Geometrical and electronic structures of the acetyl complex Re(bpy)(CO)3(COCH3) and of [M(bpy)(CO)4](OTf), M=Mn,Re

The compound fac-Re(bpy)(CO)3(COCH3) (1) (bpy=2,2′-bipyridine) with three different kinds of π-acceptor ligands coordinated to rhenium(I) has been investigated by infrared spectroelectrochemistry to reveal the occupation of the π*(bpy) MO on one-electron reduction to 1radical dot− with negligible participation of the π-accepting acetyl group. The results are discussed in relation to the spectroscopy (NMR, IR) and the crystal structure analysis of the neutral complex 1, which reveals a short CO(acetyl) (1.157(12) Å) and a long ReC(acetyl) bond (2.245(12) Å) and an orientation of the ReC(O)CH3 plane parallel to the C2 axis of the coordinated bpy. The result is an orthogonal arrangement of dxz/π*(bpy) and dxy/π*(acetyl) orbitals. This situation stands in distinct contrast to the structure reported for the complex salt [Re(L)(CO)3(COCH3)](PPN) (PPN+=bis(triphenylphosphoranylidene)ammonium) with a cyclometallated 2-phenylpyridine ligand L. The crystal structures of the related complexes [M(bpy)(CO)4](OTf), M=Re and Mn, were determined for comparison.