Synthesis and X-ray crystal structure of [Me2GaBi(SiMe3)2]3

Article abstract of DOI:10.1021/om0202569

[Me₂GaBi(SiMe₃)₂]₃ (1) was synthesized in high yield by the equimolar reaction of Me₂GaH and Bi(SiMe₃)₃ and characterized by mass and multinuclear NMR spectroscopy and by single-

Full text of DOI:10.1021/om0202569

Organometallics 2002, 21, 2793-2795
2793
Syn th esis a n d X-r a y Cr ysta l Str u ctu r e of
[Me2Ga Bi(SiMe3)2]3
Florian Thomas, Stephan Schulz,* and Martin Nieger
Institut fu¨r Anorganische Chemie, Universita¨t Bonn, Gerhard-Domagk-Strasse 1,
D-53121 Bonn, Germany
Received April 1, 2002
Summary: [Me2GaBi(SiMe3)2]3 (1) was synthesized in
high yield by the equimolar reaction of Me2GaH and Bi-
(SiMe3)3 and characterized by mass and multinuclear
NMR spectroscopy and by single-crystal X-ray diffrac-
tion. [Me2GaBi(SiMe3)2]3 represents the first Ga-Bi
heterocycle, closing the gap on structurally characterized
Ga-pnicogen compounds. The described reaction dem-
onstrates the potential application of dialkylgallanes to
serve as powerful synthons in organometallic syntheses
requiring mild reaction conditions.
is not surprising, since organometallic main-group-
element-Bi compounds containing electropositive ele-
ments in general have only been scarcely investigated.9
A few years ago we started our investigations on the
synthesis of group 13-Bi compounds in an attempt to
gain the first insights into their thermodynamic stabil-
ity, chemical reactivity, and solid-state structures.
Stable Lewis acid-base adducts of the types R3M‚
BiR′3 and [R3M]2[Bi2R′4]11 containing dative M-Bi
10
bonds (M ) Al, Ga) were obtained by reaction of
bismuthines R3Bi and dibismuthines R4Bi2 with tri-
alkylalanes and -gallanes R3M, respectively. In addition,
[Me2AlBi(SiMe3)2]3, to date the only structurally char-
acterized group 13-Bi heterocycle,12 and monomeric
Lewis base stabilized compounds of the type dmap-(R2)-
AlBi(SiMe3)2 (dmap ) 4-(dimethylamino)pyridine; R )
Me, Et)10a were synthesized by dehydrosilylation reac-
tions between R2AlH and Bi(SiMe3)3. All these reactions
were performed under very mild conditions, which were
found to be essential for the synthesis of the desired Al-
Bi compounds due to their facile thermal decomposition.
We expected the synthesis of Ga-Bi heterocycles, which
are unknown to date, also to require such mild reaction
conditions. Since the dehalosilylation reaction between
Me2GaCl and Bi(SiMe3)3 failed in our hands to give
[Me2GaBi(SiMe3)2]3, we investigated the utility of the
dehydrosilylation method in the synthesis of the desired
heterocycles. Ga-H bonds (D°298 < 274 kJ /mol) have
much lower bonding energies than Ga-Cl bonds (D°298
) 481 ( 13 kJ /mol), rendering gallanes such as di-
methylgallane, Me2GaH, very attractive reagents.13
However, to the best of our knowledge, Me2GaH, whose
synthesis was reported in 1986,14 has not been used in
In tr od u ction
Group 13/15 compounds belong to the most inten-
sively studied classes of inorganic main-group-element
compounds. Besides the simple Lewis acid-base ad-
ducts R3M‚ER′3 (M ) B, Al, Ga, In; E ) N, P, As), which
have been known for almost two centuries,1 ME
heterocycles and cages [R2MER′2]x and [RMER′]x have
been synthesized in large numbers. Four general syn-
thetic pathways, proceeding by H2, alkane, salt, or halo-
silane elimination reactions, have been developed for
the synthesis of amines, phosphines, and arsines of B,
Al, Ga, and In.2 The corresponding MSb heterocycles
were initially reported in 1988 by Cowley et al.,3 but
only within the last 5 years have dehalosilylation,4 dehy-
drosilylation,5 and distibine cleavage reactions6 been
established as general synthetic pathways. In sharp
contrast, organometallic group 13-Bi compounds have
remained almost unknown,7 most likely resulting from
their decreased thermodynamic stability.8 However, the
highly underexplored status of group 13-Bi compounds
* To whom correspondence should be addressed. Fax: +49 (0)228
73-5327. E-mail: sschulz@uni-bonn.de.
