Photoredox catalysis has gained visibility in synthetic organic chemistry due to unique reactivity patterns, product selectivity, and less toxic reagents. Much of the work in the literature centers around using ruthenium or iridium-based catalysts. Recent work has demonstrated that Cr(III) catalysts can replace Ru(II) catalysts through alternative reaction pathways. In addition to providing earth abundant alternatives, 1st-row transition metal catalysts present new conceptual challenges that complicate their use in reaction schemes. Differential long-lived excited states, variably rapid productive intersystem crossing, and delayed electron transfer are three examples of intriguing and potentially useful challenging questions. Electronic structure methods can play an important in addressing these questions if a protocol can be developed that accurately reproduces experimental observation. Here a new protocol will be outlined, validated on Cr(III) ion and chromium(III) acetylacetonate, and used to understand the ”4T” to “2E” intersystem crossing pathway for the model complex tris(1,3-propanedionato)chromium(III). The spectroscopy oriented configuration interaction (SORCI) method and core polarized cc-pVTZ basis were used to obtain the spin-orbit coupled excitation energetics along a Jahn-Teller structural distortion pathway, confirming literature hypotheses. This protocol is being used to study Cr(III) quenching by O2 quenching and apparently gated productive electron transfer occurs for Cr(III). The combination of these studies should lead to a clearer picture of Cr(III) ion based photocatalytic activity.

Theoretical study of tris(1,3-propanedionato)chromium(III) for insight into Cr(III)-based photocatalysts

253rd National Meeting (2017)

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