Mono-η⁶ complexes of chromium(II) and chromium(0). Electron demanding substituents, structural and spectroscopic data comparisons

Using thermal and photochemical methods a series of new chromium complexes has been prepared: (ν6-p-C6H4F2)Cr(CO)3; (ν6-C6H5CF3)Cr(CO)3; [m-C6H4(CF3)2]Cr(CO)3; (ν6-C6H5F)Cr(CO)2H(SiCl3); (ν6-C6H5F)Cr(CO)2(SiCl3)2; (p-C6H4F2)Cr(CO)2-H(SiCl3); (C6H5CF3)Cr(CO)2H(SiCl3(p-C6H4F2)Cr(CO)2(SiCl3)2; C6H5CF3)Cr(CO)2 (SiCl3)2; [m-C6H4(CF3)2]Cr(CO)2-H(SiCl3); [m-C6H4(CF3)2]Cr(CO) 2(SiCl3)2. Two compounds were structurally characterized by X-ray diffraction. These data combined with IR and 1H NMR have allowed assessment of some of the electronic and steric effects. The Cr-arene bond is considerably longer in the Cr(II) derivatives than in the Cr(0) species. Also the Cr center, as might be expected, is less electron rich in the Cr(II) dicarbonyl disilyl derivatives. The ν6-p-C6H4F2 ligands are slightly folded so that the C F carbons are moved further away from the Cr center. Comparison of structural and electronic effects is made with a series of similar chromium compounds reported in the literature. These new (arene)Cr(II) derivatives possess more labile ν6-arene ligands, which promise a rich chemistry at the chromium center