Early Transition Metal Alkyl and Tetrahydroborate Complexes

Jensen, James Allen

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Description

Title

Early Transition Metal Alkyl and Tetrahydroborate Complexes

Author(s)

Jensen, James Allen

Issue Date

1988

Doctoral Committee Chair(s)

Girolami, Gregory S.

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(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.

Graduation Semester

1988

Type of Resource

text

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