Cationic iridacarboranes [3-(arene)-3,1,2-IrC2B9H11]+ and [3-(MeCN)3-3,1,2-IrC2B9H11]+: Synthesis, reactivity, and bonding. Catalysis of oxidative coupling

Article abstract of DOI:10.1016/j.jorganchem.2015.01.022

(Arene)iridacarboranes [3-(arene)-3,1,2-IrC₂B₉H₁₁]⁺ (arene = benzene (1a), toluene (1b), o-xylene (1c), m-xylene (1d), durene (1e)) were synthesized by reaction of [(cod)IrCl]₂ with Tl[Tl(η-7,8-C

Full text of DOI:10.1016/j.jorganchem.2015.01.022

Journal of Organometallic Chemistry 793 (2015) 232e240
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Cationic iridacarboranes [3-(arene)-3,1,2-IrC2B9H11]þ and [3-(MeCN)3-
3,1,2-IrC2B9H11]þ: Synthesis, reactivity, and bonding. Catalysis of
oxidative coupling of benzoic acid with alkynes
Dmitry A. Loginov, Alena O. Belova, Anna V. Vologzhanina, Alexander R. Kudinov*
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 ul. Vavilova, 119991 Moscow GSP-1, Russian Federation
a r t i c l e i n f o
a b s t r a c t
þ
Article history:
(Arene)iridacarboranes [3-(arene)-3,1,2-IrC2B9H11
]
(arene ¼ benzene (1a), toluene (1b), o-xylene (1c),
Received 30 December 2014
Received in revised form
23 January 2015
Accepted 24 January 2015
Available online 19 February 2015
m-xylene (1d), durene (1e)) were synthesized by reaction of [(codꢀ)IrCl]2 with Tl[Tl(
h-7,8-C2B9H11)] with
the subsequent treatment of the anion [3-(cod)-3,1,2-IrC2B9H11
]
formed by arenes in refluxinþg tri-
fluoroacetic acid. Cation 1a reacts with acetonitrile giving complex [3-(MeCN)3-3,1,2-IrC2B9H11
]
(2).
Reactions of 2 with Cpe anions and arenes afford the cyclopentadienyl and arene derivatives 3-(
h
-
þ
C5H4R)-3,1,2-IrC2B9H11 (R ¼ H (3a), C(O)Me (3b)) and [3-(arene)-3,1,2-IrC2B9H11
]
(arene ¼ mesitylene
Dedicated to the memory of Academician,
Professor Alexander E. Shilov who contrib-
uted much to the development of the metal-
complex catalyzed CeH activation.
(1f), [2,2]paracyclophane (1g)). The structures of 1ePF6 and 2BF4 were determined by X-ray diffraction.
According to energy decomposition analysis, the metal-benzene bonding in the iridium cation 1a is
þ
stronger than in the rhodium analog [3-(
h
-C6H6)-3,1,2-RhC2B9H11
]
but weaker than in [(C5R5)
Ir(C6H6)]2þ. In the presence of Ag2CO3, iridacarboranes 1a and 2 catalyze the oxidative coupling of
benzoic acid with diphenylacetylene selectively giving 3,4-diphenylisocoumarin in 40e50% yields. In
contrast, the reactions catalyzed by [3,3-Cl2-4-SMe2-3,1,2-IrC2B9H10]2 and [CpIrI2]2 afford only 1,2,3,4-
tetraphenylnaphthalene in 10 and 35% yields, respectively. The iridium catalyzed decarboxylation of
benzoic acid was analyzed by DFT calculations.
Keywords:
CꢀH activation
Iridium
Metal complex catalysis
Metallacarboranes
© 2015 Elsevier B.V. All rights reserved.
Introduction
Although the dicarbollide anion [C2B9H11]
2ꢀ is isolobal with Cpꢀ
[5], the catalytic activity of metallacarboranes often differs from
that of cyclopentadienyl complexes [6]. Therefore, metal-
lacarboranes have found a wide range of applications in catalysis
Shilov was a pioneer in development of metal-complex cata-
lyzed CeH functionalization of hydrocarbons. In particular, he
shown that complexes of Pt(II) and Pt(IV) are capable of function-
alizing the CeH bonds of methane [1]. This work started the
extensive study of similar systems which was named “Shilov's
chemistry” [2].
The cyclopentadienyl complexes [Cp*MCl2]2 (M ¼ Rh, Ir) proved
to be effective catalysts for CeH activation [3]. In particular, they
catalyze the oxidative coupling of benzoic acids with internal al-
kynes giving isocoumarin and naphthalene derivatives [4]. The
selectivity strongly depends on metal nature. Thus, the rhodium
complex [Cp*RhCl2]2 catalyzes this reaction predominantly giving
isocoumarins, while the iridium derivative [Cp*IrCl2]2 results in
naphthalenes.
[7]. Recently, we found that rhodacarboranes [3-(
h
-C6H6)-3,1,2-
þ
RhC2B9H11
]
and [1,1-I2-12-tBuNH-1,2,4,12-RhC3B8H10 2
]
catalyze
oxidative coupling of benzoic acid with diphenylacetylene giving
1,2,3,4-tetraphenylnaphthalene in contrast to [Cp*RhCl2]2 (giving
isocoumarins) [8]. Apparently, the difference in selectivity is due to
different electronic effects of carborane and Cp ligands.
Herein we report synthesis, reactivity and catalytiþc activity of
cationic iridacarboranes [3-(arene)-3,1,2-IrC2B9H11
]
and [3-
(MeCN)3-3,1,2-IrC2B9H11]þ. The mechanisms of the reactions were
studied by DFT computation.
Results and discussion
Synthesis
Recently, we have described useful one-pot procedure for the
* Corresponding author.
E-mail address: arkudinov@ineos.ac.ru (A.R. Kudinov).
synthesis
of
(benzene)rhodacarborane
[3-(h-C6H6)-3,1,2-
http://dx.doi.org/10.1016/j.jorganchem.2015.01.022
0022-328X/© 2015 Elsevier B.V. All rights reserved.

D.A. Loginov et al. / Journal of Organometallic Chemistry 793 (2015) 232e240
233
þ
RhC2B9H11
] starting from easily available [(cod)RhCl]2 and thal-
lium dicarbollide [9]. In present work we used a similar approach
for the synthesis of (arene)iridacarboranes [3-(arene)-3,1,2-
þ
IrC2B9H11
]
(arene ¼ benzene, toluene, o- and m-xylene, durene)
(1aee) (Scheme 1). Reaction of [(cod)IrCl]2 with Tl[Tl(ꢀ
h
-7,8-
(not
C2B9H11)] preliminarily gives anion [3-(cod)-3,1,2-IrC2B9H11
]
isolated in pure form). Refluxing of the latter in the presence of
arenes in trifluoroacetic acid affords (arene)iridacarboranes 1aee
in moderate yields (20e40%).
In the 1H NMR spectra of 1aee the signals for the arene ring
protons undergo downfield shift with respect to the free arene in
contrast to other monocationic arene complexes with carbocyclic
ligands in which these signals are usually upfield shifted. Probably,
the electron-withdrawing effect of carborane ligand overrides the
opposite effect of coordination to the transition metal atom [10].
Scheme 2. Synthesis of the tris(acetonitrile) complex 2.
towards carbon atoms of the nido-carborane ligand (IreC distances
are shorter than IreB ones). In the durene cation 1e arene and C2B3
planes are almost parallel (the dihedral angle is equal to 5.2ꢁ). The
Ir/C2B3 distance in 1e (1.577 Å) is very close to that in the cyclo-
Similar pattern was observed earlier for the dicationic complexes
2þ
[CpIr(arene)]2þ and [3-(arene)-4-SMe2-3,1,2-IrC2B9H10
]
[11,12].
Earlier, we found that the rhodium benzene complex [3-(
h
-
þ
pentadienyl complexes 3-(
R ¼ Me, 1.579 Å) [13]. The Ir/C6 distance (1.758 Å) is very close to
that in the cyclopentadienyl analogs
[Cp*Ir(arene)]2þ
h-C5R5)-3,1,2-IrC2B9H11 (R ¼ H, 1.573 Å;
C6H6)-3,1,2-RhC2B9H11
]
is substitutionally labile and easily un-
dergoes the arene exchange reaction [9]. The iridium analog 1a
proved to be less reactive. In particular, after refluxing of 1a with
anisole in nitromethane during 6 h the degree of conversion for
arene exchange was ca. 14%, according to 1H NMR. Nevertheless, we
found that the refluxing of 1a in acetonitrile results in quantitative
elimination of benzene giving the tris(acetonitrile) derivative [3-
(1.744e1.763 Å) [14], but is shorter than the corresponding dis-
tances in [(diene)Ir(arene)]þ (1.770e1.810 Å) [15], suggesting
stronger Irearene bonding in the Ir(III) complexes.
Noteworthy, the Ir/C2B3 distance in the acetonitrile cation 2
(1.539 Å) is somewhat shorter than the corresponding distance in
1e (1.577 Å). Probably, the IreCarb bond strengthening is caused by
weaker bonding with acetonitrile ligands vs. durene (so called trans
influence). Moreover, the shortening of the Ir/C2B3 distance in 2 is
accompanied by significant elongation of the cage CeC bond
(1.724 Å in 2 vs. 1.664 Å in 1e).
(MeCN)3-3,1,2-IrC2B9H11]
þ (2) in high yield (89%) (Scheme 2).
The PFꢀ6 and BFꢀ4 salts of acetonitrile cation 2 are stable in air for
long time. Nevertheless, the acetonitrile ligands in 2 are much more
labile than the benzene ligand in 1a. Therefore complex 2 can be
used as a useful synthon of the cationic iridacarborane fragment
[3,1,2-IrC2B9H11]þ. In particular, it reacts with cyclopentadienide
anions and arenes giving corresponding derivatives 3-(hþ-C5H4R)-
Metal-benzene bonding in [3-(arene)-3,1,2-MC2B9H11
]
þ (M ¼ Rh, Ir)
3,1,2-IrC2B9H11 (3a,b) and [3-(arene)-3,1,2-IrC2B9H11
]
(1f,g)
(Scheme 3).
