Activation of olefin metathesis complexes containing unsymmetrical unsaturated N-heterocyclic carbenes by copper and gold transmetalation Fadwa Kamal, Sophie Colombel-Rouen, Adrien Dumas, Jean-Paul Guégan, Thierry Roisnel, Vincent Dorcet, Olivier Baslé, Mathieu Rouen, Marc Mauduit To cite this version: Fadwa Kamal, Sophie Colombel-Rouen, Adrien Dumas, Jean-Paul Guégan, Thierry Roisnel, et al.. Activation of olefin metathesis complexes containing unsymmetrical unsaturated N-heterocyclic car- benes by copper and gold transmetalation. Chemical Communications, Royal Society of Chemistry, 2019, 55 (77), pp.11583-11586. 10.1039/c9cc05776e. hal-02307034 HAL Id: hal-02307034 https://hal-univ-rennes1.archives-ouvertes.fr/hal-02307034 Submitted on 4 Dec 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. COMMUNICATION Activation of olefin metathesis complexes containing unsymmetrical unsaturated N-heterocyclic carbenes by copper Received 00th January 20xx, Accepted 00th January 20xx and gold transmetalation DOI: 10.1039/x0xx00000x Fadwa Kamal,a Sophie Colombel-Rouen,a Adrien Dumas,a Jean-Paul Guégan,a Thierry Roisnel,a a a b a www.rsc.org/ Vincent Dorcet, Olivier Baslé, † Mathieu Rouen and Marc Mauduit* The activation of ruthenium-indenylidene complexes containing required.7 Several strategies were reported to improve their two unsymmetrical unsaturated N-heterocyclic carbenes (u2- catalytic performances by facilitating the decoordination of NHCs) by a transmetalation process is reported. The use of one NHC ligand with noteworthy successes.8 Notably, the copper(I) or gold(I) chlorides promotes the rapid trapping of one introduction of electron-deficient NHC ligands9 or small NHC NHC ligand that releases the catalytic active Ru-species. units10 could enhance the activity of the related complexes Impressive initiation rates with full-conversions are observed with catalyst loadings as low as 0.05 mol% (Figure 1, a). In within one minute. This practical protocol demonstrates excellent 2011, Grubbs and Bertrand successfully reported the use of a catalytic performances in various ring-closing metathesis (RCM) Brønsted acid as external stimulus to promote the protonolysis and self-metathesis (SM). of a mesoionic carbene (MIC).11 The resulting 14e- catalytic species proved to be extremely active, surpassing current In a few decades, olefin metathesis has rapidly become one of commercial Ru-catalysts (Figure 1, b-left). More recently, our the most efficient synthetic tools in organic chemistry This group synthesised new complexes Ru-1 containing two attractiveness was mainly due to the development of efficient, unsymmetrical unsaturated N-cycloalkyl-NHCs (u2NHCs) that well-defined, air stable and easy to handle ruthenium- were activated by anhydrous HCl (Figure 1, b-right).12 These arylidene complexes with high tolerance towards many catalysts were quite efficient in various metathesis 1 organic functions. Since the pioneer works describing the manuscripttransformations, notably in macrocyclic ring-closing metathesis phosphine-based Grubbs first-generation catalyst in early (RCM) yielding various macrocyclic odorant molecules of 2 1990s, the research efforts to furnish more robust and remarkable >99% purity. Nevertheless, the use of anhydrous 1,3 powerful complexes have drastically increased. The HCl remained difficult to handle.13 development of catalysts containing a N-Heterocyclic Carbene a) Use of labile NHC ligands O2N (NHC) ligand that demonstrated higher stability and activity, NO2 Mes N N Mes N N O N N N known as Grubbs second generation catalysts, represents Mes Mes 2 NO2 Cl heating 4 NHCL = certainly the most successful achievement in this field. While Ru Rc Cl Cl Ru Rc Me N N Me NHC NHCL L Cl R : Me or Cl numerous catalysts bearing one NHC unit have been R R 5 Rc: Reactive carbene active species intensively developed, the class of Ru-complexes featuring (benzylidene or indenylidene) b) Use of protonolisable NHC ligands two NHCs has scarcely been investigated. Historically, the first N N N N members of this class were reported in 1998 by the Herrmann Mes Mes Mes R’ N N N N R’ 6 Mes Mes Cl Cl Ph Mes HCl HCl group prior to the Grubbs second generation catalyst. Ru Ru Cl Ph Cl Ph Ru Cl Cl Ru Unfortunately, due to a stronger coordination of the NHC Ph Cl N Mes Cl N N R’ ligand, a significant thermal stimulus was needed to observe active species N N active species satisfactory activities in olefin metathesis. In recent years, a Ru-1 (R’ = cycloalkyl) renewed interest has taken place for these catalysts, notably in c) Use of copper(I) or gold(I) chloride (this work) materials science, in which a full-control of the catalytic 88 N N Ar 88 N N Ar Cl Cl MCl initiation of Accepted the metathesis polymerisation is strongly Ph M + Ru Cl Ph transmetalation Ru Cl Ar (M = Cu or Au) N N 8 Cl 8 Ar N N 8 8 active species Ru-1 Fig. 1 Previously reported activation of Ru-complexes containing two NHC ligands (a and b) and the proposed transmetalation protocol (c, this work) J. Name., 2013, 00, 1-3 | 1 COMMUNICATION Journal Name We would like now to report an efficient activation of Ru- Moreover, thanks to their robustness toward silica gel, Ru-2a indenylidene complexes Ru-1 containing two u2-NHCs by a and Cu-1a were isolated in excellent 91 and 86% yields after transmetalation process involving copper(I) or gold(I) purification. Interestingly, the transmetalation process also chlorides. The rapid release of the active catalytic Ru-species in succeed with gold(I) chloride but required higher reaction time the reaction media led to impressive initiation rates with full (24 h) to reach 69% conversion. Ru-2a and gold-u2NHC Au-1a conversions that occur within a few minutes. Through this were isolated in respectively 45 and 39% yield after practical protocol, excellent catalytic performances were purification. Additionally, X-ray diffraction analysis observed in various RCM and SM. unambiguously confirmed the structure of Ru-2a and Au-1a In 1997, Grubbs and co-workers were the first to report the (Scheme 1). Unfortunately, all attempts to isolate suitable beneficial use of copper(I) chloride to enhance the initiation single crystals of Cu-1a remained unsuccessful. rates of well-defined (PR3)2X2Ru=CH-CH=Ph2 precatalysts With this efficient protocol of activation in hands, the catalytic during RCM transformations.14a Albeit the nature of the activity profile of Ru-1a was studied for the RCM of resulting species was unknown, the authors suspected that diethyldiallylmalonate (DeDAM) S1 under standard conditions CuCl could act as a phosphine scavenger. Later, Blechert and (1 mol%, 0.1 M).17a As depicted in figure 2, the critical role of co-workers used this protocol to enhance the turnover CuCl and AuCl appeared quite prominent. At 30 °C, as number (TON) of Grubbs 2nd generation precatalyst in cross- expected for a bis-NHC catalyst, Ru-1a showed a very slow metathesis of reluctant acrylonitrile.14b It is worth to underline reactivity toward diene S1 with only 10% conv. after two hours that the phosphine-scavenging effect was also successfully (67% at 24 h, Fig. S5, eSI). Addition of CuCl (5 mol%) led to a employed to improve the synthesis of phosphine-free fast initiation of the metathesis reaction, reaching up to 80% styrenylether Ru-catalysts (i.e. Hoveyda type precatalyst).15 conv. after only 20 min. and a full conversion after 40 min.17b More recently, Thuo and co-workers reported that copper(I) With gold activator, an impressive initiation rate occurred halides limited drastically the formation of isomerized by- converting up to 80% of S1 within 5 min., however the product when metathesis reaction occurred in polar protic catalytic system became rapidly less productive as a very slow solvents with phosphine-based Grubbs catalysts.16 Based on consumption was observed after 2 hours (84% conv.). these reports, we decided to examine the ability of copper(I) or gold(I) salts to activate our bis-u2NHC Ru-1 by sequestering EtO2C CO2Et Ru-1a (1 mol%) EtO2C CO2Et activator (5 mol%) one NHC ligand (Figure 1, c). First, the transmetalation process toluene (0.1 M) was investigated by reacting Ru-1a complex with 30 or 80 °C stoichiometric amounts of CuCl and 1-isopropoxy-2- S1 P1 vinylbenzene L1 in CH2Cl2 at 50 °C (Scheme 1). We were a) Reaction performed at 30 °C delighted to observe remarkable conversions for expected 100 Hoveyda-type catalyst Ru-2a and copper-u2NHC Cu-1a after 5 90 h of reaction (>95%, see eSI for details). manuscript80 70 60 N 8 N 50 Cl 40 Ru Conversion (%) 30 Cl 20 O 10 CuCl (1.2 equiv) + Ru-2a (91%)b 0 CH2Cl2, 50 °C, 5 h 0 20 40 60 80 100 120 X-ray of Ru-2a (- indenylidene) CuCl time (min) conv. >95%a N N 8 b) Reaction performed at 80 °C 8 N N 100 Cu-1a (86%)b Cl Ph 90 Ru O Cl 80 8 N N 70 N N 8 L1 (1 equiv) 60 Cl Ru 50 Ru-1a AuCl (1.2 equiv) Cl 40 O CH2Cl2, 50 °C, 24 h + Conversion (%) 30 (- indenylidene) Ru-2a (45%)b 20 conv. 69%a 10 AuCl 0 0 20 40 60 80 100 120 AcceptedN N 8 time (min) b X-ray of Au-1a Au-1a (39%) Fig.