Lanthanide complexes of a cross-bridged cyclam ligand: Isolation and structural characterization of unusual trinuclear μ3-imido Yb(III) cluster cations and a mixed valence Yb(II/III) salt containing an Yb(II) anion

Article abstract of DOI:10.1016/j.ica.2005.11.015

The reaction of the cross-bridged cyclam ligand H₂CBC with divalent ytterbium precursors, Yb[N(SiMe₃)₂]₂[L]₂ (L = THF or Et₂O) or Yb(C₅Me₅)₂(OEt₂) afforded polymeric [Yb(CBC)]_n (1), as the primary product. In addition, the Yb[N(SiMe₃)₂]₂[L]₂ reactions also afforded a small amount of an unusual mixed valence salt containing a trinuclear Yb(III) cluster cation featuring a triply bridging NH group and a mononuclear Yb(II) anion, {[Yb(CBC)]₃[μ³-NH]}⁺ {Yb[N(SiMe₃)₂]₃}^- (2). A related cluster containing an iodide counterion, {[Yb(CBC)]₃[μ³-NH]}⁺ I^- (3), was also isolated in one case. The structures of salts 2 and 3 were determined by X-ray crystallography. Reaction of [Yb(CBC)]_n with p-tolyldisulfide, (C₆H₄MeS)₂, produced burgundy crystals of [Yb(CBC)(S-p-C₆H₄Me)]_n (4). The ¹H NMR spectra of 2 suggests that the trinuclear cation remains intact in THF-d₈ solution.

Full text of DOI:10.1016/j.ica.2005.11.015

Inorganica Chimica Acta 359 (2006) 2870–2878
www.elsevier.com/locate/ica
Lanthanide complexes of a cross-bridged cyclam ligand:
Isolation and structural characterization of unusual trinuclear
l3-imido Yb(III) cluster cations and a mixed valence
Yb(II/III) salt containing an Yb(II) anion
a
a,
*
Paul E. OꢀConnor , Brendan Twamley a,b, David J. Berg
a
Department of Chemistry, University of Victoria, 1 Finnerty Road, P.O. Box 3065, Victoria, BC, Canada V8W 3V6
Single Crystal X-ray Diffraction Laboratory, University Research Office, 109 Morrill Hall, University of Idaho, Moscow, ID 83844-3010, USA
b
Received 18 October 2005; accepted 20 November 2005
Available online 6 January 2006
Dedicated to Professor Brian James for his lifelong contributions to inorganic chemistry.
Abstract
The reaction of the cross-bridged cyclam ligand H2CBC with divalent ytterbium precursors, Yb[N(SiMe3)2]2[L]2 (L = THF or Et2O)
or Yb(C5Me5)2(OEt2) afforded polymeric [Yb(CBC)]n (1), as the primary product. In addition, the Yb[N(SiMe3)2]2[L]2 reactions also
afforded a small amount of an unusual mixed valence salt containing a trinuclear Yb(III) cluster cation featuring a triply bridging
NH group and a mononuclear Yb(II) anion, {[Yb(CBC)]3[l3-NH]}+ {Yb[N(SiMe3)2]3}ꢀ (2). A related cluster containing an iodide coun-
terion, {[Yb(CBC)]3[l3-NH]}+ Iꢀ (3), was also isolated in one case. The structures of salts 2 and 3 were determined by X-ray crystallog-
raphy. Reaction of [Yb(CBC)]n with p-tolyldisulfide, (C6H4MeS)2, produced burgundy crystals of [Yb(CBC)(S-p-C6H4Me)]n (4). The 1H
NMR spectra of 2 suggests that the trinuclear cation remains intact in THF-d8 solution.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: X-ray crystal structures; Ytterbium complexes; Imide; Mixed valence; Macrocyclic ligands; Cyclam; Amide; Trinuclear cluster
1. Introduction
DAC) [3]. While ligands of this class did afford some inter-
esting chemistry including the formation of stable dialkyls
[3d], moderately stable alkyl cations [3d] and the reversible
dimerization of alkynides to butatrienediyls [3c], their flex-
ibility often resulted in polymeric products containing
bridging amido groups, especially with the larger, divalent
lanthanide ions [3a]. In addition, the six donor N2O4 array
represented in MAC and DAC was thought to be respon-
sible for the relatively low reactivity that complexes of the
type Ln(DAC)R and Ln(MAC)R2 (Ln = Y or a lantha-
nide) displayed towards unsaturated substrates such as alk-
enes and alkynes.
The development of non-cyclopentadienyl ancillary
ligand systems has been one of the major themes in lantha-
nide research over the past 15 years [1]. Lanthanide com-
plexes containing amido functionality as part of a
polydentate ligand framework have played a large role in
the development of new organometallic and coordination
chemistry of these elements [1,2]. Several years ago, we
reported a number of organolanthanide complexes con-
taining the chelating diamides derived from deprotonated
aza- and diaza-18-crown-6 ligands (Fig. 1, MAC and
With the limitations of MAC and DAC in mind, a
ligand system with fewer donors and greater rigidity
seemed attractive. The cross-bridged cyclam ligand
(Fig. 1, CBC), containing a N4 donor array and an ethylene
*
Corresponding author. Tel.: +1 250 721 7161; fax: +1 250 721 7147.
E-mail address: djberg@uvic.ca (D.J. Berg).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.11.015

P.E. OꢀConnor et al. / Inorganica Chimica Acta 359 (2006) 2870–2878
2871
under nitrogen in a glass capillary; melting points are
uncorrected. Elemental analyses were performed by Cana-
dian Microanalytical in Delta, BC, on microcrystalline
samples sealed for shipment in a glass ampoule.
H2CBC was prepared by a modification of the literature
procedure [4b,6] starting from cyclam, purchased from
Aldrich and used as received. Ln[N(SiMe3)2]3 [7], Yb[N-
(SiMe3)2]2[OEt2]2 [8], Yb[N(SiMe3)2]2[THF]2 [9] and
Yb(C5Me5)2(OEt2) [10] were prepared as described in the
literature. p-Tolyldisulfide was purchased from Aldrich
and used as received.
Fig. 1. Select macrocyclic amido ligands.
bridge that restricts macrocycle flexibility, was readily
available using literature procedures [4] and a number of
transition metal complexes were known [5], although no
lanthanide complexes had been reported. Initial attempts
to prepare trivalent lanthanide complexes by direct reac-
tion of LnCl3 with the CBC2ꢀ dianion alkali metal salts
was not successful, presumably due to our inability to
remove alkali chloride metathesis products. We experi-
enced similar problems in zirconium chemistry but we were
successful in isolating Zr(CBC)(CH2Ph)2 and Zr(CBC)Cl2
by acid–base reactions between H2CBC and Zr(CH2Ph)4
or Zr[N(SiMe3)2]2Cl2, respectively [6]. Our attempts to pre-
pare trivalent Ln(CBC)X complexes by acid–base reactions
therefore focused on the direct reaction of Ln[N(SiMe3)2]3
with H2CBC. Unfortunately, although this reaction did
proceed slowly, the products obtained were not clean. Sim-
ilar results were observed during attempts to use
Y[CH(SiMe3)2]3 or Y[CH2SiMe3]3[THF]2.
Perhaps somewhat surprisingly, direct reaction of
H2CBC with divalent Yb[N(SiMe3)2]2[L]2 (L = OEt2 or
THF) proceeds within minutes at room temperature to
afford a polymeric product {Yb[CBC]}n and an unusual
mixed valence salt containing a trinuclear Yb(III) cation
and a monomeric Yb(II) anion. The cation contains a cap-
ping l3-NH, the first structurally characterized example of
such a group in a lanthanide cluster. In this paper, we dis-
cuss the solution behaviour and solid state structure of this
unique compound as well as a related byproduct. A path-
way that explains the formation of this cluster is also
presented.
2.2. Synthesis of {Yb[CBC]}n (1)
A solution of H2CBC (0.100 g, 0.442 mmol) in 5 mL tol-
uene was added slowly to a solution of Yb[N(Si-
Me3)2]2[OEt2]2 (0.286 g, 0.435 mmol) in 3 mL toluene
with rapid stirring. An immediate color change was
observed from dark red to green–brown and precipitation
of a dark red–brown powder commenced within minutes.
The solution was allowed to stir overnight followed by col-
lection of the precipitate by vacuum filtration through a
fine sintered glass frit. The amber colored filtrate was
cooled at ꢀ30 ꢁC but no further precipitation was
observed. The dark red–brown solid was first washed with
THF, then three times with toluene and finally with hexane
before being dried under reduced pressure for several
hours. Yield: 0.122 g (71%). M.p. >275 ꢁC. Anal. Calc.
for C12H24N4Yb: C, 36.27; H, 6.09; N, 14.10. Found: C,
34.88; H, 6.15; N, 13.65%.
When the reaction was carried out on the same scale
using Yb(C5Me5)2(OEt2) (0.230 g, 0.444 mmol) as the
Yb(II) precursor, a dark rust-red precipitate formed slowly
over the course of an hour. Isolation of this solid as
described above yielded 0.145 g (84%) of 1.
2.3. Isolation of {[Yb(CBC)]3[l3-NH]}+
{Yb[N(SiMe3)2]3}ꢀ (2)
When the reaction above was carried out with Yb[N(Si-
Me3)2]2[THF]2 (0.110 g, 0.172 mmol) and H2CBC (0.050 g,
0.22 mmol) for 2 days in toluene, green crystals were easily
discernible in the reaction mixture in addition to the red–
brown powder. These crystals dissolved in THF and were
separated from the insoluble red–brown powder (1) by fil-
tration. Removal of the THF afforded 2 as a green powder.
Yield: 0.015 g (5%). M.p. >275 ꢁC. IR (Nujol mull on
2. Experimental
2.1. General
All reactions were carried out in a M. Braun glove box
under an atmosphere of nitrogen. Solvents were dried by
distillation from sodium benzophenone ketyl under argon
and used immediately or stored in the glove box until
use. THF-d8 for NMR experiments was dried by distilla-
tion from potassium metal and stored over 4 A sieves in
the glove box. Samples for NMR spectroscopy were pre-
pared in the glove box and loaded into 5 mm tubes fitted
1
NaCl): 3280 cmꢀ1 (m, NH stretch). H NMR (THF-d8,
˚
360 MHz, 293 K): d 98.3 (rel. int. = 3H, m1/2 = 220 Hz),
66.7 (3H, 400 Hz), 65.1 (3H, 260 Hz), 57.5 (3H, 680 Hz),
13.1 (3H, 180 Hz), 3.25 (3H), 3.02 (3H), 2.71 (3H), 2.58
(3H), 2.46 (3H), 0.03 (54H), ꢀ7.9 (3H, 220 Hz), ꢀ31.4
(3H, 360 Hz), ꢀ45.8 (3H, 120 Hz), ꢀ85.4 (3H, 290 Hz),
ꢀ90.9 (3H, 150), ꢀ96.1 (3H, 280 Hz), ꢀ99.6 (3H,
230 Hz), ꢀ131.3 (3H, 240 Hz), ꢀ132.0 (6H, 670), ꢀ143.4
(3H, 120 Hz), ꢀ169.0 (3H, 600 Hz). Anal. Calc. for
1
with sealable Teflon valves (Brunfeldt). H NMR spectra
were recorded on a Bruker AMX-360 MHz spectrometer
at various temperatures. FT-IR spectra were recorded as
Nujol mulls on NaCl plates. Melting points were obtained
using a Buchi melting point apparatus on samples sealed
¨

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P.E. OꢀConnor et al. / Inorganica Chimica Acta 359 (2006) 2870–2878
˚
C54H127N16Si6Yb4: C, 34.85; H, 6.88; N, 12.03. Found: C,
32.81; H, 6.45; N, 11.12%.
When the reaction was repeated with Yb[N(Si-
Me3)2]2[OEt2]2, the yield of 2 obtained by extraction of the
initial precipitate with THF was 18% (on a 0.2 mmol scale).
ment (Mo Ka radiation, k = 0.71073 A) equipped with a
Cryocool NeverIce low temperature device. A crystal of
2 was removed from a sealed glass ampoule under nitro-
gen and immediately covered with a layer of hydrocarbon
oil, mounted on a glass fiber and placed in the low tem-
perature nitrogen stream [11]. Data were measured using
omega scans of 0.3ꢁ per frame for 5 s, and a full sphere
of data were collected. A total of 2132 frames were col-
2.4. Isolation of {[Yb(CBC)]3[l3-NH]}+ Iꢀ (3)
˚
Complex 3 was isolated as yellow crystals (<2 mg) that
slowly deposited from a solution of 2 in THF-d8 over a per-
iod of several days. The crystals were only obtained with
one batch of 2, prepared from Yb[N(SiMe3)2]2[THF]2. Pre-
sumably the iodide ion was present as a minor contaminant
in the starting silylamide complex since it was prepared by
the metathesis reaction between YbI2 and NaN(SiMe3)2.
