Reactions of Electron-Deficient Benzoheterocycle Triosmium Complexes with Lithium Isobutyronitrile

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.