174265-24-8Relevant articles and documents
Siladifluoromethylation and Difluoromethylation onto C(sp3), C(sp2), and C(sp) Centers Using Ruppert-Prakash Reagent and Fluoroform
Aikawa, Kohsuke,Maruyama, Kenichi,Nitta, Junki,Hashimoto, Ryota,Mikami, Koichi
supporting information, p. 3354 - 3357 (2016/07/26)
Siladifluoromethylations and difluoromethylations on sp3, sp2, and sp carbons of lithiated carbamates, arenes, and terminal alkynes, respectively, have been attained by employing the Ruppert-Prakash reagent (CF3TMS) and fl
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).
Discovery and optimization of new chromium catalysts for ethylene oligomerization and polymerization aided by high-throughput screening
Jones, David J.,Gibson, Vernon C.,Green, Simon M.,Maddox, Peter J.,White, Andrew J. P.,Williams, David J.
, p. 11037 - 11046 (2007/10/03)
High throughput screening (HTS) of a 205 member Schiff base salicylaldimine ligand library derived from salicylaldehydes bearing bulky ortho-substituents, i.e., 9-anthracenyl, 1,4,5,8-tetramethylanthracenyl or triptycenyl, reacted in-situ with (p-tolyl)CrCl2(thf)3, identified two new classes of highly active chromium based systems for the Oligomerization and polymerization of ethylene, respectively. The polymerization system comprises bidentate ortho-substituted anthracenyl Schiff bases bearing small primary or secondary alkyl imine substituents. The Oligomerization catalysts are based upon tridentate orthotriptycenyl-substituted Schiff bases with pyridylmethyl or quinolyl substituents. Validation tests confirmed polymerization productivities of up to 3000 g·mmol-1h-1bar-1 for the polymerization catalyst systems while the oligomerization catalysts gave productivities up to 10 000 g·mmol-1h-1bar -1. Key catalyst precursors have been characterized by X-ray crystallography.
Fluorophenols and (trifluoromethyl)phenols as substrates of site-selective metalation reactions: To protect or not to protect
Marzi, Elena,Mongin, Florence,Spitaleri, Andrea,Schlosser, Manfred
, p. 2911 - 2915 (2007/10/03)
O-Methoxymethyl (MOM) protected fluorophenols can be cleanly metalated and subsequently be submitted to site-selective electrophilic substitution. The 2- and 4-isomers exhibit ambivalent reactivity: deprotonation occurs at the position adjacent to the oxygen when butyllithium is employed whereas the position adjacent to the fluorine is attacked by the superbasic mixture of butyllithium and potassium tert-butoxide (LIC-KOR). The MOM-protected (trifluoromethyl)-phenols react exclusively at oxygen-neighboring positions. The meta isomer provides another example of optional site selectivity, undergoing hydrogen/metal exchange at the 2-position with the LIC-KOR reagent and at the 6-position with sec-butyllithium. Unprotected (trifluoromethyl)phenols can also be ortho-metalated after O-deprotonation, although the products are formed in only moderate yields.
