Solar energy storage. Production of hydrogen by 546-nm irradiation of a dinuclear rhodium(I) complex in acidic aqueous solution

Abstract

We have reported1 previously on the synthesis and characterization of a novel dinuclear rhodium(I) complex, [Rh₂(bridge)₄]²⁺ (bridge = 1,3-diisocyanopropane). The orbital interactions between the directly coupled rhodium(I) centers give rise to striking electronic absorption spectral properties, the most prominent being a low-lying system (λₘₐₓ 553 nm (ϵ 14 500), [Rh₂(bridge)₄](BPh₄)₂ in acetonitrile solution) attributable to the ¹A_1g) → ¹A_(2u) (la_(2u) → 2a_(1g)) excitation. A logical avenue for exploratory research on [Rh₂(bridge)₄]²⁺ involves its excited-state reactivity behavior, as a directly coupled dinuclear redox center might be able to channel charge-transfer excitation energy into redox-substrate chemical bond formation at rates that are competitive with back electron transfer. The purpose of the present communication is to report that we have achieved this goal in one important case, namely, in the reduction of protons to hydrogen through 546-nm irradiation of [Rh₂(bridge)₄]²⁺ in aqueous HCl solution.

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