7 research outputs found
Dichotomy of Atom-Economical Hydrogen-Free Reductive Amidation vs Exhaustive Reductive Amination
Rh-catalyzed
one-step reductive amidation of aldehydes has been
developed. The protocol does not require an external hydrogen source
and employs carbon monoxide as a deoxygenative agent. The direction
of the reaction can be altered simply by changing the solvent: reaction
in THF leads to amides, whereas methanol favors formation of tertiary
amines
Ruthenium-Catalyzed Reductive Amination without an External Hydrogen Source
A ruthenium-catalyzed
reductive amination without an external hydrogen
source has been developed using carbon monoxide as the reductant and
rutheniumÂ(III) chloride (0.008–2 mol %) as the catalyst. The
method was applied to the synthesis of antianxiety agent ladasten
Atom- and Step-Economical Preparation of Reduced Knoevenagel Adducts Using CO as a Deoxygenative Agent
A highly efficient
one-step Rh-catalyzed preparation of reduced
Knoevenagel adducts of various aldehydes and ketones with active methylene
compounds has been developed. The protocol does not require an external
hydrogen source and employs carbon monoxide as a deoxygenative agent.
The use of malonic acid or cyanoacetamide enabled efficient formal
deoxygenative addition of methyl acetate or acetonitrile to aldehydes.
The developed methodology was applied to the synthesis of the precursors
of biomedically important compounds
Cyclobutadiene Arene Complexes of Rhodium and Iridium
Reactions
of [(C<sub>2</sub>H<sub>4</sub>)<sub>2</sub>RhCl]<sub>2</sub> or [(coe)<sub>2</sub>RhCl]<sub>2</sub> (coe = cyclooctene)
with AgPF<sub>6</sub> and arenes, followed by addition of 3-hexyne,
give the cyclobutadiene complexes [(C<sub>4</sub>Et<sub>4</sub>)ÂRhÂ(arene)]<sup>+</sup> in 40–65% yield (arene = <i>tert</i>-butylbenzene, <i>p</i>-xylene, mesitylene, 4-mesitylbutanoic acid). In the absence
of arenes, the hexaethylbenzene complex [(C<sub>4</sub>Et<sub>4</sub>)ÂRhÂ(C<sub>6</sub>Et<sub>6</sub>)]<sup>+</sup> is formed in 70% yield
as a result of cyclotrimerization of 3-hexyne in the coordination
sphere of rhodium. Similar reaction of [(coe)<sub>2</sub>IrCl]<sub>2</sub> with AgPF<sub>6</sub> and 3-hexyne leads to [(C<sub>4</sub>Et<sub>4</sub>)ÂIrÂ(C<sub>6</sub>Et<sub>6</sub>)]<sup>+</sup>, which
is apparently the first reported cyclobutadiene iridium complex. DFT
calculations suggest that formation of the model cyclobutadiene complex
[(C<sub>4</sub>Me<sub>4</sub>)ÂRhÂ(C<sub>6</sub>H<sub>6</sub>)]<sup>+</sup> from bisÂ(alkyne) intermediate [(C<sub>2</sub>Me<sub>2</sub>)<sub>2</sub>RhÂ(C<sub>6</sub>H<sub>6</sub>)]<sup>+</sup> can proceed
via a metallacycle transition state with a low energy barrier of 14.5
kcal mol<sup>–1</sup>
Cyclobutadiene Metal Complexes: A New Class of Highly Selective Catalysts. An Application to Direct Reductive Amination
A catalyst
of a new type, cyclobutadiene complex [(C<sub>4</sub>Et<sub>4</sub>)ÂRhÂ(<i>p</i>-xylene)]ÂPF<sub>6</sub>, was
found to promote selective reductive amination in the presence of
carbon monoxide under mild conditions (1–3 bar, 90 °C).
The reaction demonstrated perfect compatibility with a wide range
of functional groups prone to reduction by conventional reducing agents.
