Reactions of Li- and Yb-coordinated N,N′-bis(trimethylsilyl)-β- diketiminates: One- and two-electron reductions, deprotonation, and C-N bond cleavage

Article abstract of DOI:10.1039/b405554c

The synthesis and characterisation of novel Li and Yb complexes is reported, in which the monoanionic β-diketiminato ligand has been (i) reduced (SET or 2 × SET), (ii) deprotonated, or (iii) C-N bond-cleaved. Reduction of the lithium β-diketiminate Li(L

Full text of DOI:10.1039/b405554c

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F U L L P A P E R
Reactions of Li- and Yb-coordinated N,N′-bis(trimethylsilyl)--
diketiminates: one- and two-electron reductions, deprotonation,
and C–N bond cleavage
Anthony G. Avent, Peter B. Hitchcock, Alexei V. Khvostov, Michael F. Lappert* and
Andrey V. Protchenko
The Chemistry Laboratory, University of Sussex, Brighton, UK BN1 9QJ.
E-mail: m.f.lappert@sussex.ac.uk; Fax: +44 1273 677196; Tel: +44 1273 678316
Received 14th April 2004, Accepted 26th May 2004
First published as an Advance Article on the web 18th June 2004
The synthesis and characterisation of novel Li and Yb complexes is reported, in which the monoanionic -diketiminato
ligand has been (i) reduced (SET or 2 × SET), (ii) deprotonated, or (iii) C–N bond-cleaved. Reduction of the lithium -
diketiminate Li(LR,R′) [LR,R′ = N(SiMe3)C(R)CHC(R′)N(SiMe3)] with Li metal gave the dilithium derivative [Li(tmen)(-
LR,R′)Li(OEt2)] (4, R = R′ = Ph; or 5, R = Ph, R′ = But). When excess of Li was used the dimeric trilithium -diketiminate
[Li3(LR,R′)(tmen)]2 (6, R = R′ = C6H4But-4 = Ar) was obtained. Similar reduction of [Yb(LR,R′)2Cl] gave [Yb{(-
LR,R′)Li(thf)}2] (1, R = R′ = Ph; or 2, R = R′ = C6H4Ph-4 = Dph). Use of the Yb–naphthalene complex instead of Li in the
reaction with [Yb(LPh,Ph)2] led to the polynuclear Yb clusters [Yb3(LPh,Ph)3(thf)] (3), [Yb3(LPh,Ph)2(dme)2] (7), or [Yb5(LPh,Ph)-
(L1)(L2)(L3)(thf)4] (8) [L1 = N(SiMe3)C(Ph)CHC(Ph)N(SiMe2CH2), L2 = NC(Ph)CHC(Ph)H, L3 = N(SiMe2CH2)]
depending on the reaction conditions and stoichiometry. The structures of the crystalline complexes 4, 6·2ꢀ(hexane),
6·5(C6D6), 7 and 8 have been determined by X-ray crystallography (1 and 3 have been published).
bond in the di- and trianionic -diketiminates, and for the latter the
alternation of the C–C bond lengths reveals the cross-conjugation.
We now report on the synthesis and characterisation of new singly
and doubly reduced Li -diketiminates and further developments
arising from novel reductions of [Yb(LPh,Ph)2]. Experimental details
of the synthesis and characterisation of 3 are also provided.
Introduction
The chemistry of metal -diketiminates is of substantial current
interest.1 The -diketiminates have a useful role as monoanionic
spectator ligands, by virtue of their strong binding to metals, their
tuneable and extensive steric demands and the diversity of bonding
modes. In some cases, however, the coordinated ligand has been
shown to undergo fragmentation, mainly due to deprotonation of
one of the substituents on the ligand backbone.2 For example, in
the reaction of [Sc(LNN)Cl2] [LNN = {N(CH2CH2NEt2)C(Me)}2CH]
with 2NaN(SiMe3)2 deprotonation of one of the -Me substituents
led to the formation of a doubly-methylene-bridged dimer.2a Simi-
lar Me-deprotonation was also observed in an attempted synthesis
of a Ca(Dipp2nacnac)(alkyl) complex [Dipp2nacnac = {N(C6H3-
Pri2-2,6)C(Me)}2CH].2b On the other hand, the methyl group of one
Pri substituent of the Dipp2nacnac ligand was deprotonated in the
thermal decomposition of a number of scandium dialkyl complexes
[Sc(Dipp2nacnac)(CH2R)2] (R = H, Ph, But, SiMe3).2c No reduction
of the two above-mentioned ligands was observed under rather
drastic conditions.3 Indeed the LNN ligand was used to support a
Sc(I) complex,3a while the Dipp2nacnac ligand effectively stabilised
the mononuclear Al(I) compound [Al(Dipp2nacnac)].3b
(1)
(2)
Another type of bulky -diketiminato ligand, N(SiMe3)C(R)CH-
C(R′)N(SiMe3)( LR,R′), was used in our group for the synthesis of
a number of metal complexes, including those of alkali metals, mag-
nesium, aluminium, zirconium, Sn(II), Sn(IV), late transition metals,
and the lanthanides.4 In recent communications we described the
reduction of the LR,R′ ligand in its Yb complexes with the formation
of di- or trianionic -diketiminates.5,6 Thus, the synthesis [eqn. (1)]
and X-ray structures of the crystalline Yb(II)/(LR,R′ 2− complexes 1
)
and 2, their paramagnetism (SQUID, 4–300 K), and solution be-
haviour [1H/1H NOE (1) and 6Li/1H NOE {(2) and (3)}, Fig. 1 (Ph
groups omitted); consistent with the solid state structures], were
reported.5 In a follow-up paper, the synthesis [eqn. (2)] of the tri-
nuclear Yb(II, III)/(LR,R′)−(LR,R′ 3− complex 3 was described, as was
)
Fig. 1 1H/1H NOE (1) and 6Li/1H NOE [(2) and (3)] interactions in 1.5
its X-ray structure (outlined in Fig. 2); computational data on model
lithiated mono-, di-, and trianionic -diketiminates were consistent
with the structural data and the assignments, with successive one-
electron reductions of (LPh,Ph)− illustrated in Scheme 1.6 Consistent
with this, it is evident that the C–N bond length is a useful marker
as to the oxidation state of the ligand; thus reduction of (LPh,Ph)− (i.e.,
initially populating the * CN orbital of LR,R′−) lengthens the C–N
Results and discussion
Reduced homometallic -diketiminates of lithium
