Isomerization of the diphosphine ligand 3,4-bis(diphenylphosphino)-5-methoxy-2(5H)-furanone (bmf) at a triosmium cluster and P-C bond cleavage in the unsaturated cluster 1,1-Os3(CO)9(bmf): Synthesis and X-ray diffraction structures of the isomeric Os3(CO)10(bmf) clusters and HOs3(CO)8(μ-C6H4) [μ-PhPC=C(Ph2P)CH(OMe)OC(O)]

The labile cluster 1,2-Os-3(CO)(10)(MeCN)(2) (1) reacts with the chiral diphosphine ligand 3,4-bis(diphenylphosphino)-5-methoxy-2(5H)-furanone (bmf) to furnish 1,2-Os-3(CO)(10)(bmf) (2a) in high yield. Heating cluster 2a over the temperature range 358-383 K under CO leads to isomerization of the bmf ligand and formation of the diphosphine-chelated cluster 1,1-Os-3(CO)(10)(bmf) (2b) and an equilibrium mixture consisting of 2a and 2b in a 15:85 ratio. Extended thermolysis of an equilibrium mixture of Os-3(CO)(10)(bmf) is accompanied by CO loss and ortho-metalation of an aryl ring to afford an inseparable mixture of three diastereomeric hydride clusters HOs3(CO)(9)(C29H23O3P2) (3a-c). Thermolysis of HOs3 (CO)(9)(C29H23O3P2) (3a-c) in refluxing toluene leads to P-C bond cleavage and formation of the benzyne-substituted clusters HOs3(CO)(8)(mu-C6H4)(mu-C23H19O3P2) (4a,b) as a 4:1 mixture of diastereomers. The unequivocal identity of the major benzyne-substituted cluster has been determined by X-ray diffraction analysis, where the activation of one of the phenyl groups situated a to the furanone carbonyl group in the bmf ligand has been established. The isomerization and activation of the bmf ligand are contrasted with other Os-3(CO)(10)(diphosphine) derivatives prepared by our groups. (C) 2010 Elsevier Ltd. All rights reserved.