Cobalt Cage Complexes with N(3)S(3) Donor Sets and Differing Cavity Sizes: A Novel Macrobicyclic Cage with a Contracted Cap.

Abstract

Treatment of the cobalt(III) complex of the hexadentate tripodal N(3)S(3) ligand ten (4,4',4' '-ethylidynetris(3-thiabutan-1-amine) with propanal and paraformaldehyde under basic conditions, followed by borohydride reduction and reoxidation of the metal center, leads largely to the encapsulated (red) metal complex cation [Co(Me(2)-N(3)S(3)sar)](3+) (Me(2)-N(3)S(3)sar = 1,8-dimethyl-3,13,16-trithia-6,10,19-triazabicyclo[6.6.6]icosane). Unexpectedly, significant amounts of the homologous (yellow) complex cation [Co(Me(2)-N(3)S(3)absar)](3+) (Me(2)-N(3)S(3)absar = 1,8-dimethyl-3,13,16-trithia-6,10,19-triazabicyclo[6.6.5]nonadecane) were also obtained. This macrobicyclic complex has a contracted cavity resulting from a cap containing one fewer methylene units than Me(2)-N(3)S(3)sar. The structures of both cobalt(III) complexes have been determined by X-ray crystallography. [Co(Me(2)-N(3)S(3)sar)]Cl.ZnCl(4).H(2)O crystallizes in the cubic space group P2(1)3 with Z = 4, a = 13.9683(11) Å. [Co(Me(2)-N(3)S(3)absar)](ClO(4))(3).0.5CH(3)CN.0.5H(2)O crystallizes in the triclinic space group P&onemacr; with Z = 4, a = 12.036(4) Å, b = 15.932(9) Å, c = 17.212(14) Å, alpha = 64.93(7) degrees, beta = 72.77(5) degrees, gamma = 88.91(7) degrees. The surprising structural rearrangement is examined, along with the spectral and redox properties of both cobalt complexes. The influence of the reduced cavity size in the absar type cage is reflected in a shift of the bands in the electronic spectrum of both the cobalt(II) and cobalt(III) complexes to higher energy, and a more negative value for the Co(III/II) redox potential. The demetalation of the complexes is also described.