The synthesis and reactivity of bimetallic and metallacyclic manganese complexes

The coordination of Mn(CO)₃+ to conjugated polyarenes initiated several important areas of research. Two broad classes of reactions originating from the chemistry of (η6-polyarene)Mn(CO) ₃+ are the formation of bimetallic compounds and the insertion of nucleophilic metal fragments to produce metallacycles.; The synthesis of bimetallic complexes has long been investigated in order to probe the effect of electron delocalization and metal-metal interactions on a variety of physical properties, e.g. charge transfer, conductivity, non-linear optics, etc. Furthermore, bimetallic complexes have found important applications in stoichiometric and catalytic reactions and for the creation of redox switches. The synthesis and reactivity of syn-facial bimetallics of naphthalene type ligands, donor/acceptor bimetallics of joined arene systems, Lewis acid/Lewis base dimers and novel bimetallics of capped metallocenes are discussed.; The cleavage of C-X (X-C, S, O, N, Se) bonds by transition metal is primarily of interest because of it relevance to homogeneous hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) chemistry. While industrial hydroprocessing of petroleum feedstocks represents the largest volume chemical process utilizing transition metal catalysts, many important features of the process remain unknown. As currently practiced, heterogeneous HDS effects the removal of sulfur from petroleum sources such as heavy crude oil and coal derived liquids by hydrogen treatment over sulfided Co/Mo catalysts. The primary focus of homogeneous HDS research is the removal of sulfur from thiophenic molecules, especially benzothiophene (BT) and dibenzothiophene (DBT), since these are difficult for the current technology to desulfurize and therefore constitute the major source of sulfur contamination in refined fuels. A goal of the research outlined below for C-X bond activation is to better understand the complex interactions between heterocycles and transition metals, and with this knowledge to point the way to better desulfurization catalysts. The synthesis and reactivity of organometallic complexes of sulfur, oxygen and selenium heterocycles are reviewed.