Process for the manufacture of metal-azomethine complex compounds

Metal-azomethine complex compounds are prepared by condensing metal-ammonia complex compounds with organic carbonyl compounds. The azomethine complexes obtained constitute suitable catalysts for various reactions.

This invention relates to a process for the manufacture of azomethine-metal 
complex compounds by condensation of metal-ammonia complex compounds with 
organic carbonyl compounds. 
Metal complex compounds carrying azomethines as ligands are of interest as 
they can be used for examining the behaviour of azomethines which are 
unstable in the free state. For example, the azomethine deriving from 
acetone and ammonia is only known as a polymer. Therefore, many attempts 
have been made to prepare metal complex compounds carrying azomethines as 
ligands. 
It has been proposed to use ketimines as starting compounds. But this 
process is limited, of course, to such ketimines as can be isolated in 
substance. Thus, the most interesting aliphatic azomethines cannot be 
prepared in this manner. It is also possible to synthetize 
ketimine-carbonyl-metal-complex compounds by reacting metal complexes 
containing as ligands carbenes besides carbonyl groups with oximes of 
ketones. The carbene complexes to be used are, however, difficultly 
accessible and, moreover, by this method the ketimine complexes can be 
obtained in a very poor yield only. 
The present invention provides a process for the manufacture of 
metal-azomethine complex compounds by reacting metal-ammonia complexes 
with organic carbonyl compounds of the formula R--CO--R' in which R 
represents an aromatic radical, preferably the phenyl radical, or an 
aliphatic radical, preferably an alkyl radical having from 1 to 15 carbon 
atoms, preferably 1 to 3 carbon atoms, R' represents -- independent of R-- 
an aryl radical, preferably a phenyl radical, or an aliphatic radical, 
especially an alkyl radical having from 1 to 15 carbon atoms, preferably 1 
to 3 carbon atoms, or R' represents hydrogen, or the formula R--CO--R' is 
an aliphatic cyclic ketone preferably having 5 to 7 and especially 6 
carbon atoms. 
The metal-ammonia complex compounds to be used have as central atom the 
atom of an element of a subgroup, preferably of subgroups V to VIII and 
more preferably of subgroup VI of the periodic table. 
The metal-ammonia complex can carry from 1 to 6 ammonia ligands for each 
central atom, preferably from 1 to 3 and more preferably 1 ligand per 
central atom. Besides ammonia the metal-ammonia complex compounds may 
carry further ligands, which are, however, immaterial to the process of 
the invention. It proved especially advantageous to have carbonyl 
compounds as further ligands. 
The metal-ammonia complex compounds can be present as cation, as anion or 
as neutral molecule. The use of uncharged ammonia complexes proved to be 
especially advantageous. 
Suitable metal-ammonia complexes are, for example, (OC).sub.5 CrNH.sub.3, 
(OC).sub.5 MoNH.sub.3 or (OC).sub.5 WNH.sub.3. 
To carry out the reaction in the most simple case the metal-ammonia complex 
is dissolved in the respective carbonyl component and the solution is 
allowed to stand for a while. According to the preferred embodiment of the 
reaction the carbonyl compound and the metal-ammonia complex are heated to 
30.degree.-90.degree. C, in general for 2 to 20 hours, in the presence of 
a water-absorbing agent until the reaction is complete. In many cases the 
addition of a small amount of a base, for example potassium methanolate 
proved to be of advantage. 
The process proceeds according to the following reaction equation: 
##STR1## 
in which n stands for an integer of from -3 to +3, preferably zero, 
L represents identical or different ligands, 
M is a central atom (of an element of a sub group), 
y means an integer of from +1 to +6, preferably +1 to +3, more preferably 
+1, and 
x means an integer of from zero to +5 with 4 being less than or equal to 
(x+y) which is less than or equal to 6. 
It results from the above equation that a charge of the metal complex 
remains unchanged during the reaction. Furthermore, water is formed in the 
reaction. 
It proved particularly advantageous to remove the generated water from the 
reaction mixture during the reaction. 
The carbonyl compounds can be used as reaction medium either undiluted or 
in admixture with solvents which are inert under the reaction conditions. 
Suitable solvents are especially polar as well as non-polar organic 
solvents such as methanol, tetrahydrofurane, dioxane, petroleum, ether, 
benzene, or toluene. When toluene is used the water formed can be 
distilled off in the form of an azeotrope. 
The reaction in solution is carried out at a temperature of from 20.degree. 
to 150.degree. C, preferably 50.degree. to 100.degree. C. The reaction can 
be performed with equimolar amounts of the carbonyl component and ammonia 
complex, but to improve the yield an excess of the carbonyl component is 
desirable. It is advantageous to maintain a molar proportion of carbonyl 
component to ammonia complex of from 1:1 to 1,000 to 1, preferably 50:1 to 
500:1. 
In general, the metal-ammonia complexes to be used according to the 
invention are readily accessible. For example, ammonia complexes of the 
general formula (CO).sub.5 MNH.sub.3 can be easily prepared from the 
corresponding hexacarbonyl-metal compounds of the formula M(CO).sub.6 and 
ammonia. Hence, the process of the invention permits in simple manner the 
synthesis of azomethine complex compounds from starting compounds that are 
easy to obtain and in a good yield. 
When volatile metal-ammonia complexes are used the process can also be 
carried out in the gaseous phase. Difficultly volatile metal-ammonia 
complex compounds react also when a current of the gaseous carbonyl 
compound is passed thereover at elevated temperature. 
The metal-azomethine complex compounds obtained by the process of the 
invention can be used in many fields. They are suitable, for example, as 
catalysts for the oligomerization of acetylene with formation of benzene 
and cyclooctatetraene. Especially good results in this respect are 
obtained with the corresponding, nickel, cobalt, iron and chromium 
compounds. Compounds of the formula (CO).sub.5 M.sup.VI (NH=CRR'), i.e. 
compounds which still contain carbonyl groups and are derived from 
elements of subgroup VI, are expecially suitable for the trimerizatin of 
diphenylacetylene with formation of hexaphenyl benzene. 
Azomethine complex compounds containing as central atom an element of 
subgroup VIII and carbonyl groups as ligands can be used as catalysts for 
the reaction of carbon monoxide with olefins or alcohols with formation of 
carboxylic acids.

