On the reaction of C(PPh3)2 with [Co 2(CO)8]: Formation and structure of an unusual tetranuclear cluster

Article abstract of DOI:10.1515/znb-2007-0315

The reaction of the carbodiphosphorane C(PPh₃)₂ (1) with [Co₂(CO)₈] results in the formation of the salt-like complex (HC{PPh₃}₂)[Co(CO)₄] (2) in high yield if THF is used as the solvent. The proton of the cation stems from THF degradation. When the reaction is carried out in toluene, the tetranuclear cluster [Co₄(CO)₁₀(PPh₃)(μ₄- CCPPh₃)] (3) is formed in low yield as the only complex which could be identified by X-ray analysis. The solvate 3·C₇H₈ crystallizes in the triclinic space group P1? with a = 1040.8(2), b = 1387.4(2), c = 1923.0(2) pm, a = 71.96(1)°, β = 88.69(1)°, γ = 71.46(1)°, Z = 2. The structure of the cluster with 64 CVE is that of a spiked triangle in which the triphenylphosphonioacetylide CCPPh ₃ acts as a six-electron donor and the bonding mode is that of a μ₄-η² coordination.

Full text of DOI:10.1515/znb-2007-0315

On the Reaction of C(PPh3)2 with [Co2(CO)8]: Formation and
Structure of an Unusual Tetranuclear Cluster
Wolfgang Petz, Kirstin Wenck, and Bernhard Neumu¨ller
Fachbereich Chemie der Philipps-Universita¨t Marburg, Hans Meerwein-Straße, 35032 Marburg,
Germany
Reprint requests to Prof. W. Petz. E-mail: petz@staff.uni-marburg.de or
Prof. B. Neumu¨ller. E-mail: neumuell@chemie.uni-marburg.de
Z. Naturforsch. 2007, 62b, 413 – 418; received December 3, 2006
Dedicated to Prof. Helgard G. Raubenheimer on the occasion of his 65th birthday
The reaction of the carbodiphosphorane C(PPh3)2 (1) with [Co2(CO)8] results in the formation of
the salt-like complex (HC{PPh3}2)[Co(CO)4] (2) in high yield if THF is used as the solvent. The
proton of the cation stems from THF degradation. When the reaction is carried out in toluene, the
tetranuclear cluster [Co4(CO)10(PPh3)(µ4-CCPPh3)] (3) is formed in low yield as the only complex
which could be identified by X-ray analysis. The solvate 3 · C7H8 crystallizes◦in the triclinic◦space
¯
group P1 with a = 1040.8(2), b = 1387.4(2), c = 1923.0(2) pm, α = 71.96(1) , β = 88.69(1) , γ =
71.46(1)◦, Z = 2. The structure of the cluster with 64 CVE is that of a “spiked triangle” in which the
triphenylphosphonioacetylide CCPPh3 acts as a six-electron donor and the bonding mode is that of a
µ4-η2 coordination.
Key words: Tetranuclear Cobalt Cluster, Carbodiphosphorane, Phosphacumulene Ligand,
Proton Abstraction, Crystal Structure
Introduction
and [BrMn(CO)5] [13]. With the two options of reac-
tion pathways for 1, we now turned to the transition
metal carbonyl [Co2(CO)8], which is located between
the carbonyls of Fe and Ni. The results of reactions in
various solvents are reported here.
The double ylide C(PPh3)2 (1) has been known
since 1961 [1], and for its solid state a bent structure
with an approximately sp2-hybridized carbon atom
was established by X-ray diffraction [2]. Thus, in ac-
cord with a lone pair of electrons, the chemistry of
1 is mainly governed by the properties of a typi-
cal Lewis base, and various electron acceptor com-
ponents produce adducts of the type E←C(PPh3)2, in
which E can represent an element (S, Se [3]), a cation
(I+ [4], Cl+, H+ [5]), a heteroallene [6], a group 13
compound (InMe3, AlBr3 [5]), or various transition
metal fragments ([ReO3]+ [7], Cp∗Cu [8], XAu [9],
(CO)nNi [10]). Several reviews concerning the chem-
istry of ylides including 1 have been published [11].
In the case of metal carbonyl compounds the reaction
of 1 not only leads to CO substitution and formation
of ylide complexes as in [(CO)nNi(C{PPh3}2)] (n = 2,
3) [10], but to a nucleophilic attack of 1 at a carbonyl
carbon atom to produce the metal bonded triphen-
ylphosphonioacetylide ligand CCPPh3 in a “Wittig-
type” manner under elimination of OPPh3, similar to
the action of a hard base as reported for [Fe(CO)5] [12]
Results and Discussion
The results of the reaction of 1 with [Co2(CO)8]
strongly depend on the solvent and do not lead to a
CO substitution as in the case of [Ni(CO)4]. If THF
is used, H+ abstraction from the solvent is observed
with formation of the salt (HC{PPh3}2)[Co(CO)4]
(2). The 31PNMR spectrum of the solution exhibits
only one singlet at 20.3 ppm for the cation. The
formation of the cation is quantitative and can not
be explained with partial hydrolysis of an initial
reaction product. The mechanism is not clear, but
it seems likely that in the first step the complex
[Co(CO)4(C{PPh3}2)][Co(CO)4] is formed, which ap-
parently is highly reactive (eq. 1 and eq. 2).
[Co2(CO)8]+C(PPh3)2 →
(1)
[Co(CO)4(C{PPh3}2)][Co(CO)4]
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414
W. Petz et al. · On the Reaction of C(PPh3)2 with [Co2(CO)8]
[Co(CO)4(C{PPh3}2)][Co(CO)4]+H+ →
carbon atom has occurred followed by a Wittig-type re-
action with elimination of OPPh3 and formation of the
CCPPh3 ligand similar to the results of the reactions
of 1 with [Fe(CO)5] [12] or [Mn(CO)5Br] [13]. From
the solution, on layering with n-pentane and standing
for some weeks, small amounts of reddish brown crys-
tals separated, which were identified as the tetranuclear
cluster [Co4(CO)10(PPh3)(µ4-CCPPh3)] (3). Unfortu-
nately, the crystals of 3 could not be redissolved in
toluene. The initial signal in the 31P NMR spectrum
probably does not belong to the new tetranuclear clus-
ter complex which is expected to show two signals. For
compounds with a (CO)CoPPh3 fragment a low field
signal in the 31P NMR spectrum at about 70 ppm is ex-
pected [19], and the CCPPh3 group normally resonates
at about −10 ppm.
(HC{PPh3}2)[Co(CO)4]
+...
(2)
2
As yet, we were unable to confirm the existence of
this intermediate. [Co2(CO)8]is known to react with
various Lewis bases L with disproportion into salts
[Co(CO)4L][Co(CO)4] in the first step [14]. For the
formation of the cation (HC{PPh3}2)+ different path-
ways can be discussed. The cation first produced may
undergo a homolytic splitting with formation of the
radicals [Co(CO)4]• and (C{PPh3}2)+•; the latter may
than deprotonate a solvent molecule. An alternative
is taking up a proton from the solvent at the co-
ordinating carbon atom and formation of the dica-
tion [Co(CO)4(HC{PPh3}2)]2+. Very recently we have
shown that the cation (HC{PPh3}2)+ itself can serve
as a ligand for transition metals in the absence of fur-
ther coordinating anions. Thus, with AgBF4 the tri-
cation [Ag(HC{PPh3}2)2]3+was obtained upon reac-
tion with (HC{PPh3}2)[BF4] [15]. After deprotona-
tion of THF, the remaining anionic species may lose
OH− to produce 1,3-butadiene. The overall release of
H2O from THF under catalytic conditions and forma-
tion of 1,3-butadiene or other species was described
earlier [16]. Similar unusual solvent degradation reac-
tions were also observed when group 6 carbonyl com-
pounds were treated with 1 in THF solution; final sup-
port for this mechanism is the detection of carbonato
complexes in reactions of 1 with [Mo(CO)6], which
can only be rationalized by the presence of OH− ions
in the reaction mixture [17]. Thus, the colorless com-
pound 2 is finally formed through the action of water.
However, as yet we were not able to detect the
butadiene in the reaction mixture, and another mode
of degradation of THF with release of H+ may also
be considered. Theoretical considerations have shown
that 1 has a high proton affinity [18], and during our
studies concerning the chemistry of 1 and the related
CS2, CO2 and COS adducts we have often observed the
formation of the cation (HC{PPh3}2)+ if THF or halo-
genated hydrocarbons such as dichloromethane were
used as solvents [6].
The IR spectrum of 3 exhibits several strong bands
between 1948 and 2045 cm−1, which can be assigned
to vibrations of terminal CO groups. Three medium
strong bands at 1800, 1819, and 1839 cm−1 can be at-
tributed to the three bridging CO ligands. A medium
strong band at 1414 cm−1 may be due to the vibration
of the CC multiple bond of the acetylide ligand [20].
The PPh3 ligand found in 3 may originate from a re-
duction of OPPh3 with [Co2(CO)8] or other low valent
cobalt carbonyl fragments; free 1 as a PPh3 source has
not yet been observed.
The difference in the reaction of 1 with [Ni(CO)4]
and [Fe(CO)5] can be rationalized by the more elec-
trophilic nature of the carbonyl carbon atoms in the
iron species because fewer d electrons are present for
back bonding into a larger number of CO groups. For
the dimeric cobalt carbonyl complex, the experiment
establishes a close similarity to the iron carbonyl which
has in common the formation of the phosphacumulene
or acetylide ligand CCPPh3. This interesting ligand is
composed of a C2 unit, which attains 10 electrons by
means of the pair of electrons from PPh3 and thus can
To avoid any H abstraction from a source like THF
we carried out the reaction of 1 with [Co2(CO)8] in
toluene. The 31P NMR spectrum of the initial reac-
tion mixture showed two signals at 23.7 and 16.0 ppm
in an approximately 2 : 1 ratio. The low field signal
could be assigned to OPPh3, which indicates that in Scheme 1. Possible linear and bent arrangements of the
isolobal species CCPPh3, CNR, and CO.
the first step a nucleophilic attack of 1 at a carbonyl
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W. Petz et al. · On the Reaction of C(PPh3)2 with [Co2(CO)8]
Table 1. Crystal and refinement data for 2 and 3·C7H8.
415
Table 2. Selected bond lengths (pm) and angles (deg) for the
salt 2 with estimated standard deviations in parentheses.
2
3·C7H8
C41H31CoO4P2 C55H38Co4O10P2
708.57 1156.56
0.31×0.30×0.10 0.19×0.13×0.06
Cation:
Formula
Mr
P(1)-C(5)
P(1)-C(12)
P(2)-C(5)
P(2)-C(30)
C(5)-H(1)
169.3(3)
180.2(2)
168.8(3)
180.6(2)
82(3)
P(1)-C(6)
P(1)-C(18)
P(2)-C(24)
P(2)-C(36)
179.2(2)
179.8(2)
179.8(2)
179.4(2)
Crystal size [mm3]
Crystal system
Space group
a [pm]
b [pm]
c [pm]
triclinic
P1 (Nr. 2)
triclinic
P1 (Nr. 2)
¯
¯
985.2(1)
1152.0(1)
1617.6(2)
72.73(1)
80.58(1)
86.20(1)
1729.2(3)
2
1040.8(2)
1387.4(2)
1923.0(2)
71.96(1)
88.69(1)
71.46(1)
2494.5(5)
2
Anion:
Co(1)-C(1)
Co(1)-C(3)
O(1)-C(1)
O(3)-C(3)
173.6(3)
174.2(3)
116.0(3)
115.9(3)
Co(1)-C(2)
Co(1)-C(4)
O(2)-C(2)
O(4)-C(4)
175.7(3)
173.9(3)
115.4(3)
116.3(3)
α [deg]
β [deg]
γ [deg]
V [pm3 ·106]
Z
Cation:
Dcalc [g cm−3
]
1.361
1.54
C(5)-P(1)-C(6)
C(5)-P(1)-C(18)
C(6)-P(1)-C(18)
C(5)-P(2)-C(24)
C(5)-P(2)-C(36)
C(24)-P(2)-C(36)
P(1)-C(5)-P(2)
P(2)-C(5)-H(1)
111.8(1)
112.0(1)
107.6(1)
109.6(1)
113.3(1)
104.5(1)
129.3(2)
115(2)
C(5)-P(1)-C(12)
C(6)-P(1)-C(12)
C(12)-P(1)-C(18)
C(5)-P(2)-C(30)
C(24)-P(2)-C(30)
C(30)-P(2)-C(36)
P(1)-C(5)-H(1)
112.4(1)
106.6(1)
106.0(1)
114.9(1)
106.3(1)
107.6(1)
116(2)
Diffractometer
Temperature [K]
µ(MoKα ) [cm−1
Absorption correction
2θmax [deg]
hkl range
IPDS II (Stoe)
193
6.3
numerical
52.12
−11 ≤ h ≤ 11
−14 ≤ k ≤ 14
−19 ≤ l ≤ 19
17166
IPDS II (Stoe)
193
14.3
numerical
52.46
−12 ≤ h ≤ 12
−16 ≤ k ≤ 16
−23 ≤ l ≤ 22
24591
]
Anion:
Measured reflexions
Unique reflexions
Rint
C(1)-Co(1)-C(2)
C(1)-Co(1)-C(4)
C(2)-Co(1)-C(4)
109.2(1)
108.7(1)
112.0(1)
C(1)-Co(1)-C(3)
C(2)-Co(1)-C(3)
C(3)-Co(1)-C(4)
113.1(1)
106.8(1)
107.1(1)
6302
0.046
9960
0.0666
Reflexions with F0 ≥ 4σ(F0) 3883
5401
670
Refined parameters
Structure solution
438
– Patterson Method –
Crystal structures
– SHELXTL-Plus [32] –
Refinement on F2
H atoms
– SHELXL-97 [33] –
In order to get a deeper insight into the features
of the compounds, the structures of 2 and 3 · C7H8
were determined by single crystal X-ray diffraction
measurements. Colorless crystals of 2 were obtained
a
b
R1
0.0333
0.0663
0.25
0.0397
0.0641
0.43
wR2 (all data)
∆ρfin [e pm−3 ×10−6
]
a
Refined in calculated positions with a common displacement pa- at r. t. by layering the filtered THF solution with n-
rameter; free refinement of H1; b refined in calculated positions with
pentane, and brownish black crystals of 3 · C7H8 de-
a common displacement parameter.
posited on standing of a toluene solution of the reac-
tion mixture for several days. The toluene molecule
be considered to be isoelectronical with isocyanides or
in 3 · C7H8 is disordered but could be refined in two
CO as depicted in Scheme 1.
split positions (0.6: 0.4). The ORTEP views of 3 are
Efforts were also made recently to isolate free
depicted in Fig. 1. Although the salt-like solvent-free
CCPPh3, which was found to be stable only in solution
compound 2 has not been described earlier, the struc-
at very low temperature [21]. However, till now the co-
ture is not shown because cation and anion of 2 are well
ordination chemistry of CCPPh3 has been poorly de-
known and related compounds with different counte-
veloped and only few complexes are known. No com-
rions have already been published [23, 24]. Details of
plex formation was described starting from the free lig-
the structure determinations are collected in Table 1;
and. Like CO, this ligand can coordinate in a terminal
bond lengths and angles are summarized in the Ta-
manner with donation of two electrons [12, 13] or, as
bles 2 and 3.
in the trinuclear complex [Fe3(CO)9(CCPPh3)], it can
bridge the three metal atoms in a µ3-η2 manner and
act as a six-electron donor as required for a satisfac-
Molecular structure of 2
tory electron count [12]. To our knowledge, a similar
CO coordination is only realized in the trinuclear com- There are no remarkable interionic contacts; the short-
The ionic compound 2 forms colorless crystals.
plex [Cp3Nb3(CO)3(µ3-CO)], where the bridging CO est C–H···O distance occurs between a phenyl pro-
group also donates six electrons [22].
ton and an oxygen atom with a C···O separation of
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416
W. Petz et al. · On the Reaction of C(PPh3)2 with [Co2(CO)8]
Table 3. Selected bond lengths (pm) and angles (deg)
for 3 · C7H8 with estimated standard deviations in paren-
theses.
Co(1)-Co(2)
Co(2)-Co(3)
Co(1)-C(1)
Co(1)-C(9)
Co(2)-C(2)
Co(3)-C(2)
Co(3)-C(10)
Co(4)-C(2)
P(1)-C(1)
249.6(1)
249.8(1)
202.0(4)
184.4(4)
205.3(4)
197.7(4)
201.6(4)
202.7(4)
173.9(4)
117.2(5)
136.4(4)
Co(1)-Co(3)
Co(3)-Co(4)
Co(1)-C(2)
Co(2)-C(1)
Co(2)-C(7)
Co(3)-C(7)
Co(3)-C(9)
Co(4)-P(2)
Co(4)-C(10)
O(7)-C(7)
252.3(1)
252.9(1)
208.9(4)
200.9(4)
197.7(4)
187.7(4)
205.3(4)
222.4(1)
187.6(4)
118.4(4)
117.9(4)
O(10)-C(10)
C(1)-C(2)
O(9)-C(9)
C(1)-Co(1)-Co(2)
C(1)-Co(1)-Co(3)
C(1)-Co(2)-Co(1)
C(1)-Co(2)-Co(3)
C(2)-Co(3)-Co(2)
C(2)-Co(3)-Co(4)
Co(1)-Co(2)-Co(3)
Co(2)-Co(3)-Co(4)
P(2)-Co(4)-Co(3)
P(2)-Co(4)-C(10)
P(2)-Co(4)-C(11)
C(1)-Co(2)-C(2)
C(2)-Co(4)-C(11)
Co(1)-C(1)-P(1)
Co(2)-C(1)-P(1)
Co(1)-C(1)-Co(2)
Co(1)-C(2)-Co(3)
Co(1)-C(2)-Co(2)
Co(1)-C(2)-Co(4)
Co(2)-C(2)-Co(3)
Co(2)-C(2)-C(1)
51.5(1)
85.3(1)
51.9(1)
86.2(1)
53.1(1)
51.7(1)
60.7(1)
95.3(1)
122.5(1)
85.4(1)
90.1(1)
39.2(2)
88.9(2)
129.2(2)
141.2(2)
76.6(1)
76.7(1)
74.1(1)
137.9(2)
76.6(1)
68.6(2)
C(2)-Co(1)-Co(2)
C(2)-Co(1)-Co(3)
C(2)-Co(2)-Co(1)
C(2)-Co(2)-Co(3)
C(2)-Co(3)-Co(1)
C(2)-Co(4)-Co(3)
Co(2)-Co(3)-Co(1)
Co(1)-Co(3)-Co(4)
P(2)-Co(4)-C(2)
P(2)-Co(4)-C(12)
C(1)-Co(1)-C(2)
C(2)-Co(4)-C(10)
C(2)-Co(4)-C(12)
P(1)-C(1)-C(2)
Co(1)-C(1)-C(2)
Co(2)-C(1)-C(2)
Co(3)-C(2)-C(1)
Co(1)-C(2)-C(1)
Co(2)-C(2)-Co(4)
Co(3)-C(2)-Co(4)
Co(4)-C(2)-C(1)
52.3(1)
49.7(1)
53.6(1)
50.3(1)
53.7(1)
50.0(1)
59.6(1)
99.0(1)
172.3(1)
95.2(1)
38.7(2)
89.3(2)
91.9(2)
137.0(3)
73.4(2)
72.2(2)
135.5(3)
67.9(2)
131.1(2)
78.3(2)
146.0(3)
Fig. 1. Molecular structure of 3 · C7H8 showing the atom
numbering scheme. The ellipsoids are drawn at the 40 %
probability level. The H atoms at the phenyl groups are omit-
ted for clarity, and the solvent molecule is not shown.
number being attained with the CCPPh3 ligand act-
ing as a six-electron donor. All bridging CO groups
are placed asymmetrically and the differences be-
tween the Co–C bond lengths in a bridge are 10 pm
[C(7)], 14 pm [C(10)], and 21 pm [C(9)]. The trian-
gular system can be compared with the basal Co3 core
of [Co4(CO)12] [25] or of [Co3(CO)9(µ3-CR)] com-
pounds [26] containing a µ-carbyne ligand; the ligand
arrangement along the Co(3)–Co(4) bond resembles
that of [Co2(CO)8] [27].
The Co–Co bond lengths in the basal Co3 plane
of 3 are slightly longer than in related compounds.
Two CO groups bridge edges of the basal Co3 trian-
gle, whereas the third one is bridging the spiked Co–Co
bond. Molecule 3 does not contain a plane of sym-
metry indicating chirality, and the unit cell is com-
posed of a pair of enantiomers. For the CCPPh3 lig-
and the unusual and not yet described µ4-η2 coordi-
nation is achieved, and its terminal C(2) atom is con-
nected to C(1) and all four cobalt atoms; to the latter
with nearly equal distances. The carbon atoms C(1)
and C(2) form a total of six bonds to Co atoms, and
the Co–C bond lengths vary between 198 and 209 pm.
With its lone pair of electrons, the carbon atom C(2)
bridges two Co atoms symmetrically, whereas in the
related iron complex [Fe3(CO)9(C2PPh3)] this carbon
atom is only connected to one further Fe atom resulting
in a µ3-η2 coordination mode for the CCPPh3 ligand.
353 pm. The cobalt atom in the anion [Co(CO)4]− is
in a distorted tetrahedral environment; the six C–Co–C
angles vary between 106.8 and 113.0◦, the mean Co–C
and C–O distances are 175.8 and 115.6 pm, respec-
tively. In the cation (HC{PPh3}2)+ the P(1)–C(5)–P(2)
angle amounts to 128.9◦ similar to that found in related
salts with this cation [23]. The difference between the
P–C distances to C(5) and to the phenyl carbon atoms
amounts to about 10 pm, and the shorter bond lengths
to the ylidic carbon atom indicate some double bond
character; however, relative to the neutral carbodiphos-
phorane C(PPh3)2, the presence of the proton at the
ylidic carbon atom C(5) leads to an increase of these
bond lengths by about 8 pm [2].
Molecular structure of 3
The cluster core is that of a spiked triangle (Fig. 1). The C(1)–C(2) bond length amounts to 136.4(4) pm
No close intermolecular contacts exist between the corresponding to an elongated olefinic double bond,
molecules. The cluster core is electronically precise and is longer than in the related trinuclear iron com-
with a total number of 64 CVE’s, the magic electron plex [132.5(8)] [12]; the same is true for the adja-
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W. Petz et al. · On the Reaction of C(PPh3)2 with [Co2(CO)8]
417
cent P–C(1) bond, which is slightly longer in the Experimental Section
cobalt complex. Thus, the µ4 coordination mode of
All operations were carried out under an argon atmo-
sphere in dried and degassed solvents using Schlenk tech-
niques. The solvents were thoroughly dried and freshly dis-
tilled prior to use. The IR spectra were run on a Nicolet
510 spectrometer. For the NMR spectra we used the in-
struments Bruker AMX 500 and AC 200. Elemental anal-
yses were performed by the analytical service of the Fach-
the CCPPh3 ligand leads to an increased electron re-
lease with respect to the µ3 mode. A similar µ4-η2
coordination was also found by us recently with the
CO ligand, but the arrangement of the metal atoms (2
lithium atoms at the oxygen atom and an Fe2 unit at
the carbon atom) differs markedly from that in 3 [28].
Thus, the µ4-η2 coordination of the CCPPh3 ligand bereich Chemie der Universita¨t Marburg (Germany). 1 was
prepared according to a modified literature procedure [31]
from (ClC{PPh3}2)Cl and P(NMe2)3. Commercially avail-
able [Co2(CO)8] was used without further purification.
found in 3 is unique. The C–C–P angle amounts to
137.0(3)◦ and is similar to that in [Fe3(CO)9(CCPPh3)]
[138.7(5)] but more acute than in [(CO)4Fe(CCPPh3)]
[162.1(3)] and [Br(CO)4Mn(CCPPh3)] [164.0(12)],
were CCPPh3 acts as a terminal ligand. Similar as
in solid [Co2(CO)8], the spiked Co–Co bond has two
bridges, one CO and one CCPPh3 group, and the
dihedral angle between the planes C(2)Co(3)Co(4)
and C(10)Co(3)Co(4) amounts to 130◦, which is
close to the dihedral angle in [Co2(CO)8] (127◦).
The PPh3 group at Co(4) is probably formed in the
reduction of OPPh3 with cobalt carbonyl species.
The Co–P distance corresponds to that in trans-
[(Ph3P)2Co2(CO)6] [29].
Formation of (HC{PPh3}2)[Co(CO)4] (2)
A solution of 1 (0.83 g, 1.60 mmol) in 100 mL of THF
was cooled to −78 ◦C. To this solution [Co2(CO)8] (0.66 g,
1.90 mmol) was added and the mixture was stirred for 2 h.
The dark red solution was allowed to warm to r. t.. After addi-
tional 2 h the mixture was filtered over diatomaceous earth.
In the 31P NMR spectrum of the solution only a singlet at
21.0 ppm was observed. The solution was layered with n-
pentane, and after several weeks colorless crystals of 2 were
obtained. Yield: 0.88 g (77 %). – IR (Nujol mull, cm−1): ν =
1888 vs br, 1483 m, 1439 s, 1337 w, 1312 w, 1225 m, 1186 m,
1103 s, 1009 w, 989 m, 804 w, 793 w, 760 w, 743 s, 716 s,
692 ws, 554 ws, 523 s, 503 m, 490 m.
Conclusion
With the exception of the carbonyl complexes
[(CO)2Ni(C{PPh3}2)] and [(CO)3Ni(C{PPh3}2)] no
carbonyl complexes of the type [(CO)xM(C{PPh3}2)]n
(M = group 6 to group 9 transition metals) containing
C(PPh3)2, 1, as a ligand could as yet be synthesized
and their structure confirmed by X-ray diffraction. This
is probably due to the poor π acceptor properties of 1
according to the occupied p orbital at the ylidic carbon
atom. Complexes of this type are probably formed as
reaction intermediates but appear to be strong bases
with the option to abstract protons from a variety of
solvents such as THF or CH2Cl2. The resulting proton
acceptor complex [(CO)xM(HC{PPh3}2)]n+1 is less
stable than the related silver complex [15] and decom-
Formation of [Co4(CO)10(PPh3)(µ4-CCPPh3)] (3)
To a suspension of 1 (1.00 g, 1.86 mmol) in 20 mL of
toluene, which was precooled to −78 ◦C, was added 0.636 g
(1.86 mmol) of [Co2(CO)8]. The mixture was stirred me-
chanically for about 1 h at this temperature and then allowed
to warm to r. t. and stirred for additional 5 h. A brownish
black reaction mixture was obtained, which was filtered from
some insoluble material. The 31P NMR spectrum of the solu-
tion showed two signals at 16.0 and 23.7 ppm in a 1 : 2 ratio.
◦
The solution was stored at −18 C for about two weeks to
afford reddish brown crystals of 3 · C7H8. Yield: ca. 0.04 g
(3 %). The crystals could not be redissolved in toluene. – IR
(Nujol mull, cm−1): ν = 2045 s, 2000 vs br, 1987 vs, 1948 vs,
1887 m br, 1839 s, 1819 s, 1800 s, 1605 vw, 1586 vw, 1572
position occurs with elimination of (HC{PPh3}2)+. vw, 1495 w, 1480 m, 1436 s, 1414 m, 1378 m, 1097 s, 746 m,
727 vs, 692 vs, 546 m, 520 vs. – C55H38Co4O10P2(1156.56):
Even the complexes [(CO)2Ni(C{PPh3}2)] and
calcd. C 57.10, H 3.31; found C 55,78, H 3.06.
[(CO)3Ni(C{PPh3}2)] are not stable in CH2Cl2 but
immediately produce the cation (HC{PPh3}2)+.
CCDC 628555 (2) and CCDC 628556 (3) contain the
supplementary crystallographic data for this paper. These
All attempts to isolate the related complex
data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data request/cif.
[(CO)4Fe(C{PPh3}2)] have failed [30]. Further
endeavors to find the appropriate conditions for the
preparation of [(CO)xM(C{PPh3}2)]n complexes (or
related species [(CO)xM(HC{PPh3}2)]n+1) for group
Acknowledgements
6 to 9 transition metals and to prove their structure by
X-ray diffraction are currently in progress.
Financial support of this work was provided by the
Deutsche Forschungsgemeinschaft. W. P. thanks the Max-
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418
W. Petz et al. · On the Reaction of C(PPh3)2 with [Co2(CO)8]
Planck-Society, Munich, Germany, for supporting this
research project.
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