Intramolecular alkylation of α-diimine ligands giving amido-imino and diamido scandium and yttrium complexes as catalysts for intramolecular hydroamination/cyclization

Article abstract of DOI:10.1021/om1002667

Treatment of alkyl complexes M(CH₂SiMe₃) ₃(THF)₂ (1a: M = Sc; 1b: M = Y) with α-diimine ligands, N,N′-bis(2,6-dimethylphenyl)-1,4-diaza-1,3-butadiene (2a) and N,N′-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene (2b), afforded the corresponding amido-imino complexes M(CH₂SiMe₃) ₂(2,6-R₂Ph-DAB-CH₂SiMe₃)(THF) (3a: M = Sc, R = Me; 3b: M = Sc, R = ⁱPr; 4a: M = Y, R = Me; 4b: M = Y, R = ⁱPr) by selective monoalkylation of one of two C=N bonds of the ligands followed by intramolecular H migration, while in the reactions with a less bulky α-diimine ligand, N,N′-bis(4-methylphenyl)-1,4-diaza-1,3- butadiene (2c), complex 1a gave an diamido complex ScCH₂SiMe ₃(4-MePh-DAB-(CH₂SiMe₃)₂)(THF) ₂ (5c) as a product of the double alkylation. Upon heating a hexane solution of 3b, intramolecular activation of a C-H bond of an isopropyl group of the ligand proceeded to give a scandium monoalkyl complex ScCH ₂SiMe₃(CH₂C₂H₄-6- ⁱPrPh-2,6-ⁱPr₂Ph-DAB-CH₂SiMe ₃)(THF) (6b). Among them, amido-imino complexes of yttrium became catalysts for intramolecular hydroamination/cyclization of 2,2-dimethyl-4- pentenylamine at room temperature.

Full text of DOI:10.1021/om1002667

Organometallics 2010, 29, 3463–3466 3463
DOI: 10.1021/om1002667
Intramolecular Alkylation of r-Diimine Ligands Giving Amido;Imino
and Diamido Scandium and Yttrium Complexes as Catalysts for
Intramolecular Hydroamination/Cyclization
Hiroshi Kaneko, Hayato Tsurugi, Tarun K. Panda, and Kazushi Mashima*
Department of Chemistry, Graduate School of Engineering Science, Osaka University,
Toyonaka, Osaka 560-8531, Japan
Received April 5, 2010
Summary: Treatment of alkyl complexes M(CH2SiMe3)3-
non-metallocenes, have been extensively studied over the past
two decades.3 Two methods have been utilized to prepare these
catalysts and catalyst precursors of group 3 metals: a salt
metathesis reaction and an alkane or amine elimination reac-
tion. A third method, an alkylation reaction of the CdN bond
of ligand precursors, such as carbodiimides and imine-based
compounds, is anticipated to be another promising and con-
venient method for synthesizing the catalysts.4,5 In fact,
Arnold et al. prepared ((amidinate)La(N(SiMe3)2)2) complexes
using a one-pot reaction of La(N(SiMe3)2)3) with appropriate
carbodiimides via the insertion of metal-amide into the CdN
bond of carbodiimides,6 and Hessen et al. reported the reaction
of the 6-amino-1,4-diazepane moiety with 1 equiv of M(CH2-
SiMe3)3(THF)n (M = group 3 metals) to give the corres-
ponding dialkyl complexes.7
(THF)2 (1a: M = Sc; 1b: M = Y) with R-diimine ligands, N,
N0-bis(2,6-dimethylphenyl)-1,4-diaza-1,3-butadiene (2a) and N,
N0-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene (2b), af-
forded the corresponding amido-imino complexes M(CH2-
SiMe3)2(2,6-R2Ph-DAB-CH2SiMe3)(THF) (3a: M = Sc, R =
Me; 3b: M = Sc, R = iPr; 4a: M = Y, R = Me; 4b: M = Y,
R = iPr) by selective monoalkylation of one of two CdN bonds
of the ligands followed by intramolecular H migration, while in
the reactions with a less bulky R-diimine ligand, N,N0-bis(4-
methylphenyl)-1,4-diaza-1,3-butadiene (2c), complex 1a gave an
diamido complex ScCH2SiMe3(4-MePh-DAB-(CH2SiMe3)2)-
(THF)2 (5c) as a product of the double alkylation. Upon heating
a hexane solution of 3b, intramolecular activation of a C;H
bond of an isopropyl group of the ligand proceeded to give a
scandium monoalkyl complex ScCH2SiMe3(CH2C2H4-6-iPrPh-
2,6-iPr2Ph-DAB-CH2SiMe3)(THF) (6b). Amongthem, amido;
imino complexes of yttrium became catalysts for intramolecular
hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine at
room temperature.
