Titanium Alkoxides as Initiators for the Controlled Polymerization of Lactide
作者:Youngjo Kim、G. K. Jnaneshwara、John G. Verkade
DOI:10.1021/ic026139n
日期:2003.3.1
afforded polymers in higher yields and with larger molecular weights than their six-membered ring counterparts. Steric hindrance of the rings was found to significantly affect polymer yields. Increased heterotactic-biased poly(rac-LA) was formed as the number of chlorine atoms increased in TiCl(x)(O-i-Pr)(4)(-)(x). In solution polymerizations, titanium alkoxides catalyzed controlledpolymerizations of LA
Conversion of Tricoordinate to Hexacoordinate Phosphorus. Formation of a Phosphorane−Phosphatrane System<sup>1</sup>
作者:Natalya V. Timosheva、A. Chandrasekaran、Roberta O. Day、Robert R. Holmes
DOI:10.1021/ja012579m
日期:2002.6.1
tris(2-hydroxy-3-tert-butyl-5-methylbenzyl)amine (4) led to the formation of a tricoordinated phosphonite (1) when R = Ph and to a hexacoordinated phosphorane-phosphatrane (2) when R = Et. The X-ray structures showed that the unreacted hydroxyl group in 1 oxidatively added to phosphorus in 2 leading to the formation of three additional bonds, a P[bond]O, a P[bond]H, and a P[bond]N linkage. In solution, (31)P measurements
Steric Stabilization of a Monomeric Proalumatrane: Experimental and Theoretical Studies
作者:Weiping Su、Junji Kobayashi、Arkady Ellern、Takayuki Kawashima、John G. Verkade
DOI:10.1021/ic7010327
日期:2007.9.1
Treatment of tripodal tris(3-tett-butyl-2-hydroxy-5-methylbenzyl)amine (L) with 1 equiv of trimethylaluminum in toluene gave the stable proalumatrane (AIL) (1) [wherein L = tris(3-tert-butyl-5-methyl-2-oxidobenzyl)amine] featuring a distorted trigonal monopyramidal four-coordinate aluminum geometry. An analogous reaction uses the less sterically congested isomer of L, namely, tris(5-tert-butyl-2-hydroxy-3-methylbenzyl)amine provided dimeric (AIL')2 (2) [wherein L' = tris(5-tert-butyl-3-methyl-2-oxidobenzyl)amine], which contains two bridging alumatrane moieties possessing five-coordinate TBP aluminum geometries. Reaction of AIL with water provided the adduct H2O center dot AIL (3), a species that is representative of a coordinatively stabilized intermediate in the hydrolysis of an aluminum alkoxide. Theoretical calculations revealed that considerable stabilization energy is obtained by the coordination of a water molecule to the tetracoordinate aluminum in AIL and that this result is consistent with the postulate that the Lewis acidity of AIL exceeds that of boron trifluoride, despite the presence of the transannular N -> Al bond in AIL.
KOSTYUCHENKO, V. M., HOB. NAPRAVLENIYA ISPOLZ. PRODUKTOV NEFTEPERERAB. I NEFTEXIMII, M.,(1989)+