Group IV coordination chemistry of a tetradentate redox-active ligand in two oxidation states

Article abstract of DOI:10.1002/ejic.200800945

The redox-active ligand N,N′-bis(3,5-di-tert-butyl-2-phenoxy)-1,2- phenylenediamide [N₂O₂^red]^4- reacts with group IV metal salts to form six- and seven-coordinate complexes [N ₂O₂^red

Full text of DOI:10.1002/ejic.200800945

FULL PAPER
DOI: 10.1002/ejic.200800945
Group IV Coordination Chemistry of a Tetradentate Redox-Active Ligand in
Two Oxidation States
[a]
[a]
[a]
[a]
Karen J. Blackmore, Neetu Lal, Joseph W. Ziller, and Alan F. Heyduk*
0
Keywords: Redox-active ligands / Oxidation / N,O ligands / d metals / Macrocyclic ligands
The redox-active ligand N,NЈ-bis(3,5-di-tert-butyl-2-phen- nium metal center, only two pyridine solvent molecules coor-
red 4–
oxy)-1,2-phenylenediamide [N
2
O
2
]
reacts with group IV
dinate to the metal atom, leaving an open coordination site.
metal salts to form six- and seven-coordinate complexes
All three complexes react with halogen oxidants to afford
oxidative addition products [N O ]MCl L (M = Ti, n = 0;
2 2 2 n
red
ox
[
N
2
O
2
]ML
n
(M = Ti, L = py, n = 2; M = Zr, Hf, L = thf, n =
3
). The redox-active ligand occupies four equatorial coordi-
M = Zr, Hf, L = thf, n = 1), in which the redox-active ligand
is oxidized by two electrons to the cyclohexadienediimine
state.
nation sites in these complexes. In the case of the zirconium
and hafnium complexes, two axial solvent molecules coordi-
nate to the metal center with a third solvent molecule coordi- (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
nating in the equatorial plane. In the case of the smaller tita-
Germany, 2009)
with Zr[ap] (thf)
{[ap]2– = 4,6-di-tert-butyl-2-(tert-butyl-
2 2
Introduction
amido)phenolate}, resulting in ligand oxidation and halide
addition to the metal atom. This reaction resembles a tradi-
tional oxidative addition sequence in that the halides add to
the metal center; however, it is differentiated by the formal
assignment of the reducing equivalents, which come from
the amidophenolate ligands. Despite the success of this re-
action with zirconium and hafnium, similar reactions with
titanium were not successful due to ligand-exchange dy-
namics on the titanium center, which led to valence dispro-
portionation and dissociation of the redox-active ligands.
To overcome this limitation of bidentate, catecholate-type
ligands, we became interested in the coordination and reac-
tion chemistry of N,NЈ-bis(3,5-di-tert-butyl-2-phenoxy)-1,2-
Redox-active ligands derived from catechol and related
organic functionalities offer an intriguing way to approach
multi-electron reactivity at a well-defined metal complex.
For example, mid-transition metal catecholate and ortho-
amidophenolate complexes act as catalysts for oxidation re-
[
1]
actions with O2. Zirconium(IV) ene-diamide complexes
have been shown to react reversibly with O to form zirconi-
2
um(IV) bis(peroxide) complexes with concomitant oxi-
dation of the ene-diamide ligands to the corresponding α-
diimine oxidation state.[ Iridium amidophenolate com-
plexes have been developed into molecular catalysts for hy-
2]
[
3]
drogen oxidation. Bis(imino)pyridine ligands have been
found to be non-innocent in a variety of transition-metal
complexes, and in one case this behaviour leads to unusual
red 4–
phenylenediamide ([N O ] , Scheme 1), with electro-
2
2
0
philic d metals.
[4]
N activation at a single iron center. In another multi-
red
2
The [N O2 ]H ligand was first reported by Wieghardt
2 4
electron reaction, four-electron oxidation of a tantalum
imido dimer with redox-active ligands resulted in the release
of an organic diazene.[ We have been interested in de-
veloping further the coordination and reaction chemistry of
redox-active ligands with early transition metals in order
to bring late-transition-metal reactions, such as oxidative
addition, reductive elimination, and group transfer, to elec-
and co-workers, who studied complexes of the ligand with
copper and zinc. Electrochemical and spectroscopic data
[8]
5]
showed that up to four electrons could be removed from
the ligand platform with the two-electron oxidized form
represented as the cyclohexadienediimine as shown in
Scheme 1. The copper and zinc complexes serve as catalysts
for the aerobic oxidation of primary alcohols under mild
conditions. This reaction is remarkable, especially for zinc,
0
trophilic d metal complexes.
Oxidative addition and reductive elimination have been
which is a redox-inactive metal.
established as viable reaction pathways for group IV redox-
red 4–
Whereas the [N O2
]
ligand can be viewed as a dimer
2
active ligand complexes.,[
6,7]
Halogens were found to react
of two bidentate ortho-amidophenolate ligands, it has sev-
eral features that might add stability and increase reducing
power relative to the simpler derivatives. The two amido-
[
a] Department of Chemistry, University of California,
red 4–
phenolate groups of the [N O2
]
ligand are connected to
2
Irvine, CA 92697, USA
Fax: 1-949-824-2210
ortho positions of a phenyl ring, resulting in a π system
that is conjugated over three six-membered rings. Simple
E-mail: aheyduk@uci.edu
Eur. J. Inorg. Chem. 2009, 735–743
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
735

K. J. Blackmore, N. Lal, J. W. Ziller, A. F. Heyduk
FULL PAPER
Results and Discussion
Reduced-Ligand Complexes
The condensation of 2 equiv. of 3,5-di-tert-butylcatechol
with phenylenediamine affords the redox-active, tetraden-
red
tate [N O2 ]H ligand as first reported by Wieghardt and
2
4
[
8]
co-workers.
In their synthesis, the authors isolated
red
[
N O ]H as a pale yellow solid, which was analytically
2 2 4
red
pure. In our hands, [N O2 ]H prepared in this way gave
2
4
unreliable metallation results with group IV metals, and
products often were contaminated with paramagnetic impu-
rities that could not be separated from the desired products.
As such, we have added a purification step to the synthesis
red
of [N O2 ]H . When the pale-yellow, crude product was
2
4
dissolved in diethyl ether, it formed a yellow solution, which
was filtered through a plug of silica gel. Following diethyl
ether removal, the pale blue residue was washed with cold
red
pentane to afford [N O ]H as a pure white powder. Puri-
2
2
4
red
fication of [N O2 ]H in this way only resulted in the loss
2
4
of 1–2% of the crude material, but gave much more reliable
syntheses of the following coordination complexes.
red
Metallation of [N O2 ]H with group IV metals was
2
4
readily achieved by using solvent adducts of the metal tetra-
chloride salts as shown in Scheme 2. All four acidic protons
red
of [N O2 ]H may be removed with nBuLi, providing an
2
4
easy metathesis metallation route for the halide salts of tita-
nium, zirconium, and hafnium. In the case of titanium, ad-
dition of solid TiCl (thf) to a cold diethyl ether solution
4
2
red
of [N O2 ]Li resulted in a color change to deep red with
2
4
concomitant precipitation of LiCl as a white solid. After
red
Scheme 1. Oxidation states of the [N
ported in ref.
2
O
2
] ligand platform as re- filtration and solvent removal, the product, [N
2
O
2
]Ti-
[
8]
(
thf) (1a), was obtained as red crystals from pentane in
2
red
modest yields. Similarly, the bis(pyridine) adduct, [N O2 ]-
2
Ti(py) (1b), was isolated as purple crystals by using the
2
TiCl (py) starting material. In the cases of zirconium and
4
2
red
hafnium, reactions of [N O ]Li and MCl (thf) (M = Zr,
extended Hückel calculations suggest that the HOMO of Hf) gave [N O2 ]Zr(thf) (2) and [N O ]Hf(thf) (3), as
ligand resides mainly on this linking phen- yellow microcrystalline solids from diethyl ether.
ylenediamine group, and as such two-electron oxidation X-ray crystallography was used to establish the coordina-
would lead to a stable cyclohexadienediimine species as tion geometry of complexes 1–3. As shown in Figure 1, tita-
2
2
4
4
2
red
red
2
3
2
2
3
red 4–
the [N O
]
2
2
red 4–
shown in Scheme 1. Furthermore, the [N O
]
ligand co- nium complex 1b is a six-coordinate complex; selected bond
2
2
ordinates to transition metal atoms as a tertradentate che- lengths and angles can be found in Table 1. Complex 1b is
late, which should engender stability to the metal complexes a severely distorted octahedron, owing to the constrained
red 4–
regardless of ligand oxidation state. This feature should geometry imposed by the [N O2
]
ligand. The sum of
2
stop disproportionation of ligand valence states and subse- the three angles encompassed by the ligand is 233°, leaving
quent ligand dissociation events that have hampered further a rather open site between the two oxygen atoms of the
development of group IV metal chemistry with redox-active ligand [O–Ti–O 126.95(8)°]. Whereas the titanium center
red 4–
ligands. In this paper, we report the synthesis and charac- and four heteroatom donors of the [N O2
]
ligand are
2
terization of titanium, zirconium, and hafnium complexes nearly coplanar, the rest of the ligand framework shows a
red 4–
of the [N O
]
ligand, along with chlorine-based oxi- distinct ruffle, which tilts the central phenylenediamine ring
2
2
dation chemistry leading to the formation of oxidative ad- up and the two aminophenol rings down. The Ti–O and
ox 2–
[9]
red 4–
dition products with the [N O
]
ligand. This work is Ti–N bond lengths for the [N O2
]
ligand are consistent
2
2
2
the first full report on the coordination chemistry of this with these groups coordinating as phenoxide and anilide,
tetradentate, redox-active ligand platform for electrophilic respectively. The coordination sphere of 1b is completed by
0
d metals, and it established the structural and electronic two axial pyridine molecules, which are bent towards the
features of the metal complexes for two ligand oxidation open section of the equatorial plane, resulting in an N–Ta–
states.
N angle of 164.70(9)°.
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 735–743

Group IV Coordination Chemistry of a Redox-Active Ligand
red]ML
(1–3) and [N
2 2 2 n
O L (4–6).
ox]MCl
Scheme 2. Syntheses of redox-active ligand complexes [N
2
O
2
n
2 2
O (4a)
ox]TiCl
Table 1. Selected bond lengths and angles for [N
2
ox
and [N
2
O
2
]ZrCl
2
(thf) (5).
Bond lengths [Å]
red]Ti(py)
(4b)
2 2 2
[N O (4a)
ox]TiCl
[N
2
O
2
2
Ti–O(1)
Ti–O(2)
Ti–N(1)
Ti–N(2)
Ti–Cl(1)[
Ti–N(3)
Ti–N(4)[
1.9275(18)
1.9185(18)
2.002(2)
1.996(2)
–
2.217(2)
2.220(2)
1.873(2)
–
2.114(3)
–
2.3580(12)
–
–
a]
a]
Bond angles [°]
red
2 2 2
[N O (4a)
ox]TiCl
[N
2
O
2
]Ti(py)
2
(4b)
O(1)–Ti–N(1)
O(2)–Ti–N(2)
N(1)–Ti–N(2)
O(1)–Ti–O(2)[
N(3)–Ti–N(4)
78.68(8)
78.86(8)
75.66(9)
126.95(8)
164.70(9)
–
79.01(11)
–
[
b]
75.83(16)
126.17(15)[
–
b]
a]
Cl(1)–Ti–Cl(1)Ј
174.87(6)
[
a] N(3) and N(4) are pyridine nitrogen atoms. [b] Angle between
symmetry-equivalent N(1) and O(1) atoms, respectively.
parison an ORTEP plot is shown in Figure 1 alongside the
titanium congener. The coordination geometry of complex
Figure 1. ORTEP diagrams for [N
Zr(thf) (2). Ellipsoids are drawn at 50% probability. Hydrogen is coordinated in the equatorial plane, resulting in a pentag-
atoms and solvent molecules are excluded for clarity.
red]Ti(py)
red] 2 is similar to that of 1b; however, a third solvent molecule
2 2 2 2 2
O (1b) and [N O
3
onal-bipyramidal structure. By virtue of the larger zirco-
red 4–
nium radius, the [N O2
]
ligand occupies a smaller frac-
2
Zirconium and hafnium complexes, 2 and 3, respectively, tion of the equatorial plane around the zirconium center,
adopt a seven-coordinate geometry in the solid state. The which opens the O–Zr–O angle by 20° to 143° in 2, allowing
structure of 2 has been reported previously,[ but for com- the coordination of a third thf molecule. As such the angle
9]
Eur. J. Inorg. Chem. 2009, 735–743
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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737

K. J. Blackmore, N. Lal, J. W. Ziller, A. F. Heyduk
FULL PAPER
between the axial thf molecules opens to 175° reflecting the visible region of the spectrum. The titanium–pyridine ad-
more crowded equatorial plane. The Zr–O bond lengths to duct 1b shows a further absorbance at 530 nm (ε =
3
–1
–1
the coordinated thf molecule provide further evidence of 3ϫ10  cm ), consistent with ligand-to-ligand charge-
steric crowding in the equatorial plane of 2 [Zr–Oaxial transfer transitions observed in other group IV pyridine
2.235(4) and 2.252(4) Å; Zr–Oequatorial 2.369(4) Å], suggest- complexes. This absorbance likely leads to the purple colour
ing that the third thf ligand is weakly bound. All other Zr– observed for solid samples of 1b.
O and Zr–N bond lengths are in the expected range of
phenoxides and anilides bound to a zirconium atom. In the
case of hafnium derivative 3, only weakly diffracting crys-
tals were obtained after repeated crystallization attempts.
Oxidized-Ligand Complexes
red 4–
As such the diffraction data for 3 were of poor quality.
To evaluate the ability of the [N O
]
ligand to sup-
2
2
0
While this data could confirm a seven-coordinate geometry port redox reactivity at d transition metals, chlorine-based
analogous to zirconium complex 2, it was not suitable for oxidations were carried out with complexes 1–3 (Scheme 2).
examination of detailed structural features.
Previous attempts to carry out halogen oxidation reactions
Solution characterization data for 1–3 from NMR spec- with titanium complexes of redox-active ligands resulted in
[
10]
troscopy was consistent with the solid-state structural data. messy ligand disproportionation reactions.
We hoped
1
red 4–
The H NMR spectra of titanium derivatives 1a and 1b in that the tetradentate nature of the [N O2
]
ligand would
2
C D are identical, save for the resonances associated with prevent disproportionation and dissociation of the redox-
6
6
the coordinated thf and pyridine ligands, respectively. No- active ligand upon halogen oxidative addition. Thus, the
tably, the four protons of the ortho-phenylenediamide ring addition of the chlorine surrogate PhICl to a solution of
2
in 1a and 1b appear as two doublet-of-doublet resonances 1a in diethyl ether resulted in a rapid color change to dark
at δ = 6.75 and 7.30 ppm, whereas the aromatic protons of green. Storage of the reaction mixture at –35 °C overnight
the ortho-amidophenolate rings appear as two doublets at δ resulted in the precipation of dark green crystals identified
ox
=
7.06 and 7.35 ppm. Two resonances are observed for the as [N O2 ]TiCl (4a) in modest yields. A similar reaction
2 2
coordinated thf molecules of 1a at δ = 1.26 and 4.29 ppm, between PhICl and pyridine adduct 1b afforded the related
2
ox
which are shifted by less than 1 ppm from those of free thf complex [N O2 ]TiCl (py) (4b). Analogous reactivity was
2
2
in C D ; similarly small shifts are observed for the proton observed for zirconium and hafnium complexes 2 and 3,
6
6
ox
ox
resonances of the coordinated pyridine molecule in 1b. which afforded [N O2 ]ZrCl (thf) (5) and [N O2 ]-
2
2
2
Overall, the NMR spectroscopic data for complexes 1a and HfCl (thf) (6), respectively, upon treatment with PhICl .
2
2
1b is consistent with approximate C2v symmetry in solution. Attempts to generate odd-electron species through the ad-
Zirconium and hafnium derivatives 2 and 3 gave analo- dition of 0.5 or 1.5 equiv. of PhICl resulted only in reduced
2
gous NMR spectra, which were nearly superimposable. De- yields of the two-electron oxidized products 4–6.
spite the increase in coordination number to seven observed The solid-state structures of complexes 4a and 5 were
1
for 2 and 3, the H NMR resonances for the ortho-phenyl- interrogated by single-crystal X-ray diffraction methods.
enediamide ring shift further downfield to δ = 7.00 and Figure 2 gives ORTEP diagrams derived from the X-ray dif-
7
.88 ppm, suggesting a more electrophilic metal center. fraction data for complexes 4a and 5; selected metrical pa-
1
Only two H NMR resonances are observed for the coordi- rameters for 4a are shown in Table 1. The coordination en-
nated thf molecules; moreover, whereas the signal of the vironment in 4a is similar to that observed for 1a in that
protons on the β-carbon atom are shifted upfield to δ = the titanium center is six-coordinate with the redox-active
0.83 ppm, those protons on the α-carbon atom resonate ligand occupying four equatorial positions. In the case of
close to the frequency of free thf at δ = 3.79 ppm. Similarly, 4a, however, chlorido ligands from the halogen oxidation
1
3
only two C NMR resonances were observed for the coor- occupy the metal atom’s axial positions. The zirconium oxi-
dinated thf molecules in 3, whereas no signals attributable dation product 5 is structurally analogous to the reduced
1
3
to thf were observed in the C NMR spectrum of 2. These complex 2, except for the coordination of axial chlorido
NMR results are consistent with rapid exchange of the axial ligands in the place of thf molecules. As observed in 2, the
and equatorial thf ligands of 2 and 3 on the NMR time- coordination of a thf ligand in the equatorial plane of 5
scale, which probably proceeds through dissociation of a thf creates a crowded environment, which is reflected in a long
ligand. Further evidence for such an exchange process was Zr–O(thf) bond of 2.265(5) Å.
obtained for NMR spectra in [D ]thf, which showed instant
X-ray diffraction studies also provide unequivocal evi-
dence for ligand oxidation accompanying halide addition to
8
exchange of coordinated [H ]thf for the [D ]thf.
8
8
The electronic spectra of complexes 1–3 are remarkably the titanium center in complex 4a.[11] The Ti–Cl bond
similar, even though their solid-state colors vary from near- length in 4a is consistent with a chloride ion bound to a
ly colorless for hafnium complex 3 to purple for titanium titanium(IV) metal center. As shown in Table 1 the ligand–
complex 1b. The UV/Vis absorbance spectra of 1–3 are titanium angles for the redox-active ligand in 4a are nearly
dominated by an intense UV absorbance at 330 nm (ε ≈ identical to the values observed in 1b; however, the Ti–O
4
–1
–1
1
0  cm ), analogous to that reported for the copper(II) and Ti–N bond lengths are significantly different. A small
red
II 2– [8]
dianion, {[N O ]Cu } . Titanium derivatives 1a and contraction is observed in the Ti–O bond lengths, whereas
2
2
1b both show a shoulder at 380 nm, which tails into the an elongation of over 0.1 Å is observed in the Ti–N bond
738
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 735–743

Group IV Coordination Chemistry of a Redox-Active Ligand
2 2 2 2 2
O (4a) and [N O
ox]TiCl ox]-
Figure 2. ORTEP diagrams for [N
ZrCl (thf) (5). Ellipsoids are drawn at 50% probability. Hydrogen
atoms and solvent molecules are excluded for clarity.
2
Figure 3. Redox-active-ligand bond lengths from the X-ray crystal
red
ox
structures of (a) [N
2
O
2
2 2 2 2
]Ti(py) (1b) and (b) [N O ]TiCl (4a).
tert-Butyl groups, chlorido ligands, and coordinated solvent mole-
cules are omitted for clarity.
lengths of 4a. These bond length changes are consistent
with the nitrogen atoms acting as neutral imine donor in 4a,
1
and the oxygen atoms acting as anionic phenolate donors. room-temperature H NMR spectrum the pyridine protons
Figure 3 compares redox-active-ligand bond lengths from appeared as sharp triplets and singlets, suggesting that the
the structures of 1b and 4a. The C–C bond lengths within complex is seven-coordinate and static on the NMR time-
the redox-active ligand of 1b fall in the 1.39–1.41 Å range scale.
(Figure 3a), as expected for aromatic phenyl rings. In con-
In the case of zirconium dichloride complex 5 and haf-
1
trast, the central, six-membered ring of the redox-active li- nium dichloride complex 6, the H NMR spectra are indis-
gand in 4a (Figure 3b) shows C–C bond lengths that alter- tinguishable, except for the peak shape of the resonances
nate between 1.35 Å and 1.44 Å, indicative of a non-aro- for the coordinated thf molecule. In hafnium complex 6, the
matic, cyclohexadiene ring. Whereas some C–C bond- thf protons resonate as relatively sharp singlets at δ = 1.59
length variation is also observed in the ortho-amidophenol- and 4.75 ppm; in zirconium complex 5, the thf proton reso-
ate rings of 4a, the difference is much smaller and within nances are broadened significantly, suggesting that ex-
the error of the experimental measurement. The crystallo- change is occurring on the NMR timescale. This contention
graphic bond lengths observed in the structure of 4b suggest is further supported by the 13C NMR spectroscopic data.
ox
that the best resonance structure for [N O ]TiCl is that The thf carbon resonances were readily observed at δ = 25.3
2
2
2
depicted in Figure 3, namely a cyclohexadienediimine. Sim- and 74.2 ppm for 6, whereas the same resonances for 5 were
ilar metrical parameters are observed in the crystal struc- broadened into the spectral baseline.
ox
ture of 5, consistent with the formulation [N O2 ]-
Distinct changes in color accompanied the chlorine oxi-
2
ZrCl (thf).
dations of 1–3, prompting an investigation of the UV/Vis
2
NMR spectra of 4–6 show further evidence of ligand oxi- absorbance spectra of products 4–6. Figure 4 shows the
1
dation. The H NMR spectrum of 4a showed changes diag- room-temperature UV/Vis absorbance spectra of complexes
nostic for ligand oxidation in the aromatic portion of the 4–6 in thf. The spectra for zirconium complex 5 and haf-
spectrum. Notably, one proton resonance for the cyclo- nium complex 6 are dominated by an intense absorbance
4
–1
–1
hexdienediimine ring shifts upfield by 0.2 ppm to δ = near 937 nm (ε = 2.0ϫ10  cm ), with a high-energy
6.5 ppm, whereas the other proton resonance shifts down- shoulder near 750 nm, resulting in the observed dark-green
field by 0.3 ppm to δ = 7.6 ppm. In the case of the amino- color for the oxidized complexes. These absorbances are
phenolate rings, the two aromatic resonances of 4a shift consistent with ligand-based, π Ǟ π* transitions. The low-
downfield by 0.3–0.5 ppm relative to the same resonances energy absorbance for titanium complexes 4a and 4b (not
1
13
in 1a. The H and C NMR spectra of 4b are virtually shown) is slightly redshifted (λ
= 947 nm; ε =
max
4
–1
–1
the same as those observed for 4a, with the exception of 1.3ϫ10  cm ) relative to the zirconium and hafnium
resonances for the coordinated pyridine molecule. In the derivatives. Complexes 4a and 4b also show a strong transi-
Eur. J. Inorg. Chem. 2009, 735–743
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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739

K. J. Blackmore, N. Lal, J. W. Ziller, A. F. Heyduk
FULL PAPER
4
–1
–1
tion to higher energy at 427 nm (ε = 1.55ϫ10  cm ). A zirconium species identified for the reaction were dichloride
similar transition is observed in the zirconium and hafnium 5 and the unreacted zirconium starting material. Hence, the
sq1
complexes, albeit with a much lower intensity (λ
=
putative one-electron product, [N O2 ·]ZrClL , could not
max
2 2
3
–1
–1
460 nm, ε = 3ϫ10  cm ).
be isolated (although this does not preclude its formation
either as an intermediate or as a minor product).
In addition to the increased stability of metal complexes
ox 2–
of the [N O2
]
ligand, the geometry enforced by the li-
2
gand platform may have important implications for both
stoichoimetric and catalytic reactions. Superficially, the
[
N O ] ligand platform resembles a salen-type ligand. In the
2 2
ox 2–
case of the two-electron oxidized form, [N O2 ] , this re-
2
semblance extends to the ligand being isoelectronic with
ox 2–
salen ligands, as [N O2
]
has two neutral imine donors
2
and two anionic phenoxide donors. Whereas salen-type li-
gands typically form six-coordinate complexes with titani-
[
13]
um(IV),
seven-coordinate complexes are often observed
for complexes of the larger metals zirconium and haf-
[
14]
nium.
In the [N O ] ligand platform, the formation of
2 2
three five-membered chelates upon metal coordination re-
sults in access to seven-coordinate geometries for all three
metal ions. In the case of zirconium derivatives 2 and 5,
these seven-coordinate species are fluxional on the NMR
timescale. Rapid exchange of the equatorial ligand in these
Figure 4. UV/Vis absorbance spectra for [N
2
O
2
ox]TiCl
(thf) (6) in thf solution
2
(4a), seven-coordinate complexes provides an entry point for the
ox
ox
[
N
2
O
2
]ZrCl
2
(thf) (5), and [N
2
O
2
]HfCl
2
[9]
addition of substrates to the metal center, and such ad-
at room temperature.
ditions may be exploited for stoichiometric and catalytic
atom- and group-transfer studies.
Conclusions
Experimental Section
red 4–
ox 2–
The [N O ] /[N O ]
2
ligand platform provides a ro-
2
2
2
General Experimental Considerations: The complexes described be-
low are extremely air- and moisture-sensitive. Except where noted,
all manipulations were carried out under argon or nitrogen gas
0
bust framework for two-electron chemistry at d metal cen-
ters. Previous efforts in our research group focused on the
redox chemistry of zirconium with bidentate ortho-amido- by using standard Schlenk, vacuum-line, and glovebox techniques.
2
–
phenolate ligands ([ap] ). Whereas oxidative addition and High-purity solvents were first sparged with argon and then passed
0
reductive elimination chemistry were realized for d metal through activated alumina and Q5 columns to remove water and
4 4 4
oxygen, respectively. The metal salts TiCl , ZrCl , and HfCl (Alfa-
Aesar) and 3,5-di-tert-butylcatechol (Acros) were used as received.
ortho-Phenylenediamine (Alfa-Aesar) was purified by vacuum sub-
centers, the chemistry was always dominated by the imino-
semiquinonate ([isq·] ) oxidation state of the ligand, which
shows surprising stability, even in its neutral, protonated
–
limation. The starting materials TiCl
thf) , and PhICl were synthesized according to published pro-
cedures.
4 2 4 2 4
(thf) , ZrCl (thf) , HfCl -
form. Whereas oxidized complexes of the form ZrX (isq·)2
2
(
2
2
could be obtained by halogen oxidative addition reactions,
[15,16]
1
13
All complexes were characterized by H and
C
similar species were not accessible for titanium derivatives,
NMR spectroscopy, IR spectroscopy, and elemental analysis. NMR
spectra were collected with Bruker Avance 500 or 600 MHz spec-
[10]
where a titanium(III) oxidation state is viable. In the tita-
nium case, a valence tautomerization[ could give TiIII and trometers in either [D ]benzene or [D ]thf solvents that were de-
12]
6
8
an iminoquinone ligand (iq), which would readily dissociate gassed by several freeze-pump-thaw cycles, dried with sodium
0
1
from the d metal center. In contrast, the tetradentate benzophenone ketyl radical, and vacuum-distilled before use.
H
ox 2–
and 13C NMR spectra were referenced to TMS by using the resid-
[
N O
2
]
ligand cannot dissociate, even if a valence tauto-
merization is established.
2
1
13
ual H and natural abundance C impurities of the solvent. All
chemical shifts are reported by using the standard δ notation in
parts per million. IR spectra were recorded with a Perkin–Elmer
Spectrum One spectrophotometer as KBr pellets. Elemental analy-
ses were provided by Desert Analytics or Schwarzkopf Microana-
lytical Laboratory, Inc.
–
iq
TiIV ↔ TiIII [isq·][iq] Ǟ TiIIIX [isq·] ↔ TiIV
X [isq·] X X [ap]
2 2 2 2 2 2
Given the well-defined electrochemistry of metal com-
plexes of the [N O2
ox 2–
[8]
]
ligand (Scheme 1), it was surpris-
2
ing that one- and three-electron oxidation products could
not be isolated for titanium, zirconium, and hafnium. When
N,NЈ-Bis(3,5-di-tert-butyl-2-hydroxyphenyl)-1,2-phenylenediamine
red
red
(
[N
2
O
2
]H
4
): The [N
2
O
2
4
]H ligand was prepared according to
0
.5 equiv. of PhICl or 1.5 equiv. of PhICl was added to
2 2
the procedure reported by Wieghardt and co-workers with minor
complexes 1–3, only a reduced yield of the two-electron
[8]
modifications that lead to a higher-purity product. Freshly sub-
products 4–6 could be isolated. In the case of the addition limed ortho-phenylenediamine (2.06 g, 19 mmol), NEt3 (0.4 mL),
of 0.5 equiv. of PhICl to zirconium complex 2, the major and 3,5-di-tert-butylcatechol (8.9 g, 38 mmol) were dissolved in
2
740
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 735–743

Group IV Coordination Chemistry of a Redox-Active Ligand
3
heptane (150 mL). The solution was stirred open to air for 4 d,
during which time a yellow precipitate formed (the solution was
greenish-brown). The yellow solid was collected, dissolved in di-
ethyl ether (30 mL), and filtered through a silica plug. The silica
was washed with additional diethyl ether (150 mL), and all diethyl
ether fractions were combined and taken to dryness in a rotovapor.
The resulting blue residue was taken up in cold pentane and stirred,
resulting in the precipitation of a white solid from the blue solution.
The white solid was collected and washed with cold pentane until
the washings were colorless. The overall yield was 4.3 g (44%) of
6.6 and 3.6 Hz, 2 H, aryl-H), 7.93 (d, JHH = 4.2 Hz, 2 H, aryl-H)
ppm. C NMR (125.8 MHz, C
1
3
6 6 3 3
D ): δ =30.4 [C(CH ) ], 32.5
[C(CH ], 34.9 [C(CH ], 109.4 (aryl-C), 109.7 (aryl-C), 113.3
(aryl-C), 118.8 (aryl-C), 132.2 (aryl-C), 139.2 (aryl-C), 145.5 (aryl-
C), 147.2 (aryl-C), 156.3 (aryl-C). UV/Vis: λmax (ε) = 333 nm
3
)
3
3 3
)
–
1
–1
(15248  cm ).
red]Hf(thf)
ogous to that used to prepare 1a, starting with ZrCl
[N
2
O
2
3
(3): Complex 3 was prepared by a procedure anal-
(thf) (0.90 g,
(1.93 mmol) in diethyl ether (10 mL),
4
2
red
1.93 mmol) and [N
2
O
2
]Li
4
containing a few drops of thf. The product was obtained in 57%
yield (0.80 g) as yellow crystals. X-ray quality crystals were ob-
tained by chilling saturated diethyl ether solutions of the complex
to –35 °C. C H N O Hf (907.52): calcd. C 60.88, H 7.55, N 3.09;
found C 60.24, H 7.93, N 3.02. H NMR (600 MHz, C D ):
6 6
δ = 0.79 (s, 12 H, thf), 1.53 [s, 18 H, C(CH ) ], 1.69 [s, 18 H,
], 3.77 (s, 12 H, thf), 7.02 (dd, JHH = 7.2 and 4.2 Hz, 2
= 2.4 Hz, 2 H, aryl-H), 7.92 (d, J
.2 Hz, 2 H, aryl-H), 8.02 (dd, JHH = 7.2 and 4.2 Hz, 2 H, aryl-H)
red
red
analytically pure [N
2
O
2
]H
4
. Analytical data for [N
2
O
2
4
]H pre-
pared by this procedure matched the data reported in the literature.
red]Ti(thf)
[
N
2
O
2
2
(1a): In a 20-mL scintillation vial, a diethyl ether
46 68
2
5
1
red
solution (10 mL) containing [N
2
O
2
]Li
(1.00 g) and 2.71  n-butyllithium
2.86 mL)} was frozen in a liquid-nitrogen cold well. Immediately
4
{1.93 mmol; prepared in
red
situ from [N
2
O
2
]H
4
3 3
3
C(CH
H, aryl-H), 7.10 (d, J
3
)
3
(
3
3
red
HH
=
upon thawing, the [N
2
O
2
]Li
4
mixture was added to a stirred sus-
HH
3
4
pension of TiCl (thf) (0.46 g 1.93 mmol) in cold diethyl ether. The
4 2
1
3
ppm. C NMR (125.8 MHz, C
2.2 [C(CH ], 34.5 [C(CH ], 34.6 [C(CH
aryl-C), 110.2 (aryl-C), 112.6 (aryl-C), 118.2 (aryl-C), 132.6 (aryl-
C), 138.8 (aryl-C), 144.9 (aryl-C), 146.6 (aryl-C), 155.7 (aryl-C)
6
D
6
): δ = 24.9 (thf), 30.2 [C(CH
3 3
) ],
reaction mixture was warmed to 26 °C and stirred overnight to
afford a dark-red solution and a white precipitate. The white solid
was removed by filtration, and the solvent was stripped from the
red mother liquor under reduced pressure. The resulting residue
was triturated with pentane (3ϫ10 mL) and then dissolved in a
fourth aliquot of pentane, which was cooled to –35 °C overnight.
Collection of the red crystals gave 4a (0.78 g, 52% yield).
3
3
)
3
3
)
3
3 3
)
], 74.2 (thf), 109.9
(
–
1
–1
ppm. UV/Vis: λmax (ε) = 328 nm (8740  cm ).
ox]TiCl
[N
2
O
2
2
(4a): Complex 1a (0.30 g, 0.43 mmol) was dissolved
in diethyl ether (5 mL). The solution was frozen in a liquid nitrogen
cold well, and immediately upon melting, freshly-prepared PhICl
0.117 g, 0.43 mmol) was added as a solid. The solution was shaken
2
until all the PhICl had dissolved (2–3 min). The solution color
changed from yellow to dark green. A dark-green precipitate began
forming, and the mixture was stored at –35 °C. If the reaction mix-
ture warms to room temperature, the yield decreases significantly.
After 12 h at –35 °C, the cold solution was filtered to afford 5a
as a dark-green, microcrystalline solid (210 mg, 67% yield). X-ray
42 60 2 4
C H N O Ti (704.79): calcd. C 71.57, H 8.58, N 3.97; found C
2
1
7
2.01, H 8.39, N 3.42. H NMR (600 MHz, C
H, thf), 1.38 [s, 18 H, C(CH ], 1.51 [s, 18 H, C(CH
2 H, thf), 6.77 (dd, JHH = 6.0 and 3.0 Hz, 2 H, aryl-H), 7.05 (d,
6
D
6
): δ = 1.26 (s, 12
(
3
)
3
3 3
)
], 4.29 (s,
3
1
3
3
J
HH = 1.8 Hz, 2 H, aryl-H), 7.28 (dd, JHH = 6.0 and 3.0 Hz, 2
H, aryl-H), 7.31 (d, JHH = 1.8 Hz, 2 H, aryl-H) ppm. 13C NMR
150 MHz, C ): δ = 25.4 (thf), 30.1 [C(CH ], 32.2 [C(CH ],
4.8 (thf), 108.5 (aryl-C), 108.7 (aryl-C), 116.6 (aryl-C), 121.3 (aryl-
C), 132.5 (aryl-C), 141.8 (aryl-C), 146.3 (aryl-C), 149.4 (aryl-C),
3
(
3
6
D
6
3
)
3
3 3
)
quality crystals were obtained by slow concentration of a saturated
1
–1
1
59.0 (aryl-C) ppm. UV/Vis: λmax (ε) = 326 nm (21250 – cm ).
1
diethyl ether solution of the complex. H NMR (600 MHz, C
6
3
D
6
):
], 6.52 (dd, JHH
9.0 and 3.6 Hz, 2 H, aryl-H), 7.59 (d, 2 H, aryl-H), 7.61 (dd,
red]Ti(py)
3 3 3 3
δ = 1.23 [s, 18 H, C(CH ) ], 1.55 [s, 18 H, C(CH )
[
N
2
O
2
2
(1b): Complex 1b was prepared by a procedure
(py)
(1.93 mmol) in diethyl ether
10 mL). The product was obtained in 79% yield (1.1 g) as purple
=
J
analogous to that used to prepare 1a, starting from TiCl
0.672 g, 1.93 mmol) and [N
4
2
3
3
red
HH = 9.0 and 3.6 Hz, 2 H, aryl-H), 7.63 (d,
H, aryl-H) ppm. UV/Vis: λmax (ε) = 948 nm (13172  cm ), 427
15161).
JHH = 9.6 Hz, 2
(
(
2
O
2
]Li
4
–
1
–1
(
crystals. X-ray quality crystals were obtained by chilling saturated
1
diethyl ether solutions of the complex to –35 °C. H NMR
ox]TiCl
[N
2
O
2
2
(py) (4b): Complex 4b was prepared by a procedure
(
600 MHz, C
C(CH ], 6.33 (t, JHH = 6.5 Hz, 4 H, py), 6.59 (t, JHH = 7.5 Hz,
H, py), 6.70 (dd, JHH = 6.9 and 4.5 Hz, 2 H, aryl-H), 7.07 (d, 2
6 6 3 3
D ): δ = 1.34 [s, 18 H, C(CH ) ], 1.48 [s, 18 H,
analogous to that used to prepare 4a, starting from 1b (0.40 g,
.56 mmol) and PhICl (0.134 g, 0.49 mmol) in diethyl ether
5 mL). The product was obtained in 53% yield (210 mg) as dark
green crystals. C39 Cl Ti (710.58): calcd. C 65.92, H 6.95,
N 5.91; found C 65.82, H 7.26, N 5.65. H NMR (600 MHz, C
δ = 1.29 [s, 18 H, C(CH ], 1.36 [s, 18 H, C(CH ], 6.62 (dd, 2 H,
3
3
3 3
)
0
2
3
2
(
3
H, aryl-H), 7.32 (dd, JHH = 6.9 and 4.5 Hz, 2 H, aryl-H), 7.38 (d,
H
49
N
3
O
2
2
13
2
(
[
(
H, aryl-H), 9.17 (d, 3
125.8 MHz, C ): δ = 29.8 [C(CH
C(CH ], 108.7 (aryl-C), 109.0 (aryl-C), 116.6 (aryl-C), 121.2
aryl-C), 124.3 (py-C), 132.9 (aryl-C), 138.3 (py-C), 141.3 (aryl-C),
44.8 (aryl-C), 147.7 (py-C), 149.1 (aryl-C) ppm. UV/Vis: λmax (ε)
J
HH = 5.0 Hz, 4 H, py) ppm. C NMR
1
6
6
D ):
6
D
6
3
)
3
], 31.8 [C(CH ], 34.5
3 3
)
)
3
3 3
)
3
)
3
3
3
3
aryl-H, JHH = 7.0 and 3.0 Hz), 6.78 (t, 2 H, py, JHH = 8.4 Hz),
.06 (t, 2 H, py, 3JHH = 9.6 Hz), 7.64 (s, 2 H, aryl-H), 7.72 (s, 2 H,
7
1
3
aryl-H), 7.78 (dd, 2 H, aryl-H, JHH = 7.0 and 3.0 Hz), 9.80 (d, 2
–1
=
324 nm (33440 –1 cm ).
3
13
H, py, JHH = 6.0 Hz) ppm. C NMR (150 MHz, C
C(CH ], 30.9 [C(CH ], 110.0 (aryl-C), 114.3 (aryl-C), 121.1
aryl-C), 123.8 (aryl-C), 131.5 (aryl-C), 136.7 (py), 138.0 (py), 141.8
aryl-C), 147.1 (aryl-C), 150.0 (aryl-C), 150.3 (aryl-C) ppm. UV/
6 6
D ): δ = 29.4
[
3
)
3
3 3
)
[N
2
O
2
red]Zr(thf)
3
(2): Complex 2 was prepared by a procedure anal-
(
(
ogous to that used to prepare 1a, starting with ZrCl (thf) (0.46 g,
(1.93 mmol) in diethyl ether (10 mL),
4
2
red
1.93 mmol) and [N
2
O
2
]Li
4
–
1
–1
Vis: λmax (ε) = 948 nm (15480  cm ), 426 (17569).
[N (thf) (5): Complex 5 was prepared by a procedure
ox]ZrCl
analogous to that used to prepare 4a, starting from 2 (0.40 g,
(0.134 g, 0.49 mmol) in diethyl ether
(8 mL). The product was obtained in 42% yield (153 mg) as dark-
green crystals. C38 Cl Zr (746.94): calcd. C 61.10, H 7.02,
N 3.75; found C 60.87, H 7.56, N 3.68. H NMR (600 MHz, C
δ = 1.32 [s, 18 H, C(CH ], 1.64 (br. s, 4 H, thf), 1.70 [s, 18 H,
containing a few drops of thf. The product was obtained in 55%
yield (0.26 g) as yellow crystals. X-ray quality crystals were ob-
tained by chilling saturated diethyl ether solutions of the complex
2
O
2
2
2
to –35 °C. C46
found C 67.42, H 8.39, N 3.20. H NMR (600 MHz, C
δ = 0.87 (s, 12 H, thf), 1.50 [s, 18 H, C(CH ], 1.67 [s, 18 H,
], 3.81 (s, 12 H, thf), 6.98 (dd, JHH = 6.6 and 3.6 Hz, 2
68 2 5 2
H N O Zr (820.24): calcd. C 67.36, H 8.36, N 3.42; 0.49 mmol) and PhICl
1
6
6
D ):
3
)
3
H
52
N
2
O
3
2
3
1
C(CH
3
)
3
6 6
D ):
H, aryl-H), 7.08 (d, JHH = 2.4 Hz, 2 H, aryl-H), 7.83 (dd, 3JHH
3
=
3 3
)
Eur. J. Inorg. Chem. 2009, 735–743
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
741

K. J. Blackmore, N. Lal, J. W. Ziller, A. F. Heyduk
FULL PAPER
3
C(CH
H, aryl-H), 7.52 (dd, JHH = 9.0 and 3.6 Hz, 2 H, aryl-H), 7.63 (s,
H, aryl-H), 7.68 (s, 2 H, aryl-H) ppm. 13C NMR (125.8 MHz,
]thf): δ = 27.3 [C(CH ], 31.0 [C(CH ], 32.5 [C(CH
aryl-C), 124.9 (aryl-C), 129.5 (aryl-C), 129.9 (aryl-C), 134.5 (aryl-
3
)
3
], 4.79 (br. s, 4 H, thf), 6.35 (dd, JHH = 9.0 and 3.6 Hz, 2
tion symmetry was 2/m, and the systematic absences were consis-
tent with the centrosymmetric monoclinic space groups Cc and C2/
c. It was later determined that the centrosymmetric space group
3
2
[D
8
3
)
3
3
)
3
3
)
3
], 117.7 C2/c was correct. The molecule was located on a twofold rotation
axis, and there was a molecule of benzene solvent present that was
(
C), 141.0 (aryl-C), 143.1 (aryl-C), 145.9 (aryl-C), 153.8 (aryl-C) located about an inversion center. Hydrogen atoms were located
ppm. UV/Vis: λmax (ε) = 938 nm (19718 –1 cm ).
–1
from a difference-Fourier map and refined (x, y, z and Uiso). Least-
squares analysis yielded wR = 0.1662 and Goof = 1.020 for 314
variables refined against 3127 data (0.85 Å), R = 0.0579 for those
160 data with I Ն 2σ
ox]HfCl
2
[N
2
O
2
2
(thf) (6): Complex 6 was prepared by a procedure
1
analogous to that used to prepare 4a, starting from 3 (0.35 g,
.39 mmol) and PhICl (0.109 g, 0.39 mmol) in diethyl ether
15 mL). The product was obtained in 66% yield (220 mg) as dark-
green crystals. C38 Cl Hf (834.22): calcd. C 54.71, H 6.28,
N 3.36; found C 54.87, H 6.56, N 3.08. H NMR (600 MHz, C
δ = 1.31 [s, 18 H, C(CH ], 1.59 (s, 4 H, thf), 1.69 [s, 18 H,
C(CH ], 4.75 (s, 4 H, thf), 6.34 (dd, JHH = 9.0 and 4.2 Hz, 2 H,
2
I
.
0
2
(
H
52
N
2
O
3
2
Acknowledgments
1
6
6
D ):
3 3
)
3
Financial support was received from the National Science Founda-
tion (NSF-CAREER, CHE-0645685). A. F. H. is an Alfred P.
Sloan Foundation Research Fellow.
3 3
)
3
aryl-H), 7.49 (dd, JHH = 9.0 and 4.2 Hz, 2 H, aryl-H), 7.61 (s, 2
H, aryl-H), 7.69 (s, 2 H, aryl-H) ppm. 13C NMR (125.8 MHz,
[D
8
3 3 3 3
]thf): δ = 25.3 (thf), 29.7 [C(CH ) ], 31.1 [C(CH ) ], 34.6
[
C(CH ], 35.2 [C(CH ], 74.2 (thf), 116.2 (aryl-C), 123.2 (aryl-
3
)
3
3 3
)
[
1] a) C. A. Tyson, A. E. Martell, J. Am. Chem. Soc. 1972, 94,
39–945; b) M. E. Cass, D. L. Greene, R. M. Buchanan, C. G.
C), 131.6 (aryl-C), 140.4 (aryl-C), 141.6 (aryl-C), 143.8 (aryl-C),
52.1 (aryl-C), 168.2 (aryl-C) ppm. UV/Vis: λmax (ε) = 938 nm
9
1
(
Pierpont, J. Am. Chem. Soc. 1983, 105, 2680–2686; c) M. E.
Cass, C. G. Pierpont, Inorg. Chem. 1986, 25, 122–123; d) C. M.
Liu, E. Nordlander, D. Schmeh, R. Shoemaker, C. G. Pierpont,
Inorg. Chem. 2004, 43, 2114–2124; e) C. J. Rolle, K. I. Hard-
castle, J. D. Soper, Inorg. Chem. 2008, 47, 1892–1894.
24999 –1 cm ).
–1
Crystal-Structure Analyses: X-ray diffraction data were collected
on crystals mounted on glass fibers by using a Bruker CCD plat-
form diffractometer, equipped with a CCD detector. Measurements
were carried out at 163 K by using Mo-K (λ = 0.71073 Å) radia-
α
tion, which was wavelength-selected with a single-crystal graphite
monochromator. The SMART program package was used to deter-
[
2] C. Stanciu, M. E. Jones, P. E. Fanwick, M. M. Abu-Omar, J.
Am. Chem. Soc. 2007, 129, 12400–12401.
[3] M. R. Ringenberg, S. L. Kokatam, Z. M. Heiden, T. B. Rauch-
fuss, J. Am. Chem. Soc. 2008, 130, 788–789.
[
17]
mine unit-cell parameters and to collect data.
The raw frame
[4] a) S. C. Bart, E. B. Lobkovsky, P. J. Chirik, J. Am. Chem. Soc.
2004, 126, 13794–13807; b) S. C. Bart, K. Chłopek, E. Bill,
M. W. Bouwkamp, E. B. Lobkovsky, F. Neese, K. Weighardt,
P. J. Chirik, J. Am. Chem. Soc. 2006, 128, 13901–13912; c) S. C.
Bart, E. B. Lobkovsky, E. Bill, K. Wieghardt, P. J. Chirik, In-
org. Chem. 2008, 46, 7055–7063.
data were processed by using SAINT[
18]
and SADABS[19] to yield
the reflection data files. Subsequent calculations were carried out
by using the SHELXTL[
20]
program suite. Structures were solved
2
by direct methods and refined on F by full-matrix least-squares
techniques. Analytical scattering factors for neutral atoms were
used throughout the analyses.[ Hydrogen atoms were included by
[
5] R. A. Zarkesh, J. W. Ziller, A. F. Heyduk, Angew. Chem. Int.
21]
Ed. 2008, 47, 4715–4718.
using a riding model. ORTEP diagrams were generated by using
[6] K. J. Blackmore, J. W. Ziller, A. F. Heyduk, Inorg. Chem. 2005,
44, 5559–5561.
[7] M. R. Haneline, A. F. Heyduk, J. Am. Chem. Soc. 2006, 128,
ORTEP-3 for Windows.[
22]
CCDC-703149 (1b·Et
) contain the supplemen-
2
O), CCDC-
7
03148 (3), and CCDC-703150 (4a·C
6
H
6
8410–8411.
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
[
8] P. Chaudhuri, M. Hess, J. Müller, K. Hildenbrand, E. Bill, T.
Weyhermüller, K. Wieghardt, J. Am. Chem. Soc. 1999, 121,
9599–9610.
[
N
2
O
2
red]Ti(py)
data was collected on a yellow crystal of approximate dimensions
.02ϫ0.28ϫ0.30 mm by using a 35 s/frame scan time. The diffrac-
tion symmetry was 2/m, and the systematic absences were consis-
tent with the centrosymmetric monoclinic space group P2 /n, which
2
·Et
2
O (1b·Et
2
O): A complete sphere of diffraction
[9] Portions of this work have been previously reported, see: K. J.
Blackmore, N. Lal, J. W. Ziller, A. F. Heyduk, J. Am. Chem.
Soc. 2008, 130, 2728–2729.
0
[
10] K. J. Blackmore, M. B. Sly, M. R. Haneline, J. W. Ziller, A. F.
Heyduk, Inorg. Chem., in press.
11] a) P. Chaudhuri, C. N. Verani, E. Bill, E. Bothe, T.
Weyhermüller, K. Weighardt, J. Am. Chem. Soc. 2001, 123,
1
[
was later determined to be correct. There was one molecule of di-
ethyl ether solvent present per formula unit. Hydrogen atoms were
included by using a riding model. Least-squares analysis yielded
wR
8
2
213–2223; b) H. Chun, C. N. Verani, P. Chaudhuri, E. Bothe,
E. Bill, T. Weyhermüller, K. Wieghardt, Inorg. Chem. 2001, 40,
4157–4166; c) S. Bhattacharaya, P. Gupta, F. Basuli, C. G. Pier-
pont, Inorg. Chem. 2002, 41, 5810–5816.
2
= 0.1254 and Goof = 1.019 for 505 variables refined against
= 0.0496 for those 5417 data with I Ն 2σ
494 data (0.82 Å), R
1
I
.
[
12] a) C. G. Pierpont, Coord. Chem. Rev. 2001, 216–217, 99–125;
b) D. N. Hendrickson, C. G. Pierpont, Top. Curr. Chem. 2004,
[
N
2
O
2
red]Hf(thf)
(3): A complete sphere of diffraction data was
3
collected on a colorless crystal by using a 25 s/frame scan time. The
diffraction symmetry was 2/m, and the systematic absences were
consistent with the centrosymmetric monoclinic space group P2 /
1
c, which was later determined to be correct. Hydrogen atoms were
included by using a riding model. Least-squares analysis yielded
wR
6
234, 63–95.
[
13] a) C. Floriani, E. Solari, F. Corazza, A. Chiesivilla, C. Guas-
tini, Angew. Chem. Int. Ed. Engl. 1989, 28, 64–66; b) V. I. Tara-
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1998, 387–388; c) H. Y. Chen, P. S. White, M. R. Gagné, Orga-
nometallics 1998, 17, 5358–5366.
2
= 0.1661 and Goof = 1.075 for 433 variables refined against
= 0.0555 for those 4530 data with I Ն 2σ
637 data (0.90 Å), R
1
I
.
[
14] F. Corazza, E. Solari, C. Floriani, A. Chiesivilla, C. Guastini,
[
N
2
O
2
ox]TiCl
·C (4a·C
data was collected on a purple crystal of approximate dimensions
2
6
H
6
6 6
H ): A complete sphere of diffraction
J. Chem. Soc., Dalton Trans. 1990, 1335–1344.
[15] L. E. Manzer, Inorg. Synth. 1982, 21, 135–140.
[16] H. J. Lucas, E. R. Kennedy, Org. Synth. 1955, 3, 482.
0
.07ϫ0.12ϫ0.21 mm by using a 45 s/frame scan time. The diffrac-
42
7
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 735–743

Group IV Coordination Chemistry of a Redox-Active Ligand
[
17] SMART Software Users Guide, Version 5.1, Bruker Analytical
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X-ray Systems, Inc., Madison, WI, 2001.
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X-ray Systems, Inc., Madison, WI, 1999.
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[
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Received: September 23, 2008
[
[
[
Published Online: January 20, 2009
Eur. J. Inorg. Chem. 2009, 735–743
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
743