Aromatic sandwich complex

Astruc et al. [187] reported a nonairon sandwich complex by treating a nona-ol with [C5H5]Fe(q6-p-MeC6H4F)(PF6). In a subsequent report [188], Astruc and Marvaud reported the synthesis of aromatic star molecules with or without a central Fe(/f-C5H5)+ group. These bipyridine and terpyridine terminated dendrimers were further capped with [Ru(bipy)2Cl2] and [Ru(terpy)Cl3], respectively, to afford the corresponding hexa or hepta nuclear complexes. 

The reaction of aromatic amino acids, dipeptides, or protected amino acids with [Ru(Cp )(CH3CN)3]PF6 in THF (THF = tetrahydro-furan) leads to the formation of robust Ru(Cp ) sandwich complexes in which side-chain phenyl (e.g., Phe, Tyr) or indole groups (Trp) are bound 7]6 to a Ru(Cp ) center (cf. 31 AA = Phe) (75, 76). The similar... 

In most paramagnetic sandwich complexes the proton hf structure is not resolved in low temperature powder or single crystal EPR spectra. In vanadium dibenzene, a typical example of this type of compound, the poor resolution is due to the fact that the aromatic rings are rigidly frozen at T < 50 K and thus the proton hfs tensors of the benzene rings are no longer magnetically equivalent. 

A tricyclic aromatic system closely related to borole, 9-boratafluorene, might be expected to form ( -coordinated transition metal sandwich complexes, but so far only the lithium complex has been characterized.19 Monohapto aluminum adducts of neutral 9-borafluorene, in which A1 is bound only to the boron atom, have been prepared.20... 

The transfer hydrogenation of aromatic ketones, which is typically catalyzed by ruthenium half-sandwich complexes using, e.g., formic acid as hydrogen source, was chosen as another model system. After applying an appropriate TSA molecule as template, i. e., a ruthenium phosphinato complex, the resulting MIP catalyzed the hydrogenation of benzophenone approximately twice as effectively as the CP [116]. 

The dehydrodimerization reaction involving aromatic radical-cations is fast only when electron donating substituents are present in the benzene ring. These substituents stabilise the a-intermediate. Benzene, naphthalene and anthracene radical-cations form a a-sandwich complex with the substrate but lack the ability to stabilise the a-intermediate so that radical-cation substrate reactions are not observed. The energy level diagram of Scheme 6.4 illustrates the influence of electron donating substituents in stabilising the Wheland type a-intermediate. 

Effect of Ag+ complexation on relative aromaticity in various rings was examined by NICS in two representative cases. Structures and energies of the acetyl pyrene-Ag -pyrene hetero-dimer and acetyl pyrene-Ag -acetyl pyrene homo-dimer complexes were determined with the same model. Interestingly, only sandwich complexes were formed and no stable structures in which the silver ion was not sandwiched between two PAH units could be found. 

Os forms many complexes with nitnte. oxalate, carbon monoxide, amines, and thio ureas. The latter arc important analytically Osmium forms the interesting aromatic sandwich" compound, osmocene. A metallocene is described under Ruthenium. See also Chemical Elements and Platinum and Platinum Group. 

There is a certain analogy between the aromatic anions of cyclopentadienide (C5H5 ) and boratabenzene (C5H6B ). l-Methylbora-2,5-cyclohexadienehas a more acidic proton connected to the, sp3-hybridized ring carbon atom than cyclopentadi-ene, due to the same tendency of aromatic anion formation [252, 253]. The related 1-phenyl-1,4-dihydroborabenzene affords the lithium salt of 1-phenylborataben-zene on treatment with tert-butyllithium. Like metallic complexes such as ferrocene formed by cyclopentadiene, boratabenzene also forms such sandwich -complexes with iron and cobalt. The iron complex can be acetylated under Friedel-Crafts conditions. 

Additional d electrons on the metals increase the number to be counted in the aromaticity formalism. As this can be applied by two metals (d6 - d8), the family of triple-decker sandwich complexes should consist of members having 30, 31, 32, 33, and 34 valence electrons. Analogous to the 17-valence-electron ferricenium cation, obtained by oxidation of ferrocene, 29-valence-electron species ( n,8/d5/7r8/d8/7r6) would be expected to be stable, and this has been confirmed by chemical and electrochemical studies (see Section III). 

Chloroborepin and its tricarbonyl-molybdenum semi-sandwich complex are definitely planar and aromatic, as proved by X-ray diffraction (93AGE1065). However, electron-donor or sterically demanding substitution causes non-planarity of the seven-membered ring 1-dimethylaminoborepin was shown experimentally and theoretically to... 

The aromatic moiety in phenylboranes and phenylb-orates may serve as a 6-electron n donor ligand to transition-metal complexes. Half-sandwich complexes of chromium, Mes2[B( -Mes)Cr(CO)3] (56), MesB[ -MesCr(CO)3]2 (57), andB[ -MesCr(CO)3]3 (58), containing trimesitylborane as a ligand have been prepared and structurally characterized.1 1 The Cr(CO)3 moieties interact weakly in the multinnclear systems (57) and (58) as shown by... 

Treatment of 3-borolenes or 2-boraindans with bulky lithium amides yields the dihthiated aromatic borolide dianions, which are applicable as hgand precursors for transition-metal complexes. Many borole complexes including a number of unusual multidecker sandwich complexes and mixed-metal clusters have been described. 4 3,2i2 An unexpected new entry into the synthesis of borole complexes has been recently discovered. Bochmann found that attack of B(C6Fs)3 at a zirconium bound diene leads to a pentafluorophenylborole complex throngh snccessive C-H activation steps. ... 

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