Zirconium complexes with alkyl ligands

An important development over the last two years has been the confirmation that cationic Group IV metal alkyl complexes are the catalytically active species in olefin polymerizations with homogeneous Ziegler-Natta catalysts. A number of complexes of the type [Cp2MR(L)] (M = Ti, Zr, Hf) have now been prepared, particularly when stabilized by donor ligands such as L = THF. The chemistry of zirconium complexes of this type has been reviewed. Some cationic benzyl complexes with stereorigid ligands (29)... 

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]. 

The pincer like diamino functionalised carbene ligand stabilises the group 4 metal sufficiently to perform a few very interesting insertion reactions with the M-Me bond. The reactions were performed with the hafnium rather than the zirconium complexes [113]. Small molecules used for these insertion reactions include isonitriles (aryl and alkyl) and CO (see Figure 4.36). Reaction of the hafnium carbene dimethyl complex with xylyl-isonitrile results in addition of this excellent donor ligand and subsequent insertion into the Hf-Me... 

Cationic zirconium complexes (88) having diketonato ligands were examined for selective epoxide ring opening (Equation 40) [45]. The catalysts showed higher activity than simple metal halides such as TiCU and ZrCU, and various epoxides (87) were converted into (89) and/or (90) effectively. When R and R" in (87) were alkyl groups, the product selectivity of the catalyst (88) were moderate to low. But with styrene oxide (R =Ph, R" =H), alkoxy alcohol (89) was obtained with high selectivity. 

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