The stable silylene Si[(NCH2But)2C 6H4-1,2]: Reactions with Group 14 element halides

Article abstract of DOI:10.1016/j.jorganchem.2005.10.027

Reaction of the thermally stable silylene Si[(NCH₂Bu ^t)₂C₆H₄-1,2] (1) [abbrev. as Si(NN)] with SiX₄ (X = Cl or Br) afforded the disilanes (NN)SiX(SiX ₃) and [(NN)SiX]₂ (X = Br only), the trisilane (NN)SiX-[(SiX₃)Si(NN)] and the monosilane (NN)SiX₂ (X = Br only), whereas treatment of 1 with MCl₄ (M = Ge or Sn) yielded (NN)SiCl₂ and MCl₂. [(NN)SiBr]₂ and (NN)SiBr₂ were also obtained by reaction of 1 with Br₂. Reaction of 1 with PhSiCl₃ yielded the disilane (NN)SiCl(SiCl ₂Ph) and trisilane [(NN)SiCl]₂SiClPh, whereas the disilane (NN)SiCl(SiCl₂Me) was obtained with MeSiCl₃. The trisilane (NN)SiCl-[(SiCl₃)Si(NN)] was thermally labile and converted to [(NN)SiCl]₂SiCl₂.

Full text of DOI:10.1016/j.jorganchem.2005.10.027

Journal of Organometallic Chemistry 691 (2006) 811–816
www.elsevier.com/locate/jorganchem
Note
The stable silylene Si[(NCH2But)2C6H4-1,2]: Reactions with
Group 14 element halides
*
Barbara Gehrhus , Peter B. Hitchcock, Helen Jansen
Department of Chemistry, School of Life Sciences, University of Sussex, Brighton BN1 9QJ, UK
Received 24 September 2005; received in revised form 15 October 2005; accepted 15 October 2005
Available online 29 November 2005
Abstract
Reaction of the thermally stable silylene Si[(NCH2But)2C6H4-1,2] (1) [abbrev. as Si(NN)] with SiX4 (X = Cl or Br) afforded the
disilanes (NN)SiX(SiX3) and [(NN)SiX]2 (X = Br only), the trisilane (NN)SiX-[(SiX3)Si(NN)] and the monosilane (NN)SiX2 (X = Br
only), whereas treatment of 1 with MCl4 (M = Ge or Sn) yielded (NN)SiCl2 and MCl2. [(NN)SiBr]2 and (NN)SiBr2 were also obtained
by reaction of 1 with Br2. Reaction of 1 with PhSiCl3 yielded the disilane (NN)SiCl(SiCl2Ph) and trisilane [(NN)SiCl]2SiClPh, whereas
the disilane (NN)SiCl(SiCl2Me) was obtained with MeSiCl3. The trisilane (NN)SiCl-[(SiCl3)Si(NN)] was thermally labile and converted
to [(NN)SiCl]2SiCl2.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Silylene; Insertion; Group 14 halides; Disilane; Trisilane
1. Introduction
2. Results and discussion
The chemistry of stable silylenes is now well estab-
lished [1–3]. In recent years stable silylenes have been
shown to extend the scope of insertion reactions of tran-
sient silylenes, including insertions into M–N (M = Li,
Na, K) [4,5], Li–C [6], Li–Si [4], B–C [7], C–X
(X = Cl, Br) [3,8,9], M(II)–N (M = Si, Ge, Sn, Pb)
[10–13], Sn(II)–C [14], Sn(II)–Cl [15], O–H [16,17], and
Si–Cl [18] bonds. The silylene Si[(NCH2But)2C6H4-1,2]
[19] 1 [abbr. Si(NN)] also inserted into the M–Cl bond
of [MCl2(PPh3)2], concomitant with PPh3 ligand replace-
ment, leading to trans-[M{Si(NN)}2{Si(NN)Cl}2] (M =
Pd, Pt) [20].
The reaction of the silylene Si[(NCH2But)2C6H4-1,2] (1)
[abbr. as Si(NN)] with SiCl4 proceeded under mild condi-
tions and yielded as the main product the trisilane 2, irre-
spective of the relative molar ratio of the reactants.
Furthermore, in an NMR spectroscopic experiment, 1
was treated with an excess of SiCl4; the reaction mixture
showed as the major component compound 2 but also of
another product assigned as compound 3 on the basis
1
of the H and 29Si NMR spectral data (Scheme 2). The
trisilane 2 was thermally labile, being converted into the
trisilane 4 upon heating.
Treatment of a solution of 1 in C6D6 with an excess of
SiBr4 (NMR experiment) afforded a product mixture of
the trisilane 5, the disilanes 6 and 7 and the silane
(NN)SiBr2 in a ratio 1.5:2.1:1.0:2.2, respectively (Scheme
2). Alternatively, when a solution of 1 was slowly added
to an excess of SiBr4 the ratio of 5:6:7:(NN)SiBr2 was
1.7:1.1:1:5.5. Additionally, a 29Si NMR spectral signal at
d À35.7 showed the presence of (SiBr3)2 [21]. Compound
5 was independently obtained by reaction of 1 with 1/2
Reactions of stable silylenes with compounds contain-
ing a Group 14 element-halogen bond include the
insertion into a Si–Cl [18] or Sn(II)–Cl [15] bond
(Scheme 1).
*
Corresponding author.
E-mail address: b.gehrhus@sussex.ac.uk (B. Gehrhus).
0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.10.027

812
B. Gehrhus et al. / Journal of Organometallic Chemistry 691 (2006) 811–816
SiMe3
SiMe3
SiR3
Cl
SiMe3
Me3Si
Me3Si
Me3Si
R3SiCl
R3Si = Me2SiCl, SiCl3, SiH2Cl
Si
Si
Me3Si
SiMe3
But
+ (N'N')SiCl
+
+ Sn(0)
[(N'N')SiCl]2
(N'N')Si
2
N
2 SnCl2
[(N'N')SiCl]3SnCl
Si
-Sn(0)
h
N
But
[(N'N')SiCl]2
Sn(0)
+
+ SnCl2
[≡
Si(N'N')]
Scheme 1.
SiCl3
Cl3Si
Cl
SiCl4
+
(NN)Si
(NN)Si
Si(NN)
Cl
3
2
Cl Cl Cl
(NN)Si Si
Si(NN)
4
Cl
CH2But
N
Br
Br
Si(NN)
Br3Si
Br
SiBr3
Br
SiBr4
+ (NN)SiBr2
(NN)Si
(NN)Si
Si(NN)
+
Si
(NN)Si
+
7
N
6
5
CH2But
1
[≡
Si(NN)]
Br2
7 + (NN)SiBr2
GeCl4
SnCl4
(NN)SiCl2 + (GeCl2) + unidentified products
(NN)SiCl2
+ SnCl2
SiPhCl2
(ex) PhSiCl3
(NN)Si
8
Cl
Si(NN)
CH2But
N
Ph
Cl
Si
½ PhSiCl3
Si
8 (minor)
+
(NN)Si
Cl
Si(NN)
N
9
Cl
CH2But
1
[≡
Si(NN)]
SiMeCl2
MeSiCl3
(NN)Si
10
Cl
Scheme 2.
an equivalent of SiBr4. Compounds 7 and (NN)SiBr2 were
identified by comparison of spectral data with those of the
products from the reaction of 1 with bromine (Scheme 2).
Reaction of 1 with the heavier Group 14 metal chlorides
MCl4 (M = Ge or Sn) afforded as the major compound the
dichlorosilane (NN)SiCl2 [19] and a precipitate which from
GeCl4 is believed to have been GeCl2 by analogy with the for-
mation of SnCl2 in the reaction of 1 with SnCl4 (Scheme 2).
Reaction of 1 with the chlorosilane PhSiCl3 or MeSiCl3
(Scheme 2) needed more vigorous conditions. Thus, the

B. Gehrhus et al. / Journal of Organometallic Chemistry 691 (2006) 811–816
813
disilane 8 or the trisilane 9 were formed at 100 °C over a
period of two days. The formation of 8 or 9 was dependent
on the relative ratios of the reactants. Silylene 1 gave 8 with
an excess of PhSiCl3, but compound 9 was the major prod-
uct from 2(1) + PhSiCl3. Additionally, it was shown that 8
is a precursor for 9 in the reaction of 8 with 1. The reaction
of 1 with MeSiCl3 afforded the disilane 10. Attempted puri-
fication of 10 by distillation led to its partial decomposition
to H(Cl)Si[(NCH2But)2C6H4-1,2] 10a. No reaction was
observed between 1 and Me3SiCl.
substituents in a gauche relationship. The Si(1)–Si(2)
˚
[2.4025(6) A] is slightly longer than the Si(2)–Si(3)
˚
[2.3817(6) A] bond; these data may be compared with the
Si–Si bonds in related (NN)Si(R1)–(R2)Si(NN) compounds
1
2
t
1
2
˚
{R = R = Bu 2.465(7) A [6]; R = Cl, R = Pr 2.3652
1
2
˚
˚
(7) A [9]; R = Cl, R = CH2Cl 2.362(2) A [9]}.
The formation of the disilanes 2 and 5 is believed to pro-
ceed by a similar radical pathway that led to the disilanes
(NN)Si(X)–(R)Si(NN) (X = Cl or Br, R = alkyl) from 1
and an alkyl halide [3,9]. Scheme 3 shows this pathway,
adapted from the proposal by McKee et al. [22] for the
reaction of a bis(amino)silylene with an alkyl halide.
The formation of 7 and (SiBr3)2 can be explained by
dimerisation of the (NN)Si(Br) and the SiBr3 radical gener-
ated in path (a), (c) or (d), respectively, in Scheme 3.
(NN)SiBr2 is proposed to form by the halogen abstraction
of (NN)Si(Br) from SiBr4.
Compounds 2–10 have been fully characterised by mul-
tinuclear NMR spectroscopy. The structure of 2 was also
confirmed by X-ray structural analysis (Fig. 1). Viewing
the molecule along the Si–Si bond shows the Cl and SiCl3
The pathway to the trisilane 4 is believed to proceed by
extrusion of 1 from 2 (a-elimination [23,24]) and concomi-
tant insertion of 1 into the Si–Cl bond of the intermediate
(NN)Si(Cl)–SiCl3 (Scheme 4). Similar silylene extrusions
were observed when the disilanes (NN)Si(X)–(R)Si(NN)
(X = Cl or Br, R = alkyl) where heated [9].
3. Experimental
3.1. General procedures
All operations and manipulations were carried out
under purified argon, by conventional Schlenk techniques.
Solvents were dried and degassed before use. Microanaly-
ses were carried out at the University of North London.
The NMR spectra were recorded (at 298 K) using Bruker
instruments: Bruker DPX 300 [1H (300.13 MHz), 13C
(75.42 MHz)] and AMX 500 [29Si (99.36 MHz), 119Sn]
˚
Fig. 1. Molecular structure of 2. Selected bond lengths (A) and angles (°):
Si(1)–Si(2) 2.4025(6), Si(2)–Si(3) 2.3817(6), N(1)–Si(1)–N(2) 94.00(6),
N(4)–Si(2)–N(3) 93.46(6).
X
(NN)Si
(NN)Si
(a)
(NN)Si + XSiX3
SiX3 + Si(NN)
+ SiX3
SiX3
(b)
SiX3
X
SiX3
(c)
+ XSiX3
(NN)Si
+ SiX3
(NN)Si
SiX3
SiX3
(NN)Si Si(NN)
SiX3
XSiX3
(NN)Si
(NN)Si
Si(NN)
+ Si(NN)
+ SiX3
(d)
X
Scheme 3.
Cl
Cl
Cl Cl
(NN)Si SiCl2
Cl SiCl3
(NN)Si Si(NN)
Si
+ Si(NN)
(NN)Si
Cl
Si(NN)
Cl
2
4
Scheme 4.

