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Molecular alloys, linking organometallics with intermetallic Hume-Rothery phases: The highly coordinated transition metal compounds [M(ZnR)<inf>n</inf>] (n ≥ 8) containing organo-zinc ligands

Abstract:

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, η5-C5(CH 3)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], [Ru2(Ga)(GaCp*)7(H)3] or [Ru(GaCp*)6(Cl)2], [(Cp*Ga) 4RhGa(η1-Cp*)Me] and [M(GaCp*) 4] (M = Ni, Pd, Pt) with ZnMe2 or ZnEt2 in toluene solution at elevated temperatures of 80-110 °C within a few hours of reaction time. Analytical characterization was done by elemental analyses (C, H, Zn, Ga), 1H and 13C 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@Aun, 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. © 2009 American Chemical Society.