Controlling the orientation of sequential ligands in the self-assembly of binuclear coordination compounds

Article abstract of DOI:10.1021/ja963265f

The sequential ligand 5-H₃, which contains one catechol and one aminophenol unit, was prepared in a four-step sequence. The two electronically different binding sites of 5 are able to control the metal-directed self-assembly of binuclear coordi

Full text of DOI:10.1021/ja963265f

1656
J. Am. Chem. Soc. 1997, 119, 1656-1661
Controlling the Orientation of Sequential Ligands in the
Self-Assembly of Binuclear Coordination Compounds
Markus Albrecht*,† and Roland Fro1hlich‡
Institut fu¨r Organische Chemie der UniVersita¨t, Richard-Willsta¨tter-Allee,
D-76131 Karlsruhe, Germany, and Organisch-Chemisches Institut der UniVersita¨t,
Corrensstrasse 40, D-48149 Mu¨nster, Germany
ReceiVed September 16, 1996X
Abstract: The sequential ligand 5-H3, which contains one catechol and one aminophenol unit, was prepared in a
four-step sequence. The two electronically different binding sites of 5 are able to control the metal-directed self-
assembly of binuclear coordination compounds with different ligand orientations. In coordination studies with titanium-
(IV) or gallium(III) ions, this ligand 5 was used to obtain anionic homobinuclear complexes [(5)3Ti2]- and [(5)3Ga2]3-
with two ligands orientated in one and the third in the opposite direction (type II structure). On the other hand, if
the ligand 5 reacts with a 1:1 mixture of titanium(IV) and gallium(III) ions exclusively, the heterobimetallic complex
[(5)3GaTi]2- is formed in a cooperative process. In this coordination compound the three ligands are orientated in
one direction (type I structure). For K2[(5)3GaTi]‚6DMF‚ether, space group P21/c, a ) 12.868(3) Å, b ) 19.902(2)
Å, c ) 27.063(2) Å, â ) 102.22(1)°, V ) 6774(2) Å3, Z ) 4, and R ) 0.071. The structural analysis shows that
titanium(IV) binds to the catecholate moieties while gallium(III) prefers the aminophenolate binding site of the
ligand 5. Internal hydrogen bonding enhances the stability of the Λ∆ configurated binuclear complex.
Introduction
program to form only one defined species in high selectivity.2,3
The formation of oligonuclear helical coordination com-
pounds (helicates) is an excellent example where the assembly
of the supramolecular aggregates is controlled by the properties
of the molecular building blocks.4 The structure of the obtained
species is influenced by the nature of the metal (e.g., double-5
versus triple-stranded compounds6) and the ligand (e.g., heli-
cate5,6 versus meso-helicate7). If sequential ligand strands are
introduced,8 heterobinuclear complexes can be formed which
possess two or three ligands orientated in one direction (type I,
Figure 1). On the other hand, combination of sequential ligands
with only one kind of metal should lead to a type II situation
as depicted in Figure 1.9 The metal is able to bind to both
different ligand subunits, and this should lead to different
Molecular recognition plays an important role in biochemical
processes like protein folding, enzyme-substrate interaction,
or the assembling of the double-stranded DNA. Thereby protons
very often act as the connecting species between units of
complementary shape.1 In artificial supramolecular systems the
small cation H+ may be substituted by larger main group or
transition metal cations. In contrast to the proton, those cations
may possess a specific shape by means of charge, size, hardness,
or preferred coordination geometry and thus might play an active
part in the molecular recognition process. Strong interactions
only can occur with “complementary donor molecules” (ligands).
Molecular recognition between metal ions and appropriate
ligands in self-assembly processes leads to the formation of
polynuclear supramolecular coordination compounds. Hereby
the steric and electronic information which is contained in each
single molecular component forces the system to follow a
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York, 1995; p 195.
† Institut fu¨r Organische Chemie der Universita¨t Karlsruhe.
‡ Organisch-Chemisches Institut der Universita¨t Mu¨nster.
X Abstract published in AdVance ACS Abstracts, January 15, 1997.
(1) Ebert, G. Biopolymere; Teubner Verlag: Stuttgart, Germany, 1993.
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S0002-7863(96)03265-9 CCC: $14.00 © 1997 American Chemical Society

Self-Assembly of Binuclear Coordination Compounds
J. Am. Chem. Soc., Vol. 119, No. 7, 1997 1657
Scheme 2
Figure 1. Schematic representation of the two orientations of sequential
ligands in triple-stranded binuclear metal complexes.
Scheme 1
one kind of ligand in a self-assembly process which is controlled
by the electronic features of the two different binding sites.
Results and Discussion
Synthesis of Ligand 5-H3. Ligand 5-H3 was synthesized in
a four-step sequence13 as outlined in Scheme 1. Addition of
2-nitro-3-methoxybenzaldehyde (1) to (2,3-dimethoxyphenyl)-
lithium, which was generated in situ by reaction of 1,2-
dimethoxybenzene with nBuLi in ether,14 affordssafter hydro-
lytic workupsthe carbinol 2 in 42% yield. The alcohol 2 by
reaction with acetic anhydride at 100 °C quantitatively (99%)
is transformed into the acetate 3. In the following reaction step
simultaneous reductive removal of the acetate and reduction of
the nitro group with hydrogen (50 bar) in the presence of Pd-C
gives the aniline derivative 4 in 58% yield. Finally, the methyl
ethers are cleaved quantitatively (98%) to afford 5-H3, which
is the precursor for the sequential ligand 5.
