A Kumada Coupling Catalyst, [Ni{(Ph2P)2N(CH2)3Si(OCH3)3-P,P′}Cl2], Bearing a Ligand for Direct Immobilization onto Siliceous Mesoporous Molecular Sieves

Article abstract of DOI:10.1002/ejic.201500447

The ligand-exchange reaction between [Ni(PPh₃)₂Cl₂] and (Ph₂P)₂N(CH₂)₃Si(OCH₃)₃ afforded the novel Ni^II complex [Ni{(Ph₂P)₂N(CH₂)₃Si(OCH₃)₃-P,P′}Cl₂] (1) in which the square-planar NiP₂Cl₂ coordination sphere contains a four-membered Ni-P-N-P ring. Comparison of the structure of 1 and related Ni^II square-planar or Ni⁰ tetrahedral complexes containing similar P-N-P ligands shows that the magnitude of the P-Ni-P angle is controlled by the presence of the Ni-P-N-P ring, irrespective of the geometry of the nickel coordination sphere. Direct anchoring of 1 onto SBA-15 molecular sieves through the trimethoxysilyl end-group of the ligand afforded heterogeneous catalyst 1/SBA-15. Both 1 and 1/SBA-15 catalyze Kumada cross-coupling reactions, exhibiting similar activity and a slightly higher product selectivity than the [Ni{Ph₂P(CH₂)₃PPh₂-P,P′}Cl₂] and [Ni{(Ph₂P)₂N-(S)-CHMePh-P,P′}X₂] (X = Cl, Br) complexes described in the literature. The Grignard reagent employed is likely to induce leaching of the catalyst, which retains its activity in solution.

Full text of DOI:10.1002/ejic.201500447

FULL PAPER
DOI:10.1002/ejic.201500447
A Kumada Coupling Catalyst,
[Ni{(Ph2P)2N(CH2)3Si(OCH3)3-P,PЈ}Cl2], Bearing a
Ligand for Direct Immobilization Onto Siliceous
Mesoporous Molecular Sieves
Ioannis Stamatopoulos,[a] Dimitrios Giannitsios,[a]
Vassilis Psycharis,[b] Catherine P. Raptopoulou,[b] Hynek Balcar,[c]
[c]
[d]
[a]
ˇ
Arnost Zukal, Jan Svoboda,* Panayotis Kyritsis,* and
[d]
ˇ
Jirí Vohlídal*
Keywords: Homogeneous catalysis / Heterogeneous catalysis / Cross coupling / Nickel / P-N-P ligands
The ligand-exchange reaction between [Ni(PPh3)2Cl2] and
(Ph2P)2N(CH2)3Si(OCH3)3 afforded the novel NiII complex
[Ni{(Ph2P)2N(CH2)3Si(OCH3)3-P,PЈ}Cl2] (1) in which the
square-planar NiP2Cl2 coordination sphere contains a four-
membered Ni–P–N–P ring. Comparison of the structure of 1
and related NiII square-planar or Ni0 tetrahedral complexes
containing similar P–N–P ligands shows that the magnitude
of the P–Ni–P angle is controlled by the presence of the Ni–
nation sphere. Direct anchoring of 1 onto SBA-15 molecular
sieves through the trimethoxysilyl end-group of the ligand
afforded heterogeneous catalyst 1/SBA-15. Both 1 and 1/
SBA-15 catalyze Kumada cross-coupling reactions, exhibit-
ing similar activity and a slightly higher product selectivity
than the [Ni{Ph2P(CH2)3PPh2-P,PЈ}Cl2] and [Ni{(Ph2P)2N-(S)-
CHMePh-P,PЈ}X2] (X = Cl, Br) complexes described in the
literature. The Grignard reagent employed is likely to induce
P–N–P ring, irrespective of the geometry of the nickel coordi- leaching of the catalyst, which retains its activity in solution.
Introduction
as catalysts for the polymerization[7] or oligomerization[8] of
The bis(phosphanyl)amine type of ligands, (R2P)2N(RЈ), ethene. Furthermore, two [Ni(P,P)Cl2] complexes, namely
hereinafter referred to as (P,P), is a well-explored family of [Ni{(Ph2P)2N(p-C6H4OMe)-P,PЈ}Cl2][9] and [Ni[(Ph2P)2N-
chelating ligands.[1] The R groups bonded to the P atoms, (S)-CHMePh-P,PЈ]Cl2],[10] have been shown to catalyze the
as well as the RЈ group bonded to the N atom of the P–N– vinyl-type polymerization of norbornene.
P backbone, can be varied, thus conveying different struc-
In an effort to further extend the catalytic scope of this
tural and electronic properties to both the ligands and their family of NiII complexes, the catalytic activities of
metal-coordinated complexes. Certain (P,P) ligands have [Ni{(Ph2P)2N-(S)-CHMePh-P,PЈ}X2] (X = Cl, Br) have re-
been used to synthesize Cr(P,P)-type complexes, which are cently been explored in Kumada and Suzuki–Miyaura C–C
catalytically active in olefin oligomerization reactions.[2–6] coupling reactions.[11] These reactions have been extensively
In addition, [Ni(P,P)Br2] complexes have been investigated investigated during the last four decades[12–17] and a large
variety of coordination compounds containing various
metal ions, for example, CrIII, FeIII, CoII, MnII, Ru0,I,II,III
,
NiII and PdII, have been shown to afford complexes that
are catalytically active in the above reactions.[18–23]
[a] Inorganic Chemistry Laboratory, Department of Chemistry,
National and Kapodistrian University of Athens,
Panepistimiopolis, Zografou, 15771 Athens, Greece
E-mail: kyritsis@chem.uoa.gr
Homogeneous catalytic systems have been extensively
employed in these types of reactions, exhibiting, in most
cases, higher activity and product selectivity compared with
heterogeneous catalysts. On the other hand, the use of the
latter allows a simple and efficient separation of the prod-
ucts from the reaction mixture, as well as the possibility of
catalyst recycling. Various heterogeneous catalysts have
been investigated for Kumada coupling reactions, including
Ni on active charcoal,[24–26] NiII complexes covalently im-
mobilized on a Merrifield resin,[27,28] NiII acetate immobi-
lized on a cross-linked polystyrene,[29] and NiII/magnesium/
lanthanum mixed oxides.[30]
http://users.uoa.gr/~kyritsis/home.html
[b] Institute of Advanced Materials, Physicochemical Processes,
Nanotechnology and Microsystems, Department of Materials
Science, N.C.S.R. “Demokritos”,
Aghia Paraskevi, 15310 Attiki, Greece
[c] J. Heyrovský Institute of Physical Chemistry, Academy of
Sciences of the Czech Republic,
v.v.i, Dolejsˇkova 3, 18223 Prague 8, Czech Republic
[d] Charles University in Prague, Faculty of Science, Department
of Physical and Macromolecular Chemistry,
Albertov 2030, 12843 Prague 2, Czech Republic
E-mail: jan.svoboda@natur.cuni.cz
vohlidal@natur.cuni.cz
http://www.natur.cuni.cz/chemistry/fyzchem/freedom
https://www.natur.cuni.cz/chemistry/fyzchem/vohlidal/kontakt
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We report herein the preparation of the novel NiII com- mean deviation from the best plane defined by the Ni, P1,
plex [Ni{(Ph2P)2N(CH2)3Si(OCH3)3-P,PЈ}Cl2] (1), which P2, Cl1, and Cl2 atoms, with the P2 atom exhibiting the
can be directly anchored onto siliceous mesoporous molec- largest deviation (0.193 Å). The four-membered Ni–P1–N–
ular sieves through the RЈ = (CH2)3Si(OCH3)3 group. Fol- P2 ring is essentially planar, with the mean deviation from
lowing its structural and spectroscopic characterization, the best plane defined by these four atoms being only
complex 1 was immobilized onto SBA-15 mesoporous mo- 0.008 Å.
lecular sieves to afford the heterogeneous catalyst 1/SBA-
15. The structural properties of 1 have been compared with
those of previously reported [Ni(P,P)X2] (X = Cl, Br, CO)
complexes, and the catalytic activities and selectivities of
1 and 1/SBA-15 in Kumada coupling reactions have been
assessed and compared with those of other NiII catalysts.
The catalytic performance of 1/SBA-15 after recycling has
also been explored.
Results and Discussion
Synthesis and Structure of 1
The ligand-exchange reaction shown in Scheme 1 af-
forded complex 1 in nearly quantitative yield. Crystals of 1
suitable for X-ray crystallography studies were obtained by
the layering method using CH2Cl2/n-hexane (1:3, v/v) as the
solvent.
Figure 1. Molecular structure and atom numbering of 1 (ORTEP
diagram, 50% thermal ellipsoids). Hydrogen atoms have been omit-
ted for clarity. The atoms at disordered sites are shown in gray.
Structures of Complexes Bearing a Four-Membered Ni–P–
N–P Ring
A search of the Cambridge Structural Database (CSD)
found six structurally characterized [Ni(P,P)Cl2] com-
[31]
Scheme 1. Synthesis of complex 1.
plexes containing (Ph2P)2N(RЈ) ligands with different RЈ
groups bonded to the N atom of the P–N–P backbone. Se-
lected bond lengths and bond angles of these complexes are
also listed in Table 2. For a comprehensive appraisal of the
relevant literature, it should be added that the complex con-
taining a ligand with three Ph and one NH(CH)(CH3)2
moiety as R groups and CH(CH3)2 as the RЈ group has also
been structurally characterized.[32] Inspection of the data in
Table 2 shows that, to a large extent, the main structural
characteristics are well conserved within this family of com-
plexes. The endocyclic P–Ni–P angle of 1 (73.39°) seems to
be controlled by the formation of the four-membered Ni–
P–N–P ring as the range of this angle is rather narrow
(73.39–73.99°; Table 2). In a series of structurally charac-
terized analogous [Ni(P,P)Br2] complexes, this range is only
slightly wider (73.00–74.62°).[11] On the other hand, the Cl–
Ni–Cl angle of 1 (97.60°) is slightly smaller than the range
of values observed for the related complexes listed in
Table 2 (98.49–99.77°). The corresponding [Ni(P,P)Br2]
complexes show a somewhat larger range of Br–Ni–Br
angles (95.68–101.29°).[11]
The main crystallographic and structural data for 1 are
listed in Table 1 and Table 2. The structure of 1 contains
discrete molecules (Figure 1) exhibiting a distorted square-
planar NiP2Cl2 core. NiII is coordinated to the (P,P) chelate,
forming a four-membered Ni–P–N–P ring. The NiP2Cl2
core is almost planar, showing a rather small (0.021 Å)
Table 1. Crystallographic data for complex 1.
Formula
Mr
Space group
a [Å]
b [Å]
c [Å]
C30H35Cl2NO3P2SiNi
677.23
P21/c
17.1970(4)
8.53010(10)
21.8353(4)
90.364(1)
3203.0(1)
4
β [°]
V [Å3]
Z
T [°C]
–113
Cu-Kα
1.404
3.968
Radiation
ρcalcd. [gcm–3
μ [mm–1]
]
Reflections with IϾ2σ(I)
4153
0.0554
0.1468
[a]
R1
[a]
The P–N–P angle in 1 (97.47°) is significantly smaller
than the angles observed for crystallographically charac-
terized (P,P) ligands such as (Ph2P)2N[(S)-CHMePh]
(119.73°)[33] and (Ph2P)2N[C6H4Si(OEt)3] (113.66°),[34] ap-
wR2
2
2 2
[a] R1 = Σ(|Fo| – |Fc|)/Σ(|Fo|) and wR2 = {Σ[w(Fo – Fc ) ]/
Σ[w(Fo2)2]}1/2, w = 1⁄[σ2(Fo2) + (0.0718P)2 + 2.87P] and P =
2
[max(Fo2,0) + 2Fc ]/3.
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Table 2. Selected bond lengths and angles for the [Ni(P,P)Cl2] complexes.
CSD code
RЈ
Bond lengths Å
Bond angles [°]
Cl1–Ni–Cl2 Cl1–Ni–P1 Cl2–Ni–P2 P1–Ni–P2 Ni–P1–N Ni–P2–N P1–N–P2
Ni–Cl1 Ni–Cl2 Ni–P1 Ni–P2 N–P1 N–P2
N–C
1
(CH2)3Si(OCH3)3
CH(CH3)Ph
C6H4OCH3-p
CH2Ph
(CH2)2CH3
CH2C6H4CH3-p
2.196
2.206
2.192
2.203
2.198
2.191
2.190
2.188
2.217
2.190
2.199
2.196
2.215
2.199
2.126
2.135
2.115
2.135
2.127
2.126
2.128
2.131
2.129
2.123
2.124
2.124
2.135
2.116
1.694
1.705
1.711
1.706
1.695
1.693
1.696
1.690
1.706
1.712
1.702
1.697
1.697
1.686
1.474
1.501
1.425
1.488
1.481
1.485
1.480
97.60
98.49
99.14
98.30
99.22
98.68
99.77
94.13
93.89
92.01
94.29
91.96
91.25
94.62
95.07
94.55
94.96
93.79
96.11
96.31
92.00
73.39
73.39
73.99
73.64
73.41
73.69
73.69
94.60
94.92
94.98
94.10
94.75
94.40
93.99
94.53
95.05
94.64
94.60
94.80
93.94
94.68
97.47
96.64
96.32
97.02
97.03
97.85
97.60
HAFQAI[10]
MEDTAR[9]
YAFCIT[35]
YAFCOZ[36]
BIRNUN[37]
MIMNON[38] (CH2)3SCH3
parently due to the formation of the four-membered Ni–P–
Conversion curves for the cross-coupling of an iodoarene
N–P ring in 1. It should be noted that for the rest of the and an aryl Grignard catalyzed by 1 and 1/SBA-15 are
crystallographically characterized [Ni(P,P)X2] (X = Cl, Br) shown in Figure 2 and the corresponding data are presented
complexes, the P–N–P angle spans a rather wide range in Table 3. As can be seen, the final product yield was essen-
(95.73–100.98°; Table 2 and ref.[11]). These differences can tially reached in 15 min for all the reaction systems investi-
be attributed to the stereochemical effects of the respective gated. Any increase in yield observed afterwards was very
R and RЈ groups in the P–N–P backbone and the resulting small. Therefore the data shown in Table 3 correspond to
packing effects in the corresponding crystals.
the reaction time of 1 h.
A search in the CSD[31] did not show any other square-
planar [Ni(P,P)X2] (X = Cl, Br, I) complexes in which a
(CH2)3Si(OR)3 group is bonded to the N atom. The only
related compound to have been reported is the tetrahedral
Ni0 complex [Ni{(Ph2P)2N(CH2)3Si(OCH3CH2)3-P,PЈ}-
(CO)2].[34] It is of interest that the P–Ni–P angle of this
complex (73.68°) is close to that observed for 1 (73.39°),
which indicates that the presence of the four-membered Ni–
P–N–P ring controls the magnitude of the P–Ni–P angle
irrespective of the geometry of the nickel coordination
sphere (square planar or tetrahedral). On the other hand,
the P–N–P angle in the tetrahedral complex (102.13°) is
larger than the corresponding angle in the square-planar
complex 1 by 4.7°.
Figure 2. Conversion curves for the cross-coupling of 1-iodo-4-tert-
butylbenzene (1.0 mmol) and p-tolylMgBr (1.2 mmol) catalyzed by
1 and 1/SBA-15 (10 μmol of Ni) in thf (3 mL; Table 3, entries 4
and 5) with mesitylene (0.5 mmol) as internal standard at room
temperature.
Catalytic Activity of 1 and 1/SBA-15 in Kumada Coupling
Reactions
31P MAS NMR analyses of 1 (δ =42.8 ppm) and 1/SBA-
15 (δ =41.8 ppm) showed that immobilization onto SBA-15
did not affect the coordination environment of the NiII site.
