Coordinated and uncoordinated anion dictated coordination mode of PN(Me)P ligand in Pd(II) complexes and their catalytic applications

Article abstract of DOI:10.1016/j.jorganchem.2014.04.011

The PN(Me)P ligands based complexes [(η²-PN(Me)P ^Ph)PdCl₂] (1), [(η³-PN(Me)P ^Ph)PdCl](OTf) (2) and [(η³-PNP^iPr)PdCl] (3) (complexes 2 and 3 are pincer type) have been synthesized and characterized using standard analytical methods such as ¹H NMR, ³¹P NMR, elemental analysis, UV-Visible spectroscopy, cyclic voltammetry and single-crystal X-ray crystallography. Formation of complexes 1 and 2 were observed under two different reaction conditions and learned about how the anions can dictate the coordination mode of PNP ligand to have different hapticity to offer different complexes. More importantly, isolation of complexes 1 and 2 filled the gap in PNP-Pd chemistry. DFT calculations have been carried out to understand the C-N bond cleavage of PN(Me)P ligand when -Ph and - ⁱPr substituent introduced on the phosphorous. The complete reversible pattern of cyclic voltammogram of complex 3 suggests that this complex can be a better catalyst where two different oxidation states involve in the catalytic cycle. We have also performed Heck and Suzuki coupling reactions using complexes 1 and 3 and observed reasonably good yield even at relatively low temperature.

Full text of DOI:10.1016/j.jorganchem.2014.04.011

Journal of Organometallic Chemistry 763-764 (2014) 6e13
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Coordinated and uncoordinated anion dictated coordination mode of
PN(Me)P ligand in Pd(II) complexes and their catalytic applications
*
Masilamani Tamizmani, Ramakrishna Kankanala, Chinnappan Sivasankar
Catalysis and Energy Laboratory, Department of Chemistry, Pondicherry University, Puducherry 605014, India
a r t i c l e i n f o
a b s t r a c t
The PN(Me)P ligands based complexes [(h h
2-PN(Me)PPh)PdCl2] (1), [( 3-PN(Me)PPh)PdCl](OTf) (2) and
Article history:
[(h
3-PNPiPr)PdCl] (3) (complexes 2 and 3 are pincer type) have been synthesized and characterized using
Received 29 January 2014
Received in revised form
8 April 2014
standard analytical methods such as 1H NMR, 31P NMR, elemental analysis, UVeVisible spectroscopy,
cyclic voltammetry and single-crystal X-ray crystallography. Formation of complexes 1 and 2 were
observed under two different reaction conditions and learned about how the anions can dictate the
coordination mode of PNP ligand to have different hapticity to offer different complexes. More impor-
tantly, isolation of complexes 1 and 2 filled the gap in PNPePd chemistry. DFT calculations have been
carried out to understand the CeN bond cleavage of PN(Me)P ligand when ePh and eiPr substituent
introduced on the phosphorous. The complete reversible pattern of cyclic voltammogram of complex 3
suggests that this complex can be a better catalyst where two different oxidation states involve in the
catalytic cycle. We have also performed Heck and Suzuki coupling reactions using complexes 1 and 3 and
observed reasonably good yield even at relatively low temperature.
Accepted 9 April 2014
Keywords:
CeN bond cleavage
PNP pincer ligand
Palladium complex
DFT studies
CeC coupling reactions
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
this area during the past twenty five years, particularly with respect
to the synthesis of PCP and PNP pincer type transition metal
The metal-mediated activation and cleavage of strong bonds
such as CeH, CeC, CeN, and CeO is one of the most important tools
in the modern synthetic organic chemistry [1e10]. Chaudhury et al.
reported a CeN bond cleavage reaction assisted by Pd(II) center in
alcoholysis of aminal CeN bond [11]. Esteruelas et al. reported the
NeH and CeN bond cleavage of pyrimidinic nucleobases and nu-
cleosides assisted by Osmium polyhydride [12]. Bercaw et al. acti-
vated and cleaved the CeN bond in nitromethane using palladium
acetate and diimine ligand [13]. Recently Zhang et al. studied the
CeN bond cleavage of the N-allylpyrrolidine and it was activated by
hydrogen-bond, and subsequently produced a stable intermediate
Pd(II)-allylic complex [14]. In all the above mentioned complexes
the CeN bond cleavage was observed in the organic substrates in
the presence of Pd(II) catalysts.
complexes that can cleave CeH, CeC and CeN bonds under mild
experimental conditions. Shaw et al. synthesized the first PCP
pincer ligand based metal complexes in the middle of 1980s [16],
and Milstein et al. [17] developed the chemistry of these complexes.
In the recent years many chemists were attracted towards the study
of these complexes owing to the efficient catalytic properties of
these metal complexes towards the CeH and CeO bond activations,
dehydrogenation, hydrogenation and CeC bond forming reactions
such as Heck and Suzuki coupling [18e28].
