Mechanistic study on rhenium(V) dimer catalysis for the oxygen atom transfer from pyridine oxide to Ph3E (E = P, As): experiment and computational study

Abstract

The oxorhenium(V) dimer {MeReO(edt)2 3 (where edt = 1,2-ethanedithiolate) catalyzes the oxygen atom transfer reaction from nitro-pyridine oxide (NPO) to triphenylarsine (Ph3As). The rate law is given by ν = k[3][NPO] and shows zeroth order dependence on Ph3As. The value of k at 25 °C in CHCl3 is 54.50 ± 1.30 L mol−1 s−1. The activation parameters are ΔH‡ = 16.7 ± 0.9 kcal mol−1 and ΔS‡ = 6.6 ± 3.1 cal K−1 mol−1. The rate determining step is the nitro-pyridine release. The triphenylarsine enters the catalytic cycle after the rate determining step through nucleophilic addition to the π* orbital of ReVII=O orbital. The computational study on the slow and the fast step using simplified model supports the experimental finding. The computed activation barrier for the nitro pyridine release and the arsine addition are 11.72 and 8.06 kcal mol−1, respectively.