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(c) Panda, T. K.; Zulys, A.; Gamer, M. T.; Roesky, P. W. Organometallics
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€
J. Organomet. Chem. 2005, 690, 5078. (e) Rastatter, M.; Zulys, A.; Roesky,
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€
D. V.; Hessen, B. Dalton Trans. 2006, 1153. (g) Rastatter, M.; Zulys, A.;
Introduction
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(5) An alkylation of a CdN bond of a ligand backbone was reported
in several cases: Use of pyridine-bis(imine) ligands: (a) Bruce, M.;
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D. J. Chem. Commun. 1998, 2523. Use of tetradentate phenol-imine
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G.; Hammond, M. L.; Kimberley, B. S.; Scott, P. J. Organomet. Chem. 2005,
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The addition of a N-H bond across carbon-carbon un-
saturation provides an efficient and practical synthetic tool for
producing nitrogen-containing molecules. Since the initial
use of metallocene complexes of group 3 metals as catalysts
for these hydroamination reactions by Marks et al.,1 many
transition metal complexes have been used as catalysts for
intermolecular and intramolecular hydroamination/cycliza-
tion reactions of aminoalkenes, aminoalkynes, aminoallenes,
and aminodienes.2 Within group 3 metal catalyst systems,
metallocene type catalysts, as well as half-metallocenes and
*To whom correspondence should be addressed. E-mail: mashima@
chem.es.osaka-u.ac.jp. Fax: 81-6-6850-6245.
(1) (a) Gagne, M. R.; Marks, T. J. J. Am. Chem. Soc. 1989, 111, 4108.
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114, 275. (c) Li, Y.; Marks, T. J. Organometallics 1996, 15, 3770.
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(e) Molander, G. A.; Dowdy, E. D. J. Org. Chem. 1998, 63, 8983. (f) Li, Y.;
Marks, T. J. J. Am. Chem. Soc. 1998, 120, 1757. (g) M€uller, T. E.; Beller, M.
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E. D.; Pack, S. K. J. Org. Chem. 2001, 66, 4344. (j) Ryu, J. S.; Li, G. Y.;
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Chem. Soc. Rev. 2003, 32, 104. (l) Hong, S.; Kawaoka, A. M.; Marks, T. J. J.
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r
2010 American Chemical Society
Published on Web 07/02/2010
pubs.acs.org/Organometallics

3464 Organometallics, Vol. 29, No. 15, 2010
Kaneko et al.
Recently, we and the group at Dow Chemical indepen-
dently reported that a reaction of M(CH2Ph)4 (M = Zr, Hf)
with neutral R-diimine ligands produces various tribenzyl
complexes supported by monoanionic amido-imino ligands,
in which one CdN bond of the R-diimine ligand is selectively
benzylated.8-10 We reported that a rational modification of
substituents on the nitrogen atom of R-diimine ligands leads
to the selective formation of monobenzylated products as
well as double-benzylated products of zirconium and
hafnium.10 As part of our continuing studies of such selective
alkylation of R-diimine ligands, we herein report the alkyla-
tion of the CdN bond of R-di(aldimine) ligands to give
amido-imino and diamido complexes of group 3 metals
that are active catalysts for intramolecular hydroamination/
cyclization of aminoalkenes.
Results and Discussion
Reaction of Sc(CH2SiMe3)3(THF)2 (1a) with R-di(aldi-
mine) ligands, N,N0-bis(2,6-dimethylphenyl)-1,4-diaza-1,
3-butadiene (2a), N,N0-bis(2,6-diisopropylphenyl)-1,4-dia-
za-1,3-butadiene (2b), and N,N0-bis(4-methylphenyl)-1,4-diaza-
1,3-butadiene (2c), afforded monoalkylated and dialkylated
scandium complexes, in moderate yield, depending on the
steric bulkiness of the aromatic substituents at the imine
moieties. Treatment of 1a with 2a in hexane at 50 °C yielded
the corresponding amido-imino complex Sc(CH2SiMe3)2-
(2,6-Me2Ph-DAB-CH2SiMe3)(THF) (3a) in 48% yield as a
consequence of an intramolecular alkylation of one of the
two CdN bonds of 2a followed by intramolecular 1,2-
hydrogen migration (eq 1). Complex 3a was characterized
using spectral data, combustion analysis, and X-ray ana-
Figure 1. Molecular structure of 3a. All hydrogen atoms are
˚
omitted for clarity. Selected distances (A) and angles (deg):
Sc-N(1) = 2.0687(13), Sc-N(2) = 2.3474(14), N(1)-C(1) =
1.481(2), N(2)-C(2) = 1.2920(12), C(1)-C(2) = 1.489(2), N(1)-
Sc-N(2) = 74.03(5), N(1)-Sc-O(1) = 90.21(5), N(1)-Sc-
C(3) = 124.13(6), N(1)-Sc-C(4) = 121.75(6), N(2)-Sc-O(1) =
161.99(5), N(2)-Sc-C(3) = 90.94(5), N(2)-Sc-C(4) = 103.66(6),
O(1)-Sc-C(3) = 90.85(5), O(1)-Sc-C(4) = 91.94(6), C(3)-
Sc-C(4) = 114.03(6).
complexes Y(CH2SiMe3)2(2,6-Me2Ph-DAB-CH2SiMe3)(THF)
(4a) and Y(CH2SiMe3)2(2,6-iPr2Ph-DAB-CH2SiMe3)(THF)
(4b) were obtained in moderate yields as 3a and 3b. Similar
observations were reported for group 4 metal benzyl complexes
by our group and Dow Chemical Company: benzylation of one
of two CdN bonds followed by a 1,2-hydrogen shift was
observed in the reaction of 2a with either Hf(CH2Ph)4 or
Zr(CH2Ph)4 at ambient temperature.8,9b,10
1
lysis. The H NMR spectrum of 3a displayed a singlet at
δ -0.20 due to CH2SiMe3 bound to the scandium atom11
and a downfield singlet at δ 1.64 as a methylene proton of
CH2SiMe3 bound to the imine carbon atom.5f,7 Accordingly,
there was no peak assignable to the imine proton of ligand
2a. In the 13C NMR spectrum of 3a, a resonance assignable
to the imine carbon of the ligand appeared at δ 190.2,
indicating a typical downfield shift (δ 190-200).4e,f,12 These
results suggested that an alkyl group was inserted at one
of the two CdN bonds of 2b and then an imine proton
spontaneously migrated. Similarly, the reaction of 1a with
2b gave Sc(CH2SiMe3)2(2,6-iPr2Ph-DAB-CH2SiMe3)(THF)
(3b) in 25% yield. When Y(CH2SiMe3)3(THF)2 (1b) was
treated with 2a and 2b in hexane, the corresponding
Figure 1 shows the molecular structure of 3a determined
by X-ray analysis. The scandium atom of 3a adopts a
distorted trigonal bipyramidal geometry. The bond distance
(7) Ge, S.; Bambirra, S.; Meetsma, A.; Hessen, B. Chem. Commun.
2006, 3320.
(8) Mashima, K.; Ohnishi, R.; Yamagata, T.; Tsurugi, H. Chem. Lett.
˚
of Sc;N(1) (2.0687(13) A) is typical of that of Sc;
N(arylamido),11 while that of Sc;N(2) (2.3474(14) A) is
˚
2007, 36, 1420.
(9) (a) Murray, R. E. U.S. Patent 6,096,676 (Union Carbide Corp.),
2000. (b) De Waele, P.; Jazdzewski, B. A.; Klosin, J.; Murray, R. E.; Theriault,
C. N.; Vosejpka, P. C.; Petersen, J. L. Organometallics 2007, 26, 3896.
(10) Tsurugi, H.; Ohnishi, R.; Kaneko, H.; Panda, T. K.; Mashima,
K. Organometallics 2009, 28, 680.
(11) (a) Hayes, P. G.; Piers, W. E.; Lee, L. W. M.; Knight, L. K.;
Parvez, M.; Elsegood, R. J. M.; Clegg, W. Organometallics 2001, 20,
2533. (b) Estler, F.; Eickerling, G.; Herdtweck, E.; Anwander, R. Organo-
assigned to a typical distance of an σ donative Sc;N bond.4f,13
˚
Thus, the bond distance of N(2);C(2) (1.2920(12) A) is
˚
shorter than that of N(1);C(1) (1.481(2) A) and lies in the
normal range of a CdN double bond.4e,f,12 The sums of the
angles around the amido nitrogen atom N1 and the imino
nitrogen atom N2 are 359.62 and 359.73° respectively, and
the dihedral angle of the best planes of N(1);Sc;N(2) and
N(1);C(1);C(2);N(2) is 177.2°, consistent with a planar
€
metallics 2003, 22, 1212. (c) Lauterwasser, F.; Hayes, P. G.; Brase, S.; Piers,
W. E.; Schafer, L. L. Organometallics 2004, 23, 2234. (d) Bambirra, S.;
Bouwkamp, M. W.; Meetsma, A.; Hessen, B. J. Am. Chem. Soc. 2004, 126,
9182. (e) Wang, D.; Li, S.; Liu, X.; Gao, W.; Cui, D. Organometallics 2008,
27, 6531. (f) Ward, B. D.; Lukesova, L.; Wadepohl, H.; Bellemin-Laponnaz,
S.; Gade, L. H. Eur. J. Inorg. Chem. 2009, 866.
(12) (a) Liu, B.; Cui, D.; Ma, J.; Chen, X.; Jing, X. Chem. ;Eur. J.
2007, 13, 834. (b) Wang, D.; Cui, D.; Miao, W.; Li, S.; Huang, B. Dalton
Trans. 2007, 4576. (c) Gao, W.; Cui, D. J. Am. Chem. Soc. 2008, 130, 4984.
(13) (a) Emslie, D. J. H.; Piers, W. E.; Parvez, M.; McDonald, R.
Organometallics 2002, 21, 4226. (b) Gao, W.; Cui, D.; Liu, X.; Zhang, Y.;
Mu, Y. Organometallics 2008, 27, 5889. (c) Carver, T. C.; Benitez, D.;
Miller, L. K.; Williams, N. B.; Tkatchouk, E.; Goddard, A. W.; Diaconescu,
L. P. J. Am. Chem. Soc. 2009, 131, 10269.

Note
Organometallics, Vol. 29, No. 15, 2010 3465
Table 1. Intramolecular Hydroamination/Cyclization of
2,2-Dimethyl-4-pentenylamine Catalyzed by Group 3 Metal
Alkyl Complexesa
entry
cat.
temp. (°C)
time (h)
yield (%)b
1
2
3
4
5
6
7
8
3a
3a
3ac
3b
3b
3bc
4a
4b
5c
rt
60
rt
rt
60
rt
rt
rt
rt
60
rt
5
5
5
5
5
5
<5
53
10
<5
>95
48
5
10 min
64
Figure 2. Molecular structure of 5c. All hydrogen atoms are
˚
>95
<5
15
omitted for clarity. Selected distances (A) and angles (deg): Sc-
9
5
5
5
5
2
5
N(1) = 2.115(2), Sc-N(2) = 2.080(2), N(1)-C(1) = 1.481(4),
N(2)-C(2)=1.482(4), C(1)-C(2)=1.523(4), N(1)-Sc-N(2) =
81.27(11), N(1)-Sc-O(1)=89.06(10), N(1)-Sc-O(2)=130.44(10),
N(1)-Sc-C(3)=119.65(12), N(2)-Sc-O(1)=154.89(10), N(2)-
Sc-O(2) = 90.77(10), N(2)-Sc-C(3) = 113.09(12), O(1)-Sc-
O(2) = 77.94(9), O(1)-Sc-C(3) = 91.85(11), O(2)-Sc-C(3) =
108.51(11).
