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Isolation and characterization of a monomeric cationic titanium hydride
Kuangbiao Ma1, Warren E Piers, Yuan Gao
1Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4.
Journal of the American Chemical Society
|May 6, 2004
Summary
Titanium methyl cations with Cp and Cp* ligands react differently with hydrogen. The Cp* ligand provides steric and electronic advantages, leading to a stable Ti(IV) hydride, unlike the reduced Ti(III) species from the Cp ligand.
Area of Science:
- Organometallic Chemistry
- Catalysis
- Materials Science
Background:
- Methyl cations stabilized by tri-tert-butylphophinimine ligands are key intermediates.
- Understanding ligand effects on metal center reactivity is crucial in catalysis.
Purpose of the Study:
- To investigate the contrasting reactivity of methyl cations with Cp (cyclopentadienyl) and Cp* (pentamethylcyclopentadienyl) ligands upon reaction with H2.
- To characterize the resulting titanium species and elucidate the role of ligand sterics and electronics.
Main Methods:
- Generation of methyl cations from neutral dimethyl precursors using a strong boron-based anion.
- Reaction with H2 gas and characterization of products using X-ray crystallography, NMR spectroscopy, and other analytical techniques.
- Solvent cleavage studies to isolate monomeric species.
Main Results:
- The Cp-ligated methyl cation underwent hydrogenolysis, reducing to a Ti(III) dimer.
- The Cp*-ligated methyl cation formed a stable, unreactive Ti(IV) hydride, which could be isolated as a THF adduct.
- The Ti(IV) hydride reacted with haloarenes to yield cationic titanium bromide species.
Conclusions:
- The Cp* ligand's enhanced steric bulk and electron donation stabilize the Ti(IV) oxidation state and hydride product.
- Ligand choice significantly influences the reaction pathway and stability of titanium complexes.
- These findings offer insights into controlling reactivity in organometallic catalysis.