INTERMEDIATES IN THE CONVERSION OF MOLYBDENUM-BOUND DINITROGEN TO AMMONIA AND HYDRAZINE. A CHEMICAL RESEMBLANCE TO NITROGENASE? (HYDRAZIDO(2-) COMPLEXES)

Reactions of trans- Mo(N(,2))(,2)(triphos)(PPh(,3)) , 1, where triphos = Ph(CH(,2)CH(,2)PPh(,2))(,2), with an excess of anhydrous HBr have led to the formation of ammonia or hydrazine as the major reduced nitrogen-containing end-product, depending upon the choice of solvent. In Tetrahydrofuran (THF) solution, the reaction of 1 with HBr, over a period of \u3e60 h produced ammonia in high yield. Occasionally, trace amounts (\u3c1.5%) of hydrazine were also detected. The analogous reaction in benzene solution led to the formation of ammonia and hydrazine, the latter in greater yield. The first step in the reaction of 1 with HBr involved the rapid evolution of 1 mol of N(,2) and the formation of two isomeric hydrazido(2-) complexes, syn- and anti- MoBr(NNH(,2))(triphos)(PPH(,3)) Br, 1A-Br and 1B-Br. Structurally, these isomers differed in the position of the phenyl group on the middle phosphorous of the triphos ligand. Phosphine loss has been identified as the next step leading to the formation of ammonia in reaction of 1 with HBr in THF. Phosphine loss occurs much quicker from 1B-Br than from 1A-Br. Addition of phosphine inhibits further reaction. The next isolable intermediate is a gold-colored solid. If large quantities of water are added to a reaction mixture while the gold-colored solid is present hydrazine is produced in significant yield. The production of hydrazine by this intermediate upon hydrolysis resembles the behavior of nitrogenase reported by Thornelely and Lowe (Thorneley, R. N. F. and Lowe, D. J.; Biochem. J.; 1984, 224, 887-894). Work continues in this area to determine the structure of the gold-colored solid. It is hoped that his work may provide a model for one of the intermediate stages in the reduction of dinitrogen by nitrogenase