Synthesis of bismuthanyl-substituted monomeric triel hydrides

Abstract

The syntheses and characterizations of the first bismuthanylborane monomers stabilized only by a donor in D·BH₂Bi(SiMe₃)₂ (D = DMAP 1a, IDipp 1b, IMe₄1c; DMAP = 4-dimethylaminopyridine, IDipp = 1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene, IMe₄ = 1,3,4,5-tetramethylimidazol-2-ylidene) are presented. All compounds were synthesized by salt metathesis reactions between D·BH₂I and KBi(SiMe₃)₂(THF)_0.3 and represent some of the extremely rare compounds featuring a 2c–2e B–Bi bond in a molecular compound. The products display high sensitivity towards air and light and slowly decompose in solution even at −80 °C. By the reaction of IDipp·GaH₂(SO₃CF₃) with KBi(SiMe₃)₂(THF)_0.3, the synthesis of the first bismuthanylgallane IDipp·GaH₂Bi(SiMe₃)₂ (2) stabilized only by a 2-electron donor was possible, as evident from single crystal X-ray structure determination, NMR spectroscopy and mass spectrometry. Computational studies shed light on the stability of the products and the electronic nature of the compounds.

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The attention paid to the chemistry of bismuth has increased tremendously within the last decade.^1–4 As bismuth can adopt all oxidation states from +V to −III and can often feature a stereoactive 6s atomic orbital, it is capable of extraordinary structural diversity. What is more, strong spin–orbit coupling and relativistic effects influence the chemical and physical properties of bismuth compounds.⁵ Prominent representatives for this flexibility are e.g. highly charged bismuth cluster anions.^2,6 The flexibility of binding modes makes organic and inorganic bismuth compounds very useful reagents. E.g. inorganic salts BiX₃ (X = Hal, OTf, NO₃; OTf = SO₃CF₃) have been commonly employed in organic transformations either stoichiometrically or catalytically.⁷

In addition, more and more new bismuth-based catalyst systems have recently been developed, capable of impressive organic transformations.^3,8 For instance, the Cornella group has pushed the boundaries of bismuth-catalysed organic transformations ranging from transfer hydrogenations and amide reductions to oxidative coupling reactions and many other applications.^4,9–12 Significantly, it could be demonstrated that bismuth-based catalysis not only relies on the Lewis acidic properties of Bi(III), but that the latter also displays reaction behaviour similar to regular transition metals since important steps such as single-electron transfer can also be achieved.^10–12

Important contributions to the chemistry of trivalent bismuth were also attained by Chitnis and co-workers who exploited the geometric perturbation of planar trivalent bismuthanes to achieve an unusual reactivity thanks to the steric and electronic properties of these compounds.^13,14 Furthermore, planar Bi(III) complexes proved to act as tuneable platforms for catalytic ring opening polymerizations of cyclic esters with good dispersity values and high molecular weights, with only low quantities of the corresponding bismuth triamide catalyst being needed.¹⁴ The success of Bi in catalysis is based on rather strong Bi–C bonds, whereas Bi–triel bonds (triel = group 13 element) often suffer weak bonding because of rather low bond dissociation enthalpies. Thus, isolated examples of such compounds are quite rare, especially when heavy triels come into play. Therefore, such compounds are often unstable and difficult to isolate without prior decomposition.

To the best of our knowledge, the only examples of isolable compounds featuring covalent B–Bi compounds are found in a boryldiphenylbismuthane (Fig. 1, I)¹⁵ as well as in a boryl-dibismuthene (Fig. 1, II).¹⁶ Here, the B atom is incorporated in a stabilizing cycle. The von Hänisch group made important contributions to the field of covalent bismuth compounds and could obtain several highly sensitive interpnictogen chain compounds that include bismuth.¹⁷ This group was recently also able to report on donor-free bismuth cations capable of intriguing reactivity.¹⁸ The group of S. Schulz further advanced this field by the activation of bismuthanes with monovalent group 13 compounds of (Dipp₂Nacnac)M (dipp = 2,6 diisopropylphenyl, M = Al, Ga, In; Fig. 1, IIIa–c, IVa).¹⁹ R. A. Fischer and co-workers reported similar dibismuthenes supported by (Dipp₂Nacnac)Ga as well as (IVb/c).²⁰ Von Hänisch and co-workers were able to synthesize similar compounds by a related strategy (Fig. 1, V, VI, VIIa/b).²¹ Again, also in these compounds, the group 13 element is embedded in a cyclic system. Very recently, the groups of Coles and McMullin synthesized a unique bicyclic-like compound featuring a covalent 2c–2e In–Bi bond (Fig. 1, VIII).²² However, in all reports about Bi–triel bonded compounds, none of the mentioned examples contained parent H-substituted triel moieties and they were all embedded in chain compounds.

