A series of mononuclear and dinuclear complexes of silver(I), supported by an N-heterocyclic carbene and bound to sp3-, sp2-, and sp-hybridized carbanions, has been synthesized. Synthetic routes include transmetalation from organozinc, organomagnesium, and organosilicon reagents, as well as the deprotonation of a terminal alkyne. These complexes exhibit greater thermal stability than typical organosilver reagents, permitting spectroscopic and structural characterization. The carbanion-bridged disilver cations feature three-center, two-electron bonding with short Ag···Ag distances. A mononuclear vinylsilver complex releases organic homocoupling products upon thermal decomposition, while mononuclear alkylsilver complexes exhibit nucleophilic behavior, for example, inserting CO2 to form silver carboxylates.

Hydride complexes of copper, silver, and gold encompass a broad array of structures, and their distinctive reactivity has enabled dramatic recent advances in synthesis and catalysis. This Review summarizes the synthesis, characterization, and key stoichiometric reactions of isolable or observable coinage metal hydrides. It discusses catalytic processes in which coinage metal hydrides are known or probable intermediates, and presents mechanistic studies of selected catalytic reactions. The purpose of this Review is to convey how developments in coinage metal hydride chemistry have led to new organic transformations, and how developments in catalysis have in turn inspired the synthesis of reactive new complexes.

A siloxide-bridged dicopper(I) cation reacts with bis(catecholato)diboron to form the boryl-bridged dicopper cation {[(SIDipp)Cu]2(μ-Bcat)}+ (SIDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene; cat = 1,2-C6H4O2). The solid-state structure shows an acute angle about the boryl, with a short intermetallic distance. Density functional theory calculations indicate a small but significant copper–copper bond order. The boryl-bridged cation deprotonates phenylacetylene and reacts with methanol to form a hydride-bridged dicopper cation.

The expanded-ring N-heterocyclic carbenes 6Dipp and 7Dipp (6Dipp = 1,3-bis(2,6-diisopropylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene and 7Dipp = 1,3-bis(2,6-diisopropylphenyl)-4,5,6,7-tetrahydro-1,3-diazepin-2-ylidene) support isolable neutral copper hydride dimers. [(6Dipp)CuH]2 reacts with 1-hexene to give (6Dipp)copper(I) hexyl by 1,2-insertion and with benzyl isonitrile to afford an η1-formimidoyl by 1,1-insertion.

A triangular [Ag2H]+ core is stabilised by the N-heterocyclic carbene (NHC) ligand 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene (SIDipp). The X-ray crystal structure of this complex reveals a short silver–silver distance, and 109Ag NMR spectroscopy shows substantial coupling between the silver nuclei. The complex persists for hours in solution after exposure to air and moisture. When carbon dioxide is added in the form of a Lewis-basic NHC adduct, a rapid reaction results in hydride transfer to form a bis(NHC)silver(I) formate.

A triangular [Ag2H]+ core is stabilised by the N-heterocyclic carbene (NHC) ligand 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene (SIDipp). The X-ray crystal structure of this complex reveals a short silver–silver distance, and 109Ag NMR spectroscopy shows substantial coupling between the silver nuclei. The complex persists for hours in solution after exposure to air and moisture. When carbon dioxide is added in the form of a Lewis-basic NHC adduct, a rapid reaction results in hydride transfer to form a bis(NHC)silver(I) formate.