Kinetico-mechanistic studies on intramolecular C-X bond activation (X = Br, Cl) of amino-imino ligands on Pt(II) compounds. Prevalence of a concerted mechanism in nonpolar, polar and ionic liquid media

Abstract

The C–Br and C–Cl oxidative addition reactions of molecules containing a set of {N-amino,N-imino} chelating donor groups (2-X,6-YC6H4CHNCH2CH2NMe2, X = Br, Cl; Y = Cl, H) attached to a {PtII(Ar)2} (Ar = Ph, 4-MeC6H4) have been studied. The Pt(IV) complexes formed, [PtAr2X{2-YCC5H3CH═NCH2CH2NMe2}], containing a metalated tridentate [C,N,N′] ligand have been fully characterized by the usual techniques, and the X-ray crystal structure of the complex with Ar = 4-MeC6H4 and X =Y = Cl has been determined. Monitoring of the reactions at varying temperatures and pressures and in different solvents agrees with a mechanism that involves the preliminary decoordination of the N-amino donor from the ligand to produce a three-coordinated intermediate. This evolves, via a concerted C–X bond activation, to form a second pentacoordinated intermediate species that, on coordination of the N-amino donor, produces the final complex. The kinetico-mechanistic parameters measured indicate that the concerted character of the process is maintained from nonpolar (xylene and toluene) to polar (acetone) and ionic liquid ((Bmin(NTf2)) media. Furthermore, the ΔV⧧ values measured indicate that, for the (2,6-Cl)C6H3CH═NCH2CH2NMe2 ligand, the existence of hydrogen bonding within the metalating molecule is a determinant for the acceleration observed.