Fig. 1 Selected examples of stabilization motifs of molecular 13/15 compounds featuring E–Bi bonds in (a) cyclic systems, (b) stabilized by β-diketiminates and (c) in bicyclic systems (Mes = 2,4,6-trimethylphenyl, dipp = 2,6-diisopropylphenyl, E = triel, Nacnac = bis(2,6-diaryl)-2,2'dimethyl-β-diketiminate); (d) bismuthanyl-substituted triel hydrides presented in this work.

Our group is interested in the stabilization of parent group 13/15 element compounds stabilized only by Lewis acids or bases, which can be used e.g. as building blocks for selective oligo- and polymerization reactions.²³ These monomers are usually synthesized by salt metathesis or hydrogen elimination reactions and show interesting reactivities towards electrophiles and nucleophiles.²⁴ The group 15 element within such compounds also enables a broad range of coordination possibilities,^25,26 even leading to promising luminescent materials.²⁶ By varying the group 15 element, the parent phosphanyl-, arsanyl- as well as stibanylboranes stabilized only by one donor molecule D·BH₂PnH₂ (Pn = P, As, Sb) could be accessed.^27,28 The corresponding phosphanyl- and arsanylgallanes and -alanes IDipp·EH₂PnH₂ (E = Ga, Al; Pn = P, As) were also recently obtained, but only with the support of a bulky N-heterocyclic carbene (NHC) as donor.^29,30 Higher degrees of substitution at the group 13 entities could also be achieved by multiple salt metatheses, leading to the compounds IDipp·EH_3−x(PnH₂)_x (x = 2, 3) and even the triphosphanylindiumane IDipp·In(PH₂)₃.^30,31

Whereas phosphanyl-, arsanyl- and stibanylboranes have already been synthesized, the synthesis of the homologous bismuthanylboranes has so far not been realized. So, the question is whether such compounds are accessible and, if so, whether it is possible to synthesize even the parent compounds. Herein, we report on the synthesis of the first chain-like, donor-stabilized bismuthanylboranes featuring covalent 2c–2e electron B–Bi bonds which contain unique BH₂-moieties as well as on the isolation of an unprecedented bismuthanylgallane, making each of them the first representatives of their particular kinds.

The first step was to target the synthesis of a suitable bismuth source to use it to prepare the donor-stabilized bismuthanylboranes. As salt metathesis presents a reliable pathway towards this type of 13/15 compounds, we started off by investigating the salt metathesis of D·BH₂I with an alkali metal bismuthanide. Unfortunately, MBiH₂ (M = alkali metal) remains inaccessible so that we decided to introduce SiMe₃ groups by using MBi(SiMe₃)₂,³² which offers the possibility towards future Bi–Si bond cleavage. KBi(SiMe₃)₂(THF)_0.3 was prepared by the reaction of Bi(SiMe₃)₃ with KO^tBu in THF (cf. ESI‡).

Subsequently, this reagent was reacted with iodinated donor-stabilized boranes D·BH₂I (D = IDipp, IMe₄ (=1,3,4,5-tetramethylimidazol-2-ylidene), DMAP) by adding neat KBi(SiMe₃)₂(THF)_0.3 to a cold solution (−80 °C) of the corresponding boranes in THF under exclusion of light (eqn (1)). Upon reaching room temperature, full conversion of the starting materials is achieved according to NMR spectroscopy. After extraction with toluene, the donor-stabilized bismuthanylboranes D·BH₂Bi(SiMe₃)₂ (1a: D = IDipp, 1b: D = IMe₄, 1c D = DMAP) were obtained in moderate to good yields. The compounds are obtained as grey powders, which display very high sensitivity towards air and light and decompose at room temperature under visible deposition of elemental bismuth. A very slow decomposition occurs even upon prolonged storage at −30 °C, complicating the storage of the solid products for longer than a month.

Decomposition in solution happens even faster and at temperatures as low as −80 °C, with 1c displaying the highest tendency towards decomposition. Presumably, the donor strength of NHCs significantly contributes to the overall better kinetic and thermodynamic stability of the compounds which keeps the molecules intact. This is further supported by quantum chemical calculations (vide infra), which show a higher dissociation energy for the NHC adducts 1a and 1b. Furthermore, this is in line with the isolated yields from the reactions (cf.eqn (1)). The NMR spectra of solutions of 1a–c in C₆D₆ show characteristic triplet resonances in the ¹¹B NMR spectra and singlets (Si(CH₃)₃) as well as broadened quartets (BH₂) in the ¹H NMR spectra (cf.Table 1). Moreover, 1a and 1b could also be characterized by their molecular ion peaks at m/z = 756.44 (1a) and m/z = 492.20 (1b) in the LIFDI mass spectra. It was also possible to crystallize all bismuthanylboranes 1a–c by storing saturated solutions in n-hexane (1b) or toluene (1c) at −30 °C overnight or slow evaporation (1a) of n-pentane at −30 °C. By single-crystal X-ray structure determination, the structures in the solid state could be elucidated (Fig. 2).

