Co-ordination chemistry of the mixed phosphorus(III)-phosphorus(v) phosphazene ligand Ph2PNP(Ph)(2)P(Ph)(2)NPPh2: crystal structures of cis-[Pt(CH3)X{Ph2PNP(Ph)(2)P(Ph)(2)NPPh2-P,P'}] (X = CH3 or I)

The ligand Ph2PNP(Ph)(2)P(Ph)(2)NPPh2 I was smoothly oxidised at both terminal PPh2 moieties with either elemental sulfur or grey selenium to give Ph2P(E)NP(Ph)(2)P(Ph)(2)NP(E)Ph-2 (E = S II or Se III) in good yields. Oxidation of I with either aqueous H2O2 (30% w/w) or (BuOOH)-O-t (in decane) gave the known dioxide compound [Ph2P(O)](2)NH presumably via a sequence of oxidation, protonation and P-P bond-cleavage reactions. Complexation of I to several palladium(II), platinum(II) and gold(I) starting materials, at ambient temperature, afforded new metal complexes in which I adopts either P,P'-chelating or P,P'-bridging co-ordination modes. Reaction of I (1 equivalent) with the zerovalent compounds [M(PPh3)(4)] (M = Pt or Pd) in toluene proceeded cleanly, with P-P bond cleavage, and formation of the known four-membered metallacycles [M(Ph2PNPPh2-P,P')(2)]. All compounds were characterised by a combination of IR and NMR (H-1, P-31-{H-1}, Pt-195-{H-1}) spectroscopy and elemental analyses. Furthermore, the molecular structures of cis[Pt(CH3)X{Ph2PNP(Ph)(2)P(Ph)(2)NPPh2-P,P'}](X = CH3 or I) have been determined by single-crystal X-ray diffraction and represent the first examples of MP2N2 metallacycles incorporating a late transition metal. The PtP4N2 rings in both compounds adopt 'tub-like' geometries.