Synthesis and X-ray crystal structures of imido and ureato derivatives of titanium(iv) phthalocyanine and their application in the catalytic formation of carbodiimides by metathesis from isocyanates

Article abstract of DOI:10.1039/c0dt00867b

The imido titanium phthalocyanine complex [PcTi(NDip)] (Dip = 2,6-diisopropylphenyl) 2a was synthesized from [PcTiO] 1 and one eq. of DipNCO. Due to the steric demand of the Dip group, addition of another isocyanate molecule to the TiN functionality of 2a does not occur even at high molar ratios of DipNCO. However, 1 reacts with 2 eq. of arylisocyanates containing sterically less demanding aryl groups producing N,N′- diarylureatotitanium(iv)phthalocyanines [PcTi{κ²-(NR)C(O) (N′R)}] (R = p-tolyl (Tol) 3a or mesityl (Mes) 3b). The N,N′ coordination (III) of the ureato ligand in 3a and 3b was proven by a single set of resonances for the aryl groups in their ¹H-NMR spectra. An N,O coordination (IV) can therefore be excluded. This is also confirmed by the X-ray crystal structure of 3a. Upon heating [PcTiO] and an excess of aryl isocyanates for 6 days, a steady evolution of CO₂ was observed and a white precipitate, identified as the corresponding diarylcarbodiimides (V), could be isolated. Therefore this reaction was applied in the metathetic conversion of two isocyanate molecules into diarylcarbodiimides (V) and CO₂. Additionally, imido titanium Pc's 2b (R = tBu) and 2c (R = Mes) were prepared by a more general synthetic strategy, reacting the potassium salt of the ligand PcK₂ with appropriate imido titanium precursors.

Full text of DOI:10.1039/c0dt00867b

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PAPER
Synthesis and X-ray crystal structures of imido and ureato derivatives of
titanium(IV) phthalocyanine and their application in the catalytic formation of
carbodiimides by metathesis from isocyanates†
Wael Darwish, Elisabeth Seikel, Ralf Ka¨smarker, Klaus Harms and Jo¨rg Sundermeyer*
Received 19th July 2010, Accepted 9th December 2010
DOI: 10.1039/c0dt00867b
The imido titanium phthalocyanine complex [PcTi(NDip)] (Dip = 2,6-diisopropylphenyl) 2a was
synthesized from [PcTiO] 1 and one eq. of DipNCO. Due to the steric demand of the Dip group,
addition of another isocyanate molecule to the Ti N functionality of 2a does not occur even at high
molar ratios of DipNCO. However, 1 reacts with 2 eq. of arylisocyanates containing sterically less
demanding aryl groups producing N,N¢-diarylureatotitanium(IV)phthalocyanines
2
[PcTi{k -(NR)C(O)(N¢R)}] (R = p-tolyl (Tol) 3a or mesityl (Mes) 3b). The N,N¢ coordination (III) of
the ureato ligand in 3a and 3b was proven by a single set of resonances for the aryl groups in their
1H-NMR spectra. An N,O coordination (IV) can therefore be excluded. This is also confirmed by the
X-ray crystal structure of 3a. Upon heating [PcTiO] and an excess of aryl isocyanates for 6 days, a
steady evolution of CO2 was observed and a white precipitate, identified as the corresponding
diarylcarbodiimides (V), could be isolated. Therefore this reaction was applied in the metathetic
conversion of two isocyanate molecules into diarylcarbodiimides (V) and CO2. Additionally, imido
titanium Pc’s 2b (R = tBu) and 2c (R = Mes) were prepared by a more general synthetic strategy,
reacting the potassium salt of the ligand PcK2 with appropriate imido titanium precursors.
phthalocyanines, their reactions and thermochemistry and their
Introduction
use in catalysis.
