Benzene and Its Derivatives as Bridging Ligands in Transition‐Metal Complexes

Abstract

Transition-metal complexes in which two or more metal atoms are bridged by one or more arene ligands led a shadowy existence in comparison to the extensive class of mononuclear arene complexes. Arene bridges can occur in a variety of coordination modes and with almost all of the transition-metal elements of the periodic table. Nowhere else are found so many forms of distorted and bent arene rings. The binuclear compounds can be divided into two classes : adducts which show relatively weak metal-arene bonding and complexes which show strong arene-metal interaction. Most of the adducts are in equilibrium with mononuclear complexes in solution or are only stable in the solid state (often as polymers). In both classes syn and anti coordination occurs; their geometries show a wide variation between the extreme cases of '1' : Ul-bridge and q6 : q6-triple-decker structure. Metal surfaces with chemisorbed arenes can be seen as a form of multinuclear arene-metal complexes. On transition-metal surfaces, benzene can be bonded to one, two, or four surface atoms. Molecular clusters with face-capping arene ligands that are bonded to three metal atoms have until now mainly been limited to two classes. The arenes bound to {(CO),M}, (M = Ru, 0s) or (CpCo), clusters as p,-q2 : q2 : 1' ligands show only a weak trigonal distortion towards a Kekule structure. Detailed investigations of the molecular structure and ligand dynamics of [ (CpCo),(p3-arene)] complexes considerably help the understanding of the bonding of arenes to metal clusters and to metal surfaces.

Mechanisms and Beyond: Elucidation of Fluxional Dynamics by Exchange NMR Spectroscopy

“…Migration of the Cr(CO) 3 tripod moiety in 112 is much slower (kinetic energy barrier 32 kcal mol −1 ) and proceeds via an o ‐Y‐complex (a similar migration was utilised in the first organometallic latch, section 3.3). Haptotropic rotation, a close relative of trigonal rotors (sections 3.1–3.3), proceeds via six rotamers of unusual tris ‐cyclopentadienylcobalt complex 113 as shown by 1 H‐ 1 H EXSY; for R= i ‐Pr, the energy barrier is 13.6 kcal mol −1 . Independently, it was shown that five dynamic processes in a related Os carbonyl 114 remain detectable in the solid state …”

“…Haptotropic rotation, a close relative of trigonal rotors (sections 3.1-3.3), proceeds via six rotamerso fu nusual tris-cyclopentadienylcobalt complex 113 as shown by 1 H-1 HE XSY;f or R = i-Pr,t he energy barrieri s 13.6 kcal mol À1 . [183] Independently,i tw as shown that five dynamic processes in ar elated Os carbonyl 114 remaind etectable in the solid state. [184] Famously,t he s-p-s interconversion of h 1 -a nd h 3 -allylpalladium species,f or example, 115a$115b was shown to be involved in Pd-catalysed allylic substitution.…”

Nickel-Containing Carbon Monoxide Dehydrogenase/Acetyl-CoA Synthase,

“…The idea of using binuclear complexes for ligand activation has been recognized. , Understanding the properties of heterobimetallic catalysts would help explain how Ni and Fe cooperate in the various steps of acetyl-CoA synthesis. Both hetero- and homonuclear bimetallic complexes without metal−metal bonds are being studied. − In these complexes, two or more metals are bridged by a common ligand. The joint action of two metal centers could enhance the activation of an organic substrate by several mechanisms.…”

Tuning of Thiyl/Thiolate Complex Near-Infrared Chromophores of Platinum through Geometrical Constraints

“…69 General information on the purification of additional starting materials, solvents and reagents, cyclic voltammetry, X-band cw-EPR spectroscopic and XRD data, computational details, and DFT-optimized structures is provided in the Supporting Information. 1 H and 13 C{ 1 H} NMR chemical shifts (δ) are referenced to residual 1 H and naturally abundant 13 C NMR resonances of the solvents (cf. the Supporting Information).…”

“…The group of electron acceptors comprises ligands that interconvert between a neutral and a radical-anionic form. Suitable candidates are ligands with energetically accessible π* orbitals, such as (heterocyclic) arenes, − conjugated N 4 -macrocycles, azo-1,2-dicarbonyl compounds, (conjugated) N derivatives of (di)­carbonyls, ,− and small (inorganic) molecules such as CO 2 , O 2 , or NO . The second category includes electron-donor ligands that establish an isomorphic series of distinct valence states that include closed-shell and (bi)­radical forms.…”