[(η5-C5Me5)Fe(Ph2PCH 2 CH2CH2PPh2)][SO3CF3 ] (see abstract)

Article abstract of DOI:10.1021/om0108245

The iron chloro complex Cp*(dppp)FeCl (Cp* = pentamethylcyclopentadienyl, dppp = 1,3-bis(diphenylphosphino)propane; 2) was prepared from FeCl₂(dppp) and Cp*Li in 85% yield. The air-stable compound 2 was characterized by IR-FT, ¹H, ³¹P, and ¹³C NMR, cyclic voltammetry (CV), and X-ray crystal analysis. The experimental data indicate that this complex possesses the same electronic properties as its homologue Cp*(dppe)FeCl (dppe = 1,2-bis(diphenylphosphino)ethane; 2′), but shorter distances between the chlorine atom and the hydrogen atoms of the dppp ligand give rise to through-space interactions. The hydride 3 was obtained by treatment of the chloro derivative 2 with LiAlH₄ (95%). The changes in the Fe-H bond stretching and redox potential induced by replacement of dppe by dppp is in agreement with the existence of two conformers for the iron hydrides 3 and 3′. The 16-electron species [Cp*(dppp)Fe][OSO₂CF₃] (4[OTf]) is obtained by treatment of 3 with methyl triflate in diethyl ether (82%). The pseudo-C_2v conformation of 4[OTf] is established by an X-ray analysis. Complex 4[OTf] possesses a triplet ground state, as shown by the magnetic susceptibility measurements, ¹H NMR, and M?ssbauer spectroscopy. The UV-vis data obtained for 4[OTf] and its homologue 4′[PF₆] suggest that the increase of the bite angle of the bis-phosphine should produce a decrease of the HOMO-LUMO gap of the triplet ground state with a pseudo-C_2v symmetry.

Full text of DOI:10.1021/om0108245

Organometallics 2002, 21, 1341-1348
1341
[(η5-C5Me5)F e(P h 2P CH2CH2CH2P P h 2)][SO3CF 3], a Sta ble
16-Electr on Com p lex w ith a Coor d in a tin g Cou n ter a n ion
a n d w ith ou t Agostic In ter a ction : Th e Dr a m a tic Role of a
Tr ivia l Meth ylen e Gr ou p
Gilles Argouarch,† Paul Hamon,† Lo¨ıc Toupet,‡ J ean-Rene´ Hamon,† and
Claude Lapinte*,†
Organome´talliques et Catalyse: Chimie et Electrochimie Mole´culaires, UMR CNRS 6509,
Institut de Chimie de Rennes, and Groupe Matie`re Condense´e et Mate´riaux, UMR 6626,
Universite´ de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France
Received September 13, 2001
The iron chloro complex Cp*(dppp)FeCl (Cp* ) pentamethylcyclopentadienyl, dppp ) 1,3-
bis(diphenylphosphino)propane; 2) was prepared from FeCl2(dppp) and Cp*Li in 85% yield.
The air-stable compound 2 was characterized by IR-FT, 1H, 31P, and 13C NMR, cyclic
voltammetry (CV), and X-ray crystal analysis. The experimental data indicate that this
complex possesses the same electronic properties as its homologue Cp*(dppe)FeCl (dppe )
1,2-bis(diphenylphosphino)ethane; 2′), but shorter distances between the chlorine atom and
the hydrogen atoms of the dppp ligand give rise to through-space interactions. The hydride
3 was obtained by treatment of the chloro derivative 2 with LiAlH4 (95%). The changes in
the Fe-H bond stretching and redox potential induced by replacement of dppe by dppp is in
agreement with the existence of two conformers for the iron hydrides 3 and 3′. The 16-
electron species [Cp*(dppp)Fe][OSO2CF3] (4[OTf]) is obtained by treatment of 3 with methyl
triflate in diethyl ether (82%). The pseudo-C2v conformation of 4[OTf] is established by an
X-ray analysis. Complex 4[OTf] possesses a triplet ground state, as shown by the magnetic
susceptibility measurements, 1H NMR, and Mo¨ssbauer spectroscopy. The UV-vis data
obtained for 4[OTf] and its homologue 4′[P F 6] suggest that the increase of the bite angle of
the bis-phosphine should produce a decrease of the HOMO-LUMO gap of the triplet ground
state with a pseudo-C2v symmetry.
In tr od u ction
all the properties of this iron fragment, its ability to
provide 18-electron paramagnetic complexes, namely
[Cp*(dppe)Fe(OCMe2)][SO3CF3]8 and [Cp*(dppe)Fe-
(OSO2CF3)],1 remains among the most surprising fea-
ture of this family of compounds and recent DFT
calculations could not explain such an intriguing fea-
ture.9
The chemistry of the sterically crowded and electron-
rich Cp*(dppe)Fe auxiliary is particularly rich. Indeed,
this unit is stable as five-coordinate iron complexes1 and
accommodates six- and seven-coordinate derivatives,
which were isolated as iron(0),2 iron(I),1 iron(II), iron-
(III), and iron(IV) complexes with a number of valence
electrons ranging from 16 to 19.2-5 This iron building
block has also shown very attractive features for the
elaboration of organometallic molecular wires.6,7 Among
The unique behavior of the Cp*(dppe)Fe fragment
results from a subtle balance of the steric, electronic,
and geometric environment of the iron center provided
by the Cp* and dppe ligands. In particular, the dppe,
as all chelates, possesses three major characteristics:
electron-donating ability, steric properties, and a rigid
P-M-P angle often called “bite angle”. In this paper
we investigate the effect of the bite angle of the dppp
ligand by substituting dppe by dppp. We focus our effort
in the determination of the modification of the steric
and electronic properties of the iron(II) complexes
induced by the introduction of an extra methylene
fragment between the two phosphorus atoms of the
bidentate phosphine. We report here (i) the synthesis
of the entry Cp*(dppp)FeCl compound (2) and its X-ray
* To whom correspondence should be addressed. E-mail: lapinte@univ-
rennes1.fr.
† Organome´talliques et Catalyse: Chimie et Electrochimie Mole´cu-
laires.
‡ Groupe Matie`re Condense´e et Mate´riaux.
(1) Hamon, P.; Toupet, L.; Hamon, J .-R.; Lapinte, C. Organometal-
lics 1996, 15, 10-12.
(2) Hamon, P.; Hamon, J .-R.; Lapinte, C. J . Chem. Soc., Chem.
Commun. 1992, 1602-1603.
(3) Roger, C.; Hamon, P.; Toupet, L.; Rabaaˆ, H.; Saillard, J .-Y.;
Hamon, J .-R.; Lapinte, C. Organometallics 1991, 10, 1045-1054.
(4) Hamon, P.; Toupet, L.; Hamon, J .-R.; Lapinte, C. Organometal-
lics 1992, 11, 1429-1431.
(5) (a) The´pot, J .-Y.; Guerchais, V.; Lapinte, C.; Toupet, L. Orga-
nometallics 1993, 12, 4843-4853. (b) Denis, R.; Toupet, L.; Paul, F.;
Lapinte, C. Organometallics 2000, 19, 4240-4251.
(6) (a) Paul, F.; Lapinte, C. Coord. Chem. Rev. 1998, 178-180, 427-
505. (b) Le Narvor, N.; Toupet, L.; Lapinte, C. J . Am. Chem. Soc. 1995,
117, 7129-7138. (c) Coat, F.; Lapinte, C. Organometallics 1996, 15,
477-480. (d) Guillemot, M.; Toupet, L.; Lapinte, C. Organometallics
1998, 17, 1928-1930.
