Isolation and crystallographic characterization of solvate- and anion-stabilized PCP pincer complexes of palladium(II)

Article abstract of DOI:10.1016/j.jorganchem.2007.11.031

Pincer PCP-Pd(II) complex [PdCl(PCP)] (1) (PCP = ^-CH(CH₂CH₂PPh₂)₂) reacts with AgNO₃ to give [Pd(NO₃)(PCP)] (2). Similar reaction with AgBF₄ gives the aqua complex [Pd(OH₂)(PCP)][BF₄] (3) and the dinuclear complex [{Pd(PCP)}₂(μ-Cl)][BF₄] (4) with singly bridging chloro ligand. All new complexes were characterized by NMR spectroscopy, ESI-MS and single-crystal X-ray diffraction. Complex 1 and the triflate complex [Pd(OTf)(PCP)] (5) are active towards Suzuki-Miyaura coupling between aryl bromides and phenyl boronic acid.

Full text of DOI:10.1016/j.jorganchem.2007.11.031

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 1628–1635
www.elsevier.com/locate/jorganchem
Isolation and crystallographic characterization of solvate- and
anion-stabilized PCP pincer complexes of palladium(II)
Kian Eang Neo a, Han Vinh Huynh a, Lip Lin Koh a, William Henderson b, T.S. Andy Hor a,*
a Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
b Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand
Received 23 October 2007; received in revised form 14 November 2007; accepted 14 November 2007
Available online 23 November 2007
Abstract
Pincer PCP-Pd(II) complex [PdCl(PCP)] (1) (PCP = ꢀCH(CH2CH2PPh2)2) reacts with AgNO3 to give [Pd(NO3)(PCP)] (2). Similar
reaction with AgBF4 gives the aqua complex [Pd(OH2)(PCP)][BF4] (3) and the dinuclear complex [{Pd(PCP)}2(l-Cl)][BF4] (4) with singly
bridging chloro ligand. All new complexes were characterized by NMR spectroscopy, ESI-MS and single-crystal X-ray diffraction. Com-
plex 1 and the triflate complex [Pd(OTf)(PCP)] (5) are active towards Suzuki–Miyaura coupling between aryl bromides and phenyl boro-
nic acid.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Pincer; Palladium; Phosphine; Suzuki–Miyaura Coupling
1. Introduction
eties was isolated during the preparation of 3. Such unsup-
ported chloro-bridged complexes of palladium and
platinum [7] are of interest especially when they are possi-
ble intermediates in the catalyst deactivation process
involving cationic complexes [8]. Included herein is the cat-
alytic activity of 1 and the earlier reported triflate complex
[Pd(OTf)(PCP)] (5) [9] towards Suzuki–Miyaura coupling
reaction. As unsaturated metal complexes or their precur-
sors are important catalysts [10], their isolation could sug-
gest an easy access to a range of PCP-Pd(II) pincer-based
catalytic materials.
Research in PCP pincer complexes arising from coordi-
nation-assisted C–X activation (X = H, C or halogen) con-
tinues to advance at a brisk pace [1]. This is driven largely
by their catalytic capabilities [2] and their role as precursors
to a range of novel bi- and polymetallic systems [3]. We
have recently used a Pd(II) pincer viz. [PdCl(PCP)] (1) as
a model to demonstrate the utility of electrospray ioniza-
tion mass spectrometry (ESI-MS) in guiding chemical syn-
theses [4]. These complexes contain a metallated sp3 carbon
that has been reported to enhance catalytic activity [5] or to
give unique reactivity [6] due to higher electron density at
the metal centre. Herein we report the metathesis reactions
of 1 with AgX (X = NO3, BF4) to give complexes
[Pd(NO3)(PCP)] (2) and [Pd(OH2)(PCP)][BF4] (3). The
dinuclear complex [{Pd(PCP)}2(l-Cl)][BF4] (4) with a
chloro ligand bridging between the two pincer Pd(II) moi-
2. Results and discussion
2.1. Synthesis and characterization of mononuclear
complexes [Pd(NO3)(PCP)] (2), [Pd(OH2)(PCP)]
[BF4] (3) and dinuclear complex [{Pd(PCP)}2(l-Cl)]
[BF4] (4)
We have recently reported the formation of a triflate-
coordinated complex 5 (79% yield) from 1 and excess
AgOTf in CH2Cl2/H2O (Scheme 1) [9]. Similar reaction
*
Corresponding author. Tel.: +65 6516 2663; fax: +65 6873 1324.
E-mail addresses: w.henderson@waikato.ac.nz (W. Henderson),
andyhor@nus.edu.sg (T.S. Andy Hor).