The developed system represents the first systematic investigation
of cyclobutadiene metal complexes as catalysts
Indenyl Rhodium Complexes with Arene Ligands: Synthesis and Application for Reductive Amination
An
efficient protocol for synthesis of indenyl rhodium complexes
with arene ligands has been developed. The hexafluoroantimonate salts
[(η<sup>5</sup>-indenyl)ÂRhÂ(arene)]Â(SbF<sub>6</sub>)<sub>2</sub> (arene = benzene (<b>2a</b>), <i>o</i>-xylene (<b>2b</b>), mesitylene (<b>2c</b>), durene (<b>2d</b>), hexamethylbenzene (<b>2e</b>), and [2.2]Âparacyclophane (<b>2g</b>)) were obtained by iodide abstraction from [(η<sup>5</sup>-indenyl)ÂRhI<sub>2</sub>]<sub><i>n</i></sub> (<b>1</b>) with AgSbF<sub>6</sub> in the presence of benzene and its
derivatives. The procedure is also suitable for the synthesis of the
dirhodium arene complex [(μ-η:η′-1,3-dimesitylpropane)Â{RhÂ(η<sup>5</sup>-indenyl)}<sub>2</sub>]Â(SbF<sub>6</sub>)<sub>4</sub> (<b>3</b>) starting from 1,3-dimesitylpropane. The structures of [<b>2e</b>]Â(SbF<sub>6</sub>)<sub>2</sub>, [<b>2g</b>]Â(SbF<sub>6</sub>)<sub>2</sub>, and [<b>3</b>]Â(SbF<sub>6</sub>)<sub>4</sub> were determined by X-ray diffraction. The last species has a sterically
unfavorable conformation, in which the bridgehead carbon atoms of
the indenyl ligand are arranged close to the propane linker between
two mesitylene moieties. Experimental and DFT calculation data revealed
that the benzene ligand in <b>2a</b> is more labile than that
in the related cyclopentadienyl complexes [(C<sub>5</sub>R<sub>5</sub>)ÂRhÂ(C<sub>6</sub>H<sub>6</sub>)]<sup>2+</sup>. Complex <b>2c</b> effectively catalyzes the reductive amination reaction between aldehydes
and primary (or secondary) amines in the presence of carbon monoxide,
giving the corresponding secondary and tertiary amines in very high
yields (80–99%). This protocol is the most active in water
Indenyl Rhodium Complexes with Arene Ligands: Synthesis and Application for Reductive Amination
An
efficient protocol for synthesis of indenyl rhodium complexes
with arene ligands has been developed. The hexafluoroantimonate salts
[(η<sup>5</sup>-indenyl)ÂRhÂ(arene)]Â(SbF<sub>6</sub>)<sub>2</sub> (arene = benzene (<b>2a</b>), <i>o</i>-xylene (<b>2b</b>), mesitylene (<b>2c</b>), durene (<b>2d</b>), hexamethylbenzene (<b>2e</b>), and [2.2]Âparacyclophane (<b>2g</b>)) were obtained by iodide abstraction from [(η<sup>5</sup>-indenyl)ÂRhI<sub>2</sub>]<sub><i>n</i></sub> (<b>1</b>) with AgSbF<sub>6</sub> in the presence of benzene and its
derivatives. The procedure is also suitable for the synthesis of the
dirhodium arene complex [(μ-η:η′-1,3-dimesitylpropane)Â{RhÂ(η<sup>5</sup>-indenyl)}<sub>2</sub>]Â(SbF<sub>6</sub>)<sub>4</sub> (<b>3</b>) starting from 1,3-dimesitylpropane. The structures of [<b>2e</b>]Â(SbF<sub>6</sub>)<sub>2</sub>, [<b>2g</b>]Â(SbF<sub>6</sub>)<sub>2</sub>, and [<b>3</b>]Â(SbF<sub>6</sub>)<sub>4</sub> were determined by X-ray diffraction. The last species has a sterically
unfavorable conformation, in which the bridgehead carbon atoms of
the indenyl ligand are arranged close to the propane linker between
two mesitylene moieties. Experimental and DFT calculation data revealed
that the benzene ligand in <b>2a</b> is more labile than that
in the related cyclopentadienyl complexes [(C<sub>5</sub>R<sub>5</sub>)ÂRhÂ(C<sub>6</sub>H<sub>6</sub>)]<sup>2+</sup>. Complex <b>2c</b> effectively catalyzes the reductive amination reaction between aldehydes
and primary (or secondary) amines in the presence of carbon monoxide,
giving the corresponding secondary and tertiary amines in very high
yields (80–99%). This protocol is the most active in water