Chiral Tripodal Ligand Containing Three N-Heterocyclic Donor Functions and Its Copper Complexes: Crystallization of [LCu^I]₂²⁺/[L₂Cu^II]²⁺ Stereoisomers and Tyrosinase Activity

Abstract

A novel chiral ligand system L containing one pyridyl and two imidazolyl donor functions has been synthesized and investigated with respect to its Cu(I) and Cu(II) coordination chemistry. Reaction with [Cu(MeCN)4]PF6 and [Cu(MeCN)4]OTf led to the dimeric complexes [LCu]2X2 (1, X = PF6; 2, X = OTf) with the ligands L in different configurations (R,S). The ligand matrix formed in these complexes can also host a Cu(II) ion instead of two Cu(I) ions so that mixed crystals of [L2Cu]X2 and [LCu]2X2 can be produced. The pure compounds [L2Cu]X2 (3, X = PF6; 4, X = OTf) can be obtained by treatment of 1 and 2 with O2 in acetonitrile, respectively. From the corresponding solution 3 crystallizes with the two L molecules in different configurations, while 4 crystallizes with the ligands in (S,S) or (R,R) configurations, respectively. Crystals containing the analogous diastereomers of 3 were obtained, besides those isolated previously, when this compound was synthesized by reaction of 1 with AgPF6. On treating 2 with O2 as the oxidant in acetonitrile, besides formation of 4, additional evidence for oxygenation of L to L(ox), where one of the original phenyl units corresponds to a phenolate function, was found: The dinuclear complex [L(ox)Cu(OH)(OTf)CuL](OTf) (5) was isolated as the final product of O2 activation and conversion, which resembles the one of tyrosinase. In acetonitrile 5 reacts further to give 4 and [L(ox)2Cu2](OTf)2 (6), and hence, product mixtures are obtained. In CH2Cl2 decomposition can be avoided, and hence, changing the solvent from acetonitrile to CH2Cl2 leads to selective formation of 5.

Efficient Biomimetic Hydroxylation Catalysis with a Bis(pyrazolyl)imidazolylmethane Copper Peroxide Complex

“…Karlin and co‐workers followed in 2009 with an imidazolyl‐containing tris(2‐pyridylmethyl)amine (TMPA) derivative,40 and in 2012 Limberg et al. presented a tripodal ligand containing sterically demanding imidazolyl moieties for the stabilisation of Cu I and Cu II species 41. Those species were also capable of oxygen activation.…”

“…presented at ripodal ligand containing sterically demanding imidazolyl moieties for the stabilisation of Cu I and Cu II species. [41] Those species werea lso capable of oxygen activation. Earliert his year,t hey demonstrated the hydroxylationo f2 ,4-ditert-butylphenol( DTBP)t ot he corresponding quinonew itht his system.…”

Three copper complexes containing the sulfur-bridged bis-pyridine ligands, 2,2′-dithiodipyridine and di-2-pyridyl sulfide

“…There has been continuous interest in the coordination chemistry of copper complexes, and much attention has been paid to the design and synthesis of Cu(I) and Cu(II) complexes [1][2][3][4][5]. These complexes have been widely used in metal organic framework materials (MOFs), luminescent materials, magnetic materials, and efficient catalysts [6][7][8][9].…”

Ligands with Two Different Binding Sites and O2 Reactivity of their Copper(I) Complexes

“…In particular, the binding motif P was found to be relevant to biological dioxygen fixation/activation in proteins such as the abovementioned hemocyanin or the monooxygenase tyrosinase , . Moreover, studies on bioinorganic model compounds indicated that factors such as electronic and steric properties of the ligand environment, temperature,, solvent,, concentration,, and the nature of the counterion[13a], [16a], , may have a strong impact on the equilibrium position between P and O , . Having synthesized different dicopper(I) complexes of our new ligands, it was thus of interest to explore their O 2 reactivity.…”