Metal and halogen dependence of the rate effect in hydroamination/ cyclization of unactivated aminoalkenes: Synthesis, characterization, and catalytic rates of CCC-NHC hafnium and zirconium pincer complexes

Article abstract of DOI:10.1016/j.jorganchem.2013.11.001

1,3-Bis(3′-butylimidazol-1′-yl)benzene dibromide (2b) or 1,3-bis(3′-butylimidazol-1′-yl)benzene dichloride (2c) was reacted with a stoichiometric amount of Zr(NMe₂)₄ or Hf(NMe ₂)₄ yielding four new early transit

Full text of DOI:10.1016/j.jorganchem.2013.11.001

Journal of Organometallic Chemistry 751 (2014) 534e540
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Journal of Organometallic Chemistry
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Metal and halogen dependence of the rate effect in hydroamination/
cyclization of unactivated aminoalkenes: Synthesis, characterization,
and catalytic rates of CCC-NHC hafnium and zirconium pincer
complexes
,
c
Wesley D. Clark a, Joon Cho b, Henry U. Valle a, T. Keith Hollis a , Edward J. Valente
*
a Department of Chemistry, Mississippi State University, Mississippi State, MS 39762, United States
b Department of Chemistry and Biochemistry, The University of Mississippi, University, MS 38677, United States
c Department of Chemistry and Biochemistry, University of Portland Diffraction Facility, University of Portland, Portland, OR 97203, United States
a r t i c l e i n f o
a b s t r a c t
1,3-Bis(30-butylimidazol-10-yl)benzene dibromide (2b) or 1,3-bis(30-butylimidazol-10-yl)benzene
dichloride (2c) was reacted with a stoichiometric amount of Zr(NMe2)4 or Hf(NMe2)4 yielding four new
early transition metal CCC-N-heterocylic carbene (CCC-NHC) pincer complexes. Two of the CCC-NHC
pincer complexes were synthesized via a new methodology, which allowed for a room temperature
reaction, shorter reaction times, and slightly less Zr(NMe2)4 or Hf(NMe2)4. The molecular structure of 2-
(1,3-bis-30-butylimidazol-10-yl-20-ylidene)phenylene)(dimethylamido)(dibromo)zirconium(IV) (3b) was
determined by X-ray crystallography. The complexes were evaluated for hydroamination/cyclization of
unactivated aminoalkenes yielding pyrrolidines or piperidines. The hydroamination/cyclization rates
were dependent upon the halogen or the metal in the complex. The complexes with iodide ligands gave
the fastest hydroamination/cyclization rates (I > Br > Cl). The Zr complexes provided faster hydro-
amination/cyclization rates than the Hf analogs. Use of CCC-NHC ZrI3 complex 5 enhanced the rate of
reaction.
Article history:
Received 1 June 2013
Received in revised form
1 November 2013
Accepted 1 November 2013
Keywords:
N-Heterocyclic carbene
CCC-NHC pincer complex
Hydroamination
Homogenous catalysis
Pyrrolidines
Piperidines
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
been reported [6]. Furthermore, a wide variety of hydroamination/
cyclization catalysts have been reported incorporating chiral or
Pyrrolidines and piperidines are important classes of N-het-
erocycles present in many natural products, biologically active
molecules, and pharmaceuticals [1]. Hydroamination/cyclization of
unactivated aminoalkenes is an atom economical pathway to these
molecules [2]. However, a catalyst is required due to a high acti-
achiral ligands, early and late transition metals, rare earth metals,
and often halogen ligands [4e6,7]. However, the effects of halogen
ligands have received little attention [8]. Understanding the way
halogen ligands impact hydroamination/cyclization rates may lead
to improved catalysts.
vation barrier from electrostatic repulsion of the olefin
p-bond and
Over the past two decades, NHC complexes have become useful
the amine lone pair [3]. Amidate, ureate, and trans-disubstituted
cyclam early transition metal complexes were reportedly utilized
in the catalytic hydroamination/cyclization of aminoalkenes and
the asymmetric synthesis of substituted morpholines and pipera-
zines [4]. A series of chiral Zr based catalysts were recently dis-
closed that enantioselectively catalyzed the formation of 5, 6, and 7
membered N-heterocycles [5]. Yttrium, scandium, titanium, and
organolanthanide hydroamination/cyclization catalysts have also
catalytic reagents in many reactions [9]. NHCs are stronger s do-
nors and dissociate less readily than their phosphine counterparts
[10]. These properties have lead to many applications in catalysis,
solar cells, and biomedical fields [9a,11]. Additional stability can be
obtained through the use of chelating, pincer type ligands [12]. Due
to the lack of need to activate the nitrogen in the pyridylene moiety,
many CNCeNHC pincer complexes have been reported [7s,11c,13].
