Salicylidene-imine-zirconium(IV) complexes in combination with methylalumoxane as catalysts for the conversion of hexa-1,5-diene: adjusting of the catalytic activity

Abstract

Over the last decade enormous efforts and progress have been made in the investigation of metallocene-type catalysts of group IV: The discovery that methylalumoxanes (MAO) promote the formation of highly active cationic species, the design of "single site" catalysts for the polymerization of 1-olefines, the isolation of cationic species involving [Cp 2 M-R] + cations, which are responsible for the catalytic reactivity, the tuning of the catalytic reactivity by adjusting the ligands, and the development of industrial processes are some examples for this rapidly growing field [1 -5].Most recently group IV metal complexes that contain inorganic donor sets have been to focus attention as potential catalysts [2, 6 -34]. However, the coordination chemistry and organometallic chemistry of these compounds is more complicated and much less developed than the metallocene chemistry. Especially, the understanding of the controlling effects of ligands containing an inorganic donor set in group IV metal catalysts is not well understood. This might be the most important problem in the development of new highly active and selective group IV catalysts containing anionic ancillary ligands having for example N or O donor atoms. Salicylidene-imine-Zirconium(IV) Complexes in Combination with Dedicated to Professor Egon Uhlig on the Occasion of his 70th BirthdayKeywords: Cyclizations, Schiff bases, Zirconium, Catalysis Abstract. A variety of substituted Schiff base complexes of the composition ("salen")ZrCl 2 (thf) (1 -21) were synthesized, with methylalumoxane ("MAO") activated and used for a systematic study of their catalytic activity towards hexa-1,5-diene ("salen": substituted salicylidene-ethylene-iminato ligands). Main product of the catalytic cycle is methylenecyclopentane. Dimers are only formed in minor amounts. The catalytic activity and selectivity of the Ziegler-Natta systems strongly depend on the nature and the position of the peripheric substituents in the Schiff base ligands. Electron-withdrawing substituents in para-position to the phenolato oxygen (5-position) decrease the catalytic activity. Improved activity andIn this paper we report on the catalytic conversion of hexa-1,5-diene by a number of MAO-activated (salicylidene-ethylene-imine)Zr(IV)(thf) complexes in which a N 2 -O 2 donor set is coordinated as four-dentate chelate ligand opening the possibility to study the electronic and steric influence of peripheric groups on the catalytic reactivity.Our aim was to get a deeper insight into the possibility to control the catalytic reactivity of the metal center depending on the coordinative environment. Since the catalytic conversion of hexa-1,5-diene was a slow reaction it was also possible to indicate the starting steps of the catalysis. Catalytic Reactions of (Salen)ZrCl 2 (thf)/MAO with Hexa-1,5-dieneFor the preparation of the Zr(IV) complexes 1 -21 the quadridentate Schiff base N,N'-ethylene-bis(salicylideneimine) ("salen") ligands were treated with two equivalents n-butyl-lithium to form the lithium salts. Re...

Mechanistic Studies of the Cycloisomerization of Dimethyl Diallylmalonate Catalyzed by a Cationic Palladium Phenanthroline Complex

“…Intermolecular H/D Transfer . Mechanisms initiated by either hydrometalation (Scheme ) or reductive cyclization have been postulated for the cycloisomerization of enynes and dienes. − A distinguishing feature between these mechanisms is that intermolecular H/D transfer is required in the former pathway but not in the latter . Therefore, the substantial intermolecular H/D exchange which accompanied the cycloisomerization of 1 -3,3,5,5- d 4 is consistent with the proposed hydrometalation/carbometalation mechanism .…”

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FI Catalysts for Olefin Polymerization—A Comprehensive Treatment

“…These substituents effectively prevent the N 2 O 2 donors from taking a planar configuration, which is required for the trans -X geometry. It should be noted that the classical salen or salphen ligands with group 4 metals are prone to form a stable [O,N,N,O] plane with trans-oriented X ligands and that these complexes show little activity for ethylene polymerization. ,,,− …”

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