Effective new palladium catalysts for the Suzuki coupling of various haloxylenes to prepare sterically hindered bi- and triaryls

Article abstract of DOI:10.1016/j.ica.2009.06.032

Several new ortho-alkyl and heteroalkyl substituted aryl and aryl alkyl phosphanes and their palladium complexes have been selectively prepared, characterized and compared as potential catalysts for the Suzuki coupling reaction. The modification of the st

Full text of DOI:10.1016/j.ica.2009.06.032

Inorganica Chimica Acta 362 (2009) 4685–4691
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Effective new palladium catalysts for the Suzuki coupling of various haloxylenes
to prepare sterically hindered bi- and triaryls
b
a
Sauli Vuoti a, Juho Autio a, , M. Haukka , J. Pursiainen
*
a Department of Chemistry, University of Oulu, P.O. Box 3000, FIN-90014 Oulu, Finland
b Department of Chemistry, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland
a r t i c l e i n f o
a b s t r a c t
Article history:
Several new ortho-alkyl and heteroalkyl substituted aryl and aryl alkyl phosphanes and their palladium
complexes have been selectively prepared, characterized and compared as potential catalysts for the
Suzuki coupling reaction. The modification of the structures of the palladium complexes were made in
search of the best possible catalytic activity. The novel catalysts were subsequently used to synthesize
sterically hindered bi- and triaryls by coupling various bulky, unactivated bromoxylenes and chloroxyl-
enes with a range of phenyl boronic acids under microwave irradiation. We showed that under optimized
reaction conditions, very good results can be obtained with a selection of the new phosphanes and their
mononuclear palladium complexes.
Received 20 November 2008
Received in revised form 9 June 2009
Accepted 16 June 2009
Available online 25 June 2009
Keywords:
Alkyl phosphane
Palladium complex
Microwave-assisted synthesis
Cross-coupling
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
recent report the stability of these types of ligands was thor-
oughly addressed [11]. The ligands may provide coordinating
Transition-metal-catalyzed cross-coupling is now recognized
to be one of the most powerful carbon–carbon bond forming
reactions. Palladium-catalyzed carbon–carbon and carbon–nitro-
gen bond forming reactions are widely used in modern organic
chemistry. Such catalytic processes have numerous applications
in the preparation of many natural products, in addition to uses
in materials science and the agrochemical industry [1,2]. The
palladium-catalyzed coupling of aryl halides or their synthetic
equivalents are very often used in the synthesis of biaryl mole-
cules whose skeletons are found in a wide range of important
compounds including, natural products and organic functional
materials [3]. Great efforts have been directed toward the devel-
opment of efficient catalytic systems for the Suzuki cross-cou-
pling reaction. Moreover, these concepts can be applied to
other palladium-catalyzed coupling reactions, including those
that occur through C–H- or C–C cleavage. [3,4] Various bulky
and electron-rich phosphanes [2,5] and N-heterocyclic carbenes
(NHCs) [6,7] have been developed as ligands to promote the
cross-coupling reaction during the last decade. One of the advan-
tages of bulky ligands that bear the biphenyl and phenyl moie-
ties are that sterically and electronically flexible perturbations
are possible by introducing appropriate substituents on the ben-
zene rings. Furthermore, minor differences in the structures have
had magnificent effect on the catalytic activities [4,8–10]. In a
unsaturated monophosphane- or monocarbene-ligated com-
plexes and accelerate catalytic steps, such as oxidative addition,
transmetalation and reductive elimination. As
a result, even
bulky, electron-rich bromides and relatively less-reactive aryl
chlorides can be used effectively in the coupling reactions
[3,10,12]. Microwave heating has also been successfully utilized
in Suzuki–Miyaura cross-coupling reactions with these types of
substrates [13–15].
We have previously tested several quinoline moiety bearing li-
gands for the Suzuki coupling of various aryl halogens by prepar-
ing, characterizing and comparing their mono- and dinuclear
palladium complexes. The couplings proceeded mostly with mod-
erate and good yields. However, sterically more demanding sub-
strates such as chloro- and bromoxylenes were prepared with
only poor yields [16]. We have earlier prepared phosphane ligands,
which produced high yields even in more demanding coupling
reactions by further optimizing the structure of the palladium
complexes [17]. The aim of this study was to continue the research
and design new ligands and prepare their palladium complexes for
the Suzuki coupling reactions of several bulky bromoxylenes and
unactivated aryl chlorides with various phenyl boronic acids to
prepare bi- and triaryls under microwave irradiation. The struc-
tures of the palladium complexes were studied in a wide string
of tests. A series of new aryl alkyl phosphanes and their corre-
sponding palladium complexes were therefore prepared, charac-
terized and compared as potential catalysts under microwave
irradiation.
* Corresponding author. Tel.: +358 8 5531635; fax: +358 8 5531603.
E-mail address: juho.autio@oulu.fi (J. Autio).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.06.032

4686
S. Vuoti et al. / Inorganica Chimica Acta 362 (2009) 4685–4691
was then stirred at room temperature overnight. The liquid was re-
2. Experimental
2.1. General
moved, and the solid was extracted three times using diethylether
(10 ml). The liquid layers were combined and the solvent was re-
moved in vacuo. The crude product was recrystallized from etha-
nol, and if necessary, purified by column chromatography using
dichloromethane/hexane (1:2) mixture as the eluent. The pure
products were either viscous oils or white solids. The ligands 1b,
3a and 4b were very air sensitive, which made the purification pro-
cess difficult. However, these phosphanes are stable when bonded
to the palladium atom, and the palladium complexes can be then
purified efficiently. The previously known phosphanes 2b, 5b and
5c were prepared as reported by Riihimäki et al. [25]. Detailed
reaction procedures and characterization of products is presented
in Supplementary material.
The prepared phosphanes are air- and moisture sensitive as
pure solid compounds and especially in solution, and without pro-
tection these phosphanes show observable oxidation within a few
hours and in some cases as little as a few minutes. Therefore all
reactions involving the free phosphanes were carried out with
standard Schlenk techniques under nitrogen or argon atmospheres.
The palladium complexes used in this study are stable in air both
as solid compounds and in solution, and were therefore isolated
and characterized in air. Diethyl ether was distilled over sodium-
benzophenone ketyl under nitrogen before use. Nitrogen was bub-
bled through dichloromethane, ethanol and n-hexane. Other com-
mercial reagents were used as received.
2.4. Preparation of the palladium complexes
The characterization of the new phosphanes and the palladium
complexes were based on 1H, 31P{1H} and 13C NMR spectrometry.
NMR spectra were recorded on a Bruker DPX400 or DPX200 spec-
trometer at room temperature in CDCl3 (99.8% D, 0.03% TMS).
H3PO4 (85%) was used as an external standard for 31P{1H} NMR. Ex-
act mass peaks of the free ligands were determined on a Micromass
LCT, using an ESI+ method. C and H analyses were performed using
a Perkin–Elmer 2400 CHNS analyzer from the purified, solid metal
complex powders. The mass peaks for the coupling products were
determined by a Hewlett Packard HP 6890 Series GC-system cou-
pled with a 5973-MSD (Mass Selective Detector; quadrupole). Sin-
gle crystals for X-ray crystallographic analyses were obtained by
slow evaporation of the dichloromethane–hexane solvent mixture
at room temperature.
All palladium complexes were prepared by a substitution of
cyclooctadiene (cod) in [PdCl2(cod)] with a preferred phosphane li-
gand in diethyl ether, and purification by dichloromethane/hexane
(1:2) solvent mixture as previously reported by our group [26].
Single crystals for X-ray crystallographic analyses were obtained
by slow evaporation of the dichloromethane–hexane 1:2 solvent
mixture at room temperature. The palladium complexes were
not soluble enough to produce proper 1H or 13C NMR spectra. How-
ever, an overnight 1H NMR measurement of a few complexes
showed that the shifts had changed only slightly and therefore
the experiments were not carried out for the other remaining com-
plexes. Detailed reaction procedures and characterization of prod-
ucts is presented in Supplementary material.
The microwave system was Biotage Initiator Eight. The micro-
wave reactor was from Biotage (personal Chemistry) Emrys syn-
theziser, where temperature, pressure and microwave power
could be controlled. The reaction vessel used was a 2–5 ml closed
tube. The maximum pressure was 21 bars, the maximum temper-
ature 250 °C and the maximum microwave power 300 W. Temper-
ature is measured with IR. The reactor is a single mode reactor,
where the microwave cavity is tuned for every sample, so that
absorption of microwaves is at the highest possible level.
2.5. A general procedure for the Suzuki coupling reactions
A microwave pressure vessel (2–5 ml) was charged with the
aryl halogen, phenylboronic acid, K2CO3 and the corresponding
palladium complex. DMF (2.5 ml) and in some cases distilled water
(0.5 ml) was added to the vessel, and the vessel was pre-stirred for
5 min. The resulting solution was warmed at 150 °C for 40 min, un-
der standard irradiation mode. The reaction mixture was cooled to
room temperature, and water (30 ml) was added to the mixture.
The organic layer was separated, and the water extracted three
times with diethyl ether (30 ml). The ether extracts were combined
with the organic layer and dried with MgSO4, and the solvent was
removed in vacuo. The remaining residue was purified by column
chromatography using silica gel and dichloromethane/hexane
(1:3) mixture. Each experiment was repeated twice and the yields
were averaged. Detailed characterization of products is presented
in Supplementary material.
2.2. X-ray crystal structure determinations
The crystals were immersed in cryo-oil, mounted in a Nylon
loop and measured at a temperature of 120 K. The X-ray diffraction
data was collected by means of a Nonius KappaCCD diffractometer
using Mo K
a radiation (k = 0.71073 Å). The DENZO-SCALEPACK [18] pro-
gram package was used for cell refinements and data reductions.
All of the structures were solved by direct methods using the
SIR2004 [19] or SHELXS97 [20] with the WINGX [21] graphical user inter-
face. An empirical absorption correction was applied to all of the
data (SADABS [22] or XPREP in SHELXTL [23]). Structural refinements
were carried out using SHELXL97. [24] All hydrogen atoms were posi-
tioned geometrically and constrained to ride on their parent atoms,
with C–H = 0.95–1.00 Å and Uiso = 1.2–1.5Ueq (parent atom). The
crystallographic details are summarized in Table 6. Selected bond
lengths and angles are shown in the figure captions.
3. Results and discussion
3.1. Mixed aryl alkyl phosphanes and their palladium complexes
In this study we modified the ortho-substitutes of the phenyl
rings (see Scheme 1) and the alkyl groups directly attached to
the phosphorous atom in order to investigate the effects of the dif-
ferent types of alkyl groups on catalytic efficiencies. For compari-
son, some ligands have been modified with hetero atom
substitutes, which have been reported in other studies to improve
catalytic activity [27,28]. We also prepared a few aryl phosphane
ligands for comparison.
The new phosphanes were prepared according to a modified lit-
erature method [29] by lithiating the substituted bromobenzenes
with n-butyllithium followed by an overnight reaction between
the matching dichloroalkyl or dialkylchlorophosphane. The phos-
2.3. A general method for the preparation of the new ortho-alkyl
substituted aryl alkyl phosphane ligands
A solution of n-butyllithium was transferred dropwise via a can-
ula to a freshly prepared solution of bromoalkylbenzene in diethyl-
ether (30 ml) at -10 °C ? 0 °C (salted ice bath). After stirring for
3 h, a solution of the corresponding chlorophosphane in diethyl-
ether (25 ml) was slowly added to this mixture, and the mixture

S. Vuoti et al. / Inorganica Chimica Acta 362 (2009) 4685–4691
4687
phanes were characterized by 1H, 13C, 31P{1H} NMR and mass
spectrometry.
3
2 2
2
2
2
Mononuclear palladium (II) complexes were prepared by a pre-
viously reported method (see Scheme 2) of substituting cycloocta-
diene (cod) in [PdCl2(cod)] with a preferred phosphane ligand in
diethyl ether. [26] The palladium complexes were characterized
by 31P{1H} NMR, elemental analysis and X-ray crystal diffraction
(where applicable). The obtained palladium complexes are stan-
dard mononuclear trans-complexes, which resemble the structures
of complexes obtained in our previous work [16,17,26].
Scheme 2. A general reaction route for preparing mononuclear palladium
complexes.
2
3
º
3.2. Suzuki coupling of arylboronic acids with aromatic halides
As a starting point, we utilized the previously optimized K2CO3/
0.5% of Pd (II) catalyst system with DMF/H2O as a solvent [16] (see
Scheme 3). The system is extremely simple and does not require
air-sensitive conditions due to the stability of the palladium com-
plexes. Furthermore, low catalyst loadings can be used and Pd (II)
catalysts allow strict control for the palladium/ligand ratio and
therefore an excess of the ligands is not required. Microwave heat-
ing has several advantages such as shorter reaction times and im-
proved yields compared to conventional heating methods and it
has been successfully applied to Suzuki coupling reactions as well
[13,30]. Comparative studies between the traditional and micro-
wave heating methods have shown the advantages of microwave
heating in most cases [31–33] and thus it was chosen as the heat-
ing method for our experiments. However, there are some exam-
ples where the yields have been comparable or even higher with
conventional heating methods [34,35]. In most of the experiments
a small amount of water was added to further improve the yields
and the purity of the coupling products [16,36]. The results are pre-
sented in Tables 1–3.
Scheme 3. Typical reaction conditions illustrated by the coupling reaction of 3-Br-
o-xylene and 3,5-dimethylphenylboronic acid.
cient. In contrast, the aryl phosphanes and the ligands bearing het-
ero substituents produced only average to low yields. Generation
of palladium black was not observed in our coupling experiments.
In general, the electron-rich ligands with isopropyl or cyclo-
hexyl groups attached to the phosphorous atoms produced the
highest yields for all reactions. The various groups in the ortho-po-
sition of the phenyl ring affected the yields only slightly, but larger
substituents seemed to improve the yields, as has been reported
elsewhere [5,37]. The addition of a small amount of water im-
proved the yields in each case as expected.
Using various palladium catalysts and conventional heating
methods similar substituents have been coupled with comparative
yields [38–40]. However, the reaction times were considerably
longer with conventional heating methods compared to the micro-
wave heating utilized here.
Due to the promising results obtained with the ligands, the test-
ing was continued with a series of unactivated chloroxylenes and
other chlorinated organics, which are known to be more demand-
ing substrates for Suzuki coupling reactions, especially under
microwave irradiation [13–15]. The bulky 2,6-dimethyl boronic
acid was now also included in the testing. The palladium complex
of ligand 12a was used as the catalyst for these reactions due to the
The coupling of various bromoxylenes with phenyl, 3,5-di-
methyl and biphenyl boronic acids using the catalyst system gave
average to excellent yields of the corresponding biphenyls and ter-
phenyls. Overall, the palladium complexes of ligands 14b, 12a and
12b were shown to be the most effective catalysts in these cou-
pling reactions with generally only minor differences between
the yields. The ligands 10a, 11b, 14a and 13b were also highly effi-
Scheme 1. New phosphane ligands prepared in this work. The numbering of the corresponding palladium (II) complexes is shown in parenthesis.

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S. Vuoti et al. / Inorganica Chimica Acta 362 (2009) 4685–4691
Table 1
Coupling of various bromoxylenes with phenyl boronic acid.a
Entry
L
Yield
Entry
L
Yield
Entry
L
Yield
Entry
L
Yield
+
17
(
)
Br
(HO)2B
1
2
3
4
14b
12a
13b
12b
91
90
85
83
5
6
7
8
13c
11b
10a
14a
82
79
79
76
9
16
12c
9b
69
65
63
61
13
14
9a
14c
59
45
10
11
12
11a
+
(18)
Br
Br
(HO)2B
(HO)2B
15
16
17
18
14b
10a
13b
14b
95b
88
73
72
19
20
21
22
12a
12b
11b
9b
69
68
63
62
23
24
25
26
13b
9b
14a
15
60
56
54
49
27
40
16
16
43
22
+
(19)
28
29
30
31
14a
11b
13b
14b
93b
85
85
84
32
33
34
35
12a
9a
10a
9b
78
76
70
69
36
37
38
39
12b
14a
12c
13c
68
61
60
60
a
Standard reaction conditions: bromoxylene (1.45 mmol, 1.0 equiv.), phenyl boronic acid (1.65 mmol, 1.15 equiv.), K2CO3 (3.0 mmol, 2.0 equiv.), DMF (2.5 ml), 0.5 mol% of
PdCl2L2, MW (150 °C, 30 min).
b
0.5 ml H2O added.
Table 2
Coupling of various bromoxylenes with 3,5-dimethylphenyl boronic acid.a
Entry
L
Yield
Entry
L
Yield
Entry
L
Yield
Entry
L
Yield
+
20
( )
Br
(HO)2B
1
2
3
12a
12b
12c
95
88
86
4
5
6
13b
14b
11b
85
78
76
7
8
9
10a
9a
9b
75
71
70
10
11
12
16
15
13a
64
54
53
+
21
(
)
Br
Br
(HO)2B
13
14
15
12a
14a
14b
90
80
80
16
17
18
11b
10b
10a
76
76
75
19
20
21
12b
16
13b
72
65
64
22
23
24
9a
13c
14c
60
60
37
+
(22)
85
81
68
(HO)2B
25
26
27
12b
10a
13b
87
86
85
28
29
30
12a
14b
11b
31
32
33
13c
9a
14a
68
66
62
34
35
36
9b
14c
16
52
49
44
+
+
(23)
Br
Br
(HO)2B
37
38
39
40
12b
11b
12a
14b
96
90b
90
41
42
43
44
13b
10a
14a
9a
76
75
71
70
45
46
47
48
11b
13a
16
70
68
67
65
49
50
51
11a
15
9b
60
55
45
87
12c
24
(
)
(HO)2B
52
53
54
14b
13b
12b
92
81
81
55
56
57
10a
13c
10b
80
73
73
58
59
60
12a
9a
14a
72
72
70
61
62
16
9b
65
64
+
(25)
80
74
74
Br
(HO)2B
63
64
65
14b
12b
12c
92b
82
81
66
67
68
12a
13c
9b
69
70
71
16
11b
10a
69
69
68
72
73
9a
14a
62
50
a
Standard reaction conditions: bromoxylene (1.45 mmol, 1.0 equiv.), 3,5-dimethyl phenyl boronic acid (1.65 mmol, 1.15 equiv.), K2CO3 (3.0 mmol, 2.0 equiv.), DMF
(2.5 ml), 0.5 mol% of PdCl2L2, MW (150 °C, 30 min).
b
0.5 ml H2O added.

S. Vuoti et al. / Inorganica Chimica Acta 362 (2009) 4685–4691
4689
Yield
Table 3
Coupling of 2-Br-p-xylene with 2-biphenyl boronic acid.a
Entry
L
Yield
Entry
L
Yield
Entry
L
+
Br
26
(
)
(HO)2B
1
2
3
10a
12a
9a
97b
95
4
5
6
12b
14b
10a
90
7
8
9
9b
14a
16
80b
76
51
90b
82
95b
a
Standard reaction conditions: 2-Br-p-xylene (1.45 mmol, 1.0 equiv.), 2-biphenyl boronic acid (1.65 mmol, 1.15 equiv), K2CO3 (3.0 mmol, 2.0 equiv.), DMF (2.5 ml),
0.5 mol% of PdCl2L2, MW (150 °C, 30 min).
b
0.5 ml H2O added.
Table 4
Coupling of various chloroxylenes with various phenyl boronic acids.a The wavy line represents the site of the coupling.
Entry
1
Product
Yield
95
Entry
8
Product
Yield
80
Entry
15
Product
Yield
53
18
(
)
(29)
32
(
)
(22)
2
3
91
88
9
80
79
16
17
(33)
(34)
49
45
27
(
)
(23)
(28)
(17)
10
24
( )
(26)
35
)
4
5
88
85
11
12
78
71
18
19
(
46
31
20
)
(36)
(
(30)
37
(
6
85
84
13
14
59
56
20
-
)
(19)
(21)
31
(
)
7
a
Standard reaction conditions: chloroxylene (1.45 mmol, 1.0 equiv.), phenyl boronic acid (1.65 mmol, 1.15 equiv.), K2CO3 (3.0 mmol, 2.0 equiv.), DMF (2.5 ml), H2O
(0.5 ml), 0.5 mol% of [PdCl2(12a)2], MW (150 °C, 30 min).
ready availability of the starting materials. The results are pre-
sented in Tables 4 and 5.
erate yields. Recently, the tetra-methyl substituted biphenyls have
successfully synthesized utilizing an elaborate catalyst design [42].
Also, other catalyst designs have facilitated the reactions with ex-
tremely small amounts of palladium (ppm or ppb levels) [43,44].
Compared to other catalyst designs described in literature the
complexes described here promote the Suzuki coupling with com-
parative catalyst loading, similar or better yields, and shortened
reaction times, despite being fairly simple, stable and easy to
prepare.
