Synthesis and structure of the first cobalt(I)-siloxide complex

Article abstract of DOI:10.1016/S0277-5387(01)00914-7

Synthesis, spectroscopic (¹H NMR, IR) characterisation and X-ray structure of the first cobalt(I)-siloxide complex, [Co(PPh₃)₃(OSiMe₃)] (I), have been presented. Complex I is synthesised by the reaction of [CoCl(PPh₃)₃] with trimethylsilanolate. The complex occupies a special position of the space group P3? on the three-fold axis passing through the Co, O and Si atoms. The coordination of cobalt is tetrahedral.

Full text of DOI:10.1016/S0277-5387(01)00914-7

Polyhedron 20 (2001) 3015–3018
www.elsevier.com/locate/poly
Synthesis and structure of the first cobalt(I)–siloxide complex
Ireneusz Kownacki, Maciej Kubicki, Bogdan Marciniec *
Faculty of Chemistry, Adam Mickiewicz Uni6ersity, Grunwaldzka 6, 60-780 Poznan, Poland
Received 29 June 2001; accepted 21 August 2001
Abstract
Synthesis, spectroscopic (1H NMR, IR) characterisation and X-ray structure of the first cobalt(I)–siloxide complex,
[Co(PPh3)3(OSiMe3)] (I), have been presented. Complex I is synthesised by the reaction of [CoCl(PPh3)3] with trimethylsilanolate.
(
The complex occupies a special position of the space group P3 on the three-fold axis passing through the Co, O and Si atoms.
The coordination of cobalt is tetrahedral. © 2001 Published by Elsevier Science Ltd.
Keywords: Siloxides; Cobalt(I); Crystal structures
1. Introduction
according to the following equation (yield 47%)
[21]:
Molecular and macromolecular compounds, incorpo-
rating MꢀOꢀSi groups (where M=metal), have at-
tracted great interest because of their wide application
[1] in material sciences and catalysis. Transition metal
siloxides can be regarded as very good molecular mod-
els of metal complexes supported on silica and silicate
surfaces [2,3].
According to a general idea presented by Wolczan-
ski, alkoxide and siloxide ancillary ligands are alterna-
tives to cyclopentadienyl complexes of transition
metals. Thanks to a more positive character of the
silicon atom when compared to carbon, siloxide ligands
are generally less basic than alkoxides, and therefore
can bind to a TM with slightly more ionic character [4].
Siloxy derivatives of the late transition metals, e.g.
ruthenium [5–9], rhodium [10–14], nickel [15], plat-
inum [16–18] and to a minor extent iron [19], osmium
[20], iridium [18], palladium [16] and cobalt [21] have
been synthesised and characterised, and the structures
of a few of them have been resolved by X-ray examina-
tions. A dimeric complex of cobalt(II), [Co(OSiPh3)2-
THF]2, was synthesised via a cobalt silylamide complex
[m-N(SiMe3)2CoN(SiMe3)2]2+4Ph3SiOH
“[{Co(m-OSiPh3)(OSiPh3)·THF}2]+4NH(SiMe3)2
X-ray studies revealed the structure of this dimeric
complex with two siloxy groups as bridging ligands.
Each cobalt has a distorted tetrahedral geometry due to
the coordination of one THF to each cobalt giving a
central Co2O6 core.
In this paper, we present a synthetic procedure, spec-
troscopic characterisation and X-ray crystal structure
of the first cobalt(I)–siloxide complex.
2. Experimental
2.1. General procedures
All manipulations were carried out using standard
Schlenk techniques under carefully deoxygenated and
dried argon. All solvents were freshly distilled in inert
atmosphere prior to use. Triphenylphosphine (Fluka
AG) and sodium trimethylsilanolate (Hulls-Petrarch)
were used as purchased. [CoCl(PPh3)3] was prepared
according to the literature [22].
NMR spectra were recorded in a Varian 300 MHz
instrument using 5 mm NMR tubes with silicon septa.
IR spectra were recorded using a Brucker instrument.
* Corresponding author. Tel.: +48-61-8291-366; fax: +48-61-
8291-508.
E-mail address: marcinb@main.amu.edu.pl (B. Marciniec).
0277-5387/01/$ - see front matter © 2001 Published by Elsevier Science Ltd.
PII: S0277-5387(01)00914-7

3016
I. Kownacki et al. / Polyhedron 20 (2001) 3015–3018
2.2. Synthesis of [Co(PPh3)3(OSiMe3)]
cooling device. The data collection was done in four
separate runs in order to cover the symmetry-indepen-
dent part of the reciprocal space. The ꢀ-scan was used
with the step of 0.75°, two reference frames were mea-
sured after every 50 frames and they did not show any
systematic changes neither in the peak position nor in
their intensities. A total of 532 frames was collected
giving 13 670 reflections up to 2q=60°. The unit-cell
parameters were determined by least-squares treatment
of the setting angles of 1414 highest-intensity reflec-
tions, chosen from the whole experiment. Lorentz and
polarisation corrections were applied [24], and then the
reflections were merged and corrected for absorption
(Amin=0.876, Amax=0.905) with SORTAV [25]. The
merging procedure gave 4172 unique data with Rint of
0.053. The analysis of the reflection file suggested that
the diffraction was negligible for the 2q angles greater
than 50°, and consequently, only the relevant subset
was used in further calculations. The structure was
solved by direct methods with the SHELXS-97 program
[26], and refined with full-matrix least-squares by
SHELXL-97 [27]. Non-hydrogen atoms were refined with
anisotropically positions, hydrogen atoms were gener-
ated geometrically and were refined as a ‘riding model’
with their Uiso parameters set at 1.2×Ueq of the appro-
priate carrier atom. Large residual electron density in
special position (0, 0, z) may be a diffraction ripple and
has not been accounted for. Selected geometric parame-
ters are listed in Table 1.
2.2.1. Synthetic procedure
Portions of 1 g (1.14 mmol) of [CoCl(PPh3)3] and
0.38 g (3.42 mmol) of NaOSiMe3 were placed in a
Schlenk vessel (cell, tube, flask in argon atmosphere).
To the mixture 8 ml of benzene (dried and deoxy-
genated) was added. The reaction was conducted for 6
h at room temperature, while stirring the contents with
a magnetic stirrer. After the reaction benzene was evap-
orated, 5 ml of pentane was added. The orange–brown
precipitate was washed three times with pentane by
decantation. The remaining precipitate was dissolved in
toluene and filtered through a cannula system. The
solution was concentrated and the desired complex was
precipitated by addition of pentane. The yield of the
complex was 75%.
FTIR (CsBr, cm−1): 3052, 2944, 1645.8, 1481,
1434.8, 1249.5, 989.6, 820.2, 740.6, 694.8, 509.5, 485.2,
1
452.7, 405.1, 302.9. H NMR (C6D6, l, ppm): 0.45 (s,
9H) broad, 7.06 (m, 27H) broad, 7.41 (m, 18H) broad.
Anal. Calc. for C57H54CoOP3Si: C, 73.22; H, 5.82.
Found: C, 72.39; H, 5.86%.
2.3. Crystal structure determination
Diffraction data from a colourless, plate-shaped crys-
tal of size 0.1×0.25×0.3 mm, sealed in a glass capil-
lary, were collected on
a
KUMA KM4CCD
Crystallographic data for [Co(PPh3)3(OSiMe3)]: em-
diffractometer [23] at 130(1) K, using graphite-
pirical formula: CoP3OSiC57H54, trigonal, space group
,
monochromated Mo Ka radiation (u=0.71073 A). The
3
(
,
,
,
P3, a=12.970(2) A, c=17.406(3) A, V=2535.8(7) A ,
temperature was controlled by an Oxford Cryosystem
Z=2, dx=1.224 g cm−3, v(Mo Ka)=0.49 mm−1
,
Table 1
F(000)=980, R(F) [Fo\4(Fo)]=0.048, R(F) [all
data]=0.069, wR(F2)=0.118, where w−1=[|2(Fo)2+
,
Selected bond lengths (A) and bond angles (°) for
[Co(PPh3)3(OSiMe3)] with e.s.d.s in parentheses
(0.05P)2+1.8P]−1
,
P=(Max(Fo2,0)+2Fc2/3), S=
1.15, (D/|)max=0.001 in the last cycle of refinement,
Bond lengths
−3
D|max=1.80 e A−3, D|min= −0.60 e A
.
,
,
Co(1)ꢀO(1)
Co(1)ꢀP(1)
O(1)ꢀSi(1)
Si(1)ꢀC(1)
P(1)ꢀC(11)
P(1)ꢀC(21)
P(1)ꢀC(31)
1.862(4)
2.2864(9)
1.605(4)
1.881(4)
1.836(3)
1.851(3)
1.841(3)
3. Results and discussion
The reaction of [CoCl(PPh3)3] with sodium trimethyl-
silanolate was used effectively for the preparation of the
corresponding phosphine cobalt–siloxide complex ac-
cording to the following equation:
Bond angles
O(1)ꢀCo(1)ꢀP(1)
P(1)ꢀCo(1)ꢀP(1)i
Si(1)ꢀO(1)ꢀCo(1)
O(1)ꢀSi(1)ꢀC(1)
C(1)ꢀSi(1)ꢀC(1)i
C(11)ꢀP(1)ꢀC(21)
C(11)ꢀP(1)ꢀC(31)
C(11)ꢀP(1)ꢀC(21)
C(31)ꢀP(1)ꢀC(21)
C(11)ꢀP(1)ꢀCo(1)
C(31)ꢀP(1)ꢀCo(1)
C(21)ꢀP(1)ꢀCo(1)
115.33(3)
103.03(3)
180.0
110.94(13)
107.97(12)
102.87(14)
105.28(14)
102.87(14)
96.88(13)
121.36(10)
111.92(10)
115.31(10)
[CoCl(PPh3)3]+NaOSiMe3
“[Co(PPh3)3(OSiMe3)]+NaCl
The X-ray structure of the molecule is shown in Fig.
1. Bond lengths, bond angles and torsion angles are
listed in Table 1. The complex occupies a special posi-
(
tion of the space group P3, on the three-fold axis
passing through the Co, O and Si atoms. The coordina-
tion of cobalt is tetrahedral; the Cambridge Crystallo-
(i): −x+y+1, −x+1, z.

I. Kownacki et al. / Polyhedron 20 (2001) 3015–3018
3017
known that tetrahedral Co(I) compounds are high-spin,
paramagnetic. Therefore, NMR study is not quite help-
1
ful. The width of a resonance line observed in the H
NMR spectrum was greater than 30 Hz and 31P, 29Si
NMR spectra could not be taken. Besides, complex I is
extremely sensitive in solution towards traces of air
(oxygen) and gets easily oxidised to Co(II)—blue com-
plexes. The IR spectrum shows a band at 982.6 consis-
tent with the (Co)ꢀOꢀSiMe3 bond.
4. Supplementary data
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 163776. Copies of this infor-
mation may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ (fax: +44-1223-336033; e-mail: deposit@ccdc.
cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Fig. 1. The thermal ellipsoid view of the complex (at 50% probability
level) with the numbering scheme [31]. The hydrogen atoms are
omitted for clarity.
graphic Database [28] search shows that this coordina-
tion dominates for four-coordinated neutral monomeric
cobalt complexes. For 602 fragments found in the
March 2001 edition of CDB there is approximately 4:1
preference of tetrahedral over square-planar coordina-
tion, with a number of intermediate or strange confor-
mations. In the present case, due to the internal
symmetry of the complex, the tetrahedron is only
slightly distorted. The CoꢀP and CoꢀO distances of
Acknowledgements
This work was supported by a project of the State
Committee for Scientific Research (no. K012/T09/
2000).
,
2.2867(8) and 1.863(3) A, respectively, agree well with
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