Aug. 20, 1954
NOTES
that the magnitudes of the equilibria constants are determined by considerations of potential energy alone. It is clear from the observed large variations in A s 0 that this is not the case and that, in fact, the kinetic energy changes accompanying complex formation are not uniformly the same throughout this series. Under these conditions it becomes hopeless t o attempt to correlate structure and reac-
tivity toward complex formation in terms of potential energy considerations alone. The changes in equilibrium constant resulting from a particular substituent could stem from a whole series of effects amongst which we might list polar or inductive effects, resonance effects, steric hindrance effects, polarizability effects and solvent effects.
4179
NORTHADAMS,MASS.
NOTES yltitanium(1V) chloride,g (CsH&TiC12. As hydrogen halide acceptors, triethylamine, diethylamine, pyridine and sodium methoxide have been used. BY J. M. BIRMINGHAM, D. SEYFERTH AND G. WILKINSON The formation of FeClz-amine addition compounds RECEIVED MAY6, 1954 that are insoluble in the solvents tried is a competThree major types of reactions have been used to ing reaction that has thus far prevented good yields. prepare bis-cyclopentadienyl-iron(I1)and other bis- Sodium methoxide seems to cause polymerization cyclopentadienyl-metal compounds : (a) the reac- of the cyclopentadiene. It is, however, significant tion of a cyclopentadienyl organometallic reagent : that bis-cyclopentadienyl-metal compounds are C5HsMgBr in benzene' or CSHSNa in tetrahydro- formed under these conditions; in the absence of a furan2 with transitional metal halides or acetylace- hydrogen halide acceptor, none of the desired prodtonates, or C5HsKin liquid ammonia with a metal uct could be detected. Experimental t h i ~ c y a n a t e . ~Bis-indenyl derivatives of Fe and c o (1) An equimolar mixture of ( C ~ H K ) and ~ N CbHa was also have been prepared by similar reactions4; (b) the reaction of cyclopentadiene vapor with a slowly added to anhydrous FeC12 with rapid stirring under a nitrogen atmosphere. Benzene was then added and the metallic iron catalyst5" or ferrous oxide a t 350°,5b mixture was stirred overnight. The reaction mixture was and (c) the reaction of cyclopentadiene vapor with filtered and the yellow filtrate was allowed to evaporate slowly. The yellow acicular crystals that separated were a metal carbonyl.6 Method a depends upon the acidic character of identified as ferrocene by infrared spectrum and melting A yield of about 4% was thus obtained. Variathe methylene hydrogen of cyclopentadiene which point. tion of the base-(CnH&NH, C ~ H K NNaOCHa-also , gave enables the formation of an organometallic deriva- similar yields. The use of ferrous acetate in place of the tive with the evolution of hydrogen in the reaction chloride with the above bases gave ferrocene but did not with Na or K, or in the case of the Grignard re- improve the yield. ( 2 ) A benzene solution of TiC1, was added slowly with agent, where cyclopentadiene reacts with CzHaMgBr, vigorous ~N stirring to an equimolar mixture of ( C ~ H S ) and of ethane. The dissociation constant of the acidic C K H ~ .The mixture was stirred overnight. Removal of hydrogen of cyclopentadiene is very small; the pK the solvent from the red reaction mixture, extraction of the value for indene has been estimated to have a mini- resulting residue with chloroform, and slow evaporation of extracts yielded red crystals. Recrystallization from mum value of 21' and the minimum PK value for the toluene gave pure (CaHs)zTiClz,identified by its infrared cyclopentadiene should be slightly lower.* Consid- spectrum. Yields of about 3% were obtained with triethyleration of this slight acidity of cyclopentadiene amine, diethylamine or pyridine. Again, serious comsuggested that a reaction of cyclopentadiene with a peting reactions were the formation of insoluble TiClrmetal halide in the presence of a hydrogen halide amine complexes and polymerization of the cyclopentadiene. acceptor might be an alternate route for the prep(9) G. Wilkinson and J. M. Birmingham, THISJOURNAL, 76, in press aration of bis-cyclopentadienyl-metal compounds, (1954).
A New Preparation of Bis-cyclopentadienyl-Metal Compounds
e.g. 2CsHs
+ FeClp + 2 Base
= (C;H&Fe
+ 2 Base.HC1
We have found that such reactions do indeed give small yields of ferrocene and of bis-cyclopentadien(1) T. J. Kealy and P. L. Pauson, Nafurc, 168, 1039 (1951). (2) G. Wilkinson and F . A. Cotton, Chemistry and Industry, 307 (1954). (3) E. 0.Fischer and R . Jira, Z.Natuyforsch., 8b, 217 (1953). (4) (a) P. L. Pauson and G. Wilkinson, THISJOURNAL,76, 2024 (1954); (b) E.0.Fisher, et a!., Z.Naturforsch., 8b, 692,694 (1953). ( 5 ) (a) S. A , Miller, J. A. Tebboth and J. F . Tremaine, -7. Chcm. Soc., 6 3 2 ( 1 9321, (b) G. Wilkinson, unpublished observation. (ti) (a)G Wilkinson, THIS JOUKNAL, 76, 209 (1954), G.Wilkinson, P. I,. Pauson and F . A. Cotton, ibid., 76, 1970 (1954). (7) 1%'. K. RlcEwen, i b i d , 68, 1124 (1936). ( 8 ) G.W. Wheland, J . Chcin. Phys., I , 474 (1934).
DEPARTMENT OF CHEMISTRY HARVARD UNIVERSITY CAMBRIDGE, MASSACHUSETTS
The Pyrolysis of Methyl Ethyl Ketone Cyanohydrin Acetate BY EARLC. CHAPINAND RICHARD F. SMITH RECEIVED MARCH10, 1954
The pyrolysis of unsymmetrical aliphatic acetates has been reported' t o yield the olefin with the least number of alkyl groups attached to it. (1) Xi'.
J. Bailey and C. King, Abstracts of the I?2nd I l e e t l n g
of the American Chemical Society, 1952 p. 3 M .
