PMe3-induced CO insertion and CO deinsertion in the zwitterionic hydrocarbyl complex Co2(CO)4[μ-PhC{double bond, long}C(H)PPh2C{double bond, long}C(PPh2)C(O)OC(O)]: Syntheses and X-ray structures of C

Article abstract of DOI:10.1016/j.poly.2007.04.004

Full title: PMe₃-induced CO insertion and CO deinsertion in the zwitterionic hydrocarbyl complex Co₂(CO)₄[μ-PhC{double bond, long}C(H)PPh₂C{double bond, long}C(PPh₂)C(O)OC(O)]: Syntheses and X-ray str

Full text of DOI:10.1016/j.poly.2007.04.004

Polyhedron 26 (2007) 3737–3742
www.elsevier.com/locate/poly
PMe3-induced CO insertion and CO deinsertion
in the zwitterionic hydrocarbyl complex Co2(CO)4
[l-PhC@C(H)PPh2CC(PPh2)C(O)OC(O)]:
Syntheses and X-ray structures of
Co2(CO)3(PMe3)[l-PhC(CO)@C(H)PPh2C@C(PPh2)C(O)OC(O)]
and Co2(CO)3(PMe3)[l-PhC@C(H)PPh2C@C(PPh2)C(O)OC(O)]
a,
b
b,
*
Simon G. Bott *, Kaiyuan Yang , Michael G. Richmond
a
Department of Chemistry, University of Houston, Houston, TX 77004, United States
Department of Chemistry, University of North Texas, Denton, TX 76203, United States
b
Received 15 November 2006; accepted 5 April 2007
Available online 21 April 2007
Abstract
Treatment of the zwitterionic hydrocarbyl compound Co2(CO)4[l-PhC@C(H)PPh2C@C(PPh2)C(O)OC(O)] (1) with PMe3 leads to
CO insertion and formation of the acyl species Co2(CO)3(PMe3)[l-PhC(CO)@C(H)PPh2C@C(PPh2)C(O)OC(O)] (2). Compound 2
is unstable at elevated temperatures and loses CO to produce the PMe3-substituted compound Co2(CO)3(PMe3)[l-PhC@C(H)PPh2C@
C(PPh2)C(O)OC(O)] (3) as the major product. Compounds 2 and 3 have been isolated and characterized in solution by IR and NMR
(13C and 31P) spectroscopies and in the solid state by X-ray diffraction analyses.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Diphosphine ligand; CO insertion; Ligand substitution; Cobalt complexes
1. Introduction
coordinated alkynes in the dicobalt compounds
Co2(CO)4(bma)(l-RCCH) (where R = Ph, But) [2,3]. The
nucleophilic addition of one of the phosphine moieties to
the terminal alkyne carbon occurs regioselectively to
furnish the zwitterionic hydrocarbyl compounds
Co2(CO)4[l-RC@C(H)PPh2C@C(PPh2)C(O)OC(O)]. That
the nature of the alkyne ligand is critical in directing the
course of these reactions was demonstrated by thermolysis
of the related compound Co2(CO)4(bma)(l-PhCCPh),
where P–C bond cleavage instead of alkyne attack gives
Co2(CO)4[l-(Z)-Ph2PC(Ph)@C(Ph)C@C(PPh2)C(O)OC(O)]
[4]. Here, the formal insertion of the diphenylacetylene
ligand into the Ph2P–C(maleic anhydride) bond gives
Transition-metal compounds containing a hydrocarbyl
moiety remain under active investigation due to their
importance as intermediates in Fischer–Tropsch chemistry,
coupled with the fact that they serve as synthetically useful
platforms for the construction of diverse organic com-
pounds [1]. Several years ago, we published our findings
on the intramolecular attack of the diphosphine ligand
bma [2,3-bis(diphenylphosphino)maleic anhydride] on
*
Corresponding authors. Tel.: +1 713 743 2771 (S.G. Bott); +1 940 565
3548; fax: +1 940 565 4318 (M.G. Richmond).
E-mail addresses: sbott@uh.edu (S.G. Bott), cobalt@unt.edu (M.G.
