Mixed-ligand ytterbium(III) complexes incorporating one or two bidentate (N,O) amide ligands

Article abstract of DOI:10.1039/b303724j

Examples of the ability of the donor-functionalised amide ligands N-(2-methoxyphenyl)-N-(trimethylsilyl)amide (L¹) and N-(2-phenoxyphenyl)-N-(trimethylsilyl)amide (L²) to support mixed-ligand lanthanoid complexes of the type [Ln(L)₂A] or [Ln(L)AB] are described. Reaction of [Yb(OAr)₃] (Ar = C₆H₃Bu₂^t-2,6) with two equivalents of [Li(L²)]_n in hexane gave hexane-soluble, monomeric and five-coordinate [Yb(L²)₂(OAr)] (1) in high yield. Attempted preparation of an analogous [Yb(L¹)₂(MeCp)] complex by reaction of [Yb(MeCp)Cl₂(thf)] with [Li(L¹)(OEt₂)]₂ (with a Yb:Li ratio of 1:2) in thf instead gave the known [Yb(L¹)₂(μ-Cl)]₂ (2). In contrast, the stable complexes [Yb(MeCp)(L¹)(μ-Cl)]₂ (3) and [Yb(MeCp)(L²)(μ-Cl)]₂ (4) were readily obtained from 1:1 (Li:Yb) reaction of [Yb(MeCp)Cl₂(thf)] with [Li(L¹)(OEt₂)]₂ or [Li(L²)(dme)] in thf. The complexes 1, 3 and 4 have been characterised by X-ray structure determination.

Full text of DOI:10.1039/b303724j

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Mixed-ligand ytterbium(III) complexes incorporating one or two
bidentate (N,O) amide ligands
Glen B. Deacon,* Craig M. Forsyth and Natalie M. Scott
School of Chemistry, Monash University, Victoria 3800, Australia.
E-mail: glen.deacon@sci.monash.edu.au
Received 3rd April 2003, Accepted 20th June 2003
First published as an Advance Article on the web 7th July 2003
Examples of the ability of the donor-functionalised amide ligands N-(2-methoxyphenyl)-N-(trimethylsilyl)amide (L1)
and N-(2-phenoxyphenyl)-N-(trimethylsilyl)amide (L2) to support mixed-ligand lanthanoid complexes of the type
[Ln(L)2A] or [Ln(L)AB] are described. Reaction of [Yb(OAr)3] (Ar = C6H3But2-2,6) with two equivalents of [Li(L2)]n
in hexane gave hexane-soluble, monomeric and five-coordinate [Yb(L2)2(OAr)] (1) in high yield. Attempted
preparation of an analogous [Yb(L1)2(MeCp)] complex by reaction of [Yb(MeCp)Cl2(thf )] with [Li(L1)(OEt2)]2
(with a Yb : Li ratio of 1 : 2) in thf instead gave the known [Yb(L1)2(µ-Cl)]2 (2). In contrast, the stable complexes
[Yb(MeCp)(L1)(µ-Cl)]2 (3) and [Yb(MeCp)(L2)(µ-Cl)]2 (4) were readily obtained from 1 : 1 (Li : Yb) reaction of
[Yb(MeCp)Cl2(thf )] with [Li(L1)(OEt2)]2 or [Li(L2)(dme)] in thf. The complexes 1, 3 and 4 have been characterised by
X-ray structure determination.
