Rare earth metal bis(alkyl) complexes bearing a monodentate arylamido ancillary ligand: Synthesis, structure, and Olefin polymerization catalysis

Article abstract of DOI:10.1016/j.jorganchem.2006.06.048

The reaction of Ln(CH₂SiMe₃)₃(thf)₂ with 1 equiv. of the amine ligand 2,6-ⁱPr₂C₆H₃NH(SiMe₃) gave the corresponding amido-ligated rare earth metal bis(alkyl) complexes [2,6-ⁱPr₂C₆H₃N(SiMe₃)]Ln(CH₂SiMe₃)₂(thf) (Ln = Sc (1), Y (2), Ho (3), Lu (4)), which represent rare examples of bis(alkyl) rare earth metal complexes bearing a monodentate anionic ancillary ligand. In the case of Gd, a similar reaction gave the bimetallic complex Gd₂(μ-CH₂SiMe₂NC₆H₃ⁱPr₂-2,6)₃(thf)₃ (5) through intramolecular C-H activation of a methyl group of Me₃Si on the amido ligand by Gd-CH₂SiMe₃ and the subsequent ligand redistribution. Complexes 1-5 were structurally characterized by X-ray analyses. On treatment with 1 equiv of [Ph₃C][B(C₆F₅)₄] in toluene at room temperature, complexes 1-4 showed high activity for the living polymerization of isoprene. The 1/[Ph₃C][B(C₆F₅)₄] system showed high activity also for the polymerization of 1-hexene and styrene.

Full text of DOI:10.1016/j.jorganchem.2006.06.048

Journal of Organometallic Chemistry 692 (2007) 536–544
www.elsevier.com/locate/jorganchem
Rare earth metal bis(alkyl) complexes bearing a monodentate
arylamido ancillary ligand: Synthesis, structure, and
Olefin polymerization catalysis
1
*
Yunjie Luo , Masayoshi Nishiura, Zhaomin Hou
Organometallic Chemistry Laboratory, RIKEN (The Institute of Physical and Chemical Research) and PRESTO, Japan Science and
Technology Agency (JST), Hirosawa 2-1, Wako, Saitama 351-0198, Japan
Received 22 May 2006; received in revised form 12 June 2006; accepted 20 June 2006
Available online 3 September 2006
Abstract
The reaction of Ln(CH2SiMe3)3(thf)2 with 1 equiv. of the amine ligand 2,6-iPr2C6H3NH(SiMe3) gave the corresponding amido-ligated
rare earth metal bis(alkyl) complexes [2,6-iPr2C6H3N(SiMe3)]Ln(CH2SiMe3)2(thf) (Ln = Sc (1), Y (2), Ho (3), Lu (4)), which represent
rare examples of bis(alkyl) rare earth metal complexes bearing a monodentate anionic ancillary ligand. In the case of Gd, a similar reac-
i
tion gave the bimetallic complex Gd2(l-CH2SiMe2NC6H3 Pr2-2,6)3(thf)3 (5) through intramolecular C–H activation of a methyl group of
Me3Si on the amido ligand by Gd–CH2SiMe3 and the subsequent ligand redistribution. Complexes 1–5 were structurally characterized
by X-ray analyses. On treatment with 1 equiv of [Ph3C][B(C6F5)4] in toluene at room temperature, complexes 1–4 showed high activity
for the living polymerization of isoprene. The 1/[Ph3C][B(C6F5)4] system showed high activity also for the polymerization of 1-hexene
and styrene.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Amido complex; Cationic rare earth metal alkyls; 1-Hexene; Isoprene; Olefin polymerization; Styrene
1. Introduction
dienyls [2], b-diketiminates [3g,5], benzamidinates [3d],
triazacyclononane-amido [3h], deprotonated aza-crown
[6], anilido-pyridine-imine [7], aminopyridinates [8], and
amido-phosphine [9], while monodentate-ligand-supported
rare earth metal bisalkyl complexes remained scarce [10].
Changing the ligand environment of a complex to modify
its properties is usually an important strategy for the devel-
opment of more efficient or selective catalysts. During our
recent studies on cationic half-sandwich rare earth metal
alkyls in polymerization catalysis [1a,1e,2], we became
interested in analogous non-metallocene alkyl complexes.
We report here the synthesis, structure and olefin polymer-
ization catalysis of the rare earth metal bis(alkyl) com-
plexes bearing a simple monodentate arylamido ligand,
[2,6-iPr2C6H3N(SiMe3)]Ln(CH2SiMe3)2(thf) (Ln = Sc (1),
Y (2), Ho (3), Lu (4)) [11]. Formation and X-ray structure
of a related bimetallic Gd complex Gd2{l-CH2SiMe2NC6
Rare earth metal bisalkyl complexes bearing one anionic
ancillary ligand have received much current interest
because such complexes can be converted to the corre-
sponding cationic monoalkyl species by treatment with
an equimolar amount of a borate compound such as
[Ph3C][B(C6F5)4] or [HNMe2Ph][B(C6F5)4], leading to for-
mation of unique catalyst systems that differ from those
derived from the conventional metallocene complexes [1–
4]. To prevent possible ligand redistribution, most of the
rare earth bisalkyl complexes reported so far were stabi-
lized by multidentate ancillary ligands such as cyclopenta-
*
Corresponding author.
E-mail address: houz@postman.riken.go.jp (Z. Hou).
Present address: Department of Biological and Pharmaceutical Engi-
1
neering, Ningbo Institute of Technology, Zhejiang University, Ningbo
315100, China.
i
H3 Pr2-2,6}3(thf)3 (5) is also described.
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.06.048

Y. Luo et al. / Journal of Organometallic Chemistry 692 (2007) 536–544
537
Table 1
Selected bond distances (A) and angles (deg) for complexes 1–4
2. Results and discussion
˚
2.1. Synthesis and structure of [2,6-iPr2C6H3N(SiMe3)]Ln-
(CH2SiMe3)2 (thf) (Ln = Sc (1), Y (2), Ho (3), Lu (4))
Ln = Sc (1) Ln = Y (2) Ln = Ho (3) Ln = Lu (4)
Ln–N(1)
Ln–C(1)
Ln–C(5)
Ln–C(9)
Ln–O(1)
2.035(2)
2.210(2)
2.211(2)
2.837(2)
2.147(2)
2.190(2)
2.366(2)
2.367(3)
2.886(2)
2.309(2)
2.176(3)
2.366(4)
2.367(4)
2.872(3)
2.311(2)
2.153(2)
2.314(3)
2.322(3)
2.889(3)
2.256(2)
The alkane elimination reaction of Ln(CH2SiMe3)3(thf)2
with 1 equiv. of 2,6-iPr2C6H3NHSiMe3 in benzene or THF
at room temperature afforded the mono(arylamido) rare
earth metal bis(alkyl) complexes [2,6-iPr2C6H3N(Si-
Me3)]Ln(CH2SiMe3)2(thf) (Ln = Sc (1), Y (2), Ho (3), Lu
(4)) in 54–68% isolated yields (Scheme 1). All these com-
plexes showed good solubility in common organic solvents,
such as THF, toluene, and hexane. Formation of a mono(-
alkyl) bis(arylamido) rare earth metal complex was not
observed even when 2 equiv. of 2,6-iPr2C6H3NHSiMe3
were used.
N(1)–Ln–C(1) 110.02(8)
N(1)–Ln–C(5) 108.05(8)
N(1)–Ln–O(1) 115.11(7)
C(1)–Ln–C(5) 111.7(1)
C(1)–Ln–O(1) 110.01(8)
C(5)–Ln–O(1) 101.70(8)
Ln–N(1)–C(9) 109.0(1)
109.59(8)
106.85(8)
117.96(7)
108.7(1)
110.93(8)
102.22(8)
104.0(1)
108.9(1)
107.1(1)
106.1(1)
118.4(1)
108.3(1)
111.3(1)
103.0(1)
103.9(2)
109.0(1)
116.60(8)
109.7(1)
102.5(1)
111.5(1)
105.8(2)
The solid structures of complexes 1–4 were determined
by X-ray diffraction analyses. Selected bond lengths and
angles are shown in Table 1. All these complexes are
isostructural and isomorphous, and therefore only the
structure of 1 is given in Fig. 1. The metal atom is
four-coordinated by one nitrogen atom, two CH2SiMe3
ligands, and one THF molecule, forming a slightly dis-
torted tetrahedral geometry. The phenyl ring of the amido
ligand is oriented almost parallel to the plane formed by
C(1), C(5), and O(1). The average Sc–CH2SiMe3 bond
˚
distance in 1 (2.211(2) A) is very close to those found in
other scandium bis(alkyl) complexes such as [PhC(N-
i
˚
2,6- Pr2C6H3)2]Sc(CH2SiMe3)2(thf) (2.212(3) A) [3d], (1,3-
˚
(SiMe3)2C5H3)Sc(CH2SiMe3)2(thf)
[(SiMe2CH2P Pr2)2N]Sc(CH2SiMe3)2 (2.214(5) A) [9], and
(C5Me4SiMe3)Sc(CH2SiMe3)2(thf) (2.223(2) A) [2d]. The
bond distances of the Sc–N (2.035(2) A) and Sc–O
(2.215(1) A)
[2c],
i
˚
˚
˚
˚
(2.147(2) A) bonds in 1 are comparable with those in
Fig. 1. ORTEP structure of 1 (thermal ellipsoids at the 30% level,
(BDPPoxyl)ScCH2SiMe3(thf) (BDPPoxyl = o-C6H4(CH2-
hydrogen atoms are omitted for clarity).
i
˚
˚
NC6H3 Pr2-2,6)2) (av. 2.027(1) A and 2.161(1) A), respec-
tively [12]. The bond lengths around the metal center in 2
and 3 are very close to each other, in consistence with the
similarity of the ionic radius of these two metal ions (Y:
˚
˚
(2.332(4) A) [16] and (C5Me4SiMe3)Lu(CH2SiMe3)2(thf)
˚
(2.335(3) A) [17]. The Lu–N bond (2.153(2) A) in 4 can
˚
˚
be compared with that in Me2Si(C5Me4)(NC6H3Me2-
2,6)Lu(CH2SiMe3)(thf) (2.188(2) A) [18].
0.900 A, Ho: 0.901 A) [13]. The average bond length of
˚
˚
the Y–CH2SiMe3 bonds (2.367(3) A) in 2 is comparable
The diamagnetic Sc (1), Y (2), and Lu (4) complexes
to that found in (C5Me4SiMe3)Y(CH2SiMe3)2(thf) (2.381
˚
˚
showed well-resolved NMR spectra, while the paramag-
(4) A) [14]. The Y–N bond distance in 2 (2.190(2) A) can
be compared with the average bond distance of the Y–N
bonds observed in Y(ArN(CH2)3NAr)CH(SiMe3)2(thf)
1
netic Ho complex 3 did not give an informative H NMR
spectrum. Ligand redistribution was not observed in solu-
1
i
˚
tion, as shown by the NMR spectra of 1, 2 and 4. H
(Ar=2,6- Pr2C6H3) (2.173(3) A) [15]. The average Lu–
NMR and 13C NMR spectra of complexes 1, 2 and 4 in
˚
CH2SiMe3 bond distance in 4 (2.318(3) A) is comparable
C6D6 showed one set of signals for the NSiMe3,
with those found in (C5Me5)Lu(CH2SiMe3)2(thf)
SiMe3
H
Me3Si
N
N
benzene or THF
rt, SiMe4
+
Ln(CH2SiMe3)3(thf)2
Ln
thf
Me3SiCH2
CH2SiMe3
Ln = Sc (1); Y (2); Ho (3); Lu (4)
Scheme 1.

538
Y. Luo et al. / Journal of Organometallic Chemistry 692 (2007) 536–544
CH2SiMe3, and thf units, and two sets of signals for the
isopropyl groups on the phenyl ring, suggesting that rota-
tion of the phenyl ring around the N–C9 bond is highly
restricted, which is in consistence with their crystal struc-
tures. The methylene protons of the trimethylsilylmethyl
groups in complexes 1 and 4 were observed as a singlet
peak, while complex 2 showed a doublet (À0.21 ppm)
due to Y–H coupling (JY–H = 3.4 Hz). Similarly, in 13C
NMR spectra, the methylene carbon of Ln–CH2SiMe3
was observed at 44.38 ppm for 1, at 46.08 ppm for 4, and
at 38.93 ppm with JY–C = 43.5 Hz for 2. The coupling con-
stants of Y–H (3.4 Hz) and Y–C (43.5 Hz) in 2 are very
close to those observed in (C5Me4SiMe3)Y(CH2SiMe3)2-
(thf) (3.1 and 43.7 Hz), respectively [19].
2.2. Reaction of Gd(CH2SiMe3)3(thf)2 with
2,6-iPr2C6H3NH(SiMe3)
Fig. 2. ORTEP structure of 5 (thermal ellipsoids at the 30% level,
hydrogen atoms and crystal solvent are omitted for clarity).
In an attempt to prepare an analogous gadolinium
bisalkyl complex [2,6-iPr2C6H3N(SiMe3)]Gd(CH2SiMe3)2-
(thf), the reaction of Gd(CH2SiMe3)3(thf)2 with an equiva-
lent of 2,6-iPr2C6H3NH(SiMe3) was carried out similarly
(Scheme 2). However, instead of the expected bisalkyl
product, a binuclear Gd complex Gd2(l-CH2SiMe2NC6-
and one thf ligand, while the other Gd atom (Gd2) is coor-
dinated by one nitrogen atom and two thf ligands. Both Gd
atoms form a distorted trigonal prism geometry. The aver-
i
˚
H3 Pr2-2,6)3(thf)3 (5), which does not contain a terminal
age bond lengths of Gd–N (2.301(3) A) and Gd–O
˚
CH2SiMe3 group, was isolated in 62% yield (based on
Gd). The molecular structure of 5 was unambiguously
determined by an X-ray analysis (Fig. 2). Selected bond
lengths and angles of 5 are given in Table 2. The two Gd
atoms are bridged by three methylene units derived from
the SiMe3 groups of the amido ligands. In addition, one
Gd atom (Gd1) is coordinated by two nitrogen atoms
(2.477(3) A) in 5 are comparable to those of the Gd–
˚
˚
N(SiMe3)2 (2.287(2) A) and Gd–O (2.441(2) A) bonds in
{[(Me3Si)2N]2(thf)Gd}2(l-N2), respectively [20]. The Gd–
˚
C bond lengths in 5 range broadly from 2.471(4) A to
˚
˚
2.757(4) A, in which the shortest Gd–C bond distance
(2.471(4) A) is similar to that of the terminal Gd–benzyl
˚
bond in (C5Me5)Gd(CH2C6H5)2(thf) (2.470(7) A) [21].
Si
thf
Si
H
N
thf
N
Gd
Si
Gd
THF
thf
Gd(CH2SiMe3)3(thf)2
+
rt, 48 h
N
N
Si
−
SiMe4
5
(62%, based on Gd)
Gd(CH2SiMe3)3(thf)2
ligand
redistribution
Si
H
N
Si
H
N
H
−
Gd
SiMe4
H
H
thf
Gd
Me3SiCH2
thf
CH2SiMe3
Me3SiCH2
6
7
Scheme 2.

