Die Hydrierung von Bis(triphenylsilyl)calcium mit dem neutralen makrocyclischen Aminliganden 1,4,7,10-Tetramethyl-1,4,7,10-tetraazacyclododecan (Me₄TACD) vom NNNN-Typ, [Ca(Me₄TACD)(SiPh₃)₂] (2), führte zu dem kationischen zweikernigen Calciumhydrid [Ca₂H₃(Me₄TACD)₂](SiPh₃) (3), das über NMR-Spektroskopie, Einkristallstrukturanalyse und Dichtefunktionalrechnungen charakterisiert wurde. 3 reagierte mit Deuterium zu dem Deuterid [D₃]-3.

Hydrogenolysis of bis(triphenylsilyl)calcium containing the neutral NNNN-type macrocyclic amine ligand Me₄TACD [Ca(Me₄TACD)(SiPh₃)₂] (2), gave the cationic dinuclear calcium hydride [Ca₂H₃(Me₄TACD)₂](SiPh₃) (3), characterized by NMR spectroscopy, single-crystal X-ray analysis, and DFT calculations. Compound 3 reacted with deuterium to give the deuteride [D₃]-3.

Triphenylborane (BPh₃) in highly polar, aprotic solvents catalyzes hydrosilylation of CO₂ effectively under mild conditions to provide silyl formates with high chemoselectivity (>95 %) and without over-reduction. This system also promotes reductive hydrosilylation of tertiary amides as well as dehydrogenative coupling of silane with alcohols.

Large magnesium hydride aggregates [Mg₁₃(Me₃TACD)₆(μ₂-H₁₂)(μ₃-H₆)][A]₂ ((Me₃TACD)H=1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane; A=AlEt₄, AlnBu₄, B{3,5-(CF₃)₂C₆H₃}₄) were synthesized stepwise from alkyl complexes [Mg₂(Me₃TACD)R₃] (R=Et, nBu) and phenylsilane in the presence of additional Mg^II ions. The central magnesium atom is octahedrally coordinated by six hydrides as in solid α-MgH₂ of the rutile type. Further coordination to six magnesium atoms leads to a substructure of seven edge-sharing octahedra as found in the hexagonal layer of brucite (Mg(OH)₂). Upon protonolysis in the presence of 1,2-dimethoxyethane (DME), this cluster was degraded into a tetranuclear dication [Mg₂(Me₃TACD)(μ-H)₂(DME)]₂[A]₂.

Molecular hydrides of the rare-earth metals play an important role as homogeneous catalysts and as counterparts of solid-state interstitial hydrides. Structurally well-characterized non-metallocene-type hydride complexes allow the study of elementary reactions that occur at rare-earth-metal centers and of catalytic reactions involving bonds between rare-earth metals and hydrides. In addition to neutral hydrides, cationic derivatives have now become available.

Große Magnesiumhydrid-Aggregate [Mg₁₃(Me₃TACD)₆(μ₂-H₁₂)(μ₃-H₆)][A]₂ ((Me₃TACD)H=1,4,7-Trimethyl-1,4,7,10-tetraazacyclododecan; A=AlEt₄, AlnBu₄, B{3,5-(CF₃)₂C₆H₃}₄) wurden schrittweise aus Alkylkomplexen [Mg₂(Me₃TACD)R₃] (R=Et, nBu) und Phenylsilan in Gegenwart von zusätzlichen Mg^II-Ionen synthetisiert. Das zentrale Magnesiumatom ist wie in festem α-MgH₂ vom Rutil-Typ oktaedrisch von sechs Hydriden koordiniert. Weitere Koordination zu sechs Magnesiumatomen führt zu einer Unterstruktur mit sieben eckenverknüpften Oktaedern, ähnlich einer hexagonalen Schicht von Brucit (Mg(OH)₂). Durch Protonolyse in Gegenwart von 1,2-Dimethoxyethan (DME) wurde dieser Cluster zu dem vierkernigen Dikation [Mg₂(Me₃TACD)(μ-H)₂(DME)]₂[A]₂ abgebaut.

