Indenyl rhodium complexes. Synthesis and catalytic activity in reductive amination using carbon monoxide as a reducing agent

Planar Chiral Rhodium Complex Based on the Tetrahydrofluorenyl Core for Enantioselective Catalysis

A simple four-step route to a chiral tetrahydrofluorenyl rhodium catalyst from naturally occurring (-)-α-pinene was developed. Our approach does not use multistep and time-consuming procedures such as chiral HPLC or diastereomeric resolution. The key to success lies in the face-selective coordination of rhodium to the sterically hindered tetrahydrofluorenyl ligand, giving only one diastereomeric complex. This catalyst proved to be highly efficient for asymmetric C-H annulation of aryl hydroxamates with alkenes (yield up to 95%, 91% ee) at low loading (up to 0.4 mol % based on Rh).

Reductive coupling of nitroarenes with carboxylic acids - a direct route to amide synthesis

A straightforward and selective way for the preparation of amides from nitroarenes and carboxylic acids using carbon monoxide as a reductant was developed. This protocol does not require any non-gaseous additives, thus simplifying product isolation. Aliphatic carboxylic acid was modified in the presence of aromatic ones, and reducible functional groups such as CC, Ar-Br, and R-NO2 were saved.

Triphenylcyclopentadienyl Rhodium Complexes in Catalytic C-H Annulations. Application for Synthesis of Natural Isocoumarins

Efficient protocols for the synthesis of triphenylcyclopentadienyl rhodium halides [(1,2,4-C₅Ph₃H₂)RhX₂]₂ (1a,b: X = Cl, I) starting from 1,2,4-triphenylcyclopentadiene or the cyclooctadiene derivative (1,2,4-C₅Ph₃H₂)Rh(cod) (2) were developed. Iodide abstraction from 1b with thallium or silver salts allowed us to prepare rhodocenium [(1,2,4-C₅Ph₃H₂)RhCp]PF₆ (3PF₆) and mesitylene complex [(1,2,4-C₅Ph₃H₂)Rh(mesitylene)](SbF₆)₂ (4(SbF₆)₂). Halides 1a,b (at 0.5 mol % loading) showed high catalytic activity in the construction of C-C, C-O, and C-N bonds via the C(sp²)-H activation approach. Their efficiency was demonstrated in the synthesis of more than 40 examples of polycyclic organic compounds (such as isocoumarins and naphthalenes, as well as isoquinolinium and dibenzo[a,f]quinolizinium salts). The protocols developed tolerate a wide range of functional groups. In particular, they were successfully used for the atom- and step-economical synthesis of hydroxy-substituted isocoumarins, including the natural product oospalactone 7fe. The 6- or 8-hydroxy-substituted isocoumarins showed moderate antiproliferative activity against several human cell lines in vitro.

Easy Access to Versatile Catalytic Systems for C-H Activation and Reductive Amination Based on Tetrahydrofluorenyl Rhodium(III) Complexes

On the basis of the 1,2,3,4-tetrahydrofluorenyl ligand, a simple approach was developed to new effective rhodium catalysts for the construction of C-C and C-N bonds. The halide compounds [(η⁵ -tetrahydrofluorenyl)RhX₂ ]₂ (2 a: X=Br; 2 b: X=I) were synthesized by treatment of the bis(ethylene) derivative (η⁵ -tetrahydrofluorenyl)Rh(C₂ H₄ )₂ (1 a) with halogens. An analogous reaction of the cyclooctadiene complex (η⁵ -tetrahydrofluorenyl)Rh(cod) (1 b) with I₂ is complicated by the side formation of [(cod)RhI]₂ . The reaction of 2 b with 2,2'-bipyridyl leads to cation [(η⁵ -tetrahydrofluorenyl)Rh(2,2'-bipyridyl)I]⁺ (3). The halide abstraction from 2 a,b with thallium or silver salts allowed us to prepare sandwich compounds with incoming cyclopentadienyl, dicarbollide and mesityleneligands [(η⁵ -tetrahydrofluorenyl)RhCp]⁺ (4), (η⁵ -tetrahydrofluorenyl)Rh(η-7,8-C₂ B₉ H₁₁ ) (5), and [(η⁵ -tetrahydrofluorenyl)Rh(η-mesitylene)]²⁺ (6). The structures of 1 b, 2 b ⋅ 2I₂ , 3PF₆ , 4TlI₄ , 5, and [(cod)RhI]₂ were determined by X-ray diffraction. Compounds 2 a,b efficiently catalyze the oxidative coupling of benzoic acids with alkynes to selectively give isocoumarins or naphthalenes, depending on the reaction temperature. Moreover, they showed moderate catalytic activity in other annulations of alkynes with aromatic compounds (such as benzamide, acetanilide, etc.) which proceed through CH activation. Compound 2 b also effectively catalyzes the reductive amination of aldehydes and ketones in the presence of carbon monoxide and water via water-gas shift reaction, giving amines in high yields (67-99 %).

Carbon monoxide-driven osmium catalyzed reductive amination harvesting WGSR power

First osmium-catalyzed reductive amination under the water gas–shift reaction conditions was developed. Proposed catalytic system demonstrates high performance even at the catalyst loading as low as 0.0625 mol%.

The phosphinoboration of acyl chlorides

This investigation examines the reactivity of phosphinoboronate esters Ph₂PBpin (pin = 1,2-O₂C₂Me₄) and Ph₂PBcat (cat = 1,2-O₂C₆H₄), as well as other phosphinoboron species, with various aryl and aliphatic acyl chlorides.

Formal reductive addition of acetonitrile to aldehydes and ketones

An efficient and highly productive rhodium-catalyzed method for the synthesis of nitriles employing aldehydes or ketones, methyl cyanoacetate, water and carbon monoxide as starting materials has been developed. Simple rhodium chloride without any ligands can be used. The fine tuning of the substrate can lead to the activity higher than 5000 TON.