The fascinating story of olefin (or alkene) metathesis (eq
1) began almost five decades ago, when Anderson and
Merckling reported the first carbon-carbon double-bond
rearrangement reaction in the titanium-catalyzed polymerization of norbornene. Nine years later, Banks and Bailey reported “a new disproportionation reaction . . . in which olefins are converted to homologues of shorter and longer carbon chains...”. In 1967, Calderon and co-workers named this metal-catalyzed redistribution of carbon-carbon double bonds olefin metathesis, from the Greek word “μeτάθeση”, which means change of position. These contributions have since served as the foundation for an amazing research field, and olefin metathesis currently represents a powerful transformation in chemical synthesis, attracting a vast amount of interest both in industry and academia.

https://core.ac.uk/download/pdf/4884240.pdf

Ruthenium-based heterocyclic carbene-coordinated olefin metathesis catalysts.

N-Heterocyclic carbene (NHC) ligands, introduced as analogues to phosphines, are recently getting wide attention in the design of diverse homogeneous catalytic systems.1-6 During recent years, olefin metathesis has gained a position of increasing significance.7-9 The ruthenium complex (PCy3)2(Cl2)RudCHPh 1 (Cy ) cyclohexyl) developed by Grubbs et al.10 constitutes a highly efficient metathesis catalyst11 tolerating most functional groups. In spite of the generally superb application profile of 1, its limited stability and the low activity toward substituted double bonds are major drawbacks. The initial success of olefin metathesis has spurred the intense investigation of new catalysts for this transformation. Inter alia, the recent introduction of NHCs * To whom correspondence should be addressed. E-mail: klgrela@ gmail.com. † Polish Academy of Sciences. ‡ Warsaw University. Cezary Samojłowicz was born in 1983 in Sokołów Podlaski, Poland. He obtained his MSc Eng. degree in chemical technology from the Warsaw University of Technology, studying sigmatropic rearrangements of sulfur ylides under the supervision of Tadeusz Zdrojewski. Before moving to olefin metathesis, he conducted work on supramolecular chemistry with David Reinhoudt at Twente University. Since 2007, he is conducting his PhD study under the supervision of Karol Grela.

Ruthenium-based olefin metathesis catalysts bearing N-heterocyclic carbene ligands.

Synthetic routes to N-heterocyclic carbene precursors.

We have investigated the performance of eight popular density functionals, four of which are “standard” functionals not including dispersion (B3LYP, BP86, PBE, and TPSS) and four of which have been constructed to account for dispersion (B97D, wB97XD, M06, and M06L), in reproducing 18 molecular structures derived from single-crystal X-ray diffraction experiments on ruthenium-based olefin metathesis catalyst precursors. Our analysis of all the internuclear distances reveals that standard DFT predicts systematically expanded structures. In contrast, all the methods accounting for dispersion give rise to more compact structures, removing the systematic overestimation of internuclear distances. The contracting effect of dispersion is general and also affects chemical bonds, thus reducing the general overestimation of bond lengths. The best overall performance is observed for wB97XD, which offers relatively small statistical errors when considering the overall structure as well as selected distances. Only for the coordination center geometry is the accuracy of wB97XD matched by standard functionals such as PBE and TPSS, whereas M06 and M06L are associated with larger errors. At the other end of the scale, B3LYP is seen to give the largest statistical errors in general, both when considering the complete structures and the geometries of the coordination centers alone. For the organic ligands, however, B3LYP performs clearly better than the other standard functionals although not as well as the functionals accounting for dispersion. Extending the basis sets is seen to improve the structures in particular of the coordination center, thus underlining the importance of using sufficiently flexible basis sets if highly accurate geometries are to be obtained. Similar conclusions to those obtained for the ruthenium catalysts can be drawn from comparisons of the X-ray crystal structures of 10 other organometallic complexes of relevance to homogeneous catalysis, covering first (Ti, Fe, Co, Ni), second (Zr, Mo, Rh, Pd) and third (W, Ir) row transition metals, with those of DFT. The latter analyses thus offer a first indication that the picture obtained for the ruthenium alkylidene complexes may be extended to other classes of relatively large transition metal complexes.

