Metal-to-ligand alkyl migration inducing carbon-sulfur bond cleavage in dialkyl yttrium complexes supported by thiazole-containing amidopyridinate ligands: Synthesis, characterization, and catalytic activity in the intramolecular hydroamination reaction

Article abstract of DOI:10.1002/chem.201303853

Neutral Y^III dialkyl complexes supported by tridentate N ^-,N,N monoanionic methylthiazole- or benzothiazole-amidopyridinate ligands have been prepared and completely characterized. Studies on their stability in solution revealed prog

Full text of DOI:10.1002/chem.201303853

DOI: 10.1002/chem.201303853
Full Paper
&
Yttrium Complexes
Metal-to-Ligand Alkyl Migration Inducing Carbon–Sulfur Bond
Cleavage in Dialkyl Yttrium Complexes Supported by Thiazole-
Containing Amidopyridinate Ligands: Synthesis, Characterization,
and Catalytic Activity in the Intramolecular Hydroamination
Reaction
Dmitry M. Lyubov,[a] Lapo Luconi,[b] Andrea Rossin,[b] Giulia Tuci,[b] Anton V. Cherkasov,[a]
Georgy K. Fukin,[a] Giuliano Giambastiani,*[b] and Alexander A. Trifonov*[a]
Abstract: Neutral YIII dialkyl complexes supported by triden-
tate Nꢀ,N,N monoanionic methylthiazole– or benzothiazole–
amidopyridinate ligands have been prepared and complete-
ly characterized. Studies on their stability in solution re-
vealed progressive rearrangement of the coordination
sphere in the benzothiazole-containing system through an
unprecedented metal-to-ligand alkyl migration and subse-
quent thiazole ring opening. Attempts to synthesize hydrido
species from the dialkyl precursor led to the generation of
subsequent dimerization through intermolecular addition of
the residual YꢀH group to the imino fragment of a second
equivalent of the ring-opened intermediate. DFT calculations
were used to elucidate the thermodynamics and kinetics of
the process, in support of the experimental evidence. Finally,
all isolated yttrium complexes, especially their cationic forms
prepared by activation with the Lewis acid Ph3C+[B(C6F5)4]ꢀ,
were found to be good candidate catalysts for intramolecu-
lar hydroamination/cyclization reactions. Their catalytic per-
formance with a number of primary and secondary amino al-
kenes was assessed.
a
dimeric yttrium species stabilized by a trianionic
Nꢀ,N,Nꢀ,Sꢀ ligand as the result of metal-to-ligand hydride
migration with chemoselective thiazole ring opening and
Introduction
Due to the large size of rare earth metal ions, the coordina-
tion number and steric hindrance at the metal center play
a central role in controlling both their stability and chemical re-
activity. Therefore, the design and synthesis of tailored ancillary
ligands suitable for coordination to rare earth metal ions, isola-
tion of the corresponding alkyl species, and investigation of
their complex structure–reactivity relationships are currently
one of the main trends in organo rare earth metal chemistry[10]
and an essential tool for fine-tuning of the reactivity of the
complexes.
Rare earth metal alkyls have attracted a great deal of attention
due to their unique reactivity,[1] which enables difficult reac-
tions such as hydrocarbon activation[2] and alkane functionali-
zation.[3] Moreover, extensive research in the past three de-
cades has revealed the great potential of rare earth metal alkyl
derivatives as catalysts (or precatalysts) of various transforma-
tions involving alkenes and alkynes, such as polymerization,[4]
hydrogenation,[5] hydrosilylation,[6] hydroamination,[7] and hy-
droboration.[8] More recently, cationic monoalkyl rare earth
metal complexes have emerged as valuable candidates for pro-
moting catalytic homo- and copolymerization of olefins and
dienes.[9]
We have recently described the use of bulky aminopyridi-
nate ligands for the synthesis of a number of surprisingly ther-
mally stable dialkyl organolanthanide complexes.[11] Modifica-
tion of the ligand framework through introduction of a methyl-
ene or quaternary CMe2 bridge between the amido and pyri-
dine groups changes the chelate bite angle and results in de-
rivatives with modified stability and reactivity.[12] In particular,
the reaction of modified ligands with [Y(CH2SiMe3)3(thf)2][13]
does not yield the expected yttrium dialkyl complexes, but in-
stead produces the monoalkyl derivatives as a result of intra-
molecular activation of an sp2 or sp3 CꢀH bond in the dangling
substituents of the central pyridine unit.
[a] Dr. D. M. Lyubov, A. V. Cherkasov, Prof. G. K. Fukin, Prof. A. A. Trifonov
G. A. Razuvaev Institute of Organometallic Chemistry
of the Russian Academy of Sciences
Tropinina 49, GSP-445, 603950 Nizhny Novgorod (Russia)
E-mail: trif@iomc.ras.ru
[b] Dr. L. Luconi, Dr. A. Rossin, Dr. G. Tuci, Dr. G. Giambastiani
Institute of Chemistry of Organometallic Compounds
ICCOM-CNR
Via Madonna del Piano, 10, 50019 Sesto Fiorentino (Italy)
Fax: (+39)055-5225203
E-mail: giuliano.giambastiani@iccom.cnr.it
Herein, we describe the synthesis and characterization of
a new family of YIII dialkyl complexes stabilized by tridentate
Nꢀ,N,N monoanionic methylthiazole– or benzothiazole–amido-
pyridinate ligands as well as the ability of their cationic coun-
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201303853.
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terparts to perform efficiently the catalytic intramolecular hy-
droamination of a variety of primary and secondary amino al-
kenes. An in-depth evaluation of the stability of the dialkyl spe-
cies revealed the occurrence of a novel reaction path for the
benzothiazole-containing complex. As a result of an alkyl mi-
gration, ring opening of the heterocycle occurs with concomi-
tant generation of a monoalkyl aryl thiolate yttrium species
stabilized by a tetradentate Nꢀ,N,N,Sꢀ dianionic ligand. DFT cal-
culations were used to elucidate the thermodynamics and ki-
netics of the process, in support of the experimental evidence.
Finally, a full account of the catalytic performance of the neu-
tral and cationic forms of the yttrium alkyl complexes in the
hydroamination of primary and secondary amino alkene sub-
strates is given.
benzothiazole framework and two hard nitrogen coordination
sites from the pyridine central unit and the amido pendant
arm (Nꢀ).
Synthesis and characterization of dialkyl YIII amidopyridinate
complexes 8a,b and 9
The reaction of ligands 6a,b with an equimolar amount of [Y-
(CH2SiMe3)3(thf)2] proceeded smoothly in toluene at 08C for 2 h
to give dark-red solutions of the expected dialkyl compounds
8a,b (Scheme 2). The reaction course was monitored by
1H NMR spectroscopy, which revealed complete ligand com-
plexation within 2 h. After cooling to ꢀ308C overnight, both
Results and Discussion
Synthesis of the tridentate N,N,N ligands HLThia (6a),
HLThiaMe2 (6b), and HLBnThMe2 (7)
Scheme 1 illustrates the stepwise procedure developed to pre-
pare 5-methylthiazole- and benzothiazole-substituted amino-
pyridine ligands 6a,b and 7 in moderate yields. Bromo inter-
mediates 3a,b, 2-(trimethylstannyl)benzothiazole (4), and 5-
methyl-2-(trimethylstannyl)thiazole (5) were prepared accord-
ing to literature procedures,[14,15] in some cases with slight
modifications.[16] 6-Bromo-2-pyridinecarboxaldehyde (1a) and
2-acetyl-6-bromopyridine (1b) were converted to imine deriva-
tives 2a,b under classical condensation conditions in the pres-
ence of a catalytic amount of formic acid.[17] Reduction of
imines 2a and 2b by treatment with NaCNBH3/AcOH[18] or
AlMe3 resulted in formation of the corresponding secondary
aniline derivatives 3a and 3b, respectively. The aminopyridine
ligands HLThia (6a), HLThiaMe2 (6b), and HLBnThMe2 (7) were pre-
pared in the form of off-white crystals (60–80% yield) by Stille
coupling between 3a,b and 4 or 5, respectively (see Experi-
mental Section). In all three ligands, the donor-atom set con-
sists of a nitrogen donor site of the electron-poor thiazole or
Scheme 2. Synthesis of yttrium dialkyl complexes 8a,b and 9.
concentrated crude mixtures give dark red, highly air and
moisture sensitive crystals of complexes 8a,b, which were iso-
lated in 74 and 61% yield, respectively.
Both dialkyl complexes are sparingly soluble in aliphatic hy-
drocarbons (n-pentane and hexane), but fairly soluble in THF
and apolar aromatic hydrocarbons (toluene and benzene); the
latter property is the main cause of the moderate yields of the
precipitated solid compounds. Crystals of 8a,b can be conven-
iently stored for months under inert atmosphere and at room
temperature without any apparent decomposition. Similarly,
1
the H NMR spectra of both compounds in [D6]benzene solu-
tion remained unchanged at room temperature or tempera-
tures below solvent reflux.
1H NMR and 13C{1H} NMR spectra
of 8a,b showed similar patterns
with superimposable spectral re-
gions. The most relevant spectral
features are resonances for
a pair of diastereotopic isopropyl
methyl groups [two doublets
at dH =1.52/1.43 ppm (8a) and
dH =1.26/1.43 ppm
ꢀCHMe2 septet
(8b)],
[dH =4.22
a
(8a)/3.70 ppm (8b)], and a sin-
glet resonance for the bridging
PyCH2N moiety (8a: dH =
4.91 ppm). In both complexes,
the methylene protons of the
alkyl groups attached to yttrium
are diastereotopic and appear as
two doublets of doublets cen-
Scheme 1. Synthesis of ligands 6a,b and 7. i) 2,6-Diisopropylaniline, HCOOH cat., MeOH, reflux; ii) NaBH3CN, AcOH,
THF/MeOH; iii) Trimethylaluminum, toluene, 08C; iv) 2-(Trimethylstannyl)benzothiazole (4), [Pd(dba)2]/PPh3 cat., tol-
uene, reflux; v) 5-Methyl-2-(trimethylstannyl)thiazole (5) [Pd(dba)2]/PPh3 cat., toluene, reflux.
