Synthesis, structural characterization, and bonding analysis of (η4-1-azadiene)Fe(CO)3 complexes: Consequences of the electronic structure on molecular and crystal properties

Article abstract of DOI:10.1021/om980415h

A series of 1-azadiene ligands as well as the corresponding (η⁴-azadiene)Fe(CO)₃ complexes have been synthesized and structurally characterized by means of single-crystal X-ray diffraction. At the molecular level, the 1-azadiene assumes a trans conformation as free ligand, while a cis coordination is found in the organometallic complexes. In the coordinated ligand the H(C3) hydrogen is found nonplanar with respect to the C-C-C-N plane. A molecular orbital analysis has been carried out by means of extended Hu?ckel calculations. The electronic origin of the out-of-plane position of the 1-azadiene hydrogen atom H(C3) has been justified in terms of a better π*-back-bonding between the 1-azadiene and Fe(CO)₃ molecular fragments. A comparison of cis and trans conformations of the ligand has also been performed. The organometallic crystals show the presence of a large number of hydrogen bond interactions of the C-H- - -O type involving CO-ligand acceptors. Hydrogen bonding of the azadiene moiety is always realized by the hydrogen atom at the C-N double bond and the hydrogen atom in α-position with respect to the imine group.

Full text of DOI:10.1021/om980415h

736
Organometallics 1999, 18, 736-747
Syn th esis, Str u ctu r a l Ch a r a cter iza tion , a n d Bon d in g
An a lysis of (η4-1-a za d ien e)F e(CO)3 Com p lexes:
Con sequ en ces of th e Electr on ic Str u ctu r e on Molecu la r
a n d Cr ysta l P r op er ties
Wolfgang Imhof* and Angela Go¨bel
Institut fu¨r Anorganische und Analytische Chemie der Universita¨t, August-Bebel-Strasse 2,
07743 J ena, Germany
Dario Braga,* Piero De Leonardis, and Emilio Tedesco
Dipartimento di Chimica “G. Ciamician”, Universita` di Bologna, Via Selmi 2,
40126 Bologna, Italy
Received May 22, 1998
A series of 1-azadiene ligands as well as the corresponding (η4-azadiene)Fe(CO)3 complexes
have been synthesized and structurally characterized by means of single-crystal X-ray
diffraction. At the molecular level, the 1-azadiene assumes a trans conformation as free
ligand, while a cis coordination is found in the organometallic complexes. In the coordinated
ligand the H(C3) hydrogen is found nonplanar with respect to the C-C-C-N plane. A
molecular orbital analysis has been carried out by means of extended Hu¨ckel calculations.
The electronic origin of the out-of-plane position of the 1-azadiene hydrogen atom H(C3)
has been justified in terms of a better π*-back-bonding between the 1-azadiene and Fe(CO)3
molecular fragments. A comparison of cis and trans conformations of the ligand has also
been performed. The organometallic crystals show the presence of a large number of hydrogen
bond interactions of the C-H- - -O type involving CO-ligand acceptors. Hydrogen bonding
of the azadiene moiety is always realized by the hydrogen atom at the C-N double bond
and the hydrogen atom in R-position with respect to the imine group.
In tr od u ction
the structural features of these compounds.4c-e,5c All
structures of Fe(CO)3 complexes that have been reported
so far show the 1,3-butadiene, 1,4-diazadiene, or 1-aza-
diene ligands to adopt an s-cis configuration.6 This is
in agreement with the results of extended Hu¨ckel
calculations for (1,3-butadiene)Fe(CO)3 complexes.7 Buta-
dienes that are stabilized by organometallic fragments
in s-trans conformation are less common and mainly
known for Cp2M (M ) Zr, Hf)8 and CpMo(NO) moieties.9
(1,3-butadiene)Fe(CO)3 complexes are widely used as
starting materials in the synthesis of organic compounds
due to the properties of the Fe(CO)3 moiety to act not
only as an activating group but also as a protecting and
stereo directing group.1 There is also a number of
reactions starting from the isolobal (1,4-diazadiene)Fe-
(CO)3 complexes,2 but only very little is known about
the reactivity of (1-azadiene)Fe(CO)3 compounds so far.
Up to now there have been reports about the reaction
of (1-azadiene)Fe(CO)3 complexes with organo lithium
compounds.3 In these reactions the initial step is always
the attack of the organo lithium reagent toward an iron-
bound CO ligand which is, in subsequent reaction steps,
incorporated into the azadiene ligand together with the
organic group attached to lithium. (1-azadiene)Fe(CO)3
complexes have also been used as catalysts in the
synthesis of (1,3-butadiene)Fe(CO)3 compounds.4 The
synthesis and properties of some other (1-azadiene)Fe-
(CO)3 complexes have also been reported in the litera-
ture.5 Nevertheless there has been little information on
(4) (a) Kno¨lker, H.-J .; Gonser, P. Synlett 1992, 517. (b) Kno¨lker, H.-
J .; Gonser, P.; J ones, P. G. Synlett 1994, 405. (c) Kno¨lker, H.-J .; Baum,
G.; Gonser, P. Tetrahedron Lett. 1995, 36, 8191. (d) Kno¨lker, H.-J .;
Goesmann, H.; Gonser, P. Tetrahedron Lett. 1996, 37, 6543. (e) Kane-
Maguire, L. A. P.; Pyne, S. G.; Siu, A. F. H.; Skelton, B. W. J . Aust.
Chem. 1996, 49, 673. (f) Kno¨lker, H.-J .; Baum, G.; Foitzik, N.;
Goesmann, H.; Gonser, P.; J ones, P. G.; Ro¨ttele, H. Eur. J . Inorg. Chem.
1998, 993.
(5) (a) Otsuka, S.; Yoshida, T.; Nakamura, A. Inorg. Chem. 1967, 6,
20. (b) Bagga, M. M.; Flannigan, W. T.; Knox, G. R.; Pauson, P. L.;
Preston, F. J .; Reed, R. I. J . Chem. Soc (C) 1968, 36. (c) De Cian, A.;
Weiss, R. Acta Crystallogr. 1972, B28, 3264. (d) Brodie, A. M.; J ohnson,
B. F. G.; J osty, P. L.; Lewis, J . J . Chem. Soc., Dalton Trans. 1972,
2031. (e) Semmelhack, M. F.; Cheng, C. H. J . Organomet. Chem. 1990,
393, 237.
(6) Marr, G.; Rockett B. W. In The Chemistry of the Metal-Carbon
Bond; Hartley, F. R., Patai, S., Eds.; Wiley: New York, 1982; Vol. I,
Chapter 9, p 237.
(1) (a) Pearson, A. J . Acc. Chem. Res. 1980, 13, 463. (b) Gre´e, R.
Synthesis 1989, 341. (c) Kno¨lker, H.-J . Synlett 1992, 371. (d) Roush,
W. R.; Wada, C. K. J . Am. Chem. Soc. 1994, 116, 2151.
(2) Feiken, N.; Fru¨hauf, H.-W.; Vrieze, K. Organometallics 1994,
13, 2825.
(3) (a) Yin, J .; Chen, J .; Xu, W.; Zhang, Z.; Tang, Y. Organometallics
1988, 7, 21. (b) Danks, T. N.; Thomas, S. E. J . Chem. Soc., Perkin
Trans. 1990, 761.
(7) Mingos, D. M. P. J . Chem. Soc., Dalton Trans. 1977, 20.
(8) (a) Erker, G.; Kru¨ger, C.; Mu¨ller, G. Adv. Organomet. Chem.
1985, 24, 1. (b) Yasuda, H.; Tatsumi, K.; Nakamura, A. Acc. Chem.
Res. 1985, 18, 120.
(9) (a) Hunter, A. D.; Legzdins, P.; Nurse, C. R.; Einstein, F. W. B.;
Willis, A. C. J . Am. Chem. Soc. 1985, 107, 1791. (b) Hunter, A. D.;
Legzdins, P.; Einstein, F. W. B.; Willis, A. C.; Bursten, B. E.; Gatter,
M. G. J . Am. Chem. Soc. 1986, 108, 3843.
10.1021/om980415h CCC: $18.00 © 1999 American Chemical Society
Publication on Web 01/27/1999

(η4-1-azadiene)Fe(CO)3 Complexes
Organometallics, Vol. 18, No. 4, 1999 737
Sch em e 1
Calculations have also been carried out for tantalum
compounds with butadiene ligands10 in order to decide
whether these group 5 compounds have to be formulated
as η4-coordinated complexes, which is believed to be the
case for the group 8 compounds, or as a metallacyclo-
pent-3-ene, as for the group 4 complexes.
In this paper we describe the synthesis of a number
of new 1-azadienes together with their Fe(CO)3 com-
plexes. Some of the ligands and all of the Fe(CO)3
complexes have also been characterized by X-ray crys-
tallography. Their molecular and crystal structures are
presented. The results of extended Hu¨ckel calculations
on the ligand system and on the organometallic com-
pounds are discussed in order to explain some of the
common features in the molecular structures and crystal
packings of the (1-azadiene)Fe(CO)3 complexes.
The Fe(CO)3 complexes are easily prepared by react-
ing the ligands with Fe2(CO)9 in n-heptane at 50 °C.
Chromatographic workup gives the organometallic com-
pounds in reasonable to good yields. By recrystallization
from mixtures of light petroleum (bp 40-60 °C) and
CH2Cl2, the complexes are obtained as crystalline
orange solids.
The IR spectra of the ligands show as the most typical
resonance a band in the region around 1630 cm-1
representing the CdN stretching vibration. The iron
complexes are easily identified by the IR bands of the
three terminal CO ligands, which show the pattern
typical for Fe(CO)3 groups.
The NMR spectra of the mononuclear iron complexes
show significant differences compared to those of the
1
free ligands. In the H NMR spectra of the ligands the
resonance for the imine hydrogen atom is observed at
about 8 ppm; the olefinic protons show signals in the
Syn th esis a n d Sp ectr oscop ica l P r op er ties of
1-Aza d ien es a n d (1-a za d ien e)F e(CO)3 Com p lexes
region between 6.5 and 7.5 ppm. The corresponding 13
C
resonances are observed at about 160 ppm (CdN) and
between 130 and 150 ppm (dCH). These signals are
shifted to higher field by complexation of the ligand with
a Fe(CO)3 moiety. The 1H NMR spectra of the iron
compounds thus show the resonance for the imine
hydrogen atom at about 6.2-6.9 ppm, whereas the
signals representing the olefinic hydrogen atoms are
observed at about 2.9-3.4 and 5.4-6.1 ppm, respec-
tively. The same effect can be seen in the 13C NMR
spectra. Resonances of the carbon atoms of the azadiene
are shifted to higher field for 50-70 ppm and are
observed at about 110 ppm (CdN) and 75 and 60 ppm
(dCHR), respectively. The organic groups at the imino
nitrogen atom and at the C-terminal end of the 1-aza-
Scheme 1 shows the synthesis of (1-azadiene)Fe(CO)3
complexes from the corresponding ligands and Fe2(CO)9.
Three groups of organometallic compounds are de-
scribed in this paper. The first group (7-12) is derived
from ligands (1-6), which are synthesized by condensa-
tion of cinnamaldehyde with the corresponding amine.
15 and 16 are prepared by the reaction of Fe2(CO)9 and
R,â-unsaturated imines with a heteroaromatic group at
the C terminus, whereas for 19 and 20 a ferrocenyl
moiety has been introduced in the same position. The
synthesis, spectroscopical properties, and molecular
structures of the ligands and Fe(CO)3 complexes bearing
ferrocenyl groups (6, 12, 17-20) have already been
published by some of us elsewhere.11
1
diene chain give the expected signals in the H and 13C
NMR spectra. The terminal CO ligands at the iron atom
show very broad signals in the 13C NMR spectra of
7-10, 15, and 16; no resonance is observed for 11. The
corresponding signals in the 13C NMR spectra of 12 and
(10) Yasuda, H.; Tatsumi, K.; Okamoto, T.; Mashima, K.; Lee, K.;
Nakamura, A.; Kai, Y.; Kanehisa, N.; Kasai, N. J . Am. Chem. Soc.
1985, 107, 2410.
(11) Imhof, W. Inorg. Chim. Acta 1998, 282, 111.

738 Organometallics, Vol. 18, No. 4, 1999
Imhof et al.
F igu r e 1. Molecular structure of 3.
F igu r e 2. Crystal packing of 17. A combination of C-H- -N and weak C-H- -πCp interactions builds up a double-chain
arrangement.
Ta ble 1. Bon d Len gth s [p m ] a n d An gles [d eg] of
3, 4, 5, a n d 17
Ta ble 2. Sh or test In ter m olecu la r Dista n ces a n d
An gles in th e Cr ysta l P a ck in gs of 3, 5, a n d 17
3
4
5
17
C-H- - -Y
H- - -Y
[pm]
C-H- - -Y
compound
hydrogen bond
[deg]
N1-C1
C1-C2
C2-C3
C3-C4
Cipso-N1
128(2)
143(2)
134(2)
145(2)
141(2)
127.1(8)
144.9(8)
131.4(9)
145.9(8)
141.9(7)
125.6(5)
144.4(5)
131.8(5)
146.0(5)
142.0(5)
124.0(9)
146.1(9)
135.3(9)
146.3(9)
145.5(8)
3
5
C-H- - -πPh
C-H- - -F
C-H- - -F
C-H- - -F
C-H- - -N
C-H- - -πCp
268.2
253.4
265.9
247.8
264.0
264.7
130.8
173.0
147.3
166.0
148.4
177.3
17
Cipso-N1-C1
N1-C1-C2
C1-C2-C3
C2-C3-C4
121(1)
119.1(5)
120.7(3)
122.5(4)
123.1(4)
128.7(4)
116.9(6)
123.3(7)
122.2(6)
126.9(6)
122(1)
123(1)
128(1)
122.6(6)
123.4(6)
126.8(6)
the central bond between C1 and C2 shows a value
typical for a single bond.
The shortest intermolecular C-H- - -X (X ) F, N, π)
contacts in crystalline 3, 5, and 17 are reported in Table
2. In the crystal structures of 3 and 17 the shortest
intermolecular distances are those of hydrogen atoms
being orientated toward the center of a phenyl group
(πPh as in 3) or of a cyclopentadienyl ligand (πCp as in
17), respectively. These distances are about 15-20 pm
below the sum of the contact radii defined by Bondi et
al.,13 indicating a rather weak interaction.
The crystal packing of 3 shows the existence of weak
hydrogen bonding between a proton of the bromine-
substituted phenyl group and the electron density
centroid of the corresponding phenyl group in the next
molecule (C-H- - -πPh ) 268.2 pm). As a result, a chain
of molecules is formed. The angle between the two
phenyl groups is 61.7°; the bond angle between the CH
group and the center of the next phenyl ring is 130.8°.
The arrangement of 17 in the solid state (see Figure
2) shows chains built up by C-H- - -N hydrogen bonds
19 are also broad, whereas the spectrum of 20 shows
three different signals for the CO groups.11 This behav-
ior indicates that the fluxionality of the (1-azadiene)-
Fe(CO)3 complexes shows coalescence temperatures
near room temperature.4d,12
Str u ctu r a l An a lysis
1-Aza d ien e Liga n d s. Table 1 summarizes the most
important bond lengths and angles of 3, 4, 5, and 17.
The molecular structure of 3, of which the numbering
scheme for the azadiene chain has been retained for all
other compounds, is shown in Figure 1.
All the structures show some common features: the
R,â-unsaturated 1-azadiene chain N1-C1-C2-C3 pre-
sents an s-trans conformation with respect to the central
single bond C1-C2. In addition the N1-C1 and C2-
C3 bond lengths clearly indicate a double bond, whereas
(12) (a) Kruczinsky, L.; Takats, T. Inorg. Chem. 1976, 15, 3140. (b)
Leibfritz, D.; tom Dieck, H. J . Organomet. Chem. 1976, 105, 255.
(13) Bondi, A. J . Phys. Chem. 1964, 68, 441.

