Synthesis and Reactivity of an Iminoborane-Boraalkene Adduct via the Complete Cleavage of the Carbon-Nitrogen Triple Bond of Isonitrile.

The reduction of 1,3,3-tribromo-1,3-diborata-2,4-diphosphoniocyclobutane yielded the unsymmetrical 1,3-dibora-2,4-diphosphoniobicyclo[1.1.0]butane 2, which reacted with 1 equiv of tert-butylisonitrile (tBuNC) to give the first iminoborane-boraalkene adduct 4. In contrast, the reaction of 2 with 2 equiv of tBuNC afforded tBuNC-coordinated diborylimine. Notably, the mechanism for the formation of 4 involved the complete cleavage of the C≡N triple bond of isonitrile, which was studied by density functional theory (DFT) calculations. Reaction of 4 with HCl gave the 1,2-addition product. Moreover, complex 4 reacted with phenyllithium (PhLi) to afford the borataalkene via the 1,2-addition of PhLi to the B=C double bonds and sequential intramolecular nucleophilic reactions. Furthermore, the frustrated Lewis pair (FLP) type reactivity of 4 was found in the reactions of 4 with tetrahydrofuran (THF) and 3-phenylpropiolonitrile.