Synthesis, characterization and catalytic application of some novel PNP-Ni(II) complexes: Regio-selective [2+2+2] cycloaddition reaction of alkyne

Article abstract of DOI:10.1016/j.jorganchem.2017.02.039

Some novel Ni(II) complexes of PN(H)P^Ph, PN(Me)P^iPr and PN(Me)P^tBu ligands have been synthesized and characterized using standard analytical and spectroscopic methods such as ¹H NMR, ³¹P NMR, elemental analysis, ESI-MS, UV-Visible spectroscopy and single-crystal X-ray crystallography. In the presence of silver triflate, complex [PN(H)P^PhNiBr]₂NiBr₄ (5) activated the C?Cl bond of dichloromethane at room temperature and afford complex [PN(H)P^PhNiCl]OTf (6). We have also performed alkyne [2+2+2] cycloaddition reaction using Ni(II) complexes and observed high regioselectivity of the products. The observed selectivity is well correlating with the electronic feature of alkynes. The [2+2+2] cycloaddition of electron rich alkynes produced 1,3,5-substituted benzene derivatives as a major product whereas the electron deficient alkynes produced 1,2,4-substituted benzene derivatives as a major product.

Full text of DOI:10.1016/j.jorganchem.2017.02.039

Journal of Organometallic Chemistry xxx (2017) 1e8
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, characterization and catalytic application of some novel
PNP-Ni(II) complexes: Regio-selective [2þ2þ2] cycloaddition reaction
of alkyne
*
Masilamani Tamizmani, Chinnappan Sivasankar
Catalysis and Energy Laboratory, Department of Chemistry, Pondicherry University (A Central University), Puducherry, 605014, India
a r t i c l e i n f o
a b s t r a c t
Some novel Ni(II) complexes of PN(H)PPh, PN(Me)PiPr and PN(Me)PtBu ligands have been synthesized and
characterized using standard analytical and spectroscopic methods such as H NMR, P NMR, elemental
analysis, ESI-MS, UV-Visible spectroscopy and single-crystal X-ray crystallography. In the presence of
Article history:
Received 26 January 2017
Received in revised form
1
31
20 February 2017
Ph
silver triflate, complex [PN(H)P NiBr]
2
NiBr
4
(5) activated the CꢀCl bond of dichloromethane at room
Accepted 25 February 2017
Available online xxx
Ph
temperature and afford complex [PN(H)P NiCl]OTf (6). We have also performed alkyne [2þ2þ2]
cycloaddition reaction using Ni(II) complexes and observed high regioselectivity of the products. The
observed selectivity is well correlating with the electronic feature of alkynes. The [2þ2þ2] cycloaddition
of electron rich alkynes produced 1,3,5-substituted benzene derivatives as a major product whereas the
electron deficient alkynes produced 1,2,4-substituted benzene derivatives as a major product.
© 2017 Elsevier B.V. All rights reserved.
Keywords:
Ni(II) complexes
PNP pincer ligands
Alkyne trimerization
Regioselectivity
[2þ2þ2] cycloaddition reaction
1. Introduction
and characterization of pincer ligands stabilized metal complexes
and their catalytic applications towards C-C bond formation re-
The PNP pincer ligands based metal complexes play a vital role
in the modern organometallic chemistry [1e4]. Several pyridine
based PNP pincer ligands have been synthesized and extensively
studied their chemistry with various metal ions [5,6]. The PNP
ligand based transition metal complexes are found to be superior
catalysts for several chemical transformations such as hydrogena-
tion, dehydrogenation, hydroamination, C-F bond activation, Si-H
bond activation, hydrogen production, dinitrogen activation, C-N
actions [21].
Transition metal catalyzed cycloaddition reaction is one of the
powerful synthetic tools to construct the building blocks for mak-
ing natural products and biologically some important compounds
[22e25]. In this regard, transition metal catalyzed [2þ2þ2] cyclo-
addition reaction of alkynes is one of the profound methodologies
to make substituted benzenes. Nevertheless the transition metal
catalyzed cyclooligomerization of the acetylene produces mixture
of products (A-F in Scheme 1a) [26]. After the first report from
Reppe et al. [27] for cyclooligomerization of phenyl acetylene to
1,2,4-triphenylbenzene and 1,3,5,8-tetraphenylcyclooctatetraene
2
bond forming reaction, C-S bond forming reaction and CO reduc-
tion [7e12]. In this line, aliphatic PNP pincer ligands drawn much
attention owing to the nature of their flexible binding to the tran-
sition metal ions [13e18]. Recently Schneider et al. have found that
2 2
using Ni(acac) /CaC as a catalyst (Scheme 1b), research related to
selectivity of cyclooligomerization reaction products of phenyl
acetylene has become more important.
Many transition metals such as Ni, Co, Rh, Fe, Pd, Ru, Ti, Zr, Mo
and Ta with suitable ligands have been used for [2þ2þ2] cycload-
dition of different alkynes [28e34]. Majority of the nickel com-
plexes known for this reaction produced mixture of products
(Scheme 1) however some catalysts produced one or two products
t
the [Ir(COE)(HN(CH
2
CH
2
P Bu
2
)
2
)]BPh
4
(COE ¼ cyclooctene) pincer
complex is capable of activating the C-H bond of tetrahydrofuran
t
[
19]. The [( Bu
2
PCH
2
SiMe
2
)
2
N]-Ni(II) complex synthesized by
Caulton et al. cleaves the dihydrogen via oxidative addition
pathway [20]. The above mentioned reactions clearly revealed the
importance of pincer type ligands and their respective transition
metal complexes. In this regard, we were interested in synthesis
as major products. Oligomerization of terminal alkynes with
iPr
(
NDI)Ni
2
(C
6
H
6
) or (NNN)NiCl
2
type complexes produced B as a
*
Corresponding author.
