Cyclic and Linear Polyferrocenes with Silicon and Tin as Alternating Bridges

The synthesis and characterization of ferrocene-based oligomers that contained two different elements (Si and Sn) as alternating bridges is described for the first time. The salt-metathesis reaction of R2Si[(C5H4)Fe(C5H4Li)]2 (R=Me, Et) with R′2SnCl2 (R′=Me, nBu, tBu) afforded a mixture of oligomers (6MeSnMe2, 6EtSnMe2, 6MeSnnBu2, 6EtSnnBu2, 6MeSntBu2, and 6EtSntBu2). These oligomers were characterized by 1H, 13C, 29Si, and 119Sn NMR spectroscopy and by mass spectrometry. MS (MALDI-TOF) studies of 6EtSnMe2 revealed the presence of linear (l) and cyclic (c) species that contained up to 20 ferrocene moieties. The molecular weights of the polymers were determined by gel-permeation chromatography (GPC) and by dynamic-light scattering (DLS). GPC analysis revealed average molecular weights of 2100–6300 Da with respect to polystyrene as a standard. DLS analysis yielded very similar results. Some compounds, c-(6MeSnMe2)1, c-(6MeSntBu2)2, c-(6EtSnMe2)1, c-(6EtSntBu2)2, l-(6MeSnnBu2)2, and l-(6MeSnnBu2)3, which contained up to six ferrocene moieties, were isolated in their pure form either by column chromatography or by crystallization. The Si- and Sn-bridged macrocycles that contained four ferrocene units (c-(6MeSntBu2)2 and c-(6EtSntBu2)2) were structurally characterized by single-crystal X-ray analysis.