Heptacoordinate Co II Complex: A New Architecture for Photochemical Hydrogen Production.

The first heptacoordinate cobalt catalyst for light-driven hydrogen production in water has been synthesized and characterized. Photochemical experiments using [Ru(bpy)3 ]2+ as photosensitizer gave a turnover number (TON) of 16300 mol H2  (mol cat.)-1 achieved in 2 hours of irradiation with visible (475 nm) light. This promising result provides a path forward in the development of new structures to improve the efficiency of the catalysis.