Hexanuclear Copper(I) Hydride from the Reduction-Induced Decarboxylation of a Dicopper(II) Formate.

Copper(I) hydride complexes represent a promising entry into formic acid dehydrogenation catalysis. Herein we present the spontaneous decarboxylation of a μ-formate-bridged dicopper(II) complex () to a hexacopper(I) hydride cluster () upon reduction. Isotopic labeling studies revealed that both the H and CO originate from the bound μ-formate in , which represents a key step of the metal-mediated formic acid dehydrogenation. The full reaction equation for the conversion of to is established. The structure of features two Cu triangles, each capped by a hydride ligand. Typical hydride reactivity of is demonstrated by the addition of phenylacetylene, leading to the replacement of the hydrides by alkynide ligands C≡CPh () while retaining the hexacopper(I) core. Temperature-dependent dynamic behavior in solution on the NMR time scale was observed for both and , reflecting the rich structural landscape of the bis(pyrazolate)-bridged hexacopper(I) core (four isomers each for and ) predicted by DFT calculations.