Effect of Ligand Substituent Coordination on the Geometry and the Electronic Structure of Cu(II)-Diradical Complexes

Abstract

Two organic moieties, known as ligands, having -OMe and -SePh as the ortho substituent attached to the aniline moiety of the parent 2-anilino-4,6-di-tert-butylphenol ligand, were synthesized. The ligands reacted with CuCl2·2H2O in a 2:1 ratio in CH3CN in the presence of Et3N and provided the corresponding mononuclear Cu(II)-diradical complexes 1 (-OMe) and 2 (-SePh). Complex 1 was square planar, while complex 2 was in distorted square planar geometry due to the secondary coordination between the Se atom and the central Cu(II) center. Both complexes were comprised of multi-paramagnetic centers and exhibited an St = 1/2 ground state as established by variable-temperature magnetic susceptibility measurements. X-band electron paramagnetic resonance measurements indicated the presence of an unpaired electron at the Cu(II) center in complex 1 and at the ligand center (π-radical) in complex 2. The extent of the secondary interaction was found to be dependent on the "softness" of the donor atom belonging to the ortho substituent.

Electronic, charge and magnetic interactions in three-centre systems

“…As a consequence, the resulting S = 1/2 system displays a conventional copper(II) type EPR signal. 12 Other examples (3) described here now for comparison include the oxygen analogue Q n a , 13 the system Q n z with the methylthio group in the peripheral meta-position, and the case Q n M with an ortho-positioned methylthiomethyl (-CH 2 SCH 3 ) substituent on N-phenyl. Such ligands are known as ''hemilabile'' ligands, 11 i.e.…”

“…7 Our own previous modification 10 of this system has made use of substituents offering additional weak donor atoms for metal coordination. 13 with non-radical ligands would involve unlikely copper oxidation states. unsymmetrical chelate ligands of variable denticity which allow the reversible generation of open coordination sites e.g.…”

Probing the Intramolecular Metal‐Selenoether Interaction in a Bis(iminosemiquinone)copper(II) Compound

“…Summarizing, the modification of replacing S by Se in the remarkable diradicalcopper(II) systems shows surprisingly little change for the experimental results and thus for the electronic structures of directly related 1a and 1b . The main difference is the 0.1 Å longer bond from Se, effects from “higher softness” of Se versus S could not be noted. Similarly, the experimental and computational data confirm the invariance of copper(II) in the redox series from dication to monoanion, leaving the noninnocent iminoquinone ligands as the sole sites of electron transfer.…”

“…[2] Introducing a small modification of the popular 4,6-di-tert-butyl-N-arylo-iminosemiquinone ligand system [3,4] by making a thioether coordination available in ortho position, [5,6] we have previously discovered that the metal-based spin (sequence: up-updown) of planar bis(iminosemiquinone)copper(II) complexes [3] can be switched to ligand-centered spin (sequence: up-downup), in association with structural changes such as NCuO/ OCuN twisting and a very weak metal-chalcogen contact at about 3.2 Å, corresponding to the sum of the van der Waals radii according to Bondi at 1.43 (Cu) and 1.80 Å (S). [6,7] Following recent studies of the sensitivity of this phenomenon on small modifications [6,8] we have now investigated the exact selenium analogue of the original [5] thiomethyl-substituted system. Considering that sulfur and selenium are often, but not always, similar in their chemical behavior, including ligand properties, we have obtained the selenoether analogue 1a of the thioether complex [Cu(Q SMe ) 2 ] (1b) (Scheme 1) and studied its structure, electronic configuration, and electrochemical behavior in comparison to the sulfur model.…”

Regioselective Multicomponent Synthesis of 2,4,6‐Trisubstituted Phenols from Fischer Alkynyl Carbene Complexes

“…[6] These compounds are important in the defense against predators and in other survival strategies; [7] they also have synthetic applications (mimetic studies of metalloenzymes and the construction of bulky protecting groups), [8,9] and applications as anticancer drugs, [10] antioxidants, [11] biopesticides, [12] tannins, [13] and as flavor enhancers for beverages. [14] These molecules are attractive not only for their potential pharmacological uses, [15] but also as they may be transformed into other interesting substrates, such as ortho [16] and para [17] quinones, aromatic ethers, [18] and ligands for metal centers.…”