Synthesis of Pd(II) 1-alkylperimidine complexes as efficient catalysts for Suzuki reactions involving arylchlorides

Abstract

Interaction of aryl halides with arylboronic acids (via Suzuki reaction) representing one of the most general C-C coupling reactions in organic synthesis, is catalyzed by palladium complexes in homogeneous solution according to the following equation [1][2][3]:(1)The reactivity of the aryl halide component decreases drastically in the X order I > Br > Cl and electron-withdrawing substituents R are required for the chlorides to react [1][2][3][4][5][6]. The low reactivity of aryl chlorides in cross-coupling reactions is generally ascribed to their reluctance to oxidatively add to Pd(0) [4][5][6]. Current interest focuses on the use of aryl chlorides since they are cheaper and more readily accessible than bromides and iodides [7]. Significant advances have been recently achieved by use of palladacycles and especially, by use of bulky and electron-rich tertiary phosphines as catalyst modifiers systems [8][9][10][11][12][13][14]. However, the major drawback of these is that the phosphine ligands are comparatively difficult to make or rather expensive. Furthermore, tertiary phosphines require airfree handling to prevent their oxidation and are susceptible to P-C bond cleavage at elevated temperatures [15].On the other hand, transition metal complexes with ligands containing nitrogen-donor atoms have been shown their potential to successfully promote the catalytic transformation of organic compounds [16,17]. These discoveries motivate the search for the new metal complexes with N-coordinated ligands and the evaluation of their catalytic properties.] Base X = Cl, Br, I. R ROur contribution to this field has started with syntheses of 2-imidazoline and benzimidazole complexes of Pt(II), Rh(I), Ru(II), and Pd(II) which are capable of catalyzing the cyclopropanation of styrene with ethyl diazoacetate and intramolecular cyclization of (Z)-3-methylpent-2-en-4-yn-1-ol into 2,3-dimethylfuran in good yields [18][19][20][21][22]. Recently, we have developed improved procedures of Heck and Suzuki reactions of aryl chlorides making use of novel ligands 1,3-bis(2,4,6-trimethylbenzyl)imidazolium chloride, 1-alkylimidazoline, α -bis(imine) [23,24]. The 1-alkylperimidine complexes are insensitive to air and moisture and are thermally stable in both the solid state and in solution.However, the development of new ligands or the application of existing ligands in Suzuki reaction, particularly those involving aryl chlorides as substrates, is still of considerable importance.We report here the straightforward preparation of a series phosphine palladium complexes with N-coordinated 1-alkylperimidine derivatives. These complexes were shown to be effective catalysts for Suzuki reaction especially with arylchlorides. EXPERIMENTALAll reactions were performed using Schlenk-type flask under argon and standard high vacuum-line techniques. Solvents were analytical grade and distilled under argon from sodium benzophenone (Et 2 O, dioxane, toluene, n -hexane ). 1 -Substituted perimidine (A) were prepared according to the literature [25,26]. NMR spectr...

N‐functionalized azolin‐2‐ylidene‐palladium‐catalyzed heck reaction

“…Their syntheses were achieved by the reaction of N,N -dialkylethan-1,2-diamines, N,N -dialkylpropan-1,3-diamines, and N,N -dialkylbutan-1,4-diamines with triethyl orthoformate and ammonium hexafluorophosphate (Scheme 1) [14].…”

Effect of immobilization on catalytic characteristics of saturated Pd-N-heterocyclic carbenes in Mizoroki–Heck reactions

“…Fig. 2 also illustrates the kinetic profile for the reaction catalyzed by another type of Pd-NHC complex (complex 3) in which all nitrogen atoms of pentacylic rings of NHC ligands are functionalized by 2,4,6-trimethylbenzyl groups [10]:…”

Palladium(II)NHC complexes containing benzimidazole ligand as a catalyst for CN bond formation

“…The most common ligand concepts comprise a wide range of phosphines, including phosphapalladacycles, cyclodiphosphazane and Nheterocyclic carbenes. [18 -21,28 -30] Pd/imidazolium salt systems [18] and the well-defined Pd-NHCs complexes [19] were found to be highly efficient for N-arylation of a wide range of nitrogencontaining substrates. However, it has not been demonstrated yet that these systems are effective for triarylamines.…”