Rare-earth metal complexes stabilized by amino-phosphine ligand. Reaction with mesityl azide and catalysis of the cycloaddition of organic azides and aromatic alkynes

Article abstract of DOI:10.1039/b811363g

Stoichiometric reactions between mesityl azide (MesN₃, Mes = 2,4,6-C₆H₂Me₃) and amino-phosphine ligated rare-earth metal alkyl, LLn(CH₂SiMe₃)₂(THF) (L = (2,6-C₆H₃

Full text of DOI:10.1039/b811363g

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www.rsc.org/dalton | Dalton Transactions
Rare-earth metal complexes stabilized by amino-phosphine ligand. Reaction
with mesityl azide and catalysis of the cycloaddition of organic azides and
aromatic alkynes†
Bo Liua,b and Dongmei Cui*a
Received 4th July 2008, Accepted 23rd September 2008
First published as an Advance Article on the web 20th November 2008
DOI: 10.1039/b811363g
Stoichiometric reactions between mesityl azide (MesN3, Mes = 2,4,6-C6H2Me3) and amino-phosphine
ligated rare-earth metal alkyl, LLn(CH2SiMe3)2(THF) (L = (2,6-C6H3Me2)NCH2C6H4P(C6H5)2;
i
Ln = Lu (1a), Sc (1b)), amide, LLu(NH(2,6-C6H3 Pr2))2(THF) (2) and acetylide at room temperature
gave the amino-phosphazide ligated rare-earth metal bis(triazenyl) complexes, [L(MesN3)]Ln[(MesN3)-
i
(CH2SiMe3)]2 (Ln = Lu (3a); Sc (3b)), bis(amido) complex [L(MesN3)]Lu[NH(2,6-C6H3 Pr2)]2 (4), and
∫
bis(alkynyl) complex (5) (L(MesN3)Lu (C CPh)2)2, respectively. The triazenyl group in 3 coordinates
2
to the metal ion in a rare h -mode via Nb and Ng atoms, generating a triangular metallocycle. The
amino-phosphazide ligand, L(MesN3), in 3, 4 and 5 chelates to the metal ion in a h -mode via Na and
3
Ng atoms. In the presence of excess phenylacetylene, complex 3a isomerized to 3¢, where the triazenyl
group coordinates to the metal ion in a h mode via Na and Ng atoms. Complexes 1, 2, 3 and 4 have
3
shown an unprecedented catalytic activity towards the cycloaddition of organic azides and aromatic
alkynes to afford 1,5-disubstituted 1,2,3-triazoles selectively.
selective cycloaddition of organic azides and aromatic alkynes at
ambient temperature will also be presented.
Introduction
Rare-earth metal complexes have shown rich and unique
reactivities1 and distinguished catalytic capabilities toward or-
ganic synthesis.2 For instance rare-earth metal complexes can
catalyze hydrogenation, hydrosilylation, hydroamination and
hydrophosphination,3 trimerization of benzonitrile,4 and dimer-
ization of terminal alkynes1h,i as well as the addition of terminal
alkynes to carbodiimines.5 Such properties, to some extent, are
affected by the steric and electronic environment of the metal
center. Therefore, the novel reactivity and catalytic activity of
rare-earth metal complexes can be achieved through careful
ligand-design. Our group has successfully synthesized rare-earth
metal bis(alkyl) complexes bearing amino-phosphine ligands with
“large” and “soft” phosphorus donors, which have shown unique
C–H activation motivated by the insertion of carbodiimide into
the lutetium-alkyl species.6 This result interested us in exploiting
other reactivities of this series of rare-earth metal complexes.
Herein, we wish to report the reactions between these complexes
and mesityl azide to afford amino-phosphazide ligated rare-earth
metal complexes with unique coordination geometry. In addition
the unprecedented catalytic activity of these complexes for the 1,5-
Result and discussion
Reaction of the alkyl complexes with mesityl azide (MesN3)
Treatment of the lutetium bis(alkyl) complex 1a LLu(CH2-
SiMe3)2(THF) (L = (2,6-C6H3Me2)NCH2C6H4P(C6H5)2),1e with
MesN3 (Mes = 2,4,6-C6H2Me3) at a molar ratio of 1:3
gave an amino-phosphazide supported triazenyl complex 3a,
[L(MesN3)]Lu[(MesN3)(CH2SiMe3)]2. In this process, one MesN3
inserted into the Lu–P bond, whilst another two molecules
of MesN3 inserted into Lu–CH2SiMe3 bonds, which was evi-
denced by the downfield shifting of the methylene resonances of
CH2SiMe3 to 3.48 and 3.53 ppm as compared with -0.33 ppm in
1a (Scheme 1).
aState Key Laboratory of Polymer Physics and Chemistry, Changchun
Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin
Street, Changchun 130022, China. E-mail: dmcui@ciac.jl.cn; Fax: (+86)
431-8526-2773
bGraduate School of the Chinese Academy of Sciences, Beijing 100039, China
Scheme 1 Stoichiometric reaction of 1 with mesityl azide.