Molekulare Hydride der Seltenerdmetalle spielen eine wichtige Rolle als homogene Katalysatoren und als Modelle für Einlagerungshydride im Festkörper. Mit strukturell gut charakterisierten Hydridkomplexen vom Nichtmetallocen-Typ lassen sich Elementarreaktionen studieren, die an Seltenerdmetallzentren ablaufen. Untersuchen lassen sich auch katalytische Reaktionen, bei denen Seltenerdmetall-Hydrid-Bindungen beteiligt sind. Über neutrale Hydride hinaus sind nun auch kationische Derivate zugänglich.

A biohybrid ring-opening olefin metathesis polymerization catalyst based on the reengineered β-barrel protein FhuA ΔCVF^tev was chemically modified with respect to the covalently anchored Grubbs–Hoveyda type catalyst. Shortening of the spacer (1,3-propanediyl to methylene) between the N-heterocyclic carbene ligand and the cysteine site 545 increased the ROMP activity toward a water-soluble 7-oxanorbornene derivative. The cis/trans ratio of the double bond in the polymer was influenced by the hybrid catalyst.

A complex featuring a terminal magnesium hydride bond supported by an NNNN macrocyclic ligand, [Mg{Me₃TACD⋅Al(iBu)₃}H] (3), was formed from its labile Al(iBu)₃ adduct. Use of Al(iBu)₃ to block the amido nitrogen of the NNNN macrocyclic ligand was essential to prevent aggregation. The structurally characterized compound 3 reacted with BH₃ to give the BH₄ derivative, whereas Me₃SiCCH and PhSiH₃ led to the corresponding acetylide and silyl derivative under H₂ elimination. Pyridine is inserted into the MgH bond to give selectively the 1,4-dihydropyridinate.

Methylene-linked bis(N,N′-di-tert-butylimidazol-2-ylidene) 1 reacted with diethylzinc to give dinuclear zinc ethyl compound 2, which contains a formally anionic bis(carbene) ligand as a result of deprotonation of the methylene bridge. The reaction of 2 with PhSiH₃ gave the phenylsilyl compound 3. The zinc hydride 4 was obtained by the reaction of 2 with LiAlH₄ or Ph₃SiOH followed by treatment with PhSiH₃. X-ray diffraction studies show that compounds 2, 3, and 4 all have a similar dimeric structure with D_2h symmetry. The reaction of hydride 4 with carbon dioxide and N,N′-diisopropylcarbodiimide gave formato (5) and formamidinato (7) derivatives as a result of the insertion of the heterocumulene into both ZnH bonds. Reaction with Ph₂CO gave the diphenylmethoxy compound 6. Hydride 4 shows catalytic activity in the hydrosilylation of 1,1-diphenylethylene and methanolysis of silanes.

The trinuclear cationic zinc hydride cluster [(IMes)₃Zn₃H₄(THF)](BPh₄)₂ (1) was obtained either by protonation of the neutral zinc dihydride [(IMes)ZnH₂]₂ with a Brønsted acid or by addition of the putative zinc dication [(IMes)Zn(THF)]²⁺. A triply bridged thiophenolato complex 2 was formed upon oxidation of 1 with PhSSPh. Protonolysis of 1 by methanol or water gave the corresponding trinuclear dicationic derivatives. At ambient temperature, 1 catalyzed the hydrosilylation of aldehydes, ketones, and nitriles. Carbon dioxide was also hydrosilylated under forcing conditions when using (EtO)₃SiH, giving silylformate as the main product.

Hydrogenation of the neutral bis(allyl) complexes of the early lanthanides [Ln(Me₃TACD)(η³-C₃H₅)₂] [(Me₃TACD)H = 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane, Me₃[12]aneN₄] with phenylsilane gave the tetranuclear octahydrido complexes [Ln(Me₃TACD)(μ-H)₂]₄ [Ln = Ce (1-Ce), Pr (2-Pr)] or the dinuclear allyl/hydrido complexes [Ln(Me₃TACD)(η³-C₃H₅)(μ-H)]₂ [Ln = Nd (3-Nd), Sm (4-Sm)], which were isolated and characterized. The structures of 1-Ce and 2-Pr are constructed of a tetrahedral Ln₄H₈ core. Single-crystal X-ray diffraction analyses of 3-Nd and 4-Sm revealed a C₂ symmetric planar Ln₂H₂ core. The experimental structures agreed with the results of DFT calculations, which predict that the nuclearity of the dihydrido complexes depend on the ionic radius of the metal. Compounds 1-Ce, 2-Pr, 3-Nd and 4-Sm were tested as catalysts in the copolymerization of cyclohexene oxide with CO₂ to give highly carbonate-linked copolymers with moderate activities.

Metallorganische Allylverbindungen sind von Bedeutung als Allylierungsreagentien in der organischen Synthese, als Polymerisationskatalysatoren und als flüchtige Metallvorstufen in den Materialwissenschaften. Während die Allylchemie der Lanthanoide und syntheserelevanter Übergangsmetalle wie Palladium gut etabliert ist, bestand für die Allylchemie der Hauptgruppenmetalle Nachholbedarf. Jüngste Erkenntnisse über die Allylkomplexe der Gruppen 1, 2 und 12–16 zeichnen nun ein vollständigeres Bild. Dies beruht auf dem grundlegenden Verständnis der Metall-Allyl-Bindungswechselwirkungen im Festkörper und in Lösung. Außerdem wurden Reaktivitätstrends rational erklärt und neue, allylspezifische Reaktivitätsmuster aufgedeckt. Schlüsselerkenntnisse umfassen 1) die Nutzung unterschiedlicher Metall-Allyl-Wechselwirkungen (stark ionisch bis vorwiegend kovalent), 2) das Nutzen synergetischer Effekte in Heterodimetallverbindungen und 3) die Regulierung der Lewis-Acidität durch Variation der Ladung von Allylkomplexen.

Organometallic allyl compounds are important as allylation reagents in organic synthesis, as polymerization catalysts, and as volatile metal precursors in material science. Whereas the allyl chemistry of synthetically relevant transition metals such as palladium and of the lanthanoids is well-established, that of main group metals has been lagging behind. Recent progress on allyl complexes of Groups 1, 2, and 12–16 now provides a more complete picture. This is based on a fundamental understanding of metal–allyl bonding interactions in solution and in the solid state. Furthermore, reactivity trends have been rationalized and new types of allyl-specific reactivity patterns have been uncovered. Key features include 1) the exploitation of the different types of metal–allyl bonding (highly ionic to predominantly covalent), 2) the use of synergistic effects in heterobimetallic compounds, and 3) the adjustment of Lewis acidity by variation of the charge of allyl compounds.

The rare-earth-metal hydride complexes [{(1,7-Me₂TACD)LnH}₄] (Ln=La 1 a, Y 1 b; (1,7-Me₂TACD)H₂=1,7-dimethyl-1,4,7,10-tetraazacyclododecane, 1,7-Me₂[12]aneN₄) were synthesized by hydrogenolysis of [{(1,7-Me₂TACD)Ln(η³-C₃H₅)}₂] with 1 bar H₂. The tetrameric structures were confirmed by ¹H NMR spectroscopy and single-crystal X-ray diffraction of compound 1 a. Both complexes catalyze the dehydrogenation of secondary amineborane Me₂NH⋅BH₃ to afford the cyclic dimer (Me₂NBH₂)₂ and (Me₂N)₂BH under mild conditions. Whilst the complete conversion of Me₂NH⋅BH₃ was observed within 2 h with lanthanumhydride 1 a, the yttrium homologue 1 b required 48 h to reach 95 % conversion. Further reactions of compound 1 a with Me₂NH⋅BH₃ in various stoichiometric ratios gave a series of intermediate products, [{(1,7-Me₂TACD)LaH}₄](Me₂NBH₂)₂ (2 a), [(1,7-Me₂TACDH)La(Me₂NBH₃)₂] (3 a), [(1,7-Me₂TACD)(Me₂NBH₂)La(Me₂NBH₃)] (4 a), and [(1,7-Me₂TACD)(Me₂NBH₂)₂La(Me₂NBH₃)] (5 a). Complexes 2 a, 3 a, and 5 a were isolated and characterized by multinuclear NMR spectroscopy and single-crystal X-ray diffraction studies. These intermediates revealed the activation and coordination modes of “Me₂NH⋅BH₃” fragments that were trapped within the coordination sphere of a rare-earth-metal center.

