Structural effects of varied steric bulk in 2,(4),6-substituted dimethylthallium(III) phenoxides

Article abstract of DOI:10.1002/ejic.201100043

The structural effects of varied steric bulk on 2,(4),6-substituted dimethylthallium(III) phenoxides has been examined. The facile reaction of Me₃Tl with a series of 2,(4),6-substituted phenols in toluene or diethyl ether resulted in the formation of the species [Me₂TlO(2,6- R₂C₆H₃)]₂ [R = H (4), Me (5), iPr (6), Ph (7)] and [Me₂TlO(2,4,6-tBu₃C₆H ₂)] (8). All compounds have been characterized by elemental analysis as well as their melting point; FTIR, FT-Raman, solution ¹H and ¹³C{¹H} NMR spectroscopy; and X-ray crystallography. The structures of 4-7 are dimeric through short intermolecular Tl-O interactions, which yield a symmetric Tl₂O₂ unit and a distorted seesaw C₂O₂ bonding environment for thallium. An increase in the steric bulk in 4-6 has little effect on Tl-O bond lengths, whereas the C _Me-Tl-C_Me bond angle was found to significantly decrease. Further, the phenoxide ligands in 5 and 6 were found to be oriented perpendicular to the Tl₂O₂ unit to minimize steric interactions. Alternatively, compound 7 shows an increase in Tl-O bond lengths and an increase in the C_Me-Tl-C_Me bond angle compared to 4-6, and orientation of the phenoxide ligands perpendicular to the Tl ₂O₂ core. The significant steric bulk imposed by the -O(2,4,6-tBu₃C₆H₂) ligand in 8 precludes dimer formation and allows for isolation of a monomeric species that contains a three-coordinate T-shaped C₂O bonding environment for thallium. DFT calculations show that the energetic favorability of dimer formation decreases with increased phenoxide steric bulk.

Full text of DOI:10.1002/ejic.201100043

FULL PAPER
DOI: 10.1002/ejic.201100043
Structural Effects of Varied Steric Bulk in 2,(4),6-Substituted
Dimethylthallium(III) Phenoxides
Glen G. Briand,*[a] Andreas Decken,[b] J. Ian McKelvey,[a] and Yukun Zhou[a]
Keywords: Thallium / O ligands / Density functional calculations / Structure elucidation
The structural effects of varied steric bulk on 2,(4),6-substi-
tuted dimethylthallium(III) phenoxides has been examined.
The facile reaction of Me3Tl with a series of 2,(4),6-substi-
tuted phenols in toluene or diethyl ether resulted in the for-
mation of the species [Me2TlO(2,6-R2C6H3)]2 [R = H (4), Me
found to significantly decrease. Further, the phenoxide li-
gands in 5 and 6 were found to be oriented perpendicular to
the Tl2O2 unit to minimize steric interactions. Alternatively,
compound 7 shows an increase in Tl–O bond lengths and an
increase in the CMe–Tl–CMe bond angle compared to 4–6,
(5), iPr (6), Ph (7)] and [Me2TlO(2,4,6-tBu3C6H2)] (8). All com- and orientation of the phenoxide ligands perpendicular to
pounds have been characterized by elemental analysis as
well as their melting point; FTIR, FT-Raman, solution H and
the Tl2O2 core. The significant steric bulk imposed by the –
O(2,4,6-tBu3C6H2) ligand in 8 precludes dimer formation and
allows for isolation of a monomeric species that contains a
three-coordinate T-shaped C2O bonding environment for
thallium. DFT calculations show that the energetic favor-
ability of dimer formation decreases with increased phen-
oxide steric bulk.
1
13C{1H} NMR spectroscopy; and X-ray crystallography. The
structures of 4–7 are dimeric through short intermolecular Tl–
O interactions, which yield a symmetric Tl2O2 unit and a dis-
torted seesaw C2O2 bonding environment for thallium. An
increase in the steric bulk in 4–6 has little effect on Tl–O
bond lengths, whereas the CMe–Tl–CMe bond angle was
Simple dimethylthallium alkyl/aryloxide species have
been known for some time, though few examples have been
reported in the literature, namely, Me2TlOR [R = Me,[11]
Et,[12] tBu,[13] 2-ClC6H4 (3),[14] 2-(CHO)C6H4,[15] C6H5
(4)].[15,16] Further, many of these compounds are poorly
characterized and/or detailed synthetic procedures are not
provided. Structural characterization of 3 and 4 has shown
that these species are dimeric in the solid state through very
short intermolecular Tl–O bonding interactions, which
yield a strongly bonded and symmetric Tl2O2 unit.[14] These
complexes also feature near-linear CMe–Tl–CMe bond
angles and a peculiar distorted seesaw geometry at thallium,
which valence-shell electron-pair repulsion (VSEPR) theory
predicts to be tetrahedral given the absence of a valence
lone pair of electrons at the metal center. To determine the
effect of altering the steric bulk on the formation of inter-
molecular bonds and the bonding environment of thallium
in dimethylthallium phenoxide species,[17] we have prepared
and structurally characterized the complexes [Me2TlO(2,6-
R2C6H3)]2 [R = H (4), Me (5), iPr (6), Ph (7)] and
[Me2TlO(2,4,6-tBu3C6H2)] (8), which incorporate bulky
2,(4),6-substituted phenoxide ligands. Further, we have
studied the subtle changes in the resulting thallium bonding
environments by means of vibrational and solution NMR
spectroscopy, and carried out DFT calculations to rational-
ize the observed structures.
