The branched oligogermanium hydride (Ph3Ge)3GeH was synthesized via a hydrogermolysis reaction from GeH4 and Ph3GeNMe2 and was converted to the halide series of compounds (Ph3Ge)3GeX (X = Cl, Br, I) upon reaction with [Ph3C][PF6] in CH2X2 solvent (X = Cl, Br, I). These species were fully characterized by NMR (1H and 13C) and UV/visible spectroscopy, cyclic voltammetry, and elemental analysis. In addition, (Ph3Ge)3GeH was analyzed by 73Ge NMR spectroscopy and exhibits two resonances at δ −56 and −311 ppm. A Ge−H coupling constant of 191 Hz was observed in the proton-coupled 73Ge NMR spectrum of (Ph3Ge)3GeH. The X-ray crystal structures of (Ph3Ge)3GeH and (Ph3Ge)3GeX (X = Cl, Br, I) were obtained and represent the first examples of branched oligogermane hydrides or halides to be characterized in this fashion. The Ge−Ge bond distances in (Ph3Ge)3GeH are short (average value 2.4310(5) Å), while those in the halide compounds (Ph3Ge)3GeX are similar to one another and range from 2.4626(7) to 2.4699(5) Å. The UV/visible and cyclic voltammetry data for these species have been correlated with DFT computations, and excellent agreement was found between the experimental and theoretical data.

A series of rhenium tricarbonyl complexes coordinated by asymmetric diimine ligands containing a pyridine moiety bound to an oxazoline ring were synthesized, structurally and electrochemically characterized, and screened for CO reduction ability. The reported complexes are of the type Re(N-N)(CO)Cl, with N-N = 2-(pyridin-2-yl)-4,5-dihydrooxazole (1), 5-methyl-2-(pyridin-2-yl)-4,5-dihydrooxazole (2), and 5-phenyl-2-(pyridin-2-yl)-4,5-dihydrooxazole (3). The electrocatalytic reduction of CO by these complexes was observed in a variety of solvents and proceeds more quickly in acetonitrile than in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). The analysis of the catalytic cycle for electrochemical CO reduction by 1 in acetonitrile using density functional theory (DFT) supports the C-O bond cleavage step being the rate-determining step (RDS) (ΔG = 27.2 kcal mol). The dependency of the turnover frequencies (TOFs) on the donor number (DN) of the solvent also supports that C-O bond cleavage is the rate-determining step. Moreover, the calculations using explicit solvent molecules indicate that the solvent dependence likely arises from a protonation-first mechanism. Unlike other complexes derived from fac-Re(bpy)(CO)Cl (I; bpy = 2,2'-bipyridine), in which one of the pyridyl moieties in the bpy ligand is replaced by another imine, no catalytic enhancement occurs during the first reduction potential. Remarkably, catalysts 1 and 2 display relative turnover frequencies, (i/i), up to 7 times larger than that of I.

We have employed the hydrogermolysis reaction for the preparation of rare branched oligogermanes, and have obtained for the first time the X-ray crystal structures of several the ethoxyethyl substituent serves as a protecting group for a germanium-hydride active site. These reagents have been employed for the stepwise synthesis of higher branched systems having up to 13 bonded germanium atoms in the oligomer backbone. The synthesis, structures, and physical characteristics of these systems are described.

The syntheses of two linear oligogermanes, Ph3GeGePh2GePh2GePh2H and Ge5Ph12, were achieved using a hydrogermolysis reaction starting with HPh2GeGePh2GePh2H. The preparation of the hydride-terminated tetragermane indicates that selectivity is possible using the hydrogermolysis reaction, which had not been observed previously. The structures of both of these compounds were determined, and they were also characterized by UV/visible spectroscopy and electrochemical methods (CV and DPV). The pentagermane Ge5Ph12 exhibits four irreversible oxidation waves in both its CV and DPV, as was observed for other aryl-substituted oligogermanes. The successful synthesis of the neopentane analogue (Ph3Ge)4Ge was also achieved by starting from GeH4 and Ph3GeCH2CN. This material was structurally characterized; the structure of (Ph3Ge)4Ge is highly sterically congested and contains long Ge–Ge single-bond distances that average 2.497(6) Å and exhibits an nearly idealized tetrahedral geometry at the central germanium atom with an average Ge–Ge–Ge bond angle of 109.49(2)°. The UV/visible spectrum of (Ph3Ge)4Ge exhibits a broad absorbance maximum centered at 250 nm, and DFT calculations indicate that this compound has a stabilized HOMO at −6.223 eV and a large HOMO–LUMO gap relative to those in other branched oligogermanes.

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