Manganese germylene hydride complexes: reactivity with carbon dioxide, benzophenone, and diisopropylcarbodiimide

Abstract

Reactions of bis(hydrocarbyl)germylene manganese(I) hydride complexes [(dmpe)₂MnH(=GeR₂)] (1a: R = Ph, 1b: R = Et) with carbon dioxide yielded the previously reported carbonyl formate complex [(dmpe)₂Mn(κ¹-O₂CH)(CO)] (3) via the unstable κ²-formatogermyl intermediates [(dmpe)₂Mn{κ²-GeR₂(OCHO)}] (5a: R = Ph, 5b: R = Et). By contrast, addition of CO₂ to [(dmpe)₂MnH(=GeⁿBuH)] (2a), which contains a terminal GeH substitutent, resulted in the sequential formation of (i) the formatogermylene hydride complex [(dmpe)₂MnH{=GeⁿBu(κ¹-O₂CH)}] (6), (ii) the isolable metallacyclic κ²-formatogermyl complex [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(OCHO)}] (7), and with heating(III) complex 3. Exposure of 2a to benzophenone also afforded a new germylene hydride complex, [(dmpe)₂MnH{=GeⁿBu(OCHPh₂)}] (8). Reactions of 1a–b and 2a with C(NⁱPr)₂ afforded a family of stable metallacyclic κ²-amidinylgermyl complexes [(dmpe)₂Mn{κ²-GeRR′(NⁱPrCHNⁱPr)}] (9a: R = R′ = Ph, 9b: R = R′ = Et, 10: R = ⁿBu and R′ = H). Addition of carbon dioxide to 10 yielded [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(NⁱPrCHNⁱPr)}] (11), and reaction of CO₂ with the κ²-amidinylsilyl derivative [(dmpe)₂Mn{κ²-SiPhH(NⁱPrCHNⁱPr)}] afforded [(dmpe)₂Mn{κ²-SiPh(κ¹-O₂CH)(NⁱPrCHNⁱPr)}] (12). Complexes 6, 7, 8, 9a, 11, and 12 were crystallographically characterized, and DFT calculations were conducted to probe the effect that different substituents on Ge have on Mn–Ge bonding in κ²-formatogermyl, κ²-amidinylgermyl, and germylene complexes.

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Introduction

Small molecule activation of carbon dioxide is of great interest given that CO₂ is a widely available and inexpensive C1 synthon.^1–6 Thus, catalytic and stoichiometric CO₂ activation by transition metal complexes has become an area of intense and growing focus.^7–11 Germylenes (GeR₂), which feature low valent and (often) sterically accessible Ge centres, offer an intriguing platform for carbon dioxide reactivity. Over the past two decades, examples have been reported involving CO₂ insertion into a Ge–H bond to afford formate-substituted germylenes (Scheme 1(a)),^12–14 oxo-transfer reactions (Scheme 1(b)),¹⁵ and CO₂ incorporation into larger substituents on Ge (Scheme 1(c)).¹⁶ Free H-substituted germylenes (R₂NGeH or (BDI)GeH; BDI = β-diketiminate) have also demonstrated activity for catalytic reduction of CO₂ ¹⁷ and have been the subject of computational reports on catalytic CO₂ hydroboration.¹⁸ Furthermore, an oxo-transfer reaction from CO₂ to (BDI)Ga(μ-Cl)GeAr (Ar = 2,6-dimesitylphenyl) has recently been described,¹⁹ and Frustrated Lewis Pair reactivity has been demonstrated involving a free germylene and a cyclic (alkyl)(amino)carbene (cAAC).²⁰

Scheme 1 Literature examples of CO₂ reactivity with free germylenes (a–c) and d-block germylene complexes (d and e).^{12–16,21,22}

By contrast, the reactivity of carbon dioxide with d-block germylene complexes (which often contain germylene ligands which would be unstable outside of the metal's coordination sphere)²³ remains relatively unexplored. To our knowledge, the only reported examples involve a platinum germylene complex which undergoes reversible cycloaddition with carbon dioxide (Scheme 1(d))²¹ and a zinc germylene species where CO₂ insertion into both Ge–H and Zn–H bonds was observed²² (Scheme 1(e)).

Expanding the scope to reactions of transition metal germylene complexes with other organic reagents containing unsaturated C=O bonds, ketones and aldehydes have been shown to form hydrogermylation products upon reaction with the hydridogermylene hydride complexes [Cp*(OC)_nMH(=GeH{C(SiMe₃)₃})] (M = W and n = 2,²⁴ or M = Fe and n = 1;²⁵ Scheme 2). These reactions were suggested to proceed via (i) initial ketone/aldehyde coordination to Ge, (ii) 1,4-H transfer of the metal hydride to the carbonyl C atom, affording a germyl intermediate, and (iii) 1,2-H migration of the GeH substituent onto the metal to afford the germylene product.^24,25 In addition, the acetylide–germylene complexes [Cp*(OC)₂W(=GePh₂)(C≡CEMe₃)] (E = C, Si) were found to undergo cycloaddition with acetone to afford 6-membered metallacyclic vinylidene complexes (Scheme 2).²⁶

Scheme 2 Literature reactions of ketones and aldehydes with transition metal germylene complexes.^24–26 Interligand interactions between germylene and hydride ligands are not shown (in the top reaction, the W starting material features such an interaction, while the Fe starting material does not).

Reactions of transition metal germylene complexes with nitriles,^24,25,27 isocyanates,^25,27–29 and isothiocyanates,^25,28 all of which feature unsaturated C–N bonds, have also been reported. While insertion of carbodiimides {C(NR)₂}, which are isoelectronic with CO₂, into a Ge–N bond in the free germylene Ge{N(Me₂SiCH₂)₂}₂ ³⁰ or the Ge–Ga bond in the gallium-substituted germylene [(BDI)Ga(μ-Cl)GeAr]¹⁹ have been reported, to the best of our knowledge, reactions between a transition metal-coordinated germylene and a carbodiimide have not yet been published.

Our group recently reported the synthesis of diorganylgermylene manganese(I) hydride complexes [(dmpe)₂MnH(=GeRR′)] (1a: R = R′ = Ph, 1b: R = R′ = Et, 2a: R = ⁿBu and R′ = H, 2b: R = Ph and R′ = H; only 1a–b and 2a were isolated with analytical purity),³¹ as a natural outgrowth of our investigations into the synthesis and reactivity of their lighter silylene congeners [(dmpe)₂MnH(=SiR₂)] (R = Ph, Et) and the related disilyl hydride complexes [(dmpe)₂MnH(SiH₂R)₂] (R = Ph, ⁿBu; in solution, these species exist in equilibrium with silylene hydride complexes [(dmpe)₂MnH(=SiRH)]).^32–36 Reactions between these silicon-containing compounds and carbon dioxide afforded the manganese(I) formate complex [(dmpe)₂Mn(κ¹-O₂CH)(CO)] (3) and siloxane by-products; Scheme 3.³⁶ We also demonstrated that diisopropylcarbodiimide {C(NⁱPr)₂} reacts with the same silicon-containing reagents to afford the metallacyclic κ²-amidinylsilyl complexes [(dmpe)₂Mn{κ²-SiRR′(NⁱPrCHNⁱPr)}] (Scheme 3).³⁶

Scheme 3 Reactions of silylene hydride complexes [(dmpe)₂MnH(=SiR₂)] (R = Ph, Et; only one isomer is shown) and disilyl hydride complexes [(dmpe)₂MnH(SiH₂R)₂] (R = Ph, ⁿBu) with CO₂ and C(NⁱPr)₂.

The reactions of these manganese silylene and disilyl hydride complexes with CO₂ (Scheme 3) were proposed to proceed via a multi-step mechanism to form the carbonyl hydride complex [(dmpe)₂MnH(CO)] (4), which then undergoes reversible CO₂ insertion into the Mn–H bond to afford 3.³⁶ In this reaction, one equivalent of CO₂ was reduced to CO, presumably driven by energetically favourable Si–O bond formation. Using germylene derivatives in place of the silylene complexes would reduce the thermodynamic driving force for such reactivity given the lower bond energy of Ge–O versus Si–O bonds,³⁷ potentially permitting isolation and/or observation of reaction intermediates, providing greater insight into CO₂ activation by transition metal tetrylene complexes.

Results and discussion

Reactions of germylene hydride complexes with CO₂

Reactions of the bis(hydrocarbyl)germylene manganese(I) hydride complexes [(dmpe)₂MnH(=GeR₂)] (1a: R = Ph, 1b: R = Et) with carbon dioxide resulted in solution colour changes from dark bronze to bright red (within 1–2 h), and then to pale yellow (within 2 d). The germylene starting materials were consumed within 2 hours at room temperature,† affording unstable [(dmpe)₂Mn{κ²-GeR₂(OCHO)}] (5a: R = Ph, 5b: R = Et; Scheme 4) complexes. These intermediary products converted over several days to the manganese(I) carbonyl formate complex [(dmpe)₂Mn(κ¹-O₂CH)(CO)] (3) accompanied by germanium-containing byproducts (Scheme 4). Complex 3 was also formed, along with siloxane byproducts, in previously reported reactions of [(dmpe)₂MnH(=SiR₂)] or [(dmpe)₂MnH(SiH₂R)₂] with CO₂. However, these reactions proceeded rapidly at room temperature, and while silicon analogues of 5a–b were proposed as potential intermediates, they were not observed.³⁶ In the absence of CO₂, intermediate 5a (which was investigated due to greater stability relative to 5b) decomposed to afford previously reported [(dmpe)₂MnH(CO)] (4)³⁸ as the major product.

Scheme 4 Reactions of diorganylgermylene manganese(I) hydride complexes [(dmpe)₂MnH(=GeRR′)] (1a: R = R′ = Ph, 1b: R = R′ = Et, 2a: R = ⁿBu and R′ = H) with carbon dioxide. Only one diastereomer is shown for complex 7. Compounds 5a–b were not isolated; their structures are proposed based on in situ NMR spectroscopy, the preference of manganese(I) for a coordination number of six, DFT calculations, and the structure of an isolated κ²-formatogermyl complex (7). Conversion of 5a–b to 4 in the absence of carbon dioxide was only demonstrated for the more stable intermediate 5a, and unidentified impurities were also formed. Note: 4 has previously been shown to reversibly insert CO₂ to yield formate complex 3.³⁶

The [(dmpe)₂Mn{κ²-GeR₂(OCHO)}] (5a: R = Ph, 5b: R = Et) intermediates gave rise to a high frequency singlet in the ¹H NMR spectra (5a: 8.1 ppm, 5b: 7.8 ppm), suggestive of a formate group, and multiple ³¹P NMR environments indicative of disphenoidal dmpe coordination. For the slightly more stable diphenyl derivative 5a, further NMR characterization was conducted at −32 °C to limit decomposition. Additional NMR features include a high frequency formate environment in the ¹³C{¹H} NMR spectrum at 172.7 ppm, two unique sets of phenyl signals indicative of diastereotopic GeR₂ substituents, and a lack of any low frequency (hydridic) ¹H NMR signal. While an X-ray crystal structure was not obtained for 5a–b, κ²GeO-coordination of the GeR₂(OCHO) ligand is proposed based on (a) the preference of manganese(I) for an octahedral coordination environment, affording an 18-electron species, (b) computational support (these structures were the lowest energy minima located by DFT calculations), and (c) the X-ray crystal structure and comparable spectroscopic features of an isolated κ²-formatogermyl complex (7; vide infra).

Previously reported reactions of the germylene hydride complexes [Cp*(OC)_nMH(=GeH{C(SiMe₃)₃})] (M = W and n = 2, or M = Fe and n = 1) with ketones and aldehydes (Scheme 2) were proposed to proceed via initial coordination of the carbonyl substrate to germanium followed by 1,4-H transfer of the metal hydride to the C=O carbon atom.^26,27 Similar reactivity seems likely for the formation of 5a–b from 1a–b (where the final step involves coordination of the pendent oxygen to Mn, rather than α-hydride migration as observed in reactions with [Cp*(OC)_nMH(=GeH{C(SiMe₃)₃})]). However, a much broader range of mechanisms have been proposed for reactions of related silylene hydride complexes with unsaturated substrates,³⁶ and alternative pathways are plausible in this work (see SI including Scheme S1 for details).‡

While reactions of bis(hydrocarbyl)germylene manganese(I) hydride complexes 1a–b with CO₂ ultimately afforded 3 at ambient temperature, analogous reactivity involving [(dmpe)₂MnH(=GeⁿBuH)] (2a), which features a terminal GeH substituent, required elevated temperature to generate the same carbonyl formate species 3. At room temperature 2a reacted with CO₂ to generate a new germylene hydride complex, [(dmpe)₂MnH{=GeⁿBu(κ¹-O₂CH)}] (6), with a terminal formate substituent on germanium (Scheme 4). This complex is potentially formed via a mechanism analogous to that for the formation of 5a–b, followed by α-H migration from Ge to Mn (Scheme S1). Direct insertion of CO₂ into the Ge–H bond of 2a (similar to that proposed for alkene or alkyne reactivity with [Cp*(ⁱPr₃P)RuH₂(=GeHTrip)]⁺)³⁹ is unlikely given that this type of reactivity requires a highly electrophilic tetrylene center and is typically only observed in cationic complexes.^40,41

Attempts to isolate a bulk sample of the formatogermylene hydride complex [(dmpe)₂MnH{=GeⁿBu(κ¹-O₂CH)}] (6) were unsuccessful, and it was analysed in situ by NMR spectroscopy. The ¹H NMR spectrum of 6 includes a low frequency MnH signal (−11.8 ppm; a quintet with ²J_H,P of 53 Hz) and a high frequency formate (8.8 ppm) resonance, and one singlet was observed in the ³¹P{¹H} NMR spectrum at 78 ppm, indicative of equatorial dmpe coordination to Mn(I). The observation of a single ³¹P environment in compound 6 (and 2a–b) by NMR spectroscopy is indicative of a rapid fluxional process (e.g. rapid phosphine dissociation and re-coordination). X-ray quality crystals of 6 were obtained from O(SiMe₃)₂ at −30 °C (Fig. 1; left), revealing an octahedral environment with trans-disposed germylene and hydride ligands. As expected for a base-free germylene complex, the germanium environment is planar (Σ(X–Ge–Y) = 359.8(3)°) and the Mn–Ge distance of 2.201(1) Å is significantly shorter than in manganese(I) germyl complexes {Mn–Ge = 2.29–2.47 Å for GeX₃ (X = halide or H) compounds^42–46 and 2.41–2.54 Å for other germyl compounds^47–51}. Furthermore, the Mn–Ge distance in 6 is substantially shorter than in the previously reported [(dmpe)₂Mn(=GePhR)] (1a: R = Ph, 2b: R = H) derivatives which feature Mn–Ge distances of 2.2636(4) Å (1a) or 2.2462(6) Å (2b),³¹ presumably due to increased π-backdonation in 6 (vide infra).

Fig. 1 X-ray crystal structures of (left) [(dmpe)₂MnH{=GeⁿBu(κ¹-O₂CH)}] (6) and (right) [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(OCHO)}] (7). Ellipsoids are shown at 50% probability, and most hydrogen atoms were omitted for clarity (the hydride ligand in 6 was located from the difference map and refined isotropically). For complex 6, one of the dmpe ligands and the CH₂CH₂CH₃ group are disordered over two positions, and only the dominant (81.9(16) and 84.7(7)%, respectively) components are shown.

To the best of our knowledge, complex 6 is the first crystallographically characterized transition metal germylene complex with a terminal formate substituent. Notably, the formate substituent on Ge is κ¹-coordinated, in contrast to crystallographically characterized terminal formatostannylene complexes in which the formate substituent is κ²-coordinated to tin.^52,53

In the absence of a second equivalent of CO₂, complex 6 decomposed at room temperature over several days (∼30% conversion after 24 hours) to afford the previously reported³⁸ manganese(I) carbonyl hydride complex [(dmpe)₂MnH(CO)] (4) as the major product; Scheme 4. However, in the presence of excess CO₂, 6 reacted with an additional equivalent of carbon dioxide to yield the κ²-formatogermyl complex [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(OCHO)}] (7). This reaction proceeded to completion within 2 hours, presumably via a pathway analogous to that for conversion of germylene hydride complexes 1a–b into κ²-formatogermyl complexes 5a–b.

Unlike the unstable κ²-formatogermyl complexes 5a–b (where R and R′ are hydrocarbyl groups), analytically pure 7 was isolated as dark red crystals in 63% yield and is stable in solution for days (although heating the reaction mixture at 80 °C resulted in conversion to 3 accompanied by unidentified by-products; potentially germoxane oligomers “OGeⁿBuH” and/or their decomposition products). To the best of our knowledge, 7 is the first isolated example of a κ²-formatogermyl transition metal complex (containing a 5-membered M–Ge–O–C(H)–O ring), although an unstable Os(III) κ²-formatogermyl species has been characterized in situ by NMR spectroscopy (and osmium κ²-carboxylatogermyl analogues were isolated).⁵⁴ Asymmetric O–C–O vibrations were located in the IR spectrum of complex 7 at 1577 and 1649 cm⁻¹ for the bridging and terminal formate groups, respectively.

NMR spectra of 7 feature two sets of nearly overlapping environments from a pair of diastereomers in an approximate 1 : 2 ratio. Multiple ³¹P NMR environments were observed for each diastereomer, indicative of disphenoidal dmpe coordination to manganese. EXSY NMR cross-peaks between PMe protons in the minor and major diastereomer indicate that the diastereomers slowly exchange, either by dissociation (from Mn) of one formate substituent on Ge and coordination of the other formate, or inversion of chirality at Mn via a 5-coordinate intermediate. For the two diastereomers, the terminal formate group gave rise to singlets in the ¹H and ¹³C{¹H} NMR spectra at 8.78–8.79 and 164.5–164.9 ppm, respectively, similar to the singlets at 8.8–8.9 and 164–165 ppm from the terminal formate environment in 6 (and in 11; vide infra). The second set of formate NMR environments in complex 7 (a singlet at 7.83–7.84 ppm in the ¹H NMR spectrum, and a doublet at 173.0–173.1 ppm in the ¹³C{¹H} NMR spectrum with ³J_C,P = 5–6 Hz) is consistent with a bridging formate group. For comparison, in 5a the bridging formate ligand gave rise to a singlet in the ¹H NMR spectrum at 8.1 ppm and a doublet at 172.7 ppm in the ¹³C{¹H} NMR spectrum with ³J_C,P of 7 Hz.

X-ray quality crystals of κ²-formatogermyl complex 7 were obtained from hexanes at −30 °C. The structure (Fig. 1; right) features a 5-membered Mn–Ge–O–C(H)–O ring, along with terminal n-butyl and formate substituents on the Ge atom. Given the reasonably high standard deviations involving certain bond metrics, DFT calculations (adf/ams, gas phase, all-electron, PBE, TZ2P, ZORA, D3-BJ; energy minima were located for both diastereomers) were also carried out (Table 1). The Mn–Ge distance of 2.341(2) Å in complex 7 (calcd 2.34 Å, Mayer b.o. 1.01–1.03) is significantly longer than in germylene complex 6, though on the shorter end of those for manganese(I) germyl complexes (2.29–2.54 Å).⁵⁵ The Mn–O distance of 2.117(7) Å in 7 (calcd 2.11 Å, Mayer b.o. 0.46–0.47) is longer than in formate complex 3 (2.086(1)–2.096(1) Å)³⁶ and other terminal manganese(I) formate complexes (1.94–2.10 Å).⁵⁵

Table 1 Selected DFT-calculated and crystallographic bond distances in Å (and Mayer bond orders) involving the 5-membered metallacycles in κ²-formatogermyl complexes [(dmpe)₂Mn{κ²-GeRR′(OCHO)}] (5a: R = R′ = Ph, 5b: R = R′ = Et, 7: R = ⁿBu and R′ = κ¹-O₂CH) and κ²-amidinylgermyl complexes [(dmpe)₂Mn{κ²-GeRR′(NⁱPrCHNⁱPr)}] (9a: R = R′ = Ph, 9b: R = R′ = Et, 10: R = ⁿBu and R′ = H, 11: R = ⁿBu and R′ = κ¹-O₂CH). O_Ge, O_Mn, N_Ge, and N_Mn are oxygen or nitrogen atoms bonded to Ge or Mn atoms in the 5-membered metallacycle. For complexes 7, 10, and 11, DFT values for two diastereomers (arising from stereocenters on Mn and Ge) are included in the provided ranges. For complex 9a, XRD values from two independent and essentially isostructural molecules in the unit cell are provided

	RR′		Mn–Ge	Mn–OMn	Ge–OGe	C–OGe	C–OMn
5a	Ph2	DFT	2.39 (0.92)	2.20 (0.42)	2.03 (0.51)	1.28 (1.31)	1.25 (1.51)
5b	Et2	DFT	2.40 (0.96)	2.20 (0.42)	2.04 (0.51)	1.28 (1.32)	1.25 (1.51)
7	^nBu(κ^1-O2CH)	DFT	2.34 (1.01–1.03)	2.11 (0.46–0.47)	2.02–2.03 (0.55)	1.28 (1.31–1.32)	1.26 (1.48)
		XRD	2.341(2)	2.117(7)	1.987(7)	1.27(1)	1.25(1)
	RR′		Mn–Ge	Mn–NMn	Ge–NGe	C–NGe	C–NMn
9a	Ph2	DFT	2.43 (0.78)	2.15 (0.56)	1.97 (0.71)	1.34 (1.27)	1.31 (1.48)
		XRD	2.458(1)–2.461(1)	2.152(4)–2.179(8)	1.923(4)–1.946(5)	1.346(9)–1.363(7)	1.299(7)–1.319(8)
9b	Et2	DFT	2.45 (0.78)	2.14 (0.60)	1.99 (0.65)	1.34 (1.28)	1.31 (1.48)
10	^nBuH	DFT	2.39–2.40 (0.85)	2.15–2.17 (0.55–0.57)	1.96 (0.73–0.74)	1.33–1.34 (1.27–1.28)	1.31 (1.48–1.49)
11	^nBu(κ^1-O2CH)	DFT XRD	2.37–2.38 (0.90–0.91) 2.378(1)	2.15–2.16 (0.57–0.59) 2.162(5)	1.95 (0.75–0.77) 1.919(5)	1.34 (1.25–1.26) 1.343(8)	1.31 (1.48–1.49) 1.293(7)

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Within the bridging formate group in complex 7, the C–O bond closest to Ge (C–O_Ge; 1.27(1) Å, calcd 1.28 Å, Mayer b.o. 1.31–1.32) is marginally longer than that close to Mn (C–O_Mn; 1.25(1) Å, calcd 1.26 Å, Mayer b.o. 1.48), while both are intermediate between a typical single and double C–O bond.⁵⁶ This suggests that 7 can be described using the two resonance structures in Fig. 2, with the former structure playing a slightly greater role (see SI for further discussion). Analogous canonical forms have been used to describe bonding in transition metal complexes featuring M–Ge–O–C(H)–N (M = Fe, W, Mo) or W–Ge–N–C(H)–S metallacycles.^25,27,28

Fig. 2 Resonance structures for κ²-formatogermyl complexes [(dmpe)₂Mn{κ²-GeRR′(OCHO)}] (5a: R = R′ = Ph, 5b: R = R′ = Et, 7: R = ⁿBu and R′ = κ¹-O₂CH). Only one diastereomer is shown for complex 7. The O_Ge and O_Mn environments discussed in the text and in Table 1 are indicated on the left structure.

In order to probe how the substituents on Ge affect bonding in the κ²-formatogermyl complexes, the metrics discussed above for complex 7 (featuring an n-butyl and a terminal formate substituent on germanium) were compared to calculated values for the GePh₂ and GeEt₂ derivatives 5a–b (Tables 1 and S15). The substituents on germanium were found to have a limited impact on the C–O bonds in the bridging formate group or the Ge–O bond. However, both the Mn–Ge and Mn–O distances are slightly shorter (by 0.05–0.09 Å) in 7 relative to 5a–b, with Mayer bond orders that are higher by 0.04–0.09.

Reactions of germylene hydride complexes with benzophenone

Similar to reactions of transition metal germylene complexes with carbon dioxide, reactions with ketones are fairly unexplored (vide supra). The bis(hydrocarbyl)germylene manganese(I) hydride complexes 1a–b did not react with benzophenone, even at elevated temperature (60–85 °C). However, [(dmpe)₂MnH(=GeⁿBuH)] (2a), which features a terminal Ge–H bond, reacted with one equivalent of benzophenone at room temperature over 1 week (or overnight at 55 °C) to afford an alkoxygermylene complex, [(dmpe)₂MnH{=GeⁿBu(OCHPh₂)}] (8); Scheme 5. This reaction may follow a pathway similar to that of 2a with CO₂ to afford the formate-substituted germylene complex 6. Complex 8 did not react with a second equivalent of benzophenone, even at elevated temperature, and is remarkably stable (relative to formatogermylene complex 6) with only minor (<10%) decomposition overnight in solution at 100 °C.

Scheme 5 Reactions of diorganylgermylene manganese(I) hydride complexes [(dmpe)₂MnH(=GeRR′)] (1a: R = R′ = Ph, 1b: R = R′ = Et, 2a: R = ⁿBu and R′ = H) with Ph₂CO.

Alkoxygermylene hydride complex 8 was isolated in 43% yield as very dark red X-ray quality crystals. Similar to other trans-diorganylgermylene manganese(I) hydride complexes (1a–b, 2a–b, and 6), complex 8 gave rise to a quintet in the ¹H NMR spectrum at −12.2 ppm (²J_H,P = 53 Hz) arising from the metal hydride, and a singlet in the ³¹P{¹H} NMR spectrum at 78.9 ppm. The ¹H NMR spectrum also contains a reasonably high frequency singlet at 6.4 ppm due to the GeOCHPh₂ environment. As expected for a germylene complex, the crystal structure of 8 (Fig. 3; left) displays a planar Ge environment (Σ(X–Ge–Y) = 359.7(1)°) and a short Mn–Ge distance of 2.2164(7) Å, which is intermediate between that in formatogermylene complex 6 (2.201(1) Å) and previously reported³¹ GePh₂ and GePhH derivatives 1a and 2b (2.2462(6)–2.2636(4) Å). Furthermore, an Mn–H stretch was located at 1705 cm⁻¹ in the IR spectrum of complex 8 (cf. 1709 and 1685 cm⁻¹ in 1a and 1b, respectively).

Fig. 3 X-ray crystal structures of (left) [(dmpe)₂MnH{=GeⁿBu(OCHPh₂)}] (8) and (right) [(dmpe)₂Mn{κ²-GePh₂(NⁱPrCHNⁱPr)}] (9a). Ellipsoids are shown at 50% probability, and most hydrogen atoms are omitted for clarity (the hydride ligand in 8 was located from the difference map and refined isotropically). For complex 8, the CH₂CH₃ group of the n-butyl substituent and a phenyl ring are disordered, and only the major components (53.6(5) and 54.5(8)%, respectively) are shown. The unit cell of complex 9a contains two independent but essentially isostructural molecules, and only one is shown.

Reactions of germylene hydride complexes with C(NⁱPr)₂

Reactions of diorganylgermylene manganese(I) hydride complexes 1a–b and 2a with diisopropylcarbodiimide {C(NⁱPr)₂} afforded a family of metallacyclic κ²-amidinylgermyl complexes [(dmpe)₂Mn{κ²-GeRR′(NⁱPrCHNⁱPr)}] (9a: R = R′ = Ph, 9b: R = R′ = Et, 10: R = ⁿBu and R′ = H), which were isolated in 15–67% yield with (for 9a–b) analytical purity or (for 10) > 95% purity as orange solids (Scheme 6). These reactions presumably proceed via a pathway analogous to that for the synthesis of κ²-formatogermyl complexes 5a–b. Furthermore, this reactivity is directly analogous to that of the silicon congeners, which resulted in κ²-amidinylsilyl complexes [(dmpe)₂Mn{κ²-SiRR′(NⁱPrCHNⁱPr)}] (vide supra), and resembles the reactions of tungsten germylene hydride complexes with isocyanates or isothiocyanates to afford W–Ge–E–C(H)–N (E = O, S) metallacycles.^28,29

Scheme 6 Reactions of diorganylgermylene manganese(I) hydride complexes [(dmpe)₂MnH(=GeRR′)] (1a: R = R′ = Ph, 1b: R = R′ = Et, 2a: R = ⁿBu and R′ = H) with diisopropylcarbodiimide to afford κ²-amidinylgermyl complexes [(dmpe)₂Mn{κ²-GeRR′(NⁱPrCHNⁱPr)}] (9a: R = R′ = Ph, 9b: R = R′ = Et, 10: R = ⁿBu and R′ = H), and the reaction of 10 with carbon dioxide to afford [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(NⁱPrCHNⁱPr)}] (11). Only one diastereomer is shown for 10 and 11.

NMR spectra of 9a–b and 10 resemble those of the κ²-formatogermyl complexes [(dmpe)₂Mn{κ²-GeR₂(OCHO)}] (5a: R = Ph, 5b: R = Et) and [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(OCHO)}] (7), as well as the previously reported κ²-amidinylsilyl derivatives,³⁶ including high frequency signals in the ¹H (9a: 7.9 ppm, 9b: 7.8 ppm, 10: 7.6 ppm) and ¹³C{¹H} (9a: 160.7 ppm, 9b: 160.0 ppm, 10: 159.6–159.7 ppm) NMR spectra arising from the central CH group of the amidinate moiety. In each case, four ³¹P NMR environments were observed, indicative of disphenoidal dmpe coordination to manganese. Solutions containing the derivative with a terminal GeH substituent, 10, gave rise to two sets of nearly identical NMR environments in a 1 : 0.75 ratio from the two diastereomers present in solution, with the GeH ¹H NMR signals at 5.9–6.0 ppm (a broad peak assigned to the Ge–H stretch was also located in the IR spectrum of 10 at 1797 cm⁻¹). The formation of 10, rather than the [(dmpe)₂MnH{=GeⁿBu(κ¹-NⁱPrCHNⁱPr)}] isomer, contrasts the reactivity of 2a with CO₂ to form [(dmpe)₂MnH{=GeⁿBu(κ¹-O₂CH)}] (6), and suggests a stronger preference for an amidinate group to bridge between Ge and Mn relative to a formate group.§

Maintaining a solution of [(dmpe)₂Mn{κ²-GePh₂(NⁱPrCHNⁱPr)}] (9a) in hexanes at −30 °C afforded X-ray quality crystals containing two independent but essentially isostructural molecules in the unit cell (Table 1). The structure of 9a (Fig. 3; right) features a Mn–Ge–N–C(H)–N ring system analogous to the Mn–Ge–O–C(H)–O ring in 7 and the Mn–Si–N–C(H)–N ring in the κ²-amidinylsilyl complex [(dmpe)₂Mn{κ²-SiPhH(NⁱPrCHNⁱPr)}].³⁶

Consistent with bond metrics for κ²-formatogermyl complexes (vide supra), the unsaturated bonds on either side of the ring carbon in 9a are of slightly different lengths, with the one closer to the metal (C–N_Mn) lying between 1.299(7) and 1.319(8) Å (calcd 1.31 Å, Mayer b.o. 1.48), and the one closer to germanium (C–N_Ge) ranging from 1.346(9) to 1.363(7) Å (calcd 1.34 Å, Mayer b.o. 1.27). Both are intermediate between the average single (1.40 ± 0.04 Å) and double (1.28 ± 0.02 Å) bond lengths in crystallographic-characterized acyclic hydrocarbyl-saturated amidines (RN=C(R)–NR₂).⁵⁵ The trend in relative C–N bond orders (C–N_Mn > C–N_Ge) is mirrored by QTAIM ellipticity at the bond critical points (0.25 > 0.19), and together indicates that the bonding environment can be described using resonance structures analogous to those discussed for κ²-formatogermyl complexes 5a–b and 7 (Fig. 2). It is also notable that the Mn–Ge distances in 9a (2.461(1)–2.458(1) Å) are significantly longer than in κ²-formatogermyl complex 7 (2.341(2) Å), falling at the high end of the range for manganese germyl complexes (vide supra).

The κ²-amidinylgermyl complexes [(dmpe)₂Mn{κ²-GeRR′(NⁱPrCHNⁱPr)}] (9a–b and 10), like their silicon analogues,³⁶ did not react with a second equivalent of C(NⁱPr)₂. Furthermore, 9a–b (which lack a GeH substituent) did not react with carbon dioxide at ambient temperature. However, the derivative containing a terminal Ge–H bond ([(dmpe)₂Mn{κ²-GeⁿBuH(NⁱPrCHNⁱPr)}]; 10) reacted within minutes with CO₂ to afford a new κ²-amidinylgermyl complex with a terminal formate substituent on germanium: [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(NⁱPrCHNⁱPr)}] (11; Scheme 6).

Analytically pure 11 was isolated in 67% yield from in situ-generated 10 by recrystallization from hexanes at −30 °C. However, it slowly decomposed in solution at room temperature to a variety of unidentified products (∼25% conversion after 24 hours). The formation of complex 11 could proceed via isomerization of 10 to a germylene hydride isomer [(dmpe)₂MnH{=GeⁿBu(κ¹-NⁱPrCHNⁱPr)}] (the amidinate-substituted analogue of formate-substituted 6), followed by reactivity analogous to reactions of 1a–b with CO₂.

As with the GeH-containing precursor 10, NMR spectra of [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(NⁱPrCHNⁱPr)}] (11) include two sets of nearly-overlapping environments from a pair of diastereomers (in a 1 : 0.35 ratio), with NCHN environments in the ¹H and ¹³C{¹H} NMR spectra at 7.77–7.83 and 160.0–160.2 ppm, respectively, along with multiple ³¹P NMR environments. Additional high frequency peaks arising from the terminal formate substituent on Ge were observed at 8.86–8.87 (¹H NMR) and 163.7–164.1 (¹³C{¹H} NMR) ppm. Two peaks were observed in the region of the IR spectrum associated with terminal formate groups (1637 and 1658 cm⁻¹), and were assigned as asymmetric OCO vibrations from the two diastereomers of 11 (DFT calculations on these diastereomers also provided substantially different ν(OCO)_{asym(terminal)} values of 1646 and 1665 cm⁻¹).

An X-ray crystal structure of formate-substituted κ²-amidinylgermyl complex [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(NⁱPrCHNⁱPr)}] (11; Fig. 4 left; Table 1) confirmed that the amidinate and formate groups occupy bridging and terminal positions, respectively {and DFT calculations indicate that the isomer of 11 with the formate in a bridging position and a terminal amidinate group (Fig. S172) is 14 kJ mol⁻¹ higher in energy than the global minimum for complex 11}. Compound 11 is essentially isostructural to 9a, with C–N_Ge and C–N_Mn distances of 1.343(8) and 1.293(7) Å, respectively (calcd 1.34 Å with Mayer b.o. 1.25–1.26, and 1.31 Å with Mayer b.o. 1.48–1.49, respectively) and a relatively planar environment about the Ge atom, not including the amidinate group (Σ(X–Ge–Y) = 356.3(2)°).

Fig. 4 X-ray crystal structures of (left) [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(NⁱPrCHNⁱPr)}] (11) and (right) [(dmpe)₂Mn{κ²-SiPh(κ¹-O₂CH)(NⁱPrCHNⁱPr)}] (12). Ellipsoids are shown at 50% probability, and most hydrogen atoms are omitted for clarity.

As with κ²-formatogermyl complexes discussed above, the substituents on Ge do not significantly affect C–N bonding within the metallacycle; for 9a–b, 10, and 11, the corresponding C–N distances are calculated to be within 0.01 Å for each derivative (Table 1). Additionally, IR spectra of 9a–b, 10, and 11 feature asymmetric NCN stretches within a very narrow range (1589–1600 cm⁻¹). However, the Mn–Ge distances are more significantly influenced by the substitutents on Ge, with DFT-calculated distances increasing from 2.37–2.38 Å (Mayer b.o. 0.90–0.91, XRD: 2.378(1) Å) in [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(NⁱPrCHNⁱPr)}] (11), to 2.39–2.40 Å (Mayer b.o. 0.85) in [(dmpe)₂Mn{κ²-GeⁿBuH(NⁱPrCHNⁱPr)}] (10), and 2.43–2.45 Å (Mayer b.o. of 0.78) in the diethyl and diphenyl derivatives 9a–b (Table 1).

Intrigued by the reaction of 10 with CO₂, we tested analogous reactivity for the previously reported³⁶ κ²-amidinylsilyl derivative [(dmpe)₂Mn{κ²-SiPhH(NⁱPrCHNⁱPr)}]. Indeed, upon exposure to CO₂ this complex underwent immediate and quantitative conversion to the formate-substituted κ²-amidinylsilyl complex [(dmpe)₂Mn{κ²-SiPh(κ¹-O₂CH)(NⁱPrCHNⁱPr)}] (12; Scheme 7). The solid state structure (Fig. 4; right) and NMR spectra of complex 12 closely resemble those of the germanium derivative 11. Also, relative to the SiH-containing starting material, the ²⁹Si NMR signals for the two diastereomers of 12 are shifted to higher frequency (97.1–98.0 ppm, relative to 87.1 ppm), and the crystallographic Mn–Si distance of 2.3139(9) Å is significantly shorter than that in [(dmpe)₂Mn{κ²-SiPhH(NⁱPrCHNⁱPr)}] (2.347(1)–2.358(1) Å).

Scheme 7 Reaction of manganese κ²-amidinylsilyl complex [(dmpe)₂Mn{κ²-SiPhH(NⁱPrCHNⁱPr)}] with carbon dioxide. Only one diasateromer is shown for each complex.

Computational investigation of Mn=Ge bonding in germylene hydride complexes

DFT calculations (adf/ams, gas phase, all-electron, ZORA, D3-BJ) were employed to investigate the effect that installing formate or alkoxy substituents on the germylene ligand has on the strength and nature of Mn–Ge bonding in diorganylgermylene manganese(I) hydride complexes. Geometry optimization (TZ2P, PBE) of formatogermylene complex [(dmpe)₂MnH{=GeⁿBu(κ¹-O₂CH)}] (6) and alkoxygermylene complex [(dmpe)₂MnH{=GeⁿBu(OCHPh₂)}] (8) afforded structures with Mn–Ge distances (Table 2) accurate to within 0.01 Å of the crystallographically determined values. The Mn–Ge Mayer bond orders in complexes 6 and 8 (1.43 and 1.39, respectively) are similar to the values of 1.40–1.44 previously calculated for diorganylgermylene manganese(I) hydride complexes with hydrocarbyl and/or hydride substituents on Ge, [(dmpe)₂MnH(=GeRR′)] (1a: R = R′ = Ph, 1b: R = R′ = Et, 2a: R = ⁿBu and R′ = H, 2b: R = Ph and R′ = H).³¹

Table 2 Selected computational data, including fragment interaction {(dmpe)₂MnH + GeRR′} calculation data, pertaining to the Mn=Ge bonds in [(dmpe)₂MnH{=GeⁿBu(κ¹-O₂CH)}] (6) and [(dmpe)₂MnH{=GeⁿBu(OCHPh₂)}] (8), as well as previously reported data for [(dmpe)₂MnH(=GeEt₂)] (1b) and [(dmpe)₂MnH(=GeⁿBuH)] (2a).³¹ The same computational method was used for all complexes, all energies are in kJ mol⁻¹, ΔE_int values are BSSE-corrected, and for ETS-NOCV data, values in parentheses are a percentages of ΔE_orb. HC = fragment Hirshfeld charge, [M] = (dmpe)₂MnH

		1b	2a	6	8
RR′		Et2	^nBuH	^nBu(κ^1-O2CH)	^nBu(OCHPh2)
d(Mn–Ge)		2.25 Å	2.24 Å	2.20 Å	2.22 Å
Mayer b.o.		1.41	1.44	1.43	1.39
EDA	ΔEelec	−490	−484	−444	−463
	ΔEorb	−305	−317	−344	−313
	ΔEPauli	558	549	517	537
	ΔEDisp	−40	−31	−42	−52
	ΔEprep	8	17	32	20
	BSSE	1	1	2	2
	ΔEint	−267	−265	−279	−270
HC	[M]	0.26	0.29	0.34	0.27
	GeRR′	−0.26	−0.29	−0.34	−0.27
ETS-NOCV	ΔEσ	−134 (44%)	−135 (43%)	−120 (35%)	−124 (40%)
	ΔEπ⊥	−117 (38%)	−127 (40%)	−135 (39%)	−113 (36%)
	ΔEπ∥	−34 (11%)	−37 (12%)	−57 (16%)	−48 (15%)
	other	−20 (7%)	−17 (5%)	−32 (9%)	−28 (9%)

---

The nature of Mn–Ge bonding in germylene complexes 6 and 8 was further investigated via fragment interaction calculations using the energy decomposition analysis (EDA)⁵⁷ method of Ziegler and Rauk (Table 2; PBE0, QZ4P, corrected for linear dependency of the wave function). This approach affords an overall interaction energy between a neutral (dmpe)₂MnH fragment and a neutral free germylene ligand, ΔE_int, which is divided into five components (ΔE_elec, ΔE_Pauli, ΔE_orb, ΔE_disp, and ΔE_prep) as discussed in the SI.^58,59

Comparing the results of these calculations to those previously conducted³¹ on [(dmpe)₂MnH(=GeEt₂)] (1b) and [(dmpe)₂MnH(=GeⁿBuH)] (2a) allows for trends to be elucidated upon changing one of the germylene substituents (alkyl, H, formate, or alkoxide) while keeping the other substituent as an alkyl group (Et or ⁿBu) (Table 2). The overall interaction energies (ΔE_int) for the Mn=Ge bonds become more negative when changing the GeR substituent in the order H (2a; −265 kJ mol⁻¹) < alkyl (1b; −267 kJ mol⁻¹) < alkoxide (8; −270 kJ mol⁻¹) < formate (6; −279 kJ mol⁻¹). In particular, the stronger bonding involving the GeⁿBu(κ¹-O₂CH) ligand in 6 is driven largely by a stronger orbital interaction and reduced Pauli repulsion, partially offset by a diminished electrostatic contribution and a higher preparation energy.

The deformation density (Δρ) associated with the orbital interaction component (ΔE_orb) from fragment interaction calculations on 6 and 8 was further divided using the Extended Transition State and Natural Orbitals for Chemical Valence (ETS-NOCV) method (Table 2 includes the energies for each component, along with literature data³¹ for 1b and 2a). Deformation density isosurfaces and the main fragment orbital contributors are shown in Fig. 5.

Fig. 5 Deformation density contributions and the main fragment orbital contributors to bonding between the (dmpe)₂MnH and germylene fragments in [(dmpe)₂MnH{=GeⁿBu(κ¹-O₂CH)}] (6; left) or [(dmpe)₂MnH{=GeⁿBu(OCHPh₂)}] (8; right). Three major interactions were observed (Δρ_σ, Δρ_π(⊥), and Δρ_π(∥)). Deformation density isosurfaces (set to 0.003) are shown in green and yellow, corresponding to increased (green) and decreased (yellow) electron density relative to the non-interacting fragments. Orbital isosurfaces are set to 0.05. The germylene acceptor orbital for Δρ_π(∥) in complex 8 is a linear combination of the LUMO+4 and LUMO+5 (see Fig. S175). [In the ETS-NOCV calculation on complex 8, the Δρ_π(∥) contribution lists two significant acceptor orbitals for the GeⁿBu(OCHPh₂) fragment with SFO contributions of 0.010 (LUMO+4) and 0.013 (LUMO+5). Both of these orbitals are delocalized across the fragment. Linear combinations of these orbitals resulted in (i) an orbital which is σ-antibonding with respect to the Ge–O bond (included in Fig. 5) and can overlap with a donor orbital from the (dmpe)₂MnH fragment, and (ii) an orbital associated with the π systems of the phenyl rings (see Fig. S175) which does not play a significant role in Mn=Ge bonding.]

Similar to previously reported ETS-NOCV calculations for 1a–b and 2a–b (for 1b and 2a, see Table 2),³¹ the orbital component of the metal–germylene bond in 6 and 8 decomposes into three contributions; Δρ_σ involving σ donation from the HOMO of the ligand to the LUMO of the metal fragment, Δρ_π(⊥) involving π backdonation from a Mn d orbital (the HOMO of the metal-based fragment) to the LUMO of the ligand fragment, and a weaker Δρ_π(∥) interaction corresponding to π-backdonation within the plane of the germylene ligand. The acceptor orbital for the Δρ_π(⊥) interaction is π-antibonding with respect to the Ge–O bond, and is primarily composed of the vacant p orbital on germanium. By contrast, the acceptor orbital for the Δρ_π(∥) interaction is σ-antibonding with respect to the Ge–O bond, reminiscent of the acceptor orbitals for phosphine⁶⁰ and chalcogenoether^61,62 ligands, which are σ-antibonding with respect to the E–R (E = P, S, Se) bonds.

For both the formatogermylene- and alkoxygermylene-complexes (6 and 8), the Δρ_σ and Δρ_π(∥) components are weaker and stronger, respectively, than those in 1b and 2a, and in the case of 6, the Δρ_π(⊥) component is also more significant. Overall, the formatogermylene ligand in 6 is a better π-acceptor and a worse σ-donor than GeEt₂ or GeⁿBuH, highlighting the strong σ-withdrawing and weak π-donating abilities of the formate substituent. The more negative Hirshfeld charge on the germylene fragment in complex 6 (from the fragment interaction calculations; Table 2) relative to those in 1b, 2a, or 8 is also indicative of overall greater charge transfer from the (dmpe)₂MnH fragment to the germylene ligand, consistent with increased π-backdonation and decreased σ-donation.

Summary and conclusions

This work describes reactions of the bis(hydrocarbyl)germylene manganese(I) hydride complexes [(dmpe)₂MnH(=GeR₂)] (1a: R = Ph, 1b: R = Et) with CO₂ to afford κ²-formatogermyl intermediates [(dmpe)₂Mn{κ²-GeR₂(OCHO)}] (5a: R = Ph, 5b: R = Et), which ultimately converted to [(dmpe)₂Mn(κ¹-O₂CH)(CO)] (3) under an atmosphere of CO₂ (or decomposed to [(dmpe)₂MnH(CO)] (4) in the absence of CO₂). By contrast, addition of CO₂ to [(dmpe)₂MnH(=GeⁿBuH)] (2a), which contains a terminal GeH substituent, afforded the formatogermylene hydride complex [(dmpe)₂MnH{=GeⁿBu(κ¹-O₂CH)}] (6), which converted to the κ²-formatogermyl complex [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(OCHO)}] (7). Complexes 1a–b did not react with Ph₂CO, whereas 2a reacted to form the alkoxygermylene hydride complex [(dmpe)₂MnH{=GeⁿBu(OCHPh₂)}] (8). Diorganylgermylene manganese(I) hydride complexes 1a–b and 2a reacted with diisopropylcarbodiimide to afford the κ²-amidinylgermyl complexes [(dmpe)₂Mn{κ²-GeRR′(NⁱPrCHNⁱPr)}] (9a: R = R′ = Ph, 9b: R = R′ = Et, 10: R = ⁿBu and R′ = H). Compound 10 (which contains a GeH substituent) reacted with CO₂ to afford a κ²-amidinylgermyl complex with a terminal formate substituent on Ge: [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(NⁱPrCHNⁱPr)}] (11). A silicon-containing analogue of 11 (compound 12) was also synthesized. Density Functional Theory calculations were carried out to investigate the nature of Mn=Ge bonding in 6 and 8 versus 1b and 2a.

Prior to this work, only 2 examples of reactions between d-block germylene complexes and CO₂ had been described, and reactions with carbodiimides were unexplored. Key features of the work are: (a) the observation of κ²-formatogermyl intermediates [(dmpe)₂Mn{κ²-GeRR′(OCHO)}] (5a–b and 7) in reactions of 1a–b and 2a with CO₂; this contrasts the reactivity of silylene hydride analogues which rapidly eliminated siloxane byproducts to afford 3, without observable intermediates. These reactivity differences may stem from the greater strength of Si–O versus Ge–O bonds. (b) Increasing κ²-formatogermyl complex stability in the order GeRR′ = GeEt₂ (5b) < GePh₂ (5a) ≪ GeⁿBu(κ¹-O₂CH) (7). (c) The reactivity of [(dmpe)₂MnH(=GeⁿBuH)] (2a) with C(NⁱPr)₂ to form the κ²-amidinylgermyl complex [(dmpe)₂Mn{κ²-GeⁿBuH(NⁱPrCHNⁱPr)}] (10), rather than the [(dmpe)₂MnH{=GeⁿBu(κ¹-NⁱPrCHNⁱPr)}] isomer; this contrasts the reactivity of 2a with CO₂ to form [(dmpe)₂MnH{=GeⁿBu(κ¹-O₂CH)}] (6), indicating a stronger preference for an amidinate versus a formate group to bridge between Ge and Mn (this is also highlighted in the structure of 11, and for Si and Mn, in the structure of 12). (d) The GeⁿBu(κ¹-O₂CH) ligand in 6 was found to be a significantly worse σ-donor and better π-acceptor (within and perpendicular to the plane of the germylene ligand) than GeEt₂ or GeⁿBuH. It is also notable that compound 6 is the first crystallographically characterized transition metal germylene complex with a terminal formate substituent, and to the best of our knowledge, 7 is the first isolated example of a κ²-formatogermyl transition metal complex.

Experimental

General methods

See SI.

Monitoring of reactions of [(dmpe)₂MnH(=GeR₂)] (1a: R = Ph, 1b: R = Et) with CO₂ to form [(dmpe)₂Mn(κ¹-O₂CH)(CO)] (3) via the intermediates [(dmpe)₂Mn{κ²-GeR₂(OCHO)}] (5a: R = Ph, 5b: R = Et). (a) Approx. 10 mg of [(dmpe)₂MnH(=GeR₂)] (1a: R = Ph, 1b: R = Et) was dissolved in approx. 0.6 mL of C₆D₆, and the solution placed in a J-young NMR tube. The mixture was freeze/pump/thawed three times, and placed under 1 atm of CO₂ at 0 °C, sealed, and warmed to room temperature. The reaction mixture turned from bronze to bright red within 1 hour, and was monitored over time in situ by NMR spectroscopy. Complete conversion to [(dmpe)₂Mn(κ¹-O₂CH)(CO)] (3) occurred within two days, at which time the solution had turned light yellow with white precipitate. (b) 16 mg (0.03 mmol) of [(dmpe)₂MnH(=GePh₂)] (1a) was dissolved in approx. 0.6 mL of d₈-toluene, and the solution placed in a J-young NMR tube. The mixture was cooled to 0 °C and degassed under dynamic vacuum for 1 minute, after which it was placed under 1 atm of CO₂ at 0 °C, sealed, and warmed to room temperature. After 30 minutes at room temperature, the resulting red solution was cooled to −32 °C, and analyzed by NMR spectroscopy at that temperature to limit decomposition of the intermediate [(dmpe)₂Mn{κ²-GePh₂(OCHO)}] (5a) for in situ NMR analysis. Selected NMR data for the intermediate [(dmpe)₂Mn{κ²-GePh₂(OCHO)}] (5a) are as follows. 5a: ¹H NMR (d₈-toluene, 500 MHz, 298 K): δ 8.05 (s, 1H, OCH̲O), 7.99, 7.79 (2 × d, 2H, ³J_H,H 7.2 Hz, o-Ph), 1.42, 0.83 (2 × d, 3H, ²J_H,P 5.8 Hz, PCH̲₃), 1.19 (d, 3H, ²J_H,P 6.3 Hz, PCH̲₃), 1.14 (m, 6H, PCH̲₃), 1.06 (d, 6H, ²J_H,P 6.1 Hz, PCH̲₃), 0.61 (d, 3H, ²J_H,P 5.5 Hz, PCH̲₃). ¹H NMR (d₈-toluene, 500 MHz, 241 K): δ 8.08 (s, 1H, OCH̲O), 8.09 (d, 2H, ³J_H,H 6.6 Hz, o-Ph), 7.87 (d, 2H, ³J_H,H 7.0 Hz, o-Ph), 7.26 (t, 2H, ³J_H,H 7.0 Hz, m-Ph), 7.22 (t, 2H, ³J_H,H 7.2 Hz, m-Ph), 7.08 (t, ³J_H,H 7.2 Hz, p-Ph),¶ 7.04 (t, ³J_H,H 6.9 Hz, p-Ph),¶ 1.80, 1.55, 1.14, 0.55 (4 × m, PCH̲₂),¶ 1.43 (d, 3H, ²J_H,P 4.6 Hz, PCH̲₃), 1.21 (d, 3H, ²J_H,P 5.3 Hz, PCH̲₃), 1.09 (m, 9H, PCH̲₃), 1.04 (d, 3H, ²J_H,P 5.9 Hz, PCH̲₃), 0.86 (d, 3H, ²J_H,P 5.2 Hz, PCH̲₃), 0.58 (d, 3H, ²J_H,P 4.4 Hz, PCH̲₃). ¹³C{¹H} NMR (d₈-toluene, 126 MHz, 241 K): δ 172.70 (d, ³J_C,P 7.1 Hz, OC̲HO), 160.98, 160.47 (2 × s, i-Ph), 132.36, 132.12 (2 × s, o-Ph), 126.31, 125.99 (2 × s, m-Ph), 37.09 (d, J_C,P 13.6 Hz, PC̲H₃), 35.18 (app. t, J_C,P 21.8 Hz, PC̲H₂), 34.53 (m, PC̲H₂), 31.98 (m, PC̲H₂), 24.10 (d, J_C,P 13.0 Hz, PC̲H₃), 23.71, 14.07 (2 × s, PC̲H₃), 23.24 (d, J_C,P 14.4 Hz, PC̲H₃), 20.59 (PC̲H₃),¶ 17.09 (d, J_C,P 8.5 Hz, PC̲H₃), 16.62 (d, J_C,P 10.3 Hz, PC̲H₃). ³¹P{¹H} NMR (d₈-toluene, 202 MHz, 298 K): δ 82.89, 80.52, 72.66, 64.65 (4 × s, 1P). ³¹P{¹H} NMR (d₈-toluene, 202 MHz, 241 K): δ 83.19, 80.54 (2 × s, 1P), 73.27 (app. q, J_P,P 31.8 Hz, 1P), 64.86 (app. t, J_P,P 31.5 Hz, 1P). Selected NMR data for the intermediate [(dmpe)₂Mn{κ²-GeEt₂(OCHO)}] (5b) are: ¹H NMR (C₆D₆, 500 MHz, 298 K): δ 7.83 (s, 1H, OCH̲O). ³¹P{¹H} NMR (C₆D₆, 202 MHz, 298 K): δ 82.93, 78.11, 75.75, 67.87 (4 × s, 1P).

Monitoring of the reaction of [(dmpe)₂MnH(=GePh₂)] (1a) with CO₂ to form [(dmpe)₂MnH(CO)] (4) via the intermediate [(dmpe)₂Mn{κ²-GePh₂(OCHO)}] (5a). 15.9 mg (0.03 mmol) of [(dmpe)₂MnH(=GePh₂)] (1a) was dissolved in ∼0.6 mL of C₆D₆. The dark bronze reaction mixture was freeze/pump/thawed three times, and placed under 1 atm of CO₂ at 0 °C, sealed, and warmed to room temperature. After shaking, the mixture was allowed to sit at room temperature for 30 minutes to afford a royal red solution, and the solvent (and remaining CO₂) was removed in vacuo. The resulting red solid was dissolved in ∼0.6 mL of C₆D₆, and the reaction mixture was monitored in situ by NMR spectroscopy after various time intervals. After 20 minutes, the reaction mixture contained 1a, 3, 4, and 5a in an approximate 1 : 0.3 : 0.3 : 3.5 ratio. After allowing to sit for 20 hours, the ratio became 1 : 0.5 : 6.3 : 0.3 (with minor decomposition to free dmpe and unidentified impurities also apparent).

Monitoring of the reaction of [(dmpe)₂MnH(=GeⁿBuH)] (2a) with excess CO₂ to sequentially form [(dmpe)₂MnH{=GeⁿBu(κ¹-O₂CH)}] (6), [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(OCHO)}] (7), and [(dmpe)₂Mn(κ¹-O₂CH)(CO)] (3). Approx. 10 mg of [(dmpe)₂MnH(=GeⁿBuH)] (2a) was dissolved in approx. 0.6 mL of C₆D₆, and the solution placed in a J-young NMR tube. The mixture was freeze/pump/thawed three times, and placed under 1 atm of CO₂ at 0 °C, sealed, and warmed to room temperature. The reaction mixture turned from bronze to bright red within 1 hour, and was monitored over time in situ by NMR spectroscopy. After sitting for 2 days at room temperature (with periodic monitoring by NMR spectroscopy), the solution was heated at 80 °C and continued to be monitored periodically by NMR spectroscopy. Selected NMR data for [(dmpe)₂MnH{=GeⁿBu(κ¹-O₂CH)}] (6) are as follows. ¹H NMR (C₆D₆, 500 MHz, 298 K): δ 8.75 (s, 1H, OCH̲O), 1.73, 1.56 (2 × br. s, 4H, PCH̲₂), 1.52, 1.12 (2 × s, 12H, PCH̲₃), −11.76 (quin., 1H, ²J_H,P 53.1 Hz, MnH̲). ¹³C{¹H} NMR (C₆D₆, 151 MHz, 298 K): δ 165.21 (s, OC̲HO), 34.16 (m, PC̲H₂), 28.86, 27.81 (2 × s, PC̲H₃). ³¹P{¹H} NMR (C₆D₆, 243 MHz, 298 K): δ 77.66 (s).

Monitoring of the reaction of [(dmpe)₂MnH(=GeⁿBuH)] (2a) with limiting CO₂ to sequentially form [(dmpe)₂MnH{=GeⁿBu(κ¹-O₂CH)}] (6) and [(dmpe)₂MnH(CO)] (4). 11.9 mg (0.02 mmol) of [(dmpe)₂MnH(=GeⁿBuH)] (2a) was dissolved in 0.58 mL of C₆D₆ and placed in a J-young NMR tube. The mixture was freeze/pump/thawed three times, and the headspace (1.72 mL) placed under 31.7 kPa of CO₂ (0.02 mmol) at 298 K and sealed. The reaction mixture was monitored in situ periodically by NMR spectroscopy.

X-ray crystal structure of [(dmpe)₂MnH{=GeⁿBu(κ¹-O₂CH)}] (6). 15.0 mg (0.03 mmol) of [(dmpe)₂MnH(=GeⁿBuH)] (2a) was dissolved in 0.57 mL of C₆D₆ and placed in a J-young NMR tube. The mixture was freeze/pump/thawed three times, and the headspace (1.73 mL) placed under 39.7 kPa of CO₂ (0.03 mmol) at 298 K and sealed. The reaction was allowed to sit for 10 minutes, after which the solvent was removed in vacuo. X-ray quality crystals were obtained by recrystallization from a concentrated solution in hexamethyldisiloxane at −30 °C.

[(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(OCHO)}] (7). 62.8 mg (0.13 mmol) of [(dmpe)₂MnH(=GeⁿBuH)] (2a) was dissolved in 5 mL of benzene and the solution placed in a 50 mL bomb. The mixture was freeze/pump/thawed three times, and placed under 1 atm of CO₂ at 0 °C, sealed, and warmed to room temperature. Stirring for 3 hours at room temperature resulted in a bright orange solution. The solvent was removed in vacuo, and the resulting red oil was dissolved in 2 mL of hexanes. This solution was allowed to sit at −30 °C to afford 35.7 mg (0.06 mmol) of [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(OCHO)}] (7) as dark red X-ray quality crystals (upon crushing, the solid became a bright red powder). Concentrating the mother liquor and allowing it to sit again at −30 °C afforded an additional 11.1 mg (0.02 mmol) of complex 7 (total yield 63%). IR (Nujol mull): ν(OCO)_{asym(terminal)} 1649 cm⁻¹ (calcd 1639 and 1688 cm⁻¹ for the lower and higher energy diastereomers, respectively), ν(OCO)_{asym(bridging)} 1577 cm⁻¹ (calcd 1561 and 1557 cm⁻¹ for the lower and higher energy diastereomers, respectively). Vis: λ_max 476 nm. Dominant diastereomer NMR data are as follows. ¹H NMR (C₆D₆, 600 MHz, 298 K): δ 8.78 (s, 1H, OCH̲O terminal), 7.84 (s, 1H, OCH̲O bridging), 2.24, 2.11 (2 × m, 1H, CH₂CH̲₂CH₂CH₃), 2.12, 1.47 (2 × m, 1H, CH̲₂CH₂CH₂CH₃), 1.94, 0.53 (2 × m, 1H, PCH̲₂), 1.67 (m, 2H, PCH̲₂), 1.61 (m, 2H, CH₂CH₂CH̲₂CH₃), 1.57 (d, 3H, ²J_H,P 6.5 Hz, PCH̲₃), 1.52 (d, 3H, ²J_H,P 5.2 Hz, PCH̲₃), 1.48 (d, 3H, ²J_H,P 5.8 Hz, PCH̲₃), 1.15, 0.82 (2 × d, 3H, ²J_H,P 5.3 Hz, PCH̲₃), 1.14 (d, 3H, ²J_H,P 6.0 Hz, PCH̲₃), 1.09 (d, 3H, ²J_H,P 4.7 Hz, PCH̲₃), 1.06 (t, 3H, ³J_H,H 7.3 Hz, CH₂CH₂CH₂CH̲₃), 0.50 (s, 3H, PCH̲₃). ¹³C{¹H} NMR (C₆D₆, 151 MHz, 298 K): δ 173.12 (d, ³J_C,P 5.1 Hz, OC̲HO bridging), 164.92 (s, OC̲HO terminal), 36.89 (s, C̲H₂CH₂CH₂CH₃), 34.63, 34.19, 32.05 (3 × m, PC̲H₂), 31.60 (d of m, J_C,P 17.6 Hz, PC̲H₃), 27.80 (s, CH₂C̲H₂CH₂CH₃), 27.05 (s, CH₂CH₂C̲H₂CH₃), 24.12, 22.67, 16.52 (3 × m, PC̲H₃), 17.78 (d, J_C,P 12.5 Hz, PC̲H₃), 15.81 (d, J_C,P 9.1 Hz, PC̲H₃), 14.28 (s, CH₂CH₂CH₂C̲H₃). ³¹P{¹H} NMR (C₆D₆, 243 MHz, 298 K): δ 80.52 (s, 2P), 71.48, 65.54 (2 × s, 1P). Minor diastereomer NMR data are as follows. ¹H NMR (C₆D₆, 600 MHz, 298 K): δ 8.79 (s, 1H, OCH̲O terminal), 7.83 (s, 1H, OCH̲O bridging), 2.24, 2.13 (2 × m, 1H, CH₂CH̲₂CH₂CH₃), 2.23, 1.61 (2 × m, 1H, CH̲₂CH₂CH₂CH₃), 1.61 (m, 2H, CH₂CH₂CH̲₂CH₃), 1.56 (d, 3H, ²J_H,P 5.3 Hz, PCH̲₃), 1.34 (d, 3H, ²J_H,P 5.5 Hz, PCH̲₃), 1.25 (d, 3H, ²J_H,P 5.4 Hz, PCH̲₃), 1.17 (d, 3H, ²J_H,P 6.5 Hz, PCH̲₃), 1.11 (d, 3H, ²J_H,P 6.4 Hz, PCH̲₃), 1.07 (m, 6H, PCH̲₃), 1.06 (t, 3H, ³J_H,H 7.3 Hz, CH₂CH₂CH₂CH̲₃), 0.50 (s, 3H, PCH̲₃). ¹³C{¹H} NMR (C₆D₆, 151 MHz, 298 K): δ 173.00 (d, ³J_C,P 6.4 Hz, OC̲HO bridging), 164.54 (s, OC̲HO terminal), 36.10 (s, C̲H₂CH₂CH₂CH₃), 34.89, 33.52, 32.68 (3 × m, PC̲H₂), 34.26, 23.76, 22.67 (3 × m, PC̲H₃), 32.31 (d, J_C,P 17.9 Hz, PC̲H₃), 27.57 (s, CH₂C̲H₂CH₂CH₃), 27.09 (s, CH₂CH₂C̲H₂CH₃), 22.06 (d, J_C,P 22.2 Hz, PC̲H₃), 19.70 (d, J_C,P 12.1 Hz, PC̲H₃), 15.31 (d of d, J_C,P 11.8 and 3.3 Hz, PC̲H₃), 14.26 (s, CH₂CH₂CH₂C̲H₃). ³¹P{¹H} NMR (C₆D₆, 243 MHz, 298 K): δ 81.81, 78.99, 75.24, 63.29 (4 × s, 1P). Anal. found (calcd): C, 37.24 (37.60); H, 7.71 (7.54); N, 4.89 (4.57).

[(dmpe)₂MnH{=GeⁿBu(OCHPh₂)}] (8). 43.1 mg (0.09 mmol) of [(dmpe)₂MnH(=GeⁿBuH)] (2a) and 18.5 mg (0.10 mmol) of benzophenone were dissolved in 4 mL of benzene, and the reaction mixture was stirred overnight at 55 °C. The solvent was removed in vacuo, and the resulting very dark red solid was dissolved in ∼1 mL of hexamethyldisiloxane. Solid residue was removed by centrifugation, and the mother liquor left to sit at −30 °C to afford 25.3 mg (0.04 mmol, 43%) of [(dmpe)₂MnH{=GeⁿBu(OCHPh₂)}] (8) as X-ray quality dark red crystals. IR (Nujol mull): ν(Mn–H) 1705 cm⁻¹ (calcd 1792 cm⁻¹). Vis: λ_max 416 nm. ¹H NMR (C₆D₆, 500 MHz, 298 K): δ 7.60 (d, 4H, ³J_H,H 7.1 Hz, o-Ph), 7.23 (t, 4H, ³J_H,H 7.7 Hz, m-Ph), 7.07 (t, 2H, ³J_H,H 6.8 Hz, p-Ph), 6.36 (s, 1H, OCH̲Ph₂), 1.89, 1.63 (2 × m, 4H, PCH̲₂), 1.47 (m, 2H, CH₂CH̲₂CH₂CH₃), 1.44, 1.19 (2 × s, 12H, PCH̲₃), 1.36 (m, 2H, CH̲₂CH₂CH₂CH₃), 1.33 (sext., 2H, ³J_H,H 7.2 Hz, CH₂CH₂CH̲₂CH₃), 0.87 (t, 3H, ³J_H,H 7.3 Hz, CH₂CH₂CH₂CH̲₃), −12.22 (quin., ²J_H,P 52.4 Hz, MnH̲). ¹³C{¹H} NMR (C₆D₆, 126 MHz, 298 K): δ 148.96 (s, i-Ph), 128.30 (s, m-Ph), 127.35 (s, o-Ph), 126.56 (s, p-Ph), 80.20 (s, OC̲HPh₂), 46.41 (s, C̲H₂CH₂CH₂CH₃), 34.37 (m, PC̲H₂), 29.60, 28.36 (2 × m, PC̲H₃), 27.44 (s, CH₂C̲H₂CH₂CH₃), 27.08 (s, CH₂CH₂C̲H₂CH₃), 13.98 (s, CH₂CH₂CH₂C̲H₃). ³¹P{¹H} NMR (C₆D₆, 202 MHz, 298 K): δ 78.92 (s). Anal. found (calcd): C, 52.10 (52.05); H, 8.16 (7.98).

[(dmpe)₂Mn{κ²-GePh₂(NⁱPrCHNⁱPr)}] (9a). 107.1 mg (0.18 mmol) of [(dmpe)₂MnH(=GePh₂)] (1a) was dissolved in 10 mL of benzene. 69 mg (0.55 mmol) of diisopropylcarbodiimide was added to the solution, and the reaction mixture stirred at room temperature for 2 days. The solvent was removed in vacuo, then an aliquot of the resulting red oil was analyzed by NMR spectroscopy to contain a significant amount of un-reacted 1a. The oil was then dissolved in another 10 mL of benzene and an additional 70 mg (0.55 mmol) of diisopropylcarbodiimide was added. The solvent was again removed in vacuo and the resulting red oil was recrystallized from a concentrated solution in hexanes to afford 19.5 mg (0.03 mmol, 15%) of [(dmpe)₂Mn{κ²-GePh₂(NⁱPrCHNⁱPr)}] (9a) as X-ray quality orange crystals. IR (Nujol mull): ν(NCN)_{asym(bridging)} 1597 cm⁻¹ (calcd 1601 cm⁻¹). Vis: λ_max ∼470 nm (shoulder). ¹H NMR (C₆D₆, 600 MHz, 298 K): δ 7.93 (d, 2H, ³J_H,H 6.6 Hz, o-Ph), 7.93 (s, NCH̲N), 7.80 (d, 2H, ³J_H,H 6.7 Hz, o-Ph), 7.33, 7.28 (2 × t, 2H, ³J_H,H 7.4 Hz, m-Ph), 7.25 (t, 1H, ³J_H,H 7.3 Hz, p-Ph), 7.19 (t, 1H, ³J_H,H 7.4 Hz, p-Ph), 3.91 (hept., 1H, ³J_H,H 6.6 Hz, CH̲Me₂), 3.06 (hept., 1H, ³J_H,H 6.5 Hz, CH̲Me₂), 2.40 (m, 1H, PCH̲₂), 1.91, 1.60 (2 × m, 2H, PCH̲₂), 1.67 (d, 3H, ²J_H,P 5.6 Hz, PCH̲₃), 1.42, 1.10, 0.74 (3 × d, 3H, ²J_H,P 4.3 Hz, PCH̲₃), 1.40 (d, 3H, ²J_H,P 4.4 Hz, PCH̲₃), 1.39 (d, 3H, ²J_H,P 6.2 Hz, PCH̲₃), 1.31 (m, 3H, PCH̲₂), 1.27, 1.03 (2 × d, 3H, ³J_H,H 6.8 Hz, CH(CH̲₃)₂), 1.19 (d, 3H, ²J_H,P 3.2 Hz, PCH̲₃), 0.93, 0.68 (2 × d, 3H, ³J_H,H 6.5 Hz, CH(CH̲₃)₂), 0.89 (d, 3H, ²J_H,P 5.7 Hz, PCH̲₃). ¹³C{¹H} NMR (C₆D₆, 151 MHz, 298 K): δ 160.70 (s, NC̲HN), 158.94 (s, i-Ph), 154.99 (m, i-Ph), 138.08, 136.62 (2 × s, o-Ph), 127.09, 126.87 (2 × s, m-Ph), 126.80, 126.13 (2 × s, p-Ph), 59.02 (d, J_C,P 8.3 Hz, C̲HMe₂), 48.34 (s, C̲HMe₂), 36.37, 35.59, 32.71 (3 × m, PC̲H₂), 35.44, 22.36 (2 × m, PC̲H₃), 27.22 (app. t, J_C,P 8.4 Hz, PC̲H₃), 26.19, 25.80, 25.35, 24.72 (4 × s, CH(C̲H₃)₂), 25.53 (d of d, J_C,P 18.0 and 3.4 Hz, PC̲H₃), 24.63, 24.32 (2 × s, PC̲H₃), 23.08 (d, J_C,P 17.5 Hz, PC̲H₃), 18.45 (d, J_C,P 5.9 Hz, PC̲H₃). ³¹P{¹H} NMR (C₆D₆, 243 MHz, 298 K): δ 79.79, 73.93, 65.91, 61.36 (4 × s, 1P). Anal. found (calcd): C, 52.56 (52.50); H, 8.10 (8.10); N, 4.31 (3.95).

[(dmpe)₂Mn{κ²-GeEt₂(NⁱPrCHNⁱPr)}] (9b). 108.4 mg (0.22 mmol) of [(dmpe)₂MnH(=GeEt₂)] (1b) was dissolved in 10 mL of benzene. 84.3 mg (0.67 mmol) of diisopropylcarbodiimide was added, and the reaction mixture was stirred at room temperature overnight. The solvent was then removed in vacuo to afford an orange solid, which was dissolved in hexamethyldisiloxane and let sit at −30 °C to afford 61.8 mg (0.10 mmol) of [(dmpe)₂Mn{κ²-GeEt₂(NⁱPrCHNⁱPr)}] (9b) as an orange solid. Concentrating the mother liquor and letting it sit again at −30 °C afforded an additional 29.3 mg (0.05 mmol) of 9b, for a total yield of 67%. IR (Nujol mull): ν(NCN)_{asym(bridging)} 1600 cm⁻¹ (calcd 1608 cm⁻¹). Vis: λ_max 464 nm. ¹H NMR (C₆D₆, 500 MHz, 298 K): δ 7.70 (t, 1H, ⁴J_H,P 2.0 Hz, NCH̲N), 3.88, 3.06 (2 × hept., 1H, ³J_H,H 6.7 Hz, CH̲Me₂), 1.58–1.96 (m, 5H, PCH̲₂), 1.56 (m, 6H, CH₂CH̲₃), 1.53, 1.26 (2 × m, 2H, CH̲₂CH₃), 1.48 (d, 3H, ²J_H,P 5.8 Hz, PCH̲₃), 1.38 (d, 3H, ²J_H,P 5.3 Hz, PCH̲₃), 1.35 (d, 3H, ²J_H,P 6.0 Hz, PCH̲₃), 1.34 (d, 3H, ²J_H,P 4.8 Hz, PCH̲₃), 1.26 (m, 2H, PCH̲₂), 1.24 (d, 3H, ²J_H,P 4.3 Hz, PCH̲₃), 1.19 (d, 3H, ²J_H,P 3.1 Hz, PCH̲₃), 1.16, 0.96 (2 × d, 3H, ³J_H,H 6.8 Hz, CH(CH̲₃)₂), 1.14 (d, 3H, ³J_H,H 6.7 Hz, CH(CH̲₃)₂), 1.07 (d, 3H, ²J_H,P 5.0 Hz, PCH̲₃), 0.98 (m, 1H, PCH̲₂), 0.89 (d, 3H, ³J_H,H 6.6 Hz, CH(CH̲₃)₂), 0.84 (d, 3H, ²J_H,P 4.5 Hz, PCH̲₃). ¹³C{¹H} NMR (C₆D₆, 126 MHz, 298 K): δ 160.04 (s, NC̲HN), 58.76 (d, J_C,P 9.6 Hz, C̲HMe₂), 48.14 (s, C̲HMe₂), 36.78 (t of m, J_C,P 21.8 Hz, PC̲H₂), 36.09 (t of t, J_C,P 18.5 and 2.8 Hz, PC̲H₂), 35.04 (d of d, J_C,P 23.3 and 16.7 Hz, PC̲H₂), 34.14, 26.69, 24.83, 24.09, 19.76 (5 × m, PC̲H₃), 32.29 (d of d, J_C,P 21.7 and 16.4 Hz, PC̲H₂), 26.32, 25.61, 25.34, 24.48 (4 × s, CH(C̲H₃)₂), 25.98 (d of d, J_C,P 17.4 and 3.8 Hz, PC̲H₃), 25.23 (d, J_C,P 15.4 Hz, PC̲H₃), 18.37 (m, C̲H₂CH₃), 17.54 (d, J_C,P 8.0 Hz, PC̲H₃), 16.83 (app. q, J_C,P 4.9 Hz, C̲H₂CH₃), 12.24, 12.07 (2 × s, CH₂C̲H₃). ³¹P{¹H} NMR (C₆D₆, 202 MHz, 298 K): δ 76.05, 72.07, 69.92, 58.15 (4 × s, 1P). Anal. found (calcd): C, 44.92 (45.05); H, 9.49 (9.37); N, 4.69 (4.57).

[(dmpe)₂Mn{κ²-GeⁿBuH(NⁱPrCHNⁱPr)}] (10). 60.4 mg (0.12 mmol) of [(dmpe)₂MnH(=GeⁿBuH)] (2a) was dissolved in 5 mL of benzene. 50 mg (0.40 mmol) of diisopropylcarbodiimide was added, and the reaction mixture stirred for 2 days at room temperature. The solvent was removed in vacuo, and the resulting red oil was dissolved in ∼1 mL of hexanes. Solid residue was removed by centrifugation, and the mother liquor was removed in vacuo. The resulting oil was recrystallized from a minimal amount of hexamethyldisiloxane at −30 °C to afford 28.3 mg (0.05 mmol, 37%) of [(dmpe)₂Mn{κ²-GeⁿBuH(NⁱPrCHNⁱPr)}] (10) as a sticky orange powder with >95% purity by NMR spectroscopy. IR (Nujol mull): ν(Ge–H) 1797 cm⁻¹ (broad; calcd 1772 and 1781 cm⁻¹ for the lower and higher energy diastereomers, respectively), ν(NCN)_{asym(bridging)} 1594 cm⁻¹ (calcd 1600 and 1607 cm⁻¹ for the lower and higher energy diastereomers, respectively). Vis: λ_max 459 nm. Selected NMR data for the dominant diastereomer are as follows. ¹H NMR (C₆D₆, 600 MHz, 298 K): δ 7.59 (s, 1H, NCH̲N), 5.85 (m, 1H, GeH̲), 3.82 (hept, 1H, ³J_H,H 6.7 Hz, CH̲Me₂), 3.06 (hept, 1H, ³J_H,H 6.8 Hz, CH̲Me₂), 2.16, 2.02 (2 × m, 1H, CH₂CH̲₂CH₂CH₃), 1.66 (m, 2H, CH₂CH₂CH̲₂CH₃), 1.46 (d, 3H, ²J_H,P 5.8 Hz, PCH̲₃), 1.44 (d, 3H, ²J_H,P 5.6 Hz, PCH̲₃), 1.38 (d, 3H, ²J_H,P 3.9 Hz, PCH̲₃), 1.36, 1.26 (2 × m, 1H, CH̲₂CH₂CH₂CH₃), 1.24 (m, 9H, PCH̲₃), 1.11 (t, 3H, ³J_H,H 7.4 Hz, CH₂CH₂CH₂CH̲₃), 1.04 (d, 3H, ²J_H,P 4.9 Hz, PCH̲₃), 0.99 (d, 3H, ³J_H,H 6.8 Hz, CH(CH̲₃)₂), 0.86 (d, 3H, ³J_H,H 6.5 Hz, CH(CH̲₃)₂), 0.83 (d, 3H, ²J_H,P 4.6 Hz, PCH̲₃). ¹³C{¹H} NMR (C₆D₆, 151 MHz, 298 K): δ 159.71 (s, NC̲HN), 51.49 (s, C̲HMe₂), 36.18 (s, CH₂C̲H₂CH₂CH₃), 29.38, 26.07 (2 × m, PC̲H₃), 25.62, 24.23 (2 × s, CH(C̲H₃)₂), 25.25 (s, C̲H₂CH₂CH₂CH₃), 24.09 (d, J_C,P 9.8 Hz, PC̲H₃), 20.99 (d, J_C,P 12.3 Hz, PC̲H₃), 20.82 (d, J_C,P 19.6 Hz, PC̲H₃), 14.40 (s, CH₂CH₂CH₂C̲H₃). ³¹P{¹H} NMR (C₆D₆, 243 MHz, 298 K): δ 77.30, 73.03, 71.68, 58.58 (4 × s, 1P). Selected NMR data for the minor diastereomer are as follows. ¹H NMR (C₆D₆, 600 MHz, 298 K): δ 7.61 (s, 1H, NCH̲N), 5.96 (t, 1H, ³J_H,P 10.9 Hz, GeH̲), 3.85 (hept, 1H, ³J_H,H 6.7 Hz, CH̲Me₂), 3.03 (hept, 1H, ³J_H,H 6.8 Hz, CH̲Me₂), 2.15, 2.01 (2 × m, 1H, CH₂CH̲₂CH₂CH₃), 1.66 (m, 2H, CH₂CH₂CH̲₂CH₃), 1.49 (d, 3H, ²J_H,P 6.3 Hz, PCH̲₃), 1.42, 1.33 (2 × m, 1H, CH̲₂CH₂CH₂CH₃), 1.37 (d, 3H, ²J_H,P 5.0 Hz, PCH̲₃), 1.34 (d, 3H, ²J_H,P 6.4 Hz, PCH̲₃), 1.33 (d, 3H, ²J_H,P 4.0 Hz, PCH̲₃), 1.24 (m, 6H, PCH̲₃), 1.12 (t, 3H, ³J_H,H 7.4 Hz, CH₂CH₂CH₂CH̲₃), 1.04 (d, 3H, ²J_H,P 4.9 Hz, PCH̲₃), 0.95 (d, 3H, ³J_H,H 6.8 Hz, CH(CH̲₃)₂), 0.89 (d, 3H, ³J_H,H 6.5 Hz, CH(CH̲₃)₂), 0.84 (d, 3H, ²J_H,P 4.7 Hz, PCH̲₃). ¹³C{¹H} NMR (C₆D₆, 151 MHz, 298 K): δ 159.64 (s, NC̲HN), 51.30 (s, C̲HMe₂), 36.10 (s, CH₂C̲H₂CH₂CH₃), 29.38, 26.00, 23.52 (3 × m, PC̲H₃), 34.61 (d of d, J_C,P 24.4 and 15.3 Hz, PC̲H₂), 33.45 (d of d, J_C,P 23.9 and 15.1 Hz, PC̲H₂), 31.84 (d of d, J_C,P 22.3 and 16.6 Hz, PC̲H₂), 28.94 (d of d, J_C,P 24.1 and 15.7 Hz, PC̲H₂), 25.25 (s, C̲H₂CH₂CH₂CH₃), 25.07, 24.63 (2 × s, CH(C̲H₃)₂), 24.90 (d, J_C,P 16.1 Hz, PC̲H₃), 17.90 (d, J_C,P 9.6 Hz, PC̲H₃), 14.40 (s, CH₂CH₂CH₂C̲H₃), 13.51 (d, J_C,P 14.0 Hz, PC̲H₃). ³¹P{¹H} NMR (C₆D₆, 243 MHz, 298 K): δ 75.46, 73.03, 68.61, 57.97 (4 × s, 1P). NMR environments unassigned to a specific diastereomer are as follows. ¹H NMR (C₆D₆, 600 MHz, 298 K): δ 1.49–1.98, 1.22, 0.97 (3 × m, PCH̲₂), 1.26, 1.22 (2 × m, CH(CH̲₃)₂). ¹³C{¹H} NMR (C₆D₆, 151 MHz, 298 K): δ 58.61, 58.55 (2 × s, C̲HMe₂), 36.40 (m, PC̲H₂), 28.18, 28.14 (2 × s, CH₂CH₂C̲H₂CH₃), 26.92, 24.49 (2 × m, PC̲H₃), 25.55 (d of d, J_C,P 17.2 and 4.9 Hz, PC̲H₃), 25.34, 25.25, 24.54 (3 × s, CH(C̲H₃)₂), 14.23 (d, J_C,P 11.6 Hz, PC̲H₃). Anal. found (calcd): C, 44.47 (45.05); H, 9.37 (9.37); N, 4.89 (4.57).

[(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(NⁱPrCHNⁱPr)}] (11). 57.3 mg (0.12 mmol) of [(dmpe)₂MnH(=GeⁿBuH)] (2a) was dissolved in 5 mL of benzene. 45 mg (0.36 mmol) of diisopropylcarbodiimide was added, and the solution stirred for 2 days at room temperature to afford a bright orange solution containing 10. The mixture was freeze/pump/thawed three times in a 50 mL bomb, placed under 1 atm of CO₂ at 0 °C, sealed, and warmed to room temperature. Stirring for 1 hour at room temperature resulted in an orange/red solution. The solvent was removed in vacuo to afford an orange powder, which was dissolved in 5 mL of hexanes. Solid residue was removed by centrifugation, and the mother liquor was maintained at −30 °C to afford 42.2 mg (0.06 mmol) of [(dmpe)₂Mn{κ²-GeⁿBu(κ¹-O₂CH)(NⁱPrCHNⁱPr)}] (11) as X-ray quality crystals. The mother liquor was concentrated and left again at −30 °C to afford an additional 9.5 mg (0.01 mmol) of 11, for a combined yield of 67%. IR (Nujol mull): ν(OCO)_{asym(terminal)} 1658, 1637 cm⁻¹ (calcd 1646 and 1665 cm⁻¹ for the lower and higher energy diastereomers, respectively), ν(NCN)_{asym(bridging)} 1589 cm⁻¹ (calcd 1599 and 1603 cm⁻¹ for the lower and higher energy diastereomers, respectively). Vis: λ_max 465 nm. Selected major diastereomer NMR data are as follows. ¹H NMR (C₆D₆, 500 MHz, 298 K): δ 8.87 (s, 1H, OCH̲O), 7.83 (s, 1H, NCH̲N), 4.44 (hept, 1H, ³J_H,H 6.7 Hz, CH̲Me₂), 2.95 (hept, 1H, ³J_H,H 6.6 Hz, CH̲Me₂), 2.07, 0.88 (2 × m, 1H, PCH̲₂), 1.96 (m, 2H, CH₂CH̲₂CH₂CH₃), 1.69 (m, 2H, PCH̲₂), 1.61 (d, 3H, ²J_H,P 5.2 Hz, PCH̲₃), 1.60 (d, 3H, ²J_H,P 6.1 Hz, PCH̲₃), 1.57 (m, 2H, CH₂CH₂CH̲₂CH₃), 1.35 (d, 3H, ³J_H,H 6.7 Hz, CH(CH̲₃)₂), 1.33 (d, 3H, ²J_H,P 4.7 Hz, PCH̲₃), 1.22 (d, 3H, ²J_H,P 3.7 Hz, PCH̲₃), 1.18 (d, 3H, ³J_H,H 6.8 Hz, CH(CH̲₃)₂), 1.15 (d, 6H, ²J_H,P 4.0 Hz, PCH̲₃), 1.08 (d, 3H, ²J_H,P 3.2 Hz, PCH̲₃), 1.08 (t, 3H, ³J_H,H 7.4 Hz, CH₂CH₂CH₂CH̲₃), 0.98 (d, 3H, ³J_H,H 6.9 Hz, CH(CH̲₃)₂), 0.78 (d, 3H, ³J_H,H 6.6 Hz, CH(CH̲₃)₂), 0.76 (d, 3H, ²J_H,P 4.8 Hz, PCH̲₃). ¹³C{¹H} NMR (C₆D₆, 126 MHz, 298 K): δ 164.06 (s, OC̲HO), 160.23 (s, NC̲HN), 58.98 (d, J_C,P 9.0 Hz, C̲HMe₂), 48.16 (s, C̲HMe₂), 35.81, 34.48, 31.07 (3 × m, PC̲H₂), 32.76 (d, J_C,P 17.4 Hz, PC̲H₃), 32.38 (s, C̲H₂CH₂CH₂CH₃), 29.41 (s, CH₂C̲H₂CH₂CH₃), 27.76 (s, CH₂CH₂C̲H₂CH₃), 25.88, 25.75, 25.41, 24.08 (4 × s, CH(C̲H₃)₂), 25.15, 24.94, 23.92, 23.12, 19.40, 17.97 (6 × m, PC̲H₃), 14.16 (s, CH₂CH₂CH₂C̲H₃). ³¹P{¹H} NMR (C₆D₆, 202 MHz, 298 K): δ 73.94, 60.06 (2 × s, 1P), 68.31 (m, 2P). Selected minor diastereomer NMR data are as follows. ¹H NMR (C₆D₆, 500 MHz, 298 K): δ 8.86 (s, 1H, OCH̲O), 7.77 (s, 1H, NCH̲N), 4.39 (hept, 1H, ³J_H,H 6.8 Hz, CH̲Me₂), 2.93 (hept, 1H, ³J_H,H 6.5 Hz, CH̲Me₂), 1.96 (m, 2H, CH₂CH̲₂CH₂CH₃), 1.57 (m, 2H, CH₂CH₂CH̲₂CH₃), 1.49 (d, 3H, ²J_H,P 5.8 Hz, PCH̲₃), 1.48 (d, 3H, ²J_H,P 4.7 Hz, PCH̲₃), 1.45 (d, 3H, ²J_H,P 6.8 Hz, PCH̲₃), 1.32 (d, 3H, ³J_H,H 7.0 Hz, CH(CH̲₃)₂), 1.31 (d, 3H, ²J_H,P 4.9 Hz, PCH̲₃), 1.21 (d, 3H, ²J_H,P 5.4 Hz, PCH̲₃), 1.18 (d, 3H, ³J_H,H 6.7 Hz, CH(CH̲₃)₂), 1.11 (d, 3H, ²J_H,P 3.9 Hz, PCH̲₃), 1.08 (t, 3H, ³J_H,H 7.4 Hz, CH₂CH₂CH₂CH̲₃), 0.88 (d, 3H, ³J_H,H 6.9 Hz, CH(CH̲₃)₂), 0.85 (d, 3H, ³J_H,H 6.6 Hz, CH(CH̲₃)₂), 0.77 (d, 3H, ²J_H,P 6.0 Hz, PCH̲₃). ¹³C{¹H} NMR (C₆D₆, 126 MHz, 298 K): δ 163.66 (s, OC̲HO), 160.03 (s, NC̲HN), 58.60 (d, J_C,P 8.2 Hz, C̲HMe₂), 48.19 (s, C̲HMe₂), 35.81, 34.48 (2 × m, PC̲H₂), 32.38 (s, C̲H₂CH₂CH₂CH₃), 31.96, 25.15, 23.70, 23.58, 21.44, 16.61 (6 × m, PC̲H₃), 29.70 (s, CH₂C̲H₂CH₂CH₃), 27.76 (s, CH₂CH₂C̲H₂CH₃), 25.57, 25.15, 24.40 (3 × s, CH(C̲H₃)₂), 14.13 (s, CH₂CH₂CH₂C̲H₃). ³¹P{¹H} NMR (C₆D₆, 202 MHz, 298 K): δ 75.40, 69.51, 68.31, 60.06 (4 × s, 1P). NMR environments unassigned to a specific diastereomer are as follows. ¹H NMR (C₆D₆, 500 MHz, 298 K): δ 1.84, 1.56 (2 × m, CH̲₂CH₂CH₂CH₃). Anal. found (calcd): C, 43.80 (43.86); H, 8.84 (8.74); N, 4.22 (4.26).

Monitoring the reaction of [(dmpe)₂Mn{κ²-SiPhH(NⁱPrCHNⁱPr)}] with CO₂ to form [(dmpe)₂Mn{κ²-SiPh(κ¹-O₂CH)(NⁱPrCHNⁱPr)}] (12). 14.7 mg (0.02 mmol) of [(dmpe)₂Mn{κ²-SiPhH(NⁱPrCHNⁱPr)}] was dissolved in approx. 0.6 mL of C₆D₆, and the solution placed in a J-young NMR tube. The mixture was freeze/pump/thawed three times, and placed under 1 atm of CO₂ at 0 °C, sealed, and warmed to room temperature. The reaction mixture was left at room temperature and monitored by NMR spectroscopy periodically. X-ray quality crystals were obtained by removing the solvent in vacuo and recrystallization from a dilute solution in hexanes at −30 °C. Selected NMR data for the major diastereomer are as follows. ¹H NMR (C₆D₆, 600 MHz, 298 K): δ 8.72 (s, 1H, OCH̲O), 7.79 (d, 2H, ³J_H,H 6.8 Hz, o-Ph), 7.77 (s, 1H, NCH̲N), 7.26 (t, 2H, ³J_H,H 7.4 Hz, m-Ph), 7.19 (t, 1H, ³J_H,H 7.1 Hz, p-Ph), 3.39, 2.91 (2 × hept., 1H, ³J_H,H 6.6 Hz, CH̲Me₂), 2.42, 1.77 (2 × m, 1H, PCH̲₂), 1.61, (d, 3H, ²J_H,P 6.6 Hz, PCH̲₃), 1.61 (m, 2H, PCH̲₂), 1.38 (d, 3H, ²J_H,P 5.4 Hz, PCH̲₃), 1.29, 0.67 (2 × d, 3H, ²J_H,P 4.4 Hz, PCH̲₃), 1.21 (d, 3H, ²J_H,P 3.0 Hz, PCH̲₃), 1.18 (d, 3H, ²J_H,P 4.8 Hz, PCH̲₃), 1.10 (d, 3H, ²J_H,P 4.2 Hz, PCH̲₃), 1.05 (d, 3H, ³J_H,H 6.8 Hz, CH(CH̲₃)₂), 1.03, 0.93, 0.87 (3 × d, 3H, ³J_H,H 6.6 Hz, CH(CH̲₃)₂), 0.74 (m, 1H, PCH̲₂), 0.74 (d, 3H, ²J_H,P 5.5 Hz, PCH̲₃). ¹³C{¹H} NMR (C₆D₆, 151 MHz, 298 K): δ 161.14 (s, OC̲HO), 160.00 (s, NC̲HN), 148.75 (s, i-Ph), 136.20 (s, o-Ph), 127.33, 127.31 (2 × s, m-Ph and p-Ph), 59.84 (d, J_C,P 9.7 Hz, C̲HMe₂), 48.45 (s, C̲HMe₂), 35.20 (m, PC̲H₂), 31.73 (d, J_C,P 17.7 Hz, PC̲H₃), 30.22 (d of d, J_C,P 26.3 and 15.4 Hz, PC̲H₂), 26.84 (d, J_C,P 10.1 Hz, PC̲H₃), 25.87 (d, J_C,P 15.5 Hz, PC̲H₃), 25.43, 24.99, 24.90, 24.54 (4 × s, CH(C̲H₃)₂), 24.11 (d, J_C,P 8.4 Hz, PC̲H₃), 23.82 (m, PC̲H₃), 23.06 (d, J_C,P 20.0 Hz, PC̲H₃), 19.11 (d of d, J_C,P 9.4 and 4.8 Hz, PC̲H₃), 17.61 (d, J_C,P 15.5 Hz, PC̲H₃). ²⁹Si NMR (data from ²⁹Si–¹H HMBC in C₆D₆, 99 MHz, 298 K): δ 98.0. ³¹P{¹H} NMR (C₆D₆, 243 MHz, 298 K): δ 72.01 (s, 2P), 67.09, 53.47 (2 × s, 1P). Selected NMR data for the minor diastereomer are as follows. ¹H NMR (C₆D₆, 600 MHz, 298 K): δ 8.64 (s, 1H, OCH̲O), 7.85 (d, 2H, ³J_H,H 6.8 Hz, o-Ph), 7.81 (m, 1H, NCH̲N), 7.27 (t, 2H, ³J_H,H 7.2 Hz, m-Ph), 7.18 (t, 1H, ³J_H,H 7.3 Hz, p-Ph), 3.39 (hept., 1H, ³J_H,H 6.6 Hz, CH̲Me₂), 3.01 (hept., 1H, ³J_H,H 6.7 Hz, CH̲Me₂), 1.77 (m, 1H, PCH̲₂), 1.75 (d, 3H, ²J_H,P 6.4 Hz, PCH̲₃), 1.43 (d, 3H, ²J_H,P 5.5 Hz, PCH̲₃), 1.38, 1.17 (2 × m, 6H, PCH̲₃), 1.14 (d, 3H, ²J_H,P 3.0 Hz, PCH̲₃), 1.60 (d, 3H, ³J_H,H 6.8 Hz, CH(CH̲₃)₂), 1.00, 0.93, 0.87 (3 × d, 3H, ³J_H,H 6.6 Hz, CH(CH̲₃)₂), 0.97 (m, 1H, PCH̲₂), 0.74 (d, 3H, ²J_H,P 4.3 Hz, PCH̲₃), 0.74 (m, 1H, PCH̲₂). ¹³C{¹H} NMR (C₆D₆, 151 MHz, 298 K): δ 160.98 (s, OC̲HO), 160.37 (s, NC̲HN), 148.75 (s, i-Ph), 136.44 (s, o-Ph), 59.48 (d, J_C,P 8.9 Hz, C̲HMe₂), 48.55 (s, C̲HMe₂), 35.20 (m, PC̲H₂), 32.53 (d, of d, J_C,P 24.4 and 15.4 Hz, PC̲H₂), 30.64 (d, J_C,P 17.9 Hz, PC̲H₃), 26.52, 25.18, 23.82, 15.75 (4 × m, PC̲H₃), 26.06 (d of d, J_C,P 17.1 and 4.2 Hz, PC̲H₃), 25.73, 24.96, 24.65, 24.47 (4 × s, CH(C̲H₃)₂), 20.63 (d, J_C,P 12.8 Hz, PC̲H₃). ²⁹Si NMR (data from ²⁹Si–¹H HMBC in C₆D₆, 99 MHz, 298 K): δ 97.1. ³¹P{¹H} NMR (C₆D₆, 243 MHz, 298 K): δ 72.01, 69.44, 66.57, 55.14 (4 × s, 1P). NMR environments unassigned to a specific diastereomer are as follows. ¹H NMR (C₆D₆, 600 MHz, 298 K): δ 1.27–1.42 (m, PCH̲₂).

[(dmpe)₂Mn(GeH₂ⁿBu)(CN^tBu)] (13a). 16.2 mg (0.03 mmol) of [(dmpe)₂MnH(=GeEt₂)] (1b) and 24.6 mg (0.19 mmol) of H₃GeⁿBu were dissolved in approx. 0.6 mL of C₆D₆ and placed in a J-young tube. After allowing the reactions to sit at room temperature for 1.75 hours, 9.2 mg (0.11 mmol) of tert-butyl isonitrile was added, and the yellow reaction mixture was analyzed in situ by NMR spectroscopy, indicating complete conversion to 13a within 15 minutes (as a 5.6 : 1 mixture of cis-13a : trans-13a). After sitting overnight at room temperature, the solvent and free hydrogermanes were removed in vacuo, and the resulting green solid was dissolved in approx. 0.6 mL of C₆D₆ to afford a clear yellow solution which was analyzed in situ by NMR spectroscopy (as an 8 : 1 mixture of cis-13a : trans-13a). X-ray quality crystals of cis-13a were obtained by removal of the solvent in vacuo followed by recrystallization from a concentrated solution of hexamethyldisiloxane at −30 °C. cis isomer: ¹H NMR (C₆D₆, 500 MHz, 298 K): δ 3.73 3.52 (2 × m, 1H, GeH̲), 2.19 (quin., 2H, ³J_H,H 7.7 Hz, CH₂CH̲₂CH₂CH₃), 1.33–1.80 (m, 5H, PCH̲₂), 1.76 (sext., 2H, ³J_H,H 7.4 Hz, CH₂CH₂CH̲₂CH₃), 1.63, 1.58 (d, 3H, ²J_H,P 6.9 Hz, PCH̲₃), 1.31 (m, 2H, CH̲₂CH₂CH₂CH₃), 1.30, 1.28 (2 × d, 3H, ²J_H,P 6.1 Hz, PCH̲₃), 1.23 (s, 9H, C(CH̲₃)₃), 1.20 (d, 3H, ²J_H,P 6.2 Hz, PCH̲₃), 1.17 (d, 3H, ²J_H,P 6.0 Hz, PCH̲₃), 1.14 (t, 3H, ³J_H,H 7.4 Hz, CH₂CH₂CH₂CH̲₃), 0.79–1.09 (m, 3H, PCH̲₂), 1.07, 0.84 (2 × d, 3H, ²J_H,P 4.8 Hz, PCH̲₃). ¹³C{¹H} NMR (C₆D₆, 126 MHz, 298 K): δ 54.63 (s, C̲(CH₃)₃), 37.26 (s, CH₂C̲H₂CH₂CH₃), 34.76 (app. t of d, J_C,P 20.9 and 4.9 Hz, PC̲H₂), 33.70 (app. t of d, J_C,P 24.1 and 8.6 Hz, PC̲H₂), 31.98 (s, C(C̲H₃)₃), 31.78 (m, PC̲H₂), 30.06 (app. t, J_C,P 19.2 Hz, PC̲H₂), 27.61 (s, CH₂CH₂C̲H₂CH₃), 23.82 (d of d, J_C,P 13.2 and 5.5 Hz, PC̲H₃), 23.55 (d, J_C,P 10.5 Hz, PC̲H₃), 23.17 (d, J_C,P 9.0 Hz, PC̲H₃), 22.08 (d of d, J_C,P 18.5 and 6.1 Hz, PC̲H₃), 20.10 (d of d, J_C,P 11.5 and 4.2 Hz, PC̲H₃), 18.08–18.65 (m, PC̲H₃), 18.43 (s, C̲H₂CH₂CH₂CH₃), 14.65 (s, CH₂CH₂CH₂C̲H₃). ³¹P{¹H} NMR (C₆D₆, 202 MHz, 298 K): δ 64–83 (m, 3P), 57.1 (br. s, 1P). trans isomer: ¹H NMR (C₆D₆, 500 MHz, 298 K): δ 3.26 (m, 2H, GeH̲), 2.05 (quin., 2H, ³J_H,H 7.7 Hz, CH₂CH̲₂CH₂CH₃), 1.66 (sext., 2H, ³J_H,H 7.4 Hz, CH₂CH₂CH̲₂CH₃), 1.66, 1.39 (2 × m, 4H, PCH̲₂), 1.51, 1.27 (2 × s, 12H, PCH̲₃), 1.08 (t, 3H, ³J_H,H 7.4 Hz, CH₂CH₂CH₂CH̲₃), 1.05 (s, 9H, C(CH̲₃)₃), 0.89 (m, 2H, CH̲₂CH₂CH₂CH₃). ¹³C{¹H} NMR (C₆D₆, 126 MHz, 298 K): δ 54.27 (s, C̲(CH₃)₃), 38.51 (s, CH₂C̲H₂CH₂CH₃), 32.26 (m, PC̲H₂), 31.85 (s, C(C̲H₃)₃), 27.65 (s, CH₂CH₂C̲H₂CH₃), 21.83, 20.20 (2 × m, PC̲H₃), 20.97 (s, C̲H₂CH₂CH₂CH₃), 14.57 (s, CH₂CH₂CH₂C̲H₃). ³¹P{¹H} NMR (C₆D₆, 202 MHz, 298 K): δ 73.49 (s).

[(dmpe)₂Mn(GeH₂Ph)(CN^tBu)] (13b). 59.5 mg (0.12 mmol) of [(dmpe)₂MnH(=GeEt₂)] (1b) was dissolved in 5 mL benzene and placed in a 50 mL bomb. 85 mg (0.56 mmol) of H₃GePh was then added, and the reaction stirred in the dark at room temperature for 1.5 hours. 117.6 mg (1.41 mmol) of tert-butyl isonitrile was then added, and the reaction mixture was stirred at room temperature in the dark overnight. Solvent was then removed in vacuo, and the resulting powder was recrystallized from hexanes at −30 °C to afford 30.2 mg (0.05 mmol, 42%) of [(dmpe)₂Mn(GeH₂Ph)(CN^tBu)] (13b; with a 0.5 : 1 ratio of cis-13b : trans-13b) as a yellow powder with ∼95% purity by ¹H NMR spectroscopy. An additional 2.3 mg (0.004 mmol, 3%) of analytically pure 13b was isolated by dissolving the residue (which did not dissolve in the hexanes used for the initial crystallization) in 0.2 mL of toluene and cooling to −30 °C. X-ray quality crystals of cis-13b were obtained by recrystallization from a solution of toluene layered with pentane at −30 °C. X-ray quality crystals of trans-13b were obtained by dissolving approx. 10 mg of isolated [(dmpe)₂Mn(GeH₂Ph)(CN^tBu)] (13b) in approx. 0.6 mL of C₆D₆, heating in a sealed J-Young tube at 90–95 °C for 6 days (resulting in a cis : trans ratio of 8 : 92), removing the solvent in vacuo, washing the resulting solid with hexanes, and finally recrystallizing from toluene layered with hexamethyldisiloxane at −30 °C. Selected NMR data for the cis isomer: ¹H NMR (C₆D₆, 500 MHz, 298 K): δ 8.15 (d of d, 2H, ³J_H,H 7.9 Hz, ⁴J_H,H 1.3 Hz, o-Ph), 7.29 (t, 2H, ³J_H,H 7.4 Hz, m-Ph), 7.20 (p-Ph),¶ 4.72 (d of d, 1H, ³J_H,P 14.2 Hz and 7.3 Hz, GeH̲), 4.51 (q, 1H, ³J_H,P 6.4 Hz, GeH̲), 1.56–1.80 (m, 2H, PCH̲₂), 1.69 (d, 3H, ²J_H,P 7.0 Hz, PCH̲₃), 1.60 (d, 3H, ²J_H,P 6.9 Hz, PCH̲₃), 1.35, 1.29, 1.16 (3 × d, 3H, ²J_H,P 6.1 Hz, PCH̲₃), 1.26–1.49 (m, 3H, PCH̲₂), 1.19 (d, 3H, ²J_H,P 6.2 Hz, PCH̲₃), 1.03–1.13 (m, 2H, PCH̲₂), 1.02 (d, 3H, ²J_H,P 5.1 Hz, PCH̲₃), 1.01 (s, 9H, C(CH̲₃)₃), 0.92 (m, 1H, PCH̲₂), 0.83 (d, 3H, ²J_H,P 4.8 Hz, PCH̲₃). ¹³C{¹H} NMR (C₆D₆, 126 MHz, 298 K): δ 153.73 (d, ³J_C,P 5.2 Hz, i-Ph), 137.63 (s, o-Ph), 127.09 (s, m-Ph), 125.35 (s, p-Ph), 54.71 (s, C̲Me₃), 34.54 (t of d, J_C,P 20.4 and 5.9 Hz, PC̲H₂), 33.22 (t of d, J_C,P 23.8 Hz and 8.5 Hz, PC̲H₂), 32.19 (m, PC̲H₂), 30.65 (app. t, J_C,P 19.4 Hz, PC̲H₂), 23.72 (d of d, J_C,P 10.9 and 2.8 Hz, PC̲H₃), 23.39 (d of m, J_C,P 14.8 Hz, PC̲H₃), 23.05 (d, J_C,P 9.0 Hz, PC̲H₃), 22.00 (d of d, J_C,P 18.3 and 6.4 Hz, PC̲H₃), 20.30 (d of d, J_C,P 12.2 and 4.3 Hz, PC̲H₃), 20.00, 19.89 (2 × m, PC̲H₃), 18.77 (d of d, J_C,P 18.2 and 4.6 Hz, PC̲H₃). ³¹P{¹H} NMR (C₆D₆, 202 MHz, 298 K): δ 67–78 (m, 3P), 56.84 (br. s, 1P). Selected NMR data for the trans isomer: ¹H NMR (C₆D₆, 500 MHz, 298 K): δ 7.88 (d of d, 2H ³J_H,H 7.8 Hz, ⁴J_H,H 1.4 Hz, o-Ph), 7.23 (t, 2H, ³J_H,H 7.1 Hz, m-Ph), 7.16 (p-Ph),¶ 4.25 (quin., 2H, ³J_H,P 7.1 Hz, GeH̲), 1.71, 1.37 (2 × m, 4H, PCH̲₂), 1.45, 1.23 (2 × s, 12H, PCH̲₃), 1.01 (s, 9H, C(CH̲₃)₃). ¹³C{¹H} NMR (C₆D₆, 126 MHz, 298 K): δ 155.75 (s, i-Ph), 136.72 (s, o-Ph), 127.43 (s, m-Ph), 125.43 (s, p-Ph), 54.41 (s, C̲Me₃), 32.19 (m, PC̲H₂), 21.45, 19.98 (2 × m, PC̲H₃). ³¹P{¹H} NMR (C₆D₆, 202 MHz, 298 K): δ 72.08 (s). NMR environments unassigned to a specific isomer are as follows. ¹³C{¹H} NMR (C₆D₆, 126 MHz, 298 K): δ 31.73, 31.67 (2 × s, C(C̲H₃)₃). Anal. found (calcd): C, 46.69 (46.81); H, 8.08 (8.20); N, 2.15 (2.37).

Additional spectroscopic data for [(dmpe)₂MnH(=GeRR′)] (1a: R = R′ = Ph, 1b: R = R′ = Et, 2a: R = ⁿBu and R′ = H). Vis: λ_max 468 nm (1a), λ_max 431 nm (1b), and λ_max 432 nm (2a). IR (Nujol mull): 1a: ν(Mn–H) 1709 cm⁻¹ (calcd 1800 cm⁻¹), 1b: ν(Mn–H) 1685 cm⁻¹ (calcd 1772 cm⁻¹), 2a: ν(H–MnGe–H)_asym 1688 cm⁻¹ (calcd 1724 cm⁻¹); ν(H–MnGe–H)_sym 1766 cm⁻¹ (calcd 1773 cm⁻¹).

Conflicts of interest

There are no conflicts to declare.

Data availability

Data supporting this article is included in the SI.

Supplementary information: general experimental information, discussion of alternative mechanisms, selected NMR, IR, and UV-Vis spectra, SCD data, and DFT results. See DOI: https://doi.org/10.1039/d5dt01701g.

CCDC 2473080–2473088 (6, 7, 8, 9a, 11, 12, cis-13a, cis-13b, and trans-13b) contain the supplementary crystallographic data for this paper.^64a–i

Acknowledgements

D. J. H. E. thanks NSERC of Canada for a Discovery Grant and Dr Yurij Mozharivskyj for access to his X-ray diffractometer.

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Footnotes

† For the reaction of 1b with CO₂, another short lived intermediate with a ¹H NMR singlet at 8.77 ppm (and no corresponding hydride environment) was observed, but had been fully consumed within 30 minutes.

‡ Alternative mechanisms for the reactions of germylene hydride complexes with CO₂ could involve initial isomerization to a low-coordinate germyl isomer [(dmpe)₂Mn(GeHRR′)]. These species have been shown to exist in equilibrium with 1a–b or 2a–b by trapping with isonitriles, hydrogermanes, or N₂, along with reactions with D₂.^31,63 Isostructural primary germyl isonitrile complexes [(dmpe)₂Mn(GeH₂R)(CN^tBu)] (13a: R = ⁿBu, 13b: R = Ph) were prepared in this work by addition of free isonitriles to equilibrium mixtures of free hydrogermanes and germylene hydride complexes 2a–b, along with the products of hydrogermane addition to 2a–b (trans-[(dmpe)₂Mn(GeH₂R)(HGeH₂R)] and mer-[(dmpe)₂MnH(GeH₂R)₂]). X-ray crystal structures were obtained for cis-13a and both the cis and trans isomers of 13b (Fig. S165).

§ A DFT calculated energy minimum for the unobserved germylene-hydride isomer of 10, [(dmpe)₂MnH{=GeⁿBu(κ¹-NⁱPrCHNⁱPr)}] (Fig. S171), is 51 kJ mol⁻¹ higher in energy than the global minimum for 10 (a κ²-amidinylgermyl complex). For comparison, the observed formatogermylene-hydride complex [(dmpe)₂MnH{=GeⁿBu(κ¹-O₂CH)}] (6) is 22 kJ mol⁻¹ lower in energy than the unobserved κ²-formatogermyl isomer [(dmpe)₂Mn{κ²-GeⁿBuH(OCHO)}] (Fig. S170).

¶ This NMR environment was determined using TOCSY NMR spectroscopy or 2D NMR spectroscopy, so no integration is provided.

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