Copper(I)–Anilide Complex [Na(phen)₃][Cu(NPh₂)₂]: An Intermediate in the Copper‐Catalyzed N‐Arylation of N‐Phenylaniline

Abstract

Complex [Na(phen)(3)][Cu(NPh(2) )(2)](2), containing a linear bis(N-phenylanilide)copper(I) anion and a distorted octahedral tris(1,10-phenanthroline)sodium counter cation, has been isolated from the catalytic C-N cross-coupling reaction with the CuI/phen/tBuONa (phen=1,10-phenanthroline) catalytic system. Complex 2 can react with 4-iodotoluene to produce 4-methyl-N,N-diphenylaniline (3 a) with 70.6 % yield. In addition, 2 can work as an effective catalyst for C-N coupling under the same reaction conditions, thus indicating that 2 is the intermediate of the catalytic system. Both [Cu(NPh(2))(2)](-) and [Cu(NPh(2))I](-) have been observed by in situ electron ionization mass spectrometry (ESI-MS) under catalytic reaction conditions, thus confirming that they are intermediates in the reaction. A catalytic cycle has been proposed based on these observations. The molecular structure of 2 has been determined by single-crystal X-ray diffraction analysis.

Synthesis, Characterisation and Reactivity of Copper(I) Amide Complexes and Studies on Their Role in the Modified Ullmann Amination Reaction

“…This indicates that the equilibrium for the binding of phen lies almost exclusively on the non-ligated side comprising the copper(I) amide aggregate and free phen (I,S cheme 4) with no NMR spectroscopic evidence for any ligateds pecies in solution. Ionic species of general formula [CuL 2 ] + [Cu(NR 2 ) 2 ] À (III,L = phen, Scheme 4) have also been identified in similar systems where they have been proposedt oe xist in equilibrium with mono-ligated neutral [LCu(NR 2 )] complexes (II,L = phen, Scheme 4), [5,6,29,30] however such ionic species are also not observed in the 1 HNMR spectrum for either of thesem ixtures in benzene solution.F urthermore, the solutionsf ormed wereu nstable over time (more so than their parent copper(I) amide solutionsi nt he absence of phen). Monitoring by 1 HNMR spectroscopya tr oom temperature shows that after two hours of addition of phen only 81 %o ft he original copper(I) amide remained and after 18 h, just4 6% copper(I) amide remained with Cu 0 also now present.I nc omparison, the amounts of 3 and 4 remainv irtually unchanged after similars toragef or 19 h.…”

“…The effect of phen on the reactivity of 3 was more pronounced when [D 6 ]DMSO was used as the solvent, with the yield unexpectedly decreasing from 75 %t o2 6%.T he yields obtained with complexes 4 and 5 on addition of phen were also diminished in [D 6 ]DMSO compared to their ligand-free analogues.T hese resultsa re somewhat surprising in light of the prominentr ole played by phen in copper-catalysed Ullmann amination. [4][5][6][7][8][9] Nevertheless, they can be explained in the context of the solution studies which showedt he favoured formation of the ionic cuprate species (III,S cheme 4) on addition of phen to copper(I) amide in DMSO.P revious studies on the reactivity of isolatedb isamidocuprate complexes [Cu(NR 2 ) 2 ] À (NR 2 = NPh 2 ; [30] phthalimidate [29] )h ave shown these anionic speciestohave little or no reactivity in the cross-coupling reaction with aryl halides. If, as seems likely,t he bis(dialkylamino)cupratec omplexes present in the reactionm ixture here also exhibit low reactivity,t his could help explain the observed reductioni np roduct yield.…”

“…[1] However,t his classical methodf or crosscoupling aryl halidesa nd amines has many drawbacks including high (stoichiometric) copper metal loadings, highr eaction temperatures anda lso long reaction times. [2,3] More recently new protocols that incorporate the use of bidentate ligands such as 1,10-phenanthroline (phen) [4][5][6][7][8][9] have enabled these re-actions to be carried out at lower reaction temperatures ( 110 8C) with lower copper loadings ( 10 %). [10][11][12][13] This improvedc opper-catalysed reactioni sc ommonly referred to as the modified Ullmann amination reaction (Scheme 1).…”

“…[20][21][22][23][24][25] Another significant shortcoming of the modified Ullmann reactioni st hat the intermediates and steps involved in the reactionm echanism are still not fully understood,d espite some recent progress in this area. [3,5,6,[26][27][28][29][30][31][32][33][34][35][36][37][38] Ideally,arational approach based on af undamental understanding of the mechanism is crucial for the development of new catalysts and improvement of existing systems.…”

Two new copper-FOX-7 complexes: synthesis, crystal structure, and thermal behavior

“…Cu(II) phen complexes attract attention for their properties used in catalytic reaction, electrochemistry, molecular biology, and other fields [1][2][3][4][5][6][7]. Many energetic Cu(II) complexes are used as detonating explosive or combustion catalysts of solid propellant [8][9][10][11][12][13][14][15].…”