Table 1 Characteristic NMR signals of compounds 1a–2 [ppm] (C₆D₆, 298 K; s = singlet, t = triplet, br = broadened)

NMR spectrum	1a	1b	1c	2
^1H Si(CH3)3 signal	0.53, s	0.81, s	0.95, s	0.70, s
^1H EH2 signal (E = B, Ga)	2.24, q, br ^1JBH = 100 Hz	2.43, q, br ^1JBH = 107 Hz	4.74, q, br ^1JBH = 120 Hz	4.97, s, br
^11B{^1H}	−42.1, s, br	−39.5, s, br	−15.4, s, br	—
^11B	−42.1, t, br ^1JBH = 100 Hz	−39.5, t, br ^1JBH = 107 Hz	−15.2, t, br ^1JBH = 120 Hz	—

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Fig. 2 Molecular structures of 1a, 1b and 1c in the solid state. Anisotropic displacement ellipsoids are shown at 50% probability level. Hydrogen atoms bound to carbon are omitted for clarity. Dipp groups are displayed as stick models for improved clarity. Selected bond lengths and angles: 1a C40–B2 1.587(7), B2–Bi2 2.424(5), Bi2–Si2 2.639(4), Bi2–Si3 2.6494(15), C40–B2–Bi2 110.9(3), B2–Bi2–Si2 90.86(15), B2–Bi2–Si3 97.09(14). 1b C1–B1 1.569(9), B1–Bi1 2.442(7), Bi1–Si1 2.6278(17), Bi1–Si2 2.6452(18), C1–B1–Bi1 107.2(4), B1–Bi1–Si1 89.12(18), B1–Bi1–Si2 97.05(19). 1c N1–B1 1.578(5), B1–Bi1 2.424(5), Bi1–Si1 2.6331(9), Bi1–Si2 2.6322(11), N1–B1–Bi1 106.9(2), B1–Bi1–Si1 94.53(10), B1–Bi1–Si2 100.10(12).

1a and 1b show eclipsed conformations at the chain positions, whereas 1c is arranged in a gauche conformation (cf.Fig. 2 and 3). All atoms within the core structure motifs are bound in a (pseudo)tetrahedral manner, with the B–Bi–Si bond angles bent at almost 90° as a result of very poor s–p orbital mixing (1a: 90.83(13)° & 97.10(12)°; 1b: 89.12(18)° & 97.05(19)°, 1c: 94.53(10)° & 100.10(12)°), which is significantly lower than for the lighter homologs (cf. Me₃N·BH₂P(SiMe₃)₂: Si–P–B 102.30(8)°).²⁸

Fig. 3 Structural features derived by X-ray crystallographic structure determination of 1a–c including key bond distances [Å] and angles (top). Bottom: Newman projections along the B–Bi σ-bonds alongside the corresponding dihedral angles.

The B–Bi bond distances of 1a–c are between 2.423(4) Å and 2.442(7) Å and represent the first known examples of B–Bi 2c–2e bonds with tetracoordinate boron atoms within chain compounds. Compared to the B–Bi bonds in boryldiphenylbismuthane I (B–Bi: 2.343(6) Å)¹⁵ and boryldibismuthene II (B–Bi: 2.326(7)/2.317(9) Å),¹⁶ the bonds are significantly elongated due to the different electronic and steric environment of, especially, the boron atom.

The SiMe₃ groups on the Bi atom of 1a–c provided a possible opportunity to generate the only hydrogen-substituted parent compounds of 1a–c D·BH₂BiH₂ by cleavage of the SiMe₃ residues. Attempts at the cleavage of the SiMe₃ groups were performed by the addition of MeOH, mixtures of MeOH/MeONa, hexanol or KF·HF. In all cases, however, only decomposition products or unreacted starting materials could be detected. The most promising attempt was the reaction of 1a with 1,4-benzoquinone as a {SiMe₃} scavenger in the presence of MeOH-d₄ in THF (cf. ESI‡), which showed the cleavage of at least one {SiMe₃} group at the bismuth atom in the ¹H NMR spectrum of the reaction mixture. Simultaneously, besides unreacted 1a, IDipp·BH₂(OMe) and IDipp·BH₃, a new, broad signal at −31.4 ppm was detected in the ¹¹B NMR spectrum. The ²H NMR spectrum shows a broad signal at 2.96 ppm but, unfortunately, a clear identification of the product was not possible. Conceivably, IDipp·BH₂Bi(SiMe₃)_2−xD_x (x = 1–2) is formed as a transient species, but unequivocal evidence of this species could not be obtained. Hence, despite numerous efforts the parent compounds containing H₂Bi–BH₂ units have so far remained inaccessible.

