Intramolecular hydroamination catalysis using trans-N,N′- dibenzylcyclam zirconium complexes

Article abstract of DOI:10.1016/j.jorganchem.2010.08.039

The syntheses of (Bn₂Cyclam)Zr(NMe₂)₂ (1), (Bn₂Cyclam)Zr(NH^2,6-MePh)Cl (2) and (Bn ₂Cyclam)Zr(N^2,6-MePh) (3) are described. The reactivity of 1, 3, (Bn₂Cyclam)Zr(CH₂Ph)₂ (4) and ((C ₆H₄CH₂)₂Cyclam)Zr (5) as hydroamination catalysts of aminoalkenes is reported. High conversions of the primary gem-disubstituted aminoalkenes in 5- or 6-member ring N-heterocycles were observed. Reactions of 1, 4 and 5 with CH₂CHCH ₂CPh₂CH₂NH₂ gave (Bn ₂Cyclam)Zr(NHR)₂ (6) (R = CH₂CPh ₂CH₂CHCH₂) that on heating converts sequentially into the mono-ortho-metallated species ((C₆H ₄CH₂)BnCyclam)Zr(NHR) (7) and the bis-ortho-metallated ((C₆H₄CH₂)₂Cyclam)Zr (5), simultaneously with the hydroamination product.

Full text of DOI:10.1016/j.jorganchem.2010.08.039

Journal of Organometallic Chemistry 696 (2011) 2e6
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Communication
Intramolecular hydroamination catalysis using trans-N,N0-dibenzylcyclam
zirconium complexes
,
,
*
M. Augusta Antunes a, Rui F. Munhá a b, Luis G. Alves a, Laurel L. Schafer b, Ana M. Martins a
a Centro de Química Estrutural, Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
b Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1
a r t i c l e i n f o
a b s t r a c t
The syntheses of (Bn2Cyclam)Zr(NMe2)2 (1), (Bn2Cyclam)Zr(NH2,6-MePh)Cl (2) and (Bn2Cyclam)Zr(N2,6-
MePh) (3) are described. The reactivity of 1, 3, (Bn2Cyclam)Zr(CH2Ph)2 (4) and ((C6H4CH2)2Cyclam)Zr (5)
as hydroamination catalysts of aminoalkenes is reported. High conversions of the primary gem-disub-
stituted aminoalkenes in 5- or 6-member ring N-heterocycles were observed. Reactions of 1, 4 and 5 with
CH2]CHCH2CPh2CH2NH2 gave (Bn2Cyclam)Zr(NHR)2 (6) (R ¼ CH2CPh2CH2CH]CH2) that on heating
converts sequentially into the mono-ortho-metallated species ((C6H4CH2)BnCyclam)Zr(NHR) (7) and the
bis-ortho-metallated ((C6H4CH2)2Cyclam)Zr (5), simultaneously with the hydroamination product.
Ó 2010 Elsevier B.V. All rights reserved.
Article history:
Received 3 August 2010
Received in revised form
19 August 2010
Accepted 24 August 2010
Available online 8 October 2010
Keywords:
Zirconium
Cyclam
Hydroamination
Nitrogen heterocycles
Aminoalkenes
Intramolecular cyclization
1. Introduction
In this contribution we present preliminary results on amino-
alkene hydroamination using a new class of zirconium catalyst
Hydroamination is an atom-efficient procedure for the assembly
of carbonenitrogen bonds through the inter- or intramolecular
addition of an amine to a carbonecarbon unsaturated bond [1].
Although enthalpically favoured, the negative entropy balance of
the reaction requires that a catalyst activates the amine and/or the
carbonecarbon bond for the coupling process [2].
