A discrete {Co4(μ(3)-OH)(4)}(4+) cluster with an oxygen-rich coordination environment as a catalyst for the epoxidation of various olefins

Abstract

Using the sterically hindered terphenyl-based carboxylate, the tetrameric Co(II) complex [Co-4(mu(3)-OH)(4)(mu-O2CAr4F-Ph)(2)(mu-OTf)(2)(Py)(4)] (1) with an asymmetric cubane-type core has been synthesized and fully characterized by X-ray diffraction, UV-vis spectroscopy, and electron paramagnetic resonance spectroscopy. Interestingly, the cubane-type cobalt cluster 1 with 3-chloroperoxybenzoic acid as the oxidant was found to be very effective in the epoxidation of a variety of olefins, including terminal olefins which are more challenging targeting substrates. Moreover, this catalytic system showed a fast reaction rate and high epoxide yields under mild conditions. Based on product analysis and Hammett studies, the use of peroxyphenylacetic acid as a mechanistic probe, (H2O)-O-18-exchange experiments, and EPR studies, it has been proposed that multiple reactive cobalt-oxo species Co-V=O and Co-IV=O were involved in the olefin epoxidation.