Pyridyl- and diphenylphosphinoethyl-functionalised N-heterocyclic carbene platinum methyl complexes

Article abstract of DOI:10.1016/j.jorganchem.2014.07.010

The novel platinum (II) dimethyl complexes Pt(κ²-L1)Me₂ and Pt(κ²-L1)Me₂ (1), Pt(κ²-L2a)Me₂ (2a) and Pt(κ²-L2b)Me₂ (2b) bearing the functionalised N-heterocyclic carbe

Full text of DOI:10.1016/j.jorganchem.2014.07.010

Journal of Organometallic Chemistry 775 (2015) 178e187
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Pyridyl- and diphenylphosphinoethyl-functionalised N-heterocyclic
carbene platinum methyl complexes
, c, *
Nikolaos Tsoureas a, Andreas A. Danopoulos b
a School of Life Sciences, University of Sussex, Sussex House, Falmer, Brighton, BN1 9RH, UK
Institute for Advanced Study (USIAS), Universite de Strasbourg, 67081 Strasbourg, France
b
ꢀ
c
ꢀ
Laboratoire de Chimie de Coordination, Institut de Chimie UMR 5177, Universite de Strasbourg, 4 rue Blaise Pascal, 67081 Strasbourg, France
a r t i c l e i n f o
a b s t r a c t
The novel platinum (II) dimethyl complexes Pt(k k k
2-L1)Me2 and Pt( 2-L1)Me2 (1), Pt(
2-L2a)Me2 (2a) and
1-(2-
1-(2-pyridyl)-3-(2,6-
Article history:
Pt(
k
2-L2b)Me2 (2b) bearing the functionalised N-heterocyclic carbenes (NHCs), L1
¼
Received 17 February 2014
Received in revised form
9 July 2014
Accepted 10 July 2014
Available online 21 July 2014
diphenylphosphinoethyl)-3-(2,6-diisopropyl-phenyl)-imidazol-2-ylidene, L2a
¼
diisopropyl-phenyl)-imidazol-2-ylidene, L2b
¼
1-(2-(3-picolinyl))-3-(2, 6-diisopropyl-phenyl)-imida-
zol-2-ylidene, react with the acid [H(Et2O)þ2 B(ArF)ꢀ4 ], ArF ¼ 3, 5-(CF3)2C6H3, in the presence of various
neutral donors (Dn) to give the salts [{Pt(k
2-L)(Me)(Dn)}þ{B(ArF)4}ꢀ], where Dn occupies specifically the
site trans to the P and the CNHC donor atoms of the coordinated ligands L1 and L2a, L2b, respectively.
Keywords:
N-Heterocyclic carbenes
Platinum
Spectroscopic data give evidence that the same selectivity prevails when other acids are employed.
Activation of the CleCH2Cl bond by 2b led to [Pt(
k
2-L2b)(Me)Cl], while reaction of CH3I with the dimethyl
complexes led to isolable [Pt(
k
2-L)Me3I] species.
Cationic
© 2014 Elsevier B.V. All rights reserved.
Weakly coordinating
Alkyl complexes
Introduction
Pt(II) or Pt(IV) products, depending on the nature of the NHC used
[7]. Chelating bidentate bis-NHC complexes of Pt(II)/(IV) have been
studied in relation to Shilov-type CeH activation and alkane
functionalisation and as possessing unique photophysical proper-
ties [8e11]. Furthermore, Pt complexes with bidentate ligands
comprising NHCs functionalised with N-donors (pyridine, picoline,
lutidine etc.) or cyclometallated, tridentate ‘pincer’ NHC ligands
(aryl Cꢀ-donor) have been studied for catalysis applications
(hydroamination and hydrovinylation reactions) [12,13] and in
relation to their interesting photophysical properties (lumines-
cence, vapochromic behaviour etc.) [14,15], which can be com-
bined with cytotoxicity for medicinal applications [16]. Oxidative
addition and reductive elimination reactions involving Pt(II) and
Platinum N-heterocyclic carbene (NHC) complexes of the type
Pt(IMes)2, IMes ¼ 1,3-dimesitylimidazol-2-ylidene, were among
the first reported transition metal complexes with NHC ligands
after the introduction of stable imidazol-2-ylidenes [1]. Since then,
the study of Pt complexes with monodentate NHCs continued,
albeit at substantially slower pace than Pd complexes, mainly
aiming at the development of novel catalysts for the hydro-
silylation of alkenes and alkynes [2,3] and various types of CeH
bond activation, including the C2eH of imidazoliums [4]. Recently,
starting from [Pt(
m
-Me2S)Me2]2 and NHCs, NHC ¼ IBut, IPri, IMes,
diverse reactivity was observed, dependent on the steric proper-
ties of the NHCs, and led to either Pt(NHC)2Me2, coordinated NHC
wingtip metallation via CeH activation, ethane reductive elimi-
nation, or abnormal NHC coordination [5]. The Pt(III) species
[Pt(IPr)2(I)2]þ obtained by the oxidation of [Pt(IPr)2(Me)I] has been
described [6]. Small monodentate NHCs with [Pt(IV)Me3ILm] or
[Pt(IV)Me3(Me2CO)3]BF4, NHC ¼ 1,3-dimethyl-imidazol-2-ylidene,
3-methyloxazol-2-ylidene, L ¼ pyridine, m ¼ 0, 2, led to diverse
Pt(IV) methyl complexes stabilised by the linear k k
2- or 3-bis-1, 3-
di(2-picolyl)imidazol-2-ylidene ligands have also been briefly
studied [17].
We have described palladium dimethyl complexes with the
chelating bidentate 2-diphenylphosphinoethyl-, 2-pyridyl- and 2-
(3-picolyl)-functionalized NHCs (L1 and L2a, L2b, respectively, see
Scheme 1) and their protonolysis by [H(Et2O)2]þ[B(ArF)4]ꢀ followed
by association of a neutral donor (e.g. pyridine, MeCN etc.) at the
created vacant site. The regiospecificity of the substitution, although
in line with the relative trans influence of the pyridine and NHC
donors of L2a and L2b, was unexpected for the P and NHC donors of
the L1. Rationalisation of the observations by DFT methods invoked
a subtle balance of electronic and steric factors and secondary
ꢀ
* Corresponding author. Institute for Advanced Study (USIAS), Universite de
Strasbourg, 67081 Strasbourg, France.
E-mail addresses: N.Tsoureas@sussex.ac.uk (N. Tsoureas), danopoulos@unistra.fr
(A.A. Danopoulos).
http://dx.doi.org/10.1016/j.jorganchem.2014.07.010
0022-328X/© 2014 Elsevier B.V. All rights reserved.

N. Tsoureas, A.A. Danopoulos / Journal of Organometallic Chemistry 775 (2015) 178e187
179
Scheme 1. The synthesis of Pt(II) dimethyl complexes, Ar ¼ 2,6-iPr2C6H3 (DiPP): (i) 1 equiv. KN(SiMe3)2, THF; (ii) [Pt(
m-Me2S)Me2]2, THF; (iii) [Pt(
m-Me2S)Me2]2, THF; (iv) 1 equiv.
[H(Et2O)2]þ[B(ArF)4]ꢀ in CH2Cl2 (ꢀ78 ꢁC, ꢀ40 ꢁC) followed by 1 equiv. pyridine (ꢀ40 ꢁC); (v) 1 equiv. CF3COOH in CD2Cl2, room temperature.
(agostic) interactions [18,19]. Protonolysis with CF3COOH followed
the same selectivity albeit association of CF3COOꢀ with the Pd
complex at the created vacant site was observed.
by the in situ generated NHC (for L1) or the isolated free NHC (for
L2a and L2b) (Scheme 1). The new complexes were isolated in high
yields as colourless or yellow, air stable powders. Solutions of 1 and
2a, 2b in CH2Cl2 have limited stability even under inert atmosphere
(i.e. after 2e3 h the formation of a mixture of species becomes
evident by 1H NMR, see also below). However, characterisation of
the complexes was carried out by analytical, spectroscopic (taking
care to minimise the duration of the experiment) and diffraction
methods.
As an extension of these studies, herein we describe (i) novel
Pt(II) dimethyl complexes coordinated by the ligands
k -
2-L1 and k2
L2a or
k
2-L2b ligand coordination, and (ii) a range of novel cationic
derivatives obtained either by their protonolysis with
[H(Et2O)2]þ[B(ArF)4]ꢀ in the presence of neutral donors (Dn), or by
acids with coordinating anions. We also report the reactions of
Pt(II) dimethyl complexes with MeI leading to stable Pt(IV) species.
The synthetic transformations are summarised in Schemes 1e3.
The 1H NMR spectra of the complexes concur with non-
symmetric solution structures. Thus the inequivalent PteCH3 sig-
nals appeared as a pair of doublets or as a pair of singlets for 1 or 2a,
2b, respectively, accompanied by Pt satellites. The PteCH3 signals in
1 are shifted upfield relative to the corresponding signals in 2a and
Results and discussion
2b. The shielding may be ascribed to the better s-donor ability of
Neutral Pt dimethyl complexes
2
phosphine donor in 1; interestingly, the value of the JPteH of the
PteCH3 signals is larger in 2a, 2b than the in 1. The stronger elec-
tron donating character of the L1 may also be responsible for the
The synthesis of the neutral Pt dimethyl complexes involved the
substitution of the labile ligand Me2S in [Pt(m-Me2S)(CH3)2]2 either
Scheme 2. The synthesis of Pt methyl complexes containing the ligands L2a and L2b: (i) 1 equiv. [H(Et2O)2]þ[B(ArF)4]ꢀ in CH2Cl2 (ꢀ78 ꢁC, ꢀ40 ꢁC) followed by 1 equiv. pyridine
derivative (ꢀ40 ꢁC) (76e89%); (ii) 1 equiv. [H(Et2O)2]þ[B(ArF)4]ꢀ and 1 equiv. CF3CH2OH in CH2Cl2 (ꢀ78 ꢁC, room temperature) followed by crystallisation from ether (19%); (iii) H2O
in chlorobenzene-d5; (iv) B(C6F5)3, H2O, ether, (ꢀ78 ꢁC to room temperature, 40%); (v) 1 equiv. CF3COOH, CD2Cl2, room temperature.

180
N. Tsoureas, A.A. Danopoulos / Journal of Organometallic Chemistry 775 (2015) 178e187
Fig. 2. The structure of 2a; ellipsoids are at the 30% probability level. Only one position
of
disordered o-iPr is shown. Selected distances (Å) and angles (ꢁ):
Pt1eC30 ¼ 2.087(5), Pt1eC31 ¼ 2.044(5), Pt1eN3 ¼ 2.128(5), Pt1eC1 ¼ 2.006(5),
N1eC1 ¼ 1.381(7), C1eN2 ¼ 1.355(7), N3ePt1eC1 ¼ 78.2(2), C30ePt1eN3 ¼ 93.7(2),
C31ePt1eC1 ¼ 98.0(2), C30ePt1eC31 ¼ 90.1(2), N1eC1eN2 ¼ 103.0(4).
Scheme 3. Reactions of the platinum dimethyl complexes with MeI: (i) 1 equiv. MeI,
CH2Cl2, room temperature.
a
upfield shift in the 195Pt{1H} NMR spectra of 1 (
d
ꢀ4257.9, d,
1JPteP ¼ 1822.5 Hz) compared to 2a and 2b (
d
ꢀ3764.1 and
In 2a the two PteCH3 bonds exhibit significantly different bond
distances: 2.087(6) Å (trans to CNHC) and 2.044(5) Å (trans to Npy),
in line with the different trans influences of the corresponding
donors. The PteCNHC bond distances are virtually the same in 1 and
2a. In 2a the NHC plane slightly deviates from the coordination
plane, defined by the Pt and the two methyl groups, and the plane
defined by the pyridine ring by 5.44ꢁ and 2.97ꢁ, respectively.
As mentioned previously, all three platinum dimethyl com-
plexes have limited stability in chlorinated solvents. Attempts to
crystallise 2b from CH2Cl2/ether gave crystals of the complex 2bCl
the identity of which was established crystallographically (see
Fig. 3). The crystals were insoluble in all inert organic solvents,
which hampered spectroscopic characterisation.
d
ꢀ3763.9, both s), respectively.
The position of the inequivalent PteCH3 relative to the trans
donors in the complexes 2a and 2b was determined by NOESY NMR
spectroscopy: the downfield signals (0.44 and 0.45 ppm) were
assignable to methyl groups situated trans to the NHC moiety. The
coordinated phosphine in 1 appears at
d
12.4 (1JPteP ¼ 1822.5 Hz).
Surprisingly, and in contrast to 2a and 2b, the PteCH3 and PteCNHC
in the 13C{1H} NMR spectrum of 1 could not be observed.
The structures of 1 and 2a were confirmed crystallographically
(Figs. 1 and 2, respectively).
In both cases the coordination geometry at Pt is square planar,
with the donor atoms of the ligands L1 and L2a occupying two cis
positions. In 1 the two PteCH3 bond distances, (2.075(4) and
2.085(4) Å), are equal within the observed esds, a trend also
observed in the analogous Pd complex reported previously [19].
Thus, there is no significant difference in the trans influence of the
phosphine and the NHC donors. However, the PteCNHC bond is
It is clearly evident that the CH3 that was trans to the NHC in 2b
was replaced by one Cl atom originating from the CH2Cl2 solvent.
The PteCNHC, PteNpy and PteCH3 bond distances are equal to the
slightly shorter than the
s-donating PteCH3; interestingly, the
PteCNHC is significantly shorter than the corresponding bond in the
Pd analogue.
Fig. 3. The structure of 2bCl from the reaction of 2b with CH2Cl2; ellipsoids are at 40%
probability level. Only one position of a disordered o-iPr is shown. Selected distances
Fig. 1. The structure of 1; ellipsoids are at the 40% probability level. Selected distances
(Å) and angles (ꢁ): C1ePt1 ¼ 2.031(5), Pt1eC30 ¼ 2.075(5), C31ePt1 ¼ 2.085(4),
Pt1eP1 ¼ 2.249(1), C1eN1 ¼ 1.348(5), N2eC1 ¼ 1.369(6), C1ePt1eC31 ¼ 95.2(2),
(Å) and angles (ꢁ): N3ePt1
¼
2.112(5), C1ePt1 ¼ 1.935(5), Pt1eC31
Pt1eCl1 ¼ 2.335(2), N1eC1 ¼ 1.374(8), C1eN2 ¼ 1.333(7), N3ePt1eC1 ¼ 78.3(2),
C1ePt1eC31 103.5(4), C31ePt1eCl1 81.5(4), Cl1ePt1eN3 96.7(1),
N1eC1eN2 ¼ 105.5(5).
¼
2.04(1),
C31ePt1eC30
¼
84.6(2), C30ePt1eP1
¼
89.5(1), P1ePt1eC1
¼
90.9(1),
¼
¼
¼
N2eC1eN1 ¼ 102.7(3).

N. Tsoureas, A.A. Danopoulos / Journal of Organometallic Chemistry 775 (2015) 178e187
181
corresponding ones in 2a. A plausible mechanism for the formation
of the chlorinated product may involve oxidative addition of the
CleCH2Cl bond, followed by reductive elimination of chloroethane.
Attempts to substitute one methyl of 2a or 2b with Cl by reaction
with HCl (2 M solution in ether) in CH2Cl2 led to decomposition
products. Interestingly, the oxidative addition of CH2Cl2 has also
been observed with the corresponding palladium dimethyl com-
plex [19]; in either case the chloride was introduced at the site trans
to the NHC donor. It appears that the increased lability aptitude of
the PteCH3 trans to the NHC originates from the weaker PteCMe
bond and is a common feature of both the Pd and Pt complexes
with ligands L2a and L2b (see also below) and contrasts the
behaviour of the complexes with the ligand L1, where the PteCMe
bond trans to the PPh2 functionality is preferentially cleaved.
CD2Cl2 were identical to those described above, implying the
reformation of two species. A proposal to rationalise these obser-
vations may involve association of CD2Cl2 with 3 or reversible
oxidative addition/reductive elimination of CD2Cl2. Adducts of
CH2Cl2 with cationic Pt(II) complexes are rare but known [24] and
the role of oxidative addition of CH2Cl2 to Pt(II) methyl complexes
has been discussed [25]. Reversible oxidative addition of MeI to 2,6-
(bis-carbene)-pyridine ‘pincer Pt complexes has been described
briefly [12]. Attempts to detect platinum species in solution by
mass spectrometry or study the postulated equilibrium by variable
temperature 1H NMR spectroscopy were inconclusive.
The reaction of 1 with trifluoroacetic acid (1 equiv.) resulted in
the cleavage of one of the PteMe bonds and the formation of the
product formulated as 4 (Scheme 1). This was evidenced by the
disappearance of one PteCH3 signal in the 1H NMR spectrum of 1
after the addition of the acid. The protons of the remaining PteCH3
ligand resonate at 0.08 ppm (2JPteH ¼ 35.5 Hz)); furthermore the
signal in the 31P{1H} NMR spectrum of 4 revealed a downfield shift
Cationic Pt complexes
Organometallic cations are ubiquitous in homogeneous catal-
ysis, for example in reactions leading to CeY bond formation, Y ¼ H,
C, Si, polymerizations and CeH activation processes [20e23]. In the
latter process Pt complexes have been commonly employed as
catalysts. The currently studied systems use as cation precursors
symmetrical chelating N-donor (bipyridine, diimine) and P-donor
(diphosphine) Pt(II) dialkyls. Crucially, the generation of the reac-
tive cationic complex species required the use of acids with weakly
coordinating anions and weakly coordinating solvents, in order to
minimise competition with the CeH bond of the substrate to be
activated for a metal coordination site.
