Organoplatinum complexes containing bis(diphenylphosphino)amine as ligand: Uncommon case of N-H?I-Pt hydrogen bonding

Article abstract of DOI:10.1039/b700009j

The complex [PtMe₂(dppa)], 1a, dppa = Ph₂PNHPPh₂, which has previously been prepared as a mixture with the dimeric form [Pt₂Me₄(-dppa)₂], was synthesized in pure form by the reaction of [PtCl₂(dppa)] with MeLi. The aryl analogue [Pt(p-MeC₆H₄)₂(dppa)], 1b, was prepared by replacement of SMe₂in cis-[Pt(p-MeC₆H₄)₂(SMe₂)₂] with dppa. The reaction of the chelate complexes 1 with one equiv. of dppa afforded the complexes [PtR₂(dppa-P)₂], RMe, 2a and R = p-MeC₆H₄2b. The reaction of [PtR₂(dppa)], 1, with neat MeI gave the organoplatinum(iv) complexes [PtR₂MeI(dppa)], RMe, 5a and R = p-MeC₆H₄, 5b. The structure of 5a, determined by X-ray crystallography, indicated that the complex undergoes self-assembly by intermolecular N-H?I-Pt hydrogen bonding. MeI was also double oxidatively added to organodiplatinum(ii) complex cis,cis-[Me₂Pt(-SMe₂)(-dppa)PtMe₂], to give diorganoplatinum(iv) complex [Me₃Pt(-dppa)(-I)₂PtMe₃], 4. The aryl analogue organodiplatinum(ii) complex cis,cis-[(p-MeC₆H₄)₂Pt(-SMe₂)(-dppa)Pt(p-MeC₆H₄)₂], 3b, was prepared by the reaction of cis-[Pt(p-MeC₆H₄)₂(SMe₂)₂] with half equiv. of dppa, but 3b refused to react with MeI, probably because of the steric effects of the aryl ligands. The tetramethyl complex [PtMe₄(dppa)], 6, was prepared either by reaction of 5a with MeLi or by replacement of SMe₂in [Pt₂Me₈(-SMe₂)₂] with dppa. All the complexes were fully characterized in solution by multinuclear NMR (¹H,¹³C,³¹P and¹⁹⁵Pt) methods and their coordination compared with that of the corresponding known dppm complexes. The Royal Society of Chemistry.

Full text of DOI:10.1039/b700009j

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Organoplatinum complexes containing bis(diphenylphosphino)amine as
ligand: uncommon case of N–H · · · I–Pt hydrogen bonding
S. Jafar Hoseini,a Maryam Mohamadikish,a Katayon Kamali,a Frank W. Heinemannb and Mehdi Rashidi*a
Received 2nd January 2007, Accepted 20th February 2007
First published as an Advance Article on the web 15th March 2007
DOI: 10.1039/b700009j
The complex [PtMe2(dppa)], 1a, dppa = Ph2PNHPPh2, which has previously been prepared as a
mixture with the dimeric form [Pt2Me4(l-dppa)2], was synthesized in pure form by the reaction of
[PtCl2(dppa)] with MeLi. The aryl analogue [Pt(p-MeC6H4)2(dppa)], 1b, was prepared by replacement
of SMe2 in cis-[Pt(p-MeC6H4)2(SMe2)2] with dppa. The reaction of the chelate complexes 1 with one
=
equiv. of dppa afforded the complexes [PtR2(dppa-P)2], R Me, 2a and R = p-MeC6H4 2b. The reaction
=
of [PtR2(dppa)], 1, with neat MeI gave the organoplatinum(IV) complexes [PtR2MeI(dppa)], R Me, 5a
and R = p-MeC6H4, 5b. The structure of 5a, determined by X-ray crystallography, indicated that the
complex undergoes self-assembly by intermolecular N–H · · · I–Pt hydrogen bonding. MeI was also
double oxidatively added to organodiplatinum(II) complex cis,cis-[Me2Pt(l-SMe2)(l-dppa)PtMe2], to
give diorganoplatinum(IV) complex [Me3Pt(l-dppa)(l-I)2PtMe3], 4. The aryl analogue
organodiplatinum(II) complex cis,cis-[(p-MeC6H4)2Pt(l-SMe2)(l-dppa)Pt(p-MeC6H4)2], 3b,
was prepared by the reaction of cis-[Pt(p-MeC6H4)2(SMe2)2] with half equiv. of dppa, but 3b refused to
react with MeI, probably because of the steric effects of the aryl ligands. The tetramethyl complex
[PtMe4(dppa)], 6, was prepared either by reaction of 5a with MeLi or by replacement of SMe2 in
[Pt2Me8(l-SMe2)2] with dppa. All the complexes were fully characterized in solution by multinuclear
NMR (1H, 13C, 31P and 195Pt) methods and their coordination compared with that of the corresponding
known dppm complexes.
NMR studies and their structures and coordination behaviors
Introduction
are compared with those of the corresponding known dppm
complexes. The structure of one of the platinum(IV) complexes,
[PtMe3I(dppa)], 5a, has been determined by X-ray crystallography.
In designing the molecular structures of coordination complexes
suitable for special chemical and/or industrial studies, it is often
necessary to use closely related ligands in order to finely tune
the properties of the complexes. A popular ligand which has
been widely used in making many organometallic and coordi-
nation complexes, is bis(diphenylphosphino)methane, dppm =
Ph2PCH2PPh2.1 This versatile and robust ligand is normally
known to act as a bridging ligand and as such many binuclear2 and
multinuclear3 platinum complexes are reported, although there
are cases in which it acts as a chelate or a monodentate ligand.4
However, the closely related ligand bis(diphenylphosphino)amine,
dppa = Ph2PNHPPh2, which might be used in conjunction with
dppm for the above mentioned purpose, has not yet received the
same scrutiny.5 Although dppa and dppm seem to behave in a
similar way in the formation of complexes, differences do also
exist in their coordination behavior.6,7 Besides, the NH proton of
the coordinated dppa ligand has a greater acidity than the CH2
protons of dppm and this would considerably affect, for example,
N-functionalization reactions8 and hydrogen bond formation in
crystal engineering.9
Results and discussion
The synthetic routes and the related chemistry studied in this work
are described in Schemes 1 and 2. All the characterization data are
collected in the Experimental.
Synthesis and characterization of the organoplatinum(II) complexes
The starting complex [PtCl2(dppa)] and the product of its reaction
with one mole of dppa, i.e. [Pt(dppa)2][Cl]2, were prepared as
reported elsewhere.7,10 In the 1H NMR spectrum of the latter cation
in CDCl3, we have observed a broad singlet at very low field (d =
12.5) which as shown in Scheme 1, is suggested to be due to the
formation of strong N · · · H · · · Cl− hydrogen bonding.
The reaction of [PtCl2(dppa)] with MeLi or the reaction of
cis-[Pt(p-MeC6H4)2(SMe2)2] with one equiv. of dppa was used to
prepare the diorganoplatinum(II) complexes [PtMe2(dppa)], 1a,
or [Pt(p-MeC6H4)2(dppa)], 1b, respectively. Note that complex 1a
has previously been prepared with difficulty by heating its mixture
with the dimeric form [Pt2Me4(l-dppa)2].6 The complex 1a was
characterized by its NMR data.6 The observation of a singlet in
the 31P NMR spectrum of 1b at d = 30.6 accompanied by platinum
satellites with 1J(PtP) = 1463 Hz clearly confirms the dppa ligand
being chelated with the coordinating phosphorus atoms being
trans to aryl ligands having high trans influence. In the 1H NMR
In this study, several new organoplatinum complexes con-
taining dppa are synthesized and characterized by multinuclear
aDepartment of Chemistry, Faculty of Sciences, Shiraz University, Shiraz,
71454, Iran. E-mail: rashidi@chem.susc.ac.ir; Fax: +98-711-2286008;
Tel: +98-711-2284822
bInstitut fuer Anorganische Chemie, Universitaet Erlangen-Nuernberg,
Egerlandstrasse 1, D-91058, Erlangen, Germany
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Scheme 1
spectrum of 1b, a rather broad singlet with platinum satellites at
d = 5.4 with 3J(PtH) = 65 Hz was assigned to the NH proton of
dppa. The Hm resonance of the tolyl ligands appeared at 6.64 which
coupled to Ho with 3J(HH) = 6.8 Hz, while the Ho appeared at 7.18
as a multiplet (due to coupling to Hm as well as the phosphorus
atom) which then coupled to platinum with 3J(PtH) = 53 Hz.
The reaction of [PtR2(dppa)], 1, with one equiv. of dppa gave
the complexes [PtR2(dppa-P)2], 2, separated at room temperature
in pure form and good yield. In the 31P NMR spectrum of
[Pt(p-MeC6H4)2(dppa-P)2], 2b (see Fig. 1A), the co-ordinated
phosphorus atoms (indicated as Pb as compared to Pa which is
the unco-ordinated phosphorus atom) appeared as a doublet at
d = 52.2 with 1J(PtPb) = 2062 Hz and 2J(PbPa) = 17 Hz. Pa atoms
however appeared shifted to a higher field as a doublet at d = 25.2
with 2J(PtPa) approximately 74 Hz and 2J(PbPa) = 17 Hz. In the
1H NMR spectrum of 2b, the NH protons appeared as a doublet of
doublets at d = 3.9 with 2J(PH) = 7.5 and 5.0 Hz. In the 31P NMR
spectrum of [PtMe2(dppa-P)2], 2a, a 2 : 1 mixture of two isomers
was observed at d = 64.2 (Pb); 30.8 (Pa) and d = 64 (Pb); 31.3 (Pa)
(see Experimental for details) each showing an AAꢀXXꢀ pattern.4b
In accord with this, in the 1H NMR spectrum of 2a, two doublet
of doublets at d = 3.38 and 4.86 were observed for the NH protons
of the two isomers. The observation of two isomers in the case of
Scheme 2
complexes [Pt(p-MeC6H4)2(dppm-P)2] and [PtMe2(dppm-P)2], it
has been reported that they dissociate extremely rapidly in solution
and only the latter complex could be isolated and characterized
at low temperatures; the related complexes with ortho-substituted
aryl ligands, e.g. o-MeC6H4, however were readily isolated at room
temperature.4b Also, the dppm complexes [PtR2(dppm-P)2] have
been widely used to systematically synthesize the homo-bimetallic
complexes such as [Me2Pt(l-dppm)2Pt(o-tolyl)2]12a and hetero-
bimetallic complexes containing the Pt(l-dppm)2M moiety, M
being different transition metals such as Ag, Au, Rh, Ir, Mo and
W. 12 However, our similar attempts using the dppa analogues
[PtR2(dppa-P)2], 2, have led to the formation of the chelate
complexes [PtR2(dppa)], 1.
The binuclear dimethylplatinum(II) complex 3a, as described in
Scheme 1, has been reported previously.6 The new bis-tolyl ana-
logue cis,cis-[(p-MeC6H4)2Pt(l-SMe2)(l-dppa)Pt(p-MeC6H4)2],
3b, was prepared by the reaction of cis-[Pt(p-MeC6H4)2(SMe2)2]
with 1/2 equiv. of dppa in high yield. The course of the
reaction was monitored by 1H NMR spectroscopy and as
described in Scheme 2, an equivalent mixture of the chelating
complex [Pt(p-MeC6H4)2(dppa)], 1b, and the starting complex
cis-[Pt(p-MeC6H4)2(SMe2)2] was first formed which then reacted
=
complex 2a, where R Me, is probably due to the relative positions
of the two dppa ligands, something that is not happening in the
related aryl complex 2b, most likely due to the steric restriction
created by the aryl ligands. In contrast, for the analogous dppm
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1b. The conversion of 3b to 1b was completed after 10 h,
while the conversion of the related dppm dimer cis,cis-[Ph2Pt(l-
SMe2)(l-dppm)PtPh2] to the monomeric product [PtPh2(dppm)]
was completed after more than 30 h.2b We believe that the dppm
conversion takes place with a similar mechanism as described here
for the dppa complex and the faster rate of the dppa reaction
is probably due to the fact that the dppa intermediate 2b is
far more stable than the presumed dppm intermediate [Pt(p-
MeC6H4)2(dppm-P)2], which is hard to form and is not observable
at room temperature.2b
Synthesis and characterization of the organoplatinum(IV)
complexes
The oxidative addition of MeI to the monomeric complexes
[PtR2(dppa)], 1, gave the platinum(IV) complexes [PtR2MeI-
(dppa)], 5, as described in Scheme 1.
