Cyclometalation of 6-Phenyl-2,2′-Bipyridine and Iridium: Synthesis, Characterization, and Reactivity Studies

Article abstract of DOI:10.1021/om900014h

Heating the potential tridentate 6-(4-R-phenyl)-2,2′-bipyridine ligand 1a (R) H), and derivatives 1b (R) CMe₃) and 1c (R) OH), with IrCl₃ hydrate in 2-methoxyethanol or acetone/H₂O gave the unexpected bidentate cyclometalated NC dinuclear complexes [Ir(NC)Cl ₂(C₅H₅N)]₂ (2a - cPy), as the major product. Altering the ligand/metal ratio from 1:1 to 2:1 produced a mixture of bis-cyclometalated complexes, Ir(NNC)(NC)Cl (3a, b), with tridentate and bidentate binding modes. Using discrete Ir^I synthons, such as Ir(dmso)₃Cl or [Ir(cyclooctene)₂Cl]₂, gave a complicated mixture of products. However, when [Ir(C₂H ₄)₂Cl]₂was used, then the desired tridentate cyclometalated Ir(NNC) complex Ir(NNC)Et(C₂H₄)Cl (4) was synthesized cleanly. The dinuclear complex 2a-Py was converted to the corresponding mononuclear dichloride complexes Ir(NC)(NN)Cl₂ (5a) upon refluxing with 4,4′-ditert-butylbipyridine in N,N-dimethylacetamide (DMA). Treatment of 5a with ZnMe₂ gives Ir(NC)(NN^tBu)MeCl (6a). Abstraction of the chloride with AgOTF yields Ir(NC)(NN ^tBu)MeOTf (7a). Complex 7a undergoes stoichiometric CH activation with arenes and shows catalytic activity for the H/D exchange between benzene and (trifluoro)acetic acids.

Full text of DOI:10.1021/om900014h

Organometallics 2009, 28, 3395–3406
3395
Cyclometalation of 6-Phenyl-2,2′-Bipyridine and Iridium: Synthesis,
Characterization, and Reactivity Studies
Kenneth J. H. Young,† Muhammed Yousufuddin,† Daniel H. Ess,‡ and Roy A. Periana*,‡
Donald P. Katherine B. Loker Hydrocarbon Research Institute and Department of Chemistry, UniVersity of
Southern California, Los Angeles, California 90089-1661, and The Scripps Research Institute, Scripps
Florida, Jupiter, Florida 33458
ReceiVed January 8, 2009
Heating the potential tridentate 6-(4-R-phenyl)-2,2′-bipyridine ligand 1a (R ) H), and derivatives 1b
(R ) CMe3) and 1c (R ) OH), with IrCl3 hydrate in 2-methoxyethanol or acetone/H2O gave the unexpected
bidentate cyclometalated NC dinuclear complexes [Ir(NC)Cl2(C5H5N)]2 (2a-cPy), as the major product.
Altering the ligand/metal ratio from 1:1 to 2:1 produced a mixture of bis-cyclometalated complexes,
Ir(NNC)(NC)Cl (3a,b), with tridentate and bidentate binding modes. Using discrete IrI synthons, such as
Ir(dmso)3Cl or [Ir(cyclooctene)2Cl]2, gave a complicated mixture of products. However, when [Ir(C2H4)2Cl]2
was used, then the desired tridentate cyclometalated Ir(NNC) complex Ir(NNC)Et(C2H4)Cl (4) was
synthesized cleanly. The dinuclear complex 2a-Py was converted to the corresponding mononuclear
dichloride complexes Ir(NC)(NN)Cl2 (5a) upon refluxing with 4,4′-di-tert-butylbipyridine in N,N-
dimethylacetamide (DMA). Treatment of 5a with ZnMe2 gives Ir(NC)(NNtBu)MeCl (6a). Abstraction of
the chloride with AgOTF yields Ir(NC)(NNtBu)MeOTf (7a). Complex 7a undergoes stoichiometric CH
activation with arenes and shows catalytic activity for the H/D exchange between benzene and
(trifluoro)acetic acids.
Scheme 1
Introduction
The use of transition metal-mediated CH bond activation
(CHA) remains a promising paradigm to ultimately achieve
heteroatom functionalization of hydrocarbons.1,2 The most
efficient catalysts that utilize CHA are based on electrophilic,
redox-active, metals such as PdII, PtII, HgII, and AuI/III and require
strong acid solvents (due to water and methanol poisoning).3
Our group is interested in developing new CHA systems that
are thermally stable and do not show Lewis base inhibition.
Therefore we are exploring the use of less electrophilic metal
complexes4 based on complexes with electron-donating ligands
and metals to the left of platinum.
and water.5 Our group has also previously shown that the
O-donor (acac)2IrMePy complex6 is protic and thermally stable
and capable of CHA and functionalization. Given the success
of these systems, we were encouraged to investigate other
bidentate and tridentate ligands. Preliminary quantum mechan-
ical rapid prototyping (QMRP) using density functional theory
(DFT) of several ligand geometries and compositions attached
to iridium showed the pincer ligand motif to be promising for
CHA7 (Scheme 1), with the NNC ligand motif8 being the most
promising.9 The popularity of pincer ligand motifs is due to
their stability and reactivity for organic transformations, such
Several iridium complexes, such as Bergman’s Cp*Ir(PMe3)
complexes, efficiently catalyze H/D exchange between arenes
* Corresponding author. E-mail: rperiana@scripps.edu.
† University of Southern California.
‡ The Scripps Research Institute.
(1) (a) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H.
Acc. Chem. Res. 1995, 28, 154. (b) Periana, R. A.; Bhalla, G.; Tenn, W. J.,
III.; Young, K. J. H.; Liu, X. Y.; Mironov, O.; Jones, C. J.; Ziatdinov,
V. R. J. Mol. Catal. A: Chem. 2004, 220, 7. (c) Shilov, A. E.; Shul’pin,
G. B. Chem. ReV. 1997, 97, 2879.
(2) Crabtree, R. H. J. Organomet. Chem. 2004, 689, 4083.
(3) (a) Conley, B. L.; Tenn, W. J., III.; Young, K. J. H.; Ganesh, S.;
Meier, S.; Ziatdinov, V.; Mironov, O.; Oxgaard, J.; Gonzales, J.; Goddard,
W. A., III.; Periana, R. A. In ActiVation of Small Molecules; Tolman, W. B.,
Ed.; Wiley-VCH: Weinheim, Germany, 2006; pp 235-285, and references
therein. (b) Periana, R. A.; Taube, D. J.; Gamble, S.; Taube, H.; Satoh, T.;
Fuji, H. Science 1998, 280, 560. (c) An, Z.; Pan, X.; Liu, X.; Han, X.;
Bao, X. J. Am. Chem. Soc. 2006, 128, 16028.
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Ahrendt, K. A.; Ellman, J. A.; Tilley, T. D.; Bergman, R. G. In ActiVation
and Functionalization of C-H Bonds; Goldberg, K. I., Goldman, A. S., Ed.;
ACS Symposium Series No. 885; American Chemical Society: Washington
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Chem. Soc. 2004, 126, 13033. (c) Tellers, D. M.; Yung, C. M.; Arndtsen,
B. A.; Adamson, D. R.; Bergman, R. G. J. Am. Chem. Soc. 2002, 124,
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Chem. Soc. 2003, 125, 14292. (b) Bhalla, G.; Liu, X. Y.; Oxgaard, J.;
Goddard, W. A., III.; Periana, R. A. J. Am. Chem. Soc. 2005, 127, 11372.
(7) Muller, R. P.; Philipp, D. M.; Goddard, W. A. Top. Catal. 2003,
23, 81.
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2002, 124, 1378. (b) Khaskin, E.; Zavalij, P. Y.; Vedernikov, A. N. J. Am.
Chem. Soc. 2006, 128, 13054. (c) Ziatdinov, V. R.; Oxgaard, J.; Mironov,
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Soc. 2006, 128, 7404.
(8) Rietveld, M. H. P.; Grove, G. M.; van Koten, G. New J. Chem. 1997,
21, 751.
(9) Unpublished results.
10.1021/om900014h CCC: $40.75
2009 American Chemical Society
Publication on Web 05/14/2009

3396 Organometallics, Vol. 28, No. 12, 2009
Scheme 2. Ligand Synthesis and NMR Label
Young et al.
Scheme 3
as Heck and Suzuki couplings, alkane dehydrogenation, catalytic
alkane metathesis, hydrogen transfer dehydrogenation, hy-
droamination, and Kharsch addition.10
Prior to our initial communication,11 Constable et al. showed
that 6-phenyl-2,2′-bipyridine (NNC-H) binds in a tridentate NNC
fashion to give Pd(NNC)Cl, Pt(NNC)Cl, and Rh(NNC)Cl2L.12
Also, Jahng et al. showed that the corresponding annulated 3,2′-
polymethylene-6-(2′′-pyridyl)-2-phenylpyridines undergoes cy-
cloplatination.13 In our initial communication, we reported that
the pincer complex (NNC)PtIITFA (NNC ) κ3-6-phenyl-4,4′-
di-tert-butyl-2,2′-bipyridine, TFA ) trifluoroacetate) was suf-
ficiently thermally and protic stable to catalyze the CH activation
of benzene in trifluoroacetic acid-d1 (DTFA).11 It is known that
2-phenylpyridine undergoes cyclometalation when refluxed with
IrCl3 in 2-ethoxyethanol/H2O to produce the corresponding
cyclometalated dinuclear [(NC)2IrCl2]2 complexes.14 Given the
precedence that 6-phenyl-2,2′-bipyridine forms pincer complexes
with Pd, Pt, and Rh, and several examples of iridium-binding
bipyridines and terpyridines to form the corresponding coordi-
nation compounds,15 we envisioned that the corresponding
iridium NNC pincer complex, (NNC)IrIIICl2, could also be made
in a similar fashion.
or PhI(TFA)2. The methyl complex 7a is capable of stoichio-
metric and catalytic benzene CH activation, and new details
about the CH activation reaction are reported.
Here we report a cyclometalation study of para-substituted
6-phenyl-2,2′-bipyridine with iridium. Depending on ligand/
metal ratios, solvent conditions, and the iridium synthon, several
cyclometalated species, including dinuclear cyclometalated
(NC)Ir complexes [(NC)IrCl2Py]2 (2a-cPy), mixed Ir(NNC)-
(NC)Cl complexes (3a,b), and the Ir(NNC) complex
(NNC)Ir(C2H4)(C2H5)Cl (4), were formed. Since the
(acac)2IrMePy complex was active for benzene CH activation
and functionalization, we converted the dinuclear complex 2a-
Pytothemononuclearbis-bidentatemethylcomplex(NC)(NNtBu)-
IrMeOTf (7a), which is also capable of benzene CH activation
and functionalization.16 Complex 7a undergoes stoichiometric
oxy-functionalization to generate methyl acetate (MeOAc) or
methyl trifluoroacetate (MeTFA) when treated with PhI(OAc)2
Results and Discussion
1. Ligand Synthesis and Characterization. 6-Phenyl-2,2′-
bipyridines can be readily synthesized by several different
routes, such as the Kroehnke synthesis17 or by nucleophilic
substitution with lithiated arenes.18 This allows easy deriva-
tization of the NNC ligand and tuning of the electronic and
steric properties of the ligand and resultant complexes. tert-
Butyl (CMe3-NNC, 1b) and hydroxy (HO-NNC, 1c) groups
were introduced into the para position of the phenyl ring to
increase the solubility of the metal complexes in nonpolar
and polar solvents. Ligands 1a-c were synthesized by heating
N-[2-(2-pyridyl)-2-oxoethyl]pyridinium iodide with the ap-
propriate para-substituted 3-(dimethylamino-1-phenyl-1-pro-
panone hydrochloride and ammonium acetate in acetic acid
(Scheme 2). 1b was obtained in 60.8% yield and 1c in 60.5%
yield. The ligands were fully characterized by NMR, mass
spectrometry, elemental analysis, and X-ray crystallography.
(10) (a) van der Boom, M. L.; Milstein, D. Chem. ReV. 2003, 103, 1759.
(b) Goldman, A. S.; Roy, A. H.; Huang, Z.; Ahuja, R.; Schinski, W.;
Brookhart, M. Science 2006, 312, 257. (c) The Chemistry of Pincer
Compounds; Morales-Morales, D., Jensen, C. M., Eds.; Elsevier: Amster-
dam, 2007.
(11) Young, K. J. H.; Meier, S. K.; Gonzales, J. M.; Oxgaard, J.;
Goddard, W. A. III.; Periana, R. A. Organometallics 2006, 25, 4734.
(12) Constable, E. C.; Henney, R. P. G.; Leese, T. A.; Tocher, D. A.
J. Chem. Soc., Dalton Trans. 1990, 443.
(13) Jahng, Y.; Park, J. G. Inorg. Chim. Acta 1998, 267, 265.
(14) (a) Sprouse, S.; King, K. A.; Spellane, P. J.; Watts, R. J. J. Am.
Chem. Soc. 1984, 106, 6647. (b) Example with benzoquinoline: Nonoyama,
M. Bull. Chem. Soc. Jpn. 1974, 47, 767. (c) Grushin, V. V.; Herron, N.;
LeCloux, D. D.; Marshall, W. J.; Petrov, V. A.; Wang, Y. Chem. Commun.
2001, 16, 1494. (d) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq,
F.; Kwong, R.; Tsyba, I.; Bortz, M.; Mui, B.; Bau, R.; Thompson, M. E.
Inorg. Chem. 2001, 40, 1704.
(15) (a) Lee, J. R.; Liou, Y. R.; Huang, W. L. Inorg. Chim. Acta 2001,
319, 83. (b) Lo, K.K.-W.; Chung, C.-K.; Ng, D.C.-M.; Zhu, N. New J. Chem.
2002, 26, 81. (c) Yoshikawa, N.; Matsumura-Inoue, T. Anal. Sci. 2003, 19,
761. (d) Polin, J.; Schmohel, E.; Balzani, V. Synthesis 1998, 321.
(16) Young, K. J. H.; Mironov, O. A.; Periana, R. A. Organometallics
2007, 26, 2137.
1
The H NMR of 1b (R ) CMe3) in CDCl3 and 1c (R ) OH)
in dmso-d6 showed nine aromatics peaks, which is expected
for an unsymmetrical substituted bipyridine. The structures
were also confirmed by X-ray structure analysis (see Sup-
porting Information). Suitable crystals of 1b and 1c were
obtained from a CH2Cl2/hexane solution (1b) and MeOH/
hexane solution (1c) at -25 °C.
2. Cyclometalation Studies. A red precipitate formed upon
heating the NNC ligand 1a with IrCl3 in 2-methoxyethanol
(Scheme 3). This product is the undesired bidentate NC
cyclometalated dinuclear complex [Ir(NC)Cl2L]2 (2a, L ) H2O),
where cyclometalation occurs at the 3-position of the central
pyridine ring. The proposed structure is supported by 1D and
2D NMR, mass spectrometry, and X-ray structure analysis.
Upon dissolving in pyridine, the corresponding mononuclear

