Hierarchical assembly of helicate-type dinuclear titanium(IV) complexes

Article abstract of DOI:10.1021/ja052326j

The ligands 4-7-H₂ were used in coordination studies with titanium(IV) and gallium(III) ions to obtain dimeric complexes Li ₄[(4-7)₆Ti₂] and Li₆[(4/5a) ₆Ga₂]. The X-ray crystal structures of Li ₄[(4)₆Ti₂], Li₄[(5b) ₆Ti₂], and Li₄[(7a)₆Ti₂] could be obtained. While these complexes are triply lithium-bridged dimers in the solid state, a monomer/dimer equilibrium is observed in solution by NMR spectroscopy and ESI FT-ICR MS. The stability of the dimer is enhanced by high negative charges (Ti(IV) versus Ga(III)) of the monomers, when the carbonyl units are good donors (aldehydes versus ketones and esters), when the solvent does not efficiently solvate the bridging lithium ions (DMSO versus acetone), and when sterical hindrance is minimized (methyl versus primary and secondary carbon substituents). The dimer is thermodynamically favored by enthalpy as well as entropy. ESI FT-ICR mass spectrometry provides detailed insight into the mechanisms with which monomeric triscatecholate complexes as well as single catechol ligands exchange in the dimers. Tandem mass spectrometric experiments in the gas phase show the dimers to decompose either in a symmetric (Ti) or in an unsymmetric (Ga) fashion when collisionally activated. The differences between the Ti and Ga complexes can be attributed to different electronic properties and a charge-controlled reactivity of the ions in the gas phase. The complexes represent an excellent example for hierarchical self-assembly, in which two different noncovalent interactions of well balanced strengths bring together eleven individual components into one well-defined aggregate.

Full text of DOI:10.1021/ja052326j

Published on Web 06/28/2005
Hierarchical Assembly of Helicate-Type Dinuclear Titanium(IV)
Complexes
Markus Albrecht,*,† Sebastian Mirtschin,† Marita de Groot,† Ingo Janser,†
Jan Runsink,† Gerhard Raabe,† Michael Kogej,‡ Christoph A. Schalley,*,‡ and
Roland Fro¨hlich§
Contribution from the Institut fu¨r Organische Chemie, RWTH Aachen, Landoltweg 1, 52074
Aachen, Germany, Kekule´-Institut fu¨r Organische Chemie und Biochemie, UniVersita¨t Bonn,
Gerhard-Domagk-Strasse 1, 53121 Bonn, Germany, and Organisch-Chemisches Institut,
UniVersita¨t Mu¨nster, Corrensstrasse 40, 48149 Mu¨nster, Germany
Received April 11, 2005; E-mail: markus.albrecht@oc.rwth-aachen.de; c.schalley@uni-bonn.de
Abstract: The ligands 4-7-H2 were used in coordination studies with titanium(IV) and gallium(III) ions to
obtain dimeric complexes Li4[(4-7)6Ti2] and Li6[(4/5a)6Ga2]. The X-ray crystal structures of Li4[(4)6Ti2],
Li4[(5b)6Ti2], and Li4[(7a)6Ti2] could be obtained. While these complexes are triply lithium-bridged dimers in
the solid state, a monomer/dimer equilibrium is observed in solution by NMR spectroscopy and ESI FT-
ICR MS. The stability of the dimer is enhanced by high negative charges (Ti(IV) versus Ga(III)) of the
monomers, when the carbonyl units are good donors (aldehydes versus ketones and esters), when the
solvent does not efficiently solvate the bridging lithium ions (DMSO versus acetone), and when sterical
hindrance is minimized (methyl versus primary and secondary carbon substituents). The dimer is
thermodynamically favored by enthalpy as well as entropy. ESI FT-ICR mass spectrometry provides detailed
insight into the mechanisms with which monomeric triscatecholate complexes as well as single catechol
ligands exchange in the dimers. Tandem mass spectrometric experiments in the gas phase show the dimers
to decompose either in a symmetric (Ti) or in an unsymmetric (Ga) fashion when collisionally activated.
The differences between the Ti and Ga complexes can be attributed to different electronic properties and
a charge-controlled reactivity of the ions in the gas phase. The complexes represent an excellent example
for hierarchical self-assembly, in which two different noncovalent interactions of well balanced strengths
bring together eleven individual components into one well-defined aggregate.
Introduction
Self-assembly is thus an efficient strategy to create complexity
and, together with it, function in nature.
Self-assembly of suitably programmed building blocks is
ubiquitous in nature1 and often occurs on several hierarchy levels
simultaneously in order to generate functional systems. For
example, the shell-forming protein building blocks of the
tobacco mosaic virus2 need to fold into the correct tertiary
protein structure before they can be organized around a
templating RNA strand. All these processes are mediated by
noncovalent forces which guide the formation of secondary
structure elements on the lowest hierarchy level. These form
the tertiary structure on the next level which displays the
necessary binding sites for the assembly of the virus from a
total of 2131 building blocks to occur as programmed on the
highest level. Other examples for hierarchical self-assembly are
multienzyme complexes, the formation of cell membranes with
all the receptors, ion channels, or other functional entities
embedded into them, or molecular motors such as ATP synthase.
Self-assembly3 often also plays a crucial role for the specific
formation of well-defined, artificial supramolecular species.4
However, aggregation, which is based on solely one type of
interaction between the components, can only develop limited
complexity. For the generation of a higher degree of complexity,
as it is found in nature’s functional molecules, different
noncovalent interactions5 are required, which have different but
well-balanced relative strengths. On one hand, using self-
assembly strategies on several different levels of hierarchy
makes the programming of the individual components more
challenging for the synthetic chemist. On the other hand,
hierarchical self-assembly promises to simplify the creation of
complexity.6 A precise understanding of the properties of such
systems is a prerequisite for any design strategy.
(3) For example, see: (a) Lindsey, J. S. New J. Chem. 1991, 15, 153-180.
(b) Whitesides, G. M.; Mathias, J. P.; Seto, C. T. Science 1991, 254, 1312-
1319. (c) Philp, D.; Stoddart, J. F. Angew. Chem. 1996, 108, 1243-1286;
Angew. Chem., Int. Ed. Engl. 1996, 35, 1154-1196. (d) Schalley, C. A.;
Lu¨tzen, A.; Albrecht, M. Chem.sEur. J. 2004, 10, 1072-1080.
(4) (a) Lehn, J. M. Struct. Bonding 1973, 16, 1-69. (b) Lehn, J.-M.
Supramolecular Chemistry; VCH: Weinheim, 1995. (c) Vo¨gtle, F. Su-
pramolekulare Chemie; Teubner: Stuttgart, 1992. (d) Steed, J. W.; Atwood,
J. L. Supramolecular Chemistry; Wiley: Chichester, 2000.
† RWTH Aachen.
‡ Universita¨t Bonn.
§ Universita¨t Mu¨nster.
(1) Hamilton, T. D.; MacGillivray, L. R. In Self-Assembly in Biochemistry;
Atwood, J. L.; Steed, J. W., Eds.; Encyclopedia of Supramolecular
Chemistry; Dekker: New York, 2004; pp 1257-1262.
(2) Klug, A. Angew. Chem. 1983, 95, 579-596; Angew. Chem., Int. Ed. Engl.
1983, 22, 565-582.
(5) For example, see: Greig, L. M.; Philp, D. Chem. Soc. ReV. 2001, 30, 287-
302.
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A R T I C L E S
Albrecht et al.
Figure 1. Helicate-type complexes formed by hierarchical self-assembly.
Helicates7 are a class of very simple metallosupramolecular
compounds which allowed the chemists to investigate basic
aspects of supramolecular chemistry,8 such as stereochemistry,9
regiochemistry,10 or the mechanisms of self-assembly.11 Only
very few examples can be found, in which helicates are formed
by hierarchical self-assembly. Hannon12 and Nitschke13 describe
the in situ formation of dinuclear helicates by imine condensa-
tion of diamines with pyridinyl-2-carbaldehydes in the presence
of appropriate metal ions. Both metal coordination and imine
condensation are reversible, thermodynamically controlled
processes which finally give rise to the helicate products in a
one-pot hierarchical process.14
Figure 2. Ligands described in this study.
(6) Selected examples: (a) Percec, V.; Cho, W.-D.; Ungar, G.; Yeardley, D.
J. P. Angew. Chem. 2000, 112, 1662-1666; Angew. Chem., Int. Ed. 2000,
39, 1597-1602. (b) Elemans, J. A. A. W.; Rowan, A. E.; Nolte, R. J. M.
J. Mater. Chem. 2003, 13, 2661-2670. (c) Wu¨rthner, F.; Yao, S.; Beginn,
U. Angew. Chem. 2003, 115, 3368-3371; Angew. Chem., Int. Ed 2003,
42, 3247-3250. (d) Elemans, J. A. A. W.; Rowan, A. E.; Nolte, R. J. M.
J. Am. Chem. Soc. 2002, 124, 1532-1540. (e) Berl, V.; Krische, M. J.;
Huc, I.; Lehn, J.-M.; Schmutz, M. Chem.sEur. J. 2000, 6, 1938-1946.
(f) Kawasaki, T.; Tokuhiro, M.; Kimizuka, N.; Kunitake, T. J. Am. Chem.
Soc. 2001, 123, 6792-6800. (g) Ikkala, O.; ten Brinke, G. Chem. Commun.
2004, 2131-2137.
(7) (a) Lehn, J.-M.; Rigault, A.; Siegel, J.; Harrowfield, J.; Chevrier, B.; Moras,
D. Proc. Natl. Acad. Sci. U.S.A. 1987, 84, 2565-2569. For other early
examples, see: (b) Scarrow, R. C.; White, D. L.; Raymond, K. N. J. Am.
Chem. Soc. 1985, 107, 6540-6546. (c) Lehn, J.-M.; Rigault, A. Angew.
Chem. 1988, 100, 1121-1122; Angew. Chem., Int. Ed. Engl. 1988, 27,
1095-1097. (d) Constable, E. C.; Elder, S. M.; Healy, J.; Ward, M. D.;
Tocher, D. A. J. Am. Chem. Soc. 1990, 112, 4590-4592. (e) Williams, A.
F.; Piguet, C.; Bernardinelli, G. Angew. Chem. 1991, 103, 1530-1532;
Angew. Chem., Int. Ed. Engl. 1991, 30, 1490-1492. (f) Bernardinelli, G.;
Piguet, C.; Williams, A. F. Angew. Chem. 1992, 104, 1662-1664; Angew.
Chem., Int. Ed. Engl. 1992, 31, 1622-1624. (g) Saalfrank, R. W.; Seitz,
V.; Caulder, D.; Raymond, K. N.; Teichert, M.; Stalke, D. Eur. J. Inorg.
Chem. 1998, 1313-1317.
Complexes 1,15 2,16 and 317 represent examples for helicate-
type complexes which are formed by two different metal binding
events. In principle, mononuclear tris-ligand complexes are
formed which are then connected by three (1) or one metal ion
(2,3), respectively. Finally, the helicate-type compounds are
obtained (Figure 1).
In this paper, we present the lithium-controlled hierarchical
assembly of a series of dinuclear helicate-type titanium(IV) and
gallium(III) complexes with catecholate ligands,18 which bear
aldehyde (4-H2), ketone (5a-j-H2, 6a,b-H2), or ester functions
(7a,b-H2) in the 3-position of the catechol (Figure 2). The
properties of these complexes are studied in the solid state, in
solution, and in the gas phase.
Results and Discussion
(8) Reviews: (a) Constable, E. C. Tetrahedron 1992, 48, 10013-10059. (b)
Piguet, C.; Bernardinelli, G.; Hopfgartner, G. Chem. ReV. 1997, 97, 2005-
2062. (c) Albrecht, M. Chem. ReV. 2001, 101, 3457-3498. (d) Hannon,
M. J.; Childs, L. J. Supramol. Chem. 2004, 16, 7-22. (e) Albrecht, M.;
Janser, I.; Fro¨hlich, R. Chem. Commun. 2005, 157-165. (f) See also:
Saalfrank, R. W.; Demleitner, B. In Transition Metals in Supramolecular
Chemistry; Sauvage, J.-P., Ed.; John Wiley & Sons: New York, 1999;
Vol. 5, pp 1-51.
Ligand Synthesis. Aldehyde 4-H2 is commercially available
while the ligands 5-7-H2 were prepared as outlined in Scheme
(15) (a) Sun, X.; Darren, W. J.; Caulder, D.; Powers, R. E.; Raymond, K. N.;
Wong, E. H. Angew. Chem. 1999, 111, 1386-1390; Angew. Chem., Int.
Ed. 1999, 38, 1303-1306. (b) Sun, X.; Johnson, D. W.; Caulder, D.;
Raymond, K. N.; Wong, E. H. J. Am. Chem. Soc. 2001, 123, 2752-2763.
(c) Sun, X.; Johnson, D. W.; Raymond, K. N.; Wong, E. H. Inorg. Chem.
2001, 40, 4504-4506.
(9) Albrecht, M. Chem.sEur. J. 2000, 6, 3485-3489.
(10) Piguet, C.; Hopfgartner, G.; Bocquet, B.; Schaad, O.; Williams, A. F. J.
Am. Chem. Soc. 1994, 116, 9092-9102.
(11) (a) Pfeil, A.; Lehn, J.-M. J. Chem. Soc., Chem. Commun. 1992, 838-840.
(b) Albrecht, M. Top. Curr. Chem. 2004, 248, 105-139.
(16) (a) Albrecht, M.; Witt, K.; Ro¨ttele, H.; Fro¨hlich, R. Chem. Commun. 2001,
1330-1331. (b) Albrecht, M.; Witt, K.; Weis, P.; Wegelius, E.; Rissanen,
K.; Fro¨hlich, R. Inorg. Chim. Acta 2002, 25-32.
(12) (a) Childs, L. J.; Alcock, N. W.; Hannon, M. J. Angew. Chem. 2002, 114,
4418-4421; Angew. Chem., Int. Ed. 2002, 41, 4244-4247. (b) Hamblin,
J.; Childs, L. J.; Alcock, N. W.; Hannon, M. J. J. Chem. Soc., Dalton Trans.
2002, 164-169.
(17) (a) Das, A. K.; Rueda, A.; Falvello, L. R.; Peng, S.-M.; Batthacharya, S.
Inorg. Chem. 1999, 38, 4365-4368. (b) For a related recent example, see:
Heinicke, J.; Peulecke, N.; Karaghiosoff, K.; Mayer, P. Inorg. Chem. 2005,
44, 2137-2139.
(13) Nitschke, J. R.; Schultz, D.; Bernardinelli, G.; Ge´rard, D. J. Am. Chem.
Soc. 2004, 126, 16538-16543.
(14) See also: (a) Nitschke, J. R.; Lehn, J.-M. Proc. Natl. Acad. Sci. U.S.A.
2003, 100, 11970-11974. (b) Nitschke, J. R.; Hutin, M.; Bernardinelli, G.
Angew. Chem. 2004, 116, 6892-6895; Angew. Chem., Int. Ed. 2004, 43,
6724-6727.
(18) For triscatecholate complexes of titanium(IV) and gallium(III), see: (a)
Borgias, B. A.; Cooper, S. R.; Koh, Y. B.; Raymond, K. N. Inorg. Chem.
1984, 23, 1009-1016. (b) Borgias, B. A.; Barclay, S. J.; Raymond, K. N.
J. Coord. Chem. 1986, 15, 109-123.
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Hierarchical Assembly of Helicates
A R T I C L E S
Scheme 1. Preparation of the Ligands 5-7-H2
Scheme 2. Hierarchical Assembly of a Triply Lithium-Bridged Helicate-Type Complex
1. The ketones 5/6-H2 were obtained by addition of organo-
lithium or Grignard reagents to 2,3-dimethoxybenzaldehyde,
followed by Jones oxidation19 and subsequent BBr3 cleavage
of the methyl ethers.20 The initially prepared secondary alcohols
were oxidized without purification.21
7a-H2 was prepared by acidic esterification of 2,3-dihydroxy-
benzoic acid with methanol.22 The synthesis of the ester 7b-H2
followed Raymond’s procedure to generate the acid chloride
of 2,3-dihydroxybenzoic acid23 followed by in situ quenching
with the alcohol.
in a meridional fashion. Upon aggregation the meridional isomer
should lead to polymeric material, which is not observed. The
coordination of Li+ mediating dimer formation acts as a template
for the formation of the facial geometry within the monomers
at the same time. This is an example for the recursive effects
that may occur in hierarchical self-assembly: The second
assembly step influences the first one, and both are not
independent from each other. The facial and meridional isomers
of the monomeric complexes are in a dynamic equilibrium,
undergoing an associative bailar twist rearrangement.25 In the
dimerization process this equilibrium is shifted toward the facial
arrangement.
Coordination Studies. The metal complexes “Li2[(4-7)3Ti]”
were prepared by dissolving 3 equiv of the corresponding ligand
and 1 equiv of TiO(acac)2 and Li2CO3 in DMF. After stirring
overnight, the solvent is removed at 70 °C in vacuo to obtain
the complexes in quantitative yield (Scheme 2).
For comparison with the Ti complexes, the compounds
“Li3[(4)3Ga]” and “Li3[(5a)3Ga]” were made in DMF from 3
equiv of 4-H2 or 5a-H2 and Ga(acac)3. Here, the monomer
Li3[(4/5a)3Ga] and the dimer Li3[(µ-Li)3{(4/5a)3Ga}2] are
observed as well.
The formation of mononuclear titanium(IV) complexes18
A
(Li2[(4-7)3Ti]) corresponds to the first molecular recognition
event. Due to the carbonyl donors at the ligands, lithium ions
can be bound in a second recognition event, and triply bridged
dinuclear helicate-type complexes B (Li[(µ-Li)3{(4-7)3Ti}2])
are formed.24 Monomer A and dimer B are observed in solution
as well as in the gas phase. In the crystal, however, we only
find the dimeric species B (vide infra). It should be noted that
two isomers of monomer A can be formed, one of which has a
facial or all-syn arrangement of the carbonyl groups and another
one where one of them points to the opposite side of the complex
The formation of dimers in an equilibrium with the corre-
sponding monomers is highly specific for lithium counterions.
Ions such as Na+ or K+ with their larger ionic radii did not
mediate dimer formation according to the absence of any
indication for their formation in the NMR and ESI MS spectra.26
This effect is likely due to an almost perfect fit of the Li+ ions
inside the three pockets formed upon dimerization, while Na+
and K+ do not fit due to their larger spatial demand and the
preference for a higher coordination number. Therefore probably
mixtures of facial and meridional isomers are formed with those
cations.
(19) Brown, H. C.; Garg, C. P.; Liu, K.-T. J. Org. Chem. 1971, 36, 387-390.
(20) McOmie, J. F. W.; West, D. E. Org. Synth. Collect. Vol. V 1973, 412-
414.
(21) The synthesis follows a procedure described in: Awad, W. L.; El-Neweihy,
M. F.; Selim, S. F. J. Org. Chem. 1958, 23, 1783-1784.
(22) Sharma, S. K.; Miller, M. J.; Payne, S. M. J. Med. Chem. 1989, 32, 357-
367.
(23) Gramer, C. J.; Raymond, K. N. Org. Lett. 2001, 3, 2827-2830.
(24) For dinuclear helicate-type titanium(IV) complexes with three coordinated
lithium cations, see: Albrecht, M.; Kotila, S. Chem. Commun. 1996, 2309-
2310.
(25) Meyer, M.; Kersting, B.; Powers, R. E.; Raymond, K. N. Inorg. Chem.
1997, 36, 5179-5191.
(26) For examples of templating in the formation of helicates, see: (a) Albrecht,
M.; Blau, O.; Fro¨hlich, R. Chem.sEur. J. 1999, 5, 48-56. (b) Albrecht,
M.; Blau, O.; Fro¨hlich, R. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 4876-
4882.
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Figure 3. Solid-state structures of the monoanions [Li3(4)6Ti2]- (A), [Li3(5b)6Ti2]- (B), and [Li3(7a)6Ti2]- (C). Side view (top) and view along the Ti-Ti
axis (bottom; hydrogens (except at the aldehyde) are omitted).
X-ray Crystal Structures. Li2[(4)3Ti], Li2[(5b)3Ti], and
Li2[(7a)3Ti] were crystallized from DMF/diethyl ether to obtain
red crystals suitable for X-ray crystallography. X-ray crystal
structure analyses revealed the complexes to exist as dimers in
the solid state (Figure 3). Due to the poor quality of the crystal
of Li4[(5b)6Ti2], only a low-quality structure could be obtained
for this compound. Nevertheless, it unambiguously confirms
its dimeric nature.
In Li4[(4)6Ti2], two triscatecholate titanium(IV) complex units
are formed with the aldehydes of the ligands 4 all orientated in
the same direction (facial arrangement). Three pseudo-tetra-
hedrally coordinated lithium cations are bridging two of the
[(4)3Ti]2- moieties by binding to an internal catecholate oxygen
(in 2-position) and a carbonyl oxygen atom of each Ti-complex
moiety.
The structure of [Li3(4)6Ti2]- can formally be regarded as a
triple-stranded dinuclear helicate with three lithium containing
“noncovalent” ligands [4-Li-4]3-. As stated above, the formation
of this noncovalent helicate needs to be considered as a true
eleven-component self-assembly process (6 × 4, 3 × Li, 2 ×
Ti) with two different kinds of recognition events: one between
titanium(IV) and catecholate and the other between Li+ and the
salicylaldehyde units.
The structures of Li4[(5b)6Ti2] and Li4[(7a)6Ti2] are very
similar to the one of the complex of ligand 4. From the
representation in Figure 3 (B, C), the orientation of the ethyl or
methoxy substituents in the clefts of the triple-stranded helical
structure can be nicely seen. The sizes of the three dimer
structures are very similar with Ti-Ti distances of 5.522 Å
(Li4[(4)6Ti2]), 5.535 Å (Li4[(5b)6Ti2]), or 5.474 Å (Li4[(7a)6-
Ti2]).
depends on the lithium coordinating ability of the solvent, and
thus different ratios are observed in different solvents.
DMSO-d6 as a solvent is strongly competing with the
catecholate complexes for the Li+ ions and therefore destabilizes
the dimers.27 For the aldehyde derivative “Li2[(4)3Ti]”, only 1H
NMR signals of monomeric Li2[(4)3Ti] are observed in DMSO-
d6 at δ (ppm) ) 10.09 (s), 6.69 (dd, J ) 7.4, 1.3 Hz), 6.36
(t, J ) 7.4 Hz), and 6.23 (dd, J ) 7.4, 1.3 Hz). In THF-d8, on
the other hand, two sets of signals are detected (Figure 4). The
minor one is found at δ (ppm) ) 9.68 (s), 6.74 (d, J ) 7.1 Hz),
6.42 (partly hidden), and 6.30 (partly hidden). The major
component is observed at δ (ppm) ) 8.55 (s), 6.56 (dd, J )
7.7, 1.5 Hz), 6.47 (t, J ) 7.7 Hz), and 6.33 (dd, J ) 7.7, 1.5
Hz). The signal of the aldehyde proton of 4 serves as a
spectroscopic probe and allows us to distinguish between the
mono- and dinuclear complexes. In the monomer, the resonance
appears at δ (ppm) ) 9.68, a typical shift for aromatic aldehydes.
In the dimer, on the other hand, a highfield shift of more than
1 ppm to δ (ppm) ) 8.55 occurs. The crystal structure of the
dimer provides an idea why this upfield shift is observed. The
aldehyde proton of each of the six ligands is located in close
proximity to the center of the aromatic system of another ligand
at the second complex unit. Consequently, the aldehyde protons
in the dimer experience a strong anisotropic deshielding effect
which is absent in the monomer.
7Li NMR spectroscopy is a tool to distinguish between lithium
cations which are bound in the dimer and those which are
solvated.28 In DMSO-d6, only the monomer [(4)3Ti]2- is present.
7
Therefore only one signal of solvated ions is observed by Li
NMR at δ ) -0.53 ppm. In THF-d8, signals are observed at δ
) 0.41 ppm for solvated Li+ and at δ ) 1.82 ppm for Li+ bound
in the dimer (Figure 5). For the gallium(III) complex “Li3[(4)3-
Ga]” similar NMR spectroscopic results are obtained. The fact
that two distinct sets of signals are observed for monomer and
dimer in all cases provides evidence for an equilibration between
The averaged Li-O distances are found to be 1.937 Å
(Li4[(4)6Ti2]), 1.933 Å (Li4[(5b)6Ti2]), or 1.918 Å (Li4[(6a)6-
Ti2]). The shortening of these interactions from the aldehyde
to the ketone to the ester represents the increasing donor
strengths of the differently substituted carbonyl groups.
Solution Studies: NMR Spectroscopy. 1H NMR investiga-
tions of the complexes reveal the presence of dimer/monomer
equilibria in solution. The monomer/dimer ratio strongly
(27) For a related solvent effect of DMSO in the coordination of templating
cations, see: Albrecht, M.; Janser, I.; Runsink, J.; Raabe, G.; Weis, P.;
Fro¨hlich, R. Angew. Chem. 2004, 116, 6832-6836; Angew. Chem., Int.
Ed. 2004, 43, 6662-6666.
(28) Albrecht, M. Chem.sEur. J. 1997, 3, 1466-1471.
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Hierarchical Assembly of Helicates
A R T I C L E S
Figure 4. 1H NMR spectrum of “Li2[(4)3Ti]” in THF-d8 showing two sets of signals corresponding to both the monomer and the dimer.
“spherical” volumes of monomer/dimer 1:2.04. These differ-
ences in the mobility and the calculated “size ratios” between
the titanium(IV) and gallium(III) complexes are possibly due
to differences in solvation in the highly polar DMSO-d6 versus
the relatively unpolar acetone-d6 and different charges of the
compounds.
From the integral ratios of monomer and dimer signals in
1
the H NMR spectra, the dimerization constants Kdim and the
changes of free enthalpies ∆Gdim easily can be calculated (Table
1). We find the stabilization of the dimer to strongly depend
on the donating ability of the solvent. For example, only the
monomer is observed for Li2[(4)3Ti] in DMSO-d6 at 298 K.
DMSO is a good ligand for lithium and therefore is a strong
competitor for dimer formation. Lowering the donor ability of
the solvent by use of methanol-d4, THF-d8, or even acetone-d6
leads to high dimerization constants Kdim. Related solvent effects
are observed for the gallium(III) complex. However, here the
dimer is more stable than it was observed for the corresponding
titanium(IV) complexes. Probably, the higher charge of the
trianion [(4)3Ga]3- as compared to the dianion [(4)3Ti]2- leads
to a tighter “electrostatic” binding of the lithium cations and to
a higher stability of the dimer.
The influence of the solvent on the dimer-monomer equi-
librium of Li2[(4)3Ti] and Li3[(4)3Ga] allows tuning the ratio
between the two species over a wide range. Figure 7 shows the
percentage of titanium(IV) ions which are bound in the
monomeric Li2[(4)3Ti] or dimeric Li4[(4)6Ti2], respectively,
depending on the molar fraction of the solvent mixture THF-
d8/methanol-d4.
Temperature-dependent 1H NMR measurements of the dimer-
ization equilibria of Li2[(4)3Ti] (THF-d8, concnTi ) 8.0 mM)
and Li3[(4)3Ga] (DMSO-d6, concnGa ) 8.0 mM) permit extrac-
tion of thermodynamic data (see Figure 8). The data show the
dimerization of the monomers in both examples to be enthal-
pically (Ti: ∆Hdim ) -12.6(4) kJ/mol. Ga: ∆Hdim ) -9.1(2)
kJ/mol) as well as entropically (Ti: ∆Sdim ) +16(1) J/mol.
Ga: ∆Sdim ) +4(1) J/mol) favored. The latter is probably due
to the liberation of solvent molecules upon binding of lithium
cations in the dimers [Li3(4)6Ti]- and [Li3(4)6Ga2]3-, respec-
tively.30
Figure 5. 7Li NMR spectra of “Li2[(4)3Ti]” in DMSO-d6 (top) showing
the signal of solvated lithium cations and in THF-d8 (bottom) showing an
additional signal for Li+ bound in the dimer.
both which is slow on the NMR time scale of the 1H as well as
7
the Li NMR experiment.
To unambiguously ascertain the assignment of the resonances
of dimer and monomer of Li2[(4)3Ti] and Li3[(4)3Ga], we
performed DOSY NMR measurements.29 For the titanium
complexes in acetone-d6 at 298 K, we obtained diffusion
coefficients of D ) 8.94 10-10 m2/s (monomer) and of D )
7.89 10-10 m2/s (dimer). Assuming an approximate spherical
shape for the monomer as well as the dimer, we can calculate
a ratio of the volumes of monomer/dimer ) 1:1.27. In case of
the gallium analogues (Figure 6), the measurements (DMSO-
d6, 298 K) lead to D ) 1.85 10-10 m2/s for the monomer and
D ) 1.45 10-10 m2/s for the dimer with a calculated ratio of
(30) (a) Mamula, O.; Monlien, F. J.; Porquet, A.; Hopfgartner, G.; Merbach, A.
E.; von Zelewsky, A. Chem.sEur. J. 2001, 7, 533-539. (b) Bark, T.;
Duggeli, M.; Stoeckli-Evans, H.; von Zelewsky, A. Angew. Chem. 2001,
113, 2924-2927; Angew. Chem., Int. Ed. 2001, 40, 2848-2851.
(29) (a) Cohen, Y.; Avram, L.; Frish, L. Angew. Chem. 2005, 116, 524-560;
Angew. Chem., Int. Ed. 2005, 44, 520-554. (b) Johnson, C. S., Jr. Prog.
Nucl. Magn. Reson. Spectrosc. 1999, 34, 203-256.
9
J. AM. CHEM. SOC. VOL. 127, NO. 29, 2005 10375