(1) F3B‚NH3 was first synthesized by Gay-Lussac (Gay-Lussac, J .
L.; Thenard, J . L. Mem. Phys. Chim. Soc. d’Arcueil 1809, 2, 210. As
cited in: J onas, V.; Frenking, G. J . Chem. Soc., Chem. Commun. 1994,
1489).
(2) For references see: (a) Cowley, A. H.; J ones, R. A. Angew. Chem.,
Int. Ed. Engl. 1989, 28, 1208. (b) Wells, R. L. Coord. Chem. Rev. 1992,
112, 237. (c) Carmalt, C. J . Coord. Chem. Rev. 2001, 223, 217.
(3) (a) Barron, A. R.; Cowley, A. H.; J ones, R. A.; Nunn, C. M.;
Westmoreland, D. L. Polyhedron 1988, 7, 77. (b) Cowley, A. H.; J ones,
R. A.; Kidd, K. B.; Nunn, C. M.; Westmoreland, D. L. J . Organomet.
Chem. 1988, 341, C1. (c) Cowley, A. H.; J ones, R. A.; Nunn, C. M.;
Westmoreland, D. L. Chem. Mater. 1990, 2, 221.
(4) See the following and references therein: (a) Foos, E. E.; J ouet,
R. J .; Wells, R. L.; White, P. S. J . Organomet. Chem. 2000, 598, 182.
(b) Schulz, S. Coord. Chem. Rev. 2001, 215, 1. (c) Thomas, F.; Schulz,
S.; Nieger, M. Z. Anorg. Allg. Chem. 2002, 628, 235.
(5) (a) Schulz, S.; Nieger, M. Organometallics 1998, 17, 3398. (b)
Schulz, S.; Nieger, M. Organometallics 1999, 18, 315. (c) Schulz, S.;
Kuczkowski, A.; Nieger, M. Organometallics 2000, 19, 699. Dialkyl-
chloroalanes and Sb(SiMe3)3 react with formation of the simple Lewis
acid-base adducts.
(6) (a) Breunig, H. J .; Stanciu, M.; Ro¨sler, R.; Lork, E. Z. Anorg.
Allg. Chem. 1998, 624, 1965. (b) Kuczkowski, A.; Schulz, S.; Nieger,
M.; Saarenketo, P. Organometallics 2001, 20, 2000.
(7) Only some Zintl ions containing AlBi4 tetrahedra (Cordier, G.;
Scha¨fer, H.; Stelter, M. Z. Naturforsch. 1984, 39b, 727) and MBi
deltahedral clusters (M ) In, Ga; Xu, L.; Sevov, S. C. Inorg. Chem.
2000, 39, 5383) have been synthesized and structurally characterized.
(8) For instance, the stability of simple Lewis acid-base adducts
was found to decrease with increasing atomic number of the pnicogen.
Kuczkowski, A.; Schulz, S.; Nieger, M.; Schreiner, P. R. Organome-
tallics 2002, 21, 1408.
(9) Organometallic main-group-element-Bi compounds are almost
limited to those containing electronegative elements such as N, P, O,
S, and halides. Prior to our studies, [Cp*2SmBi]2 (Evans, W. J .;
Gonzales, S. L.; Ziller, J . W. J . Am. Chem. Soc. 1991, 113, 9880) and
(Me2Si)6Bi2 (Kollegger, G. M.; Siegel, H.; Hassler, K.; Gruber, K.
Organometallics 1996, 15, 4337) were the only structurally character-
ized heterocycles featuring Bi atoms linked by electropositive elements.
(10) (a) Kuczkowski, A.; Thomas, F.; Schulz, S.; Nieger, M. Orga-
nometallics 2000, 19, 5758. (b) Kuczkowski, A.; Schulz, S.; Nieger, M.
Eur. J . Inorg. Chem. 2001, 2605.
(11) Kuczkowski, A.; Schulz, S.; Nieger, M. Angew. Chem., Int. Ed.
2001, 40, 4222.
(12) Schulz, S.; Nieger, M. Angew. Chem., Int. Ed. Engl. 1998, 38,
967.
(13) Lide, D. R., Ed. CRC Handbook of Chemistry and Physics, 78th
ed.; CRC Press: New York, 1997; pp 9-53 and 9-54.
10.1021/om0202569 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 05/25/2002

2794 Organometallics, Vol. 21, No. 13, 2002
Notes
Ta ble 1. Cr ysta llogr a p h ic Deta ils for 1
Sch em e 1. Syn th esis of [Me2Ga Bi(SiMe3)2]3 (1) by
Deh yd r osilyla tion Rea ction
empirical formula
C24H72Bi3Ga3Si6
1365.46
fw
cryst syst
space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/n (No. 14)
9.5769(1)
20.8442(2)
24.4343(3)
96.077(1)
4850.23(9)
4
123(2) K
Mo KR (0.710 73)
1.870
12.649
50
synthetic chemistry, so far.15 In contrast to base-
stabilized gallanes such as H3Ga‚NMe3,16 the reactivity
of dialkyl- and diarylgallanes R2GaH generally has not
been investigated in detail, most likely a consequence
of the small number of stable compounds of this type
known to date as well as their lability toward further
decomposition reactions.17 However, our purpose re-
garding the synthesis of Ga-Bi heterocycles under mild
reaction conditions required such a highly reactive
reagent. We now report on our initial studies using
Me2GaH in preparative metalloorganic chemistry, lead-
ing to the synthesis of [Me2GaBi(SiMe3)2]3 (1), the first
Ga-Bi heterocycle. 1 was investigated in detail by mass
and multinuclear NMR spectroscopy (1H, 13C) as well
as by single-crystal X-ray diffraction.
â (deg)
V (Å3)
Z
T (K)
radiation (λ (Å))
D
calcd (g cm-3
)
µ (mm-1
)
2θmax (deg)
F(000)
2568
cryst dimens (mm)
no. of rflns
no. of unique rflns
Rmerg
no. of params refined/restraints 325/0
abs cor
0.40 × 0.20 × 0.10
65 519
8512
0.1092
empirical from multiple rflns
max and min transmission
refinement method
goodness of fit on F2 a
final R indices (I > 2σ(I))b
R indices (all data)
largest diff peak and hole
0.2534 and 0.1193
full-matrix least squares on F2
0.950
Resu lts a n d Discu ssion
R1 ) 0.0309, wR2 ) 0.0681
R1 ) 0.0483, wR2 ) 0.0720
1.067 and -1.808
1 was obtained by reaction of equimolar amounts of
Me2GaH and Bi(SiMe3)3 at -25 °C in pentane (Scheme
1). Pure 1 is stable at ambient temperature under inert
conditions for several hours, whereas solutions of 1 can
be stored even at low temperatures only for short
periods of time. Depending on the solvent, 1 decomposes
at -20 °C within 1 h (pentane or THF) or a couple of
minutes (toluene). Interestingly, the decomposition
pathway differs significantly. Temperature-dependent
1H NMR spectroscopic studies clearly reveal that in
noncoordinating solvents (pentane, toluene), Bi2(SiMe3)4,
Me3Ga, and some elemental Ga are formed in almost
quantitative yield, whereas in coordinating solvents (e.g.
THF), Bi(SiMe3)3, Me3Ga, and a large amount of dark
precipitate is obtained.
(e Å-3
)
a
2
2
Goodness of fit ) {∑[w(|Fo | - |Fc |)2]/(Nobservns - Nparams)}1/2
.
R1 ) ∑(||Fo| - |Fc||)/∑|Fo| (for I > 2σ(I)). wR2 ) {∑[w(Fo2 - Fc2)2]/
b
∑[w(Fo2)2]}1/2
.
in pentane at -30 °C. 1 is isostructural with [Me2AlBi-
(SiMe3)2]3,12 crystallizing in the monoclinic space group
P21/n (No. 14). The Ga and Bi atoms adopt distorted
tetrahedral environments, forming a distorted boat-type
ring, as was observed for other six-membered group 13/
15 heterocycles. The Ga-Bi bond distances range from
2.744(1) to 2.783(1) Å, which corresponds well to the
sum of the covalent radii for Ga and Bi (2.76 Å).
