Diphosphines Possessing Electronically Different Donor Groups: Synthesis and Coordination Chemistry of the Unsymmetrical Di(Npyrrolyl)phosphino-Functionalized dppm Analogue Ph2PCH2P(NC4H4)2

The unsymmetrical diphosphinomethane ligand Ph2PCH2P(NC4H4)2 L has been prepared from the reaction of Ph2PCH2Li with PCl (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)2P,Pʹ)] (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)1P)2] 4. Complex 4 reacts with [PdCl2(cod)] to regenerate 2, and with [Pd2(dba)3]·CHCl3 to give the palladium(I) 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(II) 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 TlPF6 to give the A-frame complex [Pd2(CH3)2((mu)Cl)( (mu)-L)2]PF6 7. The reaction of L with [RuCp*((mu)3-Cl)]4 leads to the dimer [Ru2Cp*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 [Rh2 ((mu)-Cl)(cod)2((mu)-L)]PF6 9 can be isolated. The crystal structures of 2·CHCl3, 3·CH2Cl2, 4, 5·1/4CH2Cl2, 6, 7·2CH2Cl2, 8, and 9· CH2Cl2 are reported.