Intramolecular Insertion of Alkenes into Pd-N Bonds. Effects of Substrate and Ligand Structure on the Reactivity of (P-P)Pd(Ar)[N(Ar1)(CH2)3CR=CHR′] Complexes

Studies on the synthesis and reactivity of a series of (P-P)Pd(Ar)[N(Ari)(CH2)(3)CR=CHR'] complexes 3 are described. These complexes are transformed to observable (P P)Pd(Ar)[pyrrolidin-2-ylmethyl] complexes 4 via syn insertion of the pendant alkene into the Pd N bond. Complexes 4 then undergo C C bond-forming reductive elimination to yield N-aryl-2-benzylpyrrolidine derivatives 2. Kinetic studies indicate the rates of conversion of 3 to 4 and 4 to 2 are within I order of magnitude. The effects of phosphine ligand structure, alkene substitution, and the electronic properties of the Ar and Ar-1 groups on reaction rates are reported, as are the results of deuterium isotope effect studies. The mechanism of the aminopalladation step is discussed in detail, and the results of the experiments described in this paper are most consistent with conversion of 3 to 4 via rate-determining ligand displacement followed by fast aminopalladation. These transformations represent rare examples of syn migratory insertion of unactivated alkenes into Pd N bonds.