Ring size effects in cyclic fluorophosphites: ligands that span the bonding space between phosphites and PF3

Abstract

The 5- to 8-membered cyclic fluorophosphites L5–8 have been prepared from the corresponding chlorophosphites which are derived from dihydroxyarenes or bis(trimethylsiloxy)arenes. Ligand L5 is very sensitive to hydrolysis but L6–8 are much more kinetically robust. The coordination chemistry of L5–8 has been explored with Mo(0), Pt(0) and Rh(I) and it is shown that the π-acceptor properties of L5–8 increase with decreasing ring size. The IR spectra and X-ray crystal structures of the [Mo(CO)₄L₂] complexes show that L5–8 lie between PF₃ and P(OAr)₃ in terms of their σ/π-bonding properties. The [PtL₄] complexes are readily prepared from [Pt(nbe)₃] and 4 equiv. of L5–8 whereas equilibrium mixtures of PtL_x(nbe)_y species form when 2 equiv. of L5–8 are added to [Pt(nbe)₃]. The CO substitution reactions of [Rh₂Cl₂(CO)₄] with L5–8 to give [Rh₂Cl₂L₄] are evidence of the PF₃-like ligand properties of L5–8. The trends in the properties of L5–8 are analysed in terms of their proximity to PF₃ or P(OPh)₃.