Organic syntheses via transition metal complexes. 117.1 3-Aza-1-metalla-1,3,5-hexatrienes (M = Cr, W): Generation and π-cyclization to pyrroles

Article abstract of DOI:10.1021/om011032d

The organic synthesis via transition metal complexes was studied. 3-aza-1-metallahexa-1,3,5-trienes were obtained in good yields by condensation of the (NH₂-amino)carbene complexes (CO)₅M=C(Ph)NH₂ (M = Cr, W) with α,β-unsaturated acid amides in the presence of phosphoryl chloride and triethylamine. The hexatrienes were found to undergo thermally induced π-cyclization to pyrroles.

Full text of DOI:10.1021/om011032d

Organometallics 2002, 21, 1819-1824
1819
Or ga n ic Syn th eses via Tr a n sition Meta l Com p lexes. 117.1
3-Aza -1-m eta lla -1,3,5-h exa tr ien es (M ) Cr , W):
Gen er a tion a n d π-Cycliza tion to P yr r oles
Rudolf Aumann,* Dominik Vogt, and Roland Fro¨hlich†
Organisch-Chemisches Institut der Universita¨t Mu¨nster, Corrensstrasse 40,
D-48149 Mu¨nster, Germany
Received December 4, 2001
3-Aza-1-metallahexa-1,3,5-trienes 3a -f were obtained in good yields by condensation of
the (NH2-amino)carbene complexes (CO)5MdC(Ph)NH2 (1a ,b; M ) Cr, W) with R,â-
unsaturated acid amides 2 in the presence of phosphoryl chloride and triethylamine.
Compounds 3 undergo a thermally induced π-cyclization to pyrroles 4.
In tr od u ction
tigation to 3-aza-1-metalla-1,3,5-hexatrienes of chro-
mium and tungsten.
The term “azametallahexatriene” has been estab-
lished as a convenient nomenclature for a group of metal
carbene complexes in which a nitrogen atom is incor-
porated into the ligand backbone of a metallahexatriene2
(Chart 1). Since 1-metalla-1,3,5-hexatrienes of chro-
mium and tungsten were found to readily undergo a
π-cyclization to cyclopentadiene complexes, 5-aza-1-
metalla-1,3,5-hexatrienes were considered as the most
likely candidates for the formation of N-heterocyclic
compounds in an analogous reactions. It could indeed
be shown that 5-aza-1-metalla-1,3,5-hexatrienes gave
2H-pyrrole complexes by a “typical” π-cyclization, but
in addition these compounds were found to also afford
dihydropyridones by an “atypical” π-cyclization involv-
ing a chain extension by insertion of carbon monoxide.
Generation of pyrroles and dihydropyridones by π-cy-
clization of 5-aza-1-metalla-1,3,5-trienes was achieved
by two different approaches, in which the 5-aza-1-
metalla-1,3,5-trienes were generated either by insertion
of an alkyne into the MdC bond of an iminocarbene
complex (“alkyne route to pyrroles”)3,4 or by addition of
a NH-imino group to a (1-alkynyl)carbene complex
(“imine route to pyrroles”).5,6 Following these findings,
we decided to perform some systematic studies on the
chemistry of azametallahexatrienes. Since 5-aza-1-met-
alla-1,3,5-hexatrienes and cross-conjugated azametal-
lahexatrienes7 have been the only compounds studied
so far (Chart 1), we decided to next extend our inves-
Resu lts a n d Discu ssion
3-Aza -1-m eta lla h exa -1,3,5-tr ien es. We now report
on the preparation of 3-aza-1-metallahexa-1,3,5-trienes,
which gained our interest as potential precursors to
pyrroles. Our strategy was based on the condensation
of (NH2-amino)carbene complexes (CO)5MdC(NH2)Ph
(1a ,b; M ) Cr, W) with R,â-unsaturated acid amides 2.
Related condensation reactions of (NH2-amino)carbene
complexes 1a ,b with the acid amides R1CONR2 (R )
alkyl, aryl) to give 4-amino-3-aza-1-metalla-1,2-buta-
dienes (CO)5MdC(Ph)NdC(NR2)R1,8,9 with aldehydes
RCHO (R ) aryl) to give 3-aza-1-metalla-1,2-butadienes
(CO)5MdC(Ph)NdCHR, and with acid chlorides RCOCl
(R ) aryl) to yield 4-acyloxy-3-aza-1-metalla-1,2-buta-
dienes (CO)5MdC(Ph)NdC(OCOR)R have been previ-
ously described.8,10
Condensation of the aminocarbene complex 1 with the
R,â-unsaturated acid amide 2 in the presence of phos-
phoryl chloride and triethylamine indeed afforded 3-aza-
1-metallahexa-1,3,5-trienes 3 in good yields (Scheme 1).
It is obvious that this reaction was initiated by the
transformation of the R,â-unsaturated acid amide 2 into
the iminium chloride 5, which is an electrophile strong
enough to interact with the aminocarbene complex 1.
(7) (a) Aumann, R.; J asper, B.; Fro¨hlich, R.; Zippel, F. Organome-
tallics 1995, 14, 3167. (b) Aumann, R.; Yu, Z.; Fro¨hlich, R.; Zippel, F.
Eur. J . Inorg. Chem. 1998, 1623.
(8) Aumann, R.; Althaus, S.; Kru¨ger, C.; Betz, P. Chem. Ber. 1989,
122, 357.
(9) For the generation of 4-amino-3-aza-1-metalla-1,3-butadiene
from aminocarbene complexes and inamines see: (a) Do¨tz, H. H. Chem.
