New motifs in lithium zincate chemistry: a solid-state structural study of PhC(O)N(R)ZnR'2Li*2thf (R, R'=alkyl, aryl) and [PhC(O)N(Ph)Li*thf]*[PhC(O)N(Ph)Zn(But)2Li*thf]

Article abstract of DOI:10.1039/b210479b

The facile reaction of ZnMe2 with secondary carboxylic amides of the type PhC(O)N(R)H (R = Me 14, Prⁱ 15, Ph 16) yields PhC(O)N(R)ZnMe (R = Me 17, Prⁱ 18, Ph 19). These complexes describe a hexamer (for 17) and tetramers (for 18 and 19) in the solid state which are best viewed as stacks of cyclic trimers and dimers, respectively. In turn, 17-19 react with Bu^tLi to afford either the lithium zincate PhC(O)N(R)Zn(Bu^t)2Li*2thf (R = Me 20, Prⁱ21) or the co-complex [PhC(O)N(Ph)Li*thf]*[PhC(O)N(Ph)N(Bu^t)2Li*thf] 22. In the solid state both 20 and 21 reveal dimeric structures based on a (LiO)2 core in which each alkali metal centre is doubly thf-solvated and trivalent zinc centres reside peripheral to the cluster. The structure of 22 reveals an adduct in which a dimeric lithium (carboxylic) amide core interacts with two PhC(O)N(Ph)Zn(Bu^t)2Li molecules, affording a structure intermediate between a ladder and an open pseudo-cubane. This is the first full characterisation of a complex between an alkali metal zincate and another organometallic species and it affords new insights into how these two classes of molecule interact. The straighforward formation of [PhC(O)N(R)ZnMe2]^- (R = Me 23, Ph 24) ions has been successfully achieved by treating the appropriate lithium carboxylic amide with ZnMe2. In the solid-state, PhC(O)N(Ph)ZnMe2Li*2thf 24 is revealed to be isostructural with 20 and 21.

Full text of DOI:10.1039/b210479b

View Article Online / Journal Homepage / Table of Contents for this issue
New motifs in lithium zincate chemistry: a solid-state structural
study of PhC(O)N(R)ZnRЈ2Liؒ2thf (R, RЈ ؍ alkyl, aryl) and
[PhC(O)N(Ph)Liؒthf]ؒ[PhC(O)N(Ph)Zn(But)2Liؒthf]
Sally R. Boss,a Robert Haigh,a David J. Linton,a Paul Schooler,b Gregory P. Shieldsc and
Andrew E. H. Wheatley*a
a Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge,
UK CB2 1EW
b Johnson Matthey, Orchard Road, Royston, Hertfordshire, UK SG8 5HE
c Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, UK CB2 1EZ
Received 24th October 2002, Accepted 18th December 2002
First published as an Advance Article on the web 29th January 2003
The facile reaction of ZnMe2 with secondary carboxylic amides of the type PhC(O)N(R)H (R = Me 14, Pri 15, Ph 16)
yields PhC(O)N(R)ZnMe (R = Me 17, Pri 18, Ph 19). These complexes describe a hexamer (for 17) and tetramers
(for 18 and 19) in the solid state which are best viewed as stacks of cyclic trimers and dimers, respectively. In turn,
17–19 react with ButLi to afford either the lithium zincate PhC(O)N(R)Zn(But)2Liؒ2thf (R = Me 20, Pri 21) or the
co-complex [PhC(O)N(Ph)Liؒthf]ؒ[PhC(O)N(Ph)Zn(But)2Liؒthf] 22. In the solid state both 20 and 21 reveal dimeric
structures based on a (LiO)2 core in which each alkali metal centre is doubly thf-solvated and trivalent zinc centres
reside peripheral to the cluster. The structure of 22 reveals an adduct in which a dimeric lithium (carboxylic) amide
core interacts with two PhC(O)N(Ph)Zn(But)2Li molecules, affording a structure intermediate between a ladder and
an “open” pseudo-cubane. This is the first full characterisation of a complex between an alkali metal zincate and
another organometallic species and it affords new insights into how these two classes of molecule interact. The
straightforward formation of [PhC(O)N(R)ZnMe2]Ϫ (R = Me 23, Ph 24) ions has been successfully achieved by
treating the appropriate lithium carboxylic amide with ZnMe2. In the solid-state, PhC(O)N(Ph)ZnMe2Liؒ2thf 24 is
revealed to be isostructural with 20 and 21.
Although lithium-containing heterobimetallic species are
widely used in synthetic chemistry,1,2 a recent survey of the
literature2 has shown that the structural chemistry of lithium
organozincates is not well documented. While reports exist of
ion-separated triorganozincates (ZnR3ϪLiϩ) which have been
isolated from various Lewis base media,3,4 ion-association has
been reported in (Me3Si)2N(Me3SiCH2)2ZnLiؒtmeda (tmeda =
N,N,NЈ,NЈ-tetramethylethylenediamine).4 More common than
the Zn(µ-N)Li motif noted for this complex are Zn(µ-C)nLi
(n = 1, 2) fragments.5,6 Most recently, (MeCN)Cl(µ3,η2-ddbfo)2-
(µ,η2-ddbfo)3ZnLi4 (ddbfo = 2,3-dihydro-2,2-dimethyl-7-benzo-
furanoxide) has been found to be based on an array of
Zn(µ-O)2Li-based rings.7
We report here the conversion of PhC(O)N(R)H (R = Me 14,
Pri 15, Ph 16) into the methylzinc carboxylic amides PhC(O)-
N(R)ZnMe (R = Me 17, Pri 18, Ph 19). These have been reacted
with ButLi to afford either lithium zincates PhC(O)N(R)Zn-
(But)2Liؒ2thf (R = Me 20, Pri 21) or the zincate/(carboxylic)
amide co-complex [PhC(O)N(Ph)Liؒthf]ؒ[PhC(O)N(Ph)Zn-
(But)2Liؒthf] 22. Zn(But)2 evolution is implied by the formation
of the PhC(O)N(Ph)Li component of this last species and it is
in this context that the synthesis and characterisation PhC(O)-
N(R)ZnMe2Liؒ2thf (R = Me 23, Ph 24) is discussed. Results
presented here suggest for the first time that (LiO)n rings9,15,16
can determine the structures of lithium zincates.
The oxygenation of organometallic compounds has been
probed by the synthesis of mixed s-block metal species8 and by
the derivatisation of certain lithium aluminates.9 Sequential
reaction of di(p-tolyl)formamidine with BunLi and ZnCl2 in
the presence of trace oxygen has given the N-oxygenated
Results and discussion
The reaction of N-methyl benzamide 14 with ZnMe2 in toluene
results in CH4 evolution. Reduction to dryness gives an
amorphous material which H NMR spectroscopy suggests to
1
10
formamidinate [(p-Tol)N(O)C(H)N(p-Tol)]6Zn3(µ5-O)Li2 and
be PhC(O)N(Me)ZnMe 17 (Scheme 1) and storage of the reac-
tion mixture at ambient temperature affords a crystalline
material which analyses as the same species. Retention of
the zinc-bonded methyl group is implied by the observation of
ZnMe2 has been reacted with 2-pyridylamines [HN(2-C5H4N)-
R, R = Ph 1, 3,5-xy 2 (xy = xylyl), 2,6-xy 3, Me 4], ButLi and dry
air to give a disparate set of heterometallic complexes. These
include [Ph(2-C5H4N)N]2Zn[µ3-O(But)]2(Liؒthf )2 5, which
forms concomitantly with {[Ph(2-C5H4N)N]2ZnO(Me)Liؒthf}2
6—the 3,5-xy analogue (7) of which has also been reported.11
The structures of 6 and 7 imply the formal reaction of
[R(2-C5H4N)N]2ZnMeϪ and strength has been lent to this view
by the recent characterisation and oxygenation of the related
anion [Ph(2-C5H4N)N]2ZnRϪ (R = Bun, But).12 Varying the
steric demands of the amine substrate has yielded pseudo-cubic
[(ButO)2ZnMe]2(Liؒthf )2 8, and also the oxide-alkoxide [Me(2-
C5H4N)N]6Zn3(µ6-O)Li3(µ3-O)But 9.11 Related work with N,NЈ-
diphenylbenzamidine13 (HAm) 10 has led to the isolation of
[Am2ZnO(Me)Liؒthf]2 11 from thf with toluene affording both
pseudo-octahedral (µ6-O)(Am3ZnLi2)2 12 and [(ButOZnMe)3-
(ButOLi)]∞ 13.14
singlets at δ Ϫ0.37 and Ϫ17.4 by H and 13C NMR spectro-
1
scopy, respectively. X-ray diffraction studies bear out the
suggested stoichiometry, revealing a [PhC(O)N(Me)ZnMe]6
aggregate for which there exist two molecules of lattice toluene.
The oligomer is composed of Z-configured molecules and
incorporates two, highly puckered, 12-membered (ZnNCO)3
rings (top and bottom in Fig. 1; mean Zn–O = 2.061 Å, Table 1)
Scheme 1
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 1 0 0 1 – 1 0 0 8
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Table 1 Selected bond lengths (Å) and angles (Њ) for (17)6ؒ2PhMe
Table 2 Selected bond lengths (Å) and angles (Њ) for (18)4
Zn1–O1
Zn1–O3
Zn1–N2
Zn2–O1
Zn2–O2
Zn2–N3A
Zn3–O2A
Zn3–O3
2.082(3)
2.062(3)
2.010(4)
2.063(3)
2.086(3)
2.022(4)
2.057(3)
2.089(3)
Zn3–N1
C1–O1
C1–N1
C10–O2
C10–N2
C19–O3
C19–N3
2.011(4)
1.306(6)
1.295(6)
1.307(6)
1.294(6)
1.302(6)
1.290(7)
Zn1–O2
Zn1–O3
Zn1–N1
Zn2–O1
Zn2–O4
Zn2–N2
Zn3–O2
Zn3–O4
Zn3–N3
Zn4–O1
2.072(3)
2.071(3)
2.028(3)
2.063(3)
2.086(2)
2.028(3)
2.073(2)
2.067(3)
2.031(3)
2.084(3)
Zn4–O3
Zn4–N4
C1–O1
2.064(2)
2.034(3)
1.307(5)
1.286(5)
1.309(4)
1.296(5)
1.308(4)
1.286(5)
1.304(4)
1.294(5)
C1–N1
C12–O2
C12–N2
C23–O3
C23–N3
C34–O4
C34–N4
O1–Zn1–O3
Zn1–O3–Zn3
O3–Zn3–N1
Zn3–N1–C1
N1–C1–O1
Zn1–O1–C1
O1–Zn2–O2
Zn1–O1–Zn2
O1–Zn1–N2
90.78(13)
105.59(16)
106.19(15)
124.9(3)
119.4(4)
116.7(3)
91.15(13)
105.28(15)
104.98(15)
Zn1–N2–C10
N2–C10–O2
126.5(3)
120.1(4)
116.4(3)
91.48(13)
105.16(14)
106.70(15)
125.2(3)
120.7(4)
118.6(3)
Zn2–O2–C10
O2A–Zn3–O3
Zn2A–O2A–Zn3
O2A–Zn2A–N3
Zn2A–N3–C19
N3–C19–O3
O1–Zn4–O3
Zn1–O3–Zn4
O3–Zn1–N1
Zn1–N1–C1
N1–C1–O1
Zn2–O1–C1
O2–Zn3–O4
Zn2–O4–Zn3
O4–Zn2–N2
Zn2–N2–C12
N2–C12–O2
Zn3–O2–C12
87.62(10)
113.97(11)
104.12(12)
117.6(3)
120.0(3)
125.4(2)
89.05(10)
115.61(12)
102.64(12)
121.0(3)
120.5(4)
119.5(2)
O2–Zn1–O3
Zn1–O2–Zn3
O2–Zn3–N3
Zn3–N3–C23
N3–C23–O3
Zn1–O3–C23
O1–Zn2–O4
Zn2–O1–Zn4
O1–Zn4–N4
Zn4–N4–C34
N4–C34–O4
Zn2–O4–C34
89.50(10)
112.48(12)
104.34(11)
117.9(2)
119.8(3)
119.4(2)
87.58(10)
113.85(11)
103.16(11)
118.7(3)
119.4(3)
117.8(2)
Zn3–O3–C19
Table 3 Selected bond lengths (Å) and angles (Њ) for (19)4ؒ2PhMe
Zn1–O1
Zn1–O2
Zn1–N2
Zn2–O3
Zn2–O4
Zn2–N4
Zn3–O2
Zn3–O3
Zn3–N1
Zn4–O1
2.068(2)
2.090(2)
2.037(3)
2.081(2)
2.064(2)
2.050(3)
2.068(2)
2.088(2)
2.044(3)
2.077(2)
Zn4–O4
Zn4–N3
C29–O3
C29–N2
C1–O1
2.094(2)
2.035(3)
1.300(4)
1.307(4)
1.297(4)
1.308(4)
1.306(4)
1.303(5)
1.297(4)
1.301(5)
C1–N4
C43–O4
C43–N1
C15–O2
C15–N3
O1–Zn1–O2
Zn1–O1–Zn4
O1–Zn4–N3
Zn4–N3–C15
N3–C15–O2
Zn1–O2–C15
O3–Zn2–O4
Zn2–O3–Zn3
O3–Zn3–N1
Zn3–N1–C43
N1–C43–O4
Zn2–O4–C43
88.10(9)
115.34(10)
100.78(11)
120.3(2)
119.2(3)
119.2(2)
O2–Zn3–O3
Zn1–O2–Zn3
O2–Zn1–N2
Zn1–N2–C29
N2–C29–O3
Zn3–O3–C29
O1–Zn4–O4
Zn2–O4–Zn4
O4–Zn2–N4
Zn2–N4–C1
N4–C1–O1
89.92(9)
111.11(10)
106.51(10)
119.6(2)
119.2(3)
123.2(2)
Fig. 1 Structure of (17)6ؒ2PhMe; lattice solvent and hydrogen atoms
excluded.