Introduction
Although the facile preparation of thin films of thallium-
based high-Tc superconductors (TlBaCaCuO)[1] and semi-
conductors (Tl2O3)[2] by means of metal–organic chemical-
vapor deposition (MOCVD) was first demonstrated some
time ago,[3,4] there have been very few studies of potential
organometallic thallium oxide precursors.[5,6] Potential “sin-
gle source” candidates include diorganothallium(III) com-
pounds (e.g., R2TlORЈ), which comprise the most stable
and extensively studied class of organothallium(III) spe-
cies.[7] However, intermolecular Tl···O interactions in these
compounds result in dimeric or polymeric species in the
solid state {e.g., [Ph2Tl(trop)]2 (1; trop = tropolonate),
[Me2Tl(acac)]ϱ (2; acac = acetylacetonate)}[8–10] and likely
decrease their volatility.
[a] Department of Chemistry and Biochemistry, Mount Allison
University,
Sackville, New Brunswick, E4L 1G8, Canada
Fax: +1-506-364-2313
E-mail: gbriand@mta.ca
[b] Department of Chemistry, University of New Brunswick,
Fredericton, New Brunswick, E3B 6E2, Canada
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100043.
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Varied Steric Bulk in Substituted Me2Tl(III) Phenoxides
(2882 Hz) is in a similar range. Overall, chemical-shift val-
ues and coupling constants do not appear to correspond to
changes in the CMe–Tl–CMe bond angle or Tl–O bond
lengths observed in the solid-state structures (vide infra).
Vibrational Spectroscopy
The vibrational spectra of 4–8 all show characteristic
peaks that correspond to the symmetric and asymmetric
stretching vibrations of the Me–Tl–Me unit. Due to the
near-linear and centrosymmetric nature of the dimethylthal-
lium groups in 4–7, the symmetric vibration is very strong
in the FT-Raman spectra and very weak in the correspond-
ing FTIR spectra, whereas the opposite is observed for the
asymmetric mode. The frequencies for each molecular vi-
bration in 4–8 fall in a relatively narrow range [νsym(Me–
Tl–Me)
=
473–484 cm–1; νasym(Me–Tl–Me)
=
527–
546 cm–1] and are typical for dimethylthallium spe-
cies.[15,16,20] As in the case of the solution NMR spectro-
scopic resonances, the νsym(Me–Tl–Me) and νasym(Me–Tl–
Me) do not correspond to the changes in the CMe–Tl–CMe
bond angle or Tl–O bond lengths observed in the solid-
state structures.
Results and Discussion
Syntheses
The hydrocarbon elimination reaction between trimeth-
ylthallium and the corresponding alcohol[13] is desirable due
to the high reactivity of the triorganothallium species to
rapidly yield the more stable diorganothallium alkoxide and
methane reaction byproduct. Trimethylthallium is prepared
in moderate yield by means of a redox reaction between
thallium(I) iodide, methyl iodide, and methyllithium in di-
ethyl ether, and may be isolated by means of fractional sub-
limation of the volatile product from the crude reaction
product at –26 °C.[18]
Crystal Structure Determination
Crystals suitable for X-ray crystallographic analysis were
isolated for 4–8 by the slow evaporation of reaction mix-
tures at 23 °C. Selected bond lengths and angles are given
in Table 1. The structure of 5 contains two independent mo-
lecules in the asymmetric unit. Although the structure of 4
has been reported previously,[21] structural parameters are
not available on the CCDC and we have redetermined the
structure for comparisons with 5–8.
The reaction of Me3Tl with HOPh in diethyl ether to
yield 4 occurred rapidly at room temperature with evolution
of methane gas, whereas the rate of reaction appeared to
decrease as the 2,6-disubstituted phenol steric bulk was in-
creased to yield 5–8. All reactions were complete within one
hour, and the products were isolated by slow evaporation
or cooling of reaction mixtures. All reactions were quantita-
tive, as determined from H NMR spectra of the reaction
mixtures. The reported yields (13–48%) are of crystalline
material obtained from the reaction filtrate.
The structures of [Me2TlO(2,6-R2C6H3)]2 [R = H (4), Me
(5), iPr (6), Ph (7)] (Figures 1, 2, 3, and 4) show dimeriza-
tion of the corresponding dimethylthallium phenoxide
through intermolecular Tl···O contacts. The Tl–O bond
lengths of the resulting near-planar Tl2O2 cores are similar,
and no monomeric unit can be identified. This is in contrast
to the thiolate analogue of 4, namely, [Me2TlS(C6H5)]2, in
which the Tl–S bond lengths differ by 0.243(8) Å (9%).[14]
The result is a four-coordinate C2O2 bonding environment
for Tl. Given the lack of a valence lone pair for thal-
lium(III), a tetrahedral geometry is expected at the metal
center. However, the CMe–Tl–CMe bond angles [167.8(8)
and 166.9(8)°] are significantly larger than the ideal 109.5°
1
Solution NMR Spectroscopy Studies
1
Solution H NMR studies of 4–8 in [D6]DMSO showed in 4, whereas the O–Tl–O bond angles [75.2(4)–75.5(4)°]
a narrow range of 2J(1H–203/205Tl) values (420–431 Hz), were found to be significantly smaller. The latter is likely a
whereas the Me2Tl resonance of 7 (δ = 0.47 ppm) was up- result of the constraints imposed by the formation of a
field from those of 4–6 and 8 (δ = 0.71–0.85 ppm).[19] The four-membered Tl2O2 ring. The distortion from an ideal
corresponding 13C{1H} NMR spectra show a narrow range tetrahedron is quite significant, and is best described as a
of Me2Tl– resonances for 4–7 (δ = 23.0–24.4 ppm), whereas distorted seesaw geometry at Tl (vide infra).
1
the J(13C–203/205Tl) value is significantly smaller for 7 (4–
2,6-Disubstitution of the phenoxide ligands in 5 and 6
6: 2922–2963 Hz; 7: 2811 Hz). The 13C{1H} NMR reso- yields some distortions in the molecular framework com-
nance for 8 (δ = 26.6 ppm) is slightly downfield from that pared to the unsubstituted analogue 4. Firstly, all four
1
of 4–7, whereas the corresponding J(13C–203/205Tl) value methyl groups in 4 are in the same plane, and the two CMe
–
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Table 1. Selected bond lengths [Å] and angles [°] for 4–8.
4
5
6
7
8
Tl1–C1
Tl1–C2
Tl1–C9
Tl1–C10
Tl1–O1
Tl1–O2
Tl1–O1*
Tl2–C3
Tl2–C4
Tl2–C19
Tl2–C20
Tl2–O1
Tl2–O2
Tl3–C29
Tl3–C30
Tl3–O3
Tl3–O4
Tl4–C39
Tl4–C40
Tl4–O3
Tl4–O4
2.15(2)
2.13(2)
2.132(3) 2.131(5) 2.112(5)
2.141(4) 2.130(5) 2.123(5)
2.123(1)
2.12(1)
2.39(1) 2.417(6) 2.415(2) 2.521(3) 2.283(3)
2.38(1) 2.412(6)
2.505(3)
2.397(2)
2.16(2)
2.12(2)
2.126(5)
2.130(5)
2.13(1)
2.14(1)
2.38(1) 2.386(6)
2.38(1) 2.370(6)
2.12(1)
2.532(3)
2.484(3)
2.14(1)
2.388(6)
2.393(7)
2.14(1)
2.14(1)
2.407(7)
2.399(6)
Figure 2. Crystal structure of the two crystallographically unique
molecules of 5 (50% probability ellipsoids). Hydrogen atoms are
not shown for clarity.
C1–Tl1–C2
C3–Tl2–C4
C9–Tl1–C10
C19–Tl2–C20
C29–Tl3–C30
C39–Tl4–C40
O1–Tl1–O2
O1–Tl2–O2
O3–Tl3–O4
O3–Tl4–O4
O1–Tl1–O1*
C1–Tl1–O1
C2–Tl1–O1
167.8(8)
166.9(8)
156.9(2) 169.1(2) 170.2(2)
171.9(2)
160.4(4)
158.7(4)
157.1(4)
158.0(4)
75.2(4) 73.3(2)
75.5(4) 74.6(2)
74.0(2)
88.1(1)
88.4(1)
73.6(2)
76.22(7)
88.0(2)
Figure 3. Crystal structure of 6 (50% probability ellipsoids). Hy-
drogen atoms are not shown for clarity. Symmetry transformations
used to generate equivalent atoms: (*) –x + 1, –y + 1, –z + 2.
101.8(2)
Figure 1. Crystal structure of 4 (50% probability ellipsoids). Hy-
drogen atoms are not shown for clarity.
Figure 4. Crystal structure of 7 (50% probability ellipsoids). Hy-
drogen atoms are not shown for clarity.
Tl–CMe units form 88.4(4)° and 88.7(5)° angles with the the O–Tl–O bond angles. The similar structural effects im-
Tl2O2 ring. One phenyl ring (C5–C10) is nearly coplanar posed by both the 2,6-dimethyl and 2,6-diisopropyl substi-
with the Tl2O2 core [16.4(8)°], whereas the second (C11– tution is not surprising, given the orientation of the isopro-
C15) is nearly orthogonal [84.7(4)°]. In 5 and 6, the 2,6- pyl groups away from the center of the molecule in 6 (Fig-
disubstituted phenoxide ligands are nearly coplanar with ure 3). This results in similar degrees of steric crowding at
one another and orthogonal to the distorted Tl2O2 core. the thallium-bonded methyl groups in 5 and 6. The overall
Although this presumably occurs to minimize steric crowd- structural arrangement of 5 is similar to that of the indium
ing of the CMe–Tl–CMe unit, a decrease of the CMe–Tl–CMe analogue [Me2InO(2,6-Me2C6H3)]2,[22] whereas 6 resembles
bond angle by approximately 10° is observed. Further, the the aluminum analogue [Me2AlO(2,6-iPr2C6H3)]2.[23]
two CMe–Tl–CMe units in each structure are rotated with
Contrary to the decrease in the CMe–Tl–CMe bond angle
respect to one another and are oriented 78.5(7)–83.1(4)° (5) observed in 5 and 6, that of the 2,6-diphenylphenoxide ana-
and 85.8(1)° (6) to the Tl2O2 ring. However, there are no logue 7 [C1–Tl1–C2 169.1(2)° and C3–Tl1–C4 171.9(2)°]
significant changes in the Tl–C or Tl–O bond lengths or was found to be greater than in 4–6 [156.9(2)° and
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Varied Steric Bulk in Substituted Me2Tl(III) Phenoxides
167.8(8)°]. The O–Tl–O bond angles [88.1(1) and 88.4(1)°] DFT Computational Studies
are also significantly greater than in 4–6 [73.3(2)–75.5(4)°].
DFT calculations were performed to provide insight into
Although the Tl–CMe bond lengths in 7 are similar to those
in 4–6, the Tl–O bond lengths are significantly longer [7:
2.484(3)–2.532(3) Å; 4–6: 2.38(1)–2.417(6) Å]. As with 5
and 6, the CMe–Tl–CMe units are rotated with respect to
one another [15.0(9)°] and are oriented at 85.0(6)° and
85.5(4)° to the near-planar Tl2O2 core. Perhaps the most
significant structural change is a decrease in the sum of the
bond angles at O, thereby resulting in cis-type orientation
of the phenoxide rings relative to the Tl2O2 ring, and angles
of 42.4(1)° and 51.7(1)° between the phenoxide rings and
the Tl2O2 plane. Further, unlike 5 and 6, the phenoxide
groups of 7 are not oriented orthogonal to the Tl2O2 core.
