How a Redox-Innocent Metal Promotes the Formal Reductive Elimination of Biphenyl Using Redox-Active Ligands

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One of the most compelling strategies for utilizing redox-active ligands is to perform redox events at the ligands to avoid accessing prohibitively high energy oxidation states at the metal center. This has been demonstrated experimentally in many systems, yet there is little understanding of the fundamental electronic structures involved with these transformations or how to control them. Here, the reductive elimination of biphenyl from [M(isq)(2)Ph-2] (M = Ti, Zr, and Hf and isq = 2,4-di-tert-butyl-6-tert-butyliminosemiquinone) was studied computationally. It was found that the metal remains in the + IV oxidation state and all redox chemistry was mediated by the redox-active ligands. Two types of electron-transfer mechanisms were identified, an asymmetric unpaired electron transfer (UET) and a symmetric pairwise electron transfer (PET), the former always being lower in energy. The energetic differences between these two mechanisms were explained through simple molecular orbital theory arguments. Despite the metal's redox-inactivity, it still has a marked influence on the calculated energetics of the reaction, with the Ti systems being much more reactive than the Zr/Hf systems. This primarily originates from the shorter Ti-Ph bond, which leads to a stronger filled-filled interaction between these ligands at the reactant state. This greater reactant destabilization leads to the lower activation energies.
Publisher
WILEY-V C H VERLAG GMBH
Issue Date
2015-03
Language
English
Article Type
Article
Keywords

EFFECTIVE CORE POTENTIALS; SOLVATION FREE-ENERGIES; MOLECULAR CALCULATIONS; OXIDATIVE ADDITION; ELECTRONIC-STRUCTURE; WATER OXIDATION; RADICAL LIGANDS; COMPLEXES; DENSITY; STATE

Citation

CHEMISTRY-A EUROPEAN JOURNAL, v.21, no.11, pp.4308 - 4314

ISSN
0947-6539
DOI
10.1002/chem.201406019
URI
http://hdl.handle.net/10203/203286
Appears in Collection
CH-Journal Papers(저널논문)
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