After the successful synthesis of donor-stabilized bismuthanylboranes, the question arose as to whether it is also possible to synthesize the heavier gallium homolog. Thus, a reaction between IDipp·GaH₂(OTf) and KBi(SiMe₃)₂(THF)_0.3 was attempted. After cooling a solution of IDipp·GaH₂(OTf) in tetrahydrofuran to −80 °C, the solid bismuthide was added and the mixture was slowly warmed to room temperature over the course of 18 hours (eqn (2)). The ¹H NMR spectrum of the reaction mixture showed full conversion of the starting material (0.63 ppm, CD₃CN) with a characteristic singlet including ²⁹Si satellites at 0.71 ppm for the {SiMe₃} residues (18H, ²J_HSi = 7.15 Hz).

2 is extremely air-, light- and temperature-sensitive and decomposes very slowly in solution already at −80 °C under deposition to elemental bismuth and other unidentified compounds. The ¹H NMR spectra of solutions of 2 in C₆D₆ show characteristic signals at 0.70 ppm (Si(CH₃)₃) and 4.97 ppm (GaH₂; cf.Table 1). The sensitivity of 2 greatly complicates the handling of the product, but, fortunately, by slow evaporation of a solution of 2 in n-pentane under reduced pressure at −80 °C, it was possible to grow a few single crystals of 2, which were of suitable quality for single crystal X-ray structure determination (Fig. 4). 2 crystallizes in the orthorhombic space group Pbca as clear colourless plate-shaped crystals. The structure in the solid state shows (pseudo)tetrahedral geometries at the [GaH₂Bi(SiMe₃)₂] unit with a Ga–Bi bond length of 2.7234(4) Å, which is only slightly elongated compared to the Ga–Bi bond distance of 2.7171(8) Å of {(Dipp₂NacNac)GaHBiMe}₂.²¹ The C1–Ga1–Bi1 angle (110.10(8)°) indicates a tetrahedral geometry at the Ga atom while the Ga1–Bi1–Si1 (95.26(2)°) and Ga1–Bi1–Si2 (87.85(2)°) angles are significantly distorted from a regular tetrahedral binding situation. Similar to 1a and 1b, 2 is arranged in an eclipsed conformation (C1–Ga1–Bi1–Si1: 113.33(9)°). The presence of 2 could also be confirmed by mass spectrometry, as the LIFDI-MS spectrum of a solution of 2 in toluene shows a molecular ion peak at m/z = 814.34 besides the decomposition products [IDipp-H]⁺ (m/z = 389.31) and [IDipp-GaH₂]⁺ (m/z = 459.24).

Fig. 4 Molecular structure of 2 in the solid state. Anisotropic displacement ellipsoids are shown at 50% probability level. Hydrogen atoms bound to carbon are omitted for clarity. Dipp residues are depicted as stick models for better clarity. Selected bond lengths [Å] and angles [°]: N1–C1 1.352(4), N2–C1 1.357(4), C1–Ga1 2.061(3), Ga1–Bi1 2.7234(4), Bi1–Si1 2.6487(9), Bi1–Si2 2.6403(9), N1–B1–Bi1 106.9(2), N1–C1–N2 104.2(3), N1–C1–Ga1 129.2(2), C1–Ga1–Bi1 110.10(8), Ga1–Bi1–Si1 95.26(2), B1–Bi1–Si2 87.85(2).

To analyse the stability and electronic structure of all obtained products, quantum chemical calculations were performed on 1a–2 (B3LYP/def2-TZVP, ECP on Bi; cf. ESI‡). The stability with respect to the dissociation of the Lewis acid/base adducts decreases in the order of IMe₄ > IDipp > DMAP and B > Ga, which is in line with the isolated yields and the observed stabilities in solution. The standard Gibbs energy for the dissociation of 2 into IDipp and GaH₂Bi(SiMe₃)₂ is endergonic only by +27 kJ mol⁻¹, which makes this compound the least stable one within the synthesized series with respect to dissociation. Analyses of structural characteristics, NBO and Wiberg bond indices (WBIs) indicate that upon complex formation, the E–Bi bond distances increase by 0.1–0.2 Å and the WBIs of the E–Bi bonds decrease by 0.1–0.37, in line with the above-mentioned order of thermodynamic stability (cf. ESI‡). The B–Bi bond in free BH₂Bi(SiMe₃)₂ has a partial double bond character (WBI 1.21) due to the π-interaction between the lone pair of Bi (75.5% s character) and the empty orbital of boron (99.4% p-character) with an E(2) value of 3.74 kcal mol⁻¹ (Table S6 in ESI‡). In case of the gallium analogue GaH₂Bi(SiMe₃)₂, the similar π-interaction is much less pronounced (E(2) value 1.59 kcal mol⁻¹) and the WBI value is close to one. The occupancies of vacant p-orbitals on boron (0.17ē) and gallium (0.08ē) also indicate smaller involvement of the Ga atom in π-interactions with Bi. After complexation with IDipp, π-interactions between Bi–B and Bi–Ga are absent in both 1a and 2.

