Synthesis of bis(catechol) ligands derived from Troeger's base and their dinuclear triple-stranded complexes with titanium(IV) ions

Article abstract of DOI:10.1002/ejoc.200700613

Bis(catechol) ligands derived from 2,8-disubstituted analogues of Troeger's base and monofunctionalized MOM-protected or unprotected catechols bearing both rigid and flexible spacers were synthesized, which gave rise to dissymmetric oxygen donor ligands w

Full text of DOI:10.1002/ejoc.200700613

FULL PAPER
DOI: 10.1002/ejoc.200700613
Synthesis of Bis(catechol) Ligands Derived from Tröger’s Base and Their
Dinuclear Triple-Stranded Complexes with Titanium(IV) Ions
Ulf Kiehne[a] and Arne Lützen*[a]
Keywords: Tröger’s base / Self-assembly / Catechol / Titanium / Helicates
Bis(catechol) ligands derived from 2,8-disubstituted ana- triple-stranded helicates upon coordination to titanium(IV)
logues of Tröger’s base and monofunctionalized MOM-
protected or unprotected catechols bearing both rigid and
flexible spacers were synthesized, which gave rise to dissym-
metric oxygen donor ligands whose geometry is defined by
the V-shaped and rigid structure of the core of Tröger’s base.
These racemic ligands undergo self-assembly to dinuclear
ions as was proven by NMR spectroscopy and ESI-MS ex-
periments; however, these processes are not diastereoselec-
tive.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
Introduction
The last 15 years witnessed a lot of efforts made towards
the use of chiral ligand structures to efficiently control the
stereochemistry of metal centers of coordination com-
pounds in a diastereoselective manner.[1] This is especially
true for helicates[2] and in particular chiral N-donor ligands
like 2,2Ј-bipyridines,[3–7] terpyridines,[8] quaterpyridine,[9]
oxazolines,[10,11] or pyridylmethanimines[12–15] but also P-
donor ligands,[16] and cationic complexes with suitable late-
transition-metal or lanthanide ions were shown to be very
effective in this sense. Our approach is aimed at the forma-
tion of self-assembled helical metal complexes from C2-
symmetric ligands that have cavities with inwardly directed
functionalities; we recently showed that bis(2,2Ј-bipyridyl)-
substituted 1,1-binaphthyl (BINOL) derivatives are very
versatile in this respect.[17] During the course of this study,
Tröger’s base also attracted our interest as another dissym-
metric chiral molecule.
Tröger’s base (Figure 1) was first synthesized in 1887 by
Julius Tröger,[18] and its V-shaped and rigid structure has
attracted a lot of attention in the past years[19] that has led
to applications in the design of various receptors for the
recognition of neutral organic molecules such as menthol[20]
or adenine[21] as well as for the recognition of dicarboxylic
acids,[22] and it has been used as a chiral auxiliary for the
enantioselective synthesis of aziridines.[23]
Figure 1. Tröger’s base.
Very recently potentially restrictive α-amino acid based
scaffolds were prepared starting from diiodo-substituted
analogues of Tröger’s base,[24] which were first synthesized
in 2001 by Wärnmark.[25] The ability to access dihalo-sub-
stituted compounds allowed the formation of a variety of
new valuable precursors for larger architectures with ex-
tended V-shaped cores through various cross-coupling
methodologies.[26]
Thus, we started a study to find out if metallosupramolec-
ular assemblies from ligands derived from Tröger’s base
could also be formed in a diastereoselective manner. We
first synthesized racemic ligands bearing either 2,2Ј-bipyr-
idine or 2-pyridylmethanimine moieties, and indeed we
showed that they assemble diastereoselectively to form
homoleptic D2d-symmetric dinuclear double-stranded hel-
icates upon coordination to silver(I) and copper(I) ions.[27]
This was only the second example in which derivatives of
Tröger’s base were used as ligands for the formation of oli-
gonuclear metal coordination compounds.[28]
Helicates, however, have not only been obtained from N-
or P-donor ligands, but also from O-donor ligands like cate-
chols and hard metal ions such as titanium(IV) or galli-
um(III).[2c,2g,2h] These helicates are anionic and hence do
have different properties than the cationic aggregates self-
assembled from ligands bearing N-heterocyclic metal chela-
tion units and late-transition-metal ions. After the first ex-
amples of this kind published by Raymond,[29] Albrecht in
[a] Rheinische Friedrich-Wilhelms Universität Bonn,
Kekulé-Institut für Organische Chemie und Biochemie,
Gerhard-Domagk-Str. 1, 53121 Bonn, Germany
Fax: +49-228-739608
E-mail: arne.luetzen@uni-bonn.de
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particular extensively studied a variety of helical cate- and quenching with iodine following the procedure of Thal
cholato complexes,[2c,2g,2h,30] but there are also some exam- (Scheme 1).[34] Compound 4 was transformed into 6 by ap-
ples published recently by Hahn.[31] So far, however, there plying Sonogashira conditions to yield 5, which was depro-
have only been very few reports on the use of chiral ligands tected to 6 by using potassium fluoride. A similar synthetic
to control the stereochemistry of the newly formed ste- approach from ortho-bromoveratrole and slightly different
reogenic metal centers in these types of helicates, and the reaction conditions was reported by Albrecht previously.[35]
stereogenic information was introduced in the outer periph- Our approach, however, allowed the isolation of 5 in much
ery of the bis(catechol) ligand structure[29c,32] rather than in better yield. Additionally, deprotection of 5 to 6 could also
the core structural element.[30c,33] Thus, we were eager to be achieved in a better yield.
find out if Tröger’s base substituted by catechol moieties
could also self-assemble into helical dinuclear coordination
compounds with hard titanium(IV) ions and whether these
processes still proceeded in a diastereoselective fashion.
Therefore, we prepared racemic bis(catechol) ligands 1 and
2 (Figure 2) and investigated their complexation behavior
towards TiIV ions. Although this might sound somehow
paradox, the results obtained with the use of racemic li-
gands to explore the degree of stereoselectivity of the self-
assembly processes are better than those of enantiomer-
ically pure ligands because in principle racemic ligands also
allow the formation of heteroleptic complexes with dif-
ferently configured ligands that are also diastereomers of Scheme 1. Synthesis of monofunctionalized veratrol derivatives 4–
6.
the homoleptic complexes bearing only ligands that are
equally configured.
ortho-Ethynylveratrol 6 and racemic 2,8-diiodo derivative
7 of Tröger’s base[25] were subsequently subjected to a two-
fold Sonogashira reaction with the use of [Pd2(dba3)2·
CHCl3] as the palladium source and 1,1Ј-bis(diphenyphos-
phanyl)ferrocene (dppf) as a sterically demanding ligand to
yield precursor 8 with methyl protected OH groups for the
synthesis of racemic ligand 1 in excellent yield (Scheme 2).
