Intermolecular hydroamination of oxygen-substituted allenes. New routes for the synthesis of N,O-chelated zirconium and titanium amido complexes

Article abstract of DOI:10.1039/c1dt10448a

Intermolecular hydroamination of heteroatom-substituted allenes with a bulky arylamine was carried out using a bis(amidate) bis(amido) titanium(iv) complex (1) as a precatalyst. The reaction of 2,6-dimethylaniline with oxygen-substituted allene 2c or 2d i

Full text of DOI:10.1039/c1dt10448a

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PAPER
Intermolecular hydroamination of oxygen-substituted allenes. New routes for
the synthesis of N,O-chelated zirconium and titanium amido complexes†
Rashidat O. Ayinla and Laurel L. Schafer*
Received 16th March 2011, Accepted 2nd June 2011
DOI: 10.1039/c1dt10448a
Intermolecular hydroamination of heteroatom-substituted allenes with a bulky arylamine was carried
out using a bis(amidate) bis(amido) titanium(IV) complex (1) as a precatalyst. The reaction of
2,6-dimethylaniline with oxygen-substituted allene 2c or 2d in the presence of complex 1 gives the
ketimine regioisomer as the exclusive product. Reduction of such ketimine products resulted in the
formation of amino ethers that were further employed as proligands for the formation of N,O-chelating
five-membered titana- and zirconacycles. Such sterically demanding N,O-chelating ligands result in the
high-yielding preparation of mono-ligated products. Solid-state molecular structures of all the
complexes revealed distorted trigonal bipyramidal geometry about the metal centers, with a dative
bond between the metal and the oxygen donor atom. These new complexes obtained using
hydroamination as the key-step in ligand preparation were also shown to be useful
cyclohydroamination precatalysts in their own right.
been studied by Marks and co-workers.62–66 A few exam-
ples of early transition metal-catalyzed intramolecular67–70 and
Introduction
intermolecular71–73 allene hydroamination have also been dis-
closed. All of the above reports involve alkyl- or aryl-substituted
allenes, including our work disclosing a rare example of early
transition metal-catalyzed intermolecular hydroamination of sub-
stituted allenes with less reactive alkylamine substrates.74 However,
to the best of our knowledge, the intermolecular hydroamination
of oxygen-substituted allenes, in which the heteroatom is directly
attached to the highly reactive allene moiety, has yet to be
reported.71 The product of such a reaction would provide facile
access to a new class of monoanionic N,O-chelating ligand suitable
for generating five-membered metallacycles (Scheme 1), rather
than the four-membered metallacycles of complex 1 (Fig. 1) and
other amidate and ureate complexes previously reported by our
group75–90 and others.17,91–93
The transition metal-catalyzed addition of N–H to C–C multiple
bonds such as alkynes, alkenes, and allenes is an important
transformation in organic synthesis. This reaction termed hy-
droamination presents an atom economic way of synthesizing
N-containing compounds, including amines, enamines, imines,
and hydrazones, which are valuable substrates and intermedi-
ates in research and industrial processes.1–7 A large number
of metal-containing complexes including alkali and alkaline
earth metals,1,7–15 early transition metals,1–4,16–25 late transition
metals,1,2,4,6,26–35 and lanthanides1,4–6,36–39 have been described as
competent catalysts for the hydroamination reaction. Despite
these impressive reports, the use of alkenes as co-substrate with
amines in the intermolecular variant still remains a significant
challenge.1,5,6,40 The difficulties encountered using alkenes can
be mitigated by the selection of allenes as substrates because
the C–C p-bond of an allene is about 10 kcal mol-1 less stable
in comparison to that of a simple alkene.41,42 However, the
intermolecular hydroamination of allenes has received much less
attention in comparison to alkynes and functional group tolerance
in the allene substrate has not been extensively explored.
Scheme 1 Hydroamination for a modular synthesis of N,O-chelating
ligands suitable for the formation of five-membered metallacycles.