814
B. Gehrhus et al. / Journal of Organometallic Chemistry 691 (2006) 811–816
and referenced internally to residual solvent resonances, or
externally for 29Si and 119Sn and referenced to SiMe4 and
SnMe4, respectively (data in d). Electron impact mass spec-
tra were taken from solid samples using a Kratos MS 80
RF instrument. Melting points were taken in sealed capil-
laries and are uncorrected.
shown to consist of 5, 6, 7 and (NN)SiBr2 in a ratio
1.5:2.1:1.0:2.2. Alternatively, a solution of 1 (0.59 g,
2.15 mmol) in benzene (20 ml) was slowly added to a solu-
tion of SiBr4 (1.3 ml, 10.76 mmol) in benzene (10 ml). The
mixture was stirred for 16 h and then a sample was taken
for NMR spectral analysis. The mixture contained 5, 6, 7
and (NN)SiBr2 in a ratio 1.7:1.1:1:5.5, and (SiBr3)2 [21].
Signals assigned to 6: 1H NMR (C6D6): d 1.0 (s, 18H,
CH3), 3.15 (br. s, 4H, CH2). 29Si{1H} NMR: d À26.5 (SiBr)
and À20.0 (SiN). Signal assignment could not be verified
by independent synthesis. For NMR spectral assignments
of 5, 7 and (NN)SiBr2, see below.
3.2. Reaction of 1 with SiCl4
In an NMR spectroscopic experiment, a solution of 1 in
C6D6 was treated with an excess of SiCl4. The resulting mix-
ture was shown to consist of 2 and 3 in a ratio 2.3:1. 1H NMR
for 3: d 0.95 (s, 18H, But), 3.24, 3.26, 3.28 and 3.3 (AB-type,
4H, CH2), 6.68–6.80 (m, together with signals of 2, phenyl).
29Si NMR: d À20.1 (SiN) and À4.4 (SiCl).
3.6. Reaction of 1 with Br2
In an NMR spectroscopic experiment, a solution of 1 in
3.3. [1,2-C6H4(NCH2But)2]Si(SiCl3)-Si(Cl)-
[(NCH2But)2C6H4-1,2] (2)
C6D6 was treated with an excess of Br2. The mixture was
1
shown to consist of 7 and (NN)SiBr2 in a ratio 1.5:1. H
NMR (C6D6) of 7: d 0.84 (s, 18H, But), 3.05, 3.08, 3.11
and 3.14 (AB-type, 4H, CH2) and 6.71–6.98 (m, together
with signals for (NN)SiBr2, phenyl). 29Si{1H} NMR
SiCl4 (1.25 ml, 10.94 mmol) was added to a solution of
the silylene 1 (1.00 g, 3.65 mmol) in hexane (40 ml). The
mixture was stirred for 16 h. The solvent was removed in
vacuo and the resulting solid was extracted into hexane.
The extract was filtered and cooled at À25 °C yielding yel-
low crystals of 2 (1 g, 76%) (Found: C, 53.7; H, 7.38; N,
7.73%. C32H52Cl4N4Si3: requires C, 53.5; H, 7.29; N,
7.80%), m.p. 173–175 °C.
1
(C6D6) of 7: d À23.5. H NMR (C6D6) of (NN)SiBr2: d
0.97 (s, 18H, But), 3.22 (s, 4H, CH2) and 6.71–6.98 (m,
together with signals for 7, phenyl). 29Si{1H} NMR
(C6D6) of (NN)SiBr2: d À40.8.
3.7. [1,2-C6H4(NCH2But)2]Si(SiBr3)-
Si(Br)[(NCH2But)2C6H4-1,2] (5)
1H NMR (C6D6): d 0.85 (s, 18H, CH3) 0.96 (s, 18H,
CH3), 2.99, 3.02, 3.11 and 3.14 (AB-type, 4H, CH2), 3.24,
3.27, 3.33 and 3.36 (AB-type, 4H, CH2), 6.68–6.80 (m,
8H, phenyl). 13C{1H} NMR (C6D6): d 29.2 (CMe3), 29.6
(CMe3), 33.9 (CMe3), 34.1 (CMe3), 55.5 (CH2), 56.5
(CH2), 110.7, 111.7, 118.7, 119.1, 140.2 and 141.1 (phenyl).
29Si{1H} NMR (C6D6): d À17.3 (SiCl), À14.2 (SiN) and
À2.8 (SiN). EIMS; m/z = 718 ([M]+, 20%), 583 ([M À
SiCl3]+, 14%). X-ray suitable crystals were grown at room
temperature from a concentrated hexane solution.
