Self-assembly of metallamacrocycles employing a New Benzil-based organometallic bisplatinum(II) acceptor

Article abstract of DOI:10.2533/chimia.2015.541

A benzil-based semi-rigid dinuclear organometallic acceptor 4,4′-bis[trans-Pt(PEt₃)₂(NO₃)(ethynyl)]benzil (bisPt-NO₃) containing a Pt-ethynyl functionality was synthesized in good yield and characterized by mult

Full text of DOI:10.2533/chimia.2015.541

Supramolecular chemiStry
CHIMIA 2015, 69, No. 9 541
doi:10.2533/chimia.2015.541
Chimia 69 (2015) 541–546 © Schweizerische Chemische Gesellschaft
Self-assembly of Metallamacrocycles
Employing a New Benzil-based Organo-
metallic Bisplatinum(ii) Acceptor
Bijan Roy, Sankarasekaran Shanmugaraju, Rupak Saha, and Partha Sarathi Mukherjee*
Abstract: A benzil-based semi-rigid dinuclearorganometallic acceptor 4,4'-bis[trans-Pt(PEt ) (NO )(ethynyl)]benzil
3
2
3
(
bisPt-NO ) containing a Pt-ethynyl functionality was synthesized in good yield and characterized by multinuclear
3
31
1
13
NMR ( H, P, and C), electrospray ionization mass spectrometry (ESI-MS), and single-crystal X-ray diffraction
analysis of the iodide analogue bisPt-I. The stoichiometric (1:1) combination of the acceptor bisPt-NO separately
3
with four different ditopic donors (L –L ; L = 9-ethyl-3,6-di(1H-imidazol-1-yl)-9H-carbazole, L = 1,4-bis((1H-im-
1
4
1
2
idazol-1-yl)methyl)benzene, L = 1,3-bis((1H-imidazol-1-yl)methyl)benzene and L = 9,10-bis((1H-imidazol-1-yl)
3
4
methyl)anthracene) yielded four [2 + 2] self-assembled metallacycles M –M in quantitative yields, respectively.
1
4
All these newly synthesized assemblies were characterized by various spectroscopic techniques (NMR, IR, ESI-
MS) and their sizes/shapes were predicted through geometry optimization employing the PM6 semi-empirical
method. The benzil moiety was introduced in the backbone of the acceptor bisPt-NO due to the interesting
3
structural feature of long carbonyl C–C bond (~1.54 Å), which enabled us to probe the role of conformational
flexibility on size and shapes of the resulting coordination ensembles.
Keywords: Flexible bisplatinum acceptor · Metallamacrocycle · Self-assembly
powerful strategies for one-pot synthe- pose,[6] the use of flexible metal-acceptors
sis of desired molecular architectures in is very rare. Our group has been actively
Introduction
[
4]
Chemists have long desired to develop high yield. Th e stable coordination ge-
involved in this field to develop efficient
molecular ensembles with diverse shapes, ometry of square planar Pd(ꢀꢀ) and Pt(ꢀꢀ) self-assembled 2D/3D architecture for the
sizes, and functionalities in order to mim- metal ions and their dynamic metal–ligand sensing of nitroaromatic explosives, small
ic complex biological systems and also to coordination bond formation with N/O- molecules and various anions.[ Th e pres-
7]
explore such systems for practical applica- donors gives them the potential to achieve ent study introduces a novel benzil-based
[
1]
tions. Th e rapid development of synthet-
thermodynamically stable single products semi-rigid bisplatinum(ꢀꢀ) acceptor bisPt-
ic methodologies has made it possible to over several kinetically driven possibili- NO which was utilized to obtain four new
3
synthesize various intricate macrocycles/ ties, as nicely described in the ‘Molecular [2 + 2] metallamacrocycles (M –M ) in
1
4
cages, which have found significant impor- library’ by Stang et al.[ But the rapid de- almost quantitative yields by heating with
tance for the applications in drug delivery, velopment of the field demands the design equimolar amounts of the imidazole based
sensing, catalysis and host–guest chemis- and synthesis of more sophisticated and ditopic donors (L –L ) of different size and
5]
1
4
[
2]
try. However, the conventional covalent unprecedented molecular architectures rigidity in 1:1 chloroform/acetone solvent
C–C bond formation) synthesis of such beyond the existing molecular library. For mixture (Scheme 1). All the macrocycles
(
functional smart materials often involves this purpose, the use of flexible building were fully characterized by multinuclear
multi-step reactions and hence found to be blocks is a popular approach to achieve NMR and ESI-MS spectrometry. Semi-
laborious, time consuming and results in unusual structural features. Th ough a
empirical PM6 geometry optimization was
[
3]
low yield of the targeted products. Th us,
large number of rigid/semi-rigid donors carried out for all the four macrocycles to
it remains a constant challenge for the has been extensively used for this pur- illuminate their structures.
scientific community to introduce alter-
native synthetic methodologies targeting
Scheme 1. [2 + 2]
Self-assembly of
metallamacrocycles
minimum synthetic difficulties to achieve
desired products with maximum possible
yields. In light of this, coordination-driv-
en self-assembly has become one of the
(
M −M ) using a new
1 4
benzil-based organo-
metallic bisplatinum
acceptor bisPt-NO3
in combination with
four different ditopic
imidazole donors
(
L −L ).
1 4
*
Correspondence: Dr. P. S. Mukherjee
Department of Inorganic and Physical Chemistry
Indian Institute of Science
Bangalore-560012, India
Tel.: +91 80 2293 3352
E-mail: psm@ipc.iisc.ernet.in

542 CHIMIA 2015, 69, No. 9
Supramolecular chemiStry
Experimental Section
Hz, 4H, Ar-H), 0.26 (s, 18H, Me Si-H). with 1 mL methanolic solution of silver ni-
3
13
C NMR (CDCl 100 MHz): δ = 193.44, trate (5.2 mg, 0.030 mmol) for 2 h in dark
3
,
Materials and Methods
132.84, 132.57, 130.37 130.13, 104.18, at room temperature for in situ generation
Th e bisplatinum intermediate bisPt-I
100.30, 0.23.
of the nitrate analogue bisPt-NO . Th e
3
was synthesized under dry nitrogen atmos-
A solution of 4,4'-trimethylsilyleth- resulting suspension was filtered through
phere using standard Schlenk techniques. ynylbenzil (1.5 g, 3.72 mmol) in dichlo- celite in order to remove the AgI precipi-
All the solvents were dried and freshly romethane–methanol (1:1) mixture was tate. Th e solvent was evaporated complete-
distilled prior to the reactions. Th e starting
materials 4,4'-dibromobenzil, imidazole, 3.72 mmol) for 2 h at room temperature. acetone, which was filtered through cotton
anthracene, carbazole, dibromo-p-xylene, Th e solvent was evaporated completely and and added to the chloroform solution of the
stirred with potassium carbonate (515 mg, ly and the residue was taken up in 6 mL of
dibromo-m-xylene and other reagents the solid residue was filtered through silica corresponding donor (1.0 equiv.). Th e mix-
were purchased from various commercial gel matrix using 1:1 chloroform–hexane ture was then heated at 60 °C for 12 h. Th e
sources and used without further purifica- mixture to obtain pure desilylated 4,4'-di- final clear solution was dried completely
tion. All four donors (L –L ) were synthe- ethynylbenzil (1) as a pale brown powder under vacuum and the residue was washed
1
4
[
8]
sized by following literature procedures.
(86%). Anal calcd for C H O : C, 83.71; with 4 mL chloroform and the products
18 10 2
1
NMR spectra were recorded in a Bruker H, 3.90. Found: C, 83.42; H, 4. 08. H NMR were obtained as yellow solid upon treat-
4
00 MHz spectrometer and the chemical (CDCl , 400 MHz): δ = 7.94 (d, J = 8.81 ing with cold diethyl ether.
3
1
shifts are reported in ppm with respect Hz, 4H, Ar-H), 7.62 (d, J = 8.78 Hz, 4H,
Spectral data of bisPt-NO : H NMR
3
13
to standard reference tetramethylsilane Ar-H), 3.33 (s, 2H, alkyne-H); C NMR (CDCl , 400 MHz): δ = 7.83 (d, 4H, Ar-H),
3
(
Me Si, δ = 0.00 ppm) or the solvent peaks (CDCl 100 MHz): δ = 193.42, 133.13, 7.28 (d, 4H, Ar-H), 1.91 (m, 24H, -CH -),
4
3,
2
31
arising due to their incomplete deuteration 132.95, 130.22, 129.39, 82.92, 82.25.
1.19 (m, 36H, -CH3). P NMR (CDCl ):
3
(
δ = 7.26 for CDCl , δ = 1.94 for CD CN
δ = 20.21.
3
3
Synthesis of bisPt-I
1
in case of H NMR). ESI-MS spectra were
recorded in an Agilent 6538 Ultra-High
A mixture of 4,4'-diethynylbenzil (1;
Synthesis of M1
0
.100 g, 0.38 mmol), trans-[PtI (PEt ) ]
2 3 2
Definition (UHD) Accurate Mass Q- TO F
Reaction of carbazole-based donor
(
0.796 g, 1.16 mmol) and CuI (0.0074 g,
.038 mmol) was placed in an oven-dried
spectrometer. IR experiments were done
L (4.76 mg, 0.0145 mmol) with bisPt-
1
0
in a Bruker ALPHA F TI R spectrome-
NO gave macrocycle M in an iso-
3
1
Schlenk flask and 15 mL dry toluene-di-
ethylamine (2:1) solvent mixture was add-
ter. A Perkin-Elmer Lambda 750 UV/Vis
spectrophotometer was used for recording
absorbance spectra, while the emission
spectra was obtained using HORIBA Jovin
Yvon Fluoromax-4 spectrometer. HPLC
grade solvents were used for UV/Vis and
fluorescence spectroscopic studies.
lated yield of 86%. Anal calcd for
C H N O P Pt : C, 47.42; H, 5.46; N,
1
24 170 14 16
8
4
ed to it. Th e solution was stirred for 48 h
6.24. Found: C, 47.89; H, 5.32; N, 6.11.
at room temperature under nitrogen atmos-
1
H NMR (CDCl , 400 MHz): δ = 9.25 (b,
3
phere until TL C confirmed the completion
4H), 9.01 (b, 4H), 7.84 (m, 12H), 7.60
of the reaction. Th e solvent was evaporated
(m, 8H), 7.36 (t, 8H), 7.14 (s, 4H), 4.46
completely and the crude product was puri-
(b, 4H), 1.93 (m, 48H), 1.42 (m, 6H),
fied by silica-gel column chromatography
3
1
1
.16 (m, 72H). P NMR (1:1 MeCN-d3/
using 1:9 ethyl acetate–hexane mixture
as eluent to get iodide analogue bisPt-I
as yellow solid in 64% yield (Scheme 2).
Anal calcd for C H I O P Pt : C, 36.74;
Synthesis of 4,4'-Diethynylbenzil (1)
An oven-dried 100 mL two-neck round
bottom flask was charged with 4,4'-dibro-
mobenzil (2.0 g, 5.43 mmol), trans-[P-
dCl (PPh ) ] (0.114 g, 0.16 mmol), CuI
CDCl ): δ 16.33. ESI-MS (m/z): 1508.48
3
–
2+
– 3+
[M –2NO ] ,
984.65[M –3NO ] ,
2 3
– 4+ –1
3
1
3
722.98 [M –4NO ] ; IR (υ/cm ):
3
4
2
68
2
2
4
2
2964.87, 2111.75, 1661.58.
1
H, 4.99. Found: C, 36.89; H, 4.62. H
2
3 2
NMR (CDCl , 400 MHz): δ = 7.83 (d, J
3
(
0.031 g, 0.16 mmol) and 70 mL of dry
Synthesis of M2
=
8.82 Hz, 4H Ar-H), 7.34 (d, J = 8.31
NEt under nitrogen atmosphere. Th en tri-
Reaction of donor L (3.45 mg, 0.0145
3
2
Hz, 4H, Ar-H), 2.21 (m, 24H, -CH -), 1.16
2
methylsilylacetylene (1.9 mL, 13.7 mmol)
was added to the mixture and it was re-
fluxed at 85 °C for 36 h. After completion
mmol) with bisPt-NO according to the
above-mentioned procedure gave mac-
rocycle M in 91% yield. Anal calcd for
1
3
3
(
m, 36H, -CH ); C NMR (CDCl , 100
3
3
MHz): δ = 194.55, 136.12, 131.39, 130.30,
3
1
2
1
30.12, 101.53, 100.21, 17.12, 8.73;
P
of the reaction (as monitored by TL C), the
C H N O P Pt : C, 45.40; H, 5.58; N,
1
12 164 12 16
8
4
NMR (CDCl ): δ = 8.22. IR: υ = 2105.68
3
1
solvent was evaporated completely and
the product was purified by column chro-
matography in silica gel by eluting with
chloroform-hexane (9:1) mixture to obtain
5.67. Found: C, 44.89; H, 5.30; N, 5.33. H
(
alkyne C≡C stretching), 1657.90 (C=O
NMR (CDCl , 400 MHz): δ = 8.42 (d, 4H),
7.77 (m, 8H), 7.35 (m, 20H), 6.91 (s, 4H),
5.32 (s, 8H), 1.70 (m, 48H), 1.08 (m, 72H).
3
stretching). ESI-MS: m/z = 1286 ([bisPt-I
—
+
+
CH CN — I ] ).
3
3
1
4
,4'-trimethylsilylethynylbenzil as light GeneralProcedurefortheSyntheses
P NMR (MeCN-d /CDCl ): δ 16.23. ESI-
3
3
1
– 2+
yellow powder. Isolated yield = 78%. H of the Macrocycles M –M
MS (m/z): 1418.50 [M –2NO ] , 925.67
2 3
– 3+ – 4+
1
4
NMR (CDCl , 400 MHz): δ = 7.91 (d, J
=
20 mg (0.0145 mmol) of bisPt-I was [M –3NO ] , 678.75 [M –4NO ] ; IR
2 3 2 3
–1
3
8.81 Hz, 4H, Ar-H), 7.58 (d, J = 8.31 dissolved in 6 mL of chloroform and stirred (υ/cm ): 2996.25, 2114.13, 1662.22.
Synthesis of M3
Macrocycle M was isolated in almost
3
quantitativeyieldbythereactionofL (3.45
3
mg, 0.0145 mmol) with bisPt-NO . Anal
3
calcd for C H N O P Pt : C, 45.40; H,
1
12 164 12 16
8
4
5
5
.58; N, 5.67. Found: C, 45.50; H, 5.75; N,
1
.42. H NMR (CDCl , 400 MHz): δ = 8.23
3
(
(
(
s, 4H), 7.85 (d, 8H), 7.55 (d, 4H), 7.42
d, 12H), 7.29 (d, 4H), 7.06 (s, 4H), 5.28
s, 8H), 1.76 (m, 48H), 1.10 (m, 72H). P
31
NMR (1:1 MeCN-d /CDCl ): δ 16.52. ESI-
Scheme 2. Schematic representation of the synthesis of 4,4'-bis[trans-Pt(PEt ) (NO )(ethynyl)]ben-
3
3
3
2
3
–
2+
zil (bisPt-NO ) from 4,4'-diethynylbenzil (1) and trans-PtI (PEt ) .
MS (m/z): 1418.45 [M –2NO ] , 925.64
3
2
3
2
3 3

Supramolecular chemiStry
CHIMIA 2015, 69, No. 9 543
Table 1. Crystallographic data and structure re-
finement parameters for bisPt-I
empirical formula
formula weight
crystal system
space group
T, K
C H I O P Pt
42 68 2 2 4 2
1372.82
Monoclinic
C
293(2)
0.71073
39.683(14)
8.831(3)
14.908(5)
90.0
λ(Mo Kα, Å
a, Å
b, Å
c, Å
α, deg
1
13
Fig. 1. H (left) and P (right) NMR spectra of bisPt-I recorded in CDCl3.
β, deg
95.770(10)
90.0
γ, deg
3
V, Å
5198(3)
4
–
3+
– 4+
[
(
M –3NO ] , 678.73 [M –4NO ] . IR restricted flexibility will retain its char-
3 3 3 3
Z
–
1
υ/cm ): 2965.38, 2114.79, 1660.97.
acteristic structural coding as a building
unit. After thorough survey of the liter-
ature, the benzil moiety has been judi-
–3
ρcalcd, g cm
µ, mm
1.754
6.717
1.226
–
1
Synthesis of M4
a
Macrocycle M was obtained by the re- ciously selected for this purpose due to
GOF
4
b
action of donor L (4.9 mg, 0.0145 mmol) its unique structural features (long C–C
R [I > 2σ(I)]
0.0380
0.1181
4
1
with bisPt-NO in 77% isolated yield. bond of ~1.54 Å and conformational flex-
c
3
wR2
Anal calcd for C H N O P Pt : C, ibility) as earlier reported for some of its
1
28 172 12 16
8
4
a
2
2
2
1/2
[
10]
GOF = {Σ [w(F0 – F ) ] / (n – p)} , where n
and p denotes the number of data points and
the number of parameters, respectively.
4
8.61; H, 5.48; N, 5.31. Found: C, 48.72; derivatives.
Th e C=O groups in the
c
1
H, 5.23; N, 5.08. H NMR (MeCN-d , 400 benzil moiety are found to reside in differ-
3
MHz): δ = 8.47 (m, 8H), 7.79 (b, 20H), ent planes as a consequence of the strong
b
R = (Σ IIF I – IF II) / Σ IF I;
1
0
c
2
0
0
7
4
7
.37 (m, 8H), 7.18 (m, 4H), 6.98 (m, electronic repulsion between the oxygen
c
2
2
2
2
1/2
wR = { Σ [ w(F – F ) ] / Σ[w(F ) ]} , where w
2
c
0
H), 6.38 (b, 8H), 1.63 (m, 48H), 0.97(m, atoms which make ‘cis’ conformation
2
2
2
2
=
+ 2Fc
1/ [ σ (F ) + (aP) + (bP)] and P = [max (0,F )
0
0
3
1
2H). P NMR (MeCN-d ): δ 16.02. ESI- highly unfavourable. On the other hand,
2
] / 3.
3
–
2+
MS (m/z): 1519.62 [M –2NO ] , 992.15 the strong electron withdrawing nature of
4
3
–
3+
– 4+
[
(
M –3NO ] , 728.68 [M –4NO ] . IR the oxygen restricts the delocalization of
4 3 4 3
–1
1
13
31
υ/cm ): 2996.60, 2113.69, 2662.72.
electron density between two C=O moi- nuclear ( H, C, P) NMR spectrosco-
eties effectively imposing ‘only’ single py, IR and ESI-MS spectrometry. Th e H
1
X-ray Data Collection and Structure bond character to the carbonyl C–C bond, NMR spectrum consists of two doublets in
Refinements
resulting in a twisted geometry intermedi- the aromatic region (δ = 7.83, J = 8.3Hz
A suitable single crystal of the io- ate between cis and trans conformations and 7.32 ppm, J = 8.3 Hz) along with two
dide analogue bisPt-I was mounted on a of the benzil moiety.
multiplets in the upfield region (δ = 2.25,
crystal mounting loop after coating with
To synthesize the desired bisplatinum
J = 3.8 Hz and 1.12, J = 8.0 Hz) showing
paratone oil and diffracted on a Bruker acceptor bisPt-NO , 4,4'-dibromobenzil 1:1:6:9 intensity ratios corresponding to
3
SMART
APEX CCD diffractometer us- was first converted to 4,4'-diethynylben- the aromatic and ethyl protons, respective-
ing graphite-monochromatic Mo-Kα ra- zil (1) by a Sonagashira coupling reaction ly. Moreover, a sharp singlet at δ = 8.72
3
1
1
diation (0.7107 Å) at 293 K. Th e struc-
with trimethylsilylacetylene followed by ppm in P{ H} NMR spectra along with
1
95
1
ture was solved by direct methods using desilylation of the alkyne groups with po- two concomitant Pt satellite peaks ( J
Pt-P
SHELX-97 software incorporated with tassium carbonate.
= 1153.5 Hz) confirmed its purity (Fig.
WINGX package.[ Empirical absorption
9]
–1
Subsequently, 4,4'-diethynylbenzil 1 1). Th e strong peaks at ν = 2105 cm and
–1
corrections were applied with SADABS. wasincorporatedwithtwoplatinumcentres 1657 cm in the IR spectra were assigned
All the non-hydrogen atoms were refined by Cu(ꢀ)-catalysed metal insertion reaction to the ethynyl and carbonyl vibrations, re-
with anisotropic displacement coefficients with trans-PtI (PEt ) to obtain the iodide spectively. Single crystal X-ray diffraction
2
3 2
while the hydrogen atoms were fixed to analogue bisPt-I in 64% yield (Scheme 2). experiment unambiguously established the
their geometric positions suggested by the bisPt-I was fully characterised by multi- structure of bisPt-I (Fig. 2). Th e active ac-
program.
Fig. 2. Crystal
structure of bisPt-I
Results and Discussion
showing the twisted
conformation in solid
state. Hydrogen at-
oms are omitted for
Design, Synthesis and
Characterisation of bisPt-NO3
Design of a bisplatinum(ꢀꢀ) acceptor
compatible with various type of donors
can be obtained by incorporating a ‘not
so rigid’ backbone which will allow the
acceptor to adjust its binding sites in ac-
cordance with the incoming donor co-
ordination environment. However, the
clarity.

544 CHIMIA 2015, 69, No. 9
Supramolecular chemiStry
[
10(a)]
Table 2: Selected bond lengths and bond angles compared with benzil
torsional angles in bisPt-I.
and the selected
ceptor bisPt-NO was synthesized by treat-
3
ing bisPt-I with 2.1 equiv. silver nitrate in
a chloroform–methanol mixture, which
was also characterized by multinuclear
NMR spectroscopy (Supplementary Data,
Fig. S9, S10). Interestingly, exchange of
iodine caused a shift in the peak position
from δ = 8.72 ppm to δ = 20.21 ppmin the
bisPt-I
1.535(16) Å
1.230(9) Å
1.461(10) Å
116.7(7)°
118.9(8)°
124.3(7)°
123.4(7)°
119.1(6)°
Benzil
bisPt-I
C(1)-C(1)
C(1)-O(1)
1.523(7) Å
1.210(7) Å
1.482(7) Å
118.1(4)°
119.3(4)°
122.4(4)°
119.4(4)°
118.9(4)°
O(1)-C(1)-C(1)-O(1)
C(2)-C(1)-C(1)-C(2)
O(1)-C(1)-C(2)-C(7)
O(1)-C(1)-C(2)-C(3)
C(4)-C(5)-Pt(1)-P(2)
C(6)-C(5)-Pt(1)-P(1)
-113.50(3)°
-118.69(2)°
178.24(2)°
-4.03(4)°
3
1
P NMR spectrum.
Th e diffraction quality single crystals
were obtained by the slow evaporation
of dichloromethane–hexane solution of
bisPt-I at room temperature. bisPt-I crys-
C(1)-C(2)
O(1)-C(1)-C(1)
C(2)-C(1)-C(1)
O(1)-C(1)-C(2)
C(7)-C(2)-C(1)
C(3)-C(2)-C(1)
tallised in monoclinic crystal system in
35.96(2)°
34.43(2)°
the C2/c space group ( Ta ble 1). Th e sol-
id-state structure shows that the two C=O
groups of the benzil moiety are not exactly
trans-oriented, instead twisted along the
C–C bond possessing a torsional angle of
–
113.50(3)° (ΦO-C-C-O). Moreover, the C–C
bond distance is 1.535(16) Å and hence
suggesting single bond character ( Ta ble 2).
Th e two platinum centres are 16.240(89)Å
apart from each other describing a ~122°
bite angle with respect to the centroids
of the carbonyl carbon atoms making it a
unique building block. Th e phosphorous
atoms of the trans-blocking PEt groups
3
are situated outside the benzoyl plane at
an angle of around 35°.
Synthesis and Characterisation
of [2 + 2] Self-assembled
Metallamacrocycles (M −M )
1
4
In order to check the versatility of the
acceptor bisPt-NO to become amenable
3
for a range of donor systems, four imi-
dazole-based ditopic donors (L –L ) with
1
4
different shapes, sizes and flexibility were
selected to self-assemble their correspond-
ing [2 + 2] metallamacrocycles. While L1
being a carbazole-based rigid donor pos-
sessing an almost 90° donor angle, the L –
4
2
1
31
L donors are rather flexible in their coor-
Fig. 3. H (left) and P (right) NMR spectra of M in CDCl -CD CN.
1
3
3
dination directionality. L and L are struc-
2
3
tural isomers possessing different donor
environments, while L is functionalised
4
with a fluorescent anthracene backbone.
In a general synthetic methodology, the
iodide analogue bisPt-I was converted in
situ to its nitrate analogue bisPt-NO and
3
then treated separately with an equivalent
amount of the donors L –L by heating
1
4
overnight in chloroform–acetone solvent
mixture to obtain self-assembled macro-
cycles M –M (Scheme 1). Th e sharp sin-
1
4
gle peak, along with two satellite peaks, in
3
1
1
the P{ H} NMR spectra appeared in the
shielded region compared to the acceptor
bisPt-NO due to the enhanced platinum
3
to phosphorous back donation upon ligand
coordination demonstrating the formation
of a single product in each case (Figs 3 and
S12–S19, Supplementary Data).
Diffusion
ordered
spectroscopy
(
DOSY) of M showed single diffusion
Fig. 4. Experimental (above) and theoretical (below) isotopic distribution pattern of M −M for the
4
1
4
2
+ charged species.
coefficient for all the peaks and further

Supramolecular chemiStry
CHIMIA 2015, 69, No. 9 545
confirmed its purity (Fig. S20). Th e stoi-
of the donors are oriented perpendicular metallacycles in each case was verified
chiometry of the building blocks in M1– to the longer diagonal axis (Figs 5, S31– by various spectroscopic techniques and
M were determined from the ESI-MS S34). Interestingly, M has little bending structural information of these assemblies
4
4
spectra where in each case the isotopic near the acceptor sites shaping the mole- was obtained through geometry optimisa-
distribution patterns of the peaks matched cule in a boat-like geometry (Fig. S34). In tion with the PM6 semi-empirical meth-
with their respective theoretical patterns all the cases triethylphosphine groups were od. To the best of our knowledge, these
corresponding to the expected [2 + 2] as- oriented outwards from the ring to release metallamacrocycles are the first examples
semblies (Figs 4 and S22–S25). ESI-MS steric strain. Th e torsional angles associat-
of discrete supramolecular architectures
spectra of M showed three sharp peaks at ed with the acceptor (both Φ and obtained from benzil-based semi-rigid
1
C2-C1-C1-C2
m/z = 1508.48, 984.65 and 722.98 (Fig.
ΦO1-C1-C1-O1) significantly vary in four struc- organometallic acceptor via metal–ligand
–
2+
S22) corresponding to [M –2NO ] , tures over a range from 132.6° to 140.7° coordination. Our group is now actively
1
3
–
3+
– 4+
[
M –3NO ] and [M –4NO ]
frag- for Φ
and from 133.2° to 139.4° working to design various types of flexi-
which reflects the flexible ble/semi-rigid organometallic Pt(ꢀꢀ) accep-
1
3
1
3
C2-C1-C1-C2
ments, respectively. Similarly for M and for Φ
M (having identical molecular formu- donor binding capability of the acceptor tors to generate a library of unprecedented
2
O1-C1-C1-O1
3
lae), ESI-MS peaks were obtained at m/z bisPt-NO ( Ta ble S1 Supplementary Data).
functional metallamacrocycles.
3
=
1418.50(M ) and 1418.45(M ) (theo-
2
3
Supplementary Data
retical value = 1418.45), 925.67(M ) and
2
Supplementary Data containing NMR, ESI
9
6
25.64(M ) (theoretical value = 925.64), Conclusions
3
MS, and electronic spectra and optimized co-
ordinates is provided. CCDC 966747 contains
the supplementary crystallographic data for
this paper. Th ese data can be obtained free of
charge from Th e Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_re-
78.75(M ) and 678.73(M ) (theoreti-
2
3
cal value = 678.73) corresponding to the
In conclusion, we have synthesized
new benzil-based semi-rigid Pt -
M /M –4NO ] fragments, respectively organometallic acceptor bisPt-I and its
Supplementary Data, Figs S23, S24). All nitrate analogue bisPt-NO in high yields.
–
2+
–
3+
II
[
[
(
M /M –2NO ] , [M /M –3NO ] and
a
2
3
3
2
3
3
2
–
4+
2
3
3
3
the four macrocycles absorbed at 353 nm Multinuclear NMR, and X-ray diffraction quest/cif.
owing to the π-π* transition of the ethynyl analysis of bisPt-I, unequivocally con-
conjugated backbone of the acceptor (Fig. firmed their formation. Th e benzil func-
Acknowledgements
S29). M shows strong fluorescence due tionality was chosen due to its long carbon-
to the presence of anthracene moiety with yl C–C bond and to investigate the effect
characteristic triple humped curve in the of semi-rigidness on controlling the shape
B. R. is grateful to IISc Bangalore for a re-
search fellowship. P.S.M thanks the Department
4
of Science and Te chnology (DS T) , India, for fi-
nancial support in the form of a Swarnajayanti
fellowship.
emission spectra (Fig. S30).
and size of final supramolecular architec-
In order to investigate their structural tures. Th e presence of unsaturated ethy-
nature, semi-empirical geometry optimi- nyl functionality imparts further stability
zations using PM6 method were carried to keep the final molecular architectures
Received: July 7, 2015
out which show M forming a beautiful flat intact under various experimental condi-
1
ring-shaped architecture where the furthest tions. Th e stoichiometry (1:1) combina-
[
1] a) J.-M. Lehn, Proc. Natl. Acad. Sci. USA
2002, 99, 4763; b) J. W. Steed, J. L. Atwood,
stretch is about 3.90 nm between the ethyl tion of bisPt-NO with a series of ditopic
3
‘
Supramolecular Chemistry’, John Wiley &
groups (Fig. 5) and also having inner diam- imidazole donors (L –L ) resulted in the
1
4
Sons Ltd, UK, 2009; c) Q. Gan, T. K. Ronson,
D. A. Vosburg, J. D. Th oburn, J. R. Nitschke, J.
Am. Chem. Soc. 2015, 137, 1770; d) C. J. Bruns,
D. Fujita, M. Hoshino, S. Sato, J. F. Stoddart,
eters of 2.43 nm and 1.58 nm respectively. formation of [2 + 2] self-assembled metal-
Th e M , M and M have similar kind of
lacycles M –M in quantitative yields. Th e
2
3
4
1 4
architectures where aromatic backbones purity and selective formation of [2 + 2]
M. Fujita, J. Am. Chem. Soc. 2014, 136, 12027.
[
2] a) M. Fujita, Chem. Soc. Rev. 1998, 2, 417;
b) B. H. Northrop, H.-B. Yang, P. J. Stang,
Chem. Commun. 2008, 5896; c) U. N. Nehete,
G. Anantharaman, V. Chandrasekhar, R.
Murugavel, H. W. Roesky, D. Vidovic, J.
Magull, K. Samwer, B. J. Sass, Angew. Chem.,
Int. Ed. 2004, 43, 3832; d) N. L. To h, N.
Nagarithinum, J. J. Vittal, Angew. Chem., Int.
Ed. 2005, 44, 2237; e) A. M. Spokoyny, M. S.
Rosen, P. A. Ulmann, C. Stern, C. A. Mirkin,
Inorg. Chem. 2010, 49, 1577; f) K. Acharyya,
P. S. Mukherjee, Chem.-Eur. J. 2015, 21, 1; g)
M. Yoshizawa, M. Ta mura, M. Fujita, Science
2
006, 312, 251; h) L. Xu, Y.-X. Wang, L.-J.
Chen, H.-B. Yang, Chem. Soc. Rev. 2015, 44,
148; i) L. Chen, P. S. Reiss, S. Y. Chong, D.
2
Holden, K. E. Jelfs, T. Hasell, M. A. Little, A.
Kewley, M. E. Briggs, A. Stephenson, K. M.
Th omas, J. A. Armstrong, J. Bell, J. Busto, R.
Noel, J. Liu, D. M. Strachan, P. K. Th allapally,
A. I. Cooper, Nat. Mater. 2014, 13, 954; j) I. V.
Grishagin, J. B. Pollock, S. Kushal, T. R. Cook,
P. J. Stang, B. Z. Olenyuk, Proc. Nat. Acad. Sci.
USA 2014, 111, 18448.
3] a) S. Hiraoka, Y. Yamauchi, R. Arakane, M.
[
Shionoya, J. Am. Chem. Soc. 2009, 131, 11646;
b) M. Jurícek, J. C. Barnes, N. L. Strutt, N. A.
Vermeulen, K. C. Ghooray, E. J. Dale, P. R.
McGonigal, A. K. Blackburn, A.-J. Avestro,
J. F. Stoddart, Chem. Sci. 2014, 5, 2724; c)
Fig. 5. Geometry optimized structures (PM6) of the macrocycles M , M , M and M Hydrogen
atoms have been omitted for clarity.
E. J. Dale, N. A. Vermeulen, A. A. Th omas,
J. C. Barnes, M. Jurícek, A. K. Blackburn,
1
2
3
4.

546 CHIMIA 2015, 69, No. 9
Supramolecular chemiStry
N. L. Strutt, A. A. Sarjeant, C. L. Stern, S. E.
Dalton Trans. 2011, 40, 12117; d) T. H. Noh, E. [8] a) H.-P. Zhou, P. Wang, Z.-J. Hu, L. Li, J.-J.
Denmark, J. F. Stoddart, J. Am. Chem. Soc.
Heo, K. H. Park, O.-S. Jung, J. Am. Chem. Soc.
2011, 133, 1236; e) P. J. Steel, Acc. Chem. Res.
2005, 38, 24; f) A. K. Bar, R. Chakrabarty, P. S.
Chen, Y. Cui, Y.-P Ti an, J.-Y. Wu, J.-X. Yang,
X.- T. Ta o, M.-H. Jiang, Eur. J. Inorg. Chem.
2007, 13, 1854; b) M. Yang, K. Stappert, A.-V.
2
014, 136, 10669; d) C. Zhang, C.-F. Chen, J.
Org. Chem. 2007, 72, 9339.
[
4] a) S. Li, J. Huang, F. Zhou, T. R. Cook, X.Yan,Y.
Mukherjee, Inorg. Chem. 2009, 48, 10880; g)
C. M. Hartshorn, P. J. Steel, Chem. Commun.
1997, 541; h) X.-J. Li, F.-L. Jiang, M.-Y. Wu,
S.-Q. Zhang, Y.-F. Zhou, M.-C. Hong, Inorg.
Chem. 2012, 51, 4116.
Mudring, J. Mat. Chem. C 2014, 2, 458; c) L.
Ye, B. Zhu, B. Zheng, P. J. Stang, J. Am. Chem.
Soc. 2014, 136, 5908; b) B. Sun, M. Wang, Z.
Lou, M. Huang, C. Xu, X. Li, L.-J. Chen, Y. Yu,
G. L. Davis, B. Xu, H.-B. Yang, X. Li, J. Am.
Yang, L. Luo, S. Zhang, X. Su, J. Lan, C.-T.
Chen, J. You, Chem. Commun. 2010, 46, 3938;
d) W.-Q. Kan, J. Yang, Y.-Y. Liu, J.-F. Ma,
Polyhedron 2011, 30, 2106.
Chem. Soc. 2015, 137, 1556; c) K. Harris, Q.- [7] a) S. Ghosh, P. S. Mukherjee, Organometallics [9] a) G. M. Sheldrick, Acta Crystallogr 2008, A64,
F. Sun, S. Sato, M. Fujita, J. Am. Chem. Soc.
013, 135, 1249; d) S. Chakraborty, S. Mondal,
S. Bhowmick, J. Ma, H. Ta n, S. Neogic, N. Das,
2008, 27, 316; b) S. Shanmugaraju, A. K. Bar,
K.-W. Chi, P. S. Mukherjee, Organometallics
2010, 29, 2971; c) A. K. Bar, S.Shanmugaraju, [10] a) C. J. Brown, R. Sadanaga, Acta Cryst. 1965,
112; b) L. J. Farrugia, J. Appl. Cryst. 2012, 45,
849.
2
Dalton Trans. 2014, 43, 13270; e) D. Samanta,
P. S. Mukherjee, Chem. Commun. 2014, 50,
K.-W. Chi, P. S. Mukherjee, Dalton Trans. 2011,
40, 2257; d) B. Gole, S. Shanmugaraju, A. K.
Bar, P. S. Mukherjee, Chem. Commun. 2011,
47, 10046; e) S. Shanmugaraju, D. Samanta, B.
Gole, P. S. Mukherjee, Dalton Trans. 2011, 40,
12333; f) S. Shanmugaraju, V. Vajpayee, K.-W.
Chi, P. J. Stang, P. S. Mukherjee, Inorg. Chem.
2012, 51, 4817; g) B. Roy, A. K. Bar, B. Gole, P.
S. Mukherjee, J. Org. Chem. 2013, 78, 1306; h)
S. Shanmugaraju, P. S. Mukherjee, Chem.-Eur.
J. 2015, 21, 6656.
18, 158; b) E. J. Gabe, Y. L. Page, F. L. Lee,
Acta Cryst. 1981, B37, 197; c) Q. Shen, K.
Hagen, J. Phys. Chem. 1987, 91, 1357.
1
595; f) D. Samanta, P. S. Mukherjee, Chem.-
Eur. J. 2014, 20, 5649.
[
5] R. Chakrabarty, P. S. Mukherjee, P. J. Stang,
Chem. Rev. 2011, 111, 6810.
6] a) D. K. Chand, K. Biradha, M. Fujita, S.
Sakamoto, K. Yamaguchi, Chem. Commun.
[
2
002, 2486; b) S. Ghosh, P. S. Mukherjee, J.
Org. Chem. 2006, 71, 8412; c) S. Ø. Scott, E. L.
Gavey, S. J. Lind, K. C. Gordona, J. D. Crowley,