Propan catalysts, palladium complexes

The new metallocarbene complex l,3-bis(2,6-diisopropylphcnyl)-4,5-dimethyl-3//-imidazolidenylpalladium(O) has been reported to catalyse the dimerization of butadiene in the presence of propan-2-ol to afford octa-l,3,7-triene, rather than the usual telomer-ization products, typical for other palladium catalysts. The new catalyst is characterized by an unprecedented efficiency (TON > 80000 and TOF > 5000 h 1)82... 

Palladium(O) complexes also catalyze the transfer of di-terf-butylsilylene from m-dimethylsilacyclopropane 48 to alkynes (Scheme 7.6).61 In the presence of 5 mol % of (Ph3P)2PdCl2, the formation of dimethylsilacyclopropene 51 could be achieved at 110°C. In the absence of the palladium catalyst, silylene transfer from silacyclo-propane 48 to 3-hexyne occurred over 3 days at 130°C. While a reasonable mechanism was proposed involving palladacycle 49 as an intermediate, an alternative mechanism could involve palladium silylenoid intermediate 50. 

Chiral methyl chiral lactic acid (5). This labeled molecule, useful for study of stereospecificity of enzymic reactions, has been prepared in a way that allows for synthesis of all 12 possible isomers. One key step is the stereospecific debromination of 1, accomplished by conversion to the vinyl-palladium cr-complex 2 followed by cleavage with CF3COOT to give the tritium-labeled 3. The next step is the catalytic deuteration of 3, accomplished with a rhodium(I) catalyst complexed with the ligands norbornadiene and (R)-l,2-bis(diphenylphosphino)propane. This reaction gives 4 with an optical purity of 81%. The product is hydolyzed to 5, which is obtained optically pure by cr3rstallization. 

Enantioselective allylic substitutions catalyzed by transition-metal complexes are a powerful method for constructing complex organic molecules [4f,55]. Palladium-based catalysts have often given excellent results. To expand the scope of the reaction, a new enantioselective allylic alkylation catalyzed by planar-chiral ruthenium complexes was developed [56]. For example, the reaction of l,3-diphenyl-2-propenyl ethyl carbonate with sodium dimethyl malonate in the presence of 5 mol% of a planar chiral (S)-ruthenium complex (Figure 5.3) at 20 °C for 6 h in THE resulted in the formation of the corresponding chiral allylic alkylated product of dimethyl 2-((2 )(lS)-l,3-diphenylprop-2-enyl)propane-l,3-dioate in 99% yield vsdth 96% e.e. (Eq. 5.33). 

Generally, synthesis of dianhydrides is somewhat more complex than that of diamines and until recent time pyromellitic dianhydride (PMDA) and benzophenone-3,3, 4,4 -tetracarboxylic dianhydride (BTDA) had been the only commercially produced aromatic dianhydrides. Some of the significant commercial products developed recently, are Upilex by UBE Ind. and Ultem by General Electric. The former is based on biphenyl-3,3, 4,4 -tetracarboxylic dianhydride (BPDA) and the latter on 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride or bisphenol A dianhydride (BPA-DA). BPDA is produced by oxidative coupling of inexpensive phthalic acid esters in the presence of palladium catalyst [23, 24]. 

The most generally applicable catalysts are diphosphine complexes of nickel(ll) halides, notably dichloro[l,3-bis(diphenylphosphino)propane]nickel(II), NiCl2 (dppp) , and to a lesser extent analogous palladium(ll) complexes. Many examples are listed in reviews [42-44],... 

Palladium(II) acetate and palladium(II) chloride (often applied as the soluble dibenzonitrile complex) are especially suited for cyclopropanation of strained double bonds as well as styrene and its ring-substituted derivatives.152,154,155 The good coordinating abilities of these palladium ) compounds, however, somewhat complicate the catalytic action and may even limit it. Thus, the presence of phosphane ligands in palladium(II) halides causes a significant induction period for decomposition of the diazocarbonyl compound,156 and the formation of stable palladium diene complexes may even prevent the cyclopropanation reaction.155,157 Furthermore, alkenes such as 4-dimethylaminostyrene and 4-vinylpyridine cannot be cyclo-propanated since their basic center deactivates the catalyst.155... 

A Cr(VI) sulfoxide complex has been postulated after interaction of [CrOjtClj] with MejSO (385), but the complex was uncharacterized as it was excessively unstable. It was observed that hydrolysis of the product led to the formation of dimethyl sulfone. The action of hydrogen peroxide on mesityl ferrocencyl sulfide in basic media yields both mesityl ferrocenyl sulfoxide (21%) and the corresponding sulfone (62%) via a reaction similar to the Smiles rearrangement (165). Catalytic air oxidation of sulfoxides by rhodium and iridium complexes has been observed. Rhodium(III) and iridium(III) chlorides are catalyst percursors for this reaction, but ruthenium(III), osmium(III), and palladium(II) chlorides are not (273). The metal complex and sulfoxide are dissolved in hot propan-2-ol/water (9 1) and the solution purged with air to achieve oxidation. The metal is recovered as a noncrystalline, but still catalytically active, material after reaction (272). The most active precursor was [IrHClj(S-Me2SO)3], and it was observed that alkyl sulfoxides oxidize more readily than aryl sulfoxides, while thioethers are not oxidized as complex formation occurs. 

Palladium catalysts also promote copolymerization of SO2 with alkenes analogously to copolymerization of CO and alkenes (Eq. 7.24) [119]. The catalyst activities for the polysulfone synthesis are lower by an order of magnitude than those for the polyketone synthesis. Perfectly alternating copolymers can be obtained by use of cationic methylpalladium(II) complexes, [PdMe(CH3CN)L2]BF4 (L2 = l,3-bis(diphenylphosphino)propane and 1,2-bis(2,5-dimethylphosphinolato)benzene), in contrast to a lower degree of alternation provided by a radical polymerization [120]. 

Sault A.G., Martino A., Kawola J.S., Boespflug E. Novel sol-gel-based Pt nanocluster catalysts for propane dehydrogenation. J. Catal. 2000 191 474 79 Schubert U., Amberg-Schwab S., Breitscheidel B. Metal complexes in inorganic matrixes 4 Small metal particles in palladium-silica composites by sol-gel processing of metal complexes. Chem. Mater. 1989a 1 576-578... 

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