with one ring being inverted and staggered relative to the other.
Six longer interactions between the metal centres in one such
trimer and the carbonyl O-centres in the other (mean Zn–O =
2.086 Å) link these two heterocycles and, in doing so, yield as
many more 6-membered ZnNCOZnO rings.
The use of more sterically demanding N-isopropyl benz-
amide17 15 or benzanilide 16 in conjunction with ZnMe2 has
allowed the isolation and structural characterisation of the
respective isostructural tetramers [PhC(O)N(Pri)ZnMe]4 18 and
[PhC(O)N(Ph)ZnMe]4 19 (for which formulation there are two
lattice toluene molecules) (Scheme 1, Figs. 2 and 3, Tables 2 and
3). Both 18 and 19 comprise two boat-configured (ZnNCO)2
89.24(9)
90.08(9)
113.57(10)
104.97(10)
119.8(2)
119.8(3)
125.6(2)
112.08(10)
101.82(10)
120.6(2)
118.8(3)
118.2(2)
Zn4–O1–C1
Fig. 3 The structure of (19)4ؒ2PhMe; lattice toluene molecules and
hydrogen atoms excluded.
rings (top and bottom in Figs. 2 and 3). This motif is analogous
to that seen in the (LiOCO)2 core of a tetrameric 2,3-di-
methylindole-based alkali metal carbamate complex.18 Akin to
17, these two metallocycles fuse to give a series of 6-membered
rings through the formation of long Zn–O bonds.
Fig. 2 The tetramer (18)4; hydrogen atoms excluded.
D a l t o n T r a n s . , 2 0 0 3 , 1 0 0 1 – 1 0 0 8
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Table 4 Selected bond lengths (Å) and angles (Њ) for (20)2ؒPhMe
Given that the structure-types noted for complexes 17–19
would appear to be general for secondary alkylzinc carboxylic
amides, it is surprising that they have not hitherto been noted in
organozinc chemistry. This reflects the fact that, while neutral
carboxylic amides have been used as external stabilising agents
for ZnX2 salts,19 few formally N-zincated carboxylic amides
have been structurally characterised. While structures akin to
those reported here have been previously postulated,20 to the
best of our knowledge only four N-zincated carboxylic amides
have been studied in the solid state. These have all been ion-
separated monomers, with the metal centre being N-stabilised
but not O-stabilised by virtue of the employment of extensively
coordinating, polyfunctional donors.21 More generally, and
in contrast to the structures of 17–19, previously reported
carboxylic amide–zinc complexes have revealed metal centre
stabilisation to be either N- or O-based, with the two modes
being mutually exclusive.19,21
Li1–O1
Li1–O2
Li1–O3
Li1–O4
Li2–O1
Li2–O2
Li2–O5
1.936(6)
1.910(6)
1.960(6)
1.963(6)
1.906(6)
1.934(6)
1.85(4)
Li2–O6
Zn1–N1
Zn2–N2
C7–O1
C7–N1
C23–O2
C23–N2
1.961(6)
2.078(3)
2.100(3)
1.286(4)
1.299(4)
1.283(4)
1.295(4)
O1–Li1–O2
O1–Li2–O2
Li1–O1–Li2
90.5(2)
90.7(2)
89.3(2)
Li1–O2–Li2
C9–Zn1–C13
C25–Zn2–C29
89.3(2)
135.88(19)
137.89(18)
Table 5 Selected bond lengths (Å) and angles (Њ) for 21
Li1–O1
Li1–O2
Zn1–N1
1.974(4)
1.935(4)
2.184(4)
C1–O2
C1–N1
1.292(4)
1.316(6)
The treatment of 17 or 18 with ButLi (1 equiv.) affords a
1
O2–Li1–O2A
Li1–O2–Li1A
91.3(3)
88.7(3)
C11–Zn1–C11A
132.29(16)
single type of isolable product (Scheme 2). In both cases H
NMR spectroscopy points to R (= Me, Pri) and But groups in a
1
1 : 2 ratio. For the N-methyl system, H NMR spectroscopy
contrast to recently noted lithium aluminates bearing
carboxylic amide ligands,9 adopts E-configuration (cf. also
Z-configured 17)—implying that previous observations of
cis-geometric ’ate complexes had their origins in electrostatic
stabilisation of the alkali metal centres.22 At 1.285 and 1.297 Å
(mean), the relative lengths of C7 ؒ ؒ ؒ O1, C23 ؒ ؒ ؒ O2,
C7 ؒ ؒ ؒ N1 and C23 ؒ ؒ ؒ N2 interactions point to some level of
azaenolate character in 20.23 Indeed, in spite of the different
modes of Liϩ stabilisation revealed, these azaenolate character-
istics compare closely with those seen in the dimer of
PhC(O)N(Ph)AlMe2(But)Li.9 An average Zn–N distance of
2.089 Å and a mean C–Zn–C angle of 136.89Њ are observed.
One example of a bis(quaternary carbon)-bonded zinc centre
has previously been fully characterised [in the carbenoid prod-
uct of reaction between 1,3,4,5-tetramethylimidazol-2-ylidene
and bis(pentamethylcyclopentadienyl)zinc]24 and, to the best of
our knowledge, no Zn(But)2-containing systems have previously
been studied crystallographically.
The N-isopropyl system affords a dimeric product [(21)2] with
crystallography showing organic ligands in each dimer that
occupy two planes, the torsional angle between which is 94.4Њ.
