Platinum hydrides with bridges bimetallic structure, method for their preparation and their application to the catalysis of chemical reactions

The invention relates to platinum hydrides, a process for their preparation and their use as components of catalytic systems. The platinum hydrides have a bridged bimetallic structure represented by the general formula: ##STR1## wherein: M is a metal of valence n, at least equal to 2, PA1 X is a halogen atom, and PA1 P P is a schematic representation of a ligand of the general formula: ##STR2## in which: R.sub.1, R.sub.2, R.sub.5, and R.sub.6, identical or different, are chosen from among aliphatic or cycloaliphatic hydrocarbon radicals with 1 to 8 carbon atoms and aromatic hydrocarbon radicals with 6 to 10 carbon atoms, PA1 R.sub.3 and R.sub.4, identical or different, are chosen from among a hydrogen atom and aliphatic hydrocarbon radicals with 1 to 8 carbon atoms, possibly functionalized and/or together forming a ring, and PA1 m is an integer higher than or equal to 4.

The present invention relates to novel platinum hydrides, a process for 
their preparation and their use as components of catalytic systems 
intended for the catalysis of chemical reactions, in particular the 
hydroformylation reactions of ethylenically unsaturated compounds. 
A first object of the present invention consists of a novel class of 
platinum hydrides with a bridged bimetallic structure, represented by the 
general formula: 
##STR3## 
wherein M is a metal of valence n, at least equal to 2, 
X is a halogen atom, and 
P P constitutes a schematic representation of a ligand of the general 
formula: 
##STR4## 
in which R1, R.sub.2, R.sub.5, R.sub.6, identical or different, are chosen 
from among aliphatic or cycloaliphatic hydrocarbon radicals with 1 to 8 
carbon atoms and aromatic hydrocarbon radicals with 6 to 10 carbon atoms, 
R.sub.3 and R.sub.4, identical or different, are chosen from among a 
hydrogen atom and aliphatic hydrocarbon radicals with 1 to 8 C atoms, 
possibly functionalized and/or together forming a ring, and 
m an integer higher than or equal to 4. 
In Formula (I) the platinum hydrides according to the invention, X 
preferentially is chlorine, n is preferably equal to 2 or 3 and the metal 
M is preferably chosen from the groups IVB, VIII, IB, IIB, IIIA and IVA of 
the periodic classification. Even more preferably, M may be chosen from 
among iron (II), zinc, tin, copper, aluminum and titanium (III). 
In the ligand formula (II), it is preferable that R.sub.1 =R.sub.5 and 
R.sub.2 =R.sub.6, and more particularly R.sub.1 =R.sub.2 =R.sub.5 
=R.sub.6. As examples the following radicals may be cited: methyl, ethyl, 
isopropyl, tertiobutyl, neopentyl, cyclohexyl, phenyl, etc. If the R.sub.3 
and R.sub.4 are functionalized, they may carry in particular a function 
such as thiol, alcohol, thioether, amine, imine, acid, ester, amide or 
ether. 
An even more preferred class of ligands is that represented by the general 
formula: 
EQU PR.sub.2 --CH.sub.2 --(CHR').sub.n-2 CH.sub.2 --PR.sub.2 (III) 
wherein: 
R is chosen from among aliphatic or cycloaliphatic hydrocarbon radicals 
with 1 to 8 C atoms and aromatic hydrocarbon radicals with 6 to 10 C 
atoms, 
R' is chosen from among aliphatic hydrocarbon radicals with 1 to 8 C atoms, 
possibly functionalized (the function carried being as mentioned above), 
and 
m is an integer higher than or equal to 4. 
Examples of such ligands are in particular (1S, 
2S)(+)trans-1,2-bis(diphenylphosphinometal)cyclohexane, 
1,4-bis(diphenylphosphino)-butane and 
isopropylidene-dihydroxy-2,3-bis-(diphenylphosphino)1,4-butane. 
The platinum hydrides according to the invention may be prepared by a 
number of processes. A first process comprises: 
in a first stage the reduction of a solvent containing at least one 
alkylene carbonate in an electrochemical cell, the anode of which is a 
metal M, so as to form a chemical combination between the metal M and the 
alkylene carbonate, then 
the reaction of said combination with at least one platinum complex of the 
formula 
##STR5## 
wherein C and 
##STR6## 
have the abovementioned significance and finally in a last stage the 
application of a hydrogen atmosphere. 
The process therefore comprises, in a first stage, the formation of a 
chemical combination between the metal M and an alkylene carbonate which 
may be chosen in particular from among propylene, ethylene, 1,2-butylene 
and 1,2-hexylene. According to a particular embodiment of the process, the 
reduction of the solvent may be carried out in the presence of a small 
quantity of a conducting salt soluble in said solvent, such as for example 
tetra-n-butylammonium hexafluorophosphate. The presence of this conducting 
salt makes it possible to advantageously accelerate the reaction of the 
solvent, in particular at moderate temperatures. The electrochemical 
reduction phase according to the invention is generally carried out at a 
temperature between about 10.degree. and 70.degree. C., while maintaining 
the electrochemical cell under an inert gas atmosphere, such as for 
example nitrogen, argon or carbon monoxide; it is preferable in view of 
future uses of the platinum hydrides prepared in this manner, particularly 
as components of catalytic systems for chemical reactions, that the 
electrochemical reaction be carried out in the absence of hydrogen. The 
electrochemical solvent used in this stage of the process necessarily 
contains at least one alkylene carbonate, such as defined above. It may 
further contain, in a mixture with the former, another solvent, such as 
for example an aromatic hydrocarbon (benzene, toluene, xylene, etc.). To 
carry out the process of the invention it is preferred to use a solvent 
comprising at least about 10% by volume of the alkylene carbonate. 
Within this first process, two variants may be utilized for the 
electrochemical reduction. According to the first variant, the 
electrochemical cell contains in addition to the anode of the metal M, a 
cathode and a reference electrode and the reduction is carried out by 
charging the cathode to a potential less than or equal to -1.5 Volt 
relative to the reference electrode and by maintaining this potential for 
a duration sufficient to assure the production of the desired quantity of 
the chemical "M-alkylene carbonate" combination; in this case the 
reference electrode may be for example one of the electrodes 
Ag/AgCl/Cl.sup.-, Ag/Ag.sup.+ and Hg/Hg.sub.2 Cl.sub.2 (calomel). 
According to the second variant, the electrochemical cell contains a metal 
M anode and a cathode between which a difference potential higher than or 
equal to about 10 Volts is maintained, for a duration sufficient to insure 
the production of the desired quantity of the "M-alkylene carbonate". As 
in the preceding variant, the metal M anode passes progressively into 
solution. 
As examples of cathodes that may be used in the first process, on the one 
hand graphite cathodes may be cited, and on the other, metallic cathodes 
inert relative to the solvent, such as platinum or stainless steel. 
The first process according to the invention further comprises the reaction 
of the chemical combination formed between the metal M and the alkylene 
carbonate, with the platinum complex of the formula 
##STR7## 
This reaction is preferably carried out in at least one solvent of said 
complex, at a temperature between 10.degree. C. and the boiling 
temperature of said solvent. Among the solvents of the platinum complex, 
in particular aromatic hydrocarbons (for example benzene, toluene and the 
xylenes) and the alkylene carbonates, in particular those, the alkylene 
compound of which has 2 to 6 C atoms, may be mentioned. The duration of 
the reaction between the "alkylene carbonate of M" combination and the 
platinum complex may vary, in keeping with conventional rules well known 
to those skilled in the art, as a function of the temperature chosen and 
the concentration of the reactive species in the solvent. As an example, 
this duration is generally not longer than 20 min, if the reaction 
temperature is 80.degree. C. 
Several modes of carrying out this reaction may be considered within the 
first process according to the invention. A first mode of embodiment 
consists of forming an "M-alkylene carbonate" combination by 
electrochemical reduction, then introducing the platinum complex into the 
medium in which said combination has been formed, said medium already 
containing the solvent required for the reaction. A second mode of 
embodiment consists of forming an "alkylene carbonate-M" combination by 
electrochemical reduction, separating said combination (in the powder 
form) from the medium in which it has been formed (for example by 
filtering, washing and drying the precipitate formed in the 
electrochemical cell), the introducing said powder into a solution of the 
platinum complex in the solvent required for the reaction. Finally, a 
third mode of embodiment consists of forming the "alkylene carbonate-M" 
combination in the presence of the solvent and the platinum complex, for 
example by electrochemical reduction; in this case the operation is 
carried out over a duration sufficient to insure the production of a 
quantity of electricity at least equal to 0.2 Faraday by gram-atom of 
platinum. Regardless of the mode of embodiment chosen for the process of 
the invention, it is desirable that the concentration of the platinum 
complex in the reaction solvent be between about 0.001 and 0.2 mole per 
liter. 
A second process for the preparation of platinum hydrides according to the 
invention comprises the reaction of a compound of metal M with a platinum 
complex of the formula 
##STR8## 
in which X and 
##STR9## 
have the significance explained above, in the presence of a solvent 
containing at least one alkylene carbonate, followed by the application of 
a hydrogen atmosphere. The metal M compound subjected to this reaction 
preferably is a compound containing at least one covalent M--O bond, such 
as an oxide, an alcoholate or a metallic ether. 
This second process thus comprises, firstly, a chemical reaction in a 
solvent medium containing an alkylene carbonate, the alkylene group of 
which preferably has 2 to 6 carbon atoms, possibly in a mixture with an 
aromatic hydrocarbon such as benzene, toluene or xylene, preferably, as in 
the first process of the invention, said medium contains at 10% by volume 
of the alkylene carbonate. The other reaction conditions, such as 
temperature and duration, remain the same. 
Both in the first and the second process according to the invention, the 
quantities of "M-alkylene carbonate" and the platinum complex used in the 
reaction are such that the atomic ratio M/Pt is between about 0.5 and 2 
and preferably is equal to 1. In both processes the reaction between the 
"M-alkylene carbonate" combination and the platinum complex is followed by 
a hydrogenation stage, i.e. the application of a hydrogen atmosphere; this 
last stage of the process generally takes place under pressure (up to 
about 200 bars) and possibly at an elevated temperature (up to 150.degree. 
C.). 
The platinum hydrides according to the invention have a bridged bimetallic 
structure of Formula (I) verified by the following analytical methods: 
nuclear magnetic resonance of phosphorus 31, proton, platinum 195 and the 
metal M; 
infrared spectroscopy establishing the presence of a fine absorption band 
of the platinum-hydrogen bond at 2010 cm.sup.-1 ; 
mass spectrometry. 
The platinum hydrides with a bridged bimetallic structure have a remarkable 
utility as components of catalytic systems for chemical reactions, in 
particular for the hydroformylation reactions of ethylenically unsaturated 
compounds. Another object of the present invention therefore consists of 
the application of these hydrides to the preparation of aldehydes by the 
hydroformylation of an ethylenically unsaturated organic compound, 
characterized in that said organic compound is reacted at a temperature 
between about 10.degree. C. and 300.degree. C. and a pressure of 10 to 350 
bars, with a mixture of carbon monoxide and hydrogen in the presence of an 
effective quantity of said hydride. An effective quantity of the catalytic 
system is generally such that the molar ratio of the organic compound to 
the ethylenic insaturation on the platinum is between 100 and 10,000. The 
molar ratio CO/H.sub.2 in the mixture of carbon monoxide and hydrogen in 
the hydroformylation reaction according to the invention generally is 
between about 0.5 and 2. 
Among the ethylenically unsaturated organic compounds that may be subjected 
to the hydroformylation reaction according to the invention, the following 
may be cited: 
olefins with 2 to 12 C atoms, such as in particular propylene, 1-butene, 
1-hexene, 1-4-methyl-1-pentene, 1-octene, etc., 
vinylaromatic compounds such as styrene, alphamethylstyrene, 
dienes, such as for example 4-vinyl-cyclohexane. 
The duration of the hydroformylation reaction according to the invention is 
generally between about 0.5 and 30 h, depending on temperature and 
pressure. 
The hydroformylation process according to the invention makes it possible 
to obtain, with an excellent conversion proportion, a mixture of normal 
and branched aldehydes, in which the proportion of normal aldehydes is 
especially high.

The following examples illustrate the invention without limiting it. 
EXAMPLE 1 
Into a glass electrochemical cell, the following are introduced under 
nitrogen: 64 mg of the LPtCl.sub.2 compound, the ligand being 
isopropylene-2,3-dihydroxy-bis(diphenylphosphino)-1,4-butane, then the 
solvent consisting of a mixture of 15 cm.sup.3 benzene and 10 cm.sup.3 
propylene carbonate. Following the complete dissolution of the complex, 
the cathode (consisting of a platinum basket) and the anode (consisting of 
a tin cylinder) are immersed, then the reference electrode 
(Ag/AgCl/N(C.sub.4 H.sub.9).sub.4 Cl 0.1M in propylene carbonate) are 
immersed in the solvent. The temperature is 20.degree. C., the reduction 
potential is set at -1.85 Volt between the cathode and the reference 
electrode, and the electroreduction is arrested when the quantity of the 
current having passed the circuit corresponding to an atomic Sn/Pt ratio 
is equal to 1. During the coulometry, the solution changes from colorless 
to maroon, while passing through yellow. The solution is then transferred 
to a previously degassed, 50 cm.sup.3 reaction autoclave. The reactor is 
then charged with hydrogen and to a pressure of 100 bars, then heated to a 
temperature of up to 100.degree. C. and the agitation started. After about 
2 h, the autoclave is cooled and the gaseous mixture eliminated. The 
solution is transferred to a Schlenk tube and stored under argon. 
The compound prepared has been analyzed by the following spectroscopic 
methods: 
nuclear magnetic resonance of phosphorus 31 at 162 MHz with reference to 
phosphoric acid, making it possible to observe chemical displacements at 
4.22 ppm, 8.15 ppm and 13.8 ppm, 
nuclear magnetic resonance of the proton at 400 MHz relative to 
tetramethylsulfide, making it possible to observe a chemical displacement 
at -5.15 ppm, 
nuclear magnetic resonance of platinum 195 at 87 MHz with reference to 
H.sub.2 PtCl.sub.6 to observe a chemical displacement at -5390 ppm, 
nuclear magnetic resonance of tin 119 at 149 MHz with reference to 
tetramethyltin showing a chemical displacement at 36 ppm, 
mass spectrometry establishing that the compound prepared, with a total 
weight of 2337 g, responds to the following detail formula: 
##STR10## 
in which P P designates 
isopropylidene-2,3-dihydroxy-bis(diphenylphosphino)-1,4-butane. In keeping 
with the international nomenclature this compound is designated 
dihydrido[.mu.-(2,2-dimethyl-1,3-dioxolane-4,5-diyl)bis(methylene)bis[diph 
enyl phosphine]-P: P']] bis 
[[2,2-dimethyl-1,3-dioxolane-4,5-dyl)-bis(methylene) bis[diphenyl 
phosphine]-P: P']] diplatinum (II) bis trichlorostannate, and may be 
diagrammed as follows: 
##STR11## 
EXAMPLE 2 
The platinum hydride solution prepared according to Example 1 is introduced 
into a stainless steel, 100 cm.sup.3 autoclave reactor, equipped with a 
magnetic bar agitator and styrene is added in a quantity such that the 
molar styrene/Pt ratio be equal to 100. The reactor is heated to 
80.degree. C. and the synthesis gas consisting of an equimolar mixture of 
carbon monoxide and hydrogen introduced. Finally, the mixture is agitated 
and the reaction continued at 80.degree. C. under a pressure of 50 bars 
for 24 h. A mixture is obtained, with a conversion proportion TT 
(expressed in %), of ethylbenzene, 2-phenyl-2-propanal and 3-phenyl 
propanal. Analysis of the mixture determined on the one hand the 
proportion by weight of ethylbenzene EB (expressed in %) and on the other, 
the molar ratio n/b of normal aldehyde to branched aldehyde. Table I 
compiles the results obtained. 
EXAMPLE 3 
The operating process of Example 2 is repeated, with the following 
exceptions: the reaction is carried out at 90.degree. C. under a pressure 
of 100 bars for 8 h. Results are given in Table I. 
EXAMPLE 4 
The process of Example 1 is repeated with the exception that the solvent 
consists of a mixture of 10 cm.sup.3 benzene and 15 cm.sup.3 propylene 
carbonate. The platinum hydride solution obtained in this manner is then 
used in the hydroformylation of styrene under the operating conditions of 
Example 2. Results are contained in Table I. 
EXAMPLES 5-9 
The process of Example 1 is repeated with the exception of the nature of 
the anode, in which tin is replaced by another metal indicated in Table I. 
Spectroscopic analyses carried out as in Example 1 indicate that the 
product formed is a platinum hydride with a bridged bimetallic structure 
according to Formula (I). The hydroformylation of styrene is then effected 
according to the operating process of Example 3 with the exception of the 
duration of the reaction, which is from 8 to 19 h. Results obtained are in 
Table I. 
TABLE I 
______________________________________ 
example anode TT EB n/b 
______________________________________ 
2 Sn 67 6 4,3 
3 Sn 100 8 4,0 
4 Sn 53 4 5,5 
5 Al 90 17 1,9 
6 Ti 80 14,5 2,5 
7 Fe 100 3 5,0 
8 Cu 45 18 4,8 
9 Zn 100 4 5,3 
10 Fe 100 3 9,3 
11 Fe 100 15,5 8,1 
______________________________________ 
EXAMPLE 10 
The process of the preparation of platinum hydride of Example 7 (iron 
anode) is repeated with the exception that the solvent consists of 25 
cm.sup.3 of a mixture with 75% by volume of benzene. The hydroformylation 
of styrene is then carried out according to the operating process of 
Example 3 with the exception of the duration of the reaction, which is 8 
to 24 h. Results are listed in Table I. 
EXAMPLE 11 
Example 10 is repeated with the exception of the hydroformylation reaction, 
which is effected at 110.degree. C. for 21 h. Result are listed in Table 
I. 
EXAMPLE 12 to 16 
64 mg of the LPtCl.sub.2, the ligand consisting of 
isopropylene-2,3-dihydroxy-bis(diphenylphosphino)-1,4 butane, are reacted 
in 25 cm.sup.3 of a solvent mixture containing 75% by volume benzene and 
25% by volume of propylene carbonate, with an iron compound (formula given 
in Table II) in a quantity such that the atomic ratio Fe/Pt is equal to 1. 
The reaction mixture is then contacted in an autoclave reactor with 
hydrogen under a pressure of 100 bars and at a temperature of 100.degree. 
C. for 2 h. After this, the autoclave is cooled and the gaseous mixture 
eliminated. The solution is transferred into a Schlenk tube and stored 
under argon. Spectroscopic analyses carried out as in Example 1 indicate 
that the product formed is a platinum hydride with a bridged bimetallic 
structure according to Formula (I), the combining anion being FeCl.sub.3. 
Each platinum hydride solution is then used in the hydroformylation of 
styrene by the process of Example 2, with the following exceptions: the 
reaction is carried out at 90.degree. C. under a pressure of 100 bars over 
24 h (18 h only for Example 13). Results obtained are listed in Table II. 
TABLE II 
______________________________________ 
Example Iron compound TT EB n/b 
______________________________________ 
12 Fe.sub.2 O.sub.3 
100 5,7 11,9 
13 Fe.sub.3 O.sub.4 
100 4,8 13,2 
14 Fe(OH)(OCOCH.sub.3).sub.2 
92 2,5 6,0 
15 Fe(OCOCH.sub.3).sub.2 
97 2,5 9,8 
16 Fe(OCH.sub.3).sub.2 
100 4,0 5,6 
______________________________________