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tered at dH =ꢀ0.84 (dd, 2JHH =10.7, 2JYH =2.3 Hz)/ꢀ0.67 ppm
yttrium atom adopts a strongly distorted octahedral geometry
with three nitrogen atoms from the organic ligand and one
oxygen atom from thf occupying the equatorial plane. The
apical positions are occupied by two carbon atoms from the
CH2SiMe3 substituents. As expected, only the harder N-donor
sites of the methylthiazole fragment enter the coordination
sphere of the metal center, whereas the softer S site points
away from the yttrium center. Moreover, variable temperature
1H NMR spectra of 8a (ꢀ60 to 408C) showed no evidence of
a dynamic process associated with YꢀNThia dissociation and for-
mation of a YꢀSThia coordination bond. The tridentate amido-
pyridinate ligand is nearly planar, with an average deviation of
the metal center from the N(1)N(2)N(3) plane of 0.020 ꢁ. The
YꢀC distances in 8a (2.4505(18) and 2.4522(19) ꢁ) are very sim-
ilar to each other and to those in related six-coordinate yttrium
dialkyl complexes.[19] The YꢀN distances in 8a are unequal: the
Y(1)ꢀN(3) (2.2717(14) ꢁ) bond is substantially shorter than the
others (Y(1)ꢀN(2) 2.4812(14), Y(1)ꢀN(1) 2.5271(14) ꢁ), but lies in
the range observed for related systems.[8b,12b,19f,20]
2
2
2
(dd, JHH =10.7, JYH =2.9 Hz) for 8a and dH =ꢀ0.28 (dd, JHH
=
2
2
2
11.1, JYH =3.0 Hz)/ꢀ0.16 ppm (dd, JHH =11.1, JYH =3.1 Hz) for
8b. The respective methylene carbon atoms give rise to dou-
1
blets centered at dC =27.8 (8a: d, JYC =32.8 Hz)/35.6 ppm (8b:
1
d, JYC =39.2 Hz). Sharp singlets occur for the SiMe3 groups in
the H [dH =ꢀ0.08 (8a)/0.15 ppm (8b)] and 13C{1H} NMR spec-
1
tra [dC =3.9 (8a)/4.1 ppm (8b)]. Finally, two broad signals in
8a, centered at dH =1.25 and 3.45 ppm, were assigned to the
a- and b-methylene protons of a thf ligand, respectively.
Crystals of 8a and 8b suitable for X-ray analysis were ob-
tained by prolonged cooling of concentrated solutions in tolu-
ene at ꢀ308C, and their molecular structures are shown in Fig-
ures 1 and 2, respectively. Table 1 lists crystal data and structur-
al-refinement details. Complex 8a crystallizes in space group
P21/n with four molecules in the unit cell. The six-coordinate
Complex 8b crystallizes in monoclinic space group Pn with
two molecules per unit cell. The metal center has a coordina-
tion number of five (distorted square-pyramidal coordination
geometry) with the three ligand N atoms and one CH2SiMe3
group in the equatorial positions and the other CH2SiMe3
group in the axial position.[21] Unlike 8a, complex 8b crystalli-
zes without coordinated thf. Moreover, while the tridentate N-
donor set is nearly coplanar in 8a with a slight average devia-
tion of the coordinated yttrium center from the N(1)N(2)N(3)
plane, in five-coordinate complex 8b the amido nitrogen atom
N(3) deviates significantly from the plane defined by the pyri-
dine and 5-methylthiazole rings. This results in an average de-
viation of the yttrium ion of 0.624 ꢁ from the N(1)N(2)N(3)
plane. Decreasing the coordination number from six (8a) to
five (8b) expectedly translates into shortening of the YꢀC
bonds (2.3973(15) and 2.4386(15) ꢁ). As already observed for
8a, the Y(1)ꢀN(3) bond length in 8b is also substantially short-
er (2.2297(11) ꢁ) than the others (Y(1)ꢀN(1) 2.5153(12) ꢁ, Y(1)ꢀ
N(2) 2.4386(12) ꢁ).
Figure 1. Crystal structure of 8a. Thermal ellipsoids are drawn at 40% proba-
bility. Hydrogen atoms and methylene groups of the coordinated thf mole-
cule are omitted for clarity. Selected bond lengths [ꢁ] and angles [8]: Y(1)ꢀ
N(3) 2.2717(14), Y(1)ꢀC(23) 2.4505(18), Y(1)ꢀC(27) 2.4522(19), Y(1)ꢀO(1S)
2.4664(12), Y(1)ꢀN(2) 2.4812(14), Y(1)ꢀN(1) 2.5271(14); C(23)-Y(1)-C(27)
126.61(6), N(3)-Y(1)-N(2) 67.89(5), N(3)-Y(1)-N(1) 132.52(5), N(2)-Y(1)-N(1)
64.63(5).
Dialkyl complex 9 was prepared by reaction of 7 with an
equimolar amount of [Y(CH2SiMe3)3(thf)2] under the same syn-
thetic conditions as for the 5-methylthiazole-containing ligands
(Scheme 2). Complex 9 precipitated from the mother liquor on
standing at ꢀ308C overnight as a dark purple crystalline solid
in 75% yield. Complex 9 shows moderate solubility in THF and
apolar aromatic hydrocarbons, but it is scarcely soluble in ali-
phatic ones. NMR spectra and microanalysis are consistent
with a compound that does not contain any thf. The most rele-
1
vant H NMR spectral features of 9 ([D6]benzene) are a pair of
resonances for diastereotopic isopropyl methyl groups (two
doublets at dH =1.33/1.46 ppm), a ꢀCHMe2 septet (dH =
3.86 ppm), and two doublets of doublets centered at dH =
2
2
2
ꢀ0.39 (dd, JHH =11.0, JYH =2.9 Hz)/ꢀ0.22 ppm (dd, JHH =11.0,
2JYH =2.9 Hz, 2H, YCH2) assigned to the diastereotopic methyl-
ene groups of the alkyl fragments bound to the yttrium center.
In the 13C{1H} NMR spectrum, the alkyl CH2 groups appear as
a slightly broadened doublet at dC =34.0 ppm (1JYC =34.9 Hz).
The six methyl groups of the SiMe3 moieties appear as a sharp
Figure 2. Crystal structure of 8b. Thermal ellipsoids are drawn at 40% prob-
ability. Hydrogen atoms are omitted for clarity. Selected bond lengths [ꢁ]
and angles [8]: Y(1)ꢀN(3) 2.2297(11), Y(1)ꢀC(29) 2.3973(15), Y(1)ꢀC(25)
2.4386(15), Y(1)ꢀN(2) 2.4386(12), Y(1)ꢀN(1) 2.5153(12); C(29)-Y(1)-C(25)
108.00(5), N(3)-Y(1)-N(2) 67.96(4), N(3)-Y(1)-N(1) 129.25(4), N(2)-Y(1)-N(1)
65.65(4).
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room temperature provided red
single crystals of 10 suitable for
X-ray analysis.
Table 1. Crystal data and structure refinement for complexes 8a, 8b, 10, and 12.
8a
8b
10
12
The molecular structure of 10
is shown in Figure 3, and crystal
data and structural-refinement
details are listed in Table 1. Com-
plex 10 crystallizes in space
group P21/n, with four molecules
in the unit cell. The yttrium
center in 10 has a formal coordi-
nation number of six (distorted
octahedron) with three nitrogen
atoms and one sulfur atom of
a tetradentate dianionic amido-
thiolate ligand, an alkyl group,
and one oxygen atom of a thf
ligand. The novel metal coordi-
nation sphere is the result of
empirical formula
Mr
T [K]
crystal system
space group
a [ꢁ]
b [ꢁ]
c [ꢁ]
C34H56N3OSSi2Y
699.97
100(2)
monoclinic
P21/n
11.0974(5)
27.4753(11)
13.4065(6)
90
108.9810(10)
90
3865.4(3)
4
1.203
1.653
C32H52N3SSi2Y
655.92
100(2)
monoclinic
Pn
9.38398(16)
11.56576(19)
16.6885(3)
90
91.8518(15)
90
1810.30(5)
2
1.203
1.758
C39H60N3OSSi2Y
764.05
100(2)
monoclinic
P21/n
11.0637(7)
28.4816(19)
12.8320(9)
90
95.9650(10)
90
4021.6(5)
4
1.262
1.594
C54H64N6S2Y2·(C7H8)3
1315.45
100(2)
triclinic
ꢀ
P1
10.86470(10)
13.0408(2)
13.1689(2)
114.1180(10)
100.2110(10)
97.8690(10)
1629.83(4)
1
a [8]
b [8]
g [8]
V [ꢁ3]
Z
1calcd [gcmꢀ3
]
1.340
1.884
690
m [mmꢀ1
F(000)
]
1488
696
1624
crystal size [mm]
q range for data collection [8]
index ranges
0.42ꢂ0.31ꢂ0.15 0.50ꢂ0.40ꢂ0.20 0.30ꢂ0.20ꢂ0.10 0.40ꢂ0.20ꢂ0.20
2.08–28.00
ꢀ14ꢁhꢁ14
ꢀ36ꢁkꢁ36
ꢀ17ꢁlꢁ17
38279
3.01–30.00
ꢀ13ꢁhꢁ13
ꢀ16ꢁkꢁ16
ꢀ23ꢁlꢁ22
22045
1.98–26.00
ꢀ13ꢁhꢁ13
ꢀ35ꢁkꢁ35
ꢀ15ꢁlꢁ15
34021
2.92–29.00
ꢀ14ꢁhꢁ14
ꢀ17ꢁkꢁ17
ꢀ17ꢁlꢁ17
31068
a
ligand rearrangement with
generation of tetradentate
a
reflns collected
Nꢀ,N,N,Sꢀ dianionic system,
owing to a formal 1,3-migration
of one alkyl group from the
metal center to the quaternary
ipso carbon atom of the benzo-
thiazole group, which leads to
a simultaneous opening of the
heteroaromatic ring (through Cꢀ
S bond cleavage) and formation
independent reflns
Rint
completeness to q [%]
data/restraints/parameters
GOF on F2
9308
0.0519
99.7
9308/0/390
1.007
R1 =0.0384
wR2 =0.0778
R1 =0.0641
wR2 =0.0838
0.641/ꢀ0.361
9696
0.0297
99.8
9696/2/375
1.018
R1 =0.0310
wR2 =0.0643
R1 =0.0367
wR2 =0.0663
0.483/ꢀ0.238
7904
0.0644
99.9
7904/0/434
1.021
R1 =0.0445
wR2 =0.0968
R1 =0.0772
wR2 =0.1054
0.615/ꢀ0.366
8646
0.0291
99.8
8646/12/396
1.053
R1 =0.0303
wR2 =0.0766
R1 =0.0374
wR2 =0.0787
0.595/ꢀ0.506
final R indices [I>2s(I)]
R indices (all data)
largest diff. peak/hole [eꢁ3]
1
singlet at dH =ꢀ0.01 ppm and dC =4.0 ppm in the H NMR and
13C{1H} NMR spectra, respectively.
