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 of stepwise insertion of CO2 into [(NHC)CuH](2) without complete dissociation of the dimer. The first CO2 insertion into dimeric [(IPr*OMe)CuH](2) (IPr*OMe=N,N '-bis(2,6-bis(diphenylmethyl)-4-methoxy-phenyl)imidazole-2-ylidene) produced a dicopper formate hydride [(IPr*OMe)Cu](2)(mu-1,3-O2CH)(mu-H). A second CO2 insertion produced a dicopper bis(formate), [(IPr*OMe)Cu](2)(mu-1,3-O2CH)(mu-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 cleanly ruptures to monomeric complexes when dissolved in a solvent.

Automated summary

Mechanistic studies have shown that substrate insertion into dimeric [(NHC)CuH](2) complexes requires dimer dissociation. However, using single-crystal to single-crystal transformations, a new pathway of stepwise CO2 insertion into [(NHC)CuH](2) without complete dissociation of the dimer was discovered. This approach led to the formation of dicopper formate complexes which are inaccessible through solution reactions.