Organometallic π-tweezers incorporating pyrazine- and pyridine-based bridging units

Pyrazine- and pyridine-based π-conjugated σ-donor molecules, such as 4,4′-bipyridine, 1,2-di(4-pyridyl)ethylene, 3,5-dipyridyl-1,2,4-triazole, N,N′-bis(4-pyridylmethylidene)benzene-1,4-diamine, 2,5-di(pyridylmethylidene)cyclopentanone, 2,6-di(4-pyridylmethylidene)cyclohexanone (LL, 2a–2g) can successfully be used to span heterobimetallic π-tweezer units of the type [{[Ti](μ-σ,π-Ctriple bond; length of mdashCSiMe3)2}M]+ ([Ti] = (η5-C5H4SiMe3)2Ti; M = Cu, Ag). The thus accessible di-cationic species [{[Ti](μ-σ,π-Ctriple bond; length of mdashCSiMe3)2}Msingle bondLLsingle bondM{(Me3SiCtriple bond; length of mdashC-μ-σ,π)2[Ti]}]2+ (4), which are formed via the formation of [{[Ti](μ-σ,π-Ctriple bond; length of mdashCSiMe3)2}Msingle bondLL]+ (3) complexes, can be isolated in yields between 66% and 99%. However, when C5H4Nsingle bondCHdouble bond; length as m-dashCHsingle bondC6H4single bondCHdouble bond; length as m-dashCHsingle bondNC5H4 (5a) and C5H4Nsingle bondCHdouble bond; length as m-dashNsingle bondC6H4single bondCHdouble bond; length as m-dashCHsingle bondNC5H4 (5b), respectively, are reacted with {[Ti](μ-σ,π-Ctriple bond; length of mdashCSiMe3)2}AgBF4(1c) in a 1:1 molar ratio, then the silver(I) ion is released from the organometallic π-tweezer 1c and coordination polymers [AgBF4 · 5a]n (6a) and [AgBF4 · 5b]n (6b) along with [Ti](Ctriple bond; length of mdashCSiMe3)2 (7) are formed in quantitative yield.