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 epoxid ation 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 catalys ts with the performance of known, commonly used catalysts. Catalyst st ability has been recorded and deactivation reactions are described. Th e synthesis and crystal structure (X-ray diffraction) of the (pale pin k-coloured) monomeric amino-functionalized complex O3Re-CH2CH2CH2N(C2H 5)2 (4A) and its (violet) polymeric form (4B) are reported. Only the l atter is an active epoxidation catalyst with H2O2. An improved laborat ory method of the standard catalyst MTO la is described.