A versatile diphosphine ligand: Cis and trans chelation or bridging, with self association through hydrogen bonding

Article abstract of DOI:10.1021/ic400576m

The diphosphine ligand, N,N′-bis(2-diphenylphosphinoethyl) isophthalamide, dpipa, contains two amide groups and can form cis or trans chelate complexes or cis,cis or trans,trans bridged complexes. The amide groups are likely to be involved in intramolecular or intermolecular hydrogen bonding. This combination of properties of the ligand dpipa leads to very unusual structural properties of its complexes, which often exist as mixtures of monomers and dimers in solution. In the complex [Au₂(μ-dpipa) ₂]Cl₂, the ligands adopt the trans,trans bridging mode, with linear gold(I) centers, and the amide groups hydrogen bond to the chloride anions. In [Pt₂Cl₄(μ-dpipa)₂], the ligands adopt the cis,cis bridging mode, with square planar platinum(II) centers, and the amide groups form intermolecular hydrogen bonds to the chloride ligands to form a supramolecular one-dimensional polymer. Both the monomeric and dimeric complexes [PtMe₂(dpipa)] and [Pt₂Me₄(μ- dpipa)₂] have cis-PtMe₂ units with cis chelating or cis,cis bridging dpipa ligands respectively; each forms a supramolecular dimer through hydrogen bonding between amide groups and each contains an unusual NH···Pt interaction. An attempted oxidative addition reaction with methyl iodide gave the complex [PtIMe(dpipa)], which contains trans chelating dpipa, while a reaction with bromine gave a disordered complex with approximate composition [Pt₂Me₃Br₅(μ- dpipa)₂], which contains trans,trans bridging dpipa ligands.

Full text of DOI:10.1021/ic400576m

Article
pubs.acs.org/IC
A Versatile Diphosphine Ligand: cis and trans Chelation or Bridging,
with Self Association through Hydrogen Bonding
Nasser Nasser, Aneta Borecki, Paul D. Boyle, and Richard J. Puddephatt*
Department of Chemistry, University of Western Ontario, London, Canada N6A 5B7
S
* Supporting Information
ABSTRACT: The diphosphine ligand, N,N′-bis(2-diphenylphosphinoethyl)-
isophthalamide, dpipa, contains two amide groups and can form cis or trans
chelate complexes or cis,cis or trans,trans bridged complexes. The amide groups
are likely to be involved in intramolecular or intermolecular hydrogen bonding.
This combination of properties of the ligand dpipa leads to very unusual struc-
tural properties of its complexes, which often exist as mixtures of monomers
and dimers in solution. In the complex [Au2(μ-dpipa)2]Cl2, the ligands adopt
the trans,trans bridging mode, with linear gold(I) centers, and the amide groups
hydrogen bond to the chloride anions. In [Pt2Cl4(μ-dpipa)2], the ligands adopt
the cis,cis bridging mode, with square planar platinum(II) centers, and the
amide groups form intermolecular hydrogen bonds to the chloride ligands to
form a supramolecular one-dimensional polymer. Both the monomeric and
dimeric complexes [PtMe2(dpipa)] and [Pt2Me4(μ-dpipa)2] have cis-PtMe2
units with cis chelating or cis,cis bridging dpipa ligands respectively; each forms a supramolecular dimer through hydrogen
bonding between amide groups and each contains an unusual NH···Pt interaction. An attempted oxidative addition reaction with
methyl iodide gave the complex [PtIMe(dpipa)], which contains trans chelating dpipa, while a reaction with bromine gave a
disordered complex with approximate composition [Pt2Me3Br5(μ-dpipa)2], which contains trans,trans bridging dpipa ligands.
Chart 1. Some Diphosphine-Dicarboxamide Ligands
INTRODUCTION
■
Diphosphines have played a critical role in the development of
coordination chemistry and its applications. They can be designed
to act as cis or trans chelate ligands or as bridging ligands, they
may contain additional functional groups such as hydrogen bonding
groups or nitrogen donor groups, and they bind strongly to softer
metal ions in a wide range of oxidation states.1,2 Diphosphine-
carboxamides in particular have been termed “the inconspicuous
gems” and their metal complexes have found roles in catalysis
and as potential pharmaceuticals.3,4 We have been interested in
developing the chemistry of diphosphine-dicarboxamides for use in
molecular materials.5 The strategy is to use dynamic coordination
chemistry6 or dynamic ring-opening polymerization,7 using the
phosphine donor groups, to prepare the primary structure, and then
to use the carboxamide groups to increase the dimensionality or to
engage in host−guest chemistry.8 This paper reports a new diphos-
phine ligand, N,N′-bis(2-diphenylphosphinoethyl)isophthalamide,
dpipa, and its complexes with gold(I) and platinum(II). The ligand
can be considered as analogous to the previously studied ligands
shown in Chart 1, namely, dppbH, which tends to form cis or trans
chelate complexes,9 and dppeta, which tends to act as a bridging
ligand.5 The new ligand dpipa can adopt any of these binding
modes and so promises a particularly rich coordination and
supramolecular chemistry.
2-(diphenylphosphino)ethylamine in the presence of base
(Scheme 1). It was isolated, after flash chromatography, as a
white solid. The ligand dpipa was characterized in the 1H NMR
spectrum, by well separated NH, CH2N, and CH2P resonances
at δ 6.35, 3.65, and 2.44 respectively, and, in the 31P NMR
spectrum, by a singlet at δ −21.05.
The reaction of dpipa with [AuCl(SMe2)] in a 1:1 ratio
gave complex 1, which appears to exist in solution as a
mixture of the monomer 1a and dimer 1b, as shown in
Scheme 2.
