Combining two coordinatively unsaturated diruthenium cores by the tetradentate ligand (Ph2P)2NCH2C 6H4CH2N(PPh2)2

Article abstract of DOI:10.1016/j.jorganchem.2012.05.028

The tetradentate N,N-bis(diphenylphosphanyl)amine ligand (Ph ₂P)₂NCH₂C₆H₄CH ₂N(PPh₂)₂ (1, xdppa) reacted with in situ prepared [Ru₂(μ-H)(μ-PBu^t

Full text of DOI:10.1016/j.jorganchem.2012.05.028

Journal of Organometallic Chemistry 715 (2012) 64e68
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Combining two coordinatively unsaturated diruthenium cores by the tetradentate
ligand (Ph2P)2NCH2C6H4CH2N(PPh2)2
*
Tobias Mayer, Hans-Christian Böttcher
Department of Chemistry, Ludwig Maximilian University, Butenandtstraße 5e13, 81377 Munich, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
The tetradentate N,N-bis(diphenylphosphanyl)amine ligand (Ph2P)2NCH2C6H4CH2N(PPh2)2 (1, xdppa)
reacted with in situ prepared [Ru2(
novel twofold coordinatively unsaturated tetranuclear metal complex [Ru2(
Ru2( -H)(
-PBut2)(CO)4] (3). Compound 3 was protonated by tetrafluoroboric acid at each side of the
unsaturated diruthenium frameworks affording the oxidative addition product [Ru2( -H)2(
-PBut2)(-
CO)4( -xdppa)Ru2( -H)2(
-PBut2)(CO)4](BF4)2 (4). All new compounds were characterized by spectro-
m-H)(m
-PBut2)(PBut2H)2(CO)4] (2) in a molar ratio of 1:2 affording the
Received 22 April 2012
Received in revised form
22 May 2012
m
-H)(m m-xdppa)
-PBut2)(CO)4(
m
m
Accepted 23 May 2012
m
m
m
m
m
Dedicated to Dr. Bernhard Walther on the
occasion of his 75th birthday.
scopic means and the molecular structures of compounds 1 and 4 were determined by X-ray diffraction.
Ó 2012 Elsevier B.V. All rights reserved.
Keywords:
Ruthenium
Carbonyl
Coordinative unsaturation
Tetranuclear complex
Crystal structure
1. Introduction
strategies. In this paper we describe the synthesis, spectroscopic
characterization, and the X-ray crystal structure of a novel tetrar-
Recently we reported the synthesis and X-ray crystal structures
of some new coordinatively unsaturated complexes with the
uthenium complex supported by the tetradentate bridging coor-
dination modus of the ligand N,N-bis(diphenylphosphanyl)-p-
xylylene-diamine, (Ph2P)2NCH2C6H4CH2N(PPh2)2 (1), between two
coordinatively unsaturated diruthenium frameworks.
general formula [Ru2(CO)4(
phanes or N,N-substituted bis(diphenylphosphanyl)amines) [1].
Because of the unsaturated character of the central Ru2( -H)
m-H)(
m
-PBut2)(
m-P^P)] (P^P ¼ diphos
m
moiety including the RueRu double bond, these complexes
exhibited an enhanced reactivity towards a great variety of small
molecules under mild conditions [2e10]. The most important
prerequisite for the successful synthesis of all these unsaturated
2. Experimental
2.1. General considerations
species is only given by the presence of the bulky m
-PBut2 group.
All synthetic operations were performed under anaerobic
conditions using conventional Schlenk techniques. Solvents were
dried over sodium-benzophenone ketyl or molecular sieves and
were distilled under argon prior to use. Compound 1 was prepared
as reported in the literature [12] however with some modifications
as described below. Chemicals were purchased commercially from
Aldrich. IR spectra were recorded as solid with a JASCO FT/IR-460
plus spectrometer. NMR spectra were obtained using Jeol Eclipse
270 and 400 instruments operating at 270 and 400 (1H), 69 (13C),
and at 109 MHz (31P), respectively. Chemical shifts are given in ppm
Obviously this ligand supports optimal sterical and electronical
conditions to realize coordinative unsaturation. All efforts to
prepare similar constituted diruthenium complexes with other
substituents at the bridging phosphanido group failed. The
important starting complex in the synthesis of these unsaturated
species in this mind is represented by the compound [Ru2(m-H)(m-
PBut2)(PBut2H)2(CO)4] [11]. Multidentate ligands offer the oppor-
tunity of connecting several small metal frameworks together, and
in this direction we were interested in such a kind of synthetic
from SiMe4 (1H, 13C{1H}), and 85% H3PO4 31P{1H}). Microanalyses
(
(C, H, N) were performed by the Microanalytical Laboratory of the
Department of Chemistry, LMU Munich, using a Heraeus Elementar
Vario EI instrument.
* Corresponding author. Tel.: þ49 89218077422; fax: þ49 89218077407.
E-mail address: hans.boettcher@cup.uni-muenchen.de (H.-C. Böttcher).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.05.028

T. Mayer, H.-C. Böttcher / Journal of Organometallic Chemistry 715 (2012) 64e68
65
2.2. Synthesis of (Ph2P)2NCH2C6H4CH2N(PPh2)2 (1)
solution of p-xylylenediamine (1.16 g, 8.50 mmol) in
2.5. X-ray structural determination
A
Suitable single crystals for X-ray diffraction of the compounds 1
and 4 were obtained as described in the Experimental section.
Crystals were selected by means of a polarization microscope,
mounted on the tip of a glass fiber, and investigated on a Bruker
Nonius-Kappa CCD diffractometer (1) and on an Oxford XCalibur
dichloromethane (100 mL) was treated with triethylamine (20 mL)
by stirring at 0 ꢀC. To this solution chlorodiphenylphosphane
(3.66 mL, 19.07 mmol) was added and stirred for 30 min. Then
chlorodiphenylphosphane (3.66 mL, 19.07 mmol) was added again
and the mixture was stirred for 18 h at room temperature. The
solvent was evaporated to dryness under reduced pressure, and the
remaining residue was treated with water (50 mL) by stirring. The
resulting white precipitate was filtered off and washed with water
(50 mL), twice with ethanol (40 mL), and twice with hexane
(50 mL), and dried in vacuo. The product was recrystallized from
dichloromethane/acetonitrile (1:2) affording colorless crystal
plates, m.p. 195 ꢀC.
diffractometer (4) using Mo-K
a
radiation (
l
¼ 0.71073 Å). The
structures were solved by direct methods (SHELXS) [15] and refined
by full-matrix least-squares calculations on F2 (SHELXL-97) [16].
The positions of the bridging hydrido ligands in 4 were free refined.
Thus the RueH distances were set to equal lengths and free refined.
Details of the crystal data, data collection, structure solution, and
refinement parameters of compounds 1 and 4 are summarized in
Table 1.
1: Yield: 3.90 g (53%). Anal. Calcd for C56H48N2P4 (872.91): C,
77.05; H, 5.54; N, 3.21. Found: C, 77.36; H, 5.82; N, 3.14%. 1H NMR
3. Results and discussion
(270 MHz, CD2Cl2):
d 7.32e7.23 (m, 40H, PC6H5), 6.45 (s, 4H, C6H4),
4.37 (t, 4H, 3JPH ¼ 10.5 Hz, NeCH2). 31P{1H} NMR (109 MHz, CD2Cl2):
3.1. Preparation and characterization of new compounds
d
60.3 (s). 13C{1H} NMR (69 MHz, CD2Cl2):
d
139.8, 139.0 (C6H4),
2
133.2, 129.1, 128.9 (C6H4), 128.4, 55.9 (t, JPC ¼ 12.9 Hz, CH2). Suit-
able single crystals of 1 for X-ray diffraction were obtained from
dichloromethane/acetonitrile at 4 ꢀC overnight.
During our studies on the coordination behavior of the sterically
demanding secondary phosphane PHBut2 we observed a cluster
degradation of [Ru3(CO)12] affording the coordinatively unsaturated
complex [Ru2(
species served as an useful intermediate in the synthesis of the
dinuclear complex [Ru2(CO)4( -H)( -dppm)] (Ru]Ru)
-PBut2)(
m-H)(m
-PBut2)(PBut2H)2(CO)4] (2) [11]. The latter
2.3. Synthesis of [Ru2(
m
-H)(
m
-PBut2)(CO)4
-H)(
{m-(Ph2P)2NCH2C6H4CH2N(PPh2)2}Ru2(
m
m
-PBut2)(CO)4] (3)
m
m
m
(5, dppm ¼ Ph2PCH2PPh2) [2]. Recently we could apply these find-
ings to a series of other bidentate organophosphorus ligands
bridging the unsaturated diruthenium core [1]. In this light we were
also interested to study synthetic pathways affording multinuclear
complexes supported by multidentate N,N-bis(diphenylphosphanyl)
amine ligands. In 2002 Gaw et al. described the ligand p-xylylene-
di-bis(diphenylphosphanyl)amine, (Ph2P)2NCH2C6H4CH2N(PPh2)2
(1, xdppa). This ligand afforded in the reaction with 2 mol of
A mixture of [Ru3(CO)12] (639 mg, 1.00 mmol) and PHBut2
(1.00 mL, 5.40 mmol) in THF (20 mL) was refluxed for 3 h. The
solvent was evaporated to dryness under reduced pressure and the
remaining residue was dissolved in acetone (20 mL). Then p-xyly-
lene-di-bis(diphenylphosphanyl)amine (436 mg, 0.50 mmol) was
added and the mixture was refluxed for 4 h. The solvent was
evaporated to dryness under reduced pressure and the residue was
recrystallized from diethyl ether/ethanol (1:2) affording 3 as red
powder, m.p. 215e217 ꢀC dec.
[Mo(CO)4(
h
4-nbd)] (nbd
-(Ph2P)2NCH2C6H4CH2N(PPh2)2}Mo(CO)4] [12].
¼
norbornadiene) the dinuclear
complex [Mo(CO)4{
m
3: Yield: 807 mg (45%). Anal. Calcd for C80H86N2O8P6Ru4
(1793.69): C, 53.57; H, 4.83; N, 1.56. Found: C, 53.46; H, 4.92; N,
In a similar manner we studied the reaction of compound 2 with 1 in
a molar ratio of 2:1 in refluxing acetone. Thus the tetranuclear
1.74%. IR (solid, cmꢁ1): (CO): 1974s, 1928s. 1H NMR (270 MHz,
n
CD2Cl2):
d 7.54e7.25 (m, 44H, Ph and C6H4), 4.02 (t, 4H,
Table 1
3JPH ¼ 7.1 Hz, CH2), 1.40e1.19 (m, 36H, PC4H9), ꢁ14.69 (m, 2H,
m
-H).
m-
Crystal data and structure refinement details for compounds 1 and 4.
31P{1H} NMR (109 MHz, CD2Cl2):
d
279.8 (t, JPP ¼ 143.2 Hz,
2
PBut2), 111.9 (d, 2JPP ¼ 143.2 Hz,
m-xdppa).
Compound
1
4 3CH2Cl2
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
C56H48N2P4
872.84
173(2)
Monoclinic
P21/c
16.2534(6)
9.3947(3)
16.1459(6)
90
112.289(2)
90
2281.20(14)
2
1.271
0.206
3.33e27.50
18 229
0.1054
5232
C83H94B2Cl6F8N2O8P6Ru4
2224.02
203(2)
Monoclinic
P21/c
10.3648(8)
16.4147(15)
31.926(2)
90
99.867(6)
90
2.4. Synthesis of [Ru2(
-(Ph2P)2NCH2C6H4CH2N(PPh2)2}Ru2(
(4)
m-H)2(
m
-PBut2)(CO)4
-H)2(
{m
m
m
-PBut2)(CO)4](BF4)2
b (Å)
Compound 3 (538 mg, 0.3 mmol) was dissolved in diethyl ether
(20 mL) with stirring. To this mixture a solution of HBF4 (51%,
0.6 mmol, 86.8 L) in diethyl ether (10 mL) was added. Within 1 h
the color of the solution changed from red to yellow and a yellow
precipitate was obtained. The solid was filtered off and washed
three times with diethyl ether (10 mL). The yellow powder was
dried in vacuo. The product was recrystallized from dichloro-
methane/diethyl ether affording 4 as yellow needles suitable for X-
ray diffraction, m.p. 236e238 ꢀC dec.
c (Å)
a
b
g
(ꢀ)
(ꢀ)
(ꢀ)
m
Volume (Å3)
Z
5351.4(7)
2
1.380
rcalcd (g cmꢁ3
)
m
/mmꢁ1
range for data collection (ꢀ)
0.853
q
4.16e25.43
24 880
0.0485
7987
9780
575/4
0.0597
0.1955
1.075
Reflections measured
Rint
Observed reflections
Reflections, unique
Parameters/restraints
4: Yield: 460 mg (78%). Anal. Calcd for C80H88B2F8N2O8P6Ru4
(1969.32): C, 48.79; H, 4.50; N, 1.42. Found: C, 49.06; H, 4.62; N,
9128
280/0
0.0500
0.1209
1.039
0.285
ꢁ0.301
1.49%. IR (solid, cmꢁ1):
NMR (270 MHz, CD2Cl2):
n
(CO): 2060sh, 2040s, 1995s, 1970sh. 1H
d
7.65e7.43 (m, 44H, Ph and C6H4), 4.15 (t,
R (Fobs
Rw(F2)
S
)
4H, 3JPH ¼ 6.9 Hz, CH2), 1.37 (d, 36H, 3JPH ¼ 15.8 Hz, PC4H9), ꢁ14.03
(dt, 4H, 2JPH ¼ 19.8 Hz, 2JPH ¼ 13.9 Hz,
m
-H). 31P{1H} NMR (109 MHz,
Max electron density (eꢁ3
)
)
1.688
ꢁ1.125
2
CD2Cl2):
d
240.2 (t, JPP
¼
160.8 Hz, m
-PBut2), 106.6 (d,
Min electron density (eꢁ3
2JPP ¼ 160.8 Hz,
m-xdppa).

66
T. Mayer, H.-C. Böttcher / Journal of Organometallic Chemistry 715 (2012) 64e68
Scheme 1.
Scheme 2.
complex [Ru2(
m
-H)(
m
-PBut2)(CO)4(
m
-xdppa)Ru2(
m
-H)(
m
-PBut2)(CO)4]
spectroscopic methods (see Experimental section). Moreover we
obtained suitable crystals for an X-ray diffraction study and we
could confirm the composition and the structure of 3 indirectly by
the formation of its derivative 4.
(3) was obtained in good yields (Scheme 1). The new twofold
coordinatively unsaturated complex was characterized by
3
analytical and spectroscopic methods (see Experimental section).
The 31P{1H} NMR spectrum of 3 is comparable to that of 5. Thus
a pattern of two signals was found, namely a triplet corresponding to
the m
-PBut2 group at down field and a doublet at higher field indi-
cating the bridging ligand xdppa. The found coupling constant 2JPP of
3 is comparable to the observed one of 5 (143.2 Hz vs.134.5 Hz). This
is an indication of a similar structural ligand environment in both
complexes. Even the 1H NMR data of 3 exhibited a signal corre-
sponding to hydrido ligands in the high field region at ꢁ14.69 ppm
as a multiplet (compare for 5: ꢁ14.30 ppm; CD2Cl2).
Despite of intense efforts we were unable to obtain suitable
crystals of 3 for an X-ray crystallographic study to confirm its
molecular structure. Therefore we searched for another possibility
to bring more insight in its structural elucidation. In this context we
found that compound 5 could be protonated by HBF4 in an oxida-
tive addition reaction affording the complex salt [Ru2(CO)4(
m-
H)2( -dppm)]BF4 (6) [5]. Thus we investigated the reac-
m
-PBut2)(
m
tion of 3 with tetrafluoroboric acid under similar conditions.
Indeed, treatment of 3 with HBF4 in diethyl ether (molar ratio 1:2)
resulted in an analogous oxidative addition reaction indicated by
a color change from deep red to yellow. After work up by crystal-
lization the corresponding addition product between 3 and 2 mol
HBF4 could be isolated in good yields (Scheme 2). The novel
Fig. 1. Molecular structure of 1 in the crystal. Thermal ellipsoids were drawn at the
50% probability level. The asymmetric unit contains a half molecule of 1. Symmetry
i
operation: ꢁx, ꢁy, 1 ꢁ z. Selected bond lengths (Å) and angles (ꢀ): P1eN, 1.718(2);
P2eN, 1.7225(19); NeC1, 1.489(3), P1eC5, 1.832(2); P1eC11, 1.837(2); P2eC17, 1.820(3);
P2eC23, 1.832(2). P1eNeP2, 120.55(12), P1eNeC1, 119.25(15); P2eNeC1, 114.45(16).
