Stabilization of the Triphosphallyl Ligand η3-P3{P(O)H} at Iridium via Alkaline Activation of P4

The selective functionalization of the polyphosphorus moiety Ph2PCH2PPh2PPPP present as a tetrahapto-ligand in complex [Ir(dppm)(Ph2PCH2PPh2PPPP)](+) (1, dppm=Ph2PCH2PPh2) was obtained by reaction of 1 with water under basic conditions at room temperature. The formation of the new triphosphaallyl moiety (3)-P-3{P(O)H} was determined in solution by NMR spectroscopy, and confirmed in the solid state by a single-crystal X-ray structure of the stable product [Ir((2)-dppm)((1)-dppm)((3)-P-3{P(O)H})] (2). In solution, 2 has a fluxional behavior attributable to the four P atoms belonging to the tetraphosphorus moiety in 1 and exhibits a chemical exchange process involving the two PPh2 moieties of the same bidentate ligand, as determined by 1D and 2D NMR spectroscopy experiments carried out at variable temperature. The mechanism of the reaction was investigated at the DFT level, which suggested a selective attack of an in-situ generated OH- anion on one of the non-coordinated phosphorus atoms of the P-4 moiety. The reaction then evolves through an acid-assisted tautomerization, which leads to the final compound 2. Bonding analysis pointed out that the new unsubstituted P-3-unit in the (3)-P-3{P(O)H} moiety behaves as a triphosphallyl ligand.