Syntheses, structures and solution behaviour of cyclotriphosphato complexes of Pd(ii), Pt(ii) and Pt(iv)

Abstract

The cyclotriphosphate ion (P₃O₉³⁻) as a PPN [PPN = (Ph₃P)₂N⁺] salt reacted in CH₂Cl₂ at room temperature with the cationic solvated complexes of Pd(II) and Pt(II), [M(phosphine)₂(Me₂CO)₂]²⁺ [M = Pd, Pt; phosphine = PPh₃, PMePh₂, 1/2 Ph₂P(CH₂)₂PPh₂ (dppe), 1/2 Ph₂P(CH₂)₄PPh₂ (dppb)], to give the anionic P₃O₉ complexes (PPN)[Pd(P₃O₉)(PPh₃)₂] (1), (PPN)[Pd(P₃O₉)(PMePh₂)₂] (2), (PPN)[Pt(P₃O₉)(PPh₃)₂] (3), (PPN)[Pt(P₃O₉)(PMePh₂)₂] (4), (PPN)[Pt(P₃O₉)(dppe)] (5) and (PPN)[Pt(P₃O₉)(dppb)] (6). Crystallographic studies revealed that the P₃O₉ ligand in complexes 1–4 and 6 adopts a normal chair conformation and behaves as a pseudo-tridentate ligand with two normal M–O bonds and an additional weak M⋯O interaction. In 1 and 3, the terminal P₃O₉ oxygen atom weakly bound to the metal centre forms relatively strong intramolecular CH⋯O hydrogen bonds with the phosphine ligands. In contrast, the P₃O₉ ligand in 5 is bidentate and takes a pseudo-boat conformation. Complexes 1–6 are fluxional in solution and exhibit only one singlet due to the P₃O₉ ligand in the ³¹P–{¹H} NMR spectra at room temperature; the signals of complexes 4–6 split into two at −40 to −70 °C. The activation parameters for the fluxional behaviour of 6 were determined by the line shape analysis of the variable temperature ³¹P–{¹H} NMR spectra. The Pt(IV) complex (PPN)₂[PtMe₃(P₃O₉)] (7) was also synthesised and structurally characterised.