Relative stabilities of trans-dichloro(olefin)(pyridine)platinum(II) complexes. Re-examination of hammett equation for para-substituted styrene complexes

Abstract

Relative solution stabilities of several olefin (L) complexes, trans-[PtCl₂(py)L](1)(py = pyridine) have been measured by means of ¹H n.m.r. spectroscopy by observing two separate methyl proton singlets of free CH₂CHC₆H₄Me-o and (1; L = CH₂ CHC₆H₄Me-o). Data for (1; L = CH₂CHC₆H₄Y-p, Y = NMe₂, OMe, Me, H, Cl, or NO₂) show the higher stability for the more electron-donating olefin complex, with the Hammett ρ⁺ value being –0.82. This is consistent with previous ¹³C n.m.r. and structural trends which suggest olefin-to-Pt σ donation to be much more important than π backbonding in determining the stability of (1).