Dinuclear PCP pincer complexes from Lewis acidic [Pd(OTf)(PCP)] and basic [Pd(4-Spy)(PCP)] (OTf = triflate; 4-Spy = 4-pyridinethiolate; PCP = -CH(CH2CH2PPh2)2)

Article abstract of DOI:10.1039/b710752h

The Lewis acidic pincer with a labile triflate ligand, viz. [Pd(OTf)(PCP)] (PCP = ^-CH(CH₂CH₂PPh₂)₂) 1 was prepared from [PdCl(PCP)] with AgOTf. It reacts readily with neutral bidentate ligands [L = 4,4′-bipyridine (4,4′-bpy) and 1,1′-bis(diphenylphosphino)ferrocene (dppf)] to give dinuclear PCP pincers [{Pd(PCP)}₂(μ-L)][OTf]₂ (L = 4,4′-bpy, 2; dppf, 3). [PdCl(PCP)] also reacts with 4-mercaptopyridine in the presence of KOH to give a Lewis basic pincer with a free pyridine functional group [Pd(4-Spy)(PCP)] 4. Its metalloligand character is exemplified by the isolation of an asymmetric dinuclear double-pincer complex [{Pd(PCP)}₂(μ-4-Spy)][PF ₆] 6 bridged by an ambidentate pyridinethiolato ligand. Complexes 1, 2, 3, 4 and 6 have been characterized by single-crystal X-ray diffraction analyses. The Royal Society of Chemistry.

Full text of DOI:10.1039/b710752h

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PAPER
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Dinuclear PCP pincer complexes from Lewis acidic [Pd(OTf)(PCP)] and
basic [Pd(4-Spy)(PCP)] (OTf = triflate; 4-Spy = 4-pyridinethiolate; PCP =
−CH(CH2CH2PPh2)2)†‡
Kian Eang Neo,a Han Vinh Huynh,a Lip Lin Koh,a William Hendersonb and T. S. Andy Hor*a
Received 13th July 2007, Accepted 19th September 2007
First published as an Advance Article on the web 11th October 2007
DOI: 10.1039/b710752h
−
The Lewis acidic pincer with a labile triflate ligand, viz. [Pd(OTf)(PCP)] (PCP = CH(CH2CH2PPh2)2)
1 was prepared from [PdCl(PCP)] with AgOTf. It reacts readily with neutral bidentate ligands [L =
4,4ꢀ-bipyridine (4,4ꢀ-bpy) and 1,1ꢀ-bis(diphenylphosphino)ferrocene (dppf)] to give dinuclear PCP
pincers [{Pd(PCP)}2(l-L)][OTf]2 (L = 4,4ꢀ-bpy, 2; dppf, 3). [PdCl(PCP)] also reacts with
4-mercaptopyridine in the presence of KOH to give a Lewis basic pincer with a free pyridine functional
group [Pd(4-Spy)(PCP)] 4. Its metalloligand character is exemplified by the isolation of an asymmetric
dinuclear double-pincer complex [{Pd(PCP)}2(l-4-Spy)][PF6] 6 bridged by an ambidentate
pyridinethiolato ligand. Complexes 1, 2, 3, 4 and 6 have been characterized by single-crystal X-ray
diffraction analyses.
Introduction
Results and discussions
An emerging trend in pincer chemistry is to construct function-
alized pincer complexes that can enter into an array of di- and
polynuclear pincer systems.1 Such development is encouraged by
their potential applications in catalysis2 and functional materials.3
The unique reactivity of the M–C bonds of cyclometallated pincers
is a key incentive of this development.4 One of the handicaps facing
such research is the lack of versatile and general precursors that
allow di- and polynuclear pincers to be constructed from simple
mononuclear sources. We herein demonstrate such a convenient
entry starting from the established [PdCl(PCP)]5 through Lewis
addition but via two stable intermediates with opposite behavior—
Lewis acidic and basic. This would allow general entry to symmet-
ric and asymmetric dinuclear pincers. This is achieved through the
use of homo- and hetero-difunctional spacers. This methodology
brings major advantages such as simple preparations, stable
precursors/intermediates, and very importantly, application to
substrates that can be Lewis acidic or basic.
Synthesis and characterization of triflate coordinated mononuclear
pincer Pd(II) complex and its ligand displacement with
4,4ꢀ-bipyridine and 1,1ꢀ-bis(diphenylphosphino)ferrocene
The known complex [PdCl(PCP)] readily reacts with excess
AgOTf in CH2Cl2–H2O to give the triflate coordinated complex
[Pd(OTf)(PCP)] 1 in 79% yield (Scheme 1). The changes in proton
(3.45 ppm), carbon (58.3 ppm) and phosphorus (44.84 ppm) shifts
compared to [PdCl(PCP)] (dH = 3.18 ppm, dC = 60.8 ppm,
dP = 41.79 ppm) suggested successful replacement of the chloro
ligand by OTf. Other NMR features are similar to those of
[PdCl(PCP)], suggesting that the pincer fragment is intact. The
triflate ligand of 1 gives a singlet peak at −1.74 ppm in its 19F
NMR spectrum, consistent with equivalent fluorines. Two peaks
at m/z = 545 (major) and m/z = 586 (minor) were observed in
the ESI mass spectra of complex 1. The former peak is assigned
to cationic [Pd(PCP)]+ ions (calculated m/z = 546) while the
latter peak corresponds to the acetonitrile coordinated species
[Pd(CH3CN)(PCP)]+ (calculated m/z = 586). The source of solvate
could be attributed to trace amount of residual CH3CN in the
capillary system.5
aDepartment of Chemistry, National University of Singapore, 3, Science
Drive 3, Singapore 117543. E-mail: andyhor@nus.edu.sg; Fax: +65 6873
1324; Tel: +65 6516 2663
bDepartment of Chemistry, University of Waikato, Private Bag 3105,
Hamilton, New Zealand. E-mail: w.henderson@waikato.ac.nz; Fax: +64
7838 4219; Tel: +64 7838 4656
The ligand displacement reaction of 1 with neutral bidentate
ligands readily occurs to give cationic dinuclear ligand bridged
complexes [{Pd(PCP)}2(l-L)][OTf]2 (L = 4,4ꢀ-bpy, 2; dppf, 3).
