ion using borate reagents [Ph3C][B(C6F5)4] and [PhNMe2H][B(C6F5)4], respectively, results in highly active polymerization catalysts (Table 4). Scandium bis(alkyl) complex 51Sc shows excellent activity for the syndiospecific styrene homopolymerization (activity, 1.36 × 104 (kg PS)/ (mol Sc h); Mw/Mn ) 1.37), and complexes 51, 53, and 54 proved suitable for the coand terpolymerization of a series of monomers.204,206,210-225 8.2.3. Constraint Geometry Complexes Incorporation of the cyclopentadienyl ancillary ligand into a chelate array of (pendant) donor functionalities gives access to prominent Cp derivatives. Since the original introduction by the Bercaw group, the linked amido-cyclopentadienyl (Cp) ligand has advanced to be one of the most versatile ligands for group 4 metal polymerization catalysts.235 Catalysts based on this type of ligand provide a constrained ligand environment but are anticipated to be more active toward sterically demanding monomers than metallocenes. Aminecyclopentadiene proligands react with Ln(CH2SiMe3)3(thf)x (Jthf) according to an alkane-elimination reaction in a similar manner as shown in Scheme 30. Because of the dianionic nature of the resulting ligand, only one [CH2SiMe3] ligand is retained in the resulting compounds, which allows for further derivatization (Chart 11). In the presence of Ph3SiH or H2, complexes 66-73 form dimeric hydrido complexes,176,177,204,236 showing high potential in the catalytic hydrosilylation of olefins.226,237,238 Catalytic activities and stereoselectivities are hereby influenced by the length of the linker between the cyclopentadienyl and the amido-functionality and the substituents at the amidonitrogen.237 Remarkable catalytic activity was observed for complexes 68cyclohexyl. Upon activation with equimolar amounts of [Ph3C][B(C6F5)4], such compounds polymerized ethylene and isoprene, regiospecifically yielding 3,4-polyisoprene with isotactic-rich stereo microstructures and relatively narrow molecular weight distribution (Mw/Mn ) 1.8).222 Complex 67Y was found to initiate the polymerization of the polar monomers tert-butyl acrylate and acrylonitrile, however, yielding atactic polymeric products (see Table 5).204 8.2.4. Complexes with Neutral Nitrogenand Oxygen-Based Ligands While early work in organorare-earth metal chemistry was dominated by complexes supported by cyclopentadienyl-type ligands of varying substitution and modification, the limitations inherent to these ligand sets triggered the development of alternative ancillary ligands. Particularly in the past 15 years, advanced ligand design gave access to a wide variety of rare-earth metal complexes supported by noncyclopentadienyl ligand environments. Because of the Lewis acidic nature of the rare-earth metal ions, ligands based on the hard donor elements oxygen and nitrogen are most commonly used, while some notable exceptions have been reported. To avoid ligand redistribution, multidentate ligands are generally favored. Since rare-earth metal cations are invariable in the +3 oxidation state (except Eu(II), Sm(II), Yb(II), and Ce(IV)), neutral, monoanionic, or dianionic ligand sets are the most desirable. Table 4. Further Applications of Half-Sandwich Complexes (Cp)Ln(CH2SiMe3)2(donor)x compound further application ref 50 [CH2SiMe3] exchange reactions 205-209 formation of mono(cations) alternating ethylene-norbornene copolymerization

Homoleptic Rare-Earth Metal Complexes Containing Ln−C σ-Bonds†

Synthesis, Arrangement, and Reactivity of Arene−Lanthanide Compounds

Molecular compounds of “new” divalent lanthanides

The reactivity of CO2 and COS with divalent and trivalent organosamarium complexes has been investigated. (C5Me5)2Sm(THF)2 reductively couples CO2 in THF at room temperature to form the oxalate complex, [(C5Me5)2Sm]2(μ-η2:η2-O2CCO2), 1, in >90% yield. The metal centers in 1 are formally eight-coordinate. The reaction of COS with (C5Me5)2Sm(THF)2 is more complicated and generates a disproportionation product, (C5Me5)2Sm(μ-η2:η1-S2CO)Sm(C5Me5)2(THF), 2, which has one (C5Me5)2Sm unit involved in a four-membered ring, while the other (C5Me5)2Sm unit is bound to THF and the oxygen of the S2CO ligand. CO2 reacts with [(C5Me5)2Sm]2(μ-η1:η1-N2Ph2) in >90% yield to form the asymmetrical monoinsertion product, (C5Me5)2Sm[μ-η2:η1-PhNN(CO2)Ph]Sm(C5Me5)2(THF), 3. One (C5Me5)2Sm unit is involved in a five-membered ring, and the other is attached to THF and the other oxygen originating from CO2. 1−3 were characterized by analytical methods, X-ray diffraction, and NMR and IR spectroscopy.

Organosamarium-Mediated Transformations of CO2 and COS: Monoinsertion and Disproportionation Reactions and the Reductive Coupling of CO2 to [O2CCO2]2-

The Availability of Dysprosium Diiodide as a Powerful Reducing Agent in Organic Synthesis: Reactivity Studies and Structural Analysis of DyI2((DME)3 and Its Naphthalene Reduction Product1

Synthesis and reactivity of naphthalene complexes of ytterbium

Reactions of compounds containing SnLi and GeLi bonds with organic and organometallic peroxides

Study of the mechanism of the catalytic rearrangement of triphenyl(triphenylsilylperoxy)germane

New rearrangement of triphenyl(triphenylsilylperoxy)germane catalyzed by nucleophiles

Interaction of pentafluorophenyl hydrides of germanium with triethylthallium

T.A. Basalgina

Papers

Synthesis and reactivity of naphthalene complexes of ytterbium

Reactions of compounds containing SnLi and GeLi bonds with organic and organometallic peroxides

Study of the mechanism of the catalytic rearrangement of triphenyl(triphenylsilylperoxy)germane

New rearrangement of triphenyl(triphenylsilylperoxy)germane catalyzed by nucleophiles

Interaction of pentafluorophenyl hydrides of germanium with triethylthallium