Iridium(I)-salicylaldiminato-cyclooctadiene complexes used as catalysts for phenylborylation

Article abstract of DOI:10.1016/j.jorganchem.2007.06.052

Iridium(I) salicylaldiminato-cyclooctadiene complexes, Ir(-o-O-C₆H₄-CH{double bond, long}N-R)(cod) (R = CH₂Ph (1), Ph (2); cod = 1,5-cyclooctadiene), have been prepared, characterized and used as catalysts for arylborylation via C-H activation. With 1 as a catalyst, isolated yields of up to 91% has been achieved for the borylation of benzene by bis(pinacolato)diboron in the presence of tetra-2-pyridinylpyrazine and an ionic liquid. The catalytic system could be recycled for at least three times without loss of activity.

Full text of DOI:10.1016/j.jorganchem.2007.06.052

Journal of Organometallic Chemistry 692 (2007) 4244–4250
www.elsevier.com/locate/jorganchem
Iridium(I)-salicylaldiminato-cyclooctadiene complexes used
as catalysts for phenylborylation
a,
a
a
a
a
Zhu Yinghuai *, Koh Cheng Yan , Luo Jizhong , Chong Siow Hwei , Yong Chun Hon ,
b
b
b
c
d
A. Emi , Su Zhenshun , Monalisa Winata , Narayan S. Hosmane , John A. Maguire
a
Institute of Chemical and Engineering Sciences, 1, Pesek Road, Jurong Island, Singapore 627833, Singapore
b
Singapore Polytechnic, 500 Dover Road, Singapore 139651, Singapore
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115-2862, USA
c
d
Department of Chemistry, Southern Methodist University, Dallas, TX 75275-0314, USA
Received 8 April 2007; received in revised form 15 June 2007; accepted 19 June 2007
Available online 4 July 2007
Abstract
Iridium(I) salicylaldiminato-cyclooctadiene complexes, Ir(–o-O–C6H4–CH@N–R)(cod) (R = CH2Ph (1), Ph (2); cod = 1,5-cyclooctadi-
ene), have been prepared, characterized and used as catalysts for arylborylation via C–H activation. With 1 as a catalyst, isolated yields of up
to 91% has been achieved for the borylation of benzene by bis(pinacolato)diboron in the presence of tetra-2-pyridinylpyrazine and an ionic
liquid. The catalytic system could be recycled for at least three times without loss of activity.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Iridium(I) salicylaldiminato-cyclooctadiene complexes; Arylborylation; Catalyst recycle; Ionic liquid
1. Introduction
lytic methods for the production of organoboronic acids.
Palladium(0) species produced in situ from palladium(II)
complexes, such as PdCl2 (dppf), have been reported to
be active catalysts for the cross-coupling reactions of the
pinacol esters of diboronic acid with haloarenes in homo-
geneous systems [4]. More recently, Rh, Ir, and Re com-
plexes also have been explored in the direct borylation of
hydrocarbons to provide alkyl- and aryl-boron compounds
via C–H activation (see Scheme 1) [5]. These are economi-
cal, efficient, and environmentally benign protocols for the
preparation of various organoboron compounds.
The borylations of unreactive arenes were demonstrated
in the early 1990s by Marder [6] and Hartwig [7] and co-
workers. Thermally-induced transition metal-catalyzed
aromatic C–H borylation with Ir complexes was described
by Smith and Iverson [8]. These workers obtained B–C
bond formation from the reaction of benzene and pin-
acolborane (HBpin) catalyzed by a Cp*Ir complex in the
presence of PMe3. Further work saw the development of
other active catalysts, such as, (g5-C9H7)Ir(cod) [9] and
Cp*Rh(g4-C6Me6) [10]. Although yields from the reactions
Organoboric acids constitute an important class of com-
pounds that are widely used in Suzuki cross-coupling reac-
tions to form various C–C bonds [1,2]. Commonly used
methods to synthesize arylboronic acids are the alkylation
of trialkylborates or haloboranes with organomagnesium
(Grignard) or aryl lithium reagents at low temperature
[3]. These methods are not general in that they require
the prior preparation of extremely basic and nucleophilic
organometallic species that tolerate only a restricted num-
ber of functional groups. In addition, the yields in these
reactions are usually fairly modest (ca. 50%). The prepara-
tion of the Grignard and organolithium reagents from
ArCl is difficult and often requires the use of the less readily
available arylbromides. Thus, there is a great deal of inter-
est in the development of robust and highly efficient cata-
*
Corresponding author. Tel.: +65 6796 3801/3700; fax: +65 6316 6182.
E-mail address: zhu_yinghuai@ices.a-star.edu.sg (Z. Yinghuai).
0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.06.052

Z. Yinghuai et al. / Journal of Organometallic Chemistry 692 (2007) 4244–4250
4245
Scheme 1. Direct borylation of alkene, alkyne and arenas.
were moderate to high, the elevated temperatures and long
2. Results and discussion
reaction times proved to be an inconvenience in the synthe-
sis of arylboronate compounds.
2.1. Synthesis and characterization of Ir(I) complexes
Lower temperature catalytic systems were developed by
Miyaura and co-workers from the reaction of commercially
available Ir(I) precursors [IrCl(cod)]2 (cod = 1,5-cyclooct-
adiene) or [IrCl(coe)2]2 (coe = cyclooctene) with the
strongly electron-donating 2,20-bipyridine ligand. These Ir
catalysts proved to be highly efficient in the direct boryla-
tion of arenes and heteroarenes by bis(pinacolato)diboron
(B2pin2) under mild, room temperature conditions [11].
Extended studies showed that the Ir complexes having
OH, OPh or OMe ligands in place of the Cl atom also per-
formed well in the synthesis of arylboronates at room tem-
perature [12]. Experimental and computational studies of
this catalytic system lead to the identification and isolation
of an Ir(III) tris(boryl) intermediate as well as an Ir(V)
complex thought to be important in the catalytic mecha-
nism [13]. Of late, N-heterocyclic carbene complexes of
Ir(I) were shown to exhibit high activity in aromatic bory-
lation at relatively mild temperatures (40–45 °C) and reac-
tion times of between 9 and 12 h [14]. While these systems
provide feasible synthesis conditions for arylboronation,
they are not reusable, which contributes greatly to the cost
of such synthetic schemes.
Iridium(I) salicylaldiminato-cyclooctadiene complexes,
Ir(–o-O–C6H4–CH@N–CH2Ph)(cod) 1 and Ir(–o-O–C6H4–
CH@N–Ph)(cod) 2 have been prepared in 82% and 68%
yields, respectively, from the reaction of the corresponding
Schiff bases and commercially available [IrCl(cod)]2 (see
Supplementary material for detail synthetic procedures
and characterization). The salicylidenebenzylamine and sal-
icylideneaniline were first deprotonated with NaH to pro-
duce their Na salts as intermediates, which reacted with
[IrCl(cod)]2 to produce complexes 1 and 2. The synthesis of
2 from the reaction of [IrOCH3(cod)]2 and salicylideneani-
line was reported earlier but no yields were quoted [15].
The solid state structures of 1 and 2 were determined (see
the Supplementary material) and are shown in Fig. 1. As
can be seen in Fig. 1, both complexes show that the Schiff
base and the cod ligands are arranged about the central Ir
to give a square planar coordination of the metal; the O–
Ir–N bond angles in 1 and 2 are 90.7(3)° and 90.37(14)°,
respectively. These angles are essentially the same as the
value of 90.2(4)° found for the equivalent angle in Ir(–o-O–
C6H4–CH@N–o-tol)(cod) [15]. The Ir–N bond lengths in 1
˚ ˚
Herein, we report our preliminary results regarding the
syntheses of iridium(I) salicylaldiminato-cyclooctadiene
complexes as reusable catalysts for the C–H borylation of
arenes by B2pin2 as outlined in Scheme 2.
(2.066(9) A) and 2 (2.073(3) A) are slightly greater than their
˚
˚
Ir–O bond distances (1, 2.020(7) A, 2, 2.029(3) A).