In the 31P NMR spectrum of [Pt(p-MeC6H4)2MeI(dppa)], 5b, a
1
singlet at d = 2.6 with J(PtP) = 964 Hz, typical of phosphorus
ligands trans to aryl ligands in platinum(IV) complexes, was
observed. The observation of only one singlet confirms the
existence of only one isomer in which Me and I ligands are in
trans positions with respect to each other. In line with this, in
1
the H NMR spectrum of 5b, a signal at 1.39 was observed for
the Me ligand trans to I which is a triplet due to coupling with
3
Fig. 1 The 31P NMR spectra of the reaction of cis,cis-[(p-MeC6H4)2-
Pt(l-SMe2)(l-dppa)Pt(p-MeC6H4)2], 3b (shown by s), with 1 equiv. of dppa
after (A) 5 min and (B) 2 h. The complex [Pt(p-MeC6H4)2(dppa-P)2],
2b (shown by d), is formed very fast, and the final monomeric complex
[Pt(p-MeC6H4)2(dppa)], 1b (shown by m) is then gradually formed. The
reaction was completed after 10 h. The small amount of free dppa in (A)
is indicated by #. Trace impurity is shown by the asterisks.
two equivalent phosphorus atoms with J(PH) = 7.8 Hz; the Pt
2
satellites gave J(PtH) = 67.7 Hz. A broad peak at 5.66 with
3J(PtH) = 46.6 Hz, was assigned to the NH proton of dppa.
The Hm of the tolyl ligands appeared at 6.65 which coupled to
3
Ho with J(HH) = 6.2 Hz, while the Ho appeared at 7.17 as a
multiplet (due to coupling to Hm as well as the phosphorus atom)
which then coupled to platinum with 3J(PtH) = 42 Hz. Note that,
as expected, the coupling constants of Ho protons or the NH
proton of dppa with platinum atoms in the platinum(IV) complex
5b have considerably reduced as compared to the values in the
corresponding platinum(II) complex 1b. Thus, 3J(PtH) values for
NH protons have reduced from 65 to 46.6 Hz and 3J(PtH) values
for Ho protons have reduced from 53 to 42 Hz.
to form the final dimeric product 3b, probably via the presumed
intermediate 7. In the 31P NMR spectrum of 3b, the two equivalent
phosphorus atoms resonated as a singlet at d = 63.8 and showed
platinum satellites. When one platinum atom is 195Pt, the two
phosphorus atoms are no longer equivalent and appeared as two
sets of satellites, one set is due to the short range coupling with
1J(PtP) = 2067 Hz and the other set due to long range coupling
For the methyl analogue [PtMe3I(dppa)], 5a, in the 31P NMR
spectrum, a singlet at d = 10.5 with 1J(PtP) = 927 Hz, typical of
the coupling values obtained for organoplatinum(IV) complexes
with phosphorus atoms being trans to C, was observed. In the 1H
NMR spectrum of the complex, the Me ligand trans to I appeared
at d = 0.74 as a triplet due to coupling with two equivalent cis
phosphorus atoms with 3J(PH) = 8.1 Hz, which further coupled
3
with J(PtP) = 33 Hz. The splitting in the satellites corresponds
to a 2J(PP) value of 47 Hz. Consistently, in the 195Pt NMR
spectrum of 3b, a doublet of doublets was observed at d = −4256
1
3
with J(PtP) = 2097 Hz and J(PtP) = 33 Hz, very close to the
coupling values obtained from the corresponding 31P spectrum.
In the H NMR spectrum of 3b, the Me groups of SMe2 ligand
1
2
to platinum with J(PtH) = 70.0 Hz. The two Me ligands trans
3
appeared as a multiplet at d = 1.5 with J(PtH) = 23.5 Hz, and
to P were observed as a multiplet at d = 1.26 with a considerably
lower 2J(PtH) = 63.0 Hz, and the triplet at d = 5.67 with 2J(PH) =
3.7 Hz and 3J(PtH) = 42.0 Hz was assigned to the NH proton of
dppa.
two singlets at d = 1.9 and 2.0 were assigned to the two different
Me groups on the tolyl ligands. A broad peak at d = 2.6 was
observed for the NH proton of the dppa ligand.
The reaction of the latter complex 3b with one equiv. of dppa is
interesting and was monitored by 1H and 31P NMR spectroscopy.
The 31P NMR spectra of the reaction after 5 min and after 2 h
are shown in Fig. 1. As described in Scheme 2, the complex
[Pt(p-MeC6H4)2(dppa-P)2], 2b, and the diplatinum(II) complex [(p-
MeC6H4)2Pt(l-SMe2)2Pt(p-MeC6H4)2] are first formed; the latter
dimer has of course very rapidly reacted with dppa to give back the
starting dimer 3b. Subsequently, the complex 2b, slowly reacted
with 3b to form the final chelate product [Pt(p-MeC6H4)2(dppa)],
It is interesting to note that the latter complex [PtMe3I(dppa)],
5a, was obtained in pure form when the reaction of [PtMe2(dppa)],
1a, with neat MeI was performed for at least 2 h. However, for
shorter reaction times, a second species was formed as a mixture
1
with 5a. This new species has 31P and H NMR patterns very
similar to those of 5a with almost identical coupling values, but
each peak appeared at a slightly lower chemical shift compared
to the corresponding one obtained for 5a (see Experimental for
details). The 31P NMR spectrum of the products of the reaction
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Table 1 Selected bond distances (A) and angles (◦) for complex
[PtMe3I(dppa)], 5a
˚
of [PtMe2(dppa)], 1a, with neat MeI after 15 min and after work-
up, is shown in Fig. 2. Thus, the new second species is formed
along with the first one and then gradually converted to the final
product which is the first species, called 5a. We tentatively assign
this observation to be due to some kind of change in the degree
of aggregation of the molecules of [PtMe3I(dppa)], 5a, via the
formation of intermolecular hydrogen bonding of type N–H · · · I–
Pt; the crystal structure of 5a (vide infra) indicated intermolecular
hydrogen bonding of this type in crystal state. Complex 5a can
either exist in monomeric or oligomeric form in solution although
the formation of two intermolecular hydrogen bonds to give a
dimeric form of the type shown in Scheme 3 is also a possibility.13
Pt(1)–C(2)
Pt(1)–C(1)
Pt(1)–C(3)
Pt(1)–P(1)
C(2)–Pt(1)–C(1)
C(2)–Pt(1)–C(3)
C(1)–Pt(1)–C(3)
C(2)–Pt(1)–P(1)
C(1)–Pt(1)–P(1)
C(3)–Pt(1)–P(1)
C(2)–Pt(1)–P(2)
C(1)–Pt(1)–P(2)
C(3)–Pt(1)–P(2)
2.091(5)
2.094(5)
2.095(5)
2.380(2)
85.5(2)
86.6(2)
87.1(2)
Pt(1)–P(2)
Pt(1)–I(1)
P(1)–N(1)
P(2)–N(1)
P(1)–Pt(1)–P(2)
C(2)–Pt(1)–I(1)
C(1)–Pt(1)–I(1)
C(3)–Pt(1)–I(1)
P(1)–Pt(1)–I(1)
P(2)–Pt(1)–I(1)
N(1)–P(1)–Pt(1)
N(1)–P(2)–Pt(1)
P(1)–N(1)–P(2)
2.383(2)
2.7813(4)
1.689(5)
1.690(4)
68.93(5)
174.6(2)
91.4(2)
91.2(2)
88.9(2)
169.6(2)
102.5(2)
89.7(2)
92.65(3)
95.25(3)
92.6(2)
101.2(2)
170.6(2)
92.5(2)
105.8(3)
Fig. 2 31P NMR spectrum of the products of reaction of [PtMe2(dppa)],
1a, with neat MeI after 15 min and after work-up. The second species is
shown by asterisks; it disappeared when the reaction time was at least 2 h.
