Process for converting the achiral meso form or the racemate of

Details Process for converting the achiral meso form or the racemate of Process for converting the achiral meso form or the racemate of

1998-01-08

1998-11-24

Nazario-Gonzalez, Porfirio

Organic compounds -- part of the class 532-570 series

Organic compounds

Heavy metal containing

556 7, 556 12, 556 13, 556 21, 556 28, 556 27, 556 43, 556 53, 556 54, 502103, 502117, 502152, 502162, 526160, 526943, C07F 1700, C07F 900, C07F 500

Patent

active

058409505

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for converting the achiral meso form or the racemate of an ansa-metallocene complex or a mixture thereof into one of its enantiomers.
Apart from the stereospecific polymerization of olefins, enantioselective organic synthesis increasingly offers interesting possible uses of chiral ansa-metallocene complexes of metals of transition group IV of the Periodic Table of the Elements. Examples which may be mentioned here are enantioselective hydrogenations of prochiral substrates, for example prochiral olefins as described in R. Waymouth, P. Pino, J. Am. Chem. Soc. 112 (1990), p. 4911-4914, or prochiral ketones, imines and oximes as described in WO 92/9545.
Mention may also be made of the preparation of optically active alkenes by enantioselective oligomerization as described in W. Kaminsky et al., Angew. Chem. 101 (1989), p. 1304-1306, and also the enantioselective cyclopolymerization of 1,5-hexadienes as described in R. Waymouth, G. Coates, J. Am. Chem. Soc. 113 (1991), p. 6270-6271.
Unlike stereospecific olefin polymerization, all applications in enantioselective organic synthesis require the use of an enantiomerically pure ansa-metallocene complex, ie. the meso form first has to be removed from the mixture of diastereomers (rac and meso form) obtained in the metallocene synthesis and the remaining rac form has to be subjected to resolution of the enantiomers. Since both the meso form and one of the two enantiomers have to be discarded, the yield of the enantiomerically pure ansa-metallocene complex is very low.
Diastereoselective or even enantioselective syntheses of chiral ansa-metallocene complexes are known for only very few, specific ligand systems which are described, for example, in Brintzinger et al., organometallics 11 (1992), p. 3600-3607 and in Rhein-gold et al., Organometallics 11 (1992), p. 1869-1876.
It is an object of the present invention to provide a process for the quantitative conversion of the meso form or the racemate of an ansa-metallocene complex or a mixture thereof into one of its enantiomers. This conversion should be simple in process terms and inexpensive.
We have found that this object is achieved by a process for converting the achiral meso form or the racemate of an ansa-metallocene complex or a mixture thereof into one of its enantiomers wherein the conversion is carried out photochemically in the presence of an enantiomerically pure auxiliary reagent.
The terms "meso form", "racemate" and thus also "enantiomer" in the context of ansa-metallocene complexes are known and described, for example, in Rheingold et al., Organometallics 11 (1992), p. 1869-1876.
For the purposes of the present invention, the term "enantiomerically pure" means that at least 90% of a compound is present in the form of one enantiomer.
Particularly suitable ansa-metallocene complexes which can be used 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, 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 also together form a cyclic group having from 4 to 15 carbon atoms, or Si(R.sup.11).sub.3 where -C.sub.10 -cycloalkyl, ##STR2## .dbd.BR.sup.12, .dbd.AIR.sup.12, --Ge--, --Sn--, --O--, --S--, .dbd.SO, .dbd.SO.sub.2, NR.sup.12, .dbd.CO, .dbd.PR.sup.12 or .dbd.P(O)R.sup.12, where hydrogen, halogen, C.sub.1 -C.sub.10 -alkyl, C.sub.1 -C.sub.10 -fluoroalkyl, C.sub.6 -C.sub.10 -fluoroaryl, C.sub.6 -C.sub.10 -aryl, C.sub.1 -C.sub.10 -alkoxy, C.sub.2 -C.sub.10 -alkenyl, C.sub.7 -C.sub.40 -arylalkyl, C.sub.8 -C.sub.40 -arylalkenyl or C.sub.7 -C.sub.40 -alkylaryl or R.sup.12 and R.sup.13 or R.sup.12 and R.sup.14 in each case together w

REFERENCES:
Schmidt et al., Organometallics, vol. 16, No. 8, pp. 1724-1728, 1997.
J. of Organic Chem. vol. 54, 1989, pp. 4154-4158.
Makromol. Chem. Rapid Comm, vol. 8, 1987,S.305-310.
W.Kaminsky et al., Angew.Chem.101(1989), pp. 1304-1306.
Huttenloch et al.,Organometallics 11,1992, pp. 3600-3607.
Rheingold et al., Organometallics 11, 1992, pp. 1869-1876.
Wiesenfeldt et al., J. of Organomet. Chem.,369,1989, pp. 359-370.
Brintzinger et al. J. of Organomet. Chem, 232, 1982, pp. 233-247.
J. Am. Chem. Soc. vol. 114, 1992, pp. 9300-9304.
J. of Organomet. Chem. 342 (1988), 21-29.

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