Square planar coordination of silver in a η⁴-cyclobutadiene-(η⁵-C₅H₅)ReBr₂ complex framework

Halide addition and abstraction experiments with the cationic rhenacyclopentatriene [(η⁵-C₅H₅){ReC₄(SBn)₄}Br]BF₄ and the side-on cyclobutadiene complexes [(η⁵-C₅H₅)(η⁴-C₄Ph₄)ReX₂] (X = Br, I), respectively, are described. Reversible interconversion of both coordination modes of the metal bonded C₄R₄ moiety depending on the presence or absence of the second bromide ligand is demonstrated for the sulfide derivative. However, formation of the [(η⁵-C₅H₅)(ReC₄Ph₄)X]⁺ congener by halide abstraction at [(η⁵-C₅H₅)(η⁴-C₄Ph₄)ReX₂] turned out to be impossible. Instead, formation of silver halide complexes with the halide bridging rhenium and silver under retention of the metalorganic scaffold are observed. Governed by the phenyl substituent framework a square-planar coordination environment about the Ag cation is adopted for X = Br. Changing X = Br by X = I led to the formation of a heptanuclear complex with di- and three-coordinate silver ions. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)