Pd(I) Phosphine Carbonyl and Hydride Complexes Implicated in the Palladium-Catalyzed Oxo Process
Résumé
Reduction of compound “Pd(bcope)(OTf)2” [bcope = (c-C8H14-1,5)PCH2CH2P(c-C8H14-1,5); OTf = O3SCF3] with H2/CO yields a mixture of Pd(I) compounds [Pd2(bcope)2(CO)2](OTf)2 (1) and [Pd2(bcope)2(μ-CO)(μ-H)](OTf) (2), whereas reduction with H2 or Ph3SiH in the absence of CO leads to [Pd3(bcope)3(μ3-H)2](OTf)2 (3). Exposure of 3 to CO leads to 1 and 2. The structures of 1 and 3 have been determined by X-ray diffraction. Complex [Pd2(bcope)2(CO)2]2+ displays a metal−metal bonded structure with a square planar environment for the Pd atoms and terminally bonded CO ligands and is fluxional in solution. DFT calculations aid the interpretation of this fluxional behavior as resulting from an intramolecular exchange of the two inequivalent P atom positions via a symmetric bis-CO-bridged intermediate. A cyclic voltammetric investigation reveals a very complex redox behavior for the “Pd(bcope)(OTf)2”/CO system and suggests possible pathways leading to the formation of the various observed products, as well as their relationship with the active species of the PdL22+/CO/H2-catalyzed oxo processes (L2 = diphosphine ligands).
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