Rhenium complexes arene

The stability of the polypyridyl rhenium(I) compounds mentioned above stimulated applications of this coordination chemistry. Thus, new heterotopic bis(calix[4]arene)rhenium(I) bipyridyl receptor molecules have been prepared and shown to bind a variety of anions at the upper rim and alkali metal cations at the lower rim. A cyclodextrin dimer, which was obtained by connecting two permethylated /3-cyclodextrins with a bipy ligand, was used for the preparation of a luminescent rhenium(I) complex. The system is discussed as a model conipound to study the energy transfer between active metal centers and a bound ditopic substrate. The fluorescence behavior of rhenium(I) complexes containing functionalized bipy ligands has been applied for the recognition of glucose. ... 

T -Arene complexes containing late metals have been known for many years, but the scope and utility of these complexes have increased in recent years. Copper(I) and silver form labile arene complexes of various stoichiometries that are apparently T -arene complexes. A few of these complexes have been structurally characterized. More recently, a large number of V-arene and heteroarene complexes of osmium, rhenium, molybdenum, and tungsten have been prepared for the purpose of dearomatization of the arene or heteroarenes. Two examples are shown in Figure 2.33. This dearomatization creates a diene or vinyl unit that imdergoes the organic chemistry of ttiese isolated units, instead of the chemistry of an arene. n -Arene complexes of rhodium and platinum have been characterized structurally and studied in the context of their likely intermediacy in the oxidative addition of arene C-H bonds. ... 

More mechanistic insight into the C-H functionalization process of arenes is provided by theoretical and experimental studies. Multifluorinated, electron poor, aromatic substrates readily undergo CH activation with coordina-tively unsaturated rhenium complexes, attributed to the stronger C-Re bond in the product, whereas with monofluorinated analogs, the if -complex predominates (Equation (60)).61... 

Similar effects are observed in -complexes Ag1 and Hgn coordinated to arenes exhibit bending angles of a 5° (which is symptomatic of high -character of the complex and a low degree of CT). On the other hand, in rhenium, rhodium, iridium, and nickel complexes, arenes exhibit bending angles of up to 45° [2]. 

Binuclear complexes of naphthalene (VIII) and of benzene (IX) with [Os(NH3)5]2+ and [Ru(NH3)5]2+ moieties were reported by Taube et al. (19), in which anti- //-1,2-rj2 3,4- 2) coordination of the arene is present. This bonding mode was first observed by Pasman et al. (20) in the binuclear Rhenium complex X. Wolczanski et al. (21) obtained complex XI from the mononuclear complex [Ta(0—Si Bu3)3 2-(N,C)-pyridine ] and benzene. Each tantalum atom is bound unsymmetrically to one C=C bond of benzene with a weak interaction to a third carbon atom the bonding may be described as a distorted tj3-enyl. In the dinuclear cobalt complex XII, the xylene functions as a bis(enyl)-ligand (12,22). 

Finally, photolysis of the Re(V) oxo-idodide compound (HBpz3)ReO(I)Cl in arene (ArH) solvents gives the aryl complexes (HBpz3)ReO(Ar)Cl [39], Substituted arenes react with electrophilic selectivity and the authors propose that the reactive species is a rhenium(V) 0x0 complex which can add aromatic C-H bonds aaoss the Re=0 linkage. 

This chapter will initially cover several aspects of dihapto-coordination of aromatic molecules, including the scope of the dearomatization agent and the aromatic substrate. The primary focus of this work, however, will be the fundamental organic reactions of these complexes with electrophiles and the subsequent reactions of those products. Several applications of this methodology will also be illustrated. Owing largely to its earlier discovery, the majority of the organic transformations reviewed will be with osmium(II), however, recent arene transformations promoted with rhenium(I) and molybdenum(O) will also be discussed, with an emphasis on differences in reactivity compared to those of osmium. 

Electron-rich aromatic substrates undergo direct trifluoromethylation catalyzed by a variety of Lewis acids, such as Zn salts, silanes, rhenium, or copper complexes. In the absence of an appropriate directing group, this kind of trifluoromethylation displays very low or no regioselectivity. More electron-poor arenes have to be activated first and are able to undergo trifluoromethylation in the form of aryl boronic acids or trifluoroborates (Scheme 7) [23-31]. 

Manganese and Rhenium.- New arene rhenium complexes, made... 

A study, including computational results, of the role of copper enolate complexes in the a-arylation of enolates has shown that the reaction is likely to occur through oxidative addition of the iodoarene to form an aryl-copper(III) intermediate, (46), followed by reductive elimination to give the product. Copper(III) species are also likely to be involved in the meta-selective C-H arylation of acetanilides by diaryliodonium salts. However, radical species may be involved in the rhenium-catalysed electrophilic triflu-oromethylation of arenes using hypervalent iodine reagents. 

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