Ber. 1980, 113, 3597. (b) Do¨tz, K. H. J . Organomet. Chem. 1976, 118,
C13.
(10) For earlier work on similar structures see: (a) Fischer, H. J .
Organomet. Chem. 1980, 197, 303. (b) Fischer, H.; Schubert, U.; Ma¨rkl,
R. Chem Ber. 1981, 114, 3412. (c) Fischer, H.; Ma¨rkl, R. Chem. Ber.
1985, 118, 3683. (d) Fischer, H.; Seitz, F.; Mu¨ller, G. J . Organomet.
Chem. 1987, 320, 185. (e) Fischer, H.; Schubert, U. Angew. Chem. 1981,
93, 482; Angew. Chem., Int. Ed. Engl. 1981, 20, 461. (f) Fischer, H.;
Zeuner, S.; Ackermann, K.; Schubert, U. J . Organomet. Chem. 1984,
263, 201. (g) Seitz, F.; Fischer, H.; Riede, J . J . Organomet. Chem. 1985,
287, 87. (h) Fischer, H.; Zeuner, S. J . Organomet. Chem. 1987, 327,
63. (i) Yang, D. C.; Dragisich, V.; Wulff, W. D.; Huffman, C. J . Am.
Chem. Soc. 1988, 110, 307. (j) Fischer, E. O.; Hollfelder, H.; Kreissl,
F. R.; Uedelhoven, W. J . Organomet. Chem. 1976, 113, C31. (k) Knauss,
L.; Fischer, E. O. Chem. Ber. 1970, 103, 3744.
* To whom correspondence should be addressed.
† X-ray structure analysis.
(1) For part 116 of this series see: Aumann, R.; Vogt, D.; Fu, X.;
Fro¨hlich, R.; Schwab, P. Organometallics, in press.
(2) For a recent review on metallahexatrienes see: Aumann, R. Eur.
J . Org. Chem. 2000, 17-31.
(3) Dragisich, V.; Murray, C. K.; Warner, B. P.; Wulff, W. D.; Yang,
D. C. J . Am. Chem. Soc. 1990, 112, 1251.
(4) (a) Aumann, R.; Heinen, H. J . Organomet. Chem. 1990, 389, C1.
(b) Aumann, R.; Heinen, H. J . Organomet. Chem. 1990, 391, C7. (c)
Aumann, R., Heinen, H.; Kru¨ger, C.; Betz, P. Chem. Ber. 1990, 123,
599-604. (d) Aumann, R., Heinen, H.; Kru¨ger, C.; Betz, P. Chem. Ber.
1990, 123, 605-610. (e) Aumann, R.; Heinen, H.; Dartmann, M.; Krebs,
B. Chem. Ber. 1991, 124, 2587-2593.
(5) Funke, F.; Duetsch, M.; Stein, F.; Noltemeyer, M.; de Meijere,
A. Chem. Ber. 1994, 127, 911.
(6) Aumann, R.; Fro¨hlich, R.; Zippel, F. Organometallics 1997, 16,
2571.
10.1021/om011032d CCC: $22.00 © 2002 American Chemical Society
Publication on Web 04/04/2002

1820 Organometallics, Vol. 21, No. 9, 2002
Ch a r t 1. Ba sic Str u ctu r es of Aza m eta lla h exa tr ien es (M ) Cr , W)
Aumann et al.
Sch em e 1. 3-Aza -1-m eta lla -1,3,5-h exa tr ien es 3: Gen er a tion fr om Am in oca r ben e Com p lexes 1 a n d
Tr a n sfor m a tion in to P yr r oles 4
a
b
Isolated yields in percent. Isolated in small amount from the equilibrium mixture. c Not isolated, but analyzed in a mixture
with compound 3f.
P yr r oles by Th er m olysis of 3-Aza -1-m eta lla -1,3,5-
h exatr ien es. Thermolysis of 3-aza-1-metallahexatrienes
3 requires 80-100 °C and leads to production of pyrroles
4. This process is assumed to involve the π-cyclization
of compound 3 into the zwitterionic intermediate 6, from
which the 2H-pyrrole complex 7 is obtained by a 1,2-
transfer of the M(CO)5 unit (Scheme 1). (5,6-η2)-3-
Aza-1-metallahexa-1,3,5-trienes 9 have been detected
in the reaction mixture in varying amounts, depending
on the reaction conditions. These compounds are gener-
ated in a nonproductive equilibrium by chelation of
compounds (3E)-3 involving the loss of a carbonyl ligand.
Thermally induced ligand disengagement from 2H-
pyrrole complexes 7 affords the thermolabile 2H-pyr-
roles 8 and finally the stable 1H-pyrroles 4. While 2H-
pyrrole complexes 7 could not be isolated under these
reaction conditions, it was possible to obtain and fully
characterize 2H-pyrrole complexes from π-cyclization of
5-aza-1-metallahexa-1,3,5-trienes under mild condi-
tions.4c,6 The relatively high reaction temperature of 80-
100 °C required for the π-cyclization of 3-aza-1-metal-
lahexa-1,3,5-trienes 3 is attributed not only to the low

Organic Syntheses via Transition Metal Complexes
Organometallics, Vol. 21, No. 9, 2002 1821
Ch a r t 2. Ba sic Str u ctu r es of Com p ou n d s 3 w ith Differ en t Geom etr ies: Im in oca r ben e Str u ctu r e A,
2-Aza a llen yl Str u ctu r e B, a n d Im in iu m Ca r bon ylm eta la te Str u ctu r e C
electrophilicity of aminocarbene complexes but also to
the lack of stabilization of the positive charge in the
zwitterionic intermediate 6.
