Synthesis and characterization of Ge2{Sn(X)Ar#} 3 and Ga2{Ge(X)Ar#}3 (Ar# = C6H3-2,6-Mes2), X = (Cl/I): Rare examples of mixed heavier group 14/14, 13/14 element clusters

Article abstract of DOI:10.1021/om0497137

Treatment of Ar^#ECl (Ar^# = C₆H ₃-2,6-Mes₂; E = Ge or Sn) with 1 equiv of the reducing agent KC₈ or 'GaI' led to the isolation and characterization of the two new main group clusters Ge₂{Sn(X)Ar^#}₃, 1, and Ga₂{Ge(X)Ar^#}₃, 2 (X = Cl or Cl/I), which have trigonal bypyramidal Ge₂Sn₃ or Ga₂Ge ₃ frameworks. Cluster 1 is a singlet biradicaloid, whereas 2 is a very rare heavier group 13/14 element cluster, and the first with a Ga/ Ge framework.

Full text of DOI:10.1021/om0497137

Organometallics 2004, 23, 4009-4011
4009
Syn th esis a n d Ch a r a cter iza tion of Ge2{Sn (X)Ar #}3 a n d
Ga 2{Ge(X)Ar #}3 (Ar # ) C6H3-2,6-Mes2), X ) (Cl/I): Ra r e
Exa m p les of Mixed Hea vier Gr ou p 14/14, 13/14 Elem en t
Clu ster s
A. F. Richards, M. Brynda, and P. P. Power*
Department of Chemistry, University of California, Davis, One Shields Avenue,
Davis, California 95616
Received April 20, 2004
Summary: Treatment of Ar#ECl (Ar# ) C6H3-2,6-Mes2;
E ) Ge or Sn) with 1 equiv of the reducing agent KC8 or
‘GaI’ led to the isolation and characterization of the two
new main group clusters Ge2{Sn(X)Ar#}3, 1, and Ga2-
{Ge(X)Ar#}3, 2 (X ) Cl or Cl/ I), which have trigonal
bypyramidal Ge2Sn3 or Ga2Ge3 frameworks. Cluster 1
is a singlet biradicaloid, whereas 2 is a very rare heavier
group 13/ 14 element cluster, and the first with a Ga/
Ge framework.
element clusters with two different heavier main group
elements are of interest since it is probable that they
will have interesting electronic properties.12 Such clus-
ters are relatively common for group 13 /15 element
species,13 but are quite scarce for groups 14/14 and
group 13/14 combinations.14,15 Here we report two new
structurally related clusters having heterobicyclopen-
tane frameworks that are composed of the element pairs
Ge/Sn and Ga/Ge.
The clusters Ge2{Sn(Cl)Ar#}3, 1, and Ga2{Ge(Cl/I)-
(Ar#)}3, 2, were synthesized16 by the reduction of an
Ar#SnCl/GeCl2 mixture with KC8 or by the reaction of
Ar#GeCl (Ar# ) C6H3-2,6-Mes2) with a suspension of
‘GaI’ in toluene.17 Unsuccessful attempts were also
made to prepare the corresponding Ge/Ge and Ga/Sn
clusters. Our investigation of the synthesis of 1 arose
from studies of the above-mentioned mixed octahedral
cluster Sn4(GeAr′)2,11 which featured four unsubstituted
tins. We wished to prepare the analogous species,
Ge4(SnAr′)2, for comparison. Investigation of a variety
of synthetic conditions and aryl groups led only to the
The synthesis of homonuclear clusters of the heavier
main group 13 and 14 elements, i.e., [MnRm]x-, n > m,
x ) 0, 1, 2, etc., which contain atoms unsubstituted by
organic or other groups, is a topic of considerable current
interest. An impressive number of heavier group 13
metal complexes with up to 84 metal atoms is known.1
In contrast, the corresponding group 14 element clusters
are not as well studied.2 In pioneering work, Sita and
3
co-workers synthesized the compounds Sn5Ar6 and
4
Sn7Ar8 (Ar ) C6H3-2,6-Et2) in the early 1990s, and
although the number of organic substituents exceeds the
number of tin atoms, the compounds contain at least
two unsubstituted tins. In addition a similar compound,
Sn5{C6H3-2,6-(OiPr)2)}6, has been reported recently by
Drost and co-workers.5 The tin compounds are of further
interest in that they are non-Kekule´ species with
biradical character.6,7 Other neutral heavier group 14
element clusters with unsubstituted atoms include the
(12) Lahiri, S. K.; Das, S.; Umapathi, B.; Kal, S. ETE J . Res. 1997,
43, 193-205.
