Synthesis and Structure of a Bis(indolyl)-Coordinated Titanium Diamido Complex, and Its Catalytic Applications in the Intermolecular Hydroamination of Alkynes

Article abstract of DOI:10.1246/bcsj.20180181

Titanium bis(diethylamido) complex 1, which contains a carbon-bridged bis(indolyl) ligand, was obtained in 69% yield from the reaction of Ti(NEt2)4 with the corresponding bis(indole) ligand. Its molecular structure in the crystal was unequivocally determi

Full text of DOI:10.1246/bcsj.20180181

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Synthesis and Structure of a Bis(indolyl)–Coordinated Titanium Diamido Complex,
and Its Catalytic Applications in the Intermolecular Hydroamination of Alkynes
Shun Ohta,* Masaya Shimbayashi, Ryo Miyamoto, and Masaaki Okazaki
Advance Publication on the web August 24, 2018
doi:10.1246/bcsj.20180181
© 2018 The Chemical Society of Japan
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Publication manuscripts.

Synthesis and Structure of a Bis(indolyl)–Coordinated Titanium Diamido Complex,
and Its Catalytic Applications in the Intermolecular Hydroamination of Alkynes
Shun Ohta,* Masaya Shimbayashi, Ryo Miyamoto, and Masaaki Okazaki
1Department of Frontier Materials Chemistry, Graduate School of Science and Technology, Hirosaki University, Hirosaki 036–8561, JAPAN
E-mail: <shunohta@hirosaki-u.ac.jp>
Shun Ohta
Shun Ohta received Ph.D. degree from Nagoya University under the supervision of Prof. Kazuyuki Tatsumi in 2012. He
joined in Prof. Gerhard Erker’s group at Münster University as a researcher of a JSPS program (the program for advancing
strategic international networks to accelerate the circulation of talented researchers) in 2012, and then in the group of Prof.
Zhaomin Hou at the Riken institute as a special postdoctoral researcher in 2014. In 2015, he was appointed to his current
position as assistant professor at Hirosaki University, where he has been working with Prof. Masaaki Okazaki. His current
research interests include coordination chemistry and organometallic chemistry of benzo-fused N-heterocycles.
Abstract
Titanium bis(diethylamido) complex 1, which contains a
carbon–bridged bis(indolyl) ligand, was obtained in 69% yield
from the reaction of Ti(NEt2)4 with the corresponding bis(indole)
ligand. Its molecular structure in the crystal was unequivocally
determined by a single-crystal X-ray diffraction analysis,
Furthermore, we examined applications of 1 as a catalyst for the
intermolecular hydroamination of alkynes. When using
phenylacetylene or 1–hexyne as alkynes, the Markovnikov
products were obtained selectively, while the reaction with 1–
phenyl–1–propyne afforded an imine of phenylacetone.
Keywords: titanium complex, bis(indolyl) ligand,
hydroamination
Figure 1. (a) Known coordination modes of indolyl ligands
towards metals. (b) Bis(indolyl)–coordinated titanium
complexes studied in this work.
1. Introduction
synthesized and characterized monomeric titanium and
zirconium complexes,8–10 some of which show catalytic activity
for the polymerization of ethylene.9 Moreover, the coordination
of these ligands toward main group elements has been
investigated.11 Meyer et al. have used a bis(indolyl) ligand to
obtain a synthetic analogue of Rieske-type [2Fe-2S] clusters.12
Herein, we report the synthesis and structural characterization of
The deprotonation of the N–H group in indole derivatives
generates anionic indolyls. When indolyls coordinate to a metal
center, they exhibit a variety of coordination modes (Figure 1(a))
1–5. The most common is the h1-coordination mode, where the
nitrogen atom of the indolyl is bound to a metal center as an
amido ligand.1,2 The h5-coordination is also known,3 which is
comparable to the h5-coordination of the cyclopentadienido
ligand, albeit that one carbon atom is replaced by nitrogen.
Moreover, a h6-mode has been reported, wherein p-coordination
occurs via the six-membered ring of indolyl.4 In addition, a h3-
mode is known, albeit that this mode has only been reported for
indolyl complexes of yttrium and samarium.5 The haptotropic
rearrangement of an indolyl-ligated molybdenum complex has
a
titanium(IV) complex that contains a carbon-bridged
bis(indolyl) ligand. Although this type of titanium complex (A;
Figure 1(b)) has previously been reported by Mason et al,8,9
characteristic structural features around the bis(indolyl) ancillary
ligands have not yet been described. The catalytic activity of
complexes 1 and A toward the intermolecular hydroamination of
alkynes with aniline is also discussed in this article.
been reported by Parkin,6 and
a mechanism for this
rearrangement has recently been discussed by Saillard and
Oprunenko et al. based on DFT calculations.7 It is highly
intriguing that indolyls are able to change their coordination
mode in response to the steric and electronic environment of the
metal center. Yet, the coordination chemistry of indolyl moieties
incorporated in multidentate ligands, which are often supporting
ligands in chemical transformations catalyzed by metal
complexes, is not well explored.
In this study, our interest was focused on 2,2’-
bis(indolyl)methanes (henceforth: bis(indolyl)s). Metal
complexes bearing a deprotonated bis(indolyl) have been
reported mainly by the group of Mason.8–11 They have
2. Experimental
General Procedures
All manipulations of air- and moisture-sensitive
compounds were performed under an atmosphere of nitrogen
using standard Schlenk-line or glovebox techniques. Anhydrous
solvents (toluene, pentane, and THF) were purchased from
common commercial suppliers and used without further
purification. NMR solvents were distilled from sodium–
benzophenone ketyl (C6D6 and toluene-d8) or CaH2 (CDCl3).
Alkynes (phenylacetylene, 1–hexyne, and 1–phenyl–1–propyne)
and amines (aniline, cyclohexylamine, and tert-butylamine)
were purified by distillation from CaH2. HCPh3 was dried at

reduced
pressure.
Ti(NEt2)4,13
2–methoxyphenyldi(3–
solution for 1 was not possible due to the low solubility of 1 in
toluene, the difference should not affect the principal outcome of
the study. A toluene solution (0.44 M, 30 mL) of HCPh3 was
prepared as an internal standard to determine the product yield.
A Schlenk flask with a Teflon valve was charged with alkyne
(1.3 mmol), amine (4.0 mmol), the catalyst solution (1.0 mL),
and the HCPh3 solution (3.0 mL, 1.33 mmol), and then toluene
was added to make the total volume of 6 mL. The resulting
brown solution was stirred for 8 h at 75 ºC. All volatiles were
methylindol–2–yl)methane,14 and A9 were prepared according to
literature methods. NMR spectra were recorded on a JEOL JNM-
ECZ500R spectrometer; chemical shifts are reported in d and
referenced to the H signals of residual protons or the 13C{1H}
signals of deuterated solvents as internal standards. Elemental
analyses were performed on a vario MICRO tube.
1
Synthesis of 1.
1
removed under reduced pressure, before the H NMR spectrum
of the residue was measured in CDCl3. Resonances from the
generated imines were identified by comparison with reported
data.15
Monitoring of the stepwise reaction between A with aniline
and 1–phenyl–1–propyne.
A mixture of A (30 mg, 0.06 mmol) and aniline (5 mg, 0.06
mmol) in toluene-d8 (0.6 mL) was prepared. After measurement
of the 1H NMR spectrum, the mixture was heated for 6 h. at 75
ºC. 1–phenyl–1–propyne (6 mg, 0.06 mmol) was added to the
A mixture of Ti(NEt2)4 (520 mg, 1.55 mmol) and 2–
methoxyphenyldi(3–methylindol–2–yl)methane (500 mg, 1.31
mmol) in toluene (7.5 mL) was heated to reflux for 11 h.
Removal of all volatiles in vacuo, followed by washing with cold
pentane (15 mL, 10 mL, and then 2 x 5 mL) afforded a yellow to
brown powder of 1 in 69% yield (520 mg, 0.91 mmol). Anal.
Calcd for C34H42N4OTi: C, 71.57; H, 7.42; N, 9.82, Found: C
1
mixture, and then the H NMR was measured. After heating at
75 ºC for 1 h, the 1H NMR was measured to indicate the
formation of an imine of phenylacetone.
X–ray diffraction study of 1.
Single crystals, suitable for an X–ray diffraction analysis
of 1, were obtained from THF at –30 ºC. Data were collected at
123 K on a Rigaku RAXIS RAPID imaging plate diffractometer
using graphite monochromated MoKa radiation (l = 0.71069 Å),
and corrected for Lorentz, polarization, and absorption effects.
Calculations were carried out using the CrystalStructure
program package, and the structure was solved by direct
methods and refined on F2 by full matrix least-squares (non-H
atoms: anisotropic; H atoms: riding mode). Crystallographic
Data: Empirical Formula, C34H42N4OTi; Formula weight,
570.63; Crystal System, monoclinic; Space group, P21/n; a =
12.3675(17) Å; b = 15.9091(19) Å; c = 15.1944(19) Å; a =
92.174(4)º; V = 2987.4(7) Å3; Z = 4; Density, 1.269 mg/m3;
Absorption coefficient, 1.709 mm–1; Crystal size, 0.29 x 0.19 x
0.15 mm3; Reflections collected, 42349; Independent reflections,
6725; Data / restraints / parameters, 6725 / 0 / 361; Goodness–
of–fit on F2, 1.039; R1 (I > 2s(I)) = 0.0755; wR2 (all data) =
0.1840. The CIF file has been deposited at the Cambridge
Crystallographic Data Centre (CCDC) under reference number
CCDC-1846843. The data can be obtained free of charge from
the CCDC.
1
71.10; H, 7.31; N. 9.32. H NMR (500 MHz, 25 ºC, C6D6) d =
7.66 (m, 2H, H2), 7.44 (m, 2H, H5), 7.30–7.25 (m, 4H, H3 +
H4), 7.10 (m, 1H, H10), 7.00 (m, 1H, H12), 6.67 (s, 1H, CH),
6.61 (m, 1H, H11), 6.49 (m, 1H, H13), 3.49 (q, 3JH–H = 7 Hz, 4H,
NCH2CH3), 3.42 (q, 3JH–H = 7 Hz, 4H, NCH2CH3), 3.16 (s, 3H,
OCH3), 2.50 (s, 6H, CH3), 0.90 (t, 3JH–H = 7Hz, 6H, NCH2CH3),
0.67 (t, 3JH–H = 7Hz, 6H, NCH2CH3). 13C{1H} NMR (126 MHz,
25 ºC, C6D6) d = 157.8 (C14), 145.9 (C8), 143.4 (C1), 132.9 (C9),
131.0 (C6), 129.4 (C10), 127.3 (C12, overlapping with the
solvent peak) 121.5 (C3), 120.6 (C4), 120.1 (C11), 118.5 (C2),
115.5 (C5), 110.9 (C13), 109.3 (C7), 55.0 (OCH3), 48.0
(NCH2CH3), 46.5 (NCH2CH3), 37.4 (CH), 15.2 (NCH2CH3),
1
14.9 (NCH2CH3), 9.5 (CH3). H-1H COSY (500 MHz, 25 ºC,
C6D6) d 1H / d 1H = 7.66 / 7.30–7.25 (H2 / H3), 7.44 / 7.30–7.25
(H5 / H4), 7.10 / 6.61 (H10 / H11), 7.00 / 6.61, 6.49 (H12 / H11,
H13), 3.49 / 0.90 (NCH2CH3 / NCH2CH3), 3.42 / 0.67
(NCH2CH3 / NCH2CH3). 1H-13C HMQC (500 / 126 MHz, 25 ºC,
1
C6D6) d H / d 13C = 7.66 / 118.5 (H2 / C2), 7.44 / 115.5 (H5 /
C5), 7.30–7.25 / 121.5, 120.6 (H3 + H4 / C3, C4), 7.10 / 129.4
(H10 / C10), 7.00 /127.3 (H12 / C12), 6.67 / 37.4 (CH), 6.61 /
120.1 (H11 / C11), 6.49 / 110.9 (H13 / C13), 3.49 / 46.5
(NCH2CH3), 3.42 / 48.0 (NCH2CH3), 3.16 / 55.0 (OCH3), 2.50 /
9.5 (CH3), 0.90 / 14.9 (NCH2CH3), 0.67 / 15.2 (NCH2CH3). 1H-
13C HMBC (500 / 126 MHz, 25 ºC, C6D6) d 1H / d 13C = 7.66 /
143.4, 121.5 (H2 / C1, C3), 7.44 / 131.0, 120.6 (H5 / C6, C4),
7.30–7.25 / 143.4, 131.0, 118.5, 115.5 (H3 + H4 / C1, C6, C2,
C5), 7.10 / 157.8, 127.3 37.4 (H10 / C14, C12, CH), 7.00 / 157.8,
129.4 (H12 / C14, C10), 6.67 / 157.8, 145.9, 132.9, 129.4, 109.3
(CH / C14, C8, C9, C10, C7), 6.61 / 132.9, 110.9 (H11, C9, C13),
6.49 / 157.8, 132.9, 120.1 (H13 / C14, C9, C11), 3.49 / 46.5, 14.9
3. Results and Discussion
Synthesis of complex 1.
13
A mixture of Ti(NEt2)4 and 2–methoxyphenyldi(3–
methylindol–2–yl)methane14 in a 1.2:1 molar ratio was heated to
reflux in toluene and stirred for 11 h. Even though the solubility
of the bis(indolyl)methane ligand in toluene is relatively low, it
gradually dissolved as the reaction progressed, and finally, a
homogeneous dark brown solution was obtained. Evaporation of
all volatiles in vacuo afforded a brown residue that was
subsequently washed with cold pentane to remove a small
amount of unreacted Ti(NEt2)4, resulting in pure 1 as a yellow to
brown powder in 69% yield (Scheme 1).
(NCH2CH3 / NCH2CH3,
NCH2CH3), 3.42 / 48.0, 15.2
(NCH2CH3 / NCH2CH3, NCH2CH3), 3.16 / 157.8 (OCH3 / C14),
2.50 / 145.9, 131.0, 109.3 (CH3 / C8, C6, C7), 0.90 / 46.5
(NCH2CH3 / NCH2CH3), 0.67 / 48.0 (NCH2CH3 / NCH2CH3).
Solid-state structure of 1.
Intermolecular hydroamination of alkynes
An X–ray diffraction analysis of 1 was carried out on a single
crystal obtained from THF at –30 ºC, and the thus determined
structure and the crystallographic data are given in Figure 2 and
the experimental section, respectively. The titanium center, with
a distorted tetrahedral geometry, is bound to four nitrogen atoms,
A stock catalyst solution of 1 (0.12 M) was prepared by
dissolving 1 (1.00 g, 1.75 mmol) in toluene (15 mL), while that
of A (0.13 M) was prepared from A (360 mg, 0.65 mmol) and
toluene (5 mL). Even though the preparation of 0.13 M catalyst

distance from the plane defined by the three binding atoms
(0.186 Å) is slightly shorter than that of 1 (0.254(3) Å). Although
the possibility of the crystal packing is not excluded, this
difference is probably induced by the steric repulsion between
the methyl group attached to the N4–containing indolyl ring and
the methoxy group of the aromatic ring. Indeed, the O–C17
distance (3.073(4) Å) is less than the sum of the van der Waals
radii of the oxygen (1.52 Å) and carbon (1.70 Å) atoms.17 We
also found that the Ti–C15 bond (3.024(4) Å) in 1 is
considerably shorter than the Ti–C1 bond (3.111(4) Å). The
detailed analysis of these structural differences seems to be
essential for an in-depth understanding of the behavior of
bis(indolyl)s as ancillary ligands, which are currently in progress
in our group.
Scheme 1. Synthesis of 1.
two of which are from the bis(indolyl) ligand, while the other
two belong to two NEt2 ligands. The Ti–N1 (1.878(3) Å) and Ti–
N2 (1.869(3) Å) bonds are shorter than the Ti–N3 (1.986(3) Å)
and Ti–N4 (1.960(4) Å) bonds, indicating that the pN→dTi p-
bonding interaction between Ti and N(NEt2) is higher than that
between Ti and N(indolyl). This feature is consistent with the
metric parameters observed for the relevant titanium complex A
by Mason et al. (Figure 1(b)).9 Similar to A, agostic interactions
occur between the titanium center and the CH2 groups of the
NEt2 ligands. Among the four Ti–C(CH2) bonds, the Ti–C18
(2.766(4) Å) and Ti–C20 (2.801(5) Å) bonds are significantly
shorter than the Ti–C19 (3.122(4) Å) and Ti–C21 bonds
(3.054(5) Å).
Intermolecular hydroamination of alkynes mediated by 1
and A.
Early transition metal complexes supported by indolyl-
containing ligands can serve as catalysts for e.g.
polymerizations,9,18–21 hydroaminations,22 four–component
coupling reactions,1i hydrophosphonylations,23 and olefin
epoxidations.24 Thus, we examined the catalytic activity of 1 and
A for the intermolecular hydroamination of alkynes (Table 1).
For that purpose, a mixture of substrates ([alkyne]:[aniline] =
1:3), catalyst (1: 8.6 mol%; A: 10 mol%), and HCPh3 as an
internal standard was stirred for 8 h at 75 ºC in toluene. Due to
the low solubility of 1 in toluene, the amount of dissolved
catalyst is slightly lower than that of A. The yields of the
1
produced imines were determined by H NMR measurements
(CDCl3) of the brown solid obtained after evaporation of all
volatiles from the reaction mixture.
Table 1.
1– or A–catalyzed hydroaminations of (a)
phenylacetylene or 1–hexyne and (b) 1–phenyl–1–propyne with
aniline.a
Entry
Alkyne
PhCCH
Cat. (Content)
1 (8.6 mol%)
A (10 mol%)
1 (8.6 mol%)
A (10 mol%)
1 (8.6 mol%)
A (10 mol%)
Yieldb
15
Figure 2. ORTEP drawing of 1 with thermal ellipsoids set to
30% probability. Hydrogen atoms are omitted for clarity.
Selected bond distances (Å) and angles (º): Ti–N1 = 1.878(3),
Ti–N2 = 1.869(3), Ti–N3 = 1.986(3), Ti–N4 = 1.960(4), Ti–C1
= 3.111(4), Ti–C15 = 3.024(4), Ti–C18 = 2.766(4), Ti–C20 =
2.801(5), N1–Ti–N2 = 108.33(13), N1–Ti–N3 = 110.73(12),
N1–Ti–N4 = 107.83(12), N2–Ti–N3 = 114.55(13), N2–Ti–N4 =
118.51(13), N3–Ti–N4 = 96.32(12).
1
2
3
4
5
6
10
41
nBuCCH
27
18
PhCCMe
95
a Reaction conditions: alkyne (1.3 mmol), aniline (4 mmol), 75
ºC, 8 h. b 1H NMR yield.
Amido nitrogen atoms coordinated to early transition
metals usually exhibit a planar coordination geometry, which has
been ascribed to the pN→dM p-bonding interaction.16 The N4
atom of 1, however, is pyramidalized, as evident from its
distance from the plane defined by the Ti, C15, and C16 atoms
(0.254(3) Å), while the N1, N2, and N3 atoms exhibit planar
structures. Most of the indolyl nitrogen atoms with the h1-
coordination mode adopts a planar geometry,1,2 but a few
pyramidalized examples are known.1g,1i We also investigated the
geometry of the indolyl nitrogen atoms in A9, and discovered
that one nitrogen atom therein is also pyramidalized. The
Reactions with phenylacetylene or 1–hexyne afforded the
Markovnikov products, and 1H resonances assignable to the anti-
Markovnikov products were not observed. When 1–phenyl–1–
propyne was used, an imine of phenylacetone was obtained.
These regioselectivities are similar to the results obtained when
using
Ti(NMe2)2(dpma)
(dpma
=
di(pyrrolyl–a–
methyl)methylamine) (Scheme 2).25 For the reactions with
phenylacetylene or 1–hexyne (Scheme 2(a)), the active titanium
imido species, generated by treating 1 or A with aniline, reacts

with an alkyne to afford the four-membered metallacycle.26 In
this [2+2] cycloaddition, the Markovnikov regioselectivity is
favored based on the electrostatic polarization of the Tid+=Nd–
bond.27 The resulting metallacycle is protonated by the aniline to
yield an enamine, which tautomerizes to the corresponding
imine under concomitant regeneration of the active species. In
the case of 1–phenyl–1–propyne, the mechanism depicted in
Scheme 2(b) could be considered. A reaction of the titanium
imido active species with 1–phenyl–1–propyne could induce a
1,3–hydrogen shift, giving rise to the formation of a four-
membered metallacycle with an exocyclic C=C bond.25,28 The
ensuing protonation from the intermediate should proceed in a
manner similar to that in Scheme 2(a).
on the reactivities of the tentatively assigned titanium imido
species with alkynes. The treatment of the titanium imido
species, generated in situ, with phenylacetylene gave the
unidentified products, which is in contrast to the reaction with
1–phenyl–1–propyne (see above). Although we further
examined the A-mediated hydroaminations of 1–phenyl–1–
propyne with cyclohexylamine or tert-butylamine, low activity
for cyclohexylamine (10%) or no activity for tert-butylamine
were found in these reaction conditions.
4. Conclusion
Herein, we report the coordination chemistry of carbon–
bridged bis(indolyl) ligands toward a titanium center. A
crystallographic analysis revealed that in such complexes, one of
the amido nitrogen atoms of one indolyl group is pyramidalized.
Complexes 1 and A also act as catalysts for the intermolecular
hydroamination of alkynes. Both complexes yield the
Markovnikov products when using phenylacetylene or 1–hexyne
as alkynes, while the reaction with 1–phenyl–1–propyne affords
an imine of phenylacetone. The high activity of A for the
hydroamination of 1–phenyl–1–propyne is also remarkable. In
addition to the substrate scope of such hydroamination reactions,
we currently investigate the structures and catalytic activity of
relevant zirconium complexes.
Acknowledgement
This work was financially supported by the Foundation for
Japanese Chemical Research, the Hatakeyama Culture
Foundation, the Aomori Support Center for Industrial Promotion,
and the Hirosaki University Grant for Exploratory Research by
Young Scientists and Newly-appointed Scientists.
References
1.
For examples, see: (a) F. T. Ladipo, J. S. Merola, Inorg.
Chem., 1990, 29, 4172. (b) G. C. Hsu, W. P. Kosar, W. D.
Jones, Organometallics, 1994, 13 385. (c) T. J. Johnson, A.
M. Arif, J. A. Gladysz, Organometallics, 1994, 13, 3182.
(d) K. G. Parker, B. Noll, C. G. Pierpont, M. R. DuBois,
Inorg. Chem., 1996, 35, 3228. (e) A. Frenzel, R. Herbst–
Irmer, U. Klingebiel, M. Noltemeyer, S. Rudolph, Main
Group Chem., 1996, 1, 399. (f) S. Chen, B. C. Noll, L.
Peslherbe, M. R. DuBois, Organometallics, 1997, 16, 1089.
(g) I. Heldt, T. Borrmann, U. Behrens, Z. Anorg. Allg.
Chem., 2003, 629, 1980. (h) S. C. Marinescu, R. Singh, A.
S. Hock, K. M. Wampler, R. R. Schrock, P. Müller,
Organometallics, 2008, 27, 6570. (i) E. Barnea, S.
Majumder, R. J. Staples, A. L. Odom, Organometallics,
2009, 28, 3876.
For recent examples, see: (a) A. Reyes-Sánchez, F.
Cañavera-Buelvas, R. Barrios-Francisco, O. L. Cifuentes-
Vaca, M. Flores-Alamo, J. J. García, Organometallics,
2011, 30, 3340. (b) S. A. DiFranco, N. A. Maciulis, R. J.
Staples, R. J. Batrice, A. L. Odom, Inorg. Chem., 2012, 51,
1187. (c) D. V. Partyka, M. Zeller, A. D. Hunter, T. G. Gray,
Inorg. Chem., 2012, 51, 8394. (d) X. Zhu, S. Zhou, S.
Wang, Y. Wei, L. Zhang, F. Wang, S. Wang, Z. Feng, Chem.
Commun., 2012, 48, 12020. (e) P. L. Arnold, T. Cadenbach,
I. H. Marr, A. A. Fyfe, N. L. Bell, R. Bellabarba, R. P.
Tooze, J. B. Love, Dalton Trans., 2014, 43, 14346. (f) A.
Ueno, Y. Kayaki, T. Ikariya, Organometallics, 2014, 33,
4479. (g) F. T. Ladipo, J. S. Merola, Polyhedron, 2015, 90,
131.
Scheme 2. A plausible mechanism for the hydroamination of (a)
phenylacetylene or 1–hexyne, and (b) 1–phenyl–1–propyne
catalyzed by Ti-bis(indolyl) complexes.
In order to assess the validity of the reaction mechanism
proposed in Scheme 2(b), the following experiments were
performed. When a mixture of A and aniline in a 1:1 ratio was
heated at 75 ºC, the signals of A were weakened, and new signals
appeared at d 2.46 (s, 6H) and 6.08 (s, 1H) together with the
signals of diethylamine. On the other hand, no reaction occurred
between A and 1–phenyl–1–propyne. These results demonstrate
that the A-mediated hydroamination of 1–phenyl–1–propyne
with aniline initiates from the reaction of A and aniline. The new
signals could tentatively be assigned to the titanium imido active
species. After treating the mixture at 75 ºC for 6 h, 1–phenyl–1–
propyne was further added, then the mixed sample was heated at
75 ºC for 1 h. As a result, the signals of the imine product were
observed. The observation of the proposed four-membered
metallacycle intermediate was failed probably because i) A was
partially converted into the titanium imido active species by the
addition of 1 equiv. of aniline, which remains the unreacted
aniline in the reaction mixture, and ii) the remained aniline may
react fast with the four-membered metallacycle.
The activities of 1 and A were low (10–41% NMR yield)
for the hydroamination of phenylacetylene and 1–hexyne
(entries 1–4), as well as for the 1–catalyzed hydroamination of
1-phenyl-1-propyne (18%; entry 5). Surprisingly, the
hydroamination of 1–phenyl–1–propyne with A proceeded in
high yield (95%, entry 6). Ti(NMe2)2(dpma) also exhibits a high
conversion of 1–phenyl–1–propyne into an imine of
phenylacetone (99% GC yield at 75 ºC), albeit that this requires
longer reaction times (144 h).25 The activities of A would depend
2.
3.
(a) C. White, S. J. Thompson, P. M. Maitlis, J. Chem. Soc.
Chem. Commun., 1976, 409. (b) J. A. D Jeffreys, C.
Metters, J. Chem. Soc. Dalton Trans., 1977, 1624. (c) C.
White, S. J. Thompson, P. M. Maitlis, J. Chem. Soc. Dalton

Trans., 1977, 1654–1661. (d) L. –N. Ji, D. L. Kershner, M.
E. Rerek, F. Basolo, J. Organomet. Chem., 1985, 296, 83–
94. (e) M. Suginome, G. C. Fu, Chirality, 2000, 12, 318–
324.
S. Chen, V. Carperos, B. Noll, R. J. Swope, M. R. DuBois,
Organometallics, 1995, 14, 1221.
20. For zirconium complexes, see: (a) G. Li, M. Lamberti, M.
Mazzeo, D. Pappalardo, C. Pellecchia, J. Mol. Catal. A
Chem., 2013, 370, 28. (b) G. Li, C. Zuccaccia, C. Tedesco,
I. D’Auria, A. Macchioni, C. Pellecchia, Chem.-Eur. J.,
2014, 20, 232.
21. For chromium complexes, see: (a) A. Jabri, C. B. Mason,
Y. Sim, S. Gambarotta, T. J. Burchell, R. Duchateau,
Angew. Chem., Int. Ed., 2008, 47, 9717. (b) H. Wölfle, H.
Kopacka, K. Wurst, P. Preishuber–Pflügl, B. Bildstein, J.
Organomet. Chem., 2009, 694, 2493.
22. (a) J. –J. Zhao, H. Pei, Y. –M. Chen, N. Lu, J. –N. Liu, J. –
F. Hu, W. Liu, W. Li, Y. Li, Z. Anorg. Allg. Chem., 2015,
641, 1322. (b) Z. Feng, Y. Wei, S. Zhou, G. Zhang, X. Zhu,
L. Guo, S. Wang, X. Mu, Dalton Trans., 2015, 44, 20502.
23. (a) X. Zhu, S. Wang, S. Zhou, Y. Wei, L. Zhang, F. Wang,
Z. Feng, L. Guo, X. Mu, Inorg. Chem., 2012, 51, 7134. (b)
S. Yang, X. Zhu, S. Zhou, S. Wang, Z. Feng, Y. Wei, H.
Miao, L. Guo, F. Wang, G. Zhang, X. Gu, X. Mu, Dalton
Trans., 2014, 43, 2521.
4.
5.
6.
7.
W. J. Evans, J. C. Brady, J. W. Ziller, Inorg. Chem., 2002,
41, 3340.
G. Zhu, J. M. Tanski, D. G. Churchill, K. E. Janak, G.
Parkin, J. Am. Chem. Soc., 2002, 124, 13658.
E. O. Fetisov, I. P. Gloriozov, M. S. Nechaev, S. Kahlal, J.
–Y. Saillard, Y. F. Oprunenko, J. Organomet. Chem., 2017,
830, 212.
M. R. Mason, Chemtracts, 2003, 16, 272.
M. R. Mason, B. N. Fneich, K. Kirschbaum, Inorg. Chem.,
2003, 42, 6592.
8.
9.
10. M. R. Mason, D. Ogrin, B. Fneich, T. S. Barnard, K.
Kirschbaum, J. Organomet. Chem., 2005, 690, 157.
11. (a) N. B. Kingsley, K. Kirschbaum, M. R. Mason,
Organometallics, 2010, 29, 5927. (b) B. Song, K.
Kirschbaum, M. R. Mason, Organometallics, 2012, 31,
191.
12. J. Ballmann, A. Albers, S. Demeshko, S. Dechert, E. Bill,
E. Bothe, U. Ryde, F. Meyer, Angew. Chem., Int. Ed., 2008,
47, 9537–9541.
24. S. Yadav, S. Kumar, R. Gupta, Eur. J. Inorg. Chem., 2015,
5534.
25. C. Cao, J. T. Ciszewski, A. L. Odom, Organometallics,
2001, 20, 5011.
26. A. L. Odom, T. J. McDaniel, Acc. Chem. Res., 2015, 48,
2822.
13. (a) D. C. Bradley, I. M. Thomas, J. Chem. Soc., 1960, 3857.
(b) D. Steinborn, I. Wagner, R. Taube, Synthesis, 1989, 4,
304.
14. M. R. Mason, T. S. Barnard, M. F. Segla, B. Xie, K.
Kirschbaum, J. Chem. Cryst., 2003, 33, 531.
27. A. Tillack, H. Jiao, I. G. Castro, C. G. Hartung, M. Beller,
Chem. -Eur. J., 2004, 10, 2409.
28. D. J. M. Trösch, P. E. Collier, A. Bashall, L. H. Gade, M.
McPartlin, P. Mountford, S. Radojevic, Organometallics,
2001, 20, 3308.
15. (a) F. –M. Gautier, S. Jones, S. J. Martin, Org. Biomol.
Chem., 2009, 7, 229. (b) C. G. Hartung, A. Tillack, H.
Trauthwein, M. Beller, J. Org. Chem., 2001, 66, 6339. (c)
L. L. Anderson, J. Arnold, R. G. Bergman, Org. Lett., 2004,
6, 2519. (d) M. A. Esteruelas, A. M. López, A. C. Mateo,
E. Oñate, Organometallics, 2005, 24, 5084.
16. (a) S. G. Gibbins, M. F. Lappert, J. B. Pedley, G. J. Sharp,
J. Chem. Soc. Dalton Trans., 1975, 72. (b) R. A. Andersen,
D. B. Beach, W. L. Jolly, Inorg. Chem., 1985, 24, 4741. (c)
J. Hartwig, S. B. Herzon, Organotransition Metal
Chemistry From Bonding to Catalysis, ed. by J. Hartwig,
University Science Books, Sausalito, CA, 2010, pp. 152–
154.
17. M. Mantina, A. C. Chamberlin, R. Valero, C. J. Cramer, D.
G. Truhlar, J. Phys. Chem. A, 2009, 113, 5806.
18. For rare earth metal complexes, see: (a) Y. Yang, Q. Wang,
D. Cui, J. Polym. Sci. Part A Poly. Chem., 2008, 46, 5251.
(b) G. Zhang, Y. Wei, L. Guo, X. Zhu, S. Wang, S. Zhou,
X. Mu, Chem.-Eur. J., 2015, 21, 2519. (c) L. Guo, X. Zhu,
G. Zhang, Y. Wie, L. Ning, S. Zhou, Z. Feng, S. Wang, X.
Mu, J. Chen, Y. Jiang, Inorg. Chem., 2015, 54, 5725. (d) G.
Zhang, S. Wang, S. Zhou, Y. Wei, L. Guo, X. Zhu, L.
Zhang, X. Gu, X. Mu, Organometallics, 2015, 34, 4251.
(e) G. Zhang, B. Deng, S. Wang, Y. Wei, S. Zhou, X. Zhu,
Z. Huang, X. Mu, Dalton Trans., 2016, 45, 15445. (f) G.
Zhang, S. Wang, X. Zhu, S. Zhou, Y. Wei, Z. Huang, X.
Mu, Organometallics, 2017, 36, 3812.
19. For titanium complexes, see: (a) T. Matsugi, S. Matsui, S.
Kojoh, Y. Takagi, Y. Inoue, T. Nakano, T. Fujita, N.
Kashiwa, Macromolecules, 2002, 35, 4880. (b) W. Zuo, W.
–H. Sun, S. Zhang, P. Hao, A. Shiga, J. Polym. Sci. Part A
Poly. Chem., 2007, 45, 3415. (c) W. Zuo, M. Zhang, W. –
H. Sun, J. Polym. Sci. Part A Poly. Chem., 2009, 47, 357.
(d) S. V. Kulangara, A. Jabri, Y. Yang, I. Korobkov, S.
Gambarotta, R. Duchateau, Organometallics, 2012, 31,
6085.