Unprecedented oxidative chlorosilylation addition reactions to a diarylgermylene and -stannylene

Article abstract of DOI:10.1021/om020016t

Treatment of MAr₂ [Ar^- = C?₆H₃(NMe₂)₂-2,6 and M = Ge (1) or Sn (2)] with silicon tetrachloride, or 2 with SiCl₃Me, under mild conditions in diethyl ether afforded in good yields the appropriate silylgermane or -stannane M(Ar)₂Cl(SiCl₃) [M = Ge (3), Sn (4)] and Sn(Ar)₂Cl(SiCl₂Me) (5). The X-ray structures of 3 and 5 show that while in 3 there is no very close Ge?N contact (the molecule having germanium in a distorted tetrahedral environment), 5 has a distorted pyramidal structure around the tin atom, with a Cl and a N atom in apical sites. Solutions of 3 and 4 in C₆D₆ showed the former to be stable, while the latter slowly decomposed, yielding β-tin and Sn(Ar)₂Cl₂ among the products; solutions of 5 showed the presence of the equilibrium 2 + SiCl₃Me ? 5, and in CDCl₃the mixture afforded Sn(Ar)₂Cl(CDCl₂).

Full text of DOI:10.1021/om020016t

Organometallics 2002, 21, 2095-2100
2095
Un p r eced en ted Oxid a tive Ch lor osilyla tion Ad d ition
Rea ction s to a Dia r ylger m ylen e a n d -sta n n ylen e
Christian Drost,* Peter B. Hitchcock, and Michael F. Lappert*
The Chemistry Laboratory, University of Sussex, Brighton, U.K. BN1 9QJ
Received J anuary 9, 2002
Treatment of MAr2 [Ar- ) Ch6H3(NMe2)2-2,6 and M ) Ge (1) or Sn (2)] with silicon
tetrachloride, or 2 with SiCl3Me, under mild conditions in diethyl ether afforded in good
yields the appropriate silylgermane or -stannane M(Ar)2Cl(SiCl3) [M ) Ge (3), Sn (4)] and
Sn(Ar)2Cl(SiCl2Me) (5). The X-ray structures of 3 and 5 show that while in 3 there is no
very close Ge‚‚‚N contact (the molecule having germanium in a distorted tetrahedral
environment), 5 has a distorted pyramidal structure around the tin atom, with a Cl and a
N atom in apical sites. Solutions of 3 and 4 in C6D6 showed the former to be stable, while
the latter slowly decomposed, yielding â-tin and Sn(Ar)2Cl2 among the products; solutions
of 5 showed the presence of the equilibrium 2 + SiCl3Me / 5, and in CDCl3 the mixture
afforded Sn(Ar)2Cl(CDCl2).
Ta ble 1. P r eviou sly Rep or ted Cr ysta llin e
2,6-Bis(d im eth yla m in o)p h en ylm eta l Com p lexes
In tr od u ction
The present work is a continuation of a study begun
in 1997 dealing with metal complexes of the ligand
[C6H3(NMe2)2-2,6]- (abbreviated as Ar-),1 readily pre-
pared from [Li(µ-Ar)]3.2 A feature of such complexes is
the facile on/off coordination of one of the pendant NMe2
groups. The ligand Ar- differs from the widely studied3
bis(homo)analogue [C6H3(CH2NMe2)2-2,6]- (≡ Ar′-) in
that NfM association is largely strain-free for (M -
Ar′)sbut not (M - Ar)scomplexes. Thus, we note that
in three mononuclear, crystalline tin(II) complexes the
angle subtended at the ipso-carbon atom of the five- or
four-membered metallacyclic ring is close to the sp2
value in Sn(Ar′)Cl,3 but has an average value of 104°
in SnAr2,1 while in Sn(Ar)Cl it is 112.1(4)°;4 moreover,
in toluene-d8 solution there was rapid 2-NMe2fSn to
6-Me2NfSn exchange at ambient temperature for the
latter two compounds,1,4 but not for Sn(Ar′)Cl.3
complex
coordination no. of M
ref
[Li(µ-Ar)]3
GeAr2 (1)
SnAr2 (2)
2 + 2N
2 + 1N
2 + 2N
2 + 2N
3 + 1N
3 + 2N
2 + 1N
a
2
1, 9
1
1
5
5
1, 4
1
1
6
6
7
7
9
9
8
8
PbAr2
GeAr2(BH3) (A)
SnAr2(BH3) (B)
Sn(Ar)Cl
Sn(Ar){N(SiMe3)2}
Sn(Ar){CH(SiMe3)2}
GeAr2(SnX2)b (C)
SnAr2(SnX2)b (D)
Sn(Ar){Si(NN)Ar}c
Sn(Ar){Si(NN)N(SiMe3)2}
SnAr2(NCO)2
SnAr2(NCS)2
BAr(Cl)Ph
a
a
3 + 2N
2 + 2N
2 + 2N
a
4 + 2N
3 + 1N
2
HgAr2
a
b
Not determined.
