Gallium tri-chloride derivatives of the sterically demanding pyridines 2,6-Ar2C6H3N (Ar = 2,4,6-Me3C6H2 or 2,4,6-Pri3C6H2)

Article abstract of DOI:10.1016/j.poly.2009.06.011

The sterically demanding pyridines 2,6-Ar₂C₆H₃N [Ar = 2,4,6-Me₃C₆H₂ (1) or 2,4,6-Prⁱ₃C₆H₂ (2)] were prepared by a palladium catalysed Kumada C-C coupling reaction in high yield. Pyridine 1 reacted with one equivalent of GaCl₃ to afford the tetra-chloro gallate-pyridinium ion pair complex [GaCl₄]^-[2,6-(2,4,6-Me₃C₆H₂)₂C₆H₃NH]⁺ (3). Contrastingly, pyridine 2 reacted with one equivalent of GaCl₃ to afford the anticipated donor-acceptor complex [GaCl₃{2,6-(2,4,6-Prⁱ₃C₆H₂)₂C₆H₃N}] (4). Complexes 1-4 have been characterised variously by single crystal X-ray diffraction, NMR, CHN, and mass spectrometry.

Full text of DOI:10.1016/j.poly.2009.06.011

Polyhedron 29 (2010) 120–125
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Gallium tri-chloride derivatives of the sterically demanding pyridines
2,6-Ar2C6H3N (Ar = 2,4,6-Me3C6H2 or 2,4,6-Pri3C6H2)
*
Thomas Pell, David P. Mills, Alexander J. Blake, William Lewis, Stephen T. Liddle
School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK
a r t i c l e i n f o
a b s t r a c t
The sterically demanding pyridines 2,6-Ar2C6H3N [Ar = 2,4,6-Me3C6H2 (1) or 2,4,6-Pri3C6H2 (2)] were pre-
pared by a palladium catalysed Kumada C–C coupling reaction in high yield. Pyridine 1 reacted with one
equivalent of GaCl3 to afford the tetra-chloro gallate–pyridinium ion pair complex [GaCl4]À[2,6-(2,4,6-
Me3C6H2)2C6H3NH]+ (3). Contrastingly, pyridine 2 reacted with one equivalent of GaCl3 to afford the
anticipated donor-acceptor complex [GaCl3{2,6-(2,4,6-Pri3C6H2)2C6H3N}] (4). Complexes 1–4 have been
characterised variously by single crystal X-ray diffraction, NMR, CHN, and mass spectrometry.
Ó 2009 Elsevier Ltd. All rights reserved.
Article history:
Available online 10 June 2009
Keywords:
Gallium
Pyridine
Sterically demanding
Main group
1. Introduction
Situated half way down group 13 and immediately neighbouring
the transition metal series, gallium occupies a unique place in
In recent years a ‘renaissance’ in main group chemistry has ta-
ken place which has been mainly driven by the pursuit of p-block
elements in low-oxidation states exhibiting novel coordination
motifs [1]. Arguably, the greatest progress to date has been made
with the group 13 elements, almost all of which can now be iso-
lated in oxidation states I and II in addition to III [2].
the periodic table which enables it above all other group 13 ele-
ments to frequently adopt I, II, and III oxidation states [3]. One li-
gand class which has proven exceptionally well suited to
supporting low valent gallium [4] and landmark multiply bonded
transition metal compounds [5] is the anionic terphenyl ligand
class (I) pioneered by Robinson and Power [4,6]. Emerging more
recently, Aldridge introduced bulky anionic carbazole ligands (II)
as a supporting ligand class for gallium [7]. Ligands of type II might
be regarded as the anionic N-analogue of terphenyls, but since the
central ring topology is different the cone angle of carbazoles with
sterically demanding aryl substituents far exceeds a terphenyl with
the same aryl substituents. Sterically demanding pyridines such as
III are topologically similar to terphenyls, but since the coordinat-
ing centre is nitrogen rather than carbon the ligand is neutral, and
thus ligands of type III represent a complimentary ligand class to I
and II.
