Generation and insertion reactivity of cationic palladium complexes that contain halogenated alkyl ligands

The generation of cationic palladium complexes that contain halogenated alkyl ligands (R-X) and their reactivity with vinyl chloride, ethylene, and CO are described. {((n)Hex)HC(mim)(2)}Pd(CHCl2)Cl (1; nHex = n-hexyl, mim = N-methylimidazol-2-yl) reacts with 0.5 equiv of [Li(Et2O)(2.8)] [B(C6F5)(4)] to form [{{((n)Hex)HC(mim)(2)}Pd(CHCl2)}(2)(mu-Cl)][B(C6F5)4] as a 1:1 mixture of diastereomers (3a,b). 3a,b do not react with vinyl chloride. The reaction of 1 with 1 equiv of [Li(Et2O)(2.8)][B(C6F5)(4)] in the presence of ethylene or CO yields [{((n)Hex)HC(mim)(2)}Pd(CHCl2)(L)] [B(C6F5)(4)] adducts (L = ethylene (4), CO (5)). The reaction of (dppp)Pd((C3F7)-C-n)Me (7; dppp = 1,3-bis(diphenylphosphino)propane) with [HNMePh2] [B(C6F5)41 yields [(dppp)Pd((C3F7)-C-n)(NMePh2)] [B(C6F5)(4)] (8). 8 does not react with vinyl chloride or ethylene but does react with CO to form [(dppp)Pd(nC(3)F(7))(CO)l [B(C6F5)(4)] (9). 4, 5, and 9 do not undergo insertion under mild conditions. The reaction of ((t)Bu(2)bipy)Pd(CH2Cl)Cl (10; (t)Bu(2)bipy = 4,4'di-tert-butyl-2,2'-bipyridine) with 0.5 equiv of [Li(Et2O)(2.8)][B(C6F5)(4)] yields [{((t)Bu(2)bipy)Pd(CH2Cl)}(2)(mu-Cl)] [B(C6F5)(4)] (11). In the presence of one equiv of [Li(Et2O)(2.8)][B(C6F5)(4)}, 11 reacts with vinyl chloride by net 1,2-insertion and beta-Cl elimination to generate Pd-Cl+ species and allyl chloride and with CO at -78 degreesC to form [((t)Bu(2)bipy)Pd(CH2Cl)(CO)][B(C6F5)(4)] (12). At 20 degreesC, 12 undergoes slow CO insertion followed by P-Cl elimination to generate Pd-Cl+ species and ketene. The reaction of (alpha-diimine)Pd(CH2Cl)Cl (13; alpha-diimine = (2,6-(Pr2C6H3)-Pr-i)N=CMeCMe=N(2,6-Pr-i(2)-C6H3)) with 1 equiv of [Li(Et2O)(2.8)][B(C6F5)(4)] in the presence of vinyl chloride yields Pd-Cl+ species and allyl chloride, most likely via net 1,2-insertion and P-Cl elimination of a (alpha-diimine)Pd(CH2Cl)(CH2=CHCl)(+) intermediate. In general, L-2-Pd(R-X)(substrate)(+) species undergo slower insertion than non-halogen-substituted L2Pd(R)(substrate)(+) analogues.