New titanium imido complexes containing piperazine-based diamido-diamine ligands

Article abstract of DOI:10.1016/S0022-328X(99)00447-7

Syntheses of the new piperazine derivatives 1,4-bis(2-amino-4-tert-butylbenzyl)piperazine (2) and 1,4-bis(2-trimethylsilylamino-4-R-benzyl)piperazine (R=H 3 or Bu^t 4; H₂L¹ and H₂L², respectively) are

Full text of DOI:10.1016/S0022-328X(99)00447-7

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 591 (1999) 114–126
New titanium imido complexes containing piperazine-based
diamido–diamine ligands
Julian Lloyd a, Sergei Z. Vatsadze a, David A. Robson a, Alexander J. Blake b,
Philip Mountford a,*,1
a Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, UK
b School of Chemistry, Uni6ersity of Nottingham, Uni6ersity Park, Nottingham NG7 2RD, UK
Received 15 June 1999; accepted 19 July 1999
Abstract
Syntheses of the new piperazine derivatives 1,4-bis(2-amino-4-tert-butylbenzyl)piperazine (2) and 1,4-bis(2-trimethylsilylamino-
4-R-benzyl)piperazine (R=H 3 or But 4; H2L1 and H2L2, respectively) are described along with the X-ray crystal structure of 2.
Treatment of H2L1 and H2L2 with n-butyl lithium gives the amido derivatives Li2L1 (5) and Li2L2 (6), which react with
[Ti(NBut)Cl2(py)3] to form [Ti(NBut)(L1)] (7) and [Ti(NBut)(L2)] (8). Reaction of Li2L1 with [Ti(N-4-C6H4Me)Cl2(py)3] gives the
corresponding arylimido homologue [Ti(N-4-C6H4Me)(L1)] (9). The X-ray structure of 8 shows a strongly transoid disposition of
the aryl rings of the L1 ligand and this geometry is maintained in solution. Somewhat surprisingly 7 does not undergo
tert-butylimide/arylamine exchange with 4-methylphenylamine to form 9. The related compound N,N%-bis(2-trimethylsilyl-
aminobenzyl)-N,N%-dimethyl-1,3-diaminopropane (12, H2L3) and its lithium salt Li2L3 (13) are also described. However, reaction
of 13 with [Ti(NBut)Cl2(py)3] affords no tractable product. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Titanium; Imide; Amide; Polydentate ligand; X-ray diffraction
noted with interest new complexes of tetradentate
piperazine-based ligands (III) recently developed by
1. Introduction
Wieghardt and co-workers [12].
As part of an ongoing research programme in early
transition metal imido chemistry [1–9], we recently
described the syntheses, structures and reactivity of
titanium imido complexes supported by dianionic, te-
tradentate N4-donor dibenzotetraaza [14]annulene (I)
[10] and N2O2-donor Schiff base (II) [11] ligands2.
These polydentate ligands provide a useful supporting
environment that directs reactivity towards the TiꢀNR
linkage [6]. In the context of this previous work we
* Corresponding author. Tel.: +44-1865-272679; fax: +44-1865-
272690.
E-mail address: philip.mountford@chem.ox.ac.uk (P. Mountford)
1 Philip Mountford is the Royal Society of Chemistry Sir Edward
Frankland Fellow for 1998–1999.
2 Note that although for ease of representation all titaniumꢁimido
linkages are drawn TiꢀNR, the formal TiꢁN bond order in the
complexes [Ti(NR)(tetradenate-ligand)] (R=But or aryl) described
herein is generally best thought of as three (pseudo-|2p4 triple bond)
rather than as two [7,39,40].
Although the ligands in III are neutral for the com-
plexes shown, we thought it likely that appropriate
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00447-7

J. Lloyd et al. / Journal of Organometallic Chemistry 591 (1999) 114–126
115
N-derivatisation could provide precursors to dianionic
ligands suitable for early transition metal chemistry. A
second interesting feature of the ligands in III was the
non-planar, pseudo-C2 symmetric conformation that
they adopt (with one phenyl ring tilted up and one
down), even for the four-coordinate complexes with no
additional axial donor ligand(s). We envisaged that
such a conformation might, in the long term, allow for
asymmetric synthetic applications of metal–ligand
multiply bonded complexes containing such ligands.
Finally, we noted that the coordination chemistry of
piperazines [13,14] and their open-chain [12,15–19] and
macrocyclic [20–26] derivatives has only been devel-
oped for later transition metals, and we were therefore
interested to see if analogous complexes of early transi-
tion metals could be prepared.
2. Results and discussion
Scheme 1. Reagents and conditions: (i) KOH (two equivalents),
toluene, 60°C, 20 h, 19%; (ii) hydrazine monohydrate, graphite
catalyst, refluxing ethanol, 68 h, 69%.
The compound 1,4-bis(2-aminobenzyl)piperazine (as
shown in complexes III above) was prepared according
to the method of Wieghardt and co-workers [12]. In the
previously studied systems I and II we found that the
introduction of ligand aryl ring methyl or tert-butyl
substituents frequently aided solubility and crystallisa-
tion, and could also provide useful NMR handles. We
therefore prepared tert-butyl substituted analogues of
the Wieghardt systems as shown in Scheme 1.
Coupling of 1-bromomethyl-4-tert-butyl-2-nitroben-
zene [27] with piperazine afforded the nitrobenzyl com-
pound 1 as a pale yellow solid in 19% yield. The yield
for the formation of 1 is significantly lower than that
reported by Weighardt and co-workers for the non-
tert-butyl substituted homologue, 1,4-bis(2-nitroben-
zyl)piperazine (98%) [12]. We attribute the reduced
yield of 1 to a lower electrophilicity of the benzylic
methlene in 1-bromomethyl-4-tert-butyl-2-nitrobenzene
compared to that of 1-bromomethyl-2-nitrobenzene.
Subsequent graphite-catalysed reduction of 1 with hy-
drazine monohydrate gave 1,4-bis(2-amino-4-tert-butyl-
benzyl)piperazine (2) as a colourless, crystalline solid in
69% yield after recrystallisation from ethanol. Single
crystals of 1,4-bis(2-amino-4-tert-butylbenzyl)pipera-
zine·4 CHCl3 (2·4 CHCl3) suitable for X-ray diffraction
were grown from an ethanol–chloroform (1:1) mixture
at room temperature. The molecular structure is shown
in Fig. 1, data collection and processing parameters are
listed in Table 1, and selected bond lengths and angles
are given in Table 2.
Molecules of 2 lie across crystallographic inversion
centres, and the crystals contain four CHCl3 molecules
of crystallisation for each molecule of 2. There are no
unusual contacts between 2 and CHCl3, with the
molecules of 2 and CHCl3 forming alternating sheets in
the crystal structure. The piperazine ring adopts a
thermodynamically favourable chair conformation with
the benzyl substituents occupying equatorial positions
as expected [28]. There are, in addition, weak in-
,
tramolecular hydrogen bonds [NH···N=2.4(1) A] be-
tween the piperazine nitrogen atoms and one of the
Fig. 1. Displacement ellipsoid plot of 1,4-bis(2-amino-4-tert-butylbenzyl)piperazine (2). Displacement ellipsoids are drawn at the 35% probablility
level and H atoms are drawn as spheres of arbitrary radius. Carbon-bonded hydrogen atoms and the chloroform molecules of crystallisation are
omitted. Atoms carrying the suffix B are related to their non-suffixed counterparts by the symmetry operator [−x+3/2, −y+1/2, −z].

