Synthesis and characterization of a trigallacycle

Article abstract of DOI:10.1021/om010257l

The reaction of equimolar quantities of 1,8-bis(trimethylstannyl)naphthalene (1) and GaCl₃ in toluene at -25°C yields the known stannagallacycle bis(μ-1,8-naphthalenediyl)(μ-chloride)-methyltin(IV)chlorogallium(III) (2) and a new product which has been identified as the cyclic adduct formed between two molecules of bis(μ-1,8-naphthalenediyl)bis(gallium(III)chloride) and two molecules of trimethyltin chloride (3). Interestingly, when carried out at 25°C and in the presence of water, this reaction leads to the formation of an additional product (4) that is a 12-membered macrocycle containing three gallium atoms linked by 1,8-naphthalenediyl ligands and arranged about a central oxygen atom. The charge balance of 4 is achieved by the presence of a chloride atom that occupies a bridging position between two of the gallium centers. Compounds 3 and 4 have been characterized by NMR, elemental analysis, and single-crystal X-ray analysis. In the crystal, 4 exists as a dimer wherein the monomers are bridged via a Ga-O-Ga-O four-membered ring. The solution structure of 4 in THF-d₈ has been investigated by pulse field gradient spin-echo (PGSE) methods and VT ¹H NMR spectroscopy. The PGSE measurements suggest that, in solution, 4 undergoes a rapid monomer-dimer equilibrium. VT ¹H NMR spectroscopy confirms the existence of a fluxional system. The high-temperature spectrum exhibits three sharp signals. Upon cooling, each of the three sharp signals decoalesces into three signals. Simulation of the spectra followed by an Eyring analysis afforded ΔH? = 43 ± 3 kJ·mol^-1 and ΔS^? = -36 ± 9 J·K^-1·mol^-1 for this process. As a whole, these results support the existence of an exchange between the monomeric and dimeric form of 4. The high-temperature data suggest that upon dissociation into the monomer, the chloride anion undergoes rapid exchange leading to an apparent three-fold molecular symmetry.

Full text of DOI:10.1021/om010257l

Organometallics 2001, 20, 5653-5657
5653
Syn th esis a n d Ch a r a cter iza tion of a Tr iga lla cycle
J ames D. Hoefelmeyer, Denise L. Brode, and Franc¸ois P. Gabba¨ı*
Chemistry TAMU 3255, Texas A&M University, College Station, Texas 77843-3255
Received March 28, 2001
The reaction of equimolar quantities of 1,8-bis(trimethylstannyl)naphthalene (1) and GaCl3
in toluene at -25 °C yields the known stannagallacycle bis(µ-1,8-naphthalenediyl)(µ-chloride)-
methyltin(IV)chlorogallium(III) (2) and a new product which has been identified as the cyclic
adduct formed between two molecules of bis(µ-1,8-naphthalenediyl)bis(gallium(III)chloride)
and two molecules of trimethyltin chloride (3). Interestingly, when carried out at 25 °C and
in the presence of water, this reaction leads to the formation of an additional product (4)
that is a 12-membered macrocycle containing three gallium atoms linked by 1,8-naphtha-
lenediyl ligands and arranged about a central oxygen atom. The charge balance of 4 is
achieved by the presence of a chloride atom that occupies a bridging position between two
of the gallium centers. Compounds 3 and 4 have been characterized by NMR, elemental
analysis, and single-crystal X-ray analysis. In the crystal, 4 exists as a dimer wherein the
monomers are bridged via a Ga-O-Ga-O four-membered ring. The solution structure of 4
in THF-d8 has been investigated by pulse field gradient spin-echo (PGSE) methods and VT
1H NMR spectroscopy. The PGSE measurements suggest that, in solution, 4 undergoes a
1
rapid monomer-dimer equilibrium. VT H NMR spectroscopy confirms the existence of a
fluxional system. The high-temperature spectrum exhibits three sharp signals. Upon cooling,
each of the three sharp signals decoalesces into three signals. Simulation of the spectra
followed by an Eyring analysis afforded ∆Hq ) 43 ( 3 kJ ‚mol-1 and ∆Sq ) -36 ( 9
J ‚K-1‚mol-1 for this process. As a whole, these results support the existence of an exchange
between the monomeric and dimeric form of 4. The high-temperature data suggest that upon
dissociation into the monomer, the chloride anion undergoes rapid exchange leading to an
apparent three-fold molecular symmetry.
In tr od u ction
acidic elements such as tin3,4 and mercury.1,2,5-7 Moti-
vated by the chemistry developed with small group 13
bidentate Lewis acids in the field of anion complex-
ation,9 molecular recognition,10 and catalysis,11 we have
initiated an effort focused on the synthesis and coordi-
nation chemistry of macrocyclic species containing
several group 13 elements. Herein, we wish to report
on the preparation and properties of a trigallacycle.
The chemistry of macrocyclic polydentate Lewis acids
has matured into a multifaceted area of chemistry. In
the field of molecular recognition, these species have
proved useful for the selective complexation of anionic
guests.1-4 More recently, extension of their coordination
chemistry to the case of neutral electron-rich guests1,5
has found applications in the field of supramolecular
catalysis6 and crystal engineering.7 While these achieve-
ments substantiate the fertility of the field, it is
interesting to note that the vast majority of macrocyclic
polydentate Lewis acids8 contain relatively weak Lewis
Resu lts a n d Discu ssion s
Recently, we reported that the reaction of equimolar
quantities of 1,8-bis(trimethylstannyl)naphthalene (1)12
* Corresponding author. Fax: 979-845-4719. E-mail: francois@
tamu.edu.
(8) For
a hexanuclear aluminum complex, see: Dohmeier, C.;
(1) (a) Hawthorne, M. F.; Zheng, Z. Acc. Chem. Res. 1997, 30, 267-
276. (b) Hawthorne, M. F. Pure Appl. Chem. 1994, 66, 245-254.
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Y. T.; Yanovsky, A. I.; Tikhonova, I. A.; Shur, V. B. J . Organomet. Chem
1997, 536, 413-424.
(3) (a) Altmann, R.; Gausset, O.; Horn, D.; J urkschat, K.; Schur-
mann, M.; Fontani, M.; Zanello, P. Organometallics 2000, 19, 430-443.
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1990, 381, C53-C56. (c) J urkschat, K.; Kuivila, H. G.; Liu, S.; Zubieta,
J . A. Organometallics 1989, 8, 2755-2759.
Mattes, R.; Schnoeckel, H. J . Chem. Soc., Chem. Commun. 1990, 358-
359.
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Yang, X.; Stern, C.; Marks, T. J . Organometallics 1994, 13, 3755-
3757. (c) Tschinkl, M.; Schier, A.; Riede, J .; Gabba¨ı, F. P. Inorg. Chem.
1997, 36, 5706-5711. (d) Uhl, W.; Hannemann, F.; Saak, W.; Wartchow,
R. Eur. J . Inorg. Chem. 1998, 921-926. (e) Williams, V. C.; Piers, W.
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Soc. 1999, 121, 3244-3245. (f) Cottone, A., III; Scott, M. J . Organo-
metallics 2000, 19, 5254-5256.
(10) (a) Gabba¨ı, F. P.; Schier, A.; Riede, J .; Hynes, M. J . J . Chem.
Soc., Chem. Commun. 1998, 897-898. (b) Nozaki, K.; Yoshida, M.;
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E. J . Org. Chem. 1989, 54, 2179-2183.
(4) (a) Blanda, M. T.; Newcomb, M. Tetrahedron Lett. 1989, 30,
3501-3504. (b) Newcomb, M.; Horner, J . H.; Blanda, M. T.; Squattrito,
P. J . J . Am. Chem. Soc. 1989, 111, 6294-6301.
(5) Wuest, J . D. Acc. Chem. Res. 1998, 32, 81-89.
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7651-7655.
(11) Ooi, T.; Asao, N.; Maruoka, K. J . Synth. Org. Chem. J pn. 1998,
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8336.
10.1021/om010257l CCC: $20.00 © 2001 American Chemical Society
Publication on Web 11/20/2001

5654 Organometallics, Vol. 20, No. 26, 2001
Hoefelmeyer et al.
Sch em e 1a
a
(i) GaCl3, toluene, -25 °C; (ii) H2O, GaCl3, toluene, 25 °C
Ta ble 1. Cr ysta l Da ta , Da ta Collection , a n d
Str u ctu r e Refin em en t for 3 a n d 4
and GaCl3 in toluene yields a stannagallacycle, namely,
bis(µ-1,8-naphthalenediyl)(µ-chloride)methyltin(IV)-
chlorogallium(III) (2) as a major product which was
isolated in a 65% yield when the reaction was carried
out at 65 °C.13
3-toluene
4-toluene
Crystal Data
formula
Mr
cryst syst
space group
a (Å)
C
53H50Cl6Ga4Sn2
C67H44Cl2Ga6O2
685.12
1415.89
triclinic
P1h
monoclinic
P2(1)/n
14.1965(9)
10.8316(7)
17.6306(11)
90
99.4980(10)
90
2673.9(3)
1.702
10.2387(14)
10.6114(15)
14.112(2)
78.677(2)
69.505(2)
71.642(2)
1356.7(3)
1.733
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
F
Z
calc (g‚cm-3
)
1
2
F(000) (e)
694
3.194
1364
3.128
Interestingly, when this reaction is carried out at -25
°C, the formation of a crystalline precipitate containing
two types of morphologically distinguishable crystals is
observed. Analysis of the different crystals indicates
that the main product of the reaction is 2, which is
isolated as irregular shaped crystals in a 21% yield. The
second type of crystal is clear, colorless as well as cubic
and corresponds to a new product (3) which forms in a
10% yield (Scheme 1). Compound 3 has been charac-
terized by 1H, 13C, and 119Sn NMR, elemental analy-
sis, and X-ray crystallography. This compound is an
adduct formed between bis(µ-1,8-naphthalenediyl)bis-
(gallium(III)chloride) and trimethyltin chloride. In the
crystal, this adduct adopts a dimeric structure in which
the monomers are linked via two pentacoordinated tin
atoms (Table 1, Figure 1). The resulting macrocycle is
centrosymmetric. The digallacycle units exhibit a folded
structure with a dihedral angle between the naphtha-
lene rings of 133.9°. Each gallium center features a
distorted tetrahedral geometry. The deviations from an
ideal geometry are especially manifest in the obtuse
C-Ga-C angles (av 133.3°). The geometrical con-
straints present in the structure of 3 induce distortions
of the naphthalenediyl fragments similar to those
encountered in other hindered peri-substituted naph-
thalene systems.14-16 Although 3 was isolated in low
yield, its formation indicates that the exchange of both
stannyl groups of 1 by gallium moieties is possible.
Compound 3 dissolves only in polar solvents. Its NMR
spectroscopic features have been studied in pyridine-
d5. While the 1H and 13C NMR spectrum reveals the
µ(Mo K) (mm-1
)
Data Collection
cryst size (mm3)
T (K)
scan mode
hkl range
0.67 × 0.49 × 0.52
0.76 × 0.28 × 0.17
110(2)
ω
-16f13, -12f12,
-20f20
13 423
110(2)
ω
-10f12, -12f12,
-16f15
no. of measd reflns 10 646
no. of unique
reflns, [Rint
no. of reflns used
for refinement
abs corr
5872, [Rint ) 0.0382] 4705, [Rint ) 0.0179]
]
5872
4239
ψ-scan
0.984/0.649
Sadabs
0.574731
T
min/Tmax
Refinement
refined params
final R values
[I>2σ(I)]
298
336
R1a (%)
0.0312
0.0845
0.954/-1.177
0.0494
0.1388
2.789/-0.835
wR2b (%)
F
fin(max/min)
(e‚Å-3
)
a
b
R1 ) ∑(Fo - Fc)/∑Fo. wR2 ) {[∑w(Fo2 - Fc2)2]/[∑w(Fo2)2]}1/2
;
w ) 1/[σ2(Fo2) + (ap)2 + bp]; p ) (Fo + 2Fc2)/3; a ) 0.0612 (3),
0.1011 (4), b ) 1.3991 (3), 1.7511 (4).