Finally, the 2,6-diphenyl substituents are rotated with re-
spect to the central phenoxide rings, presumably to allow
for minimum steric repulsion with the (Me2TlO)2 core, as
well as between 2,6-Ph2C6H3O groups. The structure of 7
differs from that of the aluminum analogue [Me2AlO(2,6-
Ph2C6H3)]2, which has a structural arrangement similar to
5 and 6.[24]
the observed solid-state structures. Structural representa-
tions of the geometry-optimized structures are shown in
Figure 6. Energies for geometry-optimized structures are
given in Table 2.
In contrast to 4–7, the structure of [Me2TlO(2,4,6-
tBu3C6H2)] (8) (Figure 5) shows the compound to be mono-
meric in the solid state. The Tl–CMe bond lengths [2.112(5)
and 2.123(5) Å] are slightly shorter than those observed for
4–7, while the Tl–O bond length [2.283(3) Å] is significantly
shortened. The nearest intermolecular Tl···O contact is
3.612(3) Å, and is outside of the sum of the van der Waals
radii of 3.5 Å.[25] The bond angles at thallium [C1–Tl1–C2
170.2(2)°; C1–Tl1–O1 88.0(2)°; C2–Tl1–O1 101.8(2)°] are
significantly different from 120°, as predicted by valence-
shell electron-pair repulsion (VSEPR) theory, and the ge-
ometry is best described as distorted T-shaped. The Me–Tl–
Me unit is aligned orthogonal to the phenoxy ring, which
minimizes steric repulsion with the tBu substituents. The
monomeric structure is similar to that observed for the in-
dium analogue [Me2InO(2,4,6-tBu3C6H2)].[22]
Figure 6. Geometry-optimized structures of monomeric and di-
meric Me2TlO(2,6-R2C6H3) species. Hydrogen atoms are not
shown for clarity.
In the calculated R = Me, iPr, and tBu monomers, the
phenoxide rings are near orthogonal to the Me2Tl unit, as
observed in the solid-state structure of 8. This presumably
minimizes steric repulsion among the Me2Tl methyl groups
and the phenoxide 2,6-substituents. Alternatively, the R =
H monomer, which is not sterically impeded, shows an an-
gle of around 54° between the phenoxide ring and the
Me2Tl unit. The phenoxy ring in the R = Ph monomer
shows a “twisted” orientation versus the Me2Tl unit
[Є CMe–Tl–O–Cipso 24°; Є Tl–O–Cipso–Cortho 53°], similar
to the arrangement observed in the solid-state structure of
Figure 5. Crystal structure of 8 (50% probability ellipsoids). Hy-
drogen atoms are not shown for clarity.
Table 2. Calculated energies (E) [kJmol–1] for geometry optimized monomeric (m) and dimeric (d) Me2TlO(2,6-R2C6H3) species.
E
R = H
R = Me
R = iPr
R = Ph
R = tBu
Me2Tl–O(2,6-R2C6H3) (m)
[Me2Tl–O(2,6-R2C6H3)]2 (d)
–1,019,940
–2,040,019
–1,226,248
–2,452,607
–1,638,799
–3,277,699
–2,232,777
–4,465,601
–1,845,034
–
Edimerization (d – 2m)
–139
–111
–101
–47
–
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7. This suggests that the unique structure of 7 may be the the molecular orbitals that involve Tl–O orbital overlap,
result of a weak association of monomeric [Me2TlO(2,6- HOMO–7 and HOMO–4 exhibit corresponding Tl(6p)–
Ph2C6H3)] units. The overall structural arrangements of the O(2p) π-bonding and π-antibonding interactions, respec-
R = H, Me, iPr, and Ph dimers are similar to those obtained tively, whereas HOMO–8, –11, –14, and –15 exhibit Tl(6s)–
from the X-ray crystallographic data for 4–7. It is also O(2p) σ-antibonding orbital overlap. Further, analyses of
worth noting that the phenyl rings in the R = H dimer are atomic charges shows an overall +0.543 charge for the
rotated by approximately 55° with respect to the one an- Me2Tl groups and a corresponding –0.543 charge for the
other, closely resembling the orientation found in the solid- (2,6-Me2C6H3O) ligands. These findings suggest that there
state structure of 4.
is little net orbital bonding character between the (2,6-Me2-
To rationalize the observed intermolecular Tl–O bonding C6H3O) ligands and Me2Tl groups, and the Tl–O bonding
in 4–7, the relative stabilities of the corresponding mono- interaction appears to be largely electrostatic in nature.
meric versus dimeric species may be calculated according to Therefore, the Me2Tl groups are effectively isoelectronic
Equation (1).
with Me2Tl+ group, which is predicted to adopt a linear
geometry according to VSEPR theory.
2Me2Tl–O(2,6-R2C6H3) Ǟ [Me2Tl–O(2,6-R2C6H3)]2
(1)
Negative values were obtained for Equation (1) (Table 2)
for R = H, Me, iPr, and Ph, thus indicating that dimer for-
mation is thermodynamically favorable in each case. How-
ever, the energy lost through dimerization decreases signifi-
cantly with increased steric bulk of the disubstituted phen-
oxide: R = H Ͼ Me Ͼ iPr Ͼ Ph. In the case of R = tBu,
the dimeric structure geometry optimized to two mono-
meric compounds, thereby suggesting that the increase in
energy from the steric strain imposed by the larger tBu
groups outweighs the energy decrease afforded by dimeriza-
tion, that is, the formation of two intermolecular Tl···O
bonds. This again is in agreement with the X-ray crystallo-
graphic analyses.
