Structure of a highly unsaturated anionic tetrahydridononacarbonyltrirhenate cluster

The reaction between H4Re4(CO)(12) and N,N-dimethylformamide (DMF) in chloroform yields [H4Re3(CO)(9)](-)[Re(CO)(3)(DMF)(3)](+), 1, quantitatively. The X-ray structure of 1 reveals that the three Re atoms in the 44-e anionic cluster [H4Re3(CO)(9)](-) form an isosceles triangle. Two hydrides bridge the two long Re-Re single-bonded edges, and another two hydrides bridge the Re-Re double-bonded edge. There is a coordinative unsaturation site on the rhenium atom not involved in the Re-Re double bond. However, the anionic cluster associates face-to-face antiprismatically with another identical unit to form a dimer in which there are donor-acceptor interactions between the hydrides bridging the Re-Re double bonds and the coordinative unsaturation sites on the other clusters. The anionic cluster reacts rapidly with donor ligand L (CO, Py, PPh(3), CH3CN) to form [H4Re3(CO)(9)L](-). In CD2Cl2 solution at 183 K, [H4Re3(CO)(9)](-) has a hydride NMR pattern of 3:1 and a carbonyl group C-13 NMR pattern of 6:3. These NMR spectra as well as their VT NMR results and IR spectra in the solid state and solution are consistent with a solution structure of [Re-3(mu(3)-H)(mu(2)-H)(3)(CO)(9)](-) in which two double bonds are delocalized over the rhenium triangle.