posted on 2000-11-02, 00:00authored byKristian Pignat, Jacopo Vallotto, Francesco Pinna, Giorgio Strukul
The synthesis of a series of Pd(II) and Pt(II) cationic complexes of the types [(P−P)M(solv)](Y)2, [(P−P)M(η2-Y)](Y), and [(P−P)M(μ-Cl)]2(Y)2 (where P−P = various diphosphines
including chiral diphosphines (M = Pd, Pt; Y = TfO-, ClO4-, BF4-) is reported. All complexes
are excellent catalysts for the Diels−Alder reaction between cyclopentadiene or cyclohexadiene and a number of simple dienophiles such as acrolein, methacrolein, and methylvinyl
ketone. Some of the complexes modified with chiral diphosphines can act as enantioselective
catalysts in the Diels−Alder reaction under mild condition with moderate ee's. A critical
point in this respect is the presence of only one vacant coordination site in the catalyst.