New synthetic route to polyphosphine ligands bearing 1,2,4,5-tetrakis(phosphino)benzene framework: Structural characterizations of 1,4-(PPh2)2 -2,5-(PR)2)2-C6F2 (R = Ph, iPr, Et)

Article abstract of DOI:10.1016/j.jorganchem.2004.07.042

Reactions of 1,4-dibromo-2,5-difluorobenzene with two equivalents of lithium diisopropylamide at low temperature (T< -90 °C) followed by a quench with a slight excess of ClPPh 2 afford 1,4-dibromo-2,5-bis(diphenylphosphino)-3,6-difluorobenzene (1) in good

Full text of DOI:10.1016/j.jorganchem.2004.07.042

Journal of Organometallic Chemistry 689 (2004) 3350–3356
www.elsevier.com/locate/jorganchem
New synthetic route to polyphosphine ligands bearing
1,2,4,5-tetrakis(phosphino)benzene framework: structural
i
characterizations of 1,4-(PPh2)2-2,5-(PR2)2-C6F2 (R = Ph, Pr, Et)
*
Natcharee Kongprakaiwoot, Rudy L. Luck, Eugenijus Urnezius
Department of Chemistry, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA
Received 31 May 2004; accepted 26 July 2004
Available online 28 August 2004
Abstract
Reactions of 1,4-dibromo-2,5-difluorobenzene with two equivalents of lithium diisopropylamide at low temperature (T < ꢀ90
°C) followed by a quench with a slight excess of ClPPh2 afford 1,4-dibromo-2,5-bis(diphenylphosphino)-3,6-difluorobenzene (1)
in good yields. Reacting 1 with two equivalents of BuLi followed by a quench with a slight excess of ClPR2 yield novel 1,2,4,5-tetra-
kis(phosphino)-3,6-difluorobenzenes 1,4-(PPh2)2-2,5-(PR2)2-C6F2 (R = Ph (2a); R = iPr (2b); R = Et (2c)) in moderate yields. Com-
pounds 1 and 2a–c were characterized by multinuclear NMR spectroscopy and elemental analyses. In addition, molecular structures
of 2a–c have been determined by single crystal X-ray crystallography. Phosphorus atoms of PPh2/PR2 substituents in 2a–c are dis-
placed from the plane of the central phenyl ring due to steric interactions with neighboring groups.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Phosphine ligands; Polyphosphines; Binucleating; Molecular structure
1. Introduction
transition metal complexes, and as parts of the mono-
meric units in coordination oligomers and polymers
[8–12]. Some of the latter compounds have displayed
attractive electrical and optical properties [8,11,13].
However, more detailed spectroscopic and electrochem-
ical measurements have suggested that the metal centers
in bimetallic complexes based on 3a–b lack effective elec-
tronic through-ligand coupling due to the absence of a
low energy empty ligand-based orbital [14]. In addition,
complexes with rigid 3a usually display rather low solu-
bility [12]. However, fine tuning of the electronic and
solubility properties of 3a–b has not been pursued, as
the previously used synthetic methods yielding such lig-
ands did not allow for much variation [8,15].
Tertiary phosphines PR3 are one of the most widely
used ligand classes in transition metal chemistry [1]. Me-
tal complexes with chelating polyphosphine ligands usu-
ally have more predictable geometries and better control
of the processes at the metal centers [2]. Quite surpris-
ingly relatively few polyphosphine ligands have been
used as building blocks for the backbone of coordina-
tion polymers [3–6]. Such macromolecules with transi-
tion metals in their main chains have attracted
considerable attention recently as potentially useful
materials with novel physical and chemical properties
[7]. Tetrakis(phosphino)benzenes 3a–b (Fig. 1) have
been shown to be effective binucleating ligands in some
We have developed a different synthetic route to sim-
ilar tetrakis(phosphino)benzenes of the general formula
1,4-(PPh2)2-2,5-(PR2)2-C6F2 (Fig. 1, 2a–c). These com-
pounds resemble 3a–b in arrangement of phosphino
groups, but different properties can be anticipated due
*
Corresponding author. Tel.: +1 906 487 2055; fax: +1 906 487
2061.
