Palladium acetate precursor

Figure 3. Scanning electron micrographs of palladium features on quartz substrate as a function of laser power (measured on target) and scan speed. Palladium acetate precursor film thickness is 1.5 pm (cw Ar+ laser - 5145A line, spot size —0.8 pm FWHM).

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). 

The parent TMM precursor (1), now commercially available, has played a pivotal role in the execution of many synthetic plans directed at natural and unnatural targets. Reaction of (1) with 2-(methoxycarbonyl)cyclohexenone (14, R=C02Me) in the presence of palladium acetate and triethyl phosphite produced the adduct (15) in near quantitative yield. This cycloadduct is a critical intermediate in the total synthesis of a hydroxykempenone (16), a component of the defensive substances secreted by termites (Scheme 2.5) [12]. In accord with a previous observation by Trost that unactivated 2-cyclohexenone reacts poorly with TMM-Pd [13], the substrate (14, R=Me) was essentially inert in the cycloaddition. 

In 1975, Heck described the first non-catalytic example of this reaction, nsing organoboronic acids as precursors and stoichiometric amounts of palladium acetate... 

In the early work on the thermolysis of metal complexes for the synthesis of metal nanoparticles, the precursor carbonyl complex of transition metals, e.g., Co2(CO)8, in organic solvent functions as a metal source of nanoparticles and thermally decomposes in the presence of various polymers to afford polymer-protected metal nanoparticles under relatively mild conditions [1-3]. Particle sizes depend on the kind of polymers, ranging from 5 to >100 nm. The particle size distribution sometimes became wide. Other cobalt, iron [4], nickel [5], rhodium, iridium, rutheniuim, osmium, palladium, and platinum nanoparticles stabilized by polymers have been prepared by similar thermolysis procedures. Besides carbonyl complexes, palladium acetate, palladium acetylacetonate, and platinum acetylac-etonate were also used as a precursor complex in organic solvents like methyl-wo-butylketone [6-9]. These results proposed facile preparative method of metal nanoparticles. However, it may be considered that the size-regulated preparation of metal nanoparticles by thermolysis procedure should be conducted under the limited condition. 

Results on the amination of pyridyl halides conducted with two phosphine ligands and two different palladium precursors have been published (Table 2) [123]. The most general palladium precursor proved to be palladium acetate. Again, BINAP was found to be generally effective for amination with either primary or secondary amines. However, yields were lower with unbranched primary amines than those with branched amines, such as cydo-... 

From a mechanistic point of view the first steps of the catalytic cycle should be similar to the telomerization of butadiene itself (Scheme 2). The catalytic precursor generates the Pd(0) species A that reacts to the bis-(ri -allyl) complex C. The C,C bond formation between two C4 units is followed by insertion of carbon dioxide into a Pd,C bond affording the carboxylate intermediate D. Different pathways have been discussed to describe the multiple product formation (refer to ). Interestingly, a bis-(carboxylato) complex may be prepared directly from the reaction of lactone 1, palladium acetate and P(i-Pr)3. This complex was structurally characterized by Behr and co-workers and shows good activity as catalyst. Reviewing the literature, there are some remarkable facts and open questions of theoretical and technical interest ... 

Evans J, O Neill L, Kambhampati VL, Rayner G, Turin S, Genge A, Dent AJ, Neisius T (2002) Structural characterisation of solution species implicated in the palladium-catalysed Heck reaction by Pd K-edge X-ray absorption spectroscopy palladium acetate as a catalyst precursor. J Chem Soc, Dalton Trans 10 2207... 

The last and key step in the total synthesis of mvxalamide A by C.H. Heathcock et al. was a Suzuki cross-coupling between an ( )-vinylborane and a (Z)-iodotriene. The (E)-vinylborane was prepared prior to the coupling by reacting the precursor enyne with 2 equivalents of cathecholborane. Upon completion of the hydroboration, it was combined with the (Z)-iodotriene and catalytic amounts of palladium acetate. 

At the early stage of Heathcock s biomimetic total syntheses of discorhabdins [108], a 5-ejco Heck cyclization was employed for the synthesis of 3,6,7-functionalized indole. As highlighted in Scheme 42, when precursor 237 was exposed to catalytic palladium acetate, tri-o-tolylphosphine, and stoichiometric base, indole 238 was smoothly produced in 89% yield. Subsequently, the total syntheses of discorhabdin C (239) and discorhabdin E (240) were accomplished using indole 238 as the common intermediate. 

Genet has studied the enantioselective allylation of acyclic Shiff bases. Given the discussion and results above, one would not expect significant selectivity to result from use of simple chiral hgands. However, a respectable ee of 57% was determined for the reaction at -60 °C using chiral DIOP as hgand with the hthium enolate of the imine, Eq. (11) [42]. Further work indicated that use of two moles of DIOP vs. Pd, use of palladium acetate as catalyst precursor, and hthium hex-amethyldisilazide instead of LDA as base provided an increase in ee to 68% [43,... 

The first waste-free vinylation of arenes under C—H activation is as old as the Mizoroki-Heck reaction itself already in 1967, Moritani and Fujiwara [6] revealed a stoichiometric reaction of styrene-palladium(II) chloride dimers with benzene in the presence of acetic acid to give stilbenes in a modest 24% yield. During this process, the palladium(II) precursor is reduced to palladium(O), so that the key to closing the catalytic cycle was to add an efficient reoxidation step to regenerate an active palladium(II) species. One year later, the same group presented a first approach, substoichiometric in palladium. 

An alternative method to Friedel-Crafts acylation as the final step in dione synthesis involves a Pd-mediated Heck arylation to generate the indeno[l,2-h] fluorene skeleton. In 1989, HeUwinkel and Kistenmacher showed that parent and 2,8-di -tert-butyl[l,2-b]lF diones 22 and 78, respectively, could be isolated upon reacting precursors 77a,b with palladium acetate in acetic acid (Scheme 18) [56,57]. 

The syntheses of palladium and platinum organosols [82-85] by the thermolyds of such precursors as palladium acetate, palladium acetylacetonate, and platinum acetylacetonate in hi boiling organic solvents like methyl- o-butylketone have been reported. Likewise, bimetallic colloids of copper and palladium have been prepared from the thermolysis of mixtures of their acetates in similar solvents. [86] These preparations were performed in the absence of stabilizing polymers, and as a residt, relatively broad size distributions and large partides were observed. 

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