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 ruthenium­(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 [(C₂H₄)₂RhCl]₂ or [(coe)₂RhCl]₂ (coe = cyclooctene) with AgPF₆ and arenes, followed by addition of 3-hexyne, give the cyclobutadiene complexes [(C₄Et₄)­Rh­(arene)]⁺ 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 [(C₄Et₄)­Rh­(C₆Et₆)]⁺ is formed in 70% yield as a result of cyclotrimerization of 3-hexyne in the coordination sphere of rhodium. Similar reaction of [(coe)₂IrCl]₂ with AgPF₆ and 3-hexyne leads to [(C₄Et₄)­Ir­(C₆Et₆)]⁺, which is apparently the first reported cyclobutadiene iridium complex. DFT calculations suggest that formation of the model cyclobutadiene complex [(C₄Me₄)­Rh­(C₆H₆)]⁺ from bis­(alkyne) intermediate [(C₂Me₂)₂Rh­(C₆H₆)]⁺ can proceed via a metallacycle transition state with a low energy barrier of 14.5 kcal mol^–1

Cyclobutadiene Metal Complexes: A New Class of Highly Selective Catalysts. An Application to Direct Reductive Amination

A catalyst of a new type, cyclobutadiene complex [(C₄Et₄)­Rh­(<i>p</i>-xylene)]­PF₆, 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 [(η⁵-indenyl)­Rh­(arene)]­(SbF₆)₂ (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]­paracyclophane (<b>2g</b>)) were obtained by iodide abstraction from [(η⁵-indenyl)­RhI₂]_<i>n</i> (<b>1</b>) with AgSbF₆ 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)­{Rh­(η⁵-indenyl)}₂]­(SbF₆)₄ (<b>3</b>) starting from 1,3-dimesitylpropane. The structures of [<b>2e</b>]­(SbF₆)₂, [<b>2g</b>]­(SbF₆)₂, and [<b>3</b>]­(SbF₆)₄ 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 [(C₅R₅)­Rh­(C₆H₆)]²⁺. 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 [(η⁵-indenyl)­Rh­(arene)]­(SbF₆)₂ (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]­paracyclophane (<b>2g</b>)) were obtained by iodide abstraction from [(η⁵-indenyl)­RhI₂]_<i>n</i> (<b>1</b>) with AgSbF₆ 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)­{Rh­(η⁵-indenyl)}₂]­(SbF₆)₄ (<b>3</b>) starting from 1,3-dimesitylpropane. The structures of [<b>2e</b>]­(SbF₆)₂, [<b>2g</b>]­(SbF₆)₂, and [<b>3</b>]­(SbF₆)₄ 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 [(C₅R₅)­Rh­(C₆H₆)]²⁺. 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