Room-temperature reaction of carbon monoxide with tri-tert-butylaluminum at atmospheric pressure yields the dimeric tert-butylacyl complex [tBu2AlC(O)tBu]2 (1). This unprecedented CO insertion into an aluminum-carbon bond is apparently made possible by the three-coordinate aluminum center in the tri-tert-butylaluminum starting material.

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Reactions of tris(3-methylindolyl)methane, bis(3-methylindolyl)-2-methoxyphenylmethane, and bis(3-methylindolyl)phenylmethane with THF·BH3 result in hydrogen elimination and yield the corresponding boron monohydride complexes (3-CH3C8H4NH)HC(3-CH3C8H4N)2BH (6), (2-CH3OC6H4)HC(3-CH3C8H4N)2BH (7), and PhHC(3-CH3C8H4N)2BH (8), respectively. Compositions and structures were confirmed by NMR (1H, 11B, 13C) and IR spectroscopy, elemental analysis, and X-ray crystallography. The molecular structures of 6–8 each possess a trigonal-planar boron atom which resides in the plane of a bidentate diindolylmethane ligand. This planarity, the lack of Lewis acid–base complexation in the presence of THF, and the short B–N distances suggest significant N→B π donation. Thermolysis of 6 did not produce the three-coordinate, pyramidal borane HC(3-CH3C8H4N)3B or a tripodal, four-coordinate acid–base complex, presumably due to the significant B–N π bonding in 6. The planarity of 6–8 and the isoelectronic relationship of BH to C: suggest that diindolylmethanes may be useful platforms for the preparation of a new family of N-heterocyclic carbenes.