CHEMISTRY OF COBALT-DIENE AND ACETYLENE COMPLEXES

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Our broad objectives are to explore new reaction chemistry of three classes of cobalt complexes (propargylium)Co2(CO)6-nLn+BF4-(1), (propargylium)Co4(CO)10BF4(2), and (diene)Co(CO)3-nLn(3) in order to establish their patterns of reactivity with selected nucleophilic coupling partners, especially with respect to stereo- and regiocontrol, and to develop applications of this chemistry in the synthesis of natural products and other biologically active compounds. Studies of the propargylium complexes 1 (L=CO) derived from acetylenic acetals and aldehydes will be directed towards developing new approaches to diastero- and enantioselective coupling reactions with nucleophiles. Utilization of such reactions in the synthesis of chiral building blocks containing 2-5 adjacent stereocenters (precursors to carbohydrate antibiotics) and for the synthesis of macrocycles will be examined. Studies of the novel chiral bimetallic complexes 1b,c will be directed towards examining their structures and assessing their potential for directing stereoselective (and possibly stereospecific) coupling reactions with nucleophiles. A modest effort aimed at the preparation, characterization, and reactivity screening of the unknown cluster derivatives 2 is planned in order to determine if their anticipated unique structural and electronic features will provide new, improved opportunities for stereocontrolled coupling reactions an d a future basis for cluster-based stereoselective reactions in general. Our second major emphasis will be directed towards expanding the synthetically useful chemistry of the diene complexes 3. Primary objectives include: 1) deepening our understanding of the factors controlling the regioselectivity of nucleophilic attack on 3 (and the intermediate allyl-complexes); 2) expansion of the scope of annelative bisnucleophilic additions and illustration of their application in the synthesis of prostacyclin and heterocyclic derivatives; 3) preparation and utilization of chiral, non- racemic 3 in enantioselective syntheses, including carbohydrate derivatives; and 4) development of new reactivity patterns of organometallic complexes as well as valuable new synthetic tools for the stereoselective synthesis of complex and biologically active substances.