TY - JOUR
T1 - Mechanistic insight into fragmentation reactions of titanapinacolate complexes
AU - Kingston, Jesudoss V.
AU - Ozerov, Oleg V.
AU - Parkin, Sean
AU - Brock, Carolyn P.
AU - Ladipo, Folami T.
PY - 2002/10/16
Y1 - 2002/10/16
N2 - 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.
AB - 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.
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U2 - 10.1021/ja0271577
DO - 10.1021/ja0271577
M3 - Article
C2 - 12371862
AN - SCOPUS:0037120844
SN - 0002-7863
VL - 124
SP - 12217
EP - 12224
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 41
ER -