The paramagnetic dilithium compounds [Li(tmen)(-LR,R′)Li(OEt2)]
(4, R = R′ = Ph; or 5, R = Ph, R′ = But) and the diamagnetic trilith-
2 2 7 2
D a l t o n T r a n s . , 2 0 0 4 , 2 2 7 2 – 2 2 8 0
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 4

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Table 1 Ligand bond lengths (Å) in lithium -diketiminates. Numbering is shown below, which corresponds
to that of 6
4b
Bond
[Li(LPh,Ph)]2
4
6·2ꢀ(hexane)a
6·5(C6D6)a
N1–C1
N2–C3
C1–C2
C2–C3
1.337(6)
1.299(6)
1.394(7)
1.439(6)
1.509(6)
1.511(7)
1.747(5)
1.733(5)
1.377(7)
1.366(7)
1.341(7)
1.374(7)
1.393(7)
1.390(7)
1.373(7)
1.395(7)
1.349(7)
1.385(7)
1.392(7)
1.358(7)
1.390(4)
1.386(4)
1.418(5)
1.418(4)
1.480(5)
1.483(5)
1.708(3)
1.707(3)
1.403(5)
1.382(5)
1.378(6)
1.378(6)
1.382(5)
1.397(5)
1.403(5)
1.388(5)
1.365(6)
1.376(6)
1.387(5)
1.395(5)
1.404(5), 1.407(5)
1.455(4), 1.442(4)
1.385(5), 1.383(5)
1.449(5), 1.455(5)
1.489(5), 1.482(5)
1.411(5), 1.410(5)
1.703(3), 1.700(3)
1.691(3), 1.700(3)
1.401(5), 1.393(6)
1.385(6), 1.371(6)
1.389(6), 1.407(6)
1.397(5), 1.380(6)
1.389(6), 1.397(5)
1.387(5), 1.402(5)
1.445(5), 1.455(5)
1.395(5), 1.396(5)
1.413(5), 1.418(5)
1.405(5), 1.409(5)
1.382(5), 1.368(5)
1.459(5), 1.446(5)
1.415(5), 1.416(5)
1.447(5), 1.438(5)
1.370(5), 1.371(5)
1.458(5), 1.460(5)
1.498(5), 1.490(5)
1.406(5), 1.407(5)
1.709(3), 1.706(3)
1.690(3), 1.687(3)
1.386(5), 1.390(5)
1.386(6), 1.379(6)
1.400(5), 1.405(6)
1.386(5), 1.388(6)
1.390(5), 1.392(5)
1.392(5), 1.398(5)
1.449(5), 1.455(5)
1.393(5), 1.387(5)
1.408(5), 1.406(6)
1.413(5), 1.410(6)
1.376(5), 1.384(5)
1.460(5), 1.456(5)
C1–C4
C3–C14
N1–Si1
N2–Si2
C4–C5
C5–C6
C6–C7
C7–C8
C8–C9
C9–C4
C14–C15
C15–C16
C16–C17
C17–C18
C18–C19
C19–C14
a Value of corresponding bond length of the second ligand is given after comma.
Fig. 2 Schematic representation of the structure of 3 with Yb and (LPh,Ph
)
charges.6
Scheme 2 Synthesis of complexes 4 (dark green), 5 (dark blue) and 6
(dark violet).
difficult to purify. In contrast, the tmen adducts 4–6 were obtained
as well-formed crystals and were easily recrystallised from an ap-
propriate solvent.
−
2−
Scheme 1 Successive one-electron reductions: (LR,R′
)
→ (LR,R′
)
→
The dilithium complexes 4 and 5 were readily soluble in diethyl
ether or an arene; EPR spectra of such solutions showed a singlet
EPR signal without well defined hyperfine structure; more detailed
(LR,R′)3−.6
ium complex [Li3(LAr,Ar)(tmen)]2 (6, Ar = C6H4But-4) were readily
obtained by the reduction of the appropriate monolithium -dik-
etiminate with metallic lithium in the appropriate stoichiometry in
diethyl ether, Scheme 2.
studies are projected. The H-NMR spectra of the complexes in
1
C6D6 were not informative. Monitoring the reduction in an NMR
tube (in thf-d8) showed only a very broad signal which shifted from
low to high frequency during the course of the reaction.
The starting complexes were the known Li(LPh,Ph) and Li(LPh,But),4b
or the newly synthesised Li(LAr,Ar) from LiCH(SiMe3)2 and 2ArCN.
Lithium granules were used in the reductions. The reaction time
was shown to depend on the form of the metal. If the metal surface
was tarnished, the granules were activated by scratching with a
spatula. When the reduction was complete, as evident by the ab-
sence of metal, tmen was added, yielding the new crystalline com-
plexes 4, 5, or 6, depending on the stoichiometry. In the absence
of the neutral co-ligand, the products were powders which were
The molecular structure of the crystalline dilithium complex 4
(Fig. 3 and Table 1) has a puckered Li1N1Li2N2 four-membered
ring core, with a 30° torsion angle. The endocyclic angles decrease
in the sequence Li2 > Li1 > N2 ≥ N1, and the Li2–N(1 or 2) bonds
are shorter than the Li1–N(1 or 2) and by ca. 0.05 Å are longer than
in the monolithium -diketiminate [Li(LPh,Ph)]2.4b The -diketimi-
nato ligand both chelates each lithium and bridges the two lithium
atoms; Li1 and Li2 are 1.33 Å above and below, respectively, the
N1C1C2C3N2 plane.
D a l t o n T r a n s . , 2 0 0 4 , 2 2 7 2 – 2 2 8 0
2 2 7 3

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Table 2 Parameters of multistep dynamic process in complex 3 from VT
7Li-NMR data
Step
Atoms exchanging
Tc/K
G‡/kJ mol−1
1
2
3
Li(1) and Li(2)
Li(1, 2) and Li(3, 4)
Li(1, 2, 3, 4) and Li(5, 6)
278
318
338
54
60
65
Fig. 3 Molecular structure of [Li(tmen)(-LPh,Ph)Li(OEt2)] (4). Selected
bond lengths (Å) and angles (°) (see also Table 1): Li1–N1 2.060(6), Li1–N2
2.059(6), Li2–N1 2.008(7), Li2–N2 2.000(7), Li1–C1 2.433(7), Li1–C2
2.540(8), Li1–C3 2.436(7), Li2–C1 2.649(7), Li2–C2 2.815(7), Li2–C3
2.650(7); N1–Li1–N2 92.5(3), Li2–N1–Li1 82.0(3), Li1–N2–Li2 82.3(3),
N1–Li2–N2 95.9(3).
Fig. 4 1H-NMR spectrum of complex 6 at 228 K (solvent signals are
marked with a star). A and B designate two different sides of the LAr,Ar
ligand as shown in Fig. 5.
The Li1 and Li2 atoms differ in that the former is in a four- and
the latter in a three-coordinated environment; this is reflected in
the shorter distances to Li2 than Li1 not only from N1 and N2 but
also from the C1, C2 and C3 atoms. The endocyclic -diketiminato
bond lengths reveal that there is -delocalisation in the ligand; this
is not extended to the phenyl substituents, the aromatic rings having
a ca. 36° torsion angle with the N1C1C2C3N2 plane; the Si1 and
Si2 atoms are also 0.66 and 0.62 Å, respectively, out of this plane.
The ligand geometrical parameters for the crystalline 4 are listed in
Table 1, which also shows corresponding data for [Li(LPh,Ph)]24b and
[Li3(LAr,Ar)(tmen)]2 [6 as 6·2ꢀ(hexane) and 6·5(C6D6)].
The diamagnetic complex 6 had good solubility and stability in
several aprotic solvents. Its multinuclear solution NMR spectra in
1
benzene-d6 or toluene-d8 were examined. The H-NMR variable
temperature spectra of 6 (supported by 13C{1H}- and 29Si{1H}-
Fig. 5 Schematic representation of lithium positions in a “cis-like” isomer
of complex 6. SiMe3 and But groups are omitted for clarity.
NMR data) showed that there is an exchange between the two aryl
1
rings. At ambient and higher temperatures the H-NMR spectrum
showed singlets for both the tert-butyl and the trimethylsilyl groups
and a broad signal for all the aromatic protons; at 228 K the spec-
trum revealed singlets for each of the two tert-butyl and the two
trimethylsilyl groups, two doublets (at  7.80 and 7.41) for one of
the C6 ring aromatic protons and four low frequency-shifted (at 
6.12–5.54) doublets for the other C6 ring (Fig. 4). These observa-
tions are consistent with a low temperature structure in which the
negative charge is localised at one of the C6 rings (Fig. 5). At ambi-
ent temperature each C6 ring alternates in taking part in conjuga-
tion with the NC3N array (Scheme 3). This fluxional process may
involve transfer of a lithium atom (Li5 and Li6 in Fig. 5) from one
ring to the other.
Scheme 3 Dynamic process in solution of complex 6 according to
1H-NMR spectra.
6
7
The Li- (Fig. 6) and Li-NMR spectra of 6 at low temperature
showed four signals consistent with a dimeric “cis-like” structure
(Fig. 5) having four inequivalent lithium atoms: (i) Li3 and Li4
chelated by the -diketiminato ligands, (ii) Li5 and Li6 chelated
by tmen and 5-bonded to C6H4But, (iii) Li1 bridging the two -
diketiminato ligands and adjacent to the two 5-C6H4But rings and
(iv) Li2 bridging the two -diketiminato ligands and remote from
the two 5-C6H4But rings.
7
Upon progressively raising the temperature various Li signals
sequentially coalesced until at 338 K all signals merged (Table 2).
It should be noted that for the Li1 and Li2 signals to merge it is not
inevitable that these atoms exchange positions, since the same effect
can be achieved as a result of migrating the Li5 and Li6 atoms from
one C6 ring to the other, as shown in Scheme 3. This process seems
the more likely, because Li1 and Li2 are more strongly bonded
Fig. 6 6Li-NMR spectrum of complex 6 at 208 K.
2 2 7 4
D a l t o n T r a n s . , 2 0 0 4 , 2 2 7 2 – 2 2 8 0

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between the two ligands whereas Li5 and Li6 can migrate without
breaking any Li–N bond. The equality (within the experimental
the corresponding CCN (C2C1N1 or C31C30N3) moiety by ca.
42°. The exocyclic -diketiminate C–C bonds to the aryl substituent
involved in the conjugation (C3–C14 or C32–C43) are much shorter
than those to the other (C1–C4 or C30–C33). The Li-bound C6 ring
has the C–C bond length distribution similar to that in the potassium
benzyl [K(CH2Ph)(pmdien)]∞,8 with two elongated Cipso–Cortho bonds
(C14–C15 and C14–C19, 1.45 Å) and four “normal” aromatic (av.
1.40 Å) bonds. Each of the other C6 rings has all six endocyclic
bond lengths in the narrow range of 1.38–1.40 Å.
‡
1
7
error range) of GTc for the H- and the first Li-NMR dynamic
processes supports this point of view. The movements of Li5 and
Li6 appear to occur simultaneously, because the 7Li-NMR spectra
did not reveal a significant presence of a ‘trans-like’ isomer.
The two following exchanges (between first the lithium positions
Li1/2 and Li3/4 and, finally between Li1/2/3/4 and Li5/6) may in-
volve a dissociation/association sequence of the dimeric structure
of 6 and of tmen.
In spite of this multifaceted fluxional behaviour in solution, com-
plex 6 is very robust and can be obtained from different solvents.
For example, complex 6 was recovered from an NMR tube after a
VT experiment as the crystalline complex 6·5(C6D6).
The crystal structure of 6·5(C6D6) shows the same geometric
features as described above for 6·2ꢀ(hexane).
Reduced ytterbium -diketiminates
Aspreviouslyreported,theheterometallic-diketiminatocomplexes
of lithium and ytterbium(II) [Yb{(-LR,R′)Li(thf)}2] [R = R′ = Ph (1)
or R = R′ = C6H4Ph-4 (2)] were obtained from YbCl3, by reduction
of the initially formed corresponding ytterbium(III) -diketiminate
[Yb(LR,R′)2Cl] prepared in situ, eqn. (1).5 Although this method is
most convenient, the starting complexes can be isolated before
reduction. The mono--diketiminato complex of ytterbium(III)
[Yb(LDph,Dph)Cl(-Cl)2Li(thf)(OEt2)]9 can be used as a starting ma-
terial (see Experimental). In contrast, in our hands, use of the new
ytterbium(II) precursors [{Yb(LPh,Ph)(-I)(thf)}2]9 and [Yb(LR,R′)2]4i
did not lead to isolation of reduced products.
The outcome of the reductions of [Yb(LPh,Ph)2] by the ytterbium–
naphthalene complex or Yb metal, yielding the crystalline cluster
complexes 36 and 7, or 8, respectively, is summarised in Scheme 4.
Their molecular structures, as revealed by X-ray crystallography,
are outlined in Figs. 2 (3),6 8 (7) and 9 (8).
The molecular structure of crystalline [Li3(LAr,Ar)(tmen)]2 (6 as
6·2ꢀ(hexane)) (Fig. 7, Table 1) consists of two -diketiminato
ligands connected to each other by the two lithium atoms Li1 and
Li2. Each LAr,Ar ligand chelates another lithium atom, Li3 or Li4. An
additional lithium atom, Li5 or Li6, is connected to one of the aryl
rings, with an average Li–C bond length (2.48 Å) similar to that in
[Li(tmen)]2(naphthalene) (2.42 Å).7 Each lithium atom Li5 or Li6
completes its coordination sphere by tmen chelation. Each bridging
lithium atom Li1 and Li2 has additional contacts with the carbon
atoms of the twisted N1C1C2C3N2 or N3C30C31C32N4 ligand
[the angle between the N1C1C2 (or N3C30C31) and C2C3N2 (or
C31C32N4) planes is 33° (or 35°)]; in addition, Li1 is close to the
ipso- and ortho-aryl carbon atoms. These carbon atoms are also near
to each chelated lithium atom Li3 or Li4. The Li–N bonds form an
eight-membered ring core (Fig. 3); the lithium atoms (Li1–Li4) are
coplanar with LiLi′ contacts in the range of 2.66–2.74 Å. The
Li–N bond lengths vary from 1.93 to 1.99 Å, and the average Li–N
bond length of 1.97 Å is shorter than in 2 (2.03 Å).
