Base-promoted selective activation of benzylic carbon-hydrogen bonds of toluenes by iridium(III) porphyrin

Article abstract of DOI:10.1021/om700751h

K₂CO₃ and NaOPh promoted the rate of benzylic carbon-hydrogen bond activation (BnCHA) of toluenes with iridium(III) porphyrin carbonyl chloride (Ir(ttp)Cl(CO)) to give iridium porphyrin benzyls in high yields. Mechanistic studies sug

Full text of DOI:10.1021/om700751h

Organometallics 2008, 27, 3043–3055
3043
Base-Promoted Selective Activation of Benzylic Carbon-Hydrogen
Bonds of Toluenes by Iridium(III) Porphyrin
Chi Wai Cheung and Kin Shing Chan*
Department of Chemistry, The Chinese UniVersity of Hong Kong, Shatin, New Territories, Hong Kong,
People’s Republic of China
ReceiVed July 25, 2007
K2CO3 and NaOPh promoted the rate of benzylic carbon-hydrogen bond activation (BnCHA) of
toluenes with iridium(III) porphyrin carbonyl chloride (Ir(ttp)Cl(CO)) to give iridium porphyrin benzyls
in high yields. Mechanistic studies suggested that K2CO3 initially converted Ir(ttp)Cl(CO) to Ir(ttp)X (X
) OH-, KCO3-), which reacted very fast with toluenes to yield Ir(ttp)H. Ir(ttp)H then reduced the carbonyl
ligand in unreacted Ir(ttp)Cl(CO) to yield Ir(ttp)Me. Ir(ttp)H also dimerized dehydrogenatively to give
[Ir(ttp)]2, especially promoted in the presence of base, which further reacted with toluenes to yield iridium
benzyls. Weaker base of NaOPh converted Ir(ttp)Cl(CO) to Ir(ttp)OPh, which selectively promoted BnCHA
to yield iridium benzyls.
Ir(III) products.1a,e CHA by high valent Rh(III)8,9 and Ir(III)10,11
complexes have also been investigated, and various mechanisms
are proposed: oxidative addition via M(III)-M(V)-M(III) species
(M ) Rh8 or Ir11a,c), σ-bond metathesis,8,10,11f and heterolytic
cleavage.12 Rh(V)13 and Ir(V)14 complexes were even observed
in the analogous silicon-hydrogen bond activation. However,
no Rh(V) and Ir(V) complexes formed by CHA have been
directly observed. This makes CHA by Rh(III) and Ir(III)
complexes mechanistically intriguing since the mechanistic
details of CHA by high-valent Rh(III) and Ir(III) complexes
have not been fully defined.
Introduction
Selective intermolecular carbon-hydrogen bond activation
(CHA) by transition metal complexes is an important area of
research in organometallic chemistry for the controlled activation
and functionalization of hydrocarbons.1 The activation of
toluenes is particularly important since the catalytic function-
alization of toluenes can yield industrially important chemicals
such as benzyl alcohols,2 benzaldehydes,3 and benzoic acids.4
The selectivity of benzylic CHA (BnCHA) for functionalization
is therefore important as competitive aromatic CHA (ArCHA)
has been reported.5
CHA by low valent Rh(I)6 and Ir(I)7 complexes have been
extensively studied. The commonly accepted mechanism in-
volves classical oxidative addition pathway to give Rh(III) and
We have reported that Rh(III) and Ir(III) porphyrins are
unique high valent complexes in undergoing CHA. Selective
aldehydic CHA of aryl aldehydes by RhIII(ttp)Cl8 and IrIII(ttp)-
Cl(CO)10 (ttp ) tetrakis(p-tolyl)porphyrin dianion) without
ArCHA have been observed. We have discovered that in the
absence of base, Rh(ttp)Cl reacted with toluene to give both
ArCHA and BnCHA products. With K2CO3 added, the rates of
reactions were enhanced, and only selective BnCHA products
in high yields were isolated for a variety of functionalized
toluenes.9 We thus have extended our investigation of CHA of
* Corresponding author. E-mail: ksc@cuhk.edu.hk.
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10.1021/om700751h CCC: $40.75
2008 American Chemical Society
Publication on Web 05/31/2008

3044 Organometallics, Vol. 27, No. 13, 2008
Cheung and Chan
Table 1. CHA of Toluenes with Ir(ttp)Cl(CO)
Table 3. Optimization of Base Equivalent in CHA of Toluenes with
Ir(ttp)Cl(CO)
Ir(ttp)BnCl(CO) + PhCH3 K CO , time8 Ir(ttp)Bn + Ir(ttp)Me
2
3
1
temp, N2
2b
3
(3)
entry
FG
time/d
yield 2/%
1
2
3
4
Me
H
F
3.5
9
9
2a (56)
2b (55)
2c (75)
decomp.
entry
K2CO3(equiv)
temp/°C
time
yield 2b/%
yield 3/%
1
2
3
4
10
20
20
30
150
150
200
200
3 d
2 d
3.5 h
2 h
63
66
61
60
1
3
7
7
NO2
1
Table 2. Base Effect on CHA of Toluene with Ir(ttp)Cl(CO)
Table 4. Effect of K2CO3 and NaOPh on CHA of Toluene with
Ir(ttp)Cl(CO)
base
Ir(ttp)Cl(CO) + PhCH3
8 Ir(ttp)Bn + Ir(ttp)Me
2b 3
l
200 °C, time, N2
(2)
entry
base (equiv)
time
yield 2b (%)
yield 3 (%)
1
2
3
4
5
6
NaNH2 (10)
NaOH (10)
Cs2CO3(20)
K2CO3 (20)
NaOPh (20)
NaF (20)
0.25 h
1 h
0.5 h
3 h
2 d
6 d
43
34
37
66
78
96
13
7
4
entry A (K2CO3)
time/h yield (%)
entry B (NaOPh)
3
entry
FG
time/h
yield (%)
1
2
3
4
Me
H
F
1
3.5
2
2a (41)
3 (1)
3 (7)
24
48
12
0.1
2a (67)
2b (78)
2c (78)
2d (43)
2b (61)
2c (62)
2d (80)
NO2
0.1
toluenes with iridium porphyrin. We now report that NaOPh
can promote the rate and selectivity of BnCHA with iridium
porphyrin.
1–3). NaOPh was more selective without any Ir(ttp)Me formed
and generally higher yielding in BnCHA when compared with
K2CO3. Furthermore, 4-nitrotoluene successfully reacted to give
2d (Table 4, entry 4).
Synthesis of Authentic Samples. Iridium porphyrin benzyls
2a, 2b, 2c, and 2e were successfully synthesized by reductive
benzylation of Ir(ttp)Cl(CO) (eq 5).16–18 Ir(ttp)Cl(CO) was first
reduced by NaBH4 with base to yield Ir(ttp)-, which was then
further reacted with benzyl bromides to yield iridium benzyls.
Result and Discussion
Initially, Ir(ttp)Cl(CO) did not react with toluene at 150 °C
in 3 days. A very slow reaction occurred at 200 °C in 9 days to
give Ir(ttp)Bn in 55% yield (Table 1, eq 1, entry 2). p-Xylene
and 4-fluorotoluene also reacted slowly to generate BnCHA
complexes (Table 1, entries 1 and 3). 4-Nitrotoluene decom-
posed Ir(ttp)Cl(CO) (Table 1, entry 4). Likely, the low reactivity
is due to the coordinative saturation of Ir(ttp)Cl(CO).
In view of successful base-promoted BnCHA by Rh(ttp)Cl,9
various bases were examined. Coordinating organic base,
pyridine, and noncoordinating bulky organic base, 2,6-di-tert-
butylpyridine were not effective at all. Improvements in rate
enhancement and yields were observed with inorganic bases
(Table 2, eq 2). Stronger inorganic bases15 led to shorter reaction
times but lower yields of Ir(ttp)Bn and lower selectivity as
Ir(ttp)Me also formed (Table 2, entries 1–4). Weaker bases of
NaOPh and NaF15 reacted more slowly, but they were more
selective in BnCHA to yield Ir(ttp)Bn only (Table 2, entries 5
and 6). K2CO3 and NaOPh were therefore selected as the
optimized bases to further examine the scope of base-promoted
BnCHA since they reacted sufficiently fast and gave higher
yields of Ir(ttp)Bn in higher selectivity. The optimized amount
of base was found to be 20 equivalents with reference to
Ir(ttp)Cl(CO) since a lower equivalent of K2CO3 (10 equiv)
slowed down the reaction rates (Table 3, eq 3, entries 1 and 2),
and a higher equivalent of K2CO3 (30 equiv) gave similar yields
of Ir(ttp)Bn and Ir(ttp)Me in 2 h (Table 3, entry 3 and 4).