In the following, we describe cationic Pt(II) complexes obtained
by protonolysis of the dimethyl complexes 1 and 2a, 2b in the
presence of the donor Dn. The attack of the electrophilic Hþ is
conceivable either at the metal, giving formally Pt(IV) cations,
which can reductively eliminate CH4 to Pt(II) cations and associate
Dn; alternatively, direct electrophilic attack of Hþ on the coordi-
nated CH3 in the presence of Dn can lead to the same species (see
Scheme 4).
after CH3 abstraction (
in 4.
d
11.7 ppm in 1 and
d
19.6 (1JPteP ¼ 2017.8 Hz)
The reaction of 2a and 2b with [H(Et2O)2]þ[B(ArF)4]ꢀ in the
presence of a neutral donor Dn led to the isolation of complexes
5aed (Scheme 2). Their formation was confirmed by 1H and 13C
NMR spectroscopy. Of high diagnostic value was the replacement of
the two PteMe signals of 2a and 2b by one downfield shifted,
corresponding to the single PteMe of the cations in 5aed. The
presence of only one PteMe signal in the 1H, 13C and 195Pt NMR
spectra supported the regioselectivity of the abstraction/substitu-
tion sequence. The diastereotopic methyl groups of the DiPP
wingtip appear as two doublets, even when Dn is nonsymmetric
(i.e. the 2-fluoro-pyridine in 5c), which implies rapid rotation at the
PteDn bond. The proposed geometries of the cationic complexes
were confirmed by NOESY spectroscopy. In the 19F spectra of 5aed
the noncoordinating anion appears as singlet, while in 5c and 5d
additional singlets due to fluoro-pyridines are observed; in 5d it is
accompanied by Pt satellites (JPteF ¼ 110.2 Hz), implying a long
range interaction of the o-F-substituents with Pt.
In all cases studied the preferentially abstracted Me group is
trans to the P donor (in the protonolysis with 1) or trans to the NHC
(in the protonolysis with 2a). These observations are in agreement
with observations in analogous Pd complexes [18,19].
The structures of 5b and 5c were determined crystallographi-
cally and are shown in Figs. 4 and 5.
The geometry around the metal centres is virtually square
planar with the ligand L2b occupying two cis positions, forming a
bite angle of 78.11(12)ꢁ. The pyridine Dn is situated trans to the NHC
and the plane of the heterocycle is perpendicular to the coordina-
tion plane (88.97ꢁ). The NHC and the tethered pyridine planes form
an angle of 17.18ꢁ. In 5c the 2-fluoro-pyridine is disordered over
two positions, one with the fluorine atom above the coordination
plane and the other below. This is in agreement with the NMR data
discussed above.
Monitoring the reaction of
1
with [H(Et2O)2]þ[B(ArF)4]ꢀ
(1 equiv.) and pyridine in CD2Cl2 by 1H NMR spectroscopy, showed
the formation of two species in ca. 2:1 ratio. The PteCH3 region
contained two distinct CH3 signals; four different signals assignable
to CHMe2 of the DiPP (2:2:1:1 ratio) were also seen. Other spectral
features were also doubled in 2:1 ratio. The 31P{1H} consisted of one
signal at 10.1 ppm (1JPteP ¼ 746.0 Hz), and one at 8.7 ppm
(1JPteP ¼ 1977.1 Hz). Repeating the reaction in ether followed by
work-up which included layering of the ether with pentane,
afforded crystals. An X-ray diffraction study revealed that the
crystals corresponded to the formation of 3 (Scheme 1), where
electrophilic attack and pyridine coordination has taken place at
the site trans to the phosphine moiety of the bidentate ligand.
Unfortunately, the quality of the data was not sufficient to produce
a publishable model. Elemental analytical data of the crystalline
material supported the proposed crystallographic model. Surpris-
ingly, the NMR data obtained after redissolving the crystals in
Monitoring of the protonolysis of 2a with [H(Et2O)2]þ[B(ArF)4]ꢀ
in CH2Cl2 using styrene as Dn showed broad and uninterpretable
NMR spectra, however, after evaporation of the volatiles under
reduced pressure and crystallisation of the residue from ether/
pentane gave sensitive crystals of 6 in low yields. The identity of 6
was established crystallographically (see Fig. 6).
The cation in 6 comprises a square planar Pt in which the co-
ordination site trans to the NHC donor of the ligand L2a is now
occupied by an ether molecule. The PteCNHC, PteMe and PteN
Scheme 4. Alternative sites of electrophilic attack (Pt, coordinated CH3) leading to cationic complexes stabilized by the donor Dn.

182
N. Tsoureas, A.A. Danopoulos / Journal of Organometallic Chemistry 775 (2015) 178e187
Fig. 4. The structure of the cation in 5b. Selected distances (Å) and angles (ꢁ):
Pt1eC31 ¼ 2.050(5), N4ePt1 ¼ 2.068(2), Pt1eN3 ¼ 2.130(3), C1ePt1 ¼ 1.945(2),
N2eC1 ¼ 1.349(4), C1eN1 ¼ 1.375(5), C1ePt1eN3 ¼ 78.1(1), C31ePt1eC1 ¼ 101.4(2),
N4ePt1eC31 ¼ 85.3(1), N4ePt1eN3 ¼ 95.6(1), N2eC1eN1 ¼ 104.2(3).
Fig. 6. The structure of the cation in 6. Selected distances (Å) and angles (ꢁ):
N3ePt1 2.048(8), Pt1eO1 2.180(4),
¼
2.126(5), Pt1eC1 ¼ 1.937(4), Pt1eC9
¼
¼
bond distances are equal within esds with the ones found in the
cations of 5b and 5c. Structurally characterised Pt(II)-ether cations
complexes are very rare and sometimes unstable in solution at
room temperature [24,26,27]. Pt(II)-THF complexes are also very
rare [28,29]. The structure of 6 in solution was studied by 1H NMR
spectroscopy after dissolving the crystals in commercial (not pre-
dried) d5-C6H5Cl; the presence of two ether molecules (1:1 ratio),
corresponding to one coordinated and one crystallisation ether. In
N2eC1 ¼ 1.337(6), C1eN1 ¼ 1.368(7), N3ePt1eC1 ¼ 79.4(2), C9ePt1eC1 ¼ 98.6(2),
N1eC1eN2 ¼ 104.9(4), O1ePt1eN3 ¼ 90.7(2), O1ePt1eC9 ¼ 91.2(2).
quartet at 3.4 ppm, indicating that the equilibrium was shifted
towards the H2O coordinated cationic species 7. The PteMe protons
in 6 appear at 0.22 ppm (2JPteH ¼ 35.1 Hz). This signal is shifted
upfield compared to complexes [Pt(R2PCH2CH2PR2)(CH3)(OEt2)]
BArF4] (R ¼ Et, Cy) [30]. Unlike the bisphosphine monocationic
the spectrum, two singlets in 1:1 ratio were also observed at
d 1.5
complexes, 6 is stable in the presence of water, and no (m-OH)
and 1.9, the latter accompanied by platinum satellites
(2JPteH ¼ 37.9 Hz); they were assigned to H2O in C6D5Cl and H2O
coordinated after exchange with ether, respectively, leading to the
formation of 7 (Scheme 2). When the NMR sample was shaken with
one drop of D2O, the ratio of coordinated to uncoordinated H2O
changed to 3:1, while the ratio of coordinated to uncoordinated
ether changed to 1:8. The sample was heated to 45 ꢁC for 10 min
upon which time the coordinated/uncoordinated H2O ratio
increased to 4:1, while the two ether resonances collapsed into one
decomposition complexes were observed.
The reaction of 2a with one equiv. of B(C6F5)3 in the presence of
H2O was undertaken in the absence of a donor ligand (Scheme 2).
This combination is known to provide [H]þ[(B(C6F5)3(OH)]ꢀ [31],
which has been used as acid on many occasions, including platinum
chemistry [32]. The identity of 8 was established from its 1H NMR
spectrum, in which one peak at ꢀ0.01 ppm (Pt satellites with
2JPteH ¼ 37.7 Hz) was assigned to PteMe and a broad singlet at
2.93 ppm to OH. The location of the PteMe bond relative to the
donors of ligand L2a was confirmed by NOESY experiments which
revealed that the PteMe bond that was trans to the NHC was
preferentially cleaved by the acid.
The structure of 8 was unambiguously established crystallo-
graphically (Fig. 7).
The geometry around Pt is square planar with the coordination
sphere comprising the chelating L2a, one CH3 and the
[B(OH)(C6F5)3]ꢀ. The PteCH3, PteCNHC and PteNpyridine bond dis-
tances compare to those in 5b and 5c. The PteO bond distance
(2.106(9) Å) in 8 is also the same within esds with the PteN(2-
fluoropyridine) distance (2.095(7) Å) in 5c. This is an indication
that the [B(OH)(C6F5)3)]ꢀ anion is not binding very strongly to Pt,
possibly due to the electron withdrawing pentafluorophenyl
groups.
Oxidative addition of MeI
The oxidative addition of MeI in the complexes 1 and 2a was
investigated (Scheme 3). In both cases the reaction takes place
within seconds at room temperatures affording the Pt(IV) com-
plexes 10 and 11, respectively, in good yields. The formation of 10
and 11 was established by spectroscopic methods. Their 1H NMR
spectra confirmed the formation of non-symmetric structures. The
Fig. 5. The structure of the cation in 5c. Selected distances (Å) and angles (ꢁ): Only one
disordered 2-fluoro-pyridine ligand is shown. Pt1eC1 ¼ 1.938(7), Pt1eN3 ¼ 2.131(6),
Pt1eC4
C1ePt1eC4
N5BePt1eC4 ¼ 83.6(5), N2eC1eN1 ¼ 103.7(6).