We have previously prepared 17 crystalline M-Ar
complexes,1,4-9 for 11 of which X-ray data are available,
Table 1. In general, each Ar- ligand has a close N‚‚‚M
contact, exceptions being GeAr2(BH3) (in which only one
c
* Corresponding authors.
(1) Drost, C.; Hitchcock, P. B.; Lappert, M. F.; Pierssens, L. J .-M.
Chem. Commun. 1997, 1141.
(2) Harder, S.; Boersma, J .; Brandsma, L.; Kanters, J . A.; Bauer,
W.; Schleyer, P. v. R. Organometallics 1989, 8, 1696.
(3) J astrzebski, J . T. B. H.; van der Schaaf, P. A.; Boersma, J .; van
Koten, G.; Zoutberg, M. C.; Heijdenrijk, D. Organometallics 1989, 8,
1373.
(4) Hitchcock, P. B.; Lappert, M. F.; Uiterweerd, P. G. H. Unpub-
lished work. Uiterweerd, P. G. H. D.Phil. Thesis, University of Sussex,
2001.
(5) Drost, C.; Hitchcock, P. B.; Lappert, M. F. Organometallics 1998,
17, 3838.
(6) Drost, C.; Hitchcock, P. B.; Lappert, M. F. Angew. Chem., Int.
Ed. 1999, 38, 1113.
(7) Drost, C.; Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F. Chem.
Commun. 1997, 1845.
(8) Cornu, D.; Hitchcock, P. B.; Lappert, M. F.; Uiterweerd, P. G.
H. Polyhedron 2002, 21, 635.
(9) Drost, C.; Hitchcock, P. B.; Lappert, M. F.; Pierssens, L. J .-M.
Unpublished work.
of the Ar- ligands behaves in this fashion)5 and the two-
coordinate mercury(II) complex HgAr2.8
Following the synthesis and structures of the crystal-
line complexes GeAr2 (1) and SnAr2 (2),1 three classes
of reactions of these MAr2 compounds have been estab-
lished. Their Lewis base character was shown by the
demonstration that they displaced thf from BH3(thf) to
form the adducts A5 and B,5 and they formed the 1:1
adducts C6 and D6 with the Lewis acid 1,8-naphthale-
nebis(neopentylamido)tin(II).6 They were capable of
10.1021/om020016t CCC: $22.00 © 2002 American Chemical Society
Publication on Web 04/18/2002

2096 Organometallics, Vol. 21, No. 10, 2002
Drost et al.
(3) and the silylstannanes Sn(Ar)2Cl(SiCl2R) [R ) Cl (4)
and R ) Me (5)] in good yields, Scheme 1.
Each of the compounds 3-5 gave satisfactory mi-
croanalytical as well as NMR [1H, 13C{1H}, 29Si{1H},
and (for 4 and 5) 119Sn{1H}] and EI-MS spectra.
Whereas compound 3 was thermally stable below 70 °C
both in solution and in the solid state, the solution of
the tin analogue 4 slowly deposited tin at ambient
temperature, or if exposed to light for a prolonged
period. In toluene at higher temperatures however (T
> 100 °C), compound 4 decomposed within 3 to 4 h,
Scheme 2. This thermal decomposition was also moni-
tored in an NMR-tube scale reaction (in toluene + C6D6)
by 119Sn{1H} NMR spectroscopy. Besides the formation
of sponge-type aggregated metallic â-tin (“white tin”),
confirmed by X-ray powder diffraction, the tin(IV)
complex Sn(Ar)2Cl2 (6) was the only tin-containing
complex detected and was also isolated as colorless
crystals. This behavior parallels that observed in the
Sn[CH(SiMe3)2]2 + SnCl2 system, which afforded Sn-
[CH(SiMe3)2]2Cl2 + Sn.9 Compound 6 was earlier shown
to be generated together with metallic tin in a thermal
decomposition-disproportionation reaction of the re-
cently described heteroleptic chlorostannylene Sn(Ar)-
Cl in toluene (T > 100 °C).1,9 The 29Si{1H} NMR spectra
of the reaction mixture revealed three signals at δ
-18.9, -24.7, and -26.2. The signal at δ -18.9 is
assigned to SiCl4; the latter two are close to the chemical
shift of the chlorosilane Si(Ar)Cl3 (7) [29Si{1H} δ -25.3],
undergoing redox reactions; thus SnAr2 (2) with silver
iso- or isothiocyanate yielded SnAr2(NCX)2 (X ) O or
S) and silver.9 Finally, SnAr2 behaved as a substrate
for oxidative addition by the halogenoalkane ButBr or
(Me3Si)2CHBr, yielding SnAr2(Br)R [R ) But or CH-
(SiMe3)2], respectively.9
In light of the formation of MAr2(BH3) adducts A and
B,5 we have now examined reactions of GeAr2 (1) or
SnAr2 (2) with the group 14 Lewis acids SiCl4 and SiCl3-
Me. Among carbenes or heavier group 14 metal(II)
analogues, only Arduengo-type carbene-silane adducts
E have been established for SiCl4, SiCl2Me2, and SiCl2-
Ph2;10 whereas the bis(amido)stannylene F (Z ) Sn)
reacted with SiCl4 only under forcing conditions (190
°C, autoclave, 12 h) and then yielded the product F (Z
) SiCl2) of σ-bond metathesis.11
prepared from [Li(µ-Ar)]3 and SiCl4.9
2
In contrast to the above-mentioned decomposition
reaction, a solution of colorless Sn(Ar)2Cl(SiCl2Me) (5)
in aromatic solvents at ambient temperature was stable
with respect to the formation of elemental tin, but
turned yellow as soon as it was dissolved. There was
1
clear evidence from H and heteronuclear NMR spectra
that besides the desired silylstannane 5, both starting
materials, the diarylstannylene 2 and SiCl3Me (ratio )
1:1), were present. It was also shown by NMR spectro-
scopic experiments that the 2:3 ratio between the
diarylstannylene 2 and the silylstannane 5 did not
change after 1 week at ambient temperature or 2 days
at 70 °C in benzene or toluene. However, when an excess
of SiCl3Me was added to 5 in toluene, the stannylene 2
was nearly quantitatively reconverted into the silyl-
stannane 5. These observations indicate that there was
an equilibrium between the chlorosilane/stannylene and
the silylstannane 5 in aromatic (or ethereal) solvents.
