Coordinating properties of [M(CO)5(CN)]- [M=Cr; Mo; W] ligands: Formation of ion pairs or dinuclear cyanide-bridged complexes, spectroscopic and X-ray diffraction studies

Article abstract of DOI:10.1016/j.jorganchem.2004.04.021

The reaction of sodium cyanopentacarbonylmetalates Na[M(CO)₅ (CN)] (M=Cr; Mo; W) with cationic Fe(II) complexes [Cp(CO)(L)Fe(thf)] [O₃SCF₃], [L=PPh₃ (1a), CN-Benzyl (1b), CN-2,6-Me₂C₆H

Full text of DOI:10.1016/j.jorganchem.2004.04.021

Journal of Organometallic Chemistry 689 (2004) 2324–2337
www.elsevier.com/locate/jorganchem
Coordinating properties of [M(CO)5(CN)]ꢀ [M ¼ Cr; Mo; W]
ligands: formation of ion pairs or dinuclear cyanide-bridged
complexes, spectroscopic and X-ray diffraction studies
a,
b
a
a
Antonio Palazzi *, Piera Sabatino , Stefano Stagni , Silvia Bordoni ,
b
Vincenzo G. Albano , Carlo Castellari
b
a
Dipartimento di Chimica Fisica ed Inorganica, University of Bologna, Viale Risorgimento 4, I-40136 Bologna, Italy
b
Dipartimento di Chimica ‘‘G. Ciamician’’, via Selmi 2, I-40126, Bologna, Italy
Received 24 February 2004; accepted 13 April 2004
Abstract
The reaction of sodium cyanopentacarbonylmetalates Na[M(CO)5(CN)] (M ¼ Cr; Mo; W) with cationic Fe(II) complexes
[Cp(CO)(L)Fe(thf)][O3SCF3], [L ¼ PPh3 (1a), CN-Benzyl (1b), CN-2,6-Me2C6H3 (1c); CN-But (1d), P(OMe)3 (1e), P(Me)2Ph (1f)] in
acetonitrile solution, yielded the metathesis products [Cp(CO)(L)Fe(NCCH3)][NCM(CO)5] [M ¼ W, L ¼ PPh3 (2a), CN-Benzyl
(2b), CN-2,6-Me2C6H3 (2c); CN-But (2d), P(OMe)3 (2e), P(Me)2Ph (2f); M ¼ Cr, L ¼ (PPh3) (3a), CN-2,6-Me2C6H3 (3c); M ¼ Mo,
L ¼ (PPh3) (4a), CN-2,6-Me2C6H3 (4c)]. The ionic nature of such complexes was suggested by conductivity measurements and their
main structural features were determined by X-ray diffraction studies. Well-resolved signals relative to the [M(CO)5(CN)] moieties
could be distinguished only when 13C NMR experiments were performed at low temperature (from )30 to )50 ꢀC), as in the case of
[Cp(CO)(PPh3)Fe(NCCH3)][NCW(CO)5] (2a) and [Cp(CO)(Benzyl-NC)Fe(NCCH3)][NCW(CO)5] (2b). When the same reaction
was carried out in dichloromethane solution, neutral cyanide-bridged dinuclear complexes [Cp(CO)(L)FeNCM(CO)5] [M ¼ W,
L ¼ PPh3 (5a), CN-Benzyl (5b); M ¼ Cr, L ¼ (PPh3) (6a), CN-2,6-Me2C6H3 (6c), CO (6g); M ¼ Mo, L ¼ CN-2,6-Me2C6H3 (7c), CO
(7g)] were obtained and characterized by infrared and NMR spectroscopy. In all cases, the room temperature 13C NMR mea-
surements showed no broadening of cyano pentacarbonyl signals and, relative to tungsten complexes [Cp(CO)(PPh3)FeNCW(CO)5]
(5a) and [Cp(CO)(CN-Benzyl)FeNCW(CO)5] (5b), the presence of 183W satellites of the 13CN resonances (JCW ꢁ 95 Hz) at room
temperature confirmed the formation of stable neutral species. The main 13C NMR spectroscopic properties of the latter compounds
were compared to those of the linkage isomers [Cp(CO)(PPh3)FeCNW(CO)5] (8a) and [Cp(CO)(CN-Benzyl)FeCNW(CO)5] (8b).
The characterization of the isomeric couples 5a–8a and 5b–8b was completed by the analyses of their main IR spectroscopic
properties. The crystal structures determined for 2a, 5a, 8a and 8b allowed to investigate the geometrical and electronic differences
€
between such complexes. Finally, the study was completed by extended Huckel calculations of the charge distribution among the
relevant atoms for complexes 2a, 5a and 8a.
ꢁ 2004 Elsevier B.V. All rights reserved.
Keywords: Saline compounds; Dinuclear complexes; Cyanide-bridges; IR and NMR spectroscopy; X-ray diffractometry; Theoretical studies
1. Introduction
functionalized isocyanide ligands, M–CBNX [X ¼ H, R,
R3M0 (M0 ¼ Si, Ge, Sn), PR2] [1a–1f]. The cyanide li-
gand basicities have been recently determined by Ang-
elici and co-workers [2] in a series of Cp(L)2MCN
complexes, (M ¼ Ru, Fe). Typically, the reaction with
electrophilic inorganic or organometallic substrates al-
lows the synthesis of dinuclear complexes in which the
cyanide ligand is end-on coordinated to two metal at-
oms, LnM–CN–M0Ln [3a–3k,9a–9c]. Furthermore, the
It is well known that the cyanide ligand in cyano
metal complexes reacts with a variety of electrophilic
agents. By this method, using suitable alkylating agents,
it has been possible to prepare complexes containing
* Corresponding author. Tel.: +390516446496; fax: +390512093690.
E-mail address: palazzi@ms.fci.unibo.it (A. Palazzi).
0022-328X/$ - see front matter ꢁ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.04.021

A. Palazzi et al. / Journal of Organometallic Chemistry 689 (2004) 2324–2337
2325
ambidentate character of the cyanide ligand plays a key
role in the synthesis of infinite chain-like complexes [4a–
4f]. Over the past two decades, di- or polymetallic cya-
nide-bridged systems have received massive attention in
connection with the peculiar properties of the cyanide
bridging unit [5a–5k]. Indeed, the CN bridge ability to
act as an efficient charge transfer mediator made this
class of compounds potentially useful for designing
optical and electronic devices based on the asymmetry of
the cyanide linker [6a,6b]. Moreover, studies about the
presence of magnetic exchange interaction through a
bridging CN ligand have shown that transition metal
cyanides might represent good candidates for molecule-
based magnetic materials [7a–7e]. With the aim of ex-
ploiting the spectroscopic properties of organometallic
fragments coordinated either to the nitrogen or the
carbon extremity of the bridging cyanide unit, we re-
ported a series of di- and trinuclear organometallic cy-
ano-bridged complexes of iron [8]. Among plenty of
suitable building blocks, cyanopentacarbonylmetalates
such as [M(CO)5(CN)]ꢀ (M ¼ Cr; Mo; W) represent
some of the most widely employed in the synthesis of
cyanide-bridged arrays. In the first part of this paper, we
report the study of their reactions with cationic Fe(II)-
organometallic fragments to achieve the formation ei-
ther of saline compounds [Cp(CO)(L)Fe(NCCH3)]
[NCM(CO)5] or dinuclear cyano-bridged complexes
[Cp(CO)(L)FeNCM(CO)5]. The main spectroscopic and
structural features of the obtained products are com-
pared to those of the isomeric complexes [Cp(CO)-
(L)FeCNM(CO)5], in which the electronic properties of
the iron atom are modulated by ligands with different
r=p bonding abilities. A series of analogous compounds
has been reported by Vahrenkamp and co-workers
[9a,9b,9c], who has largely contributed to the elucida-
tion of the factors determining the extent of electronic
interaction between remote metal centers in cyanide-
bridged arrays of redox-active transition metal ions
[10a–10d].
135.9 ppm; CDCl3 as solvent). In addition, conductivity
measurements showed values typical of uni-univalent
electrolytes, suggesting the formation of ion pairs such
as [Cp(CO)(L)Fe(NCCH3)][NCM(CO)5], [M ¼ W, L ¼
PPh3 (2a), CN-Benzyl (2b), CN-2,6-Me2C6H3 (2c); CN-
But (2d), P(OMe)3 (2e), P(Me)2Ph (2f); M ¼ Cr, L ¼
(PPh3) (3a), CN-2,6-Me2C6H3 (3c); M ¼ Mo, L ¼ (PPh3)
(4a), CN-2,6-Me2C6H3 (4c)]
½CpðCOÞðLÞFeðthfÞꢂ½O3SCF3ꢂ
Na½MðCOÞ5ðCNÞꢂ
½CpðCOÞðLÞFeðNCCH Þꢂ½NCMðCOÞ ꢂ
ƒƒƒƒƒƒƒ!
3
5
CH3CN r:t:
ð1Þ
The 13C NMR analyses of the latter complexes showed a
temperature-dependent behaviour and well-resolved
patterns of the cyanopentacarbonyl anions could be ob-
served only between )30 and )50 ꢀC, as in the case of [Cp
(CO)(PPh3)Fe(NCCH3)][NCW(CO)5](2a) (Fig. 1) and
[Cp(CO)(CN-Benzyl)Fe(NCCH3)][NCW(CO)5] (2b).
An analogous effect has been described by Darens-
bourg et al. [11] for the cyanide-bridged dinuclear
compound [(PPh3)3CuNCW(CO)5]. In that case, one of
the proposed mechanisms which could account for the
observed line broadening consisted in the rapid ex-
change reaction involving the insertion of a solvent
molecule in the bridging unit. In our complexes, coor-
dinated acetonitrile was detected at every temperature,
confirming the presence of stable ion pairs in solution.
In addition, the low temperature 13C NMR spectra of
complexes 2a and 2b showed shifts values (dCWCN ca.
140 ppm) in agreement with those of uncoordinated
[W(CO)5(CN)]ꢀ anion [12]. From a different viewpoint,
the observed line broadening effect might be attributed
to some carbonyl scrambling. On the other hand, it is
worth noting that many mononuclear systems of type
[M(CO)5L] are reported to be stereochemically rigid at
room temperature, as inferred by stabilization energy
considerations [13a,13b]. At the same time, carbonyl
rearrangements in [M(CO)5L] (M ¼ Cr, Mo, W) deriv-
atives have already been documented and rate constants
for cis-to-trans equilibration in [M(CO)4(13CO)PR3]
(M ¼ Cr, W) were measured, suggesting intramolecular
CO ligand rearrangements [14]. Nondissociative intra-
molecular isomerization has also been proposed by
Dombeck and Angelici [15] for the conversion of trans-
[W(CO)4(13CO)(CS)] to the corresponding cis-isomer. In
our complexes, the cyanocarbonyl counterions
[M(CO)5(CN)]ꢀ, whichever metal is employed, exhibit
fluxional behavior at room temperature.
2. Results and discussion
2.1. Ion pairs
As an initial attempt to synthesize [LnFe–NC–
M(CO)5] type complexes, we reacted the cationic pre-
cursors [CpFe(CO)(L)(thf)][O3SCF3], [L ¼ PPh3 (1a),
CN-Benzyl (1b), CN-2,6-Me2C6H3 (1c); CN-But (1d),
P(OMe)3 (1e), P(Me)2Ph (1f)] with cyano-pentacarbonyl
anions such as [M(CO)5(CN)]ꢀ, (M ¼ Cr, Mo, W) in
acetonitrile medium. Even though the analysis of IR
spectroscopic data might suggest the formation of the
expected neutral species, the NMR characterization of
the product complexes allowed to establish the presence
of coordinated acetonitrile (dH ¼ 2:0 ppm; dC ¼ 5:2 and
2.2. [Cp(CO)(L)FeNCM(CO)5] complexes (M ¼ Cr,
Mo, W)
The exclusive formation of saline species
[Cp(CO)(L)Fe(NCCH3)][M(CO)5(CN)] in place of

