Synthesis, characterisation and reactivity of copper(I) amide complexes and studies on their role in the modified Ullmann amination reaction.

Simon Sung,Andrew J P White,Alan Armstrong,Robert P Davies,David Sale,D Christopher Braddock,Colin Brennan

doi:10.1002/chem.201405699

Abstract

A series of copper(I) alkylamide complexes have been synthesised; copper(I) dicyclohexylamide (1), copper(I) 2,2,6,6-tetramethylpiperidide (2), copper(I) pyrrolidide (3), copper(I) piperidide (4), and copper(I) benzylamide (5). Their solid-state structures and structures in [D6]benzene solution are characterised, with the aggregation state in solution determined by a combination of DOSY NMR spectroscopy and DFT calculations. Complexes 1, 2 and 4 are shown to exist as tetramers in the solid state by X-ray crystallography. In [D6]benzene solution, complexes 1, 2 and 5 were found by using 1H DOSY NMR to exist in rapid equilibrium between aggregates with average aggregation numbers of 2.5, 2.4 and 3.3, respectively, at 0.05 m concentration. Conversely, distinct trimeric, tetrameric and pentameric forms of 3 and 4 were distinguishable by one-dimensional 1H and 1H DOSY NMR spectroscopy. Complexes 3–5 are found to react stoichiometrically with iodobenzene, in the presence or absence of 1,10-phenanthroline as an ancillary ligand, to give arylamine products indicative of their role as potential intermediates in the modified Ullmann reaction. The role of phenanthroline has also been explored both in the stoichiometric reaction and in the catalytic Ullmann protocol.

Highlights

Copper mediated cross-coupling reactions between aryl halides and amines to form carbon-nitrogen bonds were first reported over a century ago by Ullmann when he demonstrated the preparation of 2-(N-phenylamino)benzoic acid from ochlorobenzoic acid and aniline in the presence of stoichiometric copper metal.[1]
The copper amide complexes first showed that a copper(I) amide species, CuNR2, is initially formed and this undergoes aryl halide activation.[39]
Copper(I) amide complexes 1–5 were treated with iodobenzene at 80 8C in both [D6]benzene and [D6]DMSO to investigate their reactivity in the Ullmann aryl amination reaction (Table 7) and to ascertain their competence as intermediaries on the catalytic cycle (Scheme 2)

Summary

Introduction

Copper mediated cross-coupling reactions between aryl halides and amines to form carbon-nitrogen bonds were first reported over a century ago by Ullmann when he demonstrated the preparation of 2-(N-phenylamino)benzoic acid from ochlorobenzoic acid and aniline in the presence of stoichiometric copper metal.[1]. Copper(I) amide complexes 1–5 were treated with iodobenzene at 80 8C in both [D6]benzene and [D6]DMSO to investigate their reactivity in the Ullmann aryl amination reaction (Table 7) and to ascertain their competence as intermediaries on the catalytic cycle (Scheme 2).

Results

Conclusion