The Amine Method for Preparing Ferrocene
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R. L. PRUETT and E. L. MOREHOUSE Research Laboratories, Linde Air Products Co., Tonawanda, Ν. Y.
Ferrocene can be prepared on a laboratory or large -scale basis by the reaction of ferrous chloride and sodium cyclopentadienide in an amine solvent. The basicity of the latter is an important factor in the yield of ferrocene obtained. Other factors affecting the course of the reaction as well as the yield are dis cussed.
A recent review article by Pauson (6) describes the preparation, properties, and reactions of ferrocene [or bis (cyclopentadienyl) iron] and related compounds. Several reactions are listed as possible methods for preparing ferrocene: 1. Cyclopentadiene and iron powder at high temperature (δ). 2. Cyclopentadienylmagnesium halide with ferric halide (If). 3. Cyclopentadienylmagnesium halide with ferric acetylacetonate (7,11). 4. An alkali metal cyclopentadienide with ferrous or ferric halides (8,9). 5. A n alkali metal cyclopentadienide with iron hexammine salts (2,3). 6. Cyclopentadiene with iron halide in an amine solvent (1,10). The Linde Laboratories, early in their work on organometallic compounds, de veloped two of these methods for the preparation of ferrocene. The reaction of iron (II) chloride with sodium cyclopentadienide in ethylene glycol dimethyl ether (DMC) solvent: DMC FeCl + 2NaC H 2
6
5
> (C H ) Fe + 2NaCl 6
6
(1)
2
and the reaction of cyclopentadiene with iron halides in diethylamine solvent: 2C H + FeX + 2R N -> (C H ) Fe + 2R N H X (2) These two methods appear to be the most attractive possibilities for large-scale prepara tion of ferrocene. The second method was later published by Wilkinson and coworkers as a laboratory preparation of ferrocene (1), even though their first attempts gave very low yields. This paper shows the applicability of the amine method for the preparation of ferrocene on either a laboratory or production scale. The reaction given in Equation 2 gives excellent yields of ferrocene, 85 to 90% of theory, when a highly basic amine is used. The success of this reaction apparently depends upon the formation of an intermediate according to Equation 3: xs CH + RN > [R3NHC5H5] -> R NH+ + C H (3) Amine 6
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6
6
2
3
3
5
5
2
3
3
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6
Table I shows the results of using amines of varying basicities in this reaction. The data were taken from experiments in which stoichiometric amounts of iron (II) halide and cyclopentadiene were used. The amine was employed in considerable excess as both a reactant and a solvent for the reaction. Since the iron halide was prepared in ethylene glycol dimethyl ether, this was used as a cosolvent. Iron(II) chloride was prepared by the reaction of anhydrous iron (III) chloride with iron powder in ethylene 368
In METAL-ORGANIC COMPOUNDS; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.
PRUETT AND MOREHOUSE-THE AMINE METHOD FOR PREPARING FERROCENE Table I.
Effect of Amine Structure % Yield of Ferrocene 85 69 38 29 20 7 3 to F e X 2 2 to 1 8 to 1 2 to 1 8 to 1
Amine Triethylamine n-Butylamine
% Yield Ferrocene Based on F e X 2 20 72 7 32
° C P D = cyclopentadiene.
T h e results d e s c r i b e d t h u s f a r were o b t a i n e d f r o m e x p e r i m e n t s i n w h i c h a l a r g e excess o f t h e a m i n e w a s u s e d . T a b l e I I I gives t h e r e s u l t s o f e x p e r i m e n t s i n w h i c h
Table III. Amine Diethylamine Piperidine β
Effect of Excess Amine
Molar Ratio Amine to C P D 1 to 1 (in benzene) Large (amine as solvent) 1 to 1 (in D M C ) Large (amine as solvent)
a
% Yield of Ferrocene 15 75-85 19 69
C P D = cyclopentadiene.
s t o i c h i o m e t r i c a m o u n t s o f t h e a m i n e w e r e u s e d i n t h e presence o f a n i n e r t s o l v e n t . W i t h e i t h e r benzene o r D M C as t h e s o l v e n t t h e y i e l d s w e r e m a r k e d l y decreased. T a b l e I V shows t h e v a r i a t i o n i n y i e l d s w h e n v a r i o u s i r o n salts were e m p l o y e d .
Table IV.
Product Yield
from Various Iron Salts Iron Salt* FeCls FeBr FeS0 FeCh · 4 H 0 2
4
2
a
% Yield of Ferrocene 75-85 85 0 0
All reactions in diethylamine-DMC.
In METAL-ORGANIC COMPOUNDS; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.
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ADVANCES IN CHEMISTRY SERIES
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T h e r e w a s n o m a r k e d difference b e t w e e n i r o n ( I I ) c h l o r i d e p r e p a r e d b y r e d u c t i o n o f iron (III) chloride w i t h iron powder a n d iron (II) bromide prepared b y the bromination of i r o n . T h e b r o m i d e g a v e s l i g h t l y b e t t e r r e s u l t s , p r o b a b l y because o f t h e i n c r e a s e d s o l u b i l i t y of t h e b r o m i d e i n t h e s o l v e n t . I r o n ( I I ) s u l f a t e a n d i r o n ( I I ) c h l o r i d e t e t r a h y d r a t e f a i l e d t o p r o d u c e ferrocene. T h e results w i t h t h e h y d r a t e d salt s h o w a p o i n t t h a t w a s c o n f i r m e d i n o t h e r e x p e r i m e n t s ; i t is essential t h a t a l l m a t e r i a l s b e t h o r o u g h l y d r i e d . I n these l a b o r a t o r i e s t h e a m i n e s were d r i e d b y p a s s i n g t h e m t h r o u g h a c o l u m n p a c k e d w i t h L i n d e 4 A M o l e c u l a r S i e v e . D M C w a s d r i e d , a n d i t s p e r o x i d e s were also removed, b y the L i n d e 1 3 X M o l e c u l a r Sieve. A s a laboratory preparation, commercial anhydrous iron (III) chloride m a y be u s e d d i r e c t l y w i t h c y c l o p e n t a d i e n e i n die t h y l a m i n e s o l v e n t . Y i e l d s o f a b o u t 8 5 % m a y be o b t a i n e d , b a s e d o n i r o n . I n t h i s case i t is necessary t o use a 3 t o 1 m o l a r r a t i o of c y c l o p e n t a d i e n e t o i r o n , because 1 e q u i v a l e n t o f c y c l o p e n t a d i e n e is u s e d i n t h e r e d u c t i o n of i r o n ( I I I ) chloride t o the i r o n ( I I ) state. T h i s is a v e r y convenient l a b o r a t o r y p r e p a r a t i o n , because i t gives a h i g h y i e l d of p r o d u c t f r o m a s h o r t , o n e - s t e p process. O n a l a r g e scale i t is less a t t r a c t i v e because i t r e q u i r e s 5 0 % m o r e c y c l o p e n t a d i e n e . F o r a c o m m e r c i a l process, t h e r e is a n i m p o r t a n t m o d i f i c a t i o n i n w h i c h i r o n p o w d e r m a y b e u s e d as a r a w m a t e r i a l . T h e b y - p r o d u c t o f t h e r e a c t i o n o f i r o n ( I I ) c h l o r i d e w i t h cyclopentadiene is the amine hydrochloride. T h i s amine hydrochloride m a y be r e c o v e r e d i n u s a b l e f o r m as t h e n e u t r a l a m i n e b y t r e a t i n g i t w i t h i r o n p o w d e r . When diethylamine hydrochloride is heated w i t h i r o n powder, hydrogen is evolved a n d i r o n ( I I ) c h l o r i d e a n d d i e t h y l a m i n e are f o r m e d . T h i s i r o n ( I I ) chloride can then be used i n t h e r e g u l a r process t o f o r m ferrocene. T h u s , the diethylamine hydrochloride m a y b e r e c y c l e d , so t h a t t h e o n l y r a w m a t e r i a l r e q u i r e m e n t s a r e i r o n m e t a l a n d c y c l o p e n t a d i e n e , w i t h h y d r o g e n as a b y - p r o d u c t . T h i s o v e r - a l l process i s o u t l i n e d i n t h e f o l l o w i n g s i m p l i f i e d flow d i a g r a m .
I t m a y be c o n c l u d e d t h a t t h e a m i n e m e t h o d affords a c o n v e n i e n t a n d c h e a p process f o r t h e p r e p a r a t i o n o f ferrocene o n e i t h e r a l a b o r a t o r y scale o r p r o d u c t i o n scale.
Literature Cited (1) Birmingham, J. M . , Seyforth, D., Wilkinson, G., J. Am. Chem. Soc. 76, 4179 (1954). (2) Fischer, W. O., Hafner, W., Z. Naturforsch. 86, 444 (1953). (3) Fischer, W. O., Jira, R., Ibid., 8b, 217, 327 (1953). (4) Kealy, T. J., Pauson, P. L., Nature 168, 1039 (1951). (5) Miller, S. Α., Tebboth, J. Α., Tremaine, J. F., J. Chem. Soc. 1952, 632. (6) Pauson, P. L., Quart. Revs. 9, 391 (1955). (7) Wilkinson, G., J. Am. Chem. Soc. 74, 6148, 6146 (1952). (8) Wilkinson, G., Birmingham, J. M . , Ibid., 76, 4281 (1954). In METAL-ORGANIC COMPOUNDS; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.
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(9) Wilkinson, G., Cotton, F. Α., Chem. and Ind. (London) 1954, 307. (10) Wilkinson, G., Cotton, F. Α., Birmingham, J. M . , J. Inorg. & Nuclear Chem. 2, 95 (1956). (11) Wilkinson, G., Pauson, P. O., Cotton, F. Α., J. Am. Chem. Soc. 76, 1970 (1954).
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RECEIVED for review May 10, 1957. Accepted June 1, 1957.
In METAL-ORGANIC COMPOUNDS; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.
