Molecular Alloys, Linking Organometallics with Intermetallic Hume-Rothery Phases: The Highly Coordinated Transition Metal Compounds [M(ZnR)n] (n ≥ 8) Containing Organo-Zinc Ligands

This paper presents the preparation, characterization and bonding analyses of the closed shell 18 electron compounds [M(ZnR)(n)] (M = Mo, Ru, Rh, Ni, Pd, Pt, n = 8-12), which feature covalent bonds between n one-electron organo-zinc ligands ZnR (R = Me, Et, eta(5)-C-5(CH3)(5) = Cp*) and the central metal M. The compounds were obtained in high isolated yields (>80%) by treatment of appropriate GaCp* containing transition metal precursors 13-18, namely [Mo(GaCp*)(6)], [Ru-2(Ga)(GaCp*)(7)(H)(3)] or [Ru(GaCp*)(6)(Cl)(2)], [(Cp*Ga)(4)RhGa(eta(1)-Cp*)Me] and [M(GaCp*)(4)] (M = Ni, Pd, Pt) with ZnMe2 or ZnEt2 in toluene solution at elevated temperatures of 80-110 degrees C within a few hours of reaction time. Analytical characterization was done by elemental analyses (C, H, Zn, Ga), H-1 and C-13 NMR spectroscopy. The molecular structures were determined by single crystal X-ray diffraction. The coordination environment of the central metal M and the M-Zn and Zn-Zn distances mimic the situation in known solid state M/Zn Hume-Rothery phases. DFT calculations at the RI-BP86/def2-TZVPP and BP86/TZ2P+ levels of theory, AIM and EDA analyses were done with [M(ZnH)(n)] (M = Mo, Ru, Rh, Pd; n = 12,10, 9, 8) as models of the homologous series. The results reveal that the molecules can be compared to 18 electron gold clusters of the type M@Au-n, that is, W@Au-12, but are neither genuine coordination compounds nor interstitial cage clusters. The molecules are held together by strong radial M-Zn bonds. The tangential Zn-Zn interactions are generally very weak and the (ZnH)(n) cages are not stable without the central metal M.