Re(V)-oxo-dppf and Re(V)-imido-dppf complexes: Synthesis, structure, and properties of Re(X)Cl3(dppf) (X=O, NPh, N-C6H3-2,6-i-Pr2; Dppf=Fe(η5-C5H4PPh2) 2)

Article abstract of DOI:10.1016/S0022-328X(01)00754-9

Re(V)-imido and Re(V)-oxo complexes containing 1,1′-bis(diphenylphosphino)ferrocene (Fe(η⁵-C₅H₄PPh₂)₂, dppf) were prepared from mer,trans-Re(O)Cl₃(PPh₃)₂ (1), mer,tran

Full text of DOI:10.1016/S0022-328X(01)00754-9

Journal of Organometallic Chemistry 627 (2001) 226–232
www.elsevier.nl/locate/jorganchem
Re(V)–oxo–dppf and Re(V)–imido–dppf complexes: synthesis,
structure, and properties of Re(X)Cl3(dppf) (X=O, NPh,
N-C6H3-2,6-i-Pr2; dppf=Fe(h5-C5H4PPh2)2)
Nam-Sun Choi, Soon W. Lee *
Department of Chemistry, Sungkyunkwan Uni6ersity, Natural Science Campus, Suwon 440-746, South Korea
Received 9 January 2001; received in revised form 19 February 2001; accepted 23 February 2001
Abstract
Re(V)–imido and Re(V)–oxo complexes containing 1,1%-bis(diphenylphosphino)ferrocene (Fe(h5-C5H4PPh2)2, dppf) were
prepared from mer,trans-Re(O)Cl3(PPh3)2 (1), mer,trans-Re(NPh)Cl3(PPh3)2 (2), or mer,cis-Re(N-C6H3-2,6-i-Pr2)2Cl3(py) (3).
Compounds 1–3 reacted with dppf to give fac-Re(O)Cl3(dppf) (4), fac-Re(NPh)Cl3(dppf) (5), and mer-Re(N-C6H3-2,6-i-
Pr2)Cl3(dppf) (6), respectively. Electrochemical studies performed on Re–oxo–dppf complexes (4) and Re–imido–dppf complexes
(5 and 6) showed different redox behavior depending on the type of ligand coordinated to the Re metal. The structure of
compound 4 was determined by X-ray diffraction. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Re(V)–imido complexes; Re(V)–oxo complexes; Electrochemical studies
1. Introduction
Various redox-active ligands have been reported to
control the reactivities of transition-metal complexes
[10]. The dppf (1,1%-bis(diphenylphosphino)ferrocene)
ligand is a well known redox-active ligand, and its
complexes are expected to exhibit a ferrocene-centered
oxidation process, together with additional redox pro-
cesses at other metal centers in the molecule. Because
there have been no reports on high-oxidation-state Re-
oxo and Re–imido complexes containing the dppf lig-
and, we set out to prepare Re–oxo–dppf and
Re–imido–dppf complexes. Herein we report the
preparation and some properties of fac-Re(O)Cl3(dppf)
(4), fac-Re(NPh)Cl3(dppf) (5), and mer-Re(N-C6H3-
2,6-i-Pr2)Cl3(dppf) (6), including the structure of com-
pound 4.
Transition-metal–imido (or nitrene, LnMꢀNR) com-
plexes, which have a multiple bonding character be-
tween the metal and the imido ligand, have attracted
continuous interest [1–8]. Transition-metal–oxide
(MꢀO) complexes have frequently been used to prepare
the imido complexes by reactions with primary amines
(RNH2) or organic isocyanates (RNCO) (Eqs. (1) and
(2)) [6].
LnMꢀO+RNH2“LnMꢀNR+H2O
LnMꢀO+RNCO“LnMꢀNR+CO2
(1)
(2)
We are interested in Re–imido complexes (ReꢀNR).
