Intramolecular and intermolecular N-H···F-C hydrogen-bonding interactions in amine adducts of tris(pentafluorophenyl)borane and tris(pentafluorophenyl)alane

Mountford, Andrew J., Lancaster, Simon J., Coles, Simon J., Horton, Peter N., Hughes, David L., Hursthouse, Michael B. and Light, Mark E. (2005) Intramolecular and intermolecular N-H···F-C hydrogen-bonding interactions in amine adducts of tris(pentafluorophenyl)borane and tris(pentafluorophenyl)alane. Inorganic Chemistry, 44 (16), 5921-5933. (doi:10.1021/ic050663n).

Abstract

The reaction between B(C₆F₅)₃ and NH₃(g) in light petroleum yielded the solvated adduct H₃N · B(C₆F₅)₃· NH₃. Treatment with a second equivalent of B(C₆F5)₃ afforded H₃N · B(C₆F₅)₃. Attempts to prepare the analogous alane adduct were unsuccessful and resulted in protolysis. Related compounds of the form R'R"N(H)· M(C₆F₅)₃ were synthesized from M(C₆F₅)₃ and the corresponding primary and secondary amines (M = B, Al; R' = H, Me, CH₂Ph; R" = Me, CH₂Ph, CH(Me)(Ph); R'R" = cyclo-C₅H₁₀). The solid-state structures of 13 new compounds have been elucidated by single-crystal X-ray diffraction and are discussed. Each of the borane adducts has a significant bifurcated intramolecular hydrogen bond between an amino hydrogen and two o-fluorines, while N-H···F-C interactions in the alane adducts are weaker and more variable. F-19 NMR studies demonstrate that the borane adducts retain the bifurcated C-F···H···F-C hydrogen bond in solution. Compounds of the type R'R"N(H)·M(C₆F₅)₃ conform to Etter's rules for the prediction of hydrogen-bonding interactions.

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Contributors

Author: Simon J. Coles

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