Four-Coordinate Gold(I), Silver(I), and Copper(I) Complexes with a Large-Span Chiral Ditertiary Phosphine Ligand

The ligand L = Ph(2)PCH(2)CHEtOPPh(2) (R,S) with two chemically different donor sites and a center of chirality in the middle of the loop connecting the phosphorus atoms has been chosen for the preparation of a series of gold(I), silver(I), and copper(I) complexes. The ligand-to-metal ratio was allowed to vary between 2:1, 1:1, and 1:2. The 1:1 complexes [LAuX](2) with X = Cl, Br, I, and SCN have been found to be components of solution equilibria (in di- or trichloromethane) of various cyclic dinuclear isomers involving also several complexes generated in ligand redistribution processes. However, single crystals (X = Cl, Br) obtained from these solutions are composed solely of centrosymmetrical dimers where the two metal atoms are part of 12-membered rings and are bridged transannularly by two halogen atoms. By symmetry, the metal bridging by the two ligands L follows a head-to-tail pattern and involves a pair of enantiomers of L. The silver compound [LAgClO(4)](2) has an analogous structure with the silver atoms attaining coordination number 4 by perchlorate bridging. The copper complex [LCuCl](2) is a tricyclic binuclear compound where each copper atom is chelated by an individual ligand L and doubly halogen bridged with the second metal atom. The 2:1 complex [L(2)Au]Cl is assigned a bis-chelated structure with the tetracoordinated metal atom as a spiro center of two six-membered rings. The solution (31)P NMR spectra show the presence of various stereoisomers which are readily identified via the strong couplings mediated by the metal center. Only small J(P, P') values would be expected for P-P' coupling along the ligand PCCOP' loops. The spectrum of the dinuclear 1:2 complex L(AuCl)(2) features only two singlet (31)P resonances.