Syntheses, structures and solution behaviour of cyclotriphosphato complexes of Pd(II), Pt(II) and Pt(IV)

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.