METALATION OF BIS(CYCLOPENTADIENYL) METAL HYDRIDES BY ETA-BUTYLLITHIUM IN THE PRESENCE OF PENTAMETHYLDIETHYLENETRIAMINE - SYNTHESIS OF BIS(CYCLOPENTADIENYL)RHENIUM ALKYLS AND THE MIXED METAL-COMPLEXES - ETA-5-C5H5)2M(MU-CO)2RE(CO)ETA-5-C5H5)(M = MO, W)

n-Butyllithium in the presence of pentamethyldiethylenetriamine (PMDT) in a 1:1 ratio has been found to metalate the metal (M = Re and Mo) atom of bis(cyclopentadienyl) transition metal hydrides in hexane. The complex Cp2ReLi-PMDT (1) is pale yellow, air sensitive, and soluble in aromatic solvents. Compound 1 has been used to synthesize the previously unreported bis(cyclopentadienyl)rhenium alkyls of methyl, ethyl, n-propyl, and allyl. Triphenylcarbenium tetrafluoroborate has been reacted with selected Cp2Re-R compounds giving cationic rhenium species. Compound I also reacts with CpM(CO)3Cl (M = Mo, W) with transfer of a cyclopentadienyl ring from the rhenium atom to the molybdenum or tungsten atom resulting in Cp2M(μ-CO)2Re(CO)Cp. The molybdenum-rhenium complex has been characterized by single-crystal X-ray diffraction and has been shown to contain a metal-metal single bond that is asymmetrically bridged by two “semibridging” carbonyls. These carbonyl groups in the tungsten derivative exhibit an extremely low stretching frequency (1650 cm-1, Nujol; 1690 cm-1, THF) for a dibridging carbonyl. The structural results for the molybdenum-rhenium complex revealed a statistically elongated C-O (bridge) bond, thus implying substantial reduction of the carbon-oxygen bond order of the bridging carbonyl group by the metal fragments. © 1979, American Chemical Society. All rights reserved.