Synthesis and characterization of cyclic oligomeric [cis-Mo(CO)4(Ph2P(C4H2S)2 PPh2)]n and model complexes for the edge and corners in the cyclic oligomer

Article abstract of DOI:10.1021/om030595h

Conducting organometallic polymers are an interesting class of materials because they combine the electronic properties of metals with the simpler processing requirements of organic polymers. In an approach to incorporating poly(thiophene) segments into controlled three-dimensional environments, we have synthesized 5,5′-bis(diphenylphosphino)-2,2′-bithiophene, Ph₂P(C₄H₂S)₂PPh₂, and have reacted this ligand with Mo(CO)₄(nbd) in a 1:1 ratio. The product of this reaction is a cyclic oligomer, as indicated by the presence of only cis-Mo(CO)₄ absorptions in the IR spectrum and the absence of resonances of free phosphines in the ³¹P{¹H} NMR spectrum. Size exclusion chromatography of the polymer in THF gives an M_n value of 6.0 × 10³ and M_w value of 9.7 × 10³ for the polymer. To better understand the structural features of the polymer, model complexes for the edge, Mo(CO)₅(Ph₂P(C₄H₂S)₂ PPh₂)Mo(CO)₅, and the corner, cis-Mo(CO)₄(Ph₂P(C₄H₂S)₂ H)₂ and cis-Mo(CO)₄(Ph₂P(C₄H₂S) H)₂, of the cyclic polymer have been prepared and characterized. X-ray crystal structures of Ph₂P(C₄H₂S)₂PPh₂ and the edge model have also been determined.

Full text of DOI:10.1021/om030595h

Organometallics 2004, 23, 409-415
409
Syn th esis a n d Ch a r a cter iza tion of Cyclic Oligom er ic
[cis-Mo(CO)4(P h 2P (C4H2S)2P P h 2)]n a n d Mod el Com p lexes
for th e Ed ge a n d Cor n er s in th e Cyclic Oligom er
R. Dustan Myrex, Clark S. Colbert, and Gary M. Gray*
Department of Chemistry, University of Alabama at Birmingham, 201 Chemistry Building,
901 14th Street South, Birmingham, Alabama 35294-1240
Christina H. Duffey
Department of Chemistry, Samford University, Birmingham, Alabama 35229
Received September 9, 2003
Conducting organometallic polymers are an interesting class of materials because they
combine the electronic properties of metals with the simpler processing requirements of
organic polymers. In an approach to incorporating poly(thiophene) segments into controlled
three-dimensional environments, we have synthesized 5,5′-bis(diphenylphosphino)-2,2′-
bithiophene, Ph2P(C4H2S)2PPh2, and have reacted this ligand with Mo(CO)4(nbd) in a 1:1
ratio. The product of this reaction is a cyclic oligomer, as indicated by the presence of only
cis-Mo(CO)4 absorptions in the IR spectrum and the absence of resonances of free phosphines
in the 31P{1H} NMR spectrum. Size exclusion chromatography of the polymer in THF gives
an Mh n value of 6.0 × 103 and Mh w value of 9.7 × 103 for the polymer. To better understand
the structural features of the polymer, model complexes for the edge, Mo(CO)5(Ph2P(C4H2S)2-
PPh2)Mo(CO)5, and the corner, cis-Mo(CO)4(Ph2P(C4H2S)2H)2 and cis-Mo(CO)4(Ph2PC4H2S)H)2,
of the cyclic polymer have been prepared and characterized. X-ray crystal structures of Ph2P-
(C4H2S)2PPh2 and the edge model have also been determined.
In tr od u ction
als could exhibit novel optoelectronic behavior,9 and
host-guest binding/inclusion complex phenomena for
use as chemical sensors for a variety of materials.6-8,10
Poly(thiophenes) are of interest because they have
nondegenerate ground states and thus exhibit different
excitations responsible for conduction than do polymers
with degenerate ground states such as poly(acetyl-
enes).9,11,12 Poly(thiophenes) have seen use in metal-
containing films for use as thin-film transistors and
molecular/ion-selective sieves.8,13a-b The electrolumi-
nescent behavior may be modified via similar techniques
used for band gap control in other π-conjugated sys-
tems.11,14 Coupling of poly(thiophenes) to transition
metals has yielded materials with interesting linear and
nonlinear optical behavior as well as electrochemical
properties.3,9
Conducting polymers such as poly(acetylenes),1 poly-
(pyrroles),2 poly(thiophenes),3 and fused-ring systems
such as poly(isothianaphthenes)4 have been studied
intensely in recent years, due to their potential applica-
tions in electronics and optoelectronics. An area of
considerable current interest is the development of
materials that blend conducting polymers with inor-
ganic elements via the incorporation of the conducting
polymers into the ligands of transition-metal complexes.
This process could allow the development of controlled
nanostructures via metal-directed self-assembly,5 and
molecular recognition.6-8 Such nanostructured materi-
* Corresponding author.
