Coordination of Alkenes at a Highly Electrophilic Site. New Dicationic Platinum(II) Complexes: Synthesis, Structure, and Reactions with Nucleophiles

Abstract

Dicationic platinum(II) alkene complexes [Pt(PNP)(alkene)](BF4)2 (alkene = ethylene, propene, 1-butene, Z- and E-2-butene, styrene, norbornene; PNP = 2,6-bis(diphenylphosphinomethyl)pyridine) have been prepared and characterized by 1H and 13C NMR spectroscopy, and the molecular structure of the ethylene complex has been determined by X-ray diffraction analysis. Nucleophilic attack at the coordinated double bond takes place more readily than for known neutral and monocationic species, and a variety of protic nucleophiles NuH (MeOH, H2O, aromatic amines) give the corresponding β-functionalized σ-alkyl complexes [Pt(PNP)(CHRCHR‘Nu)]BF4 also in the absence of auxiliary bases. In the case of the styrene derivatives an unusual decomposition pathway gives the stable alkenyl complex [Pt(PNP)(CHCHPh)]BF4. A competitive equilibrium process between substitution and addition was revealed by reacting ethylene with the isolated aniline complex [Pt(PNP)(PhNH2)](BF4)2. The nucleophilic addition product was found to be th...