Synthesis, structure, and reactivity of iridium(III) complexes containing a 4,6-dimethyl-1,3-benzenediphenylimine pincer ligand

Article abstract of DOI:10.1021/ic302589b

A nonheterocyclic bis(imino)aryl ligand with blocking methyl substituents, 4,6-dimethyl-1,3-benzenediphenylimine (NCHN), has been synthesized. Metalation via oxidative addition proceeds under mild conditions with the Ir(I) reagent [Ir(CH₂-CH₂)₂(Cl)]₂ to produce the Ir(III) product (NCN)Ir(CH₂CH₃)(Cl). Neutral nucleophiles such as water or triphenylphosphine add readily to the vacant sixth coordination site. Protonation of the ethyl group results in loss of ethane and formation of a dicationic chloride-bridged (NCN)Ir dimer. Alternatively, the chloride ligand can be abstracted from (NCN)Ir(CH₂CH₃)(Cl) to provide access to various neutral and cationic species, including (NCN)Ir(CH ₂CH₃)(OAc) (OAc = acetate), [(NCN)Ir(CH₂CH ₃)(bpy)][BF₄] (bpy = 4,4′-bipyridine), [(NCN)Ir(CH₂CH₃)(NCCH₃)₂][BF ₄], and [(NCN)Ir(CH₂CH₃)(OH₂) ₂][BF₄], which is water soluble.

Full text of DOI:10.1021/ic302589b

Article
pubs.acs.org/IC
Synthesis, Structure, and Reactivity of Iridium(III) Complexes
Containing a 4,6-Dimethyl-1,3-benzenediphenylimine Pincer Ligand
Leah A. Wingard,* Mathew C. Finniss, Michael Norris, Peter S. White, Maurice Brookhart,
and Joseph L. Templeton
W. R. Kenan Laboratory, Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, United
States
S
* Supporting Information
ABSTRACT: A nonheterocyclic bis(imino)aryl ligand with
blocking methyl substituents, 4,6-dimethyl-1,3-benzenediphe-
nylimine (NCHN), has been synthesized. Metalation via
oxidative addition proceeds under mild conditions with the
Ir(I) reagent [Ir(CH2CH2)2(Cl)]2 to produce the Ir(III)
product (NCN)Ir(CH2CH3)(Cl). Neutral nucleophiles such
as water or triphenylphosphine add readily to the vacant sixth
coordination site. Protonation of the ethyl group results in loss of ethane and formation of a dicationic chloride-bridged (NCN)Ir
dimer. Alternatively, the chloride ligand can be abstracted from (NCN)Ir(CH2CH3)(Cl) to provide access to various neutral and
cationic species, including (NCN)Ir(CH2CH3)(OAc) (OAc = acetate), [(NCN)Ir(CH2CH3)(bpy)][BF4] (bpy = 4,4′-
bipyridine), [(NCN)Ir(CH2CH3)(NCCH3)2][BF4], and [(NCN)Ir(CH2CH3)(OH2)2][BF4], which is water soluble.
When occupying the central site of the tridentate pincer ligand,
the M-C bond exhibits excellent thermal stability.
INTRODUCTION
■
Designing new ligands with desirable properties is one of the
most important goals in organometallic chemistry. Altering
ligand frameworks allows for systematic variation of the
chemical properties of metal complexes in a controlled and
predictable manner. Pincer ligands, which are defined by
tridentate meridional coordination to a metal center in accord
with the picturesque name, have been known since the
1970s.1−6 Because of the ease with which synthetic variations
of pincer substituents can be accomplished and the ability of
pincer ligands to stabilize mononuclear complexes, the use of
pincer ligands has rapidly expanded across organometallic
chemistry.7,8 Pincer complexes have found widespread use as
catalysts in transition metal mediated processes such as C−C
bond forming reactions, polymerizations, transfer hydro-
genation, and dehydrogenation reactions.9,10 Pincer complexes
can also be used as sensors,11−13 and they are particularly
helpful in initiating C−C, C−H, and C−O bond activation
processes.14
The typical tridentate meridional coordination mode of a
pincer with a central aryl ring forces the aryl ring into a
conformation nearly coplanar with the coordination plane of d8
square-planar metal centers or with the basal plane of d6 square-
pyramidal metal centers.9 Pincer ligands have been successfully
coordinated to all of the group VIIIB transition metals, and the
resulting complexes have been used for numerous purposes.
Iridium pincer complexes exhibit a wide range of reactivity, with
applications which include electrocatalytic reduction of
CO2,15,16 C−H bond cleavage,17−21 alkane metathesis,22,23
and various dehydrogenation reactions.8,24−37 The pincers used
have typically been PCP16,21,37 or POCOP38,39-type ligands.
Changing to nitrogen donors from phosphorus donors may
increase ligand stability under oxidative conditions. Bis(imino)-
aryl pincer metal complexes have increased in popularity over
the past decade.40−44 Known Ir(III) complexes include pincer
ligands with heterocyclic N-donor moieties including pyr-
idyl,45,46 benzimidazolyl,47,48 and oxazolyl49 groups. Non-
heterocyclic bis(imino)aryl iridium complexes are less
common,50 and synthetic routes are limited. Metalation of
nonheterocyclic bis(imino)aryl ligands at the aryl 2- position
can be challenging because C−H activation at the 4- or 6-
position resulting in bidentate binding is kinetically favored
(Scheme 1). Since only C−H activation at the 2- position
results in tridentate ligand binding, yields of κ3 complexes are
often low. Synthetically, blocking both the 4- and the 6- sites
with substituents has resulted in more favorable metalation of
the central 2- site.49 These NCN-type pincer complexes of
iridium have been shown to have catalytic hydrogen-transfer
abilities,50 applications to asymmetric synthesis,49 and lumines-
cent and emissive properties.45−48 Herein we present the
synthesis of a bis(imino)aryl NCHN ligand with methyl groups
at the 4- and 6- sites, and metalation of this ligand by iridium
under mild conditions.
RESULTS AND DISCUSSION
■
Ligand Design and Synthesis. Pursuing a simple
nonheterocyclic bis(imino)aryl ligand for facile coordination
to Ir(III), we synthesized 4,6-dimethyl-1,3-benzenediphenyli-
Received: November 27, 2012
Published: December 24, 2012
© 2012 American Chemical Society
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Scheme 1. Bidentate Coordination of Non-Heterocyclic Bis(imino)aryl Ligands
Scheme 2. Synthetic Route to 4,6-Dimethyl-1,3-bis(phenylimino)benzene
Scheme 3. Synthetic Route to (NCN)Ir(CH2CH3)(Cl) (2)
Scheme 4. Synthetic Route to (NCN)Ir(CH2CH3)(Cl)(OH2) (3)
mine. As previously shown, C−H activation at the 4- and 6-
positions of the aryl ring is favored over the desired C−H
activation at the 2- position, resulting in formation of bidentate
CN chelates rather than the desired tridentate NCN complexes
(Scheme 1). To guide C−H activation to the 2- position,
methyl groups were placed in the 4- and 6- positions. The
methyl groups provide the additional benefit of serving as
convenient NMR handles for both proton and carbon spectra.
4,6-Dimethyl-1,3-benzenedicarboxaldehyde was synthesized
according to literature procedures.51−53 The dialdehyde reacts
with 2 equiv of aniline and a catalytic amount of p-
toluenesulfonic acid (PTSA) in refluxing toluene to produce
the electron-rich bis(imino)aryl ligand, 4,6-dimethyl-1,3-
benzenediphenylimine (1, NCHN) (Scheme 2). The diimine
product is isolated by removal of toluene followed by washing
the residue with methanol to produce an air-stable off-white
powder.
The 1H NMR spectrum of 4,6-dimethyl-1,3-bis-
(phenylimino)benzene (NCHN) shows C2v symmetry with a
downfield signal at 8.75 ppm representing the two equivalent
imino protons. The central aryl proton ortho to both imino
groups appears as a singlet at 8.66 ppm. The imino phenyl rings
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Figure 1. ORTEP diagram of (NCN)Ir(CH2CH3)(Cl)(OH2) (3).
Figure 2. ORTEP of (NCN)Ir(CH2CH3)(Cl)(PPh3) (4).
Table 1. Bond Lengths and Bond Angles of 3
bond distances (Å)
bond angles (deg)
N(1)−Ir(1)−N(2)
Table 2. Bond Lengths and Bond Angles of 4
Ir(1)−Cl(1)
2.4831(8)
2.259(2)
2.051(3)
2.056(3)
2.095(3)
1.901(3)
159.35(12)
79.75(13)
79.64(13)
99.05(10)
176.88(12)
90.02(13)
170.92(10)
88.50(11)
82.43(7)
bond distances (Å)
bond angles (deg)
Ir(1)−O(1)
Ir(1)−N(1)
Ir(1)−N(2)
Ir(1)−C(2)
Ir(1)−C(10)
N(1)−Ir(1)−C(10)
N(2)−Ir(1)−C(10)
C(10)−Ir(1)−Cl(1)
C(10)−Ir(1)−O(1)
C(10)−Ir(1)−C(2)
C(2)−Ir(1)−Cl(1)
C(2)−Ir(1)−O(1)
O(1)−Ir(1)−Cl(1)
Ir(1)−Cl(1)
2.5062(6)
2.3800(6)
2.0818(19)
2.0869(19)
2.136(2)
N(1)−Ir(1)−N(2)
N(1)−Ir(1)−C(10)
N(2)−Ir(1)−C(10)
C(10)−Ir(1)−Cl(1)
C(10)−Ir(1)−P(1)
C(10)−Ir(1)−C(2)
C(2)−Ir(1)−Cl(1)
C(2)−Ir(1)−P(1)
P(1)−Ir(1)−Cl(1)
157.76(8)
79.00(9)
78.83(9)
176.48(7)
94.54(7)
86.58(9)
90.00(7)
177.56(7)
88.844(19)
Ir(1)−P(1)
Ir(1)−N(1)
Ir(1)−N(2)
Ir(1)−C(2)
Ir(1)−C(10)
1.922(3)
are symmetric and exhibit a doublet at 7.42 ppm for the four
protons in the ortho positions, a triplet at 7.24 ppm for the two
protons in the para positions, and a triplet at 7.26 ppm for the
four protons in the meta positions. The aryl proton at the 5-
position ortho to both methyl groups of the central ring appears
at 7.15 ppm. A singlet at 2.65 integrating for six protons is
observed for the equivalent methyl groups.
Metalation of the NCHN Pincer Ligand. Attempts to
metalate the NCHN ligand with traditional iridium sources,
such as IrCl3·3H2O, [Ir(COE)2(Cl)]2 (COE = cyclooctene),
and [Ir(COD)(Cl)]2 (COD = 1,5-cyclooctadiene), result in
complex reaction mixtures regardless of reaction time or
temperature. The chloride-bridged Ir(I) ethylene dimer54
proved to be an ideal iridium source for adding the NCHN
ligand. Addition of 2 equiv of the NCHN ligand to a methylene
chloride solution of [Ir(CH2CH2)2(Cl)]2 at room temper-
ature followed by stirring for 1 h results in clean metalation of
the NCN ligand by activation of the central aryl C−H bond,
giving (NCN)Ir(CH2CH3)(Cl) (2) (Scheme 3). Complex 2 is
isolated in good yield as a red powder by removal of methylene
chloride and washing with pentane.
The metalation of 1 was monitored by NMR spectroscopy at
low temperature. Upon addition of 2 equiv of ligand 1 to a
CD2Cl2 solution of [Ir(CH2CH2)2(Cl)]2 at 215 K (a 1:1
ratio of ligand to metal), the 1H NMR spectrum shows that the
two halves of the ligand are inequivalent; the imino protons and
the methyl groups of the NCHN ligand are no longer
equivalent. The central aryl proton between the two imino
groups shifts far downfield to 11.2 ppm. Additionally, free
ethylene appears in the spectrum. We postulate that one
Scheme 5. Synthetic Route to (NCN)Ir(CH2CH3)(Cl)(PPh3) (4)
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Scheme 6. Synthetic Route to [(NCN)IrCl]2[OTf]2 (5)
Scheme 7. Synthetic Route to (NCN)Ir(CH2CH3)(OAc) (6)
Table 3. Bond Lengths and Bond Angles of
(NCN)Ir(CH2CH3)(OAc) (6)
bond distances (Å)
bond angles (deg)
Ir(1)−O(1)
2.281(3)
2.248(3)
2.067(3)
2.096(3)
2.070(4)
1.899(4)
N(1)−Ir(1)−N(2)
N(1)−Ir(1)−C(12)
N(2)−Ir(1)−C(12)
C(12)−Ir(1)−O(1)
C(12)−Ir(1)−O(2)
C(12)−Ir(1)−C(4)
C(4)−Ir(1)−O(1)
C(4)−Ir(1)−O(2)
O(1)−Ir(1)−O(2)
158.64(15)
79.31(16)
79.33(15)
166.09(14)
108.36(14)
89.56(16)
104.19(13)
162.05(14)
57.86(10)
Ir(1)−O(2)
Ir(1)−N(1)
Ir(1)−N(2)
Ir(1)−C(4)
Ir(1)−C(12)
Ir(1)−C(2)
2.627(4)
ethylene into the Ir−H bond to form the observed metal
complex (NCN)Ir(CH2CH3)(Cl), 2. Note that β-H elimi-
nation from 2 is not observed even upon heating the complex.
The 1H NMR spectrum of 2 shows a Cs symmetric
iridium(III) complex. The imino protons are equivalent and
appear as a singlet at 8.82 ppm. The signal for the remaining
proton on the central aryl ring shifts upfield to 6.8 ppm, the two
methyl groups are equivalent at 2.66 ppm, and the metal-bound
ethyl group exhibits a quartet at 0.96 ppm and a triplet at −0.16
ppm. The 13C NMR spectrum is consistent with the proton
spectrum. The resonance for the equivalent imino carbons
appears at 175.1 ppm while the phenyl and aryl carbons fall
between 152 and 123 ppm. The equivalent methyl carbons
resonate at 19.7 ppm. The signals of −CH2− and −CH3 of the
ethyl group appear at 15.2 ppm and −12.9 ppm, respectively,
Figure 3. ORTEP of (NCN)Ir(CH2CH3)(OAc) (6).
ethylene ligand is displaced from each iridium center by one
imino group, resulting in formation of an intermediate chloride-
bridged iridium(I) dimer with one η2-ethylene and a
monodentate nitrogen-bound NCHN ligand in the coordina-
tion sphere of each iridium. Although no other additional
intermediates are observed by NMR spectroscopy, some
sequence of coordination of the second imino group, dimer
dissociation, and C−H activation would result in an (NCN)-
Ir(CH2CH2)(H)(Cl) intermediate that could then insert
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Scheme 8. Synthetic Route to [(NCN)Ir(CH2CH3)(NCCH3)2][BF4] (7)
Figure 4. Cyclic voltammogram of 7 in acetonitrile at 50 mV/s.
Table 4. Bond Lengths and Bond Angles of
[(NCN)Ir(CH2CH3)(NCCH3)2][BF4] (7)
bond distances (Å)
bond angles (deg)
Ir(1)−N(1)
2.132(4)
2.144(4)
2.065(4)
2.089(4)
2.096(5)
1.931(5)
N(3)−Ir(1)−N(4)
N(3)−Ir(1)−C(13)
N(4)−Ir(1)−C(13)
C(13)−Ir(1)−C(2)
C(13)−Ir(1)−N(1)
C(13)−Ir(1)−N(2)
C(2)−Ir(1)−N(1)
C(2)−Ir(1)−N(2)
N(1)−Ir(1)−N(2)
157.90(168)
78.8(2)
Ir(1)−N(2)
Ir(1)−N(3)
Ir(1)−N(4)
Ir(1)−C(2)
Ir(1)−C(13)
79.2(2)
88.0(2)
94.96(19)
175.26(18)
176.87(18)
87.97(19)
89.17(17)
the proton NMR spectrum upon coordination of water, but the
ethyl group signals shift more noticeably to 0.50 ppm for the
−CH2-protons and to −0.10 ppm for the −CH3 protons. The
coordinated water protons appear as a broad singlet at 4.82
ppm for this molecule.
Figure 5. ORTEP of [(NCN)Ir(CH2CH3)(NCCH3)2][BF4] (7).
Crystals of aquo complex 3 were grown from a solution of 3
in methylene chloride layered with hexanes at 277 K. The
crystal structure of 3 shows tridentate coordination of the NCN
ligand and a distorted octahedral geometry for the metal
(Figure 1). The ethyl group is cis to the central aryl ring of the
NCN ligand and the −CH3 group of the ethyl is turned toward
one of the imino nitrogens. The bound NCN ligand is planar
with the exception of the imino phenyl rings, and they are
twisted from the ligand plane by 51.9° and 49.3° in opposing
directions. The Ir−C(10) (aryl sp2 carbon) bond length is
and this counter-intuitive C-13 assignment was verified by
HMQC.
The five-coordinate, sixteen-electron Ir(III) complex 2
readily adds neutral two-electron donor ligands. Addition of
water results in formation of the product (NCN)Ir(CH2CH3)-
(Cl)(OH2) (3) in which the weak σ-donating water ligand is
trans to the aryl ligand of the NCN ligand (Scheme 4),
indicating that the aryl group is a stronger trans donor than the
ethyl group. The NCN ligand resonances shift only slightly in
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Scheme 9. Synthetic Route to [(NCN)Ir(CH2CH3)(bpy)][BF4]
Scheme 10. Synthetic Route to [(NCN)Ir(CH2CH3)(OH2)2][BF4] (9)
1.901 Å while the Ir−C(2) (ethyl sp3 carbon) bond length is
longer at 2.095 Å, a distance difference largely attributable to
the difference in hybridization. The water ligand is trans to the
aryl carbon, and the iridium−oxygen bond length is 2.259 Å,
which is comparable to Ir−O bond lengths in other Ir−OH2
complexes.55−57 The iridium center sits below the N−N axis no
doubt reflecting the directional orientation of the nitrogen
donor lone pair electrons with a N(1)−Ir−N(2) bond angle of
159.35°. The N−Ir−C(10) angles are acute at 79.75° and
79.64° (Table 1).
trans to the central aryl carbon. The ethyl group and the
triphenylphosphine ligand are cis to the central aryl carbon and
trans to one another. The steric bulk and stronger electron-
donor properties of the triphenylphosphine ligand result in a
slight elongation of the iridium−nitrogen bonds by 0.03 Å and
the iridium-aryl carbon bond by 0.02 Å compared to the length
of the analogous bonds in aquo adduct 3. The iridium-ethyl
carbon bond lengthens by 0.04 Å, and the iridium-chloride
bond length is longer by 0.02 Å compared to 3. The N−Ir−N
bond angle is 157.76°, almost 2° smaller compared to the
corresponding bond angle in 3 (Table 2).
Addition of trifluoromethanesulfonic acid to a methylene
chloride solution of 2 results in formation of a dicationic
chloride-bridged iridium dimer [(NCN)Ir(Cl)]2[OTf]2 (5)
and loss of ethane (Scheme 6). The dimer does not react with
silver salts. The 1H and 13C NMR spectra indicate a C2v
symmetric molecule. The four phenyl rings are equivalent,
and the aromatic proton signals fall between 7.52 and 7.43
ppm; the four equivalent imino protons appear as a singlet at
8.48 ppm. The proton on the central aryl ring resonates at 7.00
ppm for both NCN ligands, and all four methyl groups are
reflected in a singlet at 2.80 ppm.
Addition of triphenylphosphine results in formation of
(NCN)Ir(CH2CH3)(Cl)(PPh3) (4), in which the triphenyl-
phosphine ligand is cis to the aryl moiety of the NCN ligand
(Scheme 5). The two iminophenyl groups point downward,
blocking the bulky triphenylphosphine ligand from occupying
the site trans to the aryl ring. The strong sigma donation of the
triphenylphosphine ligand together with the shielding effect of
one of the aryl rings of the PPh3 ligand (Figure 2) shifts the
1
NCN ligand proton signals upfield from those of 2 in the H
NMR spectrum. The equivalent imino protons resonate at 8.42
ppm, compared to 8.82 ppm for the same protons in 2, while
the equivalent methyl groups appear at 2.44 ppm in 4
compared to the same moieties at 2.66 ppm in 2. The ethyl
group signals shift downfield to 1.43 and 0.00 ppm, and the
−CH2− multiplet reflects three-bond coupling to phosphorus.
The 31P{1H} NMR spectrum shows a single peak at −6.82 ppm
for the bound phosphine.
Red crystals of 4 were grown by slow evaporation of a
methylene chloride solution of 4 at room temperature. The
crystal structure of 4 shows a distorted octahedral geometry
(Figure 2). The NCN pincer ligand occupies three meridional
sites as anticipated, and the weak field chloride ligand is located
Addition of a silver salt to complex 2 results in abstraction of
the chloride ligand from the coordination sphere. Silver salts
with coordinating counterions give neutral complexes; as an
example, the reaction of 2 with silver acetate gives (NCN)Ir-
1
(CH2CH3)(OAc) (6) (Scheme 7). The H NMR spectrum of
6 shows a Cs symmetric molecule. The imino protons are
equivalent at 9.14 ppm, and the equivalent methyl groups from
the NCN ligand appear at 2.64 ppm. The ethyl group appears
as a quartet at 0.45 ppm (−CH2−) and a triplet at 0.20 ppm
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1
Figure 6. Variable temperature H NMR spectrum of [(NCN)Ir(Et)(OH2)2][OTf] (9).
Scheme 11. Ligand Exchange from 9
(−CH3). The methyl group of the acetate ligand gives rise to a
singlet at 1.54 ppm.
bond lengths are comparable to the other complexes reported
here at 2.067 Å and 2.096 Å, as is the Ir−Caryl bond distance at
1.899 Å. The Ir−Cethyl bond length is slightly shorter at 2.070 Å
compared to the analogous lengths in 3 and 4. The ethyl group
is located cis to the central aryl carbon with a C(12)−Ir−C(4)
bond angle of 89.56°. The O(1)−Ir−O(2) bond angle is
57.86°, and the N(1)−Ir−N(2) bond angle is 158.64° (Table
3).
Red crystals of acetate complex 6 were grown from an NMR
tube sample of 6 in CD2Cl2 at 273 K. The crystal structure
shows a distorted octahedral geometry, and again the NCN
ligand occupies three meridional coordination sites (Figure 3).
The planar acetate ligand is bound in a bidentate fashion
through the two oxygen atoms. The plane of the acetate ligand
is perpendicular to the plane of the NCN ligand. The Ir−N
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The crystal structure of 7 exhibits a distorted octahedral
geometry where the planar NCN ligand occupies the expected
three meridional coordination sites (Figure 5). The Ir−Caryl
bond length is 1.931 Å, while the Ir−Cethyl bond length is 2.096
Å. The acetonitrile trans to the ethyl group has an Ir−N(1)
bond distance of 2.132 Å while the acetonitrile trans to the aryl
carbon has a Ir−N(2) bond distance of 2.144 Å. The N(3)−
Ir−N(4) bond angle of the NCN ligand is 157.90° while the
two acetonitrile ligand nitrogens are related by a N(1)−Ir−
N(2) bond angle of 89.17° (Table 4).
Neutral bidentate ligands are readily coordinated to iridium
by displacement of both acetonitrile ligands from 7. Cationic
[Ir(III)(NCN)(CH2CH3)(bpy)][BF4] (8) is formed within
minutes upon addition of 1 equiv of bipyridine to a methylene
chloride solution of 7 (Scheme 9).
The proton NMR spectrum of 8 shows a Cs-symmetric
molecule. The imino protons (8.80 ppm) and the methyl
groups (2.76 ppm) are equivalent. Since the bipyridine ligand
lies on the mirror plane, the eight bipyridine protons are all
inequivalent; they resonate in the range of 8.66 to 7.07 ppm.
The ethyl group appears as a quartet at 1.05 ppm and a triplet
at 0.27 ppm.
Addition of 30 mL of water to a concentrated 3 mL
methylene chloride solution of the bis-acetonitrile complex 7,
followed by vigorous stirring for 12 h at 50 °C results in
replacement of both acetonitrile ligands with aqua ligands to
form [(NCN)Ir(CH2CH3)(OH2)2][BF4] (9) (Scheme 10).
One aqua ligand is trans to the central aryl group of NCN while
the other aqua ligand is trans to the ethyl group. Complex 9 is
soluble in polar organic solvents as well as in water.
Figure 7. ORTEP of [(NCN)Ir(CH2CH3)(OH2)2][BF4] (9).
Table 5. Bond Lengths and Bond Angles of 9
bond distances (Å)
bond angles (deg)
N(1)−Ir(1)−N(2)
Ir(1)−N(1)
2.071(5)
2.056(5)
2.283(4)
2.254(5)
2.059(7)
1.896(6)
159.3(2)
79.6(2)
79.7(2)
92.3(3)
177.8(2)
91.8(2)
89.7(2)
175.4(2)
86.24(19)
Ir(1)−N(2)
Ir(1)−O(1)
Ir(1)−O(2)
Ir(1)−C(2)
Ir(1)−C(15)
N(1)−Ir(1)−C(15)
N(2)−Ir(1)−C(15)
C(15)−Ir(1)−C(2)
C(15)−Ir(1)−O(1)
C(15)−Ir(1)−O(2)
C(2)−Ir(1)−O(1)
C(2)−Ir(1)−O(2)
O(1)−Ir(1)−O(2)
The proton NMR of 9 supports a Cs-symmetric complex
with a mirror plane relating the two halves of the NCN ligand.
The two imino protons are equivalent at 8.83 ppm, and the two
methyl groups are equivalent at 2.66 ppm. The ethyl group
appears as a quartet at 0.88 ppm and as a triplet at −0.18 ppm.
All four aqua protons are represented by a broad peak at 2.20
ppm in CD2Cl2 because of rapid proton exchange. When the
tetrafluoroborate counterion is replaced with a triflate counter-
ion, the proton NMR shows two species at 210 K (Figure 6).
One species is the cationic bis-aqua [(NCN)Ir(CH2CH3)-
(OH2)2][OTf] while the second species is neutral and has
triflate bound to iridium in place of the aqua ligand trans to the
ethyl group, (NCN)Ir(CH2CH3)(OH2)(OTf) (Scheme 11).
At room temperature, the ligand exchange between water and
triflate is fast on the NMR time scale.
Red crystals of cationic bis-aqua complex 9 were grown by
slow diffusion of hexanes into a concentrated methylene
chloride solution of 9 at 273 K. The crystal structure shows a
distorted octahedral geometry. The Ir−Caryl bond length is
1.896 Å, and the Ir−Cethyl bond length is 2.059 Å; both
distances are the shortest of the observed structures (Figure 7).
The two Ir−N bond distances are likewise short at 2.071 and
2.056 Å. The Ir−O(2) bond length is 2.254 Å while the Ir−
O(1) bond length corresponding to the aqua ligand trans to the
aryl ring is longer at 2.283 Å. The N(1)−Ir−N(2) bond angle is
159.3°, and the O(1)−Ir−O(2) bond angle is 86.24° (Table 5).
Cyclic voltammetric measurements were carried out at a
glassy carbon working electrode with a Ag/AgCl (3 M NaCl)
reference (measured at 0.207 V vs NHE) and platinum counter
electrode in a phosphate buffered aqueous solution at pH =
2.15 with an ionic strength of 0.5 M. A cyclic voltammogram
(CV) of 9 shows two oxidation waves at 1.05 and 1.28 V vs Ag/
AgCl attributed to the Ir(IV)/Ir(III) couple and the Ir(V)/
Figure 8. Cyclic voltammograms of 9 in 0.5 M phosphate buffer at pH
= 2.15 with a glassy carbon working electrode at 298 3 K.
Addition of excess silver tetrafluoroborate to 2 in acetonitrile
results in abstraction of the chloride ligand and coordination of
two acetonitrile ligands to iridium to give six-coordinate
cationic [(NCN)Ir(CH2CH3)(NCCH3)2][BF4] (7) (Scheme
8). The acetonitrile ligands are cis to one another, and the ethyl
ligand is cis to the central aryl carbon of the NCN ligand. The
labile acetonitrile ligands in 7 provide convenient access to the
Ir(III) center for adding poorly coordinating ligands or
bidentate ligands.
The proton NMR spectrum of 7 indicates a Cs-symmetric
complex. The acetonitrile ligands are inequivalent, with the two
methyl resonances at 2.29 and 2.30 ppm, indicating that one is
trans to the aryl ring while the other is trans to the ethyl group.
The ethyl ligand appears as a quartet at 0.41 ppm and a triplet
at 0.08 ppm. Cyclic voltammetry of 7 in acetonitrile shows a
reversible wave at 1.03 V vs Ag/AgCl, and this one-electron
redox process is assigned to the Ir(IV)/Ir(III) couple (Figure
4).
Red crystals of 7 were grown from slow diffusion of hexanes
into a concentrated methylene chloride solution of 7 at 273 K.
522
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Inorganic Chemistry
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Table 6. Crystal and Data Collection Parameters for (NCN)Ir(Et)(Cl)(OH2) (3), (NCN)Ir(Et)(Cl)(PPh3) (4), and
(NCN)Ir(Et)(OAc) (6)
3
4
6
empirical formula
formula weight
color
C24H26ClIrN2O
586.12
C42H39ClIrN2P
830.37
C26H27IrN2O2
591.70
red
red
red
temperature
100 K
100 K
100 K
triclinic
crystal system
space group
monoclinic
monoclinic
P21/n
P21/n
P1
̅
unit cell dimensions
a = 12.5082(3) Å
b = 11.5034(3) Å
c = 14.9983(4) Å
α = 90.00°
β = 93.8010(10)°
γ = 90.00°
2153.31(10) Å3
a = 11.7273(3) Å
b = 16.9263(4) Å
c = 17.7219(4) Å
α = 90.00°
β = 95.4520(10)°
γ = 90.00°
3501.88(15) Å3
a = 10.3583(2) Å
b = 10.4763(2) Å
c = 12.0455(3) Å
α = 73.8230(10)°
β = 83.5340(10)°
γ = 62.6830(10)°
1115.21(4) Å3
2
volume
Z
4
4
density (calculated)
absorption coefficient
F(000)
1.808 mg/m3
13.275 mm−1
1144.0
0.332 × 0.304 × 0.166 mm3
9.7 to 147.42°
−15 ≤ h ≤ 15
−14 ≤ k ≤ 13
−18 ≤ l ≤ 18
19808
1.575 mg/m3
8.757 mm−1
1656.0
0.35 × 0.1 × 0.079 mm3
7.24 to 147.56°
−14 ≤ h ≤ 14
−20 ≤ k ≤ 20
−22 ≤ l ≤ 21
33963
1.762 mg/m3
11.784 mm−1
580.0
0.257 × 0.171 × 0.154 mm3
7.64 to 133.14°
−12 ≤ h ≤ 11
−12 ≤ k ≤ 12
−14 ≤ l ≤ 14
12793
crystal size
θ range
index ranges
reflections collected
data/restraints/parameters
goodness-of-fit on F2
4262/0/266
1.234
6959/0/427
1.048
3770/0/284
1.183
final R indices [I > 2σ(I)] R indices (all data)
R1 = 0.0262,
wR2 = 0.0671
R1 = 0.0264,
wR2 = 0.0672
1.41 and −0.78 e Å−3
R1 = 0.0235,
wR2 = 0.0585
R1 = 0.0260,
wR2 = 0.0600
1.13 and −0.74 e Å−3
R1 = 0.0308,
wR2 = 0.0725
R1 = 0.0310,
wR2 = 0.0727
1.91 and −0.91 e Å−3
largest diff. peak and hole
Ir(IV) couple respectively (Figure 8). The potentials for these
couples were derived from differential pulse voltammetry as the
complex did not show a significant electrochemical response in
the CV. This may be due to poor solubility of the Ir complex in
the buffered aqueous medium or slow electron transfer between
the complex and the electrode. Normalized CVs at scan rates of
10, 25, 50, and 100 mV/s show increasing normalized current
with decreasing scan rates (Figure 8). The normalized current
values were obtained by dividing the observed current by the
square root of the scan rate as is appropriate for diffusion
controlled redox couples. This is indicative of a catalytic
process, although decomposition of the catalyst cannot be ruled
out. The current remained constant (did not increase or
decrease) over multiple scans.
(NCN)Ir(CH2CH3)(Cl) to access various neutral and cationic
species, including (NCN)Ir(CH2CH3)(OAc), [(NCN)Ir-
(CH2CH3)(NCCH3)2][BF4], [(NCN)Ir(CH2CH3)(bpy)]-
[BF4], and [(NCN)Ir(CH2CH3)(OH2)2][BF4].
EXPERIMENTAL SECTION
■
General Information. Unless otherwise noted, reactions were
performed open to air. Methylene chloride, hexanes, pentane, diethyl
ether, toluene, and tetrahydrofuran were purified by passage through
an activated alumina column under a dry argon atmosphere.
Methylene chloride-d2 was dried over CaH2 and degassed using
standard freeze−pump−thaw techniques.
NMR spectra were recorded on Bruker DRX400, 500, 600 or
AVANCE400 spectrometers. The electrochemical measurements were
taken with a BAS100B electrochemical analyzer potentiostat. The
electrodes were a planar BAS MF-2012 glassy carbon electrode, a
platinum wire EG&G PARC K0266 counter electrode, and a Ag/AgCl
EG&G PARC K0265 reference electrode.
SUMMARY
■
A nonheterocyclic bis(imino)aryl ligand with blocking methyl
substituents, 4,6-dimethyl-1,3-benzenediphenylimine (NCHN),
has been synthesized. Reaction with [Ir(CH2CH2)2(Cl)]2
under mild conditions led to (NCN)Ir(CH2CH3)(Cl) via C−
H activation at the central aryl position of the NCN ligand.
This five-coordinate complex proved to be a versatile starting
material for modification of the three remaining coordination
sites. Neutral nucleophiles including water and triphenylphos-
phine could be readily added to the vacant sixth coordination
site. Protonation of the ethyl group resulted in loss of ethane
and formation of a dicationic chloride-bridged (NCN)Ir dimer.
Alternatively, the chloride ligand could be abstracted from
Crystal and data collection parameters for 3, 4, and 6 are given in
Table 6 and for 7 and 9 in Table 7.
4,6-Dimethyl-1,3-benzenediphenylimine (NCHN) (1). A 0.48
mL volume (5.34 mmol) of aniline was placed in a round-bottom flask
with 0.50 g (2.67 mmol) of 4,6-dimethyl-1,3-benzenedicarboxalde-
hyde. A 0.015 g portion of (0.08 mmol) PTSA and 30 mL of toluene
were added. The solution was refluxed for 24 h, then cooled to room
temperature. The solvent was removed in vacuo, and methanol was
added to precipitate the product. The 4,6-dimethyl-1,3-benzenediphe-
nylimine was washed with methanol to give 0.70 g (2.0 mmol) of tan
powder (78% yield). 1H NMR (CDCl3, δ): 8.75 (s, 2H, CHN) 8.66 (s,
1H, Ph CH), 7.42 (t, 4H, Ph CH), 7.26 (d, 2H, Ph CH), 7.24 (t, 4H,
Ph CH), 7.15 (s, 1H, Ph CH), 2.65 (s, 6H, −CH3). 13C{1H} NMR
523
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Inorganic Chemistry
Article
138.96, 129.63, 127.59, 123.97, 122.91 (Ar C), 19.60 (Ph-CH3), 14.34
(−CH2-), −6.19 (−CH3). Analytical data: Calculated: C, 49.18; H,
4.62; N, 4.12. Found: C, 49.34; H, 4.47; N, 4.46.
Table 7. Crystal and Data Collection Parameters for
[(NCN)Ir(Et)(NCCH2)2][BF4] (7) and
[(NCN)Ir(Et)(OH2)2][BF4] (9)
(NCN)Ir(CH2CH3)(Cl)(PPh3) (4). (NCN)Ir(Et)(Cl) (0.020 g, 0.035
mmol) was dissolved in CD2Cl2 (10 mL). Triphenylphosphine
(0.0092 g, 0.035 mmol) was added and mixed, immediately resulting
in a bright red solution. The solvent was removed in vacuo, and the
orange-red residue was triturated with hexanes to give a bright orange
7
9
empirical formula
formula weight
color
C28H30BF4IrN4
701.57
C24H28BF4IrN2O2
655.49
orange
red
1
powder (0.027 g, 0.033 mmol, 94% yield). H NMR (CD2Cl2, δ, 295
temperature
100 K
100 K
K): 8.42 (s, 2H, CHN), 7.38, 7.34, 7.31, 7.03, 6.83 (m, 25H, Ph CH),
6.54 (s, 1H, Ar CH) 2.44 (s, 6H, Ph−CH3), 1.43 (m, 2H, −CH2−),
0.00 (q, 3H, −CH3). 31P{1H} NMR (CD2Cl2, δ): −6.82 (s). 13C{1H}
NMR (CD2Cl2, δ): 173.43 (CHN), 152.16, 140.88, 138.69, 133.69,
133.62, 132.40, 129.06, 128.96, 128.62, 127.65, 127.57, 125.64, 122.97
(Ph C), 19.66 (Ph-CH3), 13.17 (−CH2-), 2.22 (−CH3). Analytical
data: Calculated: C, 60.75; H, 4.73; N, 3.37. Found: C, 60.48; H, 4.60;
N, 3.26.
crystal system
space group
triclinic
monoclinic
P21/c
P1
̅
unit cell dimensions
a = 8.9633(2) Å
b = 11.9394(2) Å
c = 12.6935(2) Å
α = 82.3830(10)°
β = 84.2520(10)°
γ = 85.7140(10)°
1337.05(4) Å3
2
a = 26.0020(6) Å
b = 11.7258(3) Å
c = 16.4472(4) Å
α = 90.00°
β = 100.461(2)°
γ = 90.00°
4931.3(2) Å3
8
[(NCN)Ir(Cl)]2[OTf]2 (5). (NCN)Ir(Et)(Cl) (0.016 g, 0.028 mmol)
was dissolved in CH2Cl2 (10 mL), and trifluoromethanesulfonic acid
(2.5 μL, 0.028 mmol) was added and mixed. The solvent was removed
in vacuo and the orange-red residue was washed once with water to
remove the excess acid. Then the residue was triturated with hexanes
volume
Z
density (calculated)
absorption coefficient
F(000)
1.743 mg/m3
10.121 mm−1
688.0
1.766 mg/m3
10.961 mm−1
2560.0
1
to give an orange powder (0.015 g, 80% yield). H NMR (CD2Cl2, δ,
293 K): 8.48 (s, 2H, CHN) 7.52 (m, 8H, imine Ph CH), 7.43 (m, 2H,
imine Ph CH), 7.00 (s, 1H, Ph CH), 2.80 (s, 6H, Ph−CH3). 13C{1H}
NMR (CD2Cl2, δ, 293 K): 180.84 (CHN), 150.41, 144.27, 140.24,
130.19, 129.06, 126.68, 123.11, 120.12 (Ph C), 19.38 (Ph-CH3).
Analytical data: Calculated: C, 40.14; H, 2.78; N, 4.07. Found: C,
40.15; H, 3.20; N, 3.64.
crystal size
0.224 × 0.095 ×
0.4 × 0.05 × 0.05
0.026 mm3
mm3
θ range
7.48 to 133.2°
−7 ≤ h ≤ 10
−14 ≤ k ≤ 14
−14 ≤ l ≤ 15
8056
3.46 to 140.16°
−31 ≤ h ≤ 31
−14 ≤ k ≤ 14
−19 ≤ l ≤ 20
28565
index ranges
(NCN)Ir(CH2CH3)(OAc) (6). (NCN)Ir(Et)(Cl) (0.020 g, 0.035
mmol) was dissolved in CH2Cl2 (10 mL), and excess silver acetate
(0.10 g, 0.60 mmol) was added and stirred for 1 h. The mixture was
filtered, and the solvent was removed in vacuo, followed by a hexanes
reflections collected
data/restraints/parameters
goodness-of-fit on F2
4431/0/348
1.078
9206/0/623
1.038
1
wash to produce a red powder (0.018 g, 0.030 mmol, 87% yield). H
final R indices [I > 2σ(I)] R
indices (all data)
R1 = 0.0353,
R1 = 0.0409,
NMR (CD2Cl2, δ, 289 K): 9.14 (s, 2H, CHN), 7.51 (d, 4H, ortho-Ph
CH), 7.46 (t, 4H, meta-Ph CH), 7.37 (t, 2H, para-Ph CH), 6.73 (s,
1H, Ar CH), 2.64 (s, 6H, Ph−CH3), 1.54 (s, 3H, OAc), 0.45 (q, 2H,
−CH2−), 0.20 (t, 3H, −CH3). 13C{1H} NMR (CDCl3, δ): 171.24
(CHN), 151.57, 139.71, 139.29, 129.32, 127.50, 123.93, 122.72 (Ph
C), 68.34 (OAc-C), 25.24 (OAc-CH3), 19.75 (Ph-CH3), 14.78 (−CH2-
), −7.86 (−CH3). Analytical data: Calculated: C, 52.77; H, 4.60; N,
4.73. Found: C, 52.32; H, 4.77; N, 5.10.
wR2 = 0.0829
R1 = 0.0419,
wR2 = 0.0867
wR2 = 0.0960
R1 = 0.0538,
wR2 = 0.1036
largest diff. peak and hole
2.15 and −0.95e Å−3 2.95 and −1.18 e
Å−3
[(NCN)Ir(CH2CH3)(NCCH3)2][BF4] (7). (NCN)Ir(CH2CH3)(Cl)
(0.20 g, 0.35 mmol) was placed in a Schlenk flask and dissolved in
acetonitrile (10 mL). Silver tetrafluoroborate (0.23 g, 1.2 mmol) was
added, and the mixture was stirred 1 h. The solution was filtered, and
the solvent was removed in vacuo. The residue was dissolved in a
minimum amount of methylene chloride and placed on a silica plug.
Hexanes and methylene chloride washed the complex, and it was
(CDCl3, δ): 159.01 (CHN), 152.82 (Ph C), 141.47 (Ph C), 134.19
(Ph C), 132.73 (Ph C), 129.36 (Ph C), 126.01 (Ph C), 121.11 (Ph C),
19.96 (−CH3). Analysis: Calculated: C, 84.58; H, 6.45; N, 8.97.
Found: C, 84.55; H, 6.15; N, 8.75.
(NCN)Ir(CH2CH3)(Cl) (2). [Ir(C2H4)2Cl]2 (0.052 g, 0.092 mmol)
was placed in a Schlenk flask under argon with 4,6-dimethyl-1,3-
benzenediphenylimine (0.072 g, 0.23 mmol). Methylene chloride (20
mL) was added, and the mixture was stirred for 1 h. The solvent was
removed in vacuo, and the dark red residue was run down an alumina
column flushed with hexanes, methylene chloride, and eluted with
methanol. Solvent was removed in vacuo, and the residue was
1
eluted with ethyl acetate (0.24 g, 0.34 mmol, 98% yield). H NMR
(CD2Cl2, δ, 293 K): 8.71 (s, 2H, CHN) 7.54 (t, 4H, meta-Ph CH),
7.43 (d, 4H, ortho-Ph CH), 7.41 (t, 2H, para-Ph CH), 6.82 (s, 1H, Ph
CH), 2.66 (s, 6H, Ph−CH3), 2.25, 2.23 (each a s, each 3H, NCCH3),
0.41 (q, 2H, −CH2−), 0.08 (t, 3H, −CH3). 13C{1H} NMR (CD2Cl2,
δ): 175.05 (CHN), 151.17, 141.61, 139.98, 129.72, 128.34, 123.91,
119.38, 117.06 (Ph C), 19.60 (Ph-CH3), 15.30 (−CH2-), 3.46, 3.30
(NCCH3), −8.71 (−CH3). Analytical data: Calculated: C, 47.97; H,
4.31; N, 7.99. Found: C, 47.72; H, 4.37; N, 7.71.
1
triturated with hexanes to yield a dark red powder (0.13 g, 80%) . H
NMR (CD2Cl2, δ): 8.82 (s, 2H, CHN) 7.48 (m, 8H, imine Ph CH),
7.41 (t, 2H, imine Ph CH), 6.80 (s, 1H, Ph CH), 2.66 (s, 6H, Ph−
CH3), 0.96 (q, 2H, −CH2−), −0.16 (t, 3H, −CH3). 13C{1H} NMR
(CD2Cl2, δ): 175.12 (CHN), 151.70, 141.05, 139.93, 130.00, 128.17,
124.08, 123.7 (Ph C), 19.74 (Ph-CH3), 15.20 (−CH2-), −12.87
(−CH3). Analysis: Calculated: C, 50.74; H, 4.26; N, 4.93. Found: C,
50.57; H, 4.52; N, 5.04.
[(NCN)Ir(CH2CH3)(bpy)][OTf] (8). [(NCN)Ir(Et)(NCCH3)2]-
[OTf] (0.020 g, 0.029 mmol) was placed in a round-bottom flask
and dissolved in CH2Cl2. Bipyridine (0.0045 g, 0.029 mmol) was
added. The mixture was stirred for 5 min, and the solvent was removed
in vacuo. The resulting bright red residue was washed with hexanes to
(NCN)Ir(CH2CH3)(Cl)(OH2) (3). (NCN)Ir(Et)(Cl) (0.0086 g,
0.0015 mmol) was dissolved in CD2Cl2 (10 mL). Water (2 μL,
0.012 mmol) was added and mixed. The solvent was removed in
vacuo, and the red residue was triturated with hexanes to give a orange
1
produce a bright red powder (0.021 g, 0.027 mmol, 93% yield). H
NMR (CD2Cl2, δ, 295 K): 8.80 (s, 2H, CHN), 8.66 (d, 1H, bpy CH),
8.37 (d, 1H, bpy CH), 8.19 (t, 1H, bpy CH), 7.97 (m, 3H, bpy CH
and Ph CH), 7.56 (t, 1H, bpy CH), 7.45 (t, 1H, bpy CH), 7.34 (t, 1H,
bpy CH), 7.07 (t, 1H, bpy CH), 7.00 (s, 1H, Ph CH), 6.99 (t, 4H, Ph
CH), 6.46 (d, 4H, Ph CH) 2.76 (s, 6H, Ph−CH3), 1.05 (q, 2H,
−CH2−), 0.27 (t, 3H, −CH3). 13C{1H} NMR (CDCl3, δ): 173.94
1
powder (0.0084 g, 96% yield). H NMR (CD2Cl2, δ, 293 K): 8.82 (s,
2H, CHN), 7.61 (d, 4H, ortho-CH), 7.45 (t, 4H, meta-CH), 7.35 (t,
2H, para-CH), 6.75 (s, 1H, Ar CH), 4.82 (broad s, 2H, Ir−OH2), 2.65
(s, 6H, Ph−CH3), 0.50 (q, 2H, −CH2−), −0.10 (t, 3H, −CH3).
13C{1H} NMR (CD2Cl2, δ, 293 K): 171.72 (CHN), 152.41, 139.79,
524
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Inorganic Chemistry
Article
(CHN), 151.75, 141.16, 139.99, 129.65, 127.83, 124.32, 123.72, 121.54
(Ph C), 19.76 (Ph-CH3), 15.17 (−CH2-), −12.66 (−CH3). Analytical
data: Calculated: C, 50.17; H, 3.85; N, 6.69. Found: C, 50.07; H, 3.97;
N, 7.30.
(17) Bernskoetter, W. H.; Hanson, S. K.; Buzak, S. K.; Davis, Z.;
White, P. S.; Swartz, R.; Goldberg, K. I.; Brookhart, M. J. Am. Chem.
Soc. 2009, 131, 8603.
(18) Mohammad, H. A. Y.; Grimm, J. C.; Eichele, K.; Mack, H.;
Speiser, B.; Novak, F.; Quintanilla, M. G.; Kaska, W. C.; Mayer, H. A.
Organometallics 2002, 21, 5775.
(19) Winter, A. M.; Eichele, K.; Mack, H.; Kaska, W. C.; Mayer, H. A.
Organometallics 2005, 24, 1837.
(20) Zhang, X.; Kanzelberger, M.; Emge, T. J.; Goldman, A. S. J. Am.
Chem. Soc. 2004, 126, 13192.
(21) Choi, J.; Choliy, Y.; Zhang, X.; Emge, T. J.; Krogh-Jespersen, K.;
Goldman, A. S. J. Am. Chem. Soc. 2009, 131, 15627.
(22) Bailey, B. C.; Schrock, R. R.; Kundu, S.; Goldman, A. S.; Huang,
Z.; Brookhart, M. Organometallics 2009, 28, 355.
(23) Goldman, A. S.; Roy, A. H.; Huang, Z.; Ahuja, R.; Schinski, W.;
Brookhart, M. Science 2006, 312, 257.
(24) Goettker-Schnetmann, I.; Brookhart, M. J. Am. Chem. Soc. 2004,
126, 9330.
(25) Goettker-Schnetmann, I.; White, P. S.; Brookhart, M.
Organometallics 2004, 23, 1766.
[(NCN)Ir(CH2CH3)(OH2)2][BF4] (9). [(NCN)Ir(CH2CH3)-
(NCCH3)2][BF4] (0.10 g, 0.143 mmol) was dissolved in methylene
chloride (3 mL) in a round-bottom flask open to the atmosphere.
Thirty milliliters of deionized water was added, and the mixture was
heated to 50 °C while stirring vigorously for 18 h. The mixture was
filtered, and the solvent was removed in vacuo and the dark red residue
was triturated with hexanes to give a dark red powder (0.076 g, 0.116
1
mmol, 81% yield). H NMR (CD2Cl2, δ, 295 K): 8.83 (s, 2H, CHN)
7.47 (m, 8H, imine Ph CH), 7.41 (t, 2H, imine Ph CH), 6.79 (s, 1H,
Ph CH), 2.66 (s, 6H, Ph−CH3), 2.2 (broad s, 4H, OH2), 0.88 (q, 2H,
−CH2−), −0.18 (t, 3H, −CH3). 13C{1H} NMR (CD2Cl2, δ): 175.12
(CHN), 151.75, 141.16, 139.99, 129.65, 127.83, 124.32, 123.72, 121.54
(Ph C), 19.76 (Ph-CH3), 15.17 (−CH2-), −12.66 (−CH3). Analytical
data: Calculated: C, 43.97; H, 4.31; N, 4.27. Found: C, 44.36; H, 4.18;
N, 4.24.
ASSOCIATED CONTENT
(26) Kundu, S.; Choliy, Y.; Zhuo, G.; Ahuja, R.; Emge, T. J.;
Warmuth, R.; Brookhart, M.; Krogh-Jespersen, K.; Goldman, A. S.
Organometallics 2009, 28, 5432.
(27) Gupta, M.; Hagen, C.; Flesher, R. J.; Kaska, W. C.; Jensen, C. M.
Chem. Commun. 1996, 17, 2083.
■
S
* Supporting Information
Crystallographic data in CIF format and representative H
NMR spectra. This material is available free of charge via the
Internet at http://pubs.acs.org.
1
(28) Gupta, M.; Hagen, C.; Kaska, W. C.; Cramer, R. E.; Jensen, C.
M. J. Am. Chem. Soc. 1997, 119, 840.
(29) Lee, D. W.; Kaska, W. C.; Jensen, C. M. Organometallics 1998,
17, 1.
(30) Bernskoetter, W. H.; Brookhart, M. Organometallics 2008, 27,
2036.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: leah.a.wingard@gmail.com.
(31) Morales-Morales, D.; Cramer, R. E.; Jensen, C. M. J. Organomet.
Chem. 2002, 654, 44.
Notes
The authors declare no competing financial interest.
(32) Morales-Morales, D.; Redon, R.; Yung, C.; Jensen, C. M. Inorg.
Chim. Acta 2004, 357, 2953.
(33) Liu, F.; Goldman, A. S. Chem. Commun. 1999, 7, 655.
(34) Renkema, K. B.; Kissin, Y. V.; Goldman, A. S. J. Am. Chem. Soc.
2003, 125, 7770.
(35) Zhu, K.; Achord, P. D.; Zhang, X.; Krogh-Jespersen, K.;
Goldman, A. S. J. Am. Chem. Soc. 2004, 126, 13044.
(36) Punji, B.; Emge, T. J.; Goldman, A. S. Organometallics 2010, 29,
2702.
ACKNOWLEDGMENTS
■
This material is based upon work wholly supported as part of
the UNC EFRC, Center for Solar Fuels, an Energy Frontier
Research Center funded by the U.S. Department of Energy,
Office of Science, Office of Basic Energy Sciences under Award
Number DE-SC0001011.
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