Reactions of Electron-Deficient Benzoheterocycle Triosmium Complexes with Lithium Isobutyronitrile

Abstract

The reactions of the electron-deficient benzoheterocycle triosmium complexes of general formula Os3(CO)9(μ3-η2-Bz)(μ-H) (BzH = phenanthridine, 3; 2-methylbenzimidazole, 4; 2,3-dimethylbenzimidazole, 5; quinoxaline, 6; 2-methylquinoxaline, 7; benzothiazole, 8; 2-methylbenzothiazole, 9) with lithium isobutyryl nitrile are reported. Nucleophilic addition at the carbocyclic rings of all the complexes is observed as for the previously reported Os3(CO)9(μ3-η2-Bz)(μ-H) (BzH = quinoline, 1; 5,6-benzoquinoline, 2), thus extending the novel alteration in the regiochemistry of nucleophilic attack to this entire class of complexes. However, in some of the complexes spontaneous rearomatization of the addition product is observed on workup or on exposure to air after addition of the carbanion. The degree to which this occurs is controlled by the steric and electronic properties of the heterocycle, and by careful adjustment of the reactions conditions either the nucleophilic addition or substitution product can be observed. The solid state structures of two of the nucleophilic addition products are reported for comparison with the previously reported analogous quinoline complexes.