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

The P–H functionalized FLPs R­(H)­PC­(AlBis₂)C­(H)-CMe₃ (<b>1a</b>, R = Bis; <b>1b</b>, 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 <b>1a</b> with R′–NCS (R′ = Ph, CMe₃) or of both FLPs with Et–NCCPh₂ afforded five-membered AlCPCS/N heterocycles (<b>4</b> and <b>5</b>) 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 (<b>6</b> and <b>7</b>) was only achieved in the presence of an auxiliary base (DABCO; 1–5 mol %). (<i>Z</i>)-<b>1a</b> coordinated CO₂ to yield the adduct <b>8</b>, 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]⁺ (<b>9a</b>, B = DABCO; <b>9b</b>, B = DBU) that displayed hydrogen bonding between the ammonium ions and the exocyclic O atom of the FLP adducts in solution and the solid state. The stronger base <i>n</i>-BuLi afforded the dimeric Li compound <b>10</b>, in which the Li cation was coordinated in a chelating manner to the oxygen atoms of one FLP adduct and additionally to the exocyclic O atom of the second adduct, resulting in a four-membered Li₂O₂ heterocycle. The related reaction of (<i>Z</i>)-<b>1a</b> with DABCO­(SO₂)₂ led in contrast to the elimination of BisH and formation of a SO₂-bridged dimer that features a central (AlOSO)₂ heterocycle with Al–O and S–O single bonds. The resulting unusual structural motifs may be derived from those of dialkylcarbamic or dialkylamidosulfinic acids with the N atoms replaced by P atoms.