DIYNE AND PHOSPHORUS-CARBON BOND REACTIVITY IN THE REACTION BETWEEN [CO-2(CO)(6)](2)(PHC(4)PH) AND 2,3-BIS(DIPHENYLPHOSPHINO)MALEIC ANHYDRIDE (BMA) - SYNTHESES, MOLECULAR-ORBITAL PROPERTIES, AND X-RAY-DIFFRACTION STRUCTURES OF )-(Z)-PH(2)P(PH)C=C(PHC(2))-C=C(PH(2)P)C(O)OC(O)], CO-2(CO)(2)(BMA)(2)CENTER-DOT-CH2CL2, AND =C(PH(2)P)C(O)OC(O)](MU(2)-PH(2)P)CENTER-DOT-C6H14

Thermolysis (>80 degrees C) of the diyne complex [Co-2(CO)(6)](2)(PhC( 4)Ph) (1) with 2,3-bis(diphenylphosphino)maleic anhydride (bma) afford s the new compounds (1)-(Z)-Ph(2)P(Ph)C=C(PhC(2))C=C(Ph(2)P)C(O)OC(O)] (3), Co-2(CO)(2)(bma)(2) (4), and CO)(2)(bma)[mu-C=C(Ph(2)P)C(O)OC(O) ](mu(2)-Ph(2)P) (5) in low yields, while [Co-2(CO)(6)](2)(PhC(4)Ph) re acts with added bma in either refluxing Ch(2)Cl(2) or in the presence of Me(3)NO to give the thermally sensitive complex [Co-2(CO)(4)(bma)(P hC(4)Ph)Co-2(CO)(6)]. (2). Independent experiments reveal that 3 arise s from 2 by loss of the Co-2(CO)(6) group, coupled with P-C bond cleav age and diyne functionalization by the transient phosphido and maleic anhydride moieties, and the reaction between 2 and excess bma leads to both 4 and 5, with 5 originating from 4. The kinetics for the reactio n of 4 to 5 have been measured by UV-vis spectroscopy, and on the basi s of the first-order rate constants and the activation parameters (Del ta H double dagger = 27.0 +/- 0.6 kcal mol(-1) and Delta S double dagg er = 1.0 +/- 0.3 eu), a mechanism involving dissociative CO loss as th e rate-determining step is presented. Binuclear 4 is extremely photose nsitive and is converted cleanly to 5 by 366 nm light with a quantum e fficiency of 0.0043. Compounds 2-5 hav been isolated and characterized in solution by IR and P-31 NMR spectroscopy. The solid-state structur es of 3-5 have been established by X-ray crystallography. The X-ray st ructure of 4 reveals the presence of two bma ligands that are attached to the Co-2 (CO)(2) unit in a head-to-tail fashion via the PPh(2) gro ups and maleic anhydride pi bond, and the X-ray structure of 5 support s the existence of a mu(2)-PPh(2) moiety and a noncomplexed maleic anh ydride pi bond, the result of P-C(maleic anhydride) bond activation. T he redox properties of 2-5 were explored by cyclic voltammetry in CH2C l2, and the oxidation/reduction behavior is discussed with respect to redox stabilization that each complex experiences, as modulated by the bma ligands(s). The orbital composition of the HOMO and LUMO levels i n 3-5 has been studied by extended Huckel calculation, and the data ar e discussed relative to the observed electrochemistry. A plausible mec hanism for the activation of Co-2(CO)(2)(bma)(2) and the formation of CO)(2)(bma)[mu-C=C(Ph(2)P)C(O)OC(O)](mu(2)-Ph(2)P) is presented.