† Electronic supplementary information (ESI) available: Molecular struc-
ture of 3b, 1H NMR and 13C NMR spectra of the isolated triazoles. CCDC
reference numbers 670207–670210 and 673960. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/b811363g
Complex 3a adopts butterfly geometry with the phosphazide
ligand forming the body and the two triazenyl moieties generating
550 | Dalton Trans., 2009, 550–556
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the wings (Fig. 1).‡ It is noteworthy that the triazenyl moiety
addition of the metal alkyl species Lu–CH2Si(CH3)3 in 1a to the
terminal nitrogen (Ng ) of mesityl azide gave 3a via intermediate
D8 (Scheme 2). It is known that an azide ligand coordinates to a
2
coordinates to the Lu ion in a h -mode via Nb and Ng atoms,
generating a rare triangular metallocycle. Azide compounds
usually exist as A and B resonances, and the latter is favored when
they are attacked by a nucleophilic agent.7 Therefore, nucleophilic
1
transition metal center in three modes: h -mode via a Na 9 or Ng 10
3
2
atom and h -mode via Na and Ng atoms.11 Thus the h -mode via
Nb and Ng atoms as seen in 3a is unprecedented, as far as we are
aware.
Scheme 2 The probable reaction pathway for the formation of com-
plex 3a.
The bond lengths formed by the Lu atom and the amido
˚
˚
nitrogen atoms, Lu–N(1) (2.151(7) A), Lu–N(5) (2.264(6) A) Lu–
12
˚
N(8) (2.228(6) A) are comparable to the values in the literature.
Fig. 1 Molecular structure of 3a (hydrogen atoms omitted for clarity,
The bond distances between the Lu atom and the imido nitrogen
thermal ellipsoids drawn to 50% probability level). Selected bond distances
˚
˚
˚
(A) and angles (deg.): Lu–N(1) 2.151(7), Lu–N(2) 2.367(7), Lu–N(4)
atoms, Lu–N(2) (2.367(7) A), Lu–N(4) (2.565(6) A), Lu–N(6)
˚
˚
2.565(6), N(2)–N(3) 1.377(8), N(3)–N(4) 1.289(8), Lu–N(5) 2.264(6),
Lu–N(6) 2.332(7), Lu–N(8) 2.228(6), Lu–N(9) 2.388(6), N(5)–N(6)
1.313(8), N(6)–N(7) 1.304(9), N(8)–N(9) 1.323(9), N(9)–N(10) 1.298(8);
N(2)–Lu–N(4) 52.1(2), N(5)–Lu–N(6) 33.14(19), N(8)–Lu–N(9) 33.1(2).
(2.332(7) A) Lu–N(9) (2.388(6) A) are within the reasonable
range for a Lu–Nimido interaction.13 The bond length of P–N(2),
1.638(7) A, is shorter than that of a P–N single bond but longer
than that of a P N double bond. The average N–N bond length
(1.310 A) in the triazenyl moieties falls in between those for the
11
˚
14
=
˚
‡ Crystal data of 3a: C62H80N10Si2PLu, Mr = 1227.48, Monoclinic, space
single bond and double bond, indicating delocalized p-electrons
over the N–N–N linkage. The bond angles of N(5)–Lu–N(6)
and N(8)–Lu–N(9) (av. 33.12◦) are much smaller than that of
˚
group P2(1), a = 12.1586(10), b = 21.8677(17), c = 12.8260(10) A, a = 90,
◦
3
b = 112.5040(10), g = 90 , V = 3150.5(4) A , Z = 2, rcalcd = 1.294 gcm-3,
˚
m(MoKa) = 1.675 mm-1, 17814 reflections measured, and 8638 reflections
with I>2s(I). R(int) = 0.0672, Final R1 = 0.0499 (observed data), wR2 =
0.0981 (all data).Crystal data of 3b: C62H80N10Si2PSc, Mr = 1097.47,
Monoclinic, space group P2(1), a = 12.0822(10), b = 21.7373(18), c =
N(2)–Lu–N(4) (52.1(2)◦), in agreement with h - and h -
coordination modes, respectively.
2
3
Following a similar procedure, the reaction of the scandium
bis(alkyl) complex 1b, LSc(CH2SiMe3)2(THF), with 3 equiv.
MesN3 gave 3b, [L(MesN3)]Sc[(MesN3)(CH2SiMe3)]2 (Scheme 1).
X-Ray analysis confirmed that 3b†‡ is an analogue of 3a. The
average bond angle of N(5)–Sc–N(6) and N(8)–Sc–N(9) (av.
34.47(8)◦) is larger than that in complex 3a and the corresponding
bond lengths of Sc–Namido and Sc–Nimino in 3b are slightly shorter
than those in 3a, which is due to the smaller radius of the scandium
ion.15
In the presence of excess phenylacetylene, 3a isomerized to
3¢, but the replacement of the triazenyl ligand by the excess
phenylacetylene as in the case of cobalt azide complex did not
happen (Scheme 3).16
◦
3
˚
˚
12.8265(10) A, a = 90, b = 112.7380(10), g = 90 , V = 3106.9(4) A ,
Z = 2, rcalcd = 1.173 gcm-3, m(MoKa) = 0.228 mm-1, 17592 reflections
measured, and 9196 reflections with I>2s(I). R(int) = 0.0424, Final
R1 = 0.0456 (observed data), wR2 = 0.0772 (all data).Crystal data of
3¢: The unit cell of 3¢ was found to contain one and a half molecules
of benzene. C71H89N10Si2PLu, Mr = 1344.64, Monoclinic, space group
˚
P2(1)/n, a = 14.5568(9), b =◦ 21.7750(13), c = 22.0756(13) A, a =
3
˚
90, b = 91.3220(10), g = 90 , V = 6995.5(7) A , Z = 4, rcalcd
=
1.277 gcm-3, m(MoKa) = 1.515 mm-1, 38977 reflections measured, and
10545 reflections with I>2s(I). R(int) = 0.0532, Final R1 = 0.0424
(observed data), wR2 = 0.0885 (all data).Crystal data of 4: C60H72N6 PLu,
Mr = 1083.18, Triclinic, space group P-1, a = 13.2430(19), b = 13.321(2),
◦
˚
c = 19.106(3) A, a = 71.435(3), b = 84.227(3), g = 83.052(3) , V =
3164.6(8) A , Z = 2, rcalcd = 1.137 gcm-3, m(MoKa) = 1.622 mm-1, 17730
3
˚
reflections measured, and 6317 reflections with I>2s(I). R(int) = 0.0914,
Final R1 = 0.0906 (observed data), wR2 = 0.2072 (all data). There is a large
void in the structure, forming a channel along the c-axis. This contains
highly disordered solvent molecules which could not be successfully
modelled.Crystal data of 5: The unit cell of 5 was found to contain two
molecules of benzene, these molecules exhibit disorder which could not
be modeled successfully. C116H104N8P2Lu2, Mr = 2021.95, Triclinic, space
The 1H NMR spectrum of 3¢ was far from that of 3a: two singlets
at 0.18 ppm and 0.21 ppm were assignable to the silylmethyl
that showed as a singlet at 0.26 ppm in 3a; the resonances
of the benzyl protons, CH2C6H4P, shifted obviously downfield
(4.33 ppm, 5.62 ppm) as compared with those in 3a (2.23 and
2.26 ppm). Complex 3¢ is an isomer of 3a with the triazenyl moities
˚
group P-1, a = 13.6136(10), b = 14.4341(11), c = 27.0624(19) A, a =
◦
3
˚
79.4710(10), b = 76.8340(10), g = 73.9160(10) , V = 4934.5(6) A , Z = 2,
rcalcd = 1.361 gcm-3, m(MoKa) = 2.074 mm-1, 27957 reflections measured,
and 13680 reflections with I>2s(I). R(int) = 0.0369, Final R1 = 0.0486
(observed data), wR2 = 0.1005 (all data).
3
coordinating to the Lu ion in h -mode via Na and Ng atoms
(Fig. 2).‡ The bond angles of N(5)–Lu–N(7) and N(8)–Lu–N(10)
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Scheme 4 Stoichiometric reaction of 2 with mesityl azide.
Scheme 3 Isomerization of complex 3a in the presence of excess
phenylacetylene.
Fig. 2 Molecular structure of 3¢ (hydrogen atoms omitted for clarity;
thermal ellipsoids drawn to 50% probability level). Selected bond dis-
Fig. 3 Molecular structure of 4 (hydrogen atoms omitted for clarity;
thermal ellipsoids drawn to 50% probability level). Selected bond distances
˚
tances (A) and angles (deg.): Lu(1)–N(1) 2.173(3), Lu(1)–N(2) 2.424(3),
˚
(A) and angles (deg.): Lu–N(1) 2.532(9), Lu–N(3) 2.407(9), Lu–N(4)
Lu(1)–N(4) 2.544(3), N(2)–N(3) 1.371(4), N(3)–N(4) 1.266(4), Lu(1)–N(5)
2.439(3), Lu(1)–N(7) 2.359(3), Lu(1)–N(8) 2.411(3), Lu(1)–N(10) 2.357(3),
N(5)–N(6) 1.294(4), N(6)–N(7) 1.327(4), N(8)–N(9) 1.302(4), N(9)–N(10)
1.322(4), N(8)–C(37) 1.461(5), N(5)–C(50) 1.463(5); N(2)–Lu(1)–N(4)
51.39(10), N(7)–Lu(1)–N(5) 53.12(11), N(10)–Lu(1)–N(8) 53.24(11).
2.175(9), Lu–N(5) 2.142(10), Lu–N(6) 2.165(9), N(1)–N(2) 1.261(11),
N(2)–N(3) 1.377(11), N(3)–P(1) 1.669(9); N(1)–Lu–N(3) 51.4(3),
N(4)–Lu–N(5) 125.7(3), N(2)–N(1)–Lu 98.6(6), N(2)–N(3)–Lu 101.0(6),
N(1)–N(2)–N(3) 108.8(8), N(2)–N(1)–C(52) 111.0(9), N(2)–N(3)–P(1)
110.9(7), P(1)–N(3)–Lu 148.1(5).
(av. 53.18(11)◦) are similar to that of N(2)–Lu–N(4) (51.39(10)◦),
in agreement with h - coordination mode.
3
are similar to those in complexes 3. The N(4)–Lu–N(5) bond
angle, 125.7(3)◦, is larger than the corresponding N(3)–Lu–N(2)
(119.7(3)◦) in 2.
Reaction of the amido complex with MesN3
Stoichiometric reaction between lutetium bis(amido) complex 2,
LLu(NH(2,6-C6H3 Pr2))2(THF), and MesN3 afforded an amino-
Reaction of the alkynyl complex with MesN3
i
phosphazide supported amido complex 4, [L(MesN3)]Lu[NH(2,6-
C6H3 Pr2)]2, indicating insertion of one MesN3 molecule into the
Lu–P bond whilst the two amido groups remained untouched
(Scheme 4).
Protonolysis of the lutetium complex 1a with phenylacetylene
led to the formation of an acetylide intermediate by release of
TMS. Upon addition of MesN3 to this acetylide intermediate, an
i
∫
amino-phosphazide ligated complex 5, (L(MesN3)Lu(C CPh)2)2,
The resonances at 3.24 and 3.45 ppm and the singlet at
6.70 ppm were assigned to the methyl and aryl protons of MesN3,
respectively. The molecular structure of 4 was figured out to be
a heteroleptic monomer (Fig. 3).‡ The monoanionic phosphazide
ligand and two amino moieties coordinate to the Lu ion, forming a
distorted trigonal-bipyramidal geometry. Atoms N(1), N(3), N(4)
was obtained via MesN3 insertion into the Lu–P bond similar to
that in 3 and 4 (Scheme 5).
X-Ray analysis confirmed that complex 5 is a dimer (Fig. 4).‡
The acetylide groups coordinate to the Lu ions in bridging
and terminal modes, respectively. The two trans-located amino
3
phosphazide moieties bond to the Lu ions in h - mode via Na
are equatorial, with Lu lying out the plane (0.875 A). While atoms
and Ng atoms. Each metal center adopts a distorted tetragonal
bipyramidal geometry. Atoms C(1), C(9), N(2) and C(17) are
equatorial, while atoms N(1) and N(4) are located at the axial
˚
N(5) and N(6) are located at the axial positions. The bond lengths
and angles of the amino-phosphazide moiety within complex 4
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Table 1 Cycloaddition of alkynes and organic azides catalyzed by rare-
earth metal complexesa
Microstructure
Entry Cat. R1
R2
Yield (%)c 1,4-c
1,5-c
Scheme 5 Synthesis of complex 5.
1b
2
3
4
5
6
7
8
9
–
Mes
Mes
Mes
Mes
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
99
93
93
94
92
93
91
92
55
0
0
0
0
0
0
0
0
0
0
0
0
45
100
100
100
100
100
100
100
100
100
100
100
100
1a
1b
2
1a
1a
1a
1a
1a
1a
3a
3b
4
C6H5
C6H5CH2
(CH2)4CH C6H5
CH3(CH2)3 C6H5
Mes
Mes
Mes
Mes
Mes
p-C6H4Me 92
m-C6H4F
C6H5
C6H5
C6H5
10
93
99
98
99
11
12
13
a Temperature: r.t.; Time: 72 h; R1N3:R2CCH:Cat. = 100:100:2; [R1N3] =
0.5 M. b Temperature: 60 ◦C. c The products were isolated through silica
gel with hexane/EtOAc (3:1) as the eluent.
[Cp*RuCl] derivatives are also efficient catalysts for the cycloaddi-
tion of alkynes and azides to give 1,5-disubstituted 1,2,3-triazoles
at high temperature, which represents the only catalytic system
providing 1,5-selectivity to date.21 Strikingly, at room temperature,
complexes 1a, 1b and 2 could catalyze the cycloaddition of azides
and alkynes to afford 1,5-disubstituted triazoles exclusively within
72 h.22
Fig.
4
Molecular structure of 5 (hydrogen atoms omitted for
clarity; thermal ellipsoids drawn to 50% probability level).
Selected bond distances (A) and angles (deg.): Lu(1)–C(1) 2.465(5),
˚
Lu(2)–C(9) 2.474(5), Lu(1)–C(17) 2.372(6), Lu(2)–C(25) 2.344(6),
Lu(1)–C(9) 2.474(6), Lu(2)–C(1) 2.482(6), C(1)–C(2) 1.212(7), C(9)–C(10)
1.219(7), C(17)–C(18) 1.211(7), C(25)–C(26) 1.224(7); C(1)–Lu(1)–C(9)
79.22(18), C(9)–Lu(2)–C(1) 78.89(18), Lu(1)–C(1)–Lu(2) 99.78(19),
Lu(2)–C(9)–Lu(1) 99.8(2), C(2)–C(1)–Lu(1) 102.2(4), C(2)–C(1)–Lu(2)
151.9(4).
The changes of central metal type from lutetium (1a) to
scandium (1b) and the s-bonded group from alkyl (1a) to amido
(2) had no influence on the catalytic activity and the selectivity
(Table 1, entries 2–4). Similarly, varying from aromatic azides
to aliphatic azides, the corresponding 1,5-disubstituted 1,2,3-
triazoles were also isolated quantitatively and selectively (Table 1,
entries 5–8),23 indicating that variation in the sterics and electronics
of the substituents of the organic azides did not induce changes in
the conversion and regio-regularity of the products, at least to the
extent represented by the cases herein. In contrast, the catalytic
performances of these complexes were strongly dependent on the
nature of the alkynes. Although treatment of mesityl azide with
different aromatic alkynes generated 1,5-selective 1,2,3-triazoles
in high yields (Table 1, entries 9,10), only traces of cycloaddition
products were obtained when switching to the aliphatic alkynes.
Moreover no cycloaddition between internal alkynes and azides
was observed with this present system. This result is in striking
contrast to the [Cp*RuCl] based system, where the regio-selectivity
and conversion are obviously influenced by the nature of azides
not alkynes.21a
positions. The Lu(1)(m–CCPh)2Lu(2) core is a twisted plane as
seen from the dihedral angle Lu(1)–C(1)–Lu(2)–C(9) of -11.70◦.