Fig. 3 Molecular structure of complex [PtMe3I(dppa)], 5a (50% proba-
bility ellipsoids, H atoms and solvent molecules omitted for clarity).
hydrogen bonding of type N–H · · · I–Pt [N(1) · · · I(1)#1 = 3.756(5)
◦
˚
A, N(1)H(1)I(1)#1 = 167.4 ], as is described in Table 2, has
caused the self-assembling of the molecules of complex 5a. The
normalized distance, RHI,14–16 calculated for this hydrogen bond
˚
is 0.915 A, which is in the hydrogen bonding viability range,
established by Brammer et al. for the N–H · · · I–M donor–acceptor
combination.14 The observed H · · · I–M angle for complex 5a is
119.9◦ which is in the preferred range of 90–130◦ established by
Brammer et al. based on their analysis of N–H · · · I–M systems.14
Note also that Rheingold et al.18 in their study of angular
preference in M–Cl · · · H–N hydrogen bonding, suggested that
an H · · · Cl–M angle close to 90◦ is preferred and ascribed the
observed angles of >90◦ to steric hindrance created by the group
attached to Cl. These are explained as probably due to higher
basicity of the p-type X lone pair relative to the sp lone pair.14,18
MeI performed double oxidative addition to the dimeric
organoplatinum(II) complex cis,cis-[Me2Pt(l-SMe2)(l-dppa)-
PtMe2], 3a, to give the diplatinum(IV) complex [Me3Pt(l-dppa)(l-
I)2PtMe3], 4, as is described in Scheme 1. In the 31P NMR spectrum
Scheme 3
The structure of complex [PtMe3I(dppa)], 5a, was determined
by X-ray crystallography and is shown in Fig. 3, with the selected
bond distances and angles in Table 1. The complex contains an
octahedral platinum(IV) centre with 3 methylplatinum groups, a
chelating dppa ligand, and an iodide ligand. Due to the presence of
the 4-membered PtPNP ring, considerable distortions are expected
for the four angles involved in the dppa chelate unit. Thus,
P(1)Pt(1)P(2) = 68.93(5)◦ is much less than the ideal angle of 90◦,
P(1)N(1)P(2) = 105.8(3)◦ is significantly less than in the free ligand
[118.9(2)◦], and the angles NPPt = 92.63(16)◦ or 92.51(16)◦ are
less than the tetrahedral angle. The formation of intermolecular
Table 2 Hydrogen bonds for complex [PtMe3I(dppa)], 5a
∠DHA/◦
˚
˚
˚
D–H · · · A
d(D–H)/A
d(H · · · A)/A
d(D · · · A)/A
N(1)–H(1) · · · I(1)a
0.88
2.89
3.756(5)
167.4
a
−x + 3/2, y + 1/2, −z + 1/2.
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of 4, the two equivalent phosphorus atoms resonated as a singlet
at d = 36.8 with the short range platinum satellites with 1J(PtP) =
1181 Hz, while the long range coupling 3J(PtP) was not resolved.
The complexes, cis-[Pt(p-MeC6H4)2(SMe2)2],23 cis,cis-[Me2Pt(l-
SMe2)2PtMe2],24 cis,cis-[Me2Pt(l-SMe2)(l-dppa)PtMe2], 3a,6
[PtCl2(dppa)],7 [Pt(dppa)2][Cl]2 and [Pt2Me8(l-SMe2)2],25 were
7
2
The splitting in the satellites corresponds to a J(PP) value of
prepared by methods described in the literature.
4.6 Hz. Consistently, in the 195Pt NMR spectrum of 4, a doublet
1
was observed at d = −3744 with J(PtP) = 1209 Hz, close to
[PtMe2(dppa)], 1a
the value obtained from the corresponding 31P spectrum. In the
3
1H NMR spectrum of 4, a doublet at d = 0.72 with J(PH) =
A solution of MeLi (10 ml) was slowly added to a stirred ice-cold
solution of [PtCl2(dppa)] (335 mg; 0.514 mmol) in dry ether (40 ml)
under Ar atmosphere. The reaction mixture was stirred for 2 h and
then hydrolyzed with water (4 ml). Separation of the organic layer,
extraction with CH2Cl2, drying over MgSO4 and evaporation of
the organic solvents gave an off-white powder which was washed
with ether (5 ml) and the product was dried under vacuum. Yield:
86%; mp 175 ◦C (decomp.). Anal. Calcd. for C26H27NP2Pt: C, 51.2;
H, 4.5; N, 2.3. Found: C, 51.3; H, 4.6; N, 2.2%. NMR in CDCl3:
d (1H) = 0.61 [m, 3J(PtH) = 74.7 Hz, 6H, 2 Me ligands], 5.28 [t,
3J(PtH) = 62.3 Hz, 2J(PH) = 9.0 Hz, 1H, NH of dppa].
7.7 Hz and 2J(PtH) = 74.4 Hz was assigned to the two equivalent
Me ligands trans to I, while the Me ligand trans to the phosphorus
atom was located at d = 1.83 as a doublet with 3J(PH) = 8.1 Hz and
2J(PtH) = 59.4 Hz. A broad peak at d = 4.0 was observed for the
NH proton of the dppa ligand. The 13C NMR spectrum of 4 was
also useful and gave a doublet at d = 9.7 for the Me groups trans
to phosphorus with 2J(CP) = 133 Hz, with coupling to platinum
with 1J(CPt) = 507 Hz. The two equivalent Me groups trans to I
did not give resolvable phosphorus couplings and appeared as a
singlet at d = 12.3 with a higher value of 1J(CPt) = 652 Hz.
