An NMR study on the reaction of substituted dimethyl zirconocenes with dimethylanilinium borate

Article abstract of DOI:10.1016/j.jorganchem.2012.02.011

The reaction of a series of dimethyl zirconocenes [Me₂Si(Cp) ₂ZrMe₂, 1; Cp^t-bu₂ZrMe₂, 2; Cp^n-bu₂ZrMe₂, 3; Ind₂ZrMe ₂, 4; Cp^Me4₂ZrMe₂, 5; Cp ₂ZrMe₂, 6] with [HNMe₂Ph][B(C₆F ₅)₄] was investigated by means of NMR spectroscopy. It was found that protonolysis of a Zr-Me group occurred generating a coordinative vacancy at the metal center and methane. Cations coming from 1-4 dimethyl precursors bound NMe₂Ph, liberated from the protonation process, and formed zirconaaziridinium ion pairs {[Me₂Si(Cp)₂Zr(η ²-CH₂NMePh)][B(C₆F₅)₄], 7; [Cp^t-bu₂Zr(η²-CH₂NMePh)] [B(C₆F₅)₄], 8; [Cp^n-bu ₂Zr(η²-CH₂NMePh)][B(C₆F ₅)₄], 9; [Ind₂Zr(η²-CH ₂NMePh)][B(C₆F₅)₄], 10}, reasonably as a consequence of CH activation of one Me group of coordinated NMe ₂Ph and methane elimination. The intramolecular/interionic structures and dynamics of 7-10 ion pairs were investigated by ¹H, ¹³C and ¹⁹F 1D-and 2D-NMR techniques. The reactions of 7 and 10 ion pairs with 2-methyl-1-heptene afforded stable diastereoisomeric ion pairs bearing a five-member azametallacycle.

Full text of DOI:10.1016/j.jorganchem.2012.02.011

Journal of Organometallic Chemistry 714 (2012) 32e40
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
An NMR study on the reaction of substituted dimethyl zirconocenes
with dimethylanilinium borate
*
Luca Rocchigiani, Gianfranco Bellachioma, Cristiano Zuccaccia, Alceo Macchioni
Dipartimento di Chimica, Università degli Studi di Perugia, Via Elce di sotto 8, I-06123, Perugia, Italy
a r t i c l e i n f o
a b s t r a c t
The reaction of a series of dimethyl zirconocenes [Me2Si(Cp)2ZrMe2, 1; Cptꢀbu2ZrMe2, 2; Cpnꢀbu2ZrMe2, 3;
Ind2ZrMe2, 4; CpMe42ZrMe2, 5; Cp*2ZrMe2, 6] with [HNMe2Ph][B(C6F5)4] was investigated by means of
NMR spectroscopy. It was found that protonolysis of a ZreMe group occurred generating a coordinative
vacancy at the metal center and methane. Cations coming from 1e4 dimethyl precursors bound NMe2Ph,
liberated from the protonation process, and formed zirconaaziridinium ion pairs {[Me2Si(Cp)2Zr(h2
eCH2NMePh)][B(C6F5)4], 7; [Cptꢀbu2Zr(h2eCH2NMePh)][B(C6F5)4], 8; [Cpnꢀbu2Zr(h2eCH2NMePh)]
[B(C6F5)4], 9; [Ind2Zr(h2eCH2NMePh)][B(C6F5)4], 10}, reasonably as a consequence of CH activation of
one Me group of coordinated NMe2Ph and methane elimination. The intramolecular/interionic structures
and dynamics of 7e10 ion pairs were investigated by 1H, 13C and 19F 1D-and 2D-NMR techniques. The
reactions of 7 and 10 ion pairs with 2-methyl-1-heptene afforded stable diastereoisomeric ion pairs
bearing a five-member azametallacycle.
Article history:
Received 21 December 2011
Received in revised form
7 February 2012
Accepted 8 February 2012
Keywords:
Zirconocenes
NMR spectroscopy
Ion pairs
CH activation
Ring substituent effect
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
though the catalytic activity is not strongly affected by the presence
of NMe2Ph in solution, the latter is far from being considered an
Many studies have been devoted to understanding the rela-
tionships between molecular structure and catalytic activity of
group IV metallocenium catalysts for olefin polymerization [1e4].
Particularly, it has been shown that the nature of Cp-substituents
can play a crucial role in tailoring the electronic and steric prop-
erties of catalysts leading to the possibility of finely controlling
their activity and selectivity [5e8]. Cp-substituents not only exert
their effect on all the steps involved in the polymerization process
but they also modulate the ion pairing phenomenon between the
cationic active species and its weakly coordinating counterion
[9e12].
innocent species toward zirconocenes. As a matter of fact, evidence
for coordination of NMe2Ph at different metallocenium cations was
reported [15,16]. Notably, Bochmann and co-workers isolated and
fully characterized the adduct [(IPCF)ZrMe(NMe2Ph)][B(C6F5)4]
[IPCF ¼ Me2C(C5H4)(fluorenyl)] [17].
During our studies on the effect of the chain length on the self-
aggregation tendency of zirconocenium ion pairs [18,19], we
investigated the activation reaction of Cp2ZrMe2 with several
[HNMeRR0][B(C6F5)4]. In line with previous findings [20,21], we
observed a quantitative coordination of the amine at the metal
center and subsequent CeH activation of the NMe group leading to
the formation of stable zirconaaziridinium ion pairs (Scheme 1)
that were characterized in terms of interionic structure [18,19],
intramolecular dynamics [22] and reactivity with olefins [23].
With the aim of evaluating the scope of such a reaction,
we decided to explore the activation reaction of differently
substituted zirconocenes [Me2Si(Cp)2ZrMe2 (1), Cptꢀbu2ZrMe2
(2),Cpnꢀbu2ZrMe2 (3), Ind2ZrMe2 (4), Cp*2ZrMe2 (5), CpMe42ZrMe2
(6), Scheme 2] with [HNMe2Ph][B(C6F5)4]. The results are reported
herein. For systems that cleanly afforded the corresponding zirco-
naaziridinium ion pairs, the interionic structure and the dynamic
behavior in solution were investigated by means of NOE NMR
spectroscopy. Finally, the reactivity of substituted metallacycles
with 2-methyl-1-heptene was explored.
Ammonium salts [HNR3][X] are commonly used as activators for
dialkyl precursors [13]; they act as Brönsted acids protonating an
alkyl group, with the formation of the catalytically-active ion pairs,
related alkane, and NR3 (1).
