The cleavage of the NN bond of N,N-disubstituted hydrazines on rhenium. The preparation, reactions and x-ray crystal structures of [ReCl2(NH3)(NNCOC6H4-4-R)(PPh3)2] (R = H, OMe, NO2), [ReCl3(NNPh2)(PPh3)2], [ReCl2(N)(NNPh2)(PPH3)] and [ReCl(N)(Me2CNNCOPh)(PPh3)2] ☆

Abstract Reaction of the N,O-chelated complexes [ReCl 2 (N 2 COC 6 H 4 -4-R)(PPh 3 ) 2 ] (R = H, Me, NO 2 ) with N,N- and certain N-substituted hydrazines gave the ammine complexes [ReCl 2 (NH 3 )(NNCOC 6 H 4 -4-R)(PPh 3 ) 2 ][R = H ( 1 ), R = Me ( 2 ), R = NO 2 ( 3 ). The mechanism is believed to involve intermolecular homolytic cleavage of the NN bond. The x-ray structure of 1 revealed a pseudo-octahedral geometry with trans -phosphines. The ammine ligand is cis to the benzoyldiazenido group and the ammine hydrogens are hydrogen-bonded to the carbonyl oxygen. Reaction of [ReOCl 3 (PPh 3 ) 2 ] with excess Ph 2 NNH 2 · HCl in ethanol gave both [ReCl 3 (NNPh 2 )(PPh 3 ) 2 ] ( 6 ) and [ReCl 2 (N)(NNPh 2 )(PPh 3 )] ( 7 ). In the presence of base the rhenium(VII) cation [ReCl 2 (NNPh 2 ) 2 (PPh 3 ) + was formed. The geometry of 7 was shown by X-ray structural determination to be a distorted square-based pyramid, with the nitride in the apical position. Attempted derivatization of 7 led to NN bond cleavage and the generation of nitrido complexes. The nitrido complex [ReCl(N)(Me 2 CNNCOPh)(PPh 3 ) 2 ] ( 8 ) was unexpectedly formed in the reaction of [ReOCl 3 (PPh 3 ) 2 ] with Me 2 CNNHCOPh in ethanol in the presence of HCl. The X-ray crystal structure of 8 showed a pseudo-octahedral geometry with the nitride ligand trans to the oxygen of the N,O-chelated hydrazonato(1-) ligand. The possible mechanisms of NN bond cleavage are discussed.