Substitution reactions of CpW2(CO)7(μ-PPh2) with diphosphine ligands

Article abstract of DOI:10.1021/om960793r

The known complex CpW₂(CO)₇(μ-PPh₂) (1) has been prepared in good yield from the reaction of CpW(CO)₃(PPh₂) and W(CO)₄(NCMe)₂. Compound 1 reacts with the diphosphines PPh₂

Full text of DOI:10.1021/om960793r

918
Organometallics 1997, 16, 918-925
Su bstitu tion Rea ction s of Cp W2(CO)7(µ-P P h 2) w ith
Dip h osp h in e Liga n d s
Wen-Yann Yeh,* Yau-J ong Cheng, and Michael Y. Chiang†
Department of Chemistry, National Sun Yat-Sen University, Kaohsiung, Taiwan 80424
Received September 17, 1996X
The known complex CpW2(CO)7(µ-PPh2) (1) has been prepared in good yield from the
reaction of CpW(CO)3(PPh2) and W(CO)4(NCMe)2. Compound 1 reacts with the diphosphines
PPh2XPPh2 (2-5 for X ) CH2, C2H4, C3H7, and (C5H4)2Fe, respectively) to produce CpW2-
(CO)6(µ-PPh2)(η1-(PPh2)2X) (2a , 3a , 4a , and 5a ), CpW2(CO)5(µ-PPh2)(η2-(PPh2)2X) (2b, 3b,
and 4b), and [CpW2(CO)6(µ-PPh2)]2(η1,η1-(PPh2)2X) (3c, 4c, and 5c). Treating compound 1
with Me3NO in acetonitrile solution gives CpW2(CO)6(µ-PPh2)(NCMe) (6). Further treatment
of compound 6 with Me3NO in acetonitrile solution affords CpW2(CO)5(µ-PPh2)(NCMe)2 (7).
Reaction of compound 7 and CpW(CO)3(PPh2) leads to [CpW(CO)2(µ-PPh2)]2W(CO)4 (8). All
1
of the new complexes have been characterized by IR and H and 31P NMR spectroscopies,
mass spectrometry, and elemental analyses. 6 was also characterized by X-ray crystal-
lography.
Ch a r t 1
In tr od u ction
The bidentate diphosphine ligands R2P(CH2)nPR2 are
interesting to chemists due to their various modes of
coordination toward metal atoms1 and possible catalytic
activities of many of their complexes.2 Recently the
organometallic diphosphine ligands, particularly the
ferrocenyl derivatives (R2PC5H4)2Fe, have attracted
considerable research attention since they also provide
a convenient route to the syntheses of bimetallic or
polymetallic cluster complexes.3 Four binding modes
have been observed for diphosphines coordinated to
bimetallic complexes: η1-pendant, η2-chelating, η1,η1-
intrabridging, and η1,η1-interbridging (Chart 1). It has
been illustrated that preference for a particular coor-
dination mode depends on the substituents of the
phosphine ligands and the ancillary ligands on the
metal atoms, as well as the length of linking chains
between the two phosphine moieties.4 For example, the
steric bulk of phenyl groups, combined with only one
methylene unit separating the two phosphine groups,
makes Ph2PCH2PPh2 (dppm) difficult to bind bulky
in tr a br id gin g
in ter br id gin g
metal complexes in an η1,η1-intrabridging or an η1,η1-
interbriding mode.5
One of the general reaction patterns for metallophos-
phines of the type [M]PPh2 ([M] ) CpW(CO)3,6 CpMo-
9
(CO)3,6 CpRu(CO)2,7 CpFe(CO)2,7,8 Co(CO)4 ) is to pre-
pare bimetallic phosphido-bridged complexes.10 We
have improved the synthesis of ditungsten phosphido
complex CpW2(CO)7(µ-PPh2)11 (1) by treating W(CO)4-
(NCMe)2 with CpW(CO)3(PPh2). As part of our general
interest in the systematic chemistry of diphosphine
ligands with homonuclear and heteronuclear metal
clusters,12 the present work explores the reactions of
† To whom inquires concerning the X-ray crystallographic work
should be addressed.
X Abstract published in Advance ACS Abstracts, February 1, 1997.
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S0276-7333(96)00793-5 CCC: $14.00 © 1997 American Chemical Society

CpW2(CO)7(µ-PPh2)
Organometallics, Vol. 16, No. 5, 1997 919
Isolation of material from the second brownish-red band gave
compound 1 with dppm, dppe, dppp, and dppf, which
lead to formation and characterization of several new
cluster complexes containing W2, W2Fe, W3, W4, and W4-
Fe metal cores.
CpW2(CO)5(µ-PPh2)(η2-dppm) (2b) (20 mg, 0.017 mmol, 7%).
Ch a r a cter iza tion of 2a . Mass spectroscopy (FAB): m/ z
1170 (M+, 184W), 1170 - 28n (n ) 1-6, M+ - nCO). IR (THF,
ν
CO): 2024 (w), 1964 (w), 1932 (s), 1914 (s, br), 1850 (m) cm-1
.
1H NMR (CDCl3, 20 °C): δ 3.55 (m, 2H, CH2), 5.07 (s, 5H, Cp),
7.82-6.90 (m, 30H, Ph). 31P{1H} NMR (CD2Cl2, 20 °C): δ
2
2
-24.79 (d, J P-P ) 78 Hz), 8.99 (dd, J P-P ) 78 and 29 Hz;
with 183W satellites, J W-P ) 261 Hz), 143.89 (d, J P-P ) 29
Hz; with 183W satellites, 1J W-P ) 157 and 305 Hz). Anal. Calcd
for C48H37O6P3W2: C, 49.26; H, 3.19. Found: C, 49.81; H, 3.47.
1
2
Ch a r a cter iza tion of 2b. Mass spectroscopy (FAB): m/ z
1142 (M+, 184W), 1142-28n (n ) 1-5, M+ - nCO). IR (THF,
1
ν
CO): 1988 (w), 1916 (s), 1890 (s), 1862 (s), 1834 (w) cm-1. H
Exp er im en ta l Section
NMR (CD2Cl2, 20 °C): δ 4.90 (m, 1H, CH2), 4.97 (s, 5H, Cp),
5.25 (m, 1H, CH2), 7.81-6.71 (m, 30H, Ph). 31P{1H} NMR
(CD2Cl2, 20 °C): δ -41.43 (dd, 2J P-P ) 7 and 33 Hz; with 183W
Gen er a l P r oced u r es. CpW(CO)3(PPh2)13 and W(CO)4-
(NCMe)2 were prepared according to the literature method.
14
1
2
satellites, J W-P ) 187 Hz), -22.12 (dd, J P-P ) 7 and 57 Hz;
Bis(diphenylphosphino)methane (dppm), bis(diphenylphosphi-
no)ethane (dppe), bis(diphenylphosphino)propane (dppp), and
1,1′-bis(diphenylphosphino)ferrocene (dppf) from Aldrich were
used as received. Tetrahydrofuran (THF) was distilled from
sodium benzophenone ketyl immediately before use. Dichlo-
romethane and acetonitrile were distilled from calcium hydride
before use. Preparative thin-layer chromatographic (TLC)
plates were prepared from silica gel (Merck, GF 254). 1H and
31P NMR spectra were obtained on a Varian VXR-300 spec-
trometer at 300 and 121.4 MHz, respectively. IR spectra were
taken on a Hitachi-2001 spectrometer. Fast-atom bombard-
ment (FAB) mass spectra were obtained on a VG-5022 mass
spectrometer. Elemental analyses were performed at the
National Science Council Regional Instrumentation Center at
National Chen-Kung University, Tainan, Taiwan.
1
2
with 183W satellites, J W-P ) 220 Hz), 115.78 (dd, J P-P ) 33
and 57 Hz; with 183W satellites, 1J W-P ) 209 and 248 Hz). Anal.
Calcd for C47H37O5P3W2: C, 49.41; H, 3.26. Found: C, 49.69;
H, 3.45.
Rea ction of Cp W2(CO)7(µ-P P h 2) (1) a n d d p p e. Com-
pound 1 (70 mg, 0.086 mmol) and dppe (37 mg, 0.092 mmol)
in THF (15 mL) solution was refluxed under nitrogen for 20 h
and worked up in a fashion identical with that above. Isolation
of the material from the first brownish-red band on TLC gave
CpW2(CO)6(µ-PPh2)(η1-dppe) (3a ) (45 mg, 0.038 mmol, 44%),
from the second brownish-red band gave [CpW2(CO)6(µ-PPh2)]2-
(η1, η1-dppe) (3c) (31 mg, 0.016 mmol, 37%), and from the third
brownish-red band gave CpW2(CO)5(µ-PPh2)(η2-dppe) (3b) (7
mg, 0.006 mmol, 7%).
Im p r oved Syn th esis of Cp W2(CO)7(µ-P P h 2) (1). An
Ch a r a cter iza tion of 3a . Mass spectroscopy (FAB): m/ z
oven-dried, 100 mL Schlenk flask was equipped with
a
1184 (M+, 184W), 1184 - 28n (n ) 1-6, M+ - nCO). IR (THF,
ν
magnetic stir bar and a rubber serum stopper. The stopper
was briefly removed, and CpW(CO)3(PPh2) (2.30 g, 2.84 mmol)
was added against a nitrogen flow. Freshly distilled dichlo-
romethane (10 mL) and THF (10 mL) were added with a
gastight syringe to dissolve Cp(CO)3W(PPh2). A THF (20 mL)
solution of W(CO)4(NCMe)2 (1.07 g, 2.84 mmol) was then
introduced slowly by means of a cannula through the serum
stopper. The flask was placed in a water bath at 40 °C for 8
h, forming a dark purple solution. The volatile materials were
removed under vacuum, and the residue was subjected to TLC,
eluting with dichloromethane/hexane (1:1, v/v). Isolation of
material from the purple band gave the known complex CpW2-
(CO)7(µ-PPh2)11 (1) (1.40 g, 1.72 mmol) in 61% yield. Mass
spectroscopy (FAB): m/ z 814 (M+, 184W), 814 - 28n (n ) 1-7,
M+ - nCO). IR (CH3CN, νCO): 2076 (m), 1963 (s, br), 1930
1
CO): 2024 (w), 1966 (w), 1932 (s), 1904 (s), 1850 (m) cm-1. H
NMR (CD2Cl2, 20 °C): δ 1.95 (m, 2H, CH2), 2.75 (m, 2H, CH2),
5.08 (s, 5H, Cp), 7.80-6.92 (m, 30H, Ph). 31P{1H} NMR (CD2-
Cl2, 20 °C): δ -12.62 (d, 3J P-P ) 38 Hz), 11.60 (dd, 2J P-P ) 28,
1
3J P-P ) 38 Hz; with 183W satellites, J W-P ) 255 Hz), 143.29
2
1
(d, J P-P ) 28 Hz; with 183W satellites, J W-P ) 158 and 310
Hz). Anal. Calcd for C49H39O6P3W2: C, 49.69; H, 3.32.
Found: C, 50.07; H, 3.51.
Ch a r a cter iza tion of 3b. Mass spectroscopy (FAB): m/ z
1156 (M+, 184W), 1156 - 28n (n ) 1-5, M+ - nCO). IR (THF,
ν
CO): 1982 (w), 1916 (s), 1880 (s), 1854 (s) cm-1 1H NMR (CD2-
.
Cl2, 20 °C): δ 2.03, 2.47 (m, 1H, CH2), 3.07 (m, 2H, CH2), 4.85
(s, 5H, Cp), 7.76-6.78 (m, 30H, Ph). 31P{1H} NMR (CD2Cl2,
20 °C): δ 26.62 (dd, J P-P ) 7 and 28 Hz; with 183W satellites,
1J W-P ) 215 Hz), 45.38 (dd, J P-P ) 7 and 59 Hz; with 183W
(m), 1857 (w) cm-1 1H NMR (CD2Cl2, 20 °C): δ 5.20 (s, 5H,
.
1
Cp), 7.65-6.90 (m, 10H, Ph). 31P{1H} NMR (CD2Cl2, 20 °C):
satellites, J W-P ) 220 Hz), 106.59 (dd, J P-P ) 28 and 59 Hz;
1
with 183W satellites, J W-P ) 222 and 234 Hz). Anal. Calcd
1
δ 149.14 (s; with 183W satellites, J W-P ) 132 and 324 Hz).
for C48H39O5P3W2: C, 49.85; H, 3.40. Found: C, 50.31; H, 3.52.
Anal. Calcd for C24H15O7PW2: C, 35.41; H, 1.86. Found: C,
35.45; H, 2.01.
Ch a r a cter iza tion of 3c. Mass spectroscopy (FAB): m/ z
1970 (M+, 184W), 1184 (M+ - [CpW2(CO)6(PPh2)]), 1184-28n
(n ) 1-6). IR (THF, νCO): 2024 (w), 1968 (w), 1932 (s), 1904
Rea ction of Cp W2(CO)7(µ-P P h 2) (1) a n d d p p m . Com-
pound 1 (210 mg, 0.26 mmol), dppm (107 mg, 0.28 mmol), and
THF (50 mL) were placed in a 100 mL round-bottomed flask,
equipped with a reflux condenser and a magnetic stir bar. The
solution was refluxed under nitrogen for 20 h. The solvent
was removed under vacuum, and the residue was subjected
to TLC, eluting with dichloromethane/hexane (1:2, v/v). Isola-
tion of material forming the first brownish-red band gave
CpW2(CO)6(µ-PPh2)(η1-dppm) (2a ) (240 mg, 0.21 mmol, 80%).
(s, br), 1850 (m) cm-1 1H NMR (CD2Cl2, 20 °C): δ 2.57 (br,
.
4H, CH2), 5.07 (s, 10H, Cp), 7.76-6.86 (m, 40H, Ph). 31P{1H}
NMR (CD2Cl2, 20 °C): δ 11.15 (d, J P-P ) 27 Hz; with 183W
satellites, 1J W-P ) 261 Hz), 143.58 (d, J P-P ) 27 Hz; with 183W
1
satellites, J W-P ) 156 and 305 Hz). Anal. Calcd for C72H54
-
O12P4W4: C, 43.89; H, 2.76. Found: C, 43.88; H, 3.10.
Rea ction of Cp W2(CO)7(µ-P P h 2) a n d d p p p . Compound
1 (81 mg, 0.1 mmol) and dppp (60 mg, 0.14 mmol) in THF (10
mL) solution was refluxed under nitrogen for 15 h and worked
up in a fashion identical with that above. Isolation of the
material from the first brownish-red band on TLC gave CpW2-
(CO)6(µ-PPh2)(η1-dppp) (4a ) (59 mg, 0.049 mmol, 49%), from
the second brownish-red band gave CpW2(CO)5(µ-PPh2)(η2-
dppp) (4b) (15 mg, 0.013 mmol, 13%), and from the third
brownish-red band gave [CpW2(CO)6(µ-PPh2)]2(η1, η1-dppp) (4c)
(28 mg, 0.014 mmol, 28%).
(12) (a) Hsu, S. C. N.; Yeh, W.-Y.; Chiang, M. Y. J . Organomet.
Chem. 1995, 492, 121. (b) Hsu, M.-A.; Yeh, W.-Y.; Chiang, M. Y. J .
Chin. Chem. Soc. 1994, 41, 741. (c) Yeh, W.-Y.; Chen, S.-B.; Peng, S.-
M.; Lee, G.-H. J . Organomet. Chem. 1944, 481, 183. (d) Hsu, M.-A.;
Yeh, W.-Y.; Peng, S.-M.; Lee, G.-H. J . Chin. Chem. Soc. 1994, 41, 441.
(13) Adams, H.; Bailey, N. A.; Day, A. N.; Morris, M. J .; Harrison,
M. M. J . Organomet. Chem. 1991, 407, 247.
(14) (a) Stolz, I. W.; Dobson, G. R.; Sheline, R. K. Inorg. Chem. 1963,
2, 323. (b) Ross, B. F.; Grasselli, J . G.; Ritchey, W. M.; Kaesz, H. D.
Inorg. Chem. 1963, 2, 1023.

920 Organometallics, Vol. 16, No. 5, 1997
Yeh et al.
Ch a r a cter iza tion of 4a . Mass spectroscopy (FAB): m/ z
1198 (M+, 184W), 1198 - 28n (n ) 1-6, M+ - nCO). IR (THF,
ν
mmol, 87%). Mass spectroscopy (FAB): m/ z 827 (M+, 184W),
786 (M+ - NCMe), 786-28n (n ) 1-6). IR (CH3CN, νCO):
CO): 2024 (w), 1967 (w), 1931 (s), 1909 (s, br), 1848 (m) cm-1
.
2018 (m), 1931 (s, br), 1881 (m), 1848 (w) cm-1 1H NMR (CD2-
.
1H NMR (CD2Cl2, 20 °C): δ 1.48 (m, 2H, CH2), 2.11 (m, 2H,
CH2), 2.89 (m, 2H, CH2), 5.03 (s, 5H, Cp), 7.76-6.92 (m, 30H,
Ph). 31P{1H} NMR (CD2Cl2, 20 °C): δ -17.82 (s), 7.20 (d, 2J P-P
) 27 Hz; with 183W satellites, 1J W-P ) 255 Hz), 143.30 (d, 2J P-P
) 27 Hz; with 183W satellites, 1J W-P ) 158 and 307 Hz). Anal.
Calcd for C50H41O6P3W2: C, 50.11; H, 3.45. Found: C, 49.62;
H, 3.66.
Cl2, 20 °C): δ 1.93 (s, 3H, Me), 5.19 (s, 5H, Cp), 7.84-7.02 (m,
10H, Ph). 31P{1H} NMR (CD2Cl2, -50 °C): δ 164.10 (s; with
183W satellites, 1J W-P ) 138 and 332 Hz). Anal. Calcd for C25
-
H
18NO6PW2: C, 36.31; H, 2.19; N, 1.69. Found: C, 35.57; H,
2.22; N, 1.76.
P r ep a r a tion of Cp W2(CO)5(µ-P P h 2)(NCMe)2 (7). CpW2-
(CO)6(µ-PPh2)(NCMe) (6) (500 mg, 0.6 mmol) and acetonitrile
(15 mL) were placed in an oven-dried 100 mL Schlenk flask,
equipped with a magnetic stir bar and a rubber serum stopper,
under nitrogen atmosphere. A solution of Me3NO (54 mg, 0.72
mmol) in acetonitrile (10 mL) was slowly introduced into the
flask over a period of 30 min. The mixture was stirred at room
temperature for 30 min, at which point the IR spectrum
showed no absorptions due to compound 6. The solution was
concentrated to ca. 10 mL, and methanol (10 mL) was added.
The flask was placed in a freezer at -20 °C for 5 days to give
dark red crystals, characterized as CpW2(CO)5(µ-PPh2)(NCMe)2
(7) (380 mg, 0.45 mmol, 75%). Mass spectroscopy (FAB): m/ z
840 (M+, 184W), 758 (M+ - 2 NCMe), 758 - 28n (n ) 1-5). IR
(CH3CN, νCO): 1958 (m), 1912 (s), 1865 (sh), 1842 (s) cm-1. 1H
NMR (CD2Cl2, 20 °C): δ 1.92 (s, br, 6H, Me), 5.14 (s, 5H, Cp),
7.78-6.94 (m, 10H, Ph). 31P{1H} NMR (CD2Cl2, -50 °C): δ
138.96 (s; with 183W satellites, 1J W-P ) 161 and 303 Hz). Anal.
Calcd for C26H21N2O5PW2: C, 37.17; H, 2.52; N, 3.33. Found:
C, 36.16; H, 2.50; N, 2.96.
Ch a r a cter iza tion of 4b. Mass spectroscopy (FAB): m/ z
1170 (M+, 184W), 1170 - 28n (n ) 1-5, M+ - nCO). IR (THF,
ν
CO): 1974 (w), 1914 (s), 1869 (s), 1851 (s) cm-1 1H NMR (CD2-
.
Cl2, 20 °C): δ 1.98 (m, 2H, CH2), 2.40, 2.51 (m, 1H, CH2), 2.76
(m, 3H, CH2), 4.83 (s, 5H, Cp), 7.58-6.81 (m, 30H, Ph).
2
31P{1H} NMR (CD2Cl2, 20 °C): δ -16.45 (t, J P-P ) 29 Hz;
1
2
with 183W satellites, J W-P ) 205 Hz), -2.64 (dd, J P-P ) 29
and 56 Hz; with 183W satellites, J W-P ) 208 Hz), 107.61 (dd,
1
2J P-P ) 29 and 56 Hz; with 183W satellites, J W-P ) 226 Hz).
1
Anal. Calcd for C49H41O5P3W2: C, 50.27; H, 3.53. Found: C,
49.62; H, 3.66.
Ch a r a cter iza tion of 4c. Mass spectroscopy (FAB): m/ z
1984 (M+, 184W). IR (THF, νCO): 2024 (w), 1964 (w), 1931 (s),
1908 (s, br), 1849 (m) cm-1 1H NMR (CD2Cl2, 20 °C): δ 2.72
.
(br, 2H, CH2), 2.84 (br, 4H, CH2), 5.32 (s, 10H, Cp), 7.74-6.88
2
(m, 40H, Ph). 31P{1H} NMR (CD2Cl2, 20 °C): δ 6.72 (d, J P-P
) 28 Hz; with 183W satellites, 1J W-P ) 255 Hz), 143.10 (d, 2J P-P
) 27 Hz; with 183W satellites, 1J W-P ) 159 and 305 Hz). Anal.
Calcd for C73H56O12P4W4: C, 44.18; H, 3.45. Found: C, 44.41;
H, 3.27.
Str u ctu r e Deter m in a tion for Cp W2(CO)6(µ-P P h 2)(NC-
Me) (6). A suitable crystal of compound 6 with approximate
dimensions of 0.25 × 0.33 × 0.33 mm was mounted on a glass
fiber and aligned on a Rigaku AFC7S diffractometer. Diffrac-
tion data were collected with graphite-monochromated Mo KR
radiation using the ω-2θ scan technique. Lattice parameters
were determined from 20 carefully centered reflections in the
range 6.9 < 2θ < 12.4°. The systematic absences of h0l (h +
l * 2n) and 0k0 (k * 2n) uniquely determine the space group
to be P21/n (No. 14, nonstandard setting). The data were
collected at 24 °C with a maximum 2θ value of 47.0°. Scans
with width of (0.94 + 0.30 tan θ)° were made at a speed of
16.0°/min (in ω). Of the 4144 reflections which were collected,
3973 were unique (Rint ) 0.079). The intensities of three
representative reflections were measured after every 150
reflections; no decay was observed. An empirical absorption
correction based on azimuthal scans of several reflections was
applied which resulted in transmission factors ranging from
0.70 to 1.00. The data were corrected for Lorentz and
polarization effects. The structure was solved by direct
methods15 and expanded using Fourier techniques.16 The non-
hydrogen atoms were refined anisotropically. Hydrogen atoms
were included but not refined. The final cycle of full-matrix
least-squares refinement was based on 3219 observed reflec-
tions (I > 3.00σ(I)) and 311 variable parameters. All calcula-
tions were carried out with the TEXSAN crystallographic
software package of the Molecular Structure Corp.17 A sum-
mary of relevant crystallographic data is provided in Table 1.
Rea ction of Cp W2(CO)7(µ-P P h 2) (1) a n d d p p f. A solu-
tion of compound 1 (91 mg, 0.11 mmol) and dppf (73 mg, 0.132
mmol) in THF (15 mL) was refluxed under nitrogen for 20 h.
The products were worked up in a fashion identical with that
above. Isolation of the material from the third, brown-red
band on TLC gave CpW2(CO)6(µ-PPh2)(η1-dppf) (5a ) (96 mg,
0.072 mmol, 65%) and from the fourth brown-red band gave
[CpW2(CO)6(µ-PPh2)]2(η1,η1-dppf) (5c) (28 mg, 0.014 mmol,
14%).
Ch a r a cter iza tion of 5a . Mass spectroscopy (FAB): m/ z
1341 (M+, 184W), 1341 - 28n (n ) 1-6, M+ - nCO), 554 (dppf).
IR (THF, νCO): 2024 (w), 1964 (w), 1932 (s), 1911 (s, br), 1849
(m) cm-1
.
1H NMR (CD2Cl2, 20 °C): δ 3.81, 4.04, 4.16, 4.40
(s, 2H, C5H4), 5.08 (s, 5H, Cp), 7.77-6.95 (m, 30H, Ph).
2
31P{1H} NMR (CD2Cl2, 20 °C): δ -17.75 (s), 9.93 (d, J P-P
)
28 Hz; with 183W satellites, J W-P ) 262 Hz), 143.80 (d, J P-P
) 28 Hz; with 183W satellites, 1J W-P ) 181 and 307 Hz). Anal.
Calcd for C57H43O6P3FeW2: C, 51.08; H, 3.23. Found: C, 51.23;
H, 3.36.
1
2
Ch a r a cter iza tion of 5c. Mass spectroscopy (FAB): m/ z
2127 (M+, 184W), 1342 (M+ - CpW2(CO)6(PPh2)). IR (THF,
ν
CO): 2024 (w), 1964 (w), 1932 (s), 1906 (s, br), 1850 (m) cm-1
.
1H NMR (CD2Cl2, 20 °C): δ 3.85-4.24 (m, C5H4), 5.06 (s, 10H,
Cp), 7.40 (m, 40H, Ph). 31P{1H} NMR (CD2Cl2, 20 °C): δ 10.72
(d, 2J P-P ) 28 Hz; with 183W satellites, 1J W-P ) 264 Hz), 143.73
(d, J P-P ) 28 Hz; with 183W satellites, J W-P ) 153 and 307
Hz). Anal. Calcd for C80H58O12P4FeW4: C, 45.19; H, 2.75.
Found: C, 45.06; H, 2.94.
2
1
Reaction s of CpW2(CO)6(µ-P P h 2)(NCMe) (6) with dppm ,
d p p e, d p p p , a n d d p p f. A typical reaction, CpW2(CO)6(µ-
PPh2)(NCMe) (6) (246 mg, 0.3 mmol) and dppm (120 mg, 0.33
mmol) were placed in a 50 mL Schlenk flask under N2, and
10 mL of THF was introduced. The solution was stirred at
room temperature for 10 min, at which point the IR spectrum
showed no absorptions due to compound 6. The solvent was
removed under vacuum and the residue separated by TLC.
CpW2(CO)6(µ-PPh2)(η1-dppm) (2a ) was isolated in 88% yield.
P r ep a r a tion of Cp W2(CO)6(µ-P P h 2)(NCMe) (6). CpW2-
(CO)7(µ-PPh2) (1) (1 g, 1.2 mmol) and acetonitrile (20 mL) were
placed in an oven-dried 100 mL Schlenk flask, equipped with
a magnetic stir bar and a rubber serum stopper, under
nitrogen atmosphere. A solution of Me3NO (110 mg, 1.45
mmol) in acetonitrile (10 mL) was slowly introduced into the
flask via a syringe over a period of 30 min. The mixture was
stirred at room temperature for 1 h, at which point the IR
spectrum showed no absorptions due to compound 1. During
reaction, the color changed from purple to dark red. The
solution was concentrated to ca. 15 mL, and methanol (15 mL)
was slowly introduced into the flask. The flask was placed in
a freezer at -20 °C overnight to form dark red crystals,
characterized as CpW2(CO)6(µ-PPh2)(NCMe) (6) (856 mg, 1.04
(15) SIR92: Altomare, A.; Cascarano, M.; Giacovazzo, C.; Guagliardi,
A. J . Appl. Crystallogr. 1993, 26, 343.
(16) DIRDIF94: Beurskens, P. T.; Admiraal, G.; Beurskens, G.;
Bosman, W. P.; de Gelder, R.; Israel, R.; Smits, J . M. M. Technical
Report of the Crystallography Laboratory, University of Nijmegen, The
Netherlands, 1994.
