Sept. 5 , 1964
3589
COMMUNICATIONS TO THE EDITOR
Finally, the ultraviolet spectrum of the triafulvene 111 in cyclohexane shows an essentially symmetric single maximum a t 246 mw (log t 4 30), in methanol the maximum is a t 245 mp (log e 4.33). There is evidence neither for absorption above 300 mp nor for a solvent effect as is found for other triafulvenes, and the position of the maximum suggests qualitative agreement with Julg's prediction'* that the longest wave length (V + N) absorption for methylenecyclopropene will fall near 200 mp ( 1 2 ) A Julg J rhrm p h y s
6 0 , 652 (1953)
ORGAXIC CHEMICAL RESEARCH SECTION LEDERLE LABORATORIES DIVISION AMERICAU C YANAMID COMPANY PEARL RIVER,SEW YORK
ANDREWS KENDE PATRICKT IZZO
RECEIVED JULY 15, 1964
The Tropylium-Iron Tricarbonyl Cation Sir: Organometallic cationic complexes of the type LM(C0)3+ in which L is a tropylium ring a-bonded to a metal ( M ) are known for the group VI-B metals chromium, molybdenum,* and tungsten. The presumed structure of these complexes is indicated in formula I . The seven carbon atoms of the ring are symmetrically bonded to the metal by means of the six x-electrons, and the metal attains the effective atomic number of the next inert g a s 4
Treatment of methyl tropyl ether with iron enneacarbonyl gave the corresponding iron tricarbonyl complex (11) which reacted with fluoroboric acid to give the fluoroborate salt of the tropylium-iron tricarbonyl cation. The salt crystallizes in yellow needles from nitromethane, m.p. 112' dec. (Anal. Calcd. for C7H7Fe(C0)3BF4: C, 37.78; H , 2.22; B, 3.18. Found: C, 37.44; 2.03; B, 3.32). I t is stable in inert atmosphere but hydrolyzes rapidly in water to give tropyl alcohol-iron tricarbonyl from which the cation can be regenerated by treatment with fluoroboric acid. As with the chromium, molybdenum, and tungsten complexes, the n.m.r. spectrum of the tropylium-iron tricarbonyl cation shows a single sharp absorption, but further comparison of these complexes reveals several significant differences. The ~ K Rvalues + listed in Table I indicate that the tropylium-iron tricarbonyl cation is slightly less stable than the tropylium cation, whereas the group VI-B metal complex cations are considerably more stable. TABLE I Complex
P
PKR+~
0.72 4.7 CjH7+BF4C7H7+Fe(C0)3BF,4.20 4 5 C?Hs+Fe(C0)3BFa.. 4.7 C?H,+Cr(C0)sBFb3.42 6 3 CjHj +Mo(C0)zBFd3 82 6.2 C?H,'W( C 0 ) s B F C 3.83 -6' * Measa Position of single n.m.r. peak measured in liquid SOz. ured in HzO a t 30.0". c Approximate value only because of secondary decomposition.