In order to evaluate the catalytic efficiencies of 1 and 2 in
aromatic C–H borylation, benzene was used as the com-
Scheme 2. Iridium(I) salicylaldiminato-cyclooctadiene complexes catalyzed borylation.

4246
Z. Yinghuai et al. / Journal of Organometallic Chemistry 692 (2007) 4244–4250
Fig. 1. Molecular structure 1 (left) and 2 (right).
mon substrate with B2pin2 as the borolating agent. The sol-
vents were either excess benzene or a mixture of the ionic
liquid, tributyltetradecylphosphonium dodecylbenzenesulf-
onate, (TBPD) and dichloromethane (see the Supplemen-
tary material for the detail catalyst evaluation). To probe
the effects of added bases, which were found to be neces-
sary by Hartwig [11,12], the reactions were run in the pres-
ence of different ligands, as listed in Table 1. The two
polydentate bases, Tpy (tetra-2-pyridinylpyrazine) and
Bpy (2,20-bipyridine) were much more effective activating
agents than were the momonentate bases, even py. Hartwig
observed that in the borylation of aromatic compounds
using the precatalyst, [IrCl(cod)]2 activated by substituted
bpy, the planarity of the activating base was important
[11,12]. On the other hand, Hermann and co-workers
found that a number of bis(carbene) Ir complexes were
effective catalysts for the syntheses of a series of arylbo-
ronic acids from their corresponding aryls and pinicolbo-
rane, without base activation [14]. The data in Table 1
show that compounds 1 and 2 required base activation sim-
ilar to the [IrCl(cod)]2, even though 1 and 2 are monomeric
compounds in which the salicylaldiminato ligands are pla-
nar. In addition, Table 1 shows that, except for the runs in
which Na2CO3 and Bpy acted as the bases, catalyst 1 was
ꢀ35% more effective than was catalyst 2.
2.2. Catalytic evaluation of Ir(I) complexes in benzylic
borylation
Since the most advantageous reaction mixture was cata-
lyst 1 with TPy, this combination was used to investigate
the advantages of different reaction conditions; the results
of this study are given in Table 2. As can be seen, normal
reaction aids such as ultrasonication and increasing the
temperature had an inverse effect on the yield [16–18].
The only yield enhancement was found on the addition
of the ionic liquid, TBPD, giving a yield of 91%.
The maximum turnover number for the phenylboryla-
tion of benzene by bis(pinacolato)diboron, in the presence
of 1 was determined by running the reaction at 100 °C for
40 h in a 0.015 mol% loading of catalyst 1 in benzene sol-
vent. After hydrolysis and flash chromatography, phen-
ylboronic acid was isolated in 67% yield (4467 turnovers).
It is of interest to note that this yield was slightly lower
than that listed in Table 1 even though the reaction time
was extended. The results to date indicate that an increase
in temperature results in lower yields. It was found that the
addition of extra TPy had no positive effect on the activity
of complex 1. On the other hand, the catalytic activity of 1
is found to be strongly influenced by the choice of solvent.
Table 2
Phenylborylation with different methodology using catalyst 1 and TPy
liganda
Table 1
MWb
17
((((c
28
Autoclaved
53
ILe
91
Standardf
70
HBping
43
Phenylborylation catalyzed by 1 and 2 with various additivesa
Method
Cat
Lb
Yield (%)
a
Conditions are same as described in Table 1.
PPh3
Py
Bpy
TPy
Cs2CO3
Na2CO3
b
c
Reaction mixture was heated at 130 °C using microwaves for 1 h.
Reaction mixture was heated at 80 °C in ultrasonic bath for 3 h.
Reaction mixture was heated at 180 °C in high pressure reactor for
1
2
a
23c
14
30
22
63
65
70
52
15
10
6
8
d
All catalytic reactions were conducted under argon atmosphere at
14 h.
e
80 °C for 21 h. Reaction mixture consisted of 1.0 mmol B2pin2,
3.0 ml benzene with additional 2.0 ml each of dichloromethane and the
0.015 mmol of Ir(I) precursor and 0.03 mmol ligand, 20.0 ml benzene.
ionic liquid TBPD as solvent at 80 °C for 21 h.
b
f
PPh3 = triphenylphosphine, Py = pyridine, TPy = tetra-2-pyridinyl-
20.0 ml benzene as solvent at 80 °C for 21 h.
Same conditions with standard method except using HBpin instead
g
pyrazine, Bpy ¼ 2; 20 ꢁ bipyridine.
c
Isolated yield (%) after hydrolysis and flash chromatography.
B2pin2.

Z. Yinghuai et al. / Journal of Organometallic Chemistry 692 (2007) 4244–4250
4247
Table 3
The results of a study of the effects of the substituent
groups on the aryl are summarized in Table 3. It can be seen
that for mono-substituted benzenes of the form C6H5R
(R = H, CH3, OCH3 and CF3), only the meta- and para-
disubstituted products were observed. The lack of
formation of any ortho-products, irrespectively of the elec-
tron-donating or electron-withdrawing properties of the
substituents, seems to be due to steric effects. Under the
same conditions as those in Table 1, the ratios of meta- to
para-isomers in the products ranged from 1.5:1 for
R = CH3 to 1.1:1 for R = OMe. These ratios are signifi-
cantly less than the values of 3.0:1, 2.3:1 and 2.2:1 for
R = OCH3, CF3 and CH3, respectively, reported by Har-
twig and co-workers, using a [IrCl(cod)]2/bpy catalyst sys-
tem [11]. Given that the statistical meta/para ratio would
be 2:1, it is not apparent why the catalytic system used by
Hartwig would favor substitution at the meta-position,
while our Ir(–o-O–C6H4–CH@N–CH2Ph)(cod)/TPy system
would give preference to para-substitution. The table also
shows that this preference for para-substitution is enhanced
by the presence of the ionic liquid (Table 3, d). It might be
that the ionic liquid can stabilize greater charge separation,
thereby favoring a more remote substitution. Table 3 also
shows that the electron withdrawing CF3 group gives rise
to an 86% yield in 8 h, while the electron-donating OCH3
group resulted in only a 67% yield after 21 h. This increased
reactivity of the electron poor arenes was also found for the
[IrCl(cod)]2/bpy catalyst system [11]. When excess arenes
(10-fold) were used, neither the yields nor the selectivity
changed materially (Table 3, c).
Effect of aromatic substituent groups on the arylborylation using catalyst
1 and TPy liganda
FG
H
Me
OMe
CF3
Yield (%, m:p)b
Yield (%, m:p)c
Yield (%, m:p)d
a
70
70
91
62 (1.5)
64 (1.6)
–
67 (1.1)
65 (1.0)
71 (0.7)
86 (1.3)
87 (1.6)
89 (0.9)
Conditions are same as described in Table 1 except for CF3 which was
operated for 8 h. Reaction mixture consisted of 1.10 mmol B2pin2,
0.015 mmol of Ir(I) precursor and 0.03 mmol ligand, 1.00 mmol arenes
and 10.0 ml dichloromethane as solvent (for FG = H, 20.0 ml benzene was
used as both substrate and solvent).
b
Isolated yield (%) after hydrolysis and flash chromatography. The
ratios of meta-/para- (m:p) were determined by NMR spectroscopy.
c
Obtained from 10-fold of arenes with B2pin2 with similar standard
process.
d
From ionic liquid medium.
In the ionic liquid, TBPD, a tremendous increase in cata-
lytic efficiency was observed, with phenylboronic acid being
formed in 91% yield. The same lot of complex 1/base could
be reused three times without any obvious drop in catalytic
activity. Compound 1/base seems to be the first reported
example of a reusable imine-based catalyst for arylboryla-
tion reactions.
It is of interest to note, that reactions using either 2 or
[IrCl(cod)]2 as the precatalyst with TPy and B2Pin2 in the
TBPD/dichloromethane solvent produced only low yields
(<15% by NMR) of the arylborylation product. It is sur-
prising that the presence of the ionic liquid produces such
dramatically different effects on the three supposedly simi-
lar catalytic systems.
In order to obtain an insight into the nature of the cat-
alytic species, the reaction of 1 with TPy in the absence of
Scheme 3. Proposed catalyst cycle.

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Z. Yinghuai et al. / Journal of Organometallic Chemistry 692 (2007) 4244–4250
a borolating agent was explored. When 1 and TPy were
mixed, the color of the solution changed smoothly from
red brown into dark green. The product was isolated,
analyzed and its NMR spectra were run. Both spectra
and analysis are consistent with an Ir(–o-O–C6H4–
CH@N–CH2Ph)(cod)(TPy) (3) complex. This suggests a
catalytic cycle shown in Scheme 3. Accordingly, B2pin2
could undergo oxidative addition promoting a loss of
cod, giving the catalytically active species, Ir(–o-O–
C6H4–CH@N–CH2Ph)(TPy)(Bpin)2 (4). It is assumed that
the addition of the B2pin2 would cause the loss of cod a
six coordinate Ir(III) species (4). Alternatively, the cod
could be converted to a monodentate ligand, yielding a
seven coordinate Ir complex. This would be consistent
with the observation of Hartwig and co-workers, that
[IrCl(coe)2]2 is just as good a catalytic precursor than is
[IrCl(cod)]2 [11]. Reaction with an arene to product Ar-
Bpin and the six coordinate (H)Ir(–o-O–C6H4–CH@N–
CH2Ph)(TPy)(Bpin) (5) could easily follow. The C–H acti-
vation could proceed through either an oxidative addi-
tion/reductive elimination involving a seven coordinate
Ir(V) intermediate, or a r-bond metathesis process. Both
processes have been postulate, for Ir-catalyzed borylations
[13,20]. The resulting hydrido complex (5) could then
react with a B2pin2 or HBpin to give (4) and HBpin or
H2, respectively. The cycle could then be repeated. During
the cycle, ionic liquid may play an important role in the
stabilization of intermediates via electrostatic interaction,
which might be crucial in the decomposition step of pro-
posed iridium(V) intermediate to form para-isomers of
boroxines. It should be stressed that Scheme 3 represents
a reasonable sequence of reactions, based on the viability
of compounds 4 and 5, neither one of these proposed
intermediates have been identified. They are similar to
other intermediates proposed for Ir(I)-catalyzed boryla-
tion reactions.
structural modifications of the catalyst is undergoing in
our laboratories.
4. Experimental
General methods. All the operations were carried out
under an argon atmosphere using standard Schlenk tech-
niques or in a glove box. Solvents diethyl ether, dichloro-
methane, toluene, n-hexane and tetrahydrofuran (THF)
were purified by a solvent purification system while ben-
zene was dried with sodium. All other reagents were used
as received. Salicylidenebenzylamine and salicylidenephe-
nylamine were prepared according to literature [19]. Ele-
mental analyses were measured in a CHNS analyzer and
melting points determined by a Buchi melting point ana-
¨
1
lyzer. H, 13C and 11B NMR were recorded on a Bruker
Advance 400 MHz spectrometer. Chemical shifts were
measured in ppm relative to TMS standard (1H:
400.2 MHz, 13C: 100.6 MHz, 11B: 128.4 MHz). Infrared
(IR) spectra were measured using a BIO-RAD spectropho-
tometer with KBr pellets. Rigaku Single Crystal Diffraction
System was used for single crystal X-ray analysis.
4.1. Synthesis of complex Ir(–o-O–C6H4–CH@N–
CH2Ph)(cod) (1)
A 0.15 g (0.71 mmol) of salicylidenebenzylamine was
treated with 0.14 g (3.55 mmol) of NaH (60% in mineral
oil) in 75 ml diethyl ether at room temperature. After 3 h
of stirring at room temperature, the mixture was filtered
to remove unreacted NaH and the resulting solution added
to 0.24 g (0.35 mmol) [IrCl(cod)]2 in 75 ml THF at ꢁ78 °C.
The mixture was kept at that temperature for 30 min and
then allowed to warm to room temperature spontaneously
and continuous stirring for 3 h. After the reaction process,
the solvents were removed under reduced pressure and the
solid was washed with benzene, filtered and dried in high
vacuum to give an orange solid 1 in 82% yield (mp, 151–
153 °C). Single crystal suitable for X-ray diffraction was
obtained from solvents evaporation from a saturated solu-
tion 1 in CH2Cl2/n-hexane. Crystal structure and refine-
ment data are described in Fig. 1 and Table 1. Anal.