lected with a final resolution of 0.83 A. The first 50 frames
were recollected at the end of data collection to monitor
for decay. Cell parameters were retrieved using SMART
[12] software and refined using SAINTPlus [13] on all
observed reflections. Data reduction and correction for
Lorentz polarization and decay were performed using
the SAINTPlus software. Absorption corrections were
applied using SADABS [14]. The structure was solved by
direct methods and refined by least squares method on
F2 using the SHELXTL program package [15]. The structure
was solved in the space group P21/n (No. 14) by analysis
of systematic absences. There is disorder in two of the
cyclam rings (C7, C11, C12, C18, C19). The occupancy
2.5. Synthesis of [Yb(CBC)(S-p-Tol)]n (4)
A deep green solution of Yb(C5Me5)2(OEt2) (0.253 g,
0.489 mmol) was prepared in 10 mL toluene in the glove-
box. To this was added 0.110 g H2CBC (0.486 mmol) in
5 mL toluene with vigorous stirring. An immediate color
change to red was observed and precipitation of rust-red 1
took place within 1 h. The suspension was stirred for a fur-
ther 3 h followed by addition of a solution of p-tolyldisul-
fide, (p-C6H4MeS)2, 0.060 g (0.244 mmol) in 5 mL toluene
by pipette. An immediate color change to a deep burgundy
and complete dissolution of all solids was observed. The
solution was stirred for 2 h, filtered through Celite and lay-
ered with hexane. Dark maroon crystals of 4 formed on
standing overnight. These were isolated by decanting off
the mother liquor and were washed with a small amount
of cold toluene followed by hexane and drying under
reduced pressure for several hours. The mother liquor affor-
ded a second crop of crystals on cooling to ꢀ30 ꢁC. Once
isolated, the crystals of 4 dissolve very sparingly in toluene
but remain very soluble in THF. Overall yield: 0.18 g (72%).
Table 1
Crystallographic data for [Yb3(l-CBC)3(l3-NH)]+ [Yb(N(SiMe3)2)3]ꢀ (2)
and [Yb3(l-CBC)3(l3-NH)]+
I
ꢀ Æ 2 THF (3)a,b
Compound no.
2
3
Formula
C
1861.4
54H127N16Si6Yb4
C44H89IN13Yb3
1478.3
Fw (g molꢀ1
)
Crystal systemc
monoclinic
P21/n(No. 14)
17.6328(7)
19.3118(7)
23.4494(9)
109.930(1)
7506.8(5)
4
monoclinic
P21/c(No. 14)
11.8789(6)
13.3853(6)
31.9485(15)
92.966(1)
5073.1(4)
4
Space group
˚
a (A)
˚
b (A)
˚
c (A)
b (ꢁ)
Volume (A )
Z
Density (calc., g/cm3)
Absorption
coefficient l (mmꢀ1
Crystal size (mm)
Crystal color and habit
h Range (ꢁ)
Reflections collected
Independent reflections
Maximum and
3
˚
1.647
5.077
1.936
6.143
)
1
M.p. 165 ꢁC (dec). H NMR (THF-d8, 333 K): d 27.9 (1H,
0.32 · 0.28 · 0.12
green prism
1.40–25.25
98901
0.21 · 0.05 · 0.05
yellow needle
1.65–25.25
61429
9181
0.733 and 0.322
m
1/2 = 17 Hz), 21.0 (1H, 34 Hz), 20.7 (2H, 42 Hz), 17.7 (2H,
70 Hz), 12.7 (1H, 12 Hz), 10.5 (1H, 20 Hz), 7.05 (2H), 7.00
(1H), 1.99 (2H), 1.60 (4H, overlaps solvent), 1.32 (1H), 0.85
(2H, m-arylH, 10 Hz), ꢀ0.24 (3H, p-Me, 18 Hz), ꢀ6.6 (2H,
o-arylH, 200 Hz). Not all resonances of the CBC ligand
were observed. At room temperature, many more reso-
nances were observed suggesting a more complex structure.
In the absence of X-ray crystallographic data, no assign-
ment of the ambient temperature structure is possible but
the observed solubility and NMR data are more consistent
with a structure involving bridging, either by the thiolate or
amide ligands (or by both). Anal. Calc. for C19H31N4SYb:
C, 43.84; H, 6.00; N, 10.76. Found: C, 43.05; H, 6.05; N,
10.25%.
13595
0.546 and 0.223
minimum transmission
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]d
13595/25/748
1.037
R1 = 0.026,
wR2 = 0.059
R1 = 0.031
2.24 and ꢀ0.54
9181/55/540
1.147
R1 = 0.044,
wR2 = 0.085
R1 = 0.056
2.73 and ꢀ1.09
R (all data)
Largest difference in
peak and hole (e A
ꢀ3
˚
)
a
˚
Mo (Ka) 0.71073 A radiation at 83(2) K on a Bruker/Siemens Smart
APEX diffractometer.
b
Data collection and reduction, direct methods structure solution and
refinement were carried out using SMART, SAINTPlus and SHELXTL soft-
ware, respectively [11–15].
2.6. X-ray crystallographic studies
c
International tables for X-ray crystallography, vol. 1: Symmetry
Groups; Henry, N.F.M.; Lonsdale, K., Eds.; Kyntoch Press, England,
1969.
X-ray diffraction experiments were carried out at
83(2) K using a Bruker/Siemens SMART APEX instru-
P
P
P
P
2
2 1=2
d
R ¼ ðjF oj ꢀ jF cjÞ= jF oj; wR ¼ ½ wðjF oj ꢀ jF cj Þ= wðjF ojÞ ꢁ
.

P.E. OꢀConnor et al. / Inorganica Chimica Acta 359 (2006) 2870–2878
2873
was refined and set at 50% for each moiety. The counter
ion also shows disorder in one SiMe3 group (Si2, C40-
C42) as well as the central Yb position. The occupancies
were refined as 57% ꢀand 50%, respectively. There are large
of this compound was extremely complex at 293 K, showing
at least 40 resonances between +100 and ꢀ150 ppm. How-
ever, on heating to 333 K, the NMR spectrum simplifies
considerably so that only 18 resonances for the CBC ligand
and 3 resonances assignable to the p-tolylthiolate group are
observed. This is consistent with a dynamic process taking
place in THF-d8 solution over this temperature range. Gi-
ven the low solubility of 4 in non-coordinating solvents,
bridging amido and (or) thiolate groups could be present
in this compound. The variable temperature behavior might
therefore be explained by reversible bridge cleavage on the
NMR timescale. Although the complexity and paramagne-
tism of this spectrum made a definitive structural assign-
ment impossible, the formation of a trivalent thiolate by
reduction of p-tolyldisulfide lends further support to the
assignment of 1 as a polymeric Yb(II)-CBC complex.
3
˚
residuals of ca. 2 e /A near Yb1 and Yb2. All non-
hydrogen atoms, except disordered carbon atoms, were
refined anisotropically. No decomposition was observed
during data collection.
Crystal mounting and data collection, reduction and
refinement for a yellow crystal of 3 were carried out in
the manner described above. The structure was solved in
the space group P21/c (No. 14) by analysis of systematic
absences. The disorder in the cyclam rings was refined as
60% for the major fraction. One of the THF molecules is
completely disordered with an occupancy of 60% for the
major fraction. Disordered atoms were held isotropic and
all other atoms were refined anisotropically. The thermal
parameters of each disordered moiety were constrained to
be approximately equal. The hydrogen atom of the NH
group was located on the difference map and rꢀestrained
ð3Þ
An interesting observation was made during the prepa-
ration of 1 from Yb[N(SiMe3)2]2[THF]2: at longer reaction
times, in addition to the rust-red powder of 1, green crys-
tals were also observed to form. These crystals dissolved
readily in THF and it was subsequently discovered that
regardless of which starting silylamide complex was used
(Eq. (1)), extraction of the rust-red precipitate with THF
afforded small, but reproducible, amounts of a green pow-
der after removal of the solvent. Recrystallization of the
green powder yielded green crystals of 2 suitable for
X-ray crystallography.
3
˚
with a riding model. Large residuals of ca. 3 e /A are
˚
located ca. 1 A from the Yb centers. These are due to
absorption effects and could not be modeled or eliminated.
No decomposition was observed during data collection. A
summary of the data collection parameters is given in
Table 1 for 2 and 3. All thermal ellipsoid plots were pre-
pared using ORTEP3 [16].
3. Results and discussion
The crystal structure of 2 reveals a unique mixed valence
salt consisting of a trinuclear Yb(III) cluster cation and a
mononuclear Yb(II) anion (Figs. 2 and 3, Table 2) [16].
The cation is made up of three Yb(III) centers in a triangu-
lar arrangement, bridged on each side by an amido N of a
CBC ligand and capped on one face by a l3-NH group.
Each six-coordinate Yb(III) center in the cation is therefore
coordinated by two bridging amido N (of two different CBC
ligands), one terminal amido and two amino N, as well as
by the capping imido N (Fig. 3). The l-amido groups of
the CBC ligand bridge asymmetrically between Yb centers
with short and long average Yb–N distances of 2.370 and
Reaction of H2CBC with either Yb(C5Me5)2(OEt2) or
Yb[N(SiMe3)2]2[L]2 (L = THF or diethyl ether) resulted
in precipitation of a dark rust-red powder (1) that was
insoluble in hydrocarbons and ethereal solvents, Eqs. (1)
and (2). This compound analyzed reasonably well for
[Yb(CBC)]n and the color is consistent with a divalent
Yb center; however, the very low solubility of this
material prevented 1H NMR analysis that would allow
unambiguous assignment of the metal oxidation state.
The low solubility of this compound is presumably due
to formation of extensive bridges by the amido nitrogens
of the CBC ligand, as might be expected for what would
otherwise be
a a
four-coordinate Yb2+ center in
˚
˚
2.427 A (D = 0.057 A), respectively. The closest comparison
to this bridging mode in a simple trivalent lanthanide
monomeric unit. Similar bridging was observed in a linear
trinuclear Yb(II) complex containing 4,13-diaza-18-
crown-6 (DAC), [(Me3Si)2N]Yb(l-DAC)Yb(l-DAC)Yb-
[N(SiMe3)2] [3a].
YB½NðSiMe3Þ ꢁ L2 þ H2CBC ꢀ2HNðSiMe Þ ½YbðCBCÞꢁn ð1Þ
3
2
ꢀꢀꢀꢀ!
2 2
ꢀ2L
L¼THF;Et2O
1
YbðC Me Þ ðOEt Þ þ H CBC ꢀ2HC Me ½YbðCBCÞꢁn
ð2Þ
5
5
ꢀꢀꢀꢀ!
5
5
2
2
2
ꢀEt2O
1
Oxidation of 1 with p-tolyldisulfide, (p-C6H4MeS)2, re-
sulted in a color change to burgundy, consistent with for-
mation of the trivalent p-tolylthiolate complex 4, Eq. (3)
[17]. This complex was soluble in toluene and showed a
paramagnetic 1H NMR spectrum. The 1H NMR spectrum
Fig. 2. ORTEP3 [16] plot of {[Yb(CBC)]3[l3-NH]}+ {Yb[N(SiMe3)2]3}ꢀ
(2) (30% probability ellipsoids).

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N atoms are not quite planar (sum of angles at N: N3,
354.5; N7, 358.1; N11, 355.6ꢁ) as is usually observed for
terminal lanthanide amides (range 358.7–360ꢁ, median =
359.9ꢁ [20]) but such a small distortion from planarity is
most likely due to the constraints imposed by the ethylene
cross-bridge of the CBC ligand. Zirconium complexes of
the type Zr(CBC) (X)2 also display similar distortions from
planarity (X = OSiH(CMe3)2, sum of angles at N = 354.7ꢁ
[21]; o-C6H3Me2O, 353.1ꢁ [6]; CH2SiMe3, 353.8ꢁ [6]; X2 =
C4Ph4, 354.4ꢁ [6]).
Fig. 3. Metal coordination in the cation of 2 (30% probability ellipsoids).
The capping l3-NH group found in 2 (and 3) is the first
structurally characterized example of a triply bridging NH
in lanthanide chemistry, although at this writing there have
been five structures reported that contain l3-NR groups:
[Ln(C5Me4SiMe3)]4(l3-NR)4 (Ln = Lu, R = CH2Ph [22];
Ln = Y, R = Et [23]), [Y(C5Me4SiMe3)]4(l3-NEt)2(l-N =
CHPh)2 [23], Yb4(THF)2(l-g2-PhNNPh)4(l3-NPh)2 [24]
and Sm4(THF)6(l-g2-PhNNPh)4(l3-NPh)2 [25]. The aver-
age Ln-l3-N distance in these complexes ranges from
Table 2
Selected distances and angles for [Yb3(l-CBC)3(l3-NH)]+[Yb(N-
(SiMe3)2)3]ꢀ (2) and [Yb3(l-CBC)3(l3-NH)]+ ꢀ Æ 2 THF (3)a
I
2
3
Distances
Yb(1)–N(16)
Yb(2)–N(16)
Yb(3)–N(16)
Yb(1)–N(1)
Yb(1)–N(5)
Yb(2)–N(5)
Yb(2)–N(9)
Yb(3)–N(9)
Yb(3)–N(1)
Yb(1)–N(3)
Yb(2)–N(7)
Yb(3)–N(11)
Yb(1)–N(2)
Yb(1)–N(4)
Yb(2)–N(6)
Yb(2)–N(8)
Yb(3)–N(10)
Yb(3)–N(12)
Yb(4A)–N(13)
Yb(4B)–N(13)
Yb(4A)–N(14)
Yb(4B)–N(14)
Yb(4A)–N(15)
Yb(4B)–N(15)
2.251(3)
2.253(3)
2.261(3)
2.367(3)
2.442(3)
2.369(3)
2.422(3)
2.374(3)
2.416(3)
2.181(3)
2.191(3)
2.185(3)
2.443(3)
2.477(3)
2.443(3)
2.459(3)
2.454(3)
2.439(3)
2.362(4)
2.344(4)
2.325(4)
2.350(4)
2.318(4)
2.349(4)
Yb(1)–N(13)
Yb(2)–N(13)
Yb(3)–N(13)
Yb(1)–N(4)
Yb(1)–N(8)
Yb(2)–N(8)
Yb(2)–N(12)
Yb(3)–N(12)
Yb(3)–N(4)
Yb(1)–N(2)
Yb(2)–N(6)
Yb(3)–N(10)
Yb(1)–N(1)
Yb(1)–N(3)
Yb(2)–N(5)
Yb(2)–N(7)
Yb(3)–N(9)
Yb(3)–N(11)
2.248(6)
2.248(6)
2.278(6)
2.352(6)
2.434(6)
2.386(6)
2.399(6)
2.382(6)
2.412(6)
2.184(7)
2.190(7)
2.181(6)
2.452(6)
2.463(6)
2.464(7)
2.462(7)
2.455(7)
2.433(6)
3
˚
2.243 to 2.363 A. These distances predict a Yb-l -N dis-
˚
tance between 2.24 and 2.28 A after correction for the dif-
ferences in metal ionic radii [19], in excellent agreement
˚
with the observed average value of 2.255 A. It should be
noted that there are two reports of structurally character-
ized l4-NH lanthanide complexes [26] but the geometry
at the imide nitrogen in these structures is not comparable
to that found here.
The anion in 2 contains a Yb(II) center coordinated to
three bis(trimethylsilyl)amido ligands. Anions of this type
have been structurally characterized in the divalent
lanthanide salts Na+{Ln[N(SiMe3)2]3}ꢀ (Ln = Yb, Eu),
although in both structures two of the amido groups bridge
between the lanthanide and the sodium cation [27]. The
average terminal Ln–N distances in these complexes are
˚
2.384 and 2.446 A for Ln = Yb and Eu, respectively. After
correction for the larger ionic radius of europium(II) [19],
the latter predicts a divalent, terminal Yb–N distance of
Angles
Yb(1)–N(16)–Yb(2)
Yb(1)–N(16)–Yb(3)
Yb(2)–N(16)–Yb(3)
Yb(1)–N(1)–Yb(3)
Yb(1)–N(5)–Yb(2)
Yb(2)–N(9)–Yb(3)
N(1)–Yb(1)–N(3)
N(5)–Yb(2)–N(7)
N(9)–Yb(3)–N(11)
a
101.54(12)
100.36(12)
100.15(12)
92.87(10)
92.95(11)
92.43(11)
144.54(11)
143.89(12)
142.82(12)
Yb(1)–N(13)–Yb(2)
Yb(1)–N(13)–Yb(3)
Yb(2)–N(13)–Yb(3)
Yb(1)–N(4)–Yb(3)
Yb(1)–N(8)–Yb(2)
Yb(2)–N(12)–Yb(3)
N(2)–Yb(1)–N(4)
N(6)–Yb(2)–N(8)
N(10)–Yb(3)–N(12)
101.4(2)
˚
˚
2.31 A. The observed average Yb–N distance of 2.341 A
falls within this range and clearly indicates that this is a diva-
lent Yb center, as required for charge balance. There are sev-
99.8(2)
100.3(2)
93.2(2)
92.4(2)
93.2(2)
145.2(2)
144.1(2)
142.8(2)
˚
eral close contacts (<3.3 A) between silyl methyl groups and
Yb4 but since there is positional disorder at this Yb site, it is
difficult to assess the significance of this observation. How-
ever, agostic interactions between silyl methyls and lantha-
nide centers have been reported in many cases [20a,28], so
these interactions could well be meaningful in 2.
Estimated standard deviations in parentheses.
While it is true that the crystal structures of 2 and 3
refine marginally better with the l3 capping group as an
NH, the distinction from a l3-O (oxo) group, which would
not alter the charge on the cation, rests on a detailed anal-
ysis of the metrical data and on the observation of an N–H
stretch at 3280 cmꢀ1 [26] in the IR spectrum of 2. There are
also five lanthanide structures reported in the literature
that contain l3-O groups [20a,20c,29]; a comparison of
the angles at the l3-E atom and the equivalent Ln–E bond
lengths (corrected to compare with Yb(III) [19]) for these
five structures, the five l3-NH structures and the two
l-NR2 amide without additional bridging ligands is found
in {Na(THF)6}+{Lu2[N(SiMe3)2]4[l-NH2] [l-N(SiMe3)]}ꢀ
[18]. The l-NH2 bridge in this compound predicts short
˚
and long Ln–N bond distances of 2.387 and 2.419 A (D =
˚
0.032 A), respectively, after correction for the difference in
ionic radii [19]. As expected, the average Yb–N bond length
for the terminal amido nitrogens of CBC is considerably
˚
shorter at 2.186 A, a value that also compares well with
other six-coordinate, Yb(III) terminal amides (range
˚
˚
2.139–2.236 A, median 2.19 A) [20]. The terminal amido

P.E. OꢀConnor et al. / Inorganica Chimica Acta 359 (2006) 2870–2878
2875
Table 3
towards any redistribution processes over the temperature
range studied. In short, it appears that the anion and cation
structures are maintained in THF-d8 solution and reorga-
nization does not occur rapidly.
Comparison of X-ray data for trivalent lanthanide l3-O and l3-NH
complexes
Average
Median
Range
Lanthanide l3-O structures [20a,20c,29]
Ln–O (A)
Sum of Ln–O–Ln angles (ꢁ)
Lanthanide l3-NH structures [22–25]
Ln–N (A)
Sum of Ln–N–Ln angles (ꢁ)
{[Yb(CBC)]3[l3-NH]}+ {Yb[N(SiMe3)2]3}ꢀ (2)
Ln–N (A)
Sum of Ln–N–Ln angles (ꢁ)
[Yb3(l-CBC)3(l3-NH)]+
Ln–N (A)
Sum of Ln–N–Ln angles (ꢁ)
In order to explain the formation of 2, we are faced with
two separate issues. The first is the fact that 2 contains
three oxidized Yb(III) centers and the second is the source
of the l3-NH group. The formation of Yb(III) may be
explained by competitive reduction of an N–H bond in
H2CBC (Eq. (4)), rather than exclusive protonolysis to
form 1 (Eq. (1)). There is good precedent for this reaction
in divalent lanthanide chemistry in the formation of
Sm[DAC][N(SiMe3)2] during the reaction of H2DAC with
Sm[N(SiMe3)2]2[THF]2 [3a] and in the reduction of water
O–H bonds by Sm(C5Me5)2(THF)2 to form the Sm(III)
cluster [(C5Me5)Sm]6O9H6 [30]. Other examples of reduc-
tion competing with hydrolysis or alcoholysis in organome-
tallic Sm(II) chemistry have also been reported [31]. The
lower reducing power of Yb(II) would explain why the
samarium reaction gives trivalent product exclusively while
II/III mixed valence compounds form in the case of ytter-
bium. We have also observed N–H bond reduction during
reaction of Yb[N(SiMe3)2]2[OEt2]2 with 2-(20-aminophe-
nyl)oxazolines to form tris[2-(20-amidophenyl)oxazoline]
complexes of Yb(III) [32]. Similarly, reduction of the C–
H bond of phenylacetylene has been shown to produce a
mixed valence acetylide product, [(C5Me5)2Yb]2-
(l-CCPh)4Yb [33]. There are several other examples of
mixed valence Yb complexes [34] but, as far as we are
aware, the cases listed above are the only ones where direct
E–H (E = O, N) bond reduction is involved in their
formation.