Richmond).
rise
to
the
eight-electron
2-[(Z)-1,2-diphenyl-2-
(diphenylphosphino)ethenyl]-3-(diphenylphosphino)maleic
0277-5387/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.04.004

3738
S.G. Bott et al. / Polyhedron 26 (2007) 3737–3742
anhydride ligand. These reactions are depicted in Eqs. (1)
and (2), respectively.
2. Experimental
2.1. General
H
Ph
The starting dicobalt compound Co2(CO)4[l-PhC@
C(H)PPh2C@C(PPh2)C(O)OC(O)] was prepared from
Co2(CO)6(l-PhCCH) and bma accordingly to the pub-
lished procedure [2]. The alkyne compound Co2(CO)6-
(l-PhCCH) was synthesized from Co2(CO)8 and phenyl-
acetylene [6], while the diphosphine ligand bma was
synthesized from 2,3-dichloromaleic anhydride and
Ph2PSiMe3 [7]. PMe3 was prepared from P(OPh)3 and
MeMgI [8]. The chemicals phenylacetylene, P(OPh)3,
and MeI were purchased from Aldrich Chemical Co. and
used as received. Co2(CO)8 was purchased from Strem
Chemicals and stored under CO and in the refrigerator
when not in use. The 13CO (99%) used in the preparation
of the 13C-enriched sample of Co2(CO)6(l-PhCCH) was
obtained from Isotec. All reaction and NMR solvents were
distilled from an appropriate drying agent using Schlenk
techniques and stored under argon in storage vessels
equipped with high-vacuum Teflon stopcocks [9]. The com-
bustion analyses were performed by Atlantic Microlab,
Norcross, GA.
Co
Co
PPh2
Ph2P
O
O
ð1Þ
O
Ph
Co
H
Ph2P
heat
Co
O
O
P
Ph2
O
Ph
Ph
The IR spectral data were recorded on a Nicolet 20
SXB FT-IR spectrometer in sealed 0.1 mm NaCl cells,
while the 13C spectral data were recorded at 50 MHz on
a Varian Gemini-200 spectrometer. The 31P NMR spectra
were collected in the proton-decoupled mode on a Varian
300-VXR spectrometer at 121 MHz, with the reported
chemical shifts referenced to external H3PO4 (85%), taken
to have d = 0.
Co
Co
PPh2
Ph2P
O
ð2Þ
O
O
2.2. Synthesis of Co2(CO)3(PMe3)
[l-PhC(CO)@C(H)PPh2C@C(PPh2)C(O)OC(O)]
(2)
Ph
O
O
Ph2
O
P
To a small Schlenk tube containing 0.20 g (0.20 mmol)
of 1 in 15 mL of CH2Cl2 at room temperature was added
1.05 equiv. of PMe3 (0.42 mL of a 0.5 M solution of
PMe3 in CH2Cl2). The reaction was instantaneous based
on TLC and IR analyses of the reaction solution, which
revealed the complete consumption of 1 and the formation
of 2. The solvent was removed under vacuum and the res-
idue was passed across a short column of silica gel using
CH2Cl2/acetone (95:5) as the eluent. Recrystallization of
crude 2 from CH2Cl2/heptane afforded the analytical sam-
ple and single crystals of 2 suitable for X-ray diffraction
analysis. Yield of black-green 2: 0.18 g (85%). IR (CH2Cl2):
m(CO) 2022 (vs), 1985 (vs), 1777 (m, symm anhydride),
heat
Ph
Co
Co
PPh2
Wishing to further explore the chemistry of our zwit-
terionic hydrocarbyl complexes, we have investigated the
substitution reactivity of Co2(CO)4[l-PhC@C(H)PPh2C@
C(PPh2)C(O)OC(O)] (1) with PMe3 [5]. The addition of
PMe3 to 1 is shown to trigger the insertion of a CO
group into one of the Co–C(hydrocarbyl) bonds to give
the acyl species Co2(CO)3(PMe3)[l-PhC(CO)@C(H)
PPh2C@ C(PPh2)C(O)OC(O)] (2). Compound 2 under-
goes a formal CO deinsertion upon thermolysis to afford
the simple PMe3-substituted derivative Co2(CO)3(P-
Me3)[l-PhC@C(H)PPh2C@C(PPh2)C(O)OC (O)] (3).
The course of these substitution reactions has been estab-
lished through NMR spectroscopy and X-ray crystallo-
graphic analyses of compounds 2 and 3.
1719 (m, antisymm anhydride), 1590 (bw, acyl) cmꢀ1 13C
.
NMR (THF, 178 K): d 197.83 (d, 1C, JP–C = 23 Hz),
206.65 (s, 2C), 234.50 (d, 1C, JP–C = 15 Hz). 31P NMR
(THF, 178 K): d 14.90 (overlapping resonances, 2P),
19.21 (d, 1P, JP–P = 61 Hz, phosphonium moiety). Anal.
Calc. for C43H35Co2O7P3: C, 59.06; H, 4.03. Found: C,
59.36; H, 4.38%.

S.G. Bott et al. / Polyhedron 26 (2007) 3737–3742
3739
Table 2
2.3. Thermolysis of Co2(CO)3(PMe3)
[l-PhC(CO)@C(H)PPh2C@C(PPh2)C(O)OC(O)] and
formation of Co2(CO)3(PMe3)
˚
Selected bond distances (A) and angles (°) in the dicobalt compounds 2
and 3
Compound 2
Bond distances
[l-PhC@C(H)PPh2C@C(PPh2)C(O)OC(O)] (3)
Co(1)–Co(2)
Co(1)–C(1)
Co(1)–C(16)
Co(2)–P(3)
Co(2)–C(4)
Co(2)–C(15)
O(4)–C(4)
2.650(2)
1.77(1)
2.030(9)
2.239(3)
1.944(9)
2.006(9)
1.23(1)
1.44(1)
1.47(1)
Co(1)–P(1)
Co(1)–C(2)
Co(1)–C(17)
Co(2)–C(3)
Co(2)–C(11)
P(2)–C(15)
C(4)–C(17)
C(11)–C(15)
C(16)–C(17)
2.187(3)
1.79(1)
2.022(9)
1.73(1)
2.095(9)
1.776(9)
1.48(1)
1.47(1)
1.43(1)
To a Schlenk tube under argon was charged 0.20 g
(0.23 mmol) of 2, followed by the addition of 20 mL of
1,2-dichloroethane (DCE) via syringe. The vessel was sealed
and then heated at 60 °C for 1 h, at which time TLC analysis
confirmed the presence of compounds 1, 2, and 3. Heating
was continued for another hour and the solution examined
again by TLC. At this point, only compounds 1 (minor)
and 3 (major) were observed (Rf = 0.80 for 1 and Rf = 0.65
for 3 using CH2Cl2 as the eluent). The desired compound 3
was isolated after solvent removal and purification by col-
umn chromatography over silica gel using CH2Cl2 as the
mobile phase. Crude 3 was subsequently recrystallized from
CH2Cl2/hexane to furnish the combustion sample and the
single crystals of 3 suitable for X-ray crystallography. Yield
of 3: 82% (0.16 g). IR (CH2Cl2): m(CO) 2001 (s), 1958 (s),
1777 (m, symm anhydride), 1721 (m, antisymm anhydride)
C(11)–C(12)
C(14)–C(15)
Bond angles
Co(2)–Co(1)–P(1)
Co(2)–Co(1)–C(2)
Co(2)–Co(1)–C(17)
Co(1)–Co(2)–P(3)
Co(1)–Co(2)–C(4)
Co(1)–Co(2)–C(15)
C(4)–Co(2)–C(15)
Co(2)–C(4)–O(4)
P(2)–C(16)–C(17)
70.08(8)
173.1(3)
75.2(3)
159.7(1)
65.7(3)
Co(2)–Co(1)–C(1)
Co(2)–Co(1)–C(16)
C(16)–Co(1)–C(17)
Co(1)–Co(2)–C(3)
Co(1)–Co(2)–C(11)
C(4)–Co(2)–C(11)
C(11)–Co(2)–C(15)
Co(2)–C(4)–C(17)
91.8(3)
83.7(3)
41.5(4)
93.1(4)
81.8(3)
135.2(4)
41.9(4)
114.7(6)
89.5(3)
105.3(4)
123.7(7)
124.5(7)
cmꢀ1
.
13C NMR (THF, 178 K): d 202.07 (d, 1C,
Compound 3
Bond distances
Co(1)–Co(2)
Co(1)–C(1)
Co(1)–C(16)
Co(2)–P(3)
Co(2)–C(11)
Co(2)–C(17)
C(11)–C(15)
C(16)–C(17)
JP–C = 20 Hz), 207.37 (d, 1C, JP–C = 21 Hz), 211.89 (s,
1C). 31P NMR (THF, 178 K): d 10.80 (overlapping reso-
nances, 2P), 33.78 (d, 1P, JP–P = 67 Hz, phosphonium moi-
ety). Anal. Calc. for for C42H35Co2O6P3: C, 59.59; H, 4.13.
Found: C, 59.29; H, 4.26%.
2.553(4)
1.80(2)
2.09(2)
2.210(6)
2.05(2)
2.00(2)
1.39(3)
1.40(3)
Co(1)–P(1)
Co(1)–C(2)
Co(1)–C(17)
Co(2)–C(3)
Co(2)–C(15)
C(11)–C(12)
C(14)–C(15)
2.197(6)
1.69(3)
1.98(2)
1.74(2)
2.06(2)
1.43(3)
1.47(3)
2.4. X-ray diffraction data
Tables 1 and 2 contain the X-ray data and processing
parameters and selected bond distances and angles, respec-
Bond angles
Co(2)–Co(1)–P(1)
Co(2)–Co(1)–C(2)
Co(2)–Co(1)–C(17)
Co(1)–Co(2)–P(3)
Co(1)–Co(2)–C(11)
Co(1)–Co(2)–C(17)
70.9(2)
164.6(9)
50.4(5)
154.0(2)
84.8(5)
49.6(4)
Co(2)–Co(1)–C(1)
Co(2)–Co(1)–C(16)
C(16)–Co(1)–C(17)
Co(1)–Co(2)–C(3)
Co(1)–Co(2)–C(15)
C(11)–Co(2)–C(15)
101.5(8)
75.2(6)
40.1(7)
92.6(7)
89.0(5)
39.5(7)
Table 1
X-ray crystallographic data and processing parameters for the dicobalt
compounds 2 and 3
Compound
2
3
Crystal system
Space group
orthorhombic
P212121
monoclinic
P21/n
˚
tively, for compounds 2 and 3. A suitable crystal was
selected and sealed inside a Lindemann capillary, followed
by mounting on an Enraf-Nonius CAD-4 diffractometer.
After the cell constants were obtained, intensity data in
the range of 2° 6 2h 6 44° (2) and 2° 6 2h 6 40° (3) were
collected at 298 K and were corrected for Lorentz, polari-
zation, and absorption (DIFABS). The structures of
compounds 2 and 3 were solved using SHELX-86. All non-
hydrogen atoms were located with difference Fourier maps
and full-matrix least-squares refinement in both com-
pounds. In the case of 2, the cobalt, phosphorus, oxygen,
and the carbonyl carbon atoms were refined anisotropi-
cally, with the phenyl, hydrocarbyl, and maleic anhydride
ring carbon atoms refined isotropically. Due to the poor
scattering displayed by the crystal of 3, only the Co and
P atoms were refined anisotropically. All hydrogen atoms
were assigned calculated positions and allowed to ride on
the attached heavy atom. Refinement on 2 converged at
R = 0.0427 and Rw = 0.0460 for 2127 unique reflections
a (A)
10.2936(7)
17.471(1)
22.294(2)
9.189(3)
19.254(4)
21.702(4)
92.00(2)
3837(2)
C42H35Co2O6P3
846.53
˚
b (A)
˚
c (A)
b (°)
3
˚
V (A )
4009.3(5)
C43H35Co2O7P3
874.54
Molecular formula
Fw
Formula units per cell (Z)
Dcalc (g/mm3)
4
4
1.449
0.71073
9.91
1.465
0.71073
10.32
˚
k (Mo Ka), A
l (cmꢀ1
Rmerge
)
n/a
0.037
Absorption correction
Absorption correction factor
Total reflections
Independent reflections
Data/residual/parameters
R
Fourier
0.90/1.13
2811
2127
2127/0/301
0.0427
0.0460
0.76
0.45 near Co(1)
Fourier
0.69/1.32
4000
1375
1375/0/238
0.0620
0.0715
0.72
0.52 near C(2)
Rw
Goodness of fit on F2
Dq(maximum), Dq(minimum)
ꢀ3
˚
(e/A
)

3740
S.G. Bott et al. / Polyhedron 26 (2007) 3737–3742
affords 2 is sensitive to the nucleophilicity of incoming
H
Ph
ligand and does not proceed via a pre-equilibrium involv-
ing the unsaturated acyl species Co2(CO)3[l-PhC(CO)@
C(H)PPh2C@C(PPh2)C(O)OC(O)], as added phosphine
would be captured without complications under these cir-
cumstances. Compound 2 was subsequently isolated in
high yield as a mildly air-sensitive solid after chromato-
graphic separation over silica using the aforementioned
eluent. Scheme 1 depicts the transformation of 1 to 2.
Compound 2 was characterized by IR and NMR spec-
troscopies, elemental analysis, and X-ray crystallography.
The IR spectrum displays terminal Co–CO bands 2022
(vs) and 1985 (vs) cmꢀ1 and two m(CO) bands for the kine-
matically coupled carbonyl groups associated with the
anhydride ring at 1777 (m) and 1719 (m) cmꢀ1 [10]. The
shift to lower energy by both sets of carbonyl groups in 2
relative to 1 is consistent with the addition of an elec-
tron-rich PMe3 ligand to 1. The acyl band in 2 appears
as a broad, weak band at 1590 cmꢀ1, in agreement with
the reported frequencies in other such acyl derivatives
[11]. The low-temperature 13C NMR spectrum of a 13CO-
enriched sample of 2 exhibits two terminal Co–CO reso-
nances at d 197.83 (1C) and 206.65 (2C) and an acyl CO
resonance at d 234.50 [12], while the 31P NMR spectrum
reveals an overlapping singlet and doublet at d 14.90 for
the cobalt-bound phosphine groups and a down-field dou-
blet at d 19.21 belonging to the phosphonium moiety. The
31P NMR data recorded for 2 parallel those data reported
by us for compound 1, which displays 31P chemical shifts at
d 4.70 and 31.30 for the phosphine and phosphonium
groups, respectively [2].
P
Ph2
O
Co
Co
compound 1
O
P
Ph2
O
+PMe3/CH2Cl2
Ph
H
Ph2P
O
Me3P
compound 2
Co
Co
O
O
P
Ph2
O
heat/-CO
Ph
H
Ph2P
Me3P
compound 3
Co
Co
O
The solid-state structure of 2 was determined by single-
crystal X-ray diffraction analysis [13].1 Single crystals of 2
exist as discrete molecules in the unit cell with no unusually
short inter- or intramolecular contacts. The ORTEP dia-
gram of 1, shown in Fig. 1, confirms the regiospecific addi-
tion of the PMe3 ligand to the Co(2) atom and the insertion
of the C(4)O(4) carbonyl group into the Co(2)–C(17) bond
O
P
Ph2
O
Scheme 1.
with I > 3r(I), while 3 afforded convergence values of
R = 0.0620 and Rw = 0.0715 for 1375 unique reflections
with I > 3r(I).