There are several methods to make pincer type transition metal
catalysts; nevertheless a widely used method is cleavage of CeH/
NeH/CeN/PeH/PeC/SieH bond in the pincer type ligands to yield
metal bound PCP/PNP/PPP/PSiP type of complexes [29e41]. Ozerov
et al. have studied a possibility of CeN bond cleavage in neutral
arylamidoamine based PN(Me)P (A) and neutral iminodibenzyl
based PN(Me)P (B) pincer ligands (Fig. 1) at Rh, Ir and Pd metal
centers (ePR2 group is diisopropylphosphine) in which the CeN
bond cleavage takes place in the ligand system. In the case of Rh
and Ir, the mechanism for the CeN bond cleavage follows the
oxidative addition owing to the low oxidation state and less coor-
dination number of Rh and Ir precursors [36]. In a similar way a
possibility of CeN bond cleavage at the PdII center has been
A large number of Pd(II) catalysts are known to promote the
above mentioned reactions and most of them are Pd(II) complexes
of pincer type ligands [15]. A significant progress has been made in
* Corresponding author. Tel.: þ91 413 2654709; fax: þ91 413 2655987.
E-mail
addresses:
siva.che@pondiuni.edu.in,
drcsivas@gmail.com
(C. Sivasankar).
http://dx.doi.org/10.1016/j.jorganchem.2014.04.011
0022-328X/Ó 2014 Elsevier B.V. All rights reserved.

M. Tamizmani et al. / Journal of Organometallic Chemistry 763-764 (2014) 6e13
7
(yield 80%) (Scheme 2). The 1H NMR spectrum of complex 1 display
a single peak at 3.88 ppm for NeMe group and a pair of multiplets
at 3.07 ppm and 3.04 ppm for eCH2eCH2e protons respectively.
The 31P{1H} NMR spectrum of complex 1 displays a single peak at
d
22.04 ppm in CDCl3 indicates that the ePPh2 is coordinated with
the Pd(II). These spectral data indicate that the complex 1 is formed
without CeN bond cleavage and the PN(Me)P ligand behaves as a
bidentate ligand (h
2) without the participation of NeMe coordi-
nation. The solid state structure of complex 1 was determined using
a single-crystal X-ray diffraction studies (Fig. 2). The PdeCl1 bond
ꢀ
and PdeCl2 bond distances are found to be 2.331(2)A and
ꢀ
2.352(2)A respectively. The P2ePdeCl1 and P1ePdeCl2 bond an-
gles are found to be 172.98ꢁ and 171.47ꢁ respectively. These struc-
tural features indicate that the geometry around the central metal
ion Pd is square planar.
Fig. 1. Ligand systems.
The reaction of complex 1 with one equivalent of silver triflate in
a dichloromethane solution at room temperature for 6 h afford [h3
-
reported with ligands A and B in which the ePR2 group is diiso-
propylphosphine. Nevertheless, when the ePR2 group is diphe-
nylphosphine, the product was unidentified [9].
PN(Me)PPhPdCl](OTf) (2) (Scheme 2). The formation of complex 2
was confirmed by NMR and X-ray crystallography techniques. The
1H NMR spectrum of complex 2 displays a pair of multiplets at
3.16 ppm and 3.72 ppm for eCH2eCH2e methyl protons and a
single peak at 3.96 ppm for NeMe methyl protons. The 31P{1H}
NMR spectrum of complex 2 displays a single peak at 28.31 ppm in
CDCl3. These spectral data indicate that the complex 2 is entirely
different from complex 1. The solid state structure of complex 2 was
determined using a single-crystal X-ray diffraction studies (Fig. 3).
In this regard, in order to gain more insight to understand the
CeN bond cleavage at the Pd(II) center, we have synthesized
bromine substituted ligand type C (Fig. 1). We have used different R
groups on the phosphine to isolate certain important complexes
which are missing in the PNPePd chemistry and also to understand
more about the CeN bond cleavage. We have used DFT calculations
to understand why the CeN bond cleavage is not observed for
diphenyl substituted phosphine ligand while diisopropyl
substituted phosphine ligand displaces the CeN bond cleavage.
Apart from these studies, we have also studied the catalytic activity
of complexes 1 and 3 towards the MizorokieHeck and Suzuki
coupling reaction.
ꢀ
The PdeCl and the PdeN bond distances are found to be 2.297 A
ꢀ
ꢀ
and 2.180 A respectively. The NeMe bond distance (1.526 A) is
increased after binding with Pd when compared to the free NeMe
bond distance (1.464 A in complex 1). The P2ePdeP1 and NePdeCl
ꢀ
bond angles are found to be 171.83ꢁ and 176.85ꢁ respectively
(Table 1). These structural features indicate that the geometry
around the central metal ion is square planar and it can be noted
that the NeMe fragment of PNP ligand coordinated to the Pd center
without undergoing CeN bond cleavage. The employed anions such
as OTfꢀ and Clꢀ dictated or controlled the PN(Me)PPh ligand (L1) to
change its hapticity from h2 to h3 in the presence of respective
anions to yield two different complexes 1 and 2, and demonstrated
that how one can synthesize a complex with desired hapticity for a
particular application.
