Titanium Cluster Nuclearity Controls the Potential of Ti(IV/III) Reduction by Transfer Hydrogenation

Titanium-containing clusters can be photoreduced in the presence of a hydrogen donor to form catalytically active Ti(III) centers. The cluster nuclearity is hypothesized to impact the thermodynamics of this process. To probe this, we examine a series of titanium polyoxometalates ranging from 3 to 17 Ti-centers. Through an examination of both compositional and structural aspects of the clusters, we compare the favorability of proton-coupled electron transfer to and from the titanium clusters. The singly reduced cluster tends to have a consistent potential (approximately -5 eV vs vacuum) regardless of structure and nuclearity. Using a principal component analysis, we show that we can predict the energy of hydrogenation of the cluster and that it depends on both cluster nuclearity and composition and provides a clear pathway for Ti-based catalyst development.