Macrocyclic Platinum(II) Complexes with a Bifunctional Diphosphine Ligand

Article abstract of DOI:10.1002/ejic.201501055

The preparation and coordination chemistry of a ditopic ligand scaffold (1^H2), containing both a phosphorus-donor (P) and a nitrogen-donor (N) binding pocket, is reported. The ligand was synthesized by reductive amination from 3-(diphenylphosphino)benzaldehyde and N-(2-aminophenyl)-N-methylbenzene-1,2-diamine. Selective coordination in the P-pocket was achieved for Pt^II, with careful control over the reaction conditions and precursor materials providing access to either the thermodynamic cis isomer, cis-PtCl₂(1^H2) (2), or the kinetic trans isomer, trans-PtCl₂(1^H2) (3). Both species have been fully characterized both in the solid state and in solution. Thermodynamic parameters for isomerization processes of 2 and 3 have been determined. Halide abstraction from 2 and 3 led to formation of cis-[Pt(CH₃CN)(Cl)(1^H2)]BF₄ and trans-[Pt(CH₃CN)(Cl)(1^H2)]BF₄. The design, synthesis and stereoselective coordination chemistry of a new ditopic diphosphine ligand toward Pt^II are described. The cis and trans isomer of the PtCl₂ complex are structurally characterized. Spectroscopic investigations on the conversion of the trans into the cis-isomer and formation of cationic derivatives are also presented.

Full text of DOI:10.1002/ejic.201501055

FULL PAPER
DOI:10.1002/ejic.201501055
Macrocyclic Platinum(II) Complexes with a Bifunctional
Diphosphine Ligand
Andrea E. Pascui,[a] Karlotta van Rees,[a] Dirk W. Zant,[a]
Daniël L. J. Broere,[a] Maxime A. Siegler,[b] and
Jarl Ivar van der Vlugt*[a]
Keywords: N,P ligands / Metallacycles / Platinum / Macrocyclic ligands / Ligand design
The preparation and coordination chemistry of a ditopic li-
gand scaffold (1H2), containing both a phosphorus-donor (P)
and a nitrogen-donor (N) binding pocket, is reported. The
to either the thermodynamic cis isomer, cis-PtCl2(1H2) (2), or
the kinetic trans isomer, trans-PtCl2(1H2) (3). Both species
have been fully characterized both in the solid state and in
ligand was synthesized by reductive amination from 3-(di- solution. Thermodynamic parameters for isomerization pro-
phenylphosphino)benzaldehyde and N-(2-aminophenyl)-N-
methylbenzene-1,2-diamine. Selective coordination in the P-
pocket was achieved for PtII, with careful control over the
reaction conditions and precursor materials providing access
cesses of 2 and 3 have been determined. Halide abstraction
from 2 and 3 led to formation of cis-[Pt(CH3CN)(Cl)(1H2)]BF4
and trans-[Pt(CH3CN)(Cl)(1H2)]BF4.
and allow bimetallic species to be constructed without di-
rect metal–metal interactions, which may be relevant for
catalytic activity. Control over metal coordination with flex-
ible ditopic ligands is not trivial, both with respect to selec-
tivity for a specific binding site as well as to the geometry
imposed on the metal center. We therefore set out to design
a ditopic ligand scaffold featuring two potential binding
sites (a P- and an N-pocket; Figure 1), bridged by a flexible
linker, to gain control over the geometry and site selectivity
of this framework. We herein discuss the selective met-
alation of the P-pocket toward PtII, including selective for-
mation of cis and trans isomers and their interconversion.
This research is expected to aid future investigations into
the preparation of bimetallic architectures based on flexible
scaffolds.
Introduction
Hybrid ligands bearing both phosphorus (soft) and
nitrogen (hard) donors continue to enjoy much attention in
areas such as coordination chemistry and catalysis.[1] Recent
examples of ditopic phosphine–nitrogen-based ligand struc-
tures highlight the potential to selectively metalate one of
the two donor groups to access monofunctionalized archi-
tectures that are of relevance for the construction of (het-
ero)bimetallic coordination compounds[2] as well as for ap-
plications in supramolecular catalysis, using host-guest or
templating principles.[3] C3-Symmetric building blocks have
received much attention for the formation of well-defined
(di)metallic complexes, but (pseudo-)C2-symmetric counter-
parts have also been successfully explored in recent years.[4]
Most of the employed ditopic P,N-ligands feature
(semi-)rigid linkers between the two donor sites, which lim-
its the number of possible geometries and hence restricts
coordination chemistry. A monoatomic linker or the ab-
sence of any linker between P and N units may induce di-
rect metal–metal bonding that could be useful in the con-
text of small-molecule activation.[5] However, straightfor-
ward access to more flexible yet site-selective frameworks
would facilitate other coordination modes and geometries
Figure 1. Schematic representation of ditopic ligand 1H2
.
