A new class of linked-bis(N,N'-dialkylamidinate) ligand: applications in the synthesis of bimetallic aluminium complexes

Article abstract of DOI:10.1016/S0022-328X(02)01922-8

The 1,4-benzenebis(N,N'-dialkylamidine) compounds, 1,4-C6H4[C{NR}{NHR}]2 (1, R = Cy; 2, R = ⁱPr) were synthesised via addition of a stoichiometric amount of water to the 1,4-benzenebis(amidinate) species, generated from the in situ reaction between 1,4-Li2C6H4 and the appropriate carbodiimide. Alternatively, the neutral silylated derivatives, 1,4-C6H4[C{NR}{N(SiMe3)R}]2 (3, R = Cy; 4, R = ⁱPr) are synthesised by quenching the 1,4-benzenebis(amidinate) with excess Me3SiCl. Structural characterisaiton of selected examples are reported, showing that the neutral NH compounds are monomeric with a E-syn: E-syn arrangement of the N-alkyl substituents, while in the silylated derivative 4, the E-anti: E-anti form is present in the solid-state. Synthesis of the bimetallic aluminium compounds 1,4-C6H4[C{NⁱPr}2AlMeX]2 (5, X = Cl; 6, X = Me) was achieved from AlMe2Cl using 2 by either the direct protonolysis of an Al-C bond (5), or the trans-metallation reaction of the in situ generated dilithio-salt (6). Structural characterisation of 6 revealed a monomeric complex with a perpendicular arrangement of the amidinate units with respect to the C6-group.

Full text of DOI:10.1016/S0022-328X(02)01922-8

Journal of Organometallic Chemistry 662 (2002) 178ꢃ187
/
www.elsevier.com/locate/jorganchem
A new class of linked-bis(N,N?-dialkylamidinate) ligand: applications
in the synthesis of bimetallic aluminium complexes
Joanna Grundy, Martyn P. Coles *, Peter B. Hitchcock
School of Chemistry, Physics and Environmental Science, University of Sussex, Falmer, Brighton BN1 9QJ, UK
Received 18 July 2002; received in revised form 17 September 2002; accepted 17 September 2002
Abstract
The 1,4-benzenebis(N,N?-dialkylamidine) compounds, 1,4-C6H4[C{NR}{NHR}]2 (1, Rꢀ
/
Cy; 2, Rꢀi
Pr) were synthesised via
addition of a stoichiometric amount of water to the 1,4-benzenebis(amidinate) species, generated from the in situ reaction between
/
1,4-Li2C6H4 and the appropriate carbodiimide. Alternatively, the neutral silylated derivatives, 1,4-C6H4[C{NR}{N(SiMe3)R}]2 (3,
Cy; 4, Rꢀi
Pr) are synthesised by quenching the 1,4-benzenebis(amidinate) with excess Me3SiCl. Structural characterisation of
selected examples are reported, showing that the neutral NH compounds are monomeric with a E-syn:E-syn arrangement of the N-
Rꢀ
/
/
alkyl substituents, while in the silylated derivative 4, the E-anti:E-anti form is present in the solid-state. Synthesis of the bimetallic
aluminium compounds 1,4-C6H4[C{Ni Pr}2AlMeX]2 (5, Xꢀ
protonolysis of an Alꢀ
characterisation of 6 revealed a monomeric complex with a perpendicular arrangement of the amidinate units with respect to the C6-
/
Cl; 6, Xꢀ
/
Me) was achieved from AlMe2Cl using 2 by either the direct
/
C bond (5), or the trans-metallation reaction of the in situ generated dilithio-salt (6). Structural
group.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Amidine; Amidinate; Linked; Silylated; Bimetallic; Aluminium; Crystal structures
1. Introduction
developments in the field have expanded the number of
ligand derivatives available through the use of various
different N- and C-substituents, and a range of different
synthetic protocols to metal amidinate complexes have
been developed, including: (i) protonolysis reactions
employing neutral amidines; (ii) insertion of carbodii-
mides into metal alkyl bonds; and (iii) salt metathesis
routes between lithium amidinates (from reaction of
alkyl lithium reagents with carbodiimides) and metal
halide species.
The early benzamidinate work was extended to
include the synthesis of multifunctional ligands that
contain greater than one amidine group around the
central C6-ring. Thus, using analogous synthetic proce-
dures, the bis- and tris-per(trimethylsilyl)amidine com-
pounds, 1,4-C6H4[C{NSiMe3}{N(SiMe3)2}]2 [6] and
1,3,5-C6H3[C{NSiMe3}{N(SiMe3)2}]3 [7] were accessed.
Despite the potential for the former ligand to act as a
bridge between two metal fragments, applications within
coordination chemistry have been limited to synthesis of
Amidinate anions, [R?C{NR}2]ꢁ, comprise a class of
ligand currently finding many applications in coordina-
tion chemistry [1,2], and more recently as ancillary
ligands in polymerisation catalysis [3]. The isolobal
relationship with [R?CO2]ꢁ has facilitated rapid devel-
opment of this area, based upon the previously well
established field of carboxylate chemistry [4]. A sig-
nificant advantage of the amidinates is the ability to
tailor the steric properties to satisfy specific require-
ments via derivitisation of the N-substituents, enabling a
degree of control to be gained over the chemistry that
occurs at the metal centre. Within the field of amidinate
chemistry initial work focused primarily on the benza-
midinate derivative [PhC{NSiMe3}2]ꢁ [2], synthesised
from the reaction between LiN(SiMe3)2 and benzoni-
trile, first reported by Sanger in 1973 [5]. Subsequent
* Corresponding author. Tel.: ꢂ
677196
E-mail address: m.p.coles@sussex.ac.uk (M.P. Coles).
/
44-1273-877339; fax: ꢂ44-1273-
/
the
Me3}2SnCl3(MeCN)]2 (A, Fig. 1) [8] and the dicationic
bis-trichlorotin
complex,
1,4-C6H4[C{NSi-
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 9 2 2 - 8

J. Grundy et al. / Journal of Organometallic Chemistry 662 (2002) 178ꢃ
/187
179
2.2. Synthesis
The compounds 1,4-Br2C6H4, RNꢁ
/
Cꢁ
/
NR (Rꢀi
/
Pr,
Cy), Me3SiCl (distilled) and AlMe2Cl (1.0 M solution in
C6H14) were purchased from Aldrich and used without
further purification, unless otherwise stated.
2.2.1. 1,4-Benzenebis(N,N?-dicyclohexylamidine) (1)
1,4-Dibromobenzene (5.0 g, 21.0 mmol) was dissolved
in C6H14 (100 ml) and 25.2 ml of nBuLi (2.5 M in C6H14,
63.0 mmol, three equivalents) was added at room
temperature (r.t.). The mixture was heated at 80 8C
for 12 h, affording a pale cream slurry of the dilithio-salt
1,4-Li2C6H4. The solvent was removed by filtration and
the remaining solid was washed with C6H14 (3ꢄ20 ml).
