A digermylene (LGe^I–Ge^IL) on an N-heterocyclic carbene–fluorenyl hybrid ligand (L) and its oxidation by TEMPO and Ph₂E₂ (E = S, Se)

Abstract

A hybrid N-heterocyclic carbene (NHC)–fluorenyl ligand (L) supported Ge^IICl complex ([LGeCl]; 1) has been made from GeCl₂(dioxane) and [LK]_n. Compound 1 is reduced by Jones’ Mg^I₂ dimer [(^MesNacnacMg)₂] (^MesNacnac = [{(Mes)NCMe}₂CH]⁻; Mes = 2,4,6-Me₃-C₆H₂) to give the digermylene [LGe^I–Ge^IL] (2) with a gauche-bent conformation. Compound 2 is oxidized by TEMPO (2,2,6,6-tetramethylpiperidinyloxy) and Ph₂E₂ (E = S, Se) to give [LGe(TEMPO)] (3) and [LGeEPh] (E = S (4), Se (5)), respectively. Overoxidation of 2 by Ph₂Se₂ to give a mixed-valent trinuclear species [{(PhSe)₂Ge^II}₂(μ-L)₂Ge^IV(SePh)₂] (6) is also noted. Besides, precursor 1 is converted into [LGeMe] (7) and [LGeOSiPh₃] (8) by treating it with MeMgBr and KOSiPh₃, respectively. However, none of these compounds leads to a desired [LGeH] species. Also, interestingly, Cl-abstraction from 1 by AgSbF₆ fails and it rather forms a 2 : 1 adduct [(LGeCl)₂Ag][SbF₆] (9).

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Introduction

The low-valent/low-oxidation state chemistry of the p-block elements, especially that of the heavier ones, has seen a remarkable rise in the recent past.¹ Ancillary ligand-supported digermylenes are one such class of compounds² receiving attention as the Ge^I–Ge^I single-bonded analogues of the relatively rarer but more reactive digermynes (Ge^I≡Ge^I).³

As highlighted in Fig. 1, various monoanionic and typically bidentate ligand types have been used to furnish digermylenes (A–H)⁴ with trans- to gauche-bent conformations. In G⁴ⁱ and H,^4j the ligands bridge between the two Ge^I centers to give a butterfly-like appearance. The digermylene I has a rare eclipsed geometry achieved with the help of two K⁺ ions.⁵J is a dicationic digermylene,⁶ while K is an unsymmetrical one with two different ligands.⁷

Fig. 1 Digermylenes (A–N) supported by ancillary ligands including a few based on NHCs. Dip = 2,6-ⁱPr₂-C₆H₃; p-tol = 4-Me-C₆H₄; Ad = adamantyl.

N-heterocyclic carbenes (NHCs) are also ubiquitous ligands in the low-valent main group domain.⁸ However, their uses in digermylenes are limited (Fig. 1). For instance, the NHCs in L are external Lewis bases. A bis(NHC)-borate supports a [Ge^I₂]²⁺ in M⁹ like J. N is an NHC-ligated sila-bis-λ³-germirane.¹⁰ A CAAC-based digermylene is also possible [CAAC: cyclic(alkyl)(amino)carbene].¹¹ Lewis base coordination can also convert a digermyne into a digermylene.¹²

Despite such ligand-driven stability and the decent numbers, reactivity-wise, digermylenes remain somewhat underexplored compared to digermynes.¹³ Among the few cases studied, both C and a variant of A oxidatively add PhN=NPh by cleaving their Ge^I–Ge^I bonds but form (CO)₄Fe ← Ge^I–Ge^I → Fe(CO)₄ type Lewis adducts in reacting with Fe₂(CO)₉.¹⁴C also reacts with excess sulfur to give a Ge-analogue of a dithiocarboxylic acid anhydride.^4dD adds CO₂ to its Ge^I–Ge^I motif reversibly and also oxidatively adds PhC≡CPh and C₆F₅-F.^4eF is further reduced by KC₈ to a K-germylidenide with a formal Ge⁰.^4hH and B(C₆F₅)₃ together induce ring-opening of THF.^4j A few monodentate bulky anilides furnish pseudo-digermylenes by circumventing the Ge^I–Ge^I multiple bonding through N → Ge^I π-donation,¹⁵ although they react mostly like the digermynes. Hence, further exploration of digermylenes, especially towards controlled oxidation of Ge^I to Ge^II, would be a worthy proposition and may potentially lead to Ge^I/Ge^II redox catalysis. Performing this on an NHC-based ligand support would be even more compelling.

Danopoulos’ (CH₂)₂-linked NHC–fluorenyl hybrid ligand [Flu-(CH₂)₂-NHC^Dipp]⁻ (L; Dipp = 2,6-ⁱPr₂-C₆H₃) has been successful in d- and f-block chemistry.¹⁶ We have lately applied it to divalent main group metals like Zn, Mg, Ca, and Sr.¹⁷ Given the relevance of NHCs in stabilizing low-valent main group species, we employ here the same L on Ge and report the digermylene [LGe^I–Ge^IL] and its oxidation by TEMPO and Ph₂E₂ (E = S, Se). In addition, a compound [LGeH] is sought but found to be elusive. A Cl-abstraction from [LGeCl] by AgSbF₆ also fails and surprisingly leads to their 2 : 1 adduct instead.

Results and discussion

[LK]_n^17b and GeCl₂(dioxane) at a 1 : 1 ratio in THF give [LGeCl] (1 (89%); Scheme 1) as a colorless monomeric solid as shown by X-ray diffraction (Fig. 2). The fluorenyl is σ-bonded to the Ge^II center, which, with a stereogenic lone pair, adopts to a distorted trigonal pyramidal geometry. 1 is THF-soluble but insoluble in benzene. Its ¹H NMR spectrum in a 2 : 1 C₆D₆/THF-d₈ solvent mixture shows the characteristic resonances of L within their expected regions. The ¹³C NMR C_NHC signal is observed at δ 172.7 ppm.

Scheme 1 Synthesis of [LGeCl] (1) and its reduction to [LGe^I–Ge^IL] (2).

Fig. 2 Molecular structure of 1. Ellipsoids are set at the 50% probability level. H atoms are omitted for clarity. Selected distances (Å): Ge–C1 2.0574(14), Ge–C2 2.0939(20), and Ge–Cl 2.3223(5).

Reducing 1 using Jones’ Mg^I₂ dimer [(^MesNacnacMg)₂] (^MesNacnac = [{(Mes)NCMe}₂CH]⁻; Mes = 2,4,6-Me₃-C₆H₂)¹⁸ in benzene gives the desired digermylene [LGe^I–Ge^IL] (2 (62%); Scheme 1) as a red solid with a gauche-bent conformation as authenticated by X-ray crystallography (Fig. 3). The L → Ge bite angles are nearly the same (∼ 88.5°). While the torsion angle ∠C_NHC–Ge1–Ge2–C_NHC is 156.4°, that of ∠C2–Ge1–Ge2–C4 is recorded as 27.5°. The Ge^I–Ge^I bond distance (2.5726(4) Å) is comparable to that of other digermylenes. Notably, the C_Flu–Ge and C_NHC–Ge distances are slightly different at the two Ge^I centers. However, the ¹H NMR spectrum of 2 in C₆D₆ shows the two ligands as chemically equivalent in solution. The ¹³C NMR C_NHC signal appears at δ 185.4 ppm.

Fig. 3 Molecular structure of 2. Ellipsoids are set at the 50% probability level. H atoms are omitted for clarity. Selected distances (Å): Ge–Ge 2.5730(4), Ge1–C1 2.0301(17), G2–C3 2.0244(17), Ge1–C2 2.1606(20), and Ge2–C4 2.1710(17).

Compound 2 has been optimized at the M06-2X/def2-SVP level of theory in the gas phase (Fig. 4). The Ge^I–Ge^I bond length in the DFT-optimized structure (2.55 Å) is in good agreement with that determined in the solid state (2.57 Å). The Kohn–Sham orbitals calculated at the M06-2X/def2-TZVP//M06-2X/def2-SVP level indicate that the HOMO is localized on the Ge^I–Ge^I σ bond, formed by the overlap of their p orbitals. The HOMO-1 is essentially derived from the Ge-lone pairs. An NBO analysis at the same level of theory shows a Wiberg bond index of 0.960 for the Ge^I–Ge^I motif. Each Ge center lends 87.8% of its p-orbital character (s: 11.8%) to the Ge^I–Ge^I bond, while the lone pairs have more of the s-orbital character (s: 67.0%, p: 33.0%). The LUMO is ligand-based, lying on the fluorenyls. A reasonably high HOMO–LUMO gap (4.61 eV) reflects the stability of 2, while the same gap between the HOMO and the HOMO-1 is only 0.77 eV, suggesting that the Ge–Ge bond and the Ge-centered lone pairs can compete in reactivity. The calculated natural charge on each Ge^I center is 0.377, while that on each C_fluorenyl and C_NHC are −0.397 and 0.161, respectively. The homolytic bond dissociation energy of the Ge^I–Ge^I bond in 2 is calculated to be 37.7 kcal mol⁻¹. The red color of 2 might originate from the S₁ ← S₀ transition at around 540 nm (see the SI).

Fig. 4 DFT-optimized HOMO (left), HOMO-1 (middle), and LUMO (right) of 2 (iso-value = 0.030).

TEMPO is a common 1e⁻ oxidant in synthetic chemistry.¹⁹ However, given the rarity of Ge^I → Ge^II oxidation by TEMPO,²⁰2 when reacted with TEMPO in a 1 : 2 ratio furnishes [LGe(TEMPO)] (3 (66%); Scheme 2) as a colorless monomeric solid, as confirmed by X-ray crystallography (Fig. 5). 2 and TEMPO in a 1 : 1 ratio still gives 3 with 0.5 equiv. of 2 remaining unreacted. As observed in 1 and 2, the fluorenyl in 3 is also σ-bonded to the Ge^II center. Like 1, 3 is also THF-soluble but benzene-insoluble and its NMR spectra are recorded using a 1 : 2 C₆D₆/THF-d₈ mixture. The ¹³C NMR C_NHC signal is seen at δ 176.4 ppm.

Scheme 2 Reactivity of 2 towards oxidation by TEMPO and Ph₂E₂ (E = S, Se).

Fig. 5 Molecular structure of 3. Ellipsoids are set at the 50% probability level. H atoms are omitted for clarity. Selected distances (Å): Ge–C1 2.071(3), Ge–C2 2.116(3) Ge–O 1.8798(19), and O–N3 1.451(3).

Oxidative addition of RE–ER (R = an organyl, E = S, Se) to low-valent metal centers is a mild and efficient route to achieve heavier chalcogenides at the metal's higher oxidation states.²¹ While this has been reported for Ge^II → Ge^IV,²² a controlled oxidation of the Ge^I–Ge^I bond to yield two Ge^II centers is rare. Reacting 2 with Ph₂E₂ in a 1 : 1 ratio gives [LGeEPh] (E = S (4; 76%); Se (5; 80%); Scheme 2) as colorless solids. Both are THF-soluble but insoluble in benzene and have similar NMR spectroscopic footprints recorded in a 1 : 1 mixture of C₆D₆/THF-d₈. The ¹³C NMR C_NHC signals appear at δ 173.0 and 173.7 ppm, respectively, for 4 and 5. 4 is additionally verified by X-ray diffraction as a monomer (Fig. S18), although the data quality is not satisfactory. Notably, a crystallization attempt from 1 with an excess (3 equiv.) of Ph₂Se₂ in benzene at room temperature reacting over a week gives a complex mixture and suggests possible overoxidation. Indeed, a few single crystals of the mixed-valent trinuclear Ge^II₂Ge^IV complex [{(PhSe)₂Ge^II}₂(μ-L)₂Ge^IV(SePh)₂] (6; Scheme 2) are obtained from the crystallization attempts and only identified by X-ray crystallography (Fig. 6). While the Ge^IV center is at the middle and σ-bonded to two fluorenyls of the two bridging L units, the two Ge^II centers at the sides exhibit dative coordination from the NHC sidearm. Each Ge center has two terminal SePh groups as well.

Fig. 6 Molecular structure of 6. Ellipsoids are set at the 50% probability level. H atoms are omitted for clarity. Selected distances (Å): Ge1–C1 2.104(3), Ge2–C3 2.079(3), Ge3–C2 2.024(2), Ge3–C4 2.019(2), G1–Se1 2.469(5), Ge1–Se2 2.465(5), Ge2–Se3 2.453(4), Ge2–Se4 2.477(4), Ge3–Se5 2.400(3), and Ge3–Se6 2.387(3).

Given the values of main group metal hydrides and the well-established precedence of heteroleptic Ge^II hydrides,²³ isolating a complex [LGeH] has been attempted but remains unsuccessful. A Cl/H exchange between 1 and hydride sources such as LiAlH₄, LiHBEt₃, and MH (M = Li–K) gives intractable mixtures in all cases. To test the alternative Ge^II–(R/OR)/H–(Si/B) metathesis,^15b,23i1 is first treated with MeMgBr and KOSiPh₃ to obtain [LGeMe] (7; 81%) and [LGeOSiPh₃] (8, 95%), respectively (Scheme 3). The ¹³C NMR C_NHC signals appear at δ 181.5 and 175.6 ppm, respectively, for 7 and 8. Complex 8 is also structurally verified by X-ray crystallography (Fig. 7). The bond connectivity in 7 is also confirmed similarly (Fig. S19), but the X-ray data quality is low. However, none of these derivatives on treating with HBpin or PhSiH₃ gives a pure GeH species. The hydrogenation of 2 is also not clean.^15b Notably, [(NHC)ArGeH₃] (Ar = 2,6-Trip₂C₆H₃, Trip = 2,4,6-ⁱPr₃-C₆H₂) is dehydrogenated with an extra equivalent of the NHC to give [(NHC)ArGeH].^23l A reaction of [{(Dipp)N(^tBu)}GeO^tBu] with HBpin gives [{(Dipp)N(^tBu)}GeH]₄, which is then monomerized by NHC coordination^15b.

