Tetra(allyl)tungsten W(h3-C3H5)4 is a white, moderately air sensitive, and volatile solid (melting point 95°C with decomposition), which can be easily sublimed in vacuum at 60 °C.
Tetraallyltungsten is synthesized by the metathesis reaction of tungsten (VI) phenoxide with Grignard reagent allyl magnesium bromide in THF as solvent at 60°C (yield 60 %): W(OPh)6 + 6 BrMgCH2CH=CH2→ W(h3-C3H5)4 +C6H10 +6 “BrMg(OPh)”
Tetraallyltungsten was applied as MOCVD precursor for the growth of various W-containing layers, like metallic W, WO3 (decomposition onset temperature in CVD conditions 95°C).
Tetra(allyl)tungsten W(h3-C3H5)4 has been tested as a precursor for the growth of tungsten films by MOCVD. High carbon content found in grown W layers, the possible explanation is α-Hydride elimination. Most probably W-carbene, -carbyne, -alkylidene and metallacycles are formed as intermediates because such complexes are relatively stable species and take part in the decomposition mechanism of W(h3-C3H5)4, for example:
W(h3-C3H5)4 → [(h3-C3H5)2W=CH-CH=CH2] + H2C=CH-CH3
[(h3-C3H5)2W=CH-CH=CH2] → WC + 2 C + C3H8 + C3H6
Less carbon is found in the deposited W films when a CO- or H2/CO-rich mixture as carrier gas; hexadiene as the main volatile compound when CO is used as carrier gas.
Tetra(allyl)tungsten was tested as MOCVD precursor for the deposition of amorphous W films on pyrex substrates. The deposited W coatings were characterized by XRD, Auger, ESCA, SEM, and resistivity measurements. Propene C3H6 was main volatile pyrolysis products.[i]
[i] R.U. Kirss, J. Chen, R.B. Hallock, MRS Proc., 1991, Vol.250, « Chemical Vapor Deposition of Tungsten and Molybdenum Films From M(η3–C3H5)4 (M=Mo, W) », DOI: http://dx.doi.org/10.1557/PROC-250-303