Synthesis and Structure of Four‐Coordinate Copper(II) Complexes Stabilized by β‐Ketiminato Ligands and Application in the Reverse Atom‐Transfer Radical Polymerization of Styrene

Abstract

The reaction of CuCl2 with R2NCH2CH2NHC(Me)=CHCO(Me) [R = Me (HL1) or Et (HL2)] in the presence of Et3N leads to the formation of complexes [CuCl(Ln)] [n = 1 (1), 2 (2)]. Whereas the solid‐state structure of compound 2 is mononuclear with a close to square‐planar arrangement of the ClON2 donor set, compound 1 adopts a dinuclear di‐μ‐chlorido arrangement in which two mononuclear units having essentially the same arrangement as in 2 establish loose axial Cu···Cl interactions, each one of them with the Cl atom of the other one. Compounds 1 and 2 have been tested as reversible trapping agents for the controlled radical polymerization of styrene under a reverse atom‐transfer radical polymerization (ATRP) approach. Reversible Cl atom transfer leading to a controlled polymerization process is observed, although the controllability is negatively affected by slow radical trapping. A moderate effect on the polymerization rate, once all the radical initiator is consumed, was observed in the presence of an excess amount of pyridine (10 equiv. per Cu) and interpreted on the basis of the stabilization of the CuI system.

Activation of the Cyano Group at Imidazole via Copper Stimulated Alcoholysis

“…The ligand coordinates to the metal center through the imidazole nitrogen N1 and the imidato nitrogen N2 to form a five-membered chelating ring in the equatorial position. The Cu1-N1 and Cu1-N2 bond lengths lie in the narrow ranges of 1.989-2.025 Å and 2.009-2.036 Å, respectively, which agree with earlier reported copper(II) complexes [20,21,23,25,[31][32][33][34][35]. The nitrogen-halogen distances at basal planes are almost symmetrical in all compounds.…”

“…Two equatorial angles O2/X'-Cu1-N1 and O2/X'-Cu1-N2 are formed with almost ideal values of 90 • , whereas X1-Cu1-X2 is slightly larger than 90 • . The bite angle N1-Cu1-N2 is thus less 90 • , which is common for this type of coordination [20,21,23,25,31,34] and the apex of the pyramid is slightly shifted towards the two nitrogen atoms. In five-coordinated complexes, the degree of distortion was evaluated by the geometry index τ depending on the two largest angles (β > α) around the metal center as τ = (β − α)/60 • , where the τ value varies from 0 to 1.37 The extreme τ values such as 0 and 1 indicate ideal square pyramidal and trigonal-bipyramidal geometries, respectively.…”

“…All calculations were performed by applying Gaussian 09 software package [53]. The optimized geometry and simulated non-scaled infrared spectra for the copper(II) complexes were obtained by PBE0 functional [54] with 6-311+(d) basis set for non-metal atoms and Def2-TZVPPD basis set [31][32][33][34][35][36] for copper atom.…”

Preparation of Diamine‐β‐diketiminato Copper(II) Complexes and Their Application in the Reverse Atom‐Transfer Radical Polymerization of Styrene

“…This structural type is quite typical for a 4-coordinated Cu II complex, [16][17][18][19][20][21][22][23] fully analogous to that of the complex with a tridentate amine-βketiminato ligand, [Et2NCH2CH2NC(Me)CHC(Me)O]CuCl, which also displays similar Cu-Cl (2.2458(4) Å) and Cu-N distances (1.9404(12) Å to the ketiminato N atom, 2.0563(12) Å to the amino N atom). [14] In the latter contribution, it was specifically shown that this 4-coordinate geometry is stabilized by bulky groups against the possible dimerization with formation of loose Cu•••Cl axial interactions, which were on the other hand seen for the related [Me2NCH2CH2NC(Me)CHC(Me)O]CuX complexes (X = Cl, [14] O2CPh [24] ) as well as for other related complexes. [25][26][27] For the present structure, the bulky ethyl groups and the pendant diethylaminoethyl arm are presumably preventing the formation of such loose Cl-bridged dimer.…”

“…[13] We have recently explored the use of a tridentate "XL2" type ligand, the amino-β-ketiminato ligand obtained by deprotonation of R2NCH2CH2NHC(Me)CHC(Me)O (R = Me, Et) and have reported the synthesis of corresponding CuCl(XL2) complexes and their preliminary application to the reverse ATRP of styrene. [14] In this contribution, we wish to extend the study to a tetradentate diamino-β-diketiminato ligand. We report the synthesis of unprecedented Cu II complexes containing the ligand [Et2NCH2CH2NC(Me)CHC(Me)NCH2CH2NEt2] -(L -), our attempts to generate a corresponding Cu I complex, and the performance of the Cu II complex CuClL, 1, as a controlling agent for the polymerization of styrene.…”