Fixation of carbon dioxide and related small molecules by a bifunctional frustrated pyrazolylborane Lewis pair?

Dalton Transactions Pub Date: 2012-04-19 DOI: 10.1039/C2DT30448A

Abstract

The bifunctional frustrated Lewis pair 1-[bis(pentafluorophenyl)boryl]-3,5-di-tert-butyl-1H-pyrazole (1) was employed for small molecule fixation by reaction with carbon dioxide, paraformaldehyde, tert-butyl isocyanate, tert-butyl isothiocyanate, methyl isothiocyanate and benzonitrile, affording the adducts 3–8 as zwitterionic, bicyclic boraheterocycles. Treatment of 1 with tert-butyl isocyanide gave the isocyanide–borane complex 9, whereas the zwitterionic alkynylborate 10 was formed by C–H bond activation of phenylacetylene. The molecular structures of all products 3–10 were established by X-ray diffraction analyses. DFT calculations at the M06-2X/6-311++G(d,p) level of theory revealed that CO2 fixation by 1 and formation of the adduct 3 is strongly exothermic and proceeds with a low energy barrier of approximately 7.3 kcal mol?1via an intermediate van der Waals complex.

Graphical abstract: Fixation of carbon dioxide and related small molecules by a bifunctional frustrated pyrazolylborane Lewis pair
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