Cyclooctadiene iridium complexes [Cp*Ir(COD)X]+ (X = Cl, Br, I): Synthesis and application for oxidative coupling of benzoic acid with alkynes

Article abstract of DOI:10.1016/j.jorganchem.2018.08.014

The cyclooctadiene iridium complexes [Cp*Ir(COD)X]PF₆ ([1a?c]PF₆; X = Cl, Br, I) were synthesized by reactions of Cp*Ir(COD) with halogens followed by a counterion exchange. The cyclooctadiene in these complexes is a thermally labile

Full text of DOI:10.1016/j.jorganchem.2018.08.014

Accepted Manuscript
+
Cyclooctadiene iridium complexes [Cp*Ir(COD)X] (X = Cl, Br, I): Synthesis and
application for oxidative coupling of benzoic acid with alkynes
Vera P. Datsenko, Yulia V. Nelyubina, Alexander F. Smol'yakov, Dmitry A. Loginov
PII:
S0022-328X(18)30541-2
10.1016/j.jorganchem.2018.08.014
JOM 20541
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 1 July 2018
Revised Date: 3 August 2018
Accepted Date: 14 August 2018
Please cite this article as: V.P. Datsenko, Y.V. Nelyubina, A.F. Smol'yakov, D.A. Loginov,
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Cyclooctadiene iridium complexes [Cp*Ir(COD)X] (X = Cl, Br, I): Synthesis and application for oxidative
coupling of benzoic acid with alkynes, Journal of Organometallic Chemistry (2018), doi: 10.1016/
j.jorganchem.2018.08.014.
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ACCEPTED MANUSCRIPT
Cyclooctadiene iridium complexes [Cp*Ir(COD)X]+ (X = Cl, Br, I): synthesis and
application for oxidative coupling of benzoic acid with alkynes
Vera P. Datsenko,[a] Yulia V. Nelyubina,[a,b] Alexander F. Smol'yakov,[a,c] Dmitry A. Loginov*[a]
Abstract
The cyclooctadiene iridium complexes [Cp*Ir(COD)X]PF6 ([1a−c]PF6; X = Cl, Br, I) were
synthesized by reactions of Cp*Ir(COD) with halogens followed by a counterion exchange. The
cyclooctadiene in these complexes is a thermally labile ligand. Complex [1b]PF6 reacts with
trimethylphosphite to give [Cp*Ir{P(OMe)3}2Br]PF6 ([2]PF6) as a result of the cyclooctadiene
replacement. The refluxing of [1b]PF6 in 1,2-dichloroethane affords the dimeric iodide
[Cp*IrI2]2. The structures of [1b]PF6, [2]PF6 and [Cp*IrI2]2 were determined by X-ray
diffraction. The Ir–COD bonding in [1a−c]+ and the related non-methylated complexes was
analyzed by energy decomposition analysis. In the presence of silver salts, complexes [1a−c]PF6
(at 2.0 mol % loading) catalyze the oxidative coupling of benzoic acid with 1-phenyl-1-propyne
in methanol at 60 ºC to selectively give 4-methyl-3-phenylisocoumarin (3) or with
diphenylacetylene in o-xylene at 160 ºC to afford 1,2,3,4-tetraphenylnaphthalene (4).
Keywords: C−H activation; Iridium; Isocoumarins; Metal complex catalysis
1. Introduction
Transition-metal-catalyzed coupling of benzene derivatives with alkenes or alkynes has
proved to be one of the most powerful strategies in terms of the efficiency and atom economy for
the construction of diverse organic molecules from simple starting materials.1 For example, an
annulation reaction of benzoic acids with internal alkynes is a very efficient tool for the
construction of isocoumarins,2 which are structural motifs of compounds with important
biological and fluorescent properties.3 This reaction proceeds via direct C–H activation and does
not require preliminary formation of C–X bonds (where X is carbon, halogen or oxygen) unlike
the conventional approaches, e.g. cyclization of 2-alkynyl benzoates with olefins4 and coupling
[a] A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
ul. Vavilova 28, Moscow, 119991, Russia
E-mail: dloginov@ineos.ac.ru
http://www.ineos.ac.ru/en
[b] Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii prosp. 31, Moscow, 117901, Russia
[c] Faculty of Science, RUDNUniversity, 6 Miklukho-Maklaya St., Moscow 117198, Russia

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of 2-halide or 2-triflate benzoates with alkynes.5 The cobalt,6 ruthenium,7 rhodium8 and iridium9
complexes can be used as catalysts. Possible mechanism involves the reduction of metal atom
(M(III)/M(I) for Co, Rh and Ir or Ru(II)/Ru(0)) in the course of the reaction. Therefore, the use
of oxidants (e.g., Cu(OAc)2, Ag2CO3 and O2) as cocatalysts is necessary for the regeneration of
catalyst.
To the best of our knowledge, so far only two types of iridium complexes were found to
be capable of catalyzing the oxidative coupling of benzoic acids with alkynes. For example, Ison
with coworkers showed that the chloride complex [Cp*IrCl2]2 effectively catalyzes this reaction
in methanol at 60 °C using AgOAc as an oxidant.9a Alkyl- and aryl-alkynes as well as benzoic
acids with methyl, methoxy, tert-butyl and chloride substituents were suitable for the reaction.
Recently, we have found that the cationic iridacarboranes [(7,8-C2B9H11)Ir(C6H6)]+ and [(7,8-
C2B9H11)Ir(MeCN)3]+ also can be used as catalysts for the preparation of isocoumarins in boiling
o-xylene in the presence of Ag2CO3.9b It should be noted that under the latter conditions the use
of complex [Cp*IrCl2]2 results in the decarboxylation of benzoic acids to give naphthalenes as a
result of annulation with two alkyne molecules.8b
On the other hand, the cyclooctadiene ruthenium complex Cp*Ru(COD)Cl is the most
efficient commercially available catalyst for various transformations of alkynes.10 For example,
this complex has considerable higher catalytic activity in the [2 + 2 + 2] cyclotrimerization of
alkynes than chloride [Cp*RuCl2]2.11 The high activity is due to easy replacement of
cyclooctadiene by alkynes. Herein we report the synthesis of iridium complexes
[Cp*Ir(COD)X]+ (X = Cl, Br, I), which are cationic structural analogs of Cp*Ru(COD)Cl, and
their application in the catalytic oxidative coupling of benzoic acids with alkynes.
2. Results and discussion
We found that reactions of Cp*Ir(COD) with halogens in petroleum ether afford
complexes [Cp*Ir(COD)X]X ([1a−c]X; X = Cl, Br, I) as a result of oxidative addition (Scheme
1). Similar approach was used earlier by us for the preparation of the non-methylated analogs
[CpIr(COD)X]X.12 Unlike related reactions of rhodium complexes,13 nucleophilic replacement
of cyclooctadiene by halide counterions does not occur in the case of iridium complexes that can
be explained by the stronger bonding of cyclooctadiene with iridium than with rhodium. At the
same time, the use of more polar solvents (e.g., ether or dichloromethane) instead of petroleum
ether gives an unidentified mixture of products, suggesting that the instantaneous precipitation of
[1a−c]X has crucial importance. Following treatment of [1a−c]X by aqueous KPF6 results in
2

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counterion exchange to give salts [1a−c]PF6 which are stable in dichloromethane and acetone
solutions.
X
X2
Ir
Ir
petroleum
ether
X
[1a_c]X
KPF6 water
PF6
X
a Cl
Ir
X
b Br
c I
[1a_c]PF6
Scheme 1. Synthesis of complexes [Cp*Ir(COD)X]PF6 ([1a−c]PF6; X = Cl, Br, I).
Expectedly, the cyclooctadiene in cations [1a−c]+ is thermally labile ligand, leading to
appearance of free coordination sites at metal atom and therefore making them catalytically
useful. For example, the cyclooctadiene lability was demonstrated by reaction of [1b]PF6 with
trimethylphosphite (Scheme 2). Complex [Cp*Ir{P(OMe)3}2Br]PF6 ([2]PF6), which is formed as
a result of the replacement of cyclooctadiene by phosphite, was isolated as a sole product.
Interestingly, similar reaction of the non-methylated analog [CpIr(COD)Br]PF6 has shown to
give the phosphite complex [(COD)Ir{P(OMe)3}3]PF6 as a result of the reduction of Ir(III) to
Ir(I) and elimination of the Cp ligand.14 Probably, the reductive ability of P(OMe)3 is insufficient
for the reduction of the more electron-rich methylated complex [1b]PF6. The formation of the
dimeric iodide [Cp*IrI2]2 under refluxing of [1c]PF6 in 1,2-dichloroethane (DCE) is an another
evidence of the cyclooctadiene lability (Scheme 3).
Scheme 2. Reaction of [1b]PF6 with trimethylphosphite.
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Scheme 3. The formation of [Cp*IrI2]2 from [1c]PF6.
All the compounds obtained are air- and moisture stable, except of the phospite complex
[2]PF6, which is prone to slow oxidation. They were characterized by 1H NMR spectroscopy as
1
well as elemental analysis. The H NMR spectra of cations [1a−c]+ display two resonances,
corresponding to the olefinic cyclooctadiene protons, they being strongly downfield shifted (by
ca 2.2 and 2.8 ppm) relative to Cp*Ir(COD).15 The non-equivalence of the olefinic
cyclooctadiene protons can be explained by the restricted rotation of this ligand. The structures
of [1a]PF6, [2]BF4 and [Cp*IrI2]2 were determined by X-ray diffraction (Figs. 1−3). The
structure of the latter was studied earlier by Churchill16 and Blacker.17 In the present study
crystal has the same crystallographic parameters.
Cation [1a]+ is the structural analog of the well-known ruthenium neutral complex
Cp*Ru(COD)Cl.18 In particular, the metal-to-ring IrꢀꢀꢀCp* distance (1.876 Å) is very close to the
RuꢀꢀꢀCp* distance (1.884 Å).18 Interestingly, although the IrꢀꢀꢀCp* distance in cation [1a]+ is
practically the same as that in the neutral precursor Cp*Ir(COD) (1.880 Å),15 the Ir−Ccod bonds
in the former (2.231−2.268 Å, av. 2.250 Å) are considerably longer than those in the latter
(2.101−2.122 Å, av. 2.108 Å).15 This correlates with the easy replacement of cyclooctadiene in
cations [1a−c]+ (vide supra).
The Ir–P bonds (2.233–2.238, av. 2.235 Å) in cation [2]+ are considerably shorter than
those in the related phosphide complexes [Cp*Ir(PR3)2Cl]+ (R = Me, Ph; 2.290–2.312, av. 2.299
Å).19
Figure 1. Structure of cation 1a. Ellipsoids are shown at the 50% level. Hydrogen atoms are
omitted for clarity. Selected bond lengths (Å): Ir1−Cl1 2.4154(7), Ir1−C1 2.254(3), Ir1−C2
4

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2.222(3), Ir1−C3 2.277(3), Ir1−C4 2.229(3), Ir1−C5 2.212(3), Ir1−C6 2.268(3), Ir1−C7
2.266(3), Ir1−С10 2.234(3), Ir1−С11 2.231(3), С6−C7 1.387(4), C10−C11 1.392(4).
Figure 2. Structure of cation 2. Ellipsoids are shown at the 50% level. Hydrogen atoms are
omitted for clarity. Selected bond lengths (Å): Ir1−Br1 2.5294(5), Ir1−P1 2.2328(13), Ir1−P2
2.2379(13), Ir1−C1 2.248(5), Ir1−C2 2.246(5), Ir1−C3 2.195(5), Ir1−C4 2.260(5), Ir1−C5
2.243(5).
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Figure 3. Structure of complex [Cp*IrI2]2. Ellipsoids are shown at the 50% level. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å): Ir1−I1 2.7189(5), Ir1−I1A 2.7145(5),
Ir1−I2 2.7024(5), Ir1−C1 2.203(6), Ir1−C2 2.184(6), Ir1−C3 2.163(6), Ir1−C4 2.174(6), Ir1−C5
2.157(6).
To estimate the lability of cyclooctadiene ligand in the complexes prepared, we
performed energy decomposition analysis (EDA) for cations [1a−c]+ and their non-methylated
analogs [CpIr(COD)X]+ (X = Cl, Br, I) as well as the neutral Ir(I) complexes (C5R5)Ir(COD) (R
= H, Me) using [(C5R5)IrX]n+ and COD as interacting fragments at the BP86/TZP level (Table
1). According to the EDA Scheme20 the energy of interaction between two fragments of the
molecule ꢁEint can be divided into three main components: ꢁEint = ꢁEelstat + ꢁEPauli + ꢁEorb,
where Eelstat is the electrostatic attraction between the fragments with a frozen electron density,
ꢁEPauli is the repulsive interactions between occupied orbitals (Pauli repulsion), and ꢁEorb is the
stabilizing orbital interactions. The ratio ꢁEelstat/ꢁEorb indicates the electrostatic/covalent
character of the bond. The bond dissociation energy can be calculated as De = –(∆Eint + ∆Eprep),
where ∆Eprep (the fragment preparation energy) is the energy that is necessary to promote the
fragments from their equilibrium geometry and electronic ground state to the geometry and
electronic state that they have in the optimized structure. This method has already proven its
usefulness for the analysis of the nature of metal–arene bonding in cationic sandwich
compounds.21
We found that cations [1a−c]+ have weaker Ir–COD bond by ca. 10 kcal mol–1 than non-
methylated analogs (Entries 2, 4 and 6 vs. 1, 3 and 5), that is mainly caused by the decrease of
ꢁEorb because the increase of ꢁEelstat is overruled by the increase of ꢁEPauli. The ∆Eprep values are
higher by ca. 5 kcal mol–1 for the methylated complexes, additionally facilitating dissociation of
the Ir–COD bond. This correlates well with the easy replacement of cyclooctadiene in [1a−c]+ by
phosphite and halide ligands (vide supra). Noteworthy, both ꢁEint and De are not dependent on
the halogen nature. In general, the Ir–COD bond in the cationic Ir(III) complexes is considerably
weaker than that in the neutral Ir(I) complexes (C5R5)Ir(COD) (Entries 1−6 vs. 7 and 8).
Table 1
Results of EDA (energy values in kcal mol–1) for cations [(C5R5)Ir(COD)X]+ (R = H, Me; X =
Cl, Br, I) and neutral compounds (C5R5)Ir(COD) using [(C5R5)IrX]n+ and COD as interacting
fragments at the BP86/TZP level.
[a]
[a]
Entry X
Cl
R
H
∆Eint
∆EPauli ∆Eelstat
∆Eorb
−251.87 (54.0%) −214.70 (46.0%)
∆Eprep De
1
343.90
69.13 53.54
−122.67
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2
3
4
5
6
7
Cl
Br
Br
I
Me (1a)
H
349.74
346.92
355.82
353.64
364.74
849.22
710.81
74.47 37.53
68.97 53.62
74.77 37.70
67.63 54.18
74.55 37.54
85.88 111.11
78.74 102.53
−112.00
−122.59
−112.47
−121.81
−112.09
−196.99
−181.27
−255.30 (55.3%) −206.44 (44.7%)
−253.99 (54.1%) −215.52 (45.9%)
−259.01 (55.3%) −209.27 (44.7%)
−259.26 (54.5%) −216.20 (45.5%)
−264.91 (55.6%) −211.93 (44.4%)
−498.12 (47.6%) −548.08 (52.4%)
−459.36 (51.5%) −432.72 (48.5%)
Me (1b)
H
I
Me (1c)
H
-
8
-
Me
a
The values in parentheses give the percentage contribution to the total attractive interactions.
Finally, we tested the catalytic activity of complexes [1a,b]PF6 for oxidative coupling of
benzoic acids with alkynes in two different conditions (AgOAc or Ag2CO3, MeOH, 60 ºC and
Ag2CO3, o-xylene, 160 ºC) using the classical catalyst [Cp*IrCl2]2 for the comparison (Table 2).
As expected, the reaction pathway strongly depends on the reaction temperature. It was found
that isocoumarins 3 are isolated as sole products in the mild conditions (Entries 1−5), while the
reactions in boiling o-xylene afford naphthalenes 4 as a result of the decarboxylation of benzoic
acid (Entries 6 and 7).
Table 2
Oxidative coupling of benzoic acids with alkynes catalyzed by iridium complexes.a
Entry Solvent,
Temperature, Time
Catalyst
Additive
AgOAc
R
Yield of 3b Yield of 4b
1
2
3
4
5
6
7
8
9
MeOH, 60ºC, 24h
MeOH, 60ºC, 24h
MeOH, 60ºC, 24h
MeOH, 60ºC, 24h
MeOH, 60ºC, 24h
[1b]PF6
Ph
17
19
64
47
87
-
-
[Cp*IrCl2]2 AgOAc
Ph
-
[1b]PF6
[1b]PF6
AgOAc
Ag2CO3
Me
Me
Me
Ph
-
-
[Cp*IrCl2]2 AgOAc
Ag2CO3
o-xylene, 160ºC, 6h [Cp*IrCl2]2 Ag2CO3
o-xylene, 160ºC, 6h [1a]PF6 Ag2CO3
o-xylene, 160ºC, 6h [Cp*IrCl2]2 Ag2CO3
-
o-xylene, 160ºC, 6h [1a]PF6
59
91
-
Ph
-
Me
Me
-
-
-
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a 0.25 mmol (31 mg) of benzoic acid, 0.5 mmol of alkyne, 1.0 mmol of the silver salt, 2 mol % of
the catalyst, 2 ml of the solvent. b Yields are given after purification.
The proposed mechanism of two reaction pathways is given in Scheme 4. In both cases
the reaction starts from the formation of the Ir(III) benzoate A as a result of coordination of
catalyst to carboxylic group. Subsequent C–H activation of ortho proton gives five-membered
iridacycle intermediate B. Then alkyne insertion leads to the seven-membered rhodacycle C. In
the case of mild conditions (MeOH, 60 ºC), the following reaction proceeds via the reductive
elimination of the Ir(I) species from intermediate C to produce isocoumarins 3. In contrast, in the
case of hard conditions (o-xylene, 160 ºC), the decarboxylation of C with formation of
intermediate D is more favorable than the reductive elimination of iridium that leads to
naphthalenes 4 after insertion of the second alkyne molecule. In both cases the resulting Ir(I)
species are oxidized by silver salts (AgOAc or Ag2CO3) to generate the starting Ir(III) complex.
For more detailed discussion of mechanism, see references.2,8,22
COOH
O
C
O
C
O
O
Ir(III)X3
IrX2
Ir
X
A
B
Ag+
O
R
Ph
R
O
Ir(I)X
Ph
Mild conditions
3
O
O
Ph
IrX
Ph
Hard conditions
R
R
R
X
Ir
C
_CO2
Ph
Ph
R
R
R
D
4
Scheme 4. Mechanism of the Ir-catalyzed coupling of benzoic acid with alkynes.
We found that the cyclooctadiene complexes [1a,b]PF6, in general, proved to be slightly
less catalytically active than [Cp*IrCl2]2 (Entries 1, 3 and 6 vs. 2, 5 and 7). The low yields of 3 in
8

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the case of diphenylacetylene (Entries 1 and 2) may be explained by lower reactivity of
diarylacetylenes as compared with alkyl-substituted derivatives. The only starting materials
(benzoic acid and diphenylacetylene) were isolated from reaction mixture along with the target
product and no any other products were detected. Noteworthy, the observed regioselective
formation of only one isomer of isocoumarine 3 in the case of 1-phenyl-1-propyne is caused by
better stabilization of α-carbon atom in an intermediate iridacycle C by phenyl substituent than
methyl one.23 At the same time, the absence of any annulation products for 1-phenyl-1-propyne
in boiling o-xylene (Entries 8 and 9) is probably due to oxidation of alkyne in such hard
conditions.
3. Conclusion
The simple procedure based on the reaction of Cp*Ir(COD) with halogens allows one to
synthesize cations [1a−c]+, which are structural analogs of the best known catalyst for the alkyne
transformations Cp*Ru(COD)Cl. The cyclooctadiene ligand in such cations is notably more
labile than in the starting complex Cp*Ir(COD) and unmethylated analogs [CpIr(COD)X]+ (X =
Cl, Br, I). Although cations [1a−c]+ were shown to be less catalytically active in the oxidative
coupling of benzoic acid with alkynes than [Cp*IrCl2]2, they still give isocoumarins or
naphthalenes depending on the reaction temperature in moderate yields.
4. Experimental section
Synthesis of complexes was realized under ambient atmosphere in commercially
available solvents. The catalytic reactions were carried out under an inert atmosphere in
anhydrous solvents, which were purified and dried using standard procedures. The isolation of
products was conducted in air. Starting complex Cp*Ir(COD) was prepared as described in the
literature.24 1H and 31P{1H} NMR spectra (δ in ppm, J in Hz) were recorded on a Bruker
Avance-400 spectrometer operating at 400.13 and 161.98 MHz, respectively.
4.1. Synthesis of [Cp*Ir(COD)X]PF6 ([1a−c]PF6; X = Cl (a), Br (b), I (c))
Cl2 (gas was passed through reaction mixture for 15 min), Br2 (29 mg, 0.18 mmol) or I2
(46 mg, 0.18 mmol) were added to solution of Cp*Ir(COD) (80 mg, 0.18 mmol) in petroleum
ether (2 ml) and reaction mixture was stirred for ca. 0.5 h. The colored precipitate of [1a−c]X
was centrifuged off, washed by ether and added to saturated solution of KPF6 in water. After
stirring overnight, the precipitate was washed by water, dried in in vacuo and repricipitated from
dichloromethane by ether. Complexes [1a−c]PF6 were obtained as colored solids.
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[1a]PF6, X = Cl, yellow solid, yield 52 mg (46%). Anal. Calc. for C18H27ClIrPF6: C, 35.09; H,
1
4.43. Found: C, 34.74; H, 3.93. H NMR (acetone-d6):
δ = 5.71 (m, 2H, COD), 4.86 (m, 2H,
COD), 2.75 (m, 2H, COD), 2.57 (m, 4H, COD), 2.32 (m, 2H, COD), 1.92 (s, 15H, Cp*).
[1b]PF6, X = Br, yellow solid, yield 58 mg (48%). Anal. Calc. for C18H27BrIrPF6: C, 32.73; H,
1
4.13. Found: C, 32.58; H, 4.19. H NMR (acetone-d6):
δ = 5.57 (m, 2H, COD), 4.98 (m, 2H,
COD), 2.84 (m, 2H, COD), 2.74 (m, 2H, COD), 2.60 (m, 2H, COD), 2.31 (m, 2H, COD), 2.00
(s, 15H, Cp*).
[1c]PF6, X = I, brown solid, yield 61 mg (47%). Anal. Calc. for C18H27IIrPF6ꢀCH2Cl2: C, 28.80;
H, 3.70. Found: C, 28.91; H, 3.37. 1H NMR (acetone-d6):
δ = 5.29 (m, 2H, COD), 5.10 (m, 2H,
COD), 3.01 (m, 4H, COD), 2.65 (m, 2H, COD), 2.35 (m, 2H, COD), 2.18 (s, 15H, Cp*).
4.2. Synthesis of [Cp*Ir{P(OMe)3}2Br]PF6 ([2]PF6)
Acetone (3 ml) was added to a mixture of complex [1b]PF6 (34 mg, 0.051 mmol) and
P(OMe)3 (0.2 ml). The reaction mixture was stirred for 3 h. The volume of solvent was reduced
in vacuo to 1 ml and excess of petroleum ether was added. Yellow precipitate formed was
centrifuged off and washed with ether to give 26 mg (63%) of [2]PF6. 1H NMR (acetone-d6):
3.94 (m, 18H, P(OMe3)3), 2.25 (s, 15H, Cp*). 31P{1H} NMR (acetone-d6):
= 54.7 (s, 3P,
δ =
δ
P(OMe3)3), −144.3 (sept., 1P, PF6). Found (%):C, 24.32; H, 4.22. Calc. for C16H33BrF6IrO6P3
(%):C, 24.01; H, 4.16.
4.3. Synthesis of [Cp*IrI2]2 from [1c]PF6
A solution of [1c]PF6 (20 mg, 0.028 mmol) in DCE (2 ml) was refluxed for 3h. The
solvent was removed in vacuo. The residue was washed by petroleum ether and extracted by
chloroform (5 ml). The solvent was removed in vacuo to give 8 mg (49%) of [Cp*IrI2]2 as a dark
violet solid. 1H NMR (CDCl3): = 1.82 (s, 15H, Cp*) (cf.17).
δ
4.4. Synthesis of 4-methyl-3-phenylisocoumarin (3)
A mixture of benzoic acid (31 mg, 0.25 mmol), 1-phenyl-1-propyne (0.038 ml, 0.3
mmol), AgOAc (84 mg, 0.5 mmol), [1b]PF6 (3.3 mg, 0.005 mmol) and methanol (2 ml) was
refluxed with vigorous stirring for 24 h. The solvent was removed in vacuo and the residue was
purified by column chromatography on SiO2 (15 cm × 1 cm) using petroleum ether/ ethyl acetate
(5/1) as the eluent to give 38 mg (64%) of 3 as a colorless oil. 1H NMR (CDCl3) δ: 8.39 (d, J =
8.0, 1H), 7.82 (t, J = 8.0, 1H), 7.65 (d, J = 8.0, 1H), 7.61 (m, 2H), 7.56 (t, J = 8.0, 1H), 7.48 (m,
3H), 2.33 (s, 3H) (cf.8b).
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4.5. Synthesis of 1,2,3,4-tetraphenylnaphthalene (4)
A mixture of benzoic acid (31 mg, 0.25 mmol), diphenylacetylene (89 mg, 0.5 mmol),
Ag2CO3 (138 mg, 0.5 mmol), [1a]PF6 (3.1 mg, 0.005 mmol) and o-xylene (2 ml) was refluxed
with vigorous stirring for 6 h. The solvent was removed in vacuo and the residue was
chromatographated on SiO2 (15 cm × 1 cm). Unreacted diphenylacetylene was washed off with
petroleum ether. Then the yellow band was collected using petroleum ether/ ethyl acetate (10/1)
as the eluent and evaporated in vacuo to give 64 mg (59%) of 4 as a pale yellow solid. 1H NMR
(CDCl3) δ: 7.67−7.70 (m, 2H), 7.42−7.44 (m, 2H), 7.23−7.29 (m, 10H), 6.86−6.90 (m, 10H)
(cf.25).
4.6. X-ray crystallography
Crystals were grown by slow diffusion in a two-layer system, petroleum ether and
a solution of the complex [1a]PF6 or [Cp*IrI2]2 in CH2Cl2 or ether and a solution of the
complex [
2
]PF6 in Me2CO. In the latter case, X-ray diffraction reveals the composition of
−
the crystals as [
2
]BF4, which may be formed as a result of hydrolysis of the PF6 anion in
the presence of glass.26 X-ray diffraction data were collected with APEX2 DUO CCD
diffractometer, using graphite monochromated Mo-K radiation ( = 0.71073 Å,
α
λ
ω-
scans) at 120 K. The structures were solved by direct method and refined by the full-
matrix least-squares technique against F2 in the anisotropic-isotropic approximation.
Positions of hydrogen atoms were calculated, and they were refined in the isotropic
approximation within the riding model. All calculations were performed using SHELXTL
PLUS 5.0.27 Experimental details and crystal parameters are listed in Table 3.
Table 3
Crystallographic data and structure refinement parameters for [1a]PF6, [2]BF4 and [Cp*IrI2]2.
Compound
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
[1a]PF6
[2]BF4
[Cp*IrI2]2
C18H27ClF6IrP
616.01
C16H33BBrF4IrO6P2 C20H30I4Ir2
742.28
1162.44
Orthorombic
Pccn
Monoclinic
P21/c
Monoclinic
P21/n
11.4678(15)
13.3100(17)
13.1004(17)
96.343(2)
11.1547(12)
15.7738(16)
13.6409(13)
91.854(3)
13.3223(9)
21.5515(15)
8.9913(6)
-
b (Å)
c (Å)
β (°)
11

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V (Å3)
1987.4(4)
2.056
2398.9(4)
2.055
74.25
1440
2581.5(3)
2.991
Dcalc (g cm–3)
Linear absorption,
F(000)
µ
(cm–3)
69.80
150.87
2064
1192
30.685
35293
58
52.0
2θmax, °
Collected reflections
19686
28186
Independent reflections
Observed reflections (I > 2σ
(I))
6168 (Rint = 0.0345) 6373 (Rint = 0.0615) 2542 (Rint = 0.0568)
5556
5069
2200
Parameters
249
304
123
R
1
0.0224
0.0352
0.0270
wR
0.0530
1.076
0.0780
0.0598
2
Goodness-of-fit
1.004
1.157
Largest diff. peak and hole 1.79 and −0.92
(e Å–3)
1.62 and −1.27
2.18 and −0.84
4.7. Computational details
The geometries have been optimized without constraints at the gradient corrected DFT level of
theory using the exchange functional of Becke28 and the correlation functional of Perdew29
(BP86). All-electron triple-ζ basis set augmented by one polarization function TZP was used.
The bonding interactions were studied by means of Morokuma-Ziegler energy decomposition
analysis.30 The calculations were carried out using the ADF 2010.01 program package.31
Acknowledgements
This work was supported by the Russian Science Foundation (grant # 17-73-20144). A.F.S.
thanks the RUDN University Program “5-100” for support. The contribution of the Center of
molecular composition studies of INEOS RAS is gratefully acknowledged.
Appendix A. Supplementary material
CCDC 1845088−1845090 contain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
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Highlights
- A general approach to new family of cyclooctadiene iridium complexes was developed.
- The complexes prepared were used as catalysts for the formation of isocoumarin or
naphthalene moieties.
- The selectivity of catalytic reactions strongly depends on the reaction temperature.