Water soluble phosphines

Details Water soluble phosphines Water soluble phosphines

2000-06-09

2001-10-23

Vollano, Jean F. (Department: 1621)

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

Organic compounds

Phosphorus acids or salts thereof

C562S008000, C558S070000, C564S015000

Reexamination Certificate

active

06307098

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to water soluble phosphines and process for their preparation.
2. Description of the Related Art
There has been considerable interest in aqueous and biphasic homogeneous transition metal catalysis as a means to both lower process costs and minimize adverse health and environmental concerns during manufacture. The most frequently used ligands in the metal complexes used for these reactions are functionalized triarylphosphines. Triarylphosphines are sufficiently good &sgr;-donors and &pgr;-acceptors to stabilize synthetically useful transition metal species, yet, compared to alkylphosphines, are relatively resistant to oxidation by adventitious oxygen. This is an important factor for aqueous catalytic reactions because it is often difficult to completely remove oxygen from aqueous media.
A wide variety of cationic, anionic and non-ionic hydrophilic functional groups have been utilized to impart water solubility to triarylphosphines. Sulfonated phosphine ligands such as P(3-C
6
H
4
SO
3
Na)
3
(triphenylphosphine trisulfonate, TPPTS) were demonstrated to be effective in the biphasic hydroformylation reaction commercialized by Rhone-Poulenc in the mid-1970s, and remain the most common. However, groups other than sulfonate are increasingly being investigated to extend the desirable properties of these ligands. In particular, anionic phosphonate groups and their corresponding salts are also capable of imparting a high degree of water-solubility to triarylphosphine ligands. Such groups offer a further advantage in being an excellent functionality for the synthesis of hybrid inorganic-organometallic materials. Specifically, compounds containing phosphonate groups have found broad application in the molecular fabrication of supported catalysts, chemical sensors, electroluminescent materials, and non-linear optical materials.
Known is the synthesis of 4-Ph
2
PC
6
H
4
PO
3
Na
2
(triphenylphosphine monophosphonate disodium salt, TPPMP) from 4-Ph
2
PC
6
H
4
Br. Metal-halogen exchange with n-butyllithium followed by subsequent reaction of the aryllithium species with diethyl chlorophosphate gave the intermediate phosphonate ester 4-Ph
2
PC
6
H
4
PO
3
Et
2
. Transesterification with BrSiMe
3
followed by hydrolysis and neutralization with NaOH gave the desired compound. The phosphonate ester has also been prepared by the Pd-catalyzed reaction of 4-PPh
2
C
6
H
4
Br and diethyl phosphite. In our hands, neither of these strategies was satisfactory for the preparation of the corresponding tris-phosphonate compounds, as they gave mixtures of products that were difficult to purify.
Nucleophilic aromatic substitution of fluoro arylsulfonates by phosphine or primary or secondary phosphines in the super basic medium KOH/DMSO has been shown to be a flexible and efficient route to secondary and tertiary phosphines with sulfonated aromatic substituents . Similarly, it has been reported that the triphenylphosphine diphosphonates PhP[4-C
6
H
4
PO
3
Na
2
]
2
and PhP[3-C
6
H
4
PO
3
Na
2
]
2
could be prepared by nucleophilic aromatic substitution of 4-FC
6
H
4
P(O)(NMe
2
)
2
or 3-FC
6
H
4
P(O)(NMe
2
)
2
by PhPLi
2
, followed by acid resulting arylphosphine-phosphonodiamide, and neutralization of the free phosphonic acid with NaOH. From these reports, it was reasonable to assume that tris(4-phosphonophenyl)phosphine and its corresponding alkali metal salts could be prepared from nucleophilic aromatic substitution of the appropriate aryl fluoride by PH
3
. We were dissuaded, however, by the toxic and pyrophoric properties of phosphine gas.
It is known that phosphide anions can be generated directly from red phosphorus by the action of alkali metals in liquid ammonia . Reduction is believed to proceed via a diphosphide anion [P—P]
4-
, which, in the absence of a proton source more acidic than ammonia, is resistant to further reduction. Addition of alkyl halides gives tetraalkyldiphosphines, R
2
P-PR
2
, along with small amounts of R
3
P. Whenever the reduction is carried out by the slow addition of one molar equivalent of a proton source such as tertiary-butyl alcohol (t-BuOH) to a 1:3 molar mixture of red phosphorus and lithium, fission of the P—P bond of the intermediate diphosphide is greatly facilitated. Subsequent addition of two equivalents of RX in Scheme 1 gives dialkylphosphines R
2
PH in good yield:
The generation of trialkyl phosphines (i.e., R
3
P) via the use of excess RX in Scheme 1 is hindered by the decreased acidity of R
2
PH relative to that of PH
3
or RPH
2
, which limits formation of the requisite R
2
P anion in amounts sufficient to yield R
3
P as the major reaction product. In contrast, the acidity of aromatic phosphines of the form Ar
x
PH
(3-x)
(where Ar is a phenyl or substituted phenyl group and x=0, 1, 2) increases with the number of Ar groups (i.e., x). We therefore hypothesized that the progressive aryl substitution of phosphide anions to form ArPH
2
and Ar
2
PH would result in phosphine hydrides that, if present, would likely undergo deprotonation in the presence of more basic species such as LiPH
2
or LiNH
2
. The resultant anions would then further react with the aryl fluoride precursors to form the desired Ar
3
P product.
OBJECTS AND BRIEF SUMMARY OF THE INVENTION
An object of this invention is a process for preparation of water-soluble triphenyl phosphines possessing acid derivatives as substituents on each of the phenyl rings.
Another object of this invention is the use of elemental phosphorus as a starting material for the preparation of the triphenylphosphine of this invention instead of the toxic and pyrophoric phosphine gas.
Another object of this invention is the preparation of novel water-soluble phosphines of this invention containing phosphonodiamide, phosphonic acids or phosphonate esters.
These and other objects of this invention are attained by the water-soluble triphenylphosphine having phosphonic acid groups or their derivatives on each phenyl ring made in a single pot reaction of red phosphorus, an alkali metal such as lithium, and a proton donor such as t-butanol, in liquid solvent such as liquid ammonia with an appropriate fluorophenyl phosphonic acid derivative.
DETAILED DESCRIPTION OF THE INVENTION
This invention pertains to product and process. The product is a water-soluble substituted triarylphosphine having phosphonic acid groups or its derivatives on each of the phenyl rings. The process is characterized by a single pot reaction of red phosphorus, an alkali metal such as lithium, and a proton donor (PD) such as t-butanol, in a solvent such as liquid ammonia, with an appropriate fluorophenyl phosphonic acid ester or N,N-dialkyl amide derivative.
The general reaction is depicted as follows:
where R
1
and R
2
are same or different and are selected from dialkylamino groups containing 1-22, preferably 1-6 carbon atoms; alkoxide groups containing 1-22, preferably 1-6 carbon atoms; A, of which more than one can be present, is a substituent group(s) at positions other than the position of the phosphonate group —P(═O)(R
1
)(R
2
) and can be any organofunctional group which is stable to the reaction conditions and which maintains or does not interfere with solubility of the precursor, such as lower alkyl groups, phenyl, ether, phenol salts, dialkylamines and phenylalkyl groups; and the phosphonate group is on the phenyl ring at positions 2, 3 or 4, particularly positions 3 or 4. Another alkali metal can be used in place of lithium. Suitable alkali metals include sodium and potassium.
The structures of the compounds of this invention are shown below in Scheme 2, together with a Ronman number al designations for each compound in boldface Arc to facilitate discussion of the invention, with the phosphonate group being at position 4:
The following standard abbreviations are used in Scheme 2 and throughout the description of the invention: CH
3
=Me; C
2
H
5
=Et; C
4
H
9
=Bu. The name of each compound is given in the

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