Three-Coordinate, 12-Electron Organometallic Complexes of Iron(II) Supported by a Bulky β-Diketiminate Ligand:  Synthesis and Insertion of CO To Give Square-Pyramidal Complexes

The preparation of a series of three-coordinate, 12-electron organometallic complexes of iron(II) supported by a bulky β-diketiminate ligand is described. The thermally stable complexes LFeR (R = Et, CH 2 t Bu, i Pr) are three-coordinate in both the solid state (single crystal X-ray diffraction) and solution. They react rapidly with CO to form the diamagnetic complexes LFe(CO) 2 (COR), which have an unusual square-pyramidal geometry. Spectroscopic and crystallographic studies show that the acyl group is in the axial position. As a result, there are two orientations of the acyl group about the Fe−C bond, and the isomeric ratio is dependent on the size of R. The two isomers are in equilibrium in solution at room temperature.