Synthesis of a new class of unsymmetrical PCP′ pincer ligands and their palladium (II) complexes: X-ray structure determination of PdCl{C6H3-2-CH2PPH2 -6-CH2PBu2t}

Article abstract of DOI:10.1016/j.jorganchem.2004.05.009

The unsymmetrical PCP′ pincer ligands and {C₆ H₄1-CH₂PPh₂-3-CH₂ PBu₂^t} and {C₆H₄-1 CH₂PPh₂-3-CH₂PPrⁱ ₂} and the corresponding palladium complexes: PdCl{C₆H₃-2-CH₂PPh₂ -6-CH₂PBu^t₂} and PdCl{C₆ H₃-2-CH₂PPh₂-6-CH₂ PPrⁱ₂} have been synthesized in good yields. The molecular structure of PdCl{C₆H₃ -2-CH₂PPh₂-6-CH₂PBu^t ₂} was determined through a single crystal X-ray diffraction study. The palladium center was found to be located into a slightly distorted square planar environment in which the {C₆ H₄-1-CH₂PPh₂-3-CH₂ PBu^t₂} ligand is coordinated as a tridentate, PCP pincer type chelate. The complex, PdCl{C₆H₃-2-CH ₂PPh₂-6-CH₂PPrⁱ₂} catalyzes the Heck coupling of iodobenzene with styrene.

Full text of DOI:10.1016/j.jorganchem.2004.05.009

Journal of Organometallic Chemistry 689 (2004) 2494–2502
www.elsevier.com/locate/jorganchem
Synthesis of a new class of unsymmetrical PCP0 pincer ligands
and their palladium (II) complexes: X-ray structure determination of
PdCl{C6H3-2-CH2PPh2-6-CH2PBut2}
a
Ali Naghipour , Seyyed Javad Sabounchei , David Morales-Morales ,
a
b
b
Simon Hernandez-Ortega , Craig M. Jensen
c,
*
´
´
a
Department of Chemistry, Science Faculty, Bu-Ali-Sina University Hamadan, Iran
´
b
´ ´ ´ ´
Instituto de Quımica, Universidad Nacional Autonoma de Mexico, Cd. Universitaria, Circuito Exterior, Coyoacan 04510, Mexico D. F.
c
Department of Chemistry, University of Hawaii, Honolulu, HI 96822, USA
Received 26 February 2004; accepted 6 May 2004
Abstract
The unsymmetrical PCP0 pincer ligands {C6H4-1-CH2PPh2-3-CH2PBut2} and {C6H4-1-CH2PPh2-3-CH2PPri2} and the corre-
sponding palladium complexes: PdCl{C6H3-2-CH2PPh2-6-CH2PBut2} and PdCl{C6H3-2-CH2PPh2-6-CH2PPri2} have been synthe-
sized in good yields. The molecular structure of PdCl{C6H3-2-CH2PPh2-6-CH2PBut2} was determined through a single crystal X-ray
diffraction study. The palladium center was found to be located into a slightly distorted square planar environment in which the
{C6H4-1-CH2PPh2-3-CH2PBut2} ligand is coordinated as a tridentate, PCP pincer type chelate. The complex, PdCl{C6H3-2-
CH2PPh2-6-CH2PPri2} catalyzes the Heck coupling of iodobenzene with styrene.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: PCP pincer ligand; Palladium complexes; Heck reaction; Catalysis
1. Introduction
Much of the research on PCP pincer complexes has
focused on complexes of diphosphinoxylenes: {C6H4-
1,3-(CH2PR2)2} (Scheme 1a). Modifications of the ben-
zylic positions and phosphino R groups have been used
to ‘‘tune’’, the steric, electronic, and stereochemical
properties of these ligands thus their metal complexes
[9]. PCP pincer ligands with anthryl backbones, as seen
in Scheme 1b, and their metal complexes were recently
prepared in an effort to generate pincer complexes of
even greater thermal stability [3]. In order to elucidate
structure–activity relationships, we have synthesized
the first examples PCP pincer ligands of the following
types: symmetrical bis-phosphinito (Scheme 2a) [6,7];
unsymmetrical bis-phosphinito (Scheme 2b) [10]; and
hybrid phosphinito-phosphino (Scheme 2c and d) [11].
We have explored the reactivity of the palladium and
In the recent years, metal complexes containing PCP
pincer ligands have been employed in a wide variety of
homogeneous and heterogenized (supported) catalytic
reactions [1]. Complexes of these tridenate pincer li-
gands are sufficiently robust to withstand the elevated
temperatures at which the activation of aliphatic C–H
and C–Cl bonds become thermodynamically favorable.
Thus, these complexes have been found to have remark-
able catalytic activity in aliphatic dehydrogenation [2–4]
and C–C coupling reactions [5–8].
*
Corresponding author. Tel.: +1-808-956-2769; fax: +1-808-956-
5908.
E-mail addresses: damor@servidor.unam.mx (D. Morales-Mor-
ales), jensen@gold.chem.hawaii.edu (C.M. Jensen).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.05.009

A. Naghipour et al. / Journal of Organometallic Chemistry 689 (2004) 2494–2502
2495
the residual hydrogen signal of the deuterated solvents
and in 13C{1H} NMR the 13C signal of the deuterated
solvents was used as a reference. 31P{1H} NMR chemi-
cal shifts are reported in ppm downfield from H3PO4
and referenced to high frequency of 85% H3PO4. Ele-
mental analyses were determined on a Perkin–Elmer
240. The starting materials 1,3-benzenedimethanol, bo-
rane-dimethylsulfide (BH3 ÆMe2S), n-BuLi, chlorodiiso-
propyl-phosphine, di-tert-butylphosphine, LiAlH4,
tetrafluoruboric acid diethylether complex (BF4 ÆEt2O),
thionylchloride (SOCl2) and triethylamine (NEt3) were
purchased from Aldrich Chemical Co. and used without
further purification. The complex [PdCl2(COD)] was
synthesized according to the published procedure [13].
PR2
PR2
PR2
PR2
(a)
(b)
Scheme 1. Structure of the most common types of PCP pincer ligands.
iridium derivatives of these novel ligands, successfully
utilizing them as catalysts for Heck couplings [6,7], ali-
phatic dehydrogenations [4], allylic alkylation [10], and
Sonagashira couplings [8]. As part of our effort to create
novel PCP pincer systems in which both the electronic
and steric properties may be easily modulated, we have
designed a novel synthetic route for the high yield syn-
thesis of unsymmetrical phosphino PCP0 pincer type li-
gands (Scheme 2e). We have also prepared palladium
complexes of these novel ligands and investigated their
activity as catalysts for the Heck coupling of halo-benz-
enes and styrene.
2.2. Synthesis of {C6H4-1-(CH2OH)-3-(CH2Cl)} (2)
[14]
To a stirred suspension of 1,3-benzenedimethanol
(2.7617 g, 20 mmol) in benzene (100 ml) concentrated hy-
drochloric acid (10 ml) was added at room temperature,
the color of the solution, initially red, was discarded after
stirring overnight. After this time, the solution is then
washed with aqueous NaHCO3 and water, the organic
phase is separated and the aqueous layer extracted twice
with CH2Cl2 (2·20 ml). The organic phase is dried over
MgSO4 and the solvent removed by rotary evaporation
to afford 2 as a colorless oil (3.13 g, 20 mmol, 100%).
1H NMR (CDCl3, 300 MHz): d 2.15 (s, 1H, OH), 4.47
(s, 2H, CH2Cl), 4.55 (s, 2H, CH2OH), 7.14–7.22 (m,
4H, ArH). 13C{1H} NMR: d 46.08 (CH2Cl), 64.71
(CH2OH), 126.84, 126.97, 127.71, 128.87, 137.66, 141.40.
2. Experimental
2.1. Materials and methods
Unless stated otherwise, all reactions were carried out
under an atmosphere of purified argon using conven-
tional Schlenk glassware and glovebox techniques, sol-
vents were dried using established procedures and
distilled under dinitrogen and freeze–pump–thaw de-
gassed immediately prior to use. The 1H, 13C{1H},
31P{1H} NMR spectra were recorded at 300, 75.4, and
121.4 MHz, respectively, at 295 K, using a Varian Unity
Inova 300 NMR spectrometer. H NMR and 13C{1H}
NMR chemical shifts are reported in ppm downfield
1
from TMS. H NMR chemical shifts are referenced to
2.3. Synthesis of {C6H4-1-(CH2OH)-3-(CH2PPh2)} (3)
To a solution of Ph2PH (1.86 g, 10 mmol) in THF
(50 ml) was added dropwise a solution of n-BuLi in hex-
ane (12.5 ml of 1.6 M/l hexane solution, 20 mmol) at
ꢀ78 ꢁC, over a period of 30 min with stirring. After this
1
O
O
O
PR2
PR2
O
PR2
O
PR2
2
PR2
PR1
2
(a)
(d)
(b)
(e)
(c)
R1
R2
O
PR2
R2
R1
R1
R2
PR1
PR1
PR2
2
P
P
2
2
2
(f)
Scheme 2. Bis-Phosphinito and unsymmetrical phosphino-phosphinito PCP ligands.

2496
A. Naghipour et al. / Journal of Organometallic Chemistry 689 (2004) 2494–2502
time, the reaction mixture was allowed to reach room
temperature. The resulting orange suspension was
cooled to ꢀ78 ꢁC and a THF solution (50 ml) of m-
(chloromethyl)benzyl alcohol (2) (1.566 g, 10 mmol)
was added dropwise with a syringe (30 min). The result-
ing mixture is allowed to reach room temperature and
the stirring continued for an additional 1 h to give a pale
yellow mixture. After this time, the resulting reaction
mixture is placed in to a salt-ice bath (0 ꢁC) and a solu-
tion of NH4Cl in water (10% wt, 60 ml) carefully added
to afford a colorless mixture. The THF layer was sepa-
rated and the aqueous layer extracted twice with ether
(2·20 ml). The combined extracts were dried over
MgSO4 and passed through a short column of alumina.
Finally, the solvent was removed under vacuum to af-
ford 3 as a colorless oil (2.8 g, 9.3 mmol, 93%): 1H
NMR (300 MHz, benzene-d6): d 1.16 (s, OH); 2.96 (s,
2H, CH2P), 3.99 (s, 2H, CH2O); 6.75 (s, 10H, Ar);
7.07 (m, 4H). 31P{1H} NMR (121 MHz, benzene-d6):
d 9.078 (s), 13C{1H} NMR (75 MHz, benzene-d6): d
36.23 (d, J=16.06, CH2P); 64.89 (CH2O); 124.61;
128.18, 128.32; 128.52; 128.60; 128.78; 133.29 (d,
J=18.33 Hz); 137.88 (d, J=7.99 Hz), 139.02 (d,
J=16.06 Hz); 141.92.
Then, SOCl2 (3.9 ml, 53 mmol) was slowly added via sy-
ringe under stirring and the resulting solution kept at
this temperature for 2 h. The solvent and excess of
SOCl2 were removed under vacuum and the residue sub-
jected to column chromatography using silica gel as a
solid support (CH2Cl2/hexane 1.1:1) to afford 5 as a
white solid (2.63 g, 88%): 1H NMR (300 MHz, CDCl3):
d 0.86 (br, q, JHP =97.95, 3H, BH3), 3.51 (d, JHP =12.0
Hz, 2H, CH2P), 4.32 (s, 2H, CH2Cl), 6.77–7.20 (m, 4H),
7.30–7.60 (m, 10H). 13C{1H} NMR (75.40 MHz,
CDCl3): d 33.93 (d, JCP =31.52 Hz, CH2P), 45.90
(CH2Cl), 127.16, 128.02, 128.41, 128.63, 128.76, 130.29
(d, J=4.0 Hz), 130.48 (d, J=4.6 Hz), 131.36, 132.60
(d, J=8.67 Hz), 137.12. 31P{1H} NMR (121 MHz,
CDCl3): d 19.30 (br, m). Anal. Calc. for C20H21ClBOP
(Mr =338.63): C, 79.94; H, 6.25. Found: C, 80.05; H,
6.17%.
