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

Abstract

Iodide is an essential promoter in the industrial production of acetic acid via methanol carbonylation, but it also contributes to reactor corrosion and catalyst deactivation. Here we report that iridium pincer complexes mediate the individual steps of methanol carbonylation to methyl acetate in the absence of methyl iodide or iodide salts. Iodide-free methylation is achieved under mild conditions by an aminophenylphosphinite pincer iridium(I) dinitrogen complex through net C−O oxidative addition of methyl acetate to produce an isolable methyliridium-(III) acetate complex. Experimental and computational studies provide evidence for methylation via initial C−H bond activation followed by acetate migration, facilitated by amine hemilability. Subsequent CO insertion and reductive elimination in methanol solution produced methyl acetate and acetic acid. The net reaction is methanol carbonylation to acetic acid using methyl acetate as a promoter alongside conversion of an iridium dinitrogen complex to an iridium carbonyl complex. Kinetic studies of migratory insertion and reductive elimination reveal essential roles of the solvent methanol and distinct features of acetate and iodide anions that are relevant to the design of future catalysts for iodide-free carbonylation.

Tunable and Switchable Catalysis Enabled by Cation-Controlled Gating with Crown Ether Ligands

“…When the blocking methoxy group is installed on the backbone, the rate of isomerization is maintained for longer periods and the catalyst can be recycled repeatedly. The methoxy group also enabled access to iridium complexes with diethylamine groups, , which can serve as useful comparisons in future studies. The methoxy blocking group design feature has been retained for most studies since its introduction.…”

Characterization of Methyl- and Acetyl-Ni Intermediates in Acetyl CoA Synthase Formed during Anaerobic CO2 and CO Fixation

“…This reaction requires C–C and C–S bond cleavage to form the state with CH 3 , CO, and CoA independently bound to ACS, 12 CO/ 14 CO exchange, then condensation of these three groups to reform acetyl-CoA . An analogous state has been observed in inorganic complexes as an intermediate in carbonyl insertion into the metal–CH 3 bond during acetate synthesis …”

“…2 An analogous state has been observed in inorganic complexes as an intermediate in carbonyl insertion into the metal−CH 3 bond during acetate synthesis. 9 Here, we describe a combination of spectroscopic experiments on trapped Ni p (II)-Me (4′, A Me ) and Ni p (II)−Ac (3′, A Ac ) intermediates in the WLP. We propose a novel electrochemical (EC) coupling mechanism to address the debate between the diamagnetic and paramagnetic mechanisms, 10 which explains how ACS transits through these Figure 2.…”

NMR spectroscopic investigations of transition metal complexes in organometallic and bioinorganic chemistry

“…110,111 As depicted in Figure 2b, δ C values of such compounds present substantial differences. [112][113][114][115][116] M-C alkyl peaks appear in a range of approximately +150 to À20 ppm, 117 which is much wider relative to alkanes. For M-C aryl complexes, δ C values are observed in a range of +180 to +130 ppm, which is relatively shielded compared with arenes.…”