Cyclobutadiene cobalt polymers

The thermal reaction of cobalt polymers 148 with isocyanates at 120 °C leads to 2-pyridone-containing polymers 149 339 Yeii characterized, yellow polyesters 150 that contain skeletal (cyclobutadiene)cobalt moieties in the main... 

Novel organometallic poly(arylene)s with 1,3-type (cyclobutadiene)cobalt moieties 27 in the main chain are prepared by Ni(0)-mediated dehalogenative polycondensation of monomers having (cyclobutadiene)cobalt moieties [51], The polymers with of 20 kDa exhibit thermotropic liquid crystallinity. The synthesis of a variety of homometallic and heterometallic oligomers and polymers such as 28 is possible via nucleophilic aromatic substitution reactions of dichlorophenylene-Fe Cp and dihydroxyphenylene-Ru Cp complexes in DMF in the presence of K2CO3 [52]. 

Sawada, Y. Tomita, I. Rozhanskii, I.L. Endo, T. Synthesis of liquid crystalline organometallic poly(aryl-ene)s containing 1,3-type ((r " -cyclobutadiene)cobalt moieties in the main chain. J. Inorg. Organomet. Polym. 2000. 10 (4). 221-230. 

The thermal reaction of cobalt polymers 4.28 with isocyanates at 120 °C leads to 2-pyridone-containing polymers such as 4.30 [70]. Well-characterized, yellow polyesters 4.31 containing skeletal (cyclobutadiene)cobalt moieties in the main chain have been prepared by interfacial polycondensation approaches [73]. The use of solubilizing alkoxy substituents R afforded materials with Mn = 5,400-16,300 (PDI = 1.3-1.8). Analogous materials to 4.31 with a 1,3-disposition of the main-chain substituents on the cyclobutadiene ligands have also been studied [73, 74]. Thermotropic liquid crystallinity was detected by polarizing microscopy, with, in some cases, mesophases stable over the temperature range from about 110 to >250°C. 

Cobaltacyclopentadiene polymers undergo thermal rearrangement to the more stable ( /" -cyclobutadiene)cobalt derivatives, and reaction with isocyanates affords new polymers containing 2-pyridone moieties in the polymer backbone (for details, see Chapter 4, Section 4,4.1) [98-100],... 

Co-free PAE). In PAE-CoCpl, the fluorescence quantum yield is only 18% of that observed for Co-free PAE, even though the quencher substitutes less than 0.1% of the aryleneethynylene units. The fluorescence in solution disappeared in PAE-CoCp4, where every fifth unit is a cyclobutadiene complex. The mechanism by which this quenching occurs is via the cobalt-centered MLCT states [82,83], conferred onto the polymer by the presence of cyclobutadiene complexes. Even in the solid state the polymers PAE-CoCpl-2 are nonemissive. It was therefore shown that incorporation of CpCo-stabilized cyclobutadiene complexes into PPEs even in small amounts leads to an efficient quenching of fluorescence in solution and in the solid state. Quenching occurs by inter- and intramolecular energy transfer [84]. 

Bunz and co-workers reported the preparation of polymers containing cyclopentadienyl-cobalt moieties coordinated to cyclobutadiene rings, using diethylnyl and dipropynyl cyclobu-... 

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