14 research outputs found
Ruthenium Catalyzed Selective α- and α,β-Deuteration of Alcohols Using D<sub>2</sub>O
Highly selective
ruthenium catalyzed α-deuteration of primary
alcohols and α,β-deuteration of secondary alcohols are
achieved using deuterium oxide (D<sub>2</sub>O) as a source of deuterium
and reaction solvent. Minimal loading of catalyst (Ru-macho), base
(KO<sup><i>t</i></sup>Bu), and low temperature heating provided
efficient selective deuteration of alcohols making the process practically
attractive and environmentally benign. Mechanistic studies indicate
the D–OÂ(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 [RuÂ(<i>p</i>-cymene)ÂCl<sub>2</sub>]<sub>2</sub> (<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 [{(η<sup>6</sup>-<i>p</i>-cymene)ÂRuCl}<sub>2</sub>Â(ÎĽ-H-ÎĽ-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
[RuÂ(<i>p</i>-cymene)ÂCl<sub>2</sub>]<sub>2</sub> complex
(<b>1</b>) is used as a catalyst precursor, which upon reaction
with pinacolborane <i>in situ</i> generates the monohydrido-bridged
complex [{(η<sup>6</sup>-<i>p</i>-cymene)ÂRuCl}<sub>2</sub>(ÎĽ-H-ÎĽ-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 [RuÂ(<i>p</i>-cymene)ÂCl<sub>2</sub>]<sub>2</sub> <b>1</b> catalyzed regioselective 1,4-dearomatization
of pyridine derivatives using pinacolborane is reported. Two catalytic
intermediates, [RuÂ(<i>p</i>-cymene)ÂCl<sub>2</sub>Py] <b>2</b> and [RuÂ(<i>p</i>-cymene)ÂCl<sub>2</sub>(PÂ(Cy)<sub>3</sub>)] <b>3</b>, involved in this process are identified,
independently synthesized, characterized, and further used directly
as effective catalysts; two more catalytic intermediates [RuÂ(<i>p</i>-cymene)ÂCl<sub>2</sub>(Py)Â(PÂ(Cy)<sub>3</sub>)] <b>4</b> and [RuÂ(<i>p</i>-cymene)Â(H)ÂClÂ(Py)Â(PÂ(Cy)<sub>3</sub>)] <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
Controlling the Product Platform of Carbon Dioxide Reduction: Adaptive Catalytic Hydrosilylation of CO2 Using a Molecular Cobalt(II) Triazine Complex
Selective α‑Deuteration of Amines and Amino Acids Using D<sub>2</sub>O
Monohydrido-bridged
ruthenium complex [{(η<sup>6</sup>-<i>p</i>-cymene)ÂRuCl}<sub>2</sub>(ÎĽ-H-ÎĽ-Cl)] catalyzes
(catalyst load: 0.5–1 mol %) α-selective deuteration
of primary and secondary amines, amino acids, and drug molecules using
deuterium oxide (D<sub>2</sub>O) 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-CH<sub>2</sub> 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