Synthesis and Characterization\nof Alkoxide-Bridged Heterometallic Clusters of Cerium and Copper

Abstract

We\nprepared alkoxide-bridged heterometallic clusters of cerium and copper\nby the complexation of two metal alkoxides: treatment of Ce­(O^<i>t</i>Bu)₄ with [Cu­(O^<i>t</i>Bu)]₄ in a 1:1 metal ratio produced an alkoxide-bridged\ntetranuclear cluster, Ce₂Cu₂(O^<i>t</i>Bu)₁₀ (<b>1</b>). Upon adding 4-substituted\npyridine derivatives to complex <b>1</b>, trinuclear clusters,\nCe₂Cu­(O^<i>t</i>Bu)₉(<b>L</b>) (<b>2a</b>: L = DMAP (4-dimethylaminopyridine); <b>2b</b>: L = BPY (4,4′-bipyridine)), were obtained along\nwith the release of 0.25 equiv of [Cu­(O^<i>t</i>Bu)]₄, in which a three-coordinated copper center was\ninvolved. In contrast, reaction of <b>1</b> with 4 equiv of\n2,6-dimethylphenylisocyanide (XylNC) and 0.5 equiv of [Cu­(O^<i>t</i>Bu)]₄ resulted in the selective formation\nof CeCu₂(O^<i>t</i>Bu)₆(CNXyl)₂ (<b>3</b>). In addition, Ce₂K­(O^<i>t</i>Bu)₉ was used for complexation with CuCl₂ by salt-elimination, giving Ce₂CuCl­(O^<i>t</i>Bu)₉ (<b>4</b>) including a five-coordinated\ncopper center. These complexes <b>1</b>–<b>4</b> were characterized by crystal structure determination as well as\ncyclic voltammetry of <b>1</b>, <b>2a</b>, and <b>4</b>. The cyclic voltammogram of <b>4</b> in CH₂Cl₂ and THF suggested that reorganization of the coordination\nsphere around the copper center was observed for <b>4</b> during\nthe Cu­(I/II) redox processes assisted by the coordination of THF.