"Bidentate" and "tridentate" sulfonamide ligands for titanium complexes: Crystal structures and solution dynamics elucidating an η2 or η3-coordination mode

Article abstract of DOI:10.1039/b110481k

Highly air- and moisture-sensitive complexes having sulfonamide ligands, (TsNR)₂Ti(NMe₂)₂ (Ts = p-MeC₆H₄SO₂), were prepared by treatment of two equivalents of TsNHR with Ti(NMe₂)₄ at room temperature. One of the compounds, where R = i-Pr (1), was studied in detail; the crystal structure of 1 revealed that both of the TsNi-Pr ligands were bound to the metal in an η²-coordination mode. Solution dynamics of 1 showed that an η¹/η² interconversion occurred above 60°C with an activation energy of 15.8 kcal mol^-1. Treatment of Ti(NMe₂)₄ with the sulfonamide TsHN(CH₂)₂O(CH₂)₂NHTs (3), led to the formation of [TsN(CH₂)₂O(CH₂)₂NTs]Ti(NMe ₂)₂ (2) in high yield, in which the sulfonamide moiety was coordinated to the titanium center in an η³ (NON) mode. No sign of η¹/η² interconversion of the sulfonamide ligands was seen in solution. Treatment of 2 with Me₃SiCl resulted in the formation of [{TsN(CH₂)₂O(CH₂)₂NTs}Ti(NMe ₂)Cl]₂ (4) and [{TsN(CH₂)₂O(CH₂)₂NTs}TiCl ₂]₂ (5). An X-ray structure determination of 4 revealed that sulfonyl oxygen bridging resulted in the formation of an eight membered ring.

Full text of DOI:10.1039/b110481k

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“Bidentate” and “tridentate” sulfonamide ligands for titanium
complexes: crystal structures and solution dynamics elucidating
an ꢀ2 or ꢀ3-coordination mode†
Satoshi Hamura,a,c Takashi Oda,a Yasuaki Shimizu,a Kouki Matsubarab
and Hideo Nagashima*a,b
a Graduate School of Engineering Science, Kyushu University, Kasuga, Fukuoka 816-8580,
Japan
b Institute of Advanced Material Study, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
c Yokkaichi Research Center, TOSOH Corporation, Yokkaichi, Mie 510-8540, Japan
Received 15th November 2001, Accepted 6th February 2002
First published as an Advance Article on the web 12th March 2002
Highly air- and moisture-sensitive complexes having sulfonamide ligands, (TsNR)2Ti(NMe2)2 (Ts = p-MeC6H4SO2),
were prepared by treatment of two equivalents of TsNHR with Ti(NMe2)4 at room temperature. One of the
compounds, where R = i-Pr (1), was studied in detail; the crystal structure of 1 revealed that both of the TsNi-Pr
ligands were bound to the metal in an η2-coordination mode. Solution dynamics of 1 showed that an η1/η2
interconversion occurred above 60 ЊC with an activation energy of 15.8 kcal molϪ1. Treatment of Ti(NMe2)4 with
the sulfonamide TsHN(CH2)2O(CH2)2NHTs (3), led to the formation of [TsN(CH2)2O(CH2)2NTs]Ti(NMe2)2 (2)
in high yield, in which the sulfonamide moiety was coordinated to the titanium center in an η3 (NON) mode.
No sign of η1/η2 interconversion of the sulfonamide ligands was seen in solution. Treatment of 2 with Me3SiCl
resulted in the formation of [{TsN(CH2)2O(CH2)2NTs}Ti(NMe2)Cl]2 (4) and [{TsN(CH2)2O(CH2)2NTs}TiCl2]2 (5).
An X-ray structure determination of 4 revealed that sulfonyl oxygen bridging resulted in the formation of an eight
membered ring.
Introduction
Hapticity changes in conjugated π-ligands are thoroughly
investigated phenomena in organometallic chemistry;1 in
particular, the η1/η3 interconversion of allyl2 and pseudo-allyl
ligands3 is often seen in a wide variety of organotransition
metal compounds. As novel types of pseudo-allyl ligands, the
coordination behavior of sulfonamides in certain titanium
complexes has attracted the attention of organic and organo-
metallic chemists in relation to their catalytic activity towards
enantioselective addition of organometallic reagents to alde-
hydes.4 Walsh5–7 and Gagné8 have reported the isolation and
structure determination of several titanium compounds
bearing sulfonamides derived from 1,2-cyclohexanediamine or
1,2-diphenylethylenediamine (see Fig. 1), in which one of the
tosylamide groups is bonded to the titanium center via N and
O (referred to as η2), and the other via N (referred to as η1).5,7,8
However, this bonding mode was not seen in solution due to the
fact that either rapid η1/η2 interconversion within the NMR
time scale occurs, or a symmetric η2:η2-coordination mode of
the ligand is lower in energy.6,7
Fig. 1 Sulfonamide complexes of titanium containing sulfonamide
ligands with various coordination modes.
We were interested in investigating the possibility of whether
substantial strain in titanacyclopentane structures derived from
tosylamide ligands could be the reason why such ligands are
bound to the metal in coordination mode B. Reaction of these
sulfonamide ligands with titanium precursors resulted in the
formation of three possible titanacyclopentane structures,
A–C, as shown in Fig. 1. The coordination modes in A, B, and
C are η2 (NN), η3 (NNO) and η4 (NONO), respectively. If one
considers coordination types B or C, the Ti–O bonds should
provide additional strain on the titanacyclic structure. We
suspected that coordination mode B might be attributed to the
fact that the electronically favorable mode C cannot be adopted
due to special structural circumstances from tosylamide ligands
producing the titanacyclopentane structures; this prompted us
to synthesize titanium compounds of type D and E, bearing
other sulfonamide ligands as shown in Fig. 1. In compound
type D, titanium and the sulfonamide ligands do not form a
titanacyclopentane structure, in which the η4 (NONO) mode
is less favorable than the η3 (NNO) or η2 (NN) modes. In
contrast, it is known that the titanium in compounds of type E
bond strongly to the central oxygen of the TsN(CH2)2O(CH2)2-
1
† Electronic supplementary information (ESI) available: the H NMR
charts of a reaction mixture of Ti(NMe2)4 and 1.1, 1.6, and 3.0 equiv.
of i-PrNHTs. See http://www.rsc.org/suppdata/dt/b1/b110481k/
DOI: 10.1039/b110481k
J. Chem. Soc., Dalton Trans., 2002, 1521–1527
This journal is © The Royal Society of Chemistry 2002
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NTs (Ts = p-MeC6H4SO2) ligand (a “tridentate” sulfonamide
ligand), providing a pentacoordinate structure.9–12 Molecular
modeling studies on compounds of type E indicate that neither
the coordination mode C nor B is favorable for the sulfonamide
moiety.