Regarding the methanolysis reactions of 1a–1c, the formation of IDipp·BH₂BiH₂, IMe₄·BH₂BiH₂ and DMAP·BH₂BiH₂, respectively, is predicted to be highly exothermic and exergonic by 187–206 kJ mol⁻¹, while the formed hydride compounds are predicted to be thermodynamically unstable with respect to the decomposition to LB·BH₃, H₂ and solid Bi (processes are exergonic by 120–150 kJ mol⁻¹) (cf. ESI‡).

In summary, it could be shown that the synthesis of donor-stabilized bismuthanylboranes and gallanes can be achieved by salt metathesis with KBi(SiMe₃)₂(THF)_0.3, yielding IDipp·BH₂Bi(SiMe₃)₂ (1a), IMe₄·BH₂Bi(SiMe₃)₂ (1b), DMAP·BH₂Bi(SiMe₃)₂ (1c), and IDipp·GaH₂Bi(SiMe₃)₂ (2). All compounds could be characterized by multinuclear NMR spectroscopy and LIFDI-MS. Moreover, the crystal structures of all products 1a–2 could be determined, representing the first solid-state structures of bismuthanyltrielanes that contain parent {EH₂} triel moieties and possess E–Bi σ-bonds in chain-like compounds. Specifically, 1a–c represent the first examples of structures containing covalent B–Bi σ-bonds where the boron atom is not embedded in a cyclic system. All compounds display a very high sensitivity towards air and light. Desilylation attempts have been unsuccessful, which is likely to be also due to the extreme instability of the potentially formed {BH₂BiH₂} moiety. Future investigations will focus on the reactivity of these compounds regarding catenation, coordination as well as deposition experiments.

Data availability

The data supporting this article have been included as part of the ESI.‡ CCDC-2347535 (1a), CCDC-2340840 (1b), CCDC-2340841 (1c), and CCDC-2340842 (2), contain the supplementary crystallographic data for this paper.

Author contributions

R. Szlosek performed the experimental work (incl. reproductions and analytical data of 1b and 1c), wrote the original draft, acquisition (1a, 2) and refinement (2) of X-ray data. C. Marquardt prepared 1c and acquisition/refinement of X-ray data for 1c. O. Hegen prepared 1b and acquisition/refinement of X-ray data for 1b. G. Balázs conceptualization and project management. C. Riesinger performed the refinement of X-ray data for 1a. A. Y. Timoshkin performed quantum chemical calculations, conceptualization, project management. M. Scheer wrote the original draft, supervised the project and conceptualization, funding and project management.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by a joint DFG-RSF project (DFG Sche 384/41-1, Russian Science Foundation (RSF) grant 21-43-04404). The use of computational resources of the research centre “Computing Center” of the St. Petersburg State University is acknowledged. R. S. is grateful to the Fonds der Chemischen Industrie (FCI) for a PhD fellowship. Matthias Hautmann is acknowledged for the preparation of KBi(SiMe₃)₂(THF)_0.3. Lisa Zimmermann and Dr Martin Weber are acknowledged for fruitful discussions.