Synthesis of Coordination Compounds. The bis(titanium)
complex K[(5)3Ti2] is prepared by stirring a mixture of 5-H3 (3
equiv), Ti(OMe)4 (2 equiv), and potassium carbonate (0.5 equiv)
for 4 days in methanol. After removal of the solvent,
K[(5)3Ti2]‚6H2O is obtained as a red hygroscopic solid in 93%
yield (Scheme 2). The corresponding binuclear gallium com-
plex also is formed quantitatively (by NMR) by reaction of 5-H3
(3 equiv), Ga(NO3)3‚9H2O (2 equiv), and lithium carbonate (4.5
equiv). LiNO3 is removed by extraction with THF to give
analytically pure Li3[(5)3Ga2]‚10H2O in 50% yield.
The heterobinuclear coordination compound K2[(5)3GaTi]‚
6H2O is formed when ligand 5-H3 (3 equiv) together with a
mixture of Ga(NO3)3‚9H2O and Ti(OMe)4 (1 equiv each) and
potassium carbonate (2.5 equiv) is stirred in methanol for 4 days
and solvent is removed. Analytically pure K2[(5)3GaTi]‚6H2O
is obtained after chromatography (Sephadex LH-20, methanol)
in 73% yield. The dianion [(5)3GaTi]2- also is formed, when
K[(5)3Ti2] and Li3[(5)3Ga2] are dissolved in methanol-d4. After
1 week, characteristic signals for [(5)3GaTi]2- are observed by
1H NMR.
The compounds Na3[(5)3Ga2], K3[(5)3Ga2], Li[(5)3Ti2],
Li2[(5)3GaTi], and Na2[(5)3GaTi] were prepared and character-
ized by NMR spectroscopy to show that the alkali metal cations
don’t have an influence on the self-assembly of the binuclear
anionic complexes (vide infra).12 Identical spectra are obtained
for the anions if different cations are present. However, the
complex salts were not isolated in analytically pure form.
orientations of the ligand strands in the binuclear complex.
Similar metal centers try to be as similar as possible.
In recent studies, Piguet and Williams took advantage of the
different coordination geometries and numbers of metal ions
to obtain double- or triple-stranded type I as well as type II
helicates from sequential ligands which contain bi- and tridentate
chelating units.10
Inspired by our results in the metal-directed self-assembly
of alkyl-bridged bis(catecholate) ligands,11,12 we synthesized (2-
amino-3-hydroxyphenyl)(2,3-dihydroxyphenyl)methane (5-H3)
as a precursor for the sequential ligand 5. Ligand 5 contains
two electronically different binding sites with very similar
sterical demands. Thus, 5 should be ideal to test the possibility
to obtain coordination compounds of type I or type II from only
(8) See, for comparison: (a) Schepartz, A.; McDevitt, J. P. J. Am. Chem.
Soc. 1989, 111, 5976. (b) Constable, E. C.; Edwards, A. J.; Raithby, P. R.;
Walker, J. V. Angew. Chem. 1993, 105, 1486; Angew. Chem., Int. Ed. Engl.
1993, 32, 1465. (c) Albrecht, M.; Riether, C. Synlett 1995, 309. (d)
Zelikovich, L.; Libman, J.; Shanzer, A. Nature 1995, 374, 790. (e) Constable,
E. C.; Heirtzler, F. R.; Neuburger, M.; Zehnder, M. Chem. Commun. 1996,
933. (f) Dietrich-Buchecker, C.-O.; Sauvage, J.-P.; Armaroli, N.; Ceroni,
P.; Balzani, V. Angew. Chem. 1996, 108, 1190; Angew. Chem., Int. Ed.
Engl. 1996, 35, 1119.
(9) See, for comparison: (a) Constable, E. C.; Elder, S. M.; Healy, J.;
Ward, M. D.; Tocher, D. A. J. Am. Chem. Soc. 1990, 112, 4590. (b)
Constable, E. C.; Heirtzler, F. R.; Neuburger, M.; Zehnder, M. Supramol.
Chem. 1995, 5, 197.
(10) (a) Piguet, C.; Bocquet, B.; Hopfgartner, G. HelV. Chim. Acta 1994,
77, 931. (b) Piguet, C.; Hopfgartner, G.; Bocquet, B.; Schaad, O.; Williams,
A. F. J. Am. Chem. Soc. 1994, 116, 9092. (c) Piguet, C.; Rivara-Minten,
E.; Hopfgartner, G.; Bu¨nzli, J.-C. G. HelV. Chim. Acta 1995, 78, 1541. (d)
Piguet, C.; Rivara-Minten, E.; Hopfgartner, G.; Bu¨nzli, J.-C. G. HelV. Chim.
Acta 1995, 78, 1651. (e) Piguet, C.; Hopfgartner, G.; Williams, A. F.; Bu¨nzli,
J.-C. G. J. Chem. Soc., Chem. Commun. 1995, 491. (f) Piguet, C.;
Bernardinelli, G.; Bu¨nzli, J.-C. G.; Petoud, S.; Hopfgartner, G. J. Chem.
Soc., Chem. Commun. 1995, 2575. (g) Piguet, C.; Bu¨nzli, J.-C. G.;
Bernardinelli, G.; Hopfgartner, G.; Petoud, S.; Schaad, O. J. Am. Chem.