116
J. Lloyd et al. / Journal of Organometallic Chemistry 591 (1999) 114–126
Table 1
X-ray data collection and processing parameters for 1,4-bis(2-amino-4-tert-butylbenzyl)piperazine·4 CHCl3 (2·4 CHCl3) and [Ti(NBut)(L1)] (8)
2·4 CHCl3
8
Molecular formula
Formula weight
Crystal system
Space group
C26H40N4·4 CHCl3
886.14
Monoclinic
C2/c
C36H63N5Si2Ti
670.01
Monoclinic
P21/c
Wavelength
0.71069
0.71069
Unit cell dimensions
,
a (A)
40.63(2)
6.137(5)
17.367(10)
108.26(6)
4112.6
4
0.84
Colourless column
0.62×0.29×0.20
2.70–25.06
ꢀ-scans with profile fitting
−485h545, 05k57, 05l520
3612
16.114(1)
10.7550(8)
23.204(1)
101.824(4)
2936.1
4
0.30
Yellow plate
0.60×0.52×0.17
1.72–26.52
ꢀ-scans
05h520, 05k513, −285l528
54927
8227
0.052
,
b (A)
,
c (A)
i (°)
V (A )
3
,
Z
Absorption coefficient (mm−1
Crystal description
Crystal size (mm)
Theta range for data collection (°)
Scan type
)
Index ranges
Reflections collected
Independent reflections
Rmerge
Observed reflections
Absorption correction
Tmin, Tmax
3612
No reflections to be merged
2360 [I\2|(I)]
Integration
5092 [I\3|(I)]
Multi-scan
0.856, 0.950
0.777, 0.851
Variation in standard reflections
No. of data used in refinement
No. of restraints applied
No. of parameters refined
Refinement method
Weighting scheme
Random94.5%
2360
21
–
5092
0
420
212
Blocked-matrix,
Chebychev polynomial
R1=0.0963, 6Rw=0.1165
[I\2|(I)]
Full-matrix,
Chebychev polynomial
R1=0.0627, Rw=0.0472
[I\3|(I)]
Final R indices a
Goodness-of-fit
0.968
1.155
Final (D/|)max
0.013
0.97 and −0.86
0.001
0.95 and −0.64
−3
,
Largest residual peaks (e A
)
2
a R=R1=S ꢀꢀFoꢀ−ꢀFcꢀꢀ/S ꢀFoꢀ; Rw=ꢁ{S w(ꢀFoꢀ−ꢀFcꢀ)2/S wꢀFoꢀ }.
2-amino group hydrogen atoms. Similar solid-state ge-
ometries were recently reported for phenolic analogues
1,4-bis(2-hydroxybenzyl)piperazine [16] and 1,4-bis-
Table 2
,
Selected bond distances (A) and angles (°) for 1,4-bis(2-amino-4-tert-
butylbenzyl)piperazine (2) a
(2-hydroxy-3-formyl-5-bromobenzyl)piperazine
[29]
Bond distances
Bond angles
which contain intramolecular OH···N hydrogen bonds.
1
In CDCl3 solution the H-NMR spectrum of 2 shows
N(1)ꢁC(1)
N(1)ꢁH(1)
N(1)ꢁH(2)
N(2)···H(1)
N(2)ꢁC(11)
N(2)ꢁC(12)
N(2)ꢁC(13)
C(1)ꢁC(2)
C(1)ꢁC(6)
C(2)ꢁC(3)
C(3)ꢁC(4)
C(3)ꢁC(7)
C(4)ꢁC(5)
C(5)ꢁC(6)
C(6)ꢁC(11)
C(12)ꢁC(13B)
1.39(1)
0.91(9)
0.8(1)
C(1)ꢁN(1)ꢁH(1)
C(1)ꢁN(1)ꢁH(2)
125(6)
108(7)
107(9)
a broad resonance at ca. 2.4 ppm for the piperazine
methylene hydrogen atoms, indicating that this com-
pound is fluxional in solution. The corresponding sig-
nals for the nitrobenzyl analogue 1 appear as a
considerably sharper signal, suggesting that the activa-
tion energy barrier to chairlboatlchair interconver-
sion in this case is lower as would be expected since 1
cannot form intramolecular NH···N bonds.
Reaction of 1,4-bis(2-aminobenzyl)piperazine with
chlorotrimethylsilane in THF in the presence of 1,4-di-
azabicyclo[2.2.2]octane (DABCO) afforded 1,4-bis(2-
trimethylsilylaminobenzyl)piperazine (H2L1 3) as a
cream solid in 75% yield after recrystallisation from
hexane (Scheme 2). The homologous proligand 1,4-
bis(2-trimethylsilylamino-4-tert-butylbenzyl)piperazine
H(1)ꢁN(1)ꢁH(2)
C(11)ꢁN(2)ꢁC(12)
C(11)ꢁN(2)ꢁC(13)
C(12)ꢁN(2)ꢁC(13)
C(11)ꢁN(2)···H(1)
C(12)ꢁN(2)···H(1)
C(13)ꢁN(2)···H(1)
N(1)ꢁH(1)···N(2)
N(2)ꢁC(11)ꢁC(6)
N(2)ꢁC(12)ꢁC(13B)
N(2)ꢁC(13)ꢁC(12B)
2.4(1)
109.9(6)
111.3(6)
108.9(5)
90.4(23)
118.0(22)
116.8(22)
115(8)
111.6(7)
109.5(7)
109.5(6)
1.47(1)
1.468(8)
1.470(8)
1.394(9)
1.40(1)
1.39(1)
1.37(1)
1.552(8)
1.41(1)
1.40(1)
1.537(9)
1.51(1)
a Atoms carrying the suffix B are related to their counterparts by
the symmetry operator [−x+3/2, −y+1/2, −z].

J. Lloyd et al. / Journal of Organometallic Chemistry 591 (1999) 114–126
117
Scheme 2. Reagents and conditions: (i) DABCO (two equivalents) and Me3SiCl (2.2 equivalents), THF or Et2O, r.t., 18–24 h, 75 or 64% for 3
and 4, respectively; (ii) nBuLi (2.2 equivalents), toluene or hexane, ca. −70°C then r.t., 17–18 h, 90 or 78% for 5 and 6, respectively.
Scheme 3. Reagents and conditions: (i) THF (for 7, 8) or benzene (for 9), r.t., 17–23 h, 31 (for 7, 8) or 22% (for 9).
(H2L2 4) was prepared in 64% yield in an analogous
manner. The compounds are expected to possess similar
structures to those proposed for 1,4-bis(2-amino-4-R-
benzyl)piperazine (R=H or But 2) with intramolecular
NH···H hydrogen bonds. The remaining aniline hydro-
gen atoms of H2L1 and H2L2 are readily removed by
reaction with n-butyl lithium in toluene (for 3) or
hexane to form the corresponding dilithium diamido
derivatives Li2L1 (5) and Li2L2 (6) in 90 and 78% yields,
respectively. The compounds 5 and 6 are air- and
moisture-sensitive, highly insoluble pale yellow pow-
ders; they were characterised by elemental analysis and
infrared spectroscopy only. Their low solubility is at-
tributed to the thermodynamic tendency of piperazine
and its derivatives to adopt a chair conformation which
can result in the formation of oligomeric derivatives.
In previous studies we found that the compounds
[Ti(NR)Cl2(py)3] (R=But or aryl) [30] are extremely
useful precursors to new imido–titanium chemistry via
salt-elimination reactions with metallated reagents
[1,10,11]. Reaction of the dilithium amides Li2L1 (5) or
Li2L2 (6) with [Ti(NBut)Cl2(py)3] in THF gave the
yellow–orange derivatives [Ti(NBut)(L1)] (7) or
[Ti(NBut)(L2)] (8) in ca. 30% yield after recrystallisation
from pentane (Scheme 3). Similarly, reaction of Li2Li1
(5) with [Ti(N-4-C6H4Me)Cl2(py)3] in benzene afforded

118
J. Lloyd et al. / Journal of Organometallic Chemistry 591 (1999) 114–126
the arylimido homologue [Ti(N-4-C6H4Me)(L1)] (9) as
an orange, microcrystalline solid in 21% yield.
TiꢀNimide triple bond. The titanium atom lies 0.59 A
,
out of the least squares plane defined by N(1)ꢁN(4)
The low isolated yields of 7–9 warrant further com-
ment. When the crude reaction mixtures were examined
by NMR spectroscopy a number of relatively intense,
broad resonances were observed; similar resonances
were seen for NMR tube-scale reactions in C6D6. The
work-up of the mixtures separated oily, poorly soluble
side-products from the desired complexes. These side-
products are most likely to be oligomeric in nature,
again reflecting the tendency of piperazine to adopt a
thermodynamically favourable chair conformation
[16,17,28]. The inclination of the piperazine moiety of
L1 and L2 to bind via a bidentate, boat conformation to
a single Ti centre is presumably further diminished by
the steric crowding (see below) around Ti in 7–9.
Slow cooling of a sub-saturated pentane solution of 8
to −35°C gave diffraction-quality crystals. The molec-
ular structure is shown in Fig. 2, data collection and
processing parameters are listed in Table 1, and selected
bond lengths and angles are given in Table 3.
(maximum deviation of these atoms from the least-
squares N4 plane=0.003 A). This is similar to the value
,
,
found (0.56 A) for [Ti(N-2,6-C6H3Me2)(Et2salen)] (II
where R=2,6-C6H3Me2, R1=R2=H, R3=Et) but
somewhat less than for the two crystallographically
characterised compounds of the type I (Ti···N4 plane=
,
,
0.75–0.76 A). The TiꢁNamide [2.027(2), 2.032(2) A] and
TiꢁNpiperazine [2.259(2), 2.267(2) A] bond lengths are
,
consistent with their description as amidoꢁ and
aminoꢁtitanium linkages; the sums of the angles sub-
tended at N(3) (357.9°) and N(4) (359.9°) reveal nearly
trigonal planar (sp2-hybridised) centres, indicating the
potential for N(pp)ꢁTi(dp) interactions in this otherwise
14 valence electron system. The piperazine fragment
adopts a boat conformation as required for bidentate
coordination; the dihedral angles N(1)ꢁC(1)ꢁC(2)ꢁN(2)
and N(1)ꢁC(3)ꢁC(4)ꢁN(2) are 6.1 and 8.4°, respectively.
The N(1)ꢁTi(1)ꢁN(2) and N(3)ꢁTi(1)ꢁN(4) bite angles
[65.07(9) and 106.41(9)°, respectively] differ from the
corresponding NimineꢁTiꢁNimine [77.97(9)°] and OꢁTiꢁO
[97.17(8)°] angles in [Ti(Nꢁ2,6-C6H3Me2)(Et2salen)] by
ca.911–13°.
The molecular structure of [Ti(NBut)(L2)] (8) consists
of a dianionic, tetradentate L2 moiety coordinated to a
TiꢀNBut fragment. The TiꢀN-But angle [176.4(2)°] and
t
,
TiꢀNBu bond length [1.716(2) A] are comparable to
Perhaps the most striking feature of the molecular
structure of 8 is the strongly transoid arrangement of
the aryl rings of the L2 ligand. These rings are inclined
down and up (with respect to the imido ligand) by ca.
those found in compounds of the type I (dibenzote-
traaza[14]annulene complexes) [10] and II (Schiff base
complexes) [11] and are consistent with a formal
Fig. 2. Displacement ellipsoid plot of [Ti(NBut)(L2)] (8). Displacement ellipsoids are drawn at the 25% probability level. Hydrogen atoms are
omitted.