Y. Luo et al. / Journal of Organometallic Chemistry 692 (2007) 536–544
539
Table 2
Selected bond distances (A) and angles (ꢁ) for complex 5
10
2.5
2.0
1.5
1.0
0.5
˚
Gd(1)–N(1)
Gd(2)–N(3)
Gd(1)–C(16)
Gd(2)–C(1)
Gd(2)–C(31)
Gd(2)–O(2)
Gd(1) Á Á Á Gd(2)
2.274(3)
2.284(3)
2.757(4)
2.635(4)
2.609(5)
2.479(3)
3.3835(5)
Gd(1)–N(2)
Gd(1)–C(1)
Gd(1)–C(31)
Gd(2)–C(16)
Gd(1)–O(1)
Gd(2)–O(3)
2.345(3)
2.616(4)
2.543(5)
2.471(4)
2.475(3)
2.476(3)
8
6
4
2
0
M
M
M
(C1)–Gd(1)–(C16)
(C16)–Gd(1)–(C31)
(C1)–Gd(2)–(C31)
(Gd1)–C(1)–(Gd2)
(Gd1)–C(31)–(Gd2)
78.9(1)
79.4(2)
83.5(2)
80.2(1)
82.1(2)
(C1)–Gd(1)–(C31)
(C1)–Gd(2)–(C31)
(C16)–Gd(2)–(C31)
(Gd1)–C(16)–(Gd2)
85.2(2)
83.9(1)
83.7(2)
80.5(1)
0
20
40
60
80
100
conversion (%)
The formation of 5 could be explained by the reaction
path shown in Scheme 2. The alkane elimination reaction
of Gd(CH2SiMe3)3(thf)2 with 1 equiv. of 2,6-iPr2C6H3NH-
SiMe3 should afford the mono(arylamido)-ligated bis(alkyl)
complex [2,6-iPr2C6H3N(SiMe3)]Gd(CH2SiMe3)2 (thf) (6),
as observed in the synthesis of 1–4. Intramolecular C–H
bond activation of a methyl group of Me3Si on the amido
ligand by CH2SiMe3 would give the silylene-linked amido-
methyl complex 7, which could undergo ligand redistribu-
tion to give 5 and Gd(CH2SiMe3)3(thf)2. The less stability
of the Gd complex 6 compared to its Sc, Y, Ho, and Lu
analogues 1–4 must be due to the larger ion radius of Gd.
Fig. 3. Plots of Mn and Mw/Mn versus isoprene conversion with 2/
[Ph3C][B(C6F5)4] at 25 ꢁC.
In the polymerization of 1-hexene, only the Sc complex
1 showed significant activity in combination with an equiv-
alent of [Ph3C][B(C6F5)4], which converted 650 equivalents
of 1-hexene into atactic poly(1-hexene) with Mn = 7300
and Mw/Mn = 2.65 at room temperature in 30 min. This
is a rare example of efficient a-olefin polymerization cata-
lyzed by a rare earth metal catalyst [23]. The polymeriza-
tion of styrene by 1/[Ph3C][B(C6F5)4] gave a mixture of
syndiotactic and atactic polystyrenes, in contrast with the
exclusive formation of syndiotactic polystyrene observed
in the case of (C5Me4SiMe3)Sc(CH2SiMe3)2(thf)/[Ph3C]-
[B(C6F5)4] [2d]. A neutral bis(alkyl) complex alone did
not show activity for the above polymerization.
2.3. Polymerization of isoprene, 1-hexene and styrene
When treated with 1 equiv. of [Ph3C][B(C6F5)4], com-
plexes 1–4 showed high activity for the polymerization of
isoprene at room temperature, with the activity being in
the order of 4 > 2 > 3 > 1 (Table 3). The average number
molecular weight (Mn) of the resulting polymers increased
linearly as the isoprene conversion was raised, while the
molecular weight distribution remained very narrow (Mw/
Mn = 1.04–1.06) during the whole period of the polymeri-
zation (Fig. 3, Table 3), demonstrating the excellent ‘‘liv-
ingness’’ of the polymerization system [22].
2.4. Characterization of a cationic scandium alkyl active
species
To gain information on the active species in the present
1
polymerization systems, H NMR monitoring of the reac-
tion of 1 with 1 equiv. of [Ph3C][B(C6F5)4] in C6D5Cl was
carried out. Rapid formation of Ph3CCH2SiMe3 together
with disappearance of 1 was observed at room tempera-
Table 3
Polymerization of isoprene by 1–4/[Ph3C][B(C6F5)4]a
1-4/[Ph3C][B(C6F5)4]
25 oC, toluene
y
x
z
n
Conversionb (%)
Activityc
Mnd · 10À4
Mw/Mn
d
Run
Complex
Ln
t (min)
1
2
3
4
5
6
7
a
1
2
2
2
2
3
4
Sc
Y
Y
Y
Y
10
5
15
12
42
74
100
28
32
49
86
76
69
1.53
0.73
3.65
6.16
8.73
5.35
2.89
1.53
1.06
1.04
1.05
1.05
1.27
1.12
10
20
30
10
5
Ho
Lu
58
412
100
Conditions: Ln, 21 lmol; [Ln]/[B] = 1/1 (mol/mol); [M]/[Ln] = 500 (mol/mol); toluene, 5 mL; 25 ꢁC. Polyisoprene microstructure: 1,4-unit:3,4-unit ꢀ
30:70.
b
Weight of polymer obtained/weight of monomer used.
Given in kg of polymer/(molÀ Ln Æ h).
Determined by GPC in THF at 40 ꢁC against polystyrene standard.
c
d

540
Y. Luo et al. / Journal of Organometallic Chemistry 692 (2007) 536–544
˚
ture. However, identification of the resulting cationic scan-
dium alkyl species was not successful because of its insta-
bility. From a THF solution, a more stable scandium
alkyl species, which could be assigned to [2,6-iPr2C6H3N-
purified by passing through a Dryclean column (4 A molec-
ular sieves, Nikka Seiko Co.) and a Gasclean GC-RX col-
umn (Nikka Seiko Co.). Solvents were distilled from
sodium/benzophenone ketyl, degassed by the freeze–
pump–thaw method, and dried over fresh Na chips in the
glovebox. Ln(CH2SiMe3)3(thf)2 [24], 2,6-iPr2C6H3NH-
(SiMe3) [11b,1c] were prepared according to the literatures.
Anhydrous LnCl3 were purchased from STREM. LiCH2-
SiMe3 (1 M solution in pentane) was obtained from
Aldrich, and used as powder after drying up the solvent
under vacuum. [Ph3C][B(C6F5)4] was purchased from
Tosoh Finechem Corporation and used without purifica-
tion. 2,6-iPr2C6H3NH2 and Me3SiCl were purchased from
TCI and used without purification. 1-Hexene (TCI), iso-
prene (TCI), and styrene (Junsei Chemical Co., Ltd.) were
dried by stirring with CaH2 for 24 h, and distilled under
reduced pressure prior to polymerization experiments.
Deuterated solvents were obtained from ISOTEC. Samples
of organo rare earth metal complexes for NMR spectro-
scopic measurements were prepared in the glovebox using
J. Young valve NMR tubes. NMR (1H, 13C) spectra were
recorded on a JNM-EX 400 or a JNM-EX 300 spectrome-
ter. The NMR spectra of poly(1-hexene) and poly(iso-
prene) were recorded in CDCl3 at 25 ꢁC. The NMR
spectra of polystyrene were measured in 1,1,2,2–tetrachlo-
roethane–d2 at 120 ꢁC. Elemental analyses were performed
on a MICRO CORDER JM10 apparatus (J-SCIENCE
LAB Co.). Molecular weights and molecular weight distri-
butions of poly(1-hexene) and poly(isoprene) were deter-
mined against polystyrene standard by gel permeation
chromatography on a HLC-8220 GPC apparatus (Tosoh
Corporation) with THF as an eluent at a flow rate of
0.35 mL/min at 40 ꢁC. Molecular weight and molecular
weight distributions of polystyrenes were determined
against polystyrene standard by high temperature gel per-
meation chromatography (HT–GPC) on a HLC–8121
GPC/HT apparatus (Tosoh Corporation). 1,2–Dichloro-
benzene was used as an eluent at a flow rate of 1.0 mL/
min at 145 ꢁC.
(SiMe3)Sc(CH2SiMe3)(thf)2][B(C6F5)4],
was
obtained
(Scheme 3). Addition of one equivalent of THF to a 1:1
reaction mixture of 1 and [Ph3C][B(C6F5)4] in C6H5Cl
or toluene also gave the same species. This bis(THF)-
coordinated cationic scandium alkyl species, however, did
not show activity for the polymerization, probably because
of the lack of a vacant coordination site on the metal cen-
ter. Therefore, the true active species in the present
polymerization catalyst system might be a cationic, THF-
free, mono-amido-ligated scandium alkyl species such as
[2,6-iPr2C6H3N(SiMe3)Sc(CH2SiMe3)][B(C6F5)4] or its
mono-THF-coordinated analogue.
3. Conclusion
The acid–base reaction of Ln(CH2SiMe3)2(thf)2 with 1
equivalent of 2,6-iPr2C6H3NH(SiMe3) afforded straightfor-
wardly the corresponding mono-amido-ligated rare earth
metal bis(alkyl) complexes [2,6-iPr2C6H3N(SiMe3)]Ln-
(CH2SiMe3)2(thf) (Ln = Sc (1), Y (2), Ho (3), Lu (4)),
which represent rare examples of the bis(alkyl) rare earth
metal complexes bearing a monodentate anionic ancillary
ligand. In the case of a larger metal such as Gd, further
reactions (intramolecular C–H activation and ligand redis-
tribution) took place to give the bimetallic complex Gd2-
i
(l-CH2SiMe2NC6H3 Pr2-2,6)3(thf)3. On treatment with 1
equiv. of [Ph3C][B(C6F5)4] in toluene, complexes 1–4 served
as active catalysts for the living polymerization of isoprene
at room temperature. The combination of the Sc complex 1
with [Ph3C][B(C6F5)4] showed high activity also for the
polymerization of 1-hexene and styrene. The active catalyst
species in the present polymerization systems might be a
cationic, THF-free, mono-amido-ligated rare earth metal
alkyl species, such as [2,6-iPr2C6H3N(SiMe3)Sc(CH2Si-
Me3)][B(C6F5)4] or its mono-THF-coordinated analogue.
4. Experimental
4.2. Synthesis of [2,6-iPr2C6H3N(SiMe3)]Sc-
(CH2SiMe3)2(thf) (1)
4.1. Materials and procedures
All manipulations were performed under pure argon
with rigorous exclusion of air and moisture using standard
Schlenk techniques and an Mbraun glovebox. Argon was
To a 10 mL of colorless benzene solution of Sc(CH2Si-
Me3)3(thf)2 (1.00 g, 2.22 mmol) was added 2,6-iPr2C6H3-
NH(SiMe3) (0.553 g, 2.22 mmol) at room temperature.
[Ph3C][B(C6F5)4]
THF
−
Ph3CCH2SiMe3
Me3Si
Me3Si
N
[B(C6F5)4]
N
Sc
1. [Ph3C][B(C6F5)4], toluene
Sc
CH2SiMe3
(thf)2
thf
Me3SiCH2
Me3SiCH2
−
Ph3CCH2SiMe3
2. 1 equiv of THF
Scheme 3.

