Transition-Metal-Catalyzed ROP

Figure 26 The transition metal-catalyzed ROP of sila[l]ferrocene in the presence of Si—H functionalized diferrocenylborane to the ferrocene polymer 37. (Adapted from ref. 59.)...

The (diaryl)stanna-[l]-ferrocenophanes are relatively more stable than the (di-/-butyl)tin analog. - The bis(triisopropylphenyl)tin-ferrocenophane is stable in the presence of both air and moisture, and does not undergo anionic or transition-metal catalyzed ROP. However, at elevated temperature it undergoes... 

Carbathioferrocenophane, 47, underwent cationic ROP with methyl triflate and boron trifluoride etherate, but was resistant to both anionic and transition-metal-catalyzed ROP.100101 However, cationic ROP initiated with methyl triflate caused oxidation of the iron centers in the polymers. Me+ and H+ were determined to initiate cationic ROP for the methyl triflate and boron trifluoride, respectively.101 Scheme 2.12 shows a proposed mechanism of the methyl triflate, 48, initiated ROP of [2]carbathioferrocenophane, 47. 

A number of poly(dimethylsiloxane) and poly(ferrocenylsilane) copolymers have been prepared using thermal, anionic, and transition metal catalyzed ROP.97,98,121,124-131 Manners et al.132 described the ring-opening of [l]thia- and [l]selenaferrocenophanes using anionic initiators. Electrochemical studies of poly(ferrocenyl sulfide)s prepared by these methods elicited two reversible oxidation processes, indicating that strong Fe-Fe interactions exist in the polymers. 

Manners first proposed that the transition-metal-catalyzed ROP occurred via a homogenous mechanism.157 However, a heterogenous catalytic cycle has been reported.158 The proposed mechanism for the Pt(l,5-cod)2 (cod-cyclooctadiene) catalyzed reaction is shown in Scheme 2.24. The Pt(l,5-cod)2 forms a [2]platinasilaferrocenophane through oxidative addition to the zero-valent Pt complex via elimination of a 1,5-cod ligand. Platinum colloids are then formed by the elimination of the second 1,5-cod ligand these platinum colloids are proposed to be the active catalysts. The polymers are then formed by subsequent oxidative addition and reductive eliminations at the colloid surface. 

Thermal ROP of silicon-bridged [1 Jferrocenophanes Thermal ROP of other strained metallocenophanes Living anionic ROP of strained metallocenophanes Transition metal-catalyzed ROP of strained metallocenophanes Other ROP methods for strained metallocenophanes Properties of polyferrocenylsilanes... 

Studies have shown that unsymmetrical [Ijferrocenophanes in which only one of the cyclopentadienyl rings is methyl-substituted yield regioregular PFSs via transition metal-catalyzed ROP, whereas thermal ROP of the same monomers yields regioirregular materials. 

Research has also focused on understanding the mechanism of the transition metal-catalyzed ROP reactions for [l]ferrocenophanes. A logical first step in the polymerization is insertion of the transition metal into the strained Cp-carbon-bridging element bond in the ferrocenophane. Polymers 93 formed in the presence of hydrosilanes are believed to result from competitive oxidative addition between the Si-H bond of the hydrosilane and the strained Gp-Si bond of the ferrocenophane at the catalytic center followed by reductive elimination. Detailed work has indicated that colloidal metal is the likely catalyst in the ROP reactions. 

Moreover, PFS block co-polymers can be accessed via transition metal-catalyzed ROP of silicon-bridged [l]ferro-cenophanes (Section 12.06.3.3.4) in the presence of a polymer terminated with a reactive Si-H bond. This technique has been used successfully for the synthesis of both diblock and triblock co-polymers. For example, water-soluble PFS-/ -PEO 106 (PEO = poly(ethylene oxide)) has been prepared from monomer 72 and commercially available poly(ethylene glycol) modified at the end group (Scheme 9). In such cases, the polydispersity of the PFS blocks is higher than that obtained from anionic ROP (typically, PDI = 1.4) and the polydispersity of the co-block is determined by that of the original Si-H functionalized material. Nevertheless, block co-polymer syntheses that use the transition metal-catalyzed approach are very convenient, as the stringent purification and experimental requirements for living anionic polymerizations are unnecessary. 

Cylindrical and tape-like morphologies have been identified in the case of PI-/ -PFS (PI = polyisoprene) where the PFS block crystallizes. " Water-soluble polyferrocenyldimethylsilane-/ -poly(aminoalkylmethacrylate) co-polymers of narrow polydispersity have also been prepared and cylindrical micelles have been identified. " Block co-polymers generated by transition metal-catalyzed ROP, such as PFS-/ -PDMS-/ -PFS triblock materials, have been shown to self-assemble in hexanes to yield a variety of remarkable architectures that include flower-like assemblies where the... 

SYNTHESIS Poly(ferrocenyldimethylsilane) can be synthesized via the thermal ring opening polymerizhon (ROP) of the strained dimethylsila[l]ferrocenophane, (C5H4)2p iMe2. Additionally, poly(ferrocenyldimethylsilane) can be prepared via anionic initiated ROP or transition metal catalyzed ROP of the strained [IJferrocenophane. 

A very convenient, transition metal-catalyzed ROP route to polymetallocenes from strained metallocenophanes was reported in 1995 [87, 88]. Various Rh , Pd", Pd ,... 

The synthesis and properties of poly(ferrocenylsilanes) have been extensively reviewed (7,11,96). Thermal, anionic, and transition-metal-catalyzed ROP of [IJsilaferrocenophanes has led to the prodnction of polymers containing a variety of functional groups attached to the sihcon atoms (96-102). The structures and morphologies of this class of polymer have been examined using X-ray diffraction, optical, atomic force, and scanning electron microscopy as well as other techniques (103-107). Pannell and co-workers have recently tested these materials as coatings for tapered optical-fiber gas sensors (108). 

Thermal ring-opening polymerization of [2]ferrocenophanes has also been reported by Manners and coworkers (20). Oxidation of the polyferrocenylethyl-ene with tetracyanoethylene resulted in antiferromagnetic interactions. Unsymmetric [2]ferrocenophanes (R=S, P) have also been synthesized and ring-opened however, a ferrocenophane containing a C-Si bridge was resistant to thermal, anionic, and transition-metal-catalyzed ROP. " The [2]carbathioferrocenophane could also be polymerized in the presence of cationic initiators. 

Thermal ROP of metallocenophanes leads to virtually no control over molecular weight and the molecular weight distribution is broad (PDI= 1.5-2.5). Subsequently, living anionic and transition metal catalyzed ROP routes to polymetallocenes have been developed. " These have permitted unprecedented control of mainchain metal-containing polymer architectures. In particular, the access provided to the first block copolymers with metals in the mainchain has created unique opportunities for the generation of self-assembled, supramolecular materials. 

Transition-metal-catalyzed ROP of silicon-bridged [l]feirocenophanes was reported in 1995 and occurs in solution at room temperature in the presence of Pt°, Pt , Rh, and Pd precatalysts. Transition-metal-catalyzed ROP is a mild metiiod that does not require monomer with an exceptional degree of purity and has now been developed to the stage where considerable control over polymetallocene architectures is possible. " On the basis of the behavior of all-organic analogs, polyferrocene block copolymers would be expected to self-assemble to form supramolecular... 

Self-assembling polyferrocene triblock copolymers are also accessible via living anionic or transition metal-catalyzed ROP. " We have reported studies of the self-assembly of PFS-Z)-PDMS-h-PFS triblock copolymers. If crystallizable PFS blocks are present, remarkable flowerlike architectures form on self-assembly in n-hexane as the PDMS-selective solvent with cylindrical micelles as a major component. " In contrast, analogs with amorphous PFS blocks form spherical micelles. In the former case it also appears that crystallization directs the self-assembly process and the ability of the... 

Transition metal-catalyzed ROP of silicon-bridged [l]-ferrocenophanes 493... 

Table 16.1 Thermal transition and molecular weight data for representative polyferrocenylsilanes (PFSs) prepared by thermal or transition-metal-catalyzed ROP ...

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