Reactions of Topologically Related “nacnacH-CN” and “P-nacnacH-CN” Chelate Ligand Systems with HB(C₆F₅)₂

The chelate bis-imine nacnacH-CN (1) and its bis-phosphinimine analogue P-nacnacH-CN (2) are shown to have similar reactivities with HB(C6F5)2. In a 1:1 stoichiometry simple Lewis acid/Lewis base adducts are observed: HB(C6F5)2 just adds to the nitrile functionality to yield compounds 3 and 6, respectively. With two molar equivalents of HB(C6F5)2, both systems 1 and 2 react at 70 °C with reduction of the nitrile group to an imine that is in both reactions found to be coordinated to a second equivalent of the HB(C6F5)2 Lewis acid. The remaining B(C6F5)2 unit becomes part of a six-membered heterocycle, where it is found to be coordinated to the pair of (C-NAr) (4) or (P-NPh) (7) units. Heating of the nacnacH-CN/HB(C6F5)2 adduct 3 results in a disproportionation reaction yielding a mixture of the heterocycle (4) and the borane-free starting material 1. In marked contrast, the thermolysis of the P-nacnacH-CN/HB(C6F5)2 adduct (6) yields a new product (8), generated via an intramolecular −Ph2PNPh vs −CHNH exchange at the boron center and a formal “Umpolung” of a hydridic to a protic hydrogen atom. The compounds 3, 4, 6, 7, and 8 were characterized spectroscopically and by X-ray diffraction.