Tungsten(0) and rhodium(I) complexes of a series of 2-(2′-halo)triarylphosphinines

A series of halo substituted triarylphosphinines have been synthesised and coordinated to tungsten(0) and rhodium(I) to give [(2-(2′-halo)-triarylphosphinine)W(CO)5] and [(2-(2′-halo)-triarylphosphinine)Rh(COD)Cl] respectively. The complexes have been examined by NMR and IR spectroscopy in an effort to elucidate the nature of the bonding between the phosphinines and the respective metal centre. The W(CO)5(L) systems reveal restricted C–C bond rotation as evidenced by temperature-dependent 31P{1H} NMR spectra. Thermodynamic barriers to the rotation are dependent upon the nature of the halide with ΔG‡ values of 72.5 kJ mol−1 and 50.8 kJ mol−1 being obtained for the chloro- and fluoro-derivatives, respectively; activation barriers for the iodo- and bromo- derivatives were beyond the accessible temperature range of the NMR experiment.