Lutetium alkyl and hydride complexes in a non-cyclopentadienyl coordination environment

Article abstract of DOI:10.1039/b710228n

Lutetium alkyl complexes [Lu(L)(CH₂SiMe₃)(THF) _n], which contain a sulfur-linked bis(phenolato) ligand such as 2,2′-thiobis(6-tert-butyl-4-methylphenolate) (L = tbmp, 1) or 1,4-dithiabutanediyl-bis(6-tert-butyl-4-methylphe

Full text of DOI:10.1039/b710228n

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www.rsc.org/dalton | Dalton Transactions
Lutetium alkyl and hydride complexes in a non-cyclopentadienyl coordination
environment†‡
Marcin Konkol, Thomas P. Spaniol, Małgorzata Kondracka and Jun Okuda*
Received 4th July 2007, Accepted 17th July 2007
First published as an Advance Article on the web 2nd August 2007
DOI: 10.1039/b710228n
Lutetium alkyl complexes [Lu(L)(CH2SiMe3)(THF)n], which contain a sulfur-linked bis(phenolato)
ligand such as 2,2ꢀ-thiobis(6-tert-butyl-4-methylphenolate) (L = tbmp, 1) or 1,4-dithiabutanediyl-
bis(6-tert-butyl-4-methylphenolate) (L = etbmp, 2), were isolated from the reaction of the lutetium
tris(alkyl) complex [Lu(CH2SiMe3)3(THF)2] with H2L. The monomeric structures of these complexes
were confirmed by X-ray diffraction studies, showing distorted octahedral geometry around the metal
centre. The reaction of [Lu(tbmp)(CH2SiMe3)(THF)2] (1) with alcohols ROH (R = iPr, CHPh2, CPh3)
results in the formation of the corresponding alkoxide complexes [Lu(tbmp)(OR)(THF)n] (4–6). With
PhSiH3 hydride complexes [Lu(L)(l-H)(THF)n]2 (L = tbmp, 7; etbmp, 8) have been prepared in
moderate to good yields. They adopt a dimeric form in the solid state as revealed by the X-ray crystal
structure of 7. The reactivity of the hydride complexes and their catalytic activity in the ring-opening
polymerisation of L-lactide and the hydrosilylation of alkenes are also discussed.
As revealed by X-ray diffraction analysis, complexes 1 and 2 are
monomeric in the solid state. The lutetium atom in both cases is six-
coordinate with a tridentate (1) or tetradentate (2) bis(phenolato)
ligand, one trimethylsilylmethyl group and two (1) or one (2)
coordinated THF molecules, adopting a distorted octahedral
geometry (Fig. 1 and 2). In the case of complex 1 both oxygen
donors are arranged trans to the THF molecules with the O(1)–
Introduction
In contrast to the intensively explored chemistry of the
cyclopentadienyl(Cp)-containing hydrido complexes of the
lanthanides,1 Cp-free hydrides are limited to those containing
ancillary ligands such as hard polydentate N and/or O donor
ligands:2 guanidinato,3 salicylaldiminato,4 benzamidinato,5 or
amido.6,7 Since the catalytic activity of alkyl and hydrido com-
plexes of group 3 metals is known to depend on the hardness of
the ancillary ligand environment,8 we became interested in using
mixed hard–soft donor ligands9 to support alkyl and hydrido
lanthanide fragments. Herein we report the synthesis and reactivity
of some new alkyl and hydrido complexes of lutetium supported
by an OSO/OSSO ligand framework.
Lu–O(3) and O(2)–Lu–O(4) angles of 150.02(18) and 156.49(18)◦,
respectively. The 1,4-dithiabutanediyl bridged complex 2 adopts
a cis-a configuration, which is also observed for group 4 metal
complexes bearing this ligand.10 The trimethylsilylmethyl ligand
in 2 is located cis to THF and trans to one of the sulfur atoms, as
indicated by the corresponding angles C(25)–Lu–S(1) 174.95(11)◦,
O(3)–Lu–C(25) 98.08(14)◦.
Results and discussion
Synthesis and characterisation of alkyl complexes
Reaction of the lutetium tris(alkyl) complex, [Lu(CH2SiMe3)3-
(THF)2] with the corresponding bis(phenol) leads, under
SiMe4 elimination, to the formation of the alkyl complexes
[Lu(CH2SiMe3)(L)(THF)n] (L = tbmp 1; tbbp 1a; etbmp 2)
(Scheme 1). Both THF ligands in 1 are labile and can be easily
exchanged for pyridine to give the alkyl complex 3. Single crystals
of 1 and 2 suitable for X-ray diffracti◦on studies were obtained
from a THF–pentane solution at −40 C. Crystallographic data
and refinement parameters are summarised in Table 1. Selected
bond lengths and angles are listed in Table 2.
Fig. 1 Molecular structure of 1 shown with 30% thermal ellipsoids.
Hydrogen atoms have been omitted for clarity.
Institute for Inorganic Chemistry, RWTH Aachen University, Landoltweg 1,
D-52074 Aachen, Germany
† CCDC reference numbers 643864–643869. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b710228n
‡ Electronic supplementary information (ESI) available: Crystal data and
The two oxygen donors of the ligand in 2 are arranged
trans to each other with the O(1)–Lu–O(2) angle of 147.93(11)◦.
The molecule of 2 shows C1 symmetry and both enantiomers are
structure refinements for 1a, 5 and 6. See DOI: 10.1039/b710228n
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Scheme 1 Formation and reactivity of lutetium alkyl complexes with bis(phenolato) ligands.
Table 1 Crystallographic data and refinement parameters for 1, 2 and 7
1
2
7
Formula
M
C34H55O4SiSLu
762.90
130(2)
0.25 × 0.12 × 0.10
Orthorhombic
Pbca
17.657(3)
18.687(3)
22.178(4)
90
90
90
7318(2)
8
1.385
C32H51O3SiS2Lu
750.94
150(2)
C39H65O5SLu
820.98
140(2)
0.60 × 0.30 × 0.30
Monoclinic
C2/c
29.835(9)
17.805(6)
18.098(6)
90
Temperature/K
Crystal size/mm
Crystal system
Space group
0.29 × 0.21 × 0.05
Triclinic
¯
P1
˚
a/A
8.7517(17)
12.703(2)
16.986(3)
75.023(4)
82.049(5)
75.436(4)
1760.1(6)
2
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
121.466(5)
90
8200(5)
3
˚
U/A
Z
8
Dc/g cm−3
1.417
2.985
1.330
2.496
l/mm−1
2.820
F(000)
3136
768
3407
h Range/◦
2.17–28.42
23, −24 to 25, 29
81 995
9170
0.1015
2.33–28.35
11, 16, 22
24 117
8702
0.0503
2.26–28.36
39, 23, −24 to 23
42 018
10 147
0.0280
Data collected (hkl)
No. of reflections collected
No. of independent reflections
Rint
Final R1, wR2[I > 2r(I)]
R1, wR2 (all data)
Goodness of fit on F2
0.0848, 0.1504
0.1013, 0.1552
1.570
1.994, −4.259
0.0413, 0.0843
0.0482, 0.0873
1.100
1.379, −1.011
0.0256, 0.0633
0.0332, 0.0682
0.987
1.783, −0.513
−3
˚
Dqmax, min/e A
found in the centrosymmetric crystal structure. The Lu–C bond
˚
2.58 A), but still much shorter than the sum of the metal radius
˚
˚
distances (1, 2.348(7) A; 2, 2.335(4) A) are comparable with those
rm(Lu) and van der Waals radius rv(S) (rm(Lu) + rv(S) = 1.738 +
11
˚
13
reported in the literature for [Lu(CH2SiMe3)3(THF)2] (2.36 A)
˚
1.80 = 3.538 A), indicating the presence of coordinative bonds.
and other lutetium complexes with the trimethylsilylmethyl ligand
The Lu–S1 and Lu–S2 bond lengths in 2 differ from each other
e.g. [Lu(CH2SiMe3)2(crown)(THF)n][B(CH2SiMe3)Ph3] (crown =
˚
by about 0.16 A, with an elongated Lu–S1 bond trans to the
12
˚
12C4, n = 1; 15C5, 18C6, n = 2) (2.34–2.37 A). The two Lu–S
CH2SiMe3 moiety. This can be explained by the stronger electron-
donating ability of the trimethylsilylmethyl group that weakens
the opposite Lu–S1 bond.
˚
distances of 2.962(1) and 2.846(1) A in 2 are apparently longer
than the sum of the covalent radii (rc(Lu) + rc(S) = 1.56 + 1.02 =
4096 | Dalton Trans., 2007, 4095–4102
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◦
˚
Table 2 Selected bond lengths (A) and angles ( ) in 1, 2 and 7
1
2
7
Lu–C(23)
Lu–S
Lu–O(1)
Lu–O(2)
Lu–O(3)
Lu–O(4)
2.348(7)
2.955(2)
2.098(5)
2.099(4)
2.332(5)
2.334(5)
Lu–C(25)
Lu–S(1)
Lu–S(2)
Lu–O(1)
Lu–O(2)
Lu–O(3)
2.335(4)
2.962(1)
2.846(1)
2.101(3)
2.115(3)
2.234(3)
Lu–H(1)
Lu–Lu#
Lu–S
Lu–O(1)
Lu–O(2)
Lu–O(3)
Lu–O(4)
2.09(3)
3.553(1)
2.919(1)
2.123(2)
2.124(2)
2.379(2)
2.346(2)
O(1)–Lu–O(2)
O(3)–Lu–O(4)
O(1)–Lu–O(3)
O(2)–Lu–O(4)
C(23)–Lu–S
97.26(18)
80.16(17)
150.02(18)
156.49(18)
173.2(2)
S(1)–Lu–C(25)
S(2)–Lu–C(25)
O(1)–Lu–O(2)
O(1)–Lu–O(3)
S(2)–Lu–O(3)
O(3)–Lu–C(25)
174.95(11)
101.76(12)
147.93(11)
92.55(11)
157.46(8)
98.08(14)
S–Lu–Lu#
S–Lu–H(1)
O(1)–Lu–O(2)
O(3)–Lu–O(4)
O(1)–Lu–O(4)
O(2)–Lu–O(4)
177.63(1)
143.8(9)
99.00(8)
77.45(8)
147.77(7)
83.02(7)
Si–C(23)–Lu
129.5(4)
(6) complexes revealed monomeric structures, the structure of
isopropoxy analogue (4) may well be dimeric.
Synthesis and characterisation of hydrido complexes
The lutetium alkyl complexes 1 and 2 were found to react
smoothly at room temperature with PhSiH3 to form the corre-
sponding hydride complexes [Lu(L)(l-H)(THF)n]2 (L = tbmp 7;
etbmp 8; Scheme 1). Complex 8 bearing the 1,4-dithiabutanediyl
bridged ligand could also be prepared in 83% yield from
[Lu(CH2SiMe3)3(THF)2] in pentane in a one-pot procedure. As
revealed by X-ray diffraction analysis complex 7 adopts a dimeric
form in the solid state (Fig. 3).
Fig. 2 Molecular structure of 2 shown with 30% thermal ellipsoids.
Hydrogen atoms have been omitted for clarity.
Both alkyl complexes 1 and 2 are fluxional in solution due to a
reversible THF-dissociation process. This fluxional phenomenon
is quite often observed for rare earth metal complexes14,15 and
other transition metal complexes.16 Analogously to the 1,4-
dithiabutanediyl bridged silylamido complexes of lutetium, yt-
trium and scandium,15 in the case of 2 the fast dissociation
of THF on the NMR time scale will lead to a pseudo-five
coordinate environment around the metal centre with either
C2 (trigonal bipyramidal, trans-(O,O)) or Cs symmetry (square
pyramidal, cis-(O,O)). This renders both phenyl moieties in the
same ligand chemically equivalent resulting in only one set of
signals being observed in the 1H NMR spectra in THF-d8 at room
temperature. Thus, four ethylene bridge protons in the backbone
of the bis(phenolato) ligand in 2 appear as a singlet at 2.71 ppm.
Variable-temperature 1H NMR studies show that the fluxionality
of the ethylene bridge is frozen out on the NMR time scale at
−90 ◦C showing two broad signals at 2.35 and 3.30 ppm.
Fig. 3 Molecular structure of 7 shown with 30% thermal ellipsoids.
Hydrogen atoms except for the bridging ones have been omitted for clarity.
Each of the two metal centres is coordinated by two oxygen
atoms and one sulfur atom of the bis(phenolato) ligand, two
THF molecules and by two bridging hydrido ligands. The S–
Lu–Lu# section is almost linear with an angle of 177.63(1)◦.
