C-F Bond Breaking through Aromatic Nucleophilic Substitution with a Hydroxo Ligand Mediated via Water Bifunctional Activation

Transformation of C-F to C-O bond mediated by bifunctional ruthenium and iridium complexes is described. This reaction proceeds through water O-H bond cleavage via metal ligand cooperation in the newly developed 16e bifunctional ruthenium and iridium complexes bearing chiral (S,S)-C6F5SO2-dpen ligand. The 16e Ru amido complex, [Ru{(S,S)-Pfbsdpen}(eta(6)-hmb)] (1a), readily reacted with water at room temperature producing oxometallacyclic compound, (R)-[Ru{kappa(3)(N,N',O)-(S,S)-OC(6)F(4)SO(2)dpen}(eta(6)-hmb)] (3a(R)), as a result of bifunctional water activation followed by ortho-oxometallation via SNAr. Complex 3a(R) can be prepared either from 1a or, more conveniently from its 18e chlorido precursor, complex (R)-[RuCl{(S,S)-Pfbsdpen}(eta(6)-hmb)]. On the contrary, the 16e Ir amido complex, [Cp*Ir{(S,S)-Pfbsdpen}] (2), is kinetically stable toward water at room temperature. Oxometallacyclic compound (R)-[Cp*Ir{kappa(3)(N,N',O)-(S,S)-OC(6)F(4)SO(2)dpen}] (4(R)) was prepared in high yield by the reaction of [Cp*IrCl2](2) with 2 equiv of (S,S)-Pfbsdpen in the presence of KOH under reflux in THF. In either case 3(R) or 4(R) is obtained as a single diastereomer, the structure of which has been determined by single-crystal X-ray diffraction studies in solid state and NMR-analysis in solution. Reaction mechanism was studied by NMR spectroscopy combined with continuum solvent reaction-field density functional theory (DFT) analysis. Experimental studies showed that diastereoselective oxocyclometallation 1a --> 3a(R) proceeds at temperatures >0 degrees C in a stepwise manner through the detectable intermediate, hydroxo complex (R)-[Ru(OH){(S,S)-Pfbsdpen} (eta(6)-hmb)] (6a(R)), which exists in equilibrium with less-populated diastereomer (S)-[Ru(OH){(S,S)-Pfbsdpen}(eta(6)-hmb)] (6a(S)) in 10:1 ratio at -80 degrees C in CD2Cl2. Computational analysis essentially explains the diastereoselectivity in this reaction via a significant difference in the stabilities of the corresponding transition states: although diastereomers 6a(R) and 6a(S) are in equilibrium via complex 1a, only 6a(R) is transformed into 3a(R) via rate-determining Meisenheimer-type transition state.