Disproportionation and radical formation in the coordination of gaI with bis(imino)pyridines

Article abstract of DOI:10.1039/b920047a

Attempted coordination of Ga^II with two new sterically bulky, aryl substituted bis(imino)pyridine ligands lead to Ga ^III species [2,6-{ArNCPh}₂(NC₅H ₃)]GaI₂⁺GaI₄^- (Ar = 2,5-^tBu₂C₆H₃, 2,6- ⁱPr₂C₆H₃ = Dipp) arising from thermodynamically favorable disproportionation reactions. Examination of these reactions lead to isolation of a neutral radical species [2,6-{DippNCPh} ₂(NC₅H₃)]GaI₂. Both EPR spectroscopy and DFT calculations on this compound indicate that the unpaired electron is localized in a di(imino)pyridine π* orbital of an anionic ligand with nearly zero contribution from the Ga or I centers. Reaction of {2,5- ^tBu₂C₆H₃NCPh}₂(NC ₅H₃) with AlCl₃ yielded an analogous Al(iii) product, [{2,5-^tBu₂C₆H₃NCPh} ₂(NC₅H₃)]AlCl₂⁺AlCl ₄^-. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b920047a

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www.rsc.org/dalton | Dalton Transactions
Disproportionation and radical formation in the coordination of “GaI” with
bis(imino)pyridines†
Titel Jurca,a Karl Dawson,a Ian Mallov,a Tara Burchell,a Glenn P. A. Yapb and Darrin S. Richeson*a
Received 25th September 2009, Accepted 20th October 2009
First published as an Advance Article on the web 24th November 2009
DOI: 10.1039/b920047a
Attempted coordination of “GaII” with two new sterically bulky, aryl substituted bis(imino)pyridine
ligands lead to GaIII species [2,6-{ArN CPh}2(NC5H3)]GaI2 GaI4 (Ar = 2,5-tBu2C6H3,
+
-
=
2,6-iPr2C6H3 = Dipp) arising from thermodynamically favorable disproportionation reactions.
=
Examination of these reactions lead to isolation of a neutral radical species [2,6-{DippN CPh}2-
(NC5H3)]GaI2. Both EPR spectroscopy and DFT calculations on this compound indicate that the
unpaired electron is localized in a di(imino)pyridine p* orbital of an anionic ligand with nearly zero
t
=
contribution from the Ga or I centers. Reaction of {2,5- Bu2C6H3N CPh}2(NC5H3) with AlCl3 yielded
t
+
-
=
an analogous Al(III) product, [{2,5- Bu2C6H3N CPh}2(NC5H3)]AlCl2 AlCl4 .
exploration of related chemistry with Ga(I). The development of a
Introduction
simple synthetic route to “GaI”, via sonication of a stoichiometric
ratio of elemental Ga and I2, has afforded synthetic chemists entry
to the fascinating realm of low oxidation state gallium chemistry.8
Although the formulation of this material has not been definitely
established, its reactivity has indicated that it can be used as a
source of Ga(I).9
We report the coordination of “GaI” with new bulky
bis(imino)pyridine ligands and show that this reaction proceeds
via a thermodynamically favored disproportionation pathway to
yield products possessing pentacoordinate cationic and neutral
The demonstration that iron and cobalt complexes bearing
=
bis(imino)pyridine ligands, 2,6-{R¢N C(R)}2NC5H3 (1), afford
exceptionally active polymerization catalysts amplified interest
in these neutral, six-electron donor ligands. Furthermore, the
modular steric and electronic features and the relative ease of
synthesis of these species inspired their application to a range of
transition metal ions.1 Some of these studies have revealed the
potential for ligand centered reactivity.2,3 In particular, for the
most commonly applied version of 1 in which R is a methyl group,
single and double deprotonation of the imine methyl groups has
been observed in the presence of strong bases. In some cases,
this ligand system undergoes electron-transfer reactions leading
to ligand reduction and, in many cases, further reaction. While
the transition metal chemistry of this ligand class has received
substantial attention, the main group chemistry of this species is
less revealed.4
=
paramagnetic [{Ar¢N CPh}2(NC5H3)]GaI2 architectures. Anal-
ogous Al(III) products were observed for reaction with AlCl3 to
t
+
-
=
yield [{2,5- Bu2C6H3N CPh}2(NC5H3)]AlCl2 AlCl4 .
Discussion
In order to maximize the stability of the targeted Ga(I)
species, we chose a 2,6-bis(imino)pyridine framework with bulky
N-substituents, to provide steric load, and imino phenyl groups, to
avoid the established deprotonation reactivity of the imino methyl
groups.2a To these ends we applied 2,5-tBu2C6H3NH2 and 2,6-
iPr2C6H3NH2 (Dipp) in the synthesis of the two new ligand scaf-
folds 2 and 3 (Scheme 1).5 Using a modified literature synthesis,10
the two bis(imino)pyridine species were prepared in good yields as
yellow powders. NMR spectroscopy and microanalyses confirmed
the identities of these two species and, in the case of 2, X-ray
crystallography provided definitive structural elucidation.5
Our interest in reactive, low oxidation state p-block metal
centers exhibiting nominal classical donor–acceptor coordi-
nation led us to the implementation of this ligand class
for the isolation of the In(I) cation complex, [2,6-{2,5-
t
+ 5,6,7
=
Bu2C6H3N CPh}2(NC5H3)]In .
These results prompted our
The steric demands of these ligand architectures were supported
by the temperature dependent appearance of the 1H and 13C NMR
spectra of 2 and 3. At ambient temperature both compounds
displayed a complex set of signals in the aliphatic and aromatic
regions of the spectrum that were attributed to hindered dynamics
of solution conformers. While heating d8-toluene solutions of 2
and 3 to 80 ◦C did lead to coalescence of the spectra, the limiting
aCentre for Catalysis Research and Innovation and Department of Chemistry,
University of Ottawa, Ottawa, Ontario, K1N 6N5. E-mail: darrin@
uottawa.ca; Fax: +1 6135625170; Tel: +1 6135625800
bDepartment of Chemistry & Biochemistry, University of Delaware Newark,
DE, 19716. E-mail: gpyap@udel.edu; Fax: +1 302-831-6335; Tel: +1 302-
831-4345
◦
† Electronic supplementary information (ESI) available: A figure of the
ESR spectrum of 7. Details for the computational studies. CIF files
for 4–7. CCDC reference numbers 738765–738767 and 749531. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/b920047a
spectra required higher temperatures (115 C) using d6-dimethyl
1
sulfoxide as the NMR solvent. Under these conditions, the H
t
NMR signals reduced to two resonances for the Bu groups of 2
and one set of signals for the iPr substituents of 3.
1266 | Dalton Trans., 2010, 39, 1266–1272
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©

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t
+
=
Fig.
1
Structure of the [2,6-{2,5- BuC6H3N CPh}2(NC5H3)]GaI2
,
-
cation of compound 4 with hydrogen atoms, the GaI4 counter-ion and
co-crystallized CHCl3 omitted for clarity.
defined by the pyridine center, N2, and the two I1 and I2 centers.
The limitations of ligand geometry led to the pseudo-axial imine
centers oriented with an N1-Ga-N3 angle of 148.8(2)◦. The two
five-membered rings resulting from the coordination of the pyridyl
and imine moieties are planar. As anticipated the equatorial Ga-
Scheme 1
t
=
Although the reaction of 2,6-{2,5- Bu2C6H3N CPh}2(NC5H3)
(2) with “GaI” proceeded smoothly, this reaction consistently
yielded a mixed product of predominantly a red solid, a more
crystalline orange material, and some insoluble gray powder that
appeared to be Ga metal. Attempts to cleanly separate the two
soluble solids have, so far, been unsuccessful and the NMR analysis
of this mixture is complicated by broadness of the observed
resonances. Fortunately, we were able to isolate a small number
of orange single crystals 4 (Scheme 1). The molecular structure
of this Ga(III) species was confirmed through single crystal X-ray
analysis as summarized in Table 1 and Fig. 1. This Ga(III) complex
˚
N2 distance of 2.017(5) A is shorter than the axial Ga-Nimine
˚
˚
distances of 2.151(5) A and 2.181(5) A.
A more direct synthesis of 4 was provided by reaction of 2
with GaI3 in a stoichiometric ratio of 1 : 2. The resulting red-
orange solution yielded bright orange 4 in 93% yield. The room
temperature NMR spectra of 4 are simplified relative to that
of the free ligand and indicate two conformers for 4. The ratio
between these species was dependent on temperature and solvent.
These observations were attributed to atropisomerism arising from
restricted rotation of the N-aryl groups in the coordinated 2,6-bis
(imino)pyridine ligands of 4.11
t
+
consisted of [2,6-{2,5- Bu2C6H3N CPh}2(NC5H3)]GaI2 GaI4- as
a well-separated cation/anion pair with the cationic portion of
compound 4, shown in Fig. 1. Selected bond distances and angles
for this species are presented in Tables 2 and 3 respectively. The
geometry of the gallium center within this cation is distorted
trigonal bipyramidal with the three-fold plane (R angles = 360◦)
=
=
Application of the related ligand 2,6-{DippN C(Me)}2-
(NC5H3) (Dipp = 2,6-iPr2C6H3), in the isolation of cationic Ga(III)
and Al(III) halide complexes ([LMX2]+MX4 , M = Ga, X = I; M =
-
Al, X = Cl) has been reported.4c,g The Ga complex was obtained
Table 1 Selected crystal data and data collection parameters for compounds 4–7
Compound
4
5
6
7
Empirical formula
Formula weight
T/K
C47H55I6Ga2N3 ◊ ◊ ◊ (CHCl3)3
C47H55Cl6Al2N3
928.64
120(2)
0.71073
Orthorhombic
Pnma
15.124(4)
18.054(5)
22.939(6)
90
90
90
6263(3)
4
1.080
0.428
C43H47I6Ga2N3 ◊ ◊ ◊ (OC4H8)
C43H47GaI2N3
929.36
202(2)
0.71073
Triclinic
P1
8.411(2)
9.720(2)
13.536(3)
76.463(4)
78.265(4)
67.402(4)
985.3(4)
1
1920.88
120(2)
0.71073
Monoclinic
P21/n
1578.78
209
˚
l/A
0.71073
Monoclinic
P212121
10.647(3)
19.533(5)
27.369(7)
90
90
90
5692(3)
4
Crystal system
Space group
˚
a/A
20.582(8)
16.057(7)
22.528(9)
90
113.432(6)
90
6831(5)
4
1.868
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
Z
r (calc)/Mg m-3
1.566
2.298
m/mm-1
3.885
4.234
Absorption correction
Flack parameter
Rint
Semi-empirical from equivalents
0.36(7)
0.136
0.02(4)
0.0495
0.0483
0.0529
Final R indices [I > 2s(I)]
a
R1
0.0638
0.1792
0.0657
0.1869
0.0897
0.2232
0.0738
0.1589
wR2b
ꢀ
ꢀ
ꢀ
ꢀ
a R1 = ꢀFo| - |Fcꢀ/ |Fo|. b wR2 = ( w(|Fo| - |Fc|)2/ w|Fo|2)1/2
.
