Metal β-diketiminates revisited: ansa-CH2-bridged bis(β-diketiminate)s of lithium and aluminium having diverse structures

Article abstract of DOI:10.1016/j.jorganchem.2004.05.042

Synthesis of the β-diketimines H[{N(R)C(Ar)}₂CH] [R = SiMe₃ and Ar = Ph (1) or C₆H₄Me-4 (2)] and the ansa-CH₂-bridged bis(β-diketimines)s [H{N(R)C(Ar)} ₂C]₂CH₂ [Ar = P

Full text of DOI:10.1016/j.jorganchem.2004.05.042

Journal of Organometallic Chemistry 689 (2004) 4357–4365
www.elsevier.com/locate/jorganchem
Metal b-diketiminates revisited: ansa-CH2-bridged
bis(b-diketiminate)s of lithium and aluminium
having diverse structures
*
Laurence Bourget-Merle, Peter B. Hitchcock, Michael F. Lappert
Department of Chemistry, School of Life Sciences, University of Sussex, Brighton BN1 9QJ, UK
Received 30 April 2004; accepted 20 May 2004
Available online 21 July 2004
Abstract
The metal b-diketiminato ligand-to-metal binding modes are briefly reviewed, with reference particularly to our previous work on
metal complexes using the ligands [{N(R1)C(R2)}2CH] (R1 =SiMe3 =R and R2 =Ph; or R1 =C6H3Pri2-2,6 and R2 =Me). The syn-
theses of the b-diketimines H[{N(R)C(Ar)}2CH] 1 (Ar=Ph) and 2 (Ar=C6H4Me-4) and the ansa-CH2-bridged bis(b-diketimine)s
3 (Ar=Ph) and 4 (Ar=C6H4Me-4) are reported. Thus, from the appropriate compound Li[{N(R)C(Ar)}2CH] and H2O, (CH2Br)2
or CH2Br2 the product was 2, 3 or 4. Compound 1 was prepared from K[{N(R)C(Ph)}2CH] and (CH2Br)2. Each of 3 or 4 with
LiBun surprisingly yielded the bicyclic dilithium compound
5 (Ar=Ph) or 6 (Ar=C H Me-4)
6 4
Li2[{N(R)C(Ar)CC(Ar)NR}2(CH2)]
in which each of the b-diketiminato fragments is an N,N0-bridge between the two lithium atoms and the CH2 moiety joins the
two ligands through their central carbon atoms. However, 4 with AlMe3 yielded the expected ansa-CH2-bridged-bis[(b-diketimina-
to)(dimethyl)alane] 7, which was also obtained from 6 and Al(Cl)Me2. X-ray structures of the known compounds 2 and 3, and of 5,
6 and 7 are presented; the 1H NMR spectra of 6 in toluene-d8 show that there is restricted rotation about the NC–C6H4Me-4 bond.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: b-Diketiminates; Lithium; Aluminium; ansa-bridged complexes
1. Introduction
ments elsewhere in a comprehensive review [2]. A ligand
which has been much used is shown in delocalised form
in B, and sometimes is abbreviated as Dipp2nacnac.
b-Diketiminates have an increasing useful role in co-
ordination chemistry especially as spectator ligands, by
virtue of their strong binding to metals, their tuneable
steric demands and their diversity of bonding modes.
Our entry into this field dates back to our first
publication in 1994 [1], when we introduced the N N0-
bis-(tri- methylsilyl)-b-diketiminato ligands shown in A
(R=SiMe3) in the monoanionic delocalised mode
(Ar=Ph or C6H4Me-4). Our published contributions
to the chemistry of b-diketiminatometal complexes up
to July 2002 were placed in the context of the develop-
2. Bonding modes
*
Corresponding author. Tel.: +0-127-367-8316; fax: +0-127-367-
The b-diketiminato ligand binds to metals in a termi-
nal or bridging mode. The terminally bound ligand is
7196.
