Promotional effect of CH3I on hydroxycarbonylation of cycloalkene using homogeneous rhodium catalysts with PPh3 ligand

Hydroxycarbonylation of Alkenes with Formic Acid Catalyzed by a Rhodium(III) Hydride Diiodide Complex Bearing a Bidentate Phosphine Ligand

“…When 1-hexene, 2-hexene, or 3-hexene were used as substrates, hydroxycarbonylation proceeded with alkene isomerization and similar ratios of heptanoic acid, 2-methylhexanoic acid, or 2-ethylpentanoic acid were obtained (entries 4–6). The reactions catalyzed by 2 had comparable yields and selectivities to previously reported Rh-catalyzed reactions requiring additives, such as MeI/PPh 3 or Me 4 NI, but with shorter reaction times. On the other hand, when the aromatic alkenes styrene and α-methylstyrene were used as substrates, almost no carboxylic acids were obtained (entries 7 and 8).…”

“…Based on this background, to achieve more environmentally benign conditions for the hydroxycarbonylation of alkenes with HCOOH, we studied the role of additives in this reaction using rhodium complex catalysts, PPh 3 ligands, and CH 3 I. 24 Both the generation of a rhodium hydride intermediate and the presence of two equivalents of iodide ions relative to the Rh atom were found to be important for the reaction. In addition, RhHI 2 (CO)(PPh 3 ) 2 (1), a Rh(III) hydride diiodide complex, was identified as the reaction intermediate.…”

Sulfur-Promoted Hydrocarboxylation of Olefins on Heterogeneous Single-Rh-Site Catalysts

“…Cycle I ended with the dehydrohalogenation of the complex D to form A again. At the same time, cycle II processed the similar procedures (A–B 2 –C 2 –D–A) to cycle I only using the iodocyclohexane, a product from the addition of HI and the reactant CE, which named “alkyl halide” mechanism. , Meanwhile, cycle III going through CE insertion of complex D, CO insertion of complex [Rh­(CO)­CyI 4 ] 2– (B 2 ), and H 2 O hydrolysis of complex [(CO)­Rh­(COCy)­I 4 ] 2– (C 2 ) to regenerate the active species D and produce the desired product cyclohexanecarboxylic acid is called the “HX-addition” mechanism (D–B 2 –C 2 –D). , In contrast, a new Rh mononuclear complex species was formed when CO–H 2 S was involved, which was proved by the EXAFS analysis of the spent Rh 1 /PIPs with H 2 S. The trace (di)­methyl sulfide species were detected and confirmed by GC–MS (Figure S15), which were easily produced by the reaction between H 2 S and CH 3 I. − As demonstrated in Scheme b, we could conclude that the alkyl sulfide coordination complex [(CH 3 ) 2 SRh­(CO)­I 3 ] 2– (A S ) was formed and participated in a similar mechanism in Scheme a. Meanwhile, the alkyl sulfide species was deemed to an electron-donating ligand, which could accelerate cycles I and II to form the active species Rh–H complex to speed up cycle III, verified later by the DFT calculation analysis. ,, It is worth noting that cycle I was just an induction process for the formation of Rh–H-active species.…”

“…At the same time, cycle II processed the similar procedures (A−B 2 −C 2 −D−A) to cycle I only using the iodocyclohexane, a product from the addition of HI and the reactant CE, which named "alkyl halide" mechanism. 60,61 Meanwhile, cycle III going through CE insertion of complex D, CO insertion of complex [Rh(CO)CyI 4 ] 2− (B 2 ), and H 2 O hydrolysis of complex [(CO)Rh(COCy)I 4 ] 2− (C 2 ) to regenerate the active species D and produce the desired product cyclohexanecarboxylic acid is called the "HX-addition" mechanism (D−B 2 −C 2 −D). 60,61 In contrast, a new Rh mononuclear complex species was formed when CO−H 2 S was involved, which was proved by the EXAFS analysis of the spent Rh 1 /PIPs with H 2 S. The trace (di)methyl sulfide species were detected and confirmed by GC−MS (Figure S15), which were easily produced by the reaction between H 2 S and CH 3 I.…”

“…60,61 Meanwhile, cycle III going through CE insertion of complex D, CO insertion of complex [Rh(CO)CyI 4 ] 2− (B 2 ), and H 2 O hydrolysis of complex [(CO)Rh(COCy)I 4 ] 2− (C 2 ) to regenerate the active species D and produce the desired product cyclohexanecarboxylic acid is called the "HX-addition" mechanism (D−B 2 −C 2 −D). 60,61 In contrast, a new Rh mononuclear complex species was formed when CO−H 2 S was involved, which was proved by the EXAFS analysis of the spent Rh 1 /PIPs with H 2 S. The trace (di)methyl sulfide species were detected and confirmed by GC−MS (Figure S15), which were easily produced by the reaction between H 2 S and CH 3 I. 62−64 As demonstrated in Scheme 1b, we could conclude that the alkyl sulfide coordination complex [(CH 3 ) 2 SRh(CO)-I 3 ] 2− (A S ) was formed and participated in a similar mechanism in Scheme 1a.…”