The synthesis of sterically demanding ligands and examples of their copper complexes

Abstract

Conditions for promoting the Pd-catalyzed arylation of (N-pyrrolyl)zinc derivatives have been established using aryl bromides, chlorides, and iodides as substrates. In most cases, 0.5 mol% Pd(OAc)₂ can achieve the desired transformation in roughly 24 hours, with the more sterically demanding substrates requiring altered conditions. Typical isolated yields are in excess of 70%. Moreover, methyl- and aryl-substituted pyrrolyl anions have been shown to display similar chemistry using 5.0 mol% Pd(OAc)₂. Though they require longer reaction times, the isolated yields rival those of the unsubstituted analogs. Two new copper(I) N-heterocyclic carbene complexes containing the 2,4,6,2",4",6"-hexaisopropyl-1,1':3',1"-terphenyl moiety have been synthesized and isolated. The LCuCl complex (92% isolated yield) was made via a one-pot synthesis from the corresponding imidazolinium tetrafluoroborate salt, NaH, and CuCl (L = [1,3-bis-(2,4,6,2",4",6"-hexaisopropyl- [1,1':3',1"]terphenyl-5'-yl)-4,5-dihydroimidazol-2-ylidene]). The LCuOAc complex (71% isolated yield) was made the same way using CuOAc in place of CuCl.