Compounds with unbridged dative metal-metal bonds of formula (R3P)2(OC)3OsW(CO)5 and related complexes

Article abstract of DOI:10.1021/om990790p

Complexes of formula (R₃P)₂(OC)₃OsW(CO)₅ and similar complexes have been prepared from W(CO)₅(THF) and Os(CO)₃(PR₃)₂ in CH₂Cl₂/hexane at room temperature. The analogous Cr complexes could not be synthesized except for [MeC(CH₂O)₃P]₂(OC)₃OsCr(CO)₅ and (Me₂PCH₂CH₂PMe₂)(OC)₃OsCr(CO)₅, that is, with sterically undemanding P substituents. Tungsten compounds with P ligands with cone angles greater than approx. 125° could also not be prepared. The crystal structures of (Me₂PCH₂CH₂PMe₂)(OC)₃OsM(CO)₅ (M = Cr, W), [MeC-(CH₂O)₃P]₂(OC)₃OsW(CO)₅ (2), (OC)₃(Me₃P)₂OsW(CO)₅, (3), [MeC(CH₂O)₃P](OC)₃(Me₃P)OsW(CO)₅, (4), and [(MeO)₃P](OC)₃(Me₃P)OsW(CO)₅ (5) reveal that all have unbridged OsM bonds that are considerably longer than the corresponding OsM bond in (Me₃P)(OC)₄OsM(CO)₅. The P ligands have an axial, radial arrangement except in 3, where the PMe₃ ligands have a trans, diradial orientation. In 4 and 5 the phosphite ligands are in the site trans to the OsW bond even though they have smaller cone angles than the PMe₃ ligand. Solution NMR data indicates that for 2 and 3 both the ax,rad and dirad isomers are present; for 4 both ax,rad forms are present, whereas for 5 only the solid state form is found. There was no evidence in solution for the dirad forms of 4 and 5. (The ¹³C NMR spectra of the compounds also indicated that ²J_PC becomes zero for PMC angles of about 103°). The unusual site preference of the P ligands in these molecules is interpreted in terms of steric effects and an electronic preference for a good π-acceptor ligand to adopt the position trans to the dative metal-metal bond. Complexes 2, 3, and 5 react with PPh₃ in CH₂Cl₂ at room temperature over 2 days to give W(CO)₅(PPh₃) and Os(CO)₃(PR₃)(PR′₃) in the order 3 > 5 > 2.

Full text of DOI:10.1021/om990790p

Organometallics 2000, 19, 5049-5062
5049
Com p ou n d s w ith Un br id ged Da tive Meta l-Meta l Bon d s
of F or m u la (R3P )2(OC)3OsW(CO)5 a n d Rela ted Com p lexes
Faming J iang,† Hilary A. J enkins,‡ Kumar Biradha,‡ Harry B. Davis,†
Roland K. Pomeroy,*,†,§ and Michael J . Zaworotko‡
The Departments of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A
1S6, Canada, and Saint Mary’s University, Halifax, Nova Scotia B3H 3C3, Canada
Received October 4, 1999
Complexes of formula (R3P)2(OC)3OsW(CO)5 and similar complexes have been prepared
from W(CO)5(THF) and Os(CO)3(PR3)2 in CH2Cl2/hexane at room temperature. The analogous
Cr complexes could not be synthesized except for [MeC(CH2O)3P]2(OC)3OsCr(CO)5 and (Me2-
PCH2CH2PMe2)(OC)3OsCr(CO)5, that is, with sterically undemanding P substituents.
Tungsten compounds with P ligands with cone angles greater than ∼125° could also not be
prepared. The crystal structures of (Me2PCH2CH2PMe2)(OC)3OsM(CO)5 (M ) Cr, W), [MeC-
(CH2O)3P]2(OC)3OsW(CO)5 (2), (OC)3(Me3P)2OsW(CO)5 (3), [MeC(CH2O)3P](OC)3(Me3P)OsW-
(CO)5 (4), and [(MeO)3P](OC)3(Me3P)OsW(CO)5 (5) reveal that all have unbridged OsM bonds
that are considerably longer than the corresponding OsM bond in (Me3P)(OC)4OsM(CO)5.
The P ligands have an axial, radial arrangement except in 3, where the PMe3 ligands have
a trans, diradial orientation. In 4 and 5 the phosphite ligands are in the site trans to the
OsW bond even though they have smaller cone angles than the PMe3 ligand. Solution NMR
data indicates that for 2 and 3 both the ax,rad and dirad isomers are present; for 4 both
ax,rad forms are present, whereas for 5 only the solid state form is found. There was no
evidence in solution for the dirad forms of 4 and 5. (The 13C NMR spectra of the compounds
2
also indicated that J PC becomes zero for PMC angles of about 103°.) The unusual site
preference of the P ligands in these molecules is interpreted in terms of steric effects and
an electronic preference for a good π-acceptor ligand to adopt the position trans to the dative
metal-metal bond. Complexes 2, 3, and 5 react with PPh3 in CH2Cl2 at room temperature
over 2 days to give W(CO)5(PPh3) and Os(CO)3(PR3)(PR′3) in the order 3 > 5 > 2.
In tr od u ction
The bis-substituted compounds Os(CO)3(PR3)2 (e.g.,
R ) Me) might be expected to act as stronger donor
ligands than the Os(CO)4(PR3) analogues because there
should be an increase in electron density at the Os atom
when a carbonyl ligand is replaced with a better σ-donor
PR3 ligand. On the other hand, steric interactions
between the PR3 ligand that is necessarily cis to the
metal-metal bond and the radial carbonyls on the
M(CO)5 acceptor fragment would disfavor metal-metal
bond formation. An initial investigation of (OC)3(Me3P)2-
OsW(CO)5 showed that in the solid state both PMe3
ligands are cis to the OsW bond and in solution this
isomer was somewhat more preferred to the form with
one PMe3 group trans to the OsW bond. This unexpected
result suggested that more subtle factors were impor-
tant in determining the isomer ratios in (R3P)2(OC)3-
OsW(CO)5 complexes that warranted further study.
Herein we report the details of this study, the results
of which may be useful in the rationalization of the
unusual distribution of isomers observed for M′2-
(CO)10-x(PR3)x (M′ ) Mn, Re; x ) 2, 3) complexes.
Over the past 15 years we have reported several
investigations on complexes with unbridged donor-
acceptor bonds between two transition metals.1-9 In one
study we reported the synthesis of complexes of the type
(R3P)(OC)4OsM(CO)5 (M ) Cr, Mo, W; PR3 ) phosphine
or phosphite) which were found to exist as two isomers
in solution.2 The predominate form has the structure
found in the solid state with the P-ligand trans to the
OsM bond; the minor isomer has this ligand cis to the
metal-metal bond.
† Simon Fraser University.
‡ Saint Mary’s University.
§ E-mail: pomeroy@sfu.ca.
(1) Einstein, F. W. B.; Pomeroy, R. K.; Rushman, P. Willis, A. C. J .
Chem. Soc., Chem. Commun. 1983, 854.
(2) Davis, H. B.; Einstein, F. W. B.; Glavina, P. G.; J ones, T.;
Pomeroy, R. K.; Rushman, P. Organometallics 1989, 8, 1030.
(3) Shipley, J . A.; Batchelor, R. J .; Einstein, F. W. B.; Pomeroy, R.
K. Organometallics 1991, 10, 3620.
(4) (a) Batchelor, R. J .; Davis, H. B.; Einstein, F. W. B.; Pomeroy,
R. K. J . Am. Chem. Soc. 1990, 112, 2036. (b) Batchelor, R. J .; Einstein,
F. W. B.; Pomeroy, R. K.; Shipley, J . A. Inorg. Chem. 1992, 31, 3155.
(5) Einstein, F. W. B.; J ennings, M. C.; Krentz, R.; Pomeroy, R. K.;
Rushman, P.; Willis, A. C. Inorg. Chem. 1987, 26, 1341.
(6) Fleming, M. M.; Pomeroy, R. K.; Rushman, P. J . Organomet.
Chem. 1984, 273, C33.
(7) Einstein, F. W. B.; Pomeroy, R. K.; Rushman, P.; Willis, A. C.
Organometallics 1985, 4, 250.
(8) Martin, L. R.; Einstein, F. W. B.; Pomeroy, R. K. Organometallics
1988, 7, 294.
(9) J iang, F.; Male, J . L.; Biradha, K.; Leong, W. K.; Pomeroy, R.
K.; Zaworotko, M. J . Organometallics 1998, 17, 5810.
Exp er im en ta l Section
Unless otherwise stated, manipulations of starting materials
and products were carried out under a nitrogen atmosphere
with the use of standard Schlenk techniques. Hydrocarbon
solvents were refluxed over potassium and distilled and stored
over molecular sieves before use. Dichloromethane was dried
in a similar manner except that P2O5 was employed as the
10.1021/om990790p CCC: $19.00 © 2000 American Chemical Society
Publication on Web 11/01/2000

