Ligands bidentate dppp

The a-vinylidene-y-lactones 80 are prepared from 5-hydroxy-2-alkynyl methyl carbonates 79 under mild conditions in good yields [19]. The reaction proceeds at room temperature under 1 10 atm of CO. Bidentate ligands, particularly DPPP and DPPF, are the best ligands. 

Studies on the controlled microwave-irradiated novel palladium-catalyzed reaction of a fluorous-tagged bidentate ligand (l,3-bis(diphenylphosphino) propane ligand, [F-dppp]) for regioselective Heck vinylations of enamides have... 

In 1990, Cabri el al. [40a] reported that the precursor Pd(OAc>2 associated with a biden-tate P P ligand as dppp (1,3-bis-diphenylphosphinopropane) appeared to be more efficient than PPhs in Mizoroki-Heck reactions performed from aryl Inflates and enol ethers (electron-rich alkenes) moreover, the regioselectivity in favour of the a-arylated alkenes was improved to 100%. Since that time, dppp associated with Pd(OAc)2 has been used extensively to catalyse Mizoroki-Heck reactions and to investigate the factors that control the regioselectivity [Ig, 40]. The chiral bidentate (7 )-Binap (2,2 -bis(diphenylphosphino)-1,1-binaphthyl) associated with Pd(OAc)2 has also been used by Shibasaki and coworkers [2b,d,41a] and Overman andPoon [41b] in intramolecular enantioselective Mizoroki-Heck reactions (also, see Link [2f] for an authorative review on the Overman-Shibasaki chemistry), as well as by Hayashi and coworkers [2a, 41c,d] to control the regioselectivity and enantioselectivity of intermolecular Mizoroki-Heck reactions performed from cyclic alkenes (see Schemes 1.3 and 1.2 (Z = O) respectively). 

In this case, bidentate ligands like dppp or dppf work better than triphenylphosphine, which gave slow reactions. 

When a bidentate phosphine is used as a ligand for the reaction of J-keto esters or /i-diketones, no dimerization takes place. Only a 2-butenyl group is introduced to give 68[49,62], Substituted dienes such as isoprene, 1,3-cyclohexa-diene, and ocimene react with carbon nucleophiles to give a mixture of possible regio- and stereoisomers of 1 1 adducts when dppp is used as a ligand[63,64]. 

Palladium(II) complexes possessing bidentate ligands are known to efficiently catalyze the copolymerization of olefins with carbon monoxide to form polyketones.594-596 Sulfur dioxide is an attractive monomer for catalytic copolymerizations with olefins since S02, like CO, is known to undergo facile insertion reactions into a variety of transition metal-alkyl bonds. Indeed, Drent has patented alternating copolymerization of ethylene with S02 using various palladium(II) complexes.597 In 1998, Sen and coworkers also reported that [(dppp)PdMe(NCMe)]BF4 was an effective catalyst for the copolymerization of S02 with ethylene, propylene, and cyclopentene.598 There is a report of the insertion reactions of S02 into PdII-methyl bonds and the attempted spectroscopic detection of the copolymerization of ethylene and S02.599... 

The domino carbonylation and Diels-Alder reaction proceed only as an intramolecular version. Attempted carbonylation and intermolecular Diels-Alder reaction of conjugated 2-yne-4-enyl carbonates 101 in the presence of various alkenes as dienophiles give entirely different carbocyclization products without undergoing the intermolecular Diels-Alder reaction. The 5-alkylidene-2-cyclopenten-4-onecarboxy-lates 102 were obtained unexpectedly by the incorporation of two molecules of CO in 82% yield from 101 at 50 °C under 1 atm [25], The use of bidentate ligands such as DPPP or DPPE is important. The following mechanism of the carbocyclization of 103 has been proposed. The formation of palladacyclopentene 105 from 104 (oxidative cyclization) is proposed as an intermediate of 108. Then CO insertion to the palladacycle 105 generates acylpalladium 106. Subsequent reductive elimination affords the cyclopentenone 107, which isomerizes to the cyclopentenone 108 as the final product. 

As shown in Table 20, the overall order of stability is as follows dpype < dppf < (-l-)-diop < dppb < dppe < dppp < dppv < dpmcb < dope < dmpe < dcpe. As the Tohnan electronic scale predicts, the relative stability of the resulting complexes is strongly influenced by the electronic donor properties of the bidentate phosphine ligand if no larger steric factors are present. For example, better a donors (see a-Donor), such as, dmpe, depe, and dcpe, give more thermodynamically stable complexes while the isosteric (see Isosteric Groups) ligand dpype, which also... 

For example, the reaction of /-PrMgCl with PhCl afforded three products, i-PrPh, n-PrPh, and PhH, depending on a choice of the catalyst (see Scheme 4), which is summarized in Eq. (124) [246,285]. Bidentate low-electron-donating phosphine ligands such as dppp, dppe, and, in addition, dppf [271,292] are particularly useful to prepare desired isopropylbenzene. 

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