[a] Homogeneous, Bio-inspired and Supramolecular Catalysis,
van’t Hoff Institute for Molecular Sciences, University of
Amsterdam,
The use of square-planar PtII complexes with long-chain
chelating (bis)phosphine ligands to generate macrocyclic
structures may result in a mixture of cis and trans isomers
and oligomeric species in solution. The choice of the metal
precursor, the size and rigidity of the chelate ring, and
changes in the reaction conditions (e.g., temperature, reac-
tion time, concentration and solvent) can alter the ratio be-
Science Park 904, 1098 XH, Amsterdam, The Netherlands
E-mail: j.i.vandervlugt@uva.nl
www.homkat.nl
[b] Department of Chemistry, John Hopkins University,
3400 N Charles Street, Baltimore, Maryland 21218, USA
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201501055.
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tween the products.[6] The isolation of pure samples of both N-(2-aminophenyl)-N-methylbenzene-1,2-diamine (A) and
cis and trans isomers with the same flexible chelating ligand 3-(diphenylphosphanyl)benzaldehyde (B) (Scheme 1). Given
remains a challenging task. To synthesize the frequently less the instability of the intermediate Schiff-base product, the
stable trans isomers, the use of trans-stabilizing groups in diimine was reduced in situ with the mild reducing agent
the metal precursors, e.g., Zeise’s salt,[7] or an additional sodium triacetoxyborohydride (STAB).[11] The 31P NMR
chromatographic step to separate the isomers[8] is often nec- spectrum of 1H2 displayed a singlet at δ = –5.37 ppm, and
essary, which can increase the time and synthetic cost re- the 1H NMR spectrum showed a broad triplet at δ =
quired to produce such complexes. Taking inspiration from 4.53 ppm attributed to the NH protons (3J = 4.0 Hz). The
known di- and tripodal P,N ligand systems, we wanted to signals of the N-methyl group and the N-methylene groups
study what would happen if the distance between both were present at δ = 2.93 and 4.08 ppm, respectively. The 13
C
binding pockets was increased. The lack of control over the (APT) NMR spectrum showed doublets for the resonances
ratio of cis/trans isomers and the formation of oligomeric of the phenylene and phenyl rings connected to the phos-
species represent major issues in the development of highly phorus atoms.
active and selective homogeneous catalysts based on flexible
diphosphine ligands.[9] In this paper, we present the success-
ful functionalization of the P-pocket to form macrocyclic
species, and we discuss selective formation of both isomers
in the flexible PtCl2(1H2) system.
Results and Discussion
Scheme 1. Reaction scheme for the synthesis of ligand 1H2
.
Initial reaction of ligand 1H2 with the commercially avail-
able PtII precursor PtCl2(CH3CN)2 (cis/trans ratio ca. 3:1)
led to the formation of both cis-PtCl2(1H2) (2) and trans-
PtCl2(1H2) (3), with no control over the ratio between the
Synthesis of Bifunctional Diphosphine Ligand 1H2 and X-
ray Crystallographic Characterization of Macrocyclic Pt
Complexes cis-PtCl2(1H2) (2) and trans-PtCl2(1H2) (3)
Initially, the formation of a tris(sec-amine) was targeted, two isomers. We therefore screened various preparative
to make use of the reported redox activity of such enti- methods
using
cis-PtCl2(CH3CN)2
and
trans-
ties.[10] However, intramolecular cyclization of the periph- PtCl2(CH3CN)2 to find the optimal synthetic routes to iso-
eral imine and the pivotal secondary amine prevented isola- late both 2 and 3 in pure form (Scheme 2).
tion of the target compound. Hence, this NH group was
To suppress the formation of oligomeric species, the reac-
replaced by an NCH3 group to avoid this undesirable reac- tions were conducted under dilute conditions in CH2Cl2.
tivity.
The cis isomer 2 could be selectively obtained by addition
Ligand 1H2 was synthesized by a one-pot reductive amin- of either cis- or trans-PtCl2(CH3CN)2 precursor to the li-
ation protocol using the readily accessible building blocks gand. Pure 3 could only be isolated when ligand 1H2 was
Scheme 2. Preparative routes for the selective formation of cis-PtCl2(1H2) (2) and trans-PtCl2(1H2) (3).
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Figure 2. ORTEP plots (50% probability of thermal ellipsoids) of complex cis-PtCl2(1H2) (2) (left) and trans-PtCl2(1H2) (3) (right).
