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3,065,250 United States Patent Office Patented Nov. 20, 1962 i 2 3,065,250 stable in air, becoming brown immediately upon contact NTRLE-METAL CARBONY, COMPLEXES with air. Dewey R. Levering, Wilisagton, Rel, assignor to Her A sample of the product was analyzed under an inert cales Powder Company, Winnington, Del, a corpora atmosphere for percent carbon, , and tio of Delaware molybdenum. The results of the analysis compared with No Brawing. Filled May 13, 1960, Ser. No. 28,841 the theoretical percentages for (CH3CN)Mo(CO)3 are 26 Caistas. (C. 260-429) tabulated below. The present invention relates to new and useful metal carbonyl complexes and to the method of their 10 Found ''neory preparation. More specifically, the invention relates to

Percent C------35.4 35.56 nitrile-metal carbonyl complexes where the metal is a Percent H. 2.4 3.0

group VI-B metal (chromium, molybdenum or tungsten) Percent N- 12.35 13.92 according to the periodic system (see Lange's Handbook Percent Mo- 32.6 31.65 of Chemistry, eighth edition, pages 56–57, 1952). Some hydrogen -metal carbonyl complexes have 5 The product was identified as (CH3CN)Mo(CO)3 been reported. However, complexes of which is in agreement with the evolution of three moles and a group VI-B metal carbonyl have never been re of per mole of molybdenum carbonyl. ported, and attempts to prepare them have been unsuc The product was insoluble in , carbon tetra cessful. The present invention is based on the unforeseen 20 chloride, and ; somewhat soluble in ; and discovery that undergo a general reaction with soluble in , glycol , group VI-B metal carbonyls to form new and useful tetrahydrofuran and dimethylformamide. nitrile-metal carbonyl complexes, which result from the The infrared spectra of the product was obtained and replacement of one or more carbonyl groups of the metal found to be greatly different from the spectra of carbonyl by the nitrile. Mo(CO)6. In both cases the determinations were made More particularly, the present invention relates to crys in acetonitrile. - talline, yellow to orange complexes of a nitrile and a It was found that when the exact same reaction was group V-B metal carbonyl, said complexes having the attempted under identical conditions in a sealed reaction general formula vessel, thereby preventing the release of carbon monoxide, LR(CN). IMCCO) 30 changed.the acetonitrile and molybdenum carbonyl remained un in which R is a hydrocarbon radical or a hydrocarbon radical containing as a substituent a nucleophilic group, EXAMPLE 2 i.e., a group that increases the electron availability in the This example shows that the reaction between the metal triple bond region of the nitrile group, M is a hexaco carbonyl and nitrile is an equilibrium reaction and can be ordinated atom of a metal of group VI-B of the periodic 35 readily reversed by a small partial pressure of carbon table, x is an integer from 1 to 2 inclusive, n is an integer monoxide. - from 1 to 3 inclusive, y is an integer from 2 to 5 inclusive A Sample of an acetonitrile-molybdenum carbonyl com and z is an integer from 1 to 2 inclusive, and to the plex (described in Example 1) in cyclohexane solution method of preparing such complexes which comprises was placed in a stainless steel autoclave in the absence of either (1) reacting a group VI-B metal carbonyl 40 air. The autoclave was flushed with carbon monoxide, M(CO)6) with a nitrile having the formula R(CN). and the complex was allowed to react at 3000 p.s.i.g. where R and x are as above defined, under conditions carbon monoxide pressure at a temperature of 80 C. for where carbon monoxide is removed as it is formed or (2) 6 hours. On cooling molybdenunn carbonyl and aceto reacting a preformed nitrile-metal carbonyl complex hav nitrile were recovered. ing the general formula 45 EXAMPLE 3 A reaction was conducted as in Example 1 using 5.2 R" (CN)] (M(CO), parts of molybdenum carbonyl, 7.8 parts of acetonitrile in which M, x, n, y and z are as above defined and R' is and 68.4 parts of n-heptane reaction medium. After 13 a hydrocarbon radical or a hydrocarbon radical contain hours at a reflux temperature of 72-74 C. the evolution