Controlled synthesis of copper halide-incorporated triiron carbonyl sulfide clusters: Synthesis, electrochemistry, and computational studies

Abstract

The reactions of sulfur-capped triiron carbonyl cluster [Et4N]2[SFe3(CO)9] with 1–6equiv of copper halides in tetrahydrofuran (THF) at 0°C led to the formation of a series of CuX-, Cu2X2-, or Cu4X2-incorporated mono- or di-SFe3-based clusters, [Et4N]2[SFe3(CO)9CuX] (X=Cl, [Et4N]2[1a]; Br, [Et4N]2[1b]; I, [Et4N]2[1c]), [Et4N]4[{SFe3(CO)9CuX}2Cu2X2] (X=Cl, [Et4N]4[2a]; Br, [Et4N]4[2b]), and [Et4N]2[{SFe3(CO)9}2Cu4X2] (X=Cl, [Et4N]2[3a]; Br, [Et4N]2[3b]). X-ray analysis showed that each SFe3 core in 1a–1c was bridged by the incoming CuX across the Fe–Fe bond (X=Cl, 1a; Br, 1b; I, 1c); in the case of 2a and 2b, the two SFe3 cores each were bridged by two CuX fragments across the Fe–Fe and S–Fe bonds to form a Cu2X2-linked di-SFe3CuX cluster (X=Cl, 2a; Br, 2b). In contrast to 2a and 2b, cluster 3a displayed a different di-SFe3-based geometry, in which the two SFe3 moieties were connected by a Cu4Cl2 hexagon. In addition, complexes 1a and 1b were found to undergo cluster expansion reactions to yield 2a and 2b or 3a and 3b upon the treatment of 1equiv or 3equiv of CuX (X=Cl, Br), respectively. Furthermore, clusters 2a and 2b could be converted to 3a or 3b upon the addition of 4equiv of CuX (X=Cl, Br). The nature, formation, and electrochemistry of these copper halide-incorporated mono- or di-SFe3 clusters are elucidated in detail with the aid of molecular calculations at the B3LYP level of the density functional theory in terms of the effects of chalcogens and halides.