Y. Luo et al. / Journal of Organometallic Chemistry 692 (2007) 536–544
541
The mixture was stirred for 2 h at room temperature. The
4.5. Synthesis of [2,6-iPr2C6H3N(SiMe3)]Lu-
(CH2SiMe3)2(thf) (4)
resulting pale yellow solution was filtered. After drying
up, the residue was dissolved in 2 mL of hexane, and was
cooled at À30 ꢁC overnight to give [2,6-iPr2C6H3N(Si-
Me3)]Sc(CH2SiMe3)2(thf) as colorless cubic crystals
(0.82 g, 1.51 mmol, 68% yield). 1H NMR (C6D6,
400 MHz, 50 ꢁC): d 0.20 (br s, 4H, CH2SiMe3), 0.31 (s,
18 H, CH2SiMe3), 0.45 (s, 9 H, NSiMe3), 1.00 (m, 4 H,
thf), 1.15 (d, 6 H, JH–H = 7.0 Hz, CH(CH3)2), 1.23 (d, 6
H, JH–H = 7.0 Hz, CH(CH3)2), 3.30 (m, 4 H, thf), 3.81
(m, 2 H, CH(CH3)2), 6.91 (t, JH–H = 7.1 Hz, 1 H, p-
C6H3), 7.02 (d, JH–H = 7.5 Hz, 2 H, m-C6H3). 13C NMR
(C6D6, 100 MHz, 25 ꢁC): d 3.68, 4.59, 25.35, 25.75, 26.88,
27.86, 44.38, 72.33, 123.69, 124.65, 144.21, 146.46. Anal.
Calcd for C27H56NOScSi3: C, 60.05; H, 10.47; N, 2.59.
Found: C, 60.07; H, 10.20; N, 2.47%.
To a 10 mL of colorless benzene solution of Lu(CH2Si-
Me3)3(thf)2 (0.90 g, 1.55 mmol) was added
2,6-iPr2C6H3NH(SiMe3) (0.39 g, 1.55 mmol) at room tem-
perature. The mixture was stirred for 16 h at room temper-
ature. The resulting pale brown solution was dried in
vacuum. After drying up, the residue was extracted with
20 mL of hexane, and concentrated. Cooling at À30 ꢁC
gave [2,6-iPr2C6H3N(SiMe3)]Lu(CH2SiMe3)2(thf) as color-
less cubic crystals (0.65 g, 0.98 mmol, 63% yield). 1H NMR
(C6D6, 400 MHz, 25 ꢁC): d À0.41 (s, 4 H, CH2SiMe3), 0.34
(s, 18 H, CH2SiMe3), 0.44 (s, 9 H, NSiMe3), 0.92 (m, 4 H,
thf), 1.13 (d, 6 H, JH–H = 6.8 Hz, CH(CH3)2), 1.23 (d, 6 H,
JH–H = 6.8 Hz, CH(CH3)2), 3.09 (m, 4 H, thf), 3.90 (m, 2
H, CH(CH3)2), 6.87 (t, JH–H = 7.1 Hz, 1 H, p-C6H3), 7.01
(d, JH–H = 7.5 Hz, 2 H, m-C6H3). 13C NMR (C6D6,
100 MHz, 25 ꢁC): d 3.27, 4.70, 24.91, 25.18, 26.92, 27.24,
46.08, 71.26, 122.75, 124.34, 143.51, 146.90. Anal. Calcd
for C27H56LuNOSi3: C, 48.40; H, 8.44; N, 2.09. Found:
C, 48.45; H, 7.96; N, 2.00%.
4.3. Synthesis of [2,6-iPr2C6H3N(SiMe3)]Y(CH2SiMe3)2-
(thf) (2)
To a 10 mL of colorless benzene solution of Y(CH2Si-
Me3)3(thf)2 (1.00 g, 2.02 mmol) was added 2,6-iPr2C6H3-
NH(SiMe3) (0.50 g, 2.02 mmol) at room temperature. The
mixture was stirred for 2 h at room temperature. The
resulting pale yellow solution was filtered. After drying
up, the residue was dissolved in 2 mL of hexane, and was
cooled at À30 ꢁC overnight to give [2,6-iPr2C6H3N(SiMe3)]-
Y(CH2SiMe3)2(thf) as colorless cubic crystals (0.80 g,
1.37 mmol, 68% yield). 1H NMR (C6D6, 400 MHz,
25 ꢁC): d À0.21 (d, 4 H, JY-H = 3.4 Hz, CH2SiMe3), 0.35
(s, 18 H, CH2SiMe3), 0.45 (s, 9 H, NSiMe3), 1.01 (br s, 4
H, thf), 1.11 (d, 6 H, JH–H = 7.0 Hz, CH(CH3)2), 1.21 (d,
6 H, JH–H = 6.8 Hz, CH(CH3)2), 3.17 (br s, 4 H, thf), 3.85
(m, 2 H, CH(CH3)2), 6.85 (t, JH–H = 7.5 Hz, 1 H, p-
C6H3), 7.01 (d, JH–H = 7.5 Hz, 2 H, m-C6H3). 13C NMR
(C6D6, 100 MHz, 25 ꢁC): d 3.07, 4.31, 24.81, 25.00, 26.52,
26.92, 38.93 (JY-C = 43.5 Hz, CH2SiMe3), 70.42, 122.60,
124.36, 142.75, 146.80. Anal. Calcd for C27H56NOSi3Y:
C, 55.53; H, 9.69; N, 2.40. Found: C, 56.01; H, 9.20; N,
2.48%.
i
4.6. Synthesis of Gd2(l-CH2SiMe2NC6H3 Pr2-2,6)3(thf)3
(5)
To a 15 mL of colorless THF solution of Gd(CH2Si-
Me3)3(thf)2 (1.28 g, 2.27 mmol) was added 2,6-iPr2C6H3-
NH(SiMe3) (0.567 g, 2.27 mmol) at room temperature.
The mixture was stirred for 48 h at room temperature.
The solvent was removed under reduced pressure. The
resulting sticky white powder was washed by hexane 2 times
to give 5 as white powder (0.897 g, 62% based on Gd). Single
crystals suitable for X-ray analysis were obtained by recrys-
tallization from a toluene/hexane solution at À30 ꢁC. The
1H NMR spectrum of 5 was not informative because of
the influence of the paramagnetic Gd(III) ion. Anal. Calcd
for C64H107Gd2N3O3Si3 5 Æ toluene: C, 56.30; H, 7.90; N,
3.08. Found: C, 55.81; H, 7.52; N, 2.96%.
4.7. Reaction of [2,6-iPr2C6H3N(SiMe3)]Sc(CH2SiMe3)2-
(thf) with [Ph3C][B(C6F5)4]
4.4. Synthesis of [2,6-iPr2C6H3N(SiMe3)]Ho-
(CH2SiMe3)2(thf) (3)
To
a
THF solution (5 mL) of [2,6-iPr2C6H3N-
To a 15 mL of pink THF solution of Ho(CH2SiMe3)3-
(thf)2 (1.00 g, 1.75 mmol) was added 2,6-iPr2C6H3NH-
(SiMe3) (0.437 g, 1.75 mmol) at room temperature. The
mixture was stirred for 40 h at room temperature. The
resulting solution was dried in vacuum. Then the pink oil
residue was extracted with 20 mL of hexane, and the clear
hexane solution was concentrated. Cooling at À30 ꢁC for
2 h gave [2,6-iPr2C6H3N(SiMe3)]Ho(CH2SiMe3)2(thf) as
pink cubic crystals (0.62 g, 0.94 mmol, 54% yield). The
1H NMR spectrum of 3 was not informative because of
the influence of the paramagnetic Ho(III) ion. Anal. Calcd
for C27H56HoNOSi3: C, 49.14; H, 8.57; N, 2.12. Found: C,
48.86; H, 7.90; N, 1.87%.
(SiMe3)]Sc(CH2SiMe3)2(thf) (51 mg, 94 lmol) was added
1 equiv. of [Ph3C][B(C6F5)4] (87 mg, 94 lmol). The reaction
mixture was stirred at room temperature for 5 min, and the
solvent was removed under reduced pressure. The residue
was washed with hexane, and then dried up under vacuum
to give a red solid product, which could be assigned
to {[2,6-iPr2C6H3N(SiMe3)]Sc(CH2SiMe3)(thf)2}[B(C6F5)4].
1H NMR (300.40 MHz, o-C6D4Cl2, 24.6 ꢁC): d 0.01 (s, 9
H, CH2SiMe3), 0.15 (s, 9 H, NSiMe3), 0.57 (s, 2 H,
CH2SiMe3), 1.03, 1.10 (d, 12 H, (CH3)2CH), 1.82 (m,
8 H, thf), 3.27 (m, 2 H, (CH3)2CH), 3.78 (m, 8 H, thf).
The aromatic protons could not be unequivocally
assigned due to overlap with those of the Ph3CCH2SiMe3

542
Y. Luo et al. / Journal of Organometallic Chemistry 692 (2007) 536–544
contamination (see below). Attempts to further purify the
cationic species were not successful because of its instabil-
ity. Evaporation of the hexane extract gave Ph3CCH2-
SiMe3 as pale-white solid (29 mg, 93%). 1H NMR
(o-C6D4Cl2, 400 MHz, 25 ꢁC): d À0.28 (s, 9 H, CH2SiMe3),
2.06 (s, 2 H, CH2SiMe3), 6.87–7.26 (m, 15 H, Ph).
4.10. Polymerization of styrene
To a toluene solution (3 mL) of [2,6-iPr2C6H3N(SiMe3)]-
Sc(CH2SiMe3)2(thf) (11 mg, 21 lmol) in a 100-mL flask was
added a toluene solution (7 mL) of [Ph3C][B(C6F5)4]
(19 mg, 21 lmol). The mixture was stirred at room temper-
ature for a few minutes, and 2.148 g (21 mmol) of styrene
was added under vigorous stirring. A precipitation of poly-
mer product was observed in one minute. After 5 min, a
large amount of methanol (60 mL) was added to terminate
the polymerization. The white polymer powder was washed
with boiling methyl ethyl ketone. The insoluble part was
collected by filtration, and dried under vacuum at 60 ꢁC to
a constant weight (0.73 g, 34%), which was confirmed to
4.8. Polymerization of isoprene
A typical polymerization reaction is given below (Table
3, run 5). [2,6-iPr2C6H3N(SiMe3)]Y(CH2SiMe3)2(thf)
(12 mg, 21 lmol) and [Ph3C][B(C6F5)4] (19 mg, 21 lmol)
were added to a 100 mL flask with a stirring bar. Then tol-
uene (5 mL) was introduced by a syringe. The mixture was
stirred at room temperature for a few minutes, and
0.715 g (10.50 mmol) of isoprene was added under vigorous
stirring. After 30 minutes, a large amount of methanol
(60 mL) was added to terminate the polymerization. The
polymer product was washed with methanol, and dried
under vacuum at 60 ꢁC to a constant weight (0.715 g, 100%).
be syndiotactic polystyrene (rrrr > 99%) by H and 13C
1
NMR. Mn = 45.1 · 103, Mw/Mn = 1.96, Tm = 267 ꢁC.
