Selective and Reversible Base-Induced Elimination of a Ruthenium Dithioether Yields a Vinyl Metallosulfonium Complex

Chemical oxidation of tris­(2-diphenylphosphinebenzenethiolato)­ruthenate­(II) [Ru-1]– with ferrocenium hexafluorophosphate
in the presence of ethylene yields [(2-diphenylphosphinebenzenethiolato)­(ethane-1,2-diylbis­(thio-2,1-phenylene)­diphenylphosphine)­ruthenium­(II)]
hexafluorophosphate, [Ru-1·C2H4]­PF6, from addition of the alkene across cis sulfur sites.
The [Ru-1·C2H4]+ complex
displays a single redox couple at +794 mV versus ferrocenium/ferrocene.
1H NMR of [Ru-1·C2H4]+ displays ethylene resonances at δ = 1.29 (td,
1H), 1.59 (td, 1H), 2.78 (dd, 1H), and 3.03 (dd, 1H). In the presence
of base [Ru-1·C2H4]+ is
selectively deprotonated at the pseudoequatorial proton on the carbon
α to the sulfur trans to phosphorus, yielding the vinyl metallosulfonium
derivative [Ru-1·C2H3]. 1H and 31P NMR spectra of [Ru-1·C2H3] are temperature
dependent, associated with inversion of the sulfur lone pair at the
vinyl metallosulfonium. The activation energy for the fluxional process
calculated using density functional theory (B3LYP/LANL2DZ+6-31g) of
14.36 kcal/mol is consistent with the experimentally determined value
of 13.08 kcal/mol. The complex [Ru-1·C2H3] crystallizes as yellow blocks in the triclinic space group P-1 with unit cell dimensions of a = 11.2718(5)
Å, b =12.0524(3) Å, c =
23.6075(10) Å, α = 101.715(3)°, β = 98.154(4)°,
and γ = 105.209(3)°. Addition of hydrochloric acid to [Ru-1·C2H3] regenerates [Ru-1·C2H4]+. Addition of DCl confirms the selectivity
of this reverse reaction.