J. Lloyd et al. / Journal of Organometallic Chemistry 591 (1999) 114–126
119
The solution 1H- and 13C-NMR data for
[Ti(NBut)(L1)] (7), [Ti(NBut)(L2)] (8), and [Ti(N-4-
C6H4Me)(L1)] (9) are consistent with the solid-state
structure found for 8, and the overall pattern and
distribution of NMR resonances for the three com-
pounds is consistent with them possessing analogous
solution structures. The NMR spectra have been fully
assigned as far as possible using a combination of
1Hꢁ1H and 1Hꢁ13C correlation spectroscopy, and
phase-sensitive nuclear Overhauser effect spectroscopy
(NOESY). Full details of the assignments (provided in
Section 4) are made with reference to Fig. 3 which
shows the H atom labelling scheme adopted.
Table 3
t
1
,
Selected distances (A) and angles (°) for [Ti(NBu )(L )] (8)
Bond distances
Ti(1)ꢁN(1)
Ti(1)ꢁN(2)
Ti(1)ꢁN(3)
Ti(1)ꢁN(4)
Ti(1)ꢁN(5)
N(5)ꢁC(33)
Ti(1)···(N4 plane)
2.259(2)
2.267(2)
2.032(2)
2.027(2)
1.716(2)
1.456(3)
0.59
Bond angles
N(1)ꢁTi(1)ꢁN(2)
N(1)ꢁTi(1)ꢁN(3)
N(2)ꢁTi(1)ꢁN(3)
N(1)ꢁTi(1)ꢁN(4)
N(2)ꢁTi(1)ꢁN(4)
N(3)ꢁTi(1)ꢁN(4)
N(1)ꢁTi(1)ꢁN(5)
N(2)ꢁTi(1)ꢁN(5)
N(3)ꢁTi(1)ꢁN(5)
N(4)ꢁTi(1)ꢁN(5)
65.07(9)
141.81(9)
86.64(9)
83.23(9)
139.41(9)
106.41(9)
99.3(1)
102.2(1)
111.9(1)
107.7(1)
Ti(1)ꢁN(1)ꢁC(1)
Ti(1)ꢁN(1)ꢁC(3)
Ti(1)ꢁN(3)ꢁSi(1)
Ti(1)ꢁN(3)ꢁC(11)
Si(1)ꢁN(3)ꢁC(11)
Ti(1)ꢁN(4)ꢁSi(2)
Ti(1)ꢁN(4)ꢁC(22)
Si(2)ꢁN(4)ꢁC(22)
Ti(1)ꢁN(5)ꢁC(33)
105.7(2)
104.6(2)
122.0(1)
120.4(2)
115.5(2)
129.8(1)
110.0(2)
120.1(2)
76.4(2)
1
The H-NMR spectra of 7–9 thus reveal eight in-
equivalent environments for the methylene H atoms of
the piperazine ring, two SiMe3 signals, four signals for
the benzyl group diastereotopic H atoms, and two
different environments for the aryl rings (and their But
substituents for 8) of the L1 or L2 ligands. The unusual
high-field shift (6.06 ppm) for the ortho-H atoms of the
4-methylphenylimido ligand in 9 is attributed to shield-
ing effects of the up aryl ring of the L1 ligand. For all
three compounds the Ha, Hb and Hi resonances consis-
tently appear at relatively low fields compared to the
other piperazine and benzyl methylene resonances. We
attribute this to the deshielding effects of the tita-
niumꢁimido nitrogen multiple bond. In contrast, He of
the piperazine ligand is consistently observed at rela-
tively high field because of the shielding influence of the
down aryl ring of L1 or L2. Further examination of the
NOESY spectrum for [Ti(NBut)(L1)] (7) showed nega-
tive cross peaks between the two SiMe3 group reso-
nances and also between certain other pairs of signals.
This indicates slow (on the NMR timescale) chemical
exchange between the up and down rings of the L1
ligand in 7, as confirmed by qualitative spin saturation
transfer (SST) experiments. We expect that the ho-
mologous compounds 8 and 9 also undergo slow ex-
change in this manner.
Angles between least-squares mean planes
[C(6), C(7), C(8), C(9), C(10), C(11)] to [N(1), N(2),
N(3), N(4)]
[C(17), C(18), C(19), C(20), C(21), C(22)] to [N(1),
N(2), N(3), N(4)]
64.2
45.7
[C(6), C(7), C(8), C(9), C(10), C(11)] to[C(17), C(18), 141.5
C(19), C(20), C(21), C(22)]
64.2 and 47.7° from the N4 plane. In the Schiff base
complex [Ti(N-2,6-C6H3Me2)(Et2salen)] the correspond-
ing angles (which are in fact typical of complexes of
these types of ligand [31,32]) are 26.7 and 9.1°. Surpris-
ingly, given the apparent steric crowding imposed by
the SiMe3 substituents, the inclination of the aryl rings
in 8 with respect to the N4 plane are not substantially
different to that found for the compounds III described
by Wieghardt and co-workers. In these five complexes
the average inclination from the N4 plane is 51.3° with
a range of values spanning 46.0–58.9°.
The TiꢀNR linkages in the compounds 7–9 appear
to be very sterically protected by the up aryl ring and
one of the SiMe3 groups of the L1 or L2 ligand.
Consistent with this we found that [Ti(NBut)(L1)] (7)
does not undergo tert-butylimide/arylamine exchange
with H2N-4-C6H4Me even after prolonged heating. This
type of exchange reaction is facile for many of the
imidoꢁtitanium complexes we have described
[1,10,11,30], including the dibenzotetraaza[14]annulene
(I) and Schiff base (II for R1, R2"But) complexes. The
expected products of the reaction between 7 and H2N-
4-C6H4Me are free ButNH2 and 9, which can clearly be
prepared via the metathetical route shown in Scheme 3.
However, attempts to make arylimido complexes of
titanium with 2,6-substituents in the aryl ring by
analogous metathetical routes (e.g. from Li2L1 and
[Ti(N-2,6-C6H3Me2)Cl2(py)3]) were unsuccessful, possi-
Fig. 3. The NMR labelling scheme used for the imido complexes
[Ti(NBut)(L1)] (7), [Ti(NBut)(L2)] (8) and [Ti(N-4-C6H4Me)(L1)] (9).
See Section 4 for further details.

120
J. Lloyd et al. / Journal of Organometallic Chemistry 591 (1999) 114–126
bly due to intolerable steric interactions in the desired
product. An NMR tube-scale reaction between Li2L1
and [Zr(N-2,6-C6H3Pr2i )Cl2(THF)2] [33] appeared to be
promising, but we were unable to separate a single
product on scale-up. The reaction of Li2L1 with other
metal complexes including [Nb(NBut)Cl3(py)2] [34] and
[ZrCl4(THF)2] also failed to yield tractable products.
In an attempt to obtain a more versatile ligand
system, while retaining some of the principal features of
the piperazine-based ligands L1 and L2, we prepared the
new compounds 10–12 (Scheme 4). We hoped that
incorporation of the more flexible CH2CH2CH2 linkage
into the backbone would allow the ligand to adopt less
sterically crowded conformations. Reaction of H2L3
(12) with n-butyl lithium gave the dilithiated derivative
Li2L3 (13) in 72% yield. In contrast to the highly
insoluble (and presumably polymeric) piperazine ana-
logues Li2L1 (5) and Li2L2 (6), compound 13 is readily
soluble in hydrocarbon solvents. Unfortunately, reac-
tion of 13 (and the protio-analogue 12) with a number
of early transition metal imido substrates including
[Ti(NR)Cl2(py)3] and [Zr(N-2,6,C6H3Pri2)Cl2(THF)2]
failed to yield any tractable product. NMR tube-scale
reactions (in C6D6) of 13 showed very complex mix-
tures with these substrates. It is possible that the greater
bite angle of the 1,3-diaminopropane moiety in the
backbone of L3 forces the two trimethylsilyamido
donor groups closer together, thereby increasing steric
hinderance between these groups.
3. Summary and conclusions
We have described syntheses of two new dianionic,
tetradentate ligand systems incorporating piperazine
rings into their backbones, along with an analogue
containing a CH2CH2CH2 link in place of the piper-
azine ring. The ligand precursor 1,4-bis(2-amino-4-tert-
butylbenzyl)piperazine (2) was crystallographically
characterised. Three new imidotitanium derivatives of
the piperazine-based ligands were prepared and fully
characterised; the X-ray structure of 8 is consistent with
the solution structures of 7–9 determined by NMR
spectroscopy. The geometries of the dianionic L1 and
L2 ligands when complexed to TiꢀNR are similar to
that found for their neutral analogues in the previously
described complexes III. The phase-sensitive NOESY
spectra for 7 shows that slow exchange of up and down
Scheme 4. Reagents and conditions: (i) KOH (two equivalents), toluene, 60°C, 24 h, 98%; (ii) hydrazine monohydrate, graphite catalyst, refluxing
ethanol, 48 h, 68%; (iii) DABCO (two equivalents) and Me3SiCl (2.2 equivalents), Et2O, r.t., 20 h, 89%; (iv) nBuLi (2.2 equivalents), pentane,
−73°C then r.t., 4 h, 72%.