The use of ligands of type III in low valent gallium chemistry is
appealing because the neutral nature of the pyridine ligand frees
up a valency which would otherwise be unavailable with a ter-
phenyl. However, despite the versatility and widespread applica-
tion of terphenyls, we were surprised to find that sterically
demanding pyridines of type III have not yet been applied to gal-
lium chemistry, and structurally characterised mono-pyridine ad-
ducts of gallium tri-halides are limited to a handful of examples
reported by Schmidbaur et al. [8,9]. Furthermore, reports of struc-
turally characterised sterically demanding pyridine ligands of type
III are apparently limited to a sole report by Bosch detailing the
synthesis of a 2,6-di-mesityl-pyridine and its use in the prepara-
tion of a cationic silver(I) complex [10]. With this in mind, and with
R
R
C
R
R
R
R
R
R
I
R
R
N
R
R
II
R
R
N
R
R
R
R
III
* Corresponding author. Tel.: +44 01158467167.
E-mail address: stephen.liddle@nottingham.ac.uk (S.T. Liddle).
a
view to comparing terphenyls with topologically similar
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.06.011

T. Pell et al. / Polyhedron 29 (2010) 120–125
121
sterically demanding pyridines, we have prepared two sterically
demanding pyridines and investigated their coordination behav-
iour towards gallium tri-chloride with the intention of using the
resultant complexes as precursors to low valent gallium chemistry.
dimerisation to occur, which might be an expected pre-requisite
for chloride transfer to proceed. However, the fact that GaCl3 more
often than not reacts from the ionic form [GaCl2]+[GaCl4]À cannot
be excluded as a possible explanation in part for the formation of
3 [8b] and GaCl3 partially exists as a dimer in toluene. Although
all the usual routine precautions were taken, and the parallel syn-
thesis of 4 was always straightforward, we cannot exclude the pos-
sibility that the incorporated proton of the pyridinium component
of 3 results from adventitious moisture rather than from solvent.
Intermediates were not observed when the experiment was mon-
itored by 1H NMR spectroscopy. In contrast, the reaction of 2 with
gallium tri-chloride proceeded as anticipated to give the donor-
acceptor complex [GaCl3{2,6-(2,4,6-Pri3C6H2)2C6H3N}] (4) in high
crystalline yield. The straightforward reaction to give 4 compared
to 3 can be directly attributed to the greater sterically demanding
nature of 2 compared to 1. Spectroscopic and analytical data for 3
and 4 were found to be consistent with the proposed formulations.
2. Results and discussion
2.1. Synthesis of 1 and 2
The two ligands employed in this study, 2,6-Ar2C6H3N
[Ar = 2,4,6-Me3C6H2 (1) or 2,4,6-Pri3C6H2 (2)], were prepared by a
straightforward, palladium catalysed Kumada coupling reaction.
Pyridine 1 was prepared as described previously, but we found that
neither CuI or NHEt2 were required as previously indicated [10]
(Scheme 1). Pyridine 2 was found to precipitate from the reaction
mixture during cooling to room temperature following reflux; cool-
ing the solution further to 0 °C resulted in the isolation of 2 in high
yield following filtration and drying, which renders the preparation
of 2 very convenient and straightforward. The 1H and 13C NMR spec-
tra of 2 were clean and as expected; in particular, the inequivalent
nature of the ortho-iso-propyl methyl groups was confirmed by the
observation of two doublets in the 1H NMR spectrum in addition
to the para-iso-propyl methyl group doublet. The 31P NMR spectrum
of 2 exhibited no resonances in the range 300 ppm which con-
firmed that no phosphine-containing products co-precipitated with
2. The identity of 2 was confirmed by ES–MS which exhibited a sin-
gle peak at m/z 483 corresponding to 2ÁH+.
2.3. Structural characterisation of 1
Colourless single crystals of 1 were obtained by slow evapora-
tion of a hexane solution of 1. The molecular structure of 1 is illus-
trated in Fig. 1 and selected bond lengths are listed in Table 1. The
asymmetric unit was found to contain two independent half mol-
ecules that are very similar to each other and each resides over a
crystallographic two-fold rotation axis. The observed bond lengths
are unremarkable, and the steric bulk of the mesityl groups pre-
vents them adopting a co-planar arrangement with the pyridine
ring to maximise conjugation; instead the mesityl rings are
approximately orthogonal to the pyridine ring and the angles be-
tween the planes defined by the mesityl and pyridine rings were
found to be 112°.
2.2. Synthesis of 3 and 4
Reactions of 1 and 2 with gallium tri-chloride apparently take
two very different courses despite both ligands being spectroscop-
ically and analytically pure. The reaction of 1 with one equivalent
of gallium tri-chloride reproducibly afforded the tetra-chloro gal-
late–pyridinium ion pair complex [GaCl4]À[2,6-(2,4,6-Me3C6H2)2
C6H3NH]+ (3) in high crystalline yield. It is thought that 1, whilst
sterically demanding, is not sterically demanding enough to pre-
vent further reaction leading to 3. Support for this suggestion is gi-
ven by the fact two of 1 were shown to easily coordinate to a
silver(I) cation, so there is clearly accessible space around gallium
in the putative complex [GaCl3{2,6-(2,4,6-Me3C6H2)2C6H3N}] for
R
R
2 mol% PdCl2(PPh3)2
N
Br
N
Br
2.2 ArMgBr
THF
R
R
R
R
R = Me (1)
Pri (2)
GaCl3
GaCl3
Pri
Me
Pri
Me
Me
Pri
Pri
Me
[GaCl4]
N
H
Me
N
GaCl3
Pri
Pri
Me
3
Fig. 1. Molecular structure of one of the two unique molecules of
asymmetric unit. The other molecule is very similar. Hydrogen atoms are omitted
for clarity.
1 in the
4
Scheme 1. Synthesis of 1–4.

122
T. Pell et al. / Polyhedron 29 (2010) 120–125
Table 1
2.5. Structural characterisation of 3
Selected bond lengths and angles for 1–4.
Colourless crystals of 3 were grown from a saturated toluene
solution at À30 °C. The molecular structure of 3 is illustrated in
Fig. 3 and selected bond lengths and angles are listed in Table 1.
The tetra-chloro gallate–pyridinium complex 3 crystallises as an
ion pair with no intermolecular contacts. In the solid state the
1
N(1)–C(1)
C(2)–C(3)
1.347(2)
1.372(2)
C(1)–C(2)
C(1)–C(4)
1.385(3)
1.487(2)
2
N(1)–C(1)
C(2)–C(3)
1.342(5)
1.390(6)
C(1)–C(2)
C(1)–C(4)
1.375(7)
1.515(6)
À
1ÁH+ and GaCl4 fragments were found to be associated together
3
by a H(1A)Á Á ÁCl(4) hydrogen bond measuring 2.405(3) Å, which
compares well to the ClÁ Á ÁH hydrogen bonding distance range of
2.124–2.273 Å observed in the complex [HB(NCHCHCButNH)3Cl]+
[AlCl4]À [11]. The presence of the hydrogen bond is supported by
inspection of the Ga–Cl bond lengths which fall into two distinct
groups: 2.1550(7)–2.1579(7) Å for Ga(1)–Cl(1), Ga(1)–Cl(2), and
Ga(1)–Cl(3) which are terminal, and 2.1992(7) Å for Ga(1)–Cl(4)
which bridges to the pyridinium proton. Interestingly, the short
range of Ga–Cl bond lengths is slightly below the sum of the cova-
lent radii for gallium and chlorine (2.24 Å) [12], but this range is in-
line with the range of observed Ga–Cl bond lengths in the tetra-
chloro gallate anion fragments in [GaCl2(4-RC5H4N)4]+[GaCl4]À
(R = H or Me) [13].
N(1)–C(1)
C(1)–C(2)
C(3)–C(4)
C(1)–C(6)
Ga(1)–Cl(1)
Ga(1)–Cl(3)
Cl(2)–Ga(1)–Cl(3)
Cl(3)–Ga(1)–Cl(1)
Cl(3)–Ga(1)–Cl(4)
1.359(3)
1.381(3)
1.385(3)
1.489(3)
2.1579(7)
2.1572(7)
109.79(3)
111.35(3)
106.08(3)
N(1)–C(5)
C(2)–C(3)
C(4)–C(5)
C(5)–C(15)
Ga(1)–Cl(2)
Ga(1)–Cl(4)
Cl(2)–Ga(1)–Cl(1)
Cl(2)–Ga(1)–Cl(4)
Cl(1)–Ga(1)–Cl(4)
1.354(3)
1.384(3)
1.378(3)
1.496(3)
2.1550(7)
2.1992(7)
112.04(4)
107.46(3)
109.86(3)
4
N(1)–C(1)
C(1)–C(2)
C(3)–C(4)
C(1)–C(6)
Ga(1)–N(1)
Ga(1)–Cl(2)
N(1)–Ga(1)–Cl(1)
Cl(1)–Ga(1)–Cl(2)
Cl(1)–Ga(1)–Cl(3)
1.371(2)
1.389(3)
1.378(3)
1.488(3)
2.0563(15)
2.1598(6)
119.86(5)
104.28(2)
108.21(2)
N(1)–C(5)
C(2)–C(3)
C(4)–C(5)
C(5)–C(21)
Ga(1)–Cl(1)
Ga(1)–Cl(3)
N(1)–Ga(1)–Cl(2)
N(1)–Ga(1)–Cl(3)
Cl(2)–Ga(1)–Cl(3)
1.371(2)
1.382(3)
1.386(3)
1.501(3)
2.1530(6)
2.1725(6)
113.97(5)
97.96(4)
112.59(2)
2.6. Structural characterisation of 4
Cooling of a saturated solution of 4 in toluene to 5 °C resulted in
the formation of colourless crystals. The molecular structure of 4 is
illustrated in Fig. 4 and selected bond lengths and angles are listed
in Table 1. Complex 4 crystallises as a monomeric, solvent-free, do-
nor–acceptor complex. The gallium centre adopts a distorted tetra-
hedral geometry. The sterically demanding nature of ligand 2 is
apparent from the fact that although the gallium coordinates
straight on to the N-centre with respect to the Ga(1)–N(1)–C(1)
and Ga(1)–N(1)–C(5) angles, which are essentially equal, the gal-
lium centre does not coordinate to the N-centre in the plane of
the pyridine ring; instead, the gallium centre pitches out of the
2.4. Structural characterisation of 2
Thin colourless needles of 2 were obtained by slow cooling of a
saturated solution of 2 in THF. The molecular structure of 2 is illus-
trated in Fig. 2 and selected bond lengths are listed in Table 1. The
asymmetric unit is composed of one half molecule of 2 which re-
sides over a crystallographic two-fold rotation axis. The observed
bond lengths in 2 are unremarkable, but it is worth noting that
-
plane by 16°. In terphenyl analogues, the gallium centre in [Ar*
the C –Cispo bond lengths are unsurprisingly longer in 2 compared
a
GaCl2] [Ar* = 2,6-(2,4,6-Pr3i C6H2)2C6H3] coordinates straight on and
in the aryl plane [14], but in dimeric [{Ar*GaCl2}2] the gallium centre
coordinates ꢀ4° out of the aryl plane [15] and in [Ar*GaCl2(Py)]
(Py = C5H5N) the gallium centre coordinates out of the aryl plane
by ꢀ8° [16]. The corresponding germanium complex [Ar*GeCl3] is
to 1 due to the greater steric demand of the aryl group in 2 com-
pared to 1. The greater steric bulk of the aryl groups in 2 enforces
a stricter orthogonal arrangement of the aryl rings with respect to
the pyridine ring, compared to 1, with the angles between the
planes defined by the aryl and pyridine rings now measured at 94°.
Fig. 3. Molecular structure of 3. Carbon-bound hydrogen atoms are omitted for
Fig. 2. Molecular structure of 2. Hydrogen atoms are omitted for clarity.
clarity.

T. Pell et al. / Polyhedron 29 (2010) 120–125
123
1H and 13C{1H} NMR spectra were recorded on a Bruker DPX
400 spectrometer operating at 400.2 and 100.6 MHz, respectively;
chemical shifts are quoted in ppm and are relative to TMS. Elemen-
tal microanalyses were carried out by Mr Stephen Boyer at the
Microanalysis Service, London Metropolitan University, UK.
4.2. Synthesis of 2,6-(2,4,6-Pri3C6H2)2C6H3N (2)
2,4,6-Pri3C6H2MgBr (30 ml of a 1.0 M solution in THF) was added
dropwise over 15 min to a cold (À10 °C) mixture of 2,6-dibromopyri-
dine (3.23 g, 13.6 mmol) and PdCl2(PPh3)2 (0.02 g, 2 mol%) in THF
(30 ml). The mixture was refluxed for 12 h, then cooled to 0 °C
resulting in precipitation of a white solid. The solid was filtered
and washed with THF (3 Â 20 ml) then dried in vacuo. Yield:
5.94 g, 90%. Anal. Calc. for C35H49N: C, 86.90; H, 10.21; N, 2.90.
Found: C, 86.12; H, 9.89; N, 2.75%. 1H NMR (CDCl3): d 1.13 (d,
3
3JHH = 6.80 Hz, 12H, ortho-Pri–Me), 1.15 (d, JHH = 6.80 Hz, 12H,
3
ortho-Pri–Me), 1.28 (d, JHH = 7.20 Hz, 12H, para-Pri–Me), 2.61 (sept,
3JHH = 6.80 Hz, 4H, ortho-Pri–CH), 2.94 (sept, 3JHH = 7.20 Hz, 2H, para-
Pri–CH), 7.05 (s, 4H, meta-CH), 7.29 (d, 3JHH = 7.20 Hz, 2H, b-CH), 7.78
3
(t, JHH = 7.20 Hz, 1H,
c
-CH). 13C{1H} NMR (CDCl3): d 23.63 (ortho-
Pri–Me), 24.14 (ortho-Pri–Me), 24.57 (para-Pri–Me), 30.45 (ortho-
Pri–CH), 30.94 (para-Pri–CH), 120.44 (meta-C), 122.87 (para-C),
Fig. 4. Molecular structure of 4. Hydrogen atoms are omitted for clarity.
135.22 (b-C), 136.79 (c-C), 146.06 (ortho-C), 148.55 (a-C), 159.99
(ipso-C). (MS/ES) m/z: 483 2ÁH+.
4.3. Synthesis of [GaCl4]À[2,6-(2,4,6-Me3C6H2)2C6H3NH]+ (3)
not structurally available for comparison, but the silicon analogue
[Ar*SiCl3] has been structurally characterised and the Si centre was
found to bend ꢀ4° out of the aryl plane [17]. The sterically demand-
ing nature of 2 is further underscored by the fact the Ga(1)–N(1)
bond length of 2.0563(15) Å is significantly longer than the Ga–N
bond length of 1.968(1) Å observed in the sterically undemanding
complex [(3,5-Me2C6H3N)GaCl3] [8b], although this does not take ac-
count of the undoubtedly different nucleophilicities of the two pyr-
idine ligands due to the different ring substituents. However, the
Ga–Cl bond distances cover the range 2.1530(6)–2.1598(6) Å, which
is comparable to the range of 2.152–2.161 Å observed in [(3,5-
Me2C6H3N)GaCl3] [8b].
Toluene (40 ml) was added to a cold (À78 °C) mixture of GaCl3
(0.35 g, 2.00 mmol) and 1 (0.63 g, 2.00 mmol). The solution was al-
lowed to warm to room temperature and was stirred for 1 h. The
solution was concentrated to incipient crystallisation, gently
warmed to afford a clear yellow solution, and stored at À30 °C
overnight to afford colourless crystals of 3. Yield: 0.55 g, 70%. Anal.
Calc. for C23H26Cl4GaN: C, 52.32; H, 4.96; N, 2.65. Found: C, 52.02;
H, 4.93; N, 2.62%. 1H NMR (C6D6): d 1.61 (s, br, 1H, NH), 2.20 (s,
3
12H, ortho-Me), 2.25 (s, 6H, para-Me), 6.57 (d, JHH = 7.60 Hz, 2H,
3
b-CH), 6.92 (s, 4H, meta-CH), 7.06 (t, JHH = 7.60 Hz, 1H,
c-CH).
13C{1H} NMR (CDCl3):
128.37 (b-C), 129.09 (meta-CH), 132.98 (
141.87 (ortho-C), 142.21 ( -C), 162.65 (ipso-C).
d
20.94 (para-Me), 21.10 (ortho-Me),
3. Conclusions
c
-C), 137.75 (para-C),
a
The sterically demanding pyridines 2,6-Ar2C6H3N [Ar = 2,4,6-
Me3C6H2 (1) or 2,4,6-Pri3C6H2 (2)] were prepared by a palladium
catalysed Kumada C–C coupling reaction in high yield. Pyridine 1
reacted with one equivalent of GaCl3 to afford the tetra-chloro gal-
late–pyridinium ion pair complex [GaCl4]À[2,6-(2,4,6-Me3C6H2)2-
C6H3NH]+ (3). Contrastingly, pyridine 2 reacted with one equivalent
of GaCl3 to afford the anticipated monomeric, donor-acceptor com-
plex [GaCl3{2,6-(2,4,6-Pr3i C6H2)2C6H3N}] (4). We are currently study-
ing the utility of 4 in preparing gallium complexes with novel
bonding and low-oxidation states by reduction, halide abstraction,
and salt metathesis reactions.
4.4. Synthesis of [GaCl3{2,6-(2,4,6-Pri3C6H2)2C6H3N}] (4)
Toluene (40 ml) was added to a cold (À78 °C) mixture of GaCl3
(0.35 g, 2.00 mmol) and 2 (0.97 g, 2.00 mmol). The solution was al-
lowed to warm to room temperature and was stirred for 1 hour.
The solution was concentrated to incipient crystallisation, gently
warmed to afford a clear yellow solution, and stored at 5 °C over-
night to afford colourless crystals of 4. Yield: 0.99 g, 75%. Anal. Calc.
for C35H49Cl3GaN: C, 63.71; H, 7.48; N, 2.12. Found: C, 63.66; H,
3
7.41; N, 2.12%. 1H NMR (C6D6): d 1.10 (d, JHH = 6.80 Hz, 12H,
3
ortho-Pri–Me), 1.34 (d, JHH = 7.20 Hz, 12H, para-Pri–Me), 1.67 (d,
3
4. Experimental
3JHH = 6.80 Hz, 12H, ortho-Pri–Me), 2.83 (sept, JHH = 6.80 Hz, 4H,
3
ortho-Pri–CH), 2.95 (sept, JHH = 7.20 Hz, 2H, para-Pri–CH), 7.05 (t,
3
4.1. General
3JHH = 7.60 Hz, 1H,
c
-CH), 7.19 (d, JHH = 7.60 Hz, 2H, b-CH), 7.33
(s, 4H, meta-CH). 13C{1H} NMR (CDCl3): d 23.22 (ortho-Pri–Me),
23.83 (ortho-Pri–Me), 25.52 (para-Pri–Me), 31.74 (ortho-Pri–CH),
34.68 (para-Pri–CH), 121.90 (meta-C), 129.53 (para-C), 131.46 (b-
All manipulations were carried out using Schlenk or Glove Box
techniques under an atmosphere of dry nitrogen. Solvents were
dried by passage through activated alumina, degassed, and stored
over potassium mirrors with the exception of THF which was
stored over activated 4 Å molecular sieves. Deuterated benzene
was distilled from potassium, degassed by three freeze-pump-
thaw cycles and stored under nitrogen. Complex 1 and 2,4,6-
Pri3C6H2MgBr were prepared according to published procedures
[10,18]. All other reagents were used as supplied.
C), 139.74 (c-C), 147.64 (ortho-C), 152.16 (a-C), 162.26 (ipso-C).
4.5. X-ray crystallography
Crystal data for compounds 1–4 are given in Table 2, and further
details of the structure determinations are in the Supplementary
information. Bond lengths and angles are listed in Table 1. Crystals

124
T. Pell et al. / Polyhedron 29 (2010) 120–125
Table 2
Crystallographic data for 1–4.
1
2
3
4
Formula
Formula weight
Crystal size (mm)
Crystal system
Space group
a (Å)
C23H25
315.44
N
C39H57NO
555.86
0.10 Â 0.01 Â 0.01
orthorhombic
P21212
16.186(12)
17.624(13)
6.017(5)
C23H26Cl4GaN
527.97
0.66 Â 0.42 Â 0.24
monoclinic
P21/c
15.1484(9)
9.3622(6)
17.7322(10)
99.622(2)
2479.4(3)
4
C40.69H55.50Cl3GaN
734.68
0.65 Â 0.17 Â 0.12
monoclinic
P21/c
9.4085(5)
13.7328(7)
30.4233(16)
92.891(2)
3925.8(4)
4
0.60 Â 0.30 Â 0.13
orthorhombic
P21212
12.5029(14)
15.5217(17)
9.8273(11)
b (Å)
c (Å)
b (°)
V (Å3)
1907.1(4)
4
1716(2)
2
Z
T (K)
150
1.099
0.063
28
1.076
0.062
150
1.414
1.551
150
1.243
0.933
qcalc (g cmÀ3
)
l
(mmÀ1
)
Number of reflections measured
13 894
11 914
12 418
28 503
Number of unique reflections, Rint
3361, 0.053
2179
3014, 0.080
2246
4339, 0.0160
4021
6912, 0.0290
5781
Number of reflections with F2 > 2 (F2)
r
Transmission coefficient range
0.96–0.98
0.0378, 0.0824
0.0777, 0.0885
0.937
0.97–0.98
0.0834, 0.1020
0.2270, 0.2420
1.090
0.42–0.70
0.0330, 0.0353
0.0901, 0.0918
1.050
0.56–0.88
0.0303, 0.0378
0.0805, 0.0832
1.060
R, Rw (F2 > 2
r
)
a
a
R, Rw (all data)
Sa
Parameters
226
0.120, À0.110
191
0.470, À0.580
271
0.960, À0.690
361
0.370, À0.270
Maximum, minimum difference map (e ÅÀ3
)
a
2
2
Conventional R =
R
||Fo| À |Fc||/
R
|Fo|; Rw = [
R
w(Fo À Fc2)2/
R
w(Fo2)2]1/2; S = [
R
w(Fo À Fc2)2/(no. data – no. params)]1/2 for all data.
(c) S. Aldridge, D.L. Kays, Main Group Chem. 5 (2006) 223;
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were examined on a Bruker APEX CCD area detector diffractometer
using graphite-monochromated MoK radiation (k = 0.71073 Å) or
on a Bruker APEX2 CCD area detector using silicon111-monochro-
mated synchrotron radiation (k = 0.6946 Å). Intensities were inte-
grated from a sphere of data recorded on narrow (0.3°) frames by
a
(i) P.P. Power, Chem. Commun. (1998) 2939.
x
rotation. Cell parameters were refined from the observed posi-
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tions of all strong reflections in each data set. Semi-empirical
absorption corrections were applied, based on symmetry-equiva-
lent and repeat reflections. The structures were solved by direct
methods and were refined by least-squares methods on all unique
F2 values, with anisotropic displacement parameters, and with
constrained riding hydrogen geometries; U(H) was set at 1.2 (1.5
for methyl groups) times Ueq of the parent atom. The largest fea-
tures in final difference syntheses were close to heavy atoms.
The Flack parameters for 1 and 2 refined to 0(4) and À9(10) (not
reliably determined). Highly disordered solvent molecules of crys-
tallisation in 1 and 4 could not be modelled and were treated with
the Platon SQUEEZE procedure [19]. Programs were Bruker AXS
SMART (control) and SAINT (integration) [20], and SHELXTL for structure
solution, refinement, and molecular graphics [21].
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Supplementary information
CCDC 728403, 728404, 728405 and 728406 contain the supple-
mentary crystallographic data for 1, 2, 3 and 4. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-
033; or e-mail: deposit@ccdc.cam.ac.uk.
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(e) J.C. Beamish, A. Boardman, R.W.H. Small, I.J. Worrall, Polyhedron 4 (1985)
983;
Acknowledgements
We thank the Royal Society and the University of Nottingham
for supporting this work and the EPSRC National Crystallography
Service for collecting the diffraction data for 2.
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