0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.11.031

K.E. Neo et al. / Journal of Organometallic Chemistry 693 (2008) 1628–1635
1629
PPh2
PPh2
(i)
Pd Cl
2
Pd ONO2
2
PPh2
PPh2
2
1
(iv)
(ii)
PPh2
Ph2P
Pd
Ph2P
PPh2
(iii)
BF4
Pd OH2
Pd
Cl
BF4
2
PPh2
PPh2
4
3
Scheme 1. Preparation of complexes 2, 3 and 4. (i) Excess AgNO3, acetone/H2O 3:1; (ii) excess AgBF4, acetone/H2O 3:1; (iii) 1, CH2Cl2; (iv) AgBF4.
with AgNO3 gives the analogous nitrato complex 2 in poor
yield. Use of AgBF4 as the chloride extracting agent in wet
solvent gives the cationic aqua complex [Pd(OH2)(PCP)]-
[BF4] (3) and the dinuclear complex [{Pd(PCP)}2-
(l-Cl)][BF4] (4). Pure complex 3 was obtained by changing
CH2Cl2/H2O to acetone/H2O mixture. Analytically pure
complex 4 can be obtained by fractional crystallization
from the reaction mixture of 1 and AgBF4 (1:2 equiv.) or
1 and 3. These complexes have been characterized by
NMR, ESI-MS and single-crystal X-ray diffraction. All
of them contain typical square-planar Pd(II) centers. Com-
plex 4 possibly arises from the addition reaction between 1
and its chloride-extracted form such as 3. A similar method
was used in the preparation of chloro-bridged
[{Pt(CH2Ph)(PCH2-ox)}2(l-Cl)]BF4 (PCH2-ox = j2-P, N-
(oxazolinylmethyl)-diphenylphosphine) [7b].
pled to 11B nuclei [11]. The possibility of aꢀn exchange
process between the free and coordinated BF4 was ruled
out since addition of excess chloride ion (in form of
aqueous NaCl solution) did not cause disappearance of
any peak. Two peaks at m/z = 545 (major) and m/z =
586 (minor) were observed in the ESI mass spectra of
complexes 2 and 3. The former is assigned to cationic
[Pd(PCP)]+ ions (calculated m/z = 546) while the latter
corresponds to the acetonitrile coordinated species
[Pd(CH3CN)(PCP)]+ (calculated m/z = 586). Trapping
of CH3CN in the capillary system by cationic pincer
Pd(II) fragment is common and has been described pre-
viously [4].
The 31P{1H} NMR spectrum of 4 recorded in CDCl3
gives a broad peak at 44.9 ppm (t1/2 = 10 Hz), different
from the mononuclear complexes which give sharper
peaks in their 31P{1H} NMR spectra. The broadness
arises possibly from the restricted rotation about the
Pd–Cl bonds as a result of the close contacts of the
two sterically bulky pincer fragments. Addition of aque-
ous NaCl solution to complex 3 gives rise to two peaks
(dP = 42.4 and 45.0 ppm) which can be assigned to com-
plexes 1 and 4. Further addition of excess of NaCl gives
complex 1, thus suggesting that the bridge cleavage can
be promoted by excess Clꢀ. However, addition of excess
AgBF4 to an acetone-d6 solution of complex 4 gives rise
to a spectrum that is similar to that of 3 dissolved in
acetone-d6 (49.0 ppm), presumably due to the formation
of an acetone-coordinated complex. These results lend
additional support to the assignment of 31P chemical
shift for complex 4. They also established the relation-
ship among 1, 3 and 4 (Scheme 2). The dinuclear molec-
ular ion of 4 is observed in the ESI mass spectrum
recorded under mild conditions (calculated m/z = 1127,
observed m/z = 1127).
The proton at the metallated carbon of complexes 1
(3.18 ppm) [4],
2 (3.35 ppm), 3 (3.53 ppm) and 5
(3.45 ppm) [9] give characteristic signals in their 1H
NMR spectra. The phosphorus chemical shifts of 2
(44.6 ppm) and 3 (46.0 ppm) are comparable to complex
5 (44.8 ppm) [9] but downfield shifted as compared to 1
(41.8 ppm) [4]. This is consistent with successful replace-
ment of chloro ligand by the oxygen-donating NO3, aqua
and OTf ligands. The metallated carbons give upfield sig-
nals in 13C{1H} NMR spectra suggesting shielding upon
chloride replacement (1 = 60.8 ppm [4]; 2 = 56.0 ppm;
3 = 58.6 ppm and 5 = 58.3 ppm [9]). Other NMR fea-
tures are similar to those of 1, suggesting that the pincer
fragment is intact. The 19F{1H} NMR spectra of 3 (dF =
ꢀ76.09 ppm and ꢀ76.14 ppm) and 4 (dF = ꢀ77.38 ppm
and ꢀ77.43 ppm) show two broad peaks which can be
explained by the 10B–11B isotopic shift with the down-
field signal corresponding to the fluorine coupled to
10B nuclei while the upfield signal is due to fluorine cou-

1630
K.E. Neo et al. / Journal of Organometallic Chemistry 693 (2008) 1628–1635
PPh2
PPh2
Pd Cl
PPh2
(i)
2
Pd OH2 BF4
PPh2
2
3
1
(ii)
(iii)
(iv)
(iv)
Ph2P
PPh2
BF4
Cl Pd
Pd
PPh2
Ph2P
4
Scheme 2. Inter-conversion of complexes 1, 3 and 4. (i) aq. AgBF4; (ii)
complex 3; (iii) aq. AgBF4; (iv) aq. NaCl.
Fig. 2. ORTEP plot of complex 3 ꢁ (C2H5)2O ꢁ CH2Cl2 with 50% thermal
2.2. Crystal structures of complexes 2, 3 ꢁ (C2H5)2O, and 4
ꢀ
ellipsoids. (The BF4 anion, diethyl ether and CH2Cl2 molecules are
omitted for clarity.)
The ORTEP plots of complexes 2 and 3 ꢁ (C2H5)2O ꢁ
CH2Cl2 are shown in Figs. 1 and 2, respectively. Selected
bond lengths and bond angles are listed in Table 1. Com-
plexes 2 and 3 show that the incoming oxygen-donors
(NO3 and H2O) are coordinated to the Pd(II) center in a
monodentate fashion. The Pd–O bond lengths of 2
˚
bis(diphenylphosphino)propane) [Pd–OH O = 2.106(4) A,
2
˚
Pd–OOTf = 2.159(3) A] [13], (dppe)Pd(NO3)2 (dppe = 1,2-
bis(diphenylphosphino)ethane) [Pd–O = 2.103(2) A and
2.114(2) A] [14] and [Pd(PPh3)2(OH2)2][OTf]2, [Pd–O =
2.130(2) A and 2.119(2) A] [15]. Nevertheless, the Pd–O
bond length is comparable to the Pd–O bond length in
˚
˚
˚
˚
[2.190(4) A] and 3 [2.200(4) A] are slightly shorter than
the bulky tert-butyl analogue [Pd(OH2)(PCP-tBu)][BPh4]
˚
˚
t
ꢀ
t
˚
(PCP- Bu = CH(CH2CH2P Bu2)2) [2.301(6) A] [12] but
longer than those in the Pd(II) complexes that are not
influenced by the labilising Pd–C bonds at trans-
position like [(dppp)Pd(OH2)(OTf)][OTf] (dppp = 1,3-
˚
complex 5 [2.211(2) A] [9].
The steric bulk of the pincer substituent also forces the
C–Pd–O angles of complex 2 to deviate significantly from
linearity [C(1)–Pd(1)–O(1) = 172.2(2)°]. Such deviation
was also observed in the analogous complex 5 [171.66
(9)°] [9], [Pd(CH3)(PCP-tBu)] [171.9(2)°] and [Pd(OH2)-
(PCP-tBu)][BPh4] [171.1(3)°] [12]. The distortion is less
apparent in 1 [177.3(2)°] [4] and 3 [177.6(2)°] in which the
anion is less sterically demanding. The P–Pd–P angles of
2 [166.8(4)°] and 3 [162.9(5)°] are comparable to that of 1
[165.9(7)°] [4] and 5 [166.2(2)°] [9] as well as the tert-butyl
complexes [PdCH3(PCP-tBu)][166.2(1)°] and [Pd(OH2)-
(PCP-tBu)][BPh4] [167.2(1)°] [12].
˚
˚
The Pd–C lengths of 2 [2.072(5) A] and 3 [2.076(4) A]
are comparable. They are intermediate between that of
t
˚
˚
˚
[Pd(OH2)(PCP- Bu)][BPh4] [2.056(6) A] [12], 5 [2.071(2) A]
t
˚
[9], 1 [2.111(7) A] [4] and [Pd(CH3)(PCP- Bu)] [2.129(4) A]
[12], reflecting the trans influence of the ligands that are
trans to the metallated carbon. The aqua ligand in 3 is
ꢀ
hydrogen bonded to the disordered BF4 [Hꢁ ꢁ ꢁF =
˚
˚
1.903 A] and the Et2O solvate [Hꢁ ꢁ ꢁO = 1.895 A]. Such
hydrogen bonding was also observed for [Pd{C6H3-
(CH2PtBu)-2, 6}(OH2)][BF4] ꢁ THF [16] and [Pd(5, 8, 11,
14, 17- pentaoxa-2,20-dithia[21]-m-cyclophane)(OH2)]
[BF4] [17]. Such bonding supplements and strengthens the
cation–anion interaction and contributes towards the for-
mation and stability of the aqua complex 3 [18].
Fig. 1. ORTEP plot of complex 2 with 50% thermal ellipsoids. (The
methylene carbons C(2X) and C(4X) are disordered into two positions
with 50:50 occupancy.)

K.E. Neo et al. / Journal of Organometallic Chemistry 693 (2008) 1628–1635
1631
Table 1
˚
Selected bond lengths (A) and bond angles (°) of complexes 2, 3 ꢁ (C2H5)2O ꢁ CH2Cl2 and 4 ꢁ CH2Cl2
Complex
2a
3 ꢁ (C2H5)2O ꢁ CH2Cl2
4 ꢁ CH2Clb2
˚
Bond lengths (A)
Pd(1)–P(1)
Pd(1)–P(2)
Pd(2)–P(3)
Pd(2)–P(4)
Pd(1)–O(1)
Pd(1)–Cl(1)
Pd(2)–Cl(1)
Pd(1)–C(1)
Pd(2)–C(6)
C(1)–C(2)
2.304(1)
2.300(1)
–
–
2.190(4)
–
–
2.072(5)
–
1.497(7) C(1)–C(2X)
2.309(1)
–
–
–
2.200(4)
–
–
2.076(4)
–
1.515(4)
2.302(9)
2.289(9)
2.292(8)
2.297(1)
–
2.453(8)
2.466(9)
2.097(3)
2.086(3)
1.552(5)
1.518(5)
1.518(5)
1.531(5)
C(1)–C(4)
C(6)–C(7)
C(6)–C(9)
1.469(7) C(1)–C(4X)
–
–
–
–
–
Bond angles (°)
Pd(1)–Cl(1)–Pd(2)
P(1)–Pd(1)–P(2)
P(3)–Pd(2)–P(4)
P(1)–Pd(1)–O(1)
P(2)–Pd(1)–O(1)
P(1)–Pd(1)–Cl(1)
P(2)–Pd(1)–Cl(1)
P(3)–Pd(2)–Cl(1)
P(4)–Pd(2)–Cl(1)
P(1)–Pd(1)–C(1)
P(2)–Pd(1)–C(1)
P(3)–Pd(2)–C(6)
P(4)–Pd(2)–C(6)
O(1)–Pd(1)–C(1)
Cl(1)–Pd(1)–C(1)
Cl(1)–Pd(2)–C(6)
Pd(1)–C(1)–C(2)
Pd(1)–C(1)–C(4)
Pd(2)–C(6)–C(7)
Pd(2)–C(6)–C(9)
C(2)–C(1)–C(4)
C(7)–C(6)–C(9)
a
–
–
123.8(4)
156.4(3)
160.5(3)
–
166.8(4)
–
95.5(1)
97.6(1)
–
–
–
–
82.9(1)
83.8(1)
–
–
172.2(2)
–
–
162.9(5) P(1)–Pd(1)–P(1)#1
–
97.2(3)
–
–
–
–
–
83.0(3)
–
–
–
177.6(2)
–
–
–
100.1(3)
95.9(3)
98.6(3)
96.4(4)
82.9(1)
82.9(1)
82.3(1)
83.1(1)
–
174.1(1)
178.5(1)
114.8(3)
114.7(2)
115.0(2)
113.9(3)
110.8(3)
111.7(3)
112.8(4) Pd(1)–C(1)–C(2X)
113.1(5) Pd(1)–C(1)–C(4X)
–
–
115.9(7) C(2X)–C(1)–C(4X)
–
113.8(2)
–
–
–
111.6(4) C(2)–C(1)–C(2)#1
–
X refers to the carbon of the methylene backbone that is disordered into two positions with 50:50 occupancy.
b
Angle between P(1)–Pd(1)–P(2)–C(1)–Cl(1) and P(3)–Pd(2)–P(4)–C(6)–Cl(1) planes = 72.6°.
The crystal structure of 4 ꢁ CH2Cl2 shows that the cation
contains two pincer Pd(II) fragments solely bridged by a
chloro ligand at a bent geometry, with a Pd(1)–Cl(1)–
Pd(2) angle of 123.8(4)° (Fig. 3 and Table 1). This angle
is within the range of the M–Cl–M angles in
[{Pt(CH2Ph)(PCH2-ox)}2(l-Cl)]BF4
(3)°] [7b] and the related NCN-pincer palladium complex
[{(C6H3(CH2NMe2)2-O, [Pd–Cl–
O0)Pd}2(l-Cl)]BF4
[Pt–Cl–Pt = 119.1
Pd = 134.8(1)°] [7g]. The metal separation distance
˚
[Pdꢁ ꢁ ꢁPd = 3.910(6) A] suggests that there is no direct
metal–metal bonding. To avoid conflict and minimize con-
tacts between the two PPh2 moieties, the two coordination
planes are twisted away from each other (interplanar angle
made by P(1)–Pd(1)–P(2)–C(1)–Cl(1) and P(3)–Pd(2)–
P(4)–C(6)–Cl(1) = 72.6°) (Fig. 4). Similar twists are
observed in [{Pt(CH2Ph)(PCH2-ox)}2(l-Cl)]BF4 [87(1)°]
[7b] and [{(C6H3(CH2NMe2)2–O, O0)Pd}2(l-Cl)]BF4
[88.5(2)°] [7g]. The two Pd–C bonds are slightly different
Fig. 3. ORTEP plot of complex 4 ꢁ CH2Cl2 with 50% thermal ellipsoids
ꢀ
(BF4 anion and solvent molecule are omitted for clarity).

1632
K.E. Neo et al. / Journal of Organometallic Chemistry 693 (2008) 1628–1635
Fig. 4. ORTEP plot of complex 4 ꢁ CH2Cl2 with 50% thermal ellipsoids showing the Pd coordination planes twisted away from each other. (The phenyl
ꢀ
rings, BF4 anion and solvent molecule are omitted for clarity.)
˚
˚
Table 2
[Pd(1)–C(1) = 2.097(3) A; Pd(2)–C(6) = 2.086(3) A] and
are shorter than that of complex [Pd(1)–
Selected catalytic data of 1 and 5 towards Suzuki–Miyaura cross coupling
reaction of phenyl boronic acid and aryl bromidesa,b
1
˚
C(1) = 2.111(7) A] [4]. As expected, the terminal Pd–Cl
bond 1 [Pd(1)–Cl(1) = 2.431(1) A] [4] is shorter than that
Entry
Aryl bromide
Time (h)
Cat
Isolated yield (%)
˚
˚
1
2
3
4
5
6
7
8
a
4-Bromoacetophenone
4-Bromobenzonitrile
Bromobenzene
16
15
16
20
17
19
15
15
1
1
1
1
5
5
5
5
90
65
52
19
78
80
72
32
of the bridging chloride in 4 [Pd(1)–Cl(1) = 2.453(8) A;
˚
Pd(2)–Cl(1) = 2.466(9) A]. Such M–Cl (M = Pd, Pt) bond
lengthening is commonly observed for this type of com-
plexes [7].
4-Bromoanisole
4-Bromoacetophenone
4-Bromobenzonitrile
Bromobenzene
2.3. Preliminary catalytic study of complexes 1 and 5 in
Suzuki–Miyaura reaction
4-Bromoanisole
Reaction conditions are generally not optimized.
Conditions: aryl bromide (1 mmol), phenyl boronic acid (1.5 mmol),
b
As complexes 1 and 5 represent a saturated and a poten-
tially unsaturated pincer in this series, and that they can be
conveniently prepared in high yields, they were chosen as
models to examine the catalytic performance of this series
of PCP pincers towards Suzuki–Miyaura reactions
(Scheme 3). Preliminary results suggested that substrates
with an electron withdrawing group in the para position
tend to give higher yields (entries 1, 2, 5, and 6) (Table 2).
Further investigations using 4-bromoacetophenone as
substrate with catalysts 1 and 5 revealed that inorganic
bases (K2CO3, Cs2CO3 and NaOH) are bases of choice
for both catalysts (Table 3). Both complexes shows good
catalytic activity when the coupling reactions are per-
formed in commonly-used solvents for this type of reac-
tion, being either polar solvent (1,4-dioxane and DMF)
or non-polar (toluene). The conversion remains quantita-
tive for catalysts 5 even when the catalyst load is reduced
to as low as 0.1 mol% (Entry 19).
catalyst (0.01 mmol), K2CO3 (2 mmol), 1,4-dioxane 110 °C (10 ml), the
reactions were conducted at atmospheric pressure.
active systems [19]. Room-temperature yields can be
improved by conducting the reaction in the presence of
water (Entries 10 vs. 9, and 21 vs. 20) [20], but some catalyst
decomposition (formation of black solid which is presum-
ably palladium metal) was also observed. The activity pro-
file of 1 and 5 under similar conditions are generally
comparable.
3. Conclusion
The chloro PCP-Pd(II) pincer complex 1 exchanges with
labile ligands to give Lewis acidic pincers that could cap-
ture a coordinatively saturated pincer to give a dinuclear
complex. Ongoing work is directed to the use of these com-
plexes as precursors to other homo- and hetero-metallic
systems.
Full conversion can be achieved within 4 h for both cat-
alysts albeit at a high temperature. The catalysts are active
at r.t. but the yields are generally lower compared to other
4. Experimental
R
R
B(OH)2
4.1. General procedures
+
Br
Complexes 1 [4] and 5 [9] were prepared according to the
reported procedures. All solvents were freshly dried using
Scheme 3. Cross coupling reaction between aryl bromides and phenyl
boronic acid.

K.E. Neo et al. / Journal of Organometallic Chemistry 693 (2008) 1628–1635
1633
Table 3
Selected catalytic data of 1 and 5 towards Suzuki–Miyaura cross coupling reaction of phenyl boronic acid and 4-bromoacetophenone under different
conditionsa
Entry
Catalyst
Base
Solvent
Temperatureb
Catalyst loadingc (mol%)
Conversion (%)d
1
2
3
4
5
6
7
8
1
1
1
1
1
1
1
1
1
1
1
5
5
5
5
5
5
5
5
5
5
5
K2CO3
Cs2CO3
NaOH
NEt3
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
Toluene
110 °C
110 °C
110 °C
110 °C
110 °C
110 °C
110 °C
110 °C
RT
1
1
1
1
1
1
0.5
0.1
1
1
1
1
1
1
1
1
1
100
100
100
46
100
81
K2CO3
K2CO3
K2CO3
K2CO3
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
Cs2CO3
NaOH
NEt3
K2CO3
K2CO3
K2CO3
K2CO3
Cs2CO3
Cs2CO3
Cs2CO3
DMF
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane/H2O (2:1 v/v)
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
Toluene
100
88
9
45
10
11
12
13
14
15
16
17
18
19
20
21
22
a
RT
92e
86
70 °C
110 °C
110 °C
110 °C
110 °C
110 °C
110 °C
110 °C
110 °C
RT
100
100
93
48
100
99
100
100
22
72e
94
DMF
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane/H2O (2:1 v/v)
1,4-Dioxane
0.5
0.1
1
1
1
RT
70 °C
Conditions: 4-Bromoacetophenone (1 mmol), phenyl boronic acid (1.5 mmol), base (2 mmol), solvent (10 ml), reaction time (16 h).
The reactions were conducted at atmospheric pressure.
Relative to 4-Bromoacetophenone used in the reaction.
Determined using GC–MS based on aryl halide with n-dodecane as internal standard.
Catalyst decomposition observed.
b
c
d
e
molecular sieves. All reagents were commercial products
4.4. Synthesis of [Pd(NO3)(PCP)] (2)
Complex (0.10 g, 0.17 mmol) was dissolved in
and were used as received. Elemental analyses were per-
formed by the Chemical, Molecular and Materials Analysis
Center (CMMAC) of NUS.
1
degassed acetone (30 ml). To this solution was added a
solution of AgNO3 (0.15 g, 0.86 mmol) in deionised H2O
(10 ml). The mixture was stirred for 4 h shielded from light,
giving a colourless solution with a brown residual solid. It
was filtered through a celite column to remove AgCl. The
filtrate was evaporated under reduced pressure. The milky
white solid obtained was washed with deionised H2O
(2 ꢂ 5 ml) followed by Et2O (2 ꢂ 5 ml). The solid was then
dissolved in acetone (5 ml) and dried with anhydrous
MgSO4. The solution was then filtered and dried under
vacuum. The milky white powder was washed with Et2O
(2 ꢂ 3 ml) to give complex 2 (0.02 g, 20%).
4.2. NMR spectroscopy
The NMR spectra were measured at 25 °C using a Bru-
ker ACF 300 NMR spectrometer. Chemical shifts are
reported relative to TMS where d CHCl3 = 7.26 ppm
(1H) or d CDCl3 = 77.1 ppm (13C{1H}). The 31P{1H}
NMR spectra were externally referenced to 85% H3PO4
at 121.39 MHz while 19F{1H} NMR spectra were refer-
enced to CF3COOH at 282.38 MHz.
4.3. Electrospray ionisation mass spectrometry (ESI-MS)
Analytical data for 2: (Found: C, 57.12; H, 4.55; N, 2.01.
Anal Calc. for C29H29P2PdNO3: C, 57.29; H, 4.82; N,
2.30%) 1H NMR (CDCl3) (d): 1.52–1.79 (m, 4H,
PCH2CH2, overlapped with H2O peak), 2.09 (t, br, 2H,
PCH2CH2), 2.58 (m, 2H, PCH2CH2), 3.35 (t, br, 1H,
PdCH), 7.39–7.90 (m, 20H, Ph). 13C{1H} NMR (CDCl3)
(d): 29.5 (t, 2C, PCH2CH2, J(C,P) = 13.2 Hz), 36.7 (t, 2C,
PCH2CH2, J(C,P) = 6.9 Hz), 56.0 (t, 1C, PdC,
J(C,P) = 3.1 Hz), 128.9 (t, 8C, Ph, J(C,P) = 5.0 Hz),
130.6 (s, 2C, Ph, overlapped with phenyl ring C1 signal),
130.7 (t, 2C, Ph, J(C,P) = 18.9 Hz, overlapped with phenyl
ring C4 signal), 130.9 (s, 2C, Ph, overlapped with phenyl
ring C1 signal), 132.1 (t, 4C, Ph, J(C,P) = 6.9 Hz), 132.5
Mass spectra were recorded in positive ion mode using a
Thermo Finningan LCQ spectrometer. MeOH or MeOH/
H2O mixture (80:20 v/v) were used as the mobile phase.
The compounds were dissolved in minimal quantities of
CH2Cl2 or acetone and diluted using the mobile phase.
The solution of complex 4 was introduced via a syringe
pump. Only the molecular ions or their related fragment
peaks are reported here. Assignment of ions was aided by
comparison with the predicted isotope distribution pat-
terns. The predicted isotope patterns were calculated using
the MS/MS ISOPRO [21] computer program.

1634
K.E. Neo et al. / Journal of Organometallic Chemistry 693 (2008) 1628–1635
(t, 2C, Ph, J(C,P) = 20.1 Hz), 133.6 (t, 4C, Ph,
4.6. Synthesis of [{Pd(PCP)}2(l-Cl)][BF4] (4)
Complex (0.05 g, 0.09 mmol) was dissolved in
degassed CH2Cl2 (30 ml). To this solution was added 3
(0.05 g, 0.08 mmol). The pale orange solution was stirred
overnight and filtered. The filtrate was concentrated under
reduced pressure. Addition of Et2O (10 ml) gave pale
orange powder, which was crystallized twice from
CH2Cl2/Et2O to give complex 4 as pale yellow crystals
(0.02 g, 22%).
J(C,P) = 7.6 Hz). 31P{1H} NMR (CDCl3) (d): 44.6 (s, 2P,
ꢀ +
PPh2). ESI-MS (m/z, %): [2–NO3
]
(545, 100), [2–
1
NO3ꢀ + CH3CN]+ (586, 23).
4.5. Synthesis of [Pd(OH2)(PCP)][BF4] ꢁ H2O ꢁ
(CH3CH2)2O (3 ꢁ H2O ꢁ (CH3CH2)2O)
Complex 3 was prepared similarly to complex 2 using
complex
1 (0.05 g, 0.09 mmol) and AgBF4 (0.08 g,
0.43 mmol). The final product was obtained by adding
Et2O into CH2Cl2 solution of 3 giving yellow crystals
(0.03 g, 50%). The presence of H2O and diethyl ether sol-
vent was confirmed by elemental analysis and NMR
spectroscopy.
Analytical data for 4: (Found: C, 57.16; H, 4.71. Anal
Calc. for C58H58P4Pd2ClBF4: C, 57.35 H, 4.82%) 31P{1H}
NMR (CDCl3) (d): 44.9 (s, br, 2P, PPh2). 19F{1H}
NMR(CDCl3) (d): ꢀ77.38 (s, br, 4F, fluorine coupled to
10B nuclei), ꢀ77.43 (s, br, 4F, fluorine coupled to 11B
nuclei). ESI-MS (m/z, %): ꢀ[1+–Clꢀ]+ (547, 25), [1–Clꢀ +
Analytical data for [3 ꢁ H2O ꢁ (CH3CH2)2O]: (Found: C,
53.17; H, 5.35. Anal Calc. for C33H43P2PdO3BF4: C, 53.35;
CH3CN]+ (585, 60), [4–BF4
] (1127, 100).
1
H, 5.85) H NMR (CDCl3) (d): 1.19 (t, 6H, CH3, diethyl
ether), 1.38–1.78 (m, 4H, PCH2CH2), 2.12 (t, br, 2H,
PCH2CH2), 2.62 (m, br, 4H, PCH2CH2 + H2O), 3.53 (q,
br, 5H, PdCH + diethyl ether), 7.45–7.83 (m, 20H, Ph).
13C{1H} NMR (CDCl3) (d): 15.3 (s, 2C, CH3, diethyl
ether), 29.1 (t, 2C, PCH2CH2, J(C,P) = 13.2 Hz), 36.7 (t,
2C, PCH2CH2, J(C,P) = 6.3 Hz), 58.6 (s, br, 1C, PdC,),
65.9 (s, 2C, CH2, diethyl ether), 129.1 (t, 2C, Ph,
J(C,P) = 20.1 Hz), 129.4 (t, 4C, Ph, J(C,P) = 5.0 Hz),
129.5 (t, 4C, Ph, J(C,P) = 5.0 Hz), 131.2 (s, 2C, Ph),
131.4 (t, 2C, Ph, J(C,P) = 20.1 Hz), 131.6 (s, 2C, Ph),
132.2 (t, 4C, Ph, J(C,P) = 6.9 Hz), 133.5 (t, 4C, Ph,
J(C,P) = 6.9 Hz). 31P{1H} NMR (CDCl3) (d): 46.0 (s, 2P,
PPh2). 19F{1H} NMR (CDCl3) (d): ꢀ76.09 (s, br, 4F, fluo-
rine coupled to 10B nuclei), ꢀ76.14 (s, br, 4F, fluorine cou-
pled to 11B nuclei). ESI-MS (m/z, %): [3–H2O–BF4ꢀ]+ (545,
100), [3–H2O–BF4ꢀ + CH3CN]+ (586, 35).
4.7. General procedure for Suzuki–Miyaura reaction
Aryl bromide (1 mmol) and phenyl boronic acid
(1.5 mmol) was added into degassed 1,4-dioxane (10 ml).
K2CO3 (2 mmol) and the palladium complex (0.01 mmol)
were introduced. The reaction mixture was refluxed under
N2 flow. Upon cooling, the solvent was removed under vac-
uum. Water was added to the residue, followed by Et2O
(2 ꢂ 10 ml) and the product extracted. The organic fractions
were combined, dried with anhydrous MgSO4, filtered, and
the solvent removed under vacuum. The crude product was
purified by column chromatography using hexane and ethyl
acetate (95:5 v/v) as eluent. The final product was weighed
before GC–MS analysis. The conversion was determined
by GC–MS based on 4-bromoacetophenone in the crude
product with n-dodecane as internal standard.
Table 4
Parameters for data collection and structure refinement of 2, 3 ꢁ (C2H5)2O ꢁ CH2Cl2 and 4 ꢁ CH2Cl2
2
3 ꢁ (C2H5)2O ꢁ CH2Cl2
4 ꢁ CH2Cl2
Chemical formula
Fw, g molꢀ1
C29H29NO3P2Pd
607.87
C33.50H42B ClF4O2P2Pd
767.27
C59H60BCl3F4P4Pd2
1298.91
Crystal system
Space group
a, A
Orthorhombic
P212121
8.6508(5)
Orthorhombic
Pnma
Monoclinic
P2(1)/c
12.5514(5)
˚
10.1550(5)
˚
b, A
15.5988(9)
16.3068(8)
23.5043(10)
˚
c, A
19.6264(12)
21.9878(11)
20.0366(9)
a, °
b, °
c, °
90
90
90
2648.4(3)
90
90
90
3641.1(3)
90
105.4860(10)
90
5696.4(4)
3
˚
Volume, A
Z
4
4
4
q
cacl, Mg mꢀ3
1.525
0.853
1.400
0.719
1.515
0.936
l, mmꢀ1
Temperature (K)
223(2)
293(2)
223(2)
No. of reflections collected
No. of independent reflections Rint
No. of parameters
18,705
6067 (0.0472)
343
24,811
4317 (0.0428)
240
74,579
13,085 (0.0294)
675
Goodness-of-fit
1.045
1.084
1.054
R1 and wR2 (I > 2 sigma(I))
R1 and wR2 (all data)
R1 = 0.0488, wR2 = 0.1120
R1 = 0.0563, wR2 = 0.1158
R1 = 0.0512, wR2 = 0.1353
R1 = 0.0620, wR2 = 0.1416
R1 = 0.0420, wR2 = 0.1074
R1 = 0.0420, wR2 = 0.1133

K.E. Neo et al. / Journal of Organometallic Chemistry 693 (2008) 1628–1635
1635
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4.8. X-ray crystallography
The X-ray quality crystals of complexes
2 and
4 ꢁ CH2Cl2 were grown by layering Et2O onto a concen-
trated CH2Cl2 solution of 2 and 4 while yellow crystals
of 3 ꢁ (C2H5)2O ꢁ CH2Cl2 was obtained by diffusing Et2O
into a CH2Cl2 solution of 3. Data were collected on a Bru-
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graphics and structure reporting. Data of complex 2
shows that the methylene carbons of the aliphatic back-
bone are disorder into two positions at 50:50 occupancy.
The parameters for crystal structure determination of
complexes 2, 3 ꢁ (C2H5)2O ꢁ CH2Cl2 and 4 ꢁ CH2Cl2 are
listed in Table 4.
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Acknowledgements
We thank the National University of Singapore (NUS),
Agency for Science, Technology & Research (A*Star)
(R143-000-277-305) and the University of Waikato for
financial assistance. We acknowledge Dr. Z.Q. Weng, Dr.
F. Li and Ms. S.H. Teo for helpful discussions. K.E.N.
thanks NUS for a research scholarship.
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Appendix A. Supplementary material
CCDC 660631, 660632 and 660633 contain the supple-
mentary crystallographic data for 1, 2 and 3. These data
can be obtained free of charge from The Cambridge Crys-
tallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this
article can be found, in the online version, at
doi:10.1016/j.jorganchem.2007.11.031.
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[21] M. Senko, ISOPRO 3.0 MS/MS Software, Isotopic Abundance Simu-
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´