SiBr4 (0.14 ml, 1.09 mmol) was added to a solution of 1
(0.6 g, 2.19 mmol) in hexane (40 ml) and stirred for 16 h.
The solvent was removed in vacuo yielding 5 as a yellow
viscous oil, which was contaminated with traces of
(NN)SiBr2. 1H NMR (C6D6): d 0.98 (br. s, 36H, But),
3.14, 3.19, 3.26 and 3.30 (AB-type, 4H, CH2), 3.31, 3.35,
3.41 and 3.46 (AB-type, 4H, CH2) and 6.72–6.82 (m, 8H,
phenyl). 13C{1H} NMR (C6D6): d 29.6 and 29.8 (CMe3),
34.0 (CMe3), 55.6 and 55.9 (CH2), 111.1, 111.4, 119.1,
119.5, 139.6 and 140.2 (phenyl). 29Si{1H} NMR (C6D6):
d À30.8 (SiBr), À27.9 (SiN) and À21.4 (SiN).
3.4. [{1,2-C6H4(NCH2But)2}Si]2SiCl2 (4)
A sample of 2 was heated in C6D6 in a sealed NMR tube
at 100 °C for 16 h. NMR spectroscopic analysis revealed
the complete rearrangement to compound 4. Alternatively,
a solution of 2 (0.36 g, 0.42 mmol) in toluene (5 ml) was
refluxed for 2 days. The solvent was removed in vacuo
and the residue was crystallised from hexane to afford 4
3.8. Reaction of 1 with GeCl4
A solution of 1 (0.27 g, 0.98 mmol) in hexane (20 ml)
was slowly added to a solution of GeCl4 (0.34 ml,
2.95 mmol) in hexane (20 ml) at À78 °C. The mixture was
allowed to come to ambient temperature and was stirred
for 16 h during which a pale yellow precipitate had formed.
1
as a yellow solid (0.26 g, 87%). H NMR (C6D6): d 0.87
(s, 36H, CH3), 3.02 (br, s, 8H, CH2), 6.60–6.63 and 6.69–
6.73 (m, 8H, phenyl). 13C{1H} NMR (C6D6): d 29.4
(CMe3), 33.9 (CMe3), 55.8 (CH2), 110.9, 119.1 and 140.1
(phenyl). 29Si{1H} NMR (C6D6): d À14.2 (SiN) and
À10.0 (SiCl). EIMS; m/z = 718 ([M]+, 43%).
1
An H NMR (C6D6) spectral sample was taken from the
reaction mixture and showed major signals corresponding
to (NN)SiCl2 [19], accompanied by unidentified products.
3.9. Reaction of 1 with SnCl4
3.5. Reaction of 1 with SiBr4
A solution of 1 (0.3 g, 1.09 mmol) in hexane (20 ml) was
slowly added to a solution of SnCl4 (0.64 ml, 5.47 mmol) in
hexane (20 ml). The mixture was stirred for 16 h during
In an NMR spectroscopic experiment, a solution of 1 in
C6D6 was treated with an excess of SiBr4. The mixture was

B. Gehrhus et al. / Journal of Organometallic Chemistry 691 (2006) 811–816
815
which time a pale green precipitate had formed. The mix-
ture was filtered and the remaining solid was dried in
vacuo. A signal at d [119Sn{1H}] À211 (THF/C6D6) con-
firmed the formation of SnCl2 (independently verified by
119Sn{1H} NMR analysis of a sample of SnCl2 in THF/
C6D6). All volatiles were removed from the filtrate in vacuo
resulting in a pale yellow oil which was confirmed to be
of 10: d À16.5 and À14.2 (SiMeCl2). EIMS; m/z = 424
([M]+, 30%). 1H NMR (C6D6) of 10a: d 0.87 (s, 18H,
But), 3.08 (s, 4H, CH2), 6.42 (s, 1H, SiH), 6.79–6.81 (m,
4H, phenyl). 13C{1H} NMR (C6D6) of 10a: d 28.4
(CMe3), 34.0 (CMe3), 54.5 (CH2), 109.8, 118.7 and 131.9
(phenyl). 29Si NMR (C6D6) of 10a:
2J(H,Si) = 318 Hz).
d
À19.7 (d,
1
(NN)SiCl2 by H and 29Si{1H} NMR spectroscopy [19].
