ORGANOMETALLIC NONLINEAR OPTICAL POLYMERS .2. SYNTHESIS OF MAIN-CHAIN ORGANOMETALLIC POLYMERS AND A STRUCTURAL STUDY OF FERROCENE NLO-PHORES

A detailed structural analysis of several ferrocene-based nonlinear optical (NLO)-phores was done by X-ray diffraction. Structures were reported for {eta5-C5H5}{eta5-C5H4CH=C(CN)(R)}Fe [1a, R = CO2Et; 1b, R = CN; 1c, R = 4-pyridyl; 1d, R = 4-bromophenyl]. The study illustrated that electron-withdrawing groups favor and control the planarity of the pi-system. Through selective functionalization of the cyclopentadienyl rings of ferrocene, new monomers, namely, {eta5-C5H4CH2O(CH2)nOH}{eta5-C5H4CH=C(CN)CO2-Et}Fe (5) and {eta5-C5H4CH2O(CH2O(CH2)nO2CCH2CN}{eta5-C5H4CHO}Fe [6, n = 6; 8, n = 1], were prepared in the study. Monomer 5 was suitable for Lewis acid catalyzed transesterification/polymerization using Ti(OC4H9)4, and 6 and 8 were appropriate for a Knoevenagel polycondensation. The transesterification polymerization resulted in formation of an intractable polymeric material of unknown structure. The homopolymerization of 6 by the Knoevenagel technique afforded the desired polymer 9a, albeit in low molecular weight {M(n) = approximately 6800}. The polymer was characterized by gel permeation chromatography and spectroscopic data. A major by product in the polymerization was the macrocyclic lactone 10a produced from an intramolecular Knoevenagel condensation. The lactone structure was confirmed by single-crystal X-ray diffraction.