Calc. for C22H24IrNO 1: C, 51.71; H, 4.73; N, 2.74. Found:
3. Conclusion
Ir(I) complexes, Ir(–o-O–C6H4–CH@N–CH2Ph)(cod) 1
and Ir(–o-O–C6H4–CH@N–Ph)(cod) 2, have been synthe-
sized by the reaction of the sodium salts of Schiff bases
salicylidenebenzylamine and salicylideneaniline with
[IrCl(cod)]2 and, on activation by bases, used as catalysts
for arylborylation reactions. Of the two precatalysts, 1,
when activated with tetra-2-pyridinylpyrazine (TPy), was
found to be the more active phenylborylation catalyst.
In contrast to 2 and [IrCl(cod)]2, the catalytic perfor-
mance of 1 was enhanced when a solvent mixture of
dichloromethane and the ionic liquid, tributyltetradecyl-
phosphonium dodecylbenzenesulfonate, TBPD, was used.
It was found that compound 1 is also active phenylbory-
lation catalyst using HBpin in the presence of tetra-2-
pyridinylpyrazine (TPy) in a yield of 43%. The different
results found in the two catalytic systems could indicate
that different mechanisms are operating. A more detailed
mechanistic study and an investigation of the effects of
1
C, 51.85; H, 4.43; N, 2.67%. H NMR (CDCl3): d = 1.725
(d, 4H, cod-CH2); 2.233 (t, 4H, cod-CH2); 3.488 (s, 2H,
cod-HC@C); 4.451 (s, 2H, cod-HC@C); 4.840 (s, 2H,
CH2); 6.627–7.495 (m, 9H, Ph-H); 8.291 (s, 1H, N@CH);
13C NMR (CDCl3): d = 29.35 (cod-CH2); 32.66 (cod-
CH2); 54.59 (cod-C@C); 61.78 (CH2); 69.90 (cod-C@C);
115.84–139.21 (Ph-C); 165.44 (Ph-C); 166.30 (N@CH). IR
(KBr pellet, cmꢁ1, vs = very strong, s = strong, m = mid-
dle, w = weak): m = 2998 (w), 2972 (w), 2914 (w), 2879
(w), 2830 (w), 2361 (vs), 2342 (s), 1590 (s), 1536 (s), 1470
(m), 1435 (m), 1406 (m), 1328 (m), 1233 (w), 1199 (w),
1151 (m), 1130 (w), 1077 (w), 1023 (w), 973 (w), 895 (w),
850 (w), 807 (w), 762 (m), 738 (m), 694 (w), 683 (w), 602
(w), 488 (w), 464 (w).

Z. Yinghuai et al. / Journal of Organometallic Chemistry 692 (2007) 4244–4250
4249
4.2. Synthesis of complex Ir(–o-O–C6H4–CH@N–Ph)(cod)
(2)
with anhydrous MgSO4. The solvent was removed under
reduced pressure and the residue was purified with flash
column chromatography (SiO2) to produce the correspond-
ing arylboronic acids (confirmed by NMR spectroscopy,
see Supplementary material). For catalyst recycle runs,
after the borylation reaction and removal of the solvent,
the crude product of boroxines were distilled from reaction
mixture under reduced pressure. The residue was reused as
a catalyst mixture to undergo further runs, and the distil-
lated sticky liquids obtained from distillation was subjected
to above hydrolysis process to form products.
A similar procedure as the preparation of 1 was used to
synthesize 2. After purification, complex 2 was obtained in
68% yield from 0.12 g (0.60 mmol) of salicylideneaniline,
0.12 g (2.98 mmol) of NaH (60% in mineral oil) and
0.20 g (0.30 mmol) [IrCl(cod)]2 in 75 ml diethyl ether. The
NMR data are consistent with literature [15]. Single crystal
suitable for X-ray diffraction was obtained from solvents
evaporation from a saturated solution 2 in CH2Cl2/n-
hexane.
4.5. Determination of the maximum turnover numbers for the
borylation of benzene with bis(pinacolato)diboron using
catalyst 1
4.3. Synthesis of Ir(–o-O–C6H4–CH@N–
CH2Ph)(cod)(TPy) (3)
In glove box, 1 (102.2 mg, 0.20 mmol) and TPy (80 mg,
0.20 mmol) were dissolved in 20 mL dry CH2Cl2. The reac-
tion mixture was stirred at room temperature for 12 h. The
solution was concentrated to 2 mL and precipitated with
dry pentane. After filtered and dry under reduced pressure,
a deep green solid was obtained in 75% yield (135 mg).
Anal. Calc. for C46H40IrN7O: C, 61.45; H, 4.48; N,
10.91. Found: C, 61.17; H, 4.41; N, 10.44%. 1H NMR
(CD2Cl2): d = 1.65 (d, 4H, cod-CH2); 2.11 (d, 4H, cod-
CH2); 3.39 (s, 2H, cod-CH@C); 4.28 (s, 2H, cod-CH@C);
4.76 (s, 2H, CH2–Ph); 6.56–8.49 (m, 30H, Ph–H, C5H4N
and N@CH); 13C NMR (CD2Cl2): d = 29.32 (cod-CH2);
32.58 (cod-CH2); 54.26 (cod-C@C); 61.83 (CH2); 69.42
(cod-C@C); 116.66–139.84 (Ph-C, C5H4N); 148.53,
149.30, 156.99 (C5H4N and C4N2); 167.10 (N@CH).
A 30.0 lL (0.15 lmol) solution of 1 (5.0 mM in ben-
zene), 15.0 lL (0.30 lmol) solution of TPy (20.0 mM in
benzene) in benzene were prepared in glove box. B2pin2
(255 mg, 1.0 mmol) in 20.0 mL benzene and prepared cata-
lyst and ligand solutions were placed in autoclave. The
reaction mixture was then heated at 100 °C for 40 h. After
hydrolysis and flash chromatography as above described,
phenylboronic acid was isolated in 67% yield.
Acknowledgement
This research was generously supported by the Institute
of Chemical and Engineering Sciences (ICES), Singapore
Polytechnic, Singapore, the Robert A. Welch Foundation
(N-1322 to J.A.M.), and The National Science Foundation
(CHE-0601023). We thank Dr. Rex Ren in IL-TECH Inc.
to provide ionic liquid TBPD.
4.4. Evaluation of catalytic activity
The borylation of arenes catalyzed by 1, 2 and [IrCl-
(cod)]2 was performed in benzene or dichloromethane
(CH2Cl2) and an ionic liquid solvents in the presence of a
basic ligand. The reactants were used in the following
amount: 1.0 mmol B2pin2, 0.015 mmol catalyst (1, 2, [IrCl-
(cod)]2), 0.03 mmol ligand, 20 ml or 3 ml (for dichloro-
methane and ionic liquid solvent) benzene, 2 ml each of
dichloromethane and ionic liquid tributyltetradecylphos-
phonium dodecylbenzenesulfonate (TBPD). The reaction
was conducted at a reflux temperature 80 °C for 21 h. In
addition, alternative methods were utilized in replace of
the conventional way: (a) in a high pressure reactor (Parr
Stirred High Pressure reactor) at 180 °C for 14 h, (b) via
ultrasonic irradiation (Transsonic T750 Ultrasonic Bath)
for 3 h, and (c) under microwaves (Milestone Microsynth
Microwave Lab station with Lab Terminal 800 Controller)
with temperature increasing from room temperature to
130 °C within 2 min and maintained at 130 °C for 1 h.
After borylation, the solvent was removed under reduced
pressure. Prior hydrolysis, diethyl ether was added to dis-
solve the obtained residue, after which 20 ml of 10% HCl
(aq) was added and the mixture stirred for 4 h. Of the
two layers formed, the organic layer was isolated and dried
Appendix A. Supplementary material
CCDC 638193 and 638194 contain the supplementary
crystallographic data for 1 and 2. The 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 doi:10.1016/
j.jorganchem.2007.06.052.
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