ing as a substituent a nucleophilic group, with a nitrile 50 of carbon monoxide ceased indicating the completion of having the formula R(CN), where R and x are as above the reaction. Approximately three moles of carbon mon defined, thereby replacing the nitrile component of the oxide were evolved per mole of molybdenum carbonyl. complex with another nitrile component. During the reaction period, the reaction medium became Before describing the invention in greater detail, the 55 yellow in color and a bright yellow crystalline solid pre following examples are presented for purpose of illustra cipitated. The solid was isolated by filtration in the ab tion, parts and percentages being by weight unless other wise specified. sence of air. The product was identified as EXAMPLE 1. (CH3CN)Mo(CO) A reaction vessel fitted with a condenser and means to 60 The results of an elementary analysis are tabulated below. measure the amount of carbon monoxide evolved was charged with 5.2 parts of mobdenum carbonyl and flushed with nitrogen. Then 78.3 parts of dry acetonitrile Found Theory were added and the reaction mixture refluxed at a tem Perent C------37.78 35.66 perature of 80-81. C. for 3 hours, carbon monoxide be Percent H------2.98 3.0 ing evolved the whole time, approximately 3 moles of 65 Percent N------13.02 13.92 carbon monoxide being evolved per mole of molybdenum EXAMPLE 4 carbonyl. The Solution became yellow soon after the A reaction was conducted as in Example 1 using 5.2 mixture began to reflux and all of the molybdenum car parts of molybdenum carbonyl, 7.8 parts of acetonitrile bonyl dissolved. After removing the excess acetonitrile 70 and 39.6 parts of methanol as diluent. The reaction mix under vacuum at room temperature, there remained 5.8 ture was refluxed for 5 hours at a temperature of 65° C. parts of a yellow crystalline solid which was very un with evolution of carbon monoxide. A light yellow solu 3,065,250 3. 4. tion resulted, and after evaporation of the solvent under as (CHCHCN)Mo(CO)4. The results of an elemen vacuum, a yellow crystalline solid, identical to the com tary analysis were as follows: plex described in Example 1, was obtained. Found Theory EXAMPLE 5 A reaction vessel fitted with a condenser and means to Percent C------35.5 37.75 measure the amount of carbon monoxide evolved was Percent H------3.08 3.17 charged with 15.6 parts of molybdenum carbonyl and Percent N------8.55 8.80 flushed with nitrogen. Then 30 parts of benzonitrile in Percent Mo------32.78 30.16 68.4 parts of n-heptane were added and the reaction mix EXAMPLE 9. ture refluxed at a temperature of 101-102 C. for 14 10 hours. Carbon monoxide equivalent to 3.06 moles per In another experiment conducted in the same manner mole of molybdenum carbonyl was evolved. During the as Example 8, 15 parts of n-capronitrile was substituted reaction a yellow crystalline solid precipitated and was for the . Refluxing was conducted at a tem isolated by filtration in the absence of air. The product perature of 101° C. A brownish yellow crystalline prod was identified as (C6H5CN)Mo(CO)3. The results of 5 uct was obtained and exhibited an infrared spectra typical an elementary analysis were as follows: of a nitrile-molybdenum carbonyl complex. EXAMPLE 10 Found Theory A reaction was conducted as in Example 1 using 5.2 20 parts of molybdenum carbonyl, 11.7 parts of p-methyl Percent C------58.69 58.90 Percent H. 3.18 3.09 benzoinitrile and 68.4 parts of heptane as the reaction Percent N.-- 8.4 S. 60 medium. After refluxing at a temperature of 101° C. Percent Mo- 20.67 19.64 for 9 hours, the reaction was stopped. Carbon monoxide equivalent to 2.1 moles per mole of molybdenum car EXAMPLE 6 25 bonyl was evolved. During the reaction a golden crys Molybdenum carbonyl (5.2 parts) was charged to a talline solid precipitated and was isolated by filtration in reaction vessel as described in Example 1. Then 9.5 the absence of air. The product was identified as parts of adiponitrile dissolved in 68.4 parts of heptane (CH3CHCN) 2.Mo(CO ) 4. were added and the reaction mixture refluxed at a tem 30 perature of 100-101° C. for about 23 hours. During The results of an elementary analysis were as follows: this time, an amount of carbon monoxide equivalent to 3.1 moles per mole of molybdenum carbonyl was evolved. Found Theory The reaction mixture separated into two phases during Percent C------54.18 53.34 the reaction, the lower phase of which crystallized on 35 Percent H------3.32 3.13 cooling. A yellow crystalline product was removed by Percent N------6, 19 6.22 filtration in the absence of air. The product was identi Percent Mo------22.2 21.33 fied as INC(CH2)4CNIMo(CO)3. The results of an elementary analysis were as follows: EXAMPLE 1. 