As mentioned above, in the absence of an excess of
methyltrichlorosilane, the dissolved crystalline complex
5 partially reverted to the starting stannylene and the
silane in aromatic solvents. When deuterated chloroform
was used in an NMR-tube scale experiment, the equi-
librium between 2 and 5 was shown to be shifted in
Resu lts a n d Discu ssion
We now draw attention to unprecedented oxidative
insertion reactions of a divalent monomeric diarylger-
mylene or -stannylene with a chlorosilane, which might
occur through the intermediacy of a transient ger-
mylene/stannylene (as donor)-silane (as acceptor) com-
plex and subsequent chloride migration from Si to Ge
or Sn. Treatment of the recently described yellow diaryl-
germylene GeAr2 (1) [Ar- ) Ch6H3(NMe2)2-2,6] or -stan-
nylene SnAr2 (2)1 with tetrachlorosilane (for 1 and 2),
or also for 2 with an excess of methyltrichlorosilane in
diethyl ether, and crystallization from Et2O afforded
colorless crystals of the silylgermane Ge(Ar)2Cl(SiCl3)
(10) Kuhn, N.; Kratz, T.; Bla¨ser, D.; Boese, R. Chem. Ber. 1995, 128,
245.
(11) Veith, M.; Lisowsky, R. Z. Anorg. Allg. Chem. 1988, 560, 59.

Unprecedented Oxidative Chlorosilylation
Organometallics, Vol. 21, No. 10, 2002 2097
Sch em e 1. Syn th esis of Ge(Ar )2Cl(SiCl)3 (3), Sn (Ar )2Cl(SiCl)3 (4), a n d Sn (Ar )2Cl(SiCl2Me) (5); Ar )
Ch 6H3(NMe2)2-2,6
Sch em e 2. Th er m a l Decom p osition of Sn (Ar )2Cl(SiCl3) (4)
Sch em e 3. F or m a tion a n d Dissocia tion of Sn (Ar )2Cl(SiCl2Me) (5)
favor of 2, which, as soon as formed, was consumed by
the CDCl3 to produce Sn(Ar)2Cl(CDCl2) (8), Scheme 3.
Crystalline 5 turned yellow upon storage at ambient
temperature and was best kept at -30 °C.
The structure of Ge(Ar)2Cl(SiCl3) (3), investigated by
single-crystal X-ray diffraction, is illustrated in Figure
1, with selected bond lengths and angles in Table 2. The
molecule 3 has the germanium atom in a distorted
tetrahedral environment; the average of the six angles
subtended at the germanium atom by the atoms C1,
C11, Cl1, and Si is 109.3° and range from 96.26(6)° (Si-
Ge-Cl1) to 115.15(13)° (Si-Ge-C1). The shortest of the
contacts between the four nitrogen atoms is 2.88(1) Å
(Ge‚‚‚N3) and is surely nonbonding, as evident from the
2.479(11) and 2.508(11) Å Ge‚‚‚N contacts in two
independent molecules of GeAr′(Cl)(Me)Ph (Ar′ ) C6H4-
CH2NMe2)12 and the 2.394(6) and 2.722(6) Å in GeAr2
1,9
[cf.1 the Sn‚‚‚N distance in SnAr2 of 2.607(5) and 2.669-
F igu r e 1. Molecular structure of Ge(Ar)2Cl(SiCl3) (3)
(5) Å]. As a result of the relatively proximate Ge‚‚‚N3
showing the atom-labeling scheme, with thermal ellipsoids
at the 50% probability level. Hydrogen atoms have been
omitted for clarity.
(12) Brelie`re, C.; Carre´, F.; Corriu, R. J . P.; de Saxce, A.; Poirier,
M.; Royo, G. J . Organomet. Chem. 1981, 205, C1.

2098 Organometallics, Vol. 21, No. 10, 2002
Drost et al.
2.718(6) Å for the Sn‚‚‚NMe2 distances in each of the
9
two Ar- ligands of Sn(Ar)2(NCS)2 ] and is much shorter
than any of the Sn‚‚‚N(1,2,3) contacts, which range from
3.111(5) Å for N1 to 3.662(5) Å for N3. As a consequence
of the short Sn‚‚‚N4 distance, the C11-Sn bond is
strongly tilted toward N4, as evident from the C16-
C11-Sn and C12-C11-Sn angles of 103.3(3)° and
135.7(3)°, respectively. The Sn-Si distance of 2.594(2)
Å is unexceptional [cf. 2.597(3) and 2.604(3) Å in SnCl2-
[Si(SiMe3)3]2,15 2.609(14) and 2.611(14) Å in [Sn-
(SiMe3)3]2,16 and 2.630(4) and 2.642(4) Å in SnCl[Si(Cl)-
{(NBut)2C2H2-1,2}]3].17
1
The H and 13C{1H} NMR spectra in C6D6 at 298 K
for each of 4 and 5 showed one sharp singlet NMe2
signal, indicating either that the Sn‚‚‚N dative contacts
are absent or there is rapid 2-Me2NfSn to 6-Me2NfSn
exchange. By contrast, the silylgermane 3 displayed a
1
broad NMe2 signal in both the corresponding H and
F igu r e 2. Molecular structure of Sn(Ar)2Cl(SiCl2Me) (5)
showing the atom-labeling scheme, with thermal ellipsoids
at the 50% probability level. Hydrogen atoms have been
omitted for clarity.
13C{1H} NMR spectra, possibly due to some C-NMe2
restricted rotation. The 119Sn{1H} chemical shifts in 4
(δ -212) and 5 (δ -208) were closely similar and for
the latter coupling was reasonably resolved, J (119Sn-
1
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Ge(Ar )2Cl(SiCl3) (3)
29Si) ) 1667 Hz. These δ[119Sn] data may be compared
with those for SnAr2 (δ ) 442)1 and SnAr2(NCS)2 (δ )
-341).9 The 29Si{1H} signal for the germane 3 was at δ
-1.8, whereas for the isoleptic stannane 4 it appeared
at higher frequency, δ 16.6, and for the stannane 5 the
signal at δ 37 showed well-resolved tin satellites, 1J (29-
Si-117/119Sn) ) 1409/1479 Hz.
Ge-C1
Ge-C11
Ge-Cl1
Ge- Si
1.936(4)
1.962(4)
2.181(1)
2.379(2)
Si-Cl2
Si-Cl3
Si-Cl4
Ge‚‚‚N3
2.046(2)
2.039(2)
2.061(2)
2.88(1)
C1-Ge-C11
C1-Ge-Cl1
C11-Ge-Cl1
C1-Ge- Si
C11-Ge- Si
111.3(2)
Cl1-Ge-Si
Cl2-Si-Ge
Cl3-Si-Ge
Cl4-Si-Ge
96.26(6)
114.14(8)
123.37(9)
104.45(7)
107.95(13)
114.22(13)
115.15(13)
111.18(13)
There was no reaction between SnAr2 and dimethyl-
dichloro- or trimethylchlorosilane, even when used in
excess. As far as oxidative chlorosilylation is concerned,
not only the choice of chlorosilane but also the nature
of the ligand X- in MX2 was crucial. Thus, under
conditions similar to those used for the synthesis of 3-5,
the bis(amido)stannylene Sn[N(SiMe3)2]2 did not react
with SiCl4 and the bis(alkyl)stannylene Sn[CH(SiMe3)2]2
yielded SnCl2 and a waxy and as yet unidentified
material. Treatment of the diarylplumbylene PbAr2 with
SiCl4 gave lead powder in quantitative yield. It is clear
that while the reactions of Scheme 1 demonstrate inter
alia a new method of Ge-Si or Sn-Si bond formation,
they are unlikely to supersede established routes to such
compounds, namely, interactions of lithium germanates
or stannates with halosilanes,14 Wurtz-type cross-
coupling of MClX3 (M ) Ge or Sn) and SiClX′3,18 or
dehydrochlorination of MClX3 with SiCl3H in the pres-
ence of triethylamine.19
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Sn (Ar )2Cl(SiCl2Me) (5)
Sn1-C1
Sn1-C11
Sn1-Cl1
Sn1-Si1
2.125(4)
Si1-Cl2
Si1-Cl3
Si1-C21
Sn1‚‚‚ N4
2.0806(16)
2.04(2)
1.901(4)
2.624(4)
2.145(4)
2.4442(15)
2.5939(14)
C1-Sn1-C11
C1-Sn1-Cl1
C11-Sn1-Cl1
C1-Sn1-Si1
C11-Sn1-Si1
114.14(15)
99.54(12)
108.25(12)
122.29(12)
116.00(10)
Cl1-Sn1-Si1
C21-Si1-Sn1
Cl3-Si1-Sn1
Cl2-Si1-Sn1
90.41(5)
115.90(14)
117.96(7)
105.01(6)
contact, the C(ortho)-C(ipso)-Ge angles in 3 [C16-
C11-Ge, 127.6(3)°; C12-C11-Ge, 112.9(3)°] deviate
significantly from the sp2 value for one of the Ar-
ligands, unlike the situation for the other [C2-C1-Ge,
121.5(3)°; C6-C1-Ge, 118.5(3)°]. The Ge-Si bond
length of 2.379(2) Å is unexceptional [cf. 2.384(1) Å in
The decomposition of Sn(Ar)2Cl(SiCl3) (4) yielding not
only â-tin but also Sn(Ar)2Cl2 (6) may indicate that the
first step in the reaction sequence was a 1,2-shift of
chloride from silicon to tin, affording transiently dichlo-
rosilylene. A parallel would be the generation of dichlo-
rosilylene from Si2Cl6.20
13
Ge(Ph)3SiMe3 and 2.326(6)-2.445(1) Å in Ge(C6H4-
NMe2-2)3(SiX2X′) (X ) H, X′ ) Me; or X ) Me, X′ ) But)
in which no close GeLN contact was noted14].