A R T I C L E S
Albrecht et al.
Figure 6. Part of the DOSY NMR spectrum (DMSO-d6, 298 K) of Li3[(4)3Ga] and Li6[(4)6Ga2].
Table 1. Dimerization Constants Kdim ) [Dimer]/[Monomer]2 and
∆Gdim Values Observed for the Monomer-Dimer Equillibria in
Different Solvents at 298 K
2Li2[(4)3Ti]
h
L4[(4)6Ti2]
Gdim
[kJ/mol]
2Li3[(4)3Ga]
h
Li6[(4)6Ga2]
Kdim
∆
Kdim
∆Gdim
1
1
solvent
[M-
]
[M-
]
[kJ/mol]
DMSO-d6
D2O
CD3OD
THF-d8
acetone-d6
only monomer
only monomer
80
1600
200.000
-10.86
-18.28
-30.24
10
-5.70
950
1330
-16.99
-17.82
low solubility
low solubility
As described for the complexes of the aldehyde-substituted
ligand 4, dimer-monomer equilibria can be also observed for
the complexes of the ketones 5a-j, 6a,b, and of the esters 7a,b
in solution. Figure 9 shows the 1H NMR signals of the n-propyl
groups of Li2[(5c)3Ti] and Li4[(5c)6Ti2] in methanol-d4. The
resonances of the monomeric species are observed at δ ) 3.06
(t, J ) 7.4 Hz, CH2), 1.59 (sextet, J ) 7.4 Hz, CH2), and 0.85
(t, J ) 7.4 Hz, CH3), while the dimer is observed as the major
species at δ ) 2.68, 1.96 (2 m, CH2), 1.10, 0.98 (2 m, CH2),
and 0.63 (t, J ) 7.7 Hz, CH3). As described for the aldehyde
protons of 4, the anisotropic high-field shift of the n-propyl
group in Li4[(5c)6Ti2] is due to its location above the center of
the aromatic ring of another ligand 5c.
Figure 7. Percentage of titanium(IV) ions bound in the monomer (b) and
dimer (9) depending on the composition of a solvent mixture of THF-d8
and methanol-d4 (concnTi ) 7.5 mmol/L).
fast inversion of configuration at the metal center. The binding
of lithium cations in the dimer slows down the racemization.
Diastereotopicity is thus observed, because this process is slow
on the NMR time scale. Similar spectroscopic behavior is
observed for the complexes of ligands 5b-j and 7b. The
A major difference between monomer Li2[(5c)3Ti] and dimer
Li4[(5c)6Ti2] is the diastereotopic splitting of the CH2 resonances
observed for the CH2 groups of the dimer.31 In the monomer,
only an averaged set of signals is observed which is due to a
(31) (a) Kersting, B.; Meyer, M.; Powers, R. E.; Raymond, K. N. J. Am. Chem.
Soc. 1996, 118, 7221-7222. (b) Albrecht, M.; Schneider, M.; Ro¨ttele, H.
Chem. Ber./Recueil 1997, 130, 615-619.
9
10376 J. AM. CHEM. SOC. VOL. 127, NO. 29, 2005

Hierarchical Assembly of Helicates
A R T I C L E S
Table 2. Dimerization Constants Kdim ) [Dimer]/[Monomer]2 and
∆Gdim Values Observed for the Monomer-Dimer Equillibria of the
Titanium Complexes Li2[(L)3Ti] in Methanol-d4 at 298 K
ligand
L
Kdim
∆
[kJ/mol]
Gdim
ligand
L
Kdim
∆Gdim
[kJ/mol]
1
1
R
[M-
]
R
[M-
]
4
H
CH3
C2H5
10 -5.7
3715 -20.4
785 -16.5
5g
5h
5i
n-C7H15
n-C8H17
n-C10H19
n-C12H25
i-C3H7
725
1425
665
-16.3
-18.0
-16.1
-17.6
5a
5b
5c
5d
5e
5f
n-C3H7 1110 -17.4
n-C4H9 1500 -18.1
n-C5H11 1015 -17.2
n-C6H13 965 -17.0
5j
1200
6a
7a
7b
3.6 -3.2
25 600 -25.2
only dimer
OCH3
OC2H5
such as 4 are the weakest donors, leading to the lowest Kdim
)
10 M-1, while the strongly donating ester groups as in 7 favor
formation of the dimer (Kdim ) 25 600 M-1). The ketones 5a-j
are donors of intermediate strengths and thus lead to intermediate
Kdim ) 665-3715 M-1
.
For the complexes of the ketones 5a-j and 6a, we further-
more observe a steric effect on the dimerization equilibrium.
Li2[(5a)3Ti], with its small methyl side chain, shows a high
tendency for dimerization (Kdim ) 3715 M-1). Steric bulk in
the longer n-alkyl substituted complexes Li2[(5b-j)3Ti] results
in a lower Kdim ) 665-1500 M-1, while for Li2[(6a)3Ti] with
the branched isopropyl substituent dimerization is highly
unfavored (Kdim ) 3.6 M-1). Within the series of n-alkyl
substituted complexes Li2[(5b-j)3Ti], quite similar free enthal-
pies of dimerization are determined and a large effect of the
chain length is not observed. The trend to higher dimerization
constants for the Ga complexes discussed above for the aldehyde
ligand 4 is also observed for ketone 5a: “Li3[(5a)3Ga]” shows
a dimerization constant in DMSO-d6 at 298 K of Kdim ) 5200
M-1, while the corresponding Ti complex Li2[(5a)3Ti] hardly
forms dimers under the same conditions (Kdim ) 10 M-1).
Our solution phase NMR spectroscopic studies clearly show
the equilibrium between monomer and dimer to depend on
different factors. Dimerization is only observed when the cation
mediating it has the appropriate size. For Na+ and K+, no dimer
formation is found, while Li+ efficiently mediates the formation
of dinuclear helicate-like complexes. Dimer formation is also
favored when the bridging lithium cations are strongly bound.
This is the case (i) if the mononuclear complex units bear a
high negative charge (e.g., Li6[(4)6Ga2] versus Li4[(4)6Ti2]), (ii)
if solvents with a low tendency to solvate lithium are present
(e.g., acetone versus DMSO), (iii) if the carbonyl oxygen is a
strong donor (e.g., ester versus aldehyde), and (iv) if the steric
bulk at the carbonyl oxygen is low (e.g., methyl ketone versus
the corresponding isopropyl analogue). Some of these effects
cancel each other to some extent. For example, aldehyde ligand
4 has a lower donor strength disfavoring dimerization as
compared to ketones 5a-j but also a low steric demand favoring
it. The detailed analysis of these effects permits control of the
dimerization equilibrium quite precisely over a wide range.
Solution Studies: ESI Mass Spectrometry. Negative ion
electrospray ionization Fourier transform ion-cyclotron-reso-
nance (ESI FT-ICR) mass spectrometry shows the presence of
dimeric as well as monomeric complexes in solution.32 The
compounds were either sprayed from THF or THF/methanol
Figure 8. Plot of ∆Gdim(T) (kJ/mol) versus temperature (K) for the
dimerization of Li2[(4)3Ti] (A) (THF-d8, concnTi ) 8.0 mmol/L) and Li3[(4)3-
Ga] (B) (DMSO-d6, concnGa ) 8.0 mmol/L).
Figure 9. Part of the NMR spectrum of Li2[(5c)3Ti] (b) and Li4[(5c)6Ti2]
(9) in methanol-d4 showing the signals of the n-propyl substituent.
surprisingly high barrier for the dimer/monomer equilibrium
should be due to the simultaneous (and probably cooperative)
formation of twelve lithium-oxygen bonds.
1
Due to the slow exchange between monomer and dimer, H
NMR measurements of Li2[(L)3Ti] (L ) 5a-j-H2, 6a-H2, 7a,b-
H2) in methanol-d4 at 298 K easily yield the dimerization
constants Kdim and the free dimerization enthalpies ∆Gdim (Table
2) and permit a comparison of different substituents at the
carbonyl group. Dimer formation correlates with the donor
strength of the type of carbonyl unit at the ligand. Aldehydes
9
J. AM. CHEM. SOC. VOL. 127, NO. 29, 2005 10377

A R T I C L E S
Albrecht et al.
(1:1). With titanium(IV) as metal center, signals for monoanions
[Li3(4-7)6Ti2]- and [Li(4-7)3Ti]- are observed in quite clean
mass spectra. In addition, sometimes low-intensity signals are
observed for monomers [H(4-7)3Ti]- that underwent the
exchange of the Li+ cation against a proton. The intensities
reflect semiquantitatively the concentrations in solution as
determined by NMR spectroscopy. However, since the ESI
response factors33 are not known, we refrain from drawing
quantitative conclusions. For the gallium(III) compounds, the
mass spectra are more complex. Monomeric [LiH(4)3Ga]- (m/z
) 485) and [LiH(5a)3Ga]- (m/z ) 527), respectively, are
detected in addition to dimeric species in several charge states:
[Li4(4)6Ga2]2- (m/z ) 491), [Li3(4)6Ga2]3- (m/z ) 326),
[Li4(5a)6Ga2]2- (m/z ) 534), and [HLi4(5b)6Ga2]- (m/z ) 1069).
In addition, monomeric species with only two ligands [(4)2Ga]-
-
(m/z ) 341) and [(5a)2Ga] (m/z ) 369) were detected as
fragments (vide infra).
As shown below, the spectra obtained under soft electrospray
ionization conditions reflect the species present in solution.
Harsher ionization conditions significantly increase the abun-
dances of mononuclear ions at the expense of the dimeric
complexes due to fragmentation during the ionization process.
Consequently, some caution is required to get a true picture of
the species present in solution.
Beyond analytical characterization, mass spectrometry is a
valuable tool for following solution phase processes kinetically
when they meet the time scale of the experiment.34 When the
crystalline dimeric complexes are dissolved in a 1:1 mixture of
THF and methanol as the spray solvent, the relatively slow
dissociation of the dimers into the corresponding monomers can
be followed easily (Figure 10). Since the crystalline material
contains only dimers (see above), initially, dimeric ions are
observed almost exclusively. During 2 days at room temperature,
the dimers almost completely dissociate into the corresponding
monomers, seemingly a contradiction to the NMR experiments
in which significant amounts of dimers were observed in
equilibrium with the monomers for this solvent mixture (for
example, see Figure 7). However, one needs to take into account
that the concentration of the solution used in the MS experiments
is lower than that used for NMR analysis by a factor of about
50. In view of the low binding constants (Li2[(5f)3Ti]: Kdim
(methanol) ) 965 M-1), the complete dissociation of the dimer
thus does not come as a surprise.
Figure 10. Negative ESI FTICR mass spectra of a 100 µM solution of
dimeric Li4[(5f)6Ti2] in THF/MeOH ) 1:1 after different time intervals.
Note that the concentrations used in the MS experiment are far below those
of the NMR experiments. Consequently, the dimer finally dissociates
completely into the two monomers.
In a second experiment, we intended to study the formation
of heterodinuclear complexes from a mixture of two different
homodimers. Two 0.4 mM solutions of the titanium(IV)
complexes Li2[(5f)3Ti] and Li2[(5g)3Ti] were mixed in THF/
MeOH ) 1:1 and the exchange behavior was followed over
time by ESI FT-ICR mass spectrometry (Figure 11a). For
comparison, the same experiment was performed in pure THF
as the spray solvent (Figure 11b). Due to the similar lengths of
the alkyl chains, similar properties, in particular similar ESI
response factors, are expected for both types of complexes.
The ESI mass spectra recorded directly after mixing the two
solutions exhibit signals for the heterodinuclear complexes
hardly above the signal-to-noise ratio (Figure 11, bottom traces).
This provides evidence for a quite slow exchange of monomers
within the dimer irrespective of the solvent mixture. Interest-
ingly, the monomer ions observed in the spectrum obtained from
the THF/MeOH mixture reveal complete exchange of the
catechol ligands. A roughly 1:3:3:1 statistical ratio is observed
for the A3, A2B, AB2, and B3 complexes (inset in Figure 11a,
bottom trace; A ) 5f, B ) 5g). The fact that the ligand exchange
(32) For recent MS studies on metallosupramolecular aggregates, see: (a)
Marquis-Rigault, A.; Dupont-Gervais, A.; Baxter, P. N. W.; Van Dorsselaer,
A.; Lehn, J.-M. Inorg. Chem. 1996, 35, 2307-2310. (b) Ko¨nig, S.;
Bru¨ckner, C.; Raymond, K. N.; Leary, J. A. J. Am. Soc. Mass Spectrom.
1998, 9, 1099-1103. (c) Hopfgartner, G.; Vilbois, F.; Piguet C. Rap.
Commun. Mass Spectrom. 1999, 13 302-306. (d) Sakamoto, S.; Fujita,
M.; Kim, K.; Yamaguchi, K. Tetrahedron 2000, 56, 955-964. (e) Ziegler,
M.; Miranda, J. J.; Andersen, U. N.; Johnson, D. W.; Leary, J. A.; Raymond,
K. N. Angew. Chem. 2001, 113, 755-758; Angew. Chem., Int Ed. 2001,
40, 733-736. (f) Schalley, C. A.; Mu¨ller, T.; Linnartz, P.; Witt, M.; Scha¨fer,
M.; Lu¨tzen, A. Chem.sEur. J. 2002, 8, 3538-3551. (g) Mu¨ller, I. M.;
Mo¨ller, D.; Schalley, C. A. Angew. Chem. 2005, 117, 485-488; Angew.
Chem., Int. Ed. 2005, 44, 480-484.
(33) Leize, E.; Jaffrezic, A.; Van Dorsselaer, A. J. Mass Spectrom. 1996, 31,
537-544.
(34) (a) Romero, F. M.; Ziessel, R.; Dupont-Gervais, A.; Van Dorsselaer, A.
Chem. Commun. 1996, 551-552. (b) Marquis-Rigault, A.; Dupont-Gervais,
A.; Van Dorsselaer, A.; Lehn, J.-M. Chem.sEur. J. 1996, 2, 1395-1398.
9
10378 J. AM. CHEM. SOC. VOL. 127, NO. 29, 2005

Hierarchical Assembly of Helicates
A R T I C L E S
Figure 11. Stack plots of the ESI FT-ICR spectra of a 1:1 mixture of Li2[(5f)3Ti] and Li2[(5g)3Ti] (a) in THF/methanol 1:1 and (b) in pure THF after
different time intervals at room temperature. The insets in the bottom spectra show the monomer region directly after mixing. While the catecholates of the
monomeric complexes are quickly exchanged in THF/MeOH, they exchange much more slowly in pure THF.
is fast for the monomeric complexes under study, while the
dimers appear only as homodinuclear complexes, confirms that
the mass spectra reflect the situation in solution. If the ionization
conditions were too harsh and the monomers were formed
during the ionization process, one would expect to see much
more intense signals for A3 and B3 complexes. If in turn the
dimers were formed from the monomers by what is often called
“unspecific aggregation” during the electrospray ionization, one
would expect to see a statistical mixture of all possible species.
Both are not the case, and we can thus safely conclude that the
monomers and dimers examined are already present in solution.
In pure THF, the A2B and AB2 monomers are hardly visible.
Consequently, the exchange of catecholate ligands is slow here.
This can easily be rationalized by invoking methanol as a solvent
which accelerates the catecholate exchange due to its protic
nature. In the absence of methanol, this exchange then slows
down significantly. In THF alone, the expected heterodinuclear
complexes are indeed formed. Initially, the signals for dimers
Li3[(5f)6Ti2]- (m/z ) 1437) and Li3[(5g)6Ti2]- (m/z ) 1521)
are observed as the dominating species. Only a minor trace of
mixed dimer Li3[(5f)3(5g)3Ti2]- (m/z ) 1480) is found. Over
time, this signal increases and the spectrum recorded 1135 min
after mixing shows three prominent signals for the two homo-
and the heterodinuclear complexes. Such a result is in agreement
with the assumption that the exchange of individual catecholate
ligands is slower than the exchange of complete monomeric
complexes for both the dimeric and the monomeric complexes.
The two monomer units incorporated in the dimer are thus
homoleptic. Catecholate exchange nevertheless occurs to some
extent, and the spectrum obtained after 3 weeks corresponds to
9
J. AM. CHEM. SOC. VOL. 127, NO. 29, 2005 10379

