Synthesis and structures of the ytterbium(II) β-diketiminates [Yb{N(SiMe3)C(R2)C(H)C(R4)N(SiMe 3)}2] (R2 = R4 = Ph, C 6H4Me-4, or C6H4

Article abstract of DOI:10.1039/b300204g

Crystalline, homoleptic mononuclear ytterbium(II) β-diketiminates [Yb{N(SiMe₃)C(R²)C(H)C(R⁴)N(SiMe ₃)}₂] (R² = R⁴ = Ph 1, R² = R⁴ = Tol 2, R² = R

Full text of DOI:10.1039/b300204g

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Synthesis and structures of the ytterbium(II) ꢀ-diketiminates
[Yb{N(SiMe3)C(R2)C(H)C(R4)N(SiMe3)}2] (R2 ؍ R4 ؍ Ph,
C6H4Me-4, or C6H4Ph-4; or R2 ؍ C6H4Me-4, R4 ؍ 1-adamantyl)
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: ϩ44-1273-677196
Received 7th January 2003, Accepted 22nd January 2003
First published as an Advance Article on the web 14th February 2003
Crystalline, homoleptic mononuclear ytterbium() β-diketiminates [Yb{N(SiMe3)C(R2)C(H)C(R4)N(SiMe3)}2]
(R2 = R4 = Ph 1, R2 = R4 = Tol 2, R2 = R4 = Dph 3, or R2 = Tol and R4 = Ad 4) (Tol = C6H4Me-4, Dph = C6H4Ph-4,
Ad = 1-adamantyl) have been prepared. They have a characteristic 171Yb{1H} chemical shift in the region δ 2650 200
relative to [Yb(η5-C5Me5)2(thf )], although for 2 and 3 this was only observed at low temperatures, indicative of a fast
fluxional process at ambient temperature; data recorded ealier for 1 are shown to have been in error. The 1H NMR
spectra of 4 showed that two isomers were present in toluene solution, in a ratio of ca. 3 : 2, which interconverted on
the spin saturation transfer scale of ca. 1 sϪ1. NOE data are presented for each of 1–4; these led to (i) assignments of
the two types of SiMe3 groups (adjacent to Tol or Ad) and (ii) the conclusion that the two isomers are conformers,
one of which probably corresponds to that found in the crystal. The molecular structures of each of 1, 3 and 4 have
the ytterbium in a distorted tetrahedral environment, the two ligand planes (1 and 3) or boats (including the Yb
atom, 4) approximate to being either orthogonal (1 and 3) or parallel (4). The ligand-to-metal bonding is close to
κ2 (1, 3) or η5 (4) and the ligands are both π-delocalised (1, 3) or only one of them in 4.
these have relatively small N,NЈ-substituents R1–R5, e.g., B;2
Introduction
and (b) if R1 = SiMe3 = R5, the 4f-metal complexes [Ln(A)2Cl]
The chemistry of metal β-diketiminates is of substantial
are monomers, e.g., C,3 whereas even the bulkiest lanthanocene
current interest.1 Up to the end of June 2002, there were about
180 publications, 38 of them in 2001 and 27 in the first half of
2002, dealing with compounds of 43 metals. The β-diketimi-
nato ligand is shown as A in its delocalised general form.
chlorides, e.g. [{Pr(η5-C5H3(SiMe3)2-1,3)2(µ-Cl)}2], are (µ-Cl)2-
bridged dimers.4 The β-diketiminato ligands are thus not
only able to stabilise compounds in an unusually low state
of molecular aggregation, but also in a low oxidation state, as
cations, and others containing multiply bonded coligands, as
exemplified by D,5 E,6 and F,7 respectively. Many such com-
plexes are coordinatively unsaturated, e.g., G,8 and H;9 and this
and other features are the key to their ability to function as
catalysts (or procatalysts) for processes as varied as olefin
oligo-, poly- and copoly-merisation, e.g., I for polyethylene,10
J for ring-opening polymerisation of lactide,11 and K for
Diketiminates are important spectator ligands by virtue of their
strong binding to metals, their tuneable (cf. variations in R1–R5)
and extensive steric demands and their diversity of bonding
modes. The steric effects are well illustrated by the fact that (a)
very few tris(diketiminato)metal complexes are known and
copolymerisation of cyclohexene oxide and carbon dioxide.12 In
each of B–K, the ligand A is bonded to the metal in a chelating
terminal mode, approximating to κ2 (B, D, G, H, J, K) or η5
(C, E, I). In all these complexes, the ligands A have behaved in
a monoanionic fashion,1 but recently we have shown that the
D a l t o n T r a n s . , 2 0 0 3 , 1 0 7 0 – 1 0 7 5
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
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ytterbium() complexes L contain dianionic β-diketiminato
ligands M.13
The synthesis and characterisation of several β-diketimi-
natolanthanoid() metal complexes have been reported,
including crystallographic data not only for B2 and C,3 but
also for three further complexes of Ce,3 Sm14a and Gd.14b We
now report data for the homoleptic Yb() β-diketiminates 1–4.
The only previous record of Ln() β-diketiminates (apart from
the crystallographically characterised L13) is of [Ln{(N(SiMe3)-
C(Ph))2CH}2(thf )2] (Ln = Sm or Yb),3 [Yb{(N(SiMe3)C(Ph))2-
CH}2] 13,15 and [Yb{N(SiMe3)C(Ph)C(H)C(But)N(SiMe3)}2]
53 for which X-ray data were not available. A curious feature
was that the 1H, 13C{1H}, 29Si{1H} and 171Yb{1H} NMR
spectra of 5 in C6D6/PhMe showed that at ambient temperature
for each of these nuclei every signal was accompanied by one of
closely similar chemical shift, the two coalescing upon heating.3
The 171Yb{1H} chemical shifts for 5 at ambient temperature
were at δ 2476 and 2513.5, whereas 1 showed a singlet at δ 870.4
{rel. to [Yb(η5-C5Me5)2(thf )]16}.3 These observations were not
convincingly rationalised,3 and hence the aim of the present
investigation was to reinvestigate the NMR spectroscopic data
in more detail and to gain access to crystallographic data for
some homoleptic ytterbium() β-diketiminates in which the
ligand was either C2- or C1-symmetric, and examine further
their solution behaviour.
Fig. 1 The structure of 1 (20% ellipsoids). Selected bond lengths (Å)
and angles (Њ): Yb–N1 2.423(9), Yb–N2 2.418(9), Yb–N3 2.396(10),
Yb–N4 2.405(9), N1–C1 1.323(14), N2–C3 1.323(14), N3–C22
1.347(15), N4–C24 1.311(14), C1–C2 1.416(17), C2–C3 1.398(17), C22–
C23 1.406(17), C23–C24 1.427(16); N1–Yb–N2 86.0(3), N3–Yb–N4
85.4(3).
Results and discussion
The homoleptic ytterbium() complexes described herein are
derived from the bidentate β-diketiminato ligand A (R1
=
R5 = SiMe3, R3 = H for all complexes): (a) APh,Ph,3 (b) ATol,Tol
(Tol = C6H4Me-4), (c) ADph,Dph (Dph = C6H4Ph-4) and (d) ATol,Ad
(Ad = 1-adamantyl). Thus, they have the molecular for-
mulae [Yb(APh,Ph)2] 1, Yb(ATol,Tol
[Yb(ATol,Ad)2] 4.
)
2, [Yb(ADph,Dph)2] 3 and
2
Fig. 2 The structure of 3 (20% ellipsoids). Selected bond lengths (Å)
and angles (Њ): Yb–N1 2.396(4), Yb–N2 2.386(4), Yb–N3 2.393(4), Yb–
N4 2.405(4), N1–C1 1.331(6), N2–C3 1.331(6), N3–C34 1.345(6), N4–
C36 1.327(6), C1–C2 1.408(6), C2–C3 1.404(8), C34–C35 1.396(7),
C35–C36 1.408(7); N1–Yb–N2 87.38(12), N3–Yb–N4 89.08(13).
A precursor to complexes 1–4 was the corresponding
potassium β-diketiminate. Of these, K(APh,Ph), from
½[Li(APh,Ph)]2 ϩ KOBut in Et2O, has been described.17 The
compounds K(ATol,Tol) and K(ATol,Ad) were made similarly from
Li(ATol,Tol
)
and the X-ray-characterised [Li(ATol,Ad)],18 respec-
17
tively. The lithium β-diketiminate Li(ADph,Dph) was prepared
as shown in eqn. (1), by a general method established for
[Li(APh,Ph)]2 and Li(ATol,Tol),17 and then converted with KOBut
into K(ADph,Dph). Complexes 1–4 were prepared from
ytterbium() iodide and the appropriate K(A) in diethyl ether,
eqn. (2).
(1)
(2)
Each of the crystalline ytterbium() β-diketiminates 1–4 gave
satisfactory microanalyses, readily assignable (see Tables 2–5
and Experimental section) multinuclear NMR spectra and
(not for 2) single crystal X-ray diffraction data.
The molecular structure and atom numbering scheme, with
selected geometrical parameters for each of 1, 3 and 4 is shown
in Figs. 1–3, respectively. Some comparative data for these and
L (R2 = R4 = Ph)13 are also listed in Table 1.
Fig. 3 The structure of 4 (20% ellipsoids). Selected bond lengths (Å)
and angles (Њ): Yb–N1 2.371(7), Yb–N2 2.378(7), Yb–N3 2.412(7), Yb–
N4 2.364(7), N1–C1 1.341(12), N2–C3 1.336(11), N3–C27 1.282(12),
N4–C29 1.337(11), C1–C2 1.432(13), C2–C3 1.406(12), C27–C28
1.460(12), C28–C29 1.390(12); N1–Yb–N2 82.4(2), N3–Yb–N4 81.7(2).
D a l t o n T r a n s . , 2 0 0 3 , 1 0 7 0 – 1 0 7 5
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Table 1 Selected average bond distances (Å) and an angle (Њ) for 1, 3, 4 and L (R2 = R4 = Ph)13 a
Compound
Yb–N
N–C
C–C
N–Yb–N
1
2.410 (Ϫ0.014)
2.395 (ϩ0.010)
2.381 (ϩ0.033)
2.326 (ϩ0.015)
1.326 (ϩ0.021)
1.334 (ϩ0.012)
1.324 (Ϫ0.042)
1.413 (ϩ0.006)
1.414 (Ϫ0.016)
1.404 (Ϫ0.008)
1.422 (ϩ0.038)
1.427 (Ϫ0.002)
85.7 ( 0.3)
88.2 ( 0.9)
82.0 ( 0.4)
79.2 ( 0.2)
3
4
L (R2 = R4 = Ph)13
a In parentheses is shown the greatest deviation from the value of the mean bond length or angle.
Table 2 Selected NMR spectral chemical shifts (δ) at 298 K (unless otherwise indicated) for 1–5
a
a
Compound
Si(C1H3)3
Si(13CH3)3
29Si(CH3)3
171Yba
Solvent
[Yb(APh,Ph)2] 1
Yb(ATol,Tol)2 2
[Yb(ADph,Dph)2] 3
[Yb(ATol,Ad)2] 4
0.19
2.99
Ϫ3.27
2634 [950]e
(840.4)3
Toluene-d8
C6D6–PhMe
Toluene-d8–thf
(0.13)3
(2.71)3
(Ϫ4.81)3
2809 [2110]e
2529 [2120]e (at 273 K)
–
0.24
0.37
2.99
3.26
Ϫ5.18
Ϫ3.99
Toluene-d8
C6D6 (1H, 13C)
2588 [1960]e (at 203 K)
2641, 2629
Toluene-d8–thf (29Si, 171Yb)
Toluene-d8, C6D6 (29Si)
0.57b and 0.60c
0.16b and 0.21c
0.39d
4.51b, 4.50c
3.12b, 3.17c
4.05d
Ϫ20.42b, Ϫ20.16c
Ϫ4.32b, Ϫ4.78c
Ϫ17.01, Ϫ17.51
Ϫ2.24, Ϫ2.91
[100, 150]e
t
[Yb(ATol,Bu )2] 53
2476, 2513
C6D6–PhMe
0.03d
3.03d
[220, 170]e
a 13C, 29Si and 171Yb: each 1H-decoupled. b Major isomer. c Minor isomer. d Centre of two closely similar signals [for 1H in ratio ca. 3 : 2 (low
frequency)]; e Signal line width [w1/2/Hz].
Table 3 Variable temperature NMR spectral chemical shifts (δ) for complex 2 in toluene-d8–thf
13C
ipso-C of
T /K
171Yb
29Si
NC(Tol)CH
CH(middle)
Tol
193
208
223
238
253
268
283
298
318
2388 [1050]a
2350 [840]a
2315 [420]a
2324 [630]a
2400 [1050]a
2519 [1460]a
2656 [1900]a
2809 [2110]a
3009 [2370]a
Ϫ4.99
Ϫ5.01
Ϫ5.05
Ϫ5.09
Ϫ5.15
Ϫ5.23
Ϫ5.33
Ϫ5.49
Ϫ5.59
171.55
171.75
171.97
172.17
172.29
172.29
172.24
172.20
172.17
104.90
104.95
104.94
104.85
104.68
104.52
104.42
104.32
104.25
146.69
146.67
146.59
146.45
146.21
145.99
145.84
145.71
145.63
a Signal line width [w1/2/Hz].
Table 4 Enhancement factors η (%) in 1H NMR NOE spectral
experiments on 1–3
84Њ (3) and 58Њ (4). The ligands are disposed towards the metal
in a κ2-mode for 1 and 3 but an approximately η5-fashion for 4.
Thus, the mean planes of the two ligands are almost orthogonal
for 1 and 3, the angle between them being 80Њ (1) or 84Њ (3),
whereas in 4 it is 15Њ—the ligand planes (excluding the central C
atom, vide infra) being almost parallel. The NCCCN atoms of
the ligands are nearly coplanar in 1 and 3, the rms deviations
being 0.03 Å (1) and 0.01 Å (3). The N1–C1–C3–N2 atoms of
one of the ligands of 4 and the N3–C27–C29–N4 atoms of the
other are both almost coplanar with rms deviations of 0.07 Å,
but the C2 and C28 atoms are out of their respective plane
by 0.21 and 0.24 Å in the direction of the Yb atom. The endo-
cyclic bond lengths show that the N1–C1–C2–C3–N2 ligand
is essentially π-delocalised, whereas the other ligand approxi-
mates to the bonding illustrated in N. The molecule of 4 has
approximate C2 symmetry with the pseudo-principal axis along
the bisector of the N2–Yb–N4 angle, and is the rac-dia-
stereoisomer.
Irradiation
SiMe3
CH
0
n.a.
0
Complex 1
SiMe3
CH
m-H and p-H of Ph
o-H of Ph
n.a.
2.0
1.1
6.1
7.4
Complex 2
SiMe3
CH
m-H of Tol
o-H of Tol
n.a.
2.4
0.7
5.3
0.4
n.a.
0
4.0
Complex 3
SiMe3
CH
pЈ-H of Dph
mЈ-H of Dph
m- and oЈ-H of Dph
o-H of Dph
n.a.
1.4
0
0
1.4
6.1
0
n.a.
0
0
0
Ϫ1.1
In each of the crystalline compounds 1, 3 and 4 the ytterbium
atom is in a distorted tetrahedral environment, the angle
between the N1–Yb–N2 and N3–Yb–N4 planes being 83Њ (1),
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Table 5 Enhancement factors η (%) in 1H NMR NOE spectral experiment on 4
Irradiation
SiMe3Tol major
SiMe3Tol minor
SiMe3Ad major
SiMe3Ad minor
CH major
CH minor
SiMe3Tol, major
SiMe3Tol, minor
SiMe3Ad, major
SiMe3Ad, minor
CH2 of Ad
CH and CH2 of Ad (ϩ CH3 of Tol)
CH, minor
CH, major
m-H of Tol, minor
m-H of Tol, major
o-H of Tol, minor
o-H of Tol, major
n.a.
0
0
0
0
0
0
1.9
0
0.7
0
0
n.a.
0
0
0
0
0.6
0
0.6
0
4.7
0
1.0
0
n.a.
0
0
2.5
0
0
0
0
0
0
1.5
0
n.a.
0
3.1
0
0
0
0
0.6
0
0
0
0
0
0
2.1
0
n.a.
0
0
0
0
0
0
0
2.9
n.a.
0
0
0
3.1
0
0
2.7
4.5
0.8
The geometric parameters for the Yb β-diketiminates 1 and L
(R2 = R4 = Ph),13 both involving the same [{N(SiMe3)C(Ph)}2-
CH]nϪ ligand are now available for comparison, Table 1. The
principal bond length differences are in the longer N–C and
shorter Yb–N bond lengths in the latter. For Yb–N this is
attributed to the fact that the ligand bridges Yb and Li atoms,
but the longer N–C bond is consistent with the ligand in L
being dianionic (cf. M), there being population of the π*(CN)
LUMO of the NCCCN array.13
4 showed that, as for 5, two isomers are present in the approxi-
mate ratio 3 : 2 (the former designated “major” in Table 2),
which interconvert on the spin saturation transfer time scale of
ca. 1 sϪ1. Thus, spin saturation transfer experiments on the pair
of CH protons (corresponding to δ 5.71 and 5.66 in toluene-d8
at 298 K) displayed the following features: Ϫ20% at 303 K,
Ϫ58% at 318 K and Ϫ89% at 333 K, thus showing an increasing
rate at higher temperatures. However, the ratio of the two iso-
mers did not change significantly in the studied temperature
range showing that neither of them is thermodynamically
preferred.
To elucidate the solution structures of Yb() β-diketiminates
multinuclear NMR studies were performed on complexes 1–4.
Whereas the 1H and 13C{1H} NMR spectral chemical shifts for
1 are in reasonable agreement with those previously recorded,3
this is not the case for the 29Si{1H} and 171Yb{1H} chemical
shifts (Table 2). This table also summarises 171Yb{1H} and for
1H NMR spectral NOE experiments were performed for
each of the Yb() β-diketiminates 1–3 (Table 4) and 4 (Table 5),
in an attempt to establish their structures in toluene solution.
The interligand contact observed was that between the protons
of the SiMe3 groups and the CH proton of the ligand A. As
the distances between them are closely similar for both the
coordination modes κ2 (O and OЉ) and η5 (OЈ) (Fig. 4, R1 =
SiMe3 = R5), these are not distinguishable by the NOE data. As
reported above, crystalline 1 and 3 show κ2-bonding of ligands
to metal, whereas 4 displays η5-bonding. The NOE experiments
for 4 revealed that for both isomers there is a contact between
the middle CH proton and SiMe3 protons adjacent to the Tol,
but not the Ad, substituent, therefore excluding the possible
presence of the meso-isomer in solution. Only the rac-isomer
with a similar substituent arrangement (SiMe3 group adjacent
to Tol substituent of one ligand is opposite to the middle CH of
another ligand) is found in the crystal, suggesting that at least
one of the isomers in solution has the same η5-coordination
mode (OЈ in Fig. 4) as in the solid-state structure. Because the
171Yb{1H} chemical shifts for the two isomers of 4 are similar
(Table 2), it is likely that they differ only in their conformation.
We suggest that the second isomer adopts the κ2-mode, the
Yb(NCCCN)-metallacycle being in the boat conformation (OЉ
in Fig. 4). Each of the diketiminato ligands is bent towards the
less crowded (i.e., Tol-substituted) side of the other ligand with
the middle CH proton of one ligand being close to the SiMe3
group adjacent to the Tol substituent of the other (cf. OЈ, where
the ligands are substituted symmetrically, R2 = R4).
1
the Si(CH3)3 groups H, 13C{1H} and 29Si{1H} chemical shifts,
as well as comparative data3 for 5.
All five compounds showed 171Yb{1H} chemical shifts as
broad signals (cf. w1/2 in Table 2) in the range δ 2476–2809,
although for 1, 2 and 3 the signals became increasingly broad
and weak when the temperature changed from 193 to 298 K.
For 3 it was not found above 243 K and for 2 the observation of
a 171Yb{1H} signal at room temperature was possible only with
a more concentrated sample prepared using thf as a co-solvent.
One possible explanation (suggested by a referee) of such a
behaviour could be the presence in some NMR samples of
a small amount of a paramagnetic Yb() impurity, which is in
a dynamic equilibrium with diamagnetic Yb() complex at
higher temperatures. To check this possibility the same NMR
sample of 3 was mixed with the sample of 1 and 171Yb{1H}
NMR spectra of the mixture were recorded in the 193–298 K
temperature range. Only an 171Yb{1H} signal corresponding
to complex 1 was observed in the entire temperature range
1
while an H NMR spectrum clearly showed the presence of
both compounds in a 1.7 : 1 mixture of 1 : 3. Thus, if a para-
magnetic Yb() impurity in 3 was the reason of 171Yb{1H}
signal broadening, it had no effect on the spectrum of
complex 1.
Variable temperature NMR spectra showed non-linear
dependence of 171Yb{1H} and 13C{1H} (ligand backbone
carbon atoms) chemical shifts for 2 (Table 3) suggesting that
some changes in the ligand coordination mode occurred at
220–260 K. At higher temperatures the ligands became labile,
resulting in formation of a mixed-ligand complex when a
mixture of 1 and 2 (or 1 and 3) in C6D6 was heated at 363 K.
Having re-examined earlier such data for 1, we now conclude
that the 171Yb chemical shift reported in 19973 was in error and
that the δ 2650 200 is characteristic for the homoleptic Yb()
mononuclear β-diketiminates [Yb(AR2,R4)2], even though these
frequencies are much higher than any previously observed for
Yb() complexes.
Fig. 4 Models demonstrating NOEs (shown as arrows) in κ2 (O and
OЉ) and η5 (OЈ) bonded complexes.
The solution NMR spectra of the C2-symmetric [Yb(ATol,Ad)2]
D a l t o n T r a n s . , 2 0 0 3 , 1 0 7 0 – 1 0 7 5
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1
C42H58N4Si4Yb requires C, 55.8; H, 6.46; N, 6.19%). H NMR
Experimental
(δ, toluene-d8): 7.49 (m, 8 H, o-H of Ph ring), 7.07 and 7.06
(two m, 12 H, m- and p-H of Ph ring), 5.52 (s, 2 H, CH), 0.19
(s, 36 H, Si(CH3)3). 13C NMR (δ, toluene-d8): 173.06 (s, NC-
(Ph)CH), 148.40 (s, ipso-C of Ph ring), 128.30, 127.93, 127.83
(three s, C of Ph ring), 105.19 (s, CH), 2.99 (s, Si(CH3)3). 29Si
NMR (δ, toluene-d8): Ϫ3.27. 171Yb NMR (δ, toluene-d8): 2634.
All manipulations were carried out under vacuum or argon
by Schlenk techniques. Solvents were dried and distilled over
sodium–potassium alloy (pentane, hexane) or sodium–benzo-
phenone (Et2O, THF) and stored over a K or Na mirror under
argon. Microanalyses were carried out by Medac Ltd. (Brunel
University). The NMR spectra were recorded using the DPX
300 and AMX 500 Bruker instruments and calibrated internally
Yb(ATol,Tol)2 2. A similar procedure, starting from YbI2 (0.30
g, 0.69 mmol) and K(ATol,Tol) (0.65 g, 1.50 mmol), followed
by crystallisation from hexane, yielded complex 2 (0.43 g, 65%)
(Found: C, 57.2; H, 7.02; N, 5.70. C46H66N4Si4Yb requires C,
to residual solvent resonances for H and 13C; external SiMe4
1
and [Yb(η5-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 other-
1
57.5; H, 6.93; N, 5.83%). H NMR (δ, toluene-d8): 7.57 (d,
wise stated. Ytterbium() iodide,19 Li(APh,Ph),17 and Li(ATol,Tol
)
17
J = 7.32 Hz, 8 H, o-H of Tol), 6.94 (d, J = 7.32 Hz, 8 H, m-H
of Tol), 5.74 (s, 2 H, CH), 2.09 (s, 12 H, CH3 of Tol), 0.24 (s,
36 H, Si(CH3)3). 13C NMR (δ, toluene-d8): 172.21 (s, NC(Tol)-
CH), 145.80 (s, ipso-C of Tol), 138.09 (s, p-C of Tol), 128.58 and
128.12 (two s, o- and m-C of Tol), 104.51 (s, CH), 21.08 (s, CH3
of Tol), 2.99 (s, Si(CH3)3). 29Si NMR (δ, toluene-d8): Ϫ5.18.