Thiazole ring opening promoted by metal-to-ligand 1,3-mi-
gration of an alkyl group: study on an unprecedented
ligand rearrangement to give a monoalkyl yttrium complex
stabilized by a tetradentate, dianionic Nꢀ,N,N,Sꢀ ligand
Scheme 3. Metal-to-ligand alkyl migration and benzothiazole ring opening
to give the yttrium thiolate complex 10.
Complex 9 is a highly air and moisture sensitive compound;
nonetheless, it can be stored under inert atmosphere for pro-
longed periods without any apparent decomposition. A solu-
tion of 9 in [D6]benzene is indefinitely stable at room tempera-
ture, but the addition of exogenous THF accelerates the pro-
gressive rearrangement of the complex to give a novel yttrium
thiolate complex, the identity of which was elucidated by X-ray
diffraction analysis (Scheme 3).
of a covalent YꢀS bond. The YꢀS bond of 10 (2.7843(8) ꢁ) is
considerably longer than those in related six-coordinate tris-
thiolato yttrium complexes [{(Et3CS)2Y(m-SCEt3)Py2}2] (2.642(3)–
2.687(3) ꢁ),[22a] but shorter than bridging covalent YꢀS bonds
in dimeric complexes [{(Et3CS)2Y(m-SCEt3)Py2}2] (2.825(3)–
2.870(3) ꢁ)[22a] and [{(Me3Si)2NC(NCy)2}2Y(m-SnBu)]2 (2.831(3),
2.804(3) ꢁ[22b]). The Y(1)ꢀN(1) bond (2.227(2) ꢁ) is shorter than
the Y(1)ꢀN(3) and Y(1)ꢀN(2) bonds (2.485(2) and 2.421(2) ꢁ, re-
spectively), in line with its covalent character.[23] Notably, the
N(3)ꢀC(21) bond originating from thiazole ring opening main-
tains the character of a C=N bond (N(3)ꢀC(21) 1.285(4) ꢁ) and
N(3) is bound to yttrium through a coordinative interaction
(Y(1)ꢀN(3) 2.485(2) ꢁ).[19a,23d,24] The distance between the yttri-
um atom and the nitrogen atom of the pyridine ring is charac-
teristic of a coordinative YꢀN bond (Y(1)ꢀN(2) 2.421(2) ꢁ),[24]
Thus, the addition at room temperature of two equivalents
of THF to the isolated dialkyl complex 9 results in its complete
rearrangement to 10 over about two months. In THF/hexane
(1/1) the transformation occurs faster with complete genera-
tion of 10 in one day. On heating the mixture at 508C the rear-
rangement is complete in less than 3 h (Scheme 3). Complex
10 was isolated in 70% yield as red microcrystals from a con-
centrated solution in THF/hexane at ꢀ308C. Successive crystal-
lization procedures from concentrated THF/hexane solutions at
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calculations were performed on model systems with the aim
of elucidating the thermodynamics and kinetics of the process.
DFT modeling of the 1,3-alkyl migration and rearrangement
of the complex
Density functional calculations carried out on simplified model
systems at the M06/6-31G* level of theory (THF/hexane, SMD
continuum model) contributed to better understanding of the
process (Scheme 4). After a preliminary assessment of the
energy profiles associated with the 1,3-alkyl migration and sub-
Figure 3. Crystal structure of 10. Thermal ellipsoids are drawn at 40% proba-
bility. Hydrogen atoms and methylene groups of the coordinated thf mole-
cule are omitted for clarity. Selected bond lengths [ꢁ] and angles [8]: Y(1)ꢀ
N(1) 2.227(2), Y(1)ꢀO(1) 2.3970(19), Y(1)ꢀC(32) 2.408(3), Y(1)ꢀN(2) 2.421(2),
Y(1)ꢀN(3) 2.485(2), Y(1)ꢀS(1) 2.7843(8), N(3)ꢀC(21) 1.285(4), C(21)ꢀC(22)
1.489(4); N(1)-Y(1)-N(2) 68.09(8), N(1)-Y(1)-N(3) 131.89(8), N(2)-Y(1)-N(3)
64.93(8), N(1)-Y(1)-S(1) 119.45(6), O(1)-Y(1)-S(1) 81.54(5), C(32)-Y(1)-S(1)
133.81(8), N(2)-Y(1)-S(1) 107.99(6), N(3)-Y(1)-S(1) 68.00(6).
and the YꢀC bond length of the residual alkyl group
(2.408(3) ꢁ) is similar to those previously reported for six-coor-
dinate monoalkyl yttrium complexes.[19,23] Finally, the 1,3-migra-
tion of one alkyl group to the ipso carbon atom of the thiazole
framework results in the formation of a CꢀC single bond
(C(21)ꢀC(22) 1.489(4) ꢁ).[25]
Scheme 4. Reaction processes analyzed by DFT modeling in this work.
sequent ligand rearrangement in the models, selected profiles
of interest were also evaluated on the real system for the sake
of completeness. Starting geometries for computational
models 9a and 9b were obtained from the crystal structure of
8b by replacing the N-coordinated 5-methylthiazole with an
N- (9a) or S-coordinated (9b) benzothiazole group and replac-
ing both the 2,6-iPr(C6H3) substituent of the amido fragment
and the methyl groups of the -CH2SiMe3 substituents with H
atoms before reoptimizing the resulting structures (see also Ex-
perimental Section). Transfer of a CH2SiH3 group from the
metal center to the ipso carbon atom of the benzothiazole
ring was then analyzed theoretically for both 9a and 9b. The
processes examined are summarized in Scheme 4, and the cal-
culated relative Gibbs energies in THF/n-hexane (1/1)[29] are
shown in Figure 4, together with the optimized geometries for
reactants, transition states, and products.
Complex 10 is highly soluble in aromatic hydrocarbons and
indefinitely stable at room temperature in [D6]benzene solu-
1
tion. Its most relevant H NMR spectral features consist of two
doublets of doublets centered at dH =ꢀ0.77 and ꢀ0.74 ppm
2
(2JHH =10.5 Hz, JYH =3.0 Hz) for the residual alkyl group bound
to the metal center and two doublets at dH =2.03 and
2.95 ppm (2JHH =12.5 Hz) for the diastereotopic methylene pro-
tons of the migrated CH2SiMe3 group; the corresponding
SiMe3 protons appear as sharp singlets at dH =0.06 and
ꢀ0.21 ppm, respectively.
Whereas there have been several reports of pyridine-based
ligands undergoing further rearrangements on coordination to
transition metals[26] or rare earth metals,[27] to the best of our
knowledge this is a unique example of quantitative thiazole
ring opening proceeding through chemoselective CꢀS bond
cleavage while keeping the imino moiety derived from the
thiazole core intact. Indeed, metal-to-ligand alkyl migrations in
rare earth metal complexes are known to promote the trans-
formation of neutral N donors into anionic amide ligands, in-
cluding processes in which such a migration is associated with
partial ligand dearomatization.[28] In the case of the yttrium-co-
ordinated benzothiazole system, the electronic requirements
of the electron-poor rare earth metal ion are assumed to drive
the process towards the generation of a sterically and electron-
ically saturated system that favors selective thiazole ring open-
ing and the generation of a tetradentate dianionic chelating
ligand while preserving the C=N imino group from reduction.
Notably, complexes 8a,b do not undergo similar rearrange-
ment even when they are heated at 508C for several hours in
THF/hexane. To gain additional insight into this reaction, DFT
Benzothiazole N coordination is much more stabilizing than
S coordination (DG=14.7 kcalmolꢀ1), and s(SiꢀH)···Y agostic in-
teractions are present in 9a (optimized d(Si···Y)=3.35,
d(SiꢀH···Y)=3.10 ꢁ), probably as
a consequence of the
SiMe3!SiH3 change on going from the real system to the DFT
model. Whereas the N-coordinated ligand has approximately
planar geometry (optimized NPy-C-C-NTh dihedral angle 5.18), in
the case of S coordination the organic fragment is far from pla-
narity (optimized NPy-C-C-S dihedral angle 22.18); the coordina-
tion number is five for both complexes. While the coordination
geometry of 9a can be considered to be (distorted) trigonal-
bipyramidal, that of 9b is closer to square-pyramidal.
As shown in Figure 4 (upper panel), the 1,3-migration of
a CH2SiH3 group to the ipso carbon atom of the benzothiazole
framework does not result in the observed ring opening but
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tion is the thermodynamic driving force for the process to
occur; in fact, although the energy barrier to be overcome is
almost identical to that of the previous case (DG# =32.1 kcal
#
molꢀ1 to reach TS2 , Figure 4, lower panel), the thermodynam-
ics is much more downhill (DG(9bꢀ10b)=ꢀ26 kcalmolꢀ1).
The comparison between the benzothiazole and the 5-methyl-
thiazole (model) systems in the CH2SiH3 migration reaction
(starting from the k-S-thiazole isomer, analogous to 9b) re-
vealed that no ring opening takes place when the simpler 5-
methylthiazole substituent is present, in line with the experi-
mental outcome. Accordingly, the transition state correspond-
#
ing to TS2 could not be found on the potential-energy sur-
face.[30]
Experiments revealed that benzothiazole ring opening
occurs faster in the presence of THF as cosolvent. Accordingly,
the effect of the presence of a coordinated thf molecule in the
computational model was analyzed, to calculate the variation
in the kinetic and thermodynamic parameters with respect to
the above case, in which no thf was included in the model. Re-
actant 9b was therefore modified by the addition of one thf
molecule coordinated to yttrium, and the new ensemble 9bthf
reoptimized. As in 9b, the ligand in 9bthf is nonplanar (opti-
mized NPy-C-C-S dihedral angle 30.78), the YꢀS bond in 9bthf is
slightly longer (d(YꢀS)=3.03 ꢁ in 9b versus 3.12 ꢁ in 9bthf),
and the new coordination number is six (distorted octahedral).
Figure 4. Gibbs energies versus reaction coordinate profiles for the two
competing processes in the 1,3-migration of an alkyl fragment to the ipso
carbon atom of the benzothiazole group. Upper panel: 1,3-Alkyl migration
in 9a and thiazole reduction/dearomatization. Lower panel: 1,3-Alkyl migra-
tion in 9b and thiazole ring opening/thiolate formation. Optimized geome-
tries of reactants, transition states, and products with selected bond lengths
are reported in the Supporting Information.
instead induces benzothiazole reduction/dearomatization with
formal generation of an anionic benzothiazoline ligand coordi-
nated to the metal center. The ipso carbon atom changes its
hybridization from sp2 to sp3 (optimized d(CꢀNBnTh)=1.44 ꢁ in
9a; d(CꢀNBnTh)=1.31 ꢁ in 11), and the more basic nature of
the N donor is mirrored in a shorter YꢀN distance in 11 com-
pared to 9a (optimized d(YꢀN)=2.51 ꢁ in 9a; d(YꢀN)=2.26 ꢁ
Figure 5. Gibbs energies versus reaction coordinate profiles for the 1,3-mi-
gration of an alkyl group to the ipso carbon atom of the benzothiazole
group in complex 9bthf. Optimized geometries of reactant, transition state,
and product with selected bond lengths are reported in the Supporting In-
formation.
#
in 11). A transition state TS1 for the process was found at
32.2 kcalmolꢀ1 above the reactant (Figure 4, upper panel) and
the complex conversion occurs almost thermoneutrally with
the product 11 lying 1.8 kcalmolꢀ1 below reactant 9a. As
a result, the process is very unlikely to occur, especially from
a kinetic point of view.
#
As shown in Figure 5, the transition state (TS3 ) lies 28.3 kcal
molꢀ1 above the reactant and the calculated thermodynamics
leading to 10bthf is still strongly favored (DG(9bthfꢀ10bthf)=
ꢀ21.7 kcalmolꢀ1). The presence of a coordinated thf molecule
lowers the activation barrier to be overcome, in line with the
experimental findings. All of these theoretical data are in line
with the experiments, in which the thiolate species was the
only isolated product.
In the case of 9b, migration of the CH2SiH3 substituent takes
place with simultaneous benzothiazole ring opening through
chemoselective CꢀS bond cleavage and generation of a benzo-
thiolate ligand on yttrium (Scheme 4 and Figure 4, lower
panel). The basic nature of the benzothiolate substituent is
confirmed by the shorter YꢀS distance in 10b compared with
9b (optimized d(YꢀSBnTh)=2.70 ꢁ in 10b; d(YꢀSBnTh)=3.03 ꢁ in
9b). The nitrogen atom coming from the thiazole ring is also
coordinated to the metal center at the end of the CH2SiH3
transfer; the presence of an imino group is confirmed by the
optimized d(C=N) bond length of 1.30 ꢁ. This double coordina-
Alkyl versus hydride metal-to-ligand migration study
To further study the unprecedented reactivity observed for dia-
lkyl complex 9, the corresponding yttrium hydrido complex
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nitrogen [N(3), N(3A)] and two sulfur atoms [S(1) and S(1A)] m2-
bridging two yttrium ions [Y(1) and Y(1A)]. Thus, each Y3+ ion
is coordinated by four nitrogen atoms and two sulfur atoms
from the two bridging trianionic tetradentate Nꢀ,N,Nꢀ,Sꢀ li-
gands with a formal coordination number of six. The YꢀN
bonds in 12 are nonequivalent, and the Y(1)ꢀN(1) covalent
bond is the shortest (2.1963(8) ꢁ). Notably, the m2-bridging co-
valent bonds Y(1)ꢀN(3) and Y(1)ꢀN(3A) (2.4451(10) and
2.4895(8) ꢁ) are markedly longer than the coordinative ones
(Y(1)ꢀN(2) and Y(1A)ꢀN(2A) 2.4019(9) ꢁ). The bond length be-
tween N(3) and the neighboring carbon atom C(21) bridging
the pyridine framework (N(3)ꢀC(21) 1.4743(14) ꢁ) is much
longer compared with the related bond length in 10
(N(3)ꢀC(21) 1.285(4) ꢁ); this indicates single-bond character of
the CꢀN bond.[25] Finally, a close h2 contact between each yttri-
um center and the phenyl moiety of the aryl thiolate group
(ipso- and ortho-C atoms) was also found (Y(1)-C(22) 2.9253(12)
and Y(1)ꢀC(27) 3.0449(12) ꢁ; Y(1A)ꢀC(22A) 2.925(1) and
Y(1A)ꢀC(27A) 3.045(1) ꢁ).
Scheme 5. Metal-to-ligand hydride migration and benzothiazole ring open-
ing to afford dimeric complex 12.
On the basis of the observed reactivity and the above-de-
scribed metal-to-ligand alkyl migration, generation of the di-
meric yttrium species stabilized by a trianionic Nꢀ,N,Nꢀ,Sꢀ
ligand is assumed to be the result of the reaction sequence
summarized in Scheme 5. Firstly, treatment of 9 with two
equivalents of PhSiH3 results in the formation of dihydrido yt-
trium intermediate 9H as the product of a s-bond metathesis
reaction.[19e,d,32] Similarly to the rearrangement described above
for 9, a metal-to-ligand 1,3-hydrido migration takes place al-
ready at room temperature with simultaneous promotion of
chemoselective thiazole ring opening and generation of inter-
mediate 10H. Finally, the latter is expected to rapidly and
quantitatively undergo intermolecular addition of the residual
YꢀH group to the imino fragment of a second equivalent of
10H to generate dimeric species 12.
was synthesized by reaction of
9
with phenylsilane
(Scheme 5).[12a,31] Treating a solution of complex 9 in toluene
with two equivalents of PhSiH3 at room temperature afforded,
after solvent evaporation, a crude crystalline product, slow
crystallization of which from toluene/THF (1/1) gave yellow mi-
crocrystals suitable for an X-ray diffraction study, which identi-
fied rare dimeric yttrium complex 12 (Figure 6). Crystal data
and structural-refinement details are listed in Table 1.
ꢀ
Complex 12 crystallizes in space group P1 as a toluene sol-
vate (1.5 molecules of toluene per yttrium atom; one molecule
per unit cell), and it adopts a dimeric structure featuring a cen-
tral rhombic Y2S2 core (YꢀS 2.8060(3) and 2.8474(3) ꢁ) with two
Neutral and cationic yttrium complexes in the intramolecu-
lar hydroamination of amino alkenes
Organolanthanide complexes are active catalysts for the intra-
molecular hydroamination of both alkynes and alkenes, as pio-
neered by Marks and co-workers with cyclopentadienyl com-
plexes.[7a,33] Since then, a number of group 3 organometallics
(including non-cyclopentadienyl-based systems) have been ex-
tensively used as catalysts for these reactions (in both stereo-
selective and nonstereoselective fashion) and generally provide
high turnover frequencies and, where applicable, good to ex-
cellent stereoselectivities.[7,34] Intermolecular hydroamination
reactions[34a,b,m] with these catalysts are generally problematic,
and most reactions catalyzed by rare earth metal complexes
have been performed in an intramolecular fashion to produce
predominantly pyrrolidine and piperidine derivatives.