Maximal deviation from the least square plane: P1eP2eNeC1, 0.171(2) Å (N).
complex salt [Ru2(
m-H)2(m m-xdppa)Ru2(m-H)2(m-
-PBut2)(CO)4(
PBut2)(CO)4](BF4)2 (4) was characterized by analytical and

T. Mayer, H.-C. Böttcher / Journal of Organometallic Chemistry 715 (2012) 64e68
67
Fig. 2. Molecular structure of the dication of 4 in the crystal. Thermal ellipsoids were drawn at the 50% probability level. Hydrogen atoms and the solvate molecules are omitted for
clarity (except hydrido ligands). Symmetry operation: i 2 ꢁ x, 1 ꢁ y ꢁ z. Selected bond lengths (Å) and angles (ꢀ): Ru1eRu2, 2.6148(7); Ru1eH1, 1.85(7); Ru1eH2, 1.75(6); Ru2eH1,
1.74(6); Ru2eH2, 1.70(6); Ru1eP1, 2.3906(14); Ru2eP1, 2.3587(15); Ru1eP2, 2.3899(14); Ru2eP3, 2.3601(14); P2eN, 1.705(5); P3eN, 1.719(4); NeC5, 1.515(7). Ru1eH1eRu2,
93.4(39), Ru1eH2eRu2, 98(4); Ru1eP1eRu2, 66.81(4); P2eNeP3, 121.9(2). Maximal deviation from the least square plane: P2eP3eNeC5, 0.120(5) Å (N).
Some remarks on the spectroscopic investigation during the
transformation from 3 to 4 in comparison with the analogous
conversion from 5 to its corresponding derivative 6 should be
given. During the protonation of the RueRu bond on going from 5
to 6, a shortening of this bond was observed: 2.6974(4) to
2.6486(6) Å. This was in accordance with a small decrease in the
nearly trigonal-planar from the carbon and the both phosphorus
atoms.
Compound 4 crystallizes from dichloromethane/diethyl ether in
the monoclinic space group P21/c with two formulas in the unit
cell. The asymmetric unit contains a half molecule of the cationic
complex
[Ru2(m-H)2(m m-xdppa)Ru2(m-H)2(m
-PBut2)(CO)4( -PBut2)
angle Rue(
31P) of the bridging phosphanido group changed from
254.2 ppm. In the literature a smaller angle Me( -P)eM was often
m
-P)eRu: 70.46 to 68.19(3)ꢀ. In contrast to this the value
292.3 to
(CO)4]2þ, one tetrafluoroborate ion, and one and a half solvate
molecule CH2Cl2. A selected representation of the dication of
compound 4 is shown in Fig. 2, selected bond lengths and angles
are summarized in the caption.
d(
d
m
discussed in connection with shifting of these resonance signals to
down field [13]. However in the present case, one should take into
account that different oxidation states have to be considered. In this
light we assume similar structural changes during the conversion of
3 to 4. Thus the RueRu bond in 3 should be longer than 2.6148(7) Å
The cationic complex of compound 4 exhibits two diruthenium
tetracarbonyl cores bridged by two hydrido ligands and a phos-
phanido group. These dimetal frameworks are connected through
the bridging ligand xdppa. The overall structural features of the
complex ion are comparable to those of the known compound
(see data of 4). Following the trend of the d(
31P) values for 5 and 6,
for which a difference of about 38 ppm was found, also for 3 and 4
a difference of about 39 ppm was observed. Moreover, a similar
comparison of the CO stretching frequencies can be made. In going
[Mo(CO)4{m-(Ph2P)2NCH2C6H4CH2N(PPh2)2}Mo(CO)4] [12]. As
observed for the dimolybdenum species, the complex cation of 4
possesses an inversion center in the middle of the central C6H4 ring,
too. Because of the formation of five-membered chelate rings in the
complex cation of 4, a greater stability in contrast to the dimo-
lybdenum complex should be assumed.
from 5 to 6, an increase of the n(CO) bands was observed (in the
average from 1955 cmꢁ1 for 5e2035 cmꢁ1 for 6). The same trend
was found for the change from 3 to 4 (in the average from
1951 cmꢁ1e2015 cmꢁ1). These findings are in accordance with
the assumption of a change in the oxidation state from RuI in the
coordinatively unsaturated species to RuII in the product of the
oxidative addition reaction. Using these aspects, the shortening of
the MeM bonds upon “protonation” is in agreement with the fact
that the radii of the central atoms should decrease with increasing
the oxidation state, and therefore they come closer to one another.
