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Recyclable and Efficient Polyurethane-Ir Catalysts for Direct Borylation of Aromatic Compounds

Abstract

Four polyurethanes having 2,2’-bipyridyl moieties incorporated in the main chain were synthesized as novel polymer ligand for Ir(I)-catalyzed direct borylation of aromatic compounds. The polyurethanes were insoluble in common organic solvents and soluble in dimethylsulfoxide. The borylation reaction of benzene catalyzed by Ir(I) in the presence of the polymer prepared from 4,4’-bis(hydroxylmethyl)-2,2’-bipyridyl and 1,6-diisocyanatohexane led to catalytic activities comparable to that in the presence of 2,2’-bipyridyl while the polymers prepared by the reactions of 4,4’-bis(hydroxylmethyl)-2,2’-bipyridyl with 1,4-diisocyanatobenzene, 1,4-diisocyanato-3-methylbenzene, and bis(4-isocyanatophenyl)methane resulted in lower catalytic activities. The high activity observed using the 1,6-diisocyanatohexane-based polyurethane catalyst may have a connection to the fact that this polymer has the highest tendency to form inter-chain hydrogen bond. The borylation reaction systems with the polymers were biphasic where the top and bottom layers contained the product and the polymer-based catalysts, respectively. Due to the phase separation, the product isolation and catalyst recycle were readily performed through simple decantation. The catalyst prepared from the 1,6-diisocyanatohexane-based polyurethane was able to be recycled at least five times without a serious decrease in activity. Further, regio-selectivity in borylation of toluene, anisole, and trifluoromethybenzene was studied using the polyurethane ligands as well as correnponding small-molecular ligands.

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Publication details

The article was received on 05 Sep 2017, accepted on 08 Nov 2017 and first published on 09 Nov 2017


Article type: Paper
DOI: 10.1039/C7PY01509G
Citation: Polym. Chem., 2017, Accepted Manuscript
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    Recyclable and Efficient Polyurethane-Ir Catalysts for Direct Borylation of Aromatic Compounds

    A. Kimura, H. Hayama, J. Hasegawa, H. Nageh, Y. Wang, N. Naga, M. Nishida and T. Nakano, Polym. Chem., 2017, Accepted Manuscript , DOI: 10.1039/C7PY01509G

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