Tungsten carbonyl, W

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. 

Finally, blanket tungsten can be deposited from tungsten carbonyl, W C0)6. Some data has been published and such depositions appear to result in films with appreciable carbon and oxygen.23... 

Tungsten carbide from the decomposition of tungsten carbonyl (W(CO)5 at 350-400 C although carbon tends to remain incorporated in the structure... 

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. 

Tungsten carbonyl may be dissolved in an organic solvent and analyzed by GC/MS. The compound should form mass spectra corresponding to the masses for W(CO)6, CO and W. The compound may be decomposed thermally and product carbon monoxide transported with helium onto a GC column to be analyzed by GC-TCD or GC/MS. Residue tungsten metal is extracted with nitric acid-hydrofluoric acid, diluted with water, and analyzed (See Tungsten). 

Group 16 metal carbonyls are also effective in the PKR. Hoye prepared a pre-activated tungsten catalyst (W(GO)sTHF) by replacing one of the COs on tungsten with THF photochemically, and successfully applied it to PKR. This semicatalytic system constitutes one of the early examples useful even for the substrates bearing electron-withdrawing groups. 

The stability of complexes of the type [W(OR)6] is quite remarkable. It has been shown28 that short exposure of [W2(OPri)6py2] to approximately two molar equivalents of CO gives two products, one of which is (1). This structure can best be viewed as a substituted tungsten carbonyl in which two cis CO groups have been replaced by donor atoms of the bidentate neutral ligand [W(OPr )6], This complex is unusual in that it contains two atoms of the same element in oxidation states that differ by six units. 

There are two general procedures for the preparation of monomeric W11 complexes.269 In one, substituted tungsten carbonyls are oxidized by halogens under controlled conditions as exemplified by equations (18) and (19). In the second, W(CO)6 is first oxidized by Cl2 or Br2 at low temperature, followed by reaction of the oxidized product with the appropriate ligands. This preparative procedure is exemplified by equation (20). 

Chromium and tungsten carbonyl complexes with 2-phenyl- (L) and 2-methylbenzo-l,3-tell-urazole (L ) were prepared in an argon atmosphere as follows. Cr(CO)6 (0.660 g, 3 mmol) or W(CO)6 (1.05g, 3 mmol) in 100 mL of dried THF saturated with argon was exposed to a mercury lamp until the evolution of 3 mmol of CO. After irradiation, the corresponding benzotellurazole (3 mmol) was added to the solution, and the mixture was stirred for 1 hr. The solution was filtered off, and the solvent was removed in a rotary evaporator. The solid residue was placed in a sublimation apparatus to remove unreacted metal carbonyl in a high vacuum and then recrystallized twice from hexane. 

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