PHOSPHAAZAALLENE DIMERIZATION AND PHOSPHAALLENE ISOMERIZATION - CATALYSIS BY ZEROVALENT PALLADIUM AND PLATINUM COMPLEXES

Several Pd(0) complexes catalyze the dimerization of MesPCNPh [2, Mes = 2,4,6-(t-Bu)(3)C6H2] to the unsymmetrical heterocycle Mes*P(mu-CNP h)NPh(mu-CPMes) (5). The. symmetrical dimer [Mes*P(mu-CNPh)](2) (7), which forms slowly by uncatalyzed dimerization of 2, does not intercon vert with 5; both 5 and 7 were structurally characterized by X-ray cry stallography. The Pt complexes PtL(2)[eta(2)-(P,C)-MesPCNPh] [8, L = 1/2 dppe (Ph(2)PCH(2)CH(2)PPh(2)); 9, L = PPh(3); 10, L = PCy(3) (Cy = c-C6H11)], models for intermediates in the catalysis, were prepared. Isomerization of MesPCCPh(2) (3) to the phosphaindan [2,4-(t-Bu)(2)C6 H2(6-CMe(2)CH(2)PCH=CPh(2))] (6), which we previously observed with Rh (I) catalysts, is catalyzed by Pt(PCy(3))(2) or the known Pt(PPh(3))(2 )[eta(2)-(P,C)-MesPCCPh(2)] (12). Comparison of the metal-mediated re actions of 2 and 3 suggests that the initial steps in the catalyses, c oordination of the phosphacumulene to M(0), followed by loss of a Liga nd, are similar.