E-mail address: siva.che@pondiuni.edu.in (C. Sivasankar).
major product (Scheme 1c) [35,36]. However the [PNPRh(H )]
2
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M. Tamizmani, C. Sivasankar / Journal of Organometallic Chemistry xxx (2017) 1e8
complex produced only dimerization product with similar sub-
strates and produced E as a major product (Scheme 1d) [37]. The
All the above discussed studies clearly revealed that the selec-
tivity is the major problem for Scheme 1 and only few complexes
are known to produce compound A with moderate yield and
4
[PNPFeH]BH complex was also used for the dimerization of the
R
terminal alkynes and produced D as a major product (Scheme 1e)
selectivity. In this regard, we have synthesized a series of PNP
[
38]. Most of the Ni(0) or Ni(II) salts catalyzed [2þ2þ2] cycload-
pincer ligands stabilized Ni(II) complexes and characterized fully
using standard analytical and spectroscopic methods and used
them as catalysts to improve the regioselectivity of [2þ2þ2]
cycloaddition reaction of various alkynes and presented the results.
dition reactions of alkyne produced only 1,2,4-substituted benzene
derivatives as a major product [35,39]. Cycloaddition reaction of
phenyl acetylene with [1,2-bis(4-methoxyphenylthio)-ethane]co-
balt bromide complex produced A (Scheme 1) as a major product in
dichloromethane whereas product B (Scheme 1) was isolated as a
major product in acetonitrile [40]. Similar scenario was observed
2. Results and discussion
for the cycloaddition reaction of alkynes with [{NbCl
Cl) -C S)] and [(Ar’O) Ti(C Et )] (Ar’
diphenylphenoxide) complexes and produced 95% of trimer A
41,42]. The selectivity of this reaction was correlated with the
features of ancillary ligands of the corresponding metal complexes
and reaction conditions [43e50].
2 4 8 2
(C H S)} (m-
The PNP pincer ligands L1-L3 were prepared according to the
modified literature procedure [51]. The reaction of L1 and L2 with
2
(m
H
4 8
2
4
4
¼
2,6-
[
2 2
NiCl $6H O in THF for 12 h at room temperature afforded desired
iPr
tBu
complexes [(PN(Me)P NiCl)Cl] (1, 85%) and [(PN(Me)P NiCl)Cl]
1
(2, 92%) respectively (Scheme 3). The H NMR spectrum of complex
Based on the postulated reaction mechanism from the literature
report [43] (Scheme 2), one can understand the product selectivity.
The first step is the reduction of PNPNi(II) complex with zinc
powder to give the possible intermediate with one equivalent of
alkyne. Subsequently the intermediate I reacts with another
equivalent of alkyne to produce intermediate II. The intermediate II
undergoes oxidative addition followed by reductive coupling to
give metallacyclopentadiene III. The metallacyclopentadiene III
may react with one more equivalent of alkyne to produce the
metallacyclohepatatriene IV or V based on the orientation and
insertion of third alkyne. Finally, reductive elimination of the
metallacycloheptatriene IV or V afford the benzene derivatives.
2 displayed a sharp peak at 4.38 ppm for NeMe protons and peaks
t
around 1.83 ppme1.69 ppm corresponds to the protons of eP Bu
2
.
The complexes 1 and 2 displayed a single peak at 51.4 ppm and
31
50.4 ppm respectively in the P NMR spectra for the coordinated
phosphines. The observed ESI-MS (high resolution) values of
complexes 1 (m/z ¼ 412.16) and 2 (m/z ¼ 468.22) are well corre-
lating with the theoretically calculated ESI-MS values of the cor-
responding complexes.
Complex 2 is further confirmed by single-crystal X-ray analysis
(Fig. 1). The NieCl and NieN bond distances are found to be 2.169 Å
and 1.955 Å respectively. The P1eNieP2 and NeNieCl bond angles
ꢁ
ꢁ
are found to be 169.14 and 169.17 respectively. One of the chloride
ion is coordinated to the nickel center and other chloride ion is
Scheme 1. Representative examples for oligomerization of alkynes.
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M. Tamizmani, C. Sivasankar / Journal of Organometallic Chemistry xxx (2017) 1e8
3
at 2.26 ppm for N-Me protons and a multiplet from 1.44 ppm to
t
1
2
.55 ppm for the butyl protons of eP Bu . The ESI-MS (high reso-
lution) values of complexes 3 (m/z ¼ 412.15) and 4 (m/z ¼ 468.22)
are well correlating with the theoretically calculated ESI-MS values
of corresponding complexes. The molecular structure of complexes
3
and 4 are further confirmed by single-crystal X-ray analysis.
The NieCl and NieN bond distances in complex 3 are found to
be 2.151 Å and 1.953 Å respectively. The P1eNieP2 and NeNieCl
ꢁ
ꢁ
bond angles for complex 3 are found to be 167.44 and 174.54
respectively (Fig. 1). The NieCl and NieN bond distances in com-
plex 4 are found to be 2.151 Å and 1.967 Å respectively. The
P1eNieP2 and NeNieCl bond angles in complex 4 are found to be
ꢁ
ꢁ
1
70.06 and 169.07 respectively (Fig. 3). The structural analysis of
complexes 3 and 4 indicate that the chloride ion is coordinated to
e
4
the nickel center and the eBPh ion is located in the lattice posi-
tion, and the R group on the coordinated phosphine does not
change the coordination environment of Ni center.
Ph
The reaction of alkyl PN(H)P (L3) with NiBr
2
in THF at room
(NiBr )] (5) as a
red solid (yield 60%) (Scheme 3). The complex 5 shows a single peak
Ph
temperature for 12 h produced [(PN(H)P NiBr)
2
4
31
at 33.5 ppm in P NMR spectrum for coordinated phosphines. The
formation of complex 5 was confirmed by single-crystal X-ray
analysis (Fig. 2 and Fig. 3). The crystal structure of complex 5
Ph
revealed that the two monomeric PNP NiBr units bridged through
4
a NiBr unit. The NieBr1 and NieN bond distances are found to be
2
.3227 Å and 2.195 Å respectively. The P2eNieP1 and NeNieBr1
ꢁ
ꢁ
bond angles are found to be 165.84 and 176.53 respectively.
The reaction of complex 5 with two equivalents of silver triflate
in a dichloromethane solution at room temperature for 12 h pro-
Ph
duced [(PN(H)P NiCl)(OTf)] (6) (Scheme 3). The complex 5 acti-
vated the CeCl bond of dichloromethane in the presence of silver
triflate as observed in the literature [52]. The formation of complex
Scheme 2. The proposed catalytic cycle for alkynes [2þ2þ2] cycloaddition.
6
was confirmed by NMR and X-ray crystallography techniques. The
1
H NMR spectrum of complex 6 displays three multiplets at
.36 ppm, 2.80 ppm and 2.40 ppm for eCH eCH e methyl protons
and a single peak at 4.86 ppm for NeMe protons. The P{ H} NMR
spectrum of complex 6 displays a single peak at 27.6 ppm in CDCl
located in the lattice position.
3
2
2
The complexes 3 and 4 have been synthesized by treating
31
1
complexes 1 and 2 with a methanol saturated solution of NaBPh
The 1H NMR spectrum of complex 3 displayed broad peaks at
.21 ppm and also from 0.84 ppm to 1.52 ppm for N-Me, eCH
4
.
3
for coordinated phosphines. These spectral data indicates that the
complex 6 is entirely different from complex 5.
2
2
e
i
1
2
and eP Pr protons. The H NMR of complex 4 displays a single peak
The solid state structure of complex 6 was determined using a
Scheme 3. Synthesis of complexes 1e6.
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4
M. Tamizmani, C. Sivasankar / Journal of Organometallic Chemistry xxx (2017) 1e8
Fig. 1. ORTEP drawing (50% probability ellipsoids) of the [PN(Me)PtBuNiCl]Cl (2), and [PN(Me)PiPrNiCl]BPh
distances (Å) and selected bond angles ( ) for 2, Ni-Cl, 2.1693(10); Ni-P1, 2.2454(9); Ni-P2, 2.2433(9); Ni-N1, 1.955(3): P1-Ni-P2, 169.14(4); P1-Ni-Cl, 93.46(4); P2-Ni-Cl, 93.49(4); N1-
Ni-Cl, 169.17(9); for 3: Ni-Cl, 2.151(0); Ni-P1, 2.212(0); Ni-P2, 2.194(1); Ni-N1, 1.953(2). P1-Ni-P2, 167.44(3); P1-Ni-Cl, 95.32(3); P2-Ni-Cl, 92.40(3); N1-Ni-Cl, 174.54(8).
(3). Omitted for clarity: solvent molecule, all H atoms. Selected bond
4
ꢁ
single-crystal X-ray diffraction studies (Fig. 4). The NieCl and the
NieN bond distances are found to be 2.182 Å and 1.954 Å respec-
tively. The P2eNieP1 and NeNieCl bond angles are found to be
ꢁ ꢁ
67.45 and 174.58 respectively. The structural parameters such as
1
bond lengths, bond angles and dihedral angles of cationic part of
complex 6 are found to be relatively similar to the structural fea-
Ph
þ
56
tures reported for [ PNPNiCl] by Walter et al. Furthermore our
solid state structure analysis confirmed the cleavage of C-Cl bond of
dichloromethane. In complex 6, the chloride ion is coordinated to
ꢀ
the nickel center and the triflate ( OTf) anion is found to be out of
the primary coordination sphere. Selected bond distances and bond
angles of complexes 2e6 are given in Table 1. The complexes 2e6
exhibits P2eNieP1 and NeNieX (X ¼ Cl, Br) angles in the range of
Fig. 3. Chemical structure of complex 5 as observed in the crystal structure.
ꢁ ꢁ ꢁ
65.84 e176.53 which is lower than the expected angle 180 . The
1
1
shows two strong absorption bands at 228 nm and 338 nm, and
geometry around the nickel center for complexes 2e6 is found to be
slightly distorted square planar as observed in similar known PNP-
NiX complexes [53e55]. Therefore the kind of distortion observed
in complexes 1e6 is not unique. The NieCl bond lengths of complex
relatively a weak absorption band at 431 nm. The corresponding t-
butyl substituted phosphine complex 2 shows two strong absorp-
tion bands at 239 nm and 355 nm, and relatively a weak absorption
band at 505 nm. The complex 3 shows an intense absorption band
at 204 nm and relatively weak intense bands at 334 nm and 474 nm.
The complex 4 shows an intense absorption band at 238 nm and
relatively weak intense bands at 358 nm and 510 nm. The ab-
sorption bands centered around 250e350 nm can be attributed to
2
(2.1693 Å) is longer than complexes 3 (2.151 Å) and 4 (2.151 Å).
This indicates that the removal of chloride counter ion from com-
plexes is responsible for shorting of NeCl bond in 3 and 4. The
NieBr and NeCl bond distances in complexes 5 and 6 are similar to
previously reported NieBr (2.3036 Å) [55] and NieCl (2.169(1) Å)
bond distances in some PNP pincer nickel(II) complexes [56]. The
average bond distance of NieP in complex 2 (2.244 Å) is found to be
longer than that of NieP distance in other complexes 3e6 (3,
the ligand centered p-p* transition while the weak bands centered
around 400e500 nm can be attributed to the d-d transition for the
square planar geometry in their respective complexes 1e4.
2
.203 Å; 4, 2.2366 Å; 5, 2.1972 Å; 6, 2.203 Å) and previously re-
ported alkyl PNP-NiBr complex (2.024 Å) [55].
2.2. Catalysis: [2þ2þ2] cycloaddition reaction of alkyne
The [2þ2þ2] cycloaddition reaction of alkyne using already
known Ni(II) complexes produces generally three products such as
A (1, 3, 5-substituted benzene), B (1, 2, 4-substituted benzene) and
C (dimer of alkyne) (Scheme 1a). We have optimized the [2þ2þ2]
cycloaddition reaction with 1 mmol of phenyl acetylene in the
2
.1. Electronic spectroscopy
The UV-Visible spectra of a dilute solution of complexes 1e6
have been recorded in acetonitrile (Fig. 5 and Fig. S1). The complex
Fig. 2. ORTEP drawing (50% probability ellipsoids) of the [PN(Me)PtBuNiCl]BPh
Selected bond distances (Å) and selected bond angles ( ) for 4: Ni-Cl, 2.151(6); Ni-P1, 2.241(5); Ni-P2, 2.231(7); Ni-N1, 1.967(2). P1-Ni-P2, 170.06(4); P1-Ni-Cl, 93.41(3); P2-Ni-Cl,
(4) and [(PN(H)PPhNiBr)
(NiBr )] (5). Omitted for clarity: solvated dichloromethane, all H atoms.
2 4
4
ꢁ
93.41(3); N1-Ni-Cl, 169.07(8); for 5: Ni-Br1, 2.3227(7); Ni-P1, 2.1950(14); Ni-P2, 2.1994(14); Ni-N1, 1.973(3). P1-Ni-P2, 165.84(5); P1-Ni-Br1, 94.03(4); P2-Ni-Br1, 94.21(4); N1-Ni-Br1,
176.53(12).
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M. Tamizmani, C. Sivasankar / Journal of Organometallic Chemistry xxx (2017) 1e8
5
Fig. 4. ORTEP drawing (55% probability ellipsoids) of the [PN(H)PPhNiCl]OTf (6).
Omitted for clarity: all H atoms. Selected bond distances (Å) and selected bond angles
ꢁ
Fig. 5. UV-Visible spectra of complexes 1e4.
(
) for 6: Ni-Cl, 2.1821(7); Ni-P1, 2.2122(8); Ni-P2, 2.1941(8); Ni-N1, 1.954(2). P1-Ni-P2,
167.45(3); P1-Ni-Cl, 95.33(3); P2-Ni-Cl, 92.39(3); N1-Ni-Cl, 174.58(9).
concentration of Ni(0) species would be less and it may not even
form.
presence of PNPNi(II) complexes (1e6) (2.5 mol%) using different
reductant (5 mol%) in different solvents (Table 2). As mentioned in
Table 2, complex 2 produced good yield in acetonitrile with two
regio isomers and 1,3,5-substituted benzene (A) as a major product
In order to demonstrate the substrate scope of our newly syn-
thesized complexes for [2þ2þ2] cycloaddition reaction, we have
used different alkynes and isolated the product and characterized
using standard analytical methods and compared with the reported
analytical data of known compounds. The [2þ2þ2] cycloaddition of
3-ethynyltoluene produced 1,3,5-substituted benzene (85%) prod-
uct (Table 3, entry 2) whereas 1-ethynyl-3,5-bis(trifluoromethyl)
benzene offered 1,2,4- substituted benzene as a major product
(Table 3, entry 7). These results revealed that the observed selec-
tivity of the [2þ2þ2] cycloaddition of alkyne using complex 2 is
also depends on the electronic nature of alkynes. We observed
1,3,5- substituted benzene as a major product while using simple
alkyl substituted alkynes (Table 3, entry 3, 4 and 5). On the other
hand, we observed 1,2,4-substituted benzene as a major product
while using methyl propiolate and ethyl propiolate as substrates
(Table 3, entry 8 and 9).
(
Table 2, entry 1 and 2). In the presence of complexes 3e6, the yield
and selectivity of [2þ2þ2] cycloaddition product goes down
Table 2, entry 3e6). Furthermore the yield and selectivity have also
(
been tested in different solvents, the dimerized product C is
observed as a major product in DCM and THF solvents with low
yields (Table 2, entry 7e8) and suggests that the solvent also plays a
role in controlling the selectivity.
From Table 2, it can be noted that the complexes 2 and 4 shows
better selectivity than complexes 1, 3, 5 and 6. Since the complexes
2
and 4 have sterically bulky donor ligand L2, the bulkiness of the
phosphine ligand seems to favors the formation of A isomer,
however more detailed mechanism related experiments need to be
carried out to fully understand the origin of the selectivity. The
electronic and structural features of the complexes may also play
significant role in controlling the reactivity of respective complexes.
Nevertheless, the reduction of Ni(II) to Ni(0) in the presence of Zn is
relatively more feasible in complexes 1 and 2 when compared to
other complexes 3e6. As the chloride ion present as a counter ion in
3. Conclusions
Some novel Ni(II) complexes 1e6 have been synthesized using
pincer ligands L1-L3. Complexes 1e6 have been characterized us-
complexes 1 and 2, the formation of ZnCl
more feasible than the formation of other zinc salts such as
ZnCl(BPh ) and ZnBr from their respective complexes (3e6). As
2
(lattice energy is more) is
1
ing standard analytical and spectroscopic techniques such as
H
31
NMR, P NMR, ESI-MS and elemental analysis. The C-Cl bond
cleavage in dichloromethane was observed with the complex 5 in
the presence of silver triflate. The complex 2 acts as a good catalyst
for regioselective [2þ2þ2] cycloaddition reaction of alkyne de-
rivatives in the presence of zinc at low temperature while other
complexes 1 and 3e6 produced relatively low yields.
4
2
mentioned in Scheme 1, the formation of Ni(0) species is important
to achieve the [2þ2þ2] cycloaddition reaction, hence concentra-
tion of Ni(0) complexes would be more in solution when we used
complexes 1 and 2 whereas in case of complexes 3e6, the
Table 1
ꢁ
Selected bond distances (Å) and bond angles ( ) from crystal structures of the nickel complexes.
Compound
2
3
4
5
6
Ni-X
Ni-P1
Ni-P2
Ni-N
P1-Ni-P2
N-Ni-X
P-Ni-X
2.1693
2.151
2.212
2.151(6)
2.241(5)
2.231(7)
1.967(2)
170.06
2.3227(7)
2.1950(1)
2.1994(1)
1.973(3)
165.84
2.1821
2.2122(8)
2.194
1.954
167.45
2.2454(9)
2.2433(9)
1.9553
169.14
169.17
2.194(1)
1.9532
167.44
174.54
95.32, 92.40
169.07
93.41, 93.41
176.53
94.21, 94.03
174.58
95.33, 92.39
93.46, 93.49
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6
M. Tamizmani, C. Sivasankar / Journal of Organometallic Chemistry xxx (2017) 1e8
Table 2
Table 3
a
Optimization of the reaction conditions for PNP-Nickel(II) complexes catalyzed
[2þ2þ2] cycloaddition of various alkynes using complex 2.
a
[2þ2þ2] addition reaction.
Yieldb (%)
A: B: Cc
Entry
R
R
0
Yieldb (%)
TONc
A: Bd
Entry
Complex
Solvent
Time (h)
Reductant
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
2
2
2
2
2
2
–
2
CH
CH
CH
CH
CH
CH
3
3
3
3
3
3
CN
CN
CN
CN
CN
CN
3
3
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Sn
Mg
Zn
e
92
95
30
40
40
38
35
40
25
40
32
e
51:49:0
75: 25:0
50:50:0
70:30:0
52:48:0
50:50:0
18:7:75
18:7: 75
34:66:0
50:50:0
35:65:0
e
1
2
3
4
Ph-
3-MeC
H
H
H
H
H
H
H
H
70
82
86
86
72
60
95
92
92
65
28.0
32.8
32.0
32.0
28.8
24.0
38.0
36.8
36.8
26.0
75: 25
85: 15
88: 12
90: 10
66: 33
e
6
H
4
-
12
12
12
12
12
12
5
12
3
12
24
24
C
C
3
H
H
5
-
8
17
-
-
e
5
6
CyCH
Me Si-
3,5-CF
MeO C-
EtO C-
MeO C-
2
f
3
DCM
THF
7
8
9
10
3
C
6
H
3
-
5: 95
5: 95
5: 95
e
2
Toluene
Dioxane
CH
CH
CH
CH
2
H
10
11
12
13
14
2
2
MeO C-
3
CN
3
CN
3
CN
3
CN
a
Reaction conditions: 2 mmol terminal alkyne, 2.5 mol % [(PNP)NiCl]Cl (2),
.0 mol% Zn in 3 mL of acetonitrile.
5
e
e
b
Isolated yield of A for entry 1e4 and B for entry 7e9.
e
e
c
TON calculated based on isolated product yield.
a
d
Product ratio determined by 1H NMR spectra.
Reaction conditions: 2 mmol terminal alkyne, 2.5 mol % of [(PNP)NiCl]Cl, 5.0 mol
e
%
Zn in 3 mL of solvent.
Combined isolated yield of A and B.
Dimerized product only formed.
b
f
Isolated yield.
c
The product ratio was determined by 1H NMR spectra.
i
4
.2.1. Synthesis of PN(Me)P Pr
2
(L1)
4
. Experimental section
Under an atmosphere of argon, chlorodiisopropyl phosphine
4.56 g, 29.9 mmol) in tetrahydrofuran (10 mL) was added through
a dropping funnel to a suspension of lithium granules (830 g,
20 mmol) in tetrahydrofuran (30 mL). The resulting solution was
stirred vigorously at room temperature for 3 days to yield a lithium
(
4
.1. General considerations
1
Unless specified otherwise, all manipulations were performed
under nitrogen atmosphere using standard Schlenk line techniques.
Toluene and THF were dried and distilled over Na/Ph CO and stored
in an N -filled solvent storage flask. CDCl , DCM and acetonitrile
were dried and then distilled or vacuum transferred over CaH
Chlorodiphenylphosphine, chlorodiisopropylphosphine, chlorodi-
t-butylphosphine and NiBr were purchased from Aldrich and used
without further purification. NMR spectra were recorded on a
Bruker 400 MHz ( H NMR, 400 MHz; C NMR, 100.62 MHz;
NMR,161.822 MHz) spectrometer. For H NMR and C NMR spectra,
the residual solvent peak was used as an internal reference. P NMR
spectra were referenced externally using 85% H PO at 0 ppm and
ESI-MS was recorded on Agilent 6540 UHD Q-TOF mass
spectrometer.
i
2
diisopropyl phosphide solution. The LiP Pr was transferred
2
through a metal cannula from unreacted Li metal and the solution
2
3
ꢁ
was cooled to ꢀ78 C. A solution of (ClCH
2 2 2
CH ) NMe$HCl (2.84 g,
2
.
1
4.9 mmol) in tetrahydrofuran (30 mL) was neutralized with n-
butyllithium (2.5 M in hexane, 6.0 mL, 15 mmol) at 0 C. Then this
solution was added to the above lithium diisopropyl phosphide
solution at ꢀ78 C with vigorous stirring. The mixture was then
ꢁ
2
ꢁ
1
13
31
P
1
13
allowed to warm to room temperature and was refluxed for 10 h.
Then the reaction mixture was cooled to room temperature, then
degassed water (50 mL) was added to the reaction mixture. The
aqueous layer was decanted through cannula and the organic layer
was washed with two portions of degassed water (10 mL ꢂ 2). The
organic layer was then dried with anhydrous magnesium sulfate.
After stirring for an hour, the magnesium sulfate was filtered off
through a pad of silica gel and the solvent was concentrated in
31
3
4
d
4.2. X-ray data collection and refinement
vacuo. The residue was dissolved with pentane and filtered to yield
Data collections were performed on an OXFORD XCALIBUR
1
a pale yellow liquid. (Yield: 3.3 g, 70%). H NMR (400 MHz, CDCl
3
):
diffractometer, equipped with a CCD area detector, using graphite-
monochromated Mo K
¼ 0.71073 Å) radiation and a low-
d
2.54 (b, 4H, eNCH
ePCH(CH ), 1.53 (b, 4H, ePCH
H} NMR (162 MHz, CDCl ): d 1.6 ppm.
2
e), 2.28 (s, 3 H, eNCH
3
), 1.73 (b, 4H,
a (l
31
3
)
2
2
), 1.01 (bd, 24 H, ePCH(CH
3
)
2
).
P
temperature device. All calculations were performed using
SHELXS-97 and SHELXL-97 respectively using Olex 2e1.1 software
package [57,58]. The structures were solved by direct methods and
successive interpretation of the difference Fourier maps, followed
by full-matrix least-squares refinement (against F2). All non-
hydrogen atoms were refined anisotropically. The crystallographic
figures have been generated using Olex 2e1.1 software package
1
{
3
t
4.2.2. Synthesis of PN(Me)P Bu (L2)
Under an atmosphere of argon, chlorodi-t-butylphosphine
(4.76 g, 4.76 mL, 31 mmol) in tetrahydrofuran (10 mL) was added
through a dropping funnel to a suspension of lithium granules
(0.85 g, 122 mmol) in tetrahydrofuran (30 mL). The resulting so-
(
1
50% probability thermalellipsoids). CCDC files 1037672, 1031834,
037671, 1440680 and 1005203 contain supplementary crystallo-
graphic data for the complexes 2, 3, 4, 5 and 6. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Center via www.ccdc.cam.ac.uk/data_request/cif.
lution was stirred vigorously at room temperature for 3 days to
t
yield a lithium di-t-butylphosphide solution. The LiP Bu
2
was
transferred through a metal cannula from unreacted Li metal and
ꢁ
the solution was then cooled to ꢀ78 C. To (ClCH
2 2 2
CH ) NMe$HCl
Please cite this article in press as: M. Tamizmani, C. Sivasankar, Journal of Organometallic Chemistry (2017), http://dx.doi.org/10.1016/
j.jorganchem.2017.02.039

M. Tamizmani, C. Sivasankar / Journal of Organometallic Chemistry xxx (2017) 1e8
7
(
3 g, 15.6 mmol) in tetrahydrofuran (30 mL) was neutralized with n-
mixture was allowed to stirrer for 6 h at room temperature. The
solvent was removed under vacuo, the solid was dissolved in
ꢁ
butyllithium (2.5 M in hexanes, 6.24 mL, 15.6 mmol) at 0 C. Then
this solution was added to the above lithium di-t-butylphosphide
3
dichloromethane and filtered through 1 cm silica gel. The red-
ꢁ
1
solution at ꢀ78 C with vigorous stirring. The workup was done as
orange solid was dried under vacuum. (Yield: 283 mg, 88%).
NMR (CDCl ):
2.21 (bs, 8H), 1.52e1.47 (b, 20H), 1.28 (b, 8H), 0.84 (b, 2H). P{ H}
H
mentioned for L1 synthesis. Bis(2-(di-t-butylphosphino)ethyl)
3
d 7.40 (bs, 8H), 7.07e7.04 (t, 8H), 6.94e6.91 (t, 4H),
1
31
1
methylamine. (yield: 3.8 g, 65%). H NMR (400 MHz, CDCl
d
3
):
iPr
þ
2.61e2.55 (m, 4H, eCH
2
CH
2
e), 2.33 (s, 3H, eNCH
3
), 1.58e1.55 (m,
NMR (CDCl
at m/z ¼ 412.15, calc. 412.16. Anal. Calcd. for C41
67.20; H, 8.12; N, 1.91. Found: C, 67.16; H, 8.15; N, 1.87.
3
):
d
54.8 (s). ESI-MS: [PN(Me)P NiCl] displays a peak
4
H, eCH CH e), 1.14 (d, 18H, eP(C(CH
2
2
3
3
)
3
)
2
), 1.11 (d, 18H,
H
59BClNNiP : C,
2
31
1
eP(C(CH
3
)
3
)
2
). P{ H} NMR (162 MHz, CDCl
): d 24.2 ppm.
4
.2.3. Synthesis of PN(H)PPh (L3)
Under an atmosphere of argon, chlorodiphenylphosphine (5.2 g,
3.6 mmol) in tetrahydrofuran (10 mL) was added through a
4.2.7. Synthesis of ([PN(Me)PtBuNiCl][BPh
Complex 2 (200 mg, 0.4 mmol) was dissolved in CH
Upon addition of NaBPh (164 mg, 0.48 mmol) in 2 mL of methanol,
4
]) (4)
3
CN (5 mL).
2
4
dropping funnel to a suspension of lithium granules (0.65 g) in
tetrahydrofuran (30 mL). The resulting solution was stirred vigor-
ously at room temperature for 2 days to yield a lithium diphenyl-
a red colour solution was slowly changed to orange solution. The
reaction mixture was allowed to stir for 6 h at room temperature.
The solvent was removed under vacuo, the solid was dissolved in
3
phosphide solution. The LiPPh
2
was transferred from unreacted Li
dichloromethane and filtered through 1 cm silica gel. The orange
ꢁ
1
metal through a cannula and the solution was cooled to ꢀ78 C. The
solid was dried under vacuum. (Yield: 285 mg, 92%). H NMR
(
ClCH
2
CH
2
)
2
NH$HCl (2.25 g, 11.8 mmol) in tetrahydrofuran (30 mL)
(400 MHz, CDCl
6.94e6.90 (t, 3H, Ph-H), 2.26 (s, 3H, N-Me), 2.00 (s, 2H, -CH
1.70 (b, 2H, -CH -), 1.55e1.51 (t, 20H, PC(CH & -CH -), 1.48e1.44
(t, 20H, -PC(CH -). P{ H} NMR (CDCl ): 53.4 (s). ESI-
3
):
d
7.38 (bs, 8H, Ph-H), 7.07e7.03 (t, 8H, Ph-H),
was neutralized with n-butyllithium (2.5 M in hexanes, 4.7 mL,
2
-),
ꢁ
1
1.8 mmol) at 0 C. Then this solution was added to the above
2
3
)
3
2
ꢁ
31
1
lithium diphenylphosphide solution at ꢀ78 C with vigorous stir-
3
)
3
& -CH
2
3
d
t
þ
ring. The workup was done as mentioned for L1 synthesis.
MS: [PN(Me)P BuNiCl] displays a peak at m/z ¼ 468.22, calc.
1
(
7
eCH
Yield:2.6 g, 59%). H NMR (400 MHz, CDCl
3
):
d
7.32 (bs, 8H, Ph-H),
e), 2.14 (bs, 4H,
468.22. Anal. Calcd. for C45
H
67BClNNiP
2
: C, 68.51; H, 8.56; N, 1.78.
.22 (bs, 12H, Ph-H), 2.64 (bs, 4H, eCH
2
CH
2
Found: C, 68.45; H, 8.55; N, 1.72.
31
2
CH
2
e). P NMR (162 MHz, CDCl
3
):
d
ꢀ20.66.
4
.2.8. Synthesis of [PN(H)PPhNiBr]
2
NiBr
4
(5)
4
.2.4. Synthesis of complex PN(Me)PiPrNiCl
2
(1)
The complex 5 was prepared similar to complex 1 with NaBr
2
iPr
Ph
Under an atmosphere of nitrogen, PN(Me)P
.56 mmol) and NiCl $6H O (372 mg, 1.56 mmol) were taken in THF
40 mL) and the reaction mixture was stirred overnight at room
L1 (500 mg,
(123 mg, 0.56 mmol), PN(H)P (250 mg, 0.56 mmol) as the starting
compound. Yield: 130 mg (60%). Its paramagnetic nature failed to
1
2
2
1
31
1
(
produce good H NMR. P{ H} NMR (CDCl
3
):
d
33.58 (s). ESI-MS:
þ
temperature. The solvent was removed under vacuo, and the pink
[C28
H29ClNNiP
2
]
displayed a peak at m/z ¼ 579.2925, calc.
colour solid was dissolved in dichloromethane (25 mL) and filtered
578.03. Anal. Calcd. for C56
H
58Br
6
N
2
3 4
Ni P : C, 43.72; H, 3.80; N, 1.82.
3
through a 1 cm silica gel. The product was precipitated from the
Found: C, 43.65; H, 3.53; N, 1.80.
filtrate with hexane. The red brown product was filtered off,
washed with hexane and dried under vacuum. (Yield: 0.6 g, 86%).
4.2.9. Synthesis of [PN(H)PPhNiCl]OTf (6)
1
H NMR (CDCl
H, ePCH(CH
2)), 1.69 (m, 2H, ePCH
NMR (CDCl ): 54.63 (t, NCH2), 24.89 (t, ePCH(CH
), 21.25 (t, ePCH ), 19.61, 19.13, 18.19 and 17.99 (s,
). P{ H} NMR (CDCl ): 51.46 (s). ESI-MS: [PN(Me)
3
):
), 2.22 (m, 6H, ePCH2(2), NCH
), 1.55e1.35 (td, 24H, ePCH(CH
d
3.8 (s, 3H, eNMe), 3.09 (m, 2H, eNCH2), 2.37 (m,
Silver triflate (129 mg, 0.5 mmol) was added to a solution of
complex 3 (200 mg, 0.25 mmol) in 10 mL of dichloromethane with
stirring and the colour of the solution immediately changed to or-
ange, the reaction mixture was stirred for 12 h at room tempera-
2
(
3
)
2
2
(2), ePCH(CH
3 2
)
13
1
2
3
)
2
). C{ H}
3
d
3 2
) ), 24.19 (t,
ePCH(CH
ePCH(CH
P
3
)
)
2
2
ture. Then the mixture was filtered through celite and dried under
31
1
1
3
2
3
d
vacuo. (Yield: 91.0 mg, 50%). H NMR (400 MHz, CDCl
3
):
d
7.82e7.71
iPr
þ
NiCl] displays a peak at m/z ¼ 412.16, calc. 412.16. Anal. Calcd.
(m, 8H), 7.54e7.12 (m, 12H), 4.86 (s, br, 1H), 3.36e3.27 (m, 2H),
31
1
for C17 NNiP : C, 45.47; H, 8.75; N, 3.12. Found: C, 45.42; H,
H39Cl
2
2
2.80e2.73 (m, 2H), 2.40e2.30 (m, 4H). P{ H} NMR (CDCl
3
):
d
27.6
þ
8
.67; N, 3.15.
.2.5. Synthesis of PN(Me)PtBuNiCl
(2)
2
(s). ESI-MS: [C28
H
29ClNNiP
2
]
displays a peak at m/z ¼ 535.632,
29ClF NNiO S: C, 50.87; H,
4.27; N, 2.05. Found: C, 50.82; H, 4.11; N, 1.93.
calc. 535.638. Anal. Calcd. for C29
H
3
3 2
P
4
tBu
Under an atmosphere of nitrogen, PN(Me)P
.33 mmol) and NiCl $6H O (316 mg, 1.33 mmol) were taken in THF
40 mL) and the reaction mixture was stirred overnight at room
(L2) (500 mg,
1
(
2
2
4.2.10. General procedure for cycloaddition reaction of alkyne
To a 50 mL Schlenk flask acetylene derivatives (1 mmol), Ni(II)
complex (2.5 mol%), Zn (5 mol%) and 3 mL acetonitrile were added.
temperature. The solvent was removed in vacuo, and the pink
ꢁ
colour solid was dissolved in dichloromethane (25 mL) and filtered
The reaction mixture was heated at 40 C using an oil bath. After
3
through a 1 cm silica gel. The product was precipitated from the
completion of the reaction, the crude reaction mixture was dried
under vacuo and dissolved in diethyl ether and filtered through
silica gel. The volatiles were removed under vacuo and column
chromatography was performed to isolate the final product.
filtrate with hexane. The pink colour product was filtered off,
washed with hexane and dried under high vacuum. (Yield: 616 mg,
1
9
2
(
2%). H NMR (400 MHz, CDCl
3
):
d
5.60 (b, 2H), 4.38 (s, 3H), 3.83 (b,
31
1
H), 2.93 (b, 2H), 2.53 (b, 2H), 1.83e1.69 (dt, 36H). P{ H} NMR
tBu
þ
CDCl
3
):
d
50.18 (s). ESI-MS: [PN(Me)P NiCl] displays a peak at
NNiP : C,
Acknowledgment
m/z ¼ 468.22, calc. 468.22. Anal. Calcd. for C21
H47Cl
2
2
4
9.93; H, 9.38; N, 2.77. Found: C, 49.89; H, 9.32; N, 2.84.
Dr. C. S gratefully acknowledges the Council of Scientific and
Industrial Research, New Delhi, India for the financial support (No.
01(2535)/11/EMR-II) and Mr. Saraswatula Viswanadha G, Depart-
ment of chemistry, Pondicherry University for the crystal data. We
thank the Central Instrumentation Facility (CIF), Pondicherry Uni-
versity for NMR spectra and DST-FIST for the single-crystal X-ray
4
.2.6. Synthesis of ([PN(Me)PiPrNiCl][BPh
4
]) (3)
Complex 1 (200 mg, 0.44 mmol) was dissolved in CH
Upon addition of NaBPh (183 mg, 0.53 mmol) in 2 mL MeOH, a red
colour solution was slowly changed to orange solution. The reaction
3
CN (5 mL).
4
Please cite this article in press as: M. Tamizmani, C. Sivasankar, Journal of Organometallic Chemistry (2017), http://dx.doi.org/10.1016/
j.jorganchem.2017.02.039

8
M. Tamizmani, C. Sivasankar / Journal of Organometallic Chemistry xxx (2017) 1e8
(2004) 117e124.
diffraction facility and ESI-MS facility.
[27] W. Reppe, O. Schlichting, K. Klager, T. Toepel, Eur. J. Org. Chem. 560 (1948)
1
e92.
Appendix A. Supplementary data
[
[
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Please cite this article in press as: M. Tamizmani, C. Sivasankar, Journal of Organometallic Chemistry (2017), http://dx.doi.org/10.1016/
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