Synthesis and reactivity of zirconium and hafnium complexes incorporating chelating diamido-N-heterocyclic-carbene ligands

Article abstract of DOI:10.1016/j.jorganchem.2005.07.121

Early transition metal complexes employing a diamido N-heterocyclic carbene (NHC) ligand set (denoted [NCN]) render the centrally disposed NHC moiety stable to dissociation. Aminolysis reactions with the mesityl-substituted ligand precursor (^Mes

Full text of DOI:10.1016/j.jorganchem.2005.07.121

Journal of Organometallic Chemistry 690 (2005) 5788–5803
www.elsevier.com/locate/jorganchem
Synthesis and reactivity of zirconium and hafnium complexes
incorporating chelating diamido-N-heterocyclic-carbene ligands
*
Liam P. Spencer, Michael D. Fryzuk
Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, Canada V6T 1Z1
Received 3 June 2005; received in revised form 14 July 2005; accepted 15 July 2005
Available online 9 November 2005
Abstract
Early transition metal complexes employing a diamido N-heterocyclic carbene (NHC) ligand set (denoted [NCN]) render the centrally
disposed NHC moiety stable to dissociation. Aminolysis reactions with the mesityl-substituted ligand precursor (Mes[NCN]H2) and
M(NMe2)4 (M = Zr, Hf) provide bis(amido)-NHC-metal complexes that can be further converted to chloro and alkyl derivatives. Acti-
vation of Mes[NCN]M(CH3)2 with [Ph3C][B(C6F5)4] yields {Mes[NCN]MCH3}{B(C6F5)4}, which is surprisingly inactive for the polymer-
ization of 1-hexene. The zirconium cation did, however, show moderate ability to catalytically polymerize ethylene. The hafnium dialkyls
are thermally stable with the exception of the diethyl complex, Mes[NCN]Hf(CH2CH3)2, which undergoes b-hydrogen transfer and sub-
sequent C–H bond activation with an ortho-methyl substituent on the mesityl group. The hafnium dialkyl complexes also insert carbon
monoxide and substituted isocyanides to yield g2-acyls and g2-iminoacyls, respectively. In some circumstances, further C–C bond cou-
pling occurs to yield enediolates and eneamidolate metallocycles. The molecular structures of Mes[NCN]Hf(CH2CHMe2)2,
Mes[NCN]Hf(g2-(2,6-Me2C6H3NCCH3)(CH3), Mes[NCN]Hf(g2-(2,6-Me2C6H3NCCH3)2, Mes[NCN]Hf(OC(CH3)@C(CH3)NXy), and
[
Mes[NCN]Hf(OC(iBu)@C(iBu)O)]2 are included.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Hafnium; Zirconium; Tridentate ligand; N-heterocyclic carbene; Amido donors; Migratory insertion; Polymerization
1. Introduction
certain late transition metal complexes, NHCs have also
been observed to undergo non-innocent migratory inser-
tion chemistry with metal alkyls and hydrides, which re-
sults in the deleterious modification of the NHC unit [3].
With respect to the early transition metals, N-heterocy-
clic-carbenes are known to be susceptible to dissociation.
For example, samarium and yttrium complexes stabilized
by a bidentate amidocarbene ancillary ligand show this ten-
dency in the presence of Me2NCH2CH2NMe2 and
Ph3P@O [4]. In an effort to prevent dissociation and further
develop early transition metal NHC chemistry, we have de-
signed and synthesized an [NCN] ligand set with an NHC
flanked by two amido units. We recently communicated the
isolation and structural characterization of several zirco-
nium amido, chloro, and alkyl derivatives and found the
carbene donor was rendered stable to dissociation due to
its central disposition between the two anionic amido units
[5]. In the present work, we have extended our studies to
N-Heterocyclic carbenes (NHCs) have found wide-
spread use as essential ancillary ligands throughout most
of the periodic table. Initially regarded as academic curios-
ities, the re-emergence of NHCs has been driven in part by
their ability to replace phosphine ligands in homogeneous
catalysis and small molecule activation [1]. In particular,
late transition metal complexes employing this ligand set
show strong metal carbene bonds and slow dissociation
rates [2], properties that furnish robust and versatile cata-
lysts. Indeed, in many cases, late transition metal NHC
complexes have shown enhanced catalytic performance as
compared to their phosphine predecessors. However, with
*
Corresponding author.
E-mail address: fryzuk@chem.ubc.ca (M.D. Fryzuk).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.07.121

L.P. Spencer, M.D. Fryzuk / Journal of Organometallic Chemistry 690 (2005) 5788–5803
5789
include the synthesis of hafnium-amido, -halide, and -alkyl
compounds and, for the alkyl derivatives report their po-
tential to polymerize ethylene and 1-hexene. We have also
investigated the migratory insertion reactivity of the dialkyl
derivatives with carbon monoxide and substituted isocya-
nides, and show that the NHC donor remains innocent
during the insertion process.
2. Results and discussion
2.1. Synthesis of the dialkyl group 4 [NCN] complexes
We have recently reported the synthesis of an [NCN] li-
gand set and several group 4 zirconium complexes, includ-
ing the first crystallographically characterized zirconium
dialkyl containing an NHC donor [5]. The synthesis of
the ligand was accomplished by reducing the carbonyl of
a substituted bis(arylamide)imidazolium chloride precursor
with BH3. However, attempts to incorporate increased ste-
ric bulk on the aryl groups (i.e., 2,4,6-Me3C6H2 or
2,6-iPrC6H3) in a similar manner were unsuccessful; in
these cases, BH3 reduction under a variety of conditions
only led to decomposition of the starting materials. Intro-
duction of mesityl (2,4,6-Me3C6H2) groups was accom-
plished by simply melting the appropriately substituted
imidazole and b-chloroethylarylamine providing the
imidazolium chloride, (Mes[NCHN]H2)+Clꢀ (1), in near
quantitative yield. Compound 1 can be selectively deproto-
nated with KN(SiMe3)2 to give the diamino-carbene (2)
(Scheme 1). Synthesis of 2 was confirmed by the disappear-
ance of the diagnostic iminium resonance of 1 at d 9.35,
along with an upfield shift in the imidazole ring proton
resonances in the 1H NMR spectrum, and a weak 13C
resonance at d 215 attributable to the carbene carbon of 2.
Protonolysis reactions involving 2 and M(NMe2)4
(M = Zr, Hf) provide for a convenient entry to Mes[NCN]
Scheme 1.
1
group 4 complexes (Scheme 2). The H NMR spectra of
the bis(dimethylamido) complexes, 3 and 4 (Zr and Hf,
respectively), suggest a C2v symmetric species in solution
with two multiplets for the equivalent ethylene spacers
and singlets for the remaining proton environments. Both
compounds also exhibit weak downfield 13C resonances
around d 190, due to the M–Ccarbene carbon. The dimethy-
lamido groups can be quantitatively removed to generate
the corresponding dichlorides, 5 and 6, with excess Me3-
SiCl. The 1H and 13C NMR spectra of both 5 and 6
confirm the loss of dimethylamido groups, and weak 13C
M–Ccarbene resonances at d 192.3 ppm and 198.2, for 5
and 6, respectively, are observed. Interestingly, there is
no change in the chemical shift of these latter resonances
in any of the zirconium or hafnium compounds even in
strongly coordinating pyridine over a period of several
months, which confirms that there is no dissociation of
the carbene carbon when flanked by two amido donors.
Scheme 2.

5790
L.P. Spencer, M.D. Fryzuk / Journal of Organometallic Chemistry 690 (2005) 5788–5803
Alkylation of the dichlorides 5 and 6 by Grignard re-
Furthermore, two multiplets at d ꢀ0.10 and 0.10 can be
assigned to the diastereotopic protons of the remaining –
HfCH2 group, an observation previously made with a
similarly metallated –HfCH2CH3 system [8]. Further proof
of ortho-methyl bond activation was observed with a
downfield shifted Hf–C 13C resonance at d 72.9, a chemical
shift similar to that found for the benzylic carbons of the
hafnium dibenzyl derivative 10. Synthesis of the deuterated
diethyl complex Mes[NCN]Hf(CD2CD3)2 (d10-12) provided
information on the mechanism of this metallation. Decom-
position of d10-12 results in the liberation of d6-ethane
(CD3CD3: identified by GC–MS), which suggests that
b-hydrogen transfer [8] has occurred to give a reactive
g2-ethylene intermediate. This intermediate was not
observed in solution but readily undergoes C–H bond acti-
vation with a neighbouring mesityl-methyl group to give
the mono-protonated product, d4-13; a broad singlet at
1.5 ppm integrating to one proton was found. Attempts
to trap the g2-ethylene intermediate with PMe3 or pyridine
have been unsuccessful.
agents proceeds smoothly to give the dialkyl products 7–
12 exclusively. The zirconium dialkyl derivatives are more
thermally sensitive in solution as compared to the hafnium
analogues, decomposing to unidentifiable products over
the period of one day; for this reason, zirconium complexes
that have ethyl or isobutyl groups could not be isolated.
With one exception, the hafnium dialkyls possess excellent
thermal stability; no apparent decomposition was noted
with the hafnium diisobutyl derivative 11 at 60 ꢁC. In
solution, the dialkyl products possess C2v symmetry with
1
diagnostic 13C and H resonances in the NMR spectra;
for example, in 7, both zirconium-methyl groups are equiv-
alent and appear as a singlet at d 0.33, and also equivalent
are the four ortho-methyls on both mesityl substituents on
the amido nitrogens. The solid-state molecular structure of
11 is shown in Fig. 1; crystallographic data are given in
Table 1. The ligand assumes a puckered orientation with
respect to a distorted trigonal bipyramidal metal centre.
The mesitylamido donors are pseudo-trans oriented with
N(4)–Hf(1)–N(3) being 151.49(8)ꢁ. The hafnium–carbene
˚
bond length (2.387(3) A) is similar to the previously
2.2. Migratory insertion of isocyanides and carbon monoxide
reported zirconium [NCN] complexes as are Hf–N amido
˚
˚
(av. 1.361(3) A) and Hf–C 2.250(3) A) alkyl bond lengths
[5,6].
2.2.1. Reactivity with aryl and alkyl isocyanides
The hafnium dimethyl derivative 8 reacts immediately in
solution with one equivalent of xylyl isocyanide (XyNC) to
In contrast to the thermal stability of the diisobutyl
derivative 11, the diethyl complex Mes[NCN]Hf(CH2CH3)2
(12) decomposes at room temperature to give the metal-
1
give the mono-insertion product 14 (Scheme 4). The H
NMR spectrum is consistent with a Cs symmetric structure
(equivalent N-mesityl groups and back bone linkers); the
iminoacyl methyl resonance is found at 0.17 ppm. The g2
coordination mode of the iminoacyl group was confirmed
1
lated species 13 and ethane (d 0.8) (Scheme 3). H NMR
studies of 13 reveal a C1 symmetric species in solution with
five inequivalent aryl-methyl resonances. There are two
doublets at d 1.00 and 2.51 indicative of two diastereotopic
protons on the metallated –CH2 resonance, consistent with
a previously described metallated mesityl group [7].
by 13C NMR (N@C, d 259) and IR (m(C@N) 1575 cmꢀ1
)
spectroscopy and is a typical outcome for this kind of reac-
tion [9]. In solution, only one of the two possible orienta-
tions of the g2-iminoacyl unit is apparent. NOE
measurements show a through space enhancement of the
ortho-methyls of the N-xylyl group upon irradiation of
the remaining Hf–Me resonance, which supports the
isomer having the N-xylyl group pointing towards the
Hf–Me. The solid-state molecular structure of 14 (Fig. 2)
also verifies the g2-iminoacyl coordination mode; crystallo-
graphic data are given in Table 1. The imino carbon atom
is directly bound to hafnium centre with the Hf(1)–C(36)
˚
bond length at 2.251(2) A, which is similar to related
˚
iminoacyl-zirconium complexes (2.23–2.25 A). The bond
angles of the triangle defined by Hf–C(28)–N(5) are typical
of other structurally characterized group 4 g2-iminoacyl
complexes as is the imino C(28)–N(5) bond length [9].
The ancillary [NCN] ligand is distorted towards facial
coordination with the N(4)–Hf(1)–N(3) angle being
133.65(7)ꢁ.
Addition of a second equivalent of xylyl isocyanide to 14
results in the exclusive formation of the bis(g2-iminoacyl)
product 15 (Scheme 4). The product contains a m(C@N)
band at 1568 cmꢀ1. The room temperature 1H NMR
spectrum of 15 in CD2Cl2 is consistent with a Cs symmetric
species; however, cooling the solution to ꢀ40 ꢁC was
Fig. 1. ORTEP view of Mes[NCN]Hf(iBu)2 (11) (1/2Et2O omitted),
depicted with 30% ellipsoids; all hydrogen atoms have been omitted for
˚
clarity. Selected bond distances (A) and angles (ꢁ): Hf(1)–C(1) 2.385(3),
Hf(1)–N(3) 2.101(2), Hf(1)–N(4) 2.126(2); N(3)–Hf(1)–N(4) 151.49(8),
N(3)–Hf(1)–C(1) 80.33(9), N(4)–Hf(1)–C(1) 80.30(9), C(30)–Hf(1)–C(1)
118.02(9), C(26)–Hf(1)–C(1) 134.32(9).

L.P. Spencer, M.D. Fryzuk / Journal of Organometallic Chemistry 690 (2005) 5788–5803
5791
Table 1
General crystallographic dataa
Compound
11
14
15
18
23
CCDC registry
Formula
271123
271124
271125
271126
271127
C
33H50HfN4 Æ C2H5O C36H47Hf N5 Æ C4H8O C90H112Hf2N12 Æ CH2Cl2 C37H47Hf N5O Æ C2H5O C70H100Hf2N8O4 Æ 4C6H6
Molecular weight
Colour, habit
Crystal size (mm)
Crystal system
Space group
726.33
800.39
1803.82
801.35
1786.99
Colourless, prism
0.15 · 0.15 · 0.15
Monoclinic
C2/c
19.9312(3)
13.7149(3)
28.0013(6)
90
113.0590(10)
90
7042.7(2)
4
Colourless, plate
0.40 · 0.30 · 0.10
Monoclinic
C2/c
32.883(5)
11.614(5)
23.793(5)
90
112.217(5)
90
8412(4)
4
Colourless, irregular
0.20 · 0.07 · 0.04
Triclinic
Yellow, irregular
0.10 · 0.05 · 0.03
Monoclinic
P21/c
10.9435(6)
20.0210(11)
17.3179(8)
90
92.451(2)
90
3790.9(3)
4
Colourless, tablet
0.15 · 0.07 · 0.04
Triclinic
ꢀ
ꢀ
P1
P1
˚
a (A)
15.6616(8)
16.3972(7)
21.5514(10)
70.757(2)
73.887(2)
68.167(2)
4774.1(4)
2
1.255
1844
2.275
0.8093–1.0000
12.377(5)
18.530(5)
21.408(5)
107.656(5)
103.930(5)
100.104(5)
4374(2)
2
1.357
1840
2.425
0.6694–1.0000
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dcalc (g cmꢀ3
F(000)
)
1.355
2952
2.991
0.8448–1.0000
1.378
3600
2.521
0.7118–1.0000
1.404
1636
2.790
0.7300–1.0000
l(Mo Ka) (mmꢀ1
Transmission
factors
)
2hmax (ꢁ)
51.40
55.24
48.10
41.20
46.92
Index ranges (h, k, l)
ꢀ25, 26; ꢀ18, 18;
ꢀ43, 43; ꢀ15, 15;
ꢀ19, 19; ꢀ20, 18;
ꢀ12, 13; ꢀ23, 23;
ꢀ13, 13; ꢀ19, 19;
ꢀ37, 37
ꢀ31, 30
ꢀ26, 25
ꢀ15, 20
ꢀ23, 22
Total number of
reflections
97131
115842
108780
25826
44117
Number of unique
reflections
Rmerge
8473
9958
19273
6703
11428
0.0396
6802
0.0388
8511
0.0649
13353
0.1030
4186
0.1051
7049
Number of
reflections
with I P 2r(I)
Number of variables
R (F2, all data)
Rw (F2, all data)
R (F, I > 2r(I))
Rw (F, I > 2r(I))
Goodness-of-fit
Largest difference
377
479
988
420
993
0.0337
0.0576
0.0217
0.0508
1.066
0.0285
0.0478
0.0203
0.0454
1.021
0.0963
0.2299
0.0656
0.2136
1.281
0.1058
0.0834
0.0479
0.0713
0.999
0.1106
0.1137
0.0473
0.0944
0.982
1.241/ꢀ0.590
0.669/ꢀ0.672
6.701/ꢀ1.140
1.033/ꢀ1.275
1.340/ꢀ1.319
ꢀ3
˚
in peak/hole (e A
)
a
˚
Data common to all structures: Diffractometer, Bruker X8 APEX CCD; temperature (K), 173(2); wavelength (A), 0.71073.
necessary to fully resolve all resonances. At this lower tem-
perature, two unique environments were observed for each
g2-iminoacyl group consistent with the solid-state molecu-
lar structure of 15 (Fig. 3); crystallographic data are given
in Table 1. Attempts to observe the characteristic iminoa-
cyl 13C resonance in solution were not possible likely due
to fast exchange under the normal acquisition conditions.
In the solid state, there are two independent molecules in
the asymmetric unit cell with subtle variations in the g2-
iminoacyl bond lengths (only one of the molecules is used
for structural analysis described below). Although formally
seven-coordinate, 15 is best described as distorted trigonal
bipyramidal about hafnium, with each of the g2-iminoacyl
groups occupying a single coordination site, one axial and
one equatorial. The Mes[NCN] ligand is puckered towards a
facial orientation with N(4)–Hf(1)–N(3) being 122.6(3)ꢁ,
presumably to accommodate the additional steric con-
straints of two xylyl units. The two iminoacyl groups are
oriented perpendicular to each other, which is further evi-
dence of the considerable steric interactions in the solid
state.
In general, thermolysis of groups 4 and 5 bis(g2-iminoa-
cyl) complexes results in the formation of enediamido
metallacycles [10,11]. However, heating 15 in refluxing
toluene resulted in no reaction, only recovery of starting
materials (110 ꢁC for >8 h). This was somewhat surprising
as this transfꢁormation is reported to be facilitated by
lowering the pC@N orbital via the presence of electron-with-
drawing substituents or by having a relatively electron-rich
metal centre [9]. Because NHCs are considered strongly
r-donating [1], this should have facilitated this transforma-
tion. To probe the effects of sterics on this process, isopro-
pylisocyanide (iPrNC) was added to 14 to generate the
mixed bis(iminoacyl) species 17 (Scheme 4). Thermolysis
of this material also resulted in no reaction even after ex-
tended reaction times at 110 ꢁC. Finally, the bis(isopropyl)

5792
L.P. Spencer, M.D. Fryzuk / Journal of Organometallic Chemistry 690 (2005) 5788–5803
Fig. 2. ORTEP view of Mes[NCN]Hf(g2-XyNCCH3)(CH3) (THF omitted)
(14), depicted with 30% ellipsoids; all hydrogen atoms and mesityl groups
˚
have been omitted for clarity. Selected bond distances (A) and angles (ꢁ):
Hf(1)–C(1) 2.387(2), Hf(1)–C(26) 2.251(2), Hf(1)–N(3) 2.1352(18), Hf(1)–
N(4) 2.1117(18), Hf(1)–N(5) 2.2461(16); N(5)–C(26)–Hf(1) 73.05(11),
N(4)–Hf(1)–N(3) 133.65(7), N(4)–Hf(1)–C(1) 77.25(7), N(3)–Hf(1)–C(1)
77.72(7).
Scheme 3.
iminoacyl was prepared by addition of two equiv of isopro-
pyl isocyanide to the dimethyl complex 8 to generate 16 in
excellent yields. This also turned out to be indefinitely
2.2.2. Formation of an eneamidolate metallacycle
1
stable to thermolysis as evidenced by no change in the H
The hafnium methyl-iminoacyl complex 14 readily re-
acts with CO (1 atm) to generate the eneamidolate complex
18 (Scheme 4). The likely first step is insertion of CO into
the remaining Hf–CH3 bond; however, monitoring of this
process by NMR spectroscopy did not provide any evi-
dence for the presence of a mixed acyl-iminoacyl com-
pound implying that the C@C bond formation process is
quite facile. To our knowledge, only one other example
of eneamidolate synthesis has been reported, but that
NMR spectrum over a period of hours at 110 ꢁC. Forma-
tion of an enediamido metallacycle is known to be affected
by the steric bulk located on the nitrogen atom [12,13].
Moreover, for enediamide formation to occur, both g2-
iminoacyls must rotate into the preferred coplanar config-
uration, which would appear to be difficult in complexes
15–17 due to increased steric bulk around the metal centre
[10,11,14–16].
Scheme 4.

L.P. Spencer, M.D. Fryzuk / Journal of Organometallic Chemistry 690 (2005) 5788–5803
5793
to a r2,p bonding interaction between the electron deficient
metal centre and the olefinic portion of the metallocyclic
backbone,aphenomenonobservedinasimilarZr–butadiene
system [17]. A fold angle of 24.0ꢁ was found for 18, signif-
icantly less than previously reported compounds (ꢂ50ꢁ)
[10,18], which may be reflective of the decreased Lewis
acidity of the metal centre and/or the different kind of
heterometallocycle. As a result, the Hf(1)ꢃ ꢃ ꢃC(26) and
˚
Hf(1)ꢃ ꢃ ꢃC(27) distances (2.728(7) and 2.660(6) A, respec-
tively) are significantly longer than the previously reported
˚
eneamidolate complex (2.549(8) and 2.581(8) A) [10]. Once
again, the Mes[NCN] ancillary ligand is distorted towards
facial coordination as evidenced by the N(4)–Hf(1)–N(3)
bond angle of 124.5(2)ꢁ. The molecule possesses C1 symme-
try in the solid state as a result of the r2,p interaction;
however, Cs symmetry was observed in solution at room
temperature due to ring flipping of this eneamidolate ring
on the NMR time scale. The DGꢀ of 54.1 kJ molꢀ1 for
the ring-flipping process (Eq. (1)) was estimated from the
coalescence temperature (268 K), and is very similar to
Fig. 3. ORTEP view of Mes[NCN]Hf(g2-XyNCCH3)2 (CH2Cl2 omitted)
(15), depicted with 30% ellipsoids; all hydrogen atoms have been omitted
for clarity. Selected bond distances (A) and angles (ꢁ): Hf(1)–N(4)
2.146(8), Hf(1)–N(3) 2.154(7), Hf(1)–C(26) 2.249(9), Hf(1)–N(5) 2.250(8),
Hf(1)–N(6) 2.305(7), Hf(1)–C(36) 2.306(10), Hf(1)–C(1) 2.377(10); N(4)–
Hf(1)–N(3) 122.6(3), C(26)–Hf(1)–N(5) 34.0(3), N(4)–Hf(1)–C(1) 78.2(3),
N(3)–Hf(1)–C(1) 76.2(3), N(6)–Hf(1)–C(36) 32.3(3).
˚
the value estimated for
a Hf–enediamide complex
(59.4 kJ molꢀ1
)
[10]. Broad resonances for the O–
C(CH3)@ and O–C(CH3)@ carbon nuclei were observed
by 13C NMR at d 137.0 and 19.4, respectively.
example required forcing conditions (200–1000 psi of CO)
[10]. The solid-state molecular structure of 18 is shown in
Fig. 4, and confirms the presence of an eneamidolate ring;
crystallographic data are given in Table 1. The C@C bond
˚
length (1.340(9) A) compares well with previously de-
scribed metallocyclopentene metallocycles [10,17]. The ene-
amidolate ring is distorted from a planar coordination, an
observation prominent in most enediolate, eneamidolate
and enediamides systems. This bending has been attributed
ð1Þ
2.2.3. Formation of a hafnium vinyl-enolate and enediolate
metallacycle
Due to its ease of preparation and its enhanced thermal
stability relative to zirconium dialkyl complexes, the haf-
nium dimethyl derivative 8 was chosen for reactivity stud-
ies with CO. Exposure of 8 to 1 atm of carbon monoxide
for one day results in the formation of Mes[NCN]Hf(CH3)-
(O–CH@CH2) (20), a hafnium vinyl-enolate (Scheme 5).
1
Diagnostic resonances appear in the H NMR spectrum
at d 3.47, 3.54, and 5.75, with appropriate geminal and
vicinal coupling constants. The downfield resonance at d
5.75, assigned to the a-O–CH@ proton, splits further when
13CO is substituted, giving typical 1J
coupling of
13C–1H
145 Hz [19]. The Mes[NCN] ligand resonances are diagnos-
tic of a Cs symmetric compound and also apparent is the
Hf–CH3 resonance located at d 0.37. The 13C NMR reveals
a Hf–NHC carbene signal at d 196.2, as well as vinyl 13C
resonances at d 120.2 and 139.0. From the solution
NMR data, we are unable to provide information on the
mer versus fac orientation of the [NCN] donors, and for
Fig. 4. ORTEP view of Mes[NCN]Hf(OC(CH3)@C(CH3)NXy) (1/2Et2O
omitted) (18), depicted with 30% ellipsoids; all hydrogen atoms have been
omitted for clarity. Selected bond distances (A) and angles (ꢁ): Hf(01)–
O(1) 2.032(4), Hf(01)–N(5) 2.061(5), Hf(01)–N(3) 2.077(5), Hf(01)–N(4)
2.082(5), Hf(01)–C(1) 2.348(6), Hf(01)–C(27) 2.660(6), Hf(01)–C(26)
2.728(7), C(26)–C(27) 1.340(9); O(1)–Hf(01)–N(5) 83.14(19), N(3)–
Hf(01)–N(4) 124.5(2), N(3)–Hf(01)–C(1) 78.1(2), N(4)–Hf(01)–C(1)
81.2(2).
˚

5794
L.P. Spencer, M.D. Fryzuk / Journal of Organometallic Chemistry 690 (2005) 5788–5803
Scheme 5.
this reason, a mer geometry is shown, despite the fact that
the mono insertion adduct of XyNC (cf., 14) has a facial
coordination of the ancillary ligand.
gen-atom shift from the methyl substituent of the carbene
carbon to generate the observed vinyl enolate (Scheme 7).
Presumably, the g2-acetyl unit of 19 is oriented in such a
Monitoring the reaction of CO with the dimethyl
complex shows the formation of the expected g2-acyl inter-
mediate Mes[NCN]Hf(g2-COCH3)(CH3) (19), as evidenced
by a singlet at d 1.62 for the acetyl methyl protons; this res-
onance splits into a doublet with the use of 13CO
1
ð J
¼ 7 HzÞ, confirming that simple insertion has
13C–1H
occurred. The 13C NMR spectrum shows a resonance at
d 339.6, and is typical for the acyl carbonyl carbon of
reported Hf(g2-acyl) complexes [9]. IR spectroscopy was
also useful in the determination of the Hf(g2-acyl) with a
m(C@O) stretch observed at 1540 cmꢀ1, characteristic of
similar compounds.
The rearrangement of the hafnium methyl–acetyl
complex 19 to the methyl–vinyl enolate derivative 20 was
unexpected. The reactivity of group 4 methyl–acetyl com-
plexes has been ascribed to the oxy-carbene resonance form
of the g2-acyl moiety [19,20], which normally undergoes
intramolecular coupling with the adjacent methyl group
[21], followed by hydrogen abstraction by the metal to gen-
erate a metal hydrido-methylvinyl-enolate (Scheme 6).
In the case of the hafnium methyl–acetyl complex 19,
the formation of the vinyl enolate suggests that the oxy-
carbene resonance form preferentially undergoes a hydro-
Scheme 7.
Scheme 6.

L.P. Spencer, M.D. Fryzuk / Journal of Organometallic Chemistry 690 (2005) 5788–5803
5795
way as to disfavour C–C coupling with the Hf–CH3 unit,
and instead, hydrogen transfer from the methyl occurs.
Whether or not this is a result of a geometric constraint
caused by the different ancillary ligands or an electronic ef-
fect is unknown. Similar hydrogen and silyl group migra-
addition, 23 exhibits a weak 13C resonance at 140.0 ppm
indicative of an olefinic C@C bond (1J13C-13C = 20 Hz
with 13CO).
The mechanism of the formation of the dinuclear
bis(enediolate) was examined by monitoring the reaction
of 11 with CO as a function of time using NMR spectros-
copy. The first intermediate formed is the hafnium isobu-
tyl–acyl species, 21, clearly distinguished by a 13C NMR
resonance at 338.4 ppm, attributed to an Hf(O@CiBu) res-
onance, analogous to other early transition metal g2-acyl
tions have been reported for Cp3ThR and CpꢁThRðClÞ
2
derivatives upon reaction with CO [22]. Continued expo-
sure of 20 towards CO results in the formation of an insol-
uble, white powder. ES-MS shows a molecular ion peak at
652 m/z indicative of a second CO insertion; however, the
insolubility of the product has hampered further character-
ization efforts.
1
complexes [9]. The H NMR spectrum reveals a Cs sym-
metric species in solution with two distinct iso-butyl reso-
nances. The methylene protons a to the acyl carbonyl of
one iso-butyl unit are observed as a doublet at 1.68 ppm,
which splits further into a doublet of doublets when
13CO was used (2J13C–H = 4.7 Hz). Again, the coordina-
tion mode of the Mes[NCN] ligand in 21, mer versus fac,
is not assignable with the NMR data available.
It has been shown that the nature of carbonylation
products is dependent on substituents on the metal [23].
With this in mind, the carbonylation of the hafnium dii-
sobutyl complex, 11, was investigated. Exposure of 11 to
1 atm of CO for an extended period (3–4 days) results in
the precipitation of colourless crystals in reasonable yield.
Analysis by solid-sate X-ray diffraction indicated that this
material is the dihafnium bis(enediolate) complex,
Continued exposure of 21 to CO results in the formation
of a new product having C2v symmetry in solution and dis-
tinct from the final dihafnium macrocycle 23. Only one iso-
butyl resonance is present in the 1H NMR spectrum at room
temperature, suggestive of a second CO molecule insertion
into the remaining Hf–C bond. The 13C NMR spectrum of
this species displays a weak resonance at d 140.6 indicative
of a new C@C bond. This spectroscopic evidence is consis-
tent with the formation of the mononuclear hafnium–enedi-
olate, 22 (Scheme 5). The synthesis of this enediolate likely
proceeds through a bis(g2-acyl) species, the presence of
(
Mes[NCN]Hf)2(l-OC(iBu)@C(Bui)O)2 (23) (see Scheme
5). The ORTEP diagram is shown in Fig. 5; crystallo-
graphic data are given in Table 1. Examination of the
C–C bond length clearly shows double bond character
˚
(av. 1.342(15) A) and along with Hf–O bond lengths (av.
˚
1.928(6) A) are similar to other early transition metal
enediolate complexes [24]. The [NCN] ligand distorts to a
facial geometry having an N(4)–Hf(01)–N(3) bond angle
of 124.4(3)ꢁ Hf–C alkyl and Hf–N amido bond lengths
are similar to previously discussed complexes. In solution,
the 1H NMR resonance spectrum was consistent a Cs
symmetric species in solution with two distinct iso-butyl
resonances, consistent with the solid-state structure. In
1
which was not observed by H NMR studies. In solution,
the nuclearity of the enediolate 22 is assumed to be mononu-
clear; however, there are early transition metal enediolates
reported in both monomeric and dimeric forms (Scheme
8), depending on the steric bulk of the alkyl group [23]. For
example, when the alkyl group is bulky (R = CH2C(CH3)3,
CH2Si(CH3)3) monomeric species have been observed, and
with smaller groups (R = H, CH3, CH2Ph), higher nuclear-
ity species have been reported. Indeed, there are several
reports of monomeric enediolates dimerizing to form dinu-
clear complexes [25,26]. In one example, such complexes
show dynamic behaviour interconverting oxygen atoms
through a low activation-energy process by a ten-membered
metallacycle intermediate, similar in structure to the final
product 23 [26].
A reasonable proposal for the formation of 23 is shown
in Scheme 8, and involves dimerization of 22 via dative
oxygen–hafnium interactions that are converted to cova-
lent bonds, followed by ring-opening to generate the 10-
membered dihafnium macrocycle. The driving force for
the formation of the dinuclear complex 23 may be provided
by better oxygen-to-hafnium p donation, an overlap that is
more difficult in the mononuclear complex 22 with the five-
membered enediolate ring [27]. Examination of the solid-
state structure of 23 reveals a average Hf–O–C bond angle
of 163.5(3)ꢁ and reflects such a p donation.
Fig. 5. ORTEP view of Mes[NCN]Hf(OC(iBu)@C(iBu)O)]2(4C6H6 omit-
ted) (23), depicted with 30% ellipsoids. For clarity, only the ipso-carbons
of the mesityl groups have been included and all hydrogen atoms have
˚
been removed. Selected bond distances (A) and angles (ꢁ): Hf(01)–O(2)
1.912(6), Hf(01)–O(1) 1.937(5), Hf(01)–N(4) 2.097(7), Hf(01)–N(3)
2.109(7), Hf(01)–C(1) 2.387(9), C(52)–C(62) 1.342(12), C(51)–C(61)
1.341(12); O(2)–Hf(01)–O(1) 105.4(2), N(4)–Hf(01)–N(3) 124.4(3), N(4)–
Hf(01)–C(1) 77.1(3), N(3)–Hf(01)–C(1) 77.8(3), C(51)–O(1)–Hf(01)
169.4(6), C(52)–O(2)–Hf(01) 163.1(6).
The reason for the differences in reactivity between alkyl
substituents may be attributed to competitive dimerization

5796
L.P. Spencer, M.D. Fryzuk / Journal of Organometallic Chemistry 690 (2005) 5788–5803
Scheme 8.
and insertion pathways. Such considerations have been
attributed to the nucleophilic character of the alkoxy-
carbene moiety and have been well documented in actinide
and tantalum metallocene systems [22,28].
active amido-based non-metallocene group 4 catalysts [29].
It was recently found that 1-hexene polymerization with
group 4 metal bearing diamido Mes[N(NMe)N] ancillary li-
gands underwent ortho-methyl C–H bond activation dur-
ing polymerization [7]. Investigation of the decomposition
products revealed an ortho-methyl C–H bond activated
compound similar to 13, in addition to other unidentifiable
materials.
Generation of 24 in chlorobenzene in the presence of
ethylene showed moderate catalytic ability to produce
polyethylene (125 g mmolꢀ1 hꢀ1 atmꢀ1). It is important to
note that immediately after exposure to ethylene, a notice-
able exotherm was observed. Halting the polymerization
experiment at increasingly longer times resulted in a de-
creased activity. This suggests that the active species, albeit
catalytically active, was short-lived in solution decompos-
ing to the previously described inactive complex.
2.2.4. Hf and Zr cation formation and polymerization studies
Group
4 transition metal complexes with aryl-
substituted amide ligands have been extensively examined
as olefin polymerization catalysts [29]. In some circum-
stances, 1-hexene can be polymerized in a living fashion
by bis(amide) substituted zirconium and hafnium
complexes [30]. With these results in mind, the polymeriza-
tion ability of zirconium and hafnium dimethyl complexes
was examined.
The methyl cations,
[
Mes[NCN]M(CH3)][B(C6F5)4]
(M = Zr, 24; M = Hf, 25), were generated in situ from di-
methyl precursors 7 and 8 at ꢀ10 ꢁC with [Ph3C][B(C6F5)4].
Due to the thermal sensitivity of the species generated, the
products were identified by 1H NMR spectroscopy in solu-
tion and not isolated. 1H NMR spectra showed Cs symmet-
ric products in solution with M–CH3 resonances at d 0.50
for 24 and d 0.26 for 25.
3. Conclusion
In this work, a new tridentate diamido-N-heterocyclic
carbene ligand precursor has been synthesized via a mod-
ification of an earlier procedure; this new method toler-
ates bulky aryl donors attached to the amine arms
flanking the NHC. Incorporation of Mes[NCN] onto zirco-
nium(IV) and hafnium(IV) complexes was accomplished
by protonolysis of M(NMe2)4 to generate the bis(dimethy-
l)amido derivatives, which in turn could be converted to
dichloro and dialkyl complexes by straightforward
procedures.
Treatment of 8 with triflic acid generates the hafnium
methyl-triflate complex, Mes[NCN]Hf(OTf)(CH3) (26),
1
which is stable at room temperature. The H NMR spec-
trum of 26 shows a Cs symmetric species in solution with
a Hf–CH3 resonance at d 0.19, which is similar to previ-
ously described complexes [31].
Cationic 24 and 25 were evaluated as 1-hexene polymer-
ization catalysts (see Section 4 for protocol). Upon work-
up, a minor amount of a viscous substance was recovered
that was identified as atactic poly-1-hexene in 4% yield
[32]. These results were quite surprising in light of the many
We have already shown that dissociation of the carbene
moiety from an electro-positive, early transition metal can
be prevented by having the NHC positioned between two

L.P. Spencer, M.D. Fryzuk / Journal of Organometallic Chemistry 690 (2005) 5788–5803
5797
amido donors. What was not known was how stable early
4.2. 2,4,6-Me3C6H2NHC(O)CH2(imidazole)
transition metal NHC interactions would be to migratory
insertion. We have investigated a variety of such funda-
mental processes and have found that the NHC moiety
remains coordinated to the metal and does not participate
in any way that disrupts or changes the NHC donor. For
example, isocyanide insertions in hafnium–sp3-carbon
bonds all occur at the alkyls and result in iminoacyl
derivatives. Tandem insertions involving isocyanides and
carbon monoxide also take place just at the sp3-metal
carbon bond and leave the NHC unscathed. In addition,
multiple insertions of CO result in the formation of enedi-
olate species, presumably via the intermediacy of oxy-
carbene resonance forms, with no involvement of the
NHC unit. Such outcomes will be important in future
designs of ancillary ligands that incorporate NHC type
donors.
Activation of the zirconium- and hafnium-dimethyl
derivatives with [Ph3C][B(C6F5)4] in the presence of 1-
hexene yields marginal polymer formation. The cationic
zirconium species does possesses moderate catalytic ability
for ethylene polymerization. Hafnium alkyl complexes
containing b-hydrogen atoms display different reactivity
depending on the substitution. Diisobutyl substituted
complexes show no decomposition, even at elevated tem-
peratures; however, ethyl substituted complexes undergo
facile b-hydrogen transfer at room temperature, presum-
ably through a reactive hafnium g2-ethylene intermediate,
to yield a metallated hafnium species.
NaH (3.8 g, 158.3 mmol) and imidazole (9.73 g,
142.9 mmol) were combined in DMF (75 mL) and stirred
for 30 min at 50 ꢁC to give a clear brown solution. 2,4,6-
Me3C6H2NHC(O)CH2Cl (28.2 g, 142.9 mmol) was added
portionwise over a period of 30 min to give an opaque solu-
tion. After stirring for 12 h, water (20 mL) was added and
all solvents were removed under reduced pressure. The
resulting brown residue was acidified with 2 M HCl
(250 mL) and washed with Et2O (3 · 150 mL). The aque-
ous solution was made basic with excess NaOH and
extracted with CH2Cl2 (3 · 250 mL). The CH2Cl2was
removed to give a white crystalline material, which was
1
washed with hexanes (28.0 g, 86%). H NMR (CDCl3): d
2.12 (s, 6H, –o-ArCH3), 2.25 (s, 3H, –p-ArCH3), 4.75 (s,
2H, –NimidCH2), 6.80 (s, 2H, –ArH), 7.05 (s, 1H, –imidH),
7.10 (s, 1H, –imidH), 7.60 (s, 1H, –NCHN). 13C NMR
(CDCl3):
d
18.2 (–o-CH3), 20.5 (–p-CH3), 57.0
(–NimidCH2), 123.0 (–imidC), 123.2 (–imidC), 128.5
(–ArC), 130.5 (–ArC), 130.7 (–ArC), 135.1 (–NCN),
140.1 (–ArC), 178.1 (–C(O)). Anal. Calc. for C14H17N3O:
C, 69.11; H, 7.04; N, 17.27. Found: C, 69.00; H, 7.01; N,
17.10%.
4.3. 2,4,6-Me3C6H2NHCH2CH2(imidazole)
2,4,6-Me3C6H2NHCOCH2(imidazole) (13.0 g, 56.8
mmol) and BH3–SMe2 (25.0 mL,125.0 mmol, 5.0 M in
Et2O) were combined in THF (500 mL) and refluxed over-
night. The THF was removed under reduced pressure and
2 M HCl (63 mL, 2.2 equivalents) was added to the white
residue. The solution was made basic with excess NaOH
(8 equivalents) and extracted with CH2Cl2 (3 · 250 mL).
The CH2Cl2was removed, and the clear oil recrystallized
We are currently exploring the potential for the [NCN]
ligand architecture to stabilize other early and late transi-
tion metal centres, with goals that involve small molecule
activation and new catalytic processes.
4. Experimental
1
with boiling hexanes (9.8 g, 80%). H NMR (d6-DMSO):
4.1. General considerations
d 2.03 (s, 6H, –o-ArCH3), 2.15 (s, 3H, –p-ArCH3), 3.19
(t, J = 8 Hz, –NArCH2), 3.68 (t, J = 8 Hz, 1H, –NH),
4.13 (t, J = 8 Hz, –NimidCH2), 6.80 (s, 2H, –ArH), 6.85
(s, 1H, –imidH), 7.20 (s, 1H, –imidH), 7.64 (s, 1H, –NC
HN). 13C NMR (d6-DMSO): d 18.9 (–o-CH3), 22.1 (–p-
CH3), 48.4 (–NArCH2), 48.9 (–NimidCH2), 121.0 (–imidC),
121.6 (–imidC), 126.4 (–ArC), 128.8 (–ArC), 129.0 (–Ar
C), 134.2 (–NCN), 142.1 (–ArC). Anal. Calc. for
C14H19N3: C, 73.33; H, 8.35; N, 18.32. Found: C, 73.05;
H, 8.09; N, 18.15%.
Unless otherwise stated, all manipulations were per-
formed under 1 atm of dry oxygen-free argon or nitrogen
by means of standard Schlenk or glovebox techniques.
Zr(NEt2)4 and Hf(NEt2)4 were purchased from Strem
Chemicals and used as received. All other chemicals were
purchased from Aldrich and used as received. 2,4,6-
Me3C6H2NHC(O)CH2Cl, 2,4,6-Me3C6H2NHCH2CH2Cl,
and (CD3CD2)MgBr were synthesized by the literature
methods [33–35]. Hexanes, toluene, and tetrahydrofuran
were purchased anhydrous from Aldrich, sparged with
nitrogen, and passed through columns containing
activated alumina and Ridox catalyst. Deuterated
solvents were dried according to the literature proce-
4.4. (Mes[NCHN]H2)+Clꢀ (1)
2,4,6-Me3C6H2NHCH2CH2Cl (6.0 g, 30.4 mmol) and
2,4,6-Me3C6H2NHCH2CH2(imidazole) (6.5 g, 30.4 mmol)
were combined and stirred at 150 ꢁC for 2 h. After cooling,
the resulting white solid was washed with THF (50 mL)
and filtered to give a white crystalline powder (11.3 g,
87%). Recrystallization with boiling acetonitrile gave long
1
dures. H and 13C{1H} NMR spectra were recorded on
a
Bruker AVANCE 400 instrument operating at
1
400.0 MHz for H. Elemental analyses, IR spectroscopy,
and mass spectrometry (EI/MS) were performed at the
Department of Chemistry at the University of British
Columbia.
1
colourless crystals. H NMR (d6-DMSO): d 2.01 (s, 12H,
–o-ArCH3), 2.12 (s, 6H, –p-ArCH3), 3.15 (q, J = 8 Hz,

5798
L.P. Spencer, M.D. Fryzuk / Journal of Organometallic Chemistry 690 (2005) 5788–5803
4H, –NArCH2), 3.92 (t, J = 8 Hz, 1H, –NH), 4.40
(t, J = 8 Hz, 4H, –NimidCH2), 6.81 (s, 4H, –ArH), 7.88 (s,
2H, –imidH), 9.35 (s, 1H, –NCHN). 13C NMR (d6-DM
SO): d 17.8 (–o-CH3), 20.2 (–p-CH3), 47.2 (–NArCH2),
49.2 (–NimidCH2), 122.6 (–imidC), 129.0 (–ArC), 130.2
(–ArC), 130.7 (–ArC), 137.2 (–NCHN), 142.4 (–ArC).
Anal. Calc. for C25H35ClN4: C, 70.32; H, 8.26; N, 13.12.
Found: C, 70.15; H, 8.13; N, 13.02%.
Calc. for C29H44HfN6: C, 53.16; H, 6.77; N, 12.83. Found:
C, 52.89; H, 6.44; N, 12.68%.
4.7. Mes[NCN]MCl2 (M = Zr (5), Hf (6))
The following procedure is representative of the synthe-
sis of 5 and 6. Chlorotrimethylsilane (1.03 mL, 8.14 mmol)
was added dropwise to a toluene (20 mL) solution of 4
(533 mg, 0.81 mmol) with vigorous stirring. The white sus-
pension was stirred overnight and collected by filtration to
give a white powder, (495 mg, 95%). 5: 1H NMR (C6D5N):
d 2.24 (s, 6H, –p-ArCH3), 2.28 (s, 12H, –o-ArCH3), 3.79
(m, 2H, –NArCH2), 4.59 (m, 4H, –NimidCH2), 6.86 (s, 4H,
–ArH), 7.26 (s, 2H, –imidH). 13C NMR (C6D5N): d 19.9
(–o-CH3), 24.7 (–p-CH3), 52.3 (–NArCH2), 54.9 (–Nimid
CH2), 127.4 (–imidC), 130.9 (–ArC), 133.6 (–ArC), 134.1
(–ArC), 144.8 (–ArC), 192.3 (–ZrCcarbene). Anal. Calc. for
C25H32Cl2N4Zr: C, 54.53; H, 5.86; N, 10.17. Found: C,
54.36; H, 5.44; N, 10.01%.
4.5. Mes[NCN]H2 (2)
A THF solution of KN(SiMe3)2 (690 mg, 3.5 mmol) was
slowly added dropwise to 1 (1.47 g, 3.5 mmol) suspended in
THF (20 mL). The resulting pale yellow solution was stir-
red for 30 min and the volatiles were removed. The oily
white solid was extracted with toluene (3 · 30 mL) and
the solvent removed to give a white powder (1.4 g,
100%). The powder could be further purified by recrystal-
lization with toluene at ꢀ30 ꢁC to give long colourless nee-
1
6: 1H NMR (C6D5N): d 2.26 (s, 6H, –p-ArCH3), 2.31 (s,
12H, –o-ArCH3), 4.09 (m, 2H, –NArCH2), 4.40 (m, 4H,
–NimidCH2), 6.91 (s, 4H, –ArH), 7.28 (s, 2H, –imidH).
13C NMR (C6D5N): d 20.1 (–o-CH3), 25.7 (–p-CH3), 54.2
(–NArCH2), 56.0 (–NimidCH2), 127.5 (–imidC), 131.2 (–Ar
C), 134.3 (–ArC), 134.8 (–ArC), 145.3 (–ArC), 198.2
(–HfCcarbene). Anal. Calc. for C25H32Cl2HfN4: C, 47.07;
H, 5.06; N, 8.78. Found: C, 46.85; H, 4.86; N, 8.53%.
dles. H NMR (C6D6): d 2.35 (s, 6H, –p-ArCH3), 2.40 (s,
12H, –o-ArCH3), 3.22 (q, J = 8 Hz, 4H, –NArCH2), 3.76
(t, J = 8 Hz, 4H, –NimidCH2), 4.15 (t, J = 8 Hz, 1H,
–NH), 6.30 (s, 2H, –imidH), 6.82 (s, 4H, –ArH). 13C NM
R (C6D6): d 20.0 (–o-CH3), 24.5 (–p-CH3), 48.5 (–NArCH2),
49.1 (–NimidCH2), 121.7 (–imidC), 126.9 (–ArC), 127.5
(–ArC), 130.1 (–ArC), 145.0 (–ArC), 215.0 (–NCN). Anal.
Calc. for C25H34N4: C, 76.88; H, 8.77; N, 14.35. Found: C,
76.54; H, 8.41; N, 14.28%.
4.8. Mes[NCN]M(CH3)2 (M = Zr (7), Hf (8))
4.6. Mes[NCN]M(NMe2)2 (M = Zr (3), Hf (4))
The following procedure is representative of the synthe-
sis of 7 and 8. The hafnium dichloride 6 (200 mg,
0.31 mmol) was dissolved in 5 mL THF and cooled to
ꢀ30 ꢁC, and CH3MgCl (0.62 mmol, 3.0 M in THF) was
added dropwise; the slightly yellow solution was stirred
in the dark for 30 min. The THF was removed under
reduced pressure and to the resulting residue was added a
few drops 1,4-dioxane and toluene (5 mL). The resulting
suspension was filtered through Celite and volatiles were
removed to give a white solid which was recrystallized in
The following procedure is representative of the synthe-
sis of 3 and 4. A cooled (ꢀ30 ꢁC) THF (10 mL) solution of
Hf(NMe2)4 (415 mg, 1.17 mmol) was slowly added drop-
wise to 2 dissolved in THF (20 mL). The mixture was
warmed to room temperature gradually and stirred over-
night. After the solvent was removed in vacuo and toluene
(15 mL) added, the solution was filtered and the solvent
removed to give a pale orange solid, which was recrystal-
lized with Et2O/hexanes at ꢀ30 ꢁC to give a white powder
(662 mg, 85%). 3: 1H NMR (C6D6): d 2.21 (s, 6H, –p-
ArCH3), 2.40 (s, 12H, –o-ArCH3), 2.67 (s, 12H, –NMe2),
3.34 (m, 4H, –NArCH2), 3.61 (m, 4H, –NimidCH2), 6.02
(s, 2H, –imidH), 6.96 (s, 4H, –ArH). 13C NMR (C6D6): d
19.6 (–o-CH3), 23.4 (–p-CH3), 45.6 (–NCH3), 48.8 (–NAr
CH2), 49.2 (–NimidCH2), 122.4 (–imidC), 130.5 (–ArC),
132.3 (–ArC), 132.9 (–ArC), 140.2 (–ArC), 190.9 (–Zr
Ccarbene). Anal. Calc. for C29H44N6Zr: C, 61.33; H, 7.81;
N, 14.80. Found: C, 61.20; H, 7.58; N, 14.45%.
1
toluene; yield (167 mg, 90%). 7: H NMR (C6D6): d 0.33
(s, 6H, –ArCH3), 2.20 (s, 6H, –p-ArCH3), 2.43 (s, 12H,
–o-ArCH3), 3.37 (m, 4H, –NArCH2), 3.45 (m, 4H, –Nimid
CH2), 5.88 (s, 2H, –imidH), 6.98 (s, 4H, –ArH). 13C NM
R (C6D6): d 18.6 (–o-CH3), 20.0 (–p-CH3), 48.4 (–ZrCH3),
51.7 (–NArCH2), 52.3 (–NimidCH2), 118.5 (–imidC), 129.9
(–ArC), 133.3 (–ArC), 135.0 (–ArC), 148.9 (–ArC), 189.8
(–ZrCcarbene). Anal. Calc. for C27H38N4Zr: C, 63.61; H,
7.51; N, 10.99. Found: C, 63.33; H, 7.32; N, 10.75%.
8: 1H NMR (C6D6): d 0.12 (s, 6H, –HfCH3), 2.17 (s, 6H,
–p-ArCH3), 2.49 (s, 12H, –o-ArCH3), 3.40 (m, 4H,
–NArCH2), 3.49 (m, 4H, –NimidCH2), 5.90 (s, 2H, –imidH),
6.99 (s, 4H, –ArH). 13C NMR (C6D6): d 19.6 (–o-CH3),
20.7 (–p-CH3), 52.2 (–NArCH2), 54.1 (–HfCH3), 54.2
(–NimidCH2), 119.5 (–imidC), 129.6 (–ArC), 132.3 (–ArC),
135.3 (–ArC), 152.1 (–ArC), 196.1 (–HfCCarbene). Anal.
1
4: H NMR (C6D6): d 2.19 (s, 6H, –p-ArCH3), 2.39 (s,
12H, –o-ArCH3), 2.70 (s, 12H, –NMe2), 3.36 (m, 4H,
–NArCH2), 3.55 (m, 4H, –NimidCH2), 5.95 (s, 2H, –imidH),
6.91 (s, 4H, –ArH). 13C NMR (C6D6): d 19.7 (–o-CH3),
24.3 (–p-CH3), 44.5 (–NCH3), 49.0 (–NArCH2), 50.1
(–NimidCH2), 122.0 (–imidC), 129.8 (–ArC), 132.8 (–ArC),
133.3 (–ArC), 142.3 (–ArC), 195.7 (–HfCcarbene). Anal.

L.P. Spencer, M.D. Fryzuk / Journal of Organometallic Chemistry 690 (2005) 5788–5803
5799
Calc. for C27H38HfN4: C, 54.31; H, 6.41; N, 9.38. Found:
C, 54.22; H, 6.26; N, 9.16%.
2H, –NArCH2), 3.67 (m, 4H, –NimidCH2), 5.86 (s, 2H,
–imidH), 7.00 (s, 4H, –ArH). 13C NMR (C6D6): d 13.7
(–CH2CH(CH3)2), 19.4 (–o-CH3), 20.5 (–pꢀCH3), 32.3
(–CH2CH(CH3)2), 50.5 (–NArCH2), 52.1 (–NimidCH2),
68.4 (–HfCH2), 118.4 (–imidC), 128.4 (–ArC), 132.1 (–Ar
C), 133.9 (–ArC), 148.4 (–ArC), 194.9 (–HfCCarbene). Anal.
Calc. for C33H50HfN4: C, 58.18; H, 7.40; N, 8.22. Found:
C, 57.91; H, 7.05; N, 8.01%.
4.9. Mes[NCN]M(CH2Ph)2 (M = Zr (9), Hf (10))
The following procedure is representative of the synthe-
sis of 9 and 10. The hafnium dichloride 6 (200 mg,
0.31 mmol) was dissolved in 5 mL THF and cooled to
ꢀ30 ꢁC. PhCH2MgCl (0.62 mmol, 1.0 M in Et2O) was
added dropwise and the slightly yellow solution was stirred
in the dark for 30 min. The THF was removed under
reduced pressure and to the resulting residue was added a
few drops 1,4-dioxane and Et2O (5 mL). The resulting
suspension was filtered through Celite and volatiles were
removed to give a white solid which was recrystallized in
12: 1H NMR (C6D6) d 0.62 (q, J = 8 Hz, 4H, –HfCH2),
1.49 (t, J = 8 Hz, 6H, –CH2CH3), 2.24 (s, 6H, –p-ArCH3),
2.46 (s, 12H, –o-ArCH3), 3.32 (m, 2H, –NArCH2), 3.55 (m,
4H, –NimidCH2), 5.90 (s, 2H, –imidH), 6.70 (s, 4H, –ArH).
13C NMR (C6D6): d 12.8 (–HfCH2CH3), 19.7 (–o-CH3),
20.9 (–p-CH3), 51.4 (–NArCH2), 52.5 (–NimidCH2), 66.1
(–HfCH2CH3), 119.9 (–imidC), 129.6 (–ArC), 131.8
(–ArC), 134.9 (–ArC), 152.9 (–ArC), 196.4 (–HfCCarbene).
Anal. Calc. for C29H42HfN4: C, 55.72; H, 6.77; N, 8.96.
Found: C, 55.24; H, 6.59; N, 8.87%.
1
Et2O; yield (210 mg, 89%). 9: H NMR (C6D6): d 1.92 (s,
4H, –ZrCH2), 2.24 (s, 6H, –p-ArCH3), 2.31 (s, 12H,
–o-ArCH3), 3.03 (m, 4H, –NArCH2), 3.56 (m, 4H,
–NimidCH2), 5.77 (s, 2H, –imidH), 6.84 (d, J = 8 Hz, 4H,
–o-CH2Ph), 6.92 (t, J = 8 Hz, 2H, –p-CH2Ph), 6.98 (s,
4H, –ArH), 7.17 (t, J = 8 Hz, 4H, –m-CH2Ph). 13C NMR
(C6D6): d 20.2 (–o-CH3), 24.3 (–p-CH3), 49.3 (–NArCH2),
52.7 (–NimidCH2), 65.6 (–ZrCH2), 121.6 (–imidC), 122.4
(–Ar C), 130.3 (–ArC), 131.5 (–ArC), 136.6 (–ArC), 148.4
(–ArC), 156.3 (–ArC), 190.1 (–ZrCCarbene). Some aromatic
resonances obscured by C6D6 solvent. Anal. Calc. for
C39H46N4Zr: C, 70.75; H, 7.00; N, 8.46. Found: C, 70.43;
H, 6.92; N, 8.35%.
d10-12: 1H and 13C NMR spectra identical to 12 with the
absence of –HfCH2CH3 resonances.
4.11. Decomposition of Mes[NCN]Hf(CH2CH3)2 to form
13 and d4-13
d10-12 (110 mg, 0.18 mmol) was dissolved in Et2O and
the pale yellow solution was stirred for 5 days. The Et2O
was removed under reduced pressure and hexanes added
to precipitate a dark orange powder (99 mg, 95%). 1H
1
10: H NMR (C6D6): d 1.85 (s, 4H, –HfCH2), 2.26 (s,
NMR (C6D6):
d
ꢀ0.10 (dq, J = 5.3, 8 Hz, 1H,
6H, –p-ArCH3), 2.36 (s, 12H, –o-ArCH3), 3.04 (m, 4H,
–NArCH2), 3.46 (m, 4H, –NimidCH2), 5.73 (s, 2H, –imidH),
6.82 (d, J = 8 Hz, 4H, –o-CH2Ph), 6.90 (t, J = 8 Hz, 2H,
–p-CH2Ph), 7.02 (s, 4H, –ArH), 7.18 (t, J = 8 Hz, 4H,
–m-CH2Ph). 13C NMR (C6D6): d 21.2 (–o-CH3), 22.1 (–p-
CH3), 50.0 (–NArCH2), 51.4 (–NimidCH2), 73.5 (–HfCH2),
121.3 (–ArC), 122.9 (–imidC), 129.6 (–ArC), 130.9
(–ArC), 135.5 (–ArC), 147.9 (–ArC), 155.6 (–ArC), 196.5
(–HfCCarbene). Some aromatic resonances obscured by
C6D6 resonances. Anal. Calc. for C39H46HfN4: C, 62.51;
H, 6.19; N, 7.48. Found: C, 62.42; H, 6.14; N, 7.42%.
–HfCH2CH3), 0.010 (dq, J = 5.3, 8 Hz, 1H, –HfCH2CH3),
1.00 (d, J = 12Hz, 1H, –HfCH2Ar), 1.01 (t, J = 8 Hz, 3H,
–HfCH2CH3), 2.23 (s, 3H, –CH3), 2.25 (s, 3H, –CH3), 2.37
(s, 3H, –CH3), 2.47 (s, 3H, –CH3), 2.51 (d, J = 12Hz, 1H, –
HfCH2Ar), 2.58 (s, 3H, –CH3), 3.19 (m, 3H, –NCH2), 3.22
(m, 3H, –NCH2), 3.27–3.31 (m, 3H, –NCH2), 3.47 (m, 3H,
–NCH2), 3.62 (m, 3H, –NCH2), 3.93 (m, 3H, –NCH2), 4.16
(m, 3H, –NCH2), 5.89 (d, J=2Hz, 1H, –imidH), 5.92 (d,
J = 2Hz, 1H, –imidH), 6.77 (s, 1H, –ArH), 6.97 (s, 1H,
–ArH), 7.04 (s, 2H, –Ar H). 13C NMR (C6D6): d 9.7
(–HfCH2CH3), 19.1 (–ArCH3), 19.3 (–ArCH3), 21.1
(–ArCH3), 21.3 (–ArCH3), 52.1 (–N CH2), 53.8 (–NCH2),
55.2 (–NCH2), 55.3 (–NCH2), 58.2 (–HfCH2CH3), 72.9
(–HfCH2Ar), 119.5 (–imidC), 129.3 (–ArC), 129.9 (–ArC),
135.0 (–ArC), 138.5 (–ArC), 138.6 (–ArC), 142.9 (–ArC),
145.6 (–ArC), 197.3 (–HfCCarbene). Some aromatic reso-
nances obscured by C6D6 solvent. Anal. Calc. for
C27H36HfN4: C, 54.49; H, 6.10; N, 9.41. Found: C, 54.13;
H, 5.86; N, 9.12%.
4.10. Mes[NCN]Hf(R)2 (R = CH2CHMe2 (11);
R = CH2CH3 (12); R = CD2CD3 d10-12)
The following procedure is representative of the synthe-
sis of 11 and 12. The hafnium dichloride 6 was dissolved in
5 mL THF and cooled to ꢀ30 ꢁC. The Grignard reagent (2
equivalents) was added dropwise and the slightly yellow
solution was stirred in the dark for 30 min. The THF was
removed under reduced pressure and to the resulting
residue was added a few drops 1,4-dioxane and Et2O
(5 mL). The resulting suspension was filtered through Cel-
ite and volatiles were removed to give a white solid, which
d4-13: 1H and 13C NMR spectra identical to 13 with the
absence of –HfCH2CH3 resonances, except for a broad-
ened singlet at d 0.9 in the 1H NMR spectrum for
HfCD2CD2H.
1
was recrystallized with Et2O. 11: H NMR (C6D6): d 0.68
4.12. Mes[NCN]Hf(g2-XyNCCH3)(CH3) (14)
(d, J = 8 Hz, 4H, –HfCH2), 1.02 (d, J = 8 Hz, 12H,
–CH(CH3)2), 2.24 (s, 6H, –p-ArCH3), 2.35 (n, J = 8 Hz,
2H, –CH2CH(CH3)2), 2.46 (s, 12H, –o-ArCH3), 3.23 (m,
To a cooled toluene (5 mL) solution of 8 (200 mg,
0.33 mmol) was added a cooled toluene (2 mL) solution

5800
L.P. Spencer, M.D. Fryzuk / Journal of Organometallic Chemistry 690 (2005) 5788–5803
of xylyl isocyanide (44 mg, 0.33 mmol). The pale yellow
solution was allowed to gradually warm to room tempera-
ture and stirred overnight. The solvent was removed and
suspended in cold (ꢀ30 ꢁC) hexanes. The solid was filtered
and washed with cold hexanes to give a white powder. The
solid was further recrystallized with Et2O at ꢀ30 ꢁC
(183 mg, 74%). 14: 1H NMR (C6D6): d 0.17 (s, 3H,
–HfCH3), 1.61 (s, 6H, –xylylCH3), 1.63 (s, 3H, –CCH3),
2.21 (s, 6H, –p-ArMes–CH3), 2.39 (s, 6H, –o-ArMes–CH3),
2.48 (s, 6H, –o-ArMes CH3), 3.08 (m, 2H, –NArCH2), 3.18
(m, 2H, –NArCH2), 3.81 (m, 2H, –NimidCH2), 4.07 (m,
2H, –NimidCH2), 6.06 (s, 2H, –imidH), 6.82–6.92 (m, 7H,
–ArH). 13C NMR (C6D6): d 18.2 (–ArCH3), 19.7 (–Ar
CH3), 19.8 (–ArCH3), 20.5 (–ArCH3), 22.4 (–ArCH3),
34.2 (–HfCH3), 52.2 (–NArCH2), 56.9 (–NimidCH2), 118.7
(–imidC), 124.3 (–ArC), 128.8 (–ArC), 129.2 (–ArC),
129.6 (–ArC), 131.1 (–ArC), 134.4 (–ArC), 134.6 (–ArC),
147.2 (–ArC), 154.8 (–ArC), 197.5 (–HfCcarbene), 259.0
(–HfCiminoacyl). IR(nujol): m(C@N) 1575 cmꢀ1. Anal. Calc.
for C36H47N5Hf: C, 59.37; H, 6.50; N, 9.62. Found: C,
59.23; H, 6.33; N, 9.46%.
2H, –NArCH2), 3.47 (sept, J = 7 Hz, 2H, –CH(CH3)2),
3.55 (m, 2H, –NArCH2), 3.67 (m, 2H, –NimidCH2), 4.01
(m, 2H, –NimidCH2), 6.07 (s, 2H, –imidH), 6.93–7.07 (m,
13H, –ArH). 13C NMR (C6D6): d 20.4 (–ArCH3), 20.9
(–ArCH3), 21.1 (–CCH3) 23.2, 48.8 (–NCH), 53.3
(–NArCH2), 56.4 (–NimidCH2), 119.4 (–imidC), 128.7
(–ArC), 129.8 (–ArC), 135.3 (–ArC), 157.6 (–ArC), 194.5
(–HfCcarbene) 266.2 (–HfCimnoacyl). IR(nujol): m(C@N)
1562 cmꢀ1. Anal. Calc. for C35H52HfN6: C, 57.17; H,
7.13; N, 11.43. Found: C, 56.89; H, 7.00; N, 11.26%.
4.14. Mes[NCN]Hf(g2-XyNCCH3)(g2-iPrNCCH3) (17)
To a toluene (2 mL) solution of 14 (100 mg, 0.14 mmol)
was added
a
toluene (2 mL) solution of iPrNC
(10 mg, mmol). No observable colour change was noted.
The solution was stirred for 1 h, whereupon the solvent
was removed quickly and Et2O (2 mL) added to precipitate
a white solid, which was washed with hexanes and dried in
vacuo (96 mg, 86%). 1H NMR (C6D6): d 0.97 (d, J = 7 Hz,
6H, –CH(CH3)2), 1.23 (s, 3H, g2-iPrNCCH3), 1.91 (s, 6H,
–xylylCH3), 2.26 (s, 6H, –p-ArMes–CH3), 2.38 (s, 6H,
–o-ArMes–CH3), 2.39 (s, 6H, –o-ArMes–CH3), 2.47 (s, 3H,
–g2-XyNCCH3), 3.10 (m, 2H, –NArCH2), 3.43 (m, 2H,
–NArCH2), 3.56 (sept, J = 7 Hz, 1H, –CH(CH3)2), 3.69
(m, 2H, –NimidCH2), 3.88 (m, 2H, –NimidCH2), 6.01 (s,
2H, –imidH), 6.89 (s, 2H, –ArMesH), 6.95 (s, 2H, –ArMesH),
6.97–7.04 (m, 3H, –ArxylylH). 13C NMR (C6D6): d 18.5
(–CCH3), 18.7 (–CCH3), 20.3 (–CH(CH3)2), 20.7 (–Ar
CH3), 20.9 (–ArCH3), 26.0 (–ArCH3), 50.3 (–NCH), 52.6
(–NArCH2), 56.5 (–NimidCH2), 118.7 (–imidC), 124.3
(–Ar C), 128.9 (–ArC), 129.4 (–ArC), 130.2 (–ArC), 134.7
(–ArC), 135.8 (–ArC), 148.9 (–ArC), 157.4 (–ArC), 195.1
(–HfCcarbene), 262.4 (–HfCiminoacyl), 264.1 (–HfCiminoacyl).
IR(nujol): m(C@N) 1558, 1570 cmꢀ1. Anal. Calc. for
C40H54HfN6: C, 60.25; H, 6.83; N, 10.54. Found: C,
60.01; H, 6.82; N, 10.36%.
NOESY NMR data (C6D6): d (1H, 1H) the Hf–CH3 res-
onance at d 0.17 correlated with the xylyl-CH3 at d 1.61.
4.13. Mes[NCN]Hf(g2-RNCCH3)2 (R = Xy (15); R = iPr
(16))
The following procedure is representative of the synthe-
sis of 15 and 16. To a toluene (2 mL) solution of 8 (200 mg,
0.33 mmol) was added a toluene (2 mL) solution of xylyl
isocyanide (92 mg, 0.70 mmol). The pale yellow solution
gradually turned dark purple (or orange in the case of
17) and was stirred overnight, whereupon the solvent was
removed quickly and Et2O (2 mL) added to precipitate a
white solid. Cooling of the solution, followed by filtration
yielded colourless microcrystals (260 mg, 92%). 16: 1H
NMR (CD2Cl2, 298 K): d 1.45 (br s, 18H, –CCH3 and
–ArXyC H3), 1.85 (br s, 12H, –o-ArMesCH3), 2.14 (br s, 6H,
–p-ArMesCH3), 4.2 (br s, 8H, –NCH2), 6.60 (br s, 4H,
–ArMesH), 6.80–6.85(brs,6H, –ArXyH),6.90(s, 2H, –imidH).
1H NMR (CD2Cl2, 233 K): d 1.21 (s, 3H, –CCH3), 1.27 (s, 6H,
—ArXyCH3), 1.57 (s, 6H, —ArXyCH3), 1.78 (s, 6H, –o-
ArMesCH3), 1.85 (s, 6H, –o-ArMesCH3), 2.10 (s, 6H, –p-
ArMesCH3), 2.24 (s, 3H, –CCH3), 2.80 (m, 2H, –NCH2),
3.98 (m, 4H, –NCH2), 4.27 (m, 1H, –NCH2), 6.56 (s, 2H,
–ArMesH), 6.64 (s, 2H, –ArMesH), 6.81 (m, 1H, –ArXyH),
6.85 (m, 2H, –ArXyH), 6.90 (s, 2H, –imidH). 13C NMR
(C6D6, 298 K): d 18.5 (–ArCH3), 20.4 (–ArCH3), 20.8
(–ArCH3), 23.6 (–ArCH3), 52.7 (–NArCH2), 57.9
(–NimidCH2), 118.5 (–imidC), 124.7 (–ArC), 125.6 (–ArC),
129.1 (–ArC), 129.9 (–ArC), 130.3 (–ArC), 135.1 (–ArC),
156.5 (–ArC), 196.5 (–HfCcarbene). IR(nujol): m(C@N)
1568 cmꢀ1. Anal. Calc. for C45H56HfN6: C, 62.89; H,
6.57; N, 9.78. Found: C, 62.54; H, 6.19; N, 9.62%.
4.15. Mes[NCN]Hf(OC(CH3)@C(CH3)NXy) (18)
A toluene (10 mL) solution of 14 (102 mg, 0.14 mmol)
was freeze–pumped–thawed with 1 atm CO several times
and left to stand for 1 day. The solvent was removed in va-
cuo and the yellow powder was washed with hexane
(5 mL). The yellow solid was recrystallized from Et2O at
ꢀ30 ꢁC to give crystals suitable for X-ray diffraction
(88 mg, 83%). 1H NMR (C6D6, 298 K): d 1.37 (s, 3H,
–NCCH3), 1.59 (s, 3H, –OCCH3), 2.21 (s, 6H,), 2.37 (s,
6H,), 3.01 (m, 4H, –NArCH2), 3.51 (m, 2H, –NimidCH2),
3.77 (m, 2H, –NimidCH2), 5.81 (s, 2H, –imidH), 6.90–6.96
(m, 5H, –ArH), 7.07–7.09 (m, 2H, –ArH). 1H NMR
(CD3C6D5, 223 K): d 1.31 (s, 3H, –NCCH3), 1.60 (s, 3H,
–OCCH3), 1.98 (s, 6H, –ArCH3), 2.24 (s, 6H, –ArCH3),
2.38 (s, 6H, –ArCH3), 2.69 (s, 6H, –ArCH3), 2.94 (m,
4H, –NCH2), 3.47 (m, 2H, –NCH2), 3.73 (m, 2H,
–NCH2), 5.74 (s, 2H, –imidH), 6.81 (s, 2H, –ArMesH),
1
17: H NMR (C6D6): d 0.88 (d, J = 7 Hz, 12H, –CH
(CH3)2), 1.32 (s, 6H, g2-iPrNCCH3), 2.25 (s, 12H,
–o-ArMes–CH3), 2.31 (s, 6H, –p-ArMes–CH3), 3.28 (m,

L.P. Spencer, M.D. Fryzuk / Journal of Organometallic Chemistry 690 (2005) 5788–5803
5801
6.99 (m, 3H, –ArxyH), 7.08 (s, 2H, –ArMesH). 13C NMR
(C6D6, 298 K): d 15.2 (–NCCH3), 17.4 (–ArCH3), 19.0
(-OCCH3), 19.4 (–ArCH3), 20.9 (–ArCH3), 52.9 (–NAr
CH2), 57.3 (–NimidCH2), 116.2 (–CN), 118.7 (–imidC),
123.1 (–ArC), 129.6 (–ArC), 131.5 (–ArC), 133.0 (–ArC),
136.0 (–ArC), 137.0 (–CO), 147.9 (–ArC), 149.6
(–ArC), 196.7 (–HfCcarbene). Anal. Calc. for C37H47HfN5O:
C, 58.76; H, 6.26; N, 9.26. Found: C, 58.29; H, 6.05; N,
9.33%.
4.18. In situ generation of Mes[NCN]Hf(g2-CO(iBu))(iBu)
(21 and 13C-21)
A C6D6 solution of 12 was freeze–pumped–thawed three
1
times with CO. The reaction was followed by H NMR
spectroscopy and upon complete conversion to the monoa-
cyl complex, a 13C NMR spectroscopy experiment was
performed. 1H NMR (C6D6): d 0.66 (d, J = 7 Hz, 6H,
–CH(CH3)2), 1.06 (d, J = 7 Hz, 2H, –HfCH2), 1.40 (d,
J = 7 Hz, 6H, –C(O)CH(CH3)2), 1.68 (d, J = 7 Hz, 2H, –
HfC(O)CH2), 1.80 (sept, J = 7 Hz, 1H, –CH(CH3)2), 2.18
(–ArCH3), 2.34 (–ArCH3), 2.38 (–ArCH3), 2.75 (sept,
J = 7 Hz, 1H, –C(O)CH(CH3)2), 3.07 (m, 2H, –NCH),
3.28 (m, 2H, –NCH), 3.51 (m, 2H, –NCH), 4.00 (m, 2H,
–NCH), 6.01 (s, 2H, –imidH), 6.78 (s, 2H, –ArH), 6.85
(s, 2H, –ArH). 13C NMR (C6D6): d 19.8 (–ArCH3), 20.0
(–ArCH3), 21.2 (–ArCH3), 32.3 (–HfC(O)CH2), 36.4 (–Hf
CH2), 54.2 (–NArCH2), 55.6 (–NimidCH2), 118.4 (–imidC),
128.4 (–ArC), 128.6 (–ArC), 129.2 (–ArC), 130.4 (–ArC),
131.2 (–ArC), 132.4 (–ArC), 149.8 (–ArC), 153.2 (–ArC),
196.1 (–HfCcarbene), 338.4 (–HfCacyl).
4.16. Mes[NCN]Hf(g2-C(O)CH3)(CH3) (19) and
(13C-19)
The product was identified in situ by NMR and IR spec-
troscopy. A C6D6 solution of 8 was freeze–pumped–thawed
three times with CO, and the solution left at 1 atm. The
solution was left to stand for 6 h and the solvent removed
in vacuo to yield a pale yellow solid. The product was
1
contaminated with ꢂ5% 8. H NMR (C6D6): d 0.56 (s,
3H, –HfCH3), 1.62 (s, 3H, –HfC(O)CH3), 2.11 (s, 6H, –p-
ArCH3), 2.34 (s, 6H, –o-ArCH3), 2.44 (s, 6H, –o-ArCH3),
2.92 (m, 2H, –CH2), 3.20 (m, 2H, –CH2), 3.65 (m, 2H,
–CH2), 3.96 (m, 2H, –CH2), 6.01 (s, 2H, –imidH), 6.76 (s,
2H, –ArH), 6.86 (s, 2H, –ArH). 13C NMR (C6D6): d 19.7
(–ArCH3), 19.8 (–ArCH3), 20.8 (–ArCH3), 31.1 (–Hf
C(O)CH3), 34.7 (–HfCH2), 53.7 (–NArCH2), 55.9 (–Nimid
CH2), 119.1 (–imidC), 128.8 (–ArC), 129.5 (–ArC), 130.0
(–ArC), 132.1 (–ArC), 134.9 (–ArC), 135.5 (–ArC), 151.5
(–ArC), 153.0 (–ArC), 195.6 (–HfCcarbene), 339.6 (–Hf
1
13C-21: H NMR resonances are identical except d 1.68
(dd, J = 4.7 Hz, 2H, –Hf13C(O)CH2).
4.19. In situ generation of Mes[NCN]Hf(OC(iBu)@C(iBu)-
O) (22 and 13C-22)
The same procedure was followed as described in the
synthesis of 21; however, the reaction was further moni-
1
tored by H NMR spectroscopy after conversion to the
Cacyl). m(C@O) 1540 cmꢀ1
.
monoacyl complex. Within 1 day, the presence of 23 (see
1
13C-19: H and 13C NMR spectra identical to 19 except
1
below) could be observed. H NMR (C6D6): d 1.06 (d,
1.62 (d, J = 7 Hz, 3H, –HfC(O)CH3).
J = 8 Hz, 12H, –CH(CH3)2), 1.99 (n, J = 8 Hz, 2H,
–CH2CH(CH3)2), 2.02 (d, J = 8 Hz, 4H, –OCCH2), 2.22
(s, 6H, –p-ArCH3), 2.40 (s, 12H, –o-ArCH3), 3.41(m, 4H,
–NCH2), 3.61 (m, 4H, –NCH2), 5.89 (s, 2H, –imidH),
6.92 (s, 4H, –ArH). 13C NMR (C6D6): d 15.5 (–CH(CH3)2),
19.0 (–o-CH3), 21.2 (–p-CH3), 33.8 (–CH(CH3)2), 38.3 (–C
CH2), 49.4 (–NArCH2), 52.1 (–NimidCH2), 120.4 (–imidC),
129.2 (–ArC), 132.1 (–ArC), 134.3 (–ArC), 140.6 (–C@C),
153.5 (–ArC), 198.5 (–HfCcarbene).
4.17. Mes[NCN]Hf(OCH@CH2)(CH3) (20) and (13C-20)
A benzene solution of 8(250 mg, 0.42 mmol) was freeze–
pumped–thawed three times with CO, and the solution left
to stir under 1 atm for three days. The solvent was removed
and the residue recrystallized with Et2O/hexanes at –30 ꢁC
1
13C-22: 13C NMR resonances are identical except d
140.6 (d, J = 30 Hz, –C@C).
(162 mg, 62%). H NMR (C6D6): d 0.37 (s, 3H, –HfCH3),
2.21 (s, 6H, –p-ArCH3), 2.34 (s, 6H, –o-ArCH3), 2.62 (s,
6H, –o-ArCH3), 2.92 (m, 2H, –NArCH2), 3.15 (m, 2H,
–NArCH2), 3.47 (d, J = 14Hz, –CH), 3.54 (d, J = 6Hz,
–CH), 3.74 (m, 2H, –NimidCH2), 3.96 (m, 2H, –NimidCH2),
5.75 (dd, J = 6,14 Hz, 1H, –CH), 5.94 (s, 2H, –imidH), 6.95
(s, 2H, –ArH), 7.01 (s, 2H, –ArH).
4.20. Isolation of (Mes[NCN]Hf)2(OC(iBu)@C(iBu)O)2
(23 and 13C-23)
A benzene solution of 12 (115 mg, 0.17 mmol) was
freeze–pumped–thawed three times with CO, and the solu-
tion left to stand under 1 atm CO for five days. Colourless
crystalline material began to precipitate after three days.
The solution was filtered and the crystalline material was
13C NMR (C6D6): d19.5 (–o-CH3), 20.9 (–p-CH3), 38.4
(–HfCH3), 52.1 (–NArCH2), 55.1 (–NimidCH2), 117.4 (–imid
C), 120.2 (–HfOCH=CH2), 129.4 (–ArC), 130.4 (–ArC),
133.7 (–ArC), 139.0 (–HfOCH@CH2), 145.3 (–ArC),
196.2 (–HfCcarbene).
1
washed with pentane (82 mg, 66%). H NMR (C6D6): d
Anal. Calc. for C28H38HfN4O: C, 53.80; H, 6.13; N,
8.96. Found: C, 53.53; H, 5.89; N, 8.61%.
0.79 (d, J = 8 Hz, 6H, –CH(CH3)2), 0.87 (d, J = 8 Hz,
6H, –CH(CH3)2), 1.09 (m, 2H, –CCH2CH), 1.51 (m, 2H,
–CCH2CH), 2.21 (s, 6H, –ArCH3), 2.33 (s, 6H, –ArCH3),
2.74 (s, 6H, –ArCH3), 3.40 (m, 4H, –NCH2), 3.55 (m,
1
13C-20. H NMR resonances are identical except d 5.75
(ddd, J = 6, 14, 145 Hz, 2H, –HfO13CH@CH2).

5802
L.P. Spencer, M.D. Fryzuk / Journal of Organometallic Chemistry 690 (2005) 5788–5803
2H, –NCH2), 4.16 (m, 2H, –NCH2), 6.01 (s, 2H, –imidH),
6.96 (s, 2H, –ArH), 7.05 (s, 2H, –ArH) (multiplet from –
CH2CH(CH3)2 obscured by aryl resonances). 13C NMR
(C6D6): d 14.6 (–CH(CH3)2), 14.8 (–CH(CH3)2), 19.6
(–ArCH3), 19.7 (–ArCH3), 20.4 (–ArCH3), 34.3 (–CH
(CH3)2), 34.6 (–CH(CH3)2), 39.4 (–CCH2), 39.6 (–CCH2),
51.3 (–NArCH2), 54.4 (–NimidCH2), 119.8 (–imidC), 130.4
(–ArC), 131.6 (–ArC), 131.8 (–ArC), 133.4 (–ArC), 134.1
(–ArC), 140.0 (–C@C), 149.4 (–ArC), 153.2 (–ArC), 195.4
(–HfCcarbene).
ene (5 mL) solution of [Ph3C][B(C6F5)4] was syringed into
the flask. The orange solution was stirred for 5 min under
ethylene. A toluene (5 mL) solution of the catalyst was
quickly added and the opaque solution stirred for 15 min.
The experiment was stopped by venting the ethylene and
quenching the reaction with 10% methanolic HCl. The
resulting polyethylene was filtered and washed with 10%
methanolic HCl and methanol and air-dried overnight.
(b) 1-Hexene polymerization: The cation was generated
in chlorobenzene by the method described in 24, and 1-
hexene added immediately (ꢂ500 equivalents). The solu-
tion was stirred for 1 h and quenched with 10% methanolic
HCl. The solvents were removed, the residue dissolved in
pentane, and filtered through silica gel. The solvents were
removed in vacuo to yield a minor amount of a viscous gel.
13C-23: 13C NMR resonances are identical except d
140.0 (d, J = 30 Hz, –C@C).
Anal. Calc. for C70H100Hf2N8O4: C, 57.02; H, 6.84; N,
7.60. Found: C, 56,72; H, 6.59; N, 7.43%.
4.21. [Mes[NCN]M(CH3)][B(C6F5)4] (M = Zr (24), Hf
(25))
Acknowledgements
The following procedure is representative of the synthe-
sis of 24 and 25. To a cooled solution of 7 (35 mg,
0.069 mmol) in CD2Cl2 (0.5 mL) was added a cooled
CD2Cl2 (0.5 mL) solution of [Ph3C][B(C6F5)4] (64 mg,
0.069 mmol). The pale orange solution was immediately
transferred to an NMR tube and then frozen in liquid
N2. The NMR was taken immediately after warming the
solution to ꢀ10 ꢁC. 24: 1H NMR (CD2Cl2): d 0.50 (s,
3H, –ZrCH3), 2.10 (br s, 12H, –o-ArCH3), 2.15 (s, 6H,
–p-ArCH3), 3.45 (m, 2H, –NArCH2), 3.94 (m, 2H, –NAr
CH2), 4.14 (m, 2H, –NimidCH2), 4.29 (m, 2H, –NimidCH2),
The authors thank NSERC of Canada for funding (Dis-
covery Grant to M.D.F. and an NSERC PGS-B Scholar-
ship to L.P.S.). We also thank Mr. Jonah Chang for help
with compound preparation.
Appendix A. Supplementary data
Complete experimental details, information on X-ray
data collection and processing for 12, 14, 15, 17, and 22,
and X-ray crystallographic data for 12, 14, 15, 17, and 22
(CIF). Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/
j.jorganchem.2005.07.121.
1
6.85 (br s, 4H, –ArH), 7.04 (s, 2H, –imidH). 25: H NMR
(CD2Cl2): d 0.26 (s, 3H, –HfCH3), 2.15 (br s, 12H, –o-
ArCH3), 2.20 (s, 6H, –p-ArCH3), 3.70 (m, 2H, –NArCH2),
4.05 (m, 2H, –NArCH2), 4.28 (m, 2H, –NimidCH2), 4.60 (m,
2H, –NimidCH2), 6.99 (br s, 4H, –ArH), 7.15 (s, 2H, –imid
H).
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