Metallocenes, theoretical studies

Petitjean, L., Pattou, D., Ruiz-Lopez, M. F., 1999, Theoretical Study of the Mechanisms of Ethylene Polymerization with Metallocene-Type Catalysts , J. Phys. Chem. B, 103, 27. 

However, more quantitative molecular orbital treatments still leave scope for improvement, and in particular a systematic treatment of the whole metallocene series, rather than of isolated members such as ferrocene, is much to be desired. Moreover, theoretical studies have generally neglected the bis-arene and mixed sandwich series, and in both cases such treatments would be of value in indicating the extent to which the mainly metal n level is or is not less anti-bonding than in the metallocenes. In this connection it is interesting to note that in the (Ch) Cr(Cp)- anion the mainly metal n dxz, dyz ) level may still lie relatively high since esr measurements 1 78) indicate the odd electron to... 

Koga, N., Yoshida, T. and Morokuma, K, Theoretical Studies on Olefin Polymerisation using Group IV Metallocene Catalysts , in Ziegler Catalysts, Springer-Verlag, Berlin, 1995, pp. 275-289. 

Michalak A, Ziegler T, Theoretical Studies on the Polymerization and Copolymerization Processes Catalyzed by the Late-Transition Metal Complexes, in Beyond Metallocenes Next-Generation Polymerization Catalysts ACS Symp Series 857, edited by AO Patil, GG Hladky (American Chemical Society, Washington 2003), pp 154-172... 

The insertion reaction of a coordinated olefin into the Mt—C a-bond, where Mt is a group 4 metallocene, or a model of it, has been the subject of several theoretical studies se, 146-1 so,152,153,156,169-171,174,176,177,185-19o... 

The main conclusion of the previously reported experimental and theoretical studies is that opposite enantiofaces are favored for primary and secondary propene insertion on C2-symmetric metallocenes, whereas the same enantioface is favored for primary and secondary insertion on Cs-symmetric metallocenes. A further proof of this mechanistic picture has been obtained by Corradini and co-workers through a combination of primary and secondary propene insertions into one single insertion step, by using 2-butene as monomer. They argued that, within the above framework, insertion of Z-butene should be favored with Q-symmetric metallocenes, whereas insertion of if-butene should be favored with Cs-symmetric metallocenes, as sketched in Scheme 38, provided that the same sterlc interactions which rule the enantioselectivity of primary and secondary propene insertions hold for 2 butene. 

Interest has also continued in studies of the aromaticity of other unsaturated cyclic phosphorus compounds. A theoretical study of the 1,2-diphosphacyclooctatetraene system (228) has concluded that the ring system is perfectly planar when it has a global charge of —2 or +2, in contrast to the 1,2-diaza analogue which adopts a distorted, non-planar structure in the same oxidation states. However, it is thought unlikely that the phosphorus heterocycle will form planar metallocene complexes with metal ions. Theoretical and experimental studies have also been reported for the lone pair 671-aromatic anions P4 (229) and the arsenic analogue As4 . Both... 

Metallocenes as homogeneous catalysts have been studied theoretically compared to heterogeneous catalysts. Most of the theoretical studies are related to the mechanism of stereoregulation in a-olefin polymer-... 

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