Mechanism and Activity of Ruthenium Olefin Metathesis Catalysts:  The Role of Ligands and Substrates from a Theoretical Perspective

Adlhart, Christian; Chen, Peter

doi:10.1021/ja0305757

Cited by 276 publications

(217 citation statements)

References 83 publications

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“…64 In order to deconvolute these potential contributions to khomo, we examined the mechanism of ROMP. Based on previously reported results for related phosphine-based catalysts, [65][66][67] we proposed a dissociative pathway ( Figure 5A 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 5 intermediate. Subsequent cycloreversion yields a Pn+1 alkylidene and regenerates the 14-electron species.…”

Section: Chart 1 Monomer Design For Ring-opening Metathesis Copolymementioning

confidence: 83%

Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions

et al. 2017

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Grafting density and graft distribution impact the chain dimensions and physical properties of polymers. However, achieving precise control over these structural parameters presents long-standing synthetic challenges. In this report, we introduce a versatile strategy to synthesize polymers with tailored architectures via grafting-through ring-opening metathesis polymerization (ROMP). One-pot copolymerization of an ω-norbornenyl macromonomer and a discrete norbornenyl co-monomer (diluent) provides opportunities to control the backbone sequence and therefore the side chain distribution. Toward sequence control, the homopolymerization kinetics of 23 diluents were studied, representing diverse variations in the stereochemistry, anchor groups, and substituents. These modifications tuned the homopolymerization rate constants over two orders of magnitude (0.36 M −1 s −1 < khomo < 82 M −1 s −1 ). Rate trends were identified and elucidated by complementary mechanistic and density functional theory (DFT) studies. Building on this foundation, complex architectures were achieved through copolymerizations of selected diluents with a poly(D,L-lactide) (PLA), polydimethylsiloxane (PDMS), or polystyrene (PS) macromonomer. The cross-propagation rate constants were obtained by non-linear least squares fitting of the instantaneous co-monomer concentrations according to the Mayo-Lewis terminal model. Indepth kinetic analyses indicate a wide range of accessible macromonomer/diluent reactivity ratios (0.08 < r1/r2 < 20), corresponding to blocky, gradient, or random backbone sequences. We further demonstrated the versatility of this copolymerization approach by synthesizing AB graft diblock polymers with tapered, uniform, and inverse-tapered molecular "shapes." Small-angle X-ray scattering analysis of the self-assembled structures illustrates effects of the graft distribution on the domain spacing and backbone conformation. Collectively, the insights provided herein into the ROMP mechanism, monomer design, and homo-and copolymerization rate trends offer a general strategy for the design and synthesis of graft polymers with arbitrary architectures. Controlled copolymerization therefore expands the parameter space for molecular and materials design.

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Section: Chart 1 Monomer Design For Ring-opening Metathesis Copolymementioning

confidence: 83%

Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions

et al. 2017

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“…The root of the lower activities of the Grubbs systems lies in their mode of initiation and the accessibility of the reactive species, which has been shown experimentally [13,14] and computationally [15,16] to be the 14-electron alkylidene [Cl 2 (L)Ru = C(H)R] formed upon reversible dissociation of L'. The reaction temperatures required to overcome this initiation step can lead to decreased catalyst lifetimes.…”

mentioning

confidence: 99%

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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“…Modelos experimentais e teóricos 7,15,16 permitiram descrever um mecanismo para trimerização do norborneno; a reação modelo é finalizada com adição de uma molécula de eteno. As estruturas presentes no mecanismo em questão são mostradas na Figura 2; o mecanismo proposto pode ser visto por completo na Figura 1S, material suplementar.…”

Section: Mecanismo Geral Para Metátese Romp Do Norbornenounclassified

Investigação do mecanismo de catálise ROMP do norborneno utilizando métodos de funcional de densidade

Silva¹,

Lima²,

Leal³

et al. 2010

Quím. Nova

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Recebido em 23/7/09; aceito em 14/3/10; publicado na web em 9/8/10INVESTIGATION OF THE ROMP CATALYSIS MECHANISM OF NORBORNENE USING METHODS OF DENSITY FUNCTIONAL. This work presents a density functional theory study of the norbornene ROMP metathesis reactions. The energies have been calculated in a Grubbs catalyst model Cl 2 (PH 3 ) 2 Ru=CH 2 . The geometries and energy profile are similar to the Grubbs metilydene (Cl 2 (PCy 3 ) 2 Ru=CH 2 real model. It was found that the metathesis reaction proceeds via associative mechanism (catalyst-norbonene) followed by dissociative substitution of a phosphine ligand with norbonene, giving a monophosphine complex. The results are in reasonable agreement with the available experimental data. The dissociation energy of the phosphines is predicted to be 23.2 kcal mol -1 .Keywords: ROMP-metathesis; molecular modeling; DFT. INTRODUÇÃODerivada das palavras gregas meta -mudança e thesis -posição, a metátese é a troca de partes de duas substâncias. 1 Quando ocorre tal troca de grupos entre duas olefinas iniciais, duas outras olefinas são produzidas. Catalisadores para metátese foram desenvolvidos como ferramentas altamente poderosas e versáteis em síntese orgânica. A grande variedade de transformações sintéticas que podem ser realizadas é surpreendente. Somente com Y. Chauvin, em 1971, que um mecanismo viável foi apresentado. Chauvin e Hérisson propuseram que a reação se iniciava com a formação de um complexo metalcarbeno 1,2 e publicaram o mecanismo da metátese como ilustrado na Figura 1.Inicialmente, ocorre uma adição do tipo 2+2 do complexo metalcarbeno com a olefina. Logo em seguida acontece a coordenação da olefina com o complexo metal-carbeno, formando um intermediário metalociclobutano. Por fim, uma cicloreversão dá origem a um novo complexo metal-carbeno. Dentre os diversos tipos de metátese destacam-se: 1 CM (cross-metathesis), metátese cruzada -ocorre entre olefinas diferentes; RCM (ring-closing metathesis), metátese de fechamento de anel -é uma metátese intramolecular que ocorre em dienos, na qual há formação de um anel; ROM (ring-opening metathesis), metátese com abertura de anel -ocorre abertura de uma ciclo-olefina formando dienos, é o inverso da RCM; ADMET (acyclic diene metathesis polymerization), polimerização via metátese entre dienos acíclicos; e ROMP (ring-opening metathesis polymerization), polimerização via metátese com abertura de anel -ocorre entre alcenos cíclicos, único método de polimerização de inúmeros polímeros que não podem ser obtidos por outros processos. 3 Grubbs e colaboradores, em 1992, publicaram o primeiro complexo molecular metal-carbeno bem definido Cl 2 (PPh 3 ) 2 Ru=CH-CH=CPh 2 , que não somente era ativo para a polimerização do norborneno como também era estável na presença de solventes próticos. 4 Para aumentar a reatividade do catalisador, os grupos fenil foram trocados por grupos ciclo-hexil (R = Cy). Em 1995, Grubbs publicou novos catalisadores molecularmente bem definidos Cl 2 (PR 3 ) 2 Ru=CHPh, R=Ph ou Cy (ciclo-hexil). 5 A combinaçã...

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Mechanism and Activity of Ruthenium Olefin Metathesis Catalysts: The Role of Ligands and Substrates from a Theoretical Perspective

Cited by 276 publications

References 83 publications

Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions

Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions

Rapidly Initiating Ruthenium Olefin‐Metathesis Catalysts

Investigação do mecanismo de catálise ROMP do norborneno utilizando métodos de funcional de densidade

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