Hydrogen atoms are omitted for clarity, except for NH. Selected bond lengths [Å] and angles [°]. For 2: Pt(1)–P(1) 2.2599(7), Pt(1)–Cl(1)
2.3568(7), Pt(1)–P(2) 2.2513(8), Pt(1)–Cl(2) 2.3340(7), N(1)···N(3) 3.452, P(1)···P(2) 3.426, C(14)···C(39) 3.516; Cl(1)–Pt(1)–Cl(2) 88.52(3),
P(1)–Pt(1)–P(2) 98.63(3), Cl(2)–Pt(1)–P(2) 90.30(3), P(1)–Pt(1)–Cl(1) 82.35(3). For 3: Pt(1)–P(1) 2.3074(12), Pt(1)–Cl(1) 2.2929(12), Pt(1)–
P(2) 2.3106(12), Pt(1)–Cl(2) 2.3087(12), N(2)···N(3) 3.528, P(1)···P(2) 4.618, C(20)···C(27) 5.164; Cl(1)–Pt(1)–Cl(2) 173.16(5), P(1)–Pt(1)–
P(2) 178.53(4), P(1)–Pt(1)–Cl(1) 93.25(4), P(1)–Pt(1)–Cl(2) 86.06(4).
added to trans-PtCl2(CH3CN)2 as the metal precursor. Col- gand 1H2, whereas for 3, pseudo-triplets are observed for the
orless crystals of 2 and 3 were obtained by diffusion of hex- same fragments, which is in agreement with the respective
ane into CH2Cl2 or toluene solutions, respectively. The re- geometries around PtII in solution and in the solid state.
spective molecular structures are shown in Figure 2.
For 2, the 31P NMR spectrum shows a singlet with Pt satel-
The geometry around the platinum center in compounds lites at δ = 14.5 ppm and a JPt,P coupling constant of
2 and 3 is slightly distorted square-planar, as indicated by 3662 Hz, supporting the coordination of the chloride ion
the bond angles around Pt. For species 2, the Pt–Cl bonds trans to the phosphorus atom and thus a mutual cis orienta-
point away from the P-pocket as a result of the cis orienta- tion of both phosphines (Figure 3, right).[12,13] For 3, a sing-
tion of the ligands. The N-pocket of 1H2 adopts a folded let at δ = 20.7 ppm with Pt satellites and a JPt,P coupling of
conformation, with intramolecular N(1)···N(3) and C(14)··· 2614 Hz is observed by 31P NMR spectroscopy, which is in
C(39) distances of 3.542 and 3.516 Å, respectively, whereas agreement with mutual trans coordination of the two phos-
the P(1)···P(2) separation is 3.426 Å. Weak π···π stacking phine donors.
interactions are observed between one of the phenylene spa-
cers and the phosphine phenyl ring (centroid···centroid dis-
tance 3.62 Å), and a weak intramolecular hydrogen bond
between N3 (donor) and N1 (acceptor) is present [H(3A)···
N(1) 2.65(4) Å; N(3)–H(3A)···N(1) 156(3)°]. For compound
3, the ligand backbone (the N-pocket) unfolds [N(2)···N(3)
3.528, C(20)···C(27) 5.164 Å] to accommodate the trans co-
ordination of both P-arms [P(1)···P(2) 4.618 Å]. A weak in-
tramolecular hydrogen bond is observed between N2
(donor) and N3 (acceptor) [H(2)···N(3) 2.701 Å;
N(2)–H(2)···N(3) 160.74°].
NMR Spectroscopic Investigations of cis-PtCl2(1H2) (2) and
trans-PtCl2(1H2) (3)
Figure 3. 1H (left) and 31P (right) NMR spectra of cis-PtCl2(1H2
(2) (top) and trans-PtCl2(1H2) (3) (bottom).
)
1
Both 2 and 3 were fully characterized in solution by H,
13C, and 31P NMR spectroscopy. The signals of the NCH3
group show similar chemical shifts in both complexes, but
1
The spectral features for 2 are broader (for both the H
the signals of the NH, CH2 and some of the aromatic pro- and 31P NMR spectra) than for 3, except for the methyl-
tons are shifted downfield in trans-PtCl2(1H2) (Figure 3, amine group. We therefore recorded variable-temperature
left). The 13C NMR spectrum of 2 contains doublets for the (VT) 31P NMR spectra of both compounds in CDCl3.
carbon atoms of the phenylene and phenyl rings attached to Upon cooling, no change was observed in the spectrum of
the phosphorus atoms, similar to that observed for free li- trans-PtCl2(1H2). In contrast, the 31P signal for cis-
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PtCl2(1H2) broadened at lower temperature, ultimately re- uene, a solution of trans-PtCl2(1H2) is stable at room tem-
sulting in two peaks at δ = 17.0 and 10.9 ppm at –60 °C perature and under mild heating (40 °C), with no irrevers-
(Figure 4). Both resonances have JP,Pt coupling constants ible isomerization being observed. The irreversible isomer-
similar to that measured at 20 °C, suggesting the presence ization of 3 in coordinating solvent at elevated temperature
of two interconverting cis isomers. Reheating the sample to suggests that 2 may be the thermodynamic product and that
room temperature resulted in the coalescence of these two 3 is the kinetic product. To support this, we performed (dis-
signals, with no further changes occurring above room tem- persion-corrected) DFT calculations (BP86-D3/def2-TZVP;
perature. The observed interconversion is probably related see the Supporting Information for the optimized geome-
to the (substantial) rotational freedom in the flexible ligand tries of 2 and 3). Complex 2 was found to be 11.4 kcalmol–1
backbone. The calculated ΔG# value at the coalescence tem- more stable than the trans isomer, partly aided by the pres-
perature[14] is 10.4 kcalmol–1 (Ϯ0.2), using Equation (1) ence of an intramolecular hydrogen bond between N(3)–H
(with Tc = 245.15 K, and kc = 2736 s–1, where kc = 2.22 Δν). and N(1), which is also observed in the solid-state structure
(Figure 2).
ΔG# = 4.58Tc [10.32 + log(Tc/kc)]
(1)
Formation of Cationic PtII Complexes by Chloride
Abstraction
Abstraction of a chloride ligand with AgPF6 led to the
formation of the cationic derivatives cis-[Pt(CH3CN)-
Cl(1H2)]PF6 (4) and trans-[Pt(CH3CN)Cl(1H2)]PF6 (5), ac-
1
cording to H and 31P NMR spectroscopic analysis (Fig-
ure 5). Abstraction of one chloride ion from 2 in aceto-
nitrile results in the non-C2-symmetric NCCH3 adduct 4.
In the 31P NMR spectrum, two doublets are present at δ =
1
12.32 ppm (2JP,P = 17.8, JP,Pt = 3506 Hz) and 4.52 ppm
1
1
(2JP,P = 19.4, JPt,P = 3817 Hz), whereas in the H NMR
spectrum, two methylene resonances are observed at δ =
3.95 and 3.57 ppm, each corresponding to two protons. A
similar reaction with 3 resulted in a signal at δ = 18.0 ppm
Figure 4. Variable-temperature 31P NMR spectra of cis-PtCl2(1H2
(2).
)
in the 31P NMR spectrum with Pt satellites (JPt,P
2365 Hz) for the symmetric species 5.
=
Heating of 3 in [D6]DMSO to 100 °C led to irreversible
isomerization to cis isomer 2 and to the formation of a sec-
ond species resonating at δ = 16.18 ppm, which is proposed
to be a solvent adduct. Coordination of solvent (either
through chloride dissociation or as a five-coordinate inter-
Conclusions
We designed a new ditopic diphosphine ligand bearing
mediate) likely accelerates ligand rearrangement. In [D8]tol- a flexible nitrogen-rich backbone and developed synthetic
1
Figure 5. H (left) and 31P (right) NMR spectra of cis-[Pt(CH3CN)Cl(1H2)]PF6 (4) (top) and trans-[Pt(CH3CN)Cl(1H2)]PF6 (5) (bottom).
A small amount of 4 can be observed in the spectra of 5.
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1
A (5.45 g, 25.4 mmol, 99%) as a beige solid. H NMR (500 MHz,
routes to selectively generate 17-membered metallacyclic
complexes 2 and 3 by metalation of the P-pocket of this
ligand. Both isomers could be isolated as spectroscopically
and analytically pure species under different reaction condi-
tions, by careful control over the addition protocol. This
allows for facile access to both structures and has allowed
spectroscopic studies to probe the cis/trans interconversion.
The cis isomer appears to be the thermodynamic product,
as deduced from spectroscopic and computational data, al-
though the trans isomer is stable against isomerization in
noncoordinating solvents. These results not only demon-
strate the potential to control the geometry around Pt with
flexible diphosphine ligands but will also aid future studies
to establish the construction of heterodimetallic architec-
tures with both phosphorus and nitrogen coordination.
These investigations are ongoing in our laboratories.
CDCl3): δ = 7.02 (dd, J = 7.8, 4J = 1.4 Hz, 2 H), 6.97 (td, J =
7.7, J = 1.4 Hz, 2 H), 6.77 (dd, J = 7.6, J = 1.4 Hz, 2 H), 6.74
3
3
4
3
4
3
3
4
(td, J = 9.5, J = 8.8, J = 1.4 Hz, 2 H), 3.82 (br. s, 4 H), 3.08 (s,
3 H) ppm. 13C NMR (126 MHz, CDCl3): δ = 140.7 (C), 136.6 (C),
124.9 (CH), 122.2 (CH), 118.9 (CH), 116.0 (CH), 40.0 (CH3) ppm.
IR (ATR): ν = 3442, 3349, 1611, 1497, 1453, 1286, 1119 cm–1.
˜
HRMS (ESI+): calcd. for [C13H15N3]+ 213.1266; found 213.11280.
Note: Precursor A is very sensitive to oxidation under ambient at-
mosphere, which limits its shelf-life considerably.
Synthesis of Ligand 1H2: A clear yellow solution of A (0.832 g,
2.97 mmol) in CH2Cl2 (40 mL) was added dropwise to a brown
suspension of
B (0.305 g, 1.43 mmol) and sodium triacet-
oxyborohydride (0.852 g, 4.02 mmol) in CH2Cl2 (60 mL). The reac-
tion mixture was stirred for 22 h, then saturated NaHCO3 solution
(10 mL) and water (10 mL) were added. The yellow suspension was
extracted with ethyl acetate (3ϫ 20 mL), and the combined organic
layers were washed with water (20 mL) and dried with MgSO4.
After filtration, the volatiles were removed, and the resulting crude
yellow foam was purified by column chromatography (CH2Cl2/hex-
ane, 7:3). Ligand 1H2 (75%) was obtained as a white powder. 1H
NMR (500 MHz, CDCl3): δ = 7.31–7.29 (m, 20 H), 7.22–7.13 (m,
6 H), 6.99 (m, 6 H), 6.69 (t, 3J = 7.5 Hz, 2 H), 6.52 (d, 3J = 8.0 Hz,
2 H), 4.53 (t, JN,H = 4.0 Hz, 2 H, NH), 4.08 (d, J = 8.0 Hz, 4 H,
CH2), 2.93 (s, 3 H, CH3) ppm. 13C NMR (125 MHz, CDCl3): δ =
141.6 (s, C), 139.6 (d, JC,P = 7.5 Hz, C), 137.5 (d, JC,P = 11.3 Hz,
C), 137.1 (d, JC,P = 11.3 Hz, C), 136.2 (s, C), 133.7 (d, JC,P = 19 Hz,
CH), 132.6 (d, JC,P = 21.3 Hz, CH), 132.3 (d, JC,P = 17.5 Hz, CH),
128.8 (s, CH), 128.7 (s, CH), 128.5 (d, JC,P = 6.3 Hz, CH), 127.7
(s, CH), 125.1 (s, CH), 121.6 (s, CH), 117.3 (s, CH), 110.9 (s, CH),
47.6 (s, CH2), 40.4 (s, CH3) ppm. 31P NMR (162 MHz, CDCl3): δ
= –5.37 (s) ppm. HRMS (CSI+): calcd. for [C51H45N3P2 + H]+
762.3089; found 762.3087. C51H45N3P2 (761.88): calcd. C 80.40, H
5.95, N 5.52; found C 79.96, H 6.37, N 5.35.
Experimental Section
General Methods: All commercial reagents were purchased from
Sigma–Aldrich or Strem and were used as received. Syntheses were
carried out under N2 using standard Schlenk techniques and an
inert-gas UniLab MBRAUN glovebox. Solvents were distilled from
sodium/benzophenone or CaH2. Glassware was dried at 130 °C un-
less otherwise stated. Column chromatography was performed on
silica gel (400–630 mesh). Analytical thin-layer chromatography
(TLC) was performed on precoated gel 60 F254 silica plates. The
TLC spots were visualized by irradiation with UV light (254 nm).
Positive-ion mass spectra were collected with an AccuTOF LC,
JMS-T100LP mass spectrometer (JEOL). Infrared spectra (ATR)
were recorded with a Bruker Alpha-p FTIR spectrophotometer.
NMR (1H, 13C, 31P) spectra were recorded with a Bruker AMX
400 MHz or a Bruker DRX 500 MHz spectrometer. Elemental
analysis was performed by the Kolbe Microanalytical Laboratory
(Mülheim an der Ruhr, Germany). Precursor A, cis-PtCl2(CH3CN)2
and trans-PtCl2(CH3CN)2 were prepared according to reported
procedures,[15] and the purity of the isomers was checked by TLC
(acetone/CH2Cl2, 9:1) and by IR spectroscopy.
3
3
Synthesis of cis-PtCl2(1H2) (2): A colorless solution of 1H2 (60 mg,
0.08 mmol) in CH2Cl2 (5 mL) was added dropwise to a solution of
cis-PtCl2(CH3CN)2 (27 mg, 0.08 mmol) in CH2Cl2 (20 mL), and
the solution was stirred at room temperature. After 4 h, the solu-
tion was concentrated in vacuo, and pentane (10 mL) was added.
An off-white precipitate formed that was filtered and dried in vacuo
(98%). 1H NMR (400 MHz, CDCl3): δ = 7.67–7.63 (m, 10 H),
7.25–7.21 (m, 8 H), 7.17–7.07 (m, 8 H), 7.01–6.99 (m, 2 H), 6.92
(t, 3J = 5.6 Hz, 2 H), 6.79 (t, 3J = 8.0 Hz, 2 H), 6.72 (t, 3J = 6.4 Hz,
2 H), 6.53 (d, J = 8.0 Hz, 2 H), 3.89 (br. s, 2 H, NH), 3.71 (d, J
= 4.0 Hz, 4 H, CH2), 2.92 (s, 3 H, CH3) ppm. 13C NMR (125 MHz,
CDCl3): δ = 142.1 (s, C), 138.2 (d, JC,P = 11.3 Hz, C), 136.8 (s, C),
134.4 (m, 2CH), 133.4 (d, JC,P = 7.6 Hz, CH), 131.1 (s, CH), 130.8
(s, CH), 130.1 (d, JC,P = 61.3 Hz, C), 129.3 (d, JC,P = 69.3 Hz, C),
129.2 (d, JC,P = 10.0 Hz, CH), 127.9 (d, JC,P = 11.3 Hz, CH), 125.3
(s, CH), 121.6 (s, CH), 117.6 (s, CH), 110.3 (s, CH), 47.5 (s, CH2),
41.3 (s, CH3) ppm. 31P NMR (162 MHz, CDCl3): δ = 14.5 (s, JP,Pt
= 3662.3 Hz) ppm. HRMS (CSI+): calcd. for [C51H45N3P2PtCl]+
992.2431; found 992.2356. C51H45Cl2N3P2Pt (1027.88): calcd. C
59.59, H 4.41, N 4.09; found C 59.61, H 4.39, N . 4.06.
Synthesis of Precursor A. Step 1:[16] KOH (8.63 g, 153.0 mmol) was
added to a stirred solution of N-methyl-2-nitroaniline (9.70 g,
63.8 mmol) and 1-fluoro-2-nitrobenzene (8.1 mL, 76.5 mmol) in
anhydrous DMSO (170 mL) under atmospheric conditions. The re-
action mixture was heated at 120 °C and stirred for 36 h. Water
(100 mL) was added, and the mixture was extracted with CH2Cl2
(3ϫ 200 mL). The combined organic extracts were washed with
water and brine and dried with NaSO4. All volatiles were removed
in vacuo, and the crude product was dry-loaded on silica and puri-
fied by column chromatography (hexanes/ethyl acetate, 8:2) to af-
ford N-methyl-2-nitro-N-(2-nitrophenyl)aniline (7.91 g, 28.9 mmol,
45%) as an orange solid. 1H NMR (500 MHz, CDCl3): δ = 7.76
3
3
3
4
3
3
4
(dd, J = 8.2, J = 1.4 Hz, 2 H), 7.53 (ddd, J = 8.5, J = 7.6, J =
1.4 Hz, 2 H), 7.24 (d, 3J = 8.2 Hz, 2 H), 7.15 (t, J = 7.8 Hz, 2 H),
3
3.39 (s, 3 H) ppm. 13C NMR (126 MHz, CDCl3): δ = 143.2 (C),
141.9 (C), 134.0 (CH), 126.4 (CH), 124.9 (CH), 123.8 (CH), 42.6
Synthesis of trans-PtCl2(1H2) (3): A yellow solution of trans-
PtCl2(CH3CN)2 (73.3 mg, 0.20 mmol) in CH2Cl2 (10 mL) was
added dropwise to a colorless solution of 1H2 (160 mg, 0.20 mmol)
(CH ) ppm. IR (ATR): ν = 1596, 1515, 1486, 1445, 1363 cm–1.
˜
3
HRMS (ESI+): calcd. for [C13H11N3O4]+ 273.0750; found
273.0742. Step 2: A mixture of N-methyl-2-nitro-N-(2-nitrophenyl)- in CH2Cl2 (10 mL), and the solution was stirred at room tempera-
aniline (7.01 g, 25.7 mmol) and Pd/C (508 mg, 10 wt.-%) was sus-
pended in EtOAc (160 mL) and stirred under hydrogen (1 atm) at
room temperature. After 24 h, the mixture was filtered through Ce-
lite under nitrogen, and the solvent was removed in vacuo to afford
ture. After 1 h, the solvent was removed in vacuo to give 3 (95%)
1
3
as a yellow solid. H NMR (400 MHz, CDCl3): δ = 8.21 (t, J =
3
6.1 Hz, 2 H), 7.78–7.74 (m, 10 H), 7.46–7.32 (m, 16 H), 7.15 (t, J
3
3
= 7.7 Hz, 2 H), 7.09 (d, J = 7.9 Hz, 2 H), 6.81 (t, J = 7.7 Hz, 2
Eur. J. Inorg. Chem. 2015, 5687–5693
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3
H), 6.75 (d, J = 7.7 Hz, 2 H), 4.52 (t, 3J = 2.5 Hz, 2 H, NH), 4.23 X-ray Crystallography. Data for 2: All reflection intensities were
(d, 3J = 1.3 Hz, 4 H, CH2), 2.98 (s, 3 H, CH3) ppm. 13C NMR measured at 110(2) K with a SuperNova diffractometer (equipped
(126 MHz, CDCl3): δ = 142.1 (C), 138.9 (app. t, C), 136.7 (C),
135.7 (app. t, CH), 134.8 (app. t, CH), 132.3 (app. t, CH), 130.6
(CH), 130.4 (CH), 129.4 (app. t, C), 128.9 (app. t, C), 128.5 (app.
with Atlas detector) with Cu-Kα radiation (λ = 1.54178 Å) under
the program CrysAlisPro (Version 1.171.36.32 Agilent Technol-
ogies, 2013). The program CrysAlisPro (Version 1.171.36.32
t, CH), 128.0 (app. t, CH), 125.0 (CH), 121.9 (CH), 117.4 (CH), Agilent Technologies, 2013) was used to refine the cell dimensions
111.0 (CH), 48.4 (CH2), 30.0 (CH3) ppm. 31P NMR (162 MHz, and for data reduction. The structure was solved with the program
CDCl3): δ = 20.7 (s, JP,Pt = 2614.2 Hz) ppm. HRMS (CSI+):
calcd. for [C51H45N3P2PtCl]+ 992.2431; found 992.2398.
C51H45Cl2N3P2Pt (1027.88): calcd. C 59.59, H 4.41, N 4.09; found
C 59.55, H 4.42, N . 4.05.
SHELXS-2013[21] and was refined on F2 with SHELXL-2013.[22]
Analytical numeric absorption corrections based on a multifaceted
crystal model were applied using CrysAlisPro (Version 1.171.36.32,
Agilent Technologies, 2013). The temperature of the data collection
was controlled with the system Cryojet (manufactured by Oxford
Instruments). H atoms were placed at calculated positions (unless
otherwise specified) using the instructions AFIX 23, AFIX 43, or
AFIX 137, with isotropic displacement parameters having values
of 1.2 or 1.5 times Ueq of the attached C atoms. The H atoms
attached to N1 and N3 were found from difference Fourier maps,
and their atomic coordinates were refined freely. Data for 3: X-ray
intensities were measured with a Bruker D8 Quest Eco dif-
fractometer equipped with a Triumph monochromator (λ =
0.71073 Å) and a CMOS Photon 50 detector at a temperature of
150(2) K. Intensity data were integrated with the Bruker APEX2
software.[23] Absorption correction and scaling were performed
with SADABS.[24] The structures were solved with the program
SHELXL.[23] Least-squares refinement was performed with
SHELXL-2013[22] against F2 of all reflections. Non-hydrogen
atoms were refined with anisotropic displacement parameters. H
atoms were placed at calculated positions using the instructions
AFIX 13, AFIX 43 or AFIX 137 with isotropic displacement pa-
rameters having values 1.2 or 1.5 times Ueq of the attached C atoms.
Details for cis-PtCl2(1H2) (2): Fw = 1112.75; colorless needle;
Synthesis of cis-[Pt(CH3CN)Cl(1H2)]PF6 (4): A solution of AgPF6
(17.2 mg, 0.068 mmol) in CH3CN (5 mL) was added dropwise to a
solution of cis-PtCl2(1H2
) (70.0 mg, 0.068 mmol) in CH3CN
(10 mL). After stirring at room temperature for 16 h, the solution
was filtered through Celite, and the solvent was removed in vacuo.
The resulting solid was washed with pentane (3ϫ 5 mL) to give 4
(99%) as a white solid. 1H NMR (400 MHz, CD3CN): δ = 7.99
(br. s, 1 H), 7.84–7.79 (m, 4 H), 7.60 (br. s, 1 H), 7.46–7.33 (m, 14
H), 7.24–7.00 (m, 7 H), 6.96 (d, 3J = 7.2 Hz, 1 H), 6.78 (t, J =
14.8 Hz, 1 H), 6.72–6.66 (m, 3 H), 6.52 (m, 2 H), 6.18 (m, 2 H),
3
3
4.26 (br. t, 2 H, NH), 3.95 (d, J = 4.0 Hz, 2 H, CH2), 3.57 (d, J
= 4.0 Hz, 2 H, CH2), 2.89 (s, 3 H, CH3) ppm. 13C NMR (125 MHz,
CD3CN): δ = 143.1 (s, C), 142.2 (s, C), 140.0 (d, JC,P = 13.3 Hz,
C), 138.7 (s, C), 137.8 (s, C), 137.1 (s, C), 135.2 (d, JC,P = 7.5 Hz,
CH), 133.2 (m, CH), 132.7 (d, JC,P = 8.7 Hz, CH), 132.2 (s, CH),
132.0 (s, CH), 131.3 (s, CH), 129.1 (m, CH), 128.4 (m, CH), 127.6
(s, C), 126.5 (s, C), 125.9 (s, CH), 124.3 (s, CH), 123.1 (s, CH),
120.6 (s, CH), 117.6 (s, CH), 116.9 (s, CH), 110.6 (s, s, 2 CH), 47.0
(s, CH2), 46.8 (s, CH2), 41.3 (s, CH3) ppm. 31P NMR (162 MHz,
CD3CN): δ = 12.32 (d, JP–P = 19.4, JP,Pt = 3506 Hz), 4.51 (d, JP–P
0.27ϫ0.05ϫ0.02 mm; orthorhombic; Pbcn (no. 60);
a
=
= 17.8, JP,Pt = 3817 Hz), –144.60 (sept, JP,F = 706.32 Hz) ppm. 19
F
19.4701(2), b = 19.2427(2), c = 24.5952(2) Å; V = 9214.77(15) Å3;
Z = 8; DX = 1.604 gcm–3; μ = 8.798 mm–1; Tmin–Tmax = 0.356–
0.839. 31918 reflections were measured up to a resolution of (sin
θ/λ)max = 0.62 Å–1. 9042 reflections were unique (Rint = 0.0382), of
which 7579 were observed [IϾ2σ(I)]. 595 parameters were refined
using 69 restraints. R1/wR2 [IϾ2σ(I)] = 0.0267/0.0572. R1/wR2 (all
refl.) = 0.0367/0.0612. S = 1.017. Residual electron density found
between –0.65 and 0.71 eÅ–3. Details for trans-PtCl2(1H2) (3): Fw =
1112.75; colorless needle; 0.10ϫ0.10ϫ0.10 mm; monoclinic; P21/n
(no. 14); a = 10.1748(2), b = 17.4455(4), c = 26.6274(6) Å, β =
94.7410(15)°; V = 4710.31(18) Å3; Z = 2; DX = 1.514 gcm–3; μ =
3.201 mm–1; Tmin–Tmax = 0.58–0.74. 45484 reflections were mea-
sured up to a resolution of (sin θ/λ)max = 0.77 Å–1. 9250 reflections
were unique (Rint = 0.0670), of which 7491 were observed
[IϾ2σ(I)]. 603 parameters were refined using 79 restraints. R1/wR2
[IϾ2σ(I)] = 0.0399/0.0717. R1/wR2 (all refl.) = 0.0594/0.0767. S =
1.112. Residual electron density found between –2.55 and
1.40 eÅ–3. CCDC-1417390 (2) and 1416667 (3) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
NMR (282 MHz, CD3CN): δ = –69.32 (d, JP,F = 705.90 Hz) ppm.
HRMS (FD+): calcd. for [C53H48N4P2PtCl]+ 1033.2640; found
1033.2623.
Synthesis of trans-[Pt(CH3CN)Cl(1H2)]PF6 (5): A solution of
AgPF6 (17.2 mg, 0.068 mmol) in CH3CN (5 mL) was added drop-
wise to a solution of trans-PtCl2(1H2) (70.0 mg, 0.068 mmol) in
CH3CN (40 mL). After stirring at room temperature for 16 h, the
solution was filtered through Celite, and the solvent was removed
in vacuo. The resulting solid was washed with pentane (3ϫ 5 mL)
1
to give 5 (99%) as a white solid. H NMR (400 MHz, CD3CN): δ
= 8.12 (t, JH,P = 16.0 Hz, 2 H), 7.66–7.46 (m, 24 H), 7.21–7.16 (m,
3
2 H), 7.03 (t, J = 16 Hz, 2 H), 6.98 (d, J = 4 Hz, 2 H), 6.73–6.70
3
(m, 2 H), 4.73 (t, 2 H, NH), 4.37 (d, J = 8.0 Hz, 2 H, CH2), 2.89
(s, 3 H, CH3) ppm. 13C NMR (125 MHz, CD3CN): δ = 143.1 (s,
C), 140.7 (app. t, JC,P = 10.6 Hz, C), 140.1 (s, C), 139.9 (s, C), 138.6
(s, C), 137.0 (s, C), 134.2 (app. t, JC,P = 12.1 Hz, CH), 133.2 (m,
CH), 132.2 (m, CH), 129.2 (m, CH), 127.4 (s, C), 127.1 (s, C), 126.8
(s, C), 126.4 (s, C), 125.2 (s, CH), 122.0 (s, CH), 111.7 (s, CH), 47.3
(s, CH2), 39.7 (s, CH3) ppm. 31P NMR (162 MHz, CD3CN): δ =
–
18.0 (s, JP,Pt = 2364.9 Hz), –144.63 (sept, JP,F = 705.8 Hz, PF6 )
ppm. 19F NMR (282 MHz, CD3CN): δ = –126.89 (d, JF,P
=
Supporting Information (see footnote on the first page of this arti-
cle): Computational details with optimized geometries of 2 and 3,
NMR spectra of new compounds.
708.7 Hz, PF6 ) ppm. HRMS (FD+): calcd. for [C53H48N4P2PtCl]
–
+
1033.2640; found 1033.2611.
DFT Calculations: Geometry optimizations were carried out by
using TURBOMOLE[17] coupled with the PQS Baker optimizer[18]
with the BOpt package[19] at the DFT level using the bp86 func-
tional and the def2-TZVP basis set. All minima (no imaginary fre-
quencies) were characterized by numerically calculating the Hessian
matrix. Grimme’s semiempirical DFT-D3 method was employed
for a better description of the hydrogen-bonding interactions.[20]
Acknowledgments
This research was supported by the European Research Council
through an ERC Starting Grant (EuReCat, Grant Agreement
279097, to J. I. v. d. V.). Professor de Bruin and Professor Reek are
thanked for scientific discussions.
Eur. J. Inorg. Chem. 2015, 5687–5693
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Received: September 14, 2015
Published Online: November 13, 2015
Eur. J. Inorg. Chem. 2015, 5687–5693
5693
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim