ADDUCTS OF TRIMETHYLAMINOXIDE WITH TETRAK IS [BIS(TRIMETHYLSILYL)METHYL]DIALUMINOXANE - R(2)AL-O-ALR(2)CENTER-DOT-ONME(3) AND R(2)AL-O-ALR(2)CENTER-DOT-2ONME(3) WITH BENT AL-O-AL GROUPS

The sterically highly shielded and monomeric tetrakis[bis(trimethylsil yl)methyl]dialuminoxane R(2)Al-O-AlR(2), (R = CH(SiMe(3))2) 1 forms 1: 1 and 1:2 adducts on treatment with trimethylamine oxide. Both product s have been characterized by crystal structure determination. Contrary to the linear educt 1, the complexes show bent Al-O-Al groups with bo nd angles of 162.3 and 161.40. The mono adduct 2 has three- and four-c oordinated Al atoms with a very short Al-O bond between the bridging o xygen and the coordinativelv unsaturated Al atom (168.7 pm), possibly indicating a pi-interaction. The second bond of the dialuminoxane frag ment is lengthened to 175.3 pm and represents a ''normal'' Al-O distan ce. The Al-O bond to the amine oxide ligand (184.6 pm) lies within the range of dative Al-O bonds. As shown by NMR spectroscopy the unsymmet rical structure is preserved in toluene solution up to 90 degrees C. I n the bis(amine-oxide) adduct 3 both Al atoms are four-coordinated wit h very similar inner Al-O bond lengths of 173.6 pm.