Phosphaazaallene Dimerization and Phosphaallene Isomerization: Catalysis by Zerovalent Palladium and Platinum Complexes

Abstract

Several Pd(0) complexes catalyze the dimerization of Mes*PCNPh [2, Mes* = 2,4,6-(t-Bu)3C6H2] to the unsymmetrical heterocycle Mes*P(μ-CNPh)NPh(μ-CPMes*) (5). The symmetrical dimer [Mes*P(μ-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 PtL2[η2-(P,C)-Mes*PCNPh] [8, L = 1/2 dppe (Ph2PCH2CH2PPh2); 9, L = PPh3; 10, L = PCy3 (Cy = c-C6H11)], models for intermediates in the catalysis, were prepared. Isomerization of Mes*PCCPh2 (3) to the phosphaindan [2,4-(t-Bu)2C6H2(6-CMe2CH2PCHCPh2)] (6), which we previously observed with Rh(I) catalysts, is catalyzed by Pt(PCy3)2 or the known Pt(PPh3)2[η2-(P,C)-Mes*PCCPh2] (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.