P–H Functionalized Al/P-Based Frustrated Lewis Pairs in Dipolar Activation and Hydrophosphination: Reactions with CO2 and SO2

Abstract

The P–H functionalized FLPs R(H)PC(AlBis2)═C(H)-CMe3 (1a, R = Bis; 1b, R = Mes; Bis = CH(SiMe3)2) combine the typical FLP properties based on Lewis acidic Al and basic P atoms with the reactivity of a P–H bond. They allow the coordination of substrates followed by hydrophosphination with the activated P–H group. Reactions of 1a with R′–N═C═S (R′ = Ph, CMe3) or of both FLPs with Et–N═C═CPh2 afforded five-membered AlCPCS/N heterocycles (4 and 5) via coordination of C═S or C═N bonds to the FLP backbone. Isomerization by a 1,3-H shift from P to N or C (6 and 7) was only achieved in the presence of an auxiliary base (DABCO; 1–5 mol %). (Z)-1a coordinated CO2 to yield the adduct 8, which features a five-membered AlCPCO heterocycle with an exocyclic C═O bond. Addition of bases such as DABCO and DBU afforded by deprotonation of the P atom the compounds [Bis-PC(AlBis2)═C(H)–CMe3(CO2)]−[HB]+ (9a, B = DABCO; 9b, B = DBU) that displayed hydrogen bonding between the ammonium ions and the exocyclic O atom of the FLP ad...