To compare the MꢀC6H6 bonding in rhoda- and iridacarboranes
with that in the cyclopentadienyl analogs [(C5R5)M(C6H6)]2þ
(M ¼ Rh, Ir; R ¼ H, Me), we carried out energy decomposition
analysis (EDA) [16]. According to the EDA method, the interaction
X-ray diffraction study
The structures of 1ePF6 and 2BF4 were investigated using X-ray
diffraction (Figs. 1 and 2). In both cased the iridium is shifted
energy between the bonding fragments
three main components:
DEint can be divided into
DEint ¼ DEelstat þ DEPauli þ DEorb
D
Eelstat is the electrostatic interaction energy between the
fragments with a frozen electron density distribution, EPauli pre-
sents the repulsive four-electron interactions between occupied
orbitals (Pauli repulsion), and Eorb refers to the stabilizing orbital
interactions. The ratio Eelstat Eorb indicates the electrostatic/co-
valent character of the bond. The bond dissociation energy
D
D
D
/D
À
Á
De ¼ ꢀ DEint þ DEprep
;
where
DEprep (the fragment preparation energy) is the energy that
is necessary to promote the fragments from their equilibrium ge-
ometry 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
metaleС6H6 bonding in the chromium [17], rhenium [18], iron [19],
ruthenium [20], and cobalt [21] complexes.
The EDA data for complexes [(L)M(C6H6)]nþ in terms of in-
teractions between [(L)M]nþ and C6H6 fragments are given in
Table 1. Let us first discuss the bonding in the cyclopentadienyl
complexes [(C5R5)M(C6H6)]2þ (M ¼ Rh, Ir; R ¼ H, Me). In general,
the iridium complexes have much stronger MꢀC6H6 bond (by
22e23 kcal molꢀ1) than the rhodium analogs. The Cp methylation
leads to considerable decrease of the attractive orbital interaction
Scheme 1. Synthesis of (arene)iridacarboranes 1aee.

234
D.A. Loginov et al. / Journal of Organometallic Chemistry 793 (2015) 232e240
Scheme 3. Reactions of 2 with Cp-anions and arenes.
(
D
Esteric
Eorb),
whereas
the
sterical
contribution
[13b,22]. Finally, the energy partitioning suggests that the attrac-
tive interactions between [(L)M]nþ and C6H6 fragments are ca. 55%
covalent and 45% electrostatic for metallacarboranes, being
considerably more covalent for the cyclopentadienyl complexes.
(D
¼
D
Eelstat EPauli) remains almost unchanged. As a result,
þ
D
for the methylated complexes [Cp*M(C6H6)]2þ the MꢀC6H6 bond is
weaker by ca. 35 kcal molꢀ1 than for the unsubstituted analogs.
Going from cyclopentadienyl complexes to the carborane ana-
logs, the steric interaction increases and, in addition, the orbital
interaction decreases explaining loosening of the MꢀC6H6 bond.
Calculations also revealed that the weakest MꢀC6H6 bonds in
þ
metallacarboranes [3-(
h
-C6H6)-3,1,2-MC2B9H11
]
(M ¼ Rh, Ir) (vs
[(C5R5)M(C6H6)]2þ) correlate with the lowest activation energies
for the benzene replacement by MeCN or H2O. Fig. 4 shows the
intrinsic reaction coordinates (IRC) for the primary step, at which
the iridium cations [(L)Ir(C6H6)]nþ are attacked by the first MeCN
molecule. This step has maximal activation energies, since it is
accompanied by the hapticity change of benzene ligand, h6 (com-
plex) / h3 (L ¼ C5R5) or h4 (L ¼ C2B9H11) (transition state TS, see
Fig. 5). Similar IRC profiles for the primary step of benzene
replacement by water (Rh and Ir complexes) and acetonitrile (Rh)
The
DEint values correlate well with the dissociation energies (De)
and the M/C6H6 distances. Interestingly, in the case of the iridium
complex 1a ([M(L)]nþ ¼ [IrCarb]þ) the preparation energy (
DEprep)
is considerably higher (by 10.9 kcal molꢀ1) than that for rhodium
analog. This is explained by different optimized geometries of the
[3,1,2-IrC2B9H11
docloso) and in complex 1a (closo) (Fig. 3). The closo#pseudocloso
transformations are well known for rhoda- and iridadicarbollides
þ
]
fragment in the equilibrium ground state (pseu-
Fig. 1. Structure of cation 1e. Atoms are represented by 50% thermal ellipsoids.
Hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and angles [ꢁ]:
Ir3eC3 2.271(5), Ir3eC4 2.244(5), Ir3eC5 2.214(5), Ir3eC6 2.271(5), Ir3eC7 2.310(5),
Ir3eC8 2.278(5), Ir3eC1 2.157(5), Ir3eC2 2.154(6), Ir3eB4 2.194(6), Ir3eB7 2.192(6),
Ir3eB8 2.193(6), C1eC2 1.664(8), C1eB4 1.744(9), C2eB7 1.772(9), B4eB8 1.818(9),
B7eB8 1.836(10), C3eC4 1.437(7), C4eC5 1.426(8), C5eC6 1.428(7), C6eC7 1.429(7),
C7eC8 1.422(8), C3eC8 1.418(8), C1eC2eB7 111.0(4), C2eB7eB8 104.7(4), B7eB8eB4
107.0(4), B8eB4eC1 105.9(4), B4eC1eC2 111.4(4).