2.6. Synthesis of {C6H4-1-(CH2But2(BH3))-3-(CH2-
PPh2(BH3))} (6)
To a mixture of compound 5 (2.63 g, 7.8 mmol) and
NaI (2.34 g, 15.6 mmol) in degassed acetone (70 ml),
HPBut2 (1.47 ml, 7.96 mmol) was added via syringe un-
der stirring. The mixture was set to reflux for 5 h. After
the prescribed reaction time the solvent was removed
under vacuum. The remaining residue was dissolved in
ether (60 ml) and degassed NEt3 (1.1 ml, 7.8 mmol)
and stirred for 1 h. The resulting reaction mixture was
filtered off, and the solvent removed from the filtrate
at reduced pressure. The remaining solid (that has mix-
ture of protected and unprotected of both tert-butylpho-
spine and diphenylphosphine is very difficult to purify so
was used without further purification) was dissolved in
50 ml of THF and borane-dimethysulfide (0.68 g, 9
mmol) added at 0 ꢁC under stirring. The reaction mix-
ture was allowed to reach room temperature and stirred
for further 2 h. The solvent was then evaporated under
vacuum and the residue re-dissolved in CH2Cl2 and fil-
tered through a short plug of silica gel. The crude prod-
uct of 5 was purified by column chromatography using
silica gel as support and eluted with a mixture
CH2Cl2/hexane (1.2:1) to afford pure 6 as a white solid
(2.99 g, 6.47 mmol, 81%): 1H NMR (300 MHz, CDCl3):
2.4. Synthesis of {C6H4-1-(CH2OH)-3-(CH2PPh2-
(BH3))} (4)
A solution of compound 3 (2.85 g, 9.3 mmol) in THF
(30 ml) was placed in a salt-ice bath (0 ꢁC), then,
BH3 ÆSMe2 (0.85 g, 11.25 mmol) was slowly added via
syringe under stirring. After the addition is completed,
the cooling bath was removed and the solution allowed
to reach room temperature. The stirring was continued
at room temperature for an extra 2 h. Then, the solvent
was evaporated and the crude product dissolved in
CH2Cl2, passed through a short path of silica gel and
the resulting solution evaporated under vacuum to af-
1
ford 4 as a white solid (2.83 g, 8.84 mmol, 95%): H
NMR (300 MHz, CDCl3): d 0.85 (br, q, JHP =94.95
Hz, 3H, BH3), 1.84 (bs, 1H, OH), 3.51 (d, JHP =12.0
Hz, CH2P), 4.41 (s, 2H, CH2O), 6.77–7.06 (m, 4H,
ArH), 7.30–7.56 (m, 10H, ArH). 13C{1H} NMR (75.40
MHz, CDCl3): d 33.85 (d, J=32.12 Hz, CH2P), 64.81
(CH2OH), 125.51, 128.15, 128.54, 128.68, 128.80 (d,
J=4.53 Hz), 129.35 (d, J=4.60 Hz), 131.27, 131.97 (d,
J=4.15 Hz), 132.57 (d, J=8.60 Hz), 140.67. 31P{1H}
NMR (121 MHz, CDCl3): d 19.15 (br, m). Anal. Calc.
for C20H22BOP (Mr =320.18): C, 75.02; H, 6.93. Found:
C, 75.10; H, 6.85%.
3
d 0.00–1.00 (m, 6H, BH3), 1.19 (d, JHP =12.60 Hz, 18
H, ((CH3)3C)2P), 2.97 (d, JHP =12.29 Hz, 2H,
2
2
CH2PBut2), 3.59 (d, JHP =12.0Hz, 2H, CH2Ph2),
6.79–7.39 (m, 4H), 7.41–7.66 (m, 10H). 13C{1H} NMR
(75 MHz, CDCl3):
d
25.60 (d, J=24.66 Hz,
((CH3)3C)2P), 28.17 (s, ((CH3)3C)2P), 32.68 (d,
J=25.26 Hz, CH2PBut2), 33.78 (d, J=32.12 Hz,
CH2PPh2), 127.78, 128.48, 128.59, 128.72, 129.08,
129.21, 131.12, 131.72, 132.58 (d, J=8.60 Hz), 134.62.
31P{1H} NMR (121 MHz, CDCl3): d 19.11 (br, m,
Ph2PBH3), 47.49 (br, m, But2PBH3). Anal. Calc. for
2.5. Synthesis of {C6H4-1-(CH2Cl)-3-(CH2PPh2-
(BH3))} (5)
A solution of compound 4 (2.83 g, 8.84 mmol) in
CH2Cl2 (70 ml) was placed in to a salt-ice bath (0 ꢁC).

A. Naghipour et al. / Journal of Organometallic Chemistry 689 (2004) 2494–2502
2497
C28H42B2P2 (Mr =462.21): C, 72.76; H, 9.16. Found: C,
72.78; H, 9.06%.
