New binucleating ligand with two [P,S] chelation pockets on a single phenyl ring: Syntheses and X-ray structures of 1,4-bis(diphenylphosphino)-2,5-difluoro-3,6-bis(methylthio)benzene and of bimetallic complex (CO)3Fe(μ-[(PPh2)(SMe)C<

Article abstract of DOI:10.1016/j.jorganchem.2006.08.076

Double deprotonations of 1,4-dibromo-2,5-difluorobenzene with LDA (2 equiv., T < -90 °C) generate a reasonably stable organodilithium intermediate. Quenching this reaction mixture with chlorophosphines ClPR₂ produce p-bis(phosphino)benzenes R

Full text of DOI:10.1016/j.jorganchem.2006.08.076

Journal of Organometallic Chemistry 691 (2006) 5024–5029
www.elsevier.com/locate/jorganchem
New binucleating ligand with two [P,S] chelation pockets on a
single phenyl ring: Syntheses and X-ray structures of
1,4-bis(diphenylphosphino)-2,5-difluoro-3,6-bis(methylthio)benzene
and of bimetallic complex
(CO)3Fe(l-[(PPh2)(SMe)C6F2(SMe)(PPh2)])Fe(CO)3
*
Natcharee Kongprakaiwoot, Rudy L. Luck, Eugenijus Urnezius
Department of Chemistry, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931, USA
Received 9 August 2006; received in revised form 20 August 2006; accepted 20 August 2006
Available online 1 September 2006
Abstract
Double deprotonations of 1,4-dibromo-2,5-difluorobenzene with LDA (2 equiv., T < ꢀ90 °C) generate a reasonably stable organodil-
ithium intermediate. Quenching this reaction mixture with chlorophosphines ClPR2 produce p-bis(phosphino)benzenes R2P–C6Br2F2–
PR2 (R = Ph, 4a; R = iPr, 4b). Facile lithium–bromine exchange occurs upon exposure of 4a to BuLi (2 equiv., ꢀ80 °C), leading to
the generation of another organodilithium intermediate. Addition of MeS–SMe (2 equiv.) to such reaction mixtures gives 1,4-bis(diph-
enylphosphino)-2,5-difluoro-3,6-bis(methylthio)benzene (2). Compound 2 is the first example of a neutral binucleating ligand featuring
the [P,S] chelating sites on the opposite sides of a single phenyl ring. Compound 4b does not undergo the analogous transformation when
subjected to the same conditions (2BuLi/2MeS–SMe). Addition of 2 to Fe(CO)5/2(Me3NO Æ 2H2O) reaction mixtures led to the isolation
of the bimetallic complex {(CO)3Fe[P,S]–C6F2–[P,S]Fe(CO)3} (3), ([P,S] represents the chelating pockets formed by adjacent –PPh2 and –
SMe groups). All of the new compounds were characterized by spectroscopic and analytical techniques (multinuclear NMR, mass-spec-
trometry, and/or elemental analysis). In addition, compounds 2 and 3 were characterized via single crystal X-ray diffraction methods.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Binucleating; Phosphorus–sulfur ligands; Bimetallic complex; Iron tricarbonyl
1. Introduction
phorus and sulfur allows for facile tuning of the steric
and electronic properties of such ligands. Most of the stud-
ies involving such [P,S] ligands have been centered on
monometallic complexes, and the number of well-defined
binucleating [P,S] ligands and their bimetallic complexes
is relatively small [7,8]. Recently, we have reported the
new syntheses of potentially binucleating ligands – sym-
metric and unsymmetric 1,2,4,5-tetrakis(phosphino)benz-
enes [9], where the sequential generation of
organodilithium intermediates from 1,4-dibromo-2,5-diflu-
Polydentate ligands containing both phosphorus(III)
and sulfur(II) groups in their architectures have been exten-
sively used in coordination chemistry [1]. Derivatives of o-
phosphinothiophenol (Fig. 1, 1) are probably the most
popular among such [P,S] ligands, as they effectively com-
plex to metal centers via the formation of a five-membered
chelate ring [2–5], and are relatively easy to synthesize [6].
Furthermore, the ability to vary the substituents on phos-
i
orobenzene followed by ClPR2 quenches (R = Ph, Et, Pr)
were utilized. Structurally analogous tetrakis(phosphino)-
or tetrakis(thio)benzenes with P- or S-donor ligands at
the 1,2,4,5 positions have been successfully used as
*
Corresponding author. Tel.: +1 906 4872055; fax: +1 906 4872061.
E-mail address: urnezius@mtu.edu (E. Urnezius).
0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.08.076

N. Kongprakaiwoot et al. / Journal of Organometallic Chemistry 691 (2006) 5024–5029
5025
have now focused our initial attention towards developing
the corresponding [P,S] ligands. The organodilithium
intermediate generated from 4a via double lithium–
halogen exchange readily reacts with dimethyldisulfide,
yielding 1,4-bis(diphenylphosphino)-2,5-difluoro-3,6-bis-
(methylthio)benzene (2) in 58% isolated yield (Eq. (1)).
The byproduct of this reaction is CH3SLi, resulting from
a heterolytic disulfide cleavage. This represents a potential
problem, as alkali metal organothiolates are known to
undergo nucleophilic substitution reactions with fluorines
of Carom–F bonds [22,23]. Hence, the reaction sequence
depicted in Eq. (1) can potentially proceed further, even-
tually producing tris(thio) and tetrakis(thio) substituted
bis(phosphino)benzenes in the reaction mixture. Although
we did not detect the formation of such products under
our conditions, alternative sources for the introduction
of the thiomethyl groups were also explored. S-methyl
methanethiosulfonate, CH3S–S(@O)2CH3, is particularly
attractive for this purpose, as the nucleophilic character
of the leaving group (CH3SO2Li) should be much less
pronounced. However, the substitution of dimethyl disul-
fide by CH3S–S(@O)2CH3 in the reaction sequence
depicted in Eq. (1) did not afford expected improvements
in the reaction yield. In fact, the opposite was observed:
reactions were more difficult to control, and the yields
were less reproducible; the reasons behind this were not
investigated
Fig. 1. General representation of o-phosphinothiophenols (1, R = aryl or
alkyl; R0 = aryl, alkyl, or a lone pair); structural drawings of 1,4-
bis(diphenylphosphino)-2,5-difluoro-3,6-bis(methylthio)benzene (2), and
its bimetallic complex 3.
binucleating ligands for the formation of bimetallic com-
plexes [10–12] and of polymetallic aggregates [13–17].
However, no 1,2,4,5-tetrasubstituted benzenes where the
chelating sites are defined by mixed P- and S-donor groups
have been reported. Herein, we present the syntheses of the
first such ligand – 1,4-bis(diphenylphosphino)-2,5-difluoro-
3,6-bis-(thiomethyl)benzene (Fig. 1, 2). Given the potential
of [P,S] chelate chemistry [1], such binucleating ligands
should be interesting building blocks for the formation of
bimetallic complexes and polymetallic arrays, especially
since the [N,S] structural analog of 2, 2,5-diamino-1,4-ben-
zenedithiol has been used for the syntheses of polymeric
transition metal complexes [18,19]. Initial coordination
studies show that compound 2 acts as an effective binucle-
ating ligand, as ascertained through the formation of the
bimetallic bis(iron tricarbonyl) complex (Fig. 1, 3).
2. Results and discussion
2.1. Syntheses and spectral properties
Organodilithium intermediates have been extensively
utilized as dianionic synthons in organic syntheses [20].
Recently, we have shown that organodilithio intermedi-
ates can be formed when selected tetrahalobenzenes fea-
turing protons flanked by F/Cl and F/Br atoms are
exposed to lithium diisopropylamide (LDA) at low tem-
peratures [9,21]. Quenching such reaction mixtures with
ð1Þ
Spectroscopic characteristics of the main functional
1
groups of 2 (d 2.17 (s) in H NMR for thiomethyl and d
ꢀ10.9 (m) in 31P NMR for phosphine) are similar to those
reported for other diphenylphosphine derivatives bearing
o-thiomethylphenyl moieties [2,24]. Thus, it appears that
the fluorines on the central phenyl ring in 2 have a negligi-
ble effect on the corresponding chemical shift values. Sig-
nals in both 31P and 19F NMR spectra of 2 are
multiplets, suggesting possible weak 31P–19F interactions,
but the coupling is unresolved.
i
chlorophosphines ClPR2 (R = Ph, Pr) allowed for the
syntheses of 1,4-bis(phosphino)benzenes containing tetra-
halogenated central phenyl rings [9,21]. The presence of
the heavier halogens (particularly bromine) in the later
compounds may be utilized for designing further synthetic
steps. For example, we have shown that 1,4-bis(diph-
Our attempts to obtain other structural analogs of
2 were less successful. A suitable starting compound,
1,4-bis(diisopropylphosphino)-2,5-dibromo-3,6-difluoro-
benzene (4b) was obtained in good (ꢁ70%) yield via the
synthetic sequence used for 4a [9] (dilithiation of 1,4-dib-
romo-2,5-difluorobenzene followed by ClPiPr2 quench).
However, substituting 4a by 4b in the reaction sequence
depicted in Eq. (1) did not produce the expected product,
enylphosphino)-2,5-dibromo-3,6-difluorobenzene
(4a)
undergoes double lithium–bromine exchange upon reac-
tions with BuLi thus generating another organodilithium
intermediate, and quenching the reaction mixtures with
i
chlorophosphines ClPR2 (R = Ph, Pr, Et) lead to the syn-
theses of novel tetrakis(phosphino)difluorobenzenes [9].
Such a synthetic approach (sequential generations of
organodilithium intermediates from 1,4-dibromo-2,5-diflu-
orobenzene, followed by electrophile quenches) may
potentially be developed into a general synthetic strategy
for the construction of other binucleating ligands bearing
1,2,4,5-tetrasubstituted benzene structural frames. We
i.e.
1,4-bis(diisopropylphosphino)-2,5-difluoro-3,6-bis-
(methylthio) benzene. Substantial amounts of unreacted
4b were recovered in all experiments, suggesting that Li
for Br exchange in 4b may be restricted or proceeded
too slowly under the reaction conditions used.

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N. Kongprakaiwoot et al. / Journal of Organometallic Chemistry 691 (2006) 5024–5029
The binucleating ability of the ligand 2 was ascer-
tained as it ligated two iron tricarbonyl fragments (Eq.
(2)). The addition of 2 to a Fe(CO)5/trimethylamine N-
oxide [25] mixture resulted in immediate formation of a
dark red solution, from which the bimetallic complex 3
was isolated (by crystallization) in moderate 32% yield
(Eq. (2)). Monometallic complexes containing metal
carbonyl fragments with [P,S] chelation of (2-thiomethyl-
phenyl)diphenylphosphine ligands have been well docu-
mented [26–28], but only one complex containing iron
tricarbonyl ligated to a neutral [P,S] ligand has been
described previously [29]. Compound 3 displays three
absorption bands (1996, 1928 (shoulder), and
1905 cmꢀ1) in the carbonyl region of the IR spectrum.
Such values are of somewhat (5–15 cmꢀ1) higher energy
than the CO absorptions observed for structurally related
iron tricarbonyl complexes with chelating diphosphine
ligands containing –PPh2 groups [11,30,31]. This shift
to higher energy may be caused by the reduced donating
abilities of our ligand 2 resulting from the presence of
highly electronegative fluorines on the central phenyl
ring. Similar changes in the carbonyl frequencies in IR
spectra have been observed when M(CO)x complexes of
fluorinated and fluorine-free chelating polyphosphines
and polythioethers [10,32] were compared. The 31P
NMR spectrum of 3 displays a signal at d 101.3 (m),
and this value is comparable to the chemical shift values
observed for iron tricarbonyl complexes with 1,2-
bis(diphenylphosphino)benzene (d 98.7) [33] and 1,2,4,5-
tetrakis(diphenylphosphino)benzene (d 92.8) [11]. The
ligation of the Fe(CO)3 fragments to ligand 2 seems to
have minimal effect on chemical shift values of fluorine,
as the 19F NMR spectrum of complex 3 (d ꢀ92.6) is very
close to that of the free ligand (d ꢀ91.8)
ð2Þ
2.2. Structural characterizations of compounds 2 and 3
Compound 2, the ligand, crystallized around an inversion
point with three contiguous carbon atoms on the central
phenyl ring and –PPh2, –SMe and F groups attached to each
carbon atom (i.e., C1, C2 and C3) comprising the asymmet-
ric unit. This central phenyl ring is almost planar with the P
atoms located 0.232(1) A above and below the plane. There
was disorder associated with the position of the –SMe and F
fragments as illustrated in Fig. 2 (see Table 1).
The model refined (as detailed in Section 4) consisted of
both F and –SMe groups (i.e., F1, S1–C11) constrained
together and situated below the central benzene plane as
represented on the left (2-a) in Fig. 2. If the model refined
consisted of atoms F2, C11 and S1, then this would have
implied an F2–C11 distance of 2.38(1) A which was consid-
ered as unrealistic. These disordered atoms (i.e., F and S
atoms) are situated some 0.5 A above or below the central
plane except for atom F2 which is only 0.257(7) A. This
can be attributed to lesser steric hindrance from the adja-
cent methyl group C21 as is evident on the representation
shown on the right (2-b) in Fig. 2. In contrast, F1 is
˚
˚
˚
˚
˚
0.502(8) A out of the plane and located closer to the –
PPh2 group as the C10–C3–F1 angle of 110.6(4)° suggests.
In both of the orientations (2-a and 2-b), the adjacent sub-
stituents F, –SCH3 and –PPh2 are located on one side of the
phenyl ring, whereas their symmetry equivalents are on the
Fig. 2. ORTEP-3 [34] illustration of the 45.6(6)% (2-a) and 54.4(6)% (2-b) orientation of the F- and MeS-disordered groups in compound 2. Ellipsoids are
˚
drawn at the 30% occupancy level and H atoms are represented by circles of arbitrary radii. Selected bond distances and angles: P1–C1 1.853(3) A, C2–S1
˚
˚
˚
˚
˚
˚
1.823(4) A, C2–S2 1.808(3) A, C3–F1 1.399(7) A, C3–F2 1.390(6) A, S1–C11 1.778(11) A, S2–C21 1.782(8) A; C11 S1 C2 100.7(4)°, C21 S2 C2 98.0(3)°, C3
C2 S1 116.9(2)°, C3 C2 S2 124.2(2)°.

N. Kongprakaiwoot et al. / Journal of Organometallic Chemistry 691 (2006) 5024–5029
5027
Table 1
Summary of crystallographic data for 2 and 3
Compound
2
3
Formula
C32H26F2P2S2
574.59
C38H26F2Fe2O6P2S2
854.34
P21/a
Formula Weight
Space group
Unit cell dimensions
ꢀ
P1
˚
a (A)
9.414(2)
9.639(2)
10.125(2)
62.49(1)
80.98(1)
61.69(2)
715.1(3)
1
1.334
0.332
293(2)
0.71073
2.28–22.46
1860/1402
8.397(2)
26.473(4)
9.316(1)
90
113.71(1)
90
1896.1(6)
2
1.496
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
3
˚
V (A )
Z
qcalc (g/cm3)
l (Mo Ka mmꢀ1
T (K)
)
1.014
293(2)
0.71073
1.54–24.97
3320/2291
˚
k (A)
h Range (°)
Measured/independent
Fig. 3. ORTEP-3 illustration of complex 3. Ellipsoids are drawn at the
reflections
30% occupancy level and H atoms are represented by circles of arbitrary
Final R indices
[I > 2sigma(I)]a
R indices (all data)
R1 = 0.038,
R1 = 0.045,
wR2 = 0.096d
R1 = 0.088,
wR2 = 0.110
0.335, ꢀ0.376
˚
wR2 = 0.090b,c
R1 = 0.066,
radii. Selected bond distances and angles: Fe1–C1 1.737(6) A, Fe1–C3
˚
˚
˚
1.770(6) A, Fe1–P1 2.2066(11) A, Fe1–S1 2.2578(12) A, C1–O1
˚
˚
˚
˚
1.146(7) A, C2–O2 1.152(7) A, C131–S1 1.791(3) A, C132–P1 1.852(3) A;
P1 Fe1 S1 88.95(4)°, C131 S1 Fe1 106.63(12)°, C132 P1 Fe1 107.41(11)°,
C1 Fe1 S1 176.8(3)°, C3 Fe1 C2 124.2(2)°.
wR2 = 0.102
0.294, ꢀ0.166
Largest difference in
peak and hole
Goodness-of-fit on F2
1.042
1.017
a
distorted trigonal bipyramidal, with one CO (i.e., C1–O1)
and –SMe ligands occupying the axial positions and the
remaining two CO’s and –PPh2 situated in the equatorial
plane. Interestingly, the only other reported Fe(CO)3 com-
plex with a neutral [P,S] ligand, 1-(diphenylphosphino)-10-
(phenylthio)ferrocene, features the iron center in a tbp
geometry as well, but with the –PPh2 group in axial and
the –SPh in equatorial positions [29]. The different coordi-
nation preferences for the ligating groups observed in 3
may be dictated by both steric and electronic effects. The
equatorial positions of trigonal bipyramidal complexes con-
taining d8–d10 metal centers are expected to be occupied by
acceptor ligands [39]. While the p-acceptor properties of ter-
tiary phosphines such as PPh3 or even P(C6F5)3 are esti-
mated as weak (at best) [40,41], the ligand coordination
mode observed in our complex 3 implies that the phosphine
moiety of the [P,S] pocket of the ligand 2 is a stronger accep-
tor that the thioether functionality. However, a significantly
bulkier phosphine group may be coordinated in the equato-
rial position to reduce steric effects.
R = R(Fo ꢀ Fc)/R(Fo).
