The vibrational spectra of isotopically substituted metal carbonyls : V. C18-O-substituted cis-Mn(CO)4LBr (L = PPh3, AsPh3, SbPh3)

The reactions of cis-Mn(CO)₄LBr (L = PPh₃, AsPh₃, SbPh₃) with 96%¹⁸O-enriched CO in cyclohexane solution at 35°C have been investigated by IR spectroscopy in the ν(CO) region and the vibrational modes of the parent molecules and the various C¹⁸O-substituted species produced have ben assigned with the aid of approximate force field calculations for the energy-factored CO stretching blocks of the (FG) matrices. The IR data for the reaction of the triphenylphosphine complex indicate that, while all four carbonyl groups are eventually replaced by C¹⁸O, there is initially a stereochemical preference for axial CO substitution. For the other two complexes, both carbonyl and L substitution take place.