St r u ct u r e of 3-Aza -1-m et a lla -1,3,5-h exa t r ien es.
The 3-aza-1-metalla-1,3,5-hexatrienes 3 were character-
ized by 1H and 13C NMR spectra, including 1J (C,H) and
2,3J (C,H) correlation experiments performed with com-
pounds 3a ,e. The temperature dependence of the NMR
spectra was extensively studied with compounds 3d -f.
Compound 3d was characterized also by a crystal
structure analysis. The 13C NMR signals of the carbene
carbon atom are observed in a narrow range character-
istic of the specific metal unit [e.g. 3a (30 °C) δ(CrdC)
253.9, 3d (30 °C) δ(WdC) 236.7]. Since this range is
appreciably shifted upfield compared to aminocarbene
complexes of the corresponding metal unit [e.g. (CO)5-
WdC(OEt)CHdC(NMe2)Ph at δ 271.5, (CO)5WdC(NH2)-
Ph at δ 264.2], it was thought that compounds 3 would
F igu r e 1. 1H NMR signals of the NCH2 group of compound
adopt the 2-azaallenyl structure B or the iminium
3f in [D8]toluene in the temperature range from -55 to
+10 °C.
carbonylmetalate structure C instead of the iminocar-
bene structure A (Chart 2). Experimental proof for this
assumption was provided both by NMR studies and by
a crystal structure analysis of compound 3a . Since
structures B and C were expected to be chiral, meth-
ylene protons attached to the terminal nitrogen atom,
as in compound 3f [NR2 ) N(Me)CH2Ph], served as a
probe for the structure elucidation by NMR experi-
ments.11
Since the 1H NMR spectrum of compound 3f exhibited
a singlet for the NCH3 group (δ 3.19) and an AB system
2
for the NCH2Ph unit (δ 4.98 and 4.63, J ) 16.5 Hz; 10
°C, 360 MHz, Figure 1), an iminocarbene structure A
of this compound was excluded.
The line shape of the proton signals of the CH2N unit
of compound 3f was strongly temperature dependent
(Figure 1). A “frozen spectrum” obtained at -55 °C
showed two AB systems at δ 5.45 and 4.25 (2J ) ca.
-15 Hz) and δ 4.86 and 4.70 (2J ) ca. -17 Hz), which
collapsed to one AB system above 10 °C and finally gave
a single signal above 75 °C. The assignment of signals
is based on spin saturation transfer experiments, in
order to minimize the uncertainty resulting from the
temperature drift of the signals. On the basis of the
coalescence temperature and the difference of chemical
shifts, it was possible to distinguish between two
different dynamic processes, for which ∆Gq values of ca.
50 and 70 kJ /mol were estimated.
F igu r e 2. Molecular structure of the 4-amino-1-metalla-
1,3,5-hexatriene 3a . Selected bond lengths (Å), bond angles
(deg), and dihedral angles (deg): Cr-C1 ) 2.114(2), C1-
N2 ) 1.282(3), N2-C3 ) 1.322(3), C3-C4 ) 1.462(3), C4-
C5 ) 1.313 (3), C5-C51 ) 1.461(3), C3-N6 ) 1.335(3),
C1-C11 ) 1.506(3); N2-C1-Cr ) 127.5(2), C1-N2-C3
)
137.9(2), N2-C3-C4 ) 118.7(2), N6-C3-C4 )
The crystal structure analysis of compound 3a (Figure
2) reveals a strongly bent CNC unit, C1-N2-C3 )
137.9°, in which the plane defined by the atoms C1, N2,
and C3 is tilted by 84.3° against the plane defined the
atoms N6, C3, and C4. The distance C1-N2 ) 1.282(3)
Å is shorter than N2-C3 ) 1.322(3) Å and also shorter
120.8(2); Cr-C1-N2-C3 ) -6.2(4), C1-N2-C3-N6 )
-84.3(4), C1-N2-C3-C4 ) 102.9(3), N2-C3-C4-C5 )
-10.2(4), N6-C3-C4-C5 ) 177.0(2), C3-C4-C5-C51 )
178.3(2), C4-C5-C51-C52 ) 173.3 (3).
than C3-N6 ) 1.335(3) Å, thus indicating a strong
charge delocalization, as is represented by the iminium
carbonylmetalate structure C (Chart 2), which according
to the dynamic NMR spectra of compound 3f (Figure 1)
(11) Do¨tz, K. H.; Muhlemeier, U.; Schubert, U.; Orama, O. J .
Organomet. Chem. 1983, 247, 187.

1822 Organometallics, Vol. 21, No. 9, 2002
Aumann et al.
(1) Å, b ) 14.935(2) Å, c ) 16.036(1) Å, â ) 102.34(1)°, V )
2226.2(4) Å3, Fcalcd ) 1.356 g cm-3, F(000) ) 936 e, µ ) 5.49
cm-1, empirical absorption correction via æ scan data (0.948
e C e 0.999), Z ) 4, monoclinic, space group P21/c (No. 14),
λ ) 0.710 73 Å, T ) 293 K, ω/2θ scans, 4790 reflections
collected (-h, -k, (l), (sin θ)/λ ) 0.62 Å-1, 4516 independent
and 2988 observed reflections (I g 2σ(I)), 282 refined param-
eters, R1 ) 0.039, wR2 ) 0.108, maximum residual electron
density 0.29 (-0.21) e Å-3, hydrogens calculated and refined
as riding atoms.
as well as the crystal structure analysis of compound
3a is considered the most adequate structural descrip-
tion of the compound 3.
