%0 Journal Article %A Parks, Daniel J. %A Piers, Warren E. %A Parvez, Masood %A Atencio, Reinaldo %A Zaworotko, Michael J. %D 1998 %T Synthesis and Solution and Solid-State Structures of Tris(pentafluorophenyl)borane Adducts of PhC(O)X (X = H, Me, OEt, NPri2) %U https://acs.figshare.com/articles/journal_contribution/Synthesis_and_Solution_and_Solid-State_Structures_of_Tris_pentafluorophenyl_borane_Adducts_of_PhC_O_X_X_H_Me_OEt_NPr_i_sup_i_sup_i_sup_sup_sub_2_sub_/3781575 %R 10.1021/om9710327.s002 %2 https://acs.figshare.com/ndownloader/files/5892540 %K basicity %K solution %K carbonyl Lewis bases benzaldehyde %K experiment %K borane coordinates syn %K syn phenyl group %K interaction %K NOE %K ethyl benzoate %K acetophenone %K adduct %K borane C 6 F 5 rings %K NPr i 2 %K OEt %K NMR %K diisopropylbenzamide %K ketone %X Reaction of the highly electrophilic borane B(C6F5)3 with the carbonyl Lewis bases benzaldehyde, acetophenone, ethyl benzoate, and N,N-diisopropylbenzamide led to isolation of the crystalline adducts 1-H, 1-Me, 1-OEt, and 1-NPr, respectively, in good to excellent yields (63−89%). Equilibrium measurements and exchange experiments indicated that the order of basicity (from highest to lowest) of these bases toward B(C6F5)3 follows the order N,N-diisopropylbenzamide > benzaldehyde > acetophenone > ethyl benzoate. The solution and solid-state structures were probed to rationalize these observations. In solution, the borane coordinates to the carbonyl lone pair syn to H and Me in the aldehyde and ketone adducts, as indicated by 1H/19F NOE difference experiments. The same coordination geometry was observed in the solid state upon X-ray diffraction analysis of the two adducts. The added front strain associated with the ketone adduct (C−O−B =133.6(3)° vs 126.7(5)° for the benzaldehyde complex) accounts for the observed order of basicity with these two bases. For ethyl benzoate and N,N-diisopropylbenzamide, the borane coordinates syn to the phenyl group in both solution and the solid state. In addition to the carbonyl oxygen−boron interaction, the two complexes engage in a π-stacking interaction between one of the borane C6F5 rings and the syn phenyl group. In addition to the structural proof of this interaction in the solid state, variable-temperature 19F NMR experiments suggest it is important in the solution structures of these adducts as well. %I ACS Publications