(η4-1-azadiene)Fe(CO)3 Complexes
Organometallics, Vol. 18, No. 4, 1999 739
F igu r e 3. Crystal packing of 5. Interactions of the C-H- -F type build up a chain of dimers.
Ta ble 3. Bon d Len gth s [p m ] a n d An gles [d eg] of 7-12, 15, 16, 19, a n d 20
7
8
9
10
11
12
15
16
19
20
Fe1-N1
Fe1-C1
Fe1-C2
Fe1-C3
N1-C1
C1-C2
C2-C3
C3-C4
Cipso-N1
208.0(1)
208.1(2)
205.0(2)
216.0(2)
134.0(2)
141.8(2)
142.1(2)
147.1(2)
146.8(2)
212.5(6)
205.4(7)
206.0(8)
214.4(8)
136(1)
141(1)
142(1)
148(1)
143(1)
207.2(3)
206.4(4)
207.2(4)
215.7(4)
135.3(5)
141.4(5)
141.5(5)
148.2(5)
141.9(5)
206.5(3)
205.7(5)
207.1(5)
215.4(4)
135.7(5)
141.9(6)
141.2(6)
148.4(6)
141.6(5)
204.2(3)
207.2(4)
206.0(4)
214.5(4)
135.8(5)
140.6(6)
140.1(5)
147.4(5)
138.8(5)
209.8(4)
206.4(5)
205.3(5)
214.7(5)
134.8(7)
140.4(7)
140.4(7)
147.8(7)
141.3(6)
207.7(2)
208.0(3)
204.9(3)
214.383)
134.1(4)
141.5(4)
141.4(4)
145.3(4)
147.3(3)
208.2(2)
208.3(2)
204.5(2)
215.7(2)
134.5(3)
141.4(3)
141.7(3)
146.1(3)
147.3(3)
208.2(3)
207.7(3)
206.9(3)
215.3(2)
134.0(4)
141.1(5)
141.9(5)
147.1(5)
146.6(4)
213.2(4)
207.5(5)
205.6(4)
213.7(4)
137.8(5)
140.0(6)
136.3(6)
142.1(6)
144.5(5)
Cipso-N1-C1
N1-C1-C2
C1-C2-C3
C2-C3-C4
116.2(1)
115.0(2)
116.0(2)
124.9(2)
117.8(6)
116.7(7)
117.9(8)
123.7(8)
118.3(3)
115.3(2)
118.2(3)
121.9(3)
118.8(3)
114.3(4)
118.3(4)
122.5(4)
119.3(3)
114.2(3)
118.6(4)
124.6(3)
118.7(4)
115.7(5)
117.8(5)
125.5(5)
116.1(2)
114.6(3)
116.6(3)
122.4(3)
116.0(2)
115.0(2)
116.3(2)
123.4(2)
114.5(3)
116.8(3)
117.4(3)
120.7(3)
118.9(4)
115.7(4)
119.0(4)
120.7(4)
Ta ble 4. Devia tion s [p m ] fr om th e P la n e
[N1-C1-H1-C2-H2-C3] of 7-12, 15, 16, 19, a n d 20
from the substituted cyclopentadienyl ligand of one
molecule to the imino nitrogen atom of the next mol-
ecule, with a resulting bond length of 264.0 pm. There
are additional weak interactions of the C-H- - -πCp type
that form chains in the solid-state structure of 17.
7
8
9
10 11 12 15 16 19 20
N1 -5.5 -1.4 -0.8 -2.1 -4.9 -1.5 -3.2 -5.5 -5.3 -2.0
C1
H1
C2
2.5
3.7 -1.1 -1.5
1.2 4.3 1.6
2.2
2.4 -0.3
2.1
3.1
2.7
1.2
0.4
0.8
3.4
0.5
1.1
2.1
4.2
0.6
0.8
4.8 -0.9
2.3 -2.9
3.0
2.2
2.1
In the X-ray structure of 5 interactions between the
CF3 groups and aromatic C-H bonds of neighboring
molecules are observed. The distances reported in Table
2 (C-H- - -F of 247.8-265.9 pm) demonstrate that
covalently bonded fluorines are poor hydrogen bond
acceptors, as it has been shown previously.14a,b On the
other hand the interactions are well in the range that
has been reported for C-H- - -F interactions in the solid-
state structures of several fluorobenzene derivatives.14c
We shall get back to this point later when considering
the corresponding organometallic complexes. The CF3
groups in ortho position with respect to the azadiene
chain in the solid-state structure of 5 form two different
kinds of dimers linked by C-H- - -F hydrogen bonds
(Figure 3). One dimer is constructed by the interaction
of one CF3 group with the aromatic C-H bond in para
position to the imine nitrogen atom. The C-H- - -F bond
length is 253.4 pm; the bond angle is 173.0°. The other
CF3 moiety builds up a second type of dimer via a
bifurcated hydrogen bond to an aromatic hydrogen atom
of the 3,5-(CF3)2-C6H3 group (C-H- - -F 247.8 pm) as
well as toward the hydrogen atom of the imine carbon
of the next molecule (C-H- - -F 265.9 pm). As a result,
a chain of dimers is formed. So the C-H- - -F interac-
H2 -5.9 -2.9 -0.9 -3.3 -6.1 -1.6 -3.3 -5.8 -6.3 -2.9
C3
H3 48.4 38.5 44.0 45.1 51.2 48.6 46.9 56.8 46.6 36.3
4.0 -1.2 -0.8
1.4
3.1
0.6
1.5
4.4
3.7 -0.4
tions in 5 are also close to the sum of the van der Waals
radii of fluorine and hydrogen.
(1-Aza d ien e)F e(CO)3 Com p lexes. The most impor-
tant bond lengths and angles of 7-12, 15, 16, 19, and
20 are reported in Table 3, while Table 4 collects the
deviation from the molecular 1-azadiene plane of the
constituent atoms found in these structures. The hy-
drogen bond distances and angles are summarized in
Table 5. The molecular structure of 7, used as a model
for the other compounds, is shown in Figure 4.
In all complexes the iron atom shows a square
pyramidal coordination sphere with the azadiene ligand
always situated in the square plane of the complex. In
contrast to the solid-state structures of the free ligands,
the complexes consist of a 1-azadiene ligand adopting
an s-cis conformation with respect to the central C1-
C2 bond in the azadiene chain. The C-N bond of the
azadiene is lengthened by about 10 pm upon coordina-
tion to the Fe(CO)3 moiety, as is the C1-C2 bond length,
while a shortening of the central C2-C3 distance is
observed. The Fe-C bond lengths of the C1 and C2
atoms are also similar for all compounds, whereas the
Fe-C3 bond is about 10 pm longer than the other bonds.
The hydrogen atoms of the azadiene chains were local-
(14) (a) Dunitz, J . D.; Taylor, R. Chem. Eur. J . 1997, 3, 89. (b)
Aakero¨y, C. B.; Seddon, K. R. Chem. Soc. Rev. 1993, 22, 397. (c)
Thalladi, V. R.; Weiss, H.-C.; Bla¨ser, D.; Boese, R.; Nangia, A.; Desiraju,
G. R. J . Am. Chem. Soc. 1998, 120, 8702.

740 Organometallics, Vol. 18, No. 4, 1999
Imhof et al.
F igu r e 4. Molecular structure of 7.
Ta ble 5. Hyd r ogen Bon d Dista n ces a n d An gles in
th e Cr ysta l Str u ctu r es of 8-12, 15, 16, 19, a n d 20
atom with a partial negative charge. Therefore the
hydrogen atoms bound to C1 and C2 are more acidic
and they are more effective C-H donor groups com-
pared to H(C3).
C-H- - -Y
hydrogen bond
H- - -Y
[pm]
C-H- - -Y
[deg]
compound
8
C-H- - -O
C-H- - -O
C-H- - -N
C-H- - -O
C-H- - -F
C-H- - -N
C-H- - -O
C-H- - -O
C-H- - -O
C-H- - -O
C-H- - -O
C-H- - -O
C-H- - -O
C-H- - -O
C-H- - -O
C-H- - -O
C-H- - -O
C-H- - -O
258.0
226.8
246.2
253.6
242.5
245.8
238.5
250.8
249.8
261.4
252.7
267.2
245.0
256.2
243.4
252.0
257.2
258.4
134.4
152.3
150.0
130.4
155.6
156.8
135.3
161.3
136.3
137.5
160.6
168.1
171.4
149.1
172.4
137.7
164.0
159.2
While in crystalline 7 there are no short intermolecu-
lar interactions worth noticing, in the crystal structure
of 10 a C-H- - -F interaction of 242.5 pm between an
aromatic C-H group and the CF3 substituent of a
neighboring molecule is observed. There is also a second
type of hydrogen bond, namely of the C2-H2- - -N1 type
(245.8 pm) responsible for building up chains of mol-
ecules (Figure 5).
9
10
11
12
The packing of 9 is similar to that described for 10.
It consists of chains linked by hydrogen bonds between
a hydrogen atom of the phenyl group and a CO ligand
of a neighboring molecule (253.6 pm). Interchain links
are provided by further hydrogen bonding (246.2 pm)
involving atom H2 and the imine nitrogen of neighbor-
ing chains.
15
16
19
20
The crystal structure of 11 shows the formation of
dimers, which are constructed by an interaction of H2
with a CO ligand of the next molecule (238.5 pm). The
dimers are connected to give infinite chains by hydrogen
bonds between the proton next to both CF3 groups
toward another CO ligand of the neighboring dimer
(250.8 pm, Figure 6). In contrast to the free ligand (5),
the CF3 groups are not involved in any significantly
short intermolecular contacts. This is a clear evidence
that CO ligands are better hydrogen bond acceptor
groups than organic fluorine.14
ized from the difference electron density map and were
refined without constraints for all complexes. The
nitrogen and carbon atoms of the azadiene as well as
the hydrogen atoms at C1 and C2 are situated in one
plane for all complexes, whereas the hydrogen atom at
C3 always shows a deviation from this plane of about
40-50 pm (see Table 4). All these structural features
will be taken into account in the molecular orbital
analysis (see below).
The hydrogen bond pattern of these complexes is
deeply modified from that of the free ligands by the
introduction of the Fe(CO)3 moiety, because the CO
ligands are good hydrogen bond acceptors,15 and by the
s-cis conformation of the 1-azadiene ligand. In eight out
of ten complexes (8, 9, 11, 12, 15, 16, 19, 20) the oxygen
atom of the CO ligands acts as the acceptor of intermo-
lecular interactions. With the exception of 8, 15, and
16 in all structures the H1 or H2 hydrogens are involved
in some hydrogen bonding. There is no short intermo-
lecular contact in which H3 takes part. These results
are consistent with the extended Hu¨ckel calculations,
which show C1 and C2 to be mostly sp2 hybridized,
whereas C3 should be considered more an sp3 carbon
The crystal packing of 8, closely related to that of 11,
contains dimeric subunits that are linked by C-H- - -O
bond between a proton of the phenyl group and a CO
ligand of the next molecule (258.0 pm). In addition these
dimers are linked in infinite chains by interaction of a
methyl group of the mesityl moiety with another CO
ligand (226.8 pm).
The structure of 12 contains a bifurcated interaction
(see Figure 7) in which the same CO-ligand interacts
simultaneously with an aromatic proton and the H2
atom (252.7 and 238.5 pm, respectively). The chains
formed by the bifurcated hydrogen bonds build up an
infinite network by combination with a second chain via
a C-H- -O interaction between a proton of the unsub-
stituted cyclopentadienyl ligand and another CO ligand
(249.8 pm).
(15) (a) Braga, D.; Grepioni, F.; K. Biradha, F.; Pedireddi, V. R.;
Desiraju, G. R. J . Am. Chem. Soc. 1995, 117, 3156. (b) Braga, D.;
Grepioni, F. Acc. Chem. Res. 1997, 30, 81. (c) Braga, D.; Grepioni, F.;
Desiraju, G. R. J . Organomet. Chem. 1997, 548, 33.

(η4-1-azadiene)Fe(CO)3 Complexes
Organometallics, Vol. 18, No. 4, 1999 741
F igu r e 5. Crystal packing of 10. A combination of C-H- -N and weak C-H- -F interactions builds up an infinite network.
F igu r e 6. Crystal packing of 11. Interactions of the C-H- -O type build up a chain of dimers.
Sch em e 2
The similarity of crystalline 15 and 16 shows that
there is no effect on the crystal packing by substitution
of sulfur for oxygen. Both compounds form infinite
chains via C-H- - -O interactions between the proton
in 4-position of the heterocycle toward a CO group of
the next molecule.
Crystalline 19 again shows a network similar to that
of 9 and 10 (Figure 5). In 19 one of the chains is formed
by interaction of a proton belonging to the cyclopenta-
arrangement of the free ligand; (ii) the out-of-plane
dienyl ligand which bears the azadiene moiety with a
displacement of the hydrogen atom bonded to C3 with
CO ligand of the next molecule with a bond length of
respect to the N-C1-C2-C3 plane of the azadiene
243.4 pm. These chains are connected by interactions
ligand.
between H2 and another CO ligand of a molecule of the
The model structures used in our extended Hu¨ckel
neighboring chain (252.0 pm). In addition, each molecule
analysis are sketched in Scheme 2 (see Experimental
Section for geometric details and parameters).
of the infinite network forms a dimeric substructure via
hydrogen bonding between H2 and another CO ligand
On the free azadiene ligand we performed a cis-trans
torsional analysis, obtaining the same qualitative trend
as observed for the butadiene torsional energy profile,
the trans-azadiene being approximately 5.8 kcal mol-1
more stable than the cis conformer. Hu¨ckel theory
predicts an energy stabilization of 7 kcal mol-1 for
butadiene, in good agreement with the experimental
of a neighboring molecule (256.2 pm).
In contrast, the crystal packing of 20 only shows the
formation of dimeric units via hydrogen bonds between
H1 and H2 with two different CO ligands of the
neighboring molecule. Both C-H- - -O bond lengths are
of nearly the same value (257.2 and 258.4 pm).
value of 3-4 kcal mol-1 16
We also compared the
.
Molecu la r Or bita l Ca lcu la tion s
coordination of the ligand bound to the Fe(CO)3 moiety
in both cis and trans conformations. The (cis-azadiene)-
Fe(CO)3 compound is more stable than the (trans-
azadiene)Fe(CO)3 by approximately 4.2 kcal mol-1
In this section we investigate the bonding interaction
in the (1-azadiene)Fe(CO)3 system starting from the
observation of the structural data described above. In
particular we will address two issues: (i) the relation-
ship between the cis conformation of the 1-azadiene
ligand when coordinated to the Fe(CO)3 and the trans
(16) Streitwieser, A., J r. Molecular Orbital Theory for Organic
Chemists; Wiley: New York, 1961.

742 Organometallics, Vol. 18, No. 4, 1999
Imhof et al.
F igu r e 7. Crystal packing of 12. A combination of different C-H- -O interactions builds up an infinite network.
Sch em e 3
stability of the system increases by about 16.2 kcal
mol-1 when the hydrogen atom is above the azadiene
molecular plane (φ ) 40°). The HOMO of the organo-
metallic complex is found responsible for this stabiliza-
tion, having a similar energy profile. Drawings of this
orbital relative to φ ) 0° and φ ) 40° values are reported
in Figure 9. The out-of-plane position of H(C3) strength-
ens the Fe-C3 bonding, as proved by the calculated
overlap populations (Fe-C3 and C3-H OP values
increase from 0.078 to 0.229 and from 0.786 to 0.806
when H(C3) is moved by 40°; the Fe-N OP keeps a
constant value of 0.216 during the process). This is in
agreement with the hypothesis that the C3 atom bears
a partial sp3 hybridization rather than a pure sp2 when
interacting with the Fe(CO)3 fragment. In fact the H(C3)
atom does not participate in any hydrogen bond interac-
tion (see above), in agreement with the sp3 character of
C3 with respect to C1 and C2.
because of better overlap between the Fe(CO)3 fragment
molecular orbitals (MOs). Therefore in the cis isomer
the peripheral azadiene atoms (in particular the N
atom) attain a better overlap than in the trans isomer,
though accompanied by a slight loss of overlap in the
Fe-C1 and Fe-C2 bonding. The reduced overlap popu-
lations (OPs) between the azadiene atoms and the iron
in the cis and trans cases are respectively Fe-N ) 0.216
and 0.025; Fe-C1 ) 0.065 and 0.197; Fe-C2 ) 0.092
and 0.141; Fe-C3 ) 0.080 and 0.045. Charges on the
bonded trans-azadiene atoms are N ) -0.96; C1 ) 0.40;
C2 ) 0.08; C3 ) 0.016. The most significant change in
the atomic charge distribution on passing from trans
to cis coordination is the charge at C3, which becomes
negative (-0.230, see also Scheme 3).
In this respect we developed a molecular orbital
analysis of (cis-azadiene)Fe(CO)3 allowing the valence
orbitals of the Fe(CO)3 fragment to interact with those
of the ligand.17 The orbital interaction diagram is shown
in Figure 10. The complex has been divided into a
1-azadiene ligand and an Fe(CO)3 fragment, the latter
To explain why the H(C3) atom is found nonplanar
in the iron complexes (Table 4), we followed the reaction
coordinate when the hydrogen atom is moved out of the
ligand plane, i.e., varying the H-C-C-C dihedral angle
(φ) by 90°. The Walsh diagram (see Figure 8) corre-
sponding to the above-mentioned process shows that the
(17) Albright, T.; Burdett, J . K.; Whangbo, M.-H. Orbital Interactions
in Chemistry; Wiley: New York, 1985.

(η4-1-azadiene)Fe(CO)3 Complexes
Organometallics, Vol. 18, No. 4, 1999 743
F igu r e 10. Orbital interaction diagram of the (1-azadi-
ene)Fe(CO)3 model structure. The complex has been divided
into an Fe(CO) 3 unit (C3v, right) and the azadiene fragment
(left); the C and O components are omitted for clarity.
Con clu sion s
F igu r e 8. Walsh diagram showing the total energy curve
(dashed line, in scale) together with the selected HOMO
(solid line) associated with the out-of-plane moving of the
H(C3) atom of 90° (φ ) 0° planar C3 hydrogen).
In this paper we have discussed the synthesis and
characterization of a series of 1-azadiene ligands as well
as the corresponding (η4-azadiene)Fe(CO)3 complexes at
the molecular and crystal level. While the 1-azadiene
moiety adopts a trans conformation as free molecule,
all complexes carry the ligand in cis conformation in
order to bind to the Fe(CO)3 unit. Besides this confor-
mational difference, a more subtle effect has been
observed. Upon coordination, the â-hydrogen atom of the
azadiene is pushed out-of-plane with respect to the
C-C-C-N plane. These two aspects have been ad-
dressed by means of extended Hu¨ckel molecular orbital
calculations. The electronic origin of the out-of-plane
position of the hydrogen atom HC(3) has been justified
in terms of a better π*-back-bonding between the
1-azadiene and Fe(CO)3 molecular fragments.
In terms of crystal structure, we have been able to
show that if the azadiene moiety is involved in hydrogen
bonding, the interactions are realized by the hydrogen
atom at the C-N double bond and the hydrogen atom
in R-position with respect to the imine group. In
agreement with the observations made in other orga-
nometallic crystals of carbonyl species, all crystalline
materials discussed herein show the presence of a large
number of weak hydrogen bond interactions of the
C-H- - -O type involving the CO-ligand acceptors.
F igu r e 9. Molecular orbital (HOMO) responsible for the
major energy stabilization of the iron complex when H(C3)
is nonplanar: (a) φ ) 0° and (b) φ ) 40°. Notice the
increased overlap between Fe and C3.
being treated as a C3v ML3 unit with a d8 electronic
configuration.
Lowering the symmetry of the azadiene ligand with
respect to 1,3-butadiene results in a more complicated
mixing of MOs of the two fragments. The HOMO and
LUMO (7e in Figure 10) of the Fe(CO)3 fragment
interact with the HOMO (2a′′) and LUMO (3a′′) of the
azadiene ligand, repectively. The bonding orbitals of the
organometallic complex are described as a π-donation
from the 1-azadiene ligand (MO 2a′′) to the empty dxz
orbital of the metal with a strongly localized Fe-C3 and
Fe-N character and a π*-back-bonding from the oc-
cupied dxy MO of the Fe(CO)3 moiety and the LUMO
(3a′′) of the organic fragment. The latter interaction,
corresponding to the (1-azadiene)Fe(CO)3 HOMO (30a
in Figures 9 and 10), is stabilized by the H(C3) nonpla-
narity as shown above. The increasing π*-back-bonding
from the Fe(CO)3 fragment to the azadiene ligand
weakens the C2-C3 and C1-N bonds and strengthens
the central C-C bond, as noted in the molecular
structures.
Exp er im en ta l Section
Rea gen ts a n d Solven ts. All procedures were carried out
under an argon atmosphere in anhydrous, freshly distilled
solvents. Chromatography was done using silica gel 60 and
silanized silica gel 60, 70-230 mesh ASTM (Merck), which
were dried at 10-2 bar (103 Pa) for 2 days before use. 3-(2-
furanyl)prop-2-enal18 and 3-(2-thiophenyl)prop-2-enal19 were
synthezised by methods described in the literature. Fe2(CO)9
was prepared from Fe(CO)5 (Lancaster) by irradiation in acetic
acid.20 The preparation of the ligands 6, 17, and 18 as well as
(18) Ko¨nig, W. Chem. Ber. 1925, 58, 2559.
(19) Aumann, R.; Hinterding, P.; Kru¨ger, C.; Goddard, R. J . Orga-
nomet. Chem. 1993, 459, 145.

744 Organometallics, Vol. 18, No. 4, 1999
Imhof et al.
of the corresponding iron carbonyl complexes 12, 19, and 20
has been published by some of us.11
(C7H5N+, 8), 77 (C6H5+, 9), 51 (C4H3+, 3). IR (in CH2Cl2, 298
K) [cm-1]: 1632 (CdN). 1H NMR (in CDCl3, 298 K) [ppm]: 7.07
3
3
(dd, 1H, J HH ) 8.5 Hz, J HH ) 15.9 Hz, dCH), 7.24 (d, 1H,
3J HH ) 15.9 Hz, dCH), 7.34-7.42 (m, 3H, Har), 7.51-7.56 (m,
4H, Har), 7.69 (s, 1H, Har), 8.22 (d, 1H, 3J HH ) 8.5 Hz, NdCH).
13C NMR (CDCl3, 298 K) [ppm]: 119.1 (3J CF ) 3.8 Hz, Car),
121.1 (3J CF ) 3.4 Hz, Car), 123.2 (1J CF ) 272.7 Hz, CF3), 127.7
(Car), 127.8 (Car), 129.0 (Car), 130.2 (dC), 132.6 (2J CF ) 33.3
Hz, Car), 135.1 (Car), 146.6 (dC), 153.2 (Car), 164.3 (NdC).
P r ep a r a tion of th e Liga n d s. Equimolar amounts (20
mmol) of the R,â-unsaturated aldehyde and the corresponding
amine are stirred together at 40 °C in just enough ethanol to
dissolve all of the starting material. If both reactants are
liquids, they are reacted without any solvent. The reaction is
monitored by thin-layer chromatography. When the reaction
is finished, 1 and 14 are purified by distillation, whereas 2, 3,
4, 5, and 13 had precipitated and were purified by recrystal-
lization from ethanol. 6, 17, and 18 had to be chromatographed
after the solvent was removed, as described in ref 11. 1, 2, 3,
and 4 have been described in the literature;21 their identity
and purity were determined by comparing their physical and
spectroscopical properties with those reported. The physical
and spectroscopical properties of 6, 17, and 18 have been
described by us.11
5: yield 5.96 g (86.9%). Anal. Calcd for C17H11NF6: C, 59.48;
H, 3.23; N, 4.08. Found: C, 59.18; H, 3.41; N, 4.06.
13: yield 1.89 g (46.6%). Anal. Calcd for C13H17NO: C, 76.81;
H, 8.43; N, 6.89. Found: C, 76.47; H, 8.64; N, 6.93.
14: yield 3.02 g (68.9%). Anal. Calcd for C13H17NS: C, 71.19;
H, 7.81; N, 6.39. Found: C, 71.03; H, 8.01; N, 6.42.
P r ep a r a tion of th e Ir on Ca r bon yl Com p lexes. The
synthesis of 12, 19, and 20 has been described previously.11
In a typical experiment 500 mg (1.4 mmol) of Fe2(CO)9 is
stirred together with an equimolar amount of the correspond-
ing ligand in 30 mL of n-heptane at 50 °C. During the reaction
the color of the solution darkens from orange to deep red and
the undissolved Fe2(CO)9 slowly disappears. After all of the
starting material is dissolved, the solvent is evaporated in
vacuo. The resulting oily residue is dissolved in 10 mL of CH2-
Cl2, and 1 g of silanized silica gel is added. Chromatography
yields an orange fraction of (η4-azadiene)Fe(CO)3 using a
mixture of light petroleum (bp 40-60 °C)/CH2Cl2 (10:1) as the
eluent. The complexes are recrystallized from light petroleum/
CH2Cl2 (20:1) at -20 °C.
7: yield 277 mg (56.2%). Anal. Calcd for C18H19NO3Fe: C,
61.21; H, 5.42; N, 3.87. Found: C, 60.96; H, 5.55; N, 3.98.
8: yield 232 mg (42.7%). Anal. Calcd for C21H19NO3Fe: C,
64.80; H, 4.92; N, 3.60. Found: C, 64.45; H, 5.03; N, 3.58.
9: yield 406 mg (68.3%). Anal. Calcd for C18H12NO3FeBr:
C, 50.74; H, 2.84; N, 3.29; Br, 18.75. Found: C, 50.53; H, 2.83;
N, 3.29; Br, 18.48.
10: yield 361 mg (62.2%). Anal. Calcd for C19H12NO3F3Fe:
C, 54.97; H, 2.91; N, 3.37. Found: C, 54.72; H, 2.90; N, 3.37.
11: yield 261 mg (38.6%). Anal. Calcd for C20H11NO3F6Fe:
C, 49.72; H, 2.29; N, 2.90. Found: C, 49.61; H, 2.41; N, 2.94.
15: yield 210 mg (43.6%). Anal. Calcd for C16H17NO4Fe: C,
56.00; H, 4.99; N, 4.08. Found: C, 56.23; H, 5.03; N, 4.09.
16: yield 350 mg (69.6%). Anal. Calcd for C16H17NO3SFe:
C, 53.50; H, 4.77; N, 3.90. Found: C, 53.71; H, 4.86; N, 3.87.
Sp ectr oscop ic Mea su r em en ts. Infrared spectra were
recorded on a Perkin-Elmer FT-IR System 2000 using 0.2 mm
KBr cuvettes; NMR spectra on a Bruker AC 200 spectrometer
(1H, 200 MHz with SiMe4 as internal standard; 13C, 50.32 MHz
with CDCl3 as internal standard); mass spectra on a Finnigan
MAT SSQ 710 instrument. Elemental analyses were carried
out at the laboratory of the Institute of Organic Chemistry
and Macromolecular Chemistry of the Friedrich-Schiller-
University J ena.
MS a n d Sp ectr oscop ica l Da ta for 13. MS (EI): m/z (%)
203 (M+, 100), 186 (C12H14NO+, 5), 174 (C11H12NO+, 59), 160
(C10H10NO+, 60), 146 (C9H8NO+, 42), 132 (C8H6NO+, 19), 120
(C7H6NO+, 47), 107 (C7H7O+, 14), 93 (C6H5O+, 35), 80 (C5H4O+,
18), 78 (C5H4N+, 26), 67 (C4H5N+, 28), 55 (C3H5N+, 30), 41
1
(C2H3N+, 25). IR (in CH2Cl2, 298 K) [cm-1]: 1624 (CdN). H
NMR (in CDCl3, 298 K) [ppm]: 1.16-1.81 (m, 10H, CH2),
2.94-3.07 (m, 1H, CH), 6.38-6.43 (m, 2H, dCH, Har), 6.69-
3
6.76 (m, 2H, dCH, Har), 7.40 (d, 1H, J HH ) 1.4 Hz, Har), 7.95
(d, 1H, 3J HH ) 7.9 Hz, NdCH). 13C NMR (CDCl3, 298 K) [ppm]:
24.8 (CH2), 25.6 (CH2), 34.5 (CH2), 69.7 (CH), 111.0, 111.8
(Car), 127.0, 127.8 (dCH), 143.5 (Car), 152.2 (Car), 159.7 (Nd
CH).
MS a n d Sp ectr oscop ica l Da ta for 14. MS (EI): m/z (%)
219 (M+, 89), 218 (M+ - H, 95), 204 (C12H14NS+, 3), 190
(C11H12NS+, 12), 176 (C10H10NS+, 23), 162 (C9H8NS+, 35), 148
(C8H6NS+, 11), 136 (C7H6NS+, 100), 121 (C7H5S+, 27), 109
(C6H5S+, 27), 97 (C5H5S+, 19), 80 (C5H6N+, 8), 77 (C5H3N+, 10),
67 (C4H7N+, 6), 55 (C3H5N+, 24), 41 (C2H3N+, 22). IR (in CH2-
1
Cl2, 298 K) [cm-1]: 1628 (CdN); H NMR (in CDCl3, 298 K)
[ppm]: 1.07-1.78 (m, 10H, CH2), 2.92-3.06 (m, 1H, CH), 6.67
3
3
(dd, 1H, J HH ) 8.7 Hz, J HH ) 15.7 Hz, dCH), 6.86-7.06 (m,
3
3H, dCH, Har), 7.20 (d, 1H, J HH ) 5.0 Hz, Har), 7.92 (d, 1H,
3J HH ) 8.7 Hz, NdCH). 13C NMR (CDCl3, 298 K) [ppm]: 24.6
(CH2), 25.5 (CH2), 34.3 (CH2), 69.4 (CH), 126.5, 127.6, 127.8,
128.0 (dCH, Car), 133.1 (Car), 141.1 (Car), 159.4 (NdCH).
MS a n d Sp ectr oscop ica l Da ta for 7. MS (EI): m/z (%)
353 (M+, 1), 325 (M+ - CO, 8); 297 (M+ - 2 CO, 18), 269 (M+
- 3 CO, 100), 187 (M+ - 3 CO - C6H10, 23), 133 (C9H11N+,
29), 115 (C8H5N+, 54), 91 (C6H5N+, 12), 56 (C3H6N+, Fe+, 26).
IR (in CH2Cl2, 298 K) [cm-1]: 2051 (vs), 1987 (vs), 1969 (s).
1H NMR (in CDCl3, 298 K) [ppm]: 1.17-1.68 (m, 11H, C6H11),
3
3
2.94 (d, 1H, J HH ) 9.2 Hz, dCH), 5.48 (dd, 1H, J HH ) 2.7
3
3
Hz, J HH ) 9.2 Hz, dCH), 6.56 (d, 1H, J HH ) 2.7 Hz, dCH),
7.13-7.24 (m, 5H, Har). 13C NMR (CDCl3, 298 K) [ppm]: 24.8
(CH2), 24.9 (CH2), 25.8 (CH2), 36.3 (CH2), 37.8 (CH2), 60.9
(dCH), 67.2 (CH), 71.9 (dCH), 111.0 (NdCH), 126.5 (Car),
126.6 (Car), 128.6 (Car), 139.5 (Car), 210.6 (CO, br).
MS a n d Sp ectr oscop ica l Da ta for 8. MS (EI): m/z (%)
389 (M+, 2), 361 (M+ - CO, 14); 333 (M+ - 2 CO, 8), 305 (M+
- 3 CO, 100), 249 (M+ - 3 CO - Fe, 52), 152 (C12H8+, 36), 130
+
(C9H8N+, 25), 115 (C8H5N+, 34), 91 (C6H5N+, 34), 78 (C6H6
,
33), 56 (C3H6N+, Fe+, 56). IR (in CH2Cl2, 298 K) [cm-1]: 2053
(vs), 1990 (vs), 1978 (sh). 1H NMR (in CDCl3, 298 K) [ppm]:
2.05 (s, 3H, CH3), 2.43 (s, 6H, CH3), 3.27 (d, 1H, J HH ) 9.5
3
3
Hz, dCH), 6.08 (d, 1H, J HH ) 9.2 Hz, dCH), 6.72 (s, 1H,
dCH), 7.26-7.53 (m, 7H, Har). 13C NMR (CDCl3, 298 K) [ppm]:
20.5 (CH3), 21.9 (CH3), 64.1 (dCH), 74.2 (dCH), 107.4 (Nd
CH), 127.5 (Car), 127.6 (Car), 129.4 (Car), 130.9 (Car), 131.1 (Car),
132.6 (Car), 139.6 (Car), 147.3 (Car), 211.0 (CO, br).
MS a n d Sp ectr oscop ica l Da ta for 9. MS (EI): m/z (79Br)
(%) 425 (M+, 5), 397 (M+ - CO, 11); 369 (M+ - 2 CO, 11), 341
(M+ - 3 CO, 100), 284 (M+ - 3 CO - FeH, 10), 264 (M+ - 3
CO - C6H5, 14), 204 (C15H10N+, 67), 170 (C6H5NBr+, 46), 155
(C6H4Br+, 16), 135 (C4H8Br+, 35), 115 (C8H5N+, 79), 103
(C7H5N+, 35), 76 (C6H4+, 48), 56 (C3H6N+, Fe+, 26). IR (in CH2-
Cl2, 298 K) [cm-1]: 2060 (vs), 1998 (vs), 1988 (sh). 1H NMR
MS a n d Sp ectr oscop ic Da ta for 5. MS (EI): m/z (%) 342
(M+ - H, 100), 324 (C17H11NF5+, 4), 272 (C16H10NF3+, 2), 213
(C14H12NF+, 8), 128 (C9H6N+, 11), 115 (C8H5N+, 13), 103
(20) Brauer, G. Handbuch der pra¨p. Anorg. Chemie, Teil C, Liefer-
ung 1, 8. Aufl.; Verlag Chemie: Weinheim, 1968; p 19.
(21) (a) Grammaticakis, P. C. R. Acad. Sci., Paris, Ser. C 1967, 265,
747. (b) Skita, A.; Wulff, C. Liebigs Ann. 1927, 455, 17. (c) Sandhu, J .
S.; Mohan, S.; Sethi, P. S.; Singh, L. J . Indian Chem. Soc. 1970, 47,
1009. (d) Maginnity, P. M.; Eisenmann, J . L. J . Am. Chem. Soc. 1952,
74, 6119.
3
(in CDCl3, 298 K) [ppm]: 3.41 (d, 1H, J HH ) 9.5 Hz, dCH),
3
3
5.79 (dd, 1H, J HH ) 2.8 Hz, J HH ) 9.5 Hz, dCH), 6.80-6.84
(m, 2H, Har), 6.92 (d, 1H, 3J HH ) 2.8 Hz, dCH), 7.21-7.38 (m,
7H, Har). 13C NMR (CDCl3, 298 K) [ppm]: 63.1 (dCH), 75.5

