Improved Oxidative C-C Bond Formation Reactivity of High-Valent Pd Complexes Supported by a Pseudo-Tridentate Ligand

Abstract

<p>There is a large interest in developing oxidative transformations catalyzed by palladium complexes that employ environmentally friendly and economical oxidizing reagents such as dioxygen. Recently, we have reported the isolation and characterization of various mononuclear Pd<sup>III</sup> and Pd<sup>IV</sup> complexes supported by the tetradentate ligands <i>N,N’</i>-di-alkyl-butyl-2,11-diaza[3.3](2,6)pyridinophane (<sup>R</sup>N4, R = <sup>t</sup>Bu, <sup>i</sup>Pr, Me), and the aerobically-induced C-C and C-heteroatom bond formation reactivity was investigated in detail. Given that the steric and electronic properties of the multidentate ligands were shown to tune the stability and reactivity of the corresponding high-valent Pd complexes, herein we report the use of an asymmetric N4 ligand, <i>N-</i>mehtyl-<i>N’</i>-tosyl-2,11-diaza[3.3](2,6)pyridinophane (<sup>TsMe</sup>N4), in which one amine N atom contains a tosyl group. The N-Ts donor atom exhibits a markedly reduced donating ability, which led to the formation of transiently stable Pd<sup>III</sup> and Pd<sup>IV</sup> complexes, and consequently the corresponding O<sub>2</sub> oxidation reactivity and the subsequent C-C bond formation was improved significantly.</p>

Electrocatalytic O2 Reduction by an Organometallic Pd(III) Complex via a Binuclear Pd(III) Intermediate

“…We have previously reported the synthesis and characterization of various organometallic Pd III complexes stabilized by the tetradentate ligand N,N′-di-tert-butyl-2,11-diaza [3.3](2,6)pyridinophane ( t BuN4) and related analogs. [25][26][27][28] These complexes were shown to react with O2 and undergo oxidativelyinduced C-C and C-heteroatom bond formation reactions in the presence of O2. These O2-induced oxidative transformations prompted us to evaluate the ORR reactivity of such organometallic complexes, which to the best of our knowledge has never been done before, for any molecular Pd catalyst.…”