Oxygen atoms of each metal unit are arranged trans to each other
with a staggered conformation. The two lutetium atoms and the
˚
two hydrido ligands are coplanar, with the Lu–H (2.09(3) A) and
˚
Lu–Lu (3.553(1) A) distances being similar to those reported re-
[Lu(tbmp)(CH2SiMe3)(THF)2] (1) was found to react with
alcohols ROH (R = iPr, CHPh2, CPh3) to form the corresponding
alkoxide complexes [Lu(tbmp)(OR)(THF)n] (Scheme 1). Although
the X-ray studies of triphenylmethoxy (5) and diphenylmethoxy
cently for the guanidinato complex [Lu{(Me3Si)2NC(NiPr)2}2(l-
3
˚
H)]2(C6H14) (Lu–H, 2.12(4), 2.04(4); Lu–Lu, 3.577(1) A) and
for other dimeric l2-hydrido bridged lutetium cyclopentadienyl
complexes.14a In the 1H NMR spectrum the low-field shifted
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hydride resonance is displayed at 11.29 (7) and 11.41 (8) ppm. At
room temperature in THF-d8 the two phenyl groups of the ligand
are already symmetrical, only the fluxionality of the ethylene
bridge in 8 is frozen out on the NMR time scale, showing two
broad singlets (d 2.24, 2.97). Moreover, a VT NMR experiment
revealed two triplet resonances at −35 ◦C as shown in Fig. 4.
Scheme 2 Reactivity of lutetium hydrido complexes with bis(phenolato)
ligands.
was also tested. The resulting polymers have narrow molecular
weight distribution (1.07–1.17), although the activity is lower than
that reported for the corresponding silylamido lutetium complexes
with a tetradentate OSSO ligand.15 For the isopropoxide complex
4, at a [LA]0/[Lu]0 ratio of 200 with [LA]0 = 0.3 M and with
10 equiv. of iPrOH per Lu, about 88% conversion to PLA was
achieved after 24 h. Surprisingly, no polymerisation was observed
with 1 equiv. of iPrOH after the same time.
The catalytic potential of the hydride complex 8 was further
tested in hydrosilylation reactions. Thus, monitoring the reaction
of hex-1-ene with PhSiH3 in C6D6 at 25 C in the presence of 8
Fig. 4 VT 1H NMR spectrum of the ethylene backbone proton reso-
nances in the hydride complex 8.
◦
([Lu]0 : [PhSiH3]0 : [Alk]0 = 1 : 20 : 20) showed the formation
of the anti-Markovnikov product, PhSiH2(CH2)5CH3, with 81%
conversion after 4 d and with 98% selectivity. At 60 ◦C 82%
conversion with maintained high selectivity could be achieved after
21 h.
The reactivity of the hydride complexes 7 and 8 is shown in
Scheme 2. The dominant reaction pathway is the insertion into
Lu–H bond. Thus, NMR investigations revealed the formation
of [Lu(tbmp)(OCHPh2)(THF)3] (6) in the reaction with ben-
zophenone and of [Lu(etbmp)(NC5H6)(NC5H5)] (9) with pyridine.
Furthermore, the formation of the formiate complex 10 is postu-
lated in the reaction of 8 with CO2 as indicated by the presence
Conclusions
1
of a single resonance at 8.78 ppm in the H NMR spectrum.
In conclusion, we have demonstrated that a tridentate OSO or
a tetradentate OSSO ligand framework is a suitable ancillary for
the stabilisation of the lutetium alkyl and hydride fragments. The
hydride complexes with the bis(phenolato) ligands show a high
tendency towards insertion reactions with a variety of substrates.
Preliminary results show also a catalytic potential of hydride
species in the ring-opening polymerisation of L-lactide as well
as in the hydrosilylation of alkenes which are currently being
investigated in more detail.
The reaction of 7 with phenylacetylene led to the formation
of the corresponding acetylide complex 11, while styrene was
found to react regioselectively yielding the 2-phenylethyl complex
[Lu(etbmp){CH(Ph)CH3}(THF)] (12).
Given the suitability of OSO- and OSSO-type rare earth
metal complexes [Ln(OZO)X] for the ring-opening polymerisation
(ROP) of lactide,17 we have studied the effect of the reactive group
X = H (Table 3). For comparison the isopropoxide complex 4
Table 3 Ring-opening polymerisation of L-lactide using complexes 4 and 8
[LA]0 : [Lu]0 : [iPrOH]0
Time/h
Conv. (%)d
Mc (theory)g
Mn (GPC)
Mw/Mn
4
8
8
8
200 : 1 : 10a
195 : 1 : 0b
100 : 1 : 1a
100 : 1 : 1c
24
42
51
51
88
2597
8878
4528
7122
3960
26 400
6180
1.09
1.08
1.07
1.17
32e,f
31
49
10 070
a [LA]0 = 0.3 M, toluene. b [LA]0 = 0.87 M, THF. c [LA]0 = 0.3 M, THF. d Monomer conversion, determined by 1H NMR spectroscopy. e Isolated yield.
f 30% of oligomers. g Mc = ([LA]0/[Lu]0) × 144.13 × conv. (%); with the presence of iPrOH, Mc = ([LA]0/[iPrOH]0) × 144.13 × conv. (%) + 60.
4098 | Dalton Trans., 2007, 4095–4102
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C6H2), 126.5 (2-C6H2), 130.5 (5-C6H2), 137.9, 138.2 (4-/6-C6H2),
166.4 (1-C6H2).
Experimental
General considerations
[Lu(etbmp)(CH2SiMe3)(THF)n] (n = 1–2) (2). A solution of
[Lu(CH2SiMe3)3(THF)2] (0.200 g, 0.344 mmol) in THF (0.2 mL)
was added dropwise to 1,4-dithiabutanediyl-bis(6-tert-butyl-4-
methylphenol) (etbmpH2) (0.144 g, 0.344 mmol). After ca. 5 min
a colourless solution formed that was stirred at room temperature
for 1.5 h. Pentane was then added (3 mL) and the solution was
stored overnight at −40 ◦C. 2 was isolated as a white powder
(0.154 g, 54% for n = 2). Anal. Calc. for C36H59O4SiS2Lu (n = 2):
C 52.54, H 7.23, Lu 21.26%; found: C 52.15, H 6.99, Lu 21.18%. dH
(400 MHz, THF-d8): −1.00 (s, 2H, LuCH2), −0.13 (s, 9H, SiMe3),
1.40 (s, 18H, CMe3), 1.72 (br s, THF), 2.10 (s, 6H, Me), 2.71 (s, 4H,
SCH2), 3.54 (br s, THF), 6.90 (m, 4H, 3-/5-C6H2); dC (100 MHz,
THF-d8): 4.7 (SiMe3), 20.7 (Me), 26.4 (THF), 28.1 (LuCH2), 30.2
(CMe3), 35.7 (CMe3), 36.9 (SCH2), 68.2 (THF), 119.1 (2-C6H2),
124.9 (4-C6H2), 129.6, 132.5 (3-/5-C6H2), 139.0 (6-C6H2), 167.5
(1-C6H2).
