The synthesis and characterisation of copper(I) complexes of chiral pyridine-containing macrocyclic ligands (Pc-L*) and their use as catalysts in asymmetric cyclopropanation reactions are reported.All ligands and metal complexes were fully characterised, including crystal structures of some species determined by X-ray diffraction on single crystals. This allowed characterising the very different conformations of the macrocycles which could be induced by different substituents or by metal complexation.The strategy adopted for the ligand synthesis is very flexible allowing several structural modifications. A small library of macrocyclic ligands possessing the same donor properties but with either C 1 or C 2 symmetry was synthesized. Cyclopropane products with both aromatic and aliphatic olefins were obtained in good yields and enantiomeric excesses up to 99%.

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.

ABSTRACT:The first study of low catalyst loading olefin metathesis reactions in air is reported. TON values of up to 7000 were obtained using non-degassed solvents with commercially available pre-catalysts Caz-1, Hov-II and Ind-II. The simple experimental conditions allow olefin metathesis reactions to be carried out on the benchtop using technical grade solvents in air. KEYWORDS olefin metathesis, homogeneous catalysis, ruthenium, phosphite, air.The olefin metathesis reaction represents a powerful tool for the formation of carbon-carbon bonds.1 Development of precatalysts by modification of the original ruthenium complex reported by Grubbs and co-workers has led to more robust and active catalysts.2 Even if ruthenium pre-catalysts display better tolerance toward water and oxygen than early transition metal complexes, 2b inert atmosphere and anhydrous solvents are generally used to carry out such reactions.2 In the last two decades, only a few studies have started to question the catalytic performance of Ru systems in the presence of air. 3a Some 10 years later, Dowden and Hoveyda independently reported the use of modified Hoveyda-Grubbs-type pre-catalysts for ring-closing metathesis (RCM) reactions affording di-substituted olefins in air with non-degassed CH 2 Cl 2 and THF using 5 mol% Ru at 22-80°C.3b-c Subsequently, Blechert and co-workers described the use of commercially available G-II and Hov-II (Figure 1) in non-degassed MeOH at 22°C affording di-substituted olefins in high yields with 3-5 mol% of Ru.3d In order to obtain systems suitable for use in protic solvents, the Raines group isolated salycilaldimine-based benzylidene ruthenium precatalysts active in the RCM of dienes and in enyne metathesis. The pre-catalysts showed moderate to high conversions in non-degassed d 4 -methanol as well as d 6 -benzene in air with 5-10 mol% Ru at 55°C.3e More recently, a Hoveyda-Grubbs type pre-catalyst immobilized on polyethylene glycol able to perform RCM in air was reported by Abell and co-workers. Diand tri-substituted olefins were reacted with the use of nondegassed CH 2 Cl 2 in air and 10 mol% Ru at reflux.3f Inspired by the Raines work with salycilaldimine derivatives, 3e Verpoort and co-workers introduced a Schiff base in the phosphine-containing indenylidene ruthenium system. This system was shown active in ring-closing metathesis (RCM) and crossmetathesis (CM) of allyl benzene and cis-1,4-diacetoxy-2-butene in air with 1-2.5 mol% Ru at 40-80°C. 3g In 2010, Tew and co-workers described the ring-opening metathesis polymerization (ROMP) of a hydrophilic norbornene monomer leading to the formation of hydrogels using the pyridinebased Grubbs pre-catalyst in air at room temperature. Despite the living polymerization nature of this specific transformation, the propagating catalyst attached to the polymer chains was found to be inactive after 1 h under these reaction conditions.3h Recently, other modified Hoveyda-Grubbs type pre-catalysts were reported independently by Jensen and Grela.3i-j Jensen and co-workers des...

ABSTRACT:The reaction of the ruthenium complex cis-Caz-1 with silver fluoride affords the first example of an active olefin metathesis pre-catalyst containing fluoride ligands. The cis geometry of the precursor complex is key to the successful fluoride exchange reaction. Computational studies highlight the stability of the new Ru-F species, due to pushpull interactions between fluoride and L-type ligands (L: N-heterocyclic carbene, phosphite). Insights into the isomerization process from trans-Caz-1 to cis-Caz-1 are given. Fluoride exchange reactions were performed involving cis-and trans-Caz-1 complexes. Catalytic tests showcase the excellent activity of the Ru-F containing complexes.

A straightforward method for the hydrophenoxylation of internal alkynes, using N-heterocyclic carbene-based copper(i) and gold(i) complexes, is described. The heterobimetallic catalytic system proceeds via dual activation of the substrates to afford the desired vinylether derivatives. This methodology is shown to be highly efficient and tolerates a wide range of substituted phenols and alkynes.