J. Lloyd et al. / Journal of Organometallic Chemistry 591 (1999) 114–126
121
resonances occurs in solution on the NMR timescale.
The ligands L1 and L2 lead to sterically crowded metal
centres in the complexes 7–9.
(MgSO4). The volatiles were removed by rotary evapo-
ration to yield an oily orange–yellow solid. This solid
was thoroughly washed with diethyl ether (ca. 350 ml in
total) and dried in vacuo, giving the desired product (1)
as a pale yellow powder. Yield: 9.85 g (19%).
4. Experimental
1H-NMR (CDCl3, 300.1 MHz): 7.79 (d, J=1.8, 2H,
3-C6H3), 7.52 (d of d, J=8.1 and 1.9, 2H, 5-C6H3),
7.47 (d, J=8.1, 2H, 6-C6H4), 3.73 (s, 4H, ArCH2N),
2.41 (br s, 8H, NCH2CH2N), 1.33 (s, 18H, CMe3).
13C-{1H} NMR (CDCl3, 75.5 MHz): 151.7 (4-C6H3),
149.8 (2-C6H3), 130.7 (CH of C6H3), 129.4 (1-C6H3),
121.3, 109.6 (2×CH of C6H3), 58.6, (ArCH2N), 53.2
(NCH2CH2N), 34.8 (CMe3), 31.1 (CMe3). Anal. Found
(Anal. Calc. for C26H36N4O4): C 66.1 (66.6); H 8.2
(7.7); N 11.7 (12.0)%. EI-MS: 468 [M+].
4.1. General
All manipulations of air- and/or moisture-sensitive
compounds were carried out under an atmosphere of
dinitrogen or argon using standard Schlenk-line or
dry-box techniques. All protio-solvents and commer-
cially available reagents were pre-dried over activated
molecular sieves and refluxed over an appropriate drying
agent under an atmosphere of dinitrogen and collected
by distillation. NMR solvents for air- and/or moisture-
sensitive compounds were dried over freshly ground
calcium hydride at room temperature (r.t.) (CDCl3) or
molten potassium (C6D6), distilled under reduced pres-
sure and stored under N2 in J. Young ampoules. NMR
samples of air- and moisture-sensitive compounds were
prepared in the dry-box in 5 mm Wilmad tubes, gener-
ally equipped with a Young’s Teflon valve.
4.3. 1,4-bis(2-amino-4-tert-butylbenzyl)piperazine (2)
A stirred mixture of 1,4-bis(2-nitro-4-tert-butylben-
zyl)piperazine (1) (9.85 g, 0.02 mol) and graphite cata-
lyst (3 g, Sigma-Aldrich) in ethanol (200 ml) was
purged with argon. Oxygen-free hydrazine monohy-
drate (22.53 g, 0.45 mol) was added and the mixture
heated to reflux under an argon atmosphere for 68 h.
The hot mixture was filtered and the residue extracted
with chloroform (3×50 ml). Upon cooling to r.t.,
colourless crystals of 2 grew from the ethanol filtrate
and were isolated. The ethanol and chloroform solu-
tions were combined and the volatiles removed by
rotary evaporation to yield an oily solid, which was
recrystallised from hot ethanol (150 ml) to yield a
second batch of 2 as colourless crystals. The product in
each case was dried in vacuo. Total yield: 5.91 g (69%).
1H-NMR (CDCl3, 300.1 MHz): 6.89 (d, J=7.5, 2H,
6-C6H3), 6.69–6.66 (m, 4H, overlapping 3- and 5-
C6H3), 4.71 (br s, 4H, NH2), 3.46 (s, 4H, ArCH2N),
2.41 (br s, 8H, NCH2CH2N), 1.28 (s, 18H, CMe3).
13C-{1H} NMR (CDCl3, 75.5 MHz): 151.6 (4-C6H3),
146.5 (2-C6H3), 130.1 (6-C6H3), 119.5 (1-C6H3), 114.7
(5-C6H3), 112.8 (3-C6H3), 61.6 (ArCH2N), 53.0
(NCH2CH2N), 34.4 (CMe3), 31.4 (CMe3). Anal. Found
(Anal. Calc. for C26H40N4): C 76.3 (76.4); H 10.0 (9.9);
N 13.5 (13.7)%. IR (KBr disc): 3443 [s, w(NꢁH)], 3325
[s, w(NꢁH)], 2960 (vs), 2903 (m), 2868 (m), 2804 (vs),
2765 (m), 1618 (s), 1576 (m), 1511 (m), 1480 (w), 1451
(m), 1427 (vs), 1386 (m), 1368 (m), 1340 (s), 1296 (vs),
1261 (m), 1245 (w), 1215 (w), 1203 (w), 1173 (w), 1150
(s), 1136 (m), 1082 (w), 1006 (vs), 951 (m), 917 (w), 870
(m), 836 (m), 804 (s), 724 (m), 682 (m), 656–425 (series
of weak peaks) cm−1. EI-MS: 408 [M+].
1H- and 13C-NMR spectra were recorded on either a
Bruker DPX 300 or a Varian Unity Plus 500 spectrom-
eter and referenced internally to residual protio-solvent
(1H) or solvent (13C) resonances. Chemical shifts are
reported relative to tetramethylsilane (l=0 ppm) in l
(ppm) and coupling constants in Hz. Assignments were
supported by DEPT-135 and DEPT-90, homo- and
hetero-nuclear, one- and two-dimensional experiments
as appropriate. IR spectra were recorded on either a
Perkin–Elmer 1600 Series or a Mattson Polaris FT-IR
spectrometer in the range 4000–400 cm−1. Samples
were prepared in the dry-box between KBr plates as
Nujol mulls or as KBr discs and data are quoted in
wavenumbers (w, cm−1). Mass spectra were recorded
on a AEI MS902 or Micomass Autospec 500 mass
spectrometer. Elemental analyses were carried out by
the analysis laboratory of this department.
[Ti(NR)Cl2(py)3] (R=But or 4-C6H4Me) [30], 1,4-
bis(2-aminobenzyl)piperazine [12] and 1-bromomethyl-
4-tert-butyl-2-nitrobenzene
[27]
were
prepared
according to literature methods.
4.2. 1,4-Bis(2-nitro-4-tert-butylbenzyl)piperazine (1)
1-Bromomethyl-4-tert-butyl-2-nitrobenzene (60 g,
0.22 mol) and powdered potassium hydroxide (13 g,
0.23 mol) were added to a stirred solution of piperazine
(9.50 g, 0.11 mol) in toluene (350 ml). The mixture was
heated to 60°C for 20 h and the contents of the flask
were then allowed to cool to r.t., yielding a red–orange
solution with solid precipitate. The mixture was filtered
and the residue extracted with toluene (2×50 ml),
before combining the toluene filtrates and drying
4.4. 1,4-bis(2-trimethylsilylaminobenzyl)piperazine
(H2L1, 3)
To a stirred solution of 1,4-diazabicyclo[2.2.2]octane
(DABCO, 1.70 g, 15.18 mmol) in THF (30 ml) was