Research on this topic showed that a wide variety of metal
compounds along the Periodic Table are suitable catalysts for these
transformations [1,3]. Although titanium derivatives proved
extremely successful in the intermolecular alkyne hydroamination
[4], expanding the general use of Group 4 metal compounds to
intramolecular hydroamination processes was attained only
recently. Cationic Zr and Ti complexes were found to catalyze the
hydroamination of secondary aminoalkenes [5], while neutral
Group 4 metal compounds were used for primary aminoalkenes
and aminoalkynes [6]. Currently, intense research efforts are being
made at the development of Group 4 metal complexes due to the
fact they combine high activity and good selectivity (regio- and
enantioselectivity) with chemical robustness.
precursors supported by a dianionic trans-disubstituted cyclam
ligand, Bn2Cyclam. The flexibility of the ancillary ligand, already
evidenced by its hemiliable behavior [7], as well as its participation
in CeH activation reactions [8] are expected to play a prominent
role in catalysis. We anticipate that these features are particularly
relevant in processes that involve proton exchange as is the case of
hydroamination.
2. Results and discussion
The syntheticroutes for the preparationof(Bn2Cyclam)Zr(NMe2)2
(1), (Bn2Cyclam)Zr(NH2,6-MePh)Cl (2), (Bn2Cyclam)Zr(N2,6-MePh) (3),
(Bn2Cyclam)Zr(CH2Ph)2 (4) and ((C6H4CH2)2Cyclam)Zr (5) are pre-
sented in Scheme 1. Complex 1 was prepared by aminolysis of Zr
(NMe2)4 with Bn2Cyclam in 82% yield. 2 and 4 were prepared by
chloride metathesis of (Bn2Cyclam)ZrCl2 [9] with LiNH2,6-MePh and
MgClCH2Ph, respectively. Addition of MgClMe to compound 2 gave
the imido derivative 3, upon methane elimination in 68% yield. As
reported previously, 5 can be obtained by heating solutions of the bis
(alkyl) complex 4 [8].
In order to evaluate the behavior of different types of zirco-
nium derivatives incorporating this macrocyclic ligand, complexes
* Corresponding author.
E-mail address: ana.martins@ist.utl.pt (A.M. Martins).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.08.039

M.A. Antunes et al. / Journal of Organometallic Chemistry 696 (2011) 2e6
3
Table 1
Synthesis of cycloalkylamine derivatives via catalytic hydroamination.
Substrate
Catalyst
Time (h)
Conversion (%)
1
3
4
5
3
7
3
7
> 98
90
> 98
> 98
1
4
5
4.5
4.5
6
> 98
> 98
90
1
4
48
48
> 98
> 98
1
4
24
24
0
0
1
4
24
24
0
0
Scheme 1.
1, 3, 4 and 5 were screened as aminoalkene hydroamination
catalysts (Eq. 1). (1)
formation of [2 þ 2] addition products but followed decomposition
pathways; exception was the reaction of the imido complex with
phenylacetylene that led to (Bn2Cyclam)Zr(CCPh)2 and 2,6-iPrPhNH2
[7]. Thus the lack of reactivity observed with secondary amines in
our case may be due to the increased steric bulk of this amine
substrate over its primary amine congener.
Stoichiometric reactions of 1, 4 and 5 with 2,2-diphenyl-pent-4-
enylamine in benzene-d6 were conducted and followed by NMR
spectroscopy to gain insight into the mechanism of alkene hydro-
amination promoted by these compounds (Scheme 2).
R'
N
R
R
[catalyst]
NHR'
n
n
R
R
The results displayed in Table 1 show that all complexes are able
to perform the intramolecular cyclization of primary aminoalkenes
leading to the formation of five-member azacycles using a 10%
catalyst load in toluene-d8 at 115 ꢀC.
