Stable, Chloride-Induced Monohapto-Bonding Mode for an Allyl Ligand in a Pd(II) Complex Bearing a New Bidentate Phosphonite−Oxazoline Ligand^†

Bidentate ligands can lead to stable η1-allyl complexes of Pd(II). A novel chelating phosphonite−oxazoline P,N ligand, abbreviated NOPOMe2, has been prepared by reaction of 6-chloro-6H-dibenz[c,e][1,2]oxaphosphorin with the lithium alcoholate derived from 4,4-dimethyl-2-(1-hydroxy-1-methylethyl)-4,5-dihydrooxazole. Its reaction with [Pd(η3-C3H5)(μ-Cl)]2 afforded the new η1-allyl Pd complex [PdCl(η1-C3H5)(NOPOMe2)] 2 in 91% yield. This constitutes a still rare example of structurally characterized η1-allyl Pd(II) complex. Chloride abstraction led to the corresponding cationic η3-allyl complex [Pd(η3-C3H5)(NOPOMe2)]PF6 3, which has also been characterized by X-ray diffraction. CO insertion into the Pd−C σ-bond of the η1-allyl ligand of 2 afforded the corresponding 3-butenoyl palladium complex [PdCl{C(O)C3H5}(NOPOMe2)] 4 under mild conditions, which supports the view that CO insertion into η3-allyl palladium cationic complexes occurs via first coordination of the counterion to form a more reactive η1-allyl intermediate.