Nucleophilic addition to a Sn(II) imido cubane, [SnNR]4; a new route to heteroleptic stannates

Article abstract of DOI:10.1039/b204340h

Nucleophilic addition to Sn(II) imido cubanes provides a novel route to heteroleptic stannates, as exemplified by the formation of [{Sn(NHmmp)(O'Bu)₂}K·thf]₂ and [{Sn(MeNCH₂CH₂NMe)(NHmmp)}Li]_∞ (3) from the in situ reactions of the imido Sn(II) cubane [Sn(Nmmp)]₄ (1) (mmp = 2-MeO-6-MeC₆H₃) with 'BuOK and [MeN(Li)CH₂CH₂(Li)NMe]. This pathway demonstrates that Sn(II) imido cubanes can act as synthons for their aza-stannylene constituents, RN=Sn:.

Full text of DOI:10.1039/b204340h

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Nucleophilic addition to a Sn(II) imido cubane, [SnNR]4;
a new route to heteroleptic stannates
Andrew D. Bond,a Eilís A. Harron,a Gavin T. Lawson,a Marta E. G. Mosquera,b
Mary McPartlinc and Dominic S. Wright*a
a Chemistry Department, University of Cambridge, Lensfield Road, Cambridge, UK CB2 1EW.
E-mail: dsw1000@cus.cam.ac.uk
b Department of Organic and Inorganic Chemistry, Universidad de Oviedo, Oviedo, 33071, Spain
c School of Chemistry, University of North London, London, UK N7 8DB
Received 3rd May 2002, Accepted 8th July 2002
First published as an Advance Article on the web 12th August 2002
Nucleophilic addition to Sn() imido cubanes provides a novel route to heteroleptic stannates, as exemplified by the
formation of [{Sn(NHmmp)(OtBu)2}Kؒthf]2 (2) and [{Sn(MeNCH2CH2NMe)(NHmmp)}Li]∞ (3) from the in situ
reactions of the imido Sn() cubane [Sn(Nmmp)]4 (1) (mmp = 2-MeO-6-MeC6H3) with tBuOK and
[MeN(Li)CH2CH2(Li)NMe]. This pathway demonstrates that Sn() imido cubanes can act as
synthons for their aza-stannylene constituents, RN᎐Sn:.
᎐
cubanes of this type can behave as synthons for the stannylene
monomer.
Introduction
Sn() imido cubanes, [SnNR]4, were first investigated by Veith
in the early 1980s.1 These species can be readily prepared by the
reactions of bases [such as Me2Si(NMe)2Sn,1 Sn{N(SiMe3)2}2
2
Results and discussion
3
and Sn(NMe2)2 ] with primary amines (RNH2) and the reac-
In light of the ability of [Sn(Nmmp)]4 (1) to coordinate a
Sn(NMe2)2 monomer unit within the structure of [{Sn-
(Nmmp)}2{(Me2N)2Sn}],9 it was decided to investigate the
reactions of 1 with a range of nucleophiles. The reactions of
1 with tBuOK (1 equiv.) and MeN(Li)CH2CH2N(Li)Me
(1 equiv.)10 both occur smoothly in thf, giving the products
[{Sn(NHmmp)(OtBu)2}Kؒthf]2 (2) (79% based on Sn) and
[{Sn(MeNCH2CH2NMe)(NHmmp)}Li]∞ (3) (14%), respec-
tively (Scheme 2). For convenience, 1 was prepared by the in situ
reaction of Sn(NMe2)2 with mmpNH2 (1 : 1 equiv.),4 prior to
reaction with the mono- and di-nucleophiles. The initial choice
of this procedure proved fortunate since later attempts to
obtain the same products from the reactions of isolated samples
of 1 with the same nucleophiles were unsuccessful. The reason
for this failure became clear from 1H and IR spectroscopic
studies of 2 and 3. These reveal the presence of NHmmp
groups in both complexes, resulting presumably from the pro-
tonation of the imido group (mmpN2Ϫ) by Me2NH [generated
as a byproduct in the formation of 1 from Sn(NMe2)2 with
mmpNH2]. Preliminary analytical and spectroscopic investi-
gations also showed that the Kϩ ions of 2 are solvated by a
thf ligand whereas the Liϩ cations of 3 are not solvated in this
manner.
tions of RNHϪ 4 or RN2Ϫ 5 anions with sources of Sn(). Until
recently, it appeared that such cubanes were chemically robust.
For example, the reactions of [SnNR]4 (R = tBu or SiMe3) with
metal salts or transition metal carbonyls result in coordination
of the Sn() lone-pairs to the metal centres, with no breakdown
of the Sn4N4 cores occurring.6 The only known reactions in
which breakdown of the Sn4N4 core occurs are those involving
alkali metal primary amides and phosphides (RЈEHM, E = N,
P; M = alkali metal).7 It was reported earlier, however, that the
presence of Sn(OtBu)2 during the formation of the cubane
[SnNtBu]4 gives [{SnNtBu}2{(OtBu)2Sn}], in which the dimeric
constituents of the cubane, [SnNtBu]2, have been intercepted.8
More recently we have observed that the stability of the cubane
core can depend on the organic substituent (R).9 For example,
addition of [Sn(NMe2)2] to the intact cubane [Sn(Nmmp)]4
(1) (mmp = 2-MeO-6-MeC6H3) results in the co-complex [{Sn-
(Nmmp)}2{(Me2N)2Sn}], again containing an apparently
‘trapped’ dimer unit. This intriguing observation has prompted
us to wonder to what extent (as Veith had first suggested) the
cubanes [SnNR]4 can be regarded as oligomeric aza-stannyl-
enes, [:Sn᎐NR] (Scheme 1).
᎐
The formation of 2 and 3 corresponds formally to nucleo-
philic addition to the Sn centre of the stannylene mmpN᎐Sn:
᎐
(see Scheme 1). However, it is unlikely that this stannylene has
any real existence in solution. Studies of the reactions of
Sn(NMe2)2 with sterically demanding primary amines suggest
that the formation of Sn4N4 cubanes occurs through a series of
oligomers rather than via oligomerisation of stannylenes.11 We
believe that a more plausible mechanism for the formation of
2 and 3 therefore involves step-wise breakdown of the Sn4N4
cubane core of 1 (as illustrated in Scheme 3). Attempts to
explore the mechanism of the reaction using in situ 119Sn NMR
spectroscopic studies proved inconclusive. It should be noted
that 2 can also be prepared in much reduced yield (15%) by the
Scheme 1 The hypothetical dissociation of a [SnNR]4 cubane into
monomers.
We report here that the cubane 1 readily undergoes addition
reactions with mono- and di-nucleophiles, leading to frag-
mentation of the Sn4N4 core and the formation of heteroleptic
stannates. This new reaction illustrates that imido Sn()
t
reaction of a mixture of Sn(NMe2)2 and BuOK (1 : 2 equiv.)
DOI: 10.1039/b204340h
J. Chem. Soc., Dalton Trans., 2002, 3525–3528
This journal is © The Royal Society of Chemistry 2002
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Scheme 2 The reactions producing 2 and 3.
Table 1 Key bond lengths (Å) and angles (Њ) for [{Sn(NHmmp)-
(OtBu)2}Kؒthf]2 (2)a
Sn(1)–O(3)
Sn(1)–O(2)
Sn(1)–N(1)
K(1)–O(1)
K(1)–N(1)
2.082(2)
2.086(2)
2.154(2)
3.075(2)
2.905(2)
K(1)–O(2)
K(1)–O(2A)
K(1)–O(3A)
K(1)–O(4)
2.734(2)
2.890(2)
2.688(2)
2.799(2)
N(1)–Sn(1)–O(2)
N(1)–Sn(1)–O(3)
O(2)–Sn(1)–O(3)
N(1)–K(1)–O(2)
N(1)–K(1)–O(4)
N(1)–K(1)–O(1)
N(1)–K(1)–O(2A)
N(1)–K(1)–O(3A)
O(1)–K(1)–O(2)
O(1)–K(1)–O(2A)
O(1)–K(1)–O(4)
O(1)–K(1)–O(3A)
90.89(8)
83.82(8)
88.08(7)
64.70(6)
100.68(7)
52.10(6)
91.03(6)
153.83(6)
70.20(6)
143.04(6)
74.29(7)
153.83(6)
O(2)–K(1)–O(2A)
O(2)–K(1)–O(4)
93.47(5)
143.05(7)
121.65(7)
110.22(6)
62.46(5)
97.17(7)
97.48(8)
107.70(7)
104.65(7)
100.81(6)
86.53(5)
O(2A)–K(1)–O(4)
O(2)–K(1)–O(3A)
O(2A)–K(1)–O(3A)
O(4)–K(1)–O(3A)
Sn(1)–N(1)–K(1)
Sn(1)–O(3)–K(1A)
Sn(1)–O(2)–K(1)
Sn(1)–O(2)–K(1A)
K(1)–O(2)–K(1A)
Scheme 3 A plausible mechanism for nucleophilic addition to the
cubane core.
with NH2mmp in thf. We believe that this reaction probably
also occurs via 1, which is formed rapidly in the reaction of
Sn(NMe2)2 with mmpNH2 even at low temperatures. In view
of the fact that 2 was obtained using the 1 : 1 : 1 reaction
a Symmetry transformations used to generate equivalent atoms labelled
A: Ϫx, Ϫy, Ϫz ϩ 2.
t
of Sn(NMe2)2, mmpNH2 and BuOK (the reaction actually
Table 2 Key bond lengths (Å) and angles (Њ) for [{Sn(MeNCH2CH2-
NMe)(NHmmp)}Li]∞ (3)a
requiring a 1 : 1 : 2 stoichiometry), we reasoned that the use
of a more sterically demanding alkoxide may allow us to trap
an intermediate of type I in Scheme 3. However, no reactions
occur between 1 and the sterically demanding aryloxides
MesOLi and Mes*OLi (Mes = 2,4,6-Me3C6H2, Mes* = 2,4,6-
tBu3C6H2) and only the cubane 1 or the lithium alkoxide com-
plexes could be isolated. This suggests that these nucleophiles
are simply too sterically bulky to allow approach at the Sn()
centres of 1.
Low-temperature (180 K) X-ray crystallographic studies
were undertaken on 2 and 3. Details of the data collections
and refinements are presented in Table 3, with key bond lengths
and angles for 2 and 3 being listed in Tables 1 and 2, respec-
tively.
Sn(1)–N(1)
Sn(1)–N(2)
Sn(1)–N(3)
Sn(1) ؒ ؒ ؒ Li(1A)
2.213(2)
2.147(2)
2.156(2)
3.278(5)
Li(1)–N(1)
Li(1)–N(3)
Li(1)–O(1)
Li(1)–N(2B)
2.065(5)
2.043(5)
2.080(5)
2.023(5)
N(1)–Sn(1)–N(2)
N(1)–Sn(1)–N(3)
N(2)–Sn(1)–N(3)
N(1)–Li(1)–O(1)
N(1)–Li(1)–N(3)
91.19(9)
86.70(8)
81.11(8)
77.6(2)
O(1)–Li(1)–N(3)
Li(1)–N(1)–Sn(1)
Li(1)–N(3)–Sn(1)
Sn(1)–N(2)–Li(1A)
103.4(2)
85.4(2)
87.4(2)
103.6(2)
93.8(2)
a Symmetry transformations used to generate equivalent atoms labelled
A: Ϫx ϩ 3/2, y ϩ 1/2, Ϫz ϩ 3/2; B: Ϫx ϩ 3/2, y Ϫ 1/2, Ϫz ϩ 3/2.
Molecules of 2 consist of centrosymmetric dimers, of for-
mula [{Sn(NHmmp)(OtBu)2}Kؒthf]2 (2), which result from the
association of two [Sn(NHmmp)(OtBu)2]Ϫ stannate ions with
two thf-solvated Kϩ cations (Fig. 1). Metal coordination by the
most closely related complexes to 2 are the dimeric, trisalkoxy-
stannates [{Sn(OtBu)3}2M2] (M = Li, Na).12 In 2, N(1) and O(3)
bond to the two separate, symmetry related, Kϩ ions, with
bridge bonding of O(2) forming the central K2O2 ring. A
similar metal-coordination mode by the three O centres of
the stannate ions in [{Sn(OtBu)3}2M2] (M = Li, Na) leads to
the same type of core structure. However, unlike the heavier
alkali metal complexes containing the [Sn(OtBu)3]Ϫ ligand,
[{Sn(OtBu)3}M]∞ (M = K, Rb, Cs), where polymerisation of
the dimer units occurs, the MeO/N chelation of the mmpNH
group to the Kϩ cations (as well as thf-solvation) ensures that a
molecular structure is retained for 2.
The pyramidal geometry of the [Sn(NHmmp)(OtBu)2]Ϫ
stannate ions of 2 [with O–Sn–O and N–Sn–O angles of
83.82(8)–90.89(8)Њ] is symptomatic of the presence of a stereo-
chemically active lone-pair on Sn(). The noticeable com-
pression of N(1)–Sn(1)–O(3) [83.82(8)Њ] well below 90Њ results
primarily from the bonding of N(1) and O(3) to the separate
Kϩ cations of the central K2O2 ring unit. However, there are no
obvious associated effects on the Sn–O [mean 2.084(2) Å] and
Sn–N [Sn(1)–N(1) 2.154(2) Å] bond lengths within the stannate
anion, which are typical of those previously observed for N
and O bonds to three-coordinate Sn().13 In particular, the
Fig. 1 Structure of centrosymmetric dimer molecules of 2.
stannate ions using their N and two O centres (as well as by thf )
results in a cage structure containing a central K2O2 ring,
possessing a very distorted six-coordinate geometry for the Kϩ
cations [O–K–O and N–K–O range 62.46(5)–153.83(6)Њ]. The
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Table 3 Crystal data and structural refinements for [{Sn(NHmmp)(OtBu)2}Kؒthf]2 (2) and [{Sn(MeNCH2CH2NMe)(NHmmp)}Li]∞ (3)
Compounda
2
3
Empirical formula
Formula weight
C40H72K2O8N2Sn2
1024.58
C12H17LiN3OSn
344.92
Crystal system
Space group
Monoclinic
P21/n
Monoclinic
P21/n
a/Å
b/Å
11.9548(3)
12.5067(4)
9.3386(2)
9.7200(3)
c/Å
16.5675(5)
92.344(2)
2475.02(13)
2
1.375
17.1794(6)
97.946(2)
1544.42(8)
4
β/Њ
V/Å3
Z
ρcalc/Mg mϪ3
1.483
Independent reflections (Rint
R indices [I > 2σ(I )]
R indices (all data)
)
4347 (0.035)
R1 = 0.028, WR2 = 0.068
R1 = 0.037, WR2 = 0.073
3505 (0.046)
R1 = 0.028, WR2 = 0.070
R1 = 0.038, WR2 = 0.075
a Data in common; λ = 0.71073 Å; T = 180(2) K.
mean Sn–O bond lengths in 2 are similar to those found in the
solid-state structure of [{Sn(OtBu)3}K]∞ (mean 2.067 Å).12
Although the range of K–O bond lengths found in 2 [2.688(2)–
3.075(2) Å] is comparatively large, these distances are within the
values found previously in K alkoxides and for donor-type K–O
bonds.14 The K(1)–N(1) bond length [2.905(2) Å] is also typical
of K amides.14
The solid-state structure of 3 is that of a polymer composed
of [{Sn(MeNCH2CH2NMe)(NHmmp)}Li] monomer units
(Fig. 2a) which aggregate via N–Li bonding (Fig. 2b). Like 2,
the range of angles about the Sn() centre of the [Sn(Me-
NCH2CH2NMe)(NHmmp)]Ϫ anion is fairly typical of struc-
turally characterised stannates [for 3, N–Sn–N range 81.11(8)–
91.19(9)Њ]. The most acute N–Sn–N angle is N(2)–Sn(1)–N(3),
reflecting the small ligand bite of the Sn-chelating [MeNCH2-
CH2NMe] diamide. The Liϩ cations within each monomer unit
of 3 are bonded to the [Sn(MeNCH2CH2NMe)(NHmmp)]Ϫ
anion by one of the anionic N centres of the chelating
[MeNCH2CH2NMe] group [N(3)–Li(1) 2.043(5) Å], and the
anionic N [N(1)–Li(1) 2.065(5) Å] and neutral MeO [O(1)–Li(1)
2.080(5) Å] centres of the mmpNH group. The four-coordinate,
pseudo-tetrahedral geometry of the Liϩ cations is completed
by inter-monomer bonding with the second N centre of the
chelating [MeNCH2CH2NMe] diamide ligand of an adjacent
molecule [Li(1)–N(2B) 2.023(5) Å], an interaction which is
responsible for the formation of a polymeric structure for 3.
The overall structure of polymeric strands of 3 is that of a
helical chain formed by the association of molecules related by
the crystallographic 21 axis (Fig. 2b). Adjacent chains, related
by inversion symmetry, consist of the opposite enantiomers.
This arrangement has a similar connectivity to that found for
[{Sn(NMe2)3}Li]∞ in the solid state.15
Fig. 2 (a) Structure of monomer units of 3, and (b) propagation of the
polymer chain along the crystallographic 21 axis parallel to the b-axis of
the unit cell.
Apart from providing unambiguous proof of the success of
t
the addition reactions of BuOK and [MeNCH2CH2NMe]-
Li2 to the cubane 1, the structures of 2 and 3 also possess
several novel features. Perhaps most importantly, to our
knowledge, these are the first structurally characterised hetero-
leptic stannates. The closest representative of this type to be
reported previously is [Cp2SnN(SiMe3)2LiؒPMDETA].16 How-
ever, although formally containing the heteroleptic [Cp2{(Me3-
Si)2N}Sn]Ϫ anion, this is better regarded as a ‘loose-contact’
complex between Cp2Sn and LiN(SiMe3)2 (into which it dis-
sociates significantly in solution). A further noteworthy feature
of 3 is the first observation of a chelating, dianionic substituent
within a stannate anion.
The new synthetic approach reported here should provide
access to a broad range of new heteroleptic stannates. A future
aim of these studies will be to explore the potential for attack of
metal-based nucleophiles in the synthesis of transition metal/
Sn() clusters, e.g., mono-nucleophiles such as [(CO)5Mn]Ϫ and
di-nucleophiles such as [(CO)4Fe]2Ϫ. A particular future pro-
spect is the observation of alkene-like, [Sn᎐NR], isonitrile-like,
᎐
Ϫ
ϩ
᎐
[Sn ᎐N R], and butadiene-like, [SnNR] , fragments within
᎐
2
these systems.
Experimental
General
Compounds 1–3 are air- and moisture-sensitive. They were
handled on a vacuum line using standard inert-atmosphere
techniques and under dry/oxygen-free argon.17 Toluene and thf
were dried by distillation over sodium/benzophenone prior to
the reactions. The products were isolated and characterized
with the aid of a nitrogen-filled glove box fitted with a Belle
Technology O2 and H2O internal recirculation system.
Sn(NMe2)2 was prepared using the literature procedure, from
the reaction of anhydrous SnCl2 with a suspension of LiNMe2
J. Chem. Soc., Dalton Trans., 2002, 3525–3528
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in Et2O.18 The amine 2-methoxy-6-methylaniline (mmpNH2)
and MeN(H)CH2CH2N(H)Me were acquired from Aldrich and
were used as supplied. Melting points were not corrected.
Elemental analyses were performed by first sealing the samples
under argon in air-tight aluminium boats (1–2 mg) and C, H
and N content was analysed using an Exeter Analytical CE-440
Elemental Analyser. Proton NMR spectra were recorded on a
Bruker AM 400 MHz spectrometer in dry deuterated DMSO
(using the solvent resonances as the internal reference
standard).
2.24 (s, 4H, CH2CH2), 2.06 (s, 3H, Me–N), Elemental analysis,
found C 41.2, H 5.8, N 12.0; calc., for 3, C 41.4, H 5.8, N 12.1%.
X-Ray crystallographic studies of 2 and 3
Crystals of 2 and 3 were mounted directly from solution under
argon using an inert oil which protects them from atmospheric
oxygen and moisture.19 X-Ray intensity data for both com-
plexes were collected using a Nonius Kappa CCD diffrac-
tometer. Details of the data collections and structural
refinements are given in Table 3. The structures were solved by
direct methods and refined by full-matrix least squares on F 2.20
CCDC reference numbers 185248 and 185249.
Synthesis of 2
Method A. A solution of 1 (1.0 mmol) was prepared by the
reaction of 2-methoxy-6-methylaniline (0.88 ml, 8.0 mmol)
with Sn(NMe2)2 (1.66 g, 8.0 mmol) in thf (40 ml) at Ϫ78 ЊC.
The suspension of 1 produced after warming to room tempera-
ture was dissolved by gentle heating. The solution was added to
a solution of tBuOK (0.90 g, 8.0 mmol) in thf (20 ml) at Ϫ78 ЊC.
The reaction was brought to room temperature and a small
quantity of insoluble white precipitate was removed by filtra-
tion (Celite, P3). The solvent volume was reduced to less than
10 ml and the golden brown solution was stored at Ϫ5 ЊC.
Colourless crystalline blocks of 2 grew after 7–14 days. Yield
1.62 g (79% based on Sn). Mp 112–114 ЊC to a brown oil. IR
(Nujol, NaCl), ν/cmϪ1 = 3355(w) (N–H str.), other bands at
See http://www.rsc.org/suppdata/dt/b2/b204340h/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
We garefully acknowledge the EPSRC (A. D. B., E. A. H.,
G. T. L.) and Ministrerio de Ciencia y tecnologia (Acciones
Integradas HB1999-009) (M. E. G. M.) for financial support.
We also thank Dr J. E. Davies for collecting X-ray data.
References and notes
1
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1054; (c) M. Veith and G. Schlemmer, Chem. Ber., 1982, 115, 2141.
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8 M. Veith and W. Frank, Angew. Chem., Int. Ed. Engl., 1984, 23, 158.
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1205(s), 1073(s), 940(s), 838(m), 733(s). H NMR (D6-DMSO,
ϩ25 ЊC, 400.129 MHz), δ = 6.65 [d, J = 4 Hz, 1H, C(3)–H of
mmp group], 6.57 [d, J = 4 Hz, 1H, C(5)–H of mmp group],
6.45 [dd, J = 4 Hz, 1H, C(4)–H], 5.34 (s., 1H, N–H), 3.74 (s, 3H,
2-MeO), 3.60 (m, ca. 3H, thf ), 2.06 (s, 3H, 6-Me), 1.76 (m,
t
ca. 3H, thf ), 1.17 (s, 18H, BuO). Elemental analysis, found
C 44.9, H 6.3, N 2.8; calc., for 2ؒthf, C 45.4, H 6.8, N 2.9%.
Method B. 2-Methoxy-6-methylaniline (0.4 ml, 4.0 mmol)
was added to a solution of Sn(NMe2)2 (0.83 g, 4.0 mmol) and
tBuOK (0.45 g, 4.0 mmol) in thf (40 ml) at Ϫ78 ЊC, producing
a pale yellow solution. The reaction was brought to room
temperature and a small quantity of insoluble white precipitate
was removed by filtration (Celite, P3). The solvent volume was
reduced to less than 10 ml and the golden brown solution was
stored at Ϫ5 ЊC. Colourless crystalline blocks of 2 grew after 7
days. Yield 0.18 g (15% based on Sn).
10 Although, to our knowledge, the structure of this dianion has not
been investigated, there are a number of well characterised relatives,
see D. R. Armstrong, D. Barr, A. T. Brooker, W. Clegg, K. Gregory,
S. M. Hodgson, R. Snaith and D. S. Wright, Inorg. Chem., 1990, 29,
410; M. G. Gardiner and C. L. Raston, Inorg. Chem., 1995, 34, 4206;
M. G. Gardiner and C. L. Raston, Inorg. Chem., 1996, 35, 4047;
M. G. Gardiner and C. L. Raston, Inorg. Chem., 1996, 35, 4162.
11 M. A. Beswick, R. E. Allan, M. A. Paver, P. R. Raithby, A. E. H.
Wheatley and D. S. Wright, Inorg. Chem., 1997, 36, 5202.
12 M. Veith and R. Rosler, Z. Naturforsch., Teil B, 1986, 41, 1071.
13 Search of the Cambridge Crystallographic Data Base; for three
coordinate Sn(): mean Sn–O 2.12 Å, mean Sn–N 2.20 Å.
14 Search of the Cambridge Crystallographic Data Base; mean
K–O 2.82 Å (range 2.32–3.42 Å), mean K–N 2.94 Å.
15 M. A. Beswick, S. J. Kidd, P. R. Raithby and D. S. Wright, Inorg.
Chem. Commun., 1999, 2, 419.
16 M. A. Paver, C. A. Russell, D. Stalke and D. S. Wright, J. Chem.
Soc., Chem. Commun., 1993, 1349.
17 D. F. Shriver and M. A. Drezdon, The Manipulation of Air-Sensitive
Compounds, 2nd edn., Wiley, New York, 1986.
18 M. M. Olmstead and P. P. Power, Inorg. Chem., 1984, 23, 413.
19 T. Kottke and D. Stalke, J. Appl. Crystallogr., 1993, 26, 615.
20 G. M. Sheldrick, SHELXTL 97, Göttingen, 1997.
Synthesis of 3
A solution of 1 (1.0 mmol) was prepared by the reaction of 2-
methoxy-6-methylaniline (0.4 ml, 4.0 mmol) with Sn(NMe2)2
(0.83 g, 4.0 mmol) in thf (20 ml) at Ϫ78 ЊC. The suspension of
1 produced after warming to room temperature was heated
gently into solution. This solution was added to a solution of
MeN(Li)CH2CH2N(Li)Me (4.0 mmol) at Ϫ78 ЊC [prepared
previously by the reaction of MeNHCH2CH2NMe (0.4 ml,
4.0 mmol) with BuLi (5.2 ml, 1.5 mol dmϪ3, 8.0 mmol) in thf
n
(20 ml)]. The reaction mixture was brought to room tempera-
ture and stirred for 2 h. A small quantity of insoluble precipi-
tate was then removed by filtration (Celite, P3), and the solvent
volume reduced to ca. 20 ml. Colourless crystalline blocks of 3
were formed after storage at Ϫ5 ЊC (24 h). Yield 0.20 g (14%).
Decomp. to a black solid 193 ЊC. IR (Nujol, NaCl), ν/cmϪ1
=
3584(w), 3482(w), 3391(w) (N–H str.), other bands at 1238(m),
1170(m), 1093(s), 1068(s), 1018(s), 780(s), 758(m), 726(s). H
NMR (D6-DMSO, ϩ25 ЊC, 400.129 MHz), δ = 6.55–6.40 [m
(overlapping doublets), 3H, aromatic C–H], 3.51 (s, 3H, MeO),
1
3528
J. Chem. Soc., Dalton Trans., 2002, 3525–3528