Manganese complexes carbonyl compounds

Generation of the carbon based radical in these processes involves the prior formation of a complex between manganese(lll) and the enol of the carbonyl reactant. Intramolecular electron transfer occurs within this complex. Addition to the olefin then takes place within the co-ordination sphere of manganese. When manganese is present in catalytic amount, the relative values of the equlibrium constants between manganese and both the carbonyl compound and the alkene arc important. If the olefm is more strongly complexed then no radical can form and reaction ceases. Reactions are usually carried out at constant current and the current used must correspond to less than the maximum possible rate for the overall chemical steps involved. Excess current caused the anode potential to rise into a region where Kolbe reaction of acetate can occur and this leads to side reactions [28]. 

The rhenium compound 10 is rather unreactive. Carbonylation (100°C, 200 atm) gives Cp Re(CO)3, while treatment with I2 affords Cp Re(CO)2-(I)2. It does not react with ethyne, diazomethane, or phosphines under conditions where other dimetal complexes with multiple MM bonds do so (78). The manganese complex 8, also somewhat unreactive, reacts with phosphites by Mn=Mn cleavage. In the case of P(OEt)3 the two products Cp Mn(CO)2[P(OEt)3] and CpMn(CO)[P(OEt)3]2 form in a 1 1 ratio (51). 

Reviews have appeared of the photophysics of molybdenum complexes, primary and secondary processes in organometallic chemistry, flash photolysis of Pe(CO)5 and Cr(CO)g, dinuclear manganese carbonyl compounds, the photochemistry of metal complexes isolated in low temperature matrices, cluster complexes, diene complexes, photoproduction of coordinativeiy unsaturated species containing rhodium or iridium, and redox chemiluminescence of organometallic compounds.Synthetic and metal organic photochemistry in industry has also been reviewed. 

Vanhoye and coworkers [402] synthesized aldehydes by using the electrogenerated radical anion of iron pentacarbonyl to reduce iodoethane and benzyl bromide in the presence of carbon monoxide. Esters can be prepared catalytically from alkyl halides and alcohols in the presence of iron pentacarbonyl [403]. Yoshida and coworkers reduced mixtures of organic halides and iron pentacarbonyl and then introduced an electrophile to obtain carbonyl compounds [404] and converted alkyl halides into aldehydes by using iron pentacarbonyl as a catalyst [405,406]. Finally, a review by Torii [407] provides references to additional papers that deal with catalytic processes involving complexes of nickel, cobalt, iron, palladium, rhodium, platinum, chromium, molybdenum, tungsten, manganese, rhenium, tin, lead, zinc, mercury, and titanium. 

Adam, W., Fell, R. T., Stegmann, V. R., Saha-Moeller, C. R. Synthesis of Opticaiiy Active a-Hydroxy Carbonyl Compounds by the Catalytic, Enantioselective Oxidation of Silyl Enol Ethers and Ketene Acetals with (Salen)manganese(lll) Complexes. J. Am. Chem. Soc. 1998,120, 708-714. 

Reduction of Cp2TiCl2 with metallic manganese generates Ti(m) catalysts for the addition of allyl bromide to carbonyl compounds. This method can be used for asymmetric reactions if Brintzinger s compound r -(ebthi)2TiCl2 or the previously synthesized chiral derivative1175 shown in Scheme 492 are used. When chiral bis-Cp complexes are employed, acceptable yields of optically active products are obtained.1176... 

In the cobalt complex, each cobalt atom has a trigonal bipyramidal coordination geometry, whereas, in the manganese complex, each manganese atom is octahedrally coordinated. In both cases, the equatorial carbonyl groups are bent towards the central mercury atom. The structures of the related compounds... 

The first mononuclear carbonyl compound of cobalt, iron or manganese known was the pentacarbonyl complex [Fe(CO)5] " with a trigonal-bipyramidal ligand field (see Fig. 2). Though related electroneutral species of cobalt and manganese are not known due to a strict observance of the 18-electron-rule in these cases, the monoanionic manganese derivative fMn(CO)5] has also been described as a trigonal-bipyramidal species. ... 

The reactions of iron carbonyls with diorgano tellurides deserve mention, for example the reaction of Fe3(CO),2 with PhjTe gives Ph2TeFe(CO>4, whilst several ruthenium-carbonyl complexes have been prepared from reactions between diphenyl telluride and alcoholic carbon monoxide-saturated solutions of ruthenium trichloride hydrate. Various other ruthenium-carbonyl complexes of diorgano teUurides, including di- and tri-substituted species, have also been described. The utility of diphenyl telluride in transition metal carbonyl chemistry has also been well illustrated during studies of manganese and rhenium compounds. 

Miscellaneous Reactions. In addition to the key reactions above, DDQ has been used for the oxidative removal of chromium, iron, and manganese from their complexes with arenes and for the oxidative formation of imidazoles and thiadia-zoles from acyclic precursors. Catal)ftic amounts of DDQ also offer a mild method for the oxidative regeneration of carbonyl compounds from acetals, which contrasts with their formation from diazo compounds on treatment with DDQ and methanol in nonpolar solvents. DDQ also provides effective catalysis for the tetrahydropyranylation of alcohols. Furthermore, the oxidation of chiral esters or amides of arylacetic acid by DDQ in acetic acid provides a mild procedure for the synthesis of chiral a-acetoxy derivatives, although the diastereoselectivity achieved so far is only 65-67%. ... 

The vanadium and manganese complexes are the least stable and least studied of the series. The compound V(NO)(CO)5, a violet solid, is made by the action of nitric oxide on vanadium carbonyl (42), while Mn(NO)-(CO)4, a red liquid freezing at -1.5° C, is best made by treating Mn2(CO)g-(PPh3)2 with nitric oxide. The mechanism of this reaction has been briefly... 

The first transition metal complex containing four different substituents to be resolved was the manganese complex shown in Scheme 2, top [6,7]. In the cation of this complex, the Mn atom is surrounded by a cyclopentadienyl, a carbonyl, a nitrosyl, and a triphenylphosphine ligand. This complex can be prepared from the commercially available compound (C5H5)Mn(CO)3 in two steps yielding [(C5H5)Mn(CO)(NO)PPh3]PF6 as a racemate [8]. 

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