These ligands are each disordered over two orientations related
by a mirror plane, such that in contrast to the structure of 20,
the asymmetric unit of 21 is racemically disordered. Neverthe-
less, the main structural features of this dimer are unambigu-
ous. Like 20, it incorporates a core (LiO)2 ring (Fig. 5, Table 5)
relative to which the zinc centres lie exocyclic. The organic
groups are again E-configured and reveal similar azaenolate
characteristics to those seen in 20. However, the observed Zn–N
length [2.184(4) Å] is greater than that which results from the
presence of sterically less demanding NMe groups in 20, while
at 132.29(16)Њ the C–Zn–C angle is smaller than that reported
in the previous compound.
reveals a singlet attributable to the NMe group. However,
repeated analysis by 13C and HMQC NMR spectroscopy fails
to locate the corresponding carbon resonance (noted at δ 38.0
in 17). In spite of this, the composition implied by NMR is
borne out crystallographically. For R = Me, a complex of form-
ulation PhC(O)N(Me)Zn(But)2Liؒ2thf 20 is revealed which is a
dimer in the solid state (Fig. 4) and for which aggregate there
exists one lattice toluene molecule. At the core of this dimer
is a (LiO)2 ring which utilises the carboxylic amide O-centres
and contains two bond types (mean Li1–O1, Li2–O2 1.935 Å;
mean Li1–O2, Li2–O1 1.908 Å; Table 4). Whereas the previ-
ously reported lithium aluminate analogue of 20—PhC(O)-
N(Ph)AlMe2(But)Li—revealed agostic stabilisation of the alkali
metal centres,9 comparable donation by Zn-bonded alkyl
groups is precluded by thf solvation (two solvent molecules per
Liϩ ion). Lying exocyclic to the (LiO)2 core, the two organic
ligands reside at 105.3Њ to each other with the crystallographic
unit cell containing one of each of the two resulting stereo-
isomers. The Group 12 metal centres reveal distorted trigonal
planar coordination with delocalisation affording a ligand
whose ZnNCO backbone is precisely planar and which, in
Scheme 2
The treatment of PhC(O)N(Ph)H 16 with 1 equiv. ZnMe2 to
give PhC(O)N(Ph)ZnMe 19 has already been described. How-
ever, instead of giving a precise analogue of either 20 or 21 the
Fig. 4 Structure of (20)2ؒPhMe; hydrogen atoms, lattice toluene
molecule and minor disorder omitted and only the thf O-centres
shown.
Fig. 5 Structure of (21)2; hydrogen atoms and disorder omitted and
only the thf O-centres shown.
D a l t o n T r a n s . , 2 0 0 3 , 1 0 0 1 – 1 0 0 8
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introduction of ButLi incurs the formation of an unusual
mixed-anion species. X-Ray crystallography reveals this to
be a dimer based on the formulation [PhC(O)N(Ph)Liؒthf]ؒ
[PhC(O)N(Ph)Zn(But)2Liؒthf] 22 (Scheme 3, Fig. 6(a), Table 6),
with the asymmetric unit containing two such aggregates—of
which one representative dimer will be discussed in detail—
along with uncoordinated thf (one molecule at half occupancy)
and toluene (two molecules at full occupancy, five molecules at
half occupancy, and half a molecule at full occupancy lying on
an inversion centre) in the crystal lattice. These uncoordinated
solvent molecules present two major analytical difficulties.
Table 6 Selected bond lengths (Å), and angles (Њ) for (22)4ؒ5PhMeؒ
0.5thf
Li1–O2
Li2–O1
Li3–O4
Li4–O3
Li1–O1
Li3–O1
Li3–O3
Li2–O2
Li2–O4
Li4–O4
Zn1–N2
1.883(13)
1.986(13)
1.992(12)
1.872(13)
2.326(15)
1.925(12)
1.984(12)
1.942(15)
1.914(12)
2.261(14)
2.155(7)
Zn2–N3
Li1–N1
Li4–N4
N1–C28
N4–C41
O1–C28
O4–C41
O2–C15
O3–C62
N2–C15
N3–C62
2.167(5)
2.029(14)
2.044(14)
1.296(9)
1.301(9)
1.293(7)
1.284(8)
1.284(9)
1.275(8)
1.315(10)
1.325(8)
1
Firstly, H NMR spectroscopy indicates that they are readily
lost in vacuo during isolation, with the spectrum suggesting the
retention of only one molecule of lattice toluene per unit cell
(elemental analysis is consistent with this partially desolvated
formulation). Secondly, thermal motion exhibited by lattice
solvent molecules incurs a high crystallographic R1 value of
0.0949. In spite of this, it is clear that the complete structure of
co-complex 22 has been unambiguously determined. Akin to 20
O1–Li1–O2
O3–Li4–O4
O1–Li2–O2
O3–Li3–O4
O1–Li2–O4
O1–Li3–O4
O1–Li1–N1
O4–Li4–N4
Li1–O2–Li2
86.6(6)
88.2(5)
95.3(6)
93.3(5)
92.0(5)
91.5(5)
60.8(4)
62.2(4)
95.9(6)
Li1–O1–Li2
Li1–O1–C28
Li2–O1–Li3
Li3–O3–Li4
Li3–O4–Li4
Li4–O4–C41
Li2–O4–Li3
C7–Zn1–C11
C54–Zn2–C58
82.0(5)
84.0(5)
88.1(5)
94.9(6)
83.6(5)
84.3(5)
88.2(5)
142.0(5)
139.7(3)
and 21, it is based on (LiO)2 rings. However, rather than
incorporating an isolated metallocycle, 22 is based on three
edge-fused (LiO)2 rings. Peripheral to this core are four mole-
cules of coordinated thf and two types of anionic ligand. The
formally N-lithiated carboxylic amide anions use their Group
15 charge centres to close four-membered OCNLi chelate rings
with Li1/4 (mean Li–N 2.04 Å). Li1–O1 and Li4–O4 inter-
actions are relatively long (mean Li–O 2.29 Å) and contrast
with Li2–O1 and Li3–O4 which are of intermediate length
(mean 1.99 Å) and Li1–O2 and Li4–O3 which are short (mean
1.88 Å). Moreover, consistent with previous observations,9
it is evidently the necessity for alkali metal stabilisation that
imposes N-coordination on the core metal centres and incurs
Z-configuration of these carboxylic amide ligands. Zincate
anions represent the second ligand-type in 22, their O-centres
bridging between the two types of Liϩ ion in the aggregate.