All operations were performed under an inert atmosphere of argon
using standard Schlenk-line or glove-box techniques. THF, n-
hexane and n-pentane were distilled under argon from sodium–
benzophenone ketyl prior to use. PhSiH3 was dried over sodium.
The following compounds were prepared according to published
procedures: [Lu(CH2SiMe3)3(THF)2],18 2,2ꢀ-thiobis(6-tert-butyl-
4-methylphenol) (tbmpH2),9 2,2ꢀ-thiobis(4,6-di-tert-butylphenol)
(tbbpH2).19 1,4-dithiabutanediyl-bis(6-tert-butyl-4-methylphenol)
(etbmpH2) was synthesised according to a modification of the
methods reported in the literature.9 All other chemicals were
commercially available and used after appropriate purification.
NMR spectra were recorded on a Bruker DRX 400 spectrometer
at 25 ◦C (1H, 400.1 MHz, 13C, 100.6 MHz) unless otherwise stated.
1
Chemical shifts for H and 13C NMR spectra were referenced
internally using the residual solvent resonances and reported
relative to tetramethylsilane. Elemental analyses were performed
by the Microanalytical Laboratory of this department. Metal
analysis was performed by complexometric titration.20 The sample
(15–30 mg) was dissolved in THF (2 mL) or acetonitrile (2 mL)
and titrated with a 0.005 M aqueous solution of EDTA using
xylenol orange as indicator and a 1 M ammonium acetate buffer
solution (20 mL).
[Lu(tbmp)(CH2SiMe3)(NC5H5)2] (3). Pyridine (0.0396 g,
40 lL, 0.500 mmol) was slowly added to a solution of 1 (0.100 g,
0.131 mmol) in THF (0.5 mL). The reaction mixture was stirred
for 1 h at room temperature and pentane (3 mL) was then
added. Upon standing overnight at −40 ◦C 3 was isolated as a
beige powder (0.094 g, 92%). Anal. Calc. for C36H49O2N2SiSLu:
Lu 22.52%; found: Lu 22.35%. dH (400 MHz, THF-d8): −0.86
(s, 2H, LuCH2), −0.01 (s, 9H, SiMe3), 1.33 (s, 18H, CMe3),
Syntheses of complexes
4
2.08 (s, 6H, Me), 6.81 (d, JHH = 2.5 Hz, 2H, 3-C6H2), 7.11
(d, 4JHH = 2.3 Hz, 2H, 5-C6H2), 7.22 (m, 4H, 3-/5-H, py), 7.62 (m,
2H, 4-H, py), 8.50 (m, 4H, 2-/6-H, py); dC (100 MHz, THF-d8): 4.5
(SiMe3), 20.8 (Me), 30.1 (CMe3), 30.5 (CH2), 35.8 (CMe3), 124.32
(4-C6H2), 124.34 (3-/5-C, py), 126.4 (2-C6H2), 129.7 (3-C6H2),
134.0 (5-C6H2), 136.3 (4-C, py), 138.9 (6-C6H2), 150.7 (2-/6-C,
py), 166.6 (1-C6H2).
[Lu(tbmp)(CH2SiMe3)(THF)2] (1). A mixture of [Lu(CH2-
SiMe3)3(THF)2] (1.166 g, 2.01 mmol) and thiobis(6-tert-butyl-4-
methylphenol) (tbmpH2) (0.721 g, 2.01 mmol) was cooled down
to −78 ◦C and pentane (40 mL, with 2 mL THF) was then added.
A reaction mixture was stirred for 15 min at −78 ◦C and for a
further 2.5 h at 0 ◦C. The volume of solvents was reduced in vacuo
to ca. 30 mL and a yellow solution with a white precipitate was
stored overnight at −30 ◦C in order to achieve precipitation. 1
was isolated as a white powder (0.955 g, 62%). Anal. Calc. for
C34H55O4SiSLu: C 53.53, H 7.27, Lu 22.93%; found: C 52.68, H
7.52, Lu 22.64%. dH (400 MHz, THF-d8): −0.87 (s, 2H, LuCH2),
−0.10 (s, 9H, SiMe3), 1.34 (s, 18H, CMe3), 1.69 (br s, THF), 2.08
(s, 6H, Me), 3.54 (br s, THF), 6.81 (d, 4JHH = 2.3 Hz, 2H, 3-C6H2),
7.11 (d, 4JHH = 2.3 Hz, 2H, 5-C6H2); dC (100 MHz, THF-d8): 4.5
(SiMe3), 20.8 (Me), 26.4 (THF), 30.1 (CMe3), 30.4 (CH2), 35.8
(CMe3), 68.2 (THF), 124.3 (4-C6H2), 126.4 (2-C6H2), 129.7 (3-
C6H2), 134.0 (5-C6H2), 138.9 (6-C6H2), 166.6 (1-C6H2).
[Lu(tbmp)(OiPr)(THF)]x (x = 1 or 2) (4). To a solution of 1
(0.100 g, 0.131 mmol) in THF (0.3 mL) 2-propanol (0.0096 g,
12 lL, 0.160 mmol) was added. The solution was stirred for 5 min
at room temperature followed by an addition of pentane (3 mL).
Upon standing overnight at −40 ◦C a white precipitate formed
that was filtered off, washed with pentane and dried (0.068 g,
78%). Anal. Calc. for C29H43O4SLu: C 52.56, H 6.54, Lu 26.40%;
found: C 52.22, H 6.57, Lu 27.03. dH (400 MHz, THF-d8): 1.27
3
(d, JHH = 6.3 Hz, 6H, CH(CH3)2), 1.32 (s, 18H, CMe3), 1.69
(br s, THF), 2.09 (s, 6H, Me), 3.54 (br s, THF), 4.61 (sep, 3JHH
=
4
6.3 Hz, 1H, CH), 6.83 (d, JHH = 2.3 Hz, 2H, 3-C6H2), 7.12 (d,
4JHH = 2.3 Hz, 2H, 5-C6H2); dC (100 MHz, THF-d8): 20.8 (Me),
26.4 (THF), 28.0 (CH(CH3)2), 30.1 (CMe3), 35.6 (CMe3), 68.1
(CH(CH3)2), 68.2 (THF), 124.4 (4-C6H2), 126.6 (2-C6H2), 129.9
(3-C6H2), 133.8 (5-C6H2), 138.6 (6-C6H2), 166.1 (1-C6H2).
