Synthesis, Structure, and Electrochemical Properties of Copper(I) Complexes with S/N Homoscorpionate and Heteroscorpionate Ligands

Abstract

Dinuclear Cu(I) complexes with bifunctionalized homoscorpionate ligands, hydrotris(thioxotriazolyl)borato [Li(Tr(Me,o)(-)(Py)) (1) and Li(Tr(Mes,Me)) (2)], and the heteroscorpionate ligand hydro[bis(thioxotriazolyl)-3-(2-pyridyl)pyrazolyl]borato [K(Br(Mes)pz(o)(-)(Py))] (3) were synthesized and crystallographically characterized. The complexes [Cu(Tr(Mes,Me))](2) (4) and [Cu(Tr(Me,o)(-)(Py))](2) (5) exhibit a similar coordination geometry where every metal is surrounded by three thioxo groups in a trigonal arrangement. The presence of a [B-H...Cu] three-center-two-electron interaction in both compounds causes the overall coordination to become tetrahedrally distorted (S(3)H coordination for each metal). The complex [Cu(Br(Mes)pz(o)(-)(Py))](2) (6) presents a trigonal geometry in which the metals interact with two thioxo groups and a bridging pyrazolyl nitrogen atom. A weak contact with a pyridine nitrogen atom completes the coordination of the metals (S(2)N,N' coordination for each metal). [Cu(Tr(Mes,Me))](2), [Cu(Tr(Me,o)(-)(Py))](2), and [Cu(Br(Mes)pz(o)(-)(Py))](2) exhibit fluxional behavior in solution as evidenced by variable-temperature NMR spectroscopy, and for 5 and 6 two species in equilibrium [in the ratio 2/1 for 5 (CDCl(3)) and 3/2 for 6 (CD(2)Cl(2))] are distinguishable in the (1)H NMR spectra at 270 K. 2D-NOESY spectra recorded at 270 K assisted in the attribution of solution molecular geometries for each isomer of 5 and 6. The free energy of activation (DeltaG()(Tc)) was determined for both equilibria from the evaluation of the coalescence temperature. DFT calculations were performed to describe plausible molecular geometry for the minor isomer of 5 and 6 and to propose a possible mechanism of interconversion between major and minor isomers. Cyclic voltammograms were recorded in CH(2)Cl(2) (3 and 6) or CH(2)Cl(2)/CH(3)CN (1/1, v/v) (2, 4, and 5) solutions using 0.1 M TBAHFP or TBAOTf as supporting electrolytes. [Cu(Tr(Mes,Me))](2), [Cu(Tr(Me,o)(-)(Py))](2), and [Cu(Br(Mes)pz(o)(-)(Py))](2) exhibit a quasi-reversible Cu(I)/Cu(II) redox behavior with E(pa) = +719 mV and E(pc) = +538 mV for 4, E(pa) = +636 mV and E(pc) = -316 mV for 5, and E(pa) = +418 mV and E(pc) = -319 mV for 6.

Copper Complexes with a Hybrid Scorpionate Ligand Containing Pyridazine‐3‐thione

“…Broad singlets are found in the 1 H NMR spectrum of 1 at 5.14 ppm and in that of 2 at 5.47 ppm, corresponding to the B–H hydrogen atoms, which are shifted to significantly lower field relative to the ligand. The higher electronegativity of Cu relative to Na causes more deshielded protons on the coordinated ligands for Cu and thus downfield shifted resonances in accordance with the literature 11l,13b–13d. The equivalence of the resonances of the two mim substituents is surprising in view of the solid‐state structure determined by X‐ray crystallography (vide infra), which revealed that one of the two mim ligands is coordinated to the copper ion, whereas the other one remains dangling.…”

Pyridazine Based Scorpionate Ligand in a Copper Boratrane Compound

“…The sulfur copper sulfur angles are deviating significantly, ranging from 114.76(1) to 123.96(1)°for S1−Cu1−S2 and S1−Cu1−S3′, respectively. This distortion can also be found in related dimeric copper compounds in the literature, where the copper center is surrounded by three sulfurs in an almost trigonal fashion exhibiting sulfur copper sulfur angles between 105.20(4) and 134.98 (4) 17 The hydrogen copper bond is almost perpendicular to the CuS 3 plane, which is confirmed by the hydrogen copper sulfur angles of 84.4(1)°for H1−Cu1−S1 and 107.9(6)°for H1−Cu1−S3′. The nitrogen boron nitrogen bonds vary between 106.3(1) and 110.8(1)°for N12−B1−N22 and N12−B1−N32, respectively, exhibiting a distorted tetrahedral geometry at the boron.…”

“…)°for [Cu{Tr Me,o-Py }] 2 17. The deviation from the ideal trigonal geometry toward the tetrahedral one can be explained by the 3-center-2-electron B−H···Cu interaction, which is evidenced by a H−Cu distance of 1.92(2) Å.…”

Soft Scorpionate Ligands Based on Imidazole‐2‐thione Donors

“…However, different groups have used alternative nomenclatures and thus there is considerable scope for confusion. For instance, the abbreviation Tt was first used by Riordan for his tris(methylthioalkyl)borates,7 but has subsequently been used by Vahrenkamp for these ligands16 and initially by Marchio et al for his 1,3,4‐triazole‐2‐thione based borate ligands,27a although this was later changed for Tr to avoid confusion 27b–27e. There is undoubted logic for both of these assignments, but the duplication leads to potential confusion.…”