Abstract
Reactions between terminal alkynes or aromatic ketones and titanapinacolate complexes (DMSC)-Ti(OCAr2CAr2O) (2, Ar = Ph, and 3, Ar = p- MeC6H4; DMSC = 1,2-alternate dimethylsilyl-bridged p-tert-butylcalix[4]arene dianion) occur via rupture of the C-C bond of the titanacycle. Thus, reactions of 2 and 3 with terminal alkynes produce 2-oxatitanacyclopent-4-ene or 2-oxatitanacycloheptadiene complexes along with free Ar2CO. These compounds have been characterized spectroscopically and by X-ray crystallography. Because metallapinacolate intermediates have been implicated in important C-C bond-forming reactions, such as pinacol coupling and McMurry chemistry, the mechanism of the fragmentation reactions was studied. Analysis of the kinetics of the reaction of (DMSC)Ti {OC(p-MeC6H4)2C (p-MeC6H4)2O} (3) with Bu1C≡CH revealed that the fragmentation reactions proceed via a preequilibrium mechanism, involving reversible dissociation of titanapinacolate complexes into (DMSC)Ti(η2-OCAr2) species with release of a ketone molecule, followed by rate-limiting reaction of (DMSC)Ti (η2-OCAr2) species with an alkyne or ketone molecule.
Original language | English |
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Pages (from-to) | 12217-12224 |
Number of pages | 8 |
Journal | Journal of the American Chemical Society |
Volume | 124 |
Issue number | 41 |
DOIs | |
State | Published - Oct 16 2002 |
ASJC Scopus subject areas
- Catalysis
- Chemistry (all)
- Biochemistry
- Colloid and Surface Chemistry