† CCDC reference numbers 654026–654029 and 661013. For crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/b710752h
1
31P{ H} NMR analysis gave a downfield shift of the chelating
1
‡ Electronic supplementary information (ESI) available: 31P{ H} NMR
phosphines dP = 49.78 and 55.11 ppm in 2 and 3 respectively
compared to 44.84 ppm in 1 thus suggesting deshielding of the
spectrum of complexes 3 (Fig. S1) and 6 (Fig. S2) recorded in CDCl3. See
DOI: 10.1039/b710752h
Scheme 1 Bridge formation in complexes 2 and 3 from the Lewis acidic 1.
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chelating phosphines upon coordination of the bipyridyl and dppf
ligands.
1
The 31P{ H} NMR spectrum of 3 (Fig. S1‡) suggests the pres-
ence of two chemically inequivalent phosphines (dPdppf = 6.63 ppm
(t); dPpincer = 55.11 ppm (d)) that are strongly coupled to each other
(2J(P,P) = 43.7 Hz is comparable to that of [Pd(Me)(PMe3)3][hfac]
(hfac = hexafluoroacetylacetonate) [2J(P,P) = 43 Hz]).6 The
bridging phosphine (dPdppf = 6.63 ppm) appears more shielded and
2
upfield shifted compared to other dppf-bridged systems, e.g. [{(g -
dppf)PdCl}2(l-dppf)][ClO4]2 (dPdppf = 26.75 ppm)7 and [Pd2(C2,N-
dmpa)2(l-dppf)Cl2] (dmpa = N,N-dimethyl-1-phenethylamine)
1
(dPdppf = 32.7 ppm).8 Its 13C{ H} NMR spectrum shows the
metallated carbon (dC = 79.3 ppm, (dt)) coupling strongly to
the trans phosphine (dppf) (2J(C,Pdppf) = 28 Hz) and weakly to
1
the cis phosphines of the pincer (2J(C,Ppincer) = 3 Hz). 31P{ H}
NMR analysis shows that both 2 and 3 are stable in CDCl3
for up to two weeks but readily undergo ligand displacement
1
in a coordinating solvent. The 31P{ H} NMR spectrum of 2 in
CD3CN shows signal of [Pd(CD3CN)(PCP)][OTf] as the major
species [and two other unidentified minor species with peaks
at 49.52 (s) and 55.51 ppm (s)]. This solvento complex can be
independently prepared from 1 in CD3CN (dP = 51.34 ppm) (cf .
dP = 44.84 ppm for 1 in CDCl3). Such displacement of phosphine
by acetonitrile in Pd(II) is a reversal of the usual observation.9
Its occurrence here is driven by the labilizing effect induced
by the trans M–C bond, and assisted by the steric release and
favourable entropy effect. The steric crowding between dppf and
the pincer moieties is also evident from the distorted geometry
of Pd(II) in 3 (described later) and the upfield proton shift for
the 1H nuclei on the cyclopentadienyl (Cp) rings (2.85 ppm
and 3.00 ppm).
Fig. 1 ORTEP plot of complex 1 with 50% thermal ellipsoids.
Table 1 Selected bond lengths and bond angles of complex 1
˚
Bond lengths/A
Pd(1)–P(1)
Pd(1)–O(1)
C(1)–C(2)
2.3028(6)
2.2106(18)
1.517(4)
Pd(1)–P(2)
Pd(1)–C(1)
C(1)–C(4)
2.3190(6)
2.071(2)
1.530(4)
Bond angles/◦
P(1)–Pd(1)–P(2)
P(2)–Pd(1)–O(1)
P(2)–Pd(1)–C(1)
Pd(1)–C(1)–C(2)
C(2)–C(1)–C(4)
166.24(2)
99.71(6)
83.46(7)
113.12(17)
114.3(2)
P(1)–Pd(1)–O(1)
P(1)–Pd(1)–C(1)
O(1)–Pd(1)–C(1)
Pd(1)–C(1)–C(4)
94.02(6)
83.05(7)
171.66(9)
113.40(17)
1
Complex 3 is largely intact in solution (evident from its 31P{ H}
NMR) but some solvent-induced bridge cleavage is apparent,
1
giving [Pd(g -dppf)(PCP)][OTf], with the pendant dppf at dPdppf
=
−18.1 ppm. The ESI mass spectrum of 3 also indicates the presence
of this mono-cationic species.
Crystal structures of complexes 2 and 3
ESI-MS analysis of 2 gave no parent ionic peak, but showed
fragments at m/z = 545, 586 and 700 corresponding to [1 − OTf−]+
(calculated m/z = 546), [1 − OTf− + CH3CN]+ (calculated m/z =
586) and [1 − OTf− + 4,4ꢀ-bpy]+ (calculated m/z = 702) ions
respectively. The molecular ion (observed m/z = 823; calculated
m/z = 823) was observed in the ESI-MS spectrum of 3 as a major
peak together with [1 − OTf− + dppf]+ (observed m/z = 1099;
calculated m/z = 1100) and [1 − OTf−]+ (observed m/z = 545;
calculated m/z = 546) ion fragments.
The crystal structure of complex 2 shows a dinuclear frame-
work with a bipyridyl ligand bridging across two square planar
Pd(II) pincers (Fig. 2). The coordination plane and pyridyl
ring are significantly deviated from 90◦ (P(1)–Pd(1)–P(2)–C(1)–
N(1)/N(1)–C(6)–C(7)–C(8)–C(9)–C(10) = 80.4◦). This value is
smaller than the angles observed for the related square pla-
nar d8 complexes [(Pt(pip2NCN))2(l-L)]2+ (pip2NCN− = 1,3-
bis(piperidylmethyl)phenyl; L = 4,4ꢀ-bipyridine, pyrazine or trans-
1,2-bis(4-pyridyl)ethylene) in which the dihedral angles between
the Pt(II) coordination planes and pyridyl rings are in the range of
83.3◦ to 89.9◦.12
Crystal structure of complex 1
˚
The Pd–C bond length in 2 [Pd(1)–C(1) = 2.088(4) A] is
The ORTEP plot of complex 1 is shown in Fig. 1. Selected
bond lengths and bond angles are listed in Table 1. The
triflate ligand is coordinated in complex 1 in a monode-
intermediate between that of the triflate complex 1 [Pd–C =
5
˚
˚
2.071(2) A] and [PdCl(PCP)] [Pd(1)–C(1)
=
2.111(7) A]
˚
(Table 2). The Pd–N bond length [Pd(1)–N(1) = 2.187(4) A]
in complex 2 is longer than the Pd–N(pyridyl) bond lengths in
the metallo macrocyclic compounds [{Pd(dppm)(l-L)}2][OTf]4
˚
nate fashion. The Pd–C length of 1 [2.071(2) A] falls in
the range of bond lengths of [Pd(OH2)(PCP-tBu)][BPh4] (PCP-
−
t
10
tBu = CH(CH2CH2P Bu2)2) [2.056(6) A] and [PdCl(PCP)]
(dppm
=
bis(diphenylphosphino)methane;
L
=
NC5H4–3-
˚
5
[2.111(7) A]. The Pd–O bond length of 1 [2.2106(18) A] is longer
than [(dppp)Pd(OH2)(OTf)][OTf] (dppp = 1, 3-bis(diphenyl-
CH2NHCOCONHCH2–3-C5H4N or N,Nꢀ-bis(pyridine-4-yl)-
pyridine-2,6-dicarboxamide) and the polymeric complex
[{Pd(dppp)(l-L)}x][OTf]2x (dppp = 1,3-bis(diphenylphosphino)-
propane; L = N,Nꢀ-bis(pyridine-4-yl)-isophthalamide)) where
˚
˚
11
˚
phosphino)propane) [Pd–OOTf = 2.159(3) A] which is not in-
fluenced by the labilising Pd–C bonds at trans-positions.
