Infrared and carbon-13 NMR study of phosphine monosubstituted group VI B metal carbonyls

Abstract

IR and 13C NMR data are presented for a series of LM(CO) 5 compounds with L = (CH 3) 3P, (C 2H 5) 3P and (C 6H 5) 3P for M = Cr, Mo, W and L = PCl 3, C 6H 5PCl 2 and (C 6H 5) 2PCl for M = Cr. The correlation between the A 1(eq) ν(CO) stretching frequency and the sum of Taft's σ * i,X parameters for the phosphorus substituents is discussed in terms of σ- and π-bonding. Relative inductive and mesomeric parameters, derived according to both the treatment of Graham and of Dobson, are compared. A linear correlation has also been found between ν(CO) and δ 13 C(O) for axial as well as equatorial CO groups. Finally 2 J PMC(O) ax, 2 J PMC(O) eq and 1 J WC(O) eq are discussed in view of the recent literature; a negative sign is proposed for some PC(O) coupling constants in LCr(CO) 5 compounds in order to obtain logical trends for the carbonyls of the three transition metals Cr, Mo and W.