In this paper we describe the crystal structures and solution
dynamics of a series of compounds of type D and E. As we
had expected, sulfonamide ligands of type D gave titanium
complexes bearing both of the sulfonamides bonding in an
η2-fashion. In contrast, the coordination mode of sulfonamide
moieties in the pentacoordinate complexes is η3 (NON). In the
cases where at least one of the NR2 groups of compounds of
type E is replaced by Cl, interaction of one titanium with the
oxygen in the sulfonamide moiety bonding to another titanium
produces dimeric structures.
Results and discussion
Preparation and characterization of (i-PrNTs)2Ti(NMe2)2 (1)
Titanium amide compounds bearing tosylamide ligands
(RNTs)2Ti(NMe2)2 and (RNTs)2Ti(NEt2)2 can generally be
synthesized by the reaction of RNHTs (2 equiv.) with either
Ti(NMe2)4 or Ti(NEt2)4 in benzene or toluene as shown
in Scheme 1. Although the characterization of the product
Fig. 2 The ORTEP24 drawing of 1 with 50% probability thermal
ellipsoids.
Table 1 Selected bond lengths (Å) and angles (Њ) for 1
Ti(1)–N(1)
Ti(1)–N(2)
Ti(1)–N(3)
Ti(1)–N(4)
Ti(1)–O(2)
Ti(1)–O(3)
1.901(5)
1.885(4)
2.103(4)
2.045(4)
2.226(4)
2.338(4)
S(1)–O(1)
S(1)–O(2)
S(2)–O(3)
S(2)–O(4)
S(1)–N(3)
S(2)–N(4)
1.442(4)
1.479(3)
1.470(3)
1.432(4)
1.568(4)
1.576(4)
N(1)–Ti(1)–N(2)
N(1)–Ti(1)–N(3)
N(1)–Ti(1)–N(4)
N(2)–Ti(1)–N(3)
N(2)–Ti(1)–N(4)
N(3)–Ti(1)–N(4)
N(1)–Ti(1)–O(2)
N(1)–Ti(1)–O(3)
N(2)–Ti(1)–O(2)
N(2)–Ti(1)–O(3)
N(3)–Ti(1)–O(2)
96.5(2)
N(3)–Ti(1)–O(3)
N(4)–Ti(1)–O(2)
N(4)–Ti(1)–O(3)
O(2)–Ti(1)–O(3)
Ti(1)–N(3)–S(1)
Ti(1)–N(4)–S(2)
N(3)–S(1)–O(1)
N(3)–S(1)–O(2)
N(4)–S(2)–O(3)
N(4)–S(2)–O(4)
89.45(15)
87.75(15)
63.84(14)
83.20(13)
98.9(2)
102.6(2)
117.3(2)
99.4(2)
99.01(19)
104.52(19)
103.26(18)
100.21(18)
144.41(17)
163.02(17)
91.64(18)
92.76(17)
163.60(16)
64.89(14)
Scheme 1 Preparation of (RЈNTs)2Ti(NR2)2 (1; R = Me, RЈ = i-Pr).
1
could be carried out unequivocally on the basis of H and 13C
NMR analyses, it was difficult to obtain a complete elemental
analysis of these products because of their high moisture
sensitivity. Complete characterization of one of the com-
pounds, (i-PrNTs)2Ti(NMe2)2 (1), which gave relatively large
crystals, was successfully performed, and thus we carried out
more detailed studies with 1 including its crystal structure and
its solution dynamics.
99.8(2)
115.4(2)
groups are planar, suggesting electron donation from the Me2N
group to the titanium atom. Although the planar dimethyl-
amino moiety is indicative of the existence of Ti–N multiple
bonds, facile rotation of the Me2N group around the Ti–N
bond in solution was evidenced by the appearance of a single
1H or 13C resonance due to the NMe2 group. This rotation could
not be stopped at Ϫ60 ЊC. The Ti–N bond distances (Table 1)
are similar to those reported in other titanium amide complexes
bearing a tosylamide ligand derived from trans-1,2-cyclo-
hexanediamine (Ti–NR2, 1.86–1.89 Å; Ti–N(R)Ts, 2.05–2.10
Å).7 In contrast, the following results are significantly different.
First, both of the oxygen atoms in the tosylamide moieties are
bonded to the Ti center (in coordination mode D). In sharp
contrast to the type A–C tosylamide ligands producing the
titanacyclopentane structure, the type D tosylamide ligands
do not provide a steric bias to the complex by their η2:η2-
coordination mode; this suggests that such a coordination
mode is electronically preferable to the others.7 Secondly, the
arrangement of four N and two O atoms is pseudo-octahedral,
and the two O atoms are in a cis orientation. In contrast, two
N(Ts) moieties are trans oriented. This arrangement could
minimize the steric repulsion between two bulky isopropyl
groups. Electronically negative oxygen atoms may be favorably
located at positions trans to electron-donating NMe2 groups. In
the cyclohexanediamide complexes, the structure of the ligand
forced two N(Ts) atoms to be located at cis positions. The Ti–O
and Ti–N distances of 1 are similar to those seen in the Ti(η2-
tosylamide) moiety in the sulfonamide complexes of Walsh
The reaction of HNTs(i-Pr) (2 equiv.) with Ti(NMe2)4 took
place instantly at room temperature, giving 1 as dark red
1
crystals in up to 76% isolated yield. H NMR and 13C NMR
spectra of 1 at Ϫ20 ЊC showed the two NMe2 groups to be
magnetically equivalent with the methyl signals appearing as
one sharp singlet. Similarly, the two i-PrNTs groups in 1 are
also magnetically equivalent, and two methyl signals due to the
i-Pr groups are diastereotopic appearing as two doublets in the
1H NMR and as two independent peaks in the13C NMR. These
spectroscopic data are consistent with those expected for 1, in
which four nitrogen ligands are arranged tetrahedrally and both
tosylamides are bonded to the titanium center in coordination
mode D as shown in Scheme 1. Replacement of the NMe2
ligands in Ti(NMe2)4 by the tosylamide is stepwise, and the
formation of [(i-Pr)NTs]Ti(NMe2)3 was detectable in the 1H
NMR by addition of 1.1 equiv. of HNTs(i-Pr) to Ti(NMe2)4.
