| Research Abstract |
1. Bridge-splitting reactions of [Pd_2(mu-Cl)_2(pi-allyl)_2] or [PtCl(allyl)]_4 with tertiary phosphines, followed by methylations with LiMe afforded the desired complexes [(pi-allyl)M(Me)(PR_3)] (M= Pd or Pt) in high yields.
2. The complexes thus obtained were characterized by IR, MS, and NMR (^1H, ^<13>C) spectroscopy.
3. Thermolysis of the complexes was carried out in the solid state and in solution. Gas-chromatographic analysis of the evolved gases was revealed that in palladium complexes the major organic product is ethane rather than 1-butene. This result was accounted for by the intermolecular reductive-elimination of ethane from the methyl-bridged pi-allylpalladium dinuclear complex, formed by dissociation of the phosphine ligand. On the other hand, the platinum complexes decompose with no evolution of ethane and with the evolution of propene and methand, exclusively.
4. Additive effects of phosphine and alkene on the thermolysis components were also examined. In the palladium case, the addition of phosphine and maleic anhydride resulted in the evolution of 1-butene in a 50% and a 90% relative ratios, respectively, while in the platinum case the additive effect of phosphine was not recognized and the coupling reaction was promoted only in the addition of maleic anhydride.
5. The controlled-potential electrolysis of the platinum complex at the anodic peak potential (1.22 V vs. Ag/AgCl) revealed the evolution of 1-butene in a 50% molar ratio. This coupling-promoting effect is comparable to that of the addition of pi-acid in the thermolysis, and a mechanism involving the cationic intermediate [(pi-allyl)Pt(Me)(PR_3)]^+ was proposed to explain the effect.
6. On the addition of diphosphines in the solutions of pi-allylplatinum complexes, stable sigma-allyl complexes were isolated, but theimolysis of their complexes revealed that no coupling reaction occurs on it; only propene and methane evolved.
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