New zirconium complexes supported by N-heterocyclic carbene (NHC) ligands: Synthesis and assessment of hydroamination catalytic properties Dedicated to Professor Maria José Calhorda on the occasion of her 65th birthday.

Article abstract of DOI:10.1016/j.jorganchem.2013.11.041

Reactions of 2-(bromomethyl)-4,6-di-tert-butylphenol or 2-(bromomethyl)-4,6-bis(2-phenylpropan-2-yl)phenol with 1H-imidazole led to syntheses of N,N-disubstituted imidazolium bromides presenting two methylene-bis(2,4-di-tert-butylphenol) ([H₂L<

Full text of DOI:10.1016/j.jorganchem.2013.11.041

Journal of Organometallic Chemistry 760 (2014) 60e66
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
New zirconium complexes supported by N-heterocyclic carbene (NHC)
ligands: Synthesis and assessment of hydroamination catalytic
properties
*
Sónia Barroso, Sara R.M.M. de Aguiar, Rui F. Munhá, Ana M. Martins
Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Avenida Rovisco Pais, 1049-001 Lisboa, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
Reactions of 2-(bromomethyl)-4,6-di-tert-butylphenol or 2-(bromomethyl)-4,6-bis(2-phenylpropan-2-
yl)phenol with 1H-imidazole led to syntheses of N,N-disubstituted imidazolium bromides presenting
two methylene-bis(2,4-di-tert-butylphenol) ([H2L1]Br) or methylene-bis(2,4-di-tert-butylphenol) ([H2L2]
Br) appended groups. Treatment of Zr(NMe2)4 with [H2L1]Br or [H2L2]Br gave tethered NHC zirconium
complexes of general formula [ZrL(NMe2)(THF)Br] (L ¼ L1, 7; L2, 8). The bonding of the tridentate ligands
to the metal adopts S-shape conformation. In solution a fluxional process between the left- and right-
handed forms of the ligand is observed for both complexes. In agreement with the NMR spectra, the
optimised structure obtained by DFT revealed octahedral geometry around zirconium with mutually
trans Br and Ccarbene donors. Complexes 7 and 8 react with 2,2-diphenylpent-4-en-1-amine in a 1:1 ratio
to give the hydroamination product 2-methyl-4,4-diphenylpyrrolidine. In catalytic conditions, the sys-
tems deactivate and catalytic conversions are not observed.
Received 10 October 2013
Received in revised form
28 November 2013
Accepted 30 November 2013
Dedicated to Professor Maria José Calhorda
on the occasion of her 65th birthday.
Keywords:
Zirconium
N-Heterocyclic ligands
Tethered NHC complexes
Carbenes
Ó 2013 Elsevier B.V. All rights reserved.
Fluxional processes
1. Introduction
stability of the anionic NHC ligand precursors [10e13] is currently
the most convenient entry into NHC early metals chemistry origi-
N-Heterocyclic carbenes (NHCs) derived from imidazolium salts
[1,2] have been widely used as supporting ligands for transition
metals with important applications in catalysis [3,4]. The good
donor properties, their chemical robustness and the possibility to
modulate either electronic or stereochemical properties are
important features of NHC ligands that are responsible for their
extensive late transition metal chemistry. On the contrary, the
stabilization of early transition metals NHC complexes revealed in
many cases critical and therefore significant applications of these
compounds are by far less developed. A usual strategy to overcome
those problems requires the functionalization of the NHC nitrogen
atoms with appended moieties that provide additional binding
points to the metals. The incorporation of one or two O- or N-based
anionic fragments, which form strong bonds with high oxidation
state early metals, proved to stabilize the carbene coordination and
yielded robust NHC-based high-oxidation-state metal complexes
[5e9]. This methodology, which strongly depends on experimental
issues as the metal precursors and the NHC scaffolds, as well as the
nating a growing number of complexes with interest in catalysis
[5,14e17].
As part of our interest in the chemistry of early transition metals
and lanthanides we explored multidentate ligands where cyclic or
tripodal amine frames were combined with ariloxide donors [18e
24]. The bonding of the phenolate moieties guaranteed the stabi-
lization of low and high oxidation state metal complexes with
diverse structures and reactivity, which were investigated in radical
reactions [18,19], olefin polymerization [20] as well as in epoxida-
tion and sulfoxidation catalysis [21,22]. Furthermore, we studied Zr
complexes anchored by cyclam diamidoediamine ligands and re-
ported the first example of an intramolecular hydroamination
catalysts supported by a macrocyclic scaffold [25]. In view of recent
reports on the catalytic activity of Group 4 NHC complexes in the
intramolecular hydroamination of aminoalkenes [14,15b,26] we
report here new tridentate bis-ariloxide NHC zirconium complexes
and their evaluation as intramolecular hydroamination catalysts.
