Is the allylpalladium structure altered between solid and solutions?
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.
Clot
Eric
E
LSDSMS (UMR 5636), case courrier 14, Université Montpellier 2, 34095 Montpellier Cedex 5, France.
Eisenstein
Odile
O
Weng
Tsu-Chien
TC
Penner-Hahn
James
J
Caulton
Kenneth G
KG
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
D000475:Alkenes; D001555:Benzene Derivatives; D009942:Organometallic Compounds; D012996:Solutions; D010165:Palladium