LnMðR0Þ2 þ ½HNR3ꢁ½Xꢁ/½LnMðR0Þꢁ½Xꢁ þ R0 ꢀ H þ NR3
(1)
Very active catalytic ion pairs are generated when [HNMe2Ph]
[B(C6F5)4] is used as activator due to the moderate basicity of
NMe2Ph [14] and weakly coordinating tendency of B(C6F5)ꢀ4 . Even
* Corresponding author. Tel.: þ39 075 5855579; fax: þ39 075 5855598.
E-mail addresses: alceo@unipg.it, alceo.macchioni@gmail.com (A. Macchioni).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.02.011

L. Rocchigiani et al. / Journal of Organometallic Chemistry 714 (2012) 32e40
33
Scheme 1. Synthesis of zirconaaziridinium ion pairs.
2. Results and discussion
Scheme 3. Structure and numbering of 7.
2.1. Reactivity of 1e6 with dimethylanilinium borate
H2u and H1u (Fig. 1). These two resonances were distinguished on
the basis of the strong NOE of H1u with the singlet at dH ¼ 0.09 ppm
that was, in turn, assigned to the methyl group of the silicon bridge
labeled as SiMeC (Fig. 1). From H2u, the resonances of H3u and H4u
were easily located at dH ¼ 5.65 and dH ¼ 5.08 ppm, respectively, by
following the scalar connectivity in the 1H COSY NMR spectrum
(Fig. 2). SiMeN resonance was identified since it showed a selective
NOE with H4u. The resonances of the four Cpd protons were
assigned similarly starting from the resonance of ZrCHd2. The
assignment of all the carbon resonances was easily achieved by
performing 1H, 13C HMBC and HMQC NMR experiment and allowed
to confirm the hypothesized structure of 7.
The activation reaction of 1e6 precursors with 1 equivalent of
[HNMe2Ph][B(C6F5)4] in C6D6 led to an instantaneous evolution of
CH4, reasonably due to the protonolysis of one of the two ZrMe
groups and the formation of the corresponding cationic species.
The subsequent course of the reaction was dependent on the nature
of the metallocenes as described in the following.
2.1.1. Me2Si(Cp)2ZrMe2 (1)
An oil precipitated from the C6D6 solution and no trace of free
NMe2Ph was observed in the 1H NMR spectrum of the supernatant.
After some workup, the oily phase was dissolved in C6D5Cl and the
1H NMR spectrum revealed the presence of two sets of signals. In
strict analogy with the results obtained for Cp2ZrMe2 [19], the most
intense resonances were due to the complex [Me2Si(Cp)2ZrMe(N-
Me2Ph)][B(C6F5)4] while the other set of signals were compatible
with the formation of the ion pair [Me2Si(Cp)2Zr(h2eCH2NMePh)]
[B(C6F5)4] (7) bearing the three-member heterocycle (Scheme 1).
Over the course of several hours, the selective CeH activation of
one of the NMe groups and methane elimination proceeded,
leading to the complete formation of 7 (Scheme 1).
Ion pair 7 was characterized by crossing the information coming
from 1D- and 2D- homo- and heteronuclear NMR experiments. The
starting point was the resonance at dH ¼ 2.43 ppm, which was
assigned to the NMe group. Such NMe moiety displayed a strong
NOE interaction with the doublet at dH ¼ 2.13 ppm which was
assigned to ZrCHu2 (see Scheme 3 for labeling of proton and carbon
atoms). The latter resonance showed strong dipolar contacts with
the two multiplets at dH ¼ 6.03 and dH ¼ 5.36 ppm that were due to
2.1.2. Cptꢀbu2ZrMe2 (2)
The reaction of NMe2Ph with Cptꢀbu2ZrMeþ occurred similarly
to that described above for 1 (Scheme 1). The 1H NMR spectrum of
the final product showed the presence of two doublets having
a scalar coupling constant of 8.7 Hz at dH ¼ 3.91 and dH ¼ 2.78 ppm.
This pattern of resonances was associated with the presence of
a ZrCH2 moiety and indicated that, also in this case, the coordina-
tion of dimethylaniline was followed by the CeH activation that
afforded the corresponding ion pair [Cptꢀbu2Zr(h2eCH2NMePh)]
[B(C6F5)4] (8). The 1H NMR spectrum of the reaction mixture con-
tained some residual resonances of [Cptꢀbu2ZrMe(NMe2Ph)]
[B(C6F5)4] (Supporting Information) after 12 h at 305 K. As seen
above, the formation of the three-member heterocycle made the
two Cp rings magnetically not equivalent. This resulted in the
presence of eight separated resonances for the Cp-hydrogen atoms
and two distinct signals for the protons of the two t-butyl groups in
Scheme 2. Sketch of 1e6 dimethyl precursors and 7e10 ion pairs.

34
L. Rocchigiani et al. / Journal of Organometallic Chemistry 714 (2012) 32e40
Scheme 4. Structure and numbering of 8.
and it was assigned to H1u (Fig. 5a), while the one at dH ¼ 6.77 ppm
interacted with ZrCH2u and was assigned to H2u. H3u and H4u were
discriminated since only the signal at dH ¼ 6.33 ppm interacted
with t-Buu, so it was identified as H4u. All the carbon resonances
were easily assigned following one-bond and multiple-bonds
proton-carbon scalar correlations in 1H, 13C HMQC and 1H, 13C
HMBC NMR spectra, respectively.
The observation of selective inter-rings NOE interactions
allowed the relative orientation of the two Cp rings in solution to be
disclosed. Dipolar contacts were observed for the pairs H3u/t-Bud
and H3d/t-Buu (Fig. 5a), H4d/H3u and H4u/H4d (Fig. 5b) suggesting
that a staggered conformation (Scheme 4) was predominant in
solution. Since dipolar interactions between t-Buu and ZrCH2u were
not observed, we concluded that the Cp in up position oriented the
t-butyl group far away from the methylenic moiety and close to the
NMe. On the contrary, the Cp on the bottom pointed the t-butyl
close to the ZrCH2 as indicated by the strong NOE between ZrCH2d
and t-Bud.
Fig. 1. A section of 1H NOESY NMR spectrum of 7 recorded in C6D5Cl at 297 K. Asterisks
denote the resonances of solvent.
the 1H NMR spectrum (Supporting Information). Assignment of
proton and carbon resonances was carried out starting from the
strong NOE contact between the singlet at dH ¼ 2.86 ppm and the
doublet at dH ¼ 2.78 ppm which were due to NMe and ZrCHu2,
respectively (see Scheme 4 for numbering).
As can be seen from the section of 1H NOESY NMR spectrum
reported in Fig. 3, a selective dipolar contact was present between
ZrCHd2 group (dH ¼ 3.91 ppm) and the singlet at dH ¼ 0.81 ppm
which was assigned to the t-butyl group of the Cp ring in down
position (t-Bud). The resonance of the quaternary carbon atom C5d
(dC ¼ 143.1 ppm) was identified from its long-range scalar corre-
lation with t-Bud in the 1H, 13C HMBC NMR spectrum (Fig. 4). From
the same spectrum, the resonances of hydrogen atoms belonging to
the same Cp ring were found at dH ¼ 6.21, 5.73, 5.66 and 5.04 ppm
by virtue of their long-range couplings with C5d (Fig. 4). These
signals were distinguished following the pattern of dipolar inter-
actions: the signal at dH ¼ 5.66 ppm displayed NOE contact with
both ZrCHd2 and t-Bud and it was assigned to H1d, while the reso-
nance at dH ¼ 5.73 ppm showed only a dipolar interaction with t-
Bud and was labeled as H4d. Finally, H2d and H3d were responsible
for the resonances at dH ¼ 5.04 and dH ¼ 6.21 ppm, respectively,
based on their selective NOE interaction with H1d and H4d (Fig. 5a).
Using the same strategy, the proton resonances of the other Cp ring
located at dH ¼ 6.77, 6.33, 6.04 and 5.39 ppm were assigned starting
from the proton signal of t-Buu at dH ¼ 0.87 ppm. The signal at
dH ¼ 6.04 ppm showed dipolar contacts both with NMe and t-Buu
2.1.3. Cpnꢀbu2ZrMe2 (3)
The reaction of 3 with dimethylanilinium borate afforded the
ion pair 9 bearing the three-member azametallacycle in 3 h. This
was deduced by the observation, in the 1H NMR spectrum
(Supporting Information), of a resonance at dH ¼ 2.51 ppm, that was
assigned to the NMe group, and two doublets at dH ¼ 2.87 and
dH ¼ 2.22 ppm (JH,H ¼ 8.4 Hz), clearly indicating the formation of an
heterocyclic CH2 moiety. Unfortunately, 9 decomposed in a few
hours preventing the possibility to acquire 2D-NMR spectra and
perform a full assignment of resonances.
2.1.4. Ind2ZrMe2 (4)
The reaction between 4 and dimethylanilinium borate afforded
the zirconaaziridinium ion pair 10 after 12 h at 308 K in a 80% yield
(based on NMR integration). The CeH activation was proved by the
formation of CH4 and the appearance of two doublets at dH ¼ 0.52
and dH ¼ ꢀ0.19 ppm in the 1H NMR spectrum, due to the diaster-
eotopic protons of the ZrCH2 moiety. The aromatic region of the
spectrum was rather complex (Supporting Information) and the full
assignment of resonances was not achieved also due to the further
Fig. 2. A section of 1H COSY NMR spectrum of 7 recorded in C6D5Cl at 297 K.
Fig. 3. A section of 1H NOESY NMR spectrum of 8 recorded at 297 K in C6D5Cl.

L. Rocchigiani et al. / Journal of Organometallic Chemistry 714 (2012) 32e40
35
Fig. 4. A section of 1H, 13C HMBC NMR spectrum of 8 recorded at 297 K in C6D5Cl.
Asterisks denote the resonances of solvent.
complication introduced by the presence of extensive chemical
exchange in the 1H NOESY NMR spectrum (Fig. 6). For example,
both protons of the ZrCH2 showed apparent dipolar interactions
with the singlet at dH ¼ 2.36 ppm that was the NMe group. Fortu-
nately, the exchange process was not fast enough to completely
delete the selectivity and it was observed that the NOE interaction
between NMe and the resonance at dH ¼ 0.52 ppm was stronger
(Fig. 7). Consequently, we assigned the latter signal to ZrCH2u
(Scheme 5). Likewise, the signal at dH ¼ 5.65 ppm was assigned to
H1u, due to its stronger NOE correlation with NMe. Starting from
Fig. 6. A section of 1H NOESY NMR spectrum of 10 recorded at 297 K in C6D5Cl.
Asterisks denote the resonances of solvent.
between genuine NOE cross peaks and apparent dipolar interac-
tions due to chemical exchange was not possible.
2.1.5. Cp*2ZrMe2 (5)
The reaction of 5 with dimethylanilinium borate proceeded
differently from the cases discussed above. After mixing the
reagents in C6D6, a vigorous gas evolution and the formation of an
oily phase were observed, in accordance with the protonolysis of
one methyl group of the precursor. The 1H NMR spectrum of the
C6D6 solution showed the presence of a large excess of free dime-
thylaniline together with a Cp* resonance at dH ¼ 1.34 ppm and
a signal at dH ¼ 0.51 ppm likely due to a ZrMe group. The evolution
of the mixture was monitored by NMR over a period of 1 h. As can
be seen from Fig. 8, the intensity of both resonances decreased and
H1u, resonances of H2u
(
dH ¼ 6.02 ppm) and H3u
dH ¼ 6.19 ppm)
(
were easily located following the pattern of scalar connectivity in
the 1H COSY NMR spectrum (Supporting Information). The reso-
nance at dH ¼ 5.45 ppm was assigned to H1d since it showed
a strong correlation with the doublet at dH ¼ 6.97 ppm, which was
due to the ortho-protons of the phenyl ring on the nitrogen atom.
Having assigned H1d, H2d (dH ¼ 5.96 ppm) and H3d (dH ¼ 5.86 ppm)
resonances were identified by analyzing the 1H COSY NMR spec-
trum as the same of the other ring (Supporting Information).
Unfortunately, the protons of the annulated phenyl rings of the
indenyl groups could not be safely assigned since a discrimination
the formation of CH4
(
dH ¼ 0.15 ppm) and CH3D (triplet at
dH ¼ 0.14 ppm) was observed. Importantly, there was no evidence
neither for dimethylaniline coordination nor for the formation of
the three-member heterocycle. The production of partially
deuterated methane was a clear indication of a CeD activation of
the C6D6 molecule. Similar reactions were observed by Jordan et al.
when C6D5Cl was used as a solvent [24,25].
2.1.6. CpMe42ZrMe2 (6)
The reaction of 6 with dimethylanilinium borate formed a large
amount of CH4, indicating also in this case the protonolysis of one
ZrMe group occurred (Supporting Information). This gas evolution
was accompanied by the separation of an oily phase at the bottom
Fig. 7. F2 trace (direct dimension) of 1H NOESY NMR spectrum recorded in C6D5Cl at
297 K showing the selective dipolar contacts of NMe in 10.
Fig. 5. Sections of 1H NOESY NMR spectrum of 8 recorded at 297 K in C6D5Cl.

