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Title:Part I. Synthesis, characterization, and reactivity of low valent organotitanium complexes. Part II. Chemical vapor deposition of rhodium metal thin films
Author(s):You, Yujian
Doctoral Committee Chair(s):Girolami, Gregory S.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Inorganic
Engineering, Materials Science
Abstract:Titanium(II) complex CpTiCl(dmpe)$\sb2$ is prepared by reducing (CpTiCl$\sb2)\sb{\rm x}$ with n-butyllithium in the presence of 1,2-bis(dimethylphosphino)ethane (dmpe). Subsequent treatment with methyllithium or n-butyllithium affords CpTiMe(dmpe)$\sb2$ and CpTiH(dmpe)$\sb2$, respectively. The crystal structures of CpTiX(dmpe)$\sb2$ (X = Cl, Me, H) show unusually long metal ligand distances. Analogous treatment of (Cp$\sp*$Ti(BH$\sb4$)Cl) $\sb2$ with n-butyllithium affords Cp$\sp*$Ti(BH$\sb4$)(PP), where PP is dmpe or (t-butyl)tris(dimethylphosphino-methyl)silane. All of these titanium(II) complexes catalyze oligomerization of ethylene to 1-butene, 2-ethyl-1-butene, and 3-methyl-1-pentene, probably via metallacyclopentane intermediates.
Oxidations of the neutral titanium(II) complexes with 1,1$\sp\prime$-dimethylferrocinium salts afford the first examples of cationic alkyltitanium(III) complexes: (CpTiX(dmpe)$\sb2\rbrack$ BAr$\sb4,$ where Ar = Ph or 3,5-(CF$\sb3)\sb2$C$\sb6$H$\sb3$ (FPB). Two other complexes, (TiMe$\rm \sb2(dmpe)\sb2\rbrack$ FPB and (Cp$\sp*$Ti(BH$\sb4$)(dmpe)) FPB, have been prepared by oxidation of the corresponding titanium(II) species. Crystallographic studies of (CpTiH(dmpe)$\sb2$) FPB, (TiMe$\sb2$(dmpe)$\sb2$) FPB, and (Cp$\sp*$Ti(BH$\sb4$)(dmpe)) FPB reveal that the titanium(III) cations show a lengthening of the Ti-P bond distances owing to a decrease in metal-ligand $\pi$-back-bonding. The cationic titanium(III) alkyls neither oligomerize nor polymerize ethylene.
Treatment of Rh(hfac)(CH$\sb2$=CH$\sb2)\sb2$ (hfac = hexafluoroacetylacetonate) with vinyl-trimethylsilane, 1,2-bis(trimethylsilyl)acetylene, Cu(hfac)(COT), or PMe$\sb3$ affords a series of new complexes. High purity rhodium films have been deposited at 200-300 $\sp\circ$C using Rh(hfac)(CH$\sb2$ = CH$\sb2)\sb2$ as a CVD precursor. The deposition occurs via the disproportionation reaction 3 Rh(hfac)(alkene)$\sb2$ $\longrightarrow$ 2 Rh + Rh(hfac)$\sb3$ + 6 alkene. Ultra high vacuum studies show that Rh(hfac)(CH$\sb2$ = CH$\sb2)\sb2$ adsorbs molecularly on copper surfaces up to 130 K. The hfac groups are oriented perpendicular to the surface at 220 K. Reduction of rhodium(I) occurs at approximately 300 K. Decomposition of surface-bound hfac groups occurs at higher temperatures. This process does not occur under CVD conditions owing to the higher coverages characteristic of this process, which favor bimolecular reactions that lead to the assembly of the observed Rh(hfac)$\sb3$ product.
Issue Date:1996
Rights Information:Copyright 1996 You, Yujian
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9712495
OCLC Identifier:(UMI)AAI9712495

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