MULTIPLE BONDS BETWEEN MAIN-GROUP ELEMENTS AND TRANSITION-METALS .125. ALKYLRHENIUM OXIDES AS HOMOGENEOUS EPOXIDATION CATALYSTS - ACTIVITY, SELECTIVITY, STABILITY, DEACTIVATION

Methyltrioxorhenium (VII) (MTO, 1a) and several congeners lb and 2a-d of formula R-ReO3 and R-ReO3.L, respectively, qualify as olefin epoxidation catalysts of high activity and selectivity. Related alkylrhenium (VI) complexes form efficient catalyst precursors as well, since they get oxidized by H2O2 to the same active species CH3ReO(O2)2.H2O (3). The present paper presents a comparison of this novel class of catalysts with the performance of known, commonly used catalysts. Catalyst stability has been recorded and deactivation reactions are described. The synthesis and crystal structure (X-ray diffraction) of the (pale pink-coloured) monomeric amino-functionalized complex O3Re-CH2CH2CH2N(C2H5)2 (4A) and its (violet) polymeric form (4B) are reported. Only the latter is an active epoxidation catalyst with H2O2. An improved laboratory method of the standard catalyst MTO la is described.