93110-33-9Relevant academic research and scientific papers
The effect of X- = Cl-, Br-, I- on the kinetics of the Arbuzov rearrangement involving [CpCo(dppe)X]+ and P(OR)3 (R = Me, Et)
Landon, Shayne J.,Brill, Thomas B.
, p. 4177 - 4181 (2008/10/08)
Rate constants and equilibrium and transition-state data for the reaction of [CpCo(dppe)X]+ (X- = Cl-, Br- I-) (1) with P(OR)3 (R = Me, Et) to produce {CpCo(dppe)[P(O)(OR)2]}+ (3) and RX have been acquired by 1H NMR spectroscopy. The rate of the overall reaction (X- = I- > Br- > Cl-) is traceable to the trend of X- as a leaving group from the Co(III) center in the preequilibrium step that leads to the intermediate complex [CpCo(dppe)P(OMe)3]2+ (2). The rate of the dealkylation of 2 to form 3 is only moderately sensitive to X-, suggesting that nucleophilicity of X- plays a subordinate role. ΔH≠ and ΔS≠ for 2 → 3 are monotonically related and give an isokinetic temperature of -45°C. ΔS≠ is large and positive owing probably to the fact that ions having 2+ and 1- charge come together in the transition state. The entropy factor strongly influences the reaction rate above -45°C. A comparison of the kinetic parameters for the Arbuzov reaction involving a transition-metal center vs. an alkyl center helps explain why the rearrangement is more facile in the former.