(13) For example: Cesari, M.; Cucinella, S. In The Chemistry of
Inorganic Homo and Heterocycles; Haiduc, I., Sowerby, B. D., Eds.;
Academic: London, 1987; Vol. 1, Chapter 6.
(14) Linti, G.; Kostler, W.; Piotrowski, H.; Rodig, A. Angew Chem
Int. Ed. 1998, 37, 2209.
(15) Purath, A.,Dohmeier, C.; Ecker, A.; Koppe, R.; Krautscheid, H.;
Schno¨ckel, H.-G.; Ahrichs, R.; Stoemer, C.; Friedrich, J .; J utzi, P. J .
Am. Chem. Soc. 2000, 122, 6955.
8
9
tin clusters Sn8{(SiMe3)3}6 and Sn8(C6H3-2,6-Mes2)4
10
and the germanium species Ge8{N(SiMe3)2}6 as well
as the octahedral Ge4(GeAr′)2 and Sn4(GeAr′)2 (Ar′ )
C6H3-2,6-Dipp2, Dipp ) C6H3-2,6-iPr2).11 The latter is
the first well-characterized cluster with two different
heavier group 14 elements in its framework. Mixed
(16) A mixture of Ar#SnCl (0.467 g, 1.0 mmol)a and GeCl2(dioxane)
(0.232 g, 1.0 mmol) was dissolved in THF and added to a well-stirred
THF suspension of KC8 in a dry ice bath. A deep red solution was
obtained, which became brown on reaching room temperature. The
volatile materials were removed under reduced pressure, and the
residue was extracted into toluene. Filtration, followed by slow cooling,
afforded almost black crystals of 1. Yield: 0.213 g 42%, mp 95-110
°C (dec); 1H NMR (C6D6, 25 °C, 399.8 MHz) δ ppm, 2.019 (s 12H,
o-CH3), 2.157(s, 6H, p-CH3), 6.814 (s, 4H, m-Mes), 6.947 (d, 2H, m-C6H3,
* Corresponding author. E-mail: pppower@ucdavis.edu.
(1) Linti, G.; Schno¨ckel, H. Coord Chem. Rev. 2000, 206-297, 285.
Schno¨ckel, H.; Schnepf, A. Adv. Organomet. Chem. 2001, 47, 235.
(2) Schnepf, A. Angew. Chem., Int. Ed. 2004, 664-666.
(3) Sita, L. R.; Bickerstaff, R. D. J . Am. Chem. Soc. 1989, 111, 6454.
Sita, L. R.; Kinoshita, I. J . Am. Chem. Soc. 1990, 112, 8839.
(4) Sita, L. R.; Kinoshita, I. J . Am. Chem. Soc. 1992, 114, 7024.
(5) Drost, C.; Hildebrand, M.; Lo¨nnecke, P. Main Group Metal Chem.
2002, 25, 93.
(6) Gordon, M. S.; Nguyen, K. A.; Carroll, M. T. Polyhedron 1991,
10, 1247.
(7) Nagase, S. Polyhedron 1991, 10, 1299.
(8) Wiberg, N.; Lerner, H.-W, Wagner, S.; Noth, H.; Seifert, T. Z.
Naturforsch. B 1999, 54877.
(9) Eichler, B. E.; Power, P. P. Angew. Chem., Int. Ed. 2001, 40,
706.
3
3J H-H ) 8.0 Hz), 7.188 (t, 1H J H-H ) 8 Hz); 13C NMR (C6D6, 25 °C,
100.59 MHz) 20.98, 23.03, 130.45, 135.57, 136.24, 137.71, 146.24; 119Sn
NMR (C6D6, 25 °C, 147.07 MHz) δ ppm 456.0 ppm. 2: A toluene
suspension of ‘GaI’ (0.196 g, 1 mmol) was added to a toluene solution
of Ar#GeCla (1 mmol, 0.421 g) dropwise at 0 °C. The solution was
allowed to reach ambient temperature and stirred for 16 h. The orange
solution was then concentrated and filtered. Storage at ca. -30 °C for
1 week yielded orange/red crystals of 2. Yield ) 56%, mp 210 °C (dec);
1H NMR (C6D6, 25 °C, 399.8 MHz) δ 2.057 (s 12H, o-CH3), 2.102 (s,
3
6H, p-CH3), 6.799 (s, 4H, m-Mes), 6.954 (d, 2H, m-C6H3, J H-H ) 8.0
3
Hz), 7.365 (t, 1H, J H-H ) 8 Hz); 13C{1H} NMR (C6D6, 25 °C, 100.59
MHz) 21.094 (p-CH3) 21.895 (o-CH3), 129.512 (m-Mes), 130.513 (m-
C6H3), 132.216 (p-C6H3), 136.424 (p-Mes), 137.981 (o-Mes), 147.552 (i-
Mes), 148.210 (o-C6H3). (a) Simons, R. S.; Pu, L.; Olmstead, M. M,
Power, P. P. Organometallics 1997, 16, 1920.
(10) Schnepf, A.; Koppe, A. Angew. Chem., Int. Ed. 2003, 42, 411.
(11) Richards, A. F.; Hope, H.; Power, P. P. Angew. Chem., Int. Ed.
2003, 42, 4071.
(17) Green, M. H. L.; Mountford, P.; Smout, G. J .; Speel, S. R.
Polyhedron 1990, 9, 2763.
10.1021/om0497137 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 07/16/2004

4010 Organometallics, Vol. 23, No. 17, 2004
Communications
F igu r e 2. Thermal ellipsoid plot (30%) of 2. H atoms and
Cl occupancy are not shown for clarity. Selected bond
distances (Å) and angles (deg): Ge(1)-Ga(1) ) 2.4934(6),
Ge(1)-C(1) ) 1.974(4), Ge(1)-Cl(1) ) 2.200(3), Ge(1)-I(1)
2.597(3), Ga(1)- -Ga(1A) ) 3.078(1), C(1)-Ge(1)-Cl(1) )
106.5(2), C(1)-Ge(1)-Ga(1) ) 127.82(8), Cl(1)-Ge(1)-
Ga(1) ) 107.41(9), Ga(1)-Ge(1)-Ga(1a) ) 76.23(3), Ge(1)-
Ga(1)-Ge(1A) ) 85.90(2).
F igu r e 1. Thermal ellipsoid plot (30%) of 1. H atoms are
not shown for clarity. Selected bond distances (Å) and
angles (deg): Sn(1)-Ge(1) ) 2.7400(6), Sn(1)-C(1) )
2.141(5), Sn(1)-Cl(1) ) 2.379(2), Ge(1)- - -Ge(1a) ) 3.363(1),
C(1)-Sn(1)-Cl(1) ) 103.8(2), C(1)-Sn(1)-Ge(1) ) 126.90(9),
Cl(1)-Sn(1)-Ge(1) ) 109.41(3), Sn(1)-Ge(1)-Sn(1A) )
84.29(2), Ge(1)-Sn(1)-Ge(1A) ) 78.42(3).
isolation of the almost black, crystalline 1 in good yield.
(by ca. 6°) Ge-Sn-Ge angle. Such differences can be
partly explained on the basis of the electronegative Cl
substituent on tin. Thus, despite the large Ar# substitu-
ent, the C-Sn-Cl angle in 1 (103.8(2)°) is less than the
average C-Sn-C angle in Sn5Ar6. This finding is in
accordance with the Walsh/Bent rule.19 The narrowing
of the angle between the tin substituents leads in turn
to a wider GeSnGe angle and thus a greater Ge-Ge
separation. The lengthened Sn-Sn bridgehead separa-
tion (3.423(1) Å, C-Sn-C ) 104.62° (av)) reported in
Sn6{C6H3-2,6-(OiPr)2}6,4 which has more electron-
withdrawing substituents than Sn5Ar6, is also in accord
with these arguments. These structural data appear to
confirm that the distance between bridgehead atoms,
and therefore the amount of biradical character, can be
systematically varied by changing the constituent atoms
of the cluster and their substituents, as demonstrated
1
It was characterized by H, 13C, and 119Sn NMR spec-
troscopy (δ ) 456 ppm) and by X-ray crystallography.15
Compound 1 crystallizes in a trigonal space group as
well-separated molecules that have a trigonal bi-
pyramidal, bicyclo[1.1.1]pentane Ge2Sn3 structure in
which the bridgehead (or axial) germaniums carry no
substituent and the equatorial tins are each bonded to
Cl and Ar# groups. The molecule is characterized by
a 3-fold axis of symmetry along the Ge-Ge vector
(Ge- -Ge separation ) 3.363(7) Å). The Ge-Sn, Sn-C,
and Sn-Cl bond lengths are 2.7400(6), 2.141(5), and
2.379(2) Å, respectively, and the Sn-Ge-Sn and Ge-
Sn-Ge angles are 82.29(2)° and 78.42(3)°. The Sn- -Sn
separation is 3.677(1) Å.
