Ring-Opening Polymerization of a Galla[1]ferrocenophane: A Gallium-Bridged Polyferrocene with Observable Tacticity Bidraha Bagh, † Joe B. Gilroy, ‡ Anne Staubitz, ‡ and Jens Mu ¨ ller* ,† Department of Chemistry, UniVersity of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan S7N 5C9, Canada, and School of Chemistry, UniVersity of Bristol, Bristol BS8 1TS, United Kingdom Received December 17, 2009; E-mail: jens.mueller@usask.ca Since Manners et al. reported that thermal ring-opening poly- merization (ROP) of dimethylsila[1]ferrocenophane (1) yields high- molecular-weight poly(ferrocenyldimethylsilane) (2), 1a the tool box for ROP of strained sandwich compounds has been developed significantly. 1 To date, in addition to thermal ROP, transition metal catalyzed-, anionic-, and photocontrolled ROP of metallacyclo- phanes are described in the literature. 1c The latter two methods are of particular interest as they can be performed as living polymeriza- tions, which give access to block copolymers. Poly(ferrocenylsilanes) are functional materials applicable as plasma-etch resists for nanopatterning, 2 precursors to ceramics, 3 a tunable component of photonic crystals displays (photonic ink), 4 redox-tunable surfaces, 5 and polyelectrolyte capsules with redox- dependable permeability. 6 Block copolymers in block-selective solvents allow control of different micelle morphologies, and poly(ferrocenyldimethylsilane) (2) containing block copolymers, which form cylindrical micelles with semicrystalline cores, 7 show significant promise for future applications in nanotechnology. 8 Despite these recent advances, the number of well-defined metallopolymers is still quite restricted. Recently, we synthesized strained sandwich compounds with aluminum or gallium in bridging positions with the aim of developing new polymeric materials through ROP. 9 In this paper, we describe the first, well-characterized polyferrocene with gallium in bridging positions. 10 In depth NMR spectroscopy studies reveal that this air-stable organometallic polymer shows a surprising sensitivity toward the stereochemistry of the polymer backbone. All known strained Al- or Ga-bridged [1]metallacyclophanes 9 were equipped with the bulky, intramolecularly coordinating, trisyl- based ligands Pytsi or Me 2 Ntsi. However, ROP attempts with these [1]ferrocenophanes and [1]ruthenocenophanes either failed or resulted in sluggish polymerizations. 9e On the other hand, employ- ing the “one-armed phenyl” ligand Ar′ or p-tBuAr′ gave [1.1]met- allacyclophanes as the only isolatable products [3 (M ) Fe) and 4 (M ) Cr, Mo)]. 11 Obviously, the bulkiness of the group-13 bound ligand has a major effect on the outcome of reactions between a dilithiated sandwich species and an aluminum or gallium dihalide. Within this paper, we report on results obtained using a new “one- armed phenyl” ligand designed to incorporate steric bulk. Starting from commercially available 3,5-di-tert-butyl-toluene, the known amine 5 12 was prepared in three steps (eq 1), from which the gallium dichloride 6 was obtained as an analytically pure solid (see Supporting Information (SI) for details). Species 6 reacted readily with dilithioferrocene to form the targeted galla[1]ferroceno- phane 7 as an intermediate (Scheme 1). Attempts to isolate this new strained sandwich compound 7 gave an orange powder, which was characterized as the poly(ferroce- nylgallane) 7 n . The formation of species 7 was confirmed by 1 H NMR spectroscopy studies. If the Et 2 O from an aliquot of the reaction mixture, taken after ca. 15 min, was quickly replaced by C 6 D 6 , intermediate 7 was observed by 1 H NMR spectroscopy with resonances in the typical Cp range at δ 4.69 (4 -H), 4.56 (2 R-H), and 4.01 (2 R-H). This pattern and the chemical shifts match very well with other gallium-bridged [1]ferrocenophanes we have characterized previously [bridging moiety Ga(Pytsi): 9b δ 4.65 (2 -H), 4.61 (2 -H), 4.45 (2 R-H), 4.08 (2 R-H); or Ga(Me 2 Ntsi): 9c δ 4.54 (4 -H), 4.24 (2 R-H), 3.90 (2 R-H)]. Polymer 7 n was purified by precipitation into MeOH (45% isolated yield) and characterized by elemental analysis, GPC, DLS, WAXS, DSC, TGA, CV, UV/vis, 1 H and 13 C NMR spectroscopy (SI). Material 7 n is an amorphous polymer with a glass transition at 205 °C. The polymer is thermally robust as it retained 98% of its mass at 340 °C; further heating to 600 °C gave a nonmagnetic char with a low yield of 14% (TGA). Electrochemical studies (cyclic voltammetry) revealed two poorly resolved oxidation waves and one broad reduction wave. The midpoint between the main redox waves was found at -0.047 V versus the couple FeCp 2 /FeCp 2 + . † University of Saskatchewan. ‡ University of Bristol. Scheme 1. Synthesis of Intermediate 7 and Polymer 7 n Published on Web 01/25/2010 10.1021/ja910648k  2010 American Chemical Society 1794 9 J. AM. CHEM. SOC. 2010, 132, 1794–1795