Process for the hydrogenation of imines

Details Process for the hydrogenation of imines Process for the hydrogenation of imines

1998-01-26

1999-11-16

Barts, Samuel

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

Organic compounds

Amino nitrogen containing

564443, 564448, 564489, 549468, C07C20900

Patent

active

059861398

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for the preparation of amines by hydrogenation of imines in the presence of dinuclear iridium complexes having ferrocenyl(di-tertiary phosphine) ligands.
U.S. Pat. No. 5,112,999 describes dinuclear Ir(III) complexes having ditertiary diphosphine ligands and halide bridges, halide and hydride ligands and Ir(III) halide complex salts containing a ditertiary diphosphine ligand that are suitable as catalysts for a hydrogenation of imines that may be an enantioselective hydrogenation. Ditertiary ferrocenyldiphosphine ligands are not mentioned. U.S. Pat. No. 5,371,256 and EP-A-0 612 758 describe iridium complexes having chiral ferrocenyldiphosphine ligands for the homogeneous enantioselective hydrogenation of imines. Those homogeneous catalysis processes have proved valuable, but the activity and selectivity of the catalysts, while already high per se, are still not entirely satisfactory. It has also been suggested that soluble halides be added to the reaction mixture in order to improve the enantioselectivity and the activity and stability of the catalysts.
It has now been found that dinuclear Ir(III) complexes having ditertiary diphosphine ligands and halide bridges, halide and hydride ligands and Ir(III) halide complex salts containing a ditertiary diphosphine ligand exhibit an unexpectedly high catalyst activity and stability in the hydrogenation of imines, on their own, without further additives. Furthermore, when chiral diphosphine ligands and prochiral imines are used, extraordinarily high enantioselectivities are achieved, which may amount to an enantiomeric excess of 80% and more. The reaction times for a one hundred percent conversion may even be considerably less than an hour and, even at low catalyst concentrations, very high yields can still be achieved in relatively short reaction times.
The present invention relates to a process for the preparation of primary or secondary amines by hydrogenation of imines with hydrogen at elevated pressure and in the presence of a dinuclear Ir(III) complex having ditertiary diphosphine ligands, halide bridges, halide and hydride ligands, or an Ir(III) halide complex salt containing ditertiary diphosphine ligands, as catalyst, wherein the catalyst corresponds to formula I or Ia or to mixtures of at least two compounds of formula I, at least two compounds of formulae I and Ia, or at least two compounds of formula Ia phosphine groups of which are either bonded directly or via a bridge group --CR.sub.v R.sub.w -- to the ortho positions of a cyclopentadienyl ring or are each bonded to a cyclopentadienyl ring of a ferrocenyl, so that a 5-, 6- or 7-membered ring is formed together with the Ir atom; -C.sub.8 alkyl, C.sub.1 -C.sub.4 fluoroalkyl, phenyl or benzyl, or are phenyl or benzyl each having from 1 to 3 C.sub.1 -C.sub.4 alkyl or C.sub.1 -C.sub.4 -alkoxy substituents; and
The iridium compounds are preferably homogeneous catalysts that are to a large extent soluble in the reaction medium. The term "catalyst" also includes catalyst precursors which are converted into an active catalyst species at the beginning of a hydrogenation reaction.
R.sub.w is preferably hydrogen. R.sub.v is preferably C.sub.1 -C.sub.4 alkyl, for example methyl, ethyl, n-propyl or n-butyl, and especially methyl.
The ditertiary ferrocenyldiphosphine preferably contains at least one chiral group, and the diphosphine is especially an optically pure stereoisomer or a pair of diastereoisomers since, with catalysts that contain chiral ligands, optical inductions are obtained in asymmetric hydrogen reactions.
The phosphine groups preferably contain two identical or different, more preferably identical, unsubstituted or substituted hydrocarbon radicals having from 1 to 20, especially from 1 to 12, carbon atoms. Preferred diphosphines are those wherein the secondary phosphine groups contain two identical or different radicals from the following group: linear or branched C.sub.1 -C.sub.12 alkyl; unsubstituted or C.sub.1 -C.sub.6 alkyl- or C.sub.1 -C.sub.6 alkoxy-s

REFERENCES:
patent: 5112999 (1992-05-01), Osborn et al.
patent: 5371256 (1994-12-01), Togni et al.
patent: 5563308 (1996-10-01), Spindler et al.

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