Peaks due to [(i-Pr)NTs]Ti(NMe2)3 [δ 0.97 and 1.18 (br d
each, J = 0.07 Hz, Me of i-Pr), 3.60 (m, CH of i-Pr), 3.27 (s,
NMe2)], 1, and unreacted Ti(NMe2)4 were visible in a ratio of 5
: 1 : 0.6. The ratio was changed to 1 : 2 : 0, when 1.6 equiv. of the
ligand was added to Ti(NMe2)4. In the presence of an excess
amount (3 equiv.) of HNTs(i-Pr), only 1 and unreacted ligand
were visible (1 : 1), and neither [(i-Pr)NTs]3Ti(NMe2) nor
[(i-Pr)NTs]4Ti could be detected.
The structure of 1 was confirmed by X-ray structure
determination as illustrated in Fig. 2. The dimethylamino
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and Gagné (Ti–O, 2.167–2.264 Å; Ti–N, 2.048–2.103 Å).5,7,8
The small Ti–N–S bond angles are another indication of η2-
coordination of the sulfonamide ligands in 1; in Gagné’s com-
plex, those of the bound and unbound sulfonamides are 99.1
and 107.5Њ, respectively.8 Shorter N–S bonds and longer O–S
bonds than those of uncoordinated sulfonamides are indicative
of contribution of the sulfonate type coordination suggested by
Anwander and coworkers.13
As described above, the crystal structure of 1 revealed the
η2:η2-coordination mode of the i-PrNTs ligands. Of interest is
the possibility of η1/η2 interconversion in solution. As shown in
Fig. 3, two of the methyl groups in the isopropyl group appear
Ti–O(SON) bond fission, was ca. 15.8 kcal molϪ1. As a close
example, Jordan and coworkers reported a racemization energy
for [(pyAr2CO)2Ti(NMe2)2], in which the reversible dissociation
of the pyridine moiety induces the racemization, to be 12–13
kcal molϪ1, and the higher dissociation/recombination energy
of the sulfonamide ligands in 1 indicates the strong coordin-
ating ability of the oxygen atoms of the sulfonamide ligands.14
Preparation and characterization of [(TsNCH2CH2)2O]Ti(X)2
(X ؍ NMe2 or Cl) 2, 4, 5
Pentacoordinated titanium complexes bearing a trigonal bipyr-
amidal structure have recently been actively investigated
by Schrock and coworkers, in which 4-oxaheptanediamine
derivatives were used as a tridentate ligand.9–12 Treatment of
(TsNHCH2CH2)2O (3) with Ti(NMe2)4 in toluene afforded the
corresponding titanium complex, [(TsNCH2CH2)2O]Ti(NMe2)2
(2), in quantitative yield (Scheme 3). The product was isolable
Scheme 3 Preparation of (TsNC2H4OC2H4NTs)Ti(NMe2)2 (2).
as orange microcrystals, and was more stable towards air and
moisture than 1 and other (RNTs)2Ti(NRЈ2)2 compounds. In
1
the H and 13C NMR spectra, peaks due to the two NMe2
1
moieties appeared equivalent, while two H resonances due to
the NCH2 and OCH2 moieties or H and 13C signals derived
1
Fig. 3 1H NMR spectra of 1 (*) at Ϫ20, 30, 50, 60, and 90 ЊC in
toluene-d8.
from the tosyl groups were also magnetically equivalent. Sig-
1
nificant downfield shift of H and 13C peaks due to the OCH2
group indicated coordination of the oxygen atom to the
titanium center. A single-crystal X-ray diffraction study of 2
revealed the distorted-trigonal bipyramidal structure shown in
Fig. 4, in which two N atoms of the NMe2 moieties and the
as two independent signals, because the η2-bonding mode
makes a cyclic structure involving Ti, O, S, and N leading to
these methyl groups becoming diastereotopic. In contrast, the
η1-bonding mode allows free rotation of the sulfonamide ligand
around the Ti–N or N–S bonds, which makes the two methyl 1H
resonances equivalent. The η1/η2 exchange process was clearly
visible in the variable temperature NMR studies as shown in
Fig. 3. The diastereotopic methyl groups appear as two
independent doublets at Ϫ20 ЊC, which become broadened at
30 ЊC, coalesced at 60 ЊC, and became a sharp single doublet
at 90 ЊC. One reasonable interpretation of these results is
conversion of one η2:η2-coordination mode to the other η2:η2-
mode via an η1:η1-transition state as shown in Scheme 2; the
Fig. 4 The ORTEP drawing of 2 with 50% probability thermal
ellipsoids. Entire view (left) and front view (right).
oxygen atom in the TsN(CH2)2O(CH2)2NTs ligand occupy
the equatorial positions, and two N atoms of the tosylamide
moieties are located at the apical positions. A striking difference
between the crystal structure of 2 and 1 and the Walsh
complexes5–7 is that no bonding interaction was seen between
the Ti atom and the oxygen atoms in the sulfonamide moieties
(Ti–O distances > 3.5 Å). The N–S or S–O bond distances in
2 (Table 2) are similar to those observed in uncoordinated
Scheme 2 Reversible η1/η2 interconversion of 1.
two coordination modes are rapidly interconverted on the
NMR time scale above 60 ЊC. Calculated ∆G‡ from the coales-
cence temperature, which corresponded to the energy of the
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Table 2 Selected bond lengths (Å) and angles (Њ) for 2
S(1)–O(2)
S(1)–O(3)
S(2)–O(4)
S(2)–O(5)
S(2)–N(3)
S(1)–N(4)
1.433(2)
1.445(2)
1.438(2)
1.440(2)
1.604(2)
1.6112
Ti(1)–N(1)
Ti(1)–N(2)
Ti(1)–N(3)
Ti(1)–N(4)
Ti(1)–O(1)
1.863(2)
1.838(2)
2.090(2)
2.083(2)
2.1651(17)
N(1)–Ti(1)–N(2)
N(1)–Ti(1)–N(3)
N(1)–Ti(1)–N(4)
N(2)–Ti(1)–N(3)
N(2)–Ti(1)–N(4)
N(3)–Ti(1)–N(4)
N(1)–Ti(1)–O(1)
N(2)–Ti(1)–O(1)
104.59(9)
103.69(9)
103.37(9)
97.67(9)
N(3)–Ti(1)–O(1)
N(4)–Ti(1)–O(1)
Ti(1)–N(3)–S(2)
Ti(1)–N(4)–S(1)
N(4)–S(1)–O(2)
N(4)–S(1)–O(3)
N(3)–S(2)–O(4)
N(3)–S(2)–O(5)
74.03(8)
74.27(7)
131.00(12)
130.45(12)
109.75(11)
110.26(12)
109.19(11)
110.98(13)
98.69(9)
143.52(8)
109.11(8)
146.29(8)
tosylamides. The TsN(CH2)2O(CH2)2NTs ligand in 2 provides a
bicyclic substructure containing one Ti, two N, one O, and four
C atoms. This bicyclic structure of 2 gave large Ti–N–S bond
angles, which are unfavorable for the η2-coordination of the
sulfonamide moieties in 2. If the η2-coordination mode, which
provides short Ti–O(sulfonamide) bonds and small Ti–N–S
angles, was adopted by 2, it would give significant ring strain to
the bicyclic substructure. We carried out variable temperature
NMR studies of 2, and found no dynamic behavior suggesting
η1/η2-interconversion in solution. Some of the pentacoordin-
ated titanium amides reported by Schrock and coworkers have
a pseudo-square pyramidal structure, and in some cases struc-
tural isomerization such as Berry rotation was observed.10 The
spectroscopic data of 2 showed no suggestion of the existence
of other structures.
Scheme
Me3SiCl.
4
Reaction of (TsNC2H4OC2H4NTs)Ti(NMe2)2 (2) with
The structures of 1 and 2 suggest that two type D sulfon-
amide ligands are bound to the Ti(NMe2)2 moiety in an η2:η2-
coordination mode, whereas the type E ligand providing
the bicyclic substructure which is unfavorable for the Ti–
O(sulfonamide) bonding adopts an NON coordination mode.
Since the tosylamide ligand derived from trans-1,2-cyclohexane-
diamine provides a coordination environment for the titanium
compounds in which the Ti–O(sulfonamide) bonding is less
unfavorable than the type E bonding, it seems reasonable to
expect to see the B-type bonding mode in many of the com-
pounds. However, it is of interest that the type C bonding
mode is seen in one of the complexes, {1,2-(TsN)2C6H10}-
Ti{O(i-Pr)}2.6 We suspected that this might be attributable to
higher Lewis acidity of the titanium center in {1,2-(TsN)2C6-
H10}Ti{O(i-Pr)}2 than that in {1,2-(TsN)2C6H10}Ti(NMe2)2,
which facilitates the coordination of sulfonamide-oxygen
atoms to the titanium center. In this context, we were interested
in the preparation of [(TsNCH2CH2)2O]TiCl(NMe2) (4) and
[(TsNCH2CH2)2O]TiCl2 (5) by replacement of one or two
NMe2 ligands in 2 by electron-withdrawing chlorine atoms.
Treatment of 2 with excess Me3SiCl12,15 at room temperature
for 15 h gave a mixture of 4 and a compound having no Me2N
group, which can be assigned as dichloride 5 from the spectro-
scopic evidence and elemental analysis, in a ratio of 31 : 69
Fig. 5 The ORTEP drawing of 4. 50% probability of the thermal
ellipsoids. Symmetry transformations generate equivalent atoms. The
oxygen atom O(3Ј) is defined as the equivalent atom of O(3). Two
CH2Cl2 molecules, which are included in the lattice, are omitted for
clarity.
Table 3 Selected bond lengths (Å) and angles (Њ) for 4
Ti(1)–N(1)
Ti(1)–N(2)
Ti(1)–N(3)
Ti(1)–O(1)
Ti(1)–O(3Ј)
Ti(1)–Cl(1)
1.871(5)
2.119(4)
2.057(4)
2.158(4)
2.116(3)
2.3332(15)
S(1)–O(2)
S(1)–O(3)
S(2)–O(4)
S(2)–O(5)
S(1)–N(2)
S(2)–N(3)
1.443(4)
1.476(3)
1.436(4)
1.437(4)
1.574(4)
1.598(4)
1
(determined by H NMR) as shown in Scheme 4. Fractional
N(1)–Ti(1)–N(2)
N(1)–Ti(1)–N(3)
N(2)–Ti(1)–N(3)
N(1)–Ti(1)–O(1)
N(2)–Ti(1)–O(1)
N(3)–Ti(1)–O(1)
N(1)–Ti(1)–O(3Ј)
N(2)–Ti(1)–O(3Ј)
N(3)–Ti(1)–O(3Ј)
O(1)–Ti(1)–O(3Ј)
N(1)–Ti(1)–Cl(1)
106.82(18)
103.27(19)
148.92(18)
175.85(17)
73.86(15)
75.57(16)
92.26(17)
86.43(15)
84.79(15)
83.68(13)
95.67(15)
N(2)–Ti(1)–Cl(1)
N(3)–Ti(1)–Cl(1)
O(3Ј)–Ti(1)–Cl(1)
O(1)–Ti(1)–Cl(1)
Ti(1)–N(3)–S(2)
Ti(1)–N(2)–S(1)
N(2)–S(1)–O(2)
N(2)–S(1)–O(3)
N(3)–S(2)–O(4)
N(3)–S(2)–O(5)
91.21(12)
93.42(13)
172.07(11)
88.39(10)
131.9(3)
129.1(3)
111.0(2)
110.5(2)
109.0(2)
110.4(2)
recrystallization of this mixture from CH2Cl2 and hexane
afforded 4 and 5 in 18 and 69% yield, respectively. The isolated
4 contained a small amount of 5 as an impurity; however,
a single crystal suitable for X-ray structure determination
was successfully grown. In contrast, 5 was isolated without
contamination of 4 by fractional recrystallization. The selective
preparation of 5 was achieved by heating a mixture of 2 and
Me3SiCl at 60 ЊC for 15 h (83% isolated yield).
