- Bis-chelated palladium(II) complexes with nitrogen-donor chelating ligands are efficient catalyst precursors for the CO/styrene copolymerization reaction
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A series of dicationic bis-chelated palladium(II) complexes [Pd(N-N)2][X]2 (N-N = 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), and their substituted derivatives; X = PF6-, BF4-, OTf-, OTs-) has been synthesized and completely characterized both in the solid state and in solution. The synthetic procedure involves a simple one-pot reaction between Pd(MeCOO)2 and [(N-N)H][X]. These compounds are very active precatalysts for the CO/ styrene copolymerization yielding perfectly alternating polyketones. The crystal structures of some complexes of the series provide evidence that a distorsion from the ideal square planar geometry toward a twist conformation occurs. In DMSO solution, one of the two nitrogen-donor ligands is involved in a dissociative equilibrium yielding a monochelated complex with two cis coordination sites available for the copolymerization catalytic process. The catalytically active species is very stable in 2,2,2-trifluoroethanol, where its activity was found unaltered for at least 48 h of reaction without apparent decomposition to palladium metal. The addition of 1,4-benzoquinone (BQ) to the catalytic system has a strong influence on the yield and, above all, on the molecular weight of polyketones. The zerovalent palladium complexes [Pd(N-N)(BQ)], which might be formed during the copolymerization process, have been synthesized and characterized. The crystal structure of [Pd(bipy)(BQ)] shows that benzoquinone acts as a mono-olefinic ligand to Pd. In the presence of protons, the Pd(0) complexes are readily oxidized to Pd(II) with the reduction of benzoquinone to hydroquinone. When [(N-N)H][X] is used as the source of protons, the resulting Pd(II) species is the precatalyst and can immediately re-enter the catalytic cycle.
- Milani, Barbara,Anzilutti, Anna,Vicentini, Lidia,O Santi, Andrea Sessanta,Zangrando, Ennio,Geremia, Silvano,Mestroni, Giovanni
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- Room-Temperature Direct β-Arylation of Thiophenes and Benzo[b]thiophenes and Kinetic Evidence for a Heck-type Pathway
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The first example of a regioselective β-arylation of benzo[b]thiophenes and thiophenes at room temperature with aryl iodides as coupling partners is reported. This methodology stands out for its operational simplicity: no prefunctionalization of either st
- Colletto, Chiara,Islam, Saidul,Juliá-Hernández, Francisco,Larrosa, Igor
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supporting information
p. 1677 - 1683
(2016/02/20)
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- Catalytic C-phenylation of methyl acrylate with tetraphenylantimony(v) halides and carboxylates
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Catalytic C-phenylation of methyl acrylate to methyl cinnamate with the Ph4SbX complexes (X = F, Cl, Br, OH, OAc, O2CEt) in the presence of the palladium compounds PdCl2, Pd(OAc)2, Pd2(dba)3, Pd(Ph3P)2Cl2, and Pd(dppf)Cl2 (dba is dibenzylideneacetone and dppf is bis(diphenylphosphinoferrocene)) was studied in organic solvents (MeCN, THF, DMF, MeOH, and AcOH). The highest yield of methyl cinnamate (73% based on the starting organometallic compound) was obtained for the Ph4SbCl- PdCl2 (1:0.04) system in acetonitrile.
- Gushchin,Grunova,Moiseev,Morozov,Shavyrin,Dodonov
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p. 1376 - 1379
(2007/10/03)
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