5050 Organometallics, Vol. 19, No. 24, 2000
J iang et al.
drying agent. Pentacarbonylosmium, Os(CO)5, and Os(CO)4-
(PMe3) were prepared by literature procedures.10,11 The pre-
cursory complexes M(CO)5(THF) (M ) Cr, W) were prepared
by a literature method;2 representative preparations of the Os-
(CO)3(PR3)2 compounds are described below. NMR spectra were
recorded on a Bruker AMX400 spectrometer at the appropriate
operating frequencies for 1H, 13C{1H}, and 31P{1H} NMR
spectra. Samples of the dinuclear complexes used for 13C{1H}
NMR spectra were enriched to ∼30% 13CO from more highly
13CO-enriched M(CO)5(THF);2 it was found that the 13CO was
equally distributed over all CO sites in the products. Spectra
that required long accumulation times often exhibited weak
peaks due to the decomposition products W(CO)6 and Os(CO)3-
(PR3)2.
PMe2) is a pale yellow solid that is extremely sensitive to air.
The following derivatives were fully characterized. The other
derivatives were characterized by IR and mass spectroscopy;
all gave a parent ion by EIMS except Os(CO)3[P(OCH2)2CMe]2.
1
Os(CO)3(PMe3)2: IR (hexanes) ν(CO) 1866 (s) cm-1; H NMR
(CD2Cl2) δ 1.80 (t, apparent J PH ) 4.1 Hz); 31P{1H} NMR (CD2-
Cl2) δ -48.75; 13C{1H} NMR (CD2Cl2/CH2Cl2, 1:4) δ 200.9 (t,
apparent J PC ) 12.2 Hz), 24.9 (t, apparent J PC ) 19.4 Hz);
triplets observed at δ 180.7 and 14.8 are attributed to Os(CO)2-
(PMe3)2(Cl)2, which results from slow reaction of Os(CO)3-
(PMe3)2 with the solvent;12 MS (EI) m/z 428 (M+). Calcd for
C9H18O3OsP2: C, 25.35; H, 4.25. Found: C, 25.46; H, 4.26. Os-
(CO)3[P(OCH2)2CMe]2: IR (CH2Cl2) ν(CO) 2012 (vw), 1930 (s)
cm-1; 1H NMR (CD2Cl2) δ 0.78 (s); 4.29 (t, apparent J PH ) 2.4
Hz); 31P{1H} NMR (CD2Cl2) δ 96.7; 13C{1H} NMR (CD2Cl2/CH2-
Cl2, 1:4) δ 192.7 (t, J PC ) 17.5 Hz), 77.9 (t, apparent J PC ) 2.3
Hz), 34.1 (t, apparent J PC ) 17.9 Hz), 17.4 (d, J PC ) 1.5 Hz).
Calcd for C13H18O9OsP2‚CH2Cl2: C, 25.65; H, 3.08. Found: C,
25.73; H, 3.03 (the presence of CH2Cl2 was confirmed by 1H
NMR spectroscopy). Os(CO)3(PMe3)[P(OCH2)2CMe]: IR (CH2-
Cl2) ν(CO) 2018 (vw), 1988 (vw), 1902 (s) cm-1; 1H NMR (CD2-
P r ep a r a tion of Os(CO)3(P Me2P h )2. Meth od A. To a
round-bottom flask (∼100 mL; fitted with a Teflon valve) was
added Os(CO)5 (∼225 mg; ∼0.68 mmol) in hexane (50 mL) and
PMe2Ph (220 mg; 1.59 mmol). The flask was cooled to -196
°C, the solution degassed with three freeze-pump-thaw
cycles, and the flask sealed under vacuum. The vessel and
contents were heated with stirring at 90 °C for 28 h (after 5 h
the vessel was evacuated and the solution degassed as previ-
ously described). After this period the evacuation and degas-
sing of the solution was repeated, and the vessel and contents
were heated at 140 °C for a further 12 h to give a yellow
solution. The flask was cooled and the solution transferred to
a Schlenk flask and the solvent removed on the vacuum line;
most of the excess PMe2Ph was removed by vacuum distillation
to a probe cooled to -78 °C. The remaining waxy solid was
recrystallized from hexane at -20 °C to yield the desired
product, Os(CO)3(PMe2Ph)2 (170 mg; 46%), as an orange oil.
2
4
Cl2) δ 0.77 (s); 1.81 (dd, J PH ) 10.2 Hz, J PH ) 2.9 Hz), 4.26
(d, J PC ) 4.9 Hz); 31P{1H} NMR (CD2Cl2) δ -49.4 (d, J PP
267 Hz), 97.2 (d); 13C{1H} NMR (CD2Cl2/CH2Cl2, 1:4) δ 196.7
(dd, J PC ) 15.6, 13.0 Hz), 77.7 (d, J PC ) 6.9 Hz), 33.9 (d, J PC
)
2
)
35.5 Hz), 24.2 (dd, J PC ) 37.7, 3.4 Hz), 17.5 (s); MS (EI) m/z
500 (M+). Calcd for C11H18O6OsP2: C, 26.51; H, 3.64. Found:
C, 26.60; H, 3.58. Method of synthesis and IR data for all the
bis-substituted mononuclear compounds are deposited as
Supporting Information.
P r ep a r a t ion of (Me2P CH2CH2P Me2)(OC)3OsCr (CO)5
(1Cr ). A quartz Carius tube was charged with Cr(CO)6 (150
mg, 0.68 mmol) and THF (25 mL) and cooled to -196 °C, and
the solution was degassed with three freeze-pump-thaw
cycles. The solution, with stirring, was then irradiated with
UV light (200 W Hanovia lamp) for approximately 2 h. The
volume of the solution of Cr(CO)5(THF) was reduced to about
1 mL and cooled to -196 °C. A solution of Os(CO)3(Me2PCH2-
CH2PMe2) (90 mg, 0.21 mmol) in CH2Cl2 (4.0 mL) and hexane
(15 mL) was added to the frozen mixture. The tube and
contents were allowed to warm to room temperature, and the
solution was stirred for 2 h. The solvent was removed on the
vacuum line and the remaining solid stirred with hexane (40
mL) to remove most of the unreacted Cr(CO)6. The hexane was
decanted from the solid that was dissolved in a minimum of
CH2Cl2 and chromatographed on silica gel (12 × 1.0 cm) with
CH2Cl2 as the eluant. The yellow fraction was collected and
concentrated in volume; hexane was added until a precipitate
just began to form, whereupon the solution was stored at -15
°C for 3 days. The yellow crystals of 1Cr (49 mg, 36%) were
washed with hexane and dried on the vacuum line. IR (CH2-
Cl2) ν(CO): 2055 (m), 1999 (m), 1979 (m), 1959 (vs), 1901 (vs),
1894 (sh), 1868 (m) cm-1. Calcd for C14H16CrO8OsP2: C, 27.27;
H, 2.60. Found: C, 27.28; H, 2.66. Complexes of the formula
(R3P)2(OC)3OsM(CO)5 (M ) Cr, W) and [(RO)3P](Me3P)(OC)3-
OsW(CO)5 along with the tungsten analogue of 1Cr (1W) were
prepared in a manner similar to the method described above;
yields ranged from a low of 28% for 1W to 50-64% for most of
the (R3P)2(OC)3OsM(CO)5 and [(RO)3P](Me3P)(OC)3OsW(CO)5
products. The complexes are stable in air for short periods and
range in color from pale yellow for [MeC(CH2O)3P]2(OC)3OsW-
(CO)5 to deep yellow for 1Cr . Selected IR data (CH2Cl2;
ν(CO)): 2, 2082 (m), 2036 (s), 2019 (sh), 1998 (s), 1911 (vs),
1864 (s); 3, 2060 (m), 2054 (w), 2012 (w), 2001 (m),1977 (sh),
1958 (vs), 1906 (vs), 1873 (sh); 4, 2070 (m), 2026 (m), 1998
(m), 1979 (vs), 1906 (vs), 1863 (m) cm-1. Complete analytical
and IR spectroscopic data for the new compounds have been
deposited as Supporting Information. NMR data are given in
Tables1 and 2.
P r ep a r a tion of Os(CO)3(P Me3)[P (OCH2)3CMe]. Meth od
B. A round-bottom flask (as previously described) was charged
with Os(CO)4(PMe3) (205 mg; 0.54 mmol), P(OCH2)3CMe (80
mg, 0.55 mmol), and hexane (45 mL). The flask was evacuated
and the solution degassed in the normal manner. The flask
and contents were heated at 140 °C for 28 h (the solution was
stirred during this time). The flask was evacuated and the
solution degassed once during the 28 h period. On cooling the
flask to room temperature, a pale yellow precipitate formed;
an IR spectrum of the reaction solution at this stage showed
only bands due to the product. The mother solution was
removed from the solid which was recrystallized from
CH2Cl2/hexane to afford Os(CO)3(PMe3)[P(OCH2)3CMe] (184
mg); a further 48 mg of product was obtained when the mother
solution was concentrated and stored at -20 °C for a total yield
of 86%.
P r ep a r a tion of Os(CO)3(Me2P CH2CH2P Me2). Meth od
C. A rocking autoclave (480 mL; Parr Instrument Co.) was
charged under a nitrogen flush with Os3(CO)12 (0.52 g; 0.57
mmol), Me2PCH2CH2PMe2 (0.53 g; 3.5 mmol), and hexane (120
mL); the autoclave was quickly sealed, flushed three times
with CO, and then pressurized with CO (∼90 atm). The
autoclave was then rocked at 290-300 °C for 24 h. The
autoclave was cooled to room temperature and the pale yellow
solution transferred to a Schlenk flask (a small quantity of
an as yet unidentified red solid remained in the autoclave).
The desired product of Os(CO)3(Me2PCH2CH2PMe2) (0.35; 61%)
was obtained upon storing the solution at -35 °C. Repeating
the preparation but with a CO pressure of 200 atm resulted
in a lower yield (21%) of the product. Similarly, use of method
A to prepare Os(CO)3(Me2PCH2CH2PMe2) resulted in a lower
yield (32%).
The phosphite derivative Os(CO)3[P(OCH2)3CMe]2 is a white
crystalline solid that showed no apparent decomposition after
several days in air; on the other hand, Os(CO)3(Me2PCH2CH2-
(10) Rushman, P.; van Buuren, G. N.; Shiralian, M.; Pomeroy, R.
K. Organometallics 1983, 2, 693.
(11) Martin, L. R.; Einstein, F. W. B.; Pomeroy, R. K. Inorg. Chem.
1985, 24, 2777.
(12) Davis, H. B.; Pomeroy, R. K. Unpublished results. See also:
Davis, H. B. Ph.D. Thesis, Simon Fraser University, 1991.