However, fewer examples of CCC-NHC pincer complexes have been
reported [11b,14]. We recently disclosed the synthesis and hydro-
amination/cyclization activity of 2-(1,3-bis(30-butyl-imidazol-20-
ylidene)phenylene)(dimethylamido)diiodozirconium(IV) (3a), and
2-(1,3-bis(30-butyl-imidazol-20-ylidene)phenylene)(dimethylami-
do)diiodohafnium(IV) (4a) [14b,c]. Herein, we report the expansion
* Corresponding author.
E-mail
addresses:
khollis@chemistry.msstate.edu,
tkhollis@gmail.com
(T.K. Hollis).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.11.001

W.D. Clark et al. / Journal of Organometallic Chemistry 751 (2014) 534e540
535
of this methodology to form the 2-(1,3-bis(30-butyl-imidazol-20-
ylidene)phenylene)(dimethylamido)dibromozirconium(IV) (3b), 2-
(1,3-bis(30-butyl-imidazol-20-ylidene)phenylene)(dimethylamido)
dichlorozirconium(IV) (3c), 2-(1,3-bis(30-butyl-imidazol-20-yli-
dene)phenylene)(dimethylamido)dibromohafnium(IV) (4b), and 2-
(1,3-bis(30-butyl-imidazol-20-ylidene)phenylene)(dimethylamido)
dichlorohafnium(IV) (4c). A large rate effect was observed in
hydroamination/cyclization of unactivated aminoalkenes, which
was dependent upon the halogen ligands or metal involved.
were consistent with the formation of CCC-NHC pincer complexes.
The appearance of a resonance at
192e200 in the 13C NMR spectra
was also consistent with the formation of CCC-NHC pincer com-
plexes. The 1H and 13C NMR spectra of pincer complexes 3b, c, 4b,
and c were consistent with previously reported and structurally
characterized pincer complexes 3a and 4a [14b,c].
d
2.2. X-ray crystallography
During the synthesis of dibromo Zr complex 3b, slow cooling of
the reaction mixture yielded crystals suitable for single crystal X-
ray diffraction. An ORTEPÒ illustration of the molecular structure of
dibromo Zr complex 3b is shown in Fig. 1. The coordination sphere
around Zr is a distorted octahedron with the amido group in an
2. Results and discussion
2.1. Synthesis and characterization
axial position. The ZreCcarbene bond lengths are very similar to the
1,3-Dibromobenzene and imidazole were heated in the pres-
ence of CuO, K2CO3, and DMSO yielding 1,3-bis(imidazol-10-yl)
benzene (1) according to the literature procedure (Scheme 1 [14c]).
The previously reported alkylation of 1,3-bis(imidazol-10-yl)ben-
zene (1) with 1-iodobutane was expanded to 1-bromobutane or 1-
chlorobutane yielding imidazolium salts 2aec in excellent yields
[14c].
ꢀ
previously published diiodo analog 3a (
D
= 0.015 A, [14b]). How-
ever, the ZreCcarbene bonds in dibromo Zr complex 3b are longer
than the ZreCcarbene bond in Cavell’s Zr hydrocarbyl bis(phos-
ꢀ
ꢀ
phoranimino) pincer carbene complex (
D = 0.139 A and 0.1668 A
[15],). The ZreC7 bond in the dibromo Zr complex 3a (ZrI1 vs. ZrI2,
ꢀ
D
= 0.1607 A longer than in the diiodo Zr complex 3a [14b]. The Zre
Br1 bond is slightly longer than the ZreBr2 bond in dibromo Zr
complex 3b, an effect that is likely due to the stronger trans in-
CCC-NHC pincer complexes 3b and 4b were obtained by heating
imidazolium salts 2b with Zr(NMe2)4 or Hf(NMe2)4 and isolated as
analytically pure crystalline solids after filtration and drying under
reduced pressure. A satisfactory elemental analysis for complex 3c
was obtained after synthesizing the complex using more polar
solvents (CH2Cl2 and THF vs toluene), slightly less Zr(NMe2)4 (1.0 eq
vs 1.1 eq) and lower temperatures (room temperature vs 160 ꢀC).
