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).