Mizoroki–Heck Cross‐Coupling of Acrylate Derivatives with Aryl Halides Catalyzed by Palladate Pre‐Catalysts

Abstract

The Mizoroki-Heck (MH) reaction involving aryl halides with various acrylates and acrylamides has been studied using air and moisture-stable imidazolium-based palladate precatalysts. These pre-catalysts can be converted into Pd-NHC species (NHC = N-heterocyclic carbene) under catalytic conditions and are capable of facilitating the Mizoroki-Heck reaction of aryl halides with various acrylates. The effects of solvent, catalyst loading, temperature and bases on the reaction out- [a] 4697 Scheme 2. Substrate scope for the MH reaction with acrylate 2a-b.General Procedure for the Mizoroki-Heck Reaction: In air, a vial was charged with [SIPr·H][Pd(η 3 -2-Me-allyl)Cl 2 ] (Pd-1) (4.4 mg, 1.4 mol%), K 2 CO 3 (2.0 equiv.), DMF (1 mL) and a magnetic stir bar. The corresponding aryl halide (0.5 mmol) was added followed by the corresponding acrylate (1.0 equiv.), and the vial was then sealed with a screw cap. The reaction was left to stir for 20 h at 100°C. Afterwards, distilled water (2 mL) was added and the products were extracted with diethyl ether (3 × 3 mL). Finally, the products were isolated by flash column chromatography. The isolated yields are average of two runs. All the related supporting data are given in the Supporting Information. Mizoroki-Heck Reaction Scale Up:Following the general procedure, [SIPr·H][Pd(η 3 -2-Me-allyl)Cl 2 ] (Pd-1) (44 mg, 1.4 mol%), K 2 CO 3 (1.38 g, 2.0 equiv.), DMF (10 mL) were charged into oven dried 20 mL screwed cap vial. 4-bromoanisol (0.93 g, 5 mmol) and n-butyl acrylate (0.64 g, 5 mmol) were added subsequently and the vial was closed and heated to 100°C for 20 h. the reaction residue was purified by column chromatography 100-200 mesh silica gel and EtOAc/n-hexane (3:97) to afford 3a in 1.13 g (97%) as a yellow liquid. 1 H NMR (400 MHz, CDCl 3 ): δ (ppm) = 7.63 (d, J = 16.4 Hz, 1H, CH=CH), 7.47 (d, J = 8.8 Hz, 2HAr), 6.90 (d, J = 8.8 Hz, 2HAr), 6.31 (d, J = 16.4 Hz, 1H, CH=CH), 4.19 (t, J = 7.2 Hz, 2H, OCH 2 ), 3.84 (s, 3H, OCH 3 ), 1.64-1.70 (m, 2H , CH 2 ), 1.40-1.46 (m, 2H , CH 2 ), 0.96 (t,

The “weak base route” leading to transition metal–N-heterocyclic carbene complexes

“…All the desired compounds were obtained in high yields (85-99%). The applicability of the described palladates was also shown for the Mizoroki-Heck, 73,74 the Buchwald-Hartwig arylamination and ketone arylation reactions. 76 The scalability of the weak base approach was also showcased.…”

“…In attempts to probe if the existence of such an intermediate, which is an "ate" complex, was more widespread than expected, Zinser et al obtained a series of Pd-NHC complexes using the same reaction conditions as for the Cu-and Au-NHC compounds. 73,74 The palladium dimers [Pd(η 3 -allyl)(μ-Cl)]2, [Pd(η 3 -cin)(μ-Cl)]2 73,74 and [Pd(η 3 -2-Me-allyl)(μ-Cl)]2 74 were reacted with various saturated and unsaturated NHC salts in acetone in the presence of K2CO3. While common NHC salts reacted well when simple heating of mixture in acetone at 60°C for 5 hours, bulkier NHC ligands (namely IPr*, IPr* OMe , IPr* 2Np , IPent, IHept) required a modified procedure.…”

Palladates of the [NHC⋅H][Pd(NH2)(CC)Cl2] Type as Effective Pre‐catalysts for the Formation of C−C and C−N Bonds

“…The simplest method to assemble palladates is to grind the NHC ligand precursors (the azolium salts) and the palladium precursor [Pd(η 3 -R-allyl)(μ-Cl)] 2 with a mortar and pestle. [23][24][25][26][27] We tested whether this solvent-free approach would be possible using the [Pd(NH 2 )(CC)Cl] 2 precursor containing a palladacyclic framework. By grinding for 5 minutes, in air, 2 equivalents of the corresponding NHC ligand precursors with the [Pd-…”

“…To permit increasingly user-friendly and greener catalytic systems, we reported recently on the use of a palladate pre-catalyst, of the formula [NHC•H][Pd(η 3 -R-allyl)Cl 2 ] (Figure 1), that exhibits, in the Suzuki-Miyaura, Heck, α-arylation reaction and Buchwald-Hartwig amination, very high activity and shows a broad functional group tolerance while making use of mild conditions and a green solvent. [23][24][25][26][27] Important advantage of such systems is their facile gramscale synthesis under solvent-free conditions, without the need for any workup, and easy activation (no need of additives or of any prior activation if the reactions are conducted under slightly basic conditions). These advantages render these complexes highly useful synthetic tools.…”

Recent Advances on N‐Heterocyclic Carbene‐Palladium‐catalyzed Heck Reaction

“…A novel idea of using palladate pre‐catalyst in the Heck coupling reaction was reported 1,3‐bis (2,6‐diisopropylphenylimidazolidene (SIPr)) as the NHC ligand [57] . The standard operating condition comprised of 1.4 mol% of [SIPr⋅H] [Pd(ŋ 3 ‐2‐Me‐allyl) Cl 2 ] Pd catalyst, with 2 equiv.…”