Kinetico-mechanistic studies on the formation of seven-membered [C,N]-platinacycles: the effect of methyl or fluoro substituents on the aryl ancillary ligands

Abstract

The reactions of dinuclear [Pt2(4-RC6H4)4(μ-SEt2)2] (R = Me or F), or mononuclear [Pt(4-RC6H4)2(SMe2)2] (R = Me or H), platinum(ii) compounds with imines of the general formula 2-X,6-YC6H3CH[double bond, length as m-dash]NCH2Ph (X = Br, Y = F; X = Cl, Y = F; X = Br, Y = H) produced seven-membered [C,N]-platinacycles. The reaction consists of the initial formation of cyclometallated platinum(iv) compounds followed by a three step process: reductive elimination, isomerisation of the resulting non-cyclometallated intermediate and a final cycloplatination process. Combined (1)H NMR and UV-Vis kinetico-mechanistic studies indicated that the rate determining step of the process depends on the nature of the aryl-Pt ligand (phenyl, p-tolyl or p-fluorophenyl).

Carbon‐iodide bond activation by cyclometalated Pt (II) complexes bearing tricyclohexylphosphine ligand: A comparative kinetic study and theoretical elucidation

“…Platinum (II) complexes provide a useful platform for kinetic and mechanistic studies of fundamental oxidative addition reactions because of their relative inertness, high stability and availability of different oxidation states . Oxidative addition of C–X bonds to platinum (II) complexes is generally enthalpically favored and produces the corresponding platinum (IV) products normally proceeding through a S N 2 type mechanism in which the Pt (II) center acts as a nucleophile via the filled d z 2 orbital . However, a radical pathway as well as concerted three‐center mechanisms have also been suggested for oxidative addition reactions …”

On the stability and biological behavior of cyclometallated Pt(IV) complexes with halido and aryl ligands in the axial positions

“…We have been involved in the use of diarylplatinum(II) complexes as precursors in the synthesis of [C,N,N′] cyclometallated platinum(II) and platinum(IV) compounds [38,39] and the study of the mechanisms involved in these processes [40][41][42]. The platinum(IV) compound 3a (Scheme 1), synthesized in previous studies [43], is a cyclometallated platinum(IV) compound with a fac-PtC3 arrangement and a meridional [C,N,N′] terdentate ligand, thus leaving one bromido and one aryl ring as axial ligands.…”

Platinum-Catalyzed C–H Functionalization

“…Among other explorations of reactivity preference, Pt­(II) complexes of a bidentate amine-imine ligand ( 8 ) with a dangling biphenyl group, generated by C–C reductive elimination from an aryl–Pt­(IV) precursor ( 7 ), undergo competing C–H activation of the proximal or distal arene ring to give five- or seven-membered metallacycles ( 9 , 10 ), respectively (Scheme ). A detailed study of kinetics led to understanding of the factors controlling product preference, including interconversion between the isomeric intermediates that are precursors to specific products. − Some of the various five- and seven-membered metallacycles have been examined as possible antitumor agents, as well as for luminescence properties potentially relevant to OLED applications . The pyridylquinoline–Pt­(II) complex 11 undergoes “rollover” cyclometalation at room temperature; under certain conditions, 12 can be protonated at the free N without disturbing the Pt–methyl bond, but when the DMSO ligand is replaced with PPh 3 , “retro-rollover” takes place spontaneously (Scheme ).…”