Bis(benzene)chromium. 2. Its Discovery by E. O. Fischer and W. Hafner and Subsequent Work by the Research Groups of E. O. Fischer, H. H. Zeiss, F. Hein, C. Elschenbroich, and Others†

Aromatic hydrocarbons as ligands. Recent advances in the synthesis, the reactivity and the applications of bis(η6-arene) complexes

After briefly reviewing the applications of the coordination ability indices proposed earlier for anions and solvents toward transition metals and lanthanides, a new analysis of crystal structures is applied now to a much larger number of coordinating species: anions (including those that are present in ionic solvents), solvents, amino acids, gases, and a sample of neutral ligands. The coordinating ability towards s-block elements is now also considered. The effect of several factors on the coordinating ability will be discussed: (a) the charge of an anion, (b) the chelating nature of anions and solvents, (c) the degree of protonation of oxo-anions, carboxylates and amino carboxylates, and (d) the substitution of hydrogen atoms by methyl groups in NH3 , ethylenediamine, benzene, ethylene, pyridine and aldehydes. Hit parades of solvents and anions most commonly used in the areas of transition metal, s-block and lanthanide chemistry are deduced from the statistics of their presence in crystal structures.

https://chemistry-europe.onlinelibrary.wiley.com/doi/pdf/10.1002/chem.202001687

Coordinating Ability of Anions, Solvents, Amino Acids, and Gases towards Alkaline and Alkaline-Earth Elements, Transition Metals, and Lanthanides.

Bis(η6-phosphabenzene)vanadium: Synthesis, Structure, Redox Properties, and Conformational Flexibility

Common and less-common coordination modes of the typical chelating and heteroaromatic ligands

Dreikomponenten-Cokondensation von Benzol, Pyridin und Chrom liefert (η6-Benzol)(η6-pyridin)chrom (5), den ersten Bis-(aren)metall-Komplex mit unsubstituiertem Pyridin. Der binare Komplex Bis(η6-pyridin)chrom (7) wird durch Desilylierung der durch Cokondensation zuganglichen Verbindung Bis[2,6-bis(trimethylsilyl)-η6-pyridin]chrom6) erhalten, wobei die sterische Abschirmung der N-Atome durch die Me3Si-Gruppen Bis-η6-Koordination im ersten Syntheseschritt gewahrleistet. Die neuen Verbindungen 5–7 werden durch 1H- und 13C-NMR, MS, ESR (Radikalkationen) und Cyclovoltammetrie charakterisiert. Gemas Rontgenstrukturanalyse kristallisiert 7 fehlgeordnet, die individuellen Molekule liegen im Gitter als synclinale oder/und als antiperiplanare Rotamere vor. 5 last sich am N-Atom protonieren. Die Bestimmung des pKs-Wertes (5-H+) aus der pH-Abhangigkeit des UV-Spektrums bzw. des Redoxpotentials fur 50/+ erweist, das η6-Pyridin in 5 2.5–3.0 pK-Einheiten basischer ist als freies Pyridin.



Metal π Complexes of Heteroarenes, II. – η6-Coordination of Unsubstituted Pyridine: (η6-Benzene)(η6-pyridine)chromium and Bis(η6-pyridine)chromium



Three-component cocondensation of benzene, pyridine, and chromium affords (η6-benzene)(η6-pyridine)chromium (5), the first bis-(arene)metal complex of unsubstituted pyridine. The binary complex bis(η6-pyridine)chromium (7) is obtained by desilylation of bis[2,6-bis(trimethylsilyl)-η6-pyridine]chromium (6), the latter being accessible through cocondensation techniques. The function of the trimethylsilyl groups is to sterically block the pyridine N atoms thereby assuring η6-coordination in the first step. The new compounds 5–7 are characterized by means of 1H and 13C NMR, MS, ESR (radical cations), and cyclic voltammetry. According to X-ray diffraction, crystals of 5 are disordered such that individual molecules exist in the lattice as synclinal or/and antiperiplanar rotamers. 5 can be protonated at nitrogen. The value of pKs (5-H+), determined from the pH dependence of the UV spectrum and of the redox potential for the couple 50/+, reveals that η6-pyridine in 5 is more basic by 2.5–3.0 pK units than free pyridine.

Metall-π-Komplexe von Heteroarenen, II. η6-Koordination von unsubstituiertem Pyridin: (η6-Benzol)(η6-pyridin)chrom und Bis(η6-pyridin)chrom

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Metall-π-Komplexe von Heteroarenen, II. η6-Koordination von unsubstituiertem Pyridin: (η6-Benzol)(η6-pyridin)chrom und Bis(η6-pyridin)chrom