Using C-(1-allyl-cyclohexyl)-methylamine as
a
reference
substrate, the results show that complexes 1 and 4 are more active
than 3 and 5. Indeed, the conversion of C-(1-allyl-cyclohexyl)-
methylamine and 2,2-diphenyl-pent-4-enylamine to the corre-
sponding hydroamination products is quantitative after 3 h and
4.5 h, respectively, when 1 and 4 are used as catalyst precursors. It
should be mentioned that regardless of the activity, all compounds
reach quantitative substrate conversion and selectivity. 1 and 4 are
also efficient catalysts for the cyclization of 2,2-diphenyl-hex-5-
enylamine but neither of them react with 2-phenyl-hex-5-enyl-
amine or 2,2-diphenyl-hex-5-enylmethylamine. The lack of reaction
with 2-phenyl-hex-5-enylamine reveals the importance of the
Thorpe-Ingold effect in intramolecular hydroamination [10]. On the
other hand, the absence of reaction with secondary amines [11] is
usually associated with the formation of terminal metal-imido
moieties. The latter are thought to undergo a [2 þ 2] cycloadition
reaction to form an azametallacyclobutene intermediate and have
been proposed as active species in Ti and Zr catalyzed hydro-
amination reactions [4e,4f,6j,12]. This type of mechanism does not
seem to be in line with our previously described results on the
reactivity of amido and imido complexes incorporating this
macrocyclic ligand. We have shown that terminal imido compounds
of general formula (Bn2Cyclam)Zr]NR are not formed by amine
elimination from (Bn2Cyclam)Zr(NHR)2 solutions [7] but require
methane elimination from putative (Bn2Cyclam)Zr(NHR)(CH3), as
described for the synthesis of 3. Moreover, reactions of (Bn2Cyclam)
Zr(N2,6-iPrPh) with acetylenes did not show any evidence for the
Scheme 2.

4
M.A. Antunes et al. / Journal of Organometallic Chemistry 696 (2011) 2e6
The addition of two equivalents of aminoalkene to the solutions
3.1.1. (Bn2Cyclam)Zr(NMe2)2 (1)
of 1 or 4, at room temperature, led to the quantitative formation of
(Bn2Cyclam)Zr(NHR)2 (R ¼ CH2CPh2CH2CH]CH2) (6). Sequential
addition of one plus one equivalents of 2,2-diphenyl-pent-4-enyl-
amine to a solution of 5 gives the mono-ortho-metallated complex
7 and then the bis-amido 6, in quantitative yield at room temper-
ature. The formation of 2-methyl-4,4-diphenylpyrrolidine and 7 is
observed when solutions of 6 are kept at room temperature for
a few hours. Upon heating the solution until 90 ꢀC, 6 is converted
quantitatively to 7 and further heating of this solution gives 5 as the
only zirconium complex.
H2(Bn2Cyclam) (0.43 g, 1.1 mmol) was dissolved in 10 mL of
toluene and slowly added to a ꢁ10 ꢀC toluene solution of
Zr(NMe2)4. The resulting pale yellow solution was left stirring
overnight. The solvent was evaporated and the residue washed
with minimal hexanes to yield (Bn2Cyclam)Zr(NMe2)2 in 82%
(0.53 g). 1H NMR (C6D6, 400.2 MHz):
d(ppm) 7.15e7.10 (over-
lapping, 6H total, H-Ph), 7.05e6.98 (overlapping, 4H total, H-Ph),
4.20 (d, 2H, PhCH2N), 4.02 (d, 2H, PhCH2N), 3.42 (s, 12H, Zr(N
(CH3)2)2), 3.40e3.23 (overlapping, 6H total, 4H, [C2]CH2N, 2H, [C3]
CH2N), 3.14 (m, 2H, [C3]CH2N), 2.86 (m, 2H, [C2]CH2N), 2.71 (m, 2H,
[C3]CH2N), 2.36 (m, 2H, [C2]CH2N), 2.18e1.98 (overlapping, 4H
total, 2H, 2H, [C3]CH2N, 2H, CH2CH2CH2), 1.64 (m, 2H, CH2CH2CH2).