As shown in Fig. 5, (see also Table 3) crystallography showed
the dimeric structure of 4, in which one of the sulfonyl oxygen
atoms in the [(TsNCH2CH2)2O]TiCl(NMe2) unit is bonding
with the titanium center of a second [(TsNCH2CH2)2O]-
TiCl(NMe2) unit. The sulfonyl oxygen bridging results in the
formation of eight-membered dimetallacycles,13,16 which have
also been seen in Anwander’s yttrium complex.13 The ligands
around the titanium atom are octahedrally arranged, and
the chlorine atom is located at a trans position to the sulfonyl
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oxygen. Interestingly, this dimeric structure was not seen in
solution. In CD2Cl2 or toluene-d8, only signals due to the
monomeric [(TsNCH2CH2)2O]TiCl(NMe2) unit were visible at
Ϫ60 to 60 ЊC. 1H and 13C NMR spectra of 4 are closely similar
to those of 2 except for a significant downfield shift of a peak
due to the NMe2 group (∆δH 0.63 ppm, ∆δC 5.8 ppm). The
results indicate that the sulfonyl oxygen bridge is easily cleaved
in solution, and 4 exists as a monomer like 2 in solution.
Formation of the dimeric form of 4 can be attributed to the
increase in Lewis acidity of the titanium center by replacement
of one NMe2 group in 2 by a more electron negative Cl atom.
This indicates that sulfonate oxygen bridging should also exist
in the dichloro analogue 5. Although a single crystal of 5 was
unfortunately unavailable, appearance of two sets of seven 13C
resonances due to the TsN(CH2)2O(CH2)2NTs ligand in 5
indicates that 5 exists as a dimer in solution. Since the spectral
data are consistent with a dimer of [(TsNCH2CH2)2O]TiCl2, we
tentatively concluded that 5 is dimeric in both solution and
solid states. We attempted to synthesise (i-PrNTs)2TiCl2 by
treatment of 1 with Me3SiCl under the same conditions used
for the preparation of 5, which might give us novel titanium
complexes having dimeric or polymeric structures via sulfonate
oxygen bridging. All of 1 was consumed after 12 h, and a
mixture of compounds including substantial amounts of
i-PrNHTs was formed. Two titanium species, which showed no
signal due to the NMe2 moiety in their 1H and 13C NMR, were
included in this mixture. 1H and 13C resonances due to the
CHMe2 group of these two titanium species showed character-
istic downfield shifts compared with those of 1; this indicates
that two isomers of (i-PrNTs)2TiCl2 may be formed. However,
the high sensitivity of the compounds to moisture prevented
detailed studies after isolation.
per h) under the same conditions. Ethylene polymerization
catalyzed by [(RNC2H4)2O]TiR2 in the presence of fluorinated
boron compounds was extensively studied by Schrock and
coworkers.10,11 Attempted syntheses of dialkyl derivatives of 5
led to decomposition of the complexes, and exploration of
highly active polymerization catalysts bearing tosylamide
ligands is at present unsuccessful.
Experimental
General methods
All manipulations were carried out under a dry argon or
nitrogen atmosphere using the combination of a nitrogen-filled
glove box, high-vacuum line, and Schlenk techniques. All of the
solvents were distilled from drying reagents (Na/Ph2CO for
toluene, hexane, THF, Et2O, C6D6, and C6D5CD3; CaH2 for
CH2Cl2 and CD2Cl2; KOH for NEt3) just before use. Ti(NMe2)4
was prepared according to the literature.18 1H NMR spectra
were taken with a JEOL Lambda 400 or 600 spectrometer at
room temperature unless otherwise noted. Chemical shifts were
recorded in ppm from the solvent signal, of which assignments
were made with the aid of H–H COSY, and C–H COSY tech-
niques. Polymer analysis was done at the TOSOH Analysis and
Research Center.
Preparation of sulfonamide ligands, i-PrNHTs and
TsHN(CH2)2O(CH2)2NHTs (3)
In a typical example, p-toluenesulfonyl chloride (2.29 g, 12
mmol) dissolved in Et2O (30 mL) was treated with iso-
propylamine (1.12 mL, 13.2 mmol) and NEt3 (1.84 mL, 13.2
mmol) at 0 ЊC, and the mixture was stirred at room temperature
for 4 h. After removal of the solvent in vacuo, the residue was
purified by column chromatography {silica gel (Wakogel
FC-60), 2.75 × 9.5 cm, eluent hexane and EtOAc (1 : 1)} to give
the desired product (2.53 g, 11.8 mmol, 98%). Using a similar
procedure, the TsHN(CH2)2O(CH2)2NHTs tosylamide ligand
was obtained from 2,2Ј-oxybis(ethylamine)dihydrochloride
(1.86 g, 4.51 mmol, 71%).
Concluding remarks
In this paper, we describe a novel titanium compound 1 which
has two η2-tosylamide ligands, whereas the two sulfonamide
moieties of the TsN(CH2)2O(CH2)2NTs tosylamide ligand in 2
were bound to the metal center in type A coordination mode.
Compared with the η1:η2-complexes reported by Walsh and
Gagné,5–8 1 does not include the titanacyclopentane structure,
whereas 2 has a bicyclic titanacycle. No ring strain due to the
titanacycle in 1 causes adoption of the type D coordinated
mode, while the special ring strain due to the bicyclic structure
in 2 is favorable for the type A coordination mode. From the
solution dynamics of 1 a reversible dissociation energy of
the Ti–O(sulfonamide) bond was first estimated as ca. 16 kcal
molϪ1. Replacement of the dimethylamide ligands in 2 by
electronically negative chlorine atoms actually increased the
Lewis acidity of the titanium center; this resulted in stabiliz-
ation of the complex by making dimeric structures via sulfon-
amide oxygen bridging as shown in the crystal structure of 4.