The mechanism of hydroamination/cyclization[33c,35] classical-
ly proceeds through formation of a metal amido species with
the protonolysis of a metal–alkyl bond in the precatalyst, fol-
lowed by insertion of the olefin into the metal–amido bond
(rate-determining step)[30b] via a seven-membered chairlike
transition state (Scheme 6, for n=1). The resulting intermedi-
Figure 6. Crystal structure of 12. Thermal ellipsoids are drawn at 40% proba-
bility. Hydrogen atoms, methyl groups of the iPr fragments, and solvent of
crystallization (toluene) are omitted for clarity. Selected bond lengths [ꢁ] and
angles [8]: Y(1)ꢀN(1) 2.1963(8), Y(1)ꢀN(2) 2.4019(9), Y(1)ꢀN(3’) 2.4451(10),
Y(1)ꢀN(3) 2.4895(8), Y(1)ꢀS(1’) 2.8060(3), Y(1)ꢀS(1) 2.8474(3), Y(1)ꢀC(22)
2.9253(12), Y(1)ꢀC(27) 3.0449(12), Y(1)ꢀY(1’) 3.13516(18) N(3)ꢀC(21)
1.4743(14); N(1)-Y(1)-N(2) 69.42(3), N(1)-Y(1)-N(3’) 125.06(3), N(2)-Y(1)-N(3’)
144.90(3), N(1)-Y(1)-N(3) 132.94(3), N(2)-Y(1)-N(3) 67.12(3), N(3’)-Y(1)-N(3)
101.11(3), N(1)-Y(1)-S(1’) 114.94(2), N(2)-Y(1)-S(1’) 77.58(2), N(3’)-Y(1)-S(1’)
67.32(2), N(3)-Y(1)-S(1’) 72.05(2), N(1)-Y(1)-S(1) 132.32(2), N(2)-Y(1)-S(1)
125.06(2), N(3’)-Y(1)-S(1) 71.93(2), N(3)-Y(1)-S(1) 66.10(2), S(1’)-Y(1)-S(1)
112.644(7).
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Table 2. Intramolecular hydroamination of primary and secondary amino
alkenes catalyzed by dialkyl neutral and monoalkyl cationic yttrium com-
plexes.[a]
Entry Catalyst Activator
Substrate Product
T
t
Conv.
[%][b]
[8C] [h]
1
8b
8b
8b
8a
9
9
9
9
9
10
10
10
10
8b
8a
9
9
9
9
–
I
I
I
I
I
I
I
I
I
I
I
I
I
VII
VII
VII
VII
VII
VII
VII
VII
VII
VII
VII
VII
VII
VIII
VIII
VIII
VIII
IX
IX
X
X
X
X
XI
XI
XII
XII
40
40
80
80
80
1.5
1.5
0.75
2
11
97
96
10
30
98
>99
54
2[c]
[Ph3C][B(C6F5)4]
[Ph3C][B(C6F5)4]
[Ph3C][B(C6F5)4]
–
[Ph3C][B(C6F5)4]
[Ph3C][B(C6F5)4]
[Ph3C][B(C6F5)4]
[Ph3C][B(C6F5)4]
–
3[c]
4[c]
5
7
6[c]
RT[d] 24
7[c]
40
40
80
40
80
80
80
40
80
40
80
40
80
80
80
40
80
80
80
80
80
1.5
24
0.75 >99
24
7
0.75
24
2
8[c,e]
9[c]
Scheme 6. Intramolecular hydroamination of primary and secondary amino
alkenes.
10
11
18
23
–
–
81
5
–
12[c]
13[c]
14[c]
15[c]
16[c]
17[c]
18[c]
19[c]
20
[Ph3C][B(C6F5)4]
[Ph3C][B(C6F5)4]
[f]
[f]
ate undergoes fast protonolysis with a second amine molecule,
which regenerates the metal amido species and releases the
heterocyclic product.
[Ph3C][B(C6F5)4] II
[Ph3C][B(C6F5)4] II
[Ph3C][B(C6F5)4] II
[Ph3C][B(C6F5)4] II
[Ph3C][B(C6F5)4] III
[Ph3C][B(C6F5)4] III
2
2
94
In this regard, all isolated neutral alkyl compounds (8a,b, 9,
and 10) and their cationic monoalkyl counterparts, prepared in
situ, were tested as catalysts for the intramolecular hydroami-
nation/cyclization of primary and secondary amines tethered
to monosubstituted alkenes (Scheme 6, Table 2). Substrate con-
0.75 >99
4
20
7
7
4
4
24
24
5
10
36
–
92
27
94
31
92
28
46
[f]
8b
8b
9
9
8b
9
–
IV
21[c]
22[c]
23[c]
24[c]
25[c]
26[c]
27[c]
[Ph3C][B(C6F5)4] IV
[Ph3C][B(C6F5)4] IV
[Ph3C][B(C6F5)4] IV
[Ph3C][B(C6F5)4]
[Ph3C][B(C6F5)4]
1
versions were determined by H NMR spectroscopy with ferro-
cene as internal standard and confirmed by gas chromatogra-
phy of the final crude reaction mixture (see Experimental Sec-
tion). Details of the catalytic reactions and optimized cycliza-
tion conditions are listed in Table 2.
V
V
8b
9
[Ph3C][B(C6F5)4] VI
[Ph3C][B(C6F5)4] VI
3
[a] Reaction conditions: substrate: 0.21 mmol, catalyst: 5 mol%
(10.5 mmol), solvent: toluene (2.5 mL). [b] Determined by in situ 1H NMR
spectroscopy with ferrocene as internal standard. [c] Cationic complexes
were generated in situ from the respective neutral counterparts (8a,b, 9
and 10), as described in the Experimental Section. [d] RT: 21–228C.
[e] Catalyst: 3 mol%. [f] No detectable amounts of cyclization products
are observed.
Cationic monoalkyl compounds were simply prepared from
the respective alkyl precursors by addition of an equimolar
amount of the Lewis acid [Ph3C][B(C6F5)4] as an alkyl abstractor
(see Experimental Section). Apparently, all cationic monoalkyl
species show significantly higher catalytic activities than their
neutral dialkyl analogues (Table 2, entries 1 versus 2, 5 versus
6, and 20 versus 21). This remarkable difference in reactivity is
reasonably ascribed to the occurrence of stereo-electronic fac-
tors in which the nature of the monoanionic tridentate ancil-
lary ligand plays a crucial role.[36] In contrast to the neutral
complexes, the higher activity of the cationic systems reflects
the beneficial effect of an additional available coordination
space at the more electron deficient metal center.[37]
ed 8a. Comparing the two parent solvent-free complexes 8b
and 9 under similar reaction conditions (Table 2, entries 1
versus 5, 2 versus 7, 14 versus 16, 21 versus 23, 24 versus 25,
and 26 versus 27) reveals that these two systems behave simi-
larly in both their neutral and cationic forms, and the monoalk-
yl cationic derivative of 9 is the most catalytically active form
for all selected runs. The isolated monoalkyl complex 10 shows
very moderate catalytic activity when employed as it is
(Table 2, entries 10 and 11), and its cationic counterpart is, as
expected, totally inactive (Table 2, entries 12 and 13).
The cationic systems resulting from the in situ activation of
8b and 9 are active catalysts for the intramolecular hydroami-
nation reaction of a number of model primary and secondary
amino alkenes and provide relatively fast and complete sub-
strate conversions under relatively mild reaction conditions
(from RT to 408C with 5 mol% of catalyst; Table 2, entries 6
and 7).
Dependence of the cyclization rate on the substrate was ob-
served on comparing different cyclization precursors. Thus,
a major kinetic Thorpe–Ingold effect in diphenyl- and cyclohex-
yl-substituted precursors I and II translates into almost quanti-
tative cyclization in short reaction times to give VII and VIII, re-
spectively (Table 2, entries 6, 7, and 17). All other scrutinized
cyclization precursors (III–VI) typically require more severe re-
action conditions (higher reaction temperature and prolonged
reaction time) to give appreciable substrate conversions. Fur-
thermore, cyclization of primary amino alkenes (generally) pro-
ceeds more efficiently than that of secondary ones (Table 2, en-
tries 3 versus 21 and 24, 7 versus 22, and 9 versus 23 and 25).
Notably, complex 8a is the least active catalyst and shows
low substrate conversions compared to analogue 8b, even
under harsher reaction conditions (Table 2, entries 3 versus 4
and 14 versus 15). This lower reactivity is ascribed to the incor-
poration of solvent (Lewis-base complexation) in the coordina-
tion sphere of the metal center.[9q] Indeed the thf ligand in 8a
is expected to influence the catalytic activity of the complex
dramatically, owing to its electron-donating nature; hence, thf-
free complex 8b shows higher catalytic activity than thf-solvat-
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struments. Yttrium analysis were carried out by complexometric ti-
tration. The N, C, H elemental analyses were carried out in the mi-
croanalytical laboratory of the IOMC or at the ICCOM by means of
a Carlo Erba Model 1106 elemental analyzer with an accepted tol-
erance of 0.4 units on C, H, and N. Melting points were determined
by using a Stuart Scientific SMP3 melting point apparatus. GC anal-
yses were performed on a Shimadzu GC-17 gas chromatograph
equipped with a flame ionization detector and a Supelco SPB-
1 fused silica capillary column (30 m length, 0.25 mm i.d., 0.25 mm
film thickness) or a HP-PLOT Al2O3 KCl column (50 m length,
0.53 mm i.d., 15 mm film thickness). The GC-MS analyses were per-
Conclusion
We have provided a full account of the unprecedented reactiv-
ity of a class of neutral ytrrium dialkyl and dihydride complexes
supported by thiazole-containing amidopyridinate ligands. In
the case of the benzothiazole-containing ligand, progressive
rearrangement of the coordination sphere of the yttrium di-
alkyl complex takes place through a metal-to-ligand 1,3-alkyl
migration with subsequent chemoselective opening of the
thiazole ring. The resulting monoalkyl aryl thiolate yttrium
complex supported by a tetradentate Nꢀ,N,N,Sꢀ dianionic
ligand was isolated and completely characterized in solution
and in the solid state. While there have been several reports of
pyridine-based ligands undergoing further rearrangements on
coordination to transition metal or rare earth ions, to the best
of our knowledge this is a unique example of a quantitative
thiazole ring opening proceeding through chemoselective CꢀS
bond cleavage while keeping the imino moiety derived from
the thiazole core untouched. Density functional calculations on
model yttrium dialkyl systems were performed to elucidate the
thermodynamics and kinetics of the process, in support of the
experimental evidence. Similarly, attempts to synthesize a dihy-
drido species from the corresponding dialkyl precursor led to
the generation of an unique dimeric yttrium complex stabilized
by a trianionic Nꢀ,N,Nꢀ,Sꢀ ligand as the result of metal-to-
ligand hydride migration, chemoselective thiazole ring open-
ing, and subsequent dimerization of the complex by intermo-
lecular addition of the residual YH group to the imino frag-
ment of a second equivalent of the monohydrido yttrium inter-
mediate. Neutral and cationic thiazole-containing yttrium alkyl
complexes promote the intramolecular hydroamination of pri-
mary and secondary amino alkenes at moderate catalyst load-
ings (5 mol%) under relatively mild (time and temperature) re-
action conditions. Other organolanthanide complexes (Lu, Yb,
and Eu) supported by analogous thiazole– and benzothiazole–
amidopyridinate ligands are currently under investigation as ef-
fective precatalysts for diene polymerization.
formed on
a Shimadzu QP2010S apparatus equipped with
a column identical to that used for GC analysis.