˚
of 1. The Co(1)–Co(2) bond distance of 2.650(2) A is
˚
0.101 A longer than the cobalt–cobalt bond length
reported for compound 1. This lengthening is attributed
3. Results and discussion
to the presence of the ancillary PMe3 ligand. The Co(1)–
˚
P(1) and Co(2)–P(3) distances of 2.187(3) A and
˚
3.1. Synthesis, spectroscopic data, and X-ray diffraction
structure of 2
2.239(3) A, respectively, fall within acceptable ranges for
such linkages [14]. The Co(2)–C(4) and C(4)–C(17) dis-
˚
˚
tances of 1.944(9) A and 1.48(1) A, respectively, and the
angles associated with the Co(2)–C(4)–C(17) [114.7(6)°]
and Co(2)–C(4)–O(4) [123.7(7)°] linkages exhibit values
consistent with other acyl-substituted cobalt compounds
Treatment of 1 with a slight excess of PMe3 at room
temperature leads to a rapid reaction based on the brown
to black-green color change exhibited by the reaction solu-
tion. TLC examination confirmed the complete consump-
tion of brown 1 and the presence of a slower moving
black-green spot corresponding to 2 at Rf = 0.50 using
CH2Cl2/acetone (95:5) as the eluent. No reaction between
1 and PMe3 was observed at 0 °C, while the reaction
between 1 and PPh3 conducted at room temperature
showed no sign for the formation of any product. This lat-
ter observation suggests that the CO insertion reaction that
1
The chiral space group P212121 exhibited by compound 2 presumably
reflects a spontaneous separation of one of the enantiomers from the bulk
sample whose composition consists of a racemic mixture of 2. Unfortu-
nately, the absolute chirality associated with the two stereocenters in the
X-ray structure 2 cannot be definitively ascertained based on the available
X-ray data.

S.G. Bott et al. / Polyhedron 26 (2007) 3737–3742
3741
Fig. 1. ORTEP diagrams of compounds 2 (left) and 3 (right) showing the thermal ellipsoids at the 30% probability level.
[15]. The three terminal CO groups display distances and
angles consistent with such groups. The remaining bond
distances and angles are unremarkable and require no
comment.
the back reaction between 1 and PMe3 would be eliminated.
Accordingly, 1 would be observed as the dominant product,
provided that the expulsion of PMe3 from 2 is favored over
CO dissociation. The significant amount of 3 that accompa-
nies this particular experiment (TLC monitoring) indicates
that the conversion of 2 to 3 proceeds primarily through
the liberation of CO and not PMe3. The bottom portion
of Scheme 1 shows the conversion of 2 to 3.
3.2. Synthesis, spectroscopic data, and X-ray diffraction
structure of 3
The temperature sensitivity of 2 was subsequently veri-
fied during a routine thermolysis study. Heating 2 in either
DCE or toluene solution over the temperature range of 50–
75 °C leads to the consumption of 2 and concurrent forma-
tion of the simple phosphine-substituted compound 3 as the
major product, as assessed by TLC and IR analyses. TLC
examination also revealed the presence of a small amount
of compound 1 and some decomposed material that
remained irreversibly bound to the TLC plate irrespective
of the mobile phase employed. The observation of 1 during
the thermolysis reaction raises an interesting aspect con-
cerning the route leading to 3. It is possible that 1 serves
as the principal product from the acyl-deinsertion reaction,
which in turn requires the expulsion of the PMe3 ligand
from 2. Once regenerated 1 could again react with the liber-
ated PMe3 to furnish 2 and then ultimately produce 3
through a slower secondary event(s). The observation of
both 1 and 3 from 2 is also consistent with a dual reaction
manifold, where the amount of each product (1 and 3)
reflects a kinetic preference associated with the acyl-deinser-
tion step [16]. Of these two general paths, we favor the latter
one based on the results obtained from the thermolysis of a
toluene solution of 2 that was purged with argon in order to
remove the liberated CO and PMe3. Under such conditions,
Compound 3 was isolated by column chromatography in
82% yield and characterized by traditional spectroscopic
methods, combustion analysis, and X-ray crystallography.
The IR spectrum of 3 showed two strong carbonyl stretch-
ing bands at 2001 and 1958 cmꢀ1 belonging to the terminal
Co–CO groups and two anhydride carbonyl bands at 1777
(m) and 1721 (m) cmꢀ1 that represent the vibrationally cou-
pled symmetric and antisymmetric anhydride stretches,
respectively. The presence of three terminal Co–CO groups
in 3 was verified by 13C NMR spectroscopy of a 13CO-
enriched sample of 3. Here, 13C resonances recorded at d
202.07, 207.37, and 211.89 support the formulated structure
of 3 and the loss of the acyl moiety. The 31P NMR spectrum
of 3 exhibits a high-field resonance at d 10.80 for the over-
lapping cobalt-bound phosphine moieties and the hydrocar-
byl-bound phosphonium ligand at d 33.78. These data are
similar to those chemical shifts recorded for compound 2.
The molecular composition of 3 was established by X-
ray diffraction analysis. The ORTEP diagram of 3 depicted
in the right-hand portion of Fig. 1 confirms the loss of the
acyl moiety in the conversion of 2 to 3. With the exception
of the ancillary PMe3 group at Co(2), the overall structure
of 3 is comparable to the published structure of 1 [2]. The
˚
2.553(4) A bond distance for the Co(1)–Co(2) vector is in

3742
S.G. Bott et al. / Polyhedron 26 (2007) 3737–3742
(d) C.S.-W. Lau, W.-T. Wong, J. Chem. Soc., Dalton Trans. (1999)
2511;
(e) R.D. Adams, L. Chen, M. Huang, Organometallics 13 (1994)
2696.
keeping with its single-bond designation and consistent
with those Co–Co bond lengths found in other dinuclear
cobalt compounds [17]. The cobalt-bound alkene moieties
defined by the atoms C(11)–C(15) and C(16)–C(17) exhibit
[2] (a) K. Yang, S.G. Bott, M.G. Richmond, Organometallics 13 (1994)
3767;
˚
bond distances of 1.39(3) and 1.40(3) A, respectively, that
(b) K. Yang, S.G. Bott, M.G. Richmond, J. Organomet. Chem. 516
(1996) 65.
are slightly shorter than those distances found in 2. The
remaining bond distances and angles are unexceptional
and require no comment.
[3] (a) For examples involving intermolecular phosphine attack on a
coordinated alkyne ligand, see D.M. Hoffman, J.C. Huffman, D.
Lappas, D.A. Wierda, Organometallics 12 (1993) 4312;
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4. Conclusions
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[12] All NMR spectrum were recorded at low temperature in order to
minimize undesirable 59Co broadening of the 13C and 31P resonances.
No noticeable fluxional behavior was observed for the CO and
phosphine ligands in 2 and 3. See M. Schwartz, M.G. Richmond,
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[13] (a) For reports of spontaneous resolution of racemic mixtures, see R.
The addition of PMe3 to Co2(CO)4[l-PhC@ C(H)PPh2
C@C(PPh2)C(O)OC(O)] (1) promotes the regiospecific
CO insertion into one of the Co-C(hydrocarbyl) bonds
and production of the acyl compound Co2(CO)3-
(PMe3)[l-PhC(CO)@C(H)PPh2C@C(PPh2)C(O)OC(O)] (2).
This represents the first example of a phosphine-induced
CO-insertion reaction in a zwitterionic hydrocarbyl com-
pound of this genre. Compound 2 is thermally unstable
and undergoes decarbonylation to furnish the PMe3-substi-
tuted compound Co2(CO)3(PMe3)[l-PhC@C(H)PPh2C@
C(PPh2)C(O)OC(O)] (3) and 1, as the major and minor
products, respectively. Our future endeavors will explore
the generality of this reaction with isonitrile ligands and
different phosphines, and the kinetics for the CO insertion
reaction will be investigated using low-temperature spec-
troscopic techniques.
Acknowledgement
´
Clerac, F.A. Cotton, K.R. Dunbar, T. Lu, C.A. Murillo, X. Wang,
Financial support from the Robert A. Welch Founda-
tion (Grant B-1093-M.G.R) is much appreciated.
Inorg. Chem. 39 (2000) 3065;
(b) A. Johansson, M. Hakansson, S. Jagner, Chem. Eur. J. 11 (2005)
˚
5311;
Appendix A. Supplementary material
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Conole, M. McPartlin, H.R. Powell, J. Chem. Soc., Dalton Trans.
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CCDC 627411 and 627412 contain the supplementary
crystallographic data for 2 and 3. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.poly.2007.
04.004.
(b) I. Moldes, J. Ros, M.R. Torres, A. Perales, R. Mathieu, J.
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