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˚
Table 2 Selected bond distances (A) for compounds 4–7
4
5
6
7
C(15)-C(22)
C(26)-C(27)
C(25)-C(26)
C(22)-C(23)
C(24)-C(25)
C(23)-C(24)
Ga(1)-I(1)
Ga(1)-I(2)
Ga(1)-N(1)
Ga(1)-N(2)
Ga(1)-N(3)
N(1)-C(6)
N(3)-C(34)
N(1)-C(15)
N(3)-C(27)
N(2)-C(26)
N(2)-C(22)
1.493(8)
1.495(9)
1.384(10)
1.396(9)
1.384(10)
1.391(9)
2.5478(12)
2.5067(12)
2.181(5)
2.017(5)
2.151(5)
1.448(7)
1.449(8)
1.278(8)
1.296(8)
1.344(8)
1.323(8)
C(4)-C(3)
—
—
1.494(4)
—
—
C(13)-C(20)
C(24)-C(25)
C(23)-C(24)
C(20)-C(21)
C(22)-C(23)
C(21)-C(22)
Ga(1)-I(1)
Ga(1)-I(2)
Ga(1)-N(1)
Ga(1)-N(2)
Ga(1)-N(3)
N(1)-C(9)
N(3)-C(32)
N(1)-C(13)
N(3)-C(25)
N(2)-C(24)
N(2)-C(20)
1.48(3)
1.50(3)
1.36(3)
1.36(3)
1.28(3)
1.46(3)
2.512(3)
2.538(2)
2.214(17)
2.022(16)
2.189(17)
1.52(3)
1.48(2)
1.27(3)
1.36(3)
1.31(2)
1.38(3)
C(13)-C(20)
C(24)-C(25)
C(20)-C(21)
C(23)-C(24)
C(21)-C(22)
C(22)-C(23)
Ga-I(1)
Ga-I(2)
Ga-N(1)
Ga–N(2)
Ga-N(3)
N(1)-C(6)
N(3)-C(37)
N(1)-C(13)
N(3)-C(25)
N(2)-C(24)
N(2)-C(20)
1.462(15)
1.473(16)
1.3900
1.3900
1.3900
C(3)-C(2)
C(1)-C(2A)
C(2)-C(1)
Al(1)-Cl(1)
Al(1)-Cl(2)
Al(1)-N(2)
Al(1)-N(1)
Al(1)-N(2A)
N(2)-C(16)
—
N(2)-C(4)
—
N(1)-C(3A)
N(1)-C(3)
1.389(4)
1.377(4)
1.377(4)
2.126(2)
2.129(2)
2.048(3)
1.947(3)
2.048(3)
1.461(4)
—
1.285(4)
—
1.333(3)
1.333(3)
1.3900
2.5230(18)
2.562(2)
2.171(13)
1.952(6)
2.334(13)
1.433(14)
1.426(14)
1.318(17)
1.321(18)
1.3900
1.3900
Table 3 Selected bond angles (◦) for compounds 4–7
4
5
6
7
N(2)-Ga(1)-N(3)
N(2)-Ga(1)-N(1)
N(2)-Ga(1)-I(2)
N(2)-Ga(1)-I(1)
N(2)-C(22)-C(23)
N(2)-C(26)-C(25)
N(2)-C(22)-C(15)
N(2)-C(26)-C(27)
N(1)-C(15)-C(22)
N(3)-C(27)-C(26)
N(1)-C(15)-C(21)
N(3)-C(27)-C(33)
C(34)-N(3)-Ga(1)
C(6)-N(1)-Ga(1)
C(15)-N(1)-Ga(1)
C(27)-N(3)-Ga(1)
C(15)-N(1)-C(6)
C(27)-N(3)-C(34)
C(22)-C(15)-C(21)
C(33)-C(27)-C(26)
C(22)-N(2)-Ga(1)
C(26)-N(2)-Ga(1)
C(22)-N(2)-C(26)
76.2(2)
75.3(2)
N(1)-Al(1)-N(2A)
N(1)-Al(1)-N(2)
N(1)-Al(1)-Cl(2)
N(1)-Al(1)-Cl(1)
N(1)-C(3)-C(2)
—
N(1)-C(3)-C(4)
—
N(2)-C(4)-C(3)
—
N(2)-C(4)-C(10)
—
C(16)-N(2)-Al(1)
—
C(4)-N(2)-Al(1)
—
C(4)-N(2)-C(16)
—
77.95(8)
77.95(8)
108.11(13)
133.82(13)
120.2(3)
—
112.5(3)
—
113.1(3)
—
127.3(3)
—
121.9(2)
—
116.7(2)
—
121.3(3)
—
N(2)-Ga(1)-N(3)
N(2)-Ga(1)-N(1)
N(2)-Ga(1)-I(2)
N(2)-Ga(1)-I(1)
N(2)-C(20)-C(21)
N(2)-C(24)-C(23)
N(2)-C(20)-C(13)
N(2)-C(24)-C(25)
N(1)-C(13)-C(20)
N(3)-C(25)-C(24)
N(1)-C(13)-C(14)
N(3)-C(25)-C(26)
C(32)-N(3)-Ga(1)
C(9)-N(1)-Ga(1)
C(13)-N(1)-Ga(1)
C(25)-N(3)-Ga(1)
C(13)-N(1)-C(9)
C(25)-N(3)-C(32)
C(20)-C(13)-C(14)
C(24)-C(25)-C(26)
C(20)-N(2)-Ga(1)
C(24)-N(2)-Ga(1)
C(20)-N(2)-C(24)
75.2(6)
76.0(6)
95.9(4)
N(2)-Ga-N(3)
N(2)-Ga-N(1)
N(2)-Ga-I(2)
N(2)-Ga-I(1)
N(2)-C(20)-C(21)
N(2)-C(24)-C(23)
N(2)-C(20)-C(13)
N(2)-C(24)-C(25)
N(1)-C(13)-C(20)
N(3)-C(25)-C(24)
N(1)-C(13)-C(19)
N(3)-C(25)-C(31)
C(37)-N(3)-Ga
C(6)-N(1)-Ga
C(13)-N(1)-Ga
C(25)-N(3)-Ga
C(13)-N(1)-C(6)
C(25)-N(3)-C(37)
C(20)-C(13)-C(19)
C(24)-C(25)-C(31)
C(20)-N(2)-Ga
C(24)-N(2)-Ga
C(20)-N(2)-C(24)
75.9(4)
77.6(4)
103.2(3)
143.8(3)
120.0
120.0
143.80(15)
100.25(15)
121.7(6)
120.7(6)
113.3(5)
113.7(6)
115.3(5)
114.2(5)
126.4(6)
126.9(6)
123.2(4)
123.3(4)
114.4(4)
115.5(4)
122.0(5)
121.2(5)
118.3(5)
118.9(6)
118.5(4)
117.5(5)
121.0(6)
144.7(4)
118.3(19)
121.6(18)
114.2(18)
112.8(18)
115.1(19)
113.5(16)
128(2)
122.5(18)
125.8(12)
123.7(13)
114.2(14)
113.1(12)
120.3(18)
121.0(16)
117(2)
112.4(7)
115.1(7)
116.7(12)
116.1(12)
126.1(12)
125.3(13)
129.7(9)
128.3(8)
111.3(9)
110.0(10)
119.6(12)
119.8(12)
117.2(10)
118.4(11)
117.3(4)
119.5(4)
120.0
C(10)-C(4)-C(3)
—
C(3)-N(1)-Al(1)
C(3A)-N(1)-Al(1)
C(3A)-N(1)-C(3)
119.5(3)
—
117.98(18)
117.98(17)
122.1(4)
124.0(17)
115.0(13)
118.5(13)
121.3(17)
as a yellow solid in only 10% yield from the reaction of the ligand
with “GaI”. The Al complex was formed from the direct reaction
of the ligand with AlCl3. Similarly, ligand 2 combines readily
with AlCl3 in a 1 : 2 stoichiometric ratio that ultimately yielded
a bright-yellow powder 5 in 96% yield (eqn (1)). Coordination
of the ligand in a symmetrical fashion was clearly indicated by
imine moieties display a sum of internal angles of 538.3, values
indicating planarity.