This angle is smaller than that found in lanthanum bis(alkynyl)
complex (-20.07(6)◦).1g The m-acetylide bridges are asymmetric,
leading to a much larger Lu(2)–C(1)–C(2) bond angle (151.9(4)◦)
as compared with Lu(1)–C(1)–C(2) (102.2(4)◦). The bond length
of Lu–m–C (av. 2.474 A) is reasonably longer than that of Lu–s–C
(av. 2.358 A), comparable to that found in the lutetium terminal
alkynyl complex bearing a Cp ligand.1d
˚
˚
Catalysis of the cycloaddition of organic azides and alkynes
1,2,3-Triazoles have received increasing attention17 owing to their
important applications in organic, organometallic and material
chemistries as well as in the pharmaceutical and agricultural
industries.18 Huisgen’s dipolar cycloaddition of organic azides and
alkynes is the most convenient route to afford 1,2,3-triazoles,
however, it generates mixtures of regioisomers.19 For instance,
when a mixture of mesityl azide (MesN3) and phenylacetylene
was stirred at 60 ◦C for 3 days, approximately equivalent 1,4- and
1,5-disubstituted 1,2,3-triazole isomers were obtained (Table 1,
entry 1). The well known synthetic method for 1,4-disubstituted
1,2,3-triazoles is the “click” reaction of alkynes and azides
catalyzed by a Cu(I) system at room temperature.20 Meanwhile,
Complex 3 provided the same catalytic performances as its
congener 1 (Table 1, entry 11,12), however, complexes 3¢ and 5
couldn’t catalyze the cycloaddition. These results suggested that
in the cycloaddition process, MesN3 reacted with 1 prior to the
phenylacetylene to form intermediate 3. This was further proved
by monitoring the reaction using NMR technique. No TMS
resonance was detected, indicating that the protonolysis reaction
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between 1 and phenylacetylene did not occur. Therefore complex
3 was the true catalyst, when the cycloaddition was catalyzed
by the alkyl complex. This is in contrast to the Cu(I) catalyzed
“click” reaction, where copper(I) firstly deprotonates the alkyne
to afford the corresponding acetylide intermediate.20 Complex 4
also provided the same catalytic performances as its congener 2
(Table 1, entry 13), acting as the true active species. The similarity
among the intermediates 3 and 4 is that both of them contain a
bulky amino phosphazide ligand. Thus, the selectivity might be
governed by the bulky environment of the metal center.24†
analyses were performed at National Analytical Research Centre
of Changchun Institute of Applied Chemistry.
Complex 3a
To a hexane suspension of complex 1a (0.15 g, 0.18 mmol),
mesityl azide (0.06 g, 0.37 mmol, 1 mL hexane) was added.
The precipitate disappeared gradually with the addition. After
30 min, an orange precipitate appeared, and the stirring of the
reaction mixture was continued for 10 h at room. Complex 3a was
1
obtained by filtration (0.14 g, 58%). H NMR (400 MHz, C6D6,
25 ◦C): d = 0.26(s, 18H, Si(CH3)3), 1.90(s, 6H, C6H3(CH3)2),
2.10(s, 3H, C6H2(CH3)3), 2.23(d, 2J(H, H) = 6.4 Hz, 1H,
CH2C6H4P), 2.26(d, 2J(H, H) = 6.4 Hz, 1H, CH2C6H4P), 2.33(s,
6H, C6H2(CH3)3, 6H, C6H2(CH3)3), 2.37(s, 12H, C6H2(CH3)3),
3.48(d, 2J(H, H) = 12.4 Hz, 2H, CH2Si), 3.53(broad, 2H, CH2Si),
6.64(s, 2H, C6H2(CH3)3), 6.66(d, 3J(H, H) = 4.8 Hz, 1H, C6H4),
6.77(td, 3J(H, H) = 6.8 Hz, 4J(H, H) = 2.8 Hz, 1H, C6H4),
Conclusions
Reactions of mesityl azide with amino-phosphine ligated rare-
earth metal alkyl, amide and acetylide, respectively, afforded
the corresponding rare-earth metal triazenyl, amido and alkynyl
complexes based on amino-phosphazide ligands. The triazenyl
moiety coordinated to the metal ion with Nb and Ng atoms,
forming a rare h - mode, which transformed into h - mode in the
presence of excess phenylacetylene. These complexes exhibited an
unprecedented catalytic activity for the cycloaddition of organic
azides and aromatic alkynes to afford 1,5-disubstituted 1,2,3-
triazoles, of which the selective formation might be governed by the
bulkiness of the metal center. We are in the process of investigating
the details of the mechanism.
3
2
3
6.83(s, 4H, C6H2(CH3)3), 6.91(t, J(H, H) = 7.6 Hz, 1H, C6H4),
3
3
7.00(dd, J(P, H) = 15.2 Hz, J(H, H) = 7.6 Hz, 1H, C6H4),
3
7.09(t, J(H, H) = 7.6 Hz, 1H, C6H3(CH3)2), 7.13(broad, 4H,
P(C6H5)2), 7.20(t, 3J(H, H) = 7.2 Hz, 2H, P(C6H5)2), 7.30(d,
3J(H, H) = 7.2 Hz, 2H, C6H3(CH3)2), 7.45(d, 3J(H, H) = 7.2 Hz,
3
2H, P(C6H5)2), 7.48 ppm(d, J(H, H) = 7.2 Hz, 2H, P(C6H5)2).
13C NMR (400 MHz, C6D6, 25 ◦C): d = 0.71(s, 6C, Si(CH3)3),
20.34(s, 4C, C6H2(CH3)3), 21.22(s, 2C, C6H2(CH3)3), 21.51(s, 1C,
C6H2(CH3)3), 21.91(s, 2C, C6H2(CH3)3), 45.33(s, 1C, CH2Si),
56.53(s, 1C, CH2Si), 118.95(s, 1C, C6H2(CH3)3), 120.06(s, 2C,
Experimental section
3
C6H2(CH3)3), 122.19(s, 1C, C6H3(CH3)2), 126.14(d, J(C, P) =
General conditions
14 Hz, 1C, C6H4), 129.42(s, 2C, C6H3(CH3)2), 129.81(s, 4C,
P(C6H5)2), 129.88(s, 4C, C6H2(CH3)3), 130.01(s, 2C, P(C6H5)2),
130.64 (s, 4C, C6H2(CH3)3), 131.0(s, 2C, C6H2(CH3)3), 131.60(s,
All reactions were carried out under a dry and oxygen-free argon
atmosphere by using Schlenk techniques or under a nitrogen
atmosphere in an MBRAUN glovebox. Solvents were purified
by MBRAUN SPS system. Starting materials for the synthesis of
compounds were purchased from Aldrich or Fluka, and distilled
before use.
