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Structural Characterization of Al10O6iBu16(μ-H)2, a High Aluminum Content Cluster:  Further Studies of Methylaluminoxane (MAO) and Related Aluminum Complexes

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journal contribution
posted on 08.01.2007, 00:00 by Feng-Jung Wu, Larry S. Simeral, Anthony A. Mrse, Jan L. Eilertsen, Lacramioara Negureanu, Zhehong Gan, Frank R. Fronczek, Randall W. Hall, Leslie G. Butler
The first structurally characterized isobutyl-containing aluminoxane compound is presented. The Al10O6iBu16(μ-H)2 (I) cluster is produced from neat octakis-isobutyltetraluminoxane (Al4O2iBu8) at 80 °C in 6−8 h followed by slow crystallization. The crystal is triclinic (space group P1̄) with the molecule lying on an inversion center. This aluminoxane contains both nearly linear, 154(2)°, aluminum-bridging hydrides and three-coordinate aluminum sites. Solid-state 27Al magic-angle spinning (MAS) NMR experiments were done at 19.6 and 40 T (833 MHz and 1.703 GHz, 1H) and at 30−35 kHz spinning speeds, leading to the determination of the Cq and η values for the two four-coordinate Al sites and a lower limit of Cq for the three-coordinate Al site. Geometry-optimized restricted Hartree−Fock calculations at the double-ζ level of an idealized structure (methyl substituted, D2h geometry) yielded Cq and η in close agreement with experiment; Cq agrees within 3 MHz.