Methyl substituted benzene adducts of trimetic perfluoro-o-phenylene mercury

Article abstract of DOI:10.1039/b304023b

Trimeric perfluoro-ortho-phenylene mercury (I) dissolves in substituted benzenes including toluene, ortho-xylene, meta-xylene, para-xylene and is sparingly soluble in mesitylene. The ¹⁹⁹Hg NMR resonance of 1 in toluene, orthoxylene, meta-xylene, and para-xylene appears at δ - 1051.8, -1053.5, -1051.4 and -1059.1 ppm, respectively. These resonances are slightly upfield from the resonance observed for 1 in CH₂Cl₂ (δ - 1045.2 ppm) and possibly indicates the solvation of the mercury centres by molecules of arenes. Slow evaporation of solutions of 1 in toluene, orthoxylene, meta-xylene, para-xylene and mesitylene affords 1·toluene (2), 1· ortho-xylene (3), 1·meta-xylene (4), 1·para-xylene (5) and 1·mesitylene (6), respectively, as crystalline complexes. These adducts have been characterized by elemental analysis and X-ray crystallography. Thermogravimetric analyses indicate that 2-5 begin to lose the coordinated arene at a temperature below 50°C; however, in the case of 6 loss begins around 91°C. The structures of 2, 4 and 5 reveals the existence of binary stacks in which the aromatic core of the benzenes approaches the mercury centres of 1. In the case of 3 and 6, the aromatic molecule appears preferentially bound to one of the two proximal molecules of 1. Hence, 3 and 6 are best described as discrete 1 : 1 complexes. In 2-6, the resulting Hg ... C_aromatic distances are in the range 3.2-3.5 A and are within the sum of the van der Waals radii. They reflect the presence of secondary polyhapto π-interactions occurring between the electron-rich aromatic molecules and the acidic mercury centres.

Full text of DOI:10.1039/b304023b

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Methyl substituted benzene adducts of trimeric perfluoro-o-
phenylene mercury
Mason R. Haneline, Julie B. King and François P. Gabbaï*
Chemistry TAMU 3255, Texas A&M University, College Station, Texas 77843-3255, USA.
E-mail: francois@tamu.edu
Received 10th April 2003, Accepted 24th May 2003
First published as an Advance Article on the web 9th June 2003
Trimeric perfluoro-ortho-phenylene mercury (1) dissolves in substituted benzenes including toluene, ortho-xylene,
meta-xylene, para-xylene and is sparingly soluble in mesitylene. The 199Hg NMR resonance of 1 in toluene, ortho-
xylene, meta-xylene, and para-xylene appears at δ Ϫ1051.8, Ϫ1053.5, Ϫ1051.4 and Ϫ1059.1 ppm, respectively. These
resonances are slightly upfield from the resonance observed for 1 in CH2Cl2 (δ Ϫ1045.2 ppm) and possibly indicates
the solvation of the mercury centres by molecules of arenes. Slow evaporation of solutions of 1 in toluene, ortho-
xylene, meta-xylene, para-xylene and mesitylene affords 1ؒtoluene (2), 1ؒortho-xylene (3), 1ؒmeta-xylene (4), 1ؒpara-
xylene (5) and 1ؒmesitylene (6), respectively, as crystalline complexes. These adducts have been characterized by
elemental analysis and X-ray crystallography. Thermogravimetric analyses indicate that 2–5 begin to lose the
coordinated arene at a temperature below 50 ЊC; however, in the case of 6 loss begins around 91 ЊC. The structures of
2, 4 and 5 reveals the existence of binary stacks in which the aromatic core of the benzenes approaches the mercury
centres of 1. In the case of 3 and 6, the aromatic molecule appears preferentially bound to one of the two proximal
molecules of 1. Hence, 3 and 6 are best described as discrete 1 : 1 complexes. In 2–6, the resulting Hg ؒ ؒ ؒ Caromatic
distances are in the range 3.2–3.5 Å and are within the sum of the van der Waals radii. They reflect the presence of
secondary polyhapto π-interactions occurring between the electron-rich aromatic molecules and the acidic mercury
centres.
1 in a µ6-η2:η2:η2:η2:η2:η2 fashion. Formation of binary stacks
Introduction
is also observed with larger arenes such as biphenyl, naphth-
The complexation of arenes to mercury() cations constitutes a
alene and triphenylene.11 In an effort to determine how steric
well established phenomenon.1–5 While original efforts focused
effects might affect complex formation, we have now turned our
on the spectroscopic characterization of the resulting arene-
attention to the case of methylated benzenes and wish to report
mercury complexes, structural studies have also been performed
and indicate that the arene ligand shows a propensity for both
on the complexation of toluene, ortho-xylene, meta-xylene,
para-xylene and mesitylene by 1.
η1/η2-coordination to the mercury centres as shown by the work
of the groups of Olah,1 Dean,2 Kochi,3 and Barron.4 The form-
ation of such complexes results in the activation of the arene
substrates toward electrophilic mercuration reactions. Further
support for electrophilic aromatic substitution reaction has
been provided by Barron and co-workers who showed that
arene mercury() cationic complexes catalyze H/D exchange
reactions of C6D6 with arenes.6 While such reactivity is appar-
ently limited to the case of arene complexes of mercury() salts,
the mercury centres of organomercurials can also bind arenes
in a π-fashion.7 Typically, however, the π-coordination of
arenes observed in organomercurials is relatively weak and
Results and discussion
results in Hg ؒ ؒ ؒ Caromatic distances in the range 3–3.4 Å. While
in most cases, arene coordination occurs intramolecularly,8 a
growing number of investigations indicate that intermolecular
π-arene complexation constitutes a viable motif.9–11 Neverthe-
less, the observation of such complexes necessitates the use of
organomercurials in which the Lewis acidity of the mercury
centre is enhanced through the use of fluorinated and therefore
electron withdrawing ligands.9–11 We first observed such a
phenomenon in the isolation of π-complexes involving ortho-
bis(chloromercurio)tetrafluorophenylene and benzene.9 Taking
advantage of favorable cooperative effects, we turned our
attention to the case of trimeric perfluoro-ortho-phenylene
Synthesis and thermal stability
Compound 1 is only sparingly soluble in benzene (<0.2 mg
mlϪ1) and mesitylene (0.34 mg mlϪ1), but dissolves in toluene
(6.5 mg mlϪ1), ortho-xylene (4.5 mg mlϪ1), meta-xylene (2.5 mg
mlϪ1), and para-xylene (4.0 mg mlϪ1). The 199Hg NMR reson-
ance of 1 in toluene, ortho-xylene, meta-xylene, and para-xylene
appears at δ Ϫ1051.8, Ϫ1053.5, Ϫ1051.4 and Ϫ1059.1 ppm,
respectively. Despite extended acquisition time, the 199Hg NMR
resonance of 1 in benzene or mesitylene could not be obtained
due to the poor solubility of 1 in those solvents. We also note
that the detection of the 199Hg NMR resonance of 1 is com-
plicated by its high multiplicity which results from Hg–F
coupling.16 Slow evaporation of solutions of 1 in toluene,
ortho-xylene, meta-xylene, para-xylene and mesitylene affords
[1ؒtoluene] (2), [1ؒortho-xylene] (3), [1ؒmeta-xylene] (4), [1ؒpara-
xylene] (5) and [1ؒmesitylene] (6), respectively, as crystalline
complexes. These colourless complexes are stable for months
at room temperature. Upon elevation of the temperature,
mercury12 (1),
a
tridentate Lewis acid13 which readily
complexes neutral14–17 and anionic substrates.18 Compound 1
crystallizes from benzene solutions to afford the complex
[1ؒbenzene].10 The resulting complex [1ؒbenzene] adopts a
stacked structure in which the benzene molecules are sand-
wiched between nearly parallel, yet staggered molecules of 1.
As a result of this arrangement, the benzene molecule interacts
with the six mercury centres of the two juxtaposed molecules of
D a l t o n T r a n s . , 2 0 0 3 , 2 6 8 6 – 2 6 9 0
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
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Table 1 Crystal data, data collection, and structure refinement for 2–6
2
3
4
5
6
Crystal data
Formula
Mr
Crystal size/mm
Crystal system
Space group
a/Å
C25H8F12Hg3
1138.08
0.44 × 0.21 × 0.16
Monoclinic
P21/c
9.514(2)
7.4205(19)
35.267(9)
93.550(4)
2485.1(11)
4
C26H10F12Hg3
1152.11
0.33 × 0.17 × 0.14
Monoclinic
P21/n
20.050(4)
6.8569(14)
20.158(4)
115.23(3)
2507.0(9)
4
C26H10F12Hg3
1152.11
0.54 × 0.06 × 0.06
Orthorhombic
Pna21
15.923(3)
21.678(4)
C26H10F12Hg3
1152.11
0.30 × 0.15 × 0.13
Orthorhombic
Pna21
16.854(3)
20.891(4)
C27H12F12Hg3
1166.14
0.25 × 0.24 × 0.40
Monoclinic
P21/c
16.453(3)
7.3780(15)
22.030(4)
96.43(3)
2657.4(9)
4
b/Å
c/Å
7.2192(14)
7.1384(14)
β/Њ
V/Å3
2491.9(9)
4
3.071
18.544
2056
2513.4(9)
4
3.045
18.385
2056
Z
Dc/g cmϪ3
µ(Mo-Kα)/mmϪ1
F(000)/e
3.042
18.592
2024
3.052
18.432
2056
2.915
17.391
2088
Data collection
T /K
Scan mode
hkl Range
110(2)
ω
Ϫ10 to 10,
Ϫ8 to 8,
Ϫ40 to 40
21172
110(2)
ω
Ϫ23 to 21,
Ϫ8 to 6,
Ϫ23 to 23
16191
200(2)
ω
Ϫ17 to 17,
Ϫ24 to 23,
Ϫ8 to 8
19871
293(2)
ω
Ϫ19 to 18,
Ϫ23 to 23,
Ϫ7 to 8
15314
293(2)
ω
Ϫ22 to 19,
Ϫ9 to 9,
Ϫ29 to 29
29640
Measured refl.
Unique refl. (Rint
Refl. used for refinement
Absorption correction
T min/T max
)
3906 (0.1125)
3906
Empirical
0.2620/0.9655
4385 (0.0440)
4385
SADABS
0.4031
3573 (0.0368)
3573
SADABS
0.326298
3779 (0.0452)
3779
SADABS
0.624366
6307 (0.0508)
6307
SADABS
0.252773
Refinement
Refined parameters
R1, wR2 [I > 2σ(I )]
∆ρ(max., min.)/e ÅϪ3
Flack parameter
361
370
370
370
379
0.0433, 0.1046
1.681, Ϫ2.237
–
0.0439, 0.1033
4.019, Ϫ2.832
–
0.0217, 0.0498
1.249, Ϫ0.562
Ϫ0.001(9)
0.0504, 0.1174
4.524, Ϫ1.364
Ϫ0.06(2)
0.0420, 0.1035
3.708, Ϫ1.449
–
a R1 = Σ(Fo Ϫ Fc)/ΣFo. b wR2 = {[Σw(Fo2 Ϫ Fc2)2]/[Σw(Fo )2]}1/2; w = 1/[σ2(Fo ) ϩ (ap)2 ϩ bp]; p = (Fo2 ϩ 2Fc2)/3; a = 0.0747 (2), 0.0700 (3), 0.0690 (4);
0.0272 (5), 0.0800 (6); b = 0 (2), 0 (3), 70 (4), 0 (5), 40 (6).
2
2
Table 2 Metrical parameters for the respective orientation of the molecular component in 2–6 (Fig. 3)
Complex
2
3
4
5
6
Interplanar angle/Њ
Intercentroid distances/Å
Interplanar separations/Å
Intercomponent offset/Å
Tilt/Њ
3.5
1.9
5.0
7.1
2.3
3.63, 3.81
3.28, 3.26
1.61, 2.04
3.28 3.99
3.23, 3.21
0.59, 2.39
3.40, 3.89
3.41, 3.33
0.90, 1.95
3.61, 3.60
3.34, 3.33
1.38, 1.38
3.39, 4.54
3.39, 3.39
0.10, 3.02
29.3
23.2
21.0
however, loss of the arene is readily observed. These adducts
have been characterized by elemental analysis and thermogravi-
metric analysis. Compounds 2–5 feature a similar behaviour
with loss of arene occurring in the temperature range of 35–125
ЊC. For compound 6, however, higher temperatures (90–160 ЊC)
are required. In all cases, heating to temperatures higher
than 160 ЊC leads to further weight loss which results from the
sublimation of the trimercury derivative 1.
structures of 2, 4 and 5 reveal the existence of binary stacks.
The dihedral angles formed between the planar trinuclear core
of 1 and the aromatic ring (3.5, 5.0 and 7.1Њ for 2, 4 and 5,
respectively) indicate that the alternating molecules are almost
parallel to one another. The distances separating the centroid
of the substituted benzene ring from the centroid of the two
proximal molecules of 1 (3.63 and 3.81 Å for 2, 3.40 and 3.89 Å,
for 4, 3.60 and 3.61 Å for 5) are relatively close; hence the stacks
are regular and do not feature any discontinuity. In each stack,
the successive molecules of 1 adopt an eclipsed rather than a
staggered arrangement. It is also worth noting that the stacks
are tilted with respect to the normal of the plane containing the
three mercury centres of 1 (Fig. 2). This tilt (29.3, 23.2 and 21.0Њ
for 2, 4 and 5, respectively) results from a moderate slippage of
the sandwiched aromatic with respect to the centroid of the Hg3
core of two closest molecules of 1. Despite this slippage which
is best measured by the offset distances defined in Fig. 3 (1.61
and 2.04 Å for 2, 0.90 and 1.95 Å, for 4, 1.38 and 1.38 Å for 5)
we note that the aromatic ring of the substituted benzene
remains situated above and below the core of the trinuclear
complexes. In each case, the substituted benzene derivatives
exhibit Hg ؒ ؒ ؒ Caromatic interactions with distances ranging
from 3.189(15) to 3.506(8) Å with the mercury centres of the
neighbouring molecules of 1. While in 2, 4 and 5, the arene is
almost equidistant from the two neighbouring molecules of 1,
The 199Hg NMR resonance of 1 in toluene, ortho-xylene,
meta-xylene and para-xylene resonance is slightly upfield from
the resonance observed for 1 in CH2Cl2 (δ Ϫ1045.2 ppm). This
phenomenon possibly reflects the solvation of the mercury
centres by molecules of arenes. The facile crystallization of
these binary solids and their thermal stability at ambient
temperature points to the affinity of 1 for aromatic substrates.
These results are in agreement with previous studies dealing
with the complexation of benzene,10 biphenyl, naphthalene and
triphenylene by 1.11
Structural studies
The crystal structures of compound 2–6 have been determined
and the pertinent crystallographic data have been assembled in
Tables 1–3 and in the captions of Figs. 1, 4 and 5. In all cases,
there is one molecule of 1ؒarene in the asymmetric unit. The
D a l t o n T r a n s . , 2 0 0 3 , 2 6 8 6 – 2 6 9 0
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Table 3 Selected intramolecular distances (Å) and angles (Њ)
2
3
4
5
6
Atom numbering scheme
Hg(1)–C(8)
Hg(1)–C(1)
Hg(2)–C(7)
Hg(2)–C(14)
Hg(3)–C(2)
Hg(3)–C(13)
2.063(13)
2.069(14)
2.046(13)
2.067(13)
2.049(13)
2.084(13)
2.065(10)
2.072(10)
2.070(11)
2.062(10)
2.086(10)
2.075(10)
2.051(9)
2.054(8)
2.076(8)
2.076(9)
2.075(9)
2.066(8)
2.086(18)
2.102(18)
2.028(18)
2.07(2)
2.07(2)
2.110(19)
2.074(8)
2.071(8)
2.078(9)
2.065(8)
2.053(8)
2.066(8)
C(8)–Hg(1)–C(1)
C(7)–Hg(2)–C(14)
C(2)–Hg(3)–C(13)
174.6(5)
173.5(6)
173.2(5)
176.6(4)
175.1(4)
174.6(4)
174.7(4)
173.6(3)
175.9(4)
177.4(8)
174.8(8)
177.0(9)
176.4(3)
174.6(3)
176.3(3)
Fig. 1 Molecular structures of compounds 2, 4 and 5. Intermolecular bond distances (Å) for each compound. Compound 2: Hg(3)–C(06)
3.189(15), Hg(3)–C(01) 3.323(15), Hg(2A)–C(05) 3.403(15), Hg(2A)–C(06) 3.387(15). Compound 4: Hg(1)–C(02) 3.359(9), Hg(2)–C(05) 3.462(11),
Hg(3A)–C(02) 3.383(11), Hg(3A)–C(03) 3.243(11). Compound 5: Hg(1)–C(02) 3.19(2), Hg(1)–C(01) 3.42(2), Hg(3A)–C(03) 3.48(3), Hg(3A)–C(04)
3.31(3).
Fig. 2 Space-filling diagrams of compounds 2, 4 and 5.
3.265(11) to 3.474(11) Å (Fig. 4). By contrast, the ortho-xylene
molecule forms a single dihapto contact between the C(01)–
C(06) atom pair and the Hg(2) centre of the most distant
neighbouring molecule of 1 ((Hg(2)–C(01) 3.324(12), Hg(2)–
C(06) 3.217(12)). The disparity found in the distances formed
between the centroid of the substituted benzene ring and those
of the closest two molecules of 1 (3.28 and 4.00 Å) corroborate
this general observation. This situation is even more acute in 6
which features very disparate inter-centroid distances of 3.41
and 4.52 Å. As a result, 6 can be described as a 1 : 1 complex
(Fig. 5). In this 1 : 1 complex, the mesitylene molecule is located
directly above of the trinuclear core of 1 and interacts with the
mercury centres via three contacts of 3.506(8), 3.445(8) and
3.443(8) Å which involve the non-substituted carbon atoms
Fig. 3 Diagram defining the tilt angle and the offsets.
of the aromatic ring. Inspection of the cell packing diagram
indicate that the 1 : 1 complexes interact with one another
the molecule of ortho-xylene in 3 appears preferentially bound
to one of the two proximal molecules of 1 with which it forms
four short Hg ؒ ؒ ؒ Caromatic contacts with distances ranging from
via an additional Hg ؒ ؒ ؒ Caromatic interaction with a distance
of 3.443(8) Å involving C(02) and the Hg(1) centre of a
neighbouring molecule.
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unsubstituted arenes,10,11 the present findings indicate that 1
tolerates increased steric bulk and readily complexes methyl
substituted benzenes. In compounds 2–6 the supramolecular
stacks are held by the presence of secondary π-interactions
between the mercury centres of 1 and the aromatic molecule.
We have previously proposed that the formation of such species
results from donor interactions involving the filled π orbitals of
the aromatic substrate and the empty 6p orbitals of the mercury
centres. While such interactions are likely to be at play in the
structure of 2–6, we note that in several cases, the aromatic
molecule appears randomly oriented above and below the
trinuclear core of 1. This feature might be taken as an evidence
for the weakness of the donor interactions and probably reflects
the participation of less directional electrostatic and dispersion
forces. DFT calculations undertaken on 1 show a positively
charged electrostatic potential surface in the centre of the
complex.24 With a negatively charged electrostatic potential
surface at their locus,25 the observed arrangement of the
aromatic molecules might also result from favourable electro-
static interactions. Finally, we note that dispersion forces
between the soft mercury atoms of 1 and the polarizable
aromatic derivatives may also be present.26
Fig. 4 Molecular structure of compound 3 showing the ortho-xylene
derivative and the closest neighboring molecule of 1. Intermolecular
bond distances (Å): Hg(1)–C(05) 3.321(12), Hg(1)–C(06) 3.451(11),
Hg(2)–C(02) 3.265(11), Hg(3)–C(04) 3.474(11).
Experimental
General
Due to the toxicity of the mercury compounds discussed
in these studies extra care was taken at all times to avoid contact
with solid, solution, and air-borne particulate mercury com-
pounds. The studies herein were carried out in a well-aerated
fume hood. Atlantic Microlab, Inc., Norcross, GA, performed
the elemental analyses. All commercially available starting
materials and solvents were purchased from Aldrich Chemical
and were used as provided. Compound 1 was prepared
according to the published procedure outlined by Sartori and
Golloch.12 All NMR measurements were acquired at ambient
temperature on an INOVA 400 MHz spectrometer.
Fig. 5 Molecular structure of compound 6. Intermolecular bond
distances (Å): Hg(1)–C(04) 3.506(8), Hg(2)–C(06) 3.445(8), Hg(3)–
C(02) 3.443(8).
General synthetic procedure
Although electrostatic forces likely contribute to the stability
of these assemblies, it is important to note that in all cases, there
are short contacts between the mercury centres of 1 and the
substituted benzene molecules. These distances are in the 3.2–
3.5 Å range and exceed the Hg–C bonds observed in arene
mercury() cation complexes by approximately 0.8 Å. Never-
theless, they remain within the sum of the van der Waals radius
of mercury (rvdw(Hg) = 1.73–2.00 Å)19,20 and that of carbon in
aromatic systems (rvdw(Caromatic) = 1.7 Å).21 They are similar to
those observed in [1ؒbenzene], [1ؒbiphenyl], [1ؒnaphthalene]
and [1ؒtriphenylene] (3.25–3.55 Å)10,11 and indicate the presence
of weak secondary π interactions. Similar contacts are present
in the structure of [1ؒ4-phenylpyridine].14 While 1ؒbenzene
features stacks whose propagation direction is perpendicular to
the plane of 1, the stacks observed in 2, 4 and 5 are tilted with
respect to the normal of the plane containing the three mercury
centres of 1. This structural difference likely arises from
the increased steric requirements of the substituted benzene
derivatives which apparently interfere with the regularity of
the stacking motif. Further increase of the steric bulk as in 6,
prevents efficient stacking and leads to the formation of 1 : 1
complexes. In a final note, although arene–fluoroarene inter-
actions are not evident in 2–6, these supramolecules are
reminiscent of those involving methyl substituted benzenes and
electron deficient molecules.22,23
Compound 1 was dissolved by boiling in the selected solvents:
toluene, o-xylene, m-xylene, p-xylene, and mesitylene. Upon
cooling, followed by slow evaporation of the solvent in a well-
aerated fume hood, crystallization occurs to afford quantitative
yields of [1ؒtoluene] (2), [1ؒortho-xylene] (3), [1ؒmeta-xylene]
(4), [1ؒpara-xylene] (5) and [1ؒmesitylene] (6). Compound 2.
Found: C, 26.42; H, 0.76. C25H8F12Hg3 requires C, 26.38; H,
0.71. Compound 3. Found C, 27.55; H, 0.86. C26H10F12Hg3
requires C, 27.10; H, 0.88. Compound 4. Found: C, 27.11; H,
0.84. C26H10F12Hg3 requires C, 27.10; H, 0.88. Compound 5.
Found: C, 27.40; H, 0.93. C26H10F12Hg3 requires C, 27.10; H,
0.88. Compound 6. Found: C, 27.71; H, 1.01. C27H12F12Hg3
requires C, 27.81; H, 1.04%.
Single-crystal X-ray analysis
X-Ray data for 2, 3, 4, 5 and 6 were collected on a Bruker
Smart-CCD diffractometer using graphite-monochromated
Mo-Kα radiation (λ = 0.71073 Å). Specimens of suitable size
and quality were selected and mounted onto a glass fibre with
either Apiezon grease (for low-temperature data collections) or
epoxy (for room-temperature data collections). The structures
were solved by direct methods, which successfully located most
of the non-hydrogen atoms. Subsequent refinement on F 2 using
the SHELXTL/PC package (version 6.1) allowed location of
the remaining non-hydrogen atoms.
Conclusion
CCDC reference numbers 208162–208166.
The results presented herein further document the affinity of 1
for aromatic derivatives. While previous studies focused on
See http://www.rsc.org/suppdata/dt/b3/b304023b/ for crystal-
lographic data in CIF or other electronic format.
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Chem. Commun., 1995, 609–610; M. Tschinkl, R. E. Bachman and
F. P. Gabbai, J. Organomet. Chem., 1999, 582, 40–44.
9 J. R. Gardinier and F. P. Gabbai, J. Chem. Soc., Dalton Trans., 2000,
2861–2865.
Solubility measurements
A weighed vial and stir bar were charged with a known amount
of 1 (approximately 20 mg for toluene, o-xylene, m-xylene, and
p-xylene and approximately 2 mg for benzene and mesitylene).
The solvent was then added incrementally to the vial while
stirring until the presence of solid 1 was no longer observed.
The vial was then reweighed to determine the amount of
solvent added.
10 M. Tsunoda and F. P. Gabbai, J. Am. Chem. Soc., 2000, 122,
8335–8336.
11 M. R. Haneline, M. Tsunoda and F. P. Gabbai, J. Am. Chem. Soc.,
2002, 124, 3737–3742.
12 P. Sartori and A. Golloch, Chem. Ber., 1968, 101, 2004–2009.
13 For a series of general reviews on this topic, see: J. D. Wuest, Acc.
Chem. Res., 1999, 32, 81–89; J. Vaugeois, M. Simard and J. D.
Wuest, Coord. Chem. Rev., 1995, 145, 55–73; M. F. Hawthorne and
Z. Zheng, Acc. Chem. Res., 1997, 30, 267–276; M. F. Hawthorne,
Pure Appl. Chem., 1994, 66, 245–254; F. P. Schmidtchen and
M. Berger, Chem. Rev., 1997, 97, 1609–1646; W. E. Piers, G. J. Irvine
and V. C. Williams, Eur. J. Inorg. Chem., 2000, 2131–2142.
14 M. C. Ball, D. S. Brown, A. G. Massey and D. A. Wickens,
J. Organomet. Chem., 1981, 206, 265–277.
Thermal gravimetric analyses
These analyses were carried out on a TA Instruments TGA
Q500 using an argon flow (rate 60 ml minϪ1), a heating rate of
2 ЊC minϪ1 and a sample size between 6 and 45 mg. The tem-
perature range in which the weight loss occurs is given for each
compound, along with the calculated and observed weight loss
(WLcalc and WLobs, respectively). 2, 37 ЊC Ϫ114 ЊC (WLcalc
8.10%; WLobs, 8.09%); 3, 47 ЊC Ϫ115 ЊC (WLcalc, 9.22%; WLobs
8.65%); 4, 42 ЊC Ϫ124 ЊC (WLcalc, 9.22%; WLobs, 8.97%); 5, 43
ЊC Ϫ117 ЊC (WLcalc, 9.22%; WLobs, 9.52%); 6, 91 ЊC Ϫ154 ЊC
(WLcalc, 10.31%; WLobs, 10.56%).
15 J. Baldamus, G. B. Deacon, E. Hey-Hawkins, P. C. Junk and
C. Martin, Aust. J. Chem., 2002, 55, 195–198.
,
,
16 I. A. Tikhonova, F. M. Dolgushin, K. I. Tugashov, P. V. Petrovskii,
G. G. Furin and V. B. Shur, J. Organomet. Chem., 2002, 654,
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G. G. Furin, P. V. Petrovskii and V. B. Shur, Russ. Chem. Bull., 2001,
50, 1673–1678; I. A. Tikhonova, F. M. Dolgushin, A. I. Yanovsky,
Z. A. Starikova, P. V. Petrovskii, G. G. Furin and V. B. Shur,
J. Organomet. Chem., 2000, 613, 60–67.
Acknowledgements
17 J. B. King, M. Tsunoda and F. P. Gabbaï, Organometallics, 2002, 21,
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We would like to thank Charles Peñaloza for his participation
to this work as well as Dr. Joy Heising and Professor
Abraham Clearfield for their help with the TGA measurements.
Acknowledgment is made to the donors of the American
Chemical Society Petroleum Research Fund for support of
this research (Grant ACS PRF#38143-AC 3). The purchase
of the X-ray diffractometers was made possible by two grants
from the National Science Foundation (CHE-9807975 and
CHE-0079822).
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