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Fig. 3 ORTEP plot of complex 3 with 50% thermal ellipsoids. (The OTf−
anions are omitted for clarity.)
Table 3 Selected bond lengths and bond angles of complex 3
˚
Bond lengths/A
Pd(1)–P(1)
Pd(2)–P(3)
Pd(1)–P(5)
Pd(1)–C(1)
C(1)–C(2)
C(6)–C(7)
2.322(2)
2.313(2)
2.3761(17)
2.122(6)
1.507(10)
1.478(12)
Pd(1)–P(2)
Pd(2)–P(4)
Pd(2)–P(6)
Pd(2)–C(6)
C(1)–C(4)
C(6)–C(9)
2.317(2)
2.303(2)
2.3628(18)
2.130(7)
1.526(9)
1.533(11)
Fig. 2 ORTEP plot of complex 2 with 50% thermal ellipsoids. (The OTf−
anions are omitted for clarity.)
Table 2 Selected bond lengths, bond angles and inter-plane angles of
complex 2
Bond angles/◦
˚
Bond lengths/A
C(1)–Pd(1)–P(5)
P(1)–Pd(1)–P(2)
P(1)–Pd(1)–C(1)
P(3)–Pd(2)–C(6)
P(1)–Pd(1)–P(5)
P(3)–Pd(2)–P(6)
Pd(1)–C(1)–C(2)
Pd(2)–C(6)–C(7)
Pd(1)–P(5)–C(11)
166.9(2)
159.74(7)
81.2(2)
C(6)–Pd(2)–P(6)
P(3)–Pd(2)–P(4)
P(2)–Pd(1)–C(1)
P(4)–Pd(2)–C(6)
P(2)–Pd(1)–P(5)
P(4)–Pd(2)–P(6)
Pd(1)–C(1)–C(4)
Pd(2)–C(6)–C(9)
Pd(2)–P(6)–C(16)
167.9(2)
159.29(8)
80.9(2)
Pd(1)–P(1)
Pd(1)–N(1)
C(1)–C(2)
C(2)–C(3)
C(8)–C(8)#1
2.3242(13)
2.187(4)
1.499(7)
1.453(8)
1.511(8)
Pd(1)–P(2)
Pd(1)–C(1)
C(1)–C(4)
C(4)–C(5)
2.3168(13)
2.088(4)
1.492(7)
1.486(8)
80.7(3)
81.7(2)
99.13(6)
99.16(7)
115.3(5)
115.7(6)
116.5(2)
100.45(7)
100.33(8)
116.8(5)
113.9(5)
118.3(2)
Bond angles/◦
P(1)–Pd(1)–P(2)
P(2)–Pd(1)–N(1)
P(2)–Pd(1)–C(1)
Pd(1)–C(1)–C(2)
C(2)–C(1)–C(4)
164.40(5)
96.42(10)
81.95(13)
113.8(3)
115.2(5)
P(1)–Pd(1)–N(1)
P(1)–Pd(1)–C(1)
N(1)–Pd(1)–C(1)
Pd(1)–C(1)–C(4)
99.04(10)
82.50(13)
176.78(17)
113.2(3)
P(2) = 159.74(7)◦; P(3)–Pd(2)–P(4) = 159.29(8)◦] are significantly
distorted compared to those of the triflate complex 1 (L = OOTf
[C–Pd–O = 171.66(9)◦; Ppincer–Pd–Ppincer = 166.24(2)◦].
)
Synthesis and characterization of mono- and di-nuclear
pyridinethiolato complexes
Inter-plane angle/◦
P(1)–Pd(1)–P(2)–C(1)–N(1)/N(1)–C(6)–C(7)–C(8)–
C(9)–C(10)
80.4
4-Pyridinethiolate (4-Spy−) is a difunctional ligand used to
support hetero-,14 mixed-valent15 and homometallic16 complexes.
Although there has been much literature concerning 4-Spy com-
plexes, pincer Pd(II) and Pt(II) pyridinethiolato complexes have
only been recently reported.17 The complex [PdCl(PCP)] reacts
readily with 4-mercaptopyridine (HSpy) in the presence of KOH18
to give 4 (Scheme 2). The product was characterized by NMR,
ESI-MS, elemental analysis and single crystal X-ray diffraction.
NMR analysis of 4 suggested that replacement of the chlo-
ride in [PdCl(PCP)] (dC = 60.8 ppm; dP = 41.79 ppm) by a
soft pyridinethiolato ligand resulted in deshielding of both the
metallated carbon (dC = 65.3 ppm) and the chelating phosphine
(dP = 46.35 ppm). A major peak at m/z = 656 in the ESI-MS
spectrum can be assigned to the [4 + H]+ ion (calculated m/z =
656). Attempted heterometallic formation with AgNO3 only
resulted in the ligand exchange product [Pd(NO3)(PCP)] 519 and an
insoluble solid that is presumably the polymeric pyridinethiolato
˚
their Pd–N bond lengths are in between 2.095(4) A and
2.114(5) A.13 The lengthening of Pd–N bond length suggests high
˚
trans influence of the metallated carbon in 2.
