Synthesis and materials science applications of highly metallized polyferrocenylsilanes and the photocontrolled polymerization and oligomerization of silicon -bridged [1]ferrocenophanes

Acetylide-substituted sila[1]ferrocenophane [Fe(eta-C5H 4)2Si(Me)C≡CPh] was reacted with dinuclear metal complexes to give highly metallized sila[1]ferrocenophanes [Fe(eta-C5H 4)2Si(Me){M2(R)C2Ph}] containing pendent cobalt [M2(R) = Co2(CO)6], molybdenum [M 2(R) = Mo2Cp2(CO)4], or nickel [M 2(R) = Ni2Cp2] clusters. The corresponding highly metallized polyferrocenylsilanes (PFSs) were prepared from acetylide-substituted PFS [Fe(eta-C5H4)2Si(Me)C≡CPh] n using a similar clusterization strategy; these polymers contain at least 25% metal by weight and have been patterned on the micron scale using electron-beam lithography and UV-photolithography.;The photocontrolled ROP of sila[1]ferrocenophane [Fe(eta-C5H 4)2SiMe2] (C) using Na[CsH5 ] as initiator was studied in detail. Although ferrocenophane C has two major absorption bands between 300 nm and 600 nm, only the band centred at 480 nm is responsible for generating photoexcited monomers that undergo polymerization. A faster propagation rate was observed at 5°C than at 20°C, presumably due to the more rapid deactivation of photoexcited monomers at higher temperatures. Since the photoexcited monomers are likely solvated, coordinating solvents such as tetrahydrofuran and pyridine are best for this reaction. The living nature of photocontrolled ROP was demonstrated by ABA triblock copolymer synthesis using difunctional initiators.;Photopolymerization of ferrocenophane C using 4,4',4"-tri- tert-butyl-2,2':6',2"-terpyridine (tBu3terpy) as a stoichiometric initiator gave the high molecular weight PFS [Fe(eta-C 5H4)2SiMe2]n. When the photolysis was performed in the presence of Me3SiCl, cleavage of both iron--cyclopentadienyl bonds in ferrocenophane C was observed. The iron(II) complex [Fe(tBu3terpy)2Cl2] was formed and the silane fragment [(C5H4SiMe3) 2SiMe2] was released.;Photoirradiation of ferrocenophane C and a stoichiometric amount of 4,4'-dimethyl-2,2'-bipyridine gave cyclic PFS and cyclic oligoferrocenylsilanes. Simulated powder X-ray diffractograms of cyclic pentaferrocenylsilane c-[Fe(eta-C 5H4)2SiMe2]5 and cyclic hexaferrocenylsilane c-[Fe(eta-C5H4)2SiMe 2]6 showed that their solid state structures have similar interplanar iron--iron distances as linear PFS [Fe(eta-C5H 4)2SiMe2]n. Cyclic voltammetry studies of the oligomers reveal that oxidation initially occurred at alternating iron centres, and the remaining iron centres were oxidized at a higher potential.;Sila[1]ferrocenophanes [Fe(eta-C5H4)2Si(C≡CBu) 2] (A) and [Fe(eta-C5H4)2 Si(Me)C≡CC≡CPh] (B) were prepared and polymerized. The presence of multiple alkyne substituents complicated the reactivity of these sila[1]ferrocenophanes in platinum-catalyzed ring-opening polymerization (ROP), leading to low yields and bimodal molecular weight distributions. However, both A and B polymerized to give monomodal, well-defined PFSs in photocontrolled ROP.