A comparative study of catalysis by light and by metals of the isomerisation of cyclododeca-l,5,9-triene has shown that both promote cis-trans double bond isomerisation, but the photochemical reaction also gives a low yield of 1,2,4-trivi nylcyclo hexane. EXPAXIOX and contraction of medium-sized unsaturated rings have been shown to occur under the influence of U.V. irradiation 2 or metal catalysts 394 [see reactions (1) and (Z)]. These results have led us to look for analogous 1

The addition of alkylchloroaluminium deri-BESTIAN and CLAUSS~ used the soluble catalyst, MeTiC1,sMevatives to ZrR, (R = ally1 or benzyl) produces active AlC1, a t low temperatures to oligomerise ethylene to precatalysts for the preparation of C4-C2, a-olefins from dominantly 2-ethyl-a-olefins. More recently, Langer2 has ethylene. used TiC14.Et,A1C1,-, and obtained high proportions of linear cc-olefins. Similar results have been patented3 for

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Aus den Organe‐zirkoniumverbindungen (I) und (II) sowie den Alkylchloraluminiumverbindungen (II)‐(V) erhält man Katalysatoren, die die Oligomerisation von Äthylen in Toluol bei 40‐80°C unter Druck zu linearen C4‐C20‐a‐Olefmen katalysieren.

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