Group 10 phosphinite POCOP pincer complexes derived from 4-n-dodecylresorcinol: An alternative way to produce non-symmetric pincer compounds

Article abstract of DOI:10.1016/j.poly.2009.07.038

Phosphinite POCOP pincer compounds [4-(n-C₁₂H ₂₅)-C₆H₃-1,3-(OPR₂)₂] R=Ph (1), Prⁱ (2) derived from 4-n-dodecylresorcinol and their group 10 derivatives [MCl{3-(n-C₁₂H₂₅)-C₆H ₂-2,6-(OPR₂)₂}] M(R)-Ni(Ph) (3), Ni(Pr ⁱ) (6), Pd(Ph) (4), Pd(Prⁱ) (7) and Pt(Ph) (5), Pt(Pr ⁱ) (8) were synthesized and the catalytic activity of the palladium species explored in the Mizoroki-Heck and Suzuki-Miyaura cross coupling reactions.

Full text of DOI:10.1016/j.poly.2009.07.038

Polyhedron 29 (2010) 592–600
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Group 10 phosphinite POCOPpincer complexes derived from 4-n-dodecylresorcinol:
An alternative way to produce non-symmetric pincer compounds
*
Moisés Agustín Solano-Prado, Fabiola Estudiante-Negrete, David Morales-Morales
Instituto de Química, Universidad Nacional Autónoma de México, Cd. Universitaria, Circuito Exterior, Coyoacán 04510, México DF, Mexico
a r t i c l e i n f o
a b s t r a c t
Phosphinite POCOP pincer compounds [4-(n-C12H25)-C6H3-1,3-(OPR2)2] R@Ph (1), Pri (2) derived from
4-n-dodecylresorcinol and their group 10 derivatives [MCl{3-(n-C12H25)-C6H2-2,6-(OPR2)2}]
M(R) = Ni(Ph) (3), Ni(Pri) (6), Pd(Ph) (4), Pd(Pri) (7) and Pt(Ph) (5), Pt(Pri) (8) were synthesized and the
catalytic activity of the palladium species explored in the Mizoroki-Heck and Suzuki-Miyaura cross
coupling reactions.
Article history:
Available online 24 July 2009
Keywords:
PCP pincer compounds
POCOP pincer compounds
Cross coupling reactions
Heck reaction
Ó 2009 Elsevier Ltd. All rights reserved.
Suzuki-Miyaura reaction
Catalysis
1. Introduction
pounds of many elements are known and their chemistries are mo-
tif of continuous and numerous studies. In this sense, phosphinite
Pincer compounds represent a group of species with very par-
ticular and interesting properties among which, their high thermal
stability and unusual reactivities that confer to the metal com-
plexes they form stand out. It is due, to these characteristics of
robustness and thermal stability that pincer compounds have at-
tracted the continuous attention of the chemistry community for
multiple applications, this being particularly true in the case of
homogeneous catalysis [1]. In the beginning, the very simple back-
bone exhibited by these compounds did not anticipate the wide
variety of possible functionalizations in the main frame of the com-
plex (Scheme 1). Thus, as up today, these ligands have been mod-
ified to include different donor groups such as NHC’s heterocyclic
carbenes [2], phosphines [3], thioethers [4], oxazolines [5], phos-
phinites [6], amines and imines [7], and so forth. Moreover, the
very same system can be modified to include functional groups
that enable these species to be anchored to solid supports [8] or
allowing further functionalization to afford dendrimeric or nano-
structured systems [9]. In many cases, these complexes have been
successfully modified to include chiral motifs that have allowed
the synthesis of enantiomerically pure systems which have been
employed successfully in asymmetric synthesis and enantioselec-
tive catalysis.
POCOP pincer compounds have been an answer for the easy syn-
thesis of pincer compounds, maintaining the same characteristics
of thermal robustness and in many occasions enhanced reactivity
when compared to their phosphine counterparts. Moreover, the
number of examples of complexes including non-symmetric pincer
type ligands is limited in comparison with those of their symmetric
analogs [10]. This is partly because their preparation is a consider-
able challenge, being laborious and requiring a series of steps to
introduce different groups or donors. Moreover complexes bearing
non-symmetric pincer ligands have shown enhanced and in many
cases markedly different reactivities, such as hemilability [11].
Thus, following our continuous interest in the development on
pincer chemistry [12], the present report describes an alternative
way for the synthesis of non-symmetric POCOP pincer compounds
their characterization and catalytic evaluation in relevant cross
coupling reactions.