Titanyl phthalocyanines ([PcTiO]) have found many applications,
Macrocycle-supported imido complexes such as porphyrins and
such as their use in the manufacture of organic photoreceptors
cumulenes could not be prepared by the direct reaction of the
in electrographic printing devices1–5 and in CD-R optical data
corresponding titanium oxo species with RNCO. For porphyrins,
storage.6 In this context, surprisingly little is known about the
functionalization of the axial oxo group in titanium phthalo-
cyanines (TiPc’s). Next to the parent compounds [PcTiO]7–9
the imido complex [(TTP)Ti(NR)] (TTP = tetratolylporphyrinato
dianion) can be prepared by the reaction of [(TTP)TiCl2] with 2
2
eq. of LiNHR16,17 or by the reaction of [(TTP)Ti(h -3-hexyne)]
and [PcTiCl2],10 other axially substituted TiPc’s reported in
the literature are oxalato, catecholato, dithiocatecholato11–13 and
chalcogenido derivatives [PcTiX] (X = S, Se, or Te).14 Recently,
we described that [PcTiO] can be activated by reaction with p-
tolyl isocyanate, and that the assumed intermediate, an N,N¢-
bis-p-tolyl ureato(2-) complex, can be used for protolytic ligand
exchange reactions with SH-, OH- and NH-acidic ligands.15
However, the isolation of this valuable ureato key compound in
pure form, its full characterization and mechanistic studies, adding
proof for terminal imido titanium phthalocyanines as reactive
intermediates, have not been accomplished so far. This report
describes the isolation of pure ureato and first imido titanium
with RNCO or RNCNR.18 Similarly, the imido porphyrins of
other group 4 metals [(TTP)M(NR)] (M = Zr or Hf) could not
be prepared from the oxo complexes and tBuNCO but from
the reaction of the dichloro complexes with 2 eq. of LiNHR.19
Another synthetic strategy leading to macrocycle-supported imido
titanium complexes is the reaction of alkaline metal ligand
salts with imido titanium precursors. Thus the imido complexes
4
[(k -Mentaa)Ti(NtBu)] (n = 4 or 8, taa = tetra- or octamethyl-
dibenzotetraaza[14]-annulene) were prepared by the reaction of
Li2[Mentaa] with [Ti(NtBu)Cl2(tBupy)2].20 A porphyrin analogue
was synthesized by a similar procedure.21 Using this compound
as starting material, Mountford et al.22 prepared the arylimido
4
derivatives [(k -Me4taa)Ti(NR)] (R = Ph, Tol). They found that the
Philipps-Universita¨t Marburg, Fachbereich Chemie, Hans-Meerwein Straße,
35043, Marburg. E-mail: jsu@staff.uni-marburg.de; Fax: + 49 6421
2825711; Tel: +49 6421 2825693
† CCDC reference numbers 269282 and 269283. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/c0dt00867b
reaction of these compounds with RNCO produces symmetric and
4
2
asymmetric N,N¢-diarylureato compounds. [(k -Me4taa)Ti{k -
(NTol)C(O)(N¢Tol)}] could also be obtained by the reaction of
the oxo derivative with TolNCNTol.23
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is possible and results in the formation of N,N¢-ureato complexes
(III). Upon heating of 1 with isocyanates containing smaller
substituents for 6 days, a steady evolution of CO2 was observed and
a white precipitate, identified as the corresponding carbodiimide
(V), could be isolated. The carbodiimide is presumably formed as
a result of slow isomerization of the N,N¢- bound ureato complex
(III) to the N,O-bound complex (IV) after which IV decomposes
into the carbodiimide and [PcTiO] upon cleavage of the Ti–N and
Ti–O bonds.24
Since the reaction of [PcTiO] with isocyanates only yields
imido compounds if very bulky aryl substituents such as Dip are
employed, we searched for a more general synthetic strategy for
the target molecules [PcTi(NR)]. Mountford et al. showed that
the reaction of dilithium salts of various macrocyclic ligands with
appropriate imido titanium precursors lead to the desired imido
compounds. In order to apply this method to phthalocyanine
chemistry, it is crucial to note, that commercially available PcLi2
commonly contains the not fully lithiated species PcLiH and PcH2.
While PcLi2 reacts with titanium precursors in the desired way,
PcLiH and PcH2 do not, and the obtained mixtures can not
be separated properly. We therefore tested various lithium bases
in the deprotonation of PcH2 to obtain pure PcLi2, but while
LiN(SiMe3)2 does not complete the reaction, stronger bases such
as LiNiPr2 or BuLi lead to ortho-directed deprotonation of the
aromatic system.25,26
Results and discussion
As one of the synthetic strategies for the replacement of the
oxo functionality and generating an organoimido group, we
chose the metathesis of [PcTiO] 1 with organic isocyanates
ArNCO (Scheme 1). This metathetic transformation was found
to depend largely on the size of the aryl group. For the bulky
2,6-diisopropylphenyl group, the imido complex [PcTi(NDip)] 2a
was the final product. For the sterically less demanding groups,
2
R = Tol or mesityl, the N,N¢-diarylureato complexes [PcTi{h -
(NR)C(O)(N¢R)}] (R = Tol 3a or Mes 3b), could be isolated in a
pure form.
Scheme 1 Reaction of [PcTiO] 1 with different arylisocyanates.
The suggested reaction mechanism (Scheme 2) includes a
[2 + 2]-cycloaddition of an isocyanate molecule with the titanyl
group forming a CO2-adduct (I) as cyclic intermediate. This
unstable metallocycle readily loses a molecule of CO2 forming
the corresponding imido complex [PcTi(NR)] (2a). In the case of
sterically demanding 2,6-diisopropylphenyl isocyanate only one
addition step occurs and the imido complex is the final product.
Addition of a second isocyanate molecule to the Ti NDip
functionality is hindered because of the high steric demand of the
two isopropyl groups. In the case of arylisocyanates containing
sterically less demanding aryl groups (Ar = Tol or Mes) a second
[2 + 2]-cycloaddition of an isocyanate molecule at the Ti N-bond
On the other hand, we found that the reaction of 2.5 eq. of
benzyl potassium with PcH2 gives pure PcK2. The absence of any
protonated Pc species is confirmed by MALDI–TOF and UV/vis
spectra. PcK2 was then reacted with titanium imido precursors
of the type [Ti(NR)Cl2py2–3] in THF. Many such precursors have
been described in the literature,27–29 and we decided to confine
ourselves to the use of [Ti(NtBu)Cl2py3] as an alkyl imdo precursor
and [Ti(NMes)Cl2py2] as an aryl imido precursor (Scheme 3).
We obtained imido titanium phthalocyanines [PcTi(NtBu)] (2b)
and [PcTi(NMes)] (2c), and we believe that our method can be
generally applied to synthesize imido titanium phthalocyanines.
Scheme 3 Formation of imido titanium Pc’s via insertion.
The 1H-NMR spectra of 2a–c, 3a and 3b show resonance at the
expected chemical shifts, and the integral values are in accordance
with the suggested structures. The phthalocyanine unit shows
the characteristic AA¢BB¢ pattern in the aromatic region typical
for unsubstituted Pc’s.30 The resonances for the eight protons in
the 1,4-positions occur at 9.64–9.93 ppm and those for the eight
protons in the 2,3-positions at 8.25–8.47 ppm. The typical, strong
downfield shift of the aromatic protons of the macrocyle is due
to the well-known ring current effect.13,30 This is also the reason
why the signals of the axial ligands, which are perpendicular to the
Scheme 2 Suggested mechanism for the reaction of [PcTiO] 1 with
arylisocyanates and catalytic carbodiimide formation.
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Table 1 Thermal analysis data of 2a, 3a and 3b
First degradation stage
Second degradation stage
Temp./◦C
Weight loss (%) (calcd.)
Lost unit
Temp./◦C
Weight loss (%) (calcd.)
Lost unit
2a
3a
3b
300–420
212–260
317–320
23.8 (24)
16.8 (18)
19.0 (22)
DipN
TolNCO
MesNCO
—
260–520
320–435
—
30.0 (30)
34.4 (35)
—
TolN
MesN
ring plane, are shifted to higher field. The single set of resonances
for the two N-bound aryl groups of the ureato ligand in 3a or 3b
reveals that these two aryl groups are equivalent. This suggests
the presence of the symmetric N,N¢-coordination (III) rather than
the unsymmetric N,O-bound one (IV) in solution, which is also
supported by the crystal structure of 3a.
The m/z values of the molecular ions of imido- and ureato-
TiPc’s 2a–c and 3a–b were observed in EI, APCI and MALDI–
TOF measurements with the expected isotopic patterns. The
molecular ion peak of 1 (M+ = 576) was not observed in the
products. Purity was confirmed by elemental analyses (C, H, N,
Ti). The IR spectra of all TiPc’s show the typical absorptions
of the basic Pc moiety, such as nC at 1608 cm-1, while the
C
characteristic Ti O stretching band (nTi at 965 cm-1) is not
O
observed.31 Additionally, the vibrations at 1683 cm-1 (3a) and
1684 cm-1 (3b) can be assigned to the carbonyl group (nC O).24
UV/vis spectra of 1, 2a and 3a (Fig. 1) show the characteristic
Fig. 2 TGA diagram of 2a.
analysis of 2a (Fig. 2) shows that the molecule loses the imido
ligand ([NDip], C12H17N) in a first degradation step in the
temperature range of 300–420 ◦C. The loss of the ureato ligand in
3a and 3b occurs in the temperature range of 220–300 ◦C within
two steps (Fig. 3). The first step can be attributed to the loss
of ArNCO molecule via a [2 + 2]-cyclo reversion and formation
of an imido complex. The second step is the loss of nitrene
fragment [ArN] producing [PcTi]. In addition, the decomposition
of the Pc macrocycle starts at about 550 ◦C, which is common
for metalphthalocyanines. The observed weight losses match well
with the theoretical values for the supposed decomposition steps
(Table 1). This controlled stepwise thermal decomposition will be
further exploited to generate highly reactive intermediates [PcTi]
and to trap these with added ligands.
absorptions for metal phthalocyanine.11–13,31,32 The Q band at lmax
=
698 nm is attributed to a p–p* transition. The shoulders at
665 nm and 628 nm can be attributed to vibronic transitions.33
A second allowed p–p* transition (B band) is observed around
340 nm. Generally, no significant changes are induced in the
absorption spectra upon replacement of the titanyl group by imido
or ureato ligands. This is attributed to the fact that the absorption
energies and patterns arise mainly from the phthalocyanine
basic moiety and are only slightly affected by the nature of the
axial ligands.11–13 No significant solvent dependence was observed
when the absorption measurements were carried out either in
chloronaphthalene, dichloromethane or chloroform.
Fig. 3 TGA diagram of 3b.