(R3P)2(OC)3OsW(CO)5 and Related Complexes
Organometallics, Vol. 19, No. 24, 2000 5051
Ta ble 1. 1H a n d 31P {1H} NMR Da ta for (R3P )2(OC)3Os M(CO)5 (M ) Cr , W) Com p lexesa
(PR3)2/M
1H NMRb
δ
31P{1H} NMRc δ
isomer ratiod
5.1
[P(OCH2)3CMe]2/Cr
ax, rad
dirad
4.32 (5.0), 4.28 (5.2), 0.83, 0.78
4.27 (3.0), 0.78
88.7 (32.0), 87.5
83.4
Me2PCH2CH2PMe2/Cr (1Cr )
[P(OCH2)3CMe]2/W
ax, rad
ax, rad (2)
1.99 (10.2), 1.88 (m), 1.74 (9.8)
4.32 (5.0), 4.27 (5.0), 0.84, 0.79;
3.44 (5.3), 3.43 (5.3), -0.29, -0.35e
4.28 (t, 2.6), 0.78
6.3 (0), 8.0
87.6 (32.9), 85.2;
1.7
∼97.5, ∼88e
0.2e,f
dirad
82.4
3.34 (t, 2.6), -0.39e
82.4e
[P(OMe)3]2/W
(PMe3)2/W
ax, rad
dirad
ax, rad
dirad (3)
ax, rad
dirad
ax, rad
ax, rad
ax, radg (4)
ax, radh,i
ax, radg
ax, radg
3.69 (7.0), 3.67 (8.2)
3.70 (t, 5.9)
1.88 (9.3), 1.79 (10.3)
1.86 (4.0)
7.38-7.02 (m), 1.86 (9.4), 1.71 (9.2)
2.12 (br t, 4.0)
1.97 (10.1), 1.89-1.85 (m), 1.78 (9.9)
7.51, 7.49, 2.66, 2.62
4.27 (5.0), 1.89(10.4), 0.80
4.33 (5.0), 1.80 (10.0), 0.85
3.68 (12.5), 1.76 (10.1)
7.28-7.07 (m), 2.33, 1.82 (10.0)
106.3 (34.3), 90.8
89.7
3.9
0.9
24
-57.8 (17.5), -62.9
-64.1
(PMe2Ph)2/W
-44.0 (18.3), -53.2
-52.7
Me2PCH2CH2PMe2/W (1W)
(Ph2PCH2CH2PPh2)/W
(PMe3)/[P(OCH2)2CMe]/W
5.5 (0), -8.0
32.5 (0), 18.1
89.7 (22.4), -53.6 (21.4)
85.4 (28.5), -60.5 (28.5)
105.7 (31.6), 59.1 (31.6)
87.7 (26.5), -61.0 (26.5)
(0.7)
(PMe3)/[P(OMe)3]/W (5)
(PMe3)/[P(O-o-C6H4Me)3]/W
i
i
a
b
c
d
CD2Cl2 solution, ambient temperature. J PH or apparent J PH in parentheses. J PP in parentheses. ax,rad/dirad (2,3/3,2) except for
4 (see text). e Toluene-d8 solution. f Determined from the 1H NMR spectrum. Axial-phosphite. Axial-PMe3, see text. Diradial isomer
g
h
i
(3,2) not detected.
X-r a y An a lyses of (Me2P CH2CH2P Me2)(OC)3OsM(CO)5
the M(CO)5 (M ) Cr, W) derivatives reported below were
(M ) Cr , 1Cr ; M ) W, 1W), [MeC(CH2O)3P ]2(OC)3OsW-
(CO)5 (2‚CH2Cl2; 2‚C7H8), (OC)3(Me3P )2OsW(CO)5 (3), [MeC-
(CH2O)3P ](OC)3](Me3P )OsW(CO)5 (4), an d [(MeO)3P ](OC)3]-
(Me3P )OsW(CO)5 (5). The crystals were grown from CH2Cl2/
hexane except those of 2‚C7H8, which were grown from
toluene/hexane. The structures were determined at St. Mary’s
University. The diffraction data were collected by using a
Siemens SMART/CCD diffractometer equipped with an LT-II
low-temperature device. The data were collected at -90 °C
except those for 2‚C7H8, where the temperature was -50 °C.
Diffraction data were corrected for absorption with the SAD-
ABS program. The program SHELXTL was used for the solu-
tions of the structures and their refinements, which were based
on F2.13 Crystal structure data can be found in Tables 3 and
4; selected bond lengths and angles are given in Tables 5
and 6.
well-behaved solids. In unpublished work, we have
found that in solution or in the solid-state Os(CO)3-
(PMe3)2 reacts with oxygen to give the carbonate
compound Os(CO)2(CO3)(PMe3)2; it also reacts slowly
with CH2Cl2 at room temperature to yield Os(CO)2-
(PMe3)2(Cl)2.12 The spectroscopic properties of the de-
rivatives with monodentate P ligands are consistent
with trigonal bipyramidal coordination for the Os atom
and a diaxial arrangement of the noncarbonyl ligands.
The (R3P)2(OC)3OsW(CO)5 (e.g., R ) Me, R ) OMe)
complexes were isolated (in moderate to good yield) from
the reaction of W(CO)5(THF) and Os(CO)3(PR3)2 (in a
1:1 molar ratio) in hexane/CH2Cl2 at room temperature
(eq 4). Some mixed derivatives of the type (Me3P)-
Os(CO)3(PR3)2 + W(CO)5(THF) 25 °C8
Resu lts a n d Discu ssion
Most of the precursory Os(CO)3(PR3)2 compounds used
in syntheses of the (R3P)2(OC)3OsW(CO)5 complexes
have not been previously reported. These compounds
were synthesized by three different reactions, examples
of which are summarized in eqs 1-3. They are air-
(R3P)2(OC)3OsW(CO)5 (4)
[(RO)3P]((OC)3OsW(CO)5 were prepared in a similar
manner.
The binuclear complexes could only be prepared when
the PR3 ligand had a cone angle (θ) of less than ∼125°.
Thus, (Me3P)2(OC)3OsW(CO)5 and (PhMe2P)2(OC)3OsW-
(CO)5 could be isolated, but the corresponding PEt3,
PMePh2, and PPh3 compounds could not be synthesized,
nor could (Ph3P)(Me3P)(OC)3OsW(CO)5. The cone angles
of PMe3, PMe2Ph, PMePh2, PEt3, and PPh3 are 118°,
122°, 132°, 136°, and 145°, respectively.14
Method A: Os(CO)5 + PMe2Ph 140 °C8
Os(CO)3(PMe2Ph)2 (1)
Method B: Os(CO)4(PMe3) +
P(OCH2)3CMe 140 °C8
Os(CO)3(PMe3)[P(OCH2)3CMe)] (2)
The only derivatives in which the acceptor moiety was
Cr(CO)5 (i.e., (R3P)2(OC)3OsCr(CO)5) that could be pre-
pared were with sterically undemanding P ligands,
namely, (dmpe)(OC)3OsCr(CO)5 (eq 5) and [MeC-
(OCH2)3P]2(OC)3OsCr(CO)5 (θ for P(OCH2)3CMe )
Method C: Os3(CO)12
Me2P(CH2)2PMe2 CO, 90 atm8
Os(CO)3[Me2P(CH2)2PMe2)] (3)
+
∼300 °C
sensitive white or pale yellow solids, except Os(CO)3-
(PMe2Ph)2, which was isolated as an orange oil. The
derivative with the chelate bisphosphine, Os(CO)3-
(dmpe) (dmpe ) Me2PCH2CH2PMe2), was particularly
air-sensitive and was not characterized fully, although
Os(CO)3[Me2P(CH2)2PMe2] + M(CO)5(THF) 25 °C8
[Me2P(CH2)2PMe2](OC)3OsM(CO)5 (5)
M ) Cr, 1Cr ; M ) W, 1W
(13) Sheldrick, G. M. SHELXTL; Siemens: Madison, WI, 1995.
(14) Tolman, C. A. Chem. Rev. 1977, 77, 313.

5052 Organometallics, Vol. 19, No. 24, 2000
J iang et al.
101°).14 No attempt was made to synthesize the molyb-
denumanalogues since it had been previously found that
yields of the similar (R3P)(OC)4OsMo(CO)5 complexes
were significantly lower than those of either of the Cr
or W congeners.2,3
Undoubtedly, the necessity of having a bulky PR3
ligand cis to the metal-metal bond causes steric inter-
actions with the radial (equatorial) carbonyls on the
group 6 atom such that for bulky phosphines the
(R3P)2(OC)3OsW(CO)5 derivatives are too unstable to
isolate. Similarly, the failure to prepare the Cr ana-
logues with still smaller P ligands can be attributed to
increased steric interactions between the PR3 and the
radial Cr carbonyls because of the shorter OsCr bond.
It may be that even in the absence of steric effects that
the OsCr bond is weaker than the OsW bond and also
contributes to the instability of the Cr compounds.
Molecular orbital calculations indicate that the OsCr
bond in (OC)5OsCr(CO)5 is weaker than the OsW bond
in (OC)5OsW(CO)5.15
All the binuclear compounds described here are
moderately air-stable, crystalline solids that range in
color from pale yellow to bright yellow. The colors
appear to correlate with the expected strength of the
dative metal-metal bond as would be predicted if the
electronic transition giving rise to the visible absorption
is due to the σ-to-σ* transition associated with the
metal-metal bond.16,17 For example, the OsW bond in
[MeC(CH2O)3P]2(OC)3OsW(CO)5 is thought to be among
the strongest of these complexes (see below), and the
complex is a much paler yellow than the corresponding
PMe3 and PMe2Ph derivatives. The chromium com-
pounds are deep yellow.
Str u ctu r a l Stu d ies. The compounds (Me2PCH2CH2-
PMe2)(OC)3OsM(CO)5 (M ) Cr, 1Cr ; M ) W; 1W) are
isostructural; a view of 1Cr is shown in Figure 1 with
selected bond length and angle data for 1Cr and 1W
given in Table 5. In each case the 18-electron compound
Os(CO)3(dmpe) acts as two-electron donor ligand toward
the 16-electron M(CO)5 moiety via an unbridged dative
metal-metal bond.
The OsCr bond length in 1Cr (3.0287(4) Å) is signifi-
cantly longer than the OsCr dative bonds in (Me3P)(OC)4-
OsCr(CO)5 (2.979(1) Å),2 (OC)4(ButNC)OsCr(CO)5 (2.966-
(2) Å), and (OC)3(ButNC)2OsCr(CO)5 (2.969(1) Å).3 (In
the last two compounds the noncarbonyl ligands are cis
to the OsCr bond.) It is tempting to attribute the
lengthening in 1Cr to the repulsive interactions be-
tween the radial carbonyls of the Cr(CO)5 moiety and
the methyl substituents on the P atom that are cis to
the OsCr bond. But as can be seen from Figure 1, the
small bite angle of the bidentate phosphine (P(1)OsP-
(2) ) 83.02(3)°) pulls these methyl groups away from
the Cr atom. As discussed below, there may be an
electronic component that contributes to the weakening
of the OsCr bond.
The OsW bond length in 1W (3.0984(5) Å) is also
longer than the corresponding bond in (Me3P)(OC)4OsW-
(CO)5 (3.0756(5) Å),2 but the difference is not as large
(15) Nakatsuji, H.; Hada, M.; Kawashima, A. Inorg. Chem. 1992,
31, 1740.
(16) Geoffroy, G. L.; Wrighton, M. S. Organometallic Photochemistry;
Academic: New York, 1979; p 20.
(17) Male, J . L.; Pomeroy R. K.; Tyler D. R. Organometallics 1997,
16, 3431.

