Ytterbium(II) amides and crown ethers: Addition versus amide substitution

Article abstract of DOI:10.1016/S0022-328X(01)01408-5

New Yb(II) amides [Yb(NPh₂)₂(THF)₄] (1) and Yb{NPh(SiMe₃)}₂(THF)_x(x = 1 or 3) (2) were obtained by the salt elimination method and the structure of the dimer [Yb{NPh(SiMe₃)}{μ-NP

Full text of DOI:10.1016/S0022-328X(01)01408-5

Journal of Organometallic Chemistry 647 (2002) 198–204
www.elsevier.com/locate/jorganchem
Ytterbium(II) amides and crown ethers: addition versus amide
substitution
Peter B. Hitchcock, Alexei V. Khvostov, Michael F. Lappert *, Andrey V. Protchenko
The Chemistry Laboratory, School of Chemistry, Physics and En6ironmental Science, Uni6ersity of Sussex, Brighton, East Sussex BN1 9QJ, UK
Received 28 September 2001; received in revised form 19 October 2001
Abstract
New Yb(II) amides [Yb(NPh2)2(THF)4] (1) and Yb{NPh(SiMe3)}2(THF)x (x=1 or 3) (2) were obtained by the salt elimination
method and the structure of the dimer [Yb{NPh(SiMe3)}{m-NPh(SiMe3)}(THF)]2 (2a) was determined. Reactions of the amides
1, 2 and [Yb{N(SiMe3)2}2(THF)2] (3) with [18]crown-6 gave the crystalline structurally characterised molecular complex
[Yb(NPh2)2([18]crown-6)] (4) in the case of the smaller NPh−2 ligand and the salt [Yb{N(SiMe3)2}([18]crown-6)][Yb{N(SiMe3)2}3]
(5) with the bulky bis(trimethylsilyl)amido ligand. Crystalline 4 has a ‘‘threaded’’ structure with the NPh2 groups on the opposite
sides of the [18]crown-6 ligand and the N−Yb−N% angle of 176.6°. An X-ray diffraction study of the related potassium amide
[K([18]crown-6)(NPh2)] (6) reveals that the K ion coordinates to one of the Ph-rings rather than to the amido nitrogen atom.
There is significant delocalisation of negative charge in the amido ligand of crystalline 6, unlike in 4. © 2002 Elsevier Science B.V.
All rights reserved.
Keywords: Ytterbium(II) amides; Crown ether; Structure; NMR spectra
1. Introduction
Bu2t -1,3)2}2(m-h6:h6-C6H6)] and [K([18]crown-6)(h2-
PhMe)2][{Ln(h5-C5H4SiMe2But-1,3)3}2(m-H)] (Ln=La
or Ce, Cp%%=C5H3(SiMe3)2-1,3). However, no reaction
The complexation of lanthanoid (Ln) ions by crown
ethers has been widely explored [1] and a number of
crystalline complexes (most of which have inorganic
counteranions, such as halide, nitrate or hydroxide)
were characterised by X-ray diffraction. Rare examples
of other anionic ligands include triflate [1d] and p-sul-
fonatocalix[4]arene in a peculiar ‘‘ferris wheel’’ type
La(III) complex [1e]. By contrast, the chemistry of
(crown ether)–Ln organometallic complexes is still un-
developed and no structural information is available on
Ln(II) compounds containing coordinated crown
ethers.
was observed when [LnCp%%] (Ln=La, Ce, Pr or Nd)
3
was treated with [18]crown-6 in benzene [2e]. By con-
trast, Ln(II) cyclopentadienides [LnCp%%] (Ln=Sm or
2
Yb) were found to react with [18]crown-6 in aromatic
solvents with the displacement of a cyclopentadienyl
ligand by the crown ether and the formation of the
crystalline salt [SmCp%%([18]crown-6)][SmCp%%]·0.5C6H6
3
or [YbCp%%([18]crown-6)][Cp%%]·3C6H6 [3]. In this paper
we describe extensions of this study to some Yb(II)
organoamides.
