Lanthanoid systems

Carboxylation reaction of active methylene compounds with lanthanoid system was first attained by using a lanthanoid complex obtained from the reaction between lanthanum isopropoxide (LalO Prlj) and 2 equiv of phenyl isocyanate (Ph-N=C=0). Under CO2 at atmospheric pressure, phenylacetonitrile, an active methylene compound (equimolar with respect to LalCyPrlj), was effectively... 

Several other reactions of organic synthesis were found which are accelerated in the presence of REM compounds. Nevertheless, the catalytic properties of lanthanoid systems are evidently investigated incompletely. 

The measurment in twophase systems is discussed by the example of dithizonate of zinc, in pseudomonophase systems - by the example of zinc and cadmium complexes with l-(2-pyridylazo)-2-naphthol, lanthanoid ion complexes with l-(2-pyridylazo)-resorcin. 

Of the remaining 26 undiscovered elements between hydrogen and uranium, 11 were lanthanoids which Mendeleev s system was unable to characterize because of their great chemical similarity and the new numerological feature dictated by the filling of the 4f orbitals. Only cerium, terbium and erbium were established with certainty in 1871, and the others (except promethium, 1945) were separated and identified in the period 1879 -1907. The isolation of the (unpredicted) noble gases also occurred at this time (1894-8). 

Spahiu, K. Carbonate complex formation in lanthanoid and actinoid systems Ph.D. thesis, Royal Institute of Technology, Stockholm 1983. 

In fact, even approximate cubic symmetry seems to be rare for lanthanoid or actinoid element complexes.50 In low symmetry the number of crystal field parameters necessary to account for the system can be quite large. On the other hand, the spectra of lanthanoid complexes contain many... 

In lower symmetries the application of the AOM in /-electron systems becomes quite a complicated matter, and it is not established that it is as successful as CFT in accounting for fine details of lanthanoid spectra. Consequently, as the aim is often to parameterize the spectra rather than to seek the chemical basis for them, the AOM has not received wide usage in dealing with /-electron systems. 

Block copolymers of olefins and acrylates or vinyl esters can be obtained with lanthanoid compounds as catalysts. Living polyethylene-biscyclopenta-dienyl samarium systems can continue the polymerization of cyclolactone monomers by ROMP (273, 274). 

Block copolymers of olefins and acrylates or vinylesters can be obtained by lanthanoid compounds. Living polyethylene-biseyclopentadienyl samarium systems can continue the polymerization with acrylate monomers by group transfer polymerization or cyclolactone monomers by ring opening polymerization [216, 217]. 

SAFETY PROFILE Human systemic effects by intracerebral route blood changes. It may be an anticoagulant lanthanoid. Care in handling is advised. Flammable in the form of dust when exposed to heat or flame. 

More recently the introduction of low-valent transition metal and lanthanoid based reducing systems, especially those based on titanium, has provided dramatic advances in efficiency and selectivity. It is now possible to select appropriate conditions for efficient coupling of all types of carbonyl compounds, often with high chemo-, regio- and stereo-selectivity. Moreover, imino- and thio-carbonyl derivatives are also coupled via pinacolic methodology. The coupling of imines to 1,2-diamines is particularly effective, with excellent control of vicinal stereochemistry. 

A number of phosphonate and phosphinate derivatives where the phosphorus atom is directly bonded to non-aromatic cyclic systems have been reported. The synthesis and reactions of a number of compounds with the general structure 103 have been reported. Enantiomerically pure cyclopropanephosphonic acids which are constrained analogues of the GABA antagonist phaclophen, have been prepared by stereocontrolled Michael addition of a-anions derived from chiral chloromethylphosphonamides 104 to a,P-unsaturated esters followed by in situ cyclisation. Other asymmetric syntheses include those of (/ )- and (S)-piper-idin-2-ylphosphonic acid (105) via the addition to trialkyl phosphites to iminium salt equivalents and 4-thiazolidinylphosphonate 106 by catalytic asymmetric hydrophosphonylation of 3-thiazoline. In the latter case both titanium and lanthanoid (which give much better e.e. values) chiral catalysts are used. 

Recently, attention has been focused on lanthanoid/crown ether complexes,5 since they may be used for lanthanoid ion separation, for stabilizing unusual oxidation states, and for studying high coordination numbers, Moreover, lan-thanoid(III) ions are increasingly used as spectroscopic probes in systems of biological interest.6... 

In the following, such a desired new and innovative multifunctional catalytic system is reviewed The chiral heterobimetallic lanthanoid complexes, developed by Shibasaki et ah, have recently been shown to catalyze a broad spectra of organic reactions including many classical carbon-carbon bond formations... 

In the presence of the sodium-containing heterobimetallic catalyst (R)-LSB (10 mol%), the reaction of enone 52 with TBHP (2 equiv) was found to give the desired epoxide with 83% ee and in 92% yield [56]. Unfortunately LSB as well as other bimetallic catalysts were not useful for many other enones. Interestingly, in marked contrast to LSB an alkali metal free lanthanoid BINOL complex, which was prepared from Ln(0- -Pr)3 and (R)-BINOL or a derivative thereof (1 or 1.25 molar equiv) in the presence of MS 4A (Scheme 17), was found to be applicable to a range of enone substrates. Regarding enones with an aryl-substitu-ent in the a-keto position, the most effective catalytic system was revealed when using a lanthanum-(.R/)-3-hydroxymethyl-BINOL complex La-51 (l-5mol%) and cumene hydroperoxide (CMHP) as oxidant. The asymmetric epoxidation proceeded with excellent enantioselectivities (ees between 85 and 94%) and yields up to 95%. 

A second technical problem has been encountered in regard to the periodicity that is basic to physical periodic systems. That periodicity is pronounced for main-group molecules (Figures 1-6). The expectation has been that periodicity would be similarly visible in transition-metal molecules. For instance, it was expected by the author that transition-metal molecules having as one atom Zn, Cd, or Hg would mark the end of a period by having low dissociation potentials. This expectation was rewarded (Hefferlin 1989a, Chapter 5). The expectation that lanthanoid molecules... 

A common interpretation of this reaction invokes the use of the cerium(lll) chloride as a Lewis acid that bonds to the carbonyl system, to make 1,2-addition favored. However, lanthanoid ions are known to preferentially bind to alcohols rather than carbonyl groups.6 Additionally, if the cerium did bind with the carbonyl, one would expect that as dilution with methanol was increased, the observed regioselectivity, presumably due to this complexation, should be reduced. However, experimental results do not support this hypothesis. Since cerium complexation with methanol would result in increased acidity of the methanolic proton, the following scheme appears to be the more likely course of the reaction. 

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