X-ray diffraction data
X-ray diffraction intensity data for compounds 8a, 8b, 10, and 12
were collected with Bruker SMART APEX (8a, 8b) and Agilent Xcali-
bur E (10, 12) diffractometers with graphite-monochromated MoKa
radiation (l=0.71073 ꢁ) by using w scans. The structures were
solved by direct methods and were refined on F2 by using the
SHELXTL (G. M. Sheldrick, SHELXTL v.6.12, Structure Determination
Software Suite, Bruker AXS, Madison, Wisconsin, USA, 2000) and
Crysalis Pro [CrysAlis Pro, Agilent Technologies Ltd, Yarnton, Eng-
land, 2011) software packages. All non-hydrogen atoms were locat-
ed from Fourier syntheses of electron density and were refined ani-
sotropically. All hydrogen atoms were placed in calculated posi-
tions and were refined in the riding model. SADABS (G. M. Shel-
drick, SADABS v.2.01, Bruker/Siemens Area Detector Absorption
Correction Program, Bruker AXS, Madison, Wisconsin, USA, 1998)
and ABSPACK (Crysalis Pro) were used to perform area-detector
scaling and absorption corrections. Crystallographic, collection, and
refinement data are listed in Table 1, and corresponding cif files are
available as supporting information. Molecular plots were pro-
duced by the program ORTEP3.[38] CCDC 962956 (8a), 962957 (8b),
962958 (10) and 962959 (12) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
ccdc.cam.ac.uk/products/csd/request.
Synthesis of HLThia (6a)
A solution of 3a (1.00 g, 2.9 mmol)
and
5-methyl-2-(trimethylstannyl)-
Experimental Section
thiazole (5; 1.14 g, 4.3 mmol) in dry
and degassed toluene (10 mL) was
treated with a solution of [Pd(dba)2]
General considerations and materials characterization
All air- and/or moisture-sensitive reactions were performed under
inert atmosphere in flame-dried flasks by using standard Schlenk-
type techniques or in a dry box filled with nitrogen. THF was puri-
fied by distillation from sodium/benzophenone ketyl after drying
over KOH. Benzene, n-hexane, and toluene were purified by distilla-
tion from sodium/triglyme/benzophenone ketyl or by means of
a MBraun solvent purification system. [D6]Benzene was dried over
sodium/benzophenone ketyl and condensed in vacuo over activat-
ed 4 ꢁ molecular sieves prior to use, and CD2Cl2 was dried over ac-
tivated 4 ꢁ molecular sieves. All other reagents and solvents were
(dba=trans,trans-dibenzylideneace-
tone; 0.050 g, 0.09 mmol) and PPh3
(0.182 g, 0.69 mmol) in toluene
(5 mL). The reaction mixture was
heated to reflux for 20 h, cooled to
room temperature, and treated with water (15 mL). The resulting
layers were separated, and the aqueous phase was extracted with
AcOEt (3ꢂ10 mL) and dried over Na2SO4. The collected organic
layers were evaporated under reduced pressure to give the crude
product. The product was purified by recrystallization from hot
MeOH by cooling the resulting solution at ꢀ208C overnight to
afford white needle crystals (0.79 g, 75.0% yield). 1H NMR
(400 MHz, CD2Cl2, 293 K): d=1.31 (d, 3JHH =6.8 Hz, 12H, CH(CH3),
1
used as purchased from commercial suppliers. H and 13C{1H} NMR
spectra were obtained on a Bruker Avance DRX-400 (400.13 and
100.62 MHz, respectively) or a Bruker Avance 300 MHz instrument
1
(300.13 and 75.47 MHz for H and 13C, respectively). Chemical shifts
H
H
15,16,18,19), 2.58 (s, 3H, H23), 3.54 (sept, 3JHH =6.8 Hz, 2H, CH(CH3),
d are reported relative to TMS, referenced to the chemical shifts of
residual solvent resonances (1H and 13C). IR spectra were recorded
as Nujol mulls or KBr plates on FSM 1201 and Bruker-Vertex 70 in-
14,17), 4.25 (s, 2H, H6), 7.09 (m, 1H, CH Ar, H11), 7.15–7.17 (2H, CH
Ar, H10,12), 7.32 (d, 3JHH =7.7 Hz, 1H, CH Ar, H2), 7.61 (m, 1H, CH thia-
zole, H22), 7.79 (t, JHH =7.7 Hz, 1H, CH Ar, H3), 8.07 ppm (d, JHH
=
3
3
Chem. Eur. J. 2014, 20, 3487 – 3499
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3495 ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
7.7 Hz, 1H, CH Ar, H4); 13C{1H} NMR (100 MHz, CD2Cl2, 293 K): d=
11.9 (C23), 24.0 (CH(CH3)2, C15,16,18,19), 27.7 (CH(CH3)2, C14,17), 55.9
(CH2NH, C6), 117.3 (C4), 122.3 (C2), 123.4 (C10,12), 123.7 (C11), 136.7
(C), 137.4 (C3), 141.9 (C22), 142.6 (C), 143.5 (C), 151.4 (C), 158.5 (C),
167.3 ppm (C); elemental analysis calcd (%) for C27H31N3S
(365.53 gmolꢀ1): C 72.29, H 7.45, N 11.50, S 8.77; found: C 72.40, H
7.65, N 11.45, S 8.50.
28.8 (C(CH3)2, C7,8), 59.2 (C(CH3)2, C6), 118.0 (C4), 121.4 (C2), 121.9
(C24), 123.0 (C12,14), 123.4 (C27), 124.5 (C13), 125.4 (C26), 126.1 (C25),
136.3 (C), 137.5 (C3), 140.0 (C), 146.5 (C), 149.7 (C), 154.4 (C), 168.5
(C), 170.1 ppm (C); elemental analysis calcd (%) for C22H27N3S
(429.62 gmolꢀ1): C 75.48, H 7.27, N 9.78, S 7.46; found: C 75.40, H
7.27, N 9.83, S 7.50.
Synthesis of 8a
Synthesis of HLThiaMe2 (6b)
A solution of 6a (0.277 g, 0.76 mmol)
A solution of 3b (1.00 g, 2.6 mmol)
and 5-methyl-2-(trimethylstannyl)th-
in dry and degassed toluene
(3 mL) was added to a solution of [Y-
iazole (5; 1.05 g, 4.0 mmol) in dry
(CH2SiMe3)3(thf)2] (0.376 g, 0.76 mmol)
and degassed toluene (10 mL) was
in dry and degassed toluene (7 mL)
treated with a solution of [Pd(dba)2]
at 08C. The resulting red-purple mix-
(0.045 g, 0.08 mmol) and PPh3
ture was stirred at 08C for 2 h, con-
(0.163 g, 0.62 mmol) in toluene
centrated to approximately one-
(5 mL). The reaction mixture was
fourth of its initial volume, and
heated to reflux for 20 h, cooled to
stored at ꢀ308C overnight. Dark red crystals of 8a formed. The
mother liquor was decanted and the crystals were washed with
cold hexane and dried in vacuum for 1 h. Complex 8a was isolated
room temperature, and treated with water (15 mL). The resulting
layers were separated; the aqueous phase was extracted with
AcOEt (3ꢂ10 mL) and then dried over Na2SO4. The collected organ-
ic layers were evaporated under reduced pressure to give a crude
product. The product was purified by recrystallization from hot
MeOH by cooling the resulting solution at ꢀ208C overnight to
afford white crystals (0.82 g, 80.0% yield). 1H NMR (400 MHz,
CD2Cl2, 293 K): d=1.10 (d, 3JHH =6.8 Hz, 12H, CH(CH3), H17,18,20,21),
1
in 74% yield (0.532 g, 0.56 mmol). H NMR (400 MHz, 293 K, C6D6):
2
2
2
d=ꢀ0.86 (dd, JHH =10.7, JYH =2.3 Hz, 2H, YCH2), ꢀ0.67 (dd, JHH
=
2
10.7, JYH =2.9 Hz, 2H, YCH2), ꢀ0.08 (s, 18H, SiMe3), 1.25 (brs, 4H,
b-CH2 thf), 1.43 (d, JHH =6.9 Hz, 6H, CH3 iPr, H19,21), 1.52 (d, JHH
=
3
3
6.9 Hz, 6H, CH3 iPr, H20,22), 1.84 (d,4JHH =0.9 Hz, 3H, CH3, H16), 3.45
(brs, 4H, a-CH2 thf), 4.22 (sept, JHH =6.9 Hz, 2H, CH iPr, H17,18), 4.91
3
3
1.50 (s, 6H, C(CH3)2, H7,8), 2.55 (s, 3H, H25), 3.32 (sept, JHH =6.8 Hz,
(s, 2H, CH2, H6), 6.49 (dd, 3JHH =6.9 Hz, 4JHH =1.7 Hz, 1H, CH, H4),
2H, CH(CH3), H16,19), 4.30 (brs, 1H, NH), 7.09 (m, 3H, CH Ar, H12,13,14),
6.81–6.73 (complex m, 2H, CH, H2,3), 7.20 (dd, JHH =8.3 Hz, JHH
=
3
3
3
3
7.61–7.58 (2H, H2,24), 7.81 (t, JHH =7.8 Hz, 1H, CH Ar, H3), 8.0 ppm
6.8 Hz, 1H, CH, H10), 7.28 (d, JHH =7.1 Hz, 2H, CH, H9,11), 7.51 ppm
(m, 1H, CH Ar, H4); 13C{1H} NMR (100 MHz, CD2Cl2, 293 K): d=11.9
(C25), 23.7 (CH(CH3)2, C17,18,20,21), 28.2 (CH(CH3)2, C16,19), 28.7 (C(CH3)2,
(d, JHH =0.9 Hz, 1H, CH, H14); 13C{1H} NMR (100 MHz, 293 K, C6D6):
4
d=3.9 (s, SiMe3), 11.1 (s, CH3, C16), 24.9 (s, CH3 iPr, C19,21), 25.0 (s, b-
1
C
7,8), 59.1 (C(CH3)2, C6), 116.4 (C4), 119.8 (C2), 122.9 (C12,14), 124.5
CH2 thf), 27.0 (s, CH iPr, C17,18), 27.1 (s, CH3 iPr, C20,22), 27.8 (d, JYC
=
(C13), 136.5 (C), 137.4 (C3), 140.2 (C), 141.8 (C24), 146.7 (C), 150.2 (C),
167.8 (C), 168.0 ppm (C); elemental analysis calcd (%) for C24H31N3S
(393.59 gmolꢀ1): C 73.24, H 7.94, N 10.68, S 8.15; found: C 73.20, H
7.93, N 10.70, S 8.17.