¼
2.053(8), Pt1eN5B
¼
2.05(1), N1eC1
¼
1.38(1), C1eN2
¼
¼
1.351(8),
98.3(5),
¼
99.3(3), C1ePt1eN3
¼
78.8(3), N3ePt1eN5B

N. Tsoureas, A.A. Danopoulos / Journal of Organometallic Chemistry 775 (2015) 178e187
183
On heating 11 in toluene-d8 (40 ꢁC, 80 ꢁC 48 h) did not result in
any reaction. Heating at 125 ꢁC for 4 h resulted in extended
decomposition as evidenced by the formation of black aggregates
and minor peaks assignable to ethane (
10.5) and CH3I ( 2.16).
d 0.83), CeH(imidazolium)
(d
d
Conclusions
Neutral, square planar Pt(II) dimethyl complexes stabilised by
the chelating bidentate diphenylphosphinoethyl- and 2-pyridyl-
functionalised imidazol-2-ylidenes undergo selective protonolysis
of the more reactive methyl group that is trans- to the P- or CNHC
-
donors, respectively. The selectivity is the same to the previously
observed in analogous Pd complexes and may be controlled by the
electronic factors and weaker intramolecular agostic interactions.
However, the reactivity of the Pt complexes is lower than the Pd
analogues as can be established by the inertness of the former to-
wards the weakly acidic (CF3)2CHOH and C6F5OH [19]. In
dichloromethane the Pt(II)-dimethyl complexes exchange their
more reactive methyl (same as in the protonolysis reactions) with
chloride. The mechanism of the exchange may involve oxidative
addition and reductive elimination from transient Pt(IV)Me(CH2Cl)
Cl species. However, oxidative addition of MeI gave isolable Pt(IV)
Me3I which on thermolysis failed to give ethane cleanly. The cata-
lytic and photophysical properties of the novel Pt complexes are
under further study.
Fig. 7. The structure of 8. Selected distances (Å) and angles (ꢁ): C1ePt1 ¼ 1.89(1),
Pt1eN3
C1eN1
¼
2.13(1), Pt1eC31
1.40(2),
¼
1.99(1), O1ePt1
¼
2.105(8), N2eC1
C31ePt1eC1
¼
1.35(1),
98.3(6),
¼
C1ePt1eN3
¼
80.3(5),
¼
O1ePt1eC31 ¼ 90.6(5), O1ePt1eN3 ¼ 90.8(4), N2eC1eN1 ¼ 100(1).
two characteristic doublets of the diastereotopic o-CHMe2 of the
DiPP wingtip in 1 and 2a, were split into four distinct doublets in 10
and 11. Furthermore, two o-CHMe2 septets were observed in their
1H NMR spectra. The PteCH3 in the Pt(IV) products were shifted
further downfield compared to the Pt(II) parent complexes. The
PteCH3 resonances in 10 and 11 were isochronous to related
complexes of the type fac-[(PP)PtMe3X] (X ¼ I, OTf, PP ¼ chelating
phosphine) [33]. The 31P{1H} NMR signal in 10 was shifted upfield
compared 1. This trend has been observed during the oxidative
addition of MeI and MeOTf to the Pt(II) complex [(dppe)PtMe2]
(dppe ¼ diphenylphosphinoethane) [34].
Experimental
Elemental analyses were carried out by the microanalytical
laboratory of London Metropolitan University. All manipulations
involving organometallics were performed under nitrogen or argon
in a Braun glove-box or using standard Schlenk techniques unless
specified otherwise. Solvents were dried using standard methods
and distilled under nitrogen prior use or passed through columns of
activated alumina and subsequently purged with nitrogen or argon.
The structure of 11 was determined crystallographically and is
shown in Fig. 8.
The geometry around the Pt is octahedral with fac-arrangement
of the methyl ligands. All PteMe distances are the same within the
measured esds and comparable to the lengths of the Pt(II) complex
2a. On the other hand the PteCNHC and PteNpyridine are longer in 11.
[Pt(m-Me2S)Me2]2 [35] the salt L1$HBr [18,19] and the NHCs
compounds L2a and L2b [36,37] were prepared according to liter-
ature procedure. The acid [H(Et2O)2]þ[B(ArF)4]ꢀ was prepared by
modification of the literature procedure [38] using a 2 M HCl so-
lution in ether instead of gaseous HCl for its generation. Iodo-
methane, dimethylsulfide, trifluoroacetic acid, 2-fluoropyridine,
tris(pentafluorophenyl)borane and all other starting materials were
from Aldrich and were used as received.
cis-Pt(
k
2-L1)(CH3)2 1
To a solution of 0.080 g (0.14 mmol) of [Pt(
m-Me2S)Me2]2 in THF
at ꢀ78 ꢁC was added a solution of the free carbene L1, generated
from 0.146 g (0.28 mmol) of imidazolium salt L1$HBr and 0.062 g of
KN(SiMe3)2 (1.1 equiv. relative to the imidazolium salt) in THF
(50 ml) at ꢀ50 ꢁC. The reaction mixture was allowed to reach room
temperature and stirred for 2 h. Removal of the volatiles under
reduced pressure, extraction of the residue with CH2Cl2 (15 ml),
filtration through Celite, evaporation of the volatiles under reduced
pressure, washing of the residue with ether (10 ml) and pentane
(2 ꢂ 10 ml), and drying under vacuum gave 1 as an off-white solid.
The product decomposes after exposure to CHCl3, prolonged
exposure to CH2Cl2; is soluble in chlorobenzene or THF. Yield:
0.150 g (81%). Crystals of 1 were grown by layering a THF solution
3
with pentane. 1H NMR (CD2Cl2),
d
: ꢀ0.18 (3H, d, JPeH ¼ 7.7 Hz,
Fig. 8. The structure of 11. Selected distances (Å) and angles (ꢁ): N3ePt1 ¼ 2.178(4),
C1ePt1 ¼ 2.078(4), I1ePt1 ¼ 2.7902(4), Pt1eC31 ¼ 2.060(5), Pt1eC30 ¼ 2.089(4),
N1eC1 ¼ 1.378(6), N2eC1 ¼ 1.342(5), N3ePt1eI1 ¼ 88.2(1), N3ePt1eC30 ¼ 97.5(2),
3
PteCH3, satellites appear as dd with JPeH
¼
7.7 Hz and
2JPteH ¼ 29.0 Hz), ꢀ0.03 (3H, d, JPeH ¼ 7.7 Hz, PteCH3, satellites
3
appear as dd with 3JPeH ¼ 7.7 Hz and 2JPteH ¼ 29.0 Hz), 0.93 (6H, d,
C30ePt1eC31
N3ePt1eC23 ¼ 89.5(2), N2eC1eN1 ¼ 104.2(4).
¼
85.9(2), C31ePt1eC1
¼
99.5(2), N3ePt1eC1
¼
77.1(2),
3JHeH ¼ 6.9 Hz, CH(CH3)2), 1.14 (6H, d, JHeH ¼ 6.9 Hz, CH(CH3)2),
3

184
N. Tsoureas, A.A. Danopoulos / Journal of Organometallic Chemistry 775 (2015) 178e187
2.30 (2H, m, [PPh2CH2CH2-ylidene]PtMe2), 2.82 (2H, sept.,
3JHeH ¼ 6.9 Hz, CH(CH3)2), 4.21 and 4.27 (1H each, m, [PPh2CH2CH2-
ylidene]PtMe2), 6.76 (1H, m, aromatic), 7.01 (1H, m, aromatic), 7.15
(2H, distorted d, aromatic), 7.37 (7H, m, aromatic), 7.64 (4H, m,
1JPtꢀC ¼ 442.7 Hz); 195Pt{1H}-NMR (D2O),
:ꢀ3763.9. Found: C,
d
50.12; H, 5.90; N, 7.80%. Calcd for C23H32N3Pt: C, 50.63; H, 5.91; N,
7.70%.
aromatic); 13C{1H} NMR (CD2Cl2),
d:
no PteCH3 resonances
General method for the synthesis of the cationic Pt complexes 3,
5aed, 6 and 8
observed, 21.8 (s, CH(CH3)2), 24.4 (s, CH(CH3)2), 26.9 (d,
1JPeC ¼ 14.2 Hz, [PPh2CH2CH2-ylidene]PtMe2), 27.5 (s, CH(CH3)2),
2
48.4 (d, JPeC ¼ 10.4 Hz, [PPh2CH2CH2-ylidene]PtMe2), 118.6 (s, ar-
Two separate Schlenk tubes were charged with one equiv. of the
dimethyl complex and the acid [H(Et2O)2]þ[B(ArF)4]ꢀ, respectively.
