Proazaphosphatrane and Bench-stable Carbon-based Lewis Acids in Frustrated Lewis Pair Chemistry

Abstract

B(C6F5)3 and P(MeNCH2CH2)3N form a classical Lewis adduct, (C6F5)3BP(MeNCH2CH2)3N. Although the adduct does not exhibit spectroscopic evidence of dissociation into its constituent Lewis acid and base, products of frustrated Lewis pair (FLP) addition reactions are observed with PhNCO, PhCH2N3, PhNSO, and CO2. Recently, a bench-stable trityl cation and P(MeNCH2CH2)3N were also found to form a classical Lewis adduct that does not exhibit spectroscopic evidence of dissociation. This adduct was able to carry out the heterolytic splitting of H2. Interestingly, when this and other newly synthesized bench-stable trityl cations were combined with phosphine bases such as P(t-Bu)3 and P(o-tol)3, FLPs capable of heterolytic splitting of H2 were generated and, in at least one case, reversible activation of H2 was observed. These recent findings open avenues towards the application of bench-stable carbon-based Lewis acids for FLP mediated hydrogenation.