Synthesis of (Adamantylimido)vanadium(V) Dimethyl Complex Containing (2-Anilidomethyl)pyridine Ligand and Selected Reactions: Exploring the Oxidation State of the Catalytically Active Species in Ethylene Dimerization

Article abstract of DOI:10.1021/acs.organomet.6b00727

V(NAd)Me₂(L) [2a, L = 2-ArNCH₂(C₅H₄N), Ar = 2,6-Me₂C₆H₃], prepared from V(NAd)Cl₂(L) (1) by reaction with LiMe (2.0 equiv), exhibited remarkable catalytic activities for ethylene dimerization in the presence of MAO affording 1-butene with high selectivity [TOF = 1 120 000-1 530 000 h^-1 (311-425 s^-1), C₄′ = 97.1-98.4%], and the catalyst performances (activity, selectivity) were similar to those by the dichloride analogue (1) under the same conditions. The dimethyl complex (2a) reacted with 1.0 equiv of R′OH to yield the mono alkoxide complexes, V(NAd)Me(OR′)(L) [R′ = OC(CF₃)₃ (3a), OC(CH₃)(CF₃)₂ (3b), OC(CH₃)₃ (3c)], and structures of these complexes (3a-c) and 2a were determined by X-ray crystallography. Reactions of 2a with [Ph₃C][B(C₆F₅)₄] in Et₂O and 3c with B(C₆F₅)₃ in THF afforded the corresponding cationic complexes confirmed by NMR spectra. Both NMR and V K-edge XANES analysis of the toluene or toluene-d₈ solution of 1 and 2a did not show any significant changes in the oxidation state upon addition of MAO, Me₂AlCl, or Et₂AlCl (10 equiv). Resonances ascribed to formation of the other vanadium(V) species were observed in the⁵¹V NMR spectra, and no significant differences in the XANES spectra (V-K pre-edge peaks and edge) were observed from 1 or 2a upon addition of Al cocatalyst. Taking into account these results and others, it is thus suggested that cationic vanadium(V) alkyl/hydride species play a role in this catalysis.

Full text of DOI:10.1021/acs.organomet.6b00727

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pubs.acs.org/Organometallics
Synthesis of (Adamantylimido)vanadium(V) Dimethyl Complex
Containing (2-Anilidomethyl)pyridine Ligand and Selected Reactions:
Exploring the Oxidation State of the Catalytically Active Species in
Ethylene Dimerization
Kotohiro Nomura,*,† Takato Mitsudome,*,‡ Atsushi Igarashi,† Go Nagai,† Ken Tsutsumi,†
Toshiaki Ina,§ Takuya Omiya,† Hikaru Takaya,*,∥ and Seiji Yamazoe*,⊥
†Department of Chemistry, Faculty of Science and Engineering, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji, Tokyo
192-0397, Japan
‡Department of Materials Engineering Science, Osaka University, 1-3, Machikaneyama, Toyonaka, Osaka 560-8531, Japan
§Japan Synchrotron Radiation Research Institute (JASRI, SPring-8), Sayo, Hyogo 679-5198, Japan
∥International Research Center for Elements Science (IRCELS), Institute for Chemical Research (ICR), Kyoto University, Uji, Kyoto
611-0011, Japan
⊥Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
S
* Supporting Information
ABSTRACT: V(NAd)Me2(L) [2a, L = 2-ArNCH2(C5H4N), Ar = 2,6-
Me2C6H3], prepared from V(NAd)Cl2(L) (1) by reaction with LiMe
(2.0 equiv), exhibited remarkable catalytic activities for ethylene
dimerization in the presence of MAO affording 1-butene with high
selectivity [TOF = 1 120 000−1 530 000 h−1 (311−425 s−1), C4′ =
97.1−98.4%], and the catalyst performances (activity, selectivity) were
similar to those by the dichloride analogue (1) under the same
conditions. The dimethyl complex (2a) reacted with 1.0 equiv of R′OH
to yield the mono alkoxide complexes, V(NAd)Me(OR′)(L) [R′ =
OC(CF3)3 (3a), OC(CH3)(CF3)2 (3b), OC(CH3)3 (3c)], and
structures of these complexes (3a−c) and 2a were determined by X-
ray crystallography. Reactions of 2a with [Ph3C][B(C6F5)4] in Et2O and
3c with B(C6F5)3 in THF afforded the corresponding cationic complexes confirmed by NMR spectra. Both NMR and V K-edge
XANES analysis of the toluene or toluene-d8 solution of 1 and 2a did not show any significant changes in the oxidation state
upon addition of MAO, Me2AlCl, or Et2AlCl (10 equiv). Resonances ascribed to formation of the other vanadium(V) species
were observed in the 51V NMR spectra, and no significant differences in the XANES spectra (V−K pre-edge peaks and edge)
were observed from 1 or 2a upon addition of Al cocatalyst. Taking into account these results and others, it is thus suggested that
cationic vanadium(V) alkyl/hydride species play a role in this catalysis.
affording 1-hexane (and 1-octene) with high selectivity. Since
metal−alkyl or metal−hydride plays an important role in the
former mechanism, synthesis and reaction chemistry of metal−
alkyl species have thus been an important subject for better
understanding in the mechanism as well as of organometallic
chemistry.
Recently, we demonstrated that (imido)vanadium(V)
complexes containing (2-anilidomethyl)-pyridine or 8-anilido-
5, 6, 7-trihydroquinoline ligands, V(NR)Cl2 [2-
ArNCH2(C5H4N)] or V(NR)Cl2[8-Ar-N(C9H10N)] [R = 1-
adamantyl (Ad), 2-MeC6H4, C6H5, etc.; Ar = 2,6-Me2C6H3],
exhibited high catalytic activities and selectivities for ethylene
dimerization in the presence of methylaluminoxane (MAO)
INTRODUCTION
■
Ethylene oligomerization, exemplified by nickel complex
catalyst containing a chelate P−O ligand (shell higher olefin
process, SHOP),1,2 for production of linear α-olefins
(intermediates such as detergents, polymers, lubricants,
surfactants, etc.) is one of the important key reactions in
chemical industry.1 The subject concerning design of the
efficient (highly active and selective) catalysts thus attract
considerable attention;2−12 examples for ethylene oligomeriza-
tion especially using nickel,2,4 iron complex catalysts,5 or
ethylene trimerization especially using chromium6−8 or
titanium complex catalysts9 have been well-known. Two
reaction mechanisms via metal−hydride (or metal−alkyl) or
metallacycle intermediate have been postulated in the ethylene
oligomerization; the latter mechanism can be especially
considered for the selective trimerization (and tetramerization)
Received: September 13, 2016
© XXXX American Chemical Society
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cocatalyst (Scheme 1).12 Through this study, it turned out that
a steric bulk in the imido ligand directly affects the ethylene
Al cocatalyst employed. Reaction with ethylene by 1 in the
presence of MAO, MMAO afforded 1-butene as the major
product, whereas the reaction in the presence of Me2AlCl,
Et2AlCl afforded polyethylene with ultrahigh molecular
weights.12b On the basis of our previous assumption observed
in the ethylene/norbornene copolymerization using (imido)-
vanadium(V) dichloride complexes containing aryloxo ligands,
V(N-2,6-Me2C6H3)Cl2(OAr),13,14 in which both the activity
and norbornene incorporations were highly affected by Al
cocatalyst (and solvent) employed,13b,c,14e we speculated that a
reason for the observed difference would be due to a formation
of different catalytically active species and catalyst/cocatalyst
nuclearity effect15 in the two catalyst systems (assumed in
Scheme 2).12b
Scheme 1. Effect of Ligand Substituents in Ethylene
Dimerization/Polymerization (MAO Cocatalyst): Selected
Examples for Effective Catalysts12a,c,d
As mentioned above, two reaction mechanisms via metal−
hydride (or metal−alkyl) or metallacycle intermediate in the
ethylene oligomerization can be considered, and the above
results (effect of Al cocatalytst toward the ethylene reactivity)
and the results in ethylene pressure dependence (first order
toward the activity) would strongly suggest a possibility of
metal−hydride (alkyl) intermediates in this catalysis.12b More-
over, no (or trace amount of) resonances ascribed to
paramagnetic [vanadium(IV)] species were observed in the
ESR spectra of toluene solution containing 1 in the presence of
Al alkyls (MMAO, Et2AlCl, 100 equiv to V), whereas the
resonances ascribed to a paramagnetic species [vanadium(IV)
species]16−18 were observed when V(NAd)Cl3 was treated with
Et2AlCl (100 equiv). Similarly, another broad resonance was
observed in the 51V NMR spectra of C6D6 solution containing
1 in the presence of 10.0 equiv of MMAO or Et2AlCl (25 °C),
whereas no resonances were observed when V(NAd)Cl3 was
treated with 10.0 equiv of Et2AlCl (under the same
concentration in C6D6 at 25 °C), suggesting a formation of
paramagnetic species as observed in the ESR resonance. These
ESR and NMR results suggest that the anionic donor ligand
plays an essential role for stabilization of the oxidation state,
vanadium(V), even in the catalyst solution. Although these
results would also suggest a possibility that the cationic
vanadium(V)−alkyl species play an important role in this
catalysis, however, we need to provide more clear evidence
concerning the catalytically active species (especially oxidation
state). This is because that in the classical Ziegler-type catalyst
reactivity (between dimerization and polymerization). 2,6-
Dimethylphenylimido analogue, V(N-2,6-Me2C6H3)Cl2[2-
ArNCH2(C5H4N)], showed the moderate activity for ethylene
polymerization, whereas not only the adamantylimido ana-
logues, V(NAd)Cl2[2-ArNCH2(C5H4N)] (1), but also the
cyclohexylimido, phenylimido, and o-tollylimido analogues
afforded 1-butene with high selectivity (Scheme 1).12a,c It also
turned out that an electronic factor in the imido ligand would
affect the catalytic activity; the adamantylimido analogues (1,
etc.) exhibited the higher catalytic activities.12a More recently,
we reported that (imido)vanadium complexes containing 8-
(2,6-dimethylanilide)-5,6,7-trihydroquinoline ligands exhibited
higher catalytic activities with high selectivity for ethylene
dimerization.12d
n
systems [V(acac)3, VOCl3, etc., and Et2AlCl, EtAlCl2, BuLi,
etc.], which display unique high reactivity toward olefins in
Moreover, it also turned out that the reaction pathway with
ethylene (dimerization vs polymerization) is highly affected by
Scheme 2. Assumed Catalytically Active Species Formed by Reaction with Al Alkyls
B
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Scheme 3. Synthesis of Dialkyl Complexes V(NAd)R2[2-ArNCH2(C5H4N)] [R = Me (2a), CH2SiMe3 (2b)] and Reactions of 2a
with Alcohols
olefin coordination/insertion polymerization,19−22 vanadium-
(III) and/or vanadium(IV) species are proposed to be as the
catalytically active species (although the catalyst systems
require addition of reoxidant such as Cl3CCO2Et to stabilize
the oxidation state of the active species).14,23
in Table 1.24 Dimethyl complex 2a folds trigonal bipyramidal
geometry around vanadium with the pyridyl N donor of the
bidentate (2-anilidomethyl)-pyridine ligand and the imido N
atom lying on the axis, and an equatorial plane consisted of the
two methyl ligands and the anilido N atom. The axial N(1)−
V−N(2) bond angle [177.73(8)°] is larger than that in the
chloride analogue (1) [174.90(4)°],12a and the sum of the
equatorial C(25)−V−C(26), C(25)−V−N(3), and C(26)−V−
N(3) bond angles is 354.94°. Moreover, the nitrogen atom in
the pyridine locates at trans-position of the imido ligand
[N(1)−V−N(2): 177.73(8)°], and the V−N(1)−C(1) bond
angle [176.36(15)°] is also larger than that in (1)
[170.94(10)°],12a clearly suggesting that complex 2a folds in
a linear structure from C(1) through N(2). The V−C bond
distances in 2a [2.092(4), 2.091(5) Å] are somewhat longer
than that in reported V(N-2,6-Me2C6H3)Me(NCtBu2)2
[2.064(2) Å]25 and V−C bond distances in V(NAd)-
(CH2SiMe3)3 [2.0267(18) Å],26 V(CHSiMe3)(NAd)-
(CH2SiMe3)(NHC) [2.069(3) Å, NHC = 1,3-bis(2,6-diisopro-
pylphenyl)-imidazol-2-ylidene]],26 but within the range of the
V−C bond lengths in (arylimido)vanadium(V)−dibenzyl
analogues [2.026(7)−2.103(8) Å].27 The C(25)−V−C(26)
bond angle [116.81(13)°] is smaller than Cl(1)−V−Cl(2)
bond angle in 1 [119.953(16)°].12a The V−N(3) bond distance
in 2a [1.886(3) Å] is apparently longer than that in 1
[1.8580(12) Å] as well as those in the other (imido)vanadium-
(V) dichloride analogues with different imido ligands, V(NR)-
Cl2[2-Ar′NCH2(C5H4N)] [R = Ad, cyclohexyl, 2-MeC6H4, 2,6-
Me2C6H3; Ar′ = 2,6-Me2C6H3, 2,6-iPr2C6H3], reported
previously [1.850(2)−1.8607(18) Å].12a,c,28
Structures of the methyl-mono alkoxide analogues, V(NAd)-
Me(OR′)[2-ArNCH2(C5H4N)] [R′ = OC(CF3)3 (3a), OC-
(CH3)(CF3)2 (3b), OC(CH3)3 (3c)], are also shown in Figure
1.24 Similarly, these complexes fold a distorted trigonal
bipyramidal geometry around vanadium consisting of two
nitrogen atoms in the pyridine and the imido ligands axis, and
an equatorial plane consisted of one methyl and alkoxo ligands
and the nitrogen in the anilide ligand [N(1)−V−N(2) =
171.35(8)° in 3a, 171.01(10)° in 3b, 167.41(8)° in 3c; total
bond angles of C(25)−V−O(1), C(25)−V−N(3), O(1)−V−
N(3): 350.48° in 3a, 351.52° in 3b, 351.83° in 3c,
respectively]; the nitrogen atom in the pyridine locates at the
trans-position of the imido ligand. The vanadium−nitrogen
bond distance in the anilido ligand and the V−O(1) bond
distance in 3a−c are affected by the alkoxo substituents [V−
N(3), V−O(1): 1.888(2), 1.8999(16) Å in 3a; 1.907(3),
1.867(2) Å in 3b; 1.9240(18), 1.8016(17) Å in 3c,
respectively]; the similar influence is also observed in the V−
As described above, since metal−alkyl, especially cationic
alkyl species, plays an important role in catalysis in ethylene
dimerization/polymerization, we thus explored a possibility for
isolation of the corresponding dimethyl and the cationic methyl
complexes and some reactions. We also explored possibilities to
obtain clear supports by in situ analysis (of catalyst solution in
toluene) for better explanation of our proposed mechanism.
We thus herein present synthesis of the dimethyl complex,
V(NAd)Me2[2-ArNCH2(C5H4N)] (2a), and some reactions
including structural analyses by X-ray crystallography. More-
over, we explored analysis of the catalyst solution in the
presence of Al cocatalysts by 51V NMR spectra and solution
XAS (X-ray absorption spectroscopy) analysis. Through these
results, we wish to demonstrate that the chelate anionic donor
ligand plays an essential role for stabilization of the oxidation
state for exhibiting both high catalytic activity and selectivity in
ethylene dimerization.
RESULTS AND DISCUSSION
■
Synthesis and Structural Analysis of V(NAd)R2[2-
ArNCH2(C5H4N)] [R = Me (2a), CH2SiMe3 (2b)] and
Some Reactions. Reactions of V(NAd)Cl2 [2-
ArNCH2(C5H4N)] (1, Ar = 2,6-Me2C6H3) with 2.0 equiv of
LiMe or LiCH2SiMe3 in toluene gave the dialkyl analogues,
V(NAd)R2[2-ArNCH2(C5H4N)] [R = Me (2a), CH2SiMe3
(2b)] (Scheme 3), and these complexes were identified by 1H,
13C, and 51V NMR spectra and elemental analysis, and the
structure of 2a could be determined by X-ray crystallography
(shown below, Figure 1).24 Resonance ascribed to the methyl
protons (0.92 ppm) was observed in the 1H NMR spectrum of
2a, whereas resonances ascribed to the SiMe3 group (0.12
ppm) in addition to the methylene (2.57 ppm) were observed
1
in the H NMR spectrum of 2b.
Reactions of 2a with 1.0 equiv of (CF3)3COH, (CH3)3COH,
(CF3)2(CH3)COH in toluene afforded the corresponding
mono alkoxo complexes, V(NAd)Me(OR′)[2-
ArNCH2(C5H4N)] [R′ = OC(CF3)3 (3a), OC(CH3)(CF3)2
(3b), OC(CH3)3 (3c)], in high yields (Scheme 3). These
1
complexes were identified by H, 13C, 19F, and 51V NMR
spectra, and their structures (3a−c) were determined by X-ray
crystallography (shown in Figure 1).24
Figure 1 shows ORTEP drawings for complexes 2a and 3a−
c, and the selected bond distances and angles are summarized
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Figure 1. ORTEP drawing for V(NAd)Me2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (2a, top left), V(NAd)Me(OR′)[2-(2,6-Me2C6H3)NCH2(C5H4N)]
[R = C(CF3)3 (3a, top right), C(CH3)(CF3)2 (3b, bottom left), and C(CH3)3 (3c, bottom right)]. Thermal ellipsoids are drawn at the 50%
probability level, and H atoms are omitted for clarity.24
N(2) in pyridine bond distance [2.2243(17), 2.234(3), and
2.251(2) Å in 3a, 3b, and 3c, respectively]. Moreover, N(1)−
V−N(2) and V−N(1)−C(1) bond angles are also influenced
by the alkoxo substituent [N(1)−V−N(2), V−N(1)−C(1):
171.35(8), 171.51(15)° in 3a; 171.01(10), 170.4(3)° in 3b;
167.41(8), 168.37(15)° in 3c, respectively]. The bond angles in
C(25)−V−O(1), N(2)−V−N(3), and C(25)−V−N(3) are
also influenced by the alkoxo ligand employed (Table 1). It
seems likely that V−O(1) bond distances in 3a−c are
influenced by the electronic (and probably steric) nature of
the alkoxo substituents, which would affect the V−N(1), V−
N(3) distances and N(1)−V−N(2), V−N(1)−C(1) bond
angles, among others.
In order to obtain further information concerning the
assumed catalytically active species, reaction of the dimethyl
complex (2a) with 1.0 equiv of [Ph3C][B(C6F5)4] was explored
in Et2O (Scheme 4).29−31 After removal of volatiles, the
resultant solid was washed with n-hexane and dried in vacuo.
51V NMR spectrum of the resultant solid (in CDCl3 at 25 °C,
Figure 2b) showed a resonance at 83.6 ppm which is apparently
D
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Table 1. Selected Bond Distances and Angles for V(NAd)Me2[2-ArNCH2(C5H4N)] (2a, Ar = 2,6-Me2C6H3),
a
V(NAd)Me(OR′)[2-ArNCH2(C5H4N)] [R′ = C(CF3)3 (3a), C(CH3)(CF3)2 (3b), and C(CH3)3 (3c)]
b
complex
1
2a
3a
3b
3c
Bond Distances (Å)
1.654(3)
V−N(1)
V−N(2)
V−N(3)
V−C(25)
1.6517(12)
2.2241(11)
1.8580(12)
1.6521(17)
2.2243(17)
1.888(2)
1.662(3)
2.234(3)
1.907(3)
2.099(4)
1.867(2)
1.6642(19)
2.251(2)
2.221(3)
1.886(3)
1.9240(18)
2.112(3)
2.2677(3), V−Cl(1)
2.2709(4), V−Cl(2)
2.092(4)
2.101(3)
V−C(26) or V−O(1)
2.091(5)
1.8999(16)
1.8016(17)
Bond Angles (deg)
176.36(15)
V−N(1)−C(1)
N(1)−V−N(2)
N(2)−V−N(3)
N(1)−V−N(3)
C(25)−V−O(1)
C(25)−V−N(3)
O(1)−V−N(3)
170.94(10)
171.51(15)
171.35(8)
77.24(7)
170.4(3)
171.01(10)
76.75(10)
97.94(11)
108.78(12)
113.69(11)
129.05(11)
168.37(15)
167.41(8)
75.46(8)
174.90(4), N(1)−V−N(3)
78.20(4), N(1)−V−N(2)
97.41(5), N(1)−V−N(3)
119.953(16), Cl(1)−V−Cl(2)
116.92(4), Cl(1)−V−N(2)
118.18(3), Cl(2)−V−N(2)
177.73(8)
78.08(9)
99.65(10)
98.13(9)
98.30(9)
116.81(13), C(25)−V−C(26)
118.11(12)
111.61(9)
109.59(9)
129.28(7)
107.56(9)
118.59(9)
125.68(8)
120.02(12), C(26)−V−N(3)
a
b
Detailed analysis data are shown in the Supporting Information.24 Data for V(NAd)Cl2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (1) reprinted with
permission in part from ref 12a. Copyright 2010 American Chemical Society.
Similarly, reaction of the OtBu analogue (3c) with 1.0 equiv
of B(C6F5)3 was explored in THF (Scheme 4).31,33c After
removal of volatiles, the resultant solid was washed with n-
hexane and dried in vacuo. 51V NMR spectrum of the resultant
solid (in CDCl3 at 25 °C) showed a resonance at −309.6 ppm
which is clearly shifted from that in the mono methyl complex
(3c, −246.5 ppm); 3 resonances ascribed to C6F5 group were
also clearly observed in the 19F NMR spectrum.31 Moreover,
resonance ascribed to the methyl group in (CH3)B(C6F5)3
(0.48 ppm) accompanied by disappearance of resonance
ascribed to protons in vanadium-methyl (0.63 ppm) was
observed; resonances ascribed to free and coordinated THF
were also observed.31 These results would suggest a formation
of cationic species, [V(NAd)(OtBu){2-ArNCH2(C5H4N)}-
(THF)]+, in situ, as shown in Scheme 4, although formation
of the cationic complex was only suggested by NMR spectra
(shown in the Supporting Information).31
Scheme 4. Reactions of V(NAd)Me2[2-ArNCH2(C5H4N)]
(2a) with [Ph3C][B(C6F5)4] and V(NAd)Me(OtBu)[2-
ArNCH2(C5H4N)] (3c) with B(C6F5)3
Reactions of Ethylene by V(NAd)Me2 [2-
ArNCH2(C5H4N)] (2a) in the Presence of Cocatalyst.
Table 2 summarizes results for reaction with ethylene by
V(NAd)Me2[2-ArNCH2(C5H4N)] (2a) in the presence of
cocatalysts. The results by dichloride analogue V(NAd)Cl2[2-
ArNCH2(C5H4N)] (1)12a,b are also placed for comparison. As
reported previously,12a,b 1 showed remarkable both catalytic
activity and selectivity for ethylene dimerization in the presence
of MAO (runs 1−3),12a whereas the reactions of 1 with
ethylene in the presence of Me2AlCl, Et2AlCl afforded
polyethylene with ultrahigh molecular weights (runs 4 and
5).12b
It turned out that the dimethyl analogue (2a) exhibited
remarkable catalytic activities for reaction with ethylene in the
presence of MAO cocatalyst (runs 6−11). The products of
those reactions conducted at rather low catalyst concentration
conditions (2a 0.2 μmol, runs 8−11) were 1-butene with high
selectivity (97.1−98.4%), whereas percentage of 1-hexene
increased if the reactions were conducted under rather high
catalyst concentration (2a 0.5 μmol; selectivity of 1-butene =
91.0, 87.9% for runs 6 and 7, respectively). As reported
previously,12a,b 1-hexene was formed after accumulation of 1-
butene in the reaction mixture (ca. 7.49 g of 1-butene and 0.7 g
of 1-hexene formed in 30 mL of toluene, run 6). Moreover, the
activity was affected by the Al/V molar ratio employed. These
different (shifted high magnetic field side) from that in the
dimethyl complex (2a, 203.1 ppm, Figure 2a); 3 resonances
ascribed to C6F5 group were also observed in the 19F NMR
spectrum.31 Moreover, resonances ascribed to protons in
Ph3C(CH3) (ca. 2.2 ppm),32 and a resonance ascribed to
vanadium−methyl protons (1.53 ppm) was also observed in the
1H NMR spectrum (in CDCl3 at 25 °C, Figure 2d); most of all
resonances were assigned to protons of an assumed cationic
complex, [V(NAd)Me{2-ArNCH2(C5H4N)}(Et2O)]+, shown
in Scheme 4.31 The similar reaction in C6D6 or toluene-d8
afforded two separated solutions consisting of toluene-soluble
portion (clear pale brown) and toluene-insoluble deep brown
tan residue at the bottom. The observed small resonances
(from the top clear brown solution) were ascribed to the
starting complex (2a), and the amount (intensity) was
significantly reduced from the initial charged amount. This is
a similar observation in the reaction of Cp*TiMe2(O-
2,6-iPr2C6H3) with [Ph3C][B(C6F5)4]33a and the others,30a,33
suggesting a formation of cationic (alkyl) species.
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Figure 2. 51V NMR spectra (in CDCl3 at 25 °C) for (a) V(NAd)Me2[2-(2,6-Me2C61H3)NCH2−(C5H4N)] (2a) and (b) 2a with 1.0 equiv of
[Ph3C][B(C6F5)4] (in Et2O, resultant reaction mixture after washing with n-hexane). H NMR spectra (expanded between 1.3 and 2.4 ppm, in
CDCl3 at 25 °C) for (c) V(NAd)Me2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (2a) and (d) 2a with 1.0 equiv of [Ph3C][B(C6F5)4] (in Et2O, resultant
reaction mixture after washing with n-hexane). More NMR data are shown in the Supporting Information.31
a
Table 2. Reaction with Ethylene by V(NAd)X2[2-(2,6-Me2C6H3)NCH2(C5H4N)] [X = Cl (1), Me (2a)]−Cocatalyst Systems
oligomer
b
c
d
e
e
c
run
cat. (μmol)
Al cocat.
molar ratio
activity
TOF
C4′ (%)
C6′ (%)
PE actvity
f
1
1 (0.5)
1 (0.5)
1 (0.1)
1 (5.0)
1 (5.0)
2a (0.5)
2a (0.5)
2a (0.2)
2a (0.2)
2a (0.2)
2a (0.2)
2a (2.0)
2a (2.0)
MAO
500
50100
50300
76500
trace
1830000
1800000
2730000
92.5
90.4
97
7.5
9.6
3.0
f
2
MAO
500
f
3
MAO
1500
200
f
g
4
Me2AlCl
Et2AlCl
MAO
704
f
g
5
100
trace
137
6
500
98800
82300
20700
43600
35700
31900
446
3460000
2880000
725000
1530000
1250000
1120000
15600
91.0
87.9
98.3
97.1
98.0
98.4
>99
>99
9.0
7
MAO
1500
1000
1500
1500
2000
100/1.5
200/1.5
12.1
1.7
8
MAO
9
MAO
2.9
10
11
12
13
MAO
2.0
MAO
1.6
h
AliBu3/B
AliBu3/B
trace
trace
42
h
128
4500
67
a
Conditions: ethylene 8 atm, toluene 30 mL, d-MAO white solid (methylaluminoxane prepared by removing AlMe3, toluene from PMAO-S), 25 °C
b
c
d
(0 °C, runs 4 and 5), 10 min (run 2, 20 min). Al/V molar ratio. Activity in kg ethylene reacted/mol V·h. TOF (turnover frequency) = (molar
amount of ethylene reacted)/(mol V·h). By GC analysis vs internal standard. Cited from our previous reports.12a,b Mη = 5.92 × 106 (run 4); 6.76
e
f
g
× 106 (run 5). Samples were insoluble in ordinary GPC analysis in o-dichlorobenzene (at 145 °C); molecular weight by viscosity.12b Samples were
h
insoluble in ordinary GPC analysis in o-dichlorobenzene (at 145 °C).
results clearly indicate that 2a is an efficient catalyst for
ethylene dimerization, and the catalyst performance (activity,
selectivity) in 2a was analogous to that in 1 under the same
conditions.
However, the reactions in the presence of [Ph3C][B(C6F5)4]
and AliBu3 afforded 1-butene and small amount of polyethylene
that were insoluble for ordinary GPC measurements (in o-
dichlorobenzene at 145 °C). Although we do not have clear
explanations for the observed results, these might be probably
speculated as due to a catalyst/cocatalyst nuclearity effect, as
shown in Scheme 2,12b,13b,c,14e,15 and we may consider that
these might be due to a degree of (contact) interaction between
the cationic alkyl species and the counteranion.
of a C6D6 solution containing the dichloro complex (1) in the
presence of 10.0 equiv of MMAO (modified MAO, methyl
isobutyl aluminoxane, at 25 °C) showed a resonance at 32 ppm
in addition to the resonance ascribed to 1 (−114 ppm), and the
C6D6 solution in the presence of 10.0 equiv of Et2AlCl showed
another resonance (at −76 ppm, 25 °C).12b,34 In contrast, no
resonances were observed when V(NAd)Cl335 was treated with
10.0 equiv of Et2AlCl under the same concentration (in C6D6 at
25 °C).12b Moreover, no resonances ascribed to formation of
paramagnetic species were observed in the ESR measurement
of the toluene solution of 1 upon addition of 100 equiv of
MMAO, Et2AlCl, whereas resonances ascribed to a para-
magnetic species [vanadium(IV) species]17,18 were observed in
the toluene solution containing V(NAd)Cl3 upon treatment
with Et2AlCl.12b These results would support our hypothesis
that the anionic ancillary donor ligand, (2-anilidomethyl)-
NMR Spectra of V(NAd)X2[2-ArNCH2(C5H4N)] [X = Cl
(1), Me (2a)] in Toluene-d8 in the Presence of Al
Cocatalysts. We previously reported that 51V NMR spectra
F
DOI: 10.1021/acs.organomet.6b00727
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
pyridine ligand, plays an essential role for stabilization of the
oxidation state in this catalysis even in the presence of Al alkyls.
Since the dimethyl complex (2a) exhibited catalyst perform-
ance similar to that of 1, we measured NMR spectra in toluene-
d8 (solvent for the reaction) upon presence of Al cocatalysts.
Figure 3 shows 51V NMR spectra of toluene-d8 solution
containing the dichloride complex (1) or dimethyl complex
ppm was observed if the dimethyl complex (2a) was treated
with Me2AlCl (10.0 equiv) in toluene-d8 (Figure 3h), and the
resonance is close to that prepared by 1 with Me2AlCl (Figure
3c). However, the spectrum of 2a treated by 10.0 equiv of
MAO showed the original resonance of 2a with low intensity
(Figures 3e−f); the resonance seems to almost have
disappeared if 2a was treated with 50.0 equiv of MAO (Figure
3g). This is because the solution consisted of two phases
(toluene-d8 soluble/insoluble), and the spectra of the soluble
portion clearly showed only a resonance ascribed to the
dimethyl complex (2a). The results are highly analogous to that
observed in the reaction of 2a with [Ph3C][B(C6F5)4] in
toluene-d8, and it seems likely that this would be due to a
formation of the cationic species, although we have no clear
explanations of observed difference between 1 and 2a in the
presence of MAO.
In contrast, no resonances were observed when V(NAd)Cl3
was treated with 10.0 equiv of Me2AlCl in toluene-d8 at 25 °C
(homogeneous solution, data shown in the Figure S2-2),34 as
observed in the reaction of V(NAd)Cl3 with Et2AlCl (10.0
equiv) in C6D6,12b As described above,12b no resonances
ascribed to formation of paramagnetic species were observed in
the ESR measurement of the toluene solution of 1 upon
addition of 100 equiv of MMAO, Et2AlCl, whereas resonances
ascribed to paramagnetic species [vanadium(IV) species] were
observed in the toluene solution containing V(NAd)Cl3 upon
treated with Et2AlCl.12b Therefore, these results could suggest
that the chelate donor ligand, (2-anilidomethyl)pyridine ligand,
plays an important role for stabilization of an oxidation state
even in the presence of Al cocatalysts (MAO, Me2AlCl,
Et2AlCl) in toluene. In addition to results in reactions of the
dimethyl complex (2a) with borates, as described above, it thus
seems highly likely that the cationic alkyl complex, [V(NAd)-
Me{2-ArNCH2(C5H4N)}]+, would play an important role in
this catalysis.
Analysis of Catalyst Solution Consisting of V(NAd)-
X2[2-ArNCH2(C5H4N)] [X = Cl (1), Me (2a)] and Al
Cocatalysts in Toluene by Solution-Phase X-ray Absorp-
tion Spectroscopy. As described above, on the basis of results
in the NMR spectra of solutions prepared by 1 or 2a with Al
cocatalysts (and ESR data reported previously12b by 1) in
toluene, we could demonstrate that the chelate anionic donor
ligand plays a key role to stabilize the oxidation state of the
Figure 3. 51V NMR spectra (in toluene-d8 at 25 °C) for (a−d)
V(NAd)Cl2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (1) upon addition of
Al cocatalyst (10.0 equiv) and (e−h) V(NAd)Me2[2-(2,6-Me2C6H3)-
NCH2(C5H4N)] (2a) upon addition of Al cocatalyst (10.0 or 50.0
equiv). More NMR data are shown in the Supporting Information.34
(2a) in the presence of 10.0 equiv of MAO, Et2AlCl, or
Me2AlCl (at 25 °C).34 A new resonance at 36.1 ppm was
observed when 1 (−120.6 ppm) was treated with MAO (10.0
equiv) with slightly decrease in the peak intensity (Figure 3d),
suggesting formation of different vanadium(V) species from 1.
The other resonances, slightly shifted to high magnetic field
side (−54.2, 14.7 ppm, respectively), were observed if 1 was
treated with 10.0 equiv of Et2AlCl or Me2AlCl in toluene-d8 at
25 °C (Figure 3b,c); significant decreases in the intensities in
the spectra were not observed when these spectra were
measured under the same vanadium concentrations (Figures
3a−c). Similar results were observed when these reactions
(with MAO, Me2AlCl, etc.) were conducted in C6D6 (data are
shown in Figure S2-1).12b,34 Moreover, a resonance at 11.1
Figure 4. Solution-phase V K-edge XANES spectra (in toluene at 25 °C) for (a) V(NAd)Cl2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (1) in the presence
of Al cocatalyst (10.0 equiv), (b) V(NAd)Me2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (2a) in the presence of Al cocatalyst (10.0 equiv), and (c)
V(NAd)Cl3 and the solution upon addition of Me2AlCl (10.0 equiv).36
G
DOI: 10.1021/acs.organomet.6b00727
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Organometallics
Article
species formed in situ. These results, in addition to that in the
reaction of 2a with borate, would suggest a possibility that the
cationic alkyl species would play a role in these catalysis.
However, we could not totally exclude the other possibilities in
vanadium catalysis. One probable reason we should take into
consideration is that we could not completely exclude
possibilities of formation of vanadium(III) and/or antiferro-
magnetically coupled vanadium(IV) dimer (ESR silent) under
these experimental conditions.
Therefore, we focus on a possibility of synchrotron X-ray
absorption spectroscopy (XAS) to explore obtainment of some
structural information concerning the prepared catalyst
solutions. In particular, the method (V−K edge analysis, 5.46
keV, through the use of synchrotron radiation at SPring-8,
BL01B1 beamline) enables us to obtain information concerning
oxidation state (by V−K pre-edge and edge peaks in XANES
analysis, XANES = X-ray absorption near edge structure) as
well as coordination atoms around the vanadium (by FT-
EXAFS analysis, EXAFS = extended X-ray absorption fine
structure).36
Figure 4a shows solution-phase V K-edge XANES spectra of
toluene solution containing the dichloride complex (1) in the
presence of MAO, Me2AlCl, and Et2AlCl (10.0 equiv), and
Figure 4b shows the spectra of toluene solution containing the
dimethyl complex (2a) in the presence of MAO, Me2AlCl (10.0
equiv). The spectra of the trichloride complex, V(NAd)Cl3, and
the solution in the presence of Me2AlCl (10.0 equiv) are also
shown in Figure 4c for comparison. The corresponding EXAFS
spectrum of the dichloride complex (1) and the spectrum in
the presence of MAO (10.0 equiv) are also shown in the
Supporting Information.36
The XANES spectrum of 1 shows pre-edge peaks at 5465.2
and 5467.3 eV, and the spectrum of 2a shows the similar pre-
edge peaks (5465.0 and 5467.1 eV), although 1 showed a
shoulder-edge peak at 5477.8 eV. It turned out that the spectra
(XANES and EXAFS) of 1 are good fittings of those based on
both X-ray crystallographic analysis12a and the DFT calculation
(details are shown in the Supporting Information);36 these
suggest that solid-phase molecular geometries (trigonal
bipyramidal geometry around V) were preserved in the
solution phase. The curve-fitting of XANES spectrum of
V(NAd)Cl3 is also in good agreement with that estimated on
the basis of DFT calculation (details are shown in the
Supporting Information).36 Two pre-edge peaks [observed at
5465.2 and 5467.3 eV (1), 5465.0 and 5467.1 eV (2a), and
5465.6 and 5467.1 eV in V(NAd)Cl3] are generally considered
as due to a transition from 1s to 3d + 4p,37 although examples
of solution V K-edge XANES spectra through the use of
synchrotron radiation still have been limited.38
4b, although the spectrum of 1 in the presence of MAO showed
a weak shoulder-edge peak at 5477.8 eV (might be
corresponded to the residual 1).39,40 Moreover, these results
are reproducible (with different independent analysis runs,
shown in the Figures S3-1 and S3-2).36 Therefore, the results
suggest in high certainty that similar catalytically active species
were formed from 1 and 2a upon addition of MAO, and the
results would meet a good agreement with the fact that similar
catalyst performances toward ethylene were observed between
1 and 2a under the same conditions in the presence of MAO
(Table 2).
Moreover, it should be noted that the spectrum of toluene
solution of 1 in the presence of Me2AlCl was very close to that
of 2a in the presence of Me2AlCl (Figures 4a,b and S3-4).36,39
Since the results would also correspond to the fact that the 51
V
NMR spectra of toluene-d8 solutions of 1 and 2a in the
presence of Me2AlCl (10.0 equiv) showed similar resonances
(Figure 3c,h), these results would also suggest a possibility that
the similar species are formed in the (catalyst) solution. The
spectrum of 1 in the presence of Et2AlCl was similar to that of 1
in the presence of Me2AlCl (Figure 4a); the results would also
assume a possibility of formation of analogous species in the
solution. Taking into account these XANES results in addition
to the results in the 51V NMR spectra shown in Figure 3 (and
our previous reported results that no paramagnetic species were
formed from 1 upon addition of MMAO, Et2AlCl in
toluene),12b it is thus clear that no significant changes in the
oxidation state were observed from 1 and 2a upon addition of
Al cocatalysts (MAO, Me2AlCl, Et2AlCl) under conditions of
reactions (dimerization or polymerization) conducted with
ethylene shown in Table 2 (and reported previously with
1).12a,b
In contrast, certain significant changes in the XANES (pre-
edge and edge region) spectrum were observed when the
trichloride complex, V(NAd)Cl3 [5465.6 and 5467.1 eV (pre-
edge), 5476.7 eV (shoulder-edge)], was treated with Me2AlCl
[5465.8 eV (pre-edge), 5475.4 eV (shoulder-edge), Figure
4c].41 Since no resonances were observed when V(NAd)Cl3
was treated with 10.0 equiv of Me2AlCl in toluene-d8 at 25 °C34
and a similar result was observed in the reaction of V(NAd)Cl3
with Et2AlCl (10.0 equiv) in C6D6 [observed formation of
paramagnetic species, V(IV), in the ESR measurement in the
toluene solution12b], the result would clearly suggest a
formation of paramagnetic species. The results also strongly
suggest that the chelate anionic donor ligand plays a role to
stabilize the oxidation state upon addition of Al cocatalysts.
Moreover, no significant changes in both the EXAFS and the
FT-EXAFS spectra were observed in toluene solutions of
containing 1 upon addition of MAO (analysis data are shown in
the Figure S3-8),36 except that the apparent decrease in the
intensity ascribed to V−Cl in 1 was observed upon addition of
MAO.36,42 Note that at least two V−N σ-bonds (corresponding
to vanadium−imido and −anilido) remained (observed) upon
addition of MAO. These facts indicate that the coordinated Cl
in 1 was removed by reaction with MAO without any changes
for V−N bonds.42 Although more detailed analyses of EXAFS
spectra in addition to XANES spectra are still in progress, we
can at least say that the basic structure consisting of both imido
and chelate anionic donor ligand would be preserved from 1
upon addition of MAO.42
Note that as shown in Figure 4a no significant differences in
the XANES spectra (pre-edge peaks and edge) from that in 1
were observed upon addition of MAO [5465.1 and 5467.6 eV
(pre-edge), 5477.8 eV (shoulder-edge)], Me2AlCl [5465.6 and
5467.4 eV (pre-edge), 5476.4 eV (shoulder-edge)], and Et2AlCl
[5465.5 and 5466.8 eV (pre-edge), 5474.7 eV (shoulder-edge),
additional data are shown in the Figures S3-1−S3-3],36
although intensity in a shoulder at the edge region (at 5477.8
eV) observed in 1 decreased upon addition of MAO.39 Also
note that the XANES spectrum of 1 in the presence of MAO is
similar to those in the homogeneous toluene solution
containing the dimethyl complex (2a) in the presence of
MAO [5465.0 and 5467.0 eV (pre-edge)]40 as well as that in 2a
itself [5465.0 and 5467.1 eV (pre-edge)], as shown in Figure
Taking into account both solution-phase V K-edge XANES
and EXAFS data (and 51V NMR spectra shown in Figure 3,
etc.), it is thus proposed that no significant changes in oxidation
H
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Article
passed through an alumina short column under N2 stream prior to use.
of the catalyst solution consisting of 1 or 2a and MAO and the
formed vanadium(V) species retains the basic structure
consisting of both imido and chelate anionic donor ligand; it
thus seems highly likely that cationic alkyl species play a role in
this catalysis.
35
V(NAd)Cl3 and V(NAd)Cl2[2-(2,6-Me2C6H3)NCH2(C5H4N)]
(1)12a were prepared according to a published method. [Ph3C][B-
(C6F5)4] (Asahi Glass Co. Ltd.) were stored in the drybox and were
used as received.
Elemental analyses were performed by using EAI CE-440 CHN/O/
1
S Elemental Analyzer (Exeter Analytical, Inc.). All H, 13C, 19F, and
51V NMR spectra were recorded on a Bruker AV500 spectrometer
CONCLUDING REMARKS
■
1
(500.13 MHz for H, 125.77 MHz for 13C and 131.55 MHz for 51V).
We have shown that the dimethyl complex, V(NAd)Me2[2-
ArNCH2(C5H4N)] (2a, Ar = 2,6-Me2C6H3), prepared from the
dichloro complex by treatment with LiMe, exhibited remark-
able catalytic activity for ethylene dimerization in the presence
of MAO [TOF = 1 120 000−1 530 000 h−1 (311−425 s−1), C4′
= 97.1−98.4%], and the catalyst performance was analogous to
that of the dichloro analogue (1) under the same conditions.
Reactions of 2a with 1.0 equiv of R′OH afforded the
corresponding mono alkoxide analogues, V(NAd)Me(OR′)-
[2-ArNCH2(C5H4N)] [R′ = C(CF3)3 (3a), C(CH3)(CF3)2
(3b), C(CH3)3 (3c)], in high yields and structures of
complexes 2a, 3a−c were determined by X-ray crystallography.
The reaction of 2a with 1.0 equiv of [Ph3C][B(C6F5)4] in Et2O
suggested formation of a cationic complex, [V(NAd)Me{2-
All spectra were obtained in the solvent indicated at 25 °C unless
otherwise noted. Chemical shifts are given in ppm and are referenced
to SiMe4 (δ 0.00 ppm, 1H, 13C), CFCl3 (δ 0.00 ppm, 19F), and VOCl3
(δ 0.00 ppm, 51V). Coupling constants and half-width values, Δν1/2
are given in Hz.
,
Synthesis of V(NAd)Me2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (2a).
Into a toluene (30 mL) and Et2O (30 mL) solution containing
V(NAd)Cl2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (675 mg, 1.40 mmol)
was added methyl lithium (2.80 mmol, Et2O solution) at −30 °C. The
reaction mixture was covered by aluminum foil to block out light and
was warmed slowly to room temperature. The mixture was then stirred
overnight. The solution was passed through a Celite pad, and the filter
cake was washed with hot toluene. The combined filtrate and wash was
placed in a rotary evaporator to remove the volatiles. The resultant
solid was dissolved in a minimum amount of toluene, and was layered
with n-hexane. The chilled solution placed in the freezer (−30 °C)
afforded yellow crystals (480 mg, 1.12 mmol). Yield: 80.2%. 1H NMR
(C6D6, δ) 8.54 (d, 1H, J = 5.35 Hz, Py−H), 7.09 (d, 2H, J = 7.55 Hz,
Ar−H), 7.01−6.95 (m, 2H, Ar−H and Py−H), 6.70 (t, 1H, J = 6.47
Hz, Py−H), 6.61 (d, 1H, J = 7.85 Hz, Py−H), 4.44 (s, 2H, NCH2),
2.17 (s, 6H, Ar−CH3), 2.07 (d, 6H, J = 2.55 Hz, Ad−H), 1.96 (brs,
3H, Ad−H), 1.58 (d, 3H, J = 11.80 Hz, Ad−H), 1.51 (d, 3H, J = 11.80
Hz, Ad−H), 0.92 (brs, 6H, VCH3). 13C NMR (C6D6, δ) 161.8, 161.2,
147.9, 136.2, 132.0, 128.4, 124.4, 122.6, 120.3, 65.5, 43.5, 36.7, 29.9,
18.7. 51V NMR (C6D6, δ) 203.1 (Δν1/2 = 829 Hz). Anal. Calcd for
C26H36N3V: C, 70.73; H, 8.22; N, 9.52. Found: C, 71.09; H, 8.35; N,
9.29.
Synthesis of V(NAd)(CH2SiMe3)2[2-(2,6-Me2C6H3)-
NCH2(C5H4N)] (2b). Into a toluene solution (35 mL) containing
V(NAd)Cl2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (462 mg, 0.958 mmol)
was added toluene solution (10 mL) containing LiCH2SiMe3 (180 mg,
1.92 mmol) at −30 °C. The reaction mixture was warmed slowly to
room temperature, and the mixture was then stirred overnight. The
solvent was removed in vacuo, and the resultant residue was extracted
with n-hexane. The solution was passed through a Celite pad, and the
filter cake was washed with n-hexane. The combined filtrate and wash
was placed in a rotary evaporator to remove the volatiles. The resultant
residue was dissolved in minimum amount of n-hexane, and yellow
crystals (420 mg, 0.717 mmol) were obtained at −30 °C. Yield: 74.8%.
1H NMR (C6D6, δ) 9.01 (d, 1H, J = 5.35 Hz, Py−H), 7.06 (d, 2H, J =
1
ArNCH2(C5H4N)}]+, on the basis of H, 19F, and 51V NMR
spectra (Figure 2). Formation of another cationic species,
[V(NAd)(OtBu){2-ArNCH2(C5H4N)}]+, was also observed in
the NMR spectra when 3c was treated with B(C6F5)3 in THF.
On the basis of 51V NMR spectra of 1 and 2a in the presence
of Al cocatalysts (in toluene-d8, Figure 3, and the data in C6D6
shown in the Supporting Information), in addition to our ESR
data reported previously,12b it was demonstrated that a chelate
anionic (2-anilidomethyl)pyridine ligand plays a role to stabilize
the oxidation state in this catalysis; these results thus suggest a
possibility that the cationic alkyl complex, [V(NAd)Me{2-
ArNCH2(C5H4N)}]+, would play an important role in this
catalysis. This hypothesis was further explored by solution-
phase V K-edge XAS analysis that showed no significant
changes in the oxidation states were observed in the XANES
spectra of 1 and 2a in the presence of Al cocatalysts; the FT-
EXAFS data also suggest a possibility that both the imido and
the (2-anilidomethyl)pyridine ligands remained in the catalyst
solution. The XAS analysis data could also exclude a possibility
of formation of vanadium(III) species (ESR silent) in situ.
Taking into account these results, it could be demonstrated
with high certainty that the cationic vanadium(V) species play a
role in this catalysis.
7.60 Hz, Ar−H), 7.03−6.97 (m, 2H, Ar−H and Py−H), 6.78 (t, 1H, J
= 6.15 Hz, Py−H), 6.65 (d, 1H, J = 7.90 Hz, Py−H), 4.47 (s, 2H,
NCH2), 2.57 (d, 2H, J = 9.45 Hz, VCH2), 2.18 (s, 6H, ArCH3), 2.09
(d, 6H, J = 2.20 Hz, Ad−H), 1.97 (brs, 3H, Ad−H), 1.60 (d, 3H, J =
11.50 Hz, Ad−H), 1.50 (d, 3H, J = 11.80 Hz, Ad−H), 0.79 (d, 2H, J =
9.45 Hz, VCH2), 0.12 (s, 18H, SiCH3). 13C NMR (C6D6, δ) 162.7,
161.8, 148.0, 136.6, 132.2, 128.5, 124.7, 122.4, 120.6, 66.4, 43.4, 36.7,
29.9, 19.7, 3.4. 51V NMR (C6D6, δ) 244.4 (Δν1/2 = 1012 Hz). Anal.
Calcd for C32H52N3Si2V: C, 65.60; H, 8.95; N, 7.17. Found: C, 65.73;
H, 9.15; N, 7.05.
We believe that the results of this study introduce an
important information for better understanding concerning a
catalytically active species, especially with vanadium, as well as
basic organometallic chemistry for the better catalyst design.
Moreover, we also believe that combination of all analyses
(NMR spectra, ESR spectra, and XAS analysis) and reaction
chemistry would be helpful for providing more clear
information for the better understanding. We are now exploring
the more details including further analyses of the catalyst
solutions (and complexes) through solution XAS (XANES,
EXAFS) analysis including assignments of resonances; these
would be introduced in the future.
Synthesis of V(NAd)Me[OC(CF3)3][2-(2,6-Me2C6H3)-
NCH2(C5H4N)] (3a). Into a toluene solution containing V(NAd)-
Me2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (100 mg, 0.23 mmol) was
added (CF3)3COH (67 mg, 0.28 mmol) at −30 °C. The reaction
mixture was warmed slowly to room temperature, and the mixture was
then stirred overnight. The reaction mixture was placed in a rotary
evaporator to remove the volatiles. The residue was dissolved in a
minimum amount of n-hexane. The chilled solution placed in the
freezer (−30 °C) afforded yellow crystals (76 mg, 0.11 mmol). Yield:
EXPERIMENTAL SECTION
■
General Procedure. All experiments were carried out under a
nitrogen atmosphere in a vacuum atmospheres drybox. Anhydrous-
grade toluene and n-hexane (Kanto Kagaku Co., Ltd.) were transferred
into a bottle containing molecular sieves (a mixture of 3A 1/16, 4A 1/
8, and 13X 1/16) in the drybox under nitrogen stream, and were
1
50%. H NMR (C6D6, δ) 8.61 (d, 1H, J = 5.05 Hz, Py−H), 7.06 (br,
1H, Ar−H), 6.99 (br, 2H, Ar−H), 6.92 (t, 1H, J = 7.58 Hz, Py−H),
I
DOI: 10.1021/acs.organomet.6b00727
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 3. Crystal Data and Collection Parameters of V(NAd)Me2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (2), V(NAd)Me(OR)[2-
a
(2,6-Me2C6H3)NCH2(C5H4N)] [R = C(CF3)3 (3a), C(CH3)(CF3)2 (3b), and C(CH3)3 (3c)]
2
3a
3b
3c
formula
C26H36N3V
C29H33F9N3OV
661.53
C29H36F6N3OV
607.55
C29H42N3OV
499.61
formula weight
crystal color, habit
crystal size (mm)
crystal system
space group
a (Å)
441.53
yellow, acicular
0.360 × 0.230 × 0.180
monoclinic
P21/c (#14)
18.88(2)
yellow, block
0.330 × 0.290 × 0.180
triclinic
yellow, block
0.241 × 0.208 × 0.200
triclinic
orange, block
0.310 × 0.250 × 0.230
monoclinic
P1 (#2)
P1 (#2)
P21/n (#14)
10.439(7)
̅
̅
9.0936(7)
11.9514(6)
14.1528(12)
82.667(10)
86.963(12)
75.467(10)
1476.4(2)
2
9.709(6)
9.814(6)
16.630(10)
73.62(2)
73.71(2)
78.33(3)
1446(2)
2
b (Å)
14.196(13)
20.00(2)
15.275(10)
c (Å)
17.444(11)
α (deg)
β (deg)
116.71(2)
97.308(7)
γ (deg)
V (Å3)
4789(8)
8
2759(3)
4
Z value
Dcalcd (g/cm3)
1.225
1888.00
93
1.488
1.395
1.203
1072.00
93
F000
680.00
93
632.00
93
temp (K)
μ (Mo Kα) (cm−1
)
4.309
49795
55.1
4.209
4.086
3.842
28471
55.0
no. of reflections measured (Rint)
2θmax (deg)
15411
15304
55.0
55.0
no. of observations [I > 2.00 σ(I)]
no. of variables
10970
980
6734
6604
6293
307
388
361
R1 [I > 2.00 σ(I)]
0.0575
0.1380
1.114
0.0474
0.1364
1.089
0.0487
0.1425
1.162
0.0453
0.1615
1.074
wR2 [I > 2.00 σ(I)]
goodness of fit
a
Detailed data are shown in the Supporting Inoformation.24
6.68 (t, 1H, J = 6.30 Hz, Py−H), 6.43 (d, 1H, J = 7.90 Hz, Py−H),
4.46 (d, 1H, J = 21.36 Hz, NCH2), 4.20 (d, 1H, J = 21.36 Hz, NCH2),
2.34 (s, 3H, ArCH3), 2.00 (s, 3H, ArCH3), 1.88−1.80 (m, 9H, Ad−H),
1.52 (s, 3H, VCH3), 1.45−1.38 (m, 6H, Ad−H). 13C NMR (C6D6, δ)
162.4, 159.1, 148.2, 137.0, 131.9, 130.9, 128.3, 128.5, 128.2, 127.9,
125.4, 123.7, 122.4, 121.3, 119.6, 67.6, 42.1, 36.3, 29.7, 18.2, 18.1. 19F
NMR (C6D6, δ) −73.7. 51V NMR (C6D6, δ) −112.1 (Δν1/2 = 1160
Hz).
with solvent), 7.05 (d, 2H, J = 7.55 Hz, Ar−H), 6.93 (t, 1H, J = 7.55
Hz, Ar−H), 4.75 (d, 1H, J = 20.81 Hz, NCH2), 4.68 (d, 1H, J = 20.81
Hz, NCH2), 2.20 (s, 3H, ArCH3), 2.19 (s, 3H, ArCH3), 1.81 (brs, 3H,
Ad−H), 1.62 (d, 6H, J = 2.55 Hz, Ad−H), 1.43 (d, 3H, J = 12.15 Hz,
Ad−H), 1.38 (d, 3H, J = 12.15 Hz, Ad−H), 1.32 (s, 9H, C(CH3)3),
0.63 (s, 3H, VCH3). 13C NMR (CDCl3, δ) 160.4, 148.5, 136.2, 132.7,
132.0, 128.3, 128.0, 128.0, 123.7, 121.9, 119.2, 66.1 (NCH2), 42.8,
36.2, 33.3, 29.4, 18.8(ArCH3), 18.2 (ArCH3). 51V NMR (C6D6, δ)
−246.5 (Δν1/2 = 687 Hz).
Reaction of V(NAd)Me2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (2a)
with Borate. [Ph3C][B(C6F5)4] (209 mg, 0.227 mmol) was added to
Et2O (40 mL) containing V(NAd)Me2[2-(2,6-Me2C6H3)-
NCH2(C5H4N)] (100 mg, 0.226 mmol) at −30 °C. The solution
was stirred 1 h at room temperature. After reaction, the solution was
placed in a rotary evaporator to remove the solvent. The residue was
dissolved in Et2O and dropped into n-hexane. Removal of hexane layer
and washing by hexane afforded the residue (265 mg). 1H NMR
([solvent], δ) 8.41 (d, 1H, J = 5.35 Hz, Py−H), 8.12 (t, 1H, J = 7.73
Hz, Py−H), 7.70 (d, 1H, J = 8.15 Hz, Py−H), 7.64 (t, 1H, J = 6.48 Hz,
Py−H), 7.25−7.09 (m, 3H, Ar−H), 5.26 (d, 1H, J = 22.71 Hz, NCH2),
5.20 (d, 1H, J = 22.71 Hz, NCH2), 4.04−3.89 (m, 4H, OCH2), 2.27 (s,
3H, Ad−H), 1.94 (brs, 6H, ArCH3), 1.69 (d, 3H, J = 12.45 Hz, Ad−
H), 1.66 (d, 3H, J = 12.45 Hz, Ad−H), 1.53 (brs, 3H, VCH3), 1.53−
1.40 (m, 6H, Ad−H), 1.32 (t, 6H, J = 7.08 Hz, OCH2CH3). 19F NMR
(CDCl3, δ) −132.6 (brs), −163.0 (t, J = 20.3 Hz), −166.8 (brs). 51V
NMR (CDCl3, δ) 83.6 (Δν1/2 = 2763 Hz).
Synthesis of V(NAd)Me[OC(CF3)2(CH3)][2-(2,6-Me2C6H3)-
NCH2(C5H4N)] (3b). Into a toluene solution containing V(NAd)-
Me2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (110 mg, 0.26 mmol) was
added (CH3)(CF3)2COH (80 mg, 0.44 mmol) at −30 °C. The
reaction mixture was warmed slowly to room temperature, and the
mixture was then stirred overnight. The reaction mixture was placed in
a rotary evaporator to remove the volatiles. The residue was dissolved
in a minimum amount of n-hexane. The chilled solution placed in the
freezer (−30 °C) afforded yellow crystals (101 mg, 0.166 mmol).
1
Yield: 65%. H NMR (C6D6, δ) 8.82 (d, 1H, J = 5.35 Hz, Py−H),
7.08−6.98 (m, 3H, Ar−H), 6.90 (t, 1H, J = 7.57 Hz, Py−H), 6.70 (t,
1H, J = 6.30 Hz, Py−H), 6.42 (d, 1H, J = 7.85 Hz, Py−H), 4.37 (d,
1H, J = 21.13 Hz, NCH2), 4.29 (d, 1H, J = 21.13 Hz, NCH2), 2.28 (s,
3H, ArCH3), 2.11 (s, 3H, OC(CH3)), 1.93 (s, 3H, ArCH3), 1.82 (brs,
3H, Ad−H), 1.80 (brs, 6H, Ad−H), 1.41 (brs, 6H, Ad−H), 1.37 (s,
3H, VCH3). 19F NMR (C6D6, δ) −78.1 (q, J = 8.66 Hz), −78.9 (q, J =
8.66 Hz). 51V NMR (C6D6, δ) −161.1 (Δν1/2 = 1118 Hz).
Synthesis of V(NAd)Me[OC(CH3)3][2-(2,6-Me2C6H3)-
NCH2(C5H4N)] (3c). Into a toluene solution containing V(NAd)-
Me2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (200 mg, 0.45 mmol) was
Reaction of V(NAd)Me[OC(CH3)3][2-(2,6-Me2C6H3)-
NCH2(C5H4N)] (3c) with B(C6F5)3. B(C6F5)3 (10 mg, 0.040 mmol)
was added to THF (2 mL) containing V(NAd)Me(OtBu)[2-(2,6-
Me2C6H3)NCH2(C5H4N)] (20 mg, 0.040 mmol) at −30 °C. The
solution was stirred 1 h at room temperature. After reaction, the
solution was placed in a rotary evaporator to remove the solvent. The
residue was dissolved in THF and dropped into n-hexane. Removal of
n-hexane layer and washing by n-hexane afforded the residue (20 mg).
1H NMR (CDCl3, δ) 8.26 (d, 1H, J = 5.35 Hz, Py−H), 7.93 (td, 1H, J
t
added BuOH (40 mg, 0.54 mmol) at −30 °C. The reaction mixture
was warmed slowly to room temperature, and the mixture was then
stirred overnight. The reaction mixture was placed in a rotary
evaporator to remove the volatiles. The resultant residue was dissolved
in a minimum amount of n-hexane, and yellow solids (132 mg, 0.264
1
mmol) were obtained at −30 °C. Yield: 58%. H NMR (CDCl3, δ)
8.84 (d, 1H, J = 5.05 Hz, Py−H), 7.76 (td, 1H, J = 7.56, 1.58 Hz, Py−
H), 7.36 (t, 1H, J = 6.32 Hz, Py−H), 7.27 (d, 1H, Py−H, overlapping
= 7.55, 1.25 Hz, Py−H), 7.48−7.43 (m, 2H, Py−H), 7.23 (t, 1H, J =
J
DOI: 10.1021/acs.organomet.6b00727
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
4.70 Hz, Ar−H), 7.14 (d, 2H, J = 4.40 Hz, Ar−H), 5.22 (d, 1H, J =
22.08 Hz, NCH2), 5.04 (d, 1H, J = 22.08 Hz, NCH2), 4.09 (br, 2H,
coordinated THF), 3.99 (br, 2H, coordinated THF), 3.77 (br, 4H, free
THF), 2.34 (s, 3H, Ad−H), 2.08 (s, 6H, ArCH3), 1.88 (br, 8H,
coordinated and free THF), 1.62−1.43 (m, 9H, Ad−H), 1.41 (s, 9H,
tBu−H), 1.34−1.26 (m, 3H, Ad−H), 0.48 (brs, 3H, BCH3). 19F NMR
(CDCl3, δ) −132.7 (d, J = 20.8 Hz), −164.7 (t, J = 19.1 Hz), −167.3
(dd, J = 20.8, 19.1 Hz). 51V NMR (CDCl3, δ) −309.6 (Δν1/2 = 1842
Hz).
extracted from V(NAd)Cl2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (1)
structure using FEFF8 (σ2 = 0.0036 (σ: Debye−Waller factor)).
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00727.
Crystallographic Analysis. All of measurements made on a
Rigaku XtaLAB mini Imaging Plate diffractometer with graphite
monochromated Mo Kα radiation. The crystal collection parameters
are listed below (Table 3). All structures were solved by direct
methods and expanded using Fourier techniques, and the non-
hydrogen atoms were refined anisotropically.43 Hydrogen atoms were
refined using the riding model. All calculations were performed using
the Crystal Structure44 crystallographic software package except for
refinement, which was performed using SHELXL-97.45 Details are
shown in the Supporting Information.24
Reaction with Ethylene. Ethylene oligomerizations were
conducted in a 100 mL scale stainless-steel autoclave, and the typical
reaction procedure is as follows. Toluene (29.0 mL) and the
prescribed amount of MAO were added into the autoclave in the
drybox. The reaction apparatus was then filled with ethylene (1 atm),
and the prescribed amount of complex, V(NAd)Me2[2-(2,6-
Me2C6H3)NCH2(C5H4N)] (2a), in toluene (1.0 mL) was added
into the autoclave. The reaction apparatus was then immediately
pressurized to 7 atm (total 8 atm), and the mixture was magnetically
stirred for 10 min (ethylene pressure was kept constant during the
reaction). After the above procedure, the remaining ethylene was
purged at −30 °C, and 0.5 g of n-heptane was added as an internal
standard. The solution was then analyzed by GC to determinate the
activity and the product distribution. In the case of reaction in the
presence of [Ph3C][B(C6F5)4], a toluene solution containing [Ph3C]-
[B(C6F5)4] was added after injecting a toluene solution containing
catalyst (2a). After the above oligomerization procedure, the
remaining mixture in autoclave was poured into MeOH containing
HCl, and the resultant polymer (white precipitate) was collected on a
filter paper by filtration and was adequately washed with MeOH. The
resultant polymer was then dried in vacuo at 60 °C for 2 h.
NMR spectra in the reactions of V(NAd)Me2[2-(2,6-
Me2C6H3)NCH2(C5H4N)] (2a) with [Ph3C][B-
(C6F5)4], V(NAd)Me(OtBu)[2-(2,6-Me2C6H3)-
NCH2(C5H4N)] (3c) with B(C6F5)3. Additional NMR
spectra of C6D6 solution of V(NAd)Me2[2-(2,6-
Me2C6H3)NCH2(C5H4N)] (2a) in the presence of Al
cocatalysts. Additional data including XANES and
EXAFS spectra and curve fittings [for V(NAd)Cl3,
V(NAd)Cl2[2-(2,6-Me2C6H3)CH2C5H4N] (1) by calcu-
lations on the basis of X-ray crystallographic structure
and/or DFT calculations]. (PDF)
Crystallographic information file for V(NAd)Me2[2-
ArNCH2(C5H4N)] (2a), V(NAd)Me(OR′)[2-
ArNCH2(C5H4N)] [R′ = OC(CF3)3 (3a), OC-
(CF3)2(CH3) (3b), OC(CH3)3 (3c)] (CIF)
Cartesian coordinates for V(NAd)Me2 [2-
ArNCH2(C5H4N)] (2a), V(NAd)Me(OR′)[2-
ArNCH2(C5H4N)] [R′ = OC(CF3)3 (3a), OC-
(CF3)2(CH3) (3b), OC(CH3)3 (3c)] (XYZ)
(PDF)
(CIF)
(XYZ)
AUTHOR INFORMATION
Corresponding Authors
*E mail: ktnomura@tmu.ac.jp. Tel./Fax: +81-42-677-2547.
*E-mail: mitsudom@cheng.es.osaka-u.ac.jp.
*E-mail: takaya@scl.kyoto-u.ac.jp.
*E-mail: yamazoe@chem.s.u-tokyo.ac.jp.
ORCID
Kotohiro Nomura: 0000-0003-3661-6328
■
51V NMR Experiments in the Reaction of V(NAd)X2[2-(2,6-
Me2C6H3)NCH2(C5H4N)] [X = Cl (1), Me (2a)] with Al Cocatalysts
in Toluene-d8. Typical procedure is as follows. Into a toluene-d8
solution (ca. 0.6 mL) containing 1 or 2a (25 μmol, ca. 42 μmol/mL)
placed in the freezer (−30 °C) was added Al cocatalyst (MAO,
Me2AlCl, or Et2AlCl; 250 μmol, 10.0 equiv). The mixture was then
measured by 51V NMR spectrum at 25 °C within 10 min after the
preparation.
Notes
The authors declare no competing financial interest.
Analysis of Catalyst Solution by Solution-Phase X-ray
Absorption Spectroscopy. V K-edge X-ray absorption fine structure
(XAFS) measurements were carried out at the BL01B1 beamline at
the SPring-8 facility of the Japan Synchrotron Radiation Research
Institute (proposal nos. 2015B1308, 2016A1455). The measurements
were conducted at room temperature. A Si (111) two-crystal
monochromator was used for the incident beam. V K-edge XAFS
spectra of V complex samples (prepared as toluene solution, 50 μmol/
mL) were recorded in the fluorescence mode using an ionization
chamber as the I0 detector and 19 solid-state detectors as the I
detector. The X-ray energy was calibrated using V2O5. Data analysis
was performed with the REX2000 ver. 2.5.9 software package (Rigaku
Co.). The X-ray absorption near edge structure (XANES) data was
analyzed by removing the atomic absorption background using a cubic
spline from the χ spectra and normalization of them to the edge
height. The extended X-ray absorption fine structure (EXAFS) data
were analyzed as follows. The χ spectra were extracted by removing
the atomic absorption background using a cubic spline and were
normalized to the edge height. The k3-weighted χ spectra were Fourier
transformed (FT) into the r space, using the FT range 3.0−12 Å−1.
The curve fitting range was 1.0−2.3 Å. The phase shift and
backscattering amplitude functions of V−N and V−Cl bonds were
ACKNOWLEDGMENTS
■
This project was partly supported by Grant-in-Aid for Scientific
Research on Innovative Areas (″3D Active-Site Science”, No.
26105003) from The Ministry of Education, Culture, Sports,
Science and Technology (MEXT). The synchrotron XAFS
analysis were performed at SPring-8 beamlines of BL01B1 with
the approval of JASRI (2015B1308, 2016A1455). A.I. expresses
his thanks to JSPS for predoctoral fellowship (DC2 26·7313).
The authors would also express their heartfelt thanks to Prof.
Zen Maeno, Prof. Koichiro Jitsukawa, and Prof. Kiyotomi
Kaneda (Osaka University) for their big supports for
collaboration of XAFS analysis at SPring 8. K.N. expresses his
thanks to Mr. Takumi Yamada, Mr. Shuta Ito, Mr. Tomohiro
Miwata, and Dr. Shunsuke Sueki (Tokyo Metropolitan Univ.,
TMU) for helping measurement of synchrotron XAFS analysis
at Spring 8, and to Prof. Masaharu Nakamura (Kyoto
University), Profs. S. Komiya, A. Inagaki (TMU) for
discussions.
K
DOI: 10.1021/acs.organomet.6b00727
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
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McMullin, C. L.; Tenza, K.; Wass, D. F. Organometallics 2011, 30, 935.
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DOI: 10.1021/acs.organomet.6b00727
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
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(24) CIF and XYZ files for V(NAd)Me2[2-ArNCH2(C5H4N)] (2a),
V(NAd)Me(OR′)[2-ArNCH2(C5H4N)] [R′ = OC(CF3)3 (3a),
OC(CF3)2(CH3) (3b), and OC(CH3)3 (3c)] are shown in the
Supporting Information.
(25) Yamada, J.; Nomura, K. Organometallics 2005, 24, 3621.
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(29) Reported examples for synthesis of cationic complexes by
reaction of vanadium-methyl complex with [Ph3C][B(C6F5)4],
[PhN(H)Me][B(C6F5)4], B(C6F5)3: Liu, G.; Beetstra, D. J.;
Meetsma, A.; Hessen, B. Organometallics 2004, 23, 3914. Syntheses
and structural analyses of the cationic complexes by reactions of V(N-
2,6-Me2C6H3)Me(NCtBu2)2 with [Ph3C][B(C6F5)4], [PhN(H)Me]
[B(C6F5)4], B(C6F5)3 are also reported in ref 25.
(30) Examples for isolation of cationic Ti-methyl complexes for
ethylene polymerization: (a) Jia, L.; Yang, X.; Stern, C. L.; Marks, T. J.
Organometallics 1997, 16, 842. (b) Lee, H.; Jordan, R. F. J. Am. Chem.
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Nomura, K.; Hasumi, S. Organometallics 2009, 28, 1942. (f) Hasumi,
S.; Itagaki, K.; Zhang, S.; Nomura, K. Macromolecules 2011, 44, 773.
(31) NMR spectra in the reactions of V(NAd)Me2[2-(2,6-Me2C6H3)
NCH2(C5H4N)] (2a) with [Ph3C][B(C6F5)4] and V(NAd)Me(OtBu)
[2-(2,6-Me2C6H3)NCH2(C5H4N)] (3c) with B(C6F5)3 are shown in
the Supporting Information.
(32) Dixon, R. E.; Streitwieser, A. J. Org. Chem. 1992, 57, 6125.
(33) For examples:30a (a) Nomura, K.; Fudo, A. Inorg. Chim. Acta
2003, 345, 37. (b) Keaton, R. J.; Jayaratne, K. C.; Fettinger, J. C.; Sita,
L. R. J. Am. Chem. Soc. 2000, 122, 12909. In ref 30a, the resultant
slurry solids in toluene, corresponding to cationic complexes, were
filtered and isolated after dried in vacuo. (c) Synthesis of cationic
zirconocene complexes containing alkoxo ligand by methyl abstraction
with B(C6F5)3: Wu, Z.; Jordan, R. F.; Petersen, J. L. J. Am. Chem. Soc.
1995, 117, 5867.
(37) (a) For example (account): Yamamoto, T. Adv. X-ray Chem.
Anal., Japan 2007, 38, 45. The transition of a 1s electron to 3d orbital
gives weak pre-edge peaks due to the electric quadrupole transition for
any symmetries. An intense pre-edge peak is assigned to an electric
dipole transition to p-character in the d-p hybridized orbital, and the
mixing of a metal 4p orbital with the 3d orbital strongly depends on
the coordination symmetry. Related references include: (b) Srivastava,
U. C.; Nigam, H. L. Coord. Chem. Rev. 1973, 9, 275. and references
cited therein.
(38) For example (solid structural analysis of vanadium compounds
by XAS spectra): (a) Wong, J.; Lytle, F. W.; Messmer, R. P.; Maylotte,
D. H. Phys. Rev. B: Condens. Matter Mater. Phys. 1984, 30, 5596.
(b) Asakura, H.; Shishido, T.; Yamazoe, S.; Teramura, K.; Tanaka, T. J.
Phys. Chem. C 2011, 115, 23653.
(39) A shoulder-edge peak observed at 5477.8 eV (1), 5476.4 eV (1
+ Me2AlCl), 5474.7 eV (1 + Et2AlCl), and 5475.5 eV (2a + Me2AlCl)
might be considered as 1s−4p transition or ascribed to V-Cl bond.
The latter explanation might be good agreement with decrease in the
intensity upon addition of MAO (Figure 4a);36 this would also be
related to the fact that the intensity of V−Cl (coordination number)
by FT-EXAFS spectrum decreased upon addition of MAO (Figure S3-
8).
(40) As shown in Figure 3, the 51V NMR spectra of toluene-d8
solution containing 2a became broad upon addition of MAO (10
equiv) with decrease in the intensity of 2a, and no clear resonances
were observed upon further addition (50 equiv) due to two-phase
separation (toluene-d8 soluble/insoluble). In contrast, a toluene
solution containing 2a with MAO became homogeneous without
phase separation. We have no clear explanation concerning the
observed difference between the 51V NMR spectrum (in toluene-d8)
and the XANES spectrum (in toluene).
(41) A rather strong intensity of the pre-edge peak in V(NAd)Cl3 is
due to the tetrahedral geometry around vanadium (eg < t2g, dominant
transition from 1s−3d transition to t2g).37 The shift of pre-edge and
edge-shoulder peaks (1.3 eV) upon addition of Me2AlCl would be due
to formation of vanadium(IV) [and vanadium(III)] species, and the
assumption would also supported by the 51V NMR spectrum and ESR
spectrum.12b
(42) As shown in Figure S3-8, EXAFS spectra for V(NAd)Cl2[2-(2,6-
Me2C6H3)CH2C5H4N] (1) and complex 1 in the presence of MAO,
two peaks at 1.2 Å and 1.9 Å were observed. The backscattering
amplitude for each peak in the complex 1, obtained by reverse Fourier
transform analysis, was compared with them of V−N and V−Cl bonds
calculated by FEFF (Figure S3−10). The backscattering amplitudes
for the peaks at 1.2 Å and 1.9 Å were close to those of the V−N and
V−Cl bonds, respectively. Therefore, we determined that the peaks at
1.2 Å and 1.9 Å are the V−N and V−Cl bonds, respectively. The peak
intensity of the V−N hardly changed by the addition of MAO whereas
that of the V−Cl bonds was reduced in Figure S3−8. Same results
were obtained for curve fitting analysis as shown in Tables S3−1 and
S3−2. This change indicates that the coordinated Cl of the complex 1
was removed by the reaction with MAO without any changes for V−N
bonds. Detailed data were shown in the Supporting Information. We
appreciate the reviewer for suggestion placing more analysis data in the
manuscript.
(43) SIR2008 Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini,
B.; Cascarano, G. L.; De Caro, L.; Giacovazzo, C.; Polidori, G.; Siliqi,
D.; Spagna, R. J. Appl. Crystallogr. 2007, 40, 609.
(44) Crystal Structure 4.0: Crystal Structure Analysis Package;
Rigaku and Rigaku Americas: Tokyo, Japan, 2000−2010; pp 196−
8666.
(34) Additional NMR spectra (in C6D6) are shown in the Supporting
Information. Samples for NMR spectra were prepared by dissolving
complex (ca. 20 mg) in toluene-d8 or C6D6, followed by addition of
prescribed Al cocatalyst in the dry box.
(35) Zhang, W.; Nomura, K. Inorg. Chem. 2008, 47, 6482.
(36) Solution XAFS (X-ray absorption fine structure) analysis
[solution phase V K-edge XANES (X-ray absorption near edge
structure) and EXAFS (extended X-ray absorption fine structure)] was
conducted through the use of synchrotron radiation at SPring-8,
BL01B1 beamline. More data including XANES, EXAFS spectra and
curve fittings [by calculations on the basis of X-ray crystallographic
structures of V(NAd)Cl3, V(NAd)Cl2[2-(2,6-Me2C6H3)CH2C5H4N]
(1), V(NAd)Me2[2-(2,6-Me2C6H3)-CH2C5H4N] (2a), and/or DFT
calculations] were shown in the Supporting Information.
(45) SHELX97: Sheldrick, G. M. Acta Crystallogr., Sect. A: Found.
Crystallogr. 2008, 64, 112.10.1107/S0108767307043930
M
DOI: 10.1021/acs.organomet.6b00727
Organometallics XXXX, XXX, XXX−XXX