Olefin Insertion Reactivity of a (Phosphine-arenesulfonate)Palladium(II) Fluoride Complex

The synthesis of the phosphine-arenesulfonate Pd­(II) fluoride complex (PO-OMe)­PdF­(lut) (2, PO-OMe = P­(2-OMe-Ph)2(2-SO3-5-Me-Ph), lut = 2,6-lutidine) and its reactions with electron-deficient olefins are described. The reaction of (PO-OMe)­PdBr­(lut) (1) with AgF affords 2 as an 82:18 mixture of cis-P,F and trans-P,F isomers. 2 isomerizes to a 1:2 cis-P,F:trans-P,F equilibrium mixture in CD2Cl2 solution at room temperature in ca. 3 days. 2 reacts with vinyl fluoride (VF) to afford (PO-OMe)­Pd­(CH2CHF2)­(lut) (3), which exists as the cis-P,C isomer. 2 reacts with vinyl bromide (VBr) to yield 1 and VF by initial fluoropalladation to form (PO-OMe)­Pd­(CH2CHBrF)­(lut) (4, not observed) followed by β-Br elimination. 2 reacts with vinyl acetate to yield (PO-OMe)­Pd­{CH2CHF­(OAc)}­(lut) (5), which reacts further to form the C-bound enolate complex (PO-OMe)­Pd­{CH2C­(O)­H}­(lut) (6) and acetyl fluoride. 2 reacts with vinyl benzoate in an analogous fashion. DFT analysis of the reaction of the model complexes cis-P,F- and trans-P,F-(PH2O)­PdF­(py) (C1 and C2, PH2O– = o-PH2C6H4SO3–) with VF supports a mechanism involving substitution of lutidine by VF followed by migratory insertion into the Pd–F bond. An alternative mechanism comprising substitution of fluoride by VF to generate (PO-OMe)­Pd­(VF)­(lut)+ and F–, followed by exo attack of F– on the bound VF was found to be energetically prohibitive. DFT analysis of the reaction of the model complexes cis-P,F- and trans-P,F-(PH2O)­PdF­(VBr) (C10 and C13) supports an insertion/β-Br elimination mechanism.