Figure 2. Bis(catechol) ligands
(iminediyl bridged) derived from analogues of Tröger’s base.
1 (ethynediyl bridged) and 2
Results and Discussion
The synthesis of the desired bis(catechol) ligands in gene-
ral requires disubstituted analogues of Tröger’s bases and
monofunctionalized catechols. As spacer units between the
core of Tröger’s base and the catechol units, we chose an
ethynyl functionality as a rigid linker and an imine moiety
as a more flexible spacer. Figure 2 shows the two ligand
structures. Protection of the OH groups of the catechol is
mandatory during the course of the synthesis of 1 as a re-
sult of lithiation and cross-coupling steps in the reaction
sequence. Thus, we regarded veratrol (1,2-dimethoxyben-
Scheme 2. Synthesis of racemic precursor 8.
Surprisingly, the fourfold demethylation of 8 with the use
zene) derivatives as especially promising OH-protected cate- of boron tribromide did not lead to the desired completely
chol derivatives for our purposes, because cleavage of the deprotected bis(catechol) ligand 1, as expected, but rather
methyl groups can usually be achieved easily by applying gave rise to a complicated mixture of different products. 1H
boron tribromide as the demethylating agent.
NMR spectroscopic analysis of this mixture showed that
Therefore, starting from commercially available veratrol the deprotection seemed to be incomplete; such an incom-
(3), ortho-iodoveratrol 4 was prepared by ortho lithiation plete deprotection may lead to nine different possible prod-
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Bis(catechol) Ligands Derived from Tröger’s Base
ucts. Unfortunately, complete deprotection could not even
be achieved when 40 equiv. of boron tribromide was used
at room temperature or when trimethylsilyl iodide was used
as a demethylating agent; this is most probably because par-
tially deprotected species precipitate from the reaction mix-
ture and thus evade further deprotection.
Because our initial approach did not yield desired eth-
ynyl-bridged ligand 1 because of the problems encountered
in the deprotection step of 8, we focused on another pro-
tecting group for the OH groups of the catechol building
block. During the course of our synthesis of the bis(bipyrid-
ine) ligands of BINOL,[17] we found the methoxymethyl
group (MOM) to be also very useful for the protection of
OH functionalities of the BINOL core. The MOM group
can be cleaved easily by traces of HCl in methanol. There-
fore, we synthesized MOM-protected catechol 9 by applying
an adapted protocol for the introduction of the MOM
groups.[36] The same reaction sequence that was used for
the synthesis of the monofunctionalized veratrol derivatives
including the iodination, Sonogashira cross-coupling reac-
tion, and cleavage of the TMS functionality was then ap- 1.
plied again and led to 1-ethynyl-2,3-bis(MOM) catechol 12
over three steps (Scheme 3).
Scheme 4. Synthesis of precursor 13 and deprotection to racemic
The reaction of 14 and 2,3-dihydroxybenzaldehyde pro-
ceeded smoothly at room temperature and yielded racemic
ligand 2 in 73% (Scheme 5).
Scheme 3. Synthesis of monofunctionalized MOM-protected cate-
chol derivatives 10–12.
Again, a twofold Sonogashira reaction of 7 and 12
yielded MOM-protected precursor 13, which finally could
be completely deprotected without any complications to
yield desired racemic ligand 1 with rigid ethynyl bridges
(Scheme 4).
Next, we wanted to synthesize an additional ligand with
a more flexible spacer as a linker between the core of
Tröger’s base and the catechol chelating units. Such a flexi-
Scheme 5. Synthesis of racemic ligand 2.
With both racemic ligands 1 and 2 in hand, we then ex-
ble spacer could be, as an example, an imine moiety, which plored their ability to form dinuclear triple-stranded metallo-
is easily introduced by reaction of an amine and an alde- supramolecular coordination compounds with titanium(IV)
hyde without any protection and deprotection steps of the ions (Figure 3).
OH groups. Recently we reported the synthesis of the race-
In earlier studies, the nature of the counterion of the base
mic 2,8-diamino derivative of Tröger’s base, 14, through re- used to deprotonate the OH groups was sometimes found
duction of its 2,8-dinitro precursor.[27] An alternative ap- to be crucial for the successful formation of the helica-
proach to a diamino-substituted analogue of Tröger’s base tes.[30b] Hence, racemic ligands 1 (3 equiv.) and 2 (3 equiv.),
was reported recently by Sergeyev, and palladium-catalyzed titanium(IV) oxide acetonylacetonate [TiO(acac)2] (2 equiv.)
C,N bond formation was the key step in the reaction se- as the TiIV source, and an alkali metal carbonate (2 equiv.;
quence, which started from a diiodo derivative of Tröger’s lithium, sodium, or potassium carbonate) were dissolved in
base.[37] However, in comparison to our approach, this se- DMF and stirred overnight. In general, in all cases a red
quence involves one more step and is much more expensive. color change of the solutions as well as for the solid com-
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U. Kiehne, A. Lützen
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the successful formation of the titanium(IV) complexes. In
addition, the proton signals of the phenolic OH groups of
free 2 completely disappeared in all cases. Generally, in the
spectra of Li4[Ti2(2)3], the signals are much sharper than
those in the spectra of Na4[Ti2(2)3] and K4[Ti2(2)3].
Figure 3. Schematic figure of dinuclear triple-stranded complex
with TiIV derived from 1.
plexes could be observed; a darker shade of red for the com-
plexes with lithium as counterions and lighter shades for
their sodium and potassium analogues.
Evaporation of the solvents yielded the desired com-
1
plexes which were studied by H NMR spectroscopy and
ESI-mass spectrometric means. The ESI-MS spectrum of
Na4[Ti2(1)3] is representatively shown in Figure 4, and it
clearly shows signals of the negatively charged triple-
stranded titanium(IV) complexes only and some water ad-
ducts of them (presumably coordinated to the nitrogen
atoms of Tröger’s base, as the first coordination sphere of
the titanium is blocked and these adducts were found for
the complexes of 1 and 2) as the major peaks. These obser-
vations could be made for all six titanium(IV) complexes
(containing lithium, sodium, or potassium counterions) of
ligands 1 and 2. In all cases, only signals for the expected
triple-stranded helicates could be observed.