A R T I C L E S
Albrecht et al.
an almost statistical mixture of all possible dimeric species, i.e.,
A6, A5B, A4B2, A3B3, A2B4, AB5, and B6 complexes (A ) 5f,
B ) 5g).
The same experiment performed in THF/MeOH ) 1:1 clearly
leads to a different result. Initially, the two homodinuclear
complexes are most prominent. Over time, however, not only
the expected heterodinuclear A3B3 ion Li3[(5f)3(5g)3Ti2]-
(m/z ) 1480) is observed but also a statistical mixture of all
possible dimers grows between the two homodimer signals. This
behavior is only in agreement with dimers dissociating into
monomers, which undergo a fast catecholate exchange and then
reassociate to some extent to yield all possible mixed dimers.
In contrast, ligand exchange within the dimer is not observed
due to the additional binding energy provided by the coordina-
tion to the bridging lithium cations. In this case, one would
expect to initially observe a “U-shaped” distribution of the
different exchange products which more and more develops
toward the statistical distribution.
Consequently, mass spectrometry is a valuable tool for
gathering qualitative mechanistic insight into the exchange
equilibria in solution. Since the two dimers initially differed
only by an additional methylene group, an NMR spectroscopic
analysis of the same processes is hampered by signal overlap
and both methods yield complementary data.
Gas-Phase Reactivity of the Dimeric Complexes. Mass
spectrometry not only permits us to examine the solution-phase
reactivity of the complexes under study but also allows us to
study their reactivity in the gas phase by tandem MS experi-
ments. The collision-induced decay (CID) of mass-selected
homodinuclear [Li3(4)6Ti2]- (m/z ) 933; Figure 12c), [Li4(4)6-
Ga2]2- (m/z ) 491), [Li3(4)6Ga2]3- (m/z ) 326; Figure 12d),
and [Li3(5-7)6Ti2]- was studied in the gas phase by MS/MS
experiments with argon as the collision gas.35 The three stages
of this experiment are shown in Figure 12. Trace a shows a
typical mass spectrum of [Li4(4)6Ti2] which contains intense
signals for dimer [Li3(4)6Ti2]-. This ion is then mass selected
(trace b) and subsequently collided with Ar gas. It fragments
(trace c) into monomeric triscatecholate complexes ([Li(4)3Ti]-,
m/z ) 463). All titanium(IV) complexes Li2[(5-7)3Ti] show
the same reactivity in CID experiments. In a quasi-symmetrical
reaction, the dimers [Li3(5-7)6Ti2]- decompose into two
monomeric units, one of which carries the negative charge
([Li(5-7)3Ti]-), while the other is neutral due to the presence
of an additional Li+ cation ([Li2(5-7)3Ti]).
Interestingly, the doubly and triply charged gallium complexes
[Li4(4)6Ga2]2- and [Li3(4)6Ga2]3- were more labile and even
at rather low collision energies decomposed in an asymmetric
fashion quite similarly to each other but significantly different
from the Ti analogues. [Li4(4)6Ga2]2- fragmented into [Li4(4)4-
Ga]- (m/z ) 635) and [(4)2Ga]- (m/z ) 341) and distributed
the two charges over both fragments in order to reduce charge
repulsion (Scheme 3). [Li3(4)6Ga2]3- gave similar fragments:
[Li3(4)4Ga]2- (m/z ) 317) and [(4)2Ga]- (m/z ) 341) are
formed. The lability of [Li3(4)6Ga2]3- is due to the higher
negative charge of the ion, which destabilizes the supramolecular
aggregate and leads to a fast decomposition. This behavior is
in contrast to the higher solution stability of the Ga complex as
compared to their Ti analogues. However, in solution, solvent
Figure 12. Spectra a-c correspond to the different stages of a tandem
MS experiment: (a) Negative ion ESI FT-ICR mass spectrum of Li4[(4)6-
Ti2] sprayed from THF. (b) Same spectrum after mass selection of the dimer
[Li3(4)3Ti]- (all isotopologues isolated). (c) Collision-induced decay (CID)
mass spectrum of mass-selected [Li3(4)3Ti]- with Ar as the collision gas.
(d) CID spectrum of mass-selected ions corresponding to the triply charged
dimer [Li3(4)6Ga2]3-. (e) CID spectrum of mass-selected ions corresponding
to the doubly charged heterodimer [Li3(4)6GaTi]2-. Insets compare the
experimental isotope patterns of the parent ions (top) with those calculated
on the basis of natural abundances (bottom).
molecules and, in particular, counterions are present which
contribute to compensating the higher negative charge and
provide additional binding energy through electrostatic interac-
tions with the counterions. In the gas phase, these counterions
are absent, and thus charge repulsion destabilizes the multiply
charged complexes.
To test, how a heterodinuclear complex Li5[(4)6GaTi] would
behave in view of these quite different fragmentation pathways,
we prepared a 1:1 mixture of the two homodimers in THF and
equilibrated it until a roughly statistical mixture of Li6[(4)6Ga2],
Li4[(4)6Ti2], and Li5[(4)6GaTi] was formed. Then, the ions
(35) (a) Schalley, C. A. Int. J. Mass Spectrom. 2000, 194, 11-39. (b) Schalley,
C. A. Mass Spectrom. ReV. 2001, 20, 253-309.
9
10380 J. AM. CHEM. SOC. VOL. 127, NO. 29, 2005

Hierarchical Assembly of Helicates
A R T I C L E S
Scheme 3. Gas-Phase Fragmentation Pathwaysa
Conclusions
In this paper, we described the eleven-component self-
assembly of helicate type complexes, which are formed from
six catechol ligands bearing carbonyl groups in their 3-position,
two titanium(IV) (or gallium(III)) ions and three lithium cations.
The formation of the compounds represents a hierarchical self-
assembly process with a strong interaction between the metals
and the catecholates and a weaker binding of the lithium cations
which leads to dimerization. The monomer-dimer equilibrium
can be observed in solution by NMR spectroscopy, and it is
found that the dimer is favored, if the monomer bears a high
negative charge, if the carbonyl units are good donor atoms for
binding the bridging Li cations, if the solvent poorly solvates
these cations and thus does not efficiently compete, and if the
sterical hindrance exerted by the side chains attached to the
carbonyl groups is minimized. ESI FT-ICR MS investigations
show that the ligands are tightly bound in the dimer, so that
ligand scrambling only occurs in the monomeric species. This
is in excellent agreement with the finding that diastereotopic
signals for the methylene groups in the side chains of the ketone
complexes are only seen in the NMR spectra for the dinuclear
complexes. Complexation to the bridging lithium cations thus
also suppresses the inversion of chirality. In the gas phase, the
dinuclear titanium(IV) and gallium(III) complexes show dif-
ferent fragmentation pathways in CID experiments, with a
symmetric cleavage in case of the titanium species and an
unsymmetric decomposition of the gallium compounds. Data
from the solid state, from solution, and from the gas phase
contribute to a detailed understanding of the structural factors
which govern thermodynamic as well as kinetic stabilities and
the exchange mechanisms operative in solution.
a (a) The singly charged homodinuclear titanium(IV) and (b) doubly and
(c) triply charged gallium(III) complexes. (d) Fragmentation pathways of
doubly charged heterodinuclear titanium(IV)/gallium(III) complexes of
ligand 4. With the number of charges, the complexity of the fragmentation
reactions increases due to charge repulsion. The sequences in gray show
consecutive decompositions of primarily formed species with the inset giving
a probable fragmentation mechanism for the loss of one catecholate ligand
from the [(4)2Ga]- anion.
corresponding to the doubly charged heterodimer [Li3(4)6GaTi]2-
at m/z ) 477 were mass selected and subjected to collision-
induced dissociation. This species decomposes following both
pathways found for the two homodimers.36 The asymmetric
cleavage into [(4)2Ga]- (m/z ) 340.96) and [Li4(4)4Ti]- (m/z
) 613) competes with dissociation into the two monomers
[Li(4)3Ti]- (m/z ) 463) and [Li2(4)3Ga]- (m/z ) 491) (Figure
12e). Both monomers appear as singly charged species minimiz-
ing charge repulsion. The observation of only one of the two
possible asymmetric cleavages is probably due to the thermo-
dynamically favored formation of [(4)2Ga]- as a stable species
which possesses a completely filled electron shell. The com-
plexity of the fragmentation patterns and the extent of consecu-
tive fragmentation reactions increase with the number of charges
present in the complexes. Also, the charge distribution within
the monomeric units appears to control the fragmentation
pathways.
The gas phase experiments reveal a quite interesting differ-
ence in the reactivity of the titanium and gallium complexes.
Significant differences in the stabilities of multiply charged ions
in the gas phase and in solution can be traced back to the absence
of the appropriate number of counterions in the gas phase. These
results underline again the importance of the environment of a
species under study. Properties observed in solution are always
properties of the molecules within their environment. The
intrinsic properties can be evaluated in the gas phase and may
differ significantly.
The complexes presented in this contribution can be switched
between their monomeric and dimeric forms by different factors.
A precise control of these factors even permits us to fine-tune
the monomer/dimer ratio. At present, we aim at substituting
the side chains of these species to introduce specific functions
which can be controlled by this switching process through
control of the monomer-dimer equilibrium.
Experimental Section
General Remarks. NMR spectra were recorded on a Varian Mercury
300, Inova 400, or a Unity 500 spectrometer. FT-IR spectra were
recorded by diffuse reflection (KBr) on a Bruker IFS spectrometer.
Mass spectra (EI, 70 eV; FAB with 3-NBA as matrix) were measured
on a Finnigan MAT 90, 95, or 212 mass spectrometer. FT-ICR ESI
mass spectra were measured on a Bruker APEX IV FT mass
spectrometer. Elemental analyses were obtained with a Heraeus CHN-
O-Rapid analyzer. Melting points: Bu¨chi B-540 (uncorrected). Chemi-
cals were used as received by commercial suppliers. 4-H2 was purchased
from Aldrich.
Negative ESI FT-ICR Mass Spectrometry. ESI mass spectra and
MS/MS spectra were recorded on a Bruker APEX IV Fourier transform
ion-cyclotron-resonance (FT-ICR) mass spectrometer with an Apollo
electrospray ion source equipped with an off axis 70° spray needle.
Typically, tetrahydrofuran (THF) or 1:1 mixtures of THF and methanol
served as the spray solvents, and 100 µM solutions of the analytes
were used. Analyte solutions were introduced into the ion source with
a Cole-Parmers Instruments (Series 74900) syringe pump at flow rates
of ca. 3-4 µL/min. Ion transfer into the first of three differential pump
stages in the ion source occurred through a glass capillary with a 0.5
mm inner diameter and nickel coatings at both ends. Ionization
parameters were adjusted as follows: capillary voltage, +4.5 kV;
(36) For a heterodimeric gallium/titanium helicate, see: Albrecht, M.; Fro¨hlich,
R. J. Am. Chem. Soc. 1997, 119, 1656-1661.
9
J. AM. CHEM. SOC. VOL. 127, NO. 29, 2005 10381

