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

Abstract

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.

Copolymerization of Ethylene and Vinyl Fluoride by Self-Assembled Multinuclear Palladium Catalysts

“…The ethylene/VF copolymers produced by C in hexanes exhibit broad MWDs (Table 1, entries 3,4; Figure 2). Given the nearly ideal single-site behavior observed in ethylene homopolymerization tral cage, leading to the formation of new active Pd species [23,25,[48][49][50][51][52]. Consistent wit sal, -CH2CH2F and -CH2CHF2 end groups, which are formed by ethylene and VF inserti pecies in copolymerization by mononuclear catalysts A, are not observed in the copol ced by C (Figure 3) [23].…”

“…Given the nearly ideal single-site behavior observed in ethylene homopolymerization by C in hexanes, it is unlikely that the broadening of the MWD of the ethylene/VF copolymers formed in this solvent is due to thermal disassembly of the cage structure (Figure 2). One possibility is that nucleophilic Pd-F species generated by 1,2-VF insertion and β-F elimination react with the Li + ions in the central cage, leading to the formation of new active Pd species [23,25,[48][49][50][51][52]. Consistent with this proposal, -CH 2 CH 2 F and -CH 2 CHF 2 end groups, which are formed by ethylene and VF insertion of Pd-F species in copolymerization by mononuclear catalysts A, are not observed in the copolymer produced by C (Figure 3) [23].…”

“…Vinyl halides are particularly challenging polar comonomers due to (i) their poor competition with ethylene for binding to Pd II catalysts [ 9 , 10 ], (ii) the formation of inactive L n Pd-X complexes by β-X elimination of L n PdCH 2 CXR species (generated by 1,2 CH 2 =CHX insertion or 2,1- CH 2 =CHX insertion followed by chain walking) [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ], and (iii) the low insertion reactivity of L n PdCHXCH 2 R species formed by 2,1 CH 2 =CHX insertion [ 16 , 21 ]. We previously reported that (PO)PdMe(L) catalysts ( A , Figure 1 ) that contain phosphine-arenesulfonate ligands (PO − ) copolymerize ethylene and vinyl fluoride (VF) to linear copolymers with up to 0.55 mol% VF incorporation [ 22 , 23 , 24 , 25 ]. The catalyst activities are significantly reduced and the polymer molecular weights (MWs) are also reduced in ethylene/VF copolymerization compared to ethylene homopolymerization under the same conditions.…”

Application of Industrially Relevant HydroFluoroOlefin (HFO) Gases in Organic Syntheses

“…44 Jordan and co-workers demonstrated that fluoroolefins can be inserted into the Pd-F bond to form fluoroalkylpalladium species. Beyond the detailed mechanistic studies of this elementary step including DFT studies, 45 this insertion step enabled the copolymerization of ethylene and fluoroolefins to generate polyethylene that contained a fluoromethyl chain end. 46 The transition-metal-mediated C-F bond activation also enables the selective transformation of fluoroalkenyl species to hydrofluorocarbons.…”