/
The dilithio-salt was subsequently reslurried in THF
(100 ml) and a solution of 1,3-dicyclohexylcarbodiimide
(8.8 g, 42.4 mmol) in THF (20 ml) was added at 0 8C
affording a beige slurry. The mixture was stirred for 12 h
followed by the slow addition of a stoichiometric
amount of distilled water (0.8 ml, 42.4 mmol) to afford
a clear orange solution that was stirred at ambient
temperature for 12 h. The solution was washed with
Fig. 1. Examples of linked amidinates: A [Ref. [8]]; B [Ref. [9]]; C [Ref.
[10]] and D [Ref. [11]].
bis(1,3-diaza-2-phosphetine), [1,4-C6H4[C{NSiMe3}2-
PNiPr2]2ꢂ (B, Fig. 1) [9]. Recently, new classes of
linked bis-amidinates have been reported, based on the
1,2-disubstituted cyclohexyl framework (C, Fig. 1) [10]
water and the product was extracted with ether (3ꢄ20
ml). Removal of the volatiles in vacuo afforded crude 1
as an opaque yellow oil that was crystallised from Et2O
/
at ꢁ30 8C as colourless crystals (3.4 g, 33%).
/
and the oxalic amidine, [PhNꢁ
/
C(NHtBu)]2 (D, Fig. 1)
Anal. Calc. for C32H50N4: C, 78.32; H, 10.27; N,
1
11.42. Found: C, 78.88; H, 10.17; N, 11.35%. H-NMR
(CDCl3, 298 K): d 7.20 (m, br, 4H, C6H4), 3.10 (m, 4H,
[11]. We have been interested in developing the ligand
based on the 1,4-disubstituted benzamidinate frame-
work, but avoiding the potentially labile nitrogenꢀ
/
NCH), 1.82ꢃ0.84 (m, 40H, Cy), *. (*NH resonance not
/
1
observed in H-NMR). 13C-NMR (CDCl3, 298 K) d
157.0 (CN2), 137.0 (C6H4ꢀCipso), 127.6 (C6H4ꢀCortho),
56.3 (Cy), 53.2 (Cy ꢀC1), 35.3 (Cy), 34.7 (Cy), 34.1
(Cy), 26.1 (Cy), 25.6 (Cy), 25.3 (Cy). MS: m/z 490
[M]ꢂ, 407 [MꢁCy]ꢂ. IR: (cmꢁ1) 3284w (Nꢀ
H),
2119m, 1626s (CꢁN), 1610s, 1518s, 1343, 1316s, 1304s,
silicon bonds present in the previously reported deriva-
tive [6]. We describe here the synthesis of two neutral
ligand precursors, 1,4-C6H4[C{NR}{NHR}]2 and 1,4-
/
/
/
C6H4[C{NR}{N(SiMe3)R}]2 (Rꢀi
Pr and Cy), and
/
demonstrate their application in the synthesis of mole-
cular aluminium derivatives.
/
/
/
1279m, 1256m, 1238m, 1169m, 1150s, 1063m, 1050m,
1023m, 991m, 978m, 928m, 888m, 849m, 836m, 724m,
647m, 630m, 504m, 434m, 397m, 382m, 376s.
2. Experimental
2.2.2. 1,4-Benzenebis(N,N?-diisopropylamidine) (2)
Compound 2 was prepared using the procedure
described for 1, using 1,4-dibromobenzene (5.0 g, 21.0
mmol), nBuLi (2.5 M in C6H14, 63.0 mmol), 1,3-
diisopropylcarbodiimide (9.9 ml, 63.0 mmol) and water
(0.8 ml, 42.4 mmol). Crystallisation from Et2O afforded
pure 2 as colourless crystals (3.0 g, 43% yield).
2.1. General experimental procedures
All manipulations were carried out under dry nitrogen
using standard Schlenk and cannula techniques, or in a
conventional, nitrogen-filled glovebox operating at less
than 1 ppm oxygen. Solvents were dried over appro-
priate drying agents and degassed prior to use. Ele-
mental analyses were performed by S. Boyer at the
University of North London. The NMR spectra were
recorded using a Bruker Avance DPX 300 at 300 (1H),
75 (13C) MHz and referenced internally to residual
solvent resonances unless otherwise stated.
Anal. Calc. for C20H34N4: C, 72.68; H, 10.37; N,
1
16.95. Found: C, 72.51; H, 10.48; N, 16.83%. H-NMR
(CDCl3, 298 K) d 7.33 (s, 4H, C6H4), 3.22 (sept, br, 4H,
3
NCH), 1.03 (d, JHH
ꢀ5.1 Hz, 24H, CHMe2), *. (*NH
/
resonance not observed in 1H-NMR). 13C-NMR
(CDCl3, 298 K) d 156.0 (CN2), 137.1 (C6H4ꢀCipso),
127.6 (C6H4ꢀCortho), 46.8 (CHMe2), 24.4 (CHMe2).
MS: m/z 330 [M]ꢂ, 315 [MꢁCH3]ꢂ, 287 [MꢁiPr]ꢂ.
/
/
/
/

180
J. Grundy et al. / Journal of Organometallic Chemistry 662 (2002) 178ꢃ187
/
IR: (cmꢁ1) 3389m (Nꢀ
1510s, 1319s, 1282s, 1265s, 1171s, 1131s, 1102s, 1024s,
975m, 954m, 858s, 822m, 723m, 693m, 518m, 516m,
464m, 411m, 397m, 385m, 373m.
/
H), 3351m (Nꢀ
/
H), 1637s (Cꢁ
/N),
945m, 884m, 847s, 769m, 729m, 690m, 675m, 636m,
526m, 447m, 376m.
2.2.5. 1,4-Benzenebis(N,N?-
2.2.3. 1,4-Benzenebis(N,N?-dicyclohexyl-N-
trimethylsilylamidine) (3)
diisopropylamidinatocholromethylaluminium) (5)
A solution of AlMe2Cl (5.6 ml of a 1 M solution in
C6H14, 5.6 mmol) was further diluted with 20 ml of
C6H14. A solution of 2 (1.6 g, 4.8 mmol) in 100 ml C6H14
was added dropwise at r.t., resulting in the immediate
formation of a pale yellow precipitate. The resultant
mixture was stirred at r.t. for 12 h. Removal of the
volatile components in vacuo afforded the crude pro-
duct as an off-white solid, that was crystallised from hot
C6H5CH3 giving analytically pure 5 as pale yellow
crystals (1.5 g, 63% yield).
1,4-Dibromobenzene (5.0 g, 21.0 mmol) was dissolved
in C6H14 (100 ml) and 25.2 ml of nBuLi (2.5 M in C6H14,
63.0 mmol, three equivalents) was added at r.t. The
mixture was heated at 80 8C for 12 h, affording a pale
cream slurry of the dilithio-salt 1,4-Li2C6H4. The
solvent was removed by filtration and the remaining
solid was washed with C6H14 (3ꢄ20 ml). The dilithio-
/
salt was subsequently reslurried in THF (100 ml) and a
solution of 1,3-dicyclohexylcarbodiimide (8.8 g, 42.4
mmol) in THF (20 ml) was added dropwise at 0 8C,
affording a beige slurry. Me3SiCl (5.9 ml, 63.6 mmol)
was added and the mixture was heated at reflux for 8 h,
affording a clear yellow solution. Removal of the
Anal. Calc. for C22H38Al2Cl2N4: C, 54.66; H, 7.92; N,
1
11.59. Found: C, 54.53; H, 7.98; N, 11.44%. H-NMR
(CDCl3, 298 K): d 7.44 (s, 4H, C6H4), 3.23 (sept,
3JHH
3
6.5 Hz, 4H, CHMe2), 1.09 (d, JHH
ꢀ
/
ꢀ6.3 Hz,
6.3 Hz, 12H CHMe2),
/
solvent in vacuo, and extraction with CH2Cl2 (3ꢄ30
/
3
12H, CHMe2), 1.04 (d, JHH
0.39 (s, 6H, AlMe). 13C-NMR (CDCl3, 298 K): d
174.9 (CN2), 131.4 (C6H4ꢀCipso), 127.6 (C6H4ꢀCortho),
45.7 (CHMe2), 25.0 (CHMe2), ꢁ10.36 (AlMe). MS: m/
z 482 [M]ꢂ, 467 [MꢁMe]ꢂ, 447 [MꢁCl]ꢂ, 405 [Mꢁ
AlMeCl]ꢂ.
ꢀ
/
ml) afforded an off-white solid that was crystallised
from CH2Cl2, yielding colourless crystals (7.0 g, 52%).
Anal. Calc. for C38H66N4Si2: C, 71.86; H, 10.47; N, 8.82.
Found: C, 71.96, H, 10.57, N, 8.69%. 1H-NMR (CDCl3,
ꢁ
/
/
/
/
/
/
/
298 K): d 7.15 (s, 4H, C6H4), 2.74 (m, 4H, Cy), 1.43ꢃ
1.63 (m, 32H, Cy), 0.88ꢃ0.96 (m, 8H, Cy), 0.64 (s, 18H,
SiMe3). 13C-NMR (CDCl3, 298 K): d 162.2 (CN2),
136.5 (C6H4ꢀCipso), 127.6 (C6H6ꢀCortho), 58.2 (CyꢀC1),
34.8 (Cy), 26.1 (Cy), 26.3 (Cy), 3.54 (SiMe3). MS: m/z
634 [M]ꢂ, 619 [MꢁCH3]ꢂ, 551 [MꢁCy]ꢂ, 561 [Mꢁ
SiMe3]ꢂ, 490 [Mꢁ2SiMe3]ꢂ, 469 [Mꢁ2Cy]ꢂ. IR:
(cmꢁ1) 1614s (Cꢁ
N), 1504m, 1406m, 1338s, 1317s,
/
/
/
/
/
2.2.6. 1,4-Benzenebis(N,N?-
diisopropylamidinatodimethylaluminium) (6)
/
/
/
/
/
nBuLi (1.3 ml, 2.5 M in C6H14, 3.3 mmol) was added
dropwise at r.t. to a solution of 2 (0.5 g, 1.5 mmol) in
C6H14. The mixture was allowed to stir for 2 h during
which time a thick white precipitate formed. The solvent
was removed by filtration and the resultant solids were
/
1304s, 1257s, 1242s, 1178s, 1156s, 1112s, 1072s, 1022s,
990s, 915m, 891m, 842s, 764m, 724m, 708m, 690m,
677m, 638m, 526m, 396m, 376s.
washed with C6H14 (2ꢄ20 ml). The white solid was
/
2.2.4. 1,4-Benzenebis(N,N?-diisopropyl-N-
trimethylsilylamidine) (4)
reslurried in C6H14 and added dropwise to 3.2 ml
AlMe2Cl (1.0 M in C6H14, 3.2 mmol) that had been
further diluted in 30 ml of C6H14. The mixture was
allowed to stir overnight, resulting in a thick white
precipitate. The volatiles were removed in vacuo and the
product was separated from lithium chloride by extrac-
tion with C6H5CH3. Analytically pure 6 was obtained by
cooling a warm, saturated C6H5CH3 solution to r.t.,
affording colourless needles (1.2 g, 65% yield).
Compound 4 was prepared using the procedure
described for 3, using 1,4-dibromobenzene (5.0 g, 21.0
mmol), 25.2 ml of nBuLi (2.5 M solution in C6H14, 63.0
mmol, three equivalents), 1,3-diisopropylcarbodiimide
(9.9 ml, 63.0 mmol) and Me3SiCl (5.9 ml, 63.6 mmol).
Crystallisation from CH2Cl2 afforded pure 4 as colour-
less crystals (6.2 g, 62% yield).
Anal. Calc. for C26H50N4Si2: C, 65.76; H, 10.71; N,
1
11.80. Found: C, 65.84; H, 10.70; N, 11.89%. H-NMR
(CDCl3, 298 K) d 7.12 (s, 4H C6H4), 3.22 (sept, 3JHH
Anal. Calc. for C24H44Al2N4: C, 65.12; H, 10.02; N,
1
12.66. Found: C, 64.93; H, 9.92; N, 12.49%. H-NMR
ꢀ
/
3
(CDCl3, 298 K): d 7.36 (s, 4H, C6H4), 3.18 (sept,
3JHH
6.3 Hz, 4H, CHMe2), 1.03 (d, JHH
ꢀ6.5 Hz, 24H,
/
3
6.3 Hz, 4H, CHMe2), 0.99 (d, JHH
CHMe2), 0.23 (s, 18H SiMe3). 13C-NMR (CDCl3, 298
K): d 161.3 (CN2), 136.3 (C6H4ꢀCipso), 127.9 (C6H4ꢀ
Cortho), 49.0 (CHMe2), 24.5 (CHMe2), 3.5 (SiMe3). MS:
m/z 474 [M]ꢂ, 459 [MꢁCH3]ꢂ, 431 [MꢁiPr]ꢂ, 401
[Mꢁ N), 1505m, 1315s,
SiMe3]ꢂ. IR (cmꢁ1): 1615s (Cꢁ
1245s, 1196m, 1169s, 1128s, 1051m, 1032m, 1013m,
ꢀ
/
ꢀ6.4 Hz,
/
24H, CHMe2), ꢁ
(CDCl3, 298 K): d 172.2 (CN2), 131.9 (C6H4ꢀ
127.5 (C6H4ꢀCortho), 45.5 (CHMe2), 25.3 (CHMe2),
10.0 (AlMe2). MS: m/z 427 [Mꢁ
Me]ꢂ, 371 [Mꢁ
AlMe2]ꢂ, 329 [Mꢁ2AlMe2]ꢂ.