32.8 Hz, YCH2), 65.7 (d, JYC =2.8 Hz, CH2, C6), 68.9 (brs, a-CH2 thf),
2
117.4 (s, CH, C2), 122.3 (s, CH, C4), 123.4 (s, CH, C10), 123.7 (s, CH,
C
9,11), 136.4 (s, C15), 138.0 (s, CH, C3), 141.2 (s, CH, C14), 147.1 (s,
2
2
C8,12), 147.5 (d, JYC =0.9 Hz, C13), 151.6 (s, C7), 164.0 (d, JYC =0.8 Hz,
C5), 168.1 ppm (d, JYC =2.1 Hz, C1); elemental analysis calcd (%) for
2
C34H56N3OSSi2Y (699.97 gmolꢀ1): C 58.34, H 8.06, N 6.00 Y 12.70;
found: C 58.70, H 8.22, N 5.97, Y 12.58.
Synthesis of HLBnThMe2 (7)
A solution of 3b (0.50 g, 1.3 mmol)
and 2-(trimethylstannyl)benzo[d]thia-
zole (4; 0.60 g, 2.0 mmol) in dry and
Synthesis of 8b
degassed toluene (5 mL) was treated
A solution of 6b (0.330 g, 0.84 mmol)
with a solution of [Pd(dba)2] (0.023 g,
in dry and degassed toluene (3 mL)
0.04 mmol) and PPh3 (0.081 g,
was added to a solution of [Y-
0.33 mmol) in toluene (5 mL). The re-
(CH2SiMe3)3(thf)2] (0.415 g, 0.84 mmol)
action mixture was heated to reflux
in dry and degassed toluene (7 mL)
for 20 h, cooled to room tempera-
at 08C. The resulting dark red mix-
ture, and treated with water (10 mL).
ture was stirred at 08C for 2 h and
The resulting layers were separated; the aqueous phase was ex-
tracted with AcOEt (3ꢂ10 mL) and then dried over Na2SO4. The col-
lected organic layers were evaporated under reduced pressure to
give the crude product. The product was purified by recrystalliza-
tion from hot MeOH, by cooling the resulting solution at ꢀ208C
overnight to afford gray crystals (0.37 g, 63.0% yield). M.p.
then was concentrated to approxi-
mately one-fourth of its initial
volume and was stored at ꢀ308C
overnight. Dark red crystals of 8b formed. The mother liquor was
decanted and the crystals were washed with cold hexane and
dried in vacuum for 1 h. Complex 8b was isolated in 61% yield
1
3
1
133.78C; H NMR (300 MHz, CD2Cl2, 293 K): d=1.11 (d, JHH =6.8 Hz,
(0.336 g, 0.51 mmol). H NMR (400 MHz, 293 K, C6D6): d=ꢀ0.28 (dd,
3
2
12H, CH(CH3), H17,18,20,21), 1.56 (s, 6H, C(CH3)2, H7,8), 3.32 (sept, JHH
6.8 Hz, 2H, CH(CH3), H16,19), 4.23 (brs, 1H, NH), 7.10 (m, 3H, CH Ar,
12,13,14), 7.46 (m, 1H, CH BnTh, H26), 7.55 (m, 1H, CH BnTh, H25),
=
2JHH =11.1, 2JYH =3.0 Hz, 2H, YCH2), ꢀ0.16 (dd, 2JHH =11.1, JYH
=
3.1 Hz, 2H, YCH2), 0.17 (s, 18H, SiMe3), 1.26 (d, 3JHH =6.9 Hz, 6H,
3
H
CH3 iPr, H19,21), 1.43 (d, JHH =6.9 Hz, 6H, CH3 iPr, H20,22), 1.51 (s, 6H,
7.75 (d, JHH =7.8 Hz, 1H, CH Ar, H2), 7.91 (t, JHH =7.8 Hz, 1H, CH
Ar, H3), 8.00 (m, 1H, CH BnTh, H24), 8.11 (1H, CH Ar BnTh, H27),
8.27 ppm (d, 3JHH =7.8 Hz, 1H, CH Ar, H4); 13C{1H} NMR (75 MHz,
CD2Cl2, 293 K): d=23.7 (CH(CH3)2, C17,18,20,21), 28.2 (CH(CH3)2, C16,19),
CMe2 H23,24), 1.60 (s, 3H, CH3, H16), 3.70 (sept, JHH =6.9 Hz, 2H, CH
3
3
3
3
3
iPr, H17,18), 6.61 (d, JHH =7.5 Hz, 1H, CH, H4), 6.78 (d, JHH =8.0 Hz,
1H, CH, H2), 6.88 (t,3JHH =7.8 Hz, 1H, CH, H3), 7.21 (dd, JHH =8.5 Hz,
3
3JHH =5.9 Hz, 1H, CH, H10), 7.26 (m, 2H, CH, H9,11), 7.83 ppm (s, 1H,
Chem. Eur. J. 2014, 20, 3487 – 3499
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3496
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
2
CH, H14); 13C{1H} NMR (100 MHz, 293 K, C6D6): d=4.1 (s, SiMe3), 10.9
(s, CH3, C16), 24.0 (s, CH3 iPr, C19,20,21,22), 26.9 (s, CH3 iPr, C19,20,21,22),
H22), 1.65 (s, 3H, CMe2 H24), 2.03 (d, JHH =12.5 Hz, 1H, CCH2SiMe3),
2.95 (d, 2JHH =12.5 Hz, 1H, CCH2SiMe3), 3.25 (brs, 4H, a-CH2 thf),
3.78 (sept, 3JHH =6.7 Hz, 1H, CH iPr, H17), 4.28 (sept, 3JHH =6.7 Hz,
1
28.1 (s, CH iPr, C17,18), 32.8 (s, C(CH3)2, C23,24), 35.6 (d, JYC =39.2 Hz,
YCH2), 66.1 (d, JYC =2.5 Hz, CH2, C6), 117.2 (s, CH, C4), 121.2 (s, CH,
1H, CH iPr, H18), 6.89–7.01 (complex m, 3H, CH Ar, H2,4,26), 7.06–7.13
2
C2), 123.5 (s, CH, C9,11), 123.9 (s, CH, C10), 137.5 (s, C15), 139.5 (s, CH,
C3), 141.4 (s, CH, C14), 144.8 (s, C7), 146.5 (s, C13), 148.7 (s, C8,12),
168.9 (s, C5), 178.9 ppm (s, C1); 89Y{1H} NMR (19.6 MHz, C6D6, 293 K):
d=1008 ppm (s); elemental analysis calcd (%) for C32H52N3SSi2Y
(655.92 gmolꢀ1): C 58.60, H 7.99, N 6.41, Y 13.55; found: C 58.72, H
7.86, N 6.33, Y 13.31.
