Structural, UV-Visible, and Electrochemical Studies on 2,3-Dicyano-5,6-di-2-pyridylpyrazine, [(CN)2Py2Pyz], Related Species and Its Complexes [(CN)2Py2PyzMCl2] (M = PtII, PdII)

2,3-Dicyano-5,6-di-2-pyridylpyrazine, [(CN)(2)Py(2)Pyz], which autocyclotetramerizes to give the macrocycle tetrakis[5,6-di(2-pyridyl)-2,3-pyrazino]porphyrazine, [Py(8)TPyzPzH(2)], bearing externally four dipyridinopyrazine fragments, reacts with bis(benzonitrile)dichloroplatinum(II), [(C6H5CN)(2)PtCl2], in CH3CN, affording the monometalated species [(CN)(2)Py(2)PyzPtCl(2)]. Single-crystal X-ray work on this compound shows that Pt-II is bound to [(CN)(2)Py(2)Pyz] through the two pyridine N atoms ("py-py" coordination) in a way similar to that found for its monopalladium analogue, ((CN)(2)Py(2)PyzPdCl(2)]. Cyclic voltammetry of [(CN)(2)Py(2)PyzPtCl(2)] and [(CN)(2)Py(2)PyzPdCl(2)] in nonaqueous media (pyridine, DMSO, and DMF) indicates that the electron-withdrawing effect of the coordinated PtCl2 and PdCl2 units results in an initial one-electron reduction (E-1/2 =-0.60 and -0.54 V vs SCE in DMSO, respectively), which is easier by 0.25-0.30 V than the unmetalated [(CN)(2)Py(2)Pyz] (first reduction: E-1/2 =-0.87 V vs SCE). These electrochemical data are analyzed along with new results for a selected number of related pyrazine and 2,3-dicyanopyrazine molecules as well as earlier reported data on the mono- and bis-N-methylated derivatives ((CN)(2)Py(2-Mepy)Pyz](+) and [(CN)(2)-(2-MePy)(2)pyz](2+), with these latter species being formed by reaction of the precursor [(CN)(2)Py(2)Pyz] with methyliodide or p-toluensulfonate. The data in this study are also compared to electrochemical data previously reported for a triad of palladium(II) porphyrazine macrocycles obtained from the precursor ((CN)(2)Py(2)Pyz], i.e., [Py8TPyzPzPd], the corresponding pentanuclear complex [(PdCl2)(4)Py(8)TPyzPzPd] (presenting "py-py" coordination at the dipyridinopyrazine fragments), and the octacation [(2-Mepy)(8)TPyzPzPd](8+) (N-methylated at the pyridine rings). Thin-layer UV-visible spectra of singly reduced [(CN)(2)Py(2)PYz](-) and its metalated analogues, [(CN)(2)Py(2)PyzPtCl(2)](-) and [(CN)(2)Py-2-PyzPdCl(2)](-), were measured in pyridine, DMF, and DMSO and show pi-pi* transitions, as well as unusually intense absorptions in the near-IR region (500-900 nm) of the spectrum.