122
J. Lloyd et al. / Journal of Organometallic Chemistry 591 (1999) 114–126
added chlorotrimethylsilane (1.81 g, 16.70 mmol) over 5
min. There was an immediate formation of a white
precipitate and the mixture was left to stir for a further
1 h. A solution of 1,4-bis(2-aminobenzyl)piperazine
(2.25 g, 7.59 mmol) in THF (80 ml) was added, result-
ing in a thickening of the white precipitate. After a
further ca. 24 h the solution was filtered and the residue
(white powder) extracted with further THF (30 ml).
The filtrates were combined and the volatiles removed
under reduced pressure to yield a waxy yellow–white
solid, which was recrystallised from hexane and dried in
vacuo to yield 3 as a cream solid. Yield: 2.50 g (75%).
1H-NMR (CDCl3, 300.1 MHz): 7.10 (apparent t,
apparent J=7.7, 2H, 4-C6H4), 6.97 (d, J=7.4, 2H,
6-C6H4), 6.71 (d, J=8.0, 2H, 3-C6H4), 6.62 (apparent t,
apparent J=7.4, 2H, 5-C6H4), 6.34 (br s, 2H, NH),
(s), 1250 (vs), 1154 (m), 1128 (m), 1096 (w), 1009 (s),
969 (vs), 931 (m), 885 (s), 856 (m), 838 (vs), 795 (m),
746 (m), 689 (w), 658 (w), 616 (w) cm−1. EI-MS: 552
[M+].
4.6. Dilithium 1,4-bis(2-trimethylsilylamidobenzyl)-
piperazine (Li2L1, 5)
To a cold (ca. −68°C), stirred solution of H2L1 (3,
1.50 g, 3.40 mmol) in toluene (40 ml) was added a 2.5
M solution of n-butyl lithium in hexanes (2.99 ml, 7.49
mmol=2.2 equivalents) over 5 min. The reaction was
allowed to warm to r.t. and the resulting yellow mixture
stirred for a further 18 h to give a colourless solution
containing a volumous oily yellow precipitate. The
mixture was filtered and the solid washed with toluene
(35 ml) and hexane (2×35 ml) before drying in vacuo,
to yield 5 as a pale yellow powder. Yield: 1.39 g (90%).
Anal. Found (Anal. Calc. for C24H38N4Si2Li2): C
64.1 (63.7); H 8.4 (8.5); N 11.9 (12.4)%. IR (KBr plates,
Nujol mull): 1590 (m), 1556 (w), 1346 (w), 1320 (w),
1290 (m), 1260 (s), 1241 (s), 1153 (w), 1103 (m), 1044
(w), 988 (m), 937 (s), 917 (s), 848 (s), 825 (vs), 777 (m),
3.50 (s, 4H, ArCH6 2N), 2.42 (br s, 8H, NCH2CH2N),
0.28 (s, 18H, SiMe3). 13C-{1H} NMR (CDCl3, 75.5
MHz): 148.3 (2-C6H4), 130.5 (6-C6H4), 128.2 (4-C6H4),
123.3 (1-C6H4), 116.5 (5-C6H4), 115.5 (3-C6H4), 62.7,
(ArCH2N), 52.7 (NCH2CH2N), 0.3 (SiMe3). Anal.
Found (Anal. Calc. for C24H40N4Si2): C 65.4 (65.4); H
9.5 (9.2); N 13.1 (12.7)%. IR (KBr plates, Nujol mull):
3223 [br m, w(NꢁH)], 1606 (m), 1583 (m), 1499 (s), 1342
(m), 1318 (w), 1299 (s), 1262 (m), 1250 (s), 1147 (w),
1104 (w), 1049 (w), 1006 (m), 939 (w), 913 (s), 838 (s),
754 (m), 689 (w) 668 (w) cm−1. EI-MS: 440 [M+].
739 (s), 663 (w), 588 (w) cm−1
.
4.7. Dilithium 1,4-bis(2-trimethylsilylamido-4-
tert-butylbenzyl)piperazine (Li2L2, 6)
4.5. 1,4-bis(2-trimethylsilylamino-4-tert-
butylbenzyl)piperazine (H2L2, 4)
To a cold (ca. −73°C) stirred solution of H2L2 (4,
0.60 g, 1.09 mmol) in hexane (35 ml) was added a 2.5
M solution of n-butyl lithium in hexanes (0.95 ml, 2.39
mmol=2.2 equivalents) over 5 min. The mixture was
allowed to warm to r.t., a further 15 ml of hexane was
added and the mixture was stirred for a further 17 h
To a stirred solution of 1,4-diazabicyclo[2.2.2]octane
(0.54 g, 4.80 mmol) in diethyl ether (15 ml) was added
chlorotrimethylsilane (0.52 g, 4.80 mmol) over 5 min
giving an immediate formation of a pale white precipi-
tate. After 1 h a solution of 2 (0.98 g, 2.40 mmol) in
diethyl ether (30 ml) was added, resulting in a thicken-
ing of the white precipitate. After ca. 18 h the mixture
was filtered and the residue (white powder) extracted
with further diethyl ether (30 ml). The ether filtrates
were combined and the volatiles removed under re-
duced pressure to yield a waxy white solid, which was
recrystallised from pentane and dried in vacuo, to give
4. Yield: 0.84 g (64%).
giving
a colourless solution, together with large
amounts of yellow precipitate. The mixture was filtered
and the solid washed with hexane (20 ml) before drying
in vacuo, to yield 6 as a pale yellow powder. Yield: 0.48
g (78%).
Anal. Found (Anal. Calc. for C32H54N4Si2Li2): C
68.2 (68.0); H 9.9 (9.6); N 9.9 (9.9)%. IR (KBr plates,
Nujol mull): 1594 (m), 1552 (w), 1342 (m), 1320 (m),
1280 (vs), 1253 (s), 1236 (vs), 1200 (m), 1096 (m), 986
(vs), 939 (w), 919 (w), 883 (vs), 866 (s), 826 (vs), 737
(m), 676 (w), 658 (w), 580 (m), 549 (m), 500 (w), 478
1H-NMR (CDCl3, 300.1 MHz): 6.91 (d, J=7.8, 2H,
6-C6H3), 6.77 (d, J=1.9, 2H, 3-C6H3), 6.66 (d of d,
J=7.8 and 1.9, 2H, 5-C6H4), 6.30 (br s, 2H, NH), 3.49
(s, 4H, ArCH2N), 2.43 (br s, 8H, NCH2CH2N), 1.32 (s,
18H, CMe3), 0.30 (s, 18H, SiMe3). 13C-{1H} NMR
(CDCl3, 75.5 MHz): 151.1 (4-C6H3), 147.8 (2-C6H3),
130.0 (6-C6H3), 120.4 (1-C6H3), 113.5 (5-C6H3), 113.1
(3-C6H3), 62.3, (ArCH2N), 52.8 (NCH2CH2N), 34.4
(CMe3), 31.4 (CMe3), 0.3 (SiMe3). Anal. Found (Anal.
Calc. for C32H56N4Si2): C 70.0 (69.5); H 10.4 (10.2); N
10.4 (10.1)%. IR (KBr plates, Nujol mull): 3212 [br m,
w(NꢁH)], 1614 (m), 1573 (s), 1507 (w), 1341 (m), 1301
(m), 452 (m) cm−1
.
4.8. Tert-butylimido-{1,4-bis(2-trimethyl-
silylamidobenzyl)piperazine}-titanium (7)
A pale orange solution of [Ti(NBut)Cl2(py)3] (0.52 g,
1.16 mmol) in THF (30 ml) was added to a stirred
yellow slurry of (Li2L1, 5) (0.53 g, 1.16 mmol) in THF
(40 ml). An immediate colour change was observed,
giving a brown solution which gradually became more
red as stirring continued. After ca. 23 h the volatiles

