title: Mechanistic insight into fragmentation reactions of titanapinacolate complexes.
abstract: Reactions between terminal alkynes or aromatic ketones and titanapinacolate complexes (DMSC)Ti(OCAr(2)CAr(2)O) (2, Ar = Ph, and 3, Ar = p-MeC(6)H(4); 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 Ar(2)CO. 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-MeC(6)H(4))(2)C(p-MeC(6)H(4))(2)O] (3) with Bu(t)Ctbd1;CH revealed that the fragmentation reactions proceed via a preequilibrium mechanism, involving reversible dissociation of titanapinacolate complexes into (DMSC)Ti(eta(2)-OCAr(2)) species with release of a ketone molecule, followed by rate-limiting reaction of (DMSC)Ti(eta(2)-OCAr(2)) species with an alkyne or ketone molecule.
authors.affiliation: Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, USA.
authors.forename: Jesudoss V
authors.initials: JV
authors.lastname: Kingston
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Ozerov
authors.forename: Sean
authors.initials: S
authors.lastname: Parkin
authors.forename: Carolyn P
authors.initials: CP
authors.lastname: Brock
authors.forename: Folami T
authors.initials: FT
authors.lastname: Ladipo