Tris(2-methoxyphenyl) phosphite complexes of platinum(II): The cis preference of triaryl phosphite ligands and the effect of oxidation state on metal phosphite bonding

The complexes cis-[PtX(2){P(OC(6)H(4)OMe-2)(3)}(2)] (X = Cl, Br or I) have been prepared by treatment of the corresponding [PtX(2)(cod)] (cod = cycloocta-1,5-diene) with P(OC(6)H(4)OMe-2)(3). That with X = Cl reacted with 1 or 2 equivalents of SnCl2 to give cis-[PtCl(SnCl3){P(OC(6)H(4)OMe-2)(3)}(2)] or trans-[Pt(SnCl3)2{P(OC(6)H(4)OMe-2)(3)}(2)]. The unstable hydride trans-[PtH(Cl){P(OC(6)H(4)OMe-2)(3)}(2)] was detected when cis-[PtCl2{P(OC(6)H(4)OMe-2)(3)}(2)] was treated with NaBH4 or [Pt{P(OC(6)H(4)OMe-2)(3)}(3)] with HCl. The organoplatinum complexes cis-[PtR(2){P(OC(6)H(4)OMe-2)(3)}(2)] and cis-[PtR(X){P(OC(6)H(4)OMe-2)(3)}(2)] (R = Me, X = Cl, I or CN; R = Et, X = Cl) were obtained from platinum-(II) and -(0) precursors. Addition of HBF4 to cis-[PtMe(2){P(OC(6)H(4)OMe-2)(3)}(2)], in the presence of H2O or MeCN, gave the cationic species cis-[PtMe(L){P(OC(6)H(4)OMe-2)(3)}(2)][BF4] (L = H2O or MeCN). The significance of the observation that complexes of the type [PtMe(L){P(OC(6)H(4)OMe-2)(3)}(2)] are invariably cis is discussed. The crystal structures of cis-[PtCl2{P(OC(6)H(4)OMe-2)(3)}(2)] and cis-[PtMe(OH2){P(OC(6)H(4)OMe-2)(3)}(2)][BF4]. CH2Cl2 have been determined. These, together with those previously reported for P(OC(6)H(4)OMe-2)(3) and [Pt(eta-C2H4){P(OC(6)H(4)OMe-2)(3)}(2)], show pronounced variation in P-O lengths and O-P-O bond angles consistent with the greater importance of Pt-P pi bonding in the platinum(0) species. The phosphite P(OC(6)H(4)OMe-2)(3) shows a range of conformations in the structures and that with anti, gauche, gauche (agg) conformation about the P-O bonds apparently favoured in general but ggg attainable in the absence of steric crowding. In cis-[PtMe(OH2){P(OC(6)H(4)OMe-2)(3)}(2)][BF4]. CH2Cl2, intramolecular hydrogen bonding leads to an unusual aag conformation. Weak Pt...O interactions involving the OMe groups of the phosphite ligand are observed in these structures. The correlation of P-O length and O-P-O angle variation is mirrored by similar behaviour for 133 Z-P(OPh)(3) (Z = O, N or metal) structures. These observations are consistent with the now conventional view of M-P pi bonding.