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A. Palazzi et al. / Journal of Organometallic Chemistry 689 (2004) 2324–2337
Fig. 1. Variable temperature 13C NMR spectra of [Cp(CO)(PPh3)Fe(NCCH3)][NCW(CO)5] (2a).
[CpFe(CO)(L)NCM(CO)5] is probably due to a mass
effect of acetonitrile as solvent or eluant in the purifi-
cation process. Thus, in order to obtain the target di-
nuclear compounds, a less coordinating solvent was
considered. In particular, the reaction of the cationic
precursors [Cp(CO)(L)Fe(thf)][O3SCF3], [L ¼ PPh3 (1a),
CN-Benzyl (1b), CN-2,6-Me2C6H3 (1c); CO (1g)] with
the appropriate amount of Na[M(CO)5(CN)] (M ¼ Cr,
Mo, W) in dichloromethane solution afforded the ex-
pected neutral cyano-bridged dinuclear complexes
[Cp(CO)(L)FeNCM(CO)5] [M ¼ W, L ¼ PPh3 (5a), CN-
Benzyl (5b); M ¼ Cr, L ¼ (PPh3) (6a), CN-2,6-Me2C6H3
(6c), CO (6g); M ¼ Mo, L ¼ CN-2,6-Me2C6H3 (7c), CO
(7g)]
nitrogen lone pairs in the metallacyanide [16a,16b] are
weak and favourable to coordination only in the ab-
sence of competitive bases. Further evidence of such
solvent-dependent behaviour is that, when the saline
compound
[Cp(CO)(PPh3)Fe(NCCH3)][NCW(CO)5]
(2a) was refluxed in toluene for 2 h, the IR spectrum
showed the carbonyl bands of the cyanide-bridged
complex [Cp(CO)(PPh3)FeNCW(CO)5] (5a). The pat-
tern of IR stretchings for the neutral cyanide-bridged
compounds 5–7 is very similar to that of the corre-
sponding saline derivatives 2–4 (Fig. 2).
The observed wavenumbers, as expected, are shifted
to lower values for the iron-coordinated carbonyl and to
higher wavenumber for the CN group (@30 cmꢀ1). This
frequency increase has been associated with a kinematic
coupling effect, i.e., a constraint of the motion of the
bridging CN due to its coordination to the second metal
center [17]. Actually, the factors affecting the stretching
frequency of bridging cyanides are more complicated
and the back-bonding from the C-bonded and the N-
bonded metal atoms should also be considered. As these
three factors operate in opposition but concomitantly,
the magnitude and direction of the frequencies shift
depend on their relative importance [18]. In light of these
considerations, the increasing of the r=p bonding ratio
of the ligand L at the iron atom (L ¼ CO, [8] CNR, PR3)
resulted not only in the expected decrease of the car-
bonyl vibration but also in a minor but significant de-
crease of the CN stretching wavenumber (i.e., 2136 cmꢀ1
in [Cp(CO)2FeNCW(CO)5] [8] versus 2127 cmꢀ1 in
[Cp(CO)(PPh3)FeNCW(CO)5] (5a)). All the [LnFe–
NC–M(CO)5]-type compounds have been characterized
½CpðCOÞðLÞFeðthfÞꢂ½O3SCF3ꢂ
Na½MðCOÞ5ðCNÞꢂ
½CpðCOÞðLÞFe–NC–MðCOÞ ꢂ
ð2Þ
ƒƒƒƒƒƒƒ!
5
CH2Cl2 r:t:
In a different approach, a dinuclear cyano bridged
complex such as [Cp(CO)(PPh3)FeNCW(CO)5] (5a)
could be obtained from its carbonyl precursor
[Cp(CO)2FeNCW(CO)5] (5g) by the well-established
procedure involving addition of triphenylphosphine in
the presence of trimethylamine N-oxide
½CpðCOÞ FeNCWðCOÞ ꢂ
2
5
Me3NO; PPh3
ƒƒƒƒƒƒƒ!
CH2Cl2 r:t:
½CpðCOÞðPPh ÞFeNCWðCOÞ ꢂ
3
5
þ CO2 þ NMe3
ð3Þ
All the neutral complexes were purified by column
chromatography by using dichloromethane as eluant.
Our results suggest that the basic properties of the

A. Palazzi et al. / Journal of Organometallic Chemistry 689 (2004) 2324–2337
2327
Fig. 2. IR spectra of [Cp(CO)(PPh3)Fe(NCCH3)][NCW(CO)5] (2a); [Cp(CO)(PPh3)FeNCW(CO)5] (5a) and [Cp(CO)(PPh3)FeCNW(CO)5] (8a).
1
by spectroscopic methods (IR, H and 13C NMR) and
no significant difference has been observed in the Fe
moieties on going from Cr, Mo, to W derivatives. The
most important feature of the 13C NMR spectra of all
the neutral cyano-bridged complexes 5–7 is given by the
presence, at room temperature, of well-resolved reso-
nances attributed to M(CO)5CN moiety (Fig. 3), being
the anchorage of the M(CO)5CN group to iron a key
factor to prevent easy CO scrambling. Moreover, in
[Cp(CO)(CN-Benzyl)FeNCW(CO)5] (5b), it has been
possible to distinguish the resonances of the isocyanide
from the cyanide bridging ligand, showing the latter a
typical pattern due to coupling with 183W (see further
on).
Fig. 3. Selected 13C NMR signals for [Cp(CO)(PPh3)Fe–NC–W(CO)5] (5a) and [Cp(CO)(PPh3)Fe–CN–W(CO)5] (8a).

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A. Palazzi et al. / Journal of Organometallic Chemistry 689 (2004) 2324–2337
2.3. [Cp(CO)(L)FeCNM(CO)5] complexes(M ¼ Cr, W)
fined a1 absorption, attributable to the axial carbonyl, is
diagnostic of the –CNM(CO)5 bonding mode. The IR
evidences are in good agreement with the geometric
features observed in the X-ray molecular structures of
5a and 8a (see next section).
(ii) Ligand substitution in the iron fragment does not
appreciably influence the carbonyl stretchings in the
M(CO)5 moieties.
The synthesis of the isomeric compounds
[Cp(CO)(L)FeCNM(CO)5] [M ¼ W, L ¼ PPh3 (8a), CN-
Benzyl (8b); M ¼ Cr, L ¼ (PPh3) (9a), CN-2,6-Me2C6H3
(9c)], required the previous preparation of precursor
complexes [Cp(CO)(L)FeCN] (L ¼ PPh3, CN-Benzyl,
CN-2,6-Me2C6H3), which were obtained by addition of
the stoichiometric amount of the desired ligand L to a
refluxing solution of [Cp(CO)2FeCN] in toluene and in
(iii) The 13C NMR resonance of the bridging CN,
which is increasingly shielded in the order Cr, Mo, W, in
[Cp(CO)(L)Fe–NC–M(CO)5] complexes, is always found
at lower field (i.e., 168.6 ppm. in complex 5a) with respect
to the corresponding isomers [Cp(CO)(L)Fe–CN–M
(CO)5] (i.e., 152.3 ppm in 8a). A further distinction be-
tween the Fe–NC–M and Fe–CN–M isomers is provided
by the coupling of the bridging cyanide carbon with
phosphine ligands (2JCP ca. 30 Hz) in complexes 8a (M ¼
W; L ¼ PPh3) and 9a (M ¼ Cr; L ¼ PPh3), which allows
the unambiguous assignment of the cyanide carbon
the presence of
a catalytic quantity of [Fe2(l-
CO)2(CO)2(Cp)2]. Thus, the reaction of precursors
[CpFe(CO)(L)CN] with a slight excess of [M(CO)5(thf)]
(M ¼ Cr, W) in tetrahydrofuran solution afforded the
target complexes 8a,b and 9a,c in acceptable yields (ca.
50%), while the synthesis of dinuclear compounds with
the Mo(CO)5 unit proved unsuccessful
½CpðCOÞðLÞFeðCNÞꢂ
½MðCOÞ5thfꢂ
bonded to iron. On the other hand, the presence of 183
W
½CpðCOÞðLÞFeCNMðCOÞ ꢂ
ð4Þ
ƒƒƒƒƒ!
5
thf r:t:
satellites is diagnostic of the Fe–NC–W bonding mode, as
in the case of 5a and 5b (1JCW ca. 95 Hz; see Fig. 3).
Furthermore, as we already reported for some related
compounds [8], the typical broadness of the isocyanide
resonance [20] in the isonitrile complexes 5b, 8b,
(M ¼ W; L ¼ CN-Benzyl) and 9c (M ¼ Cr; L ¼ CN-2,6-
Me2C6H3) makes this signal clearly distinguishable from
the one of the bridging cyanide (Fig. 4).
A comparison of the spectroscopic IR and NMR fea-
tures of 8a,b and 9a,c with those of the linkage isomers
5a,b and 6a,c, allow the following considerations:
(i) The Dm between the two a1 absorptions of the
M(CO)5 fragments is always larger in [LnFeCNM
(CO)5] complexes 8a,b and 9a,c. In particular, while the
a1 stretching absorption of the axial CO is always well
observable for the latter compounds, it appears as a
shoulder of the intense e absorption in the related iso-
mers [LnFeNCM(CO)5] (5a,b) (see Fig. 2) and 6a,c. This
feature might be explained in terms of lower p-back-
donation from the N-end of the bridging cyanide
[19a,19b,19c]. It follows that the presence of a well-de-
(iv) The 13C NMR signals of the W(CO)5 groups in
[Cp(CO)(PPh3)Fe–NC–W(CO)5] 5a and [Cp(CO)(CN-
Benzyl)Fe–NC–W(CO)5] 5b are upfield shifted with
respect to those of the related isomers [Cp(CO)(L)Fe–
CN–W(CO)5] 8a (L ¼ PPh3) and (L ¼ Benzyl-NC) 8b
and exhibit (Fig. 4) a narrower separation (DCO
¼
Fig. 4. Selected 13C NMR signals for [Cp(CO)(CN-Benzyl)Fe–NC–W(CO)5] (5b) and [Cp(CO)(CN-Benzyl)Fe–CN–W(CO)5] (8b).

A. Palazzi et al. / Journal of Organometallic Chemistry 689 (2004) 2324–2337
2329
2:7–2:8 ppm) between the signals of axial and equatorial
carbonyls (DCO ¼ 3:7 ppm in 8a; 3.4 ppm in 8b), as we
previously reported in the case of L ¼ CO [8]. This effect
is even more pronounced in the [Cp(CO)(L)Fe–NC–
Cr(CO)5] complexes 6a and 6c (DCO ¼ 3:3 and 2.9 ppm,
respectively) compared to the isomers 9a and 9c
(DCO ¼ 4:5 and 4.9 ppm). These results further confirm
that in M(CO)5L complexes the chemical shift of the
trans-CO moves downfield relative to those of the cis-
carbonyls as the r=p bonding ratio of the ligand L in-
creases [21a,21b].
C25
C19
C13
O2
C2
O3
C3
P
O1
C1
N
C7
C8
W
Fe
C6
O6
C5
C4
O4
2.4. X-ray molecular structures of 2a, 5a, 8a and 8b and
extended-H€uckel calculations
O5
Fig. 7. Molecular structure of [Cp(CO)(PPh3)FeCNW(CO)5] (8a)
showing the atom numbering (thermal ellipsoids at 50% probability
level).
The molecular structures of the title compounds are
shown in Figs. 5 (2a), 6 (5a), 7 (8a) and 8 (8b). Relevant
bond distances and angles are reported in Table 1.
C9
C10
C15
O5
C27
O2
C2
C5
C4
N2
C8
P
C21
O4
O7
O1
O1
C1
C1
C7
N2
W
O6
Fe
N1
C7
C6
Fe
W
C6
O3
C2
N1
C8
C10
C4
C3
O2
C16
C3
O3
C5
O5
O4
C9
Fig. 5. Molecular structure of [Cp(CO)(PPh3)Fe(NCCH3)][NCW-
(CO)5] (2a) showing the atom numbering (thermal ellipsoids at 50%
probability level).
Fig. 8. Molecular structure of [Cp(CO)(CN-Benzyl)FeCNW(CO)5]
(8b) showing the atom numbering (thermal ellipsoids at 50% proba-
bility level).
The following discussion will be focused on the ge-
ometry of the linear fragment M–CBN–M0, in an at-
tempt to detect electronic effects connected to structural
changes and to correlate metric and spectroscopic
features.
C20
O5
P
C14
C5
C8
O6
2.4.1. [Cp(CO)(PPh3)Fe(NCCH3)][NCW(CO)5] (2a)
This saline compound contains discrete ions and the
anion unambiguously shows a C4v symmetry with
the cyanide ligand well discernible from the CO groups.
The ordered packing of the anion clearly means that the
negative charge is significantly localized on the cyanide
ligand, as indicated by the W–C distances. The W–
O1
O3
C6
Fe
C3
C1
W
N1
C7
C26
C4
O4
C2
O2
ꢀ
ꢀ
C(cyanide) [2.198(9) A] is 0.2 A longer than the average
W–C(carbonyl) [mean value for the equatorial groups
Fig. 6. Molecular structure of [Cp(CO)(PPh3)FeNCW(CO)5] (5a)
showing the atom numbering (thermal ellipsoids at 50% probability
level).
ꢀ
2.02 A]. Such a significant difference can be attributed to
the net negative charge on the cyanide group that swells

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A. Palazzi et al. / Journal of Organometallic Chemistry 689 (2004) 2324–2337
Table 1
Relevant bond parameters in compounds 2a, 5a, 8a and 8b
Complex
Fe–C
Fe–P
Fe–C/N
W–N/C
ðCNÞ
CBN
W–COtrans
W–COcis(av)
ðCOÞ
ðCNÞ
ꢀ
Bond distances (A)
2a
5a
8a
8b
1.763(8)
1.746(7)
1.735(5)
1.767(5)
2.242(2)
2.234(2)
2.218(1)
–
1.925(7)NCMe
1.921(5)N
1.884(5)C
2.198(9)C
2.178(6)C
2.194(5)N
2.194(4)N
1.142(9)
1.158(8)
1.981(9)
1.983(8)
1.964(6)
1.972(5)
2.02(1)
2.02(1)
2.04(1)
2.035(4)
1.149(7)
1.149(5)CNW
1.144(5)CNBz
1.895(4)CðCNWÞ
1.843(4)CðCNBzÞ
W–C–N
W–N–C
Fe–C–N
Fe–N–C
Bond angles (ꢀ) in the moieties M–CBN–M0
5a
8a
8b
174.8(6)
–
–
175.5(6)
–
–
172.8(4)
173.9(4)
177.2(5)
177.8(4)
–
–
up its orbitals and, more than that, makes the ligand a
poor p acceptor. This is consistent with the W–C(car-
coordination of the N-end of the cyanide ligand in the
anion. It is of interest to study the fine structural
changes in the neutralized molecular moieties with re-
ꢀ
ꢀ
bonyl) distance trans to CN [1.981(9) A] being 0.04 A
shorter than the equatorial values, an indication of a
more consistent p back-bonding for this ligand (see also
Table 1 and the discussion later on). Substantially,
longer W–C(cyanide) and W–N(cyanide) than W–
C(CO) distances are present also in 5a, 8a, 8b (see fur-
ther on) and in all the reported W(CN)(CO)5 fragments.
In particular the [(CO)5WCNW(CO)5]ꢀ anion exhibits a
symmetrically bridging cyanide ligand [W–C 2.184(8);
ꢀ
spect to the separated ions. The Fe–C(O), 1.746(7) A
ꢀ
and the Fe–P, 2.234(2) A, interactions are slightly
ꢀ
shorter than in 2a [1.763(8) and 2.242(2) A, respectively].
ꢀ
The Fe–N(cyanide) distance [1.921(5) A] is similar to
the Fe–N(nitrile) in the cation, while the CBN value
ꢀ
[1.158(8) A] is some 0.02 A longer than in the coordi-
ꢀ
ꢀ
ꢀ
nated acetonitrile [1.131(9) A] and 0.01 A longer than
that in [W(CN)(CO)5]ꢀ. Therefore, one can infer that
the antibonding p orbitals in the bridging CN group are
more populated than in NCCH3 and monodentate CNꢀ
ꢀ
W–N 2.187(7) A] and an average W–C(carbonyl) dis-
tance 2.02 long [22]. The molecular structure of an iso-
lated [W(CN)(CO)5] anion has been recently reported
[23] but, unfortunately, a comparison is not possible
because CN/CO disorder is probable. The bond dis-
tances in the [Cp(CO)(PPh3)Fe(NCCH3)] cation will be
analyzed in comparison with the corresponding values
in 5a. It is worth citing here the significant difference
ꢀ
ligands. The W–C(cyanide) distance [2.178(6) A] is 0.02
ꢀ
A shorter than in the anion, in accord with an improved
tungsten-to-cyanide back-donation consequent to a
lower net charge on the bridging ligand. No measurable
effects are observed in the W–CO interactions. The data
discussed above are consistent with the chemical evi-
dence that the negative charge in the anion moiety is
primarily localized on the cyanide ligand, while the po-
sitive charge in the cationic moiety is reasonably more
centred at the iron atom (see later in this section).
ꢀ
between the Fe–C(carbonyl) [1.763(8) A] and Fe–N(ni-
ꢀ
trile) [1.925(7) A] distances. It is in keeping with that just
discussed for the anion, the shorter distance being found
for the better acceptor carbonyl ligand. An analysis of
the anion–cation contacts in the crystals allows to rec-
ognize the formation of a preferential ion pair, the one
shown in Fig. 5. The nitrogen atom in the cyanide li-
gand, which is the most negatively charged atom in the
anion (see Table 2), is oriented towards the cation and
2.4.3. [Cp(PPh3)(CO)FeCNW(CO)5] (8a) and [Cp
(CO)(CN-Benzyl)FeCNW(CO)5] (8b)
The molecules 8a and 8b are very similar and differ
only in the donor properties of the PPh3 and CN-Benzyl
ligands. The geometric changes induced by these ligands
are hardly detectable. The W–NBC distances are found
ꢀ
one of the closest contacts, N(1)ꢃ ꢃ ꢃC(8), is 3.24 A long.
ꢀ
2.4.2. [(Cp)(CO)(PPh3)FeNCW(CO)5] (5a)
This molecule is a condensation product of the ions in
2a by elimination of the NCCH3 ligand in the cation and
equal in the two species [W–N 2.194(5), CBN 1.149(7) A]
ꢀ
and the Fe–C(cyanide) [1.884(5) and 1.895(4) A in 8a and
ꢀ
8b, respectively] is only 0.01 A shorter in the molecule
Table 2
Net charges (e) on atoms of interest in 2a, 5a and 8a obtained by extended-Huckel calculations
€
Complex
W
CCN
NCN
Ccis CO(av)
Ocis CO(av)
Ctrans CO
Otrans CO
Fe
2a
5a
8a
)0.07
)0.02
+0.06
+0.31
+0.07
+0.28
)0.95
)0.49
)0.73
+0.66
+0.66
+0.64
)0.69
)0.69
)0.67
+0.60
+0.60
+0.53
)0.76
)0.74
)0.78
+0.77
+0.77
+0.80

A. Palazzi et al. / Journal of Organometallic Chemistry 689 (2004) 2324–2337
2331
containing the better donor phosphine ligand that im-
proves the iron-to-cyanide back-donation. It is of inter-
est to compare the bond parameters of the cyanide ligand
in the linkage isomers [Cp(CO)(PPh3)FeCNW (CO)5]
(8a) and [Cp(CO)(PPh3)FeNCW(CO)5] (5a). The differ-
charge on C is lowered by a more significant back-do-
nation from W.
(iii) When the cyanide ligand is N-bonded to W,
forming the sequence WNCFe as in 8a, the charge lo-
calization turns more similar to that in the free anion
[N )0.73 and C +0.28 e] indicating that N of the CNꢀ
ligand is a poorer donor to the almost neutral W (net
charge on the heavy metal +0.06 e) than to positively
charged Fe (net charge on the metal in the range +0.7–
0.8 e). In this context it is useful to remember that the
same kind of calculations for the cyanide anion bridg-
ing two W(CO)5 groups in the already cited
[(CO)5WCN(CO)5]ꢀ anion showed much more bal-
anced charge distribution with net charges 0 and )0.13
e at C and N, respectively [22].
ꢀ
ence in the CBN distance [1.149(7) in 8a and 1.158(8) A
in 5a] is not statistically significant, what one can say is
that the total backbonding in the two cases is compara-
ble and probably greater in 5a, where the better acceptor
C atom is linked to the zerovalent tungsten atom. The
ꢀ
ꢀ
W–C [2.178(6) A] and W–N [2.194(5) A] distances show
ꢀ
that W–N is 0.016 A longer, in spite of the smaller atomic
radius of N. The lengthening is attributable to a lower
tungsten-to-nitrogen back-donation. This consideration
is in keeping with the corresponding distances Fe–C
ꢀ
ꢀ
[1.884(5) A] and Fe–N [1.921(5) A], for which an even
ꢀ
more significant difference is observed [0.04 A] in the
3. Conclusions
same way as above. These statements are even more
significant if one remember that the W–C and W–N
distances have been found equal in [(CO)5-
The reaction between cyanopentacarbonylmetalates
[M(CO)5(CN)]ꢀ (M ¼ Cr; Mo; W) and various cationic
Fe(II) organometallic fragments can be driven to the
formation either of ion pairs such as [Cp(CO)(L)Fe-
(NCCH3)][NCM(CO)5] or neutral cyanide-bridged
complexes of the type [Cp(CO)(L)FeNCM(CO)5], the
coordinating ability of the solvent being crucial for de-
termining the [M(CO)5(CN)]ꢀ coordination. In all the
saline compounds, the 13C NMR spectroscopy suggested
the fluxionality of the cyanopentacarbonyl counterions,
which was confirmed by low-temperature experiments on
complexes [Cp(CO)(PPh3)Fe(NCCH3)] [NCW(CO)5]
(2a) and [Cp(CO)(CN-Benzyl)Fe(NCCH3)][NCW(CO)5]
(2b). In particular, the crystal structure of 2a revealed the
presence of well-defined ion pairs, the formation of
which was invoked to account for some similar line
broadening effects [11]. The absence of acetonitrile, both
as the reaction solvent and in the work-up procedures,
allowed the recovery of cyanide-bridged complexes of
the type [Cp(CO)(L)FeNCM(CO)5]. All products were
fully characterized by IR and NMR (1H; 13C) spectros-
copy and their properties compared to those of the
competitive ion pairs [Cp(CO)(L)Fe(NCCH3)][NCM-
(CO)5] and of some isomeric compounds [Cp(CO)-
(L)FeCNM(CO)5]. This study was corroborated by the
investigation of the crystal structures of complexes
[Cp(CO)(PPh3)Fe(NCCH3)][NCW(CO)5] (2a), [Cp(CO)-
(PPh3)FeNCW(CO)5] (5a), [Cp(CO)(PPh3)FeCNW-
(CO)5] (8a) and [Cp(CO)(CN-Benzyl)FeCNW(CO)5]
(8b).
WCNW(CO)5]ꢀ [average 2.18 A], as discussed above
ꢀ
[22]. Bond values in accord with those discussed in this
section
have
been
found
in
the
cation
[Fe4S4{NCW(CO)5}4]2þ, in which four WCNFe units
are present [9a]. Another pair of bridging cyanide linkage
isomers in a comparable bonding environment has been
reported, i.e., [(CO)5Cr–CN/NC–Fe(dppe)Cp] [9b].
Just one comment on the M–CBN–M0 angles re-
ported in Table 1. The angles involving W are moder-
ately but systematically more bent than those involving
Fe. This is proof that the W–cyanide interactions are
weaker than the Fe-cyanide ones and, therefore, more
sensitive to asymmetric packing forces, in accord with
what was previously observed [9c].
The results of the molecular structures are usefully
€
complemented by extended-Huckel calculations [24] of
the net charges on the relevant atoms. The figures in
Table 2 put on a quantitative basis the inferences based
on the geometric evidence and their analysis allows the
following considerations:
(i) The free anion [W(CO)5(CN)]ꢀ exhibits the highest
negative and the least positive charges at the N and C
atoms of the cyanide ligand [)0.95 and +0.31 e, re-
spectively], with a resulting net charge on the ligand of
)0.64 e. These values, if compared with the average
charges on the cis- and trans-C–O atoms (+0.66, )0.69
and +0.60, )0.76 e, respectively) quantify the charge
localization in the anion and its polarity, explaining its
ordered crystallization in the saline species 2a.
(ii) When the cyanide ligand is N-coordinated to the
iron atom, forming the sequence WCNFe as in 5a, the
negative charge on N promptly drops to )0.49 e. This
effect is accompanied by a significant lowering of the
positive charge on C [+0.07 e]. The new charge balance
on the bridging ligand indicates that while the negative
charge on N drops by donation to Fe, the positive
4. Experimental
4.1. General
All reactions with organometallic reagents or sub-
strates were carried out under argon using standard

2332
A. Palazzi et al. / Journal of Organometallic Chemistry 689 (2004) 2324–2337
Schlenk techniques. Solvents were dried and distilled
under nitrogen prior to use. The prepared deriva-
tives were characterised by elemental analysis and
spectroscopic methods. IR spectra were recorded with
a FT-IR spectrometer Perkin–Elmer Spectrum 2000.
The routine NMR spectra (1H, 13C) were always
(WCOax), 197.7 (WCOeq), 142.4 (NCW), 135.9
(CH3CN), 133.5 132.2, 131.4, 130.9 129.8 (C6H5), 84.9
(C5H5), 5.3 (CH3CN). KM (10ꢀ3 M in CH3CN, r.t.):
125 Xꢀ1 cm2 molꢀ1. Anal. Calc. for C32H23N2O6PFeW:
C, 47.9; H, 2.87; N, 3.5. Found: C, 48.1; H, 2.85; N,
3.7%. (2b) 0.195 g, 41%, red oil. IR (CH2Cl2) mmax
(cmꢀ1): 2196m, 2103w (CN), 2058w, 2024m, 1921vs
1890sh (CO); NMR: dH (CDCl3, 25 ꢀC): 7.5–7.3 (m,
5H, C6H5), 4.9 (s, 5H, C5H5) 2.2 (s, 2H, CH2-Ph), 2.0
(s, 3H, CH3CN); dC (CDCl3, r.t.), 213.5 (Fe–CO), 152.9
(CNBenzyl), 134.8 (CH3CN), 132.3, 129.9, 129.6, 127.6
(C6H5), 83.8 (C5H5), 50.1 (CH2), 5.4 (CH3CN); dC
(CDCl3 )50 ꢀC): 212.7 (Fe–CO), 200.5 (WCOax), 197.1
(WCOeq), 150.9 (CNBenzyl), 142.1 (NCW), 133.2
(CH3CN), 131.4, 129.3, 129.0, 127.0 (C6H5) (C5H5),
49.2 (CH2), 5.4 (CH3CN); KM (10ꢀ3 M in CH3CN,
recorded using
a Varian Gemini 300 instrument
(1H, 300.1; 13C, 75.5 MHz). The spectra were refer-
enced internally to residual solvent resonance, and
were recorded at 298 K for characterisation pur-
poses. Elemental analyses were performed on a Ther-
moQuest Flash 1112 Series EA Instrument. The
compounds
[CpFe(CO)2CN],
Na[M(CO)5(CN)],
(M ¼ Cr, Mo, W) were prepared by the literature
procedures. Cationic precursors like [Cp(CO)-
(L)Fe(THF)]þ, [L ¼ PPh3 (1a), CN-Benzyl (1b), CN-2,6-
Me2C6H3 (1c); CN-But (1d), P(OMe)3 (1e), P(Me)2Ph
(1f), CO (1g)] were prepared from the correspond-
r.t.): 115 Xꢀ1 cm2 molꢀ1
.
Anal. Calc. for
C22H15N3O6FeW: C, 40.2; H, 2.28; N, 6.4. Found: C,
40.5; H, 2.31; N, 6.5%. (2c) 0.200 g, 42%, dark mi-
crocrystalline powder. IR (CH2Cl2) mmax (cmꢀ1): 2157s,
2104w (CN), 2024s, 1921vs, 1890sh (CO); NMR: dH
(CDCl3): 7.3–7.1 (m, 3H, C6H3-2,6-(CH3)2), 5.2 (s, 5H,
C5H5) 2.5 (s, 6H, C6H3-2,6-(CH3)2) 2.3 (s, 3H,
CH3CN); dC (CDCl3); 212.3 (Fe–CO), 163.9
(CNC6H3(CH3)2), 134.7 (CH3CN), 134.9, 129.4, 128.1,
127.4 (C6H3(CH3)2), 84.0 (C5H5), 18.5 (C6H3(CH3)2),
5.0 (CH3CN); KM (10ꢀ3 M in CH3CN, r.t.): 115 Xꢀ1
cm2 molꢀ1. Anal. Calc. for C23H17N3O6FeW: C, 41.1;
H, 2.53; N, 6.3. Found: C, 41.5; H, 2.55; N, 6.2%. (2d)
0.150 g, 33%, yellow oil. IR(CH2Cl2) mmax (cmꢀ1):
2181m, 2104w (CN), 2056w, 2020s, 1921vs (CO);
NMR: dH (CDCl3): 5.1 (s, 5H, C5H5), 2.3 (s, 3H,
CH3CN), 1.6 (s, 9H, C(CH3)3); dC (CDCl3): 213.5 (Fe-
C O), 148.8 (CNBut), 83.7 (C5H5), 60.1 (CCH3), 30.7
(CCH3), 5.0 (CH3CN); KM (10ꢀ3 M in CH3CN, r.t.):
121 Xꢀ1 cm2 molꢀ1. Anal. Calc. for C19H17N3O6FeW:
C, 36.6, H, 2.73, N, 6.7. Found: C, 36.8; H, 2.77; N,
6.5%. (2e) 0.180 g, 38%, red oil. IR (CH2Cl2) mmax
(cmꢀ1): 2103w (CN), 2058w, 2004m, 1920vs, 1890sh
(CO); NMR: dH(CDCl3): 4.9 (s, 5H, C5H5) 3.7 (9H, d,
ing iodides [25] by reaction with
a stoichiome-
tric amount of Ag(CF3SO3) in a THF solution (15 ml)
at room temperature. Filtration through a Celite
pad and subsequent evaporation to dryness afforded
a mixture which was used without any further purifica-
tion. All reactions were monitored by IR spectroscopy.
Petroleum ether (Etp) refers to a fraction of b.p. 60–
80 ꢀC. Typically, all chromatographies were performed
on alumina column (diameter:1.5 cm; height 15 cm)
under Argon atmosphere and using petroleum ether-
dichloromethane mixtures as eluant.
4.2. Typical procedure for the preparation of
[Cp(CO)(L)Fe(NCCH3)][NCW(CO)5] [L ¼ PPh3
(2a); CN-Benzyl (2b); CN-2,6-Me2C6H3 (2c); CN-
But (2d); P(OMe)3 (2e); P(Me)2Ph (2f)]
Complexes 1a–f (0.71 mmol), dissolved in dry ace-
tonitrile (10 ml), was added dropwise to a stirred sus-
pension of Na[W(CO)5(CN)] (0.270 g, 0.71 mmol) in 15
ml of CH3CN. The resulting dark mixture was main-
tained at )30 ꢀC for 2 h, then left to warm to room
temperature. Filtration through a Celite pad and
evaporation to dryness afforded a crude product which
was purified by alumina column chromatography.
CH2Cl2 was first used as eluant to remove neutral im-
purities, after which the fractions containing the title
compounds 2a–f were obtained by eluting with
CH3CN. (2a) 0.270 g, 50%, red crystals obtained from
a dichloromethane solution of pure 2a layered with
diethyl ether at )5 ꢀC. IR (CH2Cl2) mmax (cmꢀ1): 2102w
(CN); 2057w, 1990m,1920vs,1895sh (CO); NMR: dH
(CDCl3) 7.2–7.7 (m, 15H, C6H5), 4.7 (s, 5H, C5H5), 2.0
(s, 3H, CH3CN); dC (CDCl3; 25 ꢀC): 216.4 (FeCO, d,
2JCP ¼ 40 Hz), 135.9 (CH3CN), 133.4 133.2 132.5, 131.6
131.9 129.8 (C6H5); 84.7 (C5H5) 5.2 (CH3CN); dC
3
(OCH3)3, JHP ¼ 9 Hz) 2.3 (s, 3H, CH3CN); dC
3
(CDCl3): 214.1 (FeCO, d, JCP ¼ 45 Hz), 135.3 (CH3C
3
N), 83.8 (C5H5), 53.7 (OCH3, d, JCP ¼ 5 Hz), 5.18
(CH3CN). KM (10ꢀ3 M in CH3CN, r.t.): 116 Xꢀ1 cm2
molꢀ1. Anal. Calc. for C17H17N2O9PFeW: C, 30.7; H,
2.56; N, 4.2. Found: C, 30.9; H, 2.60; N, 4.4%. (2f)
0.238 g; 50%, red oil. IR (CH2Cl2) mmax (cmꢀ1): 2104w,
2059w, 1986m, 1922vs, 1898sh (CO); NMR: dH
(CDCl3) 7.4–7.7 (m, 5H, C6H5), 4.8 (s, 5H, C5H5), 2.3
(s, 6H, CH3), 2.0 (s, 3H, CH3CN); dC (CDCl3): 215.9
(FeCO, d, 3JCP ¼ 30 Hz), 134.8 (CH3C N), 135.9, 135.3,
131.1, 129.6, 129.4, 129.3 (C6H5), 83.6 (C5H5), 16.9,
2
2
(PCH3, d, JCP ¼ 15 Hz), 17.4 (PCH3, d, JCP ¼ 15 Hz),
5.4 (CH3CN); KM (10ꢀ3 M in CH3CN, r.t.): 120 Xꢀ1
cm2 molꢀ1; Anal. Calc. for C22H19N2O6PFeW: C, 38.9;
H, 2.80; N, 4.1. Found: C, 39.1; H, 2.85; N, 4.3%.
2
(CDCl3; )30 ꢀC): 216.6 (FeCO, d, JCP ¼ 35 Hz) 201.1

A. Palazzi et al. / Journal of Organometallic Chemistry 689 (2004) 2324–2337
2333
4.3. Synthesis of complexes [Cp(CO)(L)Fe(NCCH3)]
[NCM(CO)5], [L ¼ PPh3, M ¼ Cr (3a); L ¼ CN-2,6-
Me2C6H3, M ¼ Cr (3c); L ¼ PPh3, M ¼ Mo, (4a); L ¼
CN-2,6-Me2C6H3, M ¼ Mo, (4c)]
g, 70%). IR (CH2Cl2) mmax (cmꢀ1): 2127w (CN), 2062m,
1974s, 1928vs, 1900sh (CO); NMR: dH (CDCl3): 7.6–7.2
(m, 15H, C6H5) 4.5 (5H, s, C5H5); dC (CDCl3): 217.3
2
1
(FeCO, d, JCP ¼ 30 Hz), 198.3 (WCOax, JCW ¼ 125
1
Hz), 195.5 (WCOeq, JCW ¼ 128 Hz), 168.6 (NCW,
The title saline compounds were prepared in the same
manner as reported for their tungsten homologues. (3a)
0.250 g, 60%, orange powder. IR (CH3CN) mmax (cmꢀ1):
2101w (CN), 2056m, 1985s, 1929vs, 1890sh (CO); NMR:
dH (CDCl3): 7.3–7.5 (m, 15H, C6H5) 4.7 (s, 5H, C5H5) 1.9
(s, 3H, CH3CN) dC (CD3CN): 221.5 (CrCOax) 217.4
(CrCOeq) 215.1 (FeCO, d, 2JCP ¼ 23 Hz) 134.7 (CH3CN)
132.2, 130.9 130.5 128.6 (C6H5), 83.7 (C5H5) 4.3
(CH3CN); KM (10ꢀ3 M in CH3CN, r.t.): 118 Xꢀ1 cm2
molꢀ1. Anal. Calc. for C32H23N2O6PFeCr: C, 57.3, H,
3.43, N, 4.2. Found: C, 58.1; H, 3.50; N, 4.4%. (3c) 0.471 g,
70%, orange powder. IR (CH3CN) mmax (cmꢀ1): 2155w,
2098vw (CN), 2052m, 2026s, 1928vs (CO); NMR: dH
(CDCl3): 7.3–7.1 (m, 3H, C6H3-2,6-(CH3)2), 5.1 (s, 5H,
C5H5), 2.5 (s, 6H, C6H3-2,6-(CH3)2), 2.3 (s, 3H, CH3CN);
dC (CD3CN): 213.4 (FeCO), 164.9 (CNC6H3(CH3)2),
134.9 (CH3C N), 135.3, 129.5, 128.1, 127.9, (CN
C6H3(CH3)2), 84.5 (C5H5), 17.9 (CNC6H3(CH3)2), 5.1
(CH3CN). Anal. Calc. for C23H17N3O6FeCr: C, 51.2, H,
3.15, N, 7.8. Found: C, 51.0; H, 3.20; N, 7.5%. (4a)0.322 g,
62%, orange powder. IR (CH3CN) mmax (cmꢀ1): 2102w
(CN), 2060m, 1989s, 1931vs, 1890(sh) (CO); NMR: dH
(CDCl3): 7.5–7.2 (m, 15H, C6H5), 4.71 (s, 5H, C5H5), 2.0
(s, 3H, CH3CN); dC (CD3CN): 216.9 (FeCO, d, 2JCP ¼ 28
Hz), 136.2 (CH3CN), 133.3, 133.1, 132.4, 131.8, 131.5,
129.3, 129.2 (C6H5), 84.7 (C5H5), 4.3 (C H3CN). Anal.
Calc. for C32H23N2O6FeMoP: C: 53.8, H: 3.22, N: 3.9.
Found: C, 54.0; H, 3.27; N, 4.0%. (4c) 0.312 g, 65%, or-
ange powder. IR (CH3CN) mmax (cmꢀ1): 2158w, 2100vw
(CN), 2060m, 2025s, 1929vs (CO); NMR: dH (CDCl3):
7.3–7.1 (m, 3H, C6H3-2,6-(CH3)2), 5.2 (s, 5H, C5H5), 2.5
(s, 6H, C6H3-2,6-(CH3)2), 2.4 (s, 3H, CH3CN); dC
(CD3CN): 214.1 (FeCO), 166.0 (CNC6H3(CH3)2), 135.6
(CH3C N), 136.0, 130.1, 128.8 128.6 (CNC6H3(CH3)2),
85.1 (C5H5), 18.6 (CNC6H3(CH3)2), 5.3 (CH3CN). Anal.
Calc. for C23H17N3O6FeMo: C, 47.3, H, 2.91, N, 7.2.
Found: C, 47.5; H, 2.95; N, 7.0%.
2JCW ¼ 96 Hz), 132.9, 132.3, 132.1, 130.0, 127.9, 127.6
(C6H5), 83.1 (C5H5). Anal. Calc. for C30H20NO6FePW:
C, 47.3; H, 2.63; N, 1.8. Found: C, 47.4; H, 2.70; N,
1.9%. Method (B): 0.030 g of Me3NO, dissolved in 5 ml
of CH2Cl2 were slowly added to a stirred solution of
CH2Cl2 (20 ml) containing 0.140 g (0.27.mmol) of
[Cp(CO)2FeNCW(CO)5] (5g), the preparation of which
has been reported elsewhere [8], and 0.150 gr (0.57
mmol) of PPh3. After 1 h the solvent was removed and
the residue, dissolved in CH2Cl2, was purified by alu-
mina filled column chromatography by eluting with a
Etp/CH2Cl2 (3:2, v/v) mixture. Compound 5a was ob-
tained as the first fraction (0.270 g, 50% yield). Suitable
crystals were grown by diffusion of diethyl ether into a
CH2Cl2 solution of pure 5a at )5 ꢀC.
4.4.2. Synthesis of [Cp(CO)(CN-Benzyl)FeNCW-
(CO)5] (5b)
By following method A, 0.300 g (0.6 mmol) of
[CpFe(CO)(CN-Benzyl)(thf)][O3SCF3] in 20 ml of
CH2Cl2 were slowly added to a suspension of 0.230 gr
(0.6 mmol) of Na[W(CO)5CN] in 20 ml of the same
solvent. After 30 m stirring, the reaction mixture was
filtered through Celite and chromatographed on an
alumina column. Elution with Etp/CH2Cl2 (2/1, v/v)
gave a red-orange fraction containing 5b (0.262 g, 60%).
Deep orange crystals suitable for X-ray analysis were
grown by slow diffusion of petroleum ether in a di-
chloromethane solution of pure 5b, IR (CH2Cl2) mmax
(cmꢀ1): 2187m, 2137w (CN), 2057w, 2005s, 1929vs,
1900sh (CO); NMR: dH (CDCl3): 7.4–7.2 (m, 5H,
C6H5), 4.7 (s, 5H, C5H5) 2.2 (CH2–C6H5); dC (CDCl3):
1
215.8 (FeC O), 200.0 (WCOax, JCW ¼ 125 Hz), 197.3
(WCOeq, 1JCW ¼ 127 Hz), 166.3 (NCW, 2JCW ¼ 96 Hz),
158.6 (CN-Benzyl), 132.6, 129.9, 129.4, 127.1 (C6H5),
83.5 (C5H5), 49.9 (CH2–C6H5). Anal. Calc. for
C20H12N2O6FeW: C, 39.0; H, 1.95; N, 4.5. Found: C,
39.3; H, 1.98; N, 4.7%.
4.4. Cyanide-bridged complexes
4.5. Synthesis of [Cp(CO)(PPh3)FeNCCr(CO)5] (6a),
[Cp(CO)(CN-2,6-Me2C6H3)FeNCCr(CO)5]
4.4.1. Synthesis of [Cp(CO)(PPh3)FeNCW(CO)5]
(5a)
(6c),
[Cp(CO)2FeNCCr(CO)5] (6g); [Cp(CO)(CN-2,6-
Me2C6H3)FeNCMo(CO)5] (7c) [Cp(CO)2FeNCMo-
(CO)5] (7g)
Method (A): To a suspension of 0.270 g (0.71 mmol)
of Na[W(CO)5(CN)] in 20 ml of CH2Cl2 were slowly
added 0.450 mg (0.71 mmol) of 1a dissolved in 20 ml
CH2Cl2. The reaction mixture was stirred at )30 ꢀC for
1hr and then filtered through a Celite pad to eliminate
NaO3SCF3. The solvent was evaporated under vacuum
and the residue was purified by alumina filled column
chromatography. Elution with a mixture of Etp/CH2Cl2
(2:1 v/v) gave a red-orange fraction containing 5a (0.378
The title compounds were prepared by following
method A adopted for their tungsten analogues, starting
from the cationic precursors such as [CpFe(CO)(L)(thf)]
[OSO2CF3] (L ¼ P(C6H5)3 (1a); CN-2,6-Me2C6H3 (1c);
CO (1g)) and the appropriate cyanoanions Na[M
(CO)5(CN)] (where M ¼ Cr, Mo). (6a) 0.183 g, 52%, dark

2334
A. Palazzi et al. / Journal of Organometallic Chemistry 689 (2004) 2324–2337
yellow microcrystalline powder. IR (CH2Cl2) mmax
(cmꢀ1): 2131w (CN), 2063w, 1976s, 1936vs; NMR: dH
(CDCl3): 7.4–7.6 (m, 15H, C6H5) 4.52 (C5H5); dC
(CDCl3): 219.7 (CrCOax), 218.7 (FeCO, d, 2JCP ¼ 30 Hz),
216.4 (CrCOeq), 182.1 (NCCr), 133.7–128.4 (C6H5), 84.1
(C5H5). Anal. Calc. for C30H20NO6CrFeP: C, 57.2; H,
3.18; N, 2.2. Found: C, 57.0; H, 3.12; N, 2.1%. (6c) 0.167 g,
40%, pale yellow microcrystalline powder. IR (CH2Cl2)
mmax (cmꢀ1): 2148s (CN), 2059w, 2008s, 1932vs, 1900sh
(CO); NMR: dH (CDCl3): 7.3–7.1 (m, 3H, C6H3-2,6-
(CH3)2), 4.9 (C5H5), 2.4 (s, 6H, C6H3-2,6-(CH3)2); dC
(CDCl3): 220.4 (CrCOax), 217.5 (CrCOeq), 215.2
(FeCO), 182.6 (NCCr), 169.1 (CNC6H3(CH3)2), 135.4,
129.2, 128.5, 128.3 (C6H3(CH3)2), 83.7 (C5H5), 18.9
(CNC6H3(CH3)2). Anal. Calc. for C21H14N2O6CrFe: C,
50.6; H, 2.81; N, 5.6. Found: C, 50.8; H, 2.79; N, 5.9%.
(6g) 0.229 g, 34%, orange microcrystalline powder. IR
(CH2Cl2) mmax (cmꢀ1): 2133w (CN), 2071m, 2057m,
2025m, 1935vs (CO); NMR: dH(CDCl3): 5.1 (C5H5); dC
(CDCl3): 219.7 (CrCOax), 216.7 (CrCOeq), 210.8
(FeCO), 182.7 (NCCr), 86.2 (C5H5). Anal. Calc. for
C13H5NO7CrFe: C, 39.5; H, 1.27; N, 3.5. Found: C, 39.7;
H, 1.28; N, 3.7%. (7c) 0.135 g, 71%, orange microcrys-
talline powder. IR (CH2Cl2) mmax (cmꢀ1): 2149w (CN),
2064m, 2008s, 1933vs (CO); NMR: dH (CDCl3): 7.3–7.1
(m, 3H, C6H3-2,6-(CH3)2), 4.9 (C5H5), 2.5 (s, 6H, C6H3-
2,6-(CH3)2); dC (CD3CN): 215.7 (FeCO), 209.6 (Mo-
COax) 205.2 (MoCOeq), 174.7 (NCMo), 134.9–127.6
(C6H3(CH3)2), 83.9 (C5H5), 17.7 (CNC6H3(CH3)2).
Anal. Calc. for C21H14N2O6CrMo: C, 46.8; H, 2.60; N,
5.2. Found: C, 47.0; H, 2.64; N, 5.4%. (7g) 0.287 g, 68%,
orange microcrystalline powder. IR (CH2Cl2) mmax
(cmꢀ1): 2132w (CN), 2072m, 2062m 2024m, 1937vs (CO);
NMR: dH (CDCl3): 5.1 (C5H5). dC (CDCl3): 210.6
(FeCO), 209.4 (MoCOax), 205.1 (MoCOeq), 177.8
(NCMo), 86.2 (C5H5). Anal. Calc. for C13H5NO7CrMo:
C, 25.5; H, 1.14; N, 3.2. Found: C, 25.6; H, 1.16; N, 3.0%.
L ¼ CN-2,6-Me2C6H3 (yield: 55%), IR (CH2Cl2) mmax
(cmꢀ1): 2145s, 2105m (CN), 2000s (CO).
4.7. Synthesis of [Cp(CO)(PPh3)FeCNW(CO)5] (8a)
A solution of 0.500 g (1.14 mmol) of [CpFe
(CO)(PPh3)(CN)] in 30 ml of thf was treated with a
slight excess of W(CO)5(thf), and the reaction mixture
was kept at room temperature, with stirring, for 24 h.
Evaporation to dryness afforded a residue which was
purified by alumina filled column chromatography.
Excess W(CO)6 was removed eluting with petroleum
ether and the target product 8a was obtained as a yellow
powder (0.304 g, 35%) after elution with Etp/CH2Cl2 (4/
1, v/v). Yellow crystal were obtained by slow diffusion of
petroleum ether in a dichloromethane solution of pure
8a. IR (CH2Cl2) mmax (cmꢀ1): 2129w (CN), 2072w,
1980m, 1928vs, 1878m (CO); NMR: dH (CDCl3): 7.6–
7.2 (m, 15H, C6H5), 4.5 (C5H5); dC (CDCl3): 217.3
2
(FeCO, d, JCP ¼ 30 Hz), 201.9 (WCOeq), 198.2
2
(WCOax), 152.3 (FeCN, d, JCP ¼ 30 Hz), 135.1 134.5,
133.6, 131.7 129.6, 129.5 (C6H5), 85.1 (C5H5). Anal.
Calc. for C30H20NO6CrFePW: C, 49.3; H, 2.63; N, 1.9.
Found: C, 49.1; H, 2.65; N, 2.1%.
4.8. Synthesis of [Cp(CO)(CN-Benzyl)FeCNW(CO)5]
(8b)
0.210 g (0.72 mmol) of [CpFe(CO)(CNCH2C6H5)
(CN)], dissolved in 20 ml of THF, were added of a
twofold excess of W(CO)5(THF) and the resulting
mixture was left with stirring at r.t. After 24 h, I.R.
spectrum of the reaction mixture still showed a large
presence of the starting reagents together with the ex-
pected bands due to compound 8b. Further W(CO)5(thf)
(five equivalents), freshly prepared by irradiation of
W(CO)6 in THF, was added in small portions. After two
days the reaction was stopped and the solvent stripped
out under vacuum. The excess W(CO)6 was removed by
sublimation and the resulting residue was purified by
alumina filled column chromatography. Elution with
Etp afforded a first fraction containing W(CO)6. Suc-
cessive elution with CH2Cl2 gave a yellow fraction
containing compound 8b. A further fraction containing
the starting complex [CpFe(CO)(CNCH2C6H5)(CN)]
was collected by elution with CH2Cl2/CH3CN (1/1, v/v).
Compound 8b (0.26g, 58%) was obtained as yellow
crystals by slow diffusion of petroleum ether in a di-
chloromethane solution of pure 8b. IR (CH2Cl2) mmax
(cmꢀ1): 2202m, 2135w (CN), 2068w, 2011s, 1981m,
1911vs, 1872sh (CO). NMR: dC (CD3CN): 214.5
(FeCO), 201.6 (WCOax), 198.2 (WCOeq), 157.4
(CNBenzyl), 148.1 (CNW), 132.8, 129.6, 129.1 127.0
(C6H5), 83.9 (C5H5), 49.7 (CH2). Anal. Calc. for
C20H12N2O6FeW: C, 39.2; H, 1.96; N, 4.6. Found: C,
39.1; H, 2.00; N, 4.5%.
4.6. Synthesis of [Cp(CO)(L)Fe(CN)] (L ¼ PPh3;
CN-Benzyl; CN-2,6-Me2C6H3)
L ¼ PPh3: A solution of 0.820 g (4.0 mmol) of
CpFe(CO)2CN in 50 ml of toluene was added of a slight
excess of PPh3 1.10 g (4.2 mmol) and of a catalytic
amount of [CpFe(CO)(l-CO)]2. The reaction mixture
was stirred at reflux for 2 h. Evaporation to dryness
afforded a residue which was purified by alumina filled
column chromatography. Elution with Etp/CH2Cl2 (3/1,
v/v) gave a first fraction containing [CpFe(CO)(l-CO)]2,
then the eluant was switched to pure CH2Cl2 and the
title compound was recovered (1.40 g, 63%). IR
(CH2Cl2) mmax (cmꢀ1): 2097s (CN), 1969s (CO). The
neutral precursors with L ¼ Benzyl-NC; and L ¼ CN-
2,6-Me2C6H3 were prepared in the same manner. Their
properties are: L ¼ CN-Benzyl (yield: 60%), IR
(CH2Cl2) mmax (cmꢀ1): 2181vs, 2105m (CN), 1989s (CO);

A. Palazzi et al. / Journal of Organometallic Chemistry 689 (2004) 2324–2337
2335
4.9. Synthesis of [Cp(CO)(PPh3)FeCNCr(CO)5] (9a)
and [Cp(CO)(CN-2,6-Me2C6H3)FeCNCr(CO)5] (9c)
petroleum ether into dichloromethane solutions of the
pure compounds. Diffraction intensities were collected
by the x scan method at room temperature on a
graphite monochromated Enraf-Nonius CAD-4 dif-
fractometer and reduced to Fo2 values. Structure models
were obtained by direct methods and refined by full-
matrix least-squares calculations. For all computations
SHELXS-86 and SHELXL-93 [26] were employed. No
decay correction was needed, while absorption correc-
tion was done by w-scan methods for all compounds.
Thermal vibrations for all non-H atoms were treated
anisotropically. All H atoms were found in difference
Fourier maps and refined with constraints (C–H ¼ 0.96
The procedure used to prepare these compounds is
the same adopted for their tungsten analogues, involv-
ing [CpFe(CO)(L)(CN)] (L ¼ PPh3; CN-2,6-Me2C6H3)
and [Cr(CO)5(thf)] as starting materials. Their physical
and spectroscopic properties are: (9a) 0.183 g, 52%, dark
yellow microcrystalline powder. m.p. 163–165 ꢀC (dec.).
IR (CH2Cl2) mmax (cmꢀ1): 2135w (CN), 2069w, 1980s,
1937vs, 1884sh (CO). NMR: dH (CDCl3): 7.6–7.4 (m,
15H, C6H5), 4.5 (s, 5H, C5H5); dC (CD3CN): 219.10
2
(CrCOax), 217.2 (FeCO, d, JCP ¼ 30 Hz), 214.6
2
ꢀ
(CrCOeq), 155.5 (FeCN, d, JCP ¼ 30 Hz), 128.20–
A). Cyclopentadienyl rings were treated as rigid bodies.
133.40 (C6H5), 84.5 (C5H5). Anal. Calc. for
C30H20NO6CrFeP: C, 57.2; H, 3.18; N, 2.2. Found: C,
57.4; H, 3.15; N, 2.1%.
Final difference Fourier maps showed residual peaks
ꢀꢀ3
lower than 0.7 e A in all the structures in the prox-
imity of the W atom. Table 3 reports the experimental
parameters of data collection and refinement for all
compounds. Compounds 5a and 8a are strictly isomor-
phous. In order to check the correct location of the N
and C atoms in the CBN moiety for all compounds and
especially 2a, where it had to be discerned from the CO
ligands, models were refined with inverted location of
the atomic species involved. As a result, for all the
wrong structural models the R factors increased signif-
icantly and the thermal ellipsoids of the mislabelled at-
(9c) 0.167 g, 40%, pale yellow microcrystalline pow-
der, m.p.: 107–109 ꢀC. IR (CH2Cl2) mmax (cmꢀ1): 2153m,
2138m (CN), 2067w, 2006s, 1932vs, 1879sh (CO); NMR:
dH (CDCl3): 7.3–7.1 (m, 3H, C6H3-2,6-(CH3)2), 4.9
(C5H5) 2.4 (s, 6H, C6H3-2,6-(CH3)2); dC (CD3CN):
219.7 (CrCOax), 214.8 (CrCOeq), 214.4 (FeCO), 168.5
(CN-2,6-Me2C6H3), 149.6 (CNCr), 134.8–127.7 (C6H3
(CH3)2), 84.05 (C5H5), 17.60 (CNC6H3(CH3)2). Anal.
Calc. for C21H14O6N2FeCr: C, 50.6; H, 2.81; N, 5.6.
Found: C, 50.8; H, 2.90; N, 5.3%.
€
oms became clearly unreasonable. Extended-Huckel
molecular orbital calculations [24] were carried out on
the experimental structures of 2a, 5a and 8a using the
modified Wolfberg–Helmholz formula [27]. Standard
atomic parameters were used for C, O, N and H, while
those for Fe and W were taken from the literature
4.9.1. X-ray crystallography and extended-H€uckel calcu-
lations
Crystals of 2a, 5a, 8a and 8b suitable for structural
studies were grown by slow diffusion of diethyl ether or
Table 3
Crystal data and experimental details for 2a, 5a, 8a and 8b
2a
5a
8a
8b
Formula
T (K)
C32H23FeN2O6W
293
C30H20FeNO6PW
293
Triclinic
C30H20FeNO6PW
293
Triclinic
C20H12FeN2O6W
293
Monoclinic
Crystal system
Space group
Monoclinic
P21=n
14.062(2)
7.639(1)
29.790(4)
90
ꢁ
ꢁ
P1
P1
P21=n
ꢀ
a (A)
10.345(2)
12.087(2)
12.656(2)
89.75(2)
106.91(3)
107.32(2)
1439(1)
2
10.366(2)
12.031(2)
12.651(2)
89.46(2)
106.71(2)
108.22(3)
1429(1)
2
11.084(2)
15.164(3)
12.857(2)
90
ꢀ
b (A)
ꢀ
c (A)
a (ꢀ)
ꢂ (ꢀ)
c (ꢀ)
V (A )
Z
101.88(3)
90
102.58(2)
90
3
ꢀ
3131(1)
4
1568
2109(1)
4
1176
F ð000Þ
740
740
ꢀ
k (Mo Ka) (A)
0.71069
4.09
2–25
0.71069
4.44
2–30
0.71069
4.63
2–30
0.71069
5.96
2–30
l (Mo Ka) (mmꢀ1
h Range (ꢀ)
Octants explored
)
ꢄh; þk; þl
5585
ꢄh; ꢄk; þl
8723
4325
ꢄh; ꢄk; þl
8655
5831
ꢄh; þk; þl
6615
6133
Measured reflections
Unique reflections used in the refinement 2848
Number of refined parameters
Goodness-of-fit on F 2
R1 (on F, I > 2rðIÞ)
wR2 (on F 2)
380
361
1.002
367
1.006
269
1.083
1.004
0.035
0.094
0.030
0.110
0.040
0.117
0.029
0.087

2336
A. Palazzi et al. / Journal of Organometallic Chemistry 689 (2004) 2324–2337
(b) Y. Obora, T. Ohta, C.L. Stern, T.J. Marks, J. Am. Chem. Soc.
119 (1997) 3745;
[28,29]. A self-consistent charge calculation was per-
formed assuming a quadratic dependence of Hii on
charge.
(c) D.G. Fu, J. Chen, X.S. Tan, L.J. Jiang, S.W. Zhang, P.J.
Zheng, W.X. Tang, Inorg. Chem. 36 (1997) 220;
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(f) J. Larionova, M. Gross, M. Pilkington, H. Andres, H. Stoeckli-
5. Supplementary material
€
Evans, H.U. Gudel, S. Decurtins, Angew. Chem., Int. Ed. Engl.
39 (2000) 1605.
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 230991, 230992, 230993,
230994 for compounds 2a, 5a, 8a and 8b, respectively.
Copies of the data can be obtained, free of charge, from
The Director CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (fax: +44-1223-336033 or e-mail: de-
posit@ccdc.cam.ac.uk).
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Acknowledgements
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Gatteschi, Angew. Chem., Int. Ed. Engl. 35 (1996) 1947;
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The authors thank the Ministero dell’Istruzione,
ꢃ
dell’Universita e Ricerca (MIUR) for financial support
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A.C. Loyns, A.G. Orpen, G.M. Rosair, G.H. Worth, J. Chem.
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to the National Project ‘New strategies for the control of
reactions: interactions of molecular fragments with
metallic sites in unconventional species’.
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