Structural transformation and catalytic hydrogenation activity of amidinate-protected copper hydride clusters

Copper hydrides have been studied for their exciting structural chemistry and applications in hydrogenation catalysis. Here, the authors uncover the role of the amidinate ligand in yielding two closely related copper hydride clusters with quite different catalytic hydrogenation activity. Copper hydrides are important hydrogenation catalysts, but their poor stability hinders the practical applications. Ligand engineering is an effective strategy to tackle this issue. An amidinate ligand, N,N '-Di(5-trifluoromethyl-2-pyridyl)formamidinate (Tf-dpf) with four N-donors has been applied as a protecting agent in the synthesis of stable copper hydride clusters: Cu11H3(Tf-dpf)(6)(OAc)(2) (Cu-11) with three interfacial mu(5)-H and [Cu12H3(Tf-dpf)(6)(OAc)(2)]center dot OAc (Cu-12) with three interstitial mu(6)-H. A solvent-triggered reversible interconversion between Cu-11 and Cu-12 has been observed thanks to the flexibility of Tf-dpf. Cu-11 shows high activity in the reduction of 4-nitrophenol to 4-aminophenol, while Cu-12 displays very low activity. Deuteration experiments prove that the type of hydride is the key in dictating the catalytic activity, for the interfacial mu(5)-H species in Cu-11 are involved in the catalytic cycle whereas the interstitial mu(6)-H species in Cu-12 are not. This work highlights the role of hydrides with regard to catalytic hydrogenation activity.

Automated summary

This study uncovers the role of the amidinate ligand in yielding two closely related copper hydride clusters with different catalytic hydrogenation activities. The researchers synthetized stable copper hydride clusters using ligand engineering strategy and observed reversible interconversion between the clusters triggered by solvent. Deuteration experiments demonstrated that the type of hydride in the clusters dictates the catalytic activity.