Intramolecular hydroamination reactions catalyzed by zirconium complexes bearing bridged bis(phenolato) ligands

Article abstract of DOI:10.1039/c5ra23270h

Zirconium complexes stabilized by piperazidine- and imidazolidine-bridged bis(phenolato) ligands have been synthesized and characterized. Their activities in catalyzing intramolecular hydroamination reactions have been tested and compared, which reveals the significant role that the ancillary ligands play in influencing catalytic activities. Cationic species derived from zirconium dibenzyl complexes showed good activities in catalyzing intramolecular hydroamination reactions of both primary and secondary amines, and afforded the respective N-heterocycles in 85% to 99% yields. Moreover, this catalytic system also catalyzed sequential cyclization of primary aminodienes, and generated bicyclic tertiary amines in 94-99% yields.

Full text of DOI:10.1039/c5ra23270h

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Intramolecular hydroamination reactions catalyzed
by zirconium complexes bearing bridged
bis(phenolato) ligands†
Cite this: RSC Adv., 2016, 6, 10541
*
*
Yu Zhang, Qiu Sun, Yaorong Wang, Dan Yuan, Yingming Yao and Qi Shen
Zirconium complexes stabilized by piperazidine- and imidazolidine-bridged bis(phenolato) ligands have
been synthesized and characterized. Their activities in catalyzing intramolecular hydroamination
reactions have been tested and compared, which reveals the significant role that the ancillary ligands
play in influencing catalytic activities. Cationic species derived from zirconium dibenzyl complexes
showed good activities in catalyzing intramolecular hydroamination reactions of both primary and
secondary amines, and afforded the respective N-heterocycles in 85% to 99% yields. Moreover, this
catalytic system also catalyzed sequential cyclization of primary aminodienes, and generated bicyclic
tertiary amines in 94–99% yields.
Received 5th November 2015
Accepted 15th January 2016
DOI: 10.1039/c5ra23270h
www.rsc.org/advances
Bis(phenolato) ligands are derived from readily available
bis(phenol)s and can be conveniently tuned in terms of both
Introduction
electronic and steric properties. Recently, our group have re-
ported a series of group 4 metal complexes stabilized by bridged
bis(phenolato) ligands, which showed good activities in cata-
lyzing intermolecular hydroamination reactions of both
primary and secondary amines.7 Ancillary ligands with different
backbones and substituents are found to play signicant roles
in inuencing catalytic activities of zirconium complexes.7c As
a continuation of our study, a series of bis(phenolato) ligand
stabilized zirconium complexes with different coordination
environment were synthesized, and their activities for intra-
molecular hydroamination were tested and compared.
Hydroamination reactions, which involve the direct addition of
N–H bonds over carbon–carbon unsaturated bonds, represent
one of the most atom-economic approaches to construct phar-
maceutically and biologically important nitrogen-containing
compounds.1 Over the past decades, signicant efforts have
been devoted to develop efficient catalysts to promote such
transformations, which involve early1a and late transition met-
al1b,d,e and main-group metal complexes.1f Group 4 metal
complexes have drawn great interest due to their easy avail-
ability and high activity.1a,g,2 Since the rst zirconium catalysts
for hydroamination reactions reported in the 1990s,3 zirconium
complexes of various structures and different activities have
been developed. A major limitation of zirconium complexes in
general is that they are only capable of catalyzing intra-
molecular hydroamination/cyclization of primary amines, while
they show no activity towards reactions of secondary amines.1a,g
On the other hand, cationic zirconium complexes in most
instances showed great activities for secondary amines, while
they are inactive for primary amines.4 To date, zirconium
complexes that are active for intramolecular hydroamination
reactions of both primary and secondary amines are still rela-
tively rare.5,6
Results and discussion
Synthesis and characterization of zirconium complexes
Ligand precursors L1H2 and L2H2 bearing piperazidine and
imidazolidine bridges were treated with ZrBn4, which generated
zirconium dibenzyl complexes 1 and 2 in good yields of 80%,
respectively (Scheme 1). Complexes 3–5 were synthesized
according to literature methods for comparative study.7,8
The identity of complexes 1 and 2 were conrmed by 1H, 13
C
1
NMR and X-ray diffraction analysis, respectively. The H NMR
spectrum of complex 1 suggests a C2-symmetric molecule, and
four signals at 2.90, 2.70, 2.60 and 1.04 ppm are assigned to
eight methylene groups. In contrast, more signals are observed
in the 1H NMR spectrum of complex 2, revealing a non-
symmetric structure, and seven methylene groups are found
to resonate in the range of 4.32–2.17 ppm.
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry,
Chemical Engineering and Materials Science, Dushu Lake Campus, Soochow
University, Suzhou 215123, People's Republic of China. E-mail: yuandan@suda.edu.
cn; yaoym@suda.edu.cn
† Electronic supplementary information (ESI) available: 1H and 13C NMR spectra
of complexes 1 and 2, and hydroamination products. X-ray crystallographic data of
1 and 2. CCDC 1433490 and 1433491. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c5ra23270h
The difference in solution behaviors between complexes 1
and 2 is also observed in their solid state structures. As depicted
in Fig. 1, the zirconium center in complex 1 is hexa-coordinated
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 10541–10548 | 10541

View Article Online
RSC Advances
Paper
Scheme 1 Synthesis of zirconium complexes stabilized by bis(phenolato) ligands.
