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Consecutive Nucleophilic and Electrophilic Attack on N2 Ligands Synthesis of Azo Compounds from Molecular Nitrogen.

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Table 1 . Ring systems synthesized; coalescence temperature
Cpd.
[a1
Clamp K in ( 1 )
z,and free encl-pie\
o f :IctivatioIl A c t for the ( P ) + ( M ) transition.
_ _ _ _ _ - ~ \l.
["C]
z
AGP
Yield
~.
'H-NMR
[bl
17.
L %I
(Solvent)
["CI
[kcal/mol]
(kJ/mol)
-H zC-CH2-
44 (from ( I f ) )
87 (from ( 1 d ) )
-70+_5
10.5k0.5
(43.9k 2 )
2.80
fib)
-HC=CH-
47 (from (1 a ) )
[CI
-
6.41
(1 c )
(1 d )
-HzC-S-CHz-H~C-SO~*Hz-
79 (from ( 4 b ) )
38 (from (I c ) )
-
-
-55f5
58 (from ( 4 b ) )
11.5k0.5
(48.1 f 2 )
10.7f0.5
(44.8f2)
3.39
3.94
-HzC-S(CHZ)zS-CHz-
235
(CeHdEtOH)
237-238
(C6HdEtOH)
hq.
281 -282
(glacial acetic acid)
193-194
(ethyl acetate)
-HzC-SOz(CH~)zSOz-CHz-
75 (from ( 1 e ) )
-
(1 a)
(1
el
(If)
[a]
[b]
[c]
[d]
315
(glacial acetic acid)
-70f5
[dl
-
3.54
__
Composition confirmed by correct elemental analyses and mass spectra.
80 M H z ; in CDC13 at 35°C; the &values apply to the H atoms indicated in the second column of the table.
The compound contains no diastereotopic bridge protons.
Sparingly soluble.
Halogenation and subsequent elimination transforms (1 a )
into the alkene (I b ) clamped by one CC double bond.
The (temperature dependent) 'H-NMR spectra of the ring
systems ( I a), ( 1 b), (I d), (1 e) show the molecules to be
helical at low temperatures: the signals of the benzylic CHZ
protons of (1 a), (1 d), (1 e) appear as singlets at room temperature but display considerable broadening on cooling[51.Splitting of this singlet to an AB system can be observed with
the sulfone (1 d) (z - 55 "C). Thus, as in the helicenes['],
interconversion between minus ( M ) and plus ( P ) helices is
observed, albeit below room temperature:
/PI
/la/
/MI
The 'H-NMR absorption of the terminal m-phenylene rings
of the alkene ( l b ) are shifted downfield relative to ( l a ) .
This is in accord with the widening of the bond angle at the
(Z)-stilbene group expected for ( I b ) and the consequent
increase in the distance between the m-phenylene rings.
As in a helical o-quaterphenyl skeleton prepared on a former
occasion[', 61, the racemization barrier of compounds (1)
depends upon the nature and the length of the clamp K :
the sulfone exhibits the highest (P)*(M) transition threshold
(cf. Table 1).
In the UV spectra, the transition from the open-chain hydrocarbon 3,3""-dimethyl-I : l',2': 1",3": 1"',2"': I ""-quinquephenyl ( 4 a ) (1,,,=237.5nm,
logs=4.73) to ( 1 a )
(L,,, =234 nm, logs =4.67), and the transition from (1 a ) to
( I b ) (imax=233
nm, logs=4.88) are accompanied by a hypsochromic shift (in CHCI3)['l. The former can be explained
in accord with the results of Woods et a1.r2b1for open-chain
polyphenylenes by a diminished coplanarity of the rings. In
the second case, a reduction of the bathochromic effect appears
to prevail, which is due to n-n interactions induced by clamping
by the CHzCHz chain as a result of bond angle widening
in the stilbene system ( I b). In the former case the K-K interactions appear to be overcompensated by biphenyl twisting.