4
1C, P(C6H5)2), 132.17(d, J(C, P) = 11 Hz, 1C, C6H4), 132.73(s,
1C, P(C6H5)2), 133.84(s, 2C, P(C6H5)2), 134.19(s, 2C, P(C6H5)2,
2C, C6H4), 134.76(d, 2J(C, P) = 20 Hz, 1C, C6H4), 135.15(d, J(C,
P) = 15 Hz, 4C, P(C6H5)2), 136.32(s, 4C, C6H2(CH3)3), 137.58(s,
2C, C6H2(CH3)3), 143.74(s, 2C, C6H2(CH3)3), 149.43(d, 2J(C,P) =
17.5 Hz, 1C, C6H4), 151.74(s, 1C, C6H2(CH3)3), 151.82(s, 1C,
C6H3(CH3)2), 154.39 ppm(s, 2C, C6H3(CH3)2). Anal. Calc. for
C62H80N10Si2PLu: C, 60.67; H, 6.57; N, 11.41. Found: C, 60.65; H,
6.56; N, 11.38.
Instruments and measurements
Organometallic samples for NMR spectroscopic measurements
were prepared in a glovebox by the use of NMR tubes sealed
by paraffin film. 1H and 13C NMR spectra were recorded on
Bruker AV300 (FT, 300 MHz for 1H; 75 MHz for 13C) and
Complex 3b
AV400 (FT, 400 MHz for H; 100 MHz for 13C) spectrometers.
1
NMR assignments were confirmed by 1H-1H (COSY) and 1H-13C
(HMQC) experiments when necessary. Crystals for X-ray analysis
were obtained as described in the experimental section. The
crystals were manipulated in the glovebox. Data collections were
performed at -86.5 ◦C on a Bruker SMART APEX diffractometer
with a CCD area detector, using graphite monochromated Mo
Following the same procedure, treatment of complex 1b
LSc(CH2SiMe3)2(THF) (0.11 g, mmol), with mesityl azide
(0.08 g, mmol) gave complex 3b (0.09 g, 55%). 1H NMR (400 MHz,
C6D6, 25 ◦C): d = 0.26(s, 18H, Si(CH3)3), 2.01(s, 6H, C6H3(CH3)2),
2.09(s, 3H, C6H2(CH3)3), 2.24(multi, 2H, CH2C6H4P), 2.35(s,
6H, C6H2(CH3)3, 6H, C6H2(CH3)3), 2.42(s, 12H, C6H2(CH3)3),
3.50(multi, 4H, CH2Si), 6.48(multi, 1H, C6H4), 6.70(s, 2H,
C6H2(CH3)3), 6.82(t, 3J(H, H) = 7.2 Hz, 1H, C6H4), 6.87(s,
4H, C6H2(CH3)3), 6.97(dd, 3J(P, H) = 15.2 Hz, 3J(H, H) =
7.6 Hz, 1H, C6H4), 6.91(t, 3J(H, H) = 7.6 Hz, 1H, C6H4), 7.05(t,
3J(H, H) = 7.6 Hz, 1H, C6H3(CH3)2), 7.13(broad, 4H, P(C6H5)2),
7.22(broad, 2H, P(C6H5)2, 2H, C6H3(CH3)2), 7.52(d, 3J(H, H) =
7.6 Hz, 2H, P(C6H5)2), 7.55 ppm(d, 3J(H, H) = 8.0 Hz, 2H,
P(C6H5)2). 13C NMR (400 MHz, C6D6, 25 ◦C): d = 1.02(s, 6C,
Si(CH3)3), 20.44(s, 4C, C6H2(CH3)3), 20.97(s, 2C, C6H2(CH3)3),
˚
Ka radiation (l = 0.71073 A). The determination of crystal class
and unit cell parameters was carried out by the SMART program
package. The raw frame data were processed using SAINT
and SADABS to yield the reflection data file. The structures
were solved by using the SHELXTL program. Refinement was
performed on F2 anisotropically for all non-hydrogen atoms by the
full-matrix least-squares method. The hydrogen atoms were placed
at the calculated positions and were included in the structure cal-
culation without further refinement of the parameters. Elemental
554 | Dalton Trans., 2009, 550–556
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21.51(s, 1C, C6H2(CH3)3), 22.40(s, 2C, C6H2(CH3)3), 46.04(s, 1C,
CH2Si), 56.77(s, 1C, CH2Si), 119.58(s, 1C, C6H2(CH3)3), 120.68(s,
2C, C6H2(CH3)3), 122.87(s, 1C, C6H3(CH3)2), 126.28(d, 3J(C,
P) = 15 Hz, 1C, C6H4), 128.26(s, 2C, C6H3(CH3)2), 129.02(s, 4C,
P(C6H5)2), 129.84(s, 4C, C6H2(CH3)3), 129.99(s, 2C, P(C6H5)2),
130.83(s, 4C, C6H2(CH3)3), 131.10(s, 2C, C6H2(CH3)3), 131.80(s,
immediately. After 10 h, the reaction solution was concentrated
under reduced pressure to gave an orange precipitate of complex 4
(0.10 g, 60%). 1H NMR (400 MHz, C6D6, 25 ◦C): d = 1.25(d, 3J(H,
H) = 6.8 Hz, 12H, C6H3(CH(CH3)2)2), 1.32(d, 3J(H, H) = 6.8 Hz,
12H, C6H3(CH(CH3)2)2), 2.23(multi, 4H, C6H3(CH(CH3)2)2),
2.32(s, 6H, C6H3(CH3)2), 3.20(broad, 2H, NHC6H3), 3.24(s, 6H,
C6H2(CH3)3), 3.45(s, 3H, C6H2(CH3)3), 4.76(s, 2H, CH2C6H4P),
4
1C, P(C6H5)2), 132.38(d, J(C, P) = 11 Hz, 1C, C6H4), 132.93(s,
3
1C, P(C6H5)2), 133.77(s, 2C, P(C6H5)2), 133.86(s, 2C, P(C6H5)2,
1C, C6H4, 1C, C6H4), 134.32(s, 1C, C6H4), 135.42(d, J(C, P) =
15 Hz, 4C, P(C6H5)2), 136.11(s, 4C, C6H2(CH3)3), 137.54(s, 2C,
C6H2(CH3)3), 143.86(s, 2C, C6H2(CH3)3), 148.92(s, 1C, C6H4),
151.04(s, 1C, C6H2(CH3)3), 151.13(s, 1C, C6H3Me2), 153.11 ppm(s,
2C, C6H3Me2). Anal. Calc. for C62H80N10Si2PSc: C, 67.85; H, 7.35;
N, 12.76. Found: C, 67.84; H, 7.33; N, 12.74.
6.58(multi, 1H, C6H4), 6.70(s, 2H, C6H2(CH3)3), 6.75(td, J(H,
H) = 7.2 Hz, 4J(H, H) = 2.4 Hz, 1H, C6H4), 6.90(t,
3J(H, H) = 7.2 Hz, 1H, C6H3(CH3)2), 6.92–7.08(multi, 2H,
C6H3(CH3)2, 4H, P(C6H5)2, 2H, P(C6H5)2, 1H, C6H4, 1H, C6H4),
7.10–7.20(multi, 2H, C6H3(CH(CH3)2)2, 4H, C6H3(CH(CH3)2)2),
3
3
7.49(d, J(H, H) = 7.2 Hz, 2H, P(C6H5)2), 7.52 ppm(d, J(H,
H) = 7.2 Hz, 2H, P(C6H5)2). 13C NMR(100 MHz, C6D6,
25 ◦C): d = 20.12(s, 1C, C6H2(CH3)3), 20.23(s, 2C, C6H2(CH3)3),
23.04(s, 2C, C6H3(CH3)2), 24.20(s, 4C, C6H3(CH(CH3)2)2), 24.31(s,
4C, C6H3(CH(CH3)2)2), 30.15(s, 4C, C6H3(CH(CH3)2)2), 56.62(s,
1C, CH2C6H4P), 115.82(s, 2C, C6H3(CH(CH3)2)2), 122.83(s,
1C, C6H2(CH3)3), 123.17(s, 1C, C6H3(CH3)2), 123.59(s, 4C,
C6H3(CH(CH3)2)2), 127.94(s, 1C, C6H4), 129.32(s, 2C, P(C6H5)2),
129.43(s, 4C, P(C6H5)2), 129.94(s, 1C, C6H4), 130.06(s, 2C,
Complex 3¢
A toluene solution of phenylacetylene (0.06 g, 0.58 mmol)
was dropped into a solution of 3a (0.15 g, 0.12 mmol). The
stirring of the reaction mixture was continued for 1.5 h at room
temperature. Removal of the volatiles afforded an oily residue
whic◦h was dissolved with hexane (1 mL) and then cooled to
-30 C to give complex 3¢. H NMR (400 MHz, C6D6, 25 ◦C):
1
C6H3(CH3)2), 130.65(s, 1C, C6H4), 132.28(s, 2C, C6H2(CH3)3),
3
132.66(s, 4C, P(C6H5)2), 134.20(s, 1C, C6H4), 134.29(s, 1C,
C6H4), 134.61(d, 1J(C,N) = 9 Hz, 2C, C6H3(CH(CH3)2)2),
134.86(s, 2C, P(C6H5)2), 136.80(s, 2C, C6H2(CH3)3), 137.90(s, 4C,
C6H3(CH(CH3)2)2), 149.93(d, 2J(C,P) = 17.5 Hz, 1C, C6H4),
151.70(s, 1C, C6H2(CH3)3), 153.75(s, 1C, C6H3(CH3)2), 154.79
ppm(s, 2C, C6H3(CH3)2). Anal. Calc. for C60H72N6PLu: C, 66.53;
H, 6.70; N, 7.76. Found: C, 66.51; H, 6.69; N, 7.73.