Results and discussion
Ligands L1 and L2 (belong to ligand type C in Fig. 1) were syn-
thesized (Scheme 1) using modified literature procedure and
characterized by 1H and 31P NMR spectroscopy techniques. The
ligand L1 is found to be an air and moisture stable while L2 is not.
For ligand L1, the 1H NMR spectrum shows a single peak at
2.74 ppm for NeMe protons and a pair of multiplets at 2.65 ppm
and 2.16 ppm for eCH2eCH2e linker and the aromatic protons
appeared between 7.50 and 6.92 ppm. The 31P{1H} NMR spectrum
Reaction between PN(Me)PiPr (L2) and [(COD)PdCl2] in toluene
or in acetonitrile solution at 70 ꢁC for 1.5 h afford [ 3-PNPiPrPdCl]
h
(3) as a red-orange solid (yield 90%) (Scheme 3). The formation of
complex 3 was confirmed by NMR and X-ray crystallography
techniques. The 1H NMR spectrum of complex 3 displays a pair of
multiplets at 1.42 ppm and 1.27 ppm for eCH(Me)2 methyl protons
and a multiplet at 2.55 ppm for eCH(Me)2 methylene protons and a
single peak at 3.81 ppm for eCH2eCH2e protons. The 31P{1H} NMR
spectrum of complex 3 displays a single peak at 49.53 ppm in
CDCl3. These spectral data indicate that the complex 3 is formed via
H3CeN bond cleavage and PNP ligand behave as a tridentate ligand
of ligand L1 shows a single peak at
spectral data confirmed the formation of L1. The NMR spectral data
of ligand L2 is comparable with the literature data [36].
d
ꢀ18.34 ppm in CDCl3. These
Complexation of L1 and L2 with [(COD)PdCl2]
(COD ¼ cyclooctadiene)
The reaction of PN(Me)PPh (L1) with [(COD)PdCl2] in toluene at
(h
3) by producing CH3Cl as a side product. The solid state structure
100 ꢁC for 1.5 h afford [( 2-PN(Me)PPh)PdCl2] (1) as a yellow solid
h
Scheme 1. Synthesis of PN(Me)PPh (L1) and PN(Me)PiPr (L2).

8
M. Tamizmani et al. / Journal of Organometallic Chemistry 763-764 (2014) 6e13
Scheme 2. Synthesis of [(h h
2-PN(Me)PPh)PdCl2] (1) and [( 3-PN(Me)PPh)PdCl](OTf) (2).
of complex 3 was determined using a single-crystal X-ray diffrac-
tion studies (Fig. 4). The solid state structure of complex 3 shows
be attributed to the ligand centered pep* transition while the
weak bands centered around 400e500 nm can be attributed to the
ded transition for the square planar geometry in their respective
complexes 1e3.
ꢀ
that the PdeN1 bond distance is found to be 2.063(3) A. The PdeP1
ꢀ
ꢀ
and PdeP2 distances are found to be 2.2745(1) A and 2.2757(1) A
respectively. The bond angle of N1ePdeCl1 and P1ePdeP2 are
found to be 177.9ꢁ and 167.4ꢁ respectively. The geometry around
the Pd center is found to be square planar. These observed bond
distances and bond angles are comparable with the halogen free
PNP complex of Pd(II) [36].
Electrochemistry
In order to understand the redox nature of complexes 1 and 3,
the cyclic voltammogram (CV) of complexes 1 and 3 have been
recorded in acetonitrile solution (0.5 mM) with 0.1 M Bu4NPF6 as an
electrolyte at a Pt working electrode with scan rate 50 mV (Fig. 6).
The cyclic voltammogram of complex 1 reveals the one electron
reversible reduction at ꢀ0.89 V. The cyclic voltammogram of
complex 3 shows the one electron reversible oxidation at 0.8 V and
one electron quasi-reduction at ꢀ1.2 V. These results indicate that
the ePiPr2 ligand stabilizes higher oxidation state of Pd(PdII/III) and
suggests that the complex 3 can be used as a catalyst in which two
different oxidation states involve in the catalytic cycle. Neverthe-
less complex 1 can be a moderate catalyst. The observed redox
potential for complexes 1 and 3 does not match with the reported
oxidation potential in the literature for the similar type of ligand
therefore the ligand in complexes 1 and 3 might be stable towards
the oxidation [42,43].
The CeN bond cleavage was observed when the ePR2 group is
diisopropylphosphine to yield PNP (h
3) coordinated complex 3. On
the other hand the CeN bond cleavage was not observed when the
ePR2 group is diphenylphosphine and the PN(Me)PPh ligand be-
haves as a bidentate (h h
2) and tridentate ( 3), nevertheless the
binding fashion of this ligand is also controlled by the other
ancillary ligands (complexes 1 and 2), in this case Clꢀ and OTfꢀ.
Although the eBr substitution does not alter the structural features
of complex 3, the bromine substituent on the iminodibenzyl ring
enabled us to isolate and characterize some novel missing com-
plexes in the PNPePd chemistry. Previously complexes 1 and 2
were expected to form with similar ligands, nevertheless not been
isolated in the literature [9,36].
