Synthesis and Characterization of Alkoxide-Bridged Heterometallic Clusters of Cerium and Copper.

We prepared alkoxide-bridged heterometallic clusters of cerium and copper by the complexation of two metal alkoxides: treatment of Ce(OtBu)4 with [Cu(OtBu)]4 in a 1:1 metal ratio produced an alkoxide-bridged tetranuclear cluster, Ce2Cu2(OtBu)10 (1). Upon adding 4-substituted pyridine derivatives to complex 1, trinuclear clusters, Ce2Cu(OtBu)9(L) (2a: L = DMAP (4-dimethylaminopyridine); 2b: L = BPY (4,4'-bipyridine)), were obtained along with the release of 0.25 equiv of [Cu(OtBu)]4, in which a three-coordinated copper center was involved. In contrast, reaction of 1 with 4 equiv of 2,6-dimethylphenylisocyanide (XylNC) and 0.5 equiv of [Cu(OtBu)]4 resulted in the selective formation of CeCu2(OtBu)6(CNXyl)2 (3). In addition, Ce2K(OtBu)9 was used for complexation with CuCl2 by salt-elimination, giving Ce2CuCl(OtBu)9 (4) including a five-coordinated copper center. These complexes 1-4 were characterized by crystal structure determination as well as cyclic voltammetry of 1, 2a, and 4. The cyclic voltammogram of 4 in CH2Cl2 and THF suggested that reorganization of the coordination sphere around the copper center was observed for 4 during the Cu(I/II) redox processes assisted by the coordination of THF.