Interionic solution structure of [PtMe(η2-olefin)(N,N-diimine)]BF4 complexes by 19F{1H}-HOESY NMR spectroscopy:: Effect of the substituents on the accessibility of the counterion to the metal

The relative cation-anion position in [Pt(Me)(eta(2)-olefin)(N,N)]BF4 complexes (where N,N = 2,6-(R')(2)C6H3N=C(R ")C(R ")=N-2,6-(R')(2)C6H3, R' = H, Me, Et, and i-Pr, R " = H, Me; olefin = CH2=CHR, R = H, Me, COOMe) in methylene chloride has been investigated by detecting specific interionic dipolar interactions in the F-19{H-1}-HOESY NMR spectra. The counterion shows strong interionic contacts with R " and R' protons and weak contacts with R and olefinic protons only when R' < Et and R " = Me. For R' greater than or equal to Et the accessibilty to the metal center is completely inhibited and the counterion is located above or below the backside of the diimine ligand. The same position is also observed when R " = H and R' = R = Me despite the limited steric hindrance of the substituents due to specific interactions between H " and the fluorine of BF4-. In the other cases (R' < Et), the counterion also interacts with Me, R, and olefinic protons, indicating that the accessibility to the metal center is not forbidden.