Soc. 1996, 118, 6681.
(11) (a) Albrecht, M.; Kotila, S. Angew. Chem. 1995, 107, 2285; Angew.
Chem., Int. Ed. Engl. 1995, 34, 2134. (b) Albrecht, M.; Kotila, S. Angew.
Chem. 1996, 108, 1299; Angew. Chem., Int. Ed. Engl. 1996, 35, 1208. (c)
Albrecht, M. Synlett 1996, 565. (d) Albrecht, M.; Ro¨ttele, H.; Burger, P.
Chem. Eur. J. 1996, 2, 1264.
(13) See, for comparison: Albrecht, M. Tetrahedron 1996, 52, 2385.
(14) Crowther, G. B.; Sundberg, R. J.; Sarpeshkar, A. M. J. Org. Chem.
1984, 49, 4657.
(12) Albrecht, M.; Kotila, S. Chem. Commun. 1996, 2309.

1658 J. Am. Chem. Soc., Vol. 119, No. 7, 1997
Albrecht and Fro¨hlich
Figure 3. 13C NMR spectra (125 MHz) of the crude products of
K[(5)3Ti2], Li3[(5)3Ga2], and K2[(5)3GaTi] in methanol-d4.
Figure 2. 1H NMR spectra (500 MHz) of the crude products of
K[(5)3Ti2], Li3[(5)3Ga2], and K2[(5)3GaTi] in methanol-d4.
FAB Mass Spectrometric Investigations. The composition
of the complexes K[(5)3Ti2], Li3[(5)3Ga2], and K2[(5)3GaTi] is
well demonstrated by their FAB mass spectra. For K[(5)3Ti2]
the peak of the anion [(5)3Ti2]- can be observed in its negative
ion FAB mass spectrum in glycerine at m/z ) 780. A positive
ion FAB MS was taken for Li3[(5)3Ga2] (glycerine as matrix).
Peaks at m/z ) 846 (HLi3[(5)3Ga2]+) and 852 (Li4[(5)3Ga2]+)
are observed. A peak at m/z ) 840 can be detected for the
heterobimetallic species K[(5)3GaTi]- (FAB(-) MS, glycerine),
which shows that indeed a binuclear titanium/gallium complex
is formed. No peaks of homobinuclear complexes are observed
in this case.
Figure 4. Helical and nonhelical structure of type II coordination
compounds [(5)3Ti2]- or [(5)3Ga2]3- (the spacers are only indicated).
Two of the ligands 5 are orientated in one and the third in the
opposite direction, leading to a loss of symmetry. Thus, as
proposed, type II binuclear coordination compounds are formed
by thermodynamically controlled self-assembly of three se-
quential ligands and two identical metal ions.
Due to the two different complex units of this type II complex,
it is not possible to distinguish by NMR between a helical (ΛΛ
or ∆∆) or a nonhelical (Λ∆)15 structure of [(5)3Ti2]- or
[(5)3Ga2]3-, respectively. However, in accordance with earlier
findings7,12 and because of the presence of rigid CH2 spacers,
it has to be assumed that the binuclear coordination compounds
possess the nonhelical Λ∆ structure.
NMR Spectroscopic Studies of K[(5)3Ti2] and Li3[(5)3Ga2].
1
In its H NMR spectrum in methanol-d4, K[(5)3Ti2] displays
signals at δ 7.01 (2 H), 6.91 (2 H), 6.76 (3 H), 6.48 (5 H), 6.45
(2 H), 6.26 (2 H), and 6.19 (2 H) for aromatic protons, three
doublets at δ 4.13, 3.99, and 3.98 (each J ) 13.0, each 1 H),
and a multiplet at δ 3.25 (3 H) (Figure 2). The observation of
three doublets at about 4.0 ppm and a multiplet at 3.25 ppm
for the spacer shows that the three ligands 5 are magnetically
different. In the 13C NMR spectrum, signals of 36 aromatic
carbon atoms and of three methylene units are detected (see
the Experimental Section; Figure 3). A CH-correlation NMR
experiment shows that the three protons with resonances in the
region 4.13-3.98 ppm are bound to carbon atoms of different
methylene groups. The observation of three different sets of
proton signals for the methylene spacer and of a resonance for
every single carbon atom of the complex indicates that the
formed coordination compound possesses low symmetry. The
binuclear gallium compound Li3[(5)3Ga2] gives rise to similar
spectra (for details see the Experimental Section; Figures 2 and
3) and thus possesses a similar structure as its titanium analogue.
The discussed spectroscopic findings unambiguously show
that with titanium(IV) or gallium(III) exclusively coordination
compounds with the C1 symmetric type II structure are obtained.
NMR Spectroscopic Studies of K2[(5)3GaTi]. The 1H NMR
(Figure 2) and 13C NMR spectra (Figure 3) of K2[(5)3GaTi] in
methanol-d4 display only one set of signals for the coordinated
ligands (see the Experimental Section). By 1H NMR only two
doublets can be detected for the protons of the alkyl spacer [3.97,
3.26 (J ) 12.9 Hz, 3 H each)]. This shows that in contrast to
the C1 symmetric homobinuclear complexes now a C3 sym-
metric binuclear type I coordination compound is formed. The
three ligands 5 are magnetically equivalent.
(15) von Zelewsky, A. Stereochemistry of Coordination Compounds;
Wiley: New York, 1995.

Self-Assembly of Binuclear Coordination Compounds
J. Am. Chem. Soc., Vol. 119, No. 7, 1997 1659
Figure 7. Atomic numbering scheme for K2[(5)3GaTi].
sequential ligands 5 are orientated in one direction and a type
I coordination compound is formed. Due to the presence of
methylene groups as alkyl spacers the two chiral complex units
show opposite configuration (Λ∆). This observation is in
accordance with results of investigations on the stereochemistry
of the metal-directed self-assembly of helicates and meso-
helicates of alkyl-bridged bis(catecholate) ligands.11,12
Figure 5. Formation of K2[(5)3GaTi] in methanol-d4 (1H NMR, 250
MHz) in the presence of an excess of 5-H3.
The stability of the supramolecular architecture of the anion
[(5)3GaTi]2- is further enhanced by hydrogen-bonding interac-
tions of the NH2 groups with internal oxygen atoms of the
titanium(IV) tris(catecholate) unit (N-H ) 0.91 Å; H‚‚‚O )
1.94-1.98 Å; N-H‚‚‚O ) 163-165°).19 Therefore no tem-
plating by alkali metal cations has to take place. The hydrogen
bridges of [(5)3GaTi]2- have a similar stabilizing function as
the alkali metal counterions of the dinuclear titanium compound
of a methylene-bridged bis(catecholate) ligand which is analo-
gous to 5.12
The potassium cations are exohedrally coordinated to the
“ends” of the anionic binuclear complex (K2‚‚‚Ga ) 3.573(2)
Å; K1‚‚‚Ti ) 3.472(2) Å) with six oxygen atoms (of the anion
[(5)3GaTi]2- and of DMF) coordinating to each of the K+ ions
(distorted octahedral coordination geometry). Four of the
cations form a linear arrangement with K‚‚‚K distances of
3.795(2) or 3.705(3) Å. A part of this network is presented in
Figure 8 showing the relative orientation of the anions
[(5)3GaTi]2- and the positions of the potassium cations.
Figure 6. ORTEP diagram of [(5)3GaTi]2- (only amine hydrogen
atoms are shown).
Traces of a type II complex which can be detected in the
crude product (Figures 2 and 3) are due to a slightly incorrect
titanium to gallium ratio (for a spectrum with correct Ga:Ti ratio
see Figure 5).
An additional experiment was performed with a non-
stoichiometric ligand to metal ratio. Therefore a 1:1 mixture
of titanium(IV) and gallium(III) was reacted with approximately
5 equiv of ligand 5. The obtained 1H NMR spectroscopic results
indicate that the self-assembly of [(5)3GaTi]2- proceeds with
positive cooperativity.16 Only signals of the heterobinuclear
complex and of free ligand 5 can be measured in methanol-d4
(Figure 5). No signals of mononuclear or homobinuclear metal
complexes are observable.
Crystal Structure of K2[(5)3GaTi]‚6DMF‚Ether. X-ray
quality crystals of K2[(5)3TiGa]‚6DMF‚ether were obtained by
slow diffusion of ether into a solution of the salt in DMF. The
structural analysis shows that the bis-anionic heterobinuclear
titanium/gallium complex contains one pseudo-octahedral tris-
(catecholate) titanium(IV) complex unit17 and one pseudo-
octahedral tris(o-aminophenolate) gallium(III) moiety18 (Ti‚‚‚Ga
) 5.101 Å). The latter adopts a facial geometry to enable the
formation of defined molecular species. The two different
complex units are connected by three methylene linkages. The
X-ray structure (Figure 6) shows the same C3 symmetry of the
dianion that can be observed in solution. Thus, the three
Conclusions
In this paper we described a facile synthesis of the sequential
ligand 5, which possesses two electronically different binding
sites. With titanium(IV) or gallium(III) ions this ligand
spontaneously forms binuclear triple-stranded coordination
compounds. In the homobinuclear complexes two of the three
ligands are orientated in one and the third in the other direction
(type II). If the metal-directed self-assembly process is
performed with a mixture of titanium and gallium ions (1:1)
another type of coordination compound is obtained. Now one
of the binding sites of the ligand coordinates to one kind of
metal ion and the second binding site to the other kind of metal.
A C3 symmetric complex (type I) is obtained in which all three
sequential ligands are orientated in one direction. The X-ray
structural analysis reveals that in the binuclear titanium/gallium
complex the titanium only binds to catecholate units and the
gallium only to aminophenolate moieties. The complex pos-
sesses a nonhelical pseudo-meso-type structure.
The discussed self-assembly processes cleanly lead to the
formation of two different types of structures of coordination
compounds (type I or type II complex). Thus, ligand 5 together
with gallium and/or titanium ions represents an example of a
programmed supramolecular system where different combina-
tions of the same building blocks enable the selective self-
(16) See, for comparison: Pfeil, A.; Lehn, J.-M. J. Chem. Soc., Chem.
Commun. 1992, 838.
(17) (a) Borgias, B. A.; Koh, Y. B.; Raymond, K. N. Inorg. Chem. 1984,
23, 1009. (b) Hahn, F. E.; Rupprecht, S.; Mook, K. H. J. Chem. Soc., Chem.
Commun. 1991, 224.
