Kinetics of nucleophilic attack on co-ordinated organic moieties. Part 25. A nucleophilic order for attack upon the [Fe(CO)3(1–5-η-C7H9)]+ cation

Abstract

Kinetic studies of the addition of a range of phosphine and phosphite nucleophiles (PR₃) to the cation [Fe(CO)₃(1–5-η-C₇H₉)]⁺ to give [Fe(CO)₃(1–4-η-R₃P·C₇H₉)]⁺ adducts reveal the general rate law k_obs=k₁(PR₃]. Combination of these results with analogous data for amine and anionic nucleophiles provides the first comprehensive nucleophilicity order for attack on this cycloheptadienyl substrate. For the neutral phosphorus and nitrogen nucleophiles, this nucleophilicity order quantitatively parallels that found for the related but much more reactive [Fe(CO)₃(1–5-η-C₆H₇)]⁺ substrate, indicating departure from the reactivity-selectivity principle. However, with N₃^– the C₇H₉ cation reveals exceptional reactivity, suggesting a change in mechanism for this anionic nucleophile.