The most significant differences are seen in the infrared absorption spectra. The group VI-B metal complexes each show a single strong absorption band in the C-H stretching region,? but the corresponding L i iron complex shows three strong bands which presumably reflect a lower symmetry of the C7H7 ligand in the 1 iron complex.8 Furthermore, the group VI-B metal The analogous cationic complex containing iron is of complexes are transparent in the 650-800 ern.-' region some theoretical interest for, if the bonding in such a while the iron complex shows an intense absorption complex were to be similar, the effective atomic number band a t 731 cm.-' suggestive of the presence of a cis of iron would exceed that of krypton by two. double bond. Previous attempts to prepare salts of the tropyliumOn the basis of this evidence, we propose that the iron tricarbonyl cation have been unsuc~essful.~ structure of the tropylium-iron tricarbonyl cation is Whereas the triphenylmethyl cation abstracts hydride as shown in IIIa. The iron atom is bonded to five ion from cycloheptatriene-M(C0)3 complexes (M = carbons of the ring, leaving one double bond not inCr, Mo, and W) to give t r o p y l i ~ m - M ( C 0 )complexes, ~ volved in coordination to the metal. The ligand-metal in the case of cycloheptatriene-iron tricarbonyl addibonding is then analogous to that found in other pentation occurs to give a substituted cycloheptadienyl-iron dienyl-iron tricarbonyl cationic complexes. The ~ K R + tricarbonyl cation.6 value of the C7H7-Fe(C0)3cation is very similar to that We now wish to report the synthesis of the tropyliumof the cycloheptadienyl-iron tricarbonyl cation (see tricarbonyl cation by the following route. Table I ) . The salt displays carbonyl absorption typical of dienyl-iron tricarbonyl cations (strong absorption peaks a t 2070 and 2120 cm.-l).g C7H?Fe(CO)*+BF; I1 (1) J , D . M u n r o a n d P . I,. P a u s o n , J . C h e m . S O L . 3475 , (1961). ( 2 ) H . J . D a u b e n , Jr., a n d L. R . H o n n e n , J A m . C k c m . SOC.,80, 5570 (1958). ( 3 ) H . J. D a u b e n . J r . , I,. R . H o n n e n a n d D . J Bertelli, A b s t r a c t s , 1 5 t h S o u t h w e s t Regional Meeting. American Chemical Society, B a t o n R o u g e , L a , llec. 3 , 1959, p . 89. ( 4 ) I> A . Brown, J . Inorg. N u c l . C k e m . , 10, 3 9 (1959). ( r ? ) An account of these is given in ref 6 ( 6 ) H . J D a u b e n . J r , a n d D J. Bertelli. J . A m Chem Soc , 83, 497 (1961)
(7) H P. Fritz. "Advances in Organometallic C h e m i s t r y , " Vol 1 . Academic Press. I n c , New Y o r k . N Y.. 1964. p 240. (8) Y C - ~ 3086, 3076, a n d 3086 c m - 1 f o r t h e C r . M o . and W complexes. respectively. a n d 3093, 3070. a n d 3056 c m . - 1 for t h e F e complex measured as hexachlorobutadiene mulls using a Beckman I R - 7 spectrometer ( 9 ) R P e t t i t a n d G. F Emerson, ref 7 p 1
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COMMUNICATIONS TO THE EDITOR
In order to account for the single absorption in the n.m.r. spectrum a t 4.2 T i t is proposed that in solution the system undergoes rapid valence tautomerism to produce the equivalent structilre IIIb. Extension of this rearrangement would eventually lead t o rotation of the iron tricarbonyl group around the C7H7 ring, and this would result in equivalence of the ring protons. The position of the single n.m.r. absorption is also consistent with this. If five of the protons in I11 are assumed to have the same chemical shifts as the corresponding protons in the cycloheptadienyl-iron tricarbonyl catthen the very reasonable-value of 3.8 r must be employed for the two protons of the noncoordinated olefinic bond in order that the average value of the seven protons be 4.2 r . I 1 Acknowledgment.-We thank the National Science Foundation and the Robert A. Welch Foundation for financial assistance, and the Antara Chemical Company for a gift of iron pentacarbonyl. (10) I l a t a from D a u b e n a n d Bertelli.0 (11) T h e situation for t h e C,H,Fe(CO)acation is analogous t o t h a t already seen in cyclooctatetraene-iron tricarbonyl for which a d y n a m i c effect h a s a l w been postuloted.l2 I n t h i s case a n average value of 3.9 T is required for t h e four olefinic p r o t o n s of t h e t w o double bonds n o t coordinated t o iron in order t h a t t h e total average b e equal t o 4.8 T a s observed, assuming t h a t t h e o t h e r f o u r protons h a v e t h e s a m e chemical shift a s those in cycloheptatrieneiron tricarhonyl. (12) B. Ilickens a n d W. N Lipscomb, J . Chcm. P h y s . , 37,2084 (1962).
