Zirconium complexes rearrangement

Zirconium complexes, 3, 363-440 acetylacetone, 2,372,377 ligand exchange reactions, 2, 381 rearrangement, 2, 383 alkyl... 

Fig. 6.19. Isotactic polymerization of propene with rac-l,2-ethanediyl-bis(indenyl)zirconium complexes. The plane of the drawing coincides with the plane bisecting the two planes of the indenyl ligands. Propene coordination takes place with the alkene Tt-orbitals in the plane of the drawing. The carbon atoms of the growing chain are depicted in the plane of the figure in between insertions no rearrangements to more stable conformations have been drawn. Indenyl ligand above the plane drawn in full.

The novel 7 -disilenide zirconium complex 44 is highly reactive and undergoes ready rearrangement via addition of a methyl C-H bond to the Si=Si bond to give the silyl zirconium complex 45, as a mixture of diastereoisomers, shown in Equation (5) <2005JA10174>. 

The work presented here describes the chemistry of Zr(IV) complexes anchored by dissymmetric, disubstituted, dianionic cyclam ligands. In comparison with zirconium complexes supported by unsaturated dianionic tetraazamacrocycles [4,7a,8], the compounds derived from dianionic, trans-disubstituted cyclam ancillary ligands have a more robust skeleton, which is not susceptible to nucleophilic attack and rearrangement, and higher flexibility, suitable to fit to the electronic and steric metal requirements. Part of this work has already been published and the reader will be directed to the original publications for the sake of clarity. 

Then, contrary to what was reported previously, the olefin dissociates from the zirconium metal complex. This conclusion was further supported by other experimental observations. However, it cannot be completely excluded that competition between dissociative and direct rearrangement pathways could occur with the different isomerization processes studied up to now. Note that with cationic zirconocene complexes [Cp2Zr-alkyl], DFT studies suggest that Zr-alkyl isomerizations occur by the classical reaction route, i.e. 3-H transfer, olefin rotation, and reinsertion into the Zr-H bond the olefin ligand appears to remain coordinated to the Zr metal center [89]. 

Carbon monoxide rapidly inserts into the carbon—zirconium bond of alkyl- and alkenyl-zirconocene chlorides at low temperature with retention of configuration at carbon to give acylzirconocene chlorides 17 (Scheme 3.5). Acylzirconocene chlorides have found utility in synthesis, as described elsewhere in this volume [17]. Lewis acid catalyzed additions to enones, aldehydes, and imines, yielding a-keto allylic alcohols, a-hydroxy ketones, and a-amino ketones, respectively [18], and palladium-catalyzed addition to alkyl/aryl halides and a,[5-ynones [19] are examples. The acyl complex 18 formed by the insertion of carbon monoxide into dialkyl, alkylaryl, or diaryl zirconocenes may rearrange to a r 2-ketone complex 19 either thermally (particularly when R1 = R2 = Ph) or on addition of a Lewis acid [5,20,21]. The rearrangement proceeds through the less stable... 

Only one example of electrophilic behavior of silicon-stabilized lithiooxiranes is reported. Intermolecular C—Li insertion followed by Li20 elimination occurs by raising the temperature, and ( ) vinylsilanes are obtained stereoselectively (Scheme 80). Reaction of lithiooxiranes with aluminum , zirconium and silicon reagents leads to the corresponding ate complexes, which undergo 1,2-metallate rearrangements. 

Further examples of zwitterionic products are formed by B(C6F5)3 attack on tuck-in complexes to give 20 [57-59] and 21 (Scheme 8.13) the latter is a single-component polymerisation catalyst which deactivates under rearrangement to an allyl complex [60]. Attack by B(C6F5)3 on the coordinated ethene in zirconium(II) complexes gives zwitterions of type 22 which act as single-component polymerisation catalysts [58]. 

Rearrangement processes of alkyltitanocene dichlorides that occur under electron impact have been investigated using deuterium labelling. A novel type of zirconium-mediated coupling reaction of alkynes with vinyl bromide to afford 2,3-disubstituted dienes has been reported (see Scheme 105), and an inter-intramolecular reaction sequence has been proposed for the observed formation of vinylcyclohexadienes and/or methylenecycloheptadienes from the copper-catalysed reaction of zirconacyclo-pentadienes with allylic dichlorides. The essential step in these processes appears to be transmetallation of the zirconium-carbon bond of the zirconacyclopentadiene to produce a more reactive copper-carbon bond. New phosphorus heterocycles, e.g. (417), have been constructed by the thermal rearrangement of a [l,4-bis(trimethylsilyl)->/ -cyclooctatetraene]- ,3,5-triphospha-7-hafhanorbomadiene complex (416). 

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