Although discrepancies are to be expected between cal-
culated gas-phase structures and solid-state crystal struc-
tures, the results of DFT calculations were further analyzed
in attempt to rationalize the near-linear [156.9(2)–171.9(2)°]
C
Me–Tl–CMe bond angles in the solid-state structures of di-
meric compounds 4–7. The CMe–Tl–CMe bond angles in the
geometry-optimized structures are around 10–20° less than
those in the corresponding crystal structures (see the Sup-
porting Information). The calculated bending mode [δ(Me–
Tl–Me) ≈ 150 cm–1] is of very low frequency, thereby sug-
gesting that the CMe–Tl–CMe bond angle may be easily per-
turbed by packing forces. Nevertheless, the overall sym-
Figure 7. Selected DFT-calculated molecular orbitals of
[Me2TlO(2,6-Me2C6H3)]2 (5).
Conclusion
The effect of increasing steric bulk on the dimerization of
metry of the dimeric structures is retained, and the calcu- dimethylthallium(III) phenoxides has been examined. The
lated orbitals should be largely unaffected by small changes structures of 4–7 are dimeric through short intermolecular
in the CMe–Tl–CMe bond angle. It should be noted that Tl–O interactions, which yield symmetric Tl2O2 cores. In-
[Me2AlO(2,6-R2C6H3)]2 [R = iPr, Ph] have CMe–Al–CMe creasing steric bulk in 4–6 has little effect on Tl–O bond
bond angles in the 114.3(6)–116.9(2)° range, whereas [Me2- lengths, whereas compound 7 shows an increase in Tl–O
InO(2,6-Me2C6H3)]2 has a CMe–In–CMe bond angle of bond lengths, as well as a variety of other structural distor-
131.0(2)°.[22–24] Therefore, the (acute) calculated CMe–Tl– tions to minimize steric crowding. The excessive steric bulk
C
Me angles are still significantly greater than those observed imposed by the tBu substituents in 8 allows the preclusion
for structurally characterized aluminum and indium ana- of intermolecular Tl···O contacts and the isolation of a
logues. The difference is even more significant in the mono- unique example of a monomeric species. Solution NMR
meric structures, in which the CMe–In–CMe bond angle of and solid-state vibrational spectra show characteristic reso-
[Me2InO(2,4,6-tBu3C6H2)] is 109.3(8)° and the CMe–Tl– nances for the dimethylthallium group, and are not useful
CMe bond angle of 8 is 170.2(2)°.
for probing subtle structural changes or differentiating
Analysis of the HOMO to HOMO–15 surfaces of monomer versus dimer formation. DFT calculations of 4–
[Me2TlO(2,6-Me2C6H3)]2 (5) (Figure 7; see Supporting In- 7 and their dimeric/monomeric counterparts show that
formation) shows that the majority are σ and π orbitals of thermodynamic instability imposed by a moderately steri-
the (2,6-Me2C6H3O) ligands. Alternatively, HOMO–6 is a cally bulky phenoxide ligand is more than compensated for
Tl(6p)–C(2p) σ-bonding orbital of the Me2Tl groups. Of by the formation of the intermolecular Tl···O bonds. How-
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Varied Steric Bulk in Substituted Me2Tl(III) Phenoxides
H 4.25, N 0.00; found C 34.13, H 4.26, N Ͻ 0.10; m.p. 166 °C.
ever, the structural constraints imposed by the introduction
of significant steric bulk (8) is sufficient to destabilize these
bonding interactions and yield a monomeric dimethylthal-
lium phenoxide species. It is thus clear from this study that
intermolecular thallium–oxygen bonding interactions are
very favorable, and are not effectively precluded with the
introduction of a modest amount of steric bulk. To further
explore intermolecular thallium–chalcogen bonding inter-
actions in this class of compound, we are currently examin-
FTIR: ν = 528 [w, νasym(Me–Tl–Me)]. FT-Raman: 473 [vs,
˜
νsym(Me–Tl–Me)], 527 [vw, νasym(Me–Tl–Me)]. 1H NMR ([D6]-
2
DMSO) δ = 0.73 [d, JTl,H = 421 Hz, 12 H, Me2TlO(2,6-
3
Me2C6H3)], 2.05 [s, 12 H, Me2TlO(2,6-Me2C6H3)], 6.02 [t, JH,H
=
7.2 Hz, 2 H, Me2TlO(2,6-Me2C6H3)], 6.69 [d, 3JH,H = 7.2 Hz, 4 H,
Me2TlO(2,6-Me2C6H3)] ppm. 13C{1H} NMR ([D6]DMSO): δ =
1
18.8 [s, Me2TlO(2,6-Me2C6H3)], 23.2 [d, JTl,13
= 2926 Hz,
C
Me2TlO(2,6-Me2C6H3)], 111.2 [s, Me2TlO(2,6-Me2C6H3)], 126.4 [s,
Me2TlO(2,6-Me2C6H3)], 127.5 [s, Me2TlO(2,6-Me2C6H3)], 166.4 [s,
ing analogous dimethylthallium thiolate, selenolate, and tel- Me2TlO(2,6-Me2C6H3)] ppm.
lurolate species.
[Me2TlO(2,6-iPr2C6H3)]2
(6):
2,6-iPr2C6H3OH
(0.178 g,
1.00 mmol) was added to a solution of TlMe3 (0.250 g, 1.00 mmol)
in toluene (10 mL). After stirring for 1 h, the clear solution was
concentrated to 5 mL, layered with hexane (1 mL), and allowed to
sit at –15 °C. After 7 d, the solution was filtered to yield 6 as color-
less crystals (0.196 g, 0.48 mmol, 48%). C28H46O2Tl2 (823.39):
calcd. C 40.84, H 5.63, N 0.00; found C 41.29, H 5.91, N Ͻ 0.10;
Experimental Section
General Considerations: 2,6-Dimethylphenol (99%), 2,6-diisoprop-
ylphenol (97%), 2,6-di-tert-butylphenol (98%), 2,6-diphenylphen-
ol (98%), 2,4,6-tri-tert-butylphenol (99%), methyllithium 1.6 m in
diethyl ether, thallium(I) iodide (99.999%), and iodomethane
(99.5%) were purchased from the Aldrich Chemical Co. 2,6-Di-
isopropylphenol (97%) was redistilled from CaO prior to use.
