Supramclecular Host-Guest Compounds with Tripod-Metal Templates as Building Blocks at the Corners

摘要

Tripod-metal templates tripod M~(n+) (tripod = CH_3C(CH_2-PPh_2)_3) are stable units, which, depending on the metal center M and the charge n, can form strong bonds with a multitude of donors. The coordination chemistry of these tripod-metal templatesis established by the respective metal and its charge: tripod-cobalt(II) templates form, almost without exception, five-coordinate complexes, tripod -iron(II) templates form, likewise almost without exception, six-coordinate complexes, which adopt an idealized octahedral geometry. These structure-determining properties have been detected and confirmed for many mononuclear complexes; however, these templates have not been used for the specific construction of supramolecular units. The fact that the tripod-iron(II) template binds relatively strongly to three additional ligands, and that the resulting bonds are at right angles to one another, suggests that these templates could be used for the construction of three-dimensional cage compounds. For cagesof an appropriate size, countenons of matching symmetry could be incorporated into the framework of the host molecule. We report here on the synthesis of tetrahedral host -guest complexes, which are formed by molecular self-assembly according to this principle.