Insight into the stereoelectronic parameters of N-triphos ligands via coordination to tungsten(0)

A series of new N-triphos tungsten complexes have been synthesised and structurally characterised. The coordination behaviour of a range of N-triphos (N(CH2PR2)3, NP3(R)) ligands, and a mixed-arm diphosphine-pyridyl (PPN(Cyh)) ligand were explored. The steric and electronic parameters of five N-triphos ligands: NP3(Ph), NP3(iPr), NP3(Cyp), NP3(Cyh) and NP3(PhF2), and the carbon-centred triphos ligand, CH3C(CH2PPh2)3 (MeCP3(Ph)), were established. Steric parameters were evaluated by analysing the cone angles calculated from X-ray crystal structures, whilst the electron-donating ability of the ligands was determined from (31)P-(77)Se NMR coupling constants of selenium derivatives and the IR carbonyl stretching frequencies across a series of tungsten-carbonyl complexes. In general, electron-rich phosphines formed bidentate complexes while less electron-rich ligands coordinated in a tridentate mode, regardless of steric bulk. An indirect interaction between the apical nitrogen of the ligand and metal centre is implicated for tridentate complexes and is supported through DFT calculations and analysis of N-protonated complexes. Complexes 1, 3, 4, 6-8 and 10 were characterised by single-crystal X-ray crystallography.