Recently we have reported on a variety of reactions
of some tris(cyclopentadienyl)lanthanoid(III) complexes
with potassium metal in the presence of [18]crown-6
and an arene [2]. Among the crystalline compounds
2. Results and discussion
2.1. Synthesis of Yb amides 1–3 and X-ray crystal
structure of 2a
isolated were those of formula [K([18]crown-6)][LnCp%%-
2
(C6H6-1,4)], [K([18]crown-6)(h2-C6H6)2][{Ln(h5-C5H3-
The starting Yb amides bearing different substituents
on the nitrogen atom [Yb{NRR%}2(THF)n]x (1–3)
(Scheme 1) were obtained by a salt elimination reaction
using YbI2 and the corresponding potassium amide
* Corresponding author. Tel.: +44-1273-678-316; fax: +44-1273-
677-196.
E-mail address: m.f.lappert@sussex.ac.uk (M.F. Lappert).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01408-5

P.B. Hitchcock et al. / Journal of Organometallic Chemistry 647 (2002) 198–204
199
Scheme 1.
KNRR% in THF. The extremely low solubility in THF
of the resulting KI allowed the straightforward isola-
tion of the Yb amides free from ate-complexes to be
achieved; the latter are often formed when a Li or Na
amide is used as starting material. In some early exam-
ples, isolation of either the neutral Yb(II)
bis(trimethylsilyl)amide or an ionic ate-complex was
accomplished by varying only work-up procedures [4];
whereas NaNPh2 with Ln(h5-C5H4Me)2Cl in THF gave
Fig. 1. Molecular structure and atom numbering scheme for
[Yb{NPh(SiMe3)}2(THF)]2 (2a).
Table 1
only
the
ate-complex
[Ln(NPh2)2(m-h5:h5-
,
Selected bond lengths (A) and angles (°) in 2a
C5H4Me)2Na(THF)2]ꢀ (Ln=Sm or Er) independent of
the Ln/N ratio [5]. Bis(diphenylamido)ytterbium crys-
tallised from a concentrated THF solution as the te-
trakis-THF adduct 1. The amides 2 and 3 were
recrystallised from hexane. Fractional crystallisation of
the former from hexane gave two different
Yb{NPh(SiMe3)}2–THF adducts: (i) the less soluble
were deep red blocks and needles of the 1:1 adduct 2a
Bond lengths
Yb1ꢀN4
Yb1ꢀN1
Yb1ꢀN2
Yb1ꢀO1
Yb1···C1
Yb1···C6
N1ꢀC1
2.326(4)
2.465(4)
2.499(4)
2.438(3)
2.872
2.953
1.396(6)
1.392(6)
Yb2ꢀN3
Yb2ꢀN1
Yb2ꢀN2
Yb2ꢀO2
Yb2···C10
2.353(4)
2.506(4)
2.518(4)
2.402(3)
2.763
N2ꢀC10
N4ꢀC28
1.412(5)
1.391(6)
N3ꢀC19
1
(as determined by H-NMR spectroscopy) and (ii) the
Bond angles
N1ꢀYb1ꢀN2
Yb1ꢀN1ꢀYb2
more soluble orange–brown plates of the 1:3 adduct
2b. The formation of the latter as a mononuclear
tris-THF adduct was consistent with steric effects, these
increasing in the sequence NPh2BNPh(SiMe3)B
N(SiMe3)2. Except for the above-mentioned differences
86.31(12)
94.63(13)
N1ꢀYb2ꢀN2
Yb1ꢀN2ꢀYb2
85.03(12)
93.48(12)
1
in the integration of the THF absorptions, the H- and
13C-NMR spectra of 2a and 2b were very similar. Since
these data were not structurally definitive, an X-ray
diffraction study of 2a was carried out.
The molecular structure of crystalline 2a is shown in
Fig. 1 and selected bond lengths and angles are given in
Table 1. In the crystal, compound 2a consists of
dimeric molecules, each Yb atom bearing one terminal
,
(d[YbꢀN] 2.326(4) and 2.353(4) A) and one bridging
,
(average d[YbꢀN] 2.497 A) amido ligand. The coordi-
nation sphere of the Yb atom is completed by a THF
Scheme 2.
molecule with YbꢀO distances of 2.438(3) and 2.402(3)
,
A and a close interaction with the ipso-carbon atoms of
the Ph rings of the bridging ligands (2.872 and 2.763
2.2. Reactions of Yb(II) amides with [18]crown-6
,
A), which is in the same range as the YbꢀC(Cp%%)
distances in the sterically hindered Yb(II) cationic cy-
clopentadienide [YbCp%%([18]crown-6)][Cp%%] [3]. Such a
short Ln···Cipso contact in arylamido complexes was
previously observed only in the neodymium het-
erometallic cluster [{Me2Al(m-Me)2}2Nd(m3-NPh)(m-
Me)AlMe]2 [6].
[18]Crown-6 reacted easily with each of the ytterbi-
um(II) amides 1–3, but the reaction outcome varied
with the nature of the amide substituents (Scheme 2). It
is noteworthy that trivalent Ln (Ln=La or Lu) amides
(
with bulky N(SiMe3)2 ligands did not react with
[18]crown-6 in benzene-d6 solution.

200
P.B. Hitchcock et al. / Journal of Organometallic Chemistry 647 (2002) 198–204
The diphenylamido complex 1 gave the thermally
reaction periods (more than 2 days) led to the appear-
ance of very broad paramagnetic signals with a de-
crease of signal intensity in the diamagnetic range,
Yb(II) being oxidised to paramagnetic Yb(III) species.
stable 1:1 crown ether adduct 4, which was sparingly
soluble in cold THF. The product composition was
confirmed by 1H-NMR spectroscopy, microanalysis
and finally by an X-ray diffraction study. Variable
(
In the case of the more basic N(SiMe3)2 anion, the
1
deprotonation and splitting of the crown ether in the
temperature H-NMR spectra showed that at low tem-
[Yb{NRR%}2(THF)n]/[18]crown-6 (1:1) system was
found to be faster than with complex 2b. The H-NMR
spectrum showed signals of the free amine and a vinyl
group after a few minutes. The crystalline product 5
was isolated in a good yield only when a 2:1 (Yb/
crown) stoichiometry was applied and the reaction was
carried out in cold hexane (Scheme 2). Excess Yb(II)
perature (−60 °C) two sets of Ph proton signals were
observed, which coalesced into a broad line at −5 °C
and then gave one set of three broad absorptions for
the o-, m- and p-H, respectively, at higher tempera-
tures. This behaviour suggests that there are two differ-
ent modes of amido ligand coordination in 4 which
exchange rapidly at r.t., probably through dissocia-
tion–association processes.
1
(
amide 3 was required to bind N(SiMe3)2 anions. The
Lu(III) amide [Lu{N(SiMe3)2}3] was tested as an alter-
(
The C1 symmetric amido ligand NPh(SiMe3) of com-
(
native trapping agent for N(SiMe3)2, because it was
plex 2b is probably too bulky to form a similar 1:1
adduct. No crystalline material was isolated when the
reaction was carried out in THF, Et2O or hexane.
When one equivalent of [18]crown-6 was added to a
C6D6 solution of 2b in an NMR spectral tube, a dark
brown oily precipitate formed and the major compo-
nent in the solution was free crown ether. After 30 min
of vigorous shaking the oil had dissolved yielding a
known that [M{N(SiMe3)2}3] (M=Sc, Yb, or Lu) can
be deprotonated by NaN(SiMe3)2 with the formation of
¸¹¹¹¹¹¹¹º
[MCH2SiMe2NSiMe3{N(SiMe3)2}2]− anions [9]. How-
ever, only complex 5 was obtained in hexane at −10
°C and crown ether splitting occurred when the solvent
was replaced by benzene and the mixture was warmed
up to r.t., unreacted [Lu{N(SiMe3)2}3] being recovered
in a high yield.
1
bright orange solution. The H-NMR spectrum showed
a number of broad absorptions assigned to a cleaved
crown ether with the characteristic signals for the vinyl
protons of the OCHꢁCH2 group. In a better resolved
13C-NMR spectrum, recorded after ca. 5 h, sets of
The blue crystalline complex 5 was extremely air-sen-
sitive and thermally unstable; direct light caused de-
colouration of the exposed surface. An X-ray
diffraction study showed the presence of separate an-
ions [Yb{N(SiMe3)2}3]− and highly disordered cations.