/
0.66 (s, 12H, AlMe2). 13C-NMR
Cipso),
/
/
/
/
/
/
ꢁ
/
/
/
/
/
/

J. Grundy et al. / Journal of Organometallic Chemistry 662 (2002) 178ꢃ
/187
181
2.3. X-ray structural determinations
independent molecules, each lying across an inversion
centre.
Details of the crystal data, intensity collection and
refinement are listed in Tables 1 and 6. Crystals were
covered in oil and suitable single crystals were selected
under a microscope and mounted on a Kappa CCD
diffractometer. The structures were refined with
SHELXL-97 [12].
2.3.4. 1,4-C6H4[C{NiPr}{NHiPr}]2 (2(tol)
Colourless crystals were isolated by slow cooling of a
hot (ca. 70 8C) C6H5CH3 solution containing 2 to r.t.
The molecule lies on an inversion centre.
)
2.3.5. 1,4-C6H4[C{NiPr}{N(SiMe3)iPr}]2 (4)
Colourless crystals were isolated from a CH2Cl2
2.3.1. 1,4-C6H4[C{NCy}{NHCy}]2 (1)
Colourless crystals were isolated from an MeCN
solution containing 4 that was cooled to ꢁ
/
30 8C.
solution containing 1 that was cooled to ꢁ30 8C.
/
2.3.6. 1,4-C6H4[C{NiPr}2AlMe2]2 (6)
Colourless crystals were isolated by slow cooling of a
hot (ca. 70 8C) C6H5CH3 solution of 6 to r.t. The
molecule lies on an inversion centre.
Each of the two independent molecules lies on an
inversion centre. The two molecules differ in the
conformation of the C(11)ꢀ
/
C(16) cyclohexyl ring rela-
tive to the rest of the molecule.
2.3.2. 1,4-C6H4[C{NCy}{NHCy}]2×
Colourless crystals were isolated from a C6H5CH3
solution containing 1 that was cooled to ꢁ30 8C. The
/
2(toluene) (1(tol))
3. Results and discussion
/
C6H5CH3 solvate molecule is disordered and was refined
with the C6 ring as a rigid body.
Two types of neutral ligand precursor were synthe-
sised in moderate to good yield using closely related
synthetic procedures (Scheme 1). 1,4-Dibromobenzene
was lithiated via addition of an excess of nBuLi in
hexane, followed by heating at reflux for 12 h [13]. The
dilithio-salt, 1,4-Li2C6H4, which precipitated from solu-
2.3.3. 1,4-C6H4[C{NiPr}{NHiPr}]2 (2)
Colourless crystals were isolated from a C6H14 solu-
tion containing 2 that was cooled to 0 8C. There are two
Table 1
Crystal data for 1, 1(tol), 2, 2(tol) and 4
1
1(tol)
2
2(tol)
4
Empirical formula
Formula weight
Temperature (K)
C32H50N4
490.76
173(2)
C46H66N4
675.03
173(2)
C20H34N4
330.51
173(2)
C20H34N4
330.51
173(2)
C26H50N4Si2
474.88
173(2)
˚
Wavelength (A)
Crystal system
0.71073
Triclinic
¯
P1 (No. 2)
0.71073
Orthorhombic
Pbca (No. 61)
12.9781(5)
20.2559(8)
15.7556(3)
90
0.71073
Triclinic
¯
P1 (No. 2)
0.71073
Triclinic
¯
P1 (No. 2)
0.71073
Triclinic
¯
P1 (No. 2)
Space group
˚
/
/
/
/
a (A)
˚
10.3829(10)
10.7529(18)
14.074(2)
107.764(5)
91.296(10)
99.520(9)
1471.3(4)
2
9.4330(7)
10.1043(11)
12.6424(14)
71.378(4)
71.722(6)
73.590(6)
1061.8(2)
2
5.8635(5)
7.6829(7)
12.5231(12)
105.664(5)
94.084(6)
102.803(4)
524.51(8)
1
10.3154(4)
11.7023(7)
13.9879(9)
99.448(3)
94.660(4)
110.228(3)
1545.4(2)
2
b (A)
˚
c (A)
a (8)
b (8)
g (8)
V (A )
Z
90
90
3
˚
4141.9(2)
4
1.08
Dcalc (Mg mꢁ3
)
1.11
0.07
1.03
0.06
1.05
0.06
1.02
0.13
Absorption coefficient (mmꢁ1
Crystal size (mm)
)
0.06
0.4ꢄ0.4ꢄ0.4
0.4ꢄ0.1ꢄ0.05
0.4ꢄ0.4ꢄ0.4
0.2ꢄ0.1ꢄ0.1
0.4ꢄ0.3ꢄ0.3
u Range for data collection (8) 3.75ꢃ
/22.12
4.07ꢃ/25.02
3.88ꢃ
/
27.20
3.75ꢃ/23.17
3.78ꢃ25.05
/
Reflections collected
7487
3573 [Rintꢀ0.095]
2308
20 975
3618 [Rintꢀ0.062]
2746
7539
4516 [Rintꢀ0.046]
3391
3819
1448 [Rintꢀ0.050]
1148
10 090
5348 [Rintꢀ0.053]
4165
Independent reflections
Reflections with I ꢀ2s(I)
Data/restraints/parameters
Final R indices [I ꢀ2s(I)]
3573/0/331
R1ꢀ0.066,
wR2ꢀ0.133
R1ꢀ0.120,
wR2ꢀ0.155
1.038
3618/0/200
R1ꢀ0.076,
wR2ꢀ0.201
R1ꢀ0.099,
wR2ꢀ0.220
1.033
4516/0/225
R1ꢀ0.054,
wR2ꢀ0.121
R1ꢀ0.079,
wR2ꢀ0.135
1.020
1448/0/177
R1ꢀ0.050,
wR2ꢀ0.123
R1ꢀ0.068,
wR2ꢀ0.134
1.031
5348/0/289
R1ꢀ0.083,
wR2ꢀ0.215
R1ꢀ0.102,
wR2ꢀ0.225
1.114
R indices (all data)
Goodness-of-fit on F2
Largest difference peak and hole 0.19 and ꢁ0.18
1.11 and ꢁ0.31
0.24 and ꢁ0.19
0.17 and ꢁ0.16
0.65 and ꢁ0.34
ꢁ3
˚
(e A
)

182
J. Grundy et al. / Journal of Organometallic Chemistry 662 (2002) 178ꢃ187
/
Scheme 2. Fluctional process occurring in 1 in solution.
served for 2 at low temperature (193 K), presumably due
to the smaller steric demand of the Nꢁi
/
Pr versus the
Scheme 1. (i) Excess n BuLi, hexane, reflux, 12 h; (ii) two equivalents
Nꢁ
/
Cy substituent. The silylated derivatives, 3 and 4,
RNꢁ
/
CꢁNR, THF, 12 h; (iii) two equivalents H2O, 12 h; (iv) three
/
equivalents Me3SiCl, reflux, 8 h.
exist as single species in solution at room temperature.
