Photophysical Properties and Kinetic Studies of 2-Vinylpyridine-Based Cycloplatinated(II) Complexes Containing Various Phosphine Ligands †

A series of cycloplatinated(II) complexes with general formula of [PtMe(Vpy)(PR(3))], Vpy = 2-vinylpyridine and PR(3) = PPh(3) (1a); PPh(2)Me (1b); PPhMe(2) (1c), were synthesized and characterized by means of spectroscopic methods. These cycloplatinated(II) complexes were luminescent at room temperature in the yellow–orange region’s structured bands. The PPhMe(2) derivative was the strongest emissive among the complexes, and the complex with PPh(3) was the weakest one. Similar to many luminescent cycloplatinated(II) complexes, the emission was mainly localized on the Vpy cyclometalated ligand as the main chromophoric moiety. The present cycloplatinated(II) complexes were oxidatively reacted with MeI to yield the corresponding cycloplatinated(IV) complexes. The kinetic studies of the reaction point out to an S(N)2 mechanism. The complex with PPhMe(2) ligand exhibited the fastest oxidative addition reaction due to the most electron-rich Pt(II) center in its structure, whereas the PPh(3) derivative showed the slowest one. Interestingly, for the PPhMe(2) analog, the trans isomer was stable and could be isolated as both kinetic and thermodynamic product, while the other two underwent trans to cis isomerization.