Catalyst Systems Containing Lanthanides

The scope of the reaction includes the formation of five-, six-, and seven-membered heterocycles from primary, secondary, and aromatic amines as the starting compounds, giving exclusively the exo-methyl product in agreement with Markovnikov s rule. All reactions are found to proceed equally well in toluene, benzene, pentane, and related hydrocarbon solvents. In donor solvents such as THF, catalytic rates are significantly slower. In the series of bisfpenta-methylcyclopentadienyl)lanthanide catalysts, the highest activity was observed with lanthanum and with lutetium the lowest the variation of TON spans over three orders of magnitude. 

Skeletal methyl substitution in the aminoolefin can increase the rate of cycliza-tion very strongly. Thus, for the cyclization of 2,2-dimethyl-l-amino-4-pentene (eq. (3)) the highest TON of 95 mol amine/(mol La) per h at 25 °C was obtained. By variable-temperature in-situ NMR studies of the catalytic solution 

Complexes of this type could be preparatively isolated from pentane solutions in good yields. The corresponding methylamido amine complex [(C5Me5)2La-(NHMe)(H2NMe)] was characterized by X-ray crystal structureanalysis as a model compound for the catalyst complex, which obviously contains, besides the amido group, an additional amine preserving the coordination number 8 of lanthanum. 

From the bis(ethylene) precursor complex the highly reactive unsaturated 14-electron intermediate Ir(PEt3)2Cl is generated as the actual catalyst by stepwise dissociation of ethylene. Related compounds M(Pr 3P)2Cl (M = Rh, 

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Catalyst systems containing lanthanides lanthanide oxides as the majority component. 

Meerwein-Pondorf-Verley reduction, discovered in the 1920s, is the transfer hydrogenation of carbonyl compounds by alcohols, catalyzed by basic metal compounds (e.g., alkoxides) [56-58]. The same reaction viewed as oxidation of alcohols [59] is called Oppenauer oxidation. Suitable catalysts include homogeneous as well as heterogeneous systems, containing a wide variety of metals like Li, Mg, Ca, Al, Ti, 2r and lanthanides. The subject has been reviewed recently [22]. In this review we will concentrate on homogeneous catalysis by aluminium. Most aluminium alkoxides will catalyze MPV reduction. 

The discussion of the activation of bonds containing a group 15 element is continued in chapter five. D.K. Wicht and D.S. Glueck discuss the addition of phosphines, R2P-H, phosphites, (R0)2P(=0)H, and phosphine oxides R2P(=0)H to unsaturated substrates. Although the addition of P-H bonds can be sometimes achieved directly, the transition metal-catalyzed reaction is usually faster and may proceed with a different stereochemistry. As in hydrosilylations, palladium and platinum complexes are frequently employed as catalyst precursors for P-H additions to unsaturated hydrocarbons, but (chiral) lanthanide complexes were used with great success for the (enantioselective) addition to heteropolar double bond systems, such as aldehydes and imines whereby pharmaceutically valuable a-hydroxy or a-amino phosphonates were obtained efficiently. 

Besides supported Au [39f,i,l,o], other catalysts claimed in Dow patents include Agj alkali (alkaline earths, lanthanides) over Ti-containing supports. These systems givea propene conversion lower than 1%, high PO selectivity (but lower than that achieved with Au-based systems) and a H 2O/PO ratio much higher than that obtained with Au-based systems [39c,d,h,m,nj. The co-presence of Au, however, remarkably reduces the H2O/PO ratio, thus increasing hydrogen efficiency [39g,kj. 

The polymerisation of dienes occurs when the lanthanide catalyst contains an organometallic component (usually, trialkylaluminum or dialkylaluminum hydride). Systems LnHal3 nL-AlR2lTal do not reveal catalytic activity. Moreover, dialkylaluminum... 

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