Selenophenes coordinate in Cp′(CO)2Re(Sel) (Cp′ = C5H5 or C5Me5; Sel = selenophenes) as a rapidly equilibrating mixture of η1 and η2 isomers. Increasing the electron density on the Re by replacing Cp with Cp* favors η-coordination, while addition of methyl groups to the selenophene favors the η1(Se) isomer. These shifts in the η2⇄ η(Se) equilibrium can be readily explained by noting that electron-donating methyl groups in the selenophene enhance the donor ability of the Se and reduce the π-acceptor ability of the olefin which favors Se-coordination, while increasing the electron density on the Re strengthens π-back-bonding to the η2 ligand. The uncoordinated selenophene Se atom in Cp*(CO)2Re(η2-Sel) (1) is capable of binding to M(CO)4(L)(THF) (M = Cr, Mo, W; L = CO or PPh3) to give dinuclear selenophene-bridged complexes Cp*(CO)2Re(µ2-η2(Se)-Sel)[M(CO)4(L)] in which the selenophene is η2 bonded to the Re and Se-bonded to a second metal (M). The reaction of 1 with Fe2(CO)9 gives three different types of compounds. One of them (11) results from Fe(CO)4 addition to the Se of the η2 isomer; another presumably results from coordination of Fe(CO)3 to the diene portion of the η1(Se) isomer. The third product has a thiaferrole-type structure in which a C-Se bond has been cleaved. 77Se NMR studies of these different types of selenophene complexes are also reported.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry