444095-29-8Relevant academic research and scientific papers
Asymmetric induction via short-lived chiral enolates with a chiral C-O axis
Yoshimura, Tomoyuki,Tomohara, Keisuke,Kawabata, Takeo
supporting information, p. 7102 - 7105 (2013/06/27)
A novel method has been developed for the asymmetric cyclization of alkyl aryl ethers. The reactions were assumed to proceed via short-lived chiral enolate intermediates with a chiral C-O axis to give cyclic ethers with tetrasubstituted carbon in up to 99% ee. The half-life of racemization of the chiral enolate intermediate was roughly estimated to be ～1 s at -78 C.
Stereoselective ring-opening polymerization of a racemic lactide by using achiral salen- and homosalen-aluminum complexes
Nomura, Nobuyoshi,Ishii, Ryohei,Yamamoto, Yoshihiko,Kondo, Tadao
, p. 4433 - 4451 (2008/02/09)
Highly isotactic polylactide or poly(lactic acid) is synthesized in a ring-opening polymerization (ROP) of racemic lactide with achiral salen- and homosalen-aluminum complexes (salenH2 = N,N′-bis(salicylidene) ethylene-1,2-diamine; homosalenH2 = N,N′-bis(salicylidene) trimethylene-1,3-diamine). A systematic exploration of ligands demonstrates the importance of the steric influence of the Schiff base moiety on the degree of isotacticity and the backbone for high activity. The complexes prepared in situ are pure enough to apply to the polymerizations without purification. The crystal structures of the key complexes are elucidated by X-ray diffraction, which confirms that they are chiral. However. analysis of the 1H and 13C NMR spec tra unambiguously demonstrates that their conformations are so flexible that the chiral environment of the complexes cannot be maintained in solution at 25°C and that the complexes are achiral under the polymerization conditions. The flexibility of the back-bone in the propagation steps is also documented. Hence, the isotacticity of the polymer occurs due to a chain-end control mechanism. The highest reactivity in the present system is obtained with the homosalen ligand with 2.2-dimethyl substituents in the backbone (ArCH=NCH2CMe2CH2N=CHAr), whereas tBuMe2Si substituents at the 3-positions of the salicylidene moieties lead to the highest selectivity (Pmeso,= 0.98; T m = 210°C). The ratio of the rate constants in the ROPs of racemic lactide and L-lactide is found to correlate with the stereoselectivity in the present system. The complex can be utilized in bulk polymerization, which is the most attractive in industry, although with some loss of stereoselectivity at high temperature, and the afforded polymer shows a higher melting temperature (Pmeso = 0.92, Tm up to 189°C) than that of homochiral poly(L-lactide) (Tm = 162-180°C). The "livingness" of the bulk polymerization at 130°C is maintained even at a high conversion (97-98%) and for an extended polymerization time (1-2 h).
Efficient two-step synthesis of salicylaldehydes via directed ortho-lithiation of in situ N-silylated O-aryl N-isopropylcarbamates
Kauch, Matthias,Hoppe, Dieter
, p. 1575 - 1577 (2007/10/03)
O-Aryl N-isopropylcarbamates, conveniently prepared from phenols and isopropyl isocyanate, are subjected to an efficient ortho-lithiation protocol to afford the corresponding salicylaldehydes in a one-pot operation in high yields. Georg Thieme Verlag Stuttgart.
Intramolecular [4 + 2] cycloadditions of benzynes with conjugated enynes, arenynes, and dienes
Hayes, Martin E.,Shinokubo, Hiroshi,Danheiser, Rick L.
, p. 3917 - 3920 (2007/10/03)
(Chemical Equation Presented) Benzynes generated by the reaction of o-(trimethylsilyl)aryl triflates with TBAT participate in intramolecular [4 + 2] cycloadditions with conjugated enynes, arenynes, and dienes to furnish highly condensed polycyclic aromatic compounds.