The equilibrium was most easily monitored by recording
the 31P NMR spectrum in CDCl3 at different concentrations, as
RESULTS
■
The new ligand N,N′-bis(2-diphenylphosphinoethyl)isophthalamide,
Received: March 7, 2013
dpipa, was prepared by reaction of isophthaloyl dichloride with
© XXXX American Chemical Society
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Scheme 1. Synthesis of the Ligand dpipa
Scheme 2. Proposed Equilibrium between Complexes 1a
and 1b
Figure 2. View of the structure of complex 1b. Selected bond
parameters: Au(1)−P(1) 2.308(1), Au(1)−P(2A) 2.313(1),
Au(1)···Cl(A) 3.398(2), Cl···N(2) 3.341(4), Cl···N(1) 3.377(5) Å;
P(1)−Au(1)−P(2A) 174.82(4), Cl(A)−Au(1)−P(2A) 86.50(3), Cl-
(A)−Au(1)−P(1) 90.18(3)°. Symmetry equivalent: A, 1−x, 1−y, −z.
which is a common motif for anion binding by isophtha-
lamide derivatives.7a,10 The positions of the chloride ions, with
angles Cl(A)−Au(1)−P(2A) 86.50(3) and Cl(A)−Au(1)−
P(1) 90.18(3)°, suggest there may be a weak AuCl interaction,
but this is likely to be mostly ionic in character. The gold
centers are separated by 9.00 Å. We have not been able to
crystallize complex 1a, and the structure proposed in Scheme 2
is therefore less certain. In addition, it is noted that for 1b to
give a singlet resonance in the 31P NMR spectrum the complex
must be fluxional.
shown in Figure 1. At low concentration, the complex was
present almost entirely as the monomer 1a, but at higher
The reaction of cis/trans-[PtCl2(SMe2)2] with dpipa occurred
with displacement of dimethylsulfide to give complex 2, which
existed in solution as a mixture of the monomer cis-[PtCl2-
(dpipa)], 2a, and dimer cis,cis-[Pt2Cl4(μ-dpipa)2], 2b (Scheme 3).
Scheme 3. Dichloroplatinum(II) Complexes 2a and 2b
Figure 1. 31P NMR spectrum of complex 1 as a function of
concentration in CDCl3 (0.5 mL): (a) 10 mg; (b) 50 mg; (c) 100 mg.
concentrations the dimer 1b was also observed. The monomer
1a gave a singlet at δ(31P) 31.85 while dimer 1b gave a singlet
at δ(31P) 34.24. The electrospray ionization mass spectrometry
(ESI-MS) of complex 1 dissolved in dichloromethane gave two
major peaks; one at m/z = 1605.3, which corresponds to the
+
ion [Au2(μ-dpipa)2]Cl , formed by loss of one chloride ion
As with complex 1, the relative concentrations of 2a and 2b were
concentration dependent, with 2b favored at higher concen-
trations. For example, in the 31P NMR spectrum, 2a gave δ(31P)
from 1b, and another at m/z = 785.2, which corresponds to the
ion [Au(dpipa)]+, formed by loss of chloride from 1a. The data
indicate that 1b is favored by enthalpy and 1a by entropy effects.
Recrystallization of complex 1 from dichloromethane gave
single crystals of complex 1b, whose structure is shown in
Figure 2. The stereochemistry at gold is roughly linear, with
P(1)−Au(1)−P(2A) 174.82(4)°, and the distance Au(1)···Cl(A)
3.398(2) is too long to represent a gold-chloride covalent
bond. This suggests the formulation [Au2(μ-dpipa)2]Cl2 for 1b.
The chloride ions are hydrogen bonded to the NH protons of
dpipa ligand, with Cl···N(2) 3.341(4) and Cl···N(1) 3.377(5) Å,
1
1.27, with coupling constant J(PtP) 3608 Hz, while 2b gave
1
δ(31P) 1.58, J(PtP) = 3600 Hz. The magnitudes of the values
1
of J(PtP) indicate the stereochemistry with phosphorus trans
to chloride in each case.11,12 The cis,cis stereochemistry of complex
2b was confirmed crystallographically, and the structure is shown
in Figure 3.
The structure of complex 2b contains a center of symmetry,
and the ligand is in a stretched conformation, with the distance
between the platinum atoms being 14.28 Å, compared to the
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Complex 3 was prepared by displacement of the Me2S
ligands from [Pt2Me4(μ-SMe2)2] by the ligand dpipa, and was
shown to exist as a mixture of the monomer cis-[PtMe2(dpipa)],
3a, and dimer cis,cis-[Pt2Me4(μ-dpipa)2], 3b, illustrated in Scheme 4.
Scheme 4. Equilibrium between Dimethylplatinum(II)
Complexes 3a and 3b
Figure 3. View of the structure of complex 2b. Selected bond
parameters: Pt(1)−Cl(1) 2.389(1), Pt(1)−Cl(2) 2.381(1), Pt(1)−
P(2) = 2.284(1), Pt(1)−P(1) = 2.283(1) Å; Cl(1)−Pt(1)−Cl(2)
87.36(4), P(2)−Pt(1)−P(1) 99.80(4)°. Symmetry equivalent: A, 1−x,
2−y, −z.
AuAu distance in 1b of 9.00 Å (Figure 2). Another difference
between the structures of 1b and 2b is the conformation of the
phthalamide units, which tend to have roughly coplanar C6H4-
(CONH)2 units. In 1b the symmetrical conformation, which
we label the exo,exo conformation, is present with torsion angles
OCCC = 169 and 172° (Figure 2, the terminal carbon is the C2
atom of the 1,3-phthalamide unit), but in 2b (Figure 3) the
unsymmetrical exo,endo conformation is present with corre-
sponding torsion angles of 8 and 149°. The molecules of com-
plex 2b undergo self-association through complementary
NH···Cl hydrogen bonding to give a supramolecular polymer,
as shown in Figure 4.
The NMR spectra of 3 were broad and contained minor resonances,
perhaps suggesting the presence of minor amounts of other
isomers or slowly equilibrating conformers. However, the major
isomers were clearly identified. In the 31P NMR spectrum, the
monomer 3a gave a sharp singlet at δ 11.23, 1J(PtP) = 1815 Hz,
while dimer 3b gave a broad singlet at δ 10.89, 1J(PtP) = 1800 Hz
(Figure 5). The magnitudes of the coupling constants indicate
that, in each case, the phosphorus atoms are trans to the
methyl groups.11,13 The ESI-MS of complex 3 in dichloro-
methane, in the presence of NaCl to aid ionization, gave two
major peaks; one at m/z = 1649.4, which corresponds to [Pt2Me4-
(μ-dpipa)2]Na+ and one m/z = 836.2 which corresponds to
[PtMe2(dpipa)]Na+.
Fortunately, we were able to grow single crystals of both 3a
and 3b to confirm the structures. The molecular structure of
the monomer 3a is shown in Figure 6. It confirms the expected
cis square planar stereochemistry at platinum(II), though with
the PPtP bond angle at 101.27(4)° significantly distorted from
the ideal 90°. An interesting feature of the structure in Figure 6
is that the C(O)NH groups are significantly twisted out of the
plane of the C6H4 group, in such a way as to give a short intra-
molecular Pt···HN contact, with Pt···H(1) about 2.63 Å, indicative
of the electron rich dimethylplatinum(II) center acting as a
hydrogen bond acceptor.15 The molecules of complex 3a self-
associate to form a hydrogen bonded dimer, as shown in Figure 6.
