ISSN:
0887-624X
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
The reactions occurring between the components of metallocene and methylaluminoxane (MAO) catalyst leading to the reduction of the former were studied by electron paramagnetic resonance (EPR). At low Al/Zr ratios, CpZrCl3 (Cp = η5-cyclopentadienyl) was reduced to simple trivalent Zr species (g = 1.998, a(91Zr) = 12.3 G) without other superhyperfine splittings. At higher Al/Zr ratios the reactions proceed further to form two CpZr(III) hydrides (g = 1.991, a(H) = 5.5 G; and g = 2.00, a(H) = 3 G). Two CpTi(III) hydrides were also produced by the reaction of MAO with CpTiCl3 (g = 1.989, a(H) = 7.4 G, a(Ti) = 8 G; and, g = 1.995, a(H) = 4.5 G, a(Ti) = 8 G). In the case of Cp*TiCl3 (Cp* = η5-pentamethyl cyclopentadienyl) initially a multitude of paramagnetic species were formed. After long reaction time the final products show EPR features consistent with two η3: η4-(1,2,3-trimethyl-4,5-dimethylene cyclopentadienyl)hydrido Ti(III) species: the abundant one with g = 1.999, (H, sextet) = 9.5 G, a(Ti) = 9.5 G, and a weaker one of g = 1.975, a(H) = 4.8 G. All the five protons of these species and as well as those in the Cp hydrido complexes of Ti and Zr undergo facile H—D exchanges with D2. MAO is important in the formation of these hydrides because they are not formed by trimethyl aluminum reduction. The presence of tetrahydrofuran suppresses the hydride formation. The possible structures for the hydrido species and reactions producing them are discussed.
Zusätzliches Material:
14 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pola.1989.080270506
Permalink
