Reactions of acylferrate anion [CH3COFe(CO)4]- with methyl methyl iodide and acetylenes. Synthesis of mono- and dinuclear alkenyl ketone iron complexes. X-ray structure of [NEt4][IFe(CO)3(COCPh)2)]

Article abstract of DOI:10.1016/S0022-328X(01)01177-9

Collman's reagent [NEt₄][CH₃COFe(CO)₄] (1) reacts with a half equivalent of methyl iodide and diphenylacetylene in acetone at 25 °C for 10 min to give [NEt₄][Fe₂(CO)₆(μ₂-CPhCPh COCH₃)] (2). When the reaction of [NEt₄][CH₃COFe(CO)₄] (1) was carried out with an excess of methyl iodide a mixture of [NEt₄][IFe(CO)₃(C(O)CPh)₂] (3) and Fe₂(CO)₆μ-CPhCPhCCH₃ (OCH₃) (4) complexes were obtained. Complex 3 was characterized by X-ray analyses.

Full text of DOI:10.1016/S0022-328X(01)01177-9

Journal of Organometallic Chemistry 642 (2002) 107–112
www.elsevier.com/locate/jorganchem
Reactions of acylferrate anion [CH3COFe(CO)4]− with methyl
methyl iodide and acetylenes. Synthesis of mono- and dinuclear
alkenyl ketone iron complexes. X-ray structure of
[NEt4][IFe(CO)3(COCPh)2)]
Abdelhay Elarraoui a, Josep Ros a, Ramo´n Ya´n˜ez a,*, Xavier Solans b,
Merce` Font-Bardia b
a Departament de Qu´ımica, Uni6ersitat Auto`noma de Barcelona, 08193 Cerdanyola de Valle`s, Barcelona, Spain
b Crista lografia, Mineralog´ıa i Diposits Minerals, Uni6ersitat de Barcelona, Mart´ı i Franque`s s/n, 08028 Barcelona, Spain
Received 11 June 2001; accepted 18 July 2001
Abstract
Collman’s reagent [NEt4][CH3COFe(CO)4] (1) reacts with a half equivalent of methyl iodide and diphenylacetylene in acetone
at 25 °C for 10 min to give [NEt4][Fe2(CO)6(m2-CPhꢀCPhCOCH3)] (2). When the reaction of [NEt4][CH3COFe(CO)4] (1) was
carried out with an excess of methyl iodide
CPhCPhCCH3(OCH3)}] (4) complexes were obtained. Complex 3 was characterized by X-ray analyses. © 2002 Elsevier Science
a
mixture of [NEt4][IFe(CO)3(C(O)CPh)2] (3) and [Fe2(CO)6{m-
B.V. All rights reserved.
Keywords: Iron; Alkyne; Carbonyl; Dinuclear
1. Introduction
intermediate iron species (not characterized) contained
acryloyl and ferracyclopentendienone ligands.
Alkenyl–transition-metal complexes have frequently
been assumed to be key intermediates in various cata-
lytic or non-catalytic organic syntheses by acetylenic
compounds using transition-metal complexes [1]. The
chemistry of iron and alkynes involves, amongst other
species, the formation of complexes with alkenyl, acry-
loyl and ferracyclopentadiene ligands. All these ligands
are related. Recently, it has been reported that the
reaction of undecacarbonyltriferrate with a-b-unsatu-
rated acyl-halides gives unstable acryloyl complexes
that decompose to unexpected vinyl complexes via de-
carbonylation [2]. More recently, it has been reported
that Collman’s reagent Na[RCOFe(CO)4] reacts with
alkynes followed by CuCl2·2H2O oxidation to give the
corresponding cyclobutenediones and a-b-unsaturated
carboxylic acids. It appears that in these reactions the
In the course of our studies on the chemistry of
dinuclear vinyl carbonyl ferrates [3], we prepared these
species from mononuclear iron complexes in a one-pot-
synthesis fashion. This paper deals with the reaction of
Collman’s reagent [CH3COFe(CO)4]− with alkynes and
methyl iodide in aprotic solvents, which involves the
elimination of acetone and the formation of mono and
dinuclear iron anionic or neutral species.
2. Results and discussion
First, we checked the reactivity of diphenylacetylene
towards [NEt4] [CH3COFe(CO)4] (1) [4]. No reaction
occurred at room temperature. Reactivity of 1 toward
diphenylacetylene was then studied further in the pres-
ence of unsaturated 16 e iron species that could ‘acti-
vate’ alkynes and react with 1. Acetyleneiron
tetracarbonyls Fe(CO)4(RCꢁCR) are generally thought
* Corresponding author.
E-mail address: ramon.yanez@uab.es (R. Ya´n˜ez).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01177-9

108
A. Elarraoui et al. / Journal of Organometallic Chemistry 642 (2002) 107–112
to be intermediates in reactions of acetylenes with
Fe(CO)5 and Fe2(CO)9, and there is only one well
documented stable example: Fe(CO)4(h2-C2(SiMe3)2), a
tion. Complex 2 was isolated in 81% yield by recrystal-
lization in dichloromethane–diethyl ether mixtures.
This product showed three infrared-active bands in the
1
w(CO) stretching region. The H- and 13C-NMR data
compound stabilized by
a bulky bistrimethylsily-
lacetylene. In the absence of stabilizing bulky groups on
the acetylene, these simple y-complexes Fe(CO)4-
(RCꢁCR) are thought to be exceedingly reactive to
further acetylene additions, resulting in the generation
of a multitude of coordinated organic ligands via acety-
lene coupling [5]. In a previous study we obtained
dinuclear vinyl iron complexes from hydride iron com-
plexes and ironcarbonyl y-complexes Fe(CO)4(RCꢁCR)
generated from the reaction of Fe2(CO)9 with acetyle-
nes in tetrahydrofurane. In the present report we gener-
ated these species by reacting Collman’s reagent with
alkyl iodides. It has been suggested that acetone and
‘Fe(CO)4-solvent’ species [6] are generated in the former
reaction.
gave evidence of the insertion of the alkyne by the
appearance of a multiplet centered at 6.9 ppm, charac-
1
teristic of the phenyl groups. In addition, a H-NMR
resonance at 1.96 ppm and a 13C-NMR resonance at
167.21 were specifically attributed to the coordinated
ketonic carbonyl group [7].
The data lead us to suggest for 2 the structure shown
in Fig. 1. In this structure the CPhCPh entity is y-
bonded to Fe(1), while C(CH3)O is bonded through
oxygen to Fe(2). The structure of 2 reveals a coupling
between two iron–carbonyl fragments and the forma-
tion of an alkenyl ketone diiron complex.
A possible reaction pathway for the formation of this
product is shown in Scheme 1. There is a first reaction
of 1 with methyl iodide that generates the unstable
species ‘Fe(CO)4’ and acetone. This species reacts with
acetylene to form the short-lived species Fe(CO)4-
(RCꢁCR). This type of complex has been isolated by
Carty et al. [8] and recently by Takats and co-workers
[9,10]. The alkyne intermediate Fe(CO)4(RCCR) reacts
then with a second molecule of 1 to give the dinuclear
complex 2.
2.1. Reaction of [NEt4][CH3COFe(CO)4] with a half
equi6alent of methyl iodide and diphenylacetylene
When the mononuclear anion complex [NEt4][CH3-
COFe(CO)4] (1) was treated with half an equivalent of
methyl iodide and diphenylacetylene in acetone at
25 °C for 10 min, 1 reacted completely. Infrared analy-
sis in the w(CO) stretching region of the reaction
mixture after crystallization confirms the existence of
the anionic complex [NEt4][Fe2(CO)6(m2-CPhꢀCPhCO-
CH3)] (2) as the sole product formed during the reac-
2.2. Reaction of [NEt4][CH3COFe(CO)4] with an excess
of methyl iodide and diphenylacetylene
Treatment of a solution of [NEt4][CH3COFe(CO)4]
(1) with an excess of methyl iodide in acetone for 10
min and then with diphenylacetylene at 25 °C
overnight resulted in a black solution of the complex
[NEt4][IFe(CO)3(C(O)CPh)2] (3). Complex 3 was iso-
lated in 70% yield by recrystallization in dichloro-
methane–methanol mixtures. Extraction of the residue
yielded an air-stable orange material which was iden-
tified as [Fe2(CO)6{m-CPhCPhCCH3(OCH3)}] (4)
1
Fig. 1. Structure of complex 2.
through comparison of its characteristic IR, H- and
13C-NMR spectra with the spectra reported in the
literature [11]. The IR spectrum of 3 exhibited three
characteristic absorptions due to terminal w(CO) vibra-
tions and one broad band at 1627 cm−1 characteristic
of a ketonic carbonyl. The low number of resonances in
the 13C-NMR spectrum is consistent with a symmetrical
disposition of the acetylenic fragment and ketonic car-
bonyls on the molecule. The peak at 169.39 ppm is
assigned to the sp2 carbons bearing the phenyl groups.
