Homocoupling of Arylboronic Acids Catalyzed by 1,10‐Phenanthroline‐Ligated Copper Complexes in Air

Abstract

The efficient homocoupling of arylboronic acids was achieved by using the catalytic combination of inexpensive copper salts and 1,10‐phenanthroline as a ligand. The homocoupling reaction proceeds at ambient temperature in air without any additives such as base or oxidant. This method tolerates various substituents on the arylboronic acids such as halogens, carbonyls, and a nitro group. As a result, 25 symmetrical biaryls were obtained from readily availablearylboronic acids in 19–92 % isolated yields. A binuclear (μ‐hydroxido)copper complex is assumed as the catalytically active species, which undergoes efficient transmetalation with arylboronic acids to produce dinuclear arylcopper complexes. The binuclear structure is assumed to be essential for the bimetallic reductive elimination of biaryls as well as the oxidative restoration of the catalyst.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Aerobic Copper-Catalyzed Organic Reactions

“…411 Ultimately, the copper(II) bis-μ-hydroxo adduct with a phenanthroline ligand proved the most effective providing the dimeric products under ambient conditions with as little as 2 mol% of the copper catalyst (Scheme 200). …”

Nickel-Catalyzed Cross-Couplings Involving Carbon−Oxygen Bonds

“…The latter pathway is supporting by the compatibility of the reaction with aerobic conditions. Homocoupling of boronic acids can also be achieved using similar Pd II or other transition metal catalysts such as Au,353 Cu,354 Pd,355,356,357,358,359,360361,362,363,364 and Rh 365,366. However, well-established methods for Ni-catalyzed homocoupling of aryl halides and sulfonates are available.…”

Ligand‐Assisted, Copper(II) Acetate‐Accelerated Azide–Alkyne Cycloaddition

“…[5] Our group reported the use of copper(II) acetate (Cu-A C H T U N G T R E N N U N G (OAc) 2 ) to promote CuAAC reactions in the absence of an added reducing agent, for example, sodium ascorbate. [6] We hypothesized that the catalytic copper(I) species is generated upon reduction of copper(II) by either an oxidizable solvent such as methanol [7] or the terminal alkyne substrate by means of the oxidative homocoupling reaction. [8] A subset of the azide substrates rapidly convert to triazole products under the CuA C H T U N G T R E N N U N G (OAc) 2 -mediated conditions.…”