Diphosphines possessing electronically different donor groups: Synthesis and coordination chemistry of the unsymmetrical Di(N-pyrrolyl)phosphino-functionalized dppm analogue Ph2PCH2P(NC4H4)(2)

The unsymmetrical diphosphinomethane ligand Ph2PCH2P(NC4H4)(2) L has been prepared from the reaction of Ph2P-CH2Li with PCI(NC4H4)(2). The diphenylphosphino group can be selectively oxidized with sulfur to give Ph2P(S)CH2P(NC4H4)(2) 1. The reaction of L with [MCl2(cod)] (M = Pd, Pt) gives the chelate complexes [MCl2(L-kappa(2)P,P')] (2, M = Pd; 3, M = Pt) in which the M-P bond to the di(N-pyrrolyl)phosphino group is shorter than that to the corresponding diphenylphosphino group. However, the shorter Pd-P bond is cleaved on reaction of 2 with an additional 1 equiv of L to give [PdCl2(L-kappa(1)P)(2)] 4. Complex 4 reacts with [PdCl2(cod)] to regenerate 2, and with [Pd-2(dba)(3)].CHCl3 to give the palladium(l) dimer [Pd2Cl2(mu-L)(2)] 5, which exists in solution and the solid state as a 1:1 mixture of head-to-head (HH) and head-to-tail (HT) isomers. The palladium(11) dimer [Pd2Cl2(CH3)(2)(mu-L)(2)] 6, formed by the reaction of [PdCl(CH3)(cod)] with L, also exists in solution as a mixture of HH and HT isomers, although in this case the HT isomer prevails at low temperature and crystallizes preferentially. Complex 6 reacts with TIPF6 to give the A-frame complex [Pd-2(CH3)(2)(mu-Cl)(mu-L)(2)]PF6 7. The reaction of L with [RuCp*(mu(3)-Cl)](4) leads to the dimer [(RuCp2*)-Cp-2(mu-Cl)(2)(mu-L)] 8, for which the enthalpy of reaction has been measured. The reaction of L with [Rh(mu-Cl)(cod)](2) gives a mixture of compounds from which the dimer [Rh-2(U-Cl)(cod)(2)(U-L)]PF6 9 can be isolated. The crystal structures of 2.CHCl3, 3.CH2O2, 4, 5.1/4CH(2)Cl(2), 6, 7.2CH(2)Cl(2), 8, and 9.CH2Cl2 are reported.