1436826-00-4Relevant articles and documents
The Al(ORF)3/H2O/phosphane [RF = C(CF3)3] System - Protonation of phosphanes and absolute bronsted acidity
Kraft, Anne,Possart, Josephine,Scherer, Harald,Beck, Jennifer,Himmel, Daniel,Krossing, Ingo
, p. 3054 - 3062 (2013/07/27)
The synthesis of the classical, neutral donor-acceptor adducts Ph 2MeP-/Ph3P-/Ph3As-Al(ORF) 3 and H2O-Al(ORF)3 [1, 2, 3, 4, ORF = OC(CF3)3] is reported. The intermediate H2O-Al(ORF)3 (4) was generated by substitution of PhF in PhF-Al(ORF)3 with H2O and was analyzed in a long-term NMR study over 22 days. This Bronsted acidic system was used in orienting experiments to protonate phosphanes such as PMePh2, PPh3, PCy3, P(tBu)3, and PCy2[2,4,6-(iPr)3C6H2]. Depending on the use of one or two equivalents of PhF-Al(ORF)3, the new weakly coordinating anions [(RFO)3Al(μ-OH) Al(ORF)3]- or [HOAl(ORF) 3]- were obtained. However, in dependence of the steric bulk of the phosphanes, stable and unreactive R3P-Al(OR F)3 adducts were also observed in the NMR experiments. The absolute acidity of the key H2O-Al(ORF)3 adduct was evaluated by the relaxed COSMO cluster-continuum (rCCC, COSMO = conductor-like screening model) model in fluorobenzene solution. For a 0.001 M solution of H2O-Al(ORF)3, the medium acidity resulted as -986 kJ mol-1 or a pHabs value of 173. Long-term hydrolysis of H2O-Al(ORF)3 (4), probably to give HORF and HOAl(ORF)2 followed by trimerization, gave [HOAl(ORF)2]3 (10), which was identified by X-ray diffraction. Small donor ligands such as Ph 2MeP, Ph3P, Ph3As, or even H2O form classical donor-acceptor adducts with the Lewis superacid Al(OR F)3 [RF = C(CF3)3]. FLP-like (FLP = frustrated Lewis pair) combinations of this Lewis acid, phosphanes, and water then lead to [HPR3]+ and two new weakly coordinating anions [HOAl(ORF)3]- and [(FRO)3Al(μ-OH)Al(ORF)3] -. The absolute acidity of H2O-Al(ORF) 3 is evaluated.
