Phosphine-free reactions

On the other hand, bases possessing high Lewis basicity might serve as hgands in phosphine-free protocols. For example, tetramethylguanidine (TMG) and 1,4-diazabicyclo [2.2.2]octane (DABCO) were shown to improve yields markedly in phosphine-free reactions of aryl iodides, bromides and activated chlorides, compared with identical system without additive. Representative protocols PdCla (0.1 mol%), TMG, NaOAc, NfT-dimethylacetamide (DMA), 140 °C or Pd(OAc)2 (0.0001-5 mol%), DABCO, K2CO3, dimethylformamide (DMF), 120 °C. 

The addition of quaternary ammonium salts [46 8] or LiCl [28,49-51] is practised in phosphine-free reactions of aryl iodides and bromides with unsaturated alcohols, leading to... 

ESI Charge-tagged acetate ligands for mechanistic studies, Suzuki and Heck phosphine-free reactions Oliveira et al. [316]... 

Oliveira, F.F.D., dos Santos, M.R., Lalli, P.M., Schmidt, E.M., Bakuzis, R, Lapis, A.A.M., Monteiro, A.L., Eberlin, M.N., Neto, B.A.D. (2011) Charge-tagged Acetate Ligands As Mass Spectrometry Probes for Metal Complexes Investigations Applications in Suzuki and Heck Phosphine-free Reactions. J. Org. Chem. 76 10140-10147. 

The presence of phase-transfer agents is, however, unnecessary. The addition of water to the organic solvent has often been noted to have a strong accelerating influence on Heck reactions. This influence is more strongly pronounced in phosphine-free reactions, though phosphine-assisted processes are also often notably facilitated. 

BU3P. A rapid redox reaction takes place to yield the active Pd(0) species and tributylphosphine oxide. The Pd(0) thus generated is a phosphine-free cata-lyst[341]. Severe reaction conditions are necessary, or no reaction takes place, when Pd2(dba)3 is used in the elimination reaction of cyclic allylic compounds with an excess of -Bu3P[342]. 

Isomerization and elimination reactions of alkyls and aryls Isomerizations of mono-alkyls and aryls have been widely studied [107] many ds-Pt(PR3)2ArCl undergo rapid isomerization in the presence of free phosphine, a reaction inhibited by Cl- with a mechanism believed to involve a 3-coordinate Pt(PR3)2Ar+ intermediate that is then attacked by Cl-. The cis- and trans-isomers of Pt(PEt3)2(Ph)Cl undergo reversible isomerization when irradiated at the wavelength of charge-transfer transitions (254 and 280 nm). 

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. 

Several optimization studies have been carried out under these phosphine-free conditions. The reaction of bromobenzene and styrene was studied using Pd(OAc)2 as the catalyst, and potassium phosphate and (V,(V-dimethylacetamide (DMA) were found to be the best base and solvent. Under these conditions, the Pd content can be reduced to as low as 0.025 mol %.142 The reaction of substituted bromobenzenes with methyl a-acetamidoacrylate has also been studied carefully, since the products are potential precursors of modified amino acids. Good results were obtained using either N, (V-diisopropylethylamine or NaOAc as the base. 

The synthesis and olefin metathesis activity in protic solvents of a phosphine-free ruthenium alkylidene bound to a hydrophilic solid support have been reported. This heterogeneous catalyst promotes relatively efficient ring-closing and cross-metathesis reactions in both methanol and water.200 The catalyst-catalyzed cross-metathesis of allyl alcohol in D20 gave 80% HOCH2CH=CHCH2OH. 

The X-ray structure of (347), PR3 = PMe3, confirms the trigonal-bipyramidal structure, with the olefin and phosphine ligands lying in the equatorial plane. The equilibrium between free and bound olefin depends on the size of the tertiary phosphine. Further reaction of (347) with IrCl(CO)(PMe3)2 results in formation of a bimetallic iridacyclobutene complex by a second-order process. 

Anionic complexes of boron (boronates, borinates, etc.) have been introduced as convenient reagents in cross-coupling reactions of broad scope, particularly interesting for the transfer of alkynyl and primary alkyl residues, which cannot be accomplished using the standard protocols of the Suzuki-Miyaura reaction. Readily available Ph4BNa can be used as a convenient reagent for phenylation in place of the much more expensive PhB(OH)2, and all four phenyl groups can be utilized when the reaction is carried out with a phosphine-free catalyst in aqueous solutions.244... 

Polyethylene glycol) (PEG) was used as a soluble polymeric support in the efficient preparation of the 2-benzazepine 58 via a phosphine-free palladium-catalysed Heck reaction from 57 <06T10456>. 

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