The Proton Complex Of A Diaza-Macropentacycle: Structure, Slow Formation, And Chirality Induction By Ion Pairing With The Optically Active 1,1 '-Binaphthyl-2,2 '-Diyl Phosphate Anion

The protonation of a sterically crowded [N2S6] macropentacycle (1) with 1 equiv of CF3SO3H in CDCl3 is slow and gives the singly (oo(+) [1 center dot H](+)) and doubly (o(+)o(+) [1 center dot 2H](2+)) protonated forms as kinetic products, the i(+)o form of [1 center dot H](+) being the thermodynamic product. i(+)o [1 center dot H](+) is C-3 helically chiral in the solid state and in solution. The barrier to racemization (Delta G(double dagger)) of the [1 center dot H](+) propeller is >71 kJ mol(-1). The ammonium proton is encapsulated in the tetrahedral coordination sphere provided by the endo (i) nitrogen bridgehead atom and the three proximal thioether sulfurs, which makes [1 center dot H](+) a proton complex. Use of the optically active acid (R)-(-)- or (S)-(+)-1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (BNPH) in chloroform allowed us to induce a significant diastereomeric excess (24% de), which produced a detectable ICD. The de was decreased in acetone-d(6) (10%), suggesting that the sense of chirality of [1 center dot H](+) is controlled by ion-pair interactions. Detailed NMR studies allowed us to locate the chiral anion on the endo side of [1 center dot H](+), in the cavity lined by endo t-Bu groups, and to establish that the rate of anion exchange in [1 center dot H][(S,R)-(+/-)-BNP] was higher than the rate of propeller inversion of [1 center dot H](+).