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Detection of Free Cyclobutadiene on Oxidation of a Tricarbonyl(cyclobutadiene)iron Complex.

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(CDCI,): 5 = 7.8-6.5 (m, 8 methylene-H), 3.70 (d, 4 arom.
H; J z O . 9 Hz); MS: M + 268 (base peak); the fragmentation
corresponds essentially to that of simple p-benzoquinones
(no fragmentation into halves as for true [2.2]paracyclophanes); IR (KBr): 1660 cm- S.
Catalytic hydrogenation of ( 4 ) (Pd/C, dioxane, calculated
amount of Hz) and subsequent chromatography (silica
gel, from ether/chloroform) and recrystallization from benzene/ether gave the intramolecular quinhydrone ( 1 a)[61
in 70% yield. Mass spectrum: M + found 270.0868, calc.
270.0891 ; H-NMR ([D,]-acetone) : T = 7 . 8 4 . 5 (m, 8
methylene-H), 3.95 (s, 2H), 3.80 (s, 2H), 2.22 [s, 2H (OH,
concentration-dependent, exchange with D 2 0 and
CD,OD)] ;IR (KBr): vOH = 3420cm-', vCO= 1645cm-'.
In contrast to the quinhydrones, which dissociate partially
in solution, the dark violet crystals of ( 1 a ) form wine-red
solutions in polar solvents. The absorption spectrum of
( I a ) in methanol has an extremely broad absorption band
(l,,, =515 nm, E = 170), stretching on the long-wave side
far above 600nm.
In solution, ( 1 a) is oxidized to ( 4 ) by atmospheric oxygen.
We failed in attempts to detect rapid interchange of oxidation states between the two rings, involving hydrogen
transfer, which would have been shown by coalescence of
the 'H-NMR signals at r = 3.95 and 3.80, at temperatures
up to 200°C (in hexamethylphosphorotriamide). When
treated with aqueous 0.1 N sodium hydroxide, the solution
of ( I a) in methanol changes from wine-red through green
to reddish-brown, and this change is reversed by addition
of the corresponding amount of 0.1 N hydrochloric acid.
Presumably the dianion, which may exist as a diamagnetic
donor-acceptor complex or, through complete electron
transfer, as a double semiquinone radical anion, is formed
through the monoanion stage.
in a noble-gas matrix at 8"K(*l. However, this molecule
has been postulated as intermediate in a series of reactions['"], and it has been credited with an astonishing
selectivity in cycloadditions even at room temperatureIzb1.
We have tested the possibilities that free cyclobutadiene
is actually liberated on oxidative degradation of its tricarbonyliron
or alternatively that the molecule
is still complexed during the observed additions to olefins.
Earlier experiments had not led to conclusive results[41.
If the reaction of an optically active cyclobutadiene
complex proceeds by way of free cyclobutadiene then racemic products are to be expected, but in other cases they
should be optically active.
As a model compound we synthesized optically active
tricarbonyl-( I-ethyl-2-methylcyc1obutadiene)iron ( 3 ) as
follows: Reaction of the half ester ( I a)[51 with oxalyl
chloride in pyridine led to ( I b), which with diazomethane
afforded the diazo ketone ( 1 c ) . Treatment of ( 1 c ) with
HI in acetic acid gave ( I d ) in overall yield of 72%[@.
R = CO2H
R = COCl
(1 d ) was hydrolyzed to the acid (2), which was reduced
by B,H,-BF,
in THF to racemic (3) in 95% yieldf7].
Received: July 2, 1973 [Z 881 IE]
German version: Angew. Chem. 85, 831 (1973)
[I] Transannular Interactions in [2.2]Phanes, Part 4.-Part 3: M . Hornel
and H . A . Staab, Chem. Ber. 106, 2203 (1973).
[2] H . A. Staab and M . Haenel, Chem. Ber. 106, 2190 (1973); s e e also
M . Haenel and H . A. Staah, Tetrahedron Lett. 1970. 3585.
[3] We use this term because of its simplicity, although it contains
a "contradictio in adiecto": quinhydrones are defined as dissociable
complexes of quinonoid acceptor and benzenoid donor molecules,
whereas in (1 a ) and (1 b ) the donor and the acceptor are contained
in one molecule.
[4] D. J . Cram and A . C. Duy [cf. J. Org. Chem. 31, 1227 (196611
started the synthesis of these "exotic quinhydrones" a considerable time
ago, but apparently could not complete this work.