J. Lloyd et al. / Journal of Organometallic Chemistry 591 (1999) 114–126
123
were removed under reduced pressure to yield a
brown–yellow solid which was extracted into hexane
(4×40 ml). The combined extracts were filtered
through a bed of Celite and the pale orange filtrate was
evaporated to dryness, yielding a yellow–orange solid.
Recrystallisation (twice) from pentane and drying in
vacuo yielded 7 as a yellow–orange powder. Yield: 0.20
g (31%).
1H, Hb), 3.33 (d, J=13.3, 1H, Hl), 2.72 (d, J=13.3,
1H, Hk), 2.53 (d, J=11.0, 1H, Hj), 2.22 (m, 1H, Hf),
2.03 (m, 1H, Hg), 1.73 (overlapping 2×m, 2H, Hc and
Hd), 1.47 (m, 1H, Hh), 1.46 (s, 9H, ArCMe3), 1.41 (s,
9H, ArCMe3), 0.91 (m, 1H, He), 0.84 (s, 9H, NCMe3),
0.71 (s, 9H, Hv), 0.28 (s, 9H, Hu). 13C-{1H} (C6D6, 75.5
MHz): 158.9, 155.2 (2×2-C6H4), 152.2, 151.6 (2×4-
C6H4), 129.6 (CHm or CHn), 128.7 (one of 1-C6H4),
127.5 (two signals overlapping, CHp and CHq or CHr),
126.1 (one of 1-C6H4), 123.5 (CHt), 115.7 (CHr or
CHq), 115.6 (CHn or CHm), 70.0 (NCMe3), 61.6
(CHk,l), 58.8 (CHi,j), 56.1 (CHa,c), 52.9 (CHb,d), 52.4
(CHf,h), 46.4 (CHe,g), 34.7, 34.4 (2×ArCMe3),
32.6(NCMe3), 31.8, 31.6 (2×ArCMe3), 5.2 (CHv), 3.3
(CHu). Anal. Found (Anal. Calc. for C36H63N5Si2Ti):
64.4 (64.5); 9.9 (9.5); 10.5 (10.5)%. IR (KBr plates,
Nujol mull): 1596 (m), 1574 (m), 1302 (m), 1282 (m),
1252 (s), 1235 (s), 1224 (s), 1151 (w), 1136 (w), 1116
(w), 1088 (m), 1069 (m), 1009 (w), 969 (vs), 949 (w), 934
(w), 907 (m), 891 (s), 858 (s), 837 (vs), 799 (s), 678 (w),
620 (w), 602 (m), 566 (w), 521 (w), 496 (w), 469 (w), 424
(w) cm−1. FAB-MS: 670 [MH+].
The following assignments refer to the labelling
scheme in Fig. 3. 1H-NMR (C6D6, 300.1 MHz): 7.37 (d,
J=7.8, 1H, Ht), 7.32 (apparent t, apparent J=7.4, 1H,
Hs), 7.26–7.22 (overlapping 2×m, 2H, Ho and Hp),
6.97 (d, J=6.0, 1H, Hq), 6.90–6.85 (overlapping 2×m,
2H, Hm and Hr), 6.78 (m, 1H, Hn), 4.60 (d, J=11.1,
1H, Hi), 3.73 (m, 1H, Ha), 3.63 (m, 1H, Hb), 3.34 (d,
J=13.1, 1H, Hl), 2.68 (d, J=13.1, 1H, Hk), 2.52 (d,
J=11.1, 1H, Hj), 2.20 (m, 1H, Hf), 1.99 (m, 1H, Hg),
1.71 (overlapping 2×m, 2H, Hc and Hd), 1.48 (m, 1H,
Hh), 0.92 (m, 1H, He), 0.84 (s, 9H, NCMe3), 0.68 (s,
9H, Hv), 0.25 (s, 9H, Hu). 13C-{1H} (C6D6, 75.5 MHz):
159.8, 156.0 (2×2-C6H4), 131.6 (one of 1-C6H4), 130.0
(two signals overlapping, CHm or CHr, and one of
CHo, CHp, CHs) 129.4, 129.2 (two of CHo, CHp,
CHs), 128.8 (one of 1-C6H4), 128.1 (CHq), 126.2 (CHt),
118.8 (CHr or CHm), 118.7 (CHn), 70.1 (NCMe3), 61.9
(CHk,l), 59.2 (CHi,j), 56.3 (CHa,c), 52.7 (CHb,d), 52.3
(CHf,h), 46.3 (CHe,g), 32.4 (NCMe3), 5.1 (CHv), 3.2
(CHu). Anal. Found (Anal. Calc. for C28H47N5Si2Ti): C
60.3 (60.3); H 8.9 (8.5); N 12.4 (12.6)%. IR (KBr plates,
Nujol mull): 1607 (w), 1592 (m), 1560 (w), 1298 (m),
1252 (s), 1227 (s), 1151 (w), 1088 (s), 1069 (s), 1035 (s),
935 (m), 922 (m), 902 (m), 856 (s), 837 (vs), 816 (s), 802
(s), 745 (m), 668 (m), 633 (w), 591 (w), 524 (w), 498 (w)
cm−1. FAB-MS: 558 [MH+].
4.10. 4-Methylphenylimido-{1,4-bis(2-trimethyl-
silylamidobenzyl)piperazine}-titanium (9)
A slurry of [Ti(N-4-C6H4Me)Cl2(py)3] (0.61 g, 1.33
mmol) in benzene (80 ml) was added to a stirred yellow
suspension of (Li2L1, 5) (0.60 g, 1.33 mmol) in benzene
(40 ml). A dark brown solution was formed which
became more orange in colour after 17 h. The volatiles
were removed under reduced pressure to yield an oily
brown–red solid which was extracted into hexane (4×
40 ml). The combined extracts were filtered through a
bed of Celite and evaporated to dryness, yielding an
orange–red solid. The product recrystallised from pen-
tane at −35°C and dried in vacuo, giving 9 as an
orange microcrystalline solid. Yield: 0.17 g (22%). Re-
peated fractional recrystallisations from pentane af-
forded an analytically pure sample.
4.9. Tert-butylimido-{1,4-bis(2-trimethylsilylamido-
4-tert-butylbenzyl)piperazine}-titanium (8)
A pale orange solution of [Ti(NBut)Cl2(py)3] (0.24g,
0.53 mmol) in THF (20 ml) was added to a stirred
yellow slurry of (Li2L2, 6) (0.30 g, 0.53 mmol) in THF
(25 ml). A pale orange solution was obtained, which
gradually became darker as stirring continued. After ca.
18 h, the volatiles were removed under reduced pressure
to yield a brown–yellow solid which was extracted into
hexane (4×30 ml). The combined extracts were filtered
through a bed of Celite and the pale orange–yellow
filtrate was evaporated to dryness, yielding a yellow–
orange solid. The product was purified by recrystallisa-
tion from pentane to yield 8 as yellow–orange crystals.
Yield: 0.11 g (31%).
The following assignments refer to the labelling
1
scheme in Fig. 3. H-NMR (C6D6, 500.0 MHz): 7.41–
7.36 (overlapping 2×m, 2H, Hs and Ht), 7.26–7.21
(overlapping 2×m, 2H, Ho and Hp), 7.00 (d, J=6.5,
1H, Hq), 6.95 (apparent t, apparent J=6.9, 1H, Hr),
6.89 (d, J=6.5, 1H, Hm), 6.83 (d, J=8.0, 2H, 3-
C6H4Me), 6.81 (apparent t, apparent J=7.0, 1H, Hn),
6.06 (d, J=8.5, 2H, 2-C6H4Me), 4.49 (d, J=11.0, 1H,
Hi), 3.55 (m, 1H, Ha or Hb), 3.37 (m, 1H, Hb or Ha),
3.33 (d, J=13.5, 1H, Hl), 2.68 (d, J=13.0, 1H, Hk),
2.50 (d, J=11.5, 1H, Hj), 2.29 (m, 1H, Hf), 2.15 (m,
1H, Hg), 2.09 (s, 3H, C6H4Me), 1.63 (m, 1H, Hc or Hd),
1.48 (overlapping 2×m, 2H, Hh and Hc or Hd), 0.98
(m, 1H, He), 0.58 (s, 9H, Hv), 0.25 (s, 9H, Hu). 13C-
{1H} (C6D6, 125.7 MHz): 159.2, 158.8, 154.9 (2×2-
C6H4 of L1 and 1-C6H4Me), 130.5 (one of 1-C6H4 of L1
The following assignments refer to the labelling
1
scheme in Fig. 3. H-NMR (C6D6, 300.1 MHz): 7.49 (s,
1H, Ht), 7.30 (s, 1H, Hp), 6.97 (overlapping 2×m, 2H,
Hq and Hr), 6.90 (overlapping 2×m, 2H, Hm and Hn),
4.56 (d, J=11.0, 1H, Hi), 3.75 (m, 1H, Ha), 3.67 (m,