The crystal structure of complex 3 confirmed a dinuclear
complex bridged by dppf (Fig. 3 and Table 3). As expected,
introduction of a phosphine donor has slightly lengthened and
˚
weakened the Pd–C bond from 2.071(2) A in 1 to an average of
˚
2.126(7) A in 3. This is accompanied by a long Pd–P bond (trans
˚
to Pd–C) of average 2.369(2) A compared to the Pd–P bonds cis
˚
to Pd–C in 3 (av. 2.313(2) A). This weakening is a result of both
steric crowding and trans-influence of the metallated carbon. It
also affects the linearity of C–Pd–L (L = Pdppf) and Ppincer–Pd–Ppincer
angles. The observed C–Pd–L [C(1)–Pd(1)–P(5) = 166.9(2)◦; C(6)–
Pd(2)–P(6) = 167.9(2)◦] and Ppincer–Pd–Ppincer angles [P(1)–Pd(1)–
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Scheme 2 Formation of a Lewis basic pincer metalloligand 4.
complex of Ag(I) (Scheme 3). A similar polymer obtained from
the analogous 2-pyridinethiolate with AgBF4 has been reported.20
−
Use of a weaker anion such as PF6 resulted in the Pd2 bridging
complex 6 and the Ag(I) coordination polymer. Complex 6 is
presumably formed from the addition reaction between 4 and 5,
followed by anionic exchange. To support this, we have obtained
complex 6 independently from 4 and [Pd(OH2)(PCP)][PF6] 7. The
latter could be obtained from [PdCl(PCP)] and AgPF6 in wet
acetone (Scheme 4). Similar BF4− complexes have been prepared.19
Isolation of complex 6 illustrates the potential of 4 as a pincer-
metalloligand that carries active pyridine functionality. Complexes
1 and 4 are both pincers but the former is Lewis acidic whilst the
latter is Lewis basic. As a result, both are suitable precursors
for dinuclear pincers through Lewis addition, except that 1 is
receptive to Lewis bases whilst 4 to Lewis acids. Together, they
could combine with a range of complexes to give dimetallic pincers.
Scheme 4 Synthesis of complex 6 from an addition reaction between the
Lewis basic 4 and Lewis acidic 7.
to the Pd–C bond, giving effectively a metallo-pyridine ligand
(Fig. 4 and Table 4). The C–Pd–S [C–Pd–S = 177.35(8)◦] is
closer to linear as compare to the other analogous complexes
[PdX(PCP)] [X = OTf, C–Pd–O = 171.66(9)◦; X = NO3, C–
Pd–O = 172.16(18)◦], [PdCH3(PCP-tBu)] [C–Pd–C = 171.9(2)◦]
and [Pd(OH2)(PCP-tBu)][BPh4] [C–Pd–O = 171.1(3)◦].10,19 The
Ppincer–Pd–Ppincer angle [P(1)–Pd(1)–P(2) = 155.29(3)◦] is even more
distorted than those of 3 [P(1)–Pd(1)–P(2) = 159.74(7)◦; P(3)–
Pd(2)–P(4) = 159.29(8)◦].
Scheme 3 Reactions of 4 with Ag+ resulting in ligand exchange and
dinuclear formation.
NMR analysis of 6 (1H, 13C{ H} and 31P{ H}) in CDCl3
suggested that its dinuclear framework is retained in solution.
The heterofunctionality of the pyridinethiolate spacer has resulted
in two chemically inequivalent and distinguishable pincer Pd(II)
1
1
Fig. 4 ORTEP plot of complex 4·0.5(CH3)2CO with 50% thermal
1
fragments, as shown in its 31P{ H} NMR spectrum (Fig. S2‡). This
ellipsoids. (Acetone solvate omitted for clarity.)
is an unusual entity in current pincer chemistry. ESI-MS spectrum
−
+
in acetone also gives the molecular ion [6 − PF6
] (observed
The angular geometry at S forces the pyridyl ring to skew to-
wards one half of the molecule and creates a molecular asymmetry.
However, this is not translated to NMR (31P) inequivalence of the
phosphines at either side of the pincer, possibly due to rapid ligand
dynamics in solution.
m/z = 1200; calculated = 1202). The soft–hard hybrid character
of Pd(II) is evident in the formation of 6.
Crystal structures of complexes 4 and 6
Single-crystal diffraction analysis of 4 shows the preference of
the Pd(II) center towards the more basic thiolato function trans
The crystal structure of 6 shows two pincer Pd(II) fragments
bridged by a pyridinethiolato ligand (Fig. 5 and Table 4). The
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Table 4 Selected bond lengths and bond angles of complexes
4·0.5(CH3)2CO and 6
4·0.5(CH3)2CO
6
˚
Bond lengths/A
Pd(1)–P(1)
Pd(1)–P(2)
Pd(2)–P(3)
Pd(2)–P(4)
Pd(1)–S(1)
Pd(2)–N(1)
Pd(1)–C(1)
Pd(2)–C(6)
C(1)–C(2)
C(1)–C(4)
C(6)–C(7)
C(6)–C(9)
2.3013(7)
2.2824(8)
—
—
2.4027(8)
—
2.117(3)
—
1.528(4)
1.522(4)
—
2.2896(8)
2.2804(8)
2.3036(9)
2.2832(9)
2.4298(8)
2.140(3)
2.099(3)
2.080(3)
1.520(4)
1.522(4)
1.530(5)
1.501(6)
—
Bond angles/◦
C(1)–Pd(1)–S(1)
C(6)–Pd(2)–N(1)
P(1)–Pd(1)–P(2)
P(3)–Pd(2)–P(4)
P(1)–Pd(1)–C(1)
P(2)–Pd(1)–C(1)
P(3)–Pd(2)–C(6)
P(4)–Pd(2)–C(6)
P(1)–Pd(1)–S(1)
P(2)–Pd(1)–S(1)
P(3)–Pd(2)–N(1)
P(4)–Pd(2)–N(1)
Pd(1)–C(1)–C(2)
Pd(1)–C(1)–C(4)
Pd(2)–C(6)–C(7)
Pd(2)–C(6)–C(9)
Pd(1)–S(1)–C(pyridyl):
177.35(8)
—
155.29(3)
—
82.33(8)
81.71(8)
—
175.45(8)
176.13(13)
163.43(3)
165.37(3)
82.64(9)
−
Fig. 6 View of complex 6 along the C(1)–Pd(1)–S(1) axis. (The PF6
anion are omitted for clarity.)
Ppincer angles [P(1)–Pd(1)–P(2) = 163.43(3)◦; P(3)–Pd(2)–P(4) =
165.37(3)◦] fall in the range of C–Pd–L [171.1(3)◦ –177.35(8)◦] and
Ppincer–Pd–Ppincer angles [155.29(3)◦ –167.1(1)◦] observed in similar
complexes.5,10,19 Table 5 lists selected NMR chemical shift and
crystallographic data for complexes 1, 2, 3, 4, 6 and those of
[PdCl(PCP)] for comparison.
82.97(9)
82.88(11)
82.57(11)
99.45(3)
95.51(3)
98.26(7)
96.18(7)
114.1(2)
113.7(2)
112.6(3)
—
96.31(3)
100.31(3)
—
—
113.96(18)
115.83(19)
—
Conclusions
—
114.2(3)
Pd(1)–S(1)–C(13)
104.10(10)
Pd(1)–S(1)–C(6)
112.73(11)
We have demonstrated herein how dinuclear and bimetallic pincers
can be easily prepared from either Lewis basic or acidic precursor
complexes. Both homofunctional and difunctional spacers can
be accommodated in this synthetic methodology. These successes
have opened up a number of permutations in di-pincer assemblies
in terms of the choice of metals, spacers and geometries. Our next
target is to use similar methodologies to design di- and polynuclear
pincers with specific catalytic and materials functions.
Experimental
General procedures and materials
All reagents were commercial products and were used without fur-
ther purification. Complex [PdCl(PCP)]5 was prepared according
to the reported procedure. All organic solvents were freshly dried
using molecular sieves. Elemental analyses were performed by the
Chemical, Materials and Molecular Analysis Center (CMMAC)
NUS.
−
Fig. 5 ORTEP plot of complex 6 with 50% thermal ellipsoids. (The PF6
anion are omitted for clarity.)
NMR spectroscopy
relatively small spacer allows the two bulky fragments to come
to proximity without creating steric conflict. This is achieved by
bending the pyridine ring out of the Pd(II) coordination plane, such
that the entering Pd(II) plane can anchor with maximum space.
This is best realised from the molecular view along the C–Pd–S
axis (Fig. 6). With minimal conflicts, the C–Pd–L [C(1)–Pd(1)–
S(1) = 175.45(8)◦; C(6)–Pd(2)–N(1) = 176.13(13)◦] and Ppincer–Pd–
◦
The NMR spectra were measured at 25 C using a Bruker ACF
300 NMR spectrometer. Chemical shifts are reported relative to
TMS where d CHCl3 = 7.26 ppm (1H) or d CDCl3 = 77.1 ppm
1
1
(13C{ H}) unless otherwise stated. The 31P{ H} NMR spectra were
externally referenced to 85% H3PO4 at 121.39 MHz while 19F{ H}
1
NMR spectra were referenced to CF3COOH at 282.38 MHz.
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Table 5 Comparison of selected NMR (recorded in CDCl3) and crystallographic data for complexes [PdCl(PCP)], 1, 2, 3, 4·0.5(CH3)2CO and 6
Chemical shift (ppm)
[PdCl(PCP)]b
1
2
3
4·0.5(CH3)2CO
3.20
6
dHa
dCa
dPa
3.18
3.45
3.43
3.66
3.17d
3.32e
60.8
58.3
60.2
79.3c
65.3
59.5e
66.3d
41.79
44.84
49.78
55.11
46.35
47.05d
48.29e
˚
Bond length/A
Pd–L
Pd(1)–Cl(1)
Pd(1)–O(1)
Pd(1)–N(1)
Pd(1)–P(5)
Pd(2)–P(6)
Pd(1)–S(1)
2.431(2)
—
—
—
—
—
—
—
2.187(4)
—
—
—
—
—
—
—
—
—
—
2.4027(8)
—
—
2.140(3)
—
—
2.2106(18)
—
—
—
—
2.3761(17)
2.3628(18)
—
—
—
2.4298(8)
Pd–C
Pd(1)–C(1)
Pd(2)–C(6)
2.111(7)
—
2.071(2)
—
2.088(4)
—
2.122(6)
2.130(7)
2.117(3)
—
2.099(3)
2.080(3)
Pd–Ppincer
Pd(1)–P(1)
Pd(1)–P(2)
Pd(2)–P(3)
Pd(2)–P(4)
2.313(2)
2.304(2)
—
2.3028(6)
2.3190(6)
—
2.3242(13)
2.3168(13)
—
2.322(2)
2.317(2)
2.313(2)
2.303(2)
2.3013(7)
2.2824(8)
—
2.2896(8)
2.2804(8)
2.3036(9)
2.2832(9)
—
—
—
—
a dH refers to the 1H chemical shift of the proton attached to the metallated carbon; dC refers to the 13C chemical shift of the metallated carbon; dP refers
to the 31P chemical shift of the chelating phosphine. b Reference 5. c Recorded in CD2Cl2. d S bonded pincer moiety. e N bonded pincer moiety.
X-Ray crystallography†
patterns were calculated using the MS/MS IsoPro24 computer
program.
Data were collected on a Bruker AXS CCD diffractometer with
Mo-Ka radiation (k = 0.71073 A). The software SMART
21
˚
Preparation of [Pd(OTf)(PCP)] 1
was used for data frame collection, indexing reflections, and
determining lattice parameters. The integration of intensity of
reflections and scaling was done by using SAINT21; SADABS22
was used for empirical absorption correction and SHEXTL23 for
space group determination, refinements, graphics and structure
reporting. The parameters for crystal structure determinations of
complexes 1, 2, 3, 4·0.5(CH3)2CO and 6 are listed in Table 6.
CCDC reference numbers 654026–654029 and 661013.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b710752h
Complex [PdCl(PCP)] (0.43 g, 0.74 mmol) was dissolved in
degassed CH2Cl2 (20 ml). To the solution was added a solution of
excess AgOTf (0.77 g, 3.00 mmol) in deionised water (5 ml). The
mixture was stirred overnight shielded from light. The resultant
solution was filtered through Celite to remove the AgCl formed.
The product was extracted into CH2Cl2 and the organic fraction
was dried using anhydrous MgSO4. After removing MgSO4
through filtration, the dried solution was concentrated to a small
volume under reduced pressure. Addition of Et2O (10 ml) gave
a milky white powder of 1 (0.41 g, 79%). The colorless X-ray
quality crystals of complex 1 were grown by layering Et2O onto a
concentrated CH2Cl2 solution of 1.
Electrospray ionisation mass spectrometry (ESI-MS)
Mass spectra were recorded in positive ion mode using a Thermo
Finningan LCQ spectrometer. MeOH or a MeOH–H2O mixture
(80 : 20 v/v) was used as the mobile phase. The compounds were
dissolved in CH2Cl2 or acetone and were diluted using the mobile
phase. Only the molecular ions or their related fragment ions
are reported here. Peaks were assigned from the m/z values and
confirmation of species was aided by comparison of the observed
and predicted isotope distribution patterns. The predicted isotope
Analytical data for 1. (Found: C, 51.85 H, 4.19. Anal. Calcd
for C30H29P2PdF3SO3: C, 51.85 H, 4.17) H NMR (CDCl3) (d):
1
1.58–1.71 (m, 4H, PCH2CH2), 2.10 (t, br, 2H, PCH2CH2), 2.58
(m, 2H, PCH2CH2), 3.45 (t, br, 1H, PdCH), 7.43–7.93 (m, 20H,
1
Ph). 13C{ H} NMR (CDCl3) (d): 29.2 (t, 2C, PCH2CH2, J(C,P) =
13 Hz), 36.9 (t, 2C, PCH2CH2, J(C,P) = 6 Hz), 58.3 (s, br, 1C,
PdC), 119.8 (q, 1C, OTf−, J(C,F) = 319 Hz), 128.7 (t, 4C, Ph,
J(C,P) = 6 Hz), 128.9 (t, 4C, Ph, J(C,P) = 5 Hz), 129.9 (t, 2C, Ph,
5706 | Dalton Trans., 2007, 5701–5709
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Table 6 Parameters for data collection and structure refinement of 1, 2, 3, 4·0.5(CH3)2CO and 6
1
2
3
4·0.5(CH3)2CO
6
Chemical formula
Formula weight
Crystal system
Space group
C30H29F3O3P2PdS C70H66F6N2O6P4Pd2S2
C94H86F6FeO6P6Pd2S2
1944.22
Orthorhombic
Pbca
21.0633(8)
21.6510(8)
39.0514(15)
90
C35.50H36NO0.50P2PdS
685.05
Monoclinic
C2/c
22.749(3)
9.4172(12)
29.902(4)
90
97.231(3)
90
6355.2(14)
8
C63H62F6NP5Pd2S
1346.85
Monoclinic
P2(1)/c
12.9468(5)
17.4888(7)
26.5948(11)
90
91.388(10)
90
6019.9(4)
4
694.93
Triclinic
¯
P1
1546.05
Monoclinic
P2(1)/c
10.0040(14)
17.732(2)
18.719(3)
90
101.490(4)
90
3253.9(8)
2
˚
a/A
9.4270(7)
10.6781(8)
15.8613(12)
98.489(2)
93.482(2)
114.8970(10)
1418.89(18)
2
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
90
90
3
˚
Volume/A
17 809.1(12)
8
1.450
Z
qcacld/Mg m−3
l/mm−1
1.627
0.892
1.578
0.788
1.432
0.778
1.486
0.824
0.780
T/K
223(2)
18 705
223(2)
23 012
7463
223(2)
101 270
15 676
223(2)
40 276
7280
223(2)
77 929
13 826
No. of reflections collected
No. of independent reflections 6515
R(int)
0.0272
361
1.066
0.0313
0.0726
0.0356
0.0780
0.0692
415
1.038
0.0637
0.1244
0.1025
0.1381
0.1513
1053
0.993
0.0675
0.1508
0.1336
0.1768
0.0513
388
1.149
0.0418
0.0866
0.0498
0.0897
0.0429
703
1.182
0.0482
0.1021
0.0573
0.1058
No. of parameters
Goodness-of-fit
R1 (I > 2r(I))
wR2 (I > 2r(I))
R1 (all data)
wR2 (all data)
J(C,P) = 20 Hz), 130.6 (s, 2C, Ph), 131.0 (s, 2C, Ph), 131.8 (t, 2C,
Ph, J(C,P) = 20 Hz), 132.5 (t, 4C, Ph, J(C,P) = 7 Hz), 133.7 (t,
(d): −1.97 (s, 3F, OTf). ESI-MS (m/z, %): [1 − OTf−]+ (545, 100);
[1 − OTf− + CH3CN]+ (586, 28); [1 − OTf− + 4, 4ꢀ-bpy]+ (700, 37)
1
4C, Ph, J(C,P) = 7 Hz). 31P{ H} NMR (CDCl3) (d): 44.84 (s, 2P,
1
PPh2). 19F{ H} NMR (CDCl3) (d): −1.74 (s, 3F, OTf−). ESI-MS
Preparation of [{Pd(PCP)}2(l-dppf)][OTf]2 3
(m/z, %): [1 − OTf−]+ (545, 100), [1 − OTf− + CH3CN]+ (587, 8)
The reaction and the crystallisation were carried out using
degassed solvent. Complex 1 (0.10 g, 0.14 mmol) and dppf (0.04 g,
0.07 mmol) were mixed in CH2Cl2 (20 ml) and stirred under N2
atmosphere overnight. The solution was then pumped dry to give
an orange powder and was washed with hexane (5 ml) and diethyl
ether (5 ml). The solid was dissolved in CH2Cl2 (5 ml) and addition
of diethyl ether (25 ml) gave a orange powder of complex 3 (0.09 g,
66%). Orange X-ray quality crystals were grown by diffusion of
diethyl ether into a concentrated CH2Cl2 solution of 3 under an
N2 atmosphere.
Preparation of [{Pd(PCP)}2(l-4,4ꢀ-bpy)][OTf]2 2
Complex 1 (0.10 g, 0.14 mmol) and 4,4ꢀ-bpy (0.01 g, 0.07 mmol)
were mixed in degassed acetone (20 ml). The solution was allowed
to stir for 2 h at room temperature. The colourless solution was
then filtered through Celite to remove a trace amount of solid.
The solution was then pumped dry to give a white powder. The
white powder was washed with hexane (3 ml), toluene (3 ml) and
diethyl ether (3 ml). The solid was then dissolved in acetone (5 ml)
and addition of diethyl ether (25 ml) gave a white powder of 2
(0.07 g, 65%). Colorless X-ray quality crystals of 2 were grown by
layering of hexane to a concentrated CH2Cl2 solution of 2. Signals
Analytical data for 3. (Found: C, 58.24 H, 4.66. Anal Calcd for
1
C94H86P6Pd2FeF6S2O6 : C, 58.09 H, 4.42) H NMR (CDCl3) (d):
1.31 (m, 4H, PCH2CH2), 1.82 (m, 4H, PCH2CH2 overlapped with
H2O peak), 2.28 (t, br, 4H, PCH2CH2), 2.43 (m, 4H, PCH2CH2),
2.85 (s, 4H, Cp), 3.00 (s, 4H, Cp), 3.66 (t, br, 2H, PdCH),
1
corresponding to OTf− anions were not observed in the 13C{ H}
NMR spectrum, probably due to its low intensity and overlapping
with pyridyl signals.
1
6.72–7.58 (m, 60H, PPh2). 13C{ H} NMR (CD2Cl2) (d): 35.4 (t,
Analytical data for 2. (Found: C, 54.40 H, 4.14 N, 1.89. Anal
4C, PCH2CH2, J(C,Ppincer) = 3 Hz), 35.9 (td, 4C, PCH2CH2,
J(C,Ppincer) = 13 Hz, J(C,Pdppf) = 5 Hz), 72.3 (d, 4C, Cp, J(C,Pdppf) =
8 Hz), 73.3 (d, 4C, Cp, J(C,Pdppf) = 12 Hz), 76.5 (dt, 2C, Cp,
J(C,Pdppf) = 82 Hz, J (C,Ppincer) = 5 Hz), 79.3 (dt, 2C, PdC,
J(C,Pdppf) = 28 Hz, J(C,Ppincer) = 3 Hz), 121.4 (q, 1C, OTf−,
J(C,F) = 322 Hz), 126.7 (t, 4C, PPh2, J(C,Ppincer) = 22 Hz), 128.7
(t, 8C, PPh2, J(C,Ppincer) = 5 Hz), 128.8 (d, 8C, PPh2, J(C,Ppincer) =
5 Hz), 129.3 (d, 8C, PPh2, J(C,Ppincer) = 5 Hz), 130.1 (t, 4C, PPh2,
J(C,Ppincer) = 22 Hz), 130.5 (s, 4C, PPh2), 131.0 (d, 4C, PPh2,
J(C,Ppincer) = 39 Hz), 131.4 (s, 4C, PPh2), 132.0 (t, 8C, PPh2,
J(C,Ppincer) = 6 Hz), 132.6 (s, 4C, PPh2), 133.7 (d, 8C, PPh2,
J(C,Ppincer) = 14 Hz), 135.1 (t, 8C, PPh2, J(C,Ppincer) = 7 Hz).
1
Calcd for C70H66P4Pd2N2F6S2O6 : C, 54.42 H, 4.27 N, 1.81) H
NMR (CDCl3) (d): 1.83–2.02 (m, 8H, PCH2CH2), 2.31 (t, br, 4H,
PCH2CH2), 2.63 (m, 4H, PCH2CH2), 3.43 (t, br, 2H, PdCH), 7.15–
7.52 (m, 40H, Ph), 7.71 (d, 4H, pyridyl), 8.14 (d, 4H, pyridyl).
1
13C{ H} NMR (CDCl3) (d): 30.9 (t, 4C, PCH2CH2, J(C,P) =
13 Hz), 36.9 (t, 4C, PCH2CH2, J(C,P) = 6 Hz), 60.2 (s, br, 2C,
PdC), 123.8 (s, br, 4C, pyridyl), 129.1 (t, 4C, Ph, J(C,P) = 21 Hz),
129.5 (t, 8C, Ph, J(C,P) = 5 Hz), 129.8 (t, 8C, Ph, J(C,P) = 5 Hz),
130.2 (t, 4C, Ph, J(C,P) = 20 Hz), 131.5 (s, 4C, Ph), 131.7 (t, 8C,
Ph, J(C,P) = 7 Hz), 132.0 (s, 4C, Ph), 133.0 (t, 8C, Ph, J(C,P) =
1
7 Hz), 145.0 (s, br, 2C, pyridyl), 151.8 (s, br, 4C, pyridyl). 31P{ H}
1
1
NMR (CDCl3) (d): 49.78 (s, 4P, PPh2). 19F{ H} NMR (CDCl3)
31P{ H} NMR (CDCl3) (d): 6.63 (t, 2P, PPh2, J(P,P) = 43.7 Hz),
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1
55.11 (d, 4P, PPh2, J(P,P) = 43.7 Hz). 19F{ H} NMR(CDCl3) (d):
2C, PCH2CH2, J(C,P) = 6 Hz), 36.6 (t, 2C, PCH2CH2, J(C,P) =
7 Hz), 59.5 (s, br, 1C, PdC), 66.3 (s, br, 1C, PdC), 128.1 (t, 4C, Ph,
J(C,P) = 5 Hz), 128.8 (t, 4C, Ph, J(C,P) = 5 Hz), 129.2 (t, 4C, Ph,
J(C,P) = 5 Hz), 129.3 (s, 2C, pyridyl), 129.6 (t, 4C, Ph, J(C,P) =
5 Hz), 129.8 (s, 2C, Ph), 130.3 (t, 2C, Ph, J(C,P) = 20 Hz), 130.8 (s,
2C, Ph), 130.9 (s, 2C, Ph), 131.1 (t, 2C, Ph, J(C,P) = 20 Hz), 131.2
(t, 2C, Ph, J(C,P) = 20 Hz), 131.7 (s, 2C, Ph), 132.0 (t, 4C, Ph,
J(C,P) = 6 Hz, overlapped with upper face phenyl C2/C6 signal
of Pd fragment bonded to S), 132.0 (t, 4C, Ph, J(C,P) = 6 Hz,
overlapped with upper face phenyl C2/C6 signal of Pd fragment
bonded to pyridine), 132.9 (t, 2C, Ph, J(C,P) = 20 Hz), 133.2 (t,
4C, Ph, J(C,P) = 7 Hz), 133.8 (t, 4C, Ph, J(C,P) = 7 Hz), 146.3
−1.81 (s, 3F, OTf−). ESI-MS (m/z, %): [3 − 2OTf−]2+ (823, 100),
[1 − OTf− + dppf]+ (1099, 53), [1 − OTf−]+ (545, 43)
Preparation of [Pd(4-Spy)(PCP)]·0.5 (CH3)2CO [4·0.5(CH3)2CO]
4-Mercatopyridine (0.50 g, 0.86 mmol) was dissolved in MeOH
(10 ml). To this solution was added KOH (0.07 g, 1.29 mmol).
This mixture was stirred for 15 min and then added to a solution
of [PdCl(PCP)] prepared by dissolving the complex (0.14 g,
1.29 mmol) in CH2Cl2–acetone mixture (1 : 1 v/v) (total volume =
20 ml). The yellow solution turned orange immediately after
addition. The orange solution was stirred overnight, filtered and
dried under vacuum. The orange solid was dissolved in CH2Cl2
(20 ml) and extracted with H2O (10 ml) to remove excess ligand.
The organic extract was dried using anhydrous MgSO4, filtered
through Celite and concentrated to a small volume under reduced
pressure. Addition of hexane (30 ml) followed by filtration gave a
yellow powder of complex 4 (0.49 g, 87%). Orange X-ray quality
crystals were grown by slow evaporation of an acetone solution of
4. The presence of acetone solvent in the complex was confirmed
1
(s, 1C, pyridyl), 168.2 (s, 2C, pyridyl). 31P{ H} NMR (CDCl3) (d):
−143.51 (sep, 1P, PF6−, J(F,P) = 712.5 Hz), 47.05 (s, 2P, PPh2),
1
−
48.29 (s, 2P, PPh2). 19F{ H} NMR(CDCl3) (d): 2.57 (d, 6F, PF6
,
−
+
J(F,P) = 711.6 Hz). ESI-MS (m/z, %): [1 − OTf
] (545,100),
[1 − OTf + CH3CN]+ (586, 33), [4 + H+]+ (656, 69), [6 − PF6
]
−
+
(1200, 50)
Preparation of [Pd(OH2)(PCP)][PF6] 7
by elemental analysis, 1H and 13C{ H} NMR spectroscopy.
1
[PdCl(PCP)] (0.05 g, 0.09 mmol) was dissolved in acetone (15 ml).
To this solution was then added an aqueous solution of AgPF6
(0.10g, 0.43 mmol) in deionised H2O (5 ml). The solution mixture
was stirred for 1 h and then filtered through Celite to remove
AgCl formed. The filtrate was then pumped dry and washed with
deionised water (3 × 5 ml) followed by diethyl ether (2 × 5 ml). The
solid was dissolved in acetone and dried with anhydrous MgSO4.
The solution was filtered and dried under vacuum. The brownish–
yellow powder was washed with Et2O (2 × 3 ml) to give complex
7 (0.02 g, 39%). Signals corresponding to phosphorus bound aryl
Analytical data for [4·0.5(CH3)2CO]. (Found: C, 61.45 H, 5.32
N, 1.93 S, 4.56. Anal Calcd for C34H33P2PdNS·0.5(CH3)2CO: C,
61.55 H, 5.40 N, 2.08 S, 4.76) 1H NMR (CDCl3) (d): 1.70 (m, 2H,
PCH2CH2), 1.90 (m, 2H, PCH2CH2), 2.17 (s, 6H, CH3, acetone),
2.29 (t, br, 2H, PCH2CH2), 2.70 (m, 2H, PCH2CH2), 3.20 (t, br, 1H,
PdCH), 6.94 (d, 2H, pyridyl), 7.21–7.78 (m, 22H, Ph + pyridyl).
13C{ H} NMR (CDCl3) (d): 30.9 (s, 2C, CH3, acetone), 32.3 (t,
1
2C, PCH2CH2, J(C,P) = 12 Hz), 36.4 (t, 2C, PCH2CH2, J(C,P) =
6 Hz), 65.3 (t, br, 1C, PdC, J(C,P) = 3 Hz), 128.4 (s, br, 2C, pyridyl),
128.5 (t, 4C, Ph, J(C,P) = 5 Hz), 128.8 (t, 4C, Ph, J(C,P) = 5 Hz),
130.4 (s, 2C, Ph), 130.7 (s, 2C, Ph), 131.6 (t, 2C, Ph, J(C,P) =
20 Hz), 132.3 (t, 4C, Ph, J(C,P) = 6 Hz), 132.9 (t, 2C, Ph, J(C,P) =
21 Hz), 133.6 (t, 4C, Ph, J(C,P) = 6 Hz), 143.5 (s, 1C, pyridyl),
1
carbon atoms were not observed in the 13C{ H} NMR spectrum
due to its low intensity.
1
Analytical data for 7. 13C{ H} NMR (CDCl3) (d): 29.2 (t, 2C,
PCH2CH2, J(C,P) = 13 Hz), 36.9 (t, 2C, PCH2CH2, J(C,P) =
6 Hz), 59.2 (s, br, 1C, PdC), 129.3 (t, 4C, Ph, J(C,P) = 4 Hz), 129.5
(t, 4C, Ph, J(C,P) = 6 Hz), 131.2 (s, 2C, Ph), 131.7 (s, 2C, Ph),
132.0 (t, 4C, Ph, J(C,P) = 7 Hz), 133.5 (t, 4C, Ph, J(C,P) = 7 Hz).
165.6 (s, 2C, pyridyl), 207.7 (s, 1C, CO, acetone). 31P{ H} NMR
1
(CDCl3) (d): 46.35 (s, 2P, PPh2). ESI-MS (m/z, %): [4 + H+]+ (656,
100)
1
31P{ H} NMR (CDCl3) (d): 46.46 (s, 2P, PPh2), −143.82 (sep, 1P,
1
PF6−, J(F,P) = 713.2 Hz). 19F{ H} NMR (CDCl3) (d): 3.31 (d, 6F,
Preparation of [{Pd(PCP)}2(l-4-Spy)][PF6] 6
−
+
PF6−, J(F,P) = 714.4 Hz). ESI-MS (m/z, %): [7 − H2O − PF6
]
[PdCl(PCP)] (0.05 g, 0.09 mmol) was dissolved in acetone (15 ml).
To this solution was then added an aqueous solution of AgPF6
(0.07 g, 0.26 mmol) in deionised H2O (5 ml). The solution mixture
was stirred for 1 h and then filtered through Celite to remove AgCl
formed. The filtrate was evaporated to dryness and washed with
deionised water (3 × 5 ml) followed by diethyl ether (2 × 5 ml). The
brownish yellow solid (complex 7) obtained was then dissolved in
CH2Cl2 and complex 4 (0.06 g, 0.09 mmol) was added to the
solution. After stirring at r.t. for 2 h, the solution was filtered.
The yellow filtrate was concentrated and filtered. Diffusion with
diethyl ether gave yellow crystals of complex 6 (0.02 g, 18%).
(545, 100), [7 − H2O − PF6 + CH3CN]+ (586, 19)
−
Acknowledgements
We acknowledge the National University of Singapore (NUS)
(Grant no: R143-000-200-112) and the University of Waikato for
financial and technical support. We are indebted to the assistance
of Dr L. L. Koh and Ms. G. K. Tan for X-ray analysis. K. E. N.
thanks NUS for a research scholarship.
References
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5708 | Dalton Trans., 2007, 5701–5709
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