Preparation and characterization of tris(trimethylsilyl)germylzinc chloride and bis[tris(trimethylsilyl)germyl]zinc

Article abstract of DOI:10.1246/cl.2002.108

The molecular structure of (Me₃Si)₃GeZnCl (1) has been determined by single-crystal X-ray diffraction. The germylzinc chloride 1 has a dimeric structure consisting of two μ-Cl atoms. The compound 1 reacted with (Me₃Si)₃GeLi in diethyl ether to give [(Me₃Si)₃Ge]₂Zn (2), quantitatively. The structure of bis(germyl)zinc 2 has been also elucidated by X-ray diffraction.

Full text of DOI:10.1246/cl.2002.108

108
Chemistry Letters 2002
Preparation and Characterization of Tris(trimethylsilyl)germylzinc Chloride and
Bis[tris(trimethylsilyl)germyl]zinc
Masato Nanjo,ꢀ Takashi Oda, and Kunio Mochidaꢀ
Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588
(Received October 22, 2001; CL-011029)
The molecular structure of (Me3Si)3GeZnCl (1) has been
determined by single-crystal X-ray diffraction. The germylzinc
chloride 1 has a dimeric structure consisting of two ꢀ-Cl atoms.
The compound 1 reacted with (Me3Si)3GeLi in diethyl ether to
give [(Me3Si)3Ge]2Zn (2), quantitatively. The structure of
bis(germyl)zinc 2 has been also elucidated by X-ray diffraction.
Organozinc compounds are useful reagents in organic
synthesis and organometallic chemistry.1 The well-known
Reformatsky zinc alkylation and Simmons-Smith reaction
proceed via organozincs assumed as key intermediates. Despite
the large number of reports on organozinc reagents, far less
attention has been devoted to silyl- or germyl-substituted zinc
compounds. Up to now, four bis(silyl)zinc derivatives f(t-
Bu3Si)2Zn,2a
[(Me3Si)3Si]2Zn,2b
(Me3Si)2Zn,2c
and
Figure 1. An ORTEP representation of the dimeric structure of
1 (hydrogen atoms are omitted for clarity). Selected bond length
(Ph3Si)2Zn2dg and two silylzinc halides f(t-Bu3Si)ZnCl2a and
(t-Bu3Si)ZnBr2ag have been prepared and only three X-ray crystal
structures of (t-Bu3Si)2Zn, [(Me3Si)3Si]2Zn, and (t-Bu3Si)ZnBr
have been determined. Although a few example of bis(germyl)-
zinc, (Ph3Ge)2Zn and (Et3Ge)2Zn, are known,3a{c no solid state
structure or few reactivities of bis(germyl)zinc derivatives have
been reported. Furthermore, the Reformatsky-type germylzinc
halides R3GeZnX (X ¼ halogen) have never been isolated and
characterized. We report herein the first successful isolation and
full characterization of tris(trimethylsilyl)germylzinc chloride
(1) and bis[tris(trimethylsilyl)germyl]zinc (2), together with
some reactions of 1 and 2.
The treatment of zinc chloride with one mol amount of
(Me3Si)3GeLi (thf)34 in diethyl ether produces the Reformatsky-
type metallozinc compound (Me3Si)3GeZnCl (1) as colorless
crystals in 86% isolated yield (eq 1).5 As expected, the 1H, 13C,
and 29Si NMR of the colorless crystals of 1 gave a single signal
assigned to the trimethylsilyl group, and one THF molecule was
included for a molecule 1 based on the 1H and 13C NMR.6
ꢁ
ꢀ
(A) and angles ( ): Ge1-Zn1 2.3778 (6), Ge1-Si1 2.369(1), Ge1-
Si2 2.365 (1), Ge1-Si3 2.3749(12), Zn1-Cl1 2.3560 (11), Zn1-
Cl1ꢀ 2.3999 (10), Zn1-O1 2.096 (3); Ge1-Zn1-Cl1 126.07 (3),
Ge1-Zn1-Cl1ꢀ 122.40 (3), Cl1-Zn1-Cllꢀ 92.75 (4), Ge1-Zn1-O1
117.51 (10), O1-Zn1-Cl1 96.78 (10), O1-Zn1-Cl1ꢀ 93.85 (10),
Si1-Ge1-Zn1 107.36 (4), Si2-Ge1-Zn1 108.40 (4), Si3-Ge1-Zn1
111.33 (4).
solvated by coordination to an oxygen atom of a THF molecule
ꢀ
with a Zn-O distance of 2.096 (3) A and has a distorted tetrahedral
ꢀ
configuration. The Ge-Zn bond length of 2.3778 (6) A is
obviously shorter than that expected on the basis of the sum of
ꢀ
their covalent radii (2.47 A), suggesting that the Ge-Zn bond is
comprised of a covalent one with a small ionic character due to the
attachment of the electronegative chlorine atom to the zinc metal.
The Si-Ge-Zn angle of 109.03 (4) ꢁ (av.) and the Ge-Si bond
ꢀ
length of 2.370 (1) A (av.) are quite normal.
The hydrolysis of 1 proceeded extremely slow to give
(Me3Si)3GeH in only 43% yield after 7 days of stirring. The
addition of hydrochloric acid to 1 promotes the hydrolysis
reaction up to 95% (2 h) yield. The compound 1 reacted slowly
with Me3SiCl in diethyl ether for 4 days to yield (Me3Si)4Ge
(17%). The treatment of 1 with additional (Me3Si)3GeLi(thf)3 in
diethyl ether gave [(Me3Si)3Ge]2Zn (2)8 in 93% isolated yield,
suggesting that germylzinc chloride 1 is an intermediate to form
the bis(germyl)zinc. The 1H, 13C, and 29Si NMR of 2 gave a sin-
gle signal assigned to the trimethylsilyl group.9 One of particular
interest is the fact that the redistribution reaction happened on
addition of some other lithium reagents to germylzinc chloride 1
(Scheme 1). The germylzinc chloride 1 was allowed to react with
one mol amount of (Me3Si)3SiLi(thf)3 to give not asymmetrically
bis(germyl)(silyl)zinc (Me3Si)3GeZnSi(SiMe3)3 but the symme-
trical products of [(Me3Si)3Ge]2Zn and [(Me3Si)3Si]2Zn, quan-
titatively, with the ratio of 1 : 1 determined by the 1H NMR signal
intensities. The addition of methyllithium to 1 led to the formation
The Reformatsky-type metallozinc compound 1 could be
recrystallized from THF at À20 ꢁC as air-sensitive colorless
needles. The molecular structure of 1 was unequivocally
confirmed by X-ray diffraction.7 The compound 1 is dimeric in
the solid state and its molecular structure has a crystallographic
inversion center (Figure 1). No interaction between the dimer and
another dimer was observed. The two zinc and two chlorine atoms
constitute a planar four-membered ring with Zn-Cl distances of
ꢀ
2.3560 (11) and 2.3999 (10) A, a Cl-Zn-Cl bond angle of 92.75
ꢁ
ꢀ
(4) , and a Zn-Zn distance of 3.2827 (6) A. The zinc atom is
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
109
Barton, W. D. Ollis, and D. N. Jones, Pergamon, Oxford (1979),
Vol. 3, p 987. b) D. A. Armitage, ‘‘Comprehensive Organometal-
lic Chemistry,’’ ed. by G. Wilkinson, F. G. A. Stone, and E. W.
Abel, Pergamon, New York (1982), Vol. 2, p 99.
2
3
a) N. Wiberg, K. Amelunxen, H.-W. Lerner, H. Noth, A. Appel, J.
Knizek, and K. Polborn, Z. Anorg. Allg. Chem., 623, 1861 (1997). b)
J. Arnold, T. D. Tilley, A. L. Rheingold, and S. J. Geib, J. Inorg.
Chem., 26, 2106 (1987). c) L. Rosch and G. Altnau, Angew. Chem.,
Int. Ed. Engl., 18, 60 (1979). d) E. Wiberg, O. Stecher, H.-J.
