A tetranuclear heterobimetallic square formed from the cooperative ligand binding properties of square planar and tetrahedral metal centers

Article abstract of DOI:10.1021/ic025875o

Reaction of Rh(I) and ZN(II) metal centers with a ligand containing salicylaldiminato and thioether-phosphine moieties resulted in the formation of a tetranuclear heterobimetallic molecular square. The directionality required to form these structures is imparted by both the tetrahedral and square planar metal centers acting in concert with one another.

Full text of DOI:10.1021/ic025875o

Inorg. Chem. 2002, 41, 5326−5328
A Tetranuclear Heterobimetallic Square Formed from the Cooperative
Ligand Binding Properties of Square Planar and Tetrahedral Metal
Centers
Nathan C. Gianneschi and Chad A. Mirkin*
Department of Chemistry and the Institute for Nanotechnology, Northwestern UniVersity,
2145 Sheridan Road, EVanston, Illinois 60208-3113
Lev N. Zakharov and Arnold L. Rheingold
Department of Chemistry and Biochemistry, UniVersity of Delaware, Newark, Delaware 19716
Received July 15, 2002
Reaction of Rh(I) and Zn(II) metal centers with a ligand containing
salicylaldiminato and thioether−phosphine moieties resulted in the
formation of a tetranuclear heterobimetallic molecular square. The
directionality required to form these structures is imparted by both
the tetrahedral and square planar metal centers acting in concert
with one another.
that are known to complex a variety of main group and
transition metals.3,4
Reactions between 2 equiv of 1 and 1 equiv of a
mononuclear Rh(I) source followed by addition of a second
equivalent of a Zn(II) source results in the formation of 4 in
86% isolated yield (Scheme 1). Significantly, the order of
metal addition can be reversed with 4 being obtained in
comparable yield. These reactions proceeded at room tem-
perature in dry solvents under an inert atmosphere. Com-
pound 4 was isolated as a mildly air sensitive, but thermally
stable (no decomposition observed after 5 days at 80 °C in
CH2Cl2), yellow microcrystalline solid by recrystallization
from CH2Cl2/pentane with subsequent drying of the crystals
in vacuo.5
The use of coordination chemistry to arrange molecular
building blocks has evolved into one of the most useful and
flexible strategies for the synthesis of supramolecular
structures.1 However, despite the variety of metals and
ligands that have been used to date in the synthesis of
molecular squares, there are few examples of systems in
which the metals have coordination geometries other than
octahedral or square planar.2 Here, we report the first
example of a Rh-Zn heterobimetallic molecular square.
In order to form the square, the novel bifunctional ligand
1 was synthesized in two steps and in 81% overall yield
(Supporting Information). Initially, 1-chloro-2-diphenyl-
phosphinoethane and 4-aminothiophenol are coupled to form
4-(2-diphenylphosphanylethylsulfanyl)phenylamine (DPEP).
DPEP was further reacted with 3,5-di-tert-butyl-1-hydroxy-
benzaldehyde to form the target ligand 1. Compound 1
contains a hemilabile thioether-phosphine functional group
attached to a salicylaldiminato functional group. These
functional groups provide two very different binding moieties
Intermediates 2 and 3 have been isolated and fully
characterized. Compound 2 exhibits a characteristic 31P{1H}
NMR resonance at δ 64.6 (JRhP ) 161.6 Hz), diagnostic of
(3) For recent examples of salicylaldiminato complexes, see: (a) Gibson,
V. C.; Mastroianni, S.; Newton, C.; Redshaw, C.; Solan, G. A.; White,
A. J. P.; Williams, D. J. J. Chem. Soc., Dalton Trans. 2000, 1969-
1971. (b) Strauch, J.; Warren, T. H.; Erker, G.; Frohlich, R.;
Saarenketo, P. Inorg. Chim. Acta 2000, 300-302, 810-821. (c) Tian,
J.; Coates, G. W. Angew. Chem., Int. Ed. 2000, 39, 3626-3629. (d)
Darensbourg, D. J.; Rainey, P.; Yarbrough, J. Inorg Chem. 2001, 40,
986-993. (e) Matsui, S.; Mitani, M.; Saito, J.; Tohi, Y.; Makio, H.;
Matsukawa, N.; Takagi, Y.; Tsuru, K.; Nitabaru, M.; Nakano, T.;
Tanaka, H.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2001, 123,
6847-6856. (f) Emslie, D. J.; Piers, W. E.; Macdonald, R. J. Chem.
Soc., Dalton Trans. 2002, 293-294.
(4) (a) Farrell, J. R.; Mirkin, C. A.; Liable-Sands, L. M.; Rheingold, A.
L. J. Am. Chem. Soc. 1998, 120, 11834-11835. (b) Farrell, J. R.;
Mirkin, C. A.; Guzei, I. A.; Liable-Sands, L. M.; Rheingold, A. L.
Angew. Chem., Int. Ed. 1998, 37, 465-467. (c) Farrell, J. R.;
Eisenberg, A. H.; Mirkin, C. A.; Guzei, I. A.; Liable-Sands, L. M.;
Incarvito, C. D.; Rheingold, A. L.; Stern, C. L. Organometallics 1999,
18, 4856-4868. (d) Holliday, B. J.; Farrell, J. R.; Mirkin, C. A.; Lam,
K.-C.; Rheingold, A. L. J. Am. Chem. Soc. 1999, 121, 6316-6317.
(e) Dixon, F. M.; Eisenberg, A. H.; Farrell, J. R.; Mirkin, C. A.; Liable-
Sands, L. M.; Rheingold, A. L. Inorg. Chem. 2000, 39, 3432-3433.
(f) Eisenberg, A. H.; Dixon, F. M.; Mirkin, C. A.; Stern, C. L.;
Incarvito, C. D.; Rheingold, A. L. Organometallics 2001, 20, 2052-
2058.
* Author to whom correspondence should be addressed. E-mail:
CAMirkin@chem.northwestern.edu.
(1) For recent reviews, see: (a) Caulder, D. L.; Raymond, K. N. Acc.
Chem. Res. 1999, 32, 975-982. (b) Leininger, S.; Olenyuk, B.; Stang,
P. J. Chem. ReV. 2000, 100, 853-907. (c) Swiegers, G. F.; Malefetse,
T. J. Chem ReV. 2000, 100, 3483-3538. (d) Holliday, B. J.; Mirkin,
C. A. Angew. Chem., Int. Ed. 2001, 40, 2022-2043. (e) Cotton, F.
A.; Lin, C.; Murillo, C. A. Acc. Chem. Res. 2001, 34, 759-771. (f)
Fujita, M.; Umemoto, K.; Yoshizawa, M.; Fujita, N.; Kusukawa, T.;
Biradha, K. Chem. Commun. 2001, 509-518.
(2) Stang, P. J.; Persky, N. E. Chem. Commun. 1997, 77-78.
5326 Inorganic Chemistry, Vol. 41, No. 21, 2002
10.1021/ic025875o CCC: $22.00 © 2002 American Chemical Society
Published on Web 09/17/2002

COMMUNICATION
Scheme 1. The Synthesis of 2-4a
Figure 1. Thermal ellipsoid drawing of 4 showing the labeling scheme
for selected atoms and ellipsoids at 30% probability. Hydrogens are omitted
for clarity. Selected bond angles (deg): P(2)-Rh(1)-P(1), 98.39(7); P(2)-
Rh(1)-S(2), 85.37(6); P(1)-Rh(1)-S(2), 167.30(7); P(2)-Rh(1)-S(1),
171.39(7); S(2)-Rh(1)-S(1), 92.09(6); P(1)-Rh(1)-S(1), 85.85(6); O(2)-
Zn(1)-O(1), 120.7(2); O(2)-Zn(1)-N(2), 95.4(2); O(1)-Zn(1)-N(2),
118.4(2); O(2)-Zn(1)-N(1), 119.2(2); N(2)-Zn(1)-N(1), 109.7(2); O(1)-
Zn(1)-N(1), 94.8(2).
a All reactions performed at 25 °C. All counterions are BF4-. Reagents,
conditions, and yields: (i) 1/2Rh(COE)2BF4, THF/CH2Cl2, 90%; (ii) 1/2Et2Zn,
THF, 95%; (iii) Et2Zn, THF, 95%; (iv) Rh(COE)2BF4, THF/CH2Cl2, 90%.
(II) in the salicylaldiminato portion of the ligand and Rh(I)
in the thioether/phosphine portion. Significantly, the resulting
subunits (2 and 3) are not themselves “square” corners
formed from square planar metal centers. Indeed, before the
second equivalent of metal is added, the orientations of the
ligands are flexible (Scheme 1). Hence, the resulting square
is formed by cooperative interactions throughout the mol-
ecule rather than by any specific directional bonding effect.
As opposed to assembling prefabricated corners and linkers,
we are effectively constraining flexible building blocks into
a rigid structure using complementary coordination geom-
etries. Furthermore, it is likely that this approach can be used
to create flexible macrocycles through the breakage of the
a cis-phosphine/cis-thioether complex, and compound 3
exhibits a resonance at δ -16.6, assigned as free phosphine
(1 has a resonance comparable to that of 3 at δ -16.4). The
solution structure and purity of the molecular square 4 have
1
been confirmed by H and 31P{1H} NMR spectroscopy,
elemental analysis, and ES-MS. The 31P{1H}NMR spectrum
of 4 exhibits the diagnostic resonance at δ 65.2 (JRh-P
)
162.6 Hz) for a cis-phosphine/cis-thioether complex of Rh-
(I), which compares well with the 31P{1H} NMR resonance
observed for 2. In addition, the solid-state structure of 4 has
been determined by a single-crystal X-ray diffraction study
(Figure 1).6
(6) Crystal data for 4 at 100(2) K: C73H84BF4N2O2P2RhS2Cl2Zn, Mr )
1615.27, triclinic, P1h, a ) 13.0662(8) Å, b ) 17.7855(10) Å, c )
18.3270(11) Å, R ) 105.105(1)°, â ) 95.586(1)°, γ ) 105.462(1)°,
V ) 3898.8(4) Å3, Z ) 2, Fcalcd ) 1.376 g cm-3, F(000)) 1664, µ-
(Mo KR) ) 0.87 mm-1. Data collection: X-ray diffraction intensities
were collected on a Bruker SMART APEX CCD diffractometer (T )
100(2) K, Mo KR radiation (λ ) 0.71073 Å), crystal dimensions 0.30
× 0.20 × 0.15 mm3, 2θmax ) 56.5°, total number of reflections 24289,
independent reflections 17239 [Rint ) 0.0487]). In the crystal structure
of 4 there are three disordered solvate CH2Cl2 molecules. The program
SQUEEZE (Van der Sluis, P.; Spek, A. L. Acta Crystallogr., Sect. A
1990, A46, 194-201) was used to treat the solvent molecules.
Corrections of the X-ray data for 4 by SQUEEZE (263 electrons/cell)
were close to the required values (252 electrons/cell, respectively) for
the formula above. Two Ph rings at the P atoms are disordered over
two positions with occupancies 0.33/0.67 and 0.51/0.49, respectively.
Only one position of these rings is shown in Figure 1. The final R
factors [I > 2σ(I)]: R1 ) 0.0903, wR2 ) 0.2092. All software and
scattering factors are contained in the SHELXTL (5.10) program
package (G. Sheldrick, Bruker XRD, Madison, WI). Crystallographic
data (excluding structure factors) for the structure in this paper has
been deposited with the Cambridge Crystallographic Data Centre as
Supplementary Publication No. CCDC-189343. Copies of the data can
be obtained free of charge, on application to the CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax, +44 1223 336033; e-mail,
deposit@ccdc.cam.ac.uk).
The solid-state structure of 4 shows the two square planar
Rh(I) centers and two distorted tetrahedral Zn(II) centers,
bound by four ligands. The square is slightly distorted and
is defined by a Rh-Rh distance of 11.90 Å and a Zn-Zn
distance of 11.48 Å, with Rh-Zn edge distances of 8.53 Å.
The cis-phosphine/cis-thioether arrangement of the ligands
around the Rh center is crucial in enforcing the directionality
of the ligand. The use of this arrangement in the formation
of large Rh(I) bimetallic macrocycles and homotetranuclear
squares has recently been demonstrated by our group.4,7 This
approach has allowed us to synthesize large and diverse
supramolecular species from a range of flexible ligands.8
However, here the molecule’s shape is facilitated by two
very different types of ligand-metal interactions. The
bifunctional ligand 1 is capable of specifically binding Zn-
(5) It is possible to form 4 in one pot following either path detailed in
Scheme 1; however, the reactions do not proceed as cleanly as when
intermediates 2 and 3 are isolated prior to addition of the second
equivalent of metal. This is possibly due to the less than quantitative
yield of 2 and 3 and the incompatibility of Rh(COE)2BF4 with Et2Zn.
(7) Liu, X.; Stern, C. L.; Mirkin, C. A. Organometallics 2002, 21, 1017-
1019.
(8) Ovchinnikov, M. V.; Holliday, B. J.; Mirkin, C. A.; Zakharov, L. N.;
Rheingold, A. L. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 4927-4931.
Inorganic Chemistry, Vol. 41, No. 21, 2002 5327

COMMUNICATION
Supporting Information Available: Experimental procedures
and spectral data for all new compounds. X-ray crystallographic
files, in CIF format. This material is available free of charge via
the Internet at http://pubs.acs.org.
weak thioether-Rh bonds as in the weak-link approach to
supramolecular complexes.1d,4 Efforts to evaluate this chem-
istry are underway.
Acknowledgment. C.A.M. acknowledges the NSF (CHE-
9625391) and the AFOSR for support of this research.
IC025875O
5328 Inorganic Chemistry, Vol. 41, No. 21, 2002