36
L. Rocchigiani et al. / Journal of Organometallic Chemistry 714 (2012) 32e40
Scheme 5. Structure and numbering of 10.
of the NMR tube and, as observed for 5, there was no evidence for
the coordination of the amine. The 1H NMR spectrum of the oil in
C6D5Cl was complex (Supporting Information) and it was not
possible to identify any of the products present in the mixture.
Summarizing, it appears that cations generated from 1e4
precursors are capable of coordinating and activating NMe2Ph
while cations from 5 and 6 are not. Such a different behavior is
likely due to a combination of steric and electronic effects since 1e4
are not only less encumbered than 5e6 [26] but they also bear most
acidic metal centers [27]. Once the ZreN bond is formed, the CeH
activation of one of the NMe groups of the amine leads to the
formation of the zirconaziridinium structures 7e10.
The reaction time required to obtain 7, 8 and 10 ion pairs is
considerably longer with respect to that of the unsubstituted cation
[Cp2ZrMe(NMe2Ph)] [19]. Assuming that the CeH activation
proceeds by an agostic interaction between the metal and the NMe
group, it could be speculated that in the case of 1, where a more
electron density on the metal is expected [28], the tendency to react
is lower. On the contrary, for the more electron deficient 2 and 4
complexes [31], it is reasonable to believe that the steric encum-
brance of the ligand slows down the reorientation of the NPh group
that is mandatory for the formation of the constrained heterocycle.
Fig. 9. a) 19F, 1H HOESY NMR spectrum of 7 recorded in C6D5Cl at 297 K; b) Two F1
traces (indirect dimension) relative to o-F (top) and m-F (bottom).
integration of the signals showed that the strongest heteronuclear
dipolar interactions were present between o-F/m-F and H2u, H3u/
H3d and H1u/H4d pairs, NMe, ortho and meta protons of the phenyl
ring bound to the nitrogen and the two methyl groups bound to the
silicon. By combining this pattern of dipolar interactions, it was
deduced that the anion locates close to the NMePh moiety and
shifted toward the Cpu, as indicated by the difference in the relative
intensity of the contacts between H2d and H2u (Fig. 9).
In the case of 8, the 19F, 1H HOESY NMR spectrum recorded in
C6D5Cl (Fig. 10) showed strong dipolar contacts of the fluorine
atoms of the anion with the hydrogen atoms of the NMe group and
both the tert-butyls of the cation. Interestingly, the interactions
with the other protons were much weaker and in some cases
undetectable. This suggested that the steric bulk provided by the t-
Bu groups forced the anion further away from the cation.
No selective dipolar contacts were observed for 9, where the
anion shows NOEs with almost all the cationic protons, except
those belonging to the ZrCH2 moiety (Supporting Information).
2.2. Interionic structure
The interionic structure (i.e. the relative cationeanion orienta-
tion) of 7, 8 and 10 ion pairs was investigated in C6D5Cl by means of
19F,1H HOESY NMR experiments [29e36]. The 19F,1H HOESY NMR
spectrum of 7 (Fig. 9) showed that interionic dipolar contacts
involving m-F were slightly stronger than those due to o-F, as
usually observed for ion pairs bearing the B(C6F5)4 ꢀ anion [37].
It was evident that all the protons belonging to the cation were
dipolarly coupled with the fluorine atoms of the anion and this
suggested a low selectivity in the ion pairing. However, an accurate
2.3. Intramolecular dynamics
In the 1H NOESY NMR spectra of 8 and 10 ion pairs several
exchange cross peaks were observed, indicating the presence of
dynamic processes. In particular, exchange cross peaks were
observed between the two hydrogen atoms of the ZrCH2 moiety
and the two t-butyl substituents for 8. In addition, in the Cp-region
Fig. 8. Evolution of the 1H NMR spectrum for the reaction between 5 and [HNMe2Ph]
[B(C6F5)4] in C6D6 at 297 K.
Fig. 10. A section of the 19F,1H HOESY NMR spectrum of 8 recorded in C6D5Cl at 297 K.

L. Rocchigiani et al. / Journal of Organometallic Chemistry 714 (2012) 32e40
37
of the spectrum, a selective pattern of exchanges was identified
(Fig. 5b): H2d with H3u, H2u with H3d, H1u with H4u and H4d, H1d
with H4u and H4d. A rational explanation of such fluxional behavior
can be achieved considering the lability of the ZreN interaction and
the possibility for Cp groups to rotate [38,22]. In fact, up-down
exchanges may be caused by the broken of the ZreN bond, pyra-
midal inversion and re-coordination of the chiral N-atom (PI,
Scheme 6). While back-in front exchanges of Cp protons may derive
from a readjustment of the Cp-configuration aimed at minimizing
the steric Ph/t-butyl interactions (Scheme 6). Finally, since the
intensity of exchange cross peaks between Cp and t-butyl protons is
higher than that of the ZrCH2 protons it has to be hypothesized that
a back-skip (BS) process, which exchanges only the former protons
leaving the latter unaffected, is operative (Scheme 6).
Despite the full assignment of resonances for 10 was not
possible, an inspection of the exchange cross peaks of H1, H2 and
H3 (Fig. 6) was sufficient to establish that the pattern of chemical
exchange was similar to that of 8. For example, H1u showed
chemical exchange with H1d, H3u with H3d, and H2u with H2d. Also
in this case, the signals corresponding to the two hydrogen atoms of
the ZrCH2 moiety were in mutual exchange. These observations
suggested that the exchange mechanism described in Scheme 6
was operative also for 10. In contrast, exchange cross peaks were
not observed in the 1H NOESY spectrum of 7.
By a semi-quantitative integration of the exchange cross peaks
in the spectra of 8 and 10, it was found that rates of the exchange
processes are higher in the latter. Therefore, the scale of exchange
rate is 10 > 8>7. This trend in the dynamic behavior seems to
correlate with steric effects, since the rate of the fluxional processes
increased with the steric encumbrance of the ligand on the front
side of the molecule. For 7 there are no bulky groups pointing
towards the nitrogen and this could lead to a better arrangement of
the heteroycle and a slower dinamicity. In the case of 8 and 10, the
bulky groups pushes on the NPh moiety and this could decrease the
stability of the ZreN bond; this effect seems to be higher in the case
of the bis-indenyl species.
place that did not go to completion (Supporting Information). An
inspection of the 1H NMR spectrum allowed identifying four new
doublets in the 2.5e3.0 region and other four doublets between 2.0
and 0.5 ppm that had almost the same intensity. These spectral
features suggested that a 1,2 single-insertion of 2-methyl-1-
heptene into the ZreC bond of the heterocycle occurred, resulting
in the formation of an equimolar mixture of two diastereoisomeric
azametallapentacycles 11 differing in the relative configuration of
the nitrogen and carbon stereogenic centers (RR/SS or RS/SR,
Scheme 7).
