Synthesis, Reactivity, and Ring-Opening Polymerization (ROP) of Tin-Bridged [1]Ferrocenophanes

Abstract

Abstract:The first examples of tinbridged [1]ferrocenophanes, Fe(h-C 5 H 4 ) 2 -SntBu 2 (7a) and Fe(h-C 5 H 4 ) 2 SnMes 2 (7b) have been synthesized by the low-temperature reaction of Fe(h-C 5 H 4 Li) 2´n TME-DA (TMEDA N,N,N',N'-tetramethylethylenediamine) with tBu 2 SnCl 2 and Mes 2 SnCl 2 (Mes 2,4,6-trimethylphenyl), respectively. They were isolated in 65 % (7a) and 85% (7b) yield as orange crystalline solids, which were characterized by multinuclear NMR and UV/Vis spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray diffraction. The tilt angles between the planes of the cyclopentadienyl rings are 14.1(2)8 for 7a and 15.2(2)8 (average) for the three independent molecules of 7b in the unit cell. Although they have significantly smaller tilt angles than analogous [1]ferrocenophanes with the lighter Group 14 elements silicon or germanium in the bridge, 7 a and 7 b still readily undergo ring-opening polymerization (ROP) by thermal reaction in the solid state (7 a at 150 8C; 7 b at 180 8C), to give highmolecular-weight poly(ferrocenylstannane)s [Fe(h-C 5 H 4 ) 2 SntBu 2 ] n (8 a) and [Fe(h-C 5 H 4 ) 2 SnMes 2 ] n (8 b). Remarkably, 7 a and 7 b were also found to polymerize in solution at room temperature in the absence of externally added initiators. ROP is much more rapid for 7 a than for 7 b in solution. The cyclic dimers [Fe(h-C 5 H 4 ) 2 SnR 2 ] 2 (3; R tBu, Mes) were formed as by-products in amounts which depended on the solvent. Electrochemical studies of the cyclic dimers and polymers indicated the presence of significant Fe´´´Fe interactions that are mediated by the tin-atom spacer. When benzene solutions of 7 a and 7 b were treated with small amounts of Karstedts catalyst, slower polymerization was observed. Stoichiometric reaction of Pt(1,5-cod) 2 (cod cyclooctadiene) with 7 a yielded the novel trimetallic 1-stanna-2-platina[2]ferrocenophane Fe(h-C 5 H 4 ) 2 Pt(1,5-cod)SntBu 2 (9), which functioned as a sluggish catalyst for the ROP of 7 a and 7 b.

Molecular Electrochemistry of Cyclophanes

“…They show at least one reversible oxidation wave, however, at surprisingly high anodic potentials, making formation of such complexes difficult. Tin- [1]ferrocenophanes [69,70] reveal again reversible one-electron signals in CV with E 0 close to that of the parent ferrocene, while (dimethylsilylen)-[1]ferrocenophane appears to become chemically irreversible under comparable conditions [70]. Selena-and thia- [1]ferrocenophanes are also known [71] and show similar behavior as regards reversibility.…”

Organometallic Polymers of the Transition Metals

“…[175][176][177][178] The ROP of ferrocenophanes with tin bridges has also been described by the research groups of Manners and Pannell. [179][180][181][182] It was reported that high-molecularweight polymers could be produced by thermal ROP, and that the ferrocenophanes also opened at room temperature in solution. [179][180][181] It was also discovered that the ringopening of tin-bridged [1]ferrocenophanes in solution is accelerated by the addition of amines.…”

“…[179][180][181][182] It was reported that high-molecularweight polymers could be produced by thermal ROP, and that the ferrocenophanes also opened at room temperature in solution. [179][180][181] It was also discovered that the ringopening of tin-bridged [1]ferrocenophanes in solution is accelerated by the addition of amines. [181] The same observation was noted upon the addition of pyridine to solutions of ferrocenophanes containing silicon and germanium bridges as shown in Scheme 48, however, the siliconcontaining monomer displayed much lower reactivity than the other monomers.…”

Polymer science with transition metals and main group elements: Towards functional, supramolecular inorganic polymeric materials

“…24 Comparisons of the behavior of PFSs with that of other polyferrocenes indicate that the metal-metal interactions are influenced by the silicon spacer. 27 A recent analysis discusses the influence of the spacer on the molecular scale dielectric constant of the medium between the iron centers that mediates the interactions detected. According to this approach, the presence of more polarizable atoms (e.g., Si vs C) would be expected to lead to an increased Fe•••Fe interaction, which is indeed observed.…”

“…However, polyferrocenylethylenes 9 (M ϭ Fe, E ϭ EЈ ϭ CH 2 , RЈ ϭ Me) with a CH 2 OCH 2 spacer (and other polymers derived from the ROP of [2]ferrocenophanes) possess much weaker metal-metal interactions than PFSs, whereas for polyferrocenylsulfides 7 (E ϭ S) the interaction is stronger. 27,37 Polyferrocenylphosphines (PFPs) 7 (E ϭ PR) offer additional possibilities because facile coordination of transition metals to phosphorus is possible. distribution is broad (PDI ϭ ca.…”