K2CO3 and NaOPh were also used in the reactions of
Ir(ttp)Cl(CO) with various 4-substituted toluenes (Table 4, eq
4). Both bases enhanced BnCHA with the stronger base K2CO3
showing a larger rate enhancement than NaOPh (Table 4, entries
(5)
X-ray Details. The collection and processing parameters of
single-crystal data for complexes 2a, 2d, and 2e are given in
Table 5 and Supporting Information. Table 6 lists the selected
bond lengths and angles. The bond lengths of Ir-C in
Ir(ttp)CH2Ar and Ir-C-Caryl angles are not affected by the
para-substituents (Table 6). In the solid state, 2a, 2d, and 2e
adopt monomeric structures. However, due to the rotation of
the molecule of 2d, disorder of the X-ray structure results. Both
disordered and simplified ORTEP drawings of 2d are reported
in Supporting Information. As a representative, Figure 1 shows
the molecular structure of Ir(ttp)Bn(p-tBu) (2e) (30% thermal
ellipsoids).
Mechanism: No Base. Scheme 1 illustrates the proposed
mechanism for the reactions without and with bases. In the
absence of a base (Scheme 1, Pathway I), Ir(ttp)Cl(CO)
presumably reacts with the benzylic C-H bond of toluene,
(16) Yeung, S. K.; Chan, K. S. Organometallics 2005, 24, 6426–6430.
(17) Ogoshi, H.; Setsune, J.-I.; Yoshida, Z.-I. J. Organomet. Chem. 1978,
159, 317–328.
(15) Lide, D. R., Ed. CRC Handbook of Chemistry and Physics, 85th
ed; CRC Press: Cleveland, OH, 2004.
(18) Ogoshi, H.; Setsune, J.-I.; Omura, T.; Yoshida, Z.-I. J. Am. Chem.
Soc. 1975, 97, 6461–6466.

Base-Promoted SelectiVe ActiVation
Organometallics, Vol. 27, No. 13, 2008 3045
Table 5. Crystal Data and Summary of Data Collection and Refinement for 2a, 2d, and 2e
param
2a
2d
2e
formula
cryst size (mm)
fw
C56H45N4Ir.2H2O
0.40 × 0.30 × 0.20
1002.19
C55H42N5O2Ir
0.40 × 0.30 × 0.20
997.14
C59H51N4Ir
0.40 × 0.30 × 0.20
1008.24
cryst syst
space group
a (Å)
b (Å)
c (Å)
monoclinic
P2 (1)/c
13.870 (3)
22.020 (4)
15.361 (3)
90
95.34 (3)
90
4671.3 (16)
4
monoclinic
P2(1)/c
7.6573 (12)
16.574 (3)
21.973 (3)
90
90.180 (3)
90
2788.7 (7)
2
monoclinic
P2 (1)/n
12.755 (3)
22.544 (6)
16.701 (4)
90
100.692 (6)
90
4719 (2)
4
R (deg)
ꢀ(deg)
γ (deg)
V, Å3
Z
Dcalcd, Mg/m3
radiation (λ), Å
θ range, deg
F(000)
1.425
0.71073
2.11 to 25.00
2024
1.188
0.71073
1.54 to 28.02
1000
1.419
0.71073
1.53 to 25.00
2040
reflcns collcd
indpndt rflns
data/restraints/params
goodness of fit
8575
8215
18222
6677
25303
8315
8215/0/568
1.043
0.0503/0.1372
0.0945/0.1569
0.0768/4.5632
6677/155/631
1.095
0.0582/0.1621
0.1024/0.1925
0.1088/0.0000
8315/0/577
1.074
0.0422/0.1022
0.0658/0.1198
0.0664/0.3854
b
final R1a/wR2 [I > 2σ(I)]
b
final R1a/wR2 (all data)
c
w1/w2
a R1 ) Σ (|F0| - |Fc|)/Σ |F0|. b wR2 ) Σ {Σ[w(F0 - Fc ) ]/Σ [w(F02)2]}1/2
.
c Weighting scheme w-1 ) σ2 (F02) + (w1 P)2 + w2P, where P ) (F0
+
2
2 2
2
2
2Fc )/3.
Table 6. Selected Bond Lengths and Bond Angles of Compounds 2a,
2d, and 2e
generate only Ir(ttp)(p-tol) in 26% yield via electrophilic
aromatic substitution21 without any Ir(ttp)Bn (eq 6). (ii) Ir(ttp)(p-
tol) did not further react with toluene at 200 °C in 1.5 days to
yield any Ir(ttp)Bn, and therefore it is not an intermediate to
give Ir(ttp)Bn. The dissociation of Cl– from Ir(ttp)Cl(CO) does
take part during BnCHA because of the decreased rate in the
reaction between Ir(ttp)Cl(CO) and toluene added with CsCl
(10 equiv) at 200 °C to yield Ir(ttp)Bn in 61% yield with
unreacted Ir(ttp)Cl(CO) recovered in 12% yield in 15 days (eq
7). BnCHA without base does not involve Ir(ttp)H as the
intermediate since no Ir(ttp)H was observed in the course of
the reaction of Ir(ttp)Cl(CO) with p-xylene (100 equiv) in C6D6
at 200 °C in 22 days to yield Ir(ttp)Bn(p-Me) in 47% yield.
Ir-C-Caryl bond
angle (deg)
entry
FG
Ir-C length (Å)
1
2
3
Me, 2a
NO2, 2d
tBu, 2e
2.089 (9)
2.186 (4)a
2.073 (6)
115.2 (6)
114.8 (4)b
117.1 (4)
a Average of 2 Ir-C bond lengths from 2 kinds of disordered
structures. b Average of 4 Ir-C-Caryl bond angles from 4 kinds of
disordered structures.
200 °C, 2 h, N2
(
)
(
)
Ir ttp BF4 + PhCH3
8 Ir(ttp) p - tol +
26%
“ HBF4 ” (6)
Ir(ttp)Cl(CO) + PhCH3 200 °C, CsCl (10 equiv)8
15 d, N2
unreacted
Ir(ttp)Bn + Ir(ttp)Cl(CO) (7)
12%
61%
Mechanism: Strong Base. In the presence of a strong base
(Scheme 1, Pathway II) such as K2CO3, which is a precursor
of hydroxide generated by thermal hydrolysis of carbonate at
200 °C with a small amount of water present,22 or NaOH,
Ir(ttp)X (X ) OH-, KCO3-) A probably forms first by rapid
ligand substitution.11f,23 Ir(ttp)X further reacts with toluene to
yield Ir(ttp)H.17,24 This is supported by the initial formation of
Ir(ttp)H as the only iridium porphyrin species in the independent
reaction of Ir(ttp)Cl(CO) with Ph13CH3 (50 equiv) and Cs2CO3
Figure 1. ORTEP drawing of Ir(ttp)Bn(p-tBu) (2e) in 30%
probability displacement ellipsoids.
which is a sterically more accessible bond than arene C-H
bonds, via σ-bond metathesis10,11f or its variant form of internal
electrophilic substitution (IES).19 Complete dissociation of
Ir(ttp)Cl(CO) into Ir(ttp)+10,20 for BnCHA is less probable, and
this can be attributed into 2 reasons. (i) Ir(ttp)BF4 (an inseparable
mixture of Ir(ttp)BF4 and Ir(ttp)(CO)BF4)10 with the much less
-
coordinating BF4 reacted with toluene at 200 °C in 2 h to
(21) Zhou, X.; Tse, M. K.; Wu, D.-D.; Mak, T. C. W.; Chan, K. S. J.
Organomet. Chem. 2000, 598, 80–86.
(19) In the internal electrophilic substitution (IES) mechanism, the lone
pair on an M-X ligand forms an X-H bond, while the orbital making up
the M-X bond turns into a coordinating lone pair (ref 12).
