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(PPh₂=N-aryl)₂, (BIPM; 1a,b) or 1,1-bis(iminophosphoranyl)ethane (1,1-BIPE; 1c) 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 (1a-c) or nature of the metal. The first reaction observed is a metal-assisted tautomerization of BIPM to aryl-N=PPh₂-CH=PPh₂-NH-aryl. When BIPM reacts with PdCl₂(L)₂, exclusive formation of the C,N-chelate PdCl₂{CH(PPh₂=N-aryl)(PPh₂-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(NH[-pTol)-C′H-PPh₂(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=PPh₂-CH=PPb₂-NH-aryl}-C,N]Cl (5) and [PtCl₂{aryl-N=C(R)-N=PPh₂-CH=PPh₂-NH-aryl}-C,N] (6), due to an unexpected 2 + 2 cycloaddition of a nitrile with a P=N group.