The living anionic ring-opening polymerization (ROP) of the methylated silicon-bridged [1]ferrocenophane Fe(η-C5H4)2SiMe2 1 initiated by n-BuLi, PhLi, FcLi (Fc = Fe(η-C5H4)(η-C5H5)), and 1,1‘-dilithioferrocene, fcLi2· 2/3TMEDA (fc = Fe(η-C5H4)2) in THF at 20 °C has allowed the preparation of well-defined poly(ferrocenyldimethylsilanes) [Fe(η-C5H4)2SiMe2] n 4 with control of molecular weights, narrow polydispersities, and controlled end-group structures. The living anionic ROP of 1 has also been used to prepare a variety of novel, well-defined organometallic/organic/inorganic multiblock copolymers constructed from a combination of poly(ferrocenyldimethylsilane) (PFS), polystyrene (PS), and poly(dimethylsiloxane) (PDMS). The materials prepared included PFS-b-PDMS diblock copolymers (7a and 7b), PDMS-b-PFS-b-PDMS triblock copolymers (8a and 8b), a PS-b-PFS diblock copolymer (10a), a PS-b-PFS-b-PDMS triblock copolymer (11), a PS-b-PFS-b-PDMS-b-PFS-b-PS pentablock copolymer (12), a PFS-b-PS-b-PFS triblock copolymer (15), and a PDMS-b-PFS-b-PS-b-PFS-b-PDMS pentablock copolymer (16). These materials were studied by cyclic voltammetry which afforded two reversible oxidation waves characteristic of redox-coupling arising from interactions between the skeletal iron atoms in the ferrocenylsilane blocks. The multiblock copolymers were also characterized by DSC which showed the presence of individual thermal transitions for each block which indicated that they were incompatible. In addition, the morphology of a film of PS-b-PFS (10a) was investigated by TEM which showed a high degree of phase separation leading to the formation of microdomains of polystyrene and poly(ferrocenyldimethylsilane).

In order to gain insight into the electrochemical and conformational properties of the prototypical high polymeric poly(ferrocenylsilane), poly(ferrocenyldimethylsilane) [Fe(η-C5H4)2SiMe2] n 6, three series of oligo(ferrocenylsilanes) R-fc-[SiMe2-fc] n - 1-R‘ (fc = Fe(η-C5H4)2) 7 2 −7 9 (R = R‘ = H), 8 2 −8 7 (R = H and R‘ = SiMe3), and 9 2 −9 7 (R = R‘ = SiMe3) have been prepared and studied (the subscript n in the oligomer refers to the number of ferrocene units present). These species were prepared via the anionic ring-opening oligomerization of the silicon-bridged [1]ferrocenophane Fe(η-C5H4)2SiMe2 5. Initiation with ferrocenyllithium FcLi (Fc = Fe(η-C5H5)(η-C5H4)) followed by quenching with H2O or SiMe3Cl afforded H-fc-[SiMe2-fc] n - 1-H (7 2 -9 ) or H-fc-[SiMe2-fc] n - 1-SiMe3 (8 2 -7 ), respectively. Initiation with the dilithioferrocene complex fcLi·2/3TMEDA followed by quenching with H2O or SiMe3Cl similarly afforded the oligomers H-fc-[SiMe2-fc] n - 1-H (7 2 -9 ) or alternatively the bis(silyl)-capped species Me3Si-fc-[SiMe2-fc] n - 1-SiMe3 (9 2 -7 ), respectively. The individual molecular compounds of these three series of oligomers 7 2 −7 9 , 8 2 −8 7 , and 9 2 −9 7 were isolated in pure form from the oligomeric mixtures by column chromatography and these were structurally characterized by 1H, 13C, and 29Si NMR spectroscopy, mass spectrometry, and in selected cases by elemental analysis. The structure of the linear pentamer 7 5 has also been determined by single crystal X-ray diffraction. The central portion of this species possesses a trans planar zigzag conformation in the solid state and appears to be a valuable model for the analogous conformation of the high polymer 6 in crystalline domains. The electrochemical behavior of each pure oligomer was studied by cyclic and differential pulse voltammetry and was found to depend on whether an odd or an even number of ferrocene units were present. For oligomer systems containing an odd number of iron centers two reversible redox processes of varying intensities at −0.02−0.00 V and 0.21−0.23 V (vs ferrocene) were observed with a redox splitting of 0.21−0.23 V. For oligomer systems containing an even number of iron centers larger then two, three reversible redox processes of varying intensities were observed at ca. 0.00, 0.13, and 0.24 V vs ferrocene. As the oligomer chain length increased, the electrochemical behavior for both the “odd” and “even” series approached that of the high polymer 6 for which two reversible redox processes at 0.00 and 0.24 V (vs ferrocene) of equal intensity exist. These results are completely consistent with the previously proposed theory that initial oxidation of 6 affords a product in which alternating iron sites are oxidized. Spectroelectrochemical experiments show an intervalence electron transfer absorption (1100−1350 nm, εmax ⩽ 150 M-1 cm-1) for partially oxidized oligo(ferrocenylsilanes) that is typical for class II mixed-valent compounds. Additionally, single crystals were obtained of the m...

