Letter Cite This: ACS Catal. 2018, 8, 6413−6418
pubs.acs.org/acscatalysis
Photoactivation of Ruthenium Phosphite Complexes for Olefin Metathesis Or Eivgi,† Stefano Guidone,† Alexander Frenklah,† Sebastian Kozuch,† Israel Goldberg,‡ and N. Gabriel Lemcoff*,†,§ †
Department of Chemistry, Ben Gurion University of the Negev, Beer-Sheva, Israel, 84105 School of Chemistry, Tel-Aviv University, Tel-Aviv 69978, Israel § Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer-Sheva, Israel, 84105 Downloaded via UNIV OF SOUTH DAKOTA on June 17, 2018 at 06:33:06 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
‡
S Supporting Information *
ABSTRACT: The commercially available catalyst cis-Caz-1 is extremely robust, especially when reactions are performed in an atmosphere of air. This phosphite-containing ruthenium complex only shows olefin metathesis activity at high temperatures. Herein, we report photoactivation of cis-Caz-1 at room temperature with UVA light. Thus, a wide variety of olefin metathesis reactions was performed under mild conditions with good yields. In addition, we report the synthesis, characterization, and catalytic activity of a phosphite-chelated ruthenium benzylidene complex, cis-PhosRu-1, which can be efficiently activated either by irradiation with visible light (λ = 405 nm) or by heat. KEYWORDS: latent catalysis, olefin metathesis, ruthenium, phosphites, photochemistry
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1).8 In analogy to the S-chelated benzylidene complexes, the phosphite-coordinated ruthenium indenylidenes also adopted the latent cis-dichloro configuration. Upon heating, these complexes proved to be highly active, exhibiting excellent reactivity and thermal stability. Notably, even difficult olefin
lefin metathesis is one of the most important chemical reactions used to form new carbon−carbon double bonds, and it is routinely employed in academic research, as well as in the polymer and pharmaceutical industries.1 The development of latent complexes with the ability to promote the reaction using external stimuli (heat, light, pH, ultrasound, etc.) has enabled the specific execution of olefin metathesis in focused applications.2 Naturally, the use of light as a tool to make metathesis happen is quite appealing, because light is considered to be the ultimate “green” reagent and gives access to temporal and spatial control.3 The development of efficient lightswitchable olefin metathesis catalysts led to the ingress of olefin metathesis to a new set of industrial applications, such as stereolithography and 3D printing, where light enables the patterning of surfaces with good resolution.4 A notable series of precatalysts that may be photoinitiated is the family of Schelated ruthenium benzylidenes.5 These complexes adopt a latent cis-dichloro configuration due to a trans influence repulsion between the strong sigma electron-donating NHC ligand and the chelating sulfur atom.6 When irradiated with UVA light, isomerization to the active trans dichloro isomer ensues. This specific window of photoactivation with UVA light (350−380 nm) was used in several chromatic orthogonal processes and photochemical syntheses of important natural product scaffolds.7 Following the interest in stable and latent ruthenium metathesis catalysts, Cazin and co-workers, since 2010, have reported a series of highly robust phosphitecoordinated ruthenium indenylidene complexes (see Figure © XXXX American Chemical Society
Figure 1. Ruthenium olefin metathesis catalysts containing phosphite ligands. Received: April 26, 2018 Revised: May 28, 2018 Published: June 12, 2018 6413
DOI: 10.1021/acscatal.8b01637 ACS Catal. 2018, 8, 6413−6418
Letter
ACS Catalysis
olefin metathesis activity at all, opening the door to chromatic orthogonal applications.12 As detailed in Table 1, the dark control experiments showed