Scheme 3 Syntheses and reactivity of LGeCl (1) and LGe–GeL (2).

Fig. 7 Molecular structure of 8. Ellipsoids are set at the 50% probability level. H atoms are omitted for clarity. Selected distances (Å): Ge–C1 2.0889(17), Ge–C2 2.1048(17), and Ge–O 1.8593(12).

NHC-stabilized [RGe^II(NHC)]⁺ (R = alkyl, aryl, amide, aryloxide, boryl, W(CO)₃(C₅Me₅)) cations are also of interest due to their Lewis ambiphilicity and ability to activate small molecules.²⁴ They are usually made by halide (X) abstraction from [(NHC)GeRX] using M[WCA] (M = Na, Li, Ag; WCA: weakly coordinating anion). Surprisingly, no Cl-abstraction results from 1 by either AgSbF₆ or Na[{B(3,5-(CF₃)₂-C₆H₃}₄)] in THF or bromobenzene. 1 and AgSbF₆ preferably form a 2 : 1 Lewis adduct as [{(L)GeCl}₂Ag]SbF₆ (9 (83%); Scheme 3). The ligand likely pushes the Lewis basicity of the Ge^II lone pair to prevail over the potential Cl-abstraction. Cationic 9 is soluble in THF but not in benzene. Notably, its ¹H NMR spectrum in THF-d₈ shows two closely spaced set of ligand resonances suggesting discrimination between the two LGeCl units. This could also be due to the existence of two diastereomers in solution as the two Ge^II centers bonded to the Ag would be chiral. The two ¹³C NMR C_NHC signals are observed close together at δ 160.3 and 160.1 ppm, respectively. 9 is structurally confirmed by X-ray diffraction (Fig. S20), but the data quality is again unsatisfactory. Such halide abstraction can depend on the conditions applied. For instance, Aldridge's L′GeBr (L′ = an NHC-tethered amide) is Br-abstracted by LiAl[OC(CF₃)₃]₄ in haloarenes to give [L′Ge]Al[OC(CF₃)₃]₄.^24d However, the same process in benzene gives [(L′Ge)₂(μ-Br)]Al[OC(CF₃)₃]₄ by incomplete Br-abstraction. Only a few [Ge^II–Ag–Ge^II]⁺ motifs are known.²⁵

Conclusions

In conclusion, we have isolated a digermylene on a fluorenyl–NHC hybrid ligand L and explored its preliminary reactivity towards controlled oxidation. Attempts to form [LGeH] and [LGe]⁺ were also made from the precursor [LGeCl] but these remain unsuccessful so far. Instead, the Cl-abstraction attempt results in an unusual adduct formation. We are currently focusing on establishing Ge^I/Ge^II-based redox catalytic cycles.

Experimental

General considerations

All reactions were performed under a dry argon atmosphere using standard Schlenk techniques or inside a glovebox, unless otherwise indicated. Prior to use, glassware was dried overnight at 130 °C and solvents were dried, distilled and degassed using standard methods. [LK]_n^17b and [^MesNacnacMg]₂²⁶ were prepared by following literature procedures. GeCl₂(dioxane) was purchased from Sigma and MeMgBr was purchased from TCI. ¹H and ¹³C{¹H} NMR spectra were recorded on either a Jeol (JNM ECZL-400S, 400 MHz) or Bruker (Avance NEO or Avance III, both 500 MHz) spectrometer at ambient temperature, unless otherwise mentioned. Chemical shifts (δ ppm) in the ¹H and ¹³C{¹H} NMR spectra were referenced to the residual signals of the deuterated solvents.²⁷ Abbreviations for NMR spectra: s (singlet), d (doublet), t (triplet), q (quartet), quint (quintet), p (pentate), and br (broad). X-ray data were recorded on either a Rigaku Synergy i XtaLAB or a Bruker D8 diffractometer. The diffraction data are reported in crystallographic information files (cif) accompanying this document and also deposited at the Cambridge Crystallographic Data Centre, under the deposition numbers 2480685 (1), 2480687 (2), 2480688 (3), 2480686 (6), and 2480683 (8).

[LGeCl] (1). A 3 mL THF solution of [LK]_n (0.459 g, 1.000 mmol) was added dropwise to a 1 mL THF solution of GeCl₂(dioxane) (0.232 g, 1.000 mmol). The reaction mixture was stirred for 3 h. The resulting colorless solution was filtered through Celite and the volatiles were removed from the filtrate under reduced pressure. The white residue thus obtained was washed with hexane (3 × 2 mL) followed by benzene (2 × 2 mL) before drying under vacuum to obtain 1 (0.472 g, 0.894 mmol, 89%) as a white solid.

¹H NMR (400 MHz, 2 : 1 C₆D₆/THF-d₈ mixture): δ 8.27 (d, J = 7.7 Hz, 1H, ArH), 7.91 (d, J = 7.6 Hz, 1H, ArH), 7.83 (d, J = 7.5 Hz, 1H, ArH), 7.37–7.33 (m, 1H, ArH), 7.26–7.23 (m, 2H, ArH), 7.12–7.05 (m, 2H, ArH), 7.01–6.98 (m, 1H, ArH), 6.86–6.83 (m, 1H, ArH), 6.69 (d, J = 7.8 Hz, 1H, ArH), 6.56 (t, J = 1.6 Hz, 1H, NCH), 6.39 (t, J = 1.6 Hz, 1H, NCH), 4.22–4.08 (m, 2H, CH₂), 3.92–3.88 (m, 1H, CH₂), 2.76 (p, J = 6.8 Hz, 1H, CH(CH₃)₂), 2.32 (p, J = 6.7 Hz, 1H, CH(CH₃)₂), 2.14–2.09 (m, 1H, CH₂), 1.38 (d, J = 6.7 Hz, 3H, CH(CH₃)₂), 0.98–0.94 (m, 6H, CH(CH₃)₂), 0.78 (d, J = 6.8 Hz, 3H, CH(CH₃)₂). ¹³C{¹H} NMR (126 MHz, 2 : 1 C₆D₆/THF-d₈ mixture): δ 172.7 (NCN), 152.3 (Ar, C), 147.1 (Ar, C), 146.9 (Ar, C), 145.6 (Ar, C), 140.6 (Ar, C), 137.3 (Ar, C), 132.6 (Ar, C), 131.1 (Ar, C), 126.7 (Ar, C), 125.6 (Ar, C), 124.6 (Ar, C), 124.2 (Ar, C), 124.1 (Ar, C), 123.7 (Ar, C), 122.3 (Ar, C), 122.2 (Ar, C), 121.1 (Ar, C), 119.8 (Ar, C), 54.3(fluorenyl–C), 49.3 (CH₂), 29.0 (CH₂), 28.7(CH₂), 27.7, 26.0, 25.4, 23.3, 23.1. Elemental analysis for C₃₀H₃₁N₂ClGe: calcd C, 68.29; H, 5.92; N, 5.31; found C, 67.93; H, 5.88; N, 5.29.

