The development of FLP chemistry over the last decade has helped to demonstrate that it is possible to activate H2 and Si-H bonds just using abundant and low cost p block compounds.1 However, there remain drawbacks to current FLP catalysts due to the reliance on boron Lewis acids that are highly Lewis acidic towards both hydride and hard Lewis bases (especially towards oxo based nucleophiles). High oxophilicity limits functional group tolerance and leads to catalysts that are highly sensitive to minor impurities, e.g., H2O. Developing effective FLP hydrogenation catalysts containing a hydride selective, non-oxophilic Lewis acid would circumvent these limitations. Carbon Lewis acids have been previously considered as soft electrophiles for use in FLPs for E-H activation and substrate reduction, but have included platinum group metals in the compound. We have calculated the hydride ion affinity (HIA relative to BEt3)2 of a range of cations that are the conjugate Lewis acids of organic hydride donors widely used in stoichiometric transfer hydrogenations (Figure 1). These all have HIAs comparable to that of B(C6F5)3 (HIA = - 44 kcalmol-1) indicating that H2 activation using these cations will be thermodynamically favoured when combined in FLPs with appropriate Lewis bases. More significantly, they show little propensity to bind H2O indicating low oxophilicity.3 These carbon Lewis acids have been shown to (i) activate H2 in FLPs (ii) activate Si-H and be effective catalysts for the reduction of imines. References 1 Frustrated Lewis Pairs: Uncovering and Understanding; Erker, G.; Stephan, D. W., Eds.; Springer: Berlin, 2013. 2 Clark, E. R.; Del Grosso, A.; Ingleson, M. J. Chem. Eur. J. 2013, 19, 2462 3 Clark, E. R.; Ingleson, M. J. Angew. Chem. 2014, 126, 11488

Cationic carbon Lewis acids in frustrated Lewis pairs

249th National Meeting (2015)

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