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Title:Early Transition Metal Alkyl and Tetrahydroborate Complexes
Author(s):Jensen, James Allen
Doctoral Committee Chair(s):Girolami, Gregory S.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Inorganic
Physics, Condensed Matter
Engineering, Materials Science
Abstract:An investigation of early transition metal alkyl and tetrahydroborate complexes as catalytic models and ceramic precursors has been initiated. The compounds MX$\sb2$ (dmpe)$\sb2$, dmpe = 1,2-bis(dimethylphosphino)ethane, for M = Ti, V, Cr, and X = Br, I, BH$\sb4$, have been prepared. These complexes are paramagnetic and have been shown by X-ray crystallography to have trans-octahedral structures. The BH$\sb4\sp{-}$ groups in Ti(BH$\sb4)\sb2$(dmpe)$\sb2$ bond to the metal in a bidentate manner. This structure is in marked contrast to the structure of the vanadium analogue, V(BH$\sb4)\sb2$(dmpe)$\sb2$, which displays two unidentate BH$\sb4\sp{-}$ groups.
Alkylation of Ti(BH$\sb4)\sb2$(dmpe)$\sb2$ with LiMe results in the complex TiMe$\sb2$(dmpe)$\sb2$ which is diamagnetic in both solution and solid state. Single crystal X-ray and neutron diffraction studies show that there may be strong Ti-C $\pi$-bonding. A tetragonal compression along the C-Ti-C bond vector accounts for the observed diamegnetism.
A series of complexes of the formula Ti(BH$\sb4)\sb3$(PR$\sb3)\sb2$ has been prepared where PR$\sb3$ = PMe$\sb3$, PEt$\sb3$, PMe$\sb3$Ph, and P(OMe)$\sb3$. The X-ray crystal structure of Ti(BH$\sb4)\sb3$(PMe$\sb3)\sb2$ reveals a pseudo trigonal bipyramidal geometry in which two BH$\sb4\sp{-}$ groups display an unusual "side-on" bonding mode. The "side-on" ligation mode has been attributed to a Jahn-Teller distortion of the orbitally degenerate d$\sp1$ ground state. In contrast, the non-Jahn-Teller susceptible vanadium analogue, V(BH$\sb4)\sb3$(PMe$\sb3)\sb2$, possesses a nearly ideal D$\sb{\rm 3h}$ geometry with three bidentate tetrahydroborate groups. Addition of excess PMe$\sb3$ to V(BH$\sb4)\sb3$(PMe$\sb3)\sb2$ leads to the vanadium(II) hydride-bridged dimer (V(H)(BH$\sb4$)(PMe$\sb3)\sb2\rbrack\sb2$, while addition of PMe$\sb3$ and water forms the vanadium(III) oxo dimer (V(BH$\sb4)\sb2$(PMe$\sb3)\sb2\rbrack\sb2\lbrack\mu$-O) which has been structurally characterized.
The compound Ti(CH$\sb2$CMe$\sb3)\sb4$ can be prepared by addition of Ti(OEt)$\sb4$ to LiCH$\sb2$CMe$\sb3$. Sublimation of Ti(CH$\sb2$CMe$\sb3)\sb4$ over a substrate heated to 250$\sp\circ$C results in the chemical vapor deposition of amorphous TiC thin films. This CVD approach has been extended to the Group 4 borides: Ti(BH$\sb4)\sb3$(MeOCH$\sb2$CH$\sb2$OMe) yields TiB$\sb2$ at 200$\sp\circ$C, while Zr(BH$\sb4)\sb4$ and Hf(BH$\sb4)\sb4$ yield ZrB$\sb2$ and HfB$\sb2$ at 250$\sp\circ$C using the CVD process. The X-ray crystal structure of Ti(BH$\sb4)\sb3$(MeOCH$\sb2$CH$\sb2$OMe) is reported.
Issue Date:1988
Description:198 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.
Other Identifier(s):(UMI)AAI8823157
Date Available in IDEALS:2014-12-15
Date Deposited:1988

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