Me3Tl was prepared as reported previously and isolated by frac-
tional sublimation at –26 °C.[18] All reactions were carried out un-
der dinitrogen atmosphere using standard Schlenk techniques.
m.p. 167 °C (decomp.). FTIR: ν = 479 [vw, νsym(Me–Tl–Me)],
˜
532 [s, νasym(Me–Tl–Me)]. FT-Raman: 479 vs. [νsym(Me–Tl–Me)],
538 [w, νasym(Me–Tl–Me)]. 1H NMR ([D6]DMSO): δ = 0.71 [d,
3
2JTl,H = 423 Hz, 12 H, Me2TlO(2,6-iPr2C6H3)], 1.03 [d, JH,H
=
3
6.9 Hz, 24 H, Me2TlO(2,6-iPr2C6H3)], 3.47 [sept, JH,H = 6.9 Hz,
4 H, Me2TlO(2,6-iPr2C6H3)], 6.12 [t, JH,H = 7.4 Hz, 2 H,
3
3
Me2TlO(2,6-iPr2C6H3)], 6.68 [d, JH,H = 7.4 Hz, 4 H, Me2TlO(2,6-
iPr2C6H3)] ppm. 13C{1H} NMR ([D6]DMSO): δ = 23.0 [d, JTl,13
1
Caution: Thallium is a cumulative poison that may be absorbed
through the skin. All compounds must be handled with extreme
care.
C
=
2922 Hz, Me2TlO(2,6-iPr2C6H3)], 24.5 [s, Me2TlO(2,6-
iPr2C6H3)], 26.0 [s, Me2TlO(2,6-iPr2C6H3)], 111.5 [s, Me2TlO(2,6-
iPr2C6H3)], 121.9 [s, Me2TlO(2,6-iPr2C6H3)], 137.1 [s, Me2TlO(2,6-
iPr2C6H3)], 163.6 [s, Me2TlO(2,6-iPr2C6H3)] ppm.
Solution 1H and 13C{1H} NMR spectra were recorded at 23 °C
with a JEOL GMX 270 MHz spectrometer (270.2 and 67.9 MHz,
respectively) or a Varian MERCURYplus 200 MHz spectrometer
(200.0 and 50.3 MHz, respectively), and chemical shifts are cal-
ibrated to the residual solvent signal. FTIR spectra were recorded
as Nujol mulls with KBr plates with a Mattson Genesis II FTIR
spectrometer in the range of 4000–400 cm–1. FT-Raman spectra
were recorded with a Thermo Nicolet NXR 9600 Series FT-Raman
spectrometer in the range of 3900–70 cm–1. Melting points were
recorded with an Electrothermal MEL-TEMP melting point appa-
ratus and are uncorrected. Elemental analyses were performed by
Chemisar Laboratories Inc., Guelph, Ontario.
[Me2TlO(2,6-Ph2C6H3)]2 (7): 2,6-PhC6H3OH (0.246 g, 1.00 mmol)
was added to a solution of TlMe3 (0.250 g, 1.00 mmol) in diethyl
ether (15 mL). The reaction mixture was stirred for 1 h and filtered.
The resulting white powder was dissolved in THF (8 mL), and the
solution was allowed to sit at 23 °C. After 1 d, the solution was
filtered to yield 7 as colorless crystals (0.063 g, 0.13 mmol, 13%).
C40H38O2Tl2 (959.44): calcd. C 50.06, H 3.99, N 0.00; found C
50.32, H 4.04, N Ͻ 0.10; m.p. 280 °C. FTIR: ν = 543 [w, νasym(Me–
˜
Tl–Me)]. FT-Raman: 479 [vs, νsym(Me–Tl–Me)]. 1H NMR ([D6]-
2
DMSO): δ = 0.47 [d, JTl,H = 421 Hz, 12 H, Me2TlO(2,6-
3
Ph2C6H3)], 6.31 [t, 2 H, Me2TlO(2,6-Ph2C6H3)], 7.00 [d, JH,H
=
[Me2TlO(C6H5)2 (4): C6H5OH (0.095 g, 1.0 mmol) was added to a
solution of TlMe3 (0.250 g, 1.0 mmol) in toluene (5 mL). The solu-
tion was stirred for 1 h, filtered, and concentrated to 3 mL. The
solution was allowed to sit at 23 °C for 3 d and filtered to yield 4 as
colorless crystals (0.108 g, 0.33 mmol, 33%). C16H22O2Tl2 (655.08):
calcd. C 29.33, H 3.39, N 0.00; found C 29.61, H 3.53, N Ͻ 0.10;
3
7.4 Hz, 4 H, Me2TlO(2,6-Ph2C6H3)], 7.14 [t, JH,H = 7.4 Hz, 4 H,
Me2TlO(2,6-Ph2C6H3)], 7.30 [m, 8 H, Me2TlO(2,6-Ph2C6H3)], 7.67
[d, JH,H = 6.9 Hz, 8 H, Me2TlO(2,6-Ph2C6H3)] ppm. 13C{1H}
3
1
NMR ([D6]DMSO): δ = 24.4 [d, JTl,C = 2811 Hz, Me2TlO(2,6-
Ph2C6H3)], 111.5, 125.5, 128.1, 129.6, 129.9, 131.5, 143.3, 165.5 [s,
Me2TlO(2,6-Ph2C6H3)] ppm.
