Reaction of [PdClMe(cod)] withMeO
2CC
![](/images/entities/tbd1.gif)
CCO
2Me occurs in two steps,namely, insertionof the alkyne into the Pd-Me bond followed by migratory insertion ofone of the doublebonds of the coordinated cyclooctadiene into the Pd-alkenyl bond thusformed. The resultingchloride-bridged, cyclooctenyl complex was converted to[Pd(acac){
1,
2-C
8H
12C(CO
2Me)=CMe(CO
2Me)}],
2a, which was characterizedcrystallographically. The molecular structurerevealed that each insertion took place in a cis manner. Reactionsof [PdCl
2(cod)] with arange of nucleophiles were performed, which gave analogouschloride-bridged, cyclooctenylpalladium dimers,
1, which could be converted to theiracetylacetonate derivatives,
2.The solid-state structure of the methoxy complex[Pd(acac)(
1,
2-C
8H
12OMe)],
2b, obtainedby reaction of [PdCl
2(cod)] with NaOMe followed byAg(acac), was determined. This showedthat exo attack of the OMe group occurred. In contrast, thestructure of the phenyl derivative[Pd(acac)(
1,
2-C
8H
12Ph)],
2e, produced by treatment of [PdCl
2(cod)] withPh
4Sn followed byAg(acac), indicated that the phenyl group added in an endofashion, presumably via a phenylpalladium intermediate of the type [PdClPh(cod)]. With thelarger mesityl group, the complex[PdCl(C
6H
2Me
3)(cod)]could be isolated. Each of the complexes was fully characterizedby
1H and
13C{
1H} NMRspectroscopy, and the appearance of the C
HPd signal was usedtodistinguish between the exo and endo isomers. On the basis of thecrystallographic andNMR data, it was deduced that the organometallic reagents ArMgX (Ar =Ph, 2-MeC
6H
4,2,4,6-Me
3C
6H
2),Ph
4Sn, and(4-MeC
6H
4)
2Hg generate theendo products by initial attack atthe metal. In contrast, reactions with NaOR (R = Me, Et),NaCH(CO
2Me)
2, AgOAc, andEt
2NH proceed by direct attack of the nucleophile atthe coordinated double bond to givethe exo products.