INSERTION OF CARBON-MONOXIDE AND ALKENES IN PALLADIUM-CARBON BONDS OFCOMPLEXES CONTAINING RIGID BIDENTATE NITROGEN LIGANDS - THE FIRST EXAMPLE OF ISOLATED COMPLEXES IN STEPWISE SUCCESSIVE INSERTION REACTIONS ON THE WAY TO POLYKETONES

Facile successive insertion of carbon monoxide and strained alkenes ha s been observed for both neutral Pd(R)X(Ar-BIAN) and cationic [Pd(R)(M eCN)(Ar-BIAN)]SO3CF3 complexes, i.e., complexes containing the rigid b identate nitrogen ligands bis(arylimino)acenaphthene (Ar-BIAN; Ar = p- MeOC(6)H(4) (p-An), p-MeC(6)H(4) (p-Tol), o,o'-i-Pr2C6H3), leading to the formation of new multiple insertion products of the type Pd{CH(R') CH(R')C(O)CH(R')CH(R')C(O)R}X(Ar-BIAN). It appears that the rigidly ch elating Ar-BIAN ligands have an activating effect on the insertion of CO and alkenes in palladium-carbon bonds as compared to other (bidenta te) phosphorus and nitrogen ligands and a stabilizing effect on the Pd -acyl and Pd-alkyl complexes formed. Insertion of carbon monoxide was completed within 1 min (R = Me, X = Cl, I; R = PhCH(2), X = Br; R = p- MeC(6)H(4), X = I), except in the case of RX = p-NO2C6H4CH2Br, where i nsertion required 4 h to go to completion. Insertion of norbornadiene, norbornene, and dicyclopentadiene in the cationic acyl complexes [Pd( C(O)Me)(MeCN)(Ar-BIAN)]SO3CF3 occurred instantaneously. Reaction of no rbornadiene with the neutral acyl complexes Pd(C(O)Me)Cl(Ar-BIAN) resu lted in rapid quantitative insertion, whereas in the case of norbornen e and dicyclopentadiene longer reaction times were needed and mixtures of the starting materials and the insertion products were formed. All complexes isolated after alkene insertion have a similar structure, a rising from cis addition of PdC(O)R to the exo face of the alkene, wit h the acyl oxygen atom coordinating to the palladium and the chloride or trifluoromethanesulfonate present as anion. After insertion of norb ornadiene in the neutral acyl palladium complex, the resulting alkylpa lladium compound [Pd(C7H8C(O)Me)(p-An-BIAN)] Cl reacted further with c arbon monoxide to give the isolable complex Pd(C(O)C7H8C(O)Me)Cl(p-An- BIAN) (13a), whereas the analogous trifluoromethanesulfonate complex d id not show any reaction with carbon monoxide. The acyl complexes 13a reacted again with norbornadiene to yield quantitatively [Pd(C7H8C(O)C 7H8C(O)Me) (p-An-BIAN)] Cl (14a), which reacted with AgSO3CF3 to give [Pd(C7H8C(O)C7H8C(O)Me)(p-An-BIAN)]SO3CF3 (15a). These new complexes 1 3-15a, formed by stepwise successive insertion reactions of carbon mon oxide and alkenes, have been isolated and were fully characterized for the first time and constitute a living oligomer system that may inser t further molecules of CO and norbornadiene.