Alkylation complex catalysis

Stable transition-metal complexes may act as homogenous catalysts in alkene polymerization. The mechanism of so-called Ziegler-Natta catalysis involves a cationic metallocene (typically zirconocene) alkyl complex. An alkene coordinates to the complex and then inserts into the metal alkyl bond. This leads to a new metallocei e in which the polymer is extended by two carbons, i.e. 

A review article entitled "Bulky amido ligands in rare-earth chemistry Syntheses, structures, and catalysis" has been published by Roesky. Benzamidinate ligands are briefly mentioned in this contexD The use of bulky benzamidinate ligands in organolanthanide chemistry was also briefly mentioned in a review article by Okuda et al. devoted to "Cationic alkyl complexes of the rare-earth metals S mthesis, structure, and reactivity." Particularly mentioned in this article are reactions of neutral bis(alkyl) lanthanide benzamidinates with [NMe2HPh][BPh4] which result in the formation of thermally robust ion pairs (Scheme 55). ... 

A large number of (mostly zero-valent) nickel-alkene complexes has been reported. Although these complexes have not been recently reviewed, their general properties and structures were expertly described in 1982 [21]. A complete overview of the reported nickel-alkene and nickel-alkyl complexes is beyond the scope of this section, in which a selection of nickel-alkene and nickel-alkyl complexes is described, mostly related to possible intermediates in hydrogenation catalysis. 

The detail of the structure of the polymerisation centre present in suppported Ziegler-Natta catalysts for a-olefin polymerisation has been the subject of much research effort (e.g./-/2) The catalyst consists of a solid catalyst MgC /TiC /electron donor and a co-catalyst, an aluminium alkyl complexed with an electron donor. Proposed mechanisms for the polymerisation involve a titanium species attached to magnesium chloride with the olefin coordinated to titanium. The detail of the site at which the titanium species is attached is an important area of study in understanding the mechanism of catalysis and several recent papers 10-12) have investigated the surface structure of magnesium chloride and the attachment of TiCl4, in particular the interaction of titanium species with the 100 and 110 planes of a and (3- magnesium chloride. 

The relevance of Ln/Al heterobimetallic complexes for the emulation of zirconocene-based polymerization catalysis [13-15] was later on also stressed by the Lanthanide Ziegler-Natta Model [16]. Accordingly, lanthanidocene alkyl complexes were not only successfully employed for clarifying major initiation, propagation, and termination steps (Scheme 3) [17,18]. 

Bambirra, S., van Leusen, D., Tazelaar, C.GJ. et al. (2007) Rare earth metal alkyl complexes with methyl-substituted triazacyclononane-amide ligands ligand variation and ethylene polymerization catalysis. Organometallics, 26, 1014. 

Wang, D., Li, S.H., Liu, X.L. et al. (2008) Thiophene-NPN ligand supported rare-earth metal bis(alkyl) complexes. Synthesis and catalysis toward highly trans-1,4 selective polymerization of butadiene. Organometallics, 27, 6531. 

Arndt, S. and Okuda, J. (2005) Cationic alkyl complexes of the rare-earth metals synthesis, structure, and reactivity. Advanced Synthesis and Catalysis, 347, 339. 

O-Alkylation of quinoxalines usually occurs under conditions of kinetic control, while A-alkylation proceeds under thermodynamic control. The quinoxalin-2(l H)-ones have been A-ribosylated via the silyl method under boron trifluoride-diethyl ether complex catalysis leading to the corresponding nucleosides in low to moderate yields. ... 

The insertion of CO into a metal-carbon bond in alkyl complexes is of particular interest in its potential applications to organic synthesis and catalysis (examples will be discussed in Section 14-3), and its mechanism deserves careful consideration. 

Novel C-C coupling reactions are about to enter the scope of metal complex catalysis. Examples are asymmetric aldolizations (Mukaiyama [79]), Diels-Alder reactions [80], and indium- or zinc-mediated alkylations [86]. 

Despite the ubiquity of iron phosphine complexes, few aside from the Bianchini compounds have been shown to be active for hydrogenation catalysis. In 2004, Daida and Peters [72] reported a series of pseudo-tetrahedral iton(II) alkyl complexes, [PhBP3 "]Fe-R (PhBPi = [PhB(CH2P Pr2)3], R=CH3, CHjPh, CHjCMej), that are readily hydrogenated in the presence of various phosphines to yield the corresponding Fe(lV) trihydride phosphine complexes (Scheme 4.4). 

As the next example of soft catalysis, we shall discuss the dimerization of ethylene to 1-butene, which is catalyzed by rhodium complexes in a redox cycle (Scheme 2-6). The active Rh catalyst A undergoes oxidative addition of HCl and insertion of ethylene into the Rh-H bond to give the Rh alkyl complex B. The following ethylene insertion reaction is the rate-determining step and is favored by the medium-hard Rh center. The resulting Rh butyl complex C has a hard-soft dis-... 

Tin.—Allyltin compounds, especially under rhodium-complex catalysis, react with acyl chlorides to give allyl ketones or with aryl halides to give allylarenes. Bridgehead alkyl bromides are reduced on photolysis with Bu"3SnH, whilst the system (Bu"3Sn)20-Br2 oxidizes sulphides to sulphoxides. )V-(Alkoxycar-bonyl)amino-acids are obtained upon treatment of cyclic anhydrides with Bu3SnN3 and heating in an alcohol. ... 

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