TITANIUM (II) η5-ALKYLPENTADIENYLS

Titanium (II) bis(2,4-dimethylpentadienyl) Ti(η5-2,4-Me2-C5H5)2

Fig. Titanium bis (2,4-dimethyl-pentadienyl) formula

      Bis(2,4-dimethylpentadienyl)titanium (II) Ti(2,4-Me2-C5H5)2  is a dark-green compound with low melting point (-10°C) and high vapor pressure. It has open-sandwich structure (Fig.), which contains Ti atom in oxidation state (+2) (14-electron compound), which is sandwiched between a pair of 2,4-dimethylpentadienyl ligands.

      Unlike its well-known counterpart titanocene Ti(η5-C5H5)2, bis(2,4-dimethylpentadienyl) titanium is stable compound at room temperature.

     Synthesis of Ti(2,4-Me2-C5H5)2: most easy way is reaction of  TiCl2 with 2,4-dimethylpentadienyl (synthesis details see in [[i]]).

      The divalent nature of the Ti atom in Ti(2,4-Me2-C5H5)2 , makes it an attractive candidate as precursor for preparation of Ti metal films by MOCVD, as divalent titanium is more easily reduced to Ti (0) than is Ti (+3) and Ti (+4).

[i] Organometal Synthesis, 1986, Vol. 3, pp 138-139

Ti(2,4-Me2Cp)2 for Ti metal by MOCVD

     Bis(2,4-dimethylpentadienyl) titanium Ti(2,4-Me2-C5H5)2 (or its Lewis-base-stabilized form) was applied as precursor for the growth of highly-conformal Ti-containing films by low-pressure CVD (at pressure 0.1-10 Torr), at 300-600° C deposition temperature. The bubbler containing Ti(2,4-Me2-C5H5)2 was maintained at 40-100°C temperature (carrier gas flow 20-400 sccm). Optimal process parameters were deposition temperature ~420° C, process pressure ~0.5 torr, Ti(2,4-Me2-C5H5)2 precursor bubbler temperature ~50° C, precursor carrier flow ~40 sccm. If carrier gas is noble gas or N2, the principal deposition product is Ti metal having some C contamination in the form of titanium carbide TiCx. The reaction scheme is following: Ti[2,4-Me2-C5H5]2 → Ti+CHn +CH. [[i]]

      If reducing agent such as H2 is introduced, Ti metal film having less incorporated reaction byproducts is deposited.

      Titanium precursor Ti(2,4-Me2-C5H5)2 can be also let reacted with a Lewis base, such as NH3, CN, or H2N-CH2-CH2-NH2 (EDTA). The resultant compound is somewhat more stable than unadducted Ti(2,4-Me2-C5H5)2.

      If a reactive gas like NH3 is introduced to the CVD chamber flowing Ti(2,4-Me2-C5H5)2 precusor, the TiN film is grown. When Si-containing compound (like SiH4 or Si2H6) is allowed to react with bis(2,4-dimethylpentadienyl)titanium precursor, the layer mainly consisting of titanium silicide TiSix is formed.

 [i] Brenda D. Wanner,, US5273783A, US Grant, 1993, https://patents.google.com/patent/US5273783A/en, « Chemical vapor deposition of titanium and titanium containing films using bis (2,4-dimethylpentadienyl) titanium as a precursor « , patentimages.storage.googleapis.com/39/32/c4/d0cab90ebc23bd/US5273783.pdf

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