Pyrazine as a Building Block for Molecular Architectures with Pt^II

Abstract

A series of pyrazine (pz) complexes containing cis-(NH(3))(2)Pt(II), (tmeda)Pt(II) (tmeda = N,N,N',N'-tetramethylethylenediamine), and trans-(NH(3))(2)Pt(II) entities have been prepared and characterized by X-ray crystallography and/or 1H NMR spectroscopy. In these compounds, the pz ligands act as monodentate (1-3) or bidentate bridging ligands (4-7). Three variants of the latter case are described: a dinuclear complex [Pt(II)]2 (4b), a cyclic tetranuclear [Pt(II)](4) complex (5), and a trinuclear mixed-metal complex [Pt2Ag] (7). Mono- and bidentate binding modes are readily differentiated by 1H NMR spectroscopy, and the assignment of pz protons in the case of monodentate coordination is aided by the observation of (195)Pt satellites. Formation of the open molecular box cis-[{(NH3)2Pt(pz)}4](NO3)8.3.67H2O (5) from cis-(NH3)2Pt(II) and pz follows expectations of the "molecular library approach" for the generation of a cyclic tetramer.

Synthesis, spectroscopic and X-ray characterization of various pyrazine-bridged platinum(II) complexes: 1H NMR comparative study of their catalytic abilities in the hydrolysis of methionine- and histidine-containing dipeptides

“…This is in accordance with data previously reported for similar dinuclear Pt(II) complexes [1,8,16]. Four protons of uncoordinated pyrazine appear as a singlet at 8.66 ppm and this singlet is being shifted downfield after bidentate coordination of pyrazine to two …”

“…The NMR chemical shifts for complexes 1 and 2 have been previously reported [9] and here these spectral data have been repeated and discussed in comparison with those for the uncoordinated diamine ligands and complex 3. All chemical shifts for the uncoordinated diamine X and pz ligands generally agree with the literature values [16]. After chelation of 1,3-pd ligand to Pt(II) in complex 1 its two 1 H NMR multiplets centered at 1.60 and 2.65 ppm for middle C2 and terminal C1 and C3 methylene protons, respectively, are shifted downfield (Dd = 0.29 for C2 and 0.14 ppm for C1 and C3 methylene protons).…”

“…The singlet appeared in the region at 9.02-9.06 ppm for the bridging pyrazine ligand of [{Pt(X) (H 2 O)} 2 (l-pz)] 4+ complex (chemical shifts of this singlet is dependent from the type of Pt(II) complex) decreased while two symmetric multiplets in the range 8.75-9.00 ppm increased. The appearance of these two new multiplets indicates that one Pt(II)-N(pyrazine) bond of Pt(II) complex was broken and that the four pyrazine protons of this ligand coordinated in a monotopic fashion to Pt(II) ion were split into two multiplets because of vicinal and long-range coupling [1,8,16].…”

Supramolekulare Chemie in Wasser

“…Die Arbeitsgruppen von Fujita, [224][225][226] Lippert [227,228] und Navarro [229,230] haben über die Anionenerkennung in Wasser durch schüsselförmige Moleküle berichtet. Metallacalix[n]arene (n = 3, 4, 6) -Strukturanaloga der Calixarene -, zum Beispiel die Pd-oder Pt-calix [3]arene 84, sind sehr gut wasserlöslich und binden Sulfat als 1:1-Komplexe (apparenter K a (Sulfat/Nitrat)-Wert ca.…”

Novel 18-membered hexanuclear metallamacrocycle: Synthesis, crystal structure, and magnetic properties

“…The magnetic properties of the metallacrown molecules are characterized by a weak antiferromagnetic exchange interaction, with l eff = 5.12 l B at 300 K between the Mn 3+ ion spins with S = 2 in the cyclic system. Growing interest in the rational design and construction of metallamacrocycles is motivated principally by their diverse molecular architectures [1][2][3], their utilization as motifs for coordination networks [4][5][6][7][8] and their potential as host systems in various guest recognition chemistries [9][10][11][12][13][14][15]. Metallacrowns known as the first of a new class of metallamacrocycles, have been readily assembled using a trianionic pentadentate ligand, N-acylsalicylhydrazide, with a trivalent octahedral metal ion such as manganese, iron, cobalt or gallium [16][17][18].…”