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degassed toluene (2.5 mL) was heated at 1008C. After keeping the
pre-heated catalyst solution under stirring for 10 min, a pre-heated
(808C) solution of the aminoalkene 4 (0.150 g, 0.632 mmol) in dry
and degassed toluene (0.5 mL) was added by a syringe in one por-
tion. Afterwards, the reaction course was periodically monitored by
sampling the reaction mixture and analyzing it with GC–MS, till
completeness was achieved. Finally, the reaction mixture was con-
centrated under reduced pressure and the crude material was puri-
fied by flash-chromatography (CH2Cl2 +5% MeOH) to give the final
pure pyrrolidine.
X-ray data measurements
Single crystal X-Ray data were collected at low temperature (120 K)
on an Oxford Diffraction XCALIBUR 3 diffractometer equipped with
a CCD area detector by using MoKa radiation (l=0.7107 ꢃ). The
program used for the data collection was CrysAlis CCD 1.171.[26]
Data reduction was performed with the program CrysAlis RED
1.171[27] and the absorption correction was applied with the pro-
gram ABSPACK 1.17. Direct methods implemented in Sir97[28] were
used to solve the structures and the refinements were performed
by full-matrix least-squares against F2 implemented in SHELX97.[29]
All the non-hydrogen atoms were refined anisotropically, whereas
the hydrogen atoms were fixed in calculated positions and refined
isotropically with the thermal factor depending on the atoms to
which they are bound (riding model). In the refinement of 3Ph,Zr, re-
straints on some anisotropic displacement parameters of C atoms
Kinetic measurements on 3Th,Zr/3’Th,Zr and 4Th,Zr
Kinetic studies were performed for the conversion of 4 by varying
the catalyst concentration (4, 6, or 8 mol%) or the catalyst precur-
sor (3Th,Zr/3’Th,Zr or 4Th,Zr), for all runs with a constant initial concen-
tration of 4. All measurements were performed in a sealed J-Young
NMR tube and the course of the process was monitored by
1H NMR spectra recorded at constant time intervals with ferrocene
as the internal standard. Both catalyst precursors 3Th,Zr/3’Th,Zr and
4Th,Zr showed a first order dependence in substrate consumption/
cyclization. To better compare the two catalyst precursors, 5 mol%
had to be introduced, owing to the bad crystal data quality (Rint
=
0.30) generated by the existence of different conformers in the
same lattice (see the Results and Discussion section) and by the
disorder of the dimethylamido ligands even at 120 K. Molecular
plots were produced by the program ORTEP3.[30] Catalytic reactions
were performed under an inert atmosphere in either a J-Young
NMR tube or in a 10 mL round bottom flask and the reaction
1
course was followed by H NMR spectroscopy and GC–MS analysis,
of 3Th,Zr/3’Th,Zr were compared with 3.75 mol% of the pure 4Th,Zr
.
respectively. All substrates were dried overnight over activated 4 ꢃ
molecular sieves with a few drops of [D6]benzene prior to use.
Previous studies by some of us showed a 25:75 ratio of 3Th,Zr/3’Th,Zr
at the target reaction temperature (1008C).[4] Based on this, equal
amounts of the cyclometalated species 3’Th,Zr and 4Th,Zr were then
taken into account. In a typical procedure, stock solutions of cata-
lyst precursors 3Th,Zr/3’Th,Zr and 4Th,Zr were prepared by dissolving
each complex (20 mg) in [D8]toluene (0.5 mL). 4 (20 mg) and ferro-
cene (98%, 5 mg, 26.34 mmol) (internal standard)[10j] were weighted
General procedure for intramolecular hydroamination of
aminoalkenes
into a 1 mL volumetric flask and dissolved in [D8]toluene
ꢁ0.2 mL). Afterwards, a proper amount of the stock solution of
the catalyst precursor (0.06 mL of 3Th,Zr/3’Th,Zr; 0.04 mL of VITh,Zr
(
Two different cyclization conditions were used depending on the
employed catalytic system. Both procedures were set-up under an
inert atmosphere with N2 or an Ar-filled dry box.
)
was added to the 1 mL volumetric flask and the volume was
topped to 1 mL with [D8]toluene. The as-prepared solution was
shaken and 0.8 mL were rapidly transferred into the J-Young NMR
tube. The tube was placed into a pre-heated (1008C) 300 MHz
NMR probe and the system was allowed to thermally equilibrate
for 5 min before collecting the t=0 min 1H NMR spectrum. The
1H NMR spectra (8 scans) were collected every 5–10 min up to the
almost complete substrate conversion (at least 90%). Comparison
of the integration of product and substrate peaks with internal stan-
dard peaks was used to calculate the relative percentage of sub-
strate and product at any given time (see the Supporting Information).
Procedure A: Neutral (alkyl) and cationic group IV amidopyridinate
complexes were tested as catalyst precursors in the intramolecular
hydroamination reaction with a sealed J-Young NMR tube.
For neutral complexes 1Zr and 1Hf: In an Ar-filled dry box, a solution
of isolated 1Zr or 1Hf (0.016 mmol) in C6D6 (0.6 mL) was slowly
added to
a vial containing the corresponding aminoalkene
(0.16.10À3 mol) at RT. The homogeneous reaction mixture was then
introduced into a J. Young-tap NMR tube and placed in an oil bath
heated to 1008C. The conversion of the reaction was monitored by
comparative integration of the signal relative to the olefinic pro-
tons of the substrate and the signal relative to the protons of the
product. A similar procedure was used for kinetic measurements
with precatalysts 3Th,Zr/3’Th,Zr and 4Th,Zr.
First order in catalyst concentration for the pure 4Th,Zr was deter-
mined by using a similar procedure to that described above. Three
different catalyst concentrations (4, 6 and 8 mol% of 4Th,Zr) were
used in the presence of a constant concentration of 4. In a typical
procedure, the proper amount of 4Th,Zr in [D8]toluene (stock solu-
tion) was added to a solution of 4 (20 mg, 84.27 mmol) and ferro-
cene (5 mg, 26.34 mmol, internal standard) and the volume was in-
creased to 1 mL with [D8]toluene. The solution was shaken and
0.8 mL were rapidly transferred into the J-Young NMR tube. The re-
action course was monitored by 1H NMR spectra, similarly to the
procedure described above (see the Supporting Information).
For cationic complexes 2Zr and 2Hf: In an Ar-filled dry box, [Ph3C]
[B(C6F5)4] was slowly added to a solution of 1Zr or 1Hf (0.016 mmol)
in C6D6 (0.6 mL) at RT. The solution was stirred a few minutes and
transferred into a vial containing the corresponding aminoalkene
(0.16 mmol). The heterogeneous reaction mixture was then intro-
duced into a J. Young-tap NMR tube and placed in an oil bath
heated at 1008C. The conversion of the reaction was monitored by
comparative integration of the signal relative to the olefinic pro-
tons of the substrate and the signal relative to the protons of the
product.
Acknowledgements
Procedure B: Amido precursors 3Th,M/3’Th,M and 4Th,M (M=Zr, Hf)
were tested as catalysts in the intramolecular hydroamination reac-
tion by using a two-necked 10 mL round bottom flask equipped
with a magnetic stir bar, a reflux condenser and a septum. In a typi-
cal procedure, a solution of the pre-catalyst (5 mol%) in dry and
The authors thank the Groupe de Recherche International (GDRI)
“Homogeneous Catalysis for Sustainable Development” for sup-
port.
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2013, 5, 1142 – 1151 1149
Luconi, Lapo