2
2 1=2
b
c
wR ¼ ½R½wðF 2o ꢀ F c2Þ ꢂ=R½wðF 2oÞ ꢂꢂ
.
2
w ¼ 1=½r2ðF o2Þ þ ð0:0423 ꢃ PÞ þ 0:3539Pꢂ; where P ¼ ðMaxðF 2o; 0Þþ
2 ꢃ F 2oÞ=3.
2
d
w ¼ 1=½r2ðF 2oÞ þ ð0:0430 ꢃ PÞ þ 1:7135Pꢂ.
other side of the same ring (aaabbb substitution pattern).
The existence of 2 in two orientations is most likely due
to the packing effects present in the solid state, as no signal
separation corresponding to the presence of 2-a/2-b in solu-
tion was observed by low temperature NMR measurements
(1H and 31P, ꢀ45 °C, CDCl3). Persulfurated aromatic deriv-
atives have been shown to display varying substitution pat-
terns resulting from different steric orientations of the –SR
substituents around the central aromatic core [35], and this
has been referred to as a solid state phenomenon, resulting
from packing effects.
An ORTEP-3 representation of complex 3 is shown in
Fig. 3. The molecule is situated around an inversion point
and, as was the case with the ligand 2, 50% of the molecule
comprises the asymmetric unit. The geometry around the
Fe was estimated by a s test, developed to assess the nature
of pentacoordinate geometry (trigonal bipyramidal (tbp) vs.
square pyramidal) [36]. The parameter s is expressed as
s = (a ꢀ b)/60, where a and b are the largest and the second
largest angles around the metal center. Therefore, s = 0 is
expected for an ideal square pyramidal geometry, whereas
s = 1 would represent tbp structure. The calculated s value
for the geometry at the iron center in 3 is 0.88, and similar
values have been determined for Fe(CO)3 complexes with
bidentate chelating bisphosphines [37,38]. Hence, the geom-
etry around the iron centers in 3 can be viewed as slightly
The S and P atoms in 3 are in the plane of the central phe-
nyl ring of the ligand. Iron atoms in the molecule are posi-
tioned above and below this plane, but the displacement is
very small (the angle between the planes defined by P1–Fe–
S1 and carbon atoms of the central phenyl ring is only 3.2°).
Such distortions are more strongly pronounced in the struc-
turally analogous bimetallic complex featuring Fe(CO)3
fragments ligated to 1,2,4,5-tetrakis(diphenylphosphino)-
˚
benzene [11]. The Fe–P distance (2.2066(11) A) in 3
compares well to analogous metal–ligand distances
˚
(2.184(1)–2.210(2) A) determined for phosphine ligands
at the equatorial positions in trigonal bipyramidal

5028
N. Kongprakaiwoot et al. / Journal of Organometallic Chemistry 691 (2006) 5024–5029
{[P,P]FeCO3} complexes ([P,P] represents a chelating bis-
phosphine) [11,37,38]. Also, the Fe–S bond length
ment or Perkin–Elmer Spectrum One spectrometer.
Elemental analyses were performed at Galbraith Laborato-
ries Inc. (Knoxville, TN 37950-1610).
˚
(2.2578(12) A) in 3 is comparable to the Fe–S distance
˚
(2.288(2) A) reported for (cyclo-1,3-C4H8S2)Fe(CO)4 [42],
where the thioether ligates at the axial position of the tbp
complex. Carbonyl ligands in 3 are not equivalent in the
solid state, but a single peak observed in 13C NMR spec-
trum (d 218.4 s, 31P–13C coupling not resolved) suggests a
dynamic behavior for the Fe(CO)3 moiety in solution. Such
behavior is well documented for iron tricarbonyl complexes
with chelating bidentate ligands [32], and possible mecha-
nisms have also been suggested [43].
4.2. Syntheses
4.2.1. 1,4-Bis(diphenylphosphino)-2,5-difluoro-3,6-
bis(methylthio)benzene (2)
To a stirred solution of 1,4-dibromo-2,5-bis(diph-
enylphosphino)-3,6-difluorobenzene (2.00 g, 3.12 mmol) in
THF (250 mL) at ꢀ80 °C was added 2.1 equiv. of sec-BuLi
as a 1.3 M solution in hexanes. The mixture was stirred at
ꢀ80 °C for 1 h, and then was slowly treated with a solution
of 2.1 equiv. of dimethyldisulfide in THF (10 mL) through
a cannula to yield a clear dark brown solution. The mixture
was stirred for another hour at ꢀ80 °C and then allowed to
warm up to room temperature overnight. The resulting
solution was filtered, volatiles were removed under vacuo
to yield a brown solid. Washing of the latter by hot isopro-
panol (100 mL) gave 2 as an orange solid. Yield: 1.039 g
(58 %). Melting point: 205 °C (decomp.). 1H NMR
(CDCl3): d 7.40 (m, 8H), 7.32 (m, 12H), 2.17 (s, 6H). 31P
NMR (CDCl3): d ꢀ10.9 (m). 19F NMR (CDCl3): d ꢀ91.8
(m). HRMS (FAB): Calc. for C32H27F2P2S2 575.0997;
found: m/z = 575.0996 (MH+). Crystals suitable for X-
ray diffraction experiment were obtained by crystallization
of 2 from ether/toluene (1:1) (1 week, ꢀ28 °C).
