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Catalytic Activity by Opening of Metal-Metal Bonds.

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[4] H.Basch, M . B. Robin, N . A . Kuebler, J. Chem. Phys. 47, 1201 (1967).
[5] The total electron density was calculated with the SCF part of the
POLYATOM program system (obtainable from Quantum Chemistry
Program Exchange, Indiana University, No. 199). The atomic densities
were determined by the RHF program section using the same basis
~41.
[6] H.-L. Hase, H . Reitz, A. Schweig, Chem. Phys. Lett. 39, 157 (1976).
[7] The geometry of unsubstituted cyclobutadiene optimized by the
CNDOjS procedure (bond lengths: C=C 1.349, C-C 1.515, C-H
G. Lauer, K.-W Schulte, A. Schweig, unpublished results) was
1.083
used in the quantum chemical calculations. In order to determine the
dynamic density a cubic pseudo-unit cell was constructed with the
into which a molecule of cyclobutadiene
dimensions a = b = c = 4
just fits. Temperature factors measured for ( I j are used for the carbon
atoms, and it is further assumed that the temperature factors of the
hydrogen atoms ofcyclobutadiene have the same value as the experimentally accessible temperature factors of the corresponding carbon atoms
in ( I ) .
[XI C. J . Fritchie Jr., Acta Crystallogr. 20, 27 (1966); A . Hartmann, F.
L. Hirshfeld, ibid 20, 80 (1966); D. A. Matthews, G . D. Stucky, J. Am.
Chem. SOC. 93, 5954 (1971); Z Ito, Z Sakurai, Acta Crystallogr. B29,
1594 (1974).
[9] M . Harel, F . L. Hirshfeld, Acta Crystallogr. B 31, 162 (1975).
[lo] The experimental results of Figure 1 were derived from a conventionally
refined structure analysis at room temperature. The resulting possible
errors in the atomic parameters (positional a n d temperature factors)
and scale factor can lead to inaccuracies of the derived experimental
difference electron densities. A theoretical estimate of the inaccuracies
by conventional temperature factors in the case of tetracyanoethylene
(TCNE) showed that they do not exceed 0.1 e/A3 in this system. Moreover, an exact comparison between calculated and measured difference
electron densities for TCNE and smaller model systems has also shown
that the difference densities calculated in "double C'' quality are not
falsified by more than 0.15 to 0.2 e/A3 (H.-L. Hase, K.-W Schulte,
A . Schweig, unpublished results). These experiments suggest that the
observed and calculated results are already essentially correct.
A;
A
accelerating effect on the reaction. Moreover, unlike (I), other
catalysts afford the dimer ( 4 ) always in admixture with other
dirnersI3].
13)
(4)
(5)
Reaction of norbornadiene with (2) in benzene at 55°C
affords the isolable complex ( 6 ) , which directly catalyzes the
same reactions as (2) without any induction period. The
structure of (6) has been determined by X-ray crystallography14].It confirms the opening of the metal-metal bond and
loss of a CO group at cobalt as the activating step (Fig.
1).
H3C\
/CH3
( C 0 ) 4 F e/ A s \ C
o(C0)zC~Hs
(6 i
Catalytic Activity by Opening of Metal-Metal Bonds[**]
By Hans Joachim Langenbach, Egbert Keller, and Heinrich
I/ahrenkarnp[*l
The metal-metal bonds in complexes (1) and (2) are so
reactive that they are readily opened by phosphanes at room
temperature[". Compounds ( I ) and (2) may therefore be
regarded as complexes having latent free coordination sites
capable of being exploited for catalytic reactions.
H3C\
/CH3
(CO)*F
F' - ' e
H3C\
,CH3
As
As
e( C O )2 N 0
/
(C O),F e C
-
\
o( C 0 ) 3
As an example of such a reaction we describe here the
catalyzed dimerization of norbornadiene ( 3 ) with (1) and
(2) which permitted the first characterization of a catalytically
active intermediate formed by opening of a metal-metal bond
of a polynuclear complex. Norbornadiene ( 3 ) is converted
exclusively into the exo-trans-exo dimer ( 4 ) on reaction with
(1) in benzene at 6 0 T , whereas reaction with (2) at 80°C
leads to a 1:l mixture of ( 4 ) and the dimer ( 5 ) . If the
reaction with ( I ) or (2) is carried out unter milder conditions
(CH2C12,room temperature)using equimolar amounts of catalyst and BF3-etherate, very rapid and exclusive formation
of ( 5 ) takes place. Compounds (1) and (2) surpass other
catalysts[21for the dimerization of norbornadiene in their
I*] Prof. Dr. H. Vahrenkamp, Dip1.-Chem. H. J. Langenbach,
Dipl.-Chem. E. Keller
Chemisches Laboratorium der Universitat
Albertstrasse 21, D-7800 Freiburg (Germany)
p*] This work was supported by the Deutsche Forschungsgemeinschaft,
the Fonds der Chemischen Industrie, and the Rechenzentrum der Universitat Freiburg.