2.9. Synthesis of Pri2P(H)BH3 (8)
LiAlH4 (10 mmol, 10 ml of 1 M/l ether solution) and
BH3 ÆSMe2 (1.14 ml, 12 mmol) were added consecutively
by syringe to a stirred solution of ClPPri2 (1.526 g, 1.59
ml, 10 mmol) in THF (40 ml) at 0 ꢁC. After warming to
room temperature and stirring for 2 h, the reaction mix-
ture was treated with HCl (5 ml), ice ca. 12 g and
CH2Cl2 (20 ml). The organic layer was separated, and
the aqueous layer extracted twice with CH2Cl2 (2·10
ml). The combined extracts were dried over MgSO4
and then the solvent evaporated under vacuum to afford
pure diisopropylphosphine-borane adduct as a colorless
liquid. 1H NMR (300 MHz, CDCl3): d 0.46 (br, q,
JHP =93.45 Hz, 3H, BH3), 1.30 (m, 12H, (CH3)2CH),
2.17 (m, 2H, (CH3)2CH), 4.22 (m, JHP =350.82 Hz,
1H, PH). 13C{1H} NMR (75 MHz, CDCl3): d 18.16
(d, J=138.82 Hz), 19.43 (d, J=34.46 Hz). 31P{1H}
NMR (121 MHz, CDCl3): d 28.01 (br, q, m). Anal. Calc.
for C6H18BP (Mr =131.995): C, 54.60; H, 13.75. Found:
C, 54.75; H, 13.72%.
2.7. Synthesis of {C6H4-1-(CH2But2)-3-(CH2PPh2)}
(7)
HBF4 ÆEt2O complex, 85% (5.54 ml, 32 mmol) was
added via syringe to a stirred solution of 6 (1.489g, 3.2
mmol) in 30 ml of CH2Cl2 at ꢀ5 ꢁC. The mixture was al-
lowed to reach room temperature and stirred overnight.
After the prescribed reaction time, 60 ml of ether and 160
ml of a degassed saturated aqueous solution of NaHCO3
were added with vigorous stirring for 10 min. The organ-
ic layer was separated and the aqueous layer extracted
with ether. The combined organic extracts were washed
with water, brine and dried over MgSO4. After filtration,
the solution was passed through a short plug of celite and
the solvent evaporated under vacuum to afford 7 as col-
orless oil (1.25 g, 2.87 mmol, 90%). 1H NMR (300 MHz,
3
benzene-d6): d 0.769 (d, JHP =10.50 Hz, (CH3)3C, 2.38
2
(d, JPH =1.80 Hz, 2H, CH2PBut2), 2.99 (s, 2H,
CH2PPh2), 6.58–7.44 (m, 14H, Ar). 13C{1H} NMR (75
MHz, benzene-d6): d 28.83 (d, J=25.64 Hz, (CH3)3C,
29.84 (d, J=13.20 Hz, (CH3)3C, 31.61 (d, J=24.13 Hz,
CH2PBut2), 36.16 (d, J=16.06 Hz, CH2PPh2), 126.82
(d, J=7.24 Hz), 128.49, 128.63 (d, J=4.00 Hz), 131.25,
131.37, 131.95, 133.30 (d, J=18.40 Hz), 137.63 (d,
J=8.10 Hz), 139.20 (d, J=16.60 Hz), 141.93 (d,
J=12.00 Hz). 31P{1H} NMR (121 MHz, benzene-d6): d
ꢀ9.39 (PPh2), 33.87 (PBut2).
2.10. Synthesis of {C6H4-1-(CH2PPh2(BH3))-3-(CH2-
PPri2(BH3))} (9)
To a stirred solution of phosphine 8 (0.412 g, 3.12
mmol) in THF (30 ml) was added slowly a 1.6 M solu-
tion of n-BuLi in hexane (1.95 ml, 3.12 mmol) at ꢀ78
ꢁC (dry ice–acetone bath). The reaction mixture was al-
lowed to reach room temperature to afford a colorless
mixture. The dry ice–acetone bath is replaced and a so-
lution of 5 (1.097 g, 3.12 mmol) in THF (20 ml) added
drop wise by syringe over a period of 30 min. The tem-
perature was allowed to reach room temperature over a
period of 3 h and kept at this temperature for further 2
h. The reaction mixture was quenched by adding an
aqueous solution of NH4Cl (wt 10%, 30 ml). The prod-
uct was extracted with CH2Cl2 and the combined ex-
tracts dried over MgSO4. The solvent was removed
under reduced pressure and the solid residue subjected
to column chromatography using silica gel as a solid
support and eluted with CH2Cl2/hexane (1.15:1) to af-
2.8. Synthesis of [PdCl{C6H3-2-(CH2PPh2)-6-(CH2-
PBut2)} (11)
To a stirred suspension of [PdCl2(COD)] (0.819 g,
2.87 mmol) in toluene (30 ml) a solution of ligand 7
(1.250 g, 2.87 mmol) in toluene (30 ml) was slowly add-
ed. The resulting solution was set to reflux for 5 h. After
this time, the solution was filtered over a cotton pad and
pumped off under vacuum to dryness. The crude solid
was purified by recrystallization from CHCl3/MeOH
to afford complex 11 as white crystals (1.24 g, 2.15
1
1
mmol, 75%): H NMR (300 MHz, CDCl3): d 1.37 (d,
ford 9 as a white solid (1.259 g, 2.90 mmol, 93%). H
2
3JPH =13.49 Hz, CH3, 18H), 3.23 (d, JPH =9.3 Hz,
NMR (300 MHz, CDCl3): d 0.30 (br, m, 6H, BH3),
1.01 (m, 12H, (CH3)2CH), 1.85 (m, 2H, (CH3)2CH),
2.84 (d, JHP =11.10 Hz, CH2PPri2), 3.53 (d, JHP =12.29
Hz, CH2PPh2), 6.73–7.07 (m, 4H, Ar), 7.34–7.60 (m,
10H, Ar). 13C{1H} NMR (75 MHz, CDCl3): d 16.97
(d, J=10.33 Hz, (CH3)2CH, 21.41 (d, J=32.12 Hz,
(CH3)2CH), 27.92 (d, J=27.52, CH2PPri2), 33.76 (d,
J=32.12 Hz, CH2PPh2), 128.18, 128.27, 128.63,
128.76, 128.99, 131.30, 131.39, 132.21, 132.51 (d,
J=8.60 Hz), 133.52. 31P{1H} NMR (121 MHz, CDCl3):
d 18.88 (Ph2PBH3), 35.10 (Pri2PBH3). Anal. Calc. for
C26H38B2P2 (Mr =434.16): C, 71.93; H, 8.82. Found:
C, 72.10; H, 8.75%.
2
2H, CH2PBut2), 3.84 (d, JPH =10.80 Hz, 2H,
CH2PPh2), 6.88–7.18 (m, 3H, Ar), 7.29–7.83 (m, 10H,
Ar). 13C{1H} NMR (300 MHz, CDCl3): d 29.34 (d,
J=3.5 Hz, CH3), 34.33 (dd, J=23.53 Hz, J=2.3 Hz),
35.23 (dd, J=12.1 Hz, J=3 Hz), 42.27 (d, J=3.1 Hz),
122.40, 122.58, 122.67, 122.89, 125.34, 128.60 (d,
J=9.73 Hz), 130.31, 133.00 (d, J=11.46 Hz), 147.90
(d, J=23.00 Hz), 151.30 (d, J=18.93 Hz). 31P{1H}
2
NMR (121 MHz, CDCl3): d 31.62 (d, JPP =394 Hz,
2
PPh2), 78.14 (d, JPP =394 Hz, PBut2). Anal. Calc. for
C28H35ClP2Pd (Mr =575.388): C, 58.45; H, 6.13. Found:
C, 58.40; H, 6.13%.

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A. Naghipour et al. / Journal of Organometallic Chemistry 689 (2004) 2494–2502
2.11. Synthesis of {C6H4-1-(CH2PPh2)-3-(CH2PPri2)}
(10)
(Mr =547.355): C, 55.06; H, 5.71. Found: C, 54.95;
H, 5.67%.
To a stirred solution of 9 (1.259 g, 2.90 mmol) in
CH2Cl2 (25 ml), HBF4–Et2O complex 85% (5.0 ml,
29 mmol) was added at ꢀ5 ꢁC and the resulting mix-
ture allowed to react overnight. After this time, 25 ml
of ether and 75 ml of a saturated aqueous solution of
NaHCO3 were added. The organic layer was separat-
ed and the aqueous layer extracted with ether. The
combined extracts were dried over MgSO4 and filtered
over a short plug of celite. The solvent was then re-
moved under vacuum to afford 10 as a colorless oil
2.13. Data collection and refinement for PdCl{C6H3-2-
CH2PPh2-6-CH2PBut2} (11)
Crystalline yellow prisms of 11 grown by slow dif-
fusion from a CH3Cl/MeOH solvent system; were
glued to a glass fiber. The X-ray intensity data was
measured at 293 K on a Bruker SMART APEX
CCD-based X-ray diffractometer system equipped with
˚
a Mo-target X-ray tube (k=0.71073 A). The detector
was placed at a distance of 4.837 cm from the crystal.
A total of 1800 frames were collected with a scan
width of 0.3ꢁ in x and an exposure time of 10 s/frame.
The frames were integrated with the Bruker SAINT
software package [15] using a narrow-frame integra-
tion algorithm. The integration of the data was done
using a monoclinic unit cell to yield a total of
21,167 reflections to a maximum 2h angle of 50.00ꢁ
1
(1.119 g, 2.75 mmol, 95%). H NMR (300 MHz, ben-
zene-d6): d 0.91 (dd, JHP =12.30 Hz, JCH CH=7.20
3
Hz, 12H, (CH3)2CH), 1.51 (m, 2H, (CH3)2CH), 2.54
(s, 2H, CH2PPri2), 3.21 (s, 2H, CH2PPh2), 6.81–7.00
(m, 4H, Ar), 7.01–7.34 (m, 10H, Ar). 13C{1H}
NMR (75 MHz, benzene-d6): d 19.33 (d, J=11.54
Hz, CH(CH3)2), 19.75 (d, J=14.40 Hz, CH(CH3)2),
23.66 (d, J=16.06 Hz, CH(CH3)2), 30.04 (d,
J=21.79 Hz, CH2PPri2), 36.23 (d, J=16.06 Hz,
CH2PPh2), 126.97 (d, J=6.33 Hz), 127.31 (d, J=5.20
Hz), 128.49, 128.57, 128.69, 130.85 (d, J=6.94 Hz),
133.28 (d, J=18.93), 137.72 (d, J=8.00 Hz), 139.18
(d, J=16.06 Hz), 140.38 (d, J=8.00Hz). 31P{1H}
NMR (121 MHz, benzene-d6): d ꢀ9.46 (PPh2), 10.68
(PPri2).
˚
(0.93 A resolution), of which 4657 were independent.
Analysis of the data showed negligible decays during
data collection. The structure was solved by Patterson
method using SHELXS-97 [16] program. The remaining
atoms were located via few cycles of least squares re-
finements and difference Fourier maps, using the space
Table 1
Crystal data and structure refinement for compound PdCl{C6H3-2-
CH2PPh2-6-CH2PBut2} (11)
2.12. Synthesis of [PdCl{C6H3-2-(CH2PPh2)-6-(CH2-
PPri2)}] (12)
Empirical formula
Formula weight
Temperature
C28H35Cl1P2Pd1
575.35
291(2) K
A solution of the ligand 10 (1.119 g, 2.75 mmol) in
toluene (20 ml) was added dropwise to a suspension of
[PdCl2(COD)] (0.786 g, 2.75 mmol) in toluene (30 ml).
The resulting reaction mixture was set to reflux for 5 h.
