602298-01-1

Upstream product

• 21050-13-5 bis(triphenylphosphine)iminium chloride 
• 153735-01-4 cis-bis(triphenylphosphine)iminium diiododicarbonyliridium(I) 
• 10034-85-2 hydrogen iodide 
• 74-88-4 methyl iodide 

Relevant academic research and scientific papers

Promoting role of [PtI2(CO)]2 in the iridium-catalyzed methanol carbonylation to acetic acid and its interaction with involved iridium species

The catalytic activity of the iridium complexes involved in methanol carbonylation is significantly enhanced when the carbonyliodoplatinum dimer [PtI2(CO)]2 (10′) is added to the reaction mixture. Under CO this complex readily affords the monomeric species [PtI 2(CO)2] (10). The turnover frequency value, which is 1450 h-1 for iridium alone, reaches 2400 h-1 for a Pt/Ir = 3/7 molar ratio, under 30 bar of CO and at 190 °C. To get a deeper insight into the role of the platinum cocatalyst, model conditions (dinitrogen, ambient temperature, CH2Cl2, PPN+ as counterion) have been adopted. [PtI2(CO)]2 (10′ interacts with [PPN][IrI3(CH3)(CO)2] (4-PPN), affording the monoiodo-bridged anionic species [IrI2(CH3)(CO) 2(μ-I)-PtI2(CO)]- (11), which undergoes cleavage under CO to provide [IrI2(CH3)(CO)3] (6) and PtI3(CO)]- (9). Although we have to take into account the possible iodide dissociation from 4 in the polar reaction medium (CH3COOH, CH3OH, CH3I, HI, H2O), which can be scavenged by platinum to give 9, we should not discard the intermediacy of 11, even under working catalytic conditions. The crystal structures of [PPN][IrI3(COCH3)(CO)2] (8-PPN) and [PPN][PtI3(CO)] (9-PPN), which are both involved in the overall process, were determined by X-ray diffraction analysis. A catalytic cycle is herein proposed, in which the cooperative effect between the platinum promoter and the iridium catalyst is depicted.

Isolation and structural characterization of anionic and neutral compounds resulting from the oxidative addition of HI or CH3I to [IRI 2(CO)2]-

The active iridium species in the methanol carbonylation reaction has been crystallized as the [PPN][IrI2(CO)2] complex and the X-ray structure solved, showing a cis-geometry and a square planar environment. Hydriodic acid reacts very quickly with this compound to provide [PPN][IrHI 3(CO)2], the X-ray crystal structure of which has been determined. The two CO ligands remain in mutual cis-position in a pseudooctahedral environment. The same cis-arrangement has been observed from the X-ray structure for [PPN][IrI3(CH3)(CO)2] resulting from the slower oxidative addition of CH3I to [PPN][IrI2(CO)2]. By iodide abstraction with InI 3, the anionic methyl complex gave rise to the dimeric neutral complex [Ir2(μ-I)2I2(CH3) 2(CO)4]. An X-ray structure showed that the methyl ligands are in the equatorial positions of the two octahedrons sharing an edge, formed by the two bridging iodide ligands. All these four complexes have been fully characterized by mass spectrometry, 1H and 13C NMR, and infrared both in solution and in the solid state. When necessary, the 13CO- or 13CH3-enriched complexes have been prepared and analyzed.