Ferrocenyl diphosphines as ligands for homogeneous catalysts

Details Ferrocenyl diphosphines as ligands for homogeneous catalysts Ferrocenyl diphosphines as ligands for homogeneous catalysts

2000-05-18

2001-08-28

Nazario-Gonzalez, Porfirio (Department: 1621)

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

Organic compounds

Heavy metal containing

C556S011000, C556S013000, C556S022000, C556S143000, C502S152000, C502S158000

Reissue Patent

active

RE037344

ABSTRACT:

The present invention relates to 1-[2-(diphenylphosphino)ferrocenyl]alkylidene phosphines in the form of racemates and stereoisomers, to a process for their preparation, to iridium and rhodium complexes containing these ligands, and to the use thereof as enantioselective hydrogenation catalysts for the homogeneous hydrogenation of prochiral unsaturated compounds.
T. Hayashi et al. describe in Bull. Chem. Soc. Jpn., 53, pages 1136-1151, the preparation of a chiral ferrocenyl phosphine as ligand for transition metal complexes for asymmetric synthesis, namely [(R)-[(S)-2-(diphenylphosphino)ferrocenyl]ethyl]diphenylphosphine. Our investigations have revealed that homogeneous hydrogenation of prochiral compounds with rhodium complexes, which contain these ligands give only low optical yields.
It has now been found that, in the same or seven shorter reaction times, the enantioselectivity can be substantially enhanced if the substituents in the alkylidene phosphine group are not both phenyl.
In one of its aspects, the invention relates to compounds of formula I
wherein R
1
is C
1
-C
8
alkyl, phenyl or phenyl which is substituted by 1 to 3 C
1
-C
4
, alkyl or C
1
-C
4
alkoxy groups; R
2
and R
3
are identical and are C
1
-C
12
alkyl, C
5
-C
12
cycloalkyl or C
1
-C
4
alkyl- or C
1
-C
4
-alkoxy-substituted C
5
-C
12
cycloalkyl, or phenyl which is substituted by one to three identical or different members selected from the group consisting of C
1
-C
4
alkyl, C
1
-C
4
alkoxy, —SiR
4
R
5
R
6
, halogen, —SO
3
M, —CO
2
M, —PO
3
M, —NR
7
R
8
and —[⊕NR
7
R
8
R
9
]X⊖; or R
2
and R
3
are different and are C
1
-C
12
alkyl, C
5
-C
12
cycloalkyl, C
1
-C
4
alkyl- or C
1
-C
4
alkoxy-substituted C
5
-C
12
cycloalkyl, phenyl or phenyl which is substituted by one to three identical or different members selected from the group consisting of C
1
-C
4
alkyl, C
1
-C
4
alkoxy, —SiR
4
R
5
R
6
, halogen, —SO
3
M, —CO
2
M, —PO
3
M
2
, —NR
7
R
8
and —[⊕NR
7
R
8
R
9
]X⊖; or the group —PR
2
R
3
is a radical of formula II
and R
4
, R
5
and R
6
are each independently of one another C
1
-C
12
alkyl or phenyl, R
7
and R
8
are H, C
1
-C
12
alkyl, phenyl or R
7
and R
8
, taken together, are tetramethylene, pentamethylene or 3-oxa-1,5-pentylene, R
9
is H or C
1
-C
4
alkyl, M is H or an alkali metal, X⊖ is the anion of a monobasic acid, and * is a stereogenic carbon atom, in the form of their racemates and diastereoisomers or mixtures of diasteroisomers.
R
1
as alkyl may be linear or branched and contains preferably 1 to 4 carbon atoms. Typical examples are methyl, ethyl, n- and isopropyl, n-, iso- and tert-butyl, pentyl, hexyl, heptyl and octyl. Methyl and ethyl are preferred and methyl is especially preferred.
R
1
as substituted phenyl preferably contains 1 or 2 substituents. Alkyl substituents may typically be methyl, ethyl, n- and isopropyl, n-, iso- and tert-butyl; methyl and ethyl are preferred. Alkoxy substituents may be methoxy, ethoxy, n- and isopropoxy, n-, iso- and tert-butoxy. Methoxy and ethoxy are preferred.
R
2
and R
3
as alkyl may be linear or branched and contain preferably 1 to 8, most preferably 1 to 4, carbon atoms. Typical examples are methyl, ethyl, n- and isopropyl, n-, iso- and tert-butyl, pentyl, hexyl, heptyl, octyl nonyl, decyl, undecyl and dodecyl. Methyl, ethyl, n- and isopropyl, n-, iso- and tert-butyl are preferred. When R
2
and R
3
are identical and alkyl they are most preferably isopropyl or tert-butyl.
R
2
and R
3
defined as cycloalkyl preferably contain 5 to 8, most preferably 5 or 6, ring carbon atoms. Exemplary of cycloalkyl are cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclodecyl and cyclododecyl. Cyclopentyl and cyclohexyl are preferred and cyclohexyl is especially preferred.