[LGe–GeL] (2). To a 1 mL benzene suspension of 1 (0.100 g, 0.0.189 mmol), a 2 mL benzene solution of [{(^MesNacnac)Mg}₂] (0.067 g, 0.095 mmol) was added dropwise under constant stirring, during which the reaction color turned from yellow to dark red. Resting the mixture for 10 min led to a colorless precipitate, which was filtered off. Concentrating the red filtrate to <1 mL and keeping it undisturbed for 12 h at room temperature produced red crystals of 2 (0.060 g, 0.059 mmol, 62%).

¹H NMR (400 MHz, C₆D₆): δ 7.81–7.72 (m, 4H, ArH), 7.43–7.38 (m, 2H, ArH), 7.05–6.90 (m, 10H, ArH), 6.76–6.4 (m, 6H, ArH), 6.53–6.46 (m, 4H, NCH), 4.68–4.46 (m, 4H, CH₂), 4.22–4.10 (m, 2H, CH₂), 2.53–2.46 (m, 2H, CH₂), 2.29–2.20 (m, 2H, CH(CH₃)₂), 1.14–1.06 (m, 2H, CH(CH₃)₂), 0.76–0.66 (m, 12H, CH(CH₃)₂), 0.58–0.47 (m, 12H, CH(CH₃)₂). ¹³C{¹H} NMR (101 MHz, C₆D₆): δ 185.4 (NCN), 155.2 (Ar, C), 152.2 (Ar, C), 146.4 (Ar, C), 145.7 (Ar, C), 138.7 (Ar, C), 138.1 (Ar, C), 134.4 (Ar, C), 129.1 (Ar, C), 125.3 (Ar, C), 125.0 (Ar, C), 124.3 (Ar, C), 123.5 (Ar, C), 123.2 (Ar, C), 122.8 (Ar, C), 122.7 (Ar, C), 122.5 (Ar, C), 121.8 (Ar, C), 121.4 (Ar, C), 120.1 (Ar, C), 119.7 (Ar, C), 55.0 (fluorenyl–C), 49.4 (CH₂), 33.5 (CH₂), 28.9, 28.2, 27.4, 24.8, 23.3, 22.2. Elemental analysis for C₆₀H₆₂N₄Ge₂: calcd C, 73.20; H, 6.35; N, 5.69; found C, 72.97; H, 6.43; N, 5.75.

[LGe(TEMPO)] (3). A 3 mL toluene solution of TEMPO (0.016 g, 0.102 mmol) was added dropwise to a 1 mL toluene suspension of 2 (0.050 g, 0.051 mmol). The reaction mixture was stirred for 12 h before removing the volatiles under reduced pressure. The residue was first washed with cold toluene (3 × 2 mL) followed by hexane (3 × 2 mL) before drying under vacuum to obtain 3 (0.043 g, 0.059 mmol, 66%) as a colorless solid.

¹H NMR (400 MHz, 1 : 2 C₆D₆/THF-d₈): δ 8.18 (d, J = 7.7 Hz, 1H, ArH), 7.94–7.86 (m, 2H, ArH), 7.41–7.31 (m, 1H, ArH), 7.24–7.19 (m, 3H, ArH), 7.17–7.15 (m, 1H, ArH), 7.14–7.12 (m, 2H, ArH), 7.10–7.06 (m, 2H, ArH), 6.99–6.92 (m, 1H, NCH), 6.46–6.39 (m, 1H, NCH), 4.80–4.70 (m, 1H), 4.50–4.42 (m, 1H, CH₂), 4.14–4.00 (m, 1H, CH₂), 2.78–2.68 (m, 1H, CH(CH₃)₂), 2.46–2.29 (m, 2H, CH(CH₃)₂, CH₂), 1.38 (d, J = 7.00 Hz, 6H), 1.31–1.19 (m, 6H), 1.13 (d, J = 6.76 Hz, 3H), 0.95–0.79 (m, 9H), 0.55 (d, J = 6.7 Hz, 3H), 0.25–0.13 (m, 3H). ¹³C{¹H} NMR (101 MHz, 1 : 2 C₆D₆/THF-d₈): δ 176.4 (NCN), 153.9 (Ar, C), 150.7 (Ar, C), 145.6 (Ar, C), 145.3 (Ar, C), 139.0 (Ar, C), 136.6 (Ar, C), 133.4 (Ar, C), 129.9 (Ar, C), 124.7 (Ar, C), 124.7 (Ar, C), 124.2 (Ar, C), 124.1 (Ar, C), 123.9 (Ar, C), 123.5 (Ar, C), 122.4(Ar, C), 122.4 (Ar, C), 121.2 (Ar, C), 120.5 (Ar, C), 119.8 (Ar, C), 119.0 (Ar, C), 59.6 (fluorenyl–C), 49.8 (CH₂), 40.2, 31.5, 28.6, 27.8, 20.8, 17.4, 13.6. Elemental analysis for C₃₉H₄₉N₃OGe: calcd C, 72.24; H, 7.62; N, 6.48; found C, 71.78; H, 7.79; N, 6.33.

[LGeSPh] (4). A 1 mL toluene solution of Ph₂S₂ (0.010 g, 0.046 mmol) was added dropwise to a 1 mL toluene suspension of 2 (0.045 g, 0.046 mmol), during which the color of the reaction mixture turned from red to yellow. A white precipitate was slowly deposited within 1 h of storing the reaction mixture undisturbed. The precipitate was collected by filtration, washed with cold toluene (3 × 2 mL), and dried under vacuum to give 4 (0.042 g, 0.035 mmol, 76%) as a colorless solid.

¹H NMR (500 MHz, 1 : 1 C₆D₆/THF-d₈): δ 8.15 (d, J = 7.4 Hz, 1H, ArH), 7.94 (d, J = 7.6 Hz, 1H, ArH), 7.84 (d, J = 6.7 Hz, 1H, ArH), 7.25–7.10 (m, 8H, ArH), 7.03–6.99 (m, 3H, ArH), 6.81 (d, J = 7.7, 1H, NCH), 6.77–6.71 (m, 3H, NCH, ArH), 4.57–4.50 (m, 1H, CH₂), 4.38–4.34 (m, 1H, CH₂), 4.05–3.98 (m, 1H, CH₂), 2.85 (p, J = 6.8 Hz, 1H, CH(CH₃)₂), 2.47 (p, J = 6.8 Hz, 1H, CH(CH₃)₂), 2.38–2.34 (m, 1H, CH₂), 2.24 (Tol), 1.31 (d, J = 6.7 Hz, 3H, CH(CH₃)₂), 1.11 (d, J = 6.9 Hz, 3H, CH(CH₃)₂), 1.03 (d, J = 7.0 Hz, 3H, CH(CH₃)₂), 0.84 (d, J = 6.8 Hz, 3H, CH(CH₃)₂). ¹³C{¹H} NMR (126 MHz, 1 : 1 C₆D₆/THF-d₈): δ 173.0 (NCN), 152.5 (Ar, C), 149.6 (Ar, C), 147.0 (Ar, C), 146.0 (Ar, C), 143.5 (Ar, C), 139.9 (Ar, C), 137.5 (Ar, C), 133.2 (Ar, C), 132.2 (Ar, C), 131.1 (Ar, C), 128.6 (Ar, C), 127.8 (Ar, C), 126.6 (Ar, C), 125.8 (Ar, C), 125.4 (Ar, C), 124.6 (Ar, C), 124.5 (Ar, C), 124.2 (Ar, C), 124.1 (Ar, C), 123.3 (Ar, C), 123.3 (Ar, C), 123.1 (Ar, C), 122.3 (Ar, C), 120.9 (Ar, C), 119.8 (Ar, C), 53.2 (fluorenyl–C), 49.5 (CH₂), 29.5, 29.4, 29.3, 26.3, 25.6, 23.4, 22.9. Elemental analysis for C₃₆H₃₆N₂SGe: calcd C, 71.90; H, 6.03; N, 4.66; found C, 71.23; H, 6.15; N, 4.73.

[LGeSePh] (5). Following a similar procedure to that for 4, Ph₂Se₂ (0.014 g, 0.046) and 2 (0.045 g, 0.046 mmol) were reacted to obtain 5 (0.047 g, 0.037 mmol, 80%) as a colorless solid.

¹H NMR (400 MHz, 1 : 1 C₆D₆/THF-d₈): δ 8.33–8.25 (m, 1H, ArH), 7.88 (d, J = 7.6 Hz, 1H, ArH), 7.79 (dd, J = 5.3, 3.5 Hz, 1H, ArH), 7.23–7.19 (m, 4H, ArH), 7.12–7.04 (m, 2H, ArH), 7.02–6.92 (m, 2H, ArH), 6.90–6.86 (m, 2H, ArH), 6.75–6.63 (m, 5H, ArH), 4.34–4.26 (m, 1H, CH₂), 4.03–3.98 (m, 1H, CH₂), 3.96–3.87 (m, 1H, CH₂), 2.82 (p, J = 6.7 Hz, 1H, CH(CH₃)₂), 2.49–2.37 (m, 1H, CH(CH₃)₂), 2.32–2.27 (m, 1H, CH₂), 1.35 (d, J = 6.8 Hz, 3H, CH(CH₃)₂), 1.02 (d, J = 7.0 Hz, 3H, CH(CH₃)₂), 0.93 (d, J = 6.8 Hz, 3H, CH(CH₃)₂), 0.79 (d, J = 7.1 Hz, 3H, CH(CH₃)₂). ¹³C{¹H} NMR (101 MHz, 1 : 1 C₆D₆/THF-d₈): δ 173.7 (NCN), 152.1 (Ar, C), 149.3 (Ar, C), 146.6 (Ar, C), 145.6 (Ar, C), 141.5 (Ar, C), 139.9 (Ar, C), 137.2 (Ar, C), 135.6 (Ar, C), 135.1 (Ar, C), 134.0 (Ar, C), 132.8 (Ar, C), 131.0 (Ar, C), 128.6 (Ar, C), 126.5 (Ar, C), 125.5 (Ar, C), 125.1 (Ar, C), 124.9 (Ar, C), 124.5 (Ar, C), 124.3 (Ar, C), 124.2 (Ar, C), 124.0 (Ar, C), 123.0 (Ar, C), 122.6 (Ar, C), 122.1 (Ar, C), 120.9 (Ar, C), 119.8 (Ar, C), 53.0 (fluorenyl–C), 49.3 (CH₂), 26.1, 25.4, 25.3, 23.2, 22.6, 51.6, 49.2, 30.1, 29.1, 29.1, 26.3, 25.5, 23.5, 22.6. ⁷⁷Se NMR: 204.7. Elemental analysis for C₃₆H₃₆N₂SeGe: calcd C, 66.70; H, 5.60; N, 4.32; found C, 66.09; H, 5.78; N, 4.44.

[{(PhSe)₂Ge^II}₂(μ-L)₂Ge^IV(SePh)₂] (6). A 3 mL benzene solution of Ph₂Se₂ (0.067 g, 0.215 mmol) was added dropwise to a 3 mL benzene suspension of 2 (0.070 g, 0.071 mmol). The reaction mixture was stirred for 1 h before storing undisturbed for crystallization for a week, from which a few colorless crystals of 6 were obtained.

[LGeMe] (7). A 0.19 mL heptane solution of MeMgBr (0.190 mmol) was added dropwise to a 2 mL THF solution of 1 (0.100 g, 0.190 mmol). Stirring the reaction mixture for 30 min gave an orange suspension, which was filtered. Removing the volatiles from the filtrate under reduced pressure followed by washing the residue with hexane (3 × 2 mL) and drying under vacuum gave 7 (0. 080 g, 0.153 mmol, 81%) as an orange solid.

¹H NMR (500 MHz, 2 : 1 C₆D₆/THF-d₈): δ 7.79–7.74 (m, 2H, ArH), 7.52 (d, J = 7.2 Hz, 1H, ArH), 7.22 (t, J = 7.6 Hz, 1H, ArH), 7.12 (t, J = 6.8 Hz, 3H, ArH), 7.04 (t, J = 7.2 Hz, 1H, ArH), 7.00 (d, J = 7.8 Hz, 1H, ArH), 6.97–6.95 (m, 2H, ArH), 6.91–6.84 (m, 2H, ArH), 4.39–4.34 (m, 1H, CH₂), 4.21–4.14 (m, 1H, CH₂), 3.07–3.01 (m, 1H, CH₂), 2.66 (p, J = 6.8 Hz, 1H, CH(CH₃)₂), 2.49 (p, J = 6.7 Hz, 1H, CH(CH₃)₂), 2.39–2.33 (m, 1H, CH₂), 1.21 (d, J = 6.8 Hz, 3H, CH(CH₃)₂), 1.06 (d, J = 6.8 Hz, 3H, CH(CH₃)₂), 1.02 (d, J = 6.8 Hz, 3H, CH(CH₃)₂), 0.92 (d, J = 4.8 Hz, 3H, CH(CH₃)₂) −1.03 (d, J = 6.5 Hz, 3H, Ge–Me). ¹³C{¹H} NMR (126 MHz, 2 : 1 C₆D₆/THF-d₈): δ 181.5 (NCN), 155.9 (Ar, C), 154.4 (Ar, C), 147.1 (Ar, C), 146.9 (Ar, C), 139.1 (Ar, C), 138.1 (Ar, C), 134.5 (Ar, C), 131.1 (Ar, C), 126.5 (Ar, C), 126.2 (Ar, C), 125 (Ar, C), 124.4 (Ar, C), 124.3 (Ar, C), 123.8 (Ar, C), 123.3 (Ar, C), 123.1 (Ar, C), 122.7 (Ar, C), 122.5 (Ar, C), 120.5 (Ar, C), 120.0 (Ar, C), 68.5, 67.7, 51.5 (fluorenyl–C), 49.9 (CH₂), 33.9 (CH₂), 29.5, 29.2, 26.8, 26.4, 26.1, 25.3, 23.7, 23, 1.8 (Ge–Me). Elemental analysis for C₃₁H₃₄N₂Ge: calcd C, 73.40; H, 6.76; N, 5.52; found C, 73.10; H, 6.67; N, 5.59.