A R T I C L E S
Albrecht et al.
endplate voltage, +4.0 kV; capexit voltage, -120 V; skimmer voltages,
-20 to -10 V; temperature of drying gas, 250 °C. The flow of the
drying gas was kept in a medium range, while the flow of the nebulizer
gas was low. With the gas flows and the capexit voltage, the ratio of
monomeric to dimeric ions can be changed over a wide range, since
collisions with residual gas may lead to fragmentation of the dimer
into the corresponding monomers. It is therefore crucial to set these
parameters to as soft as possible conditions. The ions were accumulated
in the instruments hexapole for 1.2 s. The ions are then introduced
into the FT-ICR cell which was operated at pressures below 10-10 mbar
and detected by a standard excitation and detection sequence. For each
measurement 16 to 64 scans were averaged to improve the signal-to-
noise ratio.
69.6 (CH), 60.8 (CH3), 55.6 (CH3), 40.5 (CH2), 19.2 (CH2), 14.0 (CH3).
IR (KBr): ν (cm-1) ) 3414, 2957, 1478, 1270, 1064, 1010, 752. MS
(EI): m/z ) 210 [M+•], 167.
1-(2,3-Dimethoxyphenyl)-1-pentanol.38 Yield: 1.53 g (85%) of
crude product, colorless liquid. 1H NMR (CDCl3, 300 MHz): δ (ppm)
) 7.05 (t, J ) 7.9 Hz, 1 H), 6.95 (dd, J ) 7.9, 1.5 Hz, 1 H), 6.84 (dd,
J ) 7.9, 1.5 Hz, 1 H), 4.92 (dd, J ) 7.7, 5.7 Hz, 1 H), 3.87 (2 s, 3 H
each), 1.76 (m, 2 H), 1.36 (m, 4 H), 0.90 (t, J ) 7.4 Hz, 3 H). 13C
NMR (CDCl3, 75 MHz): δ (ppm) ) 152.5 (C), 146.2 (C), 138.3 (C),
124.1 (CH), 118.7 (CH), 111.3 (CH), 70.1 (CH), 60.9 (CH3), 55.7
(CH3), 38.0 (CH2), 28.2 (CH2), 22.6 (CH2), 14.0 (CH3). IR (KBr): ν
(cm-1) ) 3415, 2934, 1479, 1268, 1009. MS (EI): m/z ) 224 [M+•],
167.
For the experiments aimed at following the kinetics of monomer
and ligand exchange in solution, two of the sample solutions were mixed
and mass spectra were recorded at different time intervals.
1-(2,3-Dimethoxyphenyl)-1-hexanol. Yield: 1.3 g (68%) of crude
product, colorless liquid. H NMR (CDCl3, 300 MHz): δ (ppm) )
1
7.03 (t, J ) 7.9 Hz, 1 H), 6.95 (dd, J ) 7.9, 1.5 Hz, 1 H), 6.82 (dd, J
) 7.9, 1.5 Hz, 1 H), 4.91 (dd, J ) 7.7, 5.7 Hz, 1 H), 3.87 (2 s, 3 H
each), 1.73 (m, 2 H), 1.43 (m, 1 H), 1.30 (m, 5 H), 0.88 (t, J ) 7.4 Hz,
3 H). 13C NMR (CDCl3, 75 MHz): δ (ppm) ) 152.4 (C), 146.2 (C),
138.4 (C), 124.1 (CH), 118.7 (CH), 111.3 (CH), 69.9 (CH), 60.9 (CH3),
55.7 (CH3), 38.4 (CH2), 31.8 (CH2), 25.8 (CH2), 22.5 (CH2), 14.1 (CH3).
IR (KBr): ν (cm-1) ) 3415, 2933, 2860, 1477, 1268, 1072, 1010,
751. MS (EI): m/z ) 238 [M+•], 167.
For MS/MS experiments, the whole isotope pattern of the ion of
interest was isolated by applying correlated sweeps. Isolation of only
the major isotope peak is possible, but in view of the particular isotope
patterns of Ti and Ga complexes, the analysis of the fragmentation
products is facilitated, when their isotope patterns are analyzed. Thus,
for most of the tandem MS experiments described here, all isotopo-
logues were subjected to the CID experiments. After isolation, argon
was introduced into the ICR cell through a pulsed valve at a pressure
of ca. 10-8 mbar, and the ions were accelerated by a standard excitation
protocol. A sequence of several different spectra was recorded at
different excitation pulse attenuations in order to get at least a rough
and qualitative idea of the effects of different collision energies.
Between excitation and detection, a 2 s pumping delay allowed the
ions to react.
General Procedure for the Addition of Grignard Reagents to
2,3-Dimethoxybenzaldehyde.21 A few drops of the bromide are added
to the magnesium (0.01 mol) in a small amount of ether. After the
reaction has started, the remaining bromide (in total 0.01 mol) is
dissolved in ether (10 mL) and added. The mixture is refluxed until
the magnesium is dissolved (approximately 30 min). The aldehyde is
added, and the solution is heated for an additional 2 h. After cooling,
the mixture is poured on ice, and concentrated HCl is added until the
precipitate dissolves. The water is extracted with ether (2×), and the
organic phase is washed with aqueous NaHSO3, NaHCO3, and a small
amount of water. After drying with Na2SO4, solvent is removed in
vacuo. The compounds are used without further purification. Therefore
some of the alcohols are only characterized by NMR spectroscopy.
However, if necessary, further purification can be done by column
chromatography over silica gel.
1-(2,3-Dimethoxyphenyl)-1-heptanol. Yield: 2.0 g (quant.) of crude
1
product, colorless liquid. H NMR (CDCl3, 400 MHz): δ (ppm) )
7.04 (t, J ) 7.7 Hz, 1 H), 6.95 (dd, J ) 7.7, 1.6 Hz, 1 H), 6.83 (br. d,
J ) 7.7 Hz, 1 H), 4.91 (dd, J ) 7.7, 5.5 Hz, 1 H), 3.87 (s, 3 H), 3.86
(s, 3 H), 1.74 (m, 2 H), 1.26 (m, 8H) 0.87 (t, J ) 7.1 Hz, 3 H). 13C
NMR (CDCl3, 100 MHz): δ (ppm) ) 152.2 (C), 146.0 (C), 138.1 (C),
124.0 (CH), 118.5 (CH), 111.1 (CH), 70.0 (CH), 60.8 (CH3), 55.6
(CH3), 38.3 (CH2), 31.6 (CH2), 29.2 (CH2), 26.0 (CH2), 22.6 (CH2),
14.1 (CH3).
1-(2,3-Dimethoxyphenyl)-1-octanol.38 Yield: 1.77 g (83%) of crude
1
product, colorless liquid. H NMR (CDCl3, 400 MHz): δ (ppm) )
7.04 (t, J ) 8.0 Hz, 1 H), 6.94 (dd, J ) 8.0, 1.4 Hz, 1 H), 6.83 (dd, J
) 8.0, 1.4 Hz, 1 H), 4.91 (dd, J ) 8.0, 5.8 Hz, 1 H), 3.86 (s, 3 H),
3.85 (s, 3 H), 1.74 (m, 2 H), 1.46 (m, 1 H), 1.28 (m, 9 H), 0.87 (t, J
) 8.1 Hz, 3 H). 13C NMR (CDCl3, 100 MHz): δ (ppm) ) 152.2 (C),
146.0 (C), 138.1 (C), 123.9 (CH), 118.5 (CH), 111.1 (CH), 69.9 (CH),
60.8 (CH3), 55.6 (CH3), 38.3 (CH2), 31.8 (CH2), 29.7 (CH2), 29.1 (CH2),
26.0 (CH2), 25.7 (CH2), 14.1 (CH3). IR (KBr): ν (cm-1) ) 3414, 2927,
2854, 1479, 1268, 1010. MS (EI): m/z ) 266 [M+•], 167.
1-(2,3-Dimethoxyphenyl)-1-nonanol.39 Yield: 1.88 g (84%) of
crude product, colorless liquid. 1H NMR (CDCl3, 300 MHz): δ (ppm)
) 7.03 (t, J ) 7.8 Hz, 1 H), 6.94 (dd, J ) 7.8, 1.3 Hz, 1 H), 6.82 (dd,
J ) 7.8, 1.3 Hz, 1 H), 4.91 (dd, J ) 7.9, 5.7 Hz, 1 H), 3.85 (s, 3 H),
3.84 (s, 3 H), 1.75 (m, 2 H), 1.46 (m, 1 H), 1.28 (m, 11 H), 0.87 (m,
3 H). 13C NMR (CDCl3, 75 MHz): δ (ppm) ) 152.5 (C), 146.2 (C),
138.4 (C), 124.1 (CH), 118.7 (CH), 111.3 (CH), 70.0 (CH), 60.8 (CH3),
55.7 (CH3), 38.4 (CH2), 31.8 (CH2), 29.7 (CH2), 29.6 (CH2), 29.3 (CH2),
26.1 (CH2), 22.7 (CH2), 14.1 (CH3). IR (KBr): ν (cm-1) ) 3409, 2926,
2854, 1479, 1268, 1009. MS (EI): m/z ) 280 [M+•], 167.
1-(2,3-Dimethoxyphenyl)-1-undecanol.38 Yield: 2.6 g (quant.) of
crude product, colorless liquid. 1H NMR (CDCl3, 400 MHz): δ (ppm)
) 7.05 (t, J ) 7.9 Hz, 1 H), 6.94 (dd, J ) 7.9, 1.4 Hz, 1 H), 6.84 (dd,
J ) 7.9, 1.4 Hz, 1 H), 4.91 (dd, J ) 8.0, 5.8 Hz, 1 H), 3.87 (s, 3 H),
3.86 (s, 3 H), 1.74 (m, 2 H), 1.47 (m, 1 H), 1.26 (m, 15 H), 0.87 (m,
3 H). 13C NMR (CDCl3, 100 MHz): δ (ppm) ) 152.3 (C), 146.0 (C),
138.0 (C), 123.9 (CH), 118.5 (CH), 111.2 (CH), 70.2 (CH), 60.8 (CH3),
55.7 (CH3), 38.3 (CH2), 29.6 (3 × CH2), 29.5 (CH2), 29.3 (CH2), 26.0
1-(2,3-Dimethoxyphenyl)-1-ethanol.37 Yield: 576 mg (quant) of
crude product by addition of methyllithium instead of the Grignard
1
reagent, yellow solid. H NMR (CDCl3, 400 MHz): δ (ppm) ) 7.12
(t, J ) 7.9 Hz, 1 H), 7.04 (dd, J ) 7.9, 1.7 Hz, 1 H), 6.91 (dd, J ) 7.9,
1.7 Hz, 1 H), 5.20 (q, J ) 6.4 Hz, 1 H), 3.95 (s, 3 H), 3.92 (s, 3 H),
1.56 (d, J ) 6.4 Hz, 3 H).
1-(2,3-Dimethoxyphenyl)-1-propanol.21 Yield: 1.425 g (90%) of
crude product, colorless liquid. 1H NMR (CDCl3, 400 MHz): δ (ppm)
) 7.04 (t, J ) 8.0 Hz, 1 H), 6.94 (dd, J ) 8.0, 1.5 Hz, 1 H), 6.83 (dd,
J ) 8.0, 1.5 Hz, 1 H), 4.84 (dd, J ) 7.4, 5.8 Hz, 1 H), 3.86 (2s, 3 H
each), 1.80 (m, 2 H), 0.95 (t, J ) 7.4 Hz, 3 H). 13C NMR (CDCl3, 100
MHz): δ (ppm) ) 152.2 (C), 146.2 (C), 137.7 (C), 123.9 (CH), 118.6
(CH), 111.2 (CH), 71.4 (CH), 60.8 (CH3), 55.6 (CH3), 31.1 (CH2), 10.4
(CH3).
1-(2,3-Dimethoxyphenyl)-1-butanol.21 Yield: 1.4 g (82%) of crude
1
product, colorless liquid. H NMR (CDCl3, 400 MHz): δ (ppm) )
7.03 (t, J ) 8.0 Hz, 1 H), 6.94 (dd, J ) 8.0, 1.6 Hz, 1 H), 6.83 (dd, J
) 8.0, 1.6 Hz, 1 H), 4.92 (dd, J ) 8.0, 5.5 Hz, 1 H), 3.86 (s, 3 H),
3.85 (s, 3 H), 1.77 (m, 1 H), 1.68 (m, 1 H), 1.47 (m, 1 H), 1.34 (m, 1
H), 0.93 (t, J ) 7.4 Hz, 3 H). 13C NMR (CDCl3, 100 MHz): δ (ppm)
) 152.2 (C), 145.9 (C), 138.1 (C), 123.9 (CH), 118.5 (CH), 111.1 (CH),
(37) For example, see: (a) Smith, H. E.; Russel, C. R.; Schniepp, L. E. J. Am.
Chem. Soc. 1951, 73, 793-795. (b) Kaufman, T. S. Tetrahedron Lett. 1996,
37, 5329-5332.
(38) Kurtz, P. A.; Dawson, C. R. J. Med. Chem. 1971, 14, 729-732.
(39) Brown, D. G.; Hughes, W. J. J. Z. Naturforsch., B: Chem. Sci. 1979, 34B,
1408-1412.
9
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Hierarchical Assembly of Helicates
A R T I C L E S
(CH2), 22.7 (CH2), 14.1 (CH3). IR (KBr): ν (cm-1) ) 2924, 2852,
1477, 1266, 1010, 757. MS (EI): m/z ) 308 [M+•], 167.
1H NMR (CDCl3, 300 MHz): δ (ppm) ) 7.11-7.01 (m, 3 H), 3. 90
(s, 3 H), 3.89 (s, 3 H), 2.96 (t, J ) 7.4 Hz, 2 H), 1.68 (m, 2 H), 1.38
(m, 2 H), 0.93 (t, J ) 7.4 Hz, 3 H). 13C NMR (CDCl3, 75 MHz): δ
(ppm) ) 204.0 (C), 153.0 (C), 147.8 (C), 134.6 (C), 124.1 (CH), 120.5
(CH), 115.2 (CH), 61.5 (CH3), 56.0 (CH3), 43.2 (CH2), 26.4 (CH2),
22.5 (CH2), 13.9 (CH3). IR (KBr): ν (cm-1) ) 2957, 1683, 1474, 1266,
1230, 1004, 751. MS (EI): m/z ) 222 [M+•], 165.
(2,3-Dimethoxyphenyl)pentyl Ketone.41 Yield: 390 mg (31%),
colorless oil by chromatography (dichloromethane). 1H NMR (CDCl3,
400 MHz): δ (ppm) ) 7.12-7.00 (m, 3 H), 3.88 (s, 6 H), 2.94 (t, J )
7.7 Hz, 2 H), 1.68 (m, 2 H), 1.33 (m, 4 H), 0.90 (m, 3 H). 13C NMR
(CDCl3, 100 MHz): δ (ppm) ) 203.6 (C), 152.7 (C), 147.6 (C), 134.4
(C), 123.9 (CH), 120.3 (CH), 115.0 (CH), 61.4 (CH3), 55.9 (CH3), 43.3
(CH2), 31.5 (CH2), 24.0 (CH2), 22.5 (CH2), 14.0 (CH3). IR (KBr): ν
(cm-1) ) 2936, 1684, 1472, 1264, 1005. MS (EI): m/z ) 236 [M+•],
165.
1-(2,3-Dimethoxyphenyl)-1-tridecanol.38 Yield: 1.5 g (56%) of
crude product as colorless liquid. 1H NMR (CDCl3, 300 MHz): δ (ppm)
) 7.04 (t, J ) 7.9 Hz, 1 H), 6.95 (dd, J ) 7.9, 1.6 Hz, 1 H), 6.83 (dd,
J ) 7.9, 1.6 Hz, 1 H), 4.91 (dd, J ) 7.7, 6.1 Hz, 1 H), 3.87 (s, 3 H),
3.86 (s, 3 H), 1.75 (m, 2 H), 1.25 (m, 20 H) 0.88 (t, J ) 6.9 Hz, 3 H).
13C NMR (CDCl3, 75.4 MHz): δ (ppm) ) 152.5 (C), 146.2 (C), 138.3
(C), 124.2 (CH), 118.7 (CH), 111.4 (CH), 70.2 (CH), 60.9 (CH3), 55.7
(CH3), 38.4 (CH2), 31.9 (CH2), 29.7 (4 CH2), 29.6 (2 CH2), 29.4 (CH2),
26.1 (CH2), 22.7 (CH2), 14.1 (CH3).
1-(2,3-Dimethoxyphenyl)-2-methyl-1-propanol. Yield: 0.3 g (18%)
1
after chromatography with CH2Cl2 on silica gel, colorless liquid. H
NMR (CDCl3, 300 MHz): δ (ppm) ) 7.05 (t, J ) 7.9 Hz, 1 H), 6.91
(dd, J ) 7.9, 1.5 Hz, 1 H), 6.84 (dd, J ) 7.9, 1.5 Hz, 1 H), 4.55 (d, J
) 7.7 Hz, 1 H), 3.87 (s, 6 H), 1.98 (m, 1 H), 1.06 (d, J ) 6.4 Hz, 3
H), 0.82 (d, J ) 6.9 Hz, 3 H). 13C NMR (CDCl3, 75.4 MHz): δ (ppm)
) 152.5 (C), 146.5 (C), 137.1 (C), 123.9 (CH), 119.7 (CH), 111.3 (CH),
76.0 (CH), 60.9 (CH3), 55.7 (CH3), 34.9 (CH), 19.6 (CH3), 18.5 (CH3).
IR (KBr): ν (cm-1) ) 3437.6, 2960.7, 2874.3, 1585.7, 1476.3, 1432.8,
1267.4, 1220.3, 1170.9, 1071.5, 1010.6, 754.6. MS (EI): m/z ) 210
[M+•], 167.
(2,3-Dimethoxyphenyl)phenylmethanol.40 Yield: 2.40 g (quant.)
of crude product, colorless oil. 1H NMR (CDCl3, 300 MHz): δ (ppm)
) 7.35 (m, 2 H), 7.28 (m, 2 H), 7.20 (m, 1 H), 7.02 (t, J ) 7.9 Hz, 1
H), 6.96 (dd, J ) 7.9, 1.5 Hz, 1 H), 6.82 (dd, J ) 7.9, 1.5 Hz, 1 H),
6.00 (s, 1 H), 3.79 (s, 3 H), 3.56 (s, 3 H).
(2,3-Dimethoxyphenyl)hexyl Ketone.41 Yield: 550 mg (28%) after
1
purification by chromatography (dichloromethane), colorless oil. H
NMR (CDCl3, 400 MHz): δ (ppm) ) 7.09 (m, 2 H), 7.02 (dd, J )
7.4, 2.4 Hz, 1 H), 3.88 (2 s, 3 H each), 2.94 (t, J ) 7.4 Hz, 2 H), 1.68
(m, 2 H), 1.30 (m, 6 H), 0.88 (t, J ) 6.8 Hz, 3 H). 13C NMR (CDCl3,
100 MHz): δ (ppm) ) 203.6 (C), 152.7 (C), 147.6 (C), 134.4 (C),
123.9 (CH), 120.3 (CH), 115.0 (CH), 61.4 (CH3), 55.9 (CH3), 43.4
(CH2), 31.6 (CH2), 29.0 (CH2), 24.3 (CH2), 22.5 (CH2), 14.0 (CH3).
IR (KBr): ν (cm-1) ) 2930, 1474, 1266, 1238, 1004. MS (EI): m/z )
250 [M+•], 180, 165.
(2,3-Dimethoxyphenyl)heptyl Ketone.41 Yield: 870 mg (49%) after
General Procedure for the Oxidation of the Alcohols. Jones
reagent (for 1 mmol of substrate): 100 mg of Na2Cr2O7 are dissolved
in 0.2 mL water, 136 mg of concentrated H2SO4 are added, and the
mixture is filled up with water to 0.5 mL. The alcohol (1 mmol) is
dissolved in acetone (15 mL), and at room temperature Jones reagent
is added slowly. The mixture is stirred at room temperature for 3 h
and filtered and 10 mL of water are added. Acetone is removed in
vacuo, and the residue is extracted with 10 mL of ether (3×). The
organic phase is dried over Na2SO4, and the solvent is removed. If
necessary, the crude product can be purified by column chromatography
on silica gel.
1
purification by chromatography (dichloromethane), colorless oil. H
NMR (CDCl3, 400 MHz): δ (ppm) ) 7.12-7.00 (m, 3 H), 3.88 (2 s,
3 H each), 2.94 (t, J ) 7.8 Hz, 2 H), 1.68 (m, 2 H), 1.30 (m, 8 H),
0.88 (t, J ) 6.9 Hz, 3 H). 13C NMR (CDCl3, 100 MHz): δ (ppm) )
203.6 (C), 152.7 (C), 147.6 (C), 134.4 (C), 123.9 (CH), 120.3 (CH),
115.0 (CH), 61.4 (CH3), 55.9 (CH3), 43.4 (CH2), 31.7 (CH2), 29.6 (CH2),
29.1 (CH2), 24.3 (CH2), 22.6 (CH2), 14.1 (CH3). IR (KBr): ν (cm-1
)
) 2927, 2856, 1684, 1472, 1265, 1005. MS (EI): m/z ) 264 [M+•],
180, 165.
(2,3-Dimethoxyphenyl)octyl Ketone. Yield: 1.01 g (61%) after
1
purification by chromatography (dichloromethane), colorless oil. H
(2,3-Dimethoxyphenyl)methyl Ketone.37,41 Yield: 405 mg (75%)
NMR (CDCl3, 400 MHz): δ (ppm) ) 7.12-7.00 (m, 3 H), 3.89 (s, 3
H), 3.88 (s, 3 H), 2.94 (t, J ) 7.5 Hz, 2 H), 1.68 (m, 2 H), 1.29 (m, 10
H), 0.87 (m, 3 H). 13C NMR (CDCl3, 100 MHz): δ (ppm) ) 203.6
(C), 152.7 (C), 147.6 (C), 134.4 (C), 123.9 (CH), 120.4 (CH), 115.0
(CH), 61.4 (CH3), 55.9 (CH3), 43.4 (CH2), 31.9 (CH2), 29.6 (CH2),
29.4 (CH2), 29.1 (CH2), 24.3 (CH2), 22.6 (CH2), 14.1 (CH3). IR
(KBr): ν (cm-1) ) 2926, 2855, 1684, 1471, 1264. MS (EI): m/z )
278 [M+•], 180, 165.
1
of a yellow solid. H NMR (CDCl3, 300 MHz): δ (ppm) ) 7.12 (t, J
) 7.8 Hz, 1 H), 7.08 (dd, J ) 7.8, 1.8 Hz, 1 H), 6.89 (dd, J ) 7.8, 1.8
Hz, 1 H), 4.03 (s, 3 H), 3.79 (s, 3 H), 1.60 (s, 3 H).
(2,3-Dimethoxyphenyl)ethyl Ketone.21 Yield: 120 mg (8.5%) and
0.47 g of crude product, which is purified by chromatography (ethyl
1
acetate/hexane 1:10), colorless oil. H NMR (CDCl3, 400 MHz): δ
(ppm) ) 7.14 (dd, J ) 7.7, 1.6 Hz, 1 H), 7.08 (t, J ) 7.7 Hz, 1 H),
7.02 (dd, J ) 7.7, 1.6 Hz, 1 H), 3.89 (s, 3 H), 3.88 (s, 3 H), 2.98 (q,
J ) 7.1 Hz, 2 H), 1.18 (t, J ) 7.1 Hz, 3 H). 13C NMR (CDCl3, 100
MHz): δ (ppm) ) 203.7 (C), 152.8 (C), 147.7 (C), 134.0 (C), 123.9
(CH), 120.4 (CH), 115.1 (CH), 61.4 (CH3), 55.9 (CH3), 36.5 (CH2),
8.4 (CH3). IR (KBr): ν (cm-1) ) 2975, 1938, 1686, 1580, 1474, 1427,
1308, 1266, 1239, 1004, 781. MS (EI): m/z ) 194 [M+•], 165.
(2,3-Dimethoxyphenyl)propyl Ketone.21 Yield: 0.9 g (65%) by
chromatography (dichloromethane), colorless oil. 1H NMR (CDCl3, 400
MHz): δ (ppm) ) 7.12-7.01 (m, 3 H), 3.88 (s, 6 H), 2.93 (t, J ) 7.4
(2,3-Dimethoxyphenyl)decyl Ketone. Yield: 1.0 g (40%) after
1
purification by chromatography (dichloromethane), colorless oil. H
NMR (CDCl3, 400 MHz): δ (ppm) ) 7.12-7.00 (m, 3 H), 3.89 (s, 3
H), 3.88 (s, 3 H), 2.94 (t, J ) 7.1 Hz, 2 H), 1.68 (m, 2 H), 1.29 (m, 14
H), 0.88 (t, J ) 7.1 Hz, 3 H). 13C NMR (CDCl3, 100 MHz): δ (ppm)
) 203.6 (C), 152.7 (C), 147.6 (C), 134.4 (C), 123.9 (CH), 120.3 (CH),
115.0 (CH), 61.4 (CH3), 55.9 (CH3), 43.4 (CH2), 31.9 (CH2), 29.6 (CH2),
29.5 (2 × CH2), 29.4 (CH2), 29.1 (CH2), 24.3 (CH2), 22.7 (CH2), 14.1
(CH3). IR (KBr): ν (cm-1) ) 2926, 2853, 1683, 1473, 1266, 1234,
1006. MS (EI): m/z ) 306 [M+•], 180, 165.
(2,3-Dimethoxyphenyl)dodecyl Ketone. Yield: 0.8 mg (53%) after
purification by chromatography (ethyl acetate/hexane 1:10), colorless
oil. 1H NMR (CDCl3, 300 MHz): δ (ppm) ) 7.09 (m, 2 H), 7.03 (dd,
J ) 6.9, 3.0 Hz, 1 H), 3.90 (s, 3 H), 3.89 (s, 3 H), 2.95 (t, J ) 7.2 Hz,
2 H), 1.68 (m, 2 H), 1.26 (m, 18 H), 0.89 (t, J ) 6.9 Hz, 3 H). 13C
NMR (CDCl3, 100 MHz): δ (ppm) ) 204.0 (C), 152.6 (C), 147.8 (C),
134.6 (C), 124.1 (CH), 120.5 (CH), 115.2 (CH), 61.6 (CH3), 56.0 (CH3),
43.5 (CH2), 31.9 (CH2), 29.7 (CH2), 29.6 (2 CH2), 29.5 (2 CH2), 29.3
(2 CH2), 24.3 (CH2), 22.7 (CH2), 14.1 (CH3). IR (KBr): ν (cm-1) )
Hz, 2 H), 1.71 (sextet, J ) 7.4 Hz, 2 H), 0.96 (t, J ) 7.4 Hz, 3 H). 13
C
NMR (CDCl3, 100 MHz): δ (ppm) ) 203.4 (C), 152.8 (C), 147.6 (C),
134.3 (C), 123.9 (CH), 120.3 (CH), 115.1 (CH), 61.4 (CH3), 55.9 (CH3),
45.3 (CH2), 17.7 (CH2), 13.8 (CH3). IR (KBr): ν (cm-1) ) 2963, 1683,
1473, 1267, 1234, 1007. MS (EI): m/z ) 208 [M+•], 165.
(2,3-Dimethoxyphenyl)butyl Ketone.42 Yield: 350 mg (23%),
colorless oil. The product was not pure after chromatography (dichlo-
romethane). The crude product was then overoxidized, and the product
could be isolated by filtration of the mixture and removal of solvent.
(40) Boehme, W. R.; Scharpf, W. G. J. Org. Chem. 1961, 26, 1692-1695.
9
J. AM. CHEM. SOC. VOL. 127, NO. 29, 2005 10383

