Spectroscopy and electrochemistry of new 6,6′-disubstituted-4,4′-bipyrimidine molybdenum(0) and tungsten(0) tetracarbonyl complexes

Abstract

A new family of tetracarbonyl molybdenum(0) and tungsten(0) complexes based on new 6,6′-disubstituted-4,4′-bipyrimidine ligands was synthesized and characterized. The visible region of the absorption spectrum of each complex is dominated by a metal-to-ligand charge transfer band significantly lower in energy than the corresponding transition in 2,2′-bipyridine tetracarbonyl metal complexes. The 6,6′-substituents create a larger π-electronic system in the substituted bipyrimidines and are consequently better π acceptors than even the parent 4,4′-bipyrimidine. The absorption bands are shifted bathochromically with a decrease in solvent polarity.Key words: molybdenum and tungsten, nitrogen ligands, tetracarbonyl metal complexes, absorption spectroscopy, electrochemistry.