Figure 5. 1H NMR spectroscopic complexation studies of 2 in [D6]-
DMSO: (a) K4[Ti2(2)3]; (b) Na4[Ti2(2)3]; (c) Li4[Ti2(2)3]; (d) 2.
However, a closer look at the spectra revealed that the
formation of the dinuclear titanium coordination com-
pounds is not diastereoselective in these cases. Whereas di-
nuclear double-stranded helicates derived from bis(bipyrid-
ine) ligands of the derivatives of Tröger’s base gave rise to
NMR spectra with the same number of signals as the free
ligands, which is indicative of diastereoselectively formed
helicates from dissymmetrical ligands that have equally con-
figured ligands and metal centers,[17,27] the number of sig-
nals observed for the titanium complexes, however, is much
higher than the number observed for the free ligand. This
is best seen for the imine protons shown in the inset in Fig-
ure 5c. At least 10 different imine proton resonances Ϫ al-
beit in different intensities Ϫ can be distinguished. This in-
dicates that all six possible diastereomeric homo- and hetero-
leptic coordination compounds Ϫ the (∆,∆)-, (Λ,Λ)-, and
(∆,Λ)-configured homoleptic complexes of the (5S,11S)-
Figure 4. Negative ESI-MS of a solution of Na4[Ti2(1)3] in MeOH/
DMF.
Next, we focused on the investigation of the complex- configured ligand as well as the (∆,∆)-, (Λ,Λ)-, and (∆,Λ)-
1
ation behavior by H NMR spectroscopy to elucidate their configured heteroleptic complexes containing two (5S,11S)-
1
stereochemistry. The H NMR spectra of ligand 2 and its configured ligands and one (5R,11R)-configured ligand Ϫ
titanium(IV) complexes are representatively shown in Fig- are formed (together with their respective enantiomers,
ure 5. The signals of the complexes are significantly shifted which of course cannot be distinguished by normal NMR
relative to those of the free ligand, which again confirms spectroscopy).
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Bis(catechol) Ligands Derived from Tröger’s Base
Figure 6. PM3-TM-minimized structures of diastereomeric homoleptic and heteroleptic dinuclear metal coordination compounds
[Ti2{2}3]4– formed upon self-assembly of racemic 2 and titanium(IV) ions [unlabeled ligands 2 in the structures are (5S,11S)-configured].
For these, one would expect a maximum of 12 different simply be applied to O-donor ligands and their coordina-
imine proton signals (1 + 1 + 2 + 2 + 2 + 4 = 12). Thus, tion to early-transition-metal ions like titanium(IV), at least
the self-assembly process is clearly not diastereoselective in not when 2,8-functionalized derivatives of Tröger’s base are
this case but rather leads to complex mixtures of all possible used to control the stereochemistry of the newly formed
metallosupramolecular aggregates (Figure 6 shows the stereogenic metal centers.
PM3-TM minimized structures of all six possible dia-
stereomeric triple-stranded dinuclear titanium complexes of
ligand 2). The NMR spectroscopic interpretation of ligand
1 and its complexes indicates similar results; however, the
signals were much broader than those in the spectra of the
complexes of 2.
Experimental Section
General Information: All reactions except the synthesis of 1 from
13 and the preparations of the TiIV complexes were performed un-
der an argon atmosphere by using standard Schlenk techniques and
oven-dried glassware prior to use. TLC was performed on alumin-
ium TLC plates silica gel 60 F254 from Merck. Detection was done
Conclusions
by UV light (254 and 366 nm). Products were purified by column
chromatography on silica gel 60 (70–230 mesh) from Merck. 1H
We synthesized racemic bis(catechol) ligands 1 and 2,
and 13C NMR spectra were recorded with a Bruker DRX 500 spec-
which are derivatives of Tröger’s base. These ligands un-
trometer at 300 K, at 500.1 and 125.8 MHz, respectively, with a
dergo self-assembly to form dinuclear triple-stranded com-
Bruker AM 400 at 298 K, at 400.1 and 100.6 MHz, respectively, or
plexes of helical shape upon coordination to TiIV ions. This
a Bruker Avance 300 at 298 K, at 300.1 and 75.5 MHz, respectively.
1H NMR chemical shifts are reported on the δ scale (ppm) relative
is only the third report of the formation of larger architec-
tures by the self-assembly of ligands derived from Tröger’s
to residual nondeuterated solvent as an internal standard. 13C
bases and transition-metal ions and the first one involving NMR chemical shifts are reported on the δ-scale (ppm) relative to
deuterated solvent as an internal standard. Signals were assigned
bis(catechols) as O-donor ligands. However, in contrast to
similar bis(bipyridine) ligands derived from Tröger’s base,
the self-assembly processes of these ligands are not dia-
stereoselective but lead to a complex mixture of all possible
diastereomeric homo- and heteroleptic coordination com-
pounds in racemic form instead. Although, this is a disap-
pointing result, it is still very important, because it clearly
demonstrates that the concept of diastereoselective self-as-
sembly that has been well established for N-donor ligands
1
on the basis of H, 13C, HMQC, and HMBC NMR experiments.
Mass spectra were taken with a Finnigan MAT 212 with data sys-
tem MMS-ICIS (EI, CI, isobutane, NH3) or a Finnigan MAT 95
with data system DEC-Station 5000 (CI, isobutane or NH3; HiRes-
CI, isobutane or NH3; FD) or an A.E.I. MS-50 (EI; HiRes-EI).
ESI-MS spectra were recorded with a Bruker APEX IV FT mass
spectrometer. Melting points were measured with a hot-stage
microscope SM-Lux from Leitz and are not corrected. Elemental
analyses were carried out with a Fisons Instrument EA1108 or a
and their coordination to late-transition-metal ions cannot Heraeus Vario EL. Molecular modeling studies were carried out
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with Spartan Pro (Wavefunction). The geometry optimizations of
the anionic dinuclear metal coordination complexes were per-
formed on a semiempirical level of theory without taking into ac-
count the counterions or the solvent (mixture). Most solvents were
dried, distilled, and stored under an argon atmosphere according
to standard procedures. All chemicals were used as received from
commercial sources. Compound 14 was prepared according to our
previously published procedure.[27] Numbering of the 1H and 13C
nuclei is according to Figure 1.
temperature. It was quenched with H2O, and the aqueous layer was
extracted with ethyl acetate (4ϫ). The combined organic layers
were washed with H2O, aqueous saturated NaCl, and dried with
Na2SO4. The product was purified by column chromatography on
silica gel [n-hexane/ethyl acetate (2:1) + 0.5% Et3N, Rf = 0.68] and
obtained as a colorless oil. Yield: 3.70 g (18.67 mmol, 90%). Ana-
lytical data were in accordance with those previously published.[38]
However, no NMR assignments were given. 1H NMR (500.1 MHz,
CDCl3): δ = 3.51 (s, 6 H, -OCH3), 5.22 (s, 4 H, -OCH2OCH3), 6.96
(dd, 3J = 6.0 Hz, 4J = 3.2 Hz, 2 H, 3-H, 3Ј-H), 7.16 (dd, 3J =
Synthesis of Catechol Derivatives
4
6.0 Hz, J = 3.2 Hz, 2 H, 2-H, 2Ј-H) ppm. 13C NMR (125.8 MHz,
1-Iodo-2,3-dimethoxybenzene (4): THF (20 mL) and veratrol (3.5 g,
3.27 mL, 25.33 mmol) were cooled to –10 °C. A solution of nBuli
(1.6  in n-hexane, 17.29 mL, 27.87 mmol, 1.78 g, 1.1 equiv.) was
added at this temperature, and the resulting mixture was allowed
to come to room temperature and stirred for 2 h. The solution was
then cooled to –45 °C followed by the addition of a solution of
iodine (7.07 g, 27.87 mmol, 1.1 equiv.) in THF (30 mL). The re-
sulting mixture was allowed to come to room temperature and
stirred for another 2 h. The solvents were evaporated and dichloro-
methane was added. The organic layer was washed with aqueous
NaHSO3 (20%), aqueous saturated NaHCO3, and aqueous satu-
rated NaCl, and the layer was then dried with Na2SO4. The prod-
uct was purified by column chromatography on silica gel [n-hexane/
ethyl acetate (10:1), Rf = 0.49] and isolated as a yellow oil. Yield
5.30 g (20.1 mmol, 80%). Analytical data were in accordance with
those previously published.[34] However, the 13C NMR spectro-
scopic assignments were incorrect. 1H NMR (500.1 MHz, CDCl3):
δ = 3.84 (s, 3 H, -OCH3@C-2Ph), 3.85 (s, 3 H, -OCH3@C-3Ph), 6.79
CDCl3): δ = 56.1 (-OCH3), 95.5 (-OCH2OCH3), 116.9 (C-3, C-3Ј),
122.6 (C-2, C-2Ј), 147.3 (C-1, C-1Ј) ppm.
1-Iodo-2,3-bis(methoxymethoxy)benzene (10): A solution of 9 (1.5 g,
7.57 mmol) in THF (10 mL) was cooled to –10 °C. A solution of
nBuli (1.5  in n-hexane, 5.52 mL, 8.32 mmol, 0.53 g, 1.1 equiv.)
was added at this temperature, and the resulting mixture was al-
lowed to come to room temperature and stirred for 2 h. The solu-
tion was then cooled to –45 °C followed by the addition of a solu-
tion of iodine (2.11 g, 8.32 mmol, 1.1 equiv.) in THF (30 mL). The
resulting mixture was allowed to come to room temperature and
stirred for another 2 h. The solvents were evaporated and dichloro-
methane was added. The organic layer was washed with aqueous
NaHSO3 (20%), aqueous saturated NaHCO3, and aqueous satu-
rated NaCl, and the organic layer was then dried with Na2SO4.
The product was purified by column chromatography on silica gel
[n-hexane/ethyl acetate (10:1), Rf = 0.49] and isolated as a yellowish
oil. Yield: 1.62 g (5.00 mmol, 66%). 1H NMR (500.1 MHz,
CDCl3): δ = 3.50 (s, 3 H, -OCH3@C-2Ph), 3.68 (s, 3 H, -OCH3@C-
3
3
3
4
(dd, J = 8.2 Hz, J = 8.2 Hz, 1 H, 5-H), 6.88 (dd, J = 8.2 Hz, J
3
4
= 1.1 Hz, 2 H, 4-H), 7.35 (dd, J = 8.2 Hz, J = 1.1 Hz, 2 H, 6-H)
ppm. 13C NMR (125.8 MHz, CDCl3): δ = 56.0 (-OCH3@C-3Ph), 60.4
(-OCH3@C-3Ph), 92.5 (C-1), 112.8 (C-4), 125.8 (C-5), 130.6 (C-4),
149.0 (C-2), 152.8 (C-3) ppm.
3
Ph), 5.18 (s, 2 H, -OCH2OCH3@C-2Ph), 5.19 (s, 2 H, -OCH2-
3
3
OCH3@C-3Ph), 6.78 (dd, J = 8.2 Hz, J = 8.2 Hz, 1 H, 5-H), 7.12
3
4
3
4
(dd, J = 8.2 Hz, J = 1.1 Hz, 1 H, 4-H), 7.44 (dd, J = 8.2 Hz, J
= 1.1 Hz, 1 H, 6-H) ppm. 13C NMR (125.8 MHz, CDCl3): δ = 56.3
(-OCH3@C-2Ph), 58.4 (-OCH3@C-3Ph), 92.7 (C-1), 95.3 (-OCH2-
OCH3@C-2Ph), 98.9 (-OCH2OCH3@C-3Ph), 117.0 (C-4), 126.0 (C-
5), 132.5 (C-6), 146.7 (C-2) ppm. 150.0 (C-3). MS (EI): m/z (%)
= 324.0 (100) [C10H13IO4]+. C10H13IO4(324.11)·1/9THF: calcd. C
37.77, H 4.22; found C 38.11, H 4.04. HRMS (EI): calcd. for
C10H13IO4 323.9859; found 323.9852.
[2-(2,3-Dimethoxyphenyl)ethynyl]trimethylsilane (5):
A Schlenk
flask was charged with [Pd(PPh3)2Cl2] (80 mg, 114ϫ10–3 mmol,
1 mol-%) and CuI (65 mg, 0.34 mmol, 3 mol-%). Et3N (3 g) 4
(30 mL 11.36 mmol), and trimethylsilylacetylene (TMSA) (1.23 g,
12.50 mmol, 1.1 equiv.) were added, and the solution was stirred at
room temperature for 16 h. Saturated aqueous NaCl and CH2Cl2
were added, and the reaction mixture was filtered through Celite.
Aqueous saturated NaHCO3 was added to the filtrate, the layers
were separated, and the organic layer was dried with Na2SO4. The
product was purified by column chromatography on silica gel [n-
hexane/ethyl acetate (10:1) + 0.5% Et3N, Rf = 0.35] and isolated
as a yellow oil. Yield: 2.5 g (10.67 mmol, 93%). Analytical data
were in accordance with those previously published.[34]
{2-[2,3-Bis(methoxymethoxy)phenyl]ethynyl}trimethylsilane (11): A
Schlenk flask was charged with [Pd(PPh3)2Cl2] (46 mg,
64.8ϫ10–3 mmol, 3 mol-%) and CuI (8.2 mg, 43.2ϫ10–3 mmol,
2 mol-%). Et3N (15 mL), 10 (700 mg, 2.16 mmol), and TMSA
(254.6 mg, 2.59 mmol, 1.2 equiv.) were added, and the solution was
stirred at room temperature for 16 h. Saturated aqueous NaCl and
CH2Cl2 were added, and the reaction mixture was filtered through
Celite. Aqueous saturated NaHCO3 was added to the filtrate, the
layers were separated, and the organic layer was dried with
Na2SO4. The product was purified by column chromatography on
silica gel [n-hexane/ethyl acetate (4:1) + 0.5% Et3N, Rf = 0.45] and
isolated as a yellow oil. Yield: 470 mg (1.60 mmol, 74%). 1H NMR
(500.1 MHz, CDCl3): δ = 0.24 [s, 9 H, -Si(CH3)3], 3.49 (s, 3 H,
-OCH3@C-3Ph), 3.66 (s, 3 H, -OCH3@C-2Ph), 5.18 (s, 2 H, -OCH2-
1-Ethynyl-2,3-dimethoxybenzene (6): Compound
5
(1.40 g,
5.97 mmol) and KF (1.04 g, 17.91 mmol, 3 equiv.) were dissolved
in MeOH (50 mL), and the resulting solution was stirred for 18 h at
room temperature. Evaporation of the solvent yielded the product,
which was purified by column chromatography on silica gel (n-
hexane/ethyl acetate, 2:1 + 0.5% Et3N; Rf = 0.81) and isolated as
a colorless oil. Yield: 965 mg (5.97 mmol, quantitative). Analytical
data were in accordance with those previously published.[34]
3
OCH3@C-3Ph), 5.25 (s, 2 H, -OCH2OCH3@C-2Ph), 6.96 (dd, J =
3
3
1,2-Bis(methoxymethoxy)benzene (9): To a suspension of NaH
(60% dispersion in mineral oil, 1.86 g, 1.12 g, 46.51 mmol,
2.23 equiv.) in THF (30 mL) and DMF (15 mL) was added a solu-
tion of catechol (2.29 g, 20.83 mmol) in THF (15 mL) dropwise at
0 °C. A color change from white to green was observed while stir-
ring at room temperature for 1 h. Chloromethyl methyl ether
8.2 Hz, J = 8.2 Hz, 1 H, 5-H), 7.11 (d, J = 8.2 Hz, 2 H, 4-H, 6-
H) ppm. 13C NMR (125.8 MHz, CDCl3): δ = –0.1 [Si(CH3)3], 56.2
(-OCH3@C-3Ph), 57.4 (-OCH3@C-2Ph), 95.3 (-OCH2OCH3@C-
3Ph), 98.6 (CϵCTMS), 98.7 (-OCH2OCH3@C-2Ph), 101.3
(CϵCTMS), 117.6 (C-6), 118.5 (C-1), 124.1 (C-5) 127.2 (C-4),
148.3 (C-2), 150.1 (C-3) ppm. MS (EI): m/z (%) = 294.1 (100)
(5 mL, 5.3 g, 65.83 mmol, 3.16 equiv.) was added to the mixture, [C15H22O4Si]+. HRMS (EI): calcd. for C15H22O4Si 294.1287; found
which slowly turned yellow and was then stirred for 18 h at room 294.1291.
5708
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 5703–5711

Bis(catechol) Ligands Derived from Tröger’s Base
1-Ethynyl-2,3-bis(methoxymethoxy)benzene (12): Compound 11
[C37H34N2O4]+. C37H34N2O4 (570.68)·1/4toluene: calcd. C 78.39, H
(400 mg, 1.36 mmol) and KF (158 mg, 2.70 mmol, 2 equiv.) were 6.11, N 4.72; found C 78.40, H 6.19, N 4.81. HRMS (EI): calcd.
dissolved in MeOH (30 mL), and the resulting solution was stirred
for 18 h at room temperature. Evaporation of the solvent yielded
the product, which was purified by column chromatography on sil-
ica gel [n-nexane/ethyl acetate (4:1) + 0.5% Et3N, Rf = 0.29] and
isolated as a colorless oil. Yield: 281 mg (1.26 mmol, 93%). 1H
NMR (500.1 MHz, CDCl3): δ = 3.26 (s, 1 H, CϵCH), 3.50 (s, 3
H, -OCH3@C-3Ph), 3.65 (s, 3 H, -OCH3@C-2Ph), 5.19 (s, 2 H,
-OCH2OCH3@C-3Ph), 5.26 (s, 2 H, -OCH2OCH3@C-2Ph), 6.99
(dd, J = 7.7 Hz, J = 8.2 Hz, 1 H, 5-H), 7.13–7.16 (m, 2 H, 4-H,
6-H) ppm. 13C NMR (125.8 MHz, CDCl3): δ = 56.2 (-OCH3@C-
3Ph), 57.5 (-OCH3@C-2Ph), 80.0 (CϵCH), 81.2 (CϵCH), 95.3
(-OCH2OCH3@C-3Ph), 98.8 (-OCH2OCH3@C-2Ph), 117.6 (C-1),
117.8 (C-4), 124.2 (C-5), 127.2 (C-6), 148.4 (C-2), 150.2 (C-3) ppm.
MS (EI): m/z (%) = 222.1 (100) [C12H14O4]+. C12H14O4 (222.24)·
1/3CH2Cl2: calcd. C 59.12, H 5.90; found C 58.78, H 5.88. HRMS
(EI): calcd. for C12H14O4 222.0892; found 222.0887.
for C37H34N2O4 570.2519; found 570.2521.
2,8-Bis[2,3-bis(methoxymethoxy)benzene-1-ylethynyl]-4,10-dimeth-
yl-6H,12H-5,11-methanodibenzodiazocine (13): THF (7 mL) and di-
isopropylamine (85 mg, 0.84 mmol, 3 equiv.) were added to 7
(141 mg, 0.28 mmol), CuI (2 mg, 11 ϫ 10–3 mmol, 4 mol-%),
[Pd2(dba)3·CHCl3] (9 mg, 17 ϫ 10–3 mmol, 6 mol-% Pd), dppf
(9.3 mg, 17ϫ10–3 mmol, 6 mol-%), and 12 (150 mg, 0.67 mmol,
2.4 equiv.). The resulting mixture was stirred at 60 °C for 16 h. Sat-
urated aqueous NaCl and dichloromethane were added, and the
mixture was filtered through Celite. The residue was washed with
dichloromethane. The filtrate was washed with saturated aqueous
NaHCO3, and the organic layer was dried with Na2SO4. The prod-
uct was purified by column chromatography on silica gel [toluene/
THF (9:1) + 5% Et3N, Rf = 0.56] and obtained as a yellow solid.
Yield: 148 mg (0.21 mmol, 76 %). M.p. 202–204 °C. 1H NMR
(500.1 MHz, CDCl3): δ = 2.40 (s, 6 H, -CH3), 3.50 (s, 6 H,
-OCH3@C-3Ph), 3.65 (s, 6 H, -OCH3@C-2Ph), 3.98 (d, 2J =
3
3
Synthesis of the Derivatives of Tröger’s Base
2
–17.0 Hz, 2 H, 6endo-H, 12endo-H), 4.02 (s, 2 H, 13-H), 4.58 (d, J
2,8-Diiodo-4,10-dimethyl-6H,12H-5,11-methanodibenzodiazocine
(7): 4-Iodo-2-methylaniline (7.5 g, 32.02 mmol) and paraformalde-
hyde (2.02 g, 67.25 mmol, 2.1 equiv.) were dissolved in trifluoro-
acetic acid (64 mL, 0.80 mol, 26 equiv.), which resulted in a dark-
purple-colored reaction mixture. The mixture was stirred for 16 h
and poured into H2O (200 mL) to yield a brown precipitate. Aque-
ous NaOH (6 ) was added to this suspension (pH 9), the precipi-
tate was filtered off, and recrystallized from acetone, and the solu-
tion was stored at –20 °C for 12 h. A first product fraction was
obtained by collecting the precipitate. A second crop could be iso-
lated by concentrating the mother liquor and purification of the
crude product by column chromatography on silica gel (toluene +
0.5% Et3N, Rf = 0.25). Yield: 6.03 g (12.01 mmol, 75%; 55% after
recrystallization and the remaining 20% by column chromatog-
raphy). Analytical data were in accordance with those previously
published.[25]
= –17.0 Hz, 2 H, 6exo-H, 12exo-H), 5.20 (s, 4 H, -OCH2OCH3@C-
3
Ph), 5.27 (s, 4 H, -OCH2OCH3@C-2Ph), 6.97 (s, 2 H, 1-H, 7-H),
6.99 (d, 3J = 7.7 Hz, 2 H, 5Ph-H, 5ЈPh-H), 7.11 (dd, 3J = 7.7 Hz, J
= 1.1 Hz, 4 H, 4Ph-H, 4ЈPh-H, 6Ph-H, 6ЈPh-H), 7.23 (s, 2 H, 3-H, 9-
H) ppm. 13C NMR (125.8 MHz, CDCl3): δ = 17.0 (-CH3), 54.8 (C-
6, C-12), 56.2 (-OCH3@C-3Ph), 57.5 (-OCH3@C-2Ph), 67.4 (C-13),
85.0 (CϵC-Ph), 93.3 (CϵC-Ph), 95.3 (-OCH2OCH3@C-3Ph), 98.7
(-OCH2OCH3@C-2Ph), 117.1 (C-6Ph, C-6ЈPh), 118.5 (C-2, C-8),
118.8 (C-1Ph, C-1ЈPh), 124.2 (C-5Ph, C-5ЈPh), 126.7 (C-4Ph, C-4ЈPh),
127.6 (C-1, C-7), 128.1 (C-14, C-16), 132.1 (C-3, C-9), 133.1 (C-4,
C-10), 146.4 (C-15, C-17), 147.7 (C-2Ph, C-2ЈPh), 150.2 (C-3Ph, C-
3Ph) ppm. MS (EI): m/z (%) = 690.3 (100) [C41H42N2O8]+.
C41H42N2O8 (690.78)·H2O: calcd. C 69.48, H 6.26, N 3.95; found
C 69.42, H 6.20, N 3.93. HRMS (EI): calcd. for C41H42N2O8
690.2941; found 690.2937.
4
2,8-Bis(2,3-dihydroxybenzene-1-ylethynyl)-4,10-dimethyl-6H,12H-
5,11-methanodibenzodiazocine (1): Compound 13 (340 mg,
0.49 mmol) was dissolved in MeOH (10 mL) and THF (10 mL).
Concentrated hydrochloric acid (2 mL) was added to this solution,
which was then stirred for 24 h at room temperature. The solvents
were evaporated, and the crude product was dissolved in ethyl ace-
tate. After the addition of H2O, the layers were separated, and the
aqueous phase was extracted with ethyl acetate (3ϫ). The com-
bined organic layers were dried with Na2SO4, and the product was
dried in vacuo. Yield: 226 mg (0.44 mmol, 90%). M.p. Ͼ250 °C. 1H
NMR (500.1 MHz, [D6]DMSO): δ = 2.38 (s, 6 H, -CH3), 4.12 (d,
2J = –17.0 Hz, 2 H, 6endo-H, 12endo-H), 4.38 (s, 2 H, 13-H), 4.57 (d,
2,8-Bis(2,3-dimethoxybenzene-1-ylethynyl)-4,10-dimethyl-6H,12H-
5,11-methanodibenzodiazocine (8): THF (10 mL) and diisopropyl-
amine (145 mg, 1.43 mmol, 2.4 equiv.) were added to a mixture of
7 (300 mg, 0.70 mmol), CuI (4.6 mg, 24ϫ10–3 mmol, 4 mol-%),
[Pd2(dba)3·CHCl3] (19 mg, 36 ϫ 10–3 mmol, 6 mol-% Pd), dppf
(20 mg, 36 ϫ 10–3 mmol, 6 mol-%), and 6 (214 mg, 1.31 mmol,
2.2 equiv.). The resulting mixture was stirred at 60 °C for 18 h. Sat-
urated aqueous NaCl and dichloromethane were added, and the
mixture was filtered through Celite. The residue was washed with
dichloromethane. The filtrate was washed with saturated aqueous
NaHCO3, and the organic layer was dried with Na2SO4. The prod-
uct was purified by column chromatography on silica gel [toluene/
THF (9:1) + 5% Et3N, Rf = 0.50] and obtained as a colorless solid.
