Copper Halide-Incorporated Tellurium−Iron Carbonyl Complexes: Transformation, Electrochemical Properties, and Theoretical Calculations

Abstract

When the tellurium-capped tri-iron carbonyl cluster [Et(4)N](2)[TeFe(3)(CO)(9)] was treated with 1 equiv of CuX in THF at 0 degrees C, CuX-incorporated clusters [Et(4)N](2)[TeFe(3)(CO)(9)CuX] (X = Cl, [Et(4)N](2)[1a]; Br, [Et(4)N](2)[1b]; I, [Et(4)N](2)[1c]) were formed, respectively. X-ray analysis showed that 1a-1c each exhibited a TeFe(3) core with one Fe-Fe bond bridged by one CuX fragment. When the reactions were carried out at a molar ratio of 1:2 (X = Cl, Br) or 1:3 (X = I) in tetrahydrofuran (THF) or MeCN at 0 degrees C, Cu(2)X(2)-incorporated clusters [Et(4)N](2)[TeFe(3)(CO)(9)Cu(2)X(2)] (X = Cl, [Et(4)N](2)[2a]; Br, [Et(4)N](2)[2b]; I, [Et(4)N](2)[2c]) were obtained, respectively. Cluster 2a was structurally characterized by X-ray analysis to display a TeFe(3) core, in which one TeFe(2) plane was asymmetrically bridged and capped by one mu(3)-CuCl and another mu(4)-CuCl with two Cu atoms bonded. Complexes 1a-1c underwent skeleton expansion to form Cu(3)X-incorporated di-TeFe(3) clusters [{TeFe(3)(CO)(9)}(2)Cu(3)X](2-) (X = Cl, 3a; Br, 3b; I, 3c), respectively, upon treatment with 1 equiv of [Cu(MeCN)(4)][BF(4)] at 0 degrees C. X-ray analysis showed that 3b and 3c each consisted of two TeFe(3) clusters that were linked by a Cu(3)X moiety. However, a similar reaction for 1a and 1b with 1 equiv of [Cu(MeCN)(4)][BF(4)] at room temperature produced Cu(4)X(2)-linked di-TeFe(3) clusters [{TeFe(3)(CO)(9)}(2)Cu(4)X(2)](2-) (X = Cl, 4a; Br, 4b). Cluster 4a was shown by X-ray analysis to have two TeFe(3) cores linked by a Cu(4)Cl(2) moiety. Clusters 4a and 4b were also produced directly from the reaction of [Et(4)N](2)[TeFe(3)(CO)(9)] with 4 equiv of CuX (X = Cl, Br) in THF. Furthermore, the nature, the formation, the cluster transformation, and the electrochemistry of the CuX-incorporated mono- or di-TeFe(3) clusters are explained in terms of the effects of tellurium, copper halide, and the size of the metal skeleton, all of which are elucidated by molecular calculations at the B3LYP level of density functional theory.