Theoretical study on the mechanism of catalytic reduction of hydrazine to ammonia mediated by vanadium (III) thiolate complexes

DFT calculations on the free energy profile for the catalytic reduction of hydrazine to ammonia, the late stage of nitrogen fixation, mediated by vanadium (III) thiolate complexes VPS3 (1) and VNS3 (7) were carried out. The calculated energy profile revealed that all the reduction steps were exergonic while the protonation steps were endergonic. The generation of first equivalent of ammonia and the reduction of the cationic complex V-NH₃]⁺ to the neutral V-NH₃ species were found to be the most exergonic of all the steps. Based on the calculated energy profile, both VPS3 and VNS3 were found to be catalytically active for the reduction of hydrazine to ammonia, although some quantitative differences in free energy profile had been observed.