Synthesis, structure, and electrochemical properties of copper(I) complexes with S/N homoscorpionate and heteroscorpionate ligands.
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.
Cammi
Roberto
R
Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Parco area delle Scienze 17a, 43100 Parma, Italy.
Gennari
Marcello
M
Giannetto
Marco
M
Lanfranchi
Maurizio
M
Marchio
Luciano
L
Mori
Giovanni
G
Paiola
Cristiano
C
Pellinghelli
Maria Angela
MA