The bulk of reported allene hydroamination reactions
are catalyzed by late transition metals,29,41,43–61 notably
gold29,41,44,46–48,52–52,56–61 and palladium.43,49–51 The use of lanthanide
complexes as precatalysts for allene hydroamination has also
The development of four-membered N,O-chelating metallacy-
cles of early-transition metals including amidates and ureates has
received attention in recent years.17,76,78,79,81,83–92 This is due in part to
the facile protonolysis approach to synthesizing these complexes
which allows access to well-defined monomeric species. These
complexes have been successfully applied in catalytic synthesis of a
variety of N-containing molecules.17,74–77,79,80,82,83,85,86,89–92 Similarly,
Department of Chemistry, University of British Columbia, 2036 Main Mall,
Vancouver, BC, Canada. E-mail: schafer@chem.ubc.ca; Fax: +1 604 822
2847; Tel: +1 604 822 9264
† CCDC reference numbers 817776–817778. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1dt10448a
This journal is
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Dalton Trans., 2011, 40, 7769–7776 | 7769
©

Table 1 Intermolecular hydroamination of substituted allenes with a
bulky arylamine
Fig. 1 Highly reactive and regioselective hydroamination precatalyst.
Entry Allene
1a
Product
tc/h Yieldd (%)
six-membered alkoxy-imine type, N,O-chelating complexes of
early transition metals have been widely studied for a range of
reactions with significant application in olefin polymerization.94–97
In contrast, five-membered N,O-chelating complexes of early
transition metals are much less investigated.67,98–123 In principle,
such five-membered N,O-chelating complexes should be easily
accessible via protonolysis reactions with appropriate amino ether
proligands (Scheme 1). Importantly, the development of a modular
synthetic route to this class of proligands could serve to access a
broad range of complexes suitable for investigation in catalytic
applications. Here, we report the use of 1 (Fig. 1) for the hy-
droamination reaction of oxygen-substituted allenes with a bulky
arylamine to give ketimines with excellent regioselectivity. Upon
reduction, the amino ether proligands obtained can then be used to
synthesize C1-symmetric five-membered zirconium and titanium
metallacyclic complexes with N,O-chelating ligands (Scheme 1).
The synthetic details, characterization, and application of these
new complexes in cyclohydroamination are described in this
report.
24
93
2a
7
2
76
76
3a
4b
24
68
a 5 mol% 1; allene, 1.25 mmol; amine, 1.25 mmol, 90 ◦C. b 10 mol%
1; allene, 1.50 mmol; amine, 1.25 mmol, 110 ◦C. c Time required to
reach >96% conversion. d Isolated yield of the corresponding secondary
amine following reduction with lithium aluminum hydride or sodium
cyanoborohydride/zinc chloride.
Results and discussion
Intermolecular hydroamination of heteroatom-substituted allenes
Complex 1 (Fig. 1) is an efficient precatalyst for the regioselective
intermolecular hydroamination of aryl or alkyl substituted allenes
with a bulky arylamine to exclusively afford the ketimine products
(Table 1, entries 1 & 2).74 These observations are consistent with
previous reports of early transition metal-catalyzed intermolecular
hydroamination of allenes with amines which also afford the
ketimine products.71–73 In an investigation of substrate scope we
note that complex 1 is tolerant of oxygen-substituted allenes,
thus, 1 equiv. of 2,6-dimethylphenoxyallene (2c) reacts fully with
1 equiv. of 2,6-dimethylaniline in the presence of 5 mol% of
1 within 2 h at 90 C as observed by H NMR spectroscopy
(Table 1, entry 3). The success of this reaction is consistent with
a high level of functional group tolerance of complex 1. This is in
contrast to Cp derived Ti precatalysts, which were reported to be
unsuccessful for the hydroamination of heteroatom-substituted
allenes.71 Interestingly, even with late-transition metals where
functional group tolerance is anticipated to be improved, we are
unaware of any reported examples of the catalytic intermolecular
hydroamination reaction of oxygen-substituted allenes in which
the heteroatom is directly attached to the allene moiety. By
choosing the bulky 2,6-dimethylaniline as the amine substrate we
can access a preferred substituent ideal for incorporation into a
ligand as it provides the requisite steric protection for electrophilic
early transition metals such as Ti and Zr. The reaction of 2c with
2,6-dimethylaniline proceeds efficiently at 90 ◦C (Table 1, entry
3) but can also be carried out at a lower temperature of 65 ◦C,
although a longer time of 24 h is required. The disappearance of
the allene signals between d 5.20 and 6.90 and the appearance
of new signals between d 1.91 and 4.57 (singlets) in the 1H
NMR spectrum suggests the preferential formation of ketimine
3c. The ketimine products 3 are then reduced to the corresponding
secondary amines 4 for ease of isolation and characterization.
Mechanistically, the hydroamination reaction using precatalyst
1 is postulated to proceed via a [2 + 2] cycloaddition mechanism, as
has been previously proposed for alkyne hydroamination using this
Ti catalyst system90 and other group 4 complexes.124 This mecha-
nistic proposal is supported by unproductive attempts to mediate
intermolecular hydroamination of allenes with morpholine, a
known preferred secondary amine for intermolecular alkyne77 and
allene hydroamination.29,44,55,56
The alkoxy-substituted allene, methoxyallene (2d), also reacts
with 2,6-dimethylaniline in the presence of 10 mol% of 1 to afford
ketimine 3d. Here, c◦omplete consumption of the amine is achieved
within 24 h at 110 C (Table 1, entry 4). The somewhat reduced
yield of 68% is ◦attributed to the fact that methoxyallene 2d is
volatile (b.p. 52 C)125 and at elevated reaction temperatures, an
appreciable quantity is present in the gas phase. Most importantly,
this result shows that steric protection of the oxygen substituent is
◦
1
7770 | Dalton Trans., 2011, 40, 7769–7776
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not required and that precatalyst 1 is compatible with the inclusion
of sterically accessible neutral donor atoms.
It is well known that the isomerization of alkynes is one of
the general methods of synthesizing allenes,126 and indeed this
methodology is utilized in the preparation of allenes 2c and
2d.125,127 Thus, to exclude allene-alkyne isomerization and sub-
sequent hydroamination catalysis during this reaction protocol,
control experiments with the alkyne isomer of 2d, methyl propargyl
ether, have been performed. In this case 2,6-dimethylaniline does
not react with methyl propargyl ether despite a catalyst loading
of 10 mol%, and a reaction time of 24 h at 110 ◦C. The lack
of reactivity with this alkyne eliminates the possibility of allene
isomerization to the alkyne prior to undergoing hydroamination
with the amine.
Thus by achieving the first examples of oxygen-substituted
allene hydroamination with precatalyst 1 we have established a
catalytic route for the preparation of a new family of monoanionic
N,O-chelating ligands. This class of ligand provides access to five-
membered metallacycles upon complexation of these proligands
with variable steric and electronic properties.
Scheme 2 Synthesis of zirconium and titanium (amidoether)trisamido
complexes.
suggests that there is hindered rotation about the N–Caryl bond
in L1. Recrystallization of complex 5 from hot hexanes produced
crystals that are amenable to X-ray crystallographic studies.
The solid state molecular structure of 5 reveals geometry about
zirconium that is distorted trigonal bipyramidal; with the oxygen
of L1 and one of the dimethylamido nitrogens (N2) occupying the
axial positions (Fig. 3). The crystallographic structure contains a
mirror plane that passes through the aryl ring, N2, and between
N3 and N3_8. In addition, atoms C1, C2, and O1 are disordered
about the plane. This is clearly seen when the structure is viewed
along the crystallographic a-axis. The torsion angle (43.2(5)◦) of
the five-membered chelate ring indicates significant deviation from
Zirconium and titanium amido complexes
One of our main interests is the development of bidentate N,O-
chelating ligands for early transition metal complexes.75–81,83,85–90
Previous to this work, we have only investigated four-membered
N,O-chelating ligands. Thus, by using the amino ethers 4c and
4d (Fig. 2), obtained from the reduction of ketimine products
3c and 3d respectively, we can obtain new monoanionic N,O-
chelating ligands for group 4 metal complex formation. For ease
of presentation and discussion these proligands will be referred to
as HL1 (4d) and HL2 (4c) (Fig. 2).
˚
planarity. The Zr1–N1 bond distance of 2.127(2) A (Fig. 3) of the
ligand L1 is shorter than Zr–N bond distances in N,O-chelating
˚
amidate complexes (2.183–2.470 A) that have been extensively
studied in our group.87,128 The CH3O–Zr distance (2.369(3) A) is in
˚
the range of similar dative interactions in the literature;109,119,129–132
and is also comparable to the values observed for five-membered
Zr metallacycles featuring this interaction.119,129 However, this Zr–
˚
O bond distance (2.369(3) A) is significantly longer than the Zr–O
bond distances in N,O-chelating amidate complexes (2.093–2.252
78,87,128
˚
A).
Table 2 features the experimental details of the X-ray
diffraction studies.
Fig.
2
Racemic proligands for preparing N,O-chelated group 4
complexes.
Initial synthetic efforts focused on the investigation of the least
sterically demanding proligand. Thus, the protonolysis reaction
using equimolar quantities of HL1 and Zr(NMe2)4 in toluene for
16 h at 100 ◦C gives complex 5 as a colourless solid in 78% isolated
yield (Scheme 2). Notably, attempts to install two ligands using 2
equiv. of HL1 and 1 equiv. of Zr(NMe2)4 at 100 ◦C after 16 h still
give only complex 5 with only one ancillary ligand. This is clearly
observed by 1H NMR spectroscopy of the reaction mixture, which
displays the signals associated with ZrL1(NMe2)3 (5), along with
those of the free proligand in a 1 : 1 ratio.
Fig. 3 ORTEP representation of the solid-state molecular structure of
complex 5 plotted with 50% probability ellipsoids. Symmetry equivalent
atoms are indicated with the “_8” character, and were generated with
˚
the symmetry operation (x, -y + 1/2, z). Selected bond lengths (A) and
angles (◦): Zr1–O1, 2.369(3); Zr1–N1, 2.127(2); Zr1–N2, 2.064(2); Zr1–N3,
2.068(2); N2–Zr1–N1, 100.22(9); N3–Zr1–N1, 119.45(6); N2–Zr1–O1,
167.65(9); N3–Zr1–O1, 94.30(10); O1a–C3–C1a–N1 (chelate ring dihedral
angle), 43.2(5).
1
The H NMR spectrum of complex 5 reveals that the methyl
protons adjacent to the stereogenic center in L1 resonate at a
higher field (d 0.56) relative to those of HL1 (d 1.15), whereas the
methyl protons of the N-aryl group in L1 are shifted downfield and
are inequivalent as manifested by two distinct singlets at d 2.34
and 2.45, each integrating to three protons. This inequivalence
The reaction of equimolar quantities of HL1 and Ti(NMe2)4
is much slower and does not go to completion even with a
◦
prolonged reaction time. After 48 h at 100 C, the conversion to
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Dalton Trans., 2011, 40, 7769–7776 | 7771
©

Table 2 Crystallographic parameters for ZrL1(NMe2)3 (5), TiL1(NMe2)3 (6), and ZrL2(NMe2)3 (7)
ZrL1(NMe2)3 (5)
TiL1(NMe2)3 (6)
ZrL2(NMe2)3 (7)
Formula
Fw
C18H36N4OZr
415.73
C18H36N4OTi
372.41
C25H42N4OZr
505.85
Crystal size/mm
Colour, habit
Space group
Cell setting
0.25 ¥ 0.2 ¥ 0.07
Colourless, prism
Pnma
Orthorhombic
17.2760(12)
13.5998(9)
9.8227(5)
90
90
90
2307.8(3)
4
1.196
0.2 ¥ 0.2 ¥ 0.2
Red, prism
Pnma
Orthorhombic
17.289(2)
13.0762(13)
9.6677(8)
90
90
90
2185.6(4)
4
1.132
0.25 ¥ 0.1 ¥ 0.1
Colourless, prism
Pbca
Orthorhombic
16.5820(15)
17.7264(4)
18.8172(15)
90
90
90
5531.1(7)
8
1.215
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
Z
rcalcd (g cm-1)
Radiation
˚
˚
˚
Mo-Ka (l = 0.71073 A)
173
880
Mo-Ka (l = 0.71073 A)
173
808
Mo-Ka (l = 0.71073 A)
173
2144
T/K
F(000)
m(Mo-Ka)/mm-1
q range (◦)
0.487
2.36–27.74
55.5
46 460
2818
0.0379
SIR92
139
20.27
0.0421
0.0817
0.0290
0.0744
1.069
0.403
2.36–25.23
50.5
17 022
2046
0.0585
SIR92
136
15.04
0.0611
0.1144
0.0413
0.1032
1.046
0.419
2.00–27.73
55.5
154 892
6474
0.0669
SIR92
291
22.25
0.0579
0.0764
0.0303
0.0681
1.013
2qmax (◦)
Total no. of reflns
No. of unique reflns I = 2s(I)
R (int)
Structure soln
No. of variables
Rfln/param ratio
R1 (all data)
wR2 (all data)
R1 (I > 2s(I))
wR2 (I > 2s(I))
Goodness of fit
TiL1(NMe2)3 (6) is 72% as determined by 1H NMR spectroscopy.
The 1H NMR spectrum of this particular mixture shows two
different doublets between d 0 and 1.5, with the one at higher
field (d 0.55) being assigned to the protons of the methyl group
adjacent to the stereocenter in L1. This signal is diagnostic of
the formation of metal complex 6 as it is shifted about 0.60 ppm
upfield from the proligand doublet that corresponds to the protons
of the same methyl group. Once again, the methyl protons on the
aryl group in the complex are inequivalent and appear as singlets
at d 2.27 and 2.36. They are shifted downfield from the aryl-
methyl protons of the proligand, which appear as a single signal at
d 2.20.
Crystals suitable for X-ray crystallographic studies were ob-
tained from a hot benzene solution. The complex 6 is isomorphous
to 5 (Fig. 4); a similar distorted trigonal bipyramidal coordination
geometry can be seen about the metal center, with the oxygen
atom datively bonded to the titanium center and the ligand L1
forming a five-membered chelate. The crystallographic structure
also contains a mirror plane similar to that described for complex
5, with atoms C1 and O1 being disordered about the plane.
Metrical parameters are all consistent with the smaller atomic
radius of the titanium metal center.
Amido metal complex formation with HL2 as a proligand and
Zr(NMe2)4 has also been carried out. The presence of an aryl
group as opposed to an alkyl group on the oxygen of HL2 should
result in the formation of complexes with different electronic
properties upon metal complex formation. Proligand HL2 reacts
with Zr(NMe2)4 in a 1 : 1 molar ratio at 100 ◦C in toluene to
Fig. 4 ORTEP representation of the solid-state molecular structure of
complex 6 plotted with 50% probability ellipsoids. Symmetry equivalent
atoms are indicated with the “_8” character, and were generated with
˚
the symmetry operation (x, -y + 1/2, z). Selected bond lengths (A) and
angles (◦): Ti1–O1, 2.255(3); Ti1–N1, 1.984(3); Ti1–N2, 1.925(2); Ti1–N3,
1.921(3); N3–Ti1–N1, 99.53(12); N2–Ti1–N1, 120.20(7); N3–Ti1–O1,
169.27(11); N2–Ti1–O1, 94.47(11); O1–C3–C1–N1 (chelate ring dihedral
angle), 44.3(4).
afford ZrL2(NMe2)3 (7) in 86% yield upon recrystallization from
hot hexanes.
The 1H NMR spectrum of 7 indicates hindered rotation about
the N–Caryl bond in L2 as manifested by two singlets at d 2.50
and 2.56 representing the protons of the methyl substituents on
7772 | Dalton Trans., 2011, 40, 7769–7776
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The Royal Society of Chemistry 2011
©

the phenyl ring. In contrast, the methyl protons on the phenoxy
ring appear as a singlet at d 2.26. The methyl protons of the
dimethylamido ligands are noted as a singlet at d 2.81, a likely
consequence of rapid exchange of pseudo axial and equatorial
ligands on the NMR time scale.
X-ray crystallographic analysis shows that 7 is a C1-symmetric
complex with an N,O-chelating ligand in which the oxygen atom
of the ligand interacts with the zirconium center in a dative fashion
(Fig. 5). Once again, the geometry about zirconium is a distorted
trigonal bipyramid with the oxygen of the ligand and one of the
dimethylamido nitrogens (N2) in the axial positions. The five-
membered chelate ring is significantly distorted from planarity
as indicated by the torsion angle (46.40(19)◦) between the atoms
˚
of the metallacycle. The bond distance of 2.4882(12) A between
Scheme 3 Intramolecular cyclohydroamination catalyzed by five-mem-
bered titana- and zirconacycles.
the oxygen donor atom and the zirconium metal center in 7 is
˚
much longer than the value of 2.369(3) A noted in complex 5
(Fig. 3). This suggests a much weaker interaction of the oxygen
functionality with the metal center in complex 7 and is likely due
to steric effects of the bulky aryl substituent as well as the reduced
nucleophilicity of the lone pairs on oxygen due to the conjugated
aryl ring. While this Zr–O bond distance is quite long, it should be
noted that even longer Zr–O bond distances have been previously
reported.104,133
varying substituents and on synthesizing enantiopure versions of
these proligands and complexes for subsequent use in enantiose-
lective hydroamination reactions.
Summary and future directions
In summary, the intermolecular hydroamination of oxygen-
substituted allenes with a bulky aniline using catalyst precursor
1 efficiently affords ketimine products. Thus, the hydroamination
of oxygen-substituted allenes with 2,6-dimethylaniline provides
an efficient and modular synthetic route toward amino ether
proligands for the synthesis of N,O-chelated zirconium and
titanium metal complexes. In the solid-state, these complexes
adopt distorted trigonal bipyramidal geometry about the metal
center and contain a five-membered metallacycle with dative
bonding between the oxygen donor atom and the metal center.
Interestingly, six-coordinate bis-ligated complexes could not be
prepared by protonolysis, even with high reaction temperatures
and long reaction times. Preliminary investigations revealed that
these complexes are competent precatalysts for the cyclohydroam-
ination of aminoalkenes. This family of proligands is particularly
attractive, as enantioselective reduction protocols could be used,
thereby granting access to new complexes that may be useful
for asymmetric catalysis. Thus, the investigation of a variety of
five-membered N,O-chelates including enantiopure variants is
currently underway.
Fig. 5 ORTEP representation of the solid-state molecular structure of
complex 7 plotted with 50% probability ellipsoids. Selected bond lengths
◦
˚
(A) and angles ( ): Zr1–O1, 2.4882(12); Zr1–N1, 2.1263(15); Zr1–N2,
2.0763(17); Zr1–N3, 2.0617(17); Zr1–N4, 2.0830(18); N3–Zr1–N2,
98.29(7); N3–Zr1–N4, 116.62(7); N2–Zr1–O1, 162.00(5); N3–Zr1–O1,
98.57(6); O1–C3–C2–N1 (chelate ring dihedral angle), 46.40(19).
Similar to the reaction with HL1, attempts to prepare bis-ligated
zirconium complex using HL2 were unsuccessful as only one ligand
could be installed. Furthermore, neither 1 nor 2 equiv. of HL2 react
with Ti(NMe2)4 using the established protonolysis methodology,
even at a high temperature of 100 ◦C and reaction times of up
to 24 h. Based upon the sluggish reactivity observed during the
preparation of Ti complex 6 with L1, the lack of reactivity of HL2
observed here is attributed to steric factors.
Experimental procedures
General methods
All moisture/air sensitive reactions were carried out under an
atmosphere of dry nitrogen using standard Schlenk line techniques
or an MBraun Unilab glove box unless otherwise stated. 1H and
1
13C{ H} NMR spectra were recorded on 300 MHz or 400 MHz
Preliminary catalytic investigation
Bruker Avance spectrometers at ambient temperature; chemical
shifts are reported in parts per million (ppm) relative to the
signal for the residual proton in the solvent indicated. Thin
layer chromatography was performed on silica gel (Macheney-
Nagel Silica Gel 60) aluminum plates (layer 0.20 mm). Column
chromatography was performed using SiliaFlash F60 silica gel
70–230 mesh. GC–MS spectra were obtained on an Agilent series
6890 gas chromatography system equipped with a 5973 mass
Preliminary catalytic studies with compounds 5–7 show that these
complexes are effective precatalysts for the cyclohydroamination
of aminoalkenes. Complete cyclization of aminoalkenes 8 and 9
into a-substituted pyrrolidine 10 and a-substituted piperidine 11
respectively, occurs with 5 mol% of either complex 5, 6, or 7 within
24 h at 110 ◦C (reaction time not optimized, Scheme 3). On-going
investigations focus on comparing reactivity of complexes with
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 7769–7776 | 7773
©

selective detector. Mass spectrometry and elemental analysis were
performed at the Department of Chemistry, University of British
Columbia. Single crystal X-ray diffraction measurements were
performed on a Bruker X8 APEX diffractometer using a Mo-Ka
1H NMR (CDCl3, 300 MHz, d): 1.36 (3H, d, J = 6.2 Hz,
CHCH3), 2.27 (6H, s, Ar–CH3), 2.32 (6H, s, Ar–CH3), 3.51 (1H,
br s, Ar–NH), 3.69–3.78 (2H, m, CH2CH), 3.86 (1H, m, CH2CH),
6.82 (1H, m, Ar–H), 6.93 (1H, m, Ar–H), 7.01 (4H, m, Ar–H);
1
13C{ H} NMR (CDCl3, 75 MHz, d): 16.5, 18.8, 19.2, 52.6, 75.6,
˚
radiation source (l = 0.71013 A) at 173 K.
121.6, 124.0, 129.1, 129.1, 129.3, 131.1, 144.6, 155.6; GC–MS (EI)
m/z: 283 (M+), 148 {M+–[CH2O(CH3)2C6H3]}; Anal. Calcd for
C19H25ON: C, 80.52; H, 8.89; N, 4.94. Found: C, 80.33; H, 8.83;
N, 5.20.
Materials
THF, hexanes, and toluene were purified over columns of
alumina. Amines were dried over CaH2 and distilled under
vacuum or nitrogen. Ti(NEt2)4, Ti(NMe2)4, and Zr(NMe2)4 were
purchased from Strem and used as received. d8-Toluene, and
d6-benzene, were degassed by freeze-pump-thaw process, and
ZrL1(NMe2)3 (5)
˚
stored over 4 A molecular sieves in the glove box. Bis(amidate)
A solution of 300 mg (1.55 mmol) of HL1 in 10 mL of toluene
bis(amido) precatalyst 1 was prepared as described previously.90
Phenylallene 2a,134 benzylallene 2b,135 2,6-dimethylphenoxyallene
2c,127 methoxyallene 2d,125 2,2-diphenyl-4-pentenylamine 8,136 and
2,2-diphenyl-5-hexenylamine 9136 were synthesized according to
literature procedures. Hexanes solutions of proligands HL2 and
HL1 were dried over anhydrous magnesium sulphate for 2 h after
which the solid was filtered off and the solvents removed prior to
the proligands being used in metal complex formation. All other
reagents were purchased from Aldrich, Acros, or Fisher Scientific
and used without further purification. The spectral data for the
following products are consistent with literature values: N-(4-
phenylbutan-2-yl)-2,6-dimethylaniline 4a,74 N-(1-phenylpropan-
2-yl)-2,6-dimethylaniline 4b,137 N-(1-methoxypropan-2-yl)-2,6-
dimethylaniline 4d,138 2-methyl-4,4-diphenylpyrrolidine 10,136 and
2-methyl-5,5-diphenylpiperidine 11.139
was added to 0.415 g (1.55 mmol) of Zr(NMe2)4 in 20 mL of
toluene at 0 C via cannula transfer. The reaction was stirred at
◦
100 ◦C overnight. All volatiles were removed in vacuo and the solid
product formed was dissolved in hexanes and filtered through
Celite in the glove box. The hexanes were removed in vacuo to
give a colourless solid in 78% yield (503 mg, 1.21 mmol). Crystals
were obtained by dissolving the solid in hot hexanes and slowly
cooling to room temperature. 1H NMR (C6D6, 400 MHz, d): 0.56
(3H, d, J = 6.4 Hz, CHCH3), 2.34 (3H, s, Ar–CH3), 2.45 (3H,
s, Ar–CH3), 2.92 (18H, br s, N(CH3)2), 2.99 (3H, s, OCH3), 3.19
(1H, m, CH2CH), 3.26 (1H, dd, J = 7.6, 4.6 Hz, CH2CH), 3.83
(1H, m, CH2CH), 6.88 (1H, m, Ar–H), 7.10 (1H, d, J = 7.3 Hz,
1
Ar–H), 7.19 (1H, d, J = 7.3 Hz, Ar–H); 13C{ H} NMR (C6D6,
100 MHz, d): 17.3, 19.8, 21.4, 43.3, 56.4, 60.2, 82.8, 122.8, 128.6,
128.7, 134.2, 136.2, 151.1; MS(EI) m/z: 414 (M+); Anal. Cacld for
C18H36N4OZr: C, 52.00; H, 8.73; N, 13.48. Found: C, 51.93; H,
8.69; N, 13.71.
Representative procedure for intermolecular hydroamination of
allenes
All catalytic reactions were set up inside of the glove box and then
transferred into a J. Young NMR tube equipped with a Teflon
cap for further manipulation outside of the glove box. The NMR
tubes were heated in an oil bath set at the temperature indicated
in Table 1 for the specific substrates combination.
TiL1(NMe2)3 (6)
The synthesis procedure for complex 6 is analogous to that
described above for complex 5, with Ti(NMe2)4 being used instead
of Zr(NMe2)4. Complex 6 was characterized in the presence of
unreacted proligand. 1H NMR (C6D6, 300 MHz, d): 0.55 (3H, d,
J = 6.5 Hz, CHCH3), 2.27 (3H, s, Ar–CH3), 2.36 (3H, s, Ar–CH3),
3.03 (18H, br s, N(CH3)2), 3.06 (3H, s, OCH3), 3.20–3.53 (2H,
m, CH2CH), 4.08 (1H, m, CH2CH), 6.74–7.06 (3H, m, Ar–H);
MS(EI) m/z: 372 (M+), 328 (M+–NMe2).
Example: synthesis of N-(1-(2,6-dimethylphenoxy)propan-2-yl)-2,
6-dimethylaniline (4c)
A mixture of 200 mg (1.25 mmol) of 2,6-dimethylphenoxyallene,
151 mg (1.25 mmol) of 2,6-dimethylaniline, 47 mg (5 mol%) of
1, and 0.35 mL of d8-toluene in a J. Young NMR tube equipped
with a Teflon cap (total volume in NMR tube is 0.6 mL) was
heated at 90 ◦C (in an oil bath) for 2 h. The reaction mixture
was cooled to room temperature, and then added to a mixture
of 157 mg (2.50 mmol) of sodium cyanoborohydride and 170
mg (1.25 mmol) of zinc chloride in 40 mL of THF or methanol,
followed by stirring at room temperature for 16 h. The reaction was
quenched by the addition of 20 mL of saturated aqueous sodium
carbonate solution. The precipitated was filtered and washed with
dichloromethane (25 mL). The organic layer was separated and the
aqueous layer was extracted with dichloromethane (3 ¥ 30 mL).
The combined extracts were dried over anhydrous magnesium
sulphate, the solid was filtered off and the solvents removed by
rotary evaporation. The crude product was purified by column
chromatography using hexanes/ethyl acetate 40 : 1 to give the
product in 76% yield (268 mg, 0.946 mmol).
ZrL2(NMe2)3 (7)
This complex was synthesized from HL2 (535 mg, 1.89 mmol) and
Zr(NMe2)4 (505 mg, 1.89 mmol) as colourless solid in 86% yield
(821 mg, 1.62 mmol) according to the procedure outlined above
for complex 5. 1H NMR (C6D6, 300 MHz, d): 0.63 (3H, d, J = 5.8
Hz, CHCH3), 2.29 (6H, s, Ar–CH3), 2.50 (3H, s, Ar–CH3), 2.56
(3H, s, Ar–CH3), 2.81 (18H, s, N(CH3)2), 3.47 (1H, m, CH2CH),
4.16 (2H, m, CH2CH, CH2CH), 6.86 (3H, m, Ar–H), 6.94 (1H,
m, Ar–H), 7.14 (1H, m, Ar–H), 7.24 (1H, m, Ar–H); 13C{ H}
1
NMR (C6D6, 100 MHz, d): 17.1, 17.2, 19.9, 21.6, 43.4, 57.6, 82.7,
123.2, 125.8, 128.9, 129.0, 130.0, 131.4, 134.2, 137.1, 151.4, 157.3;
MS(EI) m/z: 504 (M+); Anal. Cacld for C25H42N4OZr: C, 59.36;
H, 8.37; N, 11.08. Found: C, 58.96; H, 7.97; N, 10.74.
7774 | Dalton Trans., 2011, 40, 7769–7776
This journal is
The Royal Society of Chemistry 2011
©

40 A. L. Reznichenko, H. N. Nguyen and C. Hultzsch Kai, Angew. Chem.,
Int. Ed., 2010, 49, 8984.
Acknowledgements
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The authors thank Dr Brian O. Patrick for assistance with
X-ray crystallography and NSERC and Boehringer Ingelheim
Canada Ltd. for financial support of this work. RA thanks the
Commonwealth Scholarship program for funding.
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7776 | Dalton Trans., 2011, 40, 7769–7776
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The Royal Society of Chemistry 2011
©