The solution was filtered over a short pad of silica gel
and the solvent evaporated under vacuum. Recrystal-
ization of the crude product from CH2Cl2/hexane re-
sulted in the quantitative formation of a colorless
microcrystalline solid (1.11 g, 1.93 mmol, 70%). 1H
˚
0.71073 A
Wavelength
Crystal system
Space group
Unit cell dimensions
Monoclinic
C2/c
˚
a=25.896(2) A, a=90ꢁ
b=11.1359(7) A, b=91.608(1)ꢁ
˚
˚
c=18.305(1) A, c=90ꢁ
3
˚
Volume
Z
5276.6(6) A
8
Density (calculated)
Absorption coefficient
F(000)
1.448 Mg/m3
0.940 mmꢀ1
2368
3
NMR (300 MHz, CDCl3): d 1.10 (dd, JHP =14.40
Hz, JCHCH =6.70 Hz, 6H, CH(CH3)2), 1.37 (dd,
2
Crystal size
h range for data collection
Index ranges
0.24·0.20·0.18 mm
1.99–25.0ꢁ
ꢀ30 6 h 6 30, ꢀ13 6 k 6 13,
ꢀ21 6 l 6 21
21,167
3
3JHP =17.40 HZ, JCHCH =6.70 Hz, 6H, CH(CH3)2),
2
3
2
2.38 (m, 2H, CH(CH3)2), 3.18 (d, JHP =10.19 Hz,
CH2PPri2), 3.85 (d, JHP =10.79 Hz, CH2PPh2), 6.87–
2
Reflections collected
7.01 (m, 3H, Ar), 7.27–7.83 (m, 10H, Ar). 13C{1H}
NMR (75 MHz, CDCl3): d 17.91 (s, CH(CH3)2),
18.92 (d, J=4.60 Hz, CH(CH3)2), 24.06 (d, J=20.66
Hz, CH(CH3)2), 33.29 (d, J=26.40 Hz, CH2PPri2),
41.97 (d, J=30.39 Hz, CH2PPh2), 122.72, 122.89,
123.01, 123.18, 125.46, 128.68 (d, J=9.80 Hz), 130.32,
132.89 (d, J=12.07 Hz), 148.03 (d, J=22.40 Hz),
150.21 (d, J=19.53 Hz). 31P{1H} NMR (121 MHz,
CDCl3): d 29.92 (d, JPP =400 Hz, PPh2), 68.94 (d,
JPP =400.00 Hz, PPri2). Anal. Calc. for C26H31ClP2Pd
Independent reflections
Absorption correction
Refinement method
4657 [R(int)=0.0379]
None
Full-matrix least-squares on F2
4657/0/295
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
0.955a
R1 =0.0229, wR2 =0.0532a
R1 =0.0279, wR2 =0.0ꢀ543 1b
˚
Largest diff. peak and hole
0.316 and ꢀ0.220 eA
2
2 2
S ¼ ½wððF oÞ ꢀ ðF cÞ Þ =ðn ꢀ PÞꢁ1=2, where n is number of reflec-
a
tions and p is total number of parameters.
2
2
2
2 1=2
b
R1 ¼ jF o ꢀ F cj=jF oj; wR2 ¼ ½wððF oÞ ꢀ ðF cÞ Þ =wðF oÞ ꢁ
.

A. Naghipour et al. / Journal of Organometallic Chemistry 689 (2004) 2494–2502
2499
illary column (25.0 m) was used for quantitative GC
analysis.
Table 2
˚
Selected bond distances (A) and angles (ꢁ) for PdCl{C6H3-2-CH2PPh2-
6-CH2PBut2} (11)
˚
Bond lengths (A)
Angles (ꢁ)
3. Results and discussion
Pd(1)–C(2)
Pd(1)–P(1)
Pd(1)–P(2)
Pd(1)–Cl(1)
2.023(2)
C(2)–Pd(1)–P(1)
C(2)–Pd(1)–P(2)
P(1)–Pd(1)–Cl(1)
P(2)–Pd(1)–Cl(1)
P(1)–Pd(1)–P(2)
C(2)–Pd(1)–Cl(1)
82.82(6)
82.84(6)
94.12(2)
100.24(2)
165.65(2)
175.96(7)
2.2867(6)
2.3120(6)
2.4069(6)
3.1. Synthesis of the ligands {C6H4-1-(CH2PPh2)-3-
(CH2PBut2)} (7) and {C6H4-1-(CH2PPh2)-3-(CH2-
PPri2)} (10)
1,3-Benzenedimethanol (C6H4-1,3-(CH2OH)2) is
readily transformed to 2-(chloromethyl)benzyl alcohol
(2) {C6H4-1-(CH2OH)-3-(CH2Cl)} [14]. The chloride
can be further functionalized to unsymmetrical PCP0 pin-
cer type ligands. For example, the reaction of 2 with lith-
ium diphenylphosphide gives compound 3 in high yield.
Protection of the phosphine, by forming the borane ad-
duct, affords compound 4 in good yield. This compound,
is halogenated with SOCl2 to afford compound 5, which
in turn is reacted with the lithium salt of the borane ad-
duct of the di-tert-butylphosphine to obtain compound
6. Further deprotection of 6, with HBF4 ÆEt2O affords
the unsymmetrical ligand {C6H4-1-(CH2PPh2)-3-
(CH2PBut2)} (7) as a colorless oil in good yield (Scheme
3). Analysis by multinuclear NMR spectroscopy of this
Fig. 1. An ORTEP representation of the structure of PdCl{C6H3-2-
CH2PPh2-6-CH2PBut2} (11) at 50% of probability showing the atom
labeling scheme.
1
ligand exhibits signals in the H NMR spectra corre-
sponding to the methyls of the But groups in the P moiety
(d, 0.77 ppm) and those corresponding to the two differ-
ent CH2 groups attached to the two different phosphino
moieties, one at 2.38 ppm corresponding to the
CH2PBut2 and the other at 2.99 ppm due to the CH2PPh2.