by two N and two O atoms of the ligand L1 and two benzyl of complexes 1–5 (Table 1). In general, 5 mol% of these
groups. Complex 1 adopts an octahedral geometry. Bond complexes catalyzed this reaction, and afforded the cyclized
ꢀ
distances of Zr–N bonds amount to 2.389(5) A, while bond product 7a in 70–97% yields (entry 1, 2, 4, 5), with the exception
2
ꢀ
lengths of Zr–O bonds are 2.048(4) A. In contrast, ligand L in of complex 3 (entry 3). Clearly subtle modications in ligands
complex 2 coordinates through one N and two O atoms (Fig. 2), result in profound changes in catalytic activities. Steric
ꢀ
while the distance between Zr1 and N2 (3.907 A) is not within congestions around metal centers in complexes 2, 3 and 4 may
that of a reasonable bond. Both nitrogen atoms are reported to account for their lower activity. Moreover, with the addition of
bind to the same metal centers in mononuclear lanthanide and the cationic reagent [Ph3C][B(C6F5)4] (TB), the yields of 7a were
yttrium complexes bearing the same ligand L2, probably as largely improved to 91–99%. In situ generated cationic
a result of their larger ionic radii.9 Benzyl groups in complexes 1 complexes are believed to possess increased Lewis acidity and
and 2 are located cis to each other, as evidenced by the C–Zr–C reduced steric hindrance, which facilitates the catalytic cycli-
angles of 107.95ꢀ (for complex 1) and 120.04ꢀ (for complex 2), zation process. Similar trends have been observed for inter-
while two O atoms of phenolate groups are arranged in a trans molecular hydroamination reactions catalyzed by cationic Zr
conguration. This observation is in consistent with that of Zr complexes7 and group 3 metal complexes.10 It is noteworthy the
complexes stabilized by various bridged bis(phenolato) ligands.8 mixture of complex 1 and TB showed overall the best activity, as
the model reaction resulted in >99% yield within 4 h (entry 6).
Catalytic intramolecular hydroamination reactions of
aminoalkenes
Intramolecular hydroamination reaction of 2,2-diphenylpent-4-
enyl-amine (6a) was rst studied to compare catalytic activities
Fig. 1 Molecular structure of 1 showing 30% probability ellipsoids. Fig. 2 Molecular structure of 2 showing 30% probability ellipsoids.
ꢀ
Two phenyl groups of benzyl groups and hydrogen atoms are omitted Hydrogen atoms are omitted for clarity. Selected bond lengths (A) and
ꢀ
for clarity. Selected bond lengths (A) and bond angles (deg): Zr1–O1 bond angles (deg): Zr1–O1 2.001(3), Zr1–O2 1.999(3), Zr1–N1 2.356(3),
2.048(4), Zr1–N1 2.389(5), Zr1–C1 2.273(6), O1–Zr1–N1 73.02(17), O1– Zr1–C1 2.294(4), Zr1–C2 2.287(4), O1–Zr1–N1 75.81(12), O1–Zr1–C1
Zr1–N2 113.93(18), O1–Zr1–C1 89.9(2), O1–Zr1–C2 85.7(2), N1–Zr1– 91.22(14), O1–Zr1–C2 95.75(15), N1–Zr1–O2 85.39(11), N1–Zr1–C1
N2 61.7(3), N1–Zr1–C1 102.4(2), N1–Zr1–C2 142.6(2), C1–Zr1–C2 121.49(14), N1–Zr1–C2 118.05(14), O2–Zr1–C1 95.48(14), O2–Zr1–C2
108.0(4).
96.41(14), C1–Zr1–C2 119.92(16).
10542 | RSC Adv., 2016, 6, 10541–10548
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
Table 2 Intramolecular hydroamination reactions of primary amines
catalyzed by complex 1 and TBa
No cyclization reaction was detected in the presence of [Ph3C]
[B(C6F5)4] only (entry 11).11
Under optimal conditions, a range of primary amino-
alkenes with different functional groups were studied, and
the results are summarized in Table 2. Both aliphatic and
aromatic primary amines underwent hydroamination/
cyclization reactions to generate six- and ve-membered
N-heterocycles in 88–97% yields (Table 2, entry 1–4). The
transformation of more challenging internal alkene 6c worked
less efficiently, and afforded cyclized product 7c in 88% yield at
an elevated temperature of 135 ꢀC aer prolonged reaction
time of 48 h (entry 2). The reaction with the ortho-allylaniline
6e afforded 2-methylindoline, which required higher temper-
ature and longer reaction time than that of aliphatic analogue
6a (entry 4).
To probe the activity of Zr bis(phenolato) complexes in
catalyzing intramolecular hydroamination of secondary ami-
noalkenes, a comparative study between neutral complex 1 and
its cationic derivative was conducted. No yield was detected in
the presence of neutral complex 1 (Table 3, entry 1), while
a dramatic increase to >99% yield was observed with in situ
generated cationic species (entry 2). Comparing to complexes
2–5 under identical conditions, the mixture of 1 and TB showed
the highest catalytic activity, which is consistent with the result
obtained from primary aminoalkene cyclization (vide supra)
(entry 2–6).
Entry Aminoalkene
Conditions Product
Yieldb (%)
110 ꢀC
18 h
1
97
135 ꢀC
48 h
2
3
88
140 ꢀC
8 h
95c
140 ꢀC
48 h
4
94c,d
a
Conditions: 6 (0.5 mmol), 1 (20 mg, 0.025 mmol), [Ph3C][B(C6F5)4] (TB)
(23 mg, 0.025 mmol), PhCl (2 mL). b Isolated yield based on the mass of
c
puried products aer column chromatography. PhBr-d5 (0.7 mL),
determined by 1H NMR spectroscopy. 10 mol% catalyst loading.
d
in 95% yield within 6 h (entry 1). The piperidine derivative 7h
formed in an almost quantitative yield of 97% (entry 2).
Secondary amines with different N-substituents were also
tested, and 85–97% yields of desired products 7i–7k were iso-
lated (entry 3–5), showing a good group tolerance of the cationic
system. Bicyclic tertiary amines 7l and 7m formed in good yields
of 94 and 99%, respectively, from sequential cyclization of
aminodienes 6l and 6m (entry 7 and 8). The reaction of
Reactions with other secondary amines also worked
straightforwardly in the presence of 1 and TB, and generated
a series of tertiary amines in good to excellent yields (Table 4).
The reaction with secondary amine 6g proceeded smoothly
under room temperature, and furnished the desired product 7g
Table 1 Intramolecular hydroamination of 2,2-diphenylpent-4-enyl-
amine (6a) catalyzed by complexes 1–5a
Table 3 Intramolecular hydroamination of N-(4-chlorobenzyl)-2,2-
diphenylpent-4-enyl-amine (6f) catalyzed by complexes 1–5a
Entry
Cat.
Time
Yieldb (%)
1
2
3
4
5
6
7
8
1
2
3
4
8
12
12
12
12
4
12
12
12
12
12
94
70
Trace
82
97
>99
94
94
96
99
Entry
Cat.
Time (h)
Yieldb (%)
1
2
3
4
5
6
1
20
20
20
20
20
20
Trace
>99 (87)c
79
90
58
5
1 + TB
2 + TB
3 + TB
4 + TB
5 + TB
1 + TB
2 + TB
3 + TB
4 + TB
5 + TB
TB
9
10
11
94
a
Conditions: N-(4-chlorobenzyl)-2,2-diphenylpent-4-enyl-amine 6f (181
mol%), [Ph3C]
Trace
mg, 0.5 mmol), precatalyst 1–5 (0.025 mmol,
5
a
Conditions: 2,2-diphenylpent-4-enyl-amine 6a (118 mg, 0.5 mmol), [B(C6F5)4] (TB) (23 mg, 0.025 mmol) if necessary, PhCl (2 mL), 140 ꢀC.
b
c
precatalyst 1–5 (0.025 mmol, 5 mol%), [Ph3C][B(C6F5)4] (TB) (23 mg,
PhBr-d5 (0.7 mL), determined by 1H NMR spectroscopy. Isolated
b
0.025 mmol) if necessary, PhCl (2 mL), 100 ꢀC. Isolated yield based yield based on the mass of puried products aer column
on the mass of puried products aer column chromatography.
chromatography.
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 10541–10548 | 10543

View Article Online
RSC Advances
Paper
Table 4 Intramolecular hydroamination reactions of secondary amines catalyzed by complex 1 and TBa
Entry
Aminoalkene
Conditions
Product
Yieldb (%)
95
25 ꢀC
6 h
1
60 ꢀC
48 h
2
3
97
85
140 ꢀC
50 h
140 ꢀC
48 h
4
97
88
140 ꢀC
60 h
5
6
140 ꢀC
70 h
94c
140 ꢀC
96 h
7
99c,d
a
Conditions: 6 (0.5 mmol), 1 (20 mg, 0.025 mmol), [Ph3C][B(C6F5)4](TB) (23 mg, 0.025 mmol), PhCl (2 mL). b Isolated yield based on the mass of
puried products aer column chromatography. c PhCl-d5 (0.7 mL), determined by H NMR spectroscopy. 10 mol% catalyst loading.
1
d
To ascertain the formation of cationic complex from 1 and
1
TB, H NMR monitoring of the reaction was performed. Aer
reaction, all methylene protons of ligand L1 become diaster-
eotopic, and give rise to eight doublets/multiplets in the range
of 5.44–1.00 ppm (ESI†). Moreover, a characteristic signal cor-
responding to Ph3CCH2Ph that formed as a by-product is
detected at 3.83 ppm, which provides some indirect evidence on
cationic complex formation. However, all attempts to isolate the
cationic species failed.
Based on the afore-discussed results, it is thus conclusive
that the cationic species generated from complex 1 and TB
represents one of the most active group 4 metal systems for
cyclization of both primary and secondary amine.4 On the basis
of previous studies on an oxazolinylborate-supported Zr cata-
lyst,12 a tethered bis(ureate) Zr complex,5f and an amino acid
derived [ONO]-type ligated Zr complex2b which provide solid
evidence on a proton-assisted C–N bond formation mechanism,
a plausible mechanism involving concerted C–H and C–N bond
formation is proposed in Scheme 2. Reaction of neutral complex
1 and TB generates cationic complex A, which undergoes ami-
nolysis with excess amine to form Zr–amide complex B. Based
Fig. 3 1H NMR monitoring of sequential cyclization of 6l.
aminodiene 6l (entry 7) was monitored by 1H NMR spectroscopy
(Fig. 3), which revealed that the rst-step cyclization was
complete within the rst four hours, while the cyclization of
secondary amine took much longer time of 66 hours.
10544 | RSC Adv., 2016, 6, 10541–10548
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
(ref. 7 and 8) were prepared according to literature methods.
CHCl3 was distilled under argon from P2O5. NMR spectra were
recorded on a 400 MHz spectrometer. X-ray crystallographic
data were obtained with an AXS D8 X-ray diffractometer.
Preparation of Zr(CH2Ph2)2L1 (1)
To a solution of ZrBn4 (0.91 g, 2 mmol) in toluene (10 mL),
a solution of L1H2 (1.05 g, 2 mmol) in toluene was added at
room temperature, during which the colour of the solution
changed from orange to yellow. Aer the solution was stirred
overnight, it was ltered and concentrated to 4 mL. Crystals
suitable for X-ray diffraction analyses were obtained at room
temperature aer a few days upon standing (1.27 g, 1.6 mmol,
80%). 1H NMR (400 MHz, C6D6): d 7.60 (s, 2H, ArH), 6.97 (d, 8H,
J ¼ 23.33 Hz, ArH), 6.77 (s, 2H, ArH), 6.69 (s, 2H, ArH), 2.90 (s,
4H, ArCH2), 2.71 (s, 4H, NCH2CH2N), 2.61 (s, 4H, NCH2CH2N),
1.89 (s, 18H, o-C(CH3)3), 1.41 (s, 18H, p-C(CH3)3), 1.05 (s, 4H,
CCH2N). 13C{1H} NMR (100 MHz, C6D6): 158.2, 148.7, 140.8,
138.3, 126.9, 124.0, 123.1, 121.2 (Ar–C), 70.5 (Ar–CH2N), 59.5
(NCH2CH2N), 48.6 (NCH2CH2N), 36.1 (C(CH3)3), 34.8 (C(CH3)3),
32.4 (C(CH3)3), 30.9 (C(CH3)3). Anal. calcd for C48H66N2O2Zr: C,
72.58; H, 8.38; N, 3.53. Found: C, 72.55; H, 8.40; N, 3.51.
Scheme 2 Plausible mechanism.
on the nding that A is an active precatalyst for both primary
and secondary amine transformation, Zr–imido intermediates
are excluded in this system. Intramolecular hydroamination
reaction takes place via concerted C–H and C–N bonds forma-
tion (intermediate C),2b,5f,12 followed by the disassociation of the
cyclized product. However, the possibility of alkene insertion
into Zr–amido bond cannot be unambiguously ruled out, which
requires further mechanistic investigations.
Preparation of Zr(CH2Ph2)2 L2 (2)
Complex 2 was prepared in analogous to that of complex 1 from
ZrBn4 (0.91 g, 2 mmol) and L2H2 (1.02 g, 2 mmol). Yield: 1.25 g,
1.6 mmol, 80%. 1H NMR (400 MHz, C6D6): d 7.62 (d, 2H, J ¼ 2.66
Hz, ArH), 7.21 (d, 2H, J ¼ 8.22 Hz, ArH), 7.08 (d, 2H, J ¼ 9.05 Hz,
ArH), 7.02–6.95 (m, 4H, ArH), 6.85–6.76 (m, 3H, ArH), 6.67–6.66
(m, 1H, ArH), 4.31 (d, 1H, J ¼ 9.51 Hz, ArCH2), 2.93 (s, 2H,
CCH2N), 2.76–2.66 (m, 6H, NCH2CH2CH2N), 2.54–2.48 (m, 3H,
ArCH2), 2.19–2.17 (m, 2H, NCH2C), 1.88 (s, 18H, o-C(CH3)3), 1.37
(s, 18H, p-C(CH3)3). 13C{1H} NMR (100 MHz, C6D6): 158.5, 146.2,
142.9, 142.2, 137.7, 129.7, 129.0, 127.9, 126.0, 124.5, 123.5, 122.5
(Ar–C), 79.1 (Ar–CH2N), 66.4 (Ar–CH2N), 65.2 (NCH2N), 57.4
(NCH2CH2N), 49.6 (NCH2CH2N), 36.0 (C(CH3)3), 34.8 (C(CH3)3),
32.3 (C(CH3)3), 31.2 (C(CH3)3). Anal. calcd for C47H64N2O2Zr: C,
72.35; H, 8.27; N, 3.59. Found: C, 72.33; H, 8.29; N, 3.60.
Conclusion
In summary, zirconium complexes stabilized by bridged
bis(phenolato) ligands have been prepared, which showed good
activities in catalyzing intramolecular hydroamination reac-
tions. Ancillary ligands are found to play signicant roles in
inuencing activities of complexes through tuning the steric
and electronic environment around the metal center. Various
aminoalkenes including primary and secondary amine-tethered
terminal and internal alkenes with different functional groups
were transformed into respective N-heterocycles in 85% to 99%
yields. Sequential cyclization of primary aminodienes was also
studied, which generated bicyclic tertiary amines in 94–99%
yields. Further studies on development of application of group 4
metal complexes are ongoing in our laboratory.
General procedure for hydroamination reactions
The reactions were carried out in a glovebox lled with nitrogen.
Complex 1 (20 mg, 0.025 mmol) and [Ph3C][B(C6F5)4] (23 mg,
0.025 mmol) were mixed in PhCl (2 mL). The solution was
stirred for ve minutes, and 6 was added subsequently. The
resulting solution was stirred at the desired temperature for the
desired time. Aer reaction, the solvent was removed under
reduced pressure and the products were isolated by column
chromatography (petroleum ether/ethyl acetate 100/1, silica gel)
Experimental section
General considerations
1
and characterized by H and 13C NMR spectroscopy.
All manipulations of air- or moisture sensitive compounds were
performed under an inert atmosphere of argon or nitrogen
using ame-dried Schlenk glassware or glovebox techniques.
2-Methyl-4,4-diphenyl-pyrrolidine (7a)
Toluene and hexane were distilled over Na wire prior to use 7a was prepared from 6a (119 mg, 0.5 mmol) as a colourless oil
1
under argon. PhCl, PhBr-d5 and PhCl-d5 were dried over CaH2. in 99% yield (117 mg). H NMR (400 MHz, CDCl3): d 7.21–7.12
ZrBn4 were prepared using ZrCl4 and BnMgCl.13 Ligand (m, 8H, ArH), 7.05 (t, 2H, ArH), 3.56 (d, 2H, J ¼ 11.72 Hz,
precursors L1H2 (ref. 14) and L2H2 (ref. 9b) and complexes 3–5 NCH2C), 3.35 (d, 2H, J ¼ 11.78 Hz, NCH2C), 3.31–3.22 (m, 1H,
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 10541–10548 | 10545

View Article Online
RSC Advances
Paper
NCH), 2.66–2.51 (m, 1H, CCH2C), 2.35 (s, 1H, NH), 1.94 (t, 1H,
CCH2C), 1.09 (d, 3H, J ¼ 7.64 Hz, CH3). 13C{1H} NMR (100 MHz,
CDCl3): 147.8, 147.1, 128.4, 128.8, 127.1, 127.1, 126.1 (Ar–C),
57.9 (NCH2), 57.2 (CPh2), 53.2 (NCH), 47.1 (CH2), 22.5 (CH3).
