An orbitally adapted push-pull template for N activation and reduction to diazene-diide.

A Lewis superacidic bis(borane) CF{B(CF)} was reacted with tungsten N-complexes [W(N)(RPCHCHPR)] (R = Ph or Et), affording zwitterionic boryldiazenido W(ii) complexes -[W(L)(RPCHCHPR)(N{B(CF)(CFB(CF)})] (L = ø, N or THF). These compounds feature only one N-B linkage of the covalent type, as a result of intramolecular boron-to-boron CF transfer. Complex -[W(THF)(EtPCHCHPEt)(N{B(CF)CFB(CF)})] (5) was shown to split H, leading to a seven-coordinate complex [W(H)(EtPCHCHPEt)(N{B(CF)}CF)] (7). Interestingly, hydride storage at the metal triggers backward CF transfer. This reverts the bis(boron) moiety to its bis(borane) state, now doubly binding the distal N, with structural parameters and DFT computations pointing to dative N→B bonding. By comparison with an N complex [W(H)(EtPCHCHPEt)(N{B(CF)}] (10) differing only in the Lewis acid (LA), namely B(CF), coordinated to the distal N, we demonstrate that two-fold LA coordination imparts strong N activation up to the diazene-diide (N) state. To the best of our knowledge, this is the first example of a neutral LA coordination that induces reduction of N.