Bulky Siloxyaluminum Alkyls as Models for Al<sub>2</sub>Me<sub>6</sub>-Treated Silica Gel Surfaces. Characterization of a Dimethylaniline-Stabilized Dimethylaluminum Cation
作者:Olaf Wrobel、Frank Schaper、Hans H. Brintzinger
DOI:10.1021/om030589l
日期:2004.2.1
Reaction of a particularly bulky silanol, (2,4,6-Me3C6H2)(3)SiOH, with Al2Me6 gives, instead of the otherwise preferred unreactive binuclear siloxalanes with two siloxy bridges, a binuclear siloxalane with one siloxy and one methyl bridge, Me2Al(mu-OSi(2,4,6-Me3C6H2)(3))(mu-Me)AlMe2. This species reacts with zirconocene dichlorides under chloride/methyl exchange; with the cationizing reagent PhMe2NH+B(C6F5)(4)(-) it forms the B(C6F5)(4)(-) salt of the mononuclear cation AlMe2(NPhMe2)(2)(+).
Alkyl exchange between aluminum trialkyls and zirconocene dichloride complexes — a measure of electron densities at the Zr center
作者:Stefan Beck、Hans H. Brintzinger
DOI:10.1016/s0020-1693(97)05871-4
日期:1998.4
Equilibrium constants have been determined for the formation of 15 different zirconocene monomethyl monochloro complexes from the respective dichloride complexes and Al-2(CH3)(6). The results indicate chat the tendency of a particular zirconocene complex to exchange a chloride against a methyl ligand is a measure for the electron deficiency at its Zr center. The results indicate particularly low electron densities for complexes with indenyl instead of cyclopentadienyl ligands, especially for those containing a dimethylsilyl bridge. Only one methyl group is transferred to a zirconocene dichloride even by a large excess of Al-2(CH3)(6), while the uptake of two alkyl groups, followed by alkane evolution, is observed with triethyl and triisobutyl aluminum. (C) 1998 Elsevier Science S.A.