Lanthanide aryls

Homoleptic aryl-lanthanides are less studied then alkyl complexes. After the first lanthanide aryl complex [Li(THF)4][Lu(C6H3-2,6-Me2)4], neutral triphenyllantha-nides Ph3Ln(THF)3 (Ln = Er, Tm, Yb) were synthesized in THF by reaction of metallic lanthanides with Ph2Hg or... 

A study195 based on the NMR lanthanide-induced shifts (LIS) for a series of cis- and trans-3-substituted, and 3,3-disubstituted thietane oxides concluded that all cis-substituted oxides (5c R = CH3, t-Bu and aryl) exist exclusively in the diequatorial conformation. The trans-3-substituted isomers (185) prefer the equatorial oxygen conformation (R = CH3,86% t-Bu, 65-75% aryl, 75%), which means an axial preference for the substituents (e.g. 185d), at least when they are bound to a shift reagent (equation 75). 

In hydrogenation, early transition-metal catalysts are mainly based on metallocene complexes, and particularly the Group IV metallocenes. Nonetheless, Group III, lanthanide and even actinide complexes as well as later metals (Groups V-VII) have also been used. The active species can be stabilized by other bulky ligands such as those derived from 2,6-disubstituted phenols (aryl-oxy) or silica (siloxy) (vide infra). Moreover, the catalytic activity of these systems is not limited to the hydrogenation of alkenes, but can be used for the hydrogenation of aromatics, alkynes and imines. These systems have also been developed very successfully into their enantioselective versions. 

Porphyrazines with alkyl or aryl substituents are considerably more soluble than their unsubstituted counterparts (Section III. A). Consequently, various pz isomers with alkyl and aryl substituents, for example, symmetrical M[pz(A4)] and unsym-metrical M[pz(A3B)], have been reported. In particular, the symmetrical species M[pz( A4)] have been used both as vehicles to study the fundamental physical properties of metalated porphyrazines (52) as well as to make double decker or sandwich porphyrazines, cofacial dimers linked with lanthanide metal ions (34), while the unsymmetrical species M[pz(A3B)] have utilized the alkyl-aryl substituents as solubilizing groups and have been applied to all areas of pz chemistry. 

A more recent report by Sibi and co-workers displayed the utility of chiral lanthanide Lewis acids for addition-trapping reactions [150]. An exhaustive screening of lanthanide Lewis acids and several chiral ligands revealed that Y(OTf)3 and proline derived ligand 138 was optimal (data not shown). Upon further optimization it was discovered that achiral additives 139 and 212 increased ee s (Scheme 56, entries 2 and 3). Bulkier radicals were found to decrease the enantioselectivity (entries 4 and 5). Also, larger aryl substituents on the ligand gave similar ee s as observed for 138 (compare entries 1, 6, and 7). 

The first S5m.thetic ventures into actinide and lanthanide organometalhc chemistry were attempted during World War II and were motivated by the need for stable, volatile uranium complexes in the uranium gaseous diffusion process. It soon became apparent that the homoalkyl complexes (MR4) of uranium were extremely unstable and at best could exist only as transient intermediates at low temperatures [128). With the isolation of the tricyclopentadienides of the lanthanides in 1954, the focus of /-transition metal organometaUic chemistry shifted to the n-carbocychc complexes and has remained unchanged until the recent isolation of stable alkyls and aryls of both the lanthanides and actinides. 

The primary reason for the thermal stability or instability of the alkyls and aryls of the lanthanides and actinides is kinetic in nature. As in all kinetic processes, the rate of reaction is dependent upon the activation energy between reactants and products. By considering the various decomposition pathways and factors which enhance or inhibit these pathways one can rationalize the observed sta-bihties of the various complexes. 

In contrast to the epoxides, preparative routes to the aziridines are fairly evenly split between the [C=N + C] and the [C=C + N] routes. Among contributions in the former category, aziridine carboxylate derivatives 110 can be prepared through the lanthanide-catalyzed reaction of imines with diazo compounds, such as ethyl diazoacetate (EDA). In this protocol, iV-benzyl aryl aldimines and imines derived from aromatic amines and hindered aliphatic aldehydes are appropriate substrates <99T12929>. An intramolecular variant of this reaction (e.g.. Ill —> 112) has also been reported <990L667>. 

A Japanese group have reported an unusual reaction, mediated by lanthanide metals, involving the deoxygenative acylation of diaryl ketones with aryl acyl silanes, to give 1,1-diaryl acetophenones (Scheme 79)189. 

Carbamoyl methyl Phosphine Oxide Derivatives The physicochemical properties of various aryl derivatives of CMPO have been investigated at the Vernadsky Institute of Geochemistry and Analytical Chemistry. Extraction of americium and lanthanides from nitric acid with solutions of diphenyl- and dibutyl-(diethylcarbamoylmethyl) phosphine oxides (Ph2Et2-CMPO and Bu2Et2-CMPO) in dichloroethane have been investigated as a function of the concentrations of the extractants and nitric acid (110, 111). The observed dependences are characterized... 

Cyano compounds liquid crystals, 12, 278 in silver(III) complexes, 2, 241 Cyanocuprates, with copper, 2, 186 Cyano derivatives, a-arylation, 1, 361 Cyanosilanes, applications, 9, 322 Cyclic acetals, and Grignard reagent reactivity, 9, 53 Cyclic alkenes, asymmetric hydrosilylation, 10, 830 Cyclic alkynes, strained, with platinum, 8, 644 Cyclic allyl boronates, preparation, 9, 196 Cyclic allylic esters, alkylation, 11, 91 Cyclic amides, ring-opening polymerization, via lanthanide catalysis, 4, 145... 

Heteroleptic chromium aryl compounds, preparation and characterization, 5, 298 Heteroleptic compounds actinide complexes, 4, 193 lanthanide complexes, 4, 7... 

Homoleptic germylenes, preparation and properties, 3, 773 Homoleptic lanthanide(II) alkyl compounds, properties, 4, 4 Homoleptic manganese aryl complexes, preparation, 5, 816 Homoleptic manganese isonitrilates, preparation, 5, 773—774 Homoleptic molybdenum complexes, preparation and characteristics, 5, 514... 

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