A solid-state, solution, and theoretical structural study of kinetic and thermodynamic lithiated derivatives of a simple diazomethane and their reactivities towards aryl isothiocyanates

Article abstract of DOI:10.1002/ejic.200300244

(Trimethylsilyl)diazomethane (1-H) reacts with nBuLi in THF at elevated temperature to afford (previously reported) 1-Li·3/2 THF. However, reaction in hexane/TMEDA at low temperature affords instead the N-lithiate Me₃SiCNNLi·TMEDA (9), which is a novel open pseudo-cubic tetramer in the solid state. Variable-temperature NMR spectroscopy suggests that N-metallated 9, apparently the kinetic product of the reaction, irreversibly rearranges at high temperature in solution to give the thermodynamically preferred C-lithiated isomer. These observations, supported by DFT calculations, influence our understanding of the reactivity of lithiated diazomethanes towards aryl isothiocyanates, suggesting as they do that previously observed product selectivity in these reactions is critically dependent on temperature control exercised during the process. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).

Full text of DOI:10.1002/ejic.200300244

FULL PAPER
A Solid-State, Solution, and Theoretical Structural Study of Kinetic and
Thermodynamic Lithiated Derivatives of a Simple Diazomethane and Their
Reactivities Towards Aryl Isothiocyanates
[
a]
[b]
[c]
[c]
David R. Armstrong,* Robert P. Davies, Robert Haigh, Mark A. Hendy,
[
d]
[†]
[c]
Paul R. Raithby, Ronald Snaith, and Andrew E. H. Wheatley*
Dedicated to the memory of Ron Snaith
Keywords: Density functional calculations / Diazomethane / Lithium / Solid-state structures / Solution structure
(
Trimethylsilyl)diazomethane (1-H) reacts with nBuLi in THF
isomer. These observations, supported by DFT calculations,
influence our understanding of the reactivity of lithiated di-
azomethanes towards aryl isothiocyanates, suggesting as
at elevated temperature to afford (previously reported) 1-
3
Li· /
perature affords instead the N-lithiate Me
9), which is a novel ‘‘open’’ pseudo-cubic tetramer in the
2
THF. However, reaction in hexane/TMEDA at low tem-
3
SiCNNLi·TMEDA they do that previously observed product selectivity in these
(
reactions is critically dependent on temperature control exer-
cised during the process.
solid state. Variable-temperature NMR spectroscopy sug-
gests that N-metallated 9, apparently the kinetic product of
the reaction, irreversibly rearranges at high temperature in
solution to give the thermodynamically preferred C-lithiated
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
1-Li has found ready use in the preparation of substituted
[
7]
[8]
triazoles and tetrazoles, the syntheses of aldehydes from
[
9]
[10]
(Trimethylsilyl)diazomethane (1-H), a safe and stable ketones, Colvin rearrangements
and the formation of
[
11]
[12]
analogue of diazomethane, has many applications in, for synthetically useful silyl ketenes. These last species re-
[1]
example, ArndtϪEistert syntheses, the homologation of act with phosphorus ylides and so afford a simple route to
[
2]
[3]
[4]
[13]
[13]
ketones and aldehydes, cycloaddition reactions, and silyl allenes.
In this context, central to the synthesis
[5]
the methyl esterification of carboxylic acids. Moreover, of the disubstituted silyl ketene 3, is the formation, by the
the chemistry of its lithiated derivative (1-Li) has also been sequential treatment of 1-H with n-butyllithium and carbon
extensively studied due to its synthetic utility. This derives monoxide, of a lithium ynolate 2. This latter species is con-
[
14]
from its combination of reactivity (greater than that of 1- sidered to result from the insertion
of CO into the pro-
H) and safety (relative to diazomethane).[ In consequence, posed CϪLi bond in 1-Li, whereupon N2 is eliminated
6]
(
Scheme 1), the addition of triethylsilyl trifluoromethanes-
[
a]
Department of Pure and Applied Chemistry, University of ulfonate (Et SiOTf) and subsequent work-up affording 3.
3
Strathclyde,
2
95 Cathedral Street, Glasgow, G1 1XL, U. K.
Fax: (internat.) ϩ44-141/548-4822
E-mail: drarmstrong@strath.ac.uk
[
[
[
b]
c]
Department of Chemistry, Imperial College London,
South Kensington, London, SW7 2AZ, U. K.
Fax: (internat.) ϩ44-20/7594-5804
E-mail: r.davies@imperial.ac.uk
Department of Chemistry, University of Cambridge,
Lensfield Road, Cambridge, CB2 1EW, U. K.
Fax: (internat.) ϩ44-1223/336-362
E-mail: rh293@cam.ac.uk, aehw2@cam.ac.uk
Department of Chemistry, University of Bath,
Claverton Down, Bath, BA2 7AY, U. K.
Fax: (internat.) ϩ44-1225/386-231
d]
E-mail: p.r.raithby@bath.ac.uk
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Deceased.
Scheme 1. Proposed mechanism for the preparation of the disubsti-
[
†]
[13]
tuted silyl ketene 3
Eur. J. Inorg. Chem. 2003, 3363Ϫ3375
DOI: 10.1002/ejic.200300244
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3363

A. E. H. Wheatley et al.
FULL PAPER
Figure 1. Possible isomers of 1-H[15] (and their relative energies)[17] and 1-Li (and their relative energies, 1 kcal ϭ 4.184 kJ)
The chemistry of metallated (mono-substituted) diazo-
methane has been previously investigated[15] (Figure 1) with
results indicating that deprotonation/reprotonation of di-
azomethane 4a affords the less stable CH N N-isocy-
2
2
anoamine isomer 4c, which undergoes base-induced rever-
sion to 4a. The other possible non-cyclic CH N isomer
(
2
2
Figure 2. C- and N-lithiated isomers of 1-Li and their relative ener-
nitrile imine 4b) has not been detected experimentally. The gies[17]
structures and energies of the CH N isomers 4aϪc, as well
2
2
as those of their lithiated derivatives, 5aϪd, have recently
been modelled theoretically.[
was suggested that while N-protonation of 5d would give
c, C-protonation of 5a would yield 4a. Further, consistent
16,17]
From these calculations it
4
with experiment, theory pointed to the most stable 1-H iso-
mer (4a) being obtainable, in the presence of base, from
energetically less favourable 4c (Scheme 2). This is in spite
of the suggestion, based on calculation, that 5a (precursor
to 4a) is less stable than 5d; in other words that the reaction
is thermodynamically controlled by the stability of the final
protonated product. In contrast to the parent diazomethane
structures discussed above, calculations[ have shown that
for the lithiated mono-substituted (trimethylsilyl)diazome-
thanes 1-Li and 6 (Figure 2), the N-metallated nitrile imine
isomer was slightly more stable than the C-lithiate. How-
ever, previous attempts to isolate and crystallographically
characterise 6 have resulted only in the isolation and struc-
Figure 3. The molecular structure of (7)
2
17]
fering behaviour has not hitherto been explained in detail
and this has led us to attempt the isolation and structural
characterisation of pure lithiated (trimethylsilyl)diazome-
thane (cf. 7) in order to clarify which of the proposed model
structures, C- or N-lithiated, better describes the true struc-
ture of lithiated 1-H. In this context, we report here on the
tural
elucidation
of
{hexakis[lithio(trimethylsilyl)-
observation of both kinetic [giving Me SiCNNLi·TMEDA,
3
3
diazomethane]·bis[lithio{4,5-bis(trimethylsilyl)triazole}]·
9] and thermodynamic [giving 1-Li· / THF] metallation.
2
[17]
heptakis(diethyl ether)} [(7) ·OEt ; Figure 3].
This spec-
2
2
The latter observation has led to the isolation and structural
characterisation of an intermediate in the synthesis of dis-
ubstituted silyl ketene 3 (Scheme 1). Finally, we report here
on the reactions of lithiodiazomethanes with different iso-
thiocyanates with a view to understanding the relationship
between the site of lithiation in the substrate and the struc-
ture of the final cyclised product.
ies is composed both of 6 and lithiotriazole 8, this last com-
ponent evidently being formed by the reaction of 6 with
1-H.
Suggestions[12,18] that the reactivity of lithiated 1-H is sol-
vent dependent have been borne of the observation that
whereas it reacts with RNCS (R ϭ alkyl, aryl) in OEt to
2
afford 2-amino-1,3,4-thiadiazole (13), in THF thio-1,2,3-
triazoles 10Ϫ12 result (Scheme 3).[
18b]
However, such dif-
Results and Discussion
3
Solid-State and Theoretical Studies on 1-Li· / THF and 9
2
The reaction of 1-H with nBuLi in THF yielded large
yellow crystals of pure lithiated (trimethylsilyl)diazome-
1
3
thane / [{Me SiC(Li)N } ·3THF] (1-Li· / THF), the solid-
Scheme 2. Equilibria in the interconversion of diazomethane iso-
mers
2
3
2 2
2
[19]
state structure of which we have previously reported. X-
3364
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Eur. J. Inorg. Chem. 2003, 3363Ϫ3375

Kinetic and Thermodynamic Lithiated Derivatives of a Simple Diazomethane
FULL PAPER
Scheme 3. Proposed pathways for the reaction of different 1-Li isomers with RNCS (R ϭ Ph, Bz)[12,18]
3
ray crystallography has shown 1-Li· / THF to be a polymer for X ϭ H Si (Table 1 and Figure 5) while for X ϭ Me Si
2
3
3
based on a repeating tetramer unit (Figure 4), consisting of the computed preference for N- (IV) over C-metallation
Ϫ1
two (mono-THF) complexed lithiodiazomethane molecules (III) is 4.0 kcal·mol , illustrating the electron-donating na-
and
two
(bis-THF)
complexed
ones
i.e. ture of the methyl groups over hydrogen atoms yet still sug-
{
[Me SiC(Li·THF)N ]·[Me SiC(Li·2THF)N ]} . This revel- gesting a fine energetic balance between the differently met-
3
2
3
2
2
ation of two types of lithiodiazomethane molecule in the allated, unsolvated monomers. Calculated molecular geo-
3
solid-state structure of 1-Li· / THF is consistent with the metries show little dependence upon X. Whereas C-lithiates
2
observation of two sets of CϭNϭN stretching modes by I and III both show relatively long CϪN (1.283 and 1.282
Ϫ1
˚ ˚
A, respectively) and short NϪN (1.141 and 1.144 A, respec-
IR spectroscopy (ν
2
ϭ 2149, 2116 cm
and νasym
ϭ
sym
092, 2052 cmϪ1) which collapse to a single set upon hy- tively) bonds, the opposite is true of N-lithiates II and IV
drolysis to 1-H. The ambiguity surrounding the preferred (CϪN ϭ 1.195 A in both, NϪN ϭ 1.201 and 1.205 A,
˚
˚
site of lithiation in 1-H that results from the contrasting respectively). The structural feature most significantly de-
3
structures noted for 1-Li· / THF and 7 made it desirable to pendent on X is the SiϪC bond length. This increases sig-
2
˚
˚
theoretically probe the relative stabilities and geometries of nificantly from a mean of 1.798 A to one of 1.817 A on
both N- and C-lithiates. DFT calculations[ based on a replacing H atoms with Me groupsϪpresumably reflecting
variety of models were undertaken (B3LYP /6-311G** both the increased steric requirements of the trimethylsilyl
20]
[21]
[22]
)
. Energetic results for XCN Li·nL (X ϭ H Si, Me Si; group and its aforementioned inductive effect. The
2 3 3
n ϭ 0, 1, 2; L ϭ OEt , THF) are summarised in Table 1 metalloϪorganic bonds show no significant variation with
2
˚
with selected calculated geometrical parameters in Table E1 X. Hence, while the CϪLi bonds are 1.906 A in both I
(
see Electronic Supporting Information; see footnote on the and III, the NϪLi ones in II and IV are 1.697 and 1.692
˚
first page of this article).
A, respectively.
The extension of calculations to the simple mono-sol-
vated, monomeric lithiates Me SiCN Li·L (L ϭ OEt ,
3
2
2
THF) shows that, irrespective of the choice of L, the C-
lithiates (V, VII) are higher in energy than the N-lithiates
(VI, VIII; Table 1 and Figure 5). All of the resultant struc-
ture types are significantly more stable than either III or IV
by virtue of Lewis base coordination [∆EComplexation
(
∆E ) ϭ Ϫ21.5 (V), Ϫ22.9 (VII), Ϫ21.5 (VI), Ϫ22.7 (VIII)
C
Ϫ1
kcal·mol ]. Of note (see below) for both types of L, C-
lithiated models show more negative ∆E values than their
N-lithiated counterparts. Moreover, for both C- and N-lithi-
ates, both the magnitude of and differences between ∆EC
C
Figure 4. The molecular structure of polymeric 1-Li·3/
THF
2
Overall, calculations reported here on lithiodiazome- values are enhanced for coordination of the stronger Lewis
thanes and their complexes suggest that, while N-metal- base (THF). Thus, Ϫ∆E (V) ϭ Ϫ∆E (VI) and Ϫ∆E (VII)
C
C
C
lation is thermodynamically preferred, C-metallation be- Ͼ Ϫ∆E (VIII), Ϫ∆E (VII) Ͼ Ϫ∆E (V) and Ϫ∆E (VIII)
C
C
C
C
comes increasingly favourable in the presence of strongly Ͼ Ϫ∆E (VI) and, whereas for mono-OEt solvation VI is
C
2
Ϫ1
coordinating media. For unsolvated diazomethanes preferred to V by 4.0 kcal·mol , for mono-THF solvation
Ϫ1
Ϫ1
XCN Li (X ϭ H Si, Me Si) C-lithiation is 2.5 kcal·mol
VII is 3.8 kcal·mol more stable than VIII. This implies
2
3
3
(I; 1 kcal ϭ 4.184 kJ) more energetic than N-lithiation (II) that N-metallation is less strongly favoured over C-metal-
Eur. J. Inorg. Chem. 2003, 3363Ϫ3375
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A. E. H. Wheatley et al.
FULL PAPER
Table 1. Summary of DFT calculations (B3LYP/6-311G**)[21,22] based on XCN
TMEDA). (1 kcal ϭ 4.184 kJ.) ∆E /L quoted as enthalpy of complexation per Lewis base donor atom
c
2
3 3 2
Li·nL (X ϭ H Si, Me Si; n ϭ 0, 1, 2; L ϭ OEt , THF,
Model
Figure
Formula
Total Energy
incl. ZPE; Hartrees)
∆E
c
∆E
c
/L
Relative Energy
(kcal molϪ1)
(kcal mol LϪ1
Ϫ1
)
(kcal mol
Ϫ1 Ϫ1
L )
(
I
II
E1
E1
H
H
3
3
SiC(Li)N
SiCN Li
2
Ϫ446.410355
Ϫ446.414282
Ϫ
Ϫ
Ϫ
Ϫ
2.5
0.0
2
III
IV
E1
E1
Me
Me
3
3
SiC(Li)N
SiCN Li
2
Ϫ564.343445
Ϫ564.349859
Ϫ
Ϫ
Ϫ
Ϫ
4.0
0.0
2
V
VI
E1
E1
Me
Me
3
3
SiC(Li·OEt
2
)N
2
Ϫ797.976187
Ϫ797.982585
Ϫ21.5
Ϫ21.5
Ϫ21.5
Ϫ21.5
4.0
0.0
SiCN Li·OEt
2
2
VII
VIII
E1
E1
Me
Me
3
3
SiC(Li·THF)N
SiCN Li·THF
2
Ϫ796.779249
Ϫ796.785302
Ϫ22.9
Ϫ22.7
Ϫ22.9
Ϫ22.7
3.8
0.0
2
IX
X
E2
E2
Me
Me
3
3
SiC(Li·2OEt
2
)N
2
Ϫ1031.594155
Ϫ1031.598894
Ϫ33.7
Ϫ32.6
Ϫ16.9
Ϫ16.3
3.0
0.0
SiCN Li·2OEt
2
2
XI
XII
E2
E2
Me
Me
3
3
SiC(Li·2THF)N
SiCN Li·2THF
2
Ϫ1029.205798
Ϫ1029.209892
Ϫ40.1
Ϫ38.7
Ϫ20.1
Ϫ19.3
2.6
0.0
2
XIII
XIV
E2
E2
Me
Me
3
3
SiC(Li·TMEDA)N
SiCN Li·TMEDA
2
Ϫ912.022702
Ϫ912.025424
Ϫ35.1
Ϫ32.8
Ϫ17.6
Ϫ16.4
1.7
0.0
2
the predilection for N-metallation is minimised in this me-
Ϫ1
dium [Me SiC(Li·2THF)N (XI) is only 2.6 kcal·mol less
3
2
stable than Me SiCN Li·2THF (XII)]. The addition of a
3
2
second Lewis base molecule causes the further extension of
˚
˚
CϪLi (to, 2.055 and 2.038 A for IX and XI, respectively)
and NϪLi bonds (to 1.801 A for both of X and XII).
Figure 5. Theoretically modelled structures of the simple C- (I, III)
and N-lithiated (II, IV) diazomethanes XCN Li (X ϭ H Si, Me Si)
and III·L and IV·L complexes (VϪVIII; L ϭ OEt , THF)
2
3
3
2
lation as external solvation increases; an important infer-
ence given the previously reported reactivities of lithiated
(
trimethylsilyl)diazomethanes in different Lewis base me-
[12,18]
dia.
Differences in the calculated energies of the vari-
ously coordinated mono-solvates do not, however, translate
into significant differences in bonding parameters. Slight Figure 6. Modelled structures of monomeric III·2L and IV·2L
2
complexes IXϪXII; L ϭ OEt , THF) and III·L and IV·L (L ϭ
changes are noticeable relative to unsolvated III and IV on
TMEDA)
the inclusion of Lewis base and this is most apparent in
˚
increments to CϪLi lengths (to, 1.959 and 1.956 A for V
˚
and VII, respectively, cf. 1.906 A in III) and NϪLi distances
˚
(
1
to, 1.735 and 1.732 A for VI and VIII, respectively, cf.
.692 A in IV).
While the gas phase calculations do not account for the
˚
3
aggregation behaviour either of 1-Li· / THF or of 7 it is
2
Calculations on Me SiCN Li·2 L (L ϭ OEt , THF; nonetheless apparent that some useful correlations exist be-
3
2
2
Table 1 and Figure 6) reinforce the view that, irrespective of tween theory and experiment. Table E1 (Supp. Inf.) indi-
the choice of L, the preference for N- over C-lithiation is cates close carbonϪnitrogen and the nitrogenϪnitrogen
3
diminished as external solvation of the metal is introduced. bond length agreement both between 1-Li· / THF and I
2
3
The resultant structure types (IXϪXII) are all significantly (Figure 5) and between 7 and II. Clearly, in 1-Li· / THF
2
˚
more stable than models VϪVIII [∆EC ϭ Ϫ33.7 (IX), the carbonϪnitrogen bond (mean 1.326 A) is longer than a
Ϫ1
˚
Ϫ40.1 (XI), Ϫ32.6 (X), Ϫ38.7 (XII) kcal·mol ]. As for double one and the nitrogenϪnitrogen bond (1.182 A) is
[
23]
VϪVIII, ∆E is most negative for solvation by THF while shorter than a double one.
Furthermore in 7, the
C
3366
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Eur. J. Inorg. Chem. 2003, 3363Ϫ3375

Kinetic and Thermodynamic Lithiated Derivatives of a Simple Diazomethane
FULL PAPER
˚
˚
carbonϪnitrogen bond (mean 1.202 A) is longer than a Table 2. Selected bond lengths [A] and angles [°] in 9
˚
triple one and the nitrogenϪnitrogen bond (1.208 A) is
slightly longer than a double one.
Previously reported calculations on H SiCN Li [6-
Li(1)ϪN(1)
Li(1)ϪN(3)
Li(1)ϪN(7)
Li(1)ϪN(9)
Li(2)ϪN(1)
1.991(7)
2.108(7)
2.045(8)
2.067(7)
2.010(7)
2.042(7)
2.046(7)
2.091(7)
2.058(8)
2.011(7)
2.208(9)
2.146(8)
2.113(8)
Li(4)ϪN(5)
Li(4)ϪN(7)
Li(4)ϪN(15)
Li(4)ϪN(16)
N(1)ϪN(2)
N(2)ϪC(1)
N(3)ϪN(4)
N(4)ϪC(5)
N(5)ϪN(6)
N(6)ϪC(9)
N(7)ϪN(8)
N(8)ϪC(13)
2.211(8)
2.288(8)
2.324(8)
2.203(8)
1.204(5)
1.210(6)
1.216(5)
1.212(6)
1.219(5)
1.209(6)
1.218(5)
1.193(6)
3
2
31G(d)/MP2] have suggested (in the light of structurally
Ϫ1
characterising 7) an energetic preference of 1.4 kcal·mol
for the N- over the C-lithiate.[ However, calculations pre- Li(2)ϪN(3)
17]
Li(2)ϪN(5)
sented here clearly suggest that any such preference
Li(2)ϪN(11)
is eroded by the introduction of external solvation. This
Li(3)ϪN(5)
leads us to the view that in the presence of excess donor
(
Li(3)ϪN(7)
either solvent or, by aggregation, other molecules of lithi- Li(3)ϪN(13)
ated 1-H) the C-metallated product represents the thermo- Li(3)ϪN(14)
Li(4)ϪN(3)
dynamic product of lithiation whereas the N-metallate re-
veals kinetic control. Consistent with this is the fact that,
N(1)ϪLi(1)ϪN(3)
Li(1)ϪN(1)ϪLi(2)
97.4(3)
81.9(3)
78.4(3)
98.9(3)
97.0(3)
87.9(3)
84.8(3)
89.9(3)
N(3)ϪLi(2)ϪN(5)
Li(2)ϪN(3)ϪLi(4)
Li(2)ϪN(5)ϪLi(4)
N(3)ϪLi(4)ϪN(5)
N(5)ϪLi(3)ϪN(7)
Li(3)ϪN(5)ϪLi(4)
Li(3)ϪN(7)ϪLi(4)
N(5)ϪLi(4)ϪN(7)
97.1(3)
135.6(3)
84.8(3)
90.3(3)
98.4(3)
86.8(3)
85.8(3)
86.4(3)
3
whereas 1-Li· / THF is afforded after having heated the re-
2
action mixture to reflux (approx. 65 °C), 7 results from a Li(1)ϪN(3)ϪLi(2)
N(1)ϪLi(2)ϪN(3)
process in which the temperature never exceeds Ϫ25 °C.
N(3)ϪLi(1)ϪN(7)
In order to further probe the question of thermodynamic
Li(1)ϪN(3)ϪLi(4)
versus kinetic control in the metallation of 1-H and also in
Li(1)ϪN(7)ϪLi(4)
an attempt to obtain pure lithiated derivatives based on N(3)ϪLi(4)ϪN(7)
oligo- rather than complex polymeric structures, we have
effected the crystallisation of lithiated (trimethylsilyl)diazo-
methanes from polydentate Lewis bases. The best results
have been obtained by the reaction of 1-H with nBuLi in
TMEDA (ϭ N,N,NЈ,NЈ-tetramethylethylenediamine) at low
temperature (Ͻ Ϫ25 °C). This process achieves yellow crys-
tals of a single isolable product and these analyse as
1
Me SiCN Li·TMEDA (9). Not only does H NMR spec-
3
2
troscopy support the 1:1 TMEDA/lithiate ratio but it also,
by displaying just a single trimethylsilyl resonance, suggests
the adoption of a single aggregation state, symmetrical
species in solution. In line with the kinetic control exercised
during the reaction, the solid-state structure of 9 reveals a
tetramer (Table 2 and Figures 7 and 8) consisting of N-lithi-
ated (trimethylsilyl)diazomethane molecules arranged as an
Figure 7. The molecular structure of (9)
4
‘‘open’’ pseudo-cubane. Unusually, stabilisation of the me-
tal centres by TMEDA takes two distinct forms with both
mono- and bidentate coordination modes being observed.
Notably, such a structure is incompatible with the sym-
metry suggested by NMR spectroscopy, suggesting that the
structure is either rapidly fluxional and/or significantly de-
aggregated in solution (see below).
While Li(1), Li(2), and Li(4) are each coordinated by
three diazomethane terminal N-centres, Li(3) is coordinated
by just two; there being no interaction with N(1)
˚
[
Li(3)···N(1) ϭ 2.839(9) A]. Bis-coordination by the two
TMEDA molecules that exhibit bidentate behaviour ren-
ders Li(3) and Li(4) four and five coordinate, respectively.
ϩ
The remaining two Li ions are tetra-coordinate, each be-
ing mono complexed by one N-centre of a monodentate
TMEDA molecule. Thus the aggregate can be viewed as a
Figure 8. Solid-state structure of tetrameric 9; hydrogen atoms and
dimer of dimeric pairs [each one based on a (NLi) ring, minor disorder omitted for clarity
2
i.e. Li(3)N(5)Li(4)N(7) and Li(1)N(1)Li(2)N(3)] whereby
each one is defined by the characteristic behaviour of its most significantly, and presumably symptomatic of the pre-
[
24]
TMEDA components (Figure 8). Nevertheless, the combi- dilection of lithium for forming four bonds, pentacoordi-
nation of pseudo-cubane opening and differences in the co- nate Li(4) forms long[25] interactions both with bidentate
˚
ordinative modes adopted by TMEDA incurs significant TMEDA [mean Li(4)ϪN ϭ 2.264 A] and with three depro-
variations in core LiϪN interactions (Table 2). Perhaps tonated diazomethane monomers [mean Li(4)ϪN ϭ 2.204
Eur. J. Inorg. Chem. 2003, 3363Ϫ3375
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3367

A. E. H. Wheatley et al.
FULL PAPER
˚
A]. The remaining TMEDA-chelated metal shows similar, the coordination of TMEDA [∆E ϭ Ϫ35.1 (XIII), Ϫ32.8
C
Ϫ1
though less pronounced, lengthening of LiϪN(TMEDA) (XIV) kcal·mol ] relative to unsolvated III and IV. In line
bonds [Li(3)ϪN(13) and Li(3)ϪN(14) ϭ 2.208(9) and with earlier calculations reported here (see above)
˚
2
.146(8) A, respectively] but rather stronger bonds to the Ϫ∆E (XIII) Ͼ Ϫ∆E (XIV), pointing again to the chances
C
C
˚
cluster core [mean Li(3)ϪN ϭ 2.035 A]. It may be the case of C-metallation being enhanced by external solvation.
that the discrepancy between these two LiϪN(TMEDA) in- Whilst C-lithiate XIII is still less stable than N-lithiated ana-
teractions has its origins in the orientation of the Lewis logue XIV the introduction of TMEDA has almost com-
Ϫ1
base since the shorter of the two interactions is associated pletely negated the energy difference (1.7 kcal·mol ). The
with N(14), which can presumably closely approach Li(3) structural parameters in diazomethane anions in 9 correlate
by virtue of diminished steric interactions with the N(1)- well with those of computed XIV. Notably, in 9 (as in 7) the
containing diazomethane unitϪa result of the extended carbonϪnitrogen and the nitrogenϪnitrogen bond lengths
Li(3)···N(1) distance. A further consequence of bond-cleav- are very similar (in contrast to those in C-lithiated
3
age in the aggregate core is that N(1) becomes unique 1-Li· / THF, wherein the carbonϪnitrogen distance was sig-
2
among the terminal diazomethane N-centres in that it nificantly greater than the nitrogenϪnitrogen one).
˚
stabilises just two metal ions [mean LiϪN(1) ϭ 2.001 A].
3
Solution Studies on 1-Li· / THF and 9
2
Finally, shorter than the LiϪN(TMEDA) bonds previously
noted for the bis-coordinating Lewis base molecules are
3
The observation of 1-Li· / THF and 9 demonstrates the
2
those in which the TMEDA acts only as a monodentate viability of both C- and N-lithiated derivatives of 1-H in
˚
donor [mean LiϪN ϭ 2.079 A]. A comparison of the solid- the solid state. However, the details of their syntheses sug-
state structural parameters observed for 9 with those noted gest that the regiospecificity of metallation is critically de-
˚
in 7 reveals that both CϪN (mean 1.206 and 1.202 A pendant on reaction conditions. This observation made it
respectively for 9 and 7) and NϪN (mean 1.214 and 1.208 desirable to elucidate the structures of species obtained on
˚
3
A) bond lengths correlate well but differ significantly from dissolution of both 1-Li· / THF and 9 and to probe the
2
3
[19]
those in C-lithiated 1-Li· / THF.
possible interconversion between N- and C-lithiates. Cryo-
Coincidentally, the only other known example of an ‘‘op- scopic relative molecular mass (CRMM) measurements
en’’ (LiN) pseudo-cubane in which a single core bond is on 1-Li· / THF in benzene show both that the complex de-
2
[31]
3
4
2
absent is 7. However, bond cleavage in 7 derives from the aggregates significantly in non-donor solution and that the
mixed-anion nature of the cluster, with one vertex of the molecular mass (M ) and aggregation state (n) remain es-
r
[
otherwise lithio(trimethylsilyl)diazomethane-based] cube sentially constant at 177 Ϯ 10 and n ϭ 0.77 Ϯ 0.04, respec-
3
being defined by the deprotonated N-centre in the triazole tively [assuming n ϭ 1 for Me SiC(Li)N · / THF, M ϭ
3
2
2
r
Ϫ3
ring, the neighbouring ring-nitrogen inserting into a cubane 228] over a wide concentration range (4.55·10
to
edge. The only other discrete, related ‘‘open’’ pseudo-cub- 3.20·10 mol·dm , Table E3, Supp. Inf.). This may signify
anes reported are the (LiO) -based structures the polymer (M ϭ 912) breaking down (the chain-linking
Ϫ2
Ϫ3
4
r
(
PhOLi·THF) ·PhOH (wherein a single core interaction is LiϪN bonds cleaving) such that [Me SiC(Li·THF)N ] di-
4
3
2 2
[
26]
[27]
absent),
and
Li·THF]
[2-MeOC H C(H)(OLi)NMe(CH ) NMe ]
mers (Mr ϭ 384) and Me SiC(Li·2THF)N2 monomers
6
4
2 2
2 4
3
[PhC(O)N(Ph)Li·THF]·[PhC(O)N(Ph)Zn(tBu)2- (M ϭ 264) result. Dimerisation of these monomers, con-
(in each of which two eclipsed core bonds are comitant with the evolution of THF molecules yields fun-
r
[
28]
absent). This latter mode of separation is also noted in poly- damental mono-THF solvated dimers in solution (M ϭ
r
meric (BrLi·THF)ϱ.[ The remaining rare feature of (9)4 228). Deaggregation of — and/or loss of THF from — these
29]
in the solid state is highlighted by Cl Li ·2TMEDA· species can then explain the observed M . For 9, CRMM
6
6
r
4
[30]
/2
TMEDA.
Here variations in the mode of external measurements suggest significant deaggregation of the
Ϫ2
solvation by TMEDA allow four of the six Lewis base tetramer. Over the concentration range 4.80·10
to
molecules associated with each hexamer to bridge between 2.60·10Ϫ1 mol·dmϪ3 (Table E4, Supp. Inf.) M increases
r
aggregates affording a three-dimensional network. Con- from 425 Ϯ 5 (n ϭ 1.80 Ϯ 2 assuming n ϭ 1 for
trastingly, in (9) , Li(1) and Li(2) are each stabilised by just Me SiCN Li·TMEDA) to 494 Ϯ 3 (n ϭ 2.14 Ϯ 2). This
4
3
2
one TMEDA N-centre [N(9), N(11)]; these donors being points to substantial dislocation of the tetramer (M ϭ 945)
r
strictly monodentate with neither N(10) nor N(12) bridging to give (Me SiCN Li·TMEDA) (M ϭ 473), with limited
3
2
2
r
to adjacent aggregates.
dissociation of dimers and/or de-coordination of TMEDA
Complex 9 (like 7) results from the employment of kinetic occurring at lower concentrations. Data indicates some
control during the reaction and this, perhaps, overshadows tetramer retention at higher concentrations.
1
the true aim of employing TMEDA here. Nevertheless, the
Variable-temperature H NMR spectra of 9 in [D ]PhMe
8
solid-state structure of 9 affords us the first glance of a dis- (Figure 9) reveal broadening of the TMEDA peaks and
3
crete molecular lithiodiazomethane [cf. (1-Li· / THF) ] downfield movement of the Me Si signal as the temperature
2
ϱ
3
which incorporates no other by-products (cf. 7) and a theor- is reduced. By Ϫ25 °C new sets of Me Si and (both)
3
[
21,22]
etical probe has been undertaken [B3LYP/6-311G**;
TMEDA resonances develop, suggesting the evolution of a
Figure 6 and Table 1 and Table E2 (Supp. Inf.)].[
20Ϫ22]
The second species and, as the temperature is further reduced,
and these new signals become dominant. Such behaviour is con-
stabilities of Me SiC(Li·TMEDA)N (XIII)
3
2
Me SiCN Li·TMEDA (XIV) are significantly enhanced by sistent with the aggregation of (Me SiCN Li·TMEDA)
3
2
3
2
2
3368
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Kinetic and Thermodynamic Lithiated Derivatives of a Simple Diazomethane
FULL PAPER
(see above) to give tetramers at low temperature and, as and it seems reasonable that this already weak resonance
such, these spectral changes are thermally reversible. If, in- becomes difficult to detect.) If the same sample is heated to
stead, this sample is heated above room temperature the ϩ95 °C it is found that the Me Si resonance (dominant at
3
Me Si singlet (δ ϭ 0.28 ppm at 35 °C) is replaced by a room temperature) is completely replaced by one at high
3
second one (δ ϭ 0.34 ppm at 52 °C; both signals are present field (δ ϭ Ϫ0.7 ppm, cf. the weak δ ϭ Ϫ0.8 ppm signal
1
in the range 45Ϫ51 °C) suggesting a significant change in at room temperature). In the same way as for H NMR
the lithiodiazomethane molecule whereby kinetically fav- spectroscopic data, this encourages the view that whereas
oured N-lithiate 9 rearranges to the (thermodynamic) C- the dominant species both at and below room temperature
lithiate in situ. This view is supported by the observation is the N-lithiate, it is converted into the C-metallated isomer
that subsequent cooling of the sample to room temperature at higher temperature. While the signal for the CϭN carbon
fails to incur any further significant changes in the appear- centre does not move in a manner that might be expected
1
3
ance of the spectrum, suggesting that this thermal re- for such a rearrangement, it should be noted that the
C
3
arrangement is irreversible.
NMR spectra of both (C-lithiated) 1-Li· / THF and (N-li-
2
thiated) 9 (in [D ]DMSO at room temperature) show ex-
6
tremely similar chemical shifts for this carbon nucleus.
Figure 10. 13C NMR spectroscopic data for 9 in [D
the range 95 °C to Ϫ30 °C
]PhMe over
8
Variable-temperature 7Li NMR spectra (Figure 11) re-
inforce the information gained from 1H and C NMR
spectroscopy. The single resonance observed at δ ϭ
Ϫ1.59 ppm at room temperature broadens as the tempera-
ture is lowered until at Ϫ20 °C it splits into two separate
Si group in 9 in signals, consistent with the dimer-tetramer system impli-
cated by cryoscopy. If the temperature is reduced still
further this new peak becomes the dominant one. As the
13
1
Figure 9. H NMR spectroscopic data for the Me
3
8
[D ]PhMe over the range 60 °C to Ϫ50 °C
The room temperature 13C NMR spectrum of 9 in sample is heated to above room temperature a significant
D ]PhMe (Figure 10) shows a dominant Me Si signal at alteration in the position of the sole lithium signal can be
[
8
3
1
δ ϭ 2.2 and a significantly smaller one at δ ϭ Ϫ0.8. (This seen. Consistent with the H NMR spectra, this latter ther-
latter signal may represent a small amount of the sample mal change is irreversible.
3
converting slowly to the thermodynamic isomer at room
The observation of both 1-Li· / THF and 9 suggests a
2
temperature.) Cooling the sample to Ϫ30 °C (below the complicated chemistry for lithiated diazoalkanes and (in
1
temperature at which H NMR spectroscopy showed the tandem with calculations) challenges previous assertions
effects of aggregation, see above) causes both the main that 1-H is necessarily preferentially N- rather than C-lithi-
Me Si and the TMEDA CH -peak to split into two. (The ated. Rather, calculations now suggest metallation of the
3
2
trace signal tentatively attributed to Me Si in the C-lithiate carbon centre in the presence of excess donor. Indeed,
3
at room temperature is not observed at this lower tempera- further synthetic work, culminating in the isolation and
ture. However, at Ϫ30 °C all peaks are noticeably broader structural characterisation of N-lithiated 9 suggests that the
Eur. J. Inorg. Chem. 2003, 3363Ϫ3375
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3369

A. E. H. Wheatley et al.
FULL PAPER
crystals suitable for an unambiguous structure determi-
nation led to the replacement of phenyl isothiocyanate with
its benzylic analogue (BzNCS).
Employment of BzNCS in the above reaction sequence
yields a crystalline material that analyses as S-lithio-1-
benzyl 4-trimethylsilyl-5-thio-1,2,3-triazole [BzNNNC-
(
Me Si)C(SLi·2THF)], 11. X-ray crystallography affords
3
the first full characterisation of a lithiated thio-1,2,3-tria-
zole (Figure 12 and Table 3; the asymmetric unit incorpor-
ates two crystallographically independent but structurally
similar molecules of 11 of which a representative one is dis-
cussed). The species is rendered polymeric in the solid state
through the coordination of lithium by, for example, N(3)
˚
[
LiϪN ϭ 2.050(9) A] in the almost planar (internal angles
sum to 540.1°), aromatic triazole ring. The anion is for-
˚
mally metallated at sulfur and, at 2.460(8) A, Li(1)ϪS(1) is
consistent with metal-sulfur distances reported for lithium-
[
32]
[32j,33]
[34]
containing thiolates, thioimidates,
The only other solid-state structures to incorporate an alk-
and thioureas.
[35]
ali metallated 1,2,3-triazole ring are those of lithiated
[
36]
and potassiated
benzotriazole (the triazole ring being
pre-formed in both cases). In 7 a triazole ring is incorpor-
[
17a]
ated as a neutral adduct.
The observation of a triazole
ring in 11 has ramifications for our interpretation of the
cyclisation process by which lithiodiazomethanes and
RNCS combine to give 1-substituted 5-alkylthio-1,2,3-tria-
zoles suggesting, as it does, the action of C-lithio(trimethyl-
silyl)diazomethane in THF solution (Scheme 4).
ii) Treatment of 1-H with nBuLi and RNCS in OEt2:
Syntheses of 12 (R ؍ Bz) and 13 (R ؍ Ph)
According to previous reports, the sequential combi-
nation of 1-H with nBuLi and BzNCS in OEt affords, via
2
a postulated lithio-2-benzylamino-5-trimethylsilyl-1,3,4-thia-
diazole intermediate, 2-amino-1,3,4-thiadiazoles with re-
direction of the reaction being attributed to an ambiguous
7
Figure 11. Li NMR spectroscopic data for 9 in [D
8
]PhMe over the
range 60 °C to Ϫ50 °C
regiospecificity of metallation is temperature dependant.
Clearly, such variability in the behaviour of 1-H towards
organolithium species has consequences for our under-
standing of the reactions undergone by the subsequently
formed lithiate, and this has led us to probe the details of
representative processes.
Reactions of Lithio(trimethylsilyl)diazomethane with Aryl
Isothiocyanates
i) Treatment of 1-H with nBuLi and RNCS in THF:
Syntheses of 10 (R ؍ Ph) and 11 (R ؍ PhCH ؍ Bz)
2
Reaction of lithio(trimethylsilyl)diazomethane with phe-
nyl isothiocyanate (PhNCS)[ in THF affords a product
18]
3
that analyses as PhNNNC(Me Si)C(SLi· / THF) 10
3
2
1
(
Scheme 3). This shows a 1:1 Ph/Me Si ratio by H NMR
3
spectroscopy Ϫ consistent with expectation for the intended
Figure 12. The solid state structure of polymeric 11, showing the
association of two crystallographically independent monomer units
via N-stabilisation of the metal; for clarity hydrogen atoms have
cyclised product. That ring-formation has occurred is also
1
3
suggested by C NMR spectroscopy, which reveals peaks
2
for the sp ring-carbons. However, the failure of 10 to afford been omitted
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Eur. J. Inorg. Chem. 2003, 3363Ϫ3375

Kinetic and Thermodynamic Lithiated Derivatives of a Simple Diazomethane
FULL PAPER
˚
Table 3. Selected bond lengths [A] and angles [°] in 11
Li(1)ϪN(6)
Li(1)ϪS(1)
S(1)ϪC(1)
C(1)ϪN(1)
C(1)ϪC(2)
N(1)ϪN(2)
N(2)ϪN(3)
N(3)ϪC(2)
2.052(8)
2.460(8)
1.717(4)
1.363(5)
1.383(6)
1.365(5)
1.314(5)
1.380(5)
Li(2)ϪN(3)
Li(2)ϪS(2)
S(2)ϪC(21)
C(21)ϪN(4)
C(21)ϪC(22)
N(4)ϪN(5)
N(5)ϪN(6)
N(6)ϪC(22)
2.050(9)
2.482(8)
1.726(4)
1.347(5)
1.395(6)
1.369(5)
1.308(5)
1.374(5)
S(1)ϪLi(1)ϪN(6)
Li(1)ϪS(1)ϪC(1)
N(1)ϪC(1)ϪC(2)
C(1)ϪC(2)ϪN(3)
C(1)ϪN(1)ϪN(2)
N(1)ϪN(2)ϪN(3)
N(2)ϪN(3)ϪC(2)
124.7(4)
115.8(2)
104.2(4)
107.8(4)
111.9(3)
105.9(3)
110.3(4)
S(2)ϪLi(2)ϪN(3)
Li(2)ϪS(2)ϪC(21)
N(4)ϪC(21)ϪC(22)
C(21)ϪC(22)ϪN(6)
C(21)ϪN(4)ϪN(5)
N(4)ϪN(5)ϪN(6)
N(5)ϪN(6)ϪC(22)
124.4(4)
116.5(2)
104.8(4)
106.8(4)
111.7(4)
105.8(3)
111.0(4)
Figure 13. Molecular structure of the dimer of 12; hydrogen atoms
omitted for clarity
solvent effect.[1] However, we report here that (for R ϭ Bz)
such a reaction, if followed by reflux and the addition of
TMEDA affords S-lithio-1-benzyl 4-trimethylsilyl-5-thio-
˚
Table 4. Selected bond lengths [A] and angles [°] in 12
1
,2,3-triazole, BzNNNC(Me Si)C(SLi·TMEDA) (12) as the
3
Li(1)ϪS(1A)
Li(1)ϪN(3)
N(3)ϪN(1)
2.422(6)
2.053(6)
1.377(4)
1.285(4)
N(1)ϪC(4)
N(2)ϪC(5)
C(4)ϪC(5)
C(4)ϪS(1)
1.342(4)
1.377(4)
1.385(5)
1.722(4)
only isolable product. In the solid state 12 is dimeric (Fig-
ure 13) and consists of two (mono-TMEDA) complexed
metallo-1-benzyl-5-thio-4-trimethylsilyl-1,2,3-triazole mol- N(3)ϪN(2)
ecules. Akin to 11, 12 is an S-lithiate [LiϪS ϭ 2.422(6) A],
with metal centre stabilisation [Li(1)ϪN(3) ϭ 2.053(6) A]
incurring dimerisation. The two planar triazole systems
show aromatic character (Table 4) and, as such, are essen-
tially similar to those in 11 notwithstanding that the NϪN N(3)ϪN(2)ϪC(5)
distances in the triazole component of 12 are consistent
˚
˚
S(1A)ϪLi(1)ϪN(3)
113.8(3)
124.8(3)
107.1(3)
110.7(3)
109.9(3)
N(1)ϪC(4)ϪC(5)
N(2)ϪC(5)ϪC(4)
N(1)ϪC(4)ϪS(1)
C(4)ϪS(1)ϪLi(1A)
104.6(3)
107.7(3)
124.0(3)
111.4(2)
Li(1)ϪN(3)ϪN(1)
N(1)ϪN(3)ϪN(2)
N(3)ϪN(1)ϪC(4)
with greater localisation of electron density [viz.
C(4)ϪN(1), N(1)ϪN(2), N(2)ϪN(3) in 11 and C(1)ϪN(1), the reaction is refluxed in the presence of TMEDA prior to
N(1)ϪN(3), N(2)ϪN(3) in 12]. Dimerisation of 12 results the recrystallisation and isolation of 12 agrees with the view
in these triazole systems being linked by (and participating that preference for the N-lithiate is diminished in the pres-
in) a hitherto unknown type of 10-membered (NNCSLi)2 ence of sufficiently strong external donation. Furthermore,
heterocycle.
the reaction of BzNCS with 1-Li is apparently not facile.
Of mechanistic importance is the observation that 12 is Hence, treatment of the lithiated diazomethane in (relatively
not the expected lithio-2-benzylamino-5-trimethylsilyl- poorly donating) OEt with BzNCS at low temperature pre-
2
[
1]
1
,3,4-thiadiazole, but rather a lithio-1-benzyl 4-trimethyl- sumably gives only a slow reaction via the N-lithiate. How-
silyl-5-thio-1,2,3-triazole. This is, of course, inconsistent ever, heating of the reaction mixture immediately after in-
with the reaction of N-lithio(trimethylsilyl)diazomethane troducing BzNCS (but before the application of TMEDA)
(
cf. 9) with BzNCS but rather suggests that the reactive affords the lithio-1-benzyl-5-thio-4-trimethylsilyl-1,2,3-tria-
species in solution is the C-lithiate (cf. 1-Li) instead zole, strongly suggesting that the N-isomer has been con-
Scheme 4). This observation suggests several things. That verted into its C-congener prior to significant reaction hav-
(
Scheme 4. Proposed mechanism for the formation of 11 from a C-lithiated diazomethane precursor[18]
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Eur. J. Inorg. Chem. 2003, 3363Ϫ3375
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3371

A. E. H. Wheatley et al.
FULL PAPER
ing occurred. Notably the synthesis of 12 can be reproduced ture dependent. Thus, C- and N-metallation result from the
in THF/TMEDA (with reflux prior to introduction of the exercise of thermodynamic and kinetic control, respectively.
bidentate donor) whereas if the literature preparation (no Consistent with this is the observation, by variable tempera-
reflux) is closely adhered to then 1-H, nBuLi and PhNCS ture NMR spectroscopy, of the irreversible conversion of N-
can be sequentially combined in OEt at 0 °C and worked to C-lithiate at high temperature, a result that has signifi-
2
up to give PhNHCSCHNN 13 in high yield (its formation cant consequences for our view of the reactivity of this lithi-
requiring a lithio-2-phenylamino-1,3,4-thiadiazole precur- odiazomethane with aryl isothiocyanates.
3
sor). While it has been noted that four types of cyclic system
The solid-state structures of both 1-Li· / THF and 9 indi-
2
could reasonably result from the reaction of lithiodiazome- cate why it is that organic syntheses which involve the elim-
[
37]
thanes with aryl isothiocyanates,
only two such classes ination of N from diazomethanes require formation of the
2
have been reported.[ Reaction of the C-lithiate has been C-lithiate with its weak CϪN and strong NϭN bond. Fi-
considered (Scheme 4) to require the initial formation of a nally, such reactivity has been probed and has resulted in
CϪC bond between the diazomethane carbanionic centre the crystallographic characterisation of lithiothiotriazoles
and the isothiocyanate carbon atom. However, 2-amino-5- 11 and 12. Details of their syntheses and structures bear
trimethylsilyl-1,3,4-thiadiazole production necessitates that out the view that product selectivity in these reactions,
the N-lithio(trimethylsilyl)diazomethane molecule forms a rather than being directly solvent dependent, is in fact influ-
NϪC bond prior to ring closure by CϪS bond formation enced by temperature.
1]
(Scheme 5).
Experimental Section
General Remarks: All operations were carried out using standard
Schlenk techniques. Toluene (freshly distilled from sodium) was ad-
ded direct to the nitrogen-filled Schlenk tube using standard syr-
inge techniques. NMR spectroscopy: Bruker DPX 250
1
13
(
(
250.133 MHz for H, 62.533 MHz for
C), DRX 400
1
13
7
400.136 MHz for H, 100.614 MHz for C, 155.508 MHz for Li),
1
DRX 500 (500.050 MHz for H) at 27 °C unless otherwise stated.
For NMR spectroscopy, [D ]DMSO, [D ]THF, or [D ]PhMe as sol-
vents, TMS at 27 °C as external standard (for H and C) and
6
8
8
1
13
7
PhLi in [D
8
]PhMe at 27 °C as external standard (for Li).
Scheme 5. Proposed mechanism for the production of lithio-2-am-
ino-5-trimethylsilyl-1,3,4-thiadiazole from an N-lithiated diazo-
methane precursor
1
3
Synthesis of / [{Me SiC(Li)N } ·3THF] (1-Li· / THF): Prep-
2
3
2 2
[19]
2
Ϫ1
aration as previously reported.
IR (Nujol): ν˜ ϭ 2149 cm w,
2
8
116 m (CϭNϭN sym. str.), 2092 m, 2052 m (CϭNϭN asym. str.),
(n ϭ 3)[ str.], after air exposure 2160 w (CϭNϭ
38]
38 w [SiMe
n
1
N sym. str.), 2116 m (CϭNϭN asym. str.). H NMR (250 MHz,
[
(
D
6
]DMSO): δ ϭ 3.60 (m, 6 H, THF), 1.76 (m, 6 H, THF), 0.05
Conclusions
13
s, 3 H, Me), Ϫ0.18 (s, 6 H, Me) ppm. C NMR (63 MHz,
[
(
D
6
]DMSO): δ ϭ 103.9 (CϭN), 67.1 (THF), 25.2 (THF), 2.1
This work clearly demonstrates for the first time the vi-
SiMe), 0.4 (SiMe) ppm.
ability of both the C- and N-lithiated isomers of a simple
3
Synthesis of 6(Me
Based on the literature preparation.
hexanes, 4 mmol) was added to an OEt
3
SiCN Li)·2[(Me SiC) N Li]·7OEt [(7) ·OEt ]:
2 3 2 3 2 2 2
diazomethane both in the solid state (as, 1-Li· / THF and
2
[17a]
nBuLi (2.5 mL, 3.2  in
(0.5 mL) solution of 1-H
9, respectively) and in solution. X-ray crystallographic
2
characterisations of these two species point to bonding in
the two types of molecule being quite different (Figure 14).
New calculations corroborate these bonding patterns and
(
2 mL, 2  in hexanes, 4 mmol) at Ϫ78 °C. The resultant orange
solution was frozen in liquid nitrogen and then kept at Ϫ25 °C.
Crystals of (7) ·OEt were afforded after 2 days at this temperature.
2
2
[
17a]
also suggest that while the C-lithiated isomer of 1-Li is less The crystal structure of this compound has been reported,
stable than its N-metallated analogue, the energetic differ- supporting data has not been given previously. Yield 201 mg (30%
Si10 (1677):
but
8 18 7
ence between the two decreases with the extent of solvation based on 1-H), m.p. 106Ϫ110 °C. C68H160Li N O
calcd. C 48.66, H 9.61, N 15.02; found C 44.93, H 9.11, N 15.34.
IR (Nujol): ν˜ ϭ 2085 cm m, 2066 m (CϭNϭN sym. str.), 2047
m, 2000 br (CϭNϭN asym. str.), 1632 m (CϭC), 839 m [SiMe
by progressively stronger donors. Reaction conditions em-
ployed in the syntheses of these compounds point to the
regiospecificity of metallation being significantly tempera-
Ϫ1
n
(
n ϭ 3)[ str.], after air exposure 2066 w (CϭNϭN sym. str.). H
NMR (500 MHz, [D ]DMSO): δ ϭ 3.36 (q, 15 H, OEt ), 1.07 (t,
), 0.18 (s, 36 H, Me), Ϫ0.14 (s, 12 H, Me), Ϫ0.18 (s,
38]
1
6
2
2
4
(
(
2.5 H, OEt
2 H, Me) ppm. C NMR (100 MHz, [D
), 15.3 (OEt
2
1
3
6
]DMSO): δ ϭ 144.2
), 2.1 (SiMe ), 0.4
CϭC), 104.1 (CϭN), 65.0 (OEt
SiMe ) ppm.
2
2
3
3
Synthesis of Me
hexanes, 4 mmol) was added to a TMEDA (0.9 mL, 6 mmol) solu-
3 2
SiCN Li·TMEDA (9): nBuLi (2.5 mL, 1.6  in
Figure 14. A review of bonding in C- and N-lithiated isomers of
(
trimethylsilyl)diazomethane
3372
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 3363Ϫ3375

Kinetic and Thermodynamic Lithiated Derivatives of a Simple Diazomethane
tion of 1-H (2 mL, 2  in hexanes, 4 mmol) at Ϫ78 °C. The result- added, providing an orange solution. Storage of the resultant solu-
FULL PAPER
ant orange solution was frozen in liquid nitrogen and then kept at tion for 2 days at room temperature afforded crystals of 12: Yield
Ϫ25 °C. Crystals of 9 were afforded after storage for 24 hours at 154 mg (20%; route a), 62 mg (8%; route b), m.p. Ͼ 163Ϫ165 °C
this temperature. Yield 500 mg (53%), m.p. 122Ϫ124 °C. (decomp.). C18
25LiN Si (236): calcd. C 50.82, H 10.66, N 23.70; found C
found C 55.99, H 8.94, N 21.43. IR (Nujol, cm ): ν˜ ϭ 1735, 1403,
0.56, H 10.79, N 23.84. IR (Nujol): ν˜ ϭ 2129 cm w (CϭNϭN 1377, 842 [SiMe
(n ϭ 3) str.], after air exposure 1734, 1627 br
n
5
H32LiN SSi (385): calcd. C 56.07, H 8.37, N 18.16;
Ϫ1
C
5
10
H
4
Ϫ1
[38]
(n ϭ 3)[
38]
(CϭC str.), 1377. H NMR (400 MHz, [D
H, Ph), 7.17 (m, 2 H, Ph), 7.10 (tt, 1 H, Ph), 5.66 (s, 2 H, CH
6
]DMSO): δ ϭ 2.27 (s, 2.32 (s, 8 H, TMEDA), 2.17 (s, 24 H, TMEDA), 0.32 (s, 9 H, Me)
1
]THF): δ ϭ 7.52 (d, 2
sym. str.), 2042 s (CϭNϭN asym. str.), 835 m [SiMe
str.], after air exposure 2171 w (CϭNϭN sym. str.), 2092 m (Cϭ
n
8
2
),
1
NϭN asym. str.). H NMR (400 MHz, [D
H, CH ), 2.11 (s, 12 H, NMe), Ϫ0.18 (s, 9 H, Me) ppm.
NMR (100 MHz, [D ]DMSO): δ ϭ 104.1 (CϭN), 57.0 (TMEDA), (CϪSi), 139.7, 128.5, 127.4, 126.0 (Ph), 57.8 (TMEDA) 47.8 (CH
5.6 (TMEDA), 0.3 (SiMe ) ppm. 45.3 (TMEDA), Ϫ1.6 (Me Si) ppm.
1
3
13
4
2
C
ppm. C NMR (100 MHz, [D
8
]THF): δ ϭ 159.9 (CϪS), 140.1
),
6
2
4
3
3
Synthesis of PhNNNC(Me THF) (10): nBuLi (1.25 mL, Synthesis of PhNHCSCHNN (13): nBuLi (0.75 mL, 1.6  in hex-
Si)C(SLi·3/
3
2
1
.6  in hexanes, 2 mmol) was added to a THF (3.0 mL) solution anes, 1.2 mmol) was added to an OEt (10.0 mL) solution of 1-H
2
of 1-H (1 mL, 2  in hexanes, 2 mmol) at Ϫ78 °C whereupon the
solution was treated with phenyl isothiocyanate (PhNCS)
(0.6 mL, 2  in hexanes, 1.2 mmol) at 0 °C. After stirring for 20
minutes PhNCS (0.12 mL, 1.2 mmol) was added to the chilled solu-
tion and the mixture stirred for a further 2 hours at this tempera-
(0.24 mL, 2 mmol). The orange precipitate formed on allowing the
solution to warm to room temperature was dissolved at reflux and ture. The solution was allowed to warm to room temperature and
the reaction mixture was then cooled slowly to room temperature. NH Cl (20 mL) was added. The resultant mixture was extracted
with OEt (2 ϫ 10 mL) washed with water (2 ϫ 10 mL) and dried
deposited. Yield 225 mg (31%), m.p. Ͼ 116Ϫ118 °C (decomp.). (MgSO ). Removal of excess solvent afforded 13 as a white powder.
Si (726): calcd. C 56.17, H 7.21, N 11.56; found Yield 160 mg (75%), m.p. Ͼ 170Ϫ172 °C (decomp.). C
4
3
After 1 day needles of PhNNNC(Me
3
Si)C(SLi· /
2
THF) (10) were
2
4
C
34
H
52Li
2
N
6
O
3
S
2
2
8 7 3
H N S
Ϫ1
C 55.82, H 7.40, N 10.46. IR (Nujol): ν˜ ϭ 2116 cm , 2044, 1600, (177): calcd. C 54.22, H 3.98, N 23.71; found C 53.49, H 5.43, N
(n ϭ 3)[ str.], after air exposure
38]
21.05. IR (Nujol, cm ): ν˜ ϭ 3411, 3245 w, 3195 w (NϪH str.),
Ϫ1
1
2
499, 1402, 1378, 839 m [SiMe
n
1
1
053, 2028, 1625 br (CϭC str.), 1499. H NMR spectroscopy 1715, 1597, 1573 (CϭN str.). H NMR (400 MHz, [D
6
]DMSO):
(
400 MHz, [D
8
]THF): δ ϭ 8.12 (m, 2 H, Ph), 7.30 (m, 2 H, Ph),
δ ϭ 10.42 (s, 1 H, NϪH) 8.90 (s, 1 H, NϭCϪH), 7.65 (d, 2 H,
7
.17 (tt, 1 H, Ph), 3.59 (m, 6 H, THF), 1.75 (m, 6 H, THF), 0.33 Ph), 7.32 (m, 2 H, Ph), 7.00 (t, 1 H, Ph), 2.32 (s, 8 H, TMEDA),
s, 9 H, Me) ppm. 13C NMR (100 MHz, [D
]THF): δ ϭ 158.7
CϪS), 143.1 (CϪSi), 140.7, 129.9, 128.2, 126.5, 126.1, 125.4 (Ph),
2.17 (s, 24 H, TMEDA), 0.32 (s, 9 H, Me) ppm. C NMR
(100 MHz, [D ]DMSO): 164.3 (NϭC(N)ϪS), 144.1
13
(
(
8
6
δ
ϭ
Ϫ0.8 (Me) ppm.
(SϪC(H)ϭN), 140.8, 129.1, 121.9, 117.4 (Ph) ppm.
Synthesis of BzNNNC(Me
3
Si)C(SLi·2THF) (11): nBuLi (1.25 mL,
2 2
X-ray Crystallography: Data to check the unit cell of (7) ·OEt
1
.6  in hexanes, 2 mmol.) was added to a THF (2.0 mL) solution
8 18 7
(C68H160Li N O Si10, monoclinic, space group C2/m, a ϭ 23.05,
˚
of 1-H (1 mL, 2  in hexanes, 2 mmol) at Ϫ78 °C after which the b ϭ 15.77, c ϭ 15.05 A, β ϭ 101.9°) were collected on a Rigaku
R-Axis II imaging plate diffractometer[ at 200(2)K using graphite
39]
solution was treated with benzyl isothiocyanate (BzNCS) (0.27 mL,
mmol). The orange precipitate formed on allowing the solution
˚
2
monochromated Mo-K
α
radiation (λ ϭ 0.71069 A). This compared
with the previously published[
17a]
unit cell and so the full data were
to warm to room temperature dissolved at reflux. The reaction mix-
ture was then allowed to cool slowly to room temperature where-
not collected. Data for 9 were collected on a Rigaku R-Axis II
upon it was stored for
BzNNNC(Me
2
days, affording crystals of
imaging plate diffractometer using 45 frames, each frame covering
3
Si)C(SLi·2THF) (11). Yield 256 mg (31%), m.p. Ͼ a 4° oscillation with an exposure time of 30 minutes per frame, in
68Ϫ170 °C (decomp.). C20 32LiN SSi (413): calcd. C 58.08, H each of four orientations. Data for 11 were collected by the ω/2θ
.80, N 10.16; found C 57.15, H 7.76, N 10.39. IR (Nujol): ν˜ ϭ method on a Rigaku AFC-7R four circle diffractometer
1
7
1
H
3 2
O
[
39]
and
str.], after data for 12 were collected on a StoeϪSiemens four circle dif-
Ϫ1
[38]
n
720 cm w, 1403, 1217, 917, 841 [SiMe (n ϭ 3)
1
[40]
air exposure 1719 w, 1625 br (CϭC stretch). H NMR (400 MHz,
fractometer. All structures were solved by direct methods
and
[D
8
]THF): δ ϭ 7.28 (d, 2 H, Ph), 7.13 (m, 2 H, Ph), 7.08 (tt, 1 H, subsequent Fourier difference syntheses and refined by full-matrix
), 0.29 (s, 9 H, Me) ppm. 13C NMR least-squares on F with anisotropic thermal parameters for Li,
[41]
2
Ph), 5.35 (s, 2 H, CH
100 MHz, [D ]THF): δ ϭ 160.4 (CϪS), 141.5 (CϪSi), 140.2,
29.0, 128.5, 127.2 (Ph), 48.8 (CH ), Ϫ0.8 (Me) ppm.
2
(
1
8
N, Si, and most C atoms. A riding model with idealised geometry
2
was employed for H-atom refinement. For 9, one terminal methyl
3
group of a TMEDA molecule and three of the SiMe groups
3
Preparation of BzNNNC(Me Si)C(SLi·TMEDA) (12): (a) nBuLi
showed positional disorder with respect to the position of the C
atoms and were refined isotropically over two different sites with
partial occupancies. Crystallographic data for 9, 11 and 12 are
given in Table 5. CCDC-207850 (9), -207849 (11), and -207848 (12)
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge at www.ccdc.cam.ac.uk/
conts/retrieving.html [or from the Cambridge Crystallographic
Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; Fax:
(
(
1.25 mL, 1.6  in hexanes, 2 mmol) was added to an OEt
2.0 mL) solution of 1-H (1 mL, 2  in hexanes, 2 mmol) at
2
Ϫ78 °C. BzNCS (0.27 mL, 2 mmol) was then added to the chilled
solution, affording a clear yellow solution at room temperature.
This was heated to reflux whereupon TMEDA (0.3 mL, 2 mmol)
was added. Storage of the resultant solution for 2 days at room
temperature
afforded
crystals
of
3
BzNNNC(Me Si)C-
(SLi·TMEDA), 12.
(
internat.) ϩ44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
(
b) nBuLi (1.25 mL, 1.6  in hexanes, 2 mmol) was added to a
Computational Methods: Preliminary geometry optimisation calcu-
lations[ based on XCN
20]
THF (1.8 mL) solution of 1-H (1 mL, 2  in hexanes, 2 mmol) at
Ϫ78 °C. BzNCS (0.27 mL, 2 mmol) was then added to the chilled
solution, affording a yellow precipitate at room temperature. The
mixture was heated to reflux and TMEDA (0.3 mL, 2 mmol) was
2 3 3
Li·nL (X ϭ H Si, Me Si; n ϭ 0, 1, 2; L ϭ
[22]
OEt , THF) were done using the 6-31G* basis set
2
at the HF
level. A frequency analysis was performed on the most stable con-
formation of each structure and the geometry was refined using
Eur. J. Inorg. Chem. 2003, 3363Ϫ3375
www.eurjic.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3373

A. E. H. Wheatley et al.
FULL PAPER
Table 5. Crystallographic data for 9, 11, and 12
9
11
12
Formula
M
C
945.48
40
H
100Li
4
N16Si
4
C
413.58
20
H
32LiN
3
OSSi
C
385.58
18
H
32LiN
5
SSi
Crystal system
Space group
Triclinic
P1
Triclinic
P1
Monoclinic
C2/c
19.705(4)
11.210(2)
23.186(5)
90
114.81(3)
90
4649(2)
8
¯
¯
˚
a [A]
14.836(2)
19.893(3)
11.880(1)
99.77(1)
113.15(1)
84.15(1)
3175.7(7)
2
11.147(4)
20.679(7)
10.151(3)
97.62(3)
90.49(4)
94.42(3)
2311.9(13)
4
˚
b [A]
˚
c [A]
α [°]
β [°]
γ [°]
˚
3
U [A ]
Z
D
[g cmϪ3
]
0.989
0.71073
0.131
1.188
0.71069
0.211
1.102
0.71073
0.201
c
˚
λ [A]
µ [mmϪ1]
T [K]
180(2)
180(2)
180(2)
Refl., unique
Refl. F Ͼ 2σ(F )
12251, 7118
4822
8322, 7889
4542
4337, 4076
2875
2
2
θ [°]
int
3.59Ϫ22.02
0.0645
2.60Ϫ25.01
0.0843
4.12Ϫ25.00
0.0567
R
R, wR2
0.0692, 0.1813
606
0.371, Ϫ0.353
0.0707, 0.1755
511
0.369, Ϫ0.304
0.0665, 0.1891
235
0.839, Ϫ0.285
Parameters
Peak, hole [e·AϪ3]
˚
DFT methods (B3LYP/6-311G**).[21,22] The structural parameters
reported here were taken from the DFT calculations while the elec-
tronic energy of the DFT calculation was modified by the scaled
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 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 3363Ϫ3375

Kinetic and Thermodynamic Lithiated Derivatives of a Simple Diazomethane
FULL PAPER
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