Increased solubility of imidazolium salt 2c in the higher polarity
solvents presumably allows lower reaction temperatures. High
solubility of complex 3c in the more polar solvents hampered
efficient isolation of the complex. The yields of complexes 3aec and
4aec vary significantly, and reflect different concentrations and
solubilities of complexes 3aec and 4aec in room temperature
toluene. A satisfactory elemental analysis was not obtained for
complex 4c and this result is presumably due to extreme sensitivity
to proton sources; in particular, humid air. The elemental analysis
results of complex 4c are consistent with partial hydrolysis of
ꢀ
fluence of the amido ligand (
D
= 0.0862 A). This effect was also
ꢀ
observed in the diiodo Zr complex 3a (ZrI1 vs. ZrI2,
[14b],). The ZreN25 bond in dibromo Zr complex 3b is only slightly
longer than in the diiodo Zr complex 3a (
D
¼ 0.1607 A
ꢀ
D = 0.0337 A [14b],).
However, the ZreN25 bond is shorter than all ZreN bonds found in
two Zr complexes of a tacn-derived amido ligand [16].
2.3. Hydroamination/cyclization catalysis
2.3.1. Effect of precatalyst loading
Standard substrate, 2,2-diphenylpent-4-ene-1-amine, was used
to assay the precatalysts. Quantitative conversions (>98%) were
observed in precatalyst loading experiments with 5 mol % diiodo Zr
complex 3a after 50 min of heating (Table 1, entry 1 [14b],). The
dibromo Zr complex 3b required much longer reaction times (10 h
vs. 50 min) to achieve the same conversion (>98%, entry 1). Despite
even longer reaction times (32 h vs 2 h, entry 2), reactions using
2.5 mol % dibromo Zr complex 3b did not reach quantitative con-
version. Good conversions were still achieved even at 1 mol %
precatalyst loading but required extended reaction times. Reactions
using dibromo Zr complex 3b required much longer reaction times.
For both complexes, good conversions were achieved at 5, 2.5 and
complex 4c. The loss of imidazolium proton signals around
d 11.4e
11.6 and only 4 signals in the aromatic region in the 1H NMR spectra
10% CuO, K2CO3, Imid
DMSO, 150 °C, 48 h
Br
Br
N
N
N
N
1 Ref [14c]
BuX, MeCN
M(NMe2)4
N
N
N
N
M
X
N
Bu
N
Bu
N
Bu
N
Bu
X
NMe2
2 X
2a X=I, Ref [14c]
2b X=Br, 92%
2c X=Cl, 91%
3a X=I, M=Zr, Ref [14b]
3b X=Br, M=Zr, 41 %
3c X=Cl, M=Zr, 31%
4a X=I, M=Hf, Ref [14c]
4b X=Br, M=Hf, 52%
4c X=Cl, M=Hf, 71%
Fig. 1. ORTEP diagram of dibromo Zr complex 3b with thermal ellipsoids at 50%
confidence level. Hydrogens were omitted for clarity. Only one conformer of the
disordered butyl chain is shown. Selected bond lengths (A) and angles ( ): ZreC1
2.347(2), ZreC7 2.315(2), ZreC13 2.3748(19), ZreBr1 2.7535(3), ZreBr2 2.6673(3), Zre
N25 2.0197(18), C1eZreBr1 86.39(5), C1eZreN25 94.76(7).
ꢀ
ꢀ
Scheme 1. Synthesis of 1,3-bis(imidazol-10-yl)benzene 1, imidazolium salts 2aec, and
CCC-NHC pincer complexes 3aec and 4aec.

536
W.D. Clark et al. / Journal of Organometallic Chemistry 751 (2014) 534e540
Table 1
with various substrates to evaluate the halogen rate effect across a
Evaluation of precatalyst loading.
broader array of structures (Table 3). Pyrrolidine and piperidine
rings were successfully made in the presence of Zr pincer com-
plexes 3aec (entries 1e5, 7, 10, 11), however the azepane ring
(entry 6) was not formed in the presence of these Zr pincer com-
plexes. For each Zr pincer complex (3aec), the formation of the 6-
membered (piperidine) ring progressed much slower than the
formation of the 5-membered (pyrrolidine) ring (entry 5 vs 1).
Diiodo Zr complex 3a provided quantitative conversion (>98%) for
the formation of the 6-membered (piperidine) ring (entry 5).
However, lower conversions (83% and 46%) were obtained when
using the bromo or chloro complexes even after extended reaction
times (entry 5). Entries 7 and 8 illustrate the necessity of the
Entry
Catalyst loading
3a, [Zr]eIa
3b, [Zr]eBr
Time/conv (%)b
Time/conv (%)b
1
2
3
5 mol %
2.5 mol %
1 mol %
50 min/>98%
2 h/>98%
7.5 h/97%
10 h/>98%
32 h/94%
36 h/87%
a
Data is from Ref. [14b].
b
All conversions were determined by 1H NMR spectroscopy.
1 mol % precatalyst loadings. Based on these results, 5 mol % pre-
catalyst loading was chosen for further evaluations.
Table 3
Scope and confirmation of the halogen rate effect with various substrates.
Time/conv (%)a
2.3.2. Effect of halogen ligands and metal center
Entry
Amine
Heterocycle
CCC-NHC pincer complexes 3a, b, c, 4a, b, and c were evaluated
for hydroamination/cyclization of 2,2-diphenylpent-4-ene-1-
amine allowing direct comparison between the various halides
and metal centers (Table 2). The catalytic runs were performed in
screw cap NMR tubes with deuterated solvent, and the reaction
progress was monitored with 1H NMR spectroscopy. Dibromo Zr
complex 3b and dichloro Zr complex 3c required much longer re-
action times to reach a quantitative conversion than diiodo zirco-
nium complex 3a (>98%, 10 h and 18 h vs. 50 min, entries 1e3).
Unlike diiodo Hf complex 4a, reactions using dibromo Hf complex
4b and dichloro Hf complex 4c did not reach quantitative conver-
sions despite extending the reaction times 5 fold (4.5 h vs 23 h,
entries 4e6). This result is in contrast to the Zr based precatalysts,
which all achieved quantitative conversions (>98%, entries 1e3).
Diiodo Hf complex 4a required a much longer reaction time than
diiodo zirconium complex 3a to reach a quantitative conversion
(4.5 h vs 50 min, entries 1 and 4). The reaction using dibromo Hf
complex 4b reached only 64% conversion in 23 h despite reacting
longer than the reaction using dibromo Zr complex 3b, which
provided quantitative conversion (>98%) in 10 h. Dichloro Hf
complex 4c provided only 8% conversion, whereas the dichloro Zr
complex 3c provided quantitative conversion (>98%) in less time
(23 h vs 18 h, entries 3 and 6). The Zr pincer complexes provided
faster hydroamination/cyclization rates than their Hf analogs.
Faster hydroamination/cyclization rates were observed when using
iodide ligands (I > Br > Cl).
3a, [Zr]eIb
3b [Zr]eBr 3c, [Zr]eCl
1
2
50 min/>98% 10 h/>98% 18 h/>98%
3 h/>98%
21 h/59%
53 h/66%
3
4
18 h/92%
38 h/88%
36 h/17%
45 h/20%
63 h/16%
46 h/6%
5
6
7
8 h/>98%
49 h/0%c
11 h/18%
21 h/83%
78 h/0%c
48 h/16%
39 h/46%
39 h/0%c
18 h/6%
8
9
41 h/0%c
39 h/0%c
19 h/0%c
78 h/0%c
44 h/0%c
39 h/0%c
2.3.3. Evaluation of substrate scope
Since the Zr pincer complexes 3aec provided shorter reaction
times than their Hf analogs, Zr pincer complexes 3aec were reacted
Table 2
Impact of metal (Zr vs. Hf) and halogen (Cl, Br, I) on the rate of catalysis.
10
11
8 h/>98%
1 h/>98%
45 h/65%
39 h/35%
14 h/>98% 44 h/>98%
Entry
Precatalyst
Time/conv (%)a
1
2
3
4
5
6
3ab, [Zr]eI
3b, [Zr]eBr
3c, [Zr]eCl
4ac, [Hf]el
4b, [Hf]eBr
4c, [Hf]eCl
50 min/>98%
10 h/>98%
18 h/>98%
4.5 h/98%
23 h/64%
12
29 h/0%c
19 h/0%c
29 h/0%c
23 h/8%
a
All reactions were performed in tol-d8 at 160 ꢀC with 5 mol % precatalyst (3a, b,
a
All conversions were determined by 1H NMR spectroscopy.
Data is from Ref. [14b].
or c). All conversions were determined by 1H NMR spectroscopy.
b
c
b
Data is from Ref. [14b].
c
Data is from Ref. [14c].
No reaction.

W.D. Clark et al. / Journal of Organometallic Chemistry 751 (2014) 534e540
537
geminal dialkyl effect for cyclization with these complexes. Thus 4-
pentene-1-amine did not react even at extended times (entry 8),
whereas 2-phenyl-4-pentene-1-amine yielded low conversions
(entry 7). Internal aminoalkenes yielded no reaction in the pres-
ence of Zr pincer complexes 3aec (entry 9). However, a disubsti-
tuted, terminal aminoalkene yielded a quaternary carbon in a
pyrrolidine ring slowly (entry 10). Additionally, each complex
formed diastereomeric products in equal proportions for entries 7
and 11. Only cyclic products were observed. The basic reactivity
patternsdrequiring gem dialkyl effect, forming pyrrolidine and
piperidine rings, not forming azepane rings, and forming quater-
nary carbonsd were observed regardless of the halogen ligand.
Fig. 2. Structure of CCC-NHC Zr pincer complex 5.
24%, 5 mol % catalyst, 145 ꢀC). When 1 mol % of 5 was combined
with 5 mol % 3a, a dramatic improvement in rate was observed
(entry 3 vs 1 and 2). However, the rate of conversion declined after
76% conversion at 16 h with only 79% at 24 h. A synthetically useful
conversion rate was obtained for this substrate by using 5 mol %
each of 3a and 5 (entry 4). Similar conversions were reported using
5 mol % Zr(NMe2)4 at a slightly lower temperature although the
reaction times were greatly extended (150 ꢀC, 120 h, 97% conver-
sion, [17]).
2.3.4. Comparison to other group IV catalysts
The intramolecular hydroamination/cyclization of 2,2-
diphenylpent-4-ene-1-amine with complexes 3aec and 4a pro-
vided quantitative conversions (>98%). In a recent report, quanti-
tative conversions were also obtained using 5 mol % Zr(NMe2)4 in
1 h, albeit at a lower temperature (100 ꢀC) [17]. Recently reported
trans-N,N0-dibenzylcyclam Zr complexes also yielded quantitative
conversions of the same substrate [4a]. Additionally, it was recently
reported that the hydroamination/cyclization reaction using 2-
phenylpent-4-ene-1-amine with 5 mol % Zr(NMe2)4 was much
slower, showing 97% conversion after 120 h at 100 ꢀC [17]. Com-
plexes 3aec provided much lower conversions, although it should
be noted the reaction times were much shorter than the previously
reported work using Zr(NMe2)4 (entry 7, Table 3, [17]). Additionally,
a very slow reaction rate was reported when using pent-4-ene-1-
amine and Zr(NMe2)4 (5 mol % Zr(NMe2)4, 150 ꢀC, 28 h, 25%) [17].
Complexes 3aec provided no reaction when using the same sub-
strate. Titanium tetrakis(dimethylamido) was recently reported to
provide no hydroamination/cyclization reaction with pent-4-ene-
1-amine as well [18]. Complexes 3aec, Zr(NMe2)4, and Ti(NMe2)4
provide better hydroamination/cyclization rates when substrates
have large gem-dialkyl effects; however, the effects are more pro-
nounced when using complexes 3aec and Ti(NMe2)4 [17,18]. It is
unclear as to whether these trends are the results of steric or
electronic effects.
3. Conclusion
The synthesis and isolation of four new transition metal (group
IV) CCC-NHC pincer complexes has been reported. The complexes
were spectroscopically characterized and found to be similar to
previously reported compounds [14b,c]. The X-ray crystal structure
of
2-(1,3-bis(30-butyl-imidazol-20-ylidene)phenylene)(dimethy-
lamido)dibromo zirconium (IV) (3b) is reported. The halogen li-
gands and metal centers had large effects on the rate of the
hydroamination/cyclization. Precatalysts with iodide ligands
(I > Br > Cl) gave the fastest hydroamination/cyclization rates.
Precatalysts with a Zr metal center provided the fastest conversion
rate (Zr > Hf). Use of CCC-NHC ZrI3 complex 5 enhanced the rate of
reaction. Studies on the catalytic mechanism with the CCC-NHC
class of early transition metal complexes will be reported shortly.
4. Experimental section
2.3.5. Rationalization of the halogen dependence upon rate
4.1. General procedures
Since the hydroamination/cyclization reactions did not proceed
for a 2ꢀ amine, the formation of a catalytically relevant “imido”
complex (M]N–R) is likely (Table 3, entry 12, [7a]). Imido com-
plexes have been proposed as intermediates in catalytic hydro-
amination/cyclization cycles, although they are usually proposed as
a product of a complex with two amido groups [4c,7b]. Since Zr
pincer complexes 3aec, only have one amido ligand, Zrehalide
(ZreX) exchange processes may occur in order to form an imido
complex. The large rate effect (I > Br > Cl) observed may be the
result of slower ZreX exchange rates. We also note the relationship
between increasing ZreX BDE and decreasing reaction rate. Ex-
periments are underway to identify the pathway for the formation
of the imido complex and will be reported shortly. Additionally, the
temperatures and solvent conditions for catalytic runs were the
same as in the synthesis of complexes 3a, b, 4a, and b. Therefore,
decomposition into different species should not be occurring.
All reactions were done under an inert atmosphere using
standard Schlenk techniques or a glovebox unless noted otherwise.
Al2O3 (basic, 50e200 m
) was stored in an oven at 130 ꢀC prior to use.
Amine substrates were made by previously reported literature
procedures and distilled prior to use [14b]. 1H and 13C{1H} NMR
spectra were recorded on 300 or 500 MHz Bruker instruments.
Chemical shifts (d) were expressed in ppm downfield to TMS at
d
¼ 0 and referenced to the residual solvent peak [19]. CD2Cl2,
CH2Cl2, toluene, tol-d8 , and amine substrates were dried by passing
Table 4
Evaluation of precatalyst loading and additive effects.
2.3.6. Additive effect-[Zr]I3
Due to its relatively slow reaction rate, the unactivated amino-
alkene, 2-phenylpent-4-ene-1-amine, was chosen for additive
studies with triiodide complex 5 (Fig. 2, Table 4, [14a]). Complex 5
yielded only 20% conversion after 27 h (entry 2), as compared to
iodoamido complex 3a which yielded 44% conversion after 26 h. In
a recent report, an in-situ generated bis-amide Zr catalyst provided
minimal conversion with extended reaction times as well (96 h,
Entry
3a, [Zr]I2NMe2
5, [Zr]I3
Time/conv (%)a
1
2
3
4
5 mol %
e
e
26 h/44%
27 h/20%
16 h/76%b
26 h/94%
5 mol %
1 mol %
5 mol %
5 mol %
5 mol %
a
All conversions were determined by 1H NMR spectroscopy.
At 24 h, 79% conversion.
b

538
W.D. Clark et al. / Journal of Organometallic Chemistry 751 (2014) 534e540
through activated alumina [20]. 1,3-Bis(imidazol-10-yl)benzene (1),
1,3-bis(30-butylimidazol-10-yl)benzene diiodide (2a), 2-(1,3-bis(30-
butyl-imidazol-20-ylidene)phenylene)(dimethylamido)(diiodo)
zirconium (IV) (3a), and 2-(1,3-bis(30-butyl-imidazol-20-ylidene)
phenylene)tris(iodo) zirconium (IV) (5) were obtained via previ-
ously reported procedures [14aec,21]. Zr(NMe2)4 and Hf(NMe2)4
were freshly sublimed prior to use. All catalytic hydroamination/
cyclization reactions were performed in a screw cap NMR tube with
deuterated tol-d8 at 160 ꢀC.
CD2Cl2): d 192.4, 164.5, 147.7, 129.6, 121.9, 115.3, 110.5, 51.8, 43.3,
34.1, 20.4, 14.1.
4.5.1. Alternate procedure for 2-(1,3-bis(30-butyl-imidazol-20-
ylidene)phenylene)(dimethylamido)dichloro zirconium (IV) (3c)
1,3-Bis(30-butylimidazol-10-yl) benzene dichloride 2c (0.275 g,
0.696 mmol), Zr(NMe2)4 (0.190 g, 0.710 mmol), CH2Cl2 (15 mL) and
THF (6 mL) were combined, evacuated and stirred at room tem-
perature for 4 h. Approximately 70% of the solvent was removed in
vacuo resulting in the formation of a yellow precipitate. The pre-
cipitate was collected, washed with CH2Cl2 (5 mL) and hexanes
(3 ꢁ 5 mL) and dried in vacuo yielding a pale-yellow solid (0.083 g,
23%): Spectroscopic data of the solid was identical to Section 4.5.
Anal. Calcd For C22H31Cl2N5Zr: C, 50.08; H, 5.92; N, 13.27. Found: C,
49.98; H, 6.14; N, 12.85.
4.2. 1,3-Bis(30-butylimidazol-10-yl)benzene dibromide (2b)
1,3-Bis(imidazol-10-yl) benzene (3.73 g, 17.8 mmol), 1-
bromobutane (19.0 mL, 178 mmol) and acetonitrile (150 mL)
were combined in air and stirred at reflux for 3 h. After cooling to
room temperature, the volatiles were removed under reduced
pressure yielding a white solid (7.91 g, 92%): 1H NMR (CDCl3,
4.6. 2-(1,3-Bis(30-butyl-imidazol-20-ylidene)
phenylene)(dimethylamido)dibromo hafnium (IV) (4b)
300 MHz):
d
11.44 (s, 2H), 9.13 (s, 2H), 9.00 (s,1H), 8.36 (d, J ¼ 7.8 Hz,
2H), 7.64 (t, J ¼ 8.1 Hz,1H), 7.58 (s, 2H), 4.46 (s, 4H), 2.02 (s, 4H),1.44
(sex, J ¼ 7.8 Hz, 4H), 0.99 (t, J ¼ 7.6 Hz, 6H); 13C{1H} (75.5 MHz,
1,3-Bis(30-butylimidazol-10-yl) benzene dibromide 2b (0.594 g,
1.22 mmol), Hf(NMe2)4 (0.489 g, 1.34 mmol) and toluene (200 mL)
were combined in a sealing tube. The resulting mixture was soni-
cated for 20 min and then stirred at 160 ꢀC for 16 h. After cooling to
room temperature, a solid precipitated from the reaction mixture.
The precipitate was collected and dried under reduced pressure
yielding yellow-color crystals (0.443 g, 52%): 1H NMR (CD2Cl2,
CD2Cl2):
d 136.1, 135.9, 132.9, 122.9, 122.8, 122.6, 114.9, 50.6, 32.2,
19.7, 13.6.
4.3. 1,3-Bis(30-butylimidazol-10-yl)benzene dichloride (2c)
1,3-Bis(imidazol-10-yl) benzene (3.94 g, 18.7 mmol), 1-
chlorobutane (39.0 mL, 375 mmol) and acetonitrile (250 mL)
were combined and stirred for 24 h at 160 ꢀC in a sealed tube. After
cooling to room temperature, the volatiles were removed under
reduced pressure yielding a white solid (6.71 g, 91%): Spectroscopic
data of imidazolium salt 2c were identical to previously published
data [14d].
300 MHz):
d
7.51 (s, 2H), 7.27 (t, J ¼ 7.9 Hz, 1H), 7.14 (d, J ¼ 7.6 Hz,
2H), 7.07 (s, 2H), 4.41 (m, 2H), 4.30 (m, 2H), 3.06 (s, 6H), 1.93 (sex,
J ¼ 8.1 Hz, 4H), 1.46 (sex, J ¼ 7.5 Hz, 4H), 1.00 (t, J ¼ 7.3 Hz, 6H); 13
C
{1H} NMR (75.5 MHz, CD2Cl2):
d 199.6, 169.4, 147.2, 129.3, 122.0,
116.0, 110.8, 52.2, 44.2, 34.2, 20.3, 14.2. Anal. Calcd For
22H31Br2N5Hf: C, 37.54; H, 4.44; N, 9.95. Found: C, 37.32; H, 4.25;
C
N, 9.61.
4.4. 2-(1,3-Bis(30-butyl-imidazol-20-ylidene)
phenylene)(dimethylamido)dibromo zirconium (IV) (3b)
4.7. 2-(1,3-Bis(30-butyl-imidazol-20-ylidene)
phenylene)(dimethylamido)dichloro hafnium (IV) (4c)
1,3-Bis(30-butylimidazol-10-yl) benzene dibromide 2 (0.324 g,
0.669 mmol), Zr(NMe2)4 (0.197 g, 0.736 mmol) and toluene (40 mL)
were combined and stirred for 15 h at 160 ꢀC in a sealed tube. After
cooling to room temperature, a solid precipitated from the reaction
mixture. The precipitate was collected and dried under reduced
pressure yielding a yellow-color solid (0.273 g, 41%). A crystal
suitable for X-ray diffraction was selected from the solid. 1H NMR
1,3-Bis(30-butylimidazol-10-yl)benzene
dichloride
(2c)
(0.560 g, 1.41 mmol), Hf(NMe2)4 (0.563 g, 1.59 mmol) and
toluene (150 mL) were combined in a sealing tube. The mixture
was sonicated for 20 min and then stirred at 160 ꢀC for 15 h.
