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

Abstract

The unsymmetrical diphosphinomethane ligand Ph(2)PCH(2)P(NC(4)H(4))(2) L has been prepared from the reaction of Ph(2)PCH(2)Li with PCl(NC(4)H(4))(2). The diphenylphosphino group can be selectively oxidized with sulfur to give Ph(2)P(S)CH(2)P(NC(4)H(4))(2) 1. The reaction of L with [MCl(2)(cod)] (M = Pd, Pt) gives the chelate complexes [MCl(2)(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 [PdCl(2)(L-kappa(1)P)(2)] 4. Complex 4 reacts with [PdCl(2)(cod)] to regenerate 2, and with [Pd(2)(dba)(3)].CHCl(3) to give the palladium(I) dimer [Pd(2)Cl(2)(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(II) dimer [Pd(2)Cl(2)(CH(3))(2)(mu-L)(2)] 6, formed by the reaction of [PdCl(CH(3))(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 TlPF(6) to give the A-frame complex [Pd(2)(CH(3))(2)(mu-Cl)(mu-L)(2)]PF(6) 7. The reaction of L with [RuCp*(mu(3)-Cl)](4) leads to the dimer [Ru(2)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)(mu-Cl)(cod)(2)(mu-L)]PF(6) 9 can be isolated. The crystal structures of 2.CHCl(3), 3.CH(2)Cl(2), 4, 5.(1)/(4)CH(2)Cl(2), 6, 7.2CH(2)Cl(2), 8, and 9.CH(2)Cl(2) are reported.