Con clu sion . A new entry to the formation of pyrroles
from the readily available (NH2-amino)carbene com-
plexes (CO)5MdC(Ph)NH2 (1a ,b; M ) Cr, W) was found.
It involves generation of 3-aza-1-metallahexa-1,3,5-
trienes 3 by condensation of compounds 1 with R,â-
unsaturated acid amides 2 and subsequent π-cyclization
of these compounds to pyrroles 4. The reaction is highly
regioselective. The reaction may in principle be extended
to the synthesis of pyrroles other than those containing
amino functionalities.
4a .
Exp er im en ta l Section
In st r u m en t a t ion . NMR: Bruker AM 360, Bruker AMX
400, and Varian U 600. All new compounds were routinely
analyzed by 1H, 13C, DEPT, (1H,1H)COSY, (1H,13C)GHSQC, and
(1H,13C)GHMBC experiments on a Bruker AMX 400 instru-
ment. IR: FT-IR Bio-Rad Digilab Division FTS-45. MS:
Finnigan MAT8200. Elemental analyses: Heraeus CHN-O
Rapid. Column chromatography: Merck silica gel 60F. Flash
chromatography was performed under an argon atmosphere.
TLC: Merck silica gel 60F254. Rf values refer to TLC tests.
4-(Dim eth yla m in o)-2,6-d ip h en yl-3-a za -1-p en ta ca r bon -
ylch r om a -1,3,5-h exa tr ien e (3a ) a n d 2-(Dim eth yla m in o)-
4,5-d ip h en yl-1H -p yr r ole (4a ). To N,N-dimethyl-3-phenyl-
acrylamide (2a ; 263 mg, 1.50 mmol) and 2 mL of dry dichlo-
romethane in a 5 mL screw-top vessel was added phosphoryl
chloride (229 mg, 1.50 mmol) with stirring at 0 °C. To the pale
yellow precipitate that was formed within ca. 30 min was
added a mixture of pentacarbonyl(R-NH2-aminobenzylidene)-
chromium (1a ; 149 mg, 0.50 mmol) and triethylamine (505 mg,
5.00 mmol) in 1 mL of dry dichloromethane. Stirring was
continued at 20 °C for 24 h. Flash chromatography of the
mixture on silica gel (column 20 × 2 cm) with n-pentane
afforded colorless hexacarbonylchromium, which was dis-
carded. Elution with n-pentane/dichloromethane (3:1) yielded
a red fraction containing the 3-aza-1-chroma-1,3,5-hexatriene
3a (161 mg, 71%, Rf ) 0.4 on silica gel with n-pentane/
dichloromethane (2:1), red crystals from dichloromethane/
diethyl ether at -20 °C, dec pt 74 °C). Thermolysis of
compound 3a (150 mg, 0.33 mmol) in 2 mL of benzene at 80
°C for 14 h gave hexacarbonylchromium and 2-(dimethyl-
amino)-4,5-diphenyl-1H-pyrrole (4a ), which was isolated by
chromatography on silica gel (71 mg, 82%, pale yellow oil).
3a .
1H NMR (C6D6, 303 K, 360 MHz): δ 7.78 (1 H, NH), 7.58, 7.26,
7.20-6.90 (CH each, 2:2:6 H, 4-Ph and 5-Ph), 5.65 (1 H, d, J
4
) 3 Hz, 3-H), 2.38 (6 H, s, 2 NCH3). 13C NMR (C6D6): δ 145.1
(Cq, C2), 138.1 and 134.5 (Cq each, i-C each of 4-Ph and 5-H),
128.9, 128.7, 128.6, and 126.7 (CH each, 2:2:2:2, o-CH and
m-CH each of 2 Ph), 125.9 and 125.8 (CH each, p-C each Ph),
122.4 and 122.3 (Cq each, C4 and C5), 93.9 (CH, C3), 42.5 (2
NCH3). IR (diffuse reflection; cm-1): 3329.8 (ν(N-H)). MS (70
eV; m/e (%)): 262 (80) [M+], 247 (100), 206 (15), 131 (9), 104
(10), 103 (5).
2,6-Diph en yl-4-pyr r olidin o-3-aza-1-pen tacar bon ylch r o-
m a -1,3,5-h exa tr ien e (3b) a n d 4,5-Dip h en yl-2-p yr r olid in o-
1H-p yr r ole (4b). 3-Phenyl-1-pyrrolidinoprop-2-en-1-one (2b;
201 mg, 1.00 mmol) was reacted with phosphoryl chloride (145
mg, 0.95 mmol), pentacarbonyl(R-NH2-aminobenzylidene)-
chromium (1a ; 149 mg, 0.50 mmol), and triethylamine (505
mg, 5.00 mmol) as described above to give compound 3b (202
mg, 84%, Rf ) 0.4 on silica gel with n-pentane/dichloromethane
(2:1), red crystals from dichloromethane/diethyl ether at -20
°C, dec pt 68 °C). Thermolysis of 4-pyrrolidino-3-aza-1-chroma-
1,3,5-hexatriene (3b) in 2 mL of dry toluene at 100 °C as
described above afforded the pale yellow compound 4b in ca.
80% yield.
3b. 1H NMR (CDCl3, 303 K, 360 MHz): δ 7.57 (2 H, m, Ph),
3
7.47 (1 H, d, J ) 16 Hz, 6-H), 7.44-7.22 (8 H, m, 2-Ph and
6-Ph), 6.74 (1 H, d, 3J ) 16 Hz, 5-H), 3.69 (4 H, m broad, 2
NCH2), 2.12 (4 H, m broad, 2 NCH2CH2). 13C NMR (CDCl3):
δ 253.3 (CrdC), 224.2 and 219.0 (1:4, trans- and cis-CO Cr-
(CO)5), 153.9 and 153.3 (Cq broad each, C4 and i-C 2-Ph), 145.9
(CH, C6), 134.3 (Cq, i-C 6-Ph), 130.8, 129.1, 128.5, 128.0, 127.4
and 123.0 (1:2:2:2:1:2, CH each, 2-Ph and 6-Ph), 115.0 (CH,
C5), 48.7 (2 NCH2), 25.1 (2 NCH2CH2). IR (n-hexane; cm-1
(%)): 2048.1 (25), 1929.0 (100) (ν(CtO)). MS (70 eV; m/e (%)):
480 (0) [M+], 424 (10) [M+ - 2 CO], 340 (60) [M+ - 5 CO], 288
(100) [M+ - Cr(CO)5]. Anal. Calcd for C25H20N2CrO5 (480.4):
C, 62.50; H, 4.20; N, 5.83. Found: C, 62.31; H, 4.40; N, 5.70.
4b. 1H NMR (C6D6, 303 K, 360 MHz): δ 7.80 (1 H, NH),
7.60, 7.31, and 7.28-6.85 (CH each, 2:2:6 H, 2 Ph), 5.48 (1 H,
1H NMR (CDCl3, 303 K, 360 MHz): δ 7.57 (2 H, m, Ph), 7.46-
4
3
d, J ) 3 Hz, 3-H), 2.77 (4 H, m broad, 2 NCH2), 1.49 (4 H, m
7.33 (9 H, m, 2-Ph, 6-Ph, and 6-H), 6.82 (1 H, d, J ) 15 Hz,
broad, 2 NCH2CH2). 13C NMR (C6D6): δ 144.2 (Cq, C2), 138.5
and 134.7 (Cq each, i-C each 4-Ph and 5-Ph), 129.0, 128.8,
128.6, 126.9, 125.9, and 125.4 (CH each, 2:2:2:2:2, 2 Ph), 123.0
and 120.8 (Cq each, C4 and C5), 90.9 (CH, C3), 49.3 (2 NCH2),
25.1 (2 NCH2CH2). IR (diffuse reflection; cm-1): 3329.7 (ν(N-
H)). MS (70 eV; m/e (%)): 288 (70) [M+], 232 (100), 217 (80).
4-Mor ph olin o-2,6-diph en yl-3-aza-1-pen tacar bon ylch r o-
m a -1,3,5-h exa tr ien e (3c). 1-Morpholino-3-phenylprop-2-en-
1-one (2c; 217 mg, 1.00 mmol) was reacted with phosphoryl
chloride (145 mg, 0.95 mmol), pentacarbonyl(R-NH2-amino-
benzylidene)chromium (1a ; 149 mg, 0.50 mmol), and triethyl-
amine (505 mg, 5.00 mmol) as described above to give
5-H), 3.24 (6 H, s broad, 2 NCH3). 13C NMR (CDCl3): δ 253.9
(CrdC), 224.2 and 218.7 (1:4, trans- and cis-CO Cr(CO)5), 152.8
(Cq broad, C4), 152.3 (Cq, i-C 2-Ph), 145.4 (CH, C6), 134.4 (Cq,
i-C 6-Ph), 130.7, 129.0, 128.3, 128.1, 127.8 and 123.3 (1:2:2:
2:1:2, CH each, 2-Ph and 6-Ph), 114.4 (CH, C5), 39.2 (2 NCH3).
IR (n-hexane; cm-1 (%)): 2047.2 (30), 1928.1 (100) (ν(CtO)).
MS (70 eV; m/e (%)): 454 (0) [M+], 398 (10) [M+ - 2 CO], 342
(1) [M+ - 4 CO], 314 (52) [M+ - 5 CO], 262 (100) [M+ - Cr-
(CO)5]. Anal. Calcd for C23H18N2CrO5 (454.4): C, 60.79; H, 3.99;
N, 6.16. Found: C, 60.82; H, 3.84; N, 6.21. Crystal structure
analysis of compound 3a (code AUM_711): formula C23H18N2O5-
Cr, Mr ) 454.39, red crystal, 0.60 × 0.50 × 0.40 mm, a ) 9.515-

Organic Syntheses via Transition Metal Complexes
Organometallics, Vol. 21, No. 9, 2002 1823
compound 3c (196 mg, 79%, Rf ) 0.2 on silica gel in n-pentane/
dichloromethane (2:1), red crystals, dec pt 82 °C).
separated on silica gel (column 20 × 2 cm) with n-pentane to
afford colorless hexacarbonyltungsten. Elution with n-pentane/
dichloromethane (3:1) yielded a red fraction with compound
3e (38 mg, 8%, Rf ) 0.4 in n-pentane/dichloromethane (2:1)
and a dark brown fraction containing compound 9e (72 mg,
15%, Rf ) 0.2 in n-pentane/dichloromethane (2:1)). Subsequent
elution with n-pentane/diethyl ether (1:1) afforded a pale
yellow fraction with 4,5-diphenyl-2-pyrrolidinopyrrole (4b; 92
mg, 40%). Thermolysis of compound 3e (240 mg, 0.50 mmol)
at 100 °C for 16 h in toluene as described above gave
4,5-diphenyl-2-pyrrolidino-1H-pyrrole (4b; 112 mg, 78%).