Comparable bond distances were found for [Me2AlBi-
(SiMe3)2]3 (2.755(3)-2.793(3) Å). As was observed in
isomorphous heterocycles such as [Me2MSb(SiMe3)2]3
(M ) Al,5a Ga,18 In4c) and [Me2AlBi(SiMe3)2]3, the cen-
tral ring of 1 features two long (at Bi1) and four short
Ga-Bi distances (Bi2 and Bi3). Due to the lack of any
other organometallic compounds containing Ga-Bi σ-
bonds, only comparisons to Lewis acid-base adducts
Due to the extreme sensitivity of 1 toward air and
moisture also in its pure form, no satisfactory elemental
analyses could be obtained. The mass spectrum of 1 (EI,
+
12 eV, 40 °C) displays signals due to SiMe3 (m/z 73),
GaMe2+ (m/z 99), Si2Me5+ (m/z 131), BiSiMe3+ (m/z 282),
+
and Bi(SiMe3)3 (m/z 428), indicating the excessive
fragmentation of 1 under such conditions. The peak with
the highest mass corresponds to the fragment Me4Ga2-
Bi2(SiMe3)3+ (m/z 836); the molecular ion peak was not
detected. NMR spectra of 1 in pentane show resonances
due to the Ga-Me and Si-Me groups (1H, δ 0.43
(GaMe2), 0.61 (SiMe3); 13C, δ 5.1 (GaMe2), 6.1 (SiMe3);
29Si, δ -17.7), whereas in THF the Ga-Me resonances
are shifted to higher field (1H, δ 0.04 (GaMe2), 0.65
(SiMe3); 13C, δ 3.5 (GaMe2), 7.4 (SiMe3)).
10
R3Ga-BiR′3 and [R3Ga]2[Bi2R′4]11 are possible. As
expected, these show significantly elongated Ga-Bi
distances (2.97-3.14 Å) according to their dative
bonding character. The endocyclic Ga-Bi-Ga bond
angles found for 1 are significantly larger than the
Bi-Ga-Bi bond angles, ranging from 121.6(1) to 130.7-
(1)° and from 100.7(1) to 103.8(1)°, respectively. The
exocyclic C-Ga-C (115.4(3)-123.4(3)°) and Si-Bi-Si
bond angles (99.2(1)-101.1(1)°) consequently show the
opposite trend. The Ga-C (average 1.990 Å) and Bi-Si
bond lengths (average 2.640 Å) are within typical
ranges.
Colorless crystals of 1, suitable for a single-crystal
X-ray diffraction study, were obtained from a solution
(14) Baxter, P. L.; Downs, A. J .; Goode, M. J .; Rankin, D. W. H.;
Robertson, H. E. J . Chem. Soc., Chem. Commun. 1986, 805.
(15) Only some reactions of Me2GaH with NH3, B2H6, and Lewis
bases were performed for the purpose of its characterization.
(16) For references see: (a) J ones, C.; Koutsantonis, G. A.; Raston,
C. L. Polyhedron 1993, 12, 1829. (b) Gardiner, M. G.; Raston, C. L.
Coord. Chem. Rev. 1997, 166, 1. (c) Aldridge, S.; Downs, A. J . Chem.
Rev. 2001, 101, 3305.
(17) (a) Eisch, J . J . J . Am. Chem. Soc. 1962, 84, 3830. (b) Uhl, W.;
Cuypers, L.; Graupner, R.; Molter, J .; Vester, A.; Neumu¨ller, B. Z.
Anorg. Allg. Chem. 2001, 627, 607. (c) Wehmschulte, R. J .; Ellison, J .
J .; Ruhlandt-Senge, K.; Power, P. P. Inorg. Chem. 1994, 33, 6300.
Our studies reveal the dehydrosilylation reaction to
be the most versatile pathway for the synthesis of group
13/15 heterocycles. Its high synthetic potential is based
on the use of highly reactive reagents, allowing the
syntheses to be performed under very mild reaction
conditions. These were found to be essential for the
(18) Schulz, S.; Nieger, M. J . Organomet. Chem. 1998, 570, 275.

Notes
Organometallics, Vol. 21, No. 13, 2002 2795
methods. 1H, 13C{1H}, and 29Si{1H} NMR spectra were re-
corded using a Bruker DPX 300 spectrometer. The mass
spectrum was recorded on a VG Masslab 12-250 spectrometer
in the electron ionization mode.
[Me2Ga Bi(SiMe3)2]3 (1). At -30 °C Bi(SiMe3)3 (2 mmol,
0.86 g) was added dropwise to a solution of Me2GaH (2 mmol,
0.20 g) in pentane (10 mL) and slowly warmed to -25 °C. The
initially colorless solution turns brown, and a white solid
precipitates. This suspension is stirred for another 30 min at
-20 °C and then quickly warmed to room temperature to
dissolve the solid. Storage of the resulting brown solution at
-30 °C yields [Me2GaBi(SiMe3)2]3 (1) as colorless crystals (0.49
mmol, 0.67 g, 74%).
Mr ) 1365.4 g/mol for C24H72Bi3Ga3Si6. 1H NMR (300 MHz,
pentane, -20 °C): δ 0.43 (s, 6H, GaMe2), 0.61 (s, 18H, SiMe3).