The 1H NMR spectrum of the reaction mixture (Supporting
Information) was very complicated, since it contained resonances
of the excess of heptene and residual 7 that were partially over-
lapped to those belonging to 11(RR/SS) and 11(RS/SR). This did not
allowed to perform a full assignment of resonances. Nevertheless,
important structural information was obtained from the 1H NOESY
NMR spectrum (Fig. 11). For example, a strong NOE interaction
between the NMe resonance at dH ¼ 2.64 ppm and the CMe at
dH ¼ 1.14 ppm was observed indicating that these two resonances
are due to the 11(RR/SS) diastereoisomer. Starting from these
resonances, the entire skeleton of the RR/SS five-member hetero-
cycle was assigned: the selective NOE between the NMe at
dH ¼ 2.64 ppm and the doublet at dH ¼ 2.38 ppm allowed to label
the latter as NCHu2 while the strong dipolar interaction of the CMe at
dH ¼ 1.14 ppm with the doublet at dH ¼ 1.62 ppm assigned that
signal to ZrCHu2. The resonances of NCH2d (dH ¼ 3.06 ppm) and ZrCH2d
(
dH ¼ 0.94 ppm) were identified by 1H COSY NMR spectrum
(Supporting Information). The assignment of the doublets
belonging to 11(RS/SR) isomer was performed analogously.
No reaction was observed when 2-methyl-1-heptene was
reacted with 8, likely due to the steric hindrance of the t-Bu
substituents that inhibited olefin coordination. On the contrary, 10
reacted with 10 equivalents of 2-methyl-1-heptene affording two
diastereoisomeric five-member heterocycles. Due to the
complexity of the 1H NMR spectrum, the full resonance assignment
was not possible but crucial structural information was obtained by
1H NOESY NMR spectroscopy (Supporting Information). For
example the strong dipolar contact between the NMe group and
a CMe moiety allowed identifying the RR/SS isomer, while the
interaction of the other NMe with a CCH2 group accounted for the
formation of the RS/SR isomer.
2.4. Reaction of 7, 8 and 10 ion pairs with 2-methyl-1-heptene
Zirconaaziridinium ion pairs 7, 8 and 10 were reacted with 2-
methyl-1-heptene in C6D5Cl. In the case of 7 a fast reaction took
3. Conclusions
We have herein shown that only least encumbered and least
electron rich 1e4 dimethyl zirconocenes react with [HNMe2Ph]
[B(C6F5)4] leading to zirconaaziridinium ion pairs 7e10 by
Scheme 6. Proposed mechanism for the fluxionality of 8.
Scheme 7. Monoinsertion of 2-methyl-1-heptene into the ZreC bond of 7.

38
L. Rocchigiani et al. / Journal of Organometallic Chemistry 714 (2012) 32e40
two-dimensional Overhauser spectra were recorded by using 1s
relaxation delay and a mixing time comprised between 400 and
800 ms. NMR samples were prepared into the glovebox in J-Young
NMR tubes by dissolving the suitable amount of compound in
0.6 ml of deuterated solvent.
4.2. Preparation of 1e6 dimethyl precursors and NMR data
The synthesis of the dimethyl derivatives was performed start-
ing from the corresponding dichlorides by following the literature
procedure described by Samuel and Rausch [42]. In a 50 ml reaction
flask, connected with a J-Young valve to the high vacuum line, 1.0 g
of dichloride precursor was charged and dissolved in approxi-
mately 30 ml of dry diethyl-ether. This suspension was cooled
at ꢀ40 ꢂC and 1.5 equivalents of LiMe (1.66 M solution in diethyl-
ether) were added dropwise with a syringe in a period of 30 min.
The temperature was maintained around ꢀ40 ꢂC for 30 min and
then was allowed to raise to 0 ꢂC. After 10 min, the solvent was
removed in vacuo and the reaction mixture was dried for 30 min.
The reaction product was purified by vacuum sublimation and
collected into the glovebox. All the reaction yields were between 30
and 60%.
Fig. 11. A section of 1H NOESY NMR spectrum of 11(RR/SS and SR/RS) recorded in
C6D5Cl at 297 K. Asterisks denote resonances of unreacted 2-methyl-1-heptene while
labels “a” and “b” denote RR/SS and RS/SR diastereoisomers, respectively.
protonation of both the ZrMe groups caused by NeH and NCH2eH
activations of HNMe2Phþ and ZreNMe2Ph, respectively. The ZreN
bond is rather labile in 7e10 ion pairs as demonstrated by the
fact that they undergo a complex dynamic process involving the
dissociation of the ZreN bond, pyramidal inversion of the chiral N-
atom, back-skip of the ZreCH2N(Me)Ph chain and final adjustment
of substituted Cp rings in a conformation of minimum energy. The
ZreN labile bond is likely the key to obtain the diastereoisomeric
ion pairs, having a five-member azametallacycle, from a single 1,2-
insertion of 2-methyl-1-heptene into the ZreC bond of zirconaa-
ziridinium ion pairs.
1: 1H NMR (C6D6, 297 K, 400.13 MHz)
4H), 0.18 (s, 6H), 0.03 ppm (s, 6H). 2: 1H NMR (C6D6, 297 K,
400.13 MHz)
¼ 5.82 (s, 4H), 5.78 (s, 4H), 1.81 (s, 18H), 0.02 ppm (s,
d
¼ 6.73 (m, 4H), 5.47 (m,
d
6H). 3: 1H NMR (C6D6, 297 K, 400.13 MHz)
d
¼ 5.73 (pst, 4H,
3JH,H ¼ 2.5 Hz), 5.53 (pst, 4H, 3JH,H ¼ 2.5 Hz), 2.41 (m, 4H), 1.51 (m,
4H),1.32 (m, 4H), 0.88 (t, 6H, 3JH,H ¼ 7.3 Hz), ꢀ0.10 ppm (s, 6H). 4: 1H
NMR (CD3C6D5, 297 K, 400.13 MHz)
d
¼ 7.18 (dd, 4H, 3JH,H ¼ 6.5 Hz,
3JH,H ¼ 3.1 Hz), 6.87 (dd, 4H, 3JH,H ¼ 6.5 Hz, 3JH,H ¼ 3.1 Hz), 5.77 (d,
4H, 3JH,H ¼ 3.4 Hz), 5.61 (d, 4H, 3JH,H ¼ 3.4 Hz), ꢀ0.86 ppm (s, 6H).13
C
{1H} NMR (CD3C6D5, 297 K,100.55 MHz)
d
¼ 137.1 (s),124.6 (s),124.0
(s), 114.5 (s), 99.4 (s), 35.3 ppm (s). 5: 1H NMR (C6D6, 297 K,
4. Experimental section
400.13 MHz)
297 K, 400.13 MHz)
d
¼ 1.78 (s, 30H), ꢀ0.55 ppm (s, 6H). 6: 1H NMR (C6D6,
d
¼ 4.74 (s, 2H),1.95 (s, 24H), ꢀ0.53 ppm (s, 6H).