A R T I C L E S
Albrecht et al.
2925, 2853, 1683, 1472, 1265, 1234, 1006, 751. MS (EI): m/z ) 334
26.6 (CH2), 22.4 (CH2), 13.9 (CH3). IR (KBr): ν (cm-1) ) 3355, 2958,
1634, 1383, 1279, 1057, 730. MS (EI): m/z ) 194 [M+•], 137.
[M+•], 180, 165.
2,3-Dimethoxyphenyl)isopropyl Ketone. Yield: 270 mg (60%)
after purification by chromatography (dichloromethane), colorless oil.
1H NMR (CDCl3, 300 MHz): δ (ppm) ) 7.10-6.95 (m, 3 H), 3.89 (s,
3 H), 3.86 (s, 3 H), 3.36 (sept., J ) 7.9 Hz, 1 H), 1.16 (d, J ) 7.9 Hz,
6 H). 13C NMR (CDCl3, 75.4 MHz): δ (ppm) ) 208.6 (C), 152.8 (C),
147.1 (C), 134.8 (C), 124.2 (CH), 120.3 (CH), 114.7 (CH), 61.7 (CH3),
56.0 (CH3), 40.3 (CH), 18.5 (CH3). IR (KBr): ν (cm-1) ) 2970, 1691,
1471, 1263, 1002, 754. MS (EI): m/z ) 208 [M+•], 165.
(2,3-Dihydroxyphenyl)pentyl Ketone (5e-H2). Yield: 300 mg
(87%), brown solid. Mp ) 52 °C. H NMR (CDCl3, 400 MHz): δ
1
(ppm) ) 12.63 (s, OH), 7.32 (dd, J ) 8.2, 1.4 Hz, 1 H), 7.12 (dd, J )
8.2, 1.4 Hz, 1 H), 6.81 (t, J ) 8.2 Hz, 1 H), 5.74 (br., OH), 2.98 (t, J
) 7.3 Hz, 2 H), 1.75 (m, 2 H), 1.38 (m, 4 H), 0.92 (t, J ) 7.2 Hz, 3
H). 13C NMR (CDCl3, 100 MHz): δ (ppm) ) 207.2 (C), 149.4 (C),
145.3 (C), 120.5 (CH), 119.8 (CH), 119.0 (C), 118.7 (CH), 38.4 (CH2),
31.4 (CH2), 24.2 (CH2), 22.4 (CH2), 13.9 (CH3). IR (KBr): ν (cm-1
)
2,3-Dimethoxybenzophenone.43 Yield: 1.5 g (63%), colorless oil.
1H NMR (CDCl3, 400 MHz): δ (ppm) ) 7.83 (m, 2 H), 7.55 (m, 1
H), 7.43 (m, 2 H), 7.12 (t, J ) 7.7 Hz, 1 H), 7.05 (dd, J ) 7.7, 1.6 Hz,
) 3359, 2934, 2683, 1635, 1456, 1383, 1276, 1059. MS (EI): m/z )
208 [M+•], 137. Anal. Calcd for C12H16O3‚1/4H2O: C, 67.74; H, 7.82.
Found: C, 67.85; H, 8.12.
1 H), 6.92 (dd, J ) 7.7, 1.6 Hz, 1 H), 3.90 (s, 3 H), 3.71 (s, 3 H). 13
C
(2,3-Dihydroxyphenyl)hexyl Ketone (5f-H2). Yield: 300 mg (70%),
1
NMR (CDCl3, 100 MHz): δ (ppm) ) 196.0 (C), 152.5 (C), 146.7 (C),
brown solid. Mp ) 46 °C. H NMR (CDCl3, 300 MHz): δ (ppm) )
137.3 (C), 134.0 (C), 133.0 (CH), 129.7 (CH), 128.1 (CH), 123.8 (CH),
12.63 (s, OH), 7.32 (dd, J ) 8.1, 1.5 Hz, 1 H), 7.12 (dd, J ) 8.1, 1.5
Hz, 1 H), 6.81 (t, J ) 8.1 Hz, 1 H), 5.72 (br., OH), 2.98 (t, J ) 7.2 Hz,
2 H), 1.74 (m, 2 H), 1.34 (m, 6 H), 0.90 (t, J ) 7.0 Hz, 3 H). 13C
NMR (CDCl3, 75 MHz): δ (ppm) ) 207.5 (C), 149.7 (C), 145.6 (C),
120.7 (CH), 120.1 (CH), 119.2 (C), 118.9 (CH), 38.5 (CH2), 31.6 (CH2),
120.3 (CH), 114.1 (CH), 61.5 (CH3), 55.8 (CH3). IR (KBr): ν (cm-1
)
) 2938, 1669, 1474, 1316, 1270, 712. MS (EI): m/z ) 242 [M+•],
165, 151.
General Procedure for the Deprotection of the Methyl Ethers.
At 0 °C, BBr3 (6 mmol) is added to the dimethoxyphenyl derivative
(1 mmol) in 20 mL of dichloromethane. The mixture is stirred overnight
at room temperature. Methanol is then added to the mixture at 0 °C.
The solvent is removed in vacuo, and the residue is dissolved in ethyl
acetate, washed with water, and dried with Na2SO4. The solvent is
evaporated in vacuo again.
29.0 (CH2), 24.5 (CH2), 22.5 (CH2), 14.0 (CH3). IR (KBr): ν (cm-1
)
) 3352, 2956, 2926, 1635, 1456, 1272, 1234, 728. MS (EI): m/z )
222 [M+•], 137. Anal. Calcd for C13H18O3: C, 70.24; H, 8.16. Found:
C, 69.66; H, 8.30.
(2,3-Dihydroxyphenyl)heptyl Ketone (5g-H2). Yield: 320 mg
1
(71%), brown solid. Mp ) 47 °C. H NMR (CDCl3, 300 MHz): δ
(2,3-Dihydroxyphenyl)methyl Ketone (5a-H2).44 Yield: 228 mg
(ppm) ) 12.63 (s, OH), 7.31 (dd, J ) 8.2, 1.5 Hz, 1 H), 7.12 (dd, J )
8.2, 1.5 Hz, 1 H), 6.81 (t, J ) 8.2 Hz, 1 H), 5.76 (br., OH), 2.98 (t, J
1
(quant.), green solid. Mp ) 141 °C. H NMR (DMSO-d6, 400 MHz):
) 7.6 Hz, 2 H), 1.74 (m, 2 H), 1.40-1.26 (m, 8 H), 0.89 (m, 3 H). 13
C
δ (ppm) ) 12.01 (s, 1 H), 9.40 (s, 1 H), 7.35 (dd, J ) 8.0, 1.7 Hz, 1
H), 7.05 (dd, J ) 8.0, 1.7 Hz, 1 H), 6.77 (t, J ) 8.0 Hz, 1 H), 2.62 (s,
3 H). IR (KBr): ν (cm-1) ) 3280, 1634, 1584, 1472, 1434, 1387, 1320,
1255, 1178, 1085, 1026, 897, 826, 790, 738, 677, 617. Anal. Calcd for
C8H8O3: C, 63.16; H, 5.30. Found: C, 62.99; H, 5.44.
NMR (CDCl3, 75 MHz): δ (ppm) ) 207.5 (C), 149.7 (C), 145.6 (C),
120.7 (CH), 120.0 (CH), 119.2 (C), 118.9 (CH), 38.5 (CH2), 31.7 (CH2),
29.3 (CH2), 29.1 (CH2), 24.5 (CH2), 22.6 (CH2), 14.1 (CH3). IR
(KBr): ν (cm-1) ) 3360, 2923, 1624, 1457, 1232, 895, 727. MS (EI):
m/z ) 236 [M+•], 137. Anal. Calcd for C14H20O3‚1/4 H2O: C, 69.83;
H, 8.58. Found: C, 70.08; H, 8.80.
(2,3-Dihydroxyphenyl)ethyl Ketone (5b-H2).21 Yield: 80 mg
1
(78%), brown solid. Mp ) 56 °C. H NMR (CDCl3, 300 MHz): δ
(ppm) ) 12.58 (s, OH), 7.32 (dd, J ) 8.1, 1.5 Hz, 1 H), 7.12 (dd, J )
8.1, 1.5 Hz, 1 H), 6.82 (t, J ) 8.1 Hz, 1 H), 5.77 (br., OH), 3.05 (q, J
) 7.1 Hz, 2 H), 1.25 (t, J ) 7.1 Hz, 3 H). 13C NMR (CDCl3, 75.4
MHz): δ (ppm) ) 207.7 (C), 149.5 (C), 145.5 (C), 120.6 (CH), 120.1
(2,3-Dihydroxyphenyl)octyl Ketone (5h-H2). Yield: 500 mg (80%),
brown solid. Mp ) 41 °C. H NMR (CDCl3, 300 MHz): δ (ppm) )
1
12.64 (s, OH), 7.32 (m, 1 H), 7.12 (m, 1 H), 6.82 (m, 1 H), 5.75 (br.,
OH), 2.99 (t, J ) 7.2 Hz, 2 H), 1.75 (m, 2 H), 1.38-1.25 (m, 10 H),
0.89 (m, 3 H). 13C NMR (CDCl3, 75 MHz): δ (ppm) ) 207.5 (C),
149.7 (C), 145.5 (C), 120.7 (CH), 120.0 (CH), 119.2 (C), 118.9 (CH),
38.5 (CH2), 31.9 (CH2), 29.7 (CH2), 29.4 (CH2), 29.1 (CH2), 24.5 (CH2),
22.7 (CH2), 14.1 (CH3). IR (KBr): ν (cm-1) ) 2924, 2855, 1637, 1458,
1277. MS (EI): m/z ) 250 [M+•], 137. Anal. Calcd for C14H20O3: C,
71.97; H, 8.86. Found: C, 73.42; H, 8.85.
(CH), 119.1 (C), 118.9 (CH), 31.7 (CH2), 8.2 (CH3). IR (KBr): ν (cm-1
)
) 3489, 1637, 1454, 1268, 729. MS (EI): m/z ) 166 [M+•], 137. Anal.
Calcd for C9H10O3: C, 65.05; H, 6.07. Found: C, 65.34; H, 6.43.
(2,3-Dihydroxyphenyl)propyl Ketone (5c-H2).21 Yield: 500 mg
1
(91%), brown solid. Mp ) 59 °C. H NMR (CDCl3, 400 MHz): δ
(ppm) ) 12.63 (s, OH), 7.32 (dd, J ) 8.2, 1.4 Hz, 1 H), 7.12 (dd, J )
8.2, 1.4 Hz, 1 H), 6.81 (t, J ) 8.2 Hz, 1 H), 5.75 (br., OH), 2.97 (t, J
) 7.2 Hz, 2 H), 1.79 (sextet, J ) 7.2 Hz, 2 H), 1.02 (t, J ) 7.2 Hz, 3
H). 13C NMR (CDCl3, 100 MHz): δ (ppm) ) 207.0 (C), 149.4 (C),
145.3 (C), 120.5 (CH), 119.9 (CH), 118.8 (C), 118.7 (CH), 40.3 (CH2),
17.9 (CH2), 13.8 (CH3). IR (KBr): ν (cm-1) ) 3477, 1641, 1453, 1261,
1206, 830, 745, 570. MS (EI): m/z ) 180 [M+•], 137. Anal. Calcd for
C10H12O3: C, 66.65; H, 6.71. Found: C, 65.96; H, 7.20.
(2,3-Dihydroxyphenyl)decyl Ketone (5i-H2). Yield: 625 mg (86%),
1
brown solid. Mp ) 52 °C. H NMR (CDCl3, 400 MHz): δ (ppm) )
12.63 (s, OH), 7.32 (dd, J ) 8.2, 1.4 Hz, 1 H), 7.11 (m, 1 H), 6.81 (t,
J ) 8.2 Hz, 1 H), 5.74 (br., OH), 2.98 (t, J ) 7.4 Hz, 2 H), 1.74 (m,
2 H), 1.41-1.25 (m, 14 H), 0.88 (t, J ) 7.1 Hz, 3 H). 13C NMR (CDCl3,
100 MHz): δ (ppm) ) 207.2 (C), 149.4 (C), 145.3 (C), 120.5 (CH),
119.8 (CH), 119.0 (C), 118.7 (CH), 38.4 (CH2), 31.8 (CH2), 29.7 (CH2),
29.5 (CH2), 29.4 (2 × CH2), 29.3 (CH2), 24.5 (CH2), 22.7 (CH2), 14.1
(CH3). IR (KBr): ν (cm-1) ) 3355, 2920, 2850, 1635, 1456, 728. MS
(EI): m/z ) 278 [M+•], 137. Anal. Calcd for C17H26O3: C, 73.35; H,
9.41. Found: C, 72.75; H, 8.71.
(2,3-Dihydroxyphenyl)butyl Ketone (5d-H2). Yield: 200 mg
1
(68%), brown solid. Mp ) 50 °C. H NMR (CDCl3, 400 MHz): δ
(ppm) ) 12.63 (s, OH), 7.32 (dd, J ) 8.2, 1.4 Hz, 1 H), 7.12 (dd, J )
8.2, 1.4 Hz, 1 H), 6.81 (t, J ) 8.2 Hz, 1 H), 5.75 (br., OH), 2.99 (t, J
) 7.7 Hz, 2 H), 1.73 (m, 2 H), 1.42 (m, 2 H), 0.97 (t, J ) 7.4 Hz, 3
H). 13C NMR (CDCl3, 100 MHz): δ (ppm) ) 207.2 (C), 149.4 (C),
145.3 (C), 120.5 (CH), 119.9 (CH), 119.0 (C), 118.7 (CH), 38.1 (CH2),
(2,3-Dihydroxyphenyl)dodecyl Ketone (5j-H2). Yield: 560 mg
1
(79%), brown solid. Mp ) 60 °C. H NMR (CDCl3, 400 MHz): δ
(ppm) ) 12.63 (s, OH), 7.32 (dd, J ) 8.2, 1.4 Hz, 1 H), 7.12 (dd, J )
8.2, 1.4 Hz, 1 H), 6.81 (t, J ) 8.2 Hz, 1 H), 5.72 (br., OH), 2.98 (t, J
) 7.4 Hz, 2 H), 1.74 (m, 2 H), 1.26 (m, 18 H), 0.88 (t, J ) 7.1 Hz, 3
H). 1H NMR (methanol-d4, 300 MHz): δ (ppm) ) 7.38 (dd, J ) 8.1,
1.5 Hz, 1 H), 7.02 (dd, J ) 8.1, 1.5 Hz, 1 H), 6.78 (t, J ) 8.2 Hz, 1
H), 3.02 (t, J ) 7.4 Hz, 2 H), 1.72 (m, 2 H), 1.29 (m, 18 H), 0.89 (t,
J ) 7.1 Hz, 3 H). IR (KBr): ν (cm-1) ) 2918, 2850, 1635, 1456,
(41) Tsatsas, G.; Guioka-Dedopoulou, V. Bull. Chim. Soc. Fr. 1964, 2610-
2612.
(42) Schildknecht, H.; Schmidt, H. Z. Naturforsch., B: Chem. Sci. 1967, 22B,
287-294.
(43) Richtzenhain, H.; Nippus, P. Chem. Ber. 1949, 82, 408-417.
(44) Ghosh, S. K.; Bose, R. N.; Gould, E. S. Inorg. Chem. 1988, 27, 1620-
1625.
9
10384 J. AM. CHEM. SOC. VOL. 127, NO. 29, 2005

