Synthesis, reactivities and catalytic carbonylation of rhodium(I) carbonyl complexes containing isomeric acetylpyridine ligands

[Rh(CO)2Cl]2 reacts with two mole equivalent of 2-acetylpyridine (a), 3-acetylpyridine (b) and 4-acetylpyridine (c) to afford chelate [Rh(CO)Cl(η2-N∩O)] (1a) and non-chelate [Rh(CO)2Cl(η1-N∼O)] (1b, 1c) complexes, where, N∩O = a, N∼O = b, c. Oxidative addition (OA) of 1a–1c with CH3I and C2H5I yields penta coordinate rhodium(III) complexes, [Rh(COR)ClI(η2-N∩O)] {R = –CH3 (2a); –C2H5 (3a)} and [Rh(COR)(CO)ClI(η1-N∼O)] {R = –CH3 (2b, 2c); –C2H5 (3b, 3c)}. Kinetic study for the reaction of 1a–1c with CH3I indicates a pseudo-first order reaction. The catalytic activity of 1a–1c for the carbonylation of methanol to acetic acid and its ester was evaluated at different initial CO pressures 5, 10 and 20 bar at ∼25 °C and higher turn over numbers (TON = 1581–1654) were obtained compared to commercial Monsanto’s species [Rh(CO)2I2]− (TON = 1000) under the reaction conditions: temperature = 130 ± 1 °C, pressure = 15–32 bar, rpm = 450, time = 1 h and catalyst: substrate = 1: 1900.

Graphical abstractThree new Rh(I) carbonyl complexes of isomeric acetylpyridine ligands have been synthesized, which undergo oxidative addition (OA) reactions with different electrophiles to afford Rh(III) oxidized products. The kinetics study of the complexes with CH3I follows pseudo-first order reaction. The synthesized complexes show high catalytic activity (TON = 1581–1654) in the carbonylation of methanol to acetic acid and its ester than the well-known Monsanto’s species [Rh(CO)2I2]− (TON = 1000) under similar experimental conditions.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Synthesis and characterization of Rh(I) carbonyl complexes with N,O-donor ligands. ► Oxidative addition of electrophiles such as CH3I and C2H5I with Rh(I) carbonyl complexes. ► Kinetic study of the complexes with CH3I indicates a pseudo-first order reaction. ► Carbonylation of methanol to produce acetic acid and its ester.