(20) Aoyamac, Y.; Yoshida, T.; Sakurai, K.; Ogoshi, H. Organometallics
1986, 5, 168–173.
(22) L’vov, B. V. Thermochim. Acta 1997, 303, 161–170.
(23) (a) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G. Acc.
Chem. Res. 2002, 35, 44–56. (b) Cámpora, J.; Palma, P.; del Río, D.;
Álvarez, E. Organometallics 2004, 23, 1652–1655.
(24) Collman, J. P.; Kim, K. J. Am. Chem. Soc. 1986, 108, 7847–7849.

3046 Organometallics, Vol. 27, No. 13, 2008
Scheme 1. Mechanism of Benzylic CHA and Generation of Ir(ttp)Me
Cheung and Chan
in C6D6 at 150 °C in 30 min (eq 8). The characteristic high
field hydride signal was observed at -57.4 ppm by H NMR
Ir(ttp) anion, which is formed by deprotonation of Ir(ttp)H with
base, is probably the reacting species. The base-promoted
reduction of Ir(ttp)Cl(CO) with Ir(ttp)H was also successfully
carried out in C6D6 in 150 °C to yield Ir(ttp)Me in 10% yield
(eq 13).
1
spectroscopy. However, no benzyl alcohol was observed by GC-
MS analysis in the reaction mixture of Ir(ttp)Cl(CO) with toluene
and NaOH (20 equiv) or K2CO3 (20 equiv) at 200 °C. As the
fate of the organic coproducts remains unclear, we can only
conclude that toluene is a hydride donor or reducing agent. The
detailed mechanism of conversion of Ir(ttp)Cl(CO) to Ir(ttp)H
with toluene and bases is still unclear. As Ir(ttp)OH could not
be successfully prepared from the reaction of Ir(ttp)Cl(CO) with
KOH, its observation in the reaction mixture remains difficult.
Presumably, Ir(ttp)X reacts very rapidly with toluene to give
Ir(ttp)H (Scheme 1, Pathway IIa) which further reacts with
toluene to yield Ir(ttp)Bn (Scheme 1, Pathway IIb). The
intermediacy of Ir(ttp)H was further established by the separate
reaction of Ir(ttp)H with toluene at 200 °C in 1 h to give
Ir(ttp)Bn in 48% yield (eq 9).
Cs2CO3
13
(
)
(
)
Ir ttp Cl CO + Ph CH3
(20 equiv)8
150 °C, 2 h
Ir(ttp)13CH2Ph + Ir(ttp)CH3 (10)
8%
17%
Cs2CO3 (20 equiv), C6D5CD3
Ir(ttp)H + Ir(ttp)Cl(CO)
8
4 equiv
1 equiv
150 °C, 4 d
(
)
Ir ttp Bn-d7 + Ir(ttp)CH3 (11)
19%
10%
C6D5CD3
(
)
Ir(ttp)H + Ir(ttp)Cl(CO)
8 Ir ttp Bn-d7 +
4 equiv
1 equiv
200 °C, 19 d
23%
unreacted
unreacted
Cs2CO3 (20 equiv), C6D6
Ir(ttp)CH3 + Ir(ttp)Cl(CO) + Ir(ttp)H (12)
Ir(ttp)Cl(CO) + Ph13CH3
8 Ir(ttp)H (8)
5%
23%
19%
150 °C, 30 min
200 °C,1 h, N2
81%
50 equiv
Cs2CO3 (100 equiv), C6D6
Ir(ttp)H + Ir(ttp)Cl(CO) +
8
4 equiv
1 equiv
150 °C, 11 d
Ir(ttp)H + PhCH3
8 Ir(ttp)Bn
(9)
48%
Ir(ttp)CH3(13)
10%
Ir(ttp)Me is not an intermediate of Ir(ttp)Bn as it reacted
slowly with toluene at 200 °C in 14 days to yield only a trace
of Ir(ttp)Bn with the recovery of Ir(ttp)Me in 46% yield, and it
reacted with toluene and K2CO3(20 equiv) at 200 °C in 3 days
to yield a trace of Ir(ttp)Bn with the recovery of Ir(ttp)Me in
92% yield.
Ir(ttp)H can also reduce unreacted Ir(ttp)Cl(CO) to Ir(ttp)Me
(Scheme 1, Pathway IIc). Ph13CH3 reacted with Ir(ttp)Cl(CO)
and Cs2CO3 at 150 °C in 2 h to give Ir(ttp)13CH2Ph and
Ir(ttp)Me in 8% and 17% yield, respectively (eq 10). No Ph-
13CH3 cleavage occurred. As the reduction of CO by transition
metal hydride species to yield metal methyl complexes has been
widely reported,25,26 it is highly likely that PhCH3 reduces
Ir(ttp)Cl(CO) to Ir(ttp)H, which further reduces unreacted
Ir(ttp)Cl(CO), most likely the CO ligand, to Ir(ttp)Me. Indeed,
Ir(ttp)H (4 equiv) with Cs2CO3 (20 equiv) were found to reduce
Ir(ttp)Cl(CO) (1 equiv) in toluene-d8 at 150 °C in 4 days to
yield Ir(ttp)Bn-d7 (19%) and Ir(ttp)Me (10%) (eq 11). The
presence of base is important in the reduction of Ir(ttp)Cl(CO)
as the reaction of Ir(ttp)H (4 equiv) with Ir(ttp)Cl(CO) (1 equiv)
without any base in toluene-d8 was incomplete even at 200 °C
in 19 days, yielding Ir(ttp)Bn-d7 (23%) and Ir(ttp)-Me (5%) with
unreacted Ir(ttp)Cl(CO) and Ir(ttp)H (eq 12). Therefore, the
Mechanism of Ir(ttp)Me Generation. The source of proton
in the methyl group of Ir(ttp)Me is probably from water. In
view of the rapid generation of Ir(ttp)H without Ir(ttp)D in the
reaction of Ir(ttp)Cl(CO) with toluene-d8 (50 equiv) and Cs2CO3
(20 equiv) at 150 °C in 20 min, water, which is intrinstically
present in trace amount in base used, probably acts as an
alternative proton source for the generation of Ir(ttp)H. However,
no reaction occurred when Ir(ttp)Cl(CO) and water (100 equiv)
in benzene were heated at 200 °C for 8 days to yield Ir(ttp)Me.
Thus, water does not directly react with the CO ligand in
Ir(ttp)Cl(CO) to yield Ir(ttp)Me. Indeed, base is also essential
in the formation of Ir(ttp)Me. It is proposed that Ir(ttp)D was
generated and rapidly exchanged with the trace of water present
to yield Ir(ttp)H before reducing CO in Ir(ttp)Cl(CO) to yield
Ir(ttp)Me (eq 14). In fact, facile proton exchange of Ir(ttp)D
with H2O (50 equiv) added with Cs2CO3 (40 equiv) in C6D6 at
150 °C did occur to yield Ir(ttp)H (eq 15). Complete conversion
(25) Transition-metal coordinated CO can be reduced by hydride sources
to yield metal-methyl complexes. (a) Treichel, P. M.; Shubkin, R. L. Inorg.
Chem. 1967, 6, 1328–1334. (b) Lapinte, C.; Catheline, D.; Astruc, D.
Organometallics 1988, 7, 1683–1691.
(26) The carbonyl group of Rh(ttp)C(O)Ph was proposed to be reduced
by Rh(ttp)H to yield Rh(ttp)Bn (ref 8).

Base-Promoted SelectiVe ActiVation
Organometallics, Vol. 27, No. 13, 2008 3047
of Ir(ttp)H to Ir(ttp)D with D2O (50 equiv) in C6D6 added with
Cs2CO3 (40 equiv) in the same reaction conditions of BnCHA
confirms the occurrence of proton exchange (eq 16). Therefore,
only Ir(ttp)H was present without any Ir(ttp)D during CO
reduction (eq 14). The conversion of Ir(ttp)D to Ir(ttp)H is likely
due to the base-promoted proton transfer via Ir(ttp) dimer,
[Ir(ttp)]2,27 which was observed in the proton exchange of
Ir(ttp)D with H2O (eq 15) and Ir(ttp)H with D2O (eq 16).
