MONO-ETA(6) 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 compl exes has been prepared: (eta(6)-p-C6H4F2)Cr(CO)(3); (eta(6)-C6H4CF3)Cr (CO)(3); [m-C6H4(CF3)(2)]Cr(CO)(3); (eta(6)-C6H5F)Cr(CO)(2)H(SiCl3); ( eta(6)-C6H5F)Cr(CO)(2)(SiCl3)(2); (p-C6H4F2)Cr(CO)(2)H(SiCl3); (p-C6H4 F2)Cr(CO)(2)(SiCl3)(2); (C6H5CF3)Cr(CO)(2)H(SiCl3); (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 d iffraction. These data combined with IR and H-1 NMR have allowed asses sment of some of the electronic and steric effects. The Cr-arene bond is considerably longer in the Cr(II) derivatives than in the Cr(O) spe cies. Also the Cr center, as might be expected, is less electron rich in the Cr(II) dicarbonyl disilyl derivatives. The eta(6)-p-C6H4F2 liga nds are slightly folded so that the C-F carbons are moved further away from the Cr center. Comparison of structural and electronic effects i s made with a series of similar chromium compounds reported in the lit erature. These new (arene) Cr(II) derivatives possess more labile eta( 6)-arene ligands, which promise a rich chemistry at the chromium cente r.