A Novel Family of Binuclear Cobalt(II) Complexes with Face-to-Face Bis(cyclidene) Ligands: Structural Characterization, Unusual Reactions with Dioxygen, and a Distinctive Host-Guest Complexation with a Bridging Ligand

A series of binuclear cobalt(II) complexes has been prepared and characterized with examples of thefamily of macrotricyclic ligands containing two metal ion sites that are labeled cyclidene rings. The dimetallic complexes contain a large permanent void bounded by the cyclidene moieties and by twoidentical bridging groups. The size and shape of the void vary with the bridging groups and are very flexible in solution. The crystal structure of the compound having chloride as the counterion and m-xylylene bridging groups reveals the face-to-face structure. The cyclidene groups are offset withrespect to each other, and solvent methanol and chloride ion form a pair of hydrogen-bonded bridgesacross the cavity, between NH groups of the ligand. At low temperatures a dioxygen adduct is formed; however, it autoxidizes more rapidly than the related mononuclear com lexes. An unusual form ofhost-guest complexing has been demonstrated in which 4,4’-bipyridine is both enclosedn thecavity of the bis(cyclidene) complex and coordinated to the two metal atoms, serving as a bridging group and thereby greatly enhancing the metal-metal interaction between the two cobalt(II) atoms.