Reactions and spectroscopic studies of Group 6 metal carbonyls with pyrazinecarboxamide and certain phosphine ligands

Substitution reactions of phosphine ligands, triphenylphosphine (PPh₃), tri(m-chlorophenyl)phosphine (m-ClPPh₃), tri(p-methoxyphenyl)phosphine (p-MeOPPh₃) and tri(benzyl)phosphine (PBz₃) with [M(CO)₄(PCA)] (M?=?Cr, Mo and W, PCA?=?pyrazinecarboxamide) were found to be dependent on the type of metal and phosphine ligand. The complexes were characterized by elemental analysis, mass spectrometry, and IR and ¹H NMR spectroscopy. UV–vis spectra of the complexes in different solvents showed bands due to metal-to-ligand charge transfer.