(7) Paul, F.; Meyer, W. E.; Toupet, L.; J iao, H.; Gladysz, J . A.;
Lapinte, C. J . Am. Chem. Soc. 2000, 122, 9405-9414.
(8) Hamon, P.; Toupet, L.; Hamon, J .-R.; Lapinte, C. J . Chem. Soc.,
Chem. Commun. 1994, 931-932.
(9) Costuas, K.; Saillard, J .-Y. Organometallics 1999, 18, 2505-
2512.
10.1021/om0108245 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 03/07/2002

1342 Organometallics, Vol. 21, No. 7, 2002
Argouarch et al.
Sch em e 1
Ta ble 1. Com p a r ison of th e Cyclic Volta m m etr y
Da ta for Selected Com p lexes in th e d p p p a n d d p p e
Ser iesa
characterization which reveals the steric modification
around the iron center, (ii) the conversion of 2 into the
hydride Cp*(dppp)FeH complex (3), which presents an
unexpected change in the Fe-H bonding as shown by
IR-FT spectroscopy, (iii) the synthesis and the X-ray
analysis of the 16-electron species [Cp*(dppp)Fe][SO3-
CF3] (4[OTf]), which coordinates neither the triflate
anion nor the acetone, (iv) a full spectroscopic charac-
terization of the paramagnetic complex 4, including
UV-vis spectroscopy, which demonstrates that the
HOMO-LUMO gap in the 16-electron species decreases
when the P-Fe-P angle increases, and (v) the basic
reactivity of the coordinatively unsaturated complex 4-
[OTf]. Comparison between the compounds 2, 3, 4-
[OTf], 5, and 6 and their homologues of the dppe series,
denoted 2′, 3′, 4′[P F 6], 5′, and 6′, respectively, evidences
the role of the bite angle of the diphosphine in the
properties of these iron complexes.
Eox(X/X+)
Ered(X/X-)
compd
dppp
dppe
dppp
dppe
2/2′
3/3′
-0.059
-0.274
0.321
-0.058
-0.187
0.26b
4[OTf]/4′[P F 6]
5/5′
-0.928
-0.71
0.604
0.600
a
Conditions: measurements carried out in the range +1.2-
1.2 V vs SCE; THF/0.1 M [Bu4N][PF6]; T ) 20 °C; Pt electrode;
0.1 V/s; V vs SCE; Cp2Fe0/+ couple used as internal standard at
0.560 V vs SCE.28 b From ref 1 after correction (data were reported
for the Cp2Fe/Cp2Fe0/+ couple used as an internal standard at 0.54
V vs SCE).
Resu lts a n d Discu ssion
1. Syn th esis a n d Ch a r a cter iza tion of Cp *(d p p p )-
F eCl (2). As outlined in Scheme 1, the iron chloro
complex 2 was synthesized via a protocol similar to the
one developed for the related Cp*(dppe)FeCl (2′) previ-
ously described.3 The complex (dppp)FeCl2 (1), which
is air stable as a solid for extended periods, was reacted
with Cp*Li in THF at 20 °C. Workup gave 2 as
analytically pure black microcrystals in 85% yield. The
1H chemical shifts of complex 2 are very similar to those
of the related compound 2′ of the dppe series3 (see
Experimental Section). However, we note that the
introduction of an extra methylene group in the alkyl
chain which links the two phosphorus atoms of the dppp
ligand produces a downfield shift of the 31P resonance
from δ 91.6 (observed for 2′) to δ 50.9. Moreover,
F igu r e 1. Molecular structure of Cp*(dppp)FeCl (2). Non-
hydrogen atoms are represented by 50% probability ther-
mal ellipsoids.
are given in Table 3. The complex 2 crystallizes as its
homologue 2′ in the triclinic crystal system.3 On the
whole, the bond distances and angles are typical for
piano-stool organoiron(II) complexes. Nevertheless, slight
perturbations of the structure are induced by the
presence of a third methylene group between the two
phosphorus atoms. With respect to complex 2′, the
structure of compound 2 shows a weak shortening of
the iron C5-ring centroid distance of ca. 0.02 Å, an
increase of ca. 0.035 Å in the Fe-P bond distances,
whereas the Fe-Cl bond length remains unchanged.
The major difference between these two structures deals
with an increase of 7° of the P1-Fe-P2 angle in 2. The
metallacycle defined by the dppp ligand and the metal
presents a chair conformation typical of six-membered
cycles. Two phenyl groups and the chlorine atom occupy
the axial positions, whereas the two remaining phenyl
substituents and the Cp* ligand are located in the
equatorial sites. This chair conformation is probably
quite dominant in solution, because its inversion should
1
whereas the H resonance for the methylene protons of
the complex 2′ are observed in the range δ 1.50-2.00,
a signal corresponding to two protons is observed at δ
2.54 ppm in the case of complex 2. This upfield shift
could be due to 1,3-diaxial interactions between hydro-
gen atoms of the methylene groups bound to the
phosphorus atoms and the chlorine (see below). In the
limit of the accuracy of the cyclic voltammetry measure-
ment, both complexes 2 and 2′ possess the same revers-
ible one-electron-oxidation potential (Table 1).
2. X-r a y Cr ysta l Str u ctu r e of 2. Monocrystals of 2
were grown by slow diffusion of pentane in a concen-
trated CH2Cl2 solution, and the solid-state structure
could be solved (Figure 1). The X-ray data are listed in
Table 2, while the relevant bond angles and distances

[(η5-C5Me5)Fe(Ph2PCH2CH2CH2PPh2)][SO3CF3]
Organometallics, Vol. 21, No. 7, 2002 1343
Ta ble 2. Cr ysta llogr a p h ic Da ta for [Cp *(d p p p )F eCl]‚CH2Cl2 (2‚CH2Cl2) a n d
[Cp *(d p p p )F e][OSO2CF 3]‚(CH3)2CO (4[OTf] ‚(CH3)2CO)
4[OTf] ‚(CH3)2CO
2‚CH2Cl2
293 K
293 K
110 K
FeP2C37H41(CF3SO3)‚C3H6O
mol formula
mol wt
cryst syst
space group
cell dimens
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
FeP2C37H41Cl‚CH2Cl2
723.86
triclinic
P1h
810.64
810.64
triclinic
P1h
monoclinic
P21/m
10.500(2)
11.830(2)
16.256(2)
79.84(1)
72.42(1)
66.83(2)
1765.8(6)
2
11.0111(4)
15.4655(6)
12.7913(4)
10.8283(4)
12.6358(6)
15.2854(4)
88.171(2)
113.659(2)
67.140(2)
1925.4(1)
2
113.659(2)
1995.2(1)
2
1.349
0.564
Z
d
calcd(294 K) (g/cm3)
1.361
0.771
1.398
0.585
abs coeff (mm-1
)
F(000)
756
848
848
cryst dimens (mm)
diffractometer
0.44 × 0.37 × 0.35
0.40 × 0.35 × 0.33
0.40 × 0.35 × 0.33
CAD4
Nonius Kappa CCD
radiation (Å)
Mo KR, 0.710 73
data collection method
measmt tmax (s)
index range (h,k,l)
θ range (deg)
decay of stds (25), %
no. of rflns measd
no. of indep rflns
no. of obsd data, I > 2σ(I)
no of variables
R
ω/2θ
60
20
20
0-13, -13 to +15,-19 to +20
54
0.4
0-14, 0-20, -16 to +14
0-14, -14 to +16, -20 to +20
55
55
7684
5997
5997
398
0.042
0.113
1.019
0.61, -0.82
4746
3562
3562
25 134
9176
7773
238
470
0.086
0.252
1.183
1.44, -1.38
0.092
0.259
0.986
3.8, -1.07
Rw
GOF
largest diff peak and hole, (e Å-3
)
Ta ble 3. Com p a r ison of Key Dista n ces (Å) a n d
An gles (d eg) for Cp *F e(d p p p )Cl (2), Cp *F e(d p p e)Cl
(2′),3 [Cp *F e(d p p p )][O3SCF 3] (4[OTf]), a n d
[Cp *F e(d p p e)][P F 6] (4′[P F 6])1
Moreover, we note that the distances between the
chlorine atom and the axial methylene protons of the
P-bound methylene groups are as short as 2.72 Å, which
should give rise to through-space interactions and
explain the upfield shift observed for the methylene
2/2′
4[OTf]a/4′[P F 6]
1
distance/angle
dppp
dppe
dppp dppe
resonance in the H NMR spectrum.
