Phosphines dimethylacetamide

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 ruthenium complex-catalyzed hydroformylation of 1-alkene was first examined by Wilkinson s group. Ru(CO)3(PPh3)2/phosphine catalysts were found to have moderate catalytic activity [35-37]. Ru3(CO)i2 [38] and anionic hydridocluster complexes such as [NEt4][Ru3H(CO)ii] [39] have also been shown to have catalytic activity. In molten phosphonium salt, Ru3(CO)i2/2,2 -bipyridine has high catalytic activity [40]. The Ru3(CO)i2/l,10-phenanthroline catalyst in N,N-dimethylacetamide (DMAC) shows excellent activity and selectivity for u-aldehydes (Eq. 11.10) [41]. 

Like other actinide tetrahalides, protactinium tetrachloride and tetrabromide form stable complexes with phosphine oxides (48, 55) and iV jAT -dimethylacetamide (24), but the tetrachloride-dimethyl sulfoxide... 

Heck reactions are conducted in polar aprotic, cr-donor-type solvents such as acetonitrile, dimethyl sulfoxide, or dimethylacetamide. Reaction temperatures and times largely depend on the nature of the organic halide to be activated and on the catalyst s stability limit. lodo derivatives are much more reactive (<100 °C), so auxiliary (phosphine) ligands are not necessary here. Polar solvents such as DMF, DMAc, and A-methylpyrrolidone (NMP) in combination with NaOAc as base are specifically beneficial in all cases, and even mild phase-transfer conditions in a solid/solution system employing Pd(OAc)2 without phosphine co-ligands), [N(n-C4H9)4]X in DMF (X = Cl, Br), and K2CO3 as base ( Jeffery conditions ) [17, 18]. 

Amides. Despite many investigations in the 1970s and 1980s on Pd-catalyzed a-arylation of carboxylic acid derivatives, that of amides had not been studied until recently. In 1998, the reaction of potassium enolates of 7V,7V-dimethylacetamide (DMA) and other amides with aryl bromides in the presence of catalytic amounts of Pd(dba)2 and bidentate phosphines, such as BINAP and dppf, was shown to provide the desired a-arylated products in up to roughly 70% yields, as shown in Table Diarylation competed with monoaryladon to the extent of up to 18%. Under the conditions used, the intermolecular reactions of amides other than acetamides were rather disappointing, as indicated by the last two entries in Table 5. Clearly, additional development is desirable. Its intramolecular cyclic version, however, is considerably more favorable, as discussed in the following subsection. 

The linear dimerization of isoprene often affords mixtures of head/tail dimers. For example, [Pd(OAc)2, P(CH2CH2CN)3l catalyzes dimerization of isoprene with triethylammo-nium formate in dimethylacetamide (55 °C, 3 h), affording dimers in 91% yield as a 10 49 37 98/99/100 mixture of head/tail coupling regioisomers (Scheme 30). It is interesting to note that, as in the case of butadiene and formic acid in the presence of phosphine-modified Pd(OAc)2, only 1,7-dienes are formed in this reaction of isoprene with formic add. 

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. 

Various palladium species catalyze the reaction, and a common procedure is to start with Pd(OAc>2, PPhj, NaOAc and sometimes NEtj. The reaction generally is done at elevated temperatures (100-150 C) in a polar solvent, such as dimethylacetamide or dimethyformamide. The reaction usually proceeds with formation of at least some Pd metal. The standard reaction sequence involves first reduction of Pd(II), possibly by phosphine or amine, to a ligated Pd(0) species, often represented as PdLj. The latter is proposed to undergo oxidative addition with the aryl halide, and the resulting Pd"(Ar)(X)(L)2 species loses an L and coordinates the olefin. Then, the aryl group inserts into the Pd—olefrn bond. This is followed by p-hydride elimination, possibly assisted by base, liberation of the product and re-coordination of L to regenerate the catalyst. Further details can be found in recent reviews by Crisp, Beletskaya and Cheprakov and Amatore and Jutland. It should be noted that the electrochemical studies of the latter workers indicate that the Pd(0) is present as an anionic complex, such as Pd(L)2(OAc)", and that the oxidative addition gives a 5-coordinate Pd(II) species, such as Pd(Ar)(X)(L)2(OAc)". 

The preliminary investigations into the palladium-catalysed cyanation of vinyl halides using acetone cyanohydrin (145) as the cyanating agent were conducted using trans-f)-bromostyrene (148) as the substrate. The initial conditions tested (Table 7.2) utilised 5 mol% Pd2(dba)3 as the palladium source, 30 mol% lri(2-furyl)phosphine (TPP) as the added ligand and Na2C03 (1.1 equivalents) as the base, in a solvent system of THF and dimethylacetamide (DMAc) (2 1 ratio), and with a reaction temperature of 65 C. 

Besides LiBOB, other additives have been reported to protect the high voltage cathode and mitigate electrolyte decomposition, including LiDFOB [162], succinic anhydride [66, 122], 1,3-propane sultone [66], tris(hexafluoro- o-propyl) phosphate [127], tris(pentafluorophenyl) phosphine [156], 3-hexylthiophene [3], 1,3-propanediolcyclic sulfate [41], dimethylacetamide [13], triethyl(2-methoxyethyl) phosphonium bis(trifluoromethylsulfonyl)imide [13], glutaric anhydride [16], 4-(trifluoromethyl)-benzonitrile [55], and 1-propylphosphonic acid cyclic anhydride [ 160]. The stmctures of the additives that are not listed in the previous text are shown in Fig. 8. 

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