171Yb NMR (δ, toluene-d8–thf ) (273 K): 2529.
were prepared by published procedures. The compound
[Li(ATol,Ad)] was first made by Dr Bourget-Merle.18
Preparations
Li(ADph,Dph)(OEt2). 4-Phenylbenzonitrile (4.90 g, 27.4 mmol)
was added to a cooled (0 ЊC) and stirred solution of
LiCH(SiMe3)2 (2.12 g, 12.7 mmol) in diethyl ether (150 cm3).
The resulting solution was slowly warmed to ca. 25 ЊC and
stirred for 2 h. Volatiles were removed in vacuo until onset of
crystallisation, the mixture then set aside at Ϫ27 ЊC yielding
yellow crystals of Li(ADph,Dph)(OEt2) (6.41 g, 84%) (Found:
C, 73.3; H, 7.92; N, 4.71. C37H47LiN2OSi2: requires C, 74.2; H,
7.91; N, 4.68%). 1H NMR (δ, C6D6): 7.67 (d, J = 8.78 Hz, o-H of
Dph, 4 H), 7.51 (m, m-H and oЈ-H of Dph, 8 H), 7.23 (m, mЈ-H
and oЈ-H of Dph, 6 H), 5.69 (s, CH, 1 H), 3.37 (q, J = 7.32 Hz,
OCH2CH2, 4 H), 1.16 (t, J = 7.32 Hz, OCH2CH2, 6 H), 0.21
(s, SiMe3, 18 H).
[Yb(ADph,Dph)2] 3. A similar procedure, starting from YbI2
(0.43 g, 1.02 mmol) and K(ADph,Dph) (1.17 g, 2.10 mmol),
followed by crystallisation from hexane, yielded complex 3
(0.85 g, 69%) (Found: C, 65.2; H, 6.27; N, 4.80. C66H74N4Si4Yb
1
requires C, 65.6; H, 6.17; N, 4.63%). H NMR (δ, C6D6): 7.67
(d, J = 8.78 Hz, 8 H, o-H of Dph), 7.43 (d, J = 8.78 Hz, 16 H,
m-H and oЈ-H of Dph), 7.18 (t, J = 7.32 Hz, 8 H, mЈ-H of
Dph), 7.14 (d, J = 8.78 Hz, 4 H, oЈ-H of Dph), 5.85 (s, 2 H,
CH), 0.37 (s, 36 H, Si(CH3)3). 13C NMR (δ, C6D6): 172.96 (s,
NC(Dph)CH), 147.23 (s, ipso-C of Dph), 141.57 and 140.87
(two s, p-C and ipsoЈ-C of Dph), 129.03 and 128.54 (two s,
o- and m-C of Dph), 127.61 (s, pЈ-C of Dph), 127.40 and 126.75
(two s, oЈ- and mЈ-C of Dph), 105.09 (s, CH), 3.26 (s, Si(CH3)3).
29Si NMR (δ, C6D6): Ϫ3.99. 171Yb NMR (δ, toluene-d8–thf )
(203 K): 2588.
Li(ATol,Ad). 1-Adamantanecarbonitrile (1.64 g, 10.16 mmol)
was added to a cooled (Ϫ20 ЊC) and stirred solution of
LiCH(SiMe3)2 (1.69 g, 10.16 mmol) in diethyl ether (100 cm3).
The mixture was stirred at ca. 25 ЊC for 12 h, whereafter
4-MeC6H4CN (1.19 cm3, 10.16 mmol) was slowly added. The
resulting yellow solution was stirred for a further 12 h. Volatiles
were removed at 50 ЊC/10 Ϫ2 Torr. Crystallisation of the residue
from n-hexane yielded yellow crystals of Li(ATol,Ad) (3.39 g,
75%) (Found: C, 69.9; H, 9.20; N, 6.26. C26H41LiN2Si2 requires
C, 70.2; H, 9.29; N, 6.30%).
[Yb(ATol,Ad)2] 4. A similar procedure, starting from YbI2
(0.47 g, 1.10 mmol) and K(ATol,Ad) (1.10 g, 2.30 mmol), yielded
complex 4 (0.72 g, 63%) (Found: C, 57.7; H, 7.80; N, 5.35.