Notes and references

1. (a) M. Kanatzidis, H. Sun and S. Dehnen, Inorg. Chem., 2020, 59, 3341; (b) P. Ondet, G. Lemière and E. Duñach, Eur. J. Org Chem., 2017, 2017, 761; (c) E. Lopez, S. C. Thorp and R. S. Mohan, Polyhedron, 2022, 222, 115765.
2. F. Pan, B. Peerless and S. Dehnen, Acc. Chem. Res., 2023, 56, 1018.
3. T. Ollevier, Org. Biomol. Chem., 2013, 11, 2740.
4. H. W. Moon and J. Cornella, ACS Catal., 2022, 12, 1382.
5. (a) X. Gonze, J.-P. Michenaud and J.-P. Vigneron, Phys. Scr., 1988, 37, 785; (b) A. Isaeva and M. Ruck, Inorg. Chem., 2020, 59, 3437.
6. (a) J. Heine, B. Peerless, S. Dehnen and C. Lichtenberg, Angew. Chem., Int. Ed., 2023, 62, e202218771; (b) F. Pan, S. Wei, L. Guggolz, A. R. Eulenstein, F. Tambornino and S. Dehnen, J. Am. Chem. Soc., 2021, 143, 7176; (c) A. R. Eulenstein, Y. J. Franzke, P. Bügel, W. Massa, F. Weigend and S. Dehnen, Nat. Commun., 2020, 11, 5122; (d) A. R. Eulenstein, Y. J. Franzke, N. Lichtenberger, R. J. Wilson, H. L. Deubner, F. Kraus, R. Clérac, F. Weigend and S. Dehnen, Nat. Chem., 2021, 13, 149; (e) B. Peerless, A. Schmidt, Y. J. Franzke and S. Dehnen, Nat. Chem., 2023, 15, 347.
7. (a) J. M. Bothwell, S. W. Krabbe and R. S. Mohan, Chem. Soc. Rev., 2011, 40, 4649; (b) R. Hua, Curr. Org. Synth., 2008, 5, 1.
8. (a) D. Janssen-Müller and M. Oestreich, Angew. Chem., Int. Ed., 2020, 59, 8328; (b) B. Jousseaume, C. Laporte, T. Toupance and J.-M. Bernard, Tetrahedron Lett., 2002, 43, 6305; (c) T. Kitanosono, T. Ollevier and S. Kobayashi, Chem.–Asian J., 2013, 8, 3051; (d) C. Lichtenberg, Chem. Commun., 2021, 57, 4483; (e) H. Qin, N. Yamagiwa, S. Matsunaga and M. Shibasaki, J. Am. Chem. Soc., 2006, 128, 1611; (f) H. Qin, N. Yamagiwa, S. Matsunaga and M. Shibasaki, Angew. Chem., Int. Ed., 2007, 46, 409; (g) J. Ramler, I. Krummenacher and C. Lichtenberg, Angew. Chem., Int. Ed., 2019, 58, 12924; (h) M. Rueping, B. J. Nachtsheim and W. Ieawsuwan, Adv. Synth. Catal., 2006, 348, 1033; (i) J. A. Salvador and S. M. Silvestre, Tetrahedron Lett., 2005, 46, 2581; (j) S. Vidal, Synlett, 2001, 2001, 1194; (k) N. Worz, A. Brandner and P. Claus, J. Phys. Chem. C, 2010, 114, 1164; (l) Z.-P. Zhang, N. Dong and X. Li, Chem. Commun., 2017, 53, 1301; (m) K. Zhou, W. Wang, Z. Zhao, G. Luo, J. T. Miller, M. S. Wong and F. Wei, ACS Catal., 2014, 4, 3112; (n) M. Pramanik, M. G. Guerzoni, E. Richards and R. L. Melen, Angew Chem. Int. Ed. Engl., 2024, 63, e202316461; (o) M. Mato and J. Cornella, Angew. Chem., Int. Ed., 2024, 63, e202315046.
9. (a) M. Magre and J. Cornella, J. Am. Chem. Soc., 2021, 143, 21497; (b) M. Magre, J. Kuziola, N. Nöthling and J. Cornella, Org. Biomol. Chem., 2021, 19, 4922; (c) Y. Pang, M. Leutzsch, N. Nöthling and J. Cornella, J. Am. Chem. Soc., 2020, 142, 19473; (d) Y. Pang, M. Leutzsch, N. Nöthling, F. Katzenburg and J. Cornella, J. Am. Chem. Soc., 2021, 143, 12487; (e) F. Wang, O. Planas and J. Cornella, J. Am. Chem. Soc., 2019, 141, 4235; (f) O. Planas, F. Wang, M. Leutzsch and J. Cornella, Science, 2020, 367, 313; (g) X. Yang, J. Kuziola, V. A. Béland, J. Busch, M. Leutzsch, J. Burés and J. Cornella, Angew. Chem., Int. Ed., 2023, e202306447; (h) X. Yang, E. J. Reijerse, K. Bhattacharyya, M. Leutzsch, M. Kochius, N. Nöthling, J. Busch, A. Schnegg, A. A. Auer and J. Cornella, J. Am. Chem. Soc., 2022, 144, 16535; (i) X. Yang, E. J. Reijerse, N. Nöthling, D. J. SantaLucia, M. Leutzsch, A. Schnegg and J. Cornella, J. Am. Chem. Soc., 2023, 145, 5618; (j) H. W. Moon, F. Wang, K. Bhattacharyya, O. Planas, M. Leutzsch, N. Nöthling, A. A. Auer and J. Cornella, Angew. Chem., Int. Ed., 2023, e202313578; (k) T. Tsuruta, D. Spinnato, H. W. Moon, M. Leutzsch and J. Cornella, J. Am. Chem. Soc., 2023, 145, 25538.
