Molybdenum-carbon dioxide complex

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-... 

Molybdenum(0) complexes, 1265,1266 carbon dioxide, 1277 carbon monoxide, 1266 diphenylphosphinocthane, 1266 NMR, 1266 carbonyl sulfide, 1277 dinitrogen, 1267,1268... 

As in the monoene chapter, the stoichiometric and catalytic reactions of dienes with carbon dioxide will be discussed in the sequence of the transition metal applied. It is remarkable, that almost the same metals are described both in monoene and in diene/C02 chemistry. Two differences, however, should be stressed In the presence of molybdenum and tungsten complexes no interactions between dienes and carbon dioxide are reported (until now). On the other hand, palladium is a much more versatile and effective metal in diene/C02 than in monoene/CO chemistry. 

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). 

A general method of preparation of the zero valent metal trifluorophosphines is by ligand replacement. Under high PF3 pressure, for example, the chromium or molybdenum compound can be prepared from the dibenzene derivatives (8.175). Carbon dioxide is also displaced under high pressure (8.176), although the reaction is reversible. Under some conditions, partial replacement can be effected to produce complexes of type M(CO) j (PFslx-... 

Chatt J, Kubota M, Jeffery Leigh G, March FC, Mason R, Yarrow DJ (1974) A possible carbon dioxide complex of molybdenum and its rearrangement product di-p-carbonato-bis carbonyltris(dimethylphenylphosphine) molybdenum X-ray crystal stmcture. J Chem Soc... 

Galindo A, Pastor A, Perez PJ, Carmona E (1993) Bis(ethylene)complexes of molybdenum and tungsten and their reactivity towards CO2. New examples of acrylate formation by coupling of ethylene and carbon dioxide. Organometallics 12 4443 1451... 

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

Gomez et al. " electrodeposited Co-Mo magnetic alloys from a sulfate-citrate bath on carbon electrodes. Although the focus of their paper was not on elucidating the mechanism of induced codeposition, it was suggested that hydrogen could not be responsible for the deposition of Mo in the Co-Mo system, because its concentration was fairly low and because another mechanism should explain the need for citrate or polycarboxylate anions in solution. The deposition process was foimd to be favored when molybdate was present in solution, even at very low concentrations. Hence, the authors adopted the model of Podlaha and Landolt, according to which a mixed-metal complex of cobalt(II), citrate and molybdenum dioxide is adsorbed on the surface and promotes Mo reduction. 

---