3. Conclusions
The successful syntheses of the compound 2 suggest that
a wide range of new binucleating ligands containing chelat-
ing pockets defined by hetero-donor groups can be pro-
duced. Such ligands should be useful for the construction
of novel bimetallic complexes (e.g. 3), and for one-dimen-
sional solids.
4. Experimental
4.1. General procedure
All manipulations were carried out using Schlenk tech-
niques or in a dry box under an N2 atmosphere. Low tem-
perature reactions were performed in Schlenk flasks
immersed in an ethanol/liquid N2 slush, contained in a
Dewar flask. Solvents were purified before use by distilla-
tion from Na–benzophenone ketyl (ether, THF, hexanes,
benzene) or CaH2 (toluene, isopropanol, dichloromethane)
or Na (pyridine) under N2 atmosphere. Methanol was puri-
fied by either distillation from Mg(OCH3)2 or deoxygenated
by bubbling nitrogen through it for 1 h. 1,4-Dibromo-2,5-
bis(diphenylphosphino)-3,6-difluorobenzene has been pre-
pared utilizing a previously reported synthetic procedure
[9]. Commercially available chlorophosphines were purified
prior to usage: ClPPh2 was distilled under reduced pressure;
ClPiPr2 was frozen and degassed while thawing under vac-
uum (repeated three times). LDA (lithium diisopropyla-
mide) was freshly prepared immediately prior to use
according to a published procedure [44]. Dimethyldisulfide
4.2.2. (CO)3Fe(l ꢀ [(PPh2)(SMe)C6F2(SMe)-
(PPh2)])Fe(CO)3 (3)
A solution of Me3NO Æ 2H2O (0.75 g, 6.75 mmol) in dry
methanol (20 mL) was slowly added to a solution of
Fe(CO)5 (0.44 mL, 3.37 mmol) in THF (10 mL) kept at
ꢀ30 °C. A clear brown solution turned dark red upon addi-
tion of a solution of 2 (0.968 g, 1.69 mmol) in THF
(30 mL). Upon completion of the addition, the reaction
mixture was allowed to warm up to room temperature
overnight. Volatiles were removed under vacuo to yield a
brown solid which was washed with hot toluene (40 mL).
Dark brown crystals of 3 were obtained by hexane vapor
diffusion into a THF solution (room temperature, 3 days).
Yield: 0.464 g (32%). IR (KBr, cmꢀ1; CO; relative intensi-
ties given in parentheses): 1996 (0.72), 1928 (0.62, sh), 1905
1
(1.00). H NMR (C6D6): d 7.60 (m, 8H), 6.96 (m, 12H),
was dried over molecular sieves (4 A), and then frozen and
2.05 (s, 6H). 31P NMR (C6D6): d 101.3 (m). 19F NMR
(C6D6): d ꢀ92.6 (m). Anal. Calc. for C38H26F2Fe2O6
P2S2: C, 53.42; H, 3.07. Found: C, 53.18; H, 3.34%.
˚
degassed while thawing under vacuum (repeated twice). 1H,
31P, and 19F NMR spectra were recorded on Varian
INOVA spectrometer operating at 400, 161, 376 MHz,
respectively. Spectra are referenced to tetramethylsilane
(1H), 85% H3PO4 as an external reference (31P), and CFCl3
as an internal reference in a sealed capillary tube (19F). Low
resolution mass spectrometric measurements were per-
formed on Shimadzu QP5050A instrument; high resolution
mass spectrometric measurements were performed at Mass
Spectrometry Facility of Michigan State University (East
Lansing, MI 48824-1319). Infrared spectrometric measure-
ments were performed on either Mattson 3020 FTIR instru-
4.2.3. 1,4-Dibromo-2,5-bis(diisopropylphosphino)-3,6-
difluorobenzene (4b)
To a stirred cold (ꢀ95 °C) solution of 1,4-dibromo-2,5-
difluorobenzene (2.00 g, 7.36 mmol) in THF (250 mL) was
added (via cannula) freshly prepared LDA (2.0 equiv.) in
the same solvent. After 5 min, a solution of 2.3 equiv. of
diisopropylchlorophosphine in THF (20 mL) was slowly
introduced via a cannula. The mixture was stirred at
ꢀ95 °C for 1 h and then allowed to warm up to room tem-

N. Kongprakaiwoot et al. / Journal of Organometallic Chemistry 691 (2006) 5024–5029
5029
[2] J.S. Kim, J.H. Reibenspies, M.Y. Darensbourg, J. Am. Chem. Soc.
