Intermolecular allyl, propargyl, and allenyl ligand transfer

3 Intermolecular allyl, propargyl, and allenyl ligand transfer 

Transmetalation of jt-allyl transition metal complexes and of the complexes with related C3 ligands proceeds via unique pathways that are not found in the intermolecular transfer of -bonded organic ligands. Rich information about stereochemistry of unsymmetrically substituted rt-allyl ligands of Pd complexes provides a useful probe to investigate details of the reaction mechanism. Cationic jr-allylpalladium(II) complex reacts with ethylene-coordinated Pt(0) complex to afford the jr-allylplatinum(II) complex and Pd(0) complex via transfer of the allyl ligand from Pd to Pt (Eq. 5.57). 

The jt-allyl ligand bonded to cationic Pd(II) center tends to undergo nucleophilic substitution by organic nucleophiles from the opposite side of the metal center (Chapter 8). Attack of Pd(0) or Pt(0) complex in this fashion causes inversion of stereochemistry of the complex repetition of the reactions results in epimerization. The allyl ligand transfer between Pd centers takes place much faster than that from Pd to Pt. Isomerization between the Pt(II) complexes with a propargyl ligand and that with an allenyl ligand is catalyzed by Pd(0) complex (Eq. 5.58) [200,201]. 

The propargylplatinum(II) complex reacts with Pd(0) complex to form Pt(0) complex and allenylpalladium(II) complex, the latter of which undergoes spontaneous and/or Pd(0)-catalyzed rapid isomerization into the propargylpalladium(II) complex. The reaction of the produced Pt(0) complex and propargylpalladium(II) complex leads to the formation of allenylplatinum complex. Each of the transmetalation reactions in the above procedure is accompanied by allenyl-propargyl 

Recently, stereochemical aspect of the reversible transfer of allenyl hgands between Pd(0) and Pd(ll) complexes was reported as shown in Eq. 5.60 [202]. 

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