CARBON-DIOXIDE ACTIVATION - DEOXYGENATION AND DISPROPORTIONATION OF CARBON-DIOXIDE PROMOTED BY BIS(CYCLOPENTADIENYL)TITANIUM AND BIS(CYCLOPENTADIENYL)ZIRCONIUM DERIVATIVES - NOVEL BONDING MODE OF THE CARBONATO AND A TRIMER OF THE ZIRCONYL UNIT

Carbon dioxide is quantitatively deoxygenated to carbon monoxide by [Cp2TiCl]2 [Cp = η5-C5H5] which is converted to [Cp2TiCl]2O, while Cp2Ti(CO)2 promotes the disproportionation of CO2 to CO and carbonato. This reaction gives rise to a tetranuclear carbonato complex of titanium(III), [(Cp2Ti)2(C03)]2, in which the CO3 -2 ligand, engaged in a novel bonding mode, bridges three Cp2Ti units. The uco stretching frequencies for the coordinated CO3 2- fall at 1475 m-s and 1425 v-s cm-1, and, as confirmed by the isotopic labeling, the two bands in [(Cp2Ti)(13C03)2]2 are at 1432 and 1385 cm-1. Carbon dioxide converts Cp2ZrO3, which is unprecedented both in cyclopentadienyl and zirconium chemistry. The X-ray structural analysis showed that (Cp2ZrO)3 contains a six-membered, nearly planar ring, formally derived from the trimerization of the zirconyl unit Zr=O. Noteworthy are both the Zr-O bond distances, which are not significantly different [average value of 1.959 (3) A], and the Zr-O-Zr bond angles averaging to 142.5 (2)°. These values indicate the presence of a multiple Zr=O bond. Crystallographic details for [(Cp2Ti)2(C03)]2; space group Cmca (orthorhombic), a = 11.282 (I) Å, b = 16.038 (1) Å, it = 19.729 (2) Å, and Z = 4. The final R factor is 5.8% for 1508 observed reflections. Crystallographic details for (Cp2ZrO)3-C7H8: space group P2jc (monoclinic), a = 10.230 (1) Å, b = 18.612 (2) Å, c = 17.406 (2) Å, β = 95.27 (1)°, and Z = 4. The final R factor is 4.3% for 4153 observed reflections. © 1979, American Chemical Society. All rights reserved.