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

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)Cu-H monomers in solution. Using single-crystal to single-crystal (SC-SC) transformations, we discovered a new pathway that undergoes stepwise insertion of CO2 into [(NHC)CuH]2 without complete dissociation of the dimer. The first CO2 insertion into dimeric [(IPr*OMe)CuH]2 produced a dicopper formate-hydride [(IPr*OMe)Cu]2(u-1,3-O2CH)(u-H). A second CO2 insertion produced a dicopper bis-formate [(IPr*OMe)Cu]2(u-1,3-O2CH)(u-1,1-O2CH), containing two different bonding modes of the bridging formate. These dicopper formate complexes are inaccessible from solution reactions since the dicopper core ruptures to monomeric complexes in the presence of polar and nonpolar solvent.