Molybdenum complexes dioxide

Using this method, the electrophilic aromatic substitution of the electron-rich arylamine 578 by the molybdenum-complexed cation 577 affords regio- and stereoselectively the molybdenum complexes 579. Cyclization with concomitant aromatization and demetalation using activated manganese dioxide leads to the carbazole derivatives 568 (8,10,560) (Scheme 5.26). 

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). 

Reaction of the 5-aminochromene 1044 with the complex salt 577 provided via an electrophilic aromatic substitution regio- and diastereoselectively the molybdenum complex 1050. The oxidative cyclization of complex 1050 with concomitant aromatization and demetalation using activated manganese dioxide led directly to girinimbine (115) in 50% yield. Oxidation of girinimbine (115) with DDQ in methanol afforded murrayacine (124) in 64% yield (660) (Scheme 5.161). 

Very related to the titanium chemistry described above are experiments with resembling molybdenocene complexes. If the molybdenum-diphenyl-acetylene complex Cp2Mo(PhC=CPh) is used as starting material, no C-C linkage reaction takes place with carbon dioxide. Instead, a crystalline solid was isolated whose x-ray proved the formation of a molybdenum-carbon dioxide complex [85] (Equation 15). 

Cis-molybdenum(VI) dioxide forms biscatecholate coordination compounds. The third position is already blocked by the two cis-oriented oxo ligands. The reaction of bis(acetylacetonate) cis-dioxomolybdenum with carbonyl-substituted catecholates in the presence of lithium carbonate results in the formation of bis catecholate cis-dioxomolybdenum(VI) complexes that are in equilibrium with their dimers. 

Molybdenum complexes with two side-on coordinated carbon dioxide molecules are also known... 

The iron-mediated synthesis of 2-oxygenated carbazoles is limited. On the other hand, a molybdenum-mediated approach works as a complementary route (Scheme 23.24) [31]. Similar to iron-coordinated cation 55, molybdenum-coordinated cations 61 react with electron-rich anilines 62 to give (if-cyclohexenyl)molybdenum complex 63. Then the oxidative cyclization of 63 followed by the subsequent aromatiza-tion and demetallation using activated manganese dioxide afforded the corresponding... 

Propylene oxide is also produced in Hquid-phase homogeneous oxidation reactions using various molybdenum-containing catalysts (209,210), cuprous oxide (211), rhenium compounds (212), or an organomonovalent gold(I) complex (213). Whereas gas-phase oxidation of propylene on silver catalysts results primarily in propylene oxide, water, and carbon dioxide as products, the Hquid-phase oxidation of propylene results in an array of oxidation products, such as propylene oxide, acrolein, propylene glycol, acetone, acetaldehyde, and others. 

Although numerous advantages are associated with the use of supercritical carbon dioxide (scC02) as an ecologically benign and user friendly reaction medium, systematic applications to metal-catalyzed processes are still rare. A notable exception is a recent report on the use of scC02 for the formation of industrially relevant polymers by ROMP and the eyelization of various dienes or enynes via RCM [7]. Both Schrock s molybdenum alkylidene complex 24 and the ruthe-... 

In addition to the dioxide MoO and the disulfide. MoS . example of leLravalem molybdenum compounds include the tetrachloride. MoClj. and teurabromide. MoBr. both of which are hydrolyzed in hot l-l-O. Other tetravalent compounds include a few of the complexes. 

The reaction of tellurium dioxide, vaporized at 0.0001 torr and collected in a diethyl ether matrix at — 196°, with a solution of cycloheptatrienyldicarbonylmethylmolybdenum in tetrahydrofuran at — 78° under an argon atmosphere produced, after four weeks, cycloheptatrienyldicarbonyl(methanetellurinato)molybdenum in 6% yield3 via insertion of tellurium dioxide into the Mo-mcthyl bond. The complex was postulated to have a Mo-Te bond3. 

Few derivatives of molybdenum dioxide, MoOj, have been prepared, and it is doubtful whether simple salts containing tetravalent molybdenum can be formed in solution. By the electrolytic reduction of acid molybdate solutions, brownish-coloured liquids apparently containing the metal in this stage of oxidation have been obtained, but the evidence is insufficient to determine whether Mo ions are actually present, or whether the liquids merely contain mixed Mo and Mo ions. Potential measurements indicate the presence of mixed ions. The only simple substances containing tetravalent molybdenum, in addition to the oxide, are the sulphide, MoSj, the tetrachloride, M0CI4, and the tetra-bromide, MoBr. There are, however, two series of complex molybdo-eyanides, of the types R 4[Mo(OH)4(CN)J.aq. and R 4[Mo(CN)8].aq. respectively, which contain tetravalent molybdenum and yield well-cry stallised salts. Their existence is probably due to the resistance of the stable complex to hydrolytic decomposition. 

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