Synthesis and structural investigations of bulky imino- and amido-phosphine palladium dimers

The reactions of palladium(II) dimers [Pd2Br2(L1)(2)] and [Pd2Br2(L-2)(2)] (where L1(-) is [Ph2PCH=C(Ph)N(2,6-Pr2C6H3)](-) and L2(-) is [Ph2PCH=C(Ph)N(2,6-Me2C6H3)](-)) with AgBF4 in a mixture of CH2Cl2 and MeOH give palladium(I) dimers [Pd-2(HL1)(2)][BF4] and [Pd-2(HL2)(2)][BF4](2), respectively. These exhibit unusual coordination geometries of the metal centre. Density functional theory (DFT) and culations showed that a phenyl ring of the bridging phosphine is involved in bonding via a delocalised metal-phosphine-phenyl interaction. The remarkable kinetic stability of these palladium(l) species may explain the early termination steps in the CO/ethylene copolymerisation reaction catalysed by Pd(II)-amidophosphines or enolisable Pd(II)-iminophosphines.