2. Experimental
2.1. Material and methods
In addition, the bare inclusion of different metals in the cavity of
the ligands offers an endless possibility of a very diverse chemistry
according to the metal selected. Hence, nowadays pincer com-
Unless stated otherwise, all reactions were carried out under an
atmosphere of dinitrogen using conventional Schlenk glassware,
solvents were dried using established procedures and distilled un-
der dinitrogen immediately prior to use. The 1H NMR spectra were
recorded on a JEOL GX300 spectrometer. Chemical shifts are re-
ported in ppm down field of TMS using the residual signals in
the solvent (CDCl3, d 7.27) as internal standard. 31P{1H} NMR
* Corresponding author. Tel.: +52 55 56224514; fax: +52 55 56162217.
E-mail address: damor@unam.mx (D. Morales-Morales).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.07.038

M.A. Solano-Prado et al. / Polyhedron 29 (2010) 592–600
593
- Steric and electronic modulation
via donor groups
- Chirality
- Anchoring site
- Remote electronic
modulations
R
R
D
Y
E
MmLn
D
- Cavity for metal binding
with tunable accesibility
- Sites for counter anions or
ancillary ligands
- Chirality
- Steric modulation
Scheme 1. Versatility of the pincer backbone and potential sites for modification.
spectra were recorded with complete proton decoupling and are
reported in ppm using 85% H3PO4 as external standard. Elemental
analyses were determined on a Perkin Elmer 240. Positive-ion FAB
mass spectra were recorded on a JEOL JMS-SX102A mass spectrom-
eter operated at an accelerating voltage of 10 kV. Samples were
desorbed from a nitrobenzyl alcohol (NOBA) matrix using 3 keV
xenon atoms. Mass measurements in FAB+ are performed at a res-
olution of 3000 using magnetic field scans and the matrix ions as
the reference material or, alternatively, by electric field scans with
the sample peak bracketed by two (polyethylene glycol or cesium
iodide) reference ions. GC–MS analyses were performed on a Agi-
lent 6890 N GC with a 30.0 m DB-1MS capillary column coupled
to an Agilent 5973 Inert Mass Selective detector. The PdCl2, PtCl2
were purchased from Pressure Chemical Co., 4-n-dodecylresorcinol
was purchased from Acros Organics, and ClPPh2, ClPPri2,
NiCl2Á6H2O, and NEt3 were commercially obtained from Aldrich
Chemical Co. All compounds were used as received without further
purification. The starting materials [(COD)PdCl2] [13], cis-
[(SMe2)2PtCl2] [14], were prepared according to published
procedures.
without further purification. 1H NMR (300 MHz, CDCl3): d = 0.87
(bs, 3H, –CH3, n-dodecyl), 1.05–1.17 (bm, 24H, –CH(CH3)2, PPri2),
1.25 (bs, 18H, –CH2(CH2)7CH2–, n-dodecyl), 1.44 (bs, 2H, –CH2–,
n-dodecyl), 1.84–1.91 (bm, 4H, –CH(CH3)2, PPri2), 2.50 (bs, 2H, –
CH2–Ar, n-dodecyl), 6.56–7.26 (m, 3H, Ar). 31P{1H} NMR
(121.379 MHz, CDCl3): d = 142.38 (s, Pa), 149.42 (s, Pb). EI-MS
[M]+ = 510 (100%) m/z. Anal. Calc. for C30H56O2P2 (Mr = 510.71): C,
70.55; H, 11.05. Found: C, 70.43; H, 10.96%.
2.4. Synthesis of [NiCl{3-(n-C12H25)-C6H2-2,6-(OPPh2)2}] (3)
A solution of (1) (465 mg, 0.72 mmol) in toluene (20 mL) was
added dropwise to a suspension of NiCl2 (171 mg, 0.72 mmol) in
toluene (30 mL) and set up to reflux overnight. The solution was
then filtered over a short pad of silica gel, washed with diethyl
ether and pumped off to dryness. The resulting oily product was
extracted with CH2Cl2 (2 Â 5 mL) and then the solvent removed
under vacuum. The solvent is taken off under vacuum to afford
complex (3) as a viscous amber oil, (0.442 g, 0.597 mmol, 83.1%).
1H NMR (300 MHz, CDCl3): d = 0.87 (bs, 3H, –CH3, n-dodecyl),
1.24 (bs, 18H, –CH2(CH2)7CH2–, n-dodecyl), 1.57 (bs, 2H, –CH2–,
n-dodecyl), 2.45 (bs, 2H, –CH2–Ar, n-dodecyl), 6.66–7.77 (m, 22H,
Ar). 31P{1H} NMR (121.379 MHz, CDCl3): d = 138.76, 142.67 (s,
2.2. Synthesis of [4-(n-C12H25)-C6H3-1,3-(OPPh2)2] (1)
2
2JPaPb = 474.88 Hz, Pa) and 143.18, 147.08 (s, JPaPb = 474.88 Hz,
The title compound was synthesized by a slight modification of
the procedure described for compound [C6H4{1,3-(OPPri2)2}] [3a].
A Schlenk flask was charged with 4-n-dodecylresorcinol (400 mg,
1.436 mmol), 30 mL of freshly distilled toluene and 0.4 mL of
NEt3 (2.873 mmol). The resulting mixture is stirred for 15 min
and after this time chlorodiphenylphosphine (0.51 mL, 2.873
mmol) is added dropwise under stirring. The mixture is set to re-
flux overnight and then allowed to reach room temperature and fil-
tered via canula. The filtrated is evaporated under vacuum to afford
ligand (1) as a colorless viscous oil, (0.794 g, 1.228 mmol, 85.4%).
This compound was used in the next step without any further
purification. 1H NMR (300 MHz, CDCl3): d = 0.85 (bs, 3H, –CH3,
n-dodecyl), 1.20 (bs, 18H, –CH2(CH2)7CH2–, n-dodecyl), 1.44 (bs,
2H, –CH2–, n-dodecyl), 2.50 (bs, 2H, –CH2–Ar, n-dodecyl), 6.46–
7.72 (m, 23H, Ar). 31P{1H} NMR (121.379 MHz, CDCl3): d = 110.35
(s, Pa), 111.28 (s, Pb). EI-MS [M]+ = 646 (100%) m/z. Anal. Calc. for
C42H48O2P2 (Mr = 646.78): C, 77.99; H, 7.48. Found: C, 78.04; H,
7.46%.
Pb). FAB+-MS [M]+ = 738 (50%) m/z, [MÀCl]+ = 703 (88%) m/z. Anal.
Calc. for C42H47ClNiO2P2 (Mr = 739.92): C, 68.18; H, 6.40. Found:
C, 68.05; H, 6.43%.
2.5. Synthesis of [NiCl{3-(n-C12H25)-C6H2-2,6-(OPPri2)2}] (4)
Complex (4) was synthesized by an analogous method as that
described for the phenyl derivative (3), from ligand (2) (367 mg,
0.72 mmol) in toluene (20 mL) and NiCl2 (171 mg, 0.72 mmol) in
toluene (30 mL). Complex (4) was obtained as a viscous amber
oil, (0.397 g, 0.657 mmol, 91.4%). 1H NMR (300 MHz, CDCl3):
d = 0.86 (bs, 3H, –CH3, n-dodecyl), 1.24 (bs, 18H, –CH2(CH2)7CH2–
, n-dodecyl), 1.18–1.40 (bm, 24H, –CH(CH3)2, PPri2) 1.51 (bs, 2H,
–CH2–, n-dodecyl), 1.99–2.03 (bm, 4H, -CH(CH3)2, PPri2), 2.48 (bs,
2H, –CH2–Ar, n-dodecyl), 6.33–6.90 (m, 2H, Ar). 31P{1H} NMR
2
(121.379 MHz, CDCl3): d = 180.79, 183.46 (s, JPaPb = 324.53 Hz,
2
Pa) and 184.21, 186.88 (s, JPaPb = 324.53 Hz, Pb). FAB+-MS
[M]+ = 602 (12%) m/z, [MÀCl]+ = 567 (10%) m/z. Anal. Calc. for
C30H55ClNiO2P2 (Mr = 603.85): C, 59.67; H, 9.18. Found: C, 58.96;
H, 9.16%.
2.3. Synthesis of [4-(n-C12H25)-C6H3-1,3-(OPPri2)2] (2)
The title compound was synthesized by a similar procedure as
that described for ligand (1) from 4-n-dodecylresorcinol (400 mg,
1.436 mmol), 30 mL of freshly distilled toluene, 0.4 mL of NEt3
(2.873 mmol) and chlorodiisopropylphosphine (0.45 mL, 2.873
mmol). Ligand (2) was obtained as a colorless viscous oil, (0.68 g,
1.331 mmol, 92.6%). This compound was used in the next step
2.6. Synthesis of [PdCl{3-(n-C12H25)-C6H2-2,6-(OPPh2)2}] (5)
Complex (5) was synthesized by an analogous method as that
described for complex (3), from ligand (1) (465 mg, 0.72 mmol)
in toluene (20 mL) and [CODPdCl2] (205 mg, 0.72 mmol) in toluene

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M.A. Solano-Prado et al. / Polyhedron 29 (2010) 592–600
(30 mL). Complex (5) was obtained as a viscous amber oil, (0.508 g,
0.645 mmol, 89.7%). 1H NMR (300 MHz, CDCl3): d = 0.86 (bs, 3H, –
CH3, n-dodecyl), 1.23 (bs, 18H, –CH2(CH2)7CH2–, n-dodecyl), 1.59
(bs, 2H, –CH2–, n-dodecyl), 2.66 (bs, 2H, –CH2–Ar, n-dodecyl),
6.67–7.98 (m, 22H, Ar). 31P{1H} NMR (121.379 MHz, CDCl3):
introduced into a Schlenk tube in the open air. The tube was
charged with a magnetic stir bar and an equimolar amount of base
and (Na2CO3-0.4 g, 4 mmol), sealed, and fully immersed in a 140 °C
silicon oil bath. After the prescribed reaction time (6 h), the mix-
ture was cooled to room temperature and the organic phase ana-
lyzed by gas chromatography (GC–MS) by duplicate.
2
d = 138.75, 142.65 (s, JPaPb = 473.06 Hz, Pa) and 143.17, 147.09 (s,
2JPaPb = 473.06 Hz, Pb). FAB+-MS [M]+ = 787 (8%) m/z, [MÀCl]+ = 751
(100%) m/z. Anal. Calc. for C42H47ClO2P2Pd (Mr = 787.64): C, 64.05;
H, 6.01. Found: C, 64.08; H, 6.03%.
2.11. General method for the Suzuki-Miyaura couplings
A DMF solution (5 ml) of 4.0 mmol of halobenzene, 4.0 mmol of
phenyl boronic acid, and the prescribed amount of catalyst (0.1%
mol) was introduced into a Schlenk tube in the open air. The tube
was charged with a magnetic stir bar and an equimolar amount of
base (Na2CO3, 4 mmol), and sealed, and fully immersed in a 110 °C
silicon oil bath. After the prescribed reaction time (8 h), the mix-
ture was cooled to room temperature and the organic phase ana-
lyzed by gas chromatography (GC–MS) by duplicate.
2.7. Synthesis of [PdCl{3-(n-C12H25)-C6H2-2,6-(OPPri2)2}] (6)
Complex (6) was synthesized by an analogous method as that
described for the phenyl derivative (3), from ligand (2) (367 mg,
0.72 mmol) in toluene (20 mL) and [CODPdCl2] (205 mg,
0.72 mmol) in toluene (30 mL). Complex (6) was obtained as a vis-
cous amber oil, (0.452 g, 0.694 mmol, 96.5%). 1H NMR (300 MHz,
CDCl3): d = 0.86 (bs, 3H, –CH3, n-dodecyl), 1.24 (bs, 18H, –
CH2(CH2)7CH2–, n-dodecyl), 1.27–1.41 (bm, 24H, –CH(CH3)2, PPri2)
1.51 (bs, 2H, –CH2–, n-dodecyl), 2.11–2.22 (bm, 4H, –CH(CH3)2,
2.12. Mercury drop experiments
PPri2), 2.48 (bs, 2H, –CH2–Ar, n-dodecyl), 6.44–6.78 (m, 2H, Ar).
Following the above described procedures; additionally adding
two drops of elemental Hg to the reaction mixture. After the pre-
scribed reaction times, the solution was filtered and analyzed by
GC–MS: no significant difference in conversion between these
experiments and those in the absence of mercury was observed,
indicating that heterogeneous Pd(0) is not involved. These
experiments were performed under the optimized condition for
entries 4 in both transformations (e.g. with bromobenzene).
31P{1H} NMR (121.379 MHz, CDCl3): d = 182.71, 186.11 (s, JPaPb
=
2
2
412.36 Hz, Pa) and 186.65, 190.03 (s, JPaPb = 412.36 Hz, Pb). FAB+-
MS [M]+ = 651 (11%) m/z, [MÀCl]+ = 615 (100%) m/z. Anal. Calc.
for C30H55ClO2P2Pd (Mr = 651.58): C, 55.30; H, 8.51. Found: C,
55.25; H, 8.49%.
2.8. Synthesis of [PtCl{3-(n-C12H25)-C6H2-2,6-(OPPh2)2}] (7)
Complex (7) was synthesized by an analogous method as that
described for complex (3), from ligand (1) (465 mg, 0.72 mmol)
in toluene (20 mL) and cis-[(Me2S)PtCl2] (280 mg, 0.72 mmol) in
toluene (30 mL). Complex (7) was obtained as a viscous amber
oil, (0.532 g, 0.608 mmol, 84.5%). 1H NMR (300 MHz, CDCl3):
d = 0.88 (bs, 3H, –CH3, n-dodecyl), 1.24 (bs, 18H, –CH2(CH2)7CH2–
, n-dodecyl), 1.61 (bs, 2H, –CH2–, n-dodecyl), 2.71 (bs, 2H, –CH2–
Ar, n-dodecyl), 6.68–7.99 (m, 22H, Ar). 31P{1H} NMR
3. Results and discussion
The phosphinite POCOP pincer ligands [4-(n-C12H25)-C6H3-1,3-
(OPR2)2] R@Ph (1), Pri (2) were synthesized in a similar manner
as described by our group for [C6H4-1,3-(OPPri2)2] [3a]. Thus, the
reaction of [4-(n-C12H25)-C6H3-1,3-(OH)2] with ClPR2 (R@Ph, Pri)
in a 1:2 molar ratio in the presence of slight excess of NEt3 under
reflux in toluene (Scheme 2) affords ligands (1) and (2) in good
yields and pure enough to be used for the synthesis of the corre-
sponding group 10 transition metal complexes.
2
(121.379 MHz, CDCl3): d = 128.98, 132.88 (s, JPaPb = 473.39 Hz,
2
Pa) and 133.48, 137.37 (s, JPaPb = 473.039 Hz, Pb); d = 119.68,
1
146.08 and 120.29, 146.67 (s, JPPt = 3193 Hz). FAB+-MS [M]+ =
876 (45%) m/z, [MÀCl]+ = 841 (100%) m/z. Anal. Calc. for
C42H47ClO2P2Pt (Mr = 876.30): C, 57.57; H, 5.41. Found: C, 57.58;
H, 5.43%.
Analysis of both ligands by 1H NMR displays signals due to the
presence of phenyl rings, for (1) between d 6.46 and 7.72 ppm,
additional signals assigned to the aliphatic chain can be observed
at d 0.85, 1.20, 1.44 and 2.50 ppm due to the terminal methyl
(–CH3, n-dodecyl), middle methylenes (–CH2(CH2)7CH2–, n-dode-
cyl), methylene (–CH2–, n-dodecyl) and methylene directly bonded
to the aromatic ring (–CH2–Ar, n-dodecyl) respectively. Analo-
gously, the 1H NMR spectrum for ligand (2) exhibits signals be-
tween d 6.56 and 7.26 ppm corresponding to the aromatic ring.
Additionally, signals due to the aliphatic chain and those due to
the Pri groups in the phosphine fragment are observed at d 0.87
(–CH3, n-dodecyl), 1.05–1.17 (CH3, Pri), 1.25 (–CH2(CH2)7CH2–,
n-dodecyl), 1.44 (–CH2–, n-dodecyl), 1.84–1.91 (CH2, Pri) and
2.50 ppm (–CH2–Ar, n-dodecyl) respectively. However, more
2.9. Synthesis of [PtCl{3-(n-C12H25)-C6H2-2,6-(OPPri2)2}] (8)
Complex (8) was synthesized by an analogous method as that
described for the phenyl derivative (3), from ligand (2) (367 mg,
0.72 mmol) in toluene (20 mL) and cis-[(Me2S)PtCl2] (280 mg,
0.72 mmol) in toluene (30 mL). Complex (8) was obtained as a vis-
cous amber oil, (0.432 g, 0.584 mmol, 81.2%). 1H NMR (300 MHz,
CDCl3): d = 0.87 (bs, 3H, -CH3, n-dodecyl), 1.24 (bs, 18H,
–
CH2(CH2)7CH2–, n-dodecyl), 1.27–1.45 (bm, 24H, -CH(CH3)2, PPri2)
1.53 (bs, 2H, –CH2–, n-dodecyl), 2.17–2.24 (bm, 4H, -CH(CH3)2,
PPri2), 2.51 (bs, 2H, –CH2–Ar, n-dodecyl), 6.47–6.89 (m, 2H, Ar).
2
31P{1H} NMR (121.379 MHz, CDCl3): d = 169.86, 173.27 (s, JPaPb
=
2
414.60 Hz, Pa) and 173.87, 177.29 (s, JPaPb = 414.60 Hz, Pb);
1
d = 160.64, 185.89 and 161.26, 186.49 (s, JPPt = 3054 Hz). FAB+-
OH
OH
O
PR2
9
9
MS [M]+ = 740 (20%) m/z, [MÀCl]+ = 704 (53%) m/z. Anal. Calc. for
C30H55ClO2P2Pt (Mr = 740.24): C, 48.68; H, 7.49. Found: C, 48.55;
H, 7.43%.
2 ClPR2 / NEt3
Toluene, reflux
O
PR2
2.10. General method for the Heck reactions
R= Ph (1), Pri (2)
A DMF solution (5 ml) of 4.0 mmol of halobenzene, 4.0 mmol of
styrene, and the prescribed amount of catalyst (0.1% mol) was
Scheme 2. General synthesis of the phosphinite ligands (1) and (2).

M.A. Solano-Prado et al. / Polyhedron 29 (2010) 592–600
595
Thus, the reaction of both ligands with NiCl2Á6H2O under reflux
condition in toluene affords complexes [NiCl{3-(n-C12H25)-C6H2-
2,6-(OPPh2)2}] (3) and [NiCl{3-(n-C12H25)-C6H2-2,6-(OPPri2)2}] (4)
as dense greenish oily products in good yields. Analysis by proton
NMR of both products yield similar spectra as those determined for
the free ligands, with the signals just been slightly shifted to higher
field. Further analysis of these samples by 31P{1H} NMR reveals the
non-symmetric nature of the ligand, by displaying a spectra for an
AB system, with two signals corresponding to two different P nu-
clei. For instance for compound [NiCl{3-(n-C12H25)-C6H2-2,6-
(OPPh2)2}] (3) at d 138.76 and 142.67 ppm and 143.18 and
147.08 ppm for Pa and Pb respectively, having a 2JPaPb coupling con-
stant of 474.88 Hz this value being in agreement with both phos-
phorus nuclei to be in a mutually trans conformation.
O
O
PR2
PR2
O
PR2
M
9
9
Toluene, reflux
24 h
Cl
O
PR2
M= Ni, Pd, Pt
R= Ph, Pri
Scheme 3. General method for the synthesis of the group 10 POCOP pincer
complexes.
informative results were obtained from the analysis by 31P{1H}
NMR. In this instance for both ligands, the spectra obtained shows
two singlets at d 110.35 (Pa) and 111.28 (Pb) ppm for ligand (1) and
at d 142.38 (Pa) and 149.42 (Pb) ppm for iso-propyl derivative (2),
respectively. The later results in agreement with the two phospho-
rus being in different chemical and magnetic environments, as ex-
pected for a non-symmetric pincer ligand. Analysis of compounds
(1) and (2) by mass spectrometry affords the molecular ion in
the two cases. Elemental analysis where also in agreement with
the proposed formulations.
A similar situation stands for complex [NiCl{3-(n-C12H25)-C6H2-
2,6-(OPPri2)2}] (4) where signals in the 31P{1H} NMR are located at
d 180.79 and 183.46 ppm and at 184.21 and 186.88 ppm for Pa and
2
Pb respectively, with a JPaPb coupling constant of 324.53 Hz. The
2
values of JPaPb being in agreement with the general rule that the
2
magnitude of JPP increases as the electronegativities of groups at-
tached to phosphorus increase [15].
Analysis by FAB+-MS showed the presence of the molecular ions
in both cases at [M]+ = 738 (50%) m/z and 602 (12%) m/z for (3) and
(4) respectively. Other important peaks exhibit the losing of the Cl
in the fragmentation process to afford peaks at [MÀCl]+ = 703
(88%) m/z and 567 (10%) m/z for (3) and (4), respectively. Results
The synthesis of all group 10 complexes with ligands (1) and (2)
was carried out in a similar manner by using the corresponding
starting material NiCl2, [CODPdCl2] or cis-[(Me2S)PtCl2] respec-
tively, according to Scheme 3.
Fig. 1. 31P{1H} NMR spectrum of complex [PtCl{3-(n-C12H25)-C6H2-2,6-(OPPh2)2}] (7).

596
M.A. Solano-Prado et al. / Polyhedron 29 (2010) 592–600
2
obtained from elemental analysis of both species are also in agree-
ment with the proposed formulations.
tively with a JPaPb coupling constant of 412.36 Hz. The FAB+-MS
spectra were obtained for both complexes showing a similar frag-
mentation behavior as that observed for the Ni(II) species, with the
molecular ions [M]+ = 787 (8%) m/z and 651 (11%) m/z for (5) and
(6), respectively, being in agreement with the expected molecular
weights. In both cases, the parent peak corresponds to the frag-
ment [MÀCl]+ (751 (100%) m/z (5) and 615 (100%) m/z (6)). Ele-
mental analysis results are in agreement with the proposed
formulations.
Palladium (II) complexes [PdCl{3-(n-C12H25)-C6H2-2,6-(OPR2)2}]
R@Ph (5), Pri (6), were obtained in a similar manner as that of their
nickel analogous as viscous amber oily products, from the stoichi-
ometric reaction of [CODPdCl2] with the corresponding ligand un-
der reflux conditions in toluene. In this instance also, analysis by
1H NMR allows the identification of the aromatic and aliphatic
fragments in both complexes (see Section 2). Analysis by 31P{1H}
NMR of these compounds exhibit similar patterns (AB systems)
as those observed for the nickel counterparts, with four different
signals caused by the presence of two different phosphorus nuclei.
