Neutral and Cationic Palladium(II) Bis(pyrazolyl)methane Complexes

The synthesis, structures, and reactivity of neutral and cationic Pd(II) complexes incorporating bis(pyrazolyl)methane ligands are described. The reaction of (CH₃CN)₂PdCl₂ with the appropriate bis(pyrazoyl)methane in CH₂Cl₂ yields {Ph₂C(3-^tBu-pz)₂}PdCl₂ (1) and {Ph₂C(pz)₂}PdCl₂ (2). Steric crowding associated with the ^tBu groups of 1 increases the puckering of the chelate ring (boat conformation) and retards the chelate ring inversion relative to 2. The reaction of {Me₂C(pz)₂}PdMe₂ (3) with [HNMe₂Ph][B(C₆F₅)₄] yields {Me₂C(pz)₂}PdMe(NMe₂Ph)⁺ (4a, B(C₆F₅)₄^- salt), while treatment of 3 with [H(OEt₂)₂][B{3,5-(CF₃)₂C₆H₃}₄] yields {Me₂C(pz)₂}PdMe(OEt₂)⁺ (4b, B{3,5-(CF₃)₂C₆H₃}₄^- salt). Complex 4a reacts with ethylene at −60 °C (CD₂Cl₂) to yield {Me₂C(pz)₂}PdMe(CH₂CH₂)⁺ (5, B(C₆F₅)₄^- salt) and free NMe₂Ph. Cation 5 undergoes ethylene insertion at −10 °C and oligomerizes ethylene (1 atm) to predominantly linear internal C₈ to C₂₄ olefins (ca. 0.1 branches per 2 carbons) at 23 °C.