Xanthene-based ligand with two adjacent β-diiminato binding sites

Article abstract of DOI:10.1021/jo060394y

A novel potential ligand has been designed where two β-dialdimine units are linked by a xanthene backbone (H₂Xanthdim). The synthesis proceeds via a double vinamidinium salt and the products of its hydrolysis (containing eneamine/malonaldehyde

Full text of DOI:10.1021/jo060394y

Xanthene-Based Ligand with Two Adjacent â-Diiminato Binding
Sites
Maurice Frederic Pilz, Christian Limberg,* and Burkhard Ziemer
Humboldt-UniVersita¨t zu Berlin, Institut fu¨r Chemie, Brook-Taylor-Str. 2, 12489 Berlin
christian.limberg@chemie.hu-berlin.de
ReceiVed February 24, 2006
A novel potential ligand has been designed where two â-dialdimine units are linked by a xanthene backbone
(H2Xanthdim). The synthesis proceeds via a double vinamidinium salt and the products of its hydrolysis
(containing eneamine/malonaldehyde units), which were converted into H2Xanthdim via a reaction with
2,3-dimethylaniline. The reaction of H2Xanthdim with n-butyllithium yields ((Et2O)Li)2Xanthdim, which
was isolated and crystallized. The crystal structures of both H2Xanthdim and its lithium salt are discussed.
Introduction
low oxidation states, it can be used to prepare coordinatively
unsaturated complexes, and often its complexes show interesting
reactivities, like the catalysis of epoxide/CO2 copolymerizations
(Zn),3 ring-opening polymerizations of lactides (Zn),4 cyclo-
propanations (Cu),5 olefin polymerizations (Cr),6 or the activa-
tion of dinitrogen (Fe).7
There are many examples in coordination chemistry, proving
that the cooperative behavior of two metal sites gives way to
potentials that are not open to mononuclear complexes,8 and
the same principle is used by many dinuclear metalloenzymes.9
For a given metal ion, the chemical and physical properties
of its complexes are determined by the ligands, and conse-
quently, in the past decades, a huge amount of research has
been dedicated to ligand design: it has been recognized that
the ligands are the key to new and improved functions and
applications. This contribution describes the synthesis of a novel
potential ligand providing two neighboring diiminato binding
sites.
(2) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. ReV. 2002,
102, 3031.
(3) Cheng, M.; Moore, D. R.; Reczek, J. J.; Chamberlain, B. M.;
Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 8738. Cheng,
M.; Darling, N. A.; Lobkovsky, E. B.; Coates, G. W. Chem. Commun. 2000,
2007. Cheng, M.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc.
1998, 120, 11018. Coates, G. W.; Moore, D. R. Angew. Chem. 2004, 116,
6784. Coates, G. W.; Moore, D. R. Angew. Chem., Int. Ed. 2004, 43, 6618.
(4) Cheng, M.; Ovitt, T. M.; Hustad, P. D.; Coates, G. W. Polym. Prepr.
(Am. Chem. Soc., DiV. Polym. Chem.) 1999, 40, 542. Cheng, M.; Attygalle,
A. B.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 1999, 121,
11583.
(5) Dai, X.; Warren, T. H. J. Am. Chem. Soc. 2004, 126, 10085.
(6) Gibson, V. C.; Newton, C.; Redshaw, C.; Solan, G. A.; White, A. J.
P.; Williams, D. J. Eur. J. Inorg. Chem. 2001, 1895. Gibson, V. C.; Maddox,
P. J.; Newton, C.; Redshaw, C.; Solan, G.; White, A. J. P.; Williams, D. J.
Chem. Commun. 1998, 1651.
Deprotonation of acetylacetone yields the well-known acet-
ylacetonato ligand A (abbreviation, acac), and the replacement
of the keto functions in A by imino groups leads to the
â-diketiminato ligand B (abbreviation, nacnac;1 other names,
diazapentadienide and â-iminatoaminat). Ligand B has proven
to be a very versatile ligand in the past, both in main group
and in transition metal chemistry:2 it stabilizes high as well as
* Corresponding author. Fax: +49 30 2093 6966.
(7) Smith, J. M.; Lachicotte, R. L.; Holland, P. L. Chem. Commun. 2001,
1542. Smith, J. M.; Lachicotte, R. L.; Pittard, K. A.; Cundari, T. R.; Lukat-
Rodgers, G.; Rodgers, K. R.; Holland, P. L. J. Am. Chem. Soc. 2001, 123,
9222.
(1) The designation [nacnac]- for the unsubstituted species [HC{C(Me)-
NH}2]- was first proposed by Theopold and co-workers: Kim, W.-K.;
Fevola, M. J.; Liable-Sands, L. M.; Rheingold, A. L.; Theopold, K. H.
Organometallics 1998, 17, 4541.
(8) Bosnich, B.; Gavrilova, A. Chem. ReV. 2004, 104, 349.
10.1021/jo060394y CCC: $33.50 © 2006 American Chemical Society
Published on Web 05/17/2006
J. Org. Chem. 2006, 71, 4559-4564
4559

Pilz et al.
SCHEME 1
Against this background it seemed rewarding to develop a
potential ligand with two adjacent diiminato binding sites,
especially because it has been shown that certain functions or
reactions of mononuclear nacnac complexes likewise are enabled
only by the cooperation of two molecules. Some ligands
fulfilling this requirement have already been described; in most
of these examples, the diiminato moieties are incorporated into
a macrocyclic ring system,10 in other cases two N atoms
belonging to different diiminato units are linked,11 and in all
these compounds, the chelating functions are arranged vis-a`-
vis to each other. Here we report the synthesis of a potential
ligand with a xanthene skeletal structure positioning two
diiminato binding sites in parallel. Exemplarily, a lithium
complex has been prepared, too.
Results and Discussion
Xanthene was chosen as the backbone because it was
anticipated to fix two diiminato units (once introduced in the
4,5 positions) in a distance that, after metal complexation, would
allow diatomic units to be bound between these metals.
At the same time, the xanthene spacer should permit the
formation of dinuclear complexes with monoatomic bridging
ligands, too, as the diiminato moiety is flexible enough in its
binding properties to allow complexed metals a sufficient
approach for that.2 It was, therefore, envisaged to develop
a synthesis in which two diiminato functions are (formally)
linked to the 4 and 5 positions of xanthene via their meso carbon
atoms.
It has been reported that -CH2-COOH groups can be
converted into malonaldehyde functions, which in turn can be
transformed into dialdiminato moieties: reaction of the corre-
sponding carboxylic acid with DMF/POCl3 leads in a complex
Vilsmeier-type reaction, whose mechanism is not quite clear
yet, to a vinamidinium salt;12 after subsequent hydrolysis, the
resulting malonaldehyde derivative can be transformed directly
(in situ) into the corresponding dialdimine derivative through
treatment with a chosen aniline.13 To make use of this procedure
for the preparation of the abovementioned potential ligand, first
of all the synthesis of a doubly -CH2-COOH substituted
xanthene derivative (4 in Scheme 1) was pursued.
hydrolysis of 3 yields the dicarboxylic acid 4, whose crystal
structure has been determined (as there are no peculiarities, a
discussion is avoided here).
The proceedings of these three reactions can be nicely
followed by 1H NMR spectroscopy, studying the region between
4.8 and 3.7 ppm, where the methylene protons absorb, and this
is important because, as a matter of course, it is essential for
the successful preparation of the target ligand to make sure that
in all steps the conversions nearly reach completion (as two
functions have to be reacted, naturally each percent loss in
conversion leads to two percent loss in yield); work up of the
raw material then leads to isolated yields between 65 and 85%.
Having prepared pure 4 in an acceptable overall yield, it was
employed to obtain a double vinamidinium salt according to
the abovementioned recipe for the parent compounds containing
only one vinamidinium unit. Severe modifications of the
published procedure13 were necessary to apply it to the present
problem (working under anhydrous conditions, longer reaction
times, and with excessive POCl3), but finally it indeed proved
possible to prepare 5Cl (Scheme 1). Vinamidinium salts incor-
porating chloride counteranions as in 5Cl were reported to have
undesirable thermal properties, and it has been recommended
to avoid isolation; characterizations and also subsequent reac-
tions were, thus, usually performed with the corresponding
hexafluorophosphate or perchlorate salts.12,13 In the present
study, the dication of 5 was investigated in combination with
chloride, hexafluorophosphate, and perchlorate anions. It was
found that 5Cl is isolable and reasonably stable under anhydrous
conditions; in this form it is ideally suited for subsequent
reactions. The corresponding hexafluorophosphate and perchlo-
It was finally achieved starting from the diol 1, which can
be prepared via known procedures:14 1 was converted into the
corresponding dibromide 2 via treatment with PBr3, subsequent
reaction with KCN then leads to the dicyanide 3, and acidic
(9) ComprehensiVe Coordination Chemistry II; McCleverty, J. A., Meyer,
T. J., Eds. (Que, L., Jr., Tolman, W. B., Vol. Eds.); Elsevier: Oxford, 2004;
Vol. 8, Chapters 8.1, 8.10, 8.13, 8.15, 8.19, and 8.24.
(10) Curtis, N. F. In ComprehensiVe Coordination Chemistry II;
McCleverty, J. A., Meyer, T. J., Eds. (Lever, A. B. P., Vol. Ed.); Elsevier:
Oxford, 2004; Vol. 1, Chapter 1.20. Lee, S. Y.; Na, S. J.; Kwon, H. Y.;
Lee, B. Y.; Kang, S. O. Organometallics 2004, 23, 5382. Lee, B. Y.; Kwon,
H. Y.; Lee, S. Y.; Na, S. J.; Han, S.; Yun, H.; Lee, H.; Park, Y.-W. J. Am.
Chem. Soc. 2005, 127, 3031.
(11) Bourget-Merle, L.; Hitchcock, P. B.; Lappert, M. F. J. Organomet.
Chem. 2004, 689, 4357. Vitanova, D. V.; Hampel, F.; Hultzsch, K. C. J.
Organomet. Chem. 2005, 690, 5182. Also compare Allen, S. D.; Moore,
D. R.; Lobkovsky, E. B.; Coates, G. W. J. Organomet. Chem. 2003, 683,
137 for an alternative approach involving, however, oxo imido units.
(12) Davies, I. W.; Marcoux, J.-F.; Wu, J.; Palucki, M.; Corley, E. G.;
Robbins, M. A.; Tsou, N.; Ball, R. G.; Dormer, P.; Larsen, R. D.; Reider,
P. J. J. Org. Chem. 2000, 65, 4571.
(13) Spencer, D. J. E.; Reynolds, A. M.; Holland, P. L.; Jazdzewski, B.
A.; Duboc-Toia, C.; Le Pape, L.; Yokota, S.; Tachi, Y.; Itoh, S.; Tolman,
W. B. Inorg. Chem. 2002, 41, 6307.
(14) Scheffler, G.; Behrendt, M. E.; Schmidt, R. R. Eur. J. Org. Chem.
2000, 21, 3527.
4560 J. Org. Chem., Vol. 71, No. 12, 2006

Xanthene-Based Ligand with â-Diiminato Binding Sites
FIGURE 1. Structural representation of the dication in 5ClO (hydrogen
4
atoms omitted for clarity).
rate salts could also be isolated, but the hexafluorophosphate
salt failed to react cleanly in subsequent reactions, while the
perchlorate salt proved to be unreactive. However, the latter
formed crystals that were suitable for a single-crystal X-ray
analysis. As a result of severe disordering of the perchlorate
anions, the solution did not reach a quality that would allow a
detailed discussion of bond lengths and angles; nevertheless,
the molecular structure of the dication in the solid, crystalline
state, as shown in Figure 1, is beyond doubt. The structure
exhibits planar, all-trans “W” configurations for the delocalized
allyl cations, which are naturally oriented parallel. The aryl rings
of the xanthene backbone are positioned almost perpendicular
to the allyl chain.
FIGURE 2. Structural representation of 7 (hydrogen atoms apart from
those at the N atoms are omitted for clarity).
TABLE 1. Bond Lengths [Å] and Angles [°] of Compound 7
C(24)-C(25)
C(25)-N(1)
C(26)-N(1)
C(24)-C(34)
C(34)-N(2)
C(35)-N(2)
1.365(4) C(43)-C(44)
1.351(3) C(44)-N(3)
1.403(4) C(45)-N(3)
1.432(4) C(43)-C(53)
1.305(3) C(53)-N(4)
1.425(3) C(54)-N(4)
1.380(4)
1.339(3)
1.409(4)
1.411(4)
1.320(3)
1.419(4)
C(25)-C(24)-C(34)
N(1)-C(25)-C(24)
C(25)-N(1)-H(1N)
C(25)-N(1)-C(26)
N(2)-C(34)-C(24)
C(34)-N(2)-C(35)
123.7(2) C(44)-C(43)-C(53)
126.5(3) N(3)-C(44)-C(43)
113.9(19) C(44)-N(3)-H(3N)
126.0(2) C(44)-N(3)-C(45)
123.6(3) N(4)-C(53)-C(43)
116.8(2) C(53)-N(4)-C(54)
122.0(2)
125.2(3)
114(2)
122.5(3)
123.5(3)
120.3(2)
The hydrolysis of 5Cl, that was envisaged to lead to two
malonaldehyde moieties, proceeds incompletely and yields a
mixture of three compounds containing two malonaldehyde units
6′, one malonaldehyde unit and one oxo eneamine unit, 6′′, or
two oxo eneamine units, 6′′′ (6, Scheme 1, with varying ratios
6′/6′′/6′′′), as evidenced by ESI investigation. At first sight, the
1H and 13C NMR spectra of this mixture look surprisingly
simple, as there are no obvious signals for the NMe2 groups.
This is due to the fact that incidentally the point of coalescence
for the NMe2 rotation is reached at 20 °C so that their signals
are broadened into the baseline. However, on cooling to -20
°C, the sets of signals expected for the compounds 6 can nicely
be observed. When the reactivity of the mixture 6′, 6′′, and 6′′′
was investigated, it turned out that the residual amino groups
in 6′′ and 6′′′ do not prohibit the next step (the conversion to
diiminato moieties). Hence, the raw material obtained after
hydrolysis of 5 does not have to be worked up before the final
conversion: the treatment with a chosen aniline derivative to
obtain a bis(â-dialdiminato) ligand of type 7. Commonly,
acceptable yields in this type of condensation reaction are only
observed, when the anilines employed are relatively electron
rich, that is, it is helpful when the aryl rings are substituted by
alkyl groups. For this reason and also for reasons of steric
shielding, in many cases 2,6-diisopropylaniline or 2,6-di-tert-
butylaniline have been employed in the past.2 However, the
i-propyl and tert-butyl groups appeared to be too bulky for the
present system, considering that in the target ligand 7 four aryl
residues are located in very close proximity. Hence, a more flat
aryl residue being substituted only on one side seemed more
appropriate, and accordingly, 2,3-dimethylaniline was chosen
as the starting material. Heating 6 together with a 6-fold excess
of 2,3-dimethylaniline in cyclohexane solution leads to 7
C(3)-C(2)-C(24)-C(34)
C(24)-C(25)-N(1)-C(26) 172.7(2) C(43)-C(44)-N(3)-C(45) 171.3(2)
C(13)-C(12)-C(43)-C(44) 131.0(3) C(43)-C(53)-N(4)-C(54) 177.2(2)
123.1(3) C(24)-C(34)-N(2)-C(35) 170.4(2)
(XANTHDIM) with an isolated yield of 30%. After recrystal-
lization from EtOH, single crystals could be obtained that were
suitable for an X-ray crystal structure analysis, and the result is
shown in Figure 2 (selected bond lengths and angles are listed
in Table 1).
The diiminato moieties are almost planar, and as the vin-
amidinium units in 5 they are oriented in parallel. However,
the torsion angles of the diiminato planes with respect to the
xanthene backbone are wider than those observed in 5
(C13C12C43C44 and C3C2C24C34 torsion angles of 131.0(3)
and 123.1(3)°). The H atoms of the NsH groups were located
and refined: they were found to be bonded primarily to one of
the two diimine nitrogen atoms, that is, at N3 and N1,
respectively (N3sH, 0.88(2) Å; N1sH, 0.89(2) Å). Further-
more, each of those hydrogen atoms is located close to the plane
formed by the two nitrogen atoms belonging to a respective
dialdimine unit and their connecting carbon atoms, with the
result that there are long N‚‚‚H contacts to N2 (2.09(2) Å) and
N4 (1.99(2) Å). In effect, N1 and N3 can be designated the
amine nitrogen atoms, and this is supported by the pattern of
NsC and CsC bond lengths in both units, as exemplified in
Chart 1 (the numbers in brackets refer to the second diiminato
function within 7/8).
These distances indicate that localization of the NdC
double bonds is far advanced, and a comparison with
published structures containing diketiminato moieties with
J. Org. Chem, Vol. 71, No. 12, 2006 4561

Pilz et al.
TABLE 2. Bond Lengths [Å] and Angles [°] of 8
CHART 1
C(24)-C(25)
C(25)-N(1)
C(26)-N(1)
C(24)-C(34)
C(34)-N(2)
C(35)-N(2)
1.388(6) C(43)-C(44)
1.330(5) C(44)-N(3)
1.412(5) C(45)-N(3)
1.410(6) C(43)-C(53)
1.325(5) C(53)-N(4)
1.429(5) C(54)-N(4)
1.413(6)
1.316(5)
1.426(6)
1.389(6)
1.327(5)
1.422(6)
C(25)-C(24)-C(34)
N(1)-C(25)-C(24)
C(25)-N(1)-Li(1)
C(25)-N(1)-C(26)
N(2)-C(34)-C(24)
C(34)-N(2)-Li(1)
C(34)-N(2)-C(35)
125.4(4) C(53)-C(43)-C(44)
128.5(4) N(3)-C(44)-C(43)
118.9(4) C(44)-N(3)-Li(2)
113.4(4) C(44)-N(3)-C(45)
127.6(4) N(4)-C(53)-C(43)
119.3(4) C(53)-N(4)-Li(2)
115.0(3) C(53)-N(4)-C(54)
125.0(4)
127.6(4)
119.7(4)
115.8(4)
127.5(4)
119.1(4)
116.0(4)
localized NdC bonds15 reveals a close similarity. Surprisingly,
the bond localization in one of the units (brackets) is more
pronounced than in the other one; the reasons for that are not
clear.
The addition of n-BuLi to 7 in Et2O solution and subsequent
recrystallization of the raw material from diethyl ether afforded
the lithium etherate 8 in the form of yellow crystals, which were
examined by single-crystal X-ray crystallography, too. The
crystal structure is shown in Figure 3, and relevant bond lengths
and angles are summarized in Table 2.
C(3)-C(2)-C(24)-C(34)
124.6(4) C(43)-C(44)-N(3)-C(45) 178.3(5)
C(24)-C(25)-N(1)-Li(1) 176.8(7) C(43)-C(44)-N(3)-Li(2) 170.7(7)
C(24)-C(25)-N(1)-C(26) 171.5(5) C(43)-C(53)-N(4)-C(54) 176.8(5)
C(13)-C(12)-C(43)-C(53) 132.6(5) C(43)-C(53)-N(4)-Li(2) 170.4(7)
C(24)-C(34)-N(2)-Li(1) 174.2(7) N(1)-Li(1)-N(2)-C(34) 176.6(6)
C(24)-C(34)-N(2)-C(35) 178.1(4) N(4)-Li(2)-N(3)-C(44) 178.9(6)
bond lengths are comparable to those previously described for
lithium atoms coordinated by nacnac,15 amide, and ether
ligands.16
Conclusions
In conclusion, we have established a synthetic route to 7,
which after deprotonation should represent an interesting
potential ligand for novel dinuclear complexes. The properties
of these complexes can be anticipated to vary from analogous
mononuclear compounds incorporating only one diiminato
binding pocket; the cooperating effect of the two metal ions in
complexes of 7 may even lead to advanced properties in
applications, and especially in this respect it will be interesting
to investigate the difference the parallel arrangement of the
chelating function makes for the cooperativity of the metal ions
in comparison to the “vis-a`-vis” orientation.
Furthermore, 7 was lithiated to give 8, which can be reacted
with metal halides directly for the synthesis of corresponding
metal complexes.
Experimental Section
All manipulations were carried out by means of Schlenk-type
techniques involving the use of a dry argon atmosphere. Solvents
were purified, dried, and degassed prior to use. Reagents were
obtained commercially and used without further purification.
Infrared (IR) spectra were recorded using samples prepared as KBr
pellets. Melting points are uncorrected.
4,5-Dibromomethyl-2,7-bis(1,1-dimethylethyl)-9,9-dimethyl-
xanthene, 2. 4,5-Dihydroxymethyl-2,7-bis(1,1-dimethylethyl)-9,9-
dimethylxanthene, 1 (18.5 g (0.048 mol)), is placed into a 1 L three-
necked flask in a dry atmosphere and dissolved in 600 mL of diethyl
ether. Lithium bromide (2.0 g (0.023 mol)) is added, and the
resulting suspension is treated at rt with 12 mL (0.126 mol) PBr3
(dropwise within 10 min). After stirring overnight and subsequent
cooling with ice, 20 mL of water is added to the suspension. The
mixture is neutralized with NaHCO3, the phases are separated, and
the aqueous phase is extracted twice with 200 mL of diethyl ether.
The two organic phases are combined and dried over MgSO4.
Evaporation of the solvent from the filtrate yields 21 g (0.041 mol,
85% yield) of 2.
FIGURE 3. Structural representation of 8 (hydrogen atoms omitted
for clarity, arrows point to covered atoms).
The replacement of hydrogen by lithium leaves the planarity
of the C3N2 unit unaffected. However, it can be seen (Chart 1)
that the two C-C and the two N-C distances within each of
the C3N2Li rings equalize so that both units in 8 become even
more symmetric than the more balanced unit within 7. This
indicates that the π bonding is now more delocalized for both
units to the same degree. In effect, 8 may be described as a
dinuclear diazapentadienide alkali metal complex; the Li-N
bond lengths are all very similar and lie in the range of 1.95-
1.92 Å. The Li ion has a trigonal planar coordination, with
angles that are strongly distorted from idealized values, for
example, N1-Li1-N2 and N3-Li2-N4 amount to only
100.1(4)° and 100.0(4)°, respectively. The Li-N and Li-O
(15) Compare, for instance: Stender, M.; Wright, R. J.; Eichler, B. E.;
Prust, J.; Olmstead, M. M.; Roesky, H. W.; Power, P. P. J. Chem. Soc.,
Dalton Trans. 2001, 3465. Mair, F. S.; Scully, D.; Edwards, A. J.; Raithby,
P. R.; Snaith, R. Polyhedron 1995, 14, 2397.
(16) Gregory, K.; Schleyer, P. v. R.; Snaith, R. AdV. Inorg. Chem. 1991,
37, 47. Pauer, F.; Power, P. P. In Lithium Chemistry. A Theoretical and
Experimental OVerView; Sapse, A. M., Schleyer, P. v. R., Eds.; Wiley: New
York, 1995; Chapter 9.
4562 J. Org. Chem., Vol. 71, No. 12, 2006

Xanthene-Based Ligand with â-Diiminato Binding Sites
Mp 212-213 °C. 1H NMR (400 MHz, CDCl3): δ 1.32 (s, 18H),
1.63 (s, 6H), 4.80 (s, 4H), 7.25 (d, J ) 2.26 Hz, 2H), 7.38 (d, J )
2.26 Hz, 2H). 13C NMR (100 MHz, CDCl3): δ 29.6, 31.5, 32.7,
34.5, 34.5, 123.8, 124.3, 125.7, 129.4, 145.6, 145.9. IR (KBr): υ˜
2963, 2904, 2869, 1457, 1363, 1280, 1229, 881, 758 cm-1. HRMS
(EI; m/z): calcd for C25H32Br2O, 506.0819; found, 506.0819. MS
(EI; m/z): 508 [M+], 493 [M+ - CH3], 429 [M+ - Br], 415 [M+
- CH2Br], 414 [M+ - Br - CH3], 349, 333, 330, 319, 271. Anal.