(η4-1-azadiene)Fe(CO)3 Complexes
Organometallics, Vol. 18, No. 4, 1999 745
Ta ble 6. Cr ysta l a n d In ten sity Da ta for th e
Com p ou n d s 3, 4, a n d 5
(dCH), 103.5 (NdCH), 115.1 (Car), 123.8 (Car), 127.1 (Car), 127.5
(Car), 129.2 (Car), 132.2 (Car), 139.1 (Car), 153.3 (Car), 210.1 (CO,
br).
3
4
5
MS a n d Sp ectr oscop ica l Da ta for 10. MS (EI): m/z (%)
415 (M+, 1), 387 (M+ - CO, 5); 359 (M+ - 2 CO, 4), 331 (M+
- 3 CO, 25), 274 (M+ - 3 CO - FeH, 15), 256 (C16H12F2N+,
15), 237 (C16H12FN+, 15), 166 (C12H8N+, 15), 126 (C9H4N+, 16),
115 (C8H5N+, 100), 107 (C7H9N+, 13), 91 (C6H5N+, 9), 75
(C6H3+, 13), 56 (C3H6N+, Fe+, 26). IR (in CH2Cl2, 298 K) [cm-1]:
2062 (vs), 2000 (vs), 1990 (sh). 1H NMR (in CDCl3, 298 K)
formula
C
15H12NBr
C16H12NF3
275.27
Mo KR
graphite
293
C17H11NF6
343.27
Mo KR
graphite
183
mol weight [g mol-1
radiation
]
286.17
Mo KR
graphite
183
pale yellow
0.8 × 0.2 ×
0.2
7.617(2)
5.567(1)
29.917(6)
90
monochromator
temp [K]
cryst color
pale yellow yellow
cryst size [mm]
1.2 × 0.03 × 0.5 × 0.1 ×
3
3
0.02
6.2193(9)
15.366(3)
7.313(2)
94.979(6)
90.18(1)
91.66(1)
696.0(2)
2
0.1
[ppm]: 3.37 (d, 1H, J HH ) 8.0 Hz, dCH), 5.75 (d, 1H, J HH
)
8.0 Hz, dCH), 6.82-7.48 (m, 10H, dCH, Har). 13C NMR (CDCl3,
298 K) [ppm]: 63.1 (dCH), 75.7 (dCH), 102.1 (NdCH), 121.8
(Car), 124.1 (2J CF ) 33 Hz, Car), 125.0 (1J CF ) 272 Hz, CF3),
126.2 (Car), 126.7 (Car), 127.3 (Car), 128.9 (Car), 138.4 (Car), 156.7
(Car), 205.1 (CO, br), 208.6 (CO, br), 211.3 (CO, br).
a [Å]
b [Å]
c [Å]
R [deg]
â [deg]
γ [deg]
V [Å3]
Z
8.0648(9)
8.627(2)
11.569(2)
97.07(1)
93.20(1)
107.41(1)
758.5(2)
2
348
1.503
triclinic
P1h
0.140
90
90
MS a n d Sp ectr oscop ica l Da ta for 11. MS (EI): m/z (%)
483 (M+, 1), 455 (M+ - CO, 5); 427 (M+ - 2 CO, 6), 399 (M+
1268.6(4)
4
576
- 3 CO, 61), 342 (M+ - 3 CO - FeH, 7), 323 (C17H10NF5+, 1),
F(000)
284
1.314
æ
calc [g cm-3
cryst syst
]
1.498
+
304 (C17H10NF4+, 15), 285 (C17H10NF3+, 13), 254 (C16H10NF2
,
orthorhombic triclinic
9), 235 (C16H10NF+, 7), 213 (C14H12NF+, 13), 200 (C13H11NF+,
15), 163 (C10H10NF+, 16), 115 (C8H5N+, 46), 91 (C6H5N+, 100),
77 (C6H5+, 22), 56 (C3H6N+, Fe+, 26); IR (in CH2Cl2, 298 K)
[cm-1]: 2064 (vs), 2003 (vs), 1991 (sh). 1H NMR (in CDCl3,
298 K) [ppm]: 3.42 (d, 1H, 3J HH ) 9.4 Hz, dCH), 5.84 (d, 3J HH
) 9.2 Hz, dCH), 6.87 (s, 1H, dCH), 7.23-7.38 (m, 8H, Har).
13C NMR (CDCl3, 298 K) [ppm]: 63.8 (dCH), 77.2 (dCH), 101.1
(NdCH), 115.3 (3J FC ) 3.8 Hz, Car), 121.5 (3J CF ) 3.9 Hz, Car),
123.2 (1J CF ) 272 Hz, CF3), 126.7 (Car), 127.5 (Car), 129.0 (Car),
132.4 (2J CF ) 33 Hz, Car), 137.9 (Car), 155.0 (Car), no resonances
for CO ligands have been observed.
space group
Pna21
3.216
2.72-22.07
ω-2θ
1-10
719
719
0.0000
663
P1h
0.105
abs coeff [mm-1
θ-limit [deg]
scan mode
]
3.50-23.28 2.50-23.99
æ
ω-2θ
1-10
2560
2381
0.0135
1705
scan speed [deg min-1
no. of reflns measd
no. of ind reflns
R(int)
]
1864
1864
0.000
1407
no. of obs reflns
2
2
Fo > 2σ(Fo
)
no. of params
GOOF
R1
157
250
250
1.085
0.0453
0.1281
1.165
0.1284
0.3367
0.443
1.052
0.0716
0.1719
0.456
MS a n d Sp ectr oscop ica l Da ta for 15. MS (EI): m/z (%)
343 (M+, 3), 315 (M+ - CO, 16); 287 (M+ - 2 CO, 37), 259 (M+
- 3 CO, 100), 203 (M+ - 3 CO - Fe, 6), 176 (C11H14NO+, 14),
149 (C9H11NO+, 41), 122 (C7H8NO+, 12), 104 (C7H10NO+, 17),
93 (C6H5O+, 12), 83 (C6H11+, 9), 77 (C6H5+, 6), 56 (C3H6N+, Fe+,
26), 41 (C2H3N+). IR (in CH2Cl2, 298 K) [cm-1]: 2052 (vs), 1989
(vs), 1972 (s). 1H NMR (in CDCl3, 298 K) [ppm]: 1.14-1.71
wR2
final diff map electron 0.649
density [e Å-3
]
SHELXL93.22 Computations of the structures were done with
the program XPMA, and the molecular illustrations were
drawn using the program ZORTEP.23 The crystal and intensity
data are given in Tables 6 (3, 4, and 5) and 7 (6-10, 15, and
16). Details concerning the crystal structure analyses of 12,
17, 19, and 20 have been reported by us in ref 11. Analyses of
the packings were done using the program PLATON.24 For this
purpose the C-H distances have been normalized to 108.0 pm.
Additional material on the structure analyses is available from
the Fachinformationszentrum Chemie, Physik, Mathematik
GmbH, 76344 Eggenstein-Leopoldshafen 2, Germany, by
mentioning the deposition numbers CSD-408468 (3), -408469
(4), -408470 (5), -408471 (7), -408472 (8), -408473 (9), -408474
(10), -408475 (11), -407879 (12), -408476 (15), -408477 (16),
-407880 (17), -407881 (19), -407882 (20), the authors, and the
journal citation.
Exten d ed Hu1 ck el An a lysis. All the calculations were of
the extended Hu¨ckel type,25 with modified Hij’s.26 The basis
set used for the Fe atom consisted of 3d, 4s, and 4p orbitals.
For N, C, H, and O atoms standard parameters were used.
The following valence-state ionization potentials were used for
the Fe atom: (Hij/eV, ú), 4s, -9.10, 1.9; 4p, -5.32, 1.9; 3d,
-12.6, 5.35, 2.0 (ú2), 0.5505 (C1), 0.6260 (C2). Three-dimen-
sional representations of orbitals as well as the Walsh diagram
were drawn using the program CACAO.27
3
(m, 11H, C6H11), 2.88 (d, 1H, J HH ) 8.9 Hz, dCH), 5.44 (dd,
3
3
3
1H, J HH ) 2.7 Hz, J HH ) 8.9 Hz, dCH), 6.16 (d, 1H, J HH
)
3
3
2.7 Hz, dCH), 6.26 (dd, 1H, J HH ) 1.8 Hz, J HH ) 3.0 Hz,
3
3
H
ar), 6.50 (dd, 1H, J HH ) 0.8 Hz, J HH ) 3.0 Hz, Har), 7.24 (d,
1H, 3J HH ) 1.8 Hz, Har). 13C NMR (CDCl3, 298 K) [ppm]: 23.8
(CH2), 23.7 (CH2), 24.8 (CH2), 35.3 (CH2), 36.8 (CH2), 50.6 (d
CH), 65.8 (CH), 69.0 (dCH), 105.4 (NdCH), 109.6 (Car), 110.5
(Car), 140.2 (Car), 153.9 (Car), 207.5 (CO, br).
MS a n d Sp ectr oscop ica l Da ta for 16. MS (EI): m/z (%)
359 (M+, 1), 331 (M+ - CO, 8); 303 (M+ - 2 CO, 24), 275 (M+
- 3 CO, 100), 193 (C11H15NS+, 12), 159 (C9H5NS+, 26), 137
(C7H7NS+, 54), 104 (C7H6N+, 11), 97 (C5H5S+, 5), 56 (C3H6N+,
Fe+, 11), 41 (C3H5+, 5). IR (in CH2Cl2, 298 K) [cm-1]: 2052
(vs), 1988 (vs), 1971 (s). 1H NMR (in CDCl3, 298 K) [ppm]:
3
1.18-1.85 (m, 11H, C6H11), 3.20 (d, 1H, J HH ) 9.0 Hz, dCH),
3
3
5.36 (dd, 1H, J HH ) 2.8 Hz, J HH ) 9.0 Hz, dCH), 6.50 (d,
3
1H, J HH ) 2.8 Hz, dCH), 6.85-6.95 (m, 2H, Har), 7.09 (dd,
3
3
1H, J HH ) 1.1 Hz, J HH ) 5.0 Hz, Har). 13C NMR (CDCl3, 298
K) [ppm]: 24.7 (CH2), 24.8 (CH2), 25.7 (CH2), 36.3 (CH2), 37.8
(CH2), 56.0 (dCH), 66.9 (CH), 72.3 (dCH), 110.3 (NdCH),
123.4 (Car), 123.9 (Car), 127.5 (Car), 144.9 (Car), 209.0 (CO, br).
Cr ysta l Str u ctu r e Deter m in a tion s. Crystals suitable for
X-ray structure analysis have been grown from mixtures of
light petroleum/CH2Cl2. The crystal structure determinations
of 3, 5, 7, 9, 10, and 11 were carried out on an Enraf Nonius
CAD4 diffractometer, those of 8, 15, and 16 on a Siemens P4
diffractometer, the one of 4 on an Enraf Nonius Kappa CCD
diffractometer. In all cases graphite-monochromated Mo KR
radiation was used. The crystals were mounted in a stream of
cold nitrogen. Data were corrected for Lorentz and polarization
effects but not for absorption. The structures were solved by
direct methods and refined by full-matrix least-squares tech-
niques against F2 using the programs SHELXS86 and
(22) (a) Sheldrick, G. SHELXS 86; Universita¨t Go¨ttingen, 1986. (b)
Sheldrick, G. SHELXL93; Universita¨t Go¨ttingen, 1993.
(23) (a) Zsolnai, L.; Huttner, G. XPMA; Universita¨t Heidelberg,
1997. (b) Zsolnai, L.; Pritzkow, H.; Huttner, G. ZORTEP; Universita¨t
Heidelberg, 1997.
(24) Spek, A. L. Acta Crystallogr. 1990, A46, C31.
(25) (a) Hoffmann, R. J . Chem. Phys. 1963, 39, 1397. (b) Hoffmann,
R.; Lipscomb, W. N. J . Chem. Phys. 1962, 36, 2179 and 3489.
(26) Ammeter, J . H.; Bu¨rgi, H.-B.; Thibeault, J . C.; Hoffmann, R.
J . Am. Chem. Soc. 1978, 100, 3686.
(27) Mealli, C.; Proserpio, D. M. J . Chem. Educ. 1990, 67, 39.

746 Organometallics, Vol. 18, No. 4, 1999
Ta ble 7. Cr ysta l a n d In ten sity Da ta for th e Com p ou n d s 7-11, 15, a n d 16
Imhof et al.
7
8
9
10
11
formula
mol weight [g mol-1
radiation
monochromator
temp [K]
cryst color
cryst size [mm]
a [Å]
C
18H19NO3Fe
C21H19NO3Fe
389.22
Mo KR
graphite
183
orange
0.8 × 0.5 × 0.2
10.375(4)
9.036(4)
20.328(9)
90
C18H12NO3BrFe
426.05
Mo KR
graphite
183
orange
0.6 × 0.3 × 0.1
11.463(2)
15.677(9)
9.463(3)
90
C19H12NF3O3Fe
415.15
Mo KR
graphite
183
orange
0.6 × 0.2 × 0.1
11.631(3)
16.015(7)
9.558(6)
90
C20H11NF6O3Fe
483.15
Mo KR
graphite
183
orange
0.3 × 0.2 × 0.05
8.556(3)
9.505(6)
13.353(5)
102.35(3)
93.02(3)
110.88(4)
981.2(8)
2
]
353.19
Mo KR
graphite
183
orange
0.6 × 0.4 × 0.3
11.979(3)
7.808(1)
18.376(3)
90
b [Å]
c [Å]
R [deg]
â [deg]
104.81(2)
90
1661.6(5)
4
95.25(3)
90
1898(1)
4
100.75(2)
90
1671(1)
4
100.12(4)
90
1753(1)
4
γ [deg]
V [Å3]
Z
F(000)
736
1.412
monoclinic
P21/n
0.923
808
1.362
monoclinic
P21/n
0.816
848
1.694
monoclinic
P21/c
3.312
840
1.573
monoclinic
P21/c
0.912
484
1.635
triclinic
P1h
0.849
æ
calc [g cm-3
]
cryst syst
space group
abs coeff [mm-1
θ-limit [deg]
scan mode
]
2.29-24.68
2.13-23.50
2.55-28.48
2.51-28.62
2.50-28.49
ω-2θ
ω-2θ
ω-2θ
ω-2θ
ω-2θ
scan speed [deg min-1
no. of reflns measd
no. of ind reflns
R(int)
]
1-10
1-10
1-10
1-10
1-10
2963
2721
4437
4666
4751
2817
0.0152
2599
223
1.047
0.0248
0.0657
0.261
2721
0.0000
2038
250
1.073
0.0694
0.1859
1.118
4195
0.0407
2962
231
1.031
0.0383
0.0957
0.630
4412
0.0442
3157
282
1.228
0.0703
0.1804
0.890
4580
0.0218
3639
294
1.032
0.0436
0.0888
0.630
2
2
obs reflns Fo > 2σ(Fo
)
no. of params
GOOF
R1
wR2
final diff map electron density [e Å-3
]
15
16H17NO4Fe
343.16
Mo KR
graphite
213
orange
0.4 × 0.4 × 0.05
11.034(3)
7.647(2)
19.006(4)
90
16
formula
C
C16H17NO4Fe
359.22
Mo KR
graphite
213
orange
0.2 × 0.2 × 0.2
11.868(2)
7.853(1)
18.147(2)
90
mol weight [g mol-1
radiation
monochromator
temp [K]
cryst color
cryst size [mm]
a [Å]
]
b [Å]
c [Å]
R [deg]
â [deg]
102.17(1)
90
1567.6(7)
4
103.44(1)
90
1645.0(4)
4
γ [deg]
V [Å3]
Z
F(000)
712
1.454
monoclinic
P21/c
0.981
744
1.450
monoclinic
P21/n
1.056
æ
calc[g cm-3
]
cryst syst
space group
abs coeff [mm-1
θ-limit [deg]
scan mode
]
1.89-24.36
1.87-27.50
θ-2θ
θ-2θ
scan speed [deg min-1
no. of reflns measd
no. of ind reflns
]
3-60
3-60
3385
4948
2473
3785
R(int)
0.0566
2016
214
0.0330
2889
234
2
2
no. of obs reflns Fo > 2σ(Fo
)
no. of params
GOOF
R1
1.060
1.021
0.0332
0.0829
0.321
0.0390
0.0916
0.306
wR2
final diff map electron density [e Å-3
]
Th e Mod el. For the azadiene ligand we used the simplified
CH2dCH-CHdNH system (the hydrogen atoms bonded to the
nitrogen and terminal carbon atoms instead of the organic
substituents). The N-H and C-H bond lengths used are 1.0
and 1.08 Å, respectively; the bond length of C1-C2 is 1.34 Å,
C2-C3 1.43 Å, and N-C 1.27 Å. All the ligand atoms were
considered to be in a planar arrangement (unless otherwise
stated) with all bond angles being 120°. For the organometallic
complex the azadiene geometry was taken as previously, while
an optimization of the Fe-(azadiene) centroid along the
perpendicular from the azadiene plane to the Fe nucleus has
been carried out for both cis and trans conformers. The bond
distances of the Fe(CO)3 fragment used in the model are Fe-
centroid ) 1.5 Å (cis), 2.0 Å (trans), Fe-C1 ) 2.04 Å, Fe-C2
) 2.07 Å, Fe-C3 ) 2.07 Å, Fe-N ) 2.02 Å, Fe-C ) 1.8 Å,
C-O ) 1.3 Å.

(η4-1-azadiene)Fe(CO)3 Complexes
Organometallics, Vol. 18, No. 4, 1999 747
crystal packings, tables of crystal data and structure refine-
ment, atomic coordinates, bond lengths and angles, and
anisotropic displacement parameters for 3, 4, 5, 7, 8, 9, 10,
11, 12, 15, 16, 17, 19, and 20 (103 pages). See any current
masthead page for ordering information and Internet access
instructions.
Ack n ow led gm en t. We thank the Deutscher Aka-
demischer Austauschdienst, Bonn, and the Conferenza
Nazionale dei Rettori, Roma, for a scientific exchange
within the VIGONI program.
Su p p or tin g In for m a tion Ava ila ble: Details about the
X-ray crystal structures including ORTEP diagrams of the
OM980415H