Pd 2, PPh

Butyl-5-methyl 2-Bromo-5-methylacetanilide l-(Tri-n-butyl-stannvl)hexyne, (1) Pd(PPh,)4, (2) PdCl lCHjCN) 81,77 [1]... 

Diethoxymethyl)- 1-methanesulfonyl 2-Iodo-iV-(methane- sulfonyl)anilinc 3,3-Diethoxy propyne Pd(PPh,),Cl Cul 63 [2]... 

Methyl-5-(4-pyridyl)-7-aza- 2-Araino-3-iodo-6-methyl-,S- (4-pyridyl)pyridine Trimethylsilylethyne. Pd(PPh,)jCl4, Cut 96,40 ... 

The phosphine ligands suffer from P-C-bond cleavage, which result in the corporation of the phosphine aryl groups into an unwanted side product. This is due to the facile exchange of Ph and Ph Y between the Pd" centres and co-ordinated phosphines on an intermediates of type tranj-Pd(PPh,i)2(aryl)X ... 

The proposed mechanism (Scheme 7-20) includes (a) oxidative addition of Y-Ge (Y = S or Se) bonds to Pd(PPh3)n, (b) insertion of acetylene into the Pd-Y bond to give 92 or insertion of acetylene into the Pd-Ge bond to form 93, (c) formation of 91 by either a G-Ge or a G-Y bond-forming reductive ehmination with regeneration of Pd(PPh,),. 

Pd(PPh )2 12 catalyses the internal alkylation of the phosphonate esters (96) and the formation of the 3-methyiene-l-oxa-2-phosphacycl.oalkane 2-oxides (97 ) phosphorus-containing analogues of a-methylenelactones. Further examples of the... 

The lactam 145, bearing a terminal triple bond, is transformed into the corresponding allene derivative 146 through a Crabbe reaction (Equation 7). Using Pd(PPh ()4 as the catalyst and in the presence of phenyl iodide, the corresponding indolizine is obtained. The lactam nitrogen atom is added to the central carbon atom of the allene... 

Only Pd-PPhs compounds have been investigated. The electrochemical reduction of Pd"X2(PPh3)2 is a two-electron reduction occurring at ca. — 1 V vs SCE and leading to the corresponding Pd° reactive species. 

We can also mention that one example of electroreductive cyclization of N-alkenyl-2-bromoanilines has recently been reported using Pd-PPhs as catalyst [79]. 

The electrocarboxylation of aryl iodides or bromides can also be catalyzed by the Pd-PPhs system (Eq. 14) [101]. 

Concurrent with acetic anhydride formation is the reduction of the metal-acyl species selectively to acetaldehyde. Unlike many other soluble metal catalysts (e.g. Co, Ru), no further reduction of the aldehyde to ethanol occurs. The mechanism of acetaldehyde formation in this process is likely identical to the conversion of alkyl halides to aldehydes with one additional carbon catalyzed by palladium (equation 14) (18). This reaction occurs with CO/H2 utilizing Pd(PPh )2Cl2 as a catalyst precursor. The suggested catalytic species is (PPh3)2 Pd(CO) (18). This reaction is likely occurring in the reductive carbonylation of methyl acetate, with methyl iodide (i.e. RX) being continuously generated. 

No reaction was observed when either the Pd complex, the Lewis acid or the IL was absent. Only very low yields were observed when PdCl2 was used with Cu(OTf)2 and the IL, and no reaction was observed when Pd(PPh)3Cl2 was the catalyst. Thus, it appears that weakly coordinating ligands favor the dimerization reaction. The reaction was also not observed with Pd(OAc)2/Cu(OTf)2 when ILs with the anion Bp4 were used. Moreover, the choice of solvent appears to have an influence upon the reactivity of the preferred catalyst system, since no reaction was observed when the IL was replaced by either 1,4-dioxane or DMSO however a low conversion ( 30%) of the substrate was observed when the solvent was CH3NO2. It is clear that a solvent that stabilizes ions favors the reaction. 

A study of Pd(PPhs)4,4, reported recently by Roth and coworkers, reveals yet another mechanistic pathway for Pd° oxygenation [122]. Complete dissociation of one PPha ligand from Pd occurs in solution to produce a three-coordinate palladium(O) species, 26. Kinetic studies reveal that 26 reacts with dioxygen via parallel associative and dissociative pathways (Scheme 5). The latter dissociative pathway results in the formation of the two-coordinate complex 27, which undergoes very rapid reaction with dioxygen in a manner directly analogous to that of the well-defined two-coordinate NHC complexes 23 and 24. 

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