A bis(phosphinimino)methanide lanthanum amide as catalyst for the hydroamination/cyclisation, hydrosilylation and sequential hydroamination/ hydrosilylation catalysis

Article abstract of DOI:10.1039/b514242c

[La{N(SiHMe₂)₂}₂{CH(PPh ₂NSiMe₃)₂}], which was obtained via an amine elimination starting from [CH₂(PPh₂NSiMe₃) ₂] and [La{N(SiHMe₂)₂}₃(THF) ₂], was used as catalyst for the hydroamination/cyclisation, the hydrosilylation and the sequential hydroamination/hydrosilylation reaction. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b514242c

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A bis(phosphinimino)methanide lanthanum amide as catalyst for the
hydroamination/cyclisation, hydrosilylation and sequential
hydroamination/hydrosilylation catalysis{
Marcus Rasta¨tter, Agustino Zulys and Peter W. Roesky*
Received (in Cambridge, UK) 7th October 2005, Accepted 12th December 2005
First published as an Advance Article on the web 18th January 2006
DOI: 10.1039/b514242c
characteristic signal of the {CH(PPh2NSiMe3)2}2 ligand is
[La{N(SiHMe2)2}2{CH(PPh2NSiMe3)2}], which was obtained
observed at d 17.1 ppm.
via an amine elimination starting from [CH2(PPh2NSiMe3)2]
and [La{N(SiHMe2)2}3(THF)2], was used as catalyst for the
hydroamination/cyclisation, the hydrosilylation and the sequen-
tial hydroamination/hydrosilylation reaction.
The solid state structure of complex 1 was established by single
crystal X-ray diffraction (Fig. 1). The co-ordination polyhedron is
formed by the {N(SiHMe2)2}2 groups and the {CH(PPh2-
NSiMe3)2}2 ligand. A six-membered metallacycle (N1-P1-C1-P2-
N2-La) is formed by chelation of the two trimethlysilylimine
groups to the lanthanide atom. The ring adopts a twist boat
conformation, in which the central carbon atom and the
lanthanum atom are displaced from the N2P2 least-squares plane.
The distance between the central carbon atom (C1) and the
lanthanum atom (287.5(4) pm) is longer than the average La–C
distances; however a resultant tridentate coordination of the ligand
is observed as before.12,13 In contrast to the results obtained by 1H
NMR the two {N(SiHMe2)2}2 groups are not equivalent in the
solid state. The {N(SiHMe2)2}2 group, which is attached to the
sterically more hindered side (cis to C1) is symmetrically oriented,
whereas the other {N(SiHMe2)2}2 group (trans to C1) is
asymmetric and can best be compared to the geometry found in
[(C5HPh4)2La{N(SiHMe2)2}].16 One of the silicon atoms in this
group (Si6) is getting closer to the metal centre than the others
(La–Si6 328.48(12) pm vs. La–Si3 344.40(12) pm and La–Si4
In lanthanide chemistry alkyl, amido and hydrido cyclopentadienyl
complexes and especially metallocenes such as [(C5Me5)2LnR] (R =
CH(SiMe3)2, N(SiMe3)2, H) have proven to be highly efficient
catalysts1 for a variety of olefin transformations including
hydrogenation,2 polymerization,3 hydroamination,4 hydrosilyla-
tion,5 hydroboration,6 and hydrophosphination.7 Besides the well
established cyclopentadienyl complexes today a number of non-
cyclopentadienyl lanthanide complexes, which are based on amido
and alkoxide ligands are known to be active in the hydroamina-
tion/cyclisation catalysis.8–10 Recently, we introduced the bis-
(phosphinimino)methanide {CH(PPh2NSiMe3)2}2, into yttrium
and lanthanide chemistry as a cyclopentadienyl replacement.11–13
We have previously reported the synthesis of a series of lanthanide
bis(phosphinimino)methanide complexes including yttrium, which
were used as homogenous catalysts for a number of different
catalytic applications. Very recently, Doye et al. reported on a Ti
based catalyst for a sequential hydroamination/hydrosilylation.14
Based on these results we desired to synthesise a non-cyclopenta-
dienyl lanthanide catalyst which is useable as catalyst for
hydroamination/cyclisation and the hydrosilylation reaction.
Furthermore, we wanted to study this system for a sequential
hydroamination/hydrosilylation catalysis. In contrast to the work of
Doye et al. who did not isolate the hydrosilylation product but
instead performed a hydrolytic workup to isolate the corresponding
secondary amine we were interested for obtaining the silicon species.
