METALLOCENOPHANES .6. 5,12-METHANO[2.2.2]PARACYCLOPHANE - A NEW LIGAND FOR PI-COMPLEXATION IN A CAVITY - IMPROVED SYNTHESIS AND THE CHARACTERIZATION OF ITS SILVER(I) PERCHLORATE COMPLEX

The consequences of a bridging methylene group in 1, i.e. as in 2, on the geometry and ability to complex Ag(I) were studied. Compound 2 was prepared in three steps and 36% overall yield from 1 in a new procedure and characterized through X-ray crystallography. The X-ray crystal structure of its endo complex (3) with AgClO4 shows three independent molecules in the crystal lattice. The geometry of the ligand in 3 is like that in 2. Ag is 2.48-3.00 angstrom from the nearest Ar-C, is 0.13-0.31 angstrom outside of the cavity of 2, and binds nearly symmetrically across the C(5)-C)6), C(11)-C(12), and C(23)-C(24) bonds. Compound 2 is shown to be a weaker complexing agent for Ag(I) than [2.2.2]-paracyclophane. Practical and theoretical ramifications of the bonding mode are discussed.