Reactivity Studies of Cationic Palladium(II) Phosphine Carboxylate Complexes with Lewis Bases: Substitution versus Cyclometalation

Two classes of cationic palladium(II) phosphine carboxylate complexes were isolated and characterized.
Reactions of trans-[(R3P)2Pd(O2CR‘)2] (1) with [Li(OEt2)2.5][B(C6F5)4] in MeCN led to carboxylate
abstraction and formation of trans-[(R3P)2Pd(O2CR‘)(MeCN)][B(C6F5)4] (2) in good to excellent yields.
On the other hand, carboxylate abstraction reactions of 1 with [Me2(H)NPh][B(C6F5)4] or p-toluenesulfonic
acid (HOTs·H2O) in CH2Cl2 furnished the palladium cations [(R3P)2Pd(κ2-O,O-O2CR‘)]+ (3). The reactions
of 2 and 3 with Lewis bases were found to be different in some cases. For example, reactions of 2 with
pyridine furnished the simple products of acetonitrile substitution, trans-[(R3P)2Pd(O2CR‘)(py)][B(C6F5)4].
In contrast, the reaction of 3e (R = iPr, R‘ = CH3) with CD3CN in the presence of excess sodium carbonate
yielded a material derived from cyclometalation of one of the iPr arms of a iPr3P ligand. New complexes
were characterized by elemental analyses and NMR (1H, 13C, and 31P) spectroscopic methods and in two
cases by single-crystal X-ray structural methods.