METAL CLUSTERS IN CATALYSIS .20. CHEMISTRY OF [ETA5-C5H5CR(CO)3]2

Reaction of [C5H5Cr(CO)3]2 with 2 moi of trimethyi phosphite at 25 °C yielded the symmetric dimer [C5H5Cr(CO)2-P(OCH3)3]2, 2. Crystallographic analysis of the dimer established a very long chromium-chromium bond distance of 3.343 υ. Consistent with this distance, the dimer was largely dissociated into the mononuclear fragments, C5H5Cr(CO)2P(OCH3)3, in solution at 20 °C and exhibited a high degree of chemical reactivity. Hydrogen addition to 2 was fast at 20 °C to give C5H5CrH(CO)2P(OCH3)3. Trimethyi phosphite also reacted rapidly with 2, and cleavage of a C-O bond in a phosphite occurred. The initial products were the methyl complex C5H5Cr(CH3)(CO)2P(OCH3)3 and a phosphonate complex C5H5Cr[PO(OCH3)2](CO)2P(OCH3)3, 3. An X-ray study of 3 established a square-pyramidal geometry and a trans relationship of the two phosphorus ligands. The methyl complex was unstable and slowly yielded methane at 20 ° The ionic complex {C5H5Cr(CO)2[P(OCH3)3]2}+{C5H5Cr(CO)3}- formed from 2 by dissolution in polar solvents was a relatively stable and nonreactive complex unlike the molybdenum analogue. © 1979, American Chemical Society. All rights reserved.