Synthesis and X-ray molecular structures of p-tert-butylcalixarenes with diamide bridges spanning the 1,3-(distal) positions on the lower rim
Reaction of a 1,3-diacid dichloride 1d of p-tert-butylcalixarene with various aliphatic diamines including diaza-15-crown-5 and diaza-18-crown-6 yields calixarenes capped by diamide bridges, in yields of 19–95%. The tendency for capping is so pronounced with ethylenediamine that cyclic diamide 2a is formed even in the presence of an excess of diamine. Crystals of the ethylenediamine adduct 2a and of the N,N′-dimethylethylenediamine adduct 2c were studied by X-lay diffraction. Crystals of adduct 2a are monoclinic, space group C2/c, a= 36.140(4), b= 11.879(3), c= 25.801(6)Å, β= 114.66(2)° with R= 0.077 for 3044 observed reflections. Crystals of adduct 2c are triclinic, space group P1, a= 10.272(2), b= 12.474(3), c= 19.351 (4)Å, α= 93.799(18), β= 95.524(l 5), γ= 91.584(18)° with R= 0.076 for 2317 observed reflections. While adduct 2a includes a molecule of dichioromethane in its hydrophobic cavity, the distortion of the cone conformation in adduct 2c is too severe to allow the inclusion of a guest. This distorted chiral conformation of adduct 2c(C2 symmetry) is also stable in solution at room temperature.