(17) TEXSAN: Crystal Structure Analysis Package, Molecular
Structure Corp., 1985, 1992.

CpW2(CO)7(µ-PPh2)
Ta ble 1. Exp er im en ta l Da ta for th e X-r a y
Organometallics, Vol. 16, No. 5, 1997 921
Sch em e 1
Diffr a ction Stu d y of Com p ou n d 6
chem formula: C25H18O6NPW2
fw: 827.09
a ) 14.656(4) Å
b ) 11.524(2) Å
c ) 15.082(5) Å
â ) 92.86(3)°
V ) 2543(1) Å3
Z ) 4
space group: P21/n (No. 14)
T ) 24 °C
λ ) 0.710 69 Å
Dcalcd ) 2.159 g/cm3
µ ) 91.50 cm-1
Ra ) 0.056
b
2θ max ) 47.0°
goodness of fit: 3.35
Rw ) 0.057
a
b
2 1/2
R ) ∑||Fo| - |Fc||/∑|Fo|. Rw ) [∑w(|Fo| - |Fc|)2/∑wFo
] .
The reaction of compound 6 and dppe afforded CpW2(CO)6-
(µ-PPh2)(η1-dppe) (3a ) (43%) and [CpW2(CO)6(µ-PPh2)]2(η1,η1-
dppe) (3c) (9%).
The reaction of compound 6 and dppp afforded CpW2(CO)6-
(µ-PPh2)(η1-dppp) (4a ) (48%) and [CpW2(CO)6(µ-PPh2)]2(η1,η1-
dppp) (4c) (7%).
The reaction of compound 6 and dppf afforded CpW2(CO)6-
(µ-PPh2)(η1-dppf) (5a ) (46%) and [CpW2(CO)6(µ-PPh2)]2(η1,η1-
dppf) (5c) (11%).
ture, but producing compound 1 and CpW2(CO)8(µ-PPh2)
(9) in moderate yields (eq 2). Furthermore, irradiating
9 led to 1, while no reaction was observed upon ther-
molysis of 9.11
R ea ct ion s of Cp W2(CO)5(µ-P P h 2)(NCMe)2 (7) w it h
d p p m , d p p e, d p p p , a n d d p p f. Typically, CpW2(CO)5(µ-
PPh2)(NCMe)2 (7) (240 mg, 0.3 mmol) and dppm (120 mg, 0.33
mmol) were placed in a 50 mL Schlenk flask under N2 and 10
mL of THF was introduced. The solution was stirred at room
temperature for 30 min, at which point the IR spectrum
showed no absorptions due to compound 7. The solvent was
removed under vacuum and the residue separated by TLC.
CpW2(CO)6(µ-PPh2)(η1-dppm) (2a ) (6%) and CpW2(CO)5(µ-
PPh2)(η2-dppm) (2b) (73%) were isolated.
(1)
The reaction of compound 7 and dppe afforded CpW2(CO)6-
(µ-PPh2)(η1-dppe) (3a ) (10%), CpW2(CO)5(µ-PPh2)(η2-dppe) (3b)
(41%), and [CpW2(CO)6(µ-PPh2)]2(η1,η1-dppe) (3c) (4%).
The reaction of compound 7 and dppp afforded CpW2(CO)6-
(µ-PPh2)(η1-dppp) (4a ) (14%), CpW2(CO)5(µ-PPh2)(η2-dppp) (4b)
(37%), and [CpW2(CO)6(µ-PPh2)]2(η1,η1-dppp) (4c) (11%).
The reaction of compound 7 and dppf afforded CpW2(CO)6-
(µ-PPh2)(η1-dppf) (5a ) (21%) and [CpW2(CO)6(µ-PPh2)]2(η1,η1-
dppf) (5c) (5%).
Syn th esis of [Cp W(CO)2(µ-P P h 2)]2W(CO)4 (8). CpW2-
(CO)5(µ-PPh2)(NCMe)2 (7) (350 mg, 0.42 mmol) and THF (15
mL) were placed in an oven-dried 100 mL Schlenk flask,
equipped with a magnetic stir bar and a rubber serum stopper.
A solution of CpW(CO)3(PPh2) (260 mg, 0.5 mmol) in THF (15
mL) was slowly added into the flask. The mixture was stirred
under N2 at ambient temperature for 8 h. The solvent was
removed under vacuum, and the residue was dissolved in
dichloromethane and subjected to TLC, eluting with dichlo-
romethane/ hexane (1:2, v/v). A small amount of compound 1
(7 mg, <2%) was obtained from the first, purple band. The
material from the second, orange-red band afforded [CpW-
(CO)2(µ-PPh2)]2W(CO)4 (8) (320 mg, 0.25 mmol, 60%). Mass
spectroscopy (FAB): m/ z 1276 (M+, 184W), 1276 - 28n (n )
1-8). IR (THF, νCO): 2032 (w), 1984 (w), 1943 (s), 1930 (sh),
(2)
Obviously, forming the W-W bond from 9 to 1
requires activation of a strongly-bonded carbonyl ligand
through photolysis. In the present work two carbonyls
of W(CO)6 have been replaced by the more labile
acetonitrile ligands. Thus, the metallic phosphido spe-
cies could first attack W(CO)4(NCMe)2 to generate CpW-
(CO)3(µ-PPh2)W(CO)4(NCMe), followed by W-W bond
formation with elimination of the remaining acetonitrile
ligand and CO migration to give compound 1 (Scheme
1).
Compound 1 forms air-stable, purple crystals. The
structure of 1 consists of a bimetallic Cp(CO)2WW(CO)5
group bridged by a diphenylphosphido ligand, where the
W-W vector about bisects an edge of the W(CO)5(P)
octahedron.11
1915 (s), 1860 (m) cm-1 1H NMR (CD2Cl2, 20 °C): δ 4.93 (s,
.
5 H, Cp), 5.10 (s, 10H, Cp), 5.13 (s, 5H, Cp), 7.92-6.88 (m,
40H, Ph). 31P{1H} NMR (CD2Cl2, 20 °C): δ 132.93 (d, 2J P-P
)
1
12 Hz; with 183W satellites, J W-P ) 119 and 306 Hz), 128.59
1
(s; with 183W satellites, J W-P ) 127 and 293 Hz), 124.30 (d,
1
2J P-P ) 12 Hz; with 183W satellites, J W-P ) 127 and 303 Hz).
Anal. Calcd for C42H30O8P2W3: C, 39.53; H, 2.37. Found: C,
39.32; H, 2.56.
Rea ction s of Cp W2(CO)7(µ-P P h 2) a n d Dip h os-
p h in es. Treating CpW2(CO)7(µ-PPh2) (1) with Ph2-
PXPPh2 (X ) CH2, C2H4, C3H6, and (C5H4)2Fe) in
refluxing THF for 15-20 h generates a series of
products containing η1-pendant (a ), η2-chelating (b), and
η1,η1-interbridging (c) diphosphine ligands (eq 3). There
is no indication for forming the complexes with the
diphosphine ligands in an η1,η1-intrabridging mode,
presumably due to steric bulk of the cyclopentadienyl
Resu lts a n d Discu ssion
Syn th esis of Cp W2(CO)7(µ-P P h 2) (1). Treatment
of CpW(CO)3(PPh2) with W(CO)4(NCMe)2 at 40 °C for
8 h affords the known complex CpW2(CO)7(µ-PPh2)11 (1)
as the only metal-containing product (eq 1). Shyu and
co-workers have previously reported similar reaction of
Cp(CO)3W(PPh2) and W(CO)5(THF) at room tempera-

922 Organometallics, Vol. 16, No. 5, 1997
Yeh et al.
Sch em e 2
(3)
and phenyl groups making the CpW(CO)(PPh2) moiety
too crowded to coordinate another phosphine group. By
contrast, thermal reactions between the heterobimetal-
lic analogue (CpW)Mo(CO)7(µ-PPh2) and diphosphines
(dppm and dppe) afforded (CpW)Mo(CO)5(µ-PPh2)(η2-
dppm) and (CpW)Mo(CO)5(µ-PPh2)(η2-dppe) with dppm
and dppe ligands chelating the molybdenum atom as
the only isolated products.18 It is apparent that the
weaker Mo-CO bond strength19 relative to W-CO
accelerates substitution of two adjacent carbonyl ligands
by diphosphine at elevated temperature.
Thermolysis of a complexes results in decarbonylation
and chelation of the dangling phosphine to give b
complexes (except 5a ). However, c complexes are
obtained as major products (except 2a ) if compound 1
is present. Interestingly, heating c complexes does not
lead to CO transfer to regenerate 1 and b complexes.
The results are summarized in Scheme 2.
The ratio of b and c complexes is different, depending
on the type of linking chains between the two PPh2
moieties. It is obvious that the small bite angle of dppm
(ca. 65°)20 favors the chelated product 2b, while only a
methylene unit separating two bulky PPh2 groups
makes 2c too unstable to be isolated. On the other
hand, the two PPh2 groups in dppf are separated by a
large ferrocenyl moiety and are free to form bidentate
complex 5c, but its large bite angle (ca. 98°)12a,21 hinders
5b from being generated. Since the dppe and dppp
ligands are able to form stable five- and six-membered
chelating rings and would not impose strong steric
interactions between the two PPh2 groups, both the b-
and c-types of products result.
Ch a r a cter iza tion of 2a , 3a , 4a , a n d 5a . These
compounds show very similar 31P NMR spectra and
almost identical IR absorption patterns in the carbonyl
region, suggesting great resemblance of their structures.
It is likely that the η1-diphosphine ligand replaces a
carbonyl trans to the phosphido ligand to minimize
repulsions with the Cp and the µ-PPh2 groups. In the
analogous complexes CpW2(CO)6(µ-PPh2)(PX3) (X )
OMe, Et, and Ph) the monodentate phosphine ligands
were found trans to the bridging diphenylphosphido
group.11
The IR spectra in the CO region of a complexes are
shifted to lower energy compared with that of 1,
consistent with the stronger σ-donor and weaker π-ac-
ceptor ability of phosphine ligand relative to CO.1c,22 The
31P{1H} NMR spectrum for 4a , presented in Figure 1a,
is assigned on the basis of chemical shifts and coupling
patterns of the signals. It is apparent that W-W bond
is retained in a complexes since their phosphido reso-
nances are comparable with the parent complex 1 (δ
149.14), whereas a significant upfield 31P resonance for
PPh2 bridging two metal atoms without a metal-metal
bond has been observed for Cp(CO)3W(µ-PPh2)W(CO)5
(δ -62.72),11 Cp(CO)3W(µ-PPh2)Mo(CO)5 (δ -41.66),18
and Cp(CO)3W(µ-PPh2)Fe(CO)3 (δ -10.41).10d
Ch a r a cter iza tion of 2b, 3b, a n d 4b. The 31P NMR
spectra of these complexes are alike and their IR
absorption patterns in the carbonyl region are almost
identical, again suggesting similar structures for them.
The 31P{1H} spectrum of 4b, shown in Figure 1b,
consists of three sets of resonance signals accompanied
by 183W satellites. This indicates that all the phospho-
rus atoms are coordinated to the tungsten atoms. It is
probable the dangling phosphine in a complexes re-
places a carbonyl cis to the phosphido group to form b
complexes. We note that the resonance at δ -16.46
shows equal coupling to the other two cis phosphorus
atoms (2J P-P ) 29 Hz), thus appearing as a pseudo-
(18) Wu, W.-J .; Hsu, J .-Y.; Wen, Y.-S.; Shyu, S.-G. J . Chin. Chem.
Soc. 1995, 42, 533.
(19) Marks, T. J ., Ed. Bonding Energetics in Organometallic Com-
pounds; ACS Symposium Series 428; American Chemical Society:
Washington, DC, 1990.
(20) Darensbourg, D. J .; Zalewski, D. J .; Plepys, C.; Campana, C.
Inorg. Chem. 1987, 26, 3723.
(21) Kim, T. J .; Kwon, S. C. J . Organomet. Chem. 1992, 426, 71.
(22) Elschenbroich, C.; Salzer, A. Organometallics; VCH: New York,
1989.

CpW2(CO)7(µ-PPh2)
Organometallics, Vol. 16, No. 5, 1997 923
F igu r e 1. 31P{1H} NMR spectra of (a) CpW2(CO)6(µ-PPh2)(η1-dppp) (4a ), (b) CpW2(CO)5(µ-PPh2)(η2-dppp) (4b), and (c)
[CpW2(CO)6(µ-PPh2)]2(η1,η1-dppp) (4c) in CD2Cl2 at 20 °C.
triplet. The IR absorptions in the CO region of b
complexes are in lower energy region than those of a
complexes, in agreement with chelation of the good
electron-donating phosphine ligands.
Syn th eses a n d Ch a r a cter iza tion of Cp W2(CO)6-
(µ-P P h 2)(NCMe) (6) an d CpW2(CO)5(µ-P P h 2)(NCMe)2
(7). Since reactions of 1 and diphosphines require
elevated temperature and lead to several products, we
decided to prepare more reactive substrates by replacing
carbonyls with labile ligands. Thus, treating CpW2-
(CO)7(µ-PPh2) with 1 equiv of Me3NO in CH3CN solution
effects displacement of a CO ligand by solvent molecule
to generate CpW2(CO)6(µ-PPh2)(NCMe) (6) in 87% yield.
Further reaction of 6 and Me3NO in CH3CN affords
CpW2(CO)5(µ-PPh2)(NCMe)2 (7) in 75% yield.