[LGeOSiPh₃] (8). A 1.5 mL THF solution of 1 (0.100 g, 0.189 mmol) was added to a 0.5 mL THF suspension of KOSiPh₃ (0.059 g, 0.189 mmol) and stirred for 1 h, during which the reaction mixture became turbid. It was then filtered, and the filtrate was concentrated to dryness under reduced pressure. The residue thus obtained was washed with hexane (3 × 2 mL) before drying under vacuum to obtain 8 (0.138 g, 0.180 mmol, 95%) as a colorless solid.

¹H NMR (400 MHz, C₆D₆): δ 7.97 (d, J = 7.6 Hz, 1H, ArH), 7.91 (d, J = 7.8 Hz, 1H, ArH), 7.77 (dd, J = 7.9, 1.4 Hz, 10H, ArH 7.62 (dd, J = 8.0, 1.4 Hz, 5H, ArH), 7.29–7.25 (m, 2H, ArH), 7.14–7.12 (m, 3H, ArH), 6.99–6.87 (m, 2H, ArH), 6.83 (dd, J = 7.8, 1.4 Hz, 1H, ArH), 6.53 (d, J = 7.6 Hz, 1H, ArH), 6.34 (d, J = 1.8 Hz, 1H, NCH), 6.15 (d, J = 1.7 Hz, 1H, NCH), 4.19–4.07 (m, 1H, CH₂), 4.08–3.89 (m, 2H, CH₂), 2.49 (p, J = 6.8 Hz, 1H, CH(CH₃)₂), 2.30–2.14 (m, 2H, CH₂, CH(CH₃)₂), 0.93 (d, J = 6.9 Hz, 3H, CH(CH₃)₂)), 0.74 (d, J = 6.8 Hz, 6H, CH(CH₃)₂), 0.28 (d, J = 6.8 Hz, 3H, CH(CH₃)₂). ¹³C{¹H} NMR (101 MHz, C₆D₆): δ 175.6 (NCN), 152.8 (Ar, C), 148.8 (Ar, C), 145.9 (Ar, C), 145.7 (Ar, C), 140.8 (Ar, C), 140.2 (Ar, C), 139.7 (Ar, C), 136.9 (Ar, C), 136.1 (Ar, C), 135.8 (Ar, C), 133.5 (Ar, C), 130.7 (Ar, C), 129.4 (Ar, C), 128.5 (Ar, C), 127.6 (Ar, C), 126.8 (Ar, C), 124.9 (Ar, C), 124.5 (Ar, C), 124.4 (Ar, C), 124.3 (Ar, C), 123.6 (Ar, C), 123.5 (Ar, C), 121.8 (Ar, C), 120.9 (Ar, C), 120.6 (Ar, C), 119.7 (Ar, C), 57.8(fluorenyl–C), 49.5 (CH₂), 29.1, 28.6, 27.2, 25.7, 25.5, 22.6, 22.0. Elemental analysis for C₄₈H₄₆N₂OSiGe: calcd C, 75.11; H, 6.04; N, 3.65; found C, 74.75; H, 6.16; N, 3.78.

[(LGeCl)₂Ag][SbF₆] (9). A 1 mL THF solution of AgSbF₆ (0.012 g, 0.048 mmol) was added dropwise to a 1 mL benzene suspension of 1 (0.050 g, 0.095 mmol) and stirred for 1 h. A colorless crystalline solid was deposited overnight, which was collected by filtration, washed with toluene (3 × 2 mL) and dried under vacuum to yield 9 (0.056 g, 0.039 mmol, 83%).

¹H NMR (400 MHz, THF-d₈): δ 8.02–7.91 (m, 3H, ArH), 7.89–7.82 (m, 6H, ArH), 7.75–7.71 (m, 2H, ArH), 7.58–7.31 (m, 6H, ArH), 7.32–7.19 (m, 1H, ArH), 7.18–7.01 (m, 4H, ArH), 6.71 (d, J = 7.7 Hz, 1H, ArH), 6.69–6.60 (m, 2H, ArH), 6.56–6.52 (m, 1H, ArH), 6.19 (d, J = 7.8 Hz, 1H, ArH), 4.78–4.60 (m, 4H, CH₂), 2.54 (p, J = 6.7 Hz, 1H, CH(CH₃)₂), 2.40 (p, J = 6.9 Hz, 1H, CH(CH₃)₂), 2.05–1.80 (m, 4H, CH₂, CH(CH₃)₂), 1.71–1.62 (m, 2H, CH₂, CH(CH₃)₂), 1.26–1.19 (m, 6H, CH(CH₃)₂), 1.04–0.98 (m, 6H, CH(CH₃)₂), 0.87–0.83 (m, 6H, CH(CH₃)₂), 0.25 (d, J = 6.8 Hz, 3H, CH(CH₃)₂), 0.08 (d, J = 6.8 Hz, 3H, CH(CH₃)₂). ¹³C{¹H} NMR (101 MHz, THF-d₈): δ 160.3 (NCN), 160.1 (NCN), 150.1 (Ar, C), 149.8 (Ar, C), 146.4 (Ar, C), 146.4 (Ar, C), 146.0 (Ar, C), 145.7 (Ar, C), 145.1 (Ar, C), 144.6 (Ar, C), 141.1 (Ar, C), 140.6 (Ar, C), 139.7 (Ar, C), 139.6 (Ar, C), 133.7 (Ar, C), 132.6 (Ar, C), 130.9 (Ar, C), 130.8 (Ar, C), 128.8 (Ar, C), 128.7 (Ar, C), 127.6 (Ar, C), 127.6 (Ar, C), 127.5 (Ar, C), 127.4 (Ar, C), 127.2 (Ar, C), 127.2 (Ar, C), 126.6 (Ar, C), 125.6 (Ar, C), 125.5 (Ar, C), 125.2 (Ar, C), 125.1 (Ar, C), 125.0 (Ar, C), 125.0 (Ar, C), 124.8 (Ar, C), 124.4 (Ar, C), 123.6 (Ar, C), 123.3 (Ar, C), 121.9 (Ar, C), 121.7 (Ar, C), 121.0 (Ar, C), 120.9 (Ar, C), 50.9 (fluorenyl–C), 50.7(fluorenyl–C), 48.9 (CH₂), 29.7, 29.3, 29.1, 29.1, 28.9, 26.2, 26.2, 26.1, 24.2, 23.0, 22.8. Elemental analysis for C₆₀H₆₂N₄Cl₂F₆SbAgGe₂: calcd C, 51.51; H, 4.47; N, 4.01; found C, 51.08; H, 4.66; N, 3.94.

Conflicts of interest

There are no conflicts to declare.

Data availability

Supplementary information (SI): synthetic description of all compounds reported. Spectroscopic data and crystallographic data. See DOI: https://doi.org/10.1039/d5dt02074c.

CCDC 2480685 (1), 2480687 (2), 2480688 (3), 2480686 (6) and 2480683 (8) contain the supplementary crystallographic data for this paper.^28a–e

Acknowledgements

D. Mukherjee acknowledges SERB, India for CRG/2023/005396. D. Mallick thanks SERB, India for SRG/2019/001461 and also DST, India for DST/NSM/R&D_HPC_Applications/2021/8 for offering computing resources of ‘PARAM Shakti’ at IIT Kharagpur and of ‘PARAM Brahma’ at IISER Pune. S. M. and C. M. acknowledge their fellowships from UGC, India and S. S. from IISER Kolkata, India.

