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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. [ABSTRACT FROM AUTHOR]

The C/C coupling activity of the cationic Re(III) species [(C5H5)ReBr]+ with different heteroatom-substituted alkynes was investigated. By using the sulfide-substituted bis(benzylsulfanyl)acetylene an unprecedented rhenacyclopentatriene complex was obtained. An XRD structure determination of [(C5H5)ReBr(CSBn)4]+ uncovered the coordination of the remote ethylene moiety at Re leading to an ?4-coordination mode of the C4(SBn)4 ligand and a folded five-membered metallacycle. In contrast, reaction of the monoalkyne complex [(C5H5)ReBr(CSBn)2]+ with diphenylacetylene as well as diiodoacetylene led to the mixed bis(alkyne) complexes. The different behavior is attributed to kinetic reasons according to DFT calculations. XRD as well as IR studies with the cationic bis(alkyne) complexes [(C5H5)ReBr(CSBn)2(C2Ph2)]+ and [(C5H5)ReBr(CSBn)2(C2I2)]+ revealed clear differences in the bond strengths of the coordinated alkynes at the same metal center. Further investigations on the coupling activity resulted in addition products with H2O and a trimerization of two diphenylacetylene molecules and one bis(benzylsulfanyl)acetylene, both as byproducts and involved in a sulfide bond cleavage. [ABSTRACT FROM AUTHOR]

The cover picture shows a (distorted) square planar bromide coordination environment about a silver cation. The application of soluble silver salts for halide abstraction is a common preparative routine in organometallic chemistry. If the oxidation power of Ag+ is restricting, respective thallium salt can be an alternative. The paper of Kleinschmidt et al. presents polynuclear ReIII/AgI complexes, in which the contest between both metals for the bromide or even iodide ion remains undecided. Consequently, the cyclobutadiene complexes [(η5‐C5H5)(η4‐C4Ph4)ReX2] (X = Br, I) act as neutral halide ligands for Ag+ leading to molecular complexes. Interestingly, the organometallic scaffold of the Re complex moieties forces a square planar coordination. In addition, reversible rhenacyclopentatriene /η4‐cyclobutadiene rearrangement by successful bromide addition/abstraction is presented for sulfide‐substituted congeners. More details can be found in the article by Steffen Kleinschmidt, Alexander Hinz, Alexander Villinger, and Wolfram W. Seidel on page 1268 ff. [ABSTRACT FROM AUTHOR]