Homogeneous Pd-Catalyzed Heck Coupling in γ-Valerolactone as a Green Reaction Medium: A Catalytic, Kinetic, and Computational Study

Abstract

γ-Valerolactone (GVL) was proposed as an environmentally benign reaction medium for phosphine-free Pd-catalyzed homogeneous Heck coupling reaction of iodobenzene and styrene derivatives. Detailed catalytic, kinetic, and computational studies were performed for this industrially important transformation in GVL, which shows remarkable tolerance for the moisture content of the reaction mixture and gives good efficiency for Pd(II) catalyst precursors such as PdCl 2 and Pd(OAc) 2 . Excellent functional group tolerance for both iodoaromatic substances and styrene derivatives was shown, and the reaction efficiency was correlated by the Hammet-constant of corresponding substrates. A simplified kinetic model was subsequently found to model the transformation, which can be represented by an excellent fitting of the calculated concentration of corresponding species to the experimentally determined ones. ΔH app ⧧ = +103.0 kJ•mol −1 for the apparent overall activation enthalpy of the reaction in GVL, and ΔH app ⧧ = +103.7 kJ•mol −1 in the case of DMF have been obtained. ΔS app ⧧ = +139.7 J• mol −1 •K −1 was calculated for the apparent overall activation entropy of the reaction in the presence of GVL, and ΔS app ⧧ = +138.1 J• mol −1 •K −1 in the presence of DMF, very similar values suggesting that no medium effect on the mechanism can be proposed. The computational study confirmed the experimentally observed trends regarding the effect of electron-donating and -withdrawing substituents of iodobenzene and styrene as follows: the electron-donating substituents accelerate the reaction rate for iodobenzene but decrease the reactivity for styrene derivatives.

Alkyl Levulinates and 2-Methyltetrahydrofuran: Possible Biomass-Based Solvents in Palladium-Catalyzed Aminocarbonylation

“…Despite the promising chemoselectivity results at the elevated CO pressure, the above-mentioned low conversions inspired us to find other reaction conditions that could increase the synthetic importance of this reaction in green solvents. The aminocarbonylation of iodobenzene and tert -butylamine has been investigated by Marosvölgyi-Haskó and coworkers in DMF [ 65 ] and GVL using the Pd(OAc) 2 /PPh 3 catalyst [ 41 ]. Although the amines were different, we described similar behavior in our former research (reactivity and selectivity) under the same reaction conditions [ 66 , 67 , 68 ].…”

“…Carboxamides can be synthesized from easily available starting materials with aminocarbonylation, although the conventional carboxylic acid−carboxylic halide−carboxamide route is difficult to prepare because it has no notable yield in the implementation [ 29 , 30 ]. Moreover, our research group has been investigating this reaction in the conventional solvent DMF for years [ 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ], and thanks to the ascertainments of the groups from Skrydstrup [ 40 ] and Mika [ 41 , 42 , 43 ], our interest has been turned to the investigation of green solvents.…”

Conversion of levulinic acid to valuable chemicals: a review

“…7. 124,[127][128][129][130] GVL is also suitable for use as a green solvent 131 and an intermediate of various compounds. The GVL derived chemicals include fuel additives, 119 food ingredients, 132 duction of chemicals, 133 highgrade alkene fuels 134 and nylon intermediates.…”

1,3-Dioxolane compounds (DOXs) as biobased reaction media

“…11,12 3-Methoxybutan-2-one (MO) has been used instead of chlorinated solvents. 13 γ-Valerolactone (GVL) is a polar aprotic solvent effective in supporting cross-coupling reactions [14][15][16][17][18][19][20] and is (amongst) the best established bio-based alternatives to conventional dipolar aprotic solvents (e.g., DMF, NMP and DMSO). However, even GVL is not problem free: legal issues associated with the functioning of GVL as a prodrug 21 have led to the decision that its use should not be recommended in a Unified Solvent Selection Guide.…”