Other signals between 7.4 and 6.6 ppm are due to the ar-
omatic rings in the ligand. The 31P{1H} NMR experi-
ment is very illustrating, showing two signals (singlets)
in the spectra which are in accordance with the presence
of two different phosphorus nuclei, one located at ꢀ9.39
ppm corresponding to the P center in PPh2 and the other
at lower field (33.87 ppm) corresponding to the presence
of the P nuclei of the PBut2 moiety.
group C2/c with Z=8. Hydrogen atoms were input at
calculated positions, and allowed to ride on the atoms
to which they are attached. Thermal parameters were
refined for hydrogen atoms on the phenyl groups us-
˚
ing a Ueq =1.2 A to precedent atom. The final cycle
of refinement was carried out on all non-zero data us-
ing SHELXL-97 [17] and anisotropic thermal parame-
ters for all non-hydrogen atoms. The details of the
structure determination are given in Table 1 and se-
˚
lected bond lengths (A) and angles (ꢁ) in Table 2.
The numbering of the atoms is shown in Fig. 1 (OR-
TEP) [18].
The isopropyl derivative, {C6H4-1-(CH2PPh2)-3-
(CH2PPri2)} (10) was synthesized and isolated in an
analogous manner to that of ligand 7, in good yield as
a colorless oil (Scheme 4). Similar spectroscopic analysis
exhibits signals due to the presence of the isopropyl sub-
stitutents in the P moiety at 0.9 ((CH3)2CH) and 1.5
ppm ((CH3)2CH), respectively. Analogously to ligand
7, ligand 10 also exhibits two different signals for the
two different CH2 groups in the phosphino moieties,
one at 2.54 ppm corresponding to the CH2PPri2 and
the other at 3.21 ppm due to the CH2 in CH2PPh2. As
expected, compound 10 exhibits the same behavior in
the 31P{1H} NMR spectra as that observed for ligand
7, presenting two different singlets, one at ꢀ9.46 ppm
due to the PPh2 substituent and the other displaced to
lower field due to the presence of the PPri2 moiety at
10.68 ppm.
2.14. General procedure for the palladium catalyzed Heck
reaction
A DMF solution (3 ml) of 5.0 mmol of halogen ben-
zene, 6.0 mmol of alkene, and the prescribed amount
of catalyst (5 or 8 mol%) was introduced into a
Schlenk tube in the open air. The tube was charged
with a magnetic stir bar and 1.1 equivalent of base,
sealed, and fully immersed in a 180 ꢁC silicon oil bath.
After the prescribed reaction time, the mixture was
cooled to room temperature and the organic phase
was analyzed by gas chromatography (GC/FID, GC–
MS). A Hewlett Packard 5980A gas chromatograph
with flame ionization detector (FID), and an HP-1 cap-

2500
A. Naghipour et al. / Journal of Organometallic Chemistry 689 (2004) 2494–2502
OH
OH
Cl
PPh2
a) HCl
b) NaHCO3, H2O, CH2Cl2
a) HPPh2, n-BuLi, THF
b) aq. NH4Cl, MgSO4
OH
OH
1
2
3
BH3-SMe2
THF
Ph
Ph
Ph
Ph
Ph
Ph
P
P
P
BH3
BH3
BH3
a) NaI, HPBut2, acetone
b) NEt3
SOCl2, CH2Cl2
C) BH3-SMe2, THF
BH3
But
P
Cl
OH
But
6
5
4
a) HBF4-Et2O
b) aq. NaHCO3
PPh2
PBut2
7
Scheme 3. Synthesis of the ligand {C6H4-1-(CH2But2)-3-(CH2PPh2)} (7).
3.2. Synthesis of the complexes PdCl{C6H3-2-CH2PPh2-
6-PBut2} (11) and PdCl{C6H3)-2-(CH2PPh2)-6-
(CH2PPri2)} (12)
78.14 ppm for PPh2 and PBut2 respectively with a cou-
2
pling constant of JPP =394 Hz, which is in agreement
with a trans conformation of the two P nuclei. Complex
12 exhibits a similar pattern, with signals located at
29.92 and 68.94 ppm for PPh2 and PPri2 respectively
with a coupling constant of 2JPP =400 Hz, this value be-
ing consistent with a trans arrangements of both P nu-
clei (Scheme 5).
The reaction of stoichiometric amounts of ligands 7
or 10 with the starting material [PdCl2(COD)] under
reflux of toluene (5 h), affords complexes PdCl{C6H3-
2-CH2PPh2-6-PBut2} (11) and PdCl{C6H3)-2-(CH2-
PPh2)-6-(CH2PPri2)} (12) in good yields (Scheme 5).
Both complexes were isolated from the corresponding
reaction mixtures as colorless microcrystalline powders.
The NMR spectra of both complexes exhibits the signals
corresponding to the presence of the substituents in the
P moieties and those due to the aromatic rings present in
the backbones of the ligands. However, more informa-
tive analysis by 31P{1H} NMR spectroscopy reveals sim-
ilar patterns as those observed for the free ligands 7 and
10, however the signals in these cases are shown as
doublets, due to the coupling established by the two dif-
ferent P nuclei by having the Pd metal center coordinat-
ed to both phosphorus centers. The 31P{1H} NMR
spectrum of complex 11 exhibits signals at 31.62 and
3.3. X-ray crystal structure of PdCl{C6H3-2-CH2PPh2-6-
PBut2} (11)
Single, colorless prismatic crystals of PdCl{C6H3-2-
CH2PPh2-6-PBut2} (11), that were suitable X-ray dif-
fraction analysis were obtained from a CHCl3/MeOH
solvent system. The details of the structure determina-
tion are given in Table 1 and selected bond lengths
and angles are listed in Table 2. A thermal ellipsoid
drawing of 11 with atomic number scheme of the ob-
tained structure is presented in Fig. 1. Analysis of the
colorless crystals reveals the palladium center to be lo-
cated into a lightly distorted square planar environment,

A. Naghipour et al. / Journal of Organometallic Chemistry 689 (2004) 2494–2502
2501
Scheme 4. Synthesis of the ligand {C6H4-1-(CH2PPh2)-3-(CH2PPri2)} (10).
