Os(II)−Nitrosyl and Os(II)−Dinitrogen Complexes from Reactions between Os(VI)−Nitrido and Hydroxylamines and Methoxylamines

Reactions between the Os(VI)−nitrido salts (e.g., trans-[OsVI(tpy)(Cl)2(N)]PF6 (tpy = 2,2‘:6‘,2”-terpyridine), cis-[OsVI(tpy)(Cl)2(N)]PF6, and fac-[OsVI(tpm)(Cl)2(N)]PF6 (tpm = tris(pyrazol-1-yl)methane)) and the hydroxylamines (e.g., H2NOH and MeHNOH) and the methoxylamines (e.g., H2NOMe and MeHNOMe) in dry MeOH at room temperature give three different types of products. They are Os(II)−dinitrogen (e.g., trans-, cis-, or fac-[OsII−N2]), Os(II)−nitrosyl [OsII−NO]+ (e.g., trans- or cis-[OsII−NO]+), Os(IV)−hydroxyhydrazido (e.g., cis-[OsIV−N(H)N(Me)(OH)]+), and Os(IV)−methoxyhydrazido (e.g., trans-/cis-[OsIV−N(H)N(H)(OMe)]+, and trans-/cis-[OsIV−N(H)N(Me)(OMe)]+) adducts. The products depend in a subtle way on the electron content of the starting nitrido complexes, the nature of the hydroxylamines, the nature of the methoxylamines, and the reaction conditions. Their appearance can be rationalized by invoking the formation of a series of related Os(IV) adducts which are stable or decompose to give the final products by two different pathways. The first involves internal 2-electron transfer and extrusion of H2O, MeOH, or MeOMe to give [OsII−N2]. The second which gives [OsII−NO]+ appears to involve seven-coordinate Os(IV) intermediates based on the results of an 15N-labeling study.