m.p. 212–213 °C. FTIR: ν = 479 [w, νsym(Me–Tl–Me)] , 541 [s, νa-
˜
sym(Me–Tl–Me)]. FT-Raman: 480 [vs, νsym(Me–Tl–Me)], 538 [vw,
Me2TlO(2,4,6-tBu3C6H2)
(8):
2,4,6-tBu3C6H2OH
(0.262 g,
νasym(Me–Tl–Me)] cm–1. 1H NMR ([D6]DMSO): δ = 0.84 [d, 2JTl,H
1.00 mmol) was added to a solution of TlMe3 (0.250 g, 1.00 mmol)
in toluene (5 mL). The solution was stirred for 1 h. The light-yellow
solution was filtered and concentrated to 1 mL. After sitting at
–15 °C for 1 d, the reaction mixture was filtered to yield 8 as color-
less rodlike crystals (0.100 g, 0.202 mmol, 20%). C20H35OTl
(495.85): calcd. C 48.44, H 7.11, N 0.00; found C 48.84, H 6.92, N
3
= 426 Hz, 12 H, Me2TlO(C6H5)], 6.24 [t, JH,H = 7.0 Hz, 2 H,
Me2TlO(C6H5)], 6.39 [d, 3JH,H = 7.4 Hz, 4 H, Me2TlO(C6H5)], 6.90
[m, 4 H, Me2TlO(C6H5)] ppm. 13C{1H} NMR ([D6]DMSO): δ =
1
23.4 [d, JTl,13 = 2963 Hz, Me2TlO(C6H5)], 112.9 [s, Me2T-
C
lO(C6H5)], 119.4 [s, Me2TlO(C6H5)], 129.2 [s, Me2TlO(C6H5)],
167.9 [s, Me2TlO(C6H5)] ppm.
0.00; m.p. 176 °C. FTIR: ν = 546 [w, νasym(Me–Tl–Me)]. FT-Ra-
˜
1
[Me2TlO(2,6-Me2C6H3)]2
(5):
2,6-Me2C6H3OH
(0.120 g,
man: 484 [vs, νsym(Me–Tl–Me)]. H NMR ([D6]DMSO): δ = 0.85
2
1.00 mmol) was added to a solution of TlMe3 (0.250 g, 1.00 mmol)
in toluene (5 mL). The solution was stirred for 1 h and filtered.
The resulting colorless product was then dissolved in THF (1 mL),
layered with diethyl ether (3 mL), and was allowed to sit at 23 °C.
After 2 d, the solution was filtered to yield 5 as colorless crystals
[d, JTl,H = 431 Hz, 6 H, Me2TlO(2,4,6-tBuC6H2)], 1.15 [s, 9 H,
Me2TlO(2,4,6-tBuC6H2)], 1.32 [s, 18 H, Me2TlO(2,4,6-tBuC6H2)],
6.76 [s, 2 H, Me2TlO(2,4,6-tBuC6H2)] ppm. 13C{1H} NMR ([D6]-
1
DMSO): δ = 26.6 [d, JTl,C = 2882 Hz, Me2TlO(2,4,6-tBuC6H2)],
31.3 [s, Me2TlO(2,4,6-tBuC6H2)], 32.9 [s, Me2TlO(2,4,6-tBuC6H2)],
(0.085 g, 0.24 mmol, 24%). C20H30O2Tl2 (711.18): calcd. C 33.78, 34.0 [s, Me2TlO(2,4,6-tBuC6H2)], 35.4 [s, Me2TlO(2,4,6-tBuC6H2)],
Eur. J. Inorg. Chem. 2011, 2298–2305
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2303

G. G. Briand, A. Decken, J. I. McKelvey, Y. Zhou
FULL PAPER
Table 3. Crystallographic data for 4–8.[a]
4
5
6
7
8
Formula
Fr
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C16H22O2Tl2
655.08
monoclinic
P21/n
9.697(4)
11.302(5)
16.456(7)
90
96.594(6)
90
1792(1)
4
C20H30O2Tl2
711.18
C28H46O2Tl2
823.39
monoclinic
P21/n
9.999(2)
8.983(2)
16.357(3)
90
101.768(2)
90
1438.3(4)
2
C40H32O2Tl2
959.44
monoclinic
P21/n
15.666(7)
14.349(6)
16.251(7)
90
113.030(6)
90
3362(3)
4
C20H35OTl
495.85
orthorhombic
Pnma
10.989(1)
14.697(1)
12.618(1)
90
90
90
2037.9(3)
4
triclinic
¯
P1
7.910(1)
16.143(2)
17.949(3)
107.003(2)
90.476(2)
102.913(2)
2129.8(5)
4
α [°]
β [°]
γ [°]
V [Å3]
Z
F(000)
ρcalcd. [gcm–3]
μ [mm–1]
T [K]
1184
2.429
17.965
198(1)
0.0838
0.2291
1312
2.218
15.122
198(1)
0.0372
0.0901
784
1.901
11.210
198(1)
0.0190
0.0473
1824
1.896
9.608
173(1)
0.0280
0.0660
976
1.616
7.927
198(1)
0.0222
0.0615
[b]
R1
[c]
wR2
½
[a] In all cases, λ = 0.71073 Å. [b] R1 = [Σ||Fo| – |Fc||]/[Σ|Fo|] for [F2o Ͼ 2σ(F2o)]. [c] wR2 = {[Σw(F2o – F2c)2]/[Σw(F4o)]} .
120.0 [s,
2
H, Me2TlO(2,4,6-tBuC6H2)], 127.0 [s,
2
H, bond lengths and angles for 4–8, DFT-calculated surfaces (HOMO
to HOMO–15) of [Me2TlO(2,6-Me2C6H3)]2 (5), and X-ray crystal-
lographic data for 4–8.
Me2TlO(2,4,6-tBuC6H2)], 135.2 [s, 2 H, Me2TlO(2,4,6-tBuC6H2)],
166.8 [s, 2 H, Me2TlO(2,4,6-tBuC6H2)] ppm.