(R3P)2(OC)3OsW(CO)5 and Related Complexes
Organometallics, Vol. 19, No. 24, 2000 5053
Ta ble 3. Cr ysta l Str u ctu r e Da ta for (Me2P CH2CH2P Me2)(OC)3OsM(CO)5 (M ) Cr , 1Cr ; M ) W, 1W),
[MeC(OCH2)3P ]2(OC)3OsW(CO)5‚C6H5Me (2‚C7H8), a n d 2‚CH2Cl2
1Cr
1W
2‚C7H8
2‚CH2Cl2
empirical formula
fw
C14H16CrO8OsP2
616.41
C14H16O8OsP2W
748.26
C25H26O14OsP2W
986.45
C19H20Cl2O14OsP2W
979.24
color
yellow
monoclinic
P21/c
14.8500(7)
8.4469(4)
16.6956(8)
yellow
monoclinic
P21/c
14.9516(7)
8.5143(4)
16.8825(8)
pale yellow
monoclinic
P21/c
11.9236(6)
18.1638(9)
15.3294(8)
pale yellow
triclinic
P1h
cryst syst
space group
a (Å)
b (Å)
c (Å)
9.4407(5)
11.3968(6)
14.6652(8)
86.851(1)
78.524(1)
66.128(1)
1413.5(2), 2
2.301
R (deg)
â (deg)
γ (deg)
V (Å3), Z
102.066(1)
102.689(1)
110.8430(10)
2048.0(2), 4
1.999
6.920
4766 [R(int) ) 0.0295]
0.0216
0.0566
2096.7(2), 4
2.370
11.723
4863 [R(int) ) 0.0925]
0.0671
0.1555
3102.7(3), 4
2.112
7.964
5469 [R(int) ) 0.0538]
0.0324
0.0556
D(calcd) (Mg‚m-3
)
abs coeff (mm-1
indpdt reflns
)
8.923
4885 [R(int) ) 0.0345]
0.0566
0.1533
a
RF
b
RwF
RF ) ∑|(|Fo| - |Fc|)|/∑|Fo|. RwF ) [∑(w(|Fo| - |Fc|)2)/∑(wFo2)]1/2; w ) [σ2(Fo)2 + kFo
]
.
a
b
2 -1
Ta ble 4. Cr ysta l Str u ctu r e Da ta for (OC)3(Me3P )2OsW(CO)5 (3), [MeC(CH2O)3P ](OC)3(Me3P )OsW(CO)5 (4)
a n d [(MeO)3P ](OC)3(Me3P )OsW(CO)5 (5)
3
4
5
empirical formula
fw
C
14H20O8OsP2W
C16H18Cl0.2O11OsP2W
829.38
C14H18O11OsP2W
798.27
752.29
color
yellow
yellow
yellow
cryst syst
space group
a (Å)
b (Å)
c (Å)
monoclinic
C2/c
orthorhombic
P212121
11.4419(6)
12.5953(7)
16.2012(9)
monoclinic
P21/n
14.3551(9)
13.2658(8)
11.1820(7)
100.852(1)
2091.3(2), 4
2.389
11.754
2309 [R(int) ) 0.0290]
0.0253
10.1342(5)
19.0605(9)
12.1613(6)
103.1020(10)
2288.0(2), 4
2.317
10.761
5335 [R(int) ) 0.0407]
0.0296
â (deg)
V (Å3), Z
2334.8(2), 4
2.359
10.572
5459 [R(int) ) 0.0499]
0.0366
D(calcd) (Mg‚m-3
)
abs coeff (mm-1
indpdt reflns
)
a
RF
b
RwF
0.0656
0.0871
0.0637
RF ) ∑|(|Fo| - |Fc|)|/∑|Fo|. RwF ) [∑(w(|Fo| - |Fc|)2)/∑(wFo2)]1/2; w ) [σ2(Fo)2 + kFo
]
.
a
b
2 -1
ligand.19 This distance is within a standard deviation
of the OsW distance in 1W.
Ta ble 5. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for (Me2P CH2CH2P Me2)(OC)3OsM(CO)5 (M )
Cr , 1Cr ; M ) W, 1W)
As can be seen from Figure 1, there is a significant
leaning of the radial carbonyls on the donor Os atom
toward the acceptor Cr (or W) atom. This is observed
in all the structures described here. The distances from
the C atom of these carbonyls to the group 6 metal atom
in each case (Tables 4 and 5) are greater than 3.25 Å
and are therefore essentially nonbonding. We have
proposed that the closer the C(7)OsC(8) angle is to
octahedral geometry (i.e., 180°), the stronger the donor-
acceptor interaction.9 (Consider the precursory Os(CO)3-
(PR3)2 compound going from the trigonal bipyramidal
1Cr
1W
Bond Lengths
3.0287(4)
2.3360(7)
2.3959(7)
1.819(3)
Os-M
3.0984(5)
2.338(3)
2.395(3)
Os-P(1)
Os-P(2)
M-C(1)
1.95(1)
M-Crad (range)
Os-C (range)
1.881(3)-1.897(3)
1.918(3)-1.943(3)
2.01(2)-2.05(1)
Bond Angles
175.90(2)
99.70(2)
83.02(3)
97.37(9)
M-Os-P(1)
176.56(8)
99.07(7)
83.05(10)
98.4(3)
104.7(3)
156.7(5)
M-Os-P(2)
P(1)-Os-P(2)
P(1)-Os-C(7)
P(1)-Os-C(8)
C(7)-O-C(8)
(18) Some recent examples: (a) Shiu, C.-W.; Chi, Y.; Carty, A. J .;
Peng, S.-M.; Lee, G.-H.; Organometallics 1997, 16, 5368. (b) Chi, Y.;
Chung, C.; Chou, Y.-C.; Su, P.-C.; Chiang, S.-J .; Peng, S.-M.; Lee, G.-
H. Organometallics 1997, 16, 1702. (c) Su, C.-J .; Chi, Y.; Peng, S.-M.;
Lee, G.-H. J . Cluster Sci. 1996, 7, 85. (d) Park, J . T.; Chung, J .-H.;
Song, H.; Lee, K.; Lee, J .-H.; Park, J .-R.; Suh, I.-H. J . Organomet.
Chem. 1996, 526, 215. (e) Huang, T.-K.; Chi, Y.; Peng, S.-M.; Lee, G.-
H.; Wang, S.-L.; Liao, F.-L. Organometallics 1995, 14, 2164. (f) Su,
P.-C.; Chiang, S.-J .; Chang, L.-L.; Chi, Y.; Peng, S.-M.; Lee, G.-H.
Organometallics 1995, 14, 4844. (g) Gong, J .-H.; Hwang, D.-K.; Tsay,
C.-W.; Chi, Y.; Peng, S.-M.; Lee, G.-H. Organometallics 1994, 13, 1720.
(h) Gong, J .-H.; Chen, C. C.; Chi, Y.; Wang, S.-L.; Liao, F.-L. J . Chem.
Soc., Dalton Trans. 1993, 1829.
103.64(9)
158.6(1)
Nonbonding Contacts
C(7)‚‚‚M
C(8)‚‚‚M
3.289
3.286
3.318
3.299
as that in the Cr compounds. Nondative osmium-
tungsten bond lengths in cluster compounds are usually
in the range 2.65-3.03 Å and consequently significantly
shorter than the OsW bond in 1W.18-20 In (η-C5H5)WOs3-
(µ-H)3(µ3-CC6H4Me)(CO)12 there is, however, an OsW
bond of length 3.097(1) Å that is unsupported by other
metal-metal bonds in the cluster unit or bridged by a
(19) Chi, Y.; Shapley, J . R.; Churchill, M. R.; Li, Y. Inorg. Chem.
1986, 25, 4165.
(20) Batchelor, R. J .; Davis, H. B.; Einstein, F. W. B.; J ohnston, V.
J .; J ones, R. H.; Pomeroy, R. K.; Ramos, A. F. Organometallics 1992,
11, 3555.

5054 Organometallics, Vol. 19, No. 24, 2000
J iang et al.
Ta ble 6. Selected Bon d Len gth s (Å) a n d An gles (d eg) for [MeC(CH2O)3P ]2(OC)3OsW(CO)5‚C6H5Me (2‚C7H8),
2‚CH2Cl2, (OC)3(Me3P )2OsW(CO)5 (3), [MeC(CH2O)3P ](OC)3(Me3P )OsW(CO)5 (4), a n d
[(MeO)3P ](OC)3(Me3P )OsW(CO)5 (5)
2‚C7H8
2‚CH2Cl2
3a
4
5
Bond Lengths
3.1397(4)
Os-W
3.0831(4)
2.272(2)
2.315(2)
1.953(8)
2.009(7)-2.036(8)
1.945(7)-1.954(8)
3.0818(7)
2.276(3)
2.312(3)
1.97(1)
3.0956(5)
2.268(2)
2.419(2)
1.92(1)
2.01(1)-2.02(1)
1.92(1)-1.94(1)
3.1136(3)
2.295(1)
2.422(1)
1.960(5)
2.012(6)-2.032(7)
1.925(6)-1.938(7)
Os-P(1)
2.397(1)
Os-P(2)
W-C(1)
W-Crad (range)
Os-C (range)
1.938(8)
2.03(2)-2.05(2)
1.93(1)-1.96(1)
2.028(5)-2.029(5)
1.906(7)b-1.942(4)c
Bond Angles
W-Os-P(1)
171.73(4)
94.03(4)
93.95(6)
98.2(2)
102.3(2)
159.2(3)
173.02(8)
91.70(8)
95.10(11)
99.8(4)
99.5(4)
160.6(6)
92.85(3)
166.45(6)
100.98(6)
92.44(7)
97.9(3)
101.3(3)
160.3(4)
168.65(3)
99.83(3)
91.52(4)
101.4(2)
100.7(1)
157.2(2)
W-Os-P(2)
P(1)-Os-P(2)
P(1)-Os-C(7)
P(1)-Os-C(8)
C(7)-Os-C(8)
174.30(6)
102.3(1)
155.3(3)e
Nonbonding Contacts
3.321f
C(7)‚‚‚W
C(8)‚‚‚W
3.343
3.362
3.308
3.418
3.382
3.399
3.359
3.361
a
b
d
Molecule has a 2-fold axis. Os-C(5). c Os-C(4). C(4)-Os-C(5). e C(4)-Os-C(4′). f C(4)‚‚‚W
F igu r e 1. Molecular structure of (dmpe)(OC)3OsCr(CO)5
(1Cr ). Compound 1W, (dmpe)(OC)3OsW(CO)5, is isostruc-
tural with 1Cr .
Figu r e 2. Molecular structure of OC-6-2,3-[MeC(CH2O)3P]2-
(OC)3OsW(CO)5 (2).
geometry it has in the uncomplexed state to the geom-
etry it has in (R3P)2(OC)3OsM(CO)5.) The C(7)OsC(8)
angles in 1Cr and 1W are 158.6(1)° and 156.7(5)°,
respectively. The corresponding angles in (Me3P)(OC)4-
OsCr(CO)5 and (Me3P)(OC)4OsW(CO)5 are 167.8(4)° and
168.5(4)°, and 167.9(3)° and 169.0(3)°, respectively.2
These observations are therefore also consistent with
the view that the donor-acceptor metal-metal bond is
weaker in 1Cr and 1W than in the corresponding
(Me3P)(OC)4OsM(CO)5 compounds. As mentioned in the
Introduction, it might have been expected that the
presence of two strong donor ligands on the donor Os
atom would increase the strength of the donor-acceptor
metal-metal bond.
For reasons discussed in the spectroscopic section, two
structures of [MeC(CH2O)3P]2(OC)3OsW(CO)5 were de-
termined, one of a sample crystallized from CH2Cl2 (2‚
CH2Cl2) and the other obtained from toluene (2‚C7H8).
Each structure revealed the same isomer, but each had
a molecule of solvation in the lattice. The bond lengths
and angles in each structure of 2 are not significantly
different (Table 6). The R factor for the structure of 2‚
C7H8 (hereafter, 2) is smaller than that for 2‚CH2Cl2,
and therefore discussion is restricted to the former
structure. A view of the molecule is shown in Figure 2.
Compound 2 has the expected configuration, with one
phosphite ligand cis to the OsW bond (i.e., a radial site)
and the other trans to this bond (the axial site). We refer
to this isomer as the ax,rad isomer. The OsW bond
length 3.0831(4) Å is marginally shorter than the
corresponding distance in 1W; the C(7)-Os-C(8) angle
is 159.2(3)°.
The molecule (OC)3(Me3P)2OsW(CO)5 (3) crystallizes
with a crystallographic 2-fold axis that passes through
C(5)OsWC(1). Unexpectedly, this compound has both
phosphorus ligands in mutually trans sites that are
cis to the OsW bond (Figure 3); that is, the solid state
form of 3 is the trans diradial (dirad) isomer. Discussion
of the possible reasons for the isomer distributions in
these complexes is postponed to a subsequent section
of this paper. The OsW bond in 3 at 3.1397(4) Å (Table
6) is exceptionally long and may be compared to the
other OsW lengths reported in this study (range 3.0831-
(4)-3.1136(3) Å) and that in (Me3P)(OC)4OsW(CO)5
(3.0756(5) Å).2 The OsW distance may also be compared
to the OsW vectors, of 3.154(2) and 3.156(3) Å, in
(OC)4W[(µ-H)Os(CO)3(PMe3)]2, thought to be the longest
OsW vectors reported (it is well known that the presence
of a single bridging hydride ligand significantly length-
ens a metal-metal bond over the unbridged distance).20