The individual molecules are related by a center of inversion.
The dimer 3b in the solid state adopts a highly twisted struc-
ture (conformation 3b′ in Scheme 4) as shown in Figures 7 and 8.
Figure 4. Supramolecular polymeric structure of complex 2b, formed
by intermolecular NH···Cl hydrogen bonding. Only the ipso carbon
atoms of the phenyl groups are shown, for clarity. Hydrogen bond
distance: N(1)···Cl(1B) 3.38(1) Å.
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Figure 5. 31P NMR spectra of complex 3 at different concentrations in
CDCl3 (0.5 mL), illustrating the equilibrium between 3a and 3b:
below, 10 mg 3.; above, 100 mg 3.
Figure 7. View of the structure of complex 3b. Selected bond
parameters: Pt(1)−P(1) 2.318(2), Pt(1)−P(2) 2.296(3), Pt(2)−P(3)
2.321(2), Pt(2)−P(4) 2.301(2) Å; P(2)−Pt(1)−P(1) 98.53(8),
C(14)−Pt(1)−C(13) 82.0(3), C(51)−Pt(2)−C(52) 84.6(3)°. Rep-
resentative torsion angles: O(1)−C(29)−C(30)−C(35) 153.7, O(2)−
C(36)−C(34)−C(35) 24.6°.
Figure 8. Dimer of dimers formed by hydrogen bonding in complex
3b. Hydrogen bond distances: N(1)···O(5) 2.784(8), O(4)···N(6)
2.770(8), N(3)···O(7) 2.803(9), O(2)···N(8) 2.759(8), Pt(1)···N(4)
3.348(5), Pt(2)···N(2) 3.334(5), Pt(3)···N(5) 3.304(5), Pt(4)···N(7)
3.371(5) Å. The phenyl groups have been omitted for clarity.
Figure 6. View of the structure of complex 3a, including the intra- and
intermolecular hydrogen bonding. Selected bond parameters: Pt(1)−
C(37) 2.100(4), Pt(1)−C(38) 2.101(4), Pt(1)−P(1) 2.309(1),
Pt(1)−P(2) 2.319(1), Pt(1)···N(1) 3.461(4) Å; P(1)−Pt(1)−P(2)
101.27(4), C(37)−Pt(1)−C(38) 81.5(2)°. Hydrogen bond distance:
O(1)···N(2A) 2.918(5) Å. Torsion: O(1)−C(3)−C(4)−C(24)
148.0(6), O(2)−C(9)−C(8)−C(24) 144.6(6)°. Only the ipso carbon
atom of the phenyl groups is shown. Symmetry equivalent: A,
1−x, 1−y, 2−z.
individual molecules have no crystallographically imposed sym-
metry (Figure 7). There is a short NH···Pt contact for each
dimethylplatinum(II) center (Figure 8), and this hydrogen
bond, which is similar to that observed in the monomer 3a,
appears to control the unusual conformation of the complex.
There is no such NH···Pt hydrogen bond in complex 2b, which
contains less nucleophilic dichloroplatinum(II) centers. In each
independent pair of dimers, four of the NH groups are directed
inward, and these are involved in the intramolecular NH···Pt
hydrogen bonds, while four are directed outward and form
intermolecular NH···OC hydrogen bonds to the neighboring
dimer. This gives rise to a dimer of dimers structure (Figure 8),
which can be considered to have a “swastika” conformation. If
the Pt(1)Pt(2) and Pt(3)Pt(4) dimers are considered to have
There are two independent molecules in the unit cell, but they
have similar structures, and only one is shown in Figure 7. Each
isophthalamide unit adopts the exo,endo conformation observed
previously in 2b, but the overall conformation of each molecule
of 3b′ is helical and quite different from that in 2b (Figure 3).
There is close to a 180° twist in each molecule, as indicated by
the typical torsion angle P(1)−Pt(1)−Pt(2)−P(4) of 169°.
The lattice contains equal numbers of molecules of 3b′ in the P
and M helical conformations, related by an inversion center, but
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P, M and P′, M′ conformations respectively, each dimer
contains a P,M′ or M,P′ pair. Figure 8 illustrates a P,M′ dimer of
dimers.
assigned as the hydrogen bonded Pt··HN group in 3b′, based
on the downfield chemical shift, but no coupling to 195Pt was
resolved.15
The twisted structures observed for 3a and 3b should give
more complex NMR spectra than those observed (Figure 5),
which suggest that the complexes have effective mirror sym-
metry in solution. For complex 3a, a relatively simple twisting
motion is required to exchange the Pt··HN hydrogen bond
between the N(1)H and N(2)H donors, as indicated in Scheme 4,
leading to effective Cs symmetry. However, if the conformation of
the dimer 3b′ is retained in solution, to the P and M con-
formers would need to interchange rapidly to give a single 31P
NMR resonance, and this would require passing through a
symmetrical intermediate such as 3b in Scheme 4. To study the
potential dynamic exchange, a variable temperature NMR study
was carried out, with interesting results. Figure 9 shows the
The reaction of complex 3 with methyl iodide gave a new
platinum(II) complex trans-[PtIMe(dpipa)], 4 (Scheme 5). In
a
Scheme 5. Possible Routes to Complex 4
a
P−P represents the dpipa ligand.
1
the H NMR spectrum, complex 4 gave a triplet methylplatinum
resonance at δ 0.15, with 3J(PH) = 7 Hz and with 2J(PtH) = 80 Hz,
and in the 31P NMR spectrum it gave a singlet at δ(31P) = 16.12,
with 1J(PtP) = 2946 Hz. The magnitude of 1J(PtP) suggests the
presence of mutually trans phosphine donors.11,14 The ESI-MS
of complex 4 in dichloromethane, with NaCl present, gave a
major peak at m/z = 948.1, which corresponds to the ion
[PtIMe(dpipa)]Na+. Some possible routes to complex 4 by
oxidative addition of methyl iodide followed by reductive
elimination of ethane are shown in Scheme 5.
The structure of complex 4 is shown in Figure 10. It shows
that the ligand dpipa is acting as a trans chelate ligand. The
carboxamide groups are in the exo,exo conformation, which
allows formation of two NH···I hydrogen bonds. The complex
crystallized with a water molecule, which bridges between mono-
meric units of complex 4 by hydrogen bonding, to form a supra-
molecular dimer.
Figure 9. Variable temperature 31P NMR spectra (243 MHz) of
complex 3 in CD2Cl2 solution: (a) 25 °C; (b) 0 °C; (c) −20 °C.
