The coordination of low-valent group 13 organyls E I R [E = Al, Ga, In; R = Cp*, C(SiMe 3 ) 3 ] to transition metals has attracted increasing interest over the past decade. Complexes and cluster compounds of these new ligands with a number of transition metals have been isolated and characterised. The E I R moiety is formally isolobal with CO and PR 3 (R = alkyl, Cp*) or carbenes (R = chelating group) with varying σ-donor and π-acceptor properties depending on the organic group R

The synthesis and catalytic reactivity of a variety of new ruthenium complexes of the tris(pyrazolyl)borate ligand (HB(pz) 3 ) are reported in this paper. From the parent complex Ru(HB(pz) 3 )(COD)X (X ) Cl, Br) the cationic derivatives [Ru(HB(pz) 3 )(COD)L] + (L ) H 2 O, CH 3 CN, pyridine, dmso) have been obtained by treatment with 1 equiv of AgCF 3 SO 3 in CH 2 -Cl 2 solutions of L. Displacement of COD from these latter complexes has been accomplished in boiling dmf solutions of ligands L 2 ) Ph 2 PCH 2 PPh 2 (dppm), Ph 2 PCH 2 CH 2 NMe 2 (pn), and Me 2 NCH 2 CH 2 NMe 2 (tmeda) as well as L ) pyridine and 3-methylpyridine to give Ru(HB-(pz) 3 )(L 2 )Cl and Ru(HB(pz) 3 )(L) 2 Cl, respectively, each in high yield. From some of these complexes, in turn, the chloride ion has been abstracted with either AgCF 3 SO 3 , TlCF 3 SO 3 , or NaBPh 4 in CH 3 CN as the solvent. In this way we obtained [Ru(HB(pz) 3 )(dppm)(CH 3 -CN)]CF 3 SO 3 , [Ru(HB(pz) 3 )(pn)(CH 3 CN)]BPh 4 , and [Ru(HB(pz) 3 )(tmeda)(CH 3 CN)]BPh 4 . Selected X-ray structures are included. Some of the complexes synthesized are efficient catalysts for the formation of selectively C-O-coupled products from the reaction of phenylacetylene with either benzoic acid or allyl alcohols.

The synthesis and structural characterization of the novel homoleptic cluster complexes [Pd2(GaCp*)2(mu2-GaCp*)3] (1c), [Pd3(GaCp*)4(mu2-GaCp*)4] (2b) and [Pd3(AlCp*)2(mu2-AlCp*)2(mu3-AlCp*)2] (3) (Cp*=C5Me5) are presented. Furthermore, ligand exchange reactions of these cluster complexes are explored. In contrast to the electronically and sterically saturated complexes [M(ECp*)4] (M=Ni, Pd, Pt), the new unsaturated analogues [M(a)(ER)b] (E=Al, Ga, In) react with a variety of typical ligands (Cp*Al, CO, phosphines, isonitriles) to give new di- and tri-substituted compounds like [Pt2(GaCp*)2(mu2-AlCp*)3] (1d), [PdPt(GaCp*)(PPh3)(mu2-GaCp*)3] (4b), or [Pd3(PPh3)3(mu2-InCp*)(mu3-InCp*)2] (8). The trends of the reactivity of [M(a)(ER)b] as well as their fluxional behavior in solution has been elucidated by NMR spectroscopy, resulting in a mechanistic rationale for the ligand exchange reactions as well as the fluxional processes.

Defined molecular models for the surface chemistry of Hume-Rothery nanophases related to catalysis are very rare. The Al-Cu intermetalloid cluster [(Cp*AlCu)6H4] was selectively obtained from the clean reaction of [(Cp*Al)4] and [(Ph3PCuH)6]. The stronger affinity of Cp*Al towards Cu sweeps the phosphine ligands from the copper hydride precursor and furnishes an octahedral Al6 cage to encapsulate the Cu6 core. The resulting hydrido cluster M12H4 reacts with benzonitrile to give the stoichiometric hydrometalation product [(Cp*AlCu)6H3(N=CHPh)].

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)(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)], [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 ZnMe(2) or ZnEt(2) 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), (1)H and (13)C 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.

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Compounds Cp*AlH2 (1) and Cp*2AlH (2) reductively eliminate Cp*H in benzene or toluene under reflux conditions to give Al(s) and AlCp*, respectively.

Surrounded by zinc: The reaction of [Mo(GaCp*)6] and Zn(CH3)2 zinc yields the exceptionally high‐coordinate title compound (see picture; Mo red, Zn green, C gray). Quantum chemical analysis reveals a unique bonding situation best described as a perfectly sd5 hybridized molybdenum atom with 12 valence electrons engaged in MoZn bonding. Another six electrons are delocalized over the Zn cage, evoking only weak ZnZn interactions.