124
J. Lloyd et al. / Journal of Organometallic Chemistry 591 (1999) 114–126
or 4-C6H4Me), 130.2 (CHm) 130.0 (CHs or CHt), 129.6
(CHo or CHp), 129.4 (CHp or CHo), 128.8 (one of
1-C6H4 or 4-C6H4Me), 128.7, (two signals overlapping,
3-C6H4Me and CHq), 124.7 (CHt or CHs), 123.4 (2-
C6H4Me), 119.5 (CHn), 118.9 (CHr), 62.0 (CHk,l), 59.5
(CHi,j), 55.7 (CHa,c or CHb,d), 52.3 (CHb,d or CHa,c),
52.0 (CHf,h), 46.8 (CHe,g), 21.0 (C6H4Me), 3.9 (CHv),
2.9 (CHu). One resonance for one of 1-C6H4 or 4-
C6H4Me was not observed. Anal. Found (Anal. Calc.
for C31H45N5Si2Ti): C 62.0 (62.9); H 8.0 (7.7); N 11.5
(11.8)%. IR (KBr plates, Nujol mull): 1609 (w), 1585
(w), 1492 (s), 1341 (m), 1328 (m), 1298 (s), 1251 (s),
1149 (w), 1105 (w), 1088 (w), 1071 (w), 1046 (w), 1007
(w), 928 (s), 915 (s), 854 (s), 839 (vs), 805 (m), 750 (s),
combined and the volatiles removed by rotary evapora-
tion, giving a pale yellow oily solid, which was dried in
vacuo and then dissolved in chloroform (275 ml) and
dried (MgSO4). The solvent was removed by rotary
evaporation to give a yellow–white oil. This solidified
on standing in the cold (ca. 5°C) and was dried in
vacuo. Recrystallisation from ethanol afforded 11 as a
white crystalline solid. Yield: 6.35 g (68%).
1H-NMR (CDCl3, 500.0 MHz): 7.08 (apparent t,
apparent J=7.8, 2H, 4-C6H4), 6.95 (d, J=7.5, 2H,
6-C6H4), 6.66 (apparent t, apparent J=7.4, 2H, 5-
C6H4), 6.61 (d, J=8.0, 2H, 3-C6H4), 4.45 (br s, 4H,
NH2), 3.45 (s, 4H, ArCH2N), 2.33 (t, 4H, J=7.3,
NCH2CH2), 2.12 (s, 6H, NMe), 1.68 (quin, 2H, J=7.1,
NCH2CH2. 13C-{1H} (CDCl3, 125.7 MHz): 147.0 (2-
C6H4), 130.3, 128.2 (4- and 6-C6H4), 123.1 (1-C6H4),
117.4, 115.4 (3- and 5-C6H4), 62.1 (ArCH2N), 55.1
(NCH2CH2), 41.6 (NMe), 25.1 (NCH2CH2). Anal.
Found (Anal. Calc. for C19H28N4): C 72.8 (73.0); H 9.2
(9.0); N 17.8 (17.9)%. IR (Nujol mull, KBr plates):
3341[br s, w(NꢁH)], 3263 [br s, w(NꢁH)], 2789 (vs), 1618
(s), 1492 (vs), 1363 (vs), 1271 (s), 1250 (w), 1220 (w),
1156 (m), 1137 (w), 1115 (w), 1077 (w), 1050 (m), 1041
(w), 1024 (w), 1005 (s), 966 (m), 927 (w), 883 (m), 854
(m), 790 (w), 747 (vs), 728 (s), 628 (m), 540 (w), 449
(w), 437 (m) cm−1. CI-MS: 313 [MH+].
636 (w), 518 (w), 481 (w), 436 (w), 431 (w) cm−1
EI-MS: 591 [M+].
.
4.11. N,N%-Bis(2-nitrobenzyl)-N,N%-dimethyl-
1,3-diaminopropane (10)
1-Bromomethyl-2-nitrobenzene (12.94 g, 0.06 mol)
and powdered potassium hydroxide (3.93 g, 0.07 mol)
were added to a solution of oxygen-free N,N%-dimethyl-
1,3-diaminopropane (3.06 g, 0.03 mol) in toluene (250
ml). The resultant yellow slurry was heated to 60°C
under an argon atmosphere for 24 h. The mixture was
allowed to cool to r.t., giving a golden yellow solution
with orange precipitate. The mixture was filtered and
the residue extracted with toluene (2×100 ml). The
filtrates were combined and the volatiles removed by
rotary evaporation to yield 10 as an orange–yellow oil,
which was dried in vacuo (2×10−3 mbar) to remove
residual solvent. Yield: 10.93 g (98%).
4.13. N,N%-Bis(2-trimethylsilylaminobenzyl)-N,N%-
dimethyl-1,3-diaminopropane (H2L3, 12)
To a stirred solution of 1,4-diazabicyclo[2.2.2]octane
(1.62 g, 14.40 mmol) in diethyl ether (40 ml) was added
chlorotrimethylsilane (1.72 g, 15.84 mmol) over 5 min
giving immediate formation of a pale white precipitate.
After a further 80 min a solution of 11 (2.25 g, 7.20
mmol) in diethyl ether (50 ml) was added resulting in a
thickening of the precipitate. After a further ca. 20 h
the mixture was filtered and the residue (white powder)
extracted with diethyl ether (50 ml). The filtrates were
combined and the volatiles removed under reduced
pressure to yield a cream–white oil. Crystallisation
from pentane at −80°C for several days afforded 12 as
a pale yellow–white solid. Yield: 2.92 g (89%).
1H-NMR (CDCl3, 500.0 MHz): 7.77 (d, J=8.0, 2H,
3-C6H4), 7.56 (d, J=7.5, 2H, 6-C6H4), 7.49 (apparent t,
apparent J=7.6, 2H, 4-C6H4), 7.34 (apparent t, appar-
ent J=7.6, 2H, 5-C6H4), 3.73 (s, 4H, ArCH2N), 2.35 (t,
J=7.3, 4H, NCH2CH2), 2.11 (s, 6H, NMe), 1.59 (quin,
J=7.1, 2H, NCH2CH2). 13C-{1H} (CDCl3, 125.7
MHz): 149.6 (2-C6H4), 134.9 (1-C6H4), 132.3, 130.9,
127.6, 124.1 (4×CH of C6H4), 58.8 (ArCH2N), 55.4
(NCH2CH2), 42.1 (NMe), 25.2 (NCH2CH2). CI-MS:
373 [MH+].
4.12. N,N%-Bis(2-aminobenzyl)N,N%-dimethyl-
1,3-diaminopropane (11)
1H-NMR (CDCl3, 500.0 MHz): 7.11 (apparent t,
apparent J=7.6, 2H, 4-C6H4), 6.96 (d, J=7.5, 2H,
6-C6H4), 6.72 (d, J=8.0, 2H, 3-C6H4), 6.63 (apparent t,
apparent J=7.3, 2H, 5-C6H4), 6.15 (br s, 2H, NH),
3.45 (s, 4H, ArCH2N), 2.37 (t, J=7.5, 4H, NCH2CH2),
2.13 (s, 6H, NMe), 1.73 (quin, 2H, J=7.1, NCH2CH2),
0.27 (s, 18H, SiMe3). 13C-{1H} (CDCl3, 125.7 MHz):
148.2 (2-C6H4), 130.4, 128.0 (4- and 6-C6H4), 124.4
(1-C6H4), 116.5, 115.5 (3- and 5-C6H4), 62.9 (ArCH2N),
55.3 (NCH2CH2), 41.1 (NMe), 25.3 (NCH2CH2), 0.3
(SiMe3). Anal. Found (Anal. Calc. for C25H44N4Si2): C
65.7 (65.7); H 10.1 (9.7); N 12.2 (12.3)%. IR (KBr
A stirred mixture of N,N%-bis(2-nitrobenzyl)-N,N%-
dimethyl-1,3-diaminopropane (10) (11.10 g, 0.03 mol)
and graphite catalyst (3 g, Sigma-Aldrich) in ethanol
(400 ml) was purged with nitrogen. Oxygen-free hy-
drazine monohydrate (31.34 g, 0.63 mol) was added
and the mixture heated to reflux under a nitrogen
atmosphere for 48 h. The hot mixture was filtered,
yielding a pale yellow solution and the residue was
extracted with chloroform (250 ml). The filtrates were

