When does a nitrogen attached to a λ3-phosphorus assume a pyramidal geometry? Crystal structures of Group 6 metal carbonyl complexes of isomeric forms of λ3-cyclotriphosphazanes

Abstract

The reaction of [Mo(CO)₄(nbd)](nbd = norbornadiene) with trans-[EtNP(OC₆H₃Me₂-2,6)]₃(L¹) or cis-[EtNP(OCH₂CF₃)]₃(L²) yields the mono- and di-nuclear molybdenum(0) complexes [Mo(CO)₄(L¹)]1 and [{Mo(CO)₄(µ-L²)}₂]2, respectively. They represent the first organometallic transition-metal derivatives of λ³-cyclotriphosphazanes and have been characterised by elemental analysis and IR and NMR spectroscopy and their structures confirmed by X-ray crystallography. The different co-ordination behaviour of the cis and trans isomeric forms of this type of ligand is revealed. A pyramidal geometry observed around one of the nitrogen atoms of the P₃N₃ ring in complex 1 is unprecedented among λ³-phosphazanes.