Modulation of properties in analogues of Zeise's anion on changing the ligandtrans to ethene. X-Ray crystal structures of trans-[PtCl2(OH)(η2-C2H4)]− and trans-[PtCl2(η1-CH2NO2)(η2-C2H4)]−

Abstract

To get further insight in the reaction of nucleophilic substitution upon changing the ligand trans to a η²-olefin, the reactivity of some monoanionic platinum(II) complexes (trans-[PtCl₂X(η²-C₂H₄)]⁻, X = Cl⁻, 1, OH⁻, 2, and CH₂NO₂⁻, 3) towards pyridines with different steric hindrance (py, 4-Mepy, and 2,6-Me₂py) has been tested. All crystallographic (2 and 3 reported for the first time) and spectroscopic data are in accord with a platinum–olefin interaction decreasing in the order 2 > 1 > 3, paralleling the decreasing electronegativity of the donor atom (O > Cl > C). Not only the platinum-olefin bond but also the bond between platinum and the ligand trans to the olefin appear to be strongest in 2 (Pt–O distance at the lower limit for this type of bond). In the reaction with py, the ligand trans to the olefin is displaced in 1 and 2. Moreover the reaction is in equilibrium in the case of sterically hindered 2,6-Me₂py, the equilibrium being shifted moderately or prevalently toward the reagents in the case of 1 and 2, respectively. In the case of 3, the reaction with pyridines leads to substitution of the olefin instead of the carbanion. This is in accord with the observation that carbanions strongly weaken the transPt–olefin bond.