(1)
t
the appearance of a simplified 1H NMR spectrum of the Bu
substituents as two singlets of appropriate integration. Single-
crystal X-ray analysis for this Al complex (Table 1) revealed 5
t
+
-
=
to be [{2,5- Bu2C6H3N CPh}2(NC5H3)]AlCl2 AlCl4 as a well
separated cation/anion pair; the cationic portion of compound
5 is shown in Fig. 2 with relevant bond lengths and angles
given in Tables 2 and 3. The geometry of the aluminium center
within this constituent is distorted trigonal bipyramidal, with the
threefold plane (R angles = 360◦) defined by the N1, Cl1, and
Cl2 centers. Like 4, limitations of the ligand geometry lead to
a pseudoaxial N2-Al-N2A angle of only 153.9(2)◦. The two five-
membered rings resulting from the coordination of the pyridyl and
Clearly, the reaction between “GaI” and 2 involves more than
simple ligand coordination. In an effort to unravel the details
of this reaction, obtain simpler spectroscopic data and perhaps
determine the identity of the major red product, we replaced the
N(2,5-tBu2C6H3) groups of 2 with the more symmetrical Dipp
substituent in ligand 3. Similar to the reaction with 2, the 1 : 1
reaction between “GaI” and 3 produced a rapid color change
from the yellow color of the initial solution to red. Along with
some gray powder of elemental Ga, two soluble species, one red
1268 | Dalton Trans., 2010, 39, 1266–1272
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Excellent yields (>90%) of 6 were also obtained from reaction of
3 with GaI3.
Red crystals of 7, the second and a major product from the
reaction of “GaI” and 3, were also analyzed by single crystal
X-ray analysis and the results as well as a direct comparison with
the structure of 6 are presented in Fig. 4. Selected bond distances
and angles for this compound are presented in Tables 2 and 3.
The first notable feature of these results is the observation that 7 is
the neutral analogue of the cation of compound 6. Secondly, the
similarity of the coordination of ligand 3 to the GaI2 unit in these
two species and the apparent undistorted nature of the ligand is
significant and accentuated by the overlay of the structures of 6 and
7 shown in Fig. 4. These features indicate that 7 is a radical species.
t
+
=
Fig.
2
Structure of the [{2,5- BuC6H3N C(Me)}2(NC5H3)]AlCl2
,
-
cation of compound 5 with hydrogen atoms and the AlCl4 counter-ion
omitted for clarity.
and the other yellow-orange, were obtained. As we observed from
the reaction of ligand 2, the major product appears to be the red
material. From the reaction, a mixture of crystals of a yellow-
orange compound 6 and a red compound 7 could be isolated and
it was fortunate that both of these were suitable for single crystal
analysis (Table 1).
The structure obtained for the yellow-orange species, 6, is a
Ga(III) complex analogous to that of 4 and is depicted in Fig. 3 with
selected bond distances and angles presented in Tables 2 and 3.
The cationic component of 6 presents the Ga center in a distorted
trigonal bipyramidal geometry with an equatorial pyridyl nitrogen
(N2) and two coordinated iodide (I1, I2) centers. The pseudo-
axially coordinated imine centers (N1-Ga-N3 = 146.0(6)◦) exhibit
Fig.
4
An overlay of the structures of the cation of com-
˚
˚
slightly longer bond distances (2.189(17) A and 2.214(17) A) than
+
=
pound 6, [2,6-{DippN CPh}2(NC5H3)]GaI2 (red), and the radical 7,
˚
the Ga–Npy distance of 2.022(16) A.
=
[2,6-{DippN CPh}2(NC5H3)]GaI2 (blue). Hydrogen atoms have been
omitted for clarity.
Although it may be initially tempting to interpret these data
as compound 7 consisting of a GaIII2 radical species coordinated
by a neutral ligand 3, the alternative view that 7 is composed
+
of a GaI2 cation coordinated to an anion radical of the ligand
is certainly precedented for the non-innocent di(imino)pyridine
ligand system.2a,3a We examined 7 by EPR spectroscopy and DFT
computations in an effort to more decisively assign the unpaired
electron density.
The observation of an EPR signal with a g value of 2.0029
confirms the fact that 7 possesses radical character and indicates
that the free electron is ligand localized. A slightly asymmetric
triplet pattern further suggests that the electron predominantly
samples one N center in the ligand.
Fig. 3 Structure of the [2,6-{DippN CPh}2(NC5H3)]GaI2+, cation of
=
-
compound 6 with hydrogen atoms, the GaI4 counter-ion and co-crystal-
lized THF omitted for clarity.
The energetic features for the disproportionation reaction of
A DFT computational study was undertaken to obtain a more
thorough understanding of the electronic nature of radical 7.
Calculations were carried out with the B3LYP functional and the
DGDZVP basis set. The results of these computations place the
unpaired electron on the ligand. The SOMO is depicted in Fig. 5
and consists mainly of a delocalized di(imino)pyridine p* orbital
of an anionic ligand with nearly zero contribution from the Ga or
I centers.
=
DippN C(Me)}2(NC5H3) and “GaI” to compound 6 and Ga(0)
were examined computationally. These DFT computations using
the B3LYP functional and DGDZVP basis set supported the
thermodynamic favorability of the disproportionation process
with an enthalpy for this reaction of -28.50 kJ mol-1.12
Consideration of the route to obtain 6 lead to an investigation
of an in situ method to access 6 from the elements that is provided
by direct sonication of Ga and I2 with addition of ligand 3. The
yield of this reaction was directly linked to the stoichiometry of the
ratio Ga : I2 used in the sonication step. A lower yield was provided
by a 2 : 1 ratio of “GaI” while the 2 : 3 ratio, corresponding to
GaI3, provided a 98% yield of 6. These observations are consistent
with the observed disproportionation from the “GaI” reagent.
