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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).
DEPARTMENT O F CHEMISTRY UNIVERSITY OF TEXAS AUSTIN12, TEXAS
J. E. MAHLER D. A . R. JONES R . PETTIT
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