Fig. 2. Structure of cation 2. Atoms are represented by 50% thermal ellipsoids.
Hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and angles [ꢁ]:
Ir3eC1 2.116(2), Ir3eB4 2.170(2), Ir3eB8 2.206(3), Ir3eN1 2.061(2), Ir3eN2 2.093(2),
N1eC4 1.132(2), N2eC2 1.142(3), C1eC14)1.724 ׳), C1eB4 1.737(3), B4eB8 1.838(3),
Ir3eN1eC4 172.3(2), Ir3eN2eC2 173.9(2).

D.A. Loginov et al. / Journal of Organometallic Chemistry 793 (2015) 232e240
235
Table 1
Results of EDA (energy values in kcal molꢀ1) for the [(L)M(C6H6)]nþ (M ¼ Rh, Ir) complexes using C6H6 and the [M(L)]nþ as Interacting Fragments at BP86/TZ2P.
Fragment [M(L)]nþ
RhCarb
RhCp
RhCp*
IrCarb
IrCp
IrCp*
D
D
D
D
D
D
Eint
ꢀ71.4
ꢀ123.7
146.8
ꢀ88.4
ꢀ92.0
ꢀ146.6
203.7
ꢀ110.8
EPauli
Eelstat
Esteric
Eorb
Eprep
165.8
146.6
242.5
212.3
a
ꢀ107.7 (45.4%)
ꢀ98.2 (36.3%)
ꢀ97.4 (41.5%)
ꢀ155.2 (46.4%)
ꢀ134.3 (38.3%)
ꢀ138.0 (42.7%)
58.0
48.6
49.2
87.3
69.4
74.3
a
ꢀ129.4 (54.6%)
7.6
ꢀ172.3 (63.7%)
4.7
ꢀ137.5 (58.5%)
4.6
ꢀ179.3 (53.6%)
18.5
ꢀ216.1 (61.7%)
6.9
ꢀ185.0 (57.3%)
6.5
De
63.8
119.0
83.8
73.5
139.7
104.3
M/C6H6(centroid)
1.848
1.812
1.846
1.801
1.781
1.803
a
The values in parentheses give the percentage contribution to the total attractive interactions.
are given in the Supporting Information (Figs. S1eS3). The activa-
tion energies (including solvation) are given in Tables 2 and 3. In
overall, the barriers for the carborane complexes are ca.
5 kcal molꢀ1 lower than for the cyclopentadienyl analogs. Inter-
estingly, the activation energies for the iridium cation 1a are ca.
4 kcal molꢀ1 higher than for the rhodium analog [3-(
h-C6H6)-3,1,2-
RhC2B9H11]þ, correlating well with poorer reactivity of 1a in ben-
zene replacement.
Catalytic activity in oxidative coupling of benzoic acid with alkynes
Taking into account the lability of benzene and acetonitrile li-
gands, we examined iridacarboranes 1a and 2 as catalysts for the
oxidative coupling of benzoic acid with diphenylacetylene in
refluxing o-xylene (Scheme 4). This reaction proceeds via CeH
activation of ortho position of benzoic acid. Silver carbonate was
used as a cocatalyst (necessary for the regeneration of the initial
catalyst). As can be seen from Table 4, complexes 1a and 2 catalyze
the oxidative coupling to give isocumarin (3a) as a sole product in
40e50% yields, in contrast to the reactions catalyzed by rhoda-
carboranes, which produce mainly naphthalene (3b) [8]. The tri-
s(acetonitrile) complex 2 reveals higher catalytic activity than the
benzene derivative 1a, as a consequence of higher lability of
acetonitrile ligands. In contrast, using of the SMe2-substituted iri-
Fig. 4. Intrinsic reaction coordinates at PBE/L2 for the primary step of benzene
replacement by acetonitrile in the iridium complexes [(L)Ir(C6H6)]nþ (L ¼ C2B9H11 (1a)
red line, L ¼ Cp blue, L ¼ Cp* green). (For interpretation of the references to color in
this figure legend, the reader is referred to the web version of this article.)
B. Earlier we shown by DFT-calculations that for (cyclopentadienyl)
rhodium complexes the decarboxylation proceeds via two transi-
tion states (TS1 and TS2) and have a rather small activation free
energies (8e13 kcal molꢀ1), suggesting that the selectivity of
oxidative coupling mainly depends from oxidative potential of in-
termediate A [8]. For unsubstituted (cyclopentadienyl)iridium
analog the intrinsic reaction coordinates (IRC) have a similar
pattern (Fig. 6). In contrast, for Cp*Ir and (C2B9H11)Ir derivatives the
dadicarbollide chloride [3,3-Cl2-4-SMe2-3,1,2-IrC2B9H10]2 [23] or
the parent cyclopentadienyl complex [CpIrI2]2 in the same reaction
results in exclusive formation of naphthalene 3b. Similar result has
been previously obtained using [Cp*IrCl2]2 [4].