40 A reaction was conducted as in Example 1 using 5.2 Found Theory parts of molybdenum carbonyl, 8.0 parts of and 68.4 parts of heptane as the reaction medium. After Percent C------50.87 50.00 refluxing at a temperature of 100° C. for 14 hours, the Percent H------4.63 4.79 evolution of carbon monoxide practically ceased and the Percent N------1.93 16.66 reaction was stopped. During this time the reaction me dium became yellow in color and an orange crystalline EXAMPLE 7 solid precipitated. This crystalline solid was recovered A reaction was conducted exactly as in Example 6 ex by filtration in the absence of air. Infrared analysis of cept the amount of adiponitrile reactant was reduced to a sample of the crystalline solid failed to disclose the 3.2 parts. Carbon monoxide evolution ceased after 11 presence of unsaturation. Another sample was analyzed hours and a light yellow crystalline solid was isolated 50 for percentage carbon, hydrogen, nitrogen and molyb from the lower phase of the reaction mixture. The denum. The results of the analysis compared with the product was identified as theoretical percentages for (CH2=CHCN)Mo(CO) are (CO)3MoNC(CH2)4CNMo(CO) tabulated below: 5 5 The results of an elementary analysis were as follows: Found Theory Found Theory Percent C.------39.59 37.27 Percent H------2.85 2, 34 Percent N------0.51 0.86 Percent C------42.02 42, 12 Percent Mo------34.44 37.7 Percent H------3.26 3.53 60 Percent N------1.03 2, 28 Percent Mo------26. 48 28.04 While the exact structure of this complex is unknown, the following structure is probable. EXAMPLE 8 CO A reaction was conducted as in Example 1 using 5.2 HC-C C-CH parts of molybdenum carbonyl, 7.8 parts of propionitrile and 68.4 parts of heptane reaction medium. After re | --> fluxing at a temperature of 88°-90° C. for 9 hours, the HC N J N CH, evolution of carbon monoxide became very slow and the EXAMPLES 2-2. reaction was stopped. The total carbon monoxide evolved 70 amounted to approximately two moles per mole of molyb A series of reactions between various metal carbonyls denum carbonyl. The reaction mixture consisted of two and various nitriles was conducted by the same method liquid phases. On cooling the lower phase crystallized as described in EXAMPLE 1. The metal carbonyl, and a light yellow crystalline solid was isolated by filtra nitrile, diluent (where one is used), reaction time, reac tion in the absence of air. The product was identified 75 tion temperature, moles of carbon monoxide evolved per 5 3,035,250 R mole of metal carbonyl used and the calculated number remained dissolved throughout the hydrogenation re of carbonyl groups replaced are given in Table I. action.

TABLE I

Parts Parts Parts Reac- Reac- MolesCO Numberof car Ex. Metal car. of car- Nitrile of Diluent of dil- tion tion. evolved, bonyl Color of crystal No. bonyl bonyl nitrile lent time, temp., mole car- groups line conplex hr. o C bonyl replaced used 2--- Cr(CO)6---- 2.2 Aceto--- 39 - 25.5 82 3.0 3 Light yellow. 13--- W(CO)6----- 3.5 i----- do--- 39 2.5 84-85 2.6 3 Greenish-yellow. 14. -- Mo(CO)8--- 5.2 isobutyro- 79 - 7 04 2.4 2 Yellow. i5--- S388: - - 5.2 Succino ---- 6 Edeptane. 68.4 2 101-02 2.7 3 Greenish-yellow. 16. Mo(CO)6-- 5.2 BenZO------2 ---do------68.4 7 00 0.5 1 Deep yellow. 17--- Mo(CO)6--- 5.2 3-blatene.------O --to------68.4 12.5 90-95 3.9 4 Yellow. 18--- Mo(CO)8--- 5.2 p-Chlorobenzo.--- - 15 ---do 6S. 4 10.0 102 2.8 2 Brilliant yellow. 19 - Mo(CO)6-- 5. 2 Cyanoacetamide------3. 68.4 0.5 99 1.9 2 Yellow. 20--- Mo(CO)6--- 5.2. Ethylcyanoacetamid 10 68.4 32.6 105 2.5 3 ED.o. 21--- Mo(CO)6--- 5.2 p-Methoxybenzo.------13.3 68.4 12 100 2.9 3 light yellow.

