CO₂ and Formate Complexes of Phosphine/Borane Frustrated Lewis Pairs

摘要

The reaction of a solution of B(C₆F₄H)₃ and either iPr₃P or tBu₃P with CO₂ afforded the species R₃P(CO₂)B(C₆F₄H)₃ (R=iPr (1), tBu (2)). In a similar fashion the boranes, RB(C₆F₅)₂ (R=hexyl, cyclohexyl (Cy), norbornyl), ClB(C₆F₅)₂, or PhB(C₆F₅)₂ were combined with tBu₃P and CO₂ to give the species tBu₃P(CO₂)BR(C₆F₅)₂ (R=hexyl (3), Cy (4), norbornyl (5), Cl (6), Ph (7)). Similarly, the compounds [tBu₃PH][RBH(C₆F₅)₂] (R=hexyl (8), Cy (9), norbornyl (10)) were prepared by reaction of the precursor frustrated Lewis pair (FLP) with H₂. Subsequent reactions of 9 and 10 with CO₂ afforded the species [((C₆F₅)₂BR)₂(μ-HCO₂)][tBu₃PH] (R=Cy (11), norbornyl (12)). In related chemistry, combinations of the boranes RB(C₆F₅)₂ (R=hexyl, Cy, norbornyl) with tBu₃P treated with an equivalent of formic acid gave [(C₆F₅)₂BR(HCO₂)][tBu₃PH] (R=hexyl (13), Cy (14), norbornyl (15)). Subsequent addition of an additional equivalent of borane provides a second synthetic route to 11 and 12. Crystallographic studies of compounds 2–6 and 8–14 are reported and discussed. Further understanding of the FLP complexation and activation of CO₂ is provided by computational studies.