Hierarchical Assembly of Helicates
A R T I C L E S
1276, 1239, 728. MS (EI): m/z ) 306 [M+•], 288, 189, 165, 152, 137.
Anal. Calcd for C19H30O3: C, 74.47; H, 9.87. Found: C, 74.36; H,
9.94.
Li3[Ga(4)3]/Li6[Ga2(4)6]. 1H NMR (DMSO-d6, 300 MHz): monomer
(major component) δ (ppm) ) 10.06 (s, 3 H), 6.49 (dd, J ) 8.2, 1.7
Hz, 3 H), 6.35-6.27 (m, 6 H); dimer (minor component) δ (ppm) )
8.53 (s, 6 H), 6.35-6.27 (m, 12 H), 6.12 (t, J ) 7.7 Hz, 3 H). 13C
NMR (DMSO-d6, 75 MHz, only monomer is observed): δ (ppm) )
191.3 (CH), 159.2 (C), 157.3 (C), 120.3 (C), 118.4 (CH), 115.3 (CH),
114.9 (CH). IR (KBr): ν (cm-1) ) 3412, 1658, 1588, 1545, 1446,
1412, 1255, 789, 659, 532. Anal. Calcd for (C42H24Li6O18Ga)‚2C3H7-
NO‚4 H2O: C, 47.41; H, 3.81; N, 2.30. Found: C, 47.52; H, 3.98; N,
2.49. Negative ESI FTICR-MS (THF): m/z ) 492 [Li4(4)6Ga2]2-, 326
(2,3-Dihydroxyphenyl)isopropyl Ketone (6a-H2). Yield: 80 mg
(62%), brown wax. 1H NMR (CDCl3, 300 MHz): δ (ppm) ) 12.77 (s,
OH), 7.34 (dd, J ) 8.2, 1.5 Hz, 1 H), 7.13 (dd, J ) 8.2, 1.5 Hz, 1 H),
6.82 (t, J ) 8.2 Hz, 1 H), 5.80 (br., OH), 3.58 (sept., J ) 7.1 Hz, 1 H),
1.25 (d, J ) 7.1 Hz, 6 H). 13C NMR (CDCl3, 75.4 MHz): δ (ppm) )
211.3 (C), 150.3 (C), 145.7 (C), 120.6 (CH), 120.0 (CH), 118.8 (CH),
118.0 (C), 35.2 (CH), 19.2 (CH3). IR (KBr): ν (cm-1) ) 2976, 1637,
1452, 1269, 755. MS (EI): m/z ) 181 [MH+], 180 [M+•], 137.
2,3-Dihydroxybenzophenone (6b-H2).45 Yield: 880 mg (quant). 1H
NMR (CDCl3, 300 MHz): δ (ppm) ) 12.23 (s, OH), 7.71 (m, 2 H),
7.59 (m, 1 H), 7.51 (m, 2 H), 7.16 (m, 2 H), 7.13 (dd, J ) 8.2, 1.5 Hz,
1 H), 6.80 (t, J ) 7.9 Hz, 1 H), 5.82 (br., OH). - 13C NMR (CDCl3,
75.4 MHz,): δ (ppm) ) 201.8 (C), 150.2 (C), 145.6 (C), 137.7 (C),
132.1 (CH), 129.2 (CH), 128.3 (CH), 124.5 (CH), 120.4 (CH), 119.0
(C), 118.7 (CH). IR (KBr): ν (cm-1) ) 3383, 1623, 1449, 1326, 1260,
730. MS (EI): m/z ) 215 [MH+], 214 [M+•], 136. Anal. Calcd for
C13H10O3‚1/4H2O: C, 71.39; H, 4.84. Found: C, 71.63; H, 5.14.
2,3-Dihydroxybenzoicacid Methylester (7a-H2). 7a-H2 was pre-
pared as described in the literature.22
2,3-Dihydroxybenzoicacid Ethylester (7b-H2).46 2,3-Dihydroxy-
benzoicacid (0.01 mol) and SOCl2 (15 mL) are dissolved in CHCl3
(50 mL). The mixture is refluxed under N2 overnight. The solvent is
removed, and the residue is dissolved in CH2Cl2 and under ice cooling
slowly is added to a mixture of ethanol and CH2Cl2. After stirring
overnight and removal of the solvent, the ester is obtained in 68% yield.
Mp ) 64 °C. 1H NMR (300 MHz, CDCl3): δ (ppm) ) 11.01 (s, 1 H),
7.39 (dd, J ) 1.5, 7.8 Hz, 1 H), 7.11 (dd, J ) 1.5, 7.8 Hz, 1 H), 6.80
(t, J ) 7.8 Hz, 1 H), 5.70 (s, 1 H), 4.43 (q, J ) 7.2 Hz, 2 H), 1.43 (t,
J ) 7.2 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ (ppm) ) 170.5
(C), 149.0 (C), 144.9 (C), 120.6 (CH), 119.7 (CH), 119.1 (CH), 112.4
(C), 61.6 (CH2), 14.2 (CH2). IR (KBr): ν (cm-1) ) 3476, 1674, 1465,
1312, 1271, 1154, 759. MS (EI): m/z ) 182 [M+•], 136.
[Li3(4)6Ga2]3-
.
Li2[(5a)3Ti]/Li4[(5a)6Ti2]. 1H NMR (400 MHz, methanol-d4): mono-
mer (minor component) δ (ppm) ) 6.99 (m, 3 H), 6.45 (m, 6 H), 2.61
(s, 9 H); dimer (major component) δ (ppm) ) 7.10 (m, 6 H), 6.56 (m,
12 H), 1.87 (s, 18 H). IR (drift, KBr): ν (cm-1) ) 3429, 1654, 1592,
1430, 1294, 1255, 1217, 910, 844, 717, 534. Anal. Calcd for C48H36-
Li4O18Ti2‚4 C3H7NO‚9 H2O: C, 48.73; H, 5.59; N, 3.79. Found: C,
48.43; H, 5.19; N, 3.64. Negative ESI FTICR-MS (THF): m/z ) 1017
[Li3(5a)6Ti2]-, 505 [Li(5a)3Ti]-.
Li3[(5a)3Ga]/Li6[(5a)6Ga2]. 1H NMR (DMSO-d6, 400 MHz): mono-
mer (minor component) δ (ppm) ) 6.80-6.70 (m, 3 H), 6.53-6.44
(m, 3H), 6.22-6.19 (m, 3 H), 2.60 (br, 3 H); dimer (major component)
δ (ppm) ) 6.59 (d, J ) 8.0 Hz, 6 H), 6.30 (d, J ) 8.0 Hz, 6 H), 6.14
(t, J ) 8.0 Hz, 6H), 1.74 (s, 18 H). IR (KBr): ν (cm-1) ) 3456, 1651,
1592, 1552, 1439, 1305, 1269, 1220, 906, 734, 705. Anal. Calcd for
C48H36Li6O18Ga2‚3 C3H7NO‚9 H2O: C, 46.79; H, 5.17; N, 2.87.
Found: C, 46.51; H, 4.77; N, 2.90. Negative ESI FTICR-MS (THF):
m/z ) 534 [Li4(4)6Ga2]2-, 354 [Li3(4)6Ga2]3-
.
Li2[(5b)3Ti]/Li4[(5b)6Ti2]. 1H NMR (methanol-d4, 400 MHz): mono-
mer (minor component) δ (ppm) ) 6.96 (dd, J ) 7.3, 2.8 Hz, 3 H),
6.46 (m, 6 H), 3.11 (q, J ) 7.4 Hz, 6 H), 1.05 (t, J ) 7.4 Hz, 9 H);
dimer (major component) δ (ppm) ) 7.10 (dd, J ) 6.1, 3.8 Hz, 6 H),
6.56 (m, 12 H), 2.72 (m, 6 H), 2.12 (m, 6 H), 0.47 (t, J ) 7.2 Hz, 18
H). Negative ESI FTICR-MS (THF): m/z ) 1117 [NaLi2(L)6Ti2]-,
1101 [Li3(L)6Ti2]-, 547 [Li(L)3Ti]-. IR (KBr): ν (cm-1) ) 3447, 2930,
1655, 1432, 1259, 1216, 885, 738. - Calcd. for C27H24O9TiLi2‚9 H2O:
C 45.27, H 5.91; found: C 44.83, H 5.49. Negative ESI FTICR-MS
(THF): m/z ) 1117 [NaLi2(5b)6Ti2]-, 1101 [Li3(5b)6Ti2]-, 547
[Li(5b)3Ti]-.
General Procedure for the Preparation of Metal Complexes. 2,3-
Dihydroxyaryl ketone (1 equiv, approx 0.7 mmol), titanyl bis-
(acetylacetonate) (1 equiv), and lithium carbonate (1 equiv) are
dissolved in DMF (30 mL), and the solution is stirred overnight. The
solvent is removed, and the residue is dried in vacuo. The complexes
are obtained in quantitative yield as a red solid. Yellow gallium
complexes were analogously prepared from Ga(acac)3 in the presence
of 1.5 equiv of Li2CO3.
X-ray Crystallographic Study of Li4[(5b)6Ti2]: The data set was
collected on an Enraf-Nonius CAD4 diffractometer employing graphite-
monochromated Cu KR radiation (λ ) 1.541 79 Å). The structure has
been solved by direct methods as implemented in the Xtal3.7 suite of
crystallographic routines 49 where GENSIN has been used to generate
the structure-invariant relationships and CRISP for the tangent phasing
procedure.
1
Li2[Ti(4)3]/Li4[Ti2(4)6]. H NMR (CD3OD, 300 MHz): monomer
(major component) δ (ppm) ) 10.20 (s, 3H), 6.97 (dd, J ) 6.4, 2.5
Hz, 3 H), 6.59-6.51 (m, 6 H); dimer (minor component) δ (ppm) )
8.74 (s, 6 H), 6.89 (dd, J ) 7.7, 1.4 Hz, 6 H), 6.77 (t, J ) 7.7 Hz, 6
H), 6.59-6.51 (m, 6 H). 13C NMR (DMSO-d6, 75 MHz): only
monomer δ (ppm) ) 162.8 (CH), 161.3 (C), 153.3 (C), 118.8 (C),
116.9 (CH), 114.0 (CH), 113.1 (CH). IR (KBr): ν (cm-1) ) 1663,
1592, 1550, 1449, 1406, 1253, 1206, 747, 668, 592, 528. Anal. Calcd
for C21H12Li2O9Ti‚2 C3H7NO‚2 H2O: C, 49.71; H, 4.64; N, 4.29.
Found: C, 50.02; H, 4.44; N, 4.45. Negative ESI FTICR-MS (THF):
m/z ) 933 [Li3(4)6Ti2]-, 463 [Li(4)3Ti]-, 457 [H(4)3Ti]-.
X-ray Crystallographic Study of Li4[Ti2(4)6]: The data set was
collected with a Nonius KappaCCD diffractometer, equipped with a
rotating anode generator. Programs used: data collection COLLECT
(Nonius B. V., 1998), data reduction Denzo-SMN,47 structure solution
SHELXS-97,48 structure refinement SHELXL-97 (G. M. Sheldrick,
Universita¨t Go¨ttingen, 1997), graphics SCHAKAL (E. Keller, Univer-
sita¨t Freiburg, 1997)(Table 3).
Li2[(5c)3Ti]/Li4[(5c)6Ti2]. 1H NMR (methanol-d4, 400 MHz): mono-
mer (minor component) δ (ppm) ) 6.98 (dd, J ) 8.0, 2.2 Hz, 3 H),
6.48 (dd, J ) 8.0, 2.2 Hz, 3 H), 6.44 (t, J ) 8.0 Hz, 3 H), 3.06 (t, J )
7.4 Hz, 6 H), 1.59 (sextet, J ) 7.4 Hz, 6 H), 0.85 (t, J ) 7.4 Hz, 9 H);
dimer (major component) δ (ppm) ) 7.11 (dd, J ) 6.3, 3.6 Hz, 6 H),
6.58 (m, 12 H), 2.68 (m, 6 H), 1.96 (m, 6 H), 1.10 (m, 6 H), 0.98 (m,
6 H), 0.63 (t, J ) 7.7 Hz, 18 H). 13C NMR (methanol-d4, 100 MHz,
only dimer is observed): dimer δ (ppm) ) 201.3 (C), 159.9 (C), 159.4
(C), 120.9 (CH), 120.2 (C), 117.2 (CH), 115.9 (CH), 40.5 (CH2), 17.3
(CH2), 12.6 (CH3). IR (KBr): ν (cm-1) ) 3427, 2960, 1656, 1429,
1258, 1214, 536. Negative ESI FTICR-MS (THF): m/z ) 1185
[Li3(5c)6Ti2]-, 589 [Li(5c)3Ti]-. Anal. Calcd for C27H24O9TiLi2‚2DMF‚
H2O: C, 56.85; H, 6.10; N, 3.68. Found: C, 56.17; H, 5.86; N, 3.98.
Li2[(5d)3Ti]/Li4[(5d)6Ti2]. 1H NMR (methanol-d4, 300 MHz): mono-
mer (minor component) δ (ppm) ) 6.91 (dd, J ) 7.4, 2.0 Hz, 3 H),
6.38 (m, 6 H), 3.00 (t, J ) 6.9 Hz, 6 H), 1.45 (m, 6 H); dimer (major
component) δ (ppm) ) 7.02 (m, 6 H), 6.50 (m, 12 H), 2.64 (m, 6 H),
(45) Perez, H. I.; Luna, H.; Manjarrez, N.; Solis, A.; Nunez, M. A. Tetrahe-
dron: Asymmetry 2000, 11, 4263-4268.
(46) Wenkwert, E.; Greenberg, R. S.; Kim, H. S. HelV. Chim. Acta 1987, 70,
2159.
(47) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307-326.
(48) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467-473.
(49) Xtal3.7 System; Hall, S. R., du Boulay, D. J., Olthof-Hazekamp, R., Eds.;
University of Western Australia: 2000.
9
J. AM. CHEM. SOC. VOL. 127, NO. 29, 2005 10385

