Palladium acetate studies

In a related study, the precursor 41 could be amiulated either by irradiation or by treatment with palladium acetate in acetic acid to provide indolocarbazoles 42 and 43 in yields of 37% and 55%, respectively (Scheme 8). Both products were eventually deprotected efficiently to give 44 and transformed further under reductive conditions to staurosporinone 45, the aglycone of 8, Alternatively, a shorter route encompassing deprotection of 41, followed by cychzation by irradiation in the presence of iodine and subsequent reduction, gave 45 in an even better overall yield (98T6909). 

Kragten, D. D., van Santen, R. A., Lerou, 1999, Density Functional Study of the Palladium Acetate Catalyzed Wacker Reaction in Acetic Acid , J. Phys. Chem. A, 103, 80. 

Palladium acetate, [PdO —02CCH3)2l3, possesses a unique quality that makes it attractive for solid state decomposition studies as well as technological applications. It can be spin-coated from solution to form a homogeneous, apparently amorphous solid film. This provides large uniform areas over which we can study the effects of various irradiation sources on the chemical nature of the film. The bulky structure of palladium acetate, shown in Figure 1 (8), may offer a partial explanation of the molecule s ability to achieve an amorphous metastable phase upon rapid evaporation of solvent. 

Palladium catalyzed reaction of aryl halides and olefins provide a useful synthetic method for C-C bond formation reaction [171, 172], The commonly used catalyst is palladium acetate, although other palladium complexes have also been used. A sol-vent-free Heck reaction has been conducted in excellent yields using a household MW oven and palladium acetate as catalyst and triethylamine as base (Scheme 6.51) [173], A comparative study revealed that the longer reaction times and deployment of high pressures, typical of classical heating method, are avoided using this MW procedure. 

Insertion of the alkyne into the Pd-H bond is the first step in the proposed catalytic cycle (Scheme 8), followed by insertion of the alkene and /3-hydride elimination to yield either the 1,4-diene (Alder-ene) or 1,3-diene product. The results of a deuterium-labeling experiment performed by Trost et al.46 support this mechanism. 1H NMR studies revealed 13% deuterium incorporation in the place of Ha, presumably due to exchange of the acetylenic proton, and 32% deuterium incorporation in the place of Hb (Scheme 9). An alternative Pd(n)-Pd(iv) mechanism involving palladocycle 47 (Scheme 10) has been suggested for Alder-ene processes not involving a hydridopalladium species.47 While the palladium acetate and hydridopalladium acetate systems both lead to comparable products, support for the existence of a unique mechanism for each catalyst is derived from the observation that in some cases the efficacies of the catalysts differ dramatically.46... 

The electrochemical Wacker-type oxidation of terminal olefins (111) by using palladium chloride or palladium acetate in the presence of a suitable oxidant leading to 2-alkanones (112) has been intensively studied. As recyclable double-mediatory systems (Scheme 43), quinone, ferric chloride, copper acetate, and triphenylamine have been used as co-oxidizing agents for regeneration of the Pd(II) catalyst [151]. The palladium-catalyzed anodic oxidation of... 

Pd-catalysed chelate-directed acetoxylation of meta -substituted arenes has been studied.61 Many substituted groups are tolerated by this process and the reaction shows a high degree of regioselectivity for the less sterically hindered ortfto-position. For example, 2-(3-nitrophenyl)pyridine forms 2-(2-acetoxy-3-nitrophenyl)pyridine. Finally, density functional calculations62 on the palladium acetate-promoted cyclomet-allation of dimethylbenzylamine suggest that reaction occurs via an agostic C-H complex rather than a Wheland intermediate. An intramolecular H-transfer to a coordinated acetate via a six-membered transition state follows. 

The complexes of type 641 were obtained according to the same technique by interaction of ligands 640 with Co, Ni, Cu, Zn, and Cd acetates in methanol. In case of palladium acetate, acetone was used as solvent [95], The principal circumstance is the fact that, together with well-known and studied binuclear complexes 641 (X = Y = O) [92,93], a series of novel binuclear complexes (X = NTs, Y = 0, S) has been obtained and, in some cases, structurally characterized [94,96,98], They possess antiferromagnetic properties, which are especially characteristic for Cu, Ni, and Co complexes with M2S2bridge. Their magnetic moments at 78 K have considerably decreased magnitudes 1.45 B.M. (M = Co2+), 0.45 B.M. (M = Ni2+), and 0.41 B.M. (M = Cu2+) [95],... 