(1) (a) Ito, T.; Shirakawa, H.; Ikeda, S. J . Polym. Sci., Polym. Chem.
1974, 12, 11. (b) Chiang, C. K.; Fincher, C. R., J r.; Park, Y. W.; Heeger,
A. J .; Shirakawa, H.; Louis, E. J .; Gau, S. C.; MacDiarmid, A. G. Phys.
Rev. Lett. 1977, 39, 1098.
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Chem. Commun. 1979, 14, 635. (b) Diaz, A. F.; Lacroix, J . C. New J .
Chem. 1988, 12, 171.
One approach that has not been used to incorporate
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Langmuir 1999, 15, 837.
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(b) Stang, P. J .; Olenyuk, B. Angew. Chem., Int. Ed. Engl. 1996, 35,
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Muddiman, D. C.; Smith, R. D. J . Am. Chem. Soc. 1997, 119, 5163. (e)
Leininger, S.; Olenyuk, B.; Stang, P. J . Chem. Rev. 2000, 100, 853. (f)
Stang, P. J .; Persky, N. E. Chem. Commun. 1997, 77.
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5645.
(12) Heeger, A. J . J . Phys. Chem. B 2001, 105, 8475.
(13) (a) Fujita, M.; Yazaki, J .; Ogura, K. Chem. Lett. 1991, 1031.
(b) Katz, H. E.; Torsi, L.; Dodabalapur, A. Chem. Mater. 1995, 7, 2235.
(14) (a) Noma, N.; Kawaguchi, K.; Imae, I.; Shirota, Y. Synth. Met.
1997, 84, 597. (b) Zotti, G.; Berlin, A.; Schiavon, G.; Zecchin, S. Synth.
Met. 1999, 101, 622. (c) Meerholz, K.; Heinze, J . Electrochim. Acta
1996, 41, 1839. (d) Barth, M.; Guilerez, S.; Bidan, G.; Bras, G.;
Lapkowski, M. Electrochim. Acta 2000, 45, 4409. (e) Zhu, Y.; Wolf, M.
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10.1021/om030595h CCC: $27.50 © 2004 American Chemical Society
Publication on Web 01/07/2004

410 Organometallics, Vol. 23, No. 3, 2004
Myrex et al.
5,5′-Bis(d ip h en ylp h osp h in o)-2,2′-b it h iop h en e, P h 2P -
(C4H2S)2P P h 2 (1). A solution of 5.06 g (0.0304 mol) of 2,2′-
bithiophene in 150 mL of THF was cooled in an acetone/dry
ice slush bath as a mixture of 38.0 mL (0.0608 mol) of 1.6 M
n-butyllithium in hexanes was added dropwise. When the
addition was completed, 10.9 mL (0.0608 mol) of chlorodiphen-
ylphosphine was added, and the reaction mixture was stirred
for 60 min. Then, the solvent was removed under vacuum, and
the dark solid residue was treated with 125 mL of degassed
dichloromethane. This mixture was filtered to remove the
lithium chloride, and the filtrate was evaporated to dryness
under vacuum to yield a dark orange sticky solid. The solid
was treated with 100 mL of degassed methanol, and the
mixture was stirred for 5 h. Filtration then yielded 9.99 g
(61.5%) of crude 1 as a light orange solid. 1H NMR (CDCl3): δ
7.27-7.34 (C6H5, m, 20H); 7.04-7.18 (C4H2S, m, 4H). 31P NMR
(CDCl3): δ -18.50 (s).
5-(Diph en ylph osph in o)-2,2′-bith ioph en e, P h 2P (C4H2S)2H
(2). A solution of 1.98 g (0.0119 mol) of 2,2′-bithiophene in 25
mL of dry THF was cooled in an acetone/dry ice slush bath as
a mixture of 7.45 mL (0.0119 mol) of 1.6 M n-butyllithium in
hexanes and 12.55 mL of THF was added dropwise. During
the addition, the color of the solution darkened to a deep green.
Next, 2.21 mL (0.0123 mol) of chlorodiphenylphosphine was
added to the solution. The reaction mixture was stirred for an
additional 120 min, and then a few drops of degassed water
were added to decompose any remaining bithiophenyllithium.
The solvent was removed under vacuum to yield a viscous oily
residue. The residue was treated with 30 mL of degassed
dichloromethane, and the mixture was filtered through silica
gel. The filtrate was evaporated to dryness under vacuum to
yield crude 2 as a yellow oil in a yield of 45.9% (4.17 g). 1H
NMR (CDCl3): δ 7.27-7.36 (C6H5, m, 10H); 6.89-6.91, 7.05-
7.06 (C4H2S, m, 2H); 7.09-7.18 (C4H3S, m, 3H). 31P{1H} NMR
(CDCl3): δ -18.57 (s).
F igu r e 1. Phosphine-bithiophene and phosphine-
thiophene ligands used in this study.
plexes is to substitute phosphines at the 5-carbons of
the terminal thiophenes. Such substitutions have been
used to prepare 2-phosphinothiophenes15 that have been
incorporated into transition-metal complexes via coor-
dination of the phosphine and should work equally well
with poly(thiophenes).16 In this paper, we describe the
synthesis of the simplest of the 5,5′-bis(phosphine)poly-
(thiophene) ligands, Ph2P(C4H2S)2PPh2 (1 in Figure 1),
and an oligomeric complex of this ligand, [cis-Mo(CO)4-
(Ph2P(C4H2S)2PPh2)]n (4). To better understand the
coordination environment of the ligand in the oligomeric
complex, we have also synthesized and characterized
complexes that model the edges, Mo(CO)5(Ph2P(C4H2S)2-
PPh2)Mo(CO)5 (5), and the corners, cis-Mo(CO)4(Ph2P-
(C4H2S)2H)2 (6) and cis-Mo(CO)4(Ph2PC4H3S)2 (7), of the
oligomer.
Exp er im en ta l Section
Ma ter ia ls. THF was dried by first allowing it to stand over
MgSO4 for at least 12 h, then by refluxing over CaH2, and
finally by distilling from Na/benzophenone and was used
within a few hours. Other solvents were reagent grade and
were degassed using high-purity (99.998%) nitrogen before use.
Thiophene was distilled and stored over molecular sieves until
use, while reagent grade bithiophene, chlorodiphenylphos-
phine, and 1.6 M n-butyllithium were of sufficient purity as
received from the supplier (Aldrich). Literature methods were
used to synthesize 2-(diphenylphosphino)thiophene (3),15Mo-
(CO)4(nbd),16and cis-Mo(CO)4(Ph2PC4H3S)2 (7).17
[cis-Mo(CO)4(P h 2P (C4H2S)2P P h 2)]n (4). Solutions of 0.266
g (0.887 mmol) of Mo(CO)4(nbd) in 150 mL of degassed
dichloromethane and 0.474 g (0.887 mmol) of bis(5,5′-diphen-
ylphosphino)-2,2′-bithiophene (1) in 200 mL of degassed
dichloromethane were added simultaneously and dropwise to
150 mL of degassed dichloromethane over a period of 5 h.
When the addition was completed, the reaction mixture was
stirred for 30 min, and then the solvent was removed under
vacuum. The brown oily residue was dissolved into 60 mL of
degassed dichloromethane, and this solution was filtered
through 2 mm of silica gel in a sintered-glass funnel. The silica
gel was then rinsed with two 15 mL portions of degassed
dichloromethane. The filtrate and washes were combined to
yield a golden yellow solution. This solution was heated under
a stream of nitrogen to reduce volume to 20 mL, and then
hexanes were added until the solution became saturated.
Cooling of the solution to -5 °C yielded 0.414 g (62.8%) of
Ch a r a cter iza tion . IR spectra of nitrogen-degassed dichlo-
romethane solutions of the carbonyl complexes in an ICL 0.2
mm path length NaCl solution cell were recorded on a Nicolet
1
Nexus 470 FT-IR spectrometer. Multinuclear 31P{1H} and H
NMR spectra were recorded on a Bruker ARX-300 NMR
spectrometer. Chloroform-d solutions of the complexes were
prepared under nitrogen. The 31P{1H} NMR spectra were
referenced to external 85% phosphoric acid (H3PO4) in a coaxial
tube that also contained chloroform-d, and the 1H NMR spectra
were referenced to internal tetramethylsilane (TMS). Size
exclusion chromatography was performed on a system utilizing
a Waters 515 HPLC pump, a Waters 410 refractive index
detector, a Linear UV/vis 205 absorbance detector, and a series
of four columns (Styragel HT6E, HR5E, HT3, and HR2). This
system employed a polystyrene calibration curve.
Molecu la r Mod elin g. Molecular modeling was performed
using Spartan ‘02 for Windows. The dihedral angle containing
the S-C-C-S atoms of the bithiophene was constrained from
180 to 0° in 10° increments and the strain energy recorded.
This molecular mechanics method employed the MMFF force
field parameters for minimization.18
analytically pure 4 as
a
pale yellow powder. 1H NMR
(CDCl3): δ 7.17-7.24 (C6H5, m, 20H); 6.82-6.96 (C4H2S, m,
4H). 31P{1H} NMR (CDCl3): δ 27.56 (s). Carbonyl IR (cm-1):
2024 m, 1928 sh, 1908 s. SEC (THF-polystyrene calibration):
Mh n ) 6.0 × 103 Da, Mh w ) 9.7 × 103 Da. Anal. Calcd: C, 58.23;
H, 3.26. Found: C, 58.20; H, 3.40.
