An Anionic, Chelating C(sp 3 )/NHC ligand from the Combination of an N‑heterobicyclic Carbene and Barbituric Heterocycle

• Main Authors: Idir Benaissa (6000965), Katarzyna Gajda (1726207), Laure Vendier (1347666), Noël Lugan (1737850), Anna Kajetanowicz (4046599), Karol Grela (1478173), Véronique Michelet (1413130), Vincent César (1554919), Stéphanie Bastin (1716577)
• Format: Other Non-Article Part of Journal/Newspaper
• Language: unknown
• Published: 1753
• Subjects: Biophysics; Biochemistry; Medicine; Environmental Sciences not elsewhere classified; Chemical Sciences not elsewhere classified; Physical Sciences not elsewhere classified; strong donating character; stretching frequencies recorded; low catalyst loadings; kinetic gold ­(; isolated upon crystallization; imidazo ­[ 1; exhibited high activities; carboxylic acid derivatives; au ­( iii; antecedent gold ­(; ); ir ­(; ru ­(< b; rh ­(< b; aucl ­(< b; zwitterionic nhc precursor; appropriate metal precursor; 9 </ b; lateral barbituric heterocycle; malonic carbon atoms; co </ sub; 8 </ sup; 6 </ sup; 2 </ sub; c ­( sp; anionic barbituric heterocycle; barbituric heterocycle; malonic carbon; p </; metal centers; chelating c; barbituric moiety; anionic nhc; primary alcohols; platform substituted; free carbene; external oxidant; dehydrogenative synthesis; coordination chemistry; chelating behavior; c5 position; >]­ pyridin; 5 -<; IPY
• Online Access: https://doi.org/10.1021/acs.organomet.1c00458.s001

The coordination chemistry of the anionic NHC 1 – based on an imidazo­[1,5- a ]­pyridin-3-ylidene (IPy) platform substituted at the C5 position by an anionic barbituric heterocycle was studied with d 6 (Ru­(II), Mn­(I)) and d 8 (Pd­(II), Rh­(I), Ir­(I), Au­(III)) transition-metal centers. While the anionic barbituric heterocycle is planar in the zwitterionic NHC precursor 1 ·H, NMR spectroscopic analyses supplemented by X-ray diffraction studies evidenced the chelating behavior of ligand 1 – through the carbenic and the malonic carbon atoms in all of the complexes, resulting from a deformation of the lateral barbituric heterocycle. The complexes were obtained by reaction of the free carbene with the appropriate metal precursor, except for the Au­(III) complex 10 , which was obtained by oxidation of the antecedent gold­(I) complex [AuCl­( 1 )] − with PhICl 2 as an external oxidant. During the course of the process, the kinetic gold­(I) intermediate 9 resulting from the oxidation of the malonic carbon of the barbituric moiety was isolated upon crystallization from the reaction mixture. The ν CO stretching frequencies recorded for complex [Rh­( 1 )­(CO) 2 ] ( 5 ) demonstrated the strong donating character of the malonate-C­(sp 3 )/NHC ligand 1 – . The ruthenium complex [Ru­( 1 )­Cl­( p -cymene)] ( 11 ) was implemented as a precatalyst in the dehydrogenative synthesis of carboxylic acid derivatives from primary alcohols and exhibited high activities at low catalyst loadings (25–250 ppm) and a large tolerance toward functional groups.