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

Abstract

The ligand Ph ₂ PNP(Ph) ₂ P(Ph) ₂ NPPh ₂ I was smoothly oxidised at both terminal PPh ₂ moieties with either elemental sulfur or grey selenium to give Ph ₂ P(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 H ₂ O ₂ (30% w/w) or Bu ^t OOH (in decane) gave the known dioxide compound [Ph ₂ P(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(PPh ₃ ) ₄ ] (M = Pt or Pd) in toluene proceeded cleanly, with P–P bond cleavage, and formation of the known four-membered metallacycles [M(Ph ₂ PNPPh ₂ -P,P′) ₂ ]. All compounds were characterised by a combination of IR and NMR ( ¹ H, ³¹ P-{ ¹ H}, ¹⁹⁵ Pt-{ ¹ H}) spectroscopy and elemental analyses. Furthermore, the molecular structures of cis-[Pt(CH ₃ )X{Ph ₂ PNP(Ph) ₂ P(Ph) ₂ NPPh ₂ -P,P′ }] (X = CH ₃ or I) have been determined by single-crystal X-ray diffraction and represent the first examples of MP ₄ N ₂ metallacycles incorporating a late transition metal. The PtP ₄ N ₂ rings in both compounds adopt ‘tub-like’ geometries.