Studies of transition-metal oxo- and nitrido-complexes. Part 5. Oxo-osmium ester complexes with quinuclidine and related amines

Abstract

The osmium(VI) ester complexes [{OsO₂(O₂R)(NC₇H₁₃)}₂] formed by reaction of monoalkenes R (R = cyclohexene, ethylene, or stilbene) with the adduct OsO₄·NC₇H₁₃(NC₇H₁₃= quinuclidine) contain an asymmetric Os₂O₂ bridge; in solution they have five-co-ordinate monomeric structures. With tertiary amines L (L = pyridine, methylimidazole, 5,6-dimethylbenzimidazole, or quinuclidine) they give the corresponding trans-dioxo-complexes [OsO₂(O₂R)(NC₇H₁₃)L]. The adduct OsO₄·NC₇H₁₃ reacts with dienes R (R = cyclohexa-1,3-diene, cyclo-octa-1,5-diene, or 2,5-dimethylhexa-2,4-diene) to give products [{Os₂O₄(O₄R)(NC₇H₁₃)₂}_n] or [{OsO₂(O₂R)(NC₇H₁₃)}₂]. With alkynes R they give [{Os₂O₄(O₄R)(NC₇H₁₃)₂}_n]·nS (R = C₂H₂, S = benzene, toluene, or carbon tetrachloride) and [{Os₂O₄(O₄R)(NC₇H₁₃)₂}_n](R = PhC₂H); these products have structures closely related to those of the complexes [{OsO₂(O₂R)L}₂] derived from alkenes. Alkaloids such as strychnine and brucine which contain tertiary amine functions react with OsO₄ to give oxo-osmium(VI) esters. Structures for all these complexes are proposed on the basis of vibrational and ¹H n.m.r. spectra, and on that of an X-ray determination of the crystal structure of [{OsO₂(O₂C₆H₁₀)(NC₇H_l3)}₂].