EXAMPLES 22-24 The complexes of this invention can be characterized Three preparations were run in which nitrile-molyb by the general formula denum carbonyl complexes were prepared by the displace (ment of acetonitrile with another nitrile. In each Tun 25 a solution of acetonitrile-molybdenum carbonyl complex where R, M, x, n, y and z are as previously defined. was prepared from 5.2 parts of molybdenum carbonyl The relative values of n, x, y and z. may vary considerably and 78.3 parts of acetonitrile exactly as described in according to the nature of the nitrile employed in mak Example 1. ing the complex. Where, for instance, the nitrile is a Example 22-Benzonitrile (10 parts) was added to 30 saturated mononitrile, x and z are 1 and the sum of n the first solution containing the acetonitrile complex at and y is 6. Acetylenically unsaturated mononitriles be a temperature of 80-81 C. The excess acetonitrile have similarly. was removed under vacuum leaving a yellow crystalline In the case of a dinitrile, x is, of course, 2 and the solid which was identical with the crystalline solid pre relative values of x, n, y and z are such that there is a pared in Example 5. 35 total of at least 6 nitrile and carbonyl groups combined Example 23-n-Capronitrile (6 parts) was added to for each atom of metal. Thus, complexes having the the second solution containing the acetonitrile complex respective general formulae at a temperature of 79-80 C. The excess acetonitrile was removed under vacuum leaving a crystalline product (NC-R-CN)M(CO)6- (Example 6) identical to the product of Example 9. 40 and Example 24-Malononitrile (4 parts) was added to (CO)5-M (NC-R-CN)M(CO)6- (Example 7) the third solution containing the acetonitrile complex can be made from dinitriles, the first formula represent at a temperature of 80-82° C. The excess acetonitrile ing the type of complex obtained when an excess of was removed under vacuum leaving a crystalline Solid. dinitrile is used as a reactant and the second formula Infrared analysis revealed that the solid was a mal 45 representing the type obtained when an excess of metal ononitrile-molybdenum carbonyl complex. carbonyl is employed. In the preceding instances, the coordinate bonds are EXAMPLE 25 between the metal and the nitrile and carbonyl groups. This example shows the use of a complex of this Olefinic nitriles, on the other hand, react with group invention as a catalyst in the hydrogenation of a nitrile. 50 VI-B metal carbonyls to form complexes in which An autoclave was charged to one half its volume with each mole of nitrile replaces two carbonyl groups. The acetonitrile and flushed with nitrogen. Then an amount ostensible reason for this is that both the nitrile group of (CHCN)Mo(CO)3 (the acetonitrile-molybdenum and the olefinic bond are involved in the complex (see carbonyl complex described in Example 1) equivalent Example 11). In any event, in such complexes the to 7.5% by weight of the total reaction mixture was 55 total of nitrile groups, carbonyl groups and olefinic added under nitrogen atmosphere. The complex cat bonds is 6 per atom of metal. alyst immediately went into solution. Next, the auto In accordance with this invention, the nitrile-metal clave was evacuated and pressured to 4000 p.si. with carbonyl complexes can be prepared of any nitrile-Sub hydrogen. After 4 hours at a temperature of 200 C. stituted hydrocarbon or of a nitrile-substituted hydro the reaction was cooled and the resulting Solution frac 60 carbon that contains a nucleophilic group, i.e., a group tionally distilled. The sole reaction product was triethyl that increases the electron availability in the triple bond amine obtained at a conversion of 45%. The complex region of the nitrile group. Electrophilic groups, i.e., catalyst remained in solution throughout the hydro electron withdrawing groups, tend to decrease the ability genation. of the nitrile to form these complexes. Thus, while 65 alkyl, alkoxy and chloro-substituted aryl nitriles readily EXAMPLE 26 form these new complexes, nitro-substituted aryl nitriles A hydrogenation of benzonitrile to dibenzylamine was do not, the nitro group being a strong electrophilic group. carried out under the same general conditions described Thus, the nitrile can be a hydrocarbon nitrile, an oxyhy in Example 25. However, the nitrile reactant was first drocarbon nitrile, an alkoxyhydrocarbon nitrile, a ni diluted with an equal volume of isopropyl ether, and 70 trile-substituted aliphatic amide, a nitrile-substituted (CH3CN)Mo(CO)3 (the benzonitrile-molybdenum car aliphatic ester, a halo-substituted aromatic nitrile, etc. Hence, R in the above formulae can be alkyl, alkenyl, bonyl complex described in Example 5) was used as the alkynyl, cycloalkyl, cycloalkenyl, alkaryl, aralkyl, aryl, catalyst. The sole reaction product was dibenzylamine hydroxyalkyl, alkoxyalkyl, alkoxyaryl, haloaryl, carbam obtained at a conversion of 58%. The complex catalyst 75 ylalkyl, carbamylaryl, carbalkoxyalkyl, etc. Exemplary of 3,065,250 7 3. the nitriles of which the new nitrile-metal carbonyl depends upon the number of CN groups present on each complexes of this invention can be prepared are nitrile nitrile compound since a mononitrile does not form a substituted hydrocarbons such as acetonitrile, propioni complex with more than one metal carbonyl. However, trile, n-, isobutyronitrile, n-valeronitrile, suc the ratio of dinitrile to metal carbonyl in the reaction cinonitrile, adiponitrile, n-capronitrile, acrylonitrile, 3 mixture will effect the number of metal carbonyl groups butenenitrile, propiolonitrile, benzonitrile, p-toluonitrile, appearing in the complex as shown in Examples 6 and 7. phenylacetonitrile, naphthonitrile, etc.; nitrile-substituted B. Displacement or Indirect Method oxyhydrocarbons such as 3-hydroxy-butyronitrile, p methoxy-benzonitrile, etc.; nitrile-substituted amides such The group or groups comprising the nitrile component as cyanoacetamide, etc.; nitrile-substituted esters such as 10 of the nitrile-metal carbonyl complex of this invention ethylcyanoacetate, etc.; and halo-substituted aromatic can be displaced by another nitrile compound or com nitriles such as p-chlorobenzonitrile, etc. pounds as shown in the equation As demonstrated in the examples, the new nitrile metal carbonyl complexes of this invention are prepared by either of two methods, 5 where R, R', M, x, n, y and z are the same as defined (A) The direct reaction of a nitrile with a group VI-B above. metal carbonyl. This reaction is also an equilibrium but can be forced (B) The displacement of a nitrile from a preformed to the right by either adding an excess of the R(CN) or nitrile-metal carbonyl complex with another nitrile. removing the R' (CN), in cases where the latter is the A. Direct Method more volatile nitrile, or by both means. For example, when a low boiling nitrile is displaced, such as acetonitrile, Metal carbonyls of the group VI-B metals, i.e., the reaction can be forced to completion by evaporation molybdenum carbonyl, chromium carbonyl and tungsten or distilling the lower boiling nitrile, carbonyl react with any of the nitriles defined above. The displacement method of this invention can be con As shown in the examples, this reaction can be carried ducted, in an inert diluent or in an excess of R(CN), out in an inert liquid diluent or merely in an excess of the nitrile reactant. The same inert solvents can be em the nitrile reactant. The latter procedure is preferable ployed in this method as were employed in the direct in case of liquid, high boiling nitriles because the com method. Any reaction temperature below the lower of plexes of this invention are soluble in nitriles but not (1) the decomposition temperature of the complex being in most other diluents. However, an inert diluent can 30 be employed if the reaction is conducted at reflux tem formed and (2) the decomposition temperature of the perature and the nitrile reactant would decompose the complex from which it is being formed can be used in complex sought. Exemplary of inert diluents which can this method. In general, the reaction will be carried out be employed are hydrocarbons such as n-heptane, n at a temperature beiow 140 C. Both the reaction and hexane, n-octane, cyclohexane, etc., ethers such as di the recovery of the complex product are preferably car isopropyl ether, dipropyl ether, diisobutyl ether, etc., ried out in the absence of air because of the sensitivity and alcohols such as methanol, , isopropyl al of the complex. cohol, etc. Exemplary of some of the nitrile-metal carbonyl com The reaction between a nitrile and a group V-B metal plexes that can be prepared by this method of the inven carbonyi is an equilibrium which is normally to the left 40 tion are acetonitrile-molybdenum carbonyl, propionitrile but can be shifted in the direction of the formation of molybdenum carbonyl, isobutyronitrile-chromium car the complex by removal of carbon monoxide. Therefore, bonyl, benzonitrile-molybdenum carbonyl, benzonitrile since the method of this invention is reversible, i.e. can tungsten carbonyl, succinonitrile-molybdenum carbonyl, easily be stopped or reversed by a small partial pressure malononitrile-molybdenum carbonyl, etc. of carbon monoxide, it must of necessity be conducted 45 The method used in the preparation of a desired com under conditions in which carbon monoxide is removed. plex depends on the properties of the specific reactants The reaction between the nitrile and the metal carbonyl and the specific complex desired. While many of the is generally carried out by heating a mixture of the re nitrile-metal carbonyl complexes of this invention can actants to a temperature of from about 40 C. to about easily be prepared by the direct method, others are more 140° C. at or about atmospheric pressure, while removing 50 readily prepared by displacing the nitrile of an easily the by-product carbon monoxide as it is formed. Lower prepared complex. temperatures may be used but generally are not practical, There are, of course, still other indirect methods of unless the process is operated at reduced pressure, due preparing the complexes of this invention such as the to the slowness of the reaction at such temperatures. displacement of an aromatic component of an aromatic One of the simplest methods of carrying out the reaction metal carbonyl complex with a nitrile or the displacement is by refluxing the reaction mixture at atmospheric or of an amine component of an amine-metal carbonyl com near atmospheric pressure, whereby the carbon monoxide plex with a nitrile. For example, either mesitylene is removed as it is formed. Refluxing can be conducted molybdenum tricarbonyl complex, pyridine-molybdenum over a range of temperatures up to about 140 C., at tricarbonyl complex or n-butylamine-molybdenum tricar which temperature the complexes begin to decompose. 60 bonyl complex when treated with an excess of acetonitrile, The refluxing period will vary with various reactants, the yield the acetonitrile-molybdenum tricarbonyl complex of temperature of the reflux, etc., but a sufficient period of this invention. time is readily ascertainable since the progress of the The nitrile-metal carbonyl complexes of this invention reaction is indicated by the amount of carbon monoxide are yellow to orange crystalline solids at room tempera evolved. Another method of conducting the reaction ture which decompose on exposure to air, and exhibit while removing carbon monoxide is by sparging the reac distinctive infrared spectra. In general, they are soluble tion mixture with an inert gas such as nitrogen. in most nitriles and to some extent in methanol, ethanol, Recovery of the nitrile-metal carbonyl complex from tetrahydrofuran and the various glycol ethers but are the reaction medium can be accomplished in a number essentially insoluble in other common solvents. of ways but because of its sensitivity to , the re The complexes of this invention possess a variety of covery must be carried out in the absence of air. uses. They can, for example, be used for the homoge The number of nitrile which appear in the neous catalytic hydrogenation of nitriles to secondary or final complex depends primarily upon the ratio of nitrile tertiary amines. By homogeneous hydrogenation is meant reactant to metal carbonyl. The number of metal car the catalyst is completely soluble in the reaction medium bonyl groups which appear in the final carbonyl complex and stays in solution during the whole reaction. 8,065,250 Another example of the use of the complexes of this 10 invention as catalysts is in the field of polymerization 16. The method of claim 15 wherein the metal is molyb such as the polymerization of butadiene. Still another denum. use is in the condensation of and 17. The method of claim 15 wherein the nitrile is aceto derivatives. nitrile. What I claim and desire to protect by Letters Patent is: 18. The method of claim 15 wherein the nitrile is ben 1. A crystalline complex of a nitrile and a group VI-B Zonitrile. metal carbonyl, said complex having the general formula pionitrile.19. The method of claim 15 wherein the nitrile is pro (R(CN)M(CO)). 