Coordination and reactivity study of titanium and zirconium complexes of the first imidazol-2-imine ethenolate ligand

Article abstract of DOI:10.1021/om4004708

The synthesis and structural characterization of group 4 transition metal complexes bearing a novel imidazol-2-imine enolate ligand with different electronic properties are reported. X-ray crystallographic studies of a cyclopentadienyl zirconium complex confirmed the coordination motif of the ligand through the imine nitrogen and ethenolate oxygen atoms, yielding a new class of formally four-electron-donor monoanionic bidentate ligands. The activities of the corresponding titanium(IV) and zirconium(IV) complexes in ethylene polymerization were assessed, resulting in activities up to 170 kg PE mol^-1 h^-1.

Full text of DOI:10.1021/om4004708

Article
pubs.acs.org/Organometallics
Coordination and Reactivity Study of Titanium and Zirconium
Complexes of the First Imidazol-2-imine Ethenolate Ligand
Timothy G. Larocque, Sarim Dastgir,† and Gino G. Lavoie*
Department of Chemistry, York University, 4700 Keele Street, Toronto, Ontario, M3J 1P3, Canada
S
* Supporting Information
ABSTRACT: The synthesis and structural characterization of
group 4 transition metal complexes bearing a novel imidazol-2-
imine enolate ligand with different electronic properties are
reported. X-ray crystallographic studies of a cyclopentadienyl
zirconium complex confirmed the coordination motif of the
ligand through the imine nitrogen and ethenolate oxygen
atoms, yielding a new class of formally four-electron-donor
monoanionic bidentate ligands. The activities of the
corresponding titanium(IV) and zirconium(IV) complexes in
ethylene polymerization were assessed, resulting in activities up to 170 kg PE mol−1 h−1.
INTRODUCTION
■
N-Heterocyclic carbenes (NHC) have played a dominant role
as ligands in transition metal chemistry since their first isolation
by Arduengo in 1991.1 The strong σ-donating capability of
NHCs results in the formation of strong metal bonds, which
enhance the thermal stability of complexes.2 This has been a
key contributor to their widespread use as ancillary ligands in
transition metal catalysts.3 More recently, the reactivity of
Figure 2. Neutral (A) and anionic (B) bidentate ligands with an
imidazol-2-imine fragment.
NHCs toward azides has been explored, generating a new class
of anionic imidazol-2-iminate ligands that are analogous to
phenoxides.4−7 Because of the stability of imidazolium salts,
these imidazol-2-iminates can exist in different mesomeric
forms with unexpectedly high electron density located on the
exocyclic nitrogen (Figure 1). Several groups have recently
recently reported the related anionic ureate and thioureate
ligands (B, Figure 2).11
Other bidentate monoanionic systems, and most notably the
substituted salicylaldiminate ligands, have proven to be
extremely versatile and have led to highly active olefin
polymerization catalyst precursors based on both early and
late transition metals. Studied by Fujita12 and Grubbs,13 these
salicylaldiminate ligands coordinate to the metal through the
neutral imine nitrogen and anionic oxygen atoms (Figure 3).
While the new anionic ureate and thioureate ligands B
coordinated to both early and late transition metals in a
bidentate fashion, thereby successfully addressing the short-
comings of the first-generation neutral ligand system A, both
Figure 1. Mesomeric structures of substituted imidazole-2-iminate.
explored the possibility to utilize imidazol-2-iminates either as
ancillary monodentate monoanionic ligands4−7 or as neutral
fragments incorporated in more complex bidentate and
tridentate ligand scaffolds.6,8
∧
the desired Np‑tolyl Nimidazol‑2‑ylidene and the undesired Np‑tolyl∧E
Our group has reported the synthesis of neutral imine
imidazol-2-imine ligands (A, Figure 2) and their coordination
to titanium(IV) and palladium(II).9,10 The structural character-
ization of these complexes showed two different binding modes
depending on the metal center.9 While the ligand coordinates
to Ti(IV) in the expected N∧N chelate, the use of Pd(II) led to
the formation of a dimeric structure with monodentate
coordination of the ligand to the metal through the terminal
imine nitrogen. To enforce coordination of the ligand in a
bidentate fashion to both early and late transition metals, we
Figure 3. Early and late transition metal complexes of the
salicylaldiminate ligand system.
Received: May 25, 2013
© XXXX American Chemical Society
A
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(E = O, S) chelates, with an uncoordinated imidazol-2-imine
fragment, were observed. Inspired by the salicylaldiminate
system, we decided to design a new ligand scaffold that could
bind to the metal center in a bidentate fashion exclusively
through a neutral imine nitrogen donor and an anionic oxygen
donor. As such, the new ligand scaffold combines an imidazol-
2-imine fragment, as the neutral nitrogen donor, and an
enolate, as the anionic oxygen donor. The synthesis of these
new substituted N∧O ligands, their coordination to group 4
metals, and the potential of the resulting complexes as ethylene
polymerization catalysts are reported.
carbon atom resonating at δ 54.5. Further deprotonation of the
tautomeric mixture 2a with an additional equivalent of
NaHMDS gave 3a, as a single product, in 87% yield (Scheme
2). The proton on the α-carbon atom resonates downfield at δ
6.21 (C6D6), with the carbon nucleus observed in the expected
vinyl region of the spectrum at δ 103.8.
The sodium ethenolate salt 3a could also be prepared
directly by addition of two equivalents of base to 1a and used
with no further purification in the preparation of titanium and
zirconium complexes. Thus, addition of two equivalents of
NaHMDS at −40 °C to a THF suspension of compound 1a,
with subsequent warming to room temperature, resulted in an
intense yellow solution of 3a. Without further purification, the
sodium ethenolate solution was added to a THF solution of
ZrCl4(THF)2 in a 2:1 stoichiometric ratio, resulting in the
immediate precipitation of the desired bis(imine ethenolate)
zirconium dichloride complex 4a as a yellow solid in moderate
yield (60%) (Scheme 3). Similarly, the para-chloro derivative
4b could also be prepared from 1b, albeit in slightly lower yield
(42%). Attempts to synthesize the p-nitrophenyl analogue from
1c resulted in a mixture of reaction products that could not be
successfully isolated.
RESULTS AND DISCUSSION
■
The ketone imidazol-2-imine ligand precursors 1a−c were
prepared in good yield (75−89%) by refluxing a toluene
solution of 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-imine4
with the corresponding 2-halo-1-arylethanone for 12 h
(Scheme 1). Solution NMR spectra for compounds 1a−c are
Scheme 1. Synthesis of 2-(1,3-Bis(2,4,6-
trimethylphenyl)imidazol-2-imino)-1-arylethanone
Hydrochloride (1a−c)
Compounds 4a and 4b were characterized by NMR
spectroscopy and combustion analysis. The 1H NMR spectrum
(CDCl3) of 4a contained only one set of resonances, indicating
the selective generation of a single isomer with two sets of
ligands that are magnetically equivalent. As expected, the NMR
spectrum of 4a no longer displays the distinctive triplet at δ
7.99 corresponding to the imine proton of 1a. A singlet
observed at δ 5.91 for the vinylic protons of the ligand,
integrating to two protons (one proton for each set of ligands),
is consistent with double deprotonation of 1a and coordination
to zirconium. The azole ring backbone protons resonate at δ
6.59 as a singlet integrating to four protons (two protons for
each set of ligands). As observed for compound 4a, the 1H and
13C NMR spectra of 4b show only one set of resonances for the
enolate ligands, indicating the generation of a single
coordination isomer. Although the structure of neither 4a nor
4b could be confirmed by X-ray diffraction studies, based on
zirconium work using ureate and thioureate ligands11 and
substituted salicylaldiminate ligands,14−16 we would expect the
chloride atoms to adopt a cis conformation, with both enolate
ligands coordinated to the metal with the oxygen atoms trans to
each other. However, in bis(salicylaldiminate) metal complexes
with sterically demanding substituents on the imine nitrogen, a
trans-N/cis-O/cis-Cl isomer is in fact preferred.14,16,17 Consid-
ering that our ethenolate ligand bears most of the bulk on the
nitrogen atom, we think that complexes 4a and 4b may also
adopt a trans-N/cis-O/cis-Cl arrangement. This is supported by
consistent with their expected structure. All 1H and 13C
resonances were assigned using a series of one- and two-
dimensional 1H and 13C NMR experiments, including
heteronuclear single quantum correlation (HSQC) and
heteronuclear multiple-bond correlation (HMBC) techniques.
The characteristic iminic proton for 1a−c appears at δ 7.99,
9.71, and 8.26, respectively, as a triplet, coupled to two vicinal
methylene protons (3J = 6.4−6.9 Hz). These methylene
protons and those of the imidazole backbone resonate at
approximately δ 4.5 and 6.7, respectively.
Deprotonation of compound 1a with one equivalent of
sodium hexamethyldisilazide (NaHMDS) gave a mixture of two
tautomers, 2a1 and 2a2, in a 3:1 ratio (Scheme 2). The major
tautomer was identified spectroscopically as the enol (2a1),
with the characteristic vinyl proton and the corresponding
carbon nucleus resonating, respectively, at δ 6.39 and 108.6 in
chloroform-d1. The methylene protons of the corresponding
minor keto tautomer (2a2) were observed as a singlet at a lower
frequency (δ 4.40), integrating to two protons, with the α-
Scheme 2. Sequential Deprotonation of 1a to Generate a Tautomeric Mixture of 2-(1,3-Bis(2,4,6-trimethylphenyl)imidazol-2-
imine)-1-phenylethanone (2a1 and 2a2) and the Corresponding Ethenolate (3a)
B
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Scheme 3. Synthesis of Titanium and Zirconium Complexes of the Bis(imine ethenolate) Ligand
Figure 4. ORTEP drawing (50% probability) of 5b. Only one of two independent molecules found in the asymmetric unit cell is drawn. H atoms
and diethyl ether were omitted for clarity.
DFT (B3LYP/LanL2DZ) calculations on compound 4a, which
predicts this isomer to be 12.6 kcal/mol more stable than the
corresponding cis-N/trans-O/cis-Cl isomer. Attempts to pre-
pare the related titanium complexes using the same method-
ology led only to mixtures of species, possibly coordination
isomers, which could not be isolated and characterized.
diffusion of diethyl ether into a saturated CH2Cl2 solution.
Compound 5b exhibits a distorted piano stool geometry with
the cyclopentadienyl ligand adopting an η5 hapticity (Figure 4;
Table 1). As expected, the ligand coordinates in a bidentate
fashion though the imine nitrogen and ethenolate oxygen
atoms. The formation of a five-membered metallacycle leads to
an O1−Zr−N3 bite angle of 75.92(9)°, which is significantly
larger than that observed for the four-membered metallacycle
formed in Ti(IMesN∧Imine)Cl4 (60.50(12)°). The cyclo-
pentadienyl ligand is asymmetrically bound to zirconium,
with Zr−C bond lengths ranging from 2.481(4) to 2.534(4) Å,
with shorter bonds anti to the chloride atoms and longer ones
anti to the imine ethenolate donor atoms. The mesityl rings of
the ligand are almost orthogonal to the best plane formed by
the imidazol-2-imine ring, at 84.36° and 70.21°, respectively.
The p-chlorophenyl and azole rings slightly deviate by 9.1°
and 17.9°, respectively, from coplanarity with the best plane
Cyclopentadienyl (imine ethenolate) complexes of zirconium
(5) and titanium (6) were prepared by adding the ethenolate
salt, prepared in situ by double deprotonation of 1 with
NaHMDS, to CpMCl3 (Scheme 3). The zirconium complexes
5a and 5b were isolated as yellow solids in 47% and 59% yield,
1
respectively. The H NMR spectra of both complexes showed
characteristic resonances of the ethenolate ligand, with an
additional resonance for the cyclopentadienyl protons at δ 6.0
in chloroform-d1, integrating to five protons.
Crystals of compound 5b suitable for X-ray diffraction
studies were grown at −35 °C under nitrogen by slow liquid
C
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ethylene. While all four zirconium complexes gave only trace
amounts of polyethylene (PE), titanium complex 6a gave
polymer at a moderate rate of 110 kg PE mol cat−1 h−1. The
small electronic perturbation arising from replacing the para
hydrogen atom with the more electronegative chlorine atom led
to a slight enhancement in catalytic activity for complex 6b
(170 kg PE mol cat−1 h−1). These activities favorably compare
to the best ones reported by Lancaster and Bochmann for a
series of titanium and zirconium cyclopentadienyl salicylaldi-
minate complexes.19 While they are also comparable to those
reported for bis(salicylaldiminate)ZrCl2 complexes that have
small alkyl substituents on the phenol ring, these activities are
orders of magnitude lower than those of related complexes with
larger tert-butyl, adamantyl, and cumyl groups.14 The lower
activity observed in our complexes may therefore be a result of
an unoptimized substitution pattern on the ethenolate ligand.
Alternatively, it may also be a result of either the different
ligand arrangement (trans-N/cis-O/cis-Cl vs cis-N/trans-O/cis-
Cl) or a less electrophilic metal center, a result of electron
delocalization from the imidazole ring to the exocyclic nitrogen
atom.7,9−11
Table 1. Selected Bond Lengths and Bond Angles for
Compound 5b
a
́
selected bond lengths (Å)
selected bond angles (deg)
Zr1−Cl1
Zr1−Cl2
Zr1−O1
Zr1−N3
Zr1−C30
Zr1−C31
Zr1−C32
Zr1−C33
Zr1−C34
N1−C1
N2−C1
N3−C1
N3−C22
C22−C23
O1−C23
2.463(1)
2.4995(9)
2.059(2)
2.276(3)
2.521(4)
2.492(4)
2.481(4)
2.503(4)
2.534(4)
1.363(4)
1.377(4)
1.332(4)
1.413(4)
1.357(5)
1.356(4)
O1−Zr1−N3
O1−Zr1−Cl1
N3−Zr1−Cl1
O1−Zr1−Cl2
N3−Zr1−Cl2
Cl1−Zr1−Cl2
Zr1−N3−C1
Zr1−N3−C22
Zr1−O1−C23
C1−N3−C22
N3−C22−C23
C22−C23−O1
75.92(9)
90.80(7)
131.58(7)
145.06(7)
79.70(7)
86.95(4)
141.00(2)
83.15(2)
92.15(2)
118.65(3)
119.25(3)
117.20(3)
a
Average bond lengths and angles for both molecules present in the
asymmetric unit cell.
CONCLUSIONS
formed by N3, C22, C23, and O1, possibly indicating little
electron delocalization from the imidazole ring to the exocyclic
atoms (N3, C22, C23, and O1). However, the C1−N3 bond is
only slightly shorter than C1−N1, C1−N2, and C22−N3.
Furthermore, the length of these bonds, as well as those for
C22−C23 and O1−C23, are all intermediate to those expected
for single and double bonds,18 indicating significant bond
conjugation. Interestingly, despite the relatively long Zr1···C22
and Zr1···C23 distances (2.5 Å), the position of zirconium with
respect to the ethenolate ligand in fact resembles that of metal
bound to an η4-1,4-butadiene ligand, perhaps another
manifestation of the double-bond character between N3 and
C22, and O1 and C23, which would arise from electron
delocalization from the imidazole ring through the conjugated
system. The orientation of the ethenolate ligand results in a fold
angle between the best plane containing Zr1, N3, and O1 and
the one containing N3, C22, C23, and O1 of 68.74°.
■
The synthesis of a new monoanionic bidentate ligand structure
that incorporates the electron-rich imidazol-2-imine fragment
was reported for the first time and coordinated to zirconium
and titanium. Bis(ethenolate) and (cyclopentadienyl)-
(ethenolate) metal dichloride complexes were successfully
prepared and fully characterized. The solid-state structure of
the cyclopentadienyl zirconium complex 5b confirmed the
targeted bidentate coordination of the ligand, resulting in a
four-legged piano stool configuration. The synthesis of the
bis(imine ethenolate) zirconium dichloride complexes further-
more proved to be very selective, with the formation of one
single highly symmetric molecule. While all zirconium
complexes tested showed no activity in ethylene polymer-
ization, both titanium complexes 6a and 6b were effective
catalysts at room temperature, with activities up to 170 kg PE
mol cat−1 h−1. A decrease in the electron-donating capabilities
of the ligand through the inductive effect of a more
electronegative chlorine atom led to enhanced catalyst
activities. Work aimed at determining the effect of other ligand
subtitution patterns on catalyst performance will be reported in
due course.
While the steric influence of the bulky imidazole ring cannot
be ruled out, the weaker Coulombic interactions between the
formally charged metal center and the neutral nitrogen donor,
in constrast to the negatively charged oxygen atom, likely
account for the longer Zr1−N3 bond (2.276(3) Å), compared
to Zr1−O1. Furthermore, π-donation of the oxygen atom to
the Lewis acidity metal center leads to a Zr1−O1 bond length
of 2.059(2), which is intermediate between those for Zr−O
single (2.17 Å) and ZrO double (1.84 Å) bonds.18
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were performed
under a nitrogen atmosphere in a drybox or using standard Schlenk
techniques. Solvents used in the preparation of air- and/or moisture-
sensitive compounds were dried using an MBraun Solvent Purification
System fitted with alumina columns and stored over molecular sieves
under a positive pressure of argon. Toluene for polymerization was
distilled under argon after being dried with the MBraun SPS.
Deuterated solvents were degassed using three freeze−pump−thaw
cycles. C6D6 and CDCl3 were vacuum distilled from sodium and
CaH2, respectively, and stored under nitrogen. NMR spectra were
recorded on a Bruker DRX 600 (1H at 600 MHz, 13C at 150.9 MHz),
Bruker AV 400 (1H at 400 MHz, 13C at 100 MHz), or Bruker AV 300
(1H at 300 MHz, 13C at 75.5 MHz) spectrometer and are at room
temperature unless otherwise stated. The spectra were referenced
internally relative to the residual protio-solvent (1H) and solvent (13C)
resonances, and chemical shifts were reported with respect to δ = 0 for
tetramethylsilane. Elemental compositions were determined by
Guelph Chemical Laboratories Inc. located in Guelph, Ontario.
Addition of one equivalent of sodium ethenolate 3a and 3b,
prepared in situ, to CpTiCl3 resulted in an immediate color
change of the THF solution from yellow to deep blue,
indicative of a ligand-to-metal charge transfer, with formation of
complexes 6a and 6b in 74% and 56% yield, respectively. NMR
spectra of both complexes are in agreement with their structure,
with resonances and chemical shifts similar to those observed
for compounds 5a and 5b. Attempts to prepare the
cyclopentadienyl zirconium and titanium complexes of the p-
nitrophenyl derivative resulted in a mixture of reaction products
that could not be successfully isolated.
All titanium and zirconium complexes were evaluated for
their activity in ethylene polymerization. Complexes were
activated with methylaluminoxane (MAO) as cocatalyst in
toluene, at room temperature and at one atmosphere of
D
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All metal precursors were purchased from either BDH or Sigma-
Aldrich. All acetophenones and NaHMDS were purchased from
Sigma-Aldrich and used as received. Deuterated NMR solvents were
purchased from Cambridge Isotope Laboratories. MAO was graciously
donated by Albemarle Corp. Lastly, 1,3-bis(2,4,6-trimethylphenyl)-
The pale yellow solution was filtered, evaporated to dryness, and
extracted with pentane (2 × 30 mL). The off-white solid was dried in
vacuo, and the pale yellow pentane solution was concentrated to 15
mL and left at −78 °C for 4 h to collect additional product through
precipitation. The precipitated off-white solid was washed with cold
(−78 °C) pentane (10 mL) and dried in vacuo. Yield: 1.8 g (82%). 1H
NMR (400 MHz, CDCl3): major isomer (enol form 75%) δ 7.41 (d,
1H, J = 7.7 Hz, o-CH(phenyl)), 7.08 (t, 1H, J = 7.7 Hz, p-CH(phenyl)),
6.94−6.84 (m, 2H, m-CH(phenyl)), 6.71 (s, 4H, m-CH(mesityl)), 6.39 (s,
1H, N−CHC−), 5.60 (s, 2H, −NCHCHN−), 2.13 (s, 12H, o-
CH3(mesityl)), 2.11 (s, 6H, p-CH3(mesityl)); minor isomer (keto form, 25%)
δ 7.57 (d, 1H, J = 7.7 Hz, o-CH(phenyl)), 7.04−6.84 (m, 2H, m-
CH(phenyl) + 1H, p-CH(phenyl)), 6.62 (s, 4H, m-CH(mesityl)), 5.65 (s, 2H,
−NCHCHN−), 4.40 (s, 2H, N−CH2−C−), 2.35 (s, 12H, o-
CH3(mesityl)), 1.98 (s, 6H, p-CH3(mesityl)). 13C{1H} NMR (100 MHz,
CDCl3): major isomer δ 141.9 (−NCN−), 136.4 (C(mesityl)), 136.2 (O−
C), 133.9 (o-C(mesityl)), 128.9 (p-C(mesityl)), 126.1 (p-C(phenyl)), 129.1 (m-
C(phenyl)), 123.2 (o-C(phenyl)), 108.6 (N−CHC−), 114.7
(−NCHCHN−), 21.6 (p-CH3(mesityl)), 18.6 (o-CH3(mesityl)); minor
isomer δ 196.6 (C(ketone)), 145.5 (−NCN−), 136.7 (C(mesityl)), 136.3
(C(phenyl)) 132.7 (m-C(phenyl)), 129.1 (p-C(mesityl)), 128.8 (o-C(mesityl)),
128.7 (p-C(phenyl)), 123.2 (o-C(phenyl)), 114.2 (−NCHCHN−), 54.5 (
N−CH2−C−), 21.5 (p-CH3(mesityl)), 18.9 (o-CH3(mesityl)). Anal. Calcd
for C29H31N3O (%): C, 79.60; H, 7.14; N, 9.60. Found (%): C, 79.35;
H, 7.17; N, 9.38.
Sodium 2-(1,3-Bis(2,4,6-trimethylphenyl)imizadol-2-imine)-
1-phenylethenolate, Na[IMesN∧ethenolate], 3a. To a THF (2
mL) suspension of NaH (11.5 mg, 480 μmol) at −40 °C slowly was
added a cold (−40 °C) solution of 2a (150 mg, 343 μmol) in THF (5
mL). The reaction mixture was slowly warmed to room temperature
and stirred for 60 min, resulting in the color slowly changing to intense
yellow. Pentane (5 mL) was added to precipitate the product, which
was filtered, washed with pentane (2 × 5 mL), and dried in vacuo to
yield a yellow solid. Yield: 137 mg (87%). 1H NMR (400 MHz,
C6D6): δ 7.26 (t, 2H, J = 7.4 Hz, m-CH(phenyl)), 7.08 (t, 1H, J = 7.4 Hz,
p-CH(phenyl)), 6.98 (s, 1H, m-CH(mesityl)), 6.82 (d, 2H, J = 7.4 Hz, o-
CH(phenyl)), 6.75 (s, 1H, m-CH(mesityl)), 6.30 (s, 1H, m-CH(mesityl)), 6.21
(s, 1H, N−CHC−), 6.08 (s, 1H, m-CH(mesityl)), 5.61 (d, 1H, J =
2.7 Hz −NCHCHN−), 5.58 (d, 1H, J = 2.7 Hz −NCHCHN−), 2.49
(s, 3H, CH3(mesityl)), 2.28 (s, 3H, CH3(mesityl)), 2.16 (s, 3H, CH3(mesityl)),
2.15 (s, 3H, CH3(mesityl)), 2.05 (s, 3H, CH3(mesityl)), 1.89 (s, 3H,
CH3(mesityl)). 13C{1H} NMR (100.6 MHz, C6D6): δ 150.3 (O−C),
146.5 (ipso-C(mesityl)), 141.5 (−NCN−), 137.9 (aromatic CH), 137.7
(aromatic CH), 137.4 (aromatic CH), 136.9 (aromatic CH), 135.8
(aromatic CH), 135.5 (aromatic CH), 135.2 (aromatic CH), 133.3
(ipso-C(mesityl)), 130.3 (aromatic CH), 129.6 (aromatic CH), 129.0
(aromatic CH), 128.7 (m-CH(mesityl)), 127.7 (m-CH(phenyl)), 124.5 (o-
CH(phenyl)), 122.5 (p-CH(phenyl)), 114.3 (−NCHCHN−), 113.8
(−NCHCHN−), 103.8 (N−CHC−), 21.1 (CH3(mesityl)), 20.7
(CH3(mesityl)), 19.3 (CH3(mesityl)), 18.8 (CH3(mesityl)), 18.4 (CH3(mesityl)),
16.9 (CH3(mesityl)). Anal. Calcd for C29H30N3NaO (%): C, 75.79; H,
6.58; N, 9.14. Found (%): C, 76.04; H, 6.62; N, 8.87.
20
imidazol-2-imine4 and ZrCl4(THF)2 were prepared using published
procedures.
General Procedure for the Synthesis of 2-(1,3-Bis(2,4,6-
trimethylphenyl)imizadol-2-imine)-1-(aryl)ethanone Hydro-
chloride Salt, IMesN∧ethanone·HX, 1a−c. In a typical procedure,
the substituted 2-halo-1-(4-substituted phenyl)ethanone (3.65 mmol)
was added as a solid to a toluene (20 mL) solution of 1,3-bis(2,4,6-
trimethylphenyl)imidazol-2-imine (3.28 mmol). The solution was
refluxed for a few hours, resulting in the formation of a precipitate. The
reaction mixture was then cooled to room temperature and filtered.
The solid was washed with pentane (2 × 15 mL) and dried in vacuo to
yield the product as a powder.
2-(1,3-Bis(2,4,6-trimethylphenyl)imizadol-2-imine)-1-phenyletha-
none hydrobromide salt, 1a: 89% yield. 1H NMR (400 MHz,
CDCl3): major isomer (keto form, 82%) δ 7.99 (t, 1H, J = 6.9 Hz, NH),
7.49 (t, 1H, J = 7.8 Hz, p-CH(phenyl)), 7.46 (d, 1H, J = 7.8 Hz, o-
CH(phenyl)), 7.30 (t, 1H, J = 7.8 Hz, m-CH(phenyl)), 6.89 (s, 4H, m-
CH(mesityl)), 6.77 (s, 2H, −NCHCHN−), 4.48 (d, 2H, J = 6.9 Hz, 
NH−CH2−C−), 2.23 (s, 12H, o-CH3(mesityl)), 2.21 (s, 6H, p-
CH3(mesityl)); minor isomer (enol form, 18%; some resonances are missing
due to accidental overlap with those of the major isomer) δ 7.06 (s, 4H, m-
CH(mesityl)), 6.83 (s, 2H,, −NCHCHN−), 6.69 (s + br, 2H, NH−
CHCPh−), 4.97 (s + br, 1H, −C(Ph)OH), 2.35 (s, 6H, p-
CH3(mesityl)), 2.16 (s, 12H, o-CH3(mesityl)). 13C{1H} NMR (100 MHz,
CDCl3): major isomer δ 192.2 (OC), 144.8 (−NCN−), 141.4 (ipso-
C(mesityl)), 136.0 (o-C(mesityl)), 133.7 (p-C(phenyl)), 130.0 (p-C(mesityl)),
128.4 (o-C(phenyl)), 127.5 (m-C(phenyl)), 117.7 (−NCHCHN−), 48.6
(NH−CH2−C−), 21.1 (p-CH3(mesityl)), 17.8 (p-CH3(mesityl)); minor
isomer (some resonances are missing due to accidental overlap with those of
the major isomer) δ 145.2 (−NCN−), 141.4 (o-C(mesityl)), 135.6
(C(mesityl)), 130.4 (p-C(mesityl)), 117.2 (−NCHCHN−), 21.2 (p-
CH3(mesityl)), 17.6 (p-CH3(mesityl)). Anal. Calcd for C29H32BrN3O (%):
C, 67.18; H, 6.22; N, 8.10. Found (%): C, 67.20; H, 6.31; N, 8.35.
2-(1,3-Bis(2,4,6-trimethylphenyl)imizadol-2-imine)-1-(4-
1
chlorophenyl)ethanone hydrochloride salt, 1b: 81% yield. H NMR
(400 MHz, CDCl3): δ 9.71 (t, 1H, J = 6.4 Hz, NH), 7.42 (d, 2H, J =
8.7 Hz, o-CH(phenyl)), 7.28 (d, 2H, J = 8.7 Hz, m-CH(phenyl)), 6.91 (s,
4H, m-CH(mesityl)), 6.67 (s, 2H, −NCHCHN−), 4.47 (d, 2H, J = 6.4
Hz, NH−CH2−C−), 2.22 (s, 18H, p-CH3(mesityl) + o-CH3(mesityl)).
13C{1H} NMR (100 MHz, CDCl3): δ 191.4 (OC), 145.2
(−NCN−), 141.3 (p-C(mesityl)), 140.0 (ipso-C(phenyl)), 132.2 (p-
CH(phenyl)), 130.4 (o-C(mesityl)), 130.1 (m-CH(mesityl)), 128.9 (ipso-
C(mesityl)), 128.8 (o-CH(phenyl)), 128.7 (m-CH(phenyl)), 117.3
(−NCHCHN−), 48.5 (NH−CH2−C−), 21.1 (p-CH3(mesityl)), 17.7
(o-CH3(mesityl)). Anal. Calcd for C29H31Cl2N3O (%): C, 68.50; H, 6.14;
N, 8.26. Found (%): C, 68.66; H, 5.95; N, 8.44.
2-(1,3-Bis(2,4,6-trimethylphenyl)imizadol-2-imine)-1-(4-
1
nitrophenyl)ethanone hydrobromide salt, 1c: 75% yield. H NMR
General Procedure for the Synthesis of Bis(2-(1,3-bis(2,4,6-
(400 MHz, CDCl3): δ 8.26 (t, 1H, J = 6.4 Hz, NH), 8.16 (d, 2H, J =
8.7 Hz, m-CH(nitrophenyl)), 7.68 (d, 2H, J = 8.7 Hz, o-CH(nitrophenyl)), 6.93
(s, 4H, m-CH(mesityl)), 6.74 (s, 2H, NCHCHN), 4.60 (d, 2H, J = 6.4
Hz, NH−CH2−C−), 2.22 (s, 12H, p-CH3(mesityl)) 2.16 (s, 6H, o-
CH3(mesityl)). 13C{1H} NMR (100 MHz, CDCl3): δ 191.6 (OC),
144.8 (−NCN−), 150.5 (p-C(nitrophenyl)), 138.3 (ipso-C(nitrophenyl)),
136.0 (ipso-C(mesityl)), 135.6 (p-C(mesityl)), 130.2 (o-C(mesityl)), 128.6 (o-
CH(nitrophenyl)), 123.5 (m-CH(nitrophenyl)), 117.6 (−NCHCHN−), 49.0
(NH−CH2C−), 17.7 (o-CH3(mesityl)), 17.6 (p-CH3(mesityl)). Anal.
Calcd for C29H31BrN4O3 (%): C, 61.81; H, 5.55; N, 9.94. Found (%):
C, 61.85; H, 5.38; N, 10.12.
trimethylphenyl)imizadol-2-imine)-1-(aryl)ethenolate) Zirco-
̂
nium Dichloride, ZrCl2(IMesNethenolate)2, 4a and 4b.
NaHMDS (0.773 mmol) was slowly added at room temperature as
a solid to a THF (5 mL) suspension of compound 1 (0.386 mmol).
The solution immediately turned a bright yellow, and the reaction
mixture was allowed to stir for 30 min. The solution was then added to
a THF (2 mL) solution of ZrCl2(THF)2 (0.386 mmol). A white
precipitate formed immediately. The yellow solution was stirred for 2
h, subsequently filtered through a pad of Celite, and dried under
reduced pressure. The product was washed with Et2O (2 × 5 mL) and
dried in vacuo to yield a yellow powder.
2-(1,3-Bis(2,4,6-trimethylphenyl)imizadol-2-imine)-1-phe-
nylethanone, IMesN∧ethanone, 2a. Compound 1a (2.6 g, 5.0
mmol) was suspended in THF (30 mL), and a solution of NaHMDS
(938 mg, 5.11 mmol) in THF (10 mL) was added dropwise at −78
°C. The reaction mixture was stirred for 10 min, subsequently slowly
warmed to room temperature, and stirred for an additional 30 min.
Bis(2-(1,3-bis(2,4,6-trimethylphenyl)imizadol-2-imine)-1-phenyle-
thenolate) zirconium dichloride, 4a: 60% yield. 1H NMR (400 MHz,
CDCl3): δ 6.98 (m, 12H, m-CH(mesityl) + m-CH(phenyl)), 6.88 (d, 2H, J
= 7.4 Hz, p-CH(phenyl)), 6.74 (d, 4H, J = 7.4 Hz, o-CH(phenyl)), 6.58 (s,
4H, −NCHCHN−), 5.93 (s, 2H, N−CHC−), 2.30 (s, 12H, p-
CH3(mesityl)), 2.24 (s, 24H, o-CH3(mesityl)). 13C{1H} NMR (100 MHz,
E
dx.doi.org/10.1021/om4004708 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
CDCl3): δ 145.5 (O−C), 139.2 (p-C(mesityl)), 137.1 (ipso-C(phenyl)),
136.3 (ipso-C(mesityl)), 132.3 (−NCN−), 129.6 (m-CH(mesityl)), 126.9
(m-CH(phenyl)), 124.3 (p-CH(phenyl)), 123.5 (o-CH(phenyl)), 117.4
(−NCHCHN−), 113.0 (N−CHC−), 21.1 (p-CH3(mesityl)), 19.2
(o-CH3(mesityl)). Anal. Calcd for C58H60Cl2N6O2Zr (%): C, 67.29; H,
5.84; N, 8.12. Found (%): C, 67.48; H, 6.02; N, 7.94.
NMR (400 MHz, C6D6): δ 7.19−7.17 (m, 4H, o-CH(phenyl) + m-
CH(phenyl)), 6.90 (d, 1H, J = 8.5 Hz, p-CH(phenyl)), 6.78 (s, 1H, N−
CHC−), 6.73 (s, 4H, m-CH(mesityl)), 6.12 (s, 5H, Cp), 5.56 (s, 2H,
−NCHCHN−), 2.12 (s, 12H, o-CH3(mesityl)), 2.09 (s, 6H, p-
CH3(mesityl)). 13C{1H} NMR (100 MHz, C6D6): δ 156.8 (O−C),
144.8 (−NCN−(mesityl)), 139.1 (p-C(mesityl)), 137.7 (ipso-C(phenyl)), 136.5
(o-C(mesityl)), 133.9 (ipso-C(mesityl)), 129.6 (m-CH(mesityl)), 127.0 (m-
CH(phenyl)), 125.4 (p-CH(phenyl)), 124.2 (N−CHC), 122.3 (o-
CH(phenyl)), 120.5 (Cp), 115.0 (−NCHCHN−), 20.9 (p-CH3(mesityl)),
18.0 (o-CH3(mesityl)). Anal. Calcd for C34H35Cl2N3OTi (%): C, 65.82;
H, 5.69; N, 6.77. Found (%): C, 66.10; H, 5.90; N, 7.02.
Bis(2-(1,3-bis(2,4,6-trimethylphenyl)imizadol-2-imine)-1-(4-
1
chlorophenyl)ethenolate) zirconium dichloride, 4b: 42% yield. H
NMR (400 MHz, C6D6): δ 6.96 (s, 8H, m-CH(mesityl)) 6.92 (d, 4H, J =
8.4 Hz, m-CH(chlorophenyl)), 6.64 (d, 4H, J = 8.4 Hz, o-CH(chlorophenyl)),
6.59 (s, 4H, −NCHCHN−), 5.91 (s, 2H, N−CHC−), 2.30 (s,
12H, p-CH3(mesityl)), 2.21 (s, 24H, o-CH3(mesityl)). 13C{1H} NMR (100
MHz, CDCl3): δ 144.4 (O−C), 139.3 (p-C(mesityl)), 136.2 (ipso-C(mesityl)
+ o-C(mesityl)), 135.6 (p-C(chlorophenyl)), 132.2 (−NCN−), 129.6 (m-
CH(mesityl)), 129.5 (ipso-C(chlorophenyl)), 127.1 (m-CH(chlorophenyl)), 124.5
(o-CH(chlorophenyl)), 117.5 (−NCHCHN−), 113.4 (N−CHC−),
21.1 (p-CH3(mesityl)), 19.2 (o-CH3(mesityl)). Anal. Calcd for
C58H58Cl4N6O2Zr (%): C, 63.09; H, 5.29; N, 7.61. Found (%): C,
63.32; H, 5.01; N, 7.43.
General Procedure for the Synthesis of Cyclopentadienyl (2-
(1,3-Bis(2,4,6-trimethylphenyl)imizadol-2-imine)-1-(aryl)-
ethenolate) Zirconium Dichloride, CpZrCl2(IMesN∧ethenolate),
5a and 5b. NaHMDS (0.773 mmol) was slowly added as a solid to a
THF (5 mL) suspension of compound 1 (0.386 mmol). The solution
immediately turned a bright yellow, and the reaction mixture was
allowed to stir for 30 min. The solution was then added to a THF (2
mL) solution of CpZrCl3 (0.386 mmol). A white precipitate
immediately formed, and the reaction mixture was allowed to stir
for 2 h. The reaction mixture was then filtered through a pad of Celite
and dried under reduced pressure. The product was washed with
diethyl ether (2 × 5 mL) and dried in vacuo to yield a yellow powder.
Cyclopentadienyl (2-(1,3-bis(2,4,6-trimethylphenyl)imizadol-2-
imine)-1-phenylethenolate) zirconium dichloride, 5a: 47% yield.
1H NMR (400 MHz, CDCl3): δ 7.13−7.09 (m, 7H, m-CH(mesityl) + o-
CH(phenyl) + p-CH(phenyl)), 6.92 (dd, 2H, J = 7.2, 6.0 Hz, m-CH(phenyl)),
6.53 (s, 2H, −NCHCHN−), 6.10 (s, 1H, N−CHC−), 6.04 (s,
5H, Cp), 2.34 (s, 6H, p-CH3(mesityl)), 2.31 (s, 12H, o-CH3(mesityl)).
13C{1H} NMR (100 MHz, CDCl3): δ 147.8 (O−C), 147.4
(−NCN−), 140.5 (p-C(mesityl)), 136.2 (o-C(mesityl)), 132.9 (ipso-
C(phenyl)), 132.7 (ipso-C(mesityl)), 130.1 (m-CH(mesityl)), 128.3 (p-
CH(phenyl)), 127.5 (o-CH(phenyl)), 125.6 (m-CH(phenyl)), 117.7
(−NCHCHN−), 115.8 (Cp), 103.9 (N−CHC−), 21.0 (p-
CH3(mesityl)), 18.7 (o-CH3(mesityl)). Anal. Calcd for C34H35Cl2N3OZr
(%): C, 61.52; H, 5.31; N, 6.33. Found (%): C, 61.30; H, 5.24; N,
6.10.
Cyclopentadienyl (2-(1,3-bis(2,4,6-trimethylphenyl)imizadol-2-
imine)-1-(4-chlorophenyl)ethenolate) titanium dichloride, 6b: 56%
1
yield. H NMR (400 MHz, C6D6): δ 7.05 (d, 2H, J = 8.6 Hz, m-
CH(chlorophenyl)), 6.97 (d, 2H, J = 8.6 Hz, o-CH(chlorophenyl)), 6.71 (s, 4H,
m-CH(mesityl)), 6.68 (s, 1H, N−CHC−), 6.05 (s, 5H, Cp), 5.56 (s,
2H, −NCHCHN−), 2.09 (s, 12H, o-CH3(mesityl)), 2.06 (s, 6H, p-
CH3(mesityl)). 13C{1H} NMR (100 MHz, C6D6): δ 155.6 (O−C), 144.8
(−NCN−), 139.2 (p-C(mesityl)), 136.4 (o-C(mesityl)), 136.3 (p-
C(chlorophenyl)), 133.8 (ipso-C(mesityl)), 130.7 (ipso-C(chlorophenyl)), 129.9
(m-CH(mesityl)), 128.6 (m-CH(chlorophenyl)), 124.6 (N−CHC−),
123.4 (o-CH(chlorophenyl)), 120.6 (Cp), 115.1 (−NCHCHN−), 20.9 (p-
CH3(mesityl)), 17.9 (o-CH3(mesityl)). Anal. Calcd for C34H34Cl3N3OTi
(%): C, 62.36; H, 5.23; N, 6.42. Found (%): C, 62.15; H, 5.09; N,
6.38.
General Procedure for Ethylene Polymerization. Ethylene
polymerization was performed at atmospheric pressure and room
temperature in a 200 mL Schlenk flask containing a magnetic stir bar.
The flask was conditioned in an oven at 160 °C for at least 12 h prior
to use. The hot flask was brought to room temperature under dynamic
vacuum and backfilled with ethylene. This cycle was repeated a total of
three times. Under an atmosphere of ethylene, the flask was charged
with 20 mL of dry toluene and 1000 equivalents of MAO. The
solution was stirred for 15 min before a solution of the catalyst
precursor in toluene was introduced into the flask via a syringe. The
reaction mixture was vigorously stirred for 10 min and subsequently
quenched with a 50:50 mixture of concentrated hydrochloric acid and
methanol. The resulting mixture was filtered, and any solid collected
was washed with distilled water. Solids collected were dried under
vacuum at approximately 60 °C for several hours.
Computational Details. DFT calculations were carried out at the
hybrid B3LYP level of theory with LanL2DZ as basis set using
Gaussian 921 and GaussView 322 for computing and molecular
visualization, respectively. These calculations were performed on the
Shared Hierarchical Academic Research Computing Network
(SHARCNET: www.sharcnet.ca).
X-ray Crystallography. Detailed crystallographic data for
compound 5b (tables of atomic coordinates with isotropic and
anisotropic displacement parameters, bond lengths and angles) are
provided as Supporting Information. Crystallographic data for 5b were
collected at the University of Toronto on a Bruker-Nonius Kappa-
CCD diffractometer using monochromated Mo Kα radiation (λ =
0.71073 Å) at 150 K and were measured using a combination of ϕ
scans and ω scans with κ offsets, to fill the Ewald sphere. Intensity data
were processed using the Denzo-SMN package.23 Absorption
corrections were carried out using SORTAV.24 The structure was
solved using Superflip25 and refined using WinGX26 with SHELXS-
9727 for full-matrix least-squares refinement that was based on F2. All
H atoms were included in calculated positions and allowed to refine in
riding-motion approximation with Uiso tied to the carrier atom.
Cyclopentadienyl (2-(1,3-bis(2,4,6-trimethylphenyl)imizadol-2-
imine)-1-(4-chlorophenyl)ethenolate) zirconium dichloride, 5b:
59% yield. 1H NMR (400 MHz, CDCl3): δ 7.08 (s, 4H, m-CH(mesityl)),
7.06 (d, 2H, J = 8.5 Hz, o-CH(chlorophenyl)), 6.84 (d, 2H, J = 8.5 Hz, m-
CH(chlorophenyl)), 6.55 (s, 2H, −NCHCHN−), 6.09 (s, 1H, N−CH
C−), 6.02 (s, 5H, Cp), 2.34 (s, 6H, p-CH3(mesityl)), 2.30 (s, 12H, o-
CH3(mesityl)). 13C{1H} NMR (100 MHz, CDCl3): δ 147.5 (−NCN−),
146.6 (O−C), 140.5 (p-C(mesityl)), 136.1 (o-C(mesityl)), 133.8 (p-
C(chlorophenyl)), 132.6 (ipso-C(mesityl)), 131.6 (ipso-C(chlorophenyl)), 130.3
(m-CH(mesityl)), 127.7 (o-CH(chlorophenyl)), 126.8 (m-CH(chlorophenyl)),
117.8 (−NCHCHN−), 115.9 (Cp), 104.71 (N−CHC−), 21.0
(p-CH3(mesityl)), 18.7 (o-CH3(mesityl)). Anal. Calcd for C34H34Cl3N3OZr
(%): C, 58.49; H, 4.91; N, 6.02. Found (%): C, 58.64; H, 4.72; N,
5.76.
General Procedure for the Synthesis of Cyclopentadienyl (2-
(1,3-Bis(2,4,6-trimethylphenyl)imizadol-2-imine)-1-(aryl)-
ethenolate) Titanium Dichloride, CpTiCl2(IMesN∧ethenolate),
6a and 6b. Compounds 6a and 6b were prepared using the same
procedure used for the preparation of compounds 5a and 5b, with the
exception that the CpTiCl3 was used as metal precursor. The product
was purified by redissolving it in toluene, filtering the mixture, and
removing the volatiles in vacuo to yield blue powders. Analytically pure
samples were obtained by recrystallization from THF and pentane at
−35 °C.
ASSOCIATED CONTENT
■
S
* Supporting Information
Crystallographic data for 5b (CCDC reference number
940710). Crystallographic data in CIF and other electronic
format, including tables of crystal data and structure refinement,
bond lengths, angles, atomic coordinates and equivalent
isotropic displacement parameters, and anisotropic displace-
Cyclopentadienyl (2-(1,3-bis(2,4,6-trimethylphenyl)imizadol-2-
1
imine)-1-phenylethenolate) titanium dichloride, 6a: 74% yield; H
F
dx.doi.org/10.1021/om4004708 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
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J. Am. Chem. Soc. 2008, 130, 17636−17637. (d) Sun, J.; Cheng, Z.;
Nie, Y.; Schumann, H.; Hummert, M. Appl. Organomet. Chem. 2007,
21, 268−274. (e) Mitani, M.; Mohri, J.; Yoshida, Y.; Saito, J.; Ishii, S.;
Tsuru, K.; Matsui, S.; Furuyama, R.; Nakano, T.; Tanaka, H.; Kojoh,
S.-i.; Matsugi, T.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2002, 124,
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ment parameters. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*Tel: +1 416 736 2100, ext. 77728. Fax: +1 416 736 5936. E-
mail: glavoie@yorku.ca.
Present Address
†Department of Chemistry, College of Science, Sultan Qaboos
University, P.O. Box 36, Muscat 123, Sultanate of Oman.
(16) Parssinen, A.; Luhtanen, T.; Klinga, M.; Pakkanen, T.; Leskela,
̈
̈
M.; Repo, T. Eur. J. Inorg. Chem. 2005, 2100−2109.
Notes
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(b) Johnson, A. L.; Davidson, M. G.; Lunn, M. D.; Mahon, M. F. Eur.
J. Inorg. Chem. 2006, 3088−3098. (c) Strauch, J.; Warren, T. H.; Erker,
G.; Frohlich, R.; Saarenketo, P. Inorg. Chim. Acta 2000, 300−302,
810−821.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
G.G.L. gratefully acknowledges financial support from the
Ontario Ministry of Research and Innovation for an Early
Researcher Award, the Natural Sciences and Engineering
Research Council of Canada for a Discovery Grant and a
Research and Tools Instrumentation Grant, the Canadian
Foundation for Innovation and the Ontario Research Fund for
infrastructure funding, and York University for start-up funds.
We also wish to thank Dr. Alan J. Lough of the University of
Toronto (Toronto, Ontario) for X-ray data acquisition and his
gracious assistance in structure refinement.
(18) (a) Pyykko, P.; Atsumi, M. Chem.Eur. J. 2009, 15, 12770−
̈
12779. (b) Pyykko, P.; Atsumi, M. Chem.Eur. J. 2009, 15, 186−197.
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Lancaster, S. J. J. Organomet. Chem. 2003, 665, 135−149.
(20) Manzer, L. E. Inorg. Synth. 1982, 21, 135−140.
(21) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;
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dx.doi.org/10.1021/om4004708 | Organometallics XXXX, XXX, XXX−XXX