The structure of crystalline Sn(Ar)2Cl(SiCl2Me) (5) is
shown in Figure 2, with selected geometric parameters
in Table 3. One of the two aryl ligands is bonded in a
C,N-chelate fashion to the tin atom, which lies at the
center of a distorted trigonal bipyramid with the Cl1
and N4 atoms occupying the apical sites [Cl1-Sn-N4,
167.4(2)°]. The Sn‚‚‚N4 distance of 2.624(4) Å is ap-
propriate for a dative interaction [cf. the similar Sn‚‚‚
N distances in SnAr2 (vide supra)1 and the 2.435(5) and
It is proposed that the first step in the oxidative
chlorosilylation of the bivalent group 14 diarylmetal
(15) Mallela, S. P.; Geanangel, R. A. Inorg. Chem. 1990, 29, 3525.
(16) Mallela, S. P.; Geanangel, R. A. Inorg. Chem. 1993, 32, 5623.
(17) Denk, M. K.; Hatano, K.; Lough, A. J . Eur. J . Inorg. Chem.
1998, 1067.
(18) Hermann, U.; Schu¨rmann, M.; Uhlig, F. J . Organomet. Chem.
1999, 585, 211.
(13) Pa´rka´nyi, L.; Hernandez, C.; Pannell, K. H. J . Organomet.
Chem. 1986, 301, 145.
(14) Kawachi, A.; Tanaka, Y.; Tamao, K. J . Organomet. Chem. 1999,
590, 15.
(19) Mu¨ller, L.; du Mont, W.-W.; Ruthe, F.; J ones, P. G.; Marsmann,
H. C. J . Organomet. Chem. 1999, 579, 156.
(20) Cf.: Liu, C.-S.; Hwang, T.-L. Adv. Inorg. Chem. Radiochem.
1985, 29, 1.

Unprecedented Oxidative Chlorosilylation
Organometallics, Vol. 21, No. 10, 2002 2099
Sch em e 4. Alter n a tive Rea ction P a th w a ys a , b, a n d c for Ch lor osilyla tion of MAr 2 (X ) Cl or Me)
compounds MAr2 leading to the tetravalent M(Ar)2Cl-
(SiCl2X) is the formation of the five-coordinate 1:1
adducts 9, probably of trigonal bipyramidal structure,
with the most electronegative chloride ligands occupying
the apical sites, Scheme 4. Thus MAr2 is taken to
from the appropriate adduct 9 yielding 3-5 appears to
be energetically facile.
Con clu sion s
The unprecedented oxidative chlorosilylations of the
divalent germanium (1) and tin (2) compounds MAr2
using SiCl4 or SiCl3Me to yield the appropriate diaryl-
(silyl)metal(IV) chlorides 3-5 provide a new route to
compounds containing Ge-Si or Sn-Si bonds. It re-
mains to be established whether (i) the procedure is
general for bulky diarylmetal(II) substrates or whether
the o,o′-NMe2 groups have a significant stabilizing role,
and (ii) these reactions can be extended to Lewis acids
other than chlorosilanes, including halides or triflates
of group 13 and 14 elements.
The molecular structures of the crystalline compounds
Ge(Ar)2Cl(SiCl3) (3) and Sn(Ar)2Cl(SiCl2Me) (5) show
that the group 14 metal is in a distorted tetrahedral
(3) and trigonal bipyramidal (5) environment (only the
latter having a very short M‚‚‚N contact). Whereas the
germane 3 was thermally stable below 70 °C, the
isoleptic stannane 4 was less so and products of decom-
position included â-tin and Sn(Ar)2Cl2 (6). The 119Sn-
{1H} NMR spectral chemical shifts in C6D6 of com-
pounds 4 and 5 were closely similar (δ ) -210 ( 2 ppm),
indicating that they are structurally similar, although
it is likely that both showed a rapid 2-Me2NfSn to
6-Me2NfSn exchange for one of the two aryl ligands.
