Oxygen scavenging by lithium zincates: The synthesis, structural characterisation and derivatisation of [Ph(2-C5H4N)N]2ZnRLi·nthf (R = But, Bun; n = 1, 2)

Article abstract of DOI:10.1039/b203451d

The 1:2 reaction of ZnMe₂ with N-2-pyridylaniline, Ph(2-C₅H₄N)NH 1, affords [Ph(2-C₅H₄N)N]₂Zn 10, the treatment of which with BuLi and thf affords the diastereomeric lithium zincate [Ph(2-C

Full text of DOI:10.1039/b203451d

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Oxygen scavenging by lithium zincates: the synthesis, structural
characterisation and derivatisation of [Ph(2-C5H4N)N]2ZnRLiؒnthf
(R ؍ But, Bun; n ؍ 1, 2)
Sally R. Boss, Robert Haigh, David J. Linton and Andrew E. H. Wheatley*
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, UK CB2 1EW
Received 8th April 2002, Accepted 19th June 2002
First published as an Advance Article on the web 25th July 2002
The 1 : 2 reaction of ZnMe2 with N-2-pyridylaniline, Ph(2-C5H4N)NH 1, affords [Ph(2-C5H4N)N]2Zn 10, the
treatment of which with BuLi and thf affords the diastereomeric lithium zincate [Ph(2-C5H4N)N]2ZnRLiؒnthf
(R = Bun, n = 2; 11a; R = But, n = 1, 11b). The sequential treatment of 10 (either in situ or after isolation) with
organolithium substrates and molecular oxygen has afforded insights into the oxygen-scavenging capacity of
mixed Group 1–Group 12 species. Hence, 10 reacts with BunLi, O2 and thf or dimethoxyethane (dme) to give
{[Ph(2-C5H4N)N]2ZnOBunLiؒnL}2 (n = 1, L = thf, 12a; n = 0.5, L = dme, 12b), with the structural relationship
between 11a and 12a strongly suggesting that for R = Bun oxygenation proceeds by insertion into the Zn–C
bond of an {[Ph(2-C5H4N)N]2ZnR}Ϫ ion. The employment of ButLi, O2 and thf together with 10 affords only
the previously reported complex [Ph(2-C5H4N)N]2Zn[(µ3-O)But]2(Liؒthf )2 4, the formation of which may be
rationalised in terms of the But van der Waals radius and cone angle.
Mixed Li–Zn systems have been used to achieve a wide variety
of important chemical transformations. Conjugate addition to
enones,1 the formation of α,β-disubstituted propargylic species
and allenes,2 halogen–zinc exchange3 and metal carbenoid syn-
thesis4 have been effected, and lately dilithium tetraorgano-
zincates have also found applications.5 However, the struc-
tural chemistry of lithium organozincates is incompletely
understood.6 While Lewis bases may stabilise ion-separated
triorganozincate complexes,7 the presence of electron-rich
heteroatoms in the zinc-bonded organic residues favours ion-
association. In this context Li(µ-C)nZn (n = 1, 2) motifs domin-
ate the structures of known ion-bonded lithium zincates.
some generality to the formation of dimers such as 5 and 6,
it once more implied the formal insertion of oxygen into the
Zn–C bond of an {[R(2-C5H4N)N]2ZnMe}Ϫ anion. In order to
probe this hypothesis we have synthesised and characterised the
precursor lithium zincates [Ph(2-C5H4N)N]2ZnRLi (R = Bun,
But) and tested their reactivity towards oxygen.
Results and discussion
The treatment of ZnMe2 with 2 eq. N-2-pyridylaniline affords
an orange solution from which, after heating, a yellow precipi-
tate deposits. Characterisation (see Experimental section) of
this material suggests that it is the zinc dianilide [Ph(2-C5-
H4N)N]2Zn 10. The treatment of this with BunLi affords
a single isolable product. 1H NMR spectroscopy points to
the presence of 2-pyridylanilide and Bun ligands in a 2 : 1 ratio.
The observation of cross peaks in the NOESY between the
α-methylene resonance and aromatic signals indicates that in
[2H6]C6H6 solution this species is the expected heterobimetallic
’ate complex. Moreover, NOESY indicates that in hydrocarbon
solution this complex is able to adopt a variety of geometries.
