Palladacycle catalyst

Anderson CE, Donde Y, Douglas CJ, Overman LE (2005) Catalytic asymmetric synthesis of chiral allylic amines. Evaluation of ferrocenyloxazoline palladacycle catalysts and imidate motifs. J Org Chem 70 648-657... 

Weiss ME, Fischer DF, Xin ZQ, Jautze S, Schweizer WB, Peters R (2006) Practical, highly active, and enantioselective ferrocenyl-imidazoline palladacycle catalysts (FIPs) for the Aza-Claisen rearrangement of A-para-methoxyphenyl trifluoroacetimidates. Angew Chem Int Ed 45 5694-5698... 

Fischer DF, Barakat A, Xin ZQ, Weiss ME, Peters R (2009) The asymmetric Aza-Claisen rearrangement development of widely applicable pentaphenylferrocenyl palladacycle catalysts. Chem Eur J 15 8722-8741... 

In a recent article by Botella and Najera, controlled mono- and double-Heck arylations in water catalyzed by an oxime-derived palladacycle were described [22], When the reaction was carried out under microwave irradiation at 120 °C in the presence of dicyclohexylmethylamine with only 0.01 mol% of palladium catalyst (palladium acetate or palladacycle), monoarylation took place in only 10 min with a very high turnover frequency (TOF) of > 40000 (Scheme 6.3). As regards diarylation, 1 mol% of the palladacycle catalyst and 2 equivalents of iodobenzene had to be utilized to obtain moderate to good yields of diarylated product. Whereas microwave heating at 120 °C provided a 31% yield after 10 min, a 66% isolated yield of product was obtained by heating the reaction mixture under reflux for 13 h at 100 °C. Here, the... 

Rawal s group developed an intramolecular aryl Heck cyclization method to synthesize benzofurans, indoles, and benzopyrans [83], The rate of cyclization was significantly accelerated in the presence of bases, presumably because the phenolate anion formed under the reaction conditions was much more reactive as a soft nucleophile than phenol. In the presence of a catalytic amount of Herrmann s dimeric palladacyclic catalyst (101) [84], and 3 equivalents of CS2CO3 in DMA, vinyl iodide 100 was transformed into ortho and para benzofuran 102 and 103. In the mechanism proposed by Rawal, oxidative addition of phenolate 104 to Pd(0) is followed by nucleophilic attack of the ambident phenolate anion on o-palladium intermediate 105 to afford aryl-vinyl palladium species 106 after rearomatization of the presumed cyclohexadienone intermediate. Reductive elimination of palladium followed by isomerization of the exocyclic double bond furnishes 102. 

Other than the aforementioned ynones, P-iodo-p/y-enone 132 was also converted into a 2,5-disubstituted furan, 133, under Pd-catalyzed cyclization conditions using Herrmann s catalyst, palladacycle catalyst 101 [105]. 

Kuroboshi, M. Waki, Y. Tanaka, H. Palladium-catalyzed tetrakis(dimethylamino)ethy-lene-promoted reductive coupling of aryl halides./. Org. Chem. 2003, 68, 3938-3942. Luo, F.-T. Jeevanandam, A. Basu, M. K. Efficient and high-turnover homocoupling reaction of aryl iodides by the use of palladacycle catalysts. A convenient way to prepare poly-p-phenylene. Tetrahedron Lett. 1998, 39, 7939-7942. 

Pd(ll) catalysts can be employed as well. Compared to the standard Pd(ll) catalysts, the palladacycle catalyst 7 shows a broader compatibility with functional groups. Terminal alkynes, alkyl halides, and a-halogen ketones are tolerated <1997CB1449>. It is worth mentioning that other catalysts of Pd(ll) preferentially give dimerization products. 

The amination of aryl chlorides was first accomplished utilizing the palladacycle catalyst (12). This initial success spurred a significant amount of research that has gone into the synthesis and study of various palladacycles in order to see if the activity of this type of catalyst could be improved further. Recently, systems that consist of a palladacycle plus an added ligand have proven to be some of the most active yet. The theory here is that these species act as precursors to the actual Pd-L catalysts in which, once again, the P Pd ratio is restricted to its optimal 1 1 value. ... 

Phenylboronic and 4-chloroacetophenone combine efficiently according to eq. (2) at certain palladacycle catalysts (Structure 3), which are easily available from Pd(OAc)2 and appropriate phosphines PR3 (e. g., R = o-tolyl). Turnover numbers (TONs) of 75 000 are achieved with only 0.001 mol% 3 [3]. Several reports on the catalysts of type 3 have substantiated the discovery of 1995 [3a]. As in the Heck coupling, no aryl scrambling is observed with the palladacycle catalysts [4]. 

Rosner, T., Le Bars, J., Pfaltz, A., Blackmond, D. G. Kinetic Studies of Heck Coupling Reactions Using Palladacycle Catalysts ... 

SCHEME 2. Mechanism for the activation of the palladacyclic catalyst precursor 38 to produce [Pd P(tol-o)3 2]... 

Enones are converted into furans with much less frequency than alkynones. One example of this transformation entails conversion of P-iodo-p.y-cnone 229 into 2,5-disubstituted furan 230 via a Pd-catalyzed cyclization using Herrmann s palladacycle catalyst 168 [181]. 

Polystyrene-supported soluble palladacycle catalyst as recyclable catalyst for Heck, Suzuki and Sonogashira reactions... 

POLYSTYRENE-SUPPORTED SOLUBLE PALLADACYCLE CATALYST AS RECYCLABLE CATALYST FOR HECK,... 

A new type of soluble polystyrene-supported palladium complex was synthesised (Figure 6.1) as an excellent and recyclable palladacycle catalyst for carbon-carbon bond formation in Heck, Suzuki and Sonogashira reactions to give high yields of the desired products. 

SYNTHESIS OF 1 - [4-(2-PHEN YLETHYNYL)PHEN YL] ETHAN -1-ONE VIA SONOGASHIRA REACTION BY THE USE OF POLYMER-SUPPORTED PALLADACYCLE CATALYST... 

Polymer-supported palladacycle catalyst, 30 mg, 2 pmol palladium... 

Polystyrene-supported palladacycle catalyst (30 mg, 2 pmol Pd), l-(4-bromo-phenyl)ethan-l-one (0.20 g, 1 mmol), phenylacetylene (0.16 g, 1.5 mmol), and triethylamine (3 mL) were sequentially added into a 15 mL septum-sealed test tube under nitrogen atmosphere. The mixture was then heated at 90 °C for 72 hours. 

After cooling to the room temperature, to the mixture was added 8 mL of dry ether to precipitate the polystyrene-supported palladacycle catalyst. The catalyst was further removed by centrifugation the upper liquid layer of the reaction mixture was transferred via a syringe into another 20-mL round-bottom flask. 

The newly invented polystyrene-supported palladacycle catalyst was prepared in six steps with high yields. The simple precipitation and filtration process to recycle the catalyst after model reactions for Heck, Suzuki, and Sonogashira reactions is noteworthy.[1]... 

Many palladacycles, besides those derived from bidenate phosphines, are available for catalyzing organic reactions. These varieties include 0,N-, N,N-, N,C-, P,N-, f C-ligated. species. In the following, a selection of palladacycle catalysts bearing such as well as more exotic bidentate diphosphines are presented. 

Rawal has developed a new route to indoles and benzofurans via the anion-accelerated palladium-mediated intramolecular cyclizations of phenols containing various vinyl halide side chains <97TL6379>. For example, heating a mixture of the symmetrical phenol 70 and cesium carbonate in dimethylacetamide (DMA) in the presence of a catalytic amount of Hermann s palladacyclic catalyst (HC) promoted the cyclization to the indole 71. 

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