Redox Non‐Innocence and Isomer‐Specific Oxidative Functionalization of Ruthenium‐Coordinated β‐Ketoiminate

Abstract

This article deals with isomeric ruthenium complexes [RuIII(LR)2(acac)] (S=1/2) involving unsymmetric β‐ketoiminates (AcNac) (LR=R‐AcNac, R=H (1), Cl (2), OMe (3); acac=acetylacetonate) [R=para‐substituents (H, Cl, OMe) of N‐bearing aryl group]. The isomeric identities of the complexes, cct (cis‐cis‐trans, blue, a), ctc (cis‐trans‐cis, green, b) and ccc (cis‐cis‐cis, pink, c) with respect to oxygen (acac), oxygen (L) and nitrogen (L) donors, respectively, were authenticated by their single‐crystal X‐ray structures and spectroscopic/electrochemical features. One‐electron reversible oxidation and reduction processes of 1–3 led to the electronic formulations of [RuIII(L)(L⋅)(acac)]+ and [RuII(L)2(acac)]− for 1+‐3+ (S=1) and 1−–3− (S=0), respectively. The triplet state of 1+‐3+ was corroborated by its forbidden weak half‐field signal near g≈4.0 at 4 K, revealing the non‐innocent feature of L. Interestingly, among the three isomeric forms (a–c in 1–3), the ctc (b in 2 b or 3 b) isomer selectively underwent oxidative functionalization at the central β‐carbon (C−H→C=O) of one of the L ligands in air, leading to the formation of diamagnetic [RuII(L)(L′)(acac)] (L′=diketoimine) in 4/4′. Mechanistic aspects of the oxygenation process of AcNac in 2 b were also explored via kinetic and theoretical studies.