EFFECT OF FLUORINE SUBSTITUENTS IN INTRAMOLECULAR ACTIVATION OF C-F AND C-H BONDS BY PLATINUM(II)

The bifunctional iminic ligands C6F5CH=NCH2(2-C6H4X) (X = H, Cl, Br) and ArCH=NCH2C6H5 (Ar = 2,3,6-C6H2F3, 2,4,6-C6H2F3) react with [Pt2Me4(mu-SMe2)2] to give, via oxidative addition of the C-F bonds, platinum(IV) products in which the fluorine ligand and the aryl carbon are mutually cis. Further reaction of these compounds with PPh3 takes place to give a displacement reaction of SMe2 for PPh3 which is shown from NMR data to occur with isomerization, resulting in a trans arrangement of the fluorine ligand and the aryl carbon. No reaction is observed when the ligand 2,6-C6H3F2CH=NCH2CrH5 is treated with [Pt2Me4(mu-SMe2)2], indicating the importance of the increase of fluorination in the ring for C-F bond activation. Ligands ArCH=NCH2(2-C6H4Cl) (Ar = 2-C6H4F, 3-C6H4F, 4-C6H4F, 3,5-C6H3F2) also react with [Pt2Me4(mu-SMe2)2] to give platinum(II) complexes by ortho metalation with loss of methane. Again, the presence of fluorine substituents in the ligands is shown to increase, mainly via inductive effects, the reactivity of C-H bonds. The kinetics of formation of both types of compounds has been studied, and a trend in the activation enthalpy values that parallels the electron-withdrawing effects in the iminic ring is obtained.