High nuclearity clusters containing methyl groups. Synthesis and structures of pentaosmium-gold carbonyl cluster compounds

The compounds Oss(CO)(15)(mu(3)-AuPPh3)(2), 2 and Os-5(CO)(14)[mu(4)-Au-3(PPh3)(3)](mu(3)-AuPPh3), 3 were obtained from the reaction of [PPN](2)[Os-5(CO)(15)] using [Au(PPh3)][NO3]. Compound 2 contains two triply-bridging Au(PPh3) groups. Compound 3 contains one triply-bridging Au(PPh3) group and a quadruply-bridging Au-3(PPh3)(3) group. When the same reaction was performed in the presence of CH3Au(PPh3), the new trigold compound Os-5(CO)(14)(CH3)(mu(3)-AuPPh3)(3), 4 was obtained. Compound 4 contains three triply -bridging Au(PPh3) groups and one methyl group coordinated to one of the apical osmium atoms of the trigonal bipyramidal pentaosmium cluster. Compound 4 was not obtained by the direct reaction of 2 with CH3Au(PPh3) but it was obtained when [Au(PPh3)(1)[NO3] was added to the reaction solutions. Cationic digold species such as [CH3Au2(PPh3)(2)](+) have been proposed as a possible mechanism for the activation of CH3Au(PPh3) by [Au(PPh3)][NO3]. Compound 4 was also obtained albeit in a lower yield from the reaction of Os-6(CO)(18) with MeAu(PPh3) following treatment with Me3NO. Each of the pentaosmium products was characterized structurally by a single-crystal X-ray diffraction analysis. (C) 2015 Elsevier B.V. All rights reserved.