Grela catalyst

General aspects and new metathesis catalysts. For alkene metathesis Grubbs I (1) and Grubbs II (2, 3) complexes, and the Grubbs-Hoveyda catalyst (4A) and Grela catalyst (4B) remain the workhorses. 

Examination of the crystal structures of 3a and 2 showed that there is an open coordination site at the apical position, but it is too hindered for alkene binding. Even if an alkene bound to this site, it would not be in a position for cycloaddition with the Ru=C bond. Weakening of coordination by the 2-(isopropoxy)styrene unit produced precatalysts with faster initiation rates. For example, if the aromatic ring was electron-poor, as in the Grela catalyst 3b, the ether oxygen coordinated more weakly, and the catalyst was found to initiate 12 times faster than 3a (Chart 9.4, below) [29]. If the ether experienced steric strain, as in the Blechert-Wakamatsu complex 17 [30], the catalyst was more active, most Ukely due a dissociative process. 

In a synthesis of a pharmaceutical precursor on a 100 g scale, the more robust Grela catalyst 8311 (Z = NO2) was employed to allow lower loading and lower dilution (Scheme 8.85). ... 

The particular reactivity of free alcohols in Ru-catalyzed alkene metathesis is imder-scored by the observation Tetrahedron Lett. 2007, 48,6905) by laved Iqbal of Dr. Reddy s Laboratories, Ltd., Miyapur that attempted metathesis of the ether 4a faded, but metathesis of the diol 4b proceeded efficiently. Kazunori Koide of the University of Pittsburgh has demonstrated (Organic Lett. 2007, 9, 5235) that the yields of cross-metathesis with an alkenyl alcohol could be enhanced by binding it to a trityl resin. He observed that the Grela catalyst 8 was particularly effective in this application. 

Honda et al. carried out the dienyne metathesis of optically pure 230 using Grela catalyst [Ru]-lV to form the bicyclic furan 231 in a diastereoselective synthesis of... 

Despite those challenges, both Johnson [161] and Grela [162] performed several cross metathesis reactions with vinylhalides using phosphine free catalysts. Turnover numbers (TON) above 20 were very few, while in many cases the TON stayed below ten. The diastereoselectivity of CMs with vinylhalides is shghtly in favour of the Z product which is similar to their acrolein-counterparts. 

For a thorough review of Ru-NHC-catalysts for metathesis, see Samojlowicz C, Bieniek M, Grela K (2009) Chem Rev 109 3708-3742 for ruthenium indenylidene-complexes in cross metathesis, see Boeda F, Bantreil X, Clavier H, Nolan SP (2008) Adv Synth Catal 350 2959-2966 For Hll-types systems, see Schrodi Y, Pederson RL (2007) Aldrichimica Acta 40 45-52... 

Grela and coworkers attached (4b) to butyl diethyl silyl polystyrene to yield catalyst (289) in three steps. The catalyst had good activity toward formation of trisubstituted aUcene products in RCM and CM processes. The catalysts retained efficacy for up to 6 cycles and could be used sequentially on different substrates without cross contamination. 

Grela, K. and J. Ignatowska. 2002. An improved catalyst for ring-closing alkyne metathesis based on molybdenum hexacarbonyl/2-lluorophenol. Org Left 4 3747. 

It was demonstrated that the reaction proceeds without racemisation of the stereogenic phosphorus atom and with total selectivity towards the ( )-alke-nylphosphine oxide. Unexpectedly, it was also possible to dimerise phosphine oxide 109 (with R = Me) with 5% of 112b to obtain the corresponding optically pure ( )-diphosphine oxide in 85% yield. The crystal structure of this compound has been determined by X-ray diffraction and has been used as dipolarophile in 1,3-dipolar cycloadditions with nitrones, yielding several optically pure diphosphine oxides. Similar homometathesis reactions have been investigated in more detail by Grela, Pietrusiewicz, Butenschon and co-workers with other (racemic) substrates such as 109 and different catalysts. Gouverneur and co-workers studied a similar dimerisation of... 

Recently, Grela and coworkers [38] formed the pyridine monosolvate of a chelated complex related to the Hoveyda chelate. Exposure of the sulfoxide-based catalyst 27 to excess 3-bromopyridine resulted in the quantitative formation of complex 28 (Eq. (9.3)). In the RCM of diethyl allyl dimethallylmalonate, the initiation of complex 28 was much faster than that for the parent complex. Through various structural modifications as well as supplemental DFT calculations on the 6-coordinate complex, it was determined that 28 likely initiates by a different pathway than 27. Somewhat surprisingly, dissociation of the sulfoxide ligand from the metal center in 28 was found to precede olefin coordination and the subsequent loss of the pyridine ligand. Relative to 27, the overall initiation process was determined to be 5 kcalmol" lower for 28, having an energy barrier of 11.7 kcal mol versus 17.4 kcal mol . ... 

Samojlowicz C, Bieniek M, Grela K. Ruthenium-based olefin metathesis catalysts bearing N-heterocyclic carbene ligands. Chem Rev. 2009 109(8) 3708-3742. 

Michrowska A, Bujok R, Hamtyunyan S, Sashuk V, Dolgonos G, Grela K. Nitro-Substituted Hoveyda—Grubbs Ruthenium Carbenes Enhancement of Catalyst Activity through Electronic Activation. J Hm Chem Soc. 2004 126(30) 9318—9325. 

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