Both compounds 6 and 7 form dark red, air-stable
crystalline solids. The IR spectrum of 6 shows four CO
absorption peaks ranging from 2018 to 1848 cm-1, which
are apparently between those measured for 1 and a
complexes. This is consistent with the electron-donating
ability of the ligands in the order PR3 > NCMe > CO.23
The variable-temperature 31P{1H} NMR spectra exhibit
a broad resonance at 25 °C, while a sharp singlet at δ
Ch a r a cter iza tion of 3c, 4c, a n d 5c. The IR spectra
of 3c, 4c, and 5c in the carbonyl stretching region are
essentially identical and closely matching those of a
complexes, indicating that the CpW2(CO)6(µ-PPh2) moi-
eties in the a - and c-types of complexes are structurally
similar. Apparently, c complexes consist of two identi-
cal [CpW2(CO)6(µ-PPh2)] units bound to a diphosphine
ligand in a fashion similar to that for a complexes.
Thus, the 31P{1H} NMR spectrum of 4c, illustrated in
Figure 1c, shows two doublet signals with each ac-
companied by two pairs of 183W satellites. The 1H NMR
spectrum of 4c includes a multiplet at δ 7.30 for the
phenyl protons, a singlet at δ 5.32 for the Cp protons,
and two broad signals δ at 2.72 and 2.84 in an 1:2 ratio
for the propylene protons. An inversion center or a
plane of symmetry is apparently passing through the c
complexes to result in equivalent phosphido, phosphine,
and Cp groups.
(23) Morris, M. J . In Comprehensive Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford,
U.K., 1995; Vol. 5.

924 Organometallics, Vol. 16, No. 5, 1997
Yeh et al.
Ta ble 2. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) of Com p ou n d 6
Bond Lengths
W1-W2
W1-N1
W1-C9
W1-C11
W2-C1
W2-C3
W2-C5
W2-C7
P1-C20
O2-C7
O4-C9
O6-C11
C1-C2
C2-C3
C4-C5
3.171(1)
2.21(1)
2.08(2)
2.03(2)
2.36(2)
2.27(2)
2.38(2)
1.92(2)
1.81(1)
1.18(2)
1.12(2)
1.14(2)
1.41(2)
1.40(3)
1.35(2)
W1-P1
W1-C8
W1-C10
W2-P1
W2-C2
W2-C4
W2-C6
P1-C14
O1-C6
O3-C8
O5-C10
N1-C12
C1-C5
2.513(4)
1.94(2)
1.98(2)
2.364(4)
2.30(1)
2.36(2)
1.93(2)
1.81(1)
1.16(2)
1.19(2)
1.16(2)
1.14(2)
1.42(2)
1.41(3)
1.47(2)
C3-C4
C12-C13
Bond Angles
47.42(9)
W2-W1-P1
W2-W1-C8
W2-W1-C10
P1-W1-N1
P1-W1-C9
P1-W1-C11
N1-W1-C9
N1-W1-C11
C8-W1-C10
C9-W1-C10
C10-W1-C11
W1-W2-C1
W1-W2-C3
W1-W2-C5
W1-W2-C7
P1-W2-C2
P1-W2-C4
P1-W2-C6
C6-W2-C7
W1-P1-C14
W2-P1-C14
C14-P1-C20
W2-C6-O1
W1-C8-O3
W1-C10-O5
N1-C12-C13
W2-W1-N1
W2-W1-C9
W2-W1-C11
P1-W1-C8
P1-W1-C10
N1-W1-C8
N1-W1-C10
C8-W1-C9
C8-W1-C11
C9-W1-C11
W1-W2-P1
W1-W2-C2
W1-W2-C4
W1-W2-C6
P1-W2-C1
P1-W2-C3
P1-W2-C5
P1-W2-C7
W1-P1-W2
W1-P1-C20
W2-P1-C20
W1-N1-C12
W2-C7-O2
W1-C9-O4
W1-C11-O6
90.3(3)
65.7(5)
127.2(5)
90.1(5)
164.6(6)
177.5(6)
88.6(7)
90.1(7)
91.8(7)
167.1(7)
51.54(9)
134.1(5)
113.3(6)
120.9(4)
95.5(4)
145.0(6)
115.5(5)
107.8(5)
81.0(1)
119.3(5)
115.8(5)
177(1)
88.3(5)
147.9(6)
90.5(3)
113.0(5)
79.8(5)
87.4(6)
90.7(6)
91.5(8)
82.3(8)
84.9(8)
99.9(4)
147.3(5)
90.5(4)
84.1(5)
109.7(5)
148.5(6)
80.7(4)
79.5(7)
114.8(4)
124.7(4)
101.7(6)
178(1)
F igu r e 2. ORTEP diagram of CpW2(CO)6(µ-PPh2)(NCMe)
(6), showing the atomic labeling used in the text.
164.10 with two pairs of 183W satellites is observed at
-40 °C. The results suggest that compound 6 is
fluxional in solution, presumably through rotation of a
tungsten-phosphido bond within rapid cleavage and re-
formation of the W-W bond.24 A plausible alternative
pathway is via 3-fold rotation25 of the carbonyl and
acetonitrile ligands in the W(CO)4(NCMe) unit without
breaking the W-W bond.
The FAB mass spectrum of 7 presents the molecular
ion peak at m/ z ) 840 for 184W and ions corresponding
to loss of two acetonitriles and five carbonyls. The 31P-
{1H} NMR spectrum at 25 °C shows a broad resonance
at δ 138.94, which becomes a sharp singlet accompanied
176(1)
165(1)
176(1)
178(1)
173(2)
176(1)
shown on the right side of the pair is dominated for 6,
leading to stronger binding between the P1 and W2
atoms.
1
by two pairs of 183W satellites at -50 °C. The H NMR
spectrum shows a multiplet in the range δ 7.78-6.94
for the phenyl protons, a singlet at δ 5.14 for the Cp
protons, and a broad singlet at δ 1.92 for the acetonitrile
protons. Equivalence of the two acetonitrile ligands is
presumably through a dynamic process similar to that
proposed for 6.
Cr ysta l Str u ctu r e of Cp W2(CO)6(µ-P P h 2)(NCMe)
(6). Crystals suitable for X-ray diffraction were grown
from acetonitrile/methanol at -20 °C. An ORTEP
drawing of 6 is shown in Figure 2. Selected bond
distances and bond angles are given in Table 2. The
molecule consists of Cp(CO)2W and W(CO)4(NCMe)
units connected by a tungsten-tungsten bond and a
bridging diphenylphosphido group. The W1-W2 length
of 3.171(1) Å is between those measured for CpW2(CO)7-
(µ-PPh2) (1) (3.194(1) Å) and CpW2(CO)6(µ-PPh2)-
(P(OMe)3) (3.151(1) Å),11 consistent with strengthening
of W-W bond by stronger electron-donating ligands.
The phosphido group bridges the two tungsten atoms
unequally, such that the W2-P1 bond length (2.364(4)
Å) is significantly shorter than that of W1-P1 (2.513-
(4) Å). It is apparent that the resonance structure
W1 and W2 atoms are each linked to four and two
terminal carbonyls, respectively. The W-CO lengths
associated with the W2 atom are equal, being 1.93(2)
Å, while those associated with the W1 atom are scat-
tered from 1.94(2) to 2.08(2) Å. The W-CO angles are
in the range of 165(2) to 178(1)°. Although the angle
W1-C9-O4 ) 165(1)° might indicate a semibridging
24
structure,4,
which plausibly accounts for the IR
absorption at 1848 cm-1, the W2‚‚‚C9 distance of 2.99-
(2) Å is too long to support this suggestion.
The cyclopentadienyl ring is bonded to the W2 atom
asymmetrically, with C2-W2 (2.30(1) Å) and C3-W2
(2.27(2) Å) distances being shorter than the C1-W2
(2.36(2) Å), C4-W2 (2.36(2) Å), and C5-W2 (2.38(2) Å)
distances, presumably due to steric influence from the
adjacent C8-O3 and phenyl (C20-C25) groups. Nev-
ertheless, the observed variation of these bond lengths
is within the range typically found for metal-carbon
distances in η5-C5H5 metal complexes.
(24) Shyu, S.-G.; Hsu, J .-Y.; Lin, P.-J .; Wu, W.-J .; Peng, S.-M.; Lee,
G.-H.; Wen, Y.-S. Organometallics 1994, 13, 1699.
(25) Gavens, P. D.; Mays, M. J . J . Organomet. Chem. 1978, 162,
389.

CpW2(CO)7(µ-PPh2)
Organometallics, Vol. 16, No. 5, 1997 925
The C9, W1, W2, and P1 atoms are essentially
coplanar, so the geometry about the W1 atom can be
viewed as an edge-capped octahedron with acetonitrile
ligand occupying an axial position cis to the phosphido
group. In contrast, the P(OMe)3 ligand in CpW2(CO)6-
(µ-PPh2)(P(OMe)3) was found at an equatorial position
trans to the µ-PPh2 group.11 Since both MeCN and
P(OMe)3 ligands are better σ-donor and poorer π-accep-
tors than CO, the cis position is expected to be more
favored by these ligands to achieve stronger W to CO
back-bonding, in agreement with what is observed for
6. However, the fact that P(OMe)3 assumes a less
crowded trans position indicates that steric effects, when
present, are the governing factors in determining ligand
configuration.
Rea ction s of Com p ou n d 6 a n d 7 w ith Dip h os-
p h in es. CpW2(CO)6(µ-PPh2)(NCMe) (6) undergoes fac-
ile ligand substitution reaction with dppm at room
temperature to give 2a exclusively in 88% yield. Similar
reactions with dppe, dppp, and dppf produce 3a , 4a , and
5a , respectively, in ca. 50% yield, together with the
dimeric products, 3c, 4c, and 5c in low yields (ca. 10%).
Interestingly, running the reaction of 6 with 0.5 equiv
of dppm at 60 °C for 1 min in an NMR tube shows the
31P resonances for 2a and two small multiplets at δ
142.58 and 16.86 matching the data expected for [CpW2-
(CO)6(µ-PPh2)]2(η1,η1-dppm) (2c), but attempts to isolate
this new product have been unsuccessful. Apparently,
the short methylene chain in 2c induces strong in-
tramolecular steric repulsions between the two bimetal-
lic units and leads to ready decomposition.
Treatment of CpW2(CO)5(µ-PPh2)(NCMe)2 (7) with
dppm, dppe, dppp, and dppf at room temperature
affords the products same as from thermal reactions
shown in eq 3. There is no indication of formation of
CpW2(CO)5(µ-PPh2)(η2-dppf) (5b), though it is expected
to be a kinetic product. It is probable the large dppf
bite angle makes 5b too crowded to be obtained.
Syn th esis a n d Ch a r a cter iza tion of [Cp W2(CO)6-
(µ-P P h 2)]2W(CO)4 (8). Since treating CpW(CO)3(PPh2)
with W(CO)4(NCMe)2 yielded CpW2(CO)7(µ-PPh2) (1),
we investigated if CpW(CO)3(PPh2) could replace the
acetonitrile ligands in CpW2(CO)5(µ-PPh2)(NCMe)2 (7)
to generate a tritungsten cluster complex. Indeed,
[CpW(CO)2(µ-PPh2)]2W(CO)4 (8) is afforded in 60% by
conducting the reaction at room temperature for 8 h (eq
4). Haines has previously shown8b the reaction of CpFe-
(CO)2(PPh2) and RhCl3 to give {[CpFe(CO)2(µ-PPh2)]2-
Rh}+.
F igu r e 3. 31P{1H} NMR spectrum of [CpW(CO)2(µ-
PPh2)]2W(CO)4 (8) in CD2Cl2 at 20 °C, showing the presence
of two isomers in a 1:1 ratio.
the molecular ion peak at m/ z ) 1276 (184W) and ion
1
multiplets due to loss of eight carbonyls. The H NMR
spectrum shows a complex multiplet in the range δ
7.92-6.88 for the phenyl protons, and three singlets at
δ 5.13, 5.10, and 4.93 in an 1:2:1 ratio for the Cp protons.
Moreover, the 31P{1H} NMR spectrum, shown in Figure
3, includes two doublets at δ 132.93 and 124.30 (2J P-P
) 12 Hz) and a singlet at δ 128.59 in a 1:1:2 ratio,
indicating the presence of two isomers in equal quantity
for 8. Since all the 31P signals are accompanied by two
pairs of 183W satellites and their chemical shifts are
compatible with that recorded for 1, the two CpW(CO)2-
(PPh2) units in 8 appear to bind W(CO)4 in a fashion
similar to compound 1. It is likely that the two
phosphido groups are trans to each other and the two
external tungsten atoms cap opposite edges of W(CO)4-
(P)2 octahedron to minimize steric interactions. Thus
two isomers, 8-syn and 8-anti, can be obtained when
CpW(CO)3(PPh2) approaches 7 with their Cp groups on
the same side (syn) or opposite sides (anti) of the W3P2
plane. Since the geometry of 8-syn reveals no sym-
metry, the two Cp units and phosphido atoms are not
1
equivalent and lead to separate H and 31P resonances,
whereas an inversion center is apparently imposed at
the central tungsten atom of 8-anti to result in equiva-
lent phosphido and Cp groups. We have tried to grow
crystals suitable for X-ray diffraction study but failed,
presumably due to disorder from mixing of the two
isomers.
Ack n ow led gm en t. We are grateful for support of
this work by the National Science Council, Grant No.
NSC-84-2113-M110-009.
(4)
Su p p or tin g In for m a tion Ava ila ble: Text describing
X-ray procedures and complete tables of crystallographic data,
positional and Beq parameters, anisotropic displacement pa-
rameters, bond lengths, and bond angles (17 pages). Ordering
information is given on any current masthead page.
Compound 8 forms slightly air- and thermal-sensitive,
orange-red crystals. The FAB mass spectrum presents
OM960793R