- The reactions of [Pd2Cl2(μ-PP)2] (PP = dppm, dmpm) with Et2NC≡CNEt2 in methylene chloride solution: X-ray crystal structures of [Pd2Cl2(μ-CH2)(μ-dppm)2] and hexakis(diethylamino)benzene, C6(NEt2)6
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The binuclear palladium(I) complex, [Pd2Cl2(μ-dppm)2] (dppm = bis(diphenylphosphino)methane), has been shown to react with bis(diethylamino)acetylene, Et2NC≡CNEt2, in methylene chloride solution to yield two isolable products, the known methylene-bridged complex, [Pd2Cl2(μ-CH2)(μ-dppm)2], and hexakis(diethylamino)benzene, C6(NEt2)6, both of which have been characterized crystallographically. The source of the bridging methylene group in [Pd2Cl2(μ-CH2)(μ-dppm)2] has been shown to be the methylene chloride solvent. A mechanism that accounts for the formation of the two isolable products is proposed. The complex, [Pd2Cl2(μ-dmpm)2] (dmpm = bis(dimethylphosphino)methane), was similarly found to react with Et2NC≡CNEt2 in methylene chloride solution to yield [Pd2Cl2(μ-CH2)(μ-dmpm)2], which was identified spectroscopically.
- Klopfenstein, Sean R.,Kluwe, Constanze,Kirschbaum, Kristin,Davies, Julian A.
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p. 2331 - 2339
(2007/10/03)
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- Di(phosphine)-bridged complexes of palladium. Parahydrogen-induced polarization in hydrogenation reactions and structure determination of tris(μ-bis(diphenylphosphino)methane)dipalladium, Pd2(dppm)3
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Reduction of Pd2Cl2(dppm)2 (dppm = bis(diphenylphosphino)methane) with excess NaBH4 produces a dark purple solid, I, which shows a reaction chemistry consistent with the stoichiometry Pd2Hx(dppm)2. Reaction of I with excess dppm produces the known compound Pd2(dppm)3. Crystals of Pd2(dppm)3 are monoclinic in space group P21/c with cell dimensions a = 14.733 (5) ?, b = 14.760 (5) ?, c = 29.720 (6) ?, and β = 97.44 (1)°. The structure of Pd2(dppm)3 is similar to that of the structurally characterized Pt2(dppm)3 analogue with approximate C3h symmetry. A total of 1 equiv of H2 and 1 equiv of methane is evolved per 3 Pd(dppm) units when I is treated with aqueous HCl and methyl iodide, respectively. The corresponding metal-containing products are Pd2Cl2(dppm)2 and a mixture of [Pd2I(CH3)(dppm)2]I and PdI2(dppm). The latter compound is also obtained upon oxidation of I with I2. Reaction of I with CH2I2 in dichloromethane yields a mixture of Pd2I2(μ-CH2)(dppm)2 and Pd2Cl2(μ-CH2)(dppm)2, while reaction with either Me3SiCl or Me2SiCl2 produces Pd2Cl2(dppm)2. Complex I is active in the catalytic hydrogenation of alkenes and alkynes. Parahydrogen-induced polarization (PHIP) is observed in the styrene product when solutions of I and phenylacetylene in CDCl3 are stored at -196°C under 3-4 atm of H2 for >8 h prior to reaction at 60-70°C. Similar results are obtained when para-enriched H2 is used without the storage time. Complex I decomposes upon heating in CDCl3 to mixtures of Pd2Cl2(dppm)2, PdCl2(dppm), and an unidentified red palladium compound. While this mixture is also active in hydrogenation and gives rise to PHIP, Pd2Cl2(dppm)2 by itself gives weak polarization under hydrogenation conditions and PdCl2(dppm) gives no polarization.
- Kirss, Rein U.,Eisenberg, Richard
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p. 3372 - 3378
(2008/10/08)
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- Synthesis and Reactions of Dinuclear Palladium Complexes Containing Methyls and Hydride on Adjacent Palladium Centers: Reductive Elimination and Carbonylation Reactions
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The transmetalation reaction of trimethylaluminum with the palladium chloride dimer Pd2Cl2(μ-dppm)2 (1) (dppm = bis(diphenylphosphino)methane) at -78 deg C gave an intermediate, Pd2ClMe(μ-dppm)2 (2), which disproportionated at ca. 10 deg C to yield the trans-face-to-face palladium dimer Pd2Cl2Me2(μ-dppm)2 (3) and a palladium dimer Pd2Cl2(μ-CH2)(μ-dppm)2 (5).The use of excess trimethylaluminum at -40 deg C gave the dimethyl complex, Pd2Me2(μ-dppm)2 (7).When 2 and 7 were protonated, a stable A-frame chloro-bridged dimer + (6) and a hydride-bidged dimer + (8) were obtained.Warming 6 in solution to ambient temperature caused the reductive elimination of methane; 8 lost methane and ethane at ambient temperatures.Both reductive eliminations were strictly intramolecular as determined by crossover experiments.The reaction of 6 with CO (1 atm) at -20 deg C first gave a carbonyl-bridged complex + (10) that rearranged to the acyl complex + (11) and then on warming eliminated acetaldehyde.The carbonylation of 8 (1 atm) proceeded stepwise to give first the mono- and then the diacyl complexes.The diacyl complex + (13) underwent the reductive elimination of acetaldehyde at ambient temperatures.
- Young, S. J.,Kellenberger, B.,Reibenspies, Joseph H.,Himmel, S. E.,Manning, M.,et al.
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p. 5744 - 5753
(2007/10/02)
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