Kumada–Tamao–Corriu Coupling of Alkyl Halides Catalyzed by an Iron–Bisphosphine Complex

Abstract

An iron(II) chloride complex possessing a sterically demanding ortho-phenylene-tethered bisphosphine ligand shows a high catalytic activity in the KumadaTamaoCorriu coupling of nonactivated alkyl halides with aryl Grignard reagents. Primary, secondary, and tertiary alkyl halides can participate as an electrophilic coupling partner. A radical clock experiment using (iodomethyl)cyclopropane exclusively gives the corresponding ring-opening coupling product, suggesting intermediacy of alkyl radical species.Transition-metal-catalyzed cross-coupling is one of the most powerful tools in organic synthesis.1 After dormancy for decades, iron has attracted renewed attention as a practical coupling catalyst due to its economic and ecological advantages over the other rare metal catalysts.2,3 Moreover, iron catalyst displays characteristic reactivities and selectivities, which cannot be easily attained by the prevalent Ni-and Pd-catalysts: several research groups, including us, have reported the cross-coupling reactions of nonactivated alkyl halides with Grignard reagents by using iron catalysts. 3h3j,3m3o,3t,3u In 2004, we introduced TMEDA as a Lewis basic additive into the iron-catalyzed crosscoupling reaction to obtain the desired reactivity toward the alkyl halides.3h Although high selectivity and reactivity were achieved by using TMEDA with the optimized experimental procedure, large excess of the additive was required. In order to control the reaction by using a catalytic amount of additives instead of TMEDA, we continued the study and have developed new ortho-phenylenebisphosphine ligands, which bear peripheral steric bulk around the iron center. 4 We report herein a new KumadaTamaoCorriu coupling between various nonactivated alkyl halides and aryl Grignard reagents effected by low catalyst loading (0.5 to 3 mol %) of the ironbisphosphine complex.

Iron(II) Active Species in Iron–Bisphosphine Catalyzed Kumada and Suzuki–Miyaura Cross-Couplings of Phenyl Nucleophiles and Secondary Alkyl Halides

“…Analogous S = 1/2 iron(I) species have also been identified for this Negishi reaction with dppe. 40 Nakamura and co-workers have found that the four-coordinate (4C) iron–bisphosphine complex, FeCl 2 (SciOPP), is an effective precatalyst for Kumada, 43 , 46 Suzuki–Miyaura, 42 , 47 , 48 Negishi, 37 and Sonogashira-type 44 couplings. For iron–SciOPP cross-coupling, it has been proposed that catalysis proceeds through an Fe(II)/Fe(III) radical pathway.…”

The highly surprising behaviour of diphosphine ligands in iron-catalysed Negishi cross-coupling

“…Iron complexes of chelating diphosphines are active pre-catalysts in a range of carbon-carbon bond forming processes, [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] and as such have formed the basis of a number of mechanistic studies with magnesium-, 22,24,29,30 boron-, 27,30 and zinc-based 22 coupling partners. We now report on our detailed investigations on the use of iron diphosphine complexes as precatalysts in a representative Negishi cross-coupling reaction with benzyl halide substrates.…”

Ligand-controlled Iron-catalyzed Cross Coupling of Benzylic Chlorides with Aryl Grignard Reagents

“…Iron is an inexpensive and environmentally friendly catalyst, which shows high reactivity for the cross coupling of alkyl halides. 8,9 However, iron catalysis has not been extended successfully to the reaction between benzylic halides and aryl Grignard reagents because of the competing homocoupling reaction; 10 this was studied extensively by Kharasch 11 and was found to restrict the selective cross coupling for diarylmethane synthesis. Kozak demonstrated an iron-catalyzed selective cross coupling of benzylic chlorides and bromides with aryl Grignard reagents, which produced the corresponding diarylmethanes in moderate yields.…”