1
C52H82N4Si4Yb requires C, 59.6; H, 7.88; N, 5.34%). H NMR
(δ, toluene-d8): 7.54 (d, J = 9.09 Hz, 8 H, major o-H of
Tol), 7.49 (d, J = 8.86 Hz, 8 H, minor o-H of Tol), 7.05 (d, J =
5.81 Hz, 8 H, major m-H of Tol,), 6.98 (d, J = 7.27 Hz, 8 H,
minor m-H of Tol,), 5.71 (s, 2 H, major CH), 5.66 (s, 2 H, minor
CH), 2.10 (m, 24 H, CH (6 H) of Ad ϩ CH2 (12 H) of Ad ϩ
CH3 (6 H) of Tol), 1.79 (m, 12 H, CH2 of Ad), 0.60 (s, 18 H,
minor Si(CH3)3 connected to the Ad ligand side), 0.57 (s, 18 H,
major Si(CH3)3 connected to the Ad ligand side), 0.21 (s,
18 H, minor Si(CH3)3 connected to the Tol ligand side), 0.16 (s,
18 H, major Si(CH3)3 connected to the Tol ligand side). 13C
NMR (δ, toluene-d8): 176.20 (s, minor NC(Ad or Tol)CH),
175.27 (s, major NC(Ad or Tol)CH), 173.18 (s, major NC(Ad
or Tol)CH), 172.81 (s, minor NC(Ad or Tol)CH), 145.49
(s, major ipso-C of Tol), 145.47 (s, minor ipso-C of Tol), 138.26
(s, major p-C of Tol,), 138.23 (s, minor p-C of Tol), 128.58 (s,
major o- or m-CH of Tol), 128.47 (s, minor o- or m-CH of
Tol), 128.33 (s, minor o- or m-CH of Tol), 128.05 (s, major o- or
m-CH of Tol), 99.07 (s, minor CH), 98.55 (s, major CH), 44.80
(s, major Cquat of Ad), 44.73 (s, minor Cquat of Ad), 41.39 (s,
minor CH2 of Ad), 41.36 (s, major CH2 of Ad), 37.12 (s, major
CH2 of Ad), 37.08 (s, minor CH2 of Ad), 29.43 (s, major CH of
Ad), 29.38 (s, minor CH of Ad), 21.12 (s, major CH3 of Tol),
21.06 (s, minor CH3 of Tol), 4.51(s, major Si(CH3)3 connected
to the Ad ligand side), 4.50 (s, minor Si(CH3)3 connected to
the Ad ligand side), 3.17 (s, minor Si(CH3)3 connected to the
Tol ligand side), 3.12 (s, major Si(CH3)3 connected to the Tol
ligand side). 29Si NMR (toluene-d8): Ϫ20.63 (s, major SiMe3
connected to the Ad ligand side), Ϫ20.39 (s, minor SiMe3 con-
nected to the Ad ligand side), Ϫ4.92 (s, minor SiMe3 connected
K(APh,Ph). KOBut (0.70 g, 6.28 mmol) was added to a stirred
solution of complex Li(APh,Ph) (2.34 g, 6.28 mmol) in diethyl
ether (100 cm3). The orange solution was stirred for 2 h, then
the solvent was pumped off and the residue was washed with
hexane (2 × 50 cm3) and dried for 2 h at 50 ЊC/10 Ϫ2 Torr giving
K(APh,Ph) (1.65 g, 65%) as a yellow powder (Found: C, 61.5;
H, 7.20; N, 6.89. C21H29KN2Si2 requires C, 62.3; H, 7.22;
N, 6.92%).
K(ATol,Tol). This was synthesised analogously (Found: C, 63.1;
H, 7.61; N, 6.48. C23H33KN2Si2 requires C, 63.8; H, 7.69;
N, 6.47%).
K(ADph,Dph). This was synthesised analogously (Found: C,
70.5; H, 6.72; N, 5.01. C33H37KN2Si2 requires C, 71.2; H, 6.70;
N, 5.03%).
K(ATol,Ad). This was synthesised analogously (Found: C, 65.1;
H, 8.59; N, 5.78. C26H41KN2Si2 requires C, 65.5; H, 8.67;
N, 5.87%).
[Yb(APh,Ph)2] 1. YbI2 (0.58 g, 1.36 mmol) was added to a
stirred solution of K(APh,Ph) (1.10 g, 2.72 mmol) in diethyl ether
(100 cm3). The dark brown suspension was stirred for 24 h
and then filtered. The filtrate was concentrated to yield brown
crystals of 1 (0.91 g, 74%) (Found: C, 55.3; H, 6.56; N, 6.31.
D a l t o n T r a n s . , 2 0 0 3 , 1 0 7 0 – 1 0 7 5
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View Article Online
Table 6 Crystal data and structure refinement for 1, 3 and 4
Compound
1
3
4
Empirical formula
Formula weight
C42H58N4Si4Yb
904.32
C66H74N4Si4Yb
1208.69
C52H82N4Si4Yb
1048.62
Crystal system
Space group
Triclinic
P1 (No.2)
Orthorhombic
Pna21 (No.33)
Triclinic
P1 (No.2)
¯
¯
a/Å
b/Å
c/Å
α/Њ
13.1217(14)
13.6826(15)
14.1141(16)
103.340(5)
108.799(5)
100.987(6)
2235.5(4)
2
1.34
2.23
10932
5369 [R(int) = 0.079]
4096
5369/0/318
R1 = 0.067, wR2 = 0.152
R1 = 0.094, wR2 = 0.165
12.1373(3)
22.1348(5)
23.2872(3)
90
90
90
6256.3(2)
4
1.28
1.61
38043
13613 [R(int) = 0.057]
10281
13613/1/676
12.7363(5)
13.1615(6)
16.5277(11)
85.738(3)
82.722(4)
82.784(4)
2721.6(2)
2
1.28
1.84
18527
9531 [R(int) = 0.064]
7645
9531/0/550
β/Њ
γ/Њ
U/Å3
Z
Dc/Mg mϪ3
µ(Mo-Kα)/mmϪ1
Reflections collected
Independent reflections
Reflections with I > 2σ(I )
Data/restraints/parameters
Final R indices [I > 2σ(I )]
R indices (all data)
R1 = 0.041, wR2 = 0.076
R1 = 0.066, wR2 = 0.085
R1 = 0.074, wR2 = 0.185
R1 = 0.094, wR2 = 0.199
2 D. Drees and J. Magull, Z. Anorg. Allg. Chem., 1994, 620,
814.