Non-metallocene compounds, method for the production thereof and use of the same for the polymerisation of olefins
-
, (2008/06/13)
The invention relates to a method for producing special transition metal compounds, to novel transition metal compounds and to the use of the same for the polymerisation of olefins.
Syndiospecific living propylene polymerization catalyzed by titanium complexes having fluorine-containing phenoxy-imine chelate ligands
Mitani, Makoto,Furuyama, Rieko,Mohri, Jun-ichi,Saito, Junji,Ishii, Seiichi,Terao, Hiroshi,Nakano, Takashi,Tanaka, Hidetsugu,Fujita, Terunori
, p. 4293 - 4305 (2007/10/03)
The propylene polymerization behavior of a series of Ti complexes featuring fluorine-containing phenoxy-imine chelate ligands is reported. The Ti complexes combined with methylalumoxane (MAO) can be catalysts for living and, at the same time, stereospecific polymerization of propylene at room temperature or above. DFT calculations suggest that the attractive interaction between a fluorine ortho to the imine nitrogen and a β-hydrogen of a growing polymer chain is responsible for the achievement of room-temperature living propylene polymerization. Although the Ti complexes possess C2 symmetry, they are capable of producing highly syndiotactic polypropylenes. 13C NMR is used to demonstrate that the syndiotacticity is governed by a chain-end control mechanism and that the polymerization is initiated exclusively via 1,2-insertion followed by 2,1-insertion as the principal mode of polymerization. 13C NMR spectroscopy also elucidated that the polypropylenes produced with the Ti complexes possess regio-block structures. Substitutions on the phenoxy-imine ligands have profound effects on catalytic behavior of the Ti complexes. The steric bulk of the substituent ortho to the phenoxy oxygen plays a decisive role in achieving high syndioselectivity for the chain-end controlled polymerization. Over a temperature range of 0-50 °C, Ti complex having a trimethylsilyl group ortho to the phenoxy oxygen forms highly syndiotactic, nearly monodisperse polypropylenes (94-90% rr) with extremely high peak melting temperatures (Tm = 156- 149 °C). The polymerization behavior of the Ti complexes can be explained well by the recently proposed site-inversion mechanism for the formation of syndiotactic polypropylene by a Ti complex having a pair of fluorine-containing phenoxy-imine ligands.
Fluorine- and trimethylsilyl-containing phenoxy-imine Ti complex for highly syndiotactic living polypropylenes with extremely high melting temperatures
Mitani, Makoto,Furuyama, Rieko,Mohri, Jun-ichi,Saito, Junji,Ishii, Seiichi,Terao, Hiroshi,Kashiwa, Norio,Fujita, Terunori
, p. 7888 - 7889 (2007/10/03)
A fluorine- and trimethylsilyl-containing phenoxy-imine titanium complex was synthesized and the structure was determined by an X-ray analysis. The complex on activation with MAO initiates highly controlled syndiospecific living propylene polymerization to form extremely high Tm syndiotactic polypropylenes (Mw/Mn = 1.05-1.08, Tm = 156-152 °C) at 0 or 25 °C. Moreover, at 50 °C, the complex afforded monodisperse syndiotactic polypropylene with very high Tm's of 149, 150 °C. In contrast, complexes having a t-Bu group instead of the silyl group provided lower tacticity polymers with much lower Tm's. In addition, we revealed the substituent effect that plays a key role for the highly controlled syndiospecific polymerization displayed by the catalyst. Copyright
Alkene aziridination and epoxidation catalyzed by chiral metal salen complexes
O'Connor,Wey,Burrows
, p. 1001 - 1004 (2007/10/02)
New chiral metal salen complexes substituted in the 3 position with bulky silyl groups (TMS, TBDMS) have been synthesized. Although some of these complexes catalyzed the epoxidation of unfunctionalized olefins in moderate to high ee's, they catalyzed the aziridination of cis-β-methylstyrene without any asymmetric induction.
