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 <b>2</b>, which reacted with 1 equiv of <i>tert</i>-butylisonitrile (^<i>t</i>BuNC) to give the first iminoborane-boraalkene adduct <b>4</b>. In contrast, the reaction of <b>2</b> with 2 equiv of ^<i>t</i>BuNC afforded ^<i>t</i>BuNC-coordinated diborylimine. Notably, the mechanism for the formation of <b>4</b> involved the complete cleavage of the C≡N triple bond of isonitrile, which was studied by density functional theory (DFT) calculations. Reaction of <b>4</b> with HCl gave the 1,2-addition product. Moreover, complex <b>4</b> 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 <b>4</b> was found in the reactions of <b>4</b> with tetrahydrofuran (THF) and 3-phenylpropiolonitrile.