The two solids were dissolved in CH2Cl2, the solutions cooled
to ꢀ78 ꢁC and the acid solution was added dropwise to the dimethyl
complex. Upon addition the colour changed from yellow to almost
colourless. The reaction mixture was allowed to warm to ꢀ40 ꢁC,
when 1.1 equiv. of the dry-degassed pyridine derivative was added
by means of a microsyringe, the solution was allowed to reach room
temperature slowly and stirred for 30 min. Removal of the volatiles
under reduced pressure and washing of the solid residue with
petrol gave the pure salt, which was dried under vacuum.
omatic), 122.6 (s, aromatic), 122.9 (s, aromatic), 127.2 (d,
JPeC ¼ 3.1 Hz, aromatic), 128.1 (s, aromatic), 128.8 (s, aromatic),
1
132.3 (d, JPeC ¼ 5.0 Hz, aromatic), 132.9 (d, JPeC ¼ 11.4 Hz, aro-
matic), 136.1 (s, aromatic), 145.0 (s, aromatic); 31P{1H}-NMR
(CD2Cl2),
d
:
11.7
(s,
[PPh2CH2CH2-ylidene]PtMe2,
1JPteP ¼ 1822.5 Hz); 195Pt{1H} NMR (CD2Cl2),
d
: ꢀ4257.9 (d,
1JPteP ¼ 1822.5 Hz, [PPh2CH2CH2-ylidene]PtMe2); Anal. Found: C,
55.49; H, 5.79; N, 4.21%. Calcd for C31H39N2PPt: C, 55.93; H, 5.90; N,
4.21%.
cis-Pt(k
2-L2a)(CH3)2 2a
ꢀ
cis-[Pt(k ] 3
2-L1)(CH3)(py)]þ[BArF
4
A pre-cooled (ꢀ78 ꢁC) solution of the free carbene L2a (0.085 g,
0.28 mmol) in THF was added by cannula to a cold (ꢀ78 ꢁC) solution
This was prepared as above from 0.080 g (0.12 mmol) of com-
plex 1, 0.113 g (1 equiv.) of acid and 11
m
L (1.1 equiv) of pyridine. 1H
3
of 0.080 g (0.14 mmol) of [Pt(
m-Me2S)Me2]2. After warming to room
NMR (CD2Cl2),
d
:
ꢀ0.22 (3H, d, PteCH3, JPH
¼
3.2 Hz,
temperature the reaction mixture was stirred for 2 h and the vol-
atiles were removed under reduced pressure to give a bright yellow
solid residue, which was washed with ether and dried under vac-
2JPteH ¼ 49.9 Hz), 0.80 (6H, 3JHeH ¼ 6.4 Hz CH(CH3)2, species B), 0.93
3
3
(6H, JHeH ¼ 7.0 Hz CH(CH3)2, species A), 1.00 (3H, JHeH ¼ 7.0 Hz,
CH(CH3)2), 1.32 (3H, 3JHeH ¼ 6.4 Hz, CH(CH3)2), 2.5 (5H, m, CH(CH3)2
and ([PPh2CH2CH2-ylidene]PtMe)þ of two species), 2.84 (1H, sept.,
3JHeH ¼ 7.0 Hz, CH(CH3)2), 4.38 (2H, m, ([PPh2CH2CH2-ylidene]
PtMe)þ), 4.65 (1H, m, ([PPh2CH2CH2-ylidene]PtMe)þ), 6.89e7.88
uum. Yield: 0.115 g, (78%). 1H NMR (CD2Cl2),
d
: 0.29 (3H, s, PteCH3,
2
2JPteH ¼ 46.6 Hz), 0.45 (3H, s, JPteH ¼ 31.2 Hz), 1.09 (6H, d,
3
3JHeH ¼ 6.9 Hz, CH(CH3)2), 1.34 (6H, d, JHeH ¼ 6.9 Hz, CH(CH3)2),
3
2.75 (2H, sept., JHeH
¼
6.9 Hz, CH(CH3)2), 6.58 (1H, d,
(48H, m, aromatics); 31P{1H} (CD2Cl2),
d
: 8.7 (s, 1JPteP ¼ 1977.1 Hz),
3JHeH ¼ 2.0 Hz), 7.28 (3H, m, aromatic), 7.45 (2H, t, 3JHeH ¼ 7.9 Hz,
10.1 (s, JPteP ¼ 746.0 Hz); 19F{1H}
d
(CD2Cl2): ꢀ63.1 (s, CF3). The
1
3
aromatic pyridine), 7.63 (1H, d, JHeH ¼ 2.0 Hz, ylidene backbone),
reaction was repeated using Et2O as solvent starting from 50 mg
(0.075 mmol) of 5.6 and 70 mg (1 equiv.) of acid. Yield after crys-
tallisation: 35 mg, (29%). Anal. Found: C, 50.81; H, 3.42; N, 2.59%.
Calcd for C67H53BF24N3PPt: C, 50.52; H, 3.35; N, 2.64%. Colourless
needles were obtained by layering an Et2O solution of (3) with
pentane.
8.09 (1H, ddt, JHeH ¼ 0.7 Hz, 1.5 Hz, 7.4 Hz Hz, aromatic pyridine),
9.07 (1H, s, m, aromatic pyridine); 13C{1H} NMR (CD2Cl2),
d
: ꢀ31.4
(s, PteCH3, 1JPtꢀC ¼ 401.9 Hz), ꢀ21.8 (s, PteCH3, 1JPtꢀC ¼ 397.8 Hz),
22.2 (s, CH(CH3)2), 23.4 (s, CH(CH3)2), 27.6 (s, CH(CH3)2), 109.4 (s,
ylidene backbone), 113.5 (s, ylidene backbone), 121.8 (s, aromatic),
122.9 (s, aromatic), 124.1 (s, aromatic), 129.1 (s, aromatic), 134.9 (s,
aromatic), 137.7 (s, aromatic), 144.9 (s, aromatic), 146.2 (s, aro-
matic), 152.6 (s, aromatic), 189.5 (s, NCN, 1JPtꢀC ¼ 441.9 Hz); 195Pt
cis-[Pt(k
2-L1)(CH3)(r1-OOCCF3)] 4 (NMR scale experiment)
Complex 1 (0.020 g, 0.030 mmol) was placed in an NMR tube
and dissolved in CD2Cl2 resulting in a yellow solution. After the tube
{1H}eNMR(D2O),
Calcd for C22H29N3Pt: C, 49.80; H, 5.51; N, 7.92%. Crystals were
d
: ꢀ3764.1. Found: C, 50.45; H, 5.38; N, 7.93%.
was capped with a septum and connected to a nitrogen supply, 3 mL
grown by slow diffusion of Et2O into a CH2Cl2 solution of 2a.
(1.1 equiv.) of CF3COOH were added at room temperature by means
of a microsyringe, resulting in the colour changing to almost col-
ourless. The NMR spectra of the solution were recorded. 1H NMR
cis-Pt(k
2-L2b)(CH3)2 2b
3
2
(CD2Cl2),
d
: 0.08 (3H, d, JPeH ¼ 2.9 Hz, JPteH ¼ 35.5 Hz, PteCH3),
3
3
This was prepared by a method analogous to 2a from 0.090 g
(0.28 mmol) of the free carbene and 0.080 g (0.14 mmol) of [Pt(
Me2S)Me2]2 in THF. Yield 0.110 g, (72%) of 2b as a bright yellow air-
0.99 (6H, d, JHeH ¼ 6.9 Hz, CH(CH3)2), 1.12 (6H, d, JHeH ¼ 6.9 Hz,
CH(CH3)2), 2.39 (4H, m, CH(CH3)2 and [PPh2CH2CH2-ylidene]
PtMeO2CCF3), 4.4 (2H, m, [PPh2CH2CH2-ylidene]PtMeO2CCF3), 6.88
m-
stable solid. 1H NMR (CD2Cl2),
d
: 0.19 (3H, s, PteCH3 trans to pyri-
(1H, d, JHeH ¼ 1.9 Hz, ylidene backbone), 7.19 (2H, distorted t, ar-
3
2
3
dine, JPteH ¼ 46.1 Hz), 0.44 (3H, s, PteCH3 trans to carbene,
2JPteH ¼ 31.0 Hz), 1.11 (6H, d, 3JHeH ¼ 6.9 Hz, CH(CH3)2), 1.37 (6H, d,
3JHeH ¼ 6.9 Hz, CH(CH3)2), 2.73 (2H, sept, 3JHeH ¼ 6.9 Hz, CH(CH3)2),
omatic), 7.22 (6H, broad s, aromatic), 7.33 (1H, d, JHeH ¼ 1.8 Hz,
ylidene backbone), 7.77 (5H, m, aromatic); 31P{1H} (CD2Cl2),
d: 19.6
(s, [PPh2CH2CH2-ylidene]PtMeO2CCF3, 1JPteH ¼ 2017.8 Hz); 19F{1H}
3
2.76 (3H, s, 3-CH3-pyridine), 6.90 (1H, d, JHeH ¼ 2.2 Hz, ylidene
(CD2Cl2),
d
: ꢀ74.4 (s, [PPh2CH2CH2-ylidene]PtMeO2CCF3).
backbone), 7.22 (1H, distorted dd, JHeH ¼ 5.7 Hz, 5.4 Hz and 7.6 Hz,
3
ꢀ
pyridine), 7.35 (2H, d, JHeH ¼ 7.9 Hz, aromatic), 7.50 (1H, t,
cis-[Pt(
k
2-L2a)(CH3)(py)]þ[BArF
]
4
5a
3JHeH ¼ 7.9 Hz), 7.90 (1H, distorted dd, JHeH ¼ 1.0 Hz, 0.7 Hz and
This was prepared following the general method from 0.049 g
(0.09 mmol) of 2a, 0.085 g (0.09 mmol) acid and 8 L pyridine in
20 ml CH2Cl2. Yield: 0.117 g (88%). 1H NMR (CD2Cl2),
d: 0.13 (3H, s,
3
8.1 Hz, pyridine), 8.04 (1H, d, JHeH ¼ 2.2 Hz, ylidene backbone),
m
9.18 (1H, broad dt, pyridine); 13C{1H} NMR (CD2Cl2),
d: ꢀ31.2 (s,
PteCH3, 1JPtꢀC ¼ 402.6 Hz), ꢀ21.8 (s, PteCH3, 1JPtꢀC ¼ 397.5 Hz), 19.1
(s, CH(CH3)2), 20.3 (s, CH(CH3)2), 20.9 (s, CH(CH3)2), 23.5 (s,
CH(CH3)2), 27.5 (s, py-CH3), 116.5 (s, ylidene backbone), 120.9 (s,
ylidene backbone), 121.6 (s, aromatic), 122.7 (s, aromatic), 122.9 (s,
aromatic),129.0 (s, aromatic),135.1 (s, aromatic),141.3 (s, aromatic),
144.2 (s, aromatic), 151.4 (s, aromatic), 189.7 (s, NCN,
PteCH3, 2JPteH ¼ 40.9 Hz),1.17 (6H, d, 3JHeH ¼ 6.4 Hz, CH(CH3)2),1.33
3
3
(6H, d, JHeH ¼ 6.4 Hz, CH(CH3)2), 2.61 (2H, JHeH ¼ 6.4 Hz,
3
CH(CH3)2), 6.98 (1H, d, JHeH ¼ 1.5 Hz, imidazol-2-ylidene back-
bone), 7.23 (2H, distorted ddd, JHeH ¼ 5.7 Hz, 5.4 Hz and 7.6 Hz,
3
pyridine), 7.33 (2H, d, JHeH ¼ 7.9 Hz, aromatic), 7.49 (1H, t,
3JHeH ¼ 7.9 Hz, aromatic), 7.90 (1H, distorted ddd, JHeH ¼ 1 Hz,

N. Tsoureas, A.A. Danopoulos / Journal of Organometallic Chemistry 775 (2015) 178e187
185
ꢀ
k ] 5d
2-L2a)(CH3)(2,6-difluoro-pyridine)]þ[BArF
4
0.7 Hz and 8.2 Hz, pyridine), 8.06 (1H, d, 3JHeH ¼ 1.5 Hz, imidazol-2-
cis-[Pt(
This was prepared following the general method from 0.050 g
ylidene backbone), 9.19 (broad dt, 1H, pyridine); 13C{1H} NMR
(CD2Cl2),
d
: ꢀ16.8 (s, 1JPtꢀC ¼ 517.7 Hz, PteCH3), 19.1 (s, CH(CH3)2),
(0.09 mmol) of complex 2a, 0.088 g (1 equiv.) of acidꢀ and 6
mL
19.9 (s, CH(CH3)2), 23.5 (s, CH(CH3)2), 117.1 (s, imidazol-2-ylidene
backbone), 118.1 (imidazol-2-ylidene backbone), 120.1 (s, aro-
matic), 121.1 (s, aromatic), 122.5 (s, aromatic), 123.3 (s, aromatic),
123.8 (s, aromatic), 125.0 (s, aromatic), 125.4 (s, aromatic), 126.3 (s,
(1.3 equiv.) of 2,6-difluoro-pyridine. Yield: 0.105 g (76%). 1H NMR
2
(CD2Cl2),
d
: 0.13 (3H, s, PteCH3, JPteH ¼ 38.4 Hz), 1.11 (6H, d,
3JHeH ¼ 6.9 Hz, CH(CH3)2), 1.30 (6H, d, JHeH ¼ 6.9 Hz, CH(CH3)2),
3
3
2.65 (2H, sept., JHeH
¼
6.9 Hz, CH(CH3)2), 7.08 (1H, d,
2
aromatic), 128.2 (q, JFeC ¼ 28.3 Hz, aromatic), 130.3 (s, aromatic),
3JHeH
¼
2.2 Hz, imidazol-2-ylidene backbone), 7.21 (1H,
134.0 (s, aromatic), 138.7 (s, aromatic), 143.3 (s, aromatic), 144.1 (s,
aromatic), 144.3 (s, aromatic), 150.4 (s, aromatic), 160.9 (q,
d 3JHeH ¼ 8.2 Hz, aromatic), 7.33 (3H, m, aromatic), 7.53 (4H, broad
s., aromatic), 7.63 (1H, d, 3JHeH ¼ 8.5 Hz, aromatic), 7.70 (8H, broad
1JFeC ¼ 43.8 Hz, CF3); 19F{1H},(CD2Cl2),
d
: ꢀ63.1 (s, CF3); 195Pt{1H}
s, aromatic), 7.77 (3H, m, aromatic), 8.19 (2H, m, aromatic); 13C{1H}
1
NMR (CD2Cl2): ꢀ3495.8. Found: C, 47.25; H, 3.00; N, 3.70%. Calcd for
NMR, (CD2Cl2),
d
: ꢀ2.6 (s, PteCH3, JPtꢀC ¼ 518.1 Hz), 19.8 (s,
C
58H44BF24N4Pt: C, 47.75; H, 3.04; N, 3.84%.
CH(CH3)2), 22.6 (s, CH(CH3)2), 24.1 (s, CH(CH3)2), 116.9 (s, imidazol-
2-ylidene backbone), 117.9 (imidazol-2-ylidene backbone), 119.8 (s,
aromatic), 122.5 (s, aromatic), 123.2 (s, aromatic), 123.6 (s, aro-
matic), 125.0 (s, aromatic), 125.2 (s, aromatic), 126.3 (s, aromatic),
ꢀ
cis-[Pt(k ] 5b
2-L2b)(CH3)(py)]þ[BArF
4
This salt was prepared following the general method from
2
128.1 (q, JFeC ¼ 28.8 Hz, aromatic), 130.2 (s, aromatic), 134.0 (s,
0.050 g (0.09 mmol) of 2b, 0.085 g (0.09 mmol) acid and 8
mL
2
aromatic), 138.4 (d, JFeC ¼ 19.0 Hz, 2, 6-F2-pyridine), 143.3 (s, ar-
pyridine in 20 ml CH2Cl2. Yield: 0.118 g, (89%). 1H NMR (CD2Cl2),
d:
omatic), 144.1 (d, 1JFeC ¼ 32.9 Hz, 2, 6-F2-pyridine carbon), 144.3 (s,
2
3
0.14 (3H, s, PteCH3, JPteH ¼ 40.2 Hz), 1.15 [6H, d, JHeH ¼ 6.4 Hz,
aromatic), 150.4 (s, aromatic), 160.9 (q, JFeC ¼ 43.9 Hz, CF3); 19F
1
3
CH(CH3)2], 1.33 [6H, d, JHeH ¼ 6.4 Hz, CH(CH3)2], 2.65 [2H, sept.,
{1H}} NMR (CD2Cl2),
d
: ꢀ63.1 (s, CF3), ꢀ60.3 (s, 2, 6-F2-pyridine,
3JHeH ¼ 6.4 Hz, CH(CH3)2], 2.81 (3H, s, 3-CH3-pyridine), 7.05 (1H, m,
imidazol-2-ylidene backbone), 7.21 (1H, m, aromatic), 7.33 (2H,
distorted d., aromatic), 7.53 (6H, broad s., aromatic), 7.74 (10H,
broad s., aromatic), 7.92 (2H, m, aromatic), 8.10 (1H, d,
JHeH ¼ 2.7 Hz, aromatic), 8.52 (2H, m, aromatic); 13C{1H} NMR
JPteF ¼ 110.1 Hz). Colourless crystals were grown by layering an
ether solution of 5d with pentane. Found: C, 46.32; H, 2.65; N,
3.61%. Calcd. for C58H42BF26N4Pt: C, 46.60; H, 2.83; N, 3.75%.
ꢀ
k ] 6
2-L2a)(CH3)(Et2O)]þ[BArF
4
cis-[Pt(
This was prepared following the general method from 0.050 g
(0.09 mmol) of 2a, 0.088 g (1 equiv.) of acidꢀ and 5
L of tri-
(CD2Cl2),
d
: ꢀ16.5 (s, PteCH3, 1JPtꢀC ¼ 519.9 Hz), 19.8 [s, CH(CH3)2],
22.2 [s, CH(CH3)2], 23.6 [s, CH(CH3)2], 27.8 (s, py-CH3), 116.7 (s,
ylidene backbone), 118.1 (imidazol-2-ylidene backbone), 119.8 (s,
aromatic), 122.5 (s, aromatic), 123.2 (s, aromatic), 123.6 (s, aro-
matic), 125.0 (s, aromatic), 125.2 (s, aromatic), 126.3 (s, aromatic),
m
fluoroethanol (1 equiv.). Since the primary products from the re-
action could not be characterised, the volatiles were removed
under reduced pressure and the solid residue was dissolved in
ether and was layered with petrol to give colourless crystals of 6.
2
128.1 (q, JFeC ¼ 28.8 Hz, aromatic), 130.2 (s, aromatic), 134.0 (s,
aromatic), 138.4 (s, aromatic), 143.3 (s, aromatic), 144.1 (s, aro-
matic), 144.3 (s, aromatic), 150.4 (s, aromatic), 160.9 (q,
Yield: 0.025 g (19%). 1H NMR (d5-PhCl),
d: 0.22 (s, PteCH3,
2JPteH ¼ 35.1 Hz), 1.13 (6H, d, 3JHeH ¼ 6.9 Hz, CH(CH3)2), 1.21 (12H,
1JFeC ¼ 43.9 Hz, CF3); 19F{1H}} NMR (CD2Cl2),
d
: ꢀ63.1 (s, CF3); 195Pt
m, coordinated and uncoordinated (CH3CH2)2O), 1.32 (6H, d,
{1H} NMR (CD2Cl2),
d
: ꢀ3496.4. Colourless crystals suitable for
3
3JHeH ¼ 6.9 Hz, CH(CH3)2), 2.59 (2H, d, JHeH ¼ 6.9 Hz, CH(CH3)2),
single crystal X-ray diffraction were grown by slow diffusion of
petrol into an ether solution of 9b. Found: C, 47.82; H, 3.10; N, 3.72%.
