Metallocene allyl reactivity in the presence of alkenes tethered to cyclopentadienyl ligands

The reactions of the yttrium metallocene allyl complex [(C5Me4)SiMe2(CH2CH=CH2)](2)Y-(C3H5), 1, with ethylene, trimethylaluminum, and hydrogen have been examined to determine how the olefins tethered to the cyclopentadienyl ligands interact with these species that are typically present in olefin polymerizations. Complex 1 was prepared from allylmagnesium chloride and [(C5Me4)SiMe2(CH2CH=CH2)](2)YCL, which can be directly prepared free of solvent and alkali metal halide adducts from YCL3(THF)(x) and [(C5Me4)SiMe2(CH2CH=CH2)]K in THF. 1 was characterized by NMR spectroscopy and X-ray crystallography, and the data were compared to those of three related complexes: the pentamethyl analogue, (C5Me5)(2)Y(C3H5), 2, the ansa analogue, [Me2Si(C5Me4)(2)]Y(C3H5), 3, and the lutetium complex, (C5Me5)(2)Lu(C3H5), 4. Although 1 shows no evidence for insertion of the tethered olefins into the Y-(C3H5) bond, comparisons of the synthesis and variable-temperature NMR spectra of 1 with 2-4 suggest metal-alkene interaction. Complex 1 polymerizes ethylene and reacts with excess AL(2)Me(6) to generate the allyl-free, tetramethylaluminate-bridged dimer 1 [(C5Me4)SiMe2(CH2CH=CH2)](2)Y[(mu-Me)(2)AlMe2]}(2), 5. No involvement of the tethered olefins was observed in connection with this Y-C(allyl) bond breaking and Y-C(Me) bond making. The tethered olefins do become involved in the reaction chemistry of 1 in the presence of hydrogen: the tethered olefins of 1 are hydrogenated. A hydride derivative of 1 was not isolated, but 1 reacts with H-2 in diethyl ether to form the expected hydride decomposition product, the ethoxide, {[(C5Me4)SiMe2(CH2CH2CH3)](2)Y(OEt)}(x), 6. Reaction of 1 with hydrogen in C6D6 and with deuterium in C6H6 shows that hydrogenation of the tethered olefin occurs before D/H exchange with arenes can occur in this system.