%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