Introduction
Results and discussion
The dramatic catalytic properties of group 3 and lanthanoid
metallocenes [Ln(Cp)2R]1,2 has prompted a search for altern-
ative ancillary ligands that may further exploit new reactivity
prospects for these metals.3,4 Promising results have been
achieved for bidentate diorganoamides, such as amidinates,5–7
ketiminates,8,9 guanidinates,10–14 aminotroponimates15,16 and
aminopyridinates,17,18 as spectator groups for lanthanoid cata-
lysis.19 We have recently introduced to lanthanoid chemistry
some new amide ligands based on an ortho-disubstituted phen-
ylene backbone (Fig. 1).20,21 These have a pendant donor arm,
thus chelating to the lanthanoid cation in an ‘edge-on’ binding
mode (Fig. 1, A), in contrast to the ‘face-on’ coordination of
Cp (Fig. 1, B), the latter giving rise to the characteristic reactiv-
ity wedge in metallocene catalysts.1,2 The bulky substituents on
the amide ligand periphery provide steric protection, enabling
isolation of heterolepetic lanthanoid() complexes of the type
[Ln(L)2(X)]2 (e.g. X = Cl, OMe)21,22 and [Ln(L)2(OPh)(thf )].22
In order to further explore the potential of the new L1 and L2
ligand systems, we have investigated generation of solvent-free
species that incorporate either two ‘L’ ligands {e.g. [Ln(L)2A]-
type complexes} or complexes having three disparate ligands
{e.g. [Ln(L)AB]-type complexes}. We now report the synthesis
and structural characterisation of examples of both classes of
complex, viz. monomeric [Yb(L2)2(OAr)] (Ar = C6H3But2-2,6)
The ligands L1 and L2 form a variety of well-defined, hydro-
carbon-soluble lithium salts,21,23 of which dimeric [Li(L1)-
(OEt2)]2 and monomeric [Li(L2)(dme)] are the most suitable for
situations where isolated reactants are needed. Strict stoichio-
metric conditions are generally required for the preparation of
the target mixed-ligand complexes free from contamination by
homoleptic [Ln(L)3]. We have previously isolated the solvated
mixed-ligandaryloxidecomplex[Yb(L2)2(OPh)(thf )]22 unexpec-
tedly from oxidation of a transient [YbII(L2)2(solvent)x] species,
and considered that use of a bulkier OAr group (e.g. Ar =
C6H3But2-2,6) might yield a solvent-free derivative. Accord-
ingly, reaction of solvent-free [Li(L2)]n with [Yb(OAr)3] in a
2 : 1 molar ratio in hexane (Scheme 1) successfully afforded
hexane-soluble [Yb(L2)2(OAr)] (1) in high yield, the eliminated
LiOAr having low solubility in this medium.24
23
and dimeric [Yb(MeCp)(L)(µ-Cl)]2 (L
=
L1, L2). These
complexes demonstrate a wider applicability for the current
chelating amide ligands.
Scheme 1
Complex 1 gave satisfactory elemental analyses (C, H, N)
and the infrared spectrum showed the presence of bands attri-
butable to L2 {by comparison with that of the related
[Nd(L2)3]21}, as well as additional strong absorptions at 1411,
845, 801 and 755 cmϪ1. The last may be a γ(CH) vibration of
the 2,6-di-tert-butylphenolate ring with three adjacent hydro-
gens and is observed in the spectra of [Ln(OAr)2(s)] (s = thf or
Et2O).25,26 An X-ray crystallographic study revealed that 1 is a
monomeric five-coordinate complex comprising a central ytter-
bium atom surrounded by an oxygen-bound aryloxide group
and two chelating L2 ligands. There are two monomers in the
asymmetric unit (one of which is depicted in Fig. 2), but both
have a similar structure, the major difference being derived from
rotation of one of the But groups from an eclipsed (Fig. 2) to a
staggered arrangement. The ytterbium coordination geometry
differs from the idealised square-based pyramid shown in Fig. 1
Fig. 1 Structures of L1 and L2, and ‘edge-on’ and ‘face-on’ binding
modes of amide (A) and Cp (B) ligands, respectively, in lanthanoid
complexes.
D a l t o n T r a n s . , 2 0 0 3 , 3 2 1 6 – 3 2 2 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 3
3216

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Table 1 Ytterbium environment in [Yb(L2)2(OAr)] (1)
Bond distances/Å
[Yb(Cp)X2] (X = halide) species. However, reaction of [Yb-
(MeCp)Cl2(thf )] with [Li(L1)(OEt2)]2 in a Li : Ln ratio of 2 : 1 in
thf unexpectedly afforded the known mixed-ligand bis(amido)
chloride complex [Yb(L1)2(µ-Cl)]2 (2)21 in high yield [Scheme
2(i)]. Previously, an attempt to prepare an analogous target
complex, [Yb(L1)2(Cp)], by an oxidation reaction from [Yb-
(L1)2(s)x] also failed and gave a rearranged product, [Yb-
(Cp)2(L1)].20 Considering the structures of the two aryloxide
complexes 1 and [Yb(L2)2(OPh)(thf )], the Yb(L)2 unit appears
to accommodate the increase in coordination number in the
latter by compression of the OPh substituents of the amide
ligands into a cis array around the more saturated metal. Pre-
sumably, the extra coordination site required by a ‘face-on’ Cp
ligand destabilises the resulting [Yb(L)2(Cp)] complex by
requiring closer compression of these groups preventing its
isolation.
Yb(1)–N(1)
Yb(1)–N(2)
Yb(1)–O(1)
Yb(1)–O(2)
Yb(1)–O(3)
2.068(2)
2.215(3)
2.373(2)
2.363(2)
2.068(2)
Bond angles/Њ
N(1)–Yb(1)–N(2)
N(1)–Yb(1)–O(1)
N(1)–Yb(1)–O(2)
N(1)–Yb(1)–O(3)
N(2)–Yb(1)–O(1)
N(2)–Yb(1)–O(2)
N(2)–Yb(1)–O(3)
O(1)–Yb(1)–O(2)
O(1)–Yb(1)–O(3)
O(2)–Yb(1)–O(3)
111.62(9)
71.97(8)
109.05(8)
124.14(9)
107.35(8)
71.51(8)
124.22(9)
178.66(7)
89.61(8)
90.49(8)
Scheme 2 (i) 2 [Li(L1)(OEt2)]2, thf; crystallisation from hexane.
(ii) [Li(L1)(OEt2)]2 or 2 [Li(L2)(dme)], thf; crystallisation from hexane.
(iii) 2Yb(MeCp)(L1)Cl (3) → Yb(MeCp) ClϩYb(L1) Cl (2); rearrange-
/
ment does not occur. (iv) [Li(L1)(OEt2)]22, hexane; L2i(MeCp) removed
by filtration.
In contrast to the above reaction, treatment of [Yb(MeCp)-
Cl2(thf )] with [Li(L1)2(OEt2)]2 or [Li(L2)(dme)]23 in a 1 : 1
21
Fig. 2 Structure of one of the independent molecules of 1 with 50%
thermal ellipsoids. Hydrogen atoms are omitted for clarity.
(Li : Ln) ratio in thf afforded examples of the second type of
target mixed-ligand complexes, [Yb(MeCp)(L1)(µ-Cl)]2 (3) and
[Yb(MeCp)(L2)(µ-Cl)]2 (4), respectively [Scheme 2(ii)]. The suc-
cessful isolation of 3 and the high yield (74%) of 2 from the 2 : 1
(and approaches a trigonal bipyramid) due to a relative twisting
of the two L2 arene backbones by 50.2(2)Њ. Thus, the two
NSiMe3 groups project below the ytterbium atom, whilst the
phenyl substituents protrude above, with a resultant near-linear
O–Yb–O angle (Table 1). The aryloxide ligand fits neatly into
the remaining space; the flat face of the arene ring is flanked by
the two OPh groups, whilst the bulky But substituents are posi-
tioned directly above the NSiMe3 groups (Fig. 2). This comfort-
able accommodation of the bulky OAr ligand by the Yb(L2)2
environment is reflected in the relatively short Yb(1)–O(3)
distance (Table 1) in comparison with [Ln(OAr)3(thf )]27 and
[Ln(OAr)2(s)x] (s = thf or Et2O)25,26,28 complexes. After correc-
tions for differences in the ionic radii,29 the subtraction value
for 1 of 1.16 Å is short compared with the usual range of 1.22–
1.34 Å. This effect appears typical of mixed-ligand lanthanoid
aryloxides, e.g. [Sm(C5Me5)2(OAr)] (subtraction value 1.12 Å)30
or [YbCl2(OAr)(thf )3] (1.22 Å),31 and presumably the [Ln-
(OAr)3(thf )] or [Ln(OAr)2(s)x] complexes suffer from significant
ligand–ligand repulsions as a consequence of the presence of at
least four But groups. The Yb(L2)2 arrangement in 1 also differs
markedly from that of six-coordinate [Yb(L2)2(OPh)(thf )], with
the ytterbium atom and the two L2 ligands more in a plane in 1
rather than being almost perpendicular, as they are in the latter.
This variation contrasts with the almost unchanging Ln(Cp)2
structural fragment in metallocene systems.
(Li : Ln) reaction excludes a possible 3
2 rearrangement
[Scheme 2(iii); maximum possible yield 50%] as the source of
the latter from the 2 : 1 reaction. Thus, in the formation of 2,
the initial product is presumably 3, which subsequently elimin-
ates insoluble LiMeCp in hexane. This scenario was independ-
ently confirmed by a small scale reaction of isolated 3 with
[Li(L1)(OEt2)]2 in a 1 : 1 (Li : Yb) ratio in hexane, which gave 2
and Li(MeCp) in moderate yield [Scheme 2(iv)].
The compositions of 3 and 4 were established by elemental
analyses (C, H, N) and the presence of trivalent ytterbium
was confirmed by the observation of characteristic32
f
f
transitions around 1000 nm in the near infrared spectrum. A
ligand-to-metal charge transfer (from both MeCp and L1/L2)
absorption in the visible region at 426 (3) and 428 nm (4)
accounts for the intense red colour of the complexes. The IR
spectra show strong absorptions characteristic of L1 and L2,
and obscuring those expected for the MeCp ligand.33 The mass
spectrum of 4 exhibits no peaks for metal-containing ions
attributable to dinuclear species, but the mononuclear ion
[Yb(MeCp)(L2)Cl]ϩ was observed, in addition to the organic
fragments [L2]ϩ and [MeCp]ϩ.
The single crystal X-ray structures of 3 (Fig. 3) and 4 (Fig. 4)
were determined. The ytterbium coordination environments are
virtually the same, despite the greater steric demand of L2
compared with L1. Selected bond lengths and angles are listed
in Tables 2 and 3. The asymmetric unit of each structure
To provide a counterpoint to the mixed-ligand aryloxide
complex 1, we attempted to prepare an analogous [Ln(L)2A]
species, where A is a polyhapto-cyclopentadienyl ligand, utilis-
ing an alternative synthetic strategy, viz. metathesis from a
comprises half of
a dimeric [Yb(MeCp)(L)(µ-Cl)]2 unit,
bridged by two chloride atoms, the other half related by
D a l t o n T r a n s . , 2 0 0 3 , 3 2 1 6 – 3 2 2 0
3217

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Table
2
Selected bond distances (Å) in [Yb(MeCp)(L)(µ-Cl)]2
Table 3 Comparison of ytterbium geometries (Њ) in [Yb(L1)2(µ-Cl)]2
{L = L1 (3), L2 (4)}
(2), [Yb(MeCp)(L)(µ-Cl)]2 {L = L1 (3), L2 (4)} and [Yb(MeCp)2(µ-Cl)]2
(5)
3
4
221
3
4
534
Yb(1)–N(1)
2.207(3)
2.337(3)
2.646(1)
2.655(1)
2.307
2.637(4)
2.587(4)
2.564(5)
2.597(4)
2.624(4)
2.205(2)
2.359(2)
2.641(1)
2.647(1)
2.301
2.631(3)
2.609(3)
2.586(3)
2.565(3)
2.588(3)
Yb(1)–O(1)
Yb(1)–Cl(1)
Yb(1)–Cl(1A)a
Yb(1)–C(1C)b
Yb(1)–C(1)
Yb(1)–C(2)
Yb(1)–C(3)
Yb(1)–C(4)
Yb(1)–C(5)
A–Yb–Aa
A–Yb–Cl
113.5(3), 112.7(3) 130.9
151.2(2), 152.3(2) 117.47(11)
130.4
126.7
112.4
109.4
109.1
108.0
82.05(5)
97.95(5)
114.29(6)
92.33(6)
114.1
107.4
78.51(2)
101.49(2)
144.3(2), 143.3(2)
91.0(2), 93.8(2)
88.5(2), 86.7(2)
94.19(11)
109.4
108.1
Cl–Yb–Cl
Yb–Cl–Yb
79.55(7), 79.47(7) 79.60(5)
98.72(8), 99.12(8) 100.04(5)
a A denotes N in 2, N or centroid of C(1)–C(5) in 3 and 4, and centroid
of C(1)–C(5) or centroid of C(7)–C(11) in 5.
a Symmetry transformations used to generate equivalent atoms: Ϫx ϩ
2, Ϫy ϩ 2, Ϫz ϩ 1 (3); Ϫx ϩ 1, Ϫy, Ϫz (4). b C(1C) = centroid of C(1)–
C(5).
of the MeCp rings as ‘A’, there is an intriguing similarity in the
geometry of 3, 4 and 5, which show comparable A–Yb–A and
A–Yb–Cl angles (Table 3). In contrast, 2 has narrower A–Yb–A
angles and some considerably more transoid A–Yb–Cl angles
(Table 3). These geometrical differences between 2, and 3, 4 and
5 appear to be reflected in the bond distance patterns of the
three complexes. Thus, values derived by subtraction of the
Yb3ϩ ionic radius from the Yb–N and Yb–O distances in 3 (1.28
and 1.40 Å, respectively) and 4 (1.28 and 1.43 Å, respectively)
indicate shorter bonds than found for the respective hetero-
leptic chlorides
2 (1.32 and 1.48 Å, respectively) and
[Nd(L2)2(µ–Cl)]2ؒ2PhMe (1.33 and 1.56 Å, respectively).21 Simi-
larly, an evaluation of the metal–chloride distances in 3 (1.72 Å)
and 4 (1.71 Å) shows these bonds are also significantly shorter
than in 2 (1.81 Å) and [Nd(L2)2(µ-Cl)]2.(PhMe)2 (1.84 Å),21 but
are only marginally longer than those of 5 (1.66 Å).34 Thus, the
bonding patterns of 3 and 4 are more consistent with a bis-
(cyclopentadienyl) rather than a bis(amido) ligand set. Overall,
the Yb–N, Yb–O, and Yb–Cl bond distances in 3 and 4 are
comparable to those found in the linked cyclopentadienyl-
amide complex [Y(η5:η1-SiMe2C5Me4NCMe2Et)(thf )(µ-Cl)]2
(subtraction values Y–N 1.28, Y–O 1.45, Y–Cl 1.67 Å),35 which
parallels (3) and (4), with the coordinated thf occupying a
similar position to that of the ether substituent on L1 and L2.
Fig.
3
Molecular structure of 3 with 50% thermal ellipsoids.
Hydrogen atoms are omitted for clarity.
Conclusions
Novel, solvent-free, ytterbium() complexes were prepared via
metathesis reactions, showing that the amide ligands L1 and L2
can support a variety of mixed-ligand lanthanoid environ-
ments. Unusually low coordination number (<6) complexes,
e.g. five-coordinate [Yb(L2)2(OAr)], are also accessible. Whilst
compositionally similar to the many [Ln(Cp)2A] compounds
and the more limited [Ln(Cp)AB] complexes in terms of solvent
coordination and structural types (e.g. monomer vs. dimer), the
‘edge-on’ binding of the bidentate-amide ligands provides sub-
tle structural differences which may be exploitable as catalytic
ancillaries. The range of amido-lanthanoid complex types now
available with the present ligands include both [Ln(L)2A] and
[Ln(L)(Cp)A], analogous to [Ln(Cp)2A] and [Ln(Cp-NR)A]
(Cp-NR = ansa-cyclopentadienyl-amide ligand), both of which
are active catalytic precursors.2,36
Fig.
4
Molecular structure of 4 with 50% thermal ellipsoids.
Hydrogen atoms are omitted for clarity.
inversion, generating a planar Yb2Cl2 core. Thus, pairs of
MeCp, OR and N(SiMe3) groups have a transoid disposition
across the Yb2Cl2 bridge. The unique metal environment in
Experimental
All reactions were carried out under dry nitrogen using a dry
box and standard Schlenk techniques. Solvents were dried
by distillation from sodium wire–benzophenone. IR spectra
(4000–650cmϪ1) were recorded from Nujol mulls sandwiched
between NaCl plates with a Perkin Elmer 1600 FTIR spectro-
meter. Mass spectra were recorded using a VG Trio-1 GC mass
spectrometer. Each listed m/z value for metal-containing ions is
the most intense peak of a particular cluster pattern, in good
agreement with the calculated pattern. Elemental analyses
each complex is
a seven-coordinate pseudo-square-based
pyramid, with the centroid of the η5-methylcyclopentadienyl
ligand occupying the apical position. These two structures
clearly show the contrasting coordination modes of the MeCp
(‘face-on’) and L1 and L2 (‘edge-on’) ligands. Considering the
structures of the series of complexes [Ln(L1)2(µ-Cl)]2 (2),21
[Yb(MeCp)(L)(µ-Cl)]2 {L = L1 (3), L2 (4)} and [Yb(MeCp)2-
(µ-Cl)]2 (5),34 and denoting the amide nitrogens or the centroids
D a l t o n T r a n s . , 2 0 0 3 , 3 2 1 6 – 3 2 2 0
3218

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Table 4 Crystal and refinement data
Compound
Formula
M
[Yb(L2)2(OAr)] (1)
C44H57N2O3Si2Yb
891.14
[Yb(MeCp)(L1)(µ-Cl)]2 (3)
C16H23ClNOSiYb
481.93
[Yb(MeCp)(L2)(µ-Cl)]2 (4)
C21H25ClNOSiYb
544.00
a/Å
b/Å
c/Å
α/Њ
13.8480(1)
15.6657(2)
20.1433(2)
70.702(1)
8.5538(3)
9.7537(2)
12.0433(2)
76.953(1)
9.6568(1)
8.7267(1)
25.3241(3)
90
β/Њ
82.812(1)
88.253(1)
4233.3(15)
Triclinic
¯
P1
78.027(1)
64.868(1)
879.1(3)
98.997(1)
90
2107.9(7)
Monoclinic
P21/c
γ/Њ
V/Å3
Crystal system
Space group
Z
Triclinic
¯
P1
4
2
4
ρcalcd/g cmϪ1
µ(Mo-Kα)/mmϪ1
2ϑmax/Њ
1.398
2.305
56.6
19743, 15003
0.0316, 0.0551
0.0581, 0.0653
1.821
5.537
56.6
4293, 3835
0.0322, 0.0711
0.0394, 0.0735
1.714
4.630
56.6
5202, 4877
0.0213, 0.0500
0.0239, 0.0511
N, No
R, Rw (observed data)
R, Rw (all data)
(C, H, N) were determined by the Campbell Microanalytical
Service, University of Otago, New Zealand. Metal analyses were
carried out by complexiometric titration with Na2EDTA.37,38
The following reagents were prepared according to the reported
methods: [Li(L1)2(OEt2)]2,21 [Li(L2)(dme)],23 [Li(L2)]n;23 [Yb-
(OC6H3But2-2,6)3] was prepared analogously to the Sc, Y, La
and Sm derivatives.39
After stirring for 12 h, the solvent was removed under reduced
pressure and hexane (30 cm3) was added, giving a white precipi-
tate. The red solution was filtered and the filtrate volume
reduced to 15 cm3 under vacuum. The dark red/green dichroic
crystals of the title compound formed on standing for 2 weeks
(0.17 g, 72%). (Found: C, 39.7; H, 4.7; N, 3.0; C32H46Cl2N2-
O2Si2Yb2 requires C, 39.9; H, 4.8; N, 2.9%) IR (Nujol) ν/cmϪ1
:
1594 s, 1560 w, 1486 s, 1320 w, 1283 vs, 1247 vs, 1238 s, 1214 m,
1164 vs, 1119 vs, 1068 w, 1052 m, 1032 m 1011s, 911 vs, 897 w,
827 vs, 790 w, 768 vs, 746 w, 732 vs, 678 s, 629 s, 599 w. Vis-near
IR (DME) λmax/nm (ε/dm3 molϪ1 cmϪ1): 426 (230), 938 (4), 982
(42), 994 (18).
[Yb(L2)2(OC6H3But2-2,6)] (1)
Tris(2,6-di-tert-butylphenolato)ytterbium() (0.090 g, 0.11
mmol), [Li(L2)]n (0.060 g, 0.22 mmol) and hexane (20 cm3) were
added to a flask, and the mixture was stirred for 15 h. The red
reaction mixture was cooled to Ϫ78 ЊC, affording a white pre-
cipitate. The mixture was filtered and the filtrate allowed to
warm to room temperature. After evaporation to low volume
and standing for 2 h, orange crystals (suitable for X-ray analy-
sis) of the title complex formed (0.070 g, 73%). (Found: C, 59.0;
H, 6.8; N, 2.9; C44H57N2O3Si2Yb requires C, 59.3; H, 6.5; N,
3.1%.) IR (Nujol) ν/cmϪ1: 1594 s, 1558 w, 1478 s, 1411 vs, 1351
w, 1280 vs, 1244 s, 1183 s, 1158 s, 1098 vs, 1074 w, 1048 br m,
1022 w, 1004 w, 916 vs, 861 s, 845 s, 827 s, 801 vs, 755 s, 734 s,
693 vs, 680 w, 659 m, 628 w, 593 w.
