Hydrogenolysis of Dinuclear PCNR Ligated PdII μ‐Hydroxides and Their Mononuclear PdII Hydroxide Analogues. Issue 42 (3rd July 2019)

• Record Type: Journal Article
• Authors: Bailey, Wilson D.; Phearman, Alexander S.; Luconi, Lapo; Rossin, Andrea; Yakhvarov, Dmitry G.; D'Accolti, Lucia; Flowers, Sarah E.; Kaminsky, Werner; Kemp, Richard A.; Giambastiani, Giuliano; Goldberg, Karen I.
• Is Part Of: Chemistry. Volume 25:Issue 42(2019)
• Page Start: 9920
• Page End: 9929
• Publication Date: 2019-07-03
• Subjects: density functional calculations -- hydrogen -- hydrogenolysis -- palladium -- pincer complexes; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201900507
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: The hydrogenolysis of mono‐ and dinuclear Pd II hydroxides was investigated both experimentally and computationally. It was found that the dinuclear μ‐hydroxide complexes {[(PCN R )Pd]2 (μ‐OH)}(OTf) (PCN H =1‐[3‐[(di‐ tert ‐butylphosphino)methyl]phenyl]‐1 H ‐pyrazole; PCN Me =1‐[3‐[(di‐ tert ‐butylphosphino)methyl]phenyl]‐5‐methyl‐1 H ‐pyrazole) react with H2 to form the analogous dinuclear hydride species {[(PCN R )Pd]2 (μ‐H)}(OTf). The dinuclear μ‐hydride complexes were fully characterized, and are rare examples of structurally characterized unsupported singly bridged μ‐H Pd II dimers. The {[(PCN Me )Pd]2 (μ‐OH)}(OTf) hydrogenolysis mechanism was investigated through experiments and computations. The hydrogenolysis of the mononuclear complex (PCN H )Pd‐OH resulted in a mixed ligand dinuclear species [(PCN H )Pd](μ‐H)[(PCC)Pd] (PCC=a dianionic version of PCN H bound through phosphorus P, aryl C, and pyrazole C atoms) generated from initial ligand "rollover" C−H activation. Further exposure to H2 yields the bisphosphine Pd 0 complex Pd[(H)PCN H ]2 . When the ligand was protected at the pyrazole 5‐position in the (PCN Me )Pd−OH complex, no hydride formed under the same conditions; the reaction proceeded directly to the bisphosphine Pd 0 complex Pd[(H)PCN Me ]2 . Reaction mechanisms for the hydrogenolysis of the monomeric and dimeric hydroxides are proposed. Abstract : Unsymmetrical pincers : The hydrogenolysis of mono‐ and dinuclear Pd II hydroxides supported by unsymmetrical pyrazole‐based PCN R pincer ligands has been examined experimentally and computationally. New methods of H2 interaction and activation at late‐transition‐metal centers are discovered, supported by both experiment and theory (see scheme).