(2,4,6-Tris(trifluoromethyl)phenyl)palladium(II) Complexes

Complexes containing one or two Fmes ligands (Fmes = 2,4,6-tris(trifluoromethyl)phenyl = nonafluoromesityl) either trans or cis are obtained by treating palladium(II) chloro complexes with Li(Fmes):  trans-[PdCl₂L₂] (L = tetrahydrothiophene (tht), PPh₃) lead to trans-[Pd(Fmes)ClL₂] (L = tht, PPh₃) or trans-[Pd(Fmes)₂L₂] (L = tht); [PdCl₂(L-L)] (L-L = 1,5-cyclooctadiene, 2,2‘-bipyridine) give [Pd(Fmes)Cl(L-L)] (L-L = COD, bipy) or [Pd(Fmes)₂(bipy)]. The structures of two complexes containing two Fmes ligands in trans and cis arrangement, trans-[Pd(Fmes)₂(tht)₂] (2) and [Pd(Fmes)₂(bipy)] (6), respectively, have been determined by X-ray diffraction. In spite of the severe steric congestion the complexes are four coordinated. Distortions due to the bulkiness of the ortho substituents and short Pd···F₃C-ortho distances are observed. The high degree of steric crowding is also responsible for slow rotation around the Pd−P bonds in the complex trans-[Pd(Fmes)Cl(PPh₃)₂]. ΔG^⧧ associated with this motion is 12.8 kcal mol^-1, one of the highest values reported so far for rotation around M−PPh₃ bonds. Complexes 2 and 6 are redox inactive by cyclic voltammetry in the range −1.8 to +1.8 V.