Multifrequency EPR and Redox Reactivity Investigations of a Bis(μ-thiolato)-dicopper(II,II) Complex

Abstract

From a new tripodal ligand [N2SS'H] with mixed N, S(thioether), and S(thiolate) donor set, the corresponding bis(mu-thiolato)dicopper(II) complex has been prepared and characterized. X-ray crystallographic analysis of the complex [Cu2(N2SS')2](ClO4)2.C4H10O (1) demonstrates that the two five-coordinated Cu atoms are bridged by two thiolates leading to a nearly planar Cu2S2 core with a Cu1...Cu1* distance of 3.418(8) A and a large bridging angle Cu1S1Cu1* of 94.92 degrees. X-band (10 GHz), Q-band (34 GHz), and F-Band (115 GHz) EPR spectra of 1 are consistent with a weakly coupled dicopper(II,II) center attributed to an S = 1 state. Simulations for the three frequencies are obtained with a unique set of electronic parameters. The mean values of the spin Hamiltonian parameters for 1 are D = 0.210(3) cm(-1), E = 0.0295(5) cm(-1), |E/D| = 0.140, gx = 2.030(2), gy = 2.032(2), gz = 2.128(2). The electrochemical one-electron reduction of 1 generates the mixed-valent CuIICuI species. EPR and UV-vis spectra are consistent with a type I localized mixed-valent species, while dinuclear CuA centers of native cytochrome c oxidase (CcO)1-3 or nitrous oxide reductase (N2OR)4 have a delocalized CuIICuI mixed-valent state. After reoxidation of the CuIICuI species, the initial complex 1 is regenerated through a reversible interconversion process.

Enhanced Stereoselectivity of a Cu(II) Complex Chiral Auxiliary in the Synthesis of Fmoc-l-γ-carboxyglutamic Acid

“…48 A UV difference spectrum was generated using the complexes ( S )- 9c and ( S )- 9a in CH 3 CN and shows maxima at 309 (δε = −211) and 422 nm (Δε = 135), a shoulder at 335 nm (Δε = −761), and a broad band at 658 nm (Δε = 24). These features in the range of 300-450 nm and at 658 nm are consistent with sulfurcopper charge transfer bands and a copper d-d transition, respectively, and are consistent with assignments made for other compounds reported in the literature.…”

Catalytic catechol oxidation by copper complexes: development of a structure–activity relationship

“…The chloride ions are bridging between copper ions of neighboring dinuclear complexes resulting in infinite 1D zig-zag chains. The distance between the copper ions in the Cu(µ-Cl) 2 Fig. 4, selected bond distances and angles can be found in …”

“…7,8 Similar changes in the ligand structure can also induce a difference in coordination mode of dioxygen to copper. 9,10 Additionally, the redox conversion of a Cu 2 species has been reported [11][12][13] suggesting that copper-oxygen chemistry might be very similar to copper-sulfur chemistry. To investigate this hypothesis we undertook a study of the biomimetic catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butyl-o-benzoquinone (3,5-DTBQ) using Cu II complexes with mononucleating and dinucleating ligands containing sulfur donor atoms.…”

“…[1][2][3][4][5][6] It has been reported that small changes in the ligand structure can direct the reaction with copper salts towards the formation of either a Cu II µ-thiolate or a Cu I disulfide complex and that these species can interconvert (Fig. 1a).…”

Thiol-copper(I) and disulfide–dicopper(I) complex O2-reactivity leading to sulfonate–copper(II) complex or the formation of a cross-linked thioether–phenol product with phenol addition

“…Tolman and co-workers [35][36][37] generated a set of very interesting 'blue' copper model compounds (b), employing bidentate b-diketiminate and thiolate ligands, one also having a thioether donor as do the type 1 protein centers. As models for the dinuclear Cu A centers, a bis(lthiolato)dicopper(I,II) mixed-valent complex (c) and dicopper(II) compound (d) could be synthesized and characterized structurally and spectroscopically [38][39][40][41][42][43]. Perhaps reminiscent of the equilibrium of isoelectronic side-on peroxo dicoppper(II) and bis(l-oxo)dicopper(III) species, which are now well-established in copper/O 2 chemistry [44], disulfide-dicopper(I) complexes can transform to (thiolato)dicopper(II) species.…”