CO 2 and Formate Complexes of Phosphine/Borane Frustrated Lewis Pairs

The reaction of a solution of B(C 6 F 4 H) 3 and either i Pr 3 P or t Bu 3 P with CO 2 afforded the species R 3 P(CO 2 )B(C 6 F 4 H) 3 (R= i Pr ( 1 ), t Bu ( 2 )). In a similar fashion the boranes, RB(C 6 F 5 ) 2 (R=hexyl, cyclohexyl (Cy), norbornyl), ClB(C 6 F 5 ) 2 , or PhB(C 6 F 5 ) 2 were combined with t Bu 3 P and CO 2 to give the species t Bu 3 P(CO 2 )BR(C 6 F 5 ) 2 (R=hexyl ( 3 ), Cy ( 4 ), norbornyl ( 5 ), Cl ( 6 ), Ph ( 7 )). Similarly, the compounds [ t Bu 3 PH][RBH(C 6 F 5 ) 2 ] (R=hexyl ( 8 ), Cy ( 9 ), norbornyl ( 10 )) were prepared by reaction of the precursor frustrated Lewis pair (FLP) with H 2 . Subsequent reactions of 9 and 10 with CO 2 afforded the species [((C 6 F 5 ) 2 BR) 2 (μ‐HCO 2 )][ t Bu 3 PH] (R=Cy ( 11 ), norbornyl ( 12 )). In related chemistry, combinations of the boranes RB(C 6 F 5 ) 2 (R=hexyl, Cy, norbornyl) with t Bu 3 P treated with an equivalent of formic acid gave [(C 6 F 5 ) 2 BR(HCO 2 )][ t Bu 3 PH] (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 CO 2 is provided by computational studies.