(Mo(CO)5)2(µ-P h 2P (C4H2S)2P P h 2) (5). A mixture of 0.326
g (1.23 mmol) of molybdenum hexacarbonyl and 0.137 g (1.23
mmol) of tetramethylamine N-oxide dihydrate in 20 mL of
degassed acetonitrile was stirred at room temperature for 30
min. The solution was then added dropwise to a solution of
0.330 g (0.617 mmol) of bis(5,5′-diphenylphosphino)-2,2′-
bithiophene (1) in 30 mL of a 2:1 acetonitrile/THF mixture.
The solution was stirred for 2 h after the addition was
completed and then filtered to remove the unreacted molyb-
denum carbonyl. The filtrate was evaporated to dryness, and
(15) Allen, D. W. J . Chem. Soc. B 1970, 1490.
(16) Ehrl, W.; Ruck, R.; Vahrenkamp, H. J . Organomet. Chem. 1973,
56, 285.
the residue was recrystallized from
a dichloromethane/
(17) Varshney, A.; Gray, G. M. Inorg. Chim. Acta 1988, 148, 215.
(18) Spartan ‘02 for Windows; Wavefunction Inc., Irvine, CA, 2001.

Oligomeric [cis-Mo(CO)4(Ph2P(C4H2S)2PPh2)]n
Organometallics, Vol. 23, No. 3, 2004 411
Ta ble 1. Da ta Collection P a r a m eter s for X-r a y
Str u ctu r e Deter m in a tion
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 1
1
5
C3-C4
C3-C2
C2-C1
C4-C4′
C4-S1
1.355(4)
1.399(5)
1.364(4)
1.449(6)
1.722(3)
C1-S1
C1-P1
P1-C15
P1-C9
1.724(3)
1.804(3)
1.825(3)
1.834(3)
empirical formula
formula wt
temp, K
C
32H24P2S2
C
43H26Cl2Mo2O10P2S2
534.57
293(2)
0.710 73
1091.48
293(2)
wavelength, Å
0.710 73
triclinic, P1h
11.602(2)
15.688(3)
26.980(5)
90.97(3)
100.36(3)
109.00(3)
4552.3(16)
4; 1.593
cryst syst, space group monoclinic, P21/c
C4-C3-C2
C1-C2-C3
C3-C4-C4′
C3-C4-S1
C4′-C4-S1
C2-C1-S1
113.8(3)
113.8(3)
129.7(4)
110.0(2)
120.3(3)
109.5(2)
C2-C1-P1
S1-C1-P1
C1-P1-C15
C1-P1-C9
C15-P1-C9
C4-S1-C1
125.2(3)
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
8.9841(18)
19.670(4)
8.8902(18)
90
117.97(3)
90
125.24(18)
103.54(15)
101.36(14)
102.60(14)
92.85(15)
1387.6(5)
Z; calcd density, Mg/m3 2; 1.279
dispersion. All data were corrected for Lorentz and polarization
effects, and when necessary, empirical absorption corrections
were applied.
abs coeff, mm-1
F(000)
0.327
556
0.885
2176
cryst size, mm
θ range for data
collecn, deg
0.80 × 0.40 × 0.30
0.06 × 0.52 × 0.18
All crystallographic calculations were performed with the
Siemens SHELXTL-PC program package.20 The Mo and P
positions were located using the Patterson method, and the
remainder of the non-hydrogen atoms were located in differ-
ence Fourier maps. Full-matrix refinements of the positional
and anisotropic thermal parameters for all non-hydrogen
atoms versus F2 were carried out. All hydrogen atoms were
placed in calculated positions with the appropriate molecular
geometry and d(C-H) ) 0.96 Å. The isotropic thermal
parameter of each hydrogen atom was fixed equal to 1.2 times
the Ueq value of the atom to which it was bound. Selected bond
lengths and angles for 1 and 5 are given in Tables 2 and 3.