The title compound [La{N(SiHMe2)2}2{CH(PPh2NSiMe3)2}]
(1) was obtained via an amine elimination in boiling toluene
starting from [CH2(PPh2NSiMe3)2] and [La{N(SiHMe2)2}3-
(THF)2] (Anwander Amide).15 (Scheme 1).{ The 1H NMR
spectrum of 1 shows the characteristic signals for the two different
substituents. Thus, a singlet at d 0.13 ppm and a triplet at 2.35 ppm
are observed for the {CH(PPh2NSiMe3)2}2 ligand, whereas a
doublet at d 0.56 ppm and a septet at d 5.44 are observed for the
{N(SiHMe2)2}2 groups. In the 31P{1H} NMR spectrum the
347.68(13) pm).
A
similar effect is observed in
[(C5HPh4)2La{N(SiHMe2)2}] (326.1(2) pm vs. 347.2(2) pm for
Scheme 1
Institut fu¨r Chemie und Biochemie, Freie Universita¨t Berlin,
Fabeckstrasse 34-36, 14195, Berlin, Germany.
E-mail: roesky@chemie.fu-berlin.de; Fax: (+49)30 – 83852440;
Tel: (+49)30 – 83854004
{ Electronic supplementary information (ESI) available: Experimental
details. See DOI: 10.1039/b514242c
Fig. 1 Solid-state structure of 1, omitting hydrogen atoms.
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874 | Chem. Commun., 2006, 874–876

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one of the two independent molecules).16 Concomitant with this
effect a decrease in the La–N–Si angle (La–N4–Si6 105.6(2)u vs.
130.7(2)u for La–N4–Si5) is observed in 1. This is indicative of a
weak b-SiH monoagostic interaction as has been discussed for
other dimethylsilylamido rare-earth-metal complexes.15–17
temperature (entry 1-2). The rigorously anaerobic reaction of the
catalyst with dry, degassed aminoolefin and aminoalkyne proceeds
regiospecifically. Kinetic studies indicate zero-order behaviour in
substrate over a ten fold concentration range. Substrates bearing
bulky geminal substituents in the b-position to the amino group
(Thorpe–Ingold effect)18 could be cyclised with reasonable catalyst/
activator loadings of 1–3 mol% within good reaction times.
Substrate 5a was the most reactive of the aminoolefins, giving the
corresponding pyrrolidine within 1.5 h. Compound 8a which is
known to be a difficult substrate for this reaction, could be
converted to 2,5-dimethyl-pyrrolidine (8b) in good yield. We were
pleased to find that the formation of six membered rings can also
be performed with our catalyst (entry 6). It can be concluded that
the rate of cyclisation for aminoalkynes follows the order 5 > 6,
consistent with classical, stereoelectronically controlled, cyclisation
processes.
Since we were interested in studying the sequential hydroamina-
tion/hydrosilylation first we tested both reactions separately.
Compound 1 was used as the catalyst in the intramolecular
hydroamination/cyclisation reaction of non-activated terminal
aminoolefines and one aminoalkynes first (Table 1).§ Here we
focused on aminoalkenes because it is well known that compared
to the hydroamination of aminoalkynes, aminoalkenes exhibit
significantly lower turnover frequencies. It turned out that the
substrates are converted to the cyclic product at 60 uC in high
yield. Some compounds could be converted even at room
Beside the hydroamination, also the hydrosilylation catalysed by
1 was also investigated. The hydrosilylation of alkenes is one of the
most versatile and efficient methods for the synthesis of
alkylsilanes and their derivatives. Usually, the very air and
moisture sensitive lanthanide alkyl and hydride complexes were
used as catalysts for the hydrosilylation.19 Recently, the more
stable lanthanide amido catalyst, [La{N(SiMe3)2}3], has been
introduced as a hydrosilylation catalyst.20
Table 1 Hydroamination/cyclisation reaction of terminal aminoole-
fines and alkynes catalyzed by 1
mol% Yield
(%)a
Entry Substrate
1
Product
T/uC cat
t/h
RT
60
1.0
1.0
Quant
Quant
120
1
As substrates, we used terminal olefins and dienes, which were
used as ‘‘benchmark’’ substrates earlier (Table 2).20 All substrates
were reacted at room temperature with PhSiH3 in quantitative
yields with 1.5 mol% catalyst quantitatively to the corresponding
silanes. The catalyst loading is half of the amount used with the
[La{N(SiMe3)2}3] system. In regard of reaction temperature,
catalyst loading and yields, the activity of compound 1 is
comparable to that reported for metallocene catalysts.5 The
aliphatic substrates (entry 1-3) were converted in very high
regioselectivity to the corresponding anti-Markovnikov products.