2. Results and discussion
The ligand precursors [H3L1]Br (3) and [H3L2]Br (4) were pre-
pared by alkylation of 1H-imidazole using 2-(bromomethyl)-4,6-di-
* Corresponding author.
E-mail address: ana.martins@ist.utl.pt (A.M. Martins).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.11.041

S. Barroso et al. / Journal of Organometallic Chemistry 760 (2014) 60e66
61
tert-butylphenol
(1)
and
2-(bromomethyl)-4,6-bis(2-
diffraction. DFT calculation presented below also point out that S
shape configuration is more stable and no U shape compounds
have been identified yet. Thus, it seems plausible to assume that in
complexes 7 and 8 the ligand assumes an S shape that originates an
asymmetric zirconium centre, as observed by NMR at low tem-
perature (see below).
phenylpropan-2-yl)phenol (2), respectively (Scheme 1, top). Com-
pound 1 was obtained as described in the literature [27] by reaction
of 2-(bromomethyl)-4,6-di-tert-butylphenol, paraformaldehyde
and HBr, and compound 2 was prepared using an adaptation of that
procedure. The reaction of 1 equiv. of either 1 or 2 with imidazole,
described in the literature [28] gave, in our hands, mixtures of
mono- and disubstituted products (5 þ 3 and 6 þ 4 in Scheme 1,
bottom) but one pot dialkylation of imidazole, using 2 equiv. of 1 or
2, led cleanly to imidazolium salts [H3L1]Br (3) and [H3L2]Br (4),
respectively, in good yields. 1H and 13C-{1H} NMR spectra of 3 and 4
are consistent with C2-symmetry and in accordance with their
formulation. The resonances for the NCHN protons show up at
The 1H NMR spectra of 7 and 8 at room temperature display
broad resonances that denote a fluxional process in solution. The
proton and carbon NMR patterns of the two compounds are
essentially the same with exception of the resonances assigned to
the tert-butyl or dimethylphenyl substituents of the phenolate
rings. The tert-butyl groups of the phenolate rings of 7 give rise to
two broad signals and the dimethylphenyl groups of 8 originate
three broad resonances for the methyl groups (integrating 6H, 6H
and 12H, respectively) in addition to several aromatic resonances
due to the phenyl groups. In common the proton NMR spectra of 7
and 8 reveal two aromatic peaks corresponding to the phenolate
groups, two broad AX spin systems for the CH2 protons, one reso-
nance for the NMe2 ligand, two broad apparent singlets for the THF
and one resonance for the CH protons of the NHC core. In both 1H
NMR spectra of 7 and 8 the proton attached to the carbon atom of
d
9.48 and 9.94 ppm, respectively, while the resonances for the
NCHN carbons are observed at 137.4 and 136.6 ppm, respectively.
The NMR data of 3 are in accordance with those reported in the
literature [28].
d
Crystals of monoalkylated imidazole
6 suitable for X-ray
diffraction precipitated from a THF solution of a mixture of 6 and 4
at ꢀ20 ꢁC. Although the data obtained are of poor quality the
structure could be unequivocally determined. This data can be
found in Supporting information.
the NCN fragment is absent (at
d 9.48 and 9.94 ppm in the ligand
Crystals of [H3L2]Br (4) suitable for X-ray diffraction were also
obtained from a THF solution at ꢀ20 ꢁC. [H3L2]Br crystallizes in the
S shape conformation (Fig. 1, right) with hydrogen bonds between
the imidazolium cations and the Br anions with a O2eH2/Br1
precursors, respectively), which is an evidence of the ZreCcarbene
bond. In each AX system one of the protons is shifted to low field
(d
w 5 ppm) and very deshielded in comparison with their geminal
protons ( w 3.6 ppm). This difference indicates that the chemical
d
ꢀ
length of 2.43 A (Fig. 1, left). The phenolate rings are almost parallel
environments of the methylenic protons are very different and
reflect the influence of the NMe2 and THF ligands in complexes 7
and 8 (see DFT discussion below). The carbon NMR spectra are in
agreement with the proton data described and the most significant
resonances are those assigned to the carbene that are observed at
to each other with an angle of 22.0(3)ꢁ between the planes con-
taining the rings.