Calcd for C25H32Br2O (508.3): C, 59.07; H, 6.35. Found: C, 59.20;
H, 6.37.
4,5-Dicyanomethyl-2,7-bis(1,1-dimethylethyl)-9,9-dimethyl-
xanthene, 3. Compound 2 (20.5 g (0.04 mol)) is dissolved in 600
mL ethanol, and 21 g (0.32 mol) of KCN, dissolved in 40 mL water,
is added. After heating under reflux for 4 h, most of the ethanol is
removed under vacuum, and the residue is extracted several times
with diethyl ether. The combined organic phases are dried over
MgSO4. Evaporation of the solvent from the filtrate yields a
brownish solid, which is recrystallized from ethanol. After drying
under vacuum, 12.6 g (0.031 mol, 78% yield) of white 3 is isolated.
Mp 181-183 °C. 1H NMR (400 MHz, CDCl3): δ 1.32 (s, 18H),
1.64 (s, 6H), 3.87 (s, 4H), 7.20 (d, J ) 2.38 Hz, 2H), 7.39 (d, J )
2.38 Hz, 2H). 13C NMR (100 MHz, CDCl3): δ 19.6, 31.4, 32.9,
34.4, 34.6, 116.7, 117.9, 123.2, 125.0, 129.3, 145.1, 146.3. IR
(KBr): υ˜ 2966, 2910, 2873, 2247 (ν(CN)), 1460, 1417, 1365, 1333,
1277, 1224, 877, 848, 754 cm-1. HRMS (ESI; m/z): calcd for
C27H32N2O + Na+, 423.2407; found, 423.2407. HRMS (ESI;
m/z): calcd for C27H32N2O + K+, 439.2146; found, 439.2148. MS
(ESI; m/z): 839 [2M + K+], 823 [2M + Na+], 447, 439 [M +
K+], 423 [M + Na+], 418 [M + NH4+]. Anal. Calcd for C27H32N2O
(400.5): C, 80.96; H, 8.05; N, 6.99. Found: C, 80.02; H, 8.10; N,
6.46.
the solvent is removed, leaving behind 1.5 g of an orange solid
that mainly contains 6 (1.5 g/3.0 mmol, 85%). This raw material
can be employed directly in the synthesis of 7 without further
purification.
As pointed out in Results and Discussion, the dimethylamino
groups are coalescent at rt so that averaged spectra are observed.
Exemplarily, the NMR data for 6′′′ are: 1H NMR (300 MHz,
CD2Cl2): δ 1.33 (s, 18H), 1.67 (s, 6H), 2.3-3.3 (b, 6H), 6.79 (s,
2H), 7.04 (d, J ) 2.4 Hz, 2H), 7.37 (d, J ) 2.4 Hz, 2H), 9.03 (s,
2H). 13C{1H} NMR (75 MHz, CD2Cl2): δ 31.6, 33.1, 34.6, 34.8,
37-40 (b), 45-48 (b), 110.9, 122.1, 122.2, 128.6, 128.9, 144.8,
145.9, 159.5, 188.3. Only lowering the temperature to -20 °C
allows the observation of resolved signals for the NMe2 groups:
1H NMR (400 MHz, CD2Cl2, -20 °C): δ 1.29 (s, 18H), 1.65 (s,
6H), 2.40 (s, 6H), 3.06 (s, 6H), 6.80 (s, 2H), 7.01 (d, J ) 2.2 Hz,
2H), 7.33 (d, J ) 2.2 Hz, 2H), 8.98 (s, 2H). 13C{1H} NMR (100
MHz, CD2Cl2): δ 31.3, 33.3, 34.3, 34.3, 37.9, 47.0, 109.9, 121.6,
122.1, 128.1, 128.3, 144.3, 144.9, 159.5, 188.1. The 1H NMR
spectrum at 40 °C shows only one broad peak for the NMe2
groups: 1H NMR (300 MHz, CD2Cl2, 40 °C): δ 1.34 (s, 18H),
1.67 (s, 6H), 2.60-2.85 (b, 6H), 6.70-6.86 (b, 2H), 7.04 (d, J )
2.4 Hz, 2H), 7.38 (d, J ) 2.4 Hz, 2H), 9.04 (s, 2H).
6: HRMS (ESI; m/z): calcd for C33H45N2O3 + Na+ (6′′′),
539.3244; found, 539.3243. HRMS (ESI; m/z): calcd for C33H45N2O3,
517.3425; found, 517.3424. HRMS (neg. ESI; m/z): calcd for
C31H38NO4 (6′′), 488.2795; found, 488.2795. MS (ESI; m/z): 461
[M- - H+] (6′); 488 [M- - H+] (6′′); 516 [M+] (6′′′).
2,7-Bis(1,1-dimethylethyl)-9,9-dimethyl-4,5-bis(1-(2,3-dimethyl-
phenylamino)-3-(2,3-dimethylphenylimino)isopropenyl)-xanthene,
7. Raw material obtained in the synthesis of 6 (1.5 g) is dissolved
in 150 mL of cyclohexane and 5 mL (41 mmol) of 2,3-
dimethylaniline, and 1.5 g (7.9 mmol) of p-toluenesulfuric acid is
added. The flask is equipped with a Dean Stark apparatus and a
reflux condenser wearing a drying tube on top, and the mixture is
heated for 3 days under reflux. The resulting solution is neutralized
with a saturated solution of NaHCO3, and the aqueous phase is
extracted with a mixture of diethyl ether and tetrahydrofuran in a
ratio of 2:1. After drying the combined organic phases with MgSO4,
all volatile compounds are removed from the filtrate under vacuum.
The resulting amber oil is recrystallized several times from absolute
ethanol and dried sufficiently under vacuum so that 820 mg (0.94
mmol) of pure 7 is obtained as a yellow solid (27% starting from
the acid).
4,5-Diethylcarboxy-2,7-bis(1,1-dimethylethyl)-9,9-dimethyl-
xanthene, 4. Compound 3 (12.6 g (31.5 mmol)) is placed into a 1
L flask, and 150 mL of water and 150 mL of glacial acetic acid, as
well as 150 mL of concentrated sulfuric acid, are added. After
refluxing for 6 h, the resulting mixture is extracted three times with
100 mL of diethyl ether. The combined ether phases are dried with
MgSO4, and, after filtration, the solvent is removed. The resulting
beige solid is washed with acetone. This leads to 8.9 g (20.3 mmol,
65% yield) of white 4. Colorless crystals could be obtained by the
slow evaporation of a THF solution of 4.
1
Mp 291 °C. H NMR (400 MHz, THF-d8): δ 1.32 (s, 18H),
1.62 (s, 6H), 3.72 (s, 4H), 7.18 (d, J ) 2.38 Hz, 2H), 7.37 (d, J )
2.38 Hz, 2H), 10.78 (b, 2H). 13C NMR (100 MHz, THF-d8): δ
31.9, 32.7, 35.0, 35.4, 36.2, 122.1, 123.2, 126.7, 129.9, 145.4, 147.4,
172.7. IR (KBr): υ˜ 2963, 2907, 2872, 1715 (ν(CO)), 1458, 1278,
1225 cm-1. HRMS (EI; m/z): calcd for C27H34O5, 438.2406; found,
Mp 247 °C. 1H NMR (400 MHz, CDCl3): δ 1.34 (s, 18H), 1.73
(s, 6H), 2.01 (s, 12H), 2.12 (s, 12H), 6.65 (d, J ) 7.2 Hz, 4H),
6.73 (d, J ) 7.2 Hz, 4H), 6.79 (ps-t, J ) 7.6 Hz, 4H), 7.12 (d, J )
2.4 Hz, 2H), 7.35 (d, J ) 2.4 Hz, 2H), 7.92 (d, J ) 5.2 Hz, 1H),
12.16 (ps-t, J ) 5.2 Hz, 2H). 13C{1H} NMR (100 MHz, CDCl3):
δ 13.9, 20.3, 31.6, 33.2, 34.7, 34.8, 106.4, 114.3, 121.0, 124.8,
125.7, 126.0, 126.5, 127.7, 129.4, 136.8, 145.2, 145.3, 145.8, 150.9.
438.2406. MS (EI; m/z): 438 [M+], 423 [M+ - CH3], 281 [M+
-
CH3 - H2O]. Anal. Calcd for C27H34O5 (438.5): C, 73.94; H, 7.81.
Found: C, 73.54; H, 7.78.
IR (KBr): υ˜ 3434 (NH), 2962, 2864, 1640, 1542, 1286, 1266 cm-1
.
2,7-Bis(1,1-dimethylethyl)-9,9-dimethylxanthene-4,5-bis(1,3-
bis(dimethylamino)trimethinium Chloride), 5Cl, and Its Hy-
drolysis Products, 6. Compound 4 (1.5 g (3.4 mmol)) is dissolved
in 15 mL of dry DMF. After cooling to 0°C, 3.4 mL (37 mmol) of
phosphoryl chloride is added slowly via a syringe. Subsequently,
the solution is allowed to warm to rt (during this process it turns
yellow). The reaction vessel is equipped with a reflux condenser
wearing a drying tube on top, and the mixture is heated to 84 °C
for 17 h. A beige suspension is formed from which the solution is
removed via cannula. The beige solid residue mainly consists of
5Cl (by redissolution and addition of NaClO4, it can be converted
HRMS (EI; m/z): calcd for C61H70N4O1, 874.5549; found, 874.5549.