N-Methyl-2-methyl-5,5-diphenylpyrrolidine (7g)
7g was prepared from 6g (126 mg, 0.5 mmol) as a colourless oil
1
in 95% yield (119 mg). H NMR (400 MHz, CDCl3): d 7.33–7.13
(m, 10H, ArH), 3.82 (d, 1H, J ¼ 8.96 Hz, NCHC), 2.92–2.87 (m,
2H, NCH2C), 2.56–2.48 (m, 1H, CCH2C), 2.38 (s, 1H, NCH3),
2.27–2.21 (m, 1H, CCH2C), 1.16 (d, 3H, J ¼ 6.06 Hz, CCH3). 13
C
2-Methyl-5,5-diphenylpiperidine (7b)
{1H} NMR (100 MHz, CDCl3): 128.4, 128.3, 127.6, 127.3, 126.0,
125.7 (Ar–C), 70.5 (NCH3), 62.1 (NCH2), 52.8 (CPh2), 48.7 (NCH),
40.7 (CH2), 19.1 (CCH3).
7b was prepared from 6b (126 mg, 0.5 mmol) as a colourless oil
in 97% yield (122 mg). 1H NMR (400 MHz, CDCl3): d 7.40 (d, 2H,
J ¼ 7.28 Hz, ArH), 7.33 (t, 2H, ArH), 7.08–7.23 (m, 6H, ArH), 3.89
(dd, J ¼ 3.19 Hz, J ¼ 3.15 Hz, 1H), 3.09 (d, 1H, J ¼ 13.53 Hz,
NCH2C), 2.80–2.72 (m, 1H, NCH), 2.67–2.73 (m, 1H, CCH2C),
2.24–2.16 (m, 1H, CCH2C), 1.65–1.61 (m, 1H, CCH2C), 1.48 (s,
1H, NH), 1.20–1.10 (m, 1H, CCH2C) 0.99 (d, 3H, J ¼ 6.33 Hz,
CH3). 13C{1H} NMR (100 MHz, CDCl3): 149.0, 144.9, 128.4,
128.8, 128.4, 126.6, 126.0 (Ar–C), 56.0 (NCH2), 52.5 (CPh2), 45.4
(NCH), 35.6 (CH2), 31.6 (CH2), 22.6 (CH3).
N-Methyl-2-methyl-5,5-diphenylpiperidine (7h)
7h was prepared from 6h (132 mg, 0.5 mmol) as a colourless oil
in 97% yield (129 mg). 1H NMR (400 MHz, CDCl3): d 7.41 (d, 2H,
J ¼ 8.28 Hz, ArH), 7.27–7.11 (m, 8H, ArH), 3.47 (d, 1H, J ¼ 11.8
Hz, NCHC), 2.40–2.44 (m, 1H, NCH2C), 2.28 (s, 1H, NCH3), 2.19–
2.11 (m, 1H, NCH2C), 1.58–1.51 (m, 1H, CCH2C), 1.31–1.21 (m,
1H, CCH2C), 1.02 (d, 3H, J ¼ 6.06 Hz, CCH3). 13C{1H} NMR (100
MHz, CDCl3): 149.1, 146.9, 128.9, 128.1, 127.8, 127.2, 126.8,
125.8, 125.3 (Ar–C), 66.0 (NCH3), 59.0 (NCH2), 46.8 (CPh2), 43.2
(NCH), 35.2 (CH2), 31.0 (CH2), 19.7 (CH3).
2-Ethyl-4,4-diphenylpyrrolidine (7c)
7c was prepared from 6c (132 mg, 0.5 mmol) as a colourless oil
1
in 88% yield (117 mg). H NMR (400 MHz, CDCl3): d 7.28–7.10
1-Benzyl-2-methyl-4,4-diphenylpyrrolidine (7i)
(m, 10H, ArH), 3.64 (d, 1H, J ¼ 13.39 Hz, NCH2C), 3.35 (d, 1H, J
¼ 10.08 Hz, NCH2C), 3.13–3.08 (m, 1H, NCH), 2.74–2.70 (m, 1H,
CCH2C), 1.98–1.96 (m, 1H, CCH2C), 1.46–1.21 (m, 2H, CCH2C),
1.20 (s, 1H, NH), 0.89 (t, 3H, CH3). 13C{1H} NMR (100 MHz,
CDCl3): 147.9, 147.1, 130.0, 128.5, 128.4, 127.2, 127.1, 126.2 (Ar–
C), 59.6 (NCH2), 57.8 (NCH), 56.9 (CPh2), 45.1 (CH2), 30.5 (CH2),
11.8 (CH3).
7i was prepared from 6i (164 mg, 0.5 mmol) as a colourless oil in
85% yield (139 mg). 1H NMR (400 MHz, CDCl3): d 7.37–7.08 (m,
15H, ArH), 4.06 (d, 1H, J ¼ 14.84 Hz, NCH2C), 3.61 (d, 1H, J ¼
9.86 Hz, NCH2C), 3.22 (d, 1H, J ¼ 12.75 Hz, NCH2C), 2.93–2.88
(m, 1H, NCHC), 2.84–2.81 (m, 2H, CCH2C), 2.76 (d, 1H, J ¼ 9.66
Hz, NCH2C), 2.22–2.17 (m, 1H, CCH2C), 1.15 (d, 3H, J ¼ 6.08 Hz,
CCH3). 13C{1H} NMR (100 MHz, CDCl3): 150.8, 146.9, 148.9,
140.3, 128.8, 128.4, 128.3, 128.0, 127.6, 127.5, 127.0, 126.0, 125.6
(Ar–C), 66.7 (NCH2Ph), 59.9 (NCH2), 58.2 (NCH), 52.7 (CPh2),
48.2 (CH2), 19.7 (CH3).
3-Methyl-2-azaspiro[4.5]decane (7d)
1
7d was prepared from 6d (46 mg, 0.3 mmol) in 95% yield. H
NMR (400 MHz, PhBr-d5): d 2.85–2.76 (m, 1H, NCH), 2.48 (d, 1H,
J ¼ 10.32 Hz, NCH2), 2.28 (d, 1H, J ¼ 11.16 Hz, NCH2), 1.42–1.35
(m, 1H, CCH2C), 1.12–1.06 (m, 1H, CCH2C), 1.28 (s, 1H, NH),
1.12–1.06 (m, 10H, CCH2CH2CH2CH2CH2C), 0.83 (d, 3H, J ¼
7.64 Hz, CH3), 0.69–0.64 (m, 1H, CCH2C).
2-Methyl-1-(4-nitrobenzyl)-4,4-diphenylpyrrolidine (7j)
7j was prepared from 6j (186 mg, 0.5 mmol) as a colourless oil in
97% yield (181 mg). 1H NMR (400 MHz, CDCl3): d 8.06 (d, 2H, J
¼ 12.00 Hz, ArH), 7.42 (d, 2H, J ¼ 7.63 Hz, ArH), 7.15–7.02 (m,
10H, ArH), 3.99 (d, 1H, J ¼ 16.38 Hz, NCH2C), 3.49 (d, 1H, J ¼
11.62 Hz, NCH2C), 3.30 (d, 1H, J ¼ 13.73 Hz, NCH2C), 2.85–2.78
(m, 2H, CCH2C), 2.73 (d, 1H, J ¼ 9.79 Hz, NCH2C), 2.20–2.14 (m,
1H, NCHC), 1.07 (d, 3H, J ¼ 5.10 Hz, CCH3). 13C{1H} NMR (100
MHz, CDCl3): 150.2, 148.5, 148.4, 147.2, 129.2, 128.4, 128.1,
127.5, 127.2, 126.1, 125.8, 123.7 (Ar–C), 66.6 (NCH2Ph), 59.8
(NCH2), 57.5 (NCH), 52.8 (CPh2), 47.8 (CH2), 19.9 (CH3).
2-Methylindoline (7e)
1
7e was prepared from 6e (40 mg, 0.3 mmol) in 94% yield. H
NMR (400 MHz, PhBr-d5): d 7.19–6.44 (m, 4H, ArH), 3.39 (s, 2H,
CH2), 1.95 (s, 1H, NH), 1.65 (s, 1H, CH), 0.81 (s, 3H, CH3).
1-(4-Chlorobenzyl)-2-methyl-4,4-diphenylpyrrolidine (7f)
1-(4-Methoxybenzyl)-2-methyl-4,4-diphenylpyrrolidine (7k)
7f was prepared from 6f (181 mg, 0.5 mmol) as a colourless oil in
87% yield (157 mg). 1H NMR (400 MHz, CDCl3): d 7.21–7.05 (m, 7k was prepared from 6k (179 mg, 0.5 mmol) as a colourless oil
1
14H, ArH), 3.96 (d, 1H, J ¼ 13.69 Hz, NCH2C), 3.54 (d, 1H, J ¼ in 88% yield (157 mg). H NMR (400 MHz, CDCl3): d 7.30–7.09
9.44 Hz, NCH2C), 3.16 (d, 1H, J ¼ 14.63 Hz, NCH2C), 289–2.84 (m, 12H, ArH), 6.86 (d, 2H, J ¼ 8.18 Hz, ArH), 4.01 (d, 1H, J ¼
(m, 1H, NCH2C), 2.81–2.75 (m, 1H, CCH2C), 2.71 (d, 1H, J ¼ 9.67 14.37 Hz, NCH2C), 3.80 (s, 3H OCH3), 3.62 (d, 1H, J ¼ 10.09 Hz,
Hz, NCH2C), 2.20–2.14 (m, 1H, CCH2C), 1.10 (d, 3H, J ¼ 6.00 Hz, NCH2C), 3.18 (d, 1H, J ¼ 18.95 Hz, NCH2C), 2.95–2.89 (m, 1H,
CCH3). 13C{1H} NMR (100 MHz, CDCl3): 150.6, 148.8, 138.9, NCHC), 2.83–2.80 (m, 1H, CCH2C), 2.75 (d, 1H, J ¼ 10.20 Hz,
132.6, 130.1, 128.5, 128.1, 128.0, 127.6, 126.1, 128.0, 127.6, NCH2C), 2.23–2.18 (m, 1H, CCH2C), 1.17 (d, 3H, J ¼ 5.36 Hz,
125.7, 127.0, (Ar–C), 66.6 (NCH2Ph), 59.8 (NCH2), 57.5 (NCH), CCH3). 13C{1H} NMR (100 MHz, CDCl3): 158.7, 150.87, 149.0,
52.7 (CPh2), 48.1 (CH2), 19.7 (CH3).
132.3, 129.9, 128.3, 128.0, 127.6, 127.5, 126.0, 125.6, 113.8 (Ar–
10546 | RSC Adv., 2016, 6, 10541–10548
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
C), 66.5 (NCH2Ph), 59.8 (NCH2), 57.5 (NCH), 55.5 (OCH3), 52.6
(CPh2), 48.2 (CH2), 19.7 (CH3).
and J. Hannedouche, Catal. Sci. Technol., 2015, 5, 2017–
2037; (f) V. Rodriguez-Ruiz, R. Carlino, S. Bezzenine-
´
Lafollee, R. Gil, D. Prim, E. Schulz and J. Hannedouche,
Dalton Trans., 2015, 44, 12029–12059; (g) S. A. Ryken and
L. L. Schafer, Acc. Chem. Res., 2015, 48, 2576–2586; (h)
J. Hannedouche and E. Schulz, Chem.–Eur. J., 2013, 19,
4972–4985; (i) C.-V. T. Vo and J. W. Bode, J. Org. Chem.,
2014, 79, 2809–2815; (j) S. M. Bronner and R. H. Grubbs,
Chem. Sci., 2014, 5, 101–106; (k) X. Yang, Q. Wang, B. Zhao
and Y. Yao, Chin. J. Org. Chem., 2015, 35, 1598–1614.
2 For recent reports: (a) K. Manna, N. Eedugurala and
A. D. Sadow, J. Am. Chem. Soc., 2015, 137, 425–435; (b)
X. Zhou, B. Wei, X.-L. Sun, Y. Tang and Z. Xie, Chem.
Commun., 2015, 51, 5751–5753; (c) J. M. P. Lauzon and
L. L. Schafer, Z. Anorg. Allg. Chem., 2015, 641, 128–135; (d)
E. Chong, S. Qayyum, L. L. Schafer and R. Kempe,
Organometallics, 2013, 32, 1858–1865; (e) P. R. Payne,
R. K. Thomson, D. M. Medeiros, G. Wan and L. L. Schafer,
Dalton Trans., 2013, 42, 15670–15677; (f) A. T. Normand,
A. Massard, P. Richard, C. Canovas, C. Balan, M. Picquet,
A. Auffrant and P. L. Gendre, Dalton Trans., 2014, 43,
15098–15110; (g) I. A. Tonks, J. C. Meier and J. E. Bercaw,
Organometallics, 2013, 32, 3451–3457; (h) C. Brahms,
P. Tholen, W. Saak and S. Doye, Eur. J. Org. Chem., 2013,
2,6-Dimethyl-4-phenyl-1-azabicyclo[2.2.1]hexane (7l)
7l was prepared from 6l (60 mg, 0.3 mmol) in 94% yield. 1H
NMR (400 MHz, PhCl-d5) (7lA : 7lB z 1.2 : 1) (7lA): d 7.27–6.98
(m, 5H, ArH), 3.16–3.27 (m, 2H, NCHNCH), 2.58 (d, 2H, J ¼
11.70 Hz, NCH2C), 1.69–1.60 (m, 2H, CCH2C), 1.38–1.19 (m, 2H,
CCH2C), 1.13 (d, J ¼ 1.71 Hz, 3H CH3), 1.11 (d, J ¼ 2.52 Hz, 3H,
CH3); (7lB) d 7.27–6.98 (m, 5H, ArH), 2.84–2.71 (m, 2H,
NCHNCH), 1.89–1.84 (m, 2H, NCH2C), 1.38–1.19 (m, 2H,
CCH2C), 1.16 (s, 3H, CH3), 1.10 (s, 3H, CH3), 0.91–0.86 (m, 2H,
CCH2C).
2,8-Dimethyl-5-phenyl-1-azabicyclo[3.3.1]nonane (7m)
1
7m was prepared from 6m (69 mg, 0.3 mmol) in 99% yield. H
NMR (400 MHz, PhCl-d5): d 7.42–7.07 (m, 5H, ArH), 3.40 (d, 1H, J
¼ 13.87 Hz, NCH2), 3.03–2.96 (m, 1H, NCH), 2.86 (s, 1H, NCH),
2.63 (d, 1H, J ¼ 13.43 Hz, NCH2), 1.87–1.62 (m, 6H, CH3), 1.36–
1.06 (m, 8H, CH2).
X-ray crystallographic structure determination
Suitable single crystals of complexes 1 and 2 were sealed in
a thin-walled glass capillary for determination the single-crystal
structures. Intensity data were collected with a Rigaku Mercury
CCD area detector in u scan mode using Mo-Ka radiation (l ¼
¨
7583–7592; (i) L. H. Luhning, C. Brahms, J. P. Nimoth,
M. Schmidtmann and S. Doye, Z. Anorg. Allg. Chem., 2015,
641, 2071–2082; (j) L. Luconi, A. Rossin, A. Motta, G. Tuci
and G. Giambastiani, Chem.–Eur. J., 2013, 19, 4906–4921;
(k) W. D. Clark, J. Cho, H. U. Valle, T. K. Hollis and
E. J. Valente, J. Organomet. Chem., 2014, 751, 534–540; (l)
J. Liu, Y. Cao, L. Li, H. Pei, Y. Chen, J. Hu, Y. Qin, Y. Li,
W. Li and W. Liu, RSC Adv., 2015, 5, 10318–10325; (m)
J.-J. Zhao, H. Pei, Y.-M. Chen, N. Lu, J.-N. Liu, J.-F. Hu,
W. Liu, W. Li and Y. Li, Z. Anorg. Allg. Chem., 2015, 641,
1322–1382; (n) S. Barroso, S. R. M. M. de Aguiar,
ꢀ
0.71070 A). The diffracted intensities were corrected for Lorentz/
polarization effects and empirical absorption corrections.
The structures were solved by direct methods and rened by
full-matrix least-squares procedures based on |F|2. The
hydrogen atoms in these complexes were generated geometri-
cally, assigned appropriate isotropic thermal parameters, and
were allowed to ride on their parent carbon atoms. All of the
hydrogen atoms were held stationary and included in the
structure factor calculation in the nal stage of full-matrix least-
squares renement. The structures were solved and rened
using SHELEXL-97 programs.
´
R. F. Munha and A. M. Martins, J. Organomet. Chem., 2014,
760, 60–66; (o) K. Manna, W. C. Everett, G. Schoendorff,
A. Ellern, T. L. Windus and A. D. Sadow, J. Am. Chem. Soc.,
2013, 135, 7235–7250; (p) N. Yonson, J. C.-H. Yim and
L. L. Schafer, Inorg. Chim. Acta, 2014, 422, 14–20; (q)
J. C.-H. Yim, J. A. Bexrud, R. O. Ayinla, D. C. Leitch and
L. L. Schafer, J. Org. Chem., 2014, 79, 2015–2028.
3 (a) P. J. Walsh, A. M. Baranger and R. G. Bergman, J. Am.
Chem. Soc., 1992, 114, 1708–1719; (b) P. L. McGrane,
M. Jensen and T. Livinghouse, J. Am. Chem. Soc., 1992, 114,
5459–5460; (c) P. L. McGrane and T. Livinghouse, J. Am.
Chem. Soc., 1993, 115, 11485–11489.
Acknowledgements
Financial support from the National Natural Science Founda-
tion of China (Grants 21402135), the Natural Science Founda-
tion of the Jiangsu Higher Education Institutions of China
(14KJB150021), the China Postdoctoral Science Foundation
(2013M541712), PAPD, and the Qing Lan Project is gratefully
acknowledged.
4 (a) D. V. Gribkov and K. C. Hultzsch, Angew. Chem., Int. Ed.,
2004, 43, 5542–5546; (b) S. Tobisch, Dalton Trans., 2006,
4277–4285; (c) A. Mukherjee, T. K. Sen, S. K. Mandal,
B. Maity and D. Koley, RSC Adv., 2013, 3, 1255–1264; (d)
P. D. Knight, I. Munslow, P. N. O'Shaughnessy and
P. Scott, Chem. Commun., 2004, 894–895.
5 (a) D. C. Leitch, P. R. Payne, C. R. Dunbar and L. L. Schafer, J.
Am. Chem. Soc., 2009, 131, 18246–18247; (b) B. D. Stubbert
and T. J. Marks, J. Am. Chem. Soc., 2007, 129, 6149–6167;
(c) S. Majumder and A. L. Odom, Organometallics, 2008, 27,
Notes and references
1 For recent reviews: (a) A. L. Reznichenko and K. C. Hultzsch,
Top. Organomet. Chem., 2013, 43, 51–114; (b) N. Nishina and
Y. Yamamoto, Top. Organomet. Chem., 2013, 43, 115–144; (c)
A. L. Reznichenko, A. J. Nawara-Hultzsch and K. C. Hultzsch,
Top. Curr. Chem., 2014, 343, 191–260; (d) L. Huang, M. Arndt,
K. Gooben, H. Heydt and L. J. Gooben, Chem. Rev., 2015, 115,
2596–2697; (e) E. Bernoud, C. Lepori, M. Mellah, E. Schulz
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 10541–10548 | 10547

View Article Online
RSC Advances
Paper
¨
1174–1177; (d) C. Muller, W. Saak and S. Doye, Eur. J. Org.
Chem., 2008, 2731–2739; (e) Y.-C. Hu, C.-F. Liang,
J.-H. Tsai, G. P. A. Yap, Y.-T. Chang and T.-G. Ong,
Organometallics, 2010, 29, 3357–3361; (f) D. C. Leitch,
R. H. Platel and L. L. Schafer, J. Am. Chem. Soc., 2011, 133,
15453–15463.
E. Y. Tshuva, I. Goldberg, M. Kol and Z. Goldschmidt,
Organometallics, 2001, 20, 3017–3028.
9 (a) Z. Zhang, X. Xu, W. Li, Y. Yao, Y. Zhang, Q. Shen and
Y. Luo, Inorg. Chem., 2009, 48, 5715–5724; (b) X. Xu, Y. Yao,
Y. Zhang and Q. Shen, Inorg. Chem., 2007, 46, 3743–3751.
¨
10 (a) F. Lauterwasser, P. G. Hayes, S. Brase, W. E. Piers and
6 (a) X. Wang, Z. Chen, X.-L. Sun, Y. Tang and Z. Xie, Org. Lett.,
2011, 13, 4758–4761; (b) L. Luconi, J. Klosin, A. J. Smith,
L. L. Schafer, Organometallics, 2004, 23, 2234–2237; (b)
S. Bambirra, H. Tsurugi, D. van Leusen and B. Hessen,
Dalton Trans., 2006, 1157–1161.
S.
Germain,
E.
Schulz,
J.
Hannedouche
and
G. Giambastiani, Dalton Trans., 2013, 42, 16056–16065; (c) 11 T. Mahdi and D. W. Stephan, Chem.–Eur. J., 2015, 21, 11134–
L. Luconi, A. Rossin, G. Tuci, S. Germain, E. Schulz, 11142.
J. Hannedouche and G. Giambastiani, ChemCatChem, 2013, 12 K. Manna, S. Xu and A. D. Sadow, Angew. Chem., Int. Ed.,
5, 1142–1151. 2011, 50, 1865–1868.
7 (a) Q. Sun, Y. Wang, D. Yuan, Y. Yao and Q. Shen, 13 (a) U. Zucchini, E. Albizzati and U. Giannini, J. Organomet.
Organometallics, 2014, 33, 994–1001; (b) Q. Sun, Y. Wang,
D. Yuan, Y. Yao and Q. Shen, Chem. Commun., 2015, 51,
7633–7636; (c) Q. Sun, Y. Wang, D. Yuan, Y. Yao and
Q. Shen, Dalton Trans., 2015, 44, 20352.
Chem., 1971, 26, 357–372; (b) Y. Rong, A. Al-Harbi and
G. Parkin, Organometallics, 2012, 31, 8208–8217; (c)
M. R. Radlauer and T. Agapie, Organometallics, 2014, 33,
3247–3250.
8 (a) E. Y. Tshuva, I. Goldberg and M. Kol, J. Am. Chem. Soc., 14 (a) S. Mohanty, D. Suresh, M. S. Balakrishna and J. T. Mague,
2000, 122, 10706–10707; (b) E. Y. Tshuva, S. Groysman,
I. Goldberg and M. Kol, Organometallics, 2002, 21, 662–670;
(c) E. Y. Tshuva, I. Goldberg, M. Kol, H. Weitman and
Z. Goldschmidt, Chem. Commun., 2000, 379–380; (d)
Tetrahedron, 2008, 64, 240–247; (b) J. D. Farwell,
P. B. Hitchcock, M. F. Lappert, G. A. Luinstra,
A. V. Protchenko and X.-H. Wei, J. Organomet. Chem., 2008,
693, 1861–1869.
10548 | RSC Adv., 2016, 6, 10541–10548
This journal is © The Royal Society of Chemistry 2016