3. Syn th esis a n d Ch a r a cter iza tion of Cp *(d p p p )-
F eH (3) a n d [Cp *(d p p p )F eH][P F 6] (3+). The hydride
3 was readily obtained by treatment of the chloro
derivative 2 with a small excess of LiAlH4 (1.2 equiv)
in THF at low temperature. After in situ destruction of
the alanes by successive addition of CH3OH and CH2-
Cl2 (see Experimental Section), workup provides 3 as a
pure and thermally stable orange powder in 95% yield.
This reaction does not present any significant difference
from that previously studied in the dppe series.3 As
already noted for 2 and 2′, the 1H and 13C NMR chemical
shifts observed for 3 are quite similar to those reported
for its homologue of the dppe series 3′. We note that a
small upfield shift of 0.35 ppm for the hydride resonance
and the 31P resonance observed at δ 75.6 ppm strongly
differs from that of 3′ located at δ 107.9.
Surprisingly, the replacement of the dppe by the dppp
ligand produces a large decrease of the Fe-H bond
stretching (∆ν ) 69 cm-1). A possible explanation for
this feature, which reveals an unexpected change in the
Fe-H bonding, can be found in the existence of two
different conformers for 3 (3A and 3B, Scheme 2), as
recently proposed for 3′ on the basis of DFT calculations
on the model complex CpFe(dpe)H (3H).10 One of the
Fe-P1
Fe-P2
2.2406(8) 2.210(1) 2.2737(11) 2.126(3)
2.2388(8) 2.197(1) 2.2656(11) 2.148(3)
Fe-Cp*(centroid) 1.746(3)
1.768(4) 1.802(3)
1.722(4)
Fe-X
2.3463(8) 2.346(1) 8.173b
P1-Fe-P2
P1-Fe-Cl
P2-Fe-Cl
Rc
92.02(3)
86.80(3)
88.75(3)
84.98(5) 95.62(6)
86.03(4)
87.23(4)
86.87(8)
178.0
175.2
θc
89.1(2)
a
b
Data obtained at 110 K. X ) closest oxygen atom of the
triflate anion. c See text for the definition of the angle.
produce strong 1,3-diaxial interactions between the
bulky C5Me5 ligand and axial methylene protons.
Interestingly, the opening of the P1-Fe-P2 angle in
the dppp series induces significant modification of the
steric environment around the metal center. Indeed,
comparison of 2 and 2′ clearly shows that the metal
center and the chlorine atom are more sterically crowded
in 2 than in 2′. In particular, the two phenyl rings of
the dppp in equatorial positions are very close to the
chlorine. The through-space distances between their
ortho carbon atoms (C25 and C33) and the chlorine atom
are as short as 3.3 Å. In the complex 2′, there is more
room around chlorine, and as a result, the through-space
shortest carbon-chlorine distance is 3.5 Å. Such a steric
congestion could have an effect on the reactivity and
the stability of the complex in the Cp*(dppp)Fe series.
(10) Tilset, M.; Fjeldahl, I.; Hamon, J .-R.; Hamon, P.; Toupet, L.;
Saillard, J .-Y.; Costuas, K.; Haynes, A. J . Am. Chem. Soc. 2001, 123,
9984-10000.

1344 Organometallics, Vol. 21, No. 7, 2002
Argouarch et al.
Sch em e 2
filtration, this solid material is thermally stable, but air
sensitive. Recrystallization from an acetone solution by
addition of pentane afforded the 16-electron species
[Cp*(dppp)Fe][OSO2CF3] (4[OTf]), isolated as the tri-
flate salt in 82% yield. The IR spectrum of 4[OTf] shows
three well-defined absorption bands at 1273, 1159, and
1029 cm-1. Bands in this range of frequencies can be
observed either for triflate coordinated at a metal center
or for ionic free triflate anion.11,12 Note that these bands
are also observed in the spectra of the compounds 5 and
6 (see below). More characteristic of a noncoordinated
triflate anion is the absence of the sulfonyl stretching
conformers, denoted HA, presents a symmetry close to
Cs and adopts a three-legged piano-stool geometry
comparable to those observed for halide complexes such
as 2 and 2′. In the other one, named HB, the geometry
can be idealized by considering a four-legged piano-stool
complex in which a vacant site occupies the fourth leg.
In this conformer, the P1-Fe-P2 plane is much closer
to being perpendicular to the plane of the C5 ring of the
Cp* ligand. In the case of 3H, HB is more stable than
HA by 0.10 eV and the νFe-H stretching frequencies were
computed at 1892 and 1876 cm-1 for HA and HB,
respectively. In the case of 3, the presence of the vacant
site and its relative orientation with respect to the dppp
ligand should minimize the steric interactions in the
conformer 3B. As a consequence, the conformer B could
be more favored in 3 than in 3′. The computed Fe-H
bond stretching being smaller in HB than in HA,10 it
should result in a decrease of the experimental νFe-H
when the dppe is replaced by the dppp, as it is
experimentally observed.
The theory also predicts that the oxidized complex
3H+ does not exist with a Cs symmetry, but only as a
four-legged piano-stool conformer.10 Therefore, one can
expect that the νFe-H frequencies in the oxidized com-
plexes 3+ and 3′+ should be closer than in the reduced
forms 3 and 3′, and to verify this assumption, 3+ was
prepared. The initial scan in the cyclic voltammogram
of the complex 3 is characterized by a reversible one-
electron process with a current ratio (ip /ip ) of unity.
The anodic and cathodic peak separation (Epc - Epa) is
0.100 V in THF with a scan rate of 0.1 V/s. The
thermodynamic oxidation potential of 3 is E° ) -0.273
V vs SCE. It appears 0.087 V more negative that its
relative 3′, which means that 3 is more easily oxidized
than 3′ (Table 1).4 Possibly, the oxidation takes place
at the less stable isomer HA and the more negative
redox potential observed for the oxidation of the iron
hydride in the dppp series suggests that the HA
conformer should be less stable in this series than in
the dppe one.
mode above 1300 cm-1 13
observed in the IR spectrum of the [Cp*(dppe)Fe(OSO2-
CF3)] (4′-OTf) complex at 1305 cm-1 12,14
.
In contrast, such a feature was
.
The triflate anion was definitely demonstrated to be
not coordinated to the metal center by an X-ray crystal-
lographic analysis. Monocrystals of 4[OTf]‚(CH3)2CO
were grown by slow diffusion of pentane in a concen-
trated acetone solution, and the crystal structure was
determined at 293 and 110 K, as outlined in Table 2
and Figure 2. Key distances and angles are given in
Table 3. The complex 4[OTf]‚(CH3)2CO crystallizes in
the monoclinic crystal system and in the P21/m space
group. A phase transition occurs upon cooling, and the
molecule is found in the triclinic crystal system and P1h
space group at 110 K. On the whole, the molecule
presents the same geometric characteristics in both
structures. At 293 K, the triflate anion was found
disordered between two symmetric positions with re-
spect to the plane of symmetry of the complex. In
contrast, the triflate anions occupy well-defined posi-
tions of the unit cell in the structure recorded at 110 K.
The reversibility of the phase transition was established
by a new determination of the unit cell parameters after
warming up the crystal to room temperature (293 K).
The structure of 4[OTf] strongly contrasts with that
of the previously reported triflate complex [Cp*(dppe)-
Fe(OSO2CF3)] (4′-OTf).1 Indeed, the complex 4[OTf]
does not present a pseudo-octahedral geometry, and the
shortest iron-oxygen distance of 8.17 Å clearly shows
that neither the triflate anion nor acetone is coordinated
to the metal. General features, such as the formally
trigonal-bipyramidal geometry (hybridization dsp3) at
the metal, are in accord with a formal 16-electron
complex. The X-ray structures show a molecule close to
C2v symmetry with two almost equivalent phosphorus
atoms. The angle R, defined by the ring centroid, the
Fe atom, and the middle of the P1-P2 vector (R ) 178°),
and the dihedral angle θ, formed by the plane of the
Cp* ligand and the plane defined by the three atoms
P1, Fe, and P2 (θ ) 89.1(2)°), are close to the ideal
geometry. Moreover, the shortest distance between the
a
c
Treatment of 3 with 1 equiv of [FeCp2][PF6] in THF
resulted in a rapid color change from orange to dark
red. After precipitation by pentane and further recrys-
tallization from a THF-pentane mixture, dark red
thermally stable microcrystals of 3+ were obtained in
95% yield. The complex 3+, which shows a cyclic
voltammogram identical with that of 3, exhibits an
Fe-H bond stretching at 1859 cm-1. As expected, the
difference in the νFe-H frequencies between the oxidized
species 3+ and 3′+ (∆ν ) 27 cm-1) is much smaller than
that between the corresponding 18-electron species.
4. Syn th esis an d Ch ar acter ization of [Cp*(dppp)-
F e][OSO2CF 3] (4[OTf]). Reaction of 3 with 1.1 equiv
of methyl triflate in diethyl ether at 20 °C caused the
very slow formation of a yellow suspension. Isolated by
(11) (a) Lawrance, G. A. Chem. Rev. 1986, 86, 17-33. (b) Beck, W.;
Su¨nkel, K. Chem. Rev. 1988, 88, 1405-1421.
(12) (a) J onston, D. H.; Shriver, D. F. Inorg. Chem. 1993, 32, 1045-
1047. (b) Schwiebert, K. E.; Stryker, J . M. Organometallics 1993, 12,
600-602.
(13) Stang, P. J .; Huang, Y.; Arif, A. M. Organometallics 1992, 11,
231-237.
(14) (a) Hamon, P.; Hamon, J .-R.; Lapinte, C. Unpublished results.
(b) Blake, D. M. J . Chem. Soc., Chem. Commun. 1974, 815. (c) Blosser,
P. W.; Gallucci, J . C.; Wojcicki, A. Inorg. Chem. 1992, 31, 2376-2384.
(d) Merrifield, J . H.; Fernandez, J . M.; Buhro, W. E.; Gladysz, J . A.
Inorg. Chem. 1984, 23, 4022-4029. (e) Tolman, W. B. Inorg. Chem.
1991, 30, 4877-4880. (f) Legzdins, P.; Smith, K. M.; Rettig, S. J . Can.
J . Chem. 2001, 79, 502-509.

[(η5-C5Me5)Fe(Ph2PCH2CH2CH2PPh2)][SO3CF3]
Organometallics, Vol. 21, No. 7, 2002 1345
UV-vis spectrum of 4[OTf] in THF displays a π-π*
high-energy transition at 36 760 cm-1 (ꢀ ) 4400 M-1
cm-1) and an absorption band centered at 29 630 cm-1
(ꢀ ) 2000 M-1 cm-1) with a shoulder at 23 260 cm-1 (ꢀ
) 360 M-1 cm-1) corresponding to HOMO-LUMO
transitions. The spectrum of the corresponding 16-
electron species in the dppe series displays much more
intense transitions at 35 710 cm-1 (ꢀ ) 9200 M-1 cm-1
)
and 31 496 cm-1 (ꢀ ) 5680 M-1 cm-1) with a shoulder
at 23 250 cm-1 (ꢀ ) 900 M-1 cm-1). As a result, it
appears that the increase of the P(1)-Fe-P(2) angle
from 86.87(8)° in 4′[P F 6] to 95.50(6)° in 4[OTf] is
associated with the decrease of the HOMO-LUMO gap
of 1867 cm-1 (ca. 0.23 eV).15 According to the theoretical
approach of Saillard and Costuas, it turns out that the
phosphorus participation in the HOMO and LUMO
orbitals is 3% and 15%, respectively, for the pseudo-C2v
geometry of the [CpFe(PH3)2]+ model compound.9 There-
fore, one can predict that the decrease of the HOMO-
LUMO gap induced by the replacement of the dppe by
the dppp ligand should be mainly due to the stabiliza-
tion of the LUMO rather than an increase of the energy
level of the HOMO.
The initial scan in the cyclic voltammogram of the
complex 4[OTf] displays two reversible waves in THF
with the E° potentials at -0.928 and 0.321 V vs SCE.
The chemical reversibility at the platinum electrode is
established for both redox systems by the ratio of the
anodic and cathodic current of unity. The electron
transfer which occurs at -0.928 V vs SCE corresponds
to the one-electron reduction of 4[OTf] and the forma-
tion of the neutral 17-electron species 4• at the platinum
electrode, whereas a one-electron oxidation process
takes place at 0.321 V vs SCE with the generation of
the 15-electron species [4]2+ on the electrode surface.
Considering the high degree of reversibility of these
processes, the complexes 4• and [4]2+ should constitute
accessible synthetic targets, but their preparation was
not attempted in the context of this project. The
comparison of the reduction potentials of 4[OTf] and
4′[P F 6] shows that 4[OTf] is more difficult to oxidize
(∆E° ) +0.06 V) and more difficult to reduce (∆E° )
-0.22 V) than the corresponding compound of the dppe
series (see Table 1). This result could be considered as
not consistent with the diminution of the HOMO-
LUMO gap from 4′[P F 6] to 4[OTf]. However, electro-
chemical and spectroscopic data can only be compared
with extreme caution when spin transition occurs.
Indeed, the electron transfer between the 16-electron
compound [4]+ and the 15-electron [4]2+ or the 17-
electron 4• complex should occur between species in
their low-spin states, whereas the HOMO-LUMO gap
was determined for 4[OTf] in its ground state, which
is the triplet state (see below). Note that according to
the theoretical calculations, the singlet state possesses
a somewhat pyramidalized Cs conformation, which
enlarges the HOMO-LUMO gap.9 This result suggests
that the variation of the bite angle of the bis-phosphine
F igu r e 2. Molecular structure of [Cp*(dppp)Fe][SO3-
CF3]‚(CH3)2CO (4[OTf]) at 110 K. Non-hydrogen atoms are
represented by 50% probability thermal ellipsoids.
iron site and the ortho carbon atoms of the phenyl
groups of the dppp is 3.50 Å, definitely excluding an
agostic interaction between the electron-deficient metal
center and a C-H bond.
One can recall that crystallization of the 18-electron
compound [Cp*(dppe)Fe(OSO2CF3)] from an acetone-
pentane mixture provided the σ-acetone complex [Cp*-
(dppe)Fe{σ-OdC(CH3)2}][OSO2CF3].8 Moreover, an X-
ray crystal structure determination established the Cs
symmetry of this complex and the Fe-O distance of
2.031(4) Å. Therefore, the introduction of an extra
methylene fragment between the two phosphorus atoms
of the dppp ligand produces a dramatic change in the
coordinating properties of the iron center. This differ-
ence of behavior between the dppe and dppp series was
unpredictable but should be explained by both steric and
electronic considerations. The steric congestion observed
around the metal in the case of complex 2 should not
give enough room in the vicinity of the iron center to
allow the coordination of neutral or even anionic ligand
as large as acetone or triflate. Indeed, one can assume
that 1,3-diaxial interactions between the atoms of the
triflate group or the acetone molecule as well, and the
axial hydrogen atoms of the methylene fragments
should be too strong.
On the other hand, the opening of the P-Fe-P angle
in the dppp series should induce significant changes in
the electronic structure of the16-electron species [Cp*-
(dppp)Fe]+ with respect to that of [Cp*(dppe)Fe]+, as
suggested by their different colors. Indeed, the complex
4[OTf] is yellow, whereas the corresponding 16-electron
derivative of the dppe series 4′[P F 6] is dark red. The
(15) On the basis of the facility for 16-electron ruthenium [Cp*RuP2]+
complexes to make agostic interactions, it has recently been proposed
that a small P1-M-P2 angle lowers the energy level of the LUMO.26
This could be true for compounds of Cs symmetry with a significant
degree of pyramidalization but is not confirmed by our results on iron
complexes with pseudo-C2v symmetry.

1346 Organometallics, Vol. 21, No. 7, 2002
Argouarch et al.
Ta ble 4. 57F e Mo1ssba u er F ittin g P a r a m eter s a t 80
K for 4[OTf]a
T (K)
IS (mm/s)
QS (mm/s)
Γ (mm/s)
80
100
150
200
250
300
350
0.553
0.547
0.531
0.515
0.502
0.490
0.480
1.752
1.743
1.717
1.692
1.631
1.600
1.566
0.130
0.123
0.121
0.120
0.148
0.156
0.179
a
The area percentage in all cases is 100%.
could have opposite effects on the HOMO-LUMO gap
of the singlet and triplet states.16
F igu r e 3. Temperature dependence of the 57Fe parameters
IS (open squares) and QS (dark squares) for the complex
4[OTf].
On the other hand, DFT calculations carried out on
the real compound [Cp*(dppe)Fe]+ (4′) allowed the
determination of the optimized geometries of the singlet
(S ) 0) and the triplet states (S ) 1).9 They mainly differ
from their R angle, which are 162 and 177° for the
singlet and the triplet states, respectively. The triplet
was also found to be more stable than the singlet by
0.12 eV. In agreement with its pseudo-C2v symmetry,
the complex 4[OTf] was expected to be paramagnetic.
This was confirmed by the determination of its magnetic
susceptibility at 293 K by the Evans method.17 In an
acetone solution, the complex 4[OTf] exhibits the
magnetic moment µeff ) 2.93 µB, fully compatible with
the presence of two unpaired electrons in the ground
state. In accord with its paramagnetic behavior, any
resonance cannot be observed in the 31P and 13C NMR
spectra of 4[OTf].7,18 However, a unique and sharp
signal was observed in the 19F spectrum for the triflate
anion at δ -73.7 ppm. The presence of the unpaired
electrons affects the line width and the chemical shifts
of the proton resonances, which were observed in the
1H spectrum in the range 78 to -11 ppm. On the basis
of the relative intensity of the peaks, the â- and
R-methylene protons and the Cp* resonances were
assigned to signals at δ 77.23 (w1/2 ) 105 Hz), 47.14 (w1/2
) 105 Hz), and 44.85 (w1/2 ) 85 Hz), respectively.
The zero-field Mo¨ssbauer spectra of a powdered
sample of 4[OTf], run between 80 and 350 K, show a
unique doublet without any traces of decomposition even
after 48 h at 350 K. The values of the isomer shift (IS)
range from 0.553 to 0.480 mm/s and decrease with
temperature (Table 4). In agreement with the high-spin
configuration of the 16-electron iron(II) complex, the
isomer shifts are much larger than those found for low-
spin iron(II) derivatives.19,20 The IS values decrease
almost linearly with temperature. However, careful
examination of the data revealed a break in the linear
relationship between IS and T. Indeed, in the ranges
80-200 and 200-350 K, IS decreases as a linear
function of the temperature (R g 0.999) with a visible
break in the slope around 200 K (Figure 3). Note that
the variation of the slope is quite weak, indicating that
the phase transition is not associated with a spin
transition.
Mo¨ssbauer quadrupole splittings (QS) are quite sensi-
tive to the nature of the bonding between the metal and
the coordinated ligand.21 The QS values determined for
4[OTf] are significantly smaller than the values usually
observed for 18-electron complexes (Table 4). Moreover,
the QS value continuously decreases with temperature
in the range 80-350 K. As noted for the variation of
the IS, a break is also observed around 200 K in the
temperature dependence of QS. As Mo¨ssbauer param-
eters are also sensitive to symmetry, one can assume
that the phase transition revealed by the X-ray analyses
at 293 and 110 K should occur at a temperature close
to 200 K.19 The reversibility of this transformation has
been established by running the measurements alter-
natively above and below 200 K.
5. Ba sic Rea ctivity of [Cp *(d p p p )F e][OSO2CF 3]
(4[OTf]). Despite its exceptional robust character, the
16-electron complex 4[OTf] presents a strong Lewis acid
character. In particular, it gives adducts with small
molecules as well as its homologue 4′[P F 6]. The reaction
of 4[OTf] with H2O reversibly provides an adduct which
is thought to be [Cp*(dppp)Fe(OH2)][O3SCF3]. However,
the aqua complex was not isolated. Its formation was
1
followed by H NMR by progressive addition of H2O to
a solution of 4[OTf] in CD3C(O)CD3. As the number of
equivalents of water increases, the chemical shifts of
the protons of the molecule move toward the positions
expected for a diamagnetic compound. For example, the
resonance attributed to the Cp* ligand moves from δ
45.1 (0 equiv of H2O) to δ 11.2 (50 equiv of H2O). Our
data suggest that the reversible decoordination of H2O
should be an easier process than its coordination. We
have also found that the removal of the solvents under
vacuum provides a pure sample of 4[OTf].
In the presence of CH2Cl2, 4[OTf] reacts to give the
iron(III) derivative [Cp*(dppp)FeCl][O3SCF3], identified
by CV and comparison with an authentic sample of its
iron(II) relative 2. However, in a mixture of CH2Cl2/CH3-
CN (2:3 v/v), the reaction with the nitrile is much faster
that the reaction with CH2Cl2 and the complex [Cp*-
(dppp)Fe(NCCH3)][O3SCF3] (5) is isolated as a pure
compound in 95% yield. As depicted in Scheme 1, the
(16) Considering the very large distance determined between the
organometallic cation and its counteranion in the solid state for 4-
[OTf], charge-transfer interactions between ion pairs seem to be highly
improbable in THF. Moreover, we found that the presence of 0.5-100
equiv of [NBu4][PF6] does not modify the UV-vis spectrum of 4[OTf].
(17) (a) Bertini, I.; Luchinat, C. NMR of Paramagnetic Molecules
in Biological Systems; Benjamin/Cummings: Menlo Park, CA, 1986.
(b) Sur, S. K. J . Magn. Reson. 1989, 82, 169-173.
(18) Fettinger, J . C.; Keogh, D. W.; Poli, R. J . Am. Chem. Soc. 1996,
118, 3617-3625.
(19) Gu¨tlich, P.; Link, R.; Trautwein, A. Mo¨ssbauer Spectroscopy and
Transition Metal Chemistry; Springer-Verlag: Berlin, 1978; Vol. 3.
(20) Guillaume, V.; Mahias, V.; Mari, V.; Lapinte, C. Organometal-
lics 2000, 19, 1422-1426.
(21) Guillaume, V.; Thominot, P.; Coat, F.; Mari, A.; Lapinte, C. J .
Organomet. Chem. 1998, 565, 75-80.

[(η5-C5Me5)Fe(Ph2PCH2CH2CH2PPh2)][SO3CF3]
Organometallics, Vol. 21, No. 7, 2002 1347
1
for H and 13C NMR spectra, external 85% H3PO4 for 31P NMR
spectra, and external CFCl3 for 19F spectra. Cyclic voltammo-
grams were recorded using an EG&G-PAR Model 263 poten-
tiostat/galvanostat. The working electrode was a Pt-disk
electrode (d ) 1.0 mm), the counter electrode was a Pt wire,
and a saturated calomel electrode (SCE) was used as a
reference electrode. The Cp2Fe0/+ couple was used as an
internal calibrant for the potential measurements.28 Mo¨ss-
bauer spectra were recorded with a 2.5 × 10-2 Ci (9.25 × 108
Bq) 57Co source using a symmetric triangular sweep mode.29
Computer fitting of the Mo¨ssbauer data to Lorentzian line
shapes were carried out with a previously reported computer
program.30 The isomer shift values are reported relative to iron
foil at 298 K and were not corrected for the temperature-
dependent second-order Doppler shift. Magnetic susceptibility
measurements were conducted in solution according to the
Evans method.17 Elemental analyses were performed at the
Center for Microanalyses of the CNRS at Vernaison, France.
Reagents were obtained as follows: pentamethylcyclopenta-
diene (Cp*H)31 and dppp32 were prepared according to pub-
lished procedures, and other chemicals were purchased from
commercial sources and used as received. FeCl2(dppp) was
prepared by following a procedure similar to that used to
synthesize FeCl2(dppe),33 by refluxing overnight an equimolar
amount of FeCl2(THF)1.5 and dppp in THF. At 20 °C, the white
precipitate is filtered off, washed with diethyl ether, and dried
under vacuum.
complex 4[OTf] also reacts with carbon monoxide to
yield [Cp*(dppp)Fe(CO)][O3SCF3] (6) quantitatively. The
properties of the complexes 5 and 6 are very similar to
those of the corresponding compounds 5′ and 6′ of the
dppe series. In particular, the potentials for the oxida-
tion of 5 and 5′ are identical. We only note that the
vibration of the CO ligand increases from 1932 to 1945
cm-1 when the dppp is replaced by the dppe chelate,22
which suggests that the Lewis acid [Cp*(dppp)Fe]+
would be slightly stronger than [Cp*(dppe)Fe]+.
6. Con clu sion
Cationic 16-electron complexes of iron or ruthenium
have often been postulated as intermediates in many
reactions involving 18-electron complexes of the type
[(C5R5)M(P2)L]+ (M ) Fe, Ru; L ) neutral 2-electron
donor ligands), but so far they have proven to be elusive
to isolation and characterization. Very recently remark-
ably stable cationic 16-electron complexes of the types
[(C5R5)Ru(N-N)]+[BAr′4]- (R ) Me, N-N ) TMEDA,23
Me2NCH2CH2NBu2;24 R ) H, N-N ) TMEDA;25 Ar′ )
3,5-C6H3(CF3)2) and [Cp*Ru(P2)]+[BAr′4]- (P2 ) dippe,
(PMeiPr2)2)26 and the neutral homologue27 were isolated
and unambiguously characterized. Interestingly, it was
nicely shown that the cation [Cp*Ru(dippe)]+ is stabi-
lized by an agostic interaction with one of the hydrogen
atoms of an isopropyl group, whereas such an interac-
tion is absent in the cation [Cp*Ru(PMeiPr2)2]+. In the
Cp-iron chemistry, examples of 16-electron cations are
mainly elusive. To the best of our knowledge, the
complexes [Cp*Fe(dppe)]+[PF6]- and [Cp*Fe(dppp)]+-
[OTf]- constitute the unique examples known to date.
Moreover, considering the ability of the triflate anion
to bind coordinatively unsaturated transition-metal
complexes, the 16-electron species [Cp*Fe(dppp)]+ can
be regarded as one of the less coordinating transition
metal Lewis acids. This work also emphasizes that
playing with the bite angle of the bis-phosphine ligand
in the Cp*Fe(P)2 series allows a fine-tuning of the
HOMO-LUMO gap.
Cp *(d p p p )F eCl (2). A Schlenk tube was charged with
FeCl2(dppp) (1; 2.15 g, 4.00 mmol), Cp*Li (0.566 g, 4.00 mmol),
and a magnetic bar. Then 20 mL of THF was added under
argon. The reaction mixture, which was stirred overnight (16
h) at 20 °C, gradually turned dark. The solvent was removed
under vacuum and the residue extracted with 100 mL of
diethyl ether. Crystallization from a CH2Cl2/pentane mixture
provided 2.18 g (85% yield) of Cp*Fe(dppp)Cl (2) as air-stable
black crystals. Anal. Calcd for C37H41ClFeP2‚CH2Cl2: C, 63.05;
1
H, 5.99. Found: C, 62.38; H, 6.15. H NMR (300 MHz, C6D6):
δ 8.25 (s, 4 H, Ph), 7.48-7.11 (m, 16 H, Ph), 2.54 (m, 2 H,
CH2), 1.92 (m, 2 H, CH2), 1.35 (s, 17 H, CH2 and Cp*). 31P
NMR (121 MHz, C6D6): δ 50.9 (s, dppp). CV (THF, 20 °C, 0.1
M
nBu4NPF6, v ) 0.1 V/s): E° ) -0.059 V (∆Ep ) 0.166 V,
c
ipa/ip ) 1.0). X-ray-quality crystals of Cp*Fe(dppp)Cl‚CH2Cl2
were grown by slow diffusion of pentane into a saturated CH2-
Cl2 solution of the compound prepared above.
Cp *(d p p p )F eH (3). At -80 °C, to a 50 mL dark green THF
solution of 2 (1.12 g, 1.78 mmol) was added 0.84 g (2.20 mmol)
of LiAlH4. The color of the reaction medium turned progres-
sively orange, while the temperature was raised overnight (16
h) to 20 °C. The reaction medium was then cooled to -80 °C,
and 1 mL of MeOH was added dropwise. At room temperature,
0.5 mL of CH2Cl2 was added and the stirring was continued
for an additional 5 min. The solvents were removed under
vacuum, and the solid residue was extracted with 2 × 20 mL
portions of diethyl ether. The ethereal solution was taken to
dryness to give 1.03 g (95% yield) of an air and thermally stable
orange powder of Cp*Fe(dppp)H. Anal. Calcd for C37H42FeP2:
C, 73.51; H, 7.00; P, 10.25. Found: C, 73.10; H, 7.05; P, 10.95.
IR (KBr, cm-1): 1800 (νFe-H). 1H NMR (200 MHz, C6D6): δ
7.90-7.84 (m, 8 H, Ph), 7.30-7.25 (m, 12 H, Ph), 2.39 (m, 2
H, CH2), 1.70 (m, 4 H, CH2), 1.59 (s, 15 H, Cp*), -16.42 (t, 1
H, J PH ) 70 Hz, Fe-H). 13C NMR (50 MHz, C6D6): δ 143.4-
Exp er im en ta l Section
Gen er a l Da ta . All the manipulations and workup proce-
dures of air-sensitive compounds were carried out under inert
atmosphere in a J ACOMEX drybox filled with argon, or using
standard Schlenk techniques. Reagent grade tetrahydrofuran
(THF), pentane, and diethyl ether were predried and then
distilled under argon from sodium benzophenone ketyl prior
to use. Acetonitrile and dichloromethane were distilled under
argon from P2O5, and acetone was distilled under argon from
B2O3. All glassware was oven-dried prior to use. Infrared
spectra were obtained as KBr disks on a Bruker IFS28 FT-IR
spectrometer (400-4000 cm-1). NMR spectra were acquired
at 297 K on multinuclear Bruker DPX 200 (200 MHz) or AM
300 WB (300 MHz) instruments. Chemical shifts are given in
parts per million (ppm) relative to tetramethylsilane (TMS)
(22) While the value of νCO has been previously reported,41 we have
measured it again with a more accurate FT-IR spectrometer.
(23) Gemel, C.; Mereiter, K.; Schmid, R.; Kirchner, K. Organome-
tallics 1997, 16, 5601-5603.
(28) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877-910.
(29) Varret, F.; Mariot, J .-P.; Hamon, J .-R.; Astruc, D. Hyperfine
Interact. 1988, 39, 67-81.
(30) (a) Boinnard, D.; Boussekssou, A.; Dworkin, A.; Savariault, J .-
M.; Varret, F.; Tuchagues, J .-P. Inorg. Chem. 1994, 33, 271-281. (b)
Varret, F. In International Conference on Mo¨ssbauer Effect Applica-
tions; J aipur, India, 1981; Indian Science Academy: New Delhi, 1982.
(31) Kohl, F. X.; J utzi, P. J . Organomet. Chem. 1983, 243, 119-
121.
(24) Gemel, C.; Sapunov, V. N.; Mereiter, K.; Ferencic, M.; Schmid,
R.; Kirchner, K. Inorg. Chim. Acta 1999, 286, 114-120.
(25) Gemel, C.; Huffman, J . C.; Caulton, K. G.; Mauthner, K.;
Kirchner, K. J . Organomet. Chem. 2000, 593-594, 342-353.
(26) Tenorio, M. J .; Mereiter, K.; Puerta, M. C.; Valerga, P. J . Am.
Chem. Soc. 2000, 122, 11230-11231.
(32) Hoffmann, R. Angew. Chem., Int. Ed. Engl. 1982, 21, 711-800.
(33) Mays, M. J .; Sears, P. L. J . Chem. Soc., Dalton Trans. 1973,
1873-1875.
(27) Yamaguchi, Y.; Nagashima, H. Organometallics 2000, 19, 725-
727.

1348 Organometallics, Vol. 21, No. 7, 2002
Argouarch et al.
1
125.0 (m, Ph), 85.3 (s, C5Me5), 37.4 (tt, CH2, J CH ) 120 Hz),
progressively lightened. The solvent was removed under
reduced pressure. The solid residue was washed with 3 × 20
mL of pentane, and dried under vacuum, to give 0.076 g (97%)
of an air-stable lemon yellow powder of 6. IR (KBr, cm-1): 1932
1
1
31.2 (tm, CH2, J CH ) 139 Hz), 20.7 (t, CH2, J CH ) 129 Hz),
11.6 (q, C5Me5, J CH ) 126 Hz). 31P NMR (81 MHz, C6D6): δ
1
75.6 (dd, J HP ) 70 Hz, J PP ) 29 Hz, dppp). CV (THF, 20 °C,
0.1 M Bu4NPF6, v ) 0.1 V/s): E° ) -0.274 V (∆Ep ) 0.100 V,
n
1
(νCO), 1274 (OTf), 1155 (OTf), 1029 (OTf). H NMR (200 MHz,
c
ipa/ip ) 1.0).
CD3COCD3): δ 7.72-7.59 (m, 20 H, Ph), 2.80 (m, 2 H, CH2),
[Cp *F e(d p p p )H][P F 6] (3+). At 20 °C, 0.604 g (1.0 mmol)
of 3 was dissolved in 20 mL of THF, and 0.298 g (0.9 mmol) of
ferrocenium hexafluorophosphate was added to this orange
solution. The reaction medium was stirred for 1 h, and the
volume of the solution was reduced to 3 mL. Addition of 50
mL of pentane caused the precipitation of a red powder. After
filtration the solid was washed with 3 × 50 mL of diethyl ether,
and crystallization from a THF/pentane mixture provided
0.646 g (95% yield based on Cp2FePF6) of [Cp*Fe(dppp)H][PF6]
isolated as air-sensitive dark red crystals. Anal. Calcd for
2.21 (m, 4 H, CH2), 1.84 (s, 15 H, C5Me5). 13C NMR (50 MHz,
2
CD3COCD3): δ 221,2 (t, CO, J PC ) 25 Hz), 135.1-129.1 (m,
1
Ph), 96.8 (s, C5Me5), 32.5 (tm, CH2, J CH ) 139 Hz), 20.6 (t,
1
1
CH2, J CH ) 129 Hz), 9.7 (q, J CH ) 129 Hz, C5Me5).31P NMR
(CD3COCD3): δ 49.9 (d, J PP ) 31 Hz, dppp).
Cr ysta llogr a p h y. Data were collected on crystals of 2‚CH2-
Cl2 and 4[OTf]‚(CH3)2CO as summarized in Table 2.34 Cell
constants and an orientation matrix of 2‚CH2Cl2 were obtained
from a least-squares refinement using 25 high-θ reflections.
After Lorentz and polarization corrections35 and absorption
corrections (æ scans), the structure was solved with SIR-97,37
which revealed the non-hydrogen atoms and the CH2Cl2
solvate. After anisotropic refinements, a Fourier difference
map revealed many hydrogen atoms. Cell parameters of
4‚[OTf] are obtained with Denzo and Scalepack37 with 10
frames (psi rotation: 1° per frame). The data collection34b (2θmax
) 60°, 163 frames via 1.9° omega rotation and 38 s per frame)
gives 25 134 integrated reflections. The data reduction with
Denzo and Scalepack37 leads to 9176 independent reflections
(7773 with I > 2.0σ(I)). The structure was solved with SIR-
97,37 which revealed all the non-hydrogen atoms of the
structure. The whole structure was next refined by SHELX-
9738 by full matrix least-squares techniques (use of F2 mag-
nitude; x, y, z, âij for Fe, P, N, O, and C atoms and x, y, and z
in the riding mode for H atoms; w(calcd) ) 1/[σ2(Fo2) +
C
37H42FeF6P3: C, 59.29; H, 5.65; P, 12.40. Found: C, 59.78;
H, 5.55; P, 12.92. IR (KBr, cm-1): 1859 (νFe-H).
[Cp *(d p p p )F e][CF 3SO3] (4[OTf]). To a 30 mL orange
solution of 3 (0.18 g, 0.30 mmol) in diethyl ether was added
37 µL (0.33 mmol) of MeOTf. The reaction mixture was stirred
for 12 h at 20 °C, and a yellow suspension was formed very
slowly. The suspension was filtered off and washed with 2 ×
10 mL of pentane. The solid residue was then dissolved in 10
mL of acetone and precipitated by addition of 100 mL of cold
pentane (-80 °C). The solid material was filtered, washed with
pentane, and dried under vacuum. The compound 4[OTf] was
recovered as an air- and moisture-sensitive yellow powder
(0.187 g, 82%). Anal. Calcd for C38H41F3FeO3P2S‚0.5(CH3)2-
CO: C, 60.70, H, 5.67, P, 7.93. Found: C, 61.18, H, 5.67, P,
7.20. IR (KBr, cm-1): 3057, 2984, 2913, 2858, 1484, 1436
(dppp), 1273 (OTf), 1159 (OTf), 1029 (OTf). 1H NMR (200 MHz,
CD3COCD3): δ 77.23 (s, 2 H, CH2, w1/2 ) 105 Hz), 47.14 (s, 4
H, CH2, w1/2 ) 105 Hz), 44.85 (s, 15 H, Cp*, w1/2 ) 85 Hz),
7.77 (Ph, w1/2 ) 25 Hz), 3.96 (Ph, w1/2 ) 26 Hz), -10,96 (Ph,
w1/2 ) 158 Hz). 19F NMR (188 MHz, CD3COCD3): δ -73.7 (s,
CF3). µeff (CD3COCD3, 297 K): 2.93 µB. CV (THF, 20 °C, 0.1 M
2
(0.0911P)2 + 4.5203P], where P ) (Fo + 2Fc2)/3). Atomic
scattering factors were taken from the literature.39 Ortep views
were generated with PLATON-98.36 All calculations were
performed on a Pentium NT Server computer.
Ack n ow led gm en t. We gratefully acknowledge Drs
K. Costuas, J .-F. Halet, and J .-Y. Saillard for many
interactive and stimulating discussions.
nBu4NPF6, v ) 0.1 V/s): E°1) +0.321 V (∆Ep ) 0.164 V, ipa/ip
c
c
) 1.0); E°2) -0.928 V (∆Ep ) 0.144 V, ipa/ip ) 1.0). X-ray-
quality crystals of [Cp*Fe(dppp)][CF3SO3]‚Me2CO were grown
by slow diffusion of pentane into a saturated acetone solution
of the compound prepared above.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, atomic coordinates, bond lengths and angles, and aniso-
tropic thermal parameters for 2‚CH2Cl2 and 4[OTf]‚(CH3)2-
CO. This material is available free of charge via the Internet
at http://pubs.acs.org.
[Cp *F e(d p p p )(NCMe)][CF 3SO3] (5). At room tempera-
ture, 0.030 g (0.040 mmol) of 4[OTf] was dissolved in 2 mL of
CH2Cl2, and 3 mL (0.050 mmol) of CH3CN was added with a
syringe. The solution was stirred overnight while the color
changed from yellow to red-orange. The solvents were removed
under reduced pressure. The solid residue was washed with 2
× 10 mL of pentane and dried under vacuum to give 0.030 g
(95%) of 5 as an air- and moisture-stable red-orange powder.
Anal. Calcd for C40H44F3FeNO3P2S: C, 60.54; H, 5.59; P, 7.81.
Found: C, 61.21; H, 5.80; P, 8.13. IR (KBr, cm-1): 2240 (C-
N), 1485, 1437 (dppp), 1275 (s, OTf), 1156 (s, OTf), 1029 (OTf).
1H NMR (200 MHz, CD3COCD3): δ 8.02-7.49 (m, 20 H, Ph),
2.99 (s, 3 H, CH3), 2.49 (m, 2 H, CH2), 2.12 (m, 4 H, CH2), 1.27
(s, 15 H, C5Me5). 13C NMR (50 MHz, CD3COCD3): δ 135.1 (s,
NCMe), 134.8-128.5 (m, Ph), 87.7 (s, C5Me5), 29.8 (m, CH2),
OM0108245
(34) (a) Fair, C. K. MOLEN; An Interactive System for Crystal
Structure Analysis; Enraf-Nonius: Delft, The Netherlands, 1990. (b)
Nonius KappaCCD Software; Nonius BV: Delft, The Netherlands,
1999.
(35) Spek, A. L. HELENA; Program for the handling of CAD-4
Diffractometer Output SHELX(S/L); Utrecht University: Utrecht, The
Netherlands, 1997.
(36) Altomare, M. C.; Burla, M.; Camalli, G.; Cascarano, C.;
Giacovazzo, A.; Guagliardi, A. G. G.; Moliterni, G.; Polidori, R.; Spagna,
R. Sir97: a new tool for crystal structure determination and refine-
ment. J . Appl. Crystallogr. 1998, 31, 74-77.
(37) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected In Oscillation Mode. In Methods in Enzymology, Vol. 276,
Macromolecular Crystallography, Part A; Carter, C. W., Sweet, R. M.,
Eds.; Academic Press: London, 1997; p 307.
(38) Sheldrick, G. M. SHELX97; Program for the Refinement of
Crystal Structures; University of Go¨ttingen: Go¨ttingen, Germany,
1997.
(39) International Tables for X-ray Crystallography; Wilson, A. J .
C., Ed.; Kluwer Academic Publishers: Dordrecht, 1992; Vol. C.
(40) Spek, A. L. PLATON-98; A Multipurpose Crystallographic Tool;
Utrecht University: Utrecht, The Netherlands, 1998.
(41) Catheline, D.; Astruc, D. Organometallics 1984, 3, 1094-1100.
1
1
20.3 (m, CH2), 9.4 (q, J CH ) 128 Hz, C5Me5), 5.6 (q, J CH
)
138 Hz, CH3CN). 31P NMR (81 MHz, CD3COCD3): δ 52.5 (s,
dppp). CV (THF, 20 °C, 0.1 M nBu4NPF6, v ) 0.1 V/s): E° )
c
+0.604 V (∆Ep ) 0.088 V, ipa/ip ) 1.0).
[Cp *F e(d p p p )(CO)][CF 3SO3] (6). At room temperature
under argon, 0.075 g (0.10 mmol) of 4[OTf] was dissolved in
5 mL of THF to provide a clear yellow solution. The Schlenk
tube was then evacuated and filled with CO (1 atm) and the
stirring was maintained for 1 h, while the color of the solution