A base-stabilized silylene with a tricoordinate silicon atom as a ligand for a metal complex

Article abstract of DOI:10.1021/ic900204c

Treatment of base stabilized silylene [PhC(Nt Bu)₂]SiOt Bu (1) with a tricoordinate silicon atom and diiron nonacarbonyl [Fe ₂(CO)₉] in tetrahydrofuran led to the formation of {[PhC(NBu)₂]SiOtBu}Fe-(CO)₄

Full text of DOI:10.1021/ic900204c

5058 Inorg. Chem. 2009, 48, 5058–5060
DOI: 10.1021/ic900204c
A Base-Stabilized Silylene with a Tricoordinate Silicon Atom as a Ligand
for a Metal Complex
Wei Yang,† Hao Fu,† Haijun Wang,† Mingqing Chen,† Yuqiang Ding,*,† Herbert W. Roesky,*,†,‡ and Anukul Jana‡
†School of Chemical and Material Engineering, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu Province
214122, People’s Republic of China, and ‡Institut fuer Anorganische Chemie der Universitaet Goettingen,
Tammannstrasse 4, D 37077 Goettingen, Germany
Received February 2, 2009
Treatment of base stabilized silylene [PhC(Nt Bu)2]SiOt Bu (1) with
a tricoordinate silicon atom and diiron nonacarbonyl [Fe2(CO)9] in
tetrahydrofuran led to the formation of {[PhC(NtBu)2]SiOt Bu}Fe-
(CO)4 (2), the first stable metal complex derived from a base-
stabilized tricoordinate silylene ligand. The solid-state structure and
bonding situation of 2 were investigated with single-crystal X-ray
diffraction and quantum chemical calculations.
synthesis and structures of the first monomeric heteroleptic
silylene [{PhC(NtBu)2}SiCl],4 and the derivatives [{PhC-
(NtBu)2}SiNMe2], [{PhC(NtBu)2}SiOR] (R = tBu, iPr),
and [{PhC(NtBu)2}SiPiPr2].5 The molecular structures of
these silylenes show that the Si(II) center is tricoordinate
(with two nitrogen atoms of the amidinato ligand and
another substituent) and has a trigonal-pyramidal geometry
with a lone pair of electrons and bonded with nearly pure
p orbitals. These molecular structures are quite different from
those of the dicoordinate NHSs.
In the past 20 years, the chemistry of stable N-heterocyclic
silylenes (NHSs) has attracted much attention,1 while the
N-heterocyclic carbenes have been proven to be a versatile
and important class of ligands.2,3 Recently, we reported the
Although various stable dicoordinate NHSs and their
metal complexes are known, no metal complex supported
by tricoordinate silylene was reported. We have recently been
intrigued by the question as to whether such tricoordinate
silylenes can act as ligands to stabilize metal complexes.
Therefore, tricoordinate silylene {PhC(NtBu)2}SiOtBu
(1) and diiron nonacarbonyl, Fe2(CO)9, were selected as a
probe to investigate their reaction behavior. In this paper, we
describe the preparation and characterization of the target
*To whom correspondence should be addressed. E-mail: hroesky@
gwdg.de.
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492.
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68–79. (b) Apeloig, Y.; Pauncz, R.; Karni, M.; West, R.; Steiner, W.;
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D. R.; West, R. J. Organomet. Chem. 2001, 636, 17–25.
(7) Silylene 1 was synthesized as published.5 THF (30 mL) was added to a
mixture of silylene 1 (0.057 g, 0.17 mmol) and diiron nonacarbonyl (0.076 g,
0.21 mmol) at ambient temperature under N2. After stirring for 40 h, the
initially light orange solution became darker in color to ultimately afford a
garnet brown solution. Solvent was then removed in vacuo, and the residue
was extracted with toluene (30 mL). The insoluble solid was filtered off. The
garnet brown filtrate was concentrated and stored at -30 °C to yield red-
brown crystals of 2 (72%).
(8) {[PhC(NtBu)2]SiOtBu}Fe(CO)4 (2). Mp: 203.6 °C. Anal. calcd (%) for
C23H32FeN2O5Si (M = 500.44): C, 55.20; H, 6.45; N, 5.60. Found (%): C,
55.27; H, 6.38; N, 5.66. 1H NMR(CDCl3): δ 1.25 (s, 18 H, CMe3), 1.51 (s, 9
H, OCMe3), 7.37-7.53 (m, 5H, Ph). 13C{1H} NMR (CDCl3): δ 31.39
(CMe3), 31.42 (OCMe3), 54.95 (CMe3), 77.03 (OCMe3), 127.88, 128.28,
128.36, 128.47, 130.08, 130.73 (Ph), 171.10 (NCN), 216.69 (CO). 29Si{1H}
NMR (CDCl3): δ 40.30. IR (cm-1, KBr) 2026 (m), 1949 (s), 1899 (s). Crystal
data: empirical formula C23H32FeN2O5Si, M = 500.45, monoclinic, space
group P2(1)/n, a = 9.1551(7) A, b = 16.6045(14) A, c = 17.2613(15) A, R =
90°, β = 91.710(2)°, γ = 90°, V = 2622.8(4) A3, Z = 4, Dcalcd = 1.267 mg/
m3, μ = 0.654 mm-1, λ = 0.71073 A, F(000) = 1056. Data in the range 1.70°
e θ e 28.31° were collected with graphite monochromated Mo KR radiation
(λ = 0.71073 A) at 293(2) K (6346 reflections). Final R1 = 0.0507, wR2 =
0.1096 for 3584 reflections with I > 2σ(I).
(4) (a) So, C.-W.; Roesky, H. W.; Magull, J.; Oswald, R. B. Angew. Chem.
2006, 118, 4052–4054. So, C.-W.; Roesky, H. W.; Magull, J.; Oswald, R. B.
Angew. Chem., Int. Ed. 2006, 45, 3948–3950.
r
2009 American Chemical Society
pubs.acs.org/IC
Published on Web 05/20/2009

Communication
Inorganic Chemistry, Vol. 48, No. 12, 2009 5059
Table 1. Selected Geometric Parameter by X-Ray Single-Crystal Diffraction and
Calculations at the B3LYP/6-31G* Level for Compound 2a
bond lengths (A)
exptl
B3LYP/6-31G*
Fe(1)-C(23)
Fe(1)-Si(1)
Si(1)-O(1)
Si(1)-N(1)
Si(1)-N(2)
1.758(4)
2.237(7)
1.602(2)
1.833(2)
1.838(2)
1.7653
2.2784
1.6415
1.8854
1.8855
bond angles (deg)
exptl
B3LYP/6-31G*
O(1)-Si(1)-N(1)
O(1)-Si(1)-N(2)
N(1)-Si(1)-N(2)
O(1)-Si(1)-Fe(1)
N(2)-Si(1)-Fe(1)
C(16)-O(1)-Si(1)
O(5)-C(23)-Fe(1)
C(23)-Fe(1)-Si(1)
110.6(8)
112.8(4)
71.1(6)
114.6(2)
119.1(9)
143.5(2)
176.5(3)
85.2(4)
111.78
111.79
70.09
115.76
119.74
145.54
179.79
86.19
Figure 1. Molecular structure of 2. Thermal ellipsoids are set at the 50%
probability level. H atoms are omitted for clarity.
Scheme 1. The Synthesis of Complex {[PhC(NtBu)2]SiOtBu}Fe(CO)4
(2)
a See Figure 1 for the atom numbering scheme.
