A Low-Spin Three-Coordinate Cobalt(I) Complex and Its Reactivity toward H2 and Silane.

A three-coordinate low-spin cobalt(I) complex generated using a pincer ligand is presented. Since an empty d x 2 - y 2 orbital is sterically exposed at the site trans to the N donor of an acridane moiety, the cobalt(I) center accepts the coordination of various donors such as H2 and PhSiH3 revealing σ-complex formation. At this low-spin cobalt(I) site, homolysis of H-H and Si-H bonds preferentially occurs via bimolecular hydrogen atom transfer instead of two-electron oxidative addition. When the resulting CoII -H species was exposed to N2 , H2 evolution readily occurs at ambient conditions. These results suggest single-electron processes are favored at the structurally rigidified cobalt center.