Variously substituted titanacalixarenes were synthesised and tested for their performance as catalysts in ethylenepolymerisation: p-tert-butylcalix[4]arene was derivatised to afford distal diether p-tert-butylcalix[4]arenes L1–L4, distal dihydroxy-depleted L5, proximal dihydroxy-depleted L6, proximal diether p-tert-butylcalix[4]arene L7, proximal intrabridged disiloxane L8 and proximal monoether L9
Mechanistic Insight into Fragmentation Reactions of Titanapinacolate Complexes
作者:Jesudoss V. Kingston、Oleg V. Ozerov、Sean Parkin、Carolyn P. Brock、Folami T. Ladipo
DOI:10.1021/ja0271577
日期:2002.10.1
Reactions between terminal alkynes or aromatic ketones and titanapinacolate complexes (DMSC)Ti(OCAr(2)CAr(2)O) (2, Ar = Ph, and 3, At = p-MeC(6)H(4); DMSC = 1,2-alternate dimethylsilyl-bridged p-tertbutylcalix[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)TiOC(p-MeC(6)H(4))(2)C(p-MeC(6)H(4))(2)O} (3) with Bu(t)C=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.