Synthesis, Characterization and Aerobic Alcohol Oxidation Catalysis of Palladium(II) Complexes with a Bis(imidazolyl)borate Ligand

Chloro‐ and hydroxo‐palladium(II) complexes with an imidazole‐based scorpionate ligand bis(1‐methylimidazolyl)methylphenylborate, [B(Im N –Me ) 2 MePh] – (= L Ph ), have been synthesized. Reaction of a lithium salt of L Ph with [PdCl 2 (NCPh) 2 ] yields a miscellaneous mixture involving a homoleptic complex [Pd(L Ph ) 2 ]. Replacement of the neutral ligand (benzonitrile) in the starting material with pyridine leads to the desired chloride complex 1 . X‐ray crystallographic analysis reveals the formula of 1 to be [PdCl(L Ph )(py)] with a square‐planar palladium(II) center supported by the bidentate L Ph ligand. Treatment of 1 with NaOH yields non‐pyridine‐containing hydroxo species with L Ph such as [Pd(OH)(L Ph )(H 2 O)] and [(PdL Ph ) 2 (µ‐OH) 2 ]. The hydroxo species 2 can convert into active species for catalytic secondary alcohol oxidation with O 2 in the absence of extra base. The utility of 2 as a catalyst precursor and the inertness of chloride complex 1 suggest that the basic nature of the co‐ligand (i.e. OH – ) on the palladium center supported by L Ph is essential to the formation of a putative palladium–alkoxide intermediate.