Homoleptic silyl complexes of arsenic and antimony

Article abstract of DOI:10.1016/S0277-5387(00)00446-0

Several homoleptic silyl complexes of arsenic(III) and antimony(III), namely As(SiR₂R')₃ (R = Me, R'= cyclohexyl (Cy); R = Me, R' = Ph; R = R' = Ph) and Sb(SiPh₃)₃, have been prepared via salt elimination reactions of R₂R'SiCl and Na₃E (E = As or Sb). The structures of two complexes, As(SiMe₂Cy)₃ and Sb(SiPh₃)₃, have been determined by X-ray crystallography. Both structures possess a three-coordinate Group 15 element centre with a pyramidal geometry of the ESi₃ core. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(00)00446-0

www.elsevier.nl/locate/poly
Polyhedron 19 (2000) 1639–1642
Homoleptic silyl complexes of arsenic and antimony
Claire J. Carmalt a,*, Jonathan W. Steed b
a Department of Chemistry, Christopher Ingold Laboratories, Uni6ersity College London, 20 Gordon Street, London, WC1H 0AJ, UK
b Department of Chemistry, Kings College London, Strand, London, WC2R 2LS, UK
Received 18 February 2000; accepted 19 May 2000
Abstract
Several homoleptic silyl complexes of arsenic(III) and antimony(III), namely As(SiR2R%)3 (R=Me, R%=cyclohexyl (Cy);
R=Me, R%=Ph; R=R%=Ph) and Sb(SiPh3)3, have been prepared via salt elimination reactions of R2R%SiCl and Na3E (E=As
or Sb). The structures of two complexes, As(SiMe2Cy)3 and Sb(SiPh3)3, have been determined by X-ray crystallography. Both
structures possess a three-coordinate Group 15 element centre with a pyramidal geometry of the ESi3 core. © 2000 Elsevier
Science Ltd. All rights reserved.
Keywords: Homoleptic silyl complexes; Arsenic; Antimony
1. Introduction
limited to E2(SiMe3)4 (E=As or Sb) [16,17] and the
lithiumꢀarsenide and antimonide salts, [Li(L)n]-
[E(SiMe3)2] (where n=1, E=As or Sb, L=DME;
n=2, E=As, L=thf) and [Li(thf)2][As(SiPri3)(SiFAr2)]
(Ar=2,4,6-triisopropylphenyl) [18–20]. The only ex-
amples of structures of tris(silyl)arsenic and antimony
There has been a significant amount of interest in the
chemistry of silyl complexes of arsenic(III) and antimo-
ny(III) over the last few decades. These compounds, in
combination with Group 13 species (e.g. halides and
alkyls), are excellent starting materials for preparing
molecules containing Group 13 element-arsenic or -an-
timony bonds [1]. Such compounds have attracted a
great deal of attention due to their potential applica-
tions as single-source precursors for the deposition of
thin films of the corresponding semiconductor material
by organometallic chemical vapour deposition (OM-
CVD) [1,2]. Silylarsines have also been used for the
preparation of inter-Group 15 element phases [3].
Tris(silyl)arsenic and antimony complexes were first
synthesised about 30 years ago [4–10], with further
developments occurring some years later [11–15]. Al-
though there have been studies into the synthesis and
reactivity of silyl Group 15 complexes [4], structural
characterisation of these compounds have emerged only
very slowly. Until recently, single crystal X-ray diffrac-
tion studies of silyl complexes of As and Sb were
complexes
include
As(SiMe2But)3
(1)
[21],
As(SiMe3)2(SiPh3) (2) [21], and Sb(SiMe2Ph)3 (3) [22].
In this contribution, we present the synthesis and
characterisation of a series of tris(silyl) complexes of
arsenic(III) and antimony(III). Our motivation was to
explore further the structural characteristics of these
complexes and to isolate a range of stable silyl
complexes.
2. Results and discussion
The reaction between Na3As (generated in situ from
arsenic powder and sodium metal in thf) and
chlorodimethylcyclohexylsilane in thf at reflux tempera-
ture afforded, after work-up, colourless crystals of the
complex As(SiMe2Cy)3 (4) (Cy=cyclohexyl), according
to Eq. (1):
Na3E+3R2R%SiCl“E(SiR2R%)3+3NaCl
(1)
* Corresponding author. Tel.: +44-20-7679-7528; fax: +44-20-
7679-7463.
E-mail address: c.j.carmalt@ucl.ac.uk (C.J. Carmalt).
4; E=As, R=Me, R%=Cy
5; E=As, R=Me, R%=Ph
0277-5387/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(00)00446-0

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C.J. Carmalt, J.W. Steed / Polyhedron 19 (2000) 1639–1642
6; E=As, R=Ph, R%=Ph
7; E=Sb, R=Ph, R%=Ph
Similar methods for the preparation of other tris(si-
lyl)arsenic complexes have been described previously
[14,15]. Spectroscopic and analytical data were consis-
tent with the anticipated formula of 4 and the structure
was confirmed by X-ray crystallography, the results of
which are shown in Fig. 1. Selected bond lengths and
angles are given in Table 1. The solid state structure of
4 consists of individual molecules with no unusually
short intermolecular contacts between the monomeric
units. Although not required crystallographically, indi-
vidual molecules of 4 possess approximate C3 symme-
try. The geometry about the arsenic centre is pyramidal
[av. SiꢀAsꢀSi 101.6(3)°] with the average AsꢀSi bond
Fig. 2. Molecular structure of compound 7 showing the atom num-
bering scheme. Atoms are drawn as 30% probability ellipsoids. Hy-
drogen atoms are omitted for clarity.
,
length of 2.361(7) A being similar to those observed in
1 and 2 [21]. The relative orientation of the three
dimethylcyclohexylsilyl groups at the arsenic centre is
all-staggered with each cyclohexyl group placed be-
tween two methyl groups of a neighbouring silyl group.
As such, the structure is similar to that observed for 1
[21] and the related antimony complex Sb(SiMe2Ph)3
(3) [22].
A similar reaction between Na3As and chlorodime-
thylphenylsilane in thf at reflux temperature afforded,
after work-up, colourless crystals of the complex
As(SiMe2Ph)3 (5) (Eq. (1)). Spectroscopic and analyti-
cal data for 5 were consistent with the expected for-
mula. Unfortunately, an attempted crystal structure
determination was only partially successful due to dis-
order problems. However, the structure of 5 is appar-
ently similar to that of compound 1 [21], 4 and the
related antimony derivative 3 [22].
The analogous reaction between Na3As and chlorot-
riphenylsilane in thf at reflux temperature (Eq. (1))
resulted in a cream crystalline solid, spectroscopic and
analytical data for which were consistent with the for-
mula As(SiPh3)3 6. Unfortunately X-ray quality crystals
of 6 could not be isolated. Interestingly, previous at-
tempts to prepare 6 and the antimony analogue,
Sb(SiPh3)3 (7), via the reaction between 3 equivalents of
triphenylsilyllithium and the appropriate element(III)
chloride were reported to be unsuccessful [23]. How-
ever, compound 7 has reportedly been prepared from
the reaction of SbEt3 and 3 equivalents of triphenylsi-
lane, although 7 was poorly characterised [9]. A related
reaction between Sb(SiEt3)3 and 3 equivalents of
triphenylsilane was also reported to result in the forma-
tion of 7; no characterisation of this material was
published [7]. However, compound 7 can be prepared in
a similar manner to the arsine complexes 4–6 as de-
scribed in Section 3. Spectroscopic and analytical data
for 7 were consistent with the expected formula and the
structure was confirmed by X-ray crystallography, the
results of which are shown in Fig. 2. Selected bond
distances and angles are given in Table 1. The solid
state structure of 7 consists of individual molecules with
no unusually short intermolecular contacts between the
monomeric units. Although not required crystallo-
graphically, individual molecules of 7 possess approxi-
Fig. 1. Molecular structure of compound 4 showing the atom num-
bering scheme. Atoms are drawn as 30% probability ellipsoids. Hy-
drogen atoms are omitted for clarity.
Table 1
,
Selected bond distances (A) and angles (°) for 4 and 7
As(SiMe2Cy)3 (4)
Sb(SiPh3)3 (7)
Bond lengths
As(1)ꢀSi(1)
As(1)ꢀSi(2)
As(2)ꢀSi(3)
2.3567(8)
2.3609(7)
2.3664(7)
Sb(1)ꢀSi(1)
Sb(1)ꢀSi(2)
Sb(1)ꢀSi(3)
2.5977(12)
2.5992(12)
2.6037(12)
Bond angles
Si(1)ꢀAs(1)ꢀSi(2) 102.22(3)
Si(1)ꢀAs(1)ꢀSi(3) 100.94(3)
Si(2)ꢀAs(1)ꢀS(3) 101.74(3)
Si(1)ꢀSb(1)ꢀSi(2)
Si(1)ꢀSb(1)ꢀSi(3)
Si(2)ꢀSb(1)ꢀS(3)
103.33(4)
110.09(4)
106.48(4)

C.J. Carmalt, J.W. Steed / Polyhedron 19 (2000) 1639–1642
1641
mate C3 symmetry. The geometry about the antimony
centre is pyramidal [av. SiꢀSbꢀSi 106.60(4)°] with the
crystals of naphthalene were added. THF (40 ml) was
added and the resulting black slurry was heated at reflux
for 24 h. After cooling to r.t. chlorodimethylcyclohexyl-
silane (8 ml, 43.2 mmol) was added dropwise with stirring
and the reaction mixture was refluxed for a further 12 h.
The resulting black slurry was cooled to r.t. and pumped
to dryness in vacuo. Toluene (40 ml) was added to the
remaining black–grey solid and the mixture was filtered
through Celite. The volume of the filtrate was reduced
to ca. 15 ml and cooling of this solution to −20°C
afforded a 67% yield of colourless crystalline 4. M.p.
,
average SbꢀSi bond length of 2.600(12) A being slightly
,
longer than that observed in 3 [av. SbꢀSi 2.559 A] [22].
The greater deviation from ideal tetrahedral coordina-
tion geometry and the longer SbꢀSi bond lengths ob-
served in 7 are probably a result of the increased steric
requirements of the Ph3Si ligand. A similar effect was
noted on comparison of the AsꢀSi bond distances and
SiꢀAsꢀSi angles in compounds 1 and 2 [21].
In conclusion, several homoleptic silyl arsenic(III) and
antimony(III) compounds have been synthesised and
characterised. Two of the compounds, As(SiMe2Cy)3 and
Sb(SiPh3)3 were structurally characterised. Complexes
4–7 are possible precursors for the preparation of
arsenides and antimonides and the reactivity of these
complexes is currently being investigated.
1
80–82°C. H NMR (CDCl3): l 0.29 (s, 18H, SiMe2),
0.72–1.83 (m, 33H, SiCy). 13C{1H} NMR (CDCl3): l
0.01 (SiMe2), 26.8, 27.7, 28.1, 28.4 (SiCy). CIMS: m/z 499
[M+], 359 [M+−SiMe2Cy]. Anal. Calc. for C24H51AsSi3:
C, 57.79; H, 10.30. Found: C, 57.48; H, 10.44%.
3.3.2. Compound 5
Yield: 52% of colourless crystalline 5. M.p. 122–
124°C. 1H NMR (CD2Cl2): l 0.35 (s, 18H, SiMe2),
7.25–7.55 (m, 15H, SiPh). 13C{1H} NMR (CDCl3): l 1.7
(SiMe2), 127.5 (m-C of SiPh), 128.8 (p-C of SiPh), 133.7
(o-C of SiPh3), ipso carbon not detected. CIMS: m/z 481
[M+]. Anal. Calc. for C24H33AsSi3·0.5CH2Cl2: C, 56.25;
H, 6.55. Found: C, 56.25; H, 6.54%.
3. Experimental
3.1. General procedures
All manipulations were performed under a dry, oxy-
gen-free dinitrogen atmosphere using standard Schlenk
techniques or in a MBraun Unilab glove box. All solvents
were distilled from appropriate drying agents prior to use
(sodium–toluene and hexanes; potassium–THF; CaH2
for CH2Cl2). All other reagents were procured commer-
cially from Aldrich and used without further purification.
Microanalytical data were obtained at University College
London.
3.3.3. Compound 6
Yield: 65% of pale yellow crystalline 6. M.p. 180°C
1
(dec.). H NMR (CDCl3): l 6.98–7.30 (m, 45H, SiPh3).
13C{1H} NMR (CDCl3): l 127.2 (m-C of SiPh3), 128.8
(p-C of SiPh3), 136.2 (o-C of SiPh3), ipso carbon not
detected. CIMS: m/z 853 [M+], 595 [M+−SiPh3]. Anal.
Calc. for C54H45AsSi3: C, 76.03; H, 5.32. Found: C,
75.98; H, 5.45%.
3.2. Physical measurements
3.3.4. Compound 7
NMR spectra were recorded on Bru¨ker AMX300 or
DRX500 spectrometers at UCL. The NMR spectra are
referenced to CD2Cl2 or CDCl3, which were degassed and
Yield: 58% of colourless crystalline 7. M.p. 127°C
(dec.). 1H NMR (CD2Cl2): l 6.87–7.54 (m, 45H, SiPh3).
13C{1H} NMR (CDCl3): l 126.2 (m-C of SiPh3), 128.2
(p-C of SiPh3), 135.5 (o-C of SiPh3), ipso carbon not
detected. CIMS: m/z 901 [M+]. Anal. Calc. for
C54H45SbSi3: C, 72.07; H, 5.04. Found: C, 72.61; H,
5.08%.
1
dried over molecular sieves prior to use; H and 13C
chemical shifts are reported relative to SiMe4 (0.00 ppm).
Mass spectra (CI) were run on a micromass ZABSE
instrument, and IR spectra on a Nicolet 205 instrument.
Melting points were obtained in sealed glass capillaries
under argon and are uncorrected.
3.4. Structure determinations
3.3. Preparations
Crystals of 4 and 7 were mounted on a glass fibre using
silicones grease and cooled on the diffractometer. Crys-
tallographic measurements were carried out with a No-
nius Kappa CCD diffractometer equipped with
graphite-monochromated Mo Ka radiation using a com-
bination of ƒ and ꢀ scans with 2° frames and a
detector-to-crystal distance of 30 mm. Integration was
carried out by the program DENZO-SMN [24]. Data sets
were corrected for Lorentz and polarisation effects and
for the effects of absorption using the program
SCALEPACK [24]. The structure was solved using the
All of the compounds were synthesised by the same
general procedures, hence only one example is described
in detail below.
3.3.1. Synthesis of compound 4
A mirror of sodium metal is generated on the inner
surface of a Schlenk flask by heating and stirring sodium
(1.00 g, 43.5 mmol). After cooling to room temperature
(r.t.) arsenic powder (1.09 g, 14.5 mmol) and a few

1642
C.J. Carmalt, J.W. Steed / Polyhedron 19 (2000) 1639–1642
Table 2
References
Crystallographic data for 4 and 7
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4
7
Empirical formula
Crystal system
Space group
C24H51AsSi3
triclinic
P1
C
58H50ClSbSi3
monoclinic
P21/n
13.3164(6)
21.6196(7)
17.6477(8)
90
109.198(3)
90
4798.1(3)
1.368
(
,
a (A)
6.3863(3)
14.2940(6)
16.1607(8)
72.897(3)
89.005(3)
88.017(3)
1409.12(11)
1.176
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
Dcalc (g cm−3
)
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T (K)
2
4
100(2)
0.71073
10474
100(2)
0.71073
23285
,
u (A)
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Reflections collected
No. unique reflections
Crystal size (mm)
6451
9011
0.80×0.15×0.10
2.64–27.50
0.0429
0.40×0.10×0.10
2.48–26.00
0.0519
q Range (°)
a
R
(I\2|(I))
wR% b (I\2|(I))
0.0837
0.1008
a R=S(DF)/S(Fo).
b wR%=[S{w(DF2)2}/S{w(Fo2)2}]1/2 w=1/[|2(Fo2)+(aP)2] where
.
P=[max(Fo2)+2(Fc2)]/3 and a=0.0003.
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those of the atom to which they were attached. All
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4. Supplementary material
Crystallographic data have been deposited with the
CCDC and are available on request from: The Direc-
tor, CCDC, 12 Union Road, Cambridge, CB2 1EZ,
UK (fax: +44-1223-336033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk) by quoting
the deposition numbers 140720 and 140721.
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Acknowledgements
C.J.C. is grateful to the Royal Society for a Dorothy
Hodgkin fellowship and financial support. We thank
Kings College London and EPSRC for provision of the
diffractometer system. Dr D. Tocher is thanked for his
assistance with X-ray crystallography.