The chemical shifts in the case of the phenyl derivative (5) are lo-
cated at d 138.75 and 142.65 ppm for Pa and at d 143.17 and
Similarly, as described for the Ni(II) and Pd(II) derivatives
(3)–(6), the platinum complexes were synthesized from the reaction
of ligands (1) and (2) and the starting material cis-[(Me2S)2PtCl2]
under reflux conditions in toluene via C–H activation of the C–H
aromatic bond, affording compounds [PtCl{3-(n-C12H25)-C6H2-
2,6-(OPPh2)2}] (7) and [PtCl{3-(n-C12H25)-C6H2-2,6-(OPPri2)2}] (8)
as a colorless or amber color oily products respectively. As is the
case for the Ni(II) and Pd(II) complexes, results obtained from
the analyses by 1H NMR for both complexes are coherent with
2
147.09 ppm for Pb with a JPaPb coupling constant of 473.06 Hz.
Similarly, in the 31P{1H} RMN spectrum for complex (6) four signals
can be observed at d 182.71 and 186.11 ppm and d 186.65 and
190.03 ppm assignable to the Pa and Pb phosphorus nuclei respec-
Fig. 2. 31P{1H} NMR spectrum of complex [PtCl{3-(n-C12H25)-C6H2-2,6-(OPPri2)2}] (8).

M.A. Solano-Prado et al. / Polyhedron 29 (2010) 592–600
597
the proposed structures. However, far more interesting results the
analysis by 31P{1H} NMR experiments, were a similar pattern is ob-
served for both platinum compounds 7 (Fig. 1) and 8 (Fig. 2), both
being in agreement with the presence of two magnetically differ-
ent phosphorus nuclei with signals at d 128.98 and 132.88 ppm
(Pa) and d 133.48 and 137.37 ppm (Pb) with a coupling constant
From the results obtained some general features are clear. In
most of the cases the conversion proceeds quantitatively, except
for the cases were electron donating groups (EDG) are present in
the aromatic ring, this results can be anticipated based on the reg-
ular behavior observed for this sort of substrates based on their
Hammet parameter values. The preference for the production of
E over the Z product, being in most of the cases >90% it is also no-
ticed. When compared with compound [PdCl(C6H3{2,6-(OPPri2)2})],
complex (5) results to be a faster catalyst, attaining similar yields
for the same substrates in shorter times (compare 18 to 6 hours
reaction time). Under the very same conditions employed no
decomposition of the catalyst was observed and the performance
of the catalysts in a control experiment in the presence of Hg0 does
not change significantly.
2
of JPaÀPb = 473.39 Hz for compound [PtCl{3-(n-C12H25)-C6H2-2,6-
(OPPh2)2}] (7). While for the iso-propyl derivative [PtCl{3-(n-
C12H25)-C6H2-2,6-(OPPri2)2}] (8), the phosphorus signals are lo-
cated at
d 169.86 and 173.27 ppm (Pa) and d 173.87 and
2
177.29 ppm (Pb) with a coupling constant of JPaÀPb = 414.60 Hz
respectively. The platinum satellites are located at d 119.68 and
146.08 ppm (Pa) and d 120.29 and 146.67 ppm (Pb) with a coupling
1
constant of JPÀPt = 3193 Hz for the phenyl derivative [PtCl{3-(n-
C12H25)-C6H2-2,6-(OPPh2)2}] (7) and at d 160.64 and 185.89 ppm
A similar behavior is observed when complex (5) is used as cat-
alyst for the Suzuki-Miyaura couplings of different bromobenzenes
para substituted (Table 2). In this case, complex (5) once more re-
sults to be faster that compound [Pd(TFA)(C6H3{2,6-(OPPri2)2})] re-
ported by Bedford [16], something that is important to mention is
that in the present case the Cl substituent does not has to be
substituted by a more labile group in order to make this catalysts
faster. As was the case for the Heck couplings, no apparent decom-
position is observed on this set of experiments, and a similar con-
trol experiment in the presence of Hg0 does not lead to
deactivation of the catalyst. It is possible that the enhanced reac-
tivity observed in both transformations may be related to the high-
er solubility exhibited by palladium complex (5). Additionally,
given the structure of complex (5) and the length of the hydrocar-
bon tail on the aromatic ring, the potential formation of aggregates
(e.g. micelles) could also be conceived as a stabilization process for
this species in solution, thus also enhancing the reactivity of these
species during the catalytic process.
(Pa) and d 161.26 and 186.49 ppm (Pb) with a coupling constant
1
of JPÀPt = 3054 Hz for the iso-propyl complex [PtCl{3-(n-C12H25)-
C6H2-2,6-(OPPri2)2}] (8). Analysis of both complexes by FAB+-MS,
exhibit the molecular ions at [M]+ = 876 (45%) m/z and 740 (20%)
m/z for (7) and (8), respectively. Both values being in accordance
with the expected molecular weights for the proposed formula-
tions. Elemental analysis results were also in agreement with the
proposed formulations.
All the POCOP pincer complexes synthesized are air and mois-
ture stable. And having on hand the Pd(II) derivatives we decided
to explore their reactivity on C–C cross coupling reactions, namely
Heck reaction and Suzuki–Miyaura couplings. Experiments were
done finding the best catalyst to be the phenyl derivative
[PdCl{3-(n-C12H25)-C6H2-2,6-(OPPh2)2}] (5). Hence, complex (5)
was employed as catalyst precursor for the Heck (Scheme 4a)
and Suzuki-Miyaura (Scheme 4b) couplings of different p-substi-
tuted bromobenzenes with styrene and phenylboronic acid,
respectively.
The conditions employed for the catalytic experiments are de-
picted on Scheme 4. These conditions were chosen so the results
could be comparable to those obtained previously by our group
with [PdCl(C6H3{2,6-(OPPri2)2})] on the Heck experiments [3a].
The results are summarized on Table 1.
There has been a considerable debate in the literature about the
oxidation states of the species involved in the catalytic cycle with
Pd(IV)/Pd(II) and Pd(II)/Pd(0) both being proposed at various times
[17,3c]. Another feasible proposal for the present case is that it
might be possible that one or both arms may deligate at some
stage enabling the compound to catalyze the reaction, thus
(a)
Br
R
0.1 mol % [Pd], Na2CO3, DMF
140oC, 6 h
+
+
R
R
O
PPh2
Pd Cl
PPh2
9
[Pd] =
R= OMe, Me, H, Cl, CHO, COMe
O
(5)
(b)
OH
B
Br
OH
0.1 mol % [Pd], Na2CO3, DMF
110oC, 8 h
+
R
R
Scheme 4. Evaluation of the catalytic activity of complex [PdCl{3-(n-C12H25)-C6H2-2,6-(OPPh2)2}] (5).

598
M.A. Solano-Prado et al. / Polyhedron 29 (2010) 592–600
Table 1
Heck-Mizoroki couplings using [PdCl{3-(n-C12H25)-C6H2-2,6-(OPPh2)2}] (5).
Entry
1
p-Bromobenzene
E (%)
Z (%)
% Conversiona
>99
Br
O
O
O
9.4
90.5
91.9
2
3
4
5
>99
>99
87.6
Br
O
O
H
O
H
H
8.2
Br
Cl
Cl
Cl
13.7
86.2
Br
H
H
H
18.7
68.8
80.0
Br
70.8
9.2
6
44.8
Br
O
O
O
4.3
40.5
a
Yields obtained by GC are based on bromobenzene.
behaving as a hemilabile ligand [18]. Thus, although the precise
mechanism of the catalytic reaction using complex (5) remains
to be elucidated, efforts aimed to shed some further light regarding
this are currently under progress in our laboratories.
In summary, we have successfully synthesized in high yields a
series of non-symmetric POCOP pincer ligands and their complexes
with group 10 transition metal complexes. The non-symmetric
nature of ligands (1) and (2) and their complexes (3) trough (8)
is clearly demonstrated by the 31P{1H} NMR experiments. Preli-
minary catalytic evaluation of the Pd(II) derivatives (5) and (6),
show complex (5) to be a faster catalyst than their symmetric
counterparts
compounds
[PdCl(C6H3{2,6-(OPPri2)2})]
and
[Pd(TFA)(C6H3{2,6-(OPPri2)2})] in Heck-Mizoroki and Suzuki-Miya-
ura cross coupling reactions, respectively.
Moreover, given the physical properties and structure of the
group 10 transition metal complexes obtained, these species may
present interesting optical properties, particularly in the field of li-
quid crystals. This possibility will be explored in the near future as

M.A. Solano-Prado et al. / Polyhedron 29 (2010) 592–600
599
FAB+-Mass, IR and some NMR spectra, respectively. The financial
support of this research by CONACYT (F58692) and DGAPA-UNAM
(IN227008) is gratefully acknowledged.
Table 2
Suzuki-Miyaura couplings using [PdCl{3-(n-C12H25)-C6H2-2,6-(OPPh2)2}] (5).
Entry
1
p-Bromobenzene
% Conversiona
Br
Appendix A. Supplementary data
O
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2009.07.038.
O
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