Co-catalysis over a bi-functional ligand-based Pd-catalyst for tandem bis-alkoxycarbonylation of terminal alkynes

Abstract

The one-pot tandem bis-alkoxycarbonylation of alkynes was accomplished over a bi-functional ligand-based Pd-catalyst with co-catalysis function.

Synergetic Catalysis for One‐pot Bis‐alkoxycarbonylation of Terminal Alkynes over Pd/Xantphos−Al(OTf)3 Bi‐functional Catalytic System

“…It has been widely accepted that [Pd−H] + species is a real active catalyst for bis‐alkoxycarbonylation of alkynes . And any factor able to improve the formation and stability of such [Pd−H] + species will speed up the reaction.…”

“…It has been widely accepted that [PdÀ H] + species is a real active catalyst for bis-alkoxycarbonylation of alkynes. [6] And any factor able to improve the formation and stability of such [PdÀ H] + species will speed up the reaction. As for Bronsted acids such as HOTf, MeSO 3 H, etc, they could serve as hydridesources upon oxidizing Pd(0) to afford palladium hydride (H + + Pd 0 !…”

“…As illustrated in Figure 2, the characteristic peaks at 2177 and 2117 cm À 1 assigned to gaseous CO vibrations (i. e. symmetric stretching vibration mode and the anti-symmetric stretching vibration mode of free CO molecule) were clearly observed in each case. Over PdCl 2 (MeCN) 2 /XantphosÀ Al(OTf) 3 bi-functional system (Figure 2-A), a weak peak at 1944 cm À 1 , which was attributed to the active [PdÀ H] + species, [6] was observed initially while the temperature was increased to 50°C. As the temperature further increasing from 50 to 120°C, this absorption peak gradually grew and then reached the maximum intensity at 120°C.…”

“…In 2018, Beller's group achieved the one‐pot bi‐alkoxycarbonylation of various aromatic and aliphatic alkynes over the catalytic system containing Pd(acac) 2 , an pyridinyl‐ tailed ligand and the Bronsted acid of PTSA ⋅ H 2 O, which exhibited the good activity as well as the high chemical/regional selectivity . More recently, our group developed a bi‐functional ligand containing both tert‐phosphino‐fragment and Bronsted acid group (−SO 3 H), which was applied successfully for Pd‐catalyzed bis‐alkoxycarbonylation of alkynes towards 2‐substituted succinates (diesters) in one‐pot process . It is evident that this sequence usually requires two indispensable catalytic factors in order to initiate the unfavored second‐step alkoxycarbonylation of electron‐deficient functional alkenes (α,β‐unsaturated esters): the phosphine‐modified palladium catalyst and the Bronsted acid as co‐catalyst, wherein the Bronsted acid (MeSO 3 H, p‐TsOH, etc.)…”

“…[5] More recently, our group developed a bi-functional ligand containing both tert-phosphino-fragment and Bronsted acid group (À SO 3 H), which was applied successfully for Pd-catalyzed bisalkoxycarbonylation of alkynes towards 2-substituted succinates (diesters) in one-pot process. [6] It is evident that this sequence usually requires two indispensable catalytic factors in order to initiate the unfavored second-step alkoxycarbonylation of electron-deficient functional alkenes (α,β-unsaturated esters): the phosphine-modified palladium catalyst and the Bronsted acid as co-catalyst, wherein the Bronsted acid (MeSO 3 H, p-TsOH, etc.) serves as hydride-source by reacting with Pd(0) to form active and stable [PdÀ H] + species (H + + Pd 0 !…”