Rhenium-Germanium Triple Bonds: Syntheses and Reactions of the Germylidyne Complexesmer-[X2(PMe3)3ReGeR] (X=Cl, I, H; R=m-terphenyl)

A general approach to the first compounds that contain rhenium-germanium triple and double bonds is reported. Heating [ReCl(PMe3)5] (1) with the arylgermanium(II) chloride GeCl(C6H3-2,6-Trip2) (2; Trip=2,4,6-triisopropylphenyl) results in the germylidyne complex mer-[Cl2 (PMe3)3Re≡Ge-C6H3-2,6-Trip2] (4) upon PMe3 elimination. An equilibrium that is dependent on the PMe3 concentration exists between complexes 1 and 4. Removal of the volatile PMe3 shifts the equilibrium towards complex 4, whereas treatment of 4 with an excess of PMe3 gives a 1:1 mixture of 1 and the PMe3 adduct of 2, GeCl(C6H3-2,6-Trip2)(PMe3) (2-PMe3). Adduct 2-PMe3 can be selectively obtained by addition of PMe3 to chlorogermylidene 2. The NMR spectroscopic data for 2-PMe3 indicate an equilibrium between 2-PMe3 and its dissociation products, 2 and PMe3 , which is shifted far towards the adduct site at ambient temperature. NMR spectroscopic monitoring of the reaction of complex 1 with 2 and the reaction of complex 4 with PMe3 revealed the formation of two key intermediates, which were identified to be the chlorogermylidene complexes cis/trans-[Cl(PMe3)4 Re=Ge(Cl)C6H3-2,6-Trip2] (cis/trans-3) by using NMR spectroscopy. Labile chlorogermylidene complexes cis/trans-3 can be also generated from trans-[Cl(PMe3)4 Re≡Ge-C6H3-2,6-Trip2]BPh4 (9) and (nBu4N)Cl at low temperature, and decompose at ambient temperature to give a mixture of complexes 1 and 4. Complex 4 reacts with LiI to give the diiodido derivative mer-[I2(PMe3)3Re≡Ge-C6H3-2,6-Trip2] (5), which undergoes a metathetical iodide/hydride exchange with Na(BEt3H) to give the dihydrido germylidyne complex mer-[H2(PMe3)3Re≡Ge-C6H3-2,6-Trip2] (6). Carbonylation of 4 induces a chloride migration from rhenium to the germanium atom to afford the chlorogermylidene complex mer-[Cl(CO)(PMe3)3Re=Ge(Cl)C6H3-2,6-Trip2] (7). Similarly, MeNC converts complex 4 into the methylisocyanide analogue mer-[Cl(MeNC)(PMe3)3Re=Ge(Cl)C6H3-2,6-Trip2] (8). Chloride abstraction from 4 by NaBPh4 in the presence of PMe3 gives the cationic germylidyne complex trans-[Cl(PMe3)4 Re≡Ge-C6H3-2,6-Trip2]BPh4 (9). Heating complex 4 with cis-[Mo(PMe3)4(N2)2] induces a germylidyne ligand transfer from rhenium to molybdenum to afford the germylidyne complex trans-[Cl(PMe3)4Mo≡Ge-C6H3-2,6-Trip2] (10). All new compounds were fully characterized and their molecular structures studied by X-ray crystallography, which led to the first experimentally determined Re-Ge triple- and double-bond lengths.