31P NMR spectra as a function of temperature. As the temperature
decreases, the singlet resonances for the monomer 3a and dimer
3b broaden, but they do not split to give separate resonances at
the lowest temperature studied (−80 °C). However, two new
resonances (labeled X and Y in Figure 9) appear and grow in
intensity as the temperature is decreased. The parameters [δ(PX)
The slow reaction of the mixture of isomers 3a/3b with
excess methyl iodide was monitored by 31P NMR spectroscopy
in CDCl3 solution (Figure 11). After 30 min, about 60% of the
reagent had reacted and three major new singlet resonances
were observed, namely, a sharp resonance at δ −25.46, 1J(PtP)
996 Hz, tentatively assigned to the monomer A (Scheme 5),
and two broader resonances at δ −25.96, 1J(PtP) 1060 Hz, and
1
2
1
11.6, J(PtP) 1920 Hz, J(PP) 15 Hz, and δ(PY) 8.4, J(PtP)
2
1590 Hz, J(PP) 15 Hz] indicate an unsymmetrical arrange-
ment cis-(PtMe2PXPY) as expected for the twisted structure 3b′.
The most likely explanation of this observation is that the dimer
is present in solution at room temperature mostly as a more
symmetrical conformer (3b in Scheme 4), or a conformer (such as
one analogous to that in the dichloroplatinum(II) derivative 2b)
which can very easily equilibrate with 3b. The rigid twisted
structure 3b′, which is likely to be disfavored by entropy effects,
increases in concentration at lower temperatures but equili-
brates only relatively slowly on the NMR time scale with the
more symmetrical conformer 3b. The low temperature 1H NMR
spectra are consistent with this interpretation. At −20 °C, two new
methylplatinum resonances [δ(MeX) 0.67, 2J(PtH) 64 Hz, 3J(PH)
1
δ −26.66, J(PtP) 974 Hz, tentatively assigned to the syn and
anti dimers B, C. After 2 h, a new unassigned resonance was
1
observed at δ −23.59, J(PtP) 1119 Hz, and the first ap-
pearance of the resonance for complex 4. After 2 days, the
reaction was complete, and complex 4 was formed almost
quantitatively. The singlet resonances in the region δ −23 to
−27, with coupling constants 1J(PtP) in the range 974−1119 Hz,
are characteristic of complexes with the fac-[PtIMe3P2] stereo-
chemistry.11,16 The reductive elimination of ethane from com-
plexes A−C is likely to occur by partial dissociation of a dpipa
ligand, and a common 5-coordinate intermediate [PtIMe3(κ1-
dpipa)] could be formed, which then gives ethane and a shortlived
2
3
6 Hz; δ(MeY) 0.20, J(PtH) 68 Hz, J(PH) 8 Hz] and two new
NH resonances [δ(NHX) 10.13; δ(NHY) 9.32] appear and are
assigned to 3b′. The resonance at δ(NHX) 10.13 is tentatively
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Scheme 6. Possible Route to Complexes 5, 6, 7 (and Possibly 8)
(PP = dpipa)
Figure 10. View of the structure of complex 4. Selected bond
parameters: Pt(1)−C(1) 2.093(5), Pt(1)−I(1) 2.7035(5), Pt(1)−
P(1) 2.296(2), Pt(1)−P(2) 2.309(2) Å; P(1)−Pt(1)−I(1) 94.38(4),
P(2)−Pt(1)−I(1) 93.29(4), P(2)−Pt(1)−C(1) 85.1(2), C(1)−
Pt(1)−P(1) 86.4(2)°. Hydrogen bond distances: N(1)···I(1)
3.699(5), N(2)···I(1) 3.703(5), O(2)···O(1S) 2.953(8),
O(1)···O(1S) 2.913(8) Å.
3-coordinate [PtIMe(κ1-dpipa)], which would then give trans-
[PtIMe(κ2-dpipa)], 4.17 None of the possible cis isomer, which
should contain nonequivalent phosphorus atoms and hence
give a pair of doublets in the 31P NMR spectrum, was observed
at any stage of the reaction (Figure 11).
(IV) center, whereas both monomeric 3a and dimeric 3b
starting materials contained the cis-PtP2 stereochemistry. Each
platinum center contains four anionic ligands, of which two
refined well as bromide ions. However, the other two, labeled
C(1X) and C(2X) in Figure 12, could only be refined as
disordered CH3/Br units with occupancies of Br:C 29:71 and
25:75 in the two sites. This leads to a formula [Pt2Br5.08
-
Me2.92(dpipa)2], approximating to [Pt2Br5Me3(dpipa)2], thus
suggesting that about equal numbers of the platinum(IV)
centers have [PtBr2Me2P2] and [PtBr3MeP2] coordination.
This might suggest complex 7, with intramolecular disorder of
the PtBr2Me2 and PtBr3Me groups, but it is also consistent with
a disordered mixture of complexes [Pt2Br4Me4(dpipa)2], 6,
[Pt2Br5Me3(dpipa)2], 7, and [Pt2Br6Me2(dpipa)2], 8 (Scheme 6).
The two halves of the molecule in Figure 12 are related by a
center of symmetry, and the two platinum atoms are separated
by 12.0 Å. The isophthalamide units adopt a distorted exo,endo
conformation. The NH groups are not involved in hydrogen
bonding to either the carbonyl groups or the bromide ligands,
but may hydrogen bond to solvent molecules which could not
be identified and refined.
Figure 11. 31P NMR spectra for the reaction of 3a, 3b with excess MeI
in CDCl3: (a) before addition of MeI; (b) after 30 min; (c) after 2 h;
(d) after 24 h; (e) after 2 days.
The chemistry of complexes 3a/3b with bromine is depicted
in Scheme 6. The reaction was expected to give complexes 5a
and 5b by trans oxidative addition of bromine to 3a and 3b
respectively, but, although a reaction occurred rapidly using
several different stoichiometries, it proved difficult to character-
ize the product. Eventually, crystals of a product, formed using
about 4-fold excess of bromine, were grown from a complex
mixture of solvents, and the resulting structure is shown in
Figure 12.
If the reaction of 3a/3b with bromine was carried out in
dichloromethane solution, much of the product precipitated as
an orange solid. Recrystallization of this solid gave the single
1
crystals, from which the structure was determined. The H
NMR spectrum of this initial orange complex in dmso-d6 con-
tains broad peaks, probably due to restricted rotations, but clearly
indicates that the product contains a mixture of complexes 6 and 7
in about a 3:1 ratio. The symmetrical complex 6 gives a single
There are several surprising features of the structure in
Figure 12. Most obviously, the product is a diplatinum complex
with trans-PtP2 stereochemistry at each octahedral platinum-
2
methylplatinum resonance [δ(1H) 0.55, JPtH = 65 Hz] and a
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Figure 12. View of the structure of complex 7, showing only the
carbon atoms C(1X) and C(2X) of the disordered Me/Br groups.
Selected bond parameters: Pt(1)−Br(1) 2.557(1), Pt(1)−Br(2)
2.589(1), Pt(1)−P(1) 2.384(3), Pt(1)−P(2) 2.373(2) Å; Br(1)−
Pt(1)−Br(2) 91.08(4), P(1)−Pt(1)−P(2) 177.54(8)°. Symmetry
equivalent: A, 1−x, 1−y, −z.
Figure 13. 31P NMR spectra for the reaction of complexes 3a and 3b
in CDCl3 with Br2: (a) before the addition of Br2; (b) after 3 h; (c)
after 4 days.
the solubility was improved. Immediately after addition of
bromine, the resonances of 3a,3b disappeared, and resonances
assigned to 5a,5b [δ −11.1, 1JPtP = 1585 Hz] and 6,7 [δ −5.59,
1JPtP = 2050 Hz] were observed. Over time, the resonance for
5a,5b decayed, and the resonance for 6,7 (again with accidental
degeneracy of the chemical shifts) increased in intensity.
Once formed, the complexes 6 and 7 were unreactive to
bromine, so it is likely that the formation of methyl bromide
occurs at an early stage. One possibility is that there is a com-
petition between isomerization of 5 to 6 and reductive elimi-
nation of methyl bromide from 5 followed by further reaction
with bromine to give 7 (Scheme 6), but there may be other
potential routes.
single set of resonances for the NHCH2CH2P protons, whereas
the unsymmetrical complex 7 gave two sets of resonances for
the NHCH2CH2P protons, and two methylplatinum resonances
2
[δ(1H) 1.08, JPtH = 68 Hz, for the PtMeBr3 group and 0.59,
2JPtH = 65 Hz, for the PtMe2Br2 group], with the PtMeBr3
resonance shifted to higher δ, as expected from comparison
with related complexes.18 The surprising feature was that the
31P NMR spectrum contained only one resolved resonance at
1
δ(31P) = −5.59, JPtP = 2050 Hz, whereas three resonances are
expected for a mixture of 6 and 7. The ESI-MS of the sample,
as a dilute solution in dichloromethane with NaCl added to
promote ionization, gave peaks, with masses reported for the
195Pt,79Br isotopomer, at m/z = 994.0, 1965.1, and 2029.0 which
correspond to the ions [PtBr2Me2(dpipa)]Na+, [Pt2Br4Me4-
(μ-dpipa)2]Na+, and [Pt2Br5Me3(μ-dpipa)2]Na+, respectively. It
is likely that the ion [PtBr2Me2(dpipa)]Na+ arises from frag-
mentation of 6, because there was no evidence for the mono-
CONCLUSIONS
■
The new diphosphine-dicarboxamide ligand dpipa is shown to
be remarkably versatile in its coordination chemistry, with the
carboxamide groups playing an important role in several cases.
Ligand dpipa can act as a trans chelate ligand in the complex
trans-[PtIMe(dpipa)], 4, and probably in the gold complex [Au-
(dpipa)]Cl, 1a. In complex 4, and probably in 1a, the carboxamide
groups are hydrogen bonded to the halide ligand or anion. The
ligand acts as a cis chelate ligand in the complexes cis-[PtCl2-
(dpipa)], 2a, and cis-[PtMe2(dpipa)], 3a. In complex 3a the
carboxamide groups are bifunctional, forming an intramolecular
NH···Pt hydrogen bond and taking part in intermolecular
NH···OC hydrogen bonding to form supramolecular dimers.
The trans,trans bridging mode of binding is found in the gold(I)
complex [Au2(μ-dpipa)2]Cl2, 1b, and the platinum(IV) com-
plexes [Pt2Br4Me4(μ-dpipa)2], 6, and [Pt2Br5Me3(μ-dpipa)2],
7. Figures 2 and 12 illustrate how the flexible dpipa ligand
adapts to accommodate the 2-coordinate gold(I) center or the
more sterically demanding octahedral platinum(IV) center. The
cis,cis bridging mode of binding is found in the platinum(II)
complexes [Pt2Cl4(μ-dpipa)2], 2b, and [Pt2Me4(μ-dpipa)2], 3b,
and in the intermediate platinum(IV) complex [Pt2Br4Me4-
(μ-dpipa)2], 5b. Complex 3b adopts a more twisted conforma-
tion than 2b, apparently to allow formation of intramolecular
NH···Pt hydrogen bonds, and the carboxamide groups in both
complexes also take part in intermolecular NH···OC hydrogen
bonding.
1
meric complex in either the H or the 31P NMR spectra. The
combined spectra support the assignment of the initial orange
product as a mixture of complexes 6 and 7.
To gain further insight, the reaction of 3a/3b with bromine
was carried out in both CDCl3 and dmso-d6, with monitoring
1
by H and 31P NMR spectroscopy at room temperature. In
CDCl3, some orange precipitate formed even at room tem-
perature, and low temperature experiments were not possible
because of the limited solubility of the complexes. Immediately
after addition of bromine, a methylplatinum resonance was ob-
2
served at δ 0.68, JPtH = 64 Hz, with second order (A3A′3XX′)
appearance expected for a cis-PtMe2P2 grouping, as expected in
complexes 5a,5b .13,16,18 Over a period of about an hour, this
resonance was replaced by a triplet resonance assigned to com-
plex 6, with weaker resonances due to 7. A resonance for
methyl bromide [δ 2.69] grew during this period, but no further
growth in the resonance occurred. The 31P NMR spectrum at
intermediate stages contained a resonance at δ −13.6, 1JPtP = 1585
Hz, assigned to 5a,5b, and two closely spaced resonances at δ
1
−4.8 and −5.1, each with JPtP = 2050 Hz, assigned to 6 and 7,
respectively. Three peaks are expected for a mixture of 6 and 7
and so two are presumed to overlap. Better 31P NMR spectra were
obtained in dmso-d6 solution, as illustrated in Figure 13, because
G
dx.doi.org/10.1021/ic400576m | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
J = 8, 2 Hz, C6H4]; 7.26−7.5 [m, 21H, Ph and C6H4]; 6.35 [t, 2H, J =
6 Hz, NH]; 3.65 [m, 4H, CH2N]; 2.44 [t, 4H, J = 7 Hz, CH2P]; δ
(31P) = −21.05 [s]. Anal. Calcd. for C36H34N2O2P2: C, 73.46; H, 5.82;
N, 4.76. Found: C, 73.44; H, 5.89; N, 4.74%.
Several of the complexes exhibit facile monomer−dimer iso-
merization. In one case, it was possible to determine the struc-
tures of both of the isomers, monomer 3a and dimer 3b. In
other cases, the equilibria between 1a, 1b or 2a, 2b could be
studied by NMR spectroscopy and so clearly established. The
ability to form such facile monomer−dimer isomerization when
the stereochemistry at the metal is either cis or trans appears to
be unique to the ligand dpipa. Often chelate complexes are
relatively inert, but the very large ring sizes formed by chelating
or bridging dpipa (14- or 28-membered rings respectively) evi-
dently confer little kinetic inertness or thermodynamic stability
toward reversible dissociation of the metal−phosphorus bonds.
Facile monomer−dimer equilibria are more commonly observed
for short chain diphosphine ligands such as bis(diphenylphos-
phino)methane, dppm, for which the 4-membered chelate is
strained. For example, there is a facile equilibrium between [PtMe2-
(dppm)] and [Pt2Me4(μ-dppm)2].13 There is potential for applica-
tions of the ligand dpipa in catalysis or host−guest chemistry based
on its unique coordination chemistry
[Au(dpipa)]Cl, 1a, and [Au2(μ-dpipa)2]Cl2, 1b. A solution of
[AuCl(SMe2)] (0.05 g, 0.1697 mmol) in CH2Cl2 (5 mL) was added to
a stirring solution of dpipa (0.099 g, 0.1697 mmol) in CH2Cl2 (10 mL).
The resulting solution was allowed to stir overnight, then the solvent was
evaporated under vacuum to give the product as a white solid, which
was collected, washed with ether (3 × 5 mL) and pentane (3 × 5 mL)
and then dried under high vacuum. Yield: 0.1 g, 72%. NMR in CDCl3:
1a, δ(1H) = 9.35 [m, 2H, NH]; 9.12 [s, 1 H, C6H4]; 7.95 [dd, 2H, J =
7, 2 Hz, C6H4]; 7.30−7.71 [m, 21H, Ph and C6H4]; 3.82 [br, 2H,
NCH2CH2P]; 3.44−3.68 [m, 4H, NCH2CH2P ]; 2.96 [br, 2H,
NCH2CH2P]; δ (31P) = 31.85[s]; 1b, δ(1H) = 9.18 [m, 4H, NH]; 8.78
[s, 2H, C6H4]; 8.02 [dd, 4H, J = 7, 2 Hz, C6H4]; 7.30−7.87 [m, 42H,
Ph and C6H4]; 3.82 [br, 8H, NCH2]; 3.26 [br, 8H, CH2P]; δ(31P) =
34.24 [s]. Anal. Calcd. for C72H68Au2Cl2N4O4P4: C, 52.66; H, 4.17; N,
3.41%. Found: C, 52.59; H, 4.12; N, 3.30%. Single crystals of complex
1b were grown by slow diffusion of n-pentane into a solution of the
compound 1a/1b dissolved in dichloromethane.
[PtCl2(dpipa)], 2a, and [Pt2Cl4(μ-dpipa)2], 2b. To a solution of
dpipa (0.10 g, 0.17 mmol) in CH2Cl2 (10 mL) was added cis/trans-
[PtCl2(SMe2)2] (0.0612 g, 0.170 mmol) in CH2Cl2 (10 mL). A white
precipitate was formed immediately. After allowing the reaction con-
tents to stir for 6 h, the solvent was decanted and the white solid was
washed with ether (3 × 5 mL) and pentane (3 × 5 mL) and then dried
under high vacuum. Yield: 0.12 g, 83%. NMR in DMSO-d6: 2a, δ(1H) =
EXPERIMENTAL SECTION
■
Reagents and General Procedures. All reactions were carried
out in inert atmosphere of dry nitrogen using standard Schlenk tech-
niques, unless otherwise specified. All solvents used for air and moisture
sensitive materials were purified using an innovative Technology Inc.
PURE SOLV solvent purification system (SPS). NMR spectra were
recorded at ambient temperature, unless otherwise noted (ca. 25 °C),
by using Varian Mercury 400 or Varian Inova 400 or 600 spec-
3
8.99 [m, 2H, NH]; 8.49 [s, 1H, C6H4]; 8.03 [d, 2H, JHH = 8 Hz,
C6H4]; 7.19−7.68 [m, 21H, Ph and C6H4]; 3.61 [br, 4H, NCH2]; 2.62
1
[br, 4H, CH2P]; δ(31P) = 1.27 [s, JPtP = 3608 Hz]. 2b, δ(1H) = 8.82
3
1
trometers. H chemical shifts are reported relative to TMS, and 31P
[m, 4H, NH]; 8.33 [s, 2H, C6H4]; 7.94 [d, 4H, JHH = 8 Hz, C6H4];
7.22−7.68 [m, 42H, Ph and C6H4]; 3.61 [br, 8H, NCH2]; 2.62 [br,
chemical shifts relative to 85% H3PO4. Mass spectrometric analysis was
carried out using an electrospray PE-Sciex Mass Spectrometer (ESI-
MS) coupled with TOF detector.
1
8H, CH2P]; δ(31P) = 1.58 [s, JPtP = 3600 Hz]. Anal. Calcd. for
C72H68Cl4N4O4P4Pt2: C, 50.60; H, 4.01; N, 3.28%. Found: C, 50.40;
H, 3.97; N, 3.15%. Single crystals of complex 2b were grown by slow
diffusion of n-pentane into a solution of 2a/2b dissolved in a mixture
of equal volumes of benzene, DMSO, MeOH, acetone, CH2Cl2, and
CHCl3.
X-ray Crystallography.19 A suitable crystal of each compound was
coated in Paratone oil and mounted on a glass fiber loop. X-ray data
were collected at 150 K with ω and φ scans using a Bruker Smart Apex
II diffractometer and Bruker SMART software or Nonius Kappa-CCD
diffractometer with COLLECT software, using graphite-monochro-
mated MoKα radiation(λ = 0.71073 Å). Unit cell parameters were
calculated and refined from the full data set. Reflections were scaled
and corrected for absorption effects using SADABS. All structures
were solved by either Patterson or direct methods with SHELXS
and refined by full-matrix least−square techniques against F2 using
SHELXL. All non-hydrogen atoms were refined anisotropically. The
hydrogen atoms were placed in calculated positions and refined using
the riding model. Crystal data are summarized in the Supporting
Information, cif files. Unusual features are as follows. The structures
1b, 2b, and 7 contained regions of disordered solvent molecule(s)
which eluded sensible modeling. The data and model were subjected
to the SQUEEZE procedure as implemented in PLATON.19 Complex
1b: there was a chloroform molecule and an unidentifiable solvent
molecule in the lattice. Complex 3b: there was a chloroform and a
dichloromethane molecule for each pair of dimers. Complex 4: the
crystal was nonmerohedrally twinned and the twinning was suc-
cessfully treated. Complex 7: there was disorder of the CH3/Br atoms
over two sites, and the occupancies were refined with free variables,
and there were large voids containing disordered solvent.