Two pathways of oxidative coupling of benzoic acid with al-
kynes are well described by the mechanism proposed by Satoh and
Miura (Scheme 5) [4]. In particular, the formation of naphthalenes
includes the decarboxylation of intermediate A giving intermediate
þ
Fig. 3. The optimized geometries of the [3,1,2-IrC2B9H11
]
fragment in the equilibrium ground state (left) and in cation 1a (right) at BP86/TZ2P.

236
D.A. Loginov et al. / Journal of Organometallic Chemistry 793 (2015) 232e240
Fig. 5. Optimized structures of transition states TS for the attack of 1a (left) and [CpIr(C6H6)]2þ (right) by the first MeCN molecule.
Table 2
Table 4
Activation internal energies Ua, enthalpies Ha and free energies Ga for the primary
step of benzene replacement by acetonitrile in the [(L)M(C6H6)]2þ complexes (at
298.15 K, in kcal molꢀ1) at BPBE/def2-TZVPP//BPBE/L2.a
Catalytic activity of iridacarboranes 1a, 2 and [3,3-Cl2-4-SMe2-3,1,2-IrC2B9H10] as
2
well as their cyclopentadienyl analogs in the oxidative coupling of benzoic acid with
diphenylacetylene.
Complex
Ua
Ha
Ga
Catalyst
Yield, %
[3-(
h
-C6H6)-3,1,2-IrC2B9H11
]
þ (1a)
19.9
24.6
25.3
16.3
19.7
21.4
19.3
24.0
24.7
15.7
19.1
20.8
29.7
35.0
35.6
25.0
30.4
28.4
3a
3b
[CpIr(C6H6)]2þ
þ
þ
[3-(
h
-C6H6)-3,1,2-IrC2B9H11
]
(1
(2)
]
а
)
36
47
e
e
[Cp*Ir(C6H6)]2þ
[3-(MeCN)3-3,1,2-IrC2B9H11
]
e
þ
[3-(h-C6H6)-3,1,2-RhC2B9H11]
[3,3-Cl2-4-SMe2-3,1,2-IrC2B9H10
[CpIrI2]2
10
35
79
2
[CpRh(C6H6)]2þ
[Cp*Rh(C6H6)]2þ
e
a
[Cp*IrCl2]2
e
a
Solvation by acetonitrile is included using the PCM model.
a
Ref. [4].
formation of intermediate B proceeds via only one transition state
TS (Fig. S4 in the Supporting Information). The calculations showed
that for the iridium complexes the barriers are only slightly higher
(by 0.3e2.9 kcal molꢀ1) than those for the rhodium analogs
(Table 5).
reduces the oxidation potential of intermediate B facilitating the
reductive elimination of the Ir atom with the formation of naph-
thalene 3b.
Substitution of the Cp ligand by dicarbollide-dianion results in
the considerable increasing of the decarboxylation barrier up to
18.8 kcal molꢀ1. In addition, the total energy gain for iridacarborane
species is smaller by 10.5 kcal molꢀ1 than for cyclopentadienyl
analog. These data are well correlate with exclusively formation of
isocoumarin 3a in the oxidative coupling reactions using irida-
carboranes 1a and 2. Nevertheless, we consider that the main
reason of this selectivity is caused by the anionic charge of inter-
mediate A for the iridacarborane derivatives, which considerably
reduces its oxidation potential; this makes the reductive elimina-
tion of the Ir atom giving isocoumarin 3a more favorable than
decarboxylation.
For the pentamethylated cyclopentadienyl iridium species the
activation energy of decarboxylation is higher by 3.7 kcal molꢀ1 and
the total energy gain (D
Gr) is smaller by 1.1 kcal molꢀ1 as compared
with unsubstituted analog, which can not explain the considerable
increasing of the yield of 3b going from [CpIrI2]2 to [Cp*IrCl2]2.
Probably, the donor effect of five Me-groups of the Cp* ligand
Table 3
Activation internal energies Ua, enthalpies Ha and free energies Ga for the primary
step of benzene replacement by water in the [(L)M(C6H6)]2þ complexes (at 298.15 K,
in kcal molꢀ1) at BPBE/def2-TZVPP//BPBE/L2.a
Complex
Ua
Ha
Ga
Conclusion
[3-(
h
-C6H6)-3,1,2-IrC2B9H11
]
þ (1a)
20.5
24.9
23.9
15.8
20.2
19.4
19.9
24.3
23.3
15.2
19.6
18.8
28.9
34.6
33.7
24.1
28.0
29.2
[CpIr(C6H6)]2þ
One-pot reaction of [(cod)IrCl]2 with Tl[Tl(h-7,8-C2B9H11)] fol-
[Cp*Ir(C6H6)]2þ
þ
lowed by refluxing in trifluoroacetic acid in the presence of arenes
was shown to be efficient method for the synthesis of cationic
(arene)iridacarboranes 1aee. In accordance with stronger IreC6H6
bonding than in rhodium analogs, the cation 1a does not undergo
[3-(h-C6H6)-3,1,2-RhC2B9H11]
[CpRh(C6H6)]2þ
[Cp*Rh(C6H6)]2þ
a
Solvation by water is included using the PCM model.
Scheme 4. Oxidative coupling of benzoic acid with diphenylacetylene.

