SYNTHESIS, REACTIONS, AND SE-77 NMR-STUDIES OF ETA-5-SELENOPHENE COMPLEXES OF CHROMIUM, MANGANESE, RUTHENIUM, AND IRIDIUM

The series of eta(5)-selenophene transition metal complexes (eta(5)-Se ln)Cr(CO)(3) (1-3), [(eta(5)-Seln)Mn(CO)(3)]SO3CF3 (4-6), [(eta(5)-Sel n)RuCp]SO3CF3 (7-9), and [(eta(5)-Seln)IrCp*](BF4)(2) (10-12), where Seln = selenophene (Sel), 2-methylselenophene (2-MeSel), or 2,5-dimeth ylselenophene (2,5-Me(2)Sel), were synthesized and characterized by H- 1, C-13, and Se-77 NMR and IR spectroscopy. The molecular structure of (eta(5)-2,5-Me(2)Sel)Cr(CO)(3) (3) was determined. Reactions of [(eta (5)-Sel)Mn(CO)(3)]SO3CF3 (4) with nucleophiles (Nuc = H-, CN-) give th e neutral addition products [(Sel-Nuc)Mn(CO)(3)] [Nuc = H- (4a), Nuc = CN- (4b)] in which three carbon atoms and the Se are bonded to the Mn . The reaction of [(eta(5)-Sel)RuCp]SO3CF3 (7) with H-, however, resu lts in cleavage of the C-Se bond to form a butadiene selenide complex ((eta(5)-SeCH=CHCH=CH2)RuCp) (7a). Still another type of product resu lts from the reaction of [(eta(5)-2,5-Me(2)Sel)IrCp](BF4)(2) (12) wit h 2 equiv of H-; in this case, the H- acts as a reducing agent to give the ring-opened complex (C, Se-2,5-Me(2)Sel)IrCp (12a). All of these reactions are similar to those of the analogous eta(5)-thiophene comp lexes. The Se-77 NMR chemical shift values for the eta(5)-Seln ligands in complexes 1-12 fall within a range of 225 ppm; they are influenced by the metal and its ligands, the charge on the complex, and the numb er of methyl groups in the selenophene.