Calixarene-monophosphines as supramolecular chelators.

The calix[4]arenes 5-diphenylphosphino-17-R1-11,23-diR2-25,26,27,28-tetrapropoxycalix[4]arene (1, R1 = R2 = Br; 2, R1 = Br, R2 = H; 3, R1 = R2 = p-tolyl; 4, R1 = p-tolyl, R2 = H; 5, R1 = R2 = H; 20, R1 = p-tolyl, R2 = H), all bearing a diphenylphosphino group attached to the calixarene upper rim, have been synthesised starting from 5,11,17,23-tetrabromo-25,26,27,28-tetrapropoxycalix[4]arene. Reaction of 1-5 with [RuCl2(p-cymene)]2 leads quantitatively to monophosphine complexes, [RuCl2(p-cymene)L], in which the endo-oriented ruthenium atom unit sits inside the cone delineated by the four phenoxy rings. The particular orientation of the P-Ru vector appears to result from pi-pi interactions between the p-cymene ligand and two aromatic cavity walls.

Calix[4]arene-phosphine dimers: precursors of flexible metallo-capsules and self-compacting molecules.

The first diphosphines based on a double calixarene, namely 1,4 (or 1,3)-bis-(5-diphenylphosphino-25,26,27,28-tetrapropoxycalix[4]aren-17-yl)benzene (L(2), L(3)) were each prepared in four steps starting from 5,17-dibromo-25,26,27,28-tetrapropoxycalix[4]arene. Upon reaction of L(2) with [Au(tht)(thf)]BF(4), (tht = C(4)H(8)S) a rigid metallo-capsule was quantitatively formed, which adopts an oblique form owing to the distinct nature of the spacers linking the two calixarene half-spheres. In the solid state, the 1,4-substituted phenylene linker is turned towards the gold ion, suggesting the existence of weak bonding interactions between two aromatic CH protons of this ring and the metal centre (AuH =2.

Calix[4]arene daisychains.

Generic calix[4]arenes became readily accessible in the late 70s. With their potential eight anchoring points, their utility for the production of sophisticated, highly functionalised macrocyclic molecules was rapidly recognised. While most studies in calixarene chemistry have focused on monocalixarene derivatives, there is now an increasing interest in developing multicalixarene compounds, especially those made of several linearly-arranged calix[4]arene units, the first examples of which were reported in 1989.