Yield: 260 mg (0.46 mmol, 75 %). M.p. 179–181 °C. 1H NMR
(500.1 MHz, CDCl3): δ = 2.42 (s, 6 H, -CH3), 3.86 (s, 6 H,
-OCH3@C-3Ph), 3.95 (s, 6 H, -OCH3@C-2Ph), 4.02 (d, 2J =
3
3
2J = –17.0 Hz, 2 H, 6exo-H, 12exo-H), 6.60 (dd, J = 7.7 Hz, J =
7.7 Hz, 2 H, 5Ph-H, 5ЈPh-H), 6.77–6.78 (m, 4 H, 4Ph-H, 4ЈPh-H, 6Ph
-
H, 6ЈPh-H), 7.05 (s, 2 H, 1-H, 7-H), 7.24 (s, 2 H, 3-H, 9-H), 8.85
(br. s, 2 H, OH), 9.46 (br. s, 2 H, OH) ppm. 13C NMR (125.8 MHz,
[D6]DMSO): δ = 16.6 (-CH3), 54.0 (C-6, C-12), 67.0 (C-13), 86.1
(CϵC-Ph), 92.2 (CϵC-Ph), 110.4 (C-1Ph, C-1ЈPh), 115.9 (C-4Ph, C-
4ЈPh), 118.4 (C-2, C-8), 119.2 (C-5Ph, C-5ЈPh), 122.9 (C-6Ph, C-6ЈPh),
127.6 (C-1, C-7), 128.3 (C-14, C-16), 131.5 (C-3, C-9), 132.9 (C-4,
C-10), 144.9 (C-15, C-17), 145.5 (C-3Ph, C-3ЈPh), 152.7 (C-2Ph, C-
2ЈPh) ppm. MS (EI): m/z (%) = 514.2 (100) [C33H26N2O4]+.
C33H26N2O4 (514.57)·7/2H2O: calcd. C 68.62, H 5.76, N 4.85;
found C 68.49, H 5.56, N 4.50. HRMS (EI): calcd. for C33H26N2O4
514.1892; found 514.1894.
2
–17.0 Hz, 2 H, 6endo-H, 12endo-H), 4.37 (s, 2 H, 13-H), 4.62 (d, J
= –17.0 Hz, 2 H, 6exo-H, 12exo-H), 6.88 (s, 3J = 7.8 Hz, 4J = 1.6 Hz,
2 H, 4Ph-H,4ЈPh-H), 6.97–7.00 (m, 4 H, 1-H, 7-H, 5Ph-H, 5ЈPh-H),
3
4
7.03 (dd, J = 7.8 Hz, J = 1.6 Hz, 2 H, 6Ph-H, 6ЈPh-H), 7.26 (s, 2
H, 3-H, 9-H) ppm. 13C NMR (125.8 MHz, CDCl3): δ = 17.0
(-CH3), 54.8 (C-6, C-12), 56.0 (-OCH3@C-3Ph), 61.0 (-OCH3@C-
2Ph), 67.6 (C-13), 84.8 (CϵC-Ph), 93.2 (CϵC-Ph), 112.8 (C-4Ph, C-
4ЈPh), 118.1 (C-1Ph, C-1ЈPh), 118.7 (C-2, C-8), 123.8 (C-5Ph, C-5ЈPh),
125.0 (C-6Ph, C-6ЈPh), 127.8 (C-1, C-7), 128.0 (C-14, C-16), 132.1
(C-3, C-9), 133.0 (C-4, C-10), 146.2 (C-15, C-17), 150.3 (C-3Ph, C- 2,8-Bis(2,3-dihydroxybenzenemethanimine)-4,10-dimethyl-6H,12H-
3ЈPh), 152.7 (C-2Ph, C-2ЈPh) ppm. MS (EI): m/z (%) = 570.3 (100) 5,11-methanodibenzodiazocine (2): Compound 14 (250 mg,
Eur. J. Org. Chem. 2007, 5703–5711
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5709

U. Kiehne, A. Lützen
FULL PAPER
0.89 mmol) was dissolved in MeOH (20 mL) and Et3N (2 mL). 2,3-
Dihydroxybenzaldehyde (246 mg, 1.78 mmol, 2 equiv.) was added,
and the resulting yellowish solution was stirred at room tempera-
ture for 20 h. After a short time an intensively orange solid began
to precipitate. The precipitate was filtered off, washed with small
amounts of cold MeOH, and dried in vacuo. Yield: 338 mg
(0.65 mmol, 73 %). M.p. Ͼ250 °C. 1H NMR (500.1 MHz, [D6]-
H2O}2–, 845.7 (70) {Na2[Ti223]}2–, 854.7 (30) {Na2[Ti223]·H2O}2–.
C93H72Li4N12O12Ti2 (1673.14)·5DMF·13H2O: calcd. C 57.07, H
5.90, N 10.48; found C 56.67, H 5.65, N 10.41.
Na4[Ti2(2)3]: Compound 1 (40.5 mg, 77.73 mmol, 3 equiv.), [TiO-
(acac)2] (13.6 mg, 51.82 mmol, 2 equiv.), and Na2CO3 (5.5 mg,
51.82 mmol, 2 equiv.) were used as described above. Yield: quanti-
tative. MS (ESI): m/z (%)
=
834.7 (20) {H1Na1[Ti223]}2–,
DMSO): δ = 2.42 (s, 6 H, -CH3), 4.06 (d, 2J = –17.0 Hz, 2 H, 6endo
-
-
-
845.7 (100) {Na2[Ti223]}2–, 854.7 (40) {Na2[Ti223]·H2O}2–.
C93H72N12Na4O12Ti2 (1737.33)·5DMF·10H2O: calcd. C 56.82, H
5.61, N 10.43; found C 56.27, H 5.52, N 10.47.
2
H, 12endo-H), 4.30 (s, 2 H, 13-H), 4.58 (d, J = –17.0 Hz, 2 H, 6exo
3
3
H, 12exo-H), 6.75 (dd, J = 8.7 Hz, J = 7.2 Hz, 2 H, 5Ph-H, 5ЈPh
3
H), 6.90 (d, J = 8.7 Hz, 4 H, 4Ph-H, 4ЈPh-H), 6.93 (s, 2 H, 1-H, 7-
H), 7.01 (d, 2 H, 6Ph-H, 6ЈPh-H), 7.17 (s, 2 H, 3-H, 9-H), 8.62 (s, 2
H, -N=CH) 9.11 (br. s, 2 H, OH@C-3Ph), 13.30 (br. s, 2 H, OH@C-
K4[Ti2(2)3]: Compound
1
(40.5 mg, 77.73 mmol, 3 equiv.),
[TiO(acac)2] (13.6 mg, 51.82 mmol, 2 equiv.), and K2CO3 (7.2 mg,
51.82 mmol, 2 equiv.) were used as described above. Yield: quanti-
tative. MS (ESI): m/z (%) = 824.2 (100) {H2[Ti223]}2–, 834.7 (10)
{H1Na1[Ti223]}2–, 842.2 (60) {H1K1[Ti223]}2–, 853.7 (10)
{Na2[Ti223]·H2O}2–, 861.7 (25) {K2[Ti223]}2–. C93H72K4N12O12Ti2
(1801.77)·2DMF·13H2O: calcd. C 54.49, H 5.17, N 8.99; found C
54.65, H 5.28, N 8.91.
