Hendrik A. Martin, F. Jellinek
Apr 1, 1968
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Journal
Journal of Organometallic Chemistry
Abstract
Abstract Reaction of isopropylmagnesium bromide (2 moles) with a mixture of dicyclopentadienyltitanium dichloride (1 mole) and suitable dienes in ether gives homologues of π-allyldicyclopentadienyltitanium(III). For 1,3-dienes the yields of allyldicyclopentadienyltitanium(III) complexes are of the order of 70–80%; they are lower for 1,4-dienes and 1,5-dienes, while no complexes are obtained from allenes. The complexes isolated axe the most symmetrical ones of the possible isomers; the absorption spectrum in the visible range can be used as a guide for the identification of isomers. The substituents at carbon atoms 1 and 3 of the allyl group are in synposition. This explains why no complexes could be obtained from olefins in which the diene system is part of a five- to eight-membered ring; however, the cyclododecadienyl complex, in which ring closure at the syn-positions is possible, was obtained when 1,5,9-cyclododecatriene was used as the olefin. The mechanism of the formation of allyldicyclopentadienyltitanium(III) complexes from dienes was studied, The first mole of iso-C 3 H 7 MgBr reduces Cp 2 TiCl 2 to dicyclopentadienyltitanium(III) monobromide, which is converted to the unstable “active species” (Cp 2 Ti-iso-C 3 H 7 or Cp 2 TiH) by the second mole of the Grignard reagent. The active species is trapped by the diene to give the final π-allylic complex.