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

• Published in: Chemistry : a European journal Vol. 27; no. 42; pp. 10903 - 10912
• Main Authors: Kharitonov, Vladimir B., Runikhina, Sofiya A., Nelyubina, Yulia V., Muratov, Dmitry V., Chusov, Denis, Loginov, Dmitry A.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 26-07-2021
• Subjects: Acetanilide; Aldehydes; Alkynes; Amination; Amines; Aromatic compounds; Benzamide; Benzoic acid; Carbon monoxide; Catalysts; Catalytic activity; CH activation; Chemical bonds; Chemistry; Coupling (molecular); Halogens; homogeneous catalysis; Ketones; Mesitylene; reductive amination; Rhodium; Salts; sandwich complexes; Shift reaction; Silver; Thallium; Reductive amination; CH activation; Rhodium; Sandwich complexes; homogeneous catalysis
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202100572

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(C2H4)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 ion 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‐C2B9H11) (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 %).
A versatile rhodium catalystfor the formation C−N and C−C bonds was synthesized based on easily available 1,2,3,4‐tetrahydrofluorene. The catalyst efficiently works for the reductive amination of carbonyl compounds via elimination of the tetrahydrofluorenyl ligand as well as for CH activation of aromatic compounds with the retention of this ligand.