Copper–Ligand Cooperativity in H2 Activation Enables the Synthesis of Copper Hydride Complexes

Abstract

Copper(I) complexes of a new participative triphosphane ligand (<b>2<sup>H</sup></b>) have been prepared and structurally characterized, in particular [Cu(<b>2<sup>H</sup></b>)I] and [Cu(<b>2</b>)]<sub>2</sub>. Hydrogenation of the latter species afforded the trimetallic hydride species [Cu<sub>3</sub>(<b>2</b>)<sub>2</sub>(µ-H)] or in the presence of BEt<sub>3</sub>, [Cu(<b>2<sup>H</sup></b>)(HBEt<sub>3</sub>)]. Their formation evidences transient formation of [Cu(<b>2<sup>H</sup></b>)H] formed by hydrogenolysis of the Cu‒<br>N bond of [Cu(<b>2</b>)]<sub>2</sub>. [Cu(<b>2<sup>H</sup></b>)(HBEt<sub>3</sub>)] behaves like a hydride complex and inserts CO<sub>2</sub> to yield the formate product [Cu(<b>2<sup>H</sup></b>)(O<sub>2</sub>CH)].<br>

Additive-Free Formic Acid Dehydrogenation Catalyzed by a Cobalt Complex

“…The presence of participative ligands is a consistent feature in the majority of the reported examples, to include an internal base in the coordination sphere of the catalyst to activate FA. − A second feature of interest, especially in the case of 3d group metals, is that an external base or additives such as BF 4 salts are often necessary to retain the catalytic activity . We recently reported a new ligand featuring an N–H moiety on a triphosphane backbone that helped to stabilize copper hydride complexes . This chelating ligand presents a phosphoramine function (R 2 P-NHR′) together with two phosphines, which can act as a pendant amine and a participative ligand.…”

“…The PP­(NH)P ligand was prepared by following the literature procedure, and its coordination was investigated with two different cobalt precursors (Scheme ): cobalt­(II) chloride and cobalt­(II) acetate were readily coordinated by the PP­(NH)P ligand in a THF solution at 80 °C, to yield complexes 1 and 2 , respectively, which were isolated quantitatively as brown powders. Both complexes are paramagnetic, which prevented any conclusive NMR analysis, but single crystals of 1 ·THF were obtained from the evaporation of a saturated THF solution (Figure a).…”