Cyclometalated Bidentate Ir(III) N-C Complexes
Organometallics, Vol. 28, No. 12, 2009 3397
resulting data were of decent quality, but the structure was
refined with difficulty. Several atoms were refined using SIMU
and DELU constraints, while others (N4, C17, C18, C19) were
left isotropic. One pyridine ring was severely disordered and
was constrained using appropriate DFIX commands. The
remaining rings were only slightly disordered and were left
alone. Figure 1 shows that metalation occurred at the 3-position
of the central pyridine ring with the two chloride ligands
arranged in a trans fashion and two pyridines cis to each other.
Table 1 gives the crystallographic data and parameters.
Given the literature precedence for iridium-binding bipy-
ridines and terpyridines to form the corresponding NN and NNN
coordination compounds, as well as forming the cyclometalated
product with 2-phenylpyridine, formation of the tridentate NNC
product was expected.15 The formation of these Ir(NC) type
complexes (Scheme 4) are relatively uncommon. However, there
are some reported exceptions in which the pyridyl ring rotates
and cyclometalation occurs instead of nitrogen binding. The one
example of an Ir(NNC) complex was formed when one of the
quinoline arms of a terpyridine rotated and cyclometalation
occurred on the back side.19 There has also been a reported
case in which one of the pyridyl rings of bipyridine rotated and
formed the corresponding NC cyclometalated iridium com-
plex.14a,20
Figure 1. Thermal ellipsoid plot of Ir(NC)(C5H5N)2Cl2 complex
2a-Py2. Thermal ellipsoids are at 50% probability; hydrogens were
omitted for clarity. Selected bond lengths (Å) and angles (deg):
Ir(1)-C(7) 2.012(13), Ir(1)-N(1) 2.048(10), Ir(1)-N(3) 2.081(10),
Ir(1)-N(4) 2.203(8), Ir(1)-Cl(2) 2.352(4), Ir(1)-Cl(1) 2.350(4);
C(7)-Ir(1)-N(1) 81.1(6), C(7)-Ir(1)-N(3) 96.15), N(1)-Ir(1)-N(3)
176.6(5), C(7)-Ir(1)-N(4) 178.9(5), N(1)-Ir(1)-N(4) 98.8(5),
N(3)-Ir(1)-N(4) 84.0(4), N(3)-Ir(1)-Cl(2) 90.3(3), N(4)-Ir(1)-
Cl(2) 90.2(3), N(1)-Ir(1)-Cl(1) 92.5(3), Cl(2)-Ir(1)-Cl(1)
178.67(13).
When the ligand to metal ratio was changed from 1:1 to 2:1,
the desired tridentate NNC coordination mode was observed.
However, these complexes also have a bidentate NC cyclom-
etalated ligand (Scheme 5). These new complexes are likely
formed when the second equivalent of ligand cleaves the
dinuclear Ir(NC) complex to form the monomeric intermediate,
Ir(NC)(NN)Cl2 (an example of such a complex is discussed
later), which then undergoes CH activation of the phenyl ring
to produce the mixed tridentate-bidentate cyclometalated
iridium complex. These complexes are not expected to be
efficient CH activation catalysts since they are coordinatively
saturated. With the tert-butyl ligand 1b, several mixed
tridentate-bidentate cyclometalated iridium complexes, Ir(CMe3-
NNC)(CMe3-NC)Cl (3b), were observed. There are two possible
conformers for each pair of diastereomers. Two complexes were
pyridyl complex, Ir(NC)Cl2(C5H5N)2 (2a-Py2), is formed. This
complex is initially quite soluble in chloroform and dichlo-
romethane; however, the pyridine trans to the metalated ring is
labile and slowly over time the corresponding dinuclear complex
[Ir(NC)Cl2(C5H5N)]2 (2a-Py) forms and precipitates from the
solution. The substituted ligands 1b and 1c also form the
corresponding bidentate, cyclometalated dinuclear complexes
[Ir(CMe3-NC)Cl2(C5H5N)]2 (2b-Py) and [Ir(HO-NC)Cl2-
(C5H5N)]2 (2c-Py) when refluxed in 2-methoxyethanol.
3. Synthesis of Dinuclear Cyclometalated Iridium
Complexes 2a-c-Py (R ) H (a), CMe3 (b), OH (c)). The 1H
NMR of 2a-Py in DMSO-d6 shows nine aromatic resonances
for the ligand (total of 12 including the pyridine ring) that
integrate to 11 protons, which is expected for the proposed
bidentate NC binding mode. If the ligand were to bind in a
tridentate NNC binding mode, 11 resonances would be expected.
The doublet of doublets (H-12) at 8.20 ppm and the triplet (H-
13) at 7.52 ppm that both integrate for two protons further
support that cyclometalation has not occurred at the phenyl ring.
The gCOSY experiment (see Supporting Information) shows
three spin systems consisting of a “two”, “four”, “three” pattern,
with the doublet at 8.51 (H-8) with a cross-peak with the doublet
at 7.70 (H-9) ppm, supporting that cyclometalation occurred
on the 3-position of the central pyridine ring. In the free ligand
1a, the carbon at the 3-position (C-7) appears at 119.48 ppm
and the meta carbon (C-12) of the phenyl ring appears at 127.13
ppm. Upon cyclometalation, the signals at 119.48 ppm disap-
peared and a new resonance for the ipso carbon appears at
143.32 ppm, while the C-12 (125.94 ppm) remains, further
supporting the proposed structure.
1
cleanly isolated and characterized by H and 13C NMR, mass
spectrometry, and elemental analysis, after passing the mixture
through silica gel with dichloromethane. Unfortunately, at least
two other minor species could not be cleanly separated and
characterized. 1a also forms the bis-cyclometalated Ir(NNC)-
(NC)Cl products, on the basis of mass spectrometry. However,
these products could not be separated and isolated.
The 1H NMR of the first isomer in CDCl3 is consistent with
a bis-cyclometalated species. A total of 18 aromatic resonances
that integrate to 20 protons were observed. The two doublets at
8.24 and 7.57 ppm for the aryl ring both integrate to two protons
and are consistent with one of the ligands binding in a bidentate
NC fashion. The doublet, doublet of doublets, and doublet at
4
7.49 (3J ) 8.2 Hz), 6.87 (3J ) 8.2 Hz, J ) 1.9 Hz), and 6.65
(4J ) 2.0 Hz) ppm support that metalation has occurred on the
phenyl ring and that one of the ligands is binding in a tridentate
NNC fashion. Further evidence for the proposed Ir(CMe3-
NNC)(CMe3-NC)Cl complex is the “four”, “four”, “three”,
“three”, “two”, “two” spin systems observed in the gCOSY
experiment (see Supporting Information). Formation of the
More evidence for the proposed binding mode can be seen
in the crystal structure of 2a-Py2 (Figure 1). Yellow crystals of
2a-Py2 were grown by slow evaporation from a concentrated
pyridine solution. Large crystals of 2a-Py2 were not available,
and data collection was performed over a period of 15 h. The
1
second isomer is also supported by H and 13C NMR.
(17) Krohnke, F. Synthesis 1976, 1.
(18) Goodman, M. S.; Hamilton, A. D.; Weiss, J. J. Am. Chem. Soc.
1995, 117, 8447.
(19) Mamo, A.; Stefio, I.; Parsi, M. F.; Credi, A.; Venturi, M.; Di Pietro,
C.; Campagna, S. Inorg. Chem. 1997, 36, 5947.
(20) Garces, F. O.; Watts, R. J. Inorg. Chem. 1990, 29, 584.

3398 Organometallics, Vol. 28, No. 12, 2009
Young et al.
Table 1. Crystallographic Data and Parameters
5a(NN-trans)
2a-Py2
5a(NC-trans)
6a
formula
fw
C26H21Cl2IrN4
652.57
C34H35Cl2IrN4O0.5
770.76
C34H35Cl2IrN4
762.76
C35H38ClIrN4
742.34
T, K
298
133(2)
148(2)
153(2)
cryst syst
space group
a, Å
b, Å
c, Å
monoclinic
P21/c
12.182(5)
12.030(5)
17.428(7)
90
109.190(7)
90
2412.2(17)
4, 1.797
5.778
triclinic
P1
triclinic
P1
7.119(4)
monoclinic
P21/c
13.873(10)
27.93(2)
11.008(8)
90
109.862(13)
90
4011(5)
4, 1.229
3.419
j
j
12.0798(13)
13.2601(14)
13.3101(14)
101.207(2)
104.310(2)
110.491(2)
1840.2(3)
2, 1.391
14.764(9)
16.725(10)
78.679(8)
79.307(10)
88.769(9)
1693.6(17)
2, 1.496
4.127
1.26 to 27.70
1.023
R, deg
ꢀ, deg
γ, deg
V, Å3
Z, Dcalc, g/cm3
µ, mm-1
θ range, deg
GOF
3.800
1.66 to 26.37
1.099
1.77 to 27.64
1.036
1.46 to 25.68
1.226
R1, Rw [I > 2σ(I)]
0.0599, 0.0896
0.0568, 0.1739
0.0673, 0.1744
0.0898, 0.2216
Scheme 4
of [Ir(ethylene)2Cl]2 in CH2Cl2 at -50 °C, a mononuclear
Ir(ethylene)4Cl species is generated in situ.22 To this solution
was added 1 equiv of ligand 1a, and the solution was stirred at
ambient temperature for 16 h (Scheme 6). 1H NMR analysis of
the reaction mixture indicates that the desired monoligated
tridentate NNC binding mode was obtained and that the
Ir(NNC)Cl(ethylene)ethyl complex (4) is now formed as the
major product. Complex 4 was isolated as an orange air-stable
solid after passing through alumina and was characterized by
NMR, mass spectrometry, and elemental analysis. The 1H NMR
of 4 in CDCl3 shows all expected 11 aromatic resonances (11
H’s), which is consistent with the proposed tridentate NNC
binding mode. The ethylene was observed as a singlet at 4.03
ppm, and the CH2 group of the Ir-CH2CH3 is diastereotopic,
appearing at 0.47 and 0.21 ppm. Further evidence for the
proposed NNC binding mode is the “four”, “three”, “four” spin
systems observed in the gCOSY experiment (see Supporting
Information). Consistent with the proposed structure, 16 aro-
matic carbons were observed in the 13C NMR. The reactivity
of these monocyclometalated IrNNC complexes are reported
elsewhere.23
4. Synthesis and Characterization of Mononuclear Cyclo-
metalated Complexes. (a) Synthesis and Characterization of
Ir(NC)(NNtBu)Cl2 (5a,b). Given the previous success with our
bis-bidentate (acac)2IrRL system for CH activation and func-
tionalization, we investigated whether the stable dinuclear (NC)Ir
complexes could be converted to mononuclear bis-bidentate
complexes by treatment with bidentate ligands. This would allow
access to a vacant cis coordination site for possible C-H
activation reactions. Upon refluxing 2a-Py with 4,4′-di-tert-
butylbipyridine (NNtBu) in DMA (Scheme 7), the corresponding
mononuclear bis-bidentate iridium dichloride complex Ir(NC)(NNt-
Bu)Cl2, 5a, was obtained in good yields (70.8%) as a mixture of
two cis-dichloride isomers. There are three possible isomers,
one trans and two cis. The two cis isomers, 5a(NC-trans) and
5a(NN-trans), were isolated after passing through silica gel with
dichloromethane. The ratio of the two isomers varied from 2:1
to 1:1. 5a is soluble in halogenated solvents and is slightly
soluble in aromatic solvents such as benzene and toluene. These
complexes were fully characterized by NMR, elemental analysis,
mass spectrometry, and X-ray crystallography.
Other solvents were also investigated. When a 5:1 acetone/
H2O mixture was used, the corresponding dinuclear complexes
2a-c-Py were formed as the major product. However, when a
THF/H2O (5:1) mixture was used, a complex mixture of
products was observed depending on the ligand. With 1a (R )
H) the cyclometalated dinuclear complex 2a-Py was the major
product. However, in the case of ligand 1b (R ) CMe3), 2b-Py
and several other products were observed. One of the products
was isolated and determined to be one of the isomers of the
mixed tridentate/bidentate complex 3b previously mentioned.
In all these cases cyclometalation occurred primarily at the
central pyridine ring instead of the phenyl ring, suggesting that
the reaction may occur via an electrophilic mechanism; cyclo-
metalation is occurring at the most electron-rich ring.21 In an
attempt to disfavor this reaction, we tried several IrI synthons,
as cyclometalation with IrI could be expected to proceed by an
oxidative addition mechanism and favor cyclometalation of the
phenyl ring. When 1a,b was heated with Ir(dmso)3Cl, a
complicated mixture of products formed, and the products could
1
not be cleanly separated. However, H NMR analysis of the
reaction mixture showed two triplets between 7.3 and 7.0 ppm,
which suggested that some Ir(NNC)H(Cl) complex was formed.
Iridium(I) cyclooctene dimer ([Ir(COE)2Cl]2) gave a complex
mixture of products with 1a,b after stirring at ambient temper-
ature in CH2Cl2. In the reaction with [Ir(COE)2Cl]2 and 1b, the
undesired mixed tridentate/bidentate complex 3b was the main
1
product, based on H NMR analysis. A minor side product
(<5%) was observed and separated by column chromatography,
1
The conformation of the two isomers was confirmed by X-ray
crystal analysis. Suitable crystals for X-ray analysis of 5a(NN-
and was assigned as an Ir(NNC) complex on the basis of H
NMR. However, when an IrI synthon with a very labile ligand
is used, the desired Ir(NNC) product was obtained cleanly as
the major product. When ethylene is bubbled through a solution
(22) Onderdelinden, A. L.; van der Ent, A. Inorg. Chim. Acta 1972, 6,
420.
(23) Young, K. J. H.; Oxgaard, J.; Ess, D. H.; Stewart, T.; Goddard,
W. A., III.; Periana, R. A. Chem. Commun 2009, DOI: 10.1039/b823303a.
(21) Ryabov, A. D. Chem. ReV. 1990, 90, 403.

Cyclometalated Bidentate Ir(III) N-C Complexes
Organometallics, Vol. 28, No. 12, 2009 3399
Scheme 5. Mixed Binding Mode for Bis-cyclometalated Iridium Complexes
Scheme
6.
Synthesis
(NNC)IrEt(C2H4)Cl Complex 4
of
Mononuclear
Tridentate
constrain the geometry. Atoms C12, C13, and C14 of the tert-
butyl group were not refined anisotropically. Although the
crystal weakly diffracted, the molecular diagram (Figure 4) does
suggest that the methyl complex was formed and that the methyl
group is cis to the chloride and trans to one of the pyridines of
the bipyridine ligand. Crystallographic data and parameters can
be found in Table 1. In order to generate a more reactive
catalytic precursor, the remaining chloride was replaced with
the more labile triflate anion by halide abstraction using silver
triflate.17
trans)24 and 5a(NC-trans) were grown by slow vapor diffusion
of hexanes into a CH2Cl2 solution. Table 1 gives crystallographic
data and conditions, and Figures 2 and 3 are molecular diagram
views. Both iridium centers adopt a slightly distorted octahedral
geometry with the two chlorides cis to each other. In the case
of 5a(NN-trans), one of the tert-butyl groups was disordered
and was solved by dual occupancy. As expected, the chloride
(Cl-2) trans to the strong σ-donor C-bound pyridyl ring is
elongated 2.480 (2) Å compared to the chloride (Cl-1) trans to
the nitrogen, 2.363 (2) Å.
5. Reactivity Studies
(a) Reaction of Ir(NNtBu)(NC)MeOTf with Acids. To
determine if these complexes are sufficiently protic and ther-
mally stable, we treated these complexes with acetic, trifluo-
roacetic, and sulfuric acids. While the complex remains intact,
the methyl group is very reactive and undergoes protonalysis
with loss of methane; when D2SO4 was used, CH3D was
observed. Attesting to the thermal stability of this ligand motif,
7a can be heated in neat H2SO4 at 200 °C for 20 h; the complex
remains intact, and no loss of NC or NN ligand was observed.
However mass spectral analysis indicated that the ligand
undergoes sulfonation. Only methane loss was observed.
When 2-3 equiv of trifluoroacetic acid was used, protonolysis
occurs over the course of a few hours (<2 h); however it is
instantaneous when dissolved in neat or concentrated trifluo-
roacetic acid solutions. When trifluoroacetic acid-d1 was used,
only CH3D was observed. After workup and isolation, the
product of this reaction was determined to be a bis-trifluoro-
(b) Synthesis and Characterization of Methyl Complexes.
The previous success using Zn(Me)2 as an alkylating reagent
for generating the reactive (acac)2IrRL complex7 prompted us
to use this reagent to replace the chloride ligands with a reactive
alkyl group. The corresponding monomethyl complex 6a was
successfully synthesized by heating either isomer of the dichlo-
ride (5a) with Zn(Me)2 in either toluene or THF at 120 °C in a
sealed tube (Scheme 7). The solution turned black, and upon
quenching with methanol and passing through silica, the
monomethylated product was obtained as a red powder in good
yields (70% yield). It is important that the reaction is carried
out at these high temperatures since at lower temperatures only
low conversions were observed. The methyl complex 6a is
readily soluble in a wide range of organic solvents, such as
dichloromethane, THF, benzene, and methanol, and has been
fully characterized by NMR, mass spectrometry, and X-ray
crystallography.
1
acetate complex based on H, 13C, and 19F NMR. In the 19F
NMR, two trifluoroacetate groups were observed at -75.70 and
-75.82 ppm since the trifluoroacetate groups are inequivalent.
However, when 7a is dissolved in acetic acid, the mono-acetate
complex, Ir(NN)(NC)OAcOTf, was observed as the major
product with small amounts of the diacetate complex,
1
Ir(NN)(NC)(OAc)2. H and 19F NMR confirms the formation
1
The H NMR spectra of 6a in CDCl3 shows a new peak at
of the monoacetate complex. Both complexes were characterized
by NMR, mass spectrometry, and elemental analysis.
0.66 ppm (3H’s), which has been assigned to the iridium-bound
methyl group. The 13C NMR spectrum also supports the
proposed structure and the Ir-CH3 resonance was observed at
-16.0 ppm. Formation of the methyl complex is further
supported by X-ray crystallography. Red needles were grown
by slow evaporation from a concentrated benzene solution.
Large crystals of 6a were also not available, which necessitated
a data collection time of 15 h. However, the resulting data were
of relatively poor diffraction quality, causing higher than normal
R values. An appropriate weighting scheme was used to lower
Rw to a reasonable value. A tert-butyl group was severely
disordered, and appropriate SADI commands were used to
(b) Stoichiometric and Catalytic CH Activation Studies.
Since these bis-bidentate complexes are protic and thermally
stable in strong acids, we investigated the activation of methane
by testing for H/D exchange between methane and sulfuric acid-
d2 or trifluoroacetic acid-d1. Unfortunately all reactions with
methane at temperatures up to 208 °C showed no incorporation
of deuterium into methane after 21 h. Even though the complex
was stable under these conditions, no loss of ligand was
observed (see Supporting Information).
The more reactive substrate benzene was then tested. Upon
heating 7a in neat benzene at 170 °C, the stoichiometric C-H
activation product Ir(NN)(NC)(C6H5)OTF, 8a, was formed in
quantitative yields as a crystalline yellow solid along with
liberation of methane (Scheme 8). The formation of the phenyl
complex was confirmed by 1H and 13C NMR as well as
(24) Crystals of 5a(NN-trans) were grown in air from undried solvents.
This may have caused water molecules to appear in the crystal lattice, and
indeed large, lone residual peaks were observed. The largest of these peaks
was refined as a water molecule.

3400 Organometallics, Vol. 28, No. 12, 2009
Scheme 7. Synthesis of Mononuclear Bis-bidentate Complexes
Young et al.
elemental analysis. The disappearance of the methyl peak and
the appearance of several broad peaks between 7.1 and 6.8 ppm
support the formation of the phenyl complex. Production of
methane was also confirmed by GC/MS. After treatment of 8a
with pyridine the phenyl peaks became well resolved. The
formation of the phenyl complex was further verified by X-ray
crystallography.17 Consistent with the stoichiometry in Scheme
8, when the reaction is performed in neat C6D6, Ir(NN)-
(NC)(C6D5)OTF complex (8a-d5) as well as CH3D is formed.
The preference for arene activation versus benzylic C-H
bond activation was determined by heating 7a in neat toluene
(Scheme 8) at 170 °C for 4 h. Only the para and meta tolyl CH
activation products were observed in a 1:1.7 ratio. Upon addition
of pyridine to the reaction mixture and removal of volatiles
under vacuum, the pyridine adduct [Ir(NNtBu)(NC)(C6H4-
(CH3))(C5H5N)]OTF (9a-Py) was obtained in good yields after
passing through silica gel. The two isomers could not be
1
separated. H NMR analysis of the isolated product showed
several new aromatic resonances between 7.0 and 6.6 ppm as
well as two singlets for the methyl group of toluene, which is
consistent with the proposed arene activation product. 13C NMR
also showed two methyl peaks (confirmed by DEPT) at 21.7
and 20.8 ppm also supporting arene activation. When a more
sterically congested arene such as mesitylene was used, benzylic
CH activation is observed. Upon heating 7a in neat mesitylene,
the stoichiometric CH activation product Ir(NNtBu)-
(NC)(CH2C6H3(CH3)2)OTF is formed (Scheme 8). Addition of
pyridine to the reaction mixture followed by removal of volatiles
Figure 2. Thermal ellipsoid plot of Ir(NC)(NNtBu)Cl2 complex
5a(NN-trans). Thermal ellipsoids are at 50% probability; hydrogens
and water molecule were omitted for clarity. Selected bond lengths
(Å) and angles (deg): Ir(1)-C(25) 1.998(9), Ir(1)-N(2) 2.014(7),
Ir(1)-N(1) 2.017(7), Ir(1)-N(3) 2.060(7), Ir(1)-Cl(1) 2.363(2),
Ir(1)-Cl(2) 2.480(2); C(25)-Ir(1)-N(2) 88.7(3), C(25)-Ir(1)-N(1)
93.9(3), N(2)-Ir(1)-N(1) 79.6(3), C(25)-Ir(1)-N(3) 80.5(3),
N(2)-Ir(1)-N(3) 96.1(3), N(1)-Ir(1)-N(3) 173.1(3), C(25)-Ir(1)-
Cl(1) 90.9(3), N(2)-Ir(1)-Cl(1) 176.1(2), N(1)-Ir(1)-Cl(1) 96.6(2),
N(3)-Ir(1)-Cl(1) 87.7(2), C(25)-Ir(1)-Cl(2) 175.8(3), N(2)-
Ir(1)-Cl(2) 88.8(2), N(1)-Ir(1)-Cl(2) 88.9(2), N(3)-Ir(1)-Cl(2)
96.4(2), Cl(1)-Ir(1)-Cl(2) 91.81(9).
Figure 3. Thermal ellipsoid plot of Ir(NC)(NNtBu)Cl2 complex
5a(NC-trans). Thermal ellipsoids are at 50% probability; hydrogens
were omitted for clarity. Selected bond lengths (Å) and angles (deg):
Ir(1)-C(25) 1.990(9), Ir(1)-N(2) 2.016(8), Ir(1)-N(3) 2.023(8),
Ir(1)-N(1) 2.103(8), Ir(1)-Cl(2) 2.334(3), Ir(1)-Cl(1) 2.353(3);
C(25)-Ir(1)-N(2) 98.6(4), C(25)-Ir(1)-N(3) 80.6(4), N(2)-Ir(1)-
N(3) 90.6(3), C(25)-Ir(1)-N(1) 175.9(4), N(2)-Ir(1)-N(1) 78.2(3),
N(3)-Ir(1)-N(1) 96.9(3), C(25)-Ir(1)-Cl(2) 96.2(3), N(2)-
Ir(1)-Cl(2) 87.7(2), N(3)-Ir(1)-Cl(2) 176.1(2), N(1)-Ir(1)-Cl(2)
86.2(3), C(25)-Ir(1)-Cl(1) 88.2(3), N(2)-Ir(1)-Cl(1) 173.3(2),
N(3)-Ir(1)-Cl(1)90.7(2),N(1)-Ir(1)-Cl(1)95.1(2),Cl(2)-Ir(1)-Cl(1)
91.44(12).

Cyclometalated Bidentate Ir(III) N-C Complexes
Organometallics, Vol. 28, No. 12, 2009 3401
meta isomers in a 1:1.8 ratio. The fact that no catalytic HD
exchange is observed between tol-d8 and C6H6 suggests the
barrier for arene CH activation from the phenyl or tolyl
complex is too high. Consistent with this observation, when
8a was heated in benzene-d6 at 170 °C for 12 h, 8a-d5 was
not observed and 8a was recovered.
Significantly, the methyl triflate complex 7a catalyzes H/D
exchange between acids (acetic and trifluoroacetic acids) and
benzene. When a 3.50 mM solution of 7a in a 1:1 mixture of
C6H6/acetic acid-d4 was heated at 170 °C for 4 h, 11.2% of the
benzene (208 turnovers, TOF ) 0.014 s-1) was converted into
a mixture of deuterated isotopologues, which consisted mainly
of C6H5D1. Control reactions were performed to verify that the
H/D exchange observed was metal mediated. In the absence of
catalyst no H/D exchange between benzene and acetic acid-d4
was observed. Catalytic activity slowly drops over time,
presumably due to catalyst deactivation from formation of either
the diacetate (Ir(NN)(NC)(OAc)2) or acetate-bridged dinuclear
complex. Consistent with the diacetate complex being an
inactive species, no significant incorporation of deuterium (<1%)
into benzene was observed with Ir(NN)(NC)(OAc)2 at 170 °C
after 4 h.
Figure 4. Thermal ellipsoid plot of Ir(NC)(NNtBu)ClCH3 complex
6a. Thermal ellipsoids are at 30% probability; hydrogens were
omitted for clarity. Selected bond lengths (Å) and angles (deg):
Ir(1)-C(25) 1.94(2), Ir(1)-N(3) 2.053(17), Ir(1)-N(2) 2.064(16),
Ir(1)-N(1) 2.132(15), Ir(1)-C(35) 2.163(17), Ir(1)-Cl(1) 2.469(6);
C(25)-Ir(1)-N(3) 78.8(7), C(25)-Ir(1)-N(2) 96.3(7), N(3)-Ir(1)-
N(2) 172.2(6), C25)-Ir(1)-N(1) 95.6(6), N(3)-Ir(1)-N(1) 95.8(7),
N(2)-Ir(1)-N(1) 78.5(6), C(25)-Ir(1)-C(35) 88.5(7), N(3)-
Ir(1)-C(35) 89.4(7), N(2)-Ir(1)-C(35) 96.7(7), N(1)-Ir(1)-C(35)
174.0(6), C(25)-Ir(1)-Cl(1) 174.3(6), N(3)-Ir(1)-Cl(1) 95.8(5),
N(2)-Ir(1)-Cl(1)89.2(5),N(1)-Ir(1)-Cl(1)86.9(5),C(35)-Ir(1)-Cl(1)
89.5(6).
Analysis of the reaction products after H/D exchange was
difficult since deuteration of the ligand had occurred. To
address this, 7a was heated in a 1:1 C6H6/CH3CO2H solution
at 170 °C for 15 h. After removal of volatiles and treatment
with pyridine, 1H NMR analysis (see Supporting Information)
showed three acetate complexes, two of which are proposed
to be [Ir(NN)(NC)(OAc)(Py)]OTf (four possible complexes,
Figure 5), and the third species is one of the Ir(NN)-
(NC)(OAc)2 isomers (Figure 5). Both complexes have similar
chemical shifts to independently synthesized mono- and bis-
acetate complexes. There was no evidence of an Ir-phenyl
species; however, this is expected since such species would
not be stable in acid solvents. Consequently, when the phenyl
product 8a is dissolved in acetic acid-d4, formation of
benzene-d1 (94.4% C6H5D1, 4.3% C6H6, 0.64% C6H4D2) is
observed.
Scheme 8. Stoichiometric Benzene, Toluene, and Mesitylene
Activation
Scheme 9 shows the likely mechanism for H/D scrambling.
An active five-coordinate species is generated upon triflate
dissociation from intermediate I, which then binds (intermediate
II) and cleaves the C-H bond of benzene to the putative iridium
phenyl species (intermediate III). The iridium phenyl then
undergoes protonalysis with DOAc to give benzene-d1 and
restart the cycle. On the basis of the observation that benzene-
d1 is the main product when 8a is treated with acetic acid-d4,
and that H/D exchange follows a Schultz-Flory distribution
(reaction mechanism where each encounter between a benzene
molecule and the catalyst leads to a single H/D exchange), CH
activation is most likely the rate-limiting step. If coordination
is rate determining, then multiple deuterium incorporation into
benzene would be expected for the stoichiometric reaction. As
expected, when an H/D exchange reaction was performed with
isolated Ir(NN)(NC)(OAc)OTf (I), the same turnover frequency
(I ) 0.015 s-1 versus 7a ) 0.014 s-1) as 7a was observed.
Consistent with the proposed mechanism, and that CH activation
occurs through a metal-mediated process, when Ir(NN)(NC)-
(OAc)OTf is heated in neat benzene at 160 °C for 1 h in the
presence of a sterically hindered base such as ethyldiisopropyl-
amine (1 equiv), the stoichiometric benzene activation product
is formed in 76% yield based on 1H NMR analysis (quantified
by added mesitylene as a standard). The starting material was
the only other species observed.
under vacuum led to the isolation of the pyridine adduct
[Ir(NN)(NC)(CH2C6H3(CH3)2)(C5H5N)]OTF (10a-Py) in good
yields after passing the mixture through silica gel. Formation
of the benzylic activation product is supported by the appearance
of two new doublets at 3.36 and 3.08, which integrate to one
proton each, corresponding to the diastereotopic Ir-CH2-R group
in the 1H NMR. The remaining methyl group (6H) at 1.78 ppm
and aryl resonance signals at 6.22 (1H) and 5.66 (2H) ppm also
support benzylic activation.
Since we established that 7a is capable of performing
stoichiometric arene C-H activation, we investigated whether
the system is also able to promote catalytic C-H activation
by examining the H/D exchange reaction between benzene
and toluene-d8. Interestingly, H/D exchange studies between
benzene and toluene-d8 at temperatures as high as 200 °C
showed no observable deuterium incorporation into the
benzene. When the reaction was repeated in a 1:1 benzene-
h6/toluene-h8 mixture, analysis of the reaction mixture after
treatment with pyridine showed that both the benzene and
toluene CH activation products were formed in roughly a
1:1 ratio. Consistent with the stoichiometric toluene results,
the tolyl products were observed as a mixture of para and

3402 Organometallics, Vol. 28, No. 12, 2009
Young et al.
Figure 5. Possible isomers for the mono- and bis-acetate (NNtBu)(NC)Ir complexes.
Scheme 9. Possible Catalytic Cycle
control was performed under identical conditions and these
values were subtracted from the catalytic runs to obtain corrected
values.
Experimental Section
General Considerations. Unless otherwise noted all reactions
were performed using standard Schlenk techniques (argon) or in a
Vacuum Atmosphere glovebox (nitrogen). IrCl3 (Pressure Chemical)
and Zn(Me)2 (Aldrich) were used as is. All solvents were reagent
grade or better. Anhydrous 2-methoxyethanol and anhydrous DMA
(Sureseal bottle, Aldrich) were use as is. THF was dried over
sodium/benzophenone ketyl and distilled over argon. Dichlo-
romethane (stabilizer removed with sulfuric acid) was dried over
P2O5 and distilled over argon. Acetic and trifluoroacetic acid were
purchased from Aldrich, degassed by freeze-pump-thaw methods,
and stored under argon. Deionized water was used as is. N-[2-
Pyridyl)-2-oxoethyl]pyridinium iodide15d and 6-phenyl-2,2′-bipy-
ridine12 were prepared following literature procedures. The Mannich
salts 4′-tert-butyl-3-(dimethylamino)-1-phenyl-1-propanone hydro-
chloride and 4′-hydroxy-3-(dimethylamino)-1-phenyl-1-propanone
hydrochloride were prepared following standard procedures.25
GC/MS analysis was performed on a Shimadzu GC-MS QP5000
(ver. 2) equipped with a cross-linked methyl silicone gum capillary
column (DB5). 1H (400 MHz), 13C (100 MHz), and 19F (376.5 MHz)
NMR were collected on a Varian 400 Mercury plus spectrometer.
Chemical shifts were referenced using residual protiated solvent.
Fluorine chemical shifts were referenced to CFCl3. All coupling
constants are reported in Hz. Chemical shifts were assigned on the
basis of gCOSY, NOEDIF, gHSQC, and gHMBC or cigar experi-
ments. Mass spectrometry was performed at UCSB, UCLA, and
UCR mass spectrometry laboratories. Elemental analyses were
performed by Desert Analytical Laboratory, Inc., AZ. X-ray
crystallography data were collected on a Bruker SMART APEX
CCD diffractometer.
Another possible mechanism is that the acidity of the bound
acid increases, thus acting like a superacid that carries out the
H/D exchange by protonating benzene. However, inconsistent
with such a mechanism is the observation that H/D exchange
in a stronger acid such as trifluoroacetic acid did not accelerate
the rate of H/D exchange. Thus when a 2.16 mM solution of
7a in 1:1 C6H6/trifluoroacetic acid-d1 was heated at 170 °C, H/D
for 5.5 h, 1.13% of the benzene (29 turnovers) was converted
into a mixture of deuterated isotopologues, which consisted
mainly of C6H5D1. Benzene and trifluoroacetic acid-d1 will
undergo background H/D exchange at these temperatures, so a
X-ray Structure Data Determination. Diffraction data were
collected with graphite-monochromated Mo KR radiation (λ )
0.71073 Å) on a Bruker SMART APEX CCD diffractometer. The
cell parameters were obtained from the least-squares refinement of
the spots (collected 60 frames) using the SMART program. A
hemisphere of data was collected up to a resolution of 0.75 Å, and
(25) Org. Synth. 1943, 23, 30.

Cyclometalated Bidentate Ir(III) N-C Complexes
Organometallics, Vol. 28, No. 12, 2009 3403
1
3
4
the intensity data were processed using the Saint Plus program.
Absorption corrections were applied by using SADABS.26 All
calculations for the structure determination were carried out using
the SHELXTL package (version 5.1).27 Initial atomic positions were
located by direct methods or by the Patterson method using XS,
and the structure was refined by least-squares methods on F2 using
SHELX. Calculated hydrogen positions were input and refined in
a riding manner along with the attached carbons.
2.86; N, 7.93. H NMR (dmso-d6): δ 9.84(dd, 1H, J ) 5.9, J )
1.6, H-1), 8.81(dd, 2H, 3J ) 6.3, 4J ) 1.6, o-Py), 8.51(d, 1H, 3J )
3
4
3
8.2, H-8), 8.35(dd, 1H, J ) 7.9, J ) 1.6, H-4), 8.32(t, 1H, J )
7.8, 4J ) 1.6, p-Py), 8.20(d, 2H, 3J ) 7.9, 4J ) 1.4, H-12), 7.84(t,
3
3
4
2H, J ) 7.9, 6.3, m-Py), 7.83(dt, 1H, J ) 7.8, 7.7, J ) 1.5,
H-3), 7.70(d, 1H, 3J ) 8.1, H-9), 7.52(t, 2H, 3J ) 7.8, 7.5, H-13),
3
3
4
7.41(t, 1H, J ) 7.4, H-14), 7.37(dt, 1H, J ) 7.6, 5.9, J ) 1.7,
H-2). 13C{1H} NMR (dmso-d6): δ 166.07(C-5), 162.10(C-6),
152.94(C-1), 149.88(C-10), 144.61(o-Py), 143.32(C-7), 143.29(C-
8), 143.02(p-Py), 139.55(C-11), 137.98(C-3), 128.68(C-13), 127.98(C-
14), 126.14(m-Py), 125.94(C-12), 123.56(C-2), 120.20(C-4),
119.76(C-9).
Synthesis of 6-(4′′-R-phenyl)-2,2′-bipyridine (1b
R )
CMe3, 1c R ) OH). N-[2-(2-Pyridyl)-2-oxoethyl]pyridinium iodide
(3.08 g, 9.45 mmol), ammonium acetate (20.54 g, 28.2 equiv), and
acetic acid (19 mL) were heated at 115 °C until everything dissolved
(∼10 min). Then the appropriate 4′-subsituted-3-(dimethylamino)-
propiophenone hydrochloride (2.60 g, 9.64 mmol) was added, and
the solution was refluxed for 6 h. The dark red-brown solution was
reduced under vacuum, diluted with water, and neutralized with
NaHCO3. The solution was filtered, and the resulting red-brown
residue was extracted with CH2Cl2 (1b) or acetone (1c). The extract
was dried over MgSO4, then purified by passing through silica gel
with CH2Cl2 (1b) or acetone (1c), yielding an off-white solid.
Data for 1b. Yield: 1.69 g (60.8%). Mp ) 74-76 °C. Rf(silica,
CH2Cl2) ) 0.24. Anal. Calcd for C20H20N2: C 83.30; H 6.99; N
9.71. Found: C 83.51; H 7.28; N 9.59. HREI-MS (M)+: calcd for
C20H20N2, 288.1626; found, 288.1621. 1H NMR (CDCl3): δ 8.71(dd,
Synthesis of [Ir(NCtBu)Cl2(C5H5N)]2, 2b-Py. IrCl3 · H2O (173.4
mg, 0.55 mmol), 1b (158 mg, 0.55 mmol), and 2-methoxyethanol
(12 mL) were heated at 130 °C in a Schlenk bomb for 16 h. The
suspension was reduced to ∼1 mL, diluted with H2O (10 mL), and
then filtered. The solid was washed with H2O and then CH2Cl2.
The residue was then extracted with pyridine, filtered over Celite,
concentrated under vacuum, and then precipitated with ether. Yield:
186 mg of crude material of suitable purity for the next step.
Relatively pure material can be obtained by passing through alumina
with a dichloromethane/MeOH gradient. FAB -MS: 630.2 (M +
H)+. 1H NMR (dmso-d6): δ 9.83(dd, 1H, 3J ) 5.9, 4J ) 1.5, H-1),
8.58(dd, 2H, 3J ) 5.7, 4J ) 1.7 o-Py), 8.48(d, 1H, 3J ) 7.9, H-8),
8.28(dd, 1H, 3J ) 7.9, 4J ) 1.8, H-4), 8.11(d, 2H, 3J ) 8.6, H-12),
7.84(dt, 1H, 3J ) 7.9, 7.4, 4J ) 1.5, H-3), 7.79(tt, 1H, 3J ) 7.6, 4J
3
4
3
4
1H, J ) 4.8, J ) 1.7, H-1), 8.65(dd, 1H, J ) 7.9, J ) 2.0,
H-4), 8.37(dd, 1H, 3J ) 7.8, 4J ) 1.0, H-7), 8.11(d, 2H, 3J ) 8.7,
H-12), 7.88(t, 1H, 3J ) 7.8, H-8), 7.85(dt, 1H, 3J ) 7.8, 7.6, 4J )
1.8, H-3), 7.76(dd, 1H, 3J ) 7.8, 4J ) 1.0, H-9), 7.56(d, 2H, 3J )
8.7, H-13), 7.32(dd, 1H, 3J ) 7.5, 4.7, 4J ) 1.2, H-2), 1.41(s, 9H,
C(Me)3). 13C{1H} NMR (CDCl3): δ 156.62(C-5), 155.79(C-6),
152.30(C-11), 150.15(C-14), 149.18(C-1), 137.74(C-8), 136.95(C-
3), 136.81(C-11), 126.84(C-12), 125.83(C-13), 123.83(C-2), 121.45(C-
4), 120.25(C-9), 119.13(C-7), 34.86(CMe3), 31.49(CMe3).
3
3
) 1.7, p-Py), 7.65(d, 1H, J ) 8.0, H-9), 7.54(d, 2H, J ) 8.6,
H-13), 7.41-7.34(m, 3H, m-Py, H-2), 1.36(s, 9H, CMe3). 13C{1H}
NMR (dmso-d6): δ 166.30(C-5), 162.09(C-6), 152.92(C-1), 150.35(C-
10), 150.07(C-14), 149.62(o-Py), 143.12(C-8), 142.73(C-7), 137.92(C-
3), 136.99(p-Py), 136.14(C-11), 125.68(C-12), 125.42(C-13),
123.90(m-Py),
123.41(C-2),
120.04(C-4),
119.54(C-9),
34.35(CMe3), 31.16(CMe3).
Synthesis of [Ir(NCOH)Cl2(C5H5N)]2, 2c-Py. IrCl3 · H2O (65.1
mg, 0.21 mmol), 1c (51.0 mg, 0.21 mmol), and 2-methoxyethanol
(3 mL) were heated at 130 °C in a Schlenk bomb for 3 h. The
solvent was removed under reduced pressure, and the resulting
residue was washed with ether. The residue was extracted with
pyridine, filtered over Celite, concentrated (1.5 mL), and then added
dropwise to a 10:2 ether/methanol solution (24 mL). The precipitate
was filtered and washed with more ether. Yield: 73.1 mg of 2c-Py.
HRFAB-MS (M + H)+: calcd for C21H17N3OCl2193Ir, 590.0378;
found, 590.0379. 1H NMR (dmso-d6): δ 9.83(d, 1H, 3J ) 5.8, H-1),
8.82(dd, 2H, 3J ) 6.6, 4J ) 1.6, o-Py), 8.48(d, 1H, 3J ) 7.8, H-8),
Data for 1c. Yield: 465.5 mg (60.5%). Mp ) 209-213 °C.
HREI-MS (M)+: Anal. Calcd for C16H12N2O, 248.0950. Found:
248.0946. Anal. Calcd for C16H12N2O: C 77.40; H 4.87; N 11.28.
1
Found: C 77.20; H 4.63; N 11.28. H NMR (dmso-d6): δ 9.81(s,
1H, OH), 8.70(dd, 1H, 3J ) 4.8, 4J ) 1.8, H-1), 8.57(dt, 1H, 3J )
8.0, 4J ) 1.1, H-4), 8.25(dd, 1H, 3J ) 7.5, 4J ) 1.1, H-7), 8.10(d,
3
3
4
2H, J ) 8.9, H-12), 7.98(dt, 1H, J ) 7.8, 7.6, J ) 1.9, H-3),
3
3
4
7.95(t, 1H, J ) 7.8, 7.5, H-8), 7.90(dd, 1H, J ) 7.9, J ) 1.2,
H-9), 7.46(dd, 1H, 3J ) 7.5, 4.8, 4J ) 1.2, H-2), 6.92(d, 2H, 3J )
8.9, H-13). 13C{1H} NMR (dmso-d6): δ 158.75(C-14), 155.59(C-
5), 155.50(C-10), 154.69(C-6), 149.25(C-1), 138.17(C-8), 137.32(C-
3), 129.38(C-11), 128.09(C-12), 124.19(C-2), 120.59(C-4), 119.29-
(C-9), 117.94(C-7), 115.59(C-13).
3
4
3
8.35(tt, 1H, J ) 8.0, 6.6, J ) 1.7, p-Py), 8.31(dd, 1H, J ) 7.5,
H-4), 8.02(d, 2H, 3J ) 8.8, H-12), 7.90-7.79(m, 3H, m-Py, H-3),
3
3
4
7.60(d, 1H, J ) 8.0, H-9), 7.36(dt, 1H, J ) 7.5, 5.8, J ) 1.7,
Synthesis of [Ir(NC)Cl2(C5H5N)]2, 2a-Py. IrCl3 · H2O (4.06 g,
0.0116 mols), ligand 1a (2.71 g, 0.0128 mols), and 2-methoxy-
ethanol (50 mL) were heated at 130 °C in a Schlenk bomb28 for
60 h. The red suspension was filtered and washed with H2O (3 ×
30 mL), MeOH (3 × 20 mL), and then ether (3 × 20 mL). The
resulting red powder was extracted with pyridine, filtered over
Celite, concentrated under vacuum, and then precipitated with ether.
The precipitate was filtered and washed with ether. The product
was then redissolved in CH2Cl2 and allowed to sit in the freezer
(-25 °C), from which [Ir(NC)Cl2(C5H5N)]2 (4.49 g) fell out of
solution. Suitable crystals of 2a-Py2 were obtained by slow
evaporation from a concentrated pyridine solution. The product
obtained is of significant purity for the next step. MALDI-MS:
1111.0 (dimer - Cl)+, 1077 (dimer - 2Cl)+, 617.1 (monomer +
Py - Cl)+, 574.1 (monomer + H)+. Anal. Calcd for C21H16Cl2-
IrN3 · 0.5C5H5N: C, 46.56; H, 3.01; N, 7.92. Found: C, 46.47; H,
29
H-2), 6.90(d, 2H, J ) 8.8, H-13). 13C{1H} NMR (dmso-d6): δ
166.45(C-5), 161.74(C-6), 157.60(C-14), 152.90(C-1), 150.24(C-
10), 149.62(o-Py), 143.02(C-8), 141.52(C-7), 137.82(C-3), 136.14(p-
Py), 130.68(C-11), 127.17(C-12), 123.92(m-Py), 123.27(C-2),
120.00(C-4), 118.79(C-9),115.39(C-13).
3
Synthesis of Ir(NNCtBu)(NCtBu)Cl, 3b. IrCl3 · H2O (109.8 mg,
0.35 mmol), 1b (200 mg, 0.69 mmol), and 2-methoxyethanol (10
mL) were heated at 130 °C in a Schlenk bomb for 19 h. The solvent
was removed under reduced pressure. The red residue was then
passed through silica gel with CH2Cl2. Yield: 80.6 mg of isomer 1
and 14.2 mg of isomer 2. Data for isomer 1: HRESI-MS (M +
H)+: calcd for C40H39ClIrN4, 801.2469; found, 801.2444. 1H NMR
3
3
(CDCl3): δ 9.05(d, 1H, J ) 7.83, H-8), 8.35(d, 1H, J ) 7.43,
H-4), 8.24(d, 2H, 3J ) 8.61, H-12), 8.06(d, 1H, 3J ) 5.48, H-15),
8.04(d, 1H, 3J ) 8.22, H-18), 7.89(d, 1H, 3J ) 7.83, H-23), 7.87(d,
3
3
3
1H, J ) 7.83, H-21), 7.79(d, 1H, J ) 7.83, H-9), 7.71(t, 1H, J
) 8.0, H-22), 7.68(dt, 1H, 3J ) 8.2, 7.8, 4J ) 1.57, H-17), 7.57(d,
3
3
(26) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.
(27) Sheldrick, G. M. SHELXTL, version 5.1; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 1997.
(28) Thick glass walled ampule sealed with a resealable high-vac PTFE
valve.
2H, J ) 8.61, H-13), 7.49(d, 1H, J ) 8.22, H-26), 7.44(dt, 1H,
(29) 13C NMR shifts were assigned on the basis of the free ligand and
complexes 2a,b-Py.

3404 Organometallics, Vol. 28, No. 12, 2009
Young et al.
4
3
3J ) 8.61, 8.22, J ) 1.57, H-3), 7.30(d, 1H, J ) 5.48, H-1),
(M + K)+, 727 (M - Cl)+. 1H NMR (CDCl3): δ 10.01(dd, 1H, 3J
7.14(dd, 1H, 3J ) 7.6, 5.4, 4J ) 1.0, H-16), 6.87(dd, 1H, 3J ) 8.2,
) 5.8, J ) 1.5, H-1), 9.97(d, 1H, J ) 6.3, H-24), 8.69(bs, 1H,
H-4), 8.05(d, 1H, 4J ) 2.0, H-21), 7.98-7.92(m, 3H, H-3, H-12),
7.93(d, 1H, 4J ) 2.0, H-18), 7.71(dd, 1H, 3J ) 6.3, 4J) 2.0, H-23),
7.51(d, 1H, 3J ) 6.3, H-15), 7.50(dt, 1H, 3J ) 7.4, 5.8, H-2), 7.43(t,
4
3
4J ) 1.9, H-27), 6.65(d, 1H, J ) 2.0, H-29), 6.64(dt, 1H, J )
4
3
4
7.5, 5.8, J ) 1.6, H-2), 1.42(s, 9H, CMe3), 1.03(s, 9H, CMe3).
13C{1H} NMR (CDCl3): δ 168.30(C-5), 165.60(C-19), 161.82(C-
6), 158.83(C-20), 156.03(C-10), 154.27(C-24), 153.73(C-28),
152.79(C-15), 150.86(C-14), 149.84(C7) 148.40(C-1), 145.18(C30),
143.56(C-8), 143.06(C25), 138.36(C-11), 138.20(C-22), 137.88(C-
17), 136.08(C-3), 134.41(C-29), 126.84(C-16), 125.97(C-12),
125.89(C-13), 125.00(C-26), 123.21(C-2), 123.14(C-18), 121.86(C-
9), 121.11(C-4), 119.46(C-27), 118.54(C-23), 117.50(C-21),
34.86(CMe3), 34.78(CMe3), 31.59(CMe3), 31.29(CMe3).
3
3
4
2H, J ) 7.4, 7.2, H-13′), 7.36(t, 1H, J ) 7.2, J ) 1.4, H-14),
7.21(d, 1H, 3J ) 8.0, H-8), 7.13(dd, 1H, 3J ) 6.3, 4J ) 2.0, H-16),
6.68(d, 1H, 3J ) 8.0, H-9), 1.54(s, 9H, CMe3), 1.32(s, 9H, CMe3).
13C{1H} NMR (CDCl3): δ 165.36, 162.96, 162.74, 162.15, 157.91,
157.79, 151.82, 151.66, 151.61, 149.42, 140.07, 139.70, 138.75,
137.17, 128.77, 128.32, 126.32, 124.85, 124.80, 124.71, 121.76,
121.23, 119.83, 119.58, 35.75(CMe3), 35.52(CMe3), 30.76, (CMe3)
30.44(CMe3).
1
3
Data for isomer 2: H NMR (CDCl3): δ 10.2(dd, 1H, J ) 5.7,
4J ) 1.6, H-1), 8.55(dd, 1H, 3J ) 8.0, 4J ) 1.6, H-4), 8.03(d, 1H,
3J ) 8.1, H-18), 7.98(m, 2H, H-3,15), 7.85(d, 2H, 3J ) 8.6, H-12),
7.81-7.73(m, 3H, H-17,21,22), 7.68(t, 1H, H-23), 7.49(dt, 1H, 3J
) 7.3, 5.8, J ) 1.6, H-2), 7.47(d, 1H, J ) 8.2, H-26), 7.39(d,
2H, J ) 8.6, H-13), 7.22(m, 1H, H-16), 6.98(d, 1H, J ) 8.0,
H-8), 6.91(dd, 1H, J ) 8.2, J ) 1.9, H-27), 6.53(dd, 1H, J )
8.2, 4J ) 1.9, H-9), 6.27(d, 1H, 4J ) 1.9, H-29), 1.31(s, 9H, CMe3),
1.03(s, 9H, CMe3). 13C{1H} NMR (CDCl3): δ 167.96(Py),
165.11(Py), 161.48(Py), 157.83(Py), 155.35(Py), 153.94(Ph),
150.98(Py), 150.95(Ph), 150.34(Py), 149.92(Py), 148.68(Py),
142.06(Ph), 141.06(Py), 138.71(Ph), 137.80(Ph), 137.48(Py),
137.30(Py), 136.76(Ph), 129.00(Py), 127.04(Py), 125.84(Ph),
125.73(Ph), 125.03(Ph), 124.04(Py), 122.95(Py), 121.24(Py),
121.09(Py), 119.37(Ph), 118.11(Py), 117.05(Py), 34.77(CMe3),
34.71(CMe3), 31.48(CMe3), 31.27(CMe3).
Data for 5a(NC-trans): MALDI-MS (DHB matrix): 845 (M
-2Cl + DHB)+, 801 (M + K)+, 785 (M + Na)+, 763 (M + H)+,
1
3
727 (M - Cl)+. H NMR (CDCl3): δ 9.96(d, 1H, J ) 5.8, H24),
4
3
3
3
4
8.92(d, 1H, J ) 8.0, H8), 8.50(dd, 1H, J ) 8.0, J ) 1.5, H-1),
3
3
8.23(dd, 2H, 3J ) 8.2, 4J ) 1.3, H-12), 8.20(d, 1H, 4J ) 1.8, H21),
3
4
3
4
3
8.02(d, 1H, J ) 2.0, H18), 7.98(d, 1H, J ) 6.3, H15), 7.90(dd,
1H, J ) 5.8, J ) 1.9, H23), 7.80(d, 1H, J ) 8.0, H9),7.64(dt,
3
4
3
3
4
1H, J ) 7.8, 7.6, J ) 1.6, H2), 7.55(m, 3H, H4,13), 7.45(t, 1H,
3J ) 7.4, H14), 7.10(d, 1H, 3J ) 6.3, 4J ) 2.1, H16), 6.95(dt, 1H,
3J ) 7.4, 5.8, 4J ) 1.6, H3), 1.58(s, 9H, CMe3), 1.35(s, 9H, CMe3).
13C{1H} NMR (CDCl3): δ 167.58, 163.37, 162.83, 162.07, 158.56,
155.91, 153.76, 151.99, 149.59, 149.33, 143.18, 140.41, 137.94,
128.81, 128.18, 126.61, 125.19, 124.43, 124.02, 122.26, 121.92,
119.98, 119.51, 35.86(CMe3), 35.42(CMe3), 30.85(CMe3),
30.50(CMe3).
Synthesis of Ir(NC)(NNtBu)CH3Cl (6a). The dichloride 5a
(148.0 mg, 0.19 mmol) and Zn(Me)2 2 M in toluene (200 uL, 0.40
mmol) were heated in THF (8 mL) at 110 °C. The black solution
was quenched with methanol. The solvent was removed under
vacuum, and the red residue was extracted with CH2Cl2 and filtered
through Celite. It was then purified by passing through silica with
CH2Cl2 followed by ether. Yield: 101.8 mg (70.7% of 6a). MALDI-
MS (DHB matrix): 845.4 (M - Cl + DHB + H)+, 743.3 (M +
H)+, 727.3 (M - CH3)+, 707.4 (M - Cl)+. Anal. Calcd for
C35H38ClIrN4 · 0.25C6H6: C, 57.54; H, 5.23; N, 7.35; Cl, 4.65.
Synthesis of Ir(NNC)EtCl(C2H4), 4a. In a Schlenk bomb,
[Ir(C2H4)2Cl]2 (868 mg, 0.969 mmol) was dissolved in CH2Cl2 (35
mL) and then chilled to -50 °C, and ethylene was bubbled through.
In a second flask 6-phenyl-2,2′-bipyridine (450 mg, 1.94 mmol)
was dissolved in CH2Cl2 (10 mL) and then transferred (by cannula)
to the iridium solution. The flask was then washed with CH2Cl2 (5
mL) and then transferred over. The solution was then stirred at
-50 °C for 5 min and then slowly allowed to warm to ambient
temperature, after which it was allowed to stir for 16 h. The solvent
was removed under vacuum, and the resulting residue was washed
with ether and then passed through a silica gel plug (∼1.5 in. × 3
in.) with ether to remove a red-orange band (impurity), then ethyl
acetate to remove the product. The product was then reprecipitated
from CH2Cl2/pentane. Yield: 626.5 mg (62.7%). HRESI-MS [2M
- Cl]+ obsd 997.2178 calcd 997.220 (-2.2 ppm). Anal. Calcd for
C20H20ClIrN2: C, 46.55; H, 3.91; N, 5.43. Found: C, 45.32; H, 3.89;
1
Found: C, 57.89; H, 5.54; N, 7.25; Cl, 4.41. H NMR (CDCl3): δ
9.89(dd, 1H, 3J ) 5.7, 4J ) 1.6, H-1), 9.26(d, 1H, 3J ) 6.1, H-24),
8.47(dd, 1H, 3J ) 7.9, 4J ) 1.6, H-4), 8.11(d, 1H, 4J ) 1.9, H-21),
8.05(dd, 2H, 3J ) 8.0, 4J ) 1.6, H-12), 8.02(d, 1H, 4J ) 1.9, H-18),
7.86(dt, 1H, 3J ) 7.6, 4J ) 1.6, H-3), 7.75(d, 1H, 3J ) 5.7, H-15),
3
4
3
7.59(dd, 1H, J ) 6.1, J ) 2.0, H-23), 7.43(t, 2H, J ) 7.6, 7.4,
1
3
3
4
N, 5.12. H NMR (CDCl3): δ 9.36(d, 1H, J ) 5.7, H-1), 8.14(d,
H-13), 7.33-7.38(m, 2H, H-2,14), 7.21(dd, 1H, J ) 5.7, J )
1.9, H-16), 7.15(d, 1H, 3J ) 8.0, H-8), 6.69(d, 1H, 3J ) 8.0, H-9),
1.54(s, 9H, CMe3), 1.35(s, 9H, CMe3), 0.66(s, 3H, Ir-CH3). 13C{1H}
NMR (CDCl3): δ 165.58, 162.79, 161.04, 160.92, 159.20, 155.35,
154.06, 150.99, 150.41, 148.82, 148.06, 145.67, 140.39, 139.07,
136.58, 128.78, 127.76, 125.90, 124.45, 124.40, 124.05, 120.93,
119.75, 119.20, 35.47(CMe3), 35.37(CMe3), 30.71(CMe3),
30.52(CMe3), -16.09(Ir-Me).
1H, 3J ) 8.0, H-4), 8.02(dt, 1H, 3J ) 8.0, 4J ) 1.4, H-3), 7.94(dd,
3
4
3
4
1H, J ) 7.7, J ) 1.7, H-7), 7.85(dd, 1H, J ) 8.0, J ) 1.7,
3
3
4
H-9), 7.81(t, 1H, J ) 7.8, H-8), 7.73(dd, 1H, J ) 8.9, J ) 0.9,
3
4
3
H-15), 7.65(dd, 1H, J ) 7.9, J ) 1.7, H-12), 7.60(dt, 1H, J )
7.2, 5.7, 4J ) 1.6, H-2), 7.29(dt, 1H, 3J ) 8.0, 7.3, 4J ) 1.6, H-14),
3
4
7.14(d, 1H, J ) 7.6, J ) 1.0, H-13), 4.03(s, 4H, C2H4), 0.48(m,
1H, -CH2-CH3), 0.22(m, 1H, -CH2-CH3), -0.29(t, 3H, -CH2-
CH3), 13C{1H} NMR (CD2Cl2): δ 164.27(C-16), 158.76(C-5),
153.74(C-6), 151.94(C-1), 145.14(C-10), 144.77(C-11), 139.17(C-
3), 138.53(C-8), 135.25(C-15), 132.00(C-14), 127.80(C-13), 125.49(C-
2), 123.74(C-12), 123.20(C-4), 119.52(C-9), 118.88(C-7), 67.08-
(C2H4), 14.70(-CH2CH3), -7.13(CH2CH3).
Synthesis of Ir(NC)(NNtBu)CH3OTf (7a). Silver triflate (385.3
mg, 1.50 mmol) and 6a (1.01 g, 1.36 mmol) were stirred in the
dark for 2 days in CH2Cl2 (25 mL). The yellow-orange suspension
was filtered over Celite and washed with CH2Cl2. The solvent was
removed under reduced pressure. The orange-red residue was then
redissolved in CH2Cl2 and passed through a silica gel plug, and
the product (orange band) was removed with ether. The solvent
was removed under reduced pressure, and the product was
recrystallized from CH2Cl2/ether at -35 °C. Yield: 966.4 mg (82.8%
isolated yield). Anal. Calcd for C36H38F3IrN4O3S: C, 50.51; H, 4.47;
N, 6.55; F, 6.66. Found: C, 50.20; H, 4.75; N, 6.31; F, 6.39. ESI-
MS: 857.2 (M + H)+, 841.2 (M - CH3)+, 748.3 (M - OTf +
Synthesis of Ir(NC)(NNtBu)Cl2, 5a. 2a-Py (500 mg, 0.87 mmol)
and 4,4′-di-tert-butyldipyridyl (257.4 mg, 0.96 mmol) were heated
in DMA (10 mL) at 160 °C for 20 h. The solution was filtered
through Celite, and the solvent was removed under vacuum. The
red residue was extracted with CH2Cl2 and passed through silica
(15-40 µm) with CH2Cl2, yielding 174.4 mg of 5a(NN-trans) and
148.0 mg of 5a(NC-trans).
1
Data for 5a(NN-trans): Anal. Calcd for C34H35Cl2IrN4: C, 53.54;
H, 4.62; N, 7.34; Cl, 9.30. Found: C, 53.45; H, 4.91; N, 7.16; Cl,
9.59. MALDI-MS (DHB matrix): 845 (M - 2Cl + DHB)+, 801
NCCH3)+, 707.3 (M - OTf)+. H NMR (CD2Cl2): δ 9.21(d, 1H,
3J ) 6.2, H-24), 9.07(d, 1H, 3J ) 5.8, H-1), 8.43(d, 1H, 3J ) 8.1,
4
4
H-4), 8.17(d, 1H, J ) 2.1, H-21), 8.09(d, 1H, J ) 1.9, H-18),

Cyclometalated Bidentate Ir(III) N-C Complexes
Organometallics, Vol. 28, No. 12, 2009 3405
3
4
3
7.99(d, 2H, J ) 8.3, J ) 1.4, H-12), 7.93(dt, 1H, J ) 7.8, 7.7,
4J ) 1.5, H-3), 7.73(d, 1H, 3J ) 5.9, H-15), 7.65(dd, 1H, 3J ) 6.2,
4J ) 2.2, H-23), 7.48(dt, 1H, 3J ) 7.3, 5.8, 4J ) 1.5, H-2), 7.40(t,
8.08(d, 1H, 4J ) 1.9, NNtBu), 7.99(dd, 2H, 3J ) 7.1, H-12),
7.88-7.94(m, 2H, H-3, NNtBu), 7.85(t, 1H, 3J ) 7.8, p-Py),
3
7.52-7.60(m, 3H, H-2, NNtBu),7.56(t, 2H J ) 7, m-Py), 7.40(dt,
3
4
3
3
3
4
2H J ) 7.8, 7.0, J ) 1.5, H13), 7.33(dt, 1H, J ) 7.8, H14),
2H, J ) 8.4,7.8, H-13), 7.33(dt, 1H, J ) 7.4, J )1.5, H-14),
7.29(dd, 1H, 3J ) 5.9, 4J ) 1.8, H-16), 7.07(d, 1H, 3J ) 8.1, H-8),
6.46(d, 1H, 3J ) 8.1, H-9), 1.54(s, 9H, CMe3). 1.35(s, 9H, CMe3),
0.58(s, 3H, Ir-Me). 13C{1H} NMR (CD2Cl2): δ 164.88, 163.28,
162.84, 162.78, 160.27, 156.38, 151.23, 149.62, 149.23, 148.61,
140.39, 139.61, 137.75, 135.24, 129.15, 128.37, 126.20, 125.15,
124.90, 124.69, 121.53, 120.89, 120.75, 119.72, 35.99(CMe3),
35.89(CMe3), 30.75(CMe3), 30.56(CMe3), -14.56(Ir-Me). 19F NMR
(CDCl3): δ -79.0.
7.31(d, 1H, 3J ) 7.9, H-8), 6.93(bd, 0.7H, 3J ) 7.8, tolyl), 6.85(bd,
2H, o,p-tolyl for meta isomer), 6.77(t, 1H, J ) 7.7, 7.3, m-tolyl
3
for meta isomer), 6.66-6.73(m, 3H, o-tolyl for para isomer, o-tolyl
for meta isomer, H-9), 2.17(s, 1H, p-tolyl-CH3), 2.09(s, 2H, m-tolyl-
CH3), 1.49(s, 9H, CMe3), 1.35(s, 9H, CMe3). 13C{1H} NMR
(CDCl3): δ 166.15, 164.36, 164.33, 164.27, 162.20, 162.17, 158.36,
155.30, 155.27, 152.02, 152.01, 151.76, 151.50, 151.48, 149.33,
149.29, 148.64, 148.58, 142.99, 140.76, 140.72, 139.94, 139.62,
139.11, 139.06, 138.57, 137.17, 136.51, 135.82, 132.66, 132.30,
129.13, 128.74, 128.50, 127.49, 127.18, 127.08, 127.03, 127.00,
126.56, 126.40, 125.99, 125.93, 125.83, 125.78, 124.09, 122.45,
122.43, 121.78, 121.45, 121.57(q, J ) 320, OTf), 121.01,, 36.12,
36.10, 30.57, 30.47, 21.67, 20.83. 19F NMR (CDCl3): δ -78.5.
Reaction of 7a with Mesitylene. A Schlenk bomb containing
81.7 mg of 7a (0.0936 mmol) in 15 mL of mesitylene was heated
at 170 °C for 16 h. After cooling, ∼3 mL of pyridine was added.
The yellow solution was stirred for 30 min. Then the solvent was
removed under reduced pressure. The resulting yellow solid was
redissolved in CH2Cl2 and reprecipitated with pentane, yielding the
Synthesis of Ir(NC)(NNtBu)(C6H5)OTf (8a). In a Schlenk bomb
complex 7a (100 mg, 0.12 mmol) was heated at 170 °C in benzene
(30 mL) for 6.5 h. The solvent was then removed under reduced
pressure. The resulting yellow microcrystalline solid was redissolved
in a minimal amount of CH2Cl2 and reprecipitated with pentane,
yielding 103.9 mg (96.9%) of 8a. Anal. Calcd for 8a: C, 53.64; H,
4.39; N, 6.10,; F, 6.21. Found: C, 53.30; H, 4.31; N, 6.03; F 6.33.
1H NMR (CDCl3): δ 9.18 (d, 1H, J ) 5.9, H-1), 8.89 (d, 1H, J
3
3
) 6.1, NNtBu), 8.40 (d, 1H, J ) 8.1, H-4), 8.13 (d, 1H, J ) 2.0,
NNtBu), 8.07 (d, 1H, 4J ) 1.8, NNtBu), 8.04 (d, 2H, 3J ) 7.3, H-12),
7.82(dt, 1H, 3J ) 7.8, 4J ) 1.4, H-3), 7.61 (d, 1H, 3J ) 5.9, NNtBu),
3
4
7.46-7.32(m, 5H, H-2, 13, 14, NNtBu), 7.27(dd, 1H, J ) 5.9, J
3
4
stoichiometric
CH
activation
product
[Ir(NC)-
(NNtBu)(mesityl)(C6H5N)]OTf (10a-Py) as a yellow powder (90%
conversion by NMR). MALDI-MS (2,5-DHB matrix): 811 (M -
Py - OTf)+, 845 (M - mesityl - Py - OTf + matrix)+. 1H NMR
(CDCl3): δ 9.18(d, 1H, 3J ) 6.1, H-1), 8.65(d, 2H, o-Py), 8.20(dd,
1H, 3J ) 8.0, 4J ) 2, H-4), 8.19(d, 1H, NNtBu), 8.07(d, 1H, NNtBu),
8.00(d, 2H, H-12), 7.94(dt, 1H, 3J ) 7.6, H-3), 7.92 (d, 1H, NNtBu),
7.77(dd, 1H, NNtBu), 7.70(m, 2H, NNtBu), 7.59(t, 2H, m-Py), 7.42
(m, 4H, H-2, NNtBu), 7.35 (dt, 1H, H-14), 7.19(d, 1H, H-8), 7.11
(dt, 1H, Py), 6.53 (d, 1H, H-9), 6.24(s, 1H, mesityl), 5.65(s, 2H,
mesityl), 3.30(d, 1H 3J ) 9.2, -CH2-ArMe2), 3.03(d, 1H 3J ) 9.2,
-CH2-ArMe2), 1.79(s, 6H, -CH2-ArMe2), 1.43 (s, 9H, CMe3), 1.30
(s, 9H, CMe3). 19F NMR (CDCl3): δ -78.59.
) 1.8, NNtBu), 7.17 (d, 1H, J ) 8.2, H-8), 7.11-6.60(bs, Ph),
3
6.86(bt, 1H, 3J ) 7.0, Ph), 6.53(d, 1H, 3J ) 8.1, H-9), 1.50(s, 9H,
CMe3), 1.35(s, 9H, CMe3). 13C{1H} NMR (CDCl3): δ 161.17,
162.55, 161.90, 159.06, 156.14, 152.80, 149.82, 149.08, 148.17,
139.41, 138.97, 137.60, 137.51, 135.45, 128.64, 128.28, 128.03,
126.45, 125.72, 124.56, 124.25, 124.18, 122.39, 121.14, 120.86(q,
CF3,
J ) 318.6), 120.66, 119.31, 118.88, 35.43(CMe3),
35.36(CMe3), 30.38(CMe3), 30.26(CMe3). 19F NMR (CDCl3): δ
-78.97.
Synthesis of [Ir(NC)(NNtBu)(C6H5)(C6H5N)]OTf (8a-py). In a
Schlenk bomb 8a (20 mg, 0.0218 mmol) was dissolved in 1:1
pyridine/CH2Cl2 (4 mL). The yellow solution was stirred for 30
min. Then the solvent was removed under reduce pressure. Suitable
crystals for X-ray diffraction were grown overnight in a NMR tube
from a concentrated solution in CDCl3. 1H NMR (CDCl3): δ 9.16(d,
1H, 3J ) 6.3, H-15 or 24), 8.59(d, 1H, 3J ) 5.6, H-1), 8.50(d, 2H,
3J ) 5.4, o-Py), 8.41(dd, 1H, 3J ) 8.0, 4J ) 1.2, H-4), 8.16(d, 1H,
Reaction of 7a with Acetic Acid. In a 30 mL screw cap vial 7a
(214 mg, 0.29 mmol) was dissolved in acetic acid (10 mL) and
stirred for 2 h. The solution was then diluted with water (20 mL)
and extracted with CH2Cl2 (2 × 10 mL). The extracts were then
washed with water and dried with MgSO4. The solvent was removed
under vacuum, and the resulting orange residue was sonicated with
ether, then precipitated with pentane. The product was obtained as
a yellow-orange powder after redissolving and precipitating with
pentane. Yield: 127 mg of Ir(NN)(NC)OAcOTf (48.9%). 1H NMR
analysis of the supernatant showed some of the diacteate complex
Ir(NN)(NC)(OAc)2.
4J ) 2.0, NNtBu), 8.10(d, 1H, J ) 1.9, NNtBu), 7.99(d, 2H, J )
4
3
7.3, H-12), 7.90(dt, 1H, 3J ) 7.8, H-3), 7.90(d, 1H, 3J ) 5.9, NNtBu),
3
4
3
4
7.86(dt, 1H, J ) 7.7 J ) 1.4 p-Py), 7.60(dd, 1H, J ) 6.1, J )
2.2, NNtBu) 7.53-7.58(m, 2H, NNtBu, H-2), 7.46(t, 2H, J ) 6.7,
3
m-py), 7.40(t, 2H, 3J ) 7.7, 7.1, H-13), 7.33(dt, 1H, 3J ) 7.3, 4J )
2.3, 1.4, H-14), 7.28(d, 1H, 3J ) 7.9, H-8), 7.06(bs, 2H, Ph),
3
Data
for
Ir(NN)(NC)OAcOTf:
Anal.
Calcd
for
6.88(bm, 3H, Ph), 6.69(d, 1H, J ) 7.9, H-9), 1.49(s, 9H, CMe3),
1.35(s, 9H, CMe3). 13C{1H} NMR (CDCl3): δ 165.61, 163.78,
163.72, 162.14, 158.52, 154.38, 151.93, 151.21, 151.17, 149.18,
149.00, 142.50, 139.57, 138.79, 138.58, 137.10, 128.87, 128.47,
127.14, 126.88, 126.10, 125.90, 125.03, 122.81, 122.17, 121.40,
120.94, 120.54, 35.92, 35.86, 30.58, 30.45. 19F NMR (CDCl3): δ
-78.53.
C37H38F3IrN4O5S · H2O: C, 48.41; H, 4.39; N, 6.10. Found: C, 48.36;
H, 4.13; N, 6.06. HRESI-MS: (M - OTf)+ calc for C36H38IrN4O2
751.2624, found 751.2625 (0.1 ppm). 1H NMR (CDCl3): δ 9.27(d,
3
3
3
1H, J ) 5.4, H-1), 8.84(d, 1H, J ) 6.1, NNtBu), 8.58(dd, 1H, J
) 8.0, 4J ) 0.9, H-4), 8.23(d, 1H, 4J ) 1.9, NNtBu-H), 8.07(d, 1H,
4J ) 1.9, NNtBu), 7.99-8.04(m, 3H, H-3, o-Ph), 7.77(dd, 1H, 3J )
4
3
4
6.1, J ) 1.9, NNtBu), 7.59(dt, 1H, J ) 7.5, 5.8, J ) 1.5, H-2),
7.44(t, 2H, 3J ) 7.7, 7.1, m-Ph), 7.40(d, 1H, 3J ) 6.2, NNtBu), 7.37(t,
1H, 3J ) 7.1, p-Ph), 7.23(d, 1H, 3J ) 8.1, H-8), 7.18(dd, 1H, 3J )
6.2, 4J ) 2.1, NNtBu), 6.54(d, 1H, 3J ) 8.0, H-9), 1.86(s, 3H, OAc),
1.57(s, 3H, CMe3), 1.35(s, 3H, CMe3). 13C{1H} NMR (CDCl3): δ
184.35(OAc), 165.11, 164.91, 164.06, 163.03, 158.42, 158.27,
152.55, 150.96, 150,45, 149.16, 140.79, 139.87, 139.21, 130.47,
128.92, 128.77, 126.35, 125.07, 124.95, 122.00, 121.97, 121.24,
121.20, 120.91, 120.42(q, JC-F ) 321.7, OTF), 118.82, 36.11, 35.74,
30.64, 30.33, 24.54(OAc). 19F NMR (CDCl3): δ -78.91.
Synthesis of [Ir(NC)(NNtBu)(tolyl)(C6H5N)]OTf (9a-py). A
Schlenk bomb containing 80.1 mg of 7a (0.0936 mmol) in 15 mL
of toluene was heated at 170 °C for 4 h. After cooling, ∼3 mL of
pyridine was added. The yellow solution was stirred for 30 min.
Then the solvent was removed under reduced pressure. The resulting
yellow solid was redissolved in CH2Cl2 and reprecipitated with
pentane, yielding the stoichiometric CH activation product as a
yellow powder in quantitative yields (94.2 mg). MALDI-MS: 845
(M - tolyl - Py - OTf + matrix)+, 783 (M - Py - OTf)+, found
1
3
783.2958, calc 783.3033. H NMR (CDCl3): δ 9.19(d, 1H, J )
6.0, NNtBu), 8.60(d, 1H, J ) 6.0, H-1 for meta isomer), 8.58(d,
3
Data for Ir(NN)(NC)(OAc)2: HRESI-MS: (M - OAc)+ calc for
3
3
1H, J ) 6.0, H-1 for para isomer), 8.51(d, 2H, J ) 5.5, o-Py),
C36H38IrN4O2 751.2624, found 751.2613 (1.5 ppm). 1H NMR
8.41(dd, 1H, 3J ) 7.9, 4J ) 0.6, H-4), 8.14(d, 1H, 4J ) 1.9, NNtBu),
(CDCl3): δ 9.42(d, 1H, J ) 6.2, NNtBu-H), 9.37(d, 1H, J ) 5.9,
3
3

3406 Organometallics, Vol. 28, No. 12, 2009
Young et al.
H-1), 8.51(dd, 1H, 3J ) 8.1, H-4), 8.02(d, 1H, 4J ) 2.0, NNtBu-H),
7.99(d, 2H, 3J ) 8.0, o-Ph), 7.91(dt, 1H, 3J ) 7.8, H-3), 7.84(d, 4J
) 1.9, NNtBu-H), 7.71(dd, 1H, 3J ) 6.0, 4J ) 2.0, NNtBu-H), 7.46(dt,
on the fragmentation pattern of the benzenes due to replacement
of H with D. Fortunately, because of the relative stability of the
parent ion toward fragmentation, it can be used reliably to quantify
the exchange reactions. The mass range from 78 to 84 (for benzene)
was examined for each reaction and compared to a control reaction
where no metal catalyst was added. The program was calibrated
with known mixtures of benzene isotopoloques. The results obtained
from this method are reliable to within 5%.
3
4
3
1H, J ) 7.4, 5.9, J ) 1.8, H-2), 7.39(t, 2H, J ) 7.4, m-Ph),
7.36(d, 1H, 3J ) 5.9, NNtBu-H), 7.30(t, 1H, 3J ) 7.1, p-Ph), 7.13(dd,
1H, 3J ) 8.0, H-8), 6.98(d, 1H, 3J ) 6.0, 4J ) 2.0, NNtBu-H), 6.53(d,
3
1H, J ) 8.0, H-9), 1.93(s, 3H, OAc), 1.89(s, 3H, OAc), 1.53(s,
3H, CMe3), 1.29(s, 3H, CMe3).
H-D Exchange Experiments. In a typical experiment, a
homogeneous solution of 7a (5-10 mg) in a benzene/deuterium
source solvent mixture (toluene-d8, acetic acid-d4, or trifluoroacetic
acid-d1) (2 mL, 1:1 volume ratio) was heated at 170 °C in a Schlenk
bomb. The liquid phase was then analyzed by GC/MS to determine
the extent of H/D exchange. TON was calculated as moles of
product/moles of catalyst. Benzene and trifluoroacetic acid-d1
showed background H/D exchange, so a control was also performed.
The control values were subtracted from the catalytic values to
obtain corrected values.
Reaction of 7a with Trifluoroacetic Acid. In a 30 mL screw
cap vial 7a (183 mg, 0.25 mmol) was dissolved in trifluoroacetic
acid (10 mL) and stirred for 2 h. The solution was reduced by half,
then diluted with water (20 mL) and extracted with CH2Cl2 (2 ×
10 mL). The extracts were then washed with water and dried with
MgSO4. The solvent was removed under vacuum, and the resulting
yellow-orange residue was sonicated with ether, then precipitated
with pentane. The product was obtained as a yellow powder after
redissolving and precipitating with pentane. Yield: 172.7 mg of
Ir(NN)(NC)(TFA)2 (76.3%). Anal. Calcd for C38H35F6IrN4O4: C,
49.72; H, 3.84; N, 6.10. Found: C, 49.36; H, 3.68; N, 5.95. HRESI-
MS: calc for C36H35F3IrN4O2 805.2342, found 805.2326 (1.9 ppm).
1H NMR (CDCl3): δ 9.41(d, 1H, 3J ) 5.6, H-1), 9.36(d, 1H, 3J )
6.1, H-24), 8.55(d, 1H, 3J ) 8.0, H-4), 8.06(d, 1H, 4J ) 2.0, H-21),
Conclusions
In the attempt to synthesize discrete monoligated tridentate
iridium NNC complexes several new bindentate iridium NC
complexes, [Ir(R-NC)Cl2(C5H5N)]2 (2a-c-Py), and mixed tri-
dentate, bidentate iridium complexes, Ir(NNC)(NC)Cl (3a,b),
have been synthesized. However, when an IrI precursor such
as [Ir(ethylene)2Cl]2 was used, the desired mononuclear triden-
tate Ir(NNC)Cl(ethyl)(ethylene) complex (4) was formed cleanly.
On the basis of the previously successful cis-, bis-bidentate
motif, we were able to convert the bidentate NC dinuclear
complexes (2a,b-Py) into a thermally and protic stable cis-, bis-
bidentate complex, Ir(NNtBu)(NC)MeOTf (7a), which is stable
in acids and arene solvents at 200 °C. While these complexes
do not activate methane, they cleanly activate arene substrates
such as benzene, toluene, and mesitylene, as well as undergo
catalytic H/D exchange with benzene in the presence of acids
(acetic and trifluoroacetic acid).
4
8.01-7.96(m, 3H, H-3,12), 7.89(d, 1H, J ) 2.0, H-18), 7.82(dd,
3
1H, 3J ) 6.1, 4J ) 2.1, H-22), 7.56(t, 1H, J ) 7.4, 5.7, 4J ) 1.6,
H-2), 7.41(t, 2H, 3J ) 7.8, 7.3, H-13), 7.33(t, 1H, 3J ) 7.4, H-14),
3
3
7.31(d, 1H, J ) 6.3, H-15), 7.17(d, 1H, J ) 8.0, H-8), 7.09(dd,
3
4
3
1H, J ) 6.3, J ) 2.0, H-16), 6.41(d, 1H, J ) 8.0, H-9), 1.56(s,
9H, CMe3), 1.31(s, 9H, CMe3). 13C{1H} NMR (CDCl3): δ 165.77,
163.74, 163.71, 163.23(q, J ) 36.1, OC(O)CF3), 162.98(q, J )
37.0, OC(O)CF3), 162.77, 159.53, 158.12, 151.87, 150.00, 149.89,
149.36, 140.42, 139.45, 139.39, 131.11, 128.81, 128.52, 126.32,
124.66, 124.40, 124.34, 121.59, 120.55, 119.48, 119.17, 113.98(q,
J ) 36.1, OC(O)CF3), 116.05(q, J ) 36.1, OC(O)CF3), 35.90,
35.54, 30.76, 30.44. 19F NMR (CDCl3): δ -75.66, -75.79.
Reaction of Ir(NN)(NC)OAcOTf with Benzene and Base. In
a 10 mL Schlenk bomb Ir(NN)(NC)OAcOTf (33.1 mg, 0.0368
mmol) and Hunig’s base (6.4 uL) were heated in benzene (5 mL)
at 160 °C for 1 h. After cooling to ambient temperature, 2 mL of
pyridine was added. The product was then obtained as a yellow
power by adding the solution dropwise to pentane (∼30 mL). The
suspension was centrifuged and decanted, and 5 uL of mesitylene
and 1 mL of CDCl3 were added. The solution was then analyzed
by 1H NMR, which showed two species, 8-Py (76%) and
Ir(NN)(NC)OAcOTf (24%).
Acknowledgment. The authors acknowledge the National
Science Foundation (CHE-0328121) and Chevron Energy
Technology Company for financial support for this research.
We thank Xiang Yang Liu for synthetic help, and Dr.
William C. Kaska and William Tenn III for helpful
discussions.
H/D Exchange Studies. Catalytic H-D exchange reactions were
quantified by monitoring the increase of deuterium into C6H6 by
GC/MS analyses. This was achieved by deconvolution of the mass
fragmentation pattern obtained from the MS analysis, using a
program developed with Microsoft EXCEL.11 An important as-
sumption used in the program is that there are no isotope effects
Supporting Information Available: Crystallographic data and
parameters (cif) as well as spectroscopic details are available, free
of charge, via the Internet at http://pubs.acs.org.
OM900014H