Strained Ferrocenophanes

As will be shown in the next section, strained ferrocenophanes can be used as monomers for ring-opening polymerization to afford ferrocene-containing polymers. 

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Other Ferrocenyl Polymers Prepared from Strained Ferrocenophanes... 

Many other types of strained ferrocenophanes have been successfully polymerized [37-43, 57-58]. These include polymers that eontain boron, carbon, germanium, tin, phosphorus, sulfur as well as selenium. Some of the representative examples of the polymers of this type are shown in Fig. 8.26. 

The basic ring-opening reactions of ferrocenophanes have developed into a mature research area, the most significant work has been carried out by the Manners research group. The essential synthetic methodology is to react a ring-strained ferrocenophane with a alkyllithium reagent or a metal salt to initiate polymerization. There now exists a broad literature based on the subject, and several reviews have been published. ... 

Figure 25 The ring-opening polymerization of strained boron-bridged [ 1J ferrocenophanes (35a-c) to produce poly(ferrocenylboranes) (36a-c). (Adapted from ref. 57.)...

In addition to the common methods of synthesis, it has been shown that the desulfurization of thioacetals yields organogermanes (Equations (7) and (8)) with excellent selectivity in some cases (Equation (9)).8 Ring-opening reactions of strained [l]ferrocenophanes furnish germanium-substituted ferrocenes9,10 (Equation (10)).9... 

Braunstein and coworkers have shown (vide supra) that in the bimetallic Fe—Pt complex (CO)3(SiR3)Fe(yU.-PPh2)Pt(PPh3)CO(Fe—Pt), a silyl migration occurred from the Fe to the Pt center (Scheme 17)102. Remarkably, the first example of a well-characterized insertion of a transition-metal fragment into a strained silicon-carbon bond of a silicon-bridged [l]ferrocenophane was recently reported by Sheridan, Lough and Manners. The... 

Another impressive example is the facile cleavage of Si—C(Cp) bonds in strained [1]-ferrocenophanes with bridging silicon. This behaviour is the basis for the synthesis of high-molecular-weight poly(ferrocenylsilanes) (equation 47) and will be described in more detail in Section II.E.l. 

Both PFS-PI and PFS-PDMS are synthesized by two-step anionic polymerization. The synthetic approach for the preparation of PFS-PDMS is shown in Scheme 1 [8,9] n-butyllithium was used to initiate the polymerization of the strained silicon-bridged ferrocenophane in THF solution, while the second block was built by the subsequent addition of hexamethyltrisiloxane (D3). The reaction was terminated with chlorotrimethylsilane. To obtain PFS-PI, the PI block was initiated with butyllithium, followed by the addition of the silicon-bridged ferrocenophane. 

To date, the synthesis of strained [l]stannafeiTocenophanes as precursors for ROP is restricted to compounds with bulky substituents at tin. Previous attempts to prepare tin-bridged ferrocenophanes by the reaction of dilithioferrocene with diorganotin dichlorides, R2SnCl2, containing less bulky substituents (R = Me, Et, w-Bu, Ph) resulted in the isolation of oligomers (Mn < 4.6 x 10 ) and cyclic dimers . The crystal structure analyses of the [2]distannaferrocenophane 60 and the [3]tristannaferrocenophane 61, which are essentially unstrained, were also reported " . 

Hydrocarbon-bridged [2]ferrocenophanes 30 are quite well known and are significantly more strained than their disilane-bridged analogs because of the smaller size of carbon relative to silicon. For example, tilt angles up to around 21° are known for these species. The first ROP of a [2]metallo-... 

To prepare [2]metallocenophanes that are even more strained than [2]ferrocenophanes 30, species with a larger ruthenium atom in the place of iron have been synthesized (81). Such [2]ruthocenophanes would be expected to possess much greater ring-tilt angles moreover, because ruthenocene is known to possess significantly different electrical properties compared to ferrocene, modified polymer properties would be anticipated (57). 

Gates DP (1997) The synthesis, structure, reactivity and polymerization behavior of boron- and sulfur-nitrogen-phosphorus heterocycles and highly strained chalcogen- and boron-bridged [1], ferrocenophanes. PhD thesis, University of Toronto... 

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