(18) For tris(aminophenolate) complexes, see: (a) Stuntz, C. F.; Wood-
burn, H. M. J. Am. Chem. Soc. 1950, 72, 1364. (b) Bauer, H. F.; Drinkard,
W. C. J. Am. Chem. Soc. 1960, 82, 5031.
(19) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A.
G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1.

1660 J. Am. Chem. Soc., Vol. 119, No. 7, 1997
Albrecht and Fro¨hlich
Figure 8. Representation of the polymeric network (SCHAKAL) of K2[(5)3GaTi]‚6DMF‚ether in the solid state.
Table 1. Selected Bond Length (Å) and Angles (deg) for
K2[(5)3GaTi]‚6DMF‚Ether
eV) m/z ) 319 (29%) [M]+, 167 (95%), 84 (100%); HRMS
(C16H17NO6) calcd 319.1056, found 319.1041.
(2,3-Dimethoxyphenyl)(2-nitro-3-methoxyphenyl)methyl Acetate
(3). The carbinol 2 (1.52 g, 4.76 mmol) is dissolved in 20 mL of acetic
anhydride, and the mixture is heated overnight to 100 °C. Volatiles
are removed in vacuo, and the residue is dissolved in CH2Cl2. The
solution is washed with saturated aqueous NaHCO3 and dried (MgSO4),
and solvent is evaporated to yield 1.70 g (99%) of 3 as an off-white
first ligand
second ligand
third ligand
Ga-O1
1.944(5)
2.058(5)
1.948(5)
1.969(5)
83.5(2)
80.0(2)
118.2(6)
1.954(5)
2.098(5)
1.951(5)
1.968(5)
82.6(2)
80.0(2)
117.1(6)
1.932(5)
2.086(6)
1.953(5)
1.970(5)
83.4(2)
79.7(2)
116.1(7)
Ga-N1
Ti-O2
Ti-O3
N1-Ga-O1
O2-Ti-O3
C5-C7-C8
1
solid: mp 81-82 °C; H NMR (CDCl3) δ 7.32 (t, J ) 8.2 Hz, 1 H),
7.25 (s, 1 H), 7.05 (t, J ) 8.0 Hz, 1 H), 6.97 (d, J ) 8.2 Hz, 1 H), 6.90
(dd, J ) 8.2/1.4 Hz, 1 H), 6.85 (dd, J ) 8.0/1.3 Hz, 1 H), 6.81 (d, J
) 8.0 Hz, 1 H), 3.87 (s, 3 H), 3.85 (s, 3 H), 3.82 (s, 3 H), 2.11 (s, 3
H); 13C NMR (CDCl3) δ 169.3 (C), 152.6 (C), 151.0 (C), 146.6 (C),
140.2 (C), 132.8 (C), 131.7 (C), 130.7 (CH), 124.1 (CH), 120.3 (CH),
119.3 (CH), 112.8 (CH), 112.2 (CH), 68.1 (CH), 60.4 (CH3), 56.5
(CH3), 55.7 (CH3), 20.6 (CH3); IR (KBr) ν ) 2942, 2840, 1748, 1535,
1482, 1371, 1281, 1226, 767 cm-1; MS (EI, 70 eV) m/z ) 361 (19%)
[M]+, 43 (100%); HRMS (C18H19NO7) calcd 361.1162, found 361.1148.
Elemental anal. Calcd for C18H19NO7: C, 59.83; H, 5.30; N, 3.88.
Found: C, 59.64; H, 5.28; N, 4.39.
assembly of two structurally different aggregates. This means
that here two different supramolecular programs are available.20
Experimental Section
General Remarks. 1H NMR and 13C NMR spectra were recorded
on a Bruker DRX 500, AM 400, or WM 250 NMR spectrometer using
DEPT techniques for the assignment of the multiplicity of carbon atoms.
FT-IR spectra were recorded by diffuse reflection (KBr) or on NaCl
plates on a Bruker IFS spectrometer. UV-vis spectra were recorded
in methanol on a Perkin Elmer UV-vis Lambda 2 spectrometer. Mass
spectra (EI, 70 eV or FAB(+/-), glycerine as matrix) were taken on
a Finnigan MAT 90 mass spectrometer. Elemental analyses were
obtained with a Heraeus CHN-O-Rapid analyzer. Solvents were
purified by standard methods. Melting points: Bu¨chi 535 (uncorrected).
Air-sensitive compounds were prepared and handled under Ar using
Schlenk techniques.
(2,3-Dimethoxyphenyl)(2-nitro-3-methoxyphenyl)methanol (2).
2,3-Dimethoxybenzene (1.60 g, 11.6 mmol) and 1.6 mL of Tmeda
(tetramethylethylenediamine) are dissolved in ether (30 mL) and 7.8
mL of a 1.6 M solution of nBuLi in hexane are added at room
temperature.14 The mixture is stirred for 4 h, and solid 3-methoxy-2-
nitrobenzaldehyde (1) (2.07 g, 11.4 mmol) is added in several portions.