2.07-27.47
2.15-22.48
limiting indices
-11 e h e 10,
-25 e k e 1,
-1 e l e 11
4030/3178
(R(int) ) 0.0392)
27.47; 100
-12 e h e 12,
-16 e k e 1,
-29 e l e 28
13 435/11 869
(R(int) ) 0.0605)
22.48; 99.9
no. of rflns collected/
unique
θ, deg; completeness
to θ, %
abs cor
empirical
empirical
max, min transmissn
refinement method
no. of data/restraints/
params
0.4630, 0.4264
0.6743, 0.5296
full-matrix least squares on F2
3178/0/212
11 869/2/1100
GOF on F2
0.998
0.997
final R indices
R1 ) 0.0458,
wR2 ) 0.1223
R1 ) 0.1292,
wR2 ) 0.1633
0.003(2)
R1 ) 0.0629,
wR2 ) 0.1453
R1 ) 0.1582,
wR2 ) 0.1776
0.000 00(12)
0.783, -0.604
(I > 2σ(I))
Resu lts a n d Discu ssion
R indices (all data)
Liga n d Syn th eses a n d Ch a r a cter iza tion : The
phosphine-substituted bithiophene ligands 1 and 2 were
prepared as shown in Scheme 1. The reactions were run
in a dry ice/acetone slush bath to minimize isomeric
scrambling between the lithiated thiophenes and the
phosphinothiophene. Generation of the lithiated thio-
phenes was rapid, and addition of the phosphine was
carried out within 30 min of completion of the n-
butyllithium addition. The 31P{1H} NMR spectra of the
extinction coeff
largest diff peak,
hole, e Å-3
0.286, -0.372
methanol mixture to yield 0.423 g (68.1%) of 5 as green,
prismatic crystals. 1H{31P} NMR (CDCl3): δ 7.23 (dd, 2H); 7.31
(dd, 2H, | J (H,H)| ) 24.8 Hz, | J (H,H)| ) 3.7 Hz); 7.43-7.53
(C6H5, m, 20H). 31P{1H} NMR (CDCl3): δ 26.63 (s). Carbonyl
IR (cm-1): 2074 m, 1988 w sh, 1948 s. Anal. Calcd: C, 47.32;
H, 2.40. Found: C, 46.95; H, 2.35.
3
4
1
ligands were singlets, and the H NMR spectra of the
cis-Mo(CO)4(P h 2P (C4H2S)2H)2 (6). A solution of 0.410 g
(1.36 mmol) of Mo(CO)4(nbd) in 100 mL of dichloromethane
was added dropwise to a solution of 0.953 g (2.72 mmol) of
5-(diphenylphosphino)-2,2′-bithiophene (2) in 100 mL of de-
gassed dichloromethane at room temperature. Then the sol-
vent was then removed under vacuum to yield a pale yellow
powder. Column chromatography on a silica gel column using
a 1:4 dichloromethane/hexanes system followed by recrystal-
lization from a dichloromethane/hexanes mixture yielded 0.353
g (28.6%) of analytically pure 6. 1H NMR (CDCl3): δ 7.26-
7.40 (C6H5, m, 10H); 6.98-7.23 (C4H2S-C4H3S, m, 5H). 31P-
{1H} NMR (CDCl3): δ 27.31 (s). Carbonyl IR (cm-1): 2023 m,
1923 sh, 1910 s, 1886 m. Anal. Calcd: C, 58.15; H, 3.33.
Found: C, 57.88; H, 3.26.
X-r a y Da ta Collection a n d Solu tion . Suitable single
crystals of both 1 and 5 were glued on glass fibers with epoxy
and aligned upon an Enraf-Nonius CAD4 single-crystal dif-
fractometer under aerobic conditions. Standard peak search
and automatic indexing routines followed by least-squares fits
of 25 accurately centered reflections resulted in accurate unit
cell parameters for each. The space groups of the crystals were
assigned on the basis of systematic absences and intensity
statistics. All data collections were carried out using the CAD4-
PC software,19 and details of the data collections are given in
Table 1. The analytical scattering factors of the compounds
were corrected for both ∆f ′ and i∆f ′′ components of anomalous
ligands contained only resonances for the phenyl and
thiophenyl protons in the expected ratios. The NMR
data indicated that the crude ligands were sufficiently
pure for use in the syntheses of the complexes. Ligand
1 was recrystallized from a dichloromethane/hexanes
solvent system to obtain the crystal of 1 that was used
to determine its X-ray crystal structure.
Com p lex Syn th eses. The cis-molybdenum tetracar-
bonyl complexes of ligands 1 and 2 were synthesized
by the simultaneous additions of solutions of Mo(CO)4-
(nbd) and the ligand into the solvent via pressure-
equalizing dropping funnels, as shown in Scheme 2.
These reactions were rapid and were completed within
30 min after the additions were completed. Because of
the tendency of the liberated norbornadiene to polymer-
ize, the solvent and norbornadiene were removed as
soon as the reactions had reached completion. The edge
model, 5, was synthesized by the addition of 1 to 2 equiv
of Mo(CO)5(NCMe), as shown in Scheme 3.
Ch a r a cter iza tion : The edge (5) and corner (6 and
7) model complexes exhibited 31P{1H} NMR spectra,
summarized in Table 4, that are similar to those of
related Mo(CO)5(phosphine) and cis-Mo(CO)4(phosphine)2
(19) CAD4-PC Version 1.2; Enraf-Nonius, Delft, The Netherlands,
1988.
(20) Sheldrick, G. M. SHELXTL NT Version 6.12; Bruker AXS, Inc.,
Madison, WI, 2001.

412 Organometallics, Vol. 23, No. 3, 2004
Myrex et al.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 5
The coordination geometries of the molybdenum car-
bonyl centers in the model complexes 5-7 were char-
acterized using IR spectroscopy, and the frequencies of
the infrared absorptions in the carbonyl region for the
complexes are given in Table 5. The frequency of the
higher energy A1 absorption of each complex clearly
indicates the coordination geometry of the complex (ν-
(A1): Mo(CO)5L, ∼2074 cm-1; cis-Mo(CO)4L2, ∼2024
cm-1).
