168129-77-9Relevant academic research and scientific papers
Large kinetic isotope effects for the protonolysis of metal-methyl complexes are not reliable mechanistic indicators
Scott, Valerie J.,Labinger, Jay A.,Bercaw, John E.
, p. 4374 - 4378 (2011/10/10)
Earlier work on protonolyses of several palladium and platinum methyl complexes (with release of methane) had suggested the possibility that observation of an unusually large kinetic isotope effect, consistent with significant contributions from quantum mechanical tunneling, might be diagnostic of a mechanism involving direct protonation of the metal-methyl bond, as opposed to one proceeding via a metal hydride intermediate. By extension of these measurements to a wider set of complexes, we find no support for the proposed correlation.
In situ preparation of palladium diphosphane catalysts
Marson, Angelica,Van Oort, A. Bart,Mul, Wilhelmus P.
, p. 3028 - 3031 (2007/10/03)
The efficiency of a superficially simple preparation procedure for palladium-diphosphane catalysts has been examined. Preparation of Pd(dppe)X2 in situ by mixing equimolar amounts of Pd(OAc)2 and 1,2-bis(diphenylphosphanyl)-ethane (dppe) in methanol in the first step unexpectedly affords the bischelate [Pd(dppe)2](OAc)2 as the (main) kinetic product. Subsequently, the slow reaction of [Pd(dppe)2]-(OAc)2 and unreacted Pd(OAc)2 forms the thermodynamically favored monochelate [Pd(dppe)(OAc)2] (following first-order kinetics). Conversion of the bischelate into the monochelate stops after addition of strong acid (HX) in the second step, thus affording a mixture of active - Pd(dppe)X2 - virtually inactive - [Pd(dppe)2]X2 - and unstable - PdX2 - species. This procedure was also evaluated for some other diphosphane ligands and methods are given to overcome the encountered problem.
Studies on palladium-bisphosphine catalyzed alternating copolymerization of CO and ethylene
Luo, He-Kuan,Kou, Yuan,Wang, Xi-Wen,Li, Da-Gang
, p. 91 - 113 (2008/10/08)
Palladium(II)-bisphosphine catalyzed copolymerization of CO and ethylene was studied in detail. The results showed that DPPPr/Pd(II) mole ratio, CF3COOH/Pd(II) mole ratio and solvent greatly influence the catalytic activity. Solvent effects were studied and in detail through end group analysis. With high pressure in situ 1H-NMR technique, the signals of coordinated ethylene at 4.4 ppm and methylene linked with Pd(II) (Pd - CH2-) at 0.6 ppm were observed. With high-pressure in situ IR technique three palladium carbonyl absorptions were observed generated at 1638 cm-1, 1616 cm-1 and 1970 cm-1, which may be assigned to three intermediates (3) (5) (6). With the above results, the copolymerization mechanisms were discussed. High-pressure in situ 31P-NMR experimental result showed that only mono- chelate ring complex (1) was produced when DPPPr/Pd(II) = 1; only bis-chelate ring complex (2) was produced when DPPPr/Pd(II) = 2; equimolar complex (1) and (2) were produced when DPPPr/Pd(II) = 1.5. Extended X-ray absorption fine structure (EXAFS) was used to calculate the coordination number (CN) and shell radius (R, in ?) of complexes (DPPPr)Pd(OCOCF3)2 (a), (DPPBu)Pd(OCOCF3)2 (b), (DPPEt)Pd(OCOCF3)2 (c), (DPPPr)2Pd(OCOCF3)2 (e), and two catalyst solutions of methanol freshly taken before and in the middle of copolymerization (named S1 and S2, respectively). The Pd - P bond length of complexes (a) (b) (c) are 2.25(3) ?, 2.33(3) ?, and 2.38(2) ?, respectively, Pd - O bond length of complexes (a) (b) (c) are 2.07(3) ?, 2.06(2) ? and 2.05(3) ?, respectively. In the order of complexes (a) (b) (c), the catalytic activity increases with Pd - P bond decreasing and Pd - O bond increasing, which may show that the chelate ring is more stable, the anions can go away more easily, and the corresponding catalyst is more efficient. The coordination number of two catalyst solutions S1 and S2 are increased by 1.9 and 0.9 compared with solid complex (a), which may show that 18-electron and five-coordinated pyramidal intermediates were produced and existed in the system besides 16-electron and four-coordinated square planar intermediates. (C) 2000 Elsevier Science B.V.
