Heats of reaction of pyridine, triphenylphosphine, and triphenyl phosphite with the chloro-, bromo-, and iodo-1,5-cyclooctadienerhodium(I) dimers and dichlorobis(benzonitrile)palladium(II)

Article abstract of DOI:10.1021/ic50130a012

The heats for the following reactions in dichloromethane are reported: [RhX(COD)]₂ + 2B → 2[RhX(COD)(B)]; [RhX(P-(OC₆H₅)₃)₂]₂ + 2P(OC₆H₅)₃ → 2[RhX(P(OC₆H₅)₃)₃]; [RhX(COD)₂] + 2P(OC₆H₅)₃ → [Rh₂X₂(COD)(P(OC₆H₅) ₃)₂] + COD; [Rh₂X₂(COD)(P(OC₆H₅) ₃)₂] + 2P(OC₆H₅)₃ → [RhX(P(OC₆H₅)₃)₂]₂ + COD; [PdCl₂(C₆H₅CN)₂] + 2B → [PdCl₂B₂] + 2C₆H₅CN; and [PdCl₂(COD)] + 2P(OC₆H₅)₃ → [PdCl₂(P(OC₆H₅)₃)₂] + COD (B = pyridine, triphenylphosphine; X = Cl, Br, I; COD = 1,5-cyclooctadiene). Relative displacement energies are for the rhodium compounds, triphenyl phosphite ? 1,5-cyclooctadiene and triphenylphosphine > pyridine, and for the palladium compounds, triphenylphosphine > triphenyl phosphite > pyridine ? cyclooctadiene. Arguments are given that solvent-solute enthalpic contributions are not predominant in the displacement energies. For a given reaction, the effect of varying the halogens upon the observed enthalpies is very small or nonexistent. Equilibrium constants for the first reaction are too high to measure when B = triphenylphosphine and are approximately 5 × 10⁴ when B = pyridine.