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Pentaarylcyclopentadienyl half-sandwich complexes of iron, cobalt, and nickel were synthesized and characterized by X-ray crystallography, spectroscopic methods, and magnetic measurements. Divalent and trivalent compounds are accessible via complementary routes.
The preparation of new stable half-sandwich transition metal complexes, having a bulky cyclopentadienyl ligand C5(C6H4-4-Et)5 (CpAr1) or C5(C6H4-4-nBu)5 (CpAr2), is reported. The tetrahydrofuran (THF) adduct [CpAr1Fe(μ-Br)(THF)]2 (1a) was synthesized by reacting K[CpAr1] with [FeBr2(THF)2] in THF, and its molecular structure was determined by X-ray crystallography. Complex 1a easily loses its coordinated THF molecules under vacuum to form the solvent-free complex [CpAr1Fe(μ-Br)]2 (1b). The analogous complexes [CpAr1Co(μ-Br)]2 (2), [CpAr1Ni(μ-Br)]2 (3), and [CpAr2Ni(μ-Br)]2 (4) were synthesized from CoBr2 and [NiBr2(1,2-dimethoxyethane)]. The mononuclear, low-spin cobalt(III) and nickel(III) complexes [CpAr2MI2] (5, M = Co; 6, M = Ni) were prepared by reacting the radical CpAr2 with NiI2 and CoI2. The complexes were characterized by NMR and UV–vis spectroscopies and by elemental analyses. Single-crystal X-ray structure analyses revealed that the dimeric complexes 1a, 1b, and 3 have a planar M2Br2 core, whereas 2 and 4 feature a puckered M2Br2 ring.
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