10
11
12
13
14
5c
5cc
6b
6b
6bc
9
rt
60
rt
<5
>95
20
a Conditions: [cat]:[substrate] = 0.01:0.2 (in mmol) in toluene-d8
(0.6 mL) under Ar atmosphere using Cp2Fe as an internal standard
(1.7 mg). b NMR yield based on the intensity of the product with respect
to Cp2Fe. c 5 mol % of [Ph3C][B(C6F5)4] was used as a cocatalyst.
five-membered metallacyclic ring, indicating the presence of
π-orbitals of N(1) and N(2) at the metal center.14
similar to that for the Sc-N(arylamido) bond.11 The distances
When complex 1a was treated with less bulky compound
2c, double alkylation of both CdN bonds of 2c gave
ScCH2SiMe3(4-MePh-DAB-(CH2SiMe3)2)(THF)2 (5c) in
65% yield (eq 2), though the corresponding yttrium complex
could not be obtained. The 1H NMR spectrum of 5c displayed
an ABq [δ-0.09 and 0.19 (2JHH = 11.1 Hz)] assignable to the
methylene group of the ScCH2SiMe3 moiety11 and a doublet of
doublet signals [δ 1.35 (2JHH=14.2 Hz, 3JHH = 2.0 Hz) and
1.50 (2JHH=14.2 Hz, 3JHH=10.4 Hz)] due to binding of the
methylene proton of the CH2SiMe3 group bound to the imine
carbon of the ligand.5f,7 A similar double alkylation of a dia-
zadiene ligand was observed for the reactions of Hf(CH2Ph)4
and Zr(CH2Ph)4 with less bulky R-diimine compounds.10
˚
˚
of N(1)-C(1) (1.481(1) A) and N(2)-C(2) (1.482(4) A) of 4c
are in the normal range of a single bond.15
When a hexane solution of 3b was heated at 70 °C for 13 h,
an intramolecular C-H bond activation of a methyl moiety
of an isopropyl group of 3b proceeded along with the release
of Me4Si to give the scandium monoalkyl complex ScCH2-
SiMe3(CH2C2H4-6-iPrPh-2,6-iPr2Ph-DAB-CH2SiMe3)(THF)
(6b) in 48% yield (eq 3). Similar scandium complexes have
been reported in literature.16 In the 1H NMR spectrum of 6b,
the methylene protons of the remaining ScCH2SiMe3 group
appeared as an ABq pattern at δ -0.38 and -0.18 (2JH-H
=
11.1 Hz), and the resonance of the methylene protons of the
metalated moiety was observed as two doublets of doublets at
δ 0.31 and 0.69 (2JH-H = 12.1 Hz, 3JH-H = 3.3 Hz), which
was associated with one multiplet at δ 3.29 in a 1:1 integral
i
ratio. Moreover, there were four distinct Pr-methine reso-
nances: three septets and one multiplet for the four methyne
protons of the isopropyl groups.
The molecular structure of 5c was clarified by X-ray
crystallographic analysis (Figure 2), confirming the double
alkylation of both imine moieties of 1c with an anti-stereo-
chemistry. The geometry around the scandium atom is a
distorted trigonal bipyramidal in which N(1), C(3), and O(2)
are in equatorial positions and N(2) and O(1) occupy the
With these scandium and yttrium complexes in hand, we
tested their catalyst activity for intramolecular hydroamina-
tion/cyclization of 2,2-dimethyl-4-pentenylamine, which is a
typical substrate, to elucidate their catalytic performance,
and the results are summarized in Table 1. All four scandium
complexes 3a, 3b, 5c, and 6b were active catalysts at 60 °C,
although almost no catalytic activity for these four scandium
˚
apical positions. The bond distances of Sc-N(1) (2.115(2) A)
˚
and Sc-N(2) (2.080(2) A) are assigned to a typical distance
(14) Skinner, M. E. G.; Mountford, P. J. Chem. Soc., Dalton Trans.
2002, 1694.
(15) (a) Kliegman, J. M.; Barnes, R. K. Tetrahedron 1970, 26, 2555.
(b) Buys, I. E.; Elgafi, S.; Field, L. D.; Hambley, T. W.; Messerle, M. A.
Inorg. Chem. 1994, 33, 1539. (c) Abrams, M. B.; Scott, B. L.; Baker, R. T.
Organometallics 2000, 19, 4944. (d) Schmid, M.; Eberhardt, R.; Klinga, M.;
Leskela, M.; Rieger, B. Organometallics 2001, 20, 2321.
(16) (a) Hayes, P. G.; Piers, W. E.; Parvez, M. Organometallics 2005,
24, 1173. (b) Knight, L. K.; Piers, W. E.; McDonald, R. Organometallics
2006, 25, 3289. (c) Conroy, K. D.; Hayes, P. G.; Piers, W. E.; Parvez, M.
Organometallics 2007, 26, 4464.

3466 Organometallics, Vol. 29, No. 15, 2010
Kaneko et al.
complexes was observed at room temperature. Comparison
of the catalytic activities of 3a, 3b, and 6b with those of
literature11c revealed the catalytic activities were relatively
high. The catalytic activity of 3b was higher than that of 3a,
indicating that steric bulkiness around the metal center is
necessary for the high activity. The difference in catalytic
activities between 3b and 6b was attributed to the rate of the
formation of the Sc-N bond. The formation of the Sc-N
bond of 6b was faster than that of 3b because of the strained
Sc-C bond of 6b.17 In addition, the cationic catalyst gener-
ated from the combination of 3b with [Ph3C][B(C6F5)4]
exhibited higher catalytic activity than 3b; this trend was
similar to those of the literature.11c On the other hand, the
catalytic activities of cationic catalysts of 3a and 5c were
lower than those of 3a and 5c (entries 3, 6, 11, 14). Yttrium
complexes 4a and 4b were more active than their scandium
analogues and the yttrium complexes catalyzed hydroami-
nation at room temperature (entries 7 and 8). We presumed
that the different catalytic activities between scandium and
yttrium were due to the different ionic radii of the metal
center and the different bond strengths of the metal-nitrogen
bond. The catalytic activities of 4a and 4b were higher than
those found for the yttrium dialkyl catalyst with a N,N0-bis-
(2,6-diisopropylphenyl)benzamidinate ligand.3f
We demonstrated a one-pot synthesis of some alkyl com-
plexes of scandium and yttrium. The substituents on the
nitrogen atoms of the R-diimine ligands significantly affected
the reaction pattern upon treatment with M(CH2SiMe3)3-
(THF)2 (1a: M = Sc; 1b: M = Y): (1) single alkylation of
the diaryl R-di(aldimine) ligand gave amido-imino complexes
3a-b and, 4a-b; (2) double alkylation of the bis(4-(Me)-
phenyl)-R-di(aldimine) ligand afforded a bis(amido) complex
5c. When a hexane solution of 3b was heated, scandium
monoalkyl complex 6b was isolated by the activation of a
C-H bond of the isopropyl group. These complexes and their
cationic species served as catalyst precursors for intramolecular
hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine.
Acknowledgment. We thank the Grobal-COE Fellow-
ship to H.K. T.K.P. is thankful for the JSPS Fellowship. H.T.
acknowledges financial support by a Grant-in-Aid for Young
Scientists(B) and The Sumitomo Foundation. K.M. ac-
knowledges financial support by a Grant-in-Aid for Scientific
Research(A). This work was supported by the Core Research
for Evolutional Science and Technology (CREST) program
of the Japan Science and Technology Agency (JST), Japan.
Supporting Information Available: Experimental details for
the syntheses of all compounds, crystallographic data for 3a and
5c, and their CIF files. These material are available free of
charge via the Internet at http://pubs.acs.org.
(17) Bambirra, S.; Boot, S. J.; Leusen, D. V.; Meetsma, A.; Hessen, B.
Organometallics 2004, 23, 1891.