Using a combined experimental (inhibition, cross-over, radical trapping, EPR spectroscopy) and computational (DFT) approach, we present a detailed investigation into the plausible pathways of H2 activation at the heterometallic complex. We conclude that the most likely pathways involve (i) a closed-shell mechanism involving CO dissociation and subsequent oxidative addition at Fe, and (ii) an open-shell pathway involving homolysis of the Zn-Fe bond to form radical intermediates capable of reacting with H2. Our findings provide rare insight into a lightdriven process that operates at a heterometallic complex and add to the growing examples that invoke the formation of radical intermediates in reactions of these complexes.