Although this disorder was not resolved, the ionic
structure of 5 was confirmed by multinuclear NMR
(
signals corresponded to the coordinated NRR% ligand,
free HNRR% (as a result of the crown ether deprotona-
(
tion by the NRR% anion), cleaved [18]crown-6 and free
t
THF (from the starting 2b). Similar crown ether depro-
tonation and ring-opening by an amido anion was
observed previously in the reactions of alkali earth
metal (M) amides [M{N(SiMe3)2}2(THF)2] with crown
ethers [7]. Recently a Ba amido complex containing
cleaved [18]crown-6 was structurally characterised [8]
and our NMR spectral assignments are based on com-
parisons with data for the barium complex. Longer
spectroscopy (Table 2). A mixture of BuOMe/C6D6
(4:1) was found to be the best solvent for these NMR
studies, because the solubility of 5 in hydrocarbon
solvents was too low (especially for deriving 171Yb-
NMR spectral data). In THF-d8 (where the solubility of
5 is high) the SiMe3 protons of the cation and the anion
gave only one broad signal; the presence of solvent
residual protons at l 3.58 obscured the signal of the
Table 2
NMR spectral chemical shifts (l) for 5 (293 K)
Nucleus, solvent
[18]Crown-6
A
Anion
Cation
HN(SiMe3)2
B
Minor component
t
1H, BuOMe/C6D6
3.96
3.88
3.42
70.45
0.081
−0.002
5.32
−13.68
252
−0.060
5.16
0.167
4.75
−0.068
2.47
13C, BuOMe/C6D6
68.65
5.63
−17.03
851
t
29Si, BuOMe/C6D6
N.F. b
t
a
171Yb, BuOMe/C6D6
1H, Et2O/C6D6
13C, Et2O/C6D6
1H, C6D5CD3
t
a
3.66
68.34
3.21
67.54
4.08
3.46
3.13
3.92
N.F.
70.28
3.31
70.27
3.58
0.159
5.67
0.574
5.31
N.F.
N.F.
0.087
1.73
13C, C6D5CD3
1H, C4D8O
0.036 (broad)
−0.018
a At 298 K.
b N.F., not found.

P.B. Hitchcock et al. / Journal of Organometallic Chemistry 647 (2002) 198–204
201
coordinated crown ether (minor component), whereas
the upfield shifted OCH3 signal of BuOMe at l 2.99
left the crown ether proton area at l 3–4 clear. Two
and the two apical nitrogen atoms of the dipheny-
t
,
lamido groups. The average YbꢀO distance of 2.594 A
,
is ca. 0.04 A longer than in the cation of the only other
SiMe3 absorptions in the appropriate 1:3 ratio were
structurally characterised Yb(II)–crown ether complex,
[YbCp%%([18]crown-6)][Cp%%] [3], or in the amidoytterbiu-
m(II) complex containing the dianionic deprotonated
1
observed in the H-, 13C-, and 29Si-NMR spectra. Also
two signals but in a 1:1 ratio (l=855.2 for the anion
and l=265.8 for the cation) were found in the 171Yb-
NMR spectrum at 253 K, the former being close to the
shift of the sodium ytterbate(II) complex Na[Yb-
{N(SiMe3)2}3] and the latter outside the normal range
(at l 614–1228) for a simple Yb(II) amido complex
[10]. This, and the strongly upfield shifted 171Yb signal
for 4 (l=24.4 at 273 K), is attributed to the unusually
high (compared to other Yb diamides) Yb coordination
number (C.N.=7 or 8) in these compounds.
4,13-diaza-18-crown-6
(DAC)
ligand
Yb[Yb-
{N(SiMe3)2}(m-DAC)]2 [12]. The YbꢀN distances of
,
2.538(3) and 2.568(3) A are the longest known terminal
amido–ytterbium(II) bonds (the second longest were
found in the above-mentioned Yb–DAC complex,
,
2.43(3) and 2.44(3) A [12], and in [Yb(9-carba-
,
zolyl)2(THF)2(dme)], 2.43(3) and 2.45(2) A [13]). Such
elongation of YbꢀN and YbꢀO bond distances may be
due to the significant steric strain in complex 4.
1
The most prominent feature of the H-NMR spec-
The structure of 6 is that of a contact ion pair
comprising the [K([18]crown-6)]+ cation and NPh2−
anion (Fig. 3). In contrast to the Yb complex 4, there is
trum of 5 was an AA%BB% pattern for the crown ether
protons; the chemical shifts and A to B peak-to-peak
separation were strongly concentration and solvent de-
pendent. This observation confirms the presence in
solution of the [Yb([18]crown-6){N(SiMe3)2}]+ cation,
in which the crown ether has two different faces. Weak
cation–solvent or cation–anion interaction may be re-
sponsible for the observed variations in the position of
the [18]crown-6 1H-NMR spectral signals. A similar
AA%BB% pattern for the coordinated crown ether pro-
tons was found in R2AlX- or R2Mg-crown ether sys-
tems attributed to [RAlX(crown)]+ or [RMg(crown)]+
cations [11]. However, in the Mg system such a cation
was detected only in the non-polar solvent C6D6 but
not in Et2O-d10 [11b]. In the majority of the NMR
spectra of complex 5, a minor component (5–10%) was
detected in the crown ether area along with a small
amount of free amine (Table 2). These impurities were
formed during the sample preparation and their quan-
tity was reduced by using large crystals and by protect-
ing the samples from direct light.
Fig. 2. Molecular structure and atom numbering scheme for
[Yb([18]crown-6)(NPh2)2] (4).
2.3. X-ray crystal structures of
[Yb(NPh2)2([18]crown-6)] (4) and
[K([18]crown-6)(NPh2)] (6)
In order to compare structural features attributable
to a diphenylamido-coordinated lanthanoid or an alkali
metal–crown ether complex cation, the potassium com-
pound [K([18]crown-6)(NPh2)] (6) was prepared, by
addition of [18]crown-6 to a THF solution of KNPh2.
X-ray quality crystals were obtained by slow cooling
the hot solution of 6 in a mixture of THF and toluene.
The ORTEP drawings of 4 and 6 are shown in Figs. 2
and 3, respectively, and selected intramolecular dis-
tances and angles are presented in Table 3.
The eight-coordinate Yb atom in crystalline 4 is at
the centre of a distorted hexagonal bipyramid, formed
by the six equatorial oxygen atoms of the crown ether
Fig. 3. Molecular structure and atom numbering scheme for
[K([18]crown-6)(NPh2)] (6).

202
P.B. Hitchcock et al. / Journal of Organometallic Chemistry 647 (2002) 198–204
Table 3
2a and 5 were not obtained. The NMR spectra were
recorded using the following Bruker instruments: DPX
300 (1H, 300.1; 13C, 75.5 MHz) and AMX 500 (29Si,
49.7; 171Yb, 87.5 MHz) and calibrated internally to
,
Selected bond lengths (A) and angles (°) in 4 and 6
Bond lengths (4)
YbꢀN1
YbꢀO1
YbꢀO3
YbꢀO5
N1ꢀC1
N1ꢀC7
2.538(3)
2.605(3)
2.574(3)
2.507(3)
1.387(5)
1.403(5)
YbꢀN2
YbꢀO2
YbꢀO4
YbꢀO6
N2ꢀC13
N2ꢀC19
2.568(3)
2.574(2)
2.643(3)
2.658(3)
1.400(5)
1.398(5)
1
residual solvent resonances in the case of H and 13C
spectra; external SiMe4 and [Yb(C5Me5)2(THF)] were
used for 29Si and 171Yb spectra, respectively. All NMR
spectra other than 1H were proton-decoupled and
recorded at ambient temperature unless otherwise
stated.