(complex m, 4H, CH,
H
3,10,25,27), 7.20 (dd,3JHH =7.6 Hz, JHH
=
4
1.7 Hz,1H, CH, H9), 7.26 (dd, JHH =7.6 Hz, JHH =1.7 Hz, 1H, CH, H11),
3
4
7.83 (dd, JHH =7.6 Hz, JHH =1.5 Hz, 1H, CH, H16) ppm; 13C{1H} NMR
(100 MHz, 293 K, C6D6): d=ꢀ0.8 (s, CCH2SiMe3), 4.1 (s, YCH2SiMe3),
20.8 (s, CCH2SiMe3), 24.5 (s, CH3 iPr, C19,20,21,22), 25.0 (s, b-CH2 thf),
3
4
25.3 (s, CH3iPr, C19,20,21,22), 26.4 (d, JYC =39.2 Hz, YCH2), 26.8 (s, CH3
1
iPr, C19,20,21,22), 27.2 (s, CH iPr, C17,18), 27.9 (s, CH iPr, C17,18), 28.4 (s,
CH3 iPr, C19,20,21,22), 31.2 (s, C(CH3)2, C23,24), 32.4 (s, C(CH3)2, C23,24),
Synthesis of 9
68.5 (brs, a-CH2 thf), 69.6 (d, JYC =2.6 Hz, CMe2, C6), 120.1 (s, CH,
2
C25,26), 120.4 (s, CH, C2,4), 121.5 (s, CH, C2,4), 123.5 (s, CH, C16,27),
124.0 (s, CH, C9,11), 124.6 (s, CH, C10), 124.2 (s, CH, C9,11), 127.2 (s,
A solution of 7 (0.440 g, 1.02 mmol)
in dry and degassed toluene (3 mL)
C
25,26), 135.5 (s, C16,27), 138.5 (s, CH, C3), 144.9 (s, C14,15), 145.0 (s, C7),
was added to
a solution of [Y-
145.1 (s, C14,15), 150.2 (s, C8,12), 150.4 (s, C8,12), 153.6 (s, C13),
167.8 ppm (d,2JYC =1.0 Hz, C5), 176.9 (d,2JYC =1.3 Hz, C1); elemental
analysis calcd (%) for C39H60N3OSSi2Y (764.06 gmolꢀ1): C 61.31, H
7.92, N 5.50, Y 11.64; found: C 61.53, H 7.90, N 5.61, Y 11.35.
(CH2SiMe3)3(thf)2] (0.507 g, 1.02 mmol)
in dry and degassed toluene (7 mL)
at 08C. The resulting dark purple
mixture was stirred at 08C for 2 h,
and then was concentrated to ap-
proximately one-fourth of its initial
volume and stored at ꢀ308C overnight. Dark purple crystals of 9
formed. The mother liquor was decanted and the crystals were
washed with cold hexane and dried in vacuum for 1 h. Complex 9
General procedure for intramolecular hydroamination of
amino alkenes
1
was isolated in 75% yield (0.532 g, 0.77 mmol). H NMR (400 MHz,
Two different cyclization protocols were explored, depending on
the employed catalyst system. Both procedures were set up under
an inert atmosphere in a N2-filled dry box. The conversion of each
reaction was monitored by NMR spectroscopy (by a comparative
integration of selected proton signals on the substrate and their
corresponding protons on the cyclization product) and gas chro-
matography (by integration of the reagent and product signals).
Selected experiments were additionally monitored by 1H NMR
spectroscopy with ferrocene as internal standard (0.2 mL of a stock
0.17m ferrocene solution in [D8]toluene). The internal standard was
used to measure the substrate conversion and confirm the appro-
priate reaction mass balance. In all cases, the reaction mass bal-
ance was confirmed at the limit of the NMR spectrometer experi-
mental error (1H NMR acquisition parameters: acquisition time
(aq.): 5 s; d1: 8 s; scan number (ns): 32).
293 K, C6D6): d=ꢀ0.39 (dd, 2JHH =11.0, 2JYH =2.9 Hz, 2H, YCH2),
ꢀ0.22 (dd, 2JHH =11.0, 2JYH =2.9 Hz, 2H, YCH2), ꢀ0.01 (s, 18H,
3
SiMe3), 1.33 (d, 3JHH =6.8 Hz, 6H, CH3 iPr, H19,21), 1.46 (d, JHH
=
6.8 Hz, 6H, CH3 iPr, H20,22), 1.51 (s, 6H, CMe2 H23,24), 3.86 (sept,
3JHH =6.8 Hz, 2H, CH iPr, H17,18), 6.85–6.90 (complex m, 3H, CH,
2,3,4), 6.93(ddd, 3JHH =8.2,3JHH =7.2, 3JHH =1.0 Hz, 1H, CH, H,26),
H
7.18–7.25 (complex m, 3H, CH, H10,25,27), 7.30 (m, 2H, CH, H9,11),
8.78 ppm (d,3JHH =8.3 Hz, 1H, CH, H16); 13C{1H} NMR (100 MHz,
293 K, C6D6): d=4.0 (s, SiMe3), 24.6 (s, CH3 iPr, C19,21), 27.1 (s, CH3
iPr, C20,22), 28.0 (s, CH iPr, C17,18), 32.8 (s, C(CH3)2, C23,24), 34.0 (brd,
1JYC =34.9 Hz, YCH2), 66.8 (d, 2JYC =2.4 Hz, CH2, C6), 119.2 (s, CH,
C
2,4), 121.8 (s, C16,27), 122.6 (s, CH, C2,4), 123.8 (s, CH, C9,11), 123.9 (s,
CH, C10), 124.5 (s, C16,27), 127.5 (s, C25,26), 128.0 (s, C25,26) 133.3 (s,
C15), 139.4 (s, CH, C3), 145.8 (s, C13), 146.8 (s, C7), 149.0 (s, C8,12),
150.8 (d, JYC =0.9 Hz, C14), 168.5 (brs, C5), 179.0 ppm (brs, C1); ele-
2
mental analysis calcd (%) for C35H52N3SSi2Y (691.95 gmolꢀ1): C
60.75, H 7.57, N 6.07, Y 12.85; found: C 60.99, H 7.82, N 5.98, Y
12.67.
Procedure A: catalysis by neutral dialkyl yttrium complexes: In
a typical procedure, a solution of the selected dialkyl complex
(1.05–5 mmol%) in dry and degassed toluene (1.5 mL) was slowly
added to a two-necked 10 mL round bottom flask previously
charged with a preheated, dry, and degassed solution of the de-
sired amino alkene (0.21 mmol) and ferrocene as internal standard
(0.2 mL of a stock 0.17m ferrocene solution in toluene) in toluene
(1 mL). The system was then stirred at the desired temperature
and the course of the reaction was periodically monitored by ana-
lyzing a sample of the mixture by GC-MS until completeness or at
fixed times.
Synthesis of 10
Complex 9 (0.284 g, 0.41 mmol) was
dissolved in THF/hexane (1/1, 15 mL)
and the solution heated at 508C for
6 h. The color of the reaction mixture
changed from dark purple to dark
red. Concentration and storage of re-
Procedure B: catalysis by cationic monoalkyl yttrium complexes:
In a typical procedure, a toluene solution (0.5 mL) of the activator
Ph3C+[B(C6F5)4]ꢀ was slowly added to a solution of the dialkyl com-
plex (1.05–5 mmol%) in toluene (1 mL) at RT. The solution was rap-
idly stirred and transferred to a two-necked 10 mL round-bottom
flask previously charged with a preheated, dry, and degassed solu-
tion of the desired amino alkene (0.21 mmol) and ferrocene as in-
ternal standard (0.2 mL of a stock 0.17m ferrocene solution in tolu-
ene) in toluene (1 mL). The system was then stirred at the desired
temperature and the course of the reaction was periodically moni-
tored by analyzing a sample of the mixture by GC-MS until com-
pleteness or at fixed times.
sulting solution at ꢀ308C resulted in
formation of red crystals of 10. The
mother liquor was decanted and the
crystals were washed with cold
hexane and dried in vacuum for 1 h. Complex 10 was isolated in
1
70% yield (0.220 g, 0.29 mmol). H NMR (400 MHz, 293 K, C6D6): d=
2
2
2
ꢀ0.77 (dd, JHH =10.5 Hz, JYH =3.0 Hz, 2H, YCH2), ꢀ0.74 (dd, JHH
=
2
10.5 Hz, JYH =3.0 Hz, 2H, YCH2), ꢀ0.21 (s, 9H, CCH2SiMe3), 0.06 (s,
9H, YCH2SiMe3), 1.14 (d, 3JHH =6.7 Hz, 3H, CH3 iPr, H19), 1.22–1.36
(complex m, 10H, CMe2, H23, CH3 iPr, H21, and b-CH2 thf), 1.44 (d,
3JHH =6.7 Hz, 3H, CH3 iPr, H20), 1.47 (d, 3JHH =6.7 Hz, 3H, CH3 iPr,
Chem. Eur. J. 2014, 20, 3487 – 3499
www.chemeurj.org
3497
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Generation of cationic monoalkyl complexes by treatment
of the dialkyl precursors with Ph3C+[B(C6F5)4]ꢀ in situ
Acknowledgements
The authors thank the Russian Foundation for Basic Research
(Project 12-03-93109-NTSNIL a) and the Groupe de Recherche
International (GDRI) “Homogeneous Catalysis for Sustainable
Development” for support to this work.
The generation of the cationic monoalkyl catalysts was monitored
by 1H NMR spectroscopy on the most soluble system in
[D6]benzene. Indeed, for all cationic monoalkyl systems a dark red
rubbery precipitate started to form within a few minutes, and the
most soluble one was that resulting from activation of 9 (9+). Al-
though poorly soluble in aromatic hydrocarbons, the activated
complexes are stable as precipitates for days with no apparent de-
composition. Polar aromatics such as mono- or dihalobenzenes
(halo=Cl, Br) increase the solubility of the complex while causing
progressive catalyst degradation with the generation of untreata-
ble dark-brown semisolid materials. To improve the solubility of
the activated complex 9+ and thus allow its characterization by
1H NMR spectroscopy, Ph3C+[B(C6F5)4]ꢀ (1 equiv) was dissolved in
C6D5Br (0.2 mL) and added in one portion to a dry and degassed
dark purple solution of dialkyl complex 9 (0.021 mmol, 1 equiv) in
[D6]benzene (0.5 mL). The resulting mixture was placed in a J.
Keywords: hydroamination · N ligands · ring opening ·
tridentate ligands · yttrium
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Þ
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Published online on February 24, 2014
Chem. Eur. J. 2014, 20, 3487 – 3499
www.chemeurj.org
3499
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim