Bis{[diphenyl(piperidinomethyl)silyl]-methyl}cadmium and- magnesium

Article abstract of DOI:10.1107/S0108270102011307

The homoleptic and monomeric metal alkyls bis{[diphenyl(piperidinomethyl)silyl]methyl}cadmium, [Cd(C₁₉H₂₄NSi)₂] or [Cd{CH₂SiPh₂(CH₂NC₅H₁₀)} ₂], (I), and bis

Full text of DOI:10.1107/S0108270102011307

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
When compared with similar intramolecularly stabilized
structures, both (I) and (II) show rather small CÐMÐC
angles. In comparable structures (Henderson et al., 1986; Khan
et al., 1987; Schumann et al., 1998), these angles range from
ISSN 0108-2701
Bis{[diphenyl(piperidinomethyl)silyl]-
methyl}cadmium and -magnesium
Carsten Strohmann* and Daniel Schildbach
Institut fur Anorganische Chemie, Universitat Wurzburg, Am Hubland,
È
È
È
97074 Wurzburg, Germany
È
174 (3) to 166.2 (2)ꢀ, whereas in (I), the angle is found to be
more than 20ꢀ smaller (Table 1). In related Mg compounds, the
CÐMgÐC angle ranges from 147.68 (8) to 157.0 (7)ꢀ (Seidel
et al., 2001; Henderson et al., 1986); again, this angle is more
than 20ꢀ smaller in (II) (Table 2).
Correspondence e-mail: c.strohmann@mail.uni-wuerzburg.de
Received 18 June 2002
Accepted 24 June 2002
Online 20 July 2002
Another feature of these two compounds, as for other polar
[(aminomethyl)silylmethyl]metal compounds, is the length of
The homoleptic and monomeric metal alkyls bis{[diphenyl(pi-
peridinomethyl)silyl]methyl}cadmium, [Cd(C19H24NSi)2] or
[Cd{CH2SiPh2(CH2NC5H10)}2], (I), and bis{[diphenyl(piperi-
dinomethyl)silyl]methyl}magnesium, [Mg(C19H24NSi)2] or
[Mg{CH2SiPh2(CH2NC5H10)}2], (II), (CH2NC5H10 is piper-
idinomethyl) are isostructural, and the molecules exhibit
crystallographically imposed C2 symmetry. The metal centres
are located on special positions and, for each structure, half of
the molecule is located in the asymmetric unit. The metal
centres are intramolecularly coordinated and stabilized by two
piperidinomethyl groups (side-arm donation). The SiÐC and
MÐC bonds (M is Cd or Mg) are shortened compared with
the corresponding non-metallated compounds, indicating
stabilization by the diffuse polarizable Si centres (ꢀ effect).
The CÐMÐC angle is 140.53 (12)ꢀ in (I) and 123.39 (11)ꢀ in
(II).
Figure 1
A view of the molecule of (I), shown with 50% probability displacement
ellipsoids. H atoms are shown as small spheres of arbitrary radii. Primes
indicate atoms in the symmetry-related part of the molecule, at
Comment
We are interested in the synthesis of enantiomerically enri-
ched [(aminomethyl)silylmethyl]metal compounds bearing
metals which are essential for preparative organic and inor-
ganic chemistry. By the principle of side-arm donation, a chiral
amine can introduce stereochemical information into the
system and ®x (stabilize) the metal at the stereogenic metal-
lated carbon centre by intramolecular coordination. The
synthesis of compounds of this type starts from the corre-
sponding [(aminomethyl)silylmethyl]lithium compounds by
reaction with metal halides.
(
x; y; 12 z).
In a pre-study, we synthesized non-chiral bis{[diphenyl-
(piperidinomethyl)silyl]methyl}metal compounds to study
them in the solid state. We obtained two interesting molecules
of this type for the metals cadmium, (I), and magnesium, (II),
the metal centres being intramolecularly coordinated by two
piperidinomethyl groups. Compounds (I) and (II) are
isostructural and isomorphous. Through two MÐC and two
MÐN contacts (M is Cd or Mg), a spirocyclic system is
obtained, with Mg or Cd in the centre, exhibiting distorted
tetrahedral geometry at M.
Figure 2
A view of the molecule of (II), shown with 50% probability displacement
ellipsoids. H atoms are shown as small spheres of arbitrary radii. Primes
indicate atoms in the symmetry-related part of the molecule, at
(
x; y; 12 z).
Acta Cryst. (2002). C58, m447±m449
DOI: 10.1107/S0108270102011307
# 2002 International Union of Crystallography m447

metal-organic compounds
Data collection
the SiÐC bond between Si and the metallated carbon centre.
Since it is well known that Si centres have a stabilizing effect
on ꢀ-carbanionic centres (ꢀ effect), the SiÐC bond length
depends on the polarity of the MÐC bond. In a related non-
metallated (silylmethyl)amine (crystallized as an ammonium
Stoe IPDS diffractometer
' scans
Absorption correction: numerical
(FACEIT in IPDS; Stoe & Cie,
1997)
3736 independent re¯ections
3346 re¯ections with I > 2ꢅ(I)
Rint = 0.057
ꢃmax = 27ꢀ
h = 34 ! 34
Ê
Tmin = 0.810, Tmax = 0.868
17 317 measured re¯ections
k = 8 ! 8
salt), the SiÐC bond length is 1.914 (9) A (Strohmann et al.,
2002). The values in (I) and (II) (Tables 1 and 2) indicate a
much more polar MÐC bond in (II).
l = 25 ! 25
Re®nement
By the formal replacement of CH2 by SiPh2, the CÐCdÐC
angle decreases (accompanied by a shorter MÐN distance),
when (I) is compared with a similar structure reported by
Schumann et al. (1998). The same observation is made for the
CÐMgÐC angle of (II), considering related structures
reported by Seidel et al. (2001). Whether these interesting
angles are the result of electronic or steric effects emerging
from the presence of Si in the present structures still remains
to be established (e.g. by computational methods).
Re®nement on F2
R[F2 > 2ꢅ(F2)] = 0.039
wR(F2) = 0.103
S = 1.04
3736 re¯ections
w = 1/[ꢅ2(Fo2) + (0.0597P)2
+ 1.3741P]
where P = (Fo2 + 2Fc2)/3
(Á/ꢅ)max < 0.001
3
Ê
Áꢆmax = 1.71 e A
3
Ê
1.37 e A
291 parameters
All H-atom parameters re®ned
Áꢆmin
=
Table 1
Selected geometric parameters (A, ) for (I).
ꢀ
Ê
Experimental
CdÐC1
CdÐN
SiÐC1
2.202 (2)
2.5409 (17)
1.832 (2)
SiÐC2
SiÐC8
SiÐC14
1.880 (2)
1.892 (2)
1.912 (2)
A 1.7 M solution of t-BuLi in n-pentane (1.09 ml, 1.86 mmol) was
added to a solution of [(methyldiphenylsilyl)methyl]piperidine
(550 mg, 1.86 mmol) in n-pentane (4 ml) at 183 K. After warming to
room temperature, yellow crystals of {[(lithiomethyl)diphenylsilyl]-
methyl}piperidine (504 mg, 1.67 mmol, 90%) were isolated. These
crystals were dissolved in tetrahydrofuran (THF; 6 ml), and a
suspension of CdCl2 or [Mg(THF)4Br2] (0.835 mmol) in THF (2 ml)
was added at 183 K. The mixture was allowed to warm to room
temperature, the solvent was removed and toluene (5 ml) was added.
After removal of the lithium halide, compound (II) was crystallized
from toluene and compound (I) from toluene±n-pentane. The crystals
of both compounds were mounted at 173 K (N2 stream), using an
X-TEMP device (Kottke & Stalke, 1993).
C1iÐCdÐC1
C1iÐCdÐN
140.53 (12)
122.80 (8)
C1ÐCdÐN
NiÐCdÐN
84.56 (7)
97.15 (8)
Symmetry code: (i) x; y; 12 z.
Compound (II)
Crystal data
3
[Mg(C19H24NSi)2]
Mr = 613.27
Dx = 1.195 Mg m
Mo Kꢀ radiation
Cell parameters from 6000
re¯ections
ꢃ = 2.5±26.0ꢀ
ꢄ = 0.15 mm
T = 173 (2) K
Needle, colourless
0.6 Â 0.2 Â 0.1 mm
1
Spectroscopic data for (I): H NMR (400.1 MHz, toluene-d8, ꢁ,
2
p.p.m.): 0.06 (s, JH,Cd = 61.3 Hz, 4H, CdCH2Si), 1.13 (br, 4H,
Monoclinic, C2=c
Ê
a = 27.215 (5) A
NCCCH2C), 1.42±1.47 (m, 8H, NCCH2C), 2.28 (br, 12H, SiCH2N,
NCH2C), 7.14±7.27 (m, 12H, aromatic H), 7.71±7.73 (m, 8H, aromatic
Ê
b = 6.4100 (10) A
1
Ê
c = 19.576 (4) A
H); {1H}13C NMR (100.6 MHz, toluene-d8, ꢁ, p.p.m.): 11.7 (1JC,Cd
=
ꢂ = 93.38 (3)ꢀ
V = 3409.1 (11) A
Z = 4
3
503.1 Hz, CdCH2Si), 23.8 (NCCCH2C), 25.8 (NCCH2C), 51.6
(SiCH2N), 59.0 (NCH2C), 128.0 (C-meta), 128.8 (C-para), 134.7 (C-
ortho), 141.4 (C-ipso); {1H}29Si NMR (59.6 MHz, toluene-d8, ꢁ,
p.p.m.): 5.4 (2JSi,Cd = 35.0 Hz).
Spectroscopic data for (II): 1H NMR (300.1 MHz, THF-d8, ꢁ,
p.p.m.): 1.05 (s, 4H, MgCH2Si), 1.33±1.37 (m, 4H, NCCCH2C), 1.44±
1.49 (m, 8H, NCCH2C), 2.41±2.49 (m, 12H, SiCH2N, NCH2C), 7.54±
7.61 (m, 12H, aromatic H), 7.62±7.68 (m, 8H, aromatic H); {1H}13C
Ê
Data collection
Stoe IPDS diffractometer
' scans
Absorption correction: numerical
(FACEIT in IPDS; Stoe & Cie,
1997)
3223 independent re¯ections
2453 re¯ections with I > 2ꢅ(I)
Rint = 0.059
ꢃmax = 26ꢀ
NMR (75.5 MHz, THF-d8, ꢁ, p.p.m.):
16.5 (MgCH2Si), 24.9
h = 33 ! 33
Tmin = 0.905, Tmax = 0.975
13 184 measured re¯ections
k = 7 ! 7
(NCCCH2C), 27.4 (NCCH2C), 50.2 (SiCH2N), 59.6 (NCH2C), 128.0
(C-meta), 128.6 (C-para), 135.4 (C-ortho), 144.1 (C-ipso); {1H}29Si
NMR (59.6 MHz, THF-d8, ꢁ, p.p.m.): 9.0.
l = 22 ! 21
Compound (I)
Table 2
Selected geometric parameters (A, ) for (II).
ꢀ
Ê
Crystal data
3
[Cd(C19H24NSi)2]
Mr = 701.36
Monoclinic, C2=c
Dx = 1.351 Mg m
Mo Kꢀ radiation
Cell parameters from 7500
re¯ections
MgÐC1
MgÐN
SiÐC1
2.1816 (18)
2.2545 (17)
1.818 (2)
SiÐC2
SiÐC8
SiÐC14
1.886 (2)
1.895 (2)
1.9200 (19)
Ê
a = 27.277 (5) A
b = 6.4390 (10) A
Ê
c = 19.675 (4) A
ꢂ = 94.06 (3)ꢀ
V = 3447.0 (11) A
Z = 4
ꢃ = 2.5±27.0ꢀ
ꢄ = 0.73 mm
T = 173 (2) K
Ê
1
C1iÐMgÐC1
C1ÐMgÐNi
123.39 (11)
89.60 (7)
C1iÐMgÐN
NiÐMgÐN
124.81 (7)
107.02 (9)
3
Ê
Needle, pale yellow
0.5 Â 0.2 Â 0.2 mm
Symmetry code: (i) x; y; 12 z.
ꢁ
m448 Carsten Strohmann et al.
[Cd(C19H24NSi)2] and [Mg(C19H24NSi)2]
Acta Cryst. (2002). C58, m447±m449

metal-organic compounds
Re®nement
for ®nancial support. DS thanks the FCI for a doctoral
scholarship.
Re®nement on F2
R[F2 > 2ꢅ(F2)] = 0.044
wR(F2) = 0.115
S = 1.00
3223 re¯ections
291 parameters
All H-atom parameters re®ned
w = 1/[ꢅ2(Fo2) + (0.0760P)2]
where P = (Fo2 + 2Fc2)/3
(Á/ꢅ)max < 0.001
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: GD1214). Services for accessing these data are
described at the back of the journal.
3
Ê
Áꢆmax = 0.34 e A
3
Ê
0.38 e A
Áꢆmin
=
References
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Cie, 1997); cell re®nement: CELL in IPDS; data reduction: INTE-
GRATE in IPDS; program(s) used to solve structure: SHELXS90
(Sheldrick, 1990); program(s) used to re®ne structure: SHELXL97
(Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997);
software used to prepare material for publication: SHELXL97.
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È
Sheldrick, G. M. (1997). SHELXL97. University of Gottingen, Germany.
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È È È
Institut fur Anorganische Chemie der Universitat Wurzburg
ꢁ
Acta Cryst. (2002). C58, m447±m449
Carsten Strohmann et al.
[Cd(C19H24NSi)2] and [Mg(C19H24NSi)2] m449