188
Fig. I . Molecular structure of complex (6). Important parameters:
Fe-As=2.385 (1) A, Co-As=2.379 (1) A, Co-C (norbornadiene)=2.09,
2.10,2.17,and 2.18(1)A.
In our opinion only one of the metal atoms of ( 1 ) and
(2) can be considered as the catalytically active center of the
reaction. The unaltered presence of the (C0)4Fe-As(CH3)2
group in (6) and the inertness of (C0)4Fe-L complexes toward CO substitution, rule out participation of this
part of the molecule in the dimerizing process. It would appear,
therefore, despite the use of dinuclear complexes, that the
monomolecularmechanismuiaametallacyclicintermediate['] is
favored over the %-complexmulticenter mechanism'" 2ccordingly, like ( 1 ), Fe(C0)2(N0)2preferably dimerizes n i l t-hornadiene to (4)[31,and formation of ( 5 ) is mainly achiekcd with
cobalt catalyst^[^.'^. Thus the essential property of the complexes (1) and (2) is not their polynuclear character but
the functionality of their metal-metal bonds.
Experimental :
Synthesis of ( 6 ) : A mixture of (2) (930 mg, 2.0 mmol)
and norbornadiene (2.00 g, 22 mmol) in benzene (15 ml) is
stirred for 48 h at 55°C under nitrogen. After removal of
all volatile components in a vacuum the residue is taken
up in 1 ml of benzene. Dropwise addition of 10 ml hexane
affords (6) as a brown-violet, air-sensitive precipitate [270
mg (27%), m.p. 89-90°C], which is washed with a little
hexane and dried in a vacuum.
Received: December 22, 1976 [Z 640 IE]
German version: Angew. Chem. 89, 197 (1977)
[I] H . J . Langenbach, H . Vahrenkamp. Chem. Ber., in press.
[2] G. N . Schrauzer, Adv. Catal. 18, 373 (1968).
[3] P . W Jolly, F . G. A . Stone, K . MacKenzie, J. Chem. SOC.1965, 6416;
D. R. Arnold, D . 1. Trecker, E. B. Whipple. J. Am. Chem. SOC.87,
2596 (1965).
Angew. Chem. Int. Ed. Engl. 16 (1977) N o . 3
a=
[4] Monoclinic, P2&; a=7.289 (2), b=12.134 (l), c=21.040 (3) A.
107.78 ( 2r . Nonius-CAD4 diffractometer, 2650 reflections, R =0.040.
[5] A. R . Fraser, P . H . Bird, S . A . Bezman, J . R. Shapley, R. White, J .
A. Osborn, J. Am. Chem. SOC.95, 597 (1973).
161 G . N . Schrauzer, B . N . Bastian, G . A . Fosselius, J. Am. Chem. SOC.
88, 4890 ( 1 966).
[7] M . Ennis, A . R. Manning, J. Organomet. Chem. 116, C 31 (1976).
A Model of Internal Monooxygenase Catalyzed Reactions: Copper-Catalyzed Autoxidation of Bis(1-methyl-
ben~imidazol-2-yl)rnethane[**~
By Charles A . Sprecher and Andreas D. Zuberbuhler['l
While dioxygenase activity, e.g. the oxidative cleavage of
aromatic rings, can be mimicked closely in low molecular
weight systems"], no model studies seem to have been reported
for internal rnonooxygenases['l, a group of enzymes catalyzing
the four electron oxidation (a) of organic substrates.
(4
RH2+02+RO+H20
Here we wish to present evidence for internal monooxygenase
behavior in the copper catalyzed autoxidation of bis(l-methylbenzimidazol-2-y1)methane(1 ) to bis(1-methylbenzimidazol2-y1)ketone (2).
(1)
(2)
+ HzO
Compound (1 )(m.p.211-213 "Cfromethanol), was obtained
by condensation of 1-amino-2-(methylamino)benzene
with diethyl mal~nate[~I.
Copper(I1)perchlorate (81mol) was added to
a solution of ( I ) (3.6 mmol) in 200 ml anhydrous ethanol
and the solution stirred for 30 min at room temperature
. O2 uptake of
and atmospheric pressure under pure 0 2 An
81 ml(3.3 mmo1)indicated a 1 :1 substrate to O2 stoichiometry,
as required by eq. (a). On addition of HzO containing some
EDTA to complex Cu2+,(2) was precipitated in nearly quantitative yield [m.p. 191-192°C (from CH3CN); NMR: loss
of methylene protons at 4.65 ppm relative to TMS in CDC13);
IR: carbonyl stretchingat 1649 cm-'; mass spectrum: molecular ion at m/e=290].
The redox stoichiometry was checked using an oxygen-analyzer. In 10 runs under different conditions the consumption
of O2 was 90+2% of the theoretical value. The origin of
the carbonyl oxygen was tested with D i 8 0 . The methylene
compound was oxidized in the presence of an 80-fold excess
of 64% D 2 I 8 0and (2) isolated immediately after completion
of the reaction. Only a slight increase (8%) of the (M++2)
peak, corresponding to 13% exchange, was observed in the
mass spectrum, excluding water as the source of the carbonyl
oxygen. A considerable exchange (43%) is observed only if
(2) is treated with D2180 for 3 weeks. The concomitant
shift of the carbonyl frequency by 28 cm-' compares well
exchange in
with the shift of 29 cm-' for the 160-'80
ben~ophenone[~I.
The autoxidation of ( I ) is absolutely dependent on metal
ion impurities. In commercial p.a. ethanol, CHC13,or acetonitrile a slow, irreproducible uptake of dioxygen takes place.
This uptake is completely blocked by traces of strong chelators
p] Dip].-Chem. C. A.
Sprecher and Priv.-Doz. Dr. A. D. Zuherbiihler
Institut fur Anorganische Chemie der Universitat
CH-4056 Basel, Spitalstrasse 51 (Switzerland)
[**I We thank the Schweizerischer Nationalfonds zur Forderung der wissenschaftlichen Forschung (grant No. 2.0500.73) for financial support.
Angew. Chem. I n t . Ed. Engl. 16 (1977) No. 3
like dithizone or EDTA. Equimolar amounts of acid (H2S04)
or base (NaOH),and surprisingly, excess Cu2 strongly inhibit
the reaction. In 60% ethanol with dilute acetate buffer
([CH3COOH] = [CH3COO-] =0.0005 moljiter) at an ionic
strength of 0.1 (NaN03) the rate of the reaction is first order
with respect to [O,] and [Cu:,:]
and independent of the
substrate concentration, so long as [substrate]/[Cuk:] > 3.
According to potentiometric measurements, the formation of
a partially deprotonated species [CuL . (L-H')]
with
L = ( 1 ) is essentially complete under these conditions. (1)
is probably deprotonated at the methylene group before
reaction with the oxygen sets in.
Of the other metal ions tested, only Co2+ showed catalytic
activity comparable to Cu"; Fez+, Fe3+,Ni2', Zn2+,and
Mg2 did not significantly increase the rate of dioxygen
uptake. Methyl 2-(1-methylbenzimidazol-2-yl)acetate
and 2-(1methylbenzimidazol-2-y1)acetonitrileare oxidized at rates
comparable to those found with (1) in the presence of Cu2+.
With the second substrate and using ethanol as the solvent,
one of the carbon atoms is lost in the process. 1,2-Dimethylbenzimidazole and higher bis(l-methylbenzimidazol-2-yl)alkanes,
do not show any reactivity. We therefore suggest that the
sequence -N=C-CH2-X
(X indicating an unsaturated,
electron-withdrawing group) may be essential for the catalyzed
autoxidation.
The system described here fulfils all the basic requirements
for internal monooxygenase activity: Dioxygen is used as an
oxidant, one atom of 0 2 is incorporated into the substrate,
no external reducing agent is needed, and the oxidation is
absolutely dependent on the presence of a suitable catalyst.
+
+
+
Received: December 27, 1976 [Z 643 IE]
German version: Angew. Chem. 89, 185 (1977)
CAS Registry numbers:
( I ) , 55514-10-8; ( 2 ) , 61650-33-7; l-amino-2-(methylamino)benzene,
4760-343; diethyl malonate, 105-53-3; copperirrl perchlorate, 13770-18-8
[l] J. Tsuji, H. Takayanagi, Tetrahedron Lett. 1976, 1365.
[2] 0.Hayaishi, Molecular Mechanisms of Oxygen Activation. Academic
Press, New York 1974. p. 8.
[3] US-Pat. 3337578; Chem. Abstr. 68, P95820h (1968).
[4] M . Halman, S. Pinchas, J. Chem. SOC.1958, 1703.
Reactions of Phosgeniminium Salts with Nitriles, Imino
Ethers and Imidoyl Chlorides43ynthesis of 4,6-Dichloro-2-(dialkylamino)pyrimidines[1
By Bernard Stelander and Heinz Gunter Viehe"]
Phosgeniminium salts ( 1 ) react with nitriles, depending
on their substituents, either by addition to the CN triple
bond [Equation (a)][2v31or by condensation with the CH2
group alpha to the CN group, if this is activated by a further
substituent [Equation (b)lL31.Thus, acetonitrile ( 2 a ) does
not condense with (I), even in the presence of bases such
as tertiary amines.
0
0
(HsC)zN-C=N + (HsC)zN=CClZ -+ ( H3C) 2N-C =N-C =N(CH3)z
(1)
I
c 10
c1
B
N-C-CH2-C-N
+
(H3C)2N=CC12
c 10
+
I
c1
c 10
(H,C)zN\
/C-N
/C=C\
C1
C-N
(a)
(b)
(1)
['I
B. Stelander, lic. chimie and Prof. Dr. H. G. Viehe,
Laboratoire de Chimie Organique de I'Universit.5 de Louvain
Lavoisier C3, Place L. Pasteur, 1
B 1348 Louvain-la-Neuve (Belgium)
~
189
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