Iron-Catalyzed Cross-Coupling of Primary and Secondary Alkyl Halides with Aryl Grignard Reagents

Ionic iron(III) complexes of bis(phenol)-functionalized imidazolium cations: synthesis, structures and catalysis for aryl Grignard cross-coupling of alkyl halides

A series of bis(phenol)-functionalized imidazolium salts, 1,3-bis(4,6-di-R(1)-2-hydroxybenzyl)-2-R(2)-4,5-di-R(3)-imidazolium chlorides H(3)L(n)Cl (R(1) = (t)Bu, R(2) = R(3) = H, H(3)L(1)Cl, 1; R(1) = CH(3), R(2) = R(3) = H, H(3)L(2)Cl, 2; R(1) = (t)Bu, R(2) = H, R(3) = Cl, H(3)L(3)Cl, 3; R(1) = (t)Bu, R(2) = CH(3), R(3) = H, H(3)L(4)Cl, 4), were used to produce a novel series of ionic iron(III) complexes [H(3)L(n)][FeX(4)] (n = 1, X = Cl, 5; n = 2, X = Cl, 6; n = 3, X = Cl, 7; n = 4, X = Cl, 8; n = 1, X = Br, 9; n = 3, X = Br, 10). All of the complexes were characterized by Raman spectroscopy and electrospray ionization mass spectrometry. Elemental analysis and X-ray crystallography were also used. All of the complexes were non-hygroscopic and air-stable, with five of them existing as solids (5, 7-10) and one as an oil (6) at room temperature. A preliminary catalytic study on the cross-coupling reactions of aryl Grignard reagents with primary and secondary alkyl halides bearing β-hydrogens, revealed that all of the ionic iron(III) complexes exhibited good to excellent catalytic activity. Complexes 5, 6 and 8 exhibited optimal activity, whereas 7, 9 and 10 showed only moderate activity. Furthermore, by simply decanting the cross-coupling product in the ether layer, complexes 5 and 6 could be reused in at least seven successive runs without significant loss in catalytic activity.

Cross-coupling of aryltrimethylammonium iodides with arylzinc reagents catalyzed by amido pincer nickel complexes

The cross-coupling reaction of aryltrimethylammonium iodides with aryl- or heteroarylzinc chlorides catalyzed by amido pincer nickel complexes was performed. The reaction requires low catalyst loading and displays broad substrate scope.

The development of bulky palladium NHC complexes for the most-challenging cross-coupling reactions

Palladium-catalyzed cross-coupling reactions enable organic chemists to form C-C bonds in targeted positions and under mild conditions. Although phosphine ligands have been intensively researched, in the search for even better cross-coupling catalysts attention has recently turned to the use of N-heterocyclic carbene (NHC) ligands, which form a strong bond to the palladium center. PEPPSI (pyridine-enhanced precatalyst preparation, stabilization, and initiation) palladium precatalysts with bulky NHC ligands have established themselves as successful alternatives to palladium phosphine complexes. This Review shows the success of these species in Suzuki-Miyaura, Negishi, and Stille-Migita cross-couplings as well as in amination and sulfination reactions.

Iron-catalyzed regio- and stereoselective chlorosulfonylation of terminal alkynes with aromatic sulfonyl chlorides

Terminal alkynes react with aromatic sulfonyl chlorides in the presence of an iron(II) catalyst and a phosphine ligand to give (E)-β-chlorovinylsulfones with 100% regio- and stereoselectivity. Various functional groups, such as chloride, bromide, iodide, nitro, ketone, and aldehyde, are tolerated under the reaction conditions. Addition of tosyl chloride to a 1,6-enyne followed by radical 5-exo-trig cyclization gave an exocyclic alkenylsulfone.

Iron-catalyzed intramolecular allylic C-H amination

A highly selective C-H amination reaction under iron catalysis has been developed. This novel system, which employs an inexpensive, nontoxic [Fe(III)Pc] catalyst (typically used as an industrial ink additive), displays a strong preference for allylic C-H amination over aziridination and all other C-H bond types (i.e., allylic > benzylic > ethereal > 3° > 2° ≫ 1°). Moreover, in polyolefinic substrates, the site selectivity can be controlled by the electronic and steric character of the allylic C-H bond. Although this reaction is shown to proceed via a stepwise mechanism, the stereoretentive nature of C-H amination for 3° aliphatic C-H bonds suggests a very rapid radical rebound step.

Organozinc Chemistry Enabled by Micellar Catalysis. Palladium-Catalyzed Cross-Couplings between Alkyl and Aryl Bromides in Water at Room Temperature

Negishi-like cross-couplings between (functionalized) alkyl and aryl bromides are described. Despite the fact that organozinc reagents are intolerant of water, their formation as well as their use in an aqueous micellar environment is discussed herein. Each component of this complex series of events leading up to C-C bond formation has an important role which has been determined insofar as the type of zinc, amine ligand, surfactant, and palladium catalyst are concerned. In particular, the nature of the surfactant has been found to be crucial in order to obtain synthetically useful results involving highly reactive, moisture-sensitive organometallics. Neither organic solvent nor heat is required for these cross-couplings to occur; just add water.

Iron-catalyzed C-H bond activation for the ortho-arylation of aryl pyridines and imines with Grignard reagents

Direct arylation of the ortho-C-H bond of an aryl pyridine or an aryl imine with an aryl Grignard reagent has been achieved by using an iron-diamine catalyst and a dichloroalkane as an oxidant in a short reaction time (e.g., 5 min) under mild conditions (0 °C). The use of an aromatic co-solvent, such as chlorobenzene and benzene, and slow addition of the Grignard reagent are essential for the high efficiency of the reaction. The present arylation reaction has distinct merits over the previously developed reaction that used an arylzinc reagent, such as its reaction rate and atom economy. Selective C-H bond activation occurs in the presence of a leaving group, such as a tosyloxy, chloro, and bromo group. Studies on a stoichiometric reaction and kinetic isotope effects shed light on the reaction intermediate and the C-H bond-activation step.

Homocoupling of aryl halides in flow: Space integration of lithiation and FeCl(3) promoted homocoupling

The use of FeCl₃ resulted in a fast homocoupling of aryllithiums, and this enabled its integration with the halogen–lithium exchange reaction of aryl halides in a flow microreactor. This system allows the homocoupling of two aryl halides bearing electrophilic functional groups, such as CN and NO₂, in under a minute.