Since their discovery by Wurtz in 1844, copper hydrides have grown in popularity and have been evoked as intermediates in numerous catalytic reactions; however, these species have never been observed as monomers in the solid state or in solution. Furthermore, there are many reports detailing the exceptional reactivity of CuH oligomers, and the prevailing hypothesis is that copper hydride aggregates react as monomers in solution. Using extremely sterically encumbering N-heterocyclic carbene ligands (NHCs), we obtained spectroscopic evidence for the presence of a monomeric copper(I) hydride, which was found to be in equilibrium with its dimer. Interestingly, alteration of the reaction conditions causes a change in the ratio of monomer and dimer, a fact that ultimately allowed us to determine that the dimerization process was essentially thermoneutral. These data allowed us to definitively prove the long-standing hypothesis that copper hydride aggregates dissociate in solution, thereby rationalizing their exceptional reactivity. Unlike copper hydrides, there are no reports of neutral silver(I) hydrides of any nuclearity. Using the methodology developed to spectroscopically characterize the first copper(I) hydride, we were able to isolate and crystallographically characterize the first example of a neutral monomeric (NHC)Ag-H. This complex was found to be thermally unstable above -40 oC; however, addition of B(C6F5)3 to this silver(I) hydride generated the temperature stable (NHC)Ag-H--B(C6F5)3 adduct, which was characterized via X-ray crystallography. Overall, this project confirmed several hypotheses surrounding copper hydrides that could not be tested previously. Furthermore, using this approach, we were able to answer a fundamental question surrounding silver hydrides: does their propensity for dimerization better mimic that of their copper or gold analogues?

Characterization of monomeric copper(I) and silver(I) hydrides

256th National Meeting (2018)

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