Most coupling products gave average to good yields. As ex-
pected, the yields for the sterically hindered coupling products
were lower, especially when the more demanding biphenyl boro-
nic acid or 2,6-dimethylphenyl boronic acid were used. Similar
substituents have been coupled with comparative yields with cat-
alysts based on dialkylbiarylphosphanes, but the reaction times
were longer due to the conventional heating methods employed
[41]. The coupling of 2,6-dimethyl phenyl boronic acid with 2-Cl-
m-xylene or 4-Cl-m-xylene produced no reaction or only around
30% yields for the tetra-methyl substituted biphenyls and proved
to be the most difficult reactions in our experiments. However,
the rest of the coupling products were prepared with good or mod-
4. Conclusion
In summary, we prepared and characterized new ligands and
their palladium (II) complexes for the microwave-assisted Suzuki

4690
S. Vuoti et al. / Inorganica Chimica Acta 362 (2009) 4685–4691
Table 5
Coupling of various substituted aryl chlorides with phenyl boronic acids.a The wavy line represents the site of the coupling.
Entry
1
Product
Yield
99
Entry
7
Product
Yield
89
Entry
13
Product
OMe
Yield
69
OMe
NO2
44
(
(
(
)
50
(
)
38
(
)
MeO
(39)
45
)
51
(
)
2
3
99
98
8
9
89
84
14
15
53
O
OMe
NH2
52
(
)
40
47b
(
)
46
)
CN
47
(
)
CF3
CF3
(41)
4
5
97
10
83
16
46
(53)
(54)
NO2
CN
42
(
)
92
91
11
12
78
76
17
18
43
39
(48)
O
CN
6
55
( )
49
(
)
43
(
)
a
Standard reaction conditions: aryl chloride (1.45 mmol, 1.0 equiv.), boronic acid (1.65 mmol, 1.15 equiv.), K2CO3 (3.0 mmol, 2.0 equiv.), DMF (2.5 ml), H2O (0.5 ml),
0.5 mol% of [PdCl2(12a)2], MW (150 °C, 30 min).
b
MW (120 °C, 90 min).
ture use. Additionally, the air-sensitive ligands are stable when
bonded to the palladium atom. Therefore the Suzuki reactions
can be done in air. Minor alterations in the ligand structures had
an effect on the catalytic efficiencies of the palladium catalysts. Iso-
propyl and cyclohexyl substituted phosphane ligands were found
to be the best catalysts in our studies. By using the catalysts, it is
possible to prepare various di-, tri- and tetra-methyl substituted
bi- and triaryls with good yields using bromoxylenes or unactivat-
ed chloroxylenes and other chlorinated organics under microwave
irradiation.
Table 6
Crystal data.
12a
12b
14a
Empirical formula
Fw
T (K)
C42H58Cl2P2Pd
802.12
120(2)
0.71073
monoclinic
P21/c
19.0280(4)
12.8518(3)
16.3838(4)
90
92.3280(10)
90
4003.25(16)
4
1.331
0.705
C54H74Cl2P2Pd
962.37
120(2)
0.71073
monoclinic
C2/c
18.318(5)
17.741(5)
16.732(5)
90
117.625(5)
90
4818(2)
4
1.327
0.598
C32H50Cl2P2Pd
673.96
120(2)
0.71073
orthorhombic
Pbca
7.3437(1)
17.6427(3)
24.9209(4)
90
k (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a
(°)
Appendix A. Supplementary material
b (°)
90
90
c
(°)
V (Å3)
3228.82(9)
4
1.386
0.859
55 317
4326
CCDC 658870, 658871, 658872, 658873, 658874, 658875 and
658876 contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/da-
ta_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.ica.
2009.06.032.
Z
qcalc (Mg/m3)
l
(Mo K
No of reflections
Unique reflections
a
) (mmꢀ1
)
44 789
9165
0.0347
0.0654
39 350
5516
0.0411
0.0834
a
R1 (I ꢁ 2
r
)
0.0294
0.0621
b
wR2 (I ꢁ 2
r
)
P
P
a
R1
=
||Fo| ꢀ |Fc||/ |Fo|.
P
P
2
2 1
wR2 ¼ ½ ½wðF2o ꢀ Fc2Þ ꢂ= ½wðF2oÞ ꢂꢂ =2.
b
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