Cyclo
pentadienyl com
plexes of general formula [RuX(
5-ligand)(PR
3)
2] have been foundto catalyze the stereoselective decom
position of ethyl diazoacetate (EDA) to form diethylmaleate (DEM) in 95-99%
purity with less than 1 mol % of catalyst, at tem
peraturesde
pending on the bulkiness of the
phos
phine and the
5-ligand as well as the nature of theanionic ligand X. A detailed study of the reaction between [RuCl(
5-C
5H
5)(PPh
3)
2] and EDAsuggests that dissociation of one PPh
3 is a key ste
p of the catalytic
process, which
proceedsvia the intermediate [RuCl(
5-C
5H
5)(=CHCO
2Et)(PPh
3)]. Although this electro
philic carbenewas not detected in the reaction mixture, it was inde
pendently
pre
pared in solution at lowtem
perature starting from [Ru(
2-O
2CMe)(
5-C
5H
5)(PPh
3). The acetate reacts with EDA at-40
C to form the cyclic ester
[Ru{CH(CO2Et)OC(Me)O}(5-C5H5)(PPh3), which on treatmentwith Me
2SiCl
2 gives the metal carbene
postulated in the catalytic cycle. The stoichiometricreaction of the latter com
pound with EDA selectively affords the olefin derivative [RuCl(
5-C
5H
5)(
2-DEM)(PPh
3)], which was also detected in the catalytic cycle. The new com
plexes[RuCl(
5-C
5H
5)(PR
3)
2] (PR
3 = PPh
2(2-MeC
6H
4), PPh
2Cy, P(3-MeC
6H
4)
3), bearing
phos
phinesbulkier than PPh
3, have been
pre
pared in high yield starting from ruthenium trichloridehydrate, cyclo
pentadiene, and
phos
phine in refluxing ethanol.