The following examples illustrate the invention. 
EXAMPLE 1 
1.00 g of (OC).sub.5 CrNH.sub.3 (4.8 mmols) in 30 ml of acetone and 15 mg 
of KOCH.sub.3 and 2 g of MgSO.sub.4 were heated to boil for 4 hours, the 
reaction mixture was filtered and evaporated to dryness whereby the 
compound (OC).sub.5 Cr--NH.dbd.C(CH.sub.3).sub.2 remained behind as a 
yellow oil. After purification, preferably by chromatography in 
pentane/toluene (1:1 mixture) at -20.degree. C over SiO.sub.2, 0.89 g of 
crystalline (OC).sub.5 Cr--NH.dbd.C(CH.sub.3 ).sub.2, i.e. 75 % of the 
theory, calculated on (OC).sub.5 CrNH.sub.3, was obtained. 
EXAMPLE 2 
1.00 g of (OC).sub.5 CrNH.sub.3 (4.8 mmols) in 30 ml of cyclohexanone, 15 
mg of KOCH.sub.3 and 2 g of molecular sieve (4 A) were heated for 5 hours 
to 55.degree. C. Next, the reaction mixture was filtered and evaporated to 
dryness whereby (OC).sub.5 Cr--NH.dbd.C.sub.6 H.sub.10 remained behind as 
solid matter. After purification, preferably by chromatography in toluene 
at -20.degree. C over SiO.sub.2, 1.09 g of crystalline (OC).sub.5 
Cr--NH.dbd.C.sub.6 H.sub.10, corresponding to 78 % of the theory, 
calculated on (OC).sub.5 CrNH.sub.3, were obtained.