Bond angles (4)
N1ꢀYbꢀN2
C1ꢀN1ꢀC7
C1ꢀN1ꢀYb
C7ꢀN1ꢀYb
176.57(10)
114.8(3)
124.5(2)
120.6(2)
C19ꢀN2ꢀC13
C19ꢀN2ꢀYb
C13ꢀN2ꢀYb
116.1(3)
118.9(2)
124.9(3)
3.2. Synthesis of Yb(NPh2)2(THF)4 (1)
YbI2 (1.60 g, 3.75 mmol) was added to a stirred
solution of KNPh2 (1.55 g, 7.48 mmol) in tetrahydro-
furan (70 ml). The light orange suspension was stirred
for 24 h, and then filtered. The filtrate was concentrated
Bond lengths (6)
KꢀO1
KꢀO2
KꢀO3
KꢀO4
KꢀO5
KꢀO6
NꢀC13
2.864(3)
2.813(3)
2.882(3)
2.818(3)
2.820(3)
2.862(3)
1.368(5)
KꢀC13
KꢀC14
KꢀC15
KꢀC16
KꢀC17
KꢀC18
NꢀC19
3.390(4)
3.234(4)
3.180(4)
3.274(4)
3.358(4)
3.391(4)
1.364(5)
1
to yield orange crystals of 1 (3.82 g, 64%). H-NMR (l,
C6D6/pyridine-d5): 7.30 (d, J=7.32 Hz, 8H), 7.07 (d,
J=7.32 Hz, 8H), 6.56 (t, J=7.32 Hz, 4H), 3.51 (s,
16H, THF), 1.41 (s, 16H, THF). 13C-NMR (l, C6D6/
pyridine-d5): 157.21, 129.89, 119.88, 115.33, 67.70
(THF), 25.67 (THF). 171Yb-NMR (l, C4D8O/C4H8O):
487.1.
Bond angles (6)
C13ꢀNꢀC19
120.3(3)
no close KꢀN contact in 6, but rather a close Kꢀh6-Ph
interaction which suggests significant delocalisation of
negative charge onto the Ph-rings. As a consequence,
the CꢀN bonds are considerably shorter (1.364(5) and
3.3. Synthesis of [Yb{NPh(SiMe3)}{v-NPh(SiMe3)}-
(THF)]2 (2a) and [Yb{NPh(SiMe3)}2(THF)3] (2b)
,
,
1.368(5) A) than in 4 (average 1.397 A) or in
A solution of KNPh(SiMe3) (1.211 g, 5.52 mmol)
(prepared from 0.911 g of HNPh(SiMe3) and an excess
of KH in 20 ml of THF) was added to YbI2(THF)2
(1.557 g, 2.76 mmol) in THF (40 ml) at room tempera-
ture (r.t.) and the mixture was stirred overnight. The
bright orange mixture was filtered, the solvent was
removed under vacuum and the residue was extracted
with warm (ca. 40 °C) hexane. Crystallisation at 20 °C
gave 2a (0.11 g, 7%) as dark red blocks and needles.
1H-NMR (l, C6D6): 7.11 (t, 4H), 6.89 (d, 4H), 6.65 (t,
2H), 3.19 (s, 4H), 1.10 (s, 4H), 0.32 (s, 18H). 13C-NMR
(l, C6D6): 156.8, 130.2, 121.5, 115.8, 68.7, 24.3, 1.95.
The mother liquor was concentrated to ca. 1/4 of its
volume and stored at 0 °C for 2 days yielding 2b (1.486
,
[Li([12]crown-4)(NPh2)] (1.388 A) [14], but somewhat
,
similar to those in [PEtPh3][NPh2] (1.373 A) [15]. Fur-
ther confirmation of more substantial negative charge
delocalisation in the potassium amide 6 was obtained
by comparing the 1H-NMR spectra of 6 and 4; the
signals of the Ph protons in 6 were strongly shifted
upfield (for the p-H, the difference was 0.53 ppm).
3. Experimental
3.1. Materials and procedures
1
All manipulations were carried out under vacuum or
Ar by Schlenk techniques. Solvents were dried and
distilled over sodium–potassium alloy (pentane, hex-
ane) or sodium–benzophenone (Et2O, THF) and stored
over a K or Na mirror under Ar. The compounds
KNRR% were prepared from KH and the corresponding
amine in THF and used without isolation. [18]Crown-6
(Aldrich) was exposed to a dynamic vacuum for 1 day
and stored under an Ar atmosphere. The triamides
[Ln{N(SiMe3)2}3] (Ln=La or Lu) were prepared by a
literature procedure [16].
g, 75%), as brown–orange plates. H-NMR (l, C6D6):
7.15 (t, 4H, +C6D5H), 6.90 (d, 4H), 6.67 (t, 2H), 3.42
(s, 12H), 1.27 (s, 12H), 0.40 (s, 18H). 13C-NMR (l,
C6D6): 129.7, 121.5, 115.8, 67.8, 24.7, 2.11 (ipso-C(Ph)
was not observed). Anal. Found: C, 49.5; H, 7.14; N,
4.08. Calc. for C30H52N2O3Si2Yb: C, 50.2; H, 7.30; N,
3.90%.
