P−C Bond Activation and Phenyl Group Transfer in the Reaction of Co4(CO)9(mesitylene) with 2,3-Bis(diphenylphosphino)maleic Anhydride (bma). X-ray Diffraction Structures and Redox Properties of Co3(CO)7[μ2-η2,η1-P(Ph)CC(PPh2)C(O)OC(O)] and Co3(CO)6(PPh3)[μ2-η2,η1-P(Ph)CC(PPh2)C(O)OC(O)

Abstract

The reaction of the tetracobalt cluster Co4(CO)9(mesitylene) (1) with the diphosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride (bma) affords the recently characterized dinuclear compounds Co2(CO)2(bma)2 (2) and Co2(CO)2(bma)[μ-CC(PPh2)C(O)OC(O)](μ2-PPh2) (3), in addition to the two new tricobalt clusters Co3(CO)7[μ2-η2,η1-P(Ph)CC(PPh2)C(O)OC(O)] (4) and Co3(CO)6(PPh3)[μ2-η2,η1-P(Ph)CC(PPh2)C(O)OC(O)] (5) in low yields. The PPh3-substituted cluster 5 has also been isolated, albeit in irreproduceably low yields, when Co2(CO)8 was employed as the organometallic starting material. Clusters 4 and 5 have been isolated by preparative chromatography and characterized in solution (IR and 31P NMR). Evidence for bma ligand activation by P−Ph bond cleavage and the transfer of the phenyl group to a transient μ2-PPh2 center to form the PPh3 ligand in 5 are confirmed by X-ray diffraction analysis. The redox behavior of 4 and 5 has been explored in CH2Cl2, and these data are discussed relative to the results obtained from extended Hückel molecular orbital calculations. Electrochemical and molecular orbital comparisons between cluster 4 and the related carbene-bridged cluster Co3(CO)6[μ2-η2,η1-C(Ph)CC(PPh2)C(O)OC(O)](μ2-PPh2) (6) are presented.