In contrast using styrene as substrate a product mixture is
2
3
RT
60
1.1
1.1
91
Quant
150
3
60
1.3
Quant
6
Table 2 Hydrosilylation reaction of terminal olefins and dienes
catalyzed by 1a
4
5
6
60
60
60
2.0
1.7
2.2
Quant
1.5
Yield (%)b
(ratio)
Entry
1
Substrate
Product
T/h
16
99
(99 : 1)
82
36
22
2
3
24
22
99
(99 : 1)
99
(99 : 1)
Quant
4
5
30
36
99
(65 : 35)
7
60 3.0
100 3.0
—
81
50
35
99
(99 : 1)
(80 : 20)
(trans/cis)
a
Condition, 1.5 mol% of
Calculated by 1H NMR.
1 in C6D6 at room temperature.
a
b
Calculated by 1H NMR.
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from a concentrated pentane solution. 1H NMR (C6D6, 400 MHz, 20 uC):
d = 0.13 (s, 18H, SiH(CH3)2); 0.56 (d, 24H, Si(CH3)3, 3J(H,H) = 2.92 Hz);
2.35 (t, 1H, CH, 3J = 6.33 Hz); 5.44 (sp, 4HSiH(CH3)2, 3J(H,H) = 2.92 Hz);
6.8–7.5 (m, 20H Ph). 31P-NMR{1H} (C6D6, 161.7 MHz, 20 uC): d =
17.1 (s). for C39H67LaN4P2Si6 (961.34): calcd: C 48.73, H 7.02, N 5.83;
found: C 48.7 H 7.3 N 5.3.
Scheme 2
§ For the general procedure of the hydroamination and hydrosilyation
reaction see ESI.{ Crystal data for 1: C39H67LaN4P2Si6, M = 961.36,
monoclinic space group P21/n, a = 1177.80(7) pm, b = 2170.67(10) pm, c =
1976.88(15) pm, b = 92.381(6)u, V = 5049.8(5) 6 106 pm3, T = 200(2) K,
Z = 4, m = 1.081 mm21, 23698 reflections collected, R1 = 0.0323 for 5997
F > 2 (F), wR2 = 0.0542 for all 8793 data, 483 parameters, all non hydrogen
atoms calculated anisotropic; the positions of the H atoms were calculated
for idealised positions. The structure was solved and refined using
SHELXS-9721a and SHELXL-9721b. CCDC 286336. For crystallographic
data in CIF or other electronic format see DOI: 10.1039/b514242c
Table 3 Hydroamination/hydrosilylation of aminoalkynes catalyzed
by 1a
Entry Substrate
1
Product
Conditionsa
Yield (%)
1) 60 uC, 4 h
2) RT, 4 h
99
70b
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(Scheme 2). Phenylalkynes and PhSiH3 were used as substrates.
The reactions occur in quantitative selectivity with catalysts
loadings of 2 mol% (Table 3). Quantitative conversions are
observed in short reaction times at 60 uC (2a) and 100 uC (15a),
respectively, for the hydroamination and at room temperature for
the hydrosilylation step. A five membered (14b) and a six
membered ring (15b) were formed as products. To the best of
our knowledge, compound 1 is the first rare-earth catalyst to be
reported for the sequential hydroamination/hydrosilylation reac-
tion. Thus cyclic amines can now be either obtained by a direct
hydroamination of the corresponding aminoalkene or by a
stepwise hydroamination/hydrosilylation reaction of the corre-
sponding aminoalkynes. Since the hydroamination of amino-
alkenes is significantly slower than the hydroamination of
aminoalkynes the reported sequential hydroamination/hydrosilyla-
tion is an attractive alternative pathway for the synthesis of cyclic
amines.
We thank the Deutsche Forschungsgemeinschaft for financial
support.
Notes and references
{ Preparation of 1: 0.100 g (0.15 mmol) of [La{N(SiHMe2)2}3(THF)2] and
0.082 g (0.15 mmol) [CH2(PPh2NSiMe3)2] were dissolved in 20 ml toluene.
The clear solution was refluxed for 36 h. Afterwards the solution was
reduced to dryness, extracted with pentane and filtered. The filtrate was
concentrated, cooled to 278 uC and a white precipitate was formed. Yield:
0.133 g, 94%. Crystals suitable for X-ray crystallography were obtained
19 A. A. Tifonov, T. Spaniol and J. Okuda, Dalton Trans., 2004,
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20 Y. Horino and T. Livinghouse, Organometallics, 2004, 23, 12–14.
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876 | Chem. Commun., 2006, 874–876
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