After the solution is stirred overnight, 6 N aqueous HCl is added and
the phases are separated. The ether phase is dried (MgSO4) and solvent
is removed. Column chromatography (silica gel, CH2Cl2) affords 1.52
g (42%) of 2 as a yellow oil: 1H NMR (CDCl3) δ 7.36 (t, J ) 8.2 Hz,
1 H), 7.05 (t, J ) 8.0 Hz, 1 H), 7.00-6.88 (m, 4 H), 6.11 (s, 1 H),
3.88 (s, 3 H), 3.86 (s, 3 H), 3.65 (s, 3 H), 3.10 (br, 1 H, OH); 13C
NMR (CDCl3) δ 152.5 (C), 150.8 (C), 146.2 (C), 140.4 (C), 136.8
(C), 134.9 (C), 131.1 (CH), 124.0 (CH), 119.9 (CH), 119.4 (CH), 112.6
(CH), 111.7 (CH), 67.7 (CH), 60.4 (CH3), 56.5 (CH3), 55.8 (CH3); IR
(KBr) ν ) 3418, 2940, 1839, 1534, 1480, 1281, 762 cm-1; MS (EI, 70
(2,3-Dimethoxyphenyl)(2-amino-3-methoxyphenyl)methane (4).
The acetate 3 (1.70 g, 4.71 mmol) is dissolved in ethyl acetate/methanol
(3:1). Pd-C (480 mg) is added, and the mixture is stirred under an
hydrogen atmosphere (50 bar) for 18 h. After filtration over silica
gel, solvent is removed and the residue is applied to column chroma-
tography (silica gel, CH2Cl2) to obtain 740 mg (58%) of 4 as a slightly
1
red solid: mp 62 °C; H NMR (CDCl3) δ 6.98 (t, J ) 7.9 Hz, 1 H),
6.78 (m, 3 H), 6.71 (m, 2 H), 4.28 (br., 2 H), 3.92 (s, 2 H), 3.87 (s, 3
H), 3.86 (s, 3 H), 3.83 (s, 3 H); 13C NMR (CDCl3) δ 152.6 (C), 147.2
(C), 146.5 (C), 134.5 (C), 133.4 (C), 125.3 (C), 124.2 (CH), 122.7
(CH), 122.0 (CH), 117.2 (CH), 110.3 (CH), 108.4 (CH), 60.8 (CH3),
55.6 (CH3), 55.5 (CH3), 31.1 (CH2); IR (KBr) ν ) 3473, 3375, 2937,
2835, 1619, 1583, 1482, 1277, 1083, 1008, 751, 736 cm-1; MS (EI,
70 eV) m/z ) 273 (3%) [M]+, 196 (30%), 154 (100%), 139 (51%);
HRMS (C16H19NO3) calcd 273.1365, found 273.1348. Elemental anal.
Calcd for C16H19NO3: C, 70.31; H, 7.01; N, 5.12. Found: C, 70.09;
H, 7.14; N, 5.37.
(2,3-Dihydroxyphenyl)(2-amino-3-hydroxyphenyl)methane (5-
H3). At 0 °C, 1 M BBr3/CH2Cl2 (13.7 mL) is added to amine 4 (725
mg, 2.66 mmol) in CH2Cl2 (20 mL). The mixture is allowed to warm
to room temperature and stirred overnight. Methanol is added, and
volatiles are removed in vacuo. The residue is dissolved in ether,
washed with saturated aqueous NaHCO3, and dried (MgSO4), and
solvent is evaporated to obtain 615 mg (98%) of 5-H3 as a yellow
1
hygroscopic foam: mp 39-41 °C; H NMR (methanol-d4): δ 6.65-
(20) For examples of programmed supramolecular chemistry, see: (a)
Lehn, J.-M. Angew. Chem. 1990, 102, 1347; Angew. Chem., Int. Ed. Engl.
1990, 29, 1304. (b) Lehn, J.-M. Supramolecular ChemistrysConcepts and
PerspectiVes; VCH: Weinheim, Germany, 1995. (c) Kra¨mer, R.; Lehn, J.-
M.; Marquis-Rigault, A. Proc. Natl. Acad. Sci. U.S.A. 1993, 90, 5394. (d)
Lindsey, J. S. New. J. Chem. 1991, 15, 153. (e) Philp, D.; Stoddart, J. F.
Angew. Chem. 1996, 108, 1243; Angew. Chem., Int. Ed. Engl. 1996, 35,
1154.
6.54 (m, 6 H), 3.84 (s, 2 H); 13C NMR (methanol-d4): δ 146.7 (C),
146.0 (C), 143.9 (C), 133.2 (C), 129.4 (C), 128.2 (C), 122.6 (CH),
122.0 (CH), 120.5 (CH), 120.1 (CH), 114.0 (CH), 113.4 (CH), 32.0
(CH2); IR (KBr) ν ) 3372, 2977, 1620, 1592, 1475, 1281, 744 cm-1
;
MS (EI, 70 eV) m/z ) 231 (100%) [M]+, 109 (95%); HRMS
(C13H13NO3) calcd 231.0895, found 231.0907. Elemental anal. Calcd

Self-Assembly of Binuclear Coordination Compounds
J. Am. Chem. Soc., Vol. 119, No. 7, 1997 1661
for C13H13NO3‚1/4H2O: C, 66.23; H, 5.77; N, 5.94. Found: C, 66.17;
H, 5.62; N, 6.15.
Hz, 3 H), 6.63 (d, J ) 7.9 Hz, 6 H), 6.57 (dd, J ) 7.7/1.5 Hz, 3 H),
6.40 (t, J ) 7.7 Hz, 3 H), 6.21 (dd, J ) 7.7/1.5 Hz, 3 H), 3.97 (d, J )
12.9 Hz, 3 H), 3.26 (d, J ) 12.9 Hz, 3 H); 13C NMR (methanol-d4) δ
159.8 (C), 158.9 (C), 156.5 (C), 140.3 (C), 128.6 (CH), 125.9 (C),
125.4 (C), 121.0 (CH), 119.2 (CH), 118.0 (CH), 115.1 (CH), 111.4
(CH), 34.6 (CH2); IR (KBr) ν ) 3275, 3051, 1610, 1583, 1295, 1271,
1252, 744 cm-1; UV (methanol) λ ) 200, 282, 380 nm; MS (FAB(-),
glycerine) m/z ) 840 [M - K]-. Elemental anal. Calcd for
C39H30N3TiGaK2O9‚6H2O: C, 47.38; H, 4.28; N, 4.25. Found: C,
47.63; H, 4.47; N, 4.24.
Li2[(5)3GaTi]: 1H NMR (methanol-d4) δ 6.95 (t, J ) 7.6 Hz, 3 H),
6.65 (dd, J ) 7.6 Hz, 6 H), 6.57 (dd, J ) 7.6/1.2 Hz, 3 H), 6.40 (pseudo
t, J ) 7.6 Hz, 3 H), 6.21 (dd, J ) 7.6/1.2 Hz, 3 H), 3.98 (d, J ) 12.8
Hz, 3 H), 3.25 (d, J ) 12.8 Hz, 3 H); 13C NMR (methanol-d4) δ 159.4,
158.7, 156.3, 140.3, 128.5, 125.6, 125.3, 122.2, 119.7, 119.0, 115.0,
111.3, 34.5.
K[(5)3Ti2]. A suspension of 5-H3 (49 mg, 0.21 mmol), Ti(OMe)4
(24 mg, 0.14 mmol), and K2CO3 (5.0 mg, 0.036 mmol) in methanol
(20 mL) is stirred until a red solution is formed (4 days). Solvent is
removed, and the residue is dried in vacuo to obtain 60 mg (93%) of
K[(5)3Ti2] as a hygroscopic red solid: 1H NMR (methanol-d4) δ 7.01
(m, 2 H), 6.91 (m, 2 H), 6.76 (m, 3 H), 6.48 (m, 5 H), 6.45 (m, 2 H),
6.26 (m, 2 H), 6.19 (m, 2 H), 4.13 (d, J ) 13.0 Hz, 1 H), 3.99 (d, J )
13.0 Hz, 1 H), 3.98 (d, J ) 13.0 Hz, 1 H), 3.25 (m, 3 H); 13C NMR
(methanol-d4) δ 163.5 (C), 162.5 (C), 162.0 (C), 158.6 (C), 158.2 (C),
158.1 (C), 157.1 (C), 156.8 (C), 156.4 (C), 140.9 (C), 140.1 (C), 139.8
(C), 133.1 (C), 132.5 (C), 131.1 (C), 128.8 (CH), 128.6 (CH), 128.5
(CH), 127.2 (C), 126.3 (C), 126.1 (C), 124.3 (CH), 123.2 (CH), 123.0
(CH), 122.6 (CH), 122.3 (CH), 121.0 (CH), 120.0 (CH), 119.8 (CH),
119.6 (CH), 113.4 (CH), 113.0 (CH), 112.9 (CH), 111.5 (CH), 111.4
(CH), 111.2 (CH), 33.7 (CH2), 33.2 (CH2), 33.1 (CH2); IR (KBr) ν )
3183, 3056, 1615, 1584, 1458, 1270, 1249, 746 cm-1; UV-vis
(methanol) λ ) 198, 275, 344 nm; MS (FAB(-), glycerine) m/z )
780 [M - K]-. Elemental anal. Calcd for C39H30N3Ti2KO9‚6H2O:
C, 50.50; H, 4.56; N, 4.53. Found: C, 50.75; H, 4.47; N, 4.63.
Li[(5)3Ti2]: 1H NMR (methanol-d4) δ 7.04 (m, 2 H), 6.91 (m, 2 H),
6.78 (m, 3 H), 6.5-6.2 (br m, 9 H), 6.18 (m, 2 H), 4.13 (d, J ) 13.0
Hz, 1 H), 3.99 (d, J ) 13.1 Hz, 1 H), 3.98 (d, J ) 13.0 Hz, 1 H), 3.26
(m, 3 H).
Li3[(5)3Ga2]. Ligand 5-H3 (107 mg, 0.45 mmol), Ga(NO3)3‚9H2O
(125 mg, 0.30 mmol), and Li2CO3 (51 mg, 0.69 mmol) in methanol
are stirred for 28 h. Solvent is evaporated and LiNO3 is removed by
extraction with THF to obtain 76 mg (50%) of Li3[(5)3Ga2] as a beige
hygroscopic solid: 1H NMR (methanol-d4) δ 6.85 (m, 2 H), 6.79 (t, J
) 7.8 Hz, 1 H), 6.61 (d, J ) 7.3 Hz, 1 H), 6.58-6.44 (m, 11 H), 6.27
(m, 3 H), 4.25 (d, J ) 12.6 Hz, 1 H), 4.14 (d, J ) 12.5 Hz, 1 H), 4.07
(d, J ) 12.5 Hz, 1 H), 3.26 (m, 3 H); 13C NMR (methanol-d4) δ 161.5
(C), 160.5 (C), 160.1 (C), 159.3 (C), 153.8 (C), 153.6 (C), 153.4 (C),
153.3 (C), 152.0 (C), 151.9 (C), 141.3 (C), 140.9 (C), 140.8 (C), 128.1
(CH), 128.0 (CH), 127.8 (C), 127.7 (CH), 127.5 (C), 126.4 (C), 126.2
(C), 125.8 (C), 119.2 (CH), 119.1 (CH), 118.8 (CH), 117.8 (CH), 117.6
(CH), 116.9 (CH), 116.4 (CH, double intensity), 115.7 (CH), 114.9
(CH), 114.7 (CH), 114.4 (CH), 112.7 (CH), 112.5 (CH), 112.4 (CH),
35.5 (CH2), 35.1 (CH2), 35.0 (CH2); IR (KBr): ν ) 3269, 3057, 1463,
1256, 743 cm-1; MS (FAB(+), glycerine) m/z ) 846 [M + H]+, 852
[M + Li]+. Elemental anal. Calcd for C39H30N3Ga2Li3O9‚10H2O: C,
45.70; H, 4.92; N, 4.10. Found: C, 45.39; H, 4.61; N, 3.80.
Na3[(5)3Ga2]: 1H NMR (methanol-d4) δ 6.87-6.75 (br m, 4 H),
6.60-6.43 (m, 11 H), 6.30 (m, 3 H), 4.23 (d, J ) 12.6 Hz, 1 H), 4.15
(d, J ) 12.6 Hz, 1 H), 4.09 (d, J ) 12.5 Hz, 1 H), 3.22 (m, 3 H).
K3[(5)3Ga2]: 1H NMR (methanol-d4) δ 6.86-6.74 (br m, 4 H), 6.60-
6.42 (m, 11 H), 6.29 (m, 3 H), 4.24 (d, J ) 12.7 Hz, 1 H), 4.14 (d, J
) 12.6 Hz, 1 H), 4.08 (d, J ) 12.5 Hz, 1 H), 3.15 (m, 3 H).
K2[(5)3GaTi]. A mixture of ligand 5-H3 (52 mg, 0.22 mmol),
Ti(OMe)4 (12 mg, 0.070 mmol), Ga(NO3)3‚9H2O (31 mg, 0.075 mmol),
and K2CO3 (26 mg, 0.188 mmol) is stirred for 4 days in methanol.
Solvent is removed, and the residue is purified by chromatography
(Sephadex LH-20, methanol) to obtain 53 mg (73%) of K2[(5)3GaTi]
as a red hygroscopic solid: 1H NMR (methanol-d4) δ 6.93 (t, J ) 7.9
Na2[(5)3GaTi]: 1H NMR (methanol-d4) δ 6.95 (t, J ) 8.3 Hz, 3 H),
6.65 (d, J ) 8.2 Hz, 6 H), 6.58 (dd, J ) 7.7/1.5 Hz, 3 H), 6.40 (pseudo
t, J ) 7.7 Hz, 3 H), 6.22 (dd, J ) 7.6/1.2 Hz, 3 H), 3.96 (d, J ) 13.1
Hz, 3 H), 3.27 (d, J ) 13.1 Hz, 3 H); 13C NMR (methanol-d4) δ 159.5,
158.8, 156.2, 140.1, 128.5, 125.6, 125.3, 122.2, 119.7, 119.0, 115.1,
111.4, 34.4.
X-ray Structural Analysis of K2[(5)3GaTi]‚6DMF‚Ether. X-ray
quality crystals of K2[(5)3TiGa]‚6DMF‚ether were obtained by slow
diffusion of ether in a DMF solution of K2[(5)3TiGa]. Crystal data for
K2[(5)3TiGa]‚6DMF‚ether: formula C61H82N9O16GaTiK2, formula weight
1393.18, red blocks (0.5 × 0.4 × 0.3 mm3), monoclinic space group
P21/c (No. 14); a ) 12.868(3) Å, b ) 19.902(2) Å, c ) 27.063(2) Å,
â ) 102.22(1)°, V ) 6774(2) Å3, Z ) 4, F(000) ) 2920, T ) 223 K,
F
calcd ) 1.366 g cm-3, µ ) 7.09 cm-1, empirical absorption correction
from ψ scans (Cmin/max ) 0.901/0.999), Enraf-Nonius MACH3 diffrac-
tometer, λ ) 0.710 73 Å, ω/2θ scans, 9642 reflections measured
(-h,+k,(l), 2θmax ) 45.5°, 9163 independent and 5723 observed [I g
2σ(I)], 765 refined parameters, R ) 0.071, wR2 ) 0.187; the largest
peaks in the residual electron density map [max 1.71(-1.35) e Å-3
]
were located near the disordered solvent molecules. The structure was
solved by direct methods (SHELXS-86) and refined against F2
(SHELXL-93); hydrogens were introduced in their calculated positions
and refined isotropically as riding atoms. Two of the three DMF
molecules not located in the K coordination are disordered. The
molecules were refined by using geometric and thermal restrains where
the non-disordered one served as a structural model.
Acknowledgment. This work was supported by the Fonds
der Chemischen Industrie (Liebig Stipendium for M.A.) and
the Deutsche Forschungsgemeinschaft.
Supporting Information Available: X-ray crystallographic
data for K2[(5)3GaTi]‚6DMF‚ether, including tables of positional
parameters, anisotropic thermal parameters, and bond distances
and angles (14 pages). See any current masthead page for
ordering and Internet access instructions.
JA963265F