4.11. X-ray crystallographic study
The single crystals were sealed in a thin-walled glass
capillary under a microscope in the glove box. Data col-
lections were performed on a Bruker SMART APEX
diffractometer with a CCD area detector using graphite-
4.9. Polymerization of 1-hexene
To a toluene solution (3 mL) of [2,6-iPr2C6H3N(SiMe3)]-
Sc(CH2SiMe3)2(thf) (11 mg, 21 lmol) in a 100-mL flask was
added a toluene solution (7 mL) of [Ph3C][B(C6F5)4]
(19 mg, 21 lmol). The mixture was stirred at room temper-
ature for a few minutes, and 1.736 g (20.63 mmol) of 1-hex-
ene was added under vigorous stirring. After 30 min, a large
amount of methanol (60 mL) was added to terminate the
polymerization. The polymer product was washed with
methanol, and dried under vacuum at 60 ꢁC to a constant
weight (1.13 g, 65%).
monochromated Mo Ka radiation (k = 0.71069 A). The
˚
determination of crystal class and unit cell was carried
out by SMART program package [25]. The raw frame data
were processed using SAINT [26] and SADABS [27] to yield
the reflection data file. The structures were solved by using
SHELXTL program [28]. Refinement was performed on F2
anisotropically for all the non-hydrogen atoms by the
full-matrix least-squares method. The analytical scattering
factors for neutral atoms were used throughout the
analysis. Hydrogen atoms were placed at the calculated
Table 4
Summary of crystallographic data of 1–5
1
2
3
4
5 Æ toluene
Formula
C
539.96
Triclinic
27H56NOScSi3
C27H56NOSi3Y
583.91
Triclinic
C27H56HoNOSi3
659.93
Triclinic
C27H56LuNOSi3
669.97
Triclinic
C64H107Gd2N3O3Si3
1365.30
Monoclinic
P2(1)/n
15.172(2)
19.047(3)
23.917(3)
90
93.045(2)
90
6902(2)
4
Molecular weight
Cryst system
Space group
ꢀ
ꢀ
ꢀ
ꢀ
P1
P1
P1
P1
˚
a (A)
9.933(2)
11.098(3)
17.233(4)
97.043(3)
102.430(3)
110.889(3)
1691.3(7)
2
10.1085(9)
11.260(1)
17.323(2)
97.540(2)
102.675(2)
112.066(2)
1732.2(3)
2
10.121(1)
11.236(1)
17.301(2)
97.495(1)
102.556(2)
112.111(1)
1729.4(4)
2
10.060(1)
11.212(1)
17.296(2)
97.322(2)
102.560(1)
111.588(1)
1723.9(4)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
q (g cmÀ3
)
1.060
0.341
173(1)
1.119
1.804
173(1)
1.267
2.409
173(1)
1.291
2.985
173(1)
1.314
1.999
173(1)
l (Mo Ka) (mmÀ1
T (K)
)
Number of reflections collected
Number of reflections with I > 2r(I)
Number of parameters
R1 (I > 2r(I))
wR2 (I > 2r(I))
Goodness-of-fit
8855
5822
317
0.0397
0.0913
1.013
0.391/À0.303
9149
5997
317
0.0342
0.0638
1.056
0.533/À0.504
8354
5948
317
0.0297
0.0733
0.995
1.296/À1.694
9014
6572
317
0.0248
0.0547
1.046
1.112/À1.337
32847
12137
666
0.0323
0.0678
1.002
0.824/À0.640
À3
˚
Maximum/minimum residual density (e A
)

Y. Luo et al. / Journal of Organometallic Chemistry 692 (2007) 536–544
543
(g) P.G. Hayes, W.E. Piers, R. McDonald, J. Am. Chem. Soc. 124
(2002) 2132;
(h) S. Bambirra, D. van Leusen, A. Meetsma, B. Hessen, J.H.
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positions and were included in the structure calculation
without further refinement of the parameters. Crystal data
and processing parameters are summarized in Table 4.
(i) S. Hajela, W.P. Schaefer, J.E. Bercaw, J. Organomet. Chem. 532
(1997) 45.
5. Supplementary materials
[4] (a) For examples dicationic alkyl species with a neutral ancillary
ligand, see: S. Arndt, B.R. Elvidge, P.M. Zeimentz, T.P. Spaniol, J.
Okuda, Organometallics 25 (2006) 793;
Crystallographic data have been deposited with the
Cambridge Crystallographic Data Center, CCDC no.
295238 for complex 1, CCDC no. 295239 for complex 2,
CCDC no. 295241 for complex 3, CCDC no. 295240 for
complex 4, CCDC no. 607633 for complex 5. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK (fax: +44 1223 336033; e-mail: deposit@ccdc.cam.
ac.uk or http://www.ccdc.cam.ac.uk).
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Acknowledgements
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This work was partly supported by a Grant-in-Aid for
Scientific Research on Priority Areas (No. 14078224,
‘‘Reaction Control of Dynamic Complexes’’) from the
Ministry of Education, Culture, Sports, Science and Tech-
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for micro elemental analysis.
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