Nanosized Iron- or Copper-Catalyzed Homocoupling of Aryl, Heteroaryl, Benzyl, and Alkenyl Grignard Reagents

Abstract

Under very mild reaction conditions, iron or copper nanoparticles efficiently promoted the homocoupling of different Grignard reagents in tetrahydrofuran at room temperature. The nanosized iron or copper particles were generated in situ in a simple and economical way from commercially available FeCl₂ or CuCl₂, respectively, an excess of lithium powder, and a catalytic amount (5 mol%) of 4,4′-di-tert-butylbiphenyl (DTBB) as electron carrier. The reaction of a series of aryl, heteroaryl, benzyl, and alkenyl Grignard reagents in the presence of a substoichiometric amount of the iron or copper nanoparticles led to the formation of the corresponding homocoupling products in good yield.

Keywords:

• Copper nanoparticles
• Grignard reagents
• homocoupling
• iron nanoparticles

ACKNOWLEDGMENTS

This work was generously supported by Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) (Project PIP 5104) and SGCyT-UNS (Project PGI 24/Q026) from Argentina. Y. M. and E. M. also thank CONICET for doctoral fellowships, and F. N. is thankful to Secretaría General de Ciencia y Tecnología–Universidad Nacional del Sur (SGCyT-UNS) for a student fellowship. The authors gratefully acknowledge the Servicios Técnicos de Investigación of the University of Alicante (Spain) for TEM analysis.

Notes

^a All reactions were performed using RMgX (1.0 mmol), FeCl₂ or CuCl₂ (0.5 mmol), Li (8.0 mmol), DTBB (0.1 mmol), THF, 20 °C.

^b All products were > 95% pure (GLC); isolated yield after column chromatography (hexane-ethyl acetate), based on the starting material, unless otherwise stated.

^c Reaction performed with the FeCl₂-Li-DTBB(cat.) system.

^d Reaction performed with the CuCl₂-Li-DTBB(cat.) system.

^e A ca. 1:1 mixture of toluene and o-cresol was recovered as by-products.

^f A ca. 1:1 mixture of naphthalene and 1-naphthol was recovered as by-products.

^g GLC yield based on the starting material.

^h A 1:1 mixture of Z- and E-isomers was used.

ⁱ Diastereoisomeric ratio: E/E:E/Z = 99:1, determined by GC-MS.