Transition Metal Complexes of N-Heterocyclic Germylenes

The five-membered N-heterocyclic germylenes (NHGe) 1a-3a, with or without benzo or naphtho anellation, react with [Mo(CO)(3)(cht)] (cht = 1,3,5-cycloheptatriene) to form the fac-[(NHGe)(3)Mo(CO)(3)] complexes 1b-3b. Similarly, [Ni(bnNHGe)(4)] was obtained from the benzo-anellated germylene (bnNHGe) and Ni(1,5-cod)(2); attempts to synthesize less electron-rich complexes with mono- or divalent transition metals failed. The CO valence vibrations in the IR spectra of 1b-3b, together with their short Ge-II-Mo bonds (as determined by X-ray crystallography), hint at the weak donor and good pi-acceptor properties of the ligands. Quantum chemical studies on the benzo-anellated germylene, which are supported by the good correlation between calculated and experimental (PES) orbital ionization potentials, confirm this proposal in terms of the low energy of the Ge lone electron pair and two higher pi-MOs. The slight folding about the C-C bridging and N center dot center dot center dot N axes observed for the benzo-anellated (NHGe)molybdenum and -nickel complexes by X-ray structure analyses, may be clue to packing effects. Quantum chemical calculations on slightly bent (for dineopentyl substitution in the gas phase) and planar bnNHGe complexes show that the energy differences between the two are very small. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)