3.4. Synthesis of [Yb{N(SiMe3)2}2(THF)2] (3)
A filtered solution of KN(SiMe3)2 (1.350 g, 6.79
mmol) (prepared from 1.09 g of HNPh(SiMe3) and an
excess of KH in 20 ml of THF) was added to
YbI2(THF)2 (1.937 g, 3.39 mmol) in THF (40 ml) at r.t.
Microanalyses were carried out by Medac Ltd.
(Brunel University). Due to desolvation or instability,
satisfactory elemental analysis data for compounds 1,

P.B. Hitchcock et al. / Journal of Organometallic Chemistry 647 (2002) 198–204
203
and the mixture was stirred overnight. The brown–or-
ange mixture was filtered, the solvent was removed
from the filtrate in vacuo and the residue was extracted
with hexane. Concentration of the solution to a small
volume followed by crystallisation at −27 °C gave 3
protected from direct light by aluminium foil. During
ca. 5 min the colour of the mixture changed to blue
with simultaneous precipitation of blue oily drops and
microcrystals. The crystallisation was complete in ca. 3
h at 0 °C. The colourless supernatant liquid was re-
moved by a cannula, the residue was washed with cold
hexane and dried in vacuo, yielding complex 5 (0.4214
g, 91%), as a light blue crystalline powder. Large
crystals (which were easier to handle and less light-sen-
sitive) were obtained when the concentrated Et2O solu-
tion of 5 was layered with pentane and stored at −27
°C for 1 week. NMR-spectral data are presented in
Table 2.
1
(1.73 g, 80%), as bright orange crystals. The H- and
13C-NMR spectra of the product were identical to those
reported in the literature [10].
3.5. Synthesis of [Yb([18]crown-6)(NPh2)2] (4)
[18]Crown-6 (0.08 g, 0.3 mmol) was added to a
stirred solution of 1 (0.24 g, 0.3 mmol) in tetrahydro-
furan (70 ml). The yellow solution was stirred for 1 h.
The solvent was removed in vacuo to give a yellow
solid, which was washed with pentane (30 ml) and dried
in vacuo, yielding 4 (0.21 g, 91%). 1H-NMR (l,
C4D8O): 7.00 (br s, 8H), 6.93 (br s, 8H), 6.49 (br s, 4H),
3.60 (br s, 24H, [18]crown-6). 171Yb-NMR (l, C4D8O/
C4H8O): 24.4 (273 K), 30.8 (213 K). Anal. Found: C,
54.9; H, 5.85; N, 3.66. Calc. for C36H44N2O6Yb: C,
55.9; H, 5.73; N, 3.62%.
3.7. Synthesis of [K([18]crown-6)(NPh2)] (6)
[18]Crown-6 (2.43 g, 9.2 mmol) was added to a
stirred solution of KNPh2 (1.90 g, 9.2 mmol) (synthe-
sised from HNPh2 and KH) in tetrahydrofuran (70 ml).
The mixture was stirred for 1 h. Solvent was removed
in vacuo to yield a pale yellow solid, which was washed
with hexane (60 ml) and dried in vacuo, yielding 6 (3.99
1
3.6. Synthesis of [Yb([18]crown-6){N(SiMe3)2}]-
[Yb{N(SiMe3)2}3] (5)
g, 92%). H-NMR (l, C4D8O): 6.80 (d, J=7.32 Hz,
4H), 6.71 (t, J=7.32 Hz, 4H), 5.96 (t, J=7.32 Hz,
2H), 3.51 (br s, 24H, [18]crown-6). 13C-NMR (l,
C4D8O): 159.07, 128.78, 118.83, 110.27, 70.89. Anal.
Found: C, 60.6; H, 6.99; N, 2.99. Calc. for
C24H34KNO6: C, 61.1; H, 7.27; N, 2.97%.