The accuracy of DFT-optimized geometries of functional transition metal compounds: a validation study of catalysts for olefin metathesis and other reactions in the homogeneous phase

Ring-closing metathesis (RCM) of dienes is one of the most important methodologies now in use for the assembly of cyclic organic compounds. First employed by Villemin and by Tsuji nearly three decades ago,1,2 the reaction has risen to astonishing prominence in organic synthesis over the past decade, owing largely to the development of easily handled catalysts that enable controlled reaction.3 RCM represents a key step in many synthetic sequences: recent reviews describe its use in, inter alia, construction of synthetically valuable building blocks such as heterocyclic rings containing phosphorus,4 sulfur,4 oxygen,5 or nitrogen,5,6 including aromatic heterocycles;7 spirocyclic,8,9 cyclophane,8 and polycyclic compounds;8,9 and compounds of biological and medicinal relevance such as peptidomimetics,10,11 carbohydrate derivatives,11-14 alkaloids,11,15-19 bioactive cyclic molecules,20,21 and polycyclic ethers,22 including macrocyclic aza-crown ethers23 and topologically interesting molecules and “molecular machines”.24,25 While the common rings of 5-7 members have historically been dominant, owing in part to their greater ease of access, important advances have been made in the synthesis of medium20,26-30 and macrocyclic16,17,23,27,31-35 targets. One aspect of this review will examine the increased tendency of many medium and large rings to participate in equilibrium metathesis, and the resulting implications for selectivity and yields.

Equilibrium ring-closing metathesis.

A Thermally Switchable Latent Ruthenium Olefin Metathesis Catalyst

Gradient-corrected (BP86) and hybrid (M06-L) density functional calculations were used to study the relative stability of cis and trans-dichloro X-chelated benzylidene ruthenium complexes (X = O, S, Se, N, P). Calculations in the gas phase differed from experimental results, predicting the trans-dichloro configuration as being more stable in every case. The addition of Poisson−Boltzmann (PBF) continuum approximation (dichloromethane) corrected the disagreement and afforded energies consistent with experimental results. Novel N, Se, and P chelated ruthenium olefin metathesis complexes were synthesized to evaluate calculation predictions. These findings reinforce the importance of including solvent corrections in DFT calculations of ruthenium metathesis catalysts and predict that stronger σ donors as chelating atoms tend to electronically promote the unusual and less active cis-dichloro configuration.

Predicting the cis-trans dichloro configuration of group 15-16 chelated ruthenium olefin metathesis complexes: a DFT and experimental study.

Ruthenium olefin metathesis is without doubt one of the most thriving fields in modern synthetic chemistry. Applications in industry and recent developments in basic research make the study of alkylidene ruthenium compounds both exciting and rewarding. As usually recurrent in organometallic catalysis, the development of novel ligands, in particular alkylidene ligands, has had a pivotal role in the tremendous success of the area. This microreview details the evolution of the alkylidene ruthenium compounds, including simple alkylidenes, benzylidenes, Fischer carbenes, vinylidenes, allenylidenes, indenylidenes and the important sub-class of chelated alkylidenes, and includes a discussion of the significant effects these ligands have had on the precatalysts properties.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The Versatile Alkylidene Moiety in Ruthenium Olefin Metathesis Catalysts

A short overview on the structural design of the Hoveyda-Grubbs-type ruthenium initiators chelated through oxygen, nitrogen or sulfur atoms is presented. Our aim was to compare and contrast O-, N- and S-chelated ruthenium complexes to better understand the impact of electron-withdrawing and -donating substituents on the geometry and activity of the ruthenium complexes and to gain further insight into the trans-cis isomerisation process of the S-chelated complexes. To evaluate the different effects of chelating heteroatoms and to probe electronic effects on sulfur- and nitrogen-chelated latent catalysts, we synthesised a series of novel complexes. These catalysts were compared against two well-known oxygen-chelated initiators and a sulfoxide-chelated complex. The structures of the new complexes have been determined by single-crystal X-ray diffraction and analysed to search for correlations between the structural features and activity. The replacement of the oxygen-chelating atom by a sulfur or nitrogen atom resulted in catalysts that were inert at room temperature for typical ring-closing metathesis (RCM) and cross-metathesis reactions and showed catalytic activity only at higher temperatures. Furthermore, one nitrogen-chelated initiator demonstrated thermo-switchable behaviour in RCM reactions, similar to its sulfur-chelated counterparts.

Eyal Tzur

Papers

A Thermally Switchable Latent Ruthenium Olefin Metathesis Catalyst

Predicting the cis-trans dichloro configuration of group 15-16 chelated ruthenium olefin metathesis complexes: a DFT and experimental study.

The Versatile Alkylidene Moiety in Ruthenium Olefin Metathesis Catalysts

Studies on Electronic Effects in O‐, N‐ and S‐Chelated Ruthenium Olefin‐Metathesis Catalysts

Homodinuclear Ruthenium Catalysts for Dimer Ring‐Closing Metathesis