Acceptorless Dehydrogenation of Alcohols on a Diruthenium(II,II) Platform

Abstract

The diruthenium(II,II) complex [Ru 2 (L 1 )(OAc) 3 ]Cl (1), spanned by a naphthyridine-diimine ligand and bridged by three acetates, has been synthesized. The catalytic efficacy of complex 1 has been evaluated for the acceptorless dehydrogenation (AD) of alcohols and for the dehydrogenative coupling reactions of alcohols with Wittig reagents. The diruthenium(II,II) complex is an excellent catalyst for AD of a diverse range of alcohols, and it is shown to be particularly effective for the conversion of primary alcohols to the corresponding aldehydes without undesired side products such as esters. Triphenylphosphonium ylides in a one-pot reaction with alcohols afforded the corresponding olefins in high yields with excellent E selectivity. The liberated dihydrogen gas was identified and measured to be 1 equiv with respect to alcohol. Deuteration studies with PhCD 2 OH revealed the absence of isotope scrambling in the product, indicating the involvement of a Ru-monohydride intermediate. Kinetic studies and DFT calculations suggest a low-energy bimetallic β-hydride elimination pathway where rate-limiting intramolecular proton transfer from alcohol to metal-bound hydride constitutes the dehydrogenation step. The general utility of metal−metal bonded compounds for alcohol AD and subsequent coupling reactions is demonstrated here.

Selective Synthesis of a Series of Isostructural MIICuI Heterobimetallic Complexes Spontaneously Assembled by an Unsymmetrical Naphthyridine‐Based Ligand

“…The rigid naphthyridine core promotes a close interaction between two transition metals, and additional donor groups may be incorporated to enforce open binding sites for exploration of metal‐metal cooperativity in reaction chemistry . Moreover, naphthyridine‐based bimetallic complexes have been shown to catalyze a range of reactions . However, these mostly symmetrical systems have so far been used to study homobimetallic complexes.…”

“…[21] Rigid, naphthyridine-based ligands are suitable candidates for addressing these issues. [26][27][28][29][30][31] However, these mostly symmetrical systems have so far been used to study homobimetallic complexes. [23][24][25] Moreover,n aphthyridine-based bimetallicc omplexes have been shown to catalyzearange of reactions.…”

“…[23][24][25] Moreover,n aphthyridine-based bimetallicc omplexes have been shown to catalyzearange of reactions. [26][27][28][29][30][31] However, these mostly symmetrical systems have so far been used to study homobimetallic complexes. Indeed, upon treatment with mixtures of differentm etals, symmetrical ligandsa re expected to yield am ixture of products rather than one well-defined heterobimetallic complex.…”

Mechanisms and Activity of 1‐Phenylethanol Dehydrogenation Catalyzed by Bifunctional NHC‐IrIII Complex

“…Such reactions have potential applications in hydrogen energy storage, and readily available alcohols can serve as important sources for liquid organic hydrogen carriers which can be easily implemented in liquid fuel infrastructure , . In recent years, AAD reaction has made significant progresses, using not only noble metals (Ru, Ir, Rh, and Re) but also earth‐abundant base metals (Fe, Co, Cu, Ni, and Mn).…”

One-Pot Synthesis of α,β-Unsaturated Esters, Ketones, and Nitriles from Alcohols and Phosphonium Salts

“…13 Recently, expensive metal catalyst gold/palladium bimetallic nanoparticles were utilized to catalyze the tandem process of aerobic oxidation and Horner-Wadsworth-Emmons olefination, 14 where 1.5 equivalents of triethyl phosphonoacetate and 3 equivalents of base were added to promote the reaction smoothly. Bera and co-workers reported that a diruthenium complex catalyzed the dehydrogenative coupling reactions of alcohols with Wittig reagents, 15 where the starting material for making the catalyst was commercially unavailable, and its preparation procedure was not easy. Therefore, developing a facile, efficient, and environmentally friendly synthesis of the C=C bond using the method of oxidation-Wittig tandem reaction is still highly desired.…”