Conclusions
While in some cases “GaI” may provide synthetic access to GaI
species, the coordination of this species with two new aryl sub-
stituted bis(imino)pyridine ligands leads to a thermodynamically
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Dalton Trans., 2010, 39, 1266–1272 | 1269
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48 h. Over this time, the reaction mixture became brown and a
brown precipitate formed. The mixture was concentrated in vacuo,
resulting in a thick brown paste, which was subsequently dissolved
in cold methanol to give a yellow precipitate. The yellow solid was
collected by filtration and washed with a minimal amount of cold
hexanes : ether (9 : 1) to remove aniline impurities. The filtrate was
reduced again to a thick paste and this procedure was repeated
several times. Compound 2 was isolated as a bright yellow powder
in 67% yield (8.377 g). Analysis calcd for C47H55N3: C, 85.28; H,
8.37; N, 6.35. Found: C, 84.68; H, 8.73; N, 6.12. MS (EI) m/z
=
Fig. 5 The SOMO for the radical [2,6-{DippN CPh}2(NC5H3)]GaI2 7.
1
605 (M+). Room temperature NMR spectra, H NMR (CDCl3,
Hydrogen atoms are omitted for clarity. Isovalue = 0.0300.
300 MHz) and 13C NMR (CDCl3, 75 MHz), displayed a complex
array of resonances which could not be completely assigned due to
favorable disproportionation reaction with ultimate isolation of
the GaIII species [2,6-{Ar¢N CPh}2(NC5H3)]GaI2 GaI4 (Ar¢ =
2,5-tBu2C6H3 4, 2,6-iPr2C6H3 6). These observations allowed for
the development of a direct, “one-pot” synthesis from elemental
Ga and I2. Apparent intermediates of this reaction were isolated
and characterized as neutral radical species. Employing similar
strategies, our continuing efforts are aimed at revealing the features
that will promote isolation of new low-valent main group metal
complexes.
+
-
=
◦
rotational confomers. NMR spectra obtained at 115 C resulted
1
in simplification of the spectra. H NMR (d6-dimethyl sulfoxide,
500 MHz, T = 115 ◦C) d 8.20–6.90 (br m, 17 H, Ar–H), 6.21 (br s,
2H, Ar–H), 1.39 (br s, 18H, tBu), 0.99(br s, 18H, tBu). 13C NMR
(d6-dimethyl sulfoxide, 125 MHz, T = 115 ◦C) d 148.5 (Ar-CH),
147.9 (Ar-CH), 138.7 (Ar-CH), 129.1 (Ar-CH), 128.4 (Ar-CH),
128.3 (Ar-CH), 126.1 (Ar-CH), 120.8 (Ar-CH), 118.8 (Ar-CH),
131.6 (Ar-CH), 99.9 (Ar-CH), 35.0 (Ar-tBu, C-(CH3)3), 33.8 (Ar-
tBu, C-(CH3)3), 31.1 (Ar-tBu, CH3), 30.5 (Ar-tBu, CH3).
Experimental
2,6-Bis{[2,6-di(isopropyl)phenyl)imino]benzyl}pyridine (3)
General methods
Following a procedure similar to that described for 2, a mixture of
2,6-dibenzoylpyridine (5.0 g, 17.4 mmol), 2,6-diisopropylaniline
(7.5 g, 38.3 mmol), and p-toluenesulfonic acid (0.2 mg) in toluene
(50 mL) were placed in a round bottom flask equipped with
a Dean–Stark trap. Under a nitrogen atmosphere, the reaction
mixture was heated to reflux in an oil bath at 140 ◦C for 48 h then
cooled to room temperature and the solvent was removed under
vacuum to give a dark yellow oil. Hexanes were added and a small
quantity of a white solid was removed by filtration. The filtrate
was removed under vacuum yielding a dark yellow oil. Methanol
(~400 mL) was added to this oil and the mixture was stirred for
several minutes, causing the product to precipitate as a yellow solid
which was filtered off and rinsed with methanol. The filtrate was
reduced to about half the initial volume under vacuum, and then
placed in a refrigerator, causing additional product to precipitate,
which was filtered off and rinsed with methanol. The product
was obtained as a yellow powder. Yield: 7.2 g (68%). Elemental
analysis for C43H47N3 Calculated: C, 85.25; H, 7.82; N, 6.94 Found:
C, 85.08; H, 7.69; N, 6.86. MS (EI) m/z 605 (M+). 1H NMR (T =
115 ◦C, d6-dimethyl sulfoxide, 300 MHz) d 7.82 (br t, 1 H, py,
p-CH), 7.55–7.20 (br m, 12 H, Ar–H), 6.94 (br s, 6H, Ar–H),
Unless otherwise stated, reactions were performed in a glovebox
with a nitrogen atmosphere. All solvents were sparged with nitro-
gen and then dried by passage through a column of activated alu-
mina using an apparatus purchased from Anhydrous Engineering.
Deuterated chloroform was dried using activated molecular sieves.
Metal halides were purchased from Strem Chemicals and used as
received. All other reagents were purchased from Aldrich and used
without further purification. NMR spectra were run on a Bruker
Avance 300 MHz spectrometer with deuterated chloroform as a
solvent and internal standard. Elemental analyses were performed
by Midwest Microlab LLC, Indianapolis IN. EPR measurements
were performed using a JEOL FA-100 X-Band EPR spectrometer
equipped with a JEOL ES-UCX2 cylindrical cavity. Samples were
held in clear-fused silica tubes (5 mm diameter) purchased from
Wilmad. All spectra were recorded over 2 min at 5 mW power,
modulation width of 0.025 mT, time constant of 0.03 s, and a sweep
width of 30 mT. “GaI” was prepared according to the literature.8
Both the thermochemical analysis of the disproportionation
=
reaction of 2,6-{DippN CPh}2(NC5H3)]GaI in the presence of
GaI and the optimization of compound 6 were performed with
DFT calculations and the B3LYP functional using the Gaussian
03 (revision D.01) suite of programs.13 The DGDZVP basis set
was employed. Further details are provided in the supplementary
information (ESI†.
2.90 (m, 4H, Pr), 1.00 (d, 24H, Pr). 13C NMR (T = 115 ◦C,
i
i
=
d6-dimethyl sulfoxide, 75 MHz) d 164.6 (C N imine), 155.2 (py,
=
o-C N), 146.2 (Ar-CH), 136.8 (Ar-i-C), 135.5 (Ar-CH), 130.1
(Ar-CH), 128.9 (Ar-CH), 128.1 (Ar-CH), 123.7 (Ar-CH), 123.2
(Ar-CH), 122.7 (Ar-CH), 28.2 (Ar-iPr, CH-(CH3)2), 22.9 (Ar-iPr,
CH3), 22.3 (Ar-iPr, CH3).
2,6-Bis{1-[(2,5-ditertbutylphenyl)imino]-benzyl}pyridine (2)5
The synthetic procedure was adapted from a literature preparation
described by Kleigrewe et al.10 Under lab atmosphere, a 250 mL
round bottom flask was charged with 2,6-dibenzoylpyridine (5.4 g
18.8 mmol), 2,5-di-tert-butylaniline (7.4 g, 41.4 mmol), and
p-toluenesulfonic acid (0.1 g) in toluene (150 mL). A Dean–Stark
trap was attached to the flask and the reaction mixture was placed
under nitrogen atmosphere and heated to reflux (140 ◦C) for
t
=
Reaction of [2,6-bis{2,5- Bu2C6H3N CPh}2(NC5H3)] (2) with
“GaI”
“GaI” powder (59 mg, 0.300 mmol) was added to a clear yellow
solution of 2 (200 mg, 0.300 mmol) in 8 mL of toluene. The reaction
mixture changed color immediately from translucent yellow to a
1270 | Dalton Trans., 2010, 39, 1266–1272
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dark opaque red/purple. The reaction was sealed and allowed to
stir for 4.5 h and then cooled to -20 ◦C overnight, over which
time a dark red precipitate formed. The solution was filtered and a
red solid was washed with 10 ¥ 2 mL hexanes, and allowed to dry
under vacuum. Dark red powder (80 mg) was isolated, dissolved
in toluene and cooled to -20 ◦C to give a mixture of dark red
powder and a small amount of orange powder. Despite multiple
attempts, these two compounds could not be completely isolated
from each other. The red powder is poorly soluble and shows only
very broad 1H signals by NMR. Small dark red crystals that were
not suitable for X-ray crystallography could be grown.
mixture was filtered, washed with 10 ¥ 2 mL hexanes, and allowed
to dry under vacuum. Compound 5 was isolated as a bright
yellow powder in 96% (132 mg yield). Yellow/orange needle-like
crystals were obtained by diffusion of saturated THF solution in
hexanes, and storing at -20 ◦C for several days. Analysis calcd for
C47H55Cl6Al2N3: C 60.79, H 5.97, N 4.52. Found C 59.94, H 5.97,
1
N 4.65. H NMR (CDCl3, 300 MHz): d 8.90 (t, 1H, py, p-CH),
8.39 (d, 2H, py, m-CH), 8.20–6.90 (br m, 16H, aromatic), 1.39
(br s, 18H, tBu), 1.06 (br s, 18H, tBu).13C NMR (CDCl3, 75 MHz).
=
=
d 168.9 (C N imine), 149.3 (py, m-CH), 148.2 (py, o-C N), 138.7
(py, p-CH), 138.1 (Ph, o-CH), 133.8 (Ph, i-C), 132.9 (Ar-tBu, i-C),
131.7 (Ar-tBu, C-tBu), 129.4 (Ph, m-CH), 128.6 (Ph, p-CH), 128.2
(Ar-tBu, CH), 125.7 (Ar-tBu, C-tBu), 125.4 (Ar-tBu, CH), 123.4
(Ar-tBu, CH), 36.7 (Ar-tBu, C-(CH3)3), 34.8 (Ar-tBu, C-(CH3)3),
32.9 (Ar-tBu, CH3), 31.1 (Ar-tBu, CH3).
t
=
Synthesis of [2,6-bis{2,5- Bu2C6H3N CPh}2(NC5H3)]GaI2(GaI4)
(4)
GaI3 powder (135 mg, 0.300 mmol) was added to a clear yellow
solution of 2 (100 mg, 0.151 mmol) in 8 mL of toluene. Colour
change was immediate as the solution went from translucent
yellow to a bright translucent red, gradually becoming opaque.
The reaction mixture was sealed and allowed to stir for 6 h and
then cooled to -20 ◦C overnight, over which time a bright orange
precipitate formed. The solution was filtered, washed with 10 ¥
2 mL hexanes, and the solid was allowed to dry under vacuum.
A bright orange powder of 4 was isolated in 93% yield. Yellow-
orange needle like crystals suitable for X-ray analysis were grown
by diffusion of hexanes into a saturated CDCl3 solution held at
-20 ◦C for several days. 1H and 13C NMR point to the existence of
two conformers in solution. Conformer A: 1H NMR (CDCl3, 300
MHz): d 9.02 (br t, 1 H, py, p-CH), 8.53 (br d, 2 H, py, m-CH),
8.13 (br m, 2 H, aromatic), 7.80–7.05 (br m, 13H, aromatic), 6.48
i
=
Reaction of [2,6-bis{2,6- Pr2C6H3N CPh}2(NC5H3)] (3) and
“GaI”
“GaI” powder (65 mg, 0.331 mmol) was added to a clear yellow
solution of 3 (200 mg, 0.331 mmol) in 8 mL of toluene. The reaction
mixture changed color immediately from translucent yellow to
a dark opaque red and was allowed to stir for 6 h at room
temperature. The reaction mixture was cooled to -20 ◦C and stored
overnight. During this period a combination of bright yellow
and red precipitate formed. The reaction mixture was filtered and
the solid was washed with 10 ¥ 2 mL hexanes then dried under
vacuum to yield 160 mg of bright red powder mixed with yellow
powder. Despite multiple attempts, these two compounds could
not be completely isolated from each other. The red powder is
1
poorly soluble and showed only very broad H NMR signals.
(br s, 1 H, aromatic), 1.39 (br s, 18H, tBu), 0.95 (br s, 18H, tBu).
A combination of orange needle like crystals, and small red
rectangular plate-like crystals suitable for X-ray diffraction were
grown by diffusion of saturated solution of toluene in hexanes.
The orange needle like crystals were identified as compound 6,
13
=
C NMR (CDCl3, 75 MHz). d 164.8 (C N imine), 150.1 (py,
=
o-C N), 149.8 (Ar-CH), 145.2 (Ar-CH), 140.8 (Ar, i-C), 138.4
(Ar-CH), 134.6 (Ar-CH), 132.2 (Ar, i-C), 131.4 (Ar-CH), 130.1
(Ar-CH), 129.4 (Ar-CH), 128.6 (Ar-CH), 125.6 (Ar-tBu, C-tBu),
124.1 (Ar-tBu, C-tBu), 36.7 (Ar-tBu, C-(CH3)3), 34.9 (Ar-tBu, C-
(CH3)3), 31.6 (Ar-tBu, CH3), 31.2 (Ar-tBu, CH3). Conformer B: 1H
NMR (CDCl3, 300 MHz): d 8.63 (br t, 1 H, py, p-CH), 8.46 (br
d, 2 H, py, m-CH), 7.80–7.05 (br m, 16H, aromatic), 1.36 (br s,
+
-
=
[2,6-{DippN CPh}2(NC5H3)]GaI2 GaI4 , and the red platelets
=
as complex 7, [2,6-{DippN CPh}2(NC5H3)]GaI2.
Solution state EPR of compound 7 provided an asymmetric
triplet centered at 336.000 mT. The spectrum is shown in Figure
S1 (ESI†).
t
t
18H, Bu), 1.01 (br s, 18H, Bu).13C NMR (CDCl3, 75 MHz).
=
=
d 162.1(C N imine), 149.6 (Ar-CH), 145.3 (py, o-C N), 142.7
(Ar, i-C), 138.3 (Ar-CH), 133.6 (Ar-CH), 131.7 (Ar-CH), 130.6
(Ar, i-C), 129.9 (Ar-CH), 129.2 (Ar-tBu, C-tBu), 128.9 (Ar-tBu,
C-tBu), 126.9 (Ar-CH), 124.8 (Ar-CH), 121.1 (Ar-CH), 35.3 (Ar-
tBu, C-(CH3)3), 34.5 (Ar-tBu, C-(CH3)3), 35.3 (Ar-tBu, CH3), 30.9
(Ar-tBu, CH3). A sample for elemental analysis was obtained by
recrystallization in toluene, resulting in a 4 : 3 toluene adduct of 4.
Calculated for [C47H55I6Ga2N3]3[C7H8]4: C 40.14, H 3.93, N 2.49,
Found C 40.03, H 4.14, N 2.80.
i
=
Synthesis of [2,6-bis{2,6- Pr2C6H3N CPh}2(NC5H3)]GaI2GaI4
(6)
Method 1. Ga metal (80 mg, 1.15 mmol) and I2 (437 mg,
1.72 mmol) were added to a clear yellow solution of 3 (347 mg,
0.659 mmol) in 15 mL of toluene. The reaction mixture immedi-
ately changed color resulting in a deep red solution. The reaction
mixture was sealed and sonicated for 3 h. During this period
the solution became an intense opaque yellow/orange colored
mixture. The solution was allowed to stir overnight, then filtered,
washed with 5 ¥ 2 mL hexanes, and allowed to dry under vacuum.
A deep yellow-orange powder of 6 was isolated in 98% yield.
t
=
Synthesis of [2,6-bis{2,5- Bu2C6H3N CPh}2-
(NC5H3)]AlCl2[AlCl4] (5)
AlCl3 powder (40 mg, 0.300 mmol) was added to a clear yellow
solution of 2 (100 mg, 0.151 mmol) in 8 mL of toluene. The reaction
mixture was sealed and allowed to stir for 6 h. Colour change
was immediate as the solution went from transluc◦ent yellow to
opaque orange. The solution was then held at -20 C overnight,
over which time a bright yellow precipitate formed. The reaction
Method 2. GaI3 powder (149 mg, 0.331 mmol) was added to a
clear yellow solution of 3 (100 mg, 0.166 mmol) in 8 mL of toluene.
The reaction mixture immediately changed color from translucent
yellow to bright translucent red, which gradually become opaque
and was sealed and allowed to stir for 6 h. The reaction
◦
mixture was then cooled to -20 C overnight, over which time a
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 1266–1272 | 1271
©

View Article Online
yellow-orange precipitate formed. The reaction mixture was
filtered and the solid washed with 10 ¥ 2 mL hexanes, and allowed
to dry under vacuum. A pale yellow-orange powder of 6 was
isolated in 92% yield. Yellow-orange needle like crystals of 6,
suitable for X-ray analysis, were grown by diffusion of saturated
THF solution in hexanes.
Britovsek, M. Bruce, V. C. Gibson, B. S. Kimberby, P. J. Maddox, S.
Mastroianni, S. J. McTavish, C. Redshaw, G. A. Solan, S. Stro¨mberg,
A. J. P. White and D. J. Williams, J. Am. Chem. Soc., 1999, 121, 8728;
(e) B. L. Small, M. Brookhart and A. M. A. Bennett, J. Am. Chem. Soc.,
1998, 120, 4049; (f) G. J. P. Britovsek, V. C. Gibson, B. S. Kimberley,
P. J. Maddox, S. J. McTavish, G. A. Solan, A. J. P. White and D. J.
Williams, Chem. Commun., 1998, 849; (g) L. L. Johnson, C. M. Killian
and M. Brookhart, J. Am. Chem. Soc., 1995, 117, 6414.
2 (a) Q. Knijnenburg, S. Gambarotta and P. H. M. Budzelar, Dalton
Trans., 2006, 5442; (b) I. J. Blackmore, V. C. Gibson, P. B. Hitchcock,
C. W. Rees, D. J. Williams and A. J. P. White, J. Am. Chem. Soc., 2005,
127, 6012; (c) M. Bruce, V. C. Gibson, C. Redshaw, G. A. Solan, A. J. P.
White and D. J. Williams, Chem. Commun., 1998, 2523.
3 (a) J. Scott, S. Gambarotta, I. Korobkov, Q. Knijnenburg, B. de Bruin
and P. H. M. Budzelaar, J. Am. Chem. Soc., 2005, 127, 17204; (b) I.
Vidyaratne, S. Gambarotta, I. Korobkov and P. H. M. Budzelaar, Inorg.
Chem., 2005, 44, 1187; (c) S. C. Bart, E. Lobkovsky and P. J. Chirik,
J. Am. Chem. Soc., 2004, 126, 13794; (d) H. Sugiyama, I. Korobkov, S.
Gambarotta, A. Moeller and P. H. M. Budzelaar, Inorg. Chem., 2004,
43, 5771; (e) Q. Knijnenburg, D. Hetterscheid, T. M. Kooistra and
P. H. M. Budzelaar, Eur. J. Inorg. Chem., 2004, 1204; (f) D. Enright, S.
Gambarotta, G. P. A. Yap and P. H. M. Budzelaar, Angew. Chem., Int.
Ed., 2002, 41, 3873; (g) P. H. M. Budzelaar, B. de Bruin, A. W. Gal, K.
Wieghardt and J. H. van Lenthe, Inorg. Chem., 2001, 40, 4649; (h) B.
de Bruin, E. Bill, E. Bothe, T. Weyhermueller and K. Wieghardt, Inorg.
Chem., 2000, 39, 2936.
1H NMR (CDCl3, 23 ◦C): d 8.99 (t, 1H, py, p-CH), 8.49
(d, 2H, py, m-CH), 7.90–7.05 (br m, 16H, aromatic), 3.00 (v
i
br s, 4H, Pr-CH), 1.24 (br d, 12H, CH3), 0.89 (v br d, 12H,
13
=
=
CH3). C NMR (CDCl3). d 167.7(C N imine), 148.9 (py, o-C N),
146.3 (py, m-CH), 139.5 (py, p-CH), 134.9 (Ph, o-CH), 134.1
(Ph, m-CH), 129.4 (Ar-iPr, C-iPr), 129.2 (Ar-iPr, CH), 128.9 (Ph,
i-C), 128.6 (Ph, p-CH), 125.7 (Ar-iPr, C-iPr), 125.2 (Ar-iPr, CH),
29.7 (Ar-iPr,CH3), 26.7 (Ar-iPr, CH-(CH3)2), 24.3 (Ar-iPr,CH3).
The sample for elemental analysis was obtained from re-
crystallization in toluene. Elemental analysis calculated for
[C43H47I6Ga2N3]3[C7H8] C 35.42, H 3.26, N 2.73, Found C 35.00,
H 3.22, N 2.65.
Crystallography
4 For examples of main group bis(imino)pyridine compounds see: (a) G.
Reeske and A. H. Cowley, Chem. Commun., 2006, 1784; (b) G. Reeske
and A. H. Cowley, Chem. Commun., 2006, 4856; (c) Q. Knijnenburg,
J. M. M. Smits and P. H. M. Budzelaar, Organometallics, 2006, 25,
1036; (d) I. J. Blackmore, V. C. Gibson, P. B. Hitchcock, C. W. Rees,
D. J. Williams and A. J. P. White, J. Am. Chem. Soc., 2005, 127, 6012;
(e) J. Scott, S. Gambarotta, I. Korobkov, Q. Knijnenburg, B. de Bruin
and P. H. M. Budzelaar, J. Am. Chem. Soc., 2005, 127, 17204; (f) M.
Bruce, V. C. Gibson, C. Redshaw, G. A. Solan, A. J. P. White and D. J.
Williams, Chem. Commun., 1998, 2523; (g) R. J. Baker, C. Jones, M.
Kloth and D. P. Mills, New J. Chem., 2004, 28, 207; (h) Q. Knijnenburg,
J. M. M. Smits and P. H. M. Budzelaar, C. R. Chimie, 2004, 7, 865.
5 T. Jurca, J. Lummis, T. J. Burchell, S. I. Gorlesky and D. S. Richeson,
J. Am. Chem. Soc., 2009, 131, 4608.
6 P. A. Rupar, V. N. Staroverov and K. M. Baines, Science, 2008, 322,
1360.
7 S. T. Haubrich and P. P. Power, J. Am. Chem. Soc., 1998, 120, 2202;
R. J. Wright, A. D. Phillips, N. J. Hardman and P. P. Power, J. Am.
Chem. Soc., 2002, 124, 8538.
8 M. L. H. Green, P. Mountford, G. J. Smout and S. R. Peel, Polyhedron,
1990, 9, 2763.
9 R. J. Baker and C. Jones, Dalton Trans., 2005, 1341.
Crystals of compounds 4 to 7 were grown from slow evaporation of
saturated solutions of CDCl3 (4), THF (5,6), or toluene (7). Single
crystals were mounted on a glass fibre or plastic mesh with viscous
oil and flash cooled to the data collection temperature. Unit cell
measurements and intensity data collections were performed on a
Bruker-AXS SMART 1k or APEX CCD diffractometer using
˚
graphite monochromated Mo-Ka radiation (l = 0.71073 A).
Unit cell parameters were obtained from 60 data frames, 0.3◦
w, from three different sections of the Ewald sphere. The unit
cell parameters, equivalent reflections, and systematic absences
in the diffraction data are consistent with space groups Pna21
(Pn21a) and Pnma for 5, P21/n for 4, P212121 6, and P1 for 7. The
data-sets were treated with SADABS absorption corrections based
on redundant multiscan data.14 The crystal data and refinement
parameters for compounds 4–7 are listed in Table 1. The structures
were solved using direct methods and refined with full-matrix,
least-squares procedures on F2. All non-hydrogen atoms were
refined with anisotropic displacement parameters. All hydrogen
atoms were treated as idealized contributions. For compound 6,
10 N. Kleigrewe, W. Steffen, T. Blo¨mker, G. Kehr, R. Fro¨hlich, B.
Wibbeling, G. Erker, J.-C. Wasilke, G. Wu and G. G. C. Bazan, J. Am.
Chem. Soc., 2005, 127, 13955.
-
the GaI4 moiety was disordered over two positions and modeled
´
11 J. Ca´mpora, M. A. Cartes, A. Rodr´ıguez-Delgado, A. M. Naz, P. Palma,
as an 80 : 20 mixture with the thermals restrained with SIMU.
The C–C and C–O bond distances of the THF solvent molecule
were restrained with the commands DFIX and SADI and the
thermals were restrained with the command SIMU. The data
obtained for 7 represent the best from several trials and non-
hydrogen, covalently bonded atoms were restrained to have the
same equivalent isotropic parameter and equal components of
the anisotropic displacement parameters in the direction of the
bond. Three disordered chloroform molecules per unit cell in 5
were treated as diffused contributions.15 Atomic scattering factors
and anomalous dispersion coefficients are contained in various
versions of the SHELXTL program library.14
C. M. Pe´rez and D. del Rio, Inorg. Chem., 2009, 48, 3679.
12 Details for these computations can be found the Supplementary
Information (ESI†).
13 Gaussian 03, Revision D.01, 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. C. 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. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A.
Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich,
A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck,
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Notes and references
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1272 | Dalton Trans., 2010, 39, 1266–1272
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