J. Lloyd et al. / Journal of Organometallic Chemistry 591 (1999) 114–126
125
plates, Nujol mull): 3265 [br m, w(NꢁH)], 1606 (s), 1583
(s), 1496 (s), 1421 (w), 1402 (w), 1297 (s), 1249 (s), 1207
(w), 1167 (w), 1101 (m), 1066 (w), 1049 (m), 1033 (m),
920 (s), 843 (s), 746 (s), 630 (w), 476–428 (series of
weak peaks) cm−1. CI-MS: 457 [MH+].
Lorentz-polarisation effects and absorption were per-
formed and the structures were solved by direct meth-
ods using SIR92 [37]. Subsequent difference Fourier
syntheses revealed the positions of all other non-hydro-
gen atoms. The methyl carbons of the ring tert-butyl
groups for 2 (molecules of which lie across crystallo-
graphic inversion centres) are disordered over two sites
of equal occupancy. Residual electron density for 2 was
modelled as two CHCl3 molecules of crystallisation per
asymmetric unit (there are four CHCl3 molecules per
molecule of 2). Similarity restraints were applied to the
bond angles and/or distances of one of the CHCl3
molecules and the disordered tert-butyl groups. Car-
bon-bound hydrogen atoms for both structures were
placed geometrically and their positions allowed to vary
using a riding model. H atoms of the amino group in 2
were located from Fourier difference syntheses and
positionally refined. All H atoms for 2 were assigned
fixed U[iso] values 1.3 times the U[iso] or Uequivalent of the
supporting atom; for 8 common U[iso] parameters of
chemically related groups of H atoms were refined.
Examination of the refined extinction parameters and
agreement analyses suggested that no extinction correc-
tion was required. The relatively high final R-values for
2 are attributed to the disorder in the tert-butyl sub-
stituents and the presence of two CHCl3 molecules of
crystallisation. All crystallographic calculations were
performed using SIR92 and CRYSTALS-PC [38].
4.14. Dilithium N,N%-bis(2-trimethylsilylamidobenzyl)-
N,N%-dimethyl-1,3-diaminopropane (Li2L3, 13)
To a cold (ca. −73°C), stirred solution of (H2L3, 12)
(1 g, 2.19 mmol) in pentane (25 ml) was added a 2.5 M
solution of n-butyl lithium in hexanes (1.93 ml, 4.82
mmol=2.2 equivalents) over 5 min. After a further 5
min the yellow–white mixture was allowed to warm to
r.t. and was stirred for a further 4 h. The resulting
yellow–white suspension was filtered and the solid
dried in vacuo, to give 13 as a yellow–orange powder.
A further batch of 13 (as a pale yellow powder) was
obtained by cooling the filtrate at −80°C over several
days. Total yield: 0.74 g (72%).
1H-NMR (C6D6, 500.0 MHz): 7.19 (apparent t, ap-
parent J=7.5, 2H, 4-C6H4), 7.08 (d, J=7.3, 2H, 6-
C6H4), 6.82 (apparent t, apparent J=7.4, 2H, 5-C6H4),
6.25 (d, J=7.5, 3-C6H4), 3.96 (d, J=11.5, 2H,
ArCHaHb), 2.60 (m, 2H, NCHcHdCH2CHc%Hd%N), 2.28
(d, J=11.5, 2H, ArCHaHb), 1.89 (s, 6H, NMe), 1.79
(m, 2H, NCHcHdCH2CHc%Hd%N), 1.25 (m, 2H,
NCH2CH2), −0.11 (s, 18H, SiMe3). 13C-{1H} (C6D6,
125.7 MHz): 159.2 (2-C6H4), 133.8 (1-C6H4), 132.9,
130.6, 124.0, 117.7 (4×CH of C6H4), 64.0 (ArCH2),
55.0 (NCH2CH2), 40.4 (NMe), 22.9 (NCH2CH2), 3.0
(SiMe3). Anal. Found (Anal. Calc. for C25H42N4Si2Li2):
C 63.8 (64.1); H 8.7 (9.0); N 11.9 (12.0)%. IR (KBr
plates, Nujol mull): 1590 (m), 1444 (vs), 1420 (m), 1365
(m), 1326 (w), 1275 (vs), 1262 (vs), 1240 (s), 1154 (w),
1103 (m), 1045 (m), 1021 (w), 989 (w), 958 (s), 935 (m),
878 (m), 846 (s), 827 (vs), 784 (m), 756 (m), 734 (m),
5. Crystallographic data
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC, nos. 127479 (compound 2) and
127480 (compound 8). Copies of this information may
be obtained free of charge from The Director, CCDC,
12 Union Road, Cambridge CB2 1EZ. Fax: +44-1223-
336-033 or e-mail: deposit@ccdc.cam.ac.uk or http://
www.ccdc.cam.ac.uk.
661 (w), 586 (w), 538 (w), 446 (w) cm−1
.
4.15. Crystal structure determination of
1,4-bis(2-amino-4-tert-butylbenzyl)piperazine·4CHCl3
(2·4 CHCl3) and [Ti(NBut)(L2)] (8)
Diffraction quality crystals of 2·4 CHCl3 were grown
at r.t. from an ethanol–chloroform (1:1) mixture; those
of 8 were grown from a pentane solution at −35°C.
Crystal data collection and processing parameters are
given in Table 1. The crystals were immersed in a film
of perfluoropolyether oil on a glass fibre and trans-
ferred to a Stoe¨ Stadi-4 four-circle (for 2·4 CHCl3) or
Enraf–Nonius DIP2000 image plate diffractometer (for
8) equipped with an Oxford Cryosystems low-tempera-
ture device [35]. Data were collected at 150 K using
Mo–Ka radiation. For 8 equivalent reflections were
merged and the images were processed with the DENZO
and SCALEPACK programs [36]. Corrections for
Acknowledgements
This work was supported by grants from the EPSRC,
Leverhulme Trust and Royal Society. We also thank
Oxford University for a studentship (to J.L.).
References
[1] P. Mountford, Chem. Commun. (Cambridge) (1997) 2127 (fea-
ture article).
[2] J.M. McInnes, P. Mountford, Chem. Commun. (Cambridge)
(1998) 1669.

126
J. Lloyd et al. / Journal of Organometallic Chemistry 591 (1999) 114–126
[3] A.J. Blake, S.C. Dunn, J.C. Green, N.M. Jones, A.G. Moody, P.
Mountford, Chem. Commun. (Cambridge) (1998) 1235.
[23] R.D. Hancock, A. Evers, M.P. Ngwenya, P.W. Wade, J. Chem.
Soc. Chem. Commun. (1987) 1129.
[4] A. Bashall, P.E. Collier, L.H. Gade, M. McPartlin, P. Mount-
ford, D.T. Tro¨sch, Chem. Commun. (Cambridge) (1998)
2555.
[24] R.D. Hancock, S.M. Dobson, A. Evers, P.W. Wade, P.N. Ng-
wenya, J.C.A. Boeyens, K.P. Wainwright, J. Am. Chem. Soc.
110 (1988) 2788.
[5] P.J. Wilson, A.J. Blake, P. Mountford, M. Schro¨der, Chem.
Commun. (Cambridge) (1998) 1007.
[25] N.W. Alcock, P. Moore, C.J. Reader, S.M. Roe, J. Chem. Soc.
Dalton Trans. (1988) 2959.
[6] A.J. Blake, J.M. McInnes, P. Mountford, G.I. Nikonov, D.
Swallow, D.J. Watkin, J. Chem. Soc. Dalton Trans. (1999) 379.
[7] N. Kaltsoyannis, P. Mountford, J. Chem. Soc. Dalton Trans.
(1999) 781.
[8] P.J. Wilson, P.A. Cooke, A.J. Blake, P. Mountford, M.
Schro¨der, New J. Chem. (1999) 271.
[9] F.G.N. Cloke, P.B. Hitchcock, J.F. Nixon, D.J. Wilson, P.
Mountford, Chem. Commun. (Cambridge) (1999) 661.
[10] D. Swallow, J.M. McInnes, P. Mountford, J. Chem. Soc. Dalton
Trans. (1998) 2253.
[11] J.M. McInnes, D. Swallow, A.J. Blake, P. Mountford, Inorg.
Chem. 37 (1998) 5970.
[26] T.N. Mali, P.W. Wade, R.D. Hancock, J. Chem. Soc. Dalton
Trans. (1992) 67.
[27] B.K. Moorthy, J. Indian Chem. Soc. 67 (1990) 909.
[28] H.M. Niemeyer, J. Mol. Struct. 57 (1979) 241.
[29] R. Thirumurugan, S.S.S. Raj, G. Shanmugam, H.-K. Fun, K.
Chinnakali, S. Chantrapromma, M. Marappan, M. Kan-
daswamy, Acta Crystallogr. Sect. C 54 (1998) 780.
[30] A.J. Blake, P.E. Collier, S.C. Dunn, W.-S. Li, P. Mountford,
O.V. Shishkin, J. Chem. Soc. Dalton Trans. (1997) 1549.
[31] A.D. Garnovskii, A.L. Nivorozhkin, V.I. Minkin, Coord. Chem.
Rev. 126 (1993) 1.
[32] M. Calligaris, L. Randaccio, in: G. Wilkinson, R.D. Gillard,
J.A. McCleverty (Eds.), Comprehensive Coordination Chem-
istry, vol. 2, Pergamon, Oxford, 1987, p. 715.
[12] O. Schlager, K. Wieghardt, A. Rufinska, B. Nuber, Dalton
Trans. (1996) 1659.
[13] A. Ciccarese, D.A. Clemente, F.P. Fanizzi, A. Marzotto, G.
Valle, Acta Crystallogr. Sect. C 54 (1998) 1779.
[14] A. Marzotto, D.A. Clemente, G. Valle, Acta Crystallogr. Sect. C
53 (1997) 1580.
[33] D.J. Arney, M.A. Bruck, S.R. Huber, D.E. Wigley, Inorg.
Chem. 31 (1992) 3749.
[34] J. Sundermeyer, J. Putterlik, M. Foth, J.S. Field, N. Ramesar,
Chem. Ber. 127 (1994) 1201.
[15] K. Bertoncello, G.D. Fallon, J.H. Hodgkin, K.S. Murray, Inorg.
Chem. 27 (1988) 4750.
[16] S. Loukiala, J. Ratilainen, J. Valkonen, K. Rissanen, Acta
Chem. Scand. 51 (1997) 1162.
[35] J. Cosier, A.M. Glazer, J. Appl. Crystallogr. 19 (1986) 105.
[36] D. Gewirth, The HKL Manual, written with the co-operation of
the program authors, Z. Otwinowski and W. Minor, Yale Uni-
versity, 1995.
[17] T. Soma, T.K. Miyamoto, T. Iwamoto, Chem. Lett. (1997) 319.
[18] L. Casella, J.A. Ibers, Inorg. Chem. 20 (1981) 2438.
[19] J. Reim, B. Krebs, J. Chem. Soc. Dalton Trans. (1997) 3793.
[20] K. Fuji, K. Takasu, H. Miyamoto, K. Tanaka, Tetrahedron
Lett. 37 (1996) 7111.
[21] K.P. Wainwright, Inorg. Chem. 19 (1980) 1396.
[22] A. Ramasubbu, K.P. Wainwright, J. Chem. Soc. Chem. Com-
mun. (1982) 277.
[37] A. Altomare, G. Cascarano, G. Giacovazzo, A. Guagliardi,
M.C. Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 27
(1994) 435.
[38] D.J. Watkin, C.K. Prout, J.R. Carruthers, P.W. Betteridge,
Crystals Issue 10, Chemical Crystallography Laboratory, Uni-
versity of Oxford, 1996.
[39] D.E. Wigley, Prog. Inorg. Chem. 42 (1994) 239.
[40] Z. Lin, M.B. Hall, Coord. Chem. Rev. 123 (1993) 149.
.