Table 2. Natural Bond Orbital (NBO) Properties
a
Qp
atom
NEC (valence)b
Fe(1)
Si(1)
N(2)
C(1)
C(23)
O(1)
-1.35
1.08
-0.37
0.24
0.30
(4S)0.77(3d)8.22(4p)0.07(5S)0.01(4d)0.02(5p)0.26
(3S)1.26(3p)1.27
complex {[PhC(NtBu)2]SiOtBu}Fe(CO)4 (2), an example of
complex formation using a tricoordinate silylene ligand.
The synthetic procedure of 2 (Scheme 1) is similar to that of
the NHS analogue {(CHNtBu)2Si}Fe(CO)4.6,7 Treatment of
1 with 1.2 equiv of diiron nonacarbonyl, [Fe2(CO)9], in THF
for 40 h afforded complex 2. The solvent was then removed in
a vacuum, and the residue was extracted with toluene. The
insoluble solid was filtered off. The filtrate was concentrated
and stored at -30 °C to yield red-brown crystals of complex 2
suitable for X-ray diffraction study.8 Complex 2 was
(2S)1.46(2p)3.90
(2S)1.06(2p)2.70
(2S)1.40(2p)2.30
-0.43
(2S)1.72(2p)4.71
a NBO charge on selected atoms. b Natural electronic configuration
on selected atoms.
3 (2005 (w), 1920 (vs),1883 cm-l (vs)).9 The 13C NMR
chemical shift of the carbonyl group in 2 (216.69 ppm) is
similar to that observed for the NHS complex 4 (216.90 ppm)
with tricoordinate silicon atom.6 The 29Si NMR spectrum of
2 exhibits one singlet (40.30 ppm), which shows a low-field
shift when compared with that of 1 (-5.19 ppm) due to the
Lewis base properties of silicon, where electron density is
donated to the iron center. The chemical shift of 2 lies
between that of 3 (7.1 ppm)9 and the bis(amino)silylene metal
complex 4 (111.64 ppm).6 This indicates that the silicon
center of 2 is not purely sp2 hybridized but has also some
sp3 character. It is interesting to note that the silicon atom in
2 behaves like a Lewis base, while the silicon atoms in the
N-heterocyclic stable silylenes rather act as Lewis acids,
accepting electrons from the adjacent nitrogen atoms.
To examine the stability and bonding properties of this
stable tricoordinate silylene-transition metal complex, com-
pound 2 was investigated by means of quantum chemical
calculations (Tables 1-3), using B3LYP density functional
theory. The calculated structural parameters (Table 1) are in
good agreement with the crystallographic data and give
convincing support for quantum chemical analysis. The free
energy and thermal energy of the reaction for the synthesis of 2
are -118.02 kJ/mol and -127.09 kJ/mol, respectively. These
data show that 2 is stable and an easy-to-form compound.
The natural bond orbital analysis was carried out to explain
the bonding between Fe-Si and Si-O and to determine some
electronic properties characteristic for coordination to iron.12
1
characterized by elemental analyses; IR; and H, 13C, and
29Si NMR investigation. All of the data are in accordance
with the proposed formula of 2.
The solid-state structure of 2 as determined by single-
crystal X-ray diffraction is shown in Figure 1 with selected
bond lengths and angles. Figure 1 indicates that complex 2 is
monomeric. The silicon center is four-coordinate. The
sum of the angles N(1)-Si(1)-N(2), N(1)-Si(1)-O(1), and
N(1)-Si(1)-Fe(1) around the silicon center (333.2°) of 2
exhibits a distorted tetrahedral geometry.
The acute bond angle of N(1)-Si(1)-N(2) (71.16°) in 2
is a little larger than those of [{PhC(NtBu)2}SiCl] (68.4°),4
[{PhC(NtBu)2}SiNMe2] (68.3°), and [{PhC(NtBu)2}SiPiPr2]
(69.3°).5 The Si(1)-O(1) bond distance in 2 (1.602 A) is the
shortest compared to those of {(tBuO)2Si}Fe(CO)4 HMPT
3
(HMPT = hexamethylphosphoric triamide) (3) (1.610,
1.636, and 1.730 A)9 and of the siloxyl silylene [HC{C(Me)
NAr}2SiOSi(H){NArC(CH2)}{NArC(Me)}CH] (1.656 A).10
The Fe(1)-Si(1) bond distance in 2 (2.237 A) is slightly
longer when compared with that in the NHS complex
{Si[N(tBu)CH]2}Fe(CO)4 (4) (2.196 A)6,11 with tricoordinate
silicon atom but shorter than that in 3 (2.289 A).9
In the IR spectrum of 2, the CO stretching frequencies
(2026 (m), 1949 (s), 1899 cm-l (s)) are quite similar to those of
::
(9) Zybill, C.; Muller, G. Organometallics 1988, 7, 1368–1372.
::
(10) (a) Yao, S.; Brym, M.; Wullen, C. V.; Driess, M. Angew. Chem. 2007,
::
(12) Glendening, E. D.; Reed, A. E.; Carpenter, J. E.; Weinhold, F. NBO,
version 3.1; Theoretical Chemistry Institute, University of Wisconsin:
Madison, WI.
119, 4237–4240. Yao, S.; Brym, M.; Wullen, C. V.; Driess, M. Angew. Chem.,
Int. Ed. 2007, 46, 4159–4262.
(11) West, R.; Denk, M. Pure Appl. Chem. 1996, 68, 785–788.

5060 Inorganic Chemistry, Vol. 48, No. 12, 2009
Communication
Table 3. Selected Calculated Bond Types and Hybrid Descriptors
bond
occupancy
1.75384
MO1
Fe(1)
contr.a
type
MO2
Si(1)
contr.a
type
Fe(1)-Si(1)
51.63%
s(33.68%)
p0.08(2.85%)
48.37%
s(39.61%)
p1.52(60.39%)
d
1.88(63.47%)
Si(1)-O(1)
1.94217
Si(1)
26.34%
s(30.61%)
2.27(69.39%)
s(26.95%)
2.71(73.05%)
O(1)
N(2)
73.66%
78.22%
s(26.80%)
p2.73(73.20%)
s(3.77%)
p
Si(1)-N(2)
1.72829
1.88049
Si(1)
21.78%
28.14%
p
p25.55(96.23%)
s(60.40%)
s(58.81%)
Fe(1)-C(23)
Fe(1)
p
d
0.09(5.31%)
C(23)
71.86%
p0.66(39.60%)
0.61(35.88%)
a contr. = contribution.
The natural charge (Qp; Table 2) shows the charge on the
atoms. The natural electron configuration gives the effective
valence electron configuration for the atoms. Table 3 lists the
selected calculated bond types and hybrid descriptors. The
calculated bond can be described as c1 Â hybrid1 + c2 Â
hybrid2, where the coefficients c1 and c2 denote the polariza-
tion coefficient. The calculated Fe-Si bond is 0.7186 Â
sp0.08d1.88(Fe) + 0.6955 Â sp1.52(Si), whereas the calculated
Si-O bond is 0.5133 Â sp2.27(Si) + 0.8582 Â sp2.73(O). From
the polarization coefficient, greater electronic density can be
found on Fe than on Si.
The solid-state structure and bonding situation of 2 were
investigated with single-crystal X-ray diffraction and quan-
tum chemical calculations.
Acknowledgment. This work was supported by the
National Natural Science Foundation of China (No.
20571033) and by the Program for New Century Excel-
lent Talents in University (NCET-06-0483) and the
Deutsche Forschungsgemeinschaft.
Supporting Information Available: Further details of the
synthesis and characterization, figures, and X-ray structural
information (CIF) for complex 2. This material is available free
of charge via the Internet at http://pubs.acs.org.
In summary, we succeeded in the synthesis and character-
ization of {[PhC(NtBu)2]SiOtBu}Fe(CO)4 (2), the first stable
metal complex containing a tricoordinate silylene as a ligand.