The tetramethylplatinum(IV) complex [PtMe4(dppa)], 6, as is
described in Scheme 1, was prepared either by the replacement
of SMe2 with dppa in [Pt2Me8(l-SMe2)2] or by the reaction of
[PtMe3I(dppa)], 5a, with MeLi. In the 31P NMR spectrum of 6,
[Pt(p-MeC6H4)2(dppa)], 1b
A mixture of cis-[Pt(p-MeC6H4)2(SMe2)2] (200 mg; 0.398 mmol)
and dppa (153.6 mg; 0.398 mmol) in dry benzene (30 ml) was
stirred at room temperature for 2 h. The solvent was removed and
the product was washed with n-hexane (2 ml) and then ether (2 ml)
and dried under vacuum. Yield: 92%; mp 200 ◦C (decomp.). Anal.
Calcd. for C38H35NP2Pt: C, 59.8; H, 4.6. Found: C, 60.6; H, 4.7%.
NMR in CDCl3: d (1H) = 2.18 [s, 6H, 2 Me groups on the tolyl
1
a singlet at d = 1.1 with J(PtP) = 979 Hz was observed for the
1
two equivalent phosphorus atoms. In the H NMR spectrum of
3
6, a triplet at d = −0.14 with J(PH) = 6.9 Hz accompanied by
2
platinum satellite with J(PtH) = 45.2 Hz was assigned to the
two equivalent Me ligands trans to each other and equivalently cis
to two phosphorus atoms. The unusually low value of 2J(PtH) is
consistent with the very high trans influence of the Me ligand. The
Me ligands trans to phosphorus atoms were located at d = 0.82 as
3
2
ligands], 5.4 [br., J(PtH) = 65 Hz, J(PH) = not resolved, 1H,
3
NH], 6.64 [d, J(HH) = 6.8 Hz, 4 Hm of tolyl ligands], 7.18 [m,
2
a multiplet with platinum satellites with J(PtH) = 63.9 Hz and
3J(PtH) = 53 Hz, 4 Ho of tolyl ligands]; d(31P) = 30.6 [s, 1J(PtP) =
3
3J(PH) + J(PꢀH) = 7.5 Hz. The NH proton of dppa appeared
1463 Hz].
as a broad signal at d = 5.67 which coupled with platinum with
3J(PtH) = 52.5 Hz. The 13C NMR spectrum of 6 is also very
informative and gave a triplet at d = −5.7 for the Me groups trans
to each other and cis to two equivalent phosphorus atoms with
2J(CP) = 4 Hz, with coupling to platinum with a considerably
lower 1J(CPt) value of 398 Hz due to the very high trans influence
of the Me ligand. The Me ligands trans to phosphorus ligands
[PtMe2(dppa-P)2], 2a
A mixture of [PtMe2(dppa)], 1a, (30 mg, 0.049 mmol) and dppa
(18.9 mg, 0.049 mmol) in dry benzene (10 ml) was stirred at room
temperature for 10 min. The solvent was removed and the residue
was washed with n-hexane (2 × 2 ml) and dried under vacuum.
Yield: 88%. Anal. Calcd. for C50H48N2P4Pt; C, 60.3; H, 4.9; N, 2.8;
Found: C, 60.3; H, 4.9: N, 2.7%. 1H NMR data in C6D6: d 0.7–1.1
(overlapping multiplets, Me ligands), 4.86 [dd, 2J(PbH) = 7.5 Hz;
2
appeared at d = 0.4 as a doublet of doublets with J(CPcis) =
2
3 Hz and J(CPtrans) = 131 Hz with coupling to platinum with
1J(CPt) = 567 Hz. The PtC coupling values for complex 6 are
almost identical to the values obtained for the dppm analogue
complex [PtMe4(dppm)],19 which indicate that dppa and dppm
have probably exerted the same trans influence. However, based on
the above 31P NMR data, the 1J(PtP) value of 979 Hz for complex
2
2J(PaH) = 14.8 Hz, NH of minor isomer], 3.84 [dd, J(PbH) =
2
7.3 Hz; J(PaH) = 13.0 Hz, NH of major isomer]; 31P NMR in
C6D6: major isomer: d = 64.2[m, 1J(PtPb) = 2064 Hz, Pb], 30.8 [m,
2
4
3J(PtPa) = 43 Hz, N = J(PbPa) + J(PbPa) = 19 Hz, Pa]; minor
1
6 is nearly 5% higher than the corresponding value of J(PtP) =
isomer: d = Pb overlapped under Pb of major isomer], 31.3 [m,
936 Hz for the dppm analogue complex [PtMe4(dppm)].19 The
difference, although modest, confirms that in the dppa analogue
the four-membered chelate ring experiences less strain.
3J(PtPa) = 29 Hz, N = J(PbPa) + 4J(PbPa) = 14 Hz Pa].
2
[Pt(p-MeC6H4)2(dppa-P)2], 2b
A mixture of [Pt(p-MeC6H4)2(dppa)], 1b, (100 mg; 0.131 mmol)
and dppa (50.5 mg; 0.131 mmol) in dry benzene (30 ml) was
stirred at room temperature for 3 h. The solvent was removed and
the product was washed with n-hexane (2 × 3 ml) and then dried
under vacuum. Yield: 51%, mp 146 ◦C (decomp.). Anal. Calcd.
for C62H56N2P4Pt: C, 64.9; H, 4.9. Found: C, 65.0; H, 5.0%. NMR
in CDCl3: d (1H) = 2.0 [s, 6H, 2 Me groups on the tolyl ligands],
3.9 [dd, 2J(PH) = 7.5 and 5.0 Hz, 2H, NH groups of the 2 dppa
Experimental
The 1H and 13C NMR spectra were recorded on a Bruker
Avance DPX 250 MHz spectrometer. 31P and 195Pt NMR spectra
were recorded on a Bruker Avance DRX 500 MHz. References
were TMS (1H and 13C), H3PO4 (31P), and aqueous K2PtCl4
(
195Pt), and CDCl3 was used as solvent in all cases. All chemical
shifts and coupling constants are in ppm and Hz, respectively.
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The Royal Society of Chemistry 2007
Dalton Trans., 2007, 1697–1704 | 1701
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ligands]; d(31P) = 25.2 [d, 3J(PtPa) = 74 Hz, 2J(PbPa) = 17 Hz, 2
Pa], 52.2 [d, 1J(PtPb) = 2062 Hz, 2J(PbPa) = 17 Hz, 2 Pb.
[PtMe3I(dppa)], 5a
The complex [PtMe2(dppa)], 1a, (100 mg), in neat MeI was stirred
for 2 h. The solvent was removed and the residue was washed with
n-hexane (2 × 2 ml) and dried under vacuum. Yield: 73% (90 mg);
m.p 165◦ C (dec.). Anal. Calcd. for C27H30INP2Pt; C, 43.1; H, 4.0;
N, 1.9; Found: C, 44.2; H, 4.2: N, 1.9%. NMR in CDCl3: d(1H) =
0.74 [t, 2J(PtH) = 70.0 Hz, 3J(PH) = 8.1 Hz, 3H, Me ligand trans
cis,cis-[(p-MeC6H4)2Pt(l-SMe2)(l-dppa)Pt(p-MeC6H4)2], 3b
A mixture of cis-[Pt(p-MeC6H4)2(SMe2)2] (200 mg; 0.398 mmol)
and dppa (76.8 mg; 0.199 mmol) in dry benzene (30 ml) was
stirred at room temperature for 2 h. The solvent was removed and
the product was washed with n-hexane (5 ml) and then methanol
(3 ml) and dried under vacuum. Yield: 62%; mp 115 ◦C (decomp.).
Anal. Calcd. for C54H55NP2SPt2: C, 54.0; H, 4.6; N, 1.2. Found: C,
54.1; H, 4.7; N, 1.2%. NMR in CDCl3: d (1H) = 1.5[m, 3J(PtH) =
23.5 Hz, 6H, 2 Me groups of SMe2 ligand], 1.9 and 2.0 [s, 2 Me
2
to I], 1.50 [m, J(PtH) = 63.0 Hz, 6H, 2 Me ligands trans to P],
3
2
5.67 [t, J(PtH) = 42.0 Hz, J(PH) = 3.7 Hz, 1H, NH of dppa];
d(31P) = 10.5 [s, 1J(PtP) = 927 Hz, dppa].
When the reaction time was 15 min, the above complex 5a was
accompanied by a second species with the NMR data in CDCl3:
2
3
d (1H) = 0.44 [t, J(PtH) = 73.0 Hz, J(PH) = 8.2 Hz, 3H, Me
ligand trans to I], 1.26 [m, 2J(PtH) = 62.0 Hz, 3J(PH) + 3J(PꢀH) =
12.5 Hz, 6H, 2 Me ligands trans to P], 5.51 [t, 3J(PtH) = 40.3 Hz,
3
2
groups on the tolyl ligands], 2.6 [br, J(PtH) and J(PH) = not
1
resolved, 1H, NH of dppa]; d(31P) = 63.8 [s, J(PtP) = 2067 Hz,
2
3J(PtP) = 33 Hz, J(PP) = 47 Hz, dppa]; d(195Pt) = −4256 [dd,
2J(PH) = 3.7 Hz, 1H, NH of dppa]; d(31P) = 1.0 [s, J(PtP) =
1
1J(PtP) = 2097 Hz, 3J(PtP) = 33 Hz].
933 Hz, dppa].
Reaction of cis-[Pt(p-MeC6H4)2(SMe2)2] with dppa in NMR tube
[Pt(p-MeC6H4)2MeI(dppa)], 5b
A small sample (20 mg, 0.039 mmol) of cis-[Pt(p-MeC6H4)2-
(SMe2)2], was dissolved in CDCl3 in a sealed NMR tube, and dppa
(7.68 mg, 0.0195 mmol) was added. The reaction was followed by
1H NMR spectroscopy.
The complex [Pt(p-MeC6H4)2(dppa)], 1b, (100 mg) in neat MeI
was stirred for 8 h. The solvent was removed and the residue was
washed with dry ether (2 × 2 ml) and dried under vacuum. Yield:
◦
71% (85 mg); mp 231 C (dec). Anal. Calcd. For C39H38INP2Pt;
C, 51.8; H, 4.2; N, 1.5; Found: C, 51.9; H, 4.5: N, 1.6%. NMR
in CDCl3: d (1H) = 1.39 [t, 2J(PtH) = 67.7 Hz, 3J(PH) = 7.8 Hz,
3H, Me ligand trans to I], 2.09 [s, 6H, 2 Me groups on the tolyl
Reaction of cis,cis-[(p-MeC6H4)2Pt(l-SMe2)(l-dppa)Pt(p-
MeC6H4)2], 3b, with dppa in an NMR tube
3
ligands], 5.66 [br, J(PtH) = 46.6 Hz, 1H, NH of dppa], 6.65 [d,
A small sample (20 mg, 0.016 mmol) of cis, cis-[(p-MeC6H4)2Pt(l-
SMe2)(l-dppa)Pt(p-MeC6H4)2], 3b, was dissolved in CDCl3 in a
sealed NMR tube, and dppa (6.41 mg, 0.016 mmol) was added.
The reaction was followed by 1H and 31P NMR spectroscopy.
3J(HH) = 6.2 Hz, 4 Hm of tolyl ligands], 7.17 [m, 3J(PtH) = 42 Hz,
4 Ho of tolyl ligands]; d(31P) = 2.6 [s, 1J(PtP) = 964 Hz, dppa].
[PtMe4(dppa)], 6
(i) A mixture of [Pt2Me8(l-SMe2)2] (127 mg, 0.2 mmol) and
dppa (154 mg, 0.4 mmol) in dry ether (30 ml) was stirred at
room temperature. After 6 h a colorless solid precipitated. The
precipitate was isolated by filtration, washed with ether (2 ml),
and dried under vacuum. Yield: 78% (200 mg); mp 140 ◦C (dec.).
Anal. Calcd. for C28H33NP2Pt; C, 52.5; H, 5.2; N, 2.2; Found:
C, 52.0; H, 5.3: N, 1.8%. NMR in CDCl3: d (1H) = −0.14 [t,
Reaction of [Pt(p-MeC6H4)2(dppa-P)2], 2b, with
cis,cis-[Me2Pt(l-SMe2)2PtMe2]
A mixture of [Pt(p-MeC6H4)2(dppa-P)2] (200 mg, 0.174 mmol)
and cis,cis-[Me2Pt(l-SMe2)2PtMe2] (50 mg, 0.087 mmol) in dry
benzene (30 ml) was stirred at room temperature for 1 h. The
solvent was removed and the product was washed with n-hexane
(3 ml) and dried under vacuum.
3
2J(PtH) = 45.2 Hz, J(PH) = 6.9 Hz, 6H, Me ligands trans to
Me], 0.82 [m, 2J(PtH) = 63.9 Hz, 3J(PH) + 3J(PꢀH) = 7.5 Hz, 6H,
Me ligands trans to phosphorus], 5.67[br, 3J(PtH) = 52.5 Hz, 1H,
NH of dppa]. d(31P) = d 1.1 [s, 1J (PtP) = 979 Hz, dppa]. d(13C) =
−5.7 [t, 1J(CPt) = 398 Hz, 2J(CP) = 4 Hz, 2C trans to C], 0.4 [dd,
[Me3Pt(l-dppa)(l-I)2PtMe3], 4
To a solution of [Me2Pt(l-SMe2)(l-dppa)PtMe2], 3a, (70 mg,
◦
2
2
1J(CPt) = 567 Hz, J(CPcis) = 3 Hz, J(CPtrans) = 131, 2C trans
0.078) mmol) in benzene (10 ml) at 0 C, was added excess MeI
(2 ml) and the reaction mixture was stirred for 3 h. The solvent
and excess MeI was removed and the residue was washed twice
with methanol (2 ml) to give the product as a white solid which
was dried under vacuum. Yield: 50%; mp 215–220 ◦C (decomp.).
Anal. Calcd. for C30H39I2NP2Pt2·0.3C6H6: C, 33.4; H, 3.6; N, 1.2.
Found: C, 33.4; H, 3.8; N, 1.0%. NMR in CDCl3: d (1H) = 0.72 [d,
3J(PH) = 7.7 Hz, 2J(PtH) = 74.4 Hz, 6H, Me ligands trans to I],
1.83 [d, 3J(PH) = 8.1 Hz, 2J(PtH) = 59.4 Hz, 3H, Me ligand trans
to phosphorus], 4.0 [br, 1H, NH proton of dppa ligand]; d(31P) =
to P].
(ii) MeLi (6 ml) was added slowly to a suspension of
[PtMe3I(dppa)] (0.5 g, 0.66 mmol) in anhydrous ether (30 ml) at
0 ◦C under Ar atmosphere. The reaction mixture was stirred for 1 h
and then hydrolyzed carefully with saturated aqueous ammonium
chloride solution (10 ml). The ether layer was separated, dried over
MgSO4, and evaporated under vacuum. The product washed with
ether (5 ml) and dried under vacuum. Yield: 70%.
1
3
2
36.8 [s, J(PtP) = 1181 Hz, J(PtP) = not resolved, J(PP) =
X-Ray structure determination
4.6 Hz, dppa]; d(195Pt) = −3744 [d, 1J(PtP) = 1209 Hz]; d(13C) =
2
1
9.7 [d, J(CP) = 133 Hz, J(CPt) = 507 Hz, Me groups trans to
Single crystals of [PtMe3I(dppa)], 5a, were grown from a concen-
trated methylene chloride solution by slow diffusion of hexane. A
phosphorus], 12.3 [s, 1J(CPt) = 652 Hz, Me groups trans to I].
1702 | Dalton Trans., 2007, 1697–1704
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Table 2 Crystal data, data collection and structure refinement details for
[PtMe3I(dppa)]·CH2Cl2, 5a
from the reaction of [PtCl2(dppa)] with MeLi. This provides a nice
contrast with the work of Braunstein et al., who demonstrated that
deprotonation of the NH moiety with strong bases was possible.8
Similarly, in the chelating organoplatinum(IV) complexes, the
1J(PtP) values are more than 3% greater in the dppa analogues.
Formula
Formula weight
Temperature/K
C28 H32Cl2INP2Pt
837.38
100(2)
1
˚
Wavelength/A
0.71073
Thus, the J(PtP) values for phosphorus atoms trans to Me in
Crystal system
Space group
Monoclinic
P21/n (No. 14)
10.6200(11)
14.2098(5)
19.5531(14)
94.577(8)
2941.3(4)
4
1.891
6.129
1608
55 094
[PtMe3I(dppa)], 5a, and [PtMe3I(dppm)]19 are 927 and 897 Hz,
respectively. Despite this, based on the 13C NMR data, it is
possible to show that both dppa and dppm exert a similar trans
influence in their complexes. Thus, for the platinum(IV) complexes
[PtMe4(dppa)], 6, and [PtMe4(dppm)]19 the 1J(CPt) values for the
Me ligands trans to phosphorus for both complexes are 567 Hz.
Similarly, it has been shown that for the diplatinum(II) complexes
with the general formula cis,cis-[Me2LPt(l-PP)PtLMe2], L = P(O-
iPr)3, in which the bridging PP ligand is either dppa or dppm, the
1J(CPt) values for the Me ligands trans to PP are almost the same
(588 or 586 Hz, respectively).2d
˚
a/A
˚
b/A
˚
c/A
b/◦
Vol/A
3
˚
Z
D(calc)/Mg m−3
Abs. coeff./mm−1
F(000)
No. of reflns
No. of independent reflns
No. of observed reflns [I > 2r(I)]
6474 [R(int) = 0.0445]
5631
T
min, Tmax
0.337, 0.612
1.314
The complexes [PtR2(dppa-P)2], 2, in which R is Me or tolyl
ligand, are easily prepared at room temperature in pure form
and good yields from the reaction of [PtR2(dppa)], 1, with one
equiv. of dppa, while in a similar procedure, the dppm analogue
[PtR2(dppm-P)2] is formed at very low temperatures and in
equilibrium with the chelating starting materials, [PtR2(dppm)].4b
This indicates that the tendency of dppa to act as monodentate
ligand is greater than that of the dppm. This is confirmed by
the observation of the dppa intermediate [PtR2(dppa-P)2], 2, in
the reaction of the dimer cis,cis-[R2Pt(l-SMe2)(l-dppa)PtR2], 3a,
with one equiv. of dppa, as shown in Scheme 2; in a similar reac-
tion using the dppm analogous complex cis,cis-[R2Pt(l-SMe2)(l-
dppm)PtR2], no formation of such an intermediate was observed.2b
The reaction of the complex [PtR2(dppa-P)2], 2, with, for example,
cis,cis-[Me2Pt(l-SMe2)2PtMe2], in an attempt to form the dimeric
complexes [Me2Pt(l-dppa)2PtR2], gave instead a mixture of the
monomeric forms [PtR2(dppa)], 1, and [PtMe2(dppa)]. In contrast,
using this type of reaction, the dppm complexes [PtR2(dppm-P)2]
have been widely used to systematically synthesize a wide variety
of dimeric complexes such as [Me2Pt(l-dppm)2Pt(o-tolyl)2].12 As
mentioned before, this again is consistent with the greater chelating
preference of dppa as compared to that of dppm.
Gof (F2)
R1, wR2 [I>2r(I)]
R1, wR2 (all data)
0.0277, 0.0670
0.0378, 0.0702
colorless needle of approximate 0.25 × 0.09 × 0.08 mm in size
was coated with protective perfluoro polyalkyether and mounted
on a glass fiber. Data were collected at 100 K on a Bruker-
Nonius KappaCCD diffractometer using Mo Ka radiation (k =
˚
0.71073 A, graphite monochromator). The data were corrected for
Lorentz and polarization effects, a semiempirical absorption cor-
rection based on multiple scans was carried out using SADABS.26
The structure was solved by direct methods and refined using
full-matrix least-squares procedures on F2 with the SHELXTL
NT 6.12 software.27 Crystal data, data collection and structure
refinement details are listed in Table 3. All hydrogen atoms are
in positions of idealized geometry, their isotropic displacement
parameters were tied to the equivalent isotropic displacement
parameters of the corresponding C and N carrier atoms by a
factor of 1.2 or 1.5.
CCDC reference number 632285. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b700009j
The organoplatinum(IV) complexes containing dppa behaved
very similarly compared to the analogous complexes containing
dppm,19 except for the formation of intermolecular hydrogen
bonding of type N–H · · · I–Pt, both in solution and the solid
state, in [PtMe3I(dppa)], 5a, which caused the complex to undergo
self-assembly. Although the corresponding hydrogen bonding
involving chlorine, i.e. N–H · · · Cl–Pt, has already been observed,22
hydrogen bonding of the type N–H · · · I–Pt, involving the less
electronegative iodine with weaker proton acceptor ability, is
not common and to the best of our knowledge, only one weak
intermolecular hydrogen bonding of this type has recently been
reported for [PtIMe3(DPA)], in which DPA is di-2-pyridylamine.28
Conclusions
The 1J(PtP) values in the 31P NMR spectra of chelating
organoplatinum(II) complexes [Pt(p-MeC6H4)2(dppa)], 1b, and
[Pt(p-MeC6H4)2(dppm)], are 1463 and 1392 Hz,4b respectively.
A similar trend was also observed in the methyl analogues
[PtMe2(dppa)], 1a, 1J(PtP) = 1475 Hz, and [PtMe2(dppm)],
1J(PtP) = 1434 Hz.20 Overall the J(PtP) couplings for the dppa
1
analogues are some 3–5% more than those of the dppm analogues.
The difference, although modest, might indicate that in these
chelating diphosphine complexes, the four-membered chelate ring
experiences less strain in the dppa complexes compared to those
in the dppm ones. Note that in accord with this, when the dimeric
complex cis,cis-[Me2Pt(l-SMe2)2PtMe2] is reacted with 2 mol of
dppm, only the dimeric product cis,cis-[Me2Pt(l-dppm)2PtMe2] is
formed,21 while when it is reacted with 2 mol of dppa, the dimeric
product cis,cis-[Me2Pt(l-dppa)2PtMe2] is formed as a mixture with
a considerable amount of the monomeric form [PtMe2(dppa)].6 We
therefore synthesized the latter monomeric complex in pure form
Acknowledgements
We thank the Shiraz University Research Council for financial
support through the Grant No. 85-GR-SC-18. The generous loan
of platinum metal salts by Johnson Matthey PLC is also gratefully
appreciated. We also would like to thank Professor D. Mohadjer
for his useful suggestions.
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11 (a) M. P. Brown, R. J. Puddephatt and M. Rashidi, J. Chem. Soc., Dalton
Trans., 1977, 951; (b) M. Hashemi, PhD Thesis, Shiraz University, Iran,
2001.
12 (a) A. T. Hutton, P. G. Pringle and B. L. Shaw, J. Chem. Soc., Dalton
Trans., 1985, 1677; (b) G. R. Cooper, A. T. Hutton, C. R. Langrick,
D. M. McEwan, P. G. Pringle and B. L. Shaw, J. Chem. Soc., Dalton
Trans., 1984, 855 and references therein.
13 See for example the crystal structure of a tridentate cyclometalated
platinum(II) complex which consists of dimers formed by two inter-
molecular N–H · · · Cl–Pt hydrogen bonds: L. Mao, T. Moriuchi,
H. Sakurai, H. Fujii and T. Hirao, Tetrahedron Lett., 2005, 46,
8419.
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16 This was calculated using the normalized distance function, RHI
=
=
˚
d(H · · · I)/(rH + rI), in which d(H · · · I) = 2.89 A (see Table 2); rH
˚
˚
1.20 A and rI = 1.96 A are the van der Waals radii of H and I,
respectively (ref. 17).
17 A. J. Bondi, J. Chem. Phys., 1964, 68, 441.
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22 For example see the structure of [PtCl2(NH3)2]: G. H. W. Milburn and
M. R. Truter, J. Chem. Soc. A, 1966, 1609; see also ref. 13.
23 R. J. Puddephatt and M. A. Thomson, J. Organomet. Chem., 1982, 238,
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28 F. Zhang, E. M. Prokopchuk, M. E. Broczkowski, M. J. Jennings and
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2003, 5, 65.
10 Based on the reported procedure, ref. 7, the reaction “[Pt(COD)Cl2] + 1
equiv. of dppa” was used to prepare the starting complex [Pt(dppa)Cl2].
However, we found that when [PtCl2(SMe2)2] and 1 equiv. of dppa is
used, a very small yield of [Pt(dppa)Cl2] is precipitated along with a
solution containing a very complicated mixture of products including
monodentate and bridging dppa species. Note that the analogous dppm
complex [Pt(dppm)Cl2] is reported to be prepared by the reaction:
“[Pt(COD)Cl2] + 1 equiv. of dppm” (ref. 11a). However, we have found
that it could also be easily prepared in 90% yield by the reaction of
[PtCl2(SMe2)2] and 1 equiv. of dppm in CH2Cl2 (ref. 11b).
1704 | Dalton Trans., 2007, 1697–1704
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The Royal Society of Chemistry 2007
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