10. M. Mato, D. Spinnato, M. Leutzsch, H. W. Moon, E. J. Reijerse and J. Cornella, Nat. Chem., 2023, 15, 1138–1145.
11. O. Planas, V. Peciukenas and J. Cornella, J. Am. Chem. Soc., 2020, 142, 11382.
12. O. Planas, V. Peciukenas, M. Leutzsch, N. Nöthling, D. A. Pantazis and J. Cornella, J. Am. Chem. Soc., 2022, 144, 14489.
13. (a) S. S. Chitnis, N. Burford, A. Decken and M. J. Ferguson, Inorg. Chem., 2013, 52, 7242; (b) S. S. Chitnis, A. P. M. Robertson, N. Burford, B. O. Patrick, R. McDonald and M. J. Ferguson, Chem. Sci., 2015, 6, 6545; (c) S. S. Chitnis, K. A. Vos, N. Burford, R. McDonald and M. J. Ferguson, Chem. Commun., 2016, 52, 685; (d) T. Hynes, J. D. Masuda and S. S. Chitnis, ChemPlusChem, 2022, 87, e202200244; (e) M. B. Kindervater, T. Hynes, K. M. Marczenko and S. S. Chitnis, Dalton Trans., 2020, 49, 16072; (f) M. B. Kindervater, K. M. Marczenko, U. Werner-Zwanziger and S. S. Chitnis, Angew. Chem., Int. Ed., 2019, 58, 7850; (g) K. M. Marczenko and S. S. Chitnis, Chem. Commun., 2020, 56, 8015; (h) K. M. Marczenko, J. A. Zurakowski, M. B. Kindervater, S. Jee, T. Hynes, N. Roberts, S. Park, U. Werner-Zwanziger, M. Lumsden, D. N. Langelaan and S. S. Chitnis, Chem. - Eur. J., 2019, 25, 16414; (i) K. M. Marczenko, S. Jee and S. S. Chitnis, Organometallics, 2020, 39, 4287.
14. T. J. Hannah, W. M. McCarvell, T. Kirsch, J. Bedard, T. Hynes, J. Mayho, K. L. Bamford, C. W. Vos, C. M. Kozak, T. George, J. D. Masuda and S. S. Chitnis, Chem. Sci., 2023, 14, 4549.
15. W. Lu, H. Hu, Y. Li, R. Ganguly and R. Kinjo, J. Am. Chem. Soc., 2016, 138, 6650.
16. D. Dange, A. Davey, J. A. B. Abdalla, S. Aldridge and C. Jones, Chem. Commun., 2015, 51, 7128.
17. (a) T. Dunaj, K. Dollberg and C. von Hänisch, Dalton Trans., 2022, 51, 7551; (b) T. Dunaj, K. Dollberg, C. Ritter, F. Dankert and C. Hänisch, Eur. J. Inorg. Chem., 2021, 2021, 870; (c) T. Dunaj, M. Egorycheva, A. Arebi, K. Dollberg and C. von Hänisch, Z. Anorg. Allg. Chem., 2023, 649; (d) T. Dunaj and C. von Hänisch, Chem.–Eur. J., 2022, 28, e202202932; (e) C. Ritter, N. Michel, A. Rinow, B. Ringler and C. Hänisch, Eur. J. Inorg. Chem., 2021, 2021, 2514; (f) C. Ritter, F. Weigend and C. von Hänisch, Chem.–Eur. J., 2020, 26, 8536.
18. T. Dunaj, J. Schwarzmann, J. Ramler, A. Stoy, S. Reith, J. Nitzsche, L. Völlinger, C. von Hänisch and C. Lichtenberg, Chem.–Eur. J., 2023, 29, e202204012.
19. (a) C. Ganesamoorthy, D. Bläser, C. Wölper and S. Schulz, Chem. Commun., 2014, 50, 12382; (b) L. Tuscher, C. Helling, C. Wölper, W. Frank, A. S. Nizovtsev and S. Schulz, Chem.–Eur. J., 2018, 24, 3241.
20. G. Prabusankar, C. Gemel, P. Parameswaran, C. Flener, G. Frenking and R. A. Fischer, Angew. Chem., Int. Ed., 2009, 48, 5526.
21. S. Schneider and C. von Hänisch, Chem. Commun., 2022, 58, 1522.
22. M. D. Anker, A. O'Reilly, C. L. McMullin and M. P. Coles, Polyhedron, 2023, 246, 116695.
23. (a) C. Marquardt, O. Hegen, A. Vogel, A. Stauber, M. Bodensteiner, A. Y. Timoshkin and M. Scheer, Chem. - Eur. J., 2018, 24, 360; (b) M. Bodensteiner, A. Y. Timoshkin, E. V. Peresypkina, U. Vogel and M. Scheer, Chem.–Eur. J., 2013, 19, 957; (c) M. Bodensteiner, U. Vogel, A. Y. Timoshkin and M. Scheer, Angew. Chem., Int. Ed., 2009, 48, 4629; (d) C. Marquardt, T. Jurca, K.-C. Schwan, A. Stauber, A. V. Virovets, G. R. Whittell, I. Manners and M. Scheer, Angew. Chem., Int. Ed., 2015, 54, 13782; (e) C. Thoms, C. Marquardt, A. Y. Timoshkin, M. Bodensteiner and M. Scheer, Angew. Chem., Int. Ed., 2013, 52, 5150; (f) J. Braese, F. Lehnfeld, V. T. Annibale, T. Oswald, R. Beckhaus, I. Manners and M. Scheer, Chem. Eur. J., 2023, 29, e202301741.