[Lu(tbbp)(CH2SiMe3)(THF)2] (1a). A mixture of [Lu(CH2-
SiMe3)3(THF)2] (0.100 g, 0.172 mmol) and thiobis(4,6-di-tert-
butylphenol) (tbbpH2) (0.076 g, 0.172 mmol) was dissolved in
THF (0.2 mL). The reaction mixture was stirred for 15 min at
room temperature and pentane (3 mL) was then added. Yellow
crystals of 1a formed upon standing overnight at −40 ◦C (0.076 g,
52%). Anal. Calc. for C40H67O4SiSLu: C 56.72, H 7.97, Lu 20.66%;
found: C 55.24, H 7.57, Lu 20.95%. dH (400 MHz, THF-d8): −0.85
[Lu(tbmp)(OCPh3)(THF)2] (5).
A solution of Ph3COH
(0.0365 g, 0.140 mmol) in THF (0.2 mL) was added to 1 (0.100 g,
0.131 mmol) with stirring. A clear solution formed within 1 min.
After 5 min pentane (3 mL) was added. The solution was stirred
at room temperature for 2 h. Colourless crystals of 5 were isolated
upon standing overnight at −40 ◦C (0.100 g, 82%). Anal. Calc.
for C49H59O5SLu: C 62.94, H 6.36, Lu 18.71%; found: C 60.78,
H 6.08, Lu 18.44%. dH (400 MHz, THF-d8): 1.32 (s, 18H, CMe3),
1.69 (br s, THF), 2.09 (s, 6H, Me), 3.54 (br s, THF), 6.82 (d,
(s, 2H, LuCH2), −0.10 (s, 9H, SiMe3), 1.20, 1.36 (2 × s, 2 × 18H,
4
2 × CMe3), 1.69 (br s, THF), 3.54 (br s, THF), 7.08 (d, JHH
=
4
2.5 Hz, 2H, 3-C6H2), 7.39 (d, JHH = 2.5 Hz, 2H, 5-C6H2); dC
(100 MHz, THF-d8): 4.5 (SiMe3), 26.4 (THF), 30.2 (CMe3), 30.4
(CH2), 32.1 (CMe3), 34.6, 36.1 (CMe3), 68.2 (THF), 125.8 (3-
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4
4JHH = 2.5 Hz, 2H, 3-C6H2), 7.05 (m, 3H, p-H), 7.11 (d, JHH
=
(br s, 2H, CH2S), 3.54 (br s, THF), 6.86 (m, 4H, 3-/5-C6H2), 11.41
(s, 1H, LuH); dC (100 MHz, THF-d8): 20.7 (Me), 26.4 (THF), 29.9
(CMe3), 35.6 (CMe3), 37.0 (SCH2), 68.2 (THF), 118.7 (2-C6H2),
124.3 (4-C6H2), 129.5, 132.4 (3-/5-C6H2), 138.9 (6-C6H2), 168.6
(1-C6H2).
2.5 Hz, 2H, 5-C6H2), 7.16 (m, 6H, o/m-H), 7.52 (m, 6H, o/m-H);
dC (100 MHz, THF-d8): 20.8 (Me), 26.4 (THF), 30.0 (CMe3), 35.8
(CMe3), 68.2 (THF), 86.6 (CPh3), 124.0 (4-C6H2), 126.0 (2-C6H2),
126.2 (p-C), 127.9/129.1 (o/m-C), 129.7 (3-C6H2), 134.0 (5-C6H2),
139.2 (6-C6H2), 153.0 (i-C), 166.5 (1-C6H2).
Reaction of [Lu(etbmp)(l-H)(THF)]2 (8) with pyridine. To a
solution of 8 (0.05 g, 0.038 mmol) in THF (1.5 mL) pyridine
(0.124 mmol, 10 lL) was dropwise added with stirring. After 5 min
the solution turned yellow–orange. THF was slowly evaporated to
ca. 0.5 mL and pentane (3 mL) was added. Orange precipitate
appeared upon slow evaporation of pentane (0.03 g, 53%).
The product was found to be extremely air-sensitive, turning
immediately white on contact with air. Due to its high solubility in
organic solvents we have not succeeded in obtaining an analytically
pure sample. However, the NMR data confirm unequivocally
the formation of [Lu(etbmp)(NC5H6)(NC5H5)] (9). dH (400 MHz,
THF-d8): 1.42 (s, 18H, CMe3), 2.11 (s, 6H, Me), 2.76 (br s, 4H,
[Lu(tbmp)(OCHPh2)(THF)3] (6). Method A. In an NMR tube
equipped with a J-Young valve [Lu(tbmp)(l-H)(THF)2]2 (7)
(0.01 g, 0.0074 mmol) and PhC(O)Ph (0.003 g, 0.016 mmol)
were dissolved in THF-d8 (0.5 mL). The formation of complex
6 was monitored spectroscopically by NMR. Method B. The
procedure was analogous to that for 5, using Ph2CHOH (0.0258 g,
0.140 mmol) and 1 (0.100 g, 0.131 mmol). A white powder was
isolated upon storing the solution overnight at −40 ◦C. The
product was filtered off and subsequently recrystallised from
THF–pentane (0.060 g, 49%). Anal. Calc. for C47H63O6SLu: Lu
18.79%; found: Lu 18.54%. dH (400 MHz, THF-d8): 1.34 (s, 18H,
CMe3), 1.69 (br s, THF), 2.09 (s, 6H, Me), 3.54 (br s, THF), 6.06
2
SCH2), 3.80 (d, JHH = 4.3 Hz, 2H, H2/H2ꢀ, NC5H6), 4.31 (m,
1H, H3, NC5H6), 4.57 (td, 3JHH = 5.6 Hz, 4JHH = 1.5 Hz, 1H, H5,
4
(s, 1H, CH), 6.81 (d, JHH = 2.5 Hz, 2H, 3-C6H2), 7.00 (m, 2H,
NC5H6), 5.69 (dd, 3JHH = 5.4 Hz, 1H, H4, NC5H6), 6.82 (d, 3JHH
=
p-H), 7.09–7.13 (m, 6H, 5-C6H2 + o/m-H), 7.41 (m, 4H, o/m-
H); dC (100 MHz, THF-d8): 20.8 (Me), 26.4 (THF), 30.1 (CMe3),
35.7 (CMe3), 68.2 (THF), 82.4 (CHPh2), 123.4 (4-C6H2), 125.9 (2-
C6H2), 126.4 (p-C), 127.5/128.4 (o/m-C), 129.4 (3-C6H2), 134.0
(5-C6H2), 138.7 (6-C6H2), 151.0 (i-C), 166.7 (1-C6H2).
