MULTIPLE BONDS BETWEEN MAIN-GROUP ELEMENTS AND TRANSITION-METALS .135. OXORHENIUM(V) CATALYSTS FOR THE OLEFINATION OF ALDEHYDES

Reaction of methyltrioxorhenium (MTO) (1) and triphenylphosphine in diethyl ether gives bis(triphenylphosphine)methyldioxorhenium(V).MTO (3a), which was characterized by a single-crystal X-ray diffraction study (crystal data: space group Cc, a = 1393.5(4) pm, b = 1367.5(1) pm, c = 1928.0(5) pm, beta = 102.67(1)degrees, Z = 4). An MTO molecule acts as an axial Lewis base ligand in this mixed-valence Re-V/Re-VII complex that is structurally composed of two trigonal bipyramids joined via an unsymmetrical, slightly bent oxo bridge ligand. Both phosphine ligands of the Re-V fragment are in trans positions to each other while the methyl and oxo groups occupy equatorial sites. 3a as well as bis(triphenylphosphine)trichlororhenium(V) (4) are used as catalysts for the olefination of aldehydes with diazoalkanes.