[PtMe2(dpipa)], 3a, and [Pt2Me4(μ-dpipa)2], 3b. To a solution of
dpipa (0.10 g, 0.17 mmol) in CH2Cl2 (10 mL) was added a solution of
[Pt2Me4(μ-SMe2)2] (0.0488 g, 0.0849 mmol) in CH2Cl2 (10 mL).
The solution was allowed to stir for 12 h, and the solvent was removed
under vacuum to give a white solid product, which was washed with
ether (3 × 5 mL) and pentane (3 × 5 mL) and then dried under high
vacuum. Yield: 0.11 g, 80%. NMR in CDCl3: 3a, δ(1H) = 8.35 [s, 1H,
C6H4]; 8.04 [d, 2H, 3JHH = 8 Hz, C6H4]; 7.94 [br s, 2H, NH]; 7.54 [t,
3
1H, JHH = 8 Hz, C6H4]; 7.30−7.35 [m, 20H, Ph]; 3.74 [br, 4H,
NCH2]; 2.48 [br, 4H, CH2P]; 0.56 [m, 6H, PtCH3]; δ (31P) = 11.23
1
[s, JPtP = 1815 Hz]. 3b, δ(1H) = 8.35 [s, 2H, C6H4]; 8.04 [d, 4 H,
3
3JHH = 8 Hz, C6H4]; 7.98 [br, 4H, NH]; 7.54 [t, 2H, JHH = 8 Hz,
C6H4]; 7.30−7.35 [m, 40H, Ph]; 3.60 [br, 8H, NCH2]; 2.24 [br, 8H,
1
CH2P]; 0.50 [m, 12H, PtCH3]; δ (31P) = 10.89 [s, JPtP = 1800 Hz].
Anal. Calcd. for C76H80N4O4P4Pt2: C, 56.09; H, 4.95; N, 3.44%.
Found: C, 55.94; H, 4.92; N, 3.27%. Single crystals of both complexes
3a and 3b were grown by slow diffusion of n-pentane into a solution of
the compound dissolved in a mixture of equal volumes of benzene,
dimethylsulfoxide, methanol, acetone, dichloromethane, and chloro-
form. NMR of 3b′ in CD2Cl2 at −20 °C: δ(1H) = 10.13, 9.32 [each s,
2H, NH]; 6.4−9.1 [48H, Ph and C6H4]; 1.8−4.1 [br, 16H, CH2]; 0.67
1,3-C6H4(CONHCH2CH2PPh2)2, dpipa. To a solution of 2-
(diphenylphosphino)ethylamine (4.0 g, 17.44 mmol) and triethyl-
amine (10 mL) in CHCl3 (20 mL) was added dropwise a solution of
isophthaloyl dichloride (1.771 g, 8.723 mmol) in CH2Cl2 (20 mL).
After stirring for 12 h, the reaction mixture was washed with water
(3 × 30 mL), the organic layer was separated, dried over MgSO4, then
filtered, and the solvent was evaporated under vacuum to give an oily
product. The product was purified by flash chromatography using
70:30 ethyl acetate and hexane as eluent. The solvent was evaporated
to give dpipa as a white solid, which was dried under vacuum. Yield:
4.5 g, 88%. NMR in CDCl3: δ(1H) = 7.95 [s, 1H, C6H4]; 7.72 [dd, 2H,
2
3
2
[m, 6H, J(PtH) 64 Hz, J(PH) 6 Hz, PtCH3]; 0.20 [m, 6H, J(PtH)
3
1
68 Hz, J(PH) 8 Hz, PtCH3]; δ (31P) = 11.6 [d, J(PtP) 1920 Hz,
2J(PP) 15 Hz, PtP]; 8.4 [d, J(PtP) 1590 Hz, J(PP) 15 Hz, PtP].
[PtIMe(dpipa)], 4. To a stirred solution of complexes 3a/3b (0.10 g,
0.123 mmol) in dry CH2Cl2 (15 mL) was added a solution of MeI
(100 μL, 1.61 mmol) in CH2Cl2 (5 mL). After 18 h, the solvent was
removed under vacuum, and a white solid was obtained which was
washed with pentane (3 × 5 mL) and ether (3 × 5 mL) and then dried
under high vacuum. Yield: 0.105 g, 92%. NMR in CDCl3: δ(1H) =
1
2
3
8.17 [d, 2H, JHH = 8 Hz, C6H4]; 7.75 [s, 1H, C6H4]; 7.65−7.27
H
dx.doi.org/10.1021/ic400576m | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
[m, 21H, Ph and C6H4]; 7.34 [m, 2H, NH]; 4.15 [m, 4H, NCH2];
(3) Stepnicka, P. Chem. Soc. Rev. 2012, 41, 4273.
2
3
3.31 [m, 4H, CH2P]; 0.15 [t, JPtH = 80 Hz, JPH = 7 Hz, 3H, PtMe];
δ(31P) = 16.12 [s, 1JPPt = 2946 Hz]. Anal. Calcd. for C37H37IN2O2P2Pt:
C, 48.01; H, 4.03; N, 3.03%. Found: C, 47.84; H, 4.08; N, 2.88%.
Single crystals of complex 4 were grown by slow diffusion of n-pentane
into a solution of the compound dissolved in a mixture of equal volumes
of benzene, acetone, methanol, dichloromethane, tetrahydrofuran, and
chloroform.
(4) (a) Tauchman, J.; Therrien, B.; Suss-Fink, G.; Stepnicka, P.
Organometallics 2012, 31, 3985. (b) Tauchman, J.; Suss-Fink, G.;
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Amoroso, D.; Lough, A. J.; Abdur-Rashid, K. Dalton Trans. 2009, 8301.
(e) Ito, M.; Osaku, A.; Kobayashi, C.; Shiibashi, A.; Ikariya, T.