Calcd for C59H46BF24N4Pt: C, 48.11; H, 3.15; N, 3.80%.
3
3.40 (4H, q, JHeH ¼ 6.9 Hz, uncoordinated (CH3CH2)2O), 3.53 (4H,
3
broad q, JHeH ¼ 7.1 Hz, coordinated (CH3CH2)2O), 6.70 Hz (1H, d,
3JHeH
¼
2.2 Hz, imidazol-2-ylidene backbone), 6.78 (1H, d,
3JHeH ¼ 8.5 Hz, aromatic), 7.09 (6H, m, aromatic), 7.23 (7H, m, ar-
ꢀ
cis-[Pt(
k
2-L2a)(CH3)(2-fluoro-pyridine)]þ[BArF
]
4
5c
omatic), 7.48 (4H, m, aromatic), 8.23 (1H, m, aromatic), 8.46 (1H, m,
This was prepared following the general method from 0.050 g
(0.09 mmol) of 2a, 0.088 g (1 equiv.) of acid and 6 L (1.1 equiv.) of 2-
aromatic); 19F{1H}-NMR (d5-PhCl),
d
: ꢀ63.6 (s, CF3 s); 195Pt{1H}
NMR (d5-PhCl),
d
: ꢀ3703. Satisfactory analytical data for 6 could not
fluoro-pyridine. Yield: 0.105 g (77%). 1H NMR (CD2Cl2),
d: 0.11 (3H, s,
be obtained presumably due to the facile loss of coordinated ether.
PteCH3, 2JPteH ¼ 39.5 Hz), 1.17 [6H, d, 3JHeH ¼ 7.3 Hz, CH(CH3)2],1.25
3
3
(6H, d, JHeH ¼ 7.3 Hz, CH(CH3)2), 2.67 [2H, sept., JHeH ¼ 7.3 Hz,
cis-[Pt(
k
2-L2a)(CH3)[(C6F5)3B(OH)] 8
3
CH(CH3)2], 7.03 (1H, d, JHeH ¼ 2.2 Hz, imidazol-2-ylidene back-
In a solution of 0.060 g (0.12 mmol) of 2a and 0.061 g (1 equiv.)
of B(C6F5)3 in ether (15 ml) was added H2O (two drops) at room
temperature and the solution was immediately cooled to ꢀ78 ꢁC.
The mixture was allowed to warm slowly to room temperature
and stirred overnight. After removal of the volatiles under
reduced pressure the resulting off-white solid was dried under
vacuum, washed with petrol and dried under vacuum. Yield:
3
bone), 7.30 (3H, q, JHeH
¼
7.3 Hz, aromatic), 7.42 (1H, t,
3JHeH ¼ 6.6 Hz, aromatic), 7.55 (5H, broad s, aromatic), 7.68 (1H, d,
JHeH ¼ 8.0 Hz, aromatic), 7.84 (11H, broad s., aromatic), 7.89 (1H, d,
3JHeH
¼
2.2 Hz, imidazol-2-ylidene backbone), 8.16 (1H, dt,
JHeH ¼ 1.5 Hz, 8.0 Hz, aromatic), 8.32 (2H, m, aromatic); 13C{1H}-
1
NMR (CD2Cl2),
d
: ꢀ3.2 (s, PteCH3, JPtꢀC ¼ 542.8 Hz), 18.4 [s,
CH(CH3)2], 23.6 [s, CH(CH3)2], 27.9 [s, CH(CH3)2], 116.7 (s, imidazol-
2-ylidene backbone), 117.3 (s, imidazol-2-ylidene backbone), 119.7
(s, aromatic), 122.5 (s, imidazol-2-ylidene backbone), 122.9 (s, ar-
omatic), 123.7 (s, aromatic), 125.2 (s, aromatic), 125.9 (s, aromatic),
0.050
g
(40%). 1H NMR (CD2Cl2)
d
:
ꢀ0.01 (3H, s, PteCH3
3
2JPteH ¼ 37.7 Hz), 1.06 (6H, d, JHeH ¼ 6.8 Hz, CH(CH3)2), 1.15 (6H,
3
3
d, JHeH ¼ 6.8 Hz, CH(CH3)2), 2.49 (2H, sept., JHeH ¼ 6.8 Hz,
CH(CH3)2), 2.93 (1H, broad s., OH(B(C6F5)3), 6.89 (1H,
2
128.0 (q, JFeC ¼ 28.5 Hz, aromatic), 130.4 (s, aromatic), 132.1 (s,
3JHeH
¼
2.4 Hz, imidazol-2-ylidene backbone), 7.21 (2H,
2
aromatic), 134.0 (s, aromatic), 136.2 (d, JFeC ¼ 18.3 Hz, 2-F-pyri-
3JHeH ¼ 7.9 Hz, aromatic), 7.45 (3H, m, aromatic), 7.53 (1H, d,
3JHeH ¼ 2.4 Hz, imidazol-2-ylidene backbone), 8.12 (1H, dt,
JHeH ¼ 1.7 Hz, 8.1 Hz, aromatic), 8.56 (1H, broad d., 3JHeH ¼ 5.5 Hz,
dine), 140.3 (d, 1JFeC ¼ 33.1 Hz, 2-F-pyridine carbon), 141.1 (s, aro-
matic), 145.6 (s, aromatic), 148.3 (s, aromatic), 160.7 (q,
1JFeC ¼ 43.6 Hz, CF3 s); 19F{1H} NMR (CD2Cl2): ꢀ63.1 (s, CF3 s), -61.1
(s, 2-F-pyridine). Colourless crystals were grown by layering an
ether solution of 5c with pentane. Found: C, 46.87; H, 2.80; N,
3.67%. Calcd. for C58H43BF25N4Pt: C, 47.17; H, 2.93; N, 3.79%.
aromatic); 19F{1H} NMR (CD2Cl2),
d
: ꢀ165.9 (d, 2JFeF ¼ 19.3 Hz, o-F
of B(C6F5)3), ꢀ161.0 (t, 2JFeF ¼ 19.3 Hz, m-F of B(C6F5)3), ꢀ134.5 (m,
p-F of B(C6F5)3); I.R. (Nujol, cmꢀ1): 3599 (s, OH stretching). Col-
ourless crystals of compound 8 were grown by slow diffusion of

186
N. Tsoureas, A.A. Danopoulos / Journal of Organometallic Chemistry 775 (2015) 178e187
pentane into an ether solution. Found: C, 45.15; H, 2.93; N, 3.42%.
Calcd for C45H36BF18N3OPt: C, 45.70; H, 3.07; N, 3.55%.
aromatic), 7.42 (5H, broad m, aromatic and backbone imidazol-2-
ylidene), 8.11 (2H, m, aromatic); 31P{1H} NMR:
d, (CD2Cl2): 10.8 (s,
[PPh2CH2CH2-ylidene]PtMe3I, 1JPteP ¼ 799.6 Hz).
Reaction of 2a with MeI. Formation of 11
Formation of cis-[Pt(
experiment)
k
2-L2a)(CH3)(r1-OOCCF3) 9 (NMR scale
Complex 2a (0.015 g, 0.03 mmol) was placed in an NMR tube
and dissolved in CD2Cl2 resulting in a bright yellow solution. After
the tube was capped with a septum and connected to a nitrogen
supply, 3 mL (1.1 equiv.) of CF3COOH were added at room temper-
ature by means of a microsyringe, resulting in the colour changing
to almost colourless. The NMR spectra of the solution were recor-
Complex 2a (0.055 g (0.10 mmol) was dissolved in 15 ml of
CH2Cl2 and 9 L (1.1 equiv.) of MeI was added via a microsyringe. The
mixture was stirred at room temperature for 30 min upon which
time the colour changed from bright to pale yellow. After removal
of the volatiles under reduced pressure, the resulting pale yellow
solid was washed with petrol (2 ꢂ 10 ml) to yield 0.062 g (89%) of
ded. 1H NMR (CD2Cl2),
d
: 0.17 (3H, s, PteCH3, 2JPteH ¼ 38.6 Hz), 1.12
11. 1H NMR, (CD2Cl2),
d: 0.32e1.12 (6H, three singlets with Pt sat-
3
3
(6H, d, JHeH ¼ 6.8 Hz, CH(CH3)2), 1.29 (6H, d, JHeH ¼ 6.8 Hz,
ellites, 2JPteH ¼ 38.1 Hz, 38.1 Hz and 26.4 Hz, Pt(CN)Me3I), 1.22 (6H,
3
3
CH(CH3)2), 2.50 (2H, sept., JHeH ¼ 6.8 Hz, CH(CH3)2), 6.94 (1H, d,
apparent t, CH(CH3)2), 1.25 (3H, d, JHeH ¼ 7.3 Hz, CH(CH3)2), 1.30
3JHeH
¼
2.3 Hz, imidazol-2-ylidene backbone), 7.29 (2H, d,
(3H, d, JHeH ¼ 7.3 Hz, CH(CH3)2), 2.55 (sept., 1H, JHeH ¼ 7.3 Hz,
3
3
3JHeH ¼ 7.8 Hz, aromatic), 7.51 (3H, m, aromatic), 7.66 (1H, d,
3JHeH ¼ 2.3 Hz, imidazol-2-ylidene backbone), 8.14 (1H, ddd,
JHeH ¼ 1.6 Hz, 7.5 Hz, 9.8 Hz, aromatic), 8.59 (1H, ddd, JHeH ¼ 0.9 Hz,
CH(CH3)2), 3.41 (sept., 1H, JHeH ¼ 7.3 Hz, CH(CH3)2), 6.93 (s, 1H,
3
imidazol-2-ylidene
backbone),
7.22
(1H,
d,
aromatic,
3JHeH ¼ 7.3 Hz), 7.28 (1H, d, JHeH ¼ 7.3 Hz, aromatic), 7.38 (1H, t,
3
1.6 Hz, 4.6 Hz, aromatic); 13C{1H} NMR (CD2Cl2),
d
: ꢀ19.7 (s,
3JHeH ¼ 7.3 Hz, aromatic), 7.41 (1H, t, JHeH ¼ 8.8 Hz, py-H4), 7.59
3
PteCH3, 1JPtꢀC ¼ 266.3 Hz), 23.5 (s, CH(CH3)2), 25.0 (s, CH(CH3)2),
29.1 (s, CH(CH3)2), 110.8 (s, imidazol-2-ylidene backbone), 115.6 (s,
imidazol-2-ylidene backbone), 124.2 (s, aromatic), 124.7 (s, aro-
matic), 126.3 (s, aromatic), 131.2 (s, aromatic), 135.3 (s, aromatic),
141.0 (s, aromatic), 145.9 (s, aromatic), 147.6 (s, aromatic), 150.8 (s,
(1H, d, JHeH ¼ 8.8 Hz, py-H3), 7.77 (1H, s, imidazol-2-ylidene
3
3
backbone), 8.05 (1H, t, JHeH ¼ 8.8 Hz, py-H5), 8.61 (1H, d,
3JHeH ¼ 8.8 Hz, py-H6); 13C{1H} NMR (CD2Cl2),
d
: ꢀ32.8 (s, with one
1
Pt satellite, JPtꢀC
¼
328.5 Hz, Pt(CN)Me3I), ꢀ20.5 (s,
1JPtꢀC ¼ 146.8 Hz, Pt(CN)Me3I), ꢀ10.6 [s, 1JPtꢀC ¼ 330.4 Hz, Pt(CN)
Me3I], 20.7, 21.8, 24.1, 24.3, 26.5, 26.6 (s, CH(CH3)2)), 110.2 (s, aro-
matic), 114.2 (s, aromatic), 121.4 (s, aromatic), 121.8 (s, aromatic),
122.6 (s, aromatic), 124.8 (s, aromatic), 128.8 (s, aromatic), 132.3 (s,
aromatic), 138.9 (s, aromatic), 143.9 (s, aromatic), 145.1 (s, aro-
matic), 145.2 (s, aromatic), 149.8 (s, aromatic), 183.4 (s, NCN,
1JPtꢀC ¼ 421.8 Hz). Yellow, X-ray quality crystals were obtained by
layering a CH2Cl2 solution with light petroleum (40e60). Found: C,
40.85; H, 4.78; N, 6.10%.Calcd. for C23H33IN3Pt: C, 41.02; H, 4.94; N,
6.24%.
aromatic); 19F{1H}
d
(CD2Cl2): ꢀ75.4 (s, CF3COOꢀ).
Reaction of 1a with MeI. Formation of 10 (NMR scale experiment)
Complex 1a (20 mg (0.030 mmol) was dissolved in CD2Cl2 in a
Youngs' NMR tube. To the solution at room temperature were
added 4
(CD2Cl2),
m
d
L of MeI and the NMR spectra were recorded. 1H NMR
: 0.23 (3H, d, JPeH ¼ 8.2 Hz, JPteH ¼ 36.3 Hz, PteCH3),
3
2
0.74, 0.83, 0.98, 1.10, 1.25, 1.39 (18H, overlapping each d, remaining
3
PteCH3 and CH(CH3)2), 2.38 (1H, sept., JHeH ¼ 6.8 Hz, CH(CH3)2),
2.53 (1H, m, (PPh2CH2CH2-ylidene)PtMe3I), 2.78 (1H, sept.,
3JHeH ¼ 6.9 Hz, CH(CH3)2), 2.95 (1H, m, [PPh2CH2CH2-ylidene]
PtMe3I), 4.31 (1H, m, (PPh2CH2CH2-ylidene)PtMe3I), 5.64 (1H, m,
(PPh2CH2CH2-ylidene)PtMe3I), 6.79 (1H, broad s, imidazol-2-
ylidene backbone), 7.15 (4H, m, aromatic), 7.33 (3H, broad s,
X-ray crystallography
A summary of the crystal data, data collection and refinement
data for complexes 1, 2a, 2bCl, 5b, 5c, 6, 8, and 11 are given in
Table 1. Data sets were collected on an Enraf-Nonius Kappa CCD
Table 1
Summary of crystal data collection and refinement data for complexes 1, 2a, 2bCl, 5b, 5c, 6, 8, and 11.
Complex
1
2a
2bCl
5b
5c
6
8$ether
11
CCDC
Formula
Formula weight
986051
986052
C22H29N3Pt
530.57
0.71073
Monoclinic
P21/n
8.7905(7)
18.482(2)
12.4068(10)
90
98.768(7)
90
986053
C22H28ClN3Pt
565.01
0.71073
Monoclinic
P21/n
9.0112(8)
17.2104(16)
13.1379(12)
90
93.787(2)
90
986054
986055
986056
986057
986058
C
31H39N2PPt
C59H45BF24N4Pt C58H42BF25N4Pt C57H48BF24N3OPt C43H37BF15N3O2Pt C23H32N3Pt
665.7
1471.89
0.71073
Triclinic
P -1
13.4405(7)
15.1552(6)
15.487(1)
76.778(5)
84.170(5)
72.930(4)
2934.0(3)
2
1475.86
0.71073
Triclinic
P-1
14.1039(11)
15.1745(8)
15.231(1)
92.894(6)
96.530(6)
99.627(4)
3184.9(4)
2
1452.88
0.71073
Triclinic
P-1
14.285(2)
14.324(1)
15.645(1)
97.346(7)
96.952(9)
97.259(9)
3118.5(5)
2
1118.66
0.71073
Triclinic
P-1
10.734(6)
11.247(8)
19.611(16)
81.61(7)
79.13(5)
71.43(4)
2195(3)
2
672.51
0.71073
Monoclinic
P21/n
8.5894(6)
29.989(4)
9.633(1)
90
103.39(1)
90
2413.9(5)
4
l
(Å)
0.71073
Monoclinic
P21/n
12.5675(19)
15.1164(10)
15.212(3)
90
110.368(14)
90
2709.3(7)
4
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
Volume (Å3)
1992.1(3)
4
7.054
2033.1(3)
4
7.045
Z
m
(mmꢀ1
)
5.26
2.51
2.319
2.36
3.301
7.104
Reflections
32044
39241
24137
41301
58202
61790
29558
23820
Indepen. reflections 6307 (0.0576)
(R(int))
4620 (0.0587)
4669 (0.0534)
13520 (0.0590) 14459 (0.1395) 14423 (0.0554)
7699 (0.1070)
5495 (0.0536)
GoF
1.004
1.039
1.043
1.023 0.894
1
1.05
1.04
Final R (I > 2
s(I)
0.0317 (0.0613) 0.0362 (0.0654) 0.0421 (0.0573) 0.0368 (0.0837) 0.0673 (0.1495) 0.0534 (0.1250)
0.0842 (0.2244)
0.0320 (0.0607)
R1 (wR(F2))
Final R (all data)
0.0539 (0.0667) 0.0618 (0.0735) 0.0904 (0.0969) 0.0438 (0.0871) 0.1238 (0.1680) 0.0728 (0.1358)
0.1144 (0.2453)
0.0502 (0.0665)
R1 (wR(F2))

N. Tsoureas, A.A. Danopoulos / Journal of Organometallic Chemistry 775 (2015) 178e187
187
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operating in scanning mode with and scans to fill the Ewald
K
a
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j
u
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group that are severely disordered and were modelled by
restraining their thermal parameters. Furthermore, the coordinated
2-fluoropyridine was also disordered in two positions that were
successfully modelled using standard Shelxl methodology; finally
the structure contains one molecule of disordered solvent molecule
(corresponding to ether) which could not be modelled satisfacto-
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residual electron density. The crystals used for the determination of
the structure of 6 were of pure quality giving weak reflections at
wide angles; as a result the data set was not complete. Further-
more, the structure contains one molecule of disordered solvent
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ꢀ
A.A.D. thanks the USIAS, the CNRS and the Region Alsace,
ꢀ
Communaute Urbaine de Strasbourg for the award of fellowships
and a Gutenberg Excellence Chair (2010-11), respectively.
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CCDC 986051, 986052, 986053, 986054, 986055, 986056,
986057 and 986058 contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
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