P1-C1
1.831(10)
2.513(3)
1.840(9)
2.537(3)
P3-C43
P3-Mo3
P4-C50
P4-Mo4
1.808(10)
2.521(3)
1.815(9)
2.509(3)
P1-Mo1
P2-C8
P2-Mo2
Mo1-C33
Mo1-C34
Mo1-C35
Mo1-C36
Mo1-C37
Mo2-C38
Mo2-C39
Mo2-C40
Mo2-C41
Mo2-C42
2.017(13)
2.043(13)
2.020(16)
2.067(15)
2.036(13)
1.962(12)
2.047(14)
2.055(14)
2.029(15)
2.077(14)
Mo3-C75
Mo3-C76
Mo3-C77
Mo3-C78
Mo3-C79
Mo4-C80
Mo4-C81
Mo4-C82
Mo4-C83
Mo4-C84
1.994(13)
2.062(14)
2.051(13)
2.023(15)
2.010(16)
1.979(13)
2.037(14)
2.008(14)
2.029(15)
2.072(15)
The characterization data for the polymer 4, obtained
from the reaction of 1 and Mo(CO)4(nbd), provides
significant insight into the nature of this material. Size
exclusion chromatography (SEC) of 4 gave an Mh n value
of 6.0 × 103 Da and an Mh w of 9.7 × 103 Da, yielding a
polydispersity of 1.61. The Mh n suggests an oligomer with
eight repeat units, i.e. [cis-Mo(CO)4(Ph2P(C4H2S)2-
PPh2)]8; however, the polydispersity indicates that a
number of polymeric species are present. Neither the
Mh n value nor the polydispersity is consistent with the
formation of a cyclic tetramer.5 It is important to note
that the molecular weight values are based upon the
use of a polystyrene calibration curve employing THF
as solvent. Because SEC separates on the basis of
hydrodynamic volume and the polymer most likely does
not have the same swelling properties in THF as
polystyrene, the molecular weight values determined by
SEC may vary significantly from the absolute values.
For example, McCullough has demonstrated that more
rigid linear polymers, such as poly(alkylthiophenes), can
have their molecular weights significantly overesti-
mated through SEC.24 Future studies are planned
where increasingly larger edge and corner models of
these polymers will be synthesized in order to develop
SEC calibration curves specific to these polymers. This
will require polymers spanning a range of molecular
weights and the determination of their Mark-Hou-
wink-Sakurada coefficients (from viscosity studies).
The 31P{1H} NMR and carbonyl IR spectral data for
4 are somewhat surprising. The 31P{1H} NMR spectrum
of 4 exhibits only a sharp singlet (ν1/2 ) 5 Hz) whose
chemical shift is nearly identical with that of the corner
model complex 6. As is the case for the model complexes,
the single 31P{1H} NMR resonance indicates that all of
the environments of the phosphorus nuclei in the
polymer are chemically equivalent on the time scale of
the NMR experiment. The IR spectrum of 4 is also very
similar to that the corner models 6 and 7. The only
formulation of 4 that is consistent with the 31P{1H}
NMR and carbonyl IR spectral data and the SEC data
is that the polymer is a cyclic oligomer containing only
cis-Mo(CO)4(Ph2P(C4H2S)2PPh2) repeat units. This con-
clusion is supported by the elemental analysis of the
complex, which is consistent with that calculated for the
monomer unit.