Andrasscheck, L. Kreuzbichler, and E. Staude, Angew. Chem., Int.
Ed. Engl., 2, 507 (1963).
a) E. Amberger and W. Stoeger, Angew. Chem., Int. Ed. Engl., 5,
522 (1966). b) V. T. Bychkov, N. S. Vyazankin, and G. A.
Razuvaev, Zh. Obshch. Khim., 43, 793 (1973). c) N. S. Vyazankin,
G. A. Razuvaev, and O. A. Kruglaya, Organomet. Chem. Rev. A, 3,
323 (1968).
Scheme 1.
of [(Me3Si)3Ge]2Zn and Me2Zn (1 : 1),10 (Me3Si)3GeZnMe
could not be detected at all.11
Symmetrical bis(germyl)zinc 2 could be recrystallized from
pentane at À20 ꢁC to give colorless single crystals. The structure
of 2 was determined by X-ray diffraction (Figure 2).12
Bis(germyl)zinc 2 has a crystallographic inversion center on the
zinc atom. The two tris(trimethylsilyl)germyl ligands are bonded
in a linear fashion to the zinc atom (Ge1-Zn1-Ge1ꢀ ¼ 180:0ð0Þ ꢁ)
and are staggered with respect to each other. No coordinated
solvent to the zinc metal was observed due to the steric hindrance
between the two tris(trimethylsilyl)germyl ligands. The Ge-Zn
4
5
a) S. Freitag, R. Nerbst-Irmer, L. Lameyer, and D. Stalke,
Organometallics, 15, 2839(1966). b) A. G. Brook, F. Abdesaken,
and H. Sollradl, J. Organomet. Chem., 299, 9(1986).
The germylzinc chloride 1 could be prepared by the following
procedure. The treatment of ZnCl2 (0.30 g, 2.2 mmol) with one mol
amount of (Me3Si)3GeLi(thf)3 (1.14 g, 2.2 mmol) in diethyl ether
produces 1 (0.88 g, 1.9mmol) as flammable colorless crystals in
86% isolated yield.
6
7
Spectroscopic data for 1: 1H NMR (C6D6) ꢁ 0.48 (s, 27 H), 1.34-
ꢀ
bond length of 2.3817 (2) A is somewhat longer than that found in
1
1.36 (m, 4 H, THF), 3.60–3.62 (m, 4 H, THF); 13Cf Hg NMR
germylzinc chloride 1. The average Si-Ge-Zn angle is 106.65
ꢁ
1
(C6D6) ꢁ4.7, 25.3 (THF), 68.8 (THF); 29Si f Hg NMR (C6D6) ꢁ0.2.
ꢀ
(1) , and the mean Ge-Si bond length is 2.3804 A.
Crystal structure analysis of 1: A single crystal (0:25 ꢂ 0:20ꢂ
0:20 mm) was sealed in a capillary glass tube for the data collection.
Diffraction data were collected at 200 K on a MacScience DIP2030
image plate diffractiometer employing graphite-monochromated
ꢀ
Mo (Kꢂ) radiation (ꢃ ¼ 0:71073 A); MF ¼ C13H35ClGeOSi3Zn,
MW ¼ 465:09, monoclinic, P21/n, a ¼ 9:6390 (7), b ¼ 20:5050
ꢁ
ꢀ
ꢀ 3
(9), c ¼ 12:7720 (9) A, ꢄ ¼ 105:452 (3) , V ¼ 2433:1 (3) A ,
Z ¼ 4, Dcalcd ¼ 1:270 gꢃcmÀ3. The final R factor and goodness of fit
indicator were 0.0399 (Rw ¼ 0:1327 for all data, 3531 reflections)
and 1.104, respectively, for 3137 reflections with I > 2ꢅðIÞ.
The binary germylzinc 2 could be also prepared by the following
procedure. The treatment of ZnCl2 (0.13 g, 0.95 mmol) with two
mol amounts of (Me3Si)3GeLi(thf)3 (0.88 g, 1.7 mmol) in diethyl
ether produces 2 (0.52 g, 0.80 mmol) as flammable colorless
8
crystals in 94% isolated yield.
1
9Spectroscopic data for 2: 1H NMR (C6D6) ꢁ 0.39(s, 54 H); 13Cf Hg
1
NMR (C6D6) ꢁ 5.2; 29Si f Hg NMR (C6D6) ꢁ À 2:3.
10 Spectroscopic data for Me2Zn at 25 ꢁC: 1H NMR (THF-d8)
Figure 2. An ORTEP representation of the structure of 2
(hydrogen atoms are omitted for clarity). Selected bond
1
1
ꢁ À 1:44 (s, 6 H); 13Cf Hg NMR (THF-d8) ꢁ À 7:3. For H NMR
chemical shift of Me2Zn at À20 ꢁC, see: M. Uchiyama, M. Kameda,
O. Mishima, N. Yokoyama, M. Koike, Y. Kondo, and T. Sakamoto,
J. Am. Chem. Soc., 120, 4934 (1998).
ꢁ
length (A) and angles ( ): Ge1-Zn1 2.3817 (2), Ge1-Si1
ꢀ
2.3788 (6), Ge1-Si2 2.3863 (6), Ge1-Si3 2.3761 (6); Ge1-
Zn1-Ge1ꢀ 180.0 (0), Si1-Ge1-Zn1 107.847 (18), Si2-Ge1-
Zn1 104.496 (17), Si3-Ge1-Zn1 107.600 (18), Si1-Ge1-Si2
11 The formation of the unsymmetrical (alkyl)(germyl)zinc com-
pound was reported in Ref. 3b. Ph3GeZnEt was generated by the
reaction of Ph3GeH with Et2Zn in bis(2-methoxylethyl)ether.
Bis(germyl)zinc 2 rapidly reacted with iodine in diethyl ether
to yield (Me3Si)3GeI (91%), whereas trimethylchlorosilane did
not react with 2 at all. The reaction of 2 with iodomethane
included two steps. In 4 h, the bis(germyl)zinc 2 reacted with
idomethane to form (Me3Si)3GeI (50%) and Me2Zn as reactive
intermediates.13 Further stirring for two days led to the final
formation of (Me3Si)3GeMe (75%) with precipitation of ZnI2
salt.
12 Crystal structure analysis of 2:
0:30 ꢂ 0:30 mm) was sealed in a capillary glass tube for the data
collection. Diffraction data were collected at 120 K on
A
single crystal (0:30ꢂ
a
MacScience DIP2030 image plate diffractiometer employing
ꢀ
graphite-monochromated Mo (Kꢂ) radiation (ꢃ ¼ 0:71073 A);
MF ¼ C18H54Ge2Si6Zn, MW ¼ 649:70, triclinic, P1, a ¼ 9:3840
ꢀ
(7), b ¼ 9:4960 (6), c ¼ 12:2610 (6) A, ꢂ ¼ 68:174 (4), ꢄ ¼
ꢁ
ꢀ 3
70:732 (5), ꢆ ¼ 62:489 (4) , V ¼ 882:8 (1) A , Z ¼ 1, Dcalcd
¼
1:222 gꢃcmÀ3. The final R factor and goodness of fit indicator were
0.0399 (Rw ¼ 0:1255 for all data, 3506 reflections) and 1.141,
respectively, for 3357 reflections with I > 2ꢅðIÞ.
This work was supported by a Grant-in-Aid for Scientific
research (No. 11740344) from Ministry of Education, Culture,
Sports, Science, and Technology, Japan.
13 The formation of Me2Zn was confirmed by both NMR spectra and
cross reaction. The cross reaction is described. After the treatment
of 2 with MeI in diethyl ether for 4 h stirring, Ph3GeCl was added to
the reaction mixture to form Ph3GeMe together with (Me3Si)3GeI.
References and Notes
1
a) J. B. Wakefield, ‘‘Comprehensive Organic Chemistry,’’ed. by D.