Addition of N-H bonds to iridium: Synthesis and characterization of N-Ir-H complexes and the observation that an iridium N-bonded indole ring becomes activated for Michael addition to alkynes

Article abstract of DOI:10.1016/j.poly.2015.02.002

The thermal reaction between the electron-rich iridium complex, [IrCOD(PMe₃)₃]Cl, 1a, and pyrrolic or anilinic N-H bonds results in the oxidative addition of the N-H bond and the formation of an amido iridium hydride complex, HIr(amido)(Cl)(PMe₃)₃ with loss of COD. The only isomer formed in this reaction has a meridional arrangement of PMe₃ ligands, with H trans to Cl and the amido group trans to PMe₃. The reaction products of 1a with pyrrole, indole and 3-methyl indole were fully characterized included by single crystal X-ray diffraction. Attachment of the pyrrolic ring nitrogen to the iridium results in an electron rich ring system that is activated and adds to alkynes in a Michael addition reaction under mild conditions without a catalyst.

Full text of DOI:10.1016/j.poly.2015.02.002

Polyhedron 90 (2015) 131–138
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Polyhedron
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Addition of N–H bonds to iridium: Synthesis and characterization
of N–Ir–H complexes and the observation that an iridium N-bonded
indole ring becomes activated for Michael addition to alkynes
1
⇑
Folami T. Ladipo , Joseph S. Merola
Department of Chemistry, Virginia Tech, Blacksburg, VA 24061, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The thermal reaction between the electron-rich iridium complex, [IrCOD(PMe3)3]Cl, 1a, and pyrrolic or
anilinic N–H bonds results in the oxidative addition of the N–H bond and the formation of an amido
iridium hydride complex, HIr(amido)(Cl)(PMe3)3 with loss of COD. The only isomer formed in this
reaction has a meridional arrangement of PMe3 ligands, with H trans to Cl and the amido group trans
to PMe3. The reaction products of 1a with pyrrole, indole and 3-methyl indole were fully characterized
included by single crystal X-ray diffraction. Attachment of the pyrrolic ring nitrogen to the iridium results
in an electron rich ring system that is activated and adds to alkynes in a Michael addition reaction under
mild conditions without a catalyst.
Received 22 November 2014
Accepted 6 February 2015
Available online 14 February 2015
Keywords:
N–H activation
Oxidative addition
Indole
Ó 2015 Elsevier Ltd. All rights reserved.
Iridium
Michael addition
1. Introduction
Ir–N compounds was synthesized via N–H activation and this
report details their syntheses, structures and properties.
While much has been published in the area of C–H activation
over the past several years [1–4], there has been less published
on N–H activation [5–11]. At the time this study was begun, very
few examples of the oxidative addition of a N–H bond to a metal
had been documented in the literature. The feasibility of an inser-
tion–reductive elimination sequence for the reaction of a hydrido
amido complex has been demonstrated by Trogler and Cowan for
PtH(NHPh)(PEt3)2 and the activated olefin acrylonitrile [12]. Exam-
ples of catalytic amination based on oxidative addition of a N–H
bond followed by an insertion–reductive elimination sequence
have been reported. More recent attention to N–H activation has
increased [13–21].
Results obtained in our laboratories on the oxidative addition of
aromatic C–H bonds to iridium(I), starting with the electron rich
complex [Ir(COD)(PMe3)3]Cl (COD = 1,5-cyclooctadiene) (1a) [22],
prompted an investigation of the general oxidative addition
reactions of a series of N–H compounds. The ultimate goal was
the development of catalysts for N–H addition to unsaturates
based on a subsequent insertion–reductive elimination sequence.
While the ultimate goal was not realized, an intriguing series of
2. Results and discussion
2.1. Oxidative addition of N–H compounds
The oxidative addition of N–H compounds to the series of elec-
tron rich complexes, [Ir(COD)(PMe3)3]X [22,23] (where X = Cl, 1a;
X = I, 1b; X = BF4ꢀ, 1c; X = BPh4ꢀ, 1d) was investigated. Refluxing
[Ir(COD)(PMe3)3]Cl (1a) with the heterocyclic amines, pyrrole,
indole, 3-methylindole, 7-azaindole, or carbazole (the latter four
in mesitylene) leads to the formation of mer-hydrido amido iridiu-
m(III) complexes (2a–2e) through loss of COD, oxidative addition
of the N–H bond, and chloride coordination to the iridium
(Eq. (1)). The yields for these complexes are fair to excellent. These
complexes are stable as solids, but solutions slowly decompose,
especially on exposure to air. The acyclic amine, aniline, reacts
with [Ir(COD)(PMe3)3]Cl (1a) in mesitylene at 75 °C to give the
hydrido anilido iridium(III) complex, Ir(NHPh)H(PMe3)3Cl 2f
(Eq. (2)). This complex has previously been prepared by Milstein
and co-workers from the cyclooctene complex, Ir(PMe3)3(C8H14)Cl
and aniline [24]. [Ir(COD)(PMe3)3]I (1b) reacts with indole in
mesitylene at reflux for 18 h to give the iodido hydrido amido iri-
dium(III) complex, 2g (Eq. (3)). Neither salt, [Ir(COD)(PMe3)3]BF4
(1c) nor [Ir(COD)(PMe3)3]BPh4 (1d), reacted with indole to form
⇑
Corresponding author. Tel.: +1 540 231 4510; fax: +1 540 231 3255.
E-mail address: jmerola@vt.edu (J.S. Merola).
Current address: University of Kentucky, Lexington, KY 40506, USA.
1
http://dx.doi.org/10.1016/j.poly.2015.02.002
0277-5387/Ó 2015 Elsevier Ltd. All rights reserved.

132
F.T. Ladipo, J.S. Merola / Polyhedron 90 (2015) 131–138
the corresponding hydrido amido complex under a number of
conditions in mesitylene.
pocket defined by the trans-PMe3 ligands. This was observed to
be the case for C–H and O–H addition and results in very high
barriers to rotation about the Ir–E bonds, a feature we will see in
these Ir–N compounds as well. Although pyrrolidine, 3-pyrroline,
pyrazole or tert-butylamine did not cleanly react with
[Ir(COD)(PMe3)3]Cl via oxidative addition of the N–H bond, this
electron rich iridium(I) complex is nonetheless a versatile system.
In a previous paper, we showed that sulfur and nitrogen con-
taining rings such as thiazole resulted in a ring-opening C–S bond
cleavage reactions. So, the iridium(I) complex is capable of attack-
ing quite a number of sites in different molecules with the ultimate
product most likely being determined by the stability of the end
product. A study was done recently calculating N–H versus C–H
addition in pyrrole imines [7]. It was shown previously that
[Ir(COD)(PMe3)3]Cl reacts with aromatic C–H bonds [26–28], but
this current work shows that all of the compounds with both
C–H and N–H bonds react selectively with the N–H bond.
ð1Þ
ð2Þ
The pyrrole complex (2a) typifies these complexes and 1H, 13C
and 31P NMR spectroscopy all indicate the structure as shown in
Eq. (1). That the iridium is bonded to nitrogen in the ring is clearest
from the 13C NMR spectrum – there is no resonance attributable to
a carbon atom directly bound to iridium (a doublet of triplets due
to P–C coupling would be expected) therefore pyrrole must be
bound to iridium via the nitrogen atom. These complexes were also
characterized by IR spectroscopy. There is no N–H stretch in the IR
spectra of any of these complexes. Typically, the amine N–H
stretch appears in the 3200–3600 cmꢀ1 region of the IR spectrum.
For pyrrole, the N–H stretch appears at 3530 cmꢀ1 (CH2Cl2) but is
completely absent in the pyrrole–iridium complex, 2a. An Ir–H
stretch is observed at 2221 cmꢀ1 (CH2Cl2). This is in line with
Ir–H stretching frequencies observed for similar hydrido amido
compounds [24].
Although spectroscopy made it clear that the N–H bond was
being added to iridium in all cases, it was decided to establish this
beyond any doubt by examining the product from the reaction
with 3-methylindole, complex 2c. The point of attachment of the
ring to iridium with respect to the methyl group would
unequivocally establish the position of the nitrogen atom and the
presence or absence of an Ir–N bond. As the information presented
below concerning the X-ray crystal structure shows, the point of
attachment of iridium to the indole ring can only be the N.
ð3Þ
Only the complex salts [Ir(COD)(PMe3)3]X (X = Cl or I) undergo a
clean reaction to generate the corresponding six coordinate hydri-
do amido iridium(III) products. While the oxidative addition of
amine N–H bonds to [Ir(COD)(PMe3)3]X (X = BF4 or BPh4) may
occur, the reaction does not lead to an isolable iridium hydride.
It is likely that the N–H oxidative addition to Ir(I) proceeds through
an unsaturated 14eꢀ intermediate (resulting from loss of the
chelating COD ligand) to give an unsaturated five-coordinate,
16eꢀ Ir(III) complex, (R2N)(H)IrP+3, that is then trapped by the
counter-ion, Xꢀ. The inability of BF4ꢀ and BPh4ꢀ to coordinate
strongly to the iridium may be the reason why the hydrido amido
products are not formed or, more likely, why the resulting products
are unstable and decompose under the reaction conditions. That a
sixth ligand is required to trap the 16eꢀ Ir(III) complex is
supported by the results obtained from the reactions of the five
coordinate, bis(phosphine)-iridium(I) complex, Ir(COD)(PMe3)2Cl
[25], with indole and aniline. Refluxing a mesitylene solution of
Ir(COD)(PMe3)2Cl and indole for 8.5 h results in the isolation of
the tris(phosphine)-iridium(III) complex, 2b, as the only clean
product after work-up. Reaction of Ir(COD)(PMe3)2Cl with excess
aniline in mesitylene at 70 °C for 6 h results in the analogous
formation of the tris(phosphine)anilido iridium(III) complex, 2f.
These results support the postulate that a sixth ligand is required
to trap the five-coordinate, 16eꢀ Ir(III) complex formed as
described above. In this case, that five-coordinate intermediate
scavenges a PMe3 ligand (most likely from some decomposed
starting complex) to form the tris(phosphine) complex.
2.2. Solid state structures
Single crystal X-ray structures were obtained for 2a, 2b and 2c.
The thermal ellipsoid plot of complex 2a is depicted in Fig. 1, that
of 2b is shown in Fig. 2 and that of 2c is shown in Fig. 3. The solid-
state structure of all compounds confirmed the structure assigned
by spectroscopy: an octahedral arrangement of ligands about the
iridium with the three PMe3 groups in a meridional arrangement
and the nitrogen ring group trans to PMe3. The Ir–N distances of
the three complexes are the same within error and average 2.1 Å.
This value is in line with those found in other crystallographically
characterized Ir–N(sp2) compounds [20] and shorter than Ir–N(sp3)
compounds [6,24]. The relatively short Ir–P distance for the PMe3
trans to the heterocyclic nitrogen (2.26–2.28 Å) compared to those
for the mutually trans PMe3 ligands (2.32–2.34 Å) shows that pyr-
role and indole (unlike phenyl where the same values are
2.339(2) Å versus 2.307(2) Å and 2.306(2) Å [26]) does not exert
as strong a trans influence as phenyl and is weaker than PMe3.
The Ir–Cl bond distances range from 2.48–2.50 Å.
2.3. Solution structures
[IrCOD(PMe3)3]Cl appears to give isolable products only for N–H
substrates in which the N–Ir bonded group fits into a narrow
The NMR spectra of compounds 2a–2c show evidence for hin-
dered rotation about the Ir–N bond in solution. This is most clearly

F.T. Ladipo, J.S. Merola / Polyhedron 90 (2015) 131–138
133
the same side of the Ir as the hydride ligand and the second with
the C6 ring on the same side of the iridium as the chloride ligand.
The solid-state structures for 2b and 2c are those with the C6 ring
on the same side as hydride. The solution 1H and 13C NMR spectra
would indicate that there is only one conformation in solution and
so we conclude that the solid state structure persists in solution
due to hindered rotation about the Ir–N bond and it is this confor-
mation with the C6 ring on the same side as of the iridium as
hydride which minimizes unfavorable interactions between Cl
and the hydrogens on the C6 ring.
2.4. Reactions at the metal
Having fully characterized these complexes and established
oxidative addition of the N–H bond, an exploration of the reactivity
of these complexes was undertaken. An NMR study of the reaction
of these hydrido amido complexes with a series of alkynes was
conducted. Alkynes were used because previous studies in our
group showed that vinyl complexes formed from insertion into
either Ir–H or Ir–C bonds were stable enough to be isolated and
structurally characterized [26,28,30]. For compounds 2a–2f
described in this study, unfortunately, no reaction occurred at
the metal center with any of the alkynes (Eq. (4)) at room tem-
perature over several days as monitored by 1H NMR spectroscopy.
Fig. 1. X-ray Crystal Structure of one of the independent molecules of Ir(N1C4H4)
(H)(PMe3)3(Cl) (2a). Ellipsoids are drawn at the 50% probability level and hydrogen
atoms (with the exception of the iridium hydride) are omitted for clarity. Important
bond distances: Ir1–N1, 2.109(10); Ir1–P11, 2.333(4); Ir1–P12, 2.280(3); Ir1–P13,
2.332(4); Ir1–Cl1, 2.502(3); Ir2–N2, 2.093(11); Ir2–P21, 2.323(4); Ir2–P22, 2.260(4);
Ir2–P23, 2.335(4); Ir2–Cl2, 2.483(4); Ir3–N3, 2.106(10); Ir3–P31, 2.323(4); Ir3–P32,
2.276(4); Ir3–P33, 2.319(4); Ir3–Cl3, 2.497(4); Ir4–N4, 2.088(12); Ir4–P41,
2.321(5); Ir4–P42, 2.272(4); Ir4–P43, 2.334(4); Ir4–Cl4, 2.498(4) Å.
seen in the case of the pyrrole compound, 2a, where the four pyr-
role protons in the 1H NMR spectrum and the four pyrrole carbons
in the 13C NMR spectrum are all inequivalent. Neither 1H nor 13C
spectra of toluene-d8 solutions heated over 373 K showed evi-
dence for rotation. DFT [29] calculation of the Ir–N rotational bar-
rier predicts a large barrier – over 90 kJ/mol – for rotation about
the Ir–N bond. From examination of some of the high energy con-
formations needed for rotation, it is clear that there is significant
distortion of bonds to allow the pyrrole ring to rotate past the
flanking PMe3 groups. This distortion may account for the asym-
metry in the energy plot in the Supplementary material since it
is unlikely that these distorted structures are ever able to fully
minimize and so different calculations starting from different
angles give slightly different energies. Moreover, for the indole
compounds the barrier is much higher and could not even be cal-
culated. Because of the asymmetry of the indole system, there are
two different conformations possible: the first with the C6 ring on
ð4Þ
Our previous experience showed that the analogous system
generated by oxidative addition of catecholborane underwent
chloride loss in even low polarity solvents allowing for alkyne
insertion into the iridium–hydride bond [31]. On the other hand,
the phenyl iridium hydride complexes formed by C–H addition of
benzene did not undergo spontaneous Clꢀ dissociation but did
undergo reactions with alkynes upon removal of the chloride with
Tl+ [26,28].
Fig. 2. X-ray Crystal structure of Ir(NC8H6)(H)(PMe3)3(Cl) (2b). Ellipsoids are drawn
at the 50% probability level and hydrogen atoms (with the exception of the iridium
hydride) are omitted for clarity. Important bond distances: Ir1–N1, 2.128(4); Ir1–
P1, 2.3264(14); Ir1–P2, 2.2699(13); Ir1–P3, 2.337(14); and Ir1–Cl, 2.4914(13) Å.
Fig. 3. Structure of Ir(NC9H8)(H)(PMe3)3(Cl) product, 2c. Ellipsoids are drawn at the
50% probability level and hydrogen atoms (with the exception of the iridium
hydride) are omitted for clarity. Important bond distances: Ir1–N1, 2.112(5); Ir1–
P1, 2.340(2); Ir1–P2, 2.272(2); Ir1–P3, 2.3260(18); Ir1–Cl1, 2.5070(17) Å.

134
F.T. Ladipo, J.S. Merola / Polyhedron 90 (2015) 131–138
ð5Þ
Therefore, reactions between these amido complexes and Tl+ in
the presence of alkynes were investigated in hopes that the alkyne
could trap the 16eꢀ species generated upon loss of Clꢀ if it is
formed. The reactions were very sluggish (days to weeks at moder-
ate temperatures) and did not proceed cleanly. It was not possible
to identify a specific product as decomposition reactions set in
before the reactions could proceed very far. The carbazole complex
(2e), for example, did not react with dimethylacetylenedicarboxy-
late (DMAD) but underwent reductive elimination of carbazole.
Only in the presence of the strong sigma donor PMe3 did abstrac-
tion of the chloride by Tl+ occur leading to isolable products
(Eq. (6)). While these compounds were not isolated, the 1H NMR
resonance for the hydride (as well as other features of the spectra)
was unambiguously diagnostic for the formation of the tetrakis
PMe3 complex displaying a very large trans P–H coupling constant
and 3 smaller cis P–H coupling constants. The reactions were still
very slow for the reaction with PMe3.
Fig. 4. X-ray structure of the product of Michael addition of 2b to dimethy-
lacetylenedicarboxylate, DMAD, 4a. Ellipsoids are drawn at the 50% probability
level and hydrogen atoms with the exception of the Ir–H, are omitted for clarity.
Important bond distances: Ir1–N1, 2.135(8); Ir1–P1, 2.340(3); Ir1–P2, 2.263(3); Ir1–
P3, 2.343(3); and Ir1–Cl1, 2.479(3) Å.
ð6Þ
The pyrrole complex, 2a, reacted to completion only after five
days at room temperature. The analogous reaction of the indole
complex, 2b, was still incomplete after one week at room tem-
perature. However, the anilido complex, 2f, reacted much faster
than the heterocyclic amido complexes. The reaction proceeded
with significant formation of the tetrakis(phosphine) complex
(3f) in minutes and to completion in two days. So the reaction of
2f with PMe3 shows that it is may be possible to abstract the chlo-
ride and open up a coordination site and trap it. However, reactions
with alkynes may be too slow to lead to product formation com-
pared with decomposition pathways.
2.5. Reaction at the indole ring
Fig. 5. X-ray structure of the product of Michael addition of 2b to but-3-yn-2-one,
4b. Ellipsoids are drawn at the 50% probability level and hydrogen atoms (with the
exception of the iridium hydride) are omitted for clarity. Important bond distances:
Ir1–N1, 2.135(7), Ir1–P1, 2.335(4); Ir1–P2, 2.270(3); Ir1–P3, 2.333(3) and Ir1–Cl1,
2.508(2) Å.
The lack of reactivity of alkynes at the metal center was a
disappointment. However, when the substrate was the electron
deficient acetylene DMAD and the indole complex, 2b, was used,
an unusual reaction did occur at the indole ring. The indole com-
plex, 2b, reacted with DMAD (as well as but-3-yn-2-one) at the
indole ring at room temperature to give 4a, b (Eq. (7)). Free indole
does not react with these alkynes under the same conditions.
Usually, a Lewis acid is required for addition
to the three position of indole [32]. Therefore, the coordinated
indole ring in 2b must be more electron rich than in uncoordinated
indole providing a more activated ring for the Michael-type addi-
tion. This is consistent with a report by Trogler and Cowan that
the anilide ligand in PtH(NHPh)(Pet3)3 displayed chemistry consis-
tent with a high electron density at nitrogen [33]. 4a was fully char-
acterized and, although 4b was only characterized by single-crystal
X-ray diffraction, its formation clearly underscores the electron-rich
enhancement of the indole ring. The solid state structures of 4a and
4b (Figs. 4 and 5) show an octahedral arrangement of ligands about
the iridium with the three PMe3 groups in a meridional arrange-
ment and a vinyl group attached to the indole ring at the 3-position.
ð7Þ

F.T. Ladipo, J.S. Merola / Polyhedron 90 (2015) 131–138
135
1H NMR (CDCl3): d 1.33–1.37 (m, 27H, PMe3 ligands), 2.22–2.31
(m, 8H, COD), 3.10 (br s, 4H, COD), 6.84–6.91 (m, 4H, para protons,
phenyl rings), 6.99–7.06 (m, 8H, meta protons, phenyl rings), 7.39
(bm, 8H, ortho protons, phenyl rings).
The corresponding iodide salt 1b was prepared in an analogous
manner and identified on the basis of the following data:
1H NMR (CDCl3): d 1.63–1.63 (m, 27H, PMe3 ligands), 2.49–2.19
(m, 8H, COD), 3.22 (br s, 4H, COD).
Structural parameters are little changed in the iridium core upon
Michael addition to the alkyne. In the case of 4a, the X-ray structure
showed significant disorder of the carbomethoxy group closest to
the indole ring. The disorder was treated with a two-site model that
approximates rotation about the C9I–C22A bond and the occupan-
cies refined to a 57/43 split between the two positions. Only one
of the apparent rotamers is shown in Fig. 4.
3. Conclusions
4.1.2. General procedure for addition of N–H compounds to
[Ir(COD)(PMe3)3]Cl
The electron-rich system [Ir(COD)(PMe3)3]Cl continues to be a
valuable one for the study of oxidative addition reactions of
various element-H bonds. In this report, the oxidative addition
reactions of N–H bonds was demonstrated but, unfortunately, fur-
ther reaction chemistry that could be exploited to develop catalytic
systems for the addition of N–H bonds across alkynes or alkenes
was not realized. The activation of the indole ring toward the
Michael reaction with activated alkynes was an unusual finding
but, again, not one that could be utilized in a catalytic scheme.
Nevertheless, this body of information contributes to the
understanding of N–H additions and the chemistry of iridium
trimethylphosphine complexes.
A 10.0 mL one-necked side-armed flask, equipped with a mag-
netic stirrer and a septum, was charged with the appropriate
amount of [Ir(COD)(PMe3)3]Cl (1a) under N2 in a dry box. The flask
was then connected to a double manifold (vacuum/nitrogen)
Schlenk line and a slight excess of the N–H compound was added
by syringe. If the N–H compound were a solid, it was added in
the dry box along with 1a and 4.0 mL of mesitylene was added
by syringe. The flask was then fitted with a reflux column equipped
with a nitrogen inlet and connected to the Schlenk line. The light-
yellow slurry was stirred magnetically and heated to reflux. After
16 h at reflux, the solutions were homogeneous and an appropriate
workup was performed, usually involving isolation and recrystal-
lization of solids. The solids were then dried under reduced
pressure and analyzed by NMR spectroscopies, C,H analyses and,
in several cases, by X-ray crystallography.
4. Experimental
4.1. General
4.1.3. Synthesis of Ir(NC4H4)(H)(PMe3)3(Cl) (2a)
All reactions were carried out under an atmosphere of prepuri-
fied nitrogen. All solvents were dried by the appropriate procedure
and distilled under a nitrogen atmosphere prior to use. Conven-
tional glass vessels were used and standard Schlenk line tech-
niques were employed. IrCl3ꢁ3H2O was purchased from Johnson
Matthey.
The general procedure was followed using 0.420 g
(0.745 mmol) of [Ir(COD)(PMe3)3]Cl (1a) and 2.00 mL of dry
pyrrole. The pyrrole was removed under reduced pressure and
the resulting oil was treated with ꢂ5.0 mL of dry THF and stirred
for 5 min. The solids observed were filtered off and the solution
was concentrated to ꢂ0.5 mL. 2.0 mL of dry pentane was used to
crystallize light green solids. The solids were dried under reduced
pressure to yield 0.360 g (0.691 mmol) of Ir(NC4H4)(H)(PMe3)3(Cl),
2a, (93% based on amount of [Ir(COD)(PMe3)3]Cl) identified on the
basis of the following data:
The 1H NMR spectra were obtained on either a Bruker WP270SY
or a WP200SY instrument and referenced either to solvent reso-
nance or TMS. The 31P NMR spectra were obtained on Bruker
WP81SY instrument and referenced either to an internal or exter-
nal standard of 85% H3PO4. 13C NMR spectra were obtained on a
Bruker WP200SY (at 50 MHz), Bruker WP270SY (at 67 MHz) or a
Varian Unity 400 instrument (at 100 MHz) and referenced to
solvent resonance. FT-IR spectra were obtained on a Nicolet 5DX
W/C instrument. Elemental analyses were performed by Atlantic
Microlab Inc.
Carbazole, indole, 3-methylindole, and 7-azaindole, aniline and
pyrrole were obtained from Aldrich Chemical Company. Aniline
and pyrrole were further purified via distillation from barium
oxide (BaO). All other chemicals were of reagent grade and
used without further purification. [Ir(COD)(PMe3)3]Cl [22],
Ir(COD)(PMe3)2Cl [34] and [Ir(COD)(PMe3)3]BF4 [22] were synthe-
sized by the literature methods. [Ir(COD)(PMe3)3]X, where X = I
(1b) or BPh4 (1d), were prepared via metathetical reactions
between Ir(COD)(PMe3)3]Cl and potassium iodide or sodium
tetraphenylborate, respectively.
Anal. Calc. (Found) for C13H32ClP3IrN: C, 29.86 (29.92); H, 6.17
(6.19).
1H NMR (CDCl3): d ꢀ22.12 (dt, JP–H = 17 Hz, 15 Hz, 1H, Ir–H),
1.28 (t, JP–H = 3.6 Hz, 18H, trans PMe3),1.65 (d, JP–H = 9.4 Hz, 9H,
cis PMe3), 5.98–5.99 (m, 2H, H(3) and H(4), NC4H4), 6.39 (m, 1H,
H(5), NC4H4), 7.18 (m, 1H, H(2), NC4H4).
31P NMR (CDCl3): d ꢀ50.85 (br t, 1P, cis PMe3), ꢀ34.02 (d, JP–P
=
42 Hz, 2P, trans PMe3). 13C NMR (CDCl3): d 15.88 (t, JC–P = 18.3 Hz, 6C,
trans PMe3), 20.48 (d, JC–P = 37 Hz, 3C, cis PMe3), 104.2 (s, 1C, NC4H4),
106.9 (s, 1C, NC4H4), 128.6 (s, 1C, NC4H4), 135.1 (s, 1C, NC4H4).
4.1.4. Synthesis of Ir(NC8H6)(H)(PMe3)3(Cl) (2b)
The general procedure was followed with 1.00 g (1.78 mmol) of
[Ir(COD)(PMe3)3]Cl (1a) and 0.208 g (1.78 mmol) of indole under in
4.0 mL of mesitylene. After reflux, slightly pink solids were filtered,
washed with pentane and dried under reduced pressure to yield
0.695 g (1.21 mmol) of Ir(NC8H6)(H)(PMe3)3(Cl), (2b). (68% based
on amount of 1a) identified on the basis of the following data:
Anal. Calc. (Found) for C17H34ClP3IrN: C, 35.63 (35.36); H, 5.98
(5.85).
4.1.1. Synthesis of Ir(COD)(PMe3)3]BPh4. (1d)
0.300 g (0.532 mmol) of [Ir(COD)(PMe3)3]Cl (1a) was charged
into a 25 mL Erlenmeyer flask and dissolved in 5.0 mL of distilled
water. In a second 25 mL Erlenmeyer, 0.364 g (2 eq) of sodium
tetraphenylborate was dissolved in 5.0 mL of distilled water. The
[Ir(COD)(PMe3)3]Cl (1a) solution was then introduced into the
sodium tetraphenylborate solution. White solids immediately pre-
cipitate out of solution. The solids were filtered in air and dried in
vacuo to yield 0.360 g (0.425 mmol) of Ir(COD)(PMe3)3]BPh4 (1d)
(80% based on amount of [Ir(COD)(PMe3)3]Cl) identified on the
basis of the following data:
1H NMR (Acetone-d6): d ꢀ20.86 (dt, JP–H = 16 Hz, 14 Hz, 1H,
Ir–H), 1.15 (t, JP–H = 3.6 Hz, 18H, trans PMe3), 1.79 (d, JP–H = 9.8 Hz,
9H, cis PMe3), 6.24 (d, JH–H = 1.2 Hz, 1H, H(3), NC8H6), 6.67 (dt,
J = 7.7 Hz, 0.9 Hz, 1H, H(5), NC8H6), 6.78–6.84 (m, 1H, H(6),
NC8H6), 7.34 (dd, J = 7.7 Hz, 0.6 Hz, 1H, H(7), NC8H6), 7.43 (dd,
J = 8.3 Hz, 0.6 Hz, 1H, H(4), NC8H6), 8.04–8.03 (m, 1H, H(2),
NC8H6). 31P NMR (CDCl3): d ꢀ49.44 (br t, JP–P = 22 Hz, 1P, cis
PMe3), ꢀ33.70 (d, JP–P = 21 Hz, 2P, trans PMe3).

136
F.T. Ladipo, J.S. Merola / Polyhedron 90 (2015) 131–138
13C NMR (Acetone-d6): d 16.18 (t, JC–P = 18.5 Hz, 6C, trans PMe3),
20.20 (d, JC–P = 38 Hz, 3C, cis PMe3), 99.14 (s, 1C, C(3), NC8H6),
116.6 (s, 1C, NC8H6), 117.1 (s, 1C, NC8H6), 118.0 (s, 1C, NC8H6),
120.0 (s, 1C, NC8H6), 137.4 (s, 1C, C(2), NC8H6).
ꢀ48.22 (br t, JP–P = 23 Hz, 1P, cis PMe3), ꢀ33.77 (d, JP–P = 23 Hz,
2P, trans PMe3).
4.1.8. Synthesis of Ir(NHC6H5)(H)(PMe3)3(Cl) (2f)
The general procedure was followed with 0.478 g (0.848 mmol)
4.1.5. Synthesis of Ir(NC9H8)(H)(PMe3)3(Cl) (2c)
of [Ir(COD)(PMe3)3]Cl (1a) and 160 lL (1.70 mmol, 2 eq) of aniline
The general procedure was followed with 0.250 g (0.444 mmol)
of [Ir(COD)(PMe3)3]Cl (1a) and 0.064 g (0.488 mmol, 1.1 eq) of 3-
methylindole in 3.00 mL of mesitylene. White solids were filtered,
washed with pentane and dried under reduced pressure to yield
0.161 g (0.274 mmol) of Ir(NC9H8)(H)(PMe3)3(Cl), (2c), (62% based
on amount of [Ir(COD)(PMe3)3]Cl) identified on the basis of the
following data:
in 6.00 mL of mesitylene. After 6 h at 75o (not reflux) off-white
solids were filtered and washed with copious amounts of pentane
and then ether (3 ꢃ 5.00 mL). The off-white solids were
dried under reduced pressure to yield 0.237 g (0.432 mmol) of
Ir(NHC6H5)(H)(PMe3)3(Cl), (2f), (51% based on amount of
[Ir(COD)(PMe3)3]Cl) identified on the basis of the following data:
Analysis. Calc.(found) for C15H34ClP3IrN: C, 32.78 (32.23); H,
6.24 (6.21).
Anal. Calc. (Found) for C18H36ClP3IrN: C, 36.82 (36.86); H, 6.18
(6.22).
1H NMR (d5-pyridine): d ꢀ21.62 (dt, JP–H = 20 Hz, 14 Hz, 1H,
Ir–H), 1.45 (t, JP–H = 3.7 Hz, 18H, trans PMe3), 1.57 (d, JP–H = 9.3 Hz,
9H, cis PMe3), 2.8 (br s, 1H, NH), 6.31 (t, JH–H = 7 Hz, 1H, phenyl),
6.51 (br d, JH–H = 7.8 Hz, 1H, phenyl), 6.72 (br d, JH–H = 7.8 Hz,
1H, phenyl), 7.03 (br t, JH–H = 7.5 Hz, 1H, phenyl), 7.22 (m, 1H,
phenyl). 13C NMR (d5-pyridine): d 16.2 (t, JC–P = 18.3 Hz, 6C, trans
PMe3), 20.62 (d, JC–P = 36.6 Hz, 3C, cis PMe3), 113.2 (s, 1C, phenyl),
116.1 (s, 1C, phenyl), 116.2 (s, 1C, phenyl), 129.4 (s, 1C, phenyl),
129.8 (s, 1C, phenyl), 158.9 (s, 1C, phenyl).
1H NMR (Acetone-d6): d ꢀ20.92 (q, JP–H = 16 Hz, 1H, Ir–H), 1.14
(t, JP–H = 3.6 Hz, 18H, trans PMe3), 1.78 (d, JP–H = 9.8 Hz, 9H, cis
PMe3), 2.31 (s, 3H, 3-methyl), 6.63–6.84 (m, 2H, H(5) and H(6),
NC9H8), 7.25–7.35 (m, 2H, H(4) and H(7), NC9H8), 7.81 (s, 1H,
H(2), NC9H8). 31P NMR (CDCl3): d ꢀ49.00 (br t, JP–P = 22 Hz, 1P,
cis PMe3), ꢀ33.42 (d, JP–P = 21 Hz, 2P, trans PMe3). 13C NMR
(CD2Cl2): d 10.32 (s, 1C, 3-methyl), 16.44 (t, JC–P = 18.3 Hz, 6C, trans
PMe3), 20.47 (d, JC–P = 38 Hz, 3C, cis PMe3), 115.4 (s, 1C, NC9H8),
116.6 (s, 1C, NC9H8), 117.6 (s, 1C, NC9H8), 117.6 (s, 1C, NC9H8),
135.3 (s, 1C, C(2), NC9H8).
4.1.9. Synthesis of Ir(NC8H6)(H)(PMe3)3(I) (2g)
The general procedure was followed with 0.200 g (0.305 mmol)
[Ir(COD)(PMe3)3]I (1b)and 0.040 g (0.336 mmol, 1.1 eq) indole in
4.0 mL mesitylene and identified on the basis of the following data:
1H NMR (d6-acetone): d ꢀ18.16 (dt, JP–H = 19 Hz, 14 Hz, 1H,
Ir–H), 1.29 (t, JP–H = 3.7 Hz, 18H, trans PMe3), 1.92 (d, JP–H = 9.7 Hz,
9H, cis PMe3), 6.19 (d, 1H, H(3), NC8H6), 6.66 (dt, J = 7.5 Hz, 1H,
H(5), NC8H6), 6.80–6.87 (m, 1H, H(6), NC8H6), 7.36 (d, J = 7.7 Hz,
1H, H(7), NC8H6), 7.54 (dd, J = 8.2 Hz, 1H, H(4), NC8H6), 8.32–8.29
4.1.6. Synthesis of Ir(N2C7H5)(H)(PMe3)3(Cl) (2d)
The general procedure was followed with 0.250 g (0.444 mmol)
of [Ir(COD)(PMe3)3]Cl (1a) and 0.058 g (0.491 mmol, 1.1 eq) of
7-azaindole in 3.00 mL of mesitylene. After 15 h at reflux, white
solids were filtered, washed with pentane and dried under reduced
pressure to yield 0.132 g (0.230 mmol) of Ir(N2C7H5)(H)(PMe3)3(Cl)
(52% based on amount of [Ir(COD)(PMe3)3]Cl) identified on the
basis of the following data:
(m, 1H, H(2), NC8H6). 31P NMR (d6-acetone): d ꢀ56.40 (br t, JP–P
19 Hz, 1P, cis PMe3), ꢀ42.64 (d, JP–P = 21 Hz, 2P, trans PMe3).
=
Anal. Calc. (Found) for C16H33ClP3IrN2: C, 33.48 (33.25); H, 5.79
(5.84).
1H NMR (CDCl3): d ꢀ20.66 (q, JP–H = 16 Hz, 14 Hz, 1H, Ir–H), 1.14
4.1.10. Reaction of Ir(NC8H6)(H)(PMe3)3(Cl) (2b) and dimethyl
acetylenedicarboxylate
A 10 mL one-necked side-armed flask, equipped with a magnet-
ic stirrer and a septum, was charged with 0.215 g (0.376 mmol) of
Ir(NC8H6)(H)(PMe3)3(Cl) (2b) under N2, in a dry box. The flask was
then connected to a double manifold (vacuum/nitrogen) Schlenk
(t, JP–H = 3.5 Hz, 18H, trans PMe3), 1.72 (d, JP–H = 9.6 Hz, 9H, cis
PMe3), 6.36 (d, JH–H = 2.9 Hz, 1H, H(3), N2C7H5), 6.74 (dd, JH–H
=
7.4 Hz, 4.6 Hz, 1H, H(5), N2C7H5), 7.75 (dd, JH–H = 7.1 Hz, 1.1 Hz,
1H, H(2), N2C7H5), 8.19–8.23 (m, 2H, H(4) and H(6), N2C7H5).
31P NMR (CDCl3): d ꢀ49.09 (br t, JP–P = 22 Hz, 1P, cis PMe3),
ꢀ33.82 (d, JP–P = 22 Hz, 2P, trans PMe3). 13C NMR (CDCl3): d 16.44
(t, JC–P = 18.0 Hz, 6C, trans PMe3), 20.16 (d, JC–P = 38 Hz, 3C, cis
PMe3), 97.87 (s, 1C, C(3), N2C7H5), 112.3 (s, 1C, C(4), N2C7H5),
126.6 (s, 1C, C(5), N2C7H5), 138.0 (s, 1C, C(6), N2C7H5), 139.9 (s,
1C, C(2), N2C7H5).
line. 4.0 mL of dry acetone was added by syringe. 71.0 ll
(0.564 mmol, 1.5 eq) of dimethyl acetylenedicarboxylate was then
introduced into the yellow homogenous solution. The solution
went orange and then gradually dark red. After 6 h, acetone was
stripped off and deep orange solids were obtained. The solids were
washed three times with copious amounts of pentane and dried in
vacuo to yield 0.250 g (0.350 mmol) of 4a (93% based on amount of
Ir(NC8H6)(H)(PMe3)3(Cl)) identified on the basis of the following
data:
4.1.7. Synthesis of Ir(NC12H8)(H)(PMe3)3(Cl) (2e)
The general procedure was followed with 0.500 g (0.887 mmol)
of [Ir(COD)(PMe3)3]Cl (1a) and 0.164 g (0.976 mmol, 1.1 eq) of car-
bazole in 5.00 mL of mesitylene. After 24 h at reflux, white solids
were filtered and then dissolved in CH2Cl2 (0.5 mL). Diethyl ether
(3.0 mL) was then introduced to recrystallize solids. The off-white
solids were filtered and dried under reduced pressure to yield
0.285 g (0.458 mmol) of Ir(NC12H8)(H)(PMe3)3(Cl) (52% based on
amount of [Ir(COD)(PMe3)3]Cl) identified on the basis of the
following data:
Anal. Calc. (Found) for C23H40ClP3IrNO4: C, 38.63 (38.44); H,
5.64 (5.51)
1H NMR (CDCl3): d ꢀ20.89(dt, JP–H = 19 Hz, 14 Hz, 1H, Ir–H),
1.16 (t, JP–H = 3.5 Hz, 18H, trans PMe3), 1.73 (d, JP–H = 9.6 Hz, 9H,
cis PMe3), 3.71 (s, 3H, OCH3), 4.00 (s, 3H, OCH3), 6.19 (s, 1H, vinyl
proton), 7.02–7.06 (m, 2H, phenyl ring), 7.53–7.49 (m, 1H, phenyl
ring), 7.73–7.70 (m, 1H, phenyl ring), 8.35 ppm(d, JH–H = 1.4 Hz,
Anal. Calc. (Found) for C21H36ClP3IrN: C, 40.44 (40.34); H, 5.82
(5.85).
1H, H(2), indole ring). 31P NMR (d6-acetone): d ꢀ48.35 (br t, JP–P
=
22 Hz, 1P, cis PMe3), ꢀ34.71 (d, JP–P = 22 Hz, 2P, trans PMe3). 13C
NMR (d6-acetone): d 16.22 (t, JC–P = 18.5 Hz, 6C, trans PMe3),
20.29 (d, JC–P = 37.3 Hz, 3C, cis PMe3), 51.04 (s, 1C, OCH3), 52.32
(s, 1C, OCH3), 101.7 (s, 1C, phenyl), 117.5 (s, 1C, phenyl), 119.8
(s, 1C, phenyl), 120.0 (s, 1C, phenyl), 128.3 (s, 1C, C(2), indole ring),
144.6 (s, 1C, vinylcarbon).
1H NMR (d6-acetone): d ꢀ21.06 (q, JP–H = 15 Hz, 1H, Ir–H), 1.16
(t, JP–H = 3.7 Hz, 18H, trans PMe3), 1.82 (d, JP–H = 9.9 Hz, 9H, cis
PMe3), 6.82–6.87 (m, 2H, NC12H8), 7.09–7.23 (m, 2H, NC12H8),
7.86 (d, JH–H = 8.4 Hz, 1H, NC12H8), 7.91–7.95 (m, 2H, NC12H8),
9.34 (d, JH–H = 8.5 Hz, 1H, NC12H8). 31P NMR (d6-acetone): d

F.T. Ladipo, J.S. Merola / Polyhedron 90 (2015) 131–138
137
Table 1
Experimental details for compounds characterized by X-ray crystallography.
Compound
2a
2b
2c
4a
4b
Deposition code
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
CCDC: 1034926
CCDC: 1034944
C17H34NP3ClIr
573.01
293
monoclinic
P21/c
9.3166(3)
13.647(3)
18.288(4)
90
95.74(2)
90
CCDC: 1034928
C18H36NP3ClIr
587.04
293
monoclinic
P21/n
CCDC: 1034925
C23H40NO4P3ClIr
715.12
293.0
monoclinic
P21/c
13.136(3)
11.790(2)
19.937(4)
90.00
102.35(3)
90.00
3016.3(10)
4
1.575
CCDC: 1034927
C21H38NP3ClOIr
641.08
292.0
monoclinic
P21/c
C
13H32NP3ClIr
522.96
293
triclinic
ꢀ
P1
9.602(3)
9.008(2)
9.876(2)
b (Å)
c (Å)
21.093(7)
21.310(6)
107.33(2)
98.02(2)
90.57(3)
4074(2)
26.098(4)
10.206(2)
90.00
96.00(2)
90.00
2386.2(8)
4
1.634
15.470(3)
17.223(5)
90
94.54(2)
90
2623.1(11)
4
1.623
a
(°)
b (°)
(°)
c
Volume (Å3)
Z
2313.4(10)
4
1.645
8
qcalc (mg/mm3)
1.705
6.912
l
(mmꢀ1
)
6.094
5.910
4.701
5.387
F(000)
Crystal size (mm3)
range
2048.0
1128.0
1160.0
1424.0
12720
0.4 ꢃ 0.3 ꢃ 0.3
4.04° to 45.1°
0 6 h 6 10,
ꢀ22 6 k 6 22
ꢀ22 6 l 6 22
11371
0.3 ꢃ 0.3 ꢃ 0.2
3.74° to 50.1°
0 6 h 6 11
0 6 k 6 16,
ꢀ21 6 l 6 21
4367
0.5 ꢃ 0.2 ꢃ 0.15
4.3° to 50.1°
-0 6 h 6 10
0 6 k 6 31
ꢀ12 6 l 6 12
4508
0.4 ꢃ 0.4 ꢃ 0.2
4.04° to 50.1°
0 6 h 6 15
0 6 k 6 10
ꢀ23 6 l 6 23
4579
0.4 ꢃ 0.3 ꢃ 0.2
3.45° to 50.00°
-11 6 h 6 11,
0 6 k 6 18
0 6 l 6 20
4622
2H
Index ranges
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
10605 [Rint = 0.0446]
10605/3/734
1.064
4097 [Rint = 0.0175]
4097/1/209
1.053
4229 [Rint = 0.0450]
4229/1/231
1.0524
4395 [Rint = 0.0398]
4395/1/312
1.017
4622 [Rint = 0.0000]
4622/1/266
0.628
Final R indexes [I P 2
r
(I)]
R1 = 0.0538,
wR2 = 0.1342
R1 = 0.0737,
wR2 = 0.1488
1.84/ꢀ2.31
R1 = 0.0239,
wR2 = 0.0512
R1 = 0.0328,
wR2 = 0.0539
0.49/ꢀ0.44
R1 = 0.0348,
wR2 = 0.0776
R1 = 0.0488,
wR2 = 0.0843
0.92/ꢀ0.80
R1 = 0.0479,
wR2 = 0.1128
R1 = 0.0726,
wR2 = 0.1270
1.27/ꢀ2.77
R1 = 0.0384,
wR2 = 0.0638
R1 = 0.0974,
wR2 = 0.0715
0.76/ꢀ0.88
Final R indexes [all data]
Largest difference in peak/hole/
e Åꢀ3
General survey of reactions of 2a–f with alkynes in the presence of
Tl[PF6]. In general, a screw-capped NMR tube equipped with a sep-
tum was charged with solid reagents in a glove box and sealed. via
syringe, the solvent (CD2Cl2 or acetone-d6) and the alkyne were
introduced by syringe and the tubes were shaken vigorously to
ensure complete mixing. The reactions were monitored by NMR
spectroscopy over a period of several days.
4.1.12. Reaction of Ir(NC8H6)(H)(PMe3)3(Cl) (2b) and
trimethylphosphine in the presence of thallium hexafluorophosphate
The general procedure was followed with Ir(NC8H6)(H)(PMe3)3
(Cl) (2b) 0.010 g (0.175 mmol), trimethylphosphine 1.80 ll
(0.175 mmol) and TlPF6 0.006 g (0.175 mmol)
The reaction yielded the tetrakis(phosphine) complex, [Ir(NC8
H6)(H)(PMe3)4]PF6 (3b) which was identified on the basis of the
following data:
1H NMR (CD2Cl2): d ꢀ11.29 (dq, JP–Htrans = 142 Hz, JP–Hcis
=
General survey of reactions of 2a–f with PMe3 in the presence of
Tl[PF6]. In general, a screw-capped NMR tube equipped with a sep-
tum was charged with solid reagents in a glove box and sealed via
syringe, the solvent (CD2Cl2 or acetone-d6) and PMe3 were intro-
duced by syringe and the tubes were shaken vigorously to ensure
complete mixing. The reactions were monitored by NMR spec-
troscopy over a period of several days. No attempts were made
to isolate the products.
18.6 Hz, 1H, Ir–H), 1.29 (t, JP–H = 3.5 Hz, 18H, trans PMe3), 1.84 (d,
JP–H = 7.2 Hz, 9H, cis PMe3), 1.92 (d, JP–H = 9.1 Hz, 9H, cis PMe3)
6.47 (br s, 1H, NC8H6), 6.84–6.89 (br s, 2H, NC8H6), 7.06 (t, 1H,
JH–H = 7.7 Hz, NC8H6), 7.46–7.52 (m, 2H, NC8H6).
4.1.13. Reaction of Ir(NHC6H5)(H)(PMe3)3(Cl) (2f) and
trimethylphosphine in the presence of thallium hexafluorophosphate
The general procedure was followed with 0.010 g (0.0182 mmol)
of Ir(NHC6H5)(H)(PMe3)3(Cl) (2f) and 0.006 g (0.0182 mmol) TlPF6
2.00
l
l (ꢂ0.0200 mmol, 1.1 eq) of PMe3 and 0.50 mL d6-acetone.
4.1.11. Reaction of Ir(NC4H4)(H)(PMe3)3(Cl) (2a) and
The reaction yielded the tetrakis(phosphine) complex, [Ir(NHC6
H5)(H)(PMe3)4]PF6 (3c), which was identified on the basis of the
following data:
trimethylphosphine in the presence of thallium hexafluorophosphate
A screw-capped NMR tube, equipped with a septum, was
charged with 0.010 g (0.0191 mmol) of Ir(NC4H4)(H)(PMe3)3(Cl)
(2a) and ꢂ0.007 g (ꢂ0.0191 mmol) TlPF6 under N2 in a dry box
and brought out. 0.50 mL CD2Cl2 was introduced by syringe fol-
1H NMR (d6-acetone): d ꢀ11.25 (dq, JP–Htrans = 140 Hz, JP–Hcis
=
18.5 Hz, 1H, Ir–H), 1.68 (t, JP–H = 3.7 Hz, 18H, trans PMe3), 1.73 (d,
JP–H = 7.9 Hz, 9H, cis PMe3), 1.90 (d, JP–H = 9.4 Hz, 9H, cis PMe3)
6.04 (t, 1H, NHC6H5), 6.41–6.58 (m, 2H, NHC6H5), 6.70–6.93 (m,
2H, NHC6H5).
lowed by 2.00
l
l (ꢂ0.0191 mmol) of PMe3. The tube was shaken
vigorously and the reaction was monitored at room temperature
for ꢂ5 days. The reaction yielded the tetrakisphosphine complex,
[Ir(NC4H4)(H)(PMe3)4]PF6 (3a), which was identified on the basis
of the following data:
4.1.14. X-ray crystallography
X-ray crystal structures were obtained using a Nicolet R3 m/V
diffractometer and a Mo K
Data collected was more recently re-reduced using updated ver-
sions of SHELX [35] and graphics were created using the program
1H NMR (CD2Cl2): d ꢀ11.87 (dq, JP–Htrans = 145 Hz, JP–Hcis = 18 Hz,
1H, Ir–H), 1.42 (t, JP–H = 3.7 Hz, 18H, trans PMe3), 1.76 (d, JP–H = 7.4 Hz,
9H, cis PMe3), 1.81 (d, JP–H = 9.0 Hz, 9H, cis PMe3) 5.92 (br s, 2H,
NC4H4), 6.29 (br s, 1H, NC4H4), 6.47 (br s, 1H, NC4H4).
a (k = 0.71073 Å) radiation at 298 K.

138
F.T. Ladipo, J.S. Merola / Polyhedron 90 (2015) 131–138
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OLEX2 [36]. Hydrogen atoms attached to iridium were located on
difference Fourier maps and positional parameters were refined
with DFIX = ꢀ1.6 and Uiso = 1.5 IrUiso. Table 1 summarizes the
important parameters for the crystal structures reported in this
paper. Experimental parameters and .cif files for all structures dis-
cussed in this paper as well complete listings of bond lengths and
angles may be found in the Supplementary information.
4.1.15. Computations
Full details of the DFT [29] calculations of the barrier to rotation
about the Ir–N bond in compound 2a may be found in the Supple-
mentary information.
Acknowledgment
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Financial support for this work was provided by ACS, PRF
(Grant #23961-C1) and by the National Science Foundation
(CHE-902244). Support for the server upon which Gaussian is
run came from NSF Grant No. CHE-0741927. Dr. Carla Slebodnick
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CCDC 1034925–1034928 and 1034944 contain the supplemen-
tary crystallographic data for all structures in this paper. These
data can be obtained free of charge via http://www.ccdc.cam.ac.
uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary
data associated with this article can be found, in the online version,
at http://dx.doi.org/10.1016/j.poly.2015.02.002. These data include
MOL files and InChiKeys of the most important compounds
described in this article.
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