CO Substitution in HOs3(CO)10(μ-SC6H4Me-4) by the Diphosphine 4,5-Bis(diphenylphosphino)-4-cyclopentadiene-1,3-dione (bpcd): Structural and DFT Evaluation of the Isomeric Clusters HOs3(CO)8(bpcd)(μ-SC6H4Me-4)

摘要

The reaction of the cluster HOs3(CO)10(μ-SC6H4Me-4) (1) with the diphosphine 4,5-bis(diphenylphosphino)-4-cyclopentadiene-1,3-dione (bpcd) has been investigated. 1 reacts with bpcd at room temperature in the presence of Me3NO to give the isomeric clusters 1,2-HOs3(CO)8(bpcd)(μ-SC6H4Me-4) (2a) and 1,1-HOs3(CO)8(bpcd)(μ-SC6H4Me-4) (2b). Clusters 2a and 2b have been isolated, and the molecular structure of each compound has been established by X-ray crystallography. The X-ray structure of 2a confirms the coordination of one of the non-hydride-bridged Os–Os vectors by the bpcd ligand, while the structure of 2b exhibits a chelating bpcd ligand that is bound to one of the osmium centers ligated by the thiolate and hydrido ligands. 2a and 2b are stable in refluxing toluene and show no evidence for bridge-to-chelate isomerization of the ancillary bpcd ligand. DFT calculations on 2a and 2b indicate that the former cluster is the thermodynamically more stable isomer. Near-UV irradiation of 2b leads to CO loss and ortho metalation of the thiolate moiety, yielding the dihydride cluster H2Os3(CO)7(bpcd)(μ,σ-SC6H3Me-4) (3). The conversion of 2b to 3 and free CO is computed to be endothermic by 14.1 kcal/mol and the reaction is driven by the entropic release of CO. The photochemically promoted ortho-metalation reaction is isomer dependent since cluster 2a is inert under identical conditions.