Isolation of 1,2,4,3-Triazaborol-3-yl-metal (Li, Mg, Al, Au, Zn, Sb, Bi) Derivatives and Reactivity toward CO and Isonitriles

3,4-dihydro-2H-1,2,4,3-triazaborol-3-yl-lithium 3 was synthesized
and fully characterized. The 11B NMR spectrum, X-ray diffraction
analysis, and computational studies
revealed the ionic nature of the B–Li bond, and indeed 3 displays nucleophilic property which allowed preparation
of a series of 1,2,4,3-triazaborol-3-yl-metal complexes (Al; 5, Au; 6, Zn; 7, Mg; 8, Sb; 9, and Bi; 10). 3 reacted
with CO (1 atm) and various isonitriles under ambient condition, and
mechanistic study suggests that the reactions with CO and aryl isonitriles
proceed via an insertion of CO and isonitrile carbon into the B–Li
bond followed by isomerization to yield transient carbene species,
one of which was confirmed by trapping with S8. With PhNC,
compounds 5 and 7·(thf) underwent exchange
of THF molecule coordinating to the metal center with isonitrile,
whereas insertion of isonitrile carbon occurred at the B–Bi
bond in 10 which afforded stable bismuth (boryl)­iminomethane 20.