Reactivity of Ir(iii) carbonyl complexes with water: alternative by-product formation pathways in catalytic methanol carbonylation

Abstract

The reactions of water with a number of iridium(III) complexes relevant to the mechanism for catalytic methanol carbonylation are reported. The iridium acetyl, [Ir(CO)2I3(COMe)](-), reacts with water under mild conditions to release CO2 and CH4, rather than the expected acetic acid. Isotopic labeling and kinetic experiments are consistent with a mechanism involving nucleophilic attack by water on a terminal CO ligand of [Ir(CO)2I3(COMe)](-) to give an (undetected) hydroxycarbonyl species. Subsequent decarboxylation and elimination of methane gives [Ir(CO)2I2](-). Similar reactions with water are observed for [Ir(CO)2I3Me](-), [Ir(CO)2(NCMe)I2(COMe)] and [Ir(CO)3I2Me] with the neutral complexes exhibiting markedly higher rates. The results demonstrate that CO2 formation during methanol carbonylation is not restricted to the conventional water gas shift mechanism mediated by [Ir(CO)2I4](-) or [Ir(CO)3I3], but can arise directly from key organo-iridium(III) intermediates in the carbonylation cycle. An alternative pathway for methane formation not involving the intermediacy of H2 is also suggested. A mechanism is proposed for the conversion MeOH + CO → CO2 + CH4, which may account for the similar rates of formation of the two gaseous by-products during iridium-catalysed methanol carbonylation.

Utilization of a Methoxy Group in Lignin to Prepare Amides by the Carbonylation of Amines

“…At the beginning of the reaction, with the help of LiI, CH 3 I was formed by the cleavage of the methoxy group in lignin. Then, just like one of the most famous reactions in methanol carbonylation, a typical carbonylation process including oxidative addition, insertion of CO, and reductive elimination happens, as expected, and acetyl iodide was produced. − Meanwhile, an N -methyl reaction also proceeded, and N -methylaniline was converted to NND. Subsequently, NND reacted with acetyl iodide, and the target product of NMA was produced.…”

Stepwise Iodide-Free Methanol Carbonylation via Methyl Acetate Activation by Pincer Iridium Complexes

“…This raises the possibility that one role of iodide is to shift speciation away from iridium­(I) carbonyl, which could have important implications in catalysis. For example, hydride complexes are proposed to be responsible for catalyzing the undesired water-gas shift reaction as a side-reaction during the Cativa process. ,,, …”

“…For example, hydride complexes are proposed to be responsible for catalyzing the undesired water-gas shift reaction as a side-reaction during the Cativa process. 1,3,26,38 To better compare the influence of acetate and iodide ligands on acetyl formation, the kinetics of CO insertion of iodide (5-cis) and acetate (4-cis) complexes were studied. The kinetics were first compared in CD 3 OD/DCE (8:2) solution, since 5-cis is insoluble in pure methanol (Table 1).…”

Solvatochromism and Theoretical Studies of Dicyanobis(phenylpyridine)iridium(III) Complex Using Density Functional Theory

“…In all calculations, an extensive basis set was used, consisting of 6-311G** [11][12][13][14] on all atoms (C, H, N, O) apart from iridium, which was described using a Stuttgart-Dresden pseudo-potential [15][16][17][18]. Besides, bulk solvent effects were treated via the polarizable continuum model (PCM) [19][20][21][22]. Finally, all calculations were run using ultrafine integrals, and no symmetry was considered in the calculations.…”