These results show that the sulfonamides are unique ligands
having the capability to act as both N and NO ligands; inter-
conversion between both modes is facile. The sulfonamide
groups sometimes behave as a unique bridging ligand, when the
titanium atom is Lewis acidic enough. These findings are new
and interesting in the coordination chemistry of pseudo-allyl
ligands.
i-PrNHTs. Colorless solid (mp 50–51 ЊC). 1H NMR (CDCl3):
δ 1.07 (d, J = 6.5Hz, Me of i-Pr, 6H), 2.43 (s, Me of Ts, 3H),
3.44 (sept, J = 6.5Hz, CH of i-Pr, 1H), 4.62 (d, J = 2.4 Hz, NH,
1H), 7.28 (d, J = 8.2 Hz, m-H of Ts, 2H), 7.77 (d, J = 8.2 Hz,
o-H of Ts, 2H). 13C{1H} NMR (CDCl3): δ 21.5 (Me of Ts), 23.7
(Me of i-Pr), 46.0 (CH of i-Pr), 126.8 (CH of Ts), 127.0 (CH of
Ts) 138.1 (4Њ), 143.2 (4Њ). Anal. Calcd. for C10H15NO2S: C;
56.31, H; 7.09, N; 6.57. Found: C; 56.24, H; 7.07, N; 6.54%.
TsHN(CH2)2O(CH2)2NHTs (3). 71% yield; white solid (mp
1
105–107 ЊC). H NMR (CDCl3): δ 2.43 (s, Me of Ts, 6H), 3.08
(br q, J = 5.0 Hz, CH2N, 4H), 3.39 (br t, J = 5.0 Hz, OCH2, 4H),
4.92 (br s, NH, 2H), 7.31 (d, J = 7.8 Hz, m-H of Ts, 4H), 7.74 (d,
J = 7.8 Hz, o-H of Ts, 4H). 13C{1H} NMR (CDCl3): δ 21.5 (Me
of Ts), 42.8 (CH2N), 69.3 (OCH2), 127.1 (o-C of Ts), 129.8
(m-C of Ts), 136.9 (4Њ) 143.6 (4Њ). Anal. Calcd. for
C18H24N2O5S2: C; 52.43, H; 5.83, N; 6.80. Found: C; 52.50, H;
5.90, N; 6.85%.
We expect that these unique properties of sulfonamides as
auxiliary ligands could provide new aspects in catalysis. The
possibility of tosylamide ligands as a Cp-substitute in Ti, Zr, or
lanthanide olefin polymerization catalysts17 has been pointed
out by Walsh7 and Anwander without details.13 In this context,
ethylene polymerization was examined in the presence of 10
µmol of 1, 2, or 5 and 10 mmol of MAO at room temperature
under 10 atm of ethylene in a 100 mL stainless steel autoclave to
give polyethylene with mp > 135 ЊC and η > 4.0. Activity of the
catalyst (1; 0.070, 2; 0.026, 5; 0.124 kg per mmol Ti per h) was
much smaller than that with Cp2ZrCl2 (2.14 kg per mmol Ti
Preparation of (i-PrNTs)2Ti(NMe2)2 (1)
A 50 mL Schlenk tube was charged with Ti(NMe2)4 (100 mg,
0.45 mmol) and i-PrNHTs (178 mg, 0.89 mmol) (weighed in a
glove box) and the atmosphere was replaced by argon. Then
toluene (20 mL) was added, and the solution was stirred at
room temperature for 1 h. After removal of the solvent in vacuo,
the residue was washed with several portions of Et2O (0.5 mL
each). Recrystallization of the crude product from toluene–
hexane (1 : 2) at Ϫ30 ЊC gave dark red crystals of (i-PrNTs)2-
1
Ti(NMe2)2 (1) (189 mg, 0.33 mmol, 76%); mp 170–171 ЊC. H
J. Chem. Soc., Dalton Trans., 2002, 1521–1527
1525

View Article Online
Table 4 Crystallographic data for 1, 2 and 4
1
2
4
Empirical formula
M
Crystal system
Space group
a/Å
b/Å
c/Å
C24H40N4O4S2Ti
560.62
Monoclinic
P21/c
8.708(3)
16.383(4)
19.432(5)
90.53(4)
2772.1(14)
4
C22H34N4O5S2Ti
546.55
Monoclinic
P21/n
14.0471(9)
11.8424(6)
15.7599(9)
100.603(4)
2576.9(3)
4
C40H56Cl2N6O10S4Ti2ؒ2(CH2Cl2)
1245.70
Monoclinic
P21/c
11.1393(5)
17.965(1)
13.887(1)
91.168(3)
2778.5(3)
2
β/Њ
V/Å3
Z
Dc/Mg mϪ3
1.343
0.495
1.409
0.534
1.489
0.783
µ/mmϪ1
F(000)
1192
0.40 × 0.15 × 0.15
13280
6351 [R(int) = 0.2618]
2267
1152
0.45 × 0.30 × 0.10
6171
5886 [R(int) = 0.04244]
4027
1288
0.60 × 0.60 × 0.40
6531
6149 [R(int) = 0.11879]
2796
Crystal size/mm
Reflections measured
Independent reflections
Reflections observed (>2σ)
GOF
0.950
1.023
0.938
R1 (I > 2σ(I ))
wR2 (I > 2σ(I ))
R1 (all data)
wR2 (all data)
∆ρmax, min/e ÅϪ3
0.0568
0.1103
0.2625
0.1659
0.0395
0.0977
0.0719
0.1155
0.0744
0.1401
0.1714
0.1757
0.484, Ϫ0.682
0.331, Ϫ0.463
0.458, Ϫ0.676
NMR (C6D5CD3, Ϫ20 ЊC): δ 1.00 (d, J = 6.6 Hz, Me of i-Pr,
6H), 1.33 (d, J = 6.6 Hz, Me of i-Pr, 6H), 1.75 (s, Me of Ts, 6H),
3.45 (sept, J = 6.6 Hz, CH of i-Pr, 2H), 3.61 (s, Me of NMe2,
12H), 6.58 (d, J = 8.3 Hz, m-H of Ts, 4H), 8.22 (d, J = 8.3 Hz,
o-H of Ts, 4H). 13C{1H} NMR (C6D5CD3, Ϫ20 ЊC): δ 20.9 (Me
of Ts), 23.7 (Me of i-Pr), 25.2 (Me of i-Pr), 49.9 (CH of i-Pr),
50.2 (Me of NMe2), 128.2 (o-C of Ts), 129.3 (m-C of Ts), 138.0
(4Њ), 142.5 (4Њ). Anal. Calcd. for C24H40N4O4S2Ti: C; 51.42, H;
7.19, N; 9.99. Found: C; 51.40, H; 7.18, N; 9.66%.
mmol) and 69% (22 mg, 0.04 mmol), respectively. At 60 ЊC, only
5 was available in 83% yield after 15 h.
[{(TsNC2H4)2O}Ti(NMe2)Cl]2 (4). mp 137–139 ЊC. 1H NMR
(CD2Cl2): δ 2.44 (Me of Ts, 6H), 3.32 (br s, NCH2, 4H), 3.74 (br
s, OCH2, 4H), 3.92 (s, Me of NMe2, 6H), 7.37 (d, J = 8.6 Hz,
m-H of Ts, 4H), 8.06 (d, J = 8.6 Hz, o-H of Ts, 4H). 13C{1H}
NMR (CD2Cl2): δ 20.5 (Me of Ts), 47.6 (br s, CH2N), 50.9 (Me
of NMe2), 68.9 (br s, OCH2), 127.5 (o-C of Ts), 129.0 (m-C of
Ts), 134.0 (4Њ), 144.0 (4Њ).
Preparation of [TsN(CH2)2O(CH2)2NTs]Ti(NMe2)2 (2)
1
[{(TsNC2H4)2O}TiCl2]2 (5). mp 142–144 ЊC. H NMR (CD2-
A 50 mL Schlenk tube was charged with Ti(NMe2)4 (24 mg,
0.11 mmol) and TsHN(CH2)2O(CH2)2NHTs (44 mg, 0.11
mmol) (weighed in a globe box) and the atmosphere was
replaced by argon. Toluene (30 mL) was added, and the mixture
was stirred at room temperature for 12 h. After removal of the
solvent in vacuo, the residue was purified by recrystallization
from dichloromethane–hexane (1 : 2) to give [TsN(CH2)2O-
(CH2)2NTs]Ti(NMe2)2 (2) as orange plates (58 mg, 0.10 mmol,
90%); mp 135–136 ЊC. 1H NMR (CD2Cl2): δ 2.33 (s, Me of Ts,
6H), 3.29 (s, Me of NMe2, 12H), 3.37 (t, J = 5.4 Hz, NCH2,
4H), 3.76 (t, J = 5.4 Hz, OCH2, 4H), 7.20 (d, J = 8.1 Hz, m-H of
Ts, 4H), 7.60 (d, J = 8.1 Hz, o-H of Ts, 4H). 13C{1H} NMR
(CD2Cl2): δ 20.8 (Me of Ts), 45.1 (NMe2), 48.0 (CH2N), 74.8
(OCH2), 126.5 (o-C of Ts), 128.9 (m-C of Ts), 139.9 (4Њ), 141.3
(4Њ). Anal. Calcd. for C22H34N4O5S2Ti: C; 48.35, H; 6.27, N;
10.25. Found: C; 47.98, H; 6.17, N; 9.97%.
Cl2): δ 2.34, 2.41 (s, Me of Ts, 6H), Two pairs of NCHaHaЈ-
CHbHbЈO signals were seen. 3.26–3.34 (m, CH2 of Ha or HaЈ,
1H), 3.50–3.65 (m, CH2 of Ha or HaЈ, 2H), 3.71–3.79 (m, CH2
of Ha or HaЈ, 1H), 3.97–4.12 (m, CH2 of Hb or HbЈ, 3H), 4.30–
4.41 (m, CH2 of Hb or HbЈ, 1H), 7.22, 7.26 (d each, J = 8.6 Hz,
m-H of Ts, 4H), 7.98, 7.99 (d each, J = 8.6 Hz, o-H of Ts, 4H).
13C{1H} NMR (CD2Cl2): δ 20.9, 21.0 (Me of Ts), 50.1, 51.6
(CH2N), 74.8, 76.0 (OCH2), 127.7 (o-C of Ts), 128.3 (o-C of
Ts), 129.0 (m-C of Ts), 129.1 (m-C of Ts), 134.4 (4Њ),137.9 (4Њ),
142.2 (4Њ), 143.8 (4Њ). Anal. Calcd. for C36H44Cl4N4O10S4Ti2: C;
40.85, H; 4.19, N; 5.29. Found: C; 40.28, H; 4.48, N; 5.42%.
Typical procedure for ethylene polymerization
In a 100 mL Schlenk tube, [TsN(CH2)2O(CH2)2NTs]TiCl2 (4)
(5.29 mg, 10 µmol) was measured in a glove box and the atmos-
phere was replaced by argon. A toluene solution of 1000 equiv.
of MAO (50 mL, 0.2 M, 10 mmol) was added, and the mixture
stirred for 1 h. The resulting solution was moved to a 100 mL
autoclave fitted with a Teflon inner tube by cannula. Ethylene
(10 atm) was then applied. After 30 min, the polymerization
was quenched by stopping the ethylene supply, and the mixture
was treated with methanol (200 mL) and conc. HCl (6 mL) for
1 h in order to remove any aluminium residue. The white
precipitate formed was filtered off and washed with methanol.
The resulting powder was dried for 15 h in vacuo to give poly-
ethylene (621 mg).