3.13. X-ray structure determination for complex 2
3.10. [1,2-C6H4(NCH2But)2]Si(Cl)Si(Ph)Cl2 (8)
Data for the crystal structure determination were col-
lected on a Kappa CCD diffractometer at 173(2) K using
monochromated Mo Ka radiation (k 0.71073 A). The
structure was solved by direct methods and refined by
full-matrix least-squares on F2 using SHELXL 97 [25], with
all non-H atoms anisotropic. Crystal data and refinement
details for C32H52Cl4N4Si3: Mr 718.85, orthorhombic,
Silylene 1 (0.42 g, 1.53 mmol) was dissolved in PhSiCl3
(5 ml, 31.2 mmol) and the solution was heated at 100 °C
for two days. The excess PhSiCl3 was removed in vacuo
(10À3 Torr, 80 °C) yielding a yellow, highly viscous oil,
˚
1
which was identified as compound 8. H NMR (C6D6): d
0.87 (s, 18H, But), 3.17, 3.23, 3.26 and 3.31 (AB-type,
4H, CH2), 6.81–6.86 (m, 4H, phenyl), 7.00–7.02 (m, 3H,
phenyl), 7.71–7.74 (m, 2H, phenyl). 13C{1H} NMR
(C6D6): d 29.2 (CMe3), 33.8 (CMe3), 55.9 (CH2), 111.0,
119.1, 128.9, 132.3, 133.1, 134.2 and 140.1 (phenyl).
29Si{1H} NMR (C6D6): d À15.9 and À1.4 (SiPhCl2).
EIMS; m/z = 486 ([M]+, 20%).
space group P212121 (No. 19), a = 9.7274(1), b =
3
˚
˚
18.8759(2), c = 20.7539(3) A, U = 3810.69(8) A , Z = 4,
l = 0.43 mmÀ1, 6914 unique reflections collected, R1 =
0.023 for 6720 reflections with I > 2r(I), wR2 = 0.057 for
all reflections.
4. Supplemental material
3.11. [{1,2-C6H4(NCH2But)2}Si]2Si(Ph)Cl (9)
Crystallographic data for the structural analysis for
compound 2 have been deposited with the Cambridge
Crystallographic Data centre, CCDC No. 284464. Copies
of this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (fax: +44 1223 336033; e-mail: deposit@ccdc.
cam.ac.uk or http://www.ccdc.cam.ac.uk).
A mixture of 1 and PhSiCl3 in a ratio 2:1 was heated in
C6D6 in a sealed NMR tube at 100 °C for two days. NMR
spectroscopic analysis revealed the presence of compound 9
and small amounts of 8.1H NMR for 9: d 0.80 (s, 18H,
But), d 0.97 (s, 18H, But), 2.86, 3.91, 3.02 and 3.07 (AB-
type, 4H, CH2), 3.20, 3.25, 3.28 and 3.33 (AB-type, 4H,
CH2), 6.71–6.74 (m, 2H, phenyl), 6.74–6.84 (m, 6H, phe-
nyl), 6.94–7.01 (m, 3H, phenyl), 7.64–7.67 (m, 2H, phenyl).
13C{1H} NMR for 9: d 29.2 (CMe3), 29.5 (CMe3), 33.7
(CMe3), 33.9 (CMe3), 56.0 (CH2), 56.2 (CH2), 110.6,
110.8, 118.9, 128.7, 128.9, 131.4, 133.2, 135.2, 140.4 and
140.8 (phenyl). 29Si{1H} NMR for 9: d À24.2 (SiClPh)
and À8.7 (SiN). Alternatively, a mixture of 8 and excess
of 1 was heated in C6D6 in a sealed NMR spectral tube
at 100 °C for two days. The spectrum revealed the presence
of compound 9 together with small amounts of unreacted 8
and 1.
Acknowledgements
We thank the EPSRC for the award of an Advanced
Fellowship for B.G. and the Free University of Amsterdam
for support for H.J.
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1
2:1 mixture of 10 and 10a. H NMR (C6D6) of 10: d 0.70
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d 8.3 (CH3), 29.3 (CMe3), 33.9 (CMe3), 55.6 (CH2),
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