(R3P)2(OC)3OsW(CO)5 and Related Complexes
Organometallics, Vol. 19, No. 24, 2000 5055
F igu r e 5. Molecular structure of [MeC(CH2O)3P](OC)3-
(Me3P)OsW(CO)5 (4). The structure of [(MeO)3P](OC)3-
(Me3P)OsW(CO)5 (5) is similar to 4.
F igu r e 3. Molecular structure of OC-6-3,2-(OC)3(Me3P)2-
OsW(CO)5 (3).
(Me3P)OsW(CO)5 (5) is similar to that of 4, that is, with
the phosphite ligand trans to the OsW bond. The
structural parameters (Table 6) of 4 and 5 are as might
be expected from those obtained for compounds 2 and
3. The OsW lengths are 3.0956(4) Å in 4 and 3.1136(3)
Å in 5. The difference in these two lengths can probably
be attributed to fewer steric interactions between the
phosphite and PMe3 ligands in 4, which in turn reduces
the steric interactions between the latter ligand and the
radial carbonyls on the tungsten atom. The W-Os-
P(PMe3) angle in 4 (100.98(5)°) is slightly larger than
that in 5 (99.83(3)°) despite the shorter OsW bond in 4.
The C(7)-Os-C(8) angles are 160.3(4)° in 4 and 157.2-
(2)° in 5.
Th e OsP Dista n ces. The OsP distances in the
structures are collected in Tables 5 and 6. The OsP
lengths of the phosphite ligands are significantly shorter
than those that involve phosphine substituents. This
shortening is typical and ascribed to increased back-
donation to the phosphite ligand.22,23
F igu r e 4. Plot of the radial C-Os-C angle versus the
Os-W bond length in complexes that contain unbridged
OsW dative bonds. 6 ) (Me3P)(OC)4OsW(CO)5; 7 ) (OC)3-
[MeC(OCH2)3P]2OsOs(CO)4W(CO)5; 8 ) (OC)4(ButNC2Os-
Os(CO)3(CNBut)W(CO)5.2,4
The OsP distances (rad-OsP) to a PMe3 or dmpe
ligand that is cis to the OsW (or OsCr) bond are
exceptionally long. In 1Cr and 1W the rad-Os-P
distances are 2.3959(7) and 2.395(3) Å, respectively; in
3 the OsP distances are crystallographically equivalent
at 2.397(1) Å; in 4 and 5 the Os-P(PMe3) distances are
2.419(2) and 2.422(1) Å, respectively. We have deter-
mined the structures of nine cluster compounds con-
taining an Os-PMe3 unit; with one exception the OsP
distances are in the range 2.318(4)-2.363(2).8,20,24,25 The
exception is Os5(CO)15(eq-PMe3) (OsP ) 2.396(4) Å), in
which the phosphine occupies a sterically crowded site
in the cluster.25 In (Me3P)(OC)4OsW(CO)5 the OsP
distance (that is trans to the OsW bond) is 2.359(2) Å.2
The OsP lengths may also be compared to 2.345(2) and
2.478(1) Å, the OsP lengths in Os3(CO)11(PEt3) and Os3-
The length of the dative OsW bond in 3 indicates that
it is exceptionally weak. Also consistent with this view
is that the C(4)OsC(4′) angle is 155.3(3)°. This is some
35° from the corresponding angle in the precursory
trigonal bipyramidal Os(CO)3(PMe3)2 compound and 25°
from that for ideal octahedral coordination about the
Os atom. Figure 4 shows a plot of the radial C-Os-C
angle versus the OsW bond length in the structures with
unbridged OsW dative bonds. As can be seen from the
figure, there is a reasonably good correlation between
the two parameters given the expected variation in bond
angles due to packing forces. It has been estimated by
Martin and Orpen that packing effects can contribute
differences of 1-2° to the valence angles at a metal and
in some cases over 3°.21 (In the two forms of 2 the radial
C-Os-C angles differ by 1.6°.)
(CO)11(PBut ), respectively.23,26 The lengthening of the
3
cis-Os-P(phosphine) distances in 1W, 3, 4, and 5 can
therefore be attributed mainly to excessive steric inter-
actions between the methyl substituents and the radial
The increase in the OsW length in 3 may be readily
interpreted in terms of the large steric interactions
between the PMe3 ligands and the radial carbonyls on
the tungsten atom that weaken the OsW bond in 3.
There may, however, be an electronic component to the
weakening of the Os-W bond (see below).
(22) (a) Plastas, H. J .; Stewart, J . M.; Grim, S. O. Inorg. Chem. 1973,
12, 265. (b) Wovkulich, M. J .; Atwood, J . L.; Canada, L.; Atwood, J . D.
Organometallics 1985, 4, 867.
(23) Biradha, K.; Hansen, V. M.; Leong, W. K.; Pomeroy, R. K.;
Zaworotko, M. J . J . Clust. Sci. 2000, 11, 285.
(24) Martin, L. R.; Einstein, F. W. B.; Pomeroy, R. K. Inorg. Chem.
1988, 27, 2986.
(25) Wang, W.; Batchelor, R. J .; Einstein, F. W. B.; Lu, C.-Y.;
Pomeroy, R. K. Organometallics 1993, 12, 3598
A view of [MeC(CH2O)3P](OC)3(Me3P)OsW(CO)5 (4)
is shown in Figure 5; the structure of [(MeO)3P](OC)3-
(26) Hansen, V. M.; Ma, A. K.; Biradha, K.; Pomeroy, R. K.;
Zaworotko, M. J . Organometallics 1998, 17, 5267.
(21) Martin, A.; Orpen, A. G. J . Am. Chem. Soc. 1996, 118, 1464.

5056 Organometallics, Vol. 19, No. 24, 2000
J iang et al.
F igu r e 6. 13C{1H} NMR spectrum (carbonyl region) of
[(MeO)3P]2(OC)3OsW(CO)5 (9) in CD2Cl2/CH2Cl2. Peaks
marked with an a and r are due to the axial and radial/
diradial isomers, respectively.
F igu r e 7. 13C{1H} NMR spectrum (carbonyl region) of
[MeC(CH2O)3P](Me3P)2(OC)3OsW(CO)5 (5) in CD2Cl2/CH2-
Cl2. Peaks marked with an x and y are due to the ax-PMe3/
rad-P(OCH2)3CMe isomer and ax-P(OCH2)3CMe/rad-PMe3
isomers, respectively.
carbonyls on the W atom, although there may also be
an electronic component to the lengthening (see below).
In the structures where both P substituents are
identical, but are cis and trans to the OsM bond
(i.e.,1Cr , 1W and 2), there is a significant difference in
the length of the Os-P bonds. The Os-P(1) (i.e., trans
to the W atom) distance in 2 is 2.272(2) Å, whereas the
corresponding Os-P(2) (i.e., trans to a carbonyl) dis-
tance is 2.315(2) Å. It may be that the difference in the
OsP lengths in 2 is not entirely due to different steric
interactions given the small size of the P(OCH2)3CMe
(as mentioned above, θ for P(OCH2)3CMe ) 101°). We
have found a similar difference in the RuSi lengths in
compounds of the type (Dnr)Ru(CO)3(SiCl3)2 (Dnr ) 18e
organometallic ligand such as Os(CO)4(PMe3)).9 The
difference was rationalized in terms of π-bonding prop-
erties of the ligands involved. The metal grouping is
considered to be a π-donor ligand and is therefore
expected to increase the π back-bonding to the ligand
trans to it and thereby shorten the metal-ligand bond.
On the other hand, a carbonyl ligand will reduce the
back-bonding to the ligand trans to it and hence
lengthen the appropriate metal-ligand bond. Obviously,
the same arguments could account for part of the
difference in the OsP distances in 2. Likewise, the
different trans influences of the CO and W(CO)5 units
could contribute to the differences of the OsP lengths
in 1Cr and 1W.
Ch a r t 1
(OC)3OsW(CO)5. The fac isomer of Os(CO)3(PR3)2-
[W(CO)5] is designated according to IUPAC convention
as the OC-6-3,3 form; the mer,cis (ax,rad) isomer as OC-
6-2,3; and the mer,trans (dirad) form as OC-6-3,2.27
Here the isomers will be designated 3,3, 2,3, and 3,2,
respectively, as shown in Chart 1. The isomers may
readily be distinguished by NMR spectroscopy (Tables
1 and 2). Isomer 3,3 (i.e., the facial isomer) with the two
noncarbonyl ligands in radial sites that are mutually
cis was not observed, presumably due to the excessive
steric interactions present in this form. This isomer,
however, is the thermodynamically preferred form for
(OC)3(ButNC)2OsW(CO)5 complexes.3
For the mixed derivatives (e.g., 4 and 5) there are two
possible ax,rad isomers depending on which P ligand is
trans to the OsW bond. For complex 4, NMR evidence
indicates that both isomers with an axial P ligand are
present in solution (Tables 1 and 2; Figure 7). A detailed
analysis of the NMR spectra of 4 leads to the conclusion
that the most prevalent form in solution has the PMe3
ligand trans to the W(CO)5 grouping (i.e., (ax-Me3P)-
(OC)3[rad-MeC(CH2O)3P]Os[W(CO)5]). The preferred
isomer in solution is therefore not the form found in the
solid state. For compound 5, the only isomer that was
observed in solution was the solid state form, namely,
that with the phosphite ligand trans to the tungsten
NMR Stu d ies. The NMR spectra for 1Cr and 1W are
consistent with the solid state structure as the only
1
structure in solution (Tables 1 and 2). The H, 13C{1H},
and 31P{1H} NMR spectra of many of the other new
compounds indicate the presence of two, and only two,
isomers in solution. The solution 13C{1H} NMR spec-
trum in the carbonyl region of [(MeO)3P]2(OC)3OsW-
(CO)5 (9) in CH2Cl2/CD2Cl2 is shown in Figure 6. This
spectrum was chosen for display because the PC cou-
plings in the phosphite derivatives are larger than the
couplings in the phosphine complexes, as is typical, and
the isomer distribution in 9 is such as to make the
assignment of the resonances simple.
(27) (a) Block, B. P.; Powell, W. H.; Fernelius, W. C. Inorganic
Nomenclature: Principles and Practice; American Chemical Society:
Washington, DC, 1990. (b) Huheey, J . E.; Keiter, E. A.; Keiter, R. L.
Inorganic Chemistry, 4th ed.; HarperCollins: New York, 1993; p A-71.
If the PR3 ligands remain attached to the Os atoms,
there are three possible geometric isomers for (R3P)2-

