Synthesis and ligand properties towards gold and silver of the ferrocenylamidobenzimidazole ligand

Article abstract of DOI:10.1016/j.jorganchem.2006.06.025

The treatment of FcCOCl (Fc = (C₅H₅)Fe(C₅H₄)) with aminobenzimidazole in 1:1 or 2:1 ratio gives the ferrocenyl-amido derivatives FcCO(benzimNH₂) or (FcCO)₂(NHbenzim), respectively. The reactivity of FcCO(benzimNH₂) with silver or gold complexes has been studied. The reaction with the basic gold compounds [Au(acac)(PPh₃)] or [O(AuPPh₃)₃]ClO₄ occurs with deprotonation of the NH₂ group and coordination of one or three gold(phosphine) fragments. The treatment of this ligand with silver compounds, such as Ag(OTf) or [Ag(OTf)(PPh₃)], gives the complexes of stoichiometry [Ag(OTf)L] or [Ag(OTf)(PPh₃)L]. The ligand FcCO(benzimNH₂) and the complex [Ag(OTf){FcCO(benzimNH₂)}(PPh₃)] have been characterized by X-ray diffraction studies. DFT calculations were performed on models of this dimeric silver complex and showed that dimerization is energetically favourable, because Ag(I) achieves a four coordination environment, despite some bonds being relatively weak.

Full text of DOI:10.1016/j.jorganchem.2006.06.025

Journal of Organometallic Chemistry 691 (2006) 4181–4188
www.elsevier.com/locate/jorganchem
Synthesis and ligand properties towards gold and silver of the
ferrocenylamidobenzimidazole ligand
a,b,c
Maria Jose Calhorda a,b, Paulo J. Costa a,b, Paulo N. Martinho
´
,
´
M. Concepcion Gimeno *, Antonio Laguna , Susana Quintal a,b, M. Dolores Villacampa
c,
c
c
a
Instituto de Tecnologia Quı´mica e Biolo´gica (ITQB), Av. da Repu´blica, EAN, Apt 127, 2781-901 Oeiras, Portugal
b
ˆ
Departamento de Quı´mica e Bioquı´mica, Faculdade de Ciencias da Universidade de Lisboa, 1749-016 Lisboa, Portugal
Departamento de Quı´mica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n, Universidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain
c
Received 2 May 2006; received in revised form 9 June 2006; accepted 9 June 2006
Available online 28 June 2006
Abstract
The treatment of FcCOCl (Fc = (C5H5)Fe(C5H4)) with aminobenzimidazole in 1:1 or 2:1 ratio gives the ferrocenyl-amido derivatives
FcCO(benzimNH2) or (FcCO)2(NHbenzim), respectively. The reactivity of FcCO(benzimNH2) with silver or gold complexes has been
studied. The reaction with the basic gold compounds [Au(acac)(PPh3)] or [O(AuPPh3)3]ClO4 occurs with deprotonation of the NH2
group and coordination of one or three gold(phosphine) fragments. The treatment of this ligand with silver compounds, such as Ag(OTf)
or [Ag(OTf)(PPh3)], gives the complexes of stoichiometry [Ag(OTf)L] or [Ag(OTf)(PPh3)L]. The ligand FcCO(benzimNH2) and the com-
plex [Ag(OTf){FcCO(benzimNH2)}(PPh3)] have been characterized by X-ray diffraction studies. DFT calculations were performed on
models of this dimeric silver complex and showed that dimerization is energetically favourable, because Ag(I) achieves a four coordina-
tion environment, despite some bonds being relatively weak.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Gold; Silver; Ferrocene derivatives; DFT calculations; Azolate ligands
1. Introduction
[13,14]. Recently, the incorporation of ferrocene into
diphenols has been shown to enhance the antiproliferative
effects in vitro [15]. Additionally, compounds derived of 2-
aminobenzimidazole are know to exhibit a great spectra of
biological properties [16–20]. Therefore, the combination
of both ferrocene and 2-aminobenzimidazole moieties
may be interesting for the possible biological properties.
Some ferrocenylalkyl benzimidazoles have been described
and they present biological activity, namely ferrocenylm-
ethyl benzimidazole and ferrocenylalkyl polyfluorobenzim-
idazoles, which show antitumor properties [21–23].
Here we report on the synthesis of two ferrocene amido
derivatives obtained by reaction of the chlorocarbonyl fer-
rocene and 2-aminobenzimidazole and also their reactivity
towards gold and silver derivatives. Taking into account
that many gold complexes show antiarthritic and antican-
cer properties, together with the well known antibacterial
activity of silver compounds, we think that these ligands
Ferrocene is a very versatile molecule with important
properties such as high electron density, aromaticity and
redox reversibility. These characteristics, together with
the ease of preparation of mono substituted ferrocene
derivatives with a great variety of organic and inorganic
fragments, make ferrocene a versatile building block in
many fields of research. Then ferrocene derivatives are
important in areas requiring special properties such as
non-optical linearity, charge transport, liquid crystallinity,
electrochemical recognition, catalysis or nanoparticles [1–
12]. Furthermore, the ferrocenium ion has shown some
antitumor potential, albeit at rather high concentrations
*
Corresponding author. Tel.: +34 976762291; fax: +34 976761187.