For instance, we recently prepared several Re–imido
complexes of the type Re(NAr)(PR3)2Cl3 (PR3=PMe3,
PEt3, P(OMe)3; Ar=C6H5, 2,6-i-Pr2-C6H3) from the
reactions of Re(N-C6H3-2,6-i-Pr2)2Cl3(py) with small
phosphines or phosphites [9].
2. Experimental
Unless otherwise stated, all reactions have been per-
formed with standard Schlenk line and cannula tech-
niques under argon. Air-sensitive solids were
manipulated in a glove box filled with argon. Glassware
was soaked in KOH-saturated 2-propanol for ca. 24 h
and washed with distilled water and acetone before use.
* Corresponding author. Tel.: +82-31-2907066; Fax: +82-31-
2907075.
E-mail address: swlee@chem.skku.ac.kr (S.W. Lee).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00754-9

N.-S. Choi, S.W. Lee / Journal of Organometallic Chemistry 627 (2001) 226–232
227
Glassware was either flame or oven dried. Hydrocarbon
solvents were stirred over concentrated H2SO4 for ca.
48 h, neutralized with K2CO3, stirred over sodium
metal, and distilled by vacuum transfer. Tetrahydro-
furan (THF) was stirred over sodium metal and dis-
tilled by vacuum transfer. Benzene and diethyl ether
were distilled over sodium metal under argon.
Dichloromethane was stirred over CaH2 and distilled
by vacuum transfer. NMR solvent (CDCl3) was de-
gassed by freeze-pump-thaw cycles before use and
stored over molecular sieves under argon. Re metal,
rhenium(VII) oxide (Re2O7), triphenylphosphine
(PPh3), methyl lithium (MeLi, 1.4 M in diethyl ether),
lithium ethoxide (LiOEt, 1 M in THF), methylmagne-
sium bromide (MeMgBr, 3 M in diethyl ether), hydro-
gen chloride (HCl, 1 M in diethyl ether), and tert-butyl
isocyanate (t-BuNCO) were purchased from Aldrich
and used as received. 2,6-Diisopropylphenyl isocyanate
(2,6-i-Pr2-C6H3NCO) was purchased from Fluka.
tion became orange–brown, and deep green precipi-
tates gradually formed during 5 min. The solution was
allowed to stir for an additional 2 h at r.t. The resulting
deep green solid was collected by filtration, washed
with benzene (20 ml) and diethyl ether (2×30 ml), and
then dried under vacuum to obtain 0.55 g (0.637 mmol,
84% yield) of fac-Re(O)Cl3(dppf) (4). This product was
1
recrystallized from CH2Cl2–hexane. H-NMR (CDCl3):
l 7.92 (4H, t, J=8.5 Hz, phenyl), 7.75 (4H, t, J=8.5
Hz, phenyl), 7.46–7.33 (12H, m, phenyl), 5.31 (2H, s,
br, Cp), 4.72 (2H, s, br, Cp), 4.47 (2H, s, br, Cp), 4.43
(2H, s, br, Cp). 13C{1H}-NMR (CDCl3): l 135.80,
135.55, 132.04, 131.43, 129.02, 127.99 (phenyl), 81.41,
80.95, 76.96, 75.93, 74.33, 73.81 (Cp). 31P{1H}-NMR
(CDCl3):
l
−26.00
(s).
Anal.
Calc. for
C34H28OP2Cl3FeRe: C, 47.32; H, 3.27. Found: C, 47.34;
H, 3.55%. mp (decom.): 233–235°C. IR (KBr): 3105,
3057, 1482, 1434, 1195, 1169, 1092, 1035, 967 (ReꢀO),
829, 743, 691, 548, 517, 491, 473, 443 cm−1
.
mer,trans-Re(O)Cl3(PPh3)2
(1)
[11],
mer,trans-
Re(NPh)Cl3(PPh3)2 (2) [12], PhNꢀPPh3 [12], Fe(h5-
C5H4PPh2)2 (dppf) [13], Re(N-C6H3-2,6-i-Pr2)2(py)Cl3
(3) [14,15], and Re(NPh)(dppe)Cl3 (dppe=1,2-bis-
(diphenylphosphino)ethane) [16] were prepared by liter-
ature methods. The electrolyte tetrabutylammonium
hexafluorophophate ([n-Bu4N][PF6]) and ferrocene
(FeCp2) were recrystallized from ethanol before use.
Electrochemical measurements were performed with
a model 263A EG&G potentiostat. A standard three-
electrode system was employed with a platinum disk as
working electrode. A Pt wire was the counter electrode,
and Ag wire served as a reference electrode. Measure-
ments were carried out in CH2Cl2 containing 0.1 M
[n-Bu4N][PF6] as a supporting electrolyte and ca. 1 mM
metal complex. Instrumental iR compensation was ap-
plied in all measurements. The ferrocene/ferrocenium
couple was 0.632 V at 300 mV s−1 in this cell. All the
experiments were carried out under nitrogen.
2.2. Preparation of fac-Re(NPh)Cl3(dppf ) (5)
A benzene solution (60 ml) containing mer,trans-
ReCl3(NPh)(PPh3)2 (2) (0.29 g, 0.32 mmol) and dppf
(0.183 g, 0.33 mmol) was refluxed for 1 h. The resulting
green precipitates were filtered off and then washed
with benzene (2×30 ml), diethyl ether (2×30 ml), and
pentane (1×30 ml), and then dried under vacuum to
obtain 0.26
g (0.28 mmol, 85% yield) of fac-
Re(NPh)Cl3(dppf) (5). Recrystallization was from
CH2Cl2–hexane to give a CH2Cl2-solvated product.
1H-NMR (CDCl3): l 6.67–8.02 (25H, m, Ph), 5.27 (2H,
s, br, Cp), 4.68 (2H, s, br, Cp), 4.64 (2H, s, br, Cp),
4.58 (2H, s, br, Cp). 13C{1H}-NMR (CDCl3): l 155.13
(s, Ph), 136.02 (t, J=4.15 Hz, Ph), 135.69 (s, Ph),
134.79 (d, J=4.65 Hz, Ph), 134.36 (s, Ph), 133.90 (s,
Ph), 130.90 (d, J=13.58 Hz, Ph), 129.56 (s, Ph), 129.02
(s, Ph), 128.45 (d, J=5.16 Hz, Ph), 127.97 (t, J=5.16
Hz, Ph), 122.50 (s, Ph), 84.62 (s, Cp), 84.15 (s, Cp),
76.84 (s, Cp), 75.49 (s, Cp), 73.72 (s, Cp), 73.20 (s, Cp).
31P{1H}-NMR (CDCl3): l −17.19 (s). Anal. Calc. for
C40H33NP2Cl3FeRe: C, 51.21; H, 3.54; N, 1.49. Found:
C, 51.61; H, 3.32; N, 1.28%. mp (decom.): 239–241°C.
IR (KBr): 3060, 1577, 1480, 1434, 1387, 1309, 1192,
1163, 1091, 1031, 995, 832, 750, 693, 634, 547, 512, 492,
1H- and 13C{1H}-NMR spectra were recorded with a
Bruker AMX 500 MHz spectrometer with reference to
internal solvent resonances and are reported relative to
tetramethylsilane. 31P{1H}-NMR spectra were also
recorded with a Bruker AMX 500 MHz spectrometer
with reference to 85% H3PO4. IR spectra were recorded
with a Nicolet 205 FTIR spectrophotometer. Melting
points were measured with a Thomas Hoover capillary
melting point apparatus without calibration. Elemental
analyses were performed by the Korea Basic Science
Center.
473, 445 cm−1
.