E-mail address: urnezius@mtu.edu (E. Urnezius).
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.07.042

N. Kongprakaiwoot et al. / Journal of Organometallic Chemistry 689 (2004) 3350–3356
3351
difluorobenzene readily undergoes a double deprotona-
tion with two equivalents of LDA when the reaction
media is carefully kept around ꢀ100 °C (Scheme 1).
Dilithiotetrahalobenzene thus generated is very
unstable thermally and decomposes at temperatures
higher than ꢀ80 °C. However, if maintained around
ꢀ95 °C, reactions with electrophiles are possible, and
addition of ClPPh2 (slight excess) produces 1,4-dibro-
mo-3,6-bis(diphenylphosphino)-2,5-difluorobenzene, 1,
in good yields (ꢁ70%) (Scheme 1). Analogous reactions
of 1,4-dibromo-2,5-difluorobenzene with only one
equivalent of LDA followed by ClPPh2 quench did
not result in selective monodeprotonation and exclusive
formation of expected (2,5-dibromo-3,6-difluorophe-
nyl)diphenylphosphine, for in addition to this com-
pound, reaction mixtures also contained substantial
amounts of 1 and unreacted 1,4-dibromo-2,5-difluoro-
benzene (ascertained by GC/MS). We have also
observed similar reactivities for 1,2-dibromo-4,5-difluor-
obenzene and 1-bromo-2-chloro-4,5-difluorobenzene
[22].
F
F
R2P
PPh2
PR2
R2P
R2P
PR2
PR2
Ph2P
2a, R = Ph
2b, R = iPr
2c, R = Et
3a, R = Ph
3b, R = Me
Fig. 1. Polyphosphines with 1,2,4,5-tetrakis(phosphino)benzene frame
work.
to structural and electronic differences. The presence of
the dialkylphosphino functionalities in 2a–c is expected
to render such compounds and their transition metal
complexes more soluble in hydrocarbon solvents. The
strongly electronegative fluorine substituents on the cen-
tral phenyl rings in 2a–c are also expected to directly influ-
ence the ligating ability of the P-centers. For example,
carbonyl complexes of Cr, Mo and W with structurally
related thioethers 1,2,4,5-(SCH3)4-C6F2 and 1,2,4,5-
(SCH3)4-C6H2 have shown CO stretching frequencies
of slightly higher energy for the former, which could
be attributed to weaker r-donor or better p-acceptor
properties of the fluorinated ligand [16]. Herein we re-
port the synthetic procedures and structural characteri-
zations of tetrakis(phosphino)benzenes 2a–c.
Compound 1 displays NMR (1H, 31P and 19F) signa-
tures corresponding to the C2h symmetry of the mole-
cule. The magnitude of phosphorus–fluorine coupling
(3JPF = 12 Hz, 4JPF = 6 Hz) is similar to values observed
in structurally related compounds [15]. So far we have
not been able to obtain X-ray quality crystals of this
material.
2. Results and discussion
The presence of two bromines at ortho positions to
the PPh2 groups makes compound 1 an attractive build-
ing block for the syntheses of an entire range of novel
binucleating ligands. We found that both bromines are
readily displaced utilizing standard alkyllithium/halogen
exchange reactions (Scheme 2). Again, the choice of con-
ditions is rather critical, and such reactions are facile
only at low temperatures (T < ꢀ80 °C). The resulting
dilithiated intermediate is quite unstable thermally,
and extensive decomposition occurs if the temperature
is allowed to reach ꢀ60 °C and above. However, if the
reaction mixtures are quenched with an excess of dial-
kyl/diarylchlorophosphine before warmup (Scheme 2),
pure 2a–c can be isolated in moderate yields (ꢁ20–
40%), although the initial crude yields are higher
(ꢁ50–60%).
When flanked by two halogen atoms, protons in aro-
matic systems (especially when one of the halogens is
fluorine) display ‘‘acidity’’ towards very strong bases
[17–20]. Accordingly, the formation of highly reactive
(2-bromo-6-fluorophenyl)lithium intermediate upon
reaction of lithium diisopropylamide (LDA) with 1-bro-
mo-3-fluorobenzene has been reported [21]. Quite
surprisingly, analogous reactivity of difluorodibromo-
benzenes where each of the remaining two protons is
flanked by bromine and fluorine has received rather lim-
ited attention and an unsuccessful attempt to deproto-
nate 1,2-dibromo-4,5-difluorobenzene at ꢀ78 °C has
been reported [17]. The temperature is a crucial factor
in such reactions, and recently we found that double
deprotonations of similarly substituted benzenes bearing
two ‘‘acidic’’ protons are facile when reactions are con-
ducted at very low temperatures. Thus, 1,4-dibromo-2,5-
Tetrakis(phosphino)difluorobenzenes 2a–c are ther-
mally stable (sharp melting points have been deter-
mined), pale yellow (2a) to deep yellow (2b–c)
F
F
F
F
Br
PPh2
Br
Br
Br
Li
Li
2.5 ClPPh2
-95oC
2 LDA
-95oC
THF/Et2O
Ph2P
Br
Br
F
1
F
Scheme 1.

3352
N. Kongprakaiwoot et al. / Journal of Organometallic Chemistry 689 (2004) 3350–3356
F
F
F
Li
PPh2
Li
Br
PPh2
Br
R2P
PPh2
PR2
2.3 ClPR2
-80oC
2.1 BuLi
-80oC
THF
Ph2P
Ph2P
Ph2P
F
F
F
2a-c
Scheme 2.
crystalline solids, which are relatively air stable in the so-
lid state, but oxidize in solution if exposed to air. Com-
pound 2a displays one signal in its 31P NMR spectrum
due to the equivalent nature of all four PPh2 groups in
solution. No 3-bond 19F–31P coupling was observed in
both the 31P NMR and the 19F NMR spectra. However,
such coupling can be seen in 2b (3JPF = 13 Hz), in addi-
tion to strong 3-bond P–P coupling (3JPP = 195 Hz).
bond distances and angles are summarized in Tables 1
and 2 respectively.
According to the CSD [25], the only other structur-
ally characterized 1,2,4,5-tetrakis(phosphino)benzene
prior to our work was 1,2,4,5-tetrakis(diphenylphosph-
ino)benzene (1a) [12]. Its closest structural analog
among our compounds is 2a (Fig. 2(a)), as the two differ
only by the presence of two fluorine atoms instead of H-
atoms on the central phenyl ring of the latter.
3
Such JPP values are typical for mutually ortho P(III)
groups, when the lone pairs are directed towards each
other [15,23]. A second order 31P NMR spectrum was
resolved for 2c, and a coupling value (3JPP = 198 Hz)
was determined via spectral simulation using g NMR
software [24].
Single crystals of 2a–c were obtained during low tem-
perature (ꢀ28 °C) crystallizations under N2 (from tolu-
ene (2a) and toluene/hexanes (2b–c)). X-ray diffraction
experiments allowed the determination of their molecu-
lar structures. The final figures of merit and selected
Both compounds possess planar central phenyl rings
(average carbon atom deviation from the weighted least-
squares plane through C1–C2–C3–C4–C5–C6 atoms in
˚
2a is 0.02 A). However, the internal angles in the central
ring are more distorted in 2a (C1–C6–C5 = 117.0(6)° to
C2–C1–C6 = 126.1(6)°, see Table 2) compared to 3a
