title: Is the allylpalladium structure altered between solid and solutions?
abstract: Recent EXAFS measurements on [(Ph(2)PCH(2)CH(2)PPh(2))Pd(H(2)CCHCMe(2))]O(3)SCF(3) (Tromp et al. J. Am. Chem. Soc. 2002, 124, 14814) were interpreted as evidence that, when the complex is dissolved in THF, the allyl ligand adopts an eta(2) structure with a dangling allyl CH(2) substituent. DFT calculations of the Pd complex using H(2)P-CH(2)CH(2)-PH(2) as a model for Ph(2)P-CH(2)CH(2)-PPh(2) (dppe), in the absence or the presence of the triflate counteranion, and modeling the THF solvent by explicit Me(2)O molecules or by a continuum model give always a conventional eta(3)-H(2)CCHCMe(2) structure with equal Pd-C bonds to the terminal carbon centers of the allyl. QM/MM calculations using the dppe ligand also fail to support an eta(2)-allyl structure as a global minimum. The EXAFS parameter space is shown to have multiple minima. These have very similar overall EXAFS, but have very different structural parameters. The minimum that was the basis for the previous structural conclusion gives a slightly better fit but has unrealistic Debye-Waller factors and threshold energies.
authors.affiliation: LSDSMS (UMR 5636), case courrier 14, Université Montpellier 2, 34095 Montpellier Cedex 5, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Clot
authors.forename: Odile
authors.initials: O
authors.lastname: Eisenstein
authors.forename: Tsu-Chien
authors.initials: TC
authors.lastname: Weng
authors.forename: James
authors.initials: J
authors.lastname: Penner-Hahn
authors.forename: Kenneth G
authors.initials: KG
authors.lastname: Caulton
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D001555:Benzene Derivatives / Q000737:chemistry; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D011789:Quantum Theory; D012996:Solutions; D013057:Spectrum Analysis / Q000379:methods
chemical_list: D000475:Alkenes; D001555:Benzene Derivatives; D009942:Organometallic Compounds; D012996:Solutions; D010165:Palladium