MS (EI; m/z): 874.6 [M+], 753.5 [M+ - C8H10N - H], 633.4 [M+
- 2 C8H10N - H], 121 [C8H9NH2+]. Anal. Calcd for C61H70N4O
(875.2): C, 83.71; H, 8.06; N, 6.40. Found: C, 83.17; H, 8.56; N,
6.28.
Dilithium 2,7-Bis(1,1-dimethylethyl)-9,9-dimethyl-4,5-bis(1-
(2,3-dimethylphenylamido)-3-(2,3-dimethylphenylimino)isopro-
penyl)-xanthene, 8. Compound 7 (200 mg (0.230 mmol)) is
dissolved in 10 mL diethyl ether, and the solution is cooled to -78
°C. n-Butyllithium (0.18 mL (0.46 mmol)) is added via a syringe,
and after further 10 min of stirring, the solution is warmed to rt. It
is subsequently concentrated to a volume of about 2 mL, and storing
at rt for 3 days finally leads to the precipitation of 152 mg (0.121
mmol, 53%) of yellow crystals of 8.
into 5ClO , which can be crystallized (see Figure 1)), and for the
4
preparation of 6, it is treated directly without further purification
with a solution of 4 g (0.1 mol) of NaOH in 40 mL of a 1:1 EtOH/
water mixture. After heating for 1 h under reflux, the solution is
buffered with NaHCO3 and diluted hydrochloric acid, the EtOH is
removed under vacuum, and the resulting dispersion is extracted
several times with a mixture of diethyl ether and tetrahydrofuran
in a ratio of 2:1. After drying over magnesium sulfate and filtering,
1H NMR (400 MHz, THF-d8): δ 1.34 (s, 18H), 1.63 (s, 6H),
2.14 (s, 24H), 6.57 (d, J ) 7.6 Hz, 4H), 6.70 (ps-t, J ) 8.0 Hz,
4H), 6.90 (d, J ) 8.0 Hz, 4H), 7.09 (ps-dd, J ) 2.4, 9.00 Hz, 8H),
7.94 (s, 4H). 13C NMR (100 MHz, THF-d8): δ 14.9, 20.8, 32.1,
J. Org. Chem, Vol. 71, No. 12, 2006 4563

Pilz et al.
34.8, 35.0, 35.5, 105.2, 119.2, 121.2, 123.6, 127.0, 127.2, 128.7,
atoms of 7 were found and refined isotropically, while all hydrogen
atoms of 8 were added geometrically and refined by using a riding
model.
129.4, 134.2, 136.4, 144.0, 145.7, 157.4, 161.1. IR (KBr): υ˜ 2958,
2867, 1641, 1571, 1458, 1374, 1323, 1244, 1216, 1052, 778 cm-1
.
Anal. Calcd for C61H68Li2N4O‚(C4H10O)2 (1035.3): C, 80.04; H,
The final residuals are indicated in Table S1. The crystallographic
data (apart from structure factors) of 4, 7, and 8 were deposited at
the Cambridge Crystallographic Data Centre as supplementary
publication nos. CCDC-298178, CCDC-298176, and CCDC-
298177. Copies of the data can be ordered free of charge from the
following address in Great Britain: CCDC, 12 Union Road,
Cambridge CB2 1EZ (fax: (+44)1223-336-033; E-mail:
deposit@ccdc.cam.ac.uk).
8.56; N, 5.41. Found: C, 80.13; H, 8.31; N, 5.74.
X-ray Diffraction Data Collection for 4, 7, and 8. Single
crystals of the compounds were selected in a cold stream of
nitrogen. They were then mounted on top of a fiber and quickly
frozen to -93 °C. Centered reflections were refined by least-squares
calculations to indicate the unit cells. Unit cell and collection
parameters for the complexes are listed in Table S1 in the
Supporting Information section. Diffraction data were collected in
the appropriate hemispheres and under the conditions specified also
in Table S1.
Solution and Refinement of the Structures of 4, 7, and 8.
The structures were solved by direct methods (program, SHELXS-
97)17 and refined versus F2 (program, SHELXL-97)18 with aniso-
tropic temperature factors for all nonhydrogen atoms. The hydrogen
Acknowledgment. We are grateful to the Fonds der
Chemischen Industrie, the BMBF, and Dr. Otto Ro¨hm
Geda¨chtnisstiftung for financial support. We also would like to
thank P. Neubauer for crystal structure analyses.
Supporting Information Available: Table S1 and crystal-
lographic information files for 4, 7, and 8. This material is available
free of charge via the Internet at http://pubs.acs.org.
(17) Sheldrick, G. M. SHELXS-97; Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(18) Sheldrick, G. M. SHELXS-97; Program for Crystal Structure
Solution; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
JO060394Y
4564 J. Org. Chem., Vol. 71, No. 12, 2006