Chemistry of inorganic compounds – Carbon or compound thereof – Binary compound
Reexamination Certificate
1999-01-06
2001-10-16
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Binary compound
C423S440000
Reexamination Certificate
active
06303093
ABSTRACT:
The present invention relates to a process for the preparation of novel or known transition metal carbon compounds (transition metal carbides) and their use as catalysts.
According to U.S. Pat. No. 5,385,716 (1995) and the European Patent Application 0 469 463 (1991), soluble transition metal/magnesium chloride complexes of general formula [M(MgCl)
m
(MgCl
2
)
n
], M=transition metal, m=1, 2, 3, n=0-1, the so-called “inorganic Grignard reagents”, can be prepared by the reaction of transition metal chlorides with magnesium or organomagnesium compounds in, e.g., tetrahydrofuran (THF).
Surprisingly, it has now been found that the inorganic Grignard reagents react with perchloroalkanes or -alkenes and with perchloroaromatics in, e.g., THF with elimination of the organic chlorine in the form of MgCl
2
and with the simultaneous formation of transition metal carbides of metals of groups 4 to 10 of the Periodic Table. Preferred are metals of groups 4 and 10, of which titanium, ruthenium, iridium and rhodium are more preferred. This finding has been surprising because the mentioned organic chlorine compounds are considered rather inert towards nucleophilic reactants, such as metals or organometallic compounds. The thus prepared, novel or known metal carbides are found to be effective as highly active heterogeneous hydrogenation catalysts. In the following, the invention will be further illustrated by way of some examples.
The Grignard reagents of ruthenium and iridium, [Ru(MgCl)
3
] and [Ir(MgCl)
3
], which can be prepared according to the cited literature, react with tetrachloroethene in a molar ratio of, e.g., 4:3 with elimination of MgCl
2
to form as yet unknown ruthenium and iridium carbides of empirical composition Ru
4
C
6
(MgCl
2
)
p
(THF)
q
(1) and Ir
4
C
6
(MgCl
2
)
p
(THF)
q
(2), respectively.
The black, diamagnetic solids 1 and 2, which are insoluble in diluted acids, are X-amorphous; after annealing (600° C.), reflections from Ru or Ir metal appear in the X-ray powder diagram. An examination of 1 and 2 by means of matrix-supported laser desorption/ionization mass spectrometry (MALDI; C. A. Mitchell et al., Angew. Chem. 1996, 108, 1076) yielded mass peaks which, among others, corresponded to Ru
x
C
y
, x=1-8, y=3-8, and Ir
x
C
y
, x=1-3, y=2, 3 (measurements made by Ch. Yeretzian, Inst. für Physikal. und Theoret. Chemie der TU München, 1995).
Solid 1 was also examined by means of the extended X-ray absorption fine structure (EXAFS) method, which yielded the following result:
TABLE 1
distance of back-
back-scattering atom
scattering atom [Å]
coordination number
Ru
2.64
2-3
C
2.08
2
According to the results obtained from the EXAFS spectrum, 1 consists of extremely small Ru clusters (3-4 Ru atoms) which are bonded to carbon atoms via direct bonds.
The Ru carbide 1, which can be isolated, proves to be a highly reactive heterogeneous catalyst for the hydrogenation of substrates considered difficult to hydrogenate, such as benzene, toluene and 3-pentanone, which can be hydrogenated quantitatively using 1 as a catalyst at room temperature (RT) and normal pressure to give cyclohexane, methylcyclohexane and 3-pentanol, respectively (FIG.
1
). When toluene is hydrogenated under these conditions, the catalyst shows a higher catalytic activity than that of the commercial Ru catalysts used for comparison (FIG.
2
). A catalytic activity which is higher than that of Ru black by some orders of magnitude is found using 1 as a catalyst in the hydrogenation of pyridine to piperidine (99.7%) under pressure (
FIG. 3
; cf. Tetrahedron: Asymmetry 1996, 71, 313). Under H
2
pressure, a rapid hydrogenation of toluene to give methylcyclohexane is also possible using 1 as a catalyst (FIG.
4
). Using 1 as a catalyst, phenol can also be hydrogenated to cyclohexanol. Thymol is hydrogenated to the four stereoisomers of menthol using 1 as a catalyst.
Further examples of transition metal carbides prepared from inorganic Grignard reagents and perchloroorganic compounds include Ru carbides from Ru(MgCl)
3
and carbon tetrachloride or hexachlorobenzene, and Ti carbides from [Ti(MgCl)
2
] (J. Organometal. Chem. 1993, 459, 87) and tetrachloroethene or carbon tetrachloride. The EXAFS spectrum of the titanium carbide obtainable from [Ti(MgCl)
2
] and tetrachloroethene exhibits a carbon deficiency (TiCl
1−x
) and in addition contains another unknown Ti-C component richer in carbon.
To date, metal carbides have been prepared by any of the following methods: 1. by combining the metals or metal oxides with carbon at temperatures above 1000° C.; 2. from metals or metal compounds and a gaseous carbonaceous compound (CO, CH
4
); 3. from gaseous precursors by vapor deposition for preparing carbide thin films; 4. reduction of metal halides with LiBEt
3
H in an organic solvent, e.g., THF.
The technical progress of the present process is that novel transition metal carbides as well as the previously known ones can be produced on a new synthetic route under extremely mild reaction conditions and with beneficial application properties (high catalytic activity, finely divided condition).
The experiments described in the following were performed in an argon atmosphere. The solvents used were deaerated and anhydrous.
REFERENCES:
patent: 4789534 (1988-12-01), Laine
patent: 4812301 (1989-03-01), Davidson et al.
patent: 5338523 (1994-08-01), Kristic
patent: 2747016 (1978-04-01), None
patent: 9528352 (1995-10-01), None
Bogdanović Borislav
Schwickardi Manfred
Hendrickson Stuart L.
Norris & McLaughlin & Marcus
Studiengesellschaft Kohle MBH
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