2
presence of a symmetrically substituted naphthalene
ring, the 119Sn signal observed at -16 ppm corresponds
to that of pure Me3SnCl in the same solvent. This
observation suggests that 3 does not retain its structure
in pyridine solutions but rather dissociates to give
Me3SnCl‚py and possibly solvent-stabilized molecules
of the digallacyle.17,18
When carried out at 25 °C, the reaction of 1 with
GaCl3 in toluene led to high yield of 2 (40-55% yield)
but also afforded crystals of a new compound (4)
(13) Tschinkl, M.; Hoefelmeyer, J . D.; Cocker, T. M.; Bachman, R.
E.; Gabba¨ı, F. P. Organometallics 2000, 19, 1826-1828.
(14) Gabba¨ı, F. P.; Schier, A.; Riede, J .; Sladek, A.; Go¨rlitzer, H. W.
Inorg. Chem. 1997, 36, 5694-5698.
(15) Schro¨ck, R.; Angermaier, K.; Sladek, A.; Schmibaur, H. Organo-
metallics 1994, 13, 3399-3401.
(17) For the preparation of a digallacycle, see: Dam, M. A.; Nij-
backer, T.; de Kanter, F. J . J .; Akkerman, O. S.; Bickelhaupt, F.; Spek,
A. L.; Organometallics 1999, 18, 1706-1709.
(18) Hoefelmeyer, J . D.; Schulte, M.; Gabbaı¨, F. P. Inorg. Chem.
2001, 40, 3833-3834.
(16) Blount, J . F.; Cozzi, F.; Damewood, J . R., J r.; Iroff, L. D.;
Sjostrand, U.; Mislow, K. J . Am. Chem. Soc. 1980, 102, 99-103.

Synthesis and Characterization of a Trigallacycle
Organometallics, Vol. 20, No. 26, 2001 5655
nation sphere of Ga(1) comprises two naphthalene rings
and two oxygen atoms. In each case, the largest devia-
tion from an ideal geometry occurs in the C-Ga-C
angle (av 133.2°) as well as in the O-Ga-Cl (av 80.9°)
and the O-Ga(1)-O(A) angles (83.0(1)°). The Ga-Cl
bonds (av 2.47 Å) are longer than those observed for the
bridging chloride in the structure of 3 (av 2.38 Å),
suggesting a weaker coordination of the halide ligand.
Finally, the three gallium atoms are separated by
approximately 3 Å and form a nearly equilateral tri-
angle.
Compound 4 dissolves only in polar solvents such as
THF to yield non-conducting solutions. In an effort to
understand the structure of 4 in solution, a number of
physical measurements have been carried out. Pulse
field gradient spin-echo (PGSE) has emerged as a valid
method for the determination of diffusion coefficients
and hydrodynamic radii of organometallic compounds.20
Moreover, it has been demonstrated that an excellent
correlation exists between the molecular radius derived
from X-ray diffraction data and the hydrodynamic
radius derived from diffusion determination by PGSE.21
Thus, to evaluate the radius of 4 in solution, we decided
to compare its diffusion to that of two standards,
namely, bis(diphenylphosphino)cyclopentadiene iron(II)
(A)22 and ETHANOX 330 (B).23 These two standards
were chosen because their molecular radii (5.5 Å for A
and 6.6 Å for B), which can be calculated from their
crystal structures,22,23 are close to those of monomeric
4 (5.5-5.75 Å)24 and dimeric 4 (6.6 Å),24 respectively.
Several measurements were carried out. In all cases, 4
was found to diffuse faster than B and slower than A.
These results suggest that, in solution, 4 undergoes a
rapid monomer-dimer equilibrium that leads to the
observation of an intermediate molecular size. This view
F igu r e 1. Structure of 3 in the crystal. Selected bond
lengths (Å) and angles (deg): Sn(1)-C(33) 2.114(3), Sn(1)-
C(31) 2.115(3), Sn(1)-C(32) 2.124(3), Sn(1)-Cl(1) 2.7444(7),
Sn(1)-Cl(3A) 2.7578(7), Ga(1)-C(11) 1.955(3), Ga(1)-C(1)
1.957(3), Ga(1)-Cl(1) 2.2806(7), Ga(1)-Cl(2) 2.3803(7),
Ga(2)-C(18) 1.962(3), Ga(2)-C(8) 1.965(3), Ga(2)-Cl(3)
2.2723(7), Ga(2)-Cl(2) 2.3743(7); C(33)-Sn(1)-C(31)
121.19(12), C(33)-Sn(1)-C(32) 115.34(12), C(31)-Sn(1)-
C(32) 123.35(11), Cl(1)-Sn(1)-Cl(3A), 176.64(2), C(11)-
Ga(1)-C(1) 132.28(11), Cl(1)-Ga(1)-Cl(2) 100.07(3), C(18)-
Ga(2)-C(8) 134.43(11), Cl(3)-Ga(2)-Cl(2) 100.89(2), Ga(1)-
Cl(1)-Sn(1) 111.73(3), Ga(2)-Cl(2)-Ga(1) 76.91(2), Ga(2)-
Cl(3)-Sn(1A) 115.28(3).
(Scheme 1). Crystals of 4 are colorless planks that can
be physically separated on the basis of their appearance.
The yield of compound 4 could be greatly enhanced by
adding water to the reaction mixture. Initial optimiza-
tion of this reaction was done empirically, and the best
yields (up to 16%) were obtained for reaction mixtures
containing 1, GaCl3, and H2O in 0.06, 0.06, and 0.012
M concentration, respectively. Higher concentration of
water did not result in higher yields; rather it led to
increased formation of naphthalene. As shown, by X-ray
analysis (Table 1), elemental analysis, and NMR, 4 is a
12-membered macrocycle containing three gallium at-
oms linked by 1,8-naphthalenediyl ligands and arranged
about a central oxygen atom. The charge balance is
achieved by the presence of a chloride atom that
occupies a bridging position between two of the gallium
centers (Figure 1). In the crystal, 4 exists as a dimer
wherein the monomers are bridged via a Ga-O-Ga-O
four-membered ring involving Ga(1) (Figure 2). Conse-
quently, the oxygen is four-coordinate and adopts a
distorted tetrahedral geometry (97.04° e Ga-O-Ga e
124.48°). A Ga3O unit constitutes the core of each
monomer. In this unit, the Ga-O distances (av 1.95 Å)
are shorter than the intermolecular Ga(1)-O(A) dis-
tance of 2.028 Å. These distances fall within the range
observed for other gallium species featuring multiply
bridging oxygen atoms.19 Each gallium center adopts a
distorted tetrahedral geometry. While two naphthalene
rings, the oxygen atom, and the bridging chloride occupy
the coordination sphere of Ga(2) and Ga(3), the coordi-
1
is supported by VT H NMR studies in THF-d8 which
reveal the existence of a fluxional system (Figure 3). The
room-temperature spectrum exhibits three sharp signals
(two doublets and one pseudo-triplet). Upon cooling to
-70 °C, each of the three sharp signals decoalesces into
three signals. The rates of exchange at the different
temperatures were calculated by line shape analysis
techniques.25 The resulting rates of exchange were used
to generate an Eyring plot. A least-squares fit of the
resulting plot yielded the activation enthalpy (∆Hq
)
43 ( 3 kJ ‚mol-1) and activation entropy (∆Sq ) -36 (
9 J ‚K-1‚mol-1). As a whole, these results can be ra-
tionalized by invoking the existence of an exchange
between the monomeric and dimeric form of 4. The low-
(20) Valentini, M.; Pregosin, P. S.; Ruegger, H. Dalton Trans. 2000,
24, 4507-4510.
(21) Valentini, M.; Pregosin, P. S.; Ruegger, H. Organometallics
2000, 19, 2551-2555.
(22) Casellato, U.; Ajo, D.; Valle, G.; Corain, B.; Longato, B.;
Graziani, R. J . Crystallogr. Spectrosc. Res. 1988, 18, 583-590.
(23) ETHANOX 330 ) 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-
hydroxybenzyl)benzene. Chetkina, L. A.; Zavodnik, V. E.; Sobolev, A.
N.; Bel’skii, V. K Kristallografiya 1984, 29, 389-391.
(24) These values are obtained by compounding the molecular
volume of one or two THF molecules (Vmol(THF) ) 100 Å3) with the
estimated molecular volume of the ligand-free monomer. The volume
of the ligand-free monomer is taken as half of the volume of the dimer.