d = 0.18(s, 9H, Si(CH3)3), 0.21(s, 9H, Si(CH3)3), 2.06(s, 6H,
C6H3(CH3)2), 2.13(s, 3H, C6H2(CH3)3), 2.16(s, 3H, C6H2(CH3)3),
2.17(s, 3H, C6H2(CH3)3), 2.18(s, 3H, C6H2(CH3)3), 2.21(s, 3H,
C6H2(CH3)3), 2.23(s, 3H, C6H2(CH3)3), 2.27(s, 2H, CH2Si), 2.35(s,
6H, C6H2(CH3)3), 2.71(s, 3H, C6H2(CH3)3), 2.98(s, 1H, CH2Si),
2
3.02(s, 1H, CH2Si), 4.33(d, J(H, H) = 17 Hz, 1H, CH2C6H4P),
2
5.62(d, J(H, H) = 17 Hz, 1H, CH2NC6H3(CH3)2), 6.60(s, 2H,
C6H2(CH3)3), 6.63(s, 2H, C6H2(CH3)3), 6.78(td, 3J(H, H) = 6.8 Hz,
4J(H, H) = 2.8 Hz, 1H, C6H4), 6.83(s, 2H, C6H2(CH3)3), 6.90(d,
Complex 5
3
3J(H, H) = 8.0 Hz, 1H, C6H4), 6.95(t, J(H, H) = 8.0 Hz, 1H,
3
4
Phenylacetylene (0.03 g, 0.29 mmol) in toluene (1 mL) was dropped
into a toluene solution of 1a (0.12 g, 0.15 mmol). After 1 h, mesityl
azide (0.07 g, 0.45 mmol) was added to the above solution. The
reaction mixture was stirred for 10 h at room temperature and then
was concentrated to 0.5 mL under reduced pressure. Addition of
1 mL hexane and cooling at -30 ◦C for several days gave light
C6H3(CH3)2), 6.98(dd, J(P, H) = 7.6 Hz, J(H, H) = 3.2 Hz,
1H, C6H4), 7.30(dd, 3J(H, H) = 7.6 Hz, 4J(H, H) = 1.6 Hz, 2H,
C6H3(CH3)2), 7.14(multi, 4H, P(C6H5)2, 2H, P(C6H5)2), 7.29(d,
1H, C6H4), 7.42(d, 3J(H, H) = 7.2 Hz, 2H, P(C6H5)2), 7.52
ppm(d, 3J(H, H) = 7.2 Hz, 2H, P(C6H5)2). 13C NMR (100 MHz,
C6D6, 25 ◦C): d = 0.02(s, 3C, Si(CH3)3), 0.29(s, 3C, Si(CH3)3),
20.12(s, 2C, C6H2(CH3)3), 20.55(s, 2C, C6H2(CH3)3), 21.08(s, 1C,
C6H2(CH3)3), 21.29(s, 1C, C6H2(CH3)3), 21.34(s, 1C, C6H2(CH3)3),
21.42(s, 1C, C6H2(CH3)3), 21.74(s, 1C, C6H2(CH3)3), 48.15(s, 1C,
CH2Si), 57.62(s, 1C, CH2Si), 122.26(s, 1C, C6H2(CH3)3), 126.46(s,
2C, C6H2(CH3)3), 127.94(s, 1C, C6H3(CH3)2), 129.56(d, 3J(C,
P) = 13 Hz, 1C, C6H4), 129.83(s, 2C, C6H3(CH3)2), 129.94(s, 4C,
P(C6H5)2), 131.81(s, 4C, C6H2(CH3)3), 131.92(s, 2C, P(C6H5)2),
132.67(s, 4C, C6H2(CH3)3), 133.00(s, 2C, C6H2(CH3)3), 133.16(s,
1
yellow crystals of complex 5 (0.06 g, 41%). The H NMR and
13C NMR spectra were not informative due to lots of aryl protons.
Anal. Calc. for C104H92N8P2Lu2: C, 66.95; H, 4.97; N, 6.01. Found:
C, 66.94; H, 4.85; N, 5.76.
A typical procedure for the cycloaddition reaction
To a toluene (7 mL) solution of mesityl azide (0.59 g, 3.66 mmol)
and phenylacetylene (0.37 g, 3.66 mmol), complex 1a (0.06 g,
0.07 mmol) was added. After 3 days, the volatiles were removed
and then the residue chromatographed through silica gel with
hexane/EtOAc (3:1) as the eluent to isolate the 1,5-triazole (0.89 g,
yield: 93%).
4
1C, P(C6H5)2), 133.50(d, J(C, P) = 10 Hz, 1C, C6H4), 133.79(s,
1C, P(C6H5)2), 133.96(s, 2C, P(C6H5)2), 134.26(s, 2C, P(C6H5)2),
134.67(s, 1C, C6H4), 134.90(d, 2J(C, P) = 9 Hz, 1C, C6H4),
135.27(s, 1C, C6H4), 135.75(d, J(C, P) = 11 Hz, 4C, P(C6H5)2),
136.77(s, 4C, C6H2(CH3)3), 137.04(s, 2C, C6H2(CH3)3), 146.49(s,
2C, C6H2(CH3)3), 146.81(s, 1C, C6H4), 152.52(s, 1C, C6H2(CH3)3),
152.61(s, 1C, C6H3Me2), 155.71 ppm(s, 2C, C6H3Me2). Anal. Calc.
for C62H80N10Si2PLu: C, 60.67; H, 6.57; N, 11.41. Found: C, 60.66;
H, 6.55; N, 11.40.
Acknowledgements
We are grateful for financial support from the National Natural
Science Foundation of China for project nos. 20571072 and
20674081, the Ministry of Science and Technology of China for
project no. 2005CB623802 and the “Hundred Talent Program” of
CAS.
Complex 4
The addition of 3 equiv. mesityl azide (0.07 g, 0.45 mmol) to a
hexane suspension of 2 (0.15 g, 0.15 mmol) started the reaction
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22 The mixture of mesityl azide (MesN3) and phenylacetylene was
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detected.
23 1H NMR and 13C NMR spectra of the isolated triazoles, see
the ESI†.
24 Treatment of MesN3 with phenylacetylene in the presence of lutetium
mono(alkyl) complex stabilized by anilido-phosphinimine ligand af-
forded approximately equivalent 1,4- and 1,5-disubstituted 1,2,3-
triazole. See the ESI†.
12 (a) T. M. Cameron, J. C. Gordon, R. Michalczyk and B. L. Scott, Chem.
Commun., 2003, 2282; (b) S. Arndt, P. Voth, T. P. Spaniol and J. Okuda,
Organometallics, 2000, 19, 4690.
556 | Dalton Trans., 2009, 550–556
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