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Bis(6-arsabenzene)chromium(0).

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A-s
Since, in all cases, the corresponding formamides can be
detected in the reaction solution by gas chromatography,
the role of the catalyst is possibly to hydrogenate the isocyanate."'
Received: February 10, 1986;
revised: March 19, 1986 [Z 1665 IE]
German version: Angew. Chem. 98 (1986) 568
CAS Registry numbers:
la, 624-83-9, Ib, 109-90-0; lc, 110-78-1; 2a, 101981-14-0; Zb, 101981-15-1:
Zc, l01981-16-2: 2e, 101981-17-3; PhNCO, 103-71-9: (PhNH)?CO, 102-07-8;
3
2, X I
= Mo
4, n l = Cr
as
5
-As-Ivlo(CO),
I
r-PrNCO, 1795-48-8: (i-PrNH),CO, 4128-37-4: (EtNH),CO, 623-76-7; (iPrN H):CO. 623-95-0; [N(PPh,)Z][H,Ru,(CO),*], 70073- 17-5.
[ I ] E. L. Muetterties, Science 196 (1977) 839; Bull. Soc. Chim. Belg. 84 (1975)
959; B. F. G. Johnson, J. Lewis, Pure Appl. Chem. 44 (1975) 229; R. Whyman in B. F G Johnson (Ed.): Trunsrfion Mefal Clrrslers, Wiley, Chichester 1980.
121 E. L. Muetterties, M. J . Krause, Angew. Chem. 95 (1983) 135; Angew.
Chem. Int. Ed. Enyl. 22 (1983) 135.
[3] G. Suss-Fink, G. Herrmann, U, Thewait, Angew. Chem. 95 (1983) 899;
Angen,. C'liem. 1nf. Ed. Eng1. 22 (1983) 880; Angew. Chem. Suppl. 1982.
71.
[4] J. W. Koepke, J. R. Johnson, S. A. R. Knox, H. D. Kaesz, J . Am. Chem.
Soc. 97 (1975) 3947.
[S] Turnover number (catalytic turnover): mole product/mole catalyst.
161 H. Hoberg, B. W. Oster, C. Kruger, Y . H. Tsay, J. Orgunomef. Chem. 252
(1983) 365.
171 G. Suss-Fink, G. Herrmann, unpublished results; cf. G. Herrmann, Disserm i o n . Universitat Bayreuth 1986.
Bis($-arsabenzene)chromium(O)**
By Christoph Elschenbroich, * Jorg Kroker,
Werner Massa, Martin Wunsch, and Arthur J . Ashe I I I
The cyclovoltammetrically determined redox potential
E1/2(3/3'"))=-0.51 V (reversible, at 25°C in 1,2-dimethoxyethane (DME)/tetra-n-butylammonium perchlorate
(TBAP) versus saturated calomel electrode) displays an
anodic shift of 0.17 V compared to that of bis($-benzene)chromium. 3 can also be reduced, albeit not com( E l , 2 ( 3 / 3 0 0 ) =- 1.36 V,
25"C,
pletely
reversibly
100 mVs-', AE,=94 mV, IpJIpc=0.6). Comparison with
the electrochemical data for free arsabenzene 1
( E , , 2 ( 1 / 1 0 8 ) =- I.lOV, irrev., E , , 2 ( 1 / 1 0 0 ) = -2.08V1x1)
shows that the shifts of the redox potentials due to complexation are similar in magnitude for the transitions from
the neutral molecule to the radical cation and to the radical anion ( 0.59 V and 0.72 V, respectively).
An $-coordination of the two heteroarenes in 3 can already be inferred from the N M R spectra (Table l ) : As has
already been observed in the case of 2, the unusually large
difference in the shielding of the protons H-2,6 and H3,4,5 in the free ligand 1 is reduced in the sandwich complex 3 . According to the 'H-NMR data of
[(C,H,As)Mo(CO),] 5 this does not occur upon q '-coordination.['] The NMR spectra of 3 show no signs of freezingin of ring rotation down to T = -70°C. Such a freezing-in
could not be ruled out a priori, since a rotational barrier
had been found for open metallocenes.'"'l
To answer the related question as to whether a certain
conformation is preferred, a single crystal of 3 , twinned
along (OOI), was subjected to an X-ray crystallographic
analysis (space group P2,/n; a=658.8(5), b=783.1(5),
c=963.8(4) pm; 1=94.78(5)"; Z = 2 ; T = -90°C). The
analysis revealed a high degree of disorder of the whole
complex. In this context, note that no refined crystal structure investigations of sandwich complexes with unsubstituted heterocycles have thus far been reported in the liter-
+
+
Compared to the extensively documented organic chemistry of six-membered ring heterocycles only very few studies on the synthesis and properties of bis(q'-heteroarene)metal complexes have so far been reported in the literature.I2' The reasons for this are the limited number of synthetic routes to such complexes as well as the ambident
nature of many heteroarenes. The latter aspect requires for
the synthesis of an $'-complex the donor ability of lone
pairs, which favors classical q'-coordination, to be suppressed.13] In the case of pyridine the lone pair on the nitrogen atom could be sterically blocked by 2,6-dialkyl substitution, thus enabling the synthesis of bis(2,6-dimethyl$-pyridine)chromium as the first binary sandwich complex of a neutral heteroarene.'2e.o In our attempts to prepare the unsubstituted parent compounds ( T ~ ' - C ~ H ~ E ) ~ CTable
~ I . 'H- and "C-NMR parameters of the ligand I and the complexes 3
( E = G r o u p 5B element) we first selected arsabenzene 1 as
and 4 [a].
ligand, since the o-basicity of 1 is much lower than that of
1
3
4 Id1
pyridine,I4] and, furthermore, the ability of 1 to undergo
$-coordination has already been demonstrated in the for'H-NMR
mation of the complex [(T~'-C~H~AS)MO(CO)~]
2.IS1
6(H-2,6); (As)[bl
9.79
4.22( -5.57) [c]
5.99 -3.80)
We have now synthesized his($-arsabenzene)chrom11.1
7.0
9.5
'J(H-2,H-3)
6(H-3,5); (As)
7.90
5.10 (-2.80)
5.55 -2.35)
ium(0) 3 in 15% yield by metal atom-ligand cocondensa'J(H-3,H-4)
8.4
6.2
7.0
tion. The reddish-black, air-sensitive crystals of 3 are sub6(H-4); (As)
7.60
4.86 ( - 2.74)
5.98 - 1.62)
limable under high vacuum without decomposition."]
["I Prof. Dr. C. Elschenbroich, Dip1.-Chem. J. Kroker,
Priv.-Doz. Dr. W. Massa, DipLChem. M. Wiinsch
Fachbereich Chemie der Universitat
Hans-Meerwcin-Strasse, D-3550 Marburg 1 (FRG)
['*I
Prof. Dr. A. J. Ashe 111
Department of Chemistry, University of Michigan
Ann Arbor, MI 48 109 (USA)
Meral n-Complexes of Benzene Derivatives, Part 27. This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen 1ndustrie.-Part 26: [l].
Angen. Chem Int Ed. Engl. 25 (1986) NO. 6
"C-NMR
6(C-2,6); (As)
'J(C-2.H-2)
6(C-3,5); (AS)
'J(C-3, H-3)
6(C-4): ( A @
'J(C-4,H-4)
168.4
I58 7
133.8
156.8
129.0
159.4
86.8 (-81.6)
164.8
84.8 (-49.0)
163.2
75.7 (-53.3)
164.4
114.9 ( 53.5)
167.9
95.6 ( - 38.2)
170.3
91.1 (-37.9)
171.6
[a] I n [D8]THF at 30°C. 400 and 100 MHz, resp., 6 values relative to TMS,
coupling constants in Hz. [b] A 6 = coordination shift. [c] 6(H-2,6) is temperature dependent: 4.25 (+3O"C), 4.16 ( - 10°C). 4.06 (-40°C). [d] 4 was synthesized analogously to 2 151.
0 VCH Verlugsgesellschufi mbH. 0-6940 Wernherm, 1986
0570-0833/86/0606-0571 $ 02 50/0
57 1
ature. In the case of 3, the disorder can be described to a
good approximation in terms of a model in which half of
the As atoms occupy position 1 of the ring and the other
half position 4 of the ring (R,=0.086 for 424 reflections).
The chromium atom is located 25 pm from a crystallographic center of symmetry, so that the two alternative orientations of the complex are slightly displaced from each
other. It is therefore impossible to infer structural details
of the coordinated arsabenzene rings. However, from the
positions of the As atoms it can be concluded that either
the cis- or the trans-eclipsed form is present, and, from the
maximum Cr-As distance of 252 pm that genuine $-coordination prevails." 'I
A first indication of the electronic structure of 3 is provided by the ESR spectra of the radical cation 3'@:
Whereas the data obtained for 3" in fluid solution (dimethylformamide (DMF)/CHCl3= 1 : 1, 30"C, (g)= 1.9892,
a(53Cr)= 19.3 G, ligand hyperfine structure only partially
resolved) are consistent with the parameters of bis(q6-arene)chromium(d5) cations,["] the spectrum of 3
recorded in rigid solution (DMF/CHC13= 1 : I, - 135"C, g n =
1.9730, g L = 1.9980, A,(53Cr)=20 G) shows a g-anisotropy, typical for his($'-arene)chromium anion^.^'^] In the latter, an MO with dominant n-ligand character is singly occupied. The similar g-anisotropy thus suggests that-in
contrast to cations of the corresponding carbocyclic arene
complex-the singly occupied HOMO in 3 O @ has considerable ligand character.
''
Received: December 30, 1985;
revised: March 17, 1986 [Z 1600 IE]
German version: Angew. Chem. 98 (1986) 562
CAS Registry numbers:
1, 289-31-6; 3, 101934-66-1; 30°, 101934-67-2; Cr, 7440-47-3
[ I ] C. Elschenbroich, J. Schneider, H. Prinzbach, W.-0. Fessner, Organometallics, in press.
[2] a) G. E. Herberich, G. Greiss, H. F. Heil, J. Miiller, J . Chem. SOC.Chem.
Commun. 1971. 1328; b) G. E. Herberich, G. Greiss, Chem. Ber. 105
(1972) 3413; c) G. E. Herberich, M. J. Becker, G. Greiss, ibid. 107 (1974)
3780; d) A. J. Ashe 111, E. Myers, P. Shu, T. V. Lehmann, J . Am. Chem.
SOC.97 (1975) 6865; e) L. M. Simmons, P. E. Riley, R. E. Davies, J. J.
Lagowski, rbid. 98 (1976) 1044; f) P. E. Riley, R. E. Davies, Inorg. Chem.
15 (1976) 2735; g) A. J. Ashe 111, W. Butler, H. F. Sandford, J. Am.
Chem. SOC.101 (1979) 7066; h) binary transition metal complexes of the
h"-phosphorin anions 1-R-2,4,6-Rj-CrH2PQ undergo q'-coordination
and are to be regarded as 2,6-bridged open metallocenes: T. Dave, S .
Berger, E. Bilger, H. Kaletsch, J. Pebler, J. Knecht, K. Dimroth, Orgunometallics 4 (1985) 1565; G. Baum, W. Massa, ibid. 4 (1985) 1572; i) an
q6-bonded phosphabenzene derivative is present in the mixed sandwich
F. Nief, C. Charrier, F.
complex [(1,3,5-Phl-q6-CsH2P)(qs-CsHs)Mn]:
Mathey, M. Simalty, J . Organomet. Chem. 187(1980) 277; J. Fischer, A.
De Cian, F. Nief, Acta Crystallogr. Sect. 8 3 7 (1981) 1067.
[3] a) J. Deberitz, H. Noth, Chem. Ber. 103 (1970) 2542; 106 (1973) 2222; J.
Organornet. Chem. 49 (1973) 453; b) H. Vahrenkamp, H. Noth, Chem.
Ber. 105 (1972) 1148; 106 (1973) 2227; H.-G. Biedermann, K. Of&. J.
Tajtelbaum, Z . Naturforsch. B: Anorg. Chem. Org. Chem. 31 [ 1976)
321.
141 a) A. J. Ashe 111, Top. Curr. Chem. 105 (1982) 125; b) R. V. Hodges, J. L.
Beauchamp, A. J. Ashe 111, W:T. Chan, Organometallics 4 (1985) 457.
151 A. J. Ashe 111, J. C. Colburn, J . Am. Chem. SOC.99 (1977) 8099.
161 Procedure: The vapors of arsabenzene 1 (3 g, 36 mmol) [7] and chromium (0.3 g, 5.8 mmol) were cocondensed over a period of 1.5 h onto the
walls of a n evacuated, cooled ( - 196°C) reaction vessel. After warming
to room temperature under N2, the dark red co-condensate was taken up
in tetrahydrofuran and the solution filtered over silanated silica gel. The
solvent and unchanged 1 , which can be recovered in this way, were removed in a high vacuum. Recrystallization of the residue from toluene
afforded 3 in the form of reddish-black, analytically pure crystals (yield:
290 mg (0.87 mmol), 15% referred to vaporized Cr). M.p. 253OC (dec.);
MS (El, 70 ev): r n / z 332 (26%, Me),192 (39%, MO-L), 140 (58%. L"),
52 (100% "Cr').
[7] A. J. Ashe 111, W.-T. Chan, J. Org. Chem. 44 (1979) 1409.
IS] M. Wiinsch, C. Elschenbroich, unpublished.
572
0 VCH Verlagsgesellschaji mbH. 0-6940 Wemherm, 1986
191 'H-NMR data of 5 : 6=9.6 (H-2,6), 7.8 ( H - 3 3 , 7.5 (H-4) [5]; cf. also A.
J. Ashe 111, R. R. Sharp, J. W. Tolan, J . Am. Chem. Soc. 98 (1976)
5451.
[lo] D. R. Wilson, R. D. Ernst, T. H. Cymbaluk, Organometallics 2 (1983)
1220.
[ I 11 Other Cr-As distances: 252 pm in [(CO),C~AS(M~)~MII(CO)~]
(H. Vahrenkamp, Chem. Ber. 105 (1972) 1486), 238 pm in [C6H5As(Cr(CO)5J2J
(G. Huttner, J. von Seyerl, M. Marsili, H.-G. Schmid, Angew. Chem. 87
(1975) 455; Angew. Chem. I n [ . Ed. Engl. 14 (1975) 434).
[I21 C. Elschenbroich, R. Mockel, U. Zenneck, D. Clack, Ber. Bunsenges.
Phys. Chem. 83 (1979) 1008.
I131 C . Elschenbroich, E. Bilger, J. Koch, J. Weber, J. Am. Chem. Soc. 106
(1984) 4297, and references cited therein.
Dihydropyrazolopyridine and Bis(dihydroindo1izine)Novel Mono- and Bifunctional Photochromic
Systems**
By Heinz Diirr,* Charles Schommer, and
Thomas Miinzmay
Dedicated to Professor Heinz A. Sraab on the occasion of his
60th birthday
Photochromic systems have long claimed worldwide interest."] They are not only of great importance in fundamental research but also in practice, where they find application as light-filters, chemical actinometers, silver-free
materials for display devices in reprotechnology and more
recently in computer chips."' We recently reported on a
photochromic system based on a 1,5-electrocyclization of
spir~dihydroindolizine.~'~
The aim of our present work is to
prepare new systems that can undergo 1,5-electrocyclizations as well as molecules containing two chromophores.
We now report on the extraordinary reactivity of l-pyridinioamides ("pyridin-N-imines") 1 towards pentafulvenes such as 2. The deep-colored betaines initially
formed are converted in a 1,5-electrocyclic reaction into
the novel dihydropyrazolo[l,5-a]pyridines 4 ; these are the
first dihydropyrazole-based photochromic systems (Type
2,3-systems"').
For the synthesis of 4, the N-imines 1 were generated
from the corresponding N-aminopyridinium
with
potassium carbonate in anhydrous dimethylformamide
and allowed to react directly with 2 without prior isolati0n.1~~1
The deep-red to violet products transform within a few
hours into the yellow title compounds 4, whose structure
2
3
A . dis.
d
' h v , con.
E=COOMe
/--u
4
[*] Prof. Dr. H. Diirr, DipLChem. C . Schomrner, Dipl.-Chem. T . Miinzmay
Fachrichtung 14. I Organische Chemie der Universitat
D-6600 Saarbriicken I 1 (FRG)
[**I Photochromic Systems, Part 11. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen In.
dustrie.-Part 10: H. Diirr, V. Bach, Tetruhedron Lett.. in press.
0570-0833/86/0606-0572$ 02.50/0
Angew. Chem. Int. Ed. Engl. 25 (1986) No. 6
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