π-Arene complexes.: Part 12. Synthesis of chromiumtricarbonyl complexes of quinoline and N-methylindoles and selected metallation reactions

The lithiation of indole, using a slight excess of n-butyl lithium in THF, followed by methylation and reaction with [Cr(CO)6] in refluxing dibutyl ether, resulted in the formation of [Cr(η6-N-methylindole)(CO)3] (1a) and [Cr(η6-N-methyl-2-methylindole)(CO)3] (1b). In contrast, lithiation of quinoline in THF, silylation and the subsequent reaction with [Cr(CO)6] under similar reaction conditions, afforded [Cr(η6-N-trimethylsilyl-2-butyl-1,2-dihydroquinoline)(CO)3] (2) and [Cr(η6-{2-butyl-1,2,3,4-tetrahydroquinoline})(CO)3] (3). The formation of [Cr(η6-2,2′-bis{N-methylindolyl})(CO)3] (4) implied lithiation at the 2-position of 1a. However, metallation at the 7-position was also indicated during the same reaction. In the presence of [Mn(CO)5Br], product 4 and the transmetallation product [Cr(η6-{7-(N-methylindolyl)Mn(CO)5})(CO)3] (5) were isolated. Reaction with titanocene dichloride gave [Cr(η6-{2-(N-methylindolyl)TiCp2Cl})(CO)3] (6), which slowly converted into [TiCp2{Cr(η6-2-(N-methylindolyl)(CO)3}2] (7).