P(1) and P(2). Furthermore, while the pseudoaxial sub-
stituent on one side of the molecule is above the coordi-
nation plane, the corresponding substituent on the other
side is below the coordination plane. This imposed
asymmetric environment is expected to lead to reactivi-
ties that are different than complexes of pincer ligands
with equivalent substituents in both sides of the triden-
PPh2
PPh2
[PdCl2COD]
Pd Cl
PBut2
PBut2
7
11
PPh2
PPh2
˚
tated ligand. The Pd–P(2) bond length of 2.3120(6) A
˚
is significantly longer than the 2.2867(6) A length found
[PdCl2COD]
Pd Cl
for Pd–P(1). This is counter to the situation that would
be expected upon consideration of the relative r donor
strengths of dialkylaryl- vs. trialkyl-phosphines. Thus
the shorter Pd–P(1) distance apparently reflects that
the pendent aryl group confers P(2) with a significant
p bonding component in its interaction with the palladi-
um center. Except for the above mentioned features, the
bond angles and lengths determined for 11 are similar to
those observed in other PCP-complexes [6,9,10,12,19].
The novel PCP pincer complexes 11 and 12 were test-
ed as catalysts for the olefination of aryl halides with
styrene. Complex 12 was found to catalyze the coupling
of iodobenzene and styrene. Yields of 80% (based on
iodobenzene) were achieved in reaction mixtures con-
taining 5 mol% of 12. However, 12 was ineffective as a
catalyst for the coupling of styrene with bromo or chlo-
robenzene. Complex 11 did not exhibit any detectable
activity as a catalyst for the Heck coupling of styrene
with any of the halo-benzenes, even upon increasing
the loadings of the complex to 8 mol%. The greater bulk
of the But substituents apparently creates steric conges-
tion such that there is insufficient access of substrates to
the palladium center of 11.
PPri2
PPri2
12
10
Scheme 5. Synthesis of the complexes PdCl{C6H3-2-CH2PPh2-6-
CH2PBut2} (11) and [PdCl{C6H3-2-(CH2PPh2)-6-(CH2PPri2)}] (12).
with angles of 165.65(2)ꢁ and 175.96(7)ꢁ for P(1)–Pd(1)–
P(2) and C(1)–Pd(1)–Cl(1), respectively. Two chelated
five membered rings formed by Pd(1)–P(2)–C(7)–C(1)–
C(2) and Pd(1)–P(1)–C(8)–C(3)–C(2) are present in the
complex. These rings are quite strained due to the con-
strains imposed by the atoms forming the two adjacent,
five membered chelated rings. Part of this strain is re-
leased by formation of unequal P(1)–Pd(1)–Cl(1)
(94.12(2)ꢁ) and P(2)–Pd(1)–Cl(1) (100.24(2)ꢁ) angles be-
ing the larger angle value the reflex of the presence of the
bulkier substituents But on the P moiety, as a result of
˚
this the Pd(1)–P(2) distance (2.3120(6) A) is slightly
˚
longer than Pd(1)–P(1) (2.2867(6) A). In addition, the
methylene carbons, C(7) and C(8), are located slightly
above and below the plane defined Pd(1), C(2), Cl(1),

2502
A. Naghipour et al. / Journal of Organometallic Chemistry 689 (2004) 2494–2502
(e) F. Liu, A.S. Goldman, J. Chem. Soc., Chem. Commun. (1999)
655;
In order to extend our studies of structure–activity re-
lationships in C–C coupling reactions catalyzed by PCP
pincer complexes, efforts to synthesize other classes of
PCP ligands are currently underway in our laboratories.
(f) C.M. Jensen, J. Chem. Soc., Chem. Commun. (1999) 2443;
(g) F. Liu, E.B. Pak, B. Singh, C.M. Jensen, A.S. Goldman, J.
Am. Chem. Soc. 121 (1999) 4086;
(h) C.M. Jensen, Chem. Commun. (1999) 2443;
(i) D. Morales-Morales, D.W. Lee, Z. Wang, C.M. Jensen,
Organometallics 20 (2001) 1144.
4. Supplementary material
[3] M.W. Haenel, S. Oevers, K. Angermund, W.C. Kaska, H.J. Fan,
M.B. Hall, Angew. Chem. Int. Ed. Engl. 40 (2001) 3596.
´
[4] D. Morales-Morales, R. Redon, C. Yung, C.M. Jensen. Inorg.
Supplementary data for complex 11 have been depos-
ited at the Cambridge Crystallographic Data Centre.
Copies of this information are available free of charge
on request from The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: +44-1223-336033; e-mail
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.ca-
m.ac.uk) quoting the deposition number CCDC 225523.
Chim. Acta, in press.
[5] M.E. van der Boom, D. Milstein, Chem. Rev. 103 (2003) 1759.
´
[6] D. Morales-Morales, C. Grause, K. Kasaoka, R. Redon,
R.E. Cramer, C.M. Jensen, Inorg. Chim. Acta 300–302 (2000)
958.
´
[7] D. Morales-Morales, R. Redon, C. Yung, C.M. Jensen, Chem.
Commun. (2000) 1619.
[8] M.R. Eberhard, Z.H. Wang, C.M. Jensen, Chem. Commun.
(2002) 818.
Acknowledgement
[9] (a) C.J. Moulton, B.L. Shaw, J. Chem. Soc. Dalton Trans. (1976)
1020;
D.M.-M. would like to thank CONACYT for finan-
cial support (Grant J41206-Q). The support of this re-
search by the Office of Hydrogen, Fuel Cells, and
Infrastructure Technologies of the US Department of
Energy is gratefully acknowledged.
(b) F. Gorla, A. Togni, L.M. Venanzi, A. Albinati, F. Lianza,
Organometallics 13 (1994) 1607;
(c) J.M. Longmire, X. Zhang, Tetrahedron Lett. 38 (1997)
1725;
(d) J.M. Longmire, X. Zhang, M. Shang, Organometallics 17
(1998) 4374;
(e) B.S. Williams, P. Dani, M. Lutz, A.L. Spek, G. van Koten,
Helv. Chim. Acta 84 (2001) 3519.
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