Crystal Structure Determination: Crystals of 4–8 were isolated from
the reaction mixtures as indicated above, or from dichloromethane
(in the case of 5) at 23 °C. Single crystals were coated with Para-
tone-N oil, mounted using a 20 micron cryo-loop, and frozen in
the cold nitrogen stream of the goniometer. A hemisphere of data
was collected with a Bruker AXS P4/SMART 1000 diffractometer
using ω and θ scans with a scan width of 0.3° and 10 s exposure
times. The detector distance was 5 cm. The crystal of 4 was a mul-
tiple twin and the orientation matrix for two major components
was determined (CELL_NOW).[26] The crystal of 5 was a multiple
twin and the orientation matrix for the major component was de-
termined.[27] The structure of 5 contained two independent mole-
cules in the asymmetric unit. The data were reduced (SAINT)[28]
and corrected for absorption [TWINABS[29] (4), SADABS[30] (5–
8)]. The structure was solved by direct methods and refined by full-
matrix least-squares on F2 (SHELXTL)[31] on all data. All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
included in calculated positions and refined using a riding model.
Crystallographic data are given in Table 3.
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CCDC-740493 (for 4), -767544 (for 5), -740494 (for 6), -740495 (for
7), and -740712 (for 8) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
[9]
[10]
[11]
Computational Methods: DFT calculations were performed using
Gaussian 03[32] at the B3LYP 6-31G* level of theory for all atoms
except Tl, for which Stuttgart electron-core pseudo-potentials (sdd)
were employed. All structures were geometry-optimized, and struc-
tural parameters for input files were derived from crystal structure
data where possible. Structural parameters for proposed mono-
meric structures were derived from the crystal structure data of 5.
Frequency calculations were performed on all structures and gave
no imaginary frequencies. Energy values reported are the electronic
energy values corrected for zero-point energies derived from fre-
quency calculations.
[12]
[13]
[14]
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[15]
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[16]
[17]
G. D. Shier, R. S. Drago, J. Organomet. Chem. 1966, 330–340.
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and, A. Decken, N. S. Hamilton, Dalton Trans. 2010, 39, 3833–
3841.
Supporting Information (see footnote on the first page of this arti-
cle): Complete FTIR and FT-Raman data for 4–8, DFT-calculated
2304
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 2298–2305

Varied Steric Bulk in Substituted Me2Tl(III) Phenoxides
[18]
[19]
multiple twin crystals consistently yielded the same unit cell
and structural solution. The results of both the original incom-
plete data set and a complete multiple twin data set have been
submitted as Supporting Information
a) H. Gilman, R. G. Jones, J. Am. Chem. Soc. 1946, 68, 517–
520; b) R. Boese, A. J. Downs, T. M. Greene, A. W. Hall, C. A.
Morrison, S. Parsons, Organometallics 2003, 22, 2450–2457.
2
1
1
Individual J( H–203Tl)/2J(1H–205Tl) and J(13C–203Tl)/1J(13C–
[28] SAINT 7.23A, Bruker AXS, Inc., Madison, Wisconsin, USA,
2006.
[29] G. Sheldrick, TWINABS 1.05, Bruker Nonius, Inc., Madison,
Wisconsin, USA, 2004.
[30] G. Sheldrick, SADABS, Bruker AXS, Inc., Madison,Wiscon-
sin, USA, 2004.
[31] G. Sheldrick, SHELXTL 6.14, Bruker AXS, Inc., Madison,
Wisconsin, USA, 2000.
[32] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr., T.
Vreven, K. N. Kudin, J. R. Burant, J. M. Millam, S. S. Iyengar,
J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P.
Hratchian, J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts,
R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pom-
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Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui,
A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu,
A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J.
Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
M. Challacombe, P. M. W. Gill, B. G. Johnson, W. Chen, M. W.
Wong, C. Gonzalez, J. A. Pople, Gaussian 03, rev. D.01,
Gaussian Inc., Wallingford, CT, 2004.
205Tl) couplings could not be resolved due to peak broadening,
2
although J(1H–203Tl) values have been reported to be 2–4 Hz
less than 2J(1H–205Tl) in other dimethylthallium compounds
(see ref.[15]).
[20]
M. V. Castano, A. Sánchez, J. S. Casas, J. Sordo, J. L. Briansó,
J. F. Piniella, X. Solans, G. Germain, T. Debaerdemaeker, J.
Glaser, Organometallics 1988, 7, 1897–1904.
P. J. Burke, L. A. Gray, P. J. C. Hayward, R. W. Matthews, M.
McPartlin, J. Organomet. Chem. 1977, 136, C7–C10.
[21]
[22]
G. Briand, A. Decken, N. S. Hamilton, Dalton Trans. 2010, 39,
3833–3841.
[23] A. V. Firth, J. C. Stewart, A. J. Hoskin, D. W. Stephan, J. Or-
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[24] A. J. R. Son, M. G. Thorn, P. E. Fanwick, I. P. Rothwell, Orga-
nometallics 2003, 22, 2318–2324.
[25] H. Gilman, R. G. Jones, J. Am. Chem. Soc. 1946, 68, 517–20.
[26] G. Sheldrick, CELL_NOW, Bruker AXS, Inc., Madison, Wis-
consin, USA, 2005.
[27] For compound 5, a power failure led to incomplete data collec-
tion (82% at 50° in 2θ). The sample decomposed at room tem-
perature, and data collection could not commence after power
was restored. The compound crystallizes as bundles of fibers,
and the degree of fiber alignment results in multiple twins with
one or more major components. Despite several attempts using
various solvents and techniques (evaporation, cooling, and sol-
vent diffusion), a second sample of a multiple twin with one
major component or a single crystal could not be obtained.
Complete data collection and structural refinement for several
Received: January 13, 2011
Published Online: March 30, 2011
Eur. J. Inorg. Chem. 2011, 2298–2305
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2305