13C{1H} NMR (C6D6, 100.6 MHz): 133.5 (i-Ph), 132.1 (o-Ph), 128.1
(m-Ph), 127.8 (p-Ph), 58.8 (PhCH2N), 56.9 ([C2]CH2N), 54.6 ([C3]
CH2N), 54.2 ([C2]CH2N), 48.2 (Zr(N(CH3)2)2), 46.1 ([C3]CH2N), 24.6
(CH2CH2CH2). Anal. Calcd. for C28H46N6Zr: C 60.28, H 8.31, N 15.06.
Found: C 60.11, H 8.01, N 15.03.
Even though the NMR data do not reveal any terminal or
bridging zirconium imido species or free amine, the occurrence of
fast equilibria between 7 or 6 and (Bn2Cyclam)Zr(NR) (Scheme 2)
cannot be excluded [6m,13aed]. Alternatively the cyclization
reaction may occur through insertion of C]C in the ZreNHR bond.
This type of mechanism was proposed for the intramolecular
hydroamination of aminoalkenes catalyzed by lanthanides and by
constrained geometry zirconium and actinide complexes [6a, 6e,
14]. In this instance, the accessibility of the C]C to the metal
coordination sphere, which is an essential requirement for the
reaction to proceed, may either be supported by the ancillary ligand
through the elongation of the ZreNamine bonds [7], or by increasing
the coordination number of the metal centre. Complexes incorpo-
rating this ancillary ligand have shown to be able to accommodate
coordination numbers up to 8, which have been characterized by
either X-ray diffraction studies or DFT calculations [15]. Overall, the
two mechanistic pathways are valid and the presently available
information does not allow us to distinguish between them.
In conclusion, a new class of zirconium compounds supported
by a cyclam-based ligand was found to competently catalyze the
intramolecular hydroamination of selected primary aminoalkenes.
To the best of our knowledge this is the first example where a metal
macrocyclic complex is used to promote this transformation. The
system shows some remarkable features that make it appealing.
The fact the ancillary ligand ZreN bonds resist protonation, which
may be related to the macrocyclic effect, is encouraging if one
considers the lack of steric hindrance around the amido donors. The
absence of free ligand in solution points toward the robust nature of
the ligand framework, which is a crucial aspect considering that
under catalytic conditions sequential transamination reactions are
required for successive catalytic turnovers. We are currently
pursuing this study to clarify mechanistic aspects and optimize the
system performance, and we are also interested in broadening the
substrate scope in hydroamination reactions.
3.1.2. (Bn2Cyclam)Zr(NH2,6-MePh)Cl (2)
To a THF suspension of (Bn2Cyclam)ZrCl2 (0.40 g, 0.7 mmol) at
ꢁ30 ꢀC was slowly added a THF solution of LiNH2,6-MePh (0.09 g in
20 mL). During the addition process the suspension starts to
dissolve and a pale yellow solution is formed. The mixture was left
stirring overnight and the solvent was evaporated. The residue was
extracted with toluene, allowing the removal of LiCl. The solvent
was evaporated and 10 mL of hexanes were added to wash the
yellow residue. A pale yellow solid was obtained in 74% yield
(0.32 g). 1H NMR (toluene-d8, 400.2 MHz, 246 K):
d(ppm) 7.40e7.00
(overlapping, 12H total, 10H, H-PhCH2, 2H, m-2,6-MePh), 6.86 (t, 1H,
2
p-2,6-MePh), 5.68 (s, 1H, 2,6-MePh(H)NZr), 4.93 (d, JHH ¼ 14 Hz, 1H,
PhCH2N), 4.64e4.45 (overlapping, 2H total, 1H, PhCH2N, 1H, [C3]
2
CH2N), 4.39 (d, JHH ¼ 14 Hz, 1H, PhCH2N), 4.19e4.04 (overlapping,
2H total, 1H, PhCH2N, 1H, [C3]CH2N), 3.61e3.41 (overlapping, 3H
total, 2H [C2]CH2N, 1H, [C3]CH2N), 2.88 (s, 3H, CH3-Ph), 2.80e2.50
(overlapping, 7H total, 3H, [C3]CH2N, 4H, [C2]CH2N), 2.45e2.30
(overlapping, 4H total, 3H, CH3-Ph, 1H, [C3]CH2N), 2.27 (m, 1H, [C3]
CH2N), 2.17 (m, 1H, [C2]CH2N), 1.96 (m, 1H, [C2]CH2N), 1.57 (m, 2H,
CH2CH2CH2), 1.24 (m,1H, CH2CH2CH2),1.06 (m,1H, CH2CH2CH2). 13
C
{1H} NMR (toluene-d8, 100.6 MHz, 246 K):
d
(ppm) 155.3 (i-2,6-
MePhN), 133.5 (C-PhCH2N), 133.3 (C-PhCH2N), 132.7 (i-Ph), 132.1
(i-Ph), overlapping with toluene-d8 (i-Ph and C-Ph), 118.06 (p-2,6-
MePh), 57.5 (PhCH2N), 56.9 (PhCH2N), 56.7 ([C3]CH2N), 56.1 ([C3]
CH2N), 55.8 ([C3]CH2N), 52.7 ([C2]CH2N), 52.4 ([C2]CH2N), 48.8
([C2]CH2N), 48.6 ([C2]CH2N), 24.2 (CH2CH2CH2), 24.1 (CH2CH2CH2),
22.2 ((CH3)2Ph), 22.0 ((CH3)2Ph). Anal. Calcd. for C32H44N5ClZr: C
61.46, H 7.09, N 11.20. Found: C 61.56, H 7.49, N 11.08.
3. Experimental section
3.1. General procedures
3.1.3. (Bn2Cyclam)Zr(N2,6-MePh) (3)
To a THF solution of (Bn2Cyclam)Zr(NH2,6-MePh)Cl (0.30 g,
0.5 mmol in 10 mL) was slowly added 1 mL of a diethyl ether
solution of MgClMe (0.5 M). During the addition process the light
yellow solution becomes turbid. The mixture was allowed to stir
overnight, after which the solvent was evaporated. A mixture of
10 mL of toluene, 0.5 mL of THF and 10 mL of dioxane was added to
separate MgCl2. After 3 h, the suspension was filtered, taken to
dryness and washed with hexanes. The product was obtained in
All manipulations were performed under a dry nitrogen atmo-
sphere using standard Schlenk and glove box techniques. Solvents
were previously dried with 4 Å molecular sieves and distilled under
a dry nitrogen atmosphere over sodium/benzophenone (diethyl
ether and toluene). Toluene-d8 and benzene-d6 were dried with 4 Å
molecular sieves, degassed and stored under nitrogen. Literature
methods were used to prepare H2(Bn2Cyclam), (Bn2Cyclam)ZrCl2,
(Bn2Cyclam)Zr(CH2Ph)2, and ((C6H4CH2)2Cyclam)Zr [8,9].
68% yield (0.20 g). 1H NMR (benzene-d6, 400.1 MHz, 298 K):
d(ppm)
NMR spectra were recorded on Bruker AvanceII 300 MHz or
Bruker AvanceII 400 MHz spectrometers. Chemical shifts for 1H
were referenced to resonances of the residual protonated solvents
relative to tetramethylsilane (0 ppm), and 13C spectra were refer-
enced to the solvent carbon resonance. Elemental analysis and low
resolution electron ionization were performed at the facilities of
the Chemistry Department of the University of British Columbia.
7.55e6.95 (overlapping, 12H total, 10H, H-PhCH2, 2H, m-2,6-iPrPh),
2
6.65 (t, 1H, p-2,6-iPrPh), 4.51 (d, JHH ¼ 14 Hz, 2H, PhCH2N), 4.32 (d,
2JHH ¼ 14 Hz, 2H, PhCH2N), 3.97 (m, 2H, [C3]CH2N), 3.59 (m, 2H, [C2]
CH2N), 3.00e2.80 (overlapping, 5H total, 2H, [C3]CH2N, 3H, (CH3)
Ph), 2.72e2.50 (overlapping, 9H total, 4H, [C2]CH2N, 2H, [C3]CH2N,
3H, (CH3)Ph), 2.24 (m, 2H, [C3]CH2N), 2.11 (m, 2H, [C2]CH2N), 1.47
(m, 2H, CH2CH2CH2), 1.02 (m, 2H, CH2CH2CH2). 13C{1H} NMR

M.A. Antunes et al. / Journal of Organometallic Chemistry 696 (2011) 2e6
5
(benzene-d6, 100.6 MHz, 298 K):
d
(ppm) 163.2 (i-2,6-MePhN), 133.0
3H total, 1H, eNH, 1H, [C3]NCH2, 1H, [C2]NCH2), 3.20 (m, 1H,
eCH2eCH]), 3.04e2.96 (overlapping, 2H total, 1H, eCH2eCH],
(i-PhCH2N), 131.8 (C-Ph), 129.3 (C-Ph), 128.6 (C-Ph), 128.4 (C-Ph),
125.9 (i-Ph), 112.7 (p-2,6-MePh), 56.6 (PhCH2N), 55.8 ([C3]CH2N),
52.3 ([C2]CH2N), 50.1 ([C3]CH2N), 49.9 ([C2]CH2N), 24.8
(CH2CH2CH2), 21.4 ((CH3)2Ph). EIMS (m/z): 587 (Mþ). Anal. Calcd.
for C32H43N5Zr: C 65.26, H 7.36, N 11.89. Found: C 62.73, H 7.28, N
10.34.
2
1H, [C2]NCH2), 2.86 (m, 1H, [C3]NCH2), 2.84 (d, 1H, JHH ¼ 13 Hz,
PhCH2N), 2.77e2.67 (overlapping, 3H total, 1H, [C2]NCH2, 1H, [C2]
NCH2, 1H, [C3]NCH2), 2.62e2.45 (overlapping, 2H total, 1H, [C2]
NCH2, 1H, [C3]NCH2), 2.36 (m, 1H, [C3]NCH2), 2.24 (m, 1H, [C3]
NCH2), 2.14e2.05 (overlapping, 3H total, 1H, [C2]NCH2, 1H, [C2]
NCH2, 1H, [C3]NCH2), 1.61e1.47 (overlapping, 1H, CH2CH2CH2, 1H,
3.1.4. (Bn2Cyclam)Zr(NHCH2CPh2CH2CH]CH2)2 (6)
CH2CH2CH2),1.10 (m,1H, CH2CH2CH2), 0.79 (m,1H, CH2CH2CH2). 13
C
At room temperature, addition of two equivalents of 1-amino-
{1H} NMR (C6D6, 75.5 MHz, 296 K):
d(ppm) 187.8 (C(1)-Ph), 149.9 (C
2,2-diphenyl-4-pentene to
a
C6D6 solution of
4
(20 mg,
(2)-Ph), 148.7 (i-Ph2C), 148.6 (i-Ph2C), 139.1 (C(6)-Ph), 135.9
(eCH]), 133.3 (i-PhCH2N), 132.7, 129.3, 129.3 (C(5)-Ph), 128.2,
128.1, 128.1, 127.9, 126.8, 125.8, 125.5, 124.4, 117.5 (]CH2), 62.7
(PhCH2), 59.3 ([C3]NCH2), 58.3 (eNHeCH2), 57.1 (PhCH2), 55.2 ([C2]
NCH2), 54.6 ([C3]NCH2), 54.3 ([C3]NCH2), 53.3 (Ph2C), 52.2 ([C2]
NCH2), 52.0 (CH2N), 50.6 (CH2N), 49.1 (CH2N), 42.1 (eCH2eCH]),
24.7 (CH2CH2CH2), 24.5 (CH2CH2CH2).
0.021 mmol) led to quantitative formation of the bis(amido)
zirconium complex 6 and toluene as shown by 1H and 13C NMR
spectra.
Complex 6 was also obtained by reaction of compounds 1 and 5
with two equivalents of 1-amino-2,2-diphenyl-4-pentene in the
same experimental conditions. Formation of HNMe2 was observed
in the reaction with 1 as confirmed by a doublet at 2.20 ppm in the
1H NMR spectrum and a resonance at 39.3 ppm in the 13C spectrum
that account for the methyl groups of the secondary amine.
3.2. General procedures for catalytic hydroamination
1H NMR (C6D6, 500.1 MHz, 296 K):
d(ppm) 7.44 (m, 4H, o-Ph2C),
All hydroamination reactions were carried out in an N2-filled
glove box on an NMR-tube scale. The NMR-tubes were equipped
with a Teflon screw cap. The aminoalkene, the standard (1,3,5-tri-
methoxybenzene) and the catalysts were dissolved in toluene-d8.
The reactions were heated in an oil bath to 115 ꢀC. The heterocyclic
products were characterized by 1H and 13C NMR spectroscopy and
compared with literature data.
7.21e7.13 (overlapping, 12H total, 4H, o-PhCH2N, 4H, m-PhCH2N,
4H, m-Ph2C), 7.09 (m, 2H, p-PhCH2N or p-Ph2C), 7.03 (m, 2H, p-
PhCH2N or p-Ph2C), 5.85 (m, 2H, eCH]), 5.24 (dd, 2H, ]CH2), 5.02
(dd, 2H, ]CH2), 4.54 (m, 4H, eNHeCH2), 3.94 (AB system, 4H,
PhCH2N), 3.63 (t, 2H, [C3]NCH2), 3.38 (t, 2H, eNH), 3.33 (m, 2H,
eCH2eCH]), 3.24 (m, 2H, [C2]NCH2), 3.12 (m, 2H, eCH2eCH]),
3.03e2.99 (overlapping, 4H total, 2H, [C3]NCH2, 2H, [C2]NCH2),
2.54e2.51 (overlapping, 4H total, 2H, [C2]NCH2, 2H, [C2]NCH2), 2.47
(m, 2H, [C3]NCH2), 2.19 (t, 2H, [C3]NCH2), 1.67 (m, 2H, CH2CH2CH2),
Acknowledgements
1.57 (m, 2H, CH2CH2CH2). 13C{1H} NMR (C6D6, 75.5 MHz, 296 K):
d
The authors would like to thank to Fundação para a Ciência e
a Tecnologia, Portugal, for funding (PTDC/QUI/66187/2006; SFRH/
BPD/26745/2006; SFRH/BD/29986/2006; SFRH/BD/44295/2008)
and to the Portuguese NMR Network (IST-UTL Centre) for providing
access to the NMR facility. We would also like to thank the Schafer
group members Ms. Philippa R. Payne and Dr. Patricia Horrillo
Martinez for providing the substrates and guidance on the catalytic
reactions.
(ppm) 149.0 (i-Ph2C), 148.9 (i-Ph2C), 136.7 (eCH]), 133.2 (i-
PhCH2N), 133.0 (p-PhCH2N or p-Ph2C), 129.7 (o-Ph2C), 129.5, 126.2
(o-PhCH2N, m-PhCH2N, m-Ph2C), 126.0 (p-PhCH2N or p-Ph2C), 117.5
(]CH2), 58.5 (PhCH2N and eNHeCH2), 56.8 ([C3]NCH2), 53.8
(Ph2C), 53.6 ([C2]NCH2 and [C2]NCH2), 51.9 ([C3]NCH2), 43.0
(eCH2eCH]), 25.5 (CH2CH2CH2).
Ph
4
5
Ph
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6
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1
Zr
N
N
N
N
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C6D6 solution of
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2
NCH2), 3.52 (d, 1H, JHH ¼ 14 Hz, PhCH2N), 3.40e3.32 (overlapping,

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