24. (a) R. Szlosek, M. Seidl, G. Balázs and M. Scheer, Chem.–Eur. J., 2023, 29, e202301752; (b) O. Hegen, A. V. Virovets, A. Y. Timoshkin and M. Scheer, Eur. J. Inorg. Chem., 2018, 24, 16521–16525; (c) F. Lehnfeld, M. Seidl, A. Y. Timoshkin and M. Scheer, Eur. J. Inorg. Chem., 2022, 3, e202100930; (d) C. Marquardt, T. Kahoun, J. Baumann, A. Y. Timoshkin and M. Scheer, Z. Anorg. Allg. Chem., 2017, 643, 1326; (e) M. T. Ackermann, M. Seidl, F. Wen, M. J. Ferguson, A. Y. Timoshkin, E. Rivard and M. Scheer, Chem. - Eur. J., 2022, 28, e20210370; (f) C. Marquardt, G. Balázs, J. Baumann, A. V. Virovets and M. Scheer, Chem.–Eur. J., 2017, 23, 11423; (g) C. Marquardt, C. Thoms, A. Stauber, G. Balázs, M. Bodensteiner and M. Scheer, Angew. Chem., Int. Ed., 2014, 53, 3727; (h) M. Elsayed Moussa, T. Kahoun, M. T. Ackermann, M. Seidl, M. Bodensteiner, A. Y. Timoshkin and M. Scheer, Organometallics, 2022, 41, 1572; (i) C. Marquardt, T. Kahoun, A. Stauber, G. Balázs, M. Bodensteiner, A. Y. Timoshkin and M. Scheer, Angew. Chem., Int. Ed., 2016, 55, 14828; (j) C. Marquardt, O. Hegen, T. Kahoun and M. Scheer, Chem.–Eur. J., 2017, 23, 4397; (k) U. Vogel, A. Y. Timoshkin and M. Scheer, Angew. Chem., Int. Ed., 2001, 40, 4409; (l) U. Vogel, P. Hoemensch, K.-C. Schwan, A. Y. Timoshkin and M. Scheer, Chem.–Eur. J., 2003, 9, 515; (m) F. Lehnfeld, M. Seidl, A. Y. Timoshkin and M. Scheer, Eur. J. Inorg. Chem., 2022, 3, e202100930; (n) A. Adolf, M. Zabel and M. Scheer, Eur. J. Inorg. Chem., 2007, 2007, 2136; (o) F. Lehnfeld, M. Seidl, A. Timoshkin and M. Scheer, Eur. J. Inorg. Chem., 2023, 26, e202300338; (p) R. Szlosek, A. S. Niefanger, G. Balázs, M. Seidl, A. Y. Timoshkin and M. Scheer, Chem.–Eur. J., 2024, 30, e202303603.
25. (a) A. Besson, C. R., 1890, 516; (b) M. Elsayed Moussa, J. Braese, C. Marquardt, M. Seidl and M. Scheer, Eur. J. Inorg. Chem., 2020, 26, 2501; (c) M. Elsayed Moussa, C. Marquardt, O. Hegen, M. Seidl and M. Scheer, New J. Chem., 2021, 45, 14916; (d) K.-C. Schwan, A. Adolf, M. Bodensteiner, M. Zabel and M. Scheer, Z. Anorg. Allg. Chem., 2008, 634, 1383; (e) R. Szlosek, M. T. Ackermann, C. Marquardt, M. Seidl, A. Y. Timoshkin and M. Scheer, Chem.–Eur. J., 2023, 29, e202202911.
26. J. Braese, A. Schinabeck, M. Bodensteiner, H. Yersin, A. Y. Timoshkin and M. Scheer, Chem.–Eur. J., 2018, 24, 10073.
27. (a) K.-C. Schwan, A. Y. Timoshkin, M. Zabel and M. Scheer, Chem.–Eur. J., 2006, 12, 4900; (b) C. Marquardt, O. Hegen, M. Hautmann, G. Balázs, M. Bodensteiner, A. V. Virovets, A. Y. Timoshkin and M. Scheer, Angew. Chem., Int. Ed., 2015, 54, 13122.
28. C. Marquardt, A. Adolf, A. Stauber, M. Bodensteiner, A. V. Virovets, A. Y. Timoshkin and M. Scheer, Chem. - Eur. J., 2013, 19, 11887.
29. M. A. K. Weinhart, A. S. Lisovenko, A. Y. Timoshkin and M. Scheer, Angew. Chem., Int. Ed., 2020, 59, 5541.
30. M. A. K. Weinhart, M. Seidl, A. Y. Timoshkin and M. Scheer, Angew. Chem., 2021, 133, 3850.
31. R. Szlosek, M. A. K. Weinhart, G. Balázs, M. Seidl, L. Zimmermann and M. Scheer, Chem.–Eur. J., 2023, 29, e202300340.
32. K. Dollberg, A. Marx, R.-M. Richter, L. Erlemeier, T. Dunaj, F. Weigend and C. von Hänisch, Chem.–Eur. J., 2024, 30, e202303734.

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Footnotes

† In memoriam on Ian Manners.

‡ Electronic supplementary information (ESI) available. CCDC 2347535 and 2340840–2340842. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d4sc03926b

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