Synthesis and characterization of M and M (M = Li, Na, (PPh3)2N; DF = dimethyl fumarate, DM = dimethyl maleate) and the role of these complexes in the isomerization of free DM to DF

Article abstract of DOI:10.1016/0022-328X(92)80007-K

The complexes M (1) and M (2) (M = Li (a), Na (b), (PPh3)2N (PPN) (c); DF = dimethyl fumarate, DM = dimethyl maleate) were prepared by photochemical reactions of M with the appropriate olefin, or by the metathesis reactions of (Li or Na) and (Li or Na) with Cl.They were characterized by a combination of elemental analysis and IR and 1H and 13C<1H> NMR spectroscopy.Complexes 1a, 1b, 2a, and 2b catalyze the isomerization of free DM to DF in THF under reflux for 2-4 days.By contrast, 1c and 2c are catalytically inactive under comparable experimental conditions.Studies on the catalyzed isomerization revealed that 1a and 1b exchange ligated DF with free DM in THF at 47-50 deg C over several days, whereas 1c does not.All three complexes 2a, 2b, and 2c isomerize to 1a, 1b, and 1c, respectively, in THF at 45-55 deg C over several days.From these rather qualitative results it is suggested that the catalyzed isomerization of free DM to DF proceeds by incorporation of DM in the coordination sphere of 1, conversion of the resultant 2 back to 1, and replacement of ligated DF by free DM.