118 (1996) 4115.
[3] P. Perez-Lourido, J. Romero, J. Garcia-Vazquez, A. Sousa, K.P.
Maresca, D.J. Rose, J. Zubieta, Inorg. Chem. 37 (1998) 3331.
[4] P. Perez-Lourido, J. Romero, J.A. Garcia-Vazquez, A. Sousa, J.
Zubieta, K. Maresca, Polyhedron 17 (1998) 4457.
[5] D. Morales-Morales, S. Rodriguez-Morales, J.R. Dilworth, A.
Sousa-Pedrares, Y. Zheng, Inorg. Chim. Acta 332 (2002) 101.
[6] E. Block, G. Ofori-Okai, J. Zubieta, J. Am. Chem. Soc. 111 (1989)
2327.
[7] M.F.M. Al-Dulaymmi, P.B. Hitchcock, R.L. Richards, Polyhedron 8
(1989) 1876.
perature overnight to give a slightly cloudy yellow mixture.
The reaction mixture was filtered and all volatiles were
removed under vacuo to yield a light yellow solid, which
was purified by washing with hot methanol (70 mL). Yield:
2.575 g (69%). Melting point: 210–211 °C. 1H NMR
(CDCl3): d 2.51 (m, 4H), 1.19 (m, 12H), 0.94 (m, 12H).
31P NMR (CDCl3): d 27.5 (m). 19F NMR (CDCl3): d
ꢀ90.4 (m). HRMS (FAB): calc. for C18H28F2P2Br2
502.0001; found m/z = 501.9999 (M+).
[8] M.F.M. Al-Dulaymmi, P.B. Hitchcock, R.L. Richards, Polyhedron
10 (1991) 1549.
4.3. X-ray crystallography
[9] N. Kongprakaiwoot, R.L. Luck, E. Urnezius, J. Organomet. Chem.
689 (2004) 3350.
Suitable crystals of complexes 2 and 3 were selected,
coated with epoxy resin and placed on the heads of thin
glass fibers, which were anchored in goniometer mounting
pins. The individual pin-mounted crystal was then inserted
into the goniometer head of the X-ray diffractometer and
centered in the beam path. The procedures used to collect
the data and refine the structure were as detailed previously
for other complexes [9]. The refinement of complex 3 was
straightforward as it did not contain disorder. Ligand 2
had crystallized with disorder in the F and MeS groups.
This was accounted for by including atoms at the various
sites and refining the disordered atoms’ occupancies set to
one with the F and corresponding S atom above one plane
containing identical constrained occupancies. This resulted
in a 45.6(6)–54.4(6)% occupancy ratio for S1–C11 and S2–
C21 and also for F1 and F2, respectively. This refinement
model afforded the lowest figures of merit. Another model
(which afforded slightly higher figures of merit), tying the
occupancies of trans disposed MeS and F ligands would
have implied a very short distance between the methyl
[10] M.E. Peach, C. Bruschka, Can. J. Chem. 60 (1982) 2029.
[11] G. Hogarth, J. Organomet. Chem. 406 (1991) 391.
[12] G. Hogarth, T. Norman, Inorg. Chim. Acta 248 (1996) 167.
[13] Y. Suenaga, M. Maekawa, T. Kuroda-Sowa, M. Munakata, H.
Morimoto, N. Hiyama, S. Kitagawa, Anal. Sci. 13 (1997) 1047.
[14] P. Rosa, A. Debay, L. Capes, G. Chastanet, A. Bousseksou, P.L.
Floch, J.-F. Letard, Eur. J. Inorg. Chem. (2004) 3017.
[15] P.W. Wang, M.A. Fox, Inorg. Chim. Acta 225 (1994) 15.
[16] P.W. Wang, M.A. Fox, Inorg. Chem. 33 (1994) 2938.
[17] M.A. Fox, D.A. Chandler, Adv. Mater. 3 (1991) 381.