J . E. MAHLER D. A . R. JONES R . PETTIT
DEPARTMENT O F CHEMISTRY UNIVERSITY OF TEXAS AUSTIN12, TEXAS RECEIVED JULY6, 1964
Organometallic Complexes of the Type Triene-Fez(CO) 8
Sir : We wish to report the isolation of a series of related organometallic complexes of the general type trieneFez(CO)6 and to present data pertaining t o their structure. Reaction of cycloheptatriene, 7-methoxy-l,3,5cycloheptatriene, 1,3,5-~yclooctatriene,and cyclooctatetraene with iron enneacarbonyl produced, in each case, an orange-red crystalline complex giving satis-
..
.. ..
i , -1
0
-7
I
IO
I
Velocity in m m A , relolive lo iron
Fig. 1.-Mlisshauer
absorption spectrum of complex I
factory C, H , and Fe analyses for the substance having an Fez(CO)t, grouping attached to the corresponding triene.' The complexes are diamagnetic, they each show a similar infrared and n.m.r. absorption pattern, 11) T h e melting points of these four complexes a r e 131-133, 92-94, T h e principal infrared b a n d s f o r t h e 101-103, a n d 90--92'. respectively CO stretching frequencies a r e 1960. 1975, 1995, 201.5, a n d 2058 ( 1 5 c m . - I ) f o r each complex a n d each shows a n n . m . r absorption corresponding t o six p r o t o n s in t h e region 4.8-5.5 (ZH), 5.6-6.0 ( Z H ) , a n d 7.2-7.6 ( 2 H ) i. ( 2 ) O t h e r organometallic c o m p o u n d s , especially diene-Fe(C0)a complexes, a r e also formed in t h e reaction. T h e reaction with cyclooctatetraene gives t w o nther isomeric F e z ( C 0 j i complexes. a n d this reactinn will b e discussed in more detail in a later p a p e r
Vol. 86
f E
. .
. .
Velociiy in mm/s, relative io iron
Fig. 2.--Mossl.lauer
absorption spectrum of CaHin-Fed C O h .
and they are therefore considered to have analogous structures. The complex obtained from cyclooctatriene appears to be identical with the product derived from reaction of cyclooctatriene and Fe3(CO)12 reported by King. a By analogy with the ferrole derivative I , King proposed structure I1 for this cyclooctatriene complex. However, a comparison of the Mossbauer resonance spec-
I1 trum of I with each of the t r i e n e e F e ~ ( C 0complexes )~ suggests that structure I1 is possibly incorrect. The Mossbauer spectrum of olefin-Fe(CO)3 complexes invariably consists of two peaks resulting from an unsymmetrical electric field gradient a t the Fe n ~ c l e u s . ~ The spectrum of the-ferrole (I) (Fig. 1) displays three maxima. The most reasonable interpretation is that these three peaks arise from the two Fe atoms in the ferrole complex being chemically nonequivalent, each of the two Fe atoms giving rise to a doublet of similar b u t not identical separation and chemical shift. On the other hand, the Mossbauer resonance spectra of C8Hlo-Fez(CO)~(Fig. 2 ) and the other three complexes listed above show only two peaks. We conclude therefore that the two iron atoms are chemically equivalent in these c ~ m p l e x e s . ~ The n.m.r. spectrum of the cycloheptatriene-Fez(CO)6 complex shows the two CH2 protons to be nonequivalent ; therefore, the two equivalent iron atoms must lie on the same side of the ring. This conclusion is further. substantiated by the high dipole moment of the material (4.8 D , ) , On the basis of these data we propose that these compounds are essentially bis-r-allyl-iron carbonyl complexes as illustrated in formula I11 for cycloheptatriene-Fe2(CO)6 (R = H) and its methoxy derivative (R = OCH3). Each iron atom is bonded to three contiguous carbons of the triene in essentially the same manner as in other r-allyl-iron carbonyl complexes. An Fe-Fe bond is proposed in order to account for the diamagnetic properties and so that the two iron atoms attain the atomic number of krypton. Triphenylmethyl fluoroborate reacts with cycloheptatriene-Fe2(CO)6 to produce triphenylmethane ( 3 ) R . B . King, Inorn Chem , '2, 807 (1963). ( 4 ) I