References

1. (a) P. P. Power, Nature, 2010, 463, 171–177; (b) P. P. Power, Chem. Rec., 2012, 12, 238–255; (c) R. L. Melen, Science, 2019, 363, 479–484; (d) K. Oberdorf and C. Lichtenberg, Chem. Commun., 2023, 59, 8043–8058; (e) R. Akhtar, K. Gaurav and S. Khan, Chem. Soc. Rev., 2024, 53, 6150–6243.
2. (a) F. Hanusch, L. Groll and S. Inoue, Chem. Sci., 2021, 12, 2001–2015; (b) T. J. Hadlington, Chem. Soc. Rev., 2024, 53, 9738–9831; (c) N. Mukherjee and M. Majumdar, J. Am. Chem. Soc., 2024, 146, 24209–24232; (d) T. Sasamori, Synlett, 2024, 2217–2228; (e) X. Gao, Y. He and J. Cui, J. Organomet. Chem., 2024, 1012, 123146.
3. (a) M. Stender, A. D. Phillips, R. J. Wright and P. P. Power, Angew. Chem., Int. Ed., 2002, 41, 1785–1787; (b) Y. Sugiyama, T. Sasamori, Y. Hosoi, Y. Furukawa, N. Takagi, S. Nagase and N. Tokitoh, J. Am. Chem. Soc., 2006, 128, 1023–1031; (c) T. J. Hadlington, M. Hermann, J. Li, G. Frenking and C. Jones, Angew. Chem., Int. Ed., 2013, 52, 10199–10203.
4. (a) S. P. Green, C. Jones, P. C. Junk, K.-A. Lippert and A. Stasch, Chem. Commun., 2006, 3978–3980; (b) S. Nagendran, S. S. Sen, H. W. Roesky, D. Koley, H. Grubmüller, A. Pal and R. Herbst-Irmer, Organometallics, 2008, 27, 5459–5463; (c) C. Jones, S. J. Bonyhady, N. Holzmann, G. Frenking and A. Stasch, Inorg. Chem., 2011, 50, 12315–12325; (d) W.-P. Leung, W.-K. Chiu, K.-H. Chong and T. C. W. Mak, Chem. Commun., 2009, 6822–6824; (e) J. Fan, S. Quek, M.-C. Yang, Z.-F. Zhang, M.-D. Su and C.-W. So, Chem. Commun., 2022, 58, 1033–1036; (f) A. Caise, L. P. Griffin, A. Heilmann, C. McManus, J. Campos and S. Aldridge, Angew. Chem., Int. Ed., 2021, 60, 15606–15612; (g) M. Novak, M. Bouska, L. Dostal, A. Ruzicka, A. Hoffmann, S. Herres-Pawlis and R. Jambor, Chem. – Eur. J., 2015, 21, 7820–7829; (h) S.-P. Chia, H.-X. Yeong and C.-W. So, Inorg. Chem., 2012, 51, 1002–1010; (i) H. H. Karsch, B. Deubelly, J. Riede and G. Müller, Angew. Chem., Int. Ed., 2003, 26, 673–674; (j) C. J. Miller, U. Chadha, J. R. Ulibarri-Sanchez, D. A. Dickie and R. A. Kemp, Polyhedron, 2016, 114, 351–359.
5. Y. T. Wey, F. S. Yang, H. C. Yu, T. S. Kuo and Y. C. Tsai, Angew. Chem., Int. Ed., 2017, 56, 15108–15112.
6. V. A. Beland, Z. Wang, C. L. B. Macdonald, T. K. Sham and P. J. Ragogna, Chem. – Eur. J., 2019, 25, 14790–14800.
7. W. Wang, S. Inoue, S. Yao and M. Driess, Chem. Commun., 2009, 2661–2663.
8. (a) G. Prabusankar, A. Sathyanarayana, P. Suresh, C. Naga Babu, K. Srinivas and B. P. R. Metla, Coord. Chem. Rev., 2014, 269, 96–133; (b) V. Nesterov, D. Reiter, P. Bag, P. Frisch, R. Holzner, A. Porzelt and S. Inoue, Chem. Rev., 2018, 118, 9678–9842; (c) Y. Wang and G. H. Robinson, J. Am. Chem. Soc., 2023, 145, 5592–5612.
9. Y. Xiong, S. Yao, T. Szilvasi, E. Ballestero-Martinez, H. Grutzmacher and M. Driess, Angew. Chem., Int. Ed., 2017, 56, 4333–4336.
10. Z. Dong, J. M. Winkler, M. Schmidtmann and T. Müller, Chem. Sci., 2021, 12, 6287–6292.
11. S. Kundu, P. P. Samuel, A. Luebben, D. M. Andrada, G. Frenking, B. Dittrich and H. W. Roesky, Dalton Trans., 2017, 46, 7947–7952.
12. (a) G. H. Spikes and P. P. Power, Chem. Commun., 2007, 85–87; (b) Y. Peng, R. C. Fischer, W. A. Merrill, J. Fischer, L. Pu, B. D. Ellis, J. C. Fettinger, R. H. Herber and P. P. Power, Chem. Sci., 2010, 1, 461–468.
13. (a) C. Cui, M. M. Olmstead, J. C. Fettinger, G. H. Spikes and P. P. Power, J. Am. Chem. Soc., 2005, 127, 17530–17541; (b) G. H. Spikes, J. C. Fettinger and P. P. Power, J. Am. Chem. Soc., 2005, 127, 12232–12233; (c) T. Sugahara, J.-D. Guo, T. Sasamori, Y. Karatsu, Y. Furukawa, A. E. Ferao, S. Nagase and N. Tokitoh, Bull. Chem. Soc. Jpn., 2016, 89, 1375–1384.
14. (a) W.-P. Leung, W.-K. Chiu and T. C. W. Mak, Organometallics, 2014, 33, 225–230; (b) S. S. Sen, D. Kratzert, D. Stern, H. W. Roesky and D. Stalke, Inorg. Chem., 2010, 49, 5786–5788.
15. (a) J. Li, C. Schenk, C. Goedecke, G. Frenking and C. Jones, J. Am. Chem. Soc., 2011, 133, 18622–18625; (b) J. A. Kelly, M. Juckel, T. J. Hadlington, I. Fernandez, G. Frenking and C. Jones, Chem. – Eur. J., 2019, 25, 2773–2785; (c) J. Li, M. Hermann, G. Frenking and C. Jones, Angew. Chem., Int. Ed., 2012, 51, 8611–8614; (d) T. J. Hadlington, J. Li, M. Hermann, A. Davey, G. Frenking and C. Jones, Organometallics, 2015, 34, 3175–3185.
16. (a) B. Royo and E. Peris, Eur. J. Inorg. Chem., 2012, 2012, 1309–1318; (b) S. P. Downing and A. A. Danopoulos, Organometallics, 2006, 25, 1337–1340; (c) K. J. Evans and S. M. Mansell, Chem. – Eur. J., 2019, 25, 3766–3769.