[Yb(MeCp)(L2)(ꢀ-Cl)]2 (4)
To solid [Yb(MeCp)Cl2(thf )] (0.27 g, 0.72 mmol) and
[Li(L2)(dme)] (0.26 g, 0.72 mmol) was added thf (40 cm3), and
the mixture was stirred for 12 h. The solvent was evaporated to
dryness and hexane (30 cm3) was added giving a white precipi-
tate. The orange solution was filtered and the filtrate volume
reduced to 15 cm3 under vacuum. Dark purple crystals (suitable
for X-ray analysis) of the title compound deposited on standing
(0.24 g, 62%). (Found: C, 46.1; H, 4.7; N, 2.7; C42H50Cl2N2-
O2Si2Yb2 requires C, 46.4; H, 4.6; N, 2.6%) IR (Nujol) ν/cmϪ1
:
Synthesis and characterisation of [Yb(MeCp)Cl2(thf)]
1586 s, 1558 w, 1303 w, 1281 vs, 1245 vs, 1183 s, 1157 vs, 1100 vs,
1047 s, 1026 m, 960 w, 908 vs, 850 s, 831 vs, 786 s, 726 m, 695 s,
680 w, 632 w. MS m/z: 509 (20%) [Yb(L2)(C5H4Me)]ϩ, 464 (5)
[Yb(L2)(C5H4Me) Ϫ 3Me]ϩ, 432 (<1) [Yb(L2)(C5H4Me) Ϫ
C6H5]ϩ, 416 (<1) [Yb(L2)(C5H4Me) Ϫ OC6H5]ϩ, 337 (5)
[Yb(C6H4NSiMe3)]ϩ, 257 (10) [(L2H)]ϩ, 226 (10) [(L2) Ϫ 2Me]ϩ,
165 (15) [OC6H4NHSiMe2]ϩ, 150 (15) [C6H4ONHSiMe]ϩ, 135
(20) [C6H5ONHSi]ϩ, 73 (100) [SiMe3]ϩ, 58 (25) [SiMe2]ϩ.
Vis-near IR (DME) λmax/nm (ε/dm3 molϪ1 cmϪ1): 428 (241), 926
(6), 949 (13), 988 (78), 995 (22).
The compound [Yb(MeCp)Cl2(thf )] was prepared in
a
metathesis reaction similar to the synthesis of [Er(C5H5)Cl2-
(thf )3].40 To solid YbCl3(thf )3 (1.05 g, 2.11 mmol) and
Tl(MeCp) (0.60 g, 2.11 mmol) was added thf, and the reaction
mixture was stirred at room temperature for 12 h. Filtration and
evaporation to dryness yielded a dark red material (0.52 g,
62%). (Found: C, 29.0; H, 5.0; C10H15Cl2OYb requires C, 30.4;
H, 3.8%.) IR (Nujol) ν/cmϪ1: 1299 w, 1170 w, 1074 w, 1013 s,
921 m, 863 br s, 771 w, 722 s, 668 w.
Reaction of [Yb(MeCp)Cl2(thf)] with [Li(L1)(OEt2)]2 (Li : Yb
molar ratio of 2 : 1)
Reaction of [Yb(MeCp)(L1)(ꢀ-Cl)]2 with [Li(L1)(OEt2)]2
(1 : 1 Li : Yb ratio)
To solid [Li(L1)(OEt2)]2 (0.29 g, 0.50 mmol) and [Yb(MeCp)-
Cl2(thf )] (0.28 g, 0.50 mmol) was added thf (40 cm3). The result-
ing dark red mixture was stirred for 12 h at room temperature,
the solvent was removed under vacuum and hexane was added
(30 cm3). The mixture was filtered and the red filtrate concen-
trated to ca. 15 cm3 to yield large red crystals of (by IR) 2
(0.22 g, 74%). Unit cell data—C40H64Cl2N4O4Si4Yb2, M =
1194.3, monoclinic, a = 14.614(1), b = 18.063(1), c = 19.012(1)
Å; α = 90, β = 92.44, γ = 90Њ; V = 5015 Å3, T ≈ 123 K—are in
agreement with those reported previously.21
Treatment of [Yb(MeCp)(L2)(µ-Cl)]2 (0.10 g, 0.10 mmol) with
[Li(L1)(OEt2)]2 (0.06 g, 0.10 mmol) in hexane resulted in a white
precipitate and a red solution. The reaction mixture was filtered
and the filtrate volume reduced, affording red crystals of 2
(0.06 g, 51%). The infrared spectrum was similar to that of the
authentic compound.21
X-Ray crystallography
Under an inert atmosphere, the air- and moisture-sensitive crys-
tals were covered in viscous oil and mounted onto a glass fibre.
Low-temperature (∼123 K) data were collected on an Enraf-
Nonius CCD area-detector diffractometer (Mo-Kα radiation,
λ = 0.71073 Å; frames comprised of 1.0Њ increments in and ω,
[Yb(MeCp)(L1)(ꢀ-Cl)]2 (3)
To a thf solution (40 cm3) of [Yb(MeCp)Cl2(thf )] (0.20 g,
0.50 mmol) was added [Li(L1)(OEt2)]2 (0.14 g, 0.25 mmol).
D a l t o n T r a n s . , 2 0 0 3 , 3 2 1 6 – 3 2 2 0
3219

View Article Online
17 A. Spannerberg, M. Oberthur, H. Noss, A. Tillack, P. Arndt and
R. Kempe, Angew. Chem., Int. Ed., 1998, 37, 2079.
18 A. Spannenberg, P. Arndt and R. Kempe, Angew. Chem., Int. Ed.,
1998, 37, 832.
19 R. Anwander, Top. Organomet. Chem., 1999, 2, 1.
20 G. B. Deacon, C. M. Forsyth, N. M. Scott, B. W. Skelton and
A. H. White, Aust. J. Chem., 2001, 54, 439.
21 G. B. Deacon, C. M. Forysth and N. M. Scott, Eur. J. Inorg. Chem.,
2002, 1425.
22 G. B. Deacon, C. M. Forsyth and N. M. Scott, Eur. J. Inorg. Chem.,
2000, 2501.
yielding a sphere of data) with proprietary software (Nonius
B.V., 1998). Each data set was merged (Rint as quoted) to N
unique reflections; the structures were solved by conventional
methods and refined with anisotropic thermal parameter forms
for the non-hydrogen atoms by full-matrix least-squares on all
F 2 data using the SHELX 97 software package.41 Hydrogen
atoms were included in calculated positions and allowed to ride
on the parent carbon atom with isotropic thermal parameters.
Data were corrected for absorption by either empirical (1, 4) or
numerical (3) methods. Crystal data and refinement details for
each compound are listed in Table 4.
23 G. B. Deacon, C. M. Forsyth and N. M. Scott, J. Chem. Soc.,
Dalton Trans., 2001, 2494.
CCDC reference numbers 207491–207493.
See http://www.rsc.org/suppdata/dt/b3/b303724j/ for crystal-
lographic data in CIF or other electronic format.
24 P. B. Hitchcock, M. F. Lappert, R. G. Smith, R. A. Bartlett and
P. P. Power, J. Chem. Soc., Chem. Commun., 1988, 1007.
25 G. B. Deacon, P. B. Hitchcock, M. F. Lappert, P. MacKinnon and
R. H. Newnham, J. Chem. Soc., Chem. Commun., 1989, 935.
26 G. B. Deacon, T. Feng, P. MacKinnon, R. H. Newnham, S. Nickel,
B. W. Skelton and A. H. White, Aust. J. Chem., 1993, 46, 387.
27 G. B. Deacon, T. Feng, S. Nickel, M. I. Ogden and A. H. White,
Aust. J. Chem., 1992, 45, 671.
Acknowledgements
We are grateful to the Australian Research Council for support
and for an Australian Postgraduate Scholarship and a Monash
Publications Award to N. M. S.
28 J. R. van den Hende, P. B. Hitchcock, S. A. Holmes, M. F. Lappert,
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33 G. B. Deacon, A. J. Koplick and T. D. Tuong, Aust. J. Chem., 1984,
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