Scheme 4 Reductions of [Yb(LPh,Ph)2] by Yb or Yb(C10H8)(thf)3: syn-
thesis of complex 3 (brown),6 7 (deep red) and 8 (black) {L1 = LPh,Ph − H+,
L2 = [NC(Ph)CHC(Ph)H] and L3 = [N(SiMe2CH2)]}.
Fig. 7 Molecular structure of [Li3(LAr,Ar)(tmen)]2 (6). Selected bond
lengths (Å) and angles (°) for 6·2ꢀ(hexane) [corresponding data for
6·5(C6D6) in parentheses] (see also Table 1): Li(1)–N(2) 1.936(7) [1.990(7)],
Li(1)–N(4) 1.930(7) [1.971(7)], Li(2)–N(1) 1.983(7) [1.990(7)], Li(2)–N(3)
1.992(7) [1.979(7)], Li(3)–N(1) 1.991(8) [1.987(8)], Li(3)–N(2) 1.956(6)
[1.945(7)], Li(4)–N(3) 1.989(8) [2.005(7)], Li(4)–N(4) 1.954(8) [1.949(7)],
Li(5)–Centroid(1) 2.036(7) [1.990(7)], Li(6)–Centroid(2) 2.040(7)
[2.005(7)], Li(1)–C(3) 2.430(8) [2.331(7)], Li(1)–C(32) 2.494(7) [2.338(7)],
Li(1)–C(15) 2.556(8) [2.336(7)], Li(1)–C(14) 2.600(9) [2.394(7)], Li(1)–
C(44) 2.603(9) [2.391(7)], Li(1)–C(43) 2.697(8) [2.432(7)], Li(2)–C(30)
2.118(8) [2.203(7)], Li(2)–C(1) 2.140(8) [2.216(7)], Li(2)–C(31) 2.373(8)
[2.448(8)], Li(2)–C(2) 2.471(8) [2.474(8)], Li(3)–C(43) 2.484(8) [2.593(8)],
Li(3)–C(48) 2.628(7) [2.519(7)], Li(4)–C(14) 2.543(7) [2.597(7)],
Li(4)–C(19) 2.627(7) [2.499(7)]; N(2)–Li(1)–N(4) 131.2(4) [139.8(4)],
N(1)–Li(2)–N(3) 176.4(4) [170.8(4)], N(1)–Li(3)–N(2) 105.8(3) [106.8(3)],
N(3)–Li(4)–N(4) 106.0(3) [105.7(3)].
Fig. 8 Schematic representation of the structure of crystalline 7.
As outlined in the introduction, the reduction of [Yb(LPh,Ph)2]
with Yb(C10H8)(thf)3 in thf gave the dark brown, crystalline para-
magnetic Yb(II)/Yb(III) mixed valence cluster complex 3.6 In the
course of the reaction a labile dark blue intermediate was initially
observed, but upon removing volatiles in vacuo 3 was obtained. The
1H-NMR spectrum of the blue solution in thf-d8 showed one set of
signals of a paramagnetically shifted asymmetric -diketiminate
ligand (i.e., showing separate signals for each of the two SiMe3
and two Ph groups), suggesting that the intermediate had a rather
simple, apparently monomeric, structure: (Yb+3)(L−3)(thf)x. Loss
of coordinated thf caused aggregation and electron-redistribution
resulting in the formation of 3. In order to stabilise the monomeric
species, the chelating solvent 1,2-dimethoxyethane (dme) was
The endocyclic -diketiminato bond lengths (Table 1) reveal
substantial bond localisation, with one of the N–C bonds (N1–C1
or N3–C30) shorter than the other (N2–C3 or N4–C32), and one of
the C–C bonds (C1–C2 or C30–C31) shorter than the other (C2–C3
or C31–C32). The aryl ring (C14–C19 or C43–C48) is ca. 10° out of
the plane of the NCC (N2C3C2 or N4C32C31) moiety. In contrast,
the other aromatic ring (C4–C9 or C33–C38) is twisted relative to
D a l t o n T r a n s . , 2 0 0 4 , 2 2 7 2 – 2 2 8 0
2 2 7 5

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Table 3 Bond lengths (Å) of doubly reduceda ligands in ytterbium -diketiminates.b Numbering as in Figs. 10 and 11
Bond
3
7
8
N1–C1
N2–C3
C1–C2
C2–C3
[N3–C22]
[N4–C24]
[C22–C23]
[C23–C24]
[C22–C25]
[C24–C31]
[N3–Si3]
1.443(9) [1.456(8)]
1.412(8) [1.383(8)]
1.475(10) [1.458(9)]
1.375(9) [1.367(9)]
1.395(9) [1.396(9)]
1.487(10) [1.509(9)]
1.707(5) [1.739(6)]
1.732(5) [1.720(5)]
1.448(10) [1.466(9)]
1.385(10) [1.391(9)]
1.386(10) [1.382(10)]
1.401(11) [1.423(10)]
1.386(10) [1.372(9)]
1.445(9) [1.459(9)]
1.401(12) [1.376(12)]
1.411(15) [1.406(13)]
1.394(19) [1.33(2)]
1.298(17) [1.34(2)]
1.381(12) [1.381(16)]
1.368(11) [1.373(13)]
1.476(7) [1.471(6)]
1.405(6) [1.416(7)]
1.471(7) [1.468(7)]
1.362(7) [1.364(7)]
1.468(7) [1.477(7)]
1.484(7) [1.497(7)]
1.734(4) [1.717(4)]
1.724(4) [1.718(4)]
1.413(8) [1.423(7)]
1.376(9) [1.383(8)]
1.393(11) [1.400(9)]
1.359(11) [1.377(9)]
1.397(8) [1.401(8)]
1.418(8) [1.415(7)]
1.382(8) [1.400(8)]
1.395(8) [1.381(8)]
1.366(10) [1.389(9)]
1.378(11) [1.380(9)]
1.378(9) [1.381(8)]
1.414(8) [1.390(7)]
1.474(4) [1.464(4)]
1.394(4) [1.386(4)]
1.478(4) [1.466(4)]
1.377(4) [1.380(4)]
1.439(4) [1.401(4)]
1.492(4) [1.505(5)]
1.698(3) [1.755(3)]
1.727(3) [1.721(3)]
1.432(5) [1.460(5)]
1.367(5) [1.380(5)]
1.388(7) [1.413(6)]
1.391(7) [1.383(6)]
1.392(5) [1.396(5)]
1.420(5) [1.459(5)]
1.388(5) [1.368(6)]
1.382(5) [1.404(6)]
1.380(7) [1.361(8)]
1.376(7) [1.347(8)]
1.395(5) [1.387(6)]
1.401(5) [1.389(6)]
C1–C4
C3–C10
N1–Si1
N2–Si2
C4–C5
C5–C6
C6–C7
C7–C8
C8–C9
C9–C4
C10–C11
C11–C12
C12–C13
C13–C14
C14–C15
C15–C10
[N4–Si4]
[C25–C26]
[C26–C27]
[C27–C28]
[C28–C29]
[C29–C30]
[C30–C25]
[C31–C32]
[C32–C33]
[C33–C34]
[C34–C35]
[C35–C36]
[C36–C31]
a The third ligand in 3 is not reduced, its bond lengths are similar to those in [Li(LPh,Ph)]2 (Table 2). b Values of corresponding bond length of the second ligand
are given in square brackets.
