Palladium catalysis solvent effects

The counter-phase transfer catalysis via jr-allyl—palladium complexes exhibits an unusual solvent effect [16]. Both the reduction with sodium formate and the car-... 

The dimerization of chromium-coordinated carbene ligands typically requires temperatures above 120°C. Whereas the addition of catalytic amounts of Rh2(OAc)4 allows to only a minor decrease in temperature to 100°C, the dimerization occurs already at room temperature under palladium catalysis. [95a,96] When the reaction of chromium arylcarbene 16 was promoted by Pd(OAc)2 (10 mol-%) in the presence of NEt3 using THF as a solvent, a mixture of isomeric carbene dimers 95 was obtained with an E Z ratio of 2 1 (Scheme 42). The effects of the eatalyst load, phosphine additives, the reaction temperature, the solvent and a series of other palladium catalysts have been investigated systematically, but did not reveal significant changes. [96]... 

Bianchini, C., Lee, H.M., Meli, A., Oberhauser, W, Peruzzini, M. and Vizza, F. (2002) Ligand and solvent effects in the alternating copolymerization of carbon monoxide and olefins by palladium-diphosphine catalysis, Organometallics,... 

Ligand, Additive, and Solvent Effects in Palladium Catalysis - Mechanistic Studies En Route to Catalyst Design... 

Ionic liquids have already been demonstrated to be effective membrane materials for gas separation when supported within a porous polymer support. However, supported ionic liquid membranes offer another versatile approach by which to perform two-phase catalysis. This technology combines some of the advantages of the ionic liquid as a catalyst solvent with the ruggedness of the ionic liquid-polymer gels. Transition metal complexes based on palladium or rhodium have been incorporated into gas-permeable polymer gels composed of [BMIM][PFg] and poly(vinyli-dene fluoride)-hexafluoropropylene copolymer and have been used to investigate the hydrogenation of propene [21]. 

Nonactivated olefins fail to react even under strenuous conditions with cyanide anion catalysis. Due to this lack of reactivity coupled with the inherent desirability of the products, much research has focused on developing catalysts for the hydrocyanation of these nonactivated olefins. This has led to nickel, palladium, copper, and cobalt-based catalysts effective at 25-125°C with or without a solvent. Most were developed for the hydrocyanation of unactivated olefins, but many are equally applicable for oAer olefins. For example, much work has been reported on butadiene hydrocyanation employing all of the catalysts mentioned above except palladium. 

Phosphinocarbene or 2 -phosphaacetylene 4, which is in resonance with an ylide form and with a form containing phosphoms carbon triple bond, is a distillable red oil. Electronic and more importantly steric effects make these two compounds so stable. Carbene 4 adds to various electron-deficient olefins such as styrene and substituted styrenes. Bertrand et al. have made excellent use of the push-pull motif to produce the isolable carbenes 5 and 6, which are stable at low temperature in solutions of electron-donor solvents (THF (tetrahydrofuran), diethyl ether, toluene) but dimerizes in pentane solution. Some persistent carbenes are used as ancillary ligands in organometallic chemistry and in catalysis, for example, the ruthenium-based Grubbs catalyst and palladium-based catalysts for cross-coupling reactions. 

Subsequently, the ruthenium-catalysed alkenylation of various acrylates was accomplished with alkenyl halides [62]. Most effective catalysis was achieved with [Ru(COD)(COT)] (98) as catalyst and NEts as base in the absence of additional solvent. Interestingly, both alkenyl bromides and chlorides could be employed as electrophiles (Scheme 10.35). When using an alkenyl chloride, the catalytic activity could be improved through the addition of P(p-C6H4p)3 (99) as ligand. The efficiency of this ruthenium catalyst in the alkenylation of /3-chlorostyrene (21) compared favourably with that observed for either Pd(OAc)2 or Pd(OAc)2/P(o-Tol)3 as catalysts. With respect to the working mode of the catalyst, a radical mechanism was shown to be less likely. Instead, Mitsudo et al. [62] proposed an initial oxidative addition of the alkenyl halide to a ruthenium(O) species followed by insertion of the alkene and )8-hydride elimination, all in analogy to palladium-catalysed processes. 

---