Unsymmetrical ethylene coordination

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). 

Luo etal used both HP-IR and HP-NMR in their studies of CO-ethylene co-polymerization. Using a Pd(ll)/dppp/ CF3COOH catalyst system under GO pressure, they detected three palladium-carbonyl absorptions in the IR spectrum, and linked these to three intermediates in the proposed mechanism. In addition, H NMR revealed the presence of coordinated ethylene and a palladium-methylene species (Pd-CH2-). The co-polymerization of CO with propylene was investigated using the unsymmetrical phosphine-phosphite bidentate ligand, (RSl-BINAPHOS. Two major resting states of the catalyst were observed by HP-NMR, namely alkylpalladium and acylpalladium species which are believed to correspond to [Pd(COR)(BINAPHOS)(CO)]+[BF4]- and [Pd(CH2CHCH3(CO)R)(BINAPHOS)]+[BF4]U... 

Yang, F.-Z., Chen, Y.-C., Lin, Y.-F. et al. (2009) Nickel catalysts bearing bidentate a-aminoaldimines for ethylene polymerization—independent and cooperative structure/reactivity relationship resulting from unsymmetric square planar coordination. Dalton Transactions, 1243-1250. 

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