Fig. 1 UV/vis spectra of 1, 2a and 3a in CHCl3.
Crystal structure of 2a
The stepwise thermal degradation of a Pc molecule may be
used to give an idea about its structure.34 The thermogravimetric
Single crystals of imido titanium compound 2a could be obtained
by controlled cooling of a 1-chloronaphthalene solution. The
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◦
˚
Table 2 Selected bond lengths [A] and angles [ ] for 2a
Ti–N1
Ti–N22
Ti–N41
C42–N41–Ti
N41–Ti–N22
N41–Ti–N1
N22–Ti–N32
N12–Ti–N32
N1–Ti–N32
2.056(2)
2.057(2)
1.712(2)
179.0(2)
107.7(1)
106.0(1)
84.9(1)
Ti–N12
Ti–N32
N41–C42
N41–Ti–N12
N12–Ti–N22
N12–Ti–N1
N41–Ti–N31
N22–Ti–N32
2.054(2)
2.063(2)
1.393(4)
106.0(1)
85.4(1)
85.2(1)
107.7(1)
84.9(1)
146.3(1)
85.3(1)
crystal structure of 2a (Fig. 4) shows a very similar coordination
geometry to that of its analogue phenylimido titanium tetratoluyl-
porphyrine [(TTP)Ti(NPh)].16 The geometry around the titanium
atom is square-pyramidal with the four isoindoline nitrogen atoms
forming the basal plane and the imido group at the apical site.
Due to the presence of the axial ligand, the titanium atom is
displaced from the plane defined by the four isoindoline nitrogen
˚
atoms toward the imido ligand by 0.597 A. This in turn causes the
aromatic system to deviate from planarity and adapt a “saucer”-
like shape.35 The imido titanium group is essentially linear with a
C42–N41–Ti angle of 179.0(2)◦. The slight deviation from 180◦ is
in the typical range for imido titanium compounds.27 The imido
Fig. 5 The molecular packing of 2a. H atoms are omitted for clarity.
˚
bond length [Ti–N41] is 1.712(1) A, which corresponds to a Ti–N
The configuration around the titanium atom is best described
as a capped square pyramid with the four isoindoline nitrogen
atoms almost lying in one plane. The ureato ligand occupies
two neighboring apical coordination sites. The titanium atom in
triple bond. Selected bond lengths and bond angles of 2a are given
in Table 2.
˚
3a is more displaced from the N4 plane (0.763 A) than in 2a
˚
(0.597 A). The ureato ligand is bound to the titanium atom in
the symmetrical N,N¢-coordination (not N,O-coordinated). This
1
confirms the result of H-NMR spectroscopy. The metallacycle
fragment encloses an obtuse N–C–N angle of 100.5(5)◦ as well
as an acute N–Ti–N angle of 65.6(2)◦. Selected bond lengths
and bond angles of 3a are given in Table 3. The dihedral angle
between the two planes defined by N12,Ti1,N32 and N42,Ti1,N50
is 3.8(2)◦. Therefore, the ureato ligand lies essentially coplanar
with the N12–Ti1–N32 fragment. A comparison of the bonding
parameters of 2a and 3a with [PcTiO] 1 and [PcTiCl2]10 is displayed
in Table 4.
◦
˚
Table 3 Selected bond lengths [A] and angles [ ] for 3a
Fig. 4 Molecular structure of 2a, H atoms are omitted for clarity.
Ellipsoids are shown at 50% probability.
C41–N42
C41–O41
C41–N50
N1–Ti
1.396(7)
1.221(7)
1.402(7)
2.060(5)
2.111(1)
65.6(2)
130.6(5)
100.5(5)
82.3(2)
N22–Ti
N32–Ti
N42–Ti
N50–Ti
2.066(5)
2.104(5)
1.982(4)
1.990(5)
Fig. 5 shows the molecular arrangement in the unit cell of
2a. Due to the p–p interactions of the macrocycles the structure
consists of closely packed of face-to-face dimers with a distance
N12–Ti
N42–Ti–N50
O41–C41–N42
N42–C41–N50
N22–Ti–N12
N1–Ti–N32
N1–Ti–N12
N1–Ti–N22
C41–N42–Ti
C41–N50–Ti
82.0(2)
140.3(2)
97.1(3)
96.5(3)
˚
between two adjacent N4-planes of 3.41(1) A. The arrangement
of the molecules as face-to-face dimers is also observed for a
modification of [PcTiO]. This packing in 2a is much less dense due
to the sterically demanding 2,6-diisopropylphenyl-group, which
may explain the better solubility of 2a–c compared to [PcTiO].9,36
However, the two molecules of the dimer are related to each other
by a crystallographic inversion centre.
82.9(2)
˚
Table 4 Comparison of selected bond distances [A] in [PcTiCl2], 1, 2a
and 3a. d(Ti–Nisoindoline) refers to the average Ti–Nisoindoline distance
Complex
d(Ti–Nisoindoline
)
d(Ti–N4-plane
)
Ref.
Crystal structure of 3a
[PcTiCl2]
1
2a
3a
2.087
2.067
2.062
2.085
0.84
0.63
0.60
0.76
10
9
Suitable crystals for X-ray diffraction of ureato complound 3a
could be obtained by controlled cooling of a chlorobenzene
solution. The molecular structure of 3a is shown in Fig. 6.
This work
This work
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Table 5 Attempted [PcTiO] catalyzed synthesis of carbodiimides (0.3
mol% catalyst, 6 d)
Product RNCNR
Yield (%)
Temp./◦C
R = Ph
78
85
0
170
190
190
170
R = Tol
R = 2,6-diisopropylphenyl
R = cyclohexyl
10
alkyl, aryl).43 Transition metal imido complexes are well known as
potential reagents for N–C bond formation reactions.44–46
During the study of the reaction of [PcTiO] 1 with excess aryliso-
cyanates we found that upon six days of heating, a steady evolution
of CO2 and formation of a white precipitate of diarylcarbodiimides
Fig. 6 Molecular structure of 3a, H atoms are omitted for clarity.
Ellipsoids are shown at 50% probability.
(RN
C NR) occurs. We therefore investigated the catalytic
properties of 1 in the formation of carbodiimides. Solvent-free
heating of catalytic amounts of 1 (0.3 mol%) with cyclohexyl-,
phenyl-, and p-tolylisocyanates in a temperature range of 170–
190 ◦C for about 6 days was found to yield the corresponding
carbodiimides in high purity (Table 5). In the case of the aromatic
isocyanates, a nearly quantitative yield was achieved. The products
were isolated from the reaction mixture by vacuum distillation.
The reaction of 2,6-diisopropylphenylisocyanate with 1 does not
lead to catalytic formation of the corresponding carbodiimide be-
cause of the steric hindrance mentioned above. After the addition
of one equivalent of the isocyanate, the stable imido titanium Pc 2a
is formed and the catalytic cycle cannot be completed (Scheme 2).
This catalytic system has a lot of advantages due to the catalyst’s
extreme chemical and thermal stability. Furthermore, the pure
products can easily be isolated by distillation whereas the catalyst
is retained as a residual blue mixture that is able to react with new
reactants.
The molecular arrangement in the unit cell of 3a is displayed in
Fig. 7. Two molecules of the solvent chlorobenzene are included.
Similar to the structure of 2a, face-to-face dimers of the ureato
titanium Pc’s with a distance of 3.55(1) A between two adjacent
N4 planes are observed. The two molecules of the dimer are related
to each other by an inversion centre.
˚
Conclusion
The present work reveals that the reaction of [PcTiO] 1 with
arylisocyanates depends largely on the size of the corresponding
aryl group. For smaller groups, such as tolyl and mesityl,
ureato complexes 3a and 3b were obtained. For the large 2,6-
diisopropylphenyl group, imido complex 2a was obtained. The
X-ray crystal structures of 2a and 3a revealed the formation of
face-to-face dimers in the solid state, which is also observed for
other axially substituted phthalocyanines. Additionally, a more
general synthetic route towards imido titanium compounds (2b–
c) was developed. The metathetic reaction of 1 with isocyanates
was successfully applied in the catalytic solvent-free formation of
diaryl- and dialkylcarbodiimides.
Fig. 7 The molecular packing of 3a. H atoms and two molecules of
chlorobenzene are omitted for clarity.
[PcTiO] catalyzed synthesis of carbodiimides
Carbodiimides are important class of compounds in organic
chemistry because of their miscellaneous applications. They are
used in esterification, synthesis of heterocyclic compounds or as
coupling agents in the synthesis of peptides.37 Diaryl- and dialkyl-
carbodiimides were catalytically synthesized for the first time in
1950 from isocyanates, using phospholanes or phosphalenes as a
catalyst, in high purity and quantitative yield.38,39 The methods
used before this time led to lower yields and crude products.40,41
Since then, other catalysts have been reported such as cyclic
phosphoric acid amides, e.g. phosphatranes EP(MeNCH2CH2)3N
(E = NMe, O, S)42 or iminophosphoranes (Cl3P NR)2 (R =
Experimental
All experiments and manipulations were carried out under a
dry nitrogen atmosphere using standard Schlenk-tube or glove-
box techniques. Solvents were rigorously purified with appro-
priate drying agents, distilled and stored over molecular sieves
under nitrogen. Chloronaphthalene was purchased from Acros
as a mixture of 90% of 1-chloronaphthalene and 10% of 2-
chloronaphthalene. Phenyl-, p-tolyl- and cyclohexylisocyanate
were distilled under vacuum prior to use and kept in the
◦
dark under inert gas at -20 C. [PcTiO] 1,9 [Ti(NtBu)Cl2py3]27
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Table 6 X-Ray data collection parameters of 2a and 3a
6 h. The color turned dark green. The produced CO2-gas was
replaced by N2 from time to time. After cooling, the product was
precipitated by addition of 20 mL hexane. The precipitate was
collected on a glass frit and purified by successive extractions with
refluxing MeCN and toluene (10 ¥ 50 mL each), and finally washed
with pentane. The product 2a was then dried at 120 ◦C/10-3 mbar
for 3 h. Blue–violet needles of [PcTi(NDip)] 2a were grown ◦by
controlled cooling of a chloronaphthalene solution from 180 C
to room temperature within 6 h. Beautiful crystals of 2a could also
be obtained by controlled cooling of the reaction mixture when
the reaction was carried out in an excess (10 mL) of the isocyanate
without solvent (see Table 6).
Yield: 320 mg (0.43 mmol; 83%) blue–violet crystals. Anal. calcd
for C44H33N9Ti: C, 71.84; H, 4.52; N, 17.14; found: C, 71.81; H,
4.50; N, 16.19. UV/vis lmax(CHCl3)/nm: 698.5 (s), 665.0 (sh),
628.0 (m), 344.0 (m). IR nmax(KBr)/cm-1: 2955 (w) [CH aliph.],
1607 (w), 1476 (m), 1457 (m), 1411 (m), 1330 (vs), 1284 (s), 1160
(m), 1117 (s), 1074 (s), 892 (m), 798 (w), 771 (m), 752 (m), 725 (vs).
1H-NMR (500 MHz, C6D5Br, 373 K) d (ppm): 0.03 (d, J = 4.91 Hz,
12H, MeiPr), 0.27–0.39 (m, 2H, CHMe2), 5.88–5.97 (m, 2H, m-H),
6.02–6.11 (m, 1H, p-H), 8.36–8.47 (m, 8H, H2,3Pc), 9.83–9.93 (m,
8H, H1,4Pc). MS (EI, m/z): 735 [M]+.
Compound
2a
3a·1.5C6H5Cl
Empirical formula
Formula weight
Crystal system
Space group
C44H33N9Ti
735.69
Monoclinic
C56H37.5Cl1.5N10OTi
967.53
Triclinic
¯
P 21/n
P1
˚
a/A
10.9544(9)
17.0865(9)
19.5582(15)
12.3080(17)
12.5821(14)
16.717(2)
70.981(10)
78.757(11)
68.628(10)
2270.6(5)
2
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
104.458(6)
3
˚
V/A
3542.1(4)
4
1.379
0.289
0.0926
3550
0.866
0.0866
0.0435
Z
r (calc.)/Mg m-3
1.415
0.332
0.1148
3220
0.924
0.1321
0.0678
m/mm-1
Rint
Reflns collected
Goodness-of-fit on F2
wR2 (all data)
R1 (observed data)
and [Ti(NMes)Cl2py2]27 were prepared according to literature
methods. PcH2 was deprotonated with 2.5 eq. benzyl potassium in
THF.
[PcTi(NtBu)] (2b). 500 mg (0.85 mmol) of PcK2 were dissolved
in 50 mL THF. A solution of 467 mg (1.10 mmol) [Ti(NtBu)Cl2py3]
in 5 mL THF was added and the mixture was heated to 60 ◦C
overnight. The violet product was collected by centrifugation and
extracted with acetonitrile and toluene (3 ¥ 50 mL ea◦ch) and finally
washed with pentane. The product was dried at 120 C/10-3 mbar.
Yield: 364 mg (68%) violet solid. Anal. calcd for C36H25N9Ti:
C, 69.47; H, 3.99; N, 19.96; found: C, 66.25; H, 3.69; N, 17.20:
UV/vis lmax (CH2Cl2)/nm: 690 (s), 657 (sh), 620 (sh), 348 (s). IR
Electronic spectra were recorded on a Shimadzu UV-1601 PC-
spectrophotometer. IR spectra were recorded on a Bruker IFS
588 spectrometer or a Nicolet 510 M FT-IR- spectrometer. EI
mass spectra were taken on CH7 Mass-spectrometer, Varian
MAT. APCI mass spectra were taken on a Finnigan LTQ-FT
Spectrometer using methanol as solvent. MALDI–TOF mass
spectra were taken on a Bruker Biflex III using pyrene as the matrix
or without a matrix. The reported m/z values refer to the highest
peak of the isotopic pattern according to the natural abundance
of the isotopes. Elemental analysis of C, H and N was carried out
using an Elementar, Vario EL. Atom Absorption Spectrometry
(AAS) for the determination of the titanium content was carried
out using a Perkin Elmer Atom absorption spectrometer 5000. 1H-
NMR spectra were recorded on Bruker AMX 500 or on Bruker
AC 300. Thermal gravimetric analyses (TGA) were carried out
using a TGA/SDTA 851, Mettler. The heating range was from
n
max(Nujol)/cm-1: 1330 (m), 1313 (s), 1284 (w), 1161 (w), 1116 (s),
1072(s), 893 (w), 868 (w), 778 (m), 750 (m). 1H-NMR (300 MHz,
THF-d8, 300 K) d (ppm): -1.45 (s, 9H, Me), 8.40 (m, 8H, H2,3Pc),
9.66 (m, 8H, H1,4Pc)., MS (MALDI–TOF, m/z): 632 [M]+, 617 [M
- Me]+, 575 [M - tBu]+, 560 [M - (NtBu)]+. (APCI–HRMS, m/z):
632.1787 [M+], C36H25N9Ti requires 632.1785.
[PcTi(NMes)] (2c). 500 mg of (0.85 mmol) PcK2 were dis-
solved in 50 mL THF. A solution of 542 mg (1.10 mmol)
[Ti(NMes)Cl2py2] in 5 mL THF was added and the mixture was
heated to 60 ◦C overnight. The violet product was collected by
centrifugation and extracted with acetonitrile and toluene (3 ¥
50 mL each) and finally washed with pentane. The product was
dried at 120 ◦C/10-3 mbar.
◦
◦
◦
25 C to 800 C with a heating rate◦of 10 C min-1 and a slower
◦
rate of 1 C min-1 from 250 to 400 C. Selected crystallographic
data of 2a and 3a are given in Table 6 and complete data are given
in the CIF file (Supporting Information†). Data were collected
on an IPDS area detector system using graphite monochromated
˚
Mo-Ka X-radiation (l = 0.71073 A). The structures were solved
by direct methods (programs SHELXS-9747 or SIR200248) and
refined on F2 by full matrix least squares using SHELXL-97. All
non-hydrogen atoms were refined as anisotropic, the hydrogen
atom positions were calculated and refined using the ‘riding model’
with fixed isotropic thermal parameters. The asymmetric unit of
3a contains one molecule of chlorobenzene with occupancy 1 and
one molecule of chlorobenzene with occupancy 0.5. The latter is
disordered due to crystallographic inversion symmetry.
Yield: 390 mg (66%) violet solid. Anal. calcd for C41H27N9Ti:
C, 71.00; H, 3.92; N, 18.17; found: C, 63.60; H, 3.90; N, 18.00;
UV/vis lmax (CH2 Cl2)/nm: 689 (s), 658 (sh), 622 (sh), 334 (s).
IR nmax(KBr)/cm-1:1330 (s), 1313 (s), 1284 (m), 1161 (w), 1116
1
(s), 1072 (s), 1010 (m), 893 (w), 747 (m). H-NMR (300 MHz,
THF-d8) d (ppm): -0.3 (s, 6H, o-Me), 1.24 (s, 3H, p-Me), 5.31
(s, 2H, m-H), 8.42 (m, 8H, H2,3Pc), 9.69 (m, 8H, H1,4Pc), 13C-NMR
(100 MHz, THF-d8) d (ppm): 151.5, 139.1, 131.1, 129.1, 124.1,
121.5, 93.4 (CAr), 20.5 (p-Me), 17.7 (o-Me).
MS (MALDI–TOF, m/z): 693 [M]+, 560 [M - NMes]+, (APCI–
HRMS, m/z): 694.1946 [M+H]+, C41H27N9Ti requires 694.1942.
Syntheses
[PcTi(NDip)] (2a). A mixture of [PcTiO] (300 mg, 0.52 mmol)
and 2,6-diisopropyl-phenylisocyanate (2 mL, 10.4 mmol, 20-fold
excess) in 20 mL of chloronaphthalene was heated at 180 C for
[PcTi(N,N¢-di-p-tolylureato)] (3a). A mixture of [PcTiO]
(300 mg, 0.52 mmol) and p-tolylisocyanate (1.3 mL, 10.4 mmol,
◦
1792 | Dalton Trans., 2011, 40, 1787–1794
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20-foldexcess) in20 mL of chloronaphthalene was heatedat 180 ◦C
for 6 h. The color turned dark green. The produced CO2-gas was
replaced by N2 from time to time. After cooling, the product was
precipitated by addition of 20 mL hexane. The precipitate was
collected on a glass frit and purified by successive extractions
with refluxing MeCN (10 ¥ 50 mL) and toluene (10 ¥ 50 mL),
and◦finally washed with pentane. The product 3a was then dried at
120 C/10-3 mbar for 3 h. The same product 3a was obtained when
the reaction was carried out in excess (10 ml) of p-tolylisocyanate
without solvent. Dark blue prism shaped crystals suitable for the
crystallographic structure determination of 3a were obtained by
controlled cooling of its solution in chlorobenzene from 130 ◦C to
room temperature within 3 h (see Table 6).
Yield: 316 mg (76%) blue–green solid. Anal. calcd for
C47H30N10OTi: C, 70.68; H, 3.78; N, 17.54; Ti, 5.99; found: C,
70.56; H, 3.85; N, 17.36; Ti, 5.84. UV/vis lmax (CHCl3)/nm:
698.5 (s), 665.5 (sh), 629.0 (m), 345.0 (m). IR nmax(KBr)/cm-1:
1683(m)[C O], 1589 (m), 1503 (m), 1489 (m), 1414 (w), 1332
(vs), 1286 (m), 1160 (m), 1118 (vs), 1069 (vs), 970 (s), 894 (s),
775 (s), 751 (s), 729 (vs). 1H-NMR (500 MHz, C6D5Br, 373 K) d
(ppm): 1.99 (s, 6H, p-Me), 4.98 (d, 4H, o-H), 6.32–6.44 (d, 4H,
m-H), 8.25–8.35 (m, 8H, H2,3Pc), 9.64–9.72 (m, 8H, H1,4Pc). MS
(MALDI–TOF, m/z): 798 [M]+; 665 [M - RNCO]+.
o/p-H). 13C-NMR (75 MHz, CDCl3, 300 K) d (ppm): 138.4
(N
C
N), 135.2, 129.4, 125.5, 124.1. MS (EI, m/z): 194 [M]+.
Di(p-tolyl)carbodiimide. 10.97
g
p-tolylisocyanate (79.39
mmol) and 139.4 mg of [PcTiO] (0.24 mmol, 0.3 mol%).
Yield: 7.47 g (85%, colorless liquid) Bp. 173 ◦C (3.9 mbar). IR
1
n
max(Nujol)/cm-1: 2110, 2139 [N
C
N]. H-NMR (300 MHz,
CDCl3, 300 K) d (ppm): 6.97–7.04 (m, 8H, HAr), 2.23 (s, 6H, Me).
13C-NMR (75 MHz, CDCl3, 300 K) d (ppm): 135.9 (N
135.8, 135.2, 130.0, 123.8, 20.0. MS (EI, m/z): 222 [M]+.
C
N),
Dicyclohexylcarbodiimide. 9.88 g cyclohexylisocyanate (78.93
mmol) and 132.8 mg of [PcTiO] (0.23 mmol, 0.3 mol%). Dis-
tillation of this suspension under reduced pressure afforded two
fractions, the first being the unreacted cyclohexylisocyanate (7.86
g), and the second dicyclohexylcarbodiimide.
Yield: 0.83 g (10%, white solid.). Bp. 112 ◦C (4.7 mbar). IR
n
max(Nujol)/cm-1: 2122 [N
C
N]. 1H-NMR (300 MHz, CDCl3,
300 K) d (ppm): 2.96 (sept, 2H, ipso-H), 0.95–1.71 (m, 20H, CH2).
13C-NMR (75 MHz, CDCl3, 300 K) d (ppm) 138.9 (N
55.1, 34.4, 25.0, 24.2. MS (EI, m/z): 206 [M]+.
C
N),
Bis(2,6-diisopropylphenyl)carbodiimide. 2.37 g 2,6-diisopro-
pylphenylisocyanate (11.66 mmol) and 20.2 mg of [PcTiO]
(0.035 mmol, 0.3 mol%) were refluxed at 190 ◦C for 6 days under
inert gas atmosphere. A faint green suspension was produced.
Distillation of this suspension under reduced pressure afforded
only the starting material.
[PcTi(N,N¢-dimesitylureato)] (3b). A mixture of [PcTiO]
(300 mg, 0.52 mmol) and mesitylisocyanate (1.6 g, 10.4 mmol, 20-
fold excess) in 20 mL of chloronaphthalene was heated at 180 ◦C
for 6 h. The color turned dark green. The produced CO2-gas was
replaced by N2 from time to time. After cooling, the product was
precipitated by addition of 20 mL hexane. The precipitate was
collected on a glass frit and purified by successive extractions with
refluxing MeCN (10 ¥ 50 mL) and toluene (10 ¥ 50 mL) and
finally washed with pentane. The product 3b was then dried at
120 ◦C/10-3 mbar for 3 h.
Acknowledgements
Dr Darwish gratefully acknowledges advice and support from
Prof. Abd El-Ghaffar, NRC-Cairo.
References
Yield: 325 mg (73%) blue–green solid. Anal. calcd for
C51H38N10OTi: C, 71.66; H, 4.48; N, 16.39; Ti, 5.60; found: C,
71.24; H, 4.52; N, 16.26; Ti, 5.66. UV/vis lmax(CHCl3)/nm: 700.5
(s), 627.5 (m), 343.0 (m). IR nmax(KBr)/cm-1: 1684 (s) [C O], 1502
(w), 1469 (w), 1417 (w), 1333 (s), 1287 (w), 1259 (m), 1161 (w),
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8.36 (m, 8H, H2,3Pc), 9.67–9.73 (m, 8H, H1,4Pc). MS (MALDI–TOF,
m/z): 855 [M]+, 693 [M - RNCO]+.
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1794 | Dalton Trans., 2011, 40, 1787–1794
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The Royal Society of Chemistry 2011
©