Organometallics 2009, 28, 390. (f) Stepnicka, P.; Krupa, M.; Lamac,
M.; Cisarova, I. J. Organomet. Chem. 2009, 694, 2987. (g) Swanson, R.
A.; Patrick, B. O.; Ferguson, M. J.; Daley, C. J. A. Inorg. Chim. Acta
2007, 360, 2455. (h) Abdur-Rashid, K.; Guo, R.; Lough, A. J.; Morris,
R. H.; Song, D. Adv. Synth. Catal. 2005, 347, 571. (i) Dahlenburg, L.;
Kuehnlein, C. J. Organomet. Chem. 2005, 690, 1. (j) Campos, K. R.;
Journet, M.; Lee, S.; Grabowski, E. J. J.; Tillyer, R. D. J. Org. Chem.
2005, 70, 268. (k) Burger, S.; Therrien, B.; Suss-Fink, G. Helv. Chim.
Acta 2005, 88, 478. (l) Issleib, K. Phosphorus Sulfur 1976, 2, 219.
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Chem. Commun. 2000, 2447. (p) Trost, B. M.; Toste, D. J. Am. Chem.
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Briard, P.; Grandjean, D. Inorg. Chim. Acta 1993, 208, 5. (s) Hedden,
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Antoniadis, A. Z. Naturforsch. B 1982, 37, 560. (u) Thewissen, D. H.
M. W.; Ambrosius, H. P. M. M. Recl. Trav. Chim. Pays-Bas 1980, 99,
344.
[Pt2Br4Me4(dpipa)2], 6, and[Pt2Br5Me3(dpipa)2], 7. To a stirred
solution of 3a/3b (0.10 g, 0.123 mmol) in dry CH2Cl2 (15 mL) was
added a solution of Br2 (30 μL, 0.54 mmol) in CH2Cl2 (5 mL). The
mixture was stirred for 12 h, then the orange precipitate which formed
was separated, washed with pentane (3 × 5 mL) and ether (3 × 5 mL)
and dried under high vacuum. Yield: 0.105 g. NMR in DMSO-d6: 6,
δ(1H) = 8.78 [br, 4H, NH]; 8.23 [s, 2H, C6H4]; 8.0−7.2 [m, 46H, Ph
and C6H4]; 3.57 [br, 8H, NCH2]; 2.94 [br, 8H, CH2P]; 0.55 [br, 12H,
1
2JPtH = 65 Hz, PtMe2Br2]; δ(31P) = −5.59 [s, JPPt = 2050 Hz]. 7,
δ(1H) = 8.80 [br, 2H, NH]; 8.63 [br, 2H, NH]; 8.15 [s, 2H, C6H4];
8.0−7.2 [m, 46H, Ph and C6H4]; 3.67 [br, 4H, NCH2]; 3.42 [br, 4H,
NCH2]; 2.89 [br, 4H, CH2P]; 2.66 [br, 4H, CH2P]; 1.08 [br, 3H,
3
2
2JPtH = 68 Hz PtMeBr3]; 0.59 [t, 6H, JPH = 5 Hz, JPtH = 65 Hz,
PtMe2Br2]; δ(31P) = −5.59 [s, JPPt = 2050 Hz]. Single crystals of
1
complex 7 were grown by slow diffusion of n-pentane into a solution
of the compound dissolved in a mixture of equal volumes of benzene,
dimethylsulfoxide, methanol, acetone, dichloromethane, and chloro-
form. Anal. Calcd. for C75H77Br5N4O4P4Pt2: C, 44.77; H, 3.86; N,
2.78%. Found: C, 44.54; H, 3.90; N, 2.59%.
From the in situ formation of 5a/5b in CDCl3: δ(1H) = 8.68 [br,
4H, NH]; 8.1−6.9 [m, 48H, Ph and C6H4]; 3.75 [br, 8H, CH2P]; 3.60
3
[br, 8H, NCH2]; 0.66 [br m, 12H, JPH + 3JP′H = 4 Hz, 2JPtH = 65 Hz,
1
PtMe2Br2]; δ(31P) = −13.6 [s, JPtP = 1585 Hz].
(5) (a) Nasser, N.; Puddephatt, R. J. Chem. Commun. 2011, 47, 2808.
(b) Nasser, N.; Puddephatt, R. J. Cryst. Growth Des. 2012, 12, 4275.
(6) (a) Yang, S. K.; Ambade, A. V.; Weck, M. Chem. Soc. Rev. 2011,
40, 129. (b) Leong, W. L.; Vittal, J. J. Chem. Rev. 2011, 111, 688.
(c) Chakrabarty, R.; Mukherjee, P. S.; Stang, P. J. Chem. Rev. 2011,
111, 6810. (d) Ganguly, R.; Sreenivasulu, B.; Vittal, J. J. Coord. Chem.
Rev. 2008, 252, 1027. (e) Tanaka, D.; Kitagawa, S. Chem. Mater. 2008,
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113, 734.
ASSOCIATED CONTENT
* Supporting Information
■
S
Details of the X-ray data collection, solution, and refinement in
electronic CIF form. This material is available free of charge via
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: pudd@uwo.ca.
(7) (a) Abdul-Kabir, M.; Clements, P. R.; Hanton, L. R.; Hollis, C.
A.; Sumby, C. J. Supramol. Chem. 2012, 24, 627. (b) Zhang, Q.; Zhang,
J.; Yu, Q.-Y.; Pan, M.; Su, C. Y. Cryst. Growth Des. 2010, 10, 4076.
(c) Yue, N. L. S.; Jennings, M. C.; Puddephatt, R. J. Dalton Trans.
2010, 39, 1273. (d) Brandys, M.-C.; Puddephatt, R. J. J. Am. Chem. Soc.
2001, 123, 4839. (e) Lozano, E.; Nieuenhuyzen, M.; James, S. L.
Chem.Eur. J. 2001, 7, 2644.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank the NSERC (Canada) for financial support.
■
(8) (a) Puddephatt, R. J. Chem. Soc. Rev. 2008, 37, 2012. (b) Burchell,
T. J.; Eisler, D. J.; Jennings, M. C.; Puddephatt, R. J. J. Chem. Soc.,
Chem. Commun. 2003, 2228. (c) Qin, Z.; Jennings, M. C.; Puddephatt,
R. J.; Muir, K. W. Inorg. Chem. 2002, 41, 5174. (d) Qin, Z.; Jennings,
M. C.; Puddephatt, R .J. J. Chem. Soc., Chem. Commun. 2001, 2676.
(9) Burger, S.; Therrien, B.; Suss-Fink, G. Eur. J. Inorg. Chem. 2003,
3099.
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