A study of the olefin oxidation catalyst system, palladium acetate-MOAc (M = Li or Na), has shown that in the absence of acetate ion, Pd acetate-acetic acid exists as the trimeric species [Pd3(OAc)6].32 Reaction with MOAc is not instantaneous, and u.v.-visible spectra indicate an initial equilibrium involving trimer - dimer (9). When M = Na conversion into dimer is complete at 0.2M-NaOAc. Further addition of... 

Reaction of methyl benzoate (144) with a palladium acetate/heteropolyacid mixture has been studied by Lee and coworkers [98]. They showed that aryl-aryl coupling occurs mainly at the 2-2 positions in the presence of various heteropolyacids (HPA e.g. H3PM012O40, H5PM09V3O40, H5PM010V2O40, etc.) (Scheme 34). The selectivity in favor of the 2-2 coupling product is between 53 and 84 %, but the conversions are low (0.48 to 6.93) due to deactivation of the catalyst. The observed selectivity can be rationalized in terms of formation of the (T-palladium complex 146 with stabilization by the carbonyl group (Figure 3). 

The electron-releasing phosphine promotes oxidative addition of the bromo derivative to Pd(0) and, because of its bulkiness, readily generates free coordination sites by dissociation. Ethylene coordination and insertion then occur, followed by reductive elimination, triethylamine acting as a base to neutralize hydrogen bromide. As in most cases of transition metal-catalyzed reactions the fine details of the mechanism are still under investigation. Thus recent studies by Amatore s group suggest that the palladium(O) species formed by reduction of palladium acetate is an anionic acetato complex. 

In an effort to synthesize enantioenriched diamine complexes, prochiral diamines were mixed with K2 [( )-Me2-BINOLate] and palladium acetate resulting in the formation of the two diastereomers (Figure 9). These diastereomers were both C2-symmetric and assigned as the (R,R)/(R) and (S,S)/(R) configurations based on NMR and X-ray crystallographic studies. The major diastereomer was separated from the minor by crystallization. 

Probably the most complete study to date is that of Moiseev et ah 196) who measured the kinetics of oxidation of ethylene by palladium(II) acetate. These workers found that initially the rate increased sharply with increasing [NaOAc] until a maximum rate was reached at [NaOAc] = 0.2-0.3 M, depending on temperature further increase in [NaOAc] caused a sharp decrease in rate. Moiseev et ah attributed the initial increase in rate to the dissociation of pol3rmeric palladium acetate species to give Na2Pd(OAc)4. 

In another study, these workers found that cis complexes of palladium acetate with bidentate ligands such as o-phenanthroline will catalyze the exchange at higher temperatures (190). As trans complexes were inactive, it is likely that two adjacent cis coordination positions are required for catalysis. These new catalysts are extremely interesting and deserve further mechanistic study. 

For cases in which vinylation with higher olefins has been studied, conflicting results have been reported. In one case, it has been reported (29) that olefins give predominantly 2-substitution—e,g.y l-penten-2-yl acetate (I) from pentene when a palladium acetate-acetic acid system is used. On the other hand, a buffered (sodium acetate) acetic acid solution of palladium chloride has been reported (58) to give 1-substitu-tion—e.g., 2-hexen-l-yl acetate (II) from hexene. Propylene has been... 

The use of palladium and ruthenium as halogen-free carbonylation catalysts has been studied intensively by Shell. The catalysts were principally designed for the carbonylation of olefins in the presence of alcohols in order to yield carboxylic esters [26], but work also well for the synthesis of carboxylic acids or anhydrides. The latter are formed when the reaction is conducted in an acid as a solvent [27]. The palladium systems typically consist of palladium acetate, tertiary phosphines, and strong acids such as mineral acids or acids with weak or noncoordinating anions such as p-toluenesulfonic acid. Remarkable activities are achieved when aromatic phosphines that carry pyridines as substituents are... 

The discovery of the above-mentioned class of highly efficient alkyne carbonylation catalysts originated from a general study of reactions homogeneously catalyzed by cationic metal complexes [6, 8, 9], e. g., the methoxycarbonylation of propyne (eq. (2)). The catalysts applied were cationic palladium phosphine systems prepared in situ from three components (1) palladium acetate, (2) an excess (10-40-fold on Pd) of a (mono)phosphine ligand(L) and (3) an acid (HX) [8]. Methanol was used as both reactant and solvent, but many other solvents can also be used, such as A-methyl-2-pyrrolidone (NMP) or product MMA. 

Recent examples of experimental and computational studies showing the involvement of hypercoordinate intermediates are cyclometallation of benzylamine with palladium acetate (91) and cyclopalladation of aryl imino-phosphoranes (92). ... 

---