We consider the significance of studies on such new (flexible)
helical systems to lie not only in stereochemical parallels
to the helicenes and spectroscopic and theoretical interest
in helical compounds of varying pitch and number of turns,
Angew. Chem. Int. Ed. Engl. 17 (1978) No. 4
but above all in the fact that comparison with space filling
models provides information about the quality of agreement
between such models and the intramolecular dynamic stereochemistry, and especially the flexibility of aromatic rings and
structural units. Predictions about such intramolecular processes in the numerous conceivable "phenylenicenes"[81 yet
to be synthesized are thus facilitated.
Received: January 24, 1978 [Z 917 IE]
German version: Angew. Chem. 90. 293 (1978)
CAS Registry numbers:
(1 a), 65879-17-6; (1 b ) , 65879-18-7; (1 c ) , 65879-19-8; ( 1 d ) , 65879-20-1;
(1 e), 65879-21-2; (1 f), 65879-22-3; ( 2 ) , 65879-23-4; ( 3 ) , 65879-24-5; ( 4 a ) ,
65879-25-6; ( 4 b ) , 65899-40-3; 3-etboxy-2-cyclohexen-1-one, 5323-87-5; ethane-l,2-dithiolate, 540-63-6
Cf. F . Vogtle, M . Atzmuller, W Wehner, J . Griitze, Angew. Chem. 89,
338 (1977); Angew. Chem. Int. Ed. Engl. 16, 325 (1977).
a) G. F . Woods, I . W n c k e r , J. Am. Chem. SOC. 70, 2174 (1948); b)
G . F . Woods, A. L. van Artsdale, F. 7: Reed, ibid. 72, 3221 (1950).
Cf. a) J . Grutze, F. Vogtle, Chem. Ber. 110, 1978 (1977); b) L. Rossa,
F . Vogtle, Tetrahedron Lett. 1977, 3577.
E . Hammerschmidt, W Bieber, F. Vogtle, Chem. Ber., in press.
This also applies to some phenylene protons; however, accurate assignment is difficult.
The racemate of the ethano compound ( 7 0 ) described in ref. [l] has
meanwhile been shown to crystallize spontaneously as enantiomers. We
are indebted to Doz. Dr. H. Irngartinger, Heidelberg, for this information.
i.
and E are strongly solvent dependent.
Molecules which form helices not by ortho fusing of aromatic rings
like helicenes but instead exist as helical conformers as a result of clamping
of suitably arranged o,m,p-oligophenylene units.
Consecutive Nucleophilic and Electrophilic Attack on
N2Ligands:Synthesis of Azo Compounds from Molecular Nitrogen"]
By Dieter Sellmann and Woldemar Weiss"]
The catalytic reduction of molecular nitrogen to organic
nitrogen compounds under mild conditions is not yet possible.
We recently found the reduction of coordinated dinitrogen
by bases (Xe) and subsequent protonation to represent a
new reaction of the N2 molecule['].
This reaction proceeds at low temperatures and appears
to be of fundamental importance with regard to our under[*] Prof. Dr. D. Sellmann, Dr. W. Weiss
Laboratorium fur Anorganische und Analytische Chemie der Gesamthochschule
Warburger Str. 100, Bauteil J, 4790 Paderborn (Germany)
269
e
-[ ;
a
Xe
L,M-N=N
e
e l - ,a
e CB
L,M-N=N:
---+L,M-N=NH
(2)
(a)
+ HQ
I
-30°C
C5H5(C0)2Mn-N=NH
CH,
X
(4)
C ~ H S ( C O ) ~ M ~ - N =+NCHI
standing of the mechanism and catalysis of Nz reduction;
the reaction steps can be observed separately and the Nz-coordinating metal center is preserved in the course of the Nz
reduction, as has been shown by the reaction of
C S H ~ M ~ ( C O )with
~ N LiC6H5
Z
and
togive the phenyldiazene complex C5HsMn(C0)~[N(CgH5~NH][21.
In order to prove the general validity of reaction (a) we
have also investigated the nucleophilic addition of alkyl anions
with LiCH3. Owing to the instability of alkyldiazene complexes, the addition product formed cannot be detected by
subsequent protonation. However, its appearance is unequivocally established by alkylation with methyl cations to yield
an azomethane complex.
oC
/ I\
d
0
- 30 "C, THF
'N
/I \
..-
__i
I
THF/Et,O
(1)
The intermediacy of the methyldiazene complex ( 4 ) is supported by the reaction of the corresponding methylhydrazine
complex (6).
C5H5Mn(C0)2(MeHN-NH,)
H1O+ l 0 T
------+
( I ) + ...
THF
f6 )
-30"C,THF
C' I .N=N*.
0
$N
C
I
0 CH3
In the first step of reaction (b) the V N ~and vco bands
of ( I ) at 2165, 1962, and 1908cm-' respectively in the IR
spectrum disappear while two new vco absorptions at 1853 and
1730cm-' are observed, which we attribute to the adduct
( 2 ) . In the second step, methylation by (CH3)jOBFd yields
complex (3); after chromatography (SiOZ/toluene/- 50°C)
and separation from decomposition and by-products, e. g. the
carbene complex CsHSMn(C0),[C(OCH3)CH3], (3) is isolated as analytically pure red crystals (yield 14 %), which
are moderately air- and heat sensitive, soluble in polar as
well as nonpolar organic solvents, and may be recrystallized
from acetone at lo"/- 78 "C. Independent synthesis from N,N'dimethylhydrazine yields an identical product.
C5H5Mn(C0)2. T H F + MeHN-NHMe
0 "C
+
THF
-
+
By analogy with the equilibrium[3] ( 1 ) + THF*(5)
Nz
in tetrahydrofuran solution, a similar equilibrium should also
exist between (I), ( 3 ) , and Nz. Indeed, on applying N2 pressure to ethereal solutions of the azomethane complex (3)
the following reaction is observed:
The formation of ( 1 ) is proved by IR spectroscopy, and
that of the azomethane liberated by gas chromatography and
mass spectrometry.
Thus, in principle, azomethane can be synthesized catalytically from molecular nitrogen according to the following cycle:
C H ~ N = N C H ~ YCH3@
I ) ~
H z W - 10°C
C5H5Mn(CO)2(MeHN-NHMe)
THF
(3)
N2
The IR spectrum of (3) in acetone shows two vco bands
of equal intensity at 1925 and 1860cm-'; in KBr two characteristic VCH bands are seen at 2998 and 2930cm-' and an
intense vN=Nband due to the azomethane ligand at 1518cm-'.
The 'H-NMR spectrum (60 MHz, (CD3)2C0,3 6 T , rel. TMS)
shows three signals of the correct intensity at 6=4.46 (C5H5
ring) and 6=4.18 and 4.00 (two nonequivalent methyl groups).
Hence, the azomethane ligand must be coordinated via one
nitrogen lone pair and not "side-on", a conclusion which
is additionally supported by the strong VN=N band in the
IR spectrum. In the mass spectrum (42eV, Ts=3OoC) the
molecular ion is observed at m/e=234; after loss of CO,
[C5H5Mn(CH3N=NCH3)]+ * is observed as the first fragment ion.
Protonation of the adduct (2) with HCI or H2S04 results,
even below - 30°C, in violent evolution of gas and regeneration of ( 1 ), probably due to
270
(3T
C H3@
Extensive repetition of this catalytic cycle, however, is impeded
by side reactions which destroy the C5H5Mn(C0)zcatalyst
after a short time.
Received: February 3, 1978 [Z 919 IE]
German version: Angew. Chem. YO, 295 (1978)
___[l] Reactions at Complexed Ligands, Part 26. This work was supported
by the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen
Industrie, and the Dr. Otto Rohm Memorial Foundation.-Part 25:
D. Sellrnann, A . Brand/, R. Endell, Z. Naturforsch., in press.
[2] D. Sellrnann, 19: Weiss,Angew. Chem. 89, 918 (1977); Angew. Chem.
Int. Ed. Engl. 16, 880 (1977).
[3] D. Sellrnann, Angew. Chem. 84,549 (1972); Angew. Chem. Int. Ed. Engl.
11, 534 (1972).
Angew. Chem. lnt. Ed. Engl. 17 (1978) N o . 4
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