3e. 1H NMR (CDCl3, 303 K, 360 MHz): δ 7.59 (2 H, m, Ph),
3c. 1H NMR (CDCl3, 303 K, 360 MHz): δ 7.52 (2 H, m, Ph),
3
7.43-7.29 (8 H, m, 2-Ph and 6-Ph), 7.29 (1 H, d, J ) 15 Hz,
6-H), 6.77 (1 H, d, 3J ) 15 Hz, 5-H), 3.87 (4 H, m, 2 OCH2),
3.58 (4 H, m broad, 2 NCH2). 13C NMR (CDCl3): δ 252.9
(CrdC), 224.0 and 218.4 (1:4, trans- and cis-CO Cr(CO)5), 150.3
(Cq, i-C 2-Ph), 145.4 (Cq broad, C4), 144.6 (CH, C6), 134.3 (Cq,
i-C 6-Ph); 130.6, 129.1, 128.6, 128.3, 128.2, and 123.9
(1:2:1:2:2:2, CH each, 2-Ph and 6-Ph), 113.9 (CH, C5), 66.0 (2
OCH2), 46.8 (2 NCH2). IR (n-hexane; cm-1 (%)): 2047.3 (30),
1929.2 (100) (ν(CtO)). MS (70 eV; m/e (%)): 496 (1) [M+], 440
(2) [M+ - 2 CO], 384 (1) [M+ - 4 CO], 356 (30) [M+ - 5 CO],
304 (100) [M+ - Cr(CO)5]. Anal. Calcd for C25H20N2CrO6
(496.4): C, 60.49; H, 4.06; N, 5.64. Found: C, 60.53; H, 4.07;
N, 5.56.
3
7.53 (1 H, d, J ) 15 Hz, 6-H), 7.47-7.33 (8 H, m, 2-Ph and
6-Ph), 6.71 (1 H, d, 3J ) 15 Hz, 5-H), 3.70 (4 H, m broad, 2
NCH2), 2.14 (4 H, s broad, 2 NCH2CH2). 13C NMR (CDCl3): δ
236.5 (WdC), 204.0 and 201.0 (1:4, trans- and cis-CO W(CO)5),
158.5 (Cq broad, C4), 154.4 (Cq, i-C 2-Ph), 147.5 (CH, C6), 134.3
(Cq, i-C 6-Ph), 131.1, 129.1, 128.6, 128.2, 127.9, and 124.9 (1:
2:2:1:2:2, CH each, 2-Ph and 6-Ph), 114.7 (CH, C5), 45.4 (2
NCH2), 25.0 (2 NCH2CH2). IR (diffuse reflection; cm-1 (%)):
2052.4 (35), 1960.7 (40) 1900.4 (100) (ν(CtO)). MS (70 eV, 184W;
m/e (%)): 612 (2) [M+], 584 (1) [M+ - CO], 556 (1) [M+ - 2
4-(Dim eth yla m in o)-2,6-d ip h en yl-3-a za -1-p en ta ca r bon -
yltu n gsta -1,3,5-h exa tr ien e (3d ) a n d 2-(Dim eth yla m in o)-
4,5-d ip h en yl-1H -p yr r ole (4a ). N,N-Dimethyl-3-phenyl-
acrylamide (2a ; 175 mg, 1.00 mmol), phosphoryl chloride (145
mg, 0.95 mmol), pentacarbonyl(R-NH2-aminobenzylidene)-
tungsten (1b; 215 mg, 0.50 mmol), and triethylamine (505 mg,
5.00 mmol) were reacted as described above to give compound
3d (240 mg, 82%, Rf ) 0.4 on silica gel in n-pentane/
dichloromethane (2:1), red crystals from dichloromethane/
diethyl ether at -20 °C, dec pt 73 °C). Thermolysis of the 3-aza-
1-pentacarbonyltungsta-1,3,5-hexatriene 3d (293 mg, 0.50
mmol) in 2 mL of dry toluene at 100 °C for 14 h afforded
2-(dimethylamino)-4,5-diphenyl-1H-pyrrole (4a ; 104 mg, 79%,
pale yellow oil), which was isolated by chromatography on
silica gel.
CO], 528 (6) [M+ - 3 CO], 500 (5) [M+ - 4 CO], 472 (7) [M+
-
5 CO], 288 (100) [M+ - W(CO)5].
9e.
3d . 1H NMR (CDCl3, 303 K, 360 MHz): δ 7.59 (2 H, m, Ph),
3
7.50-7.38 (9 H, m; 2-Ph, 6-Ph and 6-H), 6.83 (1 H, d, J ) 15
Hz, 5-H), 3.32 (6 H, s, 2 NCH3). 1H NMR (C6D6, 303 K, 360
MHz): δ 7.69 (2 H, m, Ph), 7.41 (1 H, d, 3J ) 15 Hz, 6-H),
1H NMR ([D8]toluene): δ 8.37 (2 H, “d”, o-CH Ph), 7.30-7.05
(8 H, m, Ph), 4.83 and 4.29 (1 H each, AB system, 3J ) 10 Hz,
CHdCHPh), 3.42, 2.98, 2.65, and 2.51 (1:1:1:1, m each,
diastereotopic NCH2), 1.05 (4 H, m, NCH2CH2). 13C NMR
(C6D6): δ 276.3 (WdC), 222.6, 212.1, 210.8, and 209.7 (Cq each,
1:1:1:1, CO each W(CO)4), 178.1 (Cq, C4), 149.6 and 142.0 (Cq
each, i-C each, Ph), 132.1, 130.2, 129.0, 128.3, 127.4, and 125.8
(CH each, 1:2:2:2:1:2, 2-Ph and 6-Ph), 73.9 and 59.5 (CH each,
CHdCHPh), 50.3 and 49.1 (2 NCH2), 25.0 and 24.4 (2
NCH2CH2). IR (n-hexane; cm-1 (%)): 2056.2 (40), 1922.5 (100)
(ν(CtO)). MS (70 eV, 184W; m/e (%)): 584 (5) [M+], 556 (5) [M+
- CO], 528 (15) [M+ - 2 CO], 500 (10) [M+ - 3 CO], 472 (20)
[M+ - 4 CO], 288 (100) [M+ - W(CO)4], 184 (15), 149 (30).
4b. See above for spectroscopic data.
3
7.26-7.00 (8 H, m, 2-Ph and 6-Ph), 6.30 (1 H, d, J ) 15 Hz,
5-H), 2.36 (6 H, s, 2 NCH3). 13C NMR (C6D6): δ 236.7 (WdC),
203.8 and 200.8 (1:4, trans- and cis-CO W(CO)5), 156.7 (Cq
broad, C4), 153.6 (Cq, i-C 2-Ph), 146.6 (CH, C6), 134.7 (Cq, i-C
6-Ph), 130.8, 129.2, 129.0, 128.6, 128.3, and 126.0 (1:2:1:2:2:
2, CH each, 2-Ph and 6-Ph), 114.3 (CH, C5), 38.4 (2 NCH3).
IR (diffuse reflection; cm-1): 2052.4, 1960.7, 1900.4 (ν(CtO)).
IR (n-hexane; cm-1 (%)): 2056.2 (15), 1924.9 (100) (ν(CtO)).
MS (70 eV, 184W; m/e (%)): 586 (1) [M+], 530 (1) [M+ - 2 CO],
502 (1) [M+ - 3 CO], 474 (1) [M+ - 4 CO], 446 (2) [M+ - 5
CO], 262 (40) [M+ - W(CO)5], 99 (100). Anal. Calcd for
C
23H18N2O5W (586.3): C, 47.12; H, 3.09; N, 4.78. Found: C,
47.12; H, 3.87; N, 4.81.
4a . See above for spectroscopic data.
4-(Ben zylm et h yla m in o)-2,6-d ip h en yl-3-a za -1-p en t a -
2,6-Diph en yl-4-pyr r olidin o-3-aza-1-pen tacar bon yltu n g-
sta -1,3,5-h exa tr ien e (3e), η5,6-2,6-Dip h en yl-4-p yr r olid in o-
3-a za -1-tetr a ca r bon yltu n gsta -1,3,5-h exa tr ien e (9e) a n d
4,5-Dip h en yl-2-p yr r olid in op yr r ole (4b). 3-Phenyl-1-pyr-
rolidinoprop-2-en-1-one (2b; 201 mg, 1.00 mmol), phosphoryl
chloride (145 mg, 0.95 mmol), pentacarbonyl(R-NH2-aminoben-
zylidene)tungsten (1b; 215 mg, 0.50 mmol), and triethylamine
(505 mg, 5.00 mmol) were reacted as described above to give
compound 3e (129 mg, 42%, Rf ) 0.4 on silica gel in n-pentane/
dichloromethane (2:1), red crystals from dichloromethane/
diethyl ether at -20 °C, dec pt 76 °C). A suspension of
pentacarbonyl-4-pyrrolidino-3-aza-1-pentacarbonyltungsta-
1,3,5-hexatriene (3e; 490 mg, 0.80 mmol) in 2 mL of C6D6 was
heated to 80 °C. It was shown by TLC tests that the red
compound 3e (Rf ) 0.4 in n-pentane/dichloromethane (2:1))
disappears gradually, while the dark brown chelate compound
9e (Rf ) 0.2 in n-pentane/dichloromethane (2:1)) was formed.
According to an 1H NMR spectrum after 6 h at 80 °C a 3:2:1
mixture of pyrrolidino-3-aza-1-tungsta-1,3,5-hexatriene (3e),
2-pyrrolidino-1H-pyrrole (4b), and the chelate complex 9e was
obtained. A 1H NMR spectrum after 18 h at 80 °C indicated a
product ratio of 1:3:1 for these compounds. The mixture was
ca r b on ylt u n gst a -1,3,5-h exa t r ien e (3f), η
5,6-4-(Ben zyl-
m e t h y la m in o )-2,6-d ip h e n y l-3-a za -1-t e t r a c a r b o n y l-
tu n gsta-1,3,5-h exatr ien e (9f), an d 4-(Ben zylm eth ylam in o)-
2,6-d ip h en yl-1H -p yr r ole (4f). (Benzylmethylamino)-3-
phenylacrylamide (2d ; 502 mg, 2.00 mmol), phosphoryl chlo-
ride (290 mg, 1.90 mmol), pentacarbonyl(R-NH2-aminoben-
zylidene)tungsten (1b; 429 mg, 1.00 mmol), and triethylamine
(1010 mg, 10.00 mmol) were reacted as described above to give
compound 3f (337 mg, 57%, Rf ) 0.4 on silica gel in n-pentane/
dichloromethane (2:1), red crystals from dichloromethane/
diethyl ether at -20 °C, dec pt 68 °C). The NMR spectrum of
a solution resulting from thermolysis of compound 3f (169 mg,
0.25 mmol) in [D8]toluene in an NMR tube at 80 °C for 15 min
shows signals of the pyrrole 4f and the chelate compound 9f
in a molar ratio of ca. 1:6. Compound 9f exhibits two sets of
signals in a ratio of ca. 3:1, resulting from isomers due to
hindered rotation of the C-N bond. The spectra could be
assigned only partially, due to overlapping signals. Thermoly-
sis of compound 3f (169 mg, 0.25 mmol) in [D8]toluene at 80
°C for 12 h afforded the pyrrole 4f (256 mg, 78%).
3f. 1H NMR (CDCl3, 303 K, 360 MHz): δ 7.52 and 7.48 (2 H
each, m each, 2 Ph), 7.44-7.35 (8 H, m, 2-Ph, 6-Ph and 6-H),

1824 Organometallics, Vol. 21, No. 9, 2002
Aumann et al.
3
7.34-7.28 (4 H, m, Ph), 6.83 (1 H, d, J ) 15 Hz, 5-H), 4.92
each of 2-Ph and 6-Ph), 6.92 (4 H, m, Ph), 4.85 and 4.42 {4.80
and 4.49} (1 H each, d each, 3J ) 11 Hz, CHdCHPh), 4.78,
4.40, and 4.02 (m each, diastereotopic NCH2 each), 2.91 and
2.48 (1:3 H, s each, NCH3 each). 13C NMR ([D8]toluene, 300
K): δ 272.0 (WdC, broad), 222.3, 211.7, 210.7, 209.4 (Cq each,
1:1:1:1, W(CO)4), 183.6 {183.0} (Cq each, 1:3, C4), 150.3 and
142.0 {150.2 and 142.1} (Cq each, 3:3:1:1, i-C each of 2-Ph and
6-Ph), 134.9 {133.9} (Cq each, 3:1, i-C NCH2Ph each), 132.3-
130.3 (CH each, Ph), 74.5 {74.4} (CH each, 3:1, CHdCHPh),
56.2 {56.2} (NCH2 each, 3:1), 39.1 and 37.3 (NCH3 each).
4f. 1H NMR ([D8]toluene, 300 K): δ 7.50 (2 H, “d”, Ph), 7.30-
7.00 (14 H, m, Ph and NH), 5.61 (1 H, d, 4J ) 3 Hz, 3-H), 3.86
(2 H, s, NCH2), 2.46 (3 H, s, NCH3). 13C NMR ([D8]toluene,
300 K; partial assignment only): δ 144.5 (Cq, C2), 138.8, 138.1,
and 134.4 (Cq each, i-C Ph each), 122.3 and 121.8 (Cq each,
C4 and C5), 94.3 (CH, C3), 59.5 (NCH2), 39.5 (NCH3). MS (70
eV; m/e (%)): 338 (90) [M+], 233 (100).
2
and 4.57 (1 H each, d each broad, J ) 16 Hz, diastereotopic
NCH2), 3.16 (3 H, s, NCH3). 13C NMR (CDCl3): δ 237.1
(WdC), 204.0 and 199.9 (1:4, trans- and cis-CO W(CO)5), 153.7
(Cq broad, C4), 152.2 (Cq, i-C 2-Ph), 146.4 (CH, C6), 134.5 and
134.1 (each Cq, i-C 6-Ph and i-C NCH2Ph), 130.8, 129.2, 129.1,
129.0, 128.9, 128.4, 128.3, 128.0, and 127.3 (1:2:2:1:1:2:2:2:2,
CH each; 2-Ph, 6-Ph and NCH2Ph), 113.8 (CH, C5), 54.9
(NCH2), 37.1 (NCH3). IR (diffuse reflection; cm-1): 2052.4,
1960.7, 1900.4 (ν(CtO)). IR (n-hexane; cm-1 (%)): 2056.2 (15),
1924.9 (100) (ν(CtO)). MS (70 eV, 184W; m/e (%)): 662 (1) [M+],
606 (1) [M+ - 2 CO], 578 (1) [M+ - 3 CO], 550 (1) [M+ - 4
CO], 522 (2) [M+ - 5 CO], 338 (40) [M+ - W(CO)5], 99 (100).
3f (isomer ratio ca. 2:1; signals of minor isomer in braces).
1H NMR (CDCl3, 213 K, 360 MHz): δ 7.70-7.25 (32 H, m
broad, 6 Ph and 2 CHdCHPh), 5.44 and 4.25 {4.87 and 4.70}
(1 H each, d broad each, 2J ) 15 Hz each, diastereotopic NCH2
each), 3.21 {3.19} (3 H, s, NCH3). 13C NMR (CDCl3, 213 K, 90
MHz): δ 240.6 {236.2} (Cq, WdC), 204.5 and 199.8 (Cq each,
1:4, trans- and cis-CO W(CO)5), 156.6 {160.3} (Cq, C4), 152.1
{153.1} (Cq, i-C Ph), 148.3 {147.0} (CH, CHdCHPh), 133.9,
133.5, and 133.4 (Cq each, 2:1:1, i-C each of 6-Ph and CH2Ph),
131.2, 129.1, 128.6, 126.4, 125.8 {131.0, 129.0, 128.8, 128.6,
128.4, 126.4} (CH each, 2 Ph), 113.2 {112.8} (CH, CHdCHPh),
54.7 {53.9} (NCH2), 37.9 {36.5} (NCH3).
Ack n ow led gm en t. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen Industrie.
Su p p or tin g In for m a tion Ava ila ble: Tables giving de-
tails of the X-ray crystal structure analyses. This material is
available free of charge via the Internet at http://pubs.acs.org.
9f. 1H NMR ([D8]toluene, 300 K) (partial assignment, signals
of minor isomer in brackets, if observed): 8.25 (2 H, “d”, o-CH
OM011032D