A hexane solution of [18]crown-6 (0.095 g, 0.36
mmol) was added to a solution of 3 (0.4742 g, 0.74
mmol) in hexane (20 ml) at −10 °C in a Schlenk tube
Table 4
Crystal data and details of data collection and structure refinement for 2a, 4 and 6
Compound
2a
4
6
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C44H72N4O2Si4Yb2
1147.50
173(2)
Monoclinic
P21/c (No.14)
20.8915(4)
13.8636(3)
18.6723(3)
111.641(1)
5026.9(2)
C
773.77
173(2)
36H44N2O6Yb
C24H34KNO6
471.62
173(2)
Monoclinic
P21/n (No.14)
8.5368(2)
29.3406(8)
13.7061(4)
106.804(2)
3286.4(2)
4
Monoclinic
Pc (No.13)
9.6670(5)
10.1606(6)
12.3875(8)
102.186(4)
1189.3(1)
2
,
a (A)
,
b (A)
,
c (A)
i (°)
3
,
V (A )
Z
4
1.52
Dcalc (Mg m−3
)
1.56
1.32
,
u (A)
0.71073
3.83
2304
0.71073
2.89
1568
0.71073
0.26
504
v (mm−1
F(000)
)
Crystal size (mm)
Theta range for data collection (°)
Reflections collected
0.10×0.10×0.05
4.56–25.05
36 055
0.20×0.10×0.05
3.73–25.02
22 536
0.20×0.15×0.10
3.92–27.87
7119
Independent reflections
Data/restraints/parameters
Final R indices [I\2|(I)]
8823 (Rint=0.064)
8823/0/505
R1=0.033, wR2=0.061
5731 (Rint=0.058)
5731/0/406
R1=0.031, wR2=0.063
4211 (Rint=0.057)
4211/2/289
R1=0.048,
wR2=0.134
0.773
Goodness-of-fit on F2
Largest difference peak and hole (e A
1.037
0.84 and −0.78
1.008
−3
,
)
1.13 and −0.82 (near Yb)
0.24 and −0.31

204
P.B. Hitchcock et al. / Journal of Organometallic Chemistry 647 (2002) 198–204
1017 and references therein;
(d) J. Chen, Y.-F. Zhang, X. Zheng, A. Vij, D. Wingate, D.
Meng, K. White, R.L. Kirchmeier, J.M. Shreeve, Inorg. Chem.
35 (1996) 1590;
(e) A. Drljaca, M.J. Hardie, J.A. Johnson, C.L. Raston, H.R.
Webb, Chem. Commun. (1999) 1135.
3.8. X-ray structure determinations for 2a, 4 and 6
Data for the crystal structure determination were
collected on a KappaCCD area detector at 173(2) K.
Crystal data and refinement details are listed in Table 4.
Empirical absorption corrections [17] were applied for
2a and 4. The structures were solved by direct methods
and refined using SHELXL-97 [18]. All non-hydrogen
atoms were refined anisotropically; hydrogen atoms
were included in riding mode.
[2] (a) M.C. Cassani, D.J. Duncalf, M.F. Lappert, J. Am. Chem.
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(d) Yu.K. Gun’ko, P.B. Hitchcock, M.F. Lappert, Organometal-
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(e) Yu.K. Gun’ko, personal communication.
[3] Yu.K. Gun’ko, P.B. Hitchcock, M.F. Lappert, Chem. Commun.
(1998) 1843.
4. Supplementary material
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2271.
[5] Y. Wang, Q. Shen, F. Xue, K. Yu, Organometallics 19 (2000)
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[7] D.C. Bradley, M.B. Hursthouse, A.A. Ibrahim, K.M. Abdul
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Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 171222 for compound 2a,
CCDC no. 171223 for compound 4 and CCDC no.
171224 for compound 6. Copies of this information
may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(Fax:
+44-1223-336033;
e-mail:
deposit@ccdc.
cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgements
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1459;
We thank the Royal Society (A.V.K.) and EPSRC
for financial support and Dr. A.G. Avent for recording
and interpreting 29Si- and 171Yb-NMR spectra.
(b) A.D. Pajerski, M. Parvez, H.G. Richey Jr., J. Am. Chem.
Soc. 110 (1988) 2660.
[12] L. Lee, D.J. Berg, G.W. Bushnell, Inorg. Chem. 33 (1994) 5302.
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