C33-O1
C34-O2
C35-O3
C36-O4
C37-O5
C38-O6
C39-O7
C40-O8
C41-O9
C42-O10
1.126(13)
1.124(13)
1.138(15)
1.095(14)
1.137(13)
1.155(13)
1.118(13)
1.140(13)
1.162(14)
1.097(14)
C75-O11
C76-O12
C77-O13
C78-O14
C79-O15
C80-O16
C81-O17
C82-O18
C83-O19
C84-O20
1.133(12)
1.119(13)
1.128(13)
1.135(14)
1.151(15)
1.144(13)
1.121(14)
1.160(14)
1.144(15)
1.092(15)
C33-Mo1-C34
C33-Mo1-C35
C33-Mo1-C36
C33-Mo1-C37
C33-Mo1-P1
P1-Mo1-C34
P1-Mo1-C35
P1-Mo1-C36
P1-Mo1-C37
86.6(5)
89.4(5)
90.4(5)
91.8(4)
178.7(4)
92.8(3)
91.8(4)
90.2(3)
87.0(3)
C75-Mo3-C76
C75-Mo3-C77
C75-Mo3-C78
C75-Mo3-C79
C75-Mo3-P3
P3-Mo3-C76
P3-Mo3-C77
P3-Mo3-C78
P3-Mo3-C79
90.0(4)
91.5(5)
86.9(5)
89.1(5)
177.9(4)
92.0(3)
88.0(3)
91.1(3)
91.5(4)
C38-Mo2-C39
C38-Mo2-C40
C38-Mo2-C41
C38-Mo2-C42
C38-Mo2-P2
P2-Mo2-C39
P2-Mo2-C40
P2-Mo2-C41
P2-Mo2-C42
89.9(5)
88.9(5)
88.8(5)
88.2(5)
176.1(4)
93.6(4)
92.5(3)
87.7(3)
90.2(3)
C80-Mo4-C81
C80-Mo4-C82
C80-Mo4-C83
C80-Mo4-C84
C80-Mo4-P4
P4-Mo4-C81
P4-Mo4-C82
P4-Mo4-C83
P4-Mo4-C84
91.8(6)
85.2(5)
92.1(6)
88.6(5)
177.4(4)
89.5(3)
92.5(3)
86.4(4)
93.6(4)
complexes.21,22 The 31P NMR resonance of each of model
complex was a sharp singlet (ν1/2: 5, 5 Hz; 6, 5 Hz; 7, 6
Hz), indicating that the environments of the phosphorus
nuclei in each complex were chemically equivalent on
the time scale of the NMR experiment. The 31P{1H}
NMR chemical shift of the edge model 5 was ap-
proximately 1 ppm downfield of those of the corner
models 6. This is consistent with the results from 31P-
{1H} NMR studies of Mo(CO)5(phosphine) and cis-Mo-
(CO)4(phosphine)2 complexes containing the same phos-
phine ligands.21,22 The 31P{1H} coordination chemical
shift (δ(31P{1H} complex) - δ(31P{1H} free ligand)) is
approximately 46 ppm for each of the complexes. Two
factors contribute to coordination chemical shifts: a
decrease in the electron density at the phosphorus
nuclei due to donation of the electron pair to the
molybdenum and a decrease in the electron density of
the phosphorus due to a slight expansion of the sub-
stituent-phosphorus-substituent (SPS) angles, and
hence the cone angles, upon coordination.23 The very
similar coordination chemical shifts of the three com-
plexes suggest that the changes in the cone angles in
the three ligands upon coordination are very similar.
X-r a y Str u ctu r es of 1 a n d 5. As discussed above,
the characterization data for 4 indicate that the reaction
of 1 and Mo(CO)4(nbd) yields a mixture of cyclic oligo-
mers because 1 coordinates only through the phos-
phines and the rigid nature of the bithiophene group in
1 prevents the phosphines from chelating. To better
understand the structure of the oligomeric complex, the
X-ray structures of the ligand 1 and the edge model
(21) Grim, S. O.; Wheatland, D. A.; McFarlane, W. J . Am. Chem.
Soc. 1967, 89, 5573.
(22) Grim, S. O.; Wheatland, D. A. Inorg. Chem. 1969, 8, 1716.
(23) Tolman, C. A. Chem. Rev. 1977, 77, 313-348.
(24) Liu, J .; Loewe, R. S.; McCullough, R. D. Macromolecules 1999,
32, 5777-5785.

Oligomeric [cis-Mo(CO)4(Ph2P(C4H2S)2PPh2)]n
Organometallics, Vol. 23, No. 3, 2004 413
Sch em e 1. Syn th esis of Liga n d s Con ta in in g P h osp h in es a n d 2,2′-Bith iop h en es
Sch em e 2. Syn th esis of th e Cyclic Oligom er ic Com p lexes a n d Cor n er Mod el Com p lexes
Ta ble 4. 31P {1H} NMR Ch em ica l Sh ifts
Sch em e 3. Syn th esis of th e Ed ge Mod el Com p lex
compd
chem shift (ppm)a
∆(δ)a
1
2
3
4
5
6
7
-18.50
-18.57
-19.43
27.56
26.64
27.31
46.06
45.14
45.88
46.04
26.61
a
δ(31P{1H} complex) - δ(31P{1H} free ligand).
Ta ble 5. IR F r equ en cies in th e Ca r bon yl Region
CO (cm-1
ν
)
compd
A1
A1, B1, B2
4
5
6
7
2024 m
2074 m
2023 m
2023 m
1928 sh, 1908 s
1988 w sh, 1948 s
1923 sh, 1910 s, 1886 m
1922 sh, 1911 s, 1886 m
bridging the two thiophene rings. Coplanarity of the two
thiophene rings is a necessary result from this cen-
trosymmetric conformation and is confirmed by the 180°
torsion angle about the carbon-carbon bond between
the thiophene rings. This center of symmetry is also
complex 5 were determined. The structures of 1 and 5
are shown in Figures 2 and 3, respectively. The ligand
1 crystallizes in the centrosymmetric space group P21/c
with a center of symmetry at the center of the bond

414 Organometallics, Vol. 23, No. 3, 2004
Myrex et al.
F igu r e 2. Molecular structure of 1. Hydrogen atoms are omitted, and the atomic displacement ellipsoids are drawn at
50% probability.
bond between the thiophene rings (molecule 1, S1-C4-
C5-S2 torsion angle 163.5°; molecule 2, S3-C46-C47-
S4 torsion angle 176.5°). The different degrees of rotation
about the carbon-carbon bond between the two thio-
phene rings suggests that there is a relatively low
barrier to rotation about this bond. Molecular modeling
has shown that while the formation energy generally
increases as the torsion angle moves from 180 to 0°, the
energy difference between these two states is only about
1.4 kcal/mol.
The metal centers of this edge are slightly distorted
octahedra. Examination of the molybdenum-carbonyl
bond distances shows the general trend of a stronger,
shorter Mo-C bond in the carbonyl opposite the coor-
dinated phosphine. This behavior was expected, as
phosphines are better σ-donors and weaker π-acceptors
than carbonyls. This difference in bonding might also
be expected to result in longer, weaker C-O bonds for
the carbonyl opposite the coordinated phosphine. How-
ever, any differences in these bonds are obscured by
differences due to crystal-packing forces in the solid-
state crystal structure.25
The structures of 1 and 5 provide considerable insight
into the reason that the reactions of 1 and Mo(CO)4-
(nbd) yield mixtures of cyclic oligomers rather than only
cyclic tetramers (molecular squares). There appear to
be three requirements that must be met for the reaction
of 1 and Mo(CO)4(nbd) to yield a cyclic tetramer. These
are as follows: (1) the thiophene rings in the bithiophene
moiety must be coplanar, (2) the phosphorus lone pairs
must have an antiparallel orientation, and (3) the
bithiophene moieties forming opposite edges of the
tetramer must have an identical orientation. The depic-
tion of compound 4 in Scheme 2, with n ) 1, shows the
appropriate orientation. The centrosymmetric space
group P21/c of the ligand 1 enforces the first two
conditions. However, even with coplanarity of the
thiophene rings, there are 70 possible orientations of
the ligands on the edges of the cyclic tetramer, but only
4 satisfy the third requirement, giving a 5.71% prob-
F igu r e 3. Molecular structure of one of the two molecules
of 5 in the asymmetric unit. Hydrogen atoms are omitted,
and the atomic displacement ellipsoids are drawn at 50%
probability.
evidenced in the trans orientation of the sulfur atoms
as well as the antiparallel orientation of the phosphorus
lone pairs.
Coordination of Mo(CO)5 groups to the phosphines in
5 disrupts the coplanarity of the two thiophene rings.
The asymmetric unit in 5 consists of two independent
molecules, giving two different examples of the model
edge in the solid state. The two molecules have signifi-
cantly different torsion angles about the carbon-carbon
(25) Cotton, F. A.; Kraihanzel, C. S. J . Am. Chem. Soc. 1962, 84,
4432-4438.

Oligomeric [cis-Mo(CO)4(Ph2P(C4H2S)2PPh2)]n
Organometallics, Vol. 23, No. 3, 2004 415
ability of forming the cyclic tetramer.26 The probability
is certainly much lower than this because (1) the crystal
structure of the edge model demonstrates that twisting
around the C-C bond between the two thiophenes can
also occur and (2) the 31P{1H} NMR data indicate that
free rotation about the metal-phosphorus bonds is
possible.
may be possible to use similar procedures to prepare a
range of organometallic poly(thiophenes) in which both
the length of the polythiophene and the nature of the
metal center are varied.
Ack n ow led gm en t. We thank the Chemistry De-
partment of the University of Alabama at Birmingham,
the donors of the Petroleum Research Fund, adminis-
tered by the American Chemical Society (grant no.
35349-AC3), and the Army Research Office (grant nos.
DAAD 19-030100218 and DAAD 19-99-1-0119) for sup-
port of this work. R.D.M. thanks the Graduate School
of the University of Alabama at Birmingham for a
Graduate Fellowship.
Con clu sion s
The development of novel organometallic polymers is
an exciting area in current chemical research. Such
polymers may serve as organometallic semiconducting
materials that combine the electrical conductivity of
metals with the light weight, corrosion resistance, and
less demanding production requirements of organic
materials. The phosphinothiophene ligands presented
herein, and their molybdenum complexes, are the first
results of our group’s efforts in this area. The ease with
which these complexes can be prepared suggest that it
Su p p or tin g In for m a tion Ava ila ble: Crystal structure
data for 1 and 5, including tables of atomic coordinates, U
values, all bond lengths and angles, torsion angles, and
hydrogen isotropic displacement parameters; crystallographic
data are also available in electronic form as CIF files. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(26) Each of the four ligands may be either cis or trans, yielding
eight possible orientations. A combination of four orientations from a
set of eight yields 70 possible orientations.
OM030595H