Catalytic intermediates in carbonylation reactions-III. Isolation, spectroscopy, electrochemical characteristics and crystal structure of isoquinolinium dicarbonyl tetraiodo iridium(III)

Abstract

The iodocarbonyl anion of iridium(III), [Ir(CO)₂I₄]^- , was isolated and characterized as the isoquinolinium salt during carbonylation of ethanol and higher alcohols using IrCl₃ . ₃H₂O as a catalyst precursor with HI as a promoter. X-ray analysis shows the presence of discrete cationic [C₁₁H₁₂N]⁺ and cis anionic species [lr(CO)₂I₄]^- , with a distorted octahedral environment around iridium and average Ir-I and Ir-C distances of 2.702(2) and 1.86(4) Å, respectively. Spectral and electrochemical studies on the intermediates isolated during carbonylation of other higher alcohols revealed a strong influence of the counter cation on the electron-transfer processes in these halocarbonyl complex of Ir^III.