The Origins of the Differences between Alkyne Hydroalkoxylations Catalyzed by 8‐Quinolinolato‐ and Dipyrrinato‐Ligated Rh^I Complexes: A DFT Mechanistic Study

Abstract

Hydroalkoxylations of terminal alkynes with methanol, catalyzed by 8-quinolinolato-and dipyrrinato-ligated Rh I complexes, afford anti-Markovnikov (Z)-and (E)-enol ethers, respectively. Herein we performed a DFT study to gain insight into the mechanisms of the two reactions, aiming at understanding why and how the two ligands differ. Of the two possible mechanisms, namely, C -HT and Rh-HT, characterized by a Rh I Fisher carbene and vinyl Rh III -H hydride complex, respectively, the hydroalkoxylation with 8-quinolinolato prefers the C -HT mechanism, while that with dipyrrinato favors the Rh-HT mechanism. The root cause for the mechanistic difference is that the O atom in 8-quinolinolato, due to its large electronega-

Transition Metal Vinylidene- and Allenylidene-Mediated Catalysis in Organic Synthesis

“…314) reorients selectivity to (Z)-preference in the reaction with 310. 220 In addition to alcohols, epoxide and carbonyl groups have been reported to be capable of intercepting metal vinylidene intermediates. When ethynylepoxide 315 was treated with pentacarbonylmolybdenum in the presence of TEA, furan 316 was isolated in good yield (Scheme 64a).…”

“…In contrast, tautomerization of the alkenylrhodium to a rhodium carbene (cf. 314 ) reorients selectivity to ( Z )-preference in the reaction with 310 …”

Dipyrrin based metal complexes: reactivity and catalysis

“…The favored formation of the E isomer of (2-methoxyvinyl)benzene was rationalized by less steric hindrance between the methoxy and phenyl group in the trans arrangement by DFT calculations. 127 This theoretical investigation also suggests that DMA facilitates the addition of MeOH and that the mechanism involves a vinyl Rh(III)-H hydride intermediate. Khoroshutin and coworkers also described the activity of a Rh(I) compound based on dpm albeit with the bis-pyrrolic chelate not at the rhodium center.…”

Catalytic Reactions of Terminal Alkynes Using Rhodium(I) Complexes Bearing 8-Quinolinolate Ligands

“…Wang and co-workers studied the mechanism of the hydroalkoxylation reaction based on DFT calculations and proposed the catalytic cycle shown in Figure . Coordination of an alkyne to 1a gives rhodium complex 5 , which then tautomerizes to vinylidene rhodium complex 6 via an indirect 1,2-hydrogen shift.…”