2,5-Bis(pyridyl)pyrazine PtM, Pt2M and Ti2M2 transition metal complexes (M = Cu, Ag)

The synthesis, properties and characterization of a series of 2,5-bis(pyridyl)pyrazine-based heterobi-(PtM) (5, 6), tri-(Pt2M) (8) and tetra-nuclear (Ti2M2) (10) (M = Cu, Ag) transition metal complexes is reported using [(bppz)Pt(CCSiMe3)2] (2) (bppz = 2,5-bis(pyridyl)pyrazine), {[Ti](μ-σ,π-CCSiMe3)2}MX (9a, M = Cu, X = FPF5; 9b, M = Ag, X = OClO3; [Ti] = (η5-C5H4SiMe3)2Ti) and diverse copper(I) and silver(I) salts as key starting materials. Treatment of 2 with equimolar amounts of [Cu(NCMe)4]X (3a, X = BF4; 3b, X = OTf(OSO2CF3)) or [MX] (M = Cu: 3c, X = Br; M = Ag: 4a, X = ClO4; 4b, X = O2CCF3; 4c, X = NO3) gave heterobimetallic [(bppz)Pt((μ-σ,π-CCSiMe3)2MX)] (M = Cu: 5a, X = FBF3; 5b, X = OTf; 5c, X = Br. M = Ag: 6a, X = OClO3; 6b, X = O2CCF3; 6c, X = ONO2), while a 1:2 stoichiometry of, for example, 2:3a and 2:4a, respectively, produced trimetallic {[(bppz)Pt(μ-σ,π-CCSiMe3)2]2M}X (8a, M = Cu, X = BF4; 8b, M = Ag, X = ClO4). Molecules 8a and 8b are also accessible, when 5a or 6a were reacted with 2 in a 1:1 molar ratio. In 8a and 8b two (bppz)Pt(CCSiMe3)2 tweezer moieties are connected by M+ ions thus resulting in a pseudo-tetrahedral environment about M+. Complexes of general composition [([Ti](μ-σ,π-CCSiMe3)2M)2(bppz)][X]2 (10a, M = Cu, X = PF6; 10b, M = Ag, X = ClO4) were accessible by treatment of {[Ti](μ-σ,π-CCSiMe3)2}MX (9a, M = Cu, X = FPF5; 9b, M = Ag, X = OClO3) with 0.5 equivalents of bppz. The structure of 10b in the solid-state shows that bppz acts as connectivity for the bridging of two {[Ti]((μ-σ,π-CCSiMe3)2)Ag}+ building blocks, whereby the planar bppz unit is almost perpendicular oriented towards the Ti–Ag organometallic π-tweezer groups. Cyclic voltammetry measurements reveal that upon reduction of 5, 6 and 10 decomposition of these complexes occurs upon formation of elemental M and non-coordinated (bppz)Pt(CCSiMe3)2 and [Ti](CCSiMe3)2, respectively.

Graphical abstractThe synthesis, properties and characterization of a series of molecules of type [(bppz){Pt(μ-σ,π-CCSiMe3)2}MX], [{(bppz)Pt(μ-σ,π-CCSiMe3)2}2M]2][X]2 and [([Ti](μ-σ,π-CCSiMe3)2M)2(bppz)][X]2 (bppz = 2,5-bis-(pyridyl)pyrazine; M = Cu, Ag; X = Br, NO3, OTf, BF4, ClO4, PF6) is reported.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Organometallic π-tweezer chemistry for stabilizing low-valent transition metal species. ► Using the chelating effect of 2,5-bis(pyridyl)pyrazine for the synthesis of heterometallic transition metal complexes. ► Formation of heterometallic bi-, tri- and tetrametallic complexes. ► Solid state structure of a Ti2Ag2 2,5-bis(pyridyl)pyrazine system.