Cycloalkyl may be substituted, conveniently by 1 to 3 alkyl or alkoxy groups. Examples of such groups have been indicated above. Methyl and ethyl are preferred, as are also methoxy and ethoxy. Substituted cycloalkyl is typically methyl- and methoxycyclopentyl and methyl- and methoxycyclohexyl.
R
2
and R
3
defined as substituted phenyl preferably contains 1 or 2 substituents. Where phenyl contains 2 or 3 substituents, these may be identical or different.
Examples of alkyl and alkoxy substituents have been indicated above. Preferred alkyl and alkoxy substituents of phenyl are methyl, ethyl as well as methoxy and ethoxy.
Halogen as a substituent of phenyl may preferably be selected from the group consisting of —F, —Cl and —Br.
R
4
, R
5
and R
6
may be linear or branched alkyl that preferably contains 1 to 8 and, most preferably, 1 to 4, carbon atoms. Exemplary alkyl substituents have been indicated above. Preferably alkyl is methyl, ethyl, n-propyl, n-butyl and tert-butyl. The substituent —SiR
4
R
5
R
6
is most preferably trimethylsilyl.
Among the acid phenyl substituents —SO
3
M, —CO
2
M and —PO
3
M, the —SO
3
M group is preferred. M is preferably H, Li, Na and K.
R
7
and R
8
as alkyl preferably contains 1 to 6, most preferably 1 to 4, carbon atoms. Alkyl is preferably linear. Preferred examples are methyl, ethyl, n-propyl and n-butyl. R
9
as alkyl is preferably methyl.
X
⊖
as anion of a monobasic acid is preferably Cl
⊖
, Br
⊖
or the anion of a carboxylic acid, typically formate, acetate, trichloroacetate or trifluoroacetate.
Representative examples of substituted phenyl are 2-methylphen-1-yl, 3-methylphen-1-yl, 4-methylphen-1-yl, 2- or 4-ethylphen-1-yl, 2- or 4-isopropylphen-1-yl, 2- or 4-tert-butylphen-1-yl, 2-methoxyphen-1-yl, 3-methoxyphen-1-yl, 4-methoxyphen-1-yl, 2- or 4-ethoxyphen-1-yl, 4-trimethylsilylphen-1-yl, 2- or 4-fluorophen-1-yl, 2,4-difluorophen-1-yl, 2- or 4-chlorophen-1-yl, 2,4-dichlorophen-1-yl, 2,4-dimethylphen-1-yl, 3,5-dimethylphen-1-yl, 2-methoxy-4-methylphen-1-yl, 3,5-dimethyl-4-methoxyphen-1-yl, 3,5-dimethyl-4-(dimethylamino)phen-1-yl, 2- or 4-aminophen-1-yl, 2- or 4-methylaminophen-1-yl, 2- or 4-(dimethylamnio)phen-1-yl, 2- or 4—SO
3
H-phen-1-yl, 2- or 4—SO
3
Na-phen-1-yl, 2- or 4-[
⊕
NH
3
Cl
⊖
]phen-1-yl, 3,4,5-trimethylphen-1-yl or 2,4,6-trimethylphen-1-yl.
R
2
and R
3
as identical substituents are preferably cyclohexyl, 2- or 4-methylphen-1-yl, 2- or 4-methoxyphen-1-yl, 2- or 4-(dimethylamino)phen-1-yl, 3,5-dimethyl-4-(dimethylamino)phen-1-yl and 3,5-dimethyl-4-methoxyphen-1-yl.
Where R
2
and R
3
are different substituents, R
2
is preferably phenyl and R
3
is preferably cyclohexyl, 2- or 4-methylphen-1-yl, 2- or 4-methoxyphen-1-yl, 4-(dimethylamino)phen-1-yl, 3,5-dimethyl-4-(dimethylamino)phen-1-yl, 3,5-dimethyl-4-methoxyphen-1-yl or 4-tert-butyl-phen-1-yl.
In a preferred embodiment of the invention, R
2
and R
3
are identical substituents and are cyclohexyl.
In another preferred embodiment of the invention, R
2
and R
3
are identical substituents and are tert-butyl or o-anisyl.
In yet a further preferred embodiment of the invention, R
2
is phenyl and R
3
is o-anisyl.
In a particularly preferred preferred embodiment of the invention, R
1
in formula I is methyl and R
2
and R
3
are each cyclohexyl.
In another of its aspects, the invention provides a process for the preparation of compounds of formula I, which comprises reacting a compound of formula III
in the presence of an inert solvent at room temperature or at elevated temperature, with a phosphine of formula IV
HPR
2
R
3
  (IV).
The reaction is known per se and is described by T. Hayashi et al. im Bull. Chem. Soc. Jpn., 53, pp. 1136-1151. The preparation of compounds of formula III is also described in this reference or can be carried out in analogous manner. The phosphines of formula IV are known or are obtainable by known methods in analogous manner.
The reaction temperature may be in the range from 20° to 150° C., preferably from 40° to 100° C. Suitable solvents are polar protic and aprotic solvents which may be used singly or as mixtures of two or more solvents. Typical examples of solvents are alkanols such as methanol and ethanol, and c

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