Tungsten carbonyl

Table 28 Photo-driven tungsten carbonyl- assisted 1,3-dipolar cycloadditions...

Tungsten carbonyl is also used as a metal source at 350 00°C but carbon tends to remain incorporated in the stmcture.P l The reaction is as follows ... 

This reaction proceeds at a much faster rate than the hydrogen reduction of WFg. The result is erosion of the silicon substrate causing encroachment and tunnel defects. The use of a different precursor, such as tungsten carbonyl, W(CO)g, may solve this problem. CVD tungsten is presently limited mostly to multilevel-via-fill applications. 

Feldmann J, WR Cullen (1997) Occurrence of volatile transition metal compounds in landfill has synthesis of molybdenum and tungsten carbonyls in the environment. Environ Sci Technol 31 2125-2129. 

The unhindered phospha-alkene (175) has been characterised in solution as a complex involving ir-donation from the double bond to a tungsten carbonyl acceptor. This complex reacts with 1,3-dienes to give adducts e.g. (176), in which the phosphorus atom... 

The possible mechanisms which one might invoke for the activation of these transition metal slurries include (1) creation of extremely reactive dispersions, (2) improved mass transport between solution and surface, (3) generation of surface hot-spots due to cavitational micro-jets, and (4) direct trapping with CO of reactive metallic species formed during the reduction of the metal halide. The first three mechanisms can be eliminated, since complete reduction of transition metal halides by Na with ultrasonic irradiation under Ar, followed by exposure to CO in the absence or presence of ultrasound, yielded no metal carbonyl. In the case of the reduction of WClfc, sonication under CO showed the initial formation of tungsten carbonyl halides, followed by conversion of W(C0) , and finally its further reduction to W2(CO)io Thus, the reduction process appears to be sequential reactive species formed upon partial reduction are trapped by CO. 

The Group VI metal carbonyls demonstrate good activity in the WGSR, but differ significantly from ruthenium carbonyl in several ways. Tables IV and V summarize some WGSR experiments with chromium and tungsten carbonyls in a tetrahydrofuran-water solvent system. 

With Cr(C0) , base clearly promotes the WGSR. However, unlike ruthenium carbonyl, chromium and tungsten carbonyls demonstrate less activity with trimethylamine than with carbonate as base. 

Molybdenum and tungsten carbonyl hydride complexes were shown (Eqs. (16), (17), (22), (23), (24) see Schemes 7.5 and 7.7) to function as hydride donors in the presence of acids. Tungsten dihydrides are capable of carrying out stoichiometric ionic hydrogenation of aldehydes and ketones (Eq. (28)). These stoichiometric reactions provided evidence that the proton and hydride transfer steps necessary for a catalytic cycle were viable, but closing of the cycle requires that the metal hydride bonds be regenerated from reaction with H2. 

The tungsten carbonyl, Wx(CO) was synthesized and studied as a catalyst for ORR reactions.198-200 Through these studies, it was found that the tungsten carbonyl was active for ORR. The Koutecky-Levich plots showed that the electrons transferred approached four during ORR.199 It was also found that the tungsten carbonyl was active for the electrolysis of water.199... 

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 reverse sequence is also possible as was demonstrated by the attack of a vic-bisamine on a tungsten carbonyl cation [(PhCsCPh)3W(CO)]. ... 

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