The chemistry of phosphorus–fluorine compounds. Part IX. Preparation and spectroscopic studies of fluorophosphine–molydbenum carbonyl complexes

Abstract

Mixed fluorophosphine molybdenum carbonyl complexes of the type L_nMo(CO)_6–n, where L is PF₃, CF₃PF₂, CCl₃PF₂, (CF₃)₂PF, (C₃F₇)₂PF (n= 3), and PF₃, CF₃PF₂, CCl₃PF₂, (CF₃)₂PF, C₅H₁₀NPF₂, and (C₂H₅)₂NPF₂(n= 2), have been prepared by displacement reactions of the olefin from cycloheptatrienemolybdenum tricarbonyl and norbornadienemolybdenum tetracarbonyl respectively. In the former series rearrangement occurs producing exclusively trans-L₃Mo(CO)₃ complexes. Infrared and Raman data are presented, and force constant calculations, using the simplified Cotton–Kraihanzel force-field, show that fluorophosphine ligands have a very strong π-accepting ability (comparable with CO itself). Calculations on other tervalent phosphorus–fluorine ligands lead to the following decreasing order of π-accepting ability: CF₃PF₂∼(CF)₂PF > PF₃ > CCl₃PF₂ > ClCH₂PF₂ > C₆H₅PF₂ > ROPF₂ > R₂NPF₂ > RPFNR₂ > (R₂N)₂PF. The unexpected position of the trifluoromethyl fluorophosphines in the series is discussed in terms of possible competitive π-bonding of fluorine, phosphorus, and the the metal atom.