Preparation of [{TsN(CH2)2O(CH2)2NTs}Ti(NMe2)Cl]2 (4) and
[{TsN(CH2)2O(CH2)2NTs}TiCl2]2 (5)
A 50 mL Schlenk tube was charged with [TsN(CH2)2O(CH2)2-
NTs]Ti(NMe2)2 (2) (36 mg, 0.06 mmol) and the atmosphere was
replaced by argon. Toluene (30 mL) was added, and Me3SiCl
(65 mg, 0.7 mL, 0.60 mmol) was added to the resulting suspen-
sion of 2 at room temperature. The reaction mixture was stirred
at room temperature for 15 h, and the solvent was removed
in vacuo. Recrystallization from dichloromethane–hexane (1 : 1)
at room temperature gave [{TsN(CH2)2O(CH2)2NTs}TiCl2]2 (5)
(13 mg) as yellow plate crystals. Further recrystallization of the
residue produced by concentration of the supernatant from
dichloromethane–hexane (1 : 2) at room temperature gave a
mixture of [{TsN(CH2)2O(CH2)2NTs}Ti(NMe2)Cl]2 (4) as dark
red crystals (6 mg) and 5 (9 mg) (detected by 1H NMR
spectroscopy). Total yields of 4 and 5 were 18% (6 mg, 0.01
X-Ray diffraction analyses for 1, 2, and 4
A single crystal of 1 was obtained from a toluene-d8 solution at
Ϫ30 ЊC in a sealed NMR tube, whereas those of 2 and 4 were
obtained from a mixture of CH2Cl2 and hexane at room
temperature. X-Ray crystallography was performed on an
1526
J. Chem. Soc., Dalton Trans., 2002, 1521–1527

View Article Online
Adv. Inorg. Radiochem., 1986, 30, 1; H. R. Keable and M. Kilner,
Enraf-Nonius CAD4 four cycle axis diffractometer (for 1) or
Rigaku RAXIS RAPID imaging plate diffractometer (for 2 and
4) with graphite monochromated Mo-Kα radiation (λ = 0.71069
Å). The diffraction data of 1 were collected at 296(2) K using
the ω–2θ technique to a maximum 2θ value of 55.0Њ, whereas
those of 2 and 4 were collected at 223(2) K in the θ ranges 1.79 ≤
θ ≤ 27.48Њ and 2.63 ≤ θ ≤ 27.48Њ, respectively (44 oscillation
exposures). Data collection and cell refinement of 1 were
carried out using the program system ‘CAD4 Express’19 on a
MS VAX computer, whereas those of 2 and 4 were done using
“MSC/AFC Diffractometer Control”20 on a Pentium com-
puter. The structure was solved by direct methods (SIR-97, 1)21
or the Patterson method (DIRDIF-94 PATTY, 2 and 4),22 and
was refined using full-matrix least squares (SHELXL-97)23
based on F 2 for all independent reflections measured. The H
atoms were located at ideal positions except for those of the
methyl groups which were allowed to rotate about the CH3
(adjacent atom) bonds. They were included in the refinement,
but were restricted to riding on the carbons to which they were
bonded. Isotropic thermal factors for the H atoms were held to
1.2 to 1.5 times (for methyl groups) Ueq of the parent atoms.
Further details are listed in Table 4.
J. Chem. Soc., Dalton Trans., 1972, 1535.
4 M. Yoshioka, T. Kawakita and M. Ohno, Tetrahedron Lett., 1989,
30, 1657; H. Takahashi, T. Kawakita, M. Ohno, M. Yoshioka and
S. Kobayashi, Tetrahedron, 1992, 48, 5691; M. J. Rozema, A. Sidduri
and P. Knochel, J. Org. Chem., 1992, 57, 1956; W. Brieden,
R. Ostwald and P. Knochel, Angew. Chem., Int. Ed. Engl., 1993, 32,
582; S. Pritchett, D. H. Woodmansee, T. J. Davis and P. J. Walsh,
Tetrahedron Lett., 1998, 39, 5941.
5 S. Pritchett, P. Gantzel and P. J. Walsh, Organometallics, 1997, 16,
5130.
6 S. Pritchett, D. H. Woodmansee, P. Gantzel and P. J. Walsh, J. Am.
Chem. Soc., 1998, 120, 6423.
7 S. Pritchett, P. Gantzel and P. J. Walsh, Organometallics, 1999, 18,
823.
8 L. T. Armistead, P. S. White and M. R. Gagné, Organometallics,
1998, 17, 216.
9 R. Baumann, M. Davis and R. R. Schrock, J. Am. Chem. Soc., 1997,
119, 3830; R. Baumann and R. R. Schrock, J. Organomet. Chem.,
1998, 557, 69; R. R. Schrock, F. Schattenmann, M. Aizenberg
and W. M. Davis, Chem. Commun., 1998, 199; L.-C. Liang, R. R.
Schrock and W. M. Davis, Organometallics, 2000, 19, 2526; see also
ref. 12–14.
10 M. Aizenberg, L. Turculet, W. M. Davis, F. Schattenmann and
R. R. Schrock, Organometallics, 1998, 17, 4795.
11 M. A. Flores, M. R. Manzoni, R. Baumann, W. M. Davis and
R. R. Schrock, Organometallics, 1999, 18, 3220.
12 R. Baumann, R. Stumpf, W. M. Davis, L. C. Liang and
R. R. Schrock, J. Am. Chem. Soc., 1999, 121, 7822.
13 H. W. Görlitzer, M. Spiegler and R. Anwander, Eur. J. Inorg. Chem.,
1998, 1009.
CCDC reference numbers 160977–160979.
See http://www.rsc.org/suppdata/dt/b1/b110481k/ for crystal-
lographic data in CIF or other electronic format.
14 I. Kim, Y. Nishihara, R. F. Jordan, R. D. Rogers, A. L. Rheingold
and G. P. A. Yap, Organometallics, 1997, 16, 3314.
15 C. H. Lee, Y.-H. La and J. W. Park, Organometallics, 2000, 19, 344.
16 Other examples of dimeric compounds, (Al): E. J. Corey,
S. Sarshar and J. Bordner, J. Am. Chem. Soc., 1992, 114, 7938; (In):
A. Blaschette, A. Michalides and P. G. Jones, J. Organomet. Chem.,
1991, 411, 57.
Acknowledgements
A part of this study was financially supported by the Japan
Society for the Promotion of Science (10450343, 13450374,
1302090) and CREST, the Japan Science and Technology
Corporation (JST).
17 For representative reviews see: W. Kaminsky, J. Chem. Soc., Dalton
Trans., 1998, 1413; H. H. Brintzinger, D. Fischer, B. Rieger and
R. Waymouth, Angew. Chem., Int. Ed. Engl., 1995, 34, 1143; G. J. P.
Biritovsk, V. C. Gibson and D. F. Wass, Angew. Chem., Int. Ed.,
1999, 38, 428.
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