Rhenium complexes halides

Complexity in the manganese and rhenium pentarbonyl halides substitution arises from the fact that these decompose in inert solvents to form the halogen-bridged dimers [M(CO)4X]2. Both monomers and dimers react with phosphines, arsines, pyridine, aniline etc. to give the disubstituted compounds M(CO)3XL2. Thus three final products or any mixture of them may be obtained, depending upon the precise reaction conditions... 

Irradiation of [Re(CNC6Fl3-2,6-Me2)6] with UV light in CH2CI2 in the presence of halide ions yields complexes of the type [Re(CNCgH3-2,6-Me2)5X] (X = Cl, Br, or I). The quantum yield of this reaction is high and results in chemical yields between 30% and 40%. Products of the same composition have been obtained directly from the cleavage of the metal-metal bond in quadruply bonded rhenium complexes of various compositions in the presence of isocyanides. ... 

The synthesis of pentacarbonyl rhenium(I) halides, Re(CO)5X, succeeded from simple and complex rhenium halides below 200 atm of CO at 200° C. The compounds are extraordinarily stable and form easily, often quantitatively, from carbon monoxide and rhenium metal in the presence of other heavy metal halides or halogen sources such as CC14. Later we prepared the corresponding carbonyl halides of manganese (67) and technetium (68) from their respective carbonyls. It was found that the corresponding binuclear tetracarbonyl halides [M(CO)4X]2 (M = Mn, Re) could be made by heating the mononuclear M(CO)5X complexes (15, 69), as well as by other methods. 

Such complexes occur exclusively as derivatives of the rhenium(II) halides. The neutral, presumably octahedral, complexes ReX2(diars)2 and ReX2(qas) (X = Cl, Br or I diars = o-phenylene(bis-dimethylarsine) qas = tris(o-diphenylarsinophenyl)arsine) are formed by reduction of the corresponding cationic rhenium(III) species.2 The species ReX2(tas) (X = Cl, Br or I tas = bis(o-diph-enylarsinophenyl)phenylarsine) are prepared similarly but may be five-coordinate.2 The complex ReCl2(PMe2Ph)4 and some of its properties have been described (including its ESCA spectrum and electrochemical properties),11 but details of its preparation have not. 

The trinuclear rhenium(III) halides Re3X9 (X = Cl, Br or I), and the mixed halides Re3X9 Y (e.g. Re3Cl3Br6), contain Re—Re double bonds174 and are the precursors to an extensive class of coordination complexes that are formed by the addition of up to three ligands to the available... 

Complexes of the general formula /ac-Re(a-diimine)(CO)3X and Re(a-diimine)(CO)2XX (where ot-diimine = bpy, phen, substituted bpy or phen, etc. and X, X = halide, solvent, alkyl, benzyl, monodentate phosphine, CO, etc.), have attracted interest since the mid-1970s [51-53]. Many of these complexes show emission from their lowest long-lived MLCT state at room temperatme in solution. Their catalytic properties for CO2 reduction have also been investigated. Electrolysis of a solution containing/uc-Re(bpy)(CO)3 Cl and 0.1 M BU4NPF6 in freshly distilled C02 saturated MeCN at —1.5 V (vs. SCE) produces both CO and C03 with cmrent efficiencies of 98 and 110 %, respectively [54]. Further, yhc-Re(bpy)(CO)3X (X = Cl, Br ) has been used successfully as a photocatalyst for CO2 reduction to CO with TEOA in DMF [55-58]. When X = Cl , a quantiun yield of 0.14 has been measured in the presence of excess Cl". A formato-rhenium complex,/ac-Re(bpy)(C0)3(02CH), has been isolated in the absence of excess Cl". 

Herrmann and co-workers showed that the 17-electron complex 62 may be subjected to electrochemical oxidation as well as reduction (54.55). The redox potentials of the respective halo complexes follow the expected trend for change in the halide ligands. In accordance with these electrochemical studies, both chemical oxidation and reduction reactions of 62 were found [Eqs. (49) and (50)]. Oxidation of the rhenium complex Re(CCMe3)(// -C5Me5)Cl2 by dioxygen results in cleavage of the neopentylidyne ligand from the metal center as pivalic anhydride and pivaloyl chloride. 

In reactions of halogens with substituted rhenium carbonyl halides, the compounds ReX(CO) (diars)2 [X = Br, I diars = l,2-C6H4(AsMe2)2] and bromine or iodine in chloroform give the complexes [ReX2(CO) (diars)2]X3 ... 

With rhenium carbonyl halides, however, the phosphine gives monosubstitution, with excess carbonyl bromide then eliminating halosilane to give the mixed bridged complex (equation 74)93. 

A number of complexes can be derived from the trinuclear and dinuclear rhenium(m) halides and halo complexes (page 979) with retention of the Re3 and Re2 units. 

Most complexes of this oxidation state are derivatives of the rhenium(III) halides. They are classified according to the other ligands (if any) that are present. For example, ReChfPRjlj will be found under phosphine complexes rather than halide complexes . Mononuclear complexes of rhenium(III) are mostly of the types [ReX2L4]" and ReXjL, but rarely [ReX4L2] . Additionally, two very important classes of complexes exist that are derivatives of the quadruply bonded dinuclear [RcjXg] and doubly bonded trinuclear [RejX,2] anions (X = Cl, Br or I). ... 

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