20. The method of claim 15 wherein the nitrile is adipo in which R is a nucleophilic group selected from the 0. nitrile. class consisting of hydrocarbon groups, oxyhydrocarbon 21. The method of claim 15 wherein the nitrile is acry groups, alkoxyhydrocarbon groups, aliphatic amide lonitrile. groups, aliphatic ester groups, and halo-substituted aro 22. The method of preparing a crystalline complex of matic hydrocarbon groups, M is a hexacoordinated metal a nitrile and a group VI-B metal which comprises react of group VI-B of the periodic table, x is an integer from 5 ing a nitrile-metal carbonyl complex having the general 1 to 2 inclusive, n is an integer from 1 to 3 inclusive, y formula (R' (CN). IMCCO)1, in which R' is a nucleo is an integer from 2 to 5 inclusive and z is an integer philic group selected from the class consisting of hydro from 1 to 2 inclusive, wherein x, n, y and z have one of carbon groups, oxyhydrocarbon groups, alkoxyhydrocar the relationships selected from (a) x and z are each 1 bon groups, aliphatic amide groups, aliphatic ester groups, and the sum of n-y is 6, (b) x and z are each 1 and the 20 and halo-substituted aromatic hydrocarbon groups, M is sum of n--y is 4 (c) x is 2, z is 1 and the Sum of n--y a hexacoordinated metal of group VI-B of the periodic is 6, and (d) x and z are each 2 and the sum of n-hy is 6. table, x is an integer from 1 to 2 inclusive, n is an integer 2. The complex of claim 1 wherein the metal is chro from 1 to 3 inclusive, y is an integer from 2 to 5 inclu mium. sive and z is an integer from 1 to 2 inclusive with a dif 3. The complex of claim 1 wherein the metal is molyb 25 ferent nitrile from the nitrile component of said nitrile denum. metal carbonyl complex, said different nitrile having the 4. The complex of claim 1 wherein the metal is tung formula R(CN), where R is a nucleophilic group selected Stea. from the class consisting of hydrocarbon groups, oxy 5. The complex of claim 1 wherein the nitrile is an hydrocarbon groups, alkoxyhydrocarbon groups, aliphatic aliphatic hydrocarbon nitrile. , 30 amide groups, aliphatic ester groups, and halo-substituted 6. The complex of claim 1 wherein the nitrile is an aromatic hydrocarbon groups, R being a different sub aromatic hydrocarbon nitrile. stituent group from R and x is an integer from 1 to 2 7. The complex of claim 1 wherein the nitrile is an inclusive, thereby replacing the nitrile component of the alkoxy-substituted aromatic hydrocarbon nitrile. 35 complex with another nitrile component, x, n, y and z 8. The complex of claim 1 wherein the nitrile is a in said formula having one of the relationships selected chloro-substituted aromatic hydrocarbon nitrile. from (a) x and z are each 1 and the sum of n--y is 6, 9. The complex of claim 5 wherein the nitrile is aceto (b) x and z are each 1 and the sum of n-ty is 4, (c) c nitrile. is 2, z is 1 and the sum of n-ty is 6, and (d) x and z are 10. An acetonitrile-molybdenum carbonyl complex 40 each 2 and the sum of n-ty is 6. having the formula (CH3CN)3Mo(CO)3. 23. The method of claim 22 wherein said nitrile-metal 11. A benzonitrile-molybdenum carbonyl complex hav carbonyl complex is an acetonitrile-molybdenum carbonyl ing the formula (CHCN)Mo(CO)3. complex. 12. An adiponitrile-molybdenum carbonyl complex 24. The method of claim 23 wherein said different having the formula INC(CH2)CNMo(CO)3. nitrile is benzonitrile. 13. A propionitrile-molybdenum carbonyl complex hav 25. The method of claim 23 wherein said different ing the formula (CHCN)2Mo(CO)4. nitrile is capronitrile. 14. Acrylonitrile-molybdenum carbonyl complex hav 26, The method of claim 23 wherein said different ing the formula (CH=CHCN)2MoCCO)2. nitrile is malononitrile, 15. The method of preparing a crystalline complex of 50 a nitrile and a group VI-B metal which comprises react References Cited in the file of this patent ing a metal carbonyl having the formula M(CO)6 where Natta et al.: “La Chimica E L'industria," vol. 40, No. M is a hexacoordinated metal of group VI-B of the 12, pp. 1003-1007, 1958. periodic table with a nitrile having the formula R(CN). Wertheim: “Organic Chemistry,' third edition, McGraw where R is a nucleophilic group selected from the class Hill Book Co., Inc. (1951), p. 327 relied on. consisting of hydrocarbon groups, oxyhydrocarbon Klages et al.: "Chemische Berichte," vol. 83, No. 6, groups, alkoxyhydrocarbon groups, aliphatic amide October 1950, pp. 501-508 relied on. groups, aliphatic ester groups, and halo-substituted aro Hieber et al.: "Chemische Berichte,' vol. 89, No. 3, matic hydrocarbon groups, and x is an integer from 1 to March 1956, pp. 616-619 relied on. 2 inclusive under conditions where carbon monoxide is 60 Huber: “Uber Neue, nicht-Salzartige, Komplexe des removed as it is formed. Molybdan (XI)," p. 32 relied on.