A R T I C L E S
Albrecht et al.
Table 3. Crystallographic Data for Li[Li3(4)6Ti2], Li[Li3(5b)6Ti2], and Li[Li3(7a)6Ti2]
compound
Li[Li3(4)6Ti2]
Li[Li3(5b)6Ti2]
Li[Li3(7a)6Ti2]
formula
Li(C3H7NO)4-
Li3[(C7H4O3)6Ti2]
1232.56
Li(C3H7NO)4-
Li(C3H7NO)2(H2O)-
Li3[(C7H4O3)6Ti2]‚2 C3H7NO
1430.72
Li3[(C9H8O3)6Ti2]‚2 C3H7NO
1547.05
150
fw
T (K)
198(2)
198(2)
wavelength (Å)
crystal system
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
0.710 73
monoclinic
P21/c
16.943(1)
23.962(1)
14.483(1)
90
97.16(1)
90
5834.1(6)
4
1.403
0.355
2544
0.50 × 0.20 × 0.20
1.65-25.00
18 701
1.541 79
monoclinic
Cc
17.845(2)
23.754(7)
18.033(2)
90
96.43(1)
90
7596(3)
4
1.353
2.459
3248
0.4 × 0.4 × 0.4
3.11-73.07
7589
7000
0.083
0.710 73
monoclinic
P21/c
14.530(1)
21.692(1)
22.298(1)
90
108.38(1)
90
6669.5(6)
4
1.425
0.329
2968
Z
D
calcd (Mg m-3
)
µ (mm-1
F (000)
)
crystal size (mm3)
θ range (deg)
0.40 × 0.25 × 0.25
2.14-25.00
38 983
11 730
0.081
reflections coll.
independent refl.
R(int)
10 252
0.046
data/restr./param.
GOF
10 252/0/755
1.023
7000/11/684
1.011
11 730/8/854
1.024
R [I > 2σ(I)], R1, wR2
R (all data), R1, wR2
max. diff. peak/hole (e Å-3
remarks
0.095, 0.259
0.135, 0.290
2.30, -0.58
cation refined with
split positions,
occupancy 0.54/0.46(1)
0.087, 0.229
0.138, 0.263
1.66, -0.75
Free solvent molecules
refined with common
0.130, 0.198
1.31, -1.32
Free solvent molecules
and the Li+ cation plus its
four ligands refined as
rigid groups with
)
U
iso each, one with
geom. restraints (SAME)
common isotropic
displacement parameters.
Atoms Li1, Li2, O2c,
O3b, C9f, C6e, O3a, and
C6f only refined
isotropically.
1.88 (m, 6 H); overlapping signals 1.10-0.6 (m). Negative ESI FTICR-
MS (THF): m/z ) 1269 [Li3(5d)6Ti2]-, 631 [Li(5d)3Ti]-. - IR
(KBr): ν (cm-1) ) 2955, 2926, 1654, 1430, 538.
TiLi2‚DMF‚2 H2O: C, 61.86; H, 7.50; N, 1.60. Found: C, 61.96; H,
7.15; N, 1.89.
Li2[(5h)3Ti]/Li4[(5h)6Ti2]. 1H NMR (methanol-d4, 400 MHz): mono-
mer (minor component) δ (ppm) ) 7.00 (dd, J ) 8.0, 1.9 Hz, 3 H),
6.44 (m, 6 H), 3.07 (t, J ) 7.7 Hz, 6 H); dimer (major component) δ
(ppm) ) 7.09 (m, 6 H), 6.57 (m, 12 H), 2.70 (m, 6 H), 1.99 (m, 6 H),
0.85 (t, J ) 7.1, 18 H); overlapping signals 1.10-0.72 (m). IR (KBr):
ν (cm-1) ) 2924, 1655, 1432, 1258, 1217. Negative ESI FTICR-MS
(THF): m/z ) 1606 [Li3(5h)6Ti2]-, 799 [Li(5h)3Ti]-. Anal. Calcd for
C39H48O9TiLi2‚3 H2O: C, 62.79; H, 7.73. Found: C, 62.14; H, 7.12
Li2[(5i)3Ti]/Li4[(5i)6Ti2]. 1H NMR (methanol-d4, 400 MHz): mono-
mer (minor component) δ (ppm) ) 6.99 (dd, J ) 8.0, 1.6 Hz, 3 H),
6.48 (dd, J ) 8.0, 1.6 Hz, 3 H), 6.43 (t, J ) 8.0 Hz, 3 H), 3.08 (t, J )
7.4 Hz, 6 H), 1.56 (m, 6 H); dimer (major component) δ (ppm) ) 7.10
(m, 6 H), 6.58 (m, 12 H), 2.70 (m, 6 H), 1.98 (m, 6 H), 0.88 (t, J )
7.1, 18 H); overlapping signals 1.30-0.90 (m). IR (KBr): ν (cm-1) )
2924, 2852, 1655, 1431, 1258, 1217. Negative ESI FTICR-MS
(THF): m/z ) 1774 [Li3(5i)6Ti2]-, 883 [Li(5i)3Ti]-. Anal. Calcd for
C51H72O9TiLi2‚2 H2O: C, 66.08; H, 8.26. Found: C, 65.67; H, 8.18.
Li2[(5j)3Ti]/Li4[(5j)6Ti2]. 1H NMR (methanol-d4, 300 MHz): mono-
mer (minor component): δ (ppm) ) 7.00 (dd, J ) 7.2, 1.7 Hz, 3 H),
6.46 (m, 6 H), 3.08 (t, J ) 7.1 Hz, 6 H), 1.57 (m, 2H); dimer (major
component) δ (ppm) ) 7.09 (dd, J ) 6.1, 3.4 Hz, 6 H), 6.58 (m, 12
H), 2.68 (m, 6 H), 1.98 (m, 6 H), 0.89 (t, J ) 6.9, 18 H); overlapping
signals 1.40-1.00 (m). IR (KBr): ν (cm-1) ) 3405, 2924, 2853, 1654,
1432, 1259, 1217. Negative ESI FTICR-MS (THF): m/z ) 1942
[Li3(5j)6Ti2]-, 961 [Li(5j)3Ti]-. Anal. Calcd for C57H84O9TiLi2‚1/
4H2O: C, 68.24; H, 8.04. Found: C, 69.85; H, 8.69.
Li2[(5e)3Ti]/Li4[(5e)6Ti2]. 1H NMR (methanol-d4, 300 MHz): mono-
mer (minor component): δ (ppm) ) 6.91 (dd, J ) 7.4, 2.0 Hz, 3 H),
6.38 (m, 6 H), 3.00 (t, J ) 7.7 Hz, 6 H), 1.46 (m, 6 H); dimer (major
component): δ (ppm) ) 7.02 (m, 6 H), 6.50 (m, 12 H), 2.62 (m, 6 H),
1.90 (m, 6 H); overlapping signals: 1.10-0.6 (m). - IR (KBr): ν
(cm-1) ) 2926, 2860, 1650, 1429, 1257, 1215, 733. - Negative FT-
ICR ESI-MS (THF): m/z ) 1353.5 [Li3(5e)6Ti2]-, 673 [Li(5e)3Ti]-.
- Calcd. for C36H42O9TiLi2‚3 H2O: C 58.87, H 6.59; found: C 58.39,
H 6.33.
Li2[(5f)3Ti]/Li4[(5f)6Ti2]. 1H NMR (methanol-d4, 400 MHz): (minor
component): δ (ppm) ) 6.90 (m, 3 H), 6.37 (m, 6 H), 2.98 (t, J ) 7.1
Hz, 6 H); dimer (major component): δ (ppm) ) 7.01 (m, 6 H), 6.48
(m, 12 H), 2.61 (m, 6 H), 1.89 (m, 6 H), 0.69 (t, J ) 7.4, 18 H);
overlapping signals: 1.10-0.72 (m). - IR (KBr): ν (cm-1) ) 3432,
2924, 1655, 1431, 1259, 1216, 671, 538. - Negative FT-ICR ESI-MS
(THF): m/z ) 1437.6 [Li3(5f)6Ti2]-, 715 [Li(5f)3Ti]-. - Calcd. for
C39H48O9TiLi2‚DMF‚5 H2O: C 56.95, H 7.40, N 1.58; found: C 56.29,
H 7.50, N 1.41.
Li2[(5 g)3Ti]/Li4[(5 g)6Ti2]. 1H NMR (methanol-d4, 300 MHz):
monomer (minor component) δ (ppm) ) 6.98 (m, 3 H), 6.46 (m, 6 H),
3.07 (t, J ) 7.5 Hz, 6 H); (major component) δ (ppm) ) 7.10 (m, 6
H), 6.59 (m, 12 H), 2.70 (m, 6 H), 1.98 (m, 6 H), 0.82 (t, J ) 7.2, 18
H); overlapping signals 1.10-0.72 (m). IR (KBr): ν (cm-1) ) 2954,
2924, 1655, 1431, 1258, 1217, 734. Negative ESI FTICR-MS (THF):
m/z ) 1522 [Li3(5g)6Ti2]-, 757 [Li(5g)3Ti]-. Anal. Calcd for C39H48O9-
9
10386 J. AM. CHEM. SOC. VOL. 127, NO. 29, 2005

Hierarchical Assembly of Helicates
A R T I C L E S
Li2[(6a)3Ti]/Li4[(6a)6Ti2]. 1H NMR (methanol-d4, 400 MHz): mono-
mer (major component) δ (ppm) ) 6.95 (dd, J ) 7.4, 2.2 Hz, 3 H),
6.44 (m, 6 H), 4.03 (sept, J ) 6.9 Hz, 3 H), 1.02 (d, J ) 6.9 Hz, 18
H); dimer (traces) δ (ppm) ) 0.70 (d, J ) 6.5 Hz, 18 H), 0.32 (d, J )
6.5 Hz, 18 H). IR (KBr): ν (cm-1) ) 2967, 1655, 1429, 1259, 1217.
Negative ESI FTICR-MS (THF): m/z ) 1185 [Li3(6a)6Ti2]-, 1179
[HLi2(6a)6Ti2]-, 1173 [H2Li(6a)6Ti2]-, 589 [Li(6a)3Ti]-, 583 [H(6a)3Ti]-.
Anal. Calcd for C27H24O9TiLi2‚7 H2O‚DMF: C, 49.82; H, 6.46; N,
1.76. Found: C, 49.77; H, 6.76; N, 1.31.
Li2[(6b)3Ti]/Li4[(6b)6Ti2]. 1H NMR (methanol-d4, 400 MHz): δ
(ppm) ) 7.73 (m, 6 H), 7.42 (m, 3 H), 7.23 (m, 6 H), 6.70 (m, 3 H),
6.44 (m, 6 H). IR (KBr): ν (cm-1) ) 3021, 1631, 1437, 1259, 1217,
766. Negative ESI FTICR-MS (THF): m/z ) 1389 [Li3(6b)6Ti2]-, 1383
[HLi2(6b)6Ti2]-, 1377 [H2Li(6b)6Ti2]-, 691 [Li(6b)3Ti]-, 685 [H(6b)3Ti]-
(dimer signals are low in intensity).
rotating anode generator. Programs used: data collection COLLECT
(Nonius B.V., 1998), data reduction Denzo-SMN,36 structure solution
SHELXS-97,37 structure refinement SHELXL-97 (G. M. Sheldrick,
Universita¨t Go¨ttingen, 1997), graphics SCHAKAL (E. Keller, Univer-
sita¨t Freiburg, 1997).
Li2[(7b)3Ti]/Li4[(7b)6Ti2]. 1H NMR (DMSO-d6, 400 MHz): mono-
mer (minor component) δ (ppm) ) 6.76 (dd, J ) 8.2, 1.7 Hz, 3 H),
6.26 (t, J ) 8.2 Hz, 3 H), 6.12 (dd, J ) 8.2, 1.7 Hz, 3 H), 4.12 (q, J
) 7.1 Hz, 6 H), 1.22 (t, J ) 7.1 Hz, 9 H); dimer (major component)
δ (ppm) ) 6.97 (dd, J ) 8.2, 1.6 Hz, 6 H), 6.52 (t, J ) 8.2 Hz, 6 H),
6.43 (dd, J ) 8.2, 1.6 Hz, 6 H), 3.50 (m, 6 H), 3.03 (m, 6 H), 0.95 (t,
J ) 7.1 Hz, 18 H). Negative ESI FTICR-MS (THF): m/z ) 1197
[Li3(7b)6Ti2]- (no signal for monomer observed). Anal. Calcd for
C27H24O12TiLi2‚H2O‚DMF: C, 51.97; H, 4.80; N, 2.02. Found: C,
52.26; H, 5.18; N, 2.23.
Li2[(7a)3Ti]/Li4[(7a)6Ti2]. 1H NMR (DMSO-d6, 400 MHz): mono-
mer (minor component) δ (ppm) ) 6.77 (dd, J ) 8.0, 1.4 Hz, 3 H),
6.27 (t, J ) 8.0 Hz, 3 H), 6.13 (dd, J ) 8.0, 1.4 Hz, 3 H), 3.65 (s, 9
H); dimer (major component) δ (ppm) ) 6.98 (dd, J ) 8.0, 1.7 Hz, 6
H), 6.55 (t, J ) 8.0 Hz, 6 H), 6.46 (dd, J ) 8.0, 1.7 Hz, 6 H), 2.96 (s,
18 H). Negative ESI FTICR-MS (THF): m/z ) 1113 [Li3(7a)6Ti2]-
(no signal for monomer observed). Anal. Calcd for C24H18O12TiLi2‚
H2O‚2DMF: C, 49.74; H, 4.73; N, 3.87. Found: C, 49.97; H, 4.97; N,
3.50.
Acknowledgment. Funding from the Deutsche Forschungs-
gemeinschaft (inter alia SFB 624) and the Fonds der Chemischen
Industrie is acknowledged. C.A.S. thanks the DFG for a
Heisenberg fellowship and the FCI for a Dozentenstipendium.
Supporting Information Available: ORTEP Plots of the
X-ray structures of [Li3(4)6Ti2]-, [Li3(5b)6Ti2]-, and [Li3(7a)6Ti2]-
and X-ray crystallographic files (three CIF files). This material
is available free of charge via the Internet at http://pubs.acs.org.
X-ray Crystallographic Study of Li4[Ti2(7a)6]: A data set was
collected with a Nonius KappaCCD diffractometer, equipped with a
JA052326J
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J. AM. CHEM. SOC. VOL. 127, NO. 29, 2005 10387