Guanidinates: a new class of ligands for dimetal units with multiple metal-metal bonds

Abstract

This dissertation concerns the discovery of the ability of the guanidinate ligand hpp (hpp = anion of 1,3,4,6,7,8-hexahydropyrimido[1,2-a]pyrimidine) to stabilize high oxidation states of dimetal units (particularly dimolybdenum species) and attempts to control solubility and redox potential through modification of the ligand. Two general strategies were used for the ligand modifications: alteration of the ring size, and addition of alkyl substituents. All of the dimetal complexes using these ligands show a significant shift in redox potential compared to other commonly used classes of ligands (i.e. carboxylates and formamidinates) allowing access to the Mo2 4+, Mo2 5+ and Mo2 6+ oxidation states. The solubility of the complexes increases with increasing ring size, or with increasing length of the alkyl substituent. The physical and chemical properties of the ligands and their dimolybdenum complexes are described in detail.