A new weakly coordinating aluminate anion incorporating a chelating perfluoro-bis-anilido ligand

Article abstract of DOI:10.1039/c0dt00846j

The synthesis of the fully fluorinated bis-anilido ligand N,N′-bis-pentafluorophenyl-3,4,5,6-tetrafluorophenylene-1,2-diamine, 1 is described. Reaction of one or two equivalents of 1 with AlMe₃ gives aluminium compounds incorporating one or two

Full text of DOI:10.1039/c0dt00846j

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www.rsc.org/dalton | Dalton Transactions
A new weakly coordinating aluminate anion incorporating a chelating
perfluoro-bis-anilido ligand†
Joshua C. Smith,a Kuangbiao Ma,a Warren E. Piers,*‡a Masood Parveza and Robert McDonaldb
Received 14th July 2010, Accepted 18th August 2010
DOI: 10.1039/c0dt00846j
The synthesis of the fully fluorinated bis-anilido ligand
N,N¢-bis-pentafluorophenyl-3,4,5,6-tetrafluorophenylene-1,2-diamine, 1 is described. Reaction of one
or two equivalents of 1 with AlMe3 gives aluminium compounds incorporating one or two ligands, the
latter being the protonated form of a new weakly coordinating anion (WCA), 3-H. Alternatively,
reaction of 1 with LiAlH4 yields the lithium salt of this anion, 3-Li, which may be employed as a
reagent for preparing the trityl and N,N-dimethylanilinium salts of the aluminate anion. All ion pairs
are fully characterized and the use of 3-Ph3C to generate titanium-based alkyl cations is also described.
Introduction
Results and discussion
Weakly coordinating anions (WCAs) have played a crucial role in
the development of the chemistry of highly electrophilic cations,
based both on main group and transition metal elements.1–7
Critical attributes of an effective WCA include stability towards
oxidation, chemical stability (both kinetic and thermodynamic),
relatively large molecular volume and a high number of electroneg-
ative atoms over which the negative charge can be delocalized.
Early work utilized the anions of strong Brønsted acids, such
as the fluorinated anions [BF4]- or [PF6]-, but as the cations
they were meant to partner with became more electrophilic and
reactive, these WCAs proved insufficient due to the tendency to
relinquish fluoride anion to the cation. Larger WCAs with more
inert bonds became necessary, with halogenated carborane based
systems5 and perfluoroaryl substituted borates or aluminates being
the most prominent classes of modern WCAs.8 Their development
and application have resulted in major advances in the chemistry
of highly electrophilic compounds and olefin polymerization
catalysts.9–11
Synthesis and characterization of perfluoroarylamine ligands
Although partially fluorinated N,N-diphenylphenylene-1,2-
diamine has been prepared,19 the perfluorinated compound has
not, to our knowledge, appeared in the open literature. We pre-
pared N,N-bis-pentafluorophenyl-3,4,5,6-tetrafluorophenylene-
1,2-diamine (1) in 49% overall yield using a nucleophilic aro-
matic substitution strategy20,21 from readily available tetrafluoro-
phenylene-1,2-diamine22 as shown in Scheme 1.
Most commonly, the perfluoroaryl borates and aluminates
utilize E–C bonds at their core; however, perfluorophenoxy12,13
or alkoxy14–16 and perfluoroanilido17,18 groups have also been
employed. One drawback of such systems is the tendency for
transfer of the ORF or N(RF)2 groups from the anion to the
cation, i.e., lowered chemical stability, particularly at higher
temperatures. Incorporation of such anchoring groups into a
chelate array should render the resulting anions less prone to
such decomposition pathways. Here we describe the synthesis of
perfluorinated N,N-diphenylphenylene-1,2-diamine and its use in
the production of a new aluminate WCA.
Scheme 1 Synthesis of perfluorinated bis-aniline 1.
Reaction of the starting diamine with two equivalents of
n-BuLi at -78 ◦C in THF gave a bright yellow solution of
the doubly deprotonated anilide dianion as confirmed by low-
temperature 1H and 19F NMR spectroscopy. Addition of a
five-fold excess of C6F6 at -78 ◦C and subsequent warming
of the solution to -5 ◦C gave the desired product 1 as well
as the mono-arylated N-pentafluorophenyl-3,4,5,6-tetrafluoro-
phenylene-1,2-diamine upon aqueous work-up. Maintenance of
aDepartment of Chemistry, University of Calgary, 2500 University Drive
NW, Calgary, Alberta, Canada, T2N 1N4. E-mail: wpiers@ucalgary.ca;
Tel: +1 403-220-5746
bX-Ray Structure Laboratory, Department of Chemistry, University of
Alberta, Edmonton, Alberta, Canada, T6G 2G2
† CCDC reference numbers 784055–784058. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt00846j
‡ S. Robert Blair Professor of Chemistry.
◦
the reaction temperature at -5 C was critical for preventing the
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formation of a by-product identified as 1,2,3,4,6,7,8,9-octafluoro-
5-pentafluorophenyl-5,10-dihydrophenazine (I) while allowing the
desired nucleophilic substitutions to take place at reasonable rates.
The mono-arylated phenylenediamine likely arises because lithium
exchange as depicted in Scheme 1 is competitive with the second
arylation. The more thermodynamically stable bis-aryl anilide
is unreactive towards C6F6 under these conditions and simply
gets protonated in the work-up. All attempts to disfavor this by-
product failed, but it can be isolated and later converted to 1
by treating with two equivalents of n-BuLi and quenching with
C6F6 as shown. In this way, the overall yield of analytically pure 1
can be improved to a workable 49%. Compound 1 exhibits five
characteristic resonances between d -165 to -152 ppm in the
19F NMR spectrum (CD2Cl2) and a single broad peak at d 5.5,
assignable to the NH proton in the 1H NMR spectrum.
Fig. 1 Solid state molecular structure of 2 as determined by X-ray
diffraction. Thermal ellipsoids are shown at the 50% probability level
˚
and hydrogen atoms are omitted for clarity. Selected bond lengths (A):
Al1–N1, 1.854(2); Al1–N2, 2.013(2); Al1–N2*, 2.010(2); Al1–C1, 1.922(2).
◦
˚
Synthesis and characterization of aluminium complexes of ligand 1
Interatomic distances (A): Al1–Al1*, 2.912(1). Selected bond angles ( ):
N1–Al1–C1, 128.02(10); N1–Al1–N2, 88.00(8); N1–Al1–N2*, 113.53(8);
N2–Al1–C1, 121.12(10); N2–Al1–N2*, 87.28(7); C1–Al1–N2*, 110.16(9);
Al1–N2–Al1*, 92.72(7).
Molecular modeling suggested that preparation of a borate anion
using ligand 1 was going to be sterically problematic, so we focused
on an aluminate-based WCA. Accordingly, the reactivity of 1 with
AlMe3 was investigated; the chemistry is depicted in Scheme 2.
Reaction at a 1 : 1 stoichiometry in refluxing toluene results in
observable gas evolution and, upon cooling and concentration,
precipitation of an off-white solid. This compound was character-
ized by NMR spectroscopy and X-ray crystallography as the dimer
2; a thermal ellipsoid diagram and selected metrical parameters
are given in Fig. 1. In the centrosymmetric 2, the bridging
Al–N bonds of the planar four-membered Al2N2 dimeric core are
aluminium, the atoms are also essentially co-planar, with the root
mean square deviation from the plane fitted across these atoms
◦
˚
being 0.0053 A. The angle between these two planes is 113.96(6) .
The dimeric structure of 2 appears to be maintained in
solution, and the compound is stable by shock testing, despite
the propensity of other molecules of this type to explode when
struck.23 Furthermore, no reaction between 2 and an additional
equivalent of 1 was observed, even at high temperatures. This
contrasts with the finding that reaction of two equivalents of 1
with AlMe3 (under similar conditions to where 2 is produced)
gives a different product in which aluminium is ligated by two
bis-anilido donors in the Brønsted acid 3-H shown in Scheme 2.
Compound 3-H was isolated in 53% yield as a purple solid; no
distinct signal was present in the 1H NMR spectrum for the NH
proton in the chemical shift range of 0–20 ppm at room temper-
ature. 19F NMR spectroscopy revealed the typical signal pattern
observed for this anion (see below) at all accessible temperatures,
suggesting the proton is highly fluxional. Furthermore, although
single crystals were grown, the proton could not be located due
to its disordering over the four nitrogen positions; nonetheless,
this data did show conclusively that two ligands 1 were attached
to aluminium in this compound. The unusual colour of 3-H is
indicative of small amounts of a paramagnetic impurity24,25 and
indeed solutions of 3-H were not EPR silent, exhibiting a complex
peak with a g-factor of 2.003(1).
˚
ª 0.15 A longer than the terminal Al–N bonds and the intra-ring
angles are close to 90◦. In the AlN2C2 rings formed as 1 chelates to
The use of 3-H as a Brønsted acid activator was investigated,
but protonolysis reactions aimed at generating, for example, early
transition metal alkyl cations, were not clean. For this we turned
to methodology developed by Strauss et al.12 for the synthesis of
fluoroaryloxyaluminates in which LiAlH4 was employed as the
Scheme 2 Reactions of 1 with AlMe3.
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source aluminium reagent. Accordingly, reaction of two equiva-
◦
lents of 1 with LiAlH4 in toluene at 80 C overnight (Scheme 3)
gave a white suspended solid, which was isolated by filtration.
Characterization of the solid by 19F NMR spectroscopy, X-ray
crystallography, and elemental analysis confirmed the compound’s
identity as Li[Al(C6F4-1,2-(NC6F5)2)2] (3-Li), which was isolated
in 81% yield. Control of the reaction temperature is of some
importance in the preparation of pure 3-Li. If too low, the reaction
does not reach completion even during extended reaction times
and the left over LiAlH4 cannot be separated from the product
3-Li; if too high, thermal decomposition of LiAlH4 and/or 3-Li
gives a grey solid mixed in with the white product, assumed to be
Al(0) metal. Since 3-Li is used to prepare trityl and ammonium
salts, pure material is critical. Any quantity of either of these
contaminants was shown to affect subsequent reactions, and so
purification of 3-Li before carrying out further synthetic steps is
imperative.
Fig. 2 Solid state molecular structure of 3-Li as determined by X-ray
diffraction, showing F–Li–F bridges. Thermal ellipsoids are shown at
the 50% probability level and hydrogen atoms are omitted for clar-
˚
ity. Selected bond distances (A): Al1–N1, 1.859(2); Al1–N2, 1.854(2);
Al1–N3, 1.855(2); Al1–N4, 1.849(2); F7–Li1*, 1.924(5); F22–Li1, 2.809(5);
Li1–O1, 1.861(5); Li1–O2, 1.850(2). Selected bond angles (◦): N4–Al1–N2,
135.98(9); N4–Al1–N3, 87.55(9); N2–Al1–N3, 105.97(9); N4–Al1–N1,
109.63(9); N2–Al1–N1, 87.36(9); N3–Al1–N1, 139.12(9); O2–Li1–O1,
130.4(3); O2–Li1–F7**, 114.1(3); O1–Li1–F7**, 108.5(2); O2–Li1–F22,
104.7(2); O1–Li1–F22, 101.9(2); F22–Li1–F7**, 86.5(2).
of Ph3CCl in CH2Cl2. Upon work-up and removal of all traces
of solvent, 3-Ph3C was obtained in 72% yield as a dark orange
powder. The 1H NMR spectrum in CD2Cl2 of the isolated product
3-Ph3C showed three peaks ranging from d 7.6 to 8.3 ppm in
a 2 : 2 : 1 ratio, indicative of the trityl cation.26 The 13C NMR
spectrum was also consistent with the presence of a trityl cation,
with a characteristic resonance at 211 ppm to go along with the
resonances for the aromatic carbons.16 Analysis of the 19F NMR
spectrum showed little difference between 3-Li and 3-Ph3C (see
Fig. 4 below), suggesting that the identity of the counterion has
little effect on the environment of the aluminate anion. Compound
3-Ph3C is very sensitive to adventitious moisture, as even brief
exposure to air or wet solvent resulted in the appearance of
Scheme 3 Synthesis of WCA salts 3.
The 19F NMR spectrum of 3-Li in CD2Cl2 was representative
of this symmetrical D2d anion, giving four peaks from d -176 to
-151 ppm, with the signals from the para and meta fluorine atoms
of the C6F5 rings overlapping at the field strength employed. Single
crystals of 3-Li were grown from THF and crystallize as the solvate
3-Li·(THF)2 which exhibits a chain polymeric structure in the
solid state (Fig. 2). The lithium and aluminate ions are linked
through lithium–fluorine contacts between fluorine atoms F22
and F7 from different molecules; two THF molecules complete
the tetrahedral coordination of lithium. The Li–F contacts are
1
additional signals in the H NMR spectrum consistent with the
formation of Ph3COH.
X-Ray quality single crystals of 3-Ph3C were grown from a
saturated C6H5Br solution layered with iso-octane at -35 ◦C over
the course of several days; the molecular structure is shown in
Fig. 3. Metrical parameters for the trityl cation are typical; the sum
of the angles about C70 is 360.0(7)◦ indicating no pyramidalization
at the central carbon resulting from significant cation/anion
interaction. The structure of the anion here is very similar to that
in 3-Li, indicating that the nature of the cation has little structural
effect on the anion. Indeed, the closest contacts between cation
◦
˚
2.089(5) and 1.924(5) A, while the F–Li–F bond angle is 86.5(2) .
Within the anion, the Al–N bond distances in 3-Li are all similar,
˚
˚
differing only by 0.010(3) A from the shortest to the longest Al–N
and anion are 3.019(4) and 3.062(4) A (dotted lines in Fig. 3),
bond. The N–Al–N bond angles are also close to expected values,
with the five-membered rings created by each chelated ligand
resulting in nearly 90◦ angles and the exocyclic N–Al–N bond
angles ranging between 105◦ and 139◦. The distorted tetrahedral
geometry about aluminium is also influenced by apparent p-
stacking interactions between adjacent N-C6F5 groups, i.e., those
on N2/N3 and N1/N4.
again engaging the fluorine atoms on the tetrafluorophenylene
backbone. However, while these contacts are within the sum of
27,28
˚
the van der Waals radii for C and F (3.17 A),
they are at the
upper limit of that range. Thus, there appears to be very little
localized electrostatic contact within this ion pair, speaking to the
weakly coordinating nature of the aluminate anion supported by
ligand 1.
Ion pair 3-Li is a suitable starting material for the preparation of
the salts 3-Ph3C and 3-PhNHMe2 (Scheme 3). The trityl salt was
prepared by established methods26 from 3-Li and one equivalent
A
simple ion exchange reaction between 3-Li and
[PhNHMe2][Cl] yields another common activator type, the anilin-
ium salt 3-PhNHMe229–31 (Scheme 3) in 60% yield. Like some other
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Fig. 4 282.37 MHz 19F NMR spectra of salts 3-Li (top), 3-Ph3C (middle),
and 3-PhNHMe2 (bottom) in CD2Cl2.
Fig. 3 Solid state molecular structure of 3-Ph3C as determined by X-ray
diffraction. Thermal ellipsoids are shown at the 50% probability level
˚
and hydrogen atoms are omitted for clarity. Selected bond lengths (A):
NMR spectroscopy (Scheme 4). Reaction patterns analogous to
those reported for the reaction of Cp*(t-Bu3P N)TiMe2 with
[Ph3C]+[B(C6F5)4]- were observed. By 1H and 31P NMR spec-
troscopy, the cation is unaffected by the nature of the anion, since
all resonances for 3-TiCH3 are identical within experimental error
to those observed when the titanium-methyl cation is partnered
with the borate anion.35 Compound 3-TiCH3 was isolated as an
orange/red oil and neither a solid nor single crystals for X-ray
diffraction analysis could be obtained.34 The 31P NMR spectrum
also indicated the presence of small amounts of the m-methyl
dimeric cationic species [(Cp(t-Bu3P N)TiCH3)2(m-CH3)]+ with
peaks at d 48.9 and 48.3 ppm, representing the rac and meso
isomers of these cations.36
N1–Al1, 1.838(3); N2–Al1, 1.859(3); N3–Al1, 1.845(3); N4–Al1, 1.859(3);
C70–C71, 1.458(5); C70–C81, 1.442(5); C70–C91, 1.436(5). Interatomic
distances (A): C92–F13, 3.019(4); C82–F14, 3.062(4). Selected bond
˚
angles (◦): N1–Al1–N2, 87.62(14); N1–Al1–N3, 133.92(15); N1–Al1–N4,
106.06(14); N2–Al1–N3, 109.77(14); N2–Al1–N4, 139.89(15);
N3–Al1–N4, 87.83(13); C71–C70–C81, 119.7(4); C71–C70–C91, 118.8(4);
C81–C70–C91, 121.5(4).
anilinium salts, 3-PhNHMe2 is green-blue in color; it has been
suggested that the striking colour of anilinium salts of this type is
due to an electron-transfer process, which does not appear to affect
the activation abilities of these salts in most cases.32 The 1H NMR
spectrum of 3-PhNHMe2 in CD2Cl2 had a signal at d 14.64 ppm
assignable to the PhNHMe2 proton, shifted from d 12.46 ppm in
the anilinium chloride starting material, where there is presumably
significant hydrogen bonding to the chloride counteranion. Again,
the 19F NMR spectrum was essentially identical to the other salts
of this anion; a comparative series of spectra is shown in Fig. 4.
Although X-ray quality crystals of 3-PhNHMe2 were obtainable,
disorder in the cation and occluded solvent rendered the data of
poor quality; nonetheless, it was apparent that the aluminate anion
assumes a very similar structure to that found in ion pairs 3-Li and
3-Ph3C.
Application of WCA 3
With the activators 3-Ph3C and 3-PhNHMe2 in hand, we sought
to test the aluminate ions efficacy in a common application of
WCAs, namely in early transition metal cations active as olefin
polymerization catalysts. We chose to focus on 3-Ph3C and the
Cp*(t-Bu3P N)TiMe2 system33,34 given the well developed ion
pair chemistry of this catalyst precursor in the literature based on
the more common perfluoroarylborate WCAs.9 In addition, the
t-Bu3P N– phosphinimide ligand provides a useful and diag-
nostic 31P NMR spectroscopic handle for analysis. Accordingly,
3-Ph3C was reacted with Cp*(t-Bu3P N)TiMe2 in C6D5Br to
give 3-TiCH3 which was characterized in situ by multinuclear
Scheme 4 Activation of an organotitanium complex with 3-Ph3C.
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Previously we have shown that the ion pair [Cp*(t-
Bu3P N)TiMe]+[B(C6F5)4]- reacts with excess neo-hexene in a
catalytic dimerization reaction in which the resting state of the
catalyst is a cationic titanium alkyl where the alkyl group is
comprised of two neo-hexene monomers.37 This compound was
crystalline, but when partnered with the [B(C6F5)4]- counteranion,
the cation’s structure was disordered and could not precisely
be determined. Reaction of 3-TiCH3 with an excess of dry
neo-hexene yielded the same cation, this time partnered with
the aluminate WCA, i.e. 3-TiR, as shown in Scheme 4. The
NMR spectral signature of the cation was identical to what we
previously reported; the mechanism of formation of this species
has been described in detail elsewhere.37 Here, the large red crystals
formed upon recrystallization from bromobenzene layered with
iso-octane were analyzed successfully, with no disorder apparent;
the structure is shown in Fig. 5 along with selected metrical
parameters. The geometric parameters of the anion are again
similar to the other structures discussed above. The cation is a
rare example of a d0-olefin complex, as the carbon–carbon double
bond between C3 and C4 chelates the metal center through an
asymmetric close contact. For example, the Ti–C3 distance of
˚
˚
2.536(3) A is nearly 0.25 A shorter than the Ti–C4 distance, which
˚
is 2.782(3) A; both of these distances are longer than that of Ti–
˚
C1 (2.140(3) A), which is in the typical range for metal–alkyl
ligand bond distances in other titanium phosphinimide cations.38
The cause of the asymmetry in the binding of the olefinic moiety
to titanium may reside in the steric interactions between the t-
butyl group at the end of the alkyl chain and the Cp* ligand,
but other examples of olefin-coordination to d0 metal centres
also exhibit such asymmetry and is also a result of the lack
of p-backbonding.39,40 The phosphinimide ligand showed bond
distances for the Ti–N and P–N bonds, and the Ti–N–P bond
angle also fell within the expected range of values.33
In terms of cation–anion interactions, 3-TiR showed only one
contact between the cation and anion within the sum of the van
der Waals radii of the respective atoms. The interatomic distance
˚
of C7 and F66 lay at the edge of this range at 3.083(4) A,
˚
only 0.09 A short of the maximum van der Waals distance of
3
˚
3.17 A. This single interaction between an sp -hybridized carbon
atom at the end of an alkyl chain and a lone fluorine atom on
the anion, along with the fact that the C66–F66 s-bond on the
anion is not lengthened relative to the other C–F bonds suggests
that this interaction results from crystal packing and not from
significant charge attraction between the ions, supporting the
weakly coordinating ability of the aluminate anion 3.
Conclusions
The preparation of a new WCA based on a fully fluorinated,
chelating bis-anilido donor bonded to aluminium has been
described. Its partnering with a number of cations, including
the proton, Li+, the trityl cation and the N,N-dimethylanilinium
cation, shows that it is feasible to prepare a number of common
catalyst activators that allow for incorporation of this WCA into,
for example, known olefin polymerization catalysts. This has been
demonstrated for the half-sandwich titanium Cp-phosphinimide
system. All spectroscopic and structural data suggest that alu-
minate 3 is a very weakly coordinating anion; furthermore, it
is thermally quite stable and not prone to transferring amido
groups from Al to Ti in the ion pairs described. Its application
to the stabilization of other electrophiles is therefore promising
and worthy of further exploration.
Experimental section
Fig. 5 Solid state molecular structure of 3-TiR as determined by
X-ray diffraction; top: the cation-anion pair; bottom: the cation alone,
depicting the Ti–C3 relationship. Thermal ellipsoids are shown at
the 30% probability level and hydrogen atoms are omitted for clar-
Reagents and general procedures
All reactions involving oxygen- or moisture-sensitive processes or
materials were performed under a protective argon atmosphere
using either a glove box or on a double manifold high vacuum
line using standard techniques.41 Solvents were purchased from
Aldrich, Cambridge Isotopes, or EMD and were dried and
deoxygenated before use by the following procedures: hexanes,
tetrahydrofuran (THF), and toluene solvents were dried and
purified using the Grubbs/Dow purification system42 and stored
in evacuated 500 mL glass bombs over titanocene43 or sodium
˚
ity. Selected bond lengths (A): Ti1–N1, 1.797(2); Ti1–C1, 2.140(3);
Ti1–C3, 2.536(3); Ti1–C4, 2.782(3); P1–N1, 1.618(2); C1–C2, 1.531(5);
C2–C3, 1.491(4); C3–C4, 1.336(5); Al1–N51, 1.848(2); Al1–N52, 1.848(2);
˚
Al1–N61, 1.847(2); Al1–N62, 1.853(2). Interatomic distances (A):
C7–F66, 3.083(4). Selected bond angles (◦): Ti1–N1–P1, 172.50(16);
Ti1–C1–C2, 93.2(2); Ti1–C3–C2, 79.64(18); C2–C3–C4, 127.3(3);
C3–C4–C5, 127.8(8); N51–Al1–N52, 88.42(11); N61–Al1–N62, 87.99(10);
N51–Al1–N61, 110.31(11); N52–Al1–N62, 109.77(11); N51–Al1–N62,
133.46(11); N52–Al1–N61, 133.60(11).
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benzophenone ketal; diethyl ether, d8-toluene, d6-benzene,
iso-octane, pentane, benzene, C6D6, bromobenzene, and d5-
bromobenzene were dried and stored over sodium/benzophenone
ketal in glass bombs under vacuum. Methylene chloride and d2-
methylene chloride were pre-dried and stored over calcium hy-
(m, 2F, N-o-C6F4), -163.7 (tm, JFF = 21.5 Hz, 4F, N-m-C6F5),
-164.7 (tm, JFF = 21.4 Hz, 2F, N-p-C6F5). N-pentafluorophenyl-
3,4,5,6-tetrafluorophenylene-1,2-diamine: 1H NMR (CDCl3): d
4.93 (br s, 1H, NH), 4.12 (br s, 2H, NH2). 19F NMR (CDCl3):
d -150.1 (dd, JFF = 22.1 Hz, 7.9 Hz, 1F, NH-o-C6F4), -158.2
(dm, JFF = 20.5 Hz, 2F, NH-m-C6F5), -159.4 (t, JFF = 21.3 Hz,
1F, NH-p-C6F5), -161.8 (dt, JFF = 21.2 Hz, 7.6 Hz, 1F, NH2-o-
C6F4), -163.2 (td, JFF = 21.6 Hz, 4.5 Hz, 2F, NH-o-C6F5), -166.9
1
dride. Nuclear magnetic resonance spectroscopy (1H, 19F, 13C{ H},
1
31P{ H}, 27Al, 19F–19F COSY, 1H–19F decoupling experiments) was
performed on a Bruker AMX 300 (1H – 300.138 MHz, 19F –
282.371 MHz, 27Al – 78.171 MHz), Bruker DMX 300 (1H –
300.138 MHz, 13C – 75.465 MHz, 31P – 121.507 MHz), or Bruker
Avance DRX 400 (1H – 400.134 MHz, 19F – 376.448 MHz,
31P – 161.710 MHz) spectrometer. 13C NMR resonances are not
reported for carbon atoms bonded directly to fluorine atoms.
Microanalyses were performed using a Perkin Elmer Model 2400
Series II Elemental Analyzer. EPR experiments were performed
on a Bruker EMX10/12 with VT accessory and gaussmeter.
The compounds 3,4,5,6-tetrafluorophenylene-1,2-diamine22,44
(tt, JFF = 21.6 Hz, 4.4 Hz, 1F, NH2-m-C6F4), -173.3 (td, JFF
21.8 Hz, 6.1 Hz, 1F, NH-m-C6F4).
=
Synthesis of 2. A toluene (15 mL) solution containing 1
(216 mg, 0.422 mmol) and AlMe3 (2.0 M in toluene, 0.21 mL,
0.42 mmol) was heated at 110 ◦C for 2 h. During this time, bubbles
were observed, indicating the evolution of CH4. The solution was
cooled to room temperature and the solvent removed in vacuo
to give an off-white solid which was identified as 2 (144 mg,
1
0.130 mmol, 61.9% based on Al). H NMR (THF-d8): d -0.62
33
and Cp*(t-Bu3P N)TiMe2 were prepared according to liter-
(s, 6H, AlMe). 19F NMR (THF-d8): d -152.4 (d, JFF = 21.3 Hz, 8F,
N-o-C6F5), -162.0 (dd, JFF = 15.3 Hz, 10.2 Hz, 4F, N-m-C6F4),
ature procedures or slight variations thereof. The compound
PhNHMe2Cl was prepared by reaction of PhNMe2 with one
equivalent of ethereal HCl, the solvent was removed in vacuo,
and the precipitate was recrystallized from Et2O prior to use.
Hexafluorobenzene (C6F6) was purchased from Aldrich Chemicals
and dried twice over P2O5 under an inert atmosphere before being
vacuum transferred to a sealed bomb for storage. Trityl chloride
(Ph3CCl) was purchased from Aldrich Chemicals and sublimed
prior to use. Pentafluoronitrobenzene was purchased from Aldrich
Chemicals and used as received. All other reagents were purchased
from Aldrich Chemicals and, where appropriate, purified using
standard techniques.45
-166.8 (tm, JFF = 21.3 Hz, 8F, N-m-C6F5), -168.5 (tm, JFF
=
21.4 Hz, 4F, N-p-C6F5), -174.6 (dd, JFF = 15.0 Hz, 10.1 Hz, 4F,
N-m-C6F4).
Synthesis of 3-H. A toluene (15 mL) solution containing 1
(438 mg, 0.855 mmol) and AlMe3 (2.0 M in toluene, 0.21 mL,
◦
0.42 mmol) was heated at 110 C for 2 h, during which time the
colour of the solution changed from colourless to purple. During
this time, bubbles were observed, indicating the evolution of CH4.
The solution was cooled to room temperature and the solvent
removed in vacuo to give a purple solid, which was dissolved in
pentane and recrystallized at -35 ◦C. The resulting purple crystals
Synthesis of 1.
A
THF (40 mL) solution of 3,4,5,6-
were isolated and identified as 3 (229 mg, 0.218 mmol, 53.2%). 19
F
tetraflu◦orophenylene-1,2-diamine (439 mg, 2.44 mmol) was cooled
to -78 C under an argon atmosphere. A hexanes solution of n-
butyl lithium (1.6 M, 3.1 mL, 5.0 mmol) was added slowly to the
THF solution, and the stirring solution turned from colourless
to a bright canary yellow. The reaction was stirred for 20 min
NMR (C6D6): d -152.5 (m, 4F, N-m-C6F4), -154.7 (m, 8F, N-o-
C6F5), -161.9 (m, 4F, N-o-C6F4), -163.1 (ov m, 12F, N-m-C6F5,
N-p-C6F5).
Synthesis of 3-Li. Compound 1 (510 mg, 0.996 mmol) and
LiAlH4 (17 mg, 0.45 mmol) were weighed into a 50 mL round-
bottomed flask and connected to a swivel frit under an inert
atmosphere. Toluene (25 mL) was condensed onto the solids at
-78 ◦C and the resulting suspension was allowed to warm to room
temperature. The reaction flask was heated at 80 ◦C overnight
under argon, after which time a copious amount of suspended
white solid was present. The reaction mixture was cooled to room
temperature and filtered. The white solid was washed several times
with toluene to remove excess 1 and was dried in vacuo to afford
3-Li as a white powder (387 mg, 0.367 mmol, 81.0%). Single
crystals of 3-Li·(THF)2 were grown by layering hexanes onto a
◦
at -78 C, whereupon an excess of hexafluorobenzene (1.40 mL,
2.27 g, 12.2 mmol) was added dropwise to the solution turning
the reaction a deep red colour. The temperature of the solution
was raised to -5 ◦C and stirred overnight under argon. The
reaction was quenched with water (20 mL), and the resulting
mixture diluted with brine and dichloromethane (200 mL ea.).
The two layers were mixed thoroughly and the organic layer was
isolated, and the aqueous layer was re-extracted with 2 ¥ 200 mL
dichloromethane. The organic fractions were combined, dried over
magnesium sulfate, filtered, and the solvent was removed in vacuo
to give a dark red oily solid. Separation by column chromatogra-
phy on silica gel using 5–20% ethyl acetate in hexanes as the eluant
gave unreacted 3,4,5,6-tetrafluorophenylene-1,2-diamine (88 mg,
0.490 mmol, 20.1%), the by-product N-pentafluorophenyl-3,4,5,6-
tetrafluorophenylene-1,2-diamine (185 mg, 0.534 mmol, 21.9%),
and the target compound N,N¢-bis-pentafluorophenyl-3,4,5,6-
tetrafluorophenylene-1,2-diamine (1) as a pale pink powder. Re-
crystallization from hot hexanes gave diamine 1 as a white fibrous
solid (500 mg, 0.976 mmol, 40.0%). Anal. Cald. for C18H2F14N2: C,
42.21; H, 0.39; N, 5.47. Found: C, 42.38; H, 0.70; N, 5.58. 1H NMR
(CD2Cl2): d 5.47 (br s, 2H, NHC6F5). 19F NMR (CD2Cl2): d -152.4
(m, 2F, N-m-C6F4), -155.3 (d, JFF = 20.6 Hz, 4F, N-o-C6F5), -162.6
◦
THF solution of 3-Li and storing the solution at -35 C. Anal.
Calcd. for C36AlF28LiN4: C, 41.01; H, 0.00; N, 5.31. Found: C,
41.69; H, 0.64; N, 5.36. 19F NMR (CD2Cl2): d -151.1 (br, 8F,
N-o-C6F5), -164.4 (dd, JFF = 16.1 Hz, 11.2 Hz, 4F, N-m-C6F4),
-166.6 (ov, 12F, N-m-C6F5, N-p-C6F5), -176.1 (dd, JFF = 16.0 Hz,
11.2 Hz, 4F, N-o-C6F4).
Synthesis of 3-Ph3C. Compound 3-Li (720 mg, 0.683 mmol)
was weighed into a 2-neck 25 mL round-bottomed flask under
an inert atmosphere. A solid addition tube containing Ph3CCl
(200 mg, 0.717 mmol) connected to the flask and the apparatus was
attached to a swivel frit. Dichloromethane (15 mL) was condensed
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Dalton Trans., 2010, 39, 10256–10263 | 10261
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into the flask at -78 ◦C and the solution was allowed to warm to
room temperature, at which time the Ph3CCl was added and the
initially white solution immediately turned dark yellow-brown.
The solution was stirred for 45 min to ensure complete reaction.
The solution was then concentrated in vacuo to 8–10 mL and
filtered, and the precipitated LiCl was washed with small amounts
of CH2Cl2 until all the yellow colour passed through the frit. The
solvent was removed from the filtrate in vacuo, and n-pentane
(20 mL) was condensed onto the resulting brown oil. Subsequent
trituration and sonication gave a solid which was collected by
filtration, washed with pentane, and dried in vacuo to give 3-Ph3C
as a brown solid (638 mg, 0.494 mmol, 72.3%). Single crystals of
3-Ph3C were grown at -35 ◦C by layering 2,2,4-trimethylpentane
(iso-octane) onto a C6D5Br solution of 3-Ph3C. Anal. Calcd. for
C55H16AlF28N4: C, 51.14; H, 1.25; N, 4.34. Found: C, 50.36; H,
pentane washes were shown to contain Ph3CCH3 by H NMR
1
spectroscopy. The orange-red oil obtained was characterized as
the title compound 3-TiCH3. 1H NMR (C6D5Br): d 1.74 (s, 15H,
Cp*), 1.16 (d, JHP = 13.7 Hz, 27H, t-Bu3P N), 1.04 (s, 3H, Ti-
Me). 19F NMR (C6D5Br): d -151.2 (br, 8F, N-o-C6F5), -164.0 (br,
4F, N-m-C6F4), -166.5 (br, 12F, N-m-C6F5, N-p-C6F5), -175.0 (br,
1
4F, N-o-C6F4). 31P{ H} NMR (C6D5Br): d 55.8 (br s, t-BuP N).
Synthesis of 3-TiR. A C6H5Br (1 mL) solution of Cp*(t-
Bu3P N)TiMe2 (25 mg, 0.058 mmol) was added dropwise with
stirring to a C6H5Br (2 mL) solution of trityl salt 3-Ph3C
(78 mg, 0.060 mmol) under an inert atmosphere, whereupon the
solution colour changed to orange-red. Excess neo-hexene (~3 mL,
~400 eq.) was added to the reaction, whereupon the solution
turned a deep red colour. After stirring for 10 min at room
temperature, pentane (10 mL) was added to the reaction mixture
until a red oil separated below a brownish-orange supernatant.
The supernatant was removed and the oil washed several times
with pentane to ensure complete removal of Ph3CCH3 and other
alkane byproducts (i.e. 2,3,3-trimethylbutane and excess neo-
hexene). The oil, which had partially solidified, was re-dissolved
in C6H5Br and layered with iso-octane. Dark-red block single
crystals of 3-TiR suitable for X-ray crystal diffraction analysis
formed overnight (79 mg, 0.049 mmol, 84%). 1H NMR (C6D5Br): d
6.10 (br m, 1H, TiCH2CH(t-Bu)CH CH(t-Bu)), 5.94 (br m, 1H,
TiCH2CH(t-Bu)CH CH(t-Bu)), 3.30 (br m, 1H, TiCH2CH(t-
Bu)CH CH(t-Bu)), 2.05 (br m, 1H, TiCH2CH(t-Bu)CH CH(t-
Bu)) 1.78 (s, 15H, Cp*), 1.16 (d, 3JHP = 13.6 Hz, 27H, Pt-Bu3), 0.81
(s, 9H, TiCH2CH(t-Bu)CH CH(t-Bu)), 0.75 (s, 9H, TiCH2CH(t-
Bu)CH CH(t-Bu)). Proton TiCH2CH(t-Bu)CH CH(t-Bu) was
not located due to overlap with other signals. 19F NMR (C6D5Br):
d -151.6 (m, 8F, N-o-C6F5), -164.1 (dd, JFF = 15.1 Hz, 11.2 Hz, 4F,
N-m-C6F4), -166.1 (ov, 12F, N-m-C6F5, N-p-C6F5), -175.4 (dd,
1
1.50; N, 4.36. H NMR (CD2Cl2): d 8.31 (t, JHH = 7.5 Hz, 1H,
CparaH), 7.89 (t, JHH = 7.7 Hz, 2H, CmetaH), 7.66 (d, JHH = 8.1 Hz,
2H, CorthoH). 19F NMR (CD2Cl2): d -151.6 (m, 8F, N-o-C6F5),
-164.4 (dd, JFF = 15.8 Hz, 11.3 Hz, 4F, N-m-C6F4), -166.8 (ov,
12F, N-m-C6F5, N-p-C6F5), -175.3 (dd, JFF = 15.8 Hz, 11.2 Hz).
1
+
+
13C{ H} NMR (CD2Cl2): d 211.2 (CPh3 ), 144.4 (CPh3 ), 143.6
+
+
+
(CPh3 ), 139.8 (CPh3 ), 130.6 (CPh3 ).
Synthesis of 3-PhNHMe2. Compound 3-Li (429 mg,
0.236 mmol) was weighed into a 2-neck 25 mL round-bottomed
flask under an inert atmosphere. A solid addition tube containing
PhNHMe2Cl (37 mg, 0.24 mmol) connected to the flask and
the apparatus was attached to a swivel frit. Dichloromethane
(15 mL) was condensed into the flask at -78 ◦C and the solution
was allowed to warm to room temperature, at which time the
PhNHMe2Cl was added and the initially white solution slowly
turned blue-green. The solution was stirred for 45 min to ensure
complete reaction. The solution was then concentrated in vacuo
to 8–10 mL and filtered, and the precipitated LiCl was washed
with small amounts of CH2Cl2 until all the blue-green colour
passed through the frit. The solvent was removed from the filtrate
in vacuo, and n-pentane (20 mL) was condensed onto the resulting
blue-green oil. Subsequent trituration and sonication gave a solid
which was collected by filtration, and washed several times with
hot hexanes to remove traces of 1. The resulting material was
isolated as a blue-green solid (3-PhNHMe2) (164 mg, 0.140 mmol,
59.7%). Anal. Calcd. for C44H12AlF28N5: C, 45.19; H, 1.03; N,
5.99. Found: C, 44.63; H, 1.24; N, 5.75. 1H NMR (CD2Cl2):
1
JFF = 15.2 Hz, 11.2 Hz, 4F, N-o-C6F4). 31P{ H} NMR (C6D5Br):
d 55.0 (s, t-Bu3P N).
Crystal structure determinations. X-Ray crystallographic
analyses were performed on suitable crystals coated in Paraton
8277 oil (Exxon) and mounted on a glass fibre. Measurements
were collected on a Nonius Kappa CCD diffractometer at the
University of Calgary or a Bruker P4/RA/SMART 1000 CCD
diffractometer at the University of Alberta. CCDC deposition
numbers 784055–784058 contains the supplementary crystallo-
graphic data for compounds 2, 3-Li, 3-Ph3C, and 3-TiR in this
paper.†
+
+
d 12.46 (s, 1H, PhNHMe2 ), 7.45 (m, 2H, PhNHMe2 ), 7.33
+
+
(m, 2H, PhNHMe2 ), 7.23 (m, 1H, PhNHMe2 ), 3.14 (br, 6H,
PhNHMe2 ). 19F NMR (CD2Cl2): d -151.1 (m, 8F, N-o-C6F5),
+
Acknowledgements
-164.2 (dd, JFF = 15.3 Hz, 11.1 Hz, 4F, N-m-C6F4), -166.5 (ov,
12F, N-m-C6F5, N-p-C6F5), -175.7 (dd, JFF = 15.4 Hz, 11.0 Hz,
Funding for this work was provided by NSERC of Canada through
Discovery and CRD grants to WEP and a CGS-M scholarship to
JCS, and Nova Chemicals, Inc. of Calgary, Alberta.
1
+
4F, N-o-C6F4). 13C{ H} NMR (CD2Cl2): d 147.4 (PhNHMe2 ),
+
+
+
131.5 (PhNHMe2 ), 130.1 (PhNHMe2 ), 122.5 (PhNHMe2 ), 48.0
+
(PhNHMe2 ).
Synthesis of 3-TiCH3. A C6H5Br (1 mL) solution containing
Cp*(t-Bu3P N)TiMe2 (20 mg, 0.047 mmol) was added dropwise
with stirring to a C6H5Br (2 mL) solution of the trityl salt 3-Ph3C
(63 mg, 0.049 mmol) under an inert atmosphere. After 5 min,
pentane (5 mL) was added to the reaction mixture and an orange-
red oil settled to the bottom of the vessel. The supernatant was
removed and the oil washed twice more with fresh pentane to
ensure complete removal of organic byproducts; the combined
References
1 S. Strauss, Chem. Rev., 1993, 93, 927.
2 C. A. Reed, Acc. Chem. Res., 1998, 31, 133.
3 I. Krossing and I. Raabe, Angew. Chem., Int. Ed., 2004, 43, 2066.
4 I. Krossing and A. Reisinger, Coord. Chem. Rev., 2006, 250, 2721.
5 C. A. Reed, Acc. Chem. Res., 2010, 43, 121.
6 T. Chivers and J. Konu, Comments Inorg. Chem., 2009, 30, 131.
7 M. Bochmann, Coord. Chem. Rev., 2009, 253, 2000.
8 W. E. Piers, Adv. Organomet. Chem., 2005, 52, 1.
10262 | Dalton Trans., 2010, 39, 10256–10263
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
9 E. Y.-X. Chen and T. J. Marks, Chem. Rev., 2000, 100, 1391.
10 W. E. Piers and T. Chivers, Chem. Soc. Rev., 1997, 26, 345.
11 M. Bochmann, Organometallics, 2010, DOI: 10.1021/om1004447,
ASAP .
29 G. Rodriguez and P. Brant, Organometallics, 2001, 20, 2417.
30 J. Zhou, S. J. Lancaster, D. A. Walker, S. Beck, M. Thornton-Pett and
M. Bochmann, J. Am. Chem. Soc., 2001, 123, 223.
31 L. Jia, X. Yang, A. Ishihara and T. J. Marks, Organometallics, 1995,
14, 3135.
12 T. J. Barbarich, S. T. Handy, S. M. Miller, O. P. Anderson, P. A. Grieco
and S. H. Strauss, Organometallics, 1996, 15, 3776.
13 M. V. Metz, Y. Sun, C. L. Stern and T. J. Marks, Organometallics, 2002,
21, 3691.
32 N. Bavarian and M. C. Baird, Dalton Trans., 2004, 4089.
33 D. W. Stephan, J. C. Stewart, F. Guerin, S. Courtenay, J. Kickham, E.
Hollink, C. Beddie, A. Hoskin, T. Graham, P. Wei, R. E. v. Spence, W.
Xu, L. Koch, X. Gao and D. G. Harrison, Organometallics, 2003, 22,
1937.
34 D. W. Stephan, Organometallics, 2005, 24, 2548.
35 K. Ma, W. E. Piers, Y. Gao and M. Parvez, J. Am. Chem. Soc., 2004,
126, 5668.
36 L. Cabrera, E. Hollink, J. C. Stewart, P. Wei and D. W. Stephan,
Organometallics, 2005, 24, 1091.
37 D. M. Friesen, W. E. Piers and M. Parvez, Organometallics, 2008, 27,
6596.
14 I. Krossing, Chem.–Eur. J., 2001, 7, 490.
15 I. Krossing and A. Reisinger, Eur. J. Inorg. Chem., 2005, 1979.
16 I. Krossing, H. Brands, R. Feuerhake and S. Koenig, J. Fluorine Chem.,
2001, 112, 83.
17 C. Cornelissen, G. Chan, J. Masuda and D. W. Stephan, Can. J. Chem.,
2007, 85, 135.
18 A. Khvorost, P. L. Shutov, K. Harms, J. Lorberth, J. Sundermeyer, S.
S. Karlov and G. S. Zaitseva, Z. Anorg. Allg. Chem., 2004, 630, 885.
19 R. Koppang, J. Organomet. Chem., 1972, 46, 193.
20 P. G. Hayes, G. C. Welch, D. J. H. Emslie, C. L. Noack, W. E. Piers and
M. Parvez, Organometallics, 2003, 22, 1577.
38 P. Voth, C. Fraser, T. Graham, C. Zhu, J. Gauld and D. W. Stephan,
Organometallics, 2006, 25, 4779.
21 R. Koppang, Acta Chem. Scand., 1971, 25, 3872.
22 A. Heaton, M. Hill and F. Drakesmith, J. Fluorine Chem., 1997, 81,
133.
23 J. Klosin, G. R. Roof, E. Y.-X. Chen and K. A. Abboud,
Organometallics, 2000, 19, 4684.
24 M. V. Barybin, V. G. Young, Jr. and J. E. Ellis, J. Am. Chem. Soc., 1998,
120, 429.
25 J. D. Hoefelmeyer and F. P. Gabba¨ı, J. Am. Chem. Soc., 2000, 122, 9054.
26 L. Jia, X. Yang, C. L. Stern and T. J. Marks, Organometallics, 1997, 16,
842.
39 G. Erker, R. Noe, C. Krueger and S. Werner, Organometallics, 1992,
11, 4174.
40 J.-F. Carpentier, Z. Wu, C. W. Lee, S. Stro¨mberg, J. N. Christopher and
R. F. Jordan, J. Am. Chem. Soc., 2000, 122, 7750.
41 B. J. Burger and J. E. Bercaw, Experimental Organometallic Chemistry,
American Chemical Society, Washington, D.C., 1987.
42 A. B. Pangborn, M. A. Giardello, R. H. Grubbs, R. K. Rosen and F. J.
Timmers, Organometallics, 1996, 15, 1518.
43 J. E. Bercaw and H. H. Brintzinger, J. Am. Chem. Soc., 1971, 93,
2046.
27 A. Bondi, J. Phys. Chem., 1964, 68, 441.
28 CCDC, Element Data and Radii, http://www.ccdc.cam.ac.uk/
products/csd/radii/, accessed March 15, 2008.
44 G. M. Brooke, J. Burdon and J. C. Tatlow, J. Chem. Soc., 1961, 802.
45 D. D. Perrin and W. L. F. Armarego, Purification of Laboratory
Chemicals, Pergamon Press, Toronto, 1988.
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 10256–10263 | 10263
©