D.A. Loginov et al. / Journal of Organometallic Chemistry 793 (2015) 232e240
237
Scheme 5. Plausible mechanism of oxidative coupling.
the arene exchange reaction. Nevertheless, the benzene ligand in
1a is easily replaced by MeCN giving the tris(acetonitrile) complex
2. The latter can be used as a synthon of the cationic iridacarborane
fragment [3,1,2-IrC2B9H11]þ, as illustrated by the preparation of its
cyclopentadienyl and arene derivatives. Iridacarboranes 1a and 2
exhibit moderate catalytic activity in the oxidative coupling of
benzoic acid with diphenylacetylene in the presence of Ag2CO3
selectively giving 3,4-diphenylisocoumarin. On the other hand, the
use of the cyclopentadienyl complexes [(C5R5)IrCl2]2 as catalysts
gives only 1,2,3,4-tetraphenylnaphthalene. DFT-calculations sug-
gest that the selectivity of this reaction is mainly determined by the
electronic rather than steric properties of the ligand (C2B9H11 or
C5R5) at the iridium atom.
the lowest activation energies for benzene replacement in this
cation by acetonitrile or water. The attractive interactions between
[3,1,2-IrC2B9H11]
þ and C6H6 fragments are ca. 55% covalent and 45%
electrostatic, being considerably more electrostatic than similar
interactions with [(C5R5)Ir]2þ fragments.
Experimental
General
The reactions were carried out under an inert atmosphere in dry
solvents, unless otherwise stated. The isolation of products was
conducted in air. Starting materials [(cod)IrCl]2 [24] and Tl[Tl(
C2B9H11)] [25] were prepared as described in the literature. 1H and
11B{1H} NMR spectra (
in ppm) were recorded on a Bruker Avance-
h-7,8-
According to the energy decomposition scheme, the IreC6H6
bond in benzene complex 1a is weaker by 20e50 kcal molꢀ1 than in
cyclopentadienyl analogs [(C5R5)Ir(C6H6)]2þ. It correlates well with
d
400 spectrometer operating at 400.13 and 128.38 MHz,
respectively.
Synthesis of [3-(arene)-3,1,2-IrC2B9H11]PF6 (1aecPF6)
A mixture of [(cod)IrCl]2 (100 mg, 0.149 mmol), Tl[Tl(h-7,8-
C2B9H11)] (162 mg, 0.30 mmol), and THF (2 ml) was stirred for
1 h. The precipitate of TlCl was centrifuged off and the centrifugate
was evaporated in vacuo. Arene (1 ml of benzene, toluene or xylene,
Table 5
Activation enthalpies (Ha) and free energies (Ga) as well as total energy gains (Hr and
Gr) for the decarboxylation of the intermediate A in the presence of rhodium and
iridium complexes (in the case of unsubstituted acetylene) at 298.15 K, in kcal molꢀ1
.
LM
TS1
TS2
Ha
e
Total energy gain
Hr Gr
3.92
Ha
Ga
Ga
(C2B9H11)Ir
CpIr
Cp*Ir
(C2B9H11)Rh
CpRh
Cp*Rh
17.92
9.62
13.33
16.79
6.56
18.80
11.04
14.74
18.53
8.29
e
ꢀ7.88
8.61
e
10.47
e
2.36
0.88
14.43
13.33
ꢀ0.24
11.37
7.10
Fig. 6. Intrinsic reaction coordinates at PBE/L2 for the decarboxylation of intermediate
A (in the case of unsubstituted acetylene) using complexes 1a (red line), [CpIrI2]2 (blue)
and [Cp*IrCl2]2 (green). (For interpretation of the references to color in this figure
legend, the reader is referred to the web version of this article.)
e
e
ꢀ11.46
6.69
12.19
7.76
13.39
0.03
5.51
7.50
ꢀ3.60

238
D.A. Loginov et al. / Journal of Organometallic Chemistry 793 (2015) 232e240
or 300 mg of durene) was added to the residue containing Tl[3-
(cod)-3,1,2-IrC2B9H11]. After cooling to ꢀ73 ꢁC, CF3COOH (1.5 ml)
and (CF3CO)2O (0.5 ml) were added, and the reaction mixture was
refluxed with vigorous stirring for 2 h. The solvents were removed
in vacuo and the residue was extracted with water (2 ꢂ 5 ml). Then
an excess of an aqueous KPF6 solution was added. The white pre-
cipitate that formed was filtered off, washed with water and dried
in vacuo. The crude product was reprecipitated by ether from
acetone solution.
Synthesis of [3-(arene)-3,1,2-IrC2B9H11]PF6 (1f,g) from 2PF6
A mixture of 2PF6 (81 mg, 0.137 mmol), mesitylene (1 ml) or
[2,2]paracyclophane (116 mg, 0.879 mmol), and nitromethane
(1 ml) was refluxed for 1.5 h. The solvent was removed in vacuo and
the residue was reprecipitated by ether from nitromethane solution
to give white solids.
1fPF6, arene ¼ 1,3,5-C6H3Me3, yield 57%. 1H NMR (acetone-d6)
d
B
:
2.83 (s, 9H, C6H3Me3), 5.73 (br. s, 2H, CH), 7.78 (m, 3H, C6H3Me3). 11
1aPF6, arene ¼ C6H6, yield 27%. 1H NMR (acetone-d6)
d: 5.98 (br.
{1H} NMR (acetone-d6)
d
: 9.21 (1B), 3.93 (1B), ꢀ4.96 (2B), ꢀ6.92
s, 2H, CH), 8.04 (s, 6H, C6H6). 11B{1H} NMR (acetone-d6)
d: 11.05
(2B), ꢀ16.07 (2B), ꢀ22.14 (1B). Found (%): C, 22.42; H, 3.98; B, 16.51.
(1B), 2.10 (1B), ꢀ6.03 (2B), ꢀ6.68 (с, 2B), ꢀ15.91 (2B), ꢀ22.50 (1B).
Found (%): C, 17.49; H, 3.00; B, 17.74. Calc. for C8H17B9F6IrP (%): C,
17.54; H, 3.13; B, 17.77.
Calc. for C11H23B9F6IrP (%): C, 22.40; H, 3.93; B, 16.50.
1gPF6, arene
(acetone-d6) : 3.55 (m, 8H, CH2), 5.69 (s, 2H, CH), 7.21 (s, 4H, C6H4),
7.24 (s, 4H, C6H4). 11B{1H} NMR (acetone-d6)
: 10.05 (1B), 1.65
¼
[2,2]paracyclophane, yield 38%. 1H NMR
d
1bPF6, arene ¼ C6H5Me, yield 17%. 1H NMR (acetone-d6)
d: 2.89
d
(s, 3H, C6H5Me), 5.93 (br. s, 2H, CH), 7.92 (m, 5H, C6H5Me). 11B{1H}
(1В), ꢀ6.48 (2B), ꢀ7.45 (2B), ꢀ16.50 (2B), ꢀ23.40 (1B). Found (%): C,
31.63; H, 4.04; B, 14.40. Calc. for C18H27B9F6IrP (%): C, 31.89; H, 4.01;
B, 14.35.
NMR (acetone-d6)
d
: 10.40 (1B), 2.84 (1B), ꢀ5.46 (2B), ꢀ6.79
(2B), ꢀ16.02 (2B), ꢀ22.40 (1B). Found (%): C, 19.11; H, 3.37; B, 17.25.
Calc. for C9H19B9F6IrP (%): C, 19.24; H, 3.41; B, 17.32.
1сPF6, arene ¼ 1,2-C6H4Me2, yield 25%. 1H NMR (acetone-d6)
d:
Oxidative coupling of benzoic acid with diphenylacetylene (general
procedure)
2.81 (s, 6H, C6H4Me2), 5.85 (br. s, 2H, CH), 7.81 (m, 4H, C6H4Me2). 11
B
{1H} NMR (acetone-d6)
d: 9.80 (1B), 4.06 (1B), ꢀ4.82 (2B), ꢀ6.87
(2B), ꢀ16.08 (2B), ꢀ22.27 (1B). Found (%): C, 20.61; H, 3.71; B, 16.82.
A mixture of benzoic acid (31 mg, 0.25 mmol), diphenylacety-
lene (89 mg, 0.5 mmol), catalyst (0.005 mmol), Cu(OAc)2 (182 mg,
1.00 mmol), and o-xylene (2 ml) was refluxed with vigorous stirring
for 6 h. The solvent was removed in vacuo, and the residue was
extracted with diethyl ether. The extract was chromatographed on
column with silica gel (1 ꢂ 15 cm). Unreacted diphenylacetylene
was washed off with petroleum ether. Then the yellow band was
collected using diethyl ether as the eluant. After the removal of the
solvent in vacuo, isocumarin 3a or naphthalene 3b was obtained as
an yellow oil.
Calc. for C10H21B9F6IrP (%): C, 20.86; H, 3.68; B, 16.90.
1dPF6, arene ¼ 1,3-C6H4Me2, yield 37%. 1H NMR (acetone-d6)
d:
2.86 (s, 6H, C6H4Me2), 5.81 (br. s, 2H, CH), 7.78 (m, 3H, C6H4Me2),
7.84 (s, 1H, C6H4Me2). 11B{1H} NMR (acetone-d6)
d: 9.80 (1B), 3.54
(1B), ꢀ4.92 (2B), ꢀ6.82 (2B), ꢀ16.06 (2B), ꢀ22.23 (1B). Found (%): C,
20.59; H, 3.41; B,16.48. Calc. for C10H21B9F6IrP (%): C, 20.86; H, 3.68;
B, 16.90.
1ePF6, arene ¼ 1,2,4,5-C6H2Me4, yield 23%. 1H NMR (acetone-d6)
d
: 2.70 (s, 12H, C6H2Me4), 5.64 (br. s, 2H, CH), 7.73 (s, 2H, C6H2Me4).
11B{1H} NMR (acetone-d6)
(2B), ꢀ16.20 (2B), ꢀ21.94 (1B). Found (%): C, 23.91; H, 4.14; B, 15.17.
d
: 8.48 (1B), 4.02 (1B), ꢀ3.82 (2B), ꢀ6.89
3a, 1H NMR (CDCl3)
(m, 1H); 7.44 (m, 3H), 7.35 (m, 2H), 7.20e7.30 (m, 6H) (cf. [4]).
3b, 1H NMR (CDCl3)
: 6.95e6.97 (m, 10H); 7.32e7.34 (m, 10H);
d: 8.44 (d, 1H, J ¼ 8.0 Hz); 7.67 (m, 1H); 7.55
Calc. for C12H25B9F6IrP (%): C, 23.87; H, 4.17; B, 16.11.
d
7.47e7.49 (m, 2H); 7.76e7.78 (m, 2H) (cf. [26]).
X-ray crystallography
Synthesis of [3-(MeCN)3-3,1,2-IrC2B9H11]PF6 (2PF6)
Crystals of 1ePF6 were grown up by slow diffusion in two-layer
system, petroleum ether and a solution of the complex in acetone.
Crystals of 2BF4 were obtained by recrystallization from hot
nitromethane-anisole mixture (1:1). X-ray diffraction experiments
of 1ePF6 and 2BF4 were carried out with a Bruker Apex 2 diffrac-
A solution of 1aPF6 (100 mg, 0.18 mmol) in MeCN (2 ml) was
refluxed for 1.5 h. The solvent was removed in vacuo and the res-
idue was reprecipitated by ether from acetonitrile solution. Yield
95 mg (89%) of 2PF6 as a yellow solid. 1H NMR (acetonitrile-d3)
d:
1.95 (s, 9H, MeCN), 5.40 (br. s, 2H, CH). 11B{1H} NMR (acetonitrile-
d3)
tometer using graphite monochromated Mo-K
a
radiation
d
: 16.69 (1B), 6.20 (1B), 0.48 (2B), ꢀ4.99 (2B), ꢀ6.79 (2B), ꢀ22.11
(l
¼ 0.71073 Å, - scans) at 100 and 295 K, respectively. The
u
(1B). Found (%): C, 15.95; H, 3.30; N, 6.99; B, 16.42. Calc. for
C8H20N3B9F6IrP (%): C, 16.21; H, 3.40; N, 7.09; B, 16.41.
principal crystallographic data, procedures for collecting data, and
characteristics of structure refinement are listed in Table 6. The
structures were solved by direct methods and refined by the full-
matrix least-squares against F2 in anisotropic approximation for
ordered non-hydrogen atoms. H(C) and H(B) atom positions were
calculated, and they were refined in isotropic approximation in
riding model. Four fluorine atoms of the PFꢀ6 anion in 1ePF6 are
disordered over two sites with site occupancies 0.33: 0.67 and were
refined isotropically. The crystal of 1ePF6 is twinned. Collected
dataset was indexed using Cell_now software and then intensities
of collected reflections were described as superposition of two
crystal components with rotation angle equal to 179.7ꢁ using HKLF
5 format and BASF instruction. All calculations were performed
using the SHELXTL PLUS 5.0 [27] and OLEX2 [28] software.
Synthesis of 3-(
h-C5H4R)-3,1,2-IrC2B9H11 (3a,b)
A
mixture of 2PF6 (50 mg, 0.084 mmol), TlCp (30 mg,
0.112 mmol) or Na[C5H4C(O)Me] (15 mg, 0.115 mmol), and THF
(2 ml) was stirred for 2 h. The solvent was removed in vacuo and the
residue was filtered through a layer of Al2O3 (5 cm) in dichloro-
methane. The solution obtained was concentrated to ca. 0.5 ml and
an excess of petroleum ether was added. The white precipitate that
formed was filtered off, washed with petroleum ether and dried in
vacuo.
3
а
, R ¼ H, yield 64%.
3b, R ¼ C(O)Me, yield 33%. 1H NMR (CDCl3)
d
: 2.43 (s, 3H, Me),
Computational details
4.41 (s, 2H, CH), 5.96 (s, 2H, C5H4), 6.25 (s, 2H, C5H4). Found (%): C,
25.82; H, 4.17; B, 21.60. Calc. for C9H18B9IrO (%): C, 25.04; H, 4.20; B,
22.54.
Geometry optimizations were performed without constraints
using the PBE exchange-correlation functional [29], the scalar-

D.A. Loginov et al. / Journal of Organometallic Chemistry 793 (2015) 232e240
239
Table 6
Crystallographic data and structure refinement parameters for 1ePF6 and 2BF4.
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Molecular weight
Crystal system
Space group
a (Å)
C12H25B9F6IrP
603.78
Monoclinic
P21/c
10.8651(9)
9.6330(8)
19.2709(16)
92.1310(10)
2015.6(3)
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1.990
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67.54
multi-scan
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C8H20B10F4IrN3
534.57
Orthorhombic
Pnma
15.2750(7)
10.6572(5)
11.1848(5)
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1820.76(14)
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1.950
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73.67
multi-scan
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4949
3395
s
Parameters
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0.0295
135
0.0185
R1 (on F for observed
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wR2 (on F2 for all
reflections)
0.0879
0.0515
Weighting scheme
a
b
wꢀ1
0.0580
8.3585
1152
¼
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0.0370
e
F(000)
1008
1.020
3.113 and ꢀ1.398
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Largest diff. peak and
1.005
1.910 and ꢀ2.031
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This work was supported by Russian Foundation for Basic
Research (grant # 15-03-04057).
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2015.01.022.
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