Cyanide as a versatile Lewis base ligand at a dinitrogen-binding iron(II) centre: Mono- and heteronuclear adducts

Article abstract of DOI:10.1016/S0020-1693(03)00249-4

The ligated cyanide in trans-[FeH(CN)(dppe)₂] is activated towards aroylation, alkylation and addition of various transition metal Lewis acids, in particular [WCl₄(PPh₃)₂], [ReOCl ₃(PPh₃)₂], [PdCl₂(PPh ₃)₂] and [PtCl(Ph)(PPh₃)₂], to give, in the former case, mononuclear isocyanide complexes and, in the latter case, heteronuclear adducts with bridging cyanide. Their syntheses and spectroscopic characterisation are presented, as well as results of the X-ray diffraction analyses of a trinuclear complex with the {Fe-C≡N-W-N≡C-Fe} unit and of the parent cyano trans-[FeH(CN)(dppe)₂] complex. The cyanide bridge allows the electronic communication between the metal centres as indicated by a cyclic voltammetric study.

Full text of DOI:10.1016/S0020-1693(03)00249-4

Inorganica Chimica Acta 356 (2003) 259Á266
/
www.elsevier.com/locate/ica
Cyanide as a versatile Lewis base ligand at a dinitrogen-binding
iron(II) centre: mono- and heteronuclear adducts
S´ılvia S.P.R. Almeida a, M. Fa´tima C. Guedes da Silva a,b, Lucjan B. Jerzykiewicz c,
Piotr Sobota c, Armando J.L. Pombeiro a,*
a Centro de Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico, Av. Rovisco pais, 1049-001 Lisbon, Portugal
b Universidade Luso´fona de Humanidades e Tecnologias, Campo Grande, 376, 1749-024 Lisbon, Portugal
c Faculty of Chemistry, University of Wroclaw, 50-383 Wroclaw, Poland
Received 1 April 2003; accepted 5 April 2003
Dedicated to Professor Joao J.R. Frau´sto da Silva in recognition of his achievements.
¯
Abstract
The ligated cyanide in trans-[FeH(CN)(dppe)2] is activated towards aroylation, alkylation and addition of various transition
metal Lewis acids, in particular [WCl4(PPh3)2], [ReOCl3(PPh3)2], [PdCl2(PPh3)2] and [PtCl(Ph)(PPh3)2], to give, in the former case,
mononuclear isocyanide complexes and, in the latter case, heteronuclear adducts with bridging cyanide. Their syntheses and
spectroscopic characterisation are presented, as well as results of the X-ray diffraction analyses of a trinuclear complex with the
{Fe ꢀ
/
Cꢁ
/
Nꢀ
/
W ꢀ
/
Nꢁ
/
Cꢀ
/
Fe} unit and of the parent cyano trans-[FeH(CN)(dppe)2] complex. The cyanide bridge allows the electronic
communication between the metal centres as indicated by a cyclic voltammetric study.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Cyanide; Bridging cyanide; Isocyanide; Transition metal Lewis acid; Heteronuclear complexes
1. Introduction
high current interest in view of their potential use, e.g. in
molecular electronics, molecular magnetism and electro-
chromism.
From a biological point of view, it is noteworthy to
mention that aqueous cyanide is a known substrate of
nitrogenase [2] and iron-cyanide complexes have been
The coordination chemistry of cyanide is a matter of
widespread interest in various fields of chemistry and
biochemistry, its origins remitting to about three cen-
turies ago since the discovery of Prussian Blue, possibly
the oldest known coordination compound.
recognised in active sites of iron-only and ironÁ
/nickel
A number of binding modes of cyanide are known
(the most common being the terminal C-bound and the
terminal C,N-bridging ones), conferring a high synthetic
versatility to this ligand namely for the preparation of a
wide variety of types of complexes [1] with relevance,
e.g. in organometallic and inorganic chemistries, mate-
rial and medicinal sciences. Cyano-bridged mixed va-
lence complexes are within those which are attracting a
hydrogenases [3].
Within our continuous interest on the investigation of
the activation, by dinitrogen-binding metal sites, of
nitrogenase substrates, such as nitriles [4Á
mides [9Á12], isocyanides [13Á24], alkynes and alkyne-
derived species [21Á32], we have also been studying
cyanide in particular at some ReI [16,33Á36] or FeII [17]
/8], cyana-
/
/
/
/
phosphinic centres and its activation towards electro-
philes. Hence, reaction of [NBu4][trans-Re(CN)2(dppe)2]
with a protic acid (HBF4, [Et3NH][BPh4], CH3COOH),
added in stoichiometric amount, gives, on protonation
of one of the cyano-ligands, the hydrogen isocyanide
* Corresponding author. Tel.: ꢀ
64455/7.
E-mail address: pombeiro@ist.utl.pt (A.J.L. Pombeiro).
/
351-2184 19237; fax: ꢀ351-2184
/
0020-1693/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00249-4

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S.S.P.R. Almeida et al. / Inorganica Chimica Acta 356 (2003) 259Á266
/
complex trans-[Re(CN)(CNH)(dppe)2], whereas the H-
bonded cyano-adducts trans-[Re(CN×HOOCCF3)2-
(dppe)2], trans-[Re(CN×HOMe)2(dppe)2] and trans-
[Re(CN×HNEt3)(dppe)2][BPh4] are formed on reaction
of the isocyanide complex trans-[Re(CN)(CNH)(dppe)2]
with an excess of CF3COOH or of the parent dicyano-
complex with an excess of MeOH or [Et3NH][BPh4] [33]
(Scheme 1(a, b)).
2. Results and discussion
/
Treatment of a CH2Cl2 or THF solution of trans-
[FeH(CN)(dppe)2] with the appropriate aroylating or
/
/
alkylating agent (RXꢁPhCOCl, MeI or [Et3O][BF4],
/
added in a stoichiometric amount or in a slight, ca. 3:1,
molar excess) results in the electrophilic addition to the
cyano-ligand to afford the corresponding isocyanide
complex trans-[FeH(CNR)(dppe)2]X [Rꢁ
/
PhCO, Xꢁ
/
Protonation of a cyano-intermediate is believed to
occur in the formation of the isocyanide complexes
trans-[ReCl(CNH)(dppe)2] and trans-[FeH(CNH)-
(dppe)2]ꢀ on reaction of trans-[ReCl(CNSiMe3)(dppe)2]
with MeOH or HCl [16,36] or of trans-[FeHCl(dppe)2]
with NCSiMe3 in the presence of Tl[BF4] and HBF4 [17].
The isocyanide complex trans-[FeH(CNH)(dppe)2]ꢀ
can also be obtained by protonation (by HBF4) of the
cyano-complex trans-[FeH(CN)(dppe)2] which can also
add BPh3 (Scheme 1c) to give the isocyanotriphenylbo-
rate product trans-[FeH(CNBPh3)(dppe)2] [17]. At the
above ReI centre, CNH can undergo further protona-
tion to give the aminocarbyne complex trans-[Re-
Cl (1); RꢁMe, XꢁI (2); RꢁEt, XꢁBF4 (3)] (Scheme
/
/
/
/
2). The reactions proceed smoothly at room tempera-
ture, leading to the products in isolated yields up to
60%. Compound 1 is new and, to our knowledge,
provides the first example of an aroylation reaction of
the ligating cyanide at the parent hydrideÁcyanide
/
complex. The susceptibility of the CNꢂ ligand in this
complex to alkylation to afford isocyanide complexes
was first briefly reported by us [39], for instance in the
preparation of 3 by using MeI as the alkylating agent,
and later by others [40] using the organoiodide as the
reaction solvent. The alkylation reaction also occurs [40]
for other organo-iodides and -bromides as solvents. Our
method does not require the use of the organo-halide as
the solvent, the reaction proceeding in a more conve-
nient and common organic solvent like CH2Cl2 or THF.
The related compounds trans-[FeH(CNMe)(dppe)2]X
Cl(CNH2)(dppe)2]ꢀ [16,18] and the {CNHx} (xꢁ
0, 1,
/
2) ligated species can be postulated [14,15,22,37] as
sequential stages in the enzymatic reduction of cyanide.
Such reactions have been recently reviewed [14,15].
We have now extended the study of the cyano-
complex trans-[FeH(CN)(dppe)2] (whose crystal struc-
ture is also included) with the same binding metal centre
as the related dinitrogen complex trans-[FeH(N2)-
(dppe)2]ꢀ [38], to other electrophilic agents and found
that the ligated cyanide can readily undergo aroylation,
alkylation and addition of various transition metal
Lewis acids giving, in the latter case, di- or trinuclear
adducts with bridging cyanide which can allow the
interaction between the metal centres.
These studies, involving a nitrogenase substrate at a
N2-binding metal site, appear particularly timely to
celebrate the retirement of Professor Frau´sto da Silva
who, in 1971 (and following his overall and remarkable
planning to bring expertise to the research Centre he was
creating at the Instituto Superior Te´cnico) introduced
one of us (A.J.L.P., then initiating his post-graduate
training) in the area of Nitrogen Fixation.
(XꢁBF4 or PF6), with different counter-ions, were
/
prepared by our group by treating a THF solution of
trans-[FeHCl(dppe)2] with methyl isocyanide (CNMe)
in the presence of Tl[BF4] [41,42] or Tl[PF6] [42]. An
identical procedure was followed [41,42] for the synth-
esis of 3 by using ethylisocyanide.
The electrophilic addition route towards the isocya-
nide complexes described in the present work, which
involves the generation in situ of the CNR ligand, is
more convenient and versatile than that involving free
isocyanide as the starting reagent, because it does not
require the synthesis and handling of the nasty, smelly
and commonly unstable CNR compounds.
Furthermore, the nucleophilic character of the cyano-
ligand in trans-[FeH(CN)(dppe)2] can be applied to the
syntheses of di- and tri-nuclear adducts by following an
electrophilic addition route similar to that described
above, but using a transition metal Lewis acid as the
electrophile. Hence, the dinuclear complex with a
bridging cyanide [HFe(dppe)2(m-CN)PdCl2(PPh3)] (4)
is obtained (Scheme 3) on reaction of trans-
[FeH(CN)(dppe)2] with [PdCl2(PPh3)2] (used in stoichio-
Scheme 1.
Scheme 2.

S.S.P.R. Almeida et al. / Inorganica Chimica Acta 356 (2003) 259Á
/266
261
Scheme 3.
metric amount), whereas the trinuclear [{HFe(dppe)2(m-
CN)}2(ReOCl3)] (5) and [{HFe(dppe)2(m-CN)}2-
PtCl(Ph)] (6) are formed (Scheme 3) when using
[ReOCl3(PPh3)2] or [PtCl(Ph)(PPh3)2] (in ca. 0.5:1 molar
ratio, relatively to the cyano-complex), correspondingly,
as the transition metal Lewis acid source. In addition,
the trinuclear species, [{XFe(dppe)2(m-CN)}2WCl3(OH)]
paramagnetic, only a relatively small shift occurs. In the
31P{1H} NMR spectra, a singlet is observed at d ꢂ
50.1
to ꢂ59.3 relative to P(OMe)3 due to the P atoms of the
chelating diphosphine, indicating the trans geometry for
the Fe metal centres in each complex. In addition, for
complex 4 the two higher field PPh3 resonances (with
the expected 1:4 integration relatively to that of the P-
dppe signal) can possibly be ascribed to the cis and trans
geometries around the Pd atom.
/
/
(7) (Xꢁ
/
Cl or OH) was formed upon reaction of trans-
[FeH(CN)(dppe)2] with [WCl4(PPh3)2].
1
The proposed formulations are based on IR, H and
31P{1H} NMR spectroscopies, positive-ion FAB mass
spectra, elemental analysis, cyclic voltammetry and, for
one of them (7), X-ray diffraction data.
In the IR spectrum of the isocyanide complex 1, the
two strong bands observed at 1881 and 1838 cmꢂ1 are
Further evidence for the proposed formulations is
provided by the positive-ion FAB MS spectra which
show various expected metal containing fragments and
by X-ray data for complex 7. Although the X-ray
structural analysis for this compound (whose molecular
assigned to the coupled n(Cꢁ
the benzoylisocyanide ligand, whereas for the di- and
tri-nuclear adducts n(CꢁN) is detected in the 1988Á2074
cmꢂ1 range.
In the 1H NMR (CD2Cl2) spectra, the hydride
resonance is the expected high-field quintet (2JHP
46Á47 Hz) at d from ꢂ7.45 to ꢂ14.55, due to coupling
to the 4 equiv. P nuclei. In comparison with the parent
iron-cyanide complex (d ꢂ14.85) a substantial lower
field shift is observed for the cationic mononuclear
compound 1 (d ꢂ7.45), as found [42] for the related
arylisocyanide complexes trans-[FeH(CNR)(dppe)2]ꢀ
(Rꢁaryl) (d ꢂ8.6 to ꢂ9.9). However, in the case of
the neutral di- and trinuclear adducts (d ꢂ13.1 and
14.6 for 5 and 6, respectively), except for 7 which is
/
N)/n(Cꢂ
/
O) vibrations of
/
/
ꢁ
/
/
/
/
/
/
/
/
/
Fig. 1. Molecular structure of the trinuclear species [{XFe(dppe)2(m-
/
CN)}2WCl3(OH)] (7) (Xꢁ
/
Cl or OH). Crystal data: monoclinic, P21/
˚
ꢂ
/
c, aꢁ24.028(4), bꢁ18.860(4), cꢁ
/
/
/
20.319(5) A, bꢁ101.09(5)8.
/

262
S.S.P.R. Almeida et al. / Inorganica Chimica Acta 356 (2003) 259Á266
/
structure is shown in Fig. 1) could not be fully refined
due to disorder, the collected data unambiguously prove
the trinuclear character of the complex with two iron-
cyano {XFe(dppe)2(CN)} units bound, via bridging
cyanides, to a central tungsten atom. The precise nature
of X (Cl, OH or O) could not be ascertained by X-rays,
but the consideration of an oxide (either at the Fe or at
the W metals) is not supported by IR since no band that
Table 1
˚
Selected bond distances (A) and angles (8) for complex trans-
[FeH(CN)(dppe)2], with e.s.d.s. in parentheses
Bond distances
Feꢀ
Feꢀ
Feꢀ
Feꢀ
Feꢀ
Feꢀ
Nꢀ
/
P1
P2
2.227(4)
2.227(4)
2.222(4)
2.240(4)
1.903(13)
1.65(9)
/
/
P3
/
P4
/
C1N
H1
could be ascribed to n(Feꢂ
/
O) or n(Wꢂ/O) was observed.
/
/
C1N
1.164(17)
In any case, the formation of 7 formally involves
hydride abstraction from iron and metal centre hydro-
Bond angles
P1ꢀ
P1ꢀ
P1ꢀ
P2ꢀ
P2ꢀ
P3ꢀ
Feꢀ
C1Nꢀ
/
Feꢀ
Feꢀ
Feꢀ
Feꢀ
Feꢀ
Feꢀ
/
P2
P3
P4
P3
P4
P4
85.2(2)
169.9(2)
93.4(2)
95.5(2)
168.8(2)
84.0(2)
173.3(13)
176(3)
lysis, i.e. of the W centre if Xꢁ
/
Cl or of both the W and
/
/
the Fe ones if XꢁOH. In the former hypothesis (Xꢁ
/
/
/
/
Cl), iron chlorination also occurs, the {WCl4} site
conceivably behaving as the halogenating agent to give
the {WCl3} centre in 7.
/
/
/
/
/
/
/
C1Nꢀ
/
N
H1
The complex trans-[FeH(CN)(dppe)2] has been char-
acterised by X-ray diffraction analysis, although also of
a low quality crystal. The molecular structure is shown
in Fig. 2, selected bond distances and angles are given in
Table 1, and crystal data in Table 2. It presents the
expected octahedral-type geometry with the dipho-
sphines in the equatorial sites, the hydride and the
CNꢂ ligands being mutually trans in the apical posi-
tions.
/
Feꢀ
/
Table 2
Crystal data and structure refinement for trans-[FeH(CN)(dppe)2)]
Chemical formula
Formula weight
˚
l (A)
C53H48FeNP4
879.66
0.71073
100(2)
T (K)
Crystal system
Space group
The Feꢀ
/
Cꢁ
/
N moiety is essentially linear [Feꢀ
/
C1Nꢀ
/
N
N
monoclinic
P21/n
angle of 173.3(13)8], and the Feꢀ
/
C1N and C1Nꢀ
/
˚
˚
distances, 1.903(13) and 1.164(17) A, are similar to those
reported for the iron(II) complexes [FeH(CNBPh3)-
a (A)
10.665(4)
24.224(6)
16.951(4)
100.80(10)
4302(3)
4
˚
b (A)
˚
c (A)
˚
(dppe)2] [17] [1.914(3) and 1.163(4) A], [FeH(CNR)-
b (8)
(dppe)2]ꢀ [Rꢁ
(CH2)3I [40], 1.845(6) and 1.161(8) A]. Moreover, the
/
Me [43], 1.851(5) and 1.154(6) A; Rꢁ
/
˚
3
V (A )
˚
˚
Z
m (mmꢂ1
)
0.538
1.358
1840
Feꢀ
/
P (average) distance in the complex of this study,
˚
2.230(4) A, is similar to that found in the above neutral
Dcalc (g cmꢂ3
F(000)
)
uRange (8)
Number of reflections mea-
3.19Á
/28.38
9066
sured
Number of unique reflections 5553
Rint
0.0951
2306
Number of observed reflec-
tions [I ꢀ
Weighting scheme (w)
/
2s(I)]
wꢁ
Pꢁ
R1ꢁ
R1ꢁ
1.056
0.588 and ꢂ
/
1/[s2(Fo2)ꢀ
(Fo2ꢀ2Fc2)2/3
0.0956, wR2ꢁ
0.2532, wR2ꢁ
/
(0.0116P)2] where
/
/
Final R1 indices [I ꢀ
Final R1 indices (all data)
/2s(I)]
/
/
0.1056
0.1605
/
/
Goodness-of-fit
Largest difference peak and
ꢂ3
/0.406
˚
hole (e A
)
cyanotriphenylborate compound, but slightly shorter
than those in the isocyanide cationic ones as well as in
the cyanamide and phosphaalkyne complexes trans-
[FeH(NCNH2)(dppe)2][BF4] and trans-[FeH(h1-Pꢁ
/
t
˚
˚
CBu )(dppe)2][BPh4] (2.244(4) A [44a] and 2.276(2) A
[44b], respectively). These differences conceivably result
from a stronger p-electron releasing ability of the metal
Fig. 2. Molecular structure of trans-[FeH(CN)(dppe)2].

S.S.P.R. Almeida et al. / Inorganica Chimica Acta 356 (2003) 259Á
/266
263
in the neutral centres in comparison with that in the
4. Experimental
cationic ones.
˚
H1 distance, 1.65(9) A, is higher than those
The Feꢀ
/
4.1. General
reported in the aforementioned cases and than the
˚
expected value, 1.53 A, based on the sum of the iron
All the reactions were carried out under argon and
using standard inert gas flow and vacuum techniques.
Solvents were purified by standard procedures. trans-
[FeH(CN)(dppe)2] [51], [PtCl(Ph)(PPh3)2] [52] and
[WCl4(PPh3)2] [53] were prepared according to pub-
lished procedures. [PdCl2(PPh3)2], [ReOCl3(PPh3)2],
Me3SiI, MeI, [Et3O]BF4 and PhCOCl were commer-
cially available.
and hydrogen covalent radii, suggesting a significant
trans influence of the cyanide ligand.
Preliminary electrochemical studies corroborate the di
and tri-nuclear characters of complexes 4 and 5 (6 and 7
could not be studied due to their instability in the
electrolytic medium, even at low temperatures), respec-
tively.
In fact, those complexes exhibit, by cyclic voltamme-
try, in 0.2 M [NBu4][BF4]/CH2Cl2, not only the expected
reversible single-electron oxidation waves due to the
Infrared (IR) measurements were carried out in KBr
pellets (values in cmꢂ1; intensity of bands is referred as
mꢁ
/
medium, sꢁ
/
strong) on a PerkinÁElmer 683 and a
/
Bio-Rad FTS 3000 spectrophotometers and 1H, 31P{1H}
and 13C NMR spectra on a Varian Unity 300 spectro-
meter. Chemical shifts are in ppm relative to SiMe4 (1H
ox
FeII0
/
FeIII oxidations, at E in the 0.43Á
0.70 V (vs.
/
1/2
SCE) range, i.e. higher than that observed for the related
complex trans-[FeH(CN)(dppe)2] (0.33 V [17]) and
lower than that for trans-[FeH(CNR)(dppe)2]ꢀ (0.87
and 13C) or P(OMe)3 (31P) (sꢁ
triplet, qꢁquartet, qtꢁquintet, mꢁ
/
singlet, dꢁ
/
doublet, tꢁ
/
/
/
/
multiplet, brꢁ
/
V (Rꢁ
irreversible reduction waves at Epred in the range from
1.0 to ꢂ1.5 V assigned to reductions centred at the
other metal centres. This is in accord with the detection
of irreversible cathodic waves (in the ꢂ0.5 to ꢂ1.5 V
/
Me) or 0.90 V (Rꢁ
/
Et) [45,46]), but also
broad). Positive-ion FAB mass spectra were obtained
on a Trio 2000 instrument by bombarding 3-nitrobenzyl
alcohol (NBA) matrixes of the samples with 8 keV (ca.
ꢂ
/
/
1.28ꢃ
105 J) Xe atoms. Mass calibration for data system
/
/
/
acquisition was achieved using CsI. Elemental analyses
were carried out at the Laborato´rio de Ana´lises of the
Instituto Superior Te´cnico.
range) for the corresponding transition metal Lewis acid
sources [PdCl2(PPh3)2] and [ReOCl3(PPh3)2].
Interestingly, the observation of two distinct iron(II)
centred oxidation waves for the trinuclear complex 5 is
The electrochemical experiments were performed on
an EG&G PAR 173 potentiostat and an EG&G PARC
175 universal programmer, or on a EG&G PARC 273
potentiostat/galvanostat connected to a PC computer
through a GPIB interface (National Instruments PC-
2A). A two-compartment three-electrode cell, with a
platinum-wire working electrode, probed by a Luggin
capillary connected to a silver wire pseudo-reference
electrode and a platinum auxiliary electrode, was
employed. The electrochemical experiments were per-
formed in a N2 atmosphere at room temperature (r.t.).
The potentials were measured by CV in 0.2 mol dmꢂ3
[NBu4][BF4]/CH2Cl2 and the values are quoted relative
to the saturated calomel electrode (SCE) by using the
trans-[FeHCl(dppe)2]0/ꢀ or the [Fe(h5-C5H5)2]0/ꢀ redox
indicative [47Á
/
50] of an ironÁ/iron interaction between
the two iron centres through the {CNꢀ
/
Re ꢀCN} brid-
/
ging moiety. The details of the electrochemical beha-
viours of such complexes will be reported separately.
3. Final comments
This work shows that trans-[FeH(CN)(dppe)2] con-
stitutes a convenient source of a cyano-iron centre with
both Bronsted and Lewis basic properties, providing a
¨
promising and easily accessible building block for the
synthesis of cyano-bridged complexes, including mixed
valent compounds, and for the generation in situ of
isocyanide ligands which are not easily accessible by
pure organic methods. The study also indicates that the
cyano-binding metal site trans-{FeH(dppe)2]ꢀ, which is
a sufficient p-electron-donor to ligate N2, can readily
activate cyanide towards a variety of electrophiles such
as those shown above. Preliminary electrochemical
(cyclic voltammetric) results also indicate that the
cyano-bridge can allow the electronic communication
between the metal atoms, a possibility that deserves
further exploration namely towards the generation of
mixed valence FeII/FeIII complexes.
couples (E1o/2xꢁ
/
ꢂ0.143 or 0.525 V vs. SCE, in CH2Cl2,
/
respectively) as the internal standards.
4.2. Syntheses
4.2.1. trans-[HFe(CNCOC6H5)(dppe)2]Cl (1)
CH2Cl2 solution (10 cm3) of trans-
To
a
[FeH(CN)(dppe)2] (0.030 g, 0.034 mmol), C6H5COCl
(0.11 mmol in a 1:10 CH2Cl2 dilution of the pure
compound) was added and the mixture was left stirring
overnight. The solution was then concentrated under
vacuum and upon addition of Et2O complex 1 pre-
cipitated as an orange solid which was separated by

264
S.S.P.R. Almeida et al. / Inorganica Chimica Acta 356 (2003) 259Á266
/
filtration, washed with Et2O and dried in vacuum (ca.
0.015 g, 45% yield).
a purple solid of complex 6 precipitated which was
separated by filtration, washed with n-pentane and dried
in vacuum (ca. 0.026 g, 36% yield).
IR: yCN/yCO 1881s and 1838s cmꢂ1. NMR: 1H
1
(CD2Cl2): d 7.67Á
CH2), 2.23 (s,br, 4H, CH2), ꢂ
1H, Feꢀ
H). 31P{1H} (CD2Cl2): d ꢂ
m/z 985 [M]ꢀ. Anal. Calc. for C60H54NOClP4Fe×
/
6.93 (m, 45H, Harom), 2.72 (s,br, 4H,
IR: yCꢁN 2010s cmꢂ1, yReO
ꢁ
/
900w cmꢂ1 NMR: H
6.97 (m, 80H, Harom); 2.84 (s,br, 8H,
2
/
7.45 (qt, JHP
ꢁ
/
47.0 Hz,
(CD2Cl2): d 7.56Á
CH2), 2.32 (s,br, 8H, CH2); ꢂ
/
2
13.08 (qt, JHP
/
/
59.31. FABꢀ -MS:
/
ꢁ
/
46.94
/
Hz, 2H, Feꢀ
/
H). 31P{1H} (CD2Cl2): d ꢂ
/
51.20. 13C{1H}
4CH2Cl2: C, 56.49; H, 4.60; N, 1.03. Found: C, 56.69;
H, 4.70; N, 1.00%.
(CD2Cl2): d 148.65 (CN). FABꢀ -MS: m/z 1015
[{ReOCl3}2(dppe)]ꢀ, 640 [Fe(dppe)Re]ꢀ, 617 [{Re-
OCl3}2]ꢀ, 308 [ReOCl3]ꢀ. Anal. Calc. for
4.2.2. trans-[FeH(CNMe)(dppe)2]I (2) and trans-
[FeH(CNEt)(dppe)2][BF4] (3)
C106H98Cl3N2OP8ReFe2: C, 61.54; H, 4.76; N, 1.35.
Found: C, 62.00; H, 4.65; N, 1.32%.
These complexes were prepared by treatment of a
CH2Cl2 or THF solution of trans-[FeH(CN)(dppe)2]
with MeI or [Et3O][BF4], respectively (in a 1:1.1 molar
ratio). The reaction solution was left stirring at r.t. for
48 (2) or 12 h (3) and then was concentrated under
vacuum followed by addition of a precipitating solvent
(n-pentane or Et2O). The final solid thus obtained was
separated by filtration, washed with n-pentane or Et2O
4.2.5. [{HFe(dppe)2(m-CN)}2PtCl(Ph)] (6)
CH2Cl2 solution (15 cm3) of trans-
To
[FeH(CN)(dppe)2]
a
(0.030
g,
0.034
mmol),
[Pt(Ph)Cl(PPh3)2] (0.013 g, 0.015 mmol) was added.
The mixture was left stirring overnight whereafter it was
concentrated under vacuum, Et2O was added and the
mixture was cooled to ꢂ18 8C for approximately 8 h.
/
and dried under vacuum (typically, 30Á
/
60% yields). The
The white solid of PPh3 thus formed was filtered off and
discarded. Further addition of Et2O led to the precipita-
tion of complex 6 as a greenish yellow solid which was
separated by filtration, washed with Et2O and dried in
characterisation data for these complexes are identical
to those previously described [41,42] and will not be
repeated.
vacuum (ca. 0.025 g, 35% yield).
IR: yCꢁN 2044 cmꢂ1. NMR: H (CD2Cl2): d 7.39Á
1
4.2.3. [HFe(dppe)2(m-CN)PdCl2(PPh3)] (4)
THF solution (15 cm3) of trans-
/
To
a
6.99 (m, 85 H, Harom), 2.48 (s,br, 8H, CH2), 2.01 (s,br,
H). 31P{1H}
[FeH(CN)(dppe)2] (0.030 g, 0.034 mmol), [PdCl2(PPh3)2]
(0.026 g, 0.037 mmol) was added and the mixture was
left stirring overnight whereafter it was concentrated in
vacuum. Dropwise addition of Et2O led to the forma-
tion of an oil. Isolation of this oily residue by decanta-
tion of the supernatant solution, addition of Et2O
8H, CH2),
(CD2Cl2):
ꢂ
/
14.55 (m,br 2H, Feꢀ
/
d
ꢂ
52.58. FABꢀ -MS: m/z 1757
/
[{Fe(CN)(dppe)2}2]ꢀ, 880 [FeH(CN)(dppe)2]ꢀ, 471
[Fe(CN)Pt(Ph)Cl(CN) Fe]ꢀ, 360 [Pt(Ph)Cl(CN)2]ꢀ,
307
[Pt(Ph)Cl)]ꢀ.
Anal.
Calc.
3CH2Cl2: C, 59.47; H, 4.48; N,
for
C112H103ClN2P8PtFe2×
1.21. Found: C, 59.02; H, 4.91; N, 0.83%.
/
followed by the application of the freezeÁ
/
thaw techni-
que and vigorous stirring resulted in the formation of an
orange powder of 4 which was separated by filtration,
washed with Et2O and dried in vacuum (ca. 0.020 g, 45%
yield). In several attempts to perform this reaction in
CH2Cl2 the same compound could be obtained,
4.2.6. [{XFe(dppe)2(m-CN)}2WCl3(OH)] (7)
THF solution (10 cm3) of trans-
[FeH(CN)(dppe)2] (0.030 g, 0.034 mmol), [WCl4(PPh3)2]
(0.030 g, 0.037 mmol) was added. The mixture was left
stirring overnight whereafter it was taken to dryness
leading to the formation of an oily residue. Addition of
To
a
although in much lower yields.
IR: yCꢁN 2074 cmꢂ1. NMR: H (CD2Cl2): d 7.93Á
7.01 (m, 55H, Harom); 2.53 (s,br, 4H, CH2), 1.90 (s,br,
1
/
Et2O followed by the application of the freezeÁthaw
/
2
4H, CH2), ꢂ
31P{1H} (CD2Cl2): d ꢂ
117.02 (PPh3) (see text). FABꢀ -MS: m/z 1020 [Mꢂ
PPh3ꢂ 630 596
Cl]ꢀ, [Fe(dppe)PdCl2]ꢀ,
[Fe(dppe)PdCl]ꢀ. Anal. Calc. for C71H64Cl2NP5PdFe×
/
13.79 (qt, JHP
ꢁ
/
46.1 Hz, 1H, Feꢀ
/
H).
technique and vigorous stirring resulted in the formation
of a violet powder of 7 that was separated by filtration,
washed with Et2O and dried under vacuum. Purple
crystals used for X-ray analysis were grown on recrys-
tallisation from CH2Cl2/Et2O (ca. 0.031 g, 40% yield).
IR: yCꢁN 1988 cmꢂ1. Paramagnetic. Anal. Calc. for
/
50.05 (dppe); ꢂ
/
112.84 and ꢂ
/
/
/
/
2CH2Cl2: C, 58.86; H, 0.94; N, 4.34. Found: C, 58.57; H,
5.10; N, 1.11%.
C
1.31. Found: C, 58.7; H, 4.99; N, 1.19%.
106H97Cl3N2P8WFe2X2 (XꢁCl): C, 59.5; H, 4.58; N,
/
4.2.4. [{HFe(dppe)2(m-CN)}2(ReOCl3)] (5)
CH2Cl2 solution (13 cm3) of trans-
To
a
4.3. X-ray measurements and structure determination
[FeH(CN)(dppe)2] (0.031 g, 0.035 mmol), [Re-
OCl3(PPh3)] (0.021 g, 0.025 mmol) was added and the
mixture was left stirring overnight. It was then concen-
trated in vacuum and n-pentane was added, whereupon
Crystal data and refinement details are given in Table
2. The crystal was mounted on glass fibre and then flash-
frozen to 100 K (Oxford Cryosystem-Cryostream

S.S.P.R. Almeida et al. / Inorganica Chimica Acta 356 (2003) 259Á
/266
265
(d) R.P. Happe, W. Roseboom, A.J. Pierik, S.P.J. Albracht,
Nature 385 (1997) 126;
Cooler). Preliminary examination and intensities data
collections were carried out on a Kuma KM4CCD k-
axis diffractometer with graphite-monochromated Mo
Ka radiation. Crystal was positioned at 65 mm from the
KM4CCD camera. 612 frames were measured at 0.758
intervals with a counting time of 35 s. The data were
corrected for Lp. Data reduction and analysis were
carried out with the Kuma Diffraction (Wroclaw)
programs [54]. The structures were solved by
direct methods (program SHELXS-97 [55]) and
refined by the full-matrix least-squares method on
all F2 data using the SHELXL-97 programs [56].
The hydride H atom was located in a difference
electron density map and its position and isotropic
displacement parameter were refined. All other H
atoms were positioned with ideal geometry and
refined with fixed individual isotropic displacement
parameters.
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Chem. Rev. 218 (2001) 43.
Crystallographic data have been deposited with the
Cambridge Crystallographic Data Centre as supplemen-
tary publications no CCDC 207288. Copies of the data
can be obtained free of charge on application to The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
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Soc., Dalton Trans. (2000) 373.
UK (fax: ꢀ44-1223-336-033; e-mail: deposit@ccdc.ca-
/
m.ac.uk or www: http://www.ccdc.cam.ac.uk).
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Acknowledgements
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da Silva, Y. Wang, J. Chem. Soc., Dalton Trans. (1995) 1193.
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Soc., Dalton Trans. (1995) 1183.
A.J.L.P. expresses his deepest gratitude to Professor
Frau´sto da Silva who (i) brought him to academic
(teaching and research) life at the I.S.T., (ii) created, in a
remarkable way, the Research Centre and the Complexo
Interdisciplinar to which A.J.L.P. belongs, and (iii)
generously has supported his research, kindly providing
laboratory space, guidance and friendship. This work
has been supported by the Foundation for Science and
Technology, its POCTI Programme, and by the NATO
Collaborative Linkage Grant PST.CLG.979289.
[21] A.J.L. Pombeiro, in: F.R. Kreissl (Ed.), Transition Metal
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¨