4.1. General Procedures
4.3. In situ generation of 7e10 ion pairs and NMR data
All manipulations of air-sensitive materials were performed in
flamed Schlenk glassware on a Schlenk line, interfaced to a diffusive
high vacuum pump (10ꢀ5 mmHg), or in a nitrogen filled glovebox
with an high capacity recirculator (<1 ppm O2 and H2O). All
solvents were preventively distilled from Na, freeze-pump-thaw
degassed on the high vacuum line, dried over Na/K alloy and
vacuum transferred in storage Schlenk flasks with a PTFE valve.
Deuterated solvents were freeze-pump-thaw degassed on the high
vacuum line, dried over Na/K alloy (C6D6 and CD3C6D5) or CaH2
(C6D5Cl) and vacuum transferred in storage Schlenk flasks with
A suitable amount of the precatalyst and 1 equivalent of solid
[HNMe2Ph][B(C6F5)4] were loaded into a J-Young NMR tube and
dissolved in approximately 0.6 ml of C6D6 at 298 K. Immediately,
a vigorous gas evolution was observed and a red oily phase quickly
settled to the bottom of the J-Young NMR tube. The supernatant
solution was removed, the resultant oil was rinsed with benzene
(2 ꢃ 1 ml) and dissolved in approximately 0.6 ml of C6D5Cl. The
formation of the reaction product was followed by NMR as
described in the Results and Discussion section and went to the
completion in about 12 h at 305e310 K.
a
PTFE valve. Zirconocenium dichlorides Me2Si(Cp)2ZrCl2,
Cptꢀbu2ZrCl2, Cpnꢀbu2ZrCl2, Ind2ZrCl2, Cp*2ZrCl2 and CpMe42ZrCl2
were purchased from Strem Chemicals. LiMe (1.66 M solution in
ether) was obtained from Aldrich. N,N-dimethylanilinium tetrakis-
pentafluorophenylborate was purchased from Boulder Sci. and
used without further purifications. 2-methyl-1-heptene was
purchased from Aldrich and freeze-pump-thaw degassed on the
high vacuum line, dried over CaH2 and distilled in a storage Schlenk
flask with a PTFE valve.
4.3.1. [Me2Si(Cp)2ZrMe(NMe2Ph)][B(C6F5)4]
1H NMR (C6D5Cl, 297 K, 400.13 MHz)
d
¼ 7.16 (m, buried with 7),
3
7.06 (m, buried with 7), 6.55 (d, 2H, JH,H ¼ 7.9 Hz), 6.29 (m, 2H),
5.61 (m, 2H), 5.45 (m, 2H), 5.31 (m, 2H), 2.22 (s, 6H), 0.50 (s, 3H),
0.36 (s, 3H), 0.08 ppm (s, 3H).
4.3.2. [Me2Si(Cp)2Zr(h
2-CH2NMePh)][B(C6F5)4] (7)
One and two-dimensional 1H, 13C and 19F NMR spectra were
measured on a Bruker DRX 400 spectrometer and referencing is
relative to TMS (1H and 13C) and CCl3F (19F). 1H NOESY NMR [39]
experiments were acquired by the standard three-pulse sequence
or by the PFG version [40]. Two-dimensional 19F,1H HOESY NMR
spectra were recorded by using the standard four-pulse sequence
or its modified version [41]. The number of transients and data
points were chosen according to the sample concentration and
desired final digital resolution. Qualitative or semi-quantitative
1H NMR (C6D5Cl, 297 K, 400.13 MHz)
d
¼ 7.16 (m, 2H, meta-H),
3
7.07 (d, 2H, ortho-H, JH,H
¼
8.0 Hz), 7.03 (t, 1H, para-H,
3JH,H ¼ 7.5 Hz), 6.03 (m, 1H, H2u), 5.65 (m, 1H, H3u), 5.36 (m, 2H,
H1uþH4d), 5.08 (m, 1H, H4u), 5.03 (m, 1H, H1d), 4.95 (m, 1H, H2d),
2.76 (d, 1H, ZrCHd2, 2JH,H ¼ 8.1 Hz), 2.43 (s, NMe), 2.13 (d, 1H, ZrCHu2,
2JH,H ¼ 8.1 Hz), 0.12 (s, 3H, SiMeN), 0.09 ppm (s, 3H, SiMeC). 13C{1H}
NMR (C6D5Cl, 297 K, 100.55 MHz)
d
¼ 155.4 (s, ipso-C), 130.0 (s,
meta-C), 128.0 (s, para-C), 125.8 (s, C2d), 125.6 (s, C2u), 122.1 (s,
ortho-C), 120.5 (s, C3u), 120.1 (s, C3d), 110.9 (s, C1d), 108.6 (s, C1u),

L. Rocchigiani et al. / Journal of Organometallic Chemistry 714 (2012) 32e40
39
107.7 (s, C5d), 107.1 (s, C4d), 104.6 (s, C2d), 103.8 (s, C5u), 57.3 (s,
(s), 104.3 (s), 103.5 (s), 102.1 (s), 101.9 (s), 101.3 (s), 101.0 (s), 100.6
(s), 100.2 (s), 69.7 (s), 54.9 (s), 45.5 (s), 22.8 ppm (s). 19F NMR
NMe), 54.9 (s, ZrCH2), ꢀ6.7 (s, SiMeN), ꢀ7.2 ppm (s, SiMeR). 19F NMR
(C6D5Cl, 297 K, 376.65 MHz)
d
¼ ꢀ132.1 (brd, ortho-F), ꢀ162.6 (t,
(C6D5Cl, 297 K, 376.65 MHz)
d
¼ ꢀ132.0 (brd, ortho-F), ꢀ162.6 (t,
3
3
para-F, JF,F ¼ 21.3 Hz), ꢀ166.6 ppm (m, meta-F).
para-F, JF,F ¼ 21.3 Hz), ꢀ166.4 ppm (m, meta-F).
4.3.3. [(Cptꢀbu)2ZrMe(NMe2Ph)][B(C6F5)4]
4.4. Partial NMR data for the reaction of Cp*2ZrMe2 with 1
equivalent of [HNMePh][B(C6F5)4]
1H NMR (C6D5Cl, 297K, 400.13 MHz)
d
¼ 7.29 (m, buried with 8),
3
7.18 (m, buried with 8), 6.71 (d, 2H, JH,H ¼ 7.8 Hz), 6.08 (brs, 4H),
5.89 (brs, 4H), 2.56 (brs, 6H), 1.07 (s, 18H), 0.98 ppm (s, 3H).
1H NMR (C6D6, 297 K, 400.13 MHz)
d
¼ 7.22 (t, 1H, JH,H ¼ 7.8 Hz),
6.80 (m, 2H), 6.62 (d, 2H, JH,H ¼ 7.8 Hz), 2.49 (s, 6H), 1.38 (s, 2.5 H),
4.3.4. [(Cptꢀbu)2Zr(
h
2-CH2NMePh)][B(C6F5)4] (8)
1.33 (s, 2H), 1.23 (s, 1.8H), 0.15 (s, CH4), 0.14 ppm (t, CH3D).
1H NMR (C6D5Cl, 297K, 400.13 MHz)
d
¼ 7.29 (m, 2H, meta-H),
7.22 (m, 2H, para-H), 6.83 (brd, 2H, ortho-H), 6.77 (ddd, 1H, H2u,
4.5. Reaction of 7, 8 and 10 ion pairs with 2-methyl-1-heptene and
NMR data
3JH,H ¼ 2.5 Hz), 6.33 (ddd, 1H, H4u, JH,H ¼ 2.5 Hz), 6.21 (ddd, 1H,
3
3
3
H3d, JH,H ¼ 2.5 Hz), 6.04 (ddd, 1H, H2u, JH,H ¼ 2.5 Hz), 5.73 (ddd,
3
3
1H, H4d, JH,H ¼ 2.5 Hz), 5.66 (ddd, 1H, H1d, JH,H ¼ 2.5 Hz), 5.39
Into the glovebox, approximately 10 equivalents of 2-methyl-1-
heptene were charged into a micrometric syringe and added to
a solution of the azametallacycle in C6D5Cl within a J-Young NMR
tube. The sample was successively analyzed by NMR spectroscopy
after about 10 min.
3
3
(ddd, 1H, H2d, JH,H ¼ 2.5 Hz), 5.04 (ddd, 1H, H2d, JH,H ¼ 2.5 Hz),
3.91 (d, 1H, ZrCHd2, JH,H ¼ 8.7 Hz), 2.86 (s, 3H, NMe), 2.78 (d, 1H,
2
ZrCHu2, JH,H ¼ 8.7 Hz), 0.87 (s, 9H, t-Buu), 0.81 ppm (s, 9H, t-Bud).
2
13C{1H} NMR (C6D5Cl, 297 K, 100.55 MHz)
d
¼ 153.9 (s, ipso-C), 143.1
(s, C5-t-Bud), 140.9 (s, C5-t-Buu), 130.4 (s, meta-C), 128.2 (s, para-C),
121.2 (s, ortho-C), 116.7 (s, C1d), 116.5 (s, C2u), 116.0 (s, C2d), 111.8 (s,
C1u), 111.3 (s, C4d), 109.2 (s, C3u), 108.8 (s, C3d), 107.2 (s, C4u), 62.0 (s,
ZrCH2), 60.1 (s, NMe), 32.4 (s, CMe t-Bud), 32.2 (s, CMe t-Bud), 30.0
(s, Me t-Bud), 26.1 ppm (s, Me t-Buu). 19F NMR (C6D5Cl, 297 K,
4.5.1. 7 þ 2-Me-1-heptene
1H NMR (C6D5Cl, 297 K, 400.13 MHz)
d
¼ 7.25 (m, buried with
other aromatic resonances), 7.17 (m, buried with other aromatic
resonances), 6.83 (s, 1H), 6.73 (s, 1H), 6.36 (m, 4H), 6.20 (brd, 4H),
5.89 (m, 1H), 5.86 (m, 1H), 5.16 (m, 4H), 5.04 (m, 1H), 3.83 (m, 1H),
3.81 (m, 1H), 3.06 (d, 1H, JH,H ¼ 12.5 Hz), 2.94 (d, 1H, JH,H ¼ 12.5 Hz),
2.64 (s, 3H), 2.63 (s, 3H), 2.58 (d, 1H, JH,H ¼ 12.5 Hz), 2.38 (d, 1H,
JH,H ¼ 12.5 Hz), 1.62 (d, 1H), 1.12 (s, 3H), 1.06 (s, 3H), 0.63 (d, 1H,
JH,H ¼ 13.8 Hz), 0.43 (s, 6H), 0.10 (s, 3H), 0.09 ppm (s, 3H).
376.65 MHz)
d
¼ ꢀ132.2 (brd, ortho-F), ꢀ162.6 (t, para-F,
3JF,F ¼ 21.3 Hz), ꢀ166.5 ppm (m, meta-F).
4.3.5. [(Cpnꢀbu)2Zr(
h
2-CH2NMePh)][B(C6F5)4] (9)
1H NMR (C6D5Cl, 297 K, 400.13 MHz)
d
¼ 7.28 (m, buried with
other aromatic resonances), 7.17 (d, buried with other aromatic
3
resonances, JH,H ¼ 7.8 Hz), 7.15 (m, buried with other aromatic
4.5.2. 10 þ 2-Me-1-heptene
resonances), 5.68 (m, buried with other resonances), 5.48 (m, 1H),
5.37 (m, 2H), 5.28 (m, 2H), 5.21 (m, 1H), 4.93 (m, 1H), 2.87 (d, 1H,
1H NMR (C6D5Cl, 297 K, 400.13 MHz)
d
¼ 7.52 (d, 3H), 7.44 (m,
buried with other aromatic resonances), 7.37 (m, buried with other
aromatic resonances), 7.28 (m, buried with other aromatic reso-
nances), 7.18 (m, buried with other aromatic resonances), 6.98 (m,
buried with other aromatic resonances), 6.9 (m, buried with other
aromatic resonances), 6.57 (t, buried with other aromatic reso-
nances), 6.49 (s, buried with other aromatic resonances), 6.41 (t,
buried with other aromatic resonances), 6.27 (s, buried with other
aromatic resonances), 6.14 (m, buried with other aromatic reso-
nances), 6.07 (s, buried with other aromatic resonances), 5.98 (m,
buried with other aromatic resonances), 5.87 (m, 2H), 5.77 (m, 1H),
5.68 (m,1H), 5.65 (m,1H), 5.58 (m, 3H), 5.34 (m,1H), 5.30 (m, buried
with other resonances), 5.27 (m, 1H), 4.99 (m, 1H), 3.63 (d, 1H), 3.61
(d, 1H), 2.78 (s, 3H), 2.76 (s, 3H), 2.75 (d, 1H), 2.51 (d, 1H,
JH,H ¼ 12.6 Hz), 2.42 (d, 1H, JH,H ¼ 12.6 Hz), 2.36 (s, 3H), 1.06 (s), 0.85
(s, 3H), 0.52 (d, 0.5H, JH,H ¼ 8.2 Hz), ꢀ1.21 ppm (d, buried with other
2JH,H ¼ 8.4 Hz), 2.51 (s, 3H), 2.22 (d, 1H, JH,H ¼ 8.4 Hz), 1.81 (m,
2
buried with other resonances), 1.38 (m, buried with other reso-
nances), 1.31 (m, buried with other resonances), 1.21 (m, buried
with other resonances), 1.10 (m, buried with other resonances), 1.03
(m, 4H), 0.99 (m, buried with other resonances), 0.76 ppm (m, 4H).
13C{1H} NMR (C6D5Cl, 297 K, 100.55 MHz)
d
¼ 155.6 (s), 121.7 (s),
117.9 (s), 117.3 (s), 116.5 (s), 116.1 (s), 115.8 (s), 113.9 (s), 113.2 (s),
112.3 (s), 111.5 (s), 107.4 (s), 105.7 (s), 58.4 (s), 57.2 (s), 45.8 (s), 33.6
(s), 33.4 (s), 33.0 (s), 32.6 (s), 29.5 (s), 29.4 (s), 24.9 (s), 22.6 (s), 22.1
(s), 13.6 (s), 13.4 (s), 13.3 ppm (s). 19F NMR (C6D5Cl, 297 K,
376.65 MHz)
d
¼ ꢀ132.0 (brd, ortho-F), ꢀ162.6 (t, para-F,
3JF,F ¼ 21.3 Hz), ꢀ166.4 ppm (m, meta-F).
4.3.6. [(Ind)2ZrMe(NMe2Ph)][B(C6F5)4]
1H NMR (C6D5Cl, 297 K, 400.13 MHz)
d
¼ 7.2e6.66 (aromatic
resonances, JH,H
¼
14.2 Hz). 13C{1H} NMR (C6D5Cl, 297 K,
resonances buried with 10), 5.83 (s, buried with 10), 5.72
(4H), ꢀ0.91 (s, 6H), ꢀ2.5 ppm (s, 3H).
100.55 MHz)
d
¼ 152.8 (s), 148.6 (s), 147.8 (s), 145.7 (s), 132.2 (s),
132.1 (s), 128.7 (s), 127.0 (s), 126.9 (s), 126.8 (s), 126.7 (s), 126.5 (s),
126.3 (s), 125.3 (s), 125.2 (s), 124.9 (s), 124.7 (s), 124.6 (s), 124.4 (s),
124.2 (s), 124.0 (s), 123.8 (s), 123.7 (s), 123.5 (s), 122.8 (s), 121.5 (s),
119.9 (s),117.4 (s),117.3 (s),117.2 (s),116.3 (s),116.2 (s),114.6 (s),112.7
(s),109.9 (s),107.4 (s),106.7 (s),106.2 (s),106.1 (s),105.6 (s),105.4 (s),
104.8 (s), 104.2 (s), 103.9 (s), 102.2 (s), 101.3 (s), 100.4 (s), 99.9 (s),
70.2 (s), 69.8 (s), 69.1 (s), 56.3 (s), 55.7 (s), 46.6 (s), 46.4 (s), 42.8 (s),
42.6 (s), 37.9 (s), 32.7 (s), 32.5 (s), 32.2 (s), 30.2 (s), 29.8 (s), 27.9 (s),
27.4 (s), 25.6 (s), 24.1 (s), 23.6 (s), 22.7 (s), 22.2 (s), 14.1 ppm (s).
4.3.7. [(Ind)2Zr(
1H NMR (C6D5Cl, 297 K, 400.13 MHz)
h
2-CH2NMePh)][B(C6F5)4] (10)
d
¼ 7.69 (d, 1H,
JH,H ¼ 8.4 Hz), 7.65 (d, 1H, JH,H ¼ 8.2 Hz), 7.38 (d, 1H, JH,H ¼ 8.2 Hz),
7.25 (m, buried with other resonances), 7.17 (m, buried with other
resonances), 7.08 (m, buried with other resonances), 6.97 (d, 2H,
JH,H ¼ 7.6 Hz), 6.90 (m, buried with other resonances), 6.82 (m, 1H),
6.50 (s, 1H), 6.27 (m, buried with other resonances), 6.19 (s, 1H),
6.12 (m, buried with other resonances), 6.07 (s, 1H), 6.00 (m,
buried with other resonances), 5.96 (s, 1H), 5.86 (s, 1H), 5.77 (d, 1H,
Acknowledgments
JH,H
¼
8.2 Hz), 5.65 (s, 1H), 2.36 (s, 3H), 0.52 (d, 1H,
JH,H ¼ 7.8 Hz), ꢀ0.19 ppm (d, 1H, JH,H ¼ 7.8 Hz). 13C{1H} NMR
This work was supported by grants from the Ministero dell’Is-
truzione, dell’Università e della Ricerca through the PRIN 2009
LR88XR program.
(C6D5Cl, 297 K, 100.55 MHz)
(s), 123.7 (s), 121.9 (s), 120.3 (s), 119.8 (s), 116.2 (s), 114.4 (s), 112.5
d
¼ 152.6 (s), 126.6 (s), 125.5 (s), 124.2

40
L. Rocchigiani et al. / Journal of Organometallic Chemistry 714 (2012) 32e40
[19] L. Rocchigiani, G. Bellachioma, G. Ciancaleoni, A. Macchioni, D. Zuccaccia,
Appendix. Supplementary material
C. Zuccaccia, Organometallics 30 (2011) 100e114.
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Ed. 50 (2011) 11752e11755.
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