Renata Drozdzak

Latent olefin metathesis catalysts

Olefin metathesis is a versatile synthetic tool for the redistribution of alkylidene fragments at carbon-carbon double bonds. This field, and more specifically the development of task-specific, latent catalysts, attracts emerging industrial and academic interest. This tutorial review aims to provide the reader with a concise overview of early breakthroughs and recent key developments in the endeavor to develop latent olefin metathesis catalysts, and to illustrate their use by prominent examples from the literature.

Improved ruthenium catalysts for the modified Friedlaender quinoline synthesis

Herein we describe an improved ruthenium catalyst for the oxidative cyclization of 2-aminobenzylalcohol with ketones, leading to quinolines via a modified Friedlaender synthesis.

Ruthenium Complexes Containing Bidentate Schiff Base Ligands as Precursors of Homogeneous and Immobilized Catalysts

The paper presents recent work conducted in our group on the synthesis of a novel class of homogeneous and immobilized Ru- complexes containing Schiff bases as O,N-bidentate ligands benefiting from a versatile, quite general and thoroughly exemplified two- step procedure. The new Ru-complexes with improved stability incorporate a variety of Schiff bases, associated with traditional inorganic and organic ligands such as chloride, phosphanes, arenes, cyclodienes, NHC etc., and different carbenes (alkylidene, vinylidene, allenylidene and indenylidene). By a proper choice of the Schiff base, useful physical and chemical properties of the derived Ru- complexes could be induced resulting in tunable catalytic activity for metathesis and related processes. A pertinent example is the latency of selected Schiff base Ru catalysts which by becoming active only under specific conditions (heat or acid activation) are ideal for industrial applications, e.g. reaction injection molding processes. The synthetic approaches that are critically discussed in this artcile have led to a diversity of Ru-complexes of which several members have risen to the rank of commercial catalysts.

Exploring new synthetic strategies in the development of a chemically activated Ru-based olefin metathesis catalyst

The objective of this work was to develop an industrially relevant olefin metathesis initiator, which circumvents the expensive, patent protected, often cumbersome preparative routes via Grubbs benzylidene complexes. Upon coordination of a Schiff base ligand to a second-generation ruthenium allenylidene complex, the formation of three catalyst isomers was observed. The major isomer was successfully isolated, and tested in a few olefin metathesis reactions. Acids such as HCl and HSiCl(3) were found to boost the metathesis reaction but the in situ formation of a neutral Ru carbyne complex restricted the catalytic capacity. Using the Lewis acid PhSiCl(3), the formation of a carbyne species was avoided, and turnover numbers up to 30,000 were reached in the ring-opening metathesis polymerisation of cycloocta-1,5-diene.

Assignment and conformational investigation of asymmetric phenylindenylidene ruthenium complexes bearing N,O-bidentate ligands.

The NMR conformational study of three asymmetric phenylindenylidene ruthenium complexes 4.1–4.3, is presented. Complete 1H and 13C assignments could be obtained for 4.1–4.3 in benzene solution from multiple 2D homonuclear and heteronuclear NMR techniques. Our NMR analysis shows that each complex exists as a 55:45 mixture of two rotational isomers in slow exchange on the NMR chemical shift timescale. They are shown to be related by a 180° flip of the indenylidene ligand along the RuCR bond. Both rotational isomers can be discriminated by means of NOEs contacts between the various ligands coordinating to the Ru. By matching these stereospecific assignments to the chemical shift, a chemical shift based fingerprint of the isomers that may allow straightforward assignment of future asymmetric phenylindenylidene ruthenium complexes is proposed. Copyright

Synthesis, structure and luminescent properties of Cd(II) and Zn(II) complexes constructed from 3,5-dimethyl-2, 6-pyrazinedicarboxylic acid

[Cd2(phen)2(DPZDA)2(H2O)2] · 8H2O (1) and [Zn(phen)(DPZDA)(H2O)] · 2H2O (2) have been synthesized by reaction of Cd(NO3)2/Zn(NO3)2 with phen and DPZDA (where phen = 1,10-phenanthroline, H2DPZDA = 3,5-dimethyl-2,6-pyrazinedicarboxylic acid) in aqueous ethanol solution. Elemental analysis, IR spectra, thermal analyses and X-ray single crystal diffraction were carried out to determine the composition and crystal structure of 1 and 2. In 1, a 2D supramolecular network containing a novel metal-water decamer were formed by hydrogen bonds. In 2, a 2D supramolecular structure was constructed from hydrogen bonds and π·· · π interactions. Moreover, 1 and 2 displayed photoluminescent properties in the blue range at room temperature.