where the corresponding values are closer to 120°
(118.3(2)–122.6(2)°) [12]. All phosphorus atoms in 3a
are reported to be in the plane of the central phenyl ring
and such an arrangement is typically found in other
Table 1
Crystal data for 1,4-(PPh2)2-2,5-(PR2)2-C6F2 (R = Ph, Pr, Et) (2a–c)
i
Crystal data
2a
2b
2c
Formula
Formula weight
Space group
C
850.74
54H40F2P4
C42H48F2P4
714.68
C38H40F2P4
658.58
ꢀ
P21/c
10.700(2)
P21/c
10.576(2)
P1
8.441(2)
˚
a (A)
˚
b (A)
18.689(5)
22.272(5)
11.927(3)
16.405(3)
9.805(3)
11.885(3)
˚
c (A)
a (°)
b (°)
c (°)
90
97.21(2)
90
107.18(2)
74.29(2)
89.06(2)
90
4418.6(18)
90
1977.0(7)
72.69(2)
901.8(4)
3
˚
V (A )
Z
4
1.279
2
1.201
1
1.213
qcalc (g/cm3)
l (Mo Ka, mmꢀ1
T (K)
)
0.216
295(2)
0.71073
0.228
295(2)
0.71073
0.245
295(2)
0.71073
˚
k (A)
h Range (°)
1.00–22.50
1.00–22.50
1.00–25.00
Final R indices [I > 2r(I)]a
R indices (all data)
R1 = 0.066, wR2 = 0.103b,c
R1 = 0.255, wR2 = 0.148
0.375, ꢀ0.269
1.011
R1 = 0.055, wR2 = 0.086b,d
R1 = 0.175, wR2 = 0.115
0.218, ꢀ0.265
1.006
R1 = 0.036, wR2 = 0.095b,e
R1 = 0.050, wR2 = 0.102
0.300, ꢀ0.253
1.051
Largest difference peak and hole
Goodness-of-fit on F2
P
P
a
b
c
R1 = (FoꢀFc)/ (Fo).
P
P
2
2 1=2
wR ¼ ½ ½wðF 2o ꢀ F c2Þ ꢂ= ½wðF 2oÞ ꢂꢂ
.
w = 1/[r2(F 2) + (0.0378 P2 + 1.2185 P], where P = (F 2 + 2 F 2)/3.
*
*
*
c
o
o
w = 1/[r2(F 2) + (0.0147 P2 + 2.2478 P], where P = (F 2 + 2 F 2)/3.
d
e
*
*
*
c
o
o
w = 1/[r2(F 2o + (0.0485 P2 + 0.2806 P], where P = (F 2 + 2 F 2)/3.
*
*
*
c
o

N. Kongprakaiwoot et al. / Journal of Organometallic Chemistry 689 (2004) 3350–3356
3353
Table 2
Selected bond distances and angles for 2a–c
within the expected range [26]. The torsion angles P1–
C2–C3–P2 (ꢀ10.9(8)°) and P3–C5–C6–P4 (ꢀ12.2(7)°)
are another indicator of this deviation. Such differences
between the key structural parameters of 2a and 3a can
be attributed to steric crowding resulting from the fluo-
rine atoms on the central ring of the former, even
though fluorine atoms are not considered bulky substit-
2a
2b
2c
˚
Bond distances (A)
C1–C2
C2–C3
C3–C4
C4–C5
C5–C6
C1–C6
F1–C1
F2–C4
P1–C2
P2–C3
P3–C5
P4–C6
1.392(8)
1.420(8)
1.410(8)
1.381(8)
1.424(8)
1.365(8)
1.361(7)
1.353(7)
1.853(7)
1.846(7)
1.863(7)
1.855(6)
1.394(6)
1.404(6)
1.383(6)a
1.384(2)
1.405(2)
1.387(2)a
˚
uents. The distortion of the PPh2 groups (by 0.133 A)
from the plane of the central phenyl ring in 1,4-bis(diph-
enylphosphino)-2,5-difluorobenzene has been reported
[27], as well as similar distortions for the PR2 groups
caused by the steric bulk of adjacent substituents in
other related compounds [28,29]. The positioning of
the PPh2 substituents (which are adjacent to a fluorine
atom) above and below the plane of the central phenyl
ring in 2a (Fig. 2(b)) renders the Ph groups attached
to the same phosphorus atom non-equivalent. Room
temperature 1H NMR spectra of 2a consist of a complex
signal in the aromatic region and further variable tem-
perature studies are necessary to assess the nature of
2a in solution. Our data on 2b–c (discussed in later par-
agraphs) suggests that in solution these molecules clo-
sely resemble the structures observed in the solid state.
The presence of the more sterically demanding diiso-
propylphosphine groups in 2b (Fig. 3) results in more se-
vere distortions. The values for the internal angles of the
planar central phenyl ring remain similar to those ob-
served in 2a (C30–C1–C2 = 126.4(4)°, C1–C2–C3 =
117.5(4)°, see Table 2), but the bending of phosphorus
atoms away from the plane of the central ring is more
1.359(5)
1.3571(19)
1.848(5)
1.844(5)
1.8520(18)
1.8557(18)
Bond angles (°)
F1–C1–C6
F1–C1–C2
C6–C1–C2
C1–C2–C3
C1–C2–P1
C3–C2–P1
C4–C3–C2
C4–C3–P2
C2–C3–P2
F2–C4–C5
F2–C4–C3
C5–C4–C3
C4–C5–C6
C4–C5–P3
C6–C5–P3
C1–C6–C5
C1–C6–P4
C5–C6–P4
a
117.5(6)
116.4(6)
126.1(6)
117.5(6)
124.9(5)
117.5(5)
116.1(6)
125.8(5)
118.0(5)
117.9(6)
116.9(6)
125.2(6)
117.7(6)
123.2(5)
119.0(5)
117.0(6)
126.0(5)
116.8(5)
116.7(5)b
116.9(4)
126.4(4)b
117.5(4)
122.1(4)
119.8(4)
116.1(4)a
124.9(4)a
118.6(4)
116.89(15)b
117.76(14)
125.32(16)b
117.32(15)
124.57(13)
117.87(13)
117.29(15)a
124.38(13)a
118.11(12)
˚
˚
severe in 2b (ꢀ0.252(2) A (P1) and 0.271(2) A (P2)).
Accordingly, the torsion angle P1–C2–C3–P2 at
ꢀ18.7(6)° is significantly larger than the corresponding
angles in 2a. The non-equivalency of the isopropyl
groups resulting from such distortion clearly persists in
C4 represents symmetry generated C1.
C6 represents symmetry generated C3.
b
structurally characterized 1,2-diphosphinobenzenes [23].
The phosphorus atoms in 2a are shifted from the in-
˚
plane positions by 0.199(2)–0.241(2) A, although the
P–C (carbons of the central ring) bond distances remain
1
solution and two H NMR signals for CH3 groups are
observed (d 1.11 and 0.74), whereas the CH proton pro-
duced a complex multiplet (d 2.34). The combination of
Fig. 2. (a) Molecular structure of 2a (50% thermal ellipsoids) without H atoms and (b) a view of the molecule along F1–C1–C4–F2 line.

3354
N. Kongprakaiwoot et al. / Journal of Organometallic Chemistry 689 (2004) 3350–3356
Fig. 3. Molecular structures for 2b (major orientation only) and 2c (40% thermal ellipsoids) without H atoms. Illustration on the far right depicts the
arrangement of the phosphorus atoms in 2b relative to the plane of the central phenyl ring. There is a similar arrangement in 2c.
diphenylphosphino and diethylphosphino groups in 2c
(Fig. 3) produce fewer steric demands, as the distortions
from ideal geometry are less pronounced. The central
phenyl ring (planar) is still distorted from the ideal
frozen and degassed while thawing under vacuum (re-
peated three times). LDA (lithium diisopropylamide)
was freshly prepared immediately prior to use according
1
to a published procedure [17]. H, 31P, and 19F NMR
geometry
(C2–C1–C30 = 125.32(16)°,
C1–C2–
spectra were recorded on Varian INOVA spectrometer
operating at 400, 161, and 376 MHz, respectively. Spectra
are referenced to tetramethylsilane (1H), 85% H3PO4
(31P) (external reference), and CFCl3 (19F) (internal
standard in a sealed capillary tube). Mass spectrometric
C3 = 117.32(15)°), but the displacements of the phos-
phorus atoms from the plane of the central phenyl ring
˚
are smaller than in 2c: 0.1538(7) A for P1 and
˚
ꢀ0.2260(7) A for P2. This accordingly results in a smal-
ler torsion angle ((P1–C2–C3–P2) = 13.3(2)°). The non-
equivalency of the ethyl groups also persists in solution,
but the 1H NMR spectrum of 2c is not well resolved (at
room temperature and 400 MHz) with multiplets for
both the CH3 (d 0.85) and the CH2 (d 1.81) groups; com-
plex multiplets are also produced by phenyl protons in
both 2b and 2c. Finally, it is noteworthy that the PR2
groups adjacent to a fluorine atom in 2b and 2c distort
towards one another, see Fig. 3. This is in contrast to
the equivalent groups being on opposite sides of the cen-
tral phenyl ring in 2a. This illustrates the flexibility of
the phenyl ring as the substituents distort to minimize
steric interactions.
measurements were performed on
a
Shimadzu
QP5050A instrument. Elemental analyses were per-
formed at Galbraith Laboratories, Inc.
3.2. Syntheses
3.2.1. 1,4-dibromo-3,6-difluoro-2,5-bis(diphenylphosph-
ino)-benzene (1)
To a stirred solution of 1,4-dibromo-3,6-difluoroben-
zene (1.0 g, 3.68 mmol) in THF (120 ml) at ꢀ95 °C was
added (via cannula) freshly prepared LDA (2.0 equiva-
lent) in the same solvent. After stirring for 5 min, a
solution of 1.69 ml (2.5 equivalents) of diphenylchloro-
phosphine in THF (10 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 temperature overnight.
A clear yellowish brown solution was filtered, volatiles re-
moved under vaccuo to yield an oily yellow solid. Wash-
ings with methanol yielded 1 as a white powder. Yield:
1.65 g (70%). Melting point: 263–264 °C. 1H NMR
(CDCl3): d 7.34 (m). 31P NMR (CDCl3): d 0.54 (dd,
3JPF = 12 Hz, 4JPF = 6 Hz); 19F NMR (C6D6): d ꢀ88.50
3. Experimental
3.1. General procedure
Manipulations requiring inert atmospheres were car-
ried out by using Schlenk techniques or in a dry box un-
der a N2 atmosphere. Low temperature reactions were
performed in Schlenk flasks immersed in hexanes/liquid
N2 slush, contained in a Dewar flask. Solvents were puri-
fied before use by distillation from Na-benzophenone ke-
tyl (ether, THF, hexanes) or CaH2 (toluene, acetonitrile)
under N2 atmosphere. Methanol was deoxygenated by
bubbling nitrogen through it for 1 h. Commercially avail-
able chlorophosphines ClPR2 were purified prior to use:
ClPPh2 was vacuum distilled; ClPEt2 and ClPiPr2 were
3
4
(dd, JFP = 12 Hz, JFP = 6 Hz). MS (EI): m/z = 640
(M+). Anal. Calc. for C30H20Br2F2P2: C, 56.28; H, 3.15.
Found: C, 56.21; H, 3.27%.
3.2.2. 1,2,4,5-Tetrakis(phosphino)-3,6-difluorobenzenes
1,4-(PPh2)2-2,5-(PR2)2-C6F2 (2a–c)
Compounds 2a–c were prepared by the same syn-
thetic protocol. To a stirred solution of 1,4-dibromo-

N. Kongprakaiwoot et al. / Journal of Organometallic Chemistry 689 (2004) 3350–3356
3355
3,6-difluoro-2,5-bis(diphenylphosphino)benzene (1.00 g,
1.56 mmol ) in 120 ml THF at ꢀ80 °C was added n-BuLi
(2.1 equivalent) as a 1.6 M solution in hexanes. The mix-
ture was stirred for 1 h at ꢀ80 °C, and then was treated
with a solution of 2.3 equivalents of the corresponding
ClPR2 in 10 ml of THF. After stirring for another hour
at ꢀ80 °C the mixture was allowed to warm up to room
temperature overnight.
diffractometer (Enraf-Nonius CAD4) and centered in
the beam path. Standard CAD4 centering, indexing,
and data collection programs were utilized [30]. Twenty-
five reflections between 10° and 15° in h were located by
a random search pattern, centered and used in indexing.