With a stronger base, more rapid deprotonation of Ir(ttp)H
gives [Ir(ttp)]-M+17 (Scheme 2, pathway I). The Ir(ttp) anion
then attacks the CO ligand of Ir(ttp)Cl(CO) followed by
dissociation of Cl- to give presumably Ir(ttp)C(O)Ir(ttp) B28
(Scheme 2, Pathway II), which dissociates homolytically and
rapidly to yield the IrII(ttp) radical and IrIII(ttp)C(O) carbon-
centered radical29 C (Scheme 2, Pathway IIa). The IrIII(ttp)C(O)
radical probably further reacts with Ir(ttp)H to give Ir(ttp)CHO
and IrII(ttp) radicals27b,30 (Scheme 2, Pathway III). Ir(ttp)CHO
is further reduced by Ir(ttp)H to yield Ir(ttp)Me31 (Scheme 2,
pathway IV). In view of the higher yield of Ir(ttp)Me with a
stronger base in base-promoted BnCHA, the Ir(ttp) anion is
probably the reacting species for Ir(ttp)Me formation (Scheme
2, pathways II–IV).
150 °C, Cs2CO3 (20 equiv), C6D6
Ir(ttp)Cl(CO) + C6D5CD3
8
14 d
50 equiv
Ir(ttp)Bn-d7 + Ir(ttp)CH3 (14)
42%
34%
Ir(ttp)D + H2O 150 °C, Cs2CO3 40 equiv , C D68 Ir(ttp)H
(
)
6
Mechanism of Ir(ttp)Bn Formation. [Ir(ttp)]2 is probably
another reacting species to generate Ir(ttp)Bn in base-promoted
BnCHA. The formation of [Ir(ttp)]2 was supported by its
observation in 41% yield in the reaction of Ir(ttp)Cl(CO) with
toluene-d8 (50 equiv) and Cs2CO3 in C6D6 at 150 °C in 1 h (eq
13 h
43%
50 equiv
(15)
Ir(ttp)H + D2O 150 °C, Cs2CO3 40 equiv , C D68 Ir(ttp)D(16)
(
)
6
19). The spectroscopic identification of [Ir(ttp)]2 was confirmed
36 h
20%
50 equiv
27a
using an authentic sample of [Ir(ttp)]2
generated by the
The incorporation of proton from water into Ir(ttp)Me is
further confirmed by the addition of D2O to the base-promoted
reactions of toluene. When toluene-d8, Cs2CO3 (20 equiv), and
D2O (10 equiv) were reacted with Ir(ttp)Cl(CO) at 150 °C, a
mixture of Ir(ttp)CH3 and Ir(ttp)CD3 formed at a ratio of 5.45:
1 (eq 17a). When the amount of D2O was increased to 50 equiv,
the ratio of Ir(ttp)CH3/Ir(ttp)CD3 became 2.54:1 with an increase
in the proportion of Ir(ttp)CD3 (eq 17b). The addition of D2O
(50 equiv) still did not give Ir(ttp)CD3 in 100% yield.
reaction of Ir(ttp)H with 2,2,6,6-tetramethylpiperidinooxy
(TEMPO) in C6D6 at room temperature for 5 min. Indeed,
[Ir(ttp)]2 did react rapidly with toluene at 200 °C in 90 min to
yield Ir(ttp)Bn in 46% yield (eq 20).
Ir(ttp)Cl(CO) + C6D5CD3 150 °C, Cs2CO3 20 equiv , C D68
(
)
6
1 h
50 equiv
Ir(ttp)H + [Ir(ttp)]2 + Ir(ttp)Bn-d7 + Ir(ttp)Me (19)
38%
41%
2%
14%
[Ir(ttp)]2+PhCH3 1.5 h, 200 °C8 Ir(ttp)Bn
(20)
N2
46%
(17)
[Ir(ttp)]2 is formed by the thermal (eqs 21 and 22) and base-
promoted (eq 23) dehydrogenative dimer formation from
Ir(ttp)H. Ir(ttp)H remained unreacted at room temperature in
2 h but reacted rapidly at 150 °C to give [Ir(ttp)]2 in 74% yield
in 1 h (eq 21). This shows that high temperature is required for
dimer formation from Ir(ttp)H. Alternatively, in the separate
reaction of Ir(ttp)H with toluene (50 equiv) in C6D6 at 150 °C,
[Ir(ttp)]2 was formed in 66% yield as the major species in 30
min prior to reacting with toluene to yield Ir(ttp)Bn (eq 22).
Rh(oep)H (oep ) octaethylporphyrin dianion) has also been
The base-promoted reactions of toluene by Ir(ttp)Cl(CO) with
various other bases were also studied at 150 °C (Table 7, eq
18). The rates of reactions and the ratios of Ir(ttp)CH3/Ir(ttp)Bn
increased with more basic salts (MOH > M2CO3) (Table 7,
entries 2–5). Furthermore, the Ir(ttp)Me/Ir(ttp)Bn ratio increased
down the group of metal ions in the bases (Cs > K > Na > Li,
Table 7, entries 1–6). The above trends can be rationalized by
the nucleophilicity of a base. A more nucleophilic OH- reacts
2-
faster than CO3 in ligand substitution with Ir(ttp)Cl(CO) to
give Ir(ttp)X (X: OH- > MCO3-, Scheme 1, Pathway II), which
also reacts faster with toluene to produce Ir(ttp)H (Scheme 1,
pathway IIa). Further reaction of Ir(ttp)H with toluene forms
Ir(ttp)Bn (Scheme 1, Pathway IIb) or with unreacted Ir(ttp)-
Cl(CO) to yield Ir(ttp)Me (Scheme 1, Pathway IIc).
(27) The authentic sample of [Ir(ttp)]2 was synthesized using the same
method to synthesize [Ir(oep)]2 by reacting Ir(oep)H and TEMPO. (a) Chan,
K. S.; Leung, Y.-B. Inorg. Chem. 1994, 3, 3187. The chemical shifts and
splitting patterns of [Ir(ttp)]2 in 1H NMR spectrocscopy was similar to that
of [Rh(ttp)]2. For [Ir(ttp)]2: 1H NMR (C6D6) δ 9.48 (d, 4 H, o-phenyl),
8.33 (s, 8 H, pyrrole), 7.65 (d, 4 H, o′-phenyl), 2.46 (s, 12 H, p-methyl); m
and m′-phenyl hydrogens are obscured by solvent (7.15). For [Rh(ttp)]2:
1H NMR (C6D6) δ 9.64 (d, 4 H, o-phenyl), 8.63 (s, 8 H, pyrrole), 7.75 (d,
4 H, o′-phenyl), 2.50 (s, 12 H, p-methyl); m and m′-phenyl hydrogens are
obscured by solvent (7.15). (b) Wayland, B. B.; Voorhees, S. L. V.; Charles
Wilker, C. Inorg. Chem. 1986, 25, 4039–4042.
Table 7. Base Effect on the Formation of Ir(ttp)Me
base (equiv)
Ir(ttp)Cl(CO) + PhCH3
8 Ir(ttp)Bn + Ir(ttp)CH3
2b 3
150 °C,time, N2
(28) An analogue of Ir(ttp)C(O)Ir(ttp), Rh(oep)C(O)Rh(oep), had been
reported. (a) Wayland, B. B.; Woods, B. A.; Coffin, V. L. Organometallics,
1986, 5, 1059–1062. (b) Coffin, V. L.; Brennen, W.; Wayland, B. B. J. Am.
Chem. Soc. 1988, 110, 6063–6069.
(18)
base
yield
yield
total
ratio
(29) Cui, W.; Li, S.; Wayland, B. B. J. Organomet. Chem. 2007, 692,
3198–3206.
entry
(equiv)
time of 2b/% of 3/% yield/% of 2b: 3
1
2
3
4
5
6
LiOH.H2O (10)
NaOH (10)
KOH (10)
Na2CO3 (20)
K2CO3 (20)
Cs2CO3 (20)
3 d
1 d
1 h
10 d
2 d
1 h
62
44
27
79
66
46
23
21
24
10
3
85
65
51
89
69
81
2.70:1
2.10:1
1.13:1
7.90:1
22.0:1
1.31:1
(30) (a) Paonessa, R. S.; Thomas, N. C.; Halpern, J. J. Am. Chem. Soc.