After cooling to room temperature, a solid precipitated from
the reaction mixture. The precipitate was collected and dried
under reduced pressure yielding a yellow-color solid (0.613 g,
(CD2Cl2, 500 MHz):
2H), 7.08 (br s, 2H), 4.44 (br s, 2H), 4.27 (br s, 2H), 2.95 (s, 6H), 1.92
d
7.49 (s, 2H), 7.27 (t, J ¼ 8.0 Hz, 1H), 7.09 (br s,
71%): 1H NMR (CD2Cl2, 300 MHz):
d 7.49 (s, 2H), 7.27 (t,
(br s, 2H), 1.90 (br s, 2H), 1.46 (sex, J ¼ 7.6 Hz, 4H), 1.00 (t, J ¼ 7.2 Hz,
6H); 13C{1H} NMR (125 MHz, CD2Cl2):
d 192.8, 164.9, 147.3, 129.4,
J ¼ 7.1 Hz, 1H), 7.14 (d, J ¼ 7.7 Hz, 2H), 7.05 (s, 2H), 4.39 (m,
2H), 4.26 (m, 2H), 3.04 (s, 6H), 1.92 (sex, J ¼ 6.8 Hz, 4H), 1.45
(sex, J ¼ 7.4 Hz, 4H), 1.00 (t, J ¼ 7.3 Hz, 6H); 13C{1H} NMR
121.8, 115.5, 110.6, 52.1, 43.1, 34.1, 20.4, 14.1. Anal. Calcd For
22H31Br2N5Zr: C, 42.86; H, 5.07; N, 11.36. Found: C, 42.68; H, 4.84;
C
N, 11.20.
(75.5 MHz, CD2Cl2):
d 198.7, 169.4, 147.6, 129.4, 122.0, 115.8,
110.7, 51.9, 44.7, 34.1, 20.3, 14.1.
4.5. 2-(1,3-Bis(30-butyl-imidazol-20-ylidene)
phenylene)(dimethylamido)dichloro zirconium (IV) (3c)
4.7.1. Alternate procedure for 2-(1,3-bis(30-butyl-imidazol-20-
ylidene)phenylene)(dimethylamido)dichloro hafnium (IV) (4c)
1,3-Bis(30-butylimidazol-10-yl)benzene dichloride (2c) (0.224 g,
0.567 mmol) was added to a solution of Hf(NMe2)4 (0.207 g,
0.583 mmol) in THF (10 mL). The mixture was sonicated for 3 min
and then allowed to sit undisturbed for 8 h. During this time a
yellow precipitate formed. The mixture was placed in a 4 ꢀC freezer
for 1 h and the supernatant liquid was decanted. The solid was
washed with toluene (2 mL), hexanes (2 ꢁ 2 mL) and dried in vacuo
yielding a yellow, microcrystalline powder (0.090 g, 26%). Anal.
Calcd For C22H31Cl2N5Hf: C, 42.97; H, 5.08; N, 11.39. Found: C, 41.84;
H 5.30; N, 11.08.
1,3-Bis(30-butylimidazol-10-yl) benzene dichloride 2c (0.195 g,
0.493 mmol), Zr(NMe2)4 (0.145 g, 0.542 mmol) and toluene
(100 mL) were combined in a sealing tube, sonicated for 20 min and
then stirred for 15 h at 160 ꢀC. After cooling to room temperature, a
solid precipitated from the reaction mixture. The precipitate was
collected and dried under reduced pressure yielding a yellow-color
micro-crystalline solid (0.081 g, 31%): 1H NMR (300 MHz, CD2Cl2):
d
7.48 (s, 2H), 7.28 (t, J ¼ 7.8 Hz, 1H), 7.10 (s, 2H), 7.07 (s, 2H), 4.43 (br
s, 2H), 4.27 (br s, 2H), 2.93 (s, 6H), 1.91 (br s, 2H), 1.90 (br s, 2H), 1.45
(sex, J ¼ 7.5 Hz, 4H), 1.00 (t, J ¼ 7.4 Hz, 6H); 13C{1H} NMR (75.5 MHz,

W.D. Clark et al. / Journal of Organometallic Chemistry 751 (2014) 534e540
539
4.8. Representative procedure for catalytic runs in Tables 1e4:
hydroamination of 2,2-diphenylpent-4-ene-1-amine with CCC-NHC
Zr or CCC-NHC Hf complexes
obtained free of charge from the Cambridge Crystallographic Data
Centre via http://www.ccdc.cam.ac.uk/data_request/cif.
Appendix B. Supplementary material
A screw cap NMR tube was charged with CCC-NHC Zr or CCC-
NHC Hf precatalyst, 2,2-diphenylpent-4-ene-1-amine (0.040 g,
0.00017 mol), and tol-d8 (0.7 mL). The mixture was placed in a
preheated oil bath at 160 ꢀC. Conversions and product distributions
were determined by 1H NMR spectroscopy.
Supplementary material related to this article can be found at
http://dx.doi.org/10.1016/j.jorganchem.2013.11.001.
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