13C NMR (75 MHz, pentane, -20 °C): δ 5.1 (GaMe2), 6.1
(SiMe3). 29Si NMR (60 MHz, pentane, -20 °C): δ -17.7
1
(SiMe3). H NMR (300 MHz, THF-d8, -50 °C): δ 0.04 (s, 6H,
GaMe2), 0.65 (s, 18H, SiMe3). 13C NMR (75 MHz, THF-d8, -50
°C): δ 3.5 (GaMe2), 7.4 (SiMe3). MS (EI, 12 eV, 40 °C): m/z
(%) 836 (2) [Me4Ga2Bi2(SiMe3)3]+, 710 (1) [Bi2(SiMe3)4]+, 627
(2) [Me4Ga2Bi(SiMe3)3]+, 428 (28) [Bi(SiMe3)3]+, 282 (24)
[BiSiMe3]+, 267 (18) [BiSiMe2]+, 157 (23) [Me2GaSiMe3]+, 131
(100) [Me5Si2]+, 99 (92) [Me2Ga]+, 73 (90) [SiMe3]+.
X-r a y Str u ctu r e Solu tion a n d Refin em en t. Crystal-
lographic data of 1 are summarized in Table 1. Figure 1 shows
an ORTEP diagram of its solid-state structure. Data were
collected on a Nonius Kappa-CCD diffractometer. The struc-
ture was solved by Patterson methods (SHELXS-97)20 and
refined by full-matrix least squares on F2. An empirical
absorption correction was applied. All non-hydrogen atoms
were refined anisotropically and hydrogen atoms by a riding
model (SHELXL-97).21
F igu r e 1. Molecular structure and atom numbering
scheme of 1; thermal ellipsoids are drawn at the 50%
probability level. H atoms have been omitted for clarity.
Selected bond lengths (Å) and angles (deg): Bi1-Ga1
2.773(1), Bi1-Ga2 2.783(1), Bi2-Ga2 2.744(1), Bi2-Ga3
2.751(1), Bi3-Ga1 2.757(1), Bi3-Ga3 2.761(1), Bi1-Si1
2.649(2), Bi1-Si2 2.647(2), Ga1-C1 2.002(7), Ga1-C2
1.978(7); Ga1-Bi1-Ga2 130.7(1), Ga1-Bi3-Ga3 128.6(1),
Ga2-Bi2-Ga3 121.6(1), Bi1-Ga1-Bi3 103.8(1), Bi1-
Ga2-Bi2 100.7(1), Bi2-Ga3-Bi3 101.5(1), C1-Ga1-C2
115.4(3), Si1-Bi1-Si2 100.7(1).
Ack n ow led gm en t. S.S. gratefully acknowledges
financial support by the Deutsche Forschungsgemein-
schaft (DFG), the Fonds der Chemischen Industrie
(FCI), the Bundesministerium fu¨r Bildung, Wissen-
schaft, Forschung und Technologie (BMBF), and Prof.
E. Niecke, Universita¨t Bonn. F.T. is grateful to the
Fonds der Chemischen Industrie for a fellowship award.
preparation of [Me2GaBi(SiMe3)2]3, on account of its
facile thermal decomposition in solution. The X-ray
structure analysis of [Me2GaBi(SiMe3)2]3 closes the gap
on structurally characterized Ga-pnicogen compounds.
The utility of the dehydrosilylation pathway with re-
spect to the synthesis of so far unknown In-Bi hetero-
cycles is currently under investigation.
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
lengths, bond angles, anisotropic temperature factor param-
eters, and fractional coordinates for [Me2GaBi(SiMe3)2]3 (1).
This material is available free of charge via the Internet at
http://pubs.acs.org.
Exp er im en ta l Section
All manipulations were performed in a glovebox under an
N2 atmosphere or by standard Schlenk techniques. Me2GaH14
was prepared similar to the synthesis of Me2AlH by reaction
of equimolar amounts of LiGaH4 and Me3Ga followed by
fractionation in vacuo. Bi(SiMe3)319 was prepared by literature
OM0202569
(20) Sheldrick, G. M. SHELXS-97, Program for Structure Solution.
Acta Crystallogr., Sect. A 1990, 46, 467.
(21) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; Universita¨t Go¨ttingen, Go¨ttingen, Germany, 1997.
(19) Becker, G.; Ro¨ssler, M. Z. Naturforsch. 1982, 37b, 91.