3 P. B. Hitchcock, M. F. Lappert and S. Tian, J. Chem. Soc., Dalton
Trans., 1997, 1945.
4 M. F. Lappert, A. Singh, J. L. Atwood and W. E. Hunter, J. Chem.
Soc., Chem. Commun., 1981, 1190.
5 C. Cui, H. W. Roesky, H.-G. Schmidt, M. Noltemeyer, H. Hao and
F. Cimpoesu, Angew. Chem., Int. Ed., 2000, 39, 4274.
6 L. W. M. Lee, W. E. Piers, M. R. J. Elsegood, W. Clegg and
M. Parvez, Organometallics, 1999, 18, 2947.
to the Tol ligand side), Ϫ4.44 (s, major SiMe3 connected to the
Tol ligand side). 171Yb NMR (δ, toluene-d8): 2641, 2629.
1H NMR NOE Spectroscopic experiments on complexes 1–4
The results are summarised in Tables 4 and 5, showing the
enhancement (η, %) of a designated 1H signal upon irradiating
the sample at the frequency of another, using C6D6 as solvent at
ambient temperature.
7 N. J. Hardman, C. Cui, H. W. Roesky, W. H. Fink and P. P. Power,
Angew. Chem., Int. Ed., 2001, 40, 2172.
8 J. M. Smith, R. L. Lachicotte, K. A. Pittard, T. R. Cundari,
G. Lukat-Rodgers, K. R. Rodgers and P. L. Holland, J. Am. Chem.
Soc., 2001, 123, 9222.
9 U. Fekl, W. Kaminsky and K. I. Goldberg, J. Am. Chem. Soc., 2001,
123, 6423.
10 P. B. Hitchcock, M. F. Lappert and D.-S. Liu, J. Chem. Soc., Chem.
Commun., 1994, 2637.
11 B. M. Chamberlain, M. Cheng, D. R. Moore, T. M. Ovitt,
E. B. Lobkovsky and G. W. Coates, J. Am. Chem. Soc., 2001,
123, 3229.
12 D. R. Moore, M. Cheng, E. B. Lobkovsky and G. W. Coates, Angew.
Chem., Int. Ed., 2002, 41, 2599.
13 A. G. Avent, A. V. Khvostov, P. B. Hitchcock and M. F. Lappert,
Chem. Commun., 2002, 1410.
14 (a) D. Drees and J. Magull, Z. Anorg. Allg. Chem., 1995, 621,
948; (b) A. Mandel and J. Magull, Z. Anorg. Allg. Chem., 1995,
621, 941.
Crystallography
Data for the crystal structure determination of each of 1, 3 and
4 were collected on a Bruker AXS CCD area detector at 173(2)
K with Mo-Kα X-rays (λ = 0.71073 Å). Crystal data and
refinement details are listed in Table 6. The structures were
solved by direct methods and refined using SHELXL-97.20 The
phenyl groups of 1 were refined as rigid bodies with isotropic
C atoms. For two of the rings (C16–C21) and (C31–C36) two
alternative orientations were included. All other non-hydrogen
atoms were refined anisotropically; hydrogen atoms were
included in riding mode.
CCDC reference numbers 191918, 192428 and 191917 for
compounds 1, 3 and 4, respectively.
See http://www.rsc.org/suppdata/dt/b3/b300204g/ for crystal-
lographic data in CIF or other electronic format.
15 P. B. Hitchcock, S. A. Holmes, M. F. Lappert and S. Tian, J. Chem.
Soc., Chem. Commun., 1994, 2691.
16 A. G. Avent, M. A. Edelman, M. F. Lappert and G. A. Lawless,
J. Am. Chem. Soc., 1989, 111, 3423.
17 P. B. Hitchcock, M. F. Lappert and D.-S. Liu, J. Chem. Soc., Chem.
Commun., 1994, 1699.
18 L. Bourget-Merle, P. B. Hitchcock and M. F. Lappert, unpublished
work.
Acknowledgements
We thank the Royal Society for an R.S./NATO fellowship for
A. V. K. and EPSRC for financial support.
19 T. D. Tilley, J. M. Boncella, D. J. Berg, C. J. Burns and
R. A. Andersen, Inorg. Synth., 1990, 27, 146.
20 G. M. Sheldrick, SHELXL-97, University of Göttingen, Göttingen,
Germany, 1997.
References
1 L. Bourget-Merle, M. F. Lappert and J. R. Severn, Chem. Rev., 2002,
102, 3031.
D a l t o n T r a n s . , 2 0 0 3 , 1 0 7 0 – 1 0 7 5
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