6.0 Hz, 1H, H6, NC5H6), 6.91 (m, 4H, 3-/5-C6H2), 7.22 (m, 2H,
3-/5-H, py), 7.62 (m, 1H, 4-H, py), 8.50 (m, 2H, 2-/6-H, py); dC
(100 MHz, THF-d8): 20.7 (Me), 30.2 (CMe3), 35.6 (CMe3), 36.7
(SCH2), 47.6 (C2), 94.4 (C5), 97.8 (C3), 119.1 (4-C6H2), 124.3 (3-
/5-C, py), 125.1 (2-C6H2), 127.7 (C4), 129.5/132.5 (3-/5-C6H2),
136.3 (4-C, py), 139.0 (6-C6H2), 147.0 (C6), 150.8 (2-/6-C, py),
167.1 (1-C6H2).
[Lu(tbmp)(l-H)(THF)2]2 (7). To a solution of 1 (0.100 g,
0.131 mmol) in THF (0.2 mL) PhSiH3 was added (0.071 g,
81 lL, 0.655 mmol). The reaction mixture was stirred at room
temperature for 1 h followed by an addition of pentane (3 mL).
The solution was stored overnight at −40 ◦C yielding a white
precipitate that was filtered off, washed with pentane and dried
(0.04 g, 45%). Crystals of 7 were grown from a THF–pentane–
hexamethyldisiloxane mixture. Anal. Calc. for C60H90O8S2Lu2: Lu
25.86%; found: Lu 25.18%. dH (400 MHz, THF-d8): 1.32 (s, 18H,
CMe3), 1.69 (br s, THF), 2.07 (s, 6H, Me), 3.54 (br s, THF), 6.77
Reaction of [Lu(etbmp)(l-H)(THF)]2 (8) with CO2. In an
NMR tube equipped with a J-Young valve 8 (0.01 g, 0.0075 mmol)
was dissolved in THF-d8 (0.5 mL). After a freeze–pump–thaw
cycle the NMR tube was charged with CO2. The formation
of the complex [Lu(etbmp)(O2CH)(THF)n] (10) was investigated
1
using H NMR spectroscopy. After 5 min at room temperature
the spectrum was free of starting material. Besides the etbmp
ligand resonances of the compound 10 two other sets of ligand
signals were found. Due to overlapping only a single resonance at
8.78 ppm could be tentatively assigned to the O2CH fragment.
4
4
(d, JHH = 2.2 Hz, 2H, 3-C6H2), 7.11 (d, JHH = 2.3 Hz, 2H, 5-
C6H2), 11.29 (s, 1H, LuH); dC (100 MHz, THF-d8): 20.8 (Me), 26.4
(THF), 30.2 (CMe3), 35.8 (CMe3), 68.2 (THF), 123.3 (4-C6H2),
126.6 (2-C6H2), 129.3 (3-C6H2), 133.8 (5-C6H2), 138.2 (6-C6H2),
167.0 (1-C6H2).
[Lu(etbmp)(C≡CPh)(THF)2] (11). To a suspension of 8
(0.10 g, 0.075 mmol) in THF (1.5 mL) phenylacetylene
(0.228 mmol, 25 lL) was added dropwise with stirring. After
5 min the suspension turned yellow. It was stirred for a further
1.5 h at room temperature. After standing overnight at −40 ◦C
THF was slowly evaporated to ca. 0.5 mL. The product was
filtered off and recrystallised from THF–pentane (1 : 3) at
−40 ◦C. After several days a yellow microcrystalline precipitate
appeared (0.065 g, 52%). Anal. Calc. for C40H53O4S2Lu: Lu
20.90%; found: Lu 20.96%. dH (400 MHz, THF-d8): 1.42 (s, 18H,
CMe3), 1.69 (br s, THF), 2.11 (s, 6H, Me), 2.68 (br s, 4H, SCH2),
3.54 (br s, THF), 6.91 (m, 4H, 3-/5-C6H2), 6.97 (m, 1H, p-H), 7.06
(m, 2H, m-H), 7.18 (m, 2H, o-H); dC (100 MHz, THF-d8): 20.7
(Me), 26.4 (THF), 30.0 (CMe3), 35.7 (CMe3), 37.0 (SCH2), 68.2
(THF), 105.9 (Lu–C≡C), 119.1 (2-C6H2), 124.8 (4-C6H2), 125.6
(i-C), 128.4 (m-C), 129.1 (p-C), 129.5/132.7 (3-/5-C6H2), 132.1
(o-C), 139.0 (6-C6H2), 151.4 (Lu–C≡C), 167.7 (1-C6H2).
[Lu(etbmp)(l-H)(THF)]2 (8). Method A. To a solution of 2
(0.200 g, 0.243 mmol) in THF (0.4 mL) PhSiH3 was added (0.132 g,
151 lL, 1.22 mmol). The reaction mixture was stirred at room
temperature for 15 min followed by an addition of pentane (1 mL).
A white precipitate was formed. After 1 h pentane (3 mL) was
again added in order to achieve precipitation. The precipitate was
filtered off, washed with pentane and dried (0.110 g, 68%). Method
B. A solution of [Lu(CH2SiMe3)3(THF)2] (0.500 g, 8.61 mmol) in
pentane (3 mL) was added dropwise to a suspension of etbmpH2
(0.360 g, 8.61 mmol) in pentane (1 mL) at room temperature with
intensive stirring. After ca. 1 min a clear colourless solution was
formed. After 1 h PhSiH3 (0.466 g, 530 lL, 43 mmol) was added.
A white precipitate was observed within 2 h. Upon standing
overnight at −40 ◦C the precipitate was filtered off, washed
with pentane (2 mL) and dried (0.474 g, 83%). Anal. Calc. for
C56H82O6S4Lu2: C 50.59, H 6.22, Lu 26.32%; found: C 49.81, H
6.65, Lu 26.06%. dH (500 MHz, THF-d8): 1.24 (s, 18H, CMe3),
1.69 (br s, THF), 2.10 (s, 6H, Me), 2.24 (br s, 2H, SCH2), 2.97
Reaction of [Lu(etbmp)(l-H)(THF)]2 (8) with styrene. In
an NMR tube equipped with a J-Young valve 8 (0.01 g,
0.0075 mmol) was dissolved in THF-d8 (0.5 mL) and styrene
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(0.016 mmol, 1.8 lL) was added with a syringe. The solution
Typical hydrosilylation procedure
turned yellow after a while. The formation of the complex
In a glove-box the complex 8 (0.01 g, 0.0075 mmol) was placed
in an NMR tube equipped with a J-Young valve and dissolved
in 0.6 ml of C6D6. To that solution hex-1-ene (0.28 mmol) and
PhSiH3 (0.28 mmol) were added. The tube was vigorously shaken.
The reaction proceeded at room temperature and was monitored
by 1H and 13C NMR spectroscopy. The ratio of Markovnikov and
anti-Markovnikov regioisomers was calculated by integration of
the appropriate signals in the 1H NMR spectra.
1
[Lu(etbmp){CH(Ph)CH3}(THF)] (12) was investigated using H
and 13C NMR spectroscopy. After 6 d at room temperature the
spectra were free of starting material. dH (400 MHz, THF-d8):
3
1.42 (s, 18H, CMe3), 1.52 (d, JHH = 6.5 Hz, 3H, CHCH3), 1.69
(br s, THF), 2.02 (obscured q, 1H, CH), 2.11 (s, 6H, Me), 2.64
(m, 4H, SCH2), 3.54 (br s, THF), 6.35 (‘t’, 2H, o-H, Ph), 6.69 (‘d’,
1H, p-H, Ph), 6.87–6.98 (m + m, 6H, 3-/5-C6H2 + m-H, Ph). dC
(100 MHz, THF-d8): 15.2 (CHCH3), 20.7 (Me), 26.4 (THF), 30.0
(CMe3), 35.6 (CMe3), 37.1 (SCH2), 58.0 (CH), 68.2 (THF), 117.1
(o-C, Ph), 118.8 (2-C6H2), 121.2(p-C, Ph), 125.4 (4-C6H2), 130.0
(3-/5-C6H2), 130.9 (m-C, Ph), 132.6 (3-/5-C6H2), 139.0 (6-C6H2),
155.0 (i-C, Ph), 167.6 (1-C6H2).
Crystal structure analysis†
Relevant crystallographic data are summarised in Table 1. The
data of complexes 1, 2 and 7 were collected with a Bruker AXS
diffractometer and reduced with the program system SMART.21
The structures were solved by direct methods (SHELXS-86)22
and all independent reflections were used in the refinement by
full-matrix least-squares against all F2 data (SHELXL-97).23 The
hydrogen atoms were included into calculated positions except
for the bridging hydrogen atoms in 7, which were refined in their
position.
Typical polymerisation procedure
L-Lactide (Aldrich) was recrystallised from dry toluene and
sublimed at 50 ◦C under vacuum prior to use. Spectroscopic
analysis of polymers was performed in CDCl3. Molecular weights
and polydispersities were determined by size-exclusion chromatog-
raphy (SEC) in THF at a flow rate of 1 mL min−1 utilising an
Agilent 1100 Series GPC system with a refractive index detector
and a PPS linear M 5 l column (filled with SDV gel) with pore
CCDC reference numbers 643864–643869.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b710228n
sizes of 103, 104, 105 and 106 A. Calibration standards were
˚
commercially available narrowly distributed linear polystyrene
samples which cover a broad range of molar masses (104 < Mn <
2 × 106 g mol−1).
Acknowledgements
We thank the German Research Foundation (DFG) and the Fonds
der Chemischen Industrie for financial support.
Polymerisation using [Lu(etbmp)(l-H)(THF)]2 (8). In a glove-
box L-lactide (195 equiv. per Lu) was dissolved in THF (0.5 mL), a
freshly prepared catalyst solution (0.00226 mmol) in THF (0.5 mL)
was then combined and the mixture stirred at room temperature.
After 42 h the polymer solution was quenched by adding an excess
amount of n-hexane with drops of water. The collected precipitate
was dissolved in chloroform and precipitated into methanol. After
filtration the polymer was dried under vacuum at 60 ◦C to a
constant weight for SEC analysis.
References
1 For examples see: H. Schumann, J. Meese-Marktscheffel and L. Esser,
Chem. Rev., 1995, 95, 865; M. Ephritikhine, Chem. Rev., 1997, 97,
2193; F. T. Edelmann, in Comprehensive Organometallic Chemistry II,
ed. E. W. Abel, F. G. A. Stone, G. Wilkinson and M. F. Lappert,
Elsevier, Tarrytown, NY, 1995, vol. 4, p. 11; M. N. Bochkarev, L. N.
Zakharov, G. S. Kalinina, in Organoderivatives of Rare Earth Elements,
Kluwer, Dordrecht, 1995; S. Arndt and J. Okuda, Chem. Rev., 2002,
102, 1953; J. Okuda, J. Chem. Soc., Dalton Trans., 2002, 2367; P. M.
Zeimentz, S. Arndt, B. R. Elvidge and J. Okuda, Chem. Rev., 2006, 106,
2404.
Polymerisation using [Lu(etbmp)(l-H)(THF)]2 (8) in the presence
of iPrOH. In a glove-box L-lactide (100 equiv. per Lu) was
dissolved in toluene (2 mL). The catalyst solution (0.004 mmol)
in toluene (1 mL) was first treated with isopropanol (1 equiv. per
Lu) and then L-lactide was added. After 51 h the polymer solution
was quenched by adding excess amount of n-pentane with drops
of water. The solvents were evaporated and CDCl3 was added.
Monomer conversion was calculated by integration of monomer
2 For reviews, see: W. E. Piers and D. J. H. Emslie, Coord. Chem. Rev.,
2002, 233–234, 131; F. T. Edelmann, D. M. M. Freckmann and H.
Schumann, Chem. Rev., 2002, 1, 1851.
3 A. A. Trifonov, E. A. Fedorova, G. K. Fukin and M. N. Bochkarev,
Eur. J. Inorg. Chem., 2004, 4396; A. A. Trifonov, G. G. Skvortsov, D. M.
Lyubov, N. A. Skorodumova, G. K. Fukin, E. V. Baranov and V. N.
Glushakova, Chem.–Eur. J., 2006, 12, 5320.
4 D. J. H. Emslie, W. E. Piers, M. Parvez and R. McDonald,
Organometallics, 2002, 21, 4226; D. J. H. Emslie, W. E. Piers and R.
McDonald, J. Chem. Soc., Dalton Trans., 2002, 293.
5 R. Duchateau, C. T. van Wee, A. Meetsma and J. H. Teuben, J. Am.
Chem. Soc., 1993, 115, 4931; R. Duchateau, C. T. van Wee, A. Meetsma,
P. T. van Duijnen and J. H. Teuben, Organometallics, 1996, 15, 2279;
R. Duchateau, C. T. van Wee and J. H. Teuben, Organometallics, 1996,
15, 2291; J. R. Hagadorn and J. Arnold, Organometallics, 1996, 15,
984.
6 R. Duchateau, T. Tuinstra, E. A. C. Brussee, A. Meetsma, P. T. van
Duijnen and J. H. Teuben, Organometallics, 1997, 16, 3511.
7 A. G. Avent, F. G. N. Cloke, B. R. Elvidge and P. B. Hitchcock, Dalton
Trans., 2004, 1083; T. I. Gountchev and T. D. Tilley, Organometallics,
1999, 18, 2896.
8 J. W. Bruno, H. A. Stecher, L. R. Morss, D. C. Sonnenberger and T. J.
Marks, J. Am. Chem. Soc., 1986, 108, 7275; S. P. Nolan, D. Stern and
T. J. Marks, J. Am. Chem. Soc., 1989, 111, 7844; D. C. Sonnenberger,
1
vs. polymer methine resonances in the H NMR spectrum. The
polymer was isolated by precipitation into methanol and dried at
60 ◦C to a constant weight for SEC analysis.
Polymerisation using [Lu(tbmp)(OiPr)(THF)] (4). In a glove-
box L-lactide (200 equiv. per Lu) was dissolved in toluene (2.5 mL).
The catalyst solution (0.00468 mmol) in toluene (0.5 mL) was first
treated with isopropanol (10 equiv.) and then L-lactide was added.
After 24 h the polymer solution was quenched by adding excess
amount of n-pentane with drops of water. The work-up procedure
was analogous to that described above.
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The Royal Society of Chemistry 2007
Dalton Trans., 2007, 4095–4102 | 4101
©

View Article Online
L. R. Morss and T. J. Marks, Organometallics, 1985, 4, 352; Z. Lin and
T. J. Marks, J. Am. Chem. Soc., 1987, 109, 7979; L. E. Schock and T. J.
Marks, J. Am. Chem. Soc., 1988, 110, 7701; J. W. Bruno, T. J. Marks and
L. R. Morss, J. Am. Chem. Soc., 1983, 105, 6824; T. Ziegler, V. Tschinke,
L. Versluis, E. J. Baerends and W. Ravenek, Polyhedron, 1988, 7, 1625;
C. J. Schaverien, Organometallics, 1994, 13, 69; C. J. Schaverien, J. H. G.
Frijns, H. J. Heeres, J. R. van den Hende, J. H. Teuben and A. L. Spek,
J. Chem. Soc., Chem. Commun., 1991, 642.
9 tbmpH2: T. K. Prakasha, R. O. Day and R. R. Holmes, J. Am.
Chem. Soc., 1993, 115, 2690; S. Fokken, T. P. Spaniol, H.-W. Kang,
W. Massa and J. Okuda, Organometallics, 1996, 15, 5069; etbmpH2:
C. Capacchione, A. Proto, H. Ebeling, R. Mu¨lhaupt, K. Mo¨ller,
T. P. Spaniol and J. Okuda, J. Am. Chem. Soc., 2003, 125, 4964; H.
Ma, T. P. Spaniol and J. Okuda, Angew. Chem., Int. Ed., 2006, 45,
7818.
10 C. Capacchione, R. Manivannan, M. Barone, K. Beckerle, R. Centore,
L. Oliva, A. Proto, A. Tuzi, T. P. Spaniol and J. Okuda, Organometallics,
2005, 24, 2971; K. Beckerle, R. Manivannan, T. P. Spaniol and J. Okuda,
Organometallics, 2006, 25, 3019; G.-J. M. Meppelder, T. P. Spaniol and
J. Okuda, J. Organomet. Chem., 2006, 691, 3206.
11 H. Schumann, D. M. M. Freckmann and S. Dechert, Z. Anorg. Allg.
Chem., 2002, 628, 2422.
12 S. Arndt, T. P. Spaniol and J. Okuda, Chem. Commun., 2002, 896.
13 L. Pauling, in The Nature of the Chemical Bond, Cornell University
Press, Ithaca, NY, 3rd edn, 1960.
14 (a) S. Arndt, P. Voth, T. P. Spaniol and J. Okuda, Organometallics, 2000,
19, 4690; (b) T. I. Gountchev and T. D. Tilley, Organometallics, 1999,
18, 5661.
15 H. Ma, T. P. Spaniol and J. Okuda, Dalton Trans., 2003, 4770.
16 M. C. Chisholm, J. Gallucci and K. Phomphrai, Inorg. Chem., 2002,
41, 2785.
17 H. Ma and J. Okuda, Macromolecules, 2005, 38, 2665.
18 M. F. Lappert and R. Pearce, J. Chem. Soc., Chem. Commun., 1973,
126; W. J. Evans, J. C. Brady and J. W. Ziller, J. Am. Chem. Soc., 2001,
123, 7711.
19 S. D. Pastor, J. D. Spivack and L. P. Steinheubel, J. Heterocycl. Chem.,
1984, 49, 4302.
20 S. Arndt, T. P. Spaniol and J. Okuda, Organometallics, 2003, 22, 775
and references therein.
21 Siemens. ASTRO, SAINT and SADABS. Data, Collection and Pro-
cessing Software for the SMART System, Siemens Analytical X-ray
Instruments Inc., Madison, Wisconsin, USA, 1996.
22 G. M. Sheldrick, SHELXS-86, A Program for Crystal Structure
Solution, University of Go¨ttingen, Germany, 1986.
23 G. M. Sheldrick, SHELXL-97, A Program for Crystal Structure
Refinement, University of Go¨ttingen, Germany, 1997.
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