Final cell constants and orientation matrix were ob-
tained by collecting appropriate preliminary data and
refined by a least squares fit. During data collection,
three intensity standards and three orientation stand-
ards were measured at regular intervals to measure the
rate of decay of the crystal and to accommodate for
crystal movement.
3.2.3. 1,2,4,5-(PPh2)4-C6F2 (2a)
The reaction mixture contained pale yellow precipi-
tate, which was filtered off and extracted with toluene
(70 ml).
Data were first reduced and corrected for absorption
using psi-scans [31] and then solved using the program
SIR-02 [32], which afforded nearly complete solutions
for the non-H atoms in all cases. These programs were
utilized using the WinGX interface [33]. The models
were then refined using SHELXL-97 [34] first with iso-
tropic and then anisotropic thermal parameters to con-
vergence. The positions and isotropic thermal
parameters of the different H-atoms were constrained
according to the specifics arranged in the SHELXL-97
program. This constituted the final model for 2a and
2c but it was apparent that two of the C atoms in one
of the isopropyl groups in 2b were disordered. This
was accounted for by including atoms at the various
sites and refining the occupancies constrained to unity.
This resulted in a 81(2)% to 19(2)% disorder in two of
the carbon atoms in this isopropyl group.
The extract was filtered, the filtrate was placed at ꢀ28
°C, yielding pale yellow crystals after one week (isolated
by filtration). Yield: 1.07 g (40%). Melting point: 274–
276 °C. 1H NMR (CDCl3): d 7.19 (m). 31P NMR
(CDCl3): d ꢀ11.31 (s); 19F NMR (C6D6): d ꢀ78.53 (s).
MS (EI): m/z = 850 (M+). Anal. Calc. for C54H40F2P4:
C, 76.23; H, 4.74. Found: C, 74.92; H, 4.72%. (Results
consistently low on carbon were obtained on repeated
runs on two different batches of the material. Multinu-
clear NMR and GC/MS spectroscopic characterizations
revealed no impurities.)
3.2.4. 1,4-(PPh2)2-2,5-(PiPr2)2-C6F2 (2b)
The reaction mixture was filtered, volatiles removed
under vacuo to yield an oily yellow solid, which was ex-
tracted with a 1:1 mixture of hexanes and toluene (100
ml). Yellow crystals of 2b precipitated on standing at
ꢀ28 °C for one day, and were isolated by filtration.
Yield: 0.23 g (20%). Melting point 238–239 °C. 1H
NMR (CDCl3): d 7.33 (m, 20H), 2.34 (m, 4H), 1.11
(m, 12H), 0.74 (m, 12H). 31P NMR (CDCl3): d 12.64
4. Supporting information available
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC, Nos. 239506–239508 for com-
pounds 2a–2c 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: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk).
3
3
(dd, JPP = 195 Hz, JPF = 13 Hz), ꢀ12.91 (dd,
3
3JPP = 195 Hz, JPF = 13 Hz). 19F NMR (C6D6): d
ꢀ84.32 (s). MS (EI): m/z = 714 (M+). Anal. Calc. for
C42H48F2P4: C, 70.58; H, 6.77. Found: C, 70.05; H,
6.92%.
3.2.5. 1,4-(PPh2)2-2,5-(PEt2)2-C6F2 (2c)
This was isolated analogously to 2b. Yield: 0.21 g
1
(21%). Melting point 198–200 °C. H NMR (CDCl3):
d 7.33 (m, 20H), 1.81 (m, 8H), 0.85 (m, 12H). 31P
Acknowledgement
3
NMR (CDCl3): d ꢀ11.48 (dm, JPP = 198 Hz), ꢀ12.41
3
(dm, JPP = 198Hz). 19F NMR (C6D6): d ꢀ88.44 (s).
We acknowledge generous financial support by Mich-
igan Technological University.
MS (EI): m/z = 658 (M+). Anal. Calc. for C38H40F2P4:
C, 69.30; H, 6.12. Found: C, 69.22; H, 6.47%.
3.3. X-ray crystallography
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