NCN-pincer metal complexes (Ti, Cr, V, Zr, Hf, and Nb) of the phebox ligand (S,S)-2,6-bis(4′-isopropyl-2′-oxazolinyl)phenyl

Article abstract of DOI:10.1021/om200170b

Reaction of (S,S)-2,6-bis(4′-isopropyl-2′-oxazolinyl) phenyllithium (i-Pr-Phebox-Li) (2a) with 4,4′-bis[P-(chlorogold(I)) diphenylphosphino]biphenyl [(dppbp)(AuCl)₂] (5) afforded the new, bimetallic gold complex 4,4′-bis[P-(η¹-C-i-Pr

Full text of DOI:10.1021/om200170b

ARTICLE
pubs.acs.org/Organometallics
NCN-Pincer Metal Complexes (Ti, Cr, V, Zr, Hf, and Nb) of the Phebox
Ligand (S,S)-2,6-Bis(40-isopropyl-20-oxazolinyl)phenyl
||
Alexey V. Chuchuryukin,†,‡ Rubin Huang,‡,^ Martin Lutz,§, John C. Chadwick,‡,^ Anthony L. Spek,§ and
Gerard van Koten*,†
†Debye Institute for Nanomaterials Research, Organic Chemistry and Catalysis, and §Bijvoet Center for Biomolecular Research, Crystal
and Structural Chemistry, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH, Utrecht, The Netherlands
‡Dutch Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands
^Laboratory of Polymer Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands
S Supporting Information
b
ABSTRACT: Reaction of (S,S)-2,6-bis(40-isopropyl-20-oxazo-
linyl)phenyllithium (i-Pr-Phebox-Li) (2a) with 4,40-bis[P-
(chlorogold(I))diphenylphosphino]biphenyl [(dppbp)(AuCl)2]
(5) afforded the new, bimetallic gold complex 4,40-bis[P-(η1-C-
i-Pr-Phebox-gold)diphenylphosphino]biphenyl [(P-Au(η1-C-
i-Pr-Phebox))2(dppbp)] (6). Transmetalation of 6 with 2 equiv
of Cl3MX (MX = TiOi-Pr, VCl, CrPy, ZrCl, HfCl, NbO)
afforded the corresponding monopincer compounds [MCl2X(i-Pr-Phebox)] (M = Ti, V, Cr) (7) and [MCl2X(i-Pr-Phebox)]2
(M = Zr, Hf, Nb) (8) in high yields and the gold starting material 5, which could be quantitatively recovered and reused. The
structures in the solid state of the digold compound 6, the monopincer compounds R-PheboxAu(PPh3) (R = i-Pr, t-Bu), and a
number of Phebox-ETM complexes (7a, 7b, 7c, 8a, 8b, and 8c) were obtained. In each of these structures the i-Pr-Phebox
monoanion is mer-N,C,N-tridentate bonded. The monopincer Phebox-Zr and -Hf compounds are dimeric because of two bridging
chlorides, while the corresponding Nb compound has bridging oxygen atoms. Reaction of 6 with iron(III) chloride resulted in the
formation of a N4(FeCl2)2 complex, characterized by X-ray crystal structure determination, comprising a bridging, tetradentate N4
ligand formed by CꢀC coupling of two Phebox anions to a biphenyl species. The new Phebox complexes 7 and 8 have been tested as
olefin polymerization precatalysts. Rapid catalyst deactivation was observed in ethene polymerization under homogeneous
conditions, whereas stable activity was obtained after immobilization on MgCl2-based supports. From preliminary investigations
on the reaction of 8a with either methylmagnesium chloride or methyllithium we assume that the low reactivity in homogeneous
polymerization is due to the alkylation of the Phebox ligand.
’ INTRODUCTION
(Phebox)4 was chosen. A large number of Phebox complexes of late
transition metals have already been reported, which commonly were
synthesized by either direct cyclometalation5a or transmetalation
reaction from the corresponding organolithium5b or organotin
precursors.5c,d However, in a number of cases we were unsuccessful
in preparing NCN-pincer metal complexes of higher oxidation state
ETMs from the corresponding Li or Mg precursor reagents because
of the occurrence of uncontrollable reductive side reactions. Re-
cently, we found that aryl gold compounds, because of their lower
nucleophilicity than the organolithium reagents, can be convenient
precursors for the synthesis of corresponding mono-ECE-pincer
metal complexes of other transition metals via a direct transmetala-
tion reaction.6 In particular, the use of the bimetallic gold complexes
synthesized from 4,40-bis(diphenylphosphino)biphenyl bis(gold(I)
chloride) (5, (AuCl)2(dppbp), vide infra Scheme 3) is particularly
useful, due to the fact that 5, which is quantitatively re-formed as a
product of the transmetalation process, is poorly soluble in many
Design and application of novel olefin polymerization catalysts
based on pincer-type transition metal compounds has attracted
considerable attention over the past decade. In particular a large
number of NNN-pincer-type complexes of middle and late
transition metals have been reported due to the relative ease of
their preparation, accompanied in some cases by remarkable
catalytic properties.1 Much less work has concerned the synthesis
of ECE-pincer-type early transition metal (ETM) compounds
containing a σ-aryl donor ligand with two ortho-chelating sub-
stituents with neutral E (N, O, P) donor atoms. Some NCN-type
pincer metal compounds of early and middle transition metals
have been reported and tested with some success as olefin
polymerization precatalysts.2 CNN-pincer-type organozirco-
nium and organohafnium compounds have also been applied
as olefin polymerization precatalysts.3
It is well known that chiral catalysts can be particularly useful for
the stereospecific synthesis of polymers. As a relatively simple chiral,
monoanionic, NCN-type ligand, which can be prepared from
inexpensive natural chiral precursors, 2,6-bis(20-oxazolinyl)phenyl
Received: February 22, 2011
Published: April 20, 2011
r
2011 American Chemical Society
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Scheme 1. Lithiation of 1a
Conditions: (i) THF, ꢀ78 ꢀC, 10 min, yield of 3 99%, [R]25589 = ꢀ91.3;
(ii) pentane, ꢀ78 ꢀC to rt, 4 h, yield of 3 96%, [R]25589 = ꢀ79.7.
Scheme 2. Synthesis of (S,S)-Phebox-gold(I) Triphenylphos-
phine Complexes 4a and 4b
Figure 1. Displacement ellipsoid plot of 4a (50% probability). Only
one of two independent molecules is shown. Hydrogen atoms are
omitted for clarity.
organic solvents and can be easily separated and recycled.2d In this
paper we report the successful synthesis of a series of mono-Phebox
ETM complexes that otherwise are difficult to obtain via the
common Grignard or organolithium transmetalation reactions.
These complexes appear to have low catalytic activity in ethene
polymerization under homogeneous conditions, most likely because
they are highly reactive to alkyl metal cocatalysts such as methyl-
aluminoxane (MAO), as was concluded from the results of preliminary
reactions of (i-Pr-PheboxCl2ZrCl)2, 8a, with MeMgCl or MeLi.
’ RESULTS AND DISCUSSION
For the lithiation of (S,S)-R,H-PheboxBr (R= i-Pr 1a, t-Bu 1b)
a modified literature procedure was used.5d Lithiation of 1a with
n-BuLi was performed in THF at ꢀ78 ꢀC. The in situ formed
(i-Pr,H-Phebox)Li (2a) was used at the same temperature within
10 min of its preparation in subsequent experiments. In one of
these experiments the Phebox-lithium product was hydrolyzed
by water, affording i-Pr,H-PheboxH (3) in 99% yield as a white
solid (Scheme 1). The optical rotation measured for this product
Figure 2. Displacement ellipsoid plot of 4b (50% probability). Only
one of two independent molecules is shown. Hydrogen atoms are
omitted for clarity.
in dichloromethane ([R]25 = ꢀ91.3) was identical to that
Monometallic NCN-Phebox gold(I) complexes (4a and 4b)
were synthesized by reacting the corresponding organolithium
compounds (2a and 2b) with (triphenylphosphino)gold chlor-
ide. These (S,S)-Phebox-gold(I) complexes were isolated in
good yields as pure, colorless solids (Scheme 2) after recrystalli-
zation from diethyl ether solution.
