Model compounds and monomers for phenylene ether carboranylene ketone (PECK) polymer synthesis: preparation and characterization of boron-arylated ortho-carboranes bearing carboxyphenyl, phenoxyphenyl or benzoylphenyl substituents

Fourteen new derivatives of ortho-carborane, 1,2-C2B10H12, have been prepared containing functionalized aryl groups attached to one or both of the boron atoms (B9 and B12) antipodal to the carbon atoms, in order to test the suitability of such species for use in the preparation of new categories of phenylene ether carboranylene ketone (PECK) polymers. Model compounds prepared from 9-iodo-ortho-carborane 1 to test synthetic procedures and reactions included the mono-substituted carboranes 9-R-1-1,2-C2B10H11 in which the boron attached group was p-tolyl(2)p-HO(2)CC(6)H3p-MeOC(6)H(4)COC(6)H4p-PhOC(6)H5p-PhCOC6H4OC6HPhCOC6H4OC6H4 PhCOC6H4OC6H4 6 (C6H4 represents para-phenylene throughout). Formation of 3 from 2 by CrO3 oxidation showed the capacity of the boron-aryl link to withstand strongly oxidizing conditions. Formation of 4 from 3 and anisole, PhOMe, in trifluoromethane sulfonic acid (TFSA), and of 6 from 5 and benzoic acid, PhCO2H, in TFSA showed such systems could undergo the acylation reactions that would allow polymer formation from suitable diarylcarborane monomers. Compound 7, 9-(3-PhCO-4-PhO-C6H3)-1,2-C2B10H11 an isomer of 6, was also obtained during the synthesis of 6 from 5 and benzoic acid. The diarylcarboranes 9,12-R-2(2)-1,2-C2B10H10 with R-2 = p-tolyl 9, p-HO2CC6H4 10 or p-MeOC6H4COC6H4 11, bearing identical functionalised aryl groups attached to both antipodal boron atoms, were prepared from 9,12-I-2-1,2-C2B10H10 8. Further series of diarylcarboranes 1,9- and 1,12-R-2(3)-1,2-C2B10H10, bearing identical aryl groups R-3 on one carbon atom (C1) and on the antipodal boron atom (B12), or on the boron atom (B9) antipodal to the unsubstituted carbon atom (C2), have also been prepared and characterized, with R-3 = p-tolyl 12, 13, p-HO2CC6H4 14, 15 or p- MeOC6H4COC6H4 16, 17.