Polymers with skeletal transition-metal atoms are attractive materials as a result of their novel electrical, optical, magnetic, and chemical characteristics.1•2 We have previously reported the preparation of the first examples of high molecular weight poly-(ferrocenylsilanes) 1 via the thermal ring-opening polymerization (ROP) of strained, ring-tilted, silicon-bridged [ 1 ] ferrocenophanes such as 2 at elevated temperatures.3 4567These polymers display novel electrochemical properties which are indicative that the iron atoms interact with one another, and several show evidence for the formation of ordered structures in the solid state.4-7 Studies of well-defined short-chain oligomers would be expected to provide additional understanding of the characteristics of these unusual polymers, but such species are often very difficult to prepare and crystallize for X-ray diffraction studies.

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The silicon-bridged [1]ferrocenophanes Fe(η-C5H4)2SiRR‘ [3 (R = Me, R‘ = Cl), 4 (R = R‘ = Cl)] with chlorine substituent(s) at silicon were prepared via the reaction of Fe(η-C5H4Li)2·TMEDA (TMEDA = tetramethylethylenediamine) with the chlorinated silanes MeSiCl3 and SiCl4, respectively. An X-ray diffraction study of 4 indicated that the cyclopentadienyl rings in this species are tilted by an angle of 19.2(4)°, typical of other structurally characterized silicon-bridged [1]ferrocenophanes. Thermal ring-opening polymerization (ROP) of 3 and 4 at 250 °C yielded the first high molecular weight poly(ferrocenylsilanes) with halogen substituents at silicon, [Fe(η-C5H4)2SiRR‘] n [7 (R = Me, R‘ = Cl), 8 (R = R‘ = Cl)]. Transition-metal-catalyzed polymerization of 3 and 4 with Pd and Pt catalysts also yielded polymers 7 and 8 in solution at room temperature. Polymer 7 was soluble in polar organic solvents and was characterized by 1H, 29Si, and 13C NMR and elemental analysis. In contrast, poly(ferrocenylsilane) 8 was found to be insoluble in organic solvents and this material was characterized by elemental analysis and derivatization. Substitution of the chlorine side groups in polymer 7 was achieved under mild conditions via reaction with the organolithium reagents MeLi, PhLi, and LiC⋮C(CH2)4H to afford the known polymers [Fe(η-C5H4)2SiMe2] n (2a) and [Fe(η-C5H4)2SiMePh] n (2d) and the new polymer [Fe(η-C5H4)2SiMeC⋮C(CH2)4H] n (9), respectively. The molecular weights for the completely halogen-substituted poly(ferrocenylsilanes) 2a, 2d, and 9 were estimated by gel permeation chromatography in THF to be in the range of M w = 7.4 × 104 to 1.7 × 105 and M n = 3.6 × 104 to 1.1 × 105 versus polystyrene standards. Substitution of the chlorine atoms in 8 was also demonstrated by reaction of the polymer with MeLi to give 2a.

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.

The first chalcogen-bridged [1]ferrocenophanes Fe(η-C5H3R)2E (6, E = S, R = H; 7, E = Se, R = H; 12, E = S, R = Me) have been synthesized and characterized both structurally and spectroscopically. Synthesis of sulfur- and selenium-bridged species 6 and 7 was achieved by the reaction of dilithioferrocene·TMEDA (TMEDA = tetramethylethylenediamine) with bis(phenylsulfonyl) sulfide S(O2SPh)2 and selenium diethyldithiocarbamate Se(S2CNEt2)2, respectively, in 20−30% yields. Structural characterization of both 6 and 7 revealed highly strained structures with tilt-angles between the cyclopentadienyl ligands of 31.05(10)° and 26.4(2)°, respectively. Compounds 6 and 7 are purple and red-purple, respectively; comparison of the structures of known [1]ferrocenophanes 1 showed that when the second period (from group 14−16) is traversed, there is a substantial increase in cyclopentadienyl ring-tilting in main group element bridged [1]ferrocenophanes, and the lowest energy UV/vis absorption peaks become increasingly red-shifted. Extended Hückel MO calculations were performed and, consistent with this observation, predicted a decrease in the HOMO−LUMO gap as the ring-tilt increases. Thermal ring-opening polymerization (ROP) of both 6 and 7 afforded the insoluble poly(ferrocenyl sulfide) [Fe(η-C5H4)2S] n 8 and poly(ferrocenyl selenide) [Fe(η-C5H4)2Se] n 9, respectively. Differential scanning calorimetry studies of the ROP process provided estimates of the strain energies of 6 and 7 which were ca. 130(±20) and 110(±20) kJ mol-1, respectively. Anionic ROP of 6 also yielded the insoluble poly(ferrocenyl sulfide) 8. However, linear soluble dimeric and trimeric trimethylsilyl-capped oligo(ferrocenyl sulfides) 10b and 11b were synthesized by the reaction of 6 with dilithioferrocene·TMEDA followed by the addition of Me3SiCl and were characterized spectroscopically, electrochemically, and, for 11b, by X-ray diffraction, and provide useful models for the analogous high polymer. The dimethylated sulfur-bridged species 12 was prepared as a mixture of isomers from the reaction between dilithiodimethylferrocene·TMEDA and S(O2SPh)2, and X-ray structural characterization of a single isomer 12a showed the presence of a large tilt-angle of 31.46(8)°. Thermal and anionic ROP of the isomer mixture 12 afforded the first soluble poly(ferrocenyl sulfide) [Fe(η-C5H3Me)2S] n 13 which was characterized by 1H and 13C NMR, elemental analysis, thermogravimetric analysis, and gel permeation chromatography. Cyclic voltammetric studies of 13 showed the presence of two reversible oxidation waves with a redox coupling ΔE = ca. 0.32 V, which is consistent with the presence of significantly stronger M···M interactions compared to those present in other ring-opened poly(ferrocenes) derived from [1]ferrocenophanes.

Novel poly(methylphenylsilane)-poly(ferrocenyldimethylsilane) copolymers 5a-d of varying monomer composition were prepared via the thermal ring-opening polymerization of a mixture of the strained cyclic tetrasilane [MePhSi]4 (1) and the silicon-bridged [1]ferrocenophane Fe(η-C5H4)2SiMe2 (3). The resulting materials were structurally characterized by 1 H and 29 Si NMR and also by gel permeation chromatography (GPC), pyrolysis mass spectrometry (MS), and cyclic voltammetry. GPC in THF indicated that the molecular weights of the polymers 5a-d were in the range Mn ) (2.0 × 10 4 )-(8.9 × 10 4 ) with PDI values of 2.4-3.5. Polymers 5a-c were photosensitive and GPC traces of 5a-c were studied both before and after irradiation of the sample with UV light (λ ) 340 nm). The formation of short chain oligo(ferrocenylsilanes) after irradiation was consistent with exclusive photodegradation of the polysilane segments and indicated that the copolymers were random in nature. Pyrolysis MS of 5a-c also supported a random structure. Cyclic voltammetric studies of 5a-c in CH2Cl2 showed the presence of the characteristic two reversible oxidation waves arising from oligo(ferrocenylsilane) segments with interacting iron atoms at E1/2 ) 0.00 and 0.23 V (relative to ferrocene/ferrocenium) and an irreversible oxidation with Ep(ox) ) 0.39 V arising from the polysilane segments. UV/vis spectroscopy showed that the σ-electrons in the oligosilane segments are delocalized and that λmax increased from 325 to 333 nm as the proportion of the cyclotetrasilane 1 in the initial monomer mixture increased. These values suggest that the oligosilane segments are relatively short and do not approach the limit corresponding to ca. 30 silicon atoms (Mn ) ca. 3 000), which levels off at 338 nm. Attempted anionic initiation of the copolymerization of 1 and 3 was unsuccessful and led exclusively to homopolymerization. Transition metal catalyzed copolymerization of 1 and 3 using PtCl2 resulted in a copolymer which was derived almost exclusively from 3. The charge transport properties of the representative copolymer 5d were also investigated. Films of pristine 5d were insulating (conductivity <10 -14 S cm -1 ) but after exposure to iodine the conductivity increased by a factor of 10 8 to (6.5-8.2) × 10 -6 S cm -1 . In comparison, the conductivities of iodineexposed films of poly(ferrocenyldimethylsilane) (4) and poly(ferrocenyldi-n-butylsilane) (7) were ca. 2 × 10 -4 S cm -1 . The hole mobility of 5d was studied by standard time of flight techniques and was found to be appreciable with a value of 4.0 × 10 -6 cm 2 /V s.