A β-barrel protein hybrid catalyst was prepared by covalently anchoring a Grubbs–Hoveyda type olefin metathesis catalyst at a single accessible cysteine amino acid in the barrel interior of a variant of β-barrel transmembrane protein ferric hydroxamate uptake protein component A (FhuA). Activity of this hybrid catalyst type was demonstrated by ring-opening metathesis polymerization of a 7-oxanorbornene derivative in aqueous solution.

Ring-opening polymerization of rac- and meso-lactide initiated by indium bis(phenolate) isopropoxides {1,4-dithiabutanediylbis(4,6-di-tert-butylphenolate)}(isopropoxy)indium (1) and {1,4-dithiabutanediylbis(4,6-di(2-phenyl-2-propyl)phenolate)}(isopropoxy)indium (2) is found to follow first-order kinetics for monomer conversion. Activation parameters ΔH^‡ and ΔS^‡ suggest an ordered transition state. Initiators 1 and 2 polymerize meso-lactide faster than rac-lactide. In general, compound 2 with the more bulky cumyl ortho-substituents in the phenolate moiety shows higher polymerization activity than 1 with tert-butyl substituents. meso-Lactide is polymerized to syndiotactic poly(meso-lactides) in THF, while polymerization of rac-lactide in THF gives atactic poly(rac-lactides) with solvent-dependent preferences for heterotactic (THF) or isotactic (CH₂Cl₂) sequences. Indium bis(phenolate) compound rac-(1,2-cyclohexanedithio-2,2′-bis{4,6-di(2-phenyl-2-propyl)phenolato}(isopropoxy)indium (3) polymerizes meso-lactide to give syndiotactic poly(meso-lactide) with narrow molecular weight distributions and rac-lactide in THF to give heterotactically enriched poly(rac-lactides). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4983–4991

A series of 1,ω-dithiaalkanediyl-bridged bis(phenols) of the general type [OSSO]H₂ with variable steric properties and various bridges were prepared. The stoichiometric reaction of the bis(phenols) 1,3-dithiapropanediyl-2,2′-bis(4,6-di-tert-butylphenol), 1,3-dithiapropanediyl-2,2′-bis[4,6-di(2-phenyl-2-propyl)phenol], rac-2,3-trans-propanediyl-1,4-dithiabutanediyl-2,2′-bis[4,6-di(2-phenyl-2-propyl)phenol], rac-2,3-trans-butanediyl-1,4-dithiabutane diyl-2,2′-bis[4,6-di(2-phenyl-2-propyl)phenol], rac-2,3-trans-hexanediyl-1,4-dithiabutanediyl-2,2′-bis[4,6-di(2-phenyl-2-propyl)phenol], 1,3-dithiapropanediyl-2,2′-bis[6-(1-methylcyclohexyl)-4-methylphenol] (C₁, R=1-methylcyclohexyl), and 1,4-dithiabutanediyl-2,2′-bis[6-(1-methylcyclohexyl)-4-methylphenol] with rare-earth metal silylamido precursors [Ln{N(SiHMe₂)₂}₃(thf)_x] (Ln=Sc, x=1 or Ln=Y, x=2; thf=tetrahydrofuran) afforded the corresponding scandium and yttrium bis(phenolate) silylamido complexes [Ln(OSSO){N(SiHMe₂)₂}(thf)] in moderate to good yields. The monomeric nature of these complexes was shown by an X-ray diffraction study of one of the yttrium complexes. The complexes efficiently initiated the ring-opening polymerization of rac- and meso-lactide to give heterotactic-biased poly(rac-lactides) and highly syndiotactic poly(meso-lactides). Variation of the ligand backbone and the steric properties of the ortho substituents affected the level of tacticity in the polylactides.

The preparation and characterization of a series of neutral rare-earth metal complexes [Ln(Me₃TACD)(η³-C₃H₅)₂] (Ln=Y, La, Ce, Pr, Nd, Sm) supported by the 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane anion (Me₃TACD⁻) are reported. Upon treatment of the neutral allyl complexes [Ln(Me₃TACD)(η³-C₃H₅)₂] with Brønsted acids, monocationic allyl complexes [Ln(Me₃TACD)(η³-C₃H₅)(thf)₂][B(C₆X₅)₄] (Ln=La, Ce, Nd, X=H, F) were isolated and characterized. Hydrogenolysis gave the hydride complexes [Ln(Me₃TACD)H₂]_n (Ln=Y, n=3; La, n=4; Sm). X-ray crystallography showed the lanthanum hydride to be tetranuclear. Reactivity studies of [Ln(Me₃TACD)R₂]_n (R=η³-C₃H₅, n=0; R=H, n=3,4) towards furan derivatives includes hydrosilylation and deoxygenation under ring-opening conditions.

A facile and general synthetic pathway for the production of dearomatized, allylated, and CH bond activated pyridine derivatives is presented. Reaction of the corresponding derivative with the previously reported reagent bis(allyl)calcium, [Ca(C₃H₅)₂] (1), cleanly affords the product in high yield. The range of N-heterocyclic compounds studied comprised 2-picoline (2), 4-picoline (3), 2,6-lutidine (4), 4-tert-butylpyridine (5), 2,2′-bipyridine (6), acridine (7), quinoline (8), and isoquinoline (9). Depending on the substitution pattern of the pyridine derivative, either carbometalation or CH bond activation products are obtained. In the absence of methyl groups ortho or para to the nitrogen atom, carbometalation leads to dearomatized products. C(sp³)H bond activation occurs at ortho and para situated methyl groups. Steric shielding of the 4-position in pyridine yields the ring-metalated product through C(sp²)H bond activation instead. The isolated compounds [Ca(2-CH₂-C₅H₄N)₂(THF)] (2 b⋅(THF)), [Ca(4-CH₂-C₅H₄N)₂(THF)₂] (3 b⋅(THF)₂), [Ca(2-CH₂-C₅H₃N-6-CH₃)₂(THF)_n] (4 b⋅(THF)_n; n=0, 0.75), [Ca{2-C₅H₃N-4-C(CH₃)₃}₂(THF)₂] (5 c⋅(THF)₂), [Ca{4,4′-(C₃H₅)₂-(C₁₀H₈N₂)}(THF)] (6 a⋅(THF)), [Ca(NC₁₃H₉-9-C₃H₅)₂(THF)] (7 a⋅(THF)), [Ca(4-C₃H₅-C₉H₇N)₂(THF)] (8 b⋅(THF)), and [Ca(1-C₃H₅-C₉H₇N)₂(THF)₃] (9 a⋅(THF)₃) have been characterized by NMR spectroscopy and metal analysis. 9 a⋅(THF)₄ and 4 b⋅(THF)₃ were additionally characterized in the solid state by X-ray diffraction experiments. 4 b⋅(THF)₃ shows an aza-allyl coordination mode in the solid state. Based on the results, mechanistic aspects are discussed in the context of previous findings.

Cyclic polyamine 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane, (Me₃TACD)H (1), was metalated with n-butyllithium in pentane to give [Li₂(Me₃TACD)₂] (2). The structure of this compound is dimeric in the solid state as shown by single-crystal X-ray diffraction. With an excess of nBuLi, nBuLi is incorporated into the product. Depending on the stoichiometry, the compounds [Li₃(nBu)(Me₃TACD)₂] (3) or [Li₄(nBu)₂(Me₃TACD)₂] (4) are formed. As shown by single-crystal X-ray diffraction, both molecular structures show a ladder motif. (Me₃TACD)H reacted with NaI/Na₂CO₃ in acetonitrile to give benzene-soluble [NaI(Me₃TACD)H] (5).

Salt metathesis reaction of the imido complex [Ti(NR)Cl₂(NC₅H₅)₃] (R = tBu, C₆H₃iPr₂-2,6) with 1 equiv. of the lithium salt of the corresponding [OSSO]-type bis(phenol) [edtbpH₂: (HOC₆H₂-tBu₂-4,6)₂(SCH₂CH₂S); rac-(cydtbp)H₂: (HOC₆H₂-tBu₂-4,6)₂(S₂C₆H₁₀-1,2)] afforded imido titanium complexes [Ti(edtbp)(NtBu)(NC₅H₅)] (1), [Ti(edtbp)(NC₆H₃iPr₂-2,6)(NC₅H₅)] (2), and [Ti{rac-(cydtbp)}(NtBu)(NC₅H₅)] (3). The bis(dimethylamido)titanium complex [Ti(edtbp)(NMe₂)₂] (4) was synthesized by protonolysis of [Ti(NMe₂)₄] with bis(phenol) edtbpH₂. Reaction of [Ti(NMe₂)Cl₃] with the lithium salt of the bis(phenol) gave the chloro dimethylamido complex [Ti(edtbp)(NMe₂)Cl] (5) in high yield. All complexes were characterized by NMR spectroscopy and elemental analysis. Additionally, complexes 1 and 5 were studied by X-ray diffraction analysis. Imido titanium complex 1 shows moderate activity in the intramolecular hydroamination reaction of 5-phenylpent-4-ynylamine. Complexes 1–3 catalyze the intramolecular hydroamination of aminoalkenes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Reaction of group 4 metal tetrabenzyl complexes [M(CH₂Ph)₄] (M = Ti, Zr, Hf) with 1 or 2 equiv. of a thioether-functionalized phenol 2,4-tBu₂-6-(PhSCH₂)C₆H₂OH afforded dibenzyl complexes [M(L)₂(CH₂Ph)₂] (M = Ti, 1; M = Zr, 2; M = Hf, 3) and the tribenzyl zirconium complex [Zr(L)(CH₂Ph)₃] (4). Benzyl abstraction with a Lewis acid gave the zirconium monobenzyl cation [Zr(L)₂CH₂Ph]⁺[PhCH₂B(C₆F₅)₃]^– (5) and the dibenzyl cation [Zr(L)(CH₂Ph)₂]⁺[PhCH₂B(C₆F₅)₃]^– (6). The monobenzyl cation 5 oligomerized 1-hexene to low molecular-weight atactic oligo(1-hexene) (M_n = 560–820), while the dibenzyl cation 6 polymerized 1-hexene isospecifically ([mmmm] > 90 %). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Monocationic bis-allyl complexes [Ln(η³-C₃H₅)₂(thf)₃]⁺[B(C₆X₅)₄]⁻ (Ln=Y, La, Nd; X=H, F) and dicationic mono-allyl complexes of yttrium and the early lanthanides [Ln(η³-C₃H₅)(thf)₆]²⁺[BPh₄]₂⁻ (Ln=La, Nd) were prepared by protonolysis of the tris-allyl complexes [Ln(η³-C₃H₅)₃(diox)] (Ln=Y, La, Ce, Pr, Nd, Sm; diox=1,4-dioxane) isolated as a 1,4-dioxane-bridged dimer (Ln=Ce) or THF adducts [Ln(η³-C₃H₅)₃(thf)₂] (Ln=Ce, Pr). Allyl abstraction from the neutral tris-allyl complex by a Lewis acid, ER₃ (Al(CH₂SiMe₃)₃, BPh₃) gave the ion pair [Ln(η³-C₃H₅)₂(thf)₃]⁺[ER₃(η¹-CH₂CHCH₂)]⁻ (Ln=Y, La; ER₃=Al(CH₂SiMe₃)₃, BPh₃). Benzophenone inserts into the LaC_allyl bond of [La(η³-C₃H₅)₂(thf)₃]⁺[BPh₄]⁻ to form the alkoxy complex [La{OCPh₂(CH₂CHCH₂)}₂(thf)₃]⁺[BPh₄]⁻. The monocationic half-sandwich complexes [Ln(η⁵-C₅Me₄SiMe₃)(η³-C₃H₅)(thf)₂]⁺[B(C₆X₅)₄]⁻ (Ln=Y, La; X=H, F) were synthesized from the neutral precursors [Ln(η⁵-C₅Me₄SiMe₃)(η³-C₃H₅)₂(thf)] by protonolysis. For 1,3-butadiene polymerization catalysis, the yttrium-based systems were more active than the corresponding lanthanum or neodymium homologues, giving polybutadiene with approximately 90 % 1,4-cis stereoselectivity.

The cover picture shows the reactivity of half-sandwich bis(aluminate) complexes of the rare-earth metals that can be converted either into cationic methyl species by protonolysis or into dimeric dimethyl species by donor-induced cleavage of the aluminate moieties. Details are discussed in the article by J. Okuda et al. on p. 2801 ff.

Half-sandwich rare-earth metal tetramethylaluminate complexes [Ln(η⁵-C₅Me₄SiMe₃){(μ-Me)₂(AlMe₂)}₂] (Ln = Y, La, Nd, Sm, Gd, Lu) were obtained by reaction of the neutral homoleptic tetramethylaluminate complex [Ln{(μ-Me)₂(AlMe₂)}₃] with tetramethyl(trimethylsilyl)cyclopentadiene, (C₅Me₄H)SiMe₃. Protonolysis reaction of the neutral mono(cyclopentadienyl) complexes with the Brønsted acid [NEt₃H]⁺[BPh₄]^– in thf led to the formation of the monocationic methyl complexes [Ln(η⁵-C₅Me₄SiMe₃)Me(thf)₃]⁺[BPh₄]^– (Ln = Y, La, Nd, Sm, Lu). Single-crystal X-ray diffraction study on the Y, Sm, and Lu derivatives showed a four-legged piano-stool configuration. Upon activation with [Ph₃C]⁺[B(C₆F₅)₄]^–, the neutral half-sandwich tetramethylaluminate complex [La(η⁵-C₅Me₄SiMe₃){(μ-Me)₂(AlMe₂)}₂] catalyzed the polymerization of butadiene in the presence of [AliBu₃] to give trans-1,4-polybutadiene with narrow polydispersities (M_n/M_w = 1.05–1.09).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Trimethylsilylmethyl complexes of the type [Ln(η⁵-C₅Me₄CH₂SiMe₂NC₆H₄R-4-κN)(CH₂SiMe₃)(thf)_n] containing a dianionic ligand [C₅Me₄CH₂SiMe₂NC₆H₄R-4]^2– with a para-substituted anilido group and a CH₂SiMe₂ link were prepared. The yttrium complex [Y(η⁵-C₅Me₄CH₂SiMe₂NPh-κN)(CH₂SiMe₃)(thf)₂] (2a) reacts with H₂ to generate the corresponding dimeric hydride [Y(η⁵-C₅Me₄CH₂SiMe₂NPh-κN)(μ-H)(thf)]₂ (5a). Pyridine inserts into the Y–H bond in a 1,2-fashion to afford the stable 2-hydropyridyl complex [Y(η⁵-C₅Me₄CH₂SiMe₂NPh-κN)(η¹-NC₅H₆)(py)₂] (6a). Upon reaction with tBuC≡CH, protonolysis takes place to give the dimeric alkynyl complex [Y(η⁵-C₅Me₄CH₂SiMe₂NPh-κN)(μ-C≡CtBu)(thf)]₂ (7a).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Chiral 1,2-trans-dithiocyclohexanediyl-bridged bis(phenols) of the type [2,2′-{HOC₆H₂-6-R¹-4-R²}₂S₂C₆H₁₀] ([OSSO]H₂, R¹=tBu, iPr, H; R²=tBu, iPr, Me) could be conveniently and selectively synthesized in three steps, starting from cyclohexene oxide and arene thiolate. The racemic bis(phenols) could be resolved using an enantiopure (S)-camphorsulfonic ester auxiliary or by (chiral) HPLC. Complexation of the racemic bis(phenols) to TiX₄ (X=Cl, OiPr) proceeds in a diastereoselective fashion to give only the Λ,R,R and Δ,S,S enantiomers. Racemic [Ti{(OC₆H₂-6-tBu-4-Me)₂S₂C₆H₁₀}Cl₂] reacts with benzyl magnesium bromide to afford the crystallographically characterized dibenzyl complex. The benzyl cation formed using B(C₆F₅)₃ in C₆D₅Br slowly decomposes at temperatures above +10 °C. When treated with methylaluminoxane, the dichloro complexes [Ti{OSSO}Cl₂] polymerize styrene with activities up to 146 kg (mol catalyst)⁻¹ [styrene (mol L⁻¹)]⁻¹ h⁻¹; diisopropoxy complexes [Ti{OSSO}(OiPr)₂] show mere trace activity. With 1-hexene as a chain-transfer agent, activated enantiopure titanium complexes give low-molecular-weight homochiral isotactic oligostyrenes, terminated by one to five 1-hexene units with M_n values as low as 750 g mol⁻¹ for R=tBu and 1290 g mol⁻¹ for R=Me. Below M_n≈5000 these oligostyrenes show optical activity.