Electronic spectroscopy
The UVeVisible spectra of a dilute solution of complexes 1e3
have been recorded in dichloromethane (Fig. 5 and Table 2). The
complex 1 shows a strong absorption band at 265 nm and rela-
tively weak absorption band at 431 nm. The corresponding tri-
coordinate complex 2 shows two medium intense absorption
bands at 327 nm and 380 nm. The complex 3 shows an intense
absorption band at 334 nm and relatively weak intense band at
431 nm. The absorption bands centered around 250e350 nm can
Fig. 2. ORTEP drawing (50% probability ellipsoids) of the [(
h
2-PN(Me)PPh)PdCl2] (1).
Fig. 3. ORTEP drawing (50% probability ellipsoids) of the [(h
3-PN(Me)PPh)PdCl](OTf)
ꢀ
Omitted for clarity: solvated bromobenzene, all H atoms. Selected bond distances (A):
PdeP1, 2.260(2); PdeP2, 2.272(2); PdeCl2, 2.331(2); PdeCl1, 2.352(2); NeC(Methyl),
1.464(10). Selected bond angles (ꢁ): P2ePdeP1, 96.54(9); P1ePdeCl2, 172.98(9); P1e
PdeCl1, 83.34(8); P2ePdeCl2, 90.46(9); P2ePdeCl1, 171.47(8); Cl1ePdeCl2, 89.68(9).
(2). Omitted for clarity: solvated dichloromethane, all H atoms. Selected bond dis-
ꢀ
tances (A): PdeP2, 2.246(3); PdeP1, 2.250(6); PdeCl1, 2.299(8); PdeN, 2.171(4); NeC
(Methyl), 1.526(7). Selected bond angles (ꢁ): P2ePdeP1,171.83(5); P2ePdeCl1,
94.22(5); P1ePdeCl1, 93.51(5); NePdeCl1, 176.85(1).

M. Tamizmani et al. / Journal of Organometallic Chemistry 763-764 (2014) 6e13
9
Table 1
Experimental and calculated geometrical parameters of complexes 1e3.
ꢁ
ꢀ
Bond length (A) or angle ( )
Exp. value
Cal. value
Complex 1
Complex 2
Complex 3
PdeCl2
PdeCl1
PdeP1
PdeP2
P1ePdeCl2
P2ePdeCl1
Cl1ePdeCl2
PdeP2
PdeP1
PdeCl
2.331(2)
2.352(2)
2.260(2)
2.272(2)
172.98(9)
171.47(8)
89.68(9)
2.246(3)
2.250(6)
2.299(8)
2.171(4)
176.85(1)
94.22(5)
93.51(5)
2.063(3)
2.309(5)
2.275(7)
2.274(5)
177.91(9)
96.91(5)
95.64(4)
2.381
2.407
2.354
2.375
170.59
163.71
89.17
2.308
2.302
2.342
2.262
172.62
93.30
94.23
2.121
2.379
2.316
2.316
179.0
95.35
95.56
PdeN
NePdeCl
P2ePdeCl
P1ePdeCl
PdeN
PdeCl
PdeP2
PdeP1
NePdeCl
P1ePdeCl
P2ePdeCl
Catalysis
Pd complexes 1 and 3 have been used for CeC bond formation
reactions such as MizorokieHeck (Scheme 4) and SuzukieMiyaura
(Scheme 5) coupling reactions. For MizorokieHeck coupling reac-
tion, we have chosen aryl halides (iodo & bromo derivatives) and
tert-butyl acrylate as coupling pairs. As summarized in Table 3, the
catalyst 3 produced relatively more yield than the catalyst 1 as
reflected in the CV, the product yield is also observed to be strongly
depended upon the nature of the substitution on the aryl group. In
the case of para-substituted iodobenzene (entry 1 and 2 in Table 3),
the product yield is more when compared to the un-substituted
iodobenzene (entry 3 and 4 in Table 3). The product yield is
further reduced when bromobenzene was used (entry 5 and 6 in
Table 3). However the presence of eOMe group at the para position
of the phenyl ring increased the yield slightly (entry 7 and 8 in
Table 3). The turn over number (TON) has been calculated for all the
reactions (Table 3). The TON for 4-MeC6H4I is found to be more with
catalyst 3 when compared with the catalyst 1. Nevertheless for all
other substituents the TON is found to be reasonable. The catalytic
activity of catalysts 1 and 3 is found to be reasonable for Heck
coupling reaction because of the even less catalyst load is sufficient
to isolate reasonably good yield.
Fig. 4. ORTEP drawing (50% probability ellipsoids) of the [(
h
3-PNPiPr)PdCl] (3). Omitted
ꢀ
for clarity: solvated bromobenzene, all H atoms. Selected bond distances (A): PdeN1,
2.063(3); PdeP2, 2.2757(11); PdeP1, 2.2745(11); PdeCl1, 2.3095(10). Selected bond
angles [ꢁ]: P2ePdeCl1, 95.64(4); P1ePdeP2, 167.45(4); P1ePdeCl1, 96.91(4); N1ePde
Cl1, 177.91(9); N1ePdeP2, 84.13(9); N1ePdeP1, 83.33(9).
the cases iodo-substituted aryl halides were found to be more
reactive than the bromo-substituted aryl halides. From Tables 3 and
4, it can be noted that the complexes 1 and 3 may be useful catalysts
for the CeC bond formation reactions even at relatively low
temperature.
DFT studies
In order to understand why the complex 1 ([(
PdCl2] in Eq. (1)) is formed over complex 1a ([(
3-PNPPh)PdCl] in
Eq. (3)) via CeN bond cleavage with phenyl substituted phosphine
h )
2-PN(Me)PPh
h
We have chosen boronic acid and aryl halides (iodo & bromo
derivatives) for Suzuki-Miyaura coupling reaction. The catalyst 3 is
active even at 80 ꢁC but catalyst 1 is active only at 110 ꢁC (Table 4).
Relatively more yield was observed for both catalysts 1 and 3 when
4-MeC6H4I was used (entry 1, 2 in Table 4). Moderate yield was
isolated for C6H5Br and 4-MeOC6H4Br (entry 3, 4 in Table 4). In all
Scheme 3. Synthesis of
h
3-PNPiPrPdCl (3).
Fig. 5. UVeVisible spectra of complexes 1e3 in dichloromethane.

10
M. Tamizmani et al. / Journal of Organometallic Chemistry 763-764 (2014) 6e13
Table 2
UVeVisible data of complexes 1e3 in dichloromethane.
Complex
lmax (nm)
εmax (Mꢀ1 cmꢀ1
)
Complex 1
Complex 2
Complex 3
265.0 (S), 431.0 (W)
327.0 (m), 380.0 (m)
334.0 (S), 488.0 (W)
0.313, 0.24
1.16, 0.074
1.55, 0.066
Scheme 4. MizorokieHeck coupling reaction.
exergonic (
CeN bond cleavage is possible in ligand L2.
D
G ¼ ꢀ67.80 kcal/mol) in nature (Eq. (4)) therefore the
in the presence of [(COD)PdCl2], DFT calculations have been per-
formed. We have used ligands L1 and L2 and their complexes (1, 2
and 3) without any simplification for the calculations. The fully
optimized structures of all the above mentioned systems can be
seen in the supporting information (Fig. S1). We observed a good
agreement between calculated structural parameters with the
experimentally observed structural parameters (Table 1).
Conclusion
Reactions of PN(Me)P type ligands L1 and L2 with [(COD)PdCl2]
produced complexes [(
PdCl](OTf) (2) and [(
h h )
2-PN(Me)PPh)PdCl2] (1), [( 3-PN(Me)PPh
h
3-PNPiPr)PdCl] (3) under different reaction
conditions. Complexes 1e3 have been characterized using standard
techniques such as 1H NMR, 31P NMR, elemental analysis, UVe
Visible spectroscopy, cyclic voltammetry and single-crystal struc-
tural determinations. We also observed that the ePh substituted
PN(Me)P ligand is failed to undergo CeN bond cleavage while eiPr
substituted PN(Me)P ligand followed CeN bond cleavage. Owing to
this difference in the reactivity/nature of two different PN(Me)P
h
i
L1 þ ½ðCODÞPdCl2ꢂ/ h2 ꢀ PNðMeÞPPhPdCl2 ð1Þ
(1)
þ COD
D
G ¼ ꢀ12:49
h
i
h
i
h2 ꢀ PNðMeÞPPhPdCl2 ð1ÞAgOTF h3 ꢀ PNðMeÞPPhPdCl ðOTfÞð2Þ
ꢀꢀ!
ligands, we observed h h
2 and 3coordination mode for these ligands
þ AgCl
D
G ¼ ꢀ9:49
(L1 and L2) in complexes 1 and 3 respectively. On the other hand
the coordination mode of L1 changed from h2 to h3 without CeN
bond cleavage when the Clꢀ ion was removed from the Pd in
complex 1 by the addition of AgOTf. DFT calculations suggest that
the formation of complexes 1e3 are thermodynamically feasible
nevertheless the CeN bond cleavage is not possible with ligand L1
to yield complex 1a. The CV of complex 3 suggests that this com-
plex can be a better catalyst where two different oxidation states
involve in the catalytic cycle. Complexes 1 and 3 are found to be
suitable to promote Heck and Suzuki coupling reactions to form
new CeC bonds even at low temperature. More catalytic studies
using complexes 1e3 are under investigation.
(2)
(3)
h
i
L1 þ ½ðCODÞPdCl2ꢂ/ h3ꢀPNPPhPdCl ð1aÞ
þ COD þ CH3Cl
D
G ¼ þ30:69
h
i
L2 þ ½ðCODÞPdCl2ꢂ/ h3ꢀPNPiPrPdCl ð3Þ
(4)
þ COD þ CH3Cl
D
G ¼ ꢀ67:80
We have calculated
D
G for the formation of complex 1 ([(h2
-
PN(Me)PPh)PdCl2]) and found to be exergonic (
D
G ¼ ꢀ12.49 kcal/
mol) in nature (Eq. (1)). The
D
G for the formation of complex 2
Experimental section
([(h
3-PN(Me)PPh)PdCl](OTf)) (
h
3-PN(Me)PPh of L1 without CeN
bond cleavage) is also calculated to be exergonic (
mol) in nature (Eq. (2)) nevertheless, the magnitude is slightly less
when compared to the G formation of complex 1. We have also
calculated the
G for the formation of hypothetical complex 1a (h3
PNP complex of L1 via CeN bond cleavage) and found to be highly
endergonic (
G ¼ þ30.69 kcal/mol) in nature (Eq. (3)). These
calculated G values clearly indicate that the formation of complex
1a is not thermodynamically feasible over the formation of com-
plexes [(
2-PN(Me)PPh)PdCl2] (1) and [( 3-PN(Me)PPh)PdCl](OTf)
(2) therefore the NeMe bond cleavage is not possible in ligand L1.
The G for the formation of complex 3 is calculated to be highly
D
G ¼ ꢀ9.49 kcal/
General considerations
D
Unless specified otherwise, all manipulations were performed
under nitrogen atmosphere using standard Schlenk line tech-
niques. Toluene, diethyl ether, C6D6 and THF were dried and
distilled over Na/Ph2CO and stored in an N2-filled glove box. CDCl3,
DCM, Acetonitrile and Bromobenzene were dried and then
D
-
D
D
distilled
or
vacuum
transferred
over
CaH2.
Chlor-
h
h
odiisopropylphosphine, Chlorodiphenylphosphine and [(COD)
PdCl2] were purchased from Aldrich and used without further
purification. N-Methyl-tetrabromoiminodibenzyl was prepared
D
Fig. 6. Cyclic voltammetry of complexes 1e3 in acetonitrile (0.5 mM) measured at 298 K with a 0.1 M Bu4NPF6 solution at a Pt working electrode (scan rate 50 mV sꢀ1).

M. Tamizmani et al. / Journal of Organometallic Chemistry 763-764 (2014) 6e13
11
Table 4
Summary of Suzuki coupling reaction results.
Entrya Catalyst Substrates
Temp Time Yield TON
(mmol)
(ꢁC)
h
ꢃ 10ꢀ5
Scheme 5. SuzukieMuyaura coupling reaction.
1
2
3
4
5
6
7
8
0.2 (1)
0.2 (1)
0.2 (1)
0.2 (1)
0.4 (3)
0.4 (3)
0.4 (3)
0.4 (3)
4-MeC6H4I
C6H5I
C6H5Br
4-MeOC6H2Br Boronic acid
4-MeC6H4I
C6H5I
Boronic acid
Boronic acid
Boronic acid
50
50
80
80
8
89%
70%
60%
65%
95%
90%
80%
60%
445,000
8
12
12
12
12
12
12
350,000
300,000
325,000
237,500
225,000
200,000
150,000
according to the literature procedure. NMR spectra were recorded
on a Bruker 400 MHz (1H NMR, 400 MHz; 13C NMR, 100.62 MHz;
31P NMR, 161.822 MHz) spectrometer. For 1H NMR and 13C NMR
spectra, the residual solvent peak was used as an internal refer-
ence. 31P NMR spectra were referenced externally using 85% H3PO4
Boronic acid 110
Boronic acid 110
Boronic acid 110
C6H5Br
4-MeOC6H2Br Boronic acid 110
a
Reactions were performed with 1.0 equiv. of aryl halides and 1.3 equiv. of
boronic acid, 1.4 equiv. of base and 0.25 equiv. of Bu4NBr in a H2O:toluene (1:2) for
required time at 50 ꢁC or 80 ꢁC or 110 ꢁC (TON ¼ Trun Over Number).
at
d 0 ppm.
Synthesis
was evaporated in vacuo to afford pale yellowish oil. This oil was
treated with methanol to produce a white solid and the solid was
Synthesis of PN(Me)PPh (L1)
Under an atmosphere of nitrogen, n-BuLi (4.0 mL of 1.6 M so-
lution in hexane, 6.38 mmol) was slowly added to the suspension of
N-methyl tetrabromoiminodibenzyl (1.6 g, 3.04 mmol) in 30 mL of
Et2O at ꢀ35 ꢁC. The mixture was stirred for 2 h at room tempera-
ture. The solution was cooled to ꢀ35 ꢁC and chlor-
odiphenylphosphine (1.14 g, 6.38 mmol) was added and it was
stirred for overnight at room temperature. The volatiles were
removed in vacuo and the residue was re-dissolved with ether and
filtered. The resulting solution was evaporated in vacuo to yield
pale yellowish oil. This oil was treated with methanol to produce a
white solid and the solid was collected by filtration. Yield: 1.23 g
collected by filtration. Yield: 1.72 g (64%). 1H NMR (CDCl3):
d 7.38 (d,
2H, AreH), 7.19 (d, 2H, AreH), 3.31 (s, 3H, NeMe), 3.24 (m, 2H, e
CH2eCH2e), 2.73 (m, 2H, eCH2eCH2e). 2.04 (m, 4H, eCH(Me)2),
1.25e1.20 (m, 6H, eCH(Me)2), 1.20e1.19 (m, 6H, eCH(Me)2), 1.19e
1.15 (m, 6H, eCH(Me)2), 1.13e1.07 (m, 6H, eCH(Me)2). 13C NMR
(CDCl3):
d 153.4, 141.7, 141.3, 137.2, 135.1, 134.1, 133.2, 118.5 (Ph), 51.1
(t, NeMe), 33.11 (s, eCH2CH2e), 26.8, 25.9, 22.5, 21.4, 20.29 (eMe of
i
iPr), 19.9, 14.2 (CH of Pr). 31P{1H} NMR (CDCl3):
d
ꢀ8.34 (s). Anal.
Calcd. for C27H39Br2NP2: C, 54.11; H, 6.56; N, 2.34. Found: C, 54.23;
H, 6.48; N, 2.17.
(55%). 1H NMR (CDCl3):
d 7.50 (m, 4H, AreH), 7.32 (m, 2H, AreH),
Synthesis of [(h
2-PN(Me)PPh)PdCl2] (1)
7.25 (m, 4H, AreH), 7.10e6.92 (m, 14H, AreH), 2.74 (s, 3H, NeMe),
[(COD)PdCl2] (50 mg, 0.175 mmol) was added to a solution of
L2 (128 mg, 0.175 mmol) in 10 mL of toluene with stirring and the
color of the solution rapidly changed to yellow orange, it was
stirred for 30 min at room temperature. Then the mixture was
heated at 100 ꢁC for 1.5 h while stirring and then the resulting
yellow solid was filtered and washed with pentane. Yield:
2.65 (m, 2H, CH2CH2), 2.16 (m, 2H, CH2CH2). 31P{1H} NMR (CDCl3):
d
ꢀ18.34 (s). 13C NMR (CDCl3):
d 151.9, 142.2, 141.4, 140.1, 138.2,
136.9, 134.9, 134.2, 133.7, 128.9, 128.6, 120.1, 48.4 (t, NeMe), 32.2 (s,
eCH2CH2e). Anal. Calcd. for C39H31Br2NP2: C, 63.69; H, 4.25; N,
1.90. Found: C, 63.49; H, 4.19; N, 1.63.
147.0 mg (92%).1H NMR (CDCl3):
d 7.39e7.37 (m, 6H, AreH), 7.40e
Synthesis of PN(Me)PiPr (L2)
7.36 (m, 2H AreH), 7.32e7.28 (m, 4H, AreH), 7.20e7.17 (m, 4H,
AreH), 6.87e6.84 (m, 8H, AreH), 3.87 (s, 3H, NeMe), 3.75e3.68
(m, 2H, eCH2CH2e), 3.04e2.97 (m, 2H, eCH2CH2e). 31P{1H} NMR
Under an atmosphere of nitrogen, n-BuLi (6.0 mL of 1.6 M so-
lution in hexanes, 9.6 mmol) was slowly added to the suspension of
N-methyl tetrabromoiminodibenzyl (2.4 g, 4.5 mmol) in 30 mL of
Et2O at ꢀ35 ꢁC. The mixture was warm up to room temperature and
stirred for 2 h. Then the reaction mixture was cooled to ꢀ35 ꢁC and
chlorodiisopropylphosphine (1.46 g, 9.6 mmol) was added and it
was stirred for overnight at room temperature. The volatiles were
removed in vacuo, and the residue was re-dissolved with ether and
filtered. The filtrate was treated with silica gel and stirred for
30 min and then the solids were filtered off. The resulting solution
(CDCl3): d d 149.8, 143.2, 136.7, 136.5(t),
22.04 (s). 13C NMR (CDCl3):
134.12(t), 133.54(s), 131.08, 130.45, 129.17, 128.36, 128.06(t), 127.9,
121.21(t), 50.06 (s, NeMe), 31.72(s, eCH2CH2e). Anal. Calcd. for
C39H31Br2Cl2NP2Pd: C, 51.32; H, 3.42; N, 1.53. Found: C, 51.20; H,
3.28; N, 1.40.
Synthesis of [(h
3-PN(Me)PPh)PdCl](OTf) (2)
Silver triflate (37 mg, 0.14 mmol) was added to a solution of 1
(120 mg, 0.13 mmol) in 10 mL of dichloromethane with stirring and
the color of the solution immediately changed to orange, it was
stirred for 6 h at room temperature. Then the mixture is filtered and
Table 3
Summary of MizorokieHeck coupling reaction results.
evacuated completely. Yield: 80.0 mg (53%). 1H NMR (CDCl3):
d
Entrya Catalyst
Substrates
Time Yield TON
(h)
7.69e7.54 (m, 14H, AreH), 7.53e7.49 (m, 6H, AreH) 7.25e7.21 (m,
2H, AreH), 7.09e7.05 (m, 2H, AreH), 3.96 (s, 3H, NeMe), 3.72e3.65
(m, 2H, eCH2CH2e), 3.18e3.12 (m, 2H, eCH2CH2e). 31P{1H} NMR
(mmol) ꢃ 10ꢀ5
AreX
R
1
2
3
4
5
6
7
8
0.2 (1)
4-MeC6H4I
4-MeC6H4I
C6H5I
C6H5I
C6H5Br
eCOOtBu
eCOOtBu
eCOOtBu
eCOOtBu
eCOOtBu
eCOOtBu
4
4
4
4
6
6
6
6
96%
89%
76%
68%
49%
46%
50%
50%
355,500
404,500
58,500
61,800
37,700
41,800
38,500
45,500
(CDCl3): d d 142.7, 142.1 (t), 140.9, 137.5,
28.31 (s). 13C NMR (CDCl3):
0.2 (3)
1.0 (1)
1.0 (3)
1.0 (1)
1.0 (3)
1.0 (1)
1.0 (3)
136.1 (t), 134.3 (t), 133.2, 133.0, 130.3 (t), 129.7 (t), 126.2, 125.9,
125.3, 124.1 (t) (Ph), 78.6 (t, eCF3), 62.9 (s, NeMe), 34.7 (s, e
CH2CH2e). Anal. Calcd. for C40H31Br2ClF3NO3P2PdS: C, 46.81; H,
3.04; N, 1.36. Found: C, 46.68; H, 2.98; N, 1.19.
C6H5Br
4-MeOC6H2Br eCOOtBu
4-MeOC6H2Br eCOOtBu
Synthesis of [(h
3-PNPiPr)PdCl] (3)
a
Reactions were performed with 1.0 equiv. of aryl halides and 1.3 equiv. of tert-
butyl acrylate and 1.4 equiv of base in a DMF for required time at 120 ꢁC.
[(COD)PdCl2] (58 mg, 0.203 mmol) was added to a solution of L2
(TON ¼ Turn Over Number).
(120.61 mg, 0.202 mmol) in 10 mL of acetonitrile with stirring, and

12
M. Tamizmani et al. / Journal of Organometallic Chemistry 763-764 (2014) 6e13
the color of the solution rapidly changed to reddish brown. The
mixture was heated at 70 ꢁC for 1.30 h while stirring, and then the
resulting mixture was passed through celite. The volatiles were
removed from the filtrate in vacuo to produce 132.6 mg (90%) of a
All these computational procedures have been used as imple-
mented in the Gaussian-09 package [50].
Acknowledgment
red orange solid. 1H NMR (CDCl3):
d 6.82 (m, 2H, AreH), 6.48 (d, 2H,
J ¼ 2.4 Hz, AreH), 2.85 (s, 4H, eCH2CH2e), 2.55 (m, 4H, eCH(Me)2),
Dr. C. S gratefully acknowledges the Council of Scientific and
Industrial Research (CSIR), New Delhi, India for the financial
support (No. 01(2535)/11/EMR-II) and Bhattacharya, S., Depart-
ment of Chemistry, Pondicherry University, for solving the crystal
data. K. Ramakrishna gratefully acknowledges the University
Grants commission (UGC) for a Junior Research Fellowship. We
thank the Central Instrumentation Facility, Pondicherry University,
for NMR spectra and DST-FIST for the single-crystal X-ray
diffraction facility.
1.42 (app. quartet (dvt), 12H, eCH(Me)2), 1.27 (app. quartet (dvt),
12H, eCH(Me)2). 31P{1H} NMR (CDCl3):
d
49.53 (s). 13C NMR
(CDCl3): d 162.6, 160.9 (t), 135.8 (t), 135.4, 123.4 (t), 107.2 (t), 39.6 (s,
eCH2CH2e), 25.1 (br s, eCH(Me)2), 18.5 (s, eCH(Me)2), 17.8 (s, e
CH(Me)2). Anal. Calcd. for C26H36Br2ClNP2Pd: C, 43.00; H, 5.00; N,
1.93. Found: C, 43.13; H, 4.89; N, 1.68.
X-ray data collection and refinement
Data collections were performed on an OXFORD XCALIBUR
Appendix A. Supplementary material
diffractometer, equipped with a CCD area detector, using graphite-
ꢀ
monochromated Mo K
a
(l
¼ 0.71073 A) radiation and a low-
CCDC 950473 and 950472 contain the supplementary crystal-
lographic 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.
temperature device [44]. All calculations were performed using
SHELXS-97 and SHELXL-97 respectively using Olex 2-1.1 software
package [45]. 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, except the disordered bromobenzene, were
refined anisotropically. For complexes 1 and 3, one of the bromo-
benzene is highly disordered and in complex 2, the triflate ion is
highly disorded, so additional calculation has been done by
“SQUEEZE” option in PLATON [46,47]. The crystallographic figures
have been generated using Olex 2-1.1 software package (50%
probability thermalellipsoids).
Appendix B. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2014.04.011.
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