Carbon-Hydrogen Bond Activation in Novel η2-Bound Cationic Heterocycle Complexes of Pentaammineosmium(II)

Abstract: Reduction of (NH3)5Os(TFMS)3 (TFMS= trifluoromethanesulfonate) by Co(Cp)2 in the presence of cationic pyridines

L (L= jV-methylpyridinium, lutidinium, pyridinium, and A-methyl-4-picolinium) leads to the formation of isolable penta-

ammineosmium(II) complexes featuring fluxional 3,4-t;2 ligands for the former three and 2,3-t;2 for the latter. Analogously

to the previously reported i)2-lutidine analogue, activation at the C4-H bond was observed for the 3,4-rj2-bound cationic ligands,

yielding carbon-bound pyridinium ylides. In accord with observations made on other complexes containing metal-ylide carbon

bonds, the resulting pentaammineosmium(II) /V-methylpyridinium complex is unstable with respect to loss of the trans ammine.