Single‐Crystal to Single‐Crystal Transformations: Stepwise CO₂ Insertions into Bridging Hydrides of [(NHC)CuH]₂ Complexes

Abstract

Mechanistic studies of substrate insertion into dimeric [(NHC)CuH] 2 (NHC = N-heterocyclic carbene) complexes with two bridging hydrides have been shown to require dimer dissociation to generate transient, highly reactive (NHC)CuÀ H monomers in solution. Using single-crystal to single-crystal (SC-SC) transformations, we discovered a new pathway of stepwise insertion of CO 2 into [(NHC)CuH] 2 without complete dissociation of the dimer. The first CO 2 insertion into dimeric [(IPr*OMe)CuH] 2 (IPr*OMe = N,N'-bis(2,6bis(diphenylmethyl)-4-methoxy-phenyl)imidazole-2ylidene) produced a dicopper formate hydride [(IPr*OMe)Cu] 2two different bonding modes of the bridging formate. These dicopper formate complexes are inaccessible from solution reactions since the dicopper core cleanly ruptures to monomeric complexes when dissolved in a solvent.