Tungsten hexacarbonyl catalysts

Various appHcations such as lubricant additives, dyes, pigments, and catalysts are under investigation. Tungsten can be deposited from tungsten hexacarbonyl, but carbide formation and gas-phase nucleation present serious problems (1,2). As a result, tungsten halides are the preferred starting material. 

It has been known since 1975 that the photolysis of tungsten hexacarbonyl in tetrachlorocarbon solutions affords an olefin metathesis catalyst [1-3]. 

In 1964, Bank and Bailey [2] reported the first catalytic reaction on the same substrate, using heterogeneous catalysts derived from molybdenum or tungsten hexacarbonyles supported on alumina. 

Chromium, molybdenum and tungsten hexacarbonyl, and palladium oxide were purchased from Strem Chemicals (7 Mulliken Way, Dexter Industrial Park, P.O. Box 108, Newburyport, MA 01950). rm-Butylisocyanide is available commercially from Aldrich Chemical Co. (P.O. Box 355, Milwaukee, WI 53201) or it may be synthesized in 50-60-g quantities by the method of Gokel et al. ° The catalyst CoCl2 2H20 was obtained by heating CoClj HjO under vacuum (O.ltorr) at 50° for approximately 5h. This catalyst can be readily handled and stored in air. It does, however, slowly reabsorb atmospheric moisture over a period of several months, necessitating... 

Method 5. Other Methods of Initiation Catalysts were prepared by the interaction of molybdenum or tungsten hexacarbonyl with bicyclo(2.2.1]heptadiene or cycloheptatriene (Si). They were described as being effective for the cyclopolymerization of [9] and [143]. 

As the scope of the reaction increased, the name Olefin Metathesis was introduced by Goodyear, who also pioneered the use of homogeneous catalysts. The reaction had first been recognized during experiments on the development of a heterogeneous catalyst to replace mineral acids in alkylation reactions. Molybdenum hexacarbonyl catalyst supported on alumina produced 2-pentene (40%) from mixed n-butenes together with propylene (51%) and hexene (9%). Tungsten hexacarbonyl was less active than the molybdenum catalyst, and in total contrast, it was found that chromium hexacarbonyl acted as a polymerization catalyst. 

Sulfoxide adducts of chromium, molybdenum, and tungsten carbonyls have been studied as catalysts for the polymerization of monomers such as vinyl chloride (248). Simple adducts of the type [M(CO)5(Me2SO)] may be prepared by carbonyl displacement from the corresponding hexacarbonyl. Photochemical reactions are frequently necessary to cause carbonyl displacement in this manner, many carbonyl complexes of higher sulfoxides have been prepared (255, 256). Infrared (257) and mass spectral studies (154) of these complexes have appeared, and infrared data suggest that S-bonding may occur in Cr(0) sulfoxide complexes, although definitive studies have not been reported. 

The simple metal hexacarbonyls of molybdenum and tungsten will catalyze allylic alkylation, with dramatic effects on the regioselectivity. The comparison of Mo(CO)6 with Pd° shows a remarkable contrast in regioselectivity (equation 67). The basis for the selectivities is somewhat mysterious, especially considering another dramatic reversal of selectivity with change in anion, from malonate, using Mo(CO)6 and the same conditions. This regioselectivity of Mo carbonyl catalysts has been used to synthesize (7 )-baclofen, as shown in equation (68). 

The role of transition-metal carbonyls and particularly those of the Group 6 metals in homogeneous photocatalytic and catalytic processes is a matter of considerable interest [1]. UV irradiation especially provides a simple and convenient method for generation of thermally active co-ordinately unsaturated catalyst for alkenes or alkynes transformation. By using tungsten and molybdenum carbonyl compounds as catalysts, alkenes and alkynes can be metathesized, isomerised and polymerized. Photocatalytic isomerization of alkenes in the presence of molybdenum hexacarbonyl was observed by Wringhton thirty years ago [2]. Carbonyl complexes of molybdenum catalyze not only... 

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