Conversion of the clusters [Os 3(1,3-diyne)(CO) 10] into bis(alkynyl) clusters by carboncarbon bond cleavage

Abstract

The symmetrical 1,3-diynes, RC 2C 2R (RMe, Et, Ph, Bu t, SiMe 3), react with [Os 3(CO) 10(MeCN) 2] to give the clusters [Os 3(μ 3,η 2-RC 2C 2R)(μ-CO)(CO) 9]. The μ 3,η 2-coordinated alkyne group does not exchange with the non- coordinated one. As a consequence the unsymmetrical diyne, PhC 2C 2SiMe 3, gives non-interconverting and separable isomers of [Os 3(μ 3η 2-PhC 2C 2SiMe 3)(μ-CO)(CO) 9] which differ only in which of the two alkyne groups is coordinated. Thermal decarbonylations of the compounds containing RC 2C 2R (RPh, Bu t or SiMe 3) and the isomers containing the unsymmetrical diyne, PhC 2C 2SiMe 3, lead by carboncarbon bond cleavage to bis(alkynyl) clusters of the type [Os 3(μ,η 1-C 2R 1)(μ 3,η 2-C 2R 2)(CO) 9] where R 1R 2Ph, Bu t SiMe 3 and only one isomer from the mixed diyne with R 1Ph and R 2SiMe 3. XRD studies on this isomer established that C 2SiMe 3 is in the triply-bridging position and C 2Ph in the doubly-bridging position. Although the C 2Ph ligand is only bonded through the α- carbon atom, we consider it to be σ, π-bonded and a three-electron donor. It spans two osmium atoms that are not bonded (Os…OS=3.297(2) Å). Thermolysis of the EtC 2C 2Et complex leads to carbon-hydrogen rather than carboncarbon cleavage to give the allenyl cluster [Os 3H(μ 3,η 2,η 2-MeCHCCC 2Et)(CO) 9], while the MeC 2C 2Me cluster decarbonylates to [Os 3(C 4Me 2)(CO) 9] of unknown structure but which may be [Os 3(CMe)(CC 2Me)(CO) 9].