(R3P)2(OC)3OsW(CO)5 and Related Complexes
Organometallics, Vol. 19, No. 24, 2000 5057
Ch a r t 2
atom than a PMe3 bound at the axial site. This would
result in changes to the OsP bonding (e.g., the amount
of s character in the bond) so that perhaps three-bond
PC coupling is observed to the methyl groups of the
more strongly bound axial PMe3, but not to the radial
PMe3 ligand in 2,3-3.
The 31P{1H} NMR spectrum consists of a singlet at δ
-64.2 assigned to 3,2-3 and two doublets at δ -57.8 and
-62.9 assigned to 2,3-3. The resonance at δ -62.9 is
attributed to the P atom cis to the tungsten atom on
the basis that it should have a chemical shift that is
similar to that of 3,2-3 and to the resonance of the
minor, radial isomer of (Me3P)(OC)4OsW(CO)5; the
latter signal occurs at δ -62.3, whereas the resonance
of the other (major) isomer of this compound appears
at δ -53.2.2
In the 13C{1H} NMR spectrum of 13CO-enriched 3 (CO
region), the resonances to low field of 200 ppm are
readily assigned to CO ligands attached to tungsten by
analogy with the spectra of similar derivatives and
because the peaks exhibit coupling to 183W (Figure 8B;
cf. Figure 6).2,3,30,31 The W-CO signals to higher field
at δ 206.3 and 205.4 in a 4:1 ratio are assigned to the
carbonyls of the W(CO)5 moiety of 2,3-3; the more
intense signal is a triplet, but the weaker signal is a
singlet. That the chemical shift of the signal due to the
axial carbonyl is to high field of the resonance due to
the radial carbonyls is unusual. In all other complexes
reported here, and of the type (L)x(OC)5-xOsM(CO)5 (M
) Cr, Mo, W; L ) PR3, x ) 1; L ) CNBut, x ) 1, 2) and
W(CO)5(PR3), this resonance appears to low field of that
due to the radial carbonyls.2-4,30,31 The observation of
an apparent three-bond, cis, cis coupling (∼2.7 Hz) from
P to C is also unprecedented in our studies on these and
similar complexes (Figure 8B). Two-bond, PC cis cou-
plings are normally small (e.g., Table 2), and three-bond,
cis, cis couplings might therefore be expected to be so
small as to be unobservable. It is proposed that this
coupling is through-space coupling where the π-acceptor
orbitals on the PMe3 and adjacent carbonyls are linked
via the filled d orbitals on the metal atoms, as shown
in Chart 2.
F igu r e 8. 13C{1H} NMR spectrum of 3 (CD2Cl2/CH2Cl2
solution) in the methyl region (A) and the W-CO region
(B).
atom. In both cases, only very weak peaks were present
in the various NMR spectra, which might indicate the
presence of a dirad isomer. The only form of [(o-
MeC6H4O)3P](OC)3(Me3P)OsW(CO)5 detected in solution
was also the ax-phosphite/rad-phosphine isomer.
The NMR spectra of these complexes show additional
interesting features that will be illustrated here with a
detailed discussion of the spectra of 3. The 1H NMR
spectrum exhibits a triplet typical of a virtually coupled
system of a trans-(Me3P)M(PMe3) grouping.28,29 This
resonance is therefore assigned to 3,2-3, the structure
found in the solid state. The remaining resonances in
the spectrum consist of two doublets and are assigned
to the 2,3 isomer with one PMe3 grouping trans to the
OsW bond. Interestingly, the methyl region of the 13C-
{1H} NMR spectrum of 3 exhibits a similar pattern
except that the high-field doublet shows a further small
(3J PC ) 3.8 Hz) three-bond phosphorus coupling (Figure
8A). The resonance that shows the extra coupling is
probably due to the PMe3 ligand that is trans to the
OsW bond. The chemical shift of this signal (δ 23.0) is
identical to that of the major (axial) isomer of (Me3P)-
(OC)4OsW(CO)5 (δ 23.0).2 On the other hand, the chemi-
cal shift of the other doublet is to low field of δ 23.0,
the region where the resonances of the corresponding
methyl groups of 3,3-3 and 2,2-4 occur (Table 2). The
structures described above indicate that a PMe3 group
cis to the OsW bond is more weakly bound to the Os
The other two resonances in the W-CO region, due
to the axial and radial carbonyls of 2,3-3, occur at δ
207.4 and 206.6, respectively, and are doublets. The
small coupling (3.0 Hz) to the signal due to the axial
carbonyl is assigned to a conventional three-bond, trans,
trans coupling to the P atom in the radial site on the
Os atom. We have occasionally observed similar cou-
plings in (R3P)(OC)4OsM(CO)5 compounds; it is also seen
in the spectrum of 1Cr , 1W, and 9 (Table 2; Figure 6).
(28) (a) J enkins, J . M.; Shaw, B. L. J . Chem. Soc., A 1966, 770. (b)
Verkade, J . G. Coord. Chem. Rev. 1972, 9, 1. (c) Harris, R. K. Can. J .
Chem. 1964, 42, 2275.
(30) Mann, B. E.; Taylor, B. F. 13C NMR Data for Organometallic
Compounds; Academic: New York, 1981; p 159.
(31) Buchner, W.; Schenk, W. Inorg. Chem. 1984, 24, 132. See also:
Bodner, G. M.; May, M. P.; McKinney, L. E. Inorg. Chem. 1980, 19,
1951.
(29) Pregosin, P. S.; Kunz, R. W. In 31P and 13C NMR of Transition
Metal Phosphine Complexes; NMR 16; Diehl, P., Fluck, E., Kosfeld,
R., Eds.; Springer-Verlag: New York, 1979.

5058 Organometallics, Vol. 19, No. 24, 2000
J iang et al.
The coupling (∼2.3 Hz) to the signal due to the radial
carbonyls of 2,2-3 is also attributed to through-space PC
coupling. If this interpretation is correct, then these
through-space couplings in 3 would also be consistent
with severe steric interactions between the radial PMe3
groups and the radial carbonyls on tungsten. Similar
through-space PC coupling has been recently reported
for W(CO)5(η1-PPh2CH2PPh2).32
Buchner and Schenk have measured the W couplings
to the 13C NMR resonances of the carbonyls in 23
complexes of the type W(CO)5(L).31 The coupling to the
resonance due to the radial carbonyls varied over the
narrow range 124.0-131.6 Hz, whereas the couplings
to the resonance due to the carbonyl trans to L
ranged from 149 Hz for [W(CO)5(H)]- to 175.8 Hz for
[W(CO)5(I)]-. In 3 the coupling to the signals attributed
to the radial carbonyls of each isomer are ∼125 Hz. The
trans WC coupling in 2,2-3 is 178 Hz, and in 3,3-3 it is
167 Hz. The trans coupling is 179.1 Hz in (Me3P)(OC)4-
OsW(CO)5. That these trans WC couplings are, with the
exception of that in 3,2-3, outside the previous known
range illustrates the unusual character of these 18e
ligands.
The resonances between δ 175 and 200 are attributed
to carbonyls bound to the osmium atom (e.g., Figure 6).
The triplet (of intensity 1) to highest field (at δ 179.1)
is assigned to the carbonyl trans to the dative OsW bond
of 3,2-3. It has been observed previously that the
resonances of carbonyl ligands trans to dative metal-
metal bonds occur at unusually high fields.2,3,9 The
triplet of intensity 2 at δ 198.7 is attributed to the
equatorial Os-CO ligands of 3,2-3. The doublet of
doublets centered at δ 187.7 is readily assigned to the
Os-CO of 2,3-3 that is both cis and trans to a PMe3
ligand on the basis of the large (70.2 Hz) and small (4.6
Hz) couplings to the signal and its intensity of 1.
The remaining peak at δ 196.7 of intensity 2 is
therefore assigned to the two radial carbonyls on the
Os atom of 2,3-3 that are chemically equivalent. The
resonance of these carbonyls in all the complexes
studied here (Table 2; Figures 6 and 7) is a doublet
rather than the expected doublet of doublets due to
coupling to two chemically different P atoms. In other
words, one of the two-bond PC couplings is unobservable
even though both phosphorus atoms are nominally in
cis positions in the axial, radial isomer. But as is found
in the crystal structures of these complexes, the carbo-
nyls in question lean toward the W atom and the P(1)-
Os-C(radial) angle opens to between 97.9(3)° and
104.7(3)° (Tables 5 and 6) and evidently causes the
coupling to drop to zero. This type of angular depen-
dence of two bond PC coupling has been observed
previously.26,33-35 For example, in clusters of formula
Os3(CO)11(PR3) (the PR3 ligand is in an equatorial site
of the triangular Os3 skeleton) the (cis) PC coupling to
the axial carbonyls of the Os(CO)3(PR3) unit is in the
range 5.9-13.7 Hz. On the other hand, the coupling to
the equatorial carbonyl is not detectable.26,34,35 The
P-Os-CO(eq) angle in these clusters is normally in the
range 95-102°. This is because the opposing OsOsOs
angle is close to 60°, required by the triangular geometry
of the metal nucleus.23,26,36
Of the three mechanisms by which nuclear spin
coupling occurs, the mechanism that involves Fermi
contact interaction between nuclear moments and elec-
tron spins in s orbitals is believed to be the most
important.29,37 The theoretical estimation of the size of
the Fermi contact term involves mixing in contributions
from excited electronic triplet states with the ground
2
singlet state. For J PP couplings, it is assumed that an
excitation from an orbital to another of the same
symmetry makes a negative contribution to the cou-
pling, whereas a transition involving orbitals of opposite
symmetry produces a positive contribution. In this way,
2
it has been possible to rationalize why cis J PP couplings
in metal complexes are usually negative whereas the
corresponding trans couplings are usually positive.29,37
As originally suggested by Carty and co-workers, it is
2
therefore probable that the cis J PC parameters in
organometallic molecules are also negative whereas the
trans couplings are positive.33 (Note there is a phase
change of the lobe of the π MO of the metal atom that
links the C and P atoms when the configuration is
changed from cis to trans.) If this is the case, there must
be an angle between 90° and 180° where the negative
and positive contributions to the coupling exactly cancel.
2
If this is assumed and that the coupling constant J PC
follows a simple linear relationship with the P-Os-C
angle, then by using the values of the cis and trans
coupling constants in these complexes, a value of ∼103°
for the P-Os-C angles is obtained where the coupling
constant should be zero. These values are in agreement
with the angles found in the X-ray structures for these
compounds (Tables 5 and 6). The results indicate that
the distorted octahedral geometry observed for the Os
atom in the solid state structures of the (R3P)2(OC)3-
OsM(CO)5 complexes is also maintained in solution.
2
Of related interest is that the (cis) J PP coupling
constants in 1Cr and 1W are also unobservable, whereas
in the derivatives with nonchelate P ligands this
coupling is in the range 17.5-34.3 Hz. Because of the
small bite angle of the dmpe ligand, the P-Os-P angles
in 1Cr and 1W are ∼83°, whereas in the compounds
with monodentate P ligands in axial and radial sites
this angle ranges from 91.52(4)° to 95.1(1)°.
Ca r bon yl Exch a n ge in th e (R3P )2(OC)3OsW(CO)5
Com p lexes. The 13CO-enriched samples used to obtain
the 13C NMR spectra were prepared by the addition of
the appropriate unenriched Os(CO)3(PR3)2 compound to
13CO-enriched W(CO)5(THF). It is apparent from Fig-
ures 6 and 7 that the C-13 label is equally distributed
over all carbonyl sites, which indicates that CO ex-
change occurs in 9 and 5 on the synthetic time scale.
This behavior was observed for all complexes studied
by 13C NMR spectroscopy (Table 2). Isomerization and
(32) Benson, J . W.; Keiter, R. L.; Keiter, E. A.; Rheingold, A. L.;
Yap, G. P. A.; Mainz, V. V. Organometallics 1998, 17, 4275.
(33) Randall, L. H.; Cherkas, A. A.; Carty, A. J . Organometallics
1989, 8, 568.
(34) (a) J ohnson, B. F. G.; Lewis, J .; Reichert, B. E.; Schorpp, K. T.
J . Chem. Soc., Dalton Trans. 1976, 1403. (b) Alex, R. F.; Pomeroy, R.
K. Organometallics 1987, 6, 2437.
(36) For example: (a) Benfield, R. E.; J ohnson, B. F. G.; Raithy, P.
R.; Sheldrick, G. Acta Crystallogr. Crystallogr., Sect. B. Srtuct. Crys-
tallogr. Cryst. Chem. 1978, B34, 666. (b) Bruce, M. I.; Liddell, M. J .;
Hughes, C. A.; Skelton, B. W.; White, A. H. J . Organomet. Chem. 1988,
347, 157.
(37) (a) Ramsey, N. F. Phys. Rev. 1953, 91, 303. (b) Pople, J . A.;
Santry, D. P. Mol. Phys. 1964, 8, 1. (c) Pople, J . A.; Santry, D. P. Mol.
Phys. 1965, 9, 311.
(35) (a) Ma, A. K.; Hansen, V. M.; Pomeroy, R. K. To be published.
(b) Ma, A. K. Ph.D. Thesis, Simon Fraser University, 1992.

