CO2 and Formate Complexes of Phosphine/Borane Frustrated Lewis Pairs

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. No need for frustration: A series of different phosphine/borane frustrated Lewis pairs as well as their corresponding salts was synthesized in the presence of CO2 (see figure for an example; R=C and norbornyl). The complexation and activation of CO2 in these compounds was investigated by X‐ray crystallography and computational studies.