Phosphaazaallene dimerization and phosphaallene isomerization: Catalysis by zerovalent palladium and platinum complexes

Several Pd(0) complexes catalyze the dimerization of Mes*PCNPh [2, Mes* = 2,4,6-(t-Bu)(3)C6H2] to the unsymmetrical heterocycle Mes*P(mu-CNPh)NPh(mu-CPMes*) (5). The. symmetrical dimer [Mes*P(mu-CNPh)](2) (7), which forms slowly by uncatalyzed dimerization of 2, does not interconvert with 5; both 5 and 7 were structurally characterized by X-ray crystallography. The Pt complexes PtL(2)[eta(2)-(P,C)-Mes*PCNPh] [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 Mes*PCCPh(2) (3) to the phosphaindan [2,4-(t-Bu)(2)C6H2(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)-Mes*PCCPh(2)] (12). Comparison of the metal-mediated reactions of 2 and 3 suggests that the initial steps in the catalyses, coordination of the phosphacumulene to M(0), followed by loss of a Ligand, are similar.