An investigation into the allylic imidate rearrangement of trichloroacetimidates catalysed by cobalt oxazoline palladacycles

Dimeric palladacycles, di-mu-X-bis [{eta(5)-(S)-(R-p)-2-[2'-(4'-methylethy-l)oxazolinyl]cyclopentadienyl,1-C,3'- N}(eta(4)-tetraphenylcyclobutadiene)co-balt]dipalladium (COP-X), containing bridaing groups X=OAc, Cl, Br, I, O2CCF3, p-O2CC6H4F, were synthesised and compared as catalysts for the asymmetric allylic imidate rearrangement of (E)-Cl3CC(=NH)OCH2CH= CHR with R=nPr. The enantiomeric excess of the product (S)-Cl3CC(=O)NHCHRCH=CH2 was essentially invariant of X (93 - 96%) and the yield increased in the sequence I < p-O2CC6H4F < OAc < O2CCF3 approximate to Br approximate to Cl. With X=Cl (COP-Cl), the catalyst loading was reduced to 0.25 mol% (CH3CN/70 degrees C/48 h) and these conditions applied to various trichloroacetimidates (R - nPr, Me, CH2Ph, CH2CH=CH2, CH2OTBDMS) to give the corresponding (S)-trichloroacetamides (68 - 88 % yield, 84 - 94 % ee; ee = enantiomeric excess). Addition of COP-Cl to triphenylphosphinobenzoyl NovaGel AM resin gave a recyclable catalyst in which the ee was maintained over three cycles (89 - 94%). Catalysis with COP-OAc displayed a small positive non-linear effect. The factors responsible for the activity of COP-X are discussed.