Compound 5 in C6D6 solution was in equilibrium with
its precursors SnAr2 (2) and SiCl3Me, as evident from
the formation of the chloroalkylation adduct Sn(Ar)2Cl-
(CDCl2) (8) in CDCl3.
function as a base, of relative base strengths GeAr2
>
SnAr2, consistent with the premise that the Ge-Si bond
is stronger than the Sn-Si; it is also noted that whereas
GeAr2(BH3) is stable both in solution and the solid, the
Sn analogue in solution slowly decomposed, yielding a
precipitate of tin.5 As for the chlorosilanes, their Lewis
acidity is at a premium the greater the number of Si-
Cl bonds; that is, Lewis acidity decreases in the se-
quence SiCl4 > SiCl3Me > SiCl2Me2 > SiClMe3. These
considerations are consistent with the experimental
observations that (i) the diaryl(chloro)trichlorosilylger-
manium compound 3 is more robust than the isoleptic
tin compound 4, (ii) 4 is more readily formed than its
methyldi(chloro)silyl analogue 5, and (iii) SnAr2 but not
Sn[E(SiMe3)2]2 (E ) CH or N) is susceptible to oxidative
chlorosilylation. As for (iii), we note that whereas each
MAr2 (1 or 2) formed a 1:1 adduct with BH3 (Table 1),
Sn[CH(SiMe3)2]2 did not react with BH3(thf) and hence
is presumed to be a weaker base than SnAr2 (2), while
Sn[N(SiMe3)2]2 was reduced by the borane, yielding
metallic tin.5
As for the conversion of 9 to the final product 3-5,
three possible pathways a, b, and c are worthy of
consideration. Route a, the homolytic (SH2) path is
similar to that established for the oxidative addition of
a halogenoalkane RHal to the stannylene Sn[CH-
(SiMe3)2]2 yielding Sn[CH(SiMe3)2]2(Hal)R;21 this is also
often the pathway for oxidative addition of RHal to
certain Pt(0) substrates yielding alkylplatinum(II)
halides.22,23a Route b, of SN2 type, is observed in many
other transition metal(n) f transition metal(n + 2)
oxidative additions of RHal.23b However, in these cited
comparative systems, RHal is unlikely to be an ad-
equately strong Lewis base to yield an intermediate 1:1
adduct. For this reason, we suggest that the preferred
route from 9 to the appropriate oxidative adduct 3-5
is likely to be c (SNi), since five-coordination for silicon
is well established and the compounds MAr2 are known
to be effective Lewis bases [(cf. MAr2(SnX2)6 and MAr2-
(BH3),5 Table 1], and an intramolecular 1,2-shift of an
apical chloride ligand from silicon to germanium or tin
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All reactions were carried out
under argon (99.994% purity) with usual Schlenk equipment
and techniques. Solvents were predried over sodium wire and
purified by distillation over sodium-potassium alloy (toluene)
and sodium-benzophenone (diethyl ether) and stored over
molecular sieves (4 Å). Deuterated solvents were stored over
a potassium mirror and degassed prior to use. The starting
materials GeAr2 (1) and SnAr2 (2) [Ar- ) Ch6H3(NMe2)2-2,6]
were obtained according to the published procedure1 and
purified by recrystallization from n-hexane. Tetrachlorosilane
and methyltrichlorosilane were commercially available and
used after redistillation. The NMR solution spectra were
recorded on Bruker AC250 (for 1H, 13C, 29Si, and 119Sn for
compounds 3-7), AMX 500 (29Si for 2), or Avance 400 (for 8)
instruments and referenced internally (1H, 13C) or externally
(SiMe4 for 29Si or SnMe4 for 119Sn). Unless otherwise stated,
all NMR spectra were examined at 293 K in C6D6 and, except
for 1H, were proton-decoupled. Electron impact mass spectra
were taken on a Kratos MS 80 RF instrument. Elemental
(21) Gynane, M. J . S.; Lappert, M. F.; Miles, S. J .; Power, P. P. J .
Chem. Soc., Chem. Commun. 1978, 192.
(22) Lappert, M. F.; Lednor, P. W. J . Chem. Soc., Chem. Commun.
1973, 948.
(23) Cf.: Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA 94941, 1987; (a) p 307, (b)
p 306.

2100 Organometallics, Vol. 21, No. 10, 2002
Drost et al.
Ta ble 4. Molecu la r P a r a m eter s for Com p ou n d s 3
a n d 5
analyses (calculated data are for empirical formulas) were
carried out by Medac Ltd, U.K. Melting points are uncorrected.
Syn th esis of Ge(Ar )2Cl(SiCl3) (3). SiCl4 (0.51 g, 0.34 mL,
2.98 mmol) was added slowly to a solution of 1 (1.19 g, 2.98
mmol) in Et2O (20 mL). The colorless solution was set aside.
After 12 h at ambient temperature, colorless crystals of 3 were
formed, and to complete crystallization, the solution was
subsequently kept at -30 °C for a further 12 h to afford
colorless crystals of 3 (1.33 g, 78%); mp ca. 89 °C (dec). Anal.