(R3P)2(OC)3OsW(CO)5 and Related Complexes
Organometallics, Vol. 19, No. 24, 2000 5059
Sch em e 1
carbonyl scrambling are common properties of com-
plexes with dative metal-metal bonds.2,3 In (η5-C5R5)-
(OC)2IrW(CO)5 (R ) H, Me) carbonyl exchange is so
rapid at, or just below, room temperature that it can be
detected by NMR line-broadening techniques.38
stand at -10 °C for ∼3.5 h and then at 0 °C for a further
2 h. During this period 31P{1H} NMR spectra were
recorded periodically of the reaction solution, which
showed isomerization to the equilibrium mixture. From
the NMR spectra in the initial stages of the reaction a
rate of approximately 4 × 10-5 s-1 was estimated for
For CO exchange to occur between the two metals,
bridging carbonyls must of course be involved. The well-
known merry-go-round CO-exchange mechanism along
with free rotation about the Os-W bond in 3,2-
(R3P)2(OC)3OsW(CO)5 exchanges all carbonyls as shown
in Scheme 1. The polar nature of the dative metal-
metal bond probably facilitates the formation of the
bridged intermediate as originally proposed by Cotton
for (η-C5H5)(OC)2V(µ-CO)2V(CO)(η-C5H5).39 Of interest
is that the preparation of 1Cr and 1W from Os(CO)3-
(dmpe) and 13CO-enriched M(CO)5(THF) also yielded
products with the C-13 label equally scrambled over all
carbonyl sites. For the above mechanism to exchange
the carbonyls that are cis to both P ligands requires the
intermediacy of the 3,3-isomer (i.e., the cis-diradial form;
Chart 1) in the exchange. Exchange of these carbonyls
with the unique Os-CO can, however, be brought about
by a localized twist mechanism at the osmium atom,
which is proposed below to account for the isomerization
in these compounds.
the isomerization at -10 °C (∆Gq ) ∼21 kcal mol-1).
263
A similar experiment was carried out with compound 2
except that a temperature of 0 °C was maintained
throughout the experiment. In this case, the initial
spectrum exhibited only the two doublets of 2,3-2 (along
with the singlet due to the added PPh3); the equilibra-
tion was judged to be complete after approximately 1
h, that is, somewhat faster than the equilibration of 3
(allowing for the difference in temperature of the two
experiments). As expected from the reactions of 2 and
3 with PPh3 described below, there was no signal due
to W(CO)5(PPh3) observed during the isomerizations.
This indicates that the isomerization does not occur by
complete dissociation into W(CO)5 and Os(CO)3(PR3)2
fragments.
Variable-temperature 1H NMR spectra of 2 in o-
xylene-d10 showed the onset of coalescence of the signals
due to the two isomers above 100 °C. The coalescence
of the CH2 resonances due to 2,3-2 was judged to occur
at just above 125 °C (the highest temperature investi-
gated), from which a ∆Gq of ∼22 kcal mol-1 at 127 °C
for the isomerization was estimated. The 1H NMR
spectrum above 100 °C indicated extensive decomposi-
tion of 2 to Os(CO)3[P(OCH2)3CMe]2, as expected from
the experiments described below.
For (OC)5MnRe(13CO)5 carbonyl exchange occurs at
a detectable rate (4.7 × 10-5 s) at 65 °C (∆Gq ) 26.5
338
kcal mol-1).40 This is considerably slower than in the
(R3P)2(OC)3OsM(CO)5 complexes, but this may be due
to the presence of the P ligands in the latter derivatives.
It is known that CO exchange is considerably more facile
in Os3(CO)11(PR3) clusters than in the parent carbonyl
Os3(CO)12.34,35
The merry-go-round carbonyl exchange can also ac-
count for the isomerization in (R3P)(OC)4OsM(CO)5
complexes, but it cannot bring about conversion of the
two isomers observed for (R3P)2(OC)3OsW(CO)5 com-
plexes. This is because the movement of one of the P
ligands in the diradial isomer to the axial site requires
the second PR3 to bridge the two metals (Scheme 2).
Ligands of the type PR3 very rarely bridge two metal
atoms, and there is no evidence for any W-PR3 species
in these reactions.
Isom er iza t ion in (R 3P )2(OC)3OsW(CO)5 Com -
p lexes. As previously discussed, the NMR results are
consistent with the presence of two isomers in solution
for most of the (R3P)2(OC)3OsM(CO)5 complexes studied,
whereas the X-ray studies show there is only one form
in the solid state. This suggested that the isomers are
in dynamic equilibrium in solution at ambient temper-
atures. Experiments were therefore carried out to
determine an approximate rate for the isomerization.
A solution of 3 in CD2Cl2 with added PPh3 was
prepared at -40 °C and a 31P{1H} NMR spectrum
recorded at -40 °C as soon as possible after the
preparation of the sample. The spectrum of 3 showed
only the singlet due to the 3,2-form, that is, the form
found in the solid state. The sample was allowed to
A mechanism that brings about isomerization of the
2,3 and 3,2 isomers is a 3-fold twist mechanism at the
Os atom, as shown in Scheme 3. Such a mechanism has
been implicated in the isomerization of a number of
metal carbonyl derivatives.41 We have also recently
described the nondissociative rearrangement mer,cis-
(41) (a) Bond, A. M.; Colton, R.; McDonald, M. E. Inorg. Chem. 1978,
17, 2842. (b) Alex, R. F.; Pomeroy, R. K. J . Organomet. Chem. 1985,
284, 379. (c) Ismail, A. A.; Sauriol, F.; Sedman, J .; Butler, I. S.
Organometallics 1985, 4, 1914. (d) Hansen, L. M.; Marynick, D. S.
Inorg. Chem. 1990, 29, 2482. (e) Howell, J . A. S.; Yates, P. C.; Ashford,
N. F.; Dixon, D. T.; Warren, R. J . Chem. Soc., Dalton Trans. 1996,
3959, and references therein.
(38) (a) Einstein, F. W. B.; Pomeroy, R. K.; Rushman, P.; Willis, A.
C. Organometallics 1985, 4, 250. (b) J iang, F.; Biradha, K.; Leong, W.
K.; Pomeroy, R. K.; Zaworotko M. J . Can. J . Chem. 1999, 77, 1327.
(39) Cotton, F. A. Prog. Inorg. Chem. 1976, 21, 1.
(40) Schmidt, S. P.; Basolo, F.; J enson, C. M.; Trogler, W. C. J . Am.
Chem. Soc. 1986, 108, 1894.

5060 Organometallics, Vol. 19, No. 24, 2000
J iang et al.
Sch em e 2
(Me3P)(OC)4OsW(CO)5 in CH2Cl2 is 3.3.2 For a ratio-
nalization of the isomer distribution in 3 and other
(R3P)2(OC)3OsW(CO)5 complexes account must be taken
of all the various steric and electronic interactions in
each isomer. Only the W(CO)5/PR3 (S(WP)) and the PR3/
PR3 (S(PP)) steric interactions are, however, considered
important. A particular bonding interaction will depend
on the ligand trans to the bond.46 The electronic prefer-
ences in each isomer can therefore be expressed in three
terms of the type T(X,Y) where X and Y are the atoms
trans to each other. The important energy terms (E) of
each form are therefore
Sch em e 3
Os(CO)3(PMe3)(Cl)2 to the fac form.42 The geometry of
the Os atom in these complexes approximates an edge-
bridged trigonal bipyramid. The mechanism of isomer-
ization might therefore be better described as interme-
diate between a trigonal twist mechanism typical of an
octahedral molecule and the turnstile rotation mecha-
nism postulated to take place in some trigonal bipyra-
midal complexes.43
E(2,3) ) S(WP) + S(PP) -
[T(WP) + T(PC) + T(CC)]
E(3,2) ) 2S(WP) - [T(WC) + T(PP) + T(CC)]
E(3,3) ) 2S(WP) + S(PP) - [T(WC) + 2T(PC)]
Conversion of one M′2(CO)10-n(PR3)n (M′ ) Mn, Re; n
) 1-3) isomer to a second form has been occasionally
observed. The diax and ax,rad forms of Re2(CO)8(PMe2-
Ph)2 are in equilibrium in solution at 80 °C.44 Nubel and
Brown found that 1,2-rad,rad-Re2(CO)8(L)2 (L ) PMe3,
P(OMe)3, or P(OPh)3) were stable in solution at 25 °C
for at least a day, whereas 1,2-ax,rad-Re2(CO)8(L)2 (L
) PBun3, PPh3) isomerized to the diaxial isomer under
the same conditions.45 These observations indicate that
the barriers to isomerism in the group 7 derivatives are
also much higher than for the (R3P)2(OC)3OsW(CO)5
complexes.
The 3,3 compound is the least preferred from steric
considerations and is not observed for the (R3P)2(OC)3-
OsW(CO)5 complexes. The 3,3 form is however the
predominant form in solution for (OC)3(ButNC)2OsW-
(CO)5, and the 2,3 isomer is not observed.3
The difference in these terms for the 3,2 (dirad) and
2,3 (ax,rad) configurations is
[S(WP) - S(PP)] - [T(WC) +
T(PP) - T(WP) - T(PC)]
Isom er Ra tios for (R3P )2(OC)3OsW(CO)5 Com -
p lexes. The approximate 2,3/3,2 isomer ratios for the
(R3P)2(OC)3OsW(CO)5 complexes in CD2Cl2 as deter-
mined by 31P{1H} NMR spectroscopy are given in Table
1. The effect of solvent on the isomer distribution was
not investigated in detail. It was, however, observed that
the 2,3/3,2 ratio for 2 in CD2Cl2 was 1.7, whereas in the
less polar toluene-d8 the ratio had decreased to 0.2 (i.e.,
more of 3,2-2 is present in toluene). For this reason, the
crystal structure of 2 that had been recrystallized from
toluene was determined. The only crystals that were
suitable for X-ray crystallography revealed they were
also the 2,3 isomer.
The preference for the 3,3 form of 3 may be because
S(WP) is smaller than S(PP). A steric argument cannot
however be used to rationalize why 4 has the sterically
undemanding P(OCH2)3CMe in the axial site (Figure 5).
The electronic terms would be dominant in molecules
where steric interactions are small (as in (OC)3(But-
NC)2OsW(CO)5) or where S(WP) is approximately equal
to S(PP).
In terms of both σ- and π-bonding considerations,
T(PC) (i.e., a P donor ligand trans to a carbonyl) is
expected to be more preferred (more negative) than
T(PP). This leads to the conclusion that, in the absence
of steric effects, in order for the 3,2 isomer to be
preferred, T(WC) must be greater (in a negative sense)
than T(WP). It might have been expected from σ-bond-
ing arguments that there would be a preference for the
strong σ-donor P-ligand to be trans to the dative OsW
bond, but this appears not to be the case in these
compounds. That T(WC) is apparently more negative
than T(WP) can, however, be rationalized with π bond-
ing arguments. There is expected to be repulsive dπ-
Of the complexes studied, only for 3 is the 3,2 (i.e.,
dirad) isomer more prevalent in CD2Cl2 solution, and
3 was the only derivative found by X-ray crystallography
to be the 3,2 form in the solid state. The stability of this
form was unexpected given that axial/radial ratio for
(42) Male, J . L.; Einstein, F. W. B.; Leong, W. K.; Pomeroy, R. K.;
Tyler, D. R. J . Organomet. Chem. 1997, 549, 105.
(43) Ugi, I.; Marquarding, D.; Klusacek, H.; Gillespie, P. Acc. Chem.
Res. 1971, 4, 288.
(44) Harris, G. W.; Boeyens, J . C. A.; Coville, N. J . J . Chem. Soc.,
Dalton Trans. 1985, 2277.
(45) Nubel, P. O.; Brown, T. L. J . Am. Chem. Soc. 1984, 106, 644.
(46) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335.

(R3P)2(OC)3OsW(CO)5 and Related Complexes
Organometallics, Vol. 19, No. 24, 2000 5061
(R3P)2(OC)3OsW(CO)5 + PPh3 25 °C8
Ch a r t 3
Os(CO)3(PR3)2 + W(CO)5(PPh3) (6)
For 2, this peak (at 1930 cm-1) would have been
obscured by those of 2 and W(CO)5(PPh3), but strong
absorptions at 1919 and 1891 cm-1 suggested the
formation of Os(CO)3(PPh3)[P(OCH2)3CMe] in this reac-
tion. In the reaction of 3 there were also medium-weak
bands at 2034 and 2017 cm-1 attributed to Os(CO)2-
(PMe3)2(Cl)2 and Os(CO)2(CO3)(PMe3)2, respectively, due
to reaction of Os(CO)3(PMe3)2 with CH2Cl2 and with
oxygen, respectively, that has been mentioned above.12
The cleavage of 5 by PPh3 was a relatively clean
reaction, the IR spectra of which showed reasonable
isosbestic points after 68 h (Supporting Information).
For the reaction that involved 2, the solution after
44 h had IR bands due to the starting material that were
equally as strong as those of W(CO)5(PPh3); for 3 there
were no CO stretches due to the starting material,
whereas for the experiment with 5 there were only very
weak IR peaks arising from the binuclear precursor.
These observations are consistent with the view that
the OsW bond strengths decrease in the order 2 > 5 >
3, and this is the order one might have predicted on the
basis of steric arguments and the OsW bond lengths in
these complexes.
The (Me3P)(OC)4OsW(CO)5 complex also undergoes
cleavage with PPh3 in solution to give W(CO)5(PPh3).
(The reaction is complete in 30 min if the reaction is
irradiated with blue light.)17 The thermal reaction is,
however, much slower than that of 3, with IR bands due
to the starting complex still visible after 9 days.17 It
should be pointed out, however, that the latter experi-
ment was carried out in benzene rather than dichlo-
romethane and in the dark with rigorous exclusion of
oxygen. We have some evidence that complexes with
dative osmium-metal bonds are somewhat less stable
in the presence of trace oxygen, but this has not been
thoroughly investigated.
dπ interactions across the OsW bond that would be
minimized by having strong π acceptor ligands in both
sites trans to the bond (as shown in Chart 3).2,3,9 This
should also increase the back-bonding to the two ligands
trans to the OsW bond. Consistent with this view is that
the OsC distance trans to the OsW bond in 3 is
considerably shorter than the other Os-CO distances
(1.906(7) vs 1.942(4)(1) Å). Furthermore, in all the
structures the WC bond to the carbonyl trans to osmium
is significantly shorter than the other WC bonds (Tables
5 and 6).
That 3,2-(OC)3(Me3P)2OsW(CO)5 is slightly thermo-
dynamically preferred over the 2,3 form could in part
be attributed to an electronic preference to have a
carbonyl ligand (i.e., a strong π-acceptor ligand) trans
to the dative OsW bond. Likewise, this argument can
explain why the better π-acceptor phosphite ligands
have some preference for the axial site over PMe3.
Trimethylphosphine is a strong donor ligand, and in
3 these ligands would be expected to expand the Os 5d
orbitals and thereby increase the OsW dπ-dπ repulsive
interactions. Because of the increased dπ-dπ interac-
tions, Os(CO)3(PMe3)2 (or Os(CO)3[Me2P(CH2)2PMe2])
might be a weaker donor ligand than Os(CO)4(PMe3)
even if steric effects were neglected.
The arguments presented here might be useful in the
rationalization of the unusual isomer distribution in
compounds of formula M′2(CO)10-n(L)n (L ) PR3, n )
1-3: L ) CNR, n ) 1-4).44,45,47,48 In many of these
complexes, however, it has not been established that
the isomer observed is the thermodynamically pre-
ferred form. Furthermore, the M′M′ bond lengths in
M′2(CO)10-n(L)n (n ) 0, 1, 2) complexes are insensitive
to the nature of L.44,48
Rea ction of 2, 3, a n d 5 w ith P P h 3. Solutions of 2,
3, and 5 in CH2Cl2 each with an excess of PPh3 were
stirred at room temperature; the solutions were moni-
tored periodically by IR spectroscopy over 44 h. After
this period, in all cases there were intense bands due
to W(CO)5(PPh3) (at 2072 (m), 1975 (m), 1938 (s)
cm-1).2,17,49 For the reactions that involved 3 and 5 the
strong peak due to the mononuclear Os complex (i.e.,
Os(CO)3(PR3)(PR′3)) was also clearly visible, consistent
with the simple displacement of the Os ligand by PPh3
(eq 6).
Con clu sion s
Complexes of formula (R3P)2(OC)3OsM(CO)5 (M ) Cr,
W) appear less stable than the (R3P)(OC)4OsM(CO)5
analogues, especially for the Cr derivatives, where only
the Os(CO)3[P(OCH2)3CMe]2 and Os(CO)3(dmpe) de-
rivatives could be prepared. On the basis of the bonding
properties of the PR3 and CO ligands, Os(CO)3(PR3)2
might have been expected to be a better donor ligand
than Os(CO)4(PR3). There are, however, other subtle
electronic factors that may work to nullify the increased
basicity of the bis-substituted molecule. The presence
of the second PMe3 would increase the electron density
on the Os atom, which would result in expansion of the
valence orbitals of osmium. This in turn would increase
the dπ-dπ repulsive interactions between the metal
atoms and weaken the metal-metal bond (Chart 3).
Reorganizational energy is needed to go from the
uncomplexed five-coordinate state to the complexed six-
coordinate geometry of the donor moiety, and this might
be greater for Os(CO)3(PR3)2 than for the monosubsti-
tuted compound.9,15 There is also the requirement in the
(R3P)2(OC)3OsM(CO)5 complexes that one bulky PR3
ligand be cis to the OsM bond, and this will increase
(47) (a) Reimann, R. H.; Singleton, E. J . Chem. Soc., Dalton Trans.
1976, 2109. (b) Laing, M.; Singleton, E.; Reimann, R. J . Organomet.
Chem. 1973, 56, C21. (c) Churchill, M. R.; Amoh, K. N.; Wasserman,
H. J . Inorg. Chem. 1981, 20, 1609. (d) Laing, M.; Ashworth, T.;
Sommerville, P.; Singleton, E.; Reimann, R. J . Chem. Soc., Chem.
Commun. 1972, 1251. (e) Masuda, H.; Taga, T.; Sowa, T.; Kawamura,
T.; Yonezawa, T. Inorg. Chim. Acta 1985, 101, 45. (f) Giordano, R.;
Sappa, E.; Tiripicchio, A.; Tiripicchio Camellini, M.; Mays, M. J .;
Brown, M. P. Polyhedron 1989, 8, 1855. (g) Moelwyn-Hughes, J . T.;
Garner, A. W. B.; Gordon, N. J . Organomet. Chem. 1971, 26, 373. (h)
Cox, D. J .; Davis, R. J . Organomet. Chem. 1980, 186, 347.
(48) (a) Harris, G. W.; Coville, N. J . Organometallics 1985, 4, 908.
(b) Harris, G. W.; Boeyens, J . C. A.; Coville, N. J . Organometallics 1985,
4, 914.
(49) Magee, T. A.; Matthews, C. N.; Wang, T. S.; Wotiz, J . H. J . Am.
Chem. Soc. 1961, 83, 3200.

5062 Organometallics, Vol. 19, No. 24, 2000
J iang et al.
the steric interactions in the (R3P)2(OC)3OsM(CO)5
complexes compared to those in the (R3P)(OC)4OsM-
(CO)5 compounds. Increased steric repulsions may be
the major cause of decreased stability of the bis-
substituted products, but such interactions cannot
explain the isomer distribution in (R3P)2(OC)3OsM(CO)5
compounds.
the dπ-dπ repulsions between the metal atoms. This
also explains why for the (phosphite)(OC)3(Me3P)OsW-
(CO)5 complexes there is a preference for the phosphite
ligand to occupy the least sterically hindered site (i.e.,
trans to the OsW bond) even when the phosphite has a
smaller cone angle than the trimethylphosphine ligand.
In solution the (R3P)2(OC)3OsW(CO)5 derivatives
undergo intramolecular CO exchange and isomerism on
the synthetic time scale. Such behavior is also observed
for the (R3P)(OC)4OsW(CO)5 analogues.2 Carbonyl ex-
change in binuclear metal carbonyl compounds is com-
mon, but it is of interest that such exchange in MnRe-
(CO)10 only occurs at a measurable rate at 65 °C.40
The isomer distribution found for the (R3P)2(OC)3-
OsM(CO)5 complexes in solution was unexpected. For
example, in CH2Cl2 solution the dirad isomer of
(Me3P)2(OC)3OsW(CO)5 was slightly more favored over
the ax,rad form; the dirad form is also the structure
adopted in the solid state. It is proposed that if the steric
repulsions in the various isomers are roughly compa-
rable, then the best π-acceptor ligand will adopt the site
trans to the dative metal-metal bond since it reduces
Ack n ow led gm en t. We thank the Natural Sciences
and Engineering Research Council of Canada and St.
Mary’s University for financial support. We also thank
Dr. J acek Styszynski (Uniwersytet Szczecinski) for
useful discussions.
Su p p or tin g In for m a tion Ava ila ble: Figures showing
structures of 1W and 5 and IR spectra of the reaction of 5 with
PPh3; tables of crystal structure and refinement data, atomic
coordinates, thermal parameters, bond lengths and angles for
compounds 1Cr , 1W, 2, 3, 4, 5, synthetic and IR data for Os-
(CO)3(PR3)(PR′3) complexes, and analytical and IR data for
(R3P)2(OC)3OsM(CO)5 (M ) Cr, W) complexes. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM990790P