POLAR IMINOBORANES - REACTIONS OF (TERT-BUTYLIMINO)(PENTAFLUOROPHENYL)BORANE

The reactions of the iminoborane C6F5-B=N-tBu (1) with nitriles and isonitriles are studied. Nitriles RCN give cycloadducts either of the triazadiboracyclohexane type (3a; R=iPr) or of the tetrazatriborabicyclo[4.2.0]octane type [4b-d; R=Ph, p-C(6)H(4)Me, p-C6H4(CF3)] or of the (iminomethyl)borazine type (5e, f; R=Me, Et). Isonitriles RNC yield. mainly adducts of RNC to a cycloaddition product of the diazadiboracyclopentane type (6a, b; R=2,6-C(6)H(3)Me(2), tBu); the adduct of RNC to a diazadiboracyclobutane may be a side-product (7b; R=tBu). The iminoborane Me(3)Si(tBu)N-B=NtBu reacts with two molecules of (2,6-C(6)H(3)Me(2))NC to give the corresponding azaboracyclobutane 8. The iminoborane tBu-B=N-C6F5 (1'), formed by gas-phase elimination of ClSiMe(3) from Cl(tBu)B=N(C6F5)SiMe(3) (9), cyclodimerizes more readily than the isomeric borane 1. The cyclodimer 2' gives 1:1-addition reactions with tBuNC, PMe(3), and MeNC, respectively; the added components fluctuate in solutions of the products 7b'-d'. A similar fluctuation is observed with the 1:1 adduct 7c from PMe(3) and the cyclodimer 2 of the iminoborane 1. The products 3a, 5e, 6a, 8 crystallize in the space groups P2(1)/c, P2(1)/n, Pbca, and P2(1)/c, respectively.