Photo-assisted preparation of double isocyanide insertion complexes of η5-cyclopentadienyliron(II) bearing only isocyanide: The molecular structure of (η5-C5H5)Fe(XylNC) 2[C(=NXyl)C(=NXyl)CH3 (XylNC=2,6-Me2C6H3NC)

Article abstract of DOI:10.1016/S0020-1693(98)00394-6

Reaction of η⁵-C₅H₅Fe(CO)₂CH₃ (1) with xylyl isocyanide in toluene at reflux gave η⁵-C₅H₅Fe(CO)(XylNC)COCH₃ (5a) (Xyl=2,6-(CH₃)₂C₆H₃), whereas photochemical reaction underwent double insertion of isocyanide molecules into an iron-carbon bond to give a bis-imino type complex (η⁵-C₅H₅)Fe(XylNC) ₂[C(=NXyl)C(=NXyl)CH₃] (6a), determined by an X-ray analysis.

Full text of DOI:10.1016/S0020-1693(98)00394-6

Inorganica Chimica Acta 286 (1999) 233–236
Note
Photo-assisted preparation of double isocyanide insertion
complexes of h5-cyclopentadienyliron(II) bearing only isocyanide:
the molecular structure of
(h5-C5H5)Fe(XylNC)2[C(ꢀNXyl)C(ꢀNXyl)CH3
(XylNC=2,6-Me2C6H3NC)
Yasuhiro Yamamoto *, Masayuki Tsuji, Toshiaki Igoshi
Department of Chemistry, Faculty of Science, Toho Uni6ersity, Miyama, Funabashi, Chiba 274-0072, Japan
Received 1 July 1998; accepted 3 November 1998
Abstract
Reaction of h5-C5H5Fe(CO)2CH3 (1) with xylyl isocyanide in toluene at reflux gave h5-C5H5Fe(CO)(XylNC)COCH3 (5a)
(Xyl=2,6-(CH3)2C6H3), whereas photochemical reaction underwent double insertion of isocyanide molecules into an iron–carbon
bond to give a bis-imino type complex (h5-C5H5)Fe(XylNC)2[C(ꢀNXyl)C(ꢀNXyl)CH3] (6a), determined by an X-ray analysis.
© 1999 Elsevier Science S.A. All rights reserved.
Keywords: Photochemistry; Iron complexes; Cyclopentadienyl complexes; Isocyanide complexes
1. Introduction
at room temperature (r.t.) to produce the correspond-
ing acyl complexes, h5-C5H5Fe(CO)(CNR)COCH3 (2)
[3], whereas reactions at reflux gave the cyclic carbene
complexes h5-C5H5Fe(CO)[kC(ꢀNR)C(NHR)ꢀCH–kC-
(NHR)] (3) accompanying novel multiple insertion of
isocyanide molecules [4]. When the photochemical reac-
tions of (h5-C5H5)Fe(CO)2CH3 in the presence of cyclo-
hexyl isocyanide were carried out, the double insertion
of isocyanide into an iron–carbon s-bond occurred to
It is well-known that carbon monoxide inserts into
the metal–carbon s-bonds to give acyl or aroyl com-
plexes and that the ultraviolet irradiation of these acyl
or aroyl complexes eliminates CO to regenerate the
corresponding alkyl or aryl derivatives [1]. This latter
process is particularly important when applied to those
systems which can not eliminate CO under thermal
conditions. A variety of insertion reactions of iso-
cyanide, isoelectronic with carbon monoxide, into the
metal–carbon or metal–hydride bonds have been docu-
mented [2].
give
a
four-membered bis-imino cyclic complex
(h5-C5H5)Fe(CO)[kC(ꢀNC6H11)–C(ꢀkNC6H11)CH3] (4)
containing a N-coordination [5]. The photo-assisted
insertion reaction is one of the most significant features
in the isocyanide chemistry as well as the multiple
insertion, different from carbon monoxide.
We found that the photochemical reaction of 1 with
aromatic isocyanide bearing methyl groups at the two,
six-positions yielded new double insertion complexes
containing only isocyanide ligand.
We
have
previously
reported
that
h5-
C5H5Fe(CO)2CH3 (1) reacted readily with alkyl iso-
cyanide (RNC) such as cyclohexyl or t-butyl isocyanide
* Corresponding author. Tel.: +81-474-725076; fax: +81-474-
751855; e-mail: yamamoto@chem.sci.toho-u.ac.jp.
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(98)00394-6

234
Y. Yamamoto et al. / Inorganica Chimica Acta 286 (1999) 233–236
2. Experimental
6.3–7.0 ppm. Anal. Calc. for C42H44N4Fe: C, 76.35; H,
6.71; N, 8.48. Found: C, 76.51; H, 6.77; N, 8.53%.
A
(MesNC)2[C(ꢀNMes)C(ꢀNMes)Me] (6b) (53%) was also
obtained according to a procedure similar to that for 6a.
All reactions were carried out under nitrogen atmo-
sphere. (h5-C5H5)Fe(CO)2CH3 [6], and xylyl (XylNC)
and mesityl isocyanides (MesNC) [7] were prepared
according to the literature. Benzene, hexane and toluene
were distilled over CaH2 and THF was distilled over
LiAlH4. The infrared and electronic absorption spectra
were measured on FT/IR-5300 and U-best 30 spectro-
meters, respectively. NMR spectroscopy was carried out
on a Bruker AC250. 1H NMR spectra were measured at
250 MHz using tetramethylsilane as an internal reference.
The mass spectra were measured on a HITACHI GC-MS
M-80 spectrometer. A photochemical reaction was car-
ried out with an USIO high-pressure mercury lamp (100
W).
mesityl isocyanide complex (h5-C5H5)Fe-
IR (Nujol): 2085, 2027 (NC), 1637, 1581 (CꢀN) cm−1
.
1
UV–Vis (CH2Cl2): umax 350 (4.15), 295 (4.25) nm. H
NMR (CDCl3): l 1.87 (s, Me, 6H), 2.07 (s, o-Me, 12H),
2.23 (s, Me, 15H), 2.26(s, Me, 6H), 6.4–6.9 (m, Ph). Anal.
Calc. for C42H44N4Fe: C, 77.08; H, 7.31; N, 7.82. Found:
C, 76.55; H, 7.28; N, 7.17%.
2.3. Data collection
Complex 6a was recrystallized from benzene–hexane.
Cell constants (a=14.201(5), b=21.05(1), c=
3
˚
˚
12.318(7) A, V=3683(6) A , Z=4) were determined
from 25 reflections on a Rigaku four-circle automated
diffractometer AFC5S. The crystal parameters along
with data collection parameters are summarized in
Table 1. Data collection was carried out on a Rigaku
AFC5S diffractometer. Intensities were measured by
the 2q–ꢀ scan method using graphite-monochromated
2.1. Thermal reaction of 1 with xylyl isocyanide
A mixture of 1 (0.50 g, 2.60 mmol) and xylyl isocyanide
(1.77 g, 13.4 mmol) in toluene (20 ml) was refluxed for
7 h and the solvent was removed in vacuo and the residue
was chromatographed on deactivated alumina (contain
10% H2O), using hexane and benzene as eluents. Two
bands (yellow and dark violet) were observed. The first
band was eluted with hexane and the second one with
benzene. Eluting with hexane gave yellow–orange crys-
tals of (h5-C5H5)Fe(CO)(XylNC)COCH3 (5a) (0.672g,
80.2%), by recrystallization from benzene–hexane. Upon
work-up of the second eluate a trace of dark violet residue
was obtained and identified as known [(h5-
C5H5)2Fe(CO)2]2 from the infrared spectrum. 5a: Mass:
m/z 322 (M+). IR (Nujol): 2100 (NꢁC), 1950 (CꢁO), 1647
˚
Mo Ka radiation (u=0.71069 A). Throughout the data
collection the intensities of the three standard reflec-
tions were measured every 150 reflections as a check of
the stability of the crystals and no decay was observed.
Intensities were corrected for Lorentz and polarization
effects. Linear absorption coefficient is 4.4 cm−1, and
the absorption correction was made with „ empirical
rotation. Transmission factors are in the range from
0.96 to 1.00. Atomic scattering factors were taken from
the usual tabulation of Cromer and Waber [8].
1
(CꢀO) cm−1. H NMR(CDCl3): l 2.38 (s, o-Me), 2.57
Table 1
Crystal data of (h5-C5H5)Fe(XylNC)2[C(ꢀNXyl)C(ꢀNXyl)Me] (6a)
(s, Me), 4.75 (s, Cp), 6.9–7.1 (m, Ph) ppm. Anal. Calc.
for C17H17NO2Fe: C, 63.18; H, 5.30; N, 4.33. Found: C,
63.00; H, 5.55; N, 4.71%.
Formula
Molecular weight
Color
C42H44N4Fe
660.68
red
2.2. Photochemical reaction of 1 with xylyl isocyanide
Crystal dimensions (mm)
Crystal system
Space group
0.30×0.20×0.40
orthorhombic
P212121 (no. 19)
14.201(5)
21.05(1)
12.318(7)
3683(6)
4
A mixture of 1 (0.30 g, 1.56 mmol) and xylyl isocyanide
(0.823 g, 6.27 mmol) in THF (20 ml) was irradiated at
r.t. with a 100-W high-pressure mercury lamp. After 8
h, the solvent was removed in vacuo and the residue was
chromatographed on deactivated alumina (contain 10%
H2O), using benzene as the eluent. Four bands (yellow–
brown, pink–yellow–brown, yellow–brown and dark
brown) were observed. Eluting with benzene gave a
yellow–brown solution. Removal of the solvent and
crystallization of the residue gave dark brown crystals of
6a (0.633 g, 56.7%). Products from the other eluates could
not be identified, because of their trace amount. Mass:
m/z 659 (M+). IR (Nujol): 2083, 2004 (NꢁC), 1639, 1572
(CꢀN) cm−1. UV–Vis (CH2Cl2): umax 354 nm (log m 4.22).
1H NMR (CDCl3): l 1.57 (s, Me, 3H), 2.05, 2.09 (s, o-Me,
inserted, 6H), 2.25 (s, o-Me, terminal, 12H), 4.84 (s, Cp),
˚
a (A)
˚
b (A)
˚
c (A)
3
˚
V (A )
Z
Dcalc (g cm−3
)
1.191
4.40
1400
v (cm−1
F(000)
)
No. reflections
6695
No. data (I\3.0|(I))
No. variables
3575
424
0.051; 0.053
1.54
a
R; Rw
GOFb
a R=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ and Rw=[S w(ꢀFoꢀ−ꢀFcꢀ)2/S wꢀFoꢀ2]1/2 (w=
1/|2(Fo)).
b GOF=[S w(ꢀFoꢀ−ꢀFcꢀ)2/S(No−Nv)]1/2, where No=no. of data,
Nv=no. of variables.

Y. Yamamoto et al. / Inorganica Chimica Acta 286 (1999) 233–236
235
Anomalous dispersion effects were included in Fcalc [9];
the values of Df % and Df ¦ were those of Creagh and
McAuley [10]. All calculations were performed using a
Digital VAX Station 3100 M38 computer using the
TEXSAN-TEXRAY program system [11].
2.4. Determination of the structures
The structure of 6a was solved by Patterson methods
and refined by using the full-matrix least-squares meth-
ods. All non-hydrogen atoms were refined anisotropi-
cally, and hydrogen atoms were calculated at the ideal
˚
positions with the C–H distance of 0.95 A. The final
refinement converged to R=0.051 and Rw=0.053.
Number of variables and goodness-of-fit (GOF) are 424
and 1.54, respectively. Final difference Fourier synthe-
ses showed peaks at heights up to 0.44 e A−3
.
Fig. 1. Crystal structure of (h5-C5H5)Fe(XylNC)2[C(ꢀNXyl)-
C(ꢀNXyl)Me] (6a).
3. Results and discussion
When a mixture of (h5-C5H5)Fe(CO)2CH3 (1) and
excess XylNC was refluxed in toluene for 6 h, yellow–
orange crystals, formulated as (h5-C5H5)Fe(CO)2-
(XylNC)CH3 (5a) from the mass spectroscopy were
obtained in 80% yield (Eq. (1)). The IR spectrum
showed three characteristic bands at 2100, 1950 and
1647 cm−1. The bands at 2100 and 1950 cm−1 sug-
gested the presence of terminal isocyanide and carbonyl
groups, respectively. The last one is assumed to be due
to an acetyl group. The 1H NMR spectrum showed
three singlets at l 2.38, 2.57, and 4.75 ppm consisting of
a 6:3:5 intensity ratio, assignable to o-methyl protons
of xylyl isocyanide, acetyl and cyclopentadienyl groups,
respectively. From these spectroscopic results 5a was
identified as an acetyl complex. Formation of any cyclic
carbene complexes was not observed.
The infrared spectrum of 6a (R=2,6-(CH3)2C6H3)
showed two sharp bands at 2083 and 2004 cm−1 due to
the terminal isocyanide groups and two bands at 1639
1
and 1572 cm−1 due to the C–N double bonds. The H
NMR spectrum showed four singlets due to methyl
protons at l 1.57, 2.05, 2.09, and 2.25 ppm consisting
of an intensity ratio of 1:2:2:4. The first one is assigned
to the C–CH3 group, the last one to the terminal
isocyanide groups, and the other two to the inserted
isocyanide groups. On the basis of these results the
complex is assumed to have a bis-imino type structure
with two isocyanide molecules inserted doubly into a
Fe–C bond. A similar double-insertion product 6b
(R=2,4,6-(CH3)3C6H2) was prepared by using mesityl
isocyanide and characterized spectroscopically (see Sec-
tion 2). These complexes are the first examples of the
imino-type complexes of iron constructed by only iso-
cyanide molecules.
(h5-C5H5)Fe(CO)2CH3+XylNC
“(h5-C5H5)Fe(CO)(XylNC)COCH3
(1)
In an attempt to confirm the detailed structure an
X-ray analysis was carried out and was in good agree-
ment with the spectroscopic results. The molecule dis-
played a piano-stool structure whereby the iron atom
was surrounded by two terminal isocyanide ligands and
a bis-imino group (Fig. 1). The selected bond lengths
and angles are shown in Table 2. The Fe–C (terminal
A mixture of 1 and excess XylNC in THF was
irradiated with UV radiation for 8 h at r.t. and the
mixture was chromatographed on alumina, from which
dark brown crystals formulated as (h5-C5H5)Fe-
(XylNC)4CH3 (6a) from the mass spectrum of m/z=
659 were isolated (Eq. (2)). Complex 6a was also pre-
pared from the photochemical reaction of 5a in the
presence of xylyl isocyanide.
˚
isocyanide) bonds of 1.786(7) and 1.808(7) A are
shorter than those found in tris-imino palladium com-
plex [12] and the average Fe–C (terminal isocyanide)
˚
bond length (1.820 A) in Fe(t-BuNC)5 [13]. The Fe–
˚
C(3) bond length of 1.985(6) A is longer than that
˚
(1.960(3) A) [4b] of the cyclic carbene complex 3, due
to structural difference between the open-chain and
cyclic form. The Fe–C3–N3 angle of 134.6(5)° larger
than other Fe–C3–C4 (116.6°) and C4–C3–N3
(2)

236
Y. Yamamoto et al. / Inorganica Chimica Acta 286 (1999) 233–236
Table 2
transition-metal chemistry of isocyanide. The different
reactivities depending on the substituents of isocyanide
also suggest the versatility of the isocyanide chemistry.
Selected bond lengths (A) and angles (°) of (h5-
C5H5)Fe(XylNC)2[(C=NXyl)2Me] (6a)
˚
Fe(1)–C(1)
Fe(1)–C(3)
C(2)–N(2)
C(3)–C(4)
C(4)–N(4)
1.786(7)
1.985(6)
1.175(7)
1.527(9)
1.252(7)
Fe(1)–C(2)
C(1)–N(1)
C(3)–N(3)
C(4)–C(5)
1.808(7)
1.149(7)
1.275(7)
1.483(9)
5. Supplementary material
A listing of thermal parameters, bond lengths, bond
angles and torsion angles, and tables of observed and
calculated structure factors are available from the Cam-
bridge Structural Database on quoting the CCDC No.
112956.
C(1)–Fe(1)–C(2)
C(2)–Fe(1)–C(3)
Fe(1)–C(2)–N(2)
Fe(1)–C(3)–C(4)
C(2)–N(2)–C(21)
C(4)–N(4)–C(41)
C(3)–C(4)–C(5)
N(4)–C(4)–C(5)
92.7(3)
97.6(3)
C(1)–Fe(1)–C(3)
Fe(1)–C(1)–N(1)
Fe(1)–C(3)–N(3)
C(1)–N(1)C(11)
C(3)–N(3)–C(31)
C(4)–C(3)–N(3)
C(3)–C(4)–N(4)
93.2(3)
176.1(6)
134.6(5)
176.4(7)
126.2(6)
108.5(5)
119.7(6)
172.9(6)
116.6(7)
164.8(7)
120.4(6)
115.5(6)
124.8(6)
Acknowledgements
A part of this work was supported by Futaba elec-
tronics memorial foundation.
(108.5°) angles, minimizing steric repulsion between the
C21–C26 and C31–C36 planes. In fact the dihedral
angle between these two planes is nearly parallel
(13.9°). The dihedral angle between the C11–C16 and
C41–C46 planes is perpendicular (87.0°). The torsion
angles of FeC(3)C(4)C(5) and N(3)C(3)C(4)N(4) are
−107.3(6) and −104.6(6)°, being smaller than those
(−155.4 and −159.6(8)°) found in the planar bis-
imino type complex, Cl(Et3P)2PdCꢁC–C(ꢀNPh)C-
(ꢀNPh)Pd(PEt3)Cl [14], responsible for the difference of
the stereochemistry between two complexes. These tor-
sion angles are assumed to be a minimum model for
helical polymers of isocyanide. The C–N double and
triple bond lengths are usual. The Fe–C–N bond and
C–N–C angles are nearly linear except the C(2)–N(2)–
C(21) bond angle (164.8(7)°).
References
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4. Conclusion
Thermal reaction of 1 with aromatic isocyanide bear-
ing the methyl groups at the two- and six-positions at
r.t. or at reflux underwent a usual carbonyl insertion to
form an acetyl complex. The photochemical reaction
gave the open-chain double insertion product 6 without
forming a four-membered N-coordination complex
such as 4. The photo-assisted insertion of isocyanide
was revealed to be one of the significant features in the
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