2
Ph) ppm. 13C NMR (125.8 MHz, [D6]DMSO): δ = 16.8 (-CH3),
54.5 (C-6, C-12), 67.0 (C-13), 117.2 (C-1, C-7), 118.6 (C-1Ph, C-
1ЈPh, C-5Ph, C-5ЈPh), 119.3 (C-4Ph, C-4ЈPh), 121.5 (C-3, C-9), 122.5
(C-6Ph, C-6ЈPh), 129.1 (C-14, C-16), 133.5 (C-4, C-10), 142.8 (C-2,
C-8), 144.8 (C-15, C-17), 145.5 (C-3Ph, C-3ЈPh), 149.3 (C-2Ph, C-
2ЈPh), 162.4 (C=N) ppm. MS (EI): m/z (%) = 520.3 (100)
[C31H28N4O4]+, 520.3 (100) [C31H28N4O4]+, 520.3 (100)
[C31H28N4O4]+. C31H28N4O4 (520.58)·3/4H2O: calcd. C 69.71, H
5.57, N 10.49; found C 69.78, H 5.79, N 10.51. HRMS (EI): calcd.
for C31H28N4O4 520.2111; found 520.2111.
Acknowledgments
Financial support from the Deutsche Forschungsgemeinschaft
(DFG SPP 1118 and SFB 624) is gratefully acknowledged. T. Weil-
andt is thanked for performing the ESI-MS experiments of the
complexes.
Preparation of the Titanium(IV) Complexes
Either 1 or 2 (3 equiv.), titanium(IV) oxide acteylacteonate {[TiO-
(acac)2]} (2 equiv.), and Li2CO3 (or Na2CO3 or K2CO3, 3 equiv.)
were dissolved in DMF, and the resulting mixture was stirred at
room temperature for 16 h. An immediate color change to dark
red was observed upon the addition of DMF. The solvents were
evaporated and the remaining solid dried in vacuo.
[1] A. von Zelewsky, Stereochemistry of Coordination Compounds,
Wiley, Chichester, 1995.
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von Zelewsky, O. Mamula, J. Chem. Soc. Dalton Trans. 2000,
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M. Albrecht, Chem. Rev. 2001, 101, 3457–3497; i) O. Mamula,
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305; Angew. Chem. Int. Ed. 1998, 37, 289–293; c) H. Murner,
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271, 36–39; d) O. Mamula, A. von Zelewsky, T. Bark, G.
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Chem. Int. Ed. 1999, 38, 2945–2948; e) O. Mamula, F. J. Mon-
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35, 1830–1833; b) R. Annunziata, M. Benaglia, M. Cinquini,
F. Cozzi, C. R. Woods, J. S. Siegel, Eur. J. Org. Chem. 2001,
173–180.
Li4[Ti2(1)3]: Compound
1
(40 mg, 77.73 mmol, 3 equiv.),
[TiO(acac)2] (13.6 mg, 51.82 mmol, 2 equiv.), and Li2CO3 (3.8 mg,
51.82 mmol, 2 equiv.) were used as described above. Yield: quanti-
tative. MS (ESI): m/z (%) = 542.5 (70) {H[Ti213]}3–, 544.8 (100)
{Li[Ti213]}3–, 817.7 (30) {H1Li1[Ti213]}2–, 820.7 (100)
{Li2[Ti213]}2–. C99H66Li4N6O12Ti2 (1655.11)·6DMF·13H2O: calcd.
C 60.37, H 5.80, N 7.22; found C 60.16, H 5.70, N 7.11.
Na4[Ti2(1)3]: Compound
1
(40 mg, 77.73 mmol, 3 equiv.),
[TiO(acac)2] (13.6 mg, 51.82 mmol, 2 equiv.), and Na2CO3 (5.5 mg,
51.82 mmol, 2 equiv.) were used as described above. Yield: quanti-
tative. MS (ESI): m/z (%) = 542.5 (5) {H[Ti213]}3–, 550.1 (100)
{Na[Ti213]}3–, 556.1 (30) [{Na[Ti213]·H2O}3– and some
{K[Ti213]}3–], 561.4 (15) {K[Ti213]·H2O}3–, 836.7 (50) {Na2-
[Ti213]}2–, 845.2 (15) {Na2[Ti213]·H2O}2–, 853.6 (5) [{Na1K1[Ti213]·
H2O}2– and some {K2[Ti213]}2–]. C99H66Na4N6O12Ti2 (1719.31)
·4DMF·15H2O: calcd. C 58.42, H 5.48, N 6.14; found C 57.90, H
5.14, N 6.23.
K4[Ti2(1)3]: Compound 1 (40 mg, 77.73 mmol, 3 equiv.), [TiO-
(acac)2] (13.6 mg, 51.82 mmol, 2 equiv.), and K2CO3 (7.2 mg,
51.82 mmol, 2 equiv.) were used as described above. Yield: quanti-
tative. MS (ESI): m/z (%) = 542.5 (5) {H[Ti213]}3–, 555.5 (100)
{K[Ti213]}3–, 561.5 (30) {K[Ti213]·H2O}3–, 833.7 (30)
{H1K1[Ti213]}2–, 844.2 (15) {Na1K1[Ti213]}2–, 852.7 (100)
{K2[Ti213]}2–, 861.7 (10) {K2[Ti213]·H2O}2–. C99H66K4N6O12Ti2
(1783.74)·3DMF·12H2O: calcd. C 58.45, H 5.04, N 5.68; found C
58.37, H 5.01, N 5.63.
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Li4[Ti2(2)3]: Compound
1
(40.5 mg, 77.73 mmol, 3 equiv.),
[TiO(acac)2] (13.6 mg, 51.82 mmol, 2 equiv.), and Li2CO3 (3.8 mg,
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5710
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Received: July 4, 2007
Published Online: October 1, 2007
Eur. J. Org. Chem. 2007, 5703–5711
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5711