The volume of dimeric 4 (Vmol(dimeric 4) ) (Vcell/Z) - Vmol(toluene) )
1190 Å3) is deduced from the cell measurement after subtraction of
the solvate toluene component (Vmol(toluene) ) 145 Å3).
(25) (a) Sandstrøm, J . Dynamic NMR Spectroscopy; Academic
Press: New York, 1982; pp 77-92. (b) Kaplan, J . I. Fraenkel, G. NMR
of Chemically Exchanging Systems; Academic Press: New York, 1980;
pp 71-128.
(19) Kim, S.-J .; Yang, N.; Kim, D.-H.; Ook Kang, S.; Ko J . Organo-
metallics 2000, 19, 4036-4042.

5656 Organometallics, Vol. 20, No. 26, 2001
Hoefelmeyer et al.
F igu r e 2. Structure of 4 in the crystal. View of the monomeric unit (left) and the dimer (right). Selected bond lengths (Å)
and angles (deg): Sn(1)-Cl(2) 2.740(3), Sn(1)-Cl(1) 2.772(3), Sn(2)-Cl(4) 2.743(3), Sn(2)-Cl(5) 2.751(3), Ga(1)-C(1)
1.957(10), Ga(1)-C(11) 1.970(10), Ga(1)-Cl(1) 2.257(3), Ga(1)-Cl(6) 2.370(3), Ga(2)-C(31) 1.936(12), Ga(2)-C(21) 1.966(11),
Ga(2)-Cl(2) 2.279(3), Ga(2)-Cl(3) 2.396(3), Ga(3)-C(38) 1.972(11), Ga(3)-C(28) 1.979(11), Ga(3)-Cl(4) 2.289(3), Ga(3)-
Cl(3) 2.379(3), Ga(4)-C(8) 1.951(10), Ga(4)-C(18) 1.984(11), Ga(4)-Cl(5) 2.281(3), Ga(4)-Cl(6) 2.365(3); Cl(2)-Sn(1)-
Cl(1) 176.72(9), Cl(4)-Sn(2)-Cl(5) 176.53(9), C(1)-Ga(1)-C(11) 134.1(4), C(1)-Ga(1)-Cl(1) 105.8(4), C(11)-Ga(1)-Cl(1)
104.8(3), C(1)-Ga(1)-Cl(6) 104.3(3), C(11)-Ga(1)-Cl(6) 102.0(3), Cl(1)-Ga(1)-Cl(6) 101.64(11), C(31)-Ga(2)-C(21)
132.7(4), C(31)-Ga(2)-Cl(2) 107.2(3), C(21)-Ga(2)-Cl(2) 106.7(3), C(31)-Ga(2)-Cl(3) 103.7(3), C(21)-Ga(2)-Cl(3) 102.0(4),
Cl(2)-Ga(2)-Cl(3) 99.78(10), C(38)-Ga(3)-C(28) 134.5(4), C(38)-Ga(3)-Cl(4) 106.2(4), C(28)-Ga(3)-Cl(4) 105.9(4), C(38)-
Ga(3)-Cl(3) 101.9(3), C(28)-Ga(3)-Cl(3) 103.2(3), Cl(4)-Ga(3)-Cl(3) 100.19(11), C(8)-Ga(4)-C(18) 131.6(4), C(8)-Ga(4)-
Cl(5) 106.3(3), C(18)-Ga(4)-Cl(5) 106.1(3), C(8)-Ga(4)-Cl(6) 103.9(4), C(18)-Ga(4)-Cl(6) 104.4(3), Cl(5)-Ga(4)-Cl(6)
100.35(11), Ga(1)-Cl(1)-Sn(1) 114.99(11), Ga(2)-Cl(2)-Sn(1) 112.14(12), Ga(3)-Cl(3)-Ga(2) 76.51(9), Ga(3)-Cl(4)-Sn(2)
115.55(11), Ga(4)-Cl(5)-Sn(2) 111.30(12), Ga(4)-Cl(6)-Ga(1) 77.32(9).
F igu r e 3. Left: 1H NMR spectra of 4 in THF-d8 between -70 and +22.5 °C. Right: Proposed exchange process.
temperature spectrum would correspond to that of the
dimer as observed in the solid state. The high-temper-
ature data suggest that upon dissociation into the
monomer, the chloride anion undergoes rapid exchange,
leading to an apparent 3-fold molecular symmetry. In
agreement with the lack of conductivity, we propose that
the chloride exchange is intra- rather than inter-
molecular (Figure 3).
focused on the use of 4 as a receptor for polynuclear
anions.
Exp er im en ta l Section
Gen er a l P r oced u r es. All experimental manipulations
were carried out under a N2 atmosphere using standard
Schlenk procedures and a glovebox. NMR spectra were re-
corded on a Varian VXR-300 instrument at 298 K. The
chemical shifts are reported in ppm relative to SiMe4 for 1H/
13C and SnMe4 for 119Sn nuclei. Atlantic Microlab (Norcross,
GA) performed the elemental analyses. All melting points were
measured on samples in sealed capillaries and are uncorrected.
Pyridine, toluene, and THF were dried over CaH2, K, and Na/
K, respectively, and distilled before use. Compound 1 was
prepared by following the published procedure.12 Sodium
tetraphenylborate was purchased from Aldrich and used
without further purification.
Con clu sion
The results presented herein indicate that distan-
nanes constitute valuable starting materials for the
preparation of polyfunctional organogallium species. In
light of the scarcity of macrocyclic species containing
several group 13 elements, the serendipitous yet repro-
ducible formation of 4 is noteworthy. Present efforts are

Synthesis and Characterization of a Trigallacycle
Organometallics, Vol. 20, No. 26, 2001 5657
Syn th esis of 3. A cold (-25 °C) solution of gallium
trichloride (97 mg, 0.55 mmol) in toluene (1.5 mL) was added
to a cold (-25 °C) solution of 1 (250 mg, 0.55 mmol) in toluene
(3 mL). The resulting solution was kept at -25 °C for several
days, after which a precipitate formed. The precipitate is a
mixture of crystals of 2 and 3-toluene, which were separated
on the basis of morphology. Crystals of 2 are irregular and
golden-brown and are isolated in a 21% yield (30 mg). Crystals
of 3-toluene are clear, colorless, and exhibit a cubic shape.
Yield of 3-toluene: 10% (20 mg); mp 72-76 °C dec. Analytical
data for 3-toluene: Anal. Calcd for C53H50Cl6Ga4Sn2: C, 44.9;
H, 3.56. Found: C, 44.2; H, 3.50. 1H NMR (300 MHz, pyridine-
d5, 25 °C, TMS): δ 0.89 (s with satellites, 2J (H-119/117Sn) )
diffusion coefficient and inversely proportional to the molecular
hydrodynamic radius.
I
δ
3
ln
) -γδ2G2 ∆ -
D
(1)
(I )
(
)
0
Two standards (A22 and B23) with crystallographic radii (RX-ray
)
and therefore hydrodynamic radii (RH)21 approaching those
expected for monomeric 4 and dimeric 4, respectively, were
selected. The slope obtained for 4 was compared to those of
the two standards. In all measurements, the slope obtained
for 4 was well between those of A and B.
Va r ia ble-Tem p er a tu r e NMR. Proton NMR spectra of 4
in THF obtained at -70, -60, -50, -40, -30, -20, -10, 0,
10, and 22.5 °C could be successfully simulated with the
program gNMR 4.1. The resulting exchange rate constants
3
65/68 Hz, 9H, CH3), 7.52 (pseudo-t, J (H,H) ) 7.3 Hz, 7.6 Hz,
4H, CH(3,6)), 7.96 (d, 3J (H,H) ) 7.8 Hz, 4H, CH(4,5)), 8.62 (d,
3J (H,H) ) 6.6 Hz, 4H, CH(2,7)). 13C NMR (75 MHz, pyridine-
d5, 25 °C, TMS): δ 125.3 (C-3,6), 130.4 (C-4,5), 134.7 (C-10),
138.8 (C-2,7), 145.2 (C-9), 160.4 (C-1,8). 119Sn NMR (149.03
MHz, pyridine-d5): δ -16.0.
were used to generate an Eyring plot, which yielded ∆Hq
)
43 ( 3 kJ ‚mol-1 and ∆Sq ) -36 ( 9 J ‚K-1‚mol-1
.
Con d u ctivity Mea su r em en ts. The cell constant of a YSI
Model 35 conductance meter was determined by conductivity
measurement of a 0.02 M KCl solution in distilled water and
found to be 1.0855. To assess the reliability of the measure-
ment, THF solutions of sodium tetraphenylborate were pre-
pared and their conductivity was measured. The conductance
values obtained from these solutions were in close agreement
with those previously reported in the literature.26 THF solu-
tions of 4 at concentrations of 1.67 × 10-3, 8.33 × 10-4, 4.17 ×
10-4, 2.08 × 10-4, and 1.04 × 10-4 M were prepared in a dry
N2 atmosphere and transferred to the cell. The cell was sealed
and connected to the conductance meter for measurement. The
conductivity of these solutions did not differ from that of pure
THF within experimental error.
Syn th esis of 4. A solution of gallium trichloride (49 mg,
0.28 mmol) in toluene (1.5 mL) was added to a solution of 1
(125 mg, 0.28 mmol) in toluene (3 mL) containing water (1.0
µL, 56 µmol). The resulting solution was left in a vial in a
glovebox for 2 days, after which a powder of 4-toluene had
precipitated. Yield: 16% (10 mg); mp 195 °C dec. Anal. Calcd
for C67H44O2Cl2Ga6: C, 58.7; H, 3.2. Found: C, 58.3; H, 3.2.
1H NMR (300 MHz, THF-d8, 25 °C, TMS): δ 7.43 (pseudo-t,
3J (H,H) ) 6.6 Hz, 8.1 Hz, 6H, CH(3,6)), 7.79 (d, 3J (H,H) ) 7.8
3
Hz, 6H, CH(4,5)), 8.10 (d, J (H,H) ) 6.6 Hz, 6H, CH(2,7)).
Sin gle-Cr ystal X-r ay An alysis. The crystallographic meas-
urements were performed at T ) 110 K using a Siemens
SMART-CCD area detector diffractometer, with a graphite-
monochromated Mo KR radiation (λ ) 0.71069 Å). Specimens
of suitable size and quality were selected and mounted onto a
glass fiber with Apiezon grease. The structure was solved by
direct methods, which successfully located most of the non-
hydrogen atoms. Subsequent refinement on F2 using the
SHELXTL/PC package (version 5.1) allowed location of the
remaining non-hydrogen atoms. All hydrogen atoms were
included in calculated positions using a standard riding model.
In the structure of 3, however, the disordered hydrogen atom
attached to C(41) was not included in the refinement. Further
crystallographic details can be found in Table 1 and in the
Supporting Information.
Ack n ow led gm en t. We thank Paul Pregosin and
Heinz Ru¨egger from the ETH for their helpful comments
on PGSE measurements. We are grateful to Steven
Silber for his assistance in programming the pulse
sequences. Support from the National Science Founda-
tion (CAREER CHE-0094264), the Welch Foundation
(Grant A-1423), and the Department of Chemistry at
Texas A&M University is gratefully acknowledged. The
purchase of the X-ray diffractometers was made possible
by a grant from the National Science Foundation (CHE-
9807975).
P u lsed F ield Gr a d en t Sp in -Ech o NMR. All measure-
ments were performed on a Varian Inova 500 MHz spectrom-
eter using Varian’s diffusion software package. Samples were
recorded in THF-d8 at 293 K without spinning. During an
experiment, all factors were kept constant while the gradient
strength (G) was arrayed between 0 and 14 G/cm. The gradient
was calibrated using D2O. Following data collection, the
spectra were carefully integrated. The resulting data points
were subjected to a least-squares fit which produced, as per
eq 1, a regression line whose slope is proportional to the
Su p p or tin g In for m a tion Ava ila ble: Spectral data and
tables of structure refinement, atomic coordinates, bond
lengths and angles, anisotropic displacement parameters, and
hydrogen coordinates for complexes 3 and 4. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM010257L
(26) Bhattacharyya, D. N.; Lee, C. L.; Smid, J .; Szwarc, M. J . Phys.
Chem. 1965, 69, 608-611.