During the course of our studies into the application
of these ligands in coordination chemistry, several
crystal structures of the neutral bis-amidine compounds
have been obtained. These data are reported here as they
illustrate several differences associated with the metrical
parameters within the ligand framework that depend on
the nature of the nitrogen substituent, in addition to the
solvent from which the compound is crystallised. These
are compared with and contrasted to the crystal
structure of the neutral, silylated derivative 4. Thus,
the molecular structures of compounds 1, 2 and 4 are
tion, was isolated by filtration and washed with hexane
to remove any unreacted starting materials. The salt was
subsequently slurried in THF and a solution of carbo-
diimide RNꢁ
/
Cꢁ
/
NR (Rꢀi
Pr, Cy) was added, to
/
produce the lithium salt of the 1,4-benzenebis(amidi-
nate), ‘1,4-C6H4[C{NR}2Li(THF)x]2’ in situ. For sto-
rage and handling purposes, the neutral bis-amidine
species were synthesised by quenching the lithium salts
with a stoichiometric amount of water to afford 1,4-
C6H4[C{NR}{NHR}]2 (1, Rꢀ
natively, the silylated
C6H4[C{NR}{N(SiMe3)R}]2 (3, Rꢀ
were synthesised by quenching the respective lithium-
amidinate compounds with an excess of trimethylsilyl
chloride. The bis(amidine) compounds 1 and 2 are best
/
Cy; 2, Rꢀi
derivatives,
Cy; 4, Rꢀi
/
Pr). Alter-
1,4-
Pr),
illustrated in Figs. 2ꢃ
Table 1 and selected bond lengths and angles are
collected in Tables 2ꢃ4.
/4, crystal data is summarised in
/
/
/
Compound 1 crystallises from acetonitrile with two
independent molecules in the unit cell [1a and 1b], each
of which lie on an inversion centre. In contrast, crystal-
lisation from toluene gives a structure with a single
molecule in the unit cell, present as the bis-solvate [1(tol)].
Molecules 1a and 1b differ from each other in the
orientation of one of the cyclohexyl groups (Fig. 2a and
b); thus, in 1a the cyclohexyl substituents are attached to
purified by crystallisation from Et2O at ꢁ30 8C, while
the silyl derivatives 3 and 4 can be crystallised under the
same conditions using CH2Cl2 as solvent.
/
Recent NMR studies of amidinate ligands that
incorporate bulky substituents have indicated the pre-
sence of different isomers and tautomers in solution
[14,15]. It was noted in our work that the room
temperature 1H-NMR spectrum of an analytically
pure sample of 1 consists of resonances from two
separate species in solution, in a ratio of ca. 24:1. The
major component exhibits a singlet resonance in the
aromatic region of the spectrum, indicating a symme-
trical species which, on the basis of crystallographic data
(vide infra), we assign as the E-syn:E-syn isomer. The
minor component consists of a non-symmetric structure
with doublet resonances for the aromatic protons which,
on the basis of the loss of a nOe between the Cy-
substituent and the aromatic protons, we assign as the
Z-syn:E-syn isomer arising from isomerisation of one
the amidine nitrogen atoms via an equatorial [C(5)ꢀ
C(10)] and an axial [C(11)ꢀC(16)] linkage, while in 1b,
both CꢀN bonds are equatorial with respect to the
/
/
/
cyclohexyl ring. Each amidine moiety is present in the
E-syn:E-syn form, as observed in the previously struc-
turally characterised N,N?-diphenyl- and N,N?-di(p-
tolyl)benzamidine derivatives [16], and the bulky ter-
phenyl compound, [2,4,6-Ph3C6H2C{NiPr}{NHiPr}]
[17]. In contrast with the former two structures however,
no hydrogen bonding is present between neighbouring
molecules, presumably due to the steric bulk of the N-
substituents. The angle between the CN2 amidine units
and the C6-plane of the phenyl group (a) varies
considerably for each molecule, with values of 80.3
and 62.48 for 1a and 1b, respectively (see Table 5). The
of the ‘CꢁNCy’ double bonds (Scheme 2). In contrast,
the non-symmetrical Z-syn:E-syn isomer is not ob-
/

J. Grundy et al. / Journal of Organometallic Chemistry 662 (2002) 178ꢃ
/187
183
Fig. 4. Molecular structure of 4 showing 50% thermal ellipsoids.
Hydrogen atoms, omitted for clarity.
inversion centre, with no interactions between neigh-
bouring molecules (one of the independent molecules,
2a, is illustrated in Fig. 3). Crystallisation from toluene
however [2(tol)] generates a unit cell that contains one
independent molecule, with no included solvent mole-
cules. In all cases, the amidine units exist as the E-
syn:E-syn isomer. The angle between the amidines and
the phenyl ring are 66.2 (2a) and 63.08 (2b) with a
slightly larger value of 68.98 for 2(tol)
.
Comparison of the a-value between the different
structures of compounds 1 and 2 shows a significant
variation (62.4ꢃ80.38, Table 5), with none of the angles
/
small enough to suggest any conjugation to the phenyl
ring. This is markedly different from isoelectronic
phenyl carboxylic acids, where a approaches 08 and an
Fig. 2. (a) Molecular structure of 1a showing 50% thermal ellipsoids.
Hydrogen atoms, except NꢀH and cyclohexyl a-hydrogens, omitted
for clarity. (b) Molecular structure of 1b showing 50% thermal
ellipsoids. Hydrogen atoms, except NꢀH and cyclohexyl a-hydrogens,
omitted for clarity.
/
/
appreciable shortening of the Cꢀ
/
C bond between the
phenyl ring and the CO2H moiety is observed [18]. The
larger values of a for the amidine structures are
attributable to the presence of the nitrogen substituents.
However, as no trend can be rationalised between the
different values for the structures of 1 and 2, these
variations are ascribed to the different ways in which the
molecules pack within the crystal.
Inspection of the Cꢁ
lengths (Table 5), using the previously described DCN
value [where DCN N)ꢁd(CꢁN)] [19], show a
d(Cꢀ
/
Nimino and Cꢀ
/
Namino bond
ꢀ
/
/
/
/
˚
range of values from 0.008 (1b) to 0.108 A (2a).
Previously, low DCN values have been ascribed to
disorder between the Z-anti and E-syn tautomers,
that differ only in the location of the Nꢀ/H atom [14].
Investigation of the electron-density map of 1b, how-
ever, did not indicate that such disorder was present,
leading us to propose that the low DCN is therefore likely
to result from a greater delocalisation of electron density
across the ‘CN2’ moiety. As with the different values for
a, no clear trend can be deduced for the different DCN
values, again suggesting that variations may be the
result of packing effects.
Fig. 3. Molecular structure of 2a showing 50% thermal ellipsoids.
Hydrogen atoms, except NꢀH, omitted for clarity.
/
molecular structure of 1(tol) also lies on an inversion
centre, with the gross structure being similar to that of
1b. Thus the E-syn:E-syn form is present, with both of
the N-cyclohexyl bonds in the equatorial position, and a
value of 63.38 for a, close to the observed value for 1b.
The structure of the iso-propyl analogue, when
crystallised from hexane, also consists of a pair of
independent molecules [2a and 2b] that each lie on an
The presence of an Nꢀ
with the NꢀH of 1 and 2 (Fig. 4) causes the N-alkyl
substituents to adopt the E-anti configuration, due to
/SiMe3 group in 4 compared
/

184
J. Grundy et al. / Journal of Organometallic Chemistry 662 (2002) 178ꢃ187
/
Table 2
˚
Selected bond lengths (A) and angles (8) for 1a, 1b and 1(tol)
1a
1b
1(tol)
Bond lengths
C(4)ꢀN(1)
C(4)ꢀN(2)
C(1)ꢀC(4)
N(1)ꢀC(5)
N(2)ꢀC(11)
1.334(5)
1.305(4)
1.504(5)
1.462(4)
1.472(4)
C(4a)ꢀN(1a)
C(4a)ꢀN(2a)
C(1a)ꢀC(4a)
N(1a)ꢀC(5a)
N(2a)ꢀC(11a)
1.328(4)
1.320(5)
1.491(5)
1.465(5)
1.472(5)
C(1)ꢀN(2)
C(1)ꢀN(1)
C(1)ꢀC(2)
N(2)ꢀC(11)
N(1)ꢀC(5)
1.372(3)
1.274(3)
1.507(3)
1.457(3)
1.461(3)
Bond angles
C(1)ꢀC(4)ꢀN(1)
C(1)ꢀC(4)ꢀN(2)
N(1)ꢀC(4)ꢀN(2)
C(4)ꢀN(1)ꢀC(5)
C(4)ꢀN(2)ꢀC(11)
114.0(3)
123.3(3)
122.6(3)
121.8(3)
121.8(3)
C(1a)ꢀC(4a)ꢀN(1a)
C(1a)ꢀC(4a)ꢀN(2a)
N(1a)ꢀC(4a)ꢀN(2a)
C(4a)ꢀN(1a)ꢀC(5a)
C(4a)ꢀN(2a)ꢀC(11a)
116.7(3)
122.1(3)
121.1(3)
121.3(3)
121.8(3)
C(2)ꢀC(1)ꢀN(2)
C(2)ꢀC(1)ꢀN(1)
N(1)ꢀC(1)ꢀN(2)
C(1)ꢀN(2)ꢀC(11)
C(1)ꢀN(1)ꢀC(5)
112.0(2)
127.5(2)
120.5(2)
123.1(2)
121.0(2)
Symmetry elements for 1a/1b: ?ꢀꢁx, ꢁy, ꢁzꢂ1; ƒꢀꢁxꢂ1, ꢁy, ꢁzꢂ1. Symmetry elements for 1(tol): ?ꢀꢁx, ꢁy, ꢁz.
Table 3
Selected bond lengths (A) and angles (8) for 2a, 2b and 2(tol)
˚
2a
2b
2(tol)
Bond lengths
C(4)ꢀN(1)
C(4)ꢀN(2)
C(1)ꢀC(4)
N(1)ꢀC(5)
N(2)ꢀC(8)
1.3807(19)
1.2724(18)
1.5022(19)
1.4664(19)
1.467(2)
C(14)ꢀN(3)
C(14)ꢀN(4)
C(11)ꢀC(14)
N(3)ꢀC(15)
N(4)ꢀC(18)
1.3695(19)
1.281(2)
C(4)ꢀN(1)
C(4)ꢀN(2)
C(1)ꢀC(4)
N(1)ꢀC(5)
N(2)ꢀC(8)
1.362(3)
1.272(2)
1.503(3)
1.461(3)
1.463(3)
1.5046(18)
1.4591(19)
1.459(2)
Bond angles
C(1)ꢀC(4)ꢀN(1)
C(1)ꢀC(4)ꢀN(2)
N(1)ꢀC(4)ꢀN(2)
C(4)ꢀN(1)ꢀC(5)
C(4)ꢀN(2)ꢀC(8)
112.70(12)
126.96(13)
120.29(13)
121.99(13)
120.16(13)
C(11)ꢀC(14)ꢀN(3)
C(11)ꢀC(14)ꢀN(4)
N(3)ꢀC(14)ꢀN(4)
C(14)ꢀN(3)ꢀC(15)
C(14)ꢀN(4)ꢀC(18)
113.14(12)
126.71(13)
120.15(13)
122.11(14)
121.01(13)
C(1)ꢀC(4)ꢀN(1)
C(1)ꢀC(4)ꢀN(2)
N(1)ꢀC(4)ꢀN(2)
C(4)ꢀN(1)ꢀC(5)
C(4)ꢀN(2)ꢀC(8)
112.21(17)
127.06(17)
120.72(18)
124.66(19)
119.71(16)
Symmetry elements for 2a/2b: ?ꢀꢁx, ꢁyꢂ1, ꢁzꢂ1; ƒꢀꢁxꢁ2, ꢁyꢂ2, ꢁzꢂ1. Symmetry elements for 2(tol): ?ꢀꢁxꢂ1, ꢁyꢂ1, ꢁzꢂ1.
the increased bulk of the silyl group. The DCN values
˚
when compared to the parent amidines, also reflecting
the larger silyl substituent.
[0.111 and 0.109 A] are consistent with a more localised
N double bond within the amidine
To demonstrate that the 1,4-benzenebis(amidine)
compounds described above can be used in the synthesis
of coordination complexes, a brief study into the
application of 2 as a ligand precursor in aluminium
chemistry was conducted. The reaction between the
neutral amidine 1,4-C6H4[C{NiPr}{NHiPr}]2 (2) and
AlMe2Cl in toluene proceeded via protonolysis of the
Cꢀ
/
N single and Cꢁ
/
unit, and the a-values [83.6 and 75.68] are also larger
Table 4
˚
Selected bond lengths (A) and angles (8) for 4
Bond lengths
C(7)ꢀN(1)
C(7)ꢀN(2)
C(1)ꢀC(7)
N(1)ꢀSi(1)
N(1)ꢀC(11)
N(2)ꢀC(14)
1.386(5) C(17)ꢀN(3)
1.275(5) C(17)ꢀN(4)
1.498(5) C(4)ꢀC(17)
1.780(3) N(3)ꢀSi(2)
1.485(5) N(3)ꢀC(21)
1.462(5) N(4)ꢀC(24)
1.388(5)
1.279(5)
1.500(5)
1.775(3)
1.489(5)
1.467(5)
Alꢀ
/
C bond to afford the bis(aluminiumchloromethyl)
complex, 1,4-C6H4[C{NiPr}2AlMeCl]2 (5, Scheme 3).
The mass spectrum and elemental analysis were con-
sistent with two ‘AlMeCl’ units attached to the central
bis(amidinate) ligand. The 1H-NMR spectrum of 5
showed one septet for the iso-propyl methine hydrogen
and two doublets (1:1 ratio), as predicted for a non-
symmetrically substituted Al-centre and restricted rota-
Bond angles
C(1)ꢀC(7)ꢀN(1)
C(1)ꢀC(7)ꢀN(2)
N(1)ꢀC(7)ꢀN(2)
C(7)ꢀN(1)ꢀSi(1)
C(11)ꢀN(1)ꢀSi(1)
C(7)ꢀN(1)ꢀC(11)
C(7)ꢀN(2)ꢀC(14)
119.4(3) C(4)ꢀC(17)ꢀN(3)
124.0(3) C(4)ꢀC(17)ꢀN(4)
116.6(3) N(3)ꢀC(17)ꢀN(4)
112.8(2) C(17)ꢀN(3)ꢀSi(2)
126.8(2) C(21)ꢀN(3)ꢀSi(2)
119.3(3) C(17)ꢀN(3)ꢀC(21)
122.0(3) C(17)ꢀN(4)ꢀC(24)
119.2(3)
123.9(3)
116.8(3)
114.2(2)
126.6(2)
119.0(3)
122.0(3)
tion about the Nꢀ
/
iPr bonds. An X-ray structural
analysis of crystals of 5 confirmed the formulation as
1,4-C6H4[C{NiPr}2AlMeCl]2. However, disorder be-
tween the methyl and chloride sites prevented satisfac-

J. Grundy et al. / Journal of Organometallic Chemistry 662 (2002) 178ꢃ
/187
185
Table 5
a (8) and DCN (A) values for 1, 1(tol), 2, 2(tol), 4 and 6
˚
˚
˚
˚
DCN (A)
Compound
d(CꢀN) A
d(CꢁN) (A)
a (8)
1a
1b
1.334(5)
1.328(4)
1.372(3)
1.3807(19)
1.3695(19)
1.362(3)
1.386(5)
1.388(5)
1.332(4)
1.305(4)
1.320(5)
1.274(3)
1.2724(18)
1.2810(2)
1.272(2)
1.275(5)
1.279(5)
1.331(4)
0.029
0.008
0.098
0.108
0.089
0.090
0.111
0.109
0.001
80.3
62.4
63.3
66.2
63.0
68.9
83.6
75.6
89.3
1(tol)
2a
2b
2(tol)
4
6
Fig. 5. Molecular structure of 6 showing 30% thermal ellipsoids.
Hydrogen atoms omitted for clarity.
Table 6
Crystal data for 6
6
Empirical formula
Formula weight
Temperature (K)
C24H44Al2N4
442.59
173(2)
˚
Wavelength (A)
0.71073
Monoclinic
P21/c (No. 14)
10.6225(14)
8.7187(8)
16.195(2)
90
Crystal system
Space group
˚
a (A)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
V (A )
Z
105.269(5)
90
3
˚
1447.0(3)
2
1.02
Scheme 3. (i) Two equivalents AlMe2Cl, hexane, 12 h; (ii) two
equivalents n BuLi, hexane, 2 h; (iii) two equivalents AlMe2Cl, hexane,
12 h.
Dcalc (Mg mꢁ3
)
Absorption coefficient (mmꢁ1
Crystal size (mm)
)
0.12
0.2ꢄ0.2ꢄ0.1
u Range for data collection (8)
Reflections collected
4.14ꢃ
7376
/
22.96
tory refinement of the data set, precluding a detailed
discussion of bond lengths and angles.
Independent reflections
Reflections with I ꢀ2s(I)
Data/restraints/parameters
Final R indices [I ꢀ2s(I)]
R indices (all data)
Goodness-of-fit on F2
˚
Largest difference peak and hole (e A
1993 [Rintꢀ0.082]
1440
1993/0/136
To avoid the possibility of such disorder, the symme-
trical bis(aluminiumdimethyl) compound was synthe-
sised. Thus, a sample of 2 was deprotonated to generate
the dilithio-salt in situ, [20] which reacted smoothly with
AlMe2Cl to afford 1,4-C6H4[C{NiPr}2AlMe2]2 as col-
ourless crystals (6, Scheme 3). The spectroscopic data
were again consistent with a bi-metallic complex, which
was subsequently confirmed by X-ray analysis. The
molecular structure is illustrated in Fig. 5; crystal data is
summarised in Table 6 and selected bond lengths and
angles are collected in Table 7.
R1ꢀ0.066, wR2ꢀ0.146
R1ꢀ0.097, wR2ꢀ0.160
1.045
ꢁ3
)
0.21 and ꢁ0.16
˚
0.001 A] with a perpendicular arrange-
N bond [DCN
ꢀ
/
ment of the amidinate and phenyl substituents [aꢀ
89.38].
In summary, a new class of neutral, linked-bis(N,N?-
/
dialkylamidine) ligand has been developed and the
application in coordination chemistry investigated. Syn-
Compound 6 is monomeric, with the distorted tetra-
hedral aluminium atom coordinated by a dihapto-
thetic routes to the N ꢀ
described, and the solid-state structure of selected
representatives is discussed. It has been shown that the
/
H and N ꢀ
/
SiMe3 derivatives are
amidinate ligand and two methyl groups. The Alꢀ
and AlꢀC bond lengths and angles are comparable to
related aluminium amidinate species [17,21], where the
bite angle of the ligand is relatively acute [N(1)ꢀAlꢀ
N(2)ꢀ68.86(12)8], and is compensated for by an
increase in the NꢀAlꢀC angles [114.88 average]. The
‘CN2’ fragment is symmetrically delocalised in each Cꢀ
/
N
/
N ꢀ
aluminium complexes using AlMe2Cl, via protonolysis
of an AlꢀC bond, or transmetallation of the in situ
generated lithium salt. Further studies into the applica-
/
H derivative 2 may be utilised in the synthesis of di-
/
/
/
/
/
/
/

186
J. Grundy et al. / Journal of Organometallic Chemistry 662 (2002) 178ꢃ187
/
Table 7
References
˚
Selected bond lengths (A) and angles (8) for 6
[1] J. Barker, M. Kilner, Coord. Chem. Rev. 133 (1994) 219.
[2] F.T. Edelmann, Coord. Chem. Rev. 137 (1994) 403.
[3] (a) K.B. Aubrecht, M.A. Hillmyer, W.B. Tolman, Macromole-
cules 35 (2002) 644;
Bond lengths
C(1)ꢀN(1)
C(1)ꢀN(2)
C(1)ꢀC(2)
N(1)ꢀAl
1.332(4)
1.331(4)
1.492(4)
1.925(3)
1.939(3)
1.946(4)
1.943(4)
1.459(4)
1.453(4)
(b) J.R. Hagadorn, J. Arnold, J. Chem. Soc. Dalton Trans. (1997)
3087;
N(2)ꢀAl
(c) F. Benetollo, G. Cavinato, L. Crosara, F. Milani, G. Rossetto,
C. Scelza, P. Zanella, J. Organomet. Chem. 555 (1998) 177;
(d) L.R. Sita, J.R. Babcock, Organometallics 17 (1998)
5228;
AlꢀC(11)
AlꢀC(12)
N(1)ꢀC(5)
N(2)ꢀC(8)
(e) J.C. Flores, J.C.W. Chien, M.D. Rausch, Organometallics 14
(1995) 1827;
Bond angles
N(1)ꢀC(1)ꢀN(2)
C(1)ꢀN(1)ꢀAl
C(1)ꢀN(2)ꢀAl
N(1)ꢀAlꢀN(2)
C(11)ꢀAlꢀN(1)
C(11)ꢀAlꢀN(2)
C(12)ꢀAlꢀN(1)
C(12)ꢀAlꢀN(2)
C(11)ꢀAlꢀC(12)
110.3(3)
90.7(2)
90.1(2)
(f) J.C. Flores, J.C.W. Chien, M.D. Rausch, Organometallics 14
(1995) 2106;
(g) V. Volkis, M. Shmulinson, C. Averbuj, A. Lisovskii, F.T.
Edelmann, M.S. Eisen, Organometallics 17 (1998) 3155;
(h) C. Averbuj, E. Tish, M.S. Eisen, J. Am. Chem. Soc. 120 (1998)
8640.
68.86(12)
115.23(18)
116.14(16)
113.97(17)
113.94(17)
118.8(2)
[4] (a) R.C. Mehrotra, R. Bohra, Metal Carboxylates, Academic,
London, 1983;
(b) C. Oldham, Comprehensive Coordination Chemistry, vol. 2,
Pergamon, Oxford, 1987.
Symmetry elements for 6: ?ꢀꢁxꢂ1, ꢁyꢂ1, ꢁz.
[5] A.R. Sanger, Inorg. Nucl. Chem. Lett. 9 (1973) 351.
[6] R.T. Boere´, R.T. Oakley, R.W. Reed, J. Organomet. Chem. 331
(1987) 161.
tion of these ligands in the synthesis of molecular species
and extended arrays are ongoing within the group.
[7] A.W. Cordes, R.C. Haddon, R.G. Hicks, R.T. Oakley, T.T.M.
Palstra, L.F. Schneemeyer, J.V. Waszczak, J. Am. Chem. Soc. 114
(1992) 5000.
[8] S. Appel, F. Weller, K. Dehnicke, Z. Anorg. Allg. Chem. 583
(1990) 7.
[9] C. Roques, M.-R. Mazie`res, J.-P. Majoral, M. Sanchez, J. Jaud,
Inorg. Chem. 28 (1989) 3931.
4. Supplementary material
[10] (a) J.R. Hagadorn, J. Arnold, Angew. Chem. Int. Ed. 37 (1998)
1729;
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
(b) J.F. Li, L.H. Weng, X.H. Wei, D.S. Liu, J. Chem. Soc. Dalton
Trans. (2002) 1401;
Data Centre, CCDC nos. 190074ꢃ190079 for com-
/
pounds 1, 1(tol), 2, 2(tol), 4, and 6, respectively. Copies
of this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2
(c) H. Kawaguchi, T. Matsuo, Chem. Commun. (2002) 958.
[11] C.-T. Chen, L.H. Rees, A.R. Cowley, M.L.H. Green, J. Chem.
Soc. Dalton Trans. (2001) 1761.
[12] G.M. Sheldrick, SHELXL-97, Program for the Refinement of
1EZ, UK (Fax: ꢂ44-1223-336033; e-mail: deposit@
/
Crystal Structures, Gottingen, Germany, 1997.
¨
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
[13] U. Honrath, L. Shu-Tang, H. Vahrenkamp, Chem. Ber. 118
(1985) 132.
[14] R.T. Boere´, V. Klassen, G. Wolmershauser, J. Chem. Soc. Dalton
¨
Trans. (1998) 4147.
[15] (a) J.A.R. Schmidt, J. Arnold, Chem. Commun. (1999)
2149;
5. Note added in proof
(b) J.A.R. Schmidt, J. Arnold, J. Chem. Soc., Dalton Trans.
(2002) 2890.
A new class of linked bis(amidine) molecule, and
application in the synthesis of a bis(aluminium) complex
was reported during the preparation of this manuscript
[22].
[16] (a) N.W. Alcock, J. Barker, M. Kilner, Acta Crystallogr. Sect. C
44 (1988) 712;
(b) N.W. Alcock, N.C. Blacker, W. Errington, M.G.H. Wall-
bridge, Acta Crystallogr. Sect. C 50 (1994) 456.
[17] D. Abeysekera, K.N. Robertson, T.S. Cameron, J.A.C. Clyburne,
Organometallics 20 (2001) 5532.
Acknowledgements
[18] C.C. Wilson, N. Shankland, A.J. Florence, J. Chem. Soc. Faraday
Trans. 92 (1996) 5051.
[19] G. Hafelinger, K.H. Kuske, The Chemistry of the Amidines and
¨
The University of Sussex is thanked for financial
support and Dr Tony Avent is acknowledged for the
variable temperature NMR measurements. We also
wish to acknowledge the use of the EPSRC’s Chemical
Database Service at Daresbury.
Imidates, vol. 2 (Chapter 1), Wiley, Chichester, 1991.
[20] The dilithio-salt has been isolated and structurally characterised
as the TMEDA adduct, 1,4-C6H4[C{Ni Pr}2Li(TMEDA)]2 and
will appear in a future publication. M.P. Coles, P.B. Hitchcock,
unpublished results.

J. Grundy et al. / Journal of Organometallic Chemistry 662 (2002) 178ꢃ
/187
187
[21] (a) R. Lechler, H.-D. Hausen, J. Weidlein, J. Organomet. Chem.
359 (1989) 1;
(d) S. Dagorne, I.A. Guzei, M.P. Coles, R.F. Jordan, J. Am.
Chem. Soc. 122 (2000) 274;
(b) M.P. Coles, D.C. Swenson, R.F. Jordan, V.G. Young, Jr.,
Organometallics 16 (1997) 5183;
(e) J.A.R. Schmidt, J. Arnold, Organometallics 21 (2002)
2306.
(c) M.P. Coles, D.C. Swenson, R.F. Jordan, V.G. Young, Jr.,
Organometallics 17 (1998) 4042;
[22] H.A. Jenkins, D. Abeysekera, D.A. Dickie, J.A.C. Clyburne, J.
Chem. Soc., Dalton Trans. (2002) 3919.