E-mail address: m.f.lappert@sussex.ac.uk (M.F. Lappert).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.05.042

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L. Bourget-Merle et al. / Journal of Organometallic Chemistry 689 (2004) 4357–4365
usually N,N0-chelating and is attached to the metal either:
(i) in a four-electron r-bond fashion, the metallacycle be-
ing planar as in C [3], or has the metal out of the NCCCN
plane as in D [4]; or (less usually) (ii) a six-electron 2r+4p
g5-fashion with the
ring adopting a boat con-
formation as in E [1]. Rarer are the monodentate N- (as in
MNCCCN
Ph
HC
Ph
R
R
Ph
CH
Ph
H
H
C
Ph
R
Ph
R
Ph
R
Ph
R
C
C
C
N
N
N
N
C
C
C
N
C
N
C
N
C
N
Mg
Zr
Cl3
Li
(tmeda)
R
R
E [1]
D [4]
C [3]
H
P(Ph)X
Me
Sn(B){N(C6H3Pri2-2,6)C(Me)=CHC(Me)=NC6H3Pri2-2,6}
F [5]
Me
C
C
N
C
N
2,6-Pri2C6H3
C6H3Pri2-2,6
Ph
C
Ph
C
G (X = Cl) [6]
H (X = Ph) [7]
K
(thf)
N
K
N
R
C
N
R
Ph
HC
Ph
R
H
(thf)
R
Ph
Ph
R
C
C
N
N
Li(CHR2)
I [8]
Li
N
C
C
C
C
N
N
CH
Ph
HC
Ph
Li
Li
N
R
R
R
J [1]
(MeCN)3Pd
K [9]
C6H3Pri2-2,6
Pd(NCMe)2
Me
C
H
C
C
N
Me
Me
Me
[BF4]3
N
Me
C6H11
NR2
N
C6H3Pri2-2,6
Me
N
C6H11
C6H11
N
C6H11
N
Ba
Ba
L [10]
H
N
N
C
C6H11
C6H11
thf
Ph
Me
M [11]
Me
R'
Li
Ph
N
R
O
N
Ph
(LPh,Ph -
R'
N
N
Yb3
N
R
R
R
SiMe2
Me
Yb
)
R
SiMe3
R
N
N
N
Yb2
R'
Li
Yb1
N
R'
(LPh,Ph 3-
)
Me
Si
Yb1 +2
Yb2 +3
Yb3 +2
Ph
Me2
thf
N (R'= Ph) [12]
O (R'= C6H4Ph-4) [12]
(LPh,Ph 3-
P (LPh,Ph = {N(R)C(Ph)}2CH) [13]
)
N
R

L. Bourget-Merle et al. / Journal of Organometallic Chemistry 689 (2004) 4357–4365
4359
Ph
Ph
Ph
Ph
Ph
Ph
1 e
Me3SiN
NSiMe3
Me3SiN
NSiMe3
Me3SiN
NSiMe3
1 e
Ph
Ph
Ph
Me3SiN
NSiMe3
Me3SiN
NSiMe3
Scheme 1. Sucessive 1-electron reductions: [LPh,Ph ꢀ
]
! [LPh,Ph 2ꢀ
]
! [LPh,Ph 3ꢀ
] .
F [5] or C- (as in G, X=Cl [6] or H, X=Ph [7]) centered
metal b-diketiminates. Similarly, the bridging b-diketimi-
nates may be terminal as in I [8] or, more frequently, che-
lating as in J [1], K [9], L [10] or M [11].
bis(b-diketimine) 3, Scheme 2 (R=SiMe3) [1]. We now
provide the experimental details and also X-ray data
for the crystalline compounds 2 and 3. The 4-tolyl ana-
logue 4 of 3 is also reported.
Of the more than 500 known b-diketiminatometal
complexes, in every case but three the ligand has been
monoanionic. The exceptions were the ytterbium com-
plexes N [12], O [12] and P [13]. In N and O the ligand
[{N(R)C(Ph)}2CH] (”LPh,Ph) was regarded as dianionic.
In P two of the ligands were assigned as trianionic, one
bound to Yb(II) and the other to Yb(III), while the third
b-diketiminate was attached to Yb(II); these features are
indicated schematically in P. The X-ray data on the crys-
talline complexes N–P were consistent with the ligand
charge distribution shown in valence bond terms in
Scheme 1 [12,13]; particularly sensitive probes are the
values of the C–N and C–C bond lengths. Structures
N–P also illustrate thus far unique bonding modes: both
N, N0-bridging and chelating in N and O, and multicen-
tred chelating and bridging for the trianionic ligands in P.
The principal focus of this paper is on ansa-CH2-
bridged bis(b-diketiminato) ligands in the context of
lithium and aluminium chemistry.
3.2. b-Diketimines and ansa-CH2-bridged
bis(b-diketimine)s
Treatment of the potassium b-diketiminate
K[{N(R)C(Ph)}2CH] with an equimolar portion of 1,2-
dibromoethane yielded ((i) in Scheme 2) yellow needles
of the b-diketimine 1 in essentially quantitative yield. Us-
ing a 0.5 molar portion of (CH2Br)2 gave 1 in ca. 50%
yield, with the K salt not fully consumed; it is assumed
that the coproduct was bromoethene which was unreac-
tive under the mild reaction conditions. Alternatively, 1
was obtained from the potassium b-diketiminate by hy-
drolysis, but less satisfactorily; it is noteworthy that the
N-SiMe3 bonds were not cleaved. The hydrolysis method
gave an almost quantitative yield of 2 ((ii) in Scheme 2)
by bubbling moist air through a hexane solution of
Li[{N(R)C(C6H4Me-4)}2CH]. Heating the latter salt,
or the phenyl analogue, under reflux with dibromome-
thane in refluxing hexane gave ((iii) in Scheme 2) the pale
yellow crystalline complex 4 or 3, in ca. 40% yield.
3. Results and discussion
3.1. Objectives
In a preliminary publication, we described the synthe-
sis of the b-diketimines 1 and 2 and the CH2-bridged
Ar
HC
Ar
R
Ar
R
Ar
R
C
C
N
C
C
N
C
C
N
iii
i or ii
H
M
H
2
2
HC
CH2
C
N
N
N
R
R
Ar
R
2
1 Ar = Ph
2 Ar = C6H4Me-4
Q Ar = Ph
Ar = C6H4Me-4
3 Ar = Ph
4 Ar = C6H4Me-4
S
Scheme 2. Synthesis of b-diketimines (1,2) and ansa-CH2-bridged bis(b-diketimine)s (3,4) Reagents and conditions: (i) (for l) S (M=K), (CH2Br)2,
C6H14, C6H14, 5 h, 50 ꢁC; (ii) (for 2) S (M=Li), H2O, C6H14; (iii) (M=Li) Q (for 3) or S (for 4), CH2Br2, C6H14, reflux.

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L. Bourget-Merle et al. / Journal of Organometallic Chemistry 689 (2004) 4357–4365
The pale yellow crystalline compounds 1–4 melted
C6D6 (5, 7) or C7D8 (6); the EI mass spectrum of 7
showed as the parent ion [MꢀMe]+. Additionally, the
molecular structures of crystalline 5 (Fig. 1), 6 (Fig. 2),
and 7 (Fig. 3) were determined by X-ray diffraction.
The molecule of crystalline 5 is a 4,8-dilithio-3,5,7,9-
tetraazabicyclo[5.5.1]tridecane derivative, in which each
of the two ligands N1C4C1C14N4 and N2C24
C3C34N3 acts as an N,N0-bridge between the two lith-
ium atoms. The central carbon atoms C1 and C3 of
each ligand are joined through a methylene bridge.
The 3,5,7,9 nitrogen positions correspond to N1, N2,
N3 and N4, respectively of Fig. 1, while the 4- and 8-
lithium positions refer to Li1 and Li2, respectively.
The atom Li1 has short contacts to C1, C2, and C4,
whereas Li2 is close to C2 and C(13)0of an adjacent
molecule. It is evident from the key bond distances
sketched schematically in 50 and bond angles (Fig. 1)
that (i) there is significant p-delocalisation over the five
skeletal atoms of each ligand; (ii) the environments at
Li1 and Li2 are disparate, which is reflected in the very
different endocyclic angles: 158.4(4)ꢁ at Li1 and
127.6(3)ꢁ at Li2; (iii) the environment at C2 is severely
distorted tetrahedral; and (iv) whereas the sum of the
bond angles at each of N2, N3 and N4 is 359.7 0.2ꢁ,
at N1 it is 352.7ꢁ. The structure of the p-tolyl homo-
logue 6 of 5 is very similar; Fig. 2 provides two different
views, in order to indicate the conformations of the
Li1-(a) and Li2-(b)-containing rings.
without decomposition [at 120–124 ꢁC (1), 85–87 ꢁC
(2), 193–198 ꢁC (3), 196 ꢁC (4)] and gave satisfactory mi-
croanalyses and 1H and 13C NMR spectra, which
showed that at ambient temperature in C6D6 there was
rapid exchange of the proton between its two adjacent
nitrogen atoms.
The X-ray molecular structures of crystalline 2 and 3
show that each is a monomer. Selected bond lengths and
an angle are sketched schematically in 20 and 30, and il-
lustrated in greater detail in the Supplementary Infor-
mation. The mean endocyclic bond angles in 30 are
121.0(8), 122.9(9), and 121.1(9)ꢁ at C, C(NR), and
C[N(H)R], respectively.
2.10(3)
H
0.76(4)
RN
NR
1.310(6)
124.1(4) ˚
1.361(5)
1.352(5)
120.8(3) ˚
1.440(7)
126.0(4) ˚
2'
H
H
NR
RN
)
1.93(4
PhC
C
RN
CPh
C
PhC
113.7(3) ˚
C
CPh
Si4
H
H
C(13)'
1.745(2)
3'
2.457(6)
N4
Li2
C14
The phenyl rings are twisted out of the NCCCN
plane by ca. 45ꢁ in 20, but are nearly orthogonal to each
such plane in 30. In the latter, the four nitrogen atoms
are located in such a way as to offer a potentially tetrad-
entate donor site to a metal or metals.
1.
928
(6)
1.
444
(4)
2.556(2)
Si3
N3
C1
C4
C(2)H2
C34
3.3. Lithium and aluminium ansa-CH2-bridged
bis(b-diketiminate)s
1.712(2)
C3
N1
Si1
1.
412
(4)
1.895(7)
Treatment of the appropriate ansa-CH2-bridged
bis(b-diketimine) 3 or 4 with two equivalents of n-buty-
llithium yielded ((i) in Scheme 3) crystals of the mono-
meric dilithium CH2-bridged bis(b-diketiminate) in
good yield: the orange 5, m.p. 157–160 ꢁC and the deep
yellow 6, m.p. 158–160 ꢁC. Likewise, from 4 and two
equivalents of trimethylalane yellow crystals of the an-
C24
Li1
N2
1.
734
(2)
5'
Si2
sa-CH2-bridged bis[b-diketiminato(dimethyl)alane]
7
The NMR spectra of 6 in toluene-d8 at 248 K
showed that its solution structure is consistent with
that found in the crystal. Thus, there were two
29Si{1H} NMR spectral signals at d ꢀ6.90 and d
ꢀ6.19. Due to restricted rotation about the C–
C6H4Me-4 bond, each of the pairs of o- and m-protons
were obtained ((ii) in Scheme 3) in excellent yield. Com-
pound 7 was also synthesised ((iii) in Scheme 3) in nearly
quantitative yield from the dilithio precursor 6 and two
equivalents of chlorodi(methyl)alane. Each of 5–7 gave
satisfactory analyses and multinuclear NMR spectra in

L. Bourget-Merle et al. / Journal of Organometallic Chemistry 689 (2004) 4357–4365
4361
Scheme 3. Synthesis of lithium (5,6) and dimethylaluminium (7) bis(b-diketiminate)s. Reagents and conditions: (i) 2 LiBun, C6H14, ꢀ78 ꢁC; (ii) 2
AlMe3, C6H14, ꢀ78 ꢁC; (iii) 2 Al(Cl)Me2, PhMe, ꢀ20 ꢁC.
labelled ‘‘Hb’’. The central methylene group in both 5
and 6 is characterised by a somewhat high frequency
1H signal, indicative of rather acidic protons.
The crystalline ansa-CH2-bridged bis[b-diketimina-
to(dimethyl)alane] molecule 7 is C2 symmetric. Each of
the b-diketiminato-Al six-membered rings has the boat
conformation (cf. E), the Al and C2 atoms being 1.027
˚
and 0.299 A, respectively, out of the almost planar
N1N2C1C3 moiety. The aluminium atom is in a distorted
tetrahedral environment; the ring bite angle N1–Al–N2
is the smallest, 91.83(11)ꢁ. There is significant p-delocal-
isation in the b-diketiminato ligands, which does not ex-
tend to the phenyl substituents. The angle subtended at
the methylene carbon atom C4 is 116.7(3)ꢁ. The angle
between the N1N2C1C3 plane and the C1C2C3 or
Fig. 1. Molecular structure of 5 with selected bond angles (ꢁ): N1–Li1–
N2 158.4(4), N3–Li2–N4 127.6(3), Li1–N1–C4 90.2(3), Li1–N2–C24
N1AlN2 plane is 24.68(35)ꢁ or 50.30(12)ꢁ, respectively.
The metric parameters for 7 (Fig. 3) may be compared
with those for Al(Me)2[{N(R)C(Ph)}2CH]: av. Al–CH3
121.1(2), N1–C4–C1 122.5(3), N2–C24–C3 122.2(3), C4–C1–C14
122.0(2), C4–C1–C2 118.9(2), C24–C3–C34 123.4(3), C24–C3–C2
˚
1.960(5), av. Al–N 1.921(4), av. C–C 1.400(6) A; H3C–
Al–CH3 111.3(2)ꢁ, N1–Al–N2 97.1(2)ꢁ, Al–N–CH3
107.3(2)ꢁ and 116.3(2)ꢁ, av. Al–N–C 109.2(3)ꢁ, C1–C2–
C3 126.8(4)ꢁ; and the angle between the N1N2C1C3
plane and the C1C2C3 or N1AlN2 plane is 11.22(17)ꢁ
or 48.44(21)ꢁ, respectively [14].
118.3(2), C1–C2–C3 119.6(2), C2–C1–C14 119.0(2), C2–C3–C34
118.0(2), C1–C14–N4 122.1(3), C3–C34–N3 122.6(3), C14–N4–Li2
113.9(3), C34–N3–Li2 106.5(2).
is magnetically inequivalent, with two distinct aryl
rings. For each ring, the o- and m-protons on one side
were at higher frequency and well separated (d 7.1 and
d 6.7) whereas those on the other side were not re-
solved and appeared at lower frequency (d 6.3). This
is consistent with the notion that the two rings are in-
terleaved (Fig. 4), so that the protons designated ‘‘Ha’’
experience a ring current from the neighbouring ring
and hence Ha signals are at lower frequency than those
1
The H, 13C, 27Al, and 29Si NMR spectra of 7 in
C6D6 at 333 K were fully consistent with the structure
of the crystalline molecule. The bridging CH2 group
1H NMR spectral chemical shift was unexceptional
at d 2.83, in contrast to the higher frequency shifts
recorded for 5 and 6.
The reaction pathway for the formation of the bicyclic
dilithio compound 5 or 6 from the ansa-CH2-bridged

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L. Bourget-Merle et al. / Journal of Organometallic Chemistry 689 (2004) 4357–4365
˚
Fig. 2. Molecular structure of 6, showing two alternative views (a and b, ellipsoid probability 20%), with selected bond lengths (A) and angles (ꢁ):
Li1–N3 1.897(2), Li1–N4 1.910(5), Li2–N1 1.919(5), Li2–N2 1.961(5), Li1. . .C2 2.514(5), Li1. . .C3 2.439(5), Li1–C34 2.279(5), Li2. . .C4 2.617(5),
Li2. . .C2 2.541(5), Li2–C(41)0 2.427(5), N3–C34 1.339(3), N4–C14 1.331(3), N1–C4 1.335(3), N2–C24 1.311(3), C34–C3 1.418(3), C14–C1 1.422(3),
˚
C1–C4 1.418(3), C3–C24 1.452(3), C1–C2 1.528(3), C3–C2 1.535(3) A; N3–Li1–N4 160.9(3), N1–Li2–N2 126.7(3), Li1–N3–C34 88.2(2), Li1–N4–C14
121.1(2), Li2–N1–C4 105.8(2), Li2–N2–C24 115.1(2), N3–C34–C3 122.4(2), N4–C14–C1 122.2(2), N1–C4–C1 123.2(2), N2–C24–C3 121.0(2), C4–
C1–C2 119.2(2), C24–C3–C2 118.7(2), C1–C2–C3 119.7(2)ꢁ.
H
b
H
a
H
b
H
a
H
a
H
b
H
a
H
b
CH
3
CH
3
Fig. 4.
and 6 indicates that the isomer 70 is thermodynamically
less favoured than 7 and if 70 is first formed then its re-
arrangement into 7 may require a process similar in re-
verse of the final two steps of Scheme 4 with the lithium
atoms replaced by AlMe2 moieties in 70.
˚
Fig. 3. Molecular structure of 7 with selected bond lengths (A) and
angles (ꢁ): Al–N1 1.895(3), Al–N2 1.949(3), Al–C25 1.956(3), Al–C26
1.971(3), N1–Si1 1.763(2), N2–Si2 1.784(2), N1–C1 1.363(3), N2–C3
˚
1.333(4), C1–C2 1.397(4), C2–C3 1.437(4), C2–C4 1.530(3) A; N1–
Me2
R
R
Al
N
N
N
Al–N2 91.83(11), N1–Al–C25 117.67(13), N1–Al–C26 112.17(14), N2–
Al–C25 106.10(12), N2–Al–C26 123.62(14), Al–N1–C1 110.4(2),
Al–N2–C3 111.1(2), N1–C1–C2 123.2(2), N2–C3–C2 124.4(3),
C1–C2–C3 119.1(2), C1–C2–C4 120.0(2), C2–C4–C20 116.7(3).
4-MeC6H4
4-MeC6H4
C6H4Me-4
C6H4Me-4
H
C
2
bis(b-diketimine) 3 or 4 is suggested to follow the route
shown in Scheme 4 (R=SiMe3, Ar=Ph or C6H4Me-4).
The formation of 7 from 4 and AlMe3, on the other
hand, is unexceptional since no rearrangement is impli-
cated. However, that 7 is also obtained from Al(Cl)Me2
N
Al
Me2
R
R

L. Bourget-Merle et al. / Journal of Organometallic Chemistry 689 (2004) 4357–4365
4363
4. Experimental
4.4. Synthesis of [H{N(R)C(Ar)}2C]2CH2 (4)
(R=SiMe3, Ar=C6H4Me-4)
4.1. Synthesis of H[{N(R)C(Ph)}2CH] (1) (R=SiMe3)
The same method as for the synthesis of 3 was used to
prepare 4. CH2Br2 (0.42 g, 2.42 mmol) added to a solu-
tion of [Li{N(R)C(Ar)}2CH]2 (1.79 g, 4.47 mmol) in
hexane (ca. 30 mL). After refluxing for 13 h yellow crys-
tals of 4 (0.71 g, 40%), m.p. 196–198 ꢁC, were obtained.
1H (300.13 MHz, C6D6, 293 K) d 0.04 (s, 36 H, SiMe3),
2.14 (s,12 H, CH3–C6H4), 2.90 (s, 2 H, CH2); 6.79–6.95
(m, 16 H, C6H4), 11.50 (s, 2 H, NH); 13C (75.46 MHz,
C6D6, 293 K) d 2.1 (SiMe3), 21.2 (CH3–C6H4), 33.3
(CH2), 110.6 (NCCCN), 128.4, 128.7, 136.8, 140.2
(C6H4), 170.2 (NCAr). Elemental analysis for
C47H68N4Si4, found % (calculated %), C 70.0 (70.4), H
8.44 (8.55), N 7.29 (6.99).
(CH2Br)2 (0.01 mL, 0.82 mmol) was added by syringe
to a solution of [K{N(R)C(Ph)}2CH] (0.41 g, 1.01
mmol) in hexane (ca. 20 mL). The mixture was heated
at 50 ꢁC for 5 h. The white precipitate formed was fil-
tered off and evaporation of the solvent from the filtrate
in vacuo produced yellow needles of compound 1 (0.36
g, 97%), m.p. 85–87.5 ꢁC.
By using the potassium compound and (CH2Br)2 in the
proportion 2:1, the reaction, even under reflux in hexane
for 10 h, led only to 1 and unreacted potassium complex.
1H NMR (360.1 MHz, toluene-d8, 298 K) d 0.04 (s,
18 H, SiMe3), 5.39 (s, 1 H, CH), 6.99–7.21 (m, 10 H,
C6H5), 12.38 (s, 1 H, NH); 13C NMR (62.9 MHz,
C6D6, 298 K) d 1.9 (SiMe3), 102.8 (CH), 128.9 (CN),
127.4, 132.8, 143.7, 170.6 (C6H5). Elemental analysis
for C21H30N2Si2, found % (calculated %), C 68.9
(68.8), H 8.25 (8.25), N 7.82 (7.64).
Li [{N(R)C(Ar)CC(Ar)NR} (CH )]
4.5. Synthesis of
(R=SiMe3, Ar=C6H5)
(5)
2
2
2
LiBun (1.6 M in hexane, 0.70 mL, 1.12 mmol) was
added dropwise to a solution of 3 (0.4 g, 0.54 mmol)
in Et2O (ca. 10 mL) at ꢀ78 ꢁC. An immediate change
of colour from yellow to orange was observed. The so-
lution was stirred for a further 30 min more at low tem-
perature, then allowed to warm up slowly and stirred at
room temperature for 4 h. Solvents were removed in
vacuo from the dark green-yellow solution to give a yel-
low-brown powder. Orange crystals of 5 (0.25 g, 61%),
m.p. 157–160 ꢁC, were obtained from a hot hexane/tol-
uene solution by cooling slowly to room temperature.
1H (300.13 MHz, C6D6, 333 K) d ꢀ0.05 (s broad, 36
H, SiMe3), 4.78 (s, 2 H, CH2), 6.60–6.91 (m broad, 20
4.2. Synthesis of H[{N(R)C(Ar)}2CH] (2)
(R=SiMe3, Ar=C6H4Me-4)
A suspension of [Li{N(R)C(Ar)}2CH]2 (0.33 g, 0.44
mmol) in hexane (ca. 10 mL) was stirred until nearly
all the solid had dissolved; there was a change in colour
from red to yellow. Slow evaporation of the solvent in
vacuo afforded yellow crystals of 2 (0.31 g, 96%), m.p.
1
120–124 ꢁC. H NMR (360.1 MHz, CDCl3, 298 K) d
0.06 (s, 18 H, SiMe3), 2.39 (s, 6 H, CH3–C6H4), 5.28
(s, 1 H, CH), 7.16 and 7.28 (d, 8 H, C6H4Me-4), 12.08
(s, 1 H, NH); 13C NMR (62.9 MHz, CDCl3, 298 K) d
1.8 (SiMe3), 21.3 (CH3–C6H4), 102.1 (CH), 128.6
(CN), 127.2, 138.1, 140.5, 170.5 (C6H4). Elemental anal-
ysis for C23H34N2Si2, found % (calculated %), C 70.1
(70.0), H 9.17 (8.78), N 7.22 (7.10).
1
H, C6H5); H (C6D6, 300.13 MHz, 293 K) d ꢀ0.13 (s,
18 H, SiMe3), 0.05 (s, 18 H, SiMe3), 4.79 (s, 2 H,
CH2), 6.65–6.80 (m, 20 H, C6H5); 13C (75.46 MHz,
C6D6, 293 K) d 2.4 (SiMe3), 2.7 (SiMe3), 35.3 (CH2),
114.5 (NCCCN), 126.2, 127.1, 128.4, 128.5, 142.7,
148.7, 149.7 (C6H5), 182.1 (NCC6H5), 185.9 (NCC6H5);
7Li (116.6 MHz, C6D6, 293 K) d 0.40; 29Si (99.36 MHz,
C6D6, 298 K) d ꢀ6.65 (SiMe3), ꢀ6.15 (SiMe3); MS (EI,
70 eV) m/z 496 ([Mꢀ(2Li+3Me3Si+NC)]+, 35%), 190
([Me3SiNCC6H5]+, 82%). Elemental analysis for
C43H58Li2N4Si4, found % (calculated %), C 67.27
(68.21), H 7.63 (7.67), N 7.45 (7.40).
4.3. Synthesis of [H{N(R)C(Ph)}2C]2CH2 (3)
(R=SiMe3)
CH2Br2 (0.34 g, 1.95 mmol) was added to a solution of
[Li{N(R)C(Ph)}2CH]2 (1.32 g, 1.77 mmol) in hexane (ca.
20 mL). The mixture was refluxed for 10 h and the white
precipitate formed was then filtered off. Concentrating
the filtrate by slow evaporation of solvent in vacuo affor-
ded yellow crystals of 3 which were washed with hexane
(ca. 5 mL) and dried in vacuo (0.57 g, 43%), m.p. 193–198
Li [{N(R)C(Ar)CC(Ar)NR} (CH )]
4.6. Synthesis of
(R=SiMe3, Ar=C6H4Me-4)
(6)
2
2
2
1
ꢁC. H NMR (360.1 MHz, toluene-d8, 298 K) d 0.08 (s,
The method used for the synthesis of 5 was applied
for the synthesis of 6, from LiBun (1.6 M in hexane,
3.2 mL, 5.12 mmol), 4 (2.05 g, 2.56 mmol) in a mixture
Et2O (42 mL)/hexane (6 mL). Deep yellow crystals
36 H, SiMe3), 2.65 (s, 2 H, CH2), 6.76–7.01 (m, 20 H,
C6H5), 11.80 (s, 2 H, NH); 13C NMR (62.9 MHz, tolu-
ene-d8, 298 K) d 2.0 (SiMe3), 33.0 (CH2), 110.5
(NCCCN), 128.4 (CN), 127.6, 129.3, 142.9, 170.1
(C6H5). Elemental analysis for C43H60N4Si4, found %
(calculated %), C 67.9 (69.3), H 8.44 (8.12), N 7.41 (7.52).
1
of 6 (1.42 g, 68%), m.p. 158–160 ꢁC, were isolated. H
(300.13 MHz, toluene-d8, 293 K) d ꢀ0.16 (s, 18
H, SiMe3), 0.08 (s, 18 H, SiMe3), 2.07 (s,12 H,

4364
L. Bourget-Merle et al. / Journal of Organometallic Chemistry 689 (2004) 4357–4365
R
R
Ar
R
H
Ar
Ar
R
Li
R
Ar
N
N
N
N
N
N
2 LiBun
H
R
CH2
Li
R
CH2
N
N
Ar
Ar
R
Ar
N
Ar
N
3 Ar = Ph, 4 Ar = C6H4Me-4
R
R
Li
R
R
Li
N
N
Ar
Ar
Ar
Ar
Ar
Ar
H
C
2
H
C
2
R
N
N
N
Ar
N
R
Ar
Li
Li
R
R
5 Ar = Ph, 6 Ar = C6H4Me-4
Scheme 4.
CH3AC6H4), 4.65 (s, 2 H, CH2), 6.42–6.77 (m, 16 H,
C6H4); 13C (75.46 MHz, toluene-d8, 293 K) d 2.1
(SiMe3), 2.7 (SiMe3), 21.0 (CH3-C6H4), 35.4 (CH2),
4.7. Synthesis of [Me2Al{N(R)C(Ar)}2C]2CH2 (7)
(R=SiMe3, Ar=C6H4Me-4)
114.7
(NCCCN),
124.8–147.3
(C6H4),
182.0
AlMe3 (2 M in hexanes, 0.6 mL, 1.2 mmol, 30% ex-
cess) was added dropwise to a suspension of 3 (0.37 g,
0.46 mmol) in hexane (ca. 20 mL) at ꢀ78 ꢁC. After 30
min at ꢀ78 ꢁC the yellow solution was allowed to warm
up slowly and stirred for 1 h at room temperature. The
solvents were then removed in vacuo to afford 7 (0.38 g,
(NCC6H4Me-4), 186.2 (NCC6H4Me-4); 7Li (116.6
MHz, toluene-d8, 293 K) d 0.38; 29Si (99.36 MHz, tolu-
ene-d8, 298 K) d ꢀ6.92 (SiMe3), ꢀ6.38 (SiMe3). Elemen-
tal analysis for C47H66Li2N4Si4, found % (calculated %),
C 71.2 (69.4), H 8.29 (8.18), N 6.50 (6.89).
Table 1
Compound
2
3
5
6
7
Empirical formula
Formula weight
Crystal system
Space group
C
394.7
23H34N2Si2
C43H60N4Si4
745.3
Triclinic
C43H58Li2N4Si4 Æ(C5H12
829.32
Triclinic
)
C47H66Li2N4Si4
813.28
C51H78Al2N4Si4 Æ(C6H14)
999.7
Monoclinic
C2/c (No. 15)
48.282(8)
6.144(9)
16.887(4)
90
Monoclinic
P21/c (No. 14)
12.3070(4)
11.6518(4)
35.7160(13)
90
Monoclinic
C2/c (No. 15)
19.461(4)
23.237(4)
13.954(2)
90
ꢀ
P1 (No. 2)
ꢀ
P1 (No. 2)
˚
a (A)
12.285(4)
14.186(4)
14.182(4)
89.15(2)
75.00(3)
75.82(2)
2311.3(3)
2
12.0755(3)
12.6880(3)
19.5345(5)
78.286(2)
75.507(2)
63.528(2)
2579.4(1)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
106.46(2)
90
99.666(2)
90
97.75
90
3
˚
V A
4804.0(3)
8
0.15
5048.9(3)
4
0.15
6253(2)
4
0.16
Z
l (mmꢀ1
)
0.15
5630
0.15
27390
8961, [0.043]
Reflections collected
Independent reflections,
[R (int)]
4694
4650, [0.03]
26994
8784, [0.065]
5656
5492, [0.033]
5630
Reflections with I>2r(I)
Final R indices (I>2r(I))
R indices (all data)
2172
R1 0.062
–
3166
R1 0.057
–
7000
R1 0.064, wR2 0.183
R1 0.083, wR2 0.200
6270
R1 0.054, wR2 0.122
R1 0.086, wR2 0.137
3862
R1 0.055, wR2 0.136
R1 0.088, wR2 0.161

L. Bourget-Merle et al. / Journal of Organometallic Chemistry 689 (2004) 4357–4365
4365
90%), m.p. 198 ꢁC, as a yellow solid which was washed
with pentane. Crystals for X-ray structure determination
were obtained from hexane at 4 ꢁC. H (300.13 MHz,
nato fragments behaves as an N,N0-bridge between the
two lithium atoms. By contrast, from 4 and AlMe3 the
product was the ansa-CH2-bridged-bis[b-diketimina-
to(dimethyl)alane] 7. The X-ray structures of 2, 3, 5, 6
and 7 are described. The 1H NMR spectrum of 6 in tol-
uene at 248 K showed that there is restricted rotation
about the C–Ar bond.
1
C6D6, 333 K) d ꢀ0.02 (s, 12 H, AlMe2), 0.06 (s, 36 H,
SiMe3), 2.07 (s, 12 H, CH3AC6H4), 2.83 (s, 2 H, CH2),
6.68–6.82 (m, 16 H, C6H4); 13C (75.46 MHz, C6D6,
333 K) d ꢀ1.1 (AlMe2), 4.0 (SiMe3), 21.2 (CH3AC6H4),
36.1 (CH2), 116.7 (NCC(CH2)CN), 128.5, 129.9, 137.6,
134.0 (C6H4), 177.8 (NCAr); 29Si (99.36 MHz, C6D6,
333 K) d 4.77 (SiMe3); 27Al (130.31 MHz, C6D6, 333
K) d 151.4 (D1/2 ꢁ5.5 KHz); MS (EI, 70 eV) m/z 897
([MꢀMe]+, 53%). Elemental analysis for C51H78Al2N4-
Si4.(C6H14), found % (calculated %), C 68.2 (68.5), H 9.1
(9.2), N 5.8 (5.6).
6. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 236280 and 236281 for 2
and 3, respectively and 237141–237143 for 5–7, respec-
tively. Copies of this information may be obtained free
of charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44-1233-336033;
e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.
cam.ac.uk).
4.8. Crystallographic data and structure refinement
for 2, 3, 5, 6 and 7
Diffraction data for 2 and 3 were collected on an En-
raf Nonius CAD4 diffractometer at room temperature
with crystals sealed in capillaries. These structures were
refined on F using reflections with I>2r(I) with the En-
raf Nonius MolEN programs.
Acknowledgement
Crystallographic data for 5, 6 and 7 were collected at
173(2) K on a CAD4 diffractometer. The structures were
refined with full-matrix, least-squares on all F2 (SHELXL
93 for 5 and 7, SHELXL 97 for 6). The poorly defined
pentane solvate was refined isotropically with distance
constraints and no H atoms for 5. In 7, all non-hydro-
gen atoms were anisotropic, and hydrogen atoms were
included in the riding mode with Uiso(H)=1.2Ueq(C)
or 1.5Ueq for Me groups. The para-methyl groups were
included with disordered H atoms. There is a molecule
of hexane solvate disordered across an inversion centre
for which C atoms were left isotropic and H atoms were
omitted.
We are grateful to Professor D.-S. Liu for the exper-
imental data on 1, 2 and 3 (see [1]). Also acknowledged
is the award of a Marie Curie Fellowship to L.B.-M.
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the 4,8-dilithio-3,5,7,9-tetraazabicyclo[5.5.1]tridecane
derivative 5 (Ar=Ph)
Li2[{N(R)C(Ar)CC(Ar)NR}2(CH2)]
or 6 (Ar=C6H4Me-4), in which each of the b-diketimi-
´
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