[18] O.-K. Kim, T.E. Tsai, T.H. Yoon, L.S. Choi, Synth. Met. 59 (1993)
59.
[19] O.-K. Kim, T.H. Yoon, D. McDermott, Chem. Commun. (1989) 740.
[20] F. Foubelo, M. Yus, Curr. Org. Chem. 9 (2005) 459.
[21] N. Kongprakaiwoot, M.S. Bultman, R.L. Luck, E. Urnezius, Inorg.
Chim. Acta 358 (2005) 3423.
[22] M.E. Peach, E.S. Rayner, J. Fluorine Chem. 13 (1979) 447.
[23] T.R. Crowell, M.E. Peach, J. Fluorine Chem. 21 (1982) 469.
[24] R.H. Laitinen, H. Riihima¨ki, M. Haukka, S. Ja¨a¨skela¨inen, T.A.
Pakkanen, J. Pursiainen, Eur. J. Inorg. Chem. (1999) 1253.
[25] Y. Shvo, E. Hazum, J. Chem. Soc., Chem. Commun. (1975) 829.
ˇ
[26] E.W. Abel, D. Ellis, K.G. Orrell, V. Sik, Polyhedron 10 (1991) 1603.
[27] L. Hirsivaara, M. Haukka, S. Ja¨a¨skela¨inen, R.H. Laitinen, E.
Niskanen, T.A. Pakkanen, J. Pursiainen, J. Organomet. Chem. 579
(1999) 45.
[28] M.A. Moreno, M. Haukka, S. Ja¨a¨skela¨inen, S. Vuoti, J. Pursiainen,
T.A. Pakkanen, J. Organomet. Chem. 690 (2005) 3803.
[29] J.A. Adeleke, L.-K. Liu, J. Chin. Chem. Soc. 39 (1992) 61.
[30] L. Luo, S.P. Nolan, Inorg. Chem. 32 (1993) 2410.
[31] J.R. Sowa, V. Zanotti, G. Facchin, R.J. Angelici, J. Am. Chem. Soc.
114 (1992) 160.
˚
ligand and an F atom of 2.383 A. Finally, suitable conver-
gence of the data was not attained if the symmetry element
was removed (i.e., the data refined in the P1 space group
resulted in correlations of the thermal parameters).
Acknowledgements
We are grateful to Michigan Technological University
for generous financial support of this research. We also
thank Prof. D. K. Bates for some helpful suggestions.
[32] G.R. Langford, M. Akhtar, P.D. Ellis, A.G. MacDiarmid, J.D.
Odom, Inorg. Chem. 14 (1975) 2937.
[33] J.T. Lin, S.Y. Wang, S.K. Yeh, Y.L. Chow, J. Organomet. Chem.
359 (1989) C17.
[34] L.J. Farrugia, J. Appl. Cryst. 32 (1999) 837.
[35] M. Gingras, J.-M. Raimundo, Y.M. Chabre, Angew. Chem., Int. Ed.
45 (2006) 1686.
Appendix A. Supplementary material
[36] A.W. Addison, T.N. Rao, J. Reedijk, J.v. Rijn, G.C. Verschoor, J.
Chem. Soc., Dalton Trans. (1984) 1349.
[37] L.-S. Luh, L.-K. Liu, Inorg. Chim. Acta 206 (1993) 89.
[38] N. Avarvari, D. Martin, M. Fourmigue, J. Organomet. Chem. 643–
644 (2002) 292.
[39] A.R. Rossi, R. Hoffmann, Inorg. Chem. 14 (1975) 365.
[40] O. Gonzalez-Blanco, V. Branchadell, Organometallics 16 (1997) 5556.
[41] A.L. Fernandez, M.R. Wilson, A. Prock, W.P. Giering, Organomet-
allics 20 (2001) 3429.
[42] F.A. Cotton, J.R. Kolb, B.R. Stults, Inorg. Chim. Acta 15 (1975) 239.
[43] S. Aime, L. Milone, Prog. Nucl. Magn. Reson. Spectrosc. 11 (1977)
183.
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic Data
Centre, CCDC, Nos. 607215 and 607216 for compounds 2
and 3 respectively. Copies of this information may be
obtained free of charge from: The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK; fax: +44 1223
336033; e-mail: http://deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk.
References
[44] P.L. Coe, A.J. Waring, T.D. Yarwood, J. Chem. Soc. Perkin Trans. 1
(1995) 2729.
[1] J.R. Dilworth, N. Wheatley, Coord. Chem. Rev. 199 (2000) 89.