Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Patent
1997-12-17
1999-06-15
Nazario-Gonzalez, Porfirio
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
556 11, 556 12, 556 13, 556 27, 556 28, 556 43, 556 53, 556 54, 502103, 502117, 502152, 502162, 526160, 526943, C07F 1700, C07F 1100, C07F 728
Patent
active
059123737
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for converting the achiral meso form of an ansa-metallocene complex into the chiral rac form.
Chiral ansa-metallocene complexes of metals of transition group IV of the Periodic Table of the Elements have in recent years attracted great interest as effective catalysts for stereospecific olefin polymerization, as described in EP-A 444 474, EP-A 519 237 and EP-A 576 970. They make it possible to prepare chemically uniform polyolefins of high isotacticity. However, in the synthesis of such metallocene complexes, considerable amounts of the achiral meso compound are usually obtained, as a result of which the yield of chiral metallocene complexes is significantly reduced. Since these meso forms generally catalyze nonstereospecific 1-olefin polymerization, they have to be separated off before the racemate of the metallocene complex can be used as polymerization catalyst (EP-A 485 823).
There have been many attempts in the past to improve the rac/meso diastereomer ratio in the ansa-metallocene synthesis, or at least to avoid the need to remove the meso compound. Introducing an alkyl substituent in the .alpha. position of the cyclopentadienyl ring enabled the rac/meso ratio to be increased to significantly above 1.0, as described in Brintzinger et al, Journal of Organometallic Chemistry, 369 (1989), pp. 359-370. A disadvantage here is that the method significantly restricts the freedom with which the ligands may be structured. In addition, despite the improved yield of racemic diastereomers, appreciable amounts (33-15%) of the meso complex are still formed.
Better yields of the racemic diastereomers were able to be achieved by reacting Zr(NMe.sub.2).sub.4 with 1,2-bisindenylethane, as described in Jordan et al., Organometallics, 14 (1995), pp. 5-7. Disadvantages are the great sensitivity and the high price of the tetrakis(dimethylamido)zirconium used. Furthermore, diastereoselective syntheses of chiral ansa-metallocenes are known only for very few, specific ligand systems which are described, for example, in Brintzinger et al., Organometallics 11 (1992), pp. 3600-3607; S. Buchwald et al., Organometallics 13 (1994), (10), pp. 3892-3840 and in U.S. Pat. No. 5,302,733.
In some cases, the yield of racemate could be increased by photochemical conversion of the undesired meso form into the rac form, as described in S. Collins et al., Journal of Organometallic Chemistry 342 (1988), pp. 21-29. However, here too, the rac form is obtained only in thermodynamic equilibrium with the meso diastereomer. Quantitative isomerization to the rac form is not possible by this route.
It is an object of the present invention to provide a process for quantitatively converting the undesired meso form of an ansa-metallocene complex into the desired rac form; this conversion should be technically simple in terms of the process and be inexpensive.
We have found that this object is achieved by a process for converting the achiral meso form of an ansa-metallocene complex into the chiral rac form, wherein the conversion is carried out photochemically in the presence of a chiral auxiliary reagent.
The terms "meso form" and "rac form" in the context of ansa-metallocene complexes are known and described, for example, in Brintzinger et al., Journal of Organometallic Chemistry, 369 (1989), pp. 359-370.
ansa-Metallocene complexes which are particularly suitable for use in the process of the present invention are those of the formula I ##STR1## where the substituents and indices have the following meanings: M is titanium, zirconium, hafnium, vanadium, niobium or tantalum, -alkyl, C.sub.6 -C.sub.15 -aryl or --OR.sup.10, alkylaryl, arylalkyl, fluoroalkyl or fluoroaryl each having from 1 to 10 carbon atoms in the alkyl radical and from 6 to 20 carbon atoms in the aryl radical, cycloalkyl which may in turn bear a C.sub.1 -C.sub.10 -alkyl group as substituent, C.sub.6 -C.sub.15 -aryl or arylalkyl, where two adjacent radicals may together form a cyclic group having from 4 to 15 carbon atoms, or Si(R.sup.11).sub.3 wh
REFERENCES:
patent: 5302733 (1994-04-01), Diefenbach et al.
J. of Organomet. Chem., 369, 1989, pp. 359-370.
Organometallics, 11, pp. 3600-3607, 1992.
J. of Organomet. Chem., 342, pp. 21-29, 1988.
J. of Organomet. Chem., 232, 1982, pp. 233-247.
Makromol. Chem., vol. 8, 1987, pp. 305-310.
J. of Am. Chem. Soc., vol. 114, 1992, pp. 9300-9304.
Organometallics, 14, 1995, pp. 5-7.
Organometallics, 13(10), 1994, pp. 3892-3896.
J. Am. Chem. Soc., 112, 1990, pp. 4911-4914.
Brintzinger Hans-Herbert
Fischer David
Kerth Jurgen
Langhauser Franz
Schmidt Katrin
BASF - Aktiengesellschaft
Nazario-Gonzalez Porfirio
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