Heteroligated metallomacrocycles generated via the weak-link approach

Article abstract of DOI:10.1021/ic048785n

Sequential reaction of two different hemilabile ligands (Ph ₂PCH₂-CH₂X)₂Ar (X = S, Ar = C ₆H₄ or C₆(CH₃)₄; X = NCH₃, Ar = C₆H₄; X = O, Ar = 9,10-C ₁₄H₈) with a Rh(I) metal center resulted in the formation of heteroligated metallomacrocycles in high yield. The specific reaction conditions for each pair of hemilabile ligands are discussed. The solid-state structure of [(1,4-(Ph₂PCH₂CH₂S) ₂C₆H₄)-{1,4-(Ph₂PCH ₂CH₂S)₂C₆(CH₃) ₄}Rh₂](BF₄)₂, as determined by X-ray crystallography, is presented.

Full text of DOI:10.1021/ic048785n

Inorg. Chem. 2004, 43, 8233−8235
Heteroligated Metallomacrocycles Generated via the Weak-Link
Approach
Maxim V. Ovchinnikov,† Aaron M. Brown,† Xiaogang Liu,† Chad A. Mirkin,*,† Lev N. Zakharov,‡ and
Arnold L. Rheingold‡
Department of Chemistry and Institute for Nanotechnology, Northwestern UniVersity,
2145 Sheridan Road, EVanston, Illinois 60208-3113, and Department of Chemistry and
Biochemistry, UniVersity of California, San Diego, 9500 Gilman DriVe, MC 0358,
La Jolla, California 92093-0358
Received August 31, 2004
a
Scheme 1
Sequential reaction of two different hemilabile ligands (Ph2PCH2-
CH2X)2Ar (X S, Ar
)
) C6H4 or C6(CH3)4; X ) NCH3, Ar ) C6H4;
X
)
O, Ar ) 9,10-C14H8) with a Rh(I) metal center resulted in the
formation of heteroligated metallomacrocycles in high yield. The
specific reaction conditions for each pair of hemilabile ligands are
discussed. The solid-state structure of [
1,4-(Ph2PCH2CH2S)2C6(CH3)4 Rh2](BF4)2, as determined by X-ray
crystallography, is presented.
{1,4-(Ph2PCH2CH2S)2C6H4}-
{
}
Over the past two decades, several effective synthetic
strategies for forming multimetallic macrocyclic functional
architectures have been developed in the field of metallo-
supramolecular chemistry.1-6 Our group has introduced and
developed one of these synthetic strategies, termed the Weak-
Link Approach (WLA), which allows one to prepare mul-
timetallic macrocycles from flexible hemilabile ligands and
transition metal precursors. This method typically allows one
to assemble symmetric 2:2 metal-to-ligand structures with
control over many architectural parameters including mac-
rocycle size, shape, hydrophobicity, and chirality, and it has
recently led to the development of a variety of allosteric
catalysts.7-10 Thus far, no methods have been developed for
preparing macrocyclic structures with two distinct hemilabile
ligands within one structure, or so-called dissymmetric
a Key: (i) H2 (1 atm) for 3b,c, 1,4-(Ph2PCH2CH2X)2Ar (2; 1 equiv),
CH2Cl2, room temperature for 3a and -78 °C f room temperature for
3b,c; (ii) CO (1 atm), [(CH3)4N]Cl (2 equiv), CH2Cl2, room temperature.
systems. Herein, we report the first examples of such
structures prepared via the WLA in a stepwise process
(Scheme 1).
Complex 1 was prepared by treating [Rh(NBD)Cl]2 (NBD
) norbornadiene) with AgBF4 in the presence of the
hemilabile ligand 1,4-(Ph2PCH2CH2S)2C6H4.11 Complex 1
was isolated as a yellow, air-sensitive solid in 93% yield
and characterized by 1H and 31P{1H} NMR spectroscopy and
ES-MS. All data are consistent with the proposed formula-
tion. The 31P{H} NMR spectrum of 1 exhibits a doublet at
δ 57 (JRh-P ) 160 Hz) indicative of the phosphine ligand
within the five-membered chelate around Rh(I).12 Moreover,
* To whom correspondence should be addressed. E-mail: chadnano@
northwestern.edu.
† Northwestern University.
(7) Gianneschi, N. C.; Bertin, P. A.; Nguyen, S. T.; Mirkin, C. A.;
Zakharov, L. N.; Rheingold, A. L. J. Am. Chem. Soc. 2003, 125,
10508-10509.
(8) Holliday, B. J.; Ulmann, P. A.; Mirkin, C. A.; Stern, C. L.; Zakharov,
L. N.; Rheingold, A. L. Organometallics 2004, 23, 1671-1679.
(9) Masar, M. S.; Ovchinnikov, M. V.; Mirkin, C. A.; Zakharov, L. N.;
Rheingold, A. L. Inorg. Chem. 2003, 42, 6851-6858.
(10) Eisenberg, A. H.; Ovchinnikov, M. V.; Mirkin, C. A. J. Am. Chem.
Soc. 2003, 125, 2836-2837.
‡ University of California, San Diego.
(1) Seidel, S. R.; Stang, P. J. Acc. Chem. Res. 2002, 35, 972-983.
(2) Lindner, E.; Pautz, S.; Haustein, M. Coord. Chem. ReV. 1996, 155,
145-162.
(3) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem. ReV. 2000, 100, 853-
907.
(4) Holliday, B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40, 2022-
2043.
(5) Fujita, M. Acc. Chem. Res. 1999, 32, 53-61.
(6) (a) Lee, S. J.; Lin, W. J. Am. Chem. Soc. 2002, 124, 4554-4555. (b)
Lee, S. J.; Hu, A.; Lin, W. J. Am. Chem. Soc. 2002, 124, 12948-
12949.
(11) 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.
(12) Bonuzzi, C.; Bressan, M.; Morandini, F.; Morvillo, A. Inorg. Chim.
Acta 1988, 154, 41-43.
10.1021/ic048785n CCC: $27.50
Published on Web 11/26/2004
© 2004 American Chemical Society
Inorganic Chemistry, Vol. 43, No. 26, 2004 8233

COMMUNICATION
intermediate undergoes fast (t1/2 ) 1.5 h, 20 mM concentra-
tion, room temperature) rearrangement to give complex 611
and a complex mixture of products containing Rh(I), ligand
2b, and NBD. However, complexes 3b and 3c were
synthesized in excellent yields under optimized reaction
conditions when a solution of 1 in CH2Cl2 was treated with
H2 (bubbling for ∼2 min at 1 atm) and a solution of the
corresponding hemilabile ligand in CH2Cl2 was then added
rapidly at -78 °C. The complete hydrogenation of NBD,
1
which was evident from the H NMR data of the crude
reaction mixture, is crucial in obtaining high yields of
complexes 3b and 3c. Presumably, Rh(I) has a stronger
affinity toward the double bonds of the NBD ligand than
the σ-donating N and O atoms. The NMR data of 3b and 3c
are consistent with their proposed structures. For instance,
the 31P{1H} NMR spectrum of 3c exhibits two characteristic
doublets of doublets at δ 73 (JRh-P,P-P ) 200, 41 Hz) and
65 (JRh-P,P-P ) 170, 41 Hz) due to the presence of two
inequivalent P atoms in the η2-PCH2CH2S and η2-PCH2CH2O
chelates. Notably, complex 3b forms as a mixture of syn
and anti isomers in a 1:1 ratio with respect to the orientation
of the Me groups in the η2-PCH2CH2NMe chelate. Therefore,
the 31P{1H} NMR spectrum of 3b exhibits four characteristic
doublets of doublets, two for each isomer.17 The ES-MS
spectrum of 3b, which shows a single isotopically resolved
Figure 1. Thermal ellipsoid drawing of [{1,4-(Ph2PCH2CH2S)2C6H4}{1,4-
(Ph2PCH2CH2S)2C6(CH3)4}Rh2]2+, with 50% probability ellipsoids, in 3a
showing the labeling scheme. Selected distances (Å): Rh(1)-S(2) 2.364(1),
Rh(2)-S(4) 2.359(1), Rh(1)-S(1) 2.326(1), Rh(2)-S(3) 2.344(1), Rh(1)-
-Rh(2) 8.758, (C6H4)cent-(C6Me4)cent 3.591. Selected torsion angles (deg):
S(2)-(C6H4)cent-(C6Me4)cent-S(1) 5.3, S(4)-(C6H4)cent-(C6Me4)cent
-
S(3) 6.6.
the 1H NMR spectrum of 1 in CD2Cl2 indicates the presence
of the η4-NBD ligands.
The reaction between complex 1 and the hemilabile ligand
1,4-(Ph2PCH2CH2S)2C6(CH3)4 (2a) at room temperature in
CH2Cl2 results in the clean formation of the corresponding
dissymmetric binuclear complex, [{1,4-(Ph2PCH2CH2S)2-
C6H4}{1,4-(Ph2PCH2CH2S)2C6(CH3)4}Rh2]2+ (3a, Scheme
1), which was isolated in 94% yield and fully characterized.
Complex 3a exhibits a 31P NMR spectrum that is diagnostic
of the proposed structure. It shows two doublets of doublets
at δ 63 (JRh-P,P-P ) 164, 36 Hz) and 65 (JRh-P,P-P ) 162,
36 Hz) due to the presence of two magnetically inequivalent
P atoms. The ES-MS spectrum exhibited a single peak at
-
peak at m/z 666.2 [M - 2BF4 ], also confirms the proposed
bimetallic formulation for complex 3b.
-
m/z 697.2 [M - 2BF4 ] corresponding to the loss of two
BF4- counterions. The solid-state structure of 3a (Figure 1),
as determined by X-ray crystallography, is consistent with
its proposed solution structure.13 Each Rh(I) metal center is
coordinated to the PCH2CH2S fragments in a slightly
distorted square-planar geometry. The metal-metal separa-
tion is 8.758 Å, and the interplanar distance between the
nearly parallel central aryl rings of the ligands is 3.591 Å.
The Rh-S(1,3) distances are approximately 0.025 Å shorter
than Rh-S(2,4), presumably because of the stronger bonds
between the Rh(I) and S(1,3) atoms of the more electron-
rich 1,4-(Ph2PCH2CH2S)2C6(CH3)4 hemilabile ligand.
The reactions between complex 1 and the hemilabile
ligands 2b14 or 2c15 under similar conditions (room temper-
ature, CH2Cl2) failed to yield complexes analogous to 3. For
instance, complex 5 was formed as the initial product when
a solution of 2b (1 equiv) was added to a solution of 1, as
evidenced by 31P{1H} NMR spectroscopy (eq 1).16 This
Condensed macrocyclic complexes 3a-c undergo clean
expansion by selectively cleaving their Rh-heteroatom
bonds with [(CH3)4N]Cl under CO (1 atm), which results in
the quantitative formation of the neutral open macrocycles
4a,b (Scheme 1). Complexes 4a-c were characterized by
1H and 31P{1H} NMR and FTIR spectroscopies, giving
results that are consistent with their proposed structural
assignments. For example, the 31P{1H} NMR spectrum of
each complex exhibit a single resonance [δ 24 (br d, JRh-P
) 128 Hz) for 4a, δ 24 (br d, JRh-P ) 128 Hz) for 4b, and
δ 20 (br d, JRh-P ) 133 Hz) for 4c]. The broad nature of
these resonances is presumably due to the presence of two
types of magnetically inequivalent P atoms in each complex.
FTIR spectra of 4a-c exhibit characteristic νCO bands for
their terminal CO ligands at 1968 cm-1. The positions of
these bands correlate well with homoligated binuclear Rh(I)
complexes with similar coordination environments.11 Com-
plexes 4a-c are stable in CH2Cl2 solution under CO (1 atm)
(13) Crystallographic details for 3a (CH2Cl2): C75H78B2Cl6F8P4Rh2S4, M
) 1823.63, yellow block, Bruker Smart Apex CCD (Mo KR radiation),
T ) 173(2) K, triclinic, space group P1h, a ) 10.5464(7) Å, b )
14.9351(9) Å, c ) 25.1498(16) Å, R ) 86.123(1)°, â ) 78.705(1)°,
γ ) 86.780(1)°, V ) 3872.0(4) Å3, Z ) 2, Dcalc ) 1.564 g‚cm-3
,
µ(Mo KR) ) 0.886 mm-1, 25 022 measured reflections, 17 447
independent reflections [Rint ) 0.0201], θmax ) 28°, R1 ) 0.0454,
wR2 ) 10.52, GOF ) 1.024 [I > 2σ(I)].
(16) 31P{1H} NMR (121.53 MHz, CD2Cl2, δ): 53 (dd, JRh-P,P-P ) 138,
27 Hz), 9 (br dd, JRh-P,P-P ) 128, 27 Hz). Complex 5 was not
characterized further because of its fast rearrangement as shown in
eq 1.
(14) Liu, X.; Eisenberg, A. H.; Stern, C. L.; Mirkin, C. A. Inorg. Chem.
2001, 40, 2940-2941.
(15) Holliday, B. J.; Farrell, J. R.; Mirkin, C. A.; Lam, K.-C.; Rheingold,
A. L. J. Am. Chem. Soc. 1999, 121, 6316-6317.
(17) Complex 3b: 31P{1H} NMR (121.53 MHz, CD2Cl2, δ): 72 (dd,
JRh-P,P-P ) 167, 42 Hz), 70 (dd, JRh-P,
) 166, 43 Hz), 54 (dd,
J
) 178, 43 Hz), 53 (dd, JRh-P,P-P-PP) 176, 43 Hz).
Rh-P, P-P
8234 Inorganic Chemistry, Vol. 43, No. 26, 2004

COMMUNICATION
at room temperature for several days. However, exposure
of complex 4a to high vacuum or prolonged storage in the
solid state under nitrogen resulted in its conversion to the
Cl- salt, analogous to 3a.
e.g., catalytic activity and selectivity, of the macrocyclic
structures in a different yet cooperative manner. Efforts to
fully evaluate the potential of the presented synthetic strategy
are underway.
The synthetic approach described herein demonstrates a
new way of controlling chemical and physical properties of
metallomacrocyclic structures via judicious choice of ligand
building blocks. This strategy paves the way for the synthesis
of functional metallomacrocyclic entities, in which one can
incorporate functional groups capable of interaction via
energy transfer processes or can alter the overall properties,
Acknowledgment. C.A.M. acknowledges the NSF and
AFOSR for generous financial support.
Supporting Information Available: X-ray structural data for
3a in CIF format and experimental details. This material is available
free of charge via the Internet at http://pubs.acs.org.
IC048785N
Inorganic Chemistry, Vol. 43, No. 26, 2004 8235