These monoanions are analogous to those noted in 20/21, with
the combination of E-isomerism22 and coordination of the
Zn(But)2 moiety preventing the N-centres from replicating the
coordinative behaviour noted for the N-lithiated carboxylic
amide units. However, 22 reveals a larger C–Zn–C angle (mean
140.85Њ) than either 20 or 21.
Scheme 3
Formally N-lithiated carboxylic amides have hitherto been
fully characterised only rarely. [2-ArC(O)N(But)LiؒL]n [Ar =
(3-MeC4H2S),
L = N,N,NЈ,NЈЈ,NЈЈ-pentamethyldiethylene-
triamine (pmdeta), n = 1; Ar = C5H4N, L = hexamethylphos-
phoramide (hmpa), n = 2] reveal no interactions between the
formally deprotonated N-centre and the metal.22 Intramono-
mer N,O-chelation of the type seen in 22 has been noted in
25
[PhC(O)N(Pri)Li]6ؒ2thf,17 [BunC(O)N(But)Li]6 and [PhC(O)-
N(Pri)Li]8.26 However, whereas thf-solvation causes two of the
amide moieties in [PhC(O)N(Pri)Li]6ؒ2thf to adopt (non-chelat-
ing) Z-configurations,17 those in 22 retain both N-coordination
and E-configuration in spite of the presence of external donor.
The close similarity between zincate anion geometries in 20–22
suggests that the last of these species can be viewed as a co-
complex between a lithium zincate and another metallo-organic
species (an N-lithio carboxylic amide) which is (conceptually)
generated by the formation in situ of two molecules of Zn(But)2.
To the best of our knowledge this is the first time that a
co-complex such as this has been fully characterised. Both the
lithium carboxylic amide and the lithium zincate components
of 22 reveal a similar degree of azaenolate character to that
noted in 20 and 21, suggesting the retention of significant
carbonylic character in the organic fragment. This contrasts
with three of the five previously characterised N-deprotonated
lithium carboxylic amides, with only [ArC(O)N(But)LiؒL]n
revealing a like trend.
Fig. 6 (a) Structure of (22)4ؒ5PhMeؒ0.5thf; hydrogen atoms and
lattice solvent molecules omitted and only the O-centres of coordinated
thf shown. (b) Core of (22)4ؒ5PhMeؒ0.5thf.
D a l t o n T r a n s . , 2 0 0 3 , 1 0 0 1 – 1 0 0 8
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Table 7 Selected bond lengths (Å) and angles (Њ) for 24
Complex 22 also provides a structural model for the inter-
action of a lithium zincate dimer (of, say, 20) with an N-lithio
carboxylic amide dimer based on a Li2O4Li3O1 metallocycle.
Coordination of the carboxylic amide N-centres (N1/4) to the
zincate alkali metal centres (Li1/4) can be viewed as having
incurred cleavage of the lithium zincate dimer at Li1–O3 and
Li4–O2 (Fig. 6(b)). With respect to the orientations of the aza-
enolate backbones in each zincate ligand (compare Fig. 4 with
Fig. 6(a)) the bonds that have been broken correspond to the
longer lithium-oxygen bonds in the core of the dimer of 20. The
result is to afford the non-bonding lithium–oxygen fragments
in 22 and to introduce the last noteworthy feature of this co-
complex: it incorporates a structural core that reveals both
ladder and “open” pseudo cubane characteristics. Hence, rather
than pertaining to a straightforward, chair-shaped (LiO)4
ladder structure,9,16 22 reveals a boat-shaped array of edge-
fused (LiO)2 rings. In this sense it is related to the pseudo-
cubane structure-type commonly seen for a wide variety of
lithiated organics (viz. alkoxides etc.).15 While the observation
of non-bonding Li1 ؒ ؒ ؒ O3 and Li4 ؒ ؒ ؒ O2 distances (4.494
and 4.395 Å, respectively) suggest that 22 could be described
as having an “open” pseudo-cubic core in which two trans edges
of a single face have cleaved, it should be recognised that the
only precedent for such a structure-type—the alkoxide [(2-
MeO)C6H4C(H)(NMeCH2CH2NMe2)OLi]4—revealed signifi-
cantly shorter Li ؒ ؒ ؒ O non-bonding distances (mean 2.723
Å).15 Nevertheless, the long non-bonding Li ؒ ؒ ؒ O distances in
22, when considered in light of the recent structural character-
isation of lithium aluminate [PhC(O)N(Me)Al(Me)(But)OMe]-
Liؒ{PhC(O)N(Me)Al(Me)[O(But)]OMe}Li,9 suggest that that
(LiO)4-based alkali metal ’ate systems will reveal some tendency
for ladder formation.
Li1–O1
Li1–O2
Li1–O3
Li1–O4
Li2–O1
Li2–O2
Li2–O5
1.917(5)
1.975(5)
1.993(5)
1.972(5)
1.966(5)
1.933(5)
1.967(5)
Li2–O6
Zn1–N1
Zn2–N2
C9–O1
C9–N1
C24–O2
C24–N2
1.962(5)
2.135(2)
2.144(2)
1.275(3)
1.308(3)
1.278(3)
1.306(3)
O1–Li1–O2
O1–Li2–O2
Li1–O1–Li2
88.21(19)
88.40(19)
92.1(2)
Li1–O2–Li2
C1–Zn1–C2
C16–Zn2–C17
91.30(19)
144.74(12)
145.38(16)
The structure of 22 implies the evolution of dialkylzinc from
a tetrameric zincate precursor—a view reinforced by the obser-
vation that upon isolation from mother liquor, 23 fumes in an
inert atmosphere. Consequently this last complex could not be
fully (X-ray) characterised. However, the employment of benz-
anilide in place of 14 afforded PhC(O)N(Ph)ZnMe2Liؒ2thf 24,
the single crystal structure of which could be elucidated. In the
solid state it reveals a dimer (Fig. 7, Table 7) isostructural with
those noted for 20/21 with the organic ligands residing at 113.7Њ
to each other. The Zn–N bond in 24 (mean 2.140 Å) lies within
the range described by those in 20–22 [cf. mean 2.089 Å (20),
2.184 Å (21), 2.161 Å (22)]. As for 22, the length of this bond
relative to analogous interactions in 17–19 is suggestive of the
instability of 23 towards ZnMe2 evolution. Moreover, for 20–22
and 24 a correlation is observed between Zn–N bond lengths
and C–Zn–C angles. Consistent with the presence of smaller
zinc-bonded organic residues (that is, with the diminishment of
steric interference between N-bonded and Zn-bonded groups),
the C–Zn–C angles in 24 are larger than those in 20–22. Hence,
the mean C–Zn–C angle of 145.06Њ in 24 is significantly greater
than the corresponding means of 136.89Њ in 20, 132.29(16)Њ in
21, and 140.85Њ in 22. Moreover, the C–Zn–C angle in 24 is
significantly more massive than that of 131.64(13)Њ noted
recently in the triimidosulfonate MeS(NBut)2N(But)ZnMe2Liؒ
2thf [wherein Zn–N = 2.1374(17) Å].27
The observation of Zn(But)2 moieties in 20–22 raises ques-
tions about the mechanism which operates in these systems. The
isolation of 17–19 from the 1 : 1 reactions of ZnMe2 with the
appropriate carboxylic amide points to the subsequent form-
ation of 20–22 from zinc monoamide precursors rather than the
diamides Zn[N(R)C(O)Ph]2. However, the observation that 17–
19 combine with equimolar ButLi to afford PhC(O)N(R)Zn-
(But)2Liؒnthf rather than PhC(O)N(R)Zn(But)MeLiؒnthf indi-
cates the non-trivial attack of ButLi. Moreover, it contrasts
with the previously noted and straightforward reaction of ButLi
with related dimethylaluminium substrates.9 Lastly, the length
of Zn–N interactions in 20–22 [range 2.078(3)–2.184(4) Å] rel-
ative to analogous interactions [range 2.010(4)–2.050(3) Å] in
17–19 suggests the instability of certain zincates with respect to
dialkylzinc evolution and, conceivably, formation of the lithium
carboxylic amide units in 22.
The straightforward 1 : 1 : 1 reaction of PhC(O)N(R)H,
ButLi and ZnMe2 has been achieved by combining reagents in
that order (Scheme 4). The lithiation of PhC(O)N(R)H (R = Me
14, Ph 16) with ButLi can be followed by treatment of the
1
resultant slurry with ZnMe2 to yield products which H NMR
spectroscopy suggests to be lithium zincates of the type
PhC(O)N(R)ZnMe2Liؒ2thf (R = Me 23, Ph 24).
Fig. 7 Structure of (24)2; hydrogen atoms omitted and only the
O-centres of coordinated thf shown.
Lastly, the synthesis and isolation of 23/24, when taken in
conjunction with the observed instability of the former com-
plex and the observation of PhC(O)NLi moieties in 22, suggests
the intriguing possibility that a Lewis acid (ZnR2) can act
as a solvent to deaggregate a lithiated organic {in this case
[PhC(O)N(R)Liؒ2thf]n} by coordinating the negative charge
centre. Whereas repeated attempts to generate and isolate the
N-isopropyl congener of 23/24 were unsuccessful, it seems
likely that the sequential treatment of PhC(O)N(Pri)H 15 with
ButLi, ZnMe2 and thf should yield a dimer analogous to that of
24 in the solid state. This contrasts with the observation that
[PhC(O)N(Pri)Li]8 26 is deaggregated only to [PhC(O)N(Pri)Li]6ؒ
2thf17 in the presence of excess Lewis base. With this in mind,
attempts to mimic the synthesis of 22 by the 2 : 2 : 1 reaction of
Scheme 4
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benzanilide, ButLi and ZnMe2 are ongoing, though so far have
afforded only 24 in depleted yield.
4.78%. Calc. for C44H60N4O4Zn4: C 54.45, H 6.23, N 5.77%. 1H
NMR spectroscopy (400 MHz, [2H6]benzene), δ 7.81–7.79 (m,
2H, Ph), 7.21–7.06 (m, 3H, Ph), 3.88 (sept., 1H, CHMe), 1.26
(d, 3H, CHMe), 1.06 (d, 3H, CHMe), Ϫ0.32 (s, 3H, ZnMe). 13
C
Conclusions
NMR (400 MHz, [2H6]benzene), δ 174.4 (CO), 135.4 (i-Ph),
130.3, 128.7, 128.1 (o-, m-Ph), 51.0 (CHMe), 24.6, 23.9
(CHMe), Ϫ11.5 (ZnMe).
The isolation and characterisation of 17–19 provides us with
some understanding of the associative behaviour and structural
chemistry of formally N-zincated carboxylic amides, while that
of 20–24 has afforded new insights into lithium zincate stability
and chemistry and, for 22, the unexplored field of co-complex
formation between lithium zincates and other potentially
reactive molecules. However, the processes which convert 17–19
into 20–22 are plainly non-trivial and, in this context, the
straightforward preparation of [PhC(O)N(R)ZnMe2]Ϫ ions
(23/24) is noteworthy. The synthetic pathways to 20–22, along
with the stabilities (with respect to dialkylzinc emission) and
reactivities of such complexes, are the subject of ongoing study.
Combining these two approaches, attempts are being made to
generate further examples of lithium zincate-incorporating
co-complexes both utilising the route which affords 22 and also
by investigating the receptivity of lithiated organics to treat-
ment with a deficiency of diorganozinc Lewis acids. The solu-
tion behaviour of 20–22 and 24 is being probed with a view to
understanding whether the evident ability of certain lithium
zincates to emit dialkylzinc has ramifications for our view of the
form which so-called “’ate complexes” take in solution and
whether we might more generally view Lewis acid molecules as
potential stabilisers of the negative charge centres in lithiated
organics.
[PhC(O)N(ZnMe)Ph]4ؒ2PhMe (19)4ؒ2PhMe. ZnMe2 (0.5 ml,
1 mmol, 2.0 M in toluene) was added to a solution of benz-
anilide (16, 0.20 g, 1 mmol) in toluene (1 ml). The colourless
solution which formed was treated with further toluene (4 ml)
and stored at room temperature for 24 h to yield crystalline
(19)4ؒ2PhMe. Yield 183 mg (57%), mp 246–248 ЊC. Found: C
64.46, H 5.21, N 4.43%. Calc. for C70H68N4O4Zn4: C 65.13, H
5.31, N 4.34%. 1H NMR (400 MHz, [2H6]benzene), δ 7.73 (dd,
2H, Ph), 7.10–6.79 (m, 7H, Ph ϩ PhMe), 6.56 (d, 2H, Ph), 2.19
(s, 0.8H; PhMe), Ϫ0.13 (s, 3H, ZnMe). 13C NMR (400 MHz,
[2H6]benzene), δ 175.4 (CO), 147.2, 134.5 (i-Ph), 131.9, 131.3,
129.3, 125.6, 125.1, 124.7 (o-, m-Ph ϩ PhMe), 21.4 (PhMe),
Ϫ15.1 (ZnMe).
PhC(O)N(Me)Zn(But)2Liؒ2thfؒ0.5PhMe (20)2ؒPhMe. N-
Methyl benzamide 14 (0.14 g, 1 mmol) in toluene (2 ml) was
treated with ZnMe2 (0.5 ml, 1 mmol, 2.0 M in toluene). The
mixture was refluxed and then cooled to Ϫ78 ЊC whereupon
ButLi (0.59 ml, 1 mmol, 1.7 M in pentane) was added and the
resultant suspension allowed to warm to room temperature.
Dissolution was effected by adding thf (1 ml). Reduction to
half-volume, followed by storage at Ϫ30 ЊC for 2 days yielded
needles of (20)2ؒPhMe. Yield 71 mg (28% by ButLi), mp 120–
122 ЊC. Found: C 61.96, H 8.71, N 2.89%. Calc. for
Experimental
1
C55H92Li2N2O6Zn2: C 64.64, H 9.07, N 2.74%. H NMR (500
Methods and materials
MHz, [2H8]thf ), δ 7.67 (m, br, 4H, Ph), 7.27 (m, br, 6H, Ph),
7.20–7.10 (m, 5H, PhMe), 3.62 (m, 12H, thf ), 2.30 (s,
3H, PhMe), 1.78 (m, 12H, thf ), 0.81 (s, 36H, But). 13C NMR
(125 MHz, [2H8]thf ), δ 138.4, 129.6, 128.9, 128.6, 127.4,
126.0 (Ph ϩ PhMe), 68.2 (thf ), 34.4 (But), 26.4 (thf ), 22.4
(PhMe).
All reactions and manipulations were carried out under an inert
atmosphere of dry nitrogen, using standard double manifold
and glove-box techniques. Chemical reagents were used as
received from Aldrich without further purification. N-isopropyl
benzamide 15 was synthesised according to a literature pro-
cedure.17 Toluene, hexane and thf were distilled off sodium or
sodium-potassium amalgam immediately prior to use.
PhC(O)N(Pri)Zn(But)2Liؒ2thf 21. ZnMe2 (0.5 ml, 1 mmol,
2M in toluene) was added to a slurry of N-isopropyl benzamide
15 (0.14 g, 1 mmol) in toluene (2 ml). The resultant solution was
cooled to Ϫ78 ЊC whereupon ButLi (0.59 ml, 1 mmol, 1.7 M
in pentane) was added and the resultant suspension allowed to
warm to room temperature. The addition of thf (0.2 ml)
afforded a yellow solution. Reduction to half-volume, followed
by storage at Ϫ30 ЊC for 2 days yielded blocks of 21. Yield 88
mg (36% by ButLi), mp 108–110 ЊC. Found: C 62.61, H 9.04, N
3.18%. Calc. for C26H46LiNO3Zn: C 63.35, H 9.41, N 2.84%. 1H
NMR (500 MHz, [2H8]thf ), δ 7.59–7.05 (m, 6.2H, Ph ϩ PhMe),
4.14 (m, br, 1H, CHMe2), 3.59 (m, 4H, thf ), 2.28 (s, H, PhMe),
NMR data were collected on either a Bruker DPX 400 or
1
DRX 400 (400.12 MHz for H and and 100.03 for 13C) or a
1
Bruker DRX 500 FT NMR spectrometer (500.05 MHz for H
and 125.01 for 13C) at 27 ЊC. Chemical shifts are internally
referenced to deuterated solvents and calculated relative to
TMS.
Synthesis and characterisation
[PhC(O)N(ZnMe)Me]6ؒ2PhMe (17)6ؒ2PhMe. ZnMe2 (0.5
ml, 1 mmol, 2.0 M in toluene) was added to a solution of
N-methyl benzamide (14, 0.14 g, 1 mmol) in toluene (1 ml). The
resultant colourless solution was stored at ϩ5 ЊC for 24 h to
yield crystals of (17)6ؒ2PhMe. Yield 212 mg (87%), mp 192–194
ЊC. Found: C 51.57, H 5.19, N 5.85%. Calc. for C68H82N6O6Zn6:
C 52.01, H 5.77, N 5.87%. 1H NMR (400 MHz, [2H6]benzene),
δ 7.62 (dd, 2H, Ph), 7.21–7.13 (m, 4H, Ph ϩ PhMe), 2.85 (s, 3H,
NMe), 2.19 (s, 0.8H, PhMe), Ϫ0.37 (s, 3H, ZnMe). 13C NMR
(100 MHz, [2H6]benzene), δ 176.3 (CO), 135.1 (i-Ph), 130.7,
129.1, 128.6, 126.5, 125.4 (o-, m-Ph ϩ PhMe), 38.0 (NMe), 21.4
(PhMe), Ϫ17.4 (ZnMe).
1.75 (m, 4H, thf ), 1.17 (d, 6H, CHMe), 0.75 (s, 18H, But). 13
C
NMR (125 MHz, [2H8]thf ), δ 145.4 (i-Ph), 138.4 (i-PhMe),
129.7, 128.9, 128.7, 127.3, 126.0 (Ph ϩ PhMe), 68.2 (thf ), 46.2
(NCH), 34.6 (But), 26.4 (thf ), 24.0 (br, CHMe), 21.4 (PhMe).
{[PhC(O)N(Ph)Liؒthf]ؒ[PhC(O)N(Ph)Zn(But)2Liؒthf]}4ؒ
5PhMeؒ0.5thf (22)4ؒ5PhMeؒ0.5thf. ZnMe2 (0.5 ml, 1 mmol,
2.0 M in toluene) was added to benzanilide 16 (0.20 g, 1 mmol)
in toluene (2 ml). After refluxing, the mixture was reacted with
ButLi (0.59 ml, 1 mmol, 1.7 M in pentane) at Ϫ78 ЊC and the
resultant suspension was allowed to warm to room temper-
ature. The addition of thf (0.4 ml) afforded a solution which
was reduced to half-volume and stored at Ϫ30 ЊC for 2 days to
give (22)4ؒ5PhMeؒ0.5thf. Yield 74 mg [35% by ButLi assuming
Zn(But)2 elimination (see text)], mp decomp. 128–130 ЊC (loses
solvent from 95 ЊC). Found: C 66.10, H 7.91, N 3.10%. Calc. for
C173H224Li8N8O16Zn4: C 69.52, H 7.55, N 3.75%. 1H NMR (400
MHz, [2H8]thf ), δ 7.85–6.77 (m, 21H, Ph ϩ PhMe), 3.59 (m,
[PhC(O)N(ZnMe)(Pri)]4 (18)4. A solution of N-isopropyl
benzamide17 (15, 0.16 g, 1 mmol) in toluene (1 ml) was treated
with ZnMe2 (0.5 ml, 1 mmol, 2.0 M in toluene). The colourless
solution which resulted was reduced to half volume and hexane
(0.25 ml) was added. Storage at Ϫ30 ЊC for 24 h afforded crys-
tals of (18)4. Yield 42 mg [17%; this increases to 200 mg (82%)
of amorphous material which analyses as (18)4 if the reaction is
reduced to dryness], mp 116–118 ЊC. Found: C 54.01, H 6.56, N
D a l t o n T r a n s . , 2 0 0 3 , 1 0 0 1 – 1 0 0 8
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8H, thf ), 2.28 (s, 0.5H, PhMe), 1.75 (m, 8H, thf ), 0.72 (s, 18H,
But). 13C NMR (100 MHz, [2H8]thf ), δ 152.8, 144.5 (i-Ph),
129.6, 129.3, 128.9, 128.4, 128.1, 126.0, 125.6, 121.3 (Ph ϩ
PhMe), 68.2 (thf ), 34.6 (But), 26.4 (thf ), 22.5 (PhMe).
PhC(O)N(Me)ZnMe2Liؒ2thf 23. A suspension of N-methyl
benzamide 14 (0.14 g, 1 mmol) in toluene (0.75 ml) was reacted
with ButLi (0.59 ml, 1 mmol, 1.7 M in pentane) at Ϫ78 ЊC. The
resultant mixture was allowed to warm to room temperature,
whereupon the addition of ZnMe2 (0.5 ml, 1 mmol, 2.0 M in
toluene) afforded a pale yellow suspension with the addition of
thf (0.2 ml) yielding a yellow solution. Storage at Ϫ30 ЊC for
2 days gave 23. Yield 156 mg (41%), mp 88–90 ЊC. Found: C
57.84, H 7.85, N 3.14%. Calc. for C18H30LiNO3Zn: C 56.78, H
7.94, N 3.68%. 1H NMR (400 MHz, [2H8]thf ), δ 7.67–7.64 (m,
2H, Ph), 7.25–7.15 (m, 3H, Ph), 3.63 (m, 7H, thf ), 2.86 (s, 3H,
NMe), 1.79 (m, 7H, thf ), Ϫ1.17 (s, 6H, ZnMe). 13C NMR (100
MHz, [2H8]thf ), δ 172.4 (CO), 144.4 (i-Ph), 129.6, 128.9, 128.6,
128.2, 128.0, 126.0 (Ph), 68.2 (thf ), 32.4 (NMe), 26.4 (thf ),
Ϫ10.4 (ZnMe).
PhC(O)N(Ph)ZnMe2Liؒ2thf 24. A suspension of benzanilide
16 (0.20 g, 1 mmol) in toluene (0.75 ml) was reacted with
ButLi (0.59 ml, 1 mmol, 1.7 M in pentane) at Ϫ78 ЊC. The
mixture was allowed to warm to room temperature and ZnMe2
(0.5 ml, 1 mmol, 2.0 M in toluene) was added to give a
pale yellow suspension. Treatment with thf (0.2 ml) yielded a
solution from which 24 deposited after 2 days at Ϫ30 ЊC. Yield
300 mg (67%), mp 68–70 ЊC. Found: C 63.14, H 7.21, N 3.35%.
Calc. for C23H32LiNO3Zn: C 62.38, H 7.28, N 3.16%. 1H NMR
(400 MHz, [2H6]benzene), δ 7.57–6.86 (m, 11H, Ph ϩ PhMe),
3.60 (m, 8H, thf ), 2.20 (s, 1H, PhMe), 1.46 (m, 8H, thf ),
Ϫ0.54 (s, 6H, ZnMe). 13C NMR (100 MHz, [2H6]benzene),
δ 129.1, 128.5, 128.4, 125.4, 124.3, 121.8 (Ph ϩ PhMe),
1
67.6 (thf ), 21.0 (PhMe), 25.5 (thf ), Ϫ7.2 (ZnMe). H NMR
(400 MHz, [2H8]thf ), δ 7.96 (br, 2H, Ph), 7.26–7.10 (m, 9H, Ph
ϩ PhMe), 6.51 (br, 1H, Ph), 3.63 (m, 7H, thf ), 2.32 (s,
1H, PhMe), 1.79 (m, 7H, thf ), Ϫ1.04 (s, 6H, ZnMe). 13C NMR
(100 MHz, [2H8]thf ), δ 168.8 (CO), 152.8, 144.3 (i-Ph), 138.3,
129.7, 129.6, 128.8, 128.7, 128.5, 128.3, 127.9, 125.9, 125.7,
121.0 (Ph ϩ PhMe), 68.1, 26.3 (thf ), 21.4 (PhMe), Ϫ10.0
(ZnMe).
X-Ray crystallography
Crystallographic data (excluding structure factors) for (17)6ؒ
2PhMe, (18)4,(19)4ؒ2PhMe, (20)2ؒPhMe, 21, (22)4ؒ5PhMeؒ
0.5thf and 24 have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publi-
cations Data were collected using a Nonius Kappa CCD
diffractometer equipped with an Oxford Cryostream low-
temperature device (Table 8). Structures were solved by direct
methods28 and refined against F 2 using SHELXL-9729 [for
(17)6ؒ2PhMe, 21 and 24] or SHELXTL NT 5.1030 [for (22)4ؒ
5PhMeؒ0.5thf].
For all structures, hydrogen atoms were placed geometrically
and allowed to ride during subsequent refinement. The phenyl
rings in (22)4ؒ5PhMeؒ0.5thf were refined as rigid groups and thf
ligands were refined with restraints on the C–C distances. The
O-centre in the lattice thf molecule could not be identified and
the ring atoms were all refined as carbon.
CCDC reference numbers 167401, 167402 and 184194–
184198.
See http://www.rsc.org/suppdata/dt/b2/b210479b/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
Thanks go to the U.K. EPSRC (S. R. B., R. H., D. J. L., P. S.)
and the CCDC (G. P. S.) for financial support.
D a l t o n T r a n s . , 2 0 0 3 , 1 0 0 1 – 1 0 0 8
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Armstrong, R. P. Davies, P. R. Raithby, R. Snaith and A. E. H.
Wheatley, New J. Chem., 1999, 23, 499.
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