Catalysts alkyl activator-free

Reactions of lithium alkyls are generally considered to be carbanionic in nature, but in reactions with alkyl halides free radicals have been detected by electron spin resonance.32 Lithium alkyls are widely employed as stereospecific catalysts for the polymerization of alkenes, notably isoprene, which gives up to 90% of 1,4-cA-polyisoprene numerous other reactions with alkenes have been studied.33 The TMED complexes again are especially active not only will they polymerize ethylene but they will even metallate benzene and aromatic compounds, as well as reacting with hydrogen at 1 atm to give LiH and alkane. 

The highly enantioselective CDC reactions between the tertiary amines and ketones have not been realized until very recently. Wang and co orkers described a metal-free enantioselective CDC reaction of Af-aryl THIQs 23 and cyclic ketones 24 by taking advantage of L-phenylalanine (S )-C5 as a suitable catalyst to activate the ketone substrates via a chiral ion-pair catalysis strategy. This new method provides an efficient way to access diverse Cl-alkylated THIQ derivatives 25 in up to 81% yield with good stereocontrol (up to 13 1 dr and 94% ee) when anhydrous PrOH was added (Scheme 2.10). 

In the Friedel-Crafts realm, Lou and coworkers reported on the activity of Mg-phosphoric acid-based binary catalyst in the alkylation of free phenols via Michael addition of p,y-unsaturated a-ketoesters 25 [41], Despite the real structure of the binary organometallic catalytic species is still unknown, excellent levels of chemical and optical outcomes were achieved in the titled process (Scheme 5.24). To be mentioned that neither the BA nor MgF alone could promote the model reaction at any extents, proving the formation of a concertedly activated catalytic aggregate between the two acids. 

Polyphosphoric acid supported on diatomaceous earth (p. 342) is a petrochemicals catalyst for the polymerization, alkylation, dehydrogenation, and low-temperature isomerization of hydrocarbons. Phosphoric acid is also used in the production of activated carbon (p. 274). In addition to its massive use in the fertilizer industry (p. 524) free phosphoric acid can be used as a stabilizer for clay soils small additions of H3PO4 under moist conditions gradually leach out A1 and Fe from the clay and these form polymeric phosphates which bind the clay particles together. An allied though more refined use is in the setting of dental cements. 

Further evidence against the formation of a free carbonium ion in the alkylation reaction is obtained from the fact that in the presence of boron trifluoride-phosphoric acid catalyst, but-l-ene, but-2-ene, and i-butene react at different rates with alkylbenzenes, yet they would each give the same carbonium ion. In addition, only the latter alkene gave the usual activation order (in this case the hyper-... 

The use of weakly coordinating and fluorinated anions such as B(C6H4F-4)4, B(C6F5)4, and MeB(C6F5)3 further enhanced the activities of Group 4 cationic complexes for the polymerization of olefins and thereby their activity reached a level comparable to those of MAO-activated metallocene catalysts. Base-free cationic metal alkyl complexes and catalytic studies on them had mainly been concerned with cationic methyl complexes, [Cp2M-Me] +. However, their thermal instability restricts the use of such systems at technically useful temperatures. The corresponding thermally more stable benzyl complexes,... 

Noyori et al. recently used ESI-MS to characterize species present in catalytically active solutions during the hydrogenation of aryl-alkyl ketones using their base-free catalyst precursors trans-[Ru((R)-tol-BINAP)((R, RJ-dpenJfHXf/ -BH ] (tol-BI-NAP = 2,2 -bis(ditolylphosphino) -1, T-binaphthyl dpen = 1,2-diphenylethylenedia-mine) in 2-propanol [9b]. Based upon ESI-MS observations, deuterium-labeling studies, kinetics, NMR observations, and other results, the authors proposed that the cationic dihydrogen complex trans-[Ru((R)-tol-BINAP)((R, R)-dpen)(H)( 2-H2)]+ is an intermediate in hydrogenations carried out in the absence of base. 

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