2.3. Preparation of
mer-Re(N-C6H3-2,6-i-Pr2)Cl3(dppf ) (6)
2.1. Preparation of fac-Re(O)Cl3(dppf ) (4)
An opaque green solution of mer,cis-Re(N-C6H3-2,6-
i-Pr2)2(py)Cl3 (3) (0.25 g, 0.346 mmol) and dppf (0.38 g,
0.685 mmol) in CH2Cl2 (30 ml) was stirred for 48 h at
r.t. The solution gradually became transparent red–
brown. The solvent was removed under vacuum to give
a red–brown residue, which was extracted with benzene
A
mixture
of
yellow–green
mer,trans-
Re(O)Cl3(PPh3)2 (1) (0.63 g, 0.756 mmol) and yellow
dppf (0.63 g, 1.136 mmol) in benzene (60 ml) was
stirred at room temperature (r.t.). The resulting solu-

228
N.-S. Choi, S.W. Lee / Journal of Organometallic Chemistry 627 (2001) 226–232
CHMe2), 0.40 (6H, d, 3JH–H=6.5 Hz, CHMe2).
13C{1H}-NMR (CDCl3): l 155.69–124.98 (phenyl),
76.52–69.55 (Cp), 28.78 (CHMe2), 26.48 (CHMe2),
23.05 (CHMe2). 31P{1H}-NMR (CDCl3): l 40.05 (1P,
s), −32.69 (1P, s). Anal. Calc. for C46H45NP2Cl3FeRe:
C, 54.05; H, 4.44; N, 1.37. Found: C, 54.16; H, 4.52; N,
0.97%. mp (decom.): 219–221°C. IR (KBr): 3054, 2961,
2924, 2864, 1479, 1463, 1435, 1385, 1364, 1310, 1143,
Table 1
X-ray data collection and structure refinement for 4
Formula
Fw
Temperature (K)
Crystal system
Space group
Unit cell dimensions
C34H28OP2Cl3FeRe
862.90
297(2)
Orthorhombic
P212121
,
a (A)
11.519(1)
15.834(4)
17.460(2)
3184.5(9)
4
b (A)
1093, 1031, 1000, 751, 726, 696, 565, 531, 496 cm−1
.
,
,
c (A)
3
,
V (A )
2.4. X-ray structure determination of 4
Z
Dcalc (g cm−3
)
1.800
4.633
v (mm−1
Tmin
)
All X-ray data were collected using a Siemens P4
diffractometer equipped with a Mo X-ray tube and a
graphite-crystal monochromator. Details on crystal
data and intensity data are given in Table 1. The
orientation matrix and unit-cell parameters were deter-
mined by least-squares analyses of the setting angles of
37 for compound 4 in the range 15.0B2qB25.0°.
Three check-reflections were measured every 100 reflec-
tions throughout data collection and showed no signifi-
cant variations in intensity. Intensity data were
corrected for Lorenz and polarization effects. Decay
corrections were also made. The intensity data were
empirically corrected with „-scan data. All calculations
were carried out with use of the SHELXTL programs
[17].
0.0748
0.5230
1688
0.0934
3227
3208
3120
380
3.5–51.0
ꢀ
Tmax
F(000)
Rint
Reflections measured
Unique reflections
Reflections with I\2|(I)
Parameters refined
2q range (°)
Scan type
Scan speed
Variable
1.033
1.613, −1.484
0.0369
0.0969
GOF (goodness-of-fit on F2)
−3
,
Maximum, minimum in Dz (e A
)
R
wR2
a
a wR2=ꢀ[w(Fo2−Fc2)2]/ꢀ[w(Fo2)2]1/2
.
A green crystal of 4 of approximate dimensions
0.80×0.68×0.60 mm3, shaped as a block, was used
for crystal and intensity data collection. The unit-cell
parameters and systematic absences, h00 (h=2n+1),
0k0 (k=2n+1), and 00l (l=2n+1), unambiguously
indicated P212121 as a space group. The structure was
solved by the direct method. All non-hydrogen atoms
were refined anisotropically. All hydrogen atoms were
generated in idealized positions and refined in a riding
model. Selected bond distances and bond angles are
shown in Table 2.
(40 ml). The solvent (benzene) was removed under
vacuum to a give a yellow–brown solid. The resulting
solid was washed with diethyl ether (3×20 ml) and
pentane (1×20 ml), and then dried under vacuum to
obtain 0.11 g (31% yield) of mer-Re(N-C6H3-2,6-i-
Pr2)Cl3(dppf) (6). 1H-NMR (CDCl3): l 8.00–6.88 (23H,
m, phenyl), 4.98 (2H, s, br, Cp), 4.75 (2H, s, br, Cp),
4.33 (2H, s, br, Cp), 4.31 (2H, s, br, Cp), 3.78 (2H, sept,
3
3JH–H=6.5 Hz, CHMe2), 1.09 (6H, d, JH–H=6.5 Hz,
Table 2
,
Selected bond distances (A) and bond angles (°) in 4
Re1–O1
Re1–Cl3
Fe1–C1
Fe1–C4
Fe1–C7
Fe1–C10
1.719(7)
2.373(3)
2.01(1)
2.05(1)
2.04(1)
2.03(1)
Re1–Cl1
Re1–P1
Fe1–C2
Fe1–C5
Fe1–C8
P1–C1
2.349(3)
2.496(3)
2.05(1)
2.03(1)
2.08(1)
Re1–Cl2
Re1–P2
Fe1–C3
Fe1–C6
Fe1–C9
P2–C6
2.385(3)
2.491(2)
2.06(1)
2.01(1)
2.05(1)
1.791(9)
1.798(11)
O1–Re1–Cl1
Cl1–Re1–Cl3
Cl1–Re1–Cl2
O1–Re1–P2
Cl3–Re1–P2
O1–Re1–P1
Cl3–Re1–P1
P2–Re1–P1
P2–C6–Fe1
103.2(3)
90.8(1)
85.4(1)
88.9(2)
85.56(9)
85.3(2)
81.2(1)
103.01(8)
128.7(5)
O1–Re1–Cl3
O1–Re1–Cl2
Cl3–Re1–Cl2
Cl1–Re1–P2
Cl2–Re1–P2
Cl1–Re1–P1
Cl2–Re1–P1
P1–C1–Fe1
163.9(3)
98.9(2)
89.9(1)
80.9(1)
165.5(1)
170.7(1)
89.8(1)
132.9(6)

N.-S. Choi, S.W. Lee / Journal of Organometallic Chemistry 627 (2001) 226–232
229
The strong IR band at 967 cm−1, assigned to the ReꢀO
bond, is consistent with those found for mononuclear
terminal monooxo Re complexes [5].
Compound 2 reacts with dppf in refluxing benzene
for 1 h to give a Re–imido–dppf compound, fac-
Re(NPh)Cl3(dppf) (5) (Eq. (4)), which is air- and mois-
ture-stable both in solution and in the solid state and is
slightly soluble in dichloromethane. Compound 5 is
also a bimetallic (Re–Fe) complex containing three
facial chloro ligands. As expected, compound 5 exhibits
a singlet at l −17.19 ppm in its 31P{1H}-NMR spectra
and four broad singlets (Cp protons) at l 5.27, 4.68,
1
4.64, and 4.58 ppm in its H-NMR spectra.
(4)
Fig. 1. ORTEP drawing of 4, showing the atom-labeling scheme and
50% probability thermal ellipsoids.
Compound mer,cis-Re(N-C6H3-2,6-i-Pr2)2(py)Cl3 (3)
reacts with the dppf ligand in benzene at room temper-
ature to give a Re–imido–dppf compound, mer-Re(N-
C6H3-2,6-i-Pr2)Cl3(dppf) (6), in 31% yield (Eq. (5)). In
this reaction, the Re metal has been formally reduced
from +7 to +5. It is worth noting that one of the
strongly bound aryl imido ligands (N-C6H3-2,6-i-Pr2)
has been replaced during the reaction. Unfortunately,
we cannot give an explanation for the unusual stoi-
chiometry and reactivities (the imido group abstraction
and the Re metal reduction). However, these phenom-
ena have been previously observed in the reaction be-
tween compound 3 and trimethylphosphine (PMe3) that
gives mer,trans-Re(N-C6H3-2,6-i-Pr2)(PMe3)2Cl3 [9].
31P{1H}-NMR spectra of 6 exhibit two singlets at l
40.05 and −32.69 ppm, which clearly indicates the
phosphorus nuclei of the dppf ligand to be inequiva-
lent. The only structure that can explain these spectra is
the one shown in Eq. (5), in which one phosphorus
atom is trans to the chloro ligand and the other to the
imido ligand. As is the case for 4 and 5, the Cp protons
in 6 appear separately as four broad singlets at l 4.98,
4.75, 4.33, and 4.31 ppm.
3. Results and discussion
3.1. Preparation
Compound 1 reacts with dppf in benzene at room
temperature to give a Re–oxo–dppf compound, fac-
Re(O)Cl3(dppf) (4), in 84% yield (Eq. (3)). Compound 4
is air- and moisture-stable both in solution and in the
solid state, and it is slightly soluble in dichloromethane,
tetrahydrofuran, and acetone. The two monodentate
PPh3 ligands have been replaced by the bidentate dppf
ligand during the reaction.
(3)
Compound 4 is a bimetallic complex that contains
Re and Fe metals. The orientation of three chloro
ligands has been changed from meridional (in 1) to
facial (in 4) during the reaction. 31P{1H}-NMR spectra
of 4 exhibit a singlet at l −26.00 ppm, which indicates
cis-orientated phosphorus nuclei of the dppf ligand to
1
be equivalent. In H-NMR spectra of the free dppf, the
cyclopentadienyl (Cp) protons show two triplets at l
4.25 and 3.98 ppm. However, upon coordination of this
ligand to the Re metal in 4, these signals are split into
the four broad singlets at l 5.31, 4.72, 4.47, and 4.43
ppm, consistent with the lowered molecular symmetry.
(5)

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N.-S. Choi, S.W. Lee / Journal of Organometallic Chemistry 627 (2001) 226–232
3.2. Structure of 4
treated with dppf to give fac-Re(NPh)Cl3(dppf) (5) in
our study (Scheme 1). As shown in Eq. (3), compound
1 reacts with dppf to give fac-Re(O)Cl3(dppf) (4). Com-
pound 4 was treated with PhNꢀPPh3 in refluxing ben-
zene for 2 h in order to check whether compound 5 can
be prepared directly from compound 4. This reaction
gives a mixture of 4 (63%) and 5 (37%), as shown in
Scheme 1. When the reaction time is increased, the ratio
of 4 to 5 becomes 22:78 (6 h) and 13:87 (24 h),
respectively. However, the reaction never goes to com-
pletion even after extremely long reaction times (120 h).
The attempt to separate 4 and 5 was not successful
because of their similar solubility in various organic
solvents. This reaction was monitored by 31P{1H}-
NMR spectroscopy which exhibits two singlets with
different intensities corresponding to 4 and 5. Com-
pound 4 was treated with organic isocyanates such as
t-BuNCO and 2,6-i-Pr2-C6H3NCO in order to prepare
its imido analogs, but no sign of reaction was observed
even under vigorous conditions (refluxing THF or
benzene).
The molecular structure of 4 with the atom-number-
ing scheme is shown in Fig. 1. The molecular structure
of 5 has recently been reported by our group [18].
Compound 4 has three fac-chloro ligands, one oxo
ligand, and one bidentate dppf ligand. The coordina-
tion sphere of the Re metal can be described as a
distorted octahedron. The equatorial plane, defined by
Cl1, Cl2, P1, and P2, is relatively planar with an
,
average atomic displacement of 0.0256 A. The Re metal
,
lies above the equatorial plane by 0.147(2) A.
,
The bond distance (1.719(7) A) of Re–O1 is fairly
typical of the oxo ligand in a monoxo Re (d2) complex
in a +5 oxidation state, in which the Re–O bond
,
distance ranges from 1.63(7) to 1.76(1) A [3]. Nugent
and Mayer have suggested that monoxo complexes are
best thought of as having a triple bond, cis-dioxo
complexes a bond order of 2.5, and trans-dioxo and
fac-trioxo complexes a bond order of 2 [5]. Therefore,
the Re–O1 bond seems to be a ReꢁO triple bond, and
the oxo ligand can be regarded as a six-electron donor.
On the basis of these arguments, 4 can be regarded as
an 18-electron complex.
When 4 and 5 are treated with MeLi, we can only
isolate the free dppf ligand. In addition, they react with
MeMgBr to give too many intractable species. Surpris-
ingly, compound 5 is robust toward HCl and H2O; in
other words, they do not decompose in their presence.
Compound 5 reacts with an oxygen nucleophile (Li-
OEt) under refluxing ethanol for 3 h to give a mixture
of 5 (26%) and Re(NPh)(OEt)Cl2(dppf) (74%). In
31P{1H}-NMR spectra of this mixture, phosphorous
nuclei of Re(NPh)(OEt)Cl2(dppf) exhibit a singlet at l
−8.81 ppm, indicating the phosphorous nuclei of the
dppf ligand to be equivalent. The only structure that
can explain these 31P{1H}-NMR spectra is the one
shown in Eq. (6), in which the ethoxy ligand is trans to
The two Cp rings are not perfectly parallel but are
twisted from each other with a dihedral angle of 3.2(9)°.
The torsion angle of P1–C7–C12–P2 is 26.9(5)°, indi-
cating that the two Cp rings adopt a gauche (or stag-
gered) conformation. For comparison, the ideal torsion
angle for the gauche conformation is 36°. The Fe–Ct
(Ct: a centroid of the Cp ring) distances are 1.647 and
,
1.649 A, and the angle Ct1–Fe–Ct2 (Ct1: C1–C5; Ct2:
C6–C10) is 178.28°. The bite angle P1···Fe···P2 is
,
68.64(6)°, and the distance P1···P2 is 3.903(4) A. The
above bonding parameters within a ferrocene moiety
are consistent with those found in octahedral rhenium
complexes in which the dppf group acts as a ligand [10].
1
the imido ligand. In H-NMR spectra, the OEt protons
in fac,trans-Re(NPh)(OEt)Cl2(dppf) exhibit a quartet at
,
The distance Re···Fe is 4.391(2) A, which clearly rules
3
l 3.95 (CH2, JH–H=7 Hz) ppm and a triplet at l 0.94
out direct bonding interaction between the two metals.
3
(CH3, JH–H=7 Hz) ppm.
3.3. Properties
Compound 1 is known to react with PhNꢀPPh3 to
give mer-Re(NPh)Cl3(PPh3)2 (2) [12], which has been
(6)
As shown in Table 3 and Fig. 2, compound 4 con-
taining the Re–oxo fragment exhibits one reversible
oxidation, and compounds 5 and 6 containing the
Re–imido fragment exhibit two reversible oxidations.
The free dppf ligand in dichloromethane exhibits one
irreversible, ferrocene-centered oxidation [19]. Com-
pound Re(NPh)(dppe)Cl3, which has a chelating bis-
phosphine ligand (dppe=bis(diphenylphosphino)-
ethane) instead of the dppf ligand, exhibits one re-
Scheme 1.

N.-S. Choi, S.W. Lee / Journal of Organometallic Chemistry 627 (2001) 226–232
231
Table 3
Electrochemical data from cyclic voltammetry studies
Compound
Scan rate (mV s−1
)
E° (V)
I
pc/Ipa
Epa (V)
Epc (V)
4
100
200
300
500
1000
1.223
1.222
1.217
1.220
1.225
0.933
0.908
0.877
1.035
1.073
1.274
1.276
1.272
1.28
1.173
1.168
1.163
1.158
1.153
1.296
5
100
200
0.871
1.423
0.891
1.445
0.876
1.434
0.883
1.442
0.880
1.447
0.91
0.924
1.476
0.949
1.505
0.939
1.498
0.952
1.514
0.968
1.533
0.818
1.370
0.834
1.384
0.812
1.370
0.815
1.370
0.792
1.361
1.063
0.937
1.031
0.953
0.973
0.989
1.016
0.988
1.091
300
500
1000
6
100
200
0.655
1.224
0.653
1.217
0.649
1.219
0.649
1.219
0.649
1.220
0.936
0.935
0.956
0.956
0.965
0.982
0.933
1.023
0.913
1.045
0.705
1.280
0.705
1.276
0.705
1.280
0.708
1.286
0.718
1.295
0.605
1.167
0.600
1.158
0.593
1.158
0.590
1.151
0.580
1.145
300
500
1000
Re(NPh)(dppe)Cl3
100
200
300
500
1000
1.261
1.259
1.263
1.261
1.263
1.043
1.036
1.073
1.046
1.012
1.308
1.308
1.314
1.317
1.327
1.214
1.211
1.211
1.204
1.198
electron-donating isopropyl substituent on the imido
phenyl ring, is more easily oxidized than compound 5
(Table 3). At various scan rates (Table 3), the oxidation
potentials of all compounds remain constant, which
indicates that their oxidized forms are stable on the
cyclovoltammetry time scale.
In summary, we have prepared Re(V)–oxo–dppf
and Re(V)–imido–dppf compounds, one of which has
been structurally characterized. These compounds ex-
hibit interesting redox processes in which the oxidation
behavior appears to be dependent on the type of ligand
coordinated to the Re metal.
versible oxidation wave at 1.263 V at the scan rate of
300 mV s−1 (Fig. 3). The oxidation potential of
Re(NPh)(dppe)Cl3 is included to show that the Re–
imido center is not oxidized at potentials where the
ferrocene-centered oxidation occurs. On the basis of the
oxidation potential values of the free dppf and
Re(NPh)(dppe)Cl3, the second oxidation in the oxida-
tion of compounds 5 and 6 probably results from the
presence of the Re–imido fragment. Therefore, it can
be inferred that the coordinated dppf ligand in 4–6
displays a reversible oxidation process.
The oxidation potential of the free dppf ligand (0.53
V) is shifted considerably to more positive values in the
Re–oxo–dppf (4) and Re–imido–dppf (5 and 6) com-
pounds, which suggests that the Re moieties might
behave as electron-withdrawing groups as a whole. This
type of a positive shift in E° is also observed for
Re(dppf)(CO)4Cl which shows one reversible ferrocene-
centered oxidation at 0.67 V at the scan rate of 100 mV
s−1 [19]. As expected, compound 6, which has a more
4. Supplementary material
Crystallographic data for structural analysis have
been deposited at the Cambridge Crystallographic Data
Center, CCDC No. 155394 for compound 4. Copies of
this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge,

232
N.-S. Choi, S.W. Lee / Journal of Organometallic Chemistry 627 (2001) 226–232
CB2 1EZ, UK (Fax: +44-1223-336033; e-mail: de-
posit@ccdc.cam.ac.uk or www: http://www.ccdc.
cam.ac.uk).
Acknowledgements
.
This work is based on research sponsored by the
Korea Research Foundation Grant (KRF-2000-015-
DP0262).
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Fig. 3. Cyclic voltammograms (300 mV s−1
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