´
E-mail address: gimeno@unizar.es (M. Concepcion Gimeno).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.06.025

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M.J. Calhorda et al. / Journal of Organometallic Chemistry 691 (2006) 4181–4188
and their complexes can be optimal candidates for a bio-
logical screening.
cal shifts of the ferrocenyl protons at 4.89, 4.55 and
4.20 ppm, are very close to those of 1, and to those of
the additional ferrocenyl fragment (4.83, 4.49 from a and
b protons of the Cp ring and 4.30 ppm, from the unsubsti-
tuted Cp). The 13C NMR spectra of compounds 1 and 2
are consistent with the proposed formulation, the assign-
ments being based in HMQC spectra.
2. Results and discussion
The synthesis of the ferrocenyl-azolate ligands has been
carried out by reaction of Fc(COCl) with 2-aminobenzim-
idazole (NH2(benzimH)) in dichloromethane and in the
presence of NEt3. When the reaction is carried out in a
ratio 1:1 the compound FcCO(benzimNH2) (1) is obtained,
as a consequence of the reaction of the NH azole group,
and further treatment of this derivative with Fc(COCl),
or just the reaction in a 2:1 molar ratio, gives the double
amide ligand (FcCO)2(NHbenzim) (2) (see Scheme 1).
These compounds are red solids air and moisture stable.
The ligand 1 was characterized by infrared spectroscopy,
which showed the strong mC@O stretching at 1678 cmꢀ1
and the sharp mN–H(as) signal at 3415 cmꢀ1 among other
bands assigned to the ferrocenyl subunit [24]. The compar-
ison between the IR spectra of 2-aminobenzimidazole and
1 led to the assignment of the bands at 1650 (mC@N), 1540
(dN–H), 1462 (mC@C), 1304 (mC–N), to the 2-aminobenzimi-
dazole fragment. The IR spectrum of ligand 2 also shows
bands assigned to the ferrocenyl (mC@O at 1678 cmꢀ1) and
the 2-aminobenzimidazole units (mC@N at 1654, dN–H at
1540, mC@C at 1479 and 1462 and mC–N at 1346, 1304
cmꢀ1). A band at 3415 cmꢀ1 was assigned to the NH
stretching mode.
The liquid secondary mass spectra (LSIMS+) of com-
pounds 1 and 2 show the molecular peaks at m/z = 345
(1, 100%) and 558 (2, 8%), respectively.
The crystal structure of compound 1 has been estab-
lished by X-ray diffraction studies and the molecule is
shown in Fig. 1. Selected bonds lengths and angles are col-
lected in Table 1. Complex 1 crystallizes in the monoclinic
space group C2/c. The relative conformation of the Cp-
rings is almost eclipsed; the torsion angle C(1)–X(1)–
X(2)–C(6) is 0.9ꢁ (X(1) and X(2) represent the centroids
of the Cp-rings C(1–5) and C(6–10), respectively). The
benzimidazole fragment is almost ideally planar (mean
˚
deviation from plane 0.0198 A). The interplanar angle
between the substituted cyclopentadienyl ring and the
benzimidazole group is 48.3ꢁ. The distances and angles of
the benzimidazole fragment compare well with those
reported for the compound 1-(ferrocenylmethyl)benzimid-
azole, [FcCH2Bim] [22].
The aromatic region of 1H NMR spectrum of 1 in
CDCl3 shows two doublets at 7.29 and 6.93 ppm, and
two triplets at 7.06 and 6.81 ppm assigned, respectively,
to the Ha, Hd, Hb and Hc protons of the benzimidazole
fragment (see Scheme 1). A broad signal at 6.45 is assigned
to the NH2 protons. Another set of signals are observed
upfield, two multiplets at 4.89 and 4.53 ppm the for the a
and b protons of the substituted cyclopentadienyl unit
and one singlet at 4.22 ppm assigned to the unsubstituted
cyclopentadienyl ring. These are consistent with the COSY
spectrum. The 1H NMR spectrum of 2 is similar, but three
additional resonances from the additional ferrocenyl unit
are observed. The aromatic protons of the benzimidazole
ring resonate in the 7.32–6.85 ppm region, while the NH
proton appears as a broad signal at 6.21 ppm. The chemi-
Fig. 1. Structure of compound 1 in the crystal with the atom numbering
scheme. Radii are arbitrary.
COCl
β2
Fe
α2
O
i)
ii)
C
Fe
O
C
HN
O
C
NH2
α1
β1
β1
α1
2
N
N
N
e
N
f
Fe
Fe
a
1
d
1
b
c
2
1
Scheme 1. (i) 2-aminobenzimidazole + NEt3, (ii) 1/2 2-aminobenzimidazole + NEt3.

M.J. Calhorda et al. / Journal of Organometallic Chemistry 691 (2006) 4181–4188
4183
Table 1
Selected bond lengths (A) and angles (ꢁ) for compound 1
Table 2
Hydrogen bonds for compound 1 (A and ꢁ)
˚
˚
N(1)–C(12)
N(2)–C(12)
N(2)–C(11)
N(2)–C(14)
N(3)–C(12)
1.337(3)
1.403(3)
1.415(3)
1.416(3)
1.307(3)
N(3)–C(13)
O(1)–C(11)
C(10)–C(11)
C(13)–C(14)
1.397(3)
1.210(3)
1.461(3)
1.397(3)
D–H. . .A
d(D–H)
d(H. . .A)
d(D. . .A)
\(DHA)
C(15)–H(15). . .O(1)#1
N(1)–H(12). . .N(3)#2
N(1)–H(11). . .O(1)
0.94(2)
0.78(3)
0.81(3)
2.56(2)
2.19(3)
2.12(3)
3.308(3)
2.964(3)
2.710(3)
137.2(17)
178(3)
129(2)
Symmetry transformations used to generate equivalent atoms: #1 ꢀx +
1/2, y ꢀ 1/2, ꢀz + 1/2; #2 ꢀx + 1/2, ꢀy + 1/2, ꢀz + 1.
C(12)–N(2)–C(11)
C(12)–N(2)–C(14)
C(11)–N(2)–C(14)
C(12)–N(3)–C(13)
O(1)–C(11)–N(2)
123.41(18)
105.62(17)
130.76(19)
105.23(18)
119.5(2)
O(1)–C(11)–C(10)
N(2)–C(11)–C(10)
N(3)–C(12)–N(1)
N(3)–C(12)–N(2)
N(1)–C(12)–N(2)
122.8(2)
117.7(2)
125.4(2)
113.20(19)
121.2(2)
gen atoms of the ligand are available for bonding, and a
mixture of complexes is obtained. They consist of the
mononuclear complex 3, and two different trinuclear deriv-
atives, where the gold atoms either coordinate to the amino
nitrogen (4a), or to both the amino and the benzimidazole
nitrogen atom (4b), as shown in Scheme 2. The outcome of
this reaction can be followed in the 31P{1H} NMR spec-
trum, where a singlet for complex 3, a singlet for com-
pound 4a and two singlets for compound 4b appear. In
the mass spectrum several fragments appear at m/z =
1721 ([Au3{N(benzim)COFc}(PPh3)3]+, 8%), 1458 ([Au3-
{N(benzim)COFc}(PPh3)2]+, 3%) and 1262 ([Au2{N(ben-
zim)COFc}(PPh3)2]+, 9%).
In the crystal, the molecules are associated into pairs
through two short hydrogen bonds involving one of the
N–H functions of the NH2 group and the N of the imidaz-
ole ring of the adjacent molecule (Fig. 2). The other N–H
function forms an intramolecular H bond to O1. The mol-
ecules are further linked to form a 3D structure through C–
H(benzimidazole)ꢁ ꢁ ꢁO1 hydrogen bond (Table 2).
The reaction of the ferrocenylamidobenzimidazole
ligand with several gold and silver compounds has been
studied. Thus, the reaction of compound 1 with [Au-
(acac)(PPh3)] occurs with deprotonation of the NH2 group
and coordination of the AuPPhþ3 fragment giving the com-
plex [Au{NH(benzim)COFc}(PPh3)] (3) (see Scheme 2).
The reaction of compound 1 with Ag(OTf) affords the
complex [Ag(OTf){FcCO (benzim)NH2}] (5), in which
the coordination of the silver atom probably takes place
to the benzimidazole nitrogen atom. The several possibili-
ties of coordination of the silver center to the ligand suggest
1
The H NMR spectrum shows the singlet and two multi-
plets attributable to the ferrocenyl protons, a singlet for
the NH group and two doublets and two pseudo-triplets
for the benzimidazole moiety. The 31P{1H} NMR spec-
trum presents one resonance for the phosphorus atom. In
the mass spectrum (LSIMS+) the molecular peak appears
at m/z = 805 (55%).
The reaction with other basic gold complex such as
[O(AuPPh3)3]ClO4 has been carried out and led to the
deprotonation of the amino group and coordination of
up to three gold(phosphine) units to the ligand. Two nitro-
1
that a supramolecular structure may be formed. The H
NMR spectrum shows resonances similar to those of the
ligand and the gold complexes, but an upfield displacement
is observed for the NH2 protons. In the mass spectrum, the
cation molecular peak appears at m/z = 452 (15%) and also
the fragment Ag2L+ at m/z = 797 (10%).
Finally, the reaction of the ferrocene–benzimidazole
ligand with [Ag(OTf)(PPh3)] has been carried out with
Fig. 2. Association of molecules in compound 1 through H bonding.

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M.J. Calhorda et al. / Journal of Organometallic Chemistry 691 (2006) 4181–4188
PPh3
Au
O
C
NH
O
C
NH2
N
N
N
N
Ag OTf
Fe
Fe
3
5
iii)
i)
+
O
C
NH2
O
C
NH2
N
N
Ag PPh3
N
N
iv)
Fe
Fe
ii)
6
+
+
PPh3
PPh3
PPh3
Au
Ph3P
Au
Au
Au
Au
PPh3
PPh3
PPh3
Au
Au
O
C
O
C
O
C
N
N
NH
N
N
N
N
N
N
+
+
Fe
Fe
Fe
4b
3
4a
Scheme 2. (i) [Au(acac)(PPh3)], (ii) [O(AuPPh3)3]ClO4, (iii) Ag(OTf), (iv) [Ag(OTf)(PPh3)].
formation of the complex [Ag(OTf){FcCO(benzim-
1
NH2)}(PPh3)] (6). In the H NMR resonances similar to
those of complex 5 are observed, with the same upfield dis-
placement of the NH2 broad singlet, indicating coordina-
tion of the AgPPhþ3 fragment to the benzimidazole
nitrogen atom, as has been confirmed by an X-ray diffrac-
tion study. The mass spectrum shows the molecular peak
at m/z = 865 (22%) and the cation molecular peak,
[AgL(PPh3)]+, at m/z = 714 (37%).
The structure of complex 6 has been determined by X-
ray diffraction studies and shows the presence of dimers
in which the triflate anions act as bridging ligands, as
depicted in Fig. 3 (the asymmetric unit consists of one mol-
ecule of the complex). Selected bonds lengths and angles
are listed in Table 3. The silver atom adopts a strongly dis-
torted tetrahedral environment; the angles around Ag
range from 89.01(5)ꢁ [O(4)–Ag1–O(2)#2, #2 ꢀx + 1,
ꢀy + 2, ꢀz + 1] to 143.74(5)ꢁ [N(2)–Ag1–P(1)]. The N–
Ag–P angle is appreciably larger than the ideal tetrahedral
angle, possibly reflecting the great steric effect of two bulky
PPh3 and FcCO(benzimNH2) ligands. The silver atom lies
˚
0.34 A out of the plane formed by the atoms O(4), P(1) and
Fig. 3. Perspective view of compound 6 in the crystal.
N(2).
The benzimidazole fragment, almost ideally planar
(mean deviation from plane 0.026 A), has bond lengths
and angles similar to those found in the uncoordinated
ligand (compound 1). The cyclopentadienyl rings deviate
slightly from an eclipsed geometry [torsion angle C(1)–
X(1)–X(2)–C(7) 4.6ꢁ (X(1) and X(2) represent the centroids
˚

M.J. Calhorda et al. / Journal of Organometallic Chemistry 691 (2006) 4181–4188
4185
Table 3
Selected bond lengths (A) and angles (ꢁ) for compound 6
hydrogens bonds N–Hꢁ ꢁ ꢁO, C–Hꢁ ꢁ ꢁO and C–Hꢁ ꢁ ꢁF, that
are summarised in Table 4.
˚
Ag(1)–N(2)
Ag(1)–P(1)
Ag(1)–O(4)
Ag(1)–O(2)#2
C(11)–O(1)
C(11)–N(1)
2.1840(16)
2.3530(5)
2.5092(16)
2.6271(15)
1.210(2)
N(1)–C(18)
N(1)–C(12)
N(2)–C(18)
N(2)–C(17)
N(3)–C(18)
C(12)–C(17)
1.392(2)
1.412(2)
1.314(3)
1.397(2)
1.324(3)
1.392(3)
DFT calculations [33] (ADF program [34]; see Compu-
tational section for details) were performed in order to
understand the preference for the dimeric arrangement
consisting of two complex cations and two triflate ions.
The phenyl rings in the phosphine were replaced by hydro-
gens in the model used, and several possible arrangements
were studied, namely the model of complex 6 (6m) and the
cation obtained after removing the triflate anion,
[Ag{FcCO(benzimNH2)}(PH3)]+ (6m+).
1.408(2)
N(2)–Ag(1)–P(1)
N(2)–Ag(1)–O(4)
P(1)–Ag(1)–O(4)
O(4)–Ag(1)–O(2)#2
N(2)–Ag(1)–O(2)#2
P(1)–Ag(1)–O(2)#2
O(1)–C(11)–N(1)
O(1)–C(11)–C(1)
N(1)–C(11)–C(1)
C(18)–N(1)–C(11)
143.74(5)
C(18)–N(1)–C(12)
C(11)–N(1)–C(12)
C(18)–N(2)–C(17)
C(18)–N(2)–Ag(1)
C(17)–N(2)–Ag(1)
C(17)–C(12)–N(1)
C(12)–C(17)–N(2)
N(2)–C(18)–N(3)
N(2)–C(18)–N(1)
N(3)–C(18)–N(1)
106.38(16)
129.45(16)
106.12(16)
131.26(14)
122.38(13)
105.10(16)
110.28(17)
125.78(19)
112.10(17)
122.10(18)
96.16(6)
112.57(4)
89.01(5)
The optimized structure of the 6m+ cation is shown in
Fig. 4. The coordination of Ag is almost linear (N–Ag–P
angle 171ꢁ), while the Ag–N and Ag–P distances are
89.87(6)
111.42(4)
120.02(17)
124.36(18)
115.62(16)
124.07(16)
˚
2.110 and 2.361 A, respectively. The Ag–P distance is very
˚
close to those observed in the X-ray structure (2.353 A),
˚
but Ag–N is much shorter (exp 2.184 A). Mayer indices
Symmetry transformations used to generate equivalent atoms: #2 ꢀx + 1,
ꢀy + 2, ꢀz + 1.
(MI) [35], scaling as bond strength indicators, were calcu-
lated. For the Ag–N bond the MI drops from 0.315 in
6m+ to 0.249 in the X-ray structure (with PH3 ligands).
There is an intramolecular COꢁ ꢁ ꢁH–N hydrogen bond, as
observed in the X-ray structure of the ligand (Fig. 2).
The addition of one triflate anion leads to a lengthening
of the Cp-rings C(1–5) and C(6–10), respectively)]. The
dihedral angle between the benzimidazole plane and Cp-
rings are equal to 58.4ꢁ.
The Ag–O distances (2.5092(16) and 2.6271(15) A) lie
among the longest observed in literature for four-coordi-
nated silver complexes [25–27]. The longer, 2.6271(15) A
Ag–O2#, indicates a weaker bond to the second triflate
unit.
The Ag–N distance, 2.1840(16) A, is shorter than those
found in some tetracoordinated silver complexes, such as
[Ag3(l-bim)3(PPh3)5] (from 2.290(5) to 2.349(5) A for the
four-coordinated silver atoms) [28], [Ag2(pz)2(PPh3)3]
(2.295(2) and 2.323(2) A for the four-coordinated silver
atom) [29], [Ag{HB(3,5-Me2pz)3}(PMePh2)] (from
2.316(6) to 2.336(5) A) [30] or the complexes [AgX-
{Fe[C5H4CH(pz)2]2}]n (X = BF4, PF6, SO3CF3 and SbF6)
(from 2.225(3) to 2.420(4) A) [31].
˚
˚
of the Ag–N bond (2.202 A, MI 0.273), while the Ag–P
bond does not change, and the angle narrows to 142ꢁ.
˚
˚
The new Ag–O bond is relatively short (2.358 A, MI
0.221), the coordination geometry around Ag having
become a wide Y. The binding energy of triflate to the
6m+ cation, forming 6m, is ꢀ82.2 kcal molꢀ1. Two new
intramolecular hydrogen bonds (Oꢁ ꢁ ꢁH distances of
˚
˚
˚
1.879 A) are established between the second N–H bond
and two oxygen atoms of the triflate, including the one
bound to silver. When a second triflate is added to 6m,
the binding energy is much lower but still attractive
(ꢀ15.6 kcal molꢀ1). This simple model suggests that silver
has a tendency to achieve four coordination. The Ag
environment is a very distorted tetrahedron, with angles
ranging from 89ꢁ to 131ꢁ (N–Ag–P), the two triflate anions
binding very differently. The two Ag–O distance are 2.340
˚
˚
˚
˚
The Ag–P distance, 2.3530(5) A, is similar to that
reported for the complex [Ag{HB(3,5-Me2pz)3}(PMePh2)]
˚
(2.336(2) A) [30] but shorter than those found in [Ag3(l-
˚
and 2.697 A (MI 0.211 and 0.105, respectively). The
˚
bim)3(PPh3)5] or [Ag2(pz)2(PPh3)3] (from 2.4377(19) A to
2.5315(19) A for the four-coordinated silver atoms)
binding of the second OTf anion has resulted in further
˚
[28,29] or other tetrahedral silver complexes such as
˚
[Ag(dppe)2]NO3 (range 2.488(3)–2.527(3) A) [32]. In addi-
tion, complex 6 displays several intra- and intermolecular
Table 4
˚
Hydrogen bonds for compound 6 (A and ꢁ)
D–H. . .A
d(D–H)
d(H. . .A)
d(D. . .A)
\(DHA)
C(3)–H(3). . .F(3)#1
C(33)–H(33). . .O(2)#2
C(34)–H(34). . .O(1)#3
N(3)–H(3A). . .O(1)
N(3)–H(3B). . .O(2)
N(3)–H(3B). . .O(4)
C(4)–H(4). . .O(3)#1
0.95
0.95
0.95
0.84(3)
0.82(3)
0.82(3)
0.95
2.53
2.57
2.57
2.11(3)
2.56(3)
2.27(3)
2.41
3.408(3)
3.513(3)
3.411(3)
2.706(2)
3.185(2)
3.054(3)
3.196(3)
153.4
170.4
147.3
127(2)
134(2)
161(3)
139.8
Fig. 4. Molekel representation of the [Ag{FcCO(benzimNH2)}(PH3)]+
cation (6m+).
Symmetry transformations used to generate equivalent atoms: #1 x ꢀ 1, y,
z + 1; #2 ꢀx + 1, ꢀy + 2, ꢀz + 1; #3 x + 1, y, z.

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˚
weakening of the Ag–N bond (2.251 A, MI 0.241), while
the Ag–P bond remains unchanged. The intramolecular
hydrogen bond network has also changed. Besides the C–
Oꢁ ꢁ ꢁH–N bond, only one, but stronger, hydrogen bond is
formed between the second N–H of the benzimidazole
and the bound oxygen of the triflate (Oꢁ ꢁ ꢁH distance of
3.3. Synthesis
3.3.1. Synthesis of FcCO(benzimNH2) (1)
To a solution of 2-amino-benzimidazole (1.335 g,
1 mmol) and NEt3 (1.21 g, 1.2 mmol) in dichloromethane
(20 mL) at 0 ꢁC was added dropwise FcCOCl (0.247 g,
1 mmol). After the addition the mixture was allowed to
reach room temperature and stirred for 12 h. Then solution
was washed with a saturated solution of NaHCO3 in water;
the organic phase separated, dried over Na2SO4 and evap-
orated to ca. 2 mL. Addition of hexane gave compound 1
˚
1.815 A).
The X-ray structure consists of two units of 6. In order
to compare the values, single point calculations were per-
formed on a structure similar to the experimental one but
with phenyl groups replaced by hydrogen atoms. The
energy of the optimized 6m is much lower than that of
the same fragment in the X-ray structure, essentially
because the Ag–N and one of the Ag–O bonds are signifi-
cantly shorter (and stronger) and the angles may adjust.
Despite the slightly distorted geometry, the dimerization
energy was calculated as ꢀ23.8 kcal molꢀ1 (difference
between the energy of the dimer and twice the energy of
the monomers). The Ag–N and Ag–O bond lengths adapt
and Ag achieves a four coordination environment. On the
other hand, the Ag-phosphine fragment remains very rigid.
In the observed structure two sets of hydrogen bonds are
also observed: one C–Oꢁ ꢁ ꢁH–N bond and one N–Hꢁ ꢁ ꢁO
bond with the bound oxygen of the closest triflate (Oꢁ ꢁ ꢁH
as a red solid. Yield: 55%, 0.190 g. KM 3.3 Xꢀ1 cm2 molꢀ1
.
Elemental analysis (%), Found: C, 62.61; H, 4.23; N, 12.12.
Calc. for C18H15FeN3O (345.176): C, 62.63; H, 4.38; N,
1
12.17. NMR data: H NMR (ppm): 4.22 (s, 1-C5H5, 5H),
4.53 (m, b1-C5H4, 2H), 4.89 (m, a1-C5H4, 2H), 6.45 (br,
NH2), 6.81 (t, Hc, 1H), 6.93 (d, Hd, 1H), 7.06 (t, Hb,
1H), 7.29 (d, Ha, 1H). 13C NMR (ppm): 172.90 (C@O),
154.08 (C-NH2), 142.04 (Ce), 131.44 (Cf), 123.86 (Cb),
120.09 (Cc), 116.58 (Ca), 113.14 (Cd), 73.76 (C(Cp)-
C@O), 72.55 (Ca1, C5H4), 72.37 (Cb1, C5H4), 71.04 (1-
C5H5). UV/Vis (CH2Cl2): 470 nm
3.3.2. Synthesis of (FcCO)2(NHbenzim) (2)
˚
distance of 2.106 and 2.275 A). Since hydrogen bonds are
To a solution of 2-amino-benzimidazole (1.335 g,
1 mmol) and NEt3 (1.21 g, 1.2 mmol) in dichloromethane
(20 mL) at 0 ꢁC was added dropwise FcCOCl (0.494 g,
2 mmol). After the addition the mixture was allowed to
reach room temperature and stirred for 12 h. Then solution
was washed with a saturated solution of NaHCO3 in water;
the organic phase separated, dried over Na2SO4 and evap-
orated to ca. 2 mL. Addition of hexane gave compound 2
found in all models, they do not particularly contribute
to stabilize any of the possible arrangements.
3. Experimental section
3.1. Instrumentation
Infrared spectra were recorded in the range 4000–
200 cmꢀ1 on a Perkin–Elmer 883 spectrophotometer using
Nujol mulls between polyethylene sheets. Conductivities
were measured in ca. 5 · 10ꢀ4 mol dmꢀ3 solutions with a
Philips 9509 conductimeter. C, H and S analyses were car-
ried out with a Perkin–Elmer 2400 microanalyzer. Mass
spectra were recorded on a VG Autospec, with the liquid
secondary-ion mass spectra (LSIMS) technique, using
nitrobenzyl alcohol as matrix. NMR spectra were recorded
on a Varian Unity 300 spectrometer and a Bruker ARX
300 spectrometer in CDCl3. Chemical shifts are cited rela-
tive to SiMe4 (1H, 13C external), and 85% H3PO4 (31P,
external). Electronic spectra were recorded with a UNI-
CAM model UV-4 spectrophotometer.
as a red solid. Yield: 67%, 0.374 g. KM 3.0 Xꢀ1 cm2 molꢀ1
.
Elemental analysis (%), Found: C, 62.31; H, 4.09; N, 7.56.
Calc. for C29H23Fe2N3O2 (557.202): C, 62.51; H, 4.16; N,
1
7.54. NMR data. H NMR (ppm): 4.20 (s, 1-C5H5, 5H),
4.30 (s, 2-C5H5, 5H), 4.49 (m, b2-C5H4, 2H), 4.55 (m, b1-
C5H4, 2H), 4.83 (m, a1-C5H4, 2H), 4.89 (m, a2-C5H4,
2H), 6.21 (br, NH), 6.85 (t, Hc, 1H), 6.95 (d, Hd, 1H),
7.09 (t, Hb, 1H), 7.32 (d, Ha, 1H). 13C NMR (ppm):
172.80 (C@O), 167.64 (C0@O), 154.05 (C–NH), 141.84
(Ce), 131.27 (Cf), 123.76 (Cb), 119.09 (Cc), 116.42 (Ca),
113.05 (Cd), 73.62 (C(Cp)-C@O), 72.75 (C(Cp)-C0@O),
72.65 (b2-C5H4), 72.43 (a1-C5H4), 72.28 (b1-C5H4), 70.94
(1-C5H5), 70.74 (a2-C5H4), 70.13 (2-C5H5). UV/Vis
(CH2Cl2): 464 nm
3.2. Materials
3.3.3. Synthesis of [Au(PPh3){NH(benzim)COFc}]ClO4
(3)
The starting materials FcCOCl [36], [Au(acac)(PPh3)]
[37], [O(AuPPh3)3]ClO4 [38], and [Ag(OTf)(PPh3)] [39] were
prepared by published procedures. All other reagents were
commercially available.
Safety note. Caution! Perchlorate salts of metal com-
plexes with organic ligands are potentially explosive. Only
small amounts of material should be prepared, and these
should be handled with great caution.
To a solution of 1 (0.035 g, 0.1 mmol) in dichlorometh-
ane (20 mL) was added [Au(acac)(PPh3)] (0.056 g,
0.1 mmol). The mixture was stirred for 2 h. Then solution
was evaporated to ca. 5 mL and addition of hexane gave
compounds 3 as a orange solid. Yield: 58%, 0.047 g. KM
9.4 Xꢀ1 cm2 molꢀ1. Elemental analysis (%), Found: C,
53.41; H, 3.52; N, 5.37. Calc. for C36H29FeAuPN3O
(803.42): C, 53.82; H, 3.64; N, 5.23. NMR data. 1H

M.J. Calhorda et al. / Journal of Organometallic Chemistry 691 (2006) 4181–4188
4187
NMR (ppm): 1H, d: 4.27 (s, 5H, C5H5), 4.60 (m, 2H,
C5H4), 4.95 (m, 2H, C5H4), 5.95 (br, 1H, NH), 6.90 (m,
1H, benzim), 7.0 (m, 1H, benzim), 7.15 (m, 1H, benzim),
7.34 (m, 1H, benzim), 7.37–7.65 (m, 15H, Ph), ppm. 31P–
{1H} (ppm): 33.46 (s, 1P, PPh3).
Table 5
Details of data collection and structure refinement for complexes 1 and 6
Compound
1
6
Chemical formula
Crystal habit
C18H15FeN3O
Orange prism
0.38 · 0.20 · 0.10 0.44 · 0.24 · 0.20
Monoclinic
C37H30AgF3FeN3O4PS
Red prism
Crystal size (mm)
Crystal system
Space group
Triclinic
P1
3.3.4. Synthesis of [(AuPPh3)3{N(benzim)COFc}]
(4a and 4b)
ꢀ
C2/c
˚
a (A)
18.2850(19)
8.6986(9)
20.295(2)
90
114.000(2)
90
2948.8(5)
8
1.555
12.4837(9)
12.5587(9)
13.1468(10)
62.4930(10)
66.8840(10)
81.4210(10)
1680.1(2)
2
˚
To a solution of compound 1 (0.035 g, 0.1 mmol) in
dichloromethane (20 mL) was added [O(AuPPh3)3]ClO4
(0.149 g, 0.1 mmol). The mixture was stirred for 3 h. Then
solution was evaporated to ca. 5 mL and addition of
diethyl ether gave a mixture of complexes 4a and 4b as yel-
low-orange solids. NMR data. 31P–{1H} (ppm): 33.46 (s,
1P, PPh3, complex 3), 32.6 (s, 3P, PPh3, complex 4a),
31.7 (s, 2P, PPh3, complex 4b), 27.9 (s, 1P, PPh3, complex
4b).
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
U (A )
Z
Dc (g cmꢀ3
M
)
1.709
864.39
872
345.18
1424
F(000)
T (ꢁC)
2hmax (ꢁ)
ꢀ173
ꢀ173
57
57
l(Mo Ka) (mmꢀ1
)
1.030
0.81461, 1.00000
9316
1.188
0.6230, 0.7971
15463
3.3.5. Synthesis of [Ag(OTf){FcCO(benzim)NH2}] (5)
To a solution of compound 1 (0.035 g, 0.1 mmol) in
dichloromethane (20 mL) was added Ag(OTf) (0.026 g,
0.1 mmol). The mixture was stirred for 3 h. Then solution
was evaporated to ca. 5 mL and addition of diethylether
gave compound 5 as an orange solid. Yield: 91%, 0.055 g.
KM 84 Xꢀ1 cm2 molꢀ1. Elemental analysis (%), Found: C,
37.59; H, 2.49; N, 6.43; S, 5.21. Calc. for C19H15F3FeAg-
N3O4S (602.114): C, 37.90; H, 2.51; N, 6.98; S, 5.32.
Transmission
Number of reflections
measured
Number of unique
reflections
Rint
3410
7609
0.0365
0.0400
0.0900
0.0188
0.0286
0.0730
7609
468
Ra (F > 4r(F))
wR2 (F2, all refl.)
b
Number of reflections used 3410
Number of parameters
Number of restraints
Sc
268
0
0.971
0.786
1
1
NMR data. H NMR (ppm): H, d: 4.0 (br, 2H, NH2),
4.30 (s, 5H, C5H5), 4.75 (m, 2H, C5H4), 4.96 (m, 2H,
C5H4), 7.09 (m, 1H, benzim), 7.32 (m, 1H, benzim), 7.40
(m, 1H, benzim), 7.87 (m, 1H, benzim).
0
1.020
0.966
ꢀ3
˚
Max. Dq (e A
)
P
P
a
R(F) = ||Fo| ꢀ |Fc||/ |Fo|.
P
P
2
2
1=2
2
b
wRðF 2Þ ¼ ½ fwðF o2 ꢀ F c2Þ g= fwðF 2oÞ gꢂ
;
wꢀ1 ¼ s2ðF 2oÞ þ ðaPÞ þ
bP, where P ¼ ½F 2o þ 2F 2c ꢂ=3 and a and b are constants adjusted by the
3.3.6. Synthesis of
[Ag(OTf){FcCO(benzim)NH2}(PPh3)] (6)
program.
c
P
S ¼ ½ fwðF 2o ꢀ F c2Þ g=ðn ꢀ pÞꢂ0:5, where n is the number of data and p
2
To a solution of compound 1 (0.035 g, 0.1 mmol) in
dichloromethane (20 mL) was added [Ag(OTf)(PPh3)]
(0.043 g, 0.1 mmol). The mixture was stirred for 1 h and
then the solvent was evaporated to ca. 5 mL and addition
of diethylether gave compound 6 as an orange solid. Yield:
67%, 0.057 g. KM 111 Xꢀ1 cm2 molꢀ1. Elemental analysis
(%), Found: C, 51.09; H, 3.28; N, 4.56; S, 3.72. Calc. for
C37H30F3FeAgN3O4PS (864.40): C, 51.41; H, 3.49; N,
the number of parameters.
refined anisotropically. Hydrogen atoms were included
using a riding model.
3.5. Computational details
Density functional calculations [33] were carried out
with the Amsterdam Density Functional program
(ADF2005) [34]. Gradient corrected geometry optimiza-
tions, [41] [C] without any symmetry constraints, were per-
formed using the the Local Density Approximation of the
correlation energy (Vosko, Wilk and Nusair’s) [42] [D] and
the Generalized Gradient Approximation (Perdew–Wang
[43] [E] exchange and correlation corrections). A triple-f
Slater-type orbital (STO) basis set augmented by one polar-
ization function was used for all atoms. A frozen core
approximation was used to treat the core electrons: (1s)
for C, N, F and O; ([1–2]s, 2p) for S, P and Fe; ([1–3]s
[2–3]p 3d) for Ag. Relativistic effects were treated with
the ZORA approximation [44]. [F] Mayer indices [35] were
calculated and used as bond strength indicators. Three-
dimensional representations of molecules were obtained
1
4.86; S, 3.71. NMR data. H NMR (ppm): 3.8 (br, 2H,
NH2), 4.33 (s, 5H, C5H5), 4.75 (m, 2H, C5H4), 4.96 (m,
2H, C5H4), 7.11 (m, 1H, benzim), 7.25–7.53 (m, 15H,
Ph), 7.55 (m, 1H, benzim), 7.67 (m, 1H, benzim), 7.97
(m, 1H, benzim). 31P–{1H} (ppm): 12.2 (s, br, 1P, PPh3).
3.4. X-ray crystallography
The crystals were mounted in inert oil on glass fibers and
transferred to the cold gas stream of the Bruker SMART
CCD diffractometer. Crystal data and details of data col-
lection and structure refinement are given in Table 5.
Absorption corrections were based on multiple scans (pro-
gram SADABS). The structures were refined on F2 using the
program SHELXL-97 [40]. All non-hydrogen atoms were

4188
M.J. Calhorda et al. / Journal of Organometallic Chemistry 691 (2006) 4181–4188
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Acknowledgements
This work was supported by the Ministerio de Edu-
´
cacion y Ciencia-FEDER (No. CTQ2004-05495-C02-01).
´
We thank the Accion Integrada HP20030147 and Acc¸ao
˜
Integrada E-31/04. PJC acknowledges FCT for Grant
(SFRH/BD/10535/2002) and S. Quintal for Grant
(SFRH/BPD/11463/2002).
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Appendix A. Supplementary data
CCDC-278148 and 278149 contains the supplementary
crystallographic data for this paper. These data can be
obtained free of charge at www.ccdc.cam.ac.uk/conts/
retrieving.htlm [or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (internat.) +44 1223 336033; e-mail; deposit@ccdc.
cam.ac.uk]. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/
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