Mechanistische Untersuchungen zum reversiblen Gleichgewicht von metallorganischen Tripeldecker- und Sandwichkomplexen des Typs [Bis{(η⁵-Cp^R)Co}-μ-{η⁴:η⁴-aren}] und [(η⁵-Cp^R)Co(η⁶-aren)] / Mechanistic Studies towards the Reversible Equilibrium between Metal Organic Triple Decker and Sandwich Complexes [Bis{(η⁵ -Cp^R)Co}-μ-{η⁴ :η⁴-arene}] and [{(η⁵-Cp^R)Co(η⁶

Abstract

Mechanistische Untersuchungen zum reversiblen Gleichgewicht von metallorganischen Tripeldecker-und Sandwichkomplexen des Typs [Bis{(r75-CpR)Co}-/z-{774:774-aren}] und [(r75-CpR)Co(r76-aren)]Mechanistic Studies towards the Reversible Equilibrium between Metal Organic Triple Decker and Sandwich Complexes [Bis{(/75-CpR)Co}-^-{/74 :774-arene}] and [{(775-CpR)Co(776-arene)] The arene ligand exchange mechanism o f slipped arene triple deckers [Bis{(?;5-CpR)C o}-^-{r/4:?74-arene}] (R = M e5, 1,2,4 tri-tert butyl, arene = benzene, toluene) 1 was studied by 1 H-NMR spectroscopy for different concentrations and solvents. It has been found that triple deckers of type 1 decom pose slow ly in solution. A unique equilibrium, between these triple deckers and the mixed sandwich com plexes [(?/6-arene)Co(?/5-CpR)] and 14 e [(^5-Cp)Co]soW fragments generated in situ by decom position o f 1 exists. In addition to this equilibrium arene lability of the thus formed mixed sandwich com plex type has been detected by NMR making slipped triple deckers 1 ideal single source compounds for the generation o f two [(7^-Cp)Co] fragments in one reaction step. Such fragments are valuable metal ligand components with high synthetic utility in organometallic chemistry. * Sonderdruckanforderungen an Priv.-Doz. Dr. J. J. Schneider. Fax: +49 201 183 2402,

Synthesis and reactivity of molybdenum(0) complexes containing sterically expanded arene ligands

“…Based on mechanistic studies by Schneider and coworkers involving arene exchange of [(Cp*Co) 2 -μ-(η 4 :η 4 -toluene)] with benzene, ready dissociation of a Cp*Co(I) equivalent occurs at ambient temperature and results in formation of Cp*Co(η 6 -toluene), as observed by 1 H NMR spectroscopy [11]. This fragmentation likely results from the strong driving force to re-establish planarity in the toluene ligand, which is severely distorted from aromaticity in the triple decker complex.…”

Development of more labile low electron count Co(i) sources: mild, catalytic functionalization of activated alkanes using a [(Cp*Co)2-μ-(η4:η4-arene)] complex

“…18,19 Moreover, exchange of the arene ligand with solvent in benzene-d 6 is observed at ambient temperature, via detectable monomeric Cp*Co(Z 6 -arene) complexes, suggesting facile access to Cp*Co(I) equivalents. 20 Though these compounds have found utility as building blocks in macromolecular chemistry, 21 the complexes have been relatively unexplored for catalytic applications. Herein, we report improved syntheses of these Co arene complexes and their use as catalysts for activated sp 3 C-H bond functionalization at ambient and higher temperatures.…”

“…Simultaneously, the presence of paramagnetic Cp*Co(Z 6 -C 6 D 6 ) ( 13) is detected by its characteristic shift of the Cp* resonance at 152 ppm in the 1 H NMR spectrum. 20 Full characterization of the organometallic intermediates proved difficult, due in part to the overlapping resonances in the 0-3 ppm region of 4, the intermediates, and product 5. However, based on rapid formation of 13 and integration of the SiMe 2 resonances relative to the Cp* peaks of the intermediates, we tentatively propose two isomers of the bis(substrate) complex Cp*Co(Z 2 -H 2 CQCHSiMe 2 (NC 5 H 10 )) 2 (14) as these potential intermediates.…”

“…Triplet arene complex Cp*Co(Z 6 -C 6 D 6 ) (13), based on reactivity of Cp*Co(Z 6 -C 6 Me 6 ) (12), may also play a role in the catalysis, through direct arene displacement by substrate or through access to 14 via the known monomer/dimer equilibrium. 20,22 The dissociative nature of the reactive Cp*Co(I) equivalent is advantageous when considering catalytic transformations involving substrates containing less strongly binding directing groups.…”

Cyclopentadienone-like Behavior of Fluorenone and 4,5-Diazafluoren-9-one

“…It is worth addressing the last point in more detail, since it turns out that 4 and 5 are quite unique in this context. All cyclopentadienylcobalt(I) arene complexes known so far belong to one of the following four categories: (A) mononuclear complexes of the electron-poor arenes C 6 (CF 3 ) 6 and C 6 (COOMe) 6 (although crystal structure determinations have not been reported for these types of compounds, there is no doubt that the arene shows η 4 coordination in each case); (B) mononuclear complexes of the electron-rich arene C 6 Me 6 16 (it is generally accepted that this ligand is always η 6 coordinated, although no reliable structural data have been reported); (C) mononuclear complexes of polycyclic aromatic hydrocarbons such as, for example, anthracene,16e decacyclene, and angular [3]phenylene (an η 4 coordination of a single six-membered ring is observed in each case); (D) oligonuclear complexes with bridging arene ligands (an antifacial η 4 :η 4 coordination of an arene ring is commonly observed here) . In view of these facts, an η 4 coordination of a single six-membered ring might have been expected for 4 and 5 .…”