Earlier studies showed that NiII complexes containing a
four-membered Ni–P–N–P ring are active in the Kumada
coupling reaction but inactive in the Suzuki–Miyaura C–C
coupling reaction.[11] Therefore the catalytic activities of 1
and 1/SBA-15 were tested only in the Kumada reaction
(Scheme 2) and compared with the activities of the widely
exploited [Ni{Ph2P(CH2)3PPh2-P,PЈ}Cl2] complex[11,39–41]
and the recently studied [Ni{(Ph2P)2N-(S)-CHMePh-
P,PЈ}X2] (X = Cl, Br) complexes.[11] It should be emphas-
ized here that other NiII complexes have also been studied
as Kumada coupling catalysts[42–48a] as they provide a
promising alternative to much more expensive PdII-based
catalysts.[20–22]
The main product of the studied Kumada cross-cou-
pling, 4-tert-butyl-4Ј-methylbiphenyl (MT), was always ac-
companied by two homocoupling side-products, namely
4,4Ј-dimethylbiphenyl (MM) and 4,4Ј-di-tert-butylbiphenyl
(TT). All these compounds, as well as mesitylene (internal
standard), were well resolved in GC chromatograms and
clearly identified by GC–MS.
As can be seen (Table 3, entry 5a), under the same reac-
tion conditions A, the heterogeneous catalyst 1/SBA-15
gave a lower substrate conversion (42%) than 1 (79%), but
a significantly increased product selectivity (from 81 to
91%). When the concentrations of both substrates as well
as 1/SBA-15 were increased three-fold (conditions B), the
conversion rose to 64% without loss in product selectivity
(90%; entry 6a). The observed difference in catalytic ac-
tivity of 1 and 1/SBA-15 can thus be mainly ascribed to the
limitations of diffusion in each porous system.
The catalytic activity of 1/SBA-15 after recycling was
also tested. The reaction mixture from the previous test (re-
action time of 1 h) was centrifuged, its liquid part removed
Scheme 2. Kumada coupling reaction investigated in this work.
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Table 3. Results of catalytic tests of 1 and 1/SBA-15 in the Kumada coupling of iodoarene and Grignard reagent at room temperature.[a]
Reaction conditions[a] Overall conversion [%]
SMT [%]
SMM [%]
STT [%]
[b]
[b]
[b]
Entry
Catalyst
1[c]
2[c]
3[c]
4
[Ni(dppp)Cl2]
[Ni{(Ph2P)2N-(S)-CHMePh-P,PЈ}Br2]
[Ni[(Ph2P)2N-(S)-CHMePh-P,PЈ]Cl2]
1
A
A
A
A
86
63
68
79
72
66
70
81
25
31
28
17
3
3
2
3
5a
5b
5c
5d
5e
5f
1/SBA-15
1/SBA-15
1/SBA-15
1/SBA-15
1/SBA-15
1/SBA-15
A
A
A
A
A
A
42
44
45
44
35
23
91
85
84
83
84
84
7
2
2
3
3
3
3
13
14
14
14
13
6a
6b
6c
6d
1/SBA-15
1/SBA-15
1/SBA-15
1/SBA-15
B
B
B
B
64
78
75
68
90
86
85
84
9
1
2
2
2
12
13
14
7a
7b
7c
1/SBA-15
1/SBA-15
1/SBA-15
A
A
A
40
50
45
92
85
81
6
13
17
2
2
3
[a] Reagents and conditions: 1-iodo-4-tert-butylbenzene (1.0 mmol), p-tolylMgBr (1.2 mmol), Ni complex (10 μmol), mesitylene
(0.5 mmol) as internal standard in A) thf (3 mL) or B) thf (0.8 mL). [b] Selectivity with respect to the (by)product DM, MM, or TT. [c]
Reaction time 15 min, data taken from.[11]
and analyzed, and the remaining solid catalyst was redis- Thus, it can be concluded that both the leached and the
persed in a new portion of the reactant solution and again remaining anchored NiII species retain their activity. This
allowed to react for 1 h. The whole process was repeated shows that a catalytically competent first coordination
five times (Table 3, entries 5a–5f). The recycled 1/SBA-15 sphere is retained in both types of NiII species.
catalyst apparently showed an increased product yield in
To probe the integrity of 1/SBA-15 in the presence of the
the second run. However, this is most likely caused by reten- Grignard reagent, the 31P and H NMR spectra of a mix-
tion of a fraction of the products inside the pores of the ture of 1 and p-tolyl-MgBr (mole ratio 1:10) were recorded.
recycled catalyst. This fraction then contributes to the yield The presence of p-tolyl-MgBr led to a shift of the 31P signal
of the consecutive catalytic experiment. The product selec- from 42.8 to 49.8 ppm arising from [Ni{(Ph2P)2N(CH2)3Si-
tivity of recycled 1/SBA-15 somewhat decreased, but still (OCH3)3-P,PЈ}Br2].[48b] Therefore this chemical shift indi-
1
remained higher than that achieved with 1 alone.
cates the substitution of Cl– in 1 by Br– released from the
The amount of catalyst leaching from 1/SBA-15 was de- Grignard reagent, affording NiP2Br2-containing species.
termined for reactions carried out in more concentrated The catalytic activity of such species in Kumada coupling
mixtures (Table 3, entries 6a–6d). The Ni content was deter- reactions has been recently documented for [Ni{(Ph2P)2N-
mined in fresh 1/SBA-15 and the liquid phases isolated at (S)-CHMePh-P,PЈ}Br2], which contains a similar first coor-
the end of each catalytic cycle. The amount of Ni released dination sphere.[11] The 1H NMR spectrum shows a shift of
in the first to fourth cycle was found to be 47, 47, 35, and the signal of the linker OCH3 groups from 3.32 to
21 μg, respectively, which represents around 13, 13, 10, and 3.23 ppm, which may be due to a solvent effect because the
6% (about 40% in total) of the amount of Ni used. Despite Grignard reagent was added as a thf solution. Alternatively,
that, no significant decrease in the activity and product this observation may be considered as indirect evidence for
selectivity of 1/SBA-15 was observed (Table 3).
the Grignard reagent causing leaching of 1 when added to
To obtain a better insight into this behavior, a “hot fil- 1/SBA-15.
tration” experiment was carried out under reaction condi-
It is worth comparing the catalyst efficiencies of 1 and
tions A. The reaction mixture was centrifuged 5 min after 1/SBA-15 with those of similar catalysts described in the
starting the reaction and the supernatant transferred to a literature, in particular, with those of [Ni{Ph2P(CH2)3PPh2-
new test tube. GC analyses showed substrate conversion of P,PЈ}Cl2] and [Ni{(Ph2P)2N-(S)-CHMePh-P,PЈ}X2] (X =
40% (Table 3, entry 7a) with no increase in the conversion Cl, Br; Table 3, entries 1–3). As can be seen, under similar
during the next 60 min. The addition of a new portion of reaction conditions, both 1 and 1/SBA-15 showed compar-
reactants increased the overall conversion to 50% (related able activity (conversion) but significantly higher product
to the total amount of reactants added, Table 3, entry 7b). selectivity compared with those of the published catalysts.
This result proves that the leached NiII species remained
In complex 1 described herein, the NiII-coordinated li-
catalytically active. Thus, the apparent lack of activity in gand contains a linker group through which the complex
the isolated supernatant should be ascribed to the decom- can be directly anchored onto a siliceous support, thus af-
position of the Grignard reagent during centrifugation. A fording a heterogeneous catalyst. This strategy allowed a
new portion of substrate added to the centrifuged 1/SBA-15 thorough characterization of the metal complex prior to its
also reacted, giving a conversion of 45% (Table 3, entry 7c). immobilization onto the support. This approach is the op-
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of 89.3 kHz with a repetition delay of 10 s. The number of tran-
sients of signal accumulation was 5120 (total experimental time was
14 h). The SPINAL 64 decoupling was applied during the periods
of detection. The 31P NMR scale was calibrated with CaHPO4
(–0.6 ppm). The frictional heating of the spinning samples was
compensated by active cooling, and temperature calibrations were
performed with Pb(NO3)2.[57]
posite of the widely used strategy in which the catalyst sup-
port is first modified, for example, by a diphosphane ligand
containing a linker capped with anchoring Si(OR)3 groups
(R = CH3 or CH2CH3), and then treated with a metal-ion
source.[34,49–52] A similar methodology has been recently
followed for the immobilization of a PdII–edta complex
onto organo-functionalized SBA-15, which is active in
Sonogashira- and Suzuki-type of reactions.[53]
UV/Vis spectra were recorded with a Perkin–Elmer Lambda 950
spectrometer in quartz cuvettes.
[Ni{(Ph2P)2N(CH2)3Si(OCH3)3-P,PЈ}Cl2] (1):
CH2Cl2 solution (0.9 m) of (Ph2P)2N(CH2)3Si(OCH3)3 (0.2 mL,
A
concentrated
Conclusions
The synthetic protocol affording novel complex 1 is quite 0.18 mmol) was diluted with CH2Cl2 (15 mL) and, after 5 min,
[NiCl2(PPh3)2] (0.12 g, 0.18 mmol) was added to afford an orange
solution that was stirred at room temperature for 1 h. This solution
was concentrated to 5 mL and subsequent addition of n-hexane
(15 mL) afforded an orange powder that was filtered and dried un-
der vacuum (isolated yield 0.12 g, 99%). UV/Vis (CH2Cl2): λ =
simple and very efficient, as well allowing its anchoring
onto siliceous supports. The structural data for 1 has pro-
vided a deeper insight into the factors controlling the struc-
tures of square-planar and tetrahedral complexes of the
[Ni(P,P)X2] type (X = Cl, Br, CO). Complex 1 exhibits com-
parable catalytic activity and significantly higher product
selectivity compared with those of widely used catalysts,
such as [Ni{Ph2P(CH2)3PPh2-P,PЈ}Cl2], or the recently in-
vestigated [Ni{(Ph2P)2N-(S)-CHMePh-P,PЈ}X2] (X = Cl,
470 nm, ε = 2150 Lmol–1 cm–1. IR (KBr): ν = 1625, 1581, 1476,
˜
1430, 1306, 1278, 1181, 1092, 1025, 917, 865, 743, 692, 535,
1
515 cm–1. H NMR (300.0 MHz, CDCl3): δ = 0.14 (J = 7.8 Hz, 2
H, Si-CH2), 1.16 (2 H, CH2), 2.81 (2 H, N-CH2), 3.32 (9 H, Si-
OCH3), 7.55–7.99 ppm (20 H, Ar-H) ppm. 31P{1H} NMR
Br). However, 1/SBA-15 exhibits significant leaching, but (121.4 MHz, CDCl3, referenced to an external 85% w/w aq. soln.
“hot filtration” experiments revealed that the leached NiII
species retain their catalytic activity. Other experiments
of H3PO4): δ = 42.8 ppm; the corresponding peak for the free
(Ph2P)2N(CH2)3Si(OCH3)3 ligand was observed at δ = 62.2 ppm.
indicated that the Grignard reagent may contribute to cata-
lyst leaching. Efforts are currently underway in our
laboratories to immobilize 1 onto other solid supports and
to test it in other catalytic reactions.
Immobilization of 1 onto SBA-15 Mesoporous Sieves (1/SBA-15):
SBA-15 molecular sieves (580 mg), predried in vacuo at 300 °C for
3 h, was placed in a Schlenk tube under Ar. CH2Cl2 (10 mL) and
complex 1 (30.6 mg, 0.045 mmol, 2.7 mg of Ni) were added and the
resulting orange mixture was stirred for 1 h. Subsequently the solid
material was separated by filtration, washed twice with CH2Cl2
(10 mL), and dried in vacuo. 31P MAS NMR of 1/SBA-15 (room
temp.): δ = 41.8 ppm. The Ni content in 1/SBA-15 was determined
to be 0.45 wt.-% based on the Ni content in the supernatant, as
quantified by UV/Vis spectroscopy.
Experimental Section
Materials and Methods: Complex 1 was synthesized under inert
conditions (argon atmosphere). The solvents were dried and dis-
tilled according to literature procedures.[54] All chemical reagents
employed in this work were purchased from Aldrich. The (Ph2P)2N-
X-ray Crystal Structure Determination:
A
crystal of
1
(CH2)3Si(OCH3)3 ligand was synthesized by the reaction between
(0.03ϫ0.29ϫ0.804 mm) was taken from the mother liquor and im-
mediately cooled to –113 °C. Diffraction measurements were per-
Ph2PCl and NH2(CH2)Si(OCH3)3, according to
a published
method.[51]
formed with
a Rigaku R-AXIS SPIDER Image Plate dif-
Siliceous mesoporous molecular sieves SBA-15 (SBET = 829 m2 g–1,
V = 1.18 cm3 g–1, d = 6.6 nm) was prepared as described else-
where.[55,56]
fractometer using graphite-monochromated Cu-Kα radiation. Data
collection (ω scans) and processing (cell refinement, data reduction,
and numerical absorption correction) were performed by using the
CrystalClear program package.[58] The structure was solved by di-
rect methods using SHELXS-97 and refined by full-matrix least-
squares methods on F2 with SHELXL-97.[59] All hydrogen atoms
were introduced by using difference maps and refined isotropically.
All non-hydrogen atoms were refined anisotropically. One of the
phenyl rings shows disorder in two positions with occupancies of
0.617(4) and 0.383(4). Two of the methyl groups of the ligand are
also in disordered positions. In one case, both oxygen and carbon
atoms of the OCH3 group are disordered with occupancies of
0.625(7) and 0.375(7), and in the other case only the carbon atom
is disordered with occupancies of 0.81(1) and 0.19(1). The hydrogen
atoms were located with difference maps and refined by using both
models, isotropic and riding on corresponding carbon atoms. The
hydrogen atoms bonded to disordered atoms were not included in
the refinment. Important crystallographic and refinement data are
listed in Table 1. Further experimental crystallographic details for
1: 2θmax = 130°; number of reflections collected/unique/used,
27946/5254 [R(int) = 0.0635]/5254; 503 parameters refined; Δ/σ =
The Kumada coupling reactions were carried out under argon by
using Schlenk techniques and specific conditions are presented in
Table 3. The resulting reaction mixtures were analyzed by GC-FID
(Shimadzu 6000) to obtain yields of products and side-products
from the catalytic reactions. Mesitylene was used as an internal
standard. The Ni contents of both solid and liquid samples were
determined by the ICP-OES method using a ThermoScientific
iCAP 6500 radial spectrometer. Solid samples were dissolved in a
HF/HClO4 mixture and transferred to a 2% w/w aqueous solution
of HNO3.
FTIR spectra were recorded with a Shimadzu IR Affinity-1 spec-
trometer using KBr pellets. 1H and 31P NMR spectra were recorded
with a Varian V 300 MHz spectrometer at 25 °C. Solid-state NMR
spectra were recorded at 11.7 T with a Bruker Avance III HD 500
WB NMR spectrometer in 3.2 mm ZrO2 rotors at a magic angle
spinning (MAS) frequency of 20 kHz. The single-pulse 31P MAS
NMR spectrum was recorded at a B1(31P) field nutation frequency
Eur. J. Inorg. Chem. 2015, 3038–3044
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© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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FULL PAPER
0.001; (Δρ)max/(Δρ)min = 0.770/–0.641 eÅ–3; R/Rw (for all data),
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Acknowledgments
Financial support by the Special Account of the University of
Athens (grant number 7575), the Ministry of Education of Greece
and the Czech Science Foundation (project number P108/12/1143)
is gratefully acknowledged. This research was co-financed by the
European Union (EU) (European Social Fund - ESF) and Greek
National Funds through the Operational Program “Education and
Lifelong Learning” of the National Strategic Reference Framework
(NSRF) – Research Funding Program “Heracleitus II”: Investing
in knowledge society through the European Social Fund. Dr. Jirˇí
Brus is gratefully thanked for recording solid-state NMR spectra.
P. K. participated in the activities of the CM0802 Cost Action
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Received: April 23, 2015
Published Online: June 2, 2015
Eur. J. Inorg. Chem. 2015, 3038–3044
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© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim