Reactions of bis(iminophosphoranes) with palladium(II) dichloride: Metal-induced tautomerization orthopalladation and unexpected platinum-assisted [2+2]cycloaddition of an aryl-nitrile with a phosphinimine moiety

Reactions of bis(iminophosphoranyl)methane, CH2(PPh(2)=N-aryl)(2), (BIPM; 1a, b) or 1, 1-bis(iminophosphoranyl)ethane (1, 1-BIPE; Ic) with Pd- and Pt-dichlorides containing weakly coordinating ligands (L) such as nitriles or cyclo-octadiene, afforded several products depending on the reaction time, type of ligand (la-c) or nature of the metal. The first reaction observed is a metal-assisted tautomerization of BIPM to aryl-N=PPh(2)-CH=PPh(2)-NH-aryl. When BIPM reacts with PdCl2(L)(2), exclusive formation of the C, N-chelate PdCl2{CH(PPh(2)=N-aryl)(PPh(2)-NH-aryl)} (2a, b) is observed, whereas with 1, 1-BIPE(1c) a product mixture consisting of a C, N-chelate (2c) and an N, N'-chelate (3) is found. Orthometallation of the four-membered palladacycle (2) took place upon heating, giving the five-membered palladacycle [PdCl2(2-C6H4-PPh(NHI-pTol)-C'H-PPh(2)(NH-pTol)}-C, C'] (4). The molecular structure of 4 has been determined by X-ray crystallography, Reactions of BIPM (1a, b) with PtCl2(RC=N)(2) (R = phenyl, p-tolyl) afforded entirely different products: the six-membered platinacycles [PtCl(RC=N){aryl-N=C(R)-N=PPh(2)-CH=PPb2-NH-aryl}-C, N]Cl (5) and [PtCl2{aryl-N=C(R)-N=PPh(2)-CH=PPh(2)-NH-aryl}-C, N] (6), due to an unexpected 2 + 2 cycloaddition of a nitrile with a P=N group.