Oligomerizations of o-Diisocyanobenzenes by Organometallic Compounds - Synthesis of Functional Nitrogen-Containing Aromatic Polymers

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Mono-metallation of an Isocyanide with an Organozinc The reaction of a variety of isocyanides with dialkylzinc was examined and it was found that aromatic isocyanides underwent insertion into zinc-carbon bond of dialkylzinc to give [1- (arylimino)alkyl]zinc, whereas aliphatic isocyanides did not react at all. Treatment of [1- (arylimino)alkl]zinc with aromatic iodide in the presence of a catalytic amount of transition metal catalyst (1-2 mol%) produced the corresponding N-aryl aromatic imine.Synthesis of Quinoxaline Oligomers by Reaction of o-Diisocyanoarene with Grignard Reagent The reaction of 1,2-diisocyano-3.4,5,6-tetramethylbenzene with Grignard reagents resulted in aromatization to give a variety of quinoxaline oligomers. The quinoxaline skeleton was regularly constructed by successive insertion of the two ortho isocyano groups into carbon- magnesium linkage. These oligomers are separated and isolated by preparative TLC on silica gel and/or recycling HPLC on polystyrene gel. UV spectra of the quinoxaline oligomers revealed their structural feature; quinoxaline trimer showed two absorptions at 260 and 280 nm, which can be ascribed to single isolated quinoxaline chromophore and conjugated quinoxaline chromophore, respectively. Tetramer and pentamer also showed the absorption at the same positions as trimer. This may indicate that an effective resonance conjugation over more than three sequential quinoxaline rings in the polymer chain may be inhibited by steric hindrance.