Nevertheless, one set of resonances is clearly dominant and
COSY demonstrates that in this species the signal due to the
α-methylene component of the Zn-bonded Bun group is at
δ 1.75 with the corresponding α-C signal at δ 29.7 by 13C NMR
spectroscopy. X-Ray crystallography bears out this interpret-
ation, revealing the monomeric bis(thf )-solvate [Ph(2-C5-
H4N)N]2ZnBunLiؒ2thf 11a which crystallises in the space
group P21/n. The alkali metal centre is further supported by the
2-pyridylanilide groups which bridge between each of the two
metal centres in the monomer in two distinct ways (Fig. 1).
One ligand utilises its formally deprotonated N-centre (N4) to
interact with both the Li and Zn centres [Li1–N4 2.092(6),
Zn1–N4 2.135(3) Å; Li1–N4–Zn1 88.62(17)Њ (Table 1)]
while its pyridyl substituent stabilises the Group 12 metal
ion [Zn1–N3 2.188(3) Å] affording a four-membered ZnN2C
heterocycle. This 2-pyridylanilide ligand thus reveals the same
single-centre bridging motif as that shown by the only other
reported N-bridged lithium zincate;10 however the second such
Hence, [2-(NMe2CH2)C6H4]3ZnLiؒthf reveals
a mono-aryl
inter-metal bridge8 while double bridging is common for
tetraorganozincate complexes.8,9 Heteroatom bridges have
also been reported, with, for example, (Me3Si)2N(Me3SiCH2)2-
ZnLiؒL (L = 1,3,5-trimethyl-1,3,5-triazine) incorporating a
Zn(µ-N)Li linkage.10
Lewis base centres may be introduced into organometallic
molecules in a variety of ways. The insertion of oxygen into a
metal–carbon interaction is one such route that has been the
subject of much recent study.11 Whereas the oxygenation of
organometallic compounds has been probed by the synthesis of
new mixed s-block metal compounds,12 advances have also been
made in the templated derivatisation of lithium aluminates
using O2.13 Moreover the sequential reaction of 2-pyridyl-
amines [R(2-C5H4N)NH, R = Ph 1, 3,5-xy 2 (xy = xylyl), 2,6-xy
3] (1 eq.) with ZnMe2, ButLi and thereafter with dry air has
been reported to yield various heterobimetallic species.14 For R
= Ph, [Ph(2-C5H4N)N]2Zn[(µ3-O)But]2(Liؒthf )2 4 is formed
alongside {[Ph(2-C5H4N)N]2ZnOMeLiؒthf}2 5 — the R = 3,5-
xy analogue (6) of which has also been reported.14 However, the
complexity with which such oxygen-capture processes operate is
demonstrated by the observation that use of the 2,6-xylyl sub-
strate 3 gives the pseudo-cubic dimer [Me(ButO)Zn(ButO)Liؒ
thf ]2 7 instead. More recently, analogous work using PhN(H)-
C(Ph)᎐NPh (HAm) 815 has revealed solvent-dependent oxygen
᎐
sensitivity, with dimeric (Am2ZnOMeLiؒthf )2 9 (cf. 5/6)14 crys-
tallising from thf.16 While this observation not only suggested
DOI: 10.1039/b203451d
J. Chem. Soc., Dalton Trans., 2002, 3129–3134
This journal is © The Royal Society of Chemistry 2002
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Table 1 Selected bond lengths (Å) and angles (Њ) for 11a
Table 3 Selected bond lengths (Å) and angles (Њ) for 12a. Symmetry
operations which relate atoms to their _2 equivalents: Ϫx, Ϫy ϩ 1,
Ϫz Ϫ 1
Li1–N1
Li1–N4
Zn1–N2
2.054(6)
2.092(6)
2.024(3)
Zn1–N3
Zn1–N4
Zn1–C23
2.188(3)
2.135(3)
1.985(4)
Li1–O1
Li1–O2
Li1–N1
Li1–N3_2
1.916(5)
1.968(5)
2.068(5)
2.077(5)
Zn1–O1
Zn1–O1_2
Zn1–N2
Zn1–N4
2.0293(16)
2.0239(17)
1.976(2)
Li1–N4–Zn1
N1–Li1–N4
N2–Zn1–N4
N3–Zn1–N4
88.62(17)
110.9(3)
113.44(10)
62.61(10)
N2–Zn1–C23
N3–Zn1–C23
N4–Zn1–C23
120.36(13)
127.96(13)
119.17(13)
1.969(2)
O1–Zn1–O1_2
O1–Li1–N1
O1–Li1–N3_2
86.16(7)
107.9(2)
108.9(2)
O1–Zn1–N2
O1–Zn1–N4
Zn1–O1–Zn1_2
117.10(8)
112.99(9)
93.84(7)
Table 2 Selected bond lengths (Å) and angles (Њ) for 11b
Li1–N1
Li1–N2
Li1–N3
Zn1–N1
2.206(6)
2.032(6)
2.032(6)
2.049(3)
Zn1–N3
Zn1–N4
Zn1–C23
2.234(3)
2.116(2)
1.989(3)
Li1–N1–Zn1
Li1–N3–Zn1
N1–Li1–N2
N1–Li1–N3
N2–Li1–N3
N1–Zn1–N3
77.52(17)
77.24(18)
64.8(2)
103.2(3)
110.2(3)
101.72(10)
N1–Zn1–N4
N3–Zn1–N4
N1–Zn1–C23
N3–Zn1–C23
N4–Zn1–C23
104.83(10)
62.30(10)
125.96(12)
120.75(12)
123.22(12)
Fig. 2 Molecular structure of 11b; hydrogen atoms omitted for clarity.
notwithstanding that the pyridyl N-centre now supports the
zinc [Zn1–N4 2.116(2) Å] and so generates a CN2Zn ring.
The treatment of a toluene–thf solution of 11a with O2 yields
1
only one crystalline product. H NMR spectroscopy reveals
retention of the 2 : 1 2-pyridylanilide : Bun ratio. However, the
Zn-bonded methylene group is no longer observed. Instead, the
appearance of a broad signal centred at δ 4.02 and a singlet at
δ 64.8 (by 1H and 13C NMR spectroscopy, respectively)
suggests the presence of a ZnOBun moiety. Secondly only 1 eq.
thf is present in the complex relative to the other organic
components. Consistent with these observations, X-ray
crystallography reveals this material to be {[Ph(2-C5H4N)N]2-
ZnOBunLiؒthf}2 12a and, therefore, confirms that a systematic
and controllable synthesis of dimeric species of the type previ-
ously reported to result from the non-trivial oxygenation of
heterobimetallic mixtures14,16 is achievable (Scheme 1). Thus,
Fig. 1 Molecular structure of 11a; hydrogen atoms and Bun disorder
omitted.
ligand behaves in a manner akin to that noted recently in
[R2ZnOMeLiؒ thf ]2 (R = 2-pyridylanilide,14 N,NЈ-diphenyl-
benzamidinate16). Each N-centre within the organic residue
bonds to only one metal ion. So whereas (deprotonated) N2
interacts with the Zn2ϩ ion the formally neutral pyridyl
N-centre bonds to the alkali metal; the result being that in the
solid state the core of 11a is based on a six-membered ZnN3CLi
metallocycle.
In a similar vein, ButLi combines with 1 to yield a lithium
zincate complex, [Ph(2-C5H4N)N]2ZnButLiؒthf 11b, which
reveals a resonance for the Zn–C fragment at δ 33.9 by 13C
NMR spectroscopy. Once more, NOESY can be employed to
reveal through-space interaction between the But and aromatic
systems, implying retention of the ’ate complex in [2H6]C6H6
solution. The crystal structure of this compound reveals the
reasons for mono(thf )-coordination of the alkali metal centre
(Fig. 2). Whereas 11a revealed amide ligands interacting with
Liϩ through only one N-centre each, in 11b the amide groups
form three interactions with the Group 1 ion. One such ligand
bridges between the two metals utilising its deprotonated N-
centre [Li1–N1 2.206(6), Zn1–N1 2.049(3) Å; Li1–N1–Zn1
77.52(17)Њ (Table 2)], with further interaction between this resi-
due and the Group 1 metal utilising its pyridyl N-atom [Li1–N2
2.032(6) Å] and affording a four-membered CN2Li heterocycle.
