Novel multi-dentate phosphines for Pd-catalyzed alkoxycarbonylation of alkynes promoted by H2O additive

Multiple-Functional Diphosphines: Synthesis, Characterization, and Application to Pd-Catalyzed Alkoxycarbonylation of Alkynes

“…As demonstrated in Figure , characteristic peaks for gaseous CO were clearly observed with strong vibrations of 2175 and 2115 cm –1 . Over the L4 -Pd­(CH 3 CN) 2 Cl 2 system (Figure A), when the temperature increased from 40 to 120 °C gradually, a weak absorption peak at 1956 cm –1 appeared at 120 °C and then reached its maximum intensity after 10 min of continuous heating at 120 °C, which was identified as the active Pd–H (palladium–hydride) species. , However, as the reaction time prolonged, the formed Pd–H species was decomposed completely after 58 min. Concurrently, the intensive characteristic peak at 1728 cm –1 , which was assigned to the carbonyl stretching vibration absorption peak of the product methyl 2-phenylacrylate, was observed, which increased as the continuous heating time increased (Figure B).…”

“…Over the L4 -Pd­(CH 3 CN) 2 Cl 2 system (Figure A), when the temperature increased from 40 to 120 °C gradually, a weak absorption peak at 1956 cm –1 appeared at 120 °C and then reached its maximum intensity after 10 min of continuous heating at 120 °C, which was identified as the active Pd–H (palladium–hydride) species. , However, as the reaction time prolonged, the formed Pd–H species was decomposed completely after 58 min. Concurrently, the intensive characteristic peak at 1728 cm –1 , which was assigned to the carbonyl stretching vibration absorption peak of the product methyl 2-phenylacrylate, was observed, which increased as the continuous heating time increased (Figure B). In contrast, as shown in Figure B, over the L5 -Pd­(CH 3 CN) 2 Cl 2 system, the characteristic peak of the Pd–H species was more easily formed and was more stable with indications of its earlier appearance just at 108 °C and a well-maintained signal even at 120 °C after 60 min, which revealed that the presence of L5 favored the formation and stability of the active Pd–H species more compared to L4 and also corresponded to more efficient methoxycarbonylation.…”

“…Later on, universal applications of phosphine ligands in alkoxycarbonylation of alkynes to warrant the activity, selectivity, and stability of Pd catalysts developed rapidly. − It was found that 1,4-bis­(diphenylphosphino)­butane (dppb), , triphenylphosphine, − 1,2-bis­(ditert-butylphosphinomethyl)­benzene (BDTBPMB), − and 2,2,-bis­(diphenylphosphino)-1,1-binaphthyl (BINAP) are well-known phosphines to improve Pd-catalyzed carbonylation. More recently, many N,P hybrid ligands with hemilability − have been reported in the literature, ,,− as shown in Scheme . Moreover, the specific effects of some reported ligands on alkoxycarbonylation of phenylacetylene have been summarized in Table S1 in the Supporting Information.…”

“…Inspired by the previous developments, we continue our interest in the design and synthesis of novel N,P hybrid ligands applicable to alkoxycarbonylation of alkynes, 36 which are composed of more functional groups including phosphino fragments, amino moieties, and F atoms with intensive electronwithdrawing effects (Scheme 1). Herein, these developed P,N hybrid ligands with good robustness are expected not only to embody typical coordination ability to Pd catalysts with P,P-, or P,N-chelating effect but also to possess the potential to develop a hydrogen-bonding interaction.…”

Palladium-catalyzed regio- and stereoselective alkoxycarbonylation of unsymmetrical internal alkynes toward α, β-unsaturated succinates

“…To the best of our knowledge, almost all the protocols that able to properly regulate regioand stereoselectivity so far are restricted to terminal alkynes. For instance, a series of branched [15][16][17][18][19][20][21][22][23] and linear [24][25][26][27][28] selective α, β-unsaturated esters (the selectivity up to 99:1) can be obtained by designing and modifying the steric hindrance, electronic properties, and proton transfer capacity of ligands applied to enhance the catalyst reactivity and reaction selectivity for the alkoxycarbonylation of alkynes (Scheme 1A, middle). Scheme 1.…”