Lewis acid promoted titanium alkylidene formation: Off-cycle intermediates relevant to olefin trimerization catalysis

Article abstract of DOI:10.1021/ja5055687

Two new precatalysts for ethylene and α-olefin trimerization, (FI)Ti(CH₂SiMe₃)₂Me and (FI)Ti(CH₂CMe₃)₂Me (FI = phenoxy-imine), have been synthesized and structurally characterized by X-ray diffraction. (FI)Ti(CH₂SiMe₃)₂Me can be activated with 1 equiv of B(C₆F₅)₃ at room temperature to give the solvent-separated ion pair [(FI)Ti(CH₂SiMe₃)₂][MeB(C₆F₅)₃], which catalytically trimerizes ethylene or 1-pentene to produce 1-hexene or C₁₅ olefins, respectively. The neopentyl analogue (FI)Ti(CH₂CMe₃)₂Me is unstable toward activation with B(C₆F₅)₃ at room temperature, giving no discernible diamagnetic titanium complexes, but at -30 °C the following can be observed by NMR spectroscopy: (i) formation of the bis-neopentyl cation [(FI)Ti(CH₂CMe₃)₂]⁺, (ii) α-elimination of neopentane to give the neopentylidene complex [(FI)Ti(=CHCMe₃)]⁺, and (iii) subsequent conversion to the imido-olefin complex [(MeOAr₂N=)Ti(OArHC=CHCMe₃)]⁺ via an intramolecular metathesis reaction with the imine fragment of the (FI) ligand. If the reaction is carried out at low temperature in the presence of ethylene, catalytic production of 1-hexene is observed, in addition to the titanacyclobutane complex [(FI)Ti(CH(CMe₃)CH₂CH₂)]⁺, resulting from addition of ethylene to the neopentylidene [(FI)Ti(=CHCMe₃)]⁺. None of the complexes observed spectroscopically subsequent to [(FI)Ti(CH₂CMe₃)₂]⁺ is an intermediate or precursor for ethylene trimerization, but notwithstanding these off-cycle pathways, [(FI)Ti(CH₂CMe₃)₂]⁺ is a precatalyst that undergoes rapid initiation to generate a catalyst for trimerizing ethylene or 1-pentene.

Full text of DOI:10.1021/ja5055687

Subscriber access provided by Otterbein University
Article
Lewis Acid Promoted Titanium Alkylidene Formation: Off-
Cycle Intermediates Relevant to Olefin Trimerization Catalysis
Aaron Sattler, David G VanderVelde, Jay A. Labinger, and John E. Bercaw
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/ja5055687 • Publication Date (Web): 09 Jul 2014
Downloaded from http://pubs.acs.org on July 10, 2014
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Journal of the American Chemical Society is published by the American Chemical
Society. 1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 12
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
Lewis Acid Promoted Titanium Alkylidene Formation:
Off-Cycle Intermediates Relevant to Olefin Trimerization Catalysis‡
Aaron Sattler, David G. VanderVelde, Jay A. Labinger,* and John E. Bercaw*
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, California 91125, United
States
ABSTRACT: Two new precatalysts for ethylene and α-olefin trimerization, (FI)Ti(CH2SiMe3)2Me and (FI)Ti(CH2CMe3)2Me (FI =
phenoxy-imine), have been synthesized and structurally characterized by X-ray diffraction. (FI)Ti(CH2SiMe3)2Me can be activated with one
equivalent of B(C6F5)3 at room temperature to give the solvent-separated ion pair [(FI)Ti(CH2SiMe3)2][MeB(C6F5)3], which catalytically
trimerizes ethylene or 1-pentene to produce 1-hexene or C15 olefins, respectively. The neopentyl analogue, (FI)Ti(CH2CMe3)2Me, is unsta-
ble towards activation with B(C6F5)3 at room temperature, giving no discernible diamagnetic titanium complexes, but at –30 °C the following
can be observed by NMR spectroscopy: (i) formation of the bis-neopentyl cation [(FI)Ti(CH2CMe3)2]+, (ii) α-elimination of neopentane to
give the neopentylidene complex [(FI)Ti(=CHCMe3)]+, and (iii) subsequent conversion to the imido-olefin complex [(Me-
OAr2N=)Ti(OArHC=CHCMe3)]+ via an intramolecular metathesis reaction with the imine fragment of the (FI) ligand. If the reaction is
carried out at low temperature in the presence of ethylene, catalytic production of 1-hexene is observed, in addition to the titanacyclobutane
complex [(FI)Ti(CH(CMe3)CH2CH2)]+, resulting from addition of ethylene to the neopentylidene [(FI)Ti(=CHCMe3)]+. None of the
complexes observed spectroscopically subsequent to [(FI)Ti(CH2CMe3)2]+ is an intermediate or precursor for ethylene trimerization, but
notwithstanding these off-cycle pathways, [(FI)Ti(CH2CMe3)2]+ is a precatalyst that undergoes rapid initiation to generate a catalyst for
trimerizing ethylene or 1-pentene.
and is the second system known to do so.8 Trimerization of α-
olefins is important to produce value-added substances such as
diesel and/or jet fuel, and motor lubricants.9 The ability to stoichi-
INTRODUCTION
The catalytic synthesis of 1-hexene by selective ethylene trimeri-
zation, an important industrial process1 due to its use as a comon-
ometrically
produce
a
trimerization
precatalyst,
omer in the production of linear low-density polyethylene
(LLDPE), has been extensively studied.2 Although catalytic sys-
tems have been known for many years,3 there has been little ad-
vance in understanding what makes a catalyst trimerize rather than
polymerize ethylene. The rational development of new catalysts
necessitates information about the active catalytic species, which is
often difficult to observe spectroscopically or characterize structur-
ally. Often the major species that can be observed is not part of the
catalytic cycle;4 furthermore, the large excess of aluminum reagents
typically required for activation, such as methylaluminoxane
(MAO), impedes mechanistic studies.
[(FI)TiMe2][MeB(C6F5)3], allowed us to show that: (i) the rela-
tive rate of initiation is orders of magnitude slower than trimeriza-
tion; (ii) the decomposition rate is similar to that of initiation; and
(iii) initiation proceeds by a series of steps involving ethylene inser-
tion(s), β-H elimination and reductive elimination of methane.
Under
such
conditions,
only
the
precatalyst
[(FI)TiMe2][MeB(C6F5)3], the decomposition product (a TiIII
species), and 1-hexene could be experimentally observed.
In order to ascertain information about the active catalytic spe-
cies, we sought a system in which precatalyst initiation is faster than
trimerization. Previous studies on the propylene polymerization
An interesting trimerization system, reported by Fujita and co-
workers, is generated from (FI)TiCl3 [(FI = (N-(5-methyl-3-(1-
catalysts [Cp*CpZrR][MeB(C6F5)3] (R
= Me, CH2SiMe3,
CH2CMe3) have shown that insertion of propylene into the zirco-
nium-alkyl bond (i.e., catalyst initiation) is significantly faster for
Zr–CH2CMe3 compared with Zr–Me and Zr–CH2SiMe3; the
[Cp*CpZr(CH2CMe3)][MeB(C6F5)3] system thus allowed for a
detailed kinetic analysis of propylene propagation, rather than be-
ing limited by slow initiation.10 It is important to note that, based
on the proposed mechanisms for selective trimerization catalysis
(Scheme 1),5,7,11 the active catalyst should be the same (i.e.,
[(FI)TiII(C2H4)2]+), independent of the alkyl ligands in the precat-
alyst.
adamantyl)salicylidene)-2’-(2”-methoxyphenyl)anilinato)]
and
MAO (10,000 equivalents); it produces 1-hexene with a turnover
number (TON) of ~1.1×107 mmol olefin oligomerized/mmol Ti
at 49.3 atm of ethylene.5 We recently reported that (FI)TiMe3, a
putative intermediate upon treatment of (FI)TiCl3 with MAO,5, 6
can be independently synthesized and activated with just one
equivalent of B(C6F5)3 to give [(FI)TiMe2][MeB(C6F5)3], an ac-
tive precatalyst for ethylene trimerization.7 Furthermore,
(FI)TiMe3/B(C6F5)3 was shown to selectively trimerize α-olefins,
‡ Dedicated in memory of Greg Hillhouse, a friend, colleague, and outstanding organometallic chemist.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 12
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. Molecular structures of (FI)Ti(CH2SiMe3)2Cl, (FI)Ti(CH2SiMe3)2Me, (FI)Ti(CH2CMe3)2Cl and (FI)Ti(CH2CMe3)2Me (left to
right). The hydrogen atoms on the (FI) ligand, CH2SiMe3 methyls, and CH2CMe3 methyls are not shown for clarity.
Accordingly, we report here the synthesis of two new potential
trimerization precatalysts, (FI)Ti(CH2SiMe3)2Me and
methoxy-arene group (C2–Ti–N), whereas the largest angle in
(FI)TiMe3 is proximal (N–Ti–C1),7 suggesting that the sterics of
the XMe3 (X = Si, C) groups have a more significant effect on dis-
torting the geometry towards square pyramidal than does the
arene. This is most readily seen by comparing the distal and prox-
(FI)Ti(CH2CMe3)2Me, and their behavior upon activation with
one equivalent of B(C6F5)3. While both systems are complicated
by competing reactions involving the (FI) and alkyl ligands, each
selectively catalyzes trimerization of ethylene and 1-pentene and
the one based on (FI)Ti(CH2CMe3)2Me does, indeed, undergo
faster initiation.
imal angles (Δd-p) in Table 1. Although (FI)Ti(CH2CMe3)2Cl has
the same approximate geometry about the Ti center as the other
complexes above, the neopentyl ligands are related by a pseudo
mirror plane (Figure 1) such that the distal and proximal angles are
more similar (Table 1).
Scheme 1.
R
R
R
R
R
+
[Ti]
+
[Ti]
+
[Ti]
B(C6F5)3
C2H4
β-H elim.
Scheme 2.
H
[Ti]
n
R
R
R
Me
–RH
Si
O
Ti
Cl
Si
O
R
R
1. MeMgBr
2. Dioxane
Me3SiCH2MgCl
C2H4
+
+
+
[Ti]
N
C2H4
N
Ti
O
Et2O
–30 °C
Et2O
–30 °C
Si
O
Si
[Ti]
[Ti]
Me
R = Me, CH2SiMe3, CH2CMe3
(FI)Ti(CH2SiMe3)2Cl
(FI)Ti(CH2SiMe3)2Me
Propagating species
independent of R
O
Ti
[Ti] = (FI)Ti
+
[Ti] = [(FI)Ti][MeB(C6F5)3]
Cl
Cl
N
O
Cl
(FI)TiCl3
RESULTS AND DISCUSSION
O
O
1. MeMgBr
2. Dioxane
Me3CCH2MgCl
N
Ti
N
Ti
1. Synthesis and Structural Characterization of (FI)Ti
Complexes. (FI)Ti(CH2SiMe3)2Me and (FI)Ti(CH2CMe3)2Me
were synthesized by consecutive treatment of a suspension of
(FI)TiCl3 in Et2O with the appropriate Grignard reagents,
Me3SiCH2MgCl or Me3CCH2MgCl (2.5 equiv), respectively, and
MeMgBr (2.4 equiv) at –30 °C, followed by addition of 1,4-dioxane
O
O
Et2O
–30 °C
Et2O
–30 °C
Cl
Me
(FI)Ti(CH2CMe3)2Cl
(FI)Ti(CH2CMe3)2Me
1H and 13C NMR spectroscopic studies indicate that all of the
complexes are five-coordinate in solution as well, based on the
upfield chemical shift of the OMe signal relative to that of
(FI)TiCl3.5 The fluxional nature of the complexes depends on
whether the fifth ligand is a chloride or methyl group: at 25 °C
(FI)Ti(CH2SiMe3)2Me and (FI)Ti(CH2CMe3)2Me each display a
(Scheme
2).12
The
corresponding
chlorides,
(FI)Ti(CH2SiMe3)2Cl and (FI)Ti(CH2CMe3)2Cl, could be isolat-
ed and characterized when the reactions were carried out without
MeMgBr addition. All four complexes are soluble in pentane, al-
lowing for easier purification and higher isolated yields compared
with (FI)TiMe3, which is only sparingly soluble in pentane. Each
complex has been structurally characterized by X-ray diffraction,
and the molecular structures are shown in Figure 1; all are five-
coordinate with the methoxy group not coordinated to the Ti cen-
ter in the solid state, displaying approximate trigonal bipyramidal
geometries distorted towards square pyramidal. The hydrogen
atoms of the methylene groups (CH2XMe3: X = Si, C) were located
in the difference electron density map and freely refined, and show
1
single H NMR signal for their respective (CH2XMe3)2 (X = Si, C)
methyl
groups,
while
(FI)Ti(CH2SiMe3)2Cl
and
(FI)Ti(CH2CMe3)2Cl each display two signals. Furthermore, the
chloride complexes display four chemically inequivalent signals for
the methylene protons (CH2XMe3: X = Si, C) at 25 °C, one of
which is significantly upfield of the other three (δ = 0.25 and 1.04
ppm, respectively). Although upfield chemical shifts can indicate
α-agostic interactions,13 the absence of any such interaction in the
solid-state structures lead us to believe that the diamagnetic ring
current of the methoxy-arene is a more likely cause.
no indication of any α-agostic interaction.13
One structural feature of note is that the largest of the three an-
gles in the pseudo trigonal plane in (FI)Ti(CH2SiMe3)2Cl,
(FI)Ti(CH2SiMe3)2Me and (FI)Ti(CH2CMe3)2Me is distal to the
2
ACS Paragon Plus Environment

Page 3 of 12
Journal of the American Chemical Society
Table 1. Bond angles (°) of the pseudo trigonal plane of five co-
ordinate (FI)Ti complexes.
(FI)Ti(CH2SiMe3)2Me/B(C6F5)3 also trimerizes α-olefins such
1
2
3
4
5
6
7
8
as 1-pentene, giving a TON of ca. 900 (Table 2), almost three
times greater than (FI)TiMe3/B(C6F5)3.7 The higher TON is at-
tributed to greater solubility of (FI)Ti(CH2SiMe3)2Me in 1-
pentene compared with (FI)TiMe3 which forms a suspension with
some solid immobilized on the walls of the flask. It is important to
note that selectivity for trimers is greater than 95%, and that 85% of
the trimers are the same regioisomer (Scheme 4) as observed for
N-Ti-C1a
C1-Ti-C2
C2-Ti-Nb
c
Δd-p
(FI)Ti(CH2SiMe3)2Cl
(FI)Ti(CH2SiMe3)2Me
(FI)Ti(CH2CMe3)2Cl
(FI)Ti(CH2CMe3)2Me
115.71(5)
116.30(5)
132.74(4)
115.63(9)
106.15(6)
106.60(6)
100.98(4)
103.76(10)
137.96(5)
137.10(5)
126.13(4)
140.17(8)
22.25
20.80
-6.61
24.54
(FI)TiMe3/B(C6F5)3,7
strongly
suggesting
that
d
9
(FI)TiMe3
131.00(7)
107.83(8)
121.01(6)
-9.99
(FI)Ti(CH2SiMe3)2Me and (FI)TiMe3 produce the same active
catalyst. Likewise, the main decomposition product is the same for
both precatalysts: a TiIII species exhibiting a room temperature
EPR signal with an isotropic g value of 1.958.7 When monitoring
the ethylene trimerization by EPR spectroscopy, the signal intensi-
ty increases over the course of catalysis and reaches a maximum
after catalysis has stopped. All of this is consistent with the pro-
posed mechanism of trimerization initiation (Scheme 1).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
a Angle proximal to the methoxy-arene. b Angle distal to the meth-
c
d
oxy-arene. Δd-p = (C2–Ti–N) – (N–Ti–C1). The labeling for
(FI)TiMe3 is different; the angles (left to right)correspond to: N–Ti–
C2, C2–Ti–C3, C3–Ti–N (reference 7).
2. Activation and Catalysis with (FI)Ti(CH2SiMe3)2Me.
When a solution of (FI)Ti(CH2SiMe3)2Me in C6D6/o-C6H4F2 (ca.
0.65 mL/0.05 mL) is treated with one equivalent of B(C6F5)3, se-
lective methide abstraction gives the solvent-separated ion pair
[(FI)Ti(CH2SiMe3)2][MeB(C6F5)3] (Scheme 3, [MeB(C6F5)3]–
anion not shown in all Schemes). The ion pair has spectroscopic
features very similar to [(FI)TiMe2][MeB(C6F5)3]:7 (i) a down-
field OMe chemical shift compared with (FI)Ti(CH2SiMe3)2Me,
indicating coordination to the Ti center;14 (ii) a Δδ(m,p-F) of 2.5
ppm in the 19F NMR spectrum, suggesting a non-coordinating
solvent-separated anion;15 and (iii) chemically inequivalent and
1
static SiMe3 groups in the H NMR spectrum at 25 °C (δ = –0.50
1
Figure 2. H NMR spectra of (FI)Ti(CH2SiMe3)2Me in C6D6 (top)
and –0.24 ppm, Figure 2). Furthermore, there are four distinct
signals for the methylene protons (CH2SiMe3), in accord with a
non-fluxional structure (Figure 2).
and [(FI)Ti(CH2SiMe3)2][MeB(C6F5)3] in C6D6/o-C6H4F2 (bottom)
at 25 °C (aromatic region not shown).
Scheme 4.
Scheme 3.
(FI)Ti(CH2XMe3)2Me
> 95% trimer
85% 1 regioisomer
B(C6F5)3
Si
Si
Si
O
O
O
C5H10
C15H30
B(C6F5)3
+
Ti
+
Ti
Si
X= Si, C
N
Ti
N
N
O
C6D6
o-C6H4F2
Si
Si
O
O
Me
Table 2. Ethylene and 1-pentene trimerization catalysis at 25 °C.
[(FI)Ti(CH2SiMe3)2]+
[(FI-CH2SiMe3)Ti(CH2SiMe3)]+
Ethylenea
TONc
1-Penteneb
TONc
(FI)Ti(CH2SiMe3)2Me
TOFd
2.7 × 103
1.2 × 103
7.5 × 103
b
C2H4
e
8.3 × 103
4.1 × 103
2.5 × 103
3.5 × 102
9.0 × 102
5.0 × 102
(FI)TiMe3
(FI)Ti(CH2SiMe3)2Me
(FI)Ti(CH2CMe3)2Mef
+
+
+
a Reaction time is 3 hours for a typical run. Reaction time is ca. 12
Upon treatment of the [(FI)Ti(CH2SiMe3)2][MeB(C6F5)3] so-
lution with ethylene (1 atm), 1-hexene is produced rapidly, with
slow disappearance of [(FI)Ti(CH2SiMe3)2]+ as determined by 1H
NMR spectroscopy. Hence, as for [(FI)TiMe2][MeB(C6F5)3],7
the rate of trimerization is significantly greater than the rate of initi-
ation. Under a constant pressure of ethylene (1 atm), a solution of
(FI)Ti(CH2SiMe3)2Me/B(C6F5)3 (9 µmol, 9 mM) in o-C6H4F2 (1
mL) at 25 °C produces primarily 1-hexene and C10 olefins, with
only trace amounts of polyethylene formed (< 3 mg). The activity
c
hours for a typical run. TON = mmol olefin oligomerized/mmol Ti.
f
d
e
TOF = TON/h. Taken from reference 7. Reaction time is 20
minutes.
While monitoring catalysis with [(FI)Ti(CH2SiMe3)2]+ in
1
C6D6/o-C6H4F2 (ca. 0.65 mL/0.05 mL) by H NMR spectroscopy,
we observed a new diamagnetic species, which we formulate as
[(FI-CH2SiMe3)Ti(CH2SiMe3)]+, an isomer of the parent cation
[(FI)Ti(CH2SiMe3)2]+ resulting from the migration of one
CH2SiMe3 group to the imine carbon of the (FI) ligand (Scheme
(TON of ca. 4.1×103 mmol olefin oligomerized/mmol Ti after ca. 3
h) is about half that obtained with [(FI)TiMe2][MeB(C6F5)3]
(Table 2).
1
3).16 Key new H NMR spectroscopic features include (i) a me-
thine signal at δ = 4.15 ppm (δ(13C) = 79.1 ppm), originating from
the imine N=CH, (ii) two signals at δ = 0.42 and 0.14 ppm that are
3
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 12
diastereotopic methylene protons on the same carbon (δ(13C) =
Scheme 1: ethylene insertion, β-H elimination and reductive elimi-
1
2
3
4
5
6
7
8
29.7 ppm),17 and (iii) two SiMe3 signals at δ = –0.14 and –0.52
ppm (δ(13C) = 1.7 and –1.9 ppm, respectively).18 The methylene
protons each couple to the methine proton, in addition to coupling
to each other, making each signal an approximate doublet of dou-
blets, which is expected for the ABX spin system.12 Although this
species could not be isolated from the complex mixture, additional
evidence for this transformation is found by analyzing the organic
products after protonolysis with MeOH by mass spectroscopy: two
major peaks in the electrospray negative ion mode spectrum (m/z
= 450 and 538) correspond to (FI)– and (FI-CH2SiMe3)H–, re-
spectively. Also the EPR spectrum (see above) exhibits a shoulder
slightly downfield of the main signal at g ≈ 1.960, indicating the
formation of another TiIII species, suggesting that both the active
catalyst and [(FI-CH2SiMe3)Ti(CH2SiMe3)]+ are reduced in situ.
This side reaction may account for the lower ethylene trimerization
activity for [(FI)Ti(CH2SiMe3)2]+ compared with [(FI)TiMe2]+.19
nation of neopentane (CMe4). However, this hypothesis is ruled
1
out by a parallel experiment using ethylene-d4: of the five new H
NMR signals seen with C2H4, only the methine peak remains with
C2D4; the neohexene, D2C=CDCH2CMe3, should show the two
methylene signals instead (Scheme 6, top). Instead, we propose
that
[(FI)Ti(CH(CMe3)CH2CH2)]+, resulting from [2+2] cycloaddi-
tion of ethylene with transient neopentylidene,
the
new
species
is
the
titanacyclobutane
a
[(FI)Ti(=CHCMe3)]+; the isotopologue obtained with ethylene-
d4 would be expected to give the observed single 1H NMR peak
(Scheme 6, bottom).20 A number of titanacyclobutane complexes,
typically formed from an alkylidene and olefin, have been reported
previously.21 –29
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Analysis by GC/MS30 of the neopentane generated in the above
experiment, carried out under an atmosphere of ethylene-d4, indi-
cates formation of a ~1:1 mixture of neopentane-d1 and neopen-
tane-d0. This is the expected result if generation of the active tri-
merization catalyst by the mechanism (Scheme 1; Scheme 6, top)
3. Activation and Catalysis with (FI)Ti(CH2CMe3)2Me.
Unlike (FI)TiMe3 and (FI)Ti(CH2SiMe3)2Me, no titanium com-
7
previously proposed for (FI)TiMe3/B(C6F5)3 proceeds at a com-
parable rate with competitive α-abstraction (Scheme 6, bottom).
Furthermore, (FI)Ti(CH2CMe3)2Me/B(C6F5)3 under an atmos-
phere of ethylene gives the same major TiIII species (isotropic g
1
plex can be detected by H NMR spectroscopy from the reaction
between (FI)Ti(CH2CMe3)2Me and B(C6F5)3 in C6D6/o-C6H4F2
(ca. 0.65 mL, 0.05 mL) at room temperature; EPR spectroscopy
indicates that one major TiIII species is produced (g = 1.976). If,
however, the reaction is carried out at –78 °C and allowed to warm
to –20 °C in the probe of the NMR spectrometer using a C7D8/o-
7
value of 1.958) observed for both (FI)TiMe3/B(C6F5)3 and
(FI)Ti(CH2SiMe3)2Me/B(C6F5)3 (see above). All observations
are thus consistent with a common mechanism for initiation.
1
C6H4F2 (ca. 0.65 mL, 0.05 mL) solvent mixture, the H, 13C,17 and
Scheme 6.
19F
NMR
spectroscopic
features
expected
for
D2C
CH2CMe3
D
D
D
CH2CMe3
CD2
CD
CD
D
+
[Ti]
+
[Ti]
+
[Ti]
C2D4
[(FI)Ti(CH2CMe3)2][MeB(C6F5)3] can be observed (Scheme 5).
As with [(FI)TiMe2]+ and [(FI)Ti(CH2SiMe3)2]+, they indicate
OMe coordination to Ti, chemically inequivalent neopentyl
(CH2CMe3) groups, and a non-coordinated solvent-separated
anion [MeB(C6F5)3]–.7 Addition of ethylene (1 atm) at –20 °C to
this solution of [(FI)Ti(CH2CMe3)2]+ results in catalytic trimeriza-
tion with production of 1-hexene (Scheme 5).
−CH2DCMe3
D
CH2CMe3
CH2CMe3
CH2CMe3
CH2CMe3
+
[Ti]
CH2CMe3
C2D4
+
[Ti]
+
[Ti]
+
[Ti]
CHCMe3
CHCMe3
CHCMe3
CD2
–CH3CMe3
D2C
CD2
+
D2C
[Ti] = [(FI)Ti][MeB(C6F5)3]
observed
In an attempt to observe the proposed neopentylidene, we ex-
amined the reactivity of [(FI)Ti(CH2CMe3)2]+ at low temperature
Scheme 5.
in the absence of ethylene.
Indeed,
a
solution of
[(FI)Ti(CH2CMe3)2]+ in C7D8/o-C6H4F2 (ca. 0.65 mL/0.05 mL)
at –30 °C is not stable; it converts to the neopentylidene complex
[(FI)Ti(=CHCMe3)]+ by α-elimination of CMe4 over a period of
one day (Scheme 5). Characteristic NMR spectroscopic features
of the Ti=CHCMe3 fragment are 1H and 13C signals at δ = 9.91
O
O
B(C6F5
C7D8
o-C6H4F2
)
C2H4
+
Ti
3
N
Ti
N
O
C7D8
o-C6H4F2
–20 °C
O
Me
–20 °C
(FI)Ti(CH2CMe3)2Me
[(FI)Ti(CH2CMe3)2]+
1
ppm and 310.9 ppm respectively, and a JC-H coupling constant of
96 Hz,31 similar to other reported titanium alkylidenes.23,32 –36 Addi-
tion of C2H4 or C2D4 (1 atm) at –20 °C to the solution of
1
[(FI)Ti(=CHCMe3)]+ immediately produces the H NMR signals
O
O
assigned
to
[(FI)Ti(CH(CMe3)CH2CH2)]+
or
O
+
Ti
H
H
C2D4
+
Ti
C2H4
+
Ti
D
D
H
H
N
N
N
D
H
[(FI)Ti(CH(CMe3)CD2CD2)]+ (Scheme 5), with complete dis-
H
O
O
O
D
H
appearance of the signals for [(FI)Ti(=CHCMe3)]+. The 13C
NMR chemical shifts (α-C’s: 99.2 and 164.537 ppm; β-C: 6.8 ppm)
are similar to those of other titanacyclobutane complexes, which
[(FI)Ti(CH(CMe3)CD2CD2)]+
[(FI)Ti(CH(CMe3)CH2CH2)]+
[(FI)Ti(=CHCMe3)]+
1
The H NMR spectrum also shows evidence for a new diamag-
netic titanium species which exhibits, in addition to a set of (FI)
signals, five chemically inequivalent signals corresponding to two
methylenes (CH2) and one methine (CH), and one tert-butyl
resonance, based on 1H, COSY, TOCSY, HSQC and HMBC spec-
troscopies. These data could be consistent with a TiII-neohexene
(H2C=CHCH2CMe3) adduct, formed by the initiation pathway of
exhibit
upfield
β-C
signals.21-28
For
example,
Cp2Ti(CH2CH(CHMe2)CH2) has 13C NMR chemical shifts of
75.2 ppm and 13.2 ppm (α and β respectively).21
It is important to note that significantly less 1-hexene is pro-
duced when [(FI)Ti(CH2CMe3)2]+ is allowed to convert partially
to [(FI)Ti(=CHCMe3)]+ before addition of ethylene than when
4
ACS Paragon Plus Environment

Page 5 of 12
Journal of the American Chemical Society
Whereas the cation formed from (FI)Ti(CH2CMe3)2Me and
ethylene is added immediately after it is generated.38 This suggests
that [(FI)Ti(=CHCMe3)]+ and [(FI)Ti(CH(CMe3)CH2CH2)]+
are not intermediates or precursors for catalytic ethylene trimeriza-
tion, but rather off-cycle species that lead to decomposition.
To further complicate matters, [(FI)Ti(=CHCMe3)]+ is also not
stable in solution; over a period of hours at –20 °C, it converts to a
new species that we assign as the imido-olefin complex [(Me-
OAr2N=)Ti(OArHC=CHCMe3)]+. 1H NMR spectroscopic fea-
tures that support this assignment are the loss of the (FI) imine
(N=CH) signal, and the appearance of two olefinic methine CH
signals at δ = 4.72 and 4.98 ppm, with 13C NMR chemical shifts of
144.5 and 123.3 ppm, respectively. Such a product could form by
an intramolecular metathesis reaction between the neopentylidene
and imine of the (FI) ligand (Scheme 7); similar transformations
have been observed previously by Mindiola and coworkers, em-
ploying a (nacnac)Ti(=CHCMe3)(OTf) complex.32,39 While the
putative intermediate in this sequence, the aza-titanacyclobutane
complex40 –45 shown in Scheme 7, might also be consistent with the
NMR observations, important evidence for the proposed assign-
ment was obtained by treating the new species with MeOH. Pro-
tonolysis of [(MeOAr2N=)Ti(OArHC=CHCMe3)]+ would be
expected to give two organic fragments, MeOAr2NH2 and
HOArHC=CHCMe3 (Scheme 8), and both were obtained as ma-
jor products, confirmed by comparison with a pure sample or by
1H, 13C, HSQC and HMBC spectroscopies respectively, along with
GC/MS for both (m/z of 199.1 and 324.3). The olefin in
HOArHC=CHCMe3 is the Z isomer, based on the characteristical-
ly small three bond coupling constant (3JH-H = 12). 46
B(C6F5)3 in C6D6 is extremely unstable at room temperature, de-
composing in less than 1 minute, a solution of the neutral precursor
(FI)Ti(CH2CMe3)2Me in C6D6 decomposes much more slowly,
over a period of hours at 25 °C. Analysis of the resulting solution
by EPR spectroscopy shows the TiIII species with an isotropic g
value of 1.976, and after treatment with MeOH, analysis by
GC/MS shows two major peaks with m/z of 199.1 and 324.3.
1
2
3
4
5
6
7
8
These
observations
taken
together
show
that
(FI)Ti(CH2CMe3)2Me converts to the same TiIII species as does
[(FI)Ti(CH2CMe3)2]+, [(MeOAr2N=)TiIII(OArHC=CHCMe3)].
It thus appears that the Lewis acid B(C6F5)3 in effect accelerates
formation of the neopentylidene. This stands in contrast to behav-
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ior typically observed in the literature: α-hydrogen elimination is
more commonly promoted by bulky Lewis bases (e.g., phos-
phines), heat, light, Brønsted bases or oxidants.31,36,47
As noted earlier, even with all of these side reactions competing,
the combination of (FI)Ti(CH2CMe3)2Me and B(C6F5)3 still gen-
erates a species capable of catalytically trimerizing ethylene and α-
olefins. When a solution of (FI)Ti(CH2CMe3)2Me (7 µmol, 7
mM) in o-C6H4F2 (1 mL) is first saturated with ethylene (1 atm)
and then treated with one equivalent of B(C6F5)3 while still under a
constant pressure of ethylene at 25 °C, 1-hexene and C10 olefins are
rapidly produced, with the same distribution as (FI)TiMe3 and
(FI)Ti(CH2SiMe3)2Me, and only trace amounts of polyethylene (<
3 mg). Remarkably, although this system gave less product than
the other two (TON ca. 2.5×103), that degree of conversion was
complete after only 20 minutes (by which time activity had com-
pletely ceased), whereas (FI)Ti(CH2SiMe3)2Me and (FI)TiMe3
required three hours to go to completion. In fact, if the same pro-
cedure is repeated at –20 °C for 3 hours, a TON of 8.9×103 is
achieved, which is the highest for this series of precatalysts thus far.
The (FI)Ti(CH2CMe3)2Me/B(C6F5)3 system is clearly more active
than the other two (Table 2), reflecting the faster rate of initiation
(by at least an order of magnitude) for [(FI)Ti(CH2CMe3)2]+
compared with [(FI)TiMe2]+ and [(FI)Ti(CH2SiMe3)2]+.
Scheme 7.
O
O
O
+
Ti
+
Ti
+
Ti
H
H
N
N
N
O
–20 °C
–20 °C
O
O
[(MeOAr2N=)Ti(OArHC=CHCMe3)]+
[(FI)Ti(=CHCMe3)]+
aza-titanacyclobutane
The faster rate of initiation is also apparent for α-olefin oli-
gomerization with (FI)Ti(CH2CMe3)2Me. When a solution of
(FI)Ti(CH2CMe3)2Me in 1-pentene is activated with B(C6F5)3,
trimerization catalysis proceeds rapidly (Scheme 4) and is com-
plete after only 20 minutes with a TON of ca. 500. In contrast,
when 1-pentene oligomerization with (FI)Ti(CH2SiMe3)2Me/
B(C6F5)3 is analyzed after 20 minutes, negligible quantities of tri-
mers are observed. Like (FI)TiMe3 and (FI)Ti(CH2SiMe3)2Me,
the oligomer selectivity is greater than 95% for trimers, and 85% of
the trimers are one regioisomer (Scheme 4), further demonstrating
that all three precatalysts produce the same active species.
After establishing the above transformations by low temperature
NMR spectroscopy, we reexamined the room temperature reaction
of (FI)Ti(CH2CMe3)2Me and B(C6F5)3 in C6D6/o-C6H4F2. Analy-
sis of the organic material after treatment with MeOH by GC/MS
gave the same two major peaks (m/z of 199.1 and 324.3), demon-
strating that the same fragmentation occurs at room temperature.
Additionally, the TiIII species with the isotropic g value of 1.976
(see above) can be observed by room temperature EPR spectros-
copy after carrying out reactions at low temperature. This species
therefore
might
be
the
neutral
complex
[(Me-
OAr2N=)TiIII(OArHC=CHCMe3)], perhaps with solvent or an-
other L-type ligand coordinated to Ti, although we have no definite
evidence on its structure at this time.
CONCLUSIONS
Both of the two new phenoxy-imine Ti complexes synthesized here,
(FI)Ti(CH2SiMe3)2Me and (FI)Ti(CH2CMe3)2Me, generate olefin
trimerization catalysts upon activation with a stoichiometric amount of
B(C6F5)3, with selectivities virtually identical to those previously ob-
tained with (FI)TiMe3, strongly suggesting that the active species is the
same in the three systems. Whereas trimerization catalysis proceeds at
about the same rate starting with [(FI)Ti(CH2SiMe3)2]+ or
[(FI)TiMe2]+, it is significantly faster for [(FI)Ti(CH2CMe3)2]+, sug-
gesting that the initial goal of accelerating initiation was achieved for
the case of neopentyl. For [(FI)Ti(CH2CMe3)2]+ side reactions are
Scheme 8.
NH2
O
+
Ti
MeOH
Et2O
+
N
O
OH
O
[(MeOAr2N=)Ti(OArHC=CHCMe3)]+
HOArHC=CHCMe3
MeOAr2NH2
5
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 12
Table 3. Crystal, intensity collection, and refinement data.
(FI)Ti(CH2SiMe3)2Cla (FI)Ti(CH2SiMe3)2Meb (FI)Ti(CH2CMe3)2Clb (FI)Ti(CH2CMe3)2Me
1
2
3
4
5
6
7
8
9
lattice
formula
formula weight
space group
a/Å
b/Å
c/Å
α/°
β/°
Monoclinic
C43H64ClNO3Si2Ti
782.48
Triclinic
C45H69NO2Si2Ti
760.09
Triclinic
C46H66ClNO2Ti
748.34
Monoclinic
C42H57NO2Ti
655.78
P21/c
9.5811(12)
20.012(3)
19.283(2)
90
101.171(4)
90
3627.2(8)
4
P21/c
P-1
P-1
9.2620(3)
22.4163(9)
21.2155(8)
90
95.996(2)
90
4380.7(3)
4
100(2)
0.71073
1.186
0.348
35.361
166156
20105
486
0.0535
0.1353
0.0756
0.1472
1.065
9.6385(5)
11.1526(6)
20.9436(12)
97.266(3)
97.906(3)
100.804(3)
2163.4(2)
2
12.1256(9)
12.3667(10)
14.8256(11)
92.283(4)
94.294(4)
106.191(4)
2124.7(3)
2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
γ/°
V/Å3
Z
temperature (K)
radiation (λ, Å)
ρ (calcd.), g cm-3
µ (Mo Kα), mm-1
θ max, deg.
no. of data collected
no. of data
no. of parameters
R1 [I > 2σ(I)]
wR2 [I > 2σ(I)]
R1 [all data]
wR2 [all data]
GOF
100(2)
100(2)
100(2)
0.71073
1.201
0.71073
1.167
0.289
33.142
97117
16165
487
0.0469
0.1145
0.71073
1.170
0.301
0.272
41.154
28.095
61492
8174
154696
28144
486
0.0521
0.1329
0.0900
0.1548
1.025
440
0.0529
0.1008
0.1128
0.1195
1.016
0.0744
0.1280
1.023
a
b
Crystallized with one molecule of Et2O in the asymmetric unit. Crystallized with one molecule of pentane in the asymmetric unit.
the Supporting Information. X-band EPR spectra were acquired at
room temperature on a Bruker EMX spectrometer. 1,4-Dioxane,
o-C6H4F2, and 1-pentene were dried over molecular sieves (3 Å) for at
least two days, then filtered through activated alumina and stored over
molecular sieves (3 Å) prior to use. C6D6, C7D8, and C6D5Cl were
dried over molecular sieves (3 Å) for at least two days prior to use.
Me3SiCH2MgCl and Me3CCH2MgCl were purchased from Aldrich as
1.0 M solutions in Et2O. (FI)TiCl3 was synthesized by our modified7
literature method.5
rapid as well: it first undergoes α-elimination to the neopentylidene
complex [(FI)Ti(=CHCMe3)]+, which in turn leads to the titana-
cyclobutane complex [(FI)Ti(CH(CMe3)CH2CH2)]+ or the im-
ido-olefin complex [(MeOAr2N=)Ti(OArHC=CHCMe3)]+ in the
presence or absence of ethylene respectively. Unfortunately, none
of these species appears to participate in trimerization catalysis, so
the higher catalytic activity is offset by the lower catalyst stability.
Ongoing work is aimed at determining whether a suitable combina-
tion of ligands and conditions can give the desired fast initiation
and consequent higher catalytic activity without sacrificing catalyst
stability.
X-ray Structure Determinations. X-ray diffraction data were
collected on a Bruker Apex II diffractometer. Crystal data, data collec-
tion and refinement parameters are summarized in Table 3. The struc-
tures were solved using direct methods and standard difference map
techniques, and were refined by full-matrix least-squares procedures on
F2 with SHELXTL (Version 2014/2).50
EXPERIMENTAL SECTION
General Considerations. All manipulations were performed using
glovebox, high-vacuum, and/or Schlenk techniques under a nitrogen
or argon atmosphere unless otherwise specified.48 Solvents were puri-
fied and degassed by using standard procedures. NMR spectra were
acquired at 25 °C, unless otherwise specified, and measured on Varian
spectrometers at field strengths of 300 MHz, 400 MHz, 500 MHz and
Gas Chromatography Analysis. Gas chromatography (GC)
was performed on an Agilent 6890N instrument using a DB-1 capillary
column (10 m length, 0.10 mm diameter, 0.40 µm film) and a flame
ionization detector. Response factors from reference 7 were used. Gas
chromatography/mass spectrometry (GC/MS) was performed on an
Agilent 6890N instrument using a HP-5MS column (30 m length, 0.25
mm diameter, 0.50 µm film) and an Agilent 5973N mass-selective EI
detector.
1
600 MHz. H chemical shifts are reported in ppm relative to SiMe4 (δ
= 0) and were referenced internally with respect to the protio solvent
impurity (δ 7.16 for C6D5H, δ 7.14 for C6D4HCl, δ 6.97 for C7D7H).49
13C chemical shift are reported in ppm relative to SiMe4 (δ = 0) and
were referenced internally with respect to the solvent (δ 128.06 for
C6D6, δ 134.19 for C6D5Cl, δ 128.87 for C7D8).49 13C chemical shift
for all cationic complexes in this report were determined by 2D HSQC
and HMBC spectroscopies. Coupling constants are given in Hz. 19F
Synthesis of (FI)Ti(CH2SiMe3)2Cl.
A
solution of
Me3SiCH2MgCl in Et2O (0.41 mL, 1M, 0.41 mmol) was added to a
stirring suspension of (FI)TiCl3 (100 mg, 0.17 mmol) in Et2O (5 mL)
cooled to –30 °C, and was stirred for 5 minutes while warming. After
this period, 1,4-dioxane (~0.05 mL, 0.6 mmol) was added, causing a
precipitate to form, and the volatiles were removed in vacuo. The solid
was extracted with pentane (2 × 5 mL), filtered through celite, and
concentrated to ~1 mL causing crystals to form. The mixture was
cooled at –30 °C for several days, thereby depositing yellow crystals
6
1
chemical shifts are reported in ppm relative to the absolute H chemi-
cal shift reference. NMR spectra for (FI)Ti(CH2SiMe3)2Cl,
(FI)Ti(CH2SiMe3)2Me,
(FI)Ti(CH2CMe3)2Cl,
(FI)Ti(CH2CMe3)2Me and selected reaction mixtures are shown in
ACS Paragon Plus Environment

Page 7 of 12
Journal of the American Chemical Society
which were isolated, washed with cold pentane (–30 °C, ~0.5 mL), and
of Ar], 127.5 [s, 1C of Ar], 128.5 [s, 1CH of Ar], 128.7 [s, 1C of Ar],
1
2
3
4
5
6
7
8
dried in vacuo to give (FI)Ti(CH2SiMe3)2Cl as a yellow crystalline
solid (70 mg, 60% yield). X-ray quality crystals were obtained by cool-
ing a solution of (FI)Ti(CH2SiMe3)2Cl in Et2O/pentane (1:1) at –30
°C. Anal. calcd. for (FI)Ti(CH2SiMe3)2Cl: C, 66.1%; H, 7.7%; N,
129.9 [s, 1CH of Ar], 132.1 [s, 1CH of Ar], 132.7 [br s, 1C of Ar],
133.0 [s, 1CH of Ar], 133.1 [s, 1CH of Ar], 135.0 [s, 1CH of Ar],
139.2 [s, 1C of Ar], 155.6 [s, 1C of Ar], 156.2 [s, 1C of Ar], 162.5 [s,
1C of Ar], 172.4 [s, 1C of N=CH].
1
2.0%. Found: C, 65.5%; H, 7.2%; N, 1.8%. H NMR (C6D6): 0.03 [br
s, 9H of Ti(CH2SiMe3)2], 0.25 [br s, 1H of Ti(CH2SiMe3)2], 0.34 [br
Synthesis of (FI)Ti(CH2CMe3)2Cl. A solution of Me3CCH2MgCl
in Et2O (0.41 mL, 1M, 0.41 mmol) was added to a stirring suspension
of (FI)TiCl3 (100 mg, 0.17 mmol) in Et2O (5 mL) cooled to –30 °C,
and was stirred for 5 minutes while warming. After this period, 1,4-
dioxane (~0.05 mL, 0.6 mmol) was added, causing a precipitate to
form, and the volatiles were removed in vacuo. The solid was extracted
with pentane (2 × 5 mL), filtered through celite, and concentrated to
~1 mL causing crystals to form. The mixture was cooled at –30 °C for
several days, thereby depositing orange crystals which were isolated,
washed with cold pentane (–30 °C, ~0.5 mL), and dried in vacuo to
give (FI)Ti(CH2CMe3)2Cl as an orange crystalline solid (37 mg, 33%
yield). (FI)Ti(CH2CMe3)2Cl is not thermally stable, darkening in
color at room temperature, and should therefore be stored at low tem-
perature (–30 °C for this work). X-ray quality crystals were obtained
by cooling a solution of (FI)Ti(CH2CMe3)2Cl in pentane at –30 °C.
Anal. calcd. for (FI)Ti(CH2CMe3)2Cl: C, 72.8%; H, 8.1%; N, 2.1%.
Found: C, 71.0%; H, 7.8%; N, 2.1%. 1H NMR (C6D6): 0.98 [br s, 9H
2
s, 9H of Ti(CH2SiMe3)2], 1.81 [d, AB pattern, JH-H = 12, 3H of
2
C(CH2)3(CH)3(CH2)3], 1.92 [d, AB pattern, JH-H = 12, 3H of
C(CH2)3(CH)3(CH2)3], 2.17 [s, 3H of C(CH2)3(CH)3(CH2)3], 2.17
[s, 3H of ArMe], 2.45 [s, 6H of C(CH2)3(CH)3(CH2)3], 2.83 [br s, 3H
of OMe], 2.99 [br s, 1H of Ti(CH2SiMe3)2], 3.15 [br s, 1H of
Ti(CH2SiMe3)2], 3.74 [br s, 1H of Ti(CH2SiMe3)2], 6.15 [br s, 1H of
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3
Ar], 6.71 [s, 1H of Ar], 6.91 [br s, 2H of Ar], 7.02 [d, JH-H = 8, 1H of
Ar], 7.13 [t, 3JH-H = 8, 1H of Ar], 7.20 [m, 2H of Ar], 7.35 [s, 1H of Ar],
7.61 [br s, 1H of Ar], 8.52 [s, 1H of N=CH]. 13C{1H} NMR (C6D6):
1.9 [br s, 6C of Ti(CH2SiMe3)2], 20.8 [s, 1C of ArMe], 29.5 [s, 3C of
C(CH2)3(CH)3(CH2)3], 37.3 [s, 3C of C(CH2)3(CH)3(CH2)3], 37.6
[s, 1C of C(CH2)3(CH)3(CH2)3], 41.4 [s, 3C of
C(CH2)3(CH)3(CH2)3], 54.5 [s, 1C of OMe], 102.4 [very br, 2C of
Ti(CH2SiMe3)2], 110.3 [s, 1CH of Ar], 121.8 [s, 1CH of Ar], 123.3 [s,
1CH of Ar], 124.2 [s, 1C of Ar], 126.8 [s, 1CH of Ar], 128.5 [s, 1CH
of Ar], 128.7 [s, 1C of Ar], 129.1 [s, 1C of Ar], 129.6 [s, 1CH of Ar],
131.7 [s, 1CH of Ar], 133.1 [s, 1CH of Ar], 133.4 [s, 1C of Ar], 134.3
[s, 1CH of Ar], 135.6 [s, 1CH of Ar], 139.1 [s, 1C of Ar], 156.0 [s, 1C
of Ar], 156.7 [s, 1C of Ar], 161.2 [s, 1C of Ar], 173.0 [s, 1C of N=CH].
2
of Ti(CH2CMe3)2], 1.04 [d, JH-H = 10, 1H of Ti(CH2CMe3)2], 1.12
2
[br s, 9H of Ti(CH2CMe3)2], 1.81 [d, AB pattern, JH-H = 12, 3H of
2
C(CH2)3(CH)3(CH2)3], 1.94 [d, AB pattern, JH-H = 12, 3H of
C(CH2)3(CH)3(CH2)3], 2.16 [br s, 3H of C(CH2)3(CH)3(CH2)3],
2.16 [s, 3H of ArMe], 2.48 [br s, 6H of C(CH2)3(CH)3(CH2)3], 2.81
Synthesis of (FI)Ti(CH2SiMe3)2Me.
A
solution of
2
Me3SiCH2MgCl in Et2O (0.82 mL, 1M, 0.82 mmol) was added to a
stirring suspension of (FI)TiCl3 (200 mg, 0.33 mmol) in Et2O (7 mL)
cooled to –30 °C, and was stirred for 5 minutes while warming. The
mixture was then cooled to –30 °C and treated with a solution of
MeMgBr in Et2O (0.26 mL, 3M, 0.78 mmol), and was then stirred at 0
°C for 3.5 hours. After this period, 1,4-dioxane (~0.1 mL, 1.2 mmol)
was added, causing a precipitate to form, and the volatiles were re-
moved in vacuo (once the sample is dry, the next steps should be done
immediately as further evacuation at room temperature results in de-
composition). The solid was extracted with pentane (5 mL, then 10
mL), filtered through a medium porosity frit with a 0.5 cm bed of
celite, and the filtrate was concentrated to ~2 mL causing crystals to
form. The mixture was cooled at –30 °C for several days, thereby de-
positing yellow/orange crystals which were isolated, washed with cold
pentane (–30 °C, ~1 mL), and dried in vacuo to give
(FI)Ti(CH2SiMe3)2Me as a yellow/orange crystalline solid (134 mg,
59% yield). X-ray quality crystals were obtained by cooling a solution
of (FI)Ti(CH2SiMe3)2Me in pentane at –30 °C. Anal. calcd. for
(FI)Ti(CH2SiMe3)2Me•0.5(C5H12): C, 70.5%; H, 8.8%; N, 1.9%.
[d, JH-H = 10, 1H of Ti(CH2CMe3)2], 2.90 [s, 3H of OMe], 2.94 [d,
2
2JH-H = 10, 1H of Ti(CH2CMe3)2], 3.29 [d, JH-H = 10, 1H of
4
Ti(CH2CMe3)2], 6.19 [d, 3JH-H = 8, 1H of Ar], 6.73 [d, JH-H = 1, 1H of
Ar], 6.88 [t, 3JH-H = 7, 1H of Ar], 6.92 [dt, 4JH-H = 2, 3JH-H = 8, 1H of Ar],
6.98 [dd, 3JH-H = 8, 4JH-H = 1, 1H of Ar], 7.13 [dt, 4JH-H = 1, 3JH-H = 8, 1H
4
3
3
of Ar], 7.20 [dt, JH-H = 1, JH-H = 8, 1H of Ar], 7.24 [d, JH-H = 8, 1H of
4
3
Ar], 7.36 [d, JH-H = 2, 1H of Ar], 7.61 [br d, JH-H = 6, 1H of Ar], 8.63
[s, 1H of N=CH]. 13C{1H} NMR (C6D6): 20.8 [s, 1C of ArMe], 29.6
[s, 3C of C(CH2)3(CH)3(CH2)3], 33.3 [br s, 6C of Ti(CH2CMe3)2],
37.4 [s, 3C of C(CH2)3(CH)3(CH2)3], 37.6 [s, 1C of
C(CH2)3(CH)3(CH2)3], 37.7 [br s, 2C of Ti(CH2CMe3)2], 41.7 [s,
3C of C(CH2)3(CH)3(CH2)3], 54.6 [s, 1C of OMe], 110.3 [s, 1CH of
Ar], 115.6 [very br, 2C of Ti(CH2CMe3)2], 121.9 [s, 1CH of Ar],
123.8 [s, 1CH of Ar], 124.3 [s, 1C of Ar], 126.7 [s, 1CH of Ar], 128.0
[s, 1C of Ar, located using 2D HMBC], 128.3 [s, 1C of Ar, located
using 2D HMBC], 128.8 [s, 1CH of Ar], 129.4 [s, 1CH of Ar], 132.0
[s, 1CH of Ar], 133.2 [s, 1CH of Ar], 133.2 [s, 1C of Ar], 134.0 [s,
1CH of Ar], 135.7 [s, 1CH of Ar], 139.4 [s, 1C of Ar], 156.1 [s, 1C of
Ar], 156.9 [s, 1C of Ar], 161.8 [s, 1C of Ar], 173.3 [s, 1C of N=CH].
1
Found: C, 70.7%; H, 8.9%; N, 1.9%. H NMR (C6D6): 0.17 [br s, 18H
Synthesis of (FI)Ti(CH2CMe3)2Me.
A
solution of
2
of Ti(CH2SiMe3)2], 1.73 [s, 3H of TiMe], 1.81 [d, AB pattern, JH-H
=
Me3CCH2MgCl in Et2O (0.82 mL, 1M, 0.82 mmol) was added to a
stirring suspension of (FI)TiCl3 (200 mg, 0.33 mmol) in Et2O (7 mL)
cooled to –30 °C, and was stirred for 5 minutes while warming. The
mixture was then cooled to –30 °C and treated with a solution of
MeMgBr in Et2O (0.26 mL, 3M, 0.78 mmol), and was then stirred at 0
°C for 3.5 hours. After this period, 1,4-dioxane (~0.1 mL, 1.2 mmol)
was added, causing a precipitate to form, and the volatiles were re-
moved in vacuo (once the sample is dry, the next steps should be done
immediately as further evacuation at room temperature results in de-
composition). The solid was extracted with pentane (5 mL, then 10
mL), filtered through a medium porosity frit with a 0.5 cm bed of
celite, and the filtrate was concentrated to ~2 mL causing crystals to
form. The mixture was cooled at –30 °C for several days, thereby de-
positing orange crystals which were isolated, washed with cold pentane
(–30 °C, ~1 mL), and dried in vacuo to give (FI)Ti(CH2CMe3)2Me as
an orange crystalline solid (96 mg, 44% yield). (FI)Ti(CH2CMe3)2Me
2
12, 3H of C(CH2)3(CH)3(CH2)3], 1.93 [d, AB pattern, JH-H = 12, 3H
of C(CH2)3(CH)3(CH2)3], 2.18 [br s, 3H of C(CH2)3(CH)3(CH2)3],
2.20 [s, 3H of ArMe], 2.37 [br s, 6H of C(CH2)3(CH)3(CH2)3], 2.91
3
4
[s, 3H of OMe], 6.22 [d, JH-H = 8, 1H of Ar], 6.77 [d, JH-H = 2, 1H of
Ar], 6.82 [t, 3JH-H = 7, 1H of Ar], 6.92 [dt, 3JH-H = 2, 3JH-H = 8, 1H of Ar],
7.03 [dd, 3JH-H = 8, 4JH-H = 1, 1H of Ar], 7.08 [dt, 4JH-H = 1, 3JH-H = 8, 1H
of Ar], 7.16 [m, 1H of Ar], 7.19 [m, 1H of Ar], 7.23 [dd, 3JH-H = 8, 4JH-H
= 1, 1H of Ar], 7.32 [d, 4JH-H = 2, 1H of Ar], 8.55 [s, 1H of N=CH], 4H
of Ti(CH2SiMe3)2 not observed. 13C{1H} NMR (C6D6): 2.1 [s, 6C of
Ti(CH2SiMe3)2], 20.9 [s, 1C of ArMe], 29.5 [s, 3C of
C(CH2)3(CH)3(CH2)3], 37.4 [s, 3C of C(CH2)3(CH)3(CH2)3], 37.5
[s, 1C of C(CH2)3(CH)3(CH2)3], 41.2 [s, 3C of
C(CH2)3(CH)3(CH2)3], 54.6 [s, 1C of OMe], 70.7 [s, 1C of TiMe],
95.4 [very br, 2C of Ti(CH2SiMe3)2], 110.8 [s, 1CH of Ar], 121.6 [s,
1CH of Ar], 123.4 [s, 1C of Ar], 124.5 [s, 1CH of Ar], 126.4 [s, 1CH
7
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 12
3
is not thermally stable in the solid state or solution, darkening in color
= 14, JH-H = 10, 1H of (N-ArCH-CH2SiMe3)], 2.36 [d, 2JH-H = 10, 1H
of Ti(CH2SiMe3)], 2.66 [d, 2JH-H = 10, 1H of Ti(CH2SiMe3)], 3.45 [s,
1
2
3
4
5
6
7
8
at room temperature, and should therefore be stored at low tempera-
ture (–30 °C for this work). Solutions of (FI)Ti(CH2CMe3)2Me in
C6D6 decompose over a period of hours to give a TiIII species with an
isotropic g value of 1.976 at room temperature. X-ray quality crystals
were obtained by cooling a solution of (FI)Ti(CH2CMe3)2Me in pen-
3
3
3H of OMe], 4.15 [dd, JH-H = 11, JH-H = 4, 1H of (N-ArCH-
CH2SiMe3)]. Selected 13C{1H} NMR (C6D6/o-C6H4F2): –1.9 [3C of
(FI-CH2SiMe3)], 1.7 [3C of Ti(CH2SiMe3)], 29.7 [1C of (N-ArCH-
CH2SiMe3)], 70.5 [1C of OMe], 79.1 [1C of (N-ArCH-CH2SiMe3)],
105.7 [1C of Ti(CH2SiMe3)].
1
tane at –30 °C. H NMR (C6D6): 1.07 [br s, 18H of Ti(CH2CMe3)2],
2
1.78 [s, 3H of TiMe], 1.81 [d, AB pattern, JH-H = 12, 3H of
2
Ethylene
Trimerization
Catalysis
with
C(CH2)3(CH)3(CH2)3], 1.94 [d, AB pattern, JH-H = 12, 3H of
C(CH2)3(CH)3(CH2)3], 2.16 [br s, 3H of C(CH2)3(CH)3(CH2)3],
2.20 [s, 3H of ArMe], 2.39 [br s, 6H of C(CH2)3(CH)3(CH2)3], 2.93
(FI)Ti(CH2SiMe3)2Me. (i) A solution of (FI)Ti(CH2SiMe3)2Me (6
mg, 0.009 mmol) in a mixture of C6D6 (ca. 0.65 mL) and o-C6H4F2 (ca.
0.05 mL) in an NMR tube equipped with a J. Young valve was treated
with B(C6F5)3 (5 mg, 0.01 mmol) at room temperature, thereby caus-
ing an immediate color change to yellow/orange. The sample was
analyzed by 1H NMR spectroscopy, thereby demonstrating conversion
to [(FI)Ti(CH2SiMe3)2][MeB(C6F5)3]. The solution was frozen,
degassed, allowed to warm to room temperature, saturated with eth-
ylene (1 atm), shaken to promote mixing, and continually re-saturated
with ethylene until catalytic activity terminated. The sample was peri-
odically analyzed by 1H NMR spectroscopy, demonstrating the catalyt-
ic production of 1-hexene and slow disappearance of
[(FI)Ti(CH2SiMe3)2]+. The solution was also analyzed by EPR spec-
troscopy, indicating the formation of a major TiIII species, with an iso-
tropic g value of 1.958 at room temperature, which increased intensity
over the time course of the reaction. (ii) In a typical experiment, a
solution of (FI)Ti(CH2SiMe3)2Me (6 mg, 0.009 mmol) in o-C6H4F2
(1 mL) in a 15 mL ampoule was treated with B(C6F5)3 (5 mg, 0.01
mmol) at room temperature. The solution was frozen, degassed, and
allowed to warm to room temperature. The ampoule was then charged
with ethylene (1 atm) and stirred for ca. 3 hours under constant eth-
ylene pressure (1 atm) at room temperature. After this period, the
volume of the solution had increased significantly (ca. 1 mL), but only
a trace amount of polymer (< 3 mg) had formed. Adamantane was
added as an internal integration standard, and the mixture was diluted
with benzene, filtered through a plug of silica gel, and analyzed by GC.
GC analysis demonstrated the catalytic production of 1-hexene, in
addition to C10 olefins and C14 olefins, with a TON of ca. 4.1×103
mmol olefin oligomerized/mmol Ti.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3
4
[s, 3H of OMe], 6.25 [d, JH-H = 8, 1H of Ar], 6.78 [d, JH-H = 2, 1H of
3
3
Ar], 6.82 [br t, JH-H = 7, 1H of Ar], 6.93 [m, 1H of Ar], 7.02 [dd, JH-H
4
4
3
= 8, JH-H = 1, 1H of Ar], 7.09 [dt, JH-H = 1, JH-H = 8, 1H of Ar], 7.16
[m, 1H of Ar], 7.21 [br d, 3JH-H = 7, 1H of Ar], 7.27 [br d, 3JH-H = 7, 1H
4
of Ar], 7.32 [d, JH-H = 2, 1H of Ar], 8.62 [s, 1H of N=CH], 4H of
Ti(CH2CMe3)2 not observed. 13C{1H} NMR (C6D6): 20.8 [s, 1C of
ArMe], 29.5 [s, 3C of C(CH2)3(CH)3(CH2)3], 33.7 [s, 6C of
Ti(CH2CMe3)2], 37.4 [s, 2C of Ti(CH2CMe3)2], 37.4 [s, 1C of
C(CH2)3(CH)3(CH2)3], 37.5 [s, 3C of C(CH2)3(CH)3(CH2)3], 41.4
[s, 3C of C(CH2)3(CH)3(CH2)3], 54.6 [s, 1C of OMe], 71.7 [s, 1C of
TiMe], 110.6 [s, 1CH of Ar], 111.8 [s, 2C of Ti(CH2CMe3)2], 121.7
[s, 1CH of Ar], 123.7 [s, 1C of Ar], 124.4 [s, 1CH of Ar], 126.3 [s,
1CH of Ar], 127.0 [s, 1C of Ar], 128.1 [s, 1CH of Ar, located using 2D
HSQC], 128.5 [s, 1C of Ar, located using 2D HMBC], 129.7 [s, 1CH
of Ar], 132.1 [s, 1CH of Ar], 132.9 [s, 1C of Ar], 133.1 [s, 1CH of Ar],
133.3 [s, 1CH of Ar], 135.2 [s, 1CH of Ar], 139.4 [s, 1C of Ar], 156.1
[s, 1C of Ar], 156.2 [s, 1C of Ar], 162.8 [s, 1C of Ar], 172.5 [s, 1C of
N=CH].
Reaction between (FI)Ti(CH2SiMe3)2Me and B(C6F5)3. A light
yellow solution of (FI)Ti(CH2SiMe3)2Me (6 mg, 0.009 mmol) in a
mixture of C6D6 (ca. 0.65 mL) and o-C6H4F2 (ca. 0.05 mL) in an NMR
tube equipped with a J. Young valve was treated with B(C6F5)3 (5 mg,
0.01 mmol) at room temperature, resulting in an immediate color
1
19
change to yellow/orange. The sample was analyzed by H, F, COSY,
HSQC and HMBC NMR spectroscopies, thereby demonstrating con-
1
version to [(FI)Ti(CH2SiMe3)2][MeB(C6F5)3] (ca. 80% by H NMR
integration).
1H NMR (C6D6/o-C6H4F2): –0.50 [s, 9H of
1-Pentene
Trimerization
Catalysis
with
Ti(CH2SiMe3)2], –0.24 [s, 9H of Ti(CH2SiMe3)2], 1.29 [br s, 3H of
MeB(C6F5)3], 1.82 [br s, 6H of C(CH2)3(CH)3(CH2)3], 2.05 [s, 3H of
ArMe], 2.14 [s, 3H of C(CH2)3(CH)3(CH2)3], 2.24 [s, 6H of
(FI)Ti(CH2SiMe3)2Me. (i) In a typical experiment, a solution of
(FI)Ti(CH2SiMe3)2Me (3 mg, 0.004 mmol) in 1-pentene (1 – 2 mL)
was treated with B(C6F5)3 (2 mg, 0.004 mmol) at room temperature,
and was stirred for ca. 12 hours. After this period, adamantane was
added as an internal integration standard, and the solution was diluted
with benzene, filtered through a plug of silica gel, and analyzed by GC.
GC analysis demonstrated the formation of C15 olefins with a TON of
ca. 900 mmol 1-pentene oligomerized/mmol Ti, with no other detect-
ible oligomers. The C15 region of the gas chromatogram displayed one
major peak (~85%), with two other minor peaks (~15%). (ii) When
the above procedure was stirred for 20 minutes, GC analysis demon-
strated negligible C15 production.
2
C(CH2)3(CH)3(CH2)3], 2.52 [d, JH-H = 11, 1H of Ti(CH2SiMe3)2],
3.18 [AB quartet, 2JH-H = 11, 2H of Ti(CH2SiMe3)2], 3.34 [d, 2JH-H = 11,
3
1H of Ti(CH2SiMe3)2], 3.89 [s, 3H of OMe], 6.30 [d, JH-H = 8, 1H of
Ar], 6.67 [s, 1H of Ar, located by COSY], 7.08 [m, 4H of Ar], 7.17 [m,
3
2H of Ar], 7.25 [t, JH-H = 8, 1H of Ar], 7.34 [s, 1H of Ar], 7.77 [s, 1H
of N=CH]. Selected 13C{1H} NMR (C6D6/o-C6H4F2): 1.3 [3C of
Ti(CH2SiMe3)2], 1.4 [3C of Ti(CH2SiMe3)2], 11.3 [1C of
MeB(C6F5)3],
20.2
[1C
of
ArMe],
29.0
[3C
of
C(CH2)3(CH)3(CH2)3], 36.8 [3C of C(CH2)3(CH)3(CH2)3], 41.8
[3C of C(CH2)3(CH)3(CH2)3], 72.1 [1C of OMe], 109.2 [1C of
Ti(CH2SiMe3)2], 110.7 [1C of Ti(CH2SiMe3)2], 174.5 [1C of
Reaction between (FI)Ti(CH2CMe3)2Me and B(C6F5)3. (i) A
light yellow/orange solution of (FI)Ti(CH2CMe3)2Me (6 mg, 0.009
mmol) in a mixture of C6D6 (ca. 0.65 mL) and o-C6H4F2 (ca. 0.05 mL)
in an NMR tube equipped with a J. Young valve was treated with
B(C6F5)3 (5 mg, 0.01 mmol) at room temperature, resulting in an
immediate color change to orange. After ca. 1 minute, the solution
3
N=CH]. 19F NMR (C6D6/o-C6H4F2): –166.9 [t, JF-F = 20, 6F of
MeB(C6F5)3, para-F], –164.4 [t, 3JF-F = 21, 3F of MeB(C6F5)3, meta-F],
–131.7 [d, 3JF-F = 21, 6F of MeB(C6F5)3, ortho-F].
The solution described above was monitored over time, demon-
strating conversion to [(FI-CH2SiMe3)Ti(CH2SiMe3)]+. The sample
was then treated with MeOH (ca. 0.1 mL), filtered and analyzed by
several MS techniques including FAB, positive-ion mode electrospray,
and negative-ion mode electrospray, all giving m/z consistent with
(FI)H and (FI-CH2SiMe3)H2. Selected 1H NMR (C6D6/o-C6H4F2): –
0.52 [s, 9H of (FI-CH2SiMe3)], –0.14 [s, 9H of Ti(CH2SiMe3)], 0.13
1
color changed to dark brown and analysis by H NMR spectroscopy
gave no indication of any diamagnetic (FI)Ti species. The sample was
analyzed by EPR spectroscopy, indicating the formation of a TiIII spe-
cies, with an isotropic g value of 1.976 at room temperature. The sam-
ple was then treated with MeOH (ca. 0.1 mL), filtered and analyzed by
GC/MS giving two major organic fragments with m/z of 199.1 and
324.3. (ii) A light yellow/orange solution of (FI)Ti(CH2CMe3)2Me
8
3
[dd, 2JH-H = 14, JH-H = 4, 1H of (N-ArCH-CH2SiMe3)], 0.42 [dd, 2JH-H
ACS Paragon Plus Environment

Page 9 of 12
Journal of the American Chemical Society
(6 mg, 0.009 mmol) in a mixture of C7D8 (ca. 0.65 mL) and o-C6H4F2
°C): 29.9 [3C of Ti(ArHC=CHCMe3)], 72.1 [1C of OMe], 123.3 [1C
of Ti(ArHC=CHCMe3)], 144.5 [1C of Ti(ArHC=CHCMe3)].
1
2
3
4
5
6
7
8
(ca. 0.05 mL) or C6D5Cl (ca. 0.7 mL) was added to an NMR tube
equipped with a J. Young valve. The sample was cooled at –78 °C, and
then treated with B(C6F5)3 (5 mg, 0.01 mmol), resulting in a color
change to orange.51 The sample was allowed to warm to either –30 °C
or –20 °C in the probe of the NMR spectrometer, and was analyzed by
1H, 19F, COSY, HSQC and HMBC NMR spectroscopies, thereby
demonstrating conversion to [(FI)Ti(CH2CMe3)2][MeB(C6F5)3] (ca.
80% by 1H NMR integration). 1H NMR (C6D5Cl, –20 °C): 0.68 [s, 9H
of Ti(CH2CMe3)2], 0.80 [s, 9H of Ti(CH2CMe3)2], 1.26 [br s, 3H of
Isolation of HOArHC=CHCMe3. A light yellow/orange solution
of (FI)Ti(CH2CMe3)2Me (40 mg, 0.061 mmol) in Et2O (ca. 3 mL)
was added to a large vial and cooled at –30 °C. The sample was then
treated with B(C6F5)3 (40 mg, 0.078 mmol), resulting in a color change
to orange, and stored in the vial at –30 °C for ca. 4 days. After this
period, the sample was treated with MeOH (ca. 0.2 mL), filtered and
analyzed by GC/MS giving two major organic fragments with m/z of
199.1 and 324.3. The volatile components were removed under re-
duced pressure, and HOArHC=CHCMe3 was separated by flash col-
umn chromatography (silica gel, hexanes). 1H NMR of
HOArHC=CHCMe3 (CDCl3): 0.95 [s, 9H of CMe3], 1.77 [m, AB
pattern, 6H of C(CH2)3(CH)3(CH2)3], 2.06 [br s, 3H of
C(CH2)3(CH)3(CH2)3], 2.12 [br s, 6H of C(CH2)3(CH)3(CH2)3],
9
2
MeB(C6F5)3], 1.63 [d, JH-H = 11, 1H of Ti(CH2CMe3)2], 1.83 [br s,
6H of C(CH2)3(CH)3(CH2)3], 2.10 [s, 3H of ArMe], 2.13 [s, 3H of
C(CH2)3(CH)3(CH2)3], 2.27 [s, 6H of C(CH2)3(CH)3(CH2)3], 2.74
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2
2
[d, JH-H = 11, 1H of Ti(CH2CMe3)2], 2.90 [d, JH-H = 11, 1H of
2
Ti(CH2CMe3)2], 2.97 [d, JH-H = 11, 1H of Ti(CH2CMe3)2], 4.22 [s,
3
3H of OMe], 6.51 [d, JH-H = 7, 1H of Ar], 6.60 [br s, 1H of Ar], 7.21
3
2.25 [s, 3H of ArMe], 5.19 [s, 1H of ArOH], 5.92 [d, JH-H = 12, 1H of
3
[m, 3H of Ar], 7.26 [m, 2H of Ar], 7.35 [m, 2H of Ar], 7.45 [br s, 1H of
Ar], 7.99 [s, 1H of N=CH]. Selected 13C{1H} NMR (C6D5Cl, –20 °C):
10.9 [1C of MeB(C6F5)3], 20.0 [1C of ArMe], 28.6 [3C of
C(CH2)3(CH)3(CH2)3], 32.4 [3C of Ti(CH2CMe3)2], 32.4 [3C of
Ti(CH2CMe3)2], 36.4 [3C of C(CH2)3(CH)3(CH2)3], 41.5 [3C of
C(CH2)3(CH)3(CH2)3], 72.5 [1C of OMe], 121.2 [1C of
Ti(CH2CMe3)2], 130.5 [1C of Ti(CH2CMe3)2], 173.8 [1C of
ArHC=CHCMe3], 6.14 [d, JH-H = 12, 1H of ArHC=CHCMe3], 6.70
[br s, 1H of Ar], 6.91 [br s, 1H of Ar]. 13C{1H} NMR of
HOArHC=CHCMe3 (CDCl3): 21.0 [s, 1C of ArMe], 29.4 [s, 3C of
C(CH2)3(CH)3(CH2)3], 30.3 [s, 3C of CMe3], 34.9 [s, 1C of CMe3],
36.9 [s, 1C of C(CH2)3(CH)3(CH2)3], 37.4 [s, 3C of
C(CH2)3(CH)3(CH2)3], 40.6 [s, 3C of C(CH2)3(CH)3(CH2)3], 120.6
[s, 1C of ArHC=CHCMe3], 125.6 [s, 1C of Ar], 126.3 [s, 1CH of Ar],
127.3 [s, 1CH of Ar], 128.2 [s, 1C of Ar], 135.4 [s, 1C of Ar], 148.9 [s,
1C of Ar], 149.2 [s, 1C of ArHC=CHCMe3].
1
N=CH]. Selected H NMR (C7D8/o-C6H4F2, –20 °C): 0.62 [s, 9H of
2
Ti(CH2CMe3)2], 0.67 [s, 9H of Ti(CH2CMe3)2], 1.75 [d, JH-H = 11,
2
Formation of [(FI)Ti(CH(CMe3)CH2CH2)]+.
A light yel-
1H of Ti(CH2CMe3)2], 2.63 [d, JH-H = 11, 1H of Ti(CH2CMe3)2],
2.83 [d, 2JH-H = 11, 1H of Ti(CH2CMe3)2], 2.92 [d, 2JH-H = 11, 1H of
Ti(CH2CMe3)2], 3.92 [s, 3H of OMe], 7.70 [s, 1H of N=CH]. Select-
ed 13C{1H} NMR (C7D8/o-C6H4F2, –20 °C): 32.2 [3C of
Ti(CH2CMe3)2], 32.2 [3C of Ti(CH2CMe3)2], 72.6 [1C of OMe],
174.0 [1C of N=CH]. 19F NMR (C7D8/o-C6H4F2, –30 °C): –166.6 [t,
low/orange solution of (FI)Ti(CH2CMe3)2Me (6 mg, 0.009 mmol) in
a mixture of C7D8 (ca. 0.65 mL) and o-C6H4F2 (ca. 0.05 mL), or
C6D5Cl (ca 0.7 mL) was added to an NMR tube equipped with a J.
Young valve. The sample was cooled at –78 °C, and then treated with
B(C6F5)3 (5 mg, 0.01 mmol) and ethylene (1 atm), resulting in a color
change to orange.51 The sample was allowed to warm to either –30 °C
or –20 °C in the probe of the NMR spectrometer, and was analyzed by
1H, COSY, TOCSY, HSQC and HMBC NMR spectroscopies, thereby
demonstrating the catalytic production of 1-hexene and the formation
of [(FI)Ti(CH(CMe3)CH2CH2)]+. An analogous experiment was
conducted with ethylene-d4, demonstrating formation of
[(FI)Ti(CH(CMe3)CD2CD2)]+. Selected 1H NMR (C7D8/o-C6H4F2,
–20 °C): 0.67 [s, 9H of Ti(CH(CMe3)CH2CH2)], 1.01 [m, 1H of
3
3JF-F = 20, 6F of MeB(C6F5)3, para-F], –164.0 [t, JF-F = 21, 3F of
3
MeB(C6F5)3, meta-F], –131.8 [d, JF-F = 21, 6F of MeB(C6F5)3, ortho-
F].
Formation of [(FI)Ti(=CHCMe3)]+ and conversion to [(Me-
OAr2N=)Ti(OArHC=CHCMe3)]+. A light yellow/orange solution of
(FI)Ti(CH2CMe3)2Me (6 mg, 0.009 mmol) in a mixture of C7D8 (ca.
0.65 mL) and o-C6H4F2 (ca. 0.05 mL) or C6D5Cl (ca. 0.7 mL) was
added to a small vial and cooled at –30 °C. The sample was then treat-
ed with B(C6F5)3 (5 mg, 0.01 mmol), resulting in a color change to
orange, and stored in the vial at –30 °C for ca. 1 day. The solution was
then pipetted into an NMR tube equipped with a J. Young valve
(which was pre-cooled to < –78 °C), sealed, and then cooled at –78 °C.
The sample was allowed to warm to –20 °C in the probe of the NMR
Ti(CH(CMe3)CH2CH2)], 2.88 [s, 3H of OMe], 3.29 [m, 1H of
3
Ti(CH(CMe3)CH2CH2)], 3.49 [t, JH-H
=
11, 1H of
Ti(CH(CMe3)CH2CH2)], 3.82 [m, 1H of Ti(CH(CMe3)CH2CH2)],
4.56 [m, 1H of Ti(CH(CMe3)CH2CH2)], 7.79 [s, 1H of N=CH].
Selected 13C{1H} NMR (C7D8/o-C6H4F2, –20 °C): 6.8 [1C of
Ti(CH(CMe3)CH2CH2)], 30.9 [3C of Ti(CH(CMe3)CH2CH2)],
70.7 [1C of OMe], 99.2 [1C of Ti(CH(CMe3)CH2CH2)], 164.5 [1C
1
spectrometer, and was analyzed by H, COSY, HSQC and HMBC
NMR spectroscopies, thereby demonstrating formation of
[(FI)Ti(=CHCMe3)]+. Selected H NMR (C7D8/o-C6H4F2, –20 °C):
1
1
of Ti(CH(CMe3)CH2CH2)], 174.4 [1C of N=CH]. Selected H
NMR (C6D5Cl, –20 °C): 0.72 [s, 9H of Ti(CH(CMe3)CH2CH2)],
1.08 [m, 1H of Ti(CH(CMe3)CH2CH2)], 3.24 [s, 3H of OMe], 3.46
0.72 [s, 9H of Ti(=CHCMe3)], 3.49 [s, 3H of OMe], 7.75 [s, 1H of
N=CH], 9.91 [s, 1H of Ti(=CHCMe3 )]. Selected 13C{1H} NMR
(C7D8/o-C6H4F2, –20 °C): 30.3 [3C of Ti(=CHCMe3)], 72.1 [1C of
OMe], 168.6 [1C of N=CH], 311.0 [1C of Ti(=CHCMe3)]. Selected
1H NMR (C6D5Cl, –20 °C): 0.72 [s, 9H of Ti(=CHCMe3)], 4.05 [s,
3H of OMe], 8.15 [s, 1H of N=CH], 9.84 [s, 1H of Ti(=CHCMe3)].
Selected 13C{1H} NMR (C6D5Cl, –20 °C): 312.3 [1C of
Ti(=CHCMe3)].
3
[m, 1H of Ti(CH(CMe3)CH2CH2)], 3.65 [t, JH-H = 11, 1H of
Ti(CH(CMe3)CH2CH2)], 3.97 [m, 1H of Ti(CH(CMe3)CH2CH2)],
4.63 [m, 1H of Ti(CH(CMe3)CH2CH2)], 8.30 [s, 1H of N=CH].
Selected 13C{1H} NMR (C6D5Cl, –20 °C): 6.8 [1C of
Ti(CH(CMe3)CH2CH2)], 31.1 [3C of Ti(CH(CMe3)CH2CH2)],
70.9 [1C of OMe], 99.2 [1C of Ti(CH(CMe3)CH2CH2)], 164.6 [1C
of Ti(CH(CMe3)CH2CH2)], 174.4 [1C of N=CH].
At –20 °C, [(FI)Ti(=CHCMe3)]+ converted to [(Me-
OAr2N=)Ti(OArHC=CHCMe3)]+ over a period of hours, and was
Ethylene Trimerization Catalysis with (FI)Ti(CH2CMe3)2Me.
(i) A light yellow/orange solution of (FI)Ti(CH2CMe3)2Me (6 mg,
0.009 mmol) in a mixture of C7D8 (ca. 0.65 mL) and o-C6H4F2 (ca.
0.05 mL), or C6D5Cl (ca 0.7 mL) was added to an NMR tube equipped
with a J. Young valve. The sample was cooled at –78 °C, and then
treated with B(C6F5)3 (5 mg, 0.01 mmol) and ethylene (1 atm), result-
ing in a color change to orange.51 The sample was continually re-
1
analyzed by H, COSY, HSQC and HMBC NMR spectroscopies.
Selected 1H NMR (C7D8/o-C6H4F2, –20 °C): 0.76 [s, 9H of
Ti(ArHC=CHCMe3)], 3.61 [s, 3H of OMe], 4.72 [d, 3JH-H = 13, 1H of
Ti(ArHC=CHCMe3)], 4.98 [d, 3JH-H
=
13, 1H of
Ti(ArHC=CHCMe3)]. Selected 13C{1H} NMR (C7D8/o-C6H4F2, –20
9
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 10 of 12
saturated with ethylene at temperatures < –20 °C until catalytic activity
1
terminated. The sample was periodically analyzed by H NMR spec-
1
(3) (a) Briggs, J. R. J. Chem. Soc., Chem. Commun. 1989, 674-675. (b)
Carter, A.; Cohen, S. A.; Cooley, N. A.; Murphy, A.; Scutt, J.; Wass, D. F.
Chem. Commun. 2002, 858-859. (c) McGuinness, D. S.; Wasserscheid,
P.; Keim, W.; Hu, C. H.; Englert, U.; Dixon, J. T.; Grove, C. Chem. Com-
mun. 2003, 334-335. (d) McGuinness, D. S.; Wasserscheid, P.; Keim, W.;
Morgan, D.; Dixon, J. T.; Bollmann, A.; Maumela, H.; Hess, F.; Englert, U.
J. Am. Chem. Soc. 2003, 125, 5272-5273. (e) Bollmann, A.; Blann, K.;
Dixon, J. T.; Hess, F. M.; Killian, E.; Maumela, H.; McGuinness, D. S.;
Morgan, D. H.; Neveling, A.; Otto, S.; Overett, M.; Slawin, A. M. Z.; Was-
serscheid, P.; Kuhlmann, S. J. Am. Chem. Soc. 2004, 126, 14712-14713.
(f) Overett, M. J.; Blann, K.; Bollmann, A.; Dixon, J. T.; Haasbroek, D.;
Killian, E.; Maumela, H.; McGuinness, D. S.; Morgan, D. H. J. Am. Chem.
Soc. 2005, 127, 10723-10730. (g) Andes, C.; Harkins, S. B.; Murtuza, S.;
Oyler, K.; Sen, A. J. Am. Chem. Soc. 2001, 123, 7423-7424. (h) Arteaga-
Müller, R.; Tsurugi, H.; Saito, T.; Yanagawa, M.; Oda, S.; Mashima, K. J.
Am. Chem. Soc. 2009, 131, 5370-5371. (i) Chen, Y.; Callens, E.; Abou-
Hamad, E.; Merle, N.; White, A. J. P.; Taoufik, M.; Copéret, C.; Le Roux,
E.; Basset, J.-M. Angew. Chem. Int. Ed. 2012, 51, 11886-11889. (j) Deck-
ers, P. J. W.; Hessen, B.; Teuben, J. H. Angew. Chem. Int. Ed. 2001, 40,
2516-2519.
(4) Do, L. H.; Labinger, J. A.; Bercaw, J. E. ACS Catal. 2013, 3, 2582-
2585.
(5) Suzuki, Y.; Kinoshita, S.; Shibahara, A.; Ishii, S.; Kawamura, K.; In-
oue, Y.; Fujita, T. Organometallics 2010, 29, 2394-2396.
(6) Soshnikov, I. E.; Semikolenova, N. V.; Ma, J.; Zhao, K.-Q.; Zakha-
rov, V. A.; Bryliakov, K. P.; Redshaw, C.; Talsi, E. P. Organometallics
2014, 33, 1431-1439.
(7) Sattler, A.; Labinger, J. A.; Bercaw, J. E. Organometallics 2013, 32,
6899-6902.
2
3
4
5
6
7
8
9
troscopy, demonstrating the rapid catalytic production of 1-hexene (by
the time the spectra were obtained (ca. 5 minutes after ethylene addi-
tion), all of the ethylene was transformed into 1-hexene) and disap-
pearance of [(FI)Ti(CH2CMe3)2]+. The solution was analyzed by
room temperature EPR spectroscopy after catalysis had ceased, indi-
cating the formation of a major TiIII species, with an isotropic g value of
1.958 at room temperature. (ii) In a typical experiment, a solution of
(FI)Ti(CH2CMe3)2Me (6 mg, 0.009 mmol) in o-C6H4F2 (1 mL) was
added to a 15 mL ampoule and frozen at –196 °C. The solution was
degassed, and allowed to warm to room temperature. The ampoule
was then charged with ethylene (1 atm), and then treated with
B(C6F5)3 (5 mg, 0.01 mmol), and stirred for 20 minutes under con-
stant ethylene pressure (1 atm) at room temperature. After this period,
the volume of the solution had increased significantly (ca. 0.3 mL), but
only a trace amount of polymer (< 3 mg) had formed. Adamantane
was added as an internal integration standard, and the mixture was
diluted with benzene, filtered through a plug of silica gel, and analyzed
by GC. GC analysis demonstrated the catalytic production of 1-
hexene, in addition to C10 olefins and C14 olefins, with a TON of ca.
2.5×103 mmol olefin oligomerized/mmol Ti. (iii) The above proce-
dure was repeated at –20 °C for 3 hours, giving a TON of ca. 8.9×103
mmol olefin oligomerized/mmol Ti.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1-Pentene
Trimerization
Catalysis
with
(FI)Ti(CH2CMe3)2Me. In a typical experiment, a solution of
(FI)Ti(CH2CMe3)2Me (3 mg, 0.005 mmol) in 1-pentene (1 – 2 mL)
was treated with B(C6F5)3 (3 mg, 0.006 mmol) at room temperature,
and was stirred for ca. 20 minutes to 2 hours. After this period, ada-
mantane was added as an internal integration standard, and the solu-
tion was diluted with benzene, filtered through a plug of silica gel, and
analyzed by GC. GC analysis demonstrated the formation of C15 ole-
fins with a TON of ca. 500 mmol 1-pentene oligomerized/mmol Ti,
with no other detectible oligomers. The C15 region of the gas chroma-
togram displayed one major peak (~85%), with two other minor peaks
(~15%).
(8) (a) Köhn, R. D.; Haufe, M.; Kociok-Köhn, G.; Grimm, S.; Wasser-
scheid, P.; Keim, W. Angew. Chem. Int. Ed. 2000, 39, 4337-4339. (b)
Wasserscheid, P.; Grimm, S.; Köhn, R. D.; Haufe, M. Adv. Synth. Catal.
2001, 343, 814-818.
(9) For related examples of olefin oligomerization, see: (a) McGuin-
ness, D. S. Organometallics 2009, 28, 244-248. (b) Bowen, L. E.;
Charernsuk, M.; Wass, D. F. Chem. Commun. 2007, 2835-2837. (c) Bow-
en, L. E.; Charernsuk, M.; Hey, T. W.; McMullin, C. L.; Orpen, A. G.;
Wass, D. F. Dalton Trans. 2010, 39, 560-567. (d) Lian, B.; Beckerle, K.;
Spaniol, T. P.; Okuda, J. Angew. Chem. Int. Ed. 2007, 46, 8507-8510. (e)
Xu, T.; Liu, J.; Wu, G.-P.; Lu, X.-B. Inorg. Chem. 2011, 50, 10884-10892.
(f) Londaitsbehere, A.; Cuenca, T.; Mosquera, M. E. G.; Cano, J.; Milione,
S.; Grassi, A. Organometallics 2012, 31, 2108-2111. (g) Dagorne, S.;
Bellemin-Laponnaz, S.; Romain, C. Organometallics 2013, 32, 2736-2743.
(h) Broene, R. D.; Brookhart, M.; Lamanna, W. M.; Volpe, A. F., Jr. J. Am.
Chem. Soc. 2005, 127, 17194-17195. (i) Small, B. L.; Marcucci, A. J. Or-
ganometallics 2001, 20, 5738-5744. (j) Small, B. L. Organometallics
2003, 22, 3178-3183. (k) Tellmann, K. P.; Gibson, V. C.; White, A. J. P.;
Williams, D. J. Organometallics 2004, 24, 280-286.
ASSOCIATED CONTENT
Supporting Information
Selected NMR spectra and CIF files. This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
jal@caltech.edu; bercaw@caltech.edu
(10) Klamo, S. B. Direct Examination of Initiation and Propagation Ki-
netics of Zirconocene-Catalyzed Alkene Polymerization. Ph.D. Thesis,
California Institute of Technology, Pasadena, CA, 2005.
(11) For computational studies on a related titanium trimerization sys-
tem, see: Tobisch, S.; Ziegler, T. Organometallics 2003, 22, 5392-5405.
(12) See Experimental Section for additional details.
ACKNOWLEDGMENT
We thank Larry Henling and Michael Takase for assistance with
crystallographic work, Mona Shahgholi and Naseem Torian for
assistance with mass spectrometry, and Thomas S. Teets, Harry
B. Gray and Jay R. Winkler for helpful discussions. This work
was funded by BP through the XC2 program.
(13) Brookhart, M.; Green, M. L. H.; Parkin, G. Proc. Nat. Acad. Sci.
2007, 104, 6908-6914.
(14) All of the cationic complexes in this report display OMe coordina-
1
tion to the Ti center, based on the H and 13C chemical shifts of the OMe
group.
REFERENCES
(15) Δδ(m,p-F) values of 3 – 6 ppm indicate coordination. See: Hor-
ton, A. D. Organometallics 1996, 15, 2675-2677.
(16) Ethylene is not required for this transformation, as
[(FI)Ti(CH2SiMe3)2]+ converts to [(FI-CH2SiMe3)Ti(CH2SiMe3)]+
under a nitrogen atmosphere.
(1) Reagen, W. K.; McDaniel, M. P. (Phillips Petroleum Company). US
Patent 5,382,738, 1995.
(2) (a) McGuinness, D. S. Chem. Rev. 2011, 111, 2321-2341. (b) Dix-
on, J. T.; Green, M. J.; Hess, F. M.; Morgan, D. H. J. Organomet. Chem.
2004, 689, 3641-3668. (c) Agapie, T. Coord. Chem. Rev. 2011, 255, 861-
880. (d) Wass, D. F. Dalton Trans. 2007, 816-819.
10
ACS Paragon Plus Environment

Page 11 of 12
Journal of the American Chemical Society
(17) For all of the cationic complexes in this report, the 13C NMR spec-
[(FI)Ti(=CHCMe3)]+ and [(MeOAr2N=)Ti(OArHC=CHCMe3)]+ be-
fore adding ethylene, negligible quantities of 1-hexene are produced.
(39) Basuli, F.; Bailey, B. C.; Watson, L. A.; Tomaszewski, J.; Huffman,
J. C.; Mindiola, D. J. Organometallics 2005, 24, 1886-1906.
(40) Bennett, J. L.; Wolczanski, P. T. J. Am. Chem. Soc. 1994, 116,
2179-2180.
(41) Bennett, J. L.; Wolczanski, P. T. J. Am. Chem. Soc. 1997, 119,
10696-10719.
(42) Polse, J. L.; Andersen, R. A.; Bergman, R. G. J. Am. Chem. Soc.
1998, 120, 13405-13414.
(43) Bashall, A.; McPartlin, M.; E. Collier, P.; Mountford, P.; H. Gade,
L.; J. M. Trosch, D. Chem. Commun. 1998, 2555-2556.
(44) Bashall, A.; Collier, P. E.; Gade, L. H.; McPartlin, M.; Mountford,
P.; Pugh, S. M.; Radojevic, S.; Schubart, M.; Scowen, I. J.; Trösch, D. J. M.
Organometallics 2000, 19, 4784-4794.
1
2
3
4
5
6
7
8
troscopic chemical shift assignments were obtained using 2D HSQC and
HMBC spectroscopies, rather than by using 1D 13C{1H} spectra.
1
(18) For H NMR spectroscopic data for a similar fragment, see: Bar-
luenga, J.; Fananas, F. J.; Yus, M. J. Org. Chem. 1979, 44, 4798-4801.
(19) [(FI-CH2SiMe3)Ti(CH2SiMe3)]+, with two X-type ligands and
positive formal charge, might be less likely to reach a TiII oxidation state
and hence harder to activate for trimerization catalysis. Selective ethylene
trimerization has been shown to proceed via a 2-electron redox active cycle
(II/IV for titanium). See: (a) Agapie, T.; Schofer, S. J.; Labinger, J. A.;
Bercaw, J. E. J. Am. Chem. Soc. 2004, 126, 1304-1305. (b) References 2,
5-7, 11.
(20) After negligible quantities of [(FI)Ti(CH2CMe3)2]+ are present,
addition of C2H4 to [(FI)Ti(CH(CMe3)CD2CD2)]+ shows no protio
incorporation into the metallacycle, demonstrating that the addition reac-
tion is irreversible on the timescale of the reaction.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(45) For related zirconium and vanadium aza-metalacyclobutane com-
plexes, see: (a) Michael, F. E.; Duncan, A. P.; Sweeney, Z. K.; Bergman, R.
G. J. Am. Chem. Soc. 2005, 127, 1752-1764. (b) De With, J.; Horton, A.
D.; Orpen, A. G. Organometallics 1993, 12, 1493-1496.
(46) For comparison, the Z and E isomers of PhHC=CHCMe3 have
(21) Howard, T. R.; Lee, J. B.; Grubbs, R. H. J. Am. Chem. Soc. 1980,
102, 6876-6878.
(22) Lee, J. B.; Gajda, G. J.; Schaefer, W. P.; Howard, T. R.; Ikariya, T.;
Straus, D. A.; Grubbs, R. H. J. Am. Chem. Soc. 1981, 103, 7358-7361.
(23) Gilliom, L. R.; Grubbs, R. H. Organometallics 1986, 5, 721-724.
(24) Straus, D. A.; Grubbs, R. H. J. Mol. Catal. 1985, 28, 9-25.
(25) Greidanus, G.; McDonald, R.; Stryker, J. M. Organometallics
2001, 20, 2492-2504.
(26) Carter, C. A. G.; McDonald, R.; Stryker, J. M. Organometallics
1999, 18, 820-822.
(27) Polse, J. L.; Andersen, R. A.; Bergman, R. G. J. Am. Chem. Soc.
1996, 118, 8737-8738.
3
been characterized, having JH-H couplings of 13 and 16 Hz, respectively.
See: (a) Kambe, N.; Moriwaki, Y.; Fujii, Y.; Iwasaki, T.; Terao, J. Org. Let.
2011, 13, 4656-4659. (b) Delcamp, J. H.; White, M. C. J. Am. Chem. Soc.
2006, 128, 15076-15077.
(47) Feldman, J.; Schrock, R. R. Prog. Inorg. Chem. 2007, 39, 1-74.
(48) (a) McNally, J. P.; Leong, V. S.; Cooper, N. J. in Experimental Or-
ganometallic Chemistry, Wayda, A. L.; Darensbourg, M. Y., Eds.; American
Chemical Society: Washington, DC, 1987; Chapter 2, pp 6-23.
(b) Burger, B. J.; Bercaw, J. E. in Experimental Organometallic Chemistry;
Wayda, A. L.; Darensbourg, M. Y., Eds.; American Chemical Society:
Washington, DC, 1987; Chapter 4, pp 79-98. (c) Shriver, D. F.; Drezdzon,
M. A.; The Manipulation of Air-Sensitive Compounds, 2nd Edition; Wiley-
Interscience: New York, 1986.
(49) (a) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem.
1997, 62, 7512-7515. (b) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.;
Gottlieb, H. E.; Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I.
Organometallics 2010, 29, 2176-2179.
(28) Polse, J. L.; Kaplan, A. W.; Andersen, R. A.; Bergman, R. G. J. Am.
Chem. Soc. 1998, 120, 6316-6328.
(29) For examples of metallacyclobutane complexes of other transition
metals, see: (a) Jennings, P. W.; Johnson, L. L. Chem. Rev. 1994, 94,
2241-2290. (b) Feldman, J.; Schrock, R. R. Prog. Inorg. Chem. 2007, 39,
1-74. (c) Andersen, R. A.; Jones, R. A.; Wilkinson, G. J. Chem. Soc., Dalton
Trans. 1978, 446-453. (d) Statler, J. A.; Wilkinson, G.; Thornton-Pett, M.;
Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1984, 1731-1738. (e)
Diversi, P.; Ingrosso, G.; Lucherini, A.; Marchetti, F.; Adovasio, V.;
Nardelli, M. J. Chem. Soc., Dalton Trans. 1991, 203-213. (f) McNeill, K.;
Andersen, R. A.; Bergman, R. G. J. Am. Chem. Soc. 1997, 119, 11244-
11254.
(50) (a) Sheldrick, G. M. SHELXTL, An Integrated System for Solving,
Refining and Displaying Crystal Structures from Diffraction Data; Univer-
sity of Göttingen, Göttingen, Federal Republic of Germany, 1981. (b)
Sheldrick, G. M. Acta Cryst. 2008, A64, 112-122.
(30) Brainard, R. L.; Nutt, W. R.; Lee, T. R.; Whitesides, G. M. Organ-
ometallics 1988, 7, 2379-2386.
(51) In C6D5Cl, the sample was allowed to thaw to ca. –30 °C after
addition of B(C6F5)3, at which point the color change was observed.
1
(31) Low values of JC-H indicate the presence of an α-agostic interac-
tion. See: Schrock, R. R. Chem. Rev. 2001, 102, 145-180.
(32) Basuli, F.; Bailey, B. C.; Tomaszewski, J.; Huffman, J. C.; Mindiola,
D. J. J. Am. Chem. Soc. 2003, 125, 6052-6053.
(33) van der Heijden, H.; Hessen, B. J. Chem. Soc., Chem. Commun.
1995, 145-146.
(34) Bailey, B. C.; Fan, H.; Baum, E. W.; Huffman, J. C.; Baik, M.-H.;
Mindiola, D. J. J. Am. Chem. Soc. 2005, 127, 16016-16017.
(35) Bailey, B. C.; Huffman, J. C.; Mindiola, D. J. J. Am. Chem. Soc.
2007, 129, 5302-5303.
(36) Mindiola, D. J.; Bailey, B. C.; Basuli, F. Eur. J. Inorg. Chem. 2006,
2006, 3135-3146.
(37) The α-C with the CMe3 group is shifted downfield from the other
α-C (CH2) in [(FI)Ti(CH(CMe3)CH2CH2)]+. This is consistent with the
parent structure, (FI)Ti(CH2CMe3)2Me, in which the 13C signal of the Ti–
CH2CMe3 groups is also shifted downfield (~ 40 ppm) compared with the
Ti–Me group.
(38) It is difficult to achieve complete conversion to
[(FI)Ti(=CHCMe3)]+ because it is also not stable in solution; the small
remaining quantities of [(FI)Ti(CH2CMe3)2]+ appear to be responsible for
the 1-hexene production, which is three times less than when
[(FI)Ti(CH2CMe3)2]+ is treated with ethylene under similar conditions.
When [(FI)Ti(CH2CMe3)2]+ is allowed to convert fully to a mixture of
11
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 12 of 12
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Graphical TOC
O
+
N
Ti
O
O
+
O
+
Ti
O
+
Ti
H
H
N
Ti
N
N
H
H
H
H
O
O
O
12
ACS Paragon Plus Environment