Pyrazole based frustrated Lewis pair

27 November 2010 - FLP chemistry VII

FLP theuergarten 2010 replacement  More and more frustrated Lewis pairs (FLP, see part 6) see the light of day. The ultimate aim is reversible hydrogen storage but creating a metal-free hydrogenation catalyst is also worth the effort. Theuergarten et al. (DOI) have prepared pyrazolium-borate 3 from pyrazole 1 and bis(pentafluorophenyl)borane 2 as the trans isomer. Dehydrogenation with another FLP 4 forms pyrazolylborane 5 which easily takes up hydrogen again now to the cis-isomer. The trans isomer is a metal-free hydrogenation catalyst for N-(benzylidene)benzylamine 6 to dibenzylamine 7.

Update 22-02-2011: added missing bonds in image. Thanks to reader K. for spotting the error.