Ruthenium Catalyzed Selective α- and α,β-Deuteration of Alcohols Using D₂O

Highly selective ruthenium catalyzed α-deuteration of primary alcohols and α,β-deuteration of secondary alcohols are achieved using deuterium oxide (D₂O) as a source of deuterium and reaction solvent. Minimal loading of catalyst (Ru-macho), base (KO^<i>t</i>Bu), and low temperature heating provided efficient selective deuteration of alcohols making the process practically attractive and environmentally benign. Mechanistic studies indicate the D–O­(D/R) bond activations by metal–ligand cooperation and intermediacy of carbonyl compounds resulting from dehydrogenation of alcohols

Hydrosilylation of carbonyl and carboxyl groups catalysed by Mn(i) complexes bearing triazole ligands

Manganese(i) complexes bearing triazole ligands are reported as catalysts for the hydrosilylation of carbonyl and carboxyl compounds. The desired reaction proceeds readily at 80 degrees C within 3 hours at catalyst loadings as low as 0.25 to 1 mol%. Hence, good to excellent yields of alcohols could be obtained for a wide range of substrates including ketones, esters, and carboxylic acids illustrating the versatility of the metal/ligand combination

Ruthenium Catalyzed Selective Hydroboration of Carbonyl Compounds

Using the [Ru­(<i>p</i>-cymene)­Cl₂]₂ (<b>1</b>) complex, catalytic hydroboration of aldehydes and ketones with pinacolborane under neat and mild conditions is reported. At rt, chemoselective hydroboration of aldehydes over the ketones is also attained. Mechanistic studies confirmed the immediate formation of monohydride bridged dinuclear complex [{(η⁶-<i>p</i>-cymene)­RuCl}₂­(μ-H-μ-Cl)] (<b>1b</b>) from the reaction of <b>1</b> with pinacolborane, which catalyzed the highly efficient hydroboration reactions. The catalytic cycle containing mononuclear Ru–H species and intramolecular 1,3-hydride transfer is postulated

Ruthenium-Catalyzed Selective Hydroboration of Nitriles and Imines

Ruthenium-catalyzed hydroboration of nitriles and imines is attained using pinacolborane with unprecedented catalytic efficiency. Chemoselective hydroboration of nitriles over esters is also demonstrated. A simple [Ru­(<i>p</i>-cymene)­Cl₂]₂ complex (<b>1</b>) is used as a catalyst precursor, which upon reaction with pinacolborane <i>in situ</i> generates the monohydrido-bridged complex [{(η⁶-<i>p</i>-cymene)­RuCl}₂(μ-H-μ-Cl)] <b>2</b>. Further oxidative addition of pinacolborane to intermediate <b>2</b> leading to the formation of mononuclear ruthenium hydride species is suggested. Mass spectral analysis of the reaction mixture and independent experiments with phosphine-ligated ruthenium complexes indicated the involvement of mononuclear ruthenium intermediates in the catalytic cycle. Consecutive intramolecular 1,3-hydride transfers from the ruthenium center to coordinated nitrile and boronate imine ligands, leading to the reduction and resulting in the formation of diboronate amines, are proposed as a plausible reaction mechanism

Ruthenium-Catalyzed Regioselective 1,4-Hydroboration of Pyridines

Simple ruthenium precursor [Ru­(<i>p</i>-cymene)­Cl₂]₂ <b>1</b> catalyzed regioselective 1,4-dearomatization of pyridine derivatives using pinacolborane is reported. Two catalytic intermediates, [Ru­(<i>p</i>-cymene)­Cl₂Py] <b>2</b> and [Ru­(<i>p</i>-cymene)­Cl₂(P­(Cy)₃)] <b>3</b>, involved in this process are identified, independently synthesized, characterized, and further used directly as effective catalysts; two more catalytic intermediates [Ru­(<i>p</i>-cymene)­Cl₂(Py)­(P­(Cy)₃)] <b>4</b> and [Ru­(<i>p</i>-cymene)­(H)­Cl­(Py)­(P­(Cy)₃)] <b>5</b> are identified in solution. Complex <b>5</b> is the active catalytic intermediate. An intramolecular selective 1,5-hydride transfer in <b>5</b> leading to the regioselective 1,4-hydroboration of pyridine compounds is proposed

Selective α‑Deuteration of Amines and Amino Acids Using D₂O

Monohydrido-bridged ruthenium complex [{(η⁶-<i>p</i>-cymene)­RuCl}₂(μ-H-μ-Cl)] catalyzes (catalyst load: 0.5–1 mol %) α-selective deuteration of primary and secondary amines, amino acids, and drug molecules using deuterium oxide (D₂O) as a deuterium source. Mechanistic investigations revealed N–H activation of amines, which was also established by single-crystal X-ray analysis of an intermediate. β-Hydride elimination on amide ligand results in formation of imine-ligated ruthenium intermediate and subsequent 1,3-deuteride migrations to imine ligand leading to the selective deuteration at the α-CH₂ protons of amine functionality is proposed

Ruthenium-Catalyzed Urea Synthesis by N–H Activation of Amines

Activation of the N–H bond of amines by a ruthenium pincer complex operating via “amine–amide” metal–ligand cooperation is demonstrated. Catalytic formyl C–H activation of <i>N</i>,<i>N</i>-dimethylformamide (DMF) is observed in situ, which resulted in the formation of CO and dimethylamine. The scope of this new mode of bond activation is extended to the synthesis of urea derivatives from amines using DMF as a carbon monoxide (CO) surrogate. This catalytic protocol allows the synthesis of simple and functionalized urea derivatives with liberation of hydrogen, devoid of any stoichiometric activating reagents, and avoids the direct use of fatal CO. The catalytic carbonylation occurred at low temperature to provide the formamide; a formamide intermediate was isolated. The consecutive addition of different amines provided unsymmetrical urea compounds. The reactions are proposed to proceed via N–H activation of amines followed by CO insertion from DMF and with liberation of dihydrogen