title: The Reaction of Carbon Dioxide with Palladium Allyl Bonds.
abstract: A family of palladium allyl complexes of the type bis(2-methylallyl)Pd(L) (L = PMe(3) (1), PEt(3) (2), PPh(3) (3) or NHC (4); NHC = 1,3-Bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene) have been prepared through the reaction of bis(2-methylallyl)Pd with the appropriate free ligand. Compounds 1-4 contain one η(1) and one η(3)-2-methylallyl ligand and 3 was characterized by X-ray crystallography. These complexes react rapidly with CO(2) at low temperature to form well defined unidentate palladium carboxylates of the type (η(3)-2-methylallyl)Pd(OC(O)C(4)H(7))(L) (L = PMe(3) (6), PEt(3) (7), PPh(3) (8) or NHC (9). The structure of 9 was elucidated using X-ray crystallography. The mechanism of the reaction of 1-4 with CO(2) was probed using a combination of experimental and theoretical (density functional theory) studies. The coordination mode of the allyl ligand is crucial and whereas nucleophilic η(1)-allyls react rapidly with CO(2), η(3)-allyls do not react. We propose that the reaction of η(1)-palladium allyls with CO(2) does not proceed via direct insertion of CO(2) into the Pd-C bond but through nucleophilic attack of the terminal olefin on electrophilic CO(2), followed by an associative substitution at palladium.
authors.affiliation: Department of Chemistry, Yale University, P. O. Box 208107, New Haven, Connecticut, 06520, USA.
authors.forename: Jianguo
authors.initials: J
authors.lastname: Wu
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Green
authors.forename: Nilay
authors.initials: N
authors.lastname: Hazari
authors.forename: Damian P
authors.initials: DP
authors.lastname: Hruszkewycz
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Incarvito
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Schmeier