1985, 107, 4333–4335. (b) Wayland, B. B.; Sherry, A. E.; Poszmik, G.;
Bunn, A. G. J. Am. Chem. Soc. 1992, 114, 1673–1681.
(31) The reduction of a carbonyl ligand coordinated to transition metal
to yield methyl ligand had been reported to proceed via a metal-formyl
intermediate. Thus, Ir(ttp)CHO was proposed to be formed in the reduction
of Ir(ttp)Cl(CO) by Ir(ttp)H.25b
35

3048 Organometallics, Vol. 27, No. 13, 2008
Scheme 2. Mechanism of Reduction of Ir(ttp)Cl(CO) by Ir(ttp)H to Generate Ir(ttp)Me
Cheung and Chan
reported to react to yield [Rh(oep)]2 and H2.32 In the presence
of Cs2CO3 (20 equiv) (eq 23), a small amount of [Ir(ttp)]2 in
25% yield had already formed from the dehydrogenative
dimerization of Ir(ttp)H at ambient temperature, and a high yield
of [Ir(ttp)]2 in 89% yield was formed in 30 min. Thus, the base
also promoted the dimer formation of Ir(ttp)H to [Ir(ttp)]2.
Indeed, the base promoted the rate of BnCHA with Ir(ttp)H
since the reaction of Ir(ttp)H with toluene (50 equiv) in C6D6
at 150 °C with Cs2CO3 (20 equiv) was complete to yield
Ir(ttp)Bn in 55% in 6 days (eq 24), whereas the same reaction
without base was still incomplete in 6 days (eq 25). Base
probably deprotonates Ir(ttp)H to give the Ir(ttp) anion17 for
faster formation of [Ir(ttp)]2, which in turn leads to faster rate
of BnCHA.
Mechanism: Weak Base. In the presence of the weak base
of NaOPh (Scheme 1, Pathway III), Ir(ttp)Cl(CO) undergoes
ligand substitution35 with NaOPh to give Ir(ttp)OPh. This is
confirmed by the rapid conversion of Ir(ttp)Cl(CO) to Ir(ttp)OPh
in 95% yield in the reaction of Ir(ttp)Cl(CO) with toluene (100
equiv) and NaOPh (20 equiv) in benzene-d6 in 2 h as observed
1
by H NMR spectroscopy (eq 26). The identity of Ir(ttp)OPh
was confirmed by an authentic sample of Ir(ttp)OPh prepared
in 86% yield by reacting Ir(ttp)Cl(CO) with NaOPh (2 equiv)
in benzene at 150 °C for 12 h. Ir(ttp)OPh then reacts with
toluene to yield Ir(ttp)Bn (Scheme 1, Pathway IIIa). The
intermediacy of Ir(ttp)OPh was supported by the reaction of
Ir(ttp)OPh with toluene-d8 at 200 °C in 1 day to yield Ir(ttp)Bn-
d7 in 75% isolated yield and PhOH in 31% yield by GC-MS
analysis (eq 27). The absence of signals of Ir(ttp)H and benzyl
C6D6
1
phenyl ether36 by H NMR spectroscopy in the reaction of
(
)
2Ir(ttp)H
8 Ir ttp 2 + H
(21)
[
]
2
Ir(ttp)OPh with toluene (100 equiv) in C6D6 at 200 °C for 10
days further supported the direct reaction of Ir(ttp)OPh with
toluene to yield Ir(ttp)Bn and PhOH. The slower substitution
of chloride by the less nucleophilic phenoxide anion (Scheme
1, Pathway III) and the lower reactivity of Ir(ttp)OPh with its
bulky and less basic phenoxide anion (Scheme 1, Pathway IIIa)
account for the longer reaction time of BnCHA with NaOPh
than with K2CO3.
1.5 h, 150 °C
C6D6
150 °C, 30 min
74%
Ir(ttp)H + PhCH3
8 Ir(ttp)H + [Ir(ttp)]2 +
5% 66%
50 equiv
Ir(ttp)Bn (22)
4%
Cs2CO3 (20 equiv), C6D6
Ir(ttp)H + PhCH3
8 Ir(ttp)H + [Ir(ttp)]2 +
150 °C, 30 min
2%
89%
50 equiv
PhCH3 (100 equiv), C6D6
Ir(ttp)Bn (23)
Ir(ttp)Cl(CO) + NaOPh
8 Ir(ttp)OPh
20 equiv
4%
200 °C, 2 h
95%
Cs2CO3 (20 equiv), C6D6
(26)
Ir(ttp)H + PhCH3
8 Ir(ttp)Bn (24)
150 °C, 6 d
55%
50 equiv
C6D5CD3, 200 °C, 1 d, N2
(
)
Ir ttp OPh
8 Ir(ttp)Bn-d7 + PhOH
75% 31%
C6D6
Ir(ttp)H + PhCH3
8 Ir(ttp)H + Ir(ttp)Bn (25)
37% 40%
150 °C, 6 d
(27)
50 equiv
[Ir(ttp)]2 probably reacts with toluene to yield both Ir(ttp)Bn
and Ir(ttp)H, likely in a termolecular mechanism33 analogous
to BnCHA with Rh(tmp) (tmp ) tetramesitylporphyrin dianion)
radical33b and toluene. Indeed, [Ir(oep)]2 has been reported to
react with toluene to yield both Ir(oep)Bn and Ir(oep)H.34
However, direct reaction of Ir(ttp)H with toluene to yield
Ir(ttp)Bn and H2 cannot be excluded. [Ir(ttp)]2 probably reacts
faster with toluene than Ir(ttp)H. It is because Ir(ttp)H, which
was generated from the reaction of [Ir(ttp)]2 with toluene, was
consumed slowly in the reaction of Ir(ttp)H with toluene (50
equiv) in C6D6 at 150 °C (eq 25). Ir(ttp)Me was probably not
generated from [Ir(ttp)]2 as it did not form in the reaction of
[Ir(ttp)]2 with toluene (50 equiv) at 150 °C both with and without
Cs2CO3 (20 equiv) (eqs 24 and 25).
Scheme 3 lists more detailed mechanisms for the BnCHA
step with Ir(ttp)X (X ) OH-, KCO3-, OPh-) with two major
possible classes: (i) oxidative addition and (ii) σ-bond metathesis
and its variants (Scheme 3). Oxidative addition (Scheme 3,
Pathway i) involves the cis-addition of the PhCH2-H bond to
Ir(ttp)X to generate a 7-coordinate Ir(V) intermediate with three
substituents on the cis-face of a porphyrin ligand, which is too
crowded for reaction. Therefore, oxidative addition is less likely
to occur. Classical σ-bond metathesis (Scheme 3, Pathway ii),
and one of its variant forms, σ-complex-assisted metathesis (σ-
CAM)37 (Scheme 3, Pathway iii), involves the concerted
rearrangement of bonds through a 4-center, 4-electron transition
state. However, they are less favorable as suggested by the very
slow analogous reaction of Ir(ttp)Me with toluene at 200 °C in
(32) Wayland, B. B.; Del Rossi, K. J. J. Organomet. Chem. 1984, 276,
C27–C30.
(35) Rees, W. M.; Churchill, M. R.; Fettinger, J. C.; Atwood, J. D.
Organometallics 1985, 4, 2179–2185.
(33) (a) Sherry, A. E.; Wayland, B. B. J. Am. Chem. Soc. 1990, 112,
1259–1261. (b) Wayland, B. B.; Ba, S.; Sherry, A. E. J. Am. Chem. Soc.
1991, 113, 5305–5311. (c) Zhang, X.-X.; Wayland, B. B. J. Am. Chem.
Soc. 1994, 116, 7897–7898. (d) Cui, W.; Zhang, X. P.; Wayland, B. B.
J. Am. Chem. Soc. 2003, 125, 4994–4995.
(36) Wiles, C.; Watts, P.; Haswell, S. J.; Pombo-Villar, E. Tetrahedron
2005, 61, 10757–10773.
(37) The difference between σ-complex-assisted metathesis and classical
σ-bond metathesis in CHA is that the former involves the pre-coordination
of the C-H bond to the metal center before concerted bond rearrangement,
whereas the latter involves the direct concerted rearrangement of bonds. Perutz,
R. N.; Sabo-Etienne, S. Angew. Chem., Int. Ed. 2007, 46, 2578–2592.
(34) Del Rossi, K. J.; Wayland, B. B. J. Chem. Soc. Chem. Commun.
1986, 1653–1655.

Base-Promoted SelectiVe ActiVation
Organometallics, Vol. 27, No. 13, 2008 3049
Scheme 3. Four Possible Mechanisms of Base-Promoted BnCHA Steps
Scheme 4. Parallel BnCHA of Toluene with Ir(ttp)H and
[Ir(ttp)]2
14 days to give just a trace of Ir(ttp)Bn with the recovery of
Ir(ttp)Me in 46% yield. Another refinement of classical σ-bond
metathesis, the internal electrophilic substitution (IES)12 (Scheme
3, Pathway iv), is probably the more likely mechanism with
the participation of the lone electron pair of the oxygen atom
of the phenoxide ligand. The oxygen in the phenoxide ligand
in Ir(ttp)OPh is sp3 hybridized with the filled p-type lone pair
orbital of oxygen conjugated with the π system of the aromatic
group. As the distortion of the p orbital of oxygen from the π
system of the aromatic group in phenol at high temperature has
been reported38 with the low energy barrier for OH rotation
about the C-O bond in phenol (3.47 kcal/mol),39 it is highly
probable that the filled p orbital of oxygen does not further
overlap with the π system of the aromatic group in the
phenoxide ligand at the reaction temperature of 200 °C. The
electron density of the p orbital of oxygen in the phenol group
can be enhanced and freely available to abstract the proton of
toluene during IES.
suggested, the small KIE in BnCHA with iridium porphyrin
cannot be accounted totally by the analogous linear transition
state proposed in the BnCHA of toluene by [Ir(ttp)]2. Probably
a parallel pathway of BnCHA by Ir(ttp)H with a bent transition
state can rationalize the small observed values (Scheme 4,
Pathway I).
Ir(ttp)Bn did not react with 4-fluorotoluene (50 equiv) in C6D6
at 200 °C in 3 days without base. In 6 days, Ir(ttp)Bn reacted
with 4-fluorotoluene and the ratio of Ir(ttp)Bn/Ir(ttp)Bn(p-F) was
found to be 11.5:1. Ir(ttp)Bn was completely consumed only
after 70 days to yield Ir(ttp)Bn(p-F) in 92% yield (eq 28).
Besides, Ir(ttp)Bn did not react with toluene-d8 (50 equiv) added
with K2CO3 (20 equiv) in C6D6 at 200 °C in 18 h, but it reacted
at a longer time of 4 days to yield Ir(ttp)Bn-d7 with the ratio of
Ir(ttp)Bn/Ir(ttp)Bn-d7 of 26.8:1 (eq 29). After 14 days, the ratio
of Ir(ttp)Bn/Ir(ttp)Bn-d7 was found to be 3.57:1. Therefore, these
results suggest that reactions of Ir(ttp)Bn with toluene-d8 to give
Ir(ttp)Bn-d7 without and with base do not significantly affect
the (kH/kD)obs values in the time scale of BnCHA. The (kH/
kD)obsvalues are generally truly kinetic values.
Isotope Effect. The observed isotope effect (kH/kD)obs for the
BnCHA of toluene with Ir(ttp)Cl(CO) was measured by a
competition experiment with an equimolar mixture of solvent
toluene and toluene-d8. At 200 °C, (kH/kD)obs was measured to
be 2.37 without base after 9 days, 2.16 with K2CO3 after 3.5 h,
1
and 2.18 with NaOPh after 2 days by H NMR spectroscopy.
These values suggest that the cleavages of benzylic C-H bonds
are involved in or occur prior to the rate-determining steps in
the BnCHA. The observed isotope effect (kH/kD)obs for BnCHA
of toluene at 200 °C with Ir(ttp)H and [Ir(ttp)]2 was measured
to be 2.30 and 2.10, resepectively, which are similar to (kH/
kD)obs of 2.16 in BnCHA with Ir(ttp)Cl(CO) and K2CO3 at
200 °C. This implies that both Ir(ttp)H and [Ir(ttp)]2 are the
intermediates involved in the rate-determining step (RDS) in
the base-promoted BnCHA of toluene with Ir(ttp)Cl(CO)
(Scheme 1, pathway IIb). Moreover, a pre-equilibrium40 exists
between Ir(ttp)H and [Ir(ttp)]2 prior to BnCHA at 200 °C
(Scheme 4), and the generation of [Ir(ttp)]2 from Ir(ttp)H is facile
at high temperature as supported by independent experiments
(eqs 21 and 22), especially in the presence of base (eq 23).
(28)
K2CO3 (20 equiv), C6D6
(
)
Ir(ttp)Bn + C6D5CD3 50 equiv
8
2b
200 °C, 4 d
(
)
Ir(ttp)Bn:Ir(ttp)Bn-d7 29
Since the kinetic isotope effect (KIE) of the BnCHA of
toluene with Rh(tmp) is 6.533b and a linear transition state was
26.8:1
Hammett Plot. In order to gain preliminary electronic effects
of toluenes on base-promoted BnCHA, the Hammett plot was
constructed from competition experiments using an equimolar
mixture of 4-substituted toluenes (100 equiv) and toluene (100
equiv) with Ir(ttp)Cl(CO) and K2CO3 (20 equiv) at 200 °C in
benzene (Table 8, eq 30). Because of the very slow reacton of
benzyl exchange of Ir(ttp)Bn with 4-fluorotoluene (eq 28) and
(38) Pratt, D. A.; de Heer, M. I.; Mulder, P.; Ingold, K. U. J. Am. Chem.
Soc. 2001, 123, 5518–5526.
(39) Zierkiewicz, W.; Michalska, D.; Hobza, P. Chem. Phys. Lett. 2004,
386, 95–100.
(40) An anologue of Ir(ttp)H, Rh(oep)H, was in equilibrium with
[Rh(oep)]2 and H2 (ref 32).

3050 Organometallics, Vol. 27, No. 13, 2008
Cheung and Chan
H2O (10:1 v/v) and silica gel (Merck, 70-230 mesh) were used for
column chromatography.
1H NMR and 13C NMR spectra were recorded on a Bruker DPX-
300 at 300 and 75 MHz, respectively. Chemical Shifts were
referenced with the residual solvent protons in C6D6 (δ ) 7.15
ppm), CDCl3 (δ ) 7.26 ppm), or tetramethylsilane (δ ) 0.00 ppm)
in 1H NMR spectra, and CDCl3 (δ ) 77.16 ppm) or THF-d8
(δ(ꢀ–CH2) ) 25.62 ppm) in 13C NMR spectra as the internal
standards. Chemical shifts (δ) were reported as part per million
(ppm) in (δ) scale downfield from TMS. Coupling constants (J)
were reported in Hertz (Hz). High resolution mass spectra (HRMS)
were performed on a ThermoFinnigan MAT 95 XL mass spec-
trometer in fast atom bombardment (FAB) mode using 3-nitrobenzyl
alcohol (NBA) matrix and CH2Cl2 as solvent, and electrospray
ionization (ESI) mode using MeOH/CH2Cl2 (1:1) as solvent.
Figure 2. Hammett plot of base-promoted BnCHA of toluenes with
Ir(ttp)Cl(CO).
Table 8. Competition Experiments of Benzylic CHA
Independent Synthesis of (Porphyrinato)iridium(III) Ben-
zyls [Ir(por)R]. Synthesis of (5,10,15,20-tetratolylporphyrinato)(4-
methylbenzyl)iridium(III) by reductive benzylation of Ir(ttp)Cl(CO)
is described as a typical example for the preparation of (porphy-
rinato)iridium(III) benzyl complexes.16
(5,10,15,20-Tetrakis(p-tolyl)porphyrinato)(4-methylbenzyl)iri-
dium(III) [Ir(ttp)Bn(p-Me)] (2a). A suspension of Ir(ttp)Cl(CO)
(100 mg, 0.11 mmol) in THF (50 mL) and a solution of NaBH4
(153 mg, 67 µL, 1.08 mmol) in aqueous NaOH (1.0 M, 3.0 mL)
were purged separately with N2 for 15 min. The solution of NaBH4
was added slowly to the suspension of Ir(ttp)Cl(CO) via a cannula.
The mixture was heated at 70 °C under N2 for 2 h in a Teflon
screw-capped 250 mL round-bottomed flask to give a deep brown
suspension. The mixture was then cooled to room temperature under
N2, and 4-methylbenzyl bromide (200 mg, 1.08 mmol) was added.
The reaction mixture was further heated at 70 °C under N2 for 2 h.
A reddish brown suspension was formed. The reaction mixture was
worked up by extraction with CH2Cl2/H2O. The combined organic
extract was dried (MgSO4), filtered, and dried by rotary evaporation.
The reddish brown residue was purified by column chromatography
over alumina (70-230 mesh), eluting with a solvent mixture of
CH2Cl2 and hexane (1:2). The major brown fraction was collected
to give a brown solid (55 mg, 0.057 mmol, 52%) as the product
after rotary evaporation. The product was further purified by
recrystallization from CH2Cl2/CH3OH. Rf ) 0.60 (1:1 hexane/
CH2Cl2). 1H NMR (CDCl3, 300 MHz) δ -4.01 (s, 2 H, H29), 1.69
(s, 3 H, H34), 2.69 (s, 12 H, H25–28), 3.07 (d, 2 H, J ) 7.8 Hz,
a
entry
p-FG
σp
log k (HFG/HH)
1
2
3
Me
F
NO2
-0.14
0.15
0.81
0.3118
0.1149
0.7048
a σp: para-substituent constant.
toluene-d8 (eq 29), the ratios of both iridium porphyrin benzyls
formed were genuine kinetic values. Figure 2 shows a nonlinear
free energy relationship in the Hammett plot using the substitu-
ent constant σp.41 Therefore, the rate-determining step of the
multistepwise reactions likely changes with the para substituents
of toluenes.
Conclusions
In summary, we have discovered that the rates of benzylic
carbon-hydrogen bond activation of toluenes by Ir(ttp)Cl(CO)
were greatly enhanced by the presence of inorganic bases. Strong
inorganic base K2CO3 generated both benzylic CHA complexes
of iridium porphyrin benzyls and methyl. Weak inorganic base
NaOPh selectively promoted BnCHA to yield benzylic CHA
complexes only. With a strong base (e.g., Cs2CO3, KOH),
Ir(ttp)H and [Ir(ttp)]2 were the probable intermediates observed
in the formation of Ir(ttp)Me and Ir(ttp)Bn, respectively. With
a weak base NaOPh, Ir(ttp)OPh was the intermediate observed
in the reaction. Ir(ttp)OPh likely underwent internal electrophilic
substitution in BnCHA with toluene.
H
30,31), 5.69 (d, 2 H, J ) 7.8 Hz, H32,33), 7.51 (d, 4 H, J ) 5.7 Hz,
17,19,21,23), 7.53 (d, 4 H, J ) 5.7 Hz, H18,20,22,24), 7.92 (d, 4 H, J )
H
8.4 Hz, H10,12,14,16), 8.00 (d, 4 H, J ) 8.4 Hz, H9,11,13,15), 8.46 (s, 8
H, H1–8). 13C NMR (CDCl3, 75 MHz) δ -13.8, 21.2, 21.7, 124.1,
124.2, 127.1, 127.6, 131.3, 132.1, 133.7, 133.9, 137.2, 138.3, 139.0,
143.4. HRMS (ESIMS): Calcd for [C56H45N4Ir]+: m/z 966.3268.
Found: m/z 966.3262. The single crystal used for X-ray diffraction
crystallography was grown from CH2Cl2/MeOH.
(5,10,15,20-Tetrakis(p-tolyl)porphyrinato)(4-fluorobenzyl)iri-
dium(III) [Ir(ttp)Bn(p-F)] (2c). 4-Fluorobenzyl bromide (204 mg,
135 µL, 1.08 mmol) was used. Brown solid (58 mg, 0.059 mmol,
54%) was obtained. Rf ) 0.60 (1:1 hexane/CH2Cl2). 1H NMR
(CDCl3, 300 MHz) δ -4.05 (s, 2 H, H29), 2.69 (s, 12 H, H25–28),
3.07 (dd, 2 H, JHH ) 8.4 Hz, 4JHF ) 6.0 Hz, H30,31), 5.56 (dd, 2 H,
Experimental Section
3
JHH ) 8.7 Hz, JHF ) 8.9 Hz, H32,33), 7.51 (d, 4 H, J ) 7.2 Hz,
Unless otherwise noted, all reagents were purchased from
commercial suppliers and directly used without further purification.
Hexane was distilled from anhydrous calcium chloride. Benzene
and toluene were distilled from sodium. Thin layer chromatography
was performed on precoated silica gel 60 F254 plates. Ir(ttp)-
Cl(CO),16 Ir(ttp)BF4 (an inseparable mixture of Ir(ttp)(CO)BF4 and
Ir(ttp)BF4),10 Ir(ttp)Me,16 and Ir(ttp)Bn16 were prepared according
to the literature procedures. Neutral alumina (Merck, 70-230 mesh)/
H17,19,21,23), 7.53 (d, 4 H, J ) 7.2 Hz, H10,12,14,16), 7.94 (d, 4 H, J )
6.9 Hz, H10,12,14,16), 8.00 (d, 4 H, J ) 7.8 Hz, H9,11,13,15), 8.48 (s, 8
H, H1–8). 13C NMR (CDCl3, 75 MHz) δ -15.1, 21.7, 112.7 (d,
2JCF) 21 Hz), 124.2, 125.2 (d, 3JCF ) 7.7 Hz), 127.7, 131.4, 133.8,
1
137.1, 137.3, 138.9, 143.3, 157.1 (d, JCF ) 241 Hz). HRMS
(FABMS): Calcd for [C55H42N4FIr]+: m/z 970.3017. Found: m/z
970.3036.
(5,10,15,20-Tetrakis(p-tolyl)porphyrinato)(4-tert-butylben-
zyl)iridium(III) [Ir(ttp)Bn(p-tBu)] (2e). 4-tert-Butylbenzyl bro-
mide (245 mg, 1.08 mmol) was used. Brown solid (72 mg, 0.072
(41) Isaacs, N. S. Physical Organic Chemistry; ELBS, Longman: Avon,
U.K., 1987.

Base-Promoted SelectiVe ActiVation
Organometallics, Vol. 27, No. 13, 2008 3051
mmol, 65%) was obtained. Rf ) 0.62 (1:1 hexane/CH2Cl2). 1H NMR
(CDCl3, 300 MHz) δ -4.02 (s, 2 H, H29), 0.98 (s, 9 H, H34–36),
2.69 (s, 12 H, H25–28), 3.14 (d, 2 H, J ) 8.1 Hz, H30,31), 5.92 (d, 2
H, J ) 8.1 Hz, H32,33), 7.50 (d, 4 H, J ) 6.3 Hz, H17,19,21,23), 7.52
(d, 4 H, J ) 6.3 Hz, H18,20,22,24), 7.98 (d, 4 H, J ) 6.3 Hz, H10,12,14,16),
7.99 (d, 4 H, J ) 6.3 Hz, H9,11,13,15), 8.44 (s, 8 H, H1–8). 13C NMR
(CDCl3, 75 MHz) δ -13.6, 21.7, 30.9, 34.3, 123.3, 123.7, 124.2,
127.5, 127.6, 131.3, 133.7, 133.9, 137.2, 138.1, 139.0, 143.4, 145.2.
HRMS (FABMS): Calcd for [C59H51N4Ir]+: m/z 1008.3737. Found:
m/z 1008.3733. The single crystal used for X-ray diffraction
crystallography was grown from CH2Cl2/MeOH.
) 8.4 Hz), 7.50 (d, 8 H, J ) 8.1 Hz, H17,19,21,23), 8.00 (d, 8 H, J )
8.1 Hz, H17,19,21,23), 8.57 (s, 8 H). 13C NMR (CDCl3, 75 MHz) δ
19.3, 21.7, 89.8, 124.2, 124.3, 127.6, 128.6, 129.2, 131.6, 133.8,
134.2,137.4,138.8,143.1.HRMS(FABMS):Calcdfor[C55H43N4Ir]+:
m/z 952.3111. Found: m/z 952.3119.
Preparation of (5,10,15,20-Tetrakis(p-tolyl)porphyrinato)iri-
dium(II) Dimer [[Ir(ttp)]2] (7). [Ir(ttp)]2 was prepared using the
literature method for the preparation of [Ir(oep)]2.30 Ir(ttp)H (4.2
mg, 0.005 mmol) and 2,2,6,6-tetramethylpiperidinooxy (TEMPO)
(1.1 mg, 0.007 mmol) were added to a Rotaflo screw-capped NMR
tube. Benzene-d6 (0.50 mL) was added to the tube under N2. The
reaction mixture was degassed for three freeze–thaw-pump cycles
in the tube and then flame-sealed under vacuum. Compound 7 was
observed by 1H NMR spectroscopy. 1H NMR (C6D6) δ 9.48 (d, 4
H, o-phenyl), 8.33 (s, 8 H, pyrrole), 7.65 (d, 4 H, o′-phenyl), 2.46
(s, 12 H, p-methyl); m and m′-phenyl hydrogens are obscured by
solvent (7.15).
Reaction of Ir(ttp)Cl(CO) with Toluene. Ir(ttp)Cl(CO) (30.0
mg, 0.032 mmol) and toluene (2.0 mL) were degassed for three
freeze–thaw-pump cycles in a Teflon screw-capped tube. The
reaction mixture was covered by aluminum foil and heated at
200 °C under N2 for 9 days. The solvent was then removed under
vacuum, and the reddish brown residue was purified by column
chromatography over silica gel (70-230 mesh), eluting with a
solvent mixture of CH2Cl2 and hexane (1:1). The major orange
fraction was collected to give 2b (16.8 mg, 0.018 mmol, 55%).
Preparation of (5,10,15,20-Tetrakis(p-tolyl)porphyrinato)-
methyliridium(III) hydride [Ir(ttp)H] (4). Ir(ttp)H was prepared
according to the literature procedure for the synthesis of Ir(oep)H.17
A suspension of Ir(ttp)Cl(CO) (100 mg, 0.11 mmol) in THF (50
mL), a solution of NaBH4 (153 mg, 67 µL, 1.08 mmol) in aqueous
NaOH (1.0 M, 3.0 mL), and concentrated HCl (10 mL) in water
(200 mL) were purged separately with N2 for 15 min. The solution
of NaBH4 was added slowly to the suspension of Ir(ttp)Cl(CO) via
a cannula. The mixture was heated at 70 °C under N2 for 2 h in a
Teflon screw-capped 250 mL round-bottomed flask to give a deep
brown suspension. The mixture was then cooled in an ice–water
bath under N2, and HCl solution was added via a cannula. The
reaction mixture was stirred in an ice–water bath under N2 until a
reddish brown precipitate formed. The precipitate was collected
under N2 by suction filtration and washed with water to give 4 (83
1
General Procedures for Reactions of Ir(ttp)Cl(CO) with
Toluene and Various Ligands or Bases. Addition of 10 Equiv
mg, 0.097 mmol, 88%). H NMR (CDCl3, 300 MHz) δ -57.6 (s,
1 H, H29), 2.68 (s, 12 H, H25–28), 7.50 (d, 8 H, J ) 7.2 Hz, H17–24),
8.00 (d, 8 H, J ) 6.9 Hz, H9–16), 8.57 (s, 8 H, H1–8). 13C NMR
(THF-d8, 75 MHz)δ 21.9, 124.5, 128.3, 128.6, 132.0, 134.9, 138.1,
140.5, 144.8. HRMS (FABMS): Calcd for [C48H47N4Ir]-: m/z
862.2653. Found: m/z 862.2640.
of 2,6-Di-tert-butylpyridine. Ir(ttp)Cl(CO) (30.0 mg, 0.032 mmol),
2,6-di-tert-butylpyridine (61.2 mg, 72 µL, 0.32 mmol), and toluene
(2 mL) were degassed for three freeze–thaw-pump cycles in a
Teflon screw-capped tube. The reaction mixture was covered by
aluminum foil and heated at 200 °C under N2 for 10 days to give
2b (17.5 mg, 0.018 mmol, 58%).
Addition of 10 Equiv of CsCl. Ir(ttp)Cl(CO) (15.5 mg, 0.017
mmol), CsCl (28 mg, 0.17 mmol), and toluene (1.0 mL) were
degassed for three freeze–thaw-pump cycles in a Teflon screw-
capped tube. The reaction mixture was covered by aluminum foil
and heated at 200 °C under N2 for 15 days. The solvent was then
removed under vacuum, and the reddish brown residue was purified
by column chromatography over alumina (70-230 mesh), eluting
with a solvent mixture of CH2Cl2 and hexane (1:4) to obtain the
brown fraction of 2b (9.7 mg, 0.010 mmol, 61%). CH2Cl2/hexane
(1:1) was then used to isolate the red fraction of unreacted
Ir(ttp)Cl(CO) (1.8 mg, 0.002 mmol, 12%).
Addition of 10 Equiv of NaNH2. Ir(ttp)Cl(CO) (20.0 mg, 0.022
mmol), NaNH2 (8.6 mg, 0.22 mmol), and toluene (2.0 mL) were
degassed for three freeze–thaw-pump cycles in a Teflon screw-
capped tube. The reaction mixture was covered by aluminum foil
and heated at 200 °C under N2 for 15 min. The solvent was then
removed under vacuum, and the reddish brown residue was purified
by column chromatography over alumina (70-230 mesh), eluting
with a solvent mixture of CH2Cl2 and hexane (1:1). Compounds
2b and 3 with the same Rf ) 0.50 (CH2Cl2/hexane ) 1: 1) were
collected in one portion, and the ratio was determined by 1H NMR
spectroscopy from the integration of the methyl protons of the Ir-
CH2Ar group of 2b and the methyl protons of the Ir-Me group of
Ir(ttp)Me. Compound 2b (9.0 mg, 0.0095 mmol, 43%) and Ir(ttp)Me
(0.3 mg, 0.0003 mmol, 13%) were obtained.
Addition of 10 Equiv of NaOH. Ir(ttp)Cl(CO) (20.0 mg, 0.022
mmol), NaOH 12.3 mg, 0.22 mmol), and toluene (2.0 mL) were
degassed for three freeze–thaw-pump cycles in a Teflon screw-
capped tube. The reaction mixture was covered by aluminum foil
and heated at 200 °C under N2 for 1 h to give 2b (7.1 mg, 0.0075
mmol, 34%) and Ir(ttp)Me (0.1 mg, 0.0002 mmol, 7%).
Preparation of (5,10,15,20-Tetrakis(p-tolyl)porphyrinato)(phe-
noxy)iridium(III) [Ir(ttp)OPh] (5). Ir(ttp)Cl(CO) (50 mg, 0.054
mmol), NaOPh (12.5 mg, 0.11 mmol), and benzene (2.0 mL) were
degassed for three freeze–thaw-pump cycles in a Teflon screw-
capped tube. The reaction mixture was covered by aluminum foil
and heated at 150 °C under N2 for 12 h. The solvent was then
removed under vacuum, and the reddish orange residue was purified
by column chromatography over silica gel (70-230 mesh), eluting
with CHCl3. The major reddish orange fraction was collected to
give 5 (44.4 mg, 0.047 mmol, 86%). Rf ) 0.30 (CHCl3). 1H NMR
(CDCl3, 300 MHz) δ 1.89 (d, 2 H, J ) 8.1 Hz, H29,30), 2.79 (s, 12
H, H25–28), 5.66 (t, 2 H, J ) 7.8 Hz, H31,32), 5.83 (t, 1 H, J ) 7.2
Hz, H33), 7.65 (d, 8 H, J ) 7.8 Hz, H17–24), 8.14 (d, 4 H, J ) 8.1
Hz, H1–8), 8.20 (d, 4 H, J ) 8.1 Hz, H9,11,13,15), 8.99 (s, 8 H,H1–8).
13C NMR (CDCl3, 75 MHz) δ 21.7, 116.2, 119.5, 122.3, 125.7,
127.5, 127.8, 131.7, 134.2, 134.6, