An orbitally adapted push-pull template for N 2 activation and reduction to diazene-diide.

A Lewis superacidic bis(borane) C 6 F 4 {B(C 6 F 5 ) 2 } 2 was reacted with tungsten N 2 -complexes [W(N 2 ) 2 (R 2 PCH 2 CH 2 PR 2 ) 2 ] (R = Ph or Et), affording zwitterionic boryldiazenido W(ii) complexes trans -[W(L)(R 2 PCH 2 CH 2 PR 2 ) 2 (N 2 {B(C 6 F 5 ) 2 (C 6 F 4 B(C 6 F 5 ) 3 })] (L = ø, N 2 or THF). These compounds feature only one N-B linkage of the covalent type, as a result of intramolecular boron-to-boron C 6 F 5 transfer. Complex trans -[W(THF)(Et 2 PCH 2 CH 2 PEt 2 ) 2 (N 2 {B(C 6 F 5 ) 2 C 6 F 4 B(C 6 F 5 ) 3 })] (5) was shown to split H 2 , leading to a seven-coordinate complex [W(H) 2 (Et 2 PCH 2 CH 2 PEt 2 ) 2 (N 2 {B(C 6 F 5 ) 2 } 2 C 6 F 4 )] (7). Interestingly, hydride storage at the metal triggers backward C 6 F 5 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 2 complex [W(H) 2 (Et 2 PCH 2 CH 2 PEt 2 ) 2 (N 2 {B(C 6 F 5 ) 3 }] (10) differing only in the Lewis acid (LA), namely B(C 6 F 5 ) 3 , coordinated to the distal N, we demonstrate that two-fold LA coordination imparts strong N 2 activation up to the diazene-diide (N 2 2- ) state. To the best of our knowledge, this is the first example of a neutral LA coordination that induces reduction of N 2 .