First X-ray Crystallographic Study of a Benzyl Cation, Cumyl Hexafluoroantimonate(V), and Structural Implications

The crystal structure of the cumyl cation (1;
2-phenyl-2-propyl cation) has been determined at −124
°C
(as hexafluoroantimonate, 1·SbF6;
R1 = 0.0502, wR2 =
0.1054). The cation 1 is nearly planar and has a
short
C+−Cipso bond (1.41(2) Å)
and bond lengths in the phenyl ring which agree with strong benzylic
delocalization.
The weak but distinct shortening of the
C+−CH3 bonds by 0.025(12) Å indicates
weak C−H hyperconjugation.
Nearly all H atoms are involved in H···F contacts to
SbF6 anions, and one close C+···F
contact (3.11(2) Å) is
observed. The phenyl rings form infinite stacks and are shifted
against each other in the stack.