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Why Conventional Design Rules for C–H Activation Fail for Open-Shell Transition-Metal Catalysts

preprint
submitted on 02.10.2020 and posted on 05.10.2020 by Aditya Nandy, Heather Kulik
The design of selective and active C–H activation catalysts for direct methane-to-methanol conversion is challenging. Bioinspired complexes that form high valent metal-oxo intermediates capable of hydrogen abstraction and rebound hydroxylation are promising candidates. This promise has made them a target for computational high-throughput screening, typically simplified through the use of linear free energy relationships (LFERs). However, their mid-row transition-metal centers have numerous accessible spin and oxidation states that increase the combinatorial scale of design efforts. Here, we carry out a computational design screen of over 2,500 mid-row 3d transition-metal complexes with four metals in numerous spin and oxidation states. We demonstrate the importance of spin/oxidation state in dictating design principles, limiting the generalization of strategies derived for widely studied high-spin Fe(II) catalysts to other metals or spin/oxidation states. Combined assessment of the effect of ligand field tuning on reaction step energetics and on the identity of the ground state allows us to propose refined design strategies for spin-allowed methane-to-methanol catalysis. We observed weak coupling of energetics and design principles between reaction steps (e.g., oxo-formation vs methanol release), meaning that LFERs do not generalize across our larger catalyst set. To rationalize relative reactivity in known catalysts, we instead compute independent reaction energies and propose strategies for further improvements in catalyst design.

Funding

NSF CBET-1704266

NSF CBET-1846426

Inorganometallic Catalyst Design

Basic Energy Sciences

Find out more...

ONR N00014-17-1-2956

ONR N00014-18-1-2434

NSF GRFP (A.N.) Grant #1122374

AAAS Marion Milligan Mason Award

BWF CASI Award

History

Email Address of Submitting Author

hjkulik@mit.edu

Institution

Massachusetts Institute of Technology

Country

United States of America

ORCID For Submitting Author

0000-0001-9342-0191

Declaration of Conflict of Interest

The authors declare no conflict of interest.

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