[ S ] F. Vogtle. Chem. Ind. (London) 1972, 346.
[6] Correct elemental analyses were obtained for these compounds;
'H-NMR and mass spectra. as well as other spectroscopic results. are
in accordance with the structure proposed.
[7) J . Bruhin and ct: Jenny, Tetrahedron Lett. 1973, 1215.
[S] Cf. M . S. Kharash and 0.Reinmuth. Grlgnard Reactions of Nonmetallic Substances. Prentice Hall, New York 1954, p. 1013.
Detection of Free Cyclobutadiene on Oxidation of
a Tricarbonyl(cyc1obutadiene)iron Complex
Resolution of the acid by quinine afforded optically active
$ ~- 102" (in ethanol). Esterification with
diazomethanegave(-)-(Id), [a]:$, = -280" (in benzene),
whose optical purity (>99%) was determined by 'H-NMR
spectroscopy with the aid of a chiral europium
Reduction of (-)-(2) gave ( - ) - ( 3 ) , [a]& = -20.5" (in
CC1& which should be of equal optical
On oxidation of (- )-(3) in methanol at 0°C by cerium(rv)
ammonium nitrate in the presence of dimethyl maleate
(37-fold excess) the diester ( 4 ) was obtained as sole adduct
(40%)['01. A 40% solution of the adduct in benzene, in
a lOcm cuvette, showed zero rotation (within the error
of the polarimeter, +0.003°) at 578 and at 435nm. The
presumption therefrom that ( 4 ) is obtained in its racemic
form can be convincingly confirmed as follows: in the
'H-NMR spectrum addition of the above shift reagent18'
causes splitting of the enantiotopic signals (ester-methyl,
allylic methyl, and ethyl group) in the ratio 1 : 1 (accuracy
of measurement 7 YO).
By E . K . G. Schrnidtpl
Dedicated to Professor Karl Winnacker on the occasion of
his 70th birthday
Recent work has shown that unsubstituted cyclobutadiene
has a finite lifetime only under extreme conditions, e.g.
[*] Dr. E. K. G. Schmidt
Abteilung fir Chemie der Universitat
463 Bochum, Postfach 2148 (Germany)
Angew. Chem. internal. Edit. J Vol. 12 (1973) j iVo. 9
On oxidative degradation of ( - ) - ( 3 ) in the presence of
the more reactive dienophile maleic anhydride (two-fold
amount), again only one adduct was formed; this was
reduced to the diol ( 5 ) by LiAlH4 [40% yield referred
to ( -)-(3)[101]. By the criteria used for ( 4 ) , this alcohol
was also racemic. Even with the very reactive dienophile
tetracyanoethylene we obtained the optically inactive
adducts (6), (7), and (8) [SO% based on ( - ) - ( 3 ) ] , of
which the bicyclohexene (6) with two alkyl groups on
the double bond is the favored product'"]. The regiospecificity observed with the less reactive dienophiles is thus
lost in this Diels-Alder reaction[121.
Pacansky, ibid. 95, 616 (1973); A. Krantz, C . Z Lin, and M . D. Newton,
ibid. 95, 2744 (1973) and literature cited therein; S. Masamune, M . Suda,
H . Ona, and L. M . Leickter, J. C. S. Chem. Commun. 1972, 1268.
[2] a) J . Font, S. C . Bmton, and 0. P. Strausz, Chem. Commun. 1970,
499; R . Criegee and R . Huber, Chem. Ber. 103, 1862 (1970); M . F.
Semmelkack and R. J . DeFranco, J. Amer. Chem. SOC. 94, 8838 (1972);
b) L. Watts, J . D. Fitzpatrick, and R . Pettit, ibid. 88, 623 (1966); E .
K . G.Schmidt, L. Brener, and R. Pettit, ibid. 92,3240 (1970). and literature
cited therein.
[3] R. Pettit, Pure Appl. Chem. 17, 253 (1968); E. E. Nunn and R.
Warrener, J. C. S. Chem. Commun. 1972, 818; E. Vedejs, ibid. 1971,
536; L . A. Paquette and J . F. Kelly, Tetrahedron Lett. 1969,4509.
[4] W J . R . Tyerman, M . Kato, P. Kebarle, S. Masamune, 0. P. Strausz,
and H. E. Gunning, Chem. Commun. 1967,497; L. Watts, J . D. Fitzpatrick,
and R . Pettit, J. Amer. Chem. SOC.87, 3253 (1965).
The formation of racemic adducts from the optically pure
tricarbonyliron complex proves the occurrence of free cyclobutadiene. During addition of the dienophile, possible
residual bonds from the cyclobutadiene to the iron or
to the solvent are clearly too weak to maintain the original
chiral surroundings of the complex.
Received: June 25, 1973 [Z 875 IE]
German version: Angew. Chem. 85,820 (1973)
[ I ] 0. L Chapman, D. DeLaCruz, R. Rotk, and 3. Pacansky, J. Amer.
Chem. SOC.95, 1337 (1973); 0. L. Chapman, C . L. Mclntosh, and J .
[5] B. W Roberts, A . Wissner, and R . A. Rimrrmann, J. Amer. Chem.
SOC.91, 6208 (1969).
[6] The new compounds were characterized by elemental analysis and
IH-NMR, UV, and IR spectroscopy.
[7] Yellow liquid, b.p. 86"C/7 torr. IR (CCL): 2970w, 2039vs, 1966vs,
617s, 590scm-'. 'H-NMR (C6D6):ring protons 6=3.62ppm (s, IH),
3.58 (s, I H); methyl group 1.48 (s, 3H); ethyl group 1.82 (4. 2H), 0.87
(t. 3 H, J - 7.3 Hz).Typical for tricarbonyl(cyc1obutadiene) complexes is
the absence of coupling between the ring protons and the diastereotopic
splitting of the signals of the ethyl group [cf. H . A. Brune, H . P. Wow,
and H . Hiither, Tetrahedron 27, 3949 (1971)]. The mass spectrum shows
the molecular ion (m/e=234), as well as the successive loss of three
C O groups.
pium(ii1); Willow Brook Laboratories, Inc.; review: H . L. Goering, 3. N .
Eikenberry, and G. S. Koermer, J. Amer. Chem. SOC. 93, 5913 (1971).
[9] (-)-(3) is thermally very stable; a sample was recovered unchanged
after being heated in benzene for 50 h at 200 "C.
[ 101 Experiments with ELI shift reagents indicate the do-configuration,
but the validity of this assignment is of no importance for our work
1113 (6) and (7) were isolated in a state of purity, but (8) only in
admixture with (7).
[I21 With less activq dienophiles 1,2-~iphenylcyclobutadienealso gave
only one adduct, but with TCNE it gave two adducts: P. Reeves, 7:
Deuon, and R . Pettit, J. Amer. Chem. Soc. 91, 5890 (1969).
Constitution of Nonstoichiometric Compounds
and Solid Solutions
By J . S. Andersonp]
Work of recent years has shown that the structure of
nonstoichiometric solids cannot be explained only in terms
of point defect vacancies or interstitials: the host structure
is modified around a defect and a point defect is replaced
by a defect complex. Alternatively, the modification may
completely eliminate a sheet of lattice sites, by crystallographic shear.
Neutron diffraction has proved particularly suited to the
determination of defect structure. Work on anion-excess
fluorite type solid solutions has shown that these contain
defect complexes of the same type as were proposed by
Willis for u409, and that these can aggregate and extend
to larger clusters. In ferrous oxide, neutron scattering from
material at high temperatures, in an equilibrium gas buffer
[*] Prof. J. S. Anderson, F.R.S.
Inorganic Chemistry Laboratory
University of Oxford
South Parks Road, Oxford (England)
atmosphere, has shown that the ratio (cation vacancies)/tetrahedral cations) agrees with the Koch-Cohen defect
complex, with four tetrahedral cations surrounded by thirteen vacant octahedral sites. The same complex is found
for all compositions, and over a wide temperature range.
These complexes can again cluster to form incipient short
range ordering.
In other structures (the rutile and Re03 structures and
their derivatives), the anion/cation ratio is changed by
eliminating a sheet of anion sites along crystallographic
shear planes. Regularly recurrent shear planes generate
families of homologous compounds; isolated shear planes
eliminate large numbers of point defects-oxygen vacancies or interstitial cations-and are already present when
the oxygen deficit is extremely small. In reduced rutile
of composition TiO, .9986 they are already beginning to
aggregate into domains of the intermediate phases, and
the residual point defect concentration in the rutile structure is less than W4.The orientation of the shear planes
in the most reduced intermediate phases is different from
that in the less reduced phases, or that of isolated extended
defects. There is some mechanism for pivoting around
Angew. Ckem. internat. Edit. / Vol. 12 (1973) / No. 9
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oxidation, complex, free, detection, iron, tricarbonyl, cyclobutadiene
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