Treatment of Zr(NMe2)4 with 1 equiv. of [H3L]Br (L ¼ L1, 3; L2, 4)
in THF at room temperature afforded complexes [ZrL(NMe2)(THF)
Br] (L ¼ L1, 7; L2, 8) that were obtained as yellow solids in 62 and
64% yield, respectively (Scheme 2). The reaction proceeds with
HNMe2 elimination and thus avoids the use of thermally unstable
alkali metal salts of the proligands [28].
d
186.8 and 186.0 ppm for 7 and 8, respectively. The two AX systems
in both complexes and the resonances of the Me groups of the
CMe2Ph substituents in 8 observed at room temperature in the
NMR spectra reveal pseudo-C2-symmetric species with trans-
phenolate coordination.
Aiming to attain further information about the structures of 7
and 8 2D NMR experiments were performed. The NOESY NMR
spectra disclosed that the NMe2 and THF ligands are trans to each
other, as no cross peaks between the two ligands were identified,
but they are mutually cis to the phenolate moieties with which they
present spatial interactions. Thus, in the NMR time scale, the
The k3-C,O2 bonding of the bis(phenolate) NHC ligand might in
principle define a U or an S shape. In the first case the two aromatic
rings are directed to the same side and in the latter they are ori-
ented to opposite sides in relation to the plane containing the two
oxygens, the carbene carbon and the zirconium. The S configuration
was observed in analogous titanium and zirconium derived from L1
[7], and in [H3L2]Br, 4, which were characterized by X-ray
Scheme 1.

62
S. Barroso et al. / Journal of Organometallic Chemistry 760 (2014) 60e66
Fig. 1. ORTEP diagram of [H3L2]Br (4) (left) using 30% probability level ellipsoids. The hydrogen bond is represented by a dashed light-blue line. Mercury wireframe diagram (right)
showing the S shape adopted by the molecule in the solid state. Hydrogen atoms and phenyl groups of the CMe2Ph substituents of the phenolates are omitted for clarity. (For
interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Scheme 2.
bromide ligand is coordinated trans to the carbene. This result
excluded an isomer presenting cis-phenolate bonding, which
would force the NMe2 and THF ligands to be cis. Moreover, the two
AX spin systems corresponding to CH2 protons display conforma-
tional exchange peaks in the NOESY NMR spectra.
the carbene remains coordinated to the metal during the
process.
The dynamic process observed in the NMR at room temperature
may be assigned to the interconversion of the left- and right-
handed twisted forms of the ligand (A and B in Scheme 3). The
dissociation of THF promotes the interconversion between the two
S-shaped forms in A and B that involves a pentacoordinated in-
termediate (C in Scheme 3). Thus, at room temperature the fast
exchange process originates a pseudo-C2-symmetric pattern on the
1H NMR time scale with broad peaks for all protons with exception
of the CH2 protons that remain asymmetric due to the non-
planarity of the 7-atoms ring formed by ZreCcarbeneeNeCH2e
Variable-temperature 1H NMR studies of 7 confirmed the
occurrence of a fluxional process that was stopped in toluene-d8
solution at ꢀ30 ꢁC, to show the presence of a species with C1
symmetry. Both splitting and sharpening of all except the THF
resonances were observed. The two NCHCHN protons of the car-
bene ligand, which appeared superimposed at room temperature,
split in two resonances and the two signals corresponding to the
tert-butyl groups gave rise to four different resonances. The aro-
matic protons of the phenolate rings split in four non-equivalent
signals as well as the proton resonances assigned to NMe2 that
originate two singlets. The four signals due to the AX system only
suffer a small displacement with cooling. The two THF resonances
remain broad even at ꢀ30 ꢁC.
CphenolateeCphenolateeOphenolate. The exchange between A and B
generates the magnetic equivalence of protons Ha, Hb, Hc and Hd in
A with Hd, Hc, Hb and Ha in B, respectively.
Several attempts to obtain suitable crystals for X-ray diffraction
failed. All off-white crystals obtained from diethyl ether or toluene
solutions had very weak diffraction power that did not allow
structure determination and hence Density functional theory cal-
culations [29] (GAUSSIAN 03/PBE1PBE [30], see Computational
details) were performed to confirm the coordination mode of
13
The changes observed in the C-{1H} NMR spectra at ꢀ30 ꢁC
are slight but the splitting observed for the tert-butyl carbons are
significant and in accordance with an unsymmetrical species.
The unchanging carbene resonance, in particular, indicates that
complexes
7 and 8. The structures of the three possible

S. Barroso et al. / Journal of Organometallic Chemistry 760 (2014) 60e66
63
Scheme 3.
coordination isomers of a model complex of 7 and 8, in which the
R substituents in the phenolate groups were replaced by methyls
(9), were fully optimized (Scheme 4). Isomer 9A, with a bromide
ligand trans to the carbene, is more stable than 9B and C by 2.01
and 1.63 kcal molꢀ1, respectively. These differences, although
consistent with the formulation of complexes 7 and 8 described
above are very small and do not exclude the formation of any of
the isomers. However, they are in agreement with the NOESY in-
formation and may be taken as a further evidence for the pref-
erential formation 9A.
Complexes 7 and 8 might be good candidates to catalyse intra-
molecular hydroamination reactions because they have one
dimethylamido ligand that may be replaced by an aminoalkene
(either to give an amido or an imido ligand) and a labile THF
molecule that may provide a coordination position for the C]C
moiety.
Preliminary catalytic hydroamination studies were carried out
with complexes 7 and 8 using 2,2-diphenylpent-4-en-1-amine
(Scheme 5). The reactions were performed in toluene-d8 solution,
in an NMR tube equipped with a J-young valve, at 100 ꢁC using
5 mol % precatalyst loading (aminoalkene:Zr ¼ 20:1), for 72 h. The
1H NMR spectra of the reaction mixtures revealed only the ami-
noalkene resonances and no signals corresponding to the hydro-
amination product, 2-methyl-4,4-diphenylpyrrolidine.
The optimized geometry of 9A, depicted in Fig. 2, shows that
there is a significant proximity between proton Ha and atom N3 of
ꢀ
the NMe2 moiety (2.62 A) and between proton Hc and atom O3 of
ꢀ
the THF molecule (2.38 A). Such proximity is responsible for the
significant deshielding observed for those protons in the 1H NMR
The 1:1 reaction of 7 with 2,2-diphenylpent-4-en-1-amine was
also performed in toluene, at 100 ꢁC, during 48 h. The analysis of the
reaction products by 1H NMR revealed no signals due to the ami-
spectra that, as already mentioned, appear close to
whereas their geminal protons show up at w3.6 ppm.
d 5 ppm
d
NHC complexes of Zr and Hf were reported as intramolecular
noalkene and the appearance of a set of new resonances at
d 3.41
hydroamination catalysts of unactivated olefins [14,15b,26].
(CH2, C5), 3.15 (CH, C2), 2.36 (CH2, C3) and 1.04 (CH3) ppm that are
Scheme 4.

64
S. Barroso et al. / Journal of Organometallic Chemistry 760 (2014) 60e66
3.2. Synthetic procedures
3.2.1. Synthesis of 2-(bromomethyl)-4,6-bis(2-phenylpropan-2-yl)
phenol (2)
This compound was prepared using an adaptation of a proce-
dure described in the literature [27]. To a solution of 2,4-bis(2-
phenylpropan-2-yl)phenol (13.94 g, 42.17 mmol) in acetic glacial
acid (c.a. 25 mL) was added paraformaldehyde (1.40 g, 46.62 mmol)
and the mixture was stirred for 2 h at room temperature. A solution
of HBr 33% in acetic acid (22.1 mL, 126.51 mmol, 3 equiv.) was then
added dropwise and the resulting yellow solution was stirred for
30 min. The solvent was evaporated under vacuum and the orange
viscous oil obtained was stored at ꢀ20 ꢁC for 16 h. An off-white
solid that precipitate out of solution was separated from the or-
ange oil, washed with a small amount of diethyl ether and dried in
vacuum to yield 12.5 g (70% yield) of an off-white powder. 1H NMR
(300 MHz, CDCl3, ppm):
d
7.37e7.25 (m, 9H CHPh þ 1H CHAr), 7.22e
7.18 (m, 1H, CHPh), 7.14 (d, 4JHH ¼ 2.2 Hz, 1H, CHAr), 4.60 (br, 1H, OH),
4.45 (s, 2H, CH2), 1.75 (s, 6H, C(CH3)2Ph),1.63 (s, 6H, C(CH3)2Ph). 13C-
{1H} NMR (75 MHz, CDCl3, ppm):
d 150.8, 150.3, 147.9, 142.7 and
Fig. 2. DFT optimized geometry of 9A.
135.4 (Cipso Ar þ Ph), 129.5 and 128.2 (CHPh), 127.8 and 127.5 (CHAr),
126.9, 126.2, 126.1 and 125.9 (CHPh), 125.4 (Cipso Ar or Ph), 42.8 and
42.1 (C(CH3)2Ph), 31.2 (C(CH3)2Ph), 30.5 (CH2), 29.8 (C(CH3)2Ph). EA
calculated for C25H27BrO: C, 70.92; H, 6.43. Found: C, 70.86; H, 6.68.
3.2.2. Synthesis of [H3L1]Br (3)
[H3L1]Br was prepared using an adaptation of a procedure
described in the literature [28]. Imidazole (1.02 g, 15 mmol) and
anhydrous sodium bicarbonate (1.26 g, 15 mmol) were poured in a
round-bottom flask under nitrogen. THF (50 mL) was added and the
mixture was refluxed. A solution of 2-(bromomethyl)-4,6-di-tert-
butylphenol (6.19 g, 30 mmol) in THF (30 mL) was slowly added to
the suspension with a dropping funnel and the mixture was stirred
for 12 h. After cooling to room temperature, the solution was
filtered off and the solvent evaporated to dryness leading to a
viscous oil that was sequentially washed with toluene and n-hex-
ane and then dried in vacuum to give 6.20 g (70% yield) of a white
Scheme 5.
characteristic of 2-methyl-4,4-diphenylpyrrolidine. Several reso-
nances between 1.15 and 1.90 ppm, possibly due to tert-butyl
groups resulting from complex decomposition, are also observed.
These results suggest that the critical step in the system
behaviour is catalyst regeneration: complexes 7 and 8 react with
2,2-diphenylpent-4-en-1-amine to perform the cyclization reaction
but they are not active under catalytic conditions.
powder. 1H NMR (300 MHz, CDCl3, ppm):
d 9.48 (s, 1H, NCHN), 7.33
(s, 2H, CHAr), 7.19 (s, 2H, NCHCHN), 5.55 (s, 4H, CH2), 1.37 (s, 6H,
C(CH3)3), 1.25 (s, 6H, C(CH3)3). 13C-{1H} NMR (75 MHz, CDCl3, ppm):
d
151.9, 143.8 and 139.6 (Cipso Ar), 137.4 (NCHN), 126.0 and 125.7
3. Experimental
(CHAr), 121.8 (NCHCHN), 121.7 (Cipso Ar), 51.3 (CH2), 35.2 and 34.5
(C(CH3)3), 30.4 and 30.3 (C(CH3)3).
3.1. General procedures
3.2.3. Synthesis of [H3L2]Br (4)
All preparations and subsequent manipulations of air/moisture
sensitive compounds were performed under a nitrogen atmo-
sphere using standard Schlenk line and dry box techniques. THF,
toluene and Et2O were dried by standard methods and distilled
prior to use. C6D6 was dried over Na and distilled under reduced
[H3L2]Br was prepared using the procedure described for [H3L1]
Br, using 2-(bromomethyl)-4,6-bis(2-phenylpropan-2-yl)phenol:
Imidazole (0.90 g, 13.2 mmol); anhydrous sodium bicarbonate
(1.11 g, 13.2 mmol); 2-(bromomethyl)-4,6-bis(2-phenylpropan-2-
yl)phenol (10.16 g, 24 mmol). The compound was obtained as a
white powder (7.20 g, 72% yield). 1H NMR (300 MHz, CDCl3, ppm):
ꢀ
pressure. Toluene-d8 and CDCl3 were dried with 4 A molecular
sieves and degassed by freezeepumpethaw method. Unless stated
otherwise, all reagents were purchased from commercial suppliers
and used as received. 2-(Bromomethyl)-4,6-di-tert-butylphenol (1)
[27] and 2,2-diphenylpent-4-en-1-amine [31] were prepared as
described in the literature. 1D and 2D (COSY, NOESY, HSQC) NMR
spectra were recorded on a Bruker Advance IIþ 300 MHz (Ultra-
Shield Magnet) instrument at ambient temperature, unless stated
d
9.94 (s, 1H, NCHN), 7.34e7.14 (m, 20H CHPh þ 2H CHAr), 7.00 (d,
4JHH ¼ 1.8 Hz, 1H, CHAr or CHPh), 5.26 (s, 4H, CH2), 1.70 (s, 6H,
C(CH3)2Ph), 1.54 (s, 6H, C(CH3)2Ph). 13C-{1H} NMR (75 MHz, CDCl3,
ppm):
136.1 (Cipso Ar or Ph), 129.5, 128.2, 128.1, 127.5, 127.2, 126.8, 126.0,
121.5 and 125.8 (CHAr þ CHPh),121.2 (Cipso Ar or Ph), 49.6 (CH2), 42.8
and 42.0 (C(CH3)2Ph), 31.1 and 29.7 (C(CH3)2Ph). EA calculated for
d
150.5, 150.2, 147.6 and 143.8 (Cipso Ar þ Ph), 136.6 (NCHN),
otherwise. 1H and 13C chemical shifts (
d) are expressed in ppm
C53H57BrN2O2: C, 76.33; H, 6.89; N, 3.36. Found: C, 75.88; H, 6.78; N,
relative to Me4Si. The NMR-tube scale reactions were prepared in
an N2-filled glove box. The NMR-tubes were equipped with a Teflon
screw cap (J-Young). Carbon, hydrogen and nitrogen analyses were
performed in-house using an EA110 CE Instruments automatic
analyser. The results presented are, in general, the average of two
independent determinations.