589
previously reported in the literature,4 confirming that the lithia-
tion procedure followed leaves the chiral centers in the Phebox
ligand unaffected. In a further experiment lithiation of 1a was
carried out in pentane at ꢀ78 ꢀC. The resulting solution was
stirred at room temperature for 4 h followed by hydrolysis. The
yield of 3 was 96% (yellow oil slowly solidifying at room
temperature), but the optical rotation of the product in dichloro-
Structures in the solid state of both 4a and 4b were determined
by X-ray crystallography (Figure 1, Figure 2).
methane, [R]25 = ꢀ79.7, was somewhat lower than that of
The (S,S)-Phebox anions in both complexes are η1-C-bound
to the gold cations via Cipso without additional NꢀAu coordina-
tion of the ortho-oxazolinyl N-substituents, which is similar to
589
3 obtained from the reaction in THF, vide supra. These results
show that in this case the lithiation reaction caused partial
racemization of the Phebox ligand. Reasons for the lower
selectivity of the lithiation reaction in pentane are the low
solubility of 1a in this solvent at ꢀ78 ꢀC, thus requiring longer
reaction times (4 h) and higher reaction temperatures (ꢀ78 ꢀC
to room temperature) to achieve complete conversion of the
starting Phebox-aryl bromide ligand.
the bonding motifs found for (η1-C-Me,Me-Phebox)AuPPh3
2d
and for earlier synthesized (η1-C-NCN)AuPPh3 (NCN is
2,6-(Me2NCH2)2C6H3-anion)6 in the solid state.
Reaction of 4,40-bis(diphenylphosphino)biphenylbis(gold(I)
chloride) (5, (AuCl)2(dppbp))2d with 2 equiv of 2a in THF resulted
in the formation of bis{(S,S)-[2,6-bis(40-isopropyl-20-oxazolinyl)
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phenyl]gold(I) (dppbp) (6, P,P0-(η1-C-i-Pr-PheboxAu(I))2(dppbp))
in 88% yield (Scheme 3).
Initially, crude 6 was crystallized from methanol. A crystal-
Finally 6 was obtained as a benzene solvate (see Figure 3 for its
structure in the solid state), and this material was used in the
further experiments reported below.
lographic study, however, indicated that 6 crystallized as
The bis-organogold compound 6 C6H6 reacted smoothly at
3
6 3MeOH, having three methanol molecules in the lattice
room temperature with a variety of transition metal chlorides,
affording the corresponding i-Pr,H-Phebox transition metal
complexes 7 and 8, with (dppbp)gold(I) chloride (5) being
formed as coproduct (Scheme 4).
3
bound via hydrogen bonds to each molecule of 6 (Figure 3A,
SI). It is important to note that the presence of methanol would
hamper the further use of 6 in transmetalation experiments to
synthesize the corresponding ETM complexes. Whereas major
Reaction of 6 with titanium isopropoxide trichloride in THF
resulted in formation of (S,S)-[2,6-bis(40-isopropyl-20-oxazolinyl)
phenyl]titanium(IV) isopropoxide dichloride (7a) in 73% yield.
X-ray crystal structure determination was performed for a single
crystal of 7a grown from ether/pentane (Figure 4). The geome-
try of the titanium center in this compound is similar to that of
nonchiral [2,6-bis(40-dimethyl-20-oxazolinyl)phenyl]titanium
isopropoxide dichloride.2d
amounts of methanol could be removed from 6 3MeOH by
3
drying the samples under vacuum at 20ꢀ100 ꢀC, this treatment
also caused melting and partial decomposition of 6 with forma-
tion of a red glassy substance. Complete removal of residual
amounts of methanol still present in pure, predried samples of
6 could be achieved by subsequent recrystallization from benzene.
An attempt to synthesize (S,S)-[2,6-bis(40-isopropyl-20-oxa-
zolinyl)phenyl]titanium trichloride using titanium(IV) tetrachloride
Table 1. Selected Distances [Å] and Angles [deg] in the
Crystal Structures of 4a and 4ba
in a similar way failed, although reaction of 6 C6H6 with titanium(IV)
3
4a
4b
chloride did occur and precipitation of the expected (dppbp)gold(I)
chloride (5) from the reaction mixture was observed. Obviously,
together with the anticipated metal exchange reaction, other side
reactions between the starting materials occurred. A possible reaction
is cleavage of the oxazoline ring by the highly Lewis-acidic and
oxophilic titanium(IV) chloride, which is known to cleave some
ethers (e.g., diisopropyl ether, anisole).7 Moreover, 2-oxazolines are
also susceptible to cleavage in acidic media.5a
Au1ꢀC11
Au1ꢀP1
Au1ꢀN11
Au1ꢀN12
Au1ꢀO11
Au1ꢀO12
C11ꢀAu1ꢀP1
2.060(2)
2.057(7)
2.2807(18)
3.046(4)
4.285(3)
4.721(7)
3.163(3)
178.1(2)
2.2758(6)
3.049(2)
3.053(2)
4.5425(18)
4.6108(19)
172.72(7)
Reaction of 6 C6H6 with vanadium(IV) tetrachloride in
3
benzene resulted in formation of (S,S)-[2,6-bis(40-isopropyl-20-
oxazolinyl)phenyl]vanadium(IV) trichloride (7b) in 82% yield
a Only one of the two independent molecules is listed, respectively. For
full data see the SI.
Scheme 3. Synthesis of Bimetallic Bis-Phebox-gold(I) dppbp Complex 6
Figure 3. Displacement ellipsoid plot of 6 C6H6 (50% probability). Hydrogen atoms and benzene solvent molecule are omitted for clarity. Selected
3
distances [Å], angles [deg], and torsion angles [deg] of 6 C6H6: Au1ꢀC11 2.070(6), Au2ꢀC21 2.059(7), Au1ꢀP1 2.2795(17), Au2ꢀP2 2.2740(16),
3
C34ꢀC44 1.494(4), C11ꢀAu1ꢀP1 177.28(19), C21ꢀAu2ꢀP2 173.66(19), C33ꢀC34ꢀC44ꢀC45 1.3(7). (For the full data and for 6 3MeOH
3
see the SI.)
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Scheme 4. Transmetalation Reaction of Bimetallic Organogold Compound 6 C6H6
3
Figure 5. Displacement ellipsoid plot of 7b (50% probability). Hydro-
gen atoms and benzene solvent molecule are omitted for clarity.
Figure 4. Displacement ellipsoid plot of 7a (50% probability). Hydro-
gen atoms are omitted for clarity.
Reaction of 6 with Cr(THF)3Cl3 in THF resulted in forma-
tion of the corresponding pincer chromium compound, which
was isolated as a pyridine adduct in 75% yield (Figure 6).
Attempts to crystallize the reaction product (S,S)-[2,6-bis(40-
isopropyl-20-oxazolinyl)phenyl]chromium(III) dichloride itself
from dichloromethane/pentane, i.e., in the absence of pyridine,
resulted in the formation of an insoluble solid that, however,
could be redissolved in pyridine. From the latter solution crystals
of 7c were obtained. These observations suggest that the primary
transmetalation reaction indeed afforded (S,S)-[2,6-bis(40-iso-
propyl-20-oxazolinyl)phenyl]chromium dichloride, but that at-
tempts to crystallize it resulted in the formation of a coordination
polymer that can be broken up into mononuclear species by
coordination with pyridine, affording 7c.
and precipitation of 5 (99%), which could be easily separated by
filtration. Compound 7b crystallized from benzene/pentane
solution as a benzene solvate (Figure 5). Interestingly, upon
reacting 6 with V(THF)3Cl3 in THF, not a single product
separated from the solution, again indicating that a competing
reaction had occurred. In this case a disproportionation of the
vanadium(III) compound into vanadium(II) and vanadium(IV)
compounds could be responsible.
EPR spectra of 1 mM solutions of 7b in benzene and toluene
were measured. Spectra in both solvents were identical and
revealed the presence of two different species in solution with
Aiso = 101 and 111 G, respectively. This could indicate the
presence of species with either N- or O-coordination of the
oxazoline rings in solution.8
The broad applicability of the gold transmetalation method is
underlined, as zirconium(IV) and hafnium(IV) chlorides also
reacted smoothly with 6 C6H6 in THF to give the corresponding
3
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dimeric, monopincer i-Pr,H-Phebox compounds (8a,b), which
were separated as benzene solvates by crystallization from
benzene/hexane in 82% and 83% yield, respectively (Figures 7
and 8).
An attempt to synthesize heptacoordinate, monomeric
(S,S)-[2,6-bis(40-isopropyl-20-oxazolinyl)phenyl]niobium(V)
tetrachloride in a similar manner, starting from niobium(V)
chloride in THF, resulted in formation of dimeric (S,S)-[2,6-
bis(40-isopropyl-20-oxazolinyl)phenyl]niobium dichloride oxide
(8c). This is probably a result of a primary reaction of niobium-
(V) chloride with THF affording niobium trichloride oxide,9
crystallography (Figure 10). The organic components Phebox-H
and Phebox-Cl could be identified via GC-MS analysis of the
reaction mixture after hydrolysis. Complex 9 could be character-
ized by X-ray crystal structure determination. A similar product
mixture (except compound 5) was formed when the Phebox-Li
compound 2a instead of the organogold reagent was used in the
reaction with iron(III) chloride at ꢀ78 ꢀC, followed by warming
to room temperature. Complex 9 comprises a newly formed
neutral, tetradentate di(Phebox) ligand, resulting from the
oxidative CꢀC coupling reaction of two Phebox anions, that is
N,N0-chelate bonded with oxazonilyl groupings of different aryl
groupings to one FeCl2 and from the other side of the diaryl
moiety again N,N0-chelate bonded to the second FeCl2 entity.
The formation of diPhebox, Phebox-H, and Phebox-Cl indicates
that the reaction of 6 with iron(III) chloride resulted in the
formation of Phebox radicals that either dimerized, thus forming
the tetradentate neutral N4 ligand present in 9, underwent
H-abstraction, e.g., from the solvent, forming the Phebox-H
compound, or reacted by atom transfer oxidation with iron(III)
trichloride to produce Phebox-Cl.
then followed by its transmetalation with 6 C6H6. No reaction
3
occurred when tantalum(V) chloride was used instead of
niobium(V) chloride, possibly because of the low stability of
tantalum trichloride oxide.9 Organoniobium compound 8c was
crystallized from benzene/pentane. X-ray crystal structure de-
termination revealed the presence of one molecule of benzene
and one molecule of pentane in the asymmetric unit. The
molecular structure of 8c is presented in Figure 9.
Interestingly, no reaction of 6 C6H6 with iron(II) chloride in
3
THF was observed. At room temperature, reaction of 6 C6H6
Compounds 7 (aꢀc) and 8 (aꢀc) were tested as precatalysts
in ethene polymerization. It appeared that in homogeneous
polymerization experiments in toluene using PMAO as activator
only compound 7b was active. The results are summarized in
Table 4.
3
with iron(III) chloride in benzene did not occur either. However,
on refluxing the reaction mixture for 6 h, a complex mixture of
products was formed (Scheme 5), from which a number of
products could be isolated and identified.
The di-iron(II) complex 9 and recovered 5 (99%) were isolated
from the reaction mixture. Complex 9 was identified by X-ray
In both experiments an initial rapid rise in temperature was
observed. However, rapid catalyst deactivation occurred when
Figure 6. Displacement ellipsoid plot of 7c (50% probability). Only one
of two independent molecules is shown. Hydrogen atoms are omitted
for clarity.
Figure 7. Displacement ellipsoid plot of 8a (50% probability). Hydro-
gen atoms and benzene solvent molecules are omitted for clarity.
Table 2. Selected Distances [Å] and Angles [deg] in the Crystal Structures of 7a, 7b, and 7ca
7a (M = Ti)
7b (M = V)
7c (M = Cr)
1.9973(19)
MꢀC1
2.141(3)
2.0906(17)
MꢀN1
2.177(2)
2.0926(14)
2.1110(16)
MꢀN2
2.190(2)
2.0932(15)
2.1075(17)
MꢀCl
2.3610(9)ꢀ2.4223(8)
1.774(2)
2.2258(6)ꢀ2.3034(5)
2.3354(6)ꢀ2.3414(6)
MꢀO1
MꢀN3
2.2025(16)
77.58(7)
76.97(7)
C1ꢀMꢀN1
C1ꢀMꢀN2
72.63(10)
73.26(10)
73.95(6)
74.55(7)
a In 7c only one of the two independent molecules is shown; for full data see the SI.
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Table 3. Selected Distances [Å] and Angles [deg] in the
Crystal Structures of 8a, 8b, and 8ca
8a (M = Zr)
8b (M = Hf)
8c (M = Nb)
M1ꢀC11
2.2948(16)
2.2893(15)
2.3759(14)
2.3521(13)
2.3827(14)
2.3690(13)
2.4347(4)
2.4256(5)
2.4244(4)
2.4423(4)
2.6199(4)
2.6819(4)
2.6205(4)
2.6583(4)
2.275(6)
2.295(3)
2.287(2)
2.286(2)
2.301(2)
2.287(2)
2.315(2)
2.3787(7)
2.3943(7)
2.3841(7)
2.3910(7)
M2ꢀC21
2.259(5)
M1ꢀN11
2.350(5)
M1ꢀN12
2.347(6)
M2ꢀN21
2.359(5)
M2ꢀN22
2.343(5)
M1ꢀCl11
2.3927(17)
2.4176(17)
2.4060(17)
2.4060(16)
2.6352(17)
2.6108(15)
2.6431(15)
2.6183(17)
M1ꢀCl12
M2ꢀCl21
M2ꢀCl22
M1ꢀCl13
M1ꢀCl23
M2ꢀCl13
Figure 8. Displacement ellipsoid plot of 8b (50% probability). Only
one of two independent molecules is shown. Hydrogen atoms and
benzene solvent molecules are omitted for clarity.
M2ꢀCl23
M1ꢀO1
1.9459(18)
1.9572(18)
1.9468(17)
1.9478(17)
68.24(9)
M1ꢀO2
M2ꢀO1
M2ꢀO2
C11ꢀM1ꢀN11
C11ꢀM1ꢀN12
C21ꢀM2ꢀN21
C21ꢀM2ꢀN22
M1ꢀCl13ꢀM2
M1ꢀCl23ꢀM2
M1ꢀO1ꢀM2
M1ꢀO2ꢀM2
68.27(5)
69.5(2)
68.80(5)
69.3(2)
67.88(9)
68.85(5)
69.3(2)
68.42(9)
68.48(5)
68.9(2)
67.98(9)
109.133(15)
106.176(14)
106.23(6)
107.68(6)
103.24(8)
102.78(8)
a In 8b only one of the two independent molecules is shown; for full data
see the SI.
Scheme 5. Reaction of Bis-organogold(I) dppbp Compound
6 with Iron(III) Chloride
Figure 9. Displacement ellipsoid plot of 8c (50% probability). Hydro-
gen atoms, disordered pentane, and benzene solvent molecules are
omitted for clarity.
the temperature inside the reactor reached ca. 65 ꢀC (Figure 11).
The data presented in Table 4 represent average activities during
15 min of polymerization.
Rapid catalyst deactivation, leading to low polymer yield, is a
common feature in olefin polymerization with many homoge-
neous transition metal catalysts, including those based on
titanium and vanadium. In the case of vanadium-catalyzed
polymerization, this is generally ascribed to the transformation
of active species to inactive V(II).10 A potential solution to this
problem is immobilization of the catalyst on a magnesium
chloride support. This approach is effective for titanium-based
catalysts, which are less susceptible to (over)reduction on
contact with aluminum alkyls when immobilized on MgCl2.11
Metallocenes such as Cp2TiCl2 undergo rapid deactivation
under homogeneous polymerization conditions, whereas their
immobilization on MgCl2 leads to stable activity.12 Examples of
highly stable MgCl2-supported vanadium catalysts have also
been reported.13 Particularly effective supports, with almost
perfectly spherical particle morphology and having the composi-
tion MgCl2/AlEtn(OEt)3ꢀn, can be obtained by reaction of AlEt3
with MgCl2 nEtOH adducts.14 In the present work, the effect of
3
immobilizing the titanium and vanadium complexes 7a and 7b
on such supports was investigated. Immobilization was carried
out at 50 ꢀC by contacting the support overnight with a toluene
solution containing the desired quantity of the Phebox complex.
It was observed that the yellow (7a) or olive green (7b) color of
the starting solutions was transferred to the supports, giving
sandy red and brown colored solids. The slurry of immobilized
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catalyst was diluted with light petroleum and used directly in
polymerization. In addition to ethene homopolymerization,
ethene/1-hexene copolymerizations were carried out in order
to gain a first indication of the ability of these complexes to
incorporate a co-monomer and to identify differences between
the titanium and vanadium catalysts in this respect. The results of
polymerizations with the immobilized Ti complex 7a are shown
in Table 5, from which it is apparent that, in contrast to the lack of
activity observed in homogeneous polymerization, good activity
is observed when the catalyst is immobilized on a MgCl2 support.
Essentially constant activity was observed in these experiments,
illustrating the stabilizing effect of the support. The presence of
co-monomer (1-hexene) resulted in some decrease in catalyst
activity and polyethylene molecular weight, particularly in the Mw
values, giving somewhat narrower molecular weight distributions
in copolymerization. Acceleration of chain transfer in the pre-
sence of a co-monomer is a frequently observed phenomenon in
ethene polymerization with both homogeneous and immobilized
catalysts.15 Slightly lower polymer melting temperatures and
crystallinities were also obtained, consistent with incorporation
of a small quantity of co-monomer into the polyethylene chain.
13C NMR analysis revealed hexene contents of approximately
0.1 and 0.2 mol % in the copolymers prepared at 50 and 70 ꢀC,
respectively, confirming the relatively poor copolymerization
ability of this catalyst.
Polymerizations with the vanadium complex 7b immobilized
on a MgCl2/AlEtn(OEt)3ꢀn support gave the results shown in
Table 6. The activities obtained are lower than those obtained
with 7a, but around an order of magnitude higher than those
measured under homogeneous polymerization conditions.
Again, the presence of 1-hexene is seen to lead to decreased
activity, but the significantly lower melting temperatures of the
polymers prepared in ethylene/1-hexene copolymerization in-
dicate greater co-monomer incorporation with the vanadium
complex than was obtained with the titanium complex 7a. This
was confirmed by 13C NMR analysis, which revealed hexene
contents of 0.25 and 1.0 mol % in the copolymers prepared at 50
and 70 ꢀC, respectively.
Figure 10. Displacement ellipsoid plot of 9(50% probability). Only one of
two independent molecules is shown. Hydrogen atoms and disordered
solvent molecules are omitted for clarity. Selected distances [Å], angles
[deg], and torsion angles [deg] in the crystal structure of 9: Fe1ꢀN11
2.097(3), Fe1ꢀN21 2.096(3), Fe2ꢀN12 2.085(3), Fe2ꢀN22 2.095(4),
Fe1ꢀCl11 2.2680(11), Fe1ꢀCl12 2.2377(14), Fe2ꢀCl21 2.2666(13),
Fe2ꢀCl22 2.2622(15), C11ꢀC21 1.492(5), N11ꢀFe1ꢀN21 111.98(12),
N12ꢀFe2ꢀN22 108.39(12), Cl11ꢀFe1ꢀCl12 123.91(5), Cl21ꢀFe2ꢀCl22
120.54(6), C12ꢀC11ꢀC21ꢀC22 101.6(5) (for full data see the SI).
Figure 11. Temperature profiles of polymerizations carried out under
homogeneous conditions with precatalyst 7b.
Table 4. Homogeneous Polymerization Experiments with Precatalyst 7b
entry no.
start temp, ꢀC
activity, kg PE/mol h bar
Mw, g/mol
Mn, g/mol
Mw/Mn
Tm, ꢀC
χc,a %
3
3
1
2
50
20
72
785 000
673 000
395 000
340 000
2.0
2.0
135.0
135.4
39
43
118
a Crystallinity (χc) calculated from melting enthalpy (ΔH), taking a ΔH value of 293 J/g for 100% crystalline polyethylene.
Table 5. Ethene (Co-)polymerization Using Complex 7a on a MgCl2-Based Supporta
entry
temp, ꢀC
1-hexene, mL
activity, kg/mol h bar
Mw, g/mol
Mn, g/mol
Mw/Mn
Tm, ꢀC
χc, %
3
3
1
2
3
4
50
50
70
70
0
20
0
4600
3900
4100
3200
1 400 000
870 000
450 000
380 000
280 000
270 000
3.1
2.3
4.6
3.6
136.6
133.2
136.7
131.4
48
45
51
45
1 280 000
20
980 000
a Support composition: MgCl2 0.21AlEt2.38(OEt)0.62. Polymerization conditions: 500 mL of light petroleum, immobilized catalyst 100 mg (4 μmol Ti),
3
AliBu3 1 mmol, ethene pressure 5 bar, time 1 h.
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Organometallics
ARTICLE
Table 6. Ethene (Co-)polymerization Using Complex 7b on a MgCl2-Based Supporta
AlR3
temp, ꢀC
1-hexene, mL
activity, kg/mol h bar
Mw, g/mol
Mn, g/mol
Mw/Mn
Tm, ꢀC
χc, %
3
3
Ali-Bu3
Ali-Bu3
AlEt3
50
70
50
50
70
70
0
0
520
1800
1200
580
740 000
690 000
360 000
360 000
850 000
450 000
500 000
290 000
2.0
1.9
1.7
2.2
2.0
2.5
136.9
136.0
135.6
126.7
135.2
123.9
52
42
40
34
42
30
0
1 480 000
980 000
AlEt3
20
0
AlEt3
1600
1 010 000
AlEt3
20
920
730 000
a Support composition: MgCl2 0.17AlEt2.21(OEt)0.89. Polymerization conditions: 500 mL of light petroleum, immobilized catalyst 100 mg (2 μmol V),
3
AlR3 1 mmol, ethene pressure 5 bar, time 1 h.
Figure 12. Possible structures of products anticipated in methylation reactions of 8a after subsequent reaction of the alkylation mixture with water.
The molecular weight data for the polyethylenes synthesized
with the vanadium complex 7b indicate a narrow (Schulzꢀ
Flory) distribution, indicative of single-center catalysis, although
the Mw/Mn values show some broadening in distribution in the
copolymerizations, carried out with AlEt3 as cocatalyst. The broad-
er copolymer distribution appears to arise from a more significant
decrease in Mn than in Mw, in contrast to what was observed with
the Ti-Phebox complex 7a. Confirmation of the single-center
characteristics of the vanadium complex in ethene homopolymer-
ization with Ali-Bu3 as cocatalyst has been obtained from an
investigation of the polymer melt rheological properties.16 Com-
parison of a range of different MgCl2-supported titanium and
vanadium catalysts revealed that single-center behavior was
consistently retained in the case of vanadium, but not with
analogous titanium complexes.
To study possible reasons for the low activity of both 7 (aꢀc)
and 8 (aꢀc) as precatalysts in homogeneous polymerization,
reactions of 8a with either MeLi or MeMgCl were carried out. In
both cases it appeared impossible to separate pure products of
alkylation from these reaction mixtures. Subsequently these
crude product mixtures were hydrolyzed with water. The organic
products were extracted with ether, and the ether extracts
analyzed by GC-MS analysis. This revealed in each case the
presence of a complex mixture of products with m/z values of
314, 329, 347, and 406. Structures proposed for these products
are presented in Figure 12.
chlorides with a bimetallic Phebox-gold compound 6. In con-
trast to reactions with Phebox lithium compounds, which often
lead to the formation of mono-, di-, and tri-Phebox complexes,
the use of the corresponding gold(I) compounds resulted in the
selective transfer of a single Phebox group to each metal center.
This lower selectivity was very apparent in experiments with
titanium isopropoxide trichloride that afforded the mono-Phe-
box titanium compound 7a with the gold reagent 6, whereas the
reaction with the Phebox-lithium reagent provided an intract-
able mixture of mono-, di-, and tri-Phebox products. An obvious
advantage of this synthetic method is the almost quantitative re-
formation of the insoluble dimeric gold chloride material 5 at the
end of the reaction, which is easily separable and can be reused in
another reaction. However, in cases where the gold reagent is
not active enough, as is most likely the case for both iron(II) and
-(III) salts, heating of the reaction mixture caused oxidative
coupling of the Phebox ligand from the in situ formed Phebox
iron complex.
Structures of the new compounds in the solid state were
established by X-ray crystallography. The enantiopurity of the
crystal was confirmed by absolute structure determination using
the Flack x parameter;24 see the SI, Table 6. In all cases the
R-Phebox ligand appears to be mer-NCN bonded to the metal
center.
These i-Pr,H-Phebox metal complexes of early and middle
transition metals were tested as precatalysts in ethene polymer-
ization. Low stability was observed under homogeneous polym-
erization conditions, using methylaluminoxane as cocatalyst, but
immobilization of the titanium and vanadium Phebox complexes
7a and 7b on MgCl2-based supports and ethene polymerization
in the presence of Ali-Bu3 or AlEt3 led to stable catalyst activity
and more than an order of magnitude increase in polymer yield.
The immobilized vanadium complex 7b retained single-center
behavior after immobilization, producing polyethylene with
narrow (SchulzꢀFlory) molecular weight distribution.
It is noteworthy that the arene product for the ligand with m/z
300 was absent in the mixture. This indicates complete alkylation
of the ligand. The product with m/z 406 is probably the result of a
reaction of 8a with THF with subsequent hydrolysis.
’ CONCLUSION
A number of novel R-Phebox metal complexes of some early
and middle transition metals were successfully synthesized via a
transmetalation reaction of the respective transition metal
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Organometallics
ARTICLE
’ EXPERIMENTAL SECTION
The reaction mixture was allowed to warm to room temperature and
stirred for 1 h. Water (5 mL) was added, and the resulting reaction
mixture was stirred for 10 min. The organic layer was separated from
the aqueous layer, which was extracted with dichloromethane (2 ꢁ
20 mL). The combined organic extracts were dried over magnesium
sulfate and filtered, and the filtrate was concentrated to dryness in
vacuo. The crude product was dissolved in boiling methanol (70 mL)
and crystallized overnight as a methanol solvate. The mother liquor
was evaporated to dryness, and the residue was recrystallized from
methanol once again to give additional amounts of the product. The
product, 6, was dried in vacuo at 100 ꢀC until constant pressure
(0.1 mbar) for 6 h to remove most of the methanol. The product was
then dissolved in boiling benzene, and 6 crystallized as a benzene
All experiments were carried out in a dry, oxygen-free nitrogen
atmosphere, using standard Schlenk techniques. Solvents were dried
and distilled from sodium (pentane, toluene), sodium/benzophenone
(diethyl ether, tetrahydrofuran, and hexane), or CaH2 (pyridine) prior
to use. n-BuLi (1.6 M in hexanes) was supplied by Acros and used as
1
received. H and 13C NMR spectra were recorded on a Varian Inova
300 spectrometer. (S,S)-(R,H-Phebox)Br (1a, 1b)5d and 4,40-bis-
[P-(chlorogold(I))diphenylphosphino]biphenyl [(dppbp)(AuCl)2] (5)2d
were synthesized according to literature procedures. All other chemicals
were purchased from either Acros or Aldrich and used as received.
Elemental analyses were performed by H. Kolbe Mikroanalytisches
Laboratorium, M€ulheim an der Ruhr, Germany.
1
solvate by slow evaporation of the solvent. Yield: 8.3 g (88%). H
Triphenylphosphine (S,S)-[2,6-Bis(40-isopropyl-20-oxazolinyl)
phenyl]gold (4a). To a solution of (S,S)-2,6-bis(40-isopropyl-20-
oxazolinyl)phenyl bromide (1a) (760 mg, 2 mmol) in THF (10 mL)
at ꢀ78 ꢀC was added via a syringe 1.3 mL (2 mmol) of n-BuL(1.6 M) in
hexane. The resulting solution containing in situ prepared 2a was stirred
for 10 min. Subsequently (triphenylphosphine)gold chloride (1.03 g,
2.08 mmol) was added. The reaction mixture was allowed to warm to
room temperature and stirred for 1 h. Water (1 mL) was added. The
resulting reaction mixture was stirred for 10 min. The organic layer was
separated, and the aqueous layer was extracted with diethyl ether (2 ꢁ
10 mL). The combined organic extracts were separated from water,
dried over magnesium sulfate, and then concentrated in vacuo. The
residue was dried in vacuo, redissolved in benzene, and again made dry in
vacuo. This treatment was performed to convert crystalline product into
an amorphous state. It precipitated from diethyl ether in a crystalline
state. The resulting amorphous mass was dissolved in diethyl ether
(20 mL). The clear solution was decanted from the precipitate and then
left for crystallization at room temperature. Crystals were filtered off and
washed with a small amount of diethyl ether. An additional amount of
the product was obtained by recrystallization of the residue obtained
after concentration of the mother liquor. Yield: 1.17 g of 4c (77%). 1H
NMR (300 MHz, CDCl3): δ 0.72 (d, 6H, 3JHꢀH = 6.7 Hz), 0.81 (d, 6H,
3JHꢀH = 6.7 Hz), 1.58 (septet, 2H, 3JHꢀH = 6.6 Hz), 3.89ꢀ3.99 (m, 4H),
4.13ꢀ4.24 (m, 2H), 7.14 (t, 1H, 3JHꢀH = 7.6 Hz), 7.40ꢀ7.50 (m, 9H),
3
NMR (300 MHz, CDCl3): δ 0.72 (d, 12H, JHꢀH = 6.7 Hz), 0.81
3
(d, 12H, JHꢀH = 6.7 Hz), 1.66 (m, 4H), 3.90ꢀ4.00 (m, 8H),
3
4.15ꢀ4.25 (m, 4H), 7.15 (t, 2H, JHꢀH = 7.8 Hz), 7.40ꢀ7.52 (m,
3
12H), 7.60ꢀ7.82 (m, 16H), 7.90 (dd, 4H, JHꢀH = 7.7 Hz, 5JPꢀH
=
1.5 Hz). 13C{1H} NMR (75 MHz, CDCl3): δ 17.8, 19.1, 32.6, 69.7,
72.7, 100.7, 124.9, 127.4 (d, 3JPꢀC = 12 Hz), 128.8 (d, 3JPꢀC = 11 Hz),
4
4
130.6 (d, JPꢀC = 5.8 Hz), 131.0, 131.3 (d, JPꢀC = 5.5 Hz), 132.0
(d, 3JPꢀC = 5.8 Hz), 134.5 (d, 2JPꢀC = 14 Hz), 135.1 (d, 2JPꢀC = 14
Hz), 138.0, 168.7 (d, JPꢀC = 3 Hz). 31P{1H} NMR (121 MHz,
5
CDCl3): δ 42.2 ppm. Anal. Calcd for C72H74Au2N4O4P2: C, 57.07; H,
4.92; N, 3.70. Found: C, 56.88; H, 4.65; N, 3.79.
(S,S)-[2,6-Bis(40-isopropyl-20-oxazolinyl)phenyl]titanium
Isopropoxide Dichloride (7a). A solution of 6 (1.85 g, 1.16 mmol)
in THF (30 mL) was added in one portion to solid titanium isopropoxide
trichloride (507 mg, 2.38 mmol). The reaction mixture was stirred for
16 h at room temperature and centrifuged to remove insoluble 5. The
precipitate (5) was collected by decantation and was washed with THF
(15 mL). The THF was removed in vacuo. Diethyl ether (10 mL) was
added to the sticky amorphous residue, and the mixture was left to
crystallize for 60 h. The diethyl ether solution was decanted from the
crystals, which were filtered off and dried in vacuo. Yield: 0.83 g (73%).
Single crystals for X-ray crystallography were grown by vapor diffusion
of pentane into a diethyl ether solution of the product 7a. Yield of
recovered 5 was 1.14 g (99%). 1H NMR (300 MHz, C6D6): δ 0.58ꢀ0.80
(m, 8H), 0.92ꢀ1.16 (m, 10H), 1.34ꢀ1.65 (m, 1H), 2.38ꢀ2.62 (m, 1H),
2.88ꢀ3.12 (m, 1H), 3.65ꢀ4.10 (m, 4H), 4.26 (m, 1H), 4.43ꢀ4.66 (m,
3
7.61ꢀ7.73 (m, 6H), 7.90 (d, 2H, JHꢀH = 7.6 Hz). 13C{1H} NMR
(75 MHz, CDCl3): δ 17.8, 19.1, 32.6, 69.7, 72.7, 124.8, 128.7 (d, 3JPꢀC
=
11 Hz), 130.5, 130.8, 134.4 (d, 2JPꢀC = 14 Hz), 138.1, 168.7. 31P{1H}
NMR (121 MHz, CDCl3): δ 42.6 ppm.
3
3
1H), 6.67 (t, 1H, JHꢀH = 7.5 Hz), 7.26 (d, 2H, JHꢀH = 7.3 Hz).
13C{1H} NMR (75 MHz, C6D6): δ 15.5, 15.6, 15.7, 15.9, 18.7, 18.9,
19.1, 19.2, 19.4, 24.6, 24.9, 25.6, 30.2, 30.5, 33.3, 65.9, 69.8, 70.5, 70.7,
71.0, 72.7, 73.0, 73.3, 73.6, 81.6, 126.6, 129.0, 131.1. Anal. Calcd for
C21H30Cl2N2O3Ti: C, 52.85; H, 6.34; N, 5.87. Found: C, 52.66; H,
6.48; N, 5.69.
Triphenylphosphine (S,S)-[2,6-Bis(40-tert-butyl-20-oxazolinyl)
phenyl]gold (4b). (Triphenylphosphine)gold chloride (0.3 g, 0.6 mmol)
was added to a solution of 2a (vide supra) (0.6 mmol) in THF/hexanes
at ꢀ78 ꢀC. The resulting reaction mixture was allowed to warm to room
temperature and stirred for 1 h. Water (0.5 mL) was added, and the reaction
mixture was stirred for 10 min, which was followed by separation of the
organic layer. This layer was dried over magnesium sulfate, then filtered, and
the filtrate was concentrated to dryness in vacuo. Subsequent workup as
described for 4a resulted in the formation of crystals, which were filtered off
and washed with a small amount of ether. An additional amount of the
(S,S)-[2,6-Bis(40-isopropyl-20-oxazolinyl)phenyl]vanadium
Trichloride (7b). A solution of 6 (1.0 g, 0.628 mmol) in benzene
(30 mL) was added to liquid neat vanadium(IV) tetrachloride (0.245 g,
1.27 mmol). The reaction mixture was stirred overnight. The resulting
mixture was centrifuged (removal of insoluble 5) and the solution
decanted. The solution was concentrated in vacuo. The residue was
crystallized from a benzene/pentane mixture, affording a benzene
solvate of 7b as dark green needles. Yield: 550 mg (82%). Yield of
recovered 5 was 615 mg (99%). Anal. Calcd for C24H29Cl3N2O2V:
C, 53.90; H, 5.47; N, 5.24. Found: C, 53.77; H, 5.53; N, 5.18.
Pyridino (S,S)-[2,6-Bis(40-isopropyl-20-oxazolinyl)phenyl]
chromium Dichloride (7c). A solution of 6 (525 mg, 0.33 mmol)
in THF (15 mL) was added to solid CrCl3(THF)3 (245 mg, 0.66
mmol). The reaction mixture was stirred for 16 h at room temperature.
Solvent was evaporated under vacuum. The residue was dissolved in
benzene (50 mL), and the solids (5) were removed by centrifugation
and decantation of the supernatant. This solution was evaporated in
vacuo. After evaporation of benzene pyridine (0.5 mL) was added to the
1
product was separated from the mother liquor. Yield: 350 mg (72%). H
NMR (300 MHz, CDCl3): δ 0.76 (s, 18H), 3.86 (dd, 2H, 3JHꢀH = 10.1 Hz,
3JHꢀH = 7.5 Hz), 3.99ꢀ4.13 (m, 4H), 7.14 (t, 1H, JHꢀH = 7.6 Hz),
3
3
7.39ꢀ7.50 (m, 9H), 7.61ꢀ7.71 (m, 6H), 7.90 (d, 2H, JHꢀH = 7.6 Hz).
13C{1H} NMR (75 MHz, CDCl3):δ25.9, 34.0, 68.5, 76.4, 128.8 (d, 3JPꢀC
=
11 Hz), 130.8, 134.5 (d, 2JPꢀC = 14 Hz) 138.2. 31P{1H} NMR (121 MHz,
CDCl3): δ 42.6 ppm. Anal. Calcd for C38H42AuN2O2P: C, 58.02; H, 5.38;
N, 3.56. Found: C, 57.97; H, 5.46; N, 3.55.
4,40-Bis{P-((S,S)-[2,6-bis(40-isopropyl-20-oxazolinyl)phenyl]
gold)(diphenylphosphino)}biphenyl (6). 4,40-Bis(diphenyl-
phosphino)biphenylgold chloride (5) (6.16 g, 6.24 mmol) was added
to a solution of 2a (vide supra) (13 mmol) in THF/hexanes at ꢀ78 ꢀC.
2827
dx.doi.org/10.1021/om200170b |Organometallics 2011, 30, 2819–2830

Organometallics
ARTICLE
residue. The resulting mixture was dissolved in dichloromethane and
crystallized by diffusion of pentane into this solution. Yield of 7c was
0.250 g (75%), dark purple crystals. Yield of recovered 5 was 320 mg
(98%). Anal. Calcd for C23H28Cl2CrN3O2: C, 55.10; H, 5.63; N, 8.38.
Found: C, 54.95; H, 5.70; N, 8.29.
stirred overnight at room temperature. No conversion was observed.
Subsequently the reaction mixture was refluxed under stirring for 6 h.
Formation of a white precipitate (5) and a change of color of the reaction
mixture from dark brown to yellow-orange were observed. The reaction
mixture was cooled to room temperature, and 5 removed by centrifuga-
tion. A small fraction of the supernatant was diluted with dichloro-
methane, washed with water, and analyzed by GC-MS. Solvent was
evaporated in vacuo. The product was crystallized from acetonitrile/
(S,S)-[2,6-Bis(40-isopropyl-20-oxazolinyl)phenyl]zirconium
Trichloride Dimer (8a). A solution of 6 (0.525 g, 0.33 mmol) in THF
(15 mL) was added to solid ZrCl4 (154 mg, 0.66 mmol). The reaction
mixture was stirred for 16 h at room temperature. Volatiles were
removed in vacuo. The residue was extracted with benzene (50 mL)
and centrifuged. The precipitate (5) obtained after centrifugation was
flushed with a second portion of benzene (50 mL) and stirred overnight,
and the supernatant was separated from the precipitate by centrifuga-
tion. The combined benzene extracts were concentrated in vacuo. The
residue was crystallized from benzene/hexane, affording 8a as a solvate
with benzene. Colorless crystals (312 mg, 82%) were obtained. Yield
of recovered 5 was 320 mg (98%). 1H NMR (300 MHz, C6D6): δ 0.76
(d, 12H, 3JHꢀH = 7.0 Hz), 0.86 (d, 12H, 3JHꢀH = 6.7 Hz), 3.21 (m, 4H),
3.79 (t, 4H, 3JHꢀH = 9.0 Hz), 4.17 (dd, 4H, 2JHꢀH = 9.0 Hz, 3JHꢀH = 3.4
Hz), 4.96 (d, 4H, 2JHꢀH = 8.8 Hz), 6.86 (t, 2H, 3JHꢀH = 7.6 Hz), 7.56
(d, 4H, 3JHꢀH = 7.6 Hz). 13C{1H} NMR (75 MHz, C6D6): δ 14.1, 19.4,
29.9, 69.8, 71.4, 100.4, 127.5, 128.9, 130.6, 178.0. Anal. Calcd for
C48H58Cl6Zr2N4O4: C, 50.12; H, 5.08; N, 4.87. Found: C, 50.21; H,
5.05; N, 4.80.
ether and identified by X-ray crystallography as [9 2Et2O]. Yield of
3
[9 2Et2O] was 110 mg (11%).
3
Reaction of Pincer Lithium 2a with Iron(III) Chloride. A
solution of in situ prepared 2a (910 mg, 2.4 mmol) in THF (10 mL) was
added to solid iron(III) chloride (370 mg, 2.28 mmol) in THF (10 mL)
at ꢀ78 ꢀC. The reaction mixture was allowed to warm to room
temperature and was stirred for another 1 h. A small sample of the
resulting reaction mixture was diluted with dichloromethane, washed
with water, and analyzed by GC-MS. The result of this analysis is
presented in Scheme 5. Solvent of the remaining reaction mixture was
evaporated in vacuo. The residue was dissolved in benzene (50 mL;
removal of LiBr), and the precipitate removed by centrifugation and
decantation of the supernatant. The supernatant was concentrated in
vacuo, and the residue was crystallized from ether/pentane, which
afforded 9 as colorless needles. They were identified by X-ray crystal-
lography as [9 2Et2O]. Yield of [9 2Et2O] was 114 mg (9.5%).
3
3
(S,S)-[2,6-Bis(40-isopropyl-20-oxazolinyl)phenyl]hafnium
Trichloride Dimer (8b). A solution of 6 (1.59 g, 1 mmol) in THF
(20 mL) was added to solid hafnium(IV) chloride (640 mg, 2 mmol).
The reaction mixture was stirred for 40 h at room temperature. The
solvent of the reaction solution was evaporated in vacuo. Benzene
(100 mL) was added to the residue, and the mixture was stirred for
50 h at room temperature and then centrifuged. The residue (5)
obtained after decantation of the supernatant was flushed with a second
portion of hot benzene (100 mL). The resulting mixture was centri-
fuged. Combined benzene extracts were concentrated in vacuo. The
residue was crystallized from benzene/hexane, affording 8b as benzene
solvate. Colorless crystals (1.03 g, 83%) were obtained. Yield of recovered
Reactions of (S,S)-[2,6-Bis(40-isopropyl-20-oxazolinyl)phenyl]
zirconium Trichloride Dimer (8a) with Either Methylmagne-
sium Chloride or Methyllithium. To a solution of (S,S)-[2,6-bis
(40-isopropyl-20-oxazolinyl)phenyl]zirconium trichloride (8a) (200 mg,
0.4 mmol) in THF (10 mL) at ꢀ78 ꢀC was added the alkylating reagent
(either methylmagnesium chloride in THF (22 wt %, d = 1.03) (90.3 mg,
0.4 mL, 1.21 mmol) or methyllithium in diethyl ether (1.6 M, 0.8 mL,
1.28 mmol)). The reaction mixture turned bright green, but after cooling
ceased the color of the reaction mixture soon turned brown. The
reaction mixture was allowed to warm to room temperature and was
stirred at room temperature overnight. The reaction mixture was
concentrated in vacuo. Attempts to crystallize the residue from various
solvents failed. No pure, crystalline material was obtained. The remain-
ing residue was then hydrolyzed with aqueous sodium hydroxide. The
resulting aqueous solution was extracted with diethyl ether, and its
contents were analyzed by GS-MS. GC-MS analysis revealed a complex
mixture of products with m/z 314, 329, 347, 406.
1
5 was 977 mg (99%). H NMR (300 MHz, C6D6): δ 0.75 (d, 12H,
3
3JHꢀH = 7.3 Hz), 0.85 (d, 12H, JHꢀH = 6.7 Hz), 3.23 (m, 4H), 3.80
3
3
(t, 4H, JHꢀH = 9.2 Hz), 4.18 (d, 4H, JHꢀH = 7.6 Hz), 4.93 (d, 4H,
3JHꢀH = 7.0 Hz), 6.90 (t, 2H, 3JHꢀH = 7.6 Hz), 7.65 (d, 4H, 3JHꢀH
=
7.6 Hz). 13C{1H} NMR (75 MHz, C6D6): δ 14.1, 19.4, 29.9, 69.7, 71.8,
100.4, 127.5, 128.6, 129.2, 179.2. Anal. Calcd for C42H52Cl6Hf2N4O4:
C, 40.47; H, 4.20; N, 4.49. Found: C, 40.45; H, 4.42; N, 4.38.
Polymerization Experiments. All manipulations were performed
under an argon atmosphere using a glovebox (Braun MB-150 GI or
LM-130) and Schlenk techniques. Light petroleum (bp 40ꢀ60 ꢀC) and
toluene were passed over columns containing activated alumina. All
solvents were freezeꢀthawꢀdegassed twice before use. AlEt3 (1.3 M in
heptane), Ali-Bu3 (25 wt % in toluene), and polymeric methyl aluminox-
ane (PMAO, 10 wt % solution in toluene) were obtained from Acros,
Akzo Nobel, and Crompton, respectively. Ethene (3.5 grade supplied by
Air Liquide) was purified by passing over columns of BASF RS3-11-
supported Cu oxygen scavenger and 4 Å molecular sieves.
Homogeneous Polymerization Experiments. Toluene (300 mL)
was introduced into a 1 L stainless steel reactor maintained at the experiment
temperature (see Table 4), after which ethene (20 bar) was introduced.
PMAO (2.8 g, 10 wt % in toluene, 5.0 mmol Al) was added, followed by a
solution of 7b benzene solvate (5.3 mg, 10 μmol) in toluene (5 mL). The
reaction was stirred for 15 min, after which the polymerization was
terminated by venting off the volatiles. The polymer was filtered off, washed
with an aqueous HCl (1 M) solution and ethanol, dried, and weighed.
Polymerization Experiments with Supported Catalysts.
a. Support Preparation and Catalyst Immobilization. The supports
used in this work were prepared by addition of AlEt3 to the adduct
(S,S)-[2,6-Bis(40-isopropyl-20-oxazolinyl)phenyl]niobium Di-
chloride Oxide Dimer (8c). A solution of 6 (487 mg, 0.306 mmol) in
THF (10 mL) was added to solid NbCl5 (165 mg, 0.611 mmol). The
reaction mixture was stirred overnight at room temperature. Volatiles of
the reaction mixture were removed in vacuo. The residue was dissolved
in benzene and centrifuged in order to remove insoluble 5. The decanted
solution was concentrated in vacuo. The residue was crystallized from
benzene/pentane, affording 8c as a benzene and pentane solvate
(lemon-yellow needles). Yield of 8c was 256 mg (76%). Yield of
1
recovered 5 was 300 mg (99%). H NMR (300 MHz, C6D6): δ 0.77
(d, 12H, 3JHꢀH = 7.0 Hz), 0.94 (d, 12H, 3JHꢀH = 6.7 Hz), 3.28 (septet of
doublets, 4H, 3JHꢀH = 6.9 Hz, 3JHꢀH = 2.5 Hz), 4.10 (t, 4H, 3JHꢀH
=
9.5 Hz), 4.29 (dd, 4H, 2JHꢀH = 8.7 Hz, 3JHꢀH = 4.7 Hz), 5.09 (doublet of
quadruplets, 4H, 3JHꢀH = 9.9 Hz, 4JHꢀH = 2.4 Hz), 6.86 (t, 2H, 3JHꢀH
=
7.5 Hz), 7.58 (d, 4H, 3JHꢀH = 7.6 Hz). 13C{1H} NMR (75 MHz, C6D6):
δ 14.8, 20.1, 28.7, 68.1, 71.8, 99.3, 127.5, 128.9, 129.4, 176.7. Anal. Calcd
for C47H64Cl4N4Nb2O6: C, 50.92; H, 5.82; N, 5.05. Found: C, 50.69; H,
5.76; N, 4.95.
Reaction of Bis-pincer-gold Diphosphine 6 with Iron(III)
Chloride. A solution of 6 (1.6 g, 1 mmol) in benzene (20 mL) was
added to solid FeCl3 (340 mg, 2.1 mmol). The reaction mixture was
MgCl2 1.1EtOH in light petroleum (AlEt3/EtOH = 2) at 0 ꢀC, after
3
which the mixture was kept at room temperature for 2 days with
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Organometallics
ARTICLE
occasional agitation. The resultant support was washed with light
petroleum three times and dried under argon flow and subsequently
under vacuum until free-flowing. The ethoxide contents in the MgCl2/
AlEtn(OEt)3ꢀn supports were determined by gas chromatographic
(GC) analysis of the ethanol content of a solution obtained by
dissolving 100 mg of support in 5 mL of BuOH containing a known
quantity of PrOH as an internal standard.
Immobilization was carried out by contacting the support (100 mg)
with 2ꢀ4 mL of a toluene solution containing 2ꢀ4 μmol of the titanium
(7a) or vanadium (7b) Phebox complex at 50 ꢀC for 16 h. The resulting
slurry was, after dilution with light petroleum, used as such in
polymerization.
b. Polymerization Procedure. Polymerization was carried out in an l L
Premex autoclave by charging the immobilized catalyst, slurried in
approximately 100 mL of light petroleum, to a further 400 mL of light
petroleum containing 1 mmol of AlEt3 or Ali-Bu3, at the desired
temperature and at an ethene pressure of 5 bar. After catalyst injection,
polymerization was continued at constant pressure for 1 h with a stirring
rate of 1000 rpm. Copolymerization experiments were carried out under
similar conditions after addition of 20 mL of 1-hexene. After venting the
reactor, 20 mL of acidified ethanol was added, and stirring was continued
for 30 min. The polymer was recovered by filtration, washed with water
and ethanol, and dried in vacuo overnight at 60 ꢀC.
Compound 7a. All hydrogen atoms were located in difference
Fourier maps and refined with a riding model.
Compound 7b C6H6. All hydrogen atoms were located in difference
3
Fourier maps and refined with a riding model.
Compound 7c. All hydrogen atoms were located in difference Fourier
maps and refined with a riding model.
Compound 8a 2C6H6. Hydrogen atoms were introduced in calcu-
3
lated positions and refined with a riding model
Compound 8b. The crystal was cracked with a 2.1ꢀ rotation about an
arbitrary axis relating the two fragments. Refinement was performed on a
HKLF5 file.23 The asymmetric unit contains two metal complexes and
three cocrystallized benzene solvent molecules, of which two were
refined with full and one with partial occupancy. Distance and flatness
restraints were used for this benzene molecule. Hydrogen atoms were
introduced in calculated positions and refined with a riding model.
Compound 8c. Pentane and benzene molecules were refined with
disorder models, respectively. Distance and angle restraints and addi-
tional restraints to approximate isotropic displacement parameters were
used for these disordered molecules. Hydrogen atoms were introduced
in calculated positions and refined with a riding model.
Compound 9. The crystal structure contains voids filled with
disordered solvent molecules (752 Å3/unit cell). Their contribution
to the structure factors was secured by the SQUEEZE routine of the
PLATON22 software, resulting in 198 electrons/unit cell. Hydrogen
atoms were introduced in calculated positions and refined with a
riding model.
c. Polymer Characterization. Molecular weight and molecular weight
distributions of the resulting polymers were determined by means of gel
permeation chromatography on a PL-GPC210 at 135 ꢀC using 1,2,4-
trichlorobenzene as solvent. Differential scanning calorimetry (DSC)
was carried out with a Q100 differential scanning calorimeter (TA
Instruments). The samples (1.5ꢀ2.5 mg) were heated to 160 ꢀC at a rate
of 10 ꢀC/min and cooled at the same rate to 20 ꢀC. A second heating
cycle at 10 ꢀC/min was used for data analysis.
’ ASSOCIATED CONTENT
S
Supporting Information. This material is available free of
charge via the Internet at http://pubs.acs.org.
b
13C NMR analysis of ethene/1-hexene copolymers was kindly carried
out by Prof. R. Cipullo at the University of Naples. Quantitative 13C
NMR spectra were recorded at 120 ꢀC on 20 mg/mL solutions in
tetrachloroethane-1,2-d2, with a Bruker DRX 400 Avance spectrometer
operating at 100.6 MHz with a 5 mm probe, under the following
conditions: 80ꢀ pulse; acquisition time 2.7 s; relaxation delay 2.5 s; >10K
transients. Broad-band proton decoupling was achieved with a modified
WALTZ16 sequence (BI_WALTZ16_32 by Bruker).
’ AUTHOR INFORMATION
Corresponding Author
*Tel: þ3130 2533120. Fax: þ3130 2523615. E-mail: g.vankoten@
uu.nl.
Address correspondence pertaining to crystallographic studies
to this author. E-mail: m.lutz@uu.nl.
X-ray Crystal Structure Determinations. X-ray intensities were
measured on a Nonius KappaCCD diffractometer with rotating anode (λ =
0.71073 Å) at a temperature of 150(2) K. Integration was performed with
HKL200017 (compounds 4a, 7b C6H6, 8c) or EvalCCD18 (4b, 6 3MeOH,
’ ACKNOWLEDGMENT
3
3
This research was supported in part (A.V.C., R.H.) by the Dutch
Polymer Institute (DPI), projects 106 and 495, and (A.L.S.) by the
Council for Chemical Sciences of The Netherlands Organisation
for Scientific Research (CW-NWO). Prof. Dr. B. Hessen and Dr.
G. P. M. van Klink are kindly acknowledged for their suggestions
and stimulating discussions. Dr. E. van Faassen is thanked for
recording the ESR spectra of 7b. O. Staal and Dr. W. P. Kretschmer
and the COP-Center (RU Groningen) are kindly acknowledged
for providing the opportunity and help during the homogeneous
olefin polymerization experiments.
6 C6H6, 7a, 7c, 8a 2C6H6, 8b, 9). The structures were solved with
3
3
automated Patterson methods using DIRDIF-9919 (4a, 4b, 6 3MeOH,
3
6 C6H6, 8b, 9) or direct methods using SHELXS-9720 (7a, 7b C6H6, 7c,
3
3
8a 2C6H6) and SIR-9721 (8c). Least-squares refinement was performed
3
with SHELXL-9720 on F2 of all reflections. Structure calculations and
checking for higher symmetry was performed with PLATON.22 Further
details are given in the SI, Table 6.
Compound 4a. The structure was refined as a pseudo-orthorhombic
twin with a 2-fold rotation about the reciprocal c*-axis as twin operation.
The twin fraction refined to 0.0168(2). All hydrogen atoms were located
in difference Fourier maps and refined with a riding model.
Compound 4b. The tert-butyl groups were refined with distance and
angle restraints and additional restraints to approximate isotropic
displacement parameters. Hydrogen atoms were introduced in calcu-
lated positions and refined with a riding model.
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