New class of phosphine oxide donor-based supramolecular coordination complexes from an in situ phosphine oxidation reaction or phosphine oxide ligands

Article abstract of DOI:10.1021/ic401257w

A one-pot, multicomponent, coordination-driven self-assembly approach was used to synthesize the first examples of neutral bridging phosphine oxide donor-based supramolecular coordination complexes. The complexes were self-assembled from a fac-Re(CO)

Full text of DOI:10.1021/ic401257w

Communication
pubs.acs.org/IC
New Class of Phosphine Oxide Donor-Based Supramolecular
Coordination Complexes from an in Situ Phosphine Oxidation
Reaction or Phosphine Oxide Ligands
Bhaskaran Shankar, Palani Elumalai, Ramasamy Shanmugam, Virender Singh, Dhanraj T. Masram,
and Malaichamy Sathiyendiran*
Department of Chemistry, University of Delhi, Delhi 110 007, India
*
S Supporting Information
Scheme 1. Neutral Ditopic Donors
ABSTRACT: A one-pot, multicomponent, coordination-
driven self-assembly approach was used to synthesize the
first examples of neutral bridging phosphine oxide donor-
based supramolecular coordination complexes. The
complexes were self-assembled from a fac-Re(CO)3
acceptor, an anionic bridging O donor, and a neutral soft
phosphine or hard phosphine oxide donor.
thq·xH O) were explored as basic building units. In the synthetic
2
route to 1 and 2, a neutral P donor is used as the starting material,
which is transformed into a PO donor through in situ
oxidation; the PO group coordinates to the metal via the
neutral O-donor atom. This approach is different from the
ver the past 3 decades, significant research interest has
O
been shown for discrete supramolecular coordination
complexes (SCCs) because of their properties and potential
applications in sensors, catalysts, flasks, anticancer agents, light
known fac-Re(CO) -directed orthogonal bonding approach, in
3
1
,2
harvesters, and nanomaterials. The synthesis of SCCs by
coordination-driven self-assembly, using predesigned transition-
metal-based acceptors and organic donor precursors, is well-
established. Because of their high importance in many fields,
efforts are being directed toward making complex SCCs and
SCCs with functional units and finding a one-pot strategy for
multicomponent assembly. As a continuation of the research on
which the neutral ligand is limited to N donors, which coordinate
to the metal without any change in the donor properties.
Compounds 1 and 2 were prepared by treating Re (CO) , P−
2
10
P, and anionic O donors (H -CA for 1 and H -thq·xH O for 2) in
2
4
2
a one-pot procedure (Scheme 2). The products are air- and
Scheme 2. Synthesis of 1 and 2
2
the development of rhenium(I)-based SCCs, which exhibit rich
photophysical properties and potential applications in many
1
b,j−l,2
fields,
we envision that substituting the commonly used
neutral N donors with phosphine oxide (PO) donors would
result in a SCC with different photophysical properties because
of the electronic differences that exist between these
3
coordinating units. Although bis(PO) ligands have been
utilized as bridging ligands between the metal centers in
supramolecular architecture including coordination polymers,
metal−organic frameworks, and discrete lanthanide-based
4
−6
SCCs,
rhenium-based SCCs with a bis(PO)-donor
7
building unit are scarce. Herein, we report the first examples
of neutral hard PO-donor-bridged neutral and heteroleptic
rhenium(I)-based SCCs (1−3). The multicomponent assembly
of 1 and 2 was achieved by a combination of the fac-Re(CO)3
acceptor, anionic O donors, and a neutral ditopic phosphine
donor ligand, whereas 3 was assembled from fac-Re(CO)3,
anionic O donors, and a neutral tetratopic PO donor. This
report is also the first example of SCCs constructed via
transforming a soft ditopic P donor to a hard ditopic OP
donor during the self-assembly process (Scheme 1).
moisture-stable. Complex 1 is soluble in polar organic solvents,
whereas 2 is sparingly soluble. The Fourier transform infrared
(
FT-IR) spectrum of 1 exhibits strong bands at 2014, 1919, and
−1
2a
1
878 cm , characteristic of fac-Re(CO) . The band at 1522
3
−1
2−
cm indicates the presence of a bis-chelating CA unit in 1. A
−1
strong band at 1149 cm was assigned to the ν(PO)
In this study, 1,4-bis(diphenylphosphino)butane (P−P),
1
,2,4,5-tetrakis(dimethylphosphoryl)benzene (tpbO), chlora-
Received: May 18, 2013
Published: August 28, 2013
nilic acid (H -CA), and tetrahydroxy-1,4-quinone hydrate (H -
2
4
©
2013 American Chemical Society
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dx.doi.org/10.1021/ic401257w | Inorg. Chem. 2013, 52, 10217−10219

Inorganic Chemistry
Communication
5
f
1
stretching of the coordinated bis(PO) unit. The H NMR
To expand further, tpbO, which has four PO units, and H -
2
spectrum of 1 shows signals for protons of the CH and
CA were used to create [(Re(CO) ) (CA) (tpbO)] (3; Scheme
2
3 4
2
phenylene units, corresponding to 1,4-bis(diphenylphosphino)-
3). Complex 3 was air- and moisture-stable and sparingly soluble
8
31
1
butane dioxide (OP−PO). Further, the P{ H} NMR
spectrum of 1 confirms the presence of the OP−PO unit (δ
Scheme 3. Synthesis of 3
8
3
0.65). It is well-known that the highly oxophilic phosphine
9
ligand can transform into PO under thermal conditions.
3
1
Similar FT-IR and P NMR patterns were observed for complex
2
(Figures S1−S3 in the Supporting Information, SI).
The structures of 1 and 2 were confirmed with a single-crystal
X-ray diffraction (SC-XRD) study. Compound 1 adopts a
M LL′-type pseudorectangular structure (Figure 1). The
2
in polar organic solvents. Related N-donor-based SCC [(Re-
(
CO) ) (CA) (1,2,4,5-tetrakis(5,6-dimethylbenzimidazol-1-
3 4 2
10
methyl)benzene)] is insoluble. The FT-IR spectrum of 3
2−
confirms the presence of fac-Re(CO) , CA , PO, and P−
3
OMe units. Complex 3 adopts a M L L′-type double-decker
4
2
structure (Figure 3). The distance and dihedral angle between
Figure 1. Molecular structure of 1 in a ball-and-stick model.
coordination geometry around the Re center is distorted
2−
octahedral with a C O -donor environment. The CA unit is
3
3
planar and acts as a symmetrical bis-chelating unit. The bond
distances of CA2 indicate that the π electrons are confined to the
−
2−
upper and lower halves of the CA unit. The OP−PO unit
adopts a syn-conformation mode with anti cofaciality. The
aliphatic chain has the anti conformation and is planar with the P
atoms in 1. The crystal structure of 1 was stabilized by various
intra- and intermolecular noncovalent interactions (Figures S5
and S6 in the SI).
Figure 3. Molecular structure of 3 in a ball-and-stick view (OMe units
are shown as thin sticks, and H atoms are removed for clarity).
Complex 2 adopts a M LL′ -type bicyclic structure (Figure 2).
4
2
thq4 acts as a hexadentate 12-electron donor using six O atoms
−
1
2
1
CA and the phenylene unit are 4.4 Å (centroid···centroid) and
and taking two μ :η :η :η modes to coordinate four Re atoms.
2
4
6
−
3
1.5°, respectively. The size of the cycle, as measured from the Re
The π electrons in the C O unit are delocalized in the two
chelating units, contrary to the delocalization found in the CA
6
2−
and methylene C atoms, is ∼8 × 4.7 Å. tpbO in 3 adopts an
anti,syn,anti,syn-conformation mode. Similar to 1, the π
electrons are delocalized in the upper and lower halves of the
CA2 unit in 3. On the basis of the analytical and SC-XRD results,
the assembly of SCCs 1−3 can be best regarded as [1 + 1], [1 +
unit in 1. The coordination mode and arrangement of the
aliphatic chain of OP−PO in 2 are similar to those in 1.
−
2
], and [2 + 1], respectively.
Complexes 1 and 3 show strong visible-light absorption in the
−
1
−1
range of 360−700 nm (λ = 500 nm and ε = 9824 M cm for
max
−
1
−1
1
; λ = 503 nm and ε = 14768 M cm for 3). Compared to
max
−1
−1
free H -CA (λ
= 442 nm and ε = 264 M cm ), the
max
2
absorptions of 1 and 3 red-shifted by 58/61 nm with 37/56-fold
higher molar absorption coefficients, respectively (Figure S7 in
the SI). On the basis of time-dependent density functional theory
(
TDDFT) calculations, the broad absorptions in 1 and 3 are
mainly attributed to metal-to-ligand charge-transfer transitions
2−
(
MLCT; Re → CA ; Figure S8 and Tables S1 and S3 in the SI).
The molar absorption coefficients of 1 and 3 are lower than those
11
of the other rhenium(I)-based complexes but significantly
2c
higher than those of the existing rhenium(I)-based SCCs.
Complex 2 exhibits absorption (for range 385−630 nm, λ
=
max
4
84 nm and ε = 3242 M− cm ) with a smaller molar absorption
1
−1
Figure 2. Molecular structure of 2 in a ball-and-stick view (CO units are
shown as thin sticks, and H atoms are removed for clarity).
coefficient than those of 1 and 3 (Figure S9 and Table S2 in the
SI).
1
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dx.doi.org/10.1021/ic401257w | Inorg. Chem. 2013, 52, 10217−10219

Inorganic Chemistry
Communication
These results indicate that coordination of the neutral O
donors can influence the energy levels of the highest occupied
and lowest unoccupied molecular orbitals of the complexes, thus
shifting the absorption to the visible region (Figure S10 in the
SI). Although TDDFT calculations cannot explain the effect of
the absorption shift to the red region with a significant increase in
the molar absorption coefficient, the results provide the
groundwork for designing optically useful rhenium-based
supramolecules.
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donor-bridged ligands, was constructed by spontaneously
transforming the soft phosphine P donor to a hard phosphine
oxide O donor in the presence of an anionic chelating O donor
and Re (CO) using a one-step multicomponent assembly.
These results indicate that a change to the neutral O donor from
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ASSOCIATED CONTENT
Supporting Information
Experimental section, spectra, tables, and CIF data for 1−3. This
material is available free of charge via the Internet at http://pubs.
acs.org.
(5) (a) Atefi, F.; McMurtrie, J. C.; Turner, P.; Duriska, M.; Arnold, D.
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*
S
AUTHOR INFORMATION
Corresponding Author
E-mail: msathi@chemistry.du.ac.in or mvdiran@yahoo.com.
Notes
■
*
(
f) Marchetti, F.; Pettinari, C.; Pizzabiocca, A.; Drozdov, A. A.; Tryanov,
S. I.; Zhuravlev, C. O.; Semenov, S. N.; Belousov, Y. A.; Timokhin, I. G.
Inorg. Chim. Acta 2010, 363, 4038. (g) Liu, X.; Guo, G. C.; Liu, B.; Chen,
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Jancarik, A.; Mazal, C.; Pinkas, J.; Pekarkova, P.; Necas, M. Polyhedron
The authors declare no competing financial interest.
2
013, 62, 83 and references cited therein. (i) Pekarkova, P.; Spichal, Z.;
Taborsky, P.; Necas, M. Luminescence 2011, 26, 650.
6) (a) Maxim, C.; Matni, A.; Geoffroy, M.; Andruh, M.; Hearns, N. G.
ACKNOWLEDGMENTS
We are grateful to CSIR, India, for financial support and USIC,
University of Delhi, for NMR and X-ray diffraction facilities.
■
(
R.; Clerac, R.; Avarvari, N. New J. Chem. 2010, 34, 2319. (b) Sues, P. E.;
Lough, A. J.; Morris, R. H. Inorg. Chem. 2012, 51, 9322. (c) Kaempfe, P.;
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DEDICATION
■
(
We dedicate this paper to Prof. Ramaswamy Murugavel
Department of Chemistry, Indian Institute of Technology
Bombay, Bombay, India).
(
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