3.52.
3.2.4. Synthesis of [ZrL1(NMe2)(THF)Br] (7)
A THF solution of [H3L1]Br (0.586 g,1 mmol) was slowly added to
a THF solution of Zr(NMe2)4 (0.267 g, 1 mmol) at room temperature.
The mixture was stirred for 16 h and a yellow solution formed. The

S. Barroso et al. / Journal of Organometallic Chemistry 760 (2014) 60e66
65
solvent was evaporated to dryness under reduced pressure to give a
yellow crystalline powder (0.451 g, 62% yield). 1H NMR (300 MHz,
C6D6, ppm, room temperature): 7.65 (br, 2H, para-CHAr), 7.08 (br,
3.3. General procedures for X-ray crystallography
d
Crystals of 4 and 6 suitable for single-crystal X-ray analysis were
2H, ortho-CHAr), 6.15 (s, 2H, NCHCHN), 5.37 (br, 1H, CH2), 4.93 (br,
1H, CH2), 3.85 (br, 2H, CH2), 3.55 (s, 4H, THF), 2.98 (s, 6H, NMe2),
1.89 (s, 18H, C(CH3)3), 1.38 (s, 18H, C(CH3)3), 1.25 (br, 4H, THF). 13C-
obtained from THF solutions at ꢀ30 ꢁC. The data were collected
ꢀ
using graphite monochromated Mo-Ka radiation (
l
¼ 0.71073 A) on
a Bruker AXS-KAPPA APEX II diffractometer equipped with an Ox-
ford Cryosystem open-flow nitrogen cryostat. Cell parameters were
retrieved using Bruker SMART software and refined using Bruker
SAINT on all observed reflections. Absorption corrections were
applied using SADABS [32]. The structures were solved and refined
using direct methods with programs SIR2004 [33] or SHELXS-97
[34] using WINGX-Version 1.80.01 [35] SHELXL [36] system of
programs. All non-hydrogen atoms were refined anisotropically
and the hydrogen atoms were inserted in idealized positions and
allowed to refine riding on the parent carbon atom. The molecular
diagrams were drawn with ORTEP-3 for Windows [37] or Mercury
1.4.2 [38] included in the software package. For crystallographic
experimental data and structure refinement parameters see
Table 1.
{1H} NMR (75 MHz, C6D6, ppm, room temperature):
d 186.8 (C,
carbene), 160.5, 138.9 (Cipso Ar), 125.3 (CHAr), 119.5 (NCHCHN), 69.2
(THF), 52.8 (CH2), 45.3 (NMe2), 36.2 and 34.4 (C(CH3)3), 32.0 and
30.8 (C(CH3)3), 25.7 (THF). 1H NMR (300 MHz, toluene-d8,
4
ppm, ꢀ30 ꢁC):
d
7.65 (d, 2H, JHH ¼ 7.4 Hz, para-CHAr), 7.15 (d, 2H,
8.1 Hz, ortho-CHAr), 6.27 (s, 1H, NCHCHN), 6.21 (s, 1H, NCHCHN),
2
2
5.33 (d, 1H, JHH ¼ 13.4 Hz, CH2), 4.87 (d, 1H, JHH ¼ 13.4 Hz, CH2),
2
2
3.89 (d, 1H, JHH ¼ 12.3 Hz, CH2), 3.85 (d, 1H, JHH ¼ 12.9 Hz, CH2),
3.60 (br, 4H, THF), 3.38 (br, 3H, NMe2), 2.61 (br, 3H, NMe2), 1.93 (s,
9H, tBu), 1.88 (s, 9H, tBu), 1.40 (s, 9H, tBu), 1.39 (s, 9H, tBu), 1.29 (br,
4H, THF). 13C-{1H} NMR (75 MHz, toluene-d8, ppm, ꢀ30 ꢁC):
d 186.4
(C, carbene), 160.9, 160.7, 140.2, 139.8, 138.8 and 138.7 (Cipso Ar),
125.7 (CHAr), 124.5 (Cipso Ar), 120.1 (NCHCHN), 66.4 (THF), 52.7
(CH2), 45.8 (NMe2), 36.6, 36.4 and 34.7 (C(CH3)3), 32.3, 31.0 and 30.8
(C(CH3)3), 25.7 (THF). EA calculated for C39H60BrN3O3Zr: C, 59.29;
H, 7.65; N, 5.32. Found: C, 58.96; H, 7.41; N, 4.94.