A similar bonding pattern is noted for the second amide ligand
[Li1–N3 2.032(6), Zn1–N3 2.234(3) Å; Li1–N3–Zn1 77.24(18)Њ]
Scheme 1
12a is a Ci-symmetry dimer in the solid state (Fig. 3). However,
whereas the previous observation of tetrahedral metal centres
in the core (ZnO)2 ring [mean Zn–O = 2.0266 Å; O–Zn–O =
86.16(7), Zn–O–Zn = 93.84(7)Њ (Table 3)] in complexes of this
type only implied the simple inclusion of oxygen into the Zn–C
bond of a lithium triorganozincate anion, a comparison of the
structure with that of 11a clearly establishes that such a process
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Table 4 Selected bond lengths (Å) and angles (Њ) for 12b. Symmetry
operations which relate atoms to their _2 equivalents: Ϫx Ϫ 1, Ϫy,
Ϫz ϩ 1 and Ϫx, Ϫy ϩ 1, Ϫz
Li1–O2
Li1–O4
Li1–N2
Li1–N4_2
1.929(5)
2.096(5)
2.059(5)
2.055(5)
Zn1–O2
Zn1–O2_2
Zn1–N1
Zn1–N3
2.0274(18)
2.0410(19)
1.983(2)
1.987(2)
O2–Zn1–O2_2
O2–Li1–N2
O2–Li1–N4_2
87.04(8)
109.1(2)
105.5(2)
O2–Zn1–N1
O2–Zn1–N3
Zn1–O2–Zn1_2
112.59(8)
109.70(8)
92.96(7)
Fig. 4 Molecular structure of polymeric 12b; hydrogen atoms and
minor Bun and dme disorder omitted for clarity.
complex [Ph(2-C5H4N)N]2Zn[(µ3-O)But]2(Liؒthf )2 4 as the only
isolable product in spite of a 1 : 1 Li : Zn ratio in the reaction
mixture. The synthesis and isolation of 4 from 11b strongly
suggests a steric influence by the R-group on the oxygen scav-
enging chemistry of the {[Ph(2-C5H4N)N]2ZnR}Ϫ (R = Bun,
But) ion. The bridging OBun moiety in 12a is located in an
elongated enclosure defined by two pyridyl rings (N1, N3, C1,
C16), two Ph groups (C6_2, C7_2, C17, C22) and one thf com-
plexant (O2, C27) (Fig. 5). The dimensions of this cavity can be
Fig. 3 Molecular structure of dimeric 12a; hydrogen atoms omitted.
is viable. The Liϩ ions are anti-disposed about the core and
interact with the O-centres, with dimerisation allowing each
metal to also be coordinated by a single pyridyl N-centre in
either half of the dimer (mean Li–N = 2.073 Å). The result is
the formation of two LiO-edge-fused pairs of six-membered
NCNZnOLi rings where each pair displays one intra-monomer
and one inter-monomer Li–N interaction. Moreover, the
motif noted in the structure of 11a — whereby a 2-pyridyl-
anilide ligand bridges between lithium and zinc such that each
N-centre within the organic residue bonds to only one metal ion
— is retained in that of 12a. Lastly, the dimeric structure of 12a
reveals two types of 2-pyridylanilide ligand with that contain-
ing N3/4 being arranged such that its pyridyl component
projects endo to the (ZnO)2 core whereas that containing N1/2
instead reveals an exo-oriented pyridyl ring. In this context, the
observation of double peaks for each of the aromatic signals in
the 13C NMR spectrum of 12a in hydrocarbon solution is con-
sistent with retention of the solid-state structure.
The stability of the four-membered (ZnO)2 metallocycle in
dimers such as 5, 6, 9 and — in the present context — 12a can
be demonstrated by the unusual behaviour of dimethoxyethane
(dme) in the product (12b) obtained by the sequential treatment
of 10 with BunLi, dme and O2. 1H NMR spectroscopy suggests
a 4 : 2 : 1 2-pyridylanilide : Bun : dme ratio and this is borne out
crystallographically by the observation that 12b is {[Ph(2-C5-
H4N)N]2ZnOBunLiؒ0.5dme}2. Hence, 12b reveals the same
dimeric configuration and (ZnO)2 core [mean Zn–O = 2.034 Å;
O–Zn–O = 87.04(8), Zn–O–Zn = 92.96(7)Њ (Table 4)] (Fig. 4) as
that noted for its thf-solvated analogue. Rather than adopting
its more normal chelating mode,17 the preference of Liϩ for
tetrahedral coordination coupled with the presumed stability
of the (ZnO)2 core (and consequently retention of a dimeric
structure), causes dme to bridge between metal centres17,18 in
adjacent aggregates. In consequence, 12b is rendered polymeric
in the solid state.
Fig. 5 Space filling diagram of dimeric 12a showing the incorporation
of OBun in a pocket defined by three anilide ligands and one thf
molecule.
approximated from the non-bonding distances between the van
der Waals extrema of these residues, and such an analysis
reveals that the topology of the pocket renders it ideal for occu-
pation by OBun but not by OBut. Hence, the observation of
C16 ؒ ؒ ؒ C27 and N3 ؒ ؒ ؒ C27 non-bonding distances of 7.265
and 7.146 Å, respectively, with C16 ؒ ؒ ؒ H27A/B and
N3 ؒ ؒ ؒ H27A/B distances (calculated on the basis of a riding
model — see Experimental section) of 6.794/7.251 Å and 6.792/
6.953 Å, respectively. These parameters suggest a gap between
van der Waals extrema of between 3.9 Å (for N3 ؒ ؒ ؒ H27A)
and 4.4
Å (for C16 ؒ ؒ ؒ H27B). Similarly, N1 ؒ ؒ ؒ C6_2,
N1 ؒ ؒ ؒ C7_2, C6_2 ؒ ؒ ؒ C17 and C6_2 ؒ ؒ ؒ C22 are 6.833,
6.526, 7.235 and 7.807 Å, respectively (with calculated
N1 ؒ ؒ ؒ H7_2 and C6_2 ؒ ؒ ؒ H22A displacements being 6.044
and 7.358 Å), and these point to distances between van der
Waals extrema of 3.3–4.4 Å. The sterically unencumbered
n-butyl group exhibits an irregular van der Waals radius
Whereas in the case of 11a the direct insertion of an oxygen
atom into an existing Zn–C bond is observed, the oxygen-
ation of But complex 11b gives rise to more complicated
behaviour and affords the previously reported14 trigonal
J. Chem. Soc., Dalton Trans., 2002, 3129–3134
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[defined by C23–C24 1.502(4) Å and mean calculated C23–
H23, C24–H24 0.990 Å] and a Tolman cone angle19 of 138.8Њ
and is clearly able to reside in this pocket. However, the more
massive 158.0Њ cone angle19 and uniform 3.1 Å van der Waals
radius of the t-butyl fragment (mean calculated values for com-
plex 4) appear to disfavour its inclusion in a cavity of the type
revealed by 12a, thereby suggesting a thermodynamic reason
for the formation of 4. Moreover, a compelling empirical
relationship exists between the structure-types represented by
these two compounds, with the (2-pyridyl)anilide ligands in 12a
being arranged in a manner that suggests an intimate relation-
ship with the structure of 4. Formally, this can be described in
terms of the rearrangement of two Zn–O interactions and two
Li–O bonds (Fig. 6b) in response to the presence of either one
ZnORLiؒnthf monomer, ii) 10 is expelled from an unstable
dimer akin to 12a or, iii) 10 and BuLi are mutually exclusive
prior to oxygenation. On the basis of the present data, the first
of these options appears most likely, with the structure of
12b suggesting the stability of a (ZnO)2 ring and both crystallo-
graphic and solution NMR data for 11a/b pointing to the
interaction of 10 with a supplied organolithium reagent.
Experimental
Methods and materials
Reactions and manipulations were carried out under an inert
atmosphere of dry nitrogen, using double manifold and glove-
box techniques. Where appropriate the treatment of air-
sensitive reaction mixtures with oxygen was achieved using
molecular oxygen (BOC) dried over P2O5 (Lancaster). All
other chemical reagents were used as received from Aldrich or
Lancaster without further purification. Toluene and thf were
distilled off sodium or sodium–potassium alloy immediately
before use.
NMR data were collected on either a Bruker DPX 400 or
DRX 400 (400.12 MHz for 1H) or a Bruker DRX 500 FT NMR
1
spectrometer (500.05 MHz for H and 125.01 for 13C) at 27 ЊC
or 50 ЊC. Chemical shifts are internally referenced against
deuterated solvents and calculated relative to TMS.
Synthesis and characterisation
[Ph(2-C5H4N)N]2Zn, 10. ZnMe2 (0.25 ml, 0.5 mmol, 2 M in
toluene) was added to N-2-pyridylaniline (0.17 g, 1 mmol) in
toluene (1 ml). The yellow precipitate which resulted from
reflux of this mixture could be isolated or treated with toluene
(14 ml) to afford a solution which yielded colourless micro-
crystals after 3 d at Ϫ30 ЊC. Both materials analyse as 10. For
the crystalline sample: Yield 140 mg (70%), mp 238–240 ЊC.
Found: C 64.17, H 4.60, N 12.51%. Calc. for C22H18N4Zn: C
1
65.44, H 4.49, N 13.87%. H NMR spectroscopy (400 MHz,
Fig. 6 {[Ph(2-C5H4N)N]2ZnORLiؒthf}2 (a) can be viewed as incorpor-
ating the same components as [Ph(2-C5H4N)N]2Zn[(µ3-O)R]2(Liؒthf )2
(c) upon the formal abstraction (b) of 1 eq. zinc dianilide 10.
[6H6]dmso, 27 ЊC), δ 8.95 (m, br, 1H, Ar), 7.38 (dd, 1H, Ar),
7.24–7.12 (m, 4.H, Ar), 6.98–6.51 (m, 0.8H, PhMe), 6.84 (d, 1H
Ar), 6.76 (m, 1H,Ar), 6.39 (m, br, 1H, Ar), 2.27 (s, 0.5H,
PhMe).
or two molecules of [Ph(2-C5H4N)N]2Zn (10). The inclusion of
two zinc dianilide moieties appears to be concomitant with the
formation of a dimer (Fig. 6a) of the type noted for 12a/b which
incorporates the alkoxy moieties within a well defined cavity.
However, the coordination of two ROLi fragments by just one
molecule of 10 instead yields a trigonal structure (Fig. 6c), akin
to that previously seen for complex 4, in which the steric con-
straints around the alkoxy groups are considerably diminished.
[Ph(2-C5H4N)N]2ZnBunLiؒ2thf, 11a. ZnMe2 (0.25 ml,
0.5 mmol, 2 M in toluene) was added to N-2-pyridylaniline
(0.17 g, 1 mmol) in toluene (0.75 ml). The mixture was refluxed
and then treated with BunLi (0.30 ml, 0.5 mmol, 1.6 M in
hexanes) at Ϫ78 ЊC and the resultant suspension was allowed to
warm to room temperature. The addition of thf (0.08 ml)
afforded a solution which gave 11a after 2 d at Ϫ30 ЊC. Yield 80
mg (26%), mp 98–100 ЊC. Found: C 66.44, H 6.84, N 8.50%.
Calc. for C34H43LiN4O2Zn: C 66.72, H 7.08, N 9.15%. 1H NMR
spectroscopy (400 MHz, [2H6]C6H6, 27 ЊC), δ 7.94 (m, br, 2H,
Ar), 7.43 (m, br, 2H, Ar), 7.36 (dd, 2H, Ar), 7.14 (dd, 2H, Ar),
7.01 (dd, 4H, Ar), 6.83 (m, br, 2H, Ar), 6.19 (m, br, 2H, Ar),
5.99 (m, br, 2H, Ar), 3.48 (m, 8H, thf ), 1.75 (m, br, 2H, α-CH2),
1.49 (m, br, 2H, γ-CH2), 1.34 (m, 8H, thf ), 1.04 (t, 3H, CH3),
0.95 (m, 2H, β-CH2). 13C NMR spectroscopy (125 MHz,
[2H6]C6H6, 27 ЊC), δ 167.8, 152.2 (i-Ar), 147.3, 138.4, 129.6,
122.7, 120.7, 111.3, 109.7 (m/p-Ar), 67.9 (thf ), 29.7 (α-CH2),
25.6 (thf ), 25.1 (γ-CH2), 14.3 (CH3), 13.9 (β-CH2).
Conclusions
The treatment of zinc dianilide 10 (in situ or after isolation and
re-dissolution of the micro-crystalline zinc compound) with a
suitable organolithium substrate and then with O2 has estab-
lished the viability of (previously postulated)14,16 oxygen inser-
tion into the Zn–C bond of a {[Ph(2-C5H4N)N]2ZnR}Ϫ ion.
For sterically undemanding R-groups such as Bun this is
revealed by the synthesis and characterisation of 11a and 12a.
That the dimeric motif noted in the latter complex is stable is
suggested by the observation that the presence of the poten-
tially Li-chelating agent dme does not result in deaggregation
(12b).
[Ph(2-C5H4N)N]2ZnButLiؒthf, 11b. ZnMe2 (0.25 ml, 0.5
mmol, 2 M in toluene) was added to N-2-pyridylaniline (0.17 g,
1 mmol) in toluene (1.25 ml). The mixture was refluxed and
then treated with ButLi (0.30 ml, 0.5 mmol, 1.7 M in pentane) at
Ϫ78 ЊC and the resultant suspension was allowed to attain
room temperature. A solution was afforded by the addition of
thf (0.08 ml) and after 2 d at Ϫ30 ЊC, 11b deposited. Yield
146 mg (54%), mp 80–82 ЊC. Found: C 66.06, H 6.59, N 10.34%.
Calc. for C30H35LiN4OZn: C 66.73, H 6.53, N 10.38%. 1H
The presence of a sterically more demanding R-group (But)
in the {[Ph(2-C5H4N)N]2ZnR}Ϫ precursor to oxygenation leads
to a more complicated reaction as evidenced by the isolation of
4. The intuitively close relationship between the solid-state
structures of 12a and 4 (Fig. 6) is presently being explored
through elucidation of the route by which these complexes are
generated in solution. Three viable pathways can be suggested:
i) zinc dianilide 10 is expelled from an [Ph(2-C5H4N)N]2-
3132
J. Chem. Soc., Dalton Trans., 2002, 3129–3134

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Table 5 Crystallographic data for 11a–12b
11a
11b
12a
12b
Formula
Mr
C34H43LiN4O2Zn
612.03
C30H35LiN4OZn
539.93
C30H35LiN4O2Zn
555.93
C56H64Li2N8O4Zn2
1057.77
Crystal system
Space group
Monoclinic
P21/n
Monoclinic
P21/c
Triclinic
P1
Triclinic
P1
¯
¯
a/Å
b/Å
c/Å
α/Њ
12.3776(7)
18.8123(6)
14.0799(8)
90
100.231(2)
90
3226.4(3)
4
1.260
9.6358(5)
17.4699(9)
16.9408(5)
90
93.230(3)
90
2847.2(2)
4
1.260
11.715(2)
12.228(2)
12.323(2)
107.10(3)
106.27(3)
111.01(3)
1420.3(5)
2
11.9618(3)
12.7891(3)
19.3890(6)
77.647(13)
73.211(15)
74.019(14)
2700.70(12)
2
β/Њ
γ/Њ
U/Å3
Z
ρcalc
1.300
0.940
Radiation
Mo-Kα (λ = 0.71069 Å)
0.796
Mo-Kα (λ = 0.71069 Å)
0.891
Mo-Kα (λ = 0.71069 Å)
0.897
Mo-Kα (λ = 0.71069 Å)
1.301
µ/mmϪ1
T /K
180(2)
19551
5670
0.1123
0.0536, 0.1010
406
1.029
220(2)
18191
4645
0.0500
0.0597, 0.1309
334
1.076
180(2)
16302
6373
0.0559
0.0462, 0.1094
343
1.056
180(2)
12229
9177
0.0536
0.0429, 0.1509
698
1.164
Measured reflections
Unique reflections
Rint
Final R(F), wR(F 2)
Parameters
GoF
Max. peak, hole/e ÅϪ3
0.504
0.456
0.658
0.996
NMR spectroscopy (500 MHz, [2H6]C6H6, 27 ЊC), δ 7.84 (m, br,
2H, Ar), 7.45 (m, br, 4H, Ar), 7.38 (m, br, 4H, Ar), 7.02 (m, br,
6H, Ar), 6.22 (dd, br, 2H, Ar), 3.16 (m, 4H, thf ), 1.49 (s, 9H,
But), 1.08 (m, 4H, thf ). 13C NMR spectroscopy (125 MHz,
[2H6]C6H6, 27 ЊC), δ 167.7, 151.8 (i-Ar), 147.2, 138.7, 129.7,
122.3, 120.7, 111.8, 111.1 (m/p-Ar), 68.1 (thf ), 33.9 (But), 25.1
(thf ).
low-temperature device (Table 5). Structures were solved by
direct methods20 and refined against F 2 using SHELXL-97.21
Hydrogen atoms were placed geometrically and allowed to ride
during subsequent refinement.
The Bun chain in structure 11a was found to be disordered
while 12b revealed minor disorder in the Bun and dme resi-
dues. In each case, disordered groups were modelled over two
orientations, each being refined at half occupancy.
{[Ph(2-C5H4N)N]2ZnOBunLiؒthf}2, 12a. As for 11a in toluene
(1 ml) and with the addition of thf (0.4 ml) being followed by
the introduction of dry O2 (ca. 15 s), reduction to half-volume
and storage at Ϫ30 ЊC for 3 d to give 12a. Yield 131 mg (49% by
ZnMe2), mp decomp. from 165 ЊC. Found: C 63.53, H 6.23, N
10.32%. Calc. for C60H70Li2N8O4Zn2: C 64.81, H 6.35, N
CCDC reference numbers 183652–183655.
See http://www.rsc.org/suppdata/dt/b2/b203451d/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
1
10.08%. H NMR spectroscopy (400 MHz, [2H6]C6H6, 50 ЊC),
We thank the UK EPSRC (S. R. B., R. H., D. J. L.) for financial
support.
δ 8.06 (m, br, 2H, Ar), 7.06–6.97 (m, br, Ar, 6H), 6.86–6.25 (m,
8H, Ar), 6.00 (m, br, 2H, Ar), 4.02 (s, br, 2H, α-CH2), 3.63 (m,
4H, thf ), 1.72 (m, br, 2H, β-CH2), 1.52 (m, 4H, thf ), 1.32 (m, br,
2H, γ-CH2), 0.94 (m, 3H, CH3). 13C NMR spectroscopy (125
MHz, [2H6]C6H6, 50 ЊC), δ 168.8, 168.6 (i-Ar), 152.0, 151.7
(i-Ar), 146.6, 145.5, 137.5, 137.1, 129.2, 129.1, 129.0, 128.9,
124.7 124.5, 121.2, 120.8, 116.2, 115.9, 110.7, 110.5, 109.8,
109.7 (m/p-Ar), 67.6 (thf ), 64.8 (α-CH2), 39.5 (CH2), 25.6 (thf ),
19.5 (CH2), 14.1 (CH3).
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Calc. for C56H64Li2N8O4Zn2: C 63.58, H 6.10, N 10.59%. H
NMR spectroscopy (500 MHz, [2H6]C6H6, 27 ЊC), δ 8.21 (m, br,
2H, Ar), 7.26–7.19 (m, br, 2H, Ar), 7.10–6.69 (m, br, 6H, Ar),
6.54 (m, br, 2H, Ar), 6.39 (m, br, 2H, Ar), 6.27 (m, br, 2H, Ar),
5.96 (m, br, 2H, Ar), 4.07 (s, br, 2H, α-CH2), 3.35 (s, br, 2H,
dme), 3.13 (s, 3H, dme), 1.74 (m, br, 2H, β-CH2), 1.36 (m, br,
2H, γ-CH2), 0.98–0.84 (m, br, 3H, CH3). 13C NMR spectro-
scopy (100 MHz, [2H6]C6H6, 27 ЊC), δ 168.7, 156.4 (i-Ar), 148.5,
137.0, 129.1, 129.0, 122.3, 120.2, 114.6, 109.8, 108.2 (m/p-Ar),
72.0 (dme), 62.2 (α-CH2), 58.4 (dme), 35.1 (CH2), 19.0 (CH2),
13.8 (CH3).
X-Ray crystallography
Data for 11a–12b were collected using a Nonius Kappa
CCD diffractometer equipped with an Oxford Cryostream
J. Chem. Soc., Dalton Trans., 2002, 3129–3134
3133

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3134
J. Chem. Soc., Dalton Trans., 2002, 3129–3134