4. Conclusions
In this paper we described the synthesis and structural char-
acterization of two new tetranuclear ruthenium complexes con-
taining the tetradentate N,N-bis(diphenylphosphanyl)amine
ligand, (Ph2P)2NCH2C6H4CH2N(PPh2)2 (1, xdppa). As described for
coordinatively unsaturated diruthenium complexes of the type
[Ru2(CO)4(
twofold coordinatively unsaturated complex [Ru2(
CO)4( -xdppa)Ru2( -H)(
-PBut2)(CO)4] (3) showed a similar reac-
m-H)(
m
-PBut2)(
m
-P^P)] (P^P ¼ diphosphanes), the new
3.2. Molecular structures of compounds 1 and 4
m-H)(
m
-PBut2)(-
m
m
m
Compound 1 crystallizes from dichloromethane/acetonitrile in
the monoclinic space group P21/c with two formula units in the unit
cell. The asymmetric unit contains a half molecule xdppa. A
selected representation of molecule 1 is shown in Fig. 1, selected
bond lengths and angles are summarized in the caption. As found
for other similar constituted N,N-bis(diphenylphosphanyl)amines
[14], also in 1 the diphenylphosphanyl groups are staggered relative
to the PNP backbone. The angles around the central N atom (see
caption in Fig. 1) are comparable e.g. with those in N,N-bis(diphe-
nylphosphanyl)benzylamine: P1eN1eP2, 120.57(12); P2eN1eC25,
120.84(16) and P1eN1eC25, 113.29(16)ꢀ [14a]. These bonding
characteristics indicate that these molecules exhibit a distorted
trigonal-pyramidal geometry, whereas the N atom is surrounded
tivity towards HBF4 and afforded an oxidative addition pattern of
reactivity simultaneously at both unsaturated diruthenium cores.
In the future we want to look at new reactivity patterns to func-
tionalize the tetranuclear framework further, especially at the end
of the dinuclear cores.
Acknowledgments
The authors are grateful to the Department of Chemistry of the
Ludwig Maximilian University Munich for supporting these inves-
tigations. T. M. thanks Prof. P. Klüfers for financial support.
Furthermore we thank A. Gallien and P. Mayer for collecting the X-

68
T. Mayer, H.-C. Böttcher / Journal of Organometallic Chemistry 715 (2012) 64e68
[5] H.-C. Böttcher, M. Graf, K. Merzweiler, C. Wagner, J. Organomet. Chem. 628
(2001) 144.
[6] H.-C. Böttcher, M. Graf, K. Merzweiler, C. Wagner, Inorg. Chim. Acta 350 (2003)
399.
[7] H.-C. Böttcher, D. Himmel, M. Scheer, Organometallics 23 (2004) 5314.
[8] H.-C. Böttcher, M. Graf, K. Mereiter, K. Kirchner, Organometallics 23 (2004)
1269.
[9] H.-C. Böttcher, T. Mayer, Z. Anorg. Allg. Chem. 637 (2011) 1884.
[10] T. Mayer, P. Mayer, H.-C. Böttcher, J. Organomet. Chem. 700 (2012) 41.
[11] H.-C. Böttcher, G. Rheinwald, H. Stoeckli-Evans, G. Süss-Fink, B. Walther,
J. Organomet. Chem. 469 (1994) 163.
ray crystal data. The Johnson Matthey plc, Reading, UK, is grateful
acknowledged for a generous loan of hydrated RuCl3.
Appendix A. Supplementary material
CCDC-877530 (1) and CCDC-877531 (4) contain the supple-
mentary 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.
[12] K.G. Gaw, M.B. Smith, J.W. Steed, J. Organomet. Chem. 664 (2002) 294.
[13] A.J. Carty, S.A. MacLaughlin, D. Nucciarone, in: J.G. Verkade, L.D. Quin (Eds.),
Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis, VCH, New
York, 1987, p. 559 (Chapter 16).
References
[14] (a) X.-F. Liu, W.-H. Xu, H. Li, Acta Crystallogr. Sect. E 67 (2011) o370;
(b) N. Cloete, H.G. Visser, A. Roodt, J.T. Dixon, K. Blann, Acta Crystallogr. Sect. E
64 (2008) o480.
[15] G.M. Sheldrick, SHELXS, Program for Crystal Structure Solution, University of
Göttingen, Germany, 1997.
[1] T. Mayer, E. Parsa, H.-C. Böttcher, J. Organomet. Chem. 696 (2011) 3415.
[2] H.-C. Böttcher, C. Bruhn, K. Merzweiler, Z. Anorg. Allg. Chem. 625 (1999) 586.
[3] H.-C. Böttcher, M. Graf, K. Merzweiler, C. Wagner, Z. Anorg. Allg. Chem. 626
(2000) 597.
[4] H.-C. Böttcher, M. Graf, K. Merzweiler, C. Wagner, Z. Anorg. Allg. Chem. 626
(2000) 1335.
[16] G.M. Sheldrick, Acta Crystallogr. Sect. A 64 (2008) 112.