Iridium-phosphine complexes, reactions kinetics

Interestingly, Harrod and co-workers (259) also compared the kinetics of triphenylphosphine and hydrosilane addition to a neutral iridium complex (eq. [89]). The kinetic parameters for the phosphine and silane reaction were almost identical AHp - AHSi = 0 kcal/mol and A5p - ASsi = 13 e.u. This striking similarity is not necessarily proof that phosphine and silane addition are mechanistically analogous processes. However, this kinetic behavior is consistent with the above description of oxidative addition. 

Interestingly, Harrod and coworkers73 also compared the kinetics of triphenylphos-phine and hydrosilane addition to a neutral iridium complex (equation 18). The activation enthaplies for the phosphine and silane reaction were almost identical ... 

---