�SEQ CHAPTER \h \r 1Part 1.� Butylated Monomer Synthesis.� About half of our synthetic work has focused on the biphenylene-linked bis(cyclopentadienone) (CPD) monomer system (A) as shown in Scheme 1.� The bulky alkyl group (R = tert-butyl) allows attachment of only one additional substituent (Ar).� This design keeps the synthesis simple (four steps) while allowing some modularity.� We have been able to synthesize monomer A with Ar = C₆F₅, 4-C₆F₄CF₃, and 4-C₅F₄N.� All of the C-C bond forming steps are now achievable in high yields (> 75%) with one minor exception (attachment of C₅F₄N group, 50%).

Part 2.� Perfluorinated Monomers.� Our only successful perfluorinated monomer so far is B (Ar = 4-C₆F₄CF₃) shown in Scheme 1.� In the key step, the six aryl substituents are attached in one pot.� The solvent we had been using (diglyme) was reacting under the harsh conditions.� Through a lengthy process of trial-and-error, we found one substitute (HMPA), which gives 75% yield for the sequence.

Part 3.� Cyclopentadiene Oxidation Chemistry.� The last step in the synthesis of all our monomers is oxidation of a methylene group (CH₂) to a carbonyl group (C=O).� Our initial conditions (N,N-dimethyl-4-nitrosoaniline followed by acidic hydrolysis of the imine/nitrone) required forcing conditions to liberate the corresponding ketones.� Yields were limited to about 30% after silica gel chromatography, an intolerable result.� Going back to the drawing board (and to the literature), we found a copper catalyst that will enable many substituted cyclopentadienes to be oxidized to the corresponding cyclopentadienones by oxidation with O₂ in yields exceeding 75%.� Meanwhile B turns out to be made cleanly using a selenium dioxide oxidation (95%).

Part 4.� Ponytail Systems.� Because our �workhorse� monomer system (A) is relatively low in fluorine content, we worried that progress toward �highly� fluorinated polyphenylenes might be limited only to the B monomer system.� However, the modularity of A suggested an alternative approach.� The student working on the perfluoro-4-tolyl-substituted monomer (Ar = 4-C₆F₄CF₃) undertook the development of �ponytail� monomers in which the CF₃ group was exchanged for a longer fluoroaliphatic chain.� We now have a good synthesis of the required starting arene (Scheme 2).� We are ready now to incorporate this interesting arene into our other monomer syntheses, both A and B types.

Part 5.� Dead Ends and Failures.� In our proposal, we offered the an approach to an isopropylidene-linked monomer system (Scheme 3).� However, these reactions fail because the isopropylidene linkage comes apart during the reaction!� Careful observations and product analyses showed that 6,6-dimethylfulvene is formed, suggesting that the arylated cyclopentadiene is simply such a good leaving group (arrows in scheme) that the decomposition process becomes favorable and apparently more rapid even than deprotonation by sodium hydride.�

Another monomer system that we originally proposed is shown in Scheme 4.� The whole synthetic sequence worked fine, except for one nasty surprise.� The proposed trans isomer (shown below at left) was not obtained.� Instead, the cis isomer formed exclusively, and upon oxidation to the diketone it underwent an intramolecular Diels-Alder reaction (at room temperature!) to form a complicated polycyclic species that we finally had to characterize by X-ray crystallography.� This surprising self-Diels-Alder reaction has taught us something very important however:� DDiels-Alder reactions between two CPD end groups should also be possible in monomer system A because of structural similarities, and we will need to keep a sharp eye out for this reaction as a possible cause of defects or low molecular weight.

Part 6. Polymer and Solvents.� At the close of the first fiscal year, we are not yet able to prepare high molecular weight polyphenylenes by combining our monomers (A, Ar = C₆F₅) with a dialkyne such as 1,4-diethynylbenzene.� However, we now know that the monomers with Ar = 4-C₆F₄CF₃ and Ar = 4-C₅F₄N react faster based on model reactions with phenylacetylene.� We also have recently learned that the solvent of the model reactions with phenylacetylene can dramatically accelerate the reaction.� Hydrogen-bonding solvents such as meta-cresol and 2,2,2-trifluoroethanol seem to work best.� We think the CPD carbonyl oxygens are accepting hydrogen bonding from these solvents, increasing their electrophilicity and accelerating the �inverse electron demand� Diels Alder reactions.� We hope to use this new knowledge to make progress toward these polymers in the coming year.

Part 7.� Fluorinated Nanodentritic Structures.� With funding from the Summer Faculty Fellowship program, my colleague and his student made progress toward the synthesis of the species shown in Scheme 5 (Ar = C₆F₅).� Work is underway to complete this synthesis and explore its behavior in fluorous and non-fluorous solvents.