Synthesis and structures of crystalline Li, Al and Sn(ii) 1-azaallyls and β-diketiminates derived from [Li{μ,η3-N(SiMe 3)C(Ad)C(H)SiMe3}]2 (Ad = 1-adamantyl)

Article abstract of DOI:10.1039/b718728a

The crystalline dimeric 1-azaallyllithium complex [Li{μ, η³-N(SiMe₃)C(Ad)C(H)SiMe₃}]₂ (1) was prepared from equivalent portions of Li[CH(SiMe₃)₂] and 1-cyanoadamantane (AdCN). Complex 1 was used as precursor to each of the crystalline complexes 2-8 which were obtained in good yield. By 1-azaallyl ligand transfer, 1 afforded (i) [Al{η³-N(SiMe₃)C(Ad) C(H)SiMe₃}{κ¹-N(SiMe₃)C(Ad)=C(H)SiMe ₃-E}Me] (5) with [AlCl₂Me]₂, (ii) [Sn{η³-N(SiMe₃)C(Ad)C(H)SiMe₃} ₂] (7) with Sn[N(SiMe₃)₂]₂, and (iii) [Li(N{C(Ad)=C(H)SiMe₃-E}{Si(NN)SiMe₃})(thf) ₂] (8) with the silylene Si[(NCH₂Bu^t) ₂C₆H₄-1,2] [= Si(NN)]. By insertion into the C≡N bond of the appropriate cyanoarene RCN, 1 gave the β-diketiminate [Li{μ-N(SiMe₃)C(Ad)C(H)C(R)NSiMe₃}]₂ [R = Ph (2), C₆H₄Me-4 (3)], and 5 yielded [Al{κ ²-N(SiMe₃)C(Ad)C(H)C(Ph)NSiMe₃} {κ¹-N(SiMe₃)C(Ad)=C(H)SiMe₃-E}Me] (6). The β-diketiminate [Al{κ²-N(SiMe₃)C(Ad)C(H) C(Ph)NSiMe₃}Me₂] (4) was prepared from 2 and [AlClMe ₂]₂. The X-ray structures of 1 and 3-8 are presented. Multinuclear NMR spectra in C₆D₆ or C₆D ₅CD₃ have been recorded for each of 1-8; such data on 8 revealed that in solution two minor isomers were also present.

Full text of DOI:10.1039/b718728a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Synthesis and structures of crystalline Li, Al and Sn(II) 1-azaallyls and
b-diketiminates derived from [Li{l,g3-N(SiMe3)C(Ad)C(H)SiMe3}]2
(Ad = 1-adamantyl)†
Laurence Bourget-Merle, Peter B. Hitchcock, Michael F. Lappert* and Philippe G. Merle
Received 4th December 2007, Accepted 31st January 2008
First published as an Advance Article on the web 11th March 2008
DOI: 10.1039/b718728a
3
The crystalline dimeric 1-azaallyllithium complex [Li{l,g -N(SiMe3)C(Ad)C(H)SiMe3}]2 (1) was
prepared from equivalent portions of Li[CH(SiMe3)2] and 1-cyanoadamantane (AdCN). Complex 1
was used as precursor to each of the crystalline complexes 2–8 which were obtained in good yield. By
3
1
=
1-azaallyl ligand transfer, 1 afforded (i) [Al{g -N(SiMe3)C(Ad)C(H)SiMe3}{j -N(SiMe3)C(Ad)
3
C(H)SiMe3-E}Me] (5) with [AlCl2Me]2, (ii) [Sn{g -N(SiMe3)C(Ad)C(H)SiMe3}2] (7) with Sn[N(Si-
=
Me3)2]2, and (iii) [Li(N{C(Ad) C(H)SiMe3-E}{Si(NN)SiMe3})(thf)2] (8) with the silylene Si[(NC-
t
≡
H2Bu )2C6H4-1,2] [= Si(NN)]. By insertion into the C N bond of the appropriate cyanoarene RCN, 1
gave the b-diketiminate [Li{l-N(SiMe3)C(Ad)C(H)C(R)NSiMe3}]2 [R = Ph (2), C6H4Me-4 (3)], and 5
2
1
=
yielded [Al{j -N(SiMe3)C(Ad)C(H)C(Ph)NSiMe3}{j -N(SiMe3)C(Ad) C(H)SiMe3-E}Me] (6). The
b-diketiminate [Al{j2-N(SiMe3)C(Ad)C(H)C(Ph)NSiMe3}Me2] (4) was prepared from 2 and
[AlClMe2]2. The X-ray structures of 1 and 3–8 are presented. Multinuclear NMR spectra in C6D6 or
C6D5CD3 have been recorded for each of 1–8; such data on 8 revealed that in solution two minor
isomers were also present.
complexes are sterically sensitive; cf. the X-ray-characterised
Introduction
3
3
compounds Sn[g -N(SiMe3)C(But)C(H)SiMe3]2 (V), Sn[g -
1
There has been a long-standing interest in lithium 1-azaallyls (pre-
pared in situ and generally not structurally characterised) because
of their role in organic synthesis,1 undergoing a number of C–C
bond-forming reactions with electrophiles, as in controlled aldol
condensation reactions and the regioselective a-functionalisation
of ketones.1 1-Azaallylic anions have played a major role in
heterocyclic chemistry.2 A direct synthesis of enamines from olefins
has recently been reported, as in Pr CH CH2 + HN(CH2)4CH2 +
CO + H2
=
N(SiMe3)C(Ph)C(SiMe3)2][j -N(SiMe3)C(Ph) C(SiMe3)2] and
1
t
7
=
Sn[j -N(SiMe3)C(Bu ) C(H)C6H3Me2-2,5]2. The crystalline
MeAl complex VI in solution underwent rapid 1-azaallyl ligand
fluxionality8b and, on the basis of multinuclear NMR spectra,
the Me2Al complex VII was assigned to have the ligand in the
3
g -bonding mode I.8b
n
=
n
3
=
Bu CH CHN(CH2)4CH2.
A 2001 review on 1-azaallylmetal complexes had 144 literature
citations.4 A variety of metal–ligand coordination modes were
identified, including the terminal g - (I), terminal j1- (enamido)
3
(II) and C,N-chelating-N-bridging (III).
Results and discussion
Our entry into this field began in 1994, with the disclosure
that Li[CH(SiMe3)2] with ButCN in Et2O gave the X-ray-
characterised crystalline compound IV;5 related reactions
are shown in Scheme 1.6 Compound IV or its Na or K
analogue was used as ligand transfer reagent; relevant to
the present studies are data on tin(II),7 and aluminium8
compounds. The structures of crystalline bis(1-azaallyl)tin(II)
The results and discussion is divided into two parts, each based
3
on [Li{l,g -N(SiMe3)C(Ad)C(H)SiMe3}]2 (1). [Its preparation,
from Li[C(H)(SiMe3)2]9 and AdCN (Ad = 1-adamantyl), has
previously been mentioned in outline10a and it has been used
as a precursor to P{N(SiMe3)C(Ad)C(H)SiMe3}Ph2.10b] The first
part deals with the preparation of 1 and its conversion into two
lithium b-diketiminates. Succeeding sections are concerned with
its role as precursor to (i) three methylaluminium compounds,
(ii) a homoleptic tin(II) 1-azaallyl and (iii) a bulky lithium
amide derived from the reaction of 1 with the bis(amino)silylene
Si[(NCH2But)2C6H4-1,2].
Department of Chemistry, University of Sussex, Brighton, United Kingdom
BN1 9QJ. E-mail: m.f.lappert@sussex.ac.uk; Tel: +44 (0)1273 678316
† CCDC reference numbers 668981–668987. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b718728a
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 3493–3501 | 3493
©

Scheme 1 Synthesis of 1-azaallyllithium (IV)5 and some of its reactions.6
Synthesis and structures of the lithium 1-azaallyl 1 and the
b-diketiminates 2 and 3
Their syntheses are shown in Scheme 2; yields (as for 4–
8) were not optimised and refer to X-ray-quality crystalline
materials. The procedures used are related to those leading to
the tert-butyl compound IV and the b-diketiminate [Li{l,j2-
{N(SiMe3)C(Ph)CHC(But)NSiMe3}]2 rather than [Li{l,j2-
(N(SiMe3)C(Ph))2C(H)}]2.6 Each of 1–3 was characterised by
satisfactory C, H and N analyses, multinuclear NMR solution
spectra, mass spectra and for 1 and 3 by single crystal X-ray
diffraction studies.
Fig. 1 (a) ORTEP representation of the structure of 1 (50% ther-
˚
mal ellipsoids) (top); (b) bond distances (A) in the skeletal core of
3
[Li{l,g -N(SiMe3)C(Ad)C(H)SiMe3}]2 (1) (bottom).
0.9◦) wider that at each nitrogen atom (73.6 0.2 ◦). The relative
disposition of the 1-adamantyl and the adjacent C–SiMe3 is cisoid
(C9 vs. Si2) or transoid (C27 vs. Si4). Some further geometric
parameters of 1 are compared with those of 8 in Table 4.
An ORTEP representation of the molecular structure of the
centrosymmetric dimeric lithium b-diketiminate 3 is shown in
Fig. 2a; its step-like fused tricyclic skeletal core is sketched
in 2D in Fig. 2b. Selected geometric parameters for 3 are
compared with those of [Li{l,j2-(N(SiMe3)C(Ph))2C(H)}]2 in
6
Table 1. A less accurate structure of crystalline [Li{l,j2-
{N(SiMe3)C(Ph)CHC(But)NSiMe3}]2 is also available.6 The cen-
tral Li2N2 ring of 3 is rhomboidal and the adjacent fused six-
membered rings are boat-shaped with the Li and C2 atoms 0.83
˚
and 0.11 A out of the N1N2C1C3 plane respectively. The Li atom
◦
˚
Table 1 Bond distances (A) and selected angles ( ) in the skeletal core of
[Li{l,j2-N(SiMe3)C(Ad)C(H)C(C6H4Me-4)NSiMe3}]2 (3) and [Li{l,j2-
6
(N(SiMe3)C(Ph))2C(H)}]2
Compound
3
[Li{(N(SiMe3)C(Ph))2C(H)}]2
Scheme 2 Synthesis of the crystalline lithium compounds 1–3.
Li–N1
Li–N2
N1–C1
N2–C3
1.996(2)
2.015(5)
1.303(4)
1.365(3)
1.448(4)
1.378(4)
78.3(2)
1.952(10)
1.965(9)
1.299(6)
1.337(6)
1.439(6)
1.394(7)
75.0(4)
An ORTEP representation of the molecular structure of crys-
talline 1 is shown in Fig. 1a; its skeletal core, with bond distances,
is found in Fig. 1b. From the latter it is evident that each of
C1–C2
C2–C3
Li–N2–Liꢀ
N2–Li–N2ꢀ
N1–Li–N2
3
the ligands is bound to its lithium atom in an g - rather than
101.7(2)
101.2(2)
103.0(4)
105.0(4)
the enamido (j1)-fashion. The central Li2N2 ring is almost planar
with the endocyclic angle subtended at each lithium atom (106.4
3494 | Dalton Trans., 2008, 3493–3501
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The Royal Society of Chemistry 2008
©

as formerly employed for [Al{N(SiMe3)C(But)C(H)SiMe3}2Me]
(VI).8b The compound 6, chiral at the Al atom, containing both 1-
azaallyl and b-diketiminato ligands is currently without precedent.
Compounds 4–6 were characterised by microanalysis (5, 6),
multinuclear (1H, 13C, 29Al and 29Si) NMR spectra in C6D6 at
293 K (4, like VIII,11 was fluxional) and mass spectra (5, 6), as well
as single crystal X-ray diffraction.
ORTEP representations of the molecular structures of crys-
talline complexes 4–6 are shown in Fig. 3, 4 and 5, respectively.
Selected geometrical data for the AlN1C1C2C3N2 rings of 4,
VIII,11 and 6 are listed in Table 2. The Al atom is 1.0 (4), 0.95
˚
(VIII) and 1.01 (6) A out of the N1C1C3N2 plane, respectively;
for 4 the C2 atom is coplanar with the latter but for the shallow-
˚
boat rings of VIII and 6, the C2 atom is 0.12 (VIII) or 0.17 (6) A
out of the N1C1N2 plane.
Fig. 2 (a) ORTEP representation of the structure of 3 (50% ther-
mal ellipsoids) (top); (b) the centrosymmetric core of [Li{l,j2-
N(SiMe3)C(Ad)C(H)C(C6H4Me-4)NSiMe3}]2 (3) (bottom).
˚
has relatively close contacts to the C1 [2.702(6) A], C3 [2.775(6)
˚
˚
A] and C24 [2.861(6) A] atoms.
Synthesis and structures of the aluminium compounds 4, 5 and 6
The routes to the crystalline methylaluminium compounds 4–6 are
illustrated in Scheme 3. Two dimethylaluminium b-diketiminates
related to 4 had previously been reported, albeit using a different
methodology: [Al{(N(SiMe3)C(Ph))2CH}Me2] (VIII) had been
obtained by methane elimination from AlMe3 and the appropriate
b-diketimine,11 and CH2[C{C(C6H4Me-4)N(SiMe3)}2AlMe2]2 was
similarly prepared from 2AlMe3 and the corresponding CH2-
bridged bis(b-diketimine).12 The synthesis of the methylaluminium
bis(1-azaallyl) 5 involved the same strategy (Cl/ligand exchange)
Fig. 3 ORTEP representation of the structure of 4 (50% thermal
ellipsoids).
Comparative geometric data for (i) the enamido fragments
3
1
=
of [Al{g -N(SiMe3)C(R)C(H)SiMe3}{j -N(SiMe3)C(R) C(H)-
SiMe3-E}Me] [R = Ad (5), R = But (VI)8b] and [Al{j2-
1
=
N(SiMe3 )C(Ph)C(H)C(Ad)NSiMe3 }{j -N(SiMe3 )C(Ad) C-
3–
(H)SiMe3-E}Me] (6) and (ii) the g 1-azaallyl fragment of 5 and
VI8b are listed in Table 3. That the two isomeric 1-azaallyl ligands in
Scheme 3 Synthesis of the crystalline aluminium compounds 4–6.
The Royal Society of Chemistry 2008 Dalton Trans., 2008, 3493–3501 | 3495
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©

˚
˚
1.45 A out of the N2C19C20 plane for 5, and 0.66 A out of the
N1C1C2 plane or 1.63 A out of the N2C13C14 plane for VI.8b The
˚
dihedral angles between the N1C1C2 and the N2C19C20 plane of
80◦ for 5 is to be compared with the 35◦ between the N1C1C2 and
N2C13C14 planes of VI.8b
Synthesis and structure of the bis(g3-1-azaallyl)tin(II) complex 7
The crystalline homoleptic 1-azaallyltin(II) compound 7 was
prepared in high yield as shown in eqn (1). The use of a metal
bis(trimethylsilyl)amide in a hydrocarbon solvent as precursor
is novel in 1-azaallylmetal chemistry and is likely to have some
generality and not only in this area of chemistry; it has the
advantage that the co-product Li[N(SiMe3)2] is volatile and hence
readily separated in vacuo. We have previously used such a
strategy for the synthesis of the homoleptic group 14 metal alkyls
M[CH(SiMe3)2]2 (M = Ge, Sn); for the germanium alkyl, in
particular, it was the method of choice.13
Fig. 4 ORTEP representation of the structure of 5 (50% thermal
ellipsoids).
(1)
Compound 7 was characterised by microanalysis, EI-mass
spectrometry and 1H, 13C, 29Si and 119Sn NMR spectra in
deuteriotoluene. The 119Sn chemical shift (d −377.3 ppm)
establishes that in solution both the ligands are bound to the
3
tin atom in the g -1-azaallyl mode I, as also found in the
crystal (Fig. 6). In support, it is noted that similar solutions of
Fig. 5 ORTEP representation of the structure of 6 (50% thermal
ellipsoids).
3
t
1
t
=
Sn[g -N(SiMe3)C(Bu )C(H)SiMe3]2 (V), Sn[j -N(SiMe3)C(Bu )
3
C(H)C6H3Me2-2,5]2, and Sn[g -N(SiMe3)C(Ph)C(SiMe3)2][j1-
N(SiMe3)C(Ph) C(SiMe3)2] had 119Sn chemical shifts of d−387.2,
crystalline 5 and VI are distinct is attributed to steric factors which
=
3
61.5 and −37.3 ppm, respectively.7
make the formation of the isomeric bis(g -azaallyl)methylalanes
3
energetically unfavourable for steric reasons. Regarding the g -
An ORTEP representation of the molecular structure of crys-
talline 7 is shown in Fig. 6, together with selected geometric
˚
1-azaallylaluminium moiety, the Al atom is 1.55 A out of the
˚
˚
N3C29C30 plane for 6, 0.76 A out of the N1C1C2 plane and
parameters of its core skeletal atoms. The tin atom is 1.39 A
out of both the N1C2C1 and N2C20C19 planes; the dihedral
angle between these two planes is 18◦. The core structure of 7 is
similar to that of V7 or Sn[{N(C6H3Pri2-2,6)}2CMe]2 (obtained
from Sn[N(SiMe3)2]2 and H[{N(C6H3Pri2-2,6)}2CMe]).14
◦
2
˚
Table 2 Selected bond distances (A) and angles ( ) for the [Al{j -
N(SiMe3)C(R)C(H)C(Ph)NSiMe3}] fragment of 4, 6 (R = Ad) and of
[Al{j2-(N(SiMe3)C(Ph))2C(H)}Me2] (VIII) (R = Ph)11
Compound
4
6
VIII
Al–N1
Al–N2
N1–C1
N2–C3
C1–C2
C2–C3
N1–Al–N2
C1–C2–C3
1.9417(12)
1.9235(11)
1.3350(16)
1.3569(15)
1.4124(18)
1.4018(4)
97.01(5)
1.959(2)
1.924(2)
1.341(3)
1.359(3)
1.415(3)
1.383(3)
95.12(9)
1.914(4)
Synthesis, reaction pathway and structure of the crystalline lithium
silylamide 8
1.928(4)
1.331(6)
1.336(6)
1.394(6)
1.406(6)
97.1(2)
The crystalline lithium compound 8 was obtained in good yield
from equivalent portions of the 1-azaallyllithium compound 1 and
the thermally stable bis(amino)silylene Si[(NCH2But)2C6H4-1,2]
(IX)15 [abbreviated as Si(NN)] in thf, eqn (2).
128.51(12)
126.4(2)
126.8(4)
3496 | Dalton Trans., 2008, 3493–3501
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The Royal Society of Chemistry 2008
©

◦
8b
Table 3 Selected bond lengths (A) and angles ( ) for the enamidoAl fragment of 5, 6 and VI and the 1-azaallylAl fragments of 5 and VI8b
˚
Compound
6
EnamidoAl of 5
EnamidoAl of VI
1-AzaallylAl of 5
1-AzaallylAl of VI
Al–N3
1.856(2)
2.910(2)
3.736(3)
1.451(3)
1.348(4)
1.8471(16) [Al–N2]
2.8314(18) [Al · · · C19]
3.683(2) [Al · · · C20]
1.441(2) [N2–C19]
1.353(2) [C19–C20]
1.839(2)
1.9945(15) [Al–N1]
2.3748(17) [Al–C1]
2.0399(17) [Al–C2]
1.326(2) [N1–C2]
1.467(2) [C1–C2]
1.998(2) [Al–N1]
2.380(2) [Al–C1]
2.022(2) [Al–C2]
1.320(3) [N1–C1]
1.468(3) [C1–C2]
Al · · · C29
Al · · · C30
N3–C29
C29–C30
2.816(2) [Al · · · C13]
3.564(2) [Al · · · C14]
1.445(3) [N2–C13]
1.347(3) [C13–C14]
Al–N3–C29
N3–C29–C30
N3–Al–C30
122.83(17)
119.4(2)
33.49(8)
118.38(11) [Al–N2–C19]
119.50(16) [N2–C19–C20]
34.96(5) [N2–Al–C20]
117.56(14) [Al–N2–C13]
119.3(2) [N2–C13–C14]
38.4(1) [N2–Al–C14]
88.96(10) [Al–N1–C1]
111.71(14) [N1–C1–C2]
69.95(7) [N1–Al–C2]
89.2(2) [Al–N1–C1]
111.8(2) [N1–C1–C2]
70.1(7) [N1–Al–C2]
the donor–acceptor adduct X. In a, this is succeeded by (i) the
electrocyclic 1,3-N–Si(NN) bond-making with N–Li bond break-
ing yielding the intermediate XI, and (ii) a 1,2-SiMe3 shift from XI
with N–Li bond-making furnishing 8. In b, X is converted directly
into 8, the electrocyclic rearrangement involving a 1,3-N →
Si SiMe3 shift and Li–Si(NN) bond-breaking. As for route c, 1
and IX are converted directly into 8, with XII as the transition
state. The crucial part of a is the intermediate XI, which may
alternatively be derived directly by a 1,1-addition of the fragments
Li and N(SiMe3)C(Ad)C(H)SiMe3 from 1 to the silylene Si(NN)
(IX).
There are precedents for the intermediates related to X
and XI. As for X, among numerous examples of Si(NN)
(IX) behaving as a ligand are the complexes [Ni{Si(NN)}4],16a
Fig. 6 ORTEP representation of the structure◦ of 7 (50% thermal
˚
ellipsoids). Selected bond lengths (A) and angles ( ): Sn–N1 2.5466(16),
Sn–N2 2.5156(16), Sn–C1 2.312(2), Sn–C19 2.313(2), Sn–C2 2.741(2),
Sn–C20 2.718(2), N1–C2 1.309(2), N2–C20 1.309(2), C1–C2 1.454(3),
C19–C20 1.451(3); N1–Sn–C1 57.18(6), N2–Sn–C19 57.63(6), N1–Sn–N2
147.88(5), C1–Sn–C19 92.83(7), C19–Sn–N1 99.99(6), N2–Sn–C1
98.24(6), N1–C2–C1 115.18(17), N2–C20–C19 115.42(17).
5
[CuI(PPh3)2{Si(NN)}],16a and [Ln(g -C5H5)3{Si(NN)}] (Ln =
Y, Y b ) . 16b Related to XI are several compounds obtained
from Si(NN) and various salts LiRꢀ in thf, including
[Li{Si(NN)Rꢀ}(thf)n] [Rꢀ = But, n = 3;17 Rꢀ = CH(SiMe3)2, n =
2;17 Rꢀ = Si(SiMe3)3, n = 2;17 Rꢀ = NR2, n = 3 (R = Me, Pri)18]. In
contrast to the formation of such 1,1-adducts of Li-Rꢀ to Si(NN),
treatment of Si(NN) with Li[N(SiMe3)2] in thf gave XIIIa,19
an analogue of 8; likewise Si(NN) and Li[N(But)SiMe3] gave
XIIIb.19 Finally, a crucial experiment was that between Si(NN)
and Li[N(C6H3Me2-2,6)SiMe3]: mixing the reagents below 0 ◦C
gave XIV as the major product, but at higher temperatures XIV
was isomerised yielding XIIIc.18 In the light of the cited earlier
data, pathway a (or aꢀ) is the most appropriate to account for the
formation of 8 from 1 + IX.
(2)
Plausible routes a, b and c from 1 + IX → 8 are shown in
Scheme 4. The first step in pathways a and b is the formation of
The crystalline lithium amide 8 gave satisfactory micro-
analytical data (C, H, N). An ORTEP representation of
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 3493–3501 | 3497
©

Scheme 4 Alternative routes [(a), (aꢀ), (b), or (c)] from 0.5(1) + IX → 8.
its molecular structure is shown in Fig. 7. Skeletal ge-
component, ca. 55%), Z-8 (ca. 19%) and the NH-containing
compound (apparently due to adventitious hydrolysis of E-8);
assignments have been made on the basis of NOE experiments.
The presence of only two thf signals (a- and b-CH2) suggests that
the thf is not strongly bound and undergoes fast exchange even at
this temperature. Two 7Li and nine 29Si resonances are consistent
with the above assignment. Heating to 90 C simplified the H
NMR multiplets in the aromatic and adamantyl proton areas but
no coalescence of the signals belonging to different isomers was
observed.
ometrical parameters of the Li[N{Si(NN)SiMe3}] and the
=
[NC(Ad) C(H)SiMe3-E] fragments of 8 are compared with those
3
in [Li(N{Si(NN)SiMe3}SiMe3)(tmeda)] 19 (Table 4a) and [Li{l,g -
N(SiMe3)C(Ad)C(H)SiMe3}]2 (1) (Table 4b), respectively. The
three-coordinate Li and C17(Ad) atoms of 8 are each in a distorted
trigonal planar environment, while the N3 atom is 0.16 A out
◦
1
˚
of the LiC17Si1 plane. The SiMe3 and Ad substituents in 8 are
=
arranged in a cisoid manner about the C C bond. The geometrical
parameters of the Li[N{Si(NN)SiMe3}] fragment of 8 are similar
to those of [Li(N{Si(NN)SiMe3}SiMe3)(tmeda)].19
In conclusion, the synthesis, structure and a variety of insertion
3–
and ligand transfer reactions of the crystalline dimeric l,g 1-
azaallyllithium compound 1 are described. These furnished in
high yield the new crystalline lithium, aluminium and tin(II)
complexes 2–8, five of which have been X-ray-characterised. The
3
preparation of [Sn{g -N(SiMe3)C(Ad)C(H)SiMe3}2] (7) by the
[N(SiMe3)2]−/[1-azaallyl]− exchange reaction points to the wider
use of metal bis(trimethylsilyl)amides. The reaction between 1 and
the silylene Si[(NCH2But)2C6H4-1,2] [abbreviated as Si(NN)] in
=
thf gave the crystalline lithium amide [Li(N{C(Ad) C(H)SiMe3-
E}{Si(NN)SiMe3})(thf)2] (8).
Experimental
General remarks
All manipulations were carried out under argon using standard
Schlenk and vacuum line techniques. Pentane and hexane were
dried using a sodium–potassium alloy; diethyl ether and thf
were dried and distilled from sodium–benzophenone. Solvents
were then stored over a sodium mirror under argon. The ni-
triles and methylaluminium chlorides were commercial samples.
The compounds Li[CH(SiMe3)2],9 Si[(NCH2But)C6H4-1,2] 15 and
Sn[N(SiMe3)2] 13 were prepared by published procedures. Apart
from 1H, the NMR spectra were proton-decoupled and were
recorded at 293 K in C6D6 unless otherwise stated on a Bruker
Fig. 7 ORTEP representation of the structure of 7 (50% thermal
ellipsoids).
Solutions of 8 in C6D6 were examined by various NMR spectral
experiments. At ambient temperature, the 1H NMR spectrum
showed three sets of signals, which were assigned to E-8 (major
3498 | Dalton Trans., 2008, 3493–3501
This journal is
The Royal Society of Chemistry 2008
©

◦
19
˚
Table 4 Selected bond lengths (A) and angles ( ) of (a) the Li[N{Si(NN)SiMe3}] fragment of 8 and of [Li(N(SiMe3){Si(NN)SiMe3})(tmeda)] and (b)
t
=
the [N–C(Ad) C(H)SiMe3] fragment of 8 and of 1 [Si(NN) = Si{(NCH2Bu )2C6H4-1,2}]
(a) Compound
8
[Li(N(SiMe3){Si(NN)SiMe3})(tmeda)] 19
Li–N3
Si1–N3
Si1–Si3
Li–N3–Si1
N3–Si1–Si3
1.942(4)
1.6683(17)
2.3791(8)
113.48(15)
115.09(6)
Li–N3
Si1–N3
Si1–Si2
Li–N3–Si1
N3–Si1–Si2
1.936(6)
1.656(3)
2.3849(11)
113.2(2)
109.76(12)
(b) Compound
8
1
N3–C17
C17–C18
1.391(3)
1.364(3)
N1–C1
C1–C2
1.403(2)
1.372(3)
N2–C19
C19–C20
1.396(2)
1.360(3)
C17–C25
C18–Si2
1.548(3)
1.850(2)
C1–C9
C2–Si2
1.544(3)
1.871(2)
C19–C27
C20–Si4
1.560(3)
1.855(2)
N3–C17–C18
N3–C17–C25
C17–C18–Si2
C18–C17–C25
123.22(18)
113.52(16)
141.69(17)
123.25(18)
N1–C1–C2
N1–C1–C9
C1–C2–Si2
C2–C1–C9
119.29(18)
117.55(16)
142.33(16)
123.13(17)
N2–C19–C20
N2–C19–C27
C19–C20–Si4
C20–C19–C27
122.42(18)
116.97(16)
133.34(17)
120.47(17)
DPX 300 (300.1 MHz for 1H, 75.5 MHz for 13C and 116.6 MHz
29.6, 37.1, 41.9, 44.1 (Ad), 108.0 (CH), 127.2–149.3 (C6H5), 178.0
7
7
for Li) or AMX 500 (131.3 MHz for 27Al, 99.4 MHz for 29Si
(NCPh), 184.0 (NCAd); Li-NMR: d 0.18; 29Si-NMR: d −17.7
and 186.5 MHz for 119Sn) instruments and referenced externally
(7Li using LiCl, 27Al using AlCl3 with a D2O lock, 29Si using
SiMe4, 119Sn using SnMe4) or internally to the residual solvent
resonances (1H, 13C). Electron impact mass spectra were taken
from solid samples using a Kratos MS 80 RF instrument. Melting
points were measured in sealed capillaries. Elemental analyses were
determined by Medac Ltd, Brunel University, UK.
(Me3SiNCPh), −4.4 (Me3SiNCAd). MS (M denotes the parent)
m/z (assignments, %): 289 ([M/2 - (Ad + H)]+, 100%).
[Li{l,j2-N(SiMe3)C(Ad)C(H)C(C6H4Me-4)NSiMe3}]2
(3).
As for 2, from 4-MeC6H4CN (0.70 cm3, 5.86 mmol) and 1
(1.90 cm3, 2.90 mmol) in diethyl ether (35 cm3) there were
obtained X-ray quality yellow crystals of 3 (1.46, 57%) (found:
C, 69.7; H, 9.41; N, 6.53. C52H82Li2N4Si4 requires C, 70.2; H,
9.30; N, 6.30%), mp 135–140 ◦C. 1H-NMR: d 0.15 [s, 9 H,
(CH3)3SiNC(Ph)], 0.49 [s, 9 H, (CH3)3SiNC(Ad)]; 1.67, 1.99 (2
broad s, 15 H, Ad), 2.06 (s, 3 H, CH3-C6H4), 5.98 (s, 1 H, CH),
6.93–7.32 (m, 4 H, C6H4); 13C-NMR: d 2.7 [(CH3)3SiNC(Ph)],
4.8 [(CH3)3SiNC(Ad)], 21.1 (CH3-C6H4); 29.6, 37.1, 41.7, 44.0
(Ad), 109.2 (CH); 126.7, 128.8, 137.7, 145.5 (C6H4), 181.3
Preparations
[Li{l,g3-N(SiMe3)C(Ad)C(H)SiMe3}]2 (1). A solution of 1-
cyanoadamantane (0.78 g, 4.8 mmol) in diethyl ether (ca.
8
cm3) was added to
a
cooled (−20 ◦C) solution of
bis(trimethylsilyl)methyllithium (0.80 g, 4.8 mmol) in Et2O
(15 cm3). The mixture was stirred at −20 ◦C for 20 min, then
set aside for ca. 16 h at 20 ◦C. Volatiles were removed in vacuo. The
colourless residue was dissolved in hot hexane (ca. 20 cm3). Cool-
ing at 20 ◦C afforded colourless crystals of 1 (1.13 g, 73%) (found:
C, 65.0; H, 10.69; N, 4.41. C36H68Li2N2Si4 requires C, 66.0; H,
10.46; N, 4.27%), mp 155–160 ◦C. 1H-NMR (C7D8): d 0.26 [s, 9 H,
CSi(CH3)3], 0.33 [s, 9 H, NSi(CH3)3], 1.63–2.02 (m, 15 H, Ad), 4.5
(s, 1 H, CH); 13C-NMR (C7D8): d1.0 [CSi(CH3)3], 5.3 [NSi(CH3)3];
29.6, 37.1, 42.4, 43.3 (Ad), 94.8 (CHSiMe3), 185.7 [C(Ad)NSiMe3];
7Li-NMR (C7D8): d −1.20 and −1.39; 29Si NMR (C7D8): d −14.8
and −14.4 (CSiMe3), −0.7 (NSiMe3). MS (M denotes the parent)
m/z (assignments, %): 321 ([M/2 - (Li + H)]+, 20%).
7
(NCPh), 186.7 (NCAd); Li-NMR: d 0.16; 29Si-NMR: d −15.7
(Me3SiNCPh), −1.9 (Me3SiNCAd). MS (M denotes the parent)
m/z (assignments, %): 303 ([M/2 - (Ad + H)]+, 100%).
[Al{j2-N(SiMe3)C(Ad)C(H)C(Ph)NSiMe3}Me2] (4). A one
molar solution of chloro(dimethyl)alane in hexanes (0.72 cm3,
0.72 mmol) was added dropwise to a suspension of 2 (0.31 g,
0.36 mmol) in hexane (20 cm3) at 0 ◦C, then stirred at 0 ◦C
for 30 min and set aside at 20 ◦C for ca. 16 h. The mixture
was filtered. Evaporation of volatiles in vacuo from the filtrate
furnished a yellow solid, which was freed from volatiles in vacuo
yielding the yellow powder 4 (0.32, 92%). Yellow, X-ray quality
crystals wer◦e isolated by cooling a concentrated pentane solution
of 4 at −18 C. 1H-NMR: d −0.13 [s, 6 H, (CH3)2Al], 0.04 [s, 9 H,
(CH3)3SiNC(Ph)], 0.47 [s, 9 H, (CH3)3SiNC(Ad)], 1.50–1.92 (m,
15 H, Ad), 6.03 (s, 1 H, CH), 6.94–7.15 (m, 5 H, C6H5); 13C-NMR:
d −5.8 [(CH3)2Al], 2.7 [(CH3)3SiNC(Ph)], 6.0 [(CH3)3SiNC(Ad)],
29.1, 36.6, 41.5, 44.7 (Ad), 112.8 (CH), 127.0–144.7 (C6H5), 180.6
(NCPh), 192.5 (NCAd); 27Al-NMR: d 154.5 (Dm1/2 ∼ 5 KHz);
29Si-NMR: d −0.62 (Me3SiNCPh), 8.43 (Me3SiNCAd).
[Li{l,j2-N(SiMe3)C(Ad)C(H)C(Ph)NSiMe3}]2 (2). Benzoni-
trile (0.40 cm3, 3.92 mmol) was added dropwise to◦a solution of 1
(1.30 g, 1.98 mmol) in diethyl ether (25 cm3) at 0 C. The yellow
mixture was stirred at 20 ◦C for ca. 16 h. Volatiles were removed in
vacuo leaving a residual yellow powder. Yellow crystals of 2 (1.50,
89%) (found: C, 69.1; H, 9.21; N, 6.56. C50H78Li2N4Si4 requires
◦
C, 69.7; H, 9.13; N, 6.50%), mp 155–160 C were obtained from
◦
1
a hot hexane solution by cooling to −18 C. H-NMR: d 0.12
[s, 9 H, (CH3)3SiNC(Ph)], 0.48 [s, 9 H, (CH3)3SiNC(Ad)]; 1.68,
2.01 (2 broad s, 15 H, Ad), 5.90 (s, 1 H, CH), 7.13–7.45 (m, 5 H,
C6H5); 13C-NMR: d2.9 [(CH3)3SiNC(Ph)], 4.9 [(CH3)3SiNC(Ad)];
3
1
=
[Al{g -N(SiMe3)C(Ad)C(H)SiMe3}{j -N(SiMe3)C(Ad) C(H)-
SiMe3-E}Me]
(5).
A
one
molar
solution
of
dichloro(methyl)alane in hexanes (2.20 cm3, 2.20 mmol) was
This journal is
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Dalton Trans., 2008, 3493–3501 | 3499
©

added dropwise to a solution of 1 (1.44 g, 2.2 mmol) in hexane
(50 cm3) at 0 ◦C, then stirred at 20 ◦C for ca. 16 h. The mixture was
filtered. Evaporation of volatiles in vacuo from the filtrate afforded
an off-white solid, which upon crystallisation from pentane at
−18 ◦C produced colourless crystals of 5 (1.00, 66%) (found:
C, 63.7 (duplicate analysis); H, 10.60; N, 4.15. C37H71AlN2Si4
requires C, 65.0; H, 10.47; N, 4.10%), mp 120–125 ◦C. 1H-NMR:
d −0.13 [s, 2.6 H, (CH3)Al]; 0.19, 0.26, 0.32 and 0.38 [bs, 36 H,
(CH3)3SiNC(Ad)], 1.69 (bs, 15 H, Ad), 1.96 (bs, 15 H, Ad), 4.83
(bs, 1 H, CH); 13C-NMR: d 2.1 [(CH3)2Al], 3.5, 4.0, 4.2 and 4.5
[(CH3)3SiNC(Ad)], 28.3, 29.2, 36.0, 36.9, 38.5, 40.9, 41.8, 43.9
=
and 44.7 (Ad), 115.3 (CH), 137.2 (N(R)C(Ad) C(H)R), 174.9
(NCPh), 192.5 (N(R)C(Ad)C(H)R); 27Al-NMR: d 127.3 (Dm1/2
∼
4.2 KHz); 29Si-NMR: d −10.27 (Me3SiC(H)), 5.19 and 6.05
(Me3SiNCAd). MS (M denotes the parent) m/z (assignments, %):
651 ([M - 2 Me]+, 40%), 531 ([M - Me - Ad]+, 60%), 186 (100%).
[Al{j2 -N(SiMe3 )C(Ph)C(H)C(Ad)NSiMe3 }{j1 -N(SiMe3 )C-
cm3,
=
(Ad) C(H)SiMe3-E}Me]
(6). Benzonitrile
(1.00
0.98 mmol) was added dropwise to a solution of 5 (0.65 g,
0.95 mmol) in hexane (12 cm3) at 0 ◦C. The mixture was set
aside at 20 ◦C for ca. 16 h. Removal of volatiles in vacuo
yielded the yellow powder 6 (0.62 g, 80%) (found: C, 65.7;
H, 9.50; N, 5.57. C44H76AlN3Si4 requires C, 67.2; H, 9.68; N,
5.35%), mp 170–172 ◦C. Yellow X-ray quality crystals were
obtained by crystallisation from Et2O at 20 ◦C. 1H-NMR:
d 0.09 (s, 3 H, CH3Al), 0.14 [s, 9 H, (CH3)3SiNC(Ph)], 0.37
[s, 9 H, (CH3)3SiC(H)], 0.45 [s, 9 H, (CH3)3SiNC(Ad)], 0.46
[s, 9 H, (CH3)3SiNC(Ad)], 1.56–2.19 (m, 30 H, Ad), 5.31 (s,
1 H, CHenamide.), 6.10 (s, 1 H, CHdiket.), 6.95–7.12 (m, 5 H,
C6H5); 13C-NMR: d −0.7 (CH3Al), 3.2 [(CH3)3SiNC(Ph)], 4.3
[(CH3)3SiCH], 5.7 [(CH3)3SiNC(Ad)], 6.5 [(CH3)3SiNC(Ad)];
29.1, 29.7, 36.7, 37.1, 41.4, 42.7, 44.8 (Ad), 116.6 (CH), 119.3
(CH), 127.5–143.3 (C6H5), 174.5 (NCPh), 183.0 (NCAdenamine),
189.5 (NCAddiket.); 27Al-NMR: d 124 (Dm1/2 ∼ 5.4 KHz); 29Si-
NMR: d -−14.72 [Me3SiC(H)], −5.17 (Me3SiNCAdenamide), −0.84
(Me3SiNCPh), 8.52 (Me3SiNCAddiket.). MS (M denotes the
parent) m/z (assignments, %): 770 ([M - (Me + H)]+, 3%), 465
([M - {RNC(Ad)C(H)R} - H]+, 100%).
[Sn{g3-N(SiMe3)C(Ad)C(H)SiMe3}2] (7). The homoleptic
bis(trimethylsilyl)amidotin(II) compound (0.53 g, 1.20 mmol) in
hexane (20 cm3) was added to a suspension of 1 (0.79 g, 1.20 mmol)
in hexane (40 cm3) at 20 ◦◦C. The resultant yellow solution was set
aside for ca. 16 h at 20 C. Partial removal of volatiles in vacuo
yielded yellow crystals of 7 (0.83 g, 90%) (found: C, 56.3; H, 9.08;
N, 3.86. C36H68N2Si4Sn requires C, 56.9; H, 9.02; N, 3.68%), mp
154–156 ◦C. 1H-NMR (C7D8): d0.23, 0.28, 0.30 [s, 18 H, Si(CH3)3],
0.46 [s, 10 H, Si(CH3)3], 1.62 and 1.74 (bs, 13 H, Ad), 1.88–1.95
(m, 12 H, Ad), 2.73 [s, 1.4 H, C(H)R], 4.65 [s, 0.4 H, C(H)R];
13C-NMR (C7D8): d0.6, 1.6, 2.1, 2.6 and 4.7 [(CH3)3Si], 29.1, 36.9,
40.6, 41.5, 45.4, 46.6 (Ad); 29Si NMR (C7D8): d −11.8, −11.5,
1.05 and 2.3; 119Sn-NMR (C7D8): d −377.3. MS (M denotes the
parent, L denotes the ligand) m/z (assignments, %): 760 ([M]+,
75%), 692 (15%), 572 (40%), 440 ([M–L]+, 75%), 321 ([L+ H]+,
55%), 306 ([L + H - Me]+, 50%), 217 ([L + H-2Me]+, 50%), 186 ([L
+ 2 H–Ad]+, 50%).
t
=
[Li(N{C(Ad) C(H)SiMe3}{Si((NCH2Bu )2C6H4-1,2)SiMe3})-
(thf)2] (8). The azaallyllithium compound 1 (0.48 g, 0.73 mmol)
3500 | Dalton Trans., 2008, 3493–3501
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The Royal Society of Chemistry 2008
©

in thf (15 cm3) was added dropwise to the benzo-1,2-
di(neopentylamino)silylene (IX) (0.40 g, 1.46 mmol) in thf (20 cm3)
at −30 ◦C. Volatiles were removed in vacuo yielding a cream solid
(1.13 g) which was dissolved in hot hexane (5 cm3) and afforded
upon cooling white crystals of 8 (0.99, 90%) (found: C, 66.7; H,
10.11; N, 6.13. C42H76LiN3O2Si3 requires C, 67.6; H, 10.26; N,
5.63%), mp 119–121 ◦C. 1H-NMR: d0.08 and 0.18 (two s, [E-8]H),
0.31 and 0.47 (two s, Z-8), 0.41 and 0.52 (two s, E-8) (together 18
H, SiMe3); 1.08 (s, H[8]), 1.17 (s, E-8) and 1.32 (s, Z-8) (together 18
H, But); 1.26 (br s, 8 H, thf); 1.52–2.12 (br multiplets, 15 H, Ad),
3.56 (br s, 8 H, thf), 3.08–3.47 (3 AB systems partly overlapped
with thf, 4 H, CH2But); 4.02 (br s, NH of H[8]); 4.04, 4.13 and
Dr B. Gehrhus for a gift of the silylene Si[(NCH2But)2C6H4-
1,2], Dr A. G. Avent for NMR spectral data on 8 and
Dr A. V. Protchenko for useful discussion.
Notes and references
1 (a) J. K. Whitesell and M. A. Whitesell, Synthesis, 1983, 517; (b) A. Job,
C. F. Janeck, W. Bettray, R. Peters and D. Enders, Tetrahedron, 2002,
58, 2253 and references therein.
2 S. Mangelinckx, N. Giubellina and N. De Kimpe, Chem. Rev., 2004,
104, 2353.
3 M. Ahmed, A. M. Seayad, R. Jackstell and M. Beller, Angew. Chem.,
Int. Ed., 2003, 42, 5615.
4 C. F. Caro, M. F. Lappert and P. G. Merle, Coord. Chem. Rev., 2001,
219–221, 605.
5 P. B. Hitchcock, M. F. Lappert and D.-S. Liu, J. Chem. Soc., Chem.
Commun., 1994, 2637.
6 P. B. Hitchcock, M. F. Lappert, M. Layh, D.-S. Liu, R. Sablong and T.
Shun, J. Chem. Soc., Dalton Trans., 2000, 2301.
7 P. B. Hitchcock, J. Hu, M. F. Lappert, M. Layh and J. R. Severn, Chem.
Commun., 1997, 1189.
8 (a) C. Cui, H. W. Roesky, M. Noltemeyer, M. F. Lappert, H.-G. Schmidt
and H. Hao, Organometallics, 1999, 18, 2256; (b) L. Bourget, P. B.
Hitchcock and M. F. Lappert, J. Chem. Soc., Dalton Trans., 1999,
2645.
9 N. Wiberg and G. Wagner, Chem. Ber., 1986, 119, 1455.
10 (a) L. Bourget, P. B. Hitchcock, and M. F. Lappert, cited as un-
published work in ref. 4; (b) R. J. Bowen, M. A. Fernandes, P. W.
Gitari, M. Layh and R. M. Moutloali, Eur. J. Inorg. Chem., 2005,
1955.
=
4.29 [s, 1 H, C C(H)SiMe3]; 6.7, 6.8 and 6.9 (multiplets, 4 H,
C6H4); 13C-NMR: d 0.5, 2.7 and 4.8 (SiMe3), 25.1 (thf), 29.7, 29.0,
34.4, 36.9, 37.7, 41.8, 42.9, 57.1, 68.3 (thf), 94.9, 108.2, 109.6,
7
=
116.7, 117.8 and 143.8 (C6H4), 177.9 (C CHR); Li-NMR: d 0.76
and 0.18; 29Si-NMR (inverse gated): d −9.9, −12.6, −14.9, −17.3,
−18.1, −22.0, −24.7, −27.4, −37.4. MS (M denotes the parent)
m/z (assignments, %): 595 ([M–Li-2 thf]+, 60), 580 ([M–Li - 2
thf - MeH]+, 50), 522 ([M–Li-2 thf - SiMe3]+, 45), 347 ([M–Li-2
thf -{NNp}2C6H4-1,2)]+, 20).
Crystal data and refinement details for 1 and 3–8†
Diffraction data for each compound were collected on an Enraf-
Nonius Kappa-CCD diffractometer, using monochromated Mo
11 F. Cosle´dan, P. B. Hitchcock and M. F. Lappert, Chem. Commun., 1999,
705.
˚
Ka radiation, k 0.71073 A. Crystals were directly mounted on
12 L. Bourget-Merle, P. B. Hitchcock and M. F. Lappert, J. Organomet.
Chem., 2004, 689, 4357.
13 P. J. Davidson, D. H. Harris and M. F. Lappert, J. Chem. Soc., Dalton
Trans., 1976, 2268.
14 N. Nimitsiriwat, V. C. Gibson, E. L. Marshall, A. J. P. White,
S. H. Dale and M. R. J. J. Elsegood, Dalton Trans., 2007,
4464.
15 B. Gehrhus, P. B. Hitchcock, M. F. Lappert, J. Heinicke, R. Boese and
D. Bla¨ser, J. Organomet. Chem., 1996, 521, 211.
16 (a) A. G. Avent, B. Gehrhus, P. B. Hitchcock and H. Maciejewski,
J. Organomet. Chem., 2003, 686, 321; (b) X. Cai, B. Gherhus,
P. B. Hitchcock and M. F. Lappert, Can. J. Chem., 2000, 78,
1484.
the diffractometer under a stream of cold nitrogen gas. For 3,
the hexane solvate was disordered across an inversion centre; it
was included with its C atoms (the terminal C atom was not
located) having a common isotropic displacement parameter, the
H atoms were omitted: 1,2-C–C distances were restrained to be
equal, as were 1,3 C · · · C distances. For 6, there was disorder
of the substituent at Al: 90% methyl at C37 and 10% with a Cl
atom in that position; the disorder was not resolved. Absorption
correction was applied for 7 only. The structures were refined on
all F2 using SHELXL-97.20 Further details are given in Table 5.
Illustrations of structures are shown using ORTEP-3 for Windows.
17 X. Cai, B. Gehrhus, P. B. Hitchcock, M. F. Lappert and J. C. Slootweg,
J. Organomet. Chem., 2002, 643–644, 272.
18 B. Gehrhus, P. B. Hitchcock and M. Parruci, Dalton Trans., 2005,
2720.
19 F. Antolini, B. Gehrhus, P. B. Hitchcock, M. F. Lappert and J. C.
Slootweg, Dalton Trans., 2004, 3288.
20 G. M. Sheldrick, SHELXL-97, Program for refinement of crystal
structures, University of Go¨ttingen, Germany, 1997.
Acknowledgements
We gratefully acknowledge the European Commission for the
award of Marie Curie fellowships to both L. B.-M. and P. G. M.,
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 3493–3501 | 3501
©