of the -diketiminate–SiMe3 substituent was observed in the at-
tempted synthesis of theYb(III) tris--diketiminateYb(LPh,Ph)3;10 Ln-
{N(SiMe3)2}3] also underwent such a transformation when treated
with an excess of NaN(SiMe3)2.11 N–C bond cleavage was observed
in another -diketiminato ligand, Dipp2nacnac, when its Mn(II)
complex was treated with Na/K alloy, but only the amido fragment
[as N(H)C6H3Pri2-2,6] was found in the reaction product.12
The molecular structures and atom numbering schemes, with
selected geometric parameters for complexes 7 and 8 are shown in
Figs. 10 and 11, respectively. Comparative data on the bond lengths
of the doubly reduced ligands LPh,Ph in complexes 3, 7 and 8 are
given in Table 3.
Fig. 9 Schematic representation of the structure of crystalline 8, with Yb
charges.
added to the reaction mixture. The removal of volatiles in vacuo was
accompanied by a colour change: from blue–violet to red–brown.†
Crystallisation from benzene gave deep red crystals of the trinuclear
cluster complex [Yb3(LPh,Ph)2(dme)2] (7).
Compound 7 was shown (NMR) to be diamagnetic and of bet-
ter stability and solubility in benzene than 3, which allowed the
assignment of its 1H-NMR spectral signals. As for the spectrum of
complex 6, the 1H-NMR spectrum of 7 in C6D6 also showed two sets
of signals for the ligand substituents: albeit the signals of the Yb-
bound Ph ring aromatic protons (at  6.84–6.31) were not signifi-
cantly shifted to lower frequency. These observations indicate that
the LPh,Ph ligand in 7 is trianionic. In accordance with the solid state
Fig. 10 Molecular structure of [Yb3(LPh,Ph)2(dme)2] (7). Selected bond
lengths (Å) and angles (°): Yb1–N2 2.526(4), Yb1–N3 2.415(4), Yb1–O3
structure of 7, two 29Si- and two 171Yb-NMR signals were observed
in toluene/toluene-d8 solution.
2.459(4), Yb1–O4 2.585(4), Yb1–C1 2.805(5), Yb1–C2 2.659(5), Yb1–C3
2.670(5), Yb1–C22 2.671(5), Yb1–C25 2.825(5), Yb1–C30 2.851(5),
Yb2–N1 2.414(4), Yb2–N2 2.519(4), Yb2–N3 2.397(4), Yb2–N4 2.547(4),
Yb3–N1 2.399(4), Yb3–N4 2.495(4), Yb3–O1 2.511(4), Yb3–O2 2.521(4),
Yb3–C1 2.673(5), Yb3–C4 2.837(5), Yb3–C9 2.844(5), Yb3–C22 2.816(5),
Yb3–C23 2.667(5), Yb3–C24 2.661(5), Yb1–C22–C25 80.3(3), Yb3–C1–
C4 80.8(3).
The ease of -diketiminate reduction was further demonstrated
by the reduction of [Yb(LPh,Ph)2] with Yb metal in thf. The reac-
tion proceeded slowly, with the colour changing successively from
green–brown to blue, violet and finally red–brown. Black shiny
crystals of complex 8 precipitated in low yield from benzene solu-
tion (once crystallised, 8 was no longer soluble in common organic
solvents), which were characterised by X-ray diffraction (Fig. 9)
as the pentanuclear cluster [Yb5(LPh,Ph)(L1)(L2)(L3)(thf)4] [L1 =
N(SiMe3)C(Ph)CHC(Ph)N(SiMe2CH2), L2 = NC(Ph)CHC(Ph)H,
L3 = N(SiMe2CH2)] containing one doubly reduced -diketiminato
ligand [LPh,Ph]2−, the second (L1) doubly reduced and deprotonated on
one SiMe3 group, and two fragments (L2 and L3) of the third ligand
as a result of N–Si and N–C bond cleavage. Similar deprotonation
The molecule of complex 3 has the Yb(LPh,Ph)(THF) moiety
(see Yb3 in Fig. 2) 5-coordinated by one of the C6H5 rings of
the tightly packed Yb2(LPh,Ph)2 cluster (see Yb1 and Yb2 in Fig. 2).
The geometric parameters of the Yb(LPh,Ph)(THF) moiety are very
4b
similar to those in the Li and Yb(II) -diketiminates [Li(LPh,Ph)]2
and [Yb(LPh,Ph)2],4i which suggests that the Yb3 atom is in the +2
oxidation state and the ligand is a “normal” monoanionic -diketi-
minate (LPh,Ph)−. Both ligands in the Yb2(LPh,Ph)2 moiety are bridging
and the changes in the C–N and C–C bond lengths, compared to
those in [Li(LPh,Ph)]2 (Table 1), indicate that a two-electron reduc-
† If the polar solvent was not removed completely, only non-crystalline
products were obtained.
2 2 7 6
D a l t o n T r a n s . , 2 0 0 4 , 2 2 7 2 – 2 2 8 0

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complexes: C—with the negative charge delocalised onto one of
the Ph substituents and a metal cation 5- or 6-coordinated to this
Ph ring (complexes 3 and 6); D—with the negative charge largely
localised on the -diketiminate backbone carbon atom and a metal
cation interacting only with the Cipso and Cortho of the adjacent Ph
ring (complex 7). Apparently, the geometric constraints of the latter
complex prevent the close approach ofYb cations and Ph rings, thus
facilitating the D-type electron distribution in the ligand.
Fig. 12 Negative charge distribution in the two types of -diketiminato
ligand C and D.
In the molecule of complex 8 (Fig. 9) there are five Yb atoms
coordinated by two different -diketiminato-based ligands: LPh,Ph
and the deprotonated ligand L1, and two ligand fragments, L2
[NC(Ph)CHC(Ph)H] and L3 [N(SiMe2CH2)]. Bond length data
(Table 3) show that L1 has the D-type charge distribution with
non-coordinating Ph substituents while LPh,Ph is of the C-type with
the negatively charged Ph ring (C25–C30) 5-bonded to the atom
Yb5, which has no Yb–N bond. The ligands L2 and L3 are trianionic
fragments of a cleaved -diketiminato ligand: (i) L2 (Figs. 9 and
13) with a triply-bridging (to Yb1, Yb3 and Yb4) dianionic imido
function, the third negative charge being delocalised on the Ph ring
(C55–C60) 6-bonded to the atom Yb5; and (ii) L3 with a triply-
bridging (to Yb1, Yb2 and Yb3) imido function and a bridging
Fig. 11 Molecular structure of complex 8. Selected bond lengths (Å):
Yb1–N5 2.267(2), Yb1–N6 2.334(2), Yb1–N3 2.377(2), Yb1–C45
2.535(3), Yb1–C46 2.582(3), Yb1–C47 2.621(3), Yb1–C48 2.592(3),
Yb1–C22 2.716(3), Yb1–C25 2.836(3), Yb1–C30 2.737(3), Yb2–N5
2.184(2), Yb2–N4 2.251(2), Yb2–N3 2.358(2), Yb2–O2 2.384(2), Yb2–
C21 2.394(3), Yb2–C24 2.752(3), Yb2–C23 2.839(3), Yb2–C22 2.844(3),
Yb3–N1 2.168(3), Yb3–N6 2.174(2), Yb3–N5 2.298(2), Yb3–N2 2.416(3),
Yb3–C1 2.570(3), Yb3–C21 2.590(3), Yb4–N6 2.462(2), Yb4–N2 2.577(3),
Yb4–O3 2.485(2), Yb4–O4 2.478(2), Yb4–C1 2.679(3), Yb4–C2 2.685(3),
Yb4–C3 2.754(3), Yb4–C4 2.951(3), Yb5–O1 2.391(2), Yb5–C45 2.511(3),
Yb5–C26 2.989(4), Yb5–C27 2.809(4), Yb5–C28 2.683(4), Yb5–C29
2.725(3), Yb5–C30 2.886(3), Yb5–C55 2.707(3), Yb5–C56 2.790(3), Yb5–
C57 2.882(3), Yb5–C58 2.893(3), Yb5–C59 2.856(3), Yb5–C60 2.777(3),
Yb3Yb4 3.17723(18).
−
(to Yb1 and Yb5) CH2 group (−2NSiMe2CH2 ). Imido ligands are
quite rare in organolanthanide chemistry; only a few complexes,
containing NSiMe3,14 NPh15 and NC6H3Pri-2,616 ligands have been
structurally characterised.
tion of (LPh,Ph)− had occurred with one negative charge delocalised
on a C6H5 ring (C4–C9 and C25–C30 rings, Table 3). In these two
C6H5 rings, coordinated to Yb1 and Yb3, the Cipso–Cortho bonds are
slightly longer and the exocyclic Cipso–C bonds are shorter than in
the (LPh,Ph)− of [Li(LPh,Ph)]2.4b A similar C–C bond length pattern was
found in complex 6. The short Yb2–N bonds and the computational
study6 confirmed that the Yb2 atom is in the +3 oxidation state. The
only possible oxidant in these highly reductive reaction conditions
is the singly reduced -diketiminato ligand [i.e., (LPh,Ph)2−], which is
relatively robust in complexes 4 and 5 with a lithium countercation.
3−
In Yb complexes it can either disproportionate into (LPh,Ph
(LPh,Ph)− (both are present in 3) or oxidise Yb(II) to Yb(III).
) and
The molecule of complex 7 consists (see Fig. 8) of two very
similar (but not crystallographically identical) -diketiminato li-
gands and three Yb atoms; each of two of them (Yb1 and Yb3) is
4-bonded to the endocyclic atoms of one ligand and also 4-bonded
to two endocyclic and two exocyclic (Cipso and Cortho) atoms of the
other ligand as well as to the chelating dme molecules; while Yb2,
situated above the skeletal atoms of the ligands, is connected only
to the N atoms of the -diketiminates with two close contacts to
Me groups of SiMe3 substituents (2.929 and 2.920 Å to C21 and
C40, respectively, not shown in Fig. 8). The -diketiminato skeletal
atoms of both ligands are not co-planar: the four atoms C1, C2, C3,
N2 connected to the Yb1 atom form one plane (N1 is 1.03 Å out of
this plane), while the four atoms N1, C1, C4 and C9 connected to the
Yb3 atom form another plane with the dihedral angle of 44.3° be-
tween them; a similar arrangement was found in the second ligand.
The C–N and C–C bond lengths data (Table 3) support the sugges-
tion that the -diketiminato ligands in 7 are trianionic with the third
negative charge located on C1 (C22 for the second ligand). The
Cipso–Cortho bond length elongation of the adjacent Ph ring is not so
pronounced as in the complexes 3 and 6, indicating a smaller extent
of negative charge delocalisation in 7. The Yb3–C1 [2.673(5) Å]
and Yb1–C22 [2.671(5) Å] bond lengths may be compared with
the Yb–C bond length (2.679 Å) in a closely related complex hav-
ing an N,C-bonded dianionic ligand [Yb(2-Ph2CNPh)(hmpa)3].13
Thus, we conclude that two structurally different types of trian-
ionic -diketiminato ligands (Fig. 12) are found in its Li and Yb
Fig. 13 Bond lengths (Å) in the ligand L2 of the complex 8.
The sum of the negative charges on the ligands of complex 8
is −13, which means that three Yb atoms are in the +3 and two
Yb atoms are in the +2 oxidation state (3 × 3 + 2 × 2 = 13). Three
Yb atoms (Yb1, Yb2 and Yb3) have shorter Yb–N bonds, than
Yb(II)–N in [Yb(LPh,Ph)2],4i while the Yb4–N bonds are even longer,
suggesting that the Yb1, Yb2 and Yb3 atoms are in the +3 oxida-
tion state with +2 for Yb4. The Yb5 atom has a rather long bond to
the bridging CH2 group [Yb5–C45, 2.511(3) Å], which is similar
to the Yb1–C45 and Yb3–C21 bonds but longer than the Yb2–C21
[2.394(3) Å]; the Yb5–C(5- and 6-Ph) bond lengths are similar
to Yb(II)–C(5-Cp) (2.66–2.78 Å)17 but significantly longer than
the Yb–C bonds in the Yb(III) compound [YbCp″2I(thf)]18 (2.59–
2.69 Å), where theYb atom is in a similar coordination environment
as the Yb5 atom in 8. We conclude that the Yb5 atom is in the +2
oxidation state.
An unusual feature of complexes 3 and 8 is the presence of a
very short contact between the Yb(II) and Yb(III) atoms: 3.275 and
3.177 Å, respectively. The next shortestYbYb contact of 3.301 Å
was found in the Yb(III) complex [{YbCp(thf)}2(Ph2N2)2].19
Conclusions
In conclusion, we have shown that (i) the -diketiminato ligand of
the type N(SiMe3)C(R)CHC(R′)N(SiMe3) is readily reduced in its
D a l t o n T r a n s . , 2 0 0 4 , 2 2 7 2 – 2 2 8 0
2 2 7 7

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Li or Yb complexes to a paramagnetic dianion or diamagnetic trian-
ion; (ii) the trianion has two structural types C and D depending on
the negative charge delocalisation and the nature of the metal coor-
dination; and (iii) further reduction of the trianion in its Yb complex
leads to ligand fragmentation (C–N and N–Si bond-cleavage and
Me group deprotonation) with the formation of new imido ligands.
cooling dark green crystals of 4 (4.30 g, 74%) (Found: C, 65.1; H,
9.70; N, 9.81. C31H55Li2N4OSi2 requires C, 65.3; H, 9.73; N, 9.83%).
EPR spectrum (C6H6 solution): s, g = 2.0029; (methylcyclohexane
solution): s, g = 2.0030.
[Li(tmen)(-LPh,But)Li(OEt2)] (5)
Similarly, from Li (0.028 g, 4.03 mmol), Li(LPh,But) (1.40 g,
3.97 mmol) and tmen (0.60 cm3, 3.97 mmol), dark blue crystals
were obtained of 5 (3.52 g, 62%) (Found: C, 63.0; H, 10.79; N,
10.18. C29H59Li2N4OSi2 requires C, 63.4; H, 10.82; N, 10.19%).
EPR spectrum (diethyl ether solution): s, g = 2.00305.
Experimental
All manipulations were carried out under an inert atmosphere using
vacuum/argon line and Schlenk techniques. Solvents were dried
and distilled over sodium–potassium alloy (pentane, hexane) or
sodium-benzophenone (Et2O, thf) and stored over a K or Na mirror
under argon. Tmen (99%, Acros Organics) was dried and distilled
over calcium hydride. LiCH(SiMe3)2,20 Li(LPh,Ph),4b Li(LPh,But),4b and
[Li3(LAr,Ar)(tmen)]2 (6)
Similarly, from Li (0.072 g, 10.37 mmol), Li(LAr,Ar) (2.49 g,
5.14 mmol) and tmen (0.79 cm3, 5.21 mmol), after crystallisation
from hexane there were obtained dark violet crystals of 6·2ꢀ(hex-
ane), which upon being desolvated in a vacuum (10−2 Torr) at room
temperature gave 6 (0.76 g, 48%) (Found: C, 67.9; H, 10.07; N, 9.28.
C70H122Li6N8Si4 requires C, 68.4; H, 10.00; N, 9.11%). 1H-NMR (,
C6D6): 6.75 (br. s, 8 H; o- and m-C6H4But-4), 5.17 (s, 1 H; CH), 1.85
and 1.74 (two br. s, 16 H; tmen), 1.21 (s, 18 H; C6H4But-4), 0.44 (s,
18 H; SiMe3); 1H-NMR (, toluene-d8, 228 K):‡ 7.80 (d, J = 6.58,
2 H; o-H of neutral C6H4But-4), 7.41 (d, J = 7.85, 2 H; m-H of neu-
tral C6H4But-4), 6.12 (d, J = 7.89, 1 H; m′-H of negatively charged
C6H4But-4), 6.01 (d, J = 8.50, 1 H; m-H of negatively charged
C6H4But-4), 5.86 (d, J = 8.14, 1 H; o-H of negatively charged
C6H4But-4), 5.54 (d, J = 7.31 Hz, 1 H; o′-H of negatively charged
C6H4But-4), 5.12 (s, 1 H; CH), 1.76 and 1.64 (two s, 16 H; tmen),
1.25 (s, 9 H; neutral C6H4But-4), 1.09 (s, 9 H; negatively charged
C6H4But-4), 0.55 (s, 9 H; SiMe3 connected to the neutral C6H4But-4
side of the ligand), 0.44 (s, 9 H; SiMe3 connected to the negatively
charged C6H4But-4 side of the ligand); 13C-NMR (, C6D6): 110.92
(s; CH), 56 (br. s; CH2, tmen), 46 (br. s; CH3, tmen), 33.59 (s;
C(CH3)3), 31.66 (s; C(CH3)3), 5.25 (s; SiMe3); 29Si-NMR (, C6D6,
308 K): −10.08 (s; SiMe3); 29Si-NMR (, toluene-d8, 223 K): −9.25
and −9.63 (two s; SiMe3); 7Li-NMR (, C6D6): 1.86 (br. s, Li3 and
Li4), −0.21 (br. s, Li1 and Li2), −0.86 (s, Li5 and Li6); 7Li-NMR (,
toluene-d8, 208 K): 1.86 (s, Li3 and Li4), 0.44 (s, Li2 or Li1), −0.95
(s, Li5 and Li6), −1.17 (s, Li1 or Li2); 6Li-NMR (, toluene-d8, 208
K): 1.85 (s, Li3 and Li4), 0.44 (s, Li2 or Li1), −0.99 (s, Li5 and
Li6), −1.13 (s, Li1 or Li2). X-Ray quality crystals of 6·5(C6D6) were
isolated from the NMR tube solution of 6.
Yb(LPh,Ph 4i were prepared by published procedures. 4-tert-Butyl-
)
2
benzonitrile (97%, Aldrich) and lithium (high sodium, granule,
99%, Aldrich) were used without purification. Microanalyses were
carried out by Medac Ltd. (Brunel University). The NMR spectra
were recorded using the DPX 300 and AMX 500 Bruker instru-
ments and calibrated internally to residual solvent resonances for 1H
and 13C; external SiMe4, LiCl and [Yb(5-C5Me5)2(thf)] were used
as references for 29Si, 7Li (and 6Li) and 171Yb spectra, respectively.
All NMR spectra other than 1H were proton-decoupled and recorded
at ambient temperature unless otherwise stated.
Preparations
Li(LAr,Ar
)
4-tert-Butylbenzonitrile (3.46 g, 22.15 mmol) was added to a cooled
(0 °C) and stirred solution of LiCH(SiMe3)2 (1.85 g, 11.12 mmol) in
diethyl ether (50 cm3). The resulting solution was slowly warmed
to ca. 25 °C and stirred for 2 h. Volatiles were removed in vacuo
at 70 °C. The product was crystallised from hexane in a freezer
at −27 °C yielding yellow crystals of Li(LAr,Ar) (4.35 g, 81%)
(Found: C, 71.5; H, 9.21; N, 5.69. C29H45LiN2Si2: requires C, 71.9;
H, 9.36; N, 5.78%). 1H-NMR (, C6D6): 7.56 (d, J = 8.35 Hz, o-H of
C6H4But-4, 4 H), 7.24 (d, J = 8.37 Hz, m-H of C6H4But-4, 4 H), 5.62
(s, CH, 1 H), 1.23 (s, But, 18 H), 0.22 (s, SiMe3, 18 H); 13C-NMR
(, C6D6): 175.27 (NC(C6H4But-4)), 150.00 and 147.03 (ipso- and
p-C6H4But-4), 127.51 and 124.62 (o- and m-C6H4But-4), 105.66
7
(CH), 34.49 (C(CH3)3), 31.53 (C(CH3)3), 3.28 (SiMe3); Li-NMR
(, C6D6): 2.73.
[Yb{(-LPh,Ph)Li(thf)}2] (1)
[Yb3(LPh,Ph)3(thf)] (3)
Li (0.017 g, 2.50 mmol) was added to a stirred solution of
[Yb(LPh,Ph)2Cl] (0.78 g, 0.83 mmol) in thf (100 cm3) at ca. 20 °C.
The dark blue reaction mixture was stirred until the metal had dis-
solved, then solvent was evaporated and the residue was extracted
by pentane (100 cm3). The extract was concentrated to yield upon
cooling dark violet crystals of 1 (0.43 g, 49%). Analytical data of 1
were identical to those published previously.5
Solid Yb(C10H8)(thf)3 (0.120 g, 0.23 mmol) was added to a frozen
solution of [YbL2] (0.189 g, 0.21 mmol) in thf (10 cm3) and the
mixture was warmed up to room temperature with vigorous stir-
ring. Removing the solvent left a deep blue oil, which turned brown
while being dried under vacuum. Addition of pentane (10 cm3) led
to crystallisation of the product, which was washed with pentane to
remove free naphthalene. X-ray quality crystals of 3 (black needles,
0.045 g, 20%) were obtained from the concentrated pentane extract
after it had been stored at 20 °C overnight. Longer storage led
to dissolution of the crystals and decomposition of the product.
The pentane-washed microcrystalline product was identified as 3
(0.092 g, 41%), on the basis of the strong similarity of its 1H-NMR
spectrum with that of the larger crystals. However, a limited stabil-
ity and solubility of 3 in C6D6 and its paramagnetism prevented
further NMR-characterisation.
[Yb{(-LDph,Dph)Li(thf)}2] (2)
Li (0.010 g, 1.50 mmol) was added to a stirred solution of
[Yb(LDph,Dph)Cl(-Cl)2Li(thf)(OEt2)] (0.77 g, 0.74 mmol) in thf
(100 cm3) at ca. 20 °C. The dark blue reaction mixture was stirred
until the metal had dissolved, then solvent was evaporated and the
residue was extracted by ether (100 cm3). The extract was con-
centrated to yield upon cooling dark blue crystals of 2·thf (0.36 g,
67%). Analytical data of 2·thf were identical to those published
previously.5
[Yb3(LPh,Ph)2(dme)2]·3(C6H6) (7)
Solid Yb(C10H8)(thf)3 (0.233 g, 0.45 mmol) was added to a frozen
solution of [Yb(LPh,Ph)2] (0.199 g, 0.22 mmol) in thf (10 cm3); dme
(2 cm3) was added by vacuum transfer and the mixture was warmed
up to room temperature with vigorous stirring. Removing the sol-
[Li(tmen)(-LPh,Ph)Li(OEt2)] (4)
Lithium (0.053 g, 7.64 mmol) was added to a stirred solution of
Li(LPh,Ph) (2.82 g, 7.57 mmol) in diethyl ether (100 cm3) at ambient
temperature. The mixture was stirred until the metal had dissolved.
Tmen (1.14 cm3, 7.55 mmol) was added with stirring to the dark
green solution, which was concentrated in a vacuum to yield upon
‡ Assignment of the signals was based on selective decoupling at 228 K and
NOE experiments at 213 K.
2 2 7 8
D a l t o n T r a n s . , 2 0 0 4 , 2 2 7 2 – 2 2 8 0

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vent yielded a deep violet oil, which turned red–brown upon expo-
sure for 1 h to a dynamic vacuum. Addition of benzene (10 cm3)
gave a dark brown solution, from which X-ray quality crystals of 7
(0.275 g, 75% as black needles, red in thin layer) were formed after
storage at room temperature overnight. 1H-NMR (, C6D6): 7.69 (d,
J = 6.9, 2 H, o-H of neutral Ph), 7.15–7.09 (overlapped C6H6 and
m- and p-H of neutral Ph), 6.84 (t, J = 6.6, 2 H, m-H of negatively
charged Ph), 6.75 (br. s, 2 H, o-H of negatively charged Ph), 6.31 (t,
J = 6.6, 1 H, p-H of negatively charged Ph), 5.53 (s, 1 H; CH), 2.86
(br. s, 6 H CH3, dme), 2.61 and 2.29 (two m, AA′BB′, 4 H, dme),
0.52 and 0.49 (two s, 18 H, SiMe3); 29Si-NMR (, toluene/toluene-
d8): −3.08 and −13.67 (two s, SiMe3); 171Yb-NMR (, toluene/
toluene-d8): 1167 (s, Yb2) and 1107 (s, Yb1 and Yb3).
[Yb5(LPh,Ph)(L1)(L2)(L3)(thf)4]·2.5(C6H6) (8)
Yb metal (0.110 g, 0.64 mmol) was stirred with dry PbI2 (0.002 g)
in thf (10 cm3) for 1 h, in order to induce activation. [Yb(LPh,Ph)2]
(0.262 g, 0.29 mmol) was added, the ampoule was sealed and the
reaction mixture was stirred at room temperature for 3 months.
Volatiles were removed from the dark red–brown solution in vacuo
and the residue was extracted with benzene (5 cm3). Storing the
benzene solution for 3 d under ambient conditions produced black
shiny crystals of complex 8 (0.020 g, 4% based on LPh,Ph and its
fragments), suitable for X-ray crystallography.
Crystallography
Data for the crystal structure determination of 4, 6·2ꢀ(hexane),
6·5(C6D6), 7 and 8 were collected on a Nonius Kappa CCD diffrac-
tometer at 173(2) K with Mo–K X-rays ( = 0.71073 Å). Crystal
data and refinement details are listed in Table 4. The structures
were solved by a direct method and refined using SHELXL-97.21 In
complex 6·2ꢀ(hexane), there were poorly defined hexane solvate
molecules, two in general positions and one on an inversion centre.
They were included with a common isotropic displacement param-
eter, and 1,2 and 1,3 distance constraints. All other non-hydrogen
atoms were refined anisotropically; hydrogen atoms were included
in riding mode. In complex 8 the hydrogen atoms on C(21) and
C(45) (two each); and C(47) and C(48) (one each) were located on
a difference map and refined. Other H atoms were riding. One thf
ligand and one of the benzene solvate molecules were disordered.
CCDC reference numbers 217238, 223191 and 236144–236146
for compounds 4, 6·2ꢀ(hexane), 6·5(C6D6), 7 and 8, respectively.
See http://www.rsc.org/suppdata/dt/b4/b405554c/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
We thank EPSRC for the award of a fellowship to A. V. K. and to
the Royal Society for earlier support and the Leverhulme Trust for
grant to A. V. P.
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2 2 8 0
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