We recently demonstrated that significantly weaker Lewis acids, most of which are cheap and readily available, can be active FLP components in the heterolytic cleavage of H2, provided a sufficiently strong and bulky base is used [1, 2]. Here, we report on the catalytic hydrogenation of imines using Verkade’s superbase P[N(Pri)CH2CH2]3N (pKa = 33.4; in CH3CN) and phosphazene base ButN=P(pyrr)3 (pKa = 28.4; in CH3CN) with various alkyl-BBN and aryl-BBN derivatives. All 9-BBN derived Lewis acids forms an active FLPs with Verkade’s superbase and Phopshazene base and most of the FLPs engages in the H2 cleavage. But not all the FLPs acts as an active catalyst for imine hydrogenation reaction. The ability of an FLP to hydrogenate imine depends on the streric and electronic nature of the Lewis acid. For example, 9-Ph-BBN (hydride affinity, ΔHHA = -67 kcal/mol) with Verkade base cleaves the H2 also hydrogenates imine (PhCH=NPh) to &gt;99% in 17 hours, whereas 9-cyclohexyl-BBN (hydride affinity, ΔHHA = -65 kcal/mol) with verkade’s base does the hydrogenation of imine (PhCH=NPh) to &gt;40% in 19 hours. More results with other Lewis acids and the mechanistic and theoretical aspects of the catalytic reactions will be discussed in this presentation.

Inverse frustrated Lewis pair (FLP) approach for catalytic metal-free hydrogenation of imines

254th National Meeting (2017)

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