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An orbitally adapted push–pull template for N<sub>2</sub> activation and reduction to diazene-diide

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18

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97

References

2023

Year

David Specklin, Marie‐Christine Boegli, Anaïs Coffinet, Léon Escomel, Laure Vendier, Mary Grellier, Antoine Simonneau
Chemical Science

Abstract

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

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