The reaction of ‘GaI’ and Ar#GeCl in toluene afforded
orange crystals of 2 in moderate yield. The crystals were
found to be isomorphous to those of 1 with almost equal
unit cell parameters. The structures are very similar
and there is a 3-fold axis of symmetry along the
Ga- -Ga vector (Ga-Ga separation ) 3.078(1) Å). The
Ga-Ge and Ge-C bond lengths are 2.4934(6) and
1.974(4) Å, with a Ge- -Ge separation of 3.398(2) Å. The
halide site at each germanium has a mixed occupancy
composed of 81% chlorine and 19% iodine, which prob-
ably arises from exchange of the Ge-Cl moiety with the
‘GaI’. The Ge-Ga-Ge and Ga-Ge-Ga angles are
85.90(2)° and 76.23(3)°.
recently by Bertrand and co-workers for boron-phos-
20
phorus diradicaloids.
Compound 1 has an intense
color which arises from an orbitally allowed HOMO-
LUMO transition. The chemical shift of the 119Sn NMR
signal is in the same region observed for Sn5Ar6 (350.0
ppm) and Sn5{C6H3-2,6(OPri)2}6 (328.4 ppm) and is
5
shifted approximately 100 ppm downfield due to the
deshielding effect of the halide substituent.
The Ga/Ge compound 2 is a very rare example of a
cluster with a framework of heavier group 13 and 14
elements. Although there are several heavier group 13
The Ge2{Sn(Cl)Ar#}3 species 1 is only the second
example of a cluster with a framework of two different
heavier group 14 elements (cf. Sn4(GeAr′)2).11 It bears
a structural resemblance to the corresponding all tin
(18) Crystal data for 1:
M ) 1457.92, trigonal, P63/m, a )
13.0931(13) Å, c ) 22.405(3) Å, Z ) 2, Dc ) 1.545 Mg m-3, µ(Mo KR)
) 0.503 mm-1, T ) 91 K, 3471 independent reflections collected on a
Bruker Smart 1000 instrument. Refinement of 3471 reflections (127
parameters) with I > 2.0σ(I) converged at final R1 ) 0.0435, wR2 )
0.1585. Crystal data for 2: M ) 1459.49, trigonal, P63/m, a ) 12.943(3)
2
Sn5Ar6 cluster of Sita. Remarkably, the distance be-
Å, c ) 22.537(6) Å, Z ) 2, Dc ) 1.482 Mg m-3, µ(Mo KR) ) 0.503 mm-1
,
tween the bridgehead germaniums, 3.363(2) Å, is simi-
lar to that between the bridgehead tins in Sn5Ar6
(3.361(1) Å) and the related Sn7Ar8 (3.348(1) Å), even
though the Ge-Sn bond in 1 is ca. 0.1 Å shorter than
the corresponding Sn-Sn bonds in Sn5Ar6.3 The longer
bridgehead distance in 1 is accompanied by a narrower
angle (by ca. 5°) at the bridgehead Ge atom and a wider
T ) 91 K, 36 951 (2584 independent) reflections collected on an Bruker
Smart 1000 instrument. Refinement of 2584 reflections (143 param-
eters) with
0.0693.
I > 2.0σ(I) converged at final R1 ) 0.0334, wR2 )
(19) Walsh, A. D. Discuss. Faraday Soc. 1947, 2, 18. Bent, H. Chem.
Rev. 1961, 61, 275.
(20) Scheschkewitz, D.; Amil, H.; Gornitzka, H.; Schoeller, W.;
Bourissou, D.; Bertrand, G. Angew. Chem., Int. Ed. 2004, 43, 585.

Communications
Organometallics, Vol. 23, No. 17, 2004 4011
clusters with peripheral silyl or germyl substituents,1
only two heavier group 13/14 clusters have been struc-
turally characterized: the anion [{GaSi(SiMe3)3}3-
(GaSiMe2)(SiSiMe3)]- 14 and the neutral SiAl14(η5-
C5Me5)6.15 Compound 2 is the first structurally charac-
terized group 13/14 cluster with a Ga-Ge framework.
