Oxidation reactions of a nucleophilic palladium carbene: mono and bi-radical carbenes

Abstract

Palladium(II) cationic carbene radical and neutral bi-radical complexes were synthesized from a previously reported Pd(II) carbene in the presence of one and two electron oxidants. When [{PC(sp²)P}^tBuPd(PMe₃)] (1, [PC(sp²)P]^tBu = (bis[2-(di-iso-propylphosphino)-4-tertbutylphenyl]methylene)) was treated with [Cp₂Fe][X] (X = BAr^F₄, Ar^F = 3,5-(CF₃)₂C₆H₃, or PF₆), the corresponding radical cationic complexes [{PC˙(sp²)P}^tBuPd(PMe₃)][X] (2: X = BAr^F₄, 3: PF₆) were isolated and characterized. Magnetic moment measurements and EPR spectroscopy indicated the presence of a ligand centered unpaired electron. In the presence of two electron oxidants such as 1,8-naphthylene disulfide or 9,10-anthracenedione, 1 converts to [{PC˙(sp²)P}^tBuPdS(C₁₀H₆)SPd{PC˙(sp²)P}^tBu] (4) or [{PC˙(sp²)P}^tBuPdO(C₁₄H₁₀)OPd{PC˙(sp²)P}^tBu] (5), respectively. Single crystal X-ray diffraction and EPR spectroscopy confirmed the bi-radical nature of 4 and 5.