P-C BOND ACTIVATION AND PHENYL GROUP-TRANSFER IN THE REACTION OF CO-4(CO)(9)(MESITYLENE) WITH 2,3-BIS(DIPHENYLPHOSPHINO)MALEIC ANHYDRIDE (BMA) - X-RAY-DIFFRACTION STRUCTURES AND REDOX PROPERTIES OF (7)[MU(2)-ETA(2),ETA(1)-P(PH)C=C(PPH(2))C(O)OC(O)] AND 3))[MU(2)-ETA(2),ETA(1)-P(PH)C=C(PPH(2))C(O)OC(O)]

The reaction of the tetracobalt cluster Co-4(CO)(9)(mesitylene) (1) wi th the diphosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride ( bma) affords the recently characterized di-nuclear compounds Co-2(CO)( 2)(bma)(2) (2) and CO)(2)(bma)[mu-C=C(PPh(2))C(O)OC(O)](mu(2)-PPh(2)) (3), in addition to the two new tricobalt clusters 7)[mu(2)-eta(2),eta (1)-P(Ph)C=C(PPh(2))C(O)OC-(O)] (4) and Co-3(CO)(6)(PPh(3))[mu(2)-eta( 2),eta(1)-P(Ph)C=C (PPh(2))C(O)OC(O)] (5) in low yields. The PPh(3)- s ubstituted cluster 5 has also been isolated, albeit in irreproduceably low yields, when Co-2(CO)(8) was employed as the organometallic start ing material. Clusters 4 and 5 have been isolated by preparative chrom atography and characterized in solution (IR and P-31 NMR). Evidence fo r bma ligand activation by P-Ph bond cleavage and the transfer of the phenyl group to a transient mu(2)-PPh(2) center to form the PPh(3) lig and in 5 are confirmed by X-ray diffraction analysis. The redox behavi or of 4 and 5 has been explored in CH2Cl2, and these data are discusse d relative to the results obtained from extended Huckel molecular orbi tal calculations. Electrochemical and molecular orbital comparisons be tween cluster 4 and the related carbene-bridged cluster 2),eta(1)-C(Ph )C=C(PPh(2))C(O)OC(O)](mu(2)-PPh(2)) (6) are presented.