Molybdenum complexes pyridine

Electrophilic substitution of 3-methoxy-4-methylaniline (655) by the complex 663 leads to the molybdenum complex 664. Oxidative cyclization of complex 664 with concomitant aromatization using activated commercial manganese dioxide provides 2-methoxy-3-methylcarbazole (37) in 53% yield (560). In contrast, cyclization of the corresponding tricarbonyliron complex to 37 was achieved in a maximum yield of 11 % on a small scale using iodine in pyridine as the oxidizing agent (see Scheme 5.49). 

CsHuN, Ethanamine, A-ethyl-A-methyl-tungsten complex, 26 40, 42 C6HF5, Benzene, pentafluoro-gold complexes, 26 86-90 C H4I2, Benzene, 1,2-diido-iridium complex, 26 125 CJT, Phenyl platinum complex, 26 136 C,H,N, Pyridine osmium complex, 26 291 OHtS, Benzenethiol osmium complex, 26 304 QH7P, Phosphine, phenyl-cobalt-iron complex, 26 353 QH 1-Butyne, 3,3-dimethyl-mercury-molybdenum-ruthenium complex, 26 329-335 C6H 4P, Phosphine, triethyl-platinum complex, 26 126 platinum complexes, 26 135-140 CsHisPO, Triethyl phosphite iron complex, 26 61... 

While arsabenzene does not act as a nucleophile toward hard acids, it does form a-Mo(CO)5 complex 57 on treatment with pyridine-Mo(CO) and boron trifluoride etherate100). Qualitatively complex 57 seems rather weak since on heating it is destroyed, forming small quantities of tc-Mo(CO)3complex 58 101). This rt-complex is more conveniently prepared directly from arsabenzene and Mo(CO)6 or from acid-catalyzed displacement from tris-(pyridine)molybdenum tricarbonyl. 

One approach to limit dimer formation in model complexes involves the use of bulky ligands and weakly coordinating solvents. Holm and coworkers [196,198-201] have studied oxygen atom transfer reactions of 2,6-bis(2,2-diphe-nyl-2-thioethyl)pyridinate [2] molybdenum oxo complexes. In contrast to the structurally similar dithiocarbamate molybdenum complexes, the tendency of the 2,6-bis(2,2-dipheny 1-2-thioethy l)pyridinate MoIV monoxo complex to undergo di-... 

As indicated in Section 14.20.3.4, borepins can react with organometallics to form complexes in which the borepin ring serves as an rf ligand to the metal. Thus, 1-methylborepin 15 reacted with tris(pyridine)molybdenum tricarbonyl to afford the corresponding molybdenum complex 16 as a red, air-sensitive oil, as in Equation (1) <19970M1884>. 

More recently, a new molybdenum complex, oxodiperoxymolybdenum-pyridine 3,4,5,6-tetrahydro-1,3-dimcthyl-2-(l //)-pyrimidinonc (MoOs py DMPU = MoOPD) has been introduced in which 1,3-dimethyl-3,4,5,6-tetrahydro-2(lf/>pyrimidinone (DMPU) is used as a non-carcinogenic alternative to HMPA54. This reagent offers comparable results to MoOPH reagent in the oxygenation of enolates (Table 4). 

The conversion of ketones into a-hydroxy ketones can be achieved by the oxidation of enolates or enol ethers. A special reagent for enolates is the oxodiperoxy molybdenum complex with pyridine and hexamethylphos-phoramide. The reaction is applied to aromatic aliphatic ketones and cyclic ketones and furnishes 34-81% yields of a-hydroxy ketones with up to 26% of a-diketones (equation 401) [531]. 

The a-hydrogens of nitroalkanes are appreciably acidic due to resonance stabilization of the anion [CH3NO2, 10.2 CH3CH2NO2, 8.5]. The anions derived from nitroalkanes give typical nucleophilic addition reactions with aldehydes (the Henry-Nef tandem reaction). Note that the nitro group can be changed directly to a carbonyl group via the Nef reaction (acidic conditions). Under basic conditions, salts of secondary nitro compounds are converted into ketones by the pyridine-HMPA complex of molybdenum (VI) peroxide. Nitronates from primary nitro compounds yield carboxylic acids since the initially formed aldehyde is rapidly oxidized under the reaction conditions. 

Over the past year, there continues to be a constant stream of methods for the deoxygenation of pyridine A-oxides. Two groups have demonstrated facile deoxygenation with molybdenum complexes <05TL125, 05SL1389>, while Sandhu et al. have accomplished this transformation with ruthenium <05TL8737>. 

NC2H7, Methaneamine, A -methyl-, molybdenum complex, 21 54 NC H , Pyridine, rhenium complex, 21 116, 117... 

Chloroborepin (17) is readily converted to the corresponding Mo(CO)3 complex (Equation (4)) by reaction with tricarbonyl-tris(pyridine)molybdenum and BF3 Et20 in ether. This Mo(CO)3 derivative is smoothly converted to the corresponding 1 /f-borepin-molybdenum complex (18) by reduction with lithium triethylborohydride (Super-Hydride) in THF (Equation (5)). This is noteworthy as (18) cannot be prepared directly from the highly labile 1//-borepin itself <93AG(E)1065>. 

More recent work has shown that direct hydroxylation of enolate anions can be achieved with a molybdenum peroxide reagent, which consists of M0O5 as a complex with pyridine (C5H5N) and hexamethylphosphoric acid triamide (hexameth-ylphosphoramidate [HMPA], 0=P[N(CH3)2]3). As shown in Scheme 8.12, phenylcy-clohexanone is first converted to the corresponding anion (e.g., with n-butyUithium, BuLi, CH3CH2CH2CH2Li) and the latter is treated with the molybdenum complex... 

Oxidations of cyclic ketones to lactones by H2O2 take place in the presence of catalytic amounts of certain molybdenum complexes. The catalysts are peroxo-molybdenum complexes stabilized by picolinato- and pyridine-2,6-dicarboxyl-ato-ligands, e.g. [Mo(0)(02) CsH3N(C02)2 ]- Although the reaction is catalytic, turnover numbers are low (25 or less) and chemical yields are variable. Moreover, competing reactions are the formation of oligomeric peroxides and ring-opened products. 

Another approach to an oxidative desulphonylation reaction is to oxidize an a-sulphonyl carbanion with an oxidizing agent that is also nucleofugal. An example of this was presented by Little and Sun Ok Myong203 who used a molybdenum peroxide complex (M0O5.Pyridine.HMPA) as the oxidant. However, this reagent is expensive and... 

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