Agostische Wechselwirkungen in d<sup>0</sup>‐Alkylmetallkomplexen

Scherer, Wolfgang; McGrady, G. Sean

doi:10.1002/ange.200200548

Cited by 68 publications

(42 citation statements)

References 209 publications

(167 reference statements)

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“…No evidence for a CÀH agostic interaction is observed in the proton NMR spectra, nor are lowfrequency CÀH vibrations apparent in the IR spectra of compounds 3, which would be expected if any of the CÀH bonds were donating electron density to the unsaturated ruthenium center. [29] Four-coordinate ruthenium complexes not stabilized by CÀH agostic interactions are rare; [30] thus, apart from being models for the 14-electron active species in olefin metathesis, compounds 3 are unusual coordination compounds.…”

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Rapidly Initiating Ruthenium Olefin‐Metathesis Catalysts

2004

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Olefin metathesis is arguably the most powerful carboncarbon bond breaking and making reaction in chemical synthesis.[1] Depending on the nature of the reacting partners, olefin metathesis can be used for ring-opening polymerization (ROMP), [2] to create advanced polymeric materials, [3] transformation of acyclic diene substrates into complex cyclic organic molecules (in ring-closing metathesis (RCM)) [4] or polymers (in acyclic diene metathesis (ADMET)) [5] or in cross metathesis (CM) to generate unsymmetrical olefins. [6,7] Although olefin metathesis is fully reversible, RCM, ADMET, and CM rely on the elimination of ethylene, the simplest olefin, as a thermodynamic driving force. Used by itself or in tandem with other synthetic transformations, [8,9] olefin metathesis is a versatile method for the modern synthetic chemist.It is generally acknowledged that a metal carbene species, {L n M=CRR'}, is required and that interaction with an olefin substrate leads to four-membered metallacyclobutane intermediates or transition states, {L n M(CRR') 3 }, by a 2+2 cycloaddition; cleavage of this intermediate in the opposite sense by which it was formed leads to olefin metathesis, creating a new carbon-carbon double bond and regenerating an active metal carbene. Metal carbenes are generally classified as being nucleophilic (electron rich) or electrophilic (electron poor) in character at the carbene carbon atom, but an effective olefin-metathesis catalyst exhibits behavior between these two extremes. Two carefully tuned classes of mediator have evolved into the catalysts of choice for olefin metathesis. Schrock catalysts [10,11] are molybdenum-or tungsten-based alkylidenes with a fairly specific ligand set designed to modulate the properties of the carbene (Figure 1). These catalysts display high activities and stabilities, but are sensitive to ambient air and moisture and are relatively intolerant of polar functionalities. The Grubbs-catalyst portfolio [12] consists of a variety of ruthenium-based systems of general formula [Cl 2 (L)(L')Ru = C(H)R] (compounds 1) which are significantly more functional-group tolerant, but do not exhibit the same levels of activity or longevity as the Schrock catalysts.

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Rapidly Initiating Ruthenium Olefin‐Metathesis Catalysts

2004

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“…[29] Eines der Methylenprotonen orientiert sich in Richtung des Lanthanzentrums, was an eine a-agostische La-(HC)-Wechselwirkung erinnert (La-H25B 2.60(3) und La-C25-H25B 84 (2)8). [30] (7) ) [16] sowie in [Cp* 3 La 3 (m-Cl) 3 (m 3 -Cl)(m 3 -CH 2 )(thf) 3 ] (2.537(3) bis 2.635(3) ) beobachtet. [13] Die beiden La-(m-CH 3 )-Bindungslängen in 3 (La-C26 2.809(2), La-C29 2.833(2) ) liegen im erwarteten Bereich.…”

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Eine Seltenerdmetallvariante des Tebbe‐Reagens

et al. 2008

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Das Tebbe-Reagens [Cp 2 Ti{(m-CH 2 )(m-Cl)Al(CH 3 ) 2 }] (A; Cp = Cyclopentadienyl) gehört zu den schillerndsten metallorganischen Verbindungen.[ [3] und Wolfram-Methylen-Verbindungen (vorgeschlagen als Olefinmetathese-Katalysatoren) [4] röntgenographisch charakterisiert.[3] Obgleich katalytisch aktiv in der Olefinmetathese, [5] wird das Tebbe-Reagens derzeit als effizientes Carbonyl-Methylenierungsreagens eingesetzt. [9, 10] Vorangegangene Untersuchungen unserer Arbeitsgruppe befassten sich mit Seltenerdmetall(III)-TetramethylaluminatKomplexen [L x Ln{Al(CH 3 ) 4 } y ] (y = 1, 2, 3; x + y = 3, L = einzähniger Hilfsligand, Ln = Seltenerdmetall und Sc, Y, La) als Polymerisationskatalysatoren [11,12] und führten zur Isolation von Ln III -Clustern mit Methylen-, [13,14] Methin- [15] und Carbidfunktionalitäten.[

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“…Reactions of laser-ablated thorium and uranium atoms with chlorofluoromethane (CH 2 FCl) have formed new actinide methylidene complexes [H 2 C = AnFCl], where An = Th and U. Through relativistic density functional theory (DFT) and ab initio studies at the CCSD(T) level, we find that these two actinide molecules have strong agostic interactions [5,6] and display pyramidalization. These effects lead to chiral actinide complexes with C = An bonds.…”

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confidence: 99%