3.4. Computational details
3.2.5. Synthesis of [ZrL2(NMe2)(THF)Br] (8)
DFT [29] calculations for 9A, B and C were performed using the
GAUSSIAN 03 software package [30] and the PBE1PBE functional,
without symmetry constraints. That functional uses a hybrid
[ZrL2(NMe2)(THF)Br] was prepared using the procedure
described above to [ZrL1(NMe2)(THF)Br] using [H3L2]Br: [H3L2]Br
(0.754 g,1 mmol); Zr(NMe2)4 (0.267 g,1 mmol). The compound was
obtained as a yellow crystalline powder (0.662 g, 64% yield). 1H
generalized gradient approximation (GGA), including
a 25%
mixture of HartreeeFock [39] exchange with DFT [29] exchange
correlation, given by the Perdew, Burke, and Ernzerhof functional
(PBE) [40]. The optimized geometries were obtained with the
LanL2DZ [41] basis set augmented with an f-polarization function
[42] for Zr and a standard 6-31G(d,p) [43] for the remaining ele-
ments (basis b1). Single point energy calculations were performed
using an improved basis set (basis b2) and the geometries opti-
mized at the PBE1BPE/b1 level. Basis b2 consisted of the Stuttgart/
NMR (300 MHz, C6D6, ppm): d 7.85e7.63 (m, 4H, CHPh), 7.48 (s, 2H,
para-CHAr), 7.37e7.21 (m, 8H, CHPh), 7.14e7.00 (m, 8H, CHPh), 6.86
(s, 2H, para-CHAr), 5.86 (br, 2H, NCHCHN), 5.18 (br, 1H, CH2), 4.67
(br, 1H, CH2), 3.60 (br, 1H, CH2), 3.55 (br, 1H, CH2), 3.50 (s, 4H, THF),
2.69 (s, 6H, NMe2), 2.26 (br, 6H, C(CH3)2Ph), 2.11 (br, 6H, C(CH3)2Ph),
1.62 (br, 12H, C(CH3)2Ph), 1.35 (br, 4H, THF). 13C-{1H} NMR (75 MHz,
C6D6, ppm): d 186.0 (C, carbene), 151.5, 138.4 (Cipso Ar), 128.3 (CHAr),
Dresden ECP with valence triple-z (SDD) [44] and an added f-po-
127.6 and 127.4 (CHPh), 127.2 (CHAr), 125.5 (CHPh), 119.3 (NCHCHN),
68.3 (THF), 52.4 (CH2), 44.7 (NMe2), 44.7 and 42.8 (C(CH3)2Ph), 31.4
(C(CH3)2Ph), 25.7 (THF). EA calculated for C59H68BrN3O3Zr: C,
68.25; H, 6.60; N, 4.05. Found: C, 67.89; H, 6.50; N, 4.01.
larization function [42] for Zr and standard 6-311þþG(d,p) [45]
basis sets for the remaining elements. Three-dimensional struc-
tures were obtained with Chemcraft [46].
3.2.6. General procedure for NMR-tube scale hydroamination tests
2,2-Diphenylpent-4-en-1-amine (0.5 mmol), the internal stan-
dard (1,3,5-trimethoxybenzene, 0.5 mmol) and the complex (7 or 8,
0.025 mmol) were dissolved in toluene-d8. The NMR tube was
closed and heated at 100 ꢁC for 72 h. The mixture was monitored by
1H NMR.
Table 1
Selected crystallographic experimental data and structure refinement parameters
for 4 and 6.
4
6
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C
35H57N2O2Br
C28H30N2O
410.54
150(2)
Monoclinic
C2/c
5357.7(10)
34.217(4)
8.7210(10)
20.987(2)
90
121.185(5)
90
8, 1.018
0.062
833.92
150(2)
Monoclinic
C2/c
10119.7(14)
54.983(4)
11.5230(9)
16.1810(14)
90
99.206(6)
90
8, 1.095
0.850
3.2.7. NMR-tube scale stoichiometric reactions of 2,2-diphenylpent-
4-en-1-amine with 7 and 8
3
ꢀ
V (A )
The 2,2-diphenylpent-4-en-1-amine (5.9 mg, 0.025 mmol) and
the complex (7: 20 mg, 0.025 mmol; 8: 26 mg, 0.025 mmol) were
dissolved in toluene-d8. The tube was heated to 100 ꢁC for 48 h. The
products were analysed by 1H NMR. After 48 h the signals of 2,2-
diphenylpent-4-en-1-amine disappear and the signals of the 2-
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
Z, rcalc (gcmꢀ3
)
methyl-4,4-diphenylpyrrolidine
diphenylpent-4-en-1-amine before reaction: 1H NMR (300 MHz,
toluene-d8, ppm): 7.28e6.91 (m, CHPh), 5.55e5.27 (m, CH2), 5.14e
appear.
Signals
of
2,2-
m
(mmꢀ1
)
Crystal size
0.25 ꢂ 0.18 ꢂ 0.05
Colourless
Plate
0.40 ꢂ 0.10 ꢂ 0.10
Colourless
Needle
d
Crystal colour
Crystal shape
Refl. collected
4.74 (dd, ]CH2), 3.17 (s, CH2), 2.85 (d, CH2), 0.45 (NH2). Signals of 2-
methyl-4,4-diphenylpyrrolidine after reaction: 1H NMR (300 MHz,
22,150
14,879
toluene-d8, ppm):
d 3.41 (dd, CH2), 3.19e3.11 (m, CH), 2.36 (dd,
Unique refl. [R(int)]
R1 [I > 2 (I)]
5231 [0.0570]
0.0984
0.2735
2105 [0.0787]
0.2088
0.5279
s
CH2). The signal of the NH is not observed in the spectra and one of
the diasteriomeric protons bonded to C3 that may be hindered by
the solvent.
wR2 [I > 2
s(I)]
GooF
1.080
1.718

66
S. Barroso et al. / Journal of Organometallic Chemistry 760 (2014) 60e66
[23] L. Maria, I.C. Santos, L.G. Alves, J. Marçalo, A.M. Martins, J. Organomet. Chem.
Acknowledgements
728 (2013) 57e67.
[24] J.M. Carretas, S. Barroso, J. Cui, A. Cruz, I.C. Santos, A.M. Martins, Inorg. Chim.
Acta 407 (2013) 175e180.
[25] M.A. Antunes, R.F. Munhá, L.G. Alves, L.L. Schafer, A.M. Martins, J. Organomet.
Chem. 696 (2011) 2e6.
[26] J. Cho, T.K. Hollis, T.R. Helgert, E.J. Valente, Chem. Commun. (2008) 5001e
5003.
[27] M. Konkol, M. Nabika, T. Kohno, T. Hino, T. Miyatake, J. Organomet. Chem. 696
(2011) 1792e1802.
The authors thank the Fundação para a Ciência e a Tecnologia,
Lisbon, Portugal, for funding (SFRH/BPD/7394/2010 and PEst-OE/
QUI/UI0100/2013 and RECI/QEQ-QIN70189/2012). S. Barroso thanks
Prof. M. J. Calhorda for her initiation and training in DFT
calculations.
[28] H. Aihara, T. Matsuo, H. Kawaguchi, Chem. Commun. (2003) 2204e2205.
[29] R.G. Parr, W. Young, Density Functional Theory of Atoms and Molecules,
Oxford University Press, New York, 1989.
Appendix A. Supplementary material
[30] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb,
J.R. Cheeseman, J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant,
J.M. Millam, S.S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi,
G. Scalmani, N. Rega, G.A. Petersson, H. Nakatsuji, M. Hada, M. Ehara,
K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, M. Klene, X. Li, J.E. . Knox, H.P. Hratchian, J.B. Cross, C. Adamo,
J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi,
C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth, P. Salvador,
J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels, M.C. Strain,
O. Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz,
Q. Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng,
A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen,
M.W. Wong, C. Gonzalez, J.A. Pople, Gaussian 03, Revision C.02, Gaussian, Inc.,
Wallingford, CT, 2004.
CCDC 963630e963631 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
Appendix B. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.11.041.
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