The lowest-field signal at 257.5 ppm is then attributed
to the ketonic carbons. The resulting complex can be
described as an anionic ferracyclopentendione complex.
Few examples of this type of structure have been
reported in the literature [12].
Scheme 1.

A. Elarraoui et al. / Journal of Organometallic Chemistry 642 (2002) 107–112
109
values found in the FeꢂC(sp2) bonds, though slightly
shorter than the mean values. This could indicate some
y-interaction between these carbons and the metal, and
thus explain the low field resonance in the 13C spectra.
Comparable FeꢂC distances were observed in
[Fe(CO)4{(CO)2C4Me2}] and [Fe(CO)4{(CO)2C4Et2}]
[16,17].
Table 1
Crystallographic data and refinement parameters for 3
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group
C19H10Fe2IO6·C8H20N
717.13
293(2)
0.71069
Triclinic
,
(
P1
Unit cell dimensions
,
a (A)
10.877(2)
11.325(2)
13.445(2)
73.47(2)
83.07(2)
64.49(2)
1432.9(4)
2
,
b (A)
Table 2
,
c (A)
h (°)
i (°)
k (°)
V (A )
,
Selected bond lengths (A) and angles (°) for 3
Bond lengths
IꢂFe
FeꢂC(19)
FeꢂC(17)
FeꢂC(18)
FeꢂC(4)
3
2.622(3)
1.54(2)
1.76(2)
,
Z
Dcalc (mg m−3
)
1.662
2.116
718
Absorption coefficient (mm−1
F(000)
)
1.835(13)
1.960(10)
1.993(10)
1.182(11)
1.204(10)
1.155(14)
1.082(11)
1.25(2)
FeꢂC(1)
Crystal size (mm)
Theta range for data collection (°)
0.1×0.2×0.2
1.6–30
O(1)ꢂC(1)
O(2)ꢂC(4)
O(3)ꢂC(17)
O(4)ꢂC(18)
O(5)ꢂC(19)
Index ranges
−155h515, −155k515,
05l55
Reflections collected
Independent reflections
Refinement method
3448
3448
Full-matrix least-squares on
Bond angles
F2
C(19)ꢂFeꢂC(17)
C(19)ꢂFeꢂC(18)
C(17)ꢂFeꢂC(18)
C(19)ꢂFeꢂC(4)
C(17)ꢂFeꢂC(4)
C(18)ꢂFeꢂC(4)
C(1)ꢂFeꢂI
O(1)ꢂC(1)ꢂC(2)
O(1)ꢂC(1)ꢂFe
C(2)ꢂC(1)ꢂFe
C(3)ꢂC(2)ꢂC(5)
C(3)ꢂC(2)ꢂC(1)
C(5)ꢂC(2)ꢂC(1)
C(2)ꢂC(3)ꢂC(4)
C(2)ꢂC(3)ꢂC(11)
C(4)ꢂC(3)ꢂC(11)
O(2)ꢂC(4)ꢂC(3)
O(2)ꢂC(4)ꢂFe
C(3)ꢂC(4)ꢂFe
96.8(8)
94.8(7)
96.2(5)
88.2(7)
90.0(5)
Data/parameters
3398/344
1.075
R1=0.0355, wR2=0.0768
R1=0.1933, wR2=0.1464
0.0000(6)
Goodness-of-fit on F2
Final R indices [I\2|(I)]
R indices (all data)
Extinction coefficient
172.8(4)
88.2(4)
Largest difference peak and hole
0.274 and −0.242
−3
,
(e A
)
120.8(9)
126.6(8)
112.2(8)
126.5(10)
113.2(8)
120.2(10)
116.5(9)
125.2(8)
117.8(9)
118.7(9)
127.9(7)
113.3(7)
3. X-ray structure determination of
[NEt4][IFe(CO)3(COCPh)2)]
Suitable single crystals of the titled complex were
obtained by slow evaporation of a dichloromethane–
methanol solution at room temperature. Crystallo-
graphic data, selected distances and angles are listed in
Tables 1 and 2.
A perspective view of [IFe(CO)3(COCPh)2)]− with
the labeling scheme is shown in Fig. 2. The anion
consists of one iron atom coordinated to a iodine atom,
three terminal CO groups and two CO groups inserted
between the metal and the alkyne molecule, forming a
five-member heterocyclic ring. The FeꢂI bond is ap-
proximately perpendicular to the herocyclic ring. The
,
distance FeꢂI (2.622 A) is within the normal range of
other FeꢂI mononuclear complexes [13–15]. The iron is
in a slightly distorted octahedral environment. As the
two FeꢂCO bond lengths trans to the heterocyclic ring
,
are slightly asymmetrical (1.76(2), 1.835(23) A), the api-
cal FeꢂC(19) distance trans to the iodine is shorter than
,
the others (1.54(2) A). The FeꢂCO (ketonic) bond
Fig. 2. View of the molecular structure of 3 together with the atomic
numberic scheme.
,
lengths, 1.993 and 1.960 A, are within the range of

110
A. Elarraoui et al. / Journal of Organometallic Chemistry 642 (2002) 107–112
Scheme 2.
4. Conclusion
6. X-ray crystal structure determination of 3
In summary, we showed that the one-pot reaction of
diphenylacetylene and CH3I in an equimolar or in
excess amount with the Collman’s reagent could be
modulated to obtain mono or dinuclear complexes of
iron with alkene ligands (Scheme 2). Recently, a similar
reaction with [HFe(CO)4]− and CH3I, which after
workup with CuCl2·H2O led to the corresponding cy-
clobutenediones, has been reported [18]. Complex 3
could be the intermediate of the above reactions and
supports the significance of h2-alkynyl ligands as inter-
mediates in the conversion of alkynes to organic cyclic
compounds.
6.1. Data collection and processing
A prismatic crystal (0.1×0.1×0.2 mm) was selected
and mounted on a Philips PW-1100 four-circle diffrac-
tometer. Unit-cell parameters were determined from
automatic centering of 25 reflections (8BqB12°) and
refined by least-squares method. Intensities were col-
lected with graphite monochromatized Mo–Ka radia-
tion, using ꢀ–2q scan-technique. Three thousand four
hundred and forty-eight reflections were measured in
the range 1.6BqB30.0°. One thousand one hundred
and ninety-three reflections were assumed as observed
applying the condition I\2 |(I). Three reflections were
measured every 2 h as orientation and intensity control,
significant intensity decay was not observed. Lorentz-
polarization and absorption corrections were made.
The structure was solved by Patterson synthesis, us-
ing SHELXS computer program [19] and refined by
full-matrix least-squares method with SHELX93 com-
puter program [20], using 3398 reflections, (very nega-
tive intensities were not assumed). The function
5. Experimental
5.1. General data
All reactions were performed under nitrogen by using
standard Schlenk tube techniques. All the solvents were
distilled and dried before use. Infrared spectra were
recorded on a Perkin–Elmer FT 1710 spectrophotome-
ter on KBr disks or with CH2Cl2 solutions. Mass
spectra were obtained on a Hewlett Packard H.P. 2985
GC/MS. NMR spectra were recorded on a Bruker
AC-250 (1H, 250 MHz; 13C, 62 MHz) spectrometer in
CDCl3 or (CD3)2CO solutions. Elemental analyses were
obtained by the staff of the Chemical Analysis Service
of the University Autonoma de Barcelona. Iron pen-
tacarbonyl was purchased commercially.
2
2 2
minimized was ꢀ w [ꢁFoꢁ −ꢁFcꢁ ] , where w=|2(I)+
[(0.0529 P)2+0.1390 P]−1, and P=(ꢁFoꢁ +2ꢁFcꢁ )/3, f,
f % and f ¦ were taken from International Tables of
X-Ray Crystallography (International Tables of X-Ray
Crystallography, (1974), Ed. Kynoch press, Vol. IV, pp.
99–100 and 149). The extinction coefficient was
2
2
2
O.OflO, wR(on ꢁFꢁ )=0.076 and goodness of fit=
1.075 for all observed reflections. Number of refined
parameters was 344. Maximum shift/Estimated S.D.=
2.5, Mean shift/Estimated S.D.=0.10. Maximum and

A. Elarraoui et al. / Journal of Organometallic Chemistry 642 (2002) 107–112
111
minimum peaks in final difference synthesis was 0.274
Anal. Calc. for C23H16Fe2O7: C, 53.53; H, 3.10.
Found: C, 53.55; H, 3.14%. IR: w(CO) (cm−1 1H-
and −0.242 eA−3, respectively. Tables of atomic coor-
)
,
dinates, thermal parameters, bond lenghts and angles
are deposited as supplementary material.
NMR (CDCl3): l 1.9 (s, 3H, CCH3), 2.81 (s, 3H,
CH3O “ Fe), 7–7.8 (m, 10H, C6H5)) ppm. 13C-NMR
(CDCl3): l 19.26 (CCH3), 70.47 (CH3O “ Fe), 89.7
(CPhꢀCPh), 109.70 (CCH3), 123.14–148.60 (C6H5),
175.45 (CPhꢀCPh), 221.57 (CO) ppm. Mass Spectrum
m/z 515.95 (M+), 178 (B).
7. Reaction of [NEt4][CH3COFe(CO)4] with CH3I and
diphenylacetylene
To a solution of [NEt4][CH3COFe(CO)4] (1 g, 2.93
mmol) in 30 ml of acetone was added CH3I (0.09 ml,
1.47 mmol). The contents were stirred for 10 min at
25 °C. Subsequently, diphenylacetylene (0.26 g, 1.47
mmol) was added, and the mixture was stirred for a
further 6 h at 25 °C. The black solution was filtered off
and the solvent was evaporated. The residue was crys-
tallized in dichloromethane–diethyl ether mixtures and
the resulting black solid was isolated in 81% yield.
Anal. Calc. for C30H33Fe2NO7: C, 57.08; H, 5.27; N,
2.22. Found: C, 57.12; H, 5.15; N, 2.22%. IR: w(CO)
Acknowledgements
We gratefully acknowledge support from the Minis-
terio de Educacio´n y Cultura of Spain, project PB96-
1146 and BQU2000-0238.
References
1
(CH2Cl2) 2025(s), 1957(vs), 1884(w), (cm−1) H-NMR
[1] (a) R.F. Heck, Organotransition Metal Chemistry, Academic
Press, New York, 1974, p. 167;
((CD3)2CO): l 1.4 (t, J=7.3 Hz, 12H, N−(CH2CH3),
1.96 (s, 3H, CH3C(O “ Fe)), 3.45 (q, J=7.3 Hz, 8H,
N+(CH2CH3), 6.8–7.7 (m, 10H, C6H5) ppm. 13C-NMR
((CD3)2CO): l 7.48 (N+(CH2CH3)), 23.16 (CH3C(O “
Fe)), 52.80 (N+(CH2CH3)), 86.31 (CPhꢀCPhꢂ
C(CH3)C(O “ Fe)), 122.31–152.59 (C6H5), 162.62
(b) D. Seyferth, News Applications of Organometallic Reagents
in Organic Synthesis, vol. 1, Elsevier, Amsterdam, 1976;
(c) H. Alper, Transition Metal Organometallics in Organic Syn-
thesis, vol. 1, Academic Press, New York, 1976;
(d) J.J. Brunet, Chem. Rev. 90 (1990) 1041.
[2] A. Ishihara, T. Mitsudo, Y. Watanabe, J. Organomet. Chem.
368 (1989) 199.
(CPhꢀCPhꢂC(CH3)O “ Fe),
167.21
(CPhꢀCPhꢂ
[3] (a) R. Ya´n˜ez, J. Ros, R. Mathieu, J. Organomet. Chem. 389
(1990) 197;
C(CH3)O “ Fe)), 221 (CO) ppm.
(b) I. Moldes, J. Ros, R. Ya´n˜ez, R. Mathieu, X. Solans, M.
Font-Bard´ıa, J. Organomet. Chem. 395 (1990) 305;
(c) R. Ya´n˜ez, J. Ros, I. Moldes, R. Mathieu, X. Solans, M.
Font-Bard´ıa, J. Chem. Soc. Dalton Trans. (1990) 3147.
[4] (a) J.P. Collman, S.R. Winter, D.R. Clark, J. Am. Chem. Soc. 94
(1972) 1788;
(b) J.P. Collman, Acc. Chem. Res. 8 (1971) 342.
[5] A.J. Carty, W.F. Smith, N. Taylor, J. Organomet. Chem. 146
(1978) C1.
[6] K.H. Whitmire, T. Randall, E.S. Lewis, Organometallics 5
(1986) 987.