Ruthenium–Indenylidene Complexes Bearing Saturated N-Heterocyclic Carbenes: Synthesis and Application in Ring-Closing Metathesis Reactions

The synthesis of complexes of the general formula Cl2Ru(SIMes)(L)(3-phenylinden-1-ylidene), 3a (L = PCy3), 3b (L = PPh3), 3c (L = py) and Cl2Ru(SIMe)(L)(3-phenylinden-1-ylidene), 4c (L = PCy3), 4b (L = PPh3), 4c (L = py) from commercially available Cl2Ru(PR3)2(3-phenylinden-1-ylidene), 2a (R = Cy), 2b (R = Ph), is reported, and the summed complexes proved to be useful catalysts for various ring-closing metathesis reactions. The catalytic data reported furthermore demonstrate that the substitution pattern of the N-aryl group has a definite influence on the activity of the second generation indenylidene catalysts for a given metathesis reaction, i.e. catalysts containing the SIMe-ligand showed improved initiation compared to the more robust SIMes substituted catalysts. A strong temperature effect was observed on all of the reactions tested. It is shown that complexes containing the SIMe-ligand display higher initiation efficiency then their corresponding SIMes analogues.

New N-Heterocyclic Carbene Ligands in Grubbs and Hoveyda–Grubbs Catalysts

A series of N-heterocyclic carbene (NHC) ligands bearing aliphatic amino side groups were synthesized and reacted with the Grubbs first generation catalyst. Reactions involving symmetrical, aliphatic NHCs did not allow the isolation of any pure NHC substituted complexes due to their instability. Unsymmetrical NHCs having a planar mesityl group on one amino side reacted with Grubbs catalyst in a favorable manner, and the resulting complexes were stable enough to be isolated. X-ray crystallographic analysis demonstrated that the mesityl group is co-planar with the phenyl ring of the benzylidene, which indicates that a π–π interaction between the mesityl arm and the benzylidene moiety might constitute an important structural element. Catalysts substituted with an NHC derived from a primary or secondary amino-group were found to surpass the parent-complex for the ROMP of cycloocta-1,5-diene. The catalyst substituted with an NHC derived from tBu-NH2 was considerably less metathesis active. Also new N-alkyl-N′-(2,6-diisopropylphenyl) heterocyclic carbenes were synthesized. These NHC ligands revealed a different reactivity towards Grubbs complexes than the hitherto reported imidazolinylidenes: (i) facile bis(NHC) coordination was found, and (ii) both NHCs on the bis(NHC) complexes can be exchanged with a phosphine, thereupon regenerating the Grubbs first generation complex. Furthermore, a comparison between the classical Hoveyda–Grubbs complexes and complexes substituted with N-alkyl-N′-(aryl) heterocyclic carbenes demonstrates that the introduction of one aliphatic group into the NHC framework does not improve the catalytic activity in any of the tested metathesis reactions. The introduction of two aliphatic amino side groups enhances the reactivity in the ROMP reaction while the increase of steric interactions lowers the CM activity. The lower activity of the N-alkyl-N′-(2,6-diisopropylphenyl) heterocyclic carbene complexes compared with the N-alkyl-N′-mesityl heterocyclic carbene complexes, may analogously be attributed to a more demanding steric environment. While small differences in donor capacities might cause a significantly different catalytic behavior, it is thus plausible that subtle steric differences exert a more determining influence on the activity of the catalysts. In addition, the obtained results confirm that the NHCs amino side groups play a pivotal role in determining the reactivity, selectivity as well as the stability of the corresponding catalysts.

Olefin Metathesis Mediated By: - Schiff Base Ru-Alkylidenes -Ru-Alkylidenes Bearing Unsymmetrical NH Ligands

The classic Grubbs second-generation complex 2 was modified through 1. The introduction of a bidentate Schiff base ligand 2. Changes in the amino side groups of the NHC ligand Representative olefin metathesis test reactions show the effects induced by the ligand modifications and demonstrate some interesting new properties of the described catalysts. catalysts.

Towards New Generations of Metathesis Metal–Carbene Pre-catalysts

A short general introduction combined with some historical milestones in the field of olefin metathesis is presented followed by an overview of recent repre- contributions and overwhelming work invested in intelligent design and innovative synthesis in this area. Despites of recent advances there is still a great interest in the generation of new, better performing, and more environment friendly metathesis.