Current single molecule photocatalysts are rare, unstable, inefficient and operate under high energy light irradiation. A new, air-stable, bimetallic dirhodium paddlewheel photocatalyst [Rh2(Form)2(bncn)2][PF6]2(1, Form=formamidinate, bncn=benzo[c]cinnoline) was synthesized and characterized that absorbs ultraviolet to near-IR wavelengths of light. The shortened Rh-Rh bond in 1results in a higher-energy metal centered state that leads to a decrease in nonradiative decay, and extends the excited state lifetime of 1. This complex acts as both the photosensitizer and catalyst for H2generation from acidic solutions photo- and electrochemically. In the presence of a sacrificial electron donor in acidic solution, 1results in catalytic H2production exceeding 170 turnovers in 24 hours with an initial rate of 28 TON/h upon 655 nm irradiation. Under near-IR irradiation of 735 nm, 1still yields over 70 turnovers. Mechanistic studies show that 1proceeds through two stepwise redox events, which was unknown in previous homogeneous photocatalytic systems. This allows for the efficient storage of multiple redox equivalents on one catalyst molecule using low energy excitation.

Efficient single molecule dirhodium photocatalyst for H2 generation using low energy visible to near-IR light

2019 Fall National Meeting

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