Regiospecific and sequential P-C bond activation/cluster transformations in the reaction of PhCCo2MoCP(CO)8 with the diphosphine ligands 2,3-bis(diphenylphosphino)maleic anhydride (bma) and 3,4-bis(diphenylphosphino)-5-methoxy-2(5H)-furanone (bmf)

Thermolysis of the mixed-metal cluster PhCCo2MoCp(CO)(8) (1) with the diphosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride (bma) in CH2Cl2 leads to the sequential formation of the phosphido-bridged cluster Co2MoCp(CO)(5)[mu(2),eta(2), eta(1)-C(Ph)C=C(PPh2)C(O)OC(O)](mu-PPh2) (3) and the bis(phosphido)-bridged cluster Co2MoCp(CO)(4)[eta(3), eta(1), eta(1)-C(Ph)C=CC(O)O-C(O)](mu-PPh2)(2) (4). 3 and 4 have been isolated and characterized in solution by IR and NMR (H-1, C-13, and P-31) spectroscopies, and the solid-state structures have been established by X-ray diffraction analyses. Both clusters contain 48e- and exhibit triangular Co2Mo cores. The structure of 3 reveals the presence of a phosphido moiety that bridges the Co-Co vector and a six-electron mu(2), eta(2), eta(1)-C(Ph)C=C(PPh2)C(O)OC(O) ligand that caps one of the Co2Mo faces. The X-ray structure of 4 confirms that the five-electron eta(3), eta(1), eta(1)-C(Ph)C=CC(O)OC(O) ligand is sigma-bound to the two cobalt centers in an eta(1) fashion and pi-coordinated to the molybdenum center through a traditional eta(3)-allylic interaction. The reaction between PhCCo2MoCp(CO)(8) and the chiral diphosphine ligand 3,4-bis(diphenylphosphino)-5-methoxy-2(5H)-furanone (bmf) proceeds similarly, furnishing the phosphido-bridged cluster Co2MoCp(CO)(5) [mu(2), eta(2),eta(1)-C(Ph)C=C(PPh2)C(O)OCH(OMe)](mu-PPh2) (6), followed by conversion to Co2MoCp(CO)(4)[eta(3), eta(1), eta(1)-C(Ph)C=CC(O)O-CH(OMe)](mu-PPh2)(2) (7). The identities of clusters 6 and 7 have been ascertained by solution spectroscopic methods and X-ray crystallography. The overall molecular structure of cluster 6 is similar to that of cluster 3, except that the P-C(furanone ring) bond cleavage occurs with high regioselectivity and high diastereoselectivity. The cleavage of the remaining P-C(furanone ring) bond in cluster 6 gives rise to the bis(phosphido) -bridged cluster 7, whose structure is discussed relative to its bma-derived analogue 4. The diastereoselectivity that accompanies the formation of 6 and 7 is discussed relative to steric effects within the Co2Mo polyhedron. The cyclic voltammetric properties of cluster 3 have been examined, with three well-defined one-electron processes for the 0/+1, 0/-1, -1/-2 redox couples found. The composition of the HOMO and LUMO in 3 was established by extended Hockel MO calculations, with the data discussed relative to the parent tetrahedrane cluster 1. (c) 2006 Elsevier B.V. All rights reserved.