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

Abstract

The complexes cis-[PtX₂{P(OC₆H₄OMe-2)₃}₂](X = Cl, Br or I) have been prepared by treatment of the corresponding [PtX₂(cod)](cod = cycloocta-1,5-diene) with P(OC₆H₄OMe-2)₃. That with X = Cl reacted with 1 or 2 equivalents of SnCl₂ to give cis-[PtCl(SnCl₃){P(OC₆H₄OMe-2)₃}₂] or trans-[Pt(SnCl₃)₂{P(OC₆H₄OMe-2)₃}₂]. The unstable hydride trans-[PtH(Cl){P(OC₆H₄OMe-2)₃}₂] was detected when cis-[PtCl₂{P(OC₆H₄OMe-2)₃}₂] was treated with NaBH₄ or [Pt{P(OC₆H₄OMe-2)₃}₃] with HCl. The organoplatinum complexes cis-[PtR₂{P(OC₆H₄OMe-2)₃}₂] and cis-[PtR(X){P(OC₆H₄OMe-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-[PtMe₂{P(OC₆H₄OMe-2)₃}₂], in the presence of H₂O or MeCN, gave the cationic species cis-[PtMe(L){P(OC₆H₄OMe-2)₃}₂][BF₄](L = H₂O or MeCN). The significance of the observation that complexes of the type [PtMe(L){P(OC₆H₄OMe-2)₃}₂] are invariably cis is discussed. The crystal structures of cis-[PtCl₂{P(OC₆H₄OMe-2)₃}₂] and cis-[PtMe(OH₂){P(OC₆H₄OMe-2)₃}₂][BF₄]·CH₂Cl₂ have been determined. These, together with those previously reported for P(OC₆H₄OMe-2)₃ and [Pt(η-C₂H₄){P(OC₆H₄OMe-2)₃}₂], show pronounced variation in P–O lengths and O–P–O bond angles consistent with the greater importance of Pt–P π bonding in the platinum(0) species. The phosphite P(OC₆H₄OMe-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(OC₆H₄OMe-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 π bonding.