The overall structural motif of 2 is very similar to that
of 1. The Ga-Ge distance (2.4934(6) Å) is marginally
longer than the sum of the covalent radii21 and is
consistent with single bonding. This is in agreement
with the fact that the number of available framework
electrons remains sufficient to form six two center-
electron bonds between the Ga and Ge atoms. The
trigonal pyramidal geometry at formally trivalent gal-
lium is unusual (Ga- - -Ga ) 3.078(1) Å). However
pyramidal gallium geometry, in which gallium is bound
to three, four, or five neighboring atoms, has been
observed in the numerous clusters of Schno¨ckel, Linti,
and co-workers.1 The appearance of 2 differs consider-
ably from that of 1 in that it has an orange color. This
difference is more likely due to the fact that the
framework of 2 has two electrons less than 1 and that
the HOMO-LUMO energy difference as reflected in the
Ge2Sn3H6 and Ga2Ge3H6 models shows the chromophore
is quite different in each molecule. Calculations22 on 1
and 2 reproduce the Ge-Sn (2.743 Å) and Ge-Ga (2.476
Å) distances quite accurately. The calculated distances
between the bridgehead atoms Ge-Ge ) 3.282 Å in 1
and Ga-Ga ) 2.675 Å are significantly (0.2-0.4 Å)
shorter than the experimentally observed values. How-
ever, such differences are probably due to the electronic
properties of the ligands in 1 and 2, which, as already
discussed, have longer bridgehead distances than in
previously reported species for electronic reasons.
Ack n ow led gm en t. We are grateful to the National
Science Foundation Collaborative Research in Chemis-
try Program and the Swiss National Science Foundation
(M.B.) for financial support.
Su p p or tin g In for m a tion Ava ila ble: CIF data for 1 and
2. This material is available free of charge via the Internet at
http://pubs.acs.org.
OM0497137
(22) The geometry optimizations were performed in gaseous phase
using DFT theory with the hybrid B3LYP functional. In the molecular
structures used for the theoretical investigations the bulky groups
connected to the Ge (or Sn) atoms were replaced with the hydrogens.
The structure containing the Sn and Ge atoms (M1) was optimized
with Los Alamos LanL2DZ basis set using an effective core potential
(ECP) approximation due to the size of the Sn atoms, while for the
Ga-Ge model cluster (M2) the 6-31g* basis set was used. The
symmetry for both structures was constrained to D3h for all the
optimization steps. All the calculations were performed with the
Gaussian03 package,a and the representations of the molecular
structures were generated with the MOLEKEL program.b The opti-
mized geometrical parameters (bond distances [Å] and angles [deg])
are close to those found in the crystal structures of 1 and 2. M1: Ge-
Ge 3.282, Ge-Sn 2.743, Sn-Ge-Sn 87.9, Ge-Sn-Ge 73.5. M2: Ga-
Ga 2.675, Ga-Ge 2.476, Ga-Ge-Ga 65.4, Ge-Ga-Ge 95.7. The
calculated Ge-Ge (Ga-Ga) distances in M1 and M2 are shorter than
those found in the X-ray crystal structures of the corresponding
clusters. The longest distances found in the crystalline matrix are most
probably related to the more important sterical constraints imposed
by the bulky ligands. (a) M. J . Frisch, G. W. Trucks, H. B. Schlegel, G.
E. Scuseria, M. A. Robb, J . R. Cheeseman, V. G. Zakrzewski, J . A.
Montgomery, J r., R. E. Stratmann, J . C. Burant, S. Dapprich, J . M.
Millam, A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J . Tomasi,
V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomeli, C. Adamo, S.
Clifford, J . Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui, K.
Morokuma, D. K. Malick, A. D. Rabuck,K. Raghavachari, J . B.
Foresman, J . Ciolowski, J . V. Ortiz, A. G. Baboul, B. B. Stefanov, G.
Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R. L. Martin,
D. J . Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C.
Gonzalez, M. Challacombe, P. M. W. Gill, B. J ohnson, W. Chen, M. W.
Wong, J . L. Andres, M. Head-Gordon, E. S. Reploge, and J . A. Pople.
Gaussian 98, Revision A.7; Gaussian, Inc.: Pittsburgh, PA, 1998. (b)
MOLEKEL 4.3, P. Flukiger, H. P. Luthi, S. Portmann, J . Weber; Swiss
Center for Scientific Computing: Manno (Switzerland), 2000-2002.
(21) Using covalent radii of 1.22 Å for Ge and 1.25 Å for Ga.