[7] T. Mitsudo, A. Ishihara, M. Kadokura, Organometallics 5
(1986) 238.
[8] A.J. Carty, W.F. Smith, N.J. Taylor, J. Organomet. Chem. 146
(1978) C1.
[9] M.J. Burns, G.Y. Kiel, I. Seils, J. Takats, J. Washington, J. Am.
Chem. Soc. 111 (1989) 6850.
[10] J. Cooke, J. Takats, J. Am. Chem. Soc. 119 (1997) 11 088.
[11] R. Ya´n˜ez, J. Ros, X. Solans, M. Font-Bard´ıa, R. Mathieu, J.
Organomet. Chem. 388 (1990) 169.
[12] (a) F.H. Herbstein, M. Kaftory, Acta Crystallogr. Sect. B 33
(1977) 3318;
8. Reaction of [NEt4][CH3COFe(CO)4] with an excess
of CH3I and diphenylacetylene
To a solution of [NEt4][CH3COFe(CO)4] (1 g, 2.93
mmol) in 30 ml of acetone was added CH3I (0.27 ml,
4.4 mmol). The contents were stirred for 10 min at
25 °C. Subsequently, diphenylacetylene (0.26 g, 1.47
mmol) was added, and the mixture was stirred
overnight at 25 °C. The black solution was filtered off
and the solvent was evaporated. The residue was crys-
tallized in dichloromethane–methanol mixtures and the
resulting black solid [NEt4][IFe(CO)3(COCPh)2)] was
isolated in 70% yield. The mother solution was evapo-
rated to dryness and extracted with pentane (2×10
ml). Concentration of this solution and cooling to
−20 °C gave 53 mg of [Fe2(CO)6{m-CPhCPh-
CCH3(OCH3)}].
(b) S. Aime, L. Milone, E. Sappa, A. Tiripicchio, A.M.M.
Lanfredi, J. Chem. Soc. Dalton Trans. (1979) 1664;
(c) K. Hoffmann, E. Weiss, J. Organomet. Chem. 128 (1977)
399;
(d) R.C. Pettersen, R.A. Levenson, Acta Crystallogr. Sect. B 32
(1976) 723.
Anal. Calc. for C27H32FeINO5: C, 51.21; H, 5.09; N,
2.21. Found: C, 51.42; H, 4.99; N, 2.10%. IR: w(CO)
(cm−1 1H-NMR ((CD3)2CO): l 1.39 (t, J=7.3 Hz,
)
12H, N+(CH2CH3), 3.43 (q, J=7.3 Hz, 8H, N+
(CH2CH3), 6.8–7.7 (m, 10H, C6H5)) ppm. 13C-NMR
[13] C. Lowe, H.-U. Hund, H. Berke, J. Organomet. Chem. 372
(1989) 295.
((CD3)2CO):
l
7.46 (N+(CH2CH3)), 52.78 (N+
(CH2CH3)), 124.05–136.40 (C6H5), 169.39 (CPh),
205.88, 216.7 (CꢁO), 257.5 (FeꢂCꢀO), ppm.
[14] M.J. Begley, S.G. Puntambekar, A.H.J. Wright, Organomet.
Chem. 329 (1987) C7.

112
A. Elarraoui et al. / Journal of Organometallic Chemistry 642 (2002) 107–112
[15] G. Cardaci, G. Bellachioma, P. Zanazzi, Organometallics 7
(1988) 172.
(b) M. Periasamy, C. Rameshkumar, Tetrahedron Lett. 41
(2000) 2719;
[16] S. Aime, L. Milone, E. Sappa, A. Tiripicchio, A.M.M. Lanfredi,
J. Chem. Soc. Dalton Trans. (1979) 1664.
(c) M. Periasamy, C. Rameshkumar, Organometallics 19 (2000)
2400.
[17] R.C. Pettersen, J.L. Cihonsky, F.R. Young, R.A. Levenson, J.
Chem. Soc. Chem. Comm. (1975) 370.
[19] G.M. Sheldrick, Acta Cryst. A46 (1990) 467–473.
[20] G.M. Sheldrick, SHELXL. A computer program for crystal
[18] (a) M. Periasamy, C. Rameshkumar, U. Radhakrishnan, J.-J.
Brunet, J. Org. Chem. 63 (1998) 4930;
structure refinement, University of Go¨ttingen, Germany,
1994.