Calcd for C20H30Cl4GeN4Si: C, 42.2; H, 5.31; N, 9.85. Found:
C, 42.3; H, 5.53; N, 9.89. NMR (C6D6, 293 K): 1H, δ 2.40 (s,
C20H30Cl4GeN4Si (3) C21H33Cl3N4SiSn (5)
Mr
T (K)
568.96
293(2)
594.653
217(2)
cryst size (mm)
cryst syst
space group
a (Å)
0.25 × 0.25 × 0.20
triclinic
P1h (No. 2)
9.440(4)
10.821(4)
14.241(4)
72.84(3)
84.85(3)
68.43(3)
1292.3(8)
2
0.70 × 0.40 × 0.40
monoclinic
Cc
1.4350(3)
1.3078(3)
1.4838(3)
90
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
3
br, 24H, NMe2), 6.66 [d, 4H, H-3/5, J (1H-1H) ) 7.9 Hz), 7.03
103.12(3)
90
(t, 2H, H-4, 3J (1H-1H) ) 7.9 Hz]; 13C{1H}, δ 47.1 (br, NC2),
117.2, 132.6, 135.8, and 161.2 (Caryl); 29Si{1H}, δ -1.85. MS:
m/z (%, assignment): 532 (3, [M - H - Cl]+), 435 (20, [M -
SiCl3]+), 400 (35, M - SiCl3 - Cl]+), 237 (85, [M - SiCl3 - Cl
- Ar]+).
2711.9(9)
4
Z
Dcalc (g cm-3
)
1.46
1.456
abs. coeff (mm-1
)
1.66
24.97
1.297
θmax for data colln
(deg)
28.57
Syn th esis of Sn (Ar )2Cl(SiCl3) (4). A slight excess of SiCl4
(0.42 g, 0.28 mL, 2.47 mmol) was added slowly to a solution of
2 (1.04 g, 2.34 mmol) in Et2O (35 mL) at ca. 25 °C. The colorless
solution was stirred overnight, whereupon a colorless micro-
crystalline precipitate of 4 was formed. To complete the
crystallization, the mixture was kept at -30 °C for 12 h to
yield compound 4 (1.32 g, 92%); mp ca. 75 °C (dec). Anal. Calcd
for C20H30Cl4N4SiSn: C, 39.1; H, 4.92; N, 9.10. Found: C, 39.5;
H, 5.52; N, 9.11. NMR (C6D6, 293 K): 1H, δ 2.44 (s, 24H, NMe2),
6.61 [d, 4H, H-3/5, 3J (1H-1H) ) 7.8 Hz], 7.04 [t, 2H, H-4,
3J (1H-1H) ) 7.8 Hz]; 13C{1H}, δ 47.8 (NC2), 116.5, 133.6, 138.3,
and 160.8 (Caryl); 29Si{1H}, δ 16.6 [SiCl3, 1J (29Si-117/119Sn) )
1511/1584 Hz]; 119Sn{1H}, δ -212 [1J (119Sn-13C) ) 758 Hz].
MS m/z (%, assignment): 480 (5, [M - SiCl3]+), 446 (8, [M -
SiCl3 - Cl]+), 318 (15, [M - SiCl3 - Ar]+), 283 (33, [M - SiCl3
- Cl - Ar]+).
no. of ind reflns
no. of reflns with
I > 2σI
4528
3224
4057 (Rint ) 0.0475)
3990
no. of data/
4528/0/271
4057/2/280
restraints/
params
R1 (I > 2σI)
wR2 (all data)
goodness-of-fit
largest diff peak
and hole (e Å-3
0.045
0.0327
0.095
0.0854
1.023
1.064
0.33 and -0.31
0.923 and -0.954
)
3J (1H-1H) ) 7.9 Hz], 7.04 [t, 2H, H-4, J (1H-1H) ) 7.9 Hz];
13C{1H}, δ 46.2 (NC2), 113.7, 120.2, 135.1, and 161.8 (Caryl);
29Si{1H}, δ -25.0. MS m/z (%, assignment): 298 (43, [M]+),
261 (30, [M - Cl]+), 245 (12, [M - Cl - Cl]+).
3
Sn Ar 2(Cl)CDCl2 (8). A slight excess of CDCl3 (0.1 g, 0.85
mmol) was added to a yellow solution of 2 (0.31 g, 0.67 mmol)
in Et2O (20 mL) at ca. 25 °C. The resulting colorless solution
was stirred for a further 2 h and the solvent removed in vacuo.
The residual crystalline colorless precipitate was treated with
a small quantitiy of hexane and kept at -30 °C for 12 h to
Syn th esis of Sn (Ar )2Cl(SiCl2Me) (5). An excess of Me-
SiCl3 (0.63 g, 0.5 mL, 4.25 mmol) was added to a solution of 2
(1.10 g, 2.47 mmol) in Et2O (40 mL) at ambient temperature
without stirring. The resulting pale yellow solution was set
aside for 15 h at room temperature and subsequently placed
in a freezer at -30 °C for 24 h, whereupon colorless crystals
of 5 (1.09 g, 74%) were formed; mp > 70 °C (dec). Anal. Calcd
for C21H33Cl3N4SiSn: C, 42.4; H, 5.59; N, 9.42. Found: C, 42.6;
H, 5.70; N, 9.49. NMR (C6D6, 293 K): 1H, δ 2.48 (s, 24H, NMe2),
6.64 [d, 4H, H-3/5, 3J (1H-1H) ) 8.0 Hz], 7.07 [t, 2H, H-4,
3J (1H-1H) ) 8.0 Hz]; 13C{1H}, δ 12.2 (CH3, [2J (13C-117/119Sn)
yield compound 8 (0.36 g, 96%); mp > ca. 105 °C (dec), C21
-
DH30Cl3N4Sn. NMR (C6D6, 300 K): 1H, δ 2.44 (s, 24H, NMe2),
6.63 [d, 4H, H-3/5, 3J (1H-1H) ) 8.0 Hz], 7.01 [t, 2H, H-4,
3J (1H-1H) ) 8.0 Hz]; 13C{1H}, δ 47.3 (NC2), 116.8, 132.3, 141.6
[1J (13C-117/119Sn) ) 769/804 Hz] and 160.5 (Caryl); 119Sn{1H}, δ
-185. MS m/z (%, assignment): 563 (20, [M]+) 481 (53, [M -
CDCl2]+), 444 (8, [M - CDCl2 - Cl]+), 325 (25, [M - 2Ar]+),
163 (70, [Ar]+).
) 109 Hz], 47.7 (NC2), 116.2, 128.6, 141.0, and 161,0 (Caryl);
1
29Si{1H}, δ 37.0 [SiCl3, J (29Si-117/119Sn) ) 1409/1479 Hz]; 119
-
Sn{1H}, δ -208 [1J (119Sn-29Si) ) 1467 Hz, 1J (119Sn-13C) )
710 Hz]. MS m/z (%, assignment): 516 (0.5, [M - SiCl2]+), 480
(4, [M - SiCl3]+), 446 (17, [M - SiCl3 - Cl]+), 318 (28, [M -
SiCl3 - Ar]+), 283 (76, [M - SiCl3 - Cl - Ar]+).
X-r a y Str u ctu r e Deter m in a tion s of Com p ou n d s 3 a n d
5. Unique data sets were collected with an Enraf-Nonius CAD4
(3) diffractometer or a Bruker AXS CCD area detector (5) using
a crystal in a sealed capillary at 293(2) K (3) or a crystal coated
with a perfluorinated ether at 217(2) K (5). Refinement was
on F2 for all reflections using SHELXL-93 for 324 or SHELXL-
9725 for 5. All non-H atoms were anisotropic, and the hydrogen
atoms were included in the riding mode. Parameters are listed
in Table 4.
Syn th esis of Sn (Ar )2Cl2 (6). A solution of Sn(Ar)2Cl(SiCl3)
(4) (1.2 g, 1.96 mmol) in toluene (20 mL) was heated above
100 °C for 4 h. After filtration of the reaction mixture, the
obtained solution was evaporated to dryness. The colorless
residue was finally recrystallized from Et2O/hexane (3:1) to
afford compound 6 (0.37 g, 37%); mp 155 °C. Anal. Calcd for
C
20H30Cl2N4Sn: C, 46.6; H, 5.86; N, 10.85. Found: C, 46.6; H,
5.95; N, 10.83. NMR (C6D6, 293 K): 1H, δ 2.49 (s, 24H, NMe2),
6.64 [d, 4H, H-3/5, 3J (1H-1H) ) 7.9 Hz], 7.04 [t, 2H, H-4,
3J (1H-1H) ) 7.9 Hz]; 119Sn{1H}, δ -245. MS m/z (%, assign-
ment): 515 (0.5, [M]+), 480 (26, [M - Cl]+), 444 (4, [M - Cl -
Cl]+), 325 (43, [Ar2]+), 281 (5, [M - Cl - Cl - Ar]+).
Ack n ow led gm en t. We thank the European Com-
mission for the award of a category 30 fellowship to C.D.
and EPSRC for other support. We are grateful to Dr.
Peter Lo¨nnecke for the X-ray data for compound 5.
Syn th esis of SiAr Cl3 (7). Addition of SiCl4 (2.36 g, 14.1
mmol) to a solution of [Li(µ-Ar)]32 (2.3 g, 13.53 mmol) in diethyl
ether (60 mL) at room temperature and subsequent refluxing
for 1 h afforded 8 as a colorless crystalline material (3.55 g,
88%), after filtration through a glass filter to remove LiCl,
removal of the solvent in vacuo, and recrystallization from
hexane; mp 165-169 °C. Anal. Calcd for C10H15Cl3N2Si: C,
40.4; H, 5.08; N, 9.41. Found: C, 40.4; H, 5.16; N, 9.44. NMR
(C6D6, 293 K): 1H, δ 2.49 (s, 24H, NMe2), 6.64 [d, 4H, H-3/5,
Su p p or tin g In for m a tion Ava ila ble: Tables giving X-ray
crystallographic data for compounds 3 and 5. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM020016T
(24) Sheldrick, G. M. SHELXL-93, Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1993.
(25) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.