Theoretical studies on the β-hydrogen elimination reactions of palladium and platinum alkoxide complexes containing bidentate ligands

The selection of reaction pathways between the β-hydrogen elimination and σ-bond metathesis followed by reductive elimination of palladium and platinum alkoxide complexes containing bidentate ligands, L2MX(OCY2H) (L2=CH2NCHCHNCH2 and PH2CH2CH2PH2; M=Pd and Pt; X=CH3, OCH3, NH2, OH, HCOO, Cl and Br; Y=H and F), have been investigated by density functional theory calculations at the level of B3LYP. The effects of cis-ligand X, bidentate ligand L2, transition metal M and substituents Y have been examined. The results show that Pd complexes with ligands X=OCH3, NH2, OH and HCOO favor the σ-bond metathesis followed by a reductive elimination reaction pathway leading to the metal-hydride products while complexes with ligand X=CH3 favor the β-hydrogen elimination pathway. Both reaction pathways are found possible for complexes with ligands X=Cl and Br when M=Pd and Y=H. It is also found that Pt complexes have higher reaction barriers and complexes with phosphine bidentate ligands have lower reaction barriers when compared to their analogous Pd complexes containing amine bidentate ligands. F substituted alkoxy ligands decrease the β-hydrogen elimination pathways barriers. It is also found that the β-hydrogen elimination pathway is always preferred when the ligand dissociation from the four-coordinate complexes is the initial event for the reactions.