˚
2.13
111
2.14
111
2.08–2.20
99–120
˚
2.27
99
2.27
98
2.24–2.28
96–102
˚
2.255
100.7
2.253
100.4
2.251–2.261
100.2–101.5
I
ꢀ Æ 2 THF (3)
2.258
˚
2.248
100.3
2.248–2.278
99.8–101.4
100.5
structures in this work are summarized in Table 3. It is
quite clear from the available structural data and from
IR (for 2) that 2 and 3 contain triply bridging NH groups.
The 1H NMR spectrum of 2 in THF-d8 shows the
expected wide chemical shift range (+90 to ꢀ170 ppm)
and Curie–Weiss behavior (Fig. 4) expected of a compound
containing paramagnetic Yb(III) centers. There are 24 res-
onances observed in solution. The largest resonance, with a
relative integration of 54 protons, corresponds to the
N(SiMe3)2 groups and shows a typical diamagnetic shift
(0.03 ppm) consistent with coordination to the diamagnetic
Yb(II) center of the anion. The other 23 resonances inte-
grate to 3 protons each and most of these show significant
paramagnetic shifts. This is consistent with an intact C3
symmetric cation in solution since the 24 protons on a
given CBC ligand are all inequivalent in this structure
but all CBC ligands are related by symmetry. Not surpris-
ingly given its proximity to three Yb(III) centers, the NH
proton is not observed. The observation of Curie–Weiss
behavior implies that the species observed are stable
Yb½NðSiMe Þ ꢁ L þ H CBC ꢀ1=2 H YbðCBCÞ½NðSiMe Þ ꢁ
2
ꢀꢀꢀ!
3
2
2
3
2 2
2
ꢀ2L
ð4Þ
To address the second point, we note that 2 appears to
form reproducibly in reactions between H2CBC and
Yb[N(SiMe3)2]2[L]2 (L = THF or Et2O) but not when
Yb(C5Me5)2(OEt2) is used as the Yb(II) precursor – a fact
that suggests to us that the l3-NH might arise from cleav-
age of an N(SiMe3)2 group. This could occur by a proton-
olysis reaction with trace water since the N–Si bond is well
known to be susceptible to hydrolysis, Eq. (5) [35]. Of
course, hydrolysis of the Yb–N bond to produce ꢁYb–
OHꢀ and HN(SiMe3)2 would normally be expected to occur
more rapidly unless the water molecule is unable to access
this bond due to steric effects which seems unlikely in the
present case. Another option might be exchange of a trim-
ethylsilyl group between an NH group of H2CBC and
N(SiMe3)2, Scheme 1. The only similar silyl transfer reac-
tion between nitrogens in a metal complex [36] was re-
ported earlier this year involving migration of a silyl
from an N(SiMe3)2 group to an anionic Zr–NHꢀ group.
There are also examples of trimethylsilyl transfer from a
M-N(SiMe3)2 to a thiol with formation of M-NH2 and 2
equivalents of RSSiMe3 [37].
Fig. 4. Variable temperature 1H NMR data for the furthest upfield
resonances of 2 in THF-d8.

2876
P.E. OꢀConnor et al. / Inorganica Chimica Acta 359 (2006) 2870–2878
Scheme 1.
Fig. 5. ORTEP3 [16] plot of {[Yb(CBC)]3[l3-NH]}+ Iꢀ (3) (30% prob-
ability ellipsoids).
ꢀMe3SiOSiMe3
YbðCBCÞ½NðSiMe3Þ2ꢁ þ H2O ꢀꢀꢀꢀꢀꢀꢀꢀ! YbðCBCÞðNH2Þ
ð5Þ
of Yb[N(SiMe3)2]2[THF]2 making it impossible to carry out
a full characterization. The metrical parameters associated
with the cation in the structure of 3 are very similar to
those observed for 2 and do not warrant any additional
discussion.
Regardless of the pathway by which it forms,
Yb[CBC][NH2] could react with Yb[CBC][N(SiMe3)2] by
loss of HN(SiMe3)2 and formation of a bridging NH unit,
Scheme 2. Addition of another equivalent of Yb[CBC][N-
(SiMe3)2] could form a crowded, neutral trimer Yb3[CBC]3-
4. Conclusions
[l3-NH][N(SiMe3)2]. Abstraction of a N(SiMe3)2 group
ꢀ
by Yb[N(SiMe3)2]2 to form the mixed valence salt 2 would
then complete the sequence. The exact pathway by which 2
forms is obviously difficult to establish with certainly but
its formation seems to indicate that reduction of N–H
bonds by Yb(II) may be significant in some cases and that
the N–Si bond of N(SiMe3)2 ligands may be more reactive
in the presence of amines than generally supposed.
In one case, a green solution of 2 in THF-d8 left to stand
for several days slowly deposited a small number of yellow
needles of 3 on the walls of the NMR tube. The X-ray
structure of these crystals revealed that 3 contained the
same trinuclear Yb(III) cluster cation as in 2 but with a
The primary product of the acid–base reaction between
H2CBC and Yb[N(SiMe3)2]2[L]2 or Yb(C5Me5)2(OEt2) is
the polymeric amide-bridged [Yb(CBC)2]n (1). However,
the consistent observation of small amounts of the mixed
valence salt 2 that contains a l3-NH group in reactions
involving Yb[N(SiMe3)2]2[L]2 suggests that silyl transfer
between H2CBC and a Yb-N(SiMe3)2 unit may be a com-
petitive process. This is noteworthy in view of the wide-
spread use of N(SiMe3)2 as an ancillary ligand in
lanthanide chemistry in that it suggests this ligand may
not be as inert as previously supposed.
simple iodide counterion rather than
a
divalent
Acknowledgements
{Yb[N(SiMe3)2]3}ꢀ anion (Fig. 5 and Table 2).
The iodide counterion most likely arises from trace con-
tamination of the starting Yb[N(SiMe3)2]2[THF]2 since this
compound is prepared from YbI2 and NaN(SiMe3)2 in
THF. Anionic ꢁateꢀ complexes such as Na+{Yb[N-
(SiMe3)2]2X}ꢀ (X = halide) are very common side products
in metathesis reactions of the lanthanides [38]. Compound
3 was produced in very small quantity from only one batch
The authors wish to thank the University of Victoria
and the Natural Sciences and Engineering Research Coun-
cil of Canada for financial support and a post-graduate fel-
lowship (PEO). The Bruker SMART APEX diffraction
facility was established at the University of Idaho with
the assistance of the NSF-EPSCoR program and the
M.J. Murdoch Charitable Trust, Vancouver, WA, USA.
Appendix A. Supplementary material
Crystallographic data in CIF format are available from
the Cambridge Crystallographic Data Center, 12 Union
Road, Cambridge, CB2 1EZ, UK (e-mail: deposit@ccdc.
cam.ac.uk) under CCDC numbers 286754 and 286753 for
2 and 3, respectively. Supplementary data associated with
this article can be found, in the online version, at
doi:10.1016/j.ica.2005.11.015.
References
[1] (a) S.A. Cotton, Annu. Rep. Prog. Chem. Sect. A 100 (2004) 303;
(b) P. Mountford, B.D. Ward, Chem. Commun. (2003) 1797;
Scheme 2.

P.E. OꢀConnor et al. / Inorganica Chimica Acta 359 (2006) 2870–2878
2877
(c) F.T. Edelmann, Angew. Chem. Int. Ed. 34 (1995) 2466;
(d) C. Eaborn, K. Izod, J.D. Smith, J. Organomet. Chem. 500 (1995)
89;
(e) M.P. Hogerheide, J. Boersma, G. van Koten, Coord. Chem. Rev.
155 (1996) 87;
[14] G.M. Sheldrick, SADABS: v.2.01, Empirical Absorption Correction
Program, Bruker AXS, Madison, WI, 2001.
[15] G.M. Sheldrick, SHELXTL: v.6.10, Structure Determination Software
Suite, Bruker AXS, Madison, WI, 2001.
[16] ORTEP3 for Windows: L.J. Farrugia, J. Appl. Cryst. 30 (1997) 565.
[17] D.J. Berg, R.A. Andersen, A. Zalkin, Organometallics 7 (1988) 1858.
[18] M. Karl, G. Seybert, W. Massa, K. Harms, S. Agrawal, R. Maleika,
W. Stelter, A. Greiner, W. Heitz, B. Neumuller, K. Dehnicke, Z.
Anorg. Allg. Chem. 625 (1999) 1301.
[19] R.D. Shannon, Acta Cryst. A 32 (1976) 751.
[20] (a) M. Niemeyer, Z. Anorg. Allg. Chem. 628 (2002) 647;
(b) Y. Yao, Y. Zhang, Q. Shen, K. Yu, Organometallics 21 (2002)
819;
(f) S.A. Cotton, Coord. Chem. Rev. 160 (1997) 93;
(g) W.J. Evans, New J. Chem. 19 (1995) 525;
(h) F. Nief, Coord. Chem. Rev. 178–180 (1998) 13;
(i) F.G.N. Cloke, Chem. Soc. Rev. 22 (1993) 17.
[2] (a) J. Okuda, Dalton Trans. (2003) 2367;
(b) P.W. Roesky, Z. Anorg. Allg. Chem. 629 (2003) 1881;
(c) J.L. Sessler, D. Seidel, Angew. Chem. Int. Ed. 42 (2003) 5106.
[3] (a) L. Lee, D.J. Berg, G.W. Bushnell, Inorg. Chem. 33 (1994) 5302;
(b) L. Lee, D.J. Berg, G.W. Bushnell, Organometallics 14 (1995) 8;
(c) L. Lee, D.J. Berg Bushnell, G.W. Bushnell, Organometallics 14
(1995) 5021;
(d) L. Lee, D.J. Berg, F.W. Einstein, R.J. Batchelor, Organometallics
16 (1997) 1819.
[4] (a) G.R. Weisman, E.H. Wong, D.C. Hill, M.E. Rogers, D.P. Reed,
J.C. Calabrese, Chem. Commun. (1996) 947;
(c) M. Karl, B. Neumuller, G. Seybert, W. Massa, K. Dehnicke, Z.
Anorg. Allg. Chem. 623 (1997) 1203;
(d) L. Mao, Q. Shen, S. Jin, Polyhedron 13 (1994) 1023;
(e) S. Wang, H. Li, Z. Xie, Organometallics 23 (2004) 3780;
(f) H. Li, Q. Xu, J. Chen, M. Cheng, Y. Zhang, W. Zhang, J. Lang,
Q. Shen, J. Organomet. Chem. 689 (2004) 3438.
[21] P.E. OꢀConnor, Ph.D. thesis, University of Victoria, 2004.
[22] D. Cui, O. Tardif, Z. Hou, J. Am. Chem. Soc. 126 (2004) 1312.
[23] D. Cui, M. Nishiura, Z. Hou, Angew. Chem., Int. Ed. 44 (2005) 959.
[24] A.A. Trifonov, M.N. Bochkarev, H. Schumann, J. Loebel, Angew.
Chem., Int. Ed. 30 (1991) 1149.
[25] N.S. Emelꢀyanova, M.N. Bochkarev, H. Schumann, J. Loebel, L.
Esser, Russ. Coord. Chem. 20 (1994) 789.
[26] (a) Z. Xie, S. Wang, Q. Yang, T.C.W. Mak, Organometallics 18
(1999) 1578;
(b) E.H. Wong, G.R. Weisman, D.C. Hill, D.P. Reed, M.E. Rogers,
J.S. Condon, M.A. Fagan, J.C. Calabrese, K. Lam, I.A. Guzei, A.L.
Rheingold, J. Am. Chem. Soc. 122 (2000) 10561.
[5] (a) G.R. Weisman, M.E. Rogers, E.H. Wong, J.P. Jasinski, E.S.
Paight, J. Am. Chem. Soc. 112 (1990) 8604;
(b) T.J. Hubin, J.M. McCormick, N.W. Alcock, H.J. Clase, D.H.
Busch, Inorg. Chem. 38 (1999) 4435;
(c) T.J. Hubin, J.M. McCormick, S.R. Collison, N.W. Alcock, D.H.
Busch, Chem. Commun. (1998) 1675;
(d) X. Sun, M. Wuest, G.R. Weisman, E.H. Wong, D.P. Reed, C.A.
Boswell, R. Motekaitis, A.E. Martell, M.J. Welch, C.J. Andersen, J.
Med. Chem. 45 (2002) 469;
(e) W. Niu, E.H. Wong, G.R. Weisman, L.N. Zakharov, C.D.
Incarvito, A.L. Rheingold, Polyhedron 23 (2004) 1019;
(f) C.A. Boswell, X. Sun, W. Niu, G.R. Weisman, E.H. Wong, A.L.
Rheingold, C.J. Anderson, J. Med. Chem. 47 (2004) 1465;
(g) T.J. Hubin, N.W. Alcock, D.H. Busch, Acta Cryst., Sect. C 56
(2000) 37;
(h) T.J. Hubin, J.M. McCormick, S.R. Collinson, M. Buchalova,
C.M. Perkins, N.W. Alcock, P.W. Kahol, A. Raghunatan, D.H.
Busch, J. Am. Chem. Soc. 122 (2000) 2512;
(i) T.J. Hubin, J.M. McCormick, N.W. Alcock, D.H. Busch, Inorg.
Chem. 40 (2001) 435;
(j) W. Niu, E.H. Wong, G.R. Weisman, K. Lam, A.L. Rheingold,
Inorg. Chem. Commun. 2 (1999) 361;
(k) W. Niu, E.H. Wong, G.R. Weisman, Y. Peng, C.J. Anderson,
L.N. Zakharova, J.A. Golen, A.L. Rheingold, Eur, J. Inorg. Chem.
(2004) 3310;
(b) S. Wang, Q. Yang, T.C.W. Mak, Z. Xie, Organometallics 18
(1999) 5511.
[27] T.D. Tilley, R.A. Andersen, A. Zalkin, Inorg. Chem. 23 (1984) 2271.
[28] (a) A.T. Gilbert, B.L. Davis, T.J. Emge, R.D. Broene, Organomet-
allics 18 (1999) 2125;
(b) G.W. Rabe, C.S. Strissel, L.M. Liable-Sands, T.E. Concolino,
A.L. Rheingold, Inorg. Chem. 38 (1999) 3446;
(c) W.T. Klooster, L. Brammer, C.J. Schaverien, P.H.M. Budzelaar,
J. Am. Chem. Soc. 121 (1999) 1381;
(d) C.J. Schaverien, Organometallics 13 (1994) 69;
(e) H. Van der Heijden, C.J. Schaverien, A.G. Orpen, Organomet-
allics 8 (1989) 255.
[29] (a) H. Schumann, P.R. Lee, J. Loebel, Angew. Chem., Int. Ed. 28
(1999) 1033;
(b) S.A. Schuetz, C.M. Silvernail, C.D. Incarvito, A.L. Rheingold,
J.L. Clark, V.W. Day, J.A. Belot, Inorg. Chem. 43 (2004) 6203;
(c) C. Yan, Z. Liu, Z. Wang, C. Liao, private communication: CSD
Code QUKXOJ.
[30] W.J. Evans, N.T. Allen, M.A. Greci, J.W. Ziller, Organometallics 20
(2001) 2936.
(l) T.J. Hubin, N.W. Alcock, H.J. Clase, D.H. Busch, Supramol.
Chem. 13 (2001) 261;
(m) T.J. Hubin, N.W. Alcock, D.H. Busch, Acta Cryst., Sect. C 55
(1999) 1404;
[31] (a) W.J. Evans, Polyhedron 6 (1987) 803;
(b) W.J. Evans, Coord. Chem. Rev. 206 (2000) 263;
(c) W.J. Evans, T.P. Hanusa, K.R. Levan, Inorg. Chim. Acta 110
(1985) 191.
(n) W. Niu, E.H. Wong, G.R. Weisman, R.D. Sommer, A.L.
Rheingold, Inorg. Chem. Commun. 5 (2002) 1.
[6] P.E. OꢀConnor, D.J. Berg, B. Twamley, Organometallics 24 (2005)
28.
[7] D.C. Bradley, J.S. Ghotra, F.A. Hart, Chem. Commun. (1972) 349.
[8] T.D. Tilley, R.A. Andersen, A. Zalkin, J. Am. Chem. Soc. 104 (1982)
3725.
[9] Y.F. Radꢀkov, E.A. Fedorova, S.Y. Khorshev, G.S. Kalinina, M.N.
Bochkarev, G.A. Razuvaev, Russ. J. Gen. Chem. 55 (1985) 1911.
[10] T.D. Tilley, R.A. Andersen, B. Spenser, H. Ruben, A. Zalkin, D.H.
Templeton, Inorg. Chem. 19 (1980) 2999.
[32] K.M. Button, R.G. Gossage, D.J. Berg, unpublished results.
[33] J.M. Boncella, T.D. Tilley, R.A. Andersen, Chem. Commun. (1984)
710.
[34] (a) C.J. Burns, D.J. Berg, R.A. Andersen, Chem. Commun. (1987)
272;
(b) W.J. Evans, T.A. Ulibarri, J. Am. Chem. Soc. 109 (1987) 4292;
(c) C.J. Burns, R.A. Andersen, Chem. Commun. (1989) 136;
(d) M.N. Bochkarev, V.V. Khramenkov, Y.F. Radꢀkov, L.N.
Zakharov, Y.T. Struchkov, J. Organomet. Chem. 429 (1992) 27;
(e) W.J. Evans, K.J. Forrestal, J.W. Ziller, Polyhedron 17 (1998)
4015;
[11] H. Hope, Progr. Inorg. Chem. 41 (1995) 1.
[12] SMART: v.5.626, Bruker Molecular Analysis Research Tool, Bruker
AXS, Madison, WI, 2002.
[13] SAINTPlus: v.6.22, Data Reduction and Correction Program, Bruker
AXS, Madison, WI, 2001.
(f) G.B. Deacon, A. Gitlits, B.W. Skelton, A.H. White, Chem.
Commun. (1999) 1213;
(g) D. Freeman, S. Sayan, T.J. Emge, M. Croft, J.G. Brennan, J.
Am. Chem. Soc. 121 (1999) 11713;
(h) J. Janczak, R. Kubiak, A. Jezierski, Inorg. Chem. 38 (1999) 2043;

2878
P.E. OꢀConnor et al. / Inorganica Chimica Acta 359 (2006) 2870–2878
´
´
´
(i) D.M.M. Freckmann, T. Dube, C.D. Berube, S. Gambarotta,
[37] S. Chadwick, U. Englich, K. Ruhlandt-Senge, Angew. Chem., Int.
Ed. 37 (1998) 3007.
G.P.A. Yap, Organometallics 21 (2002) 1240;
(j) O. Eisenstein, P.B. Hitchcock, A.V. Khvostov, M.F. Lappert, L.
Maron, L. Perrin, A.V. Protchenko, J. Am. Chem. Soc. 125 (2003)
10790;
[38] (a) S.A. Cotton, F.A. Hart, M.B. Hursthouse, A.J. Welch, Chem.
Commun. (1979) 1225;
(b) H. Schumann, J. Muller, Angew. Chem., Int. Ed. 17 (1978) 276;
¨
(k) G.B. Deacon, C.M. Forsyth, Chem. Eur. J. 10 (2004) 1798.
[35] K. Ruhmann, Chem. Ber. 94 (1961) 2311.
[36] X. Yu, Z. Xue, Inorg. Chem. 44 (2005) 1505.
(c) A.L. Wayda, W.J. Evans, J. Am. Chem. Soc. 100 (1978) 7119;
(d) J. Holton, M.F. Lappert, D.G. Ballard, R. Pearse, J.L. Atwood,
W.E. Hunter, Dalton Trans. (1979) 4554.