17. (a) S. Mondal, T. Singh, S. Baguli, S. Ghosh and D. Mukherjee, Chem. – Eur. J., 2023, 29, e202300508; (b) S. Mondal, S. Sarkar, D. Mallick and D. Mukherjee, Polyhedron, 2024, 251, 116849; (c) S. Mondal, S. Sarkar, C. Mandal, D. Mallick and D. Mukherjee, Chem. Commun., 2024, 60, 4553–4556.
18. C. Jones, Nat. Rev. Chem., 2017, 1, 0059.
19. S. Barriga, Synlett, 2001, 0563.
20. (a) G. H. Spikes, Y. Peng, J. C. Fettinger, J. Steiner and P. P. Power, Chem. Commun., 2005, 6041–6043; (b) M. Novak, T. Mikysek, A. Ruzicka, L. Dostal and R. Jambor, Chem. – Eur. J., 2018, 24, 1104–1111.
21. P. K. Dutta, A. K. Asatkar, S. S. Zade and S. Panda, Dalton Trans., 2014, 43, 1736–1743.
22. (a) E. N. Nikolaevskaya, M. A. Syroeshkin, M. P. Egorov and S. S. Karlov, Coord. Chem. Rev., 2025, 530, 216469; (b) N. Weyer, R. Guthardt, B. A. Correia Bicho, J. Oetzel, C. Bruhn and U. Siemeling, Z. Anorg. Allg. Chem., 2019, 645, 188–197; (c) J. Böserle, M. Alonso, R. Jambor, A. Růžička and L. Dostál, RSC Adv., 2016, 6, 19377–19388; (d) A. Pop, L. Wang, V. Dorcet, T. Roisnel, J.-F. Carpentier, A. Silvestru and Y. Sarazin, Dalton Trans., 2014, 43, 16459–16474; (e) S. R. Foley, G. P. A. Yap and D. S. Richeson, J. Chem. Soc., Dalton Trans., 2000, 1663–1668.
23. (a) M. M. D. Roy, A. A. Omaña, A. S. S. Wilson, M. S. Hill, S. Aldridge and E. Rivard, Chem. Rev., 2021, 121, 12784–12965; (b) S. K. Mandal and H. W. Roesky, Acc. Chem. Res., 2012, 45, 298–307; (c) T. J. Hadlington, M. Driess and C. Jones, Chem. Soc. Rev., 2018, 47, 4176–4197; (d) L. W. Pineda, V. Jancik, K. Starke, R. B. Oswald and H. W. Roesky, Angew. Chem., Int. Ed., 2006, 45, 2602–2605; (e) S. L. Choong, W. D. Woodul, C. Schenk, A. Stasch, A. F. Richards and C. Jones, Organometallics, 2011, 30, 5543–5550; (f) S. M. Al-Rafia, R. McDonald, M. J. Ferguson and E. Rivard, Chem. – Eur. J., 2012, 18, 13810–13820; (g) S. Khan, P. P. Samuel, R. Michel, J. M. Dieterich, R. A. Mata, J.-P. Demers, A. Lange, H. W. Roesky and D. Stalke, Chem. Commun., 2012, 48, 4890–4892; (h) Y. Xiong, T. Szilvási, S. Yao, G. Tan and M. Driess, J. Am. Chem. Soc., 2014, 136, 11300–11303; (i) T. J. Hadlington, B. Schwarze, E. I. Izgorodina and C. Jones, Chem. Commun., 2015, 51, 6854–6857; (j) A. R. Leverett, V. Diachenko, M. L. Cole and A. I. McKay, Dalton Trans., 2019, 48, 13197–13204; (k) J. Tremmel, J. Tydlitat, L. Dostal, A. Ruzicka, X. Deraet, J. Turek and R. Jambor, Chem. – Eur. J., 2020, 26, 6070–6075; (l) M. Auer, F. Diab, K. Eichele, H. Schubert and L. Wesemann, Dalton Trans., 2022, 51, 5950–5961.
24. (a) T. A. Engesser, M. R. Lichtenthaler, M. Schleep and I. Krossing, Chem. Soc. Rev., 2016, 45, 789–899; (b) H. Fang, Z. Wang and X. Fu, Coord. Chem. Rev., 2017, 344, 214–237; (c) R. J. Mangan, A. R. Davies, J. Hicks, C. P. Sindlinger, A. L. Thompson and S. Aldridge, Polyhedron, 2021, 196, 115006; (d) X. Zhou, P. Vasko, J. Hicks, M. Á. Fuentes, A. Heilmann, E. L. Kolychev and S. Aldridge, Dalton Trans., 2020, 49, 9495–9504; (e) R. J. Mangan, A. Rit, C. P. Sindlinger, R. Tirfoin, J. Campos, J. Hicks, K. E. Christensen, H. Niu and S. Aldridge, Chem. – Eur. J., 2020, 26, 306–315; (f) D. Paul, F. Heins, S. Krupski, A. Hepp, C. G. Daniliuc, K. Klahr, J. Neugebauer, F. Glorius and F. E. Hahn, Organometallics, 2017, 36, 1001–1008; (g) K. Inomata, T. Watanabe, Y. Miyazaki and H. Tobita, J. Am. Chem. Soc., 2015, 137, 11935–11937; (h) A. Rit, R. Tirfoin and S. Aldridge, Angew. Chem., Int. Ed., 2016, 55, 378–382.
25. (a) Z. Dong, L. Albers, M. Schmidtmann and T. Muller, Chem. – Eur. J., 2019, 25, 1098–1105; (b) N. Zhao, J. Zhang, Y. Yang, G. Chen, H. Zhu and H. W. Roesky, Organometallics, 2013, 32, 762–769; (c) L. Álvarez-Rodríguez, J. A. Cabeza, P. García-Álvarez and D. Polo, Organometallics, 2015, 34, 5479–5484; (d) R. K. Raut and M. Majumdar, Chem. Commun., 2017, 53, 1467–1469.
26. J. Hicks, M. Juckel, A. Paparo, D. Dange and C. Jones, Organometallics, 2018, 37, 4810–4813.
27. G. R. Fulmer, A. J. M. Miller, N. H. Sherden, H. E. Gottlieb, A. Nudelman, B. M. Stoltz, J. E. Bercaw and K. I. Goldberg, Organometallics, 2010, 29, 2176–2179.
28. (a) CCDC 2480685: Experimental Crystal Structure Determination, 2025,  DOI:10.5517/ccdc.csd.cc2p8c3g; (b) CCDC 2480687: Experimental Crystal Structure Determination, 2025,  DOI:10.5517/ccdc.csd.cc2p8c5j; (c) CCDC 2480688: Experimental Crystal Structure Determination, 2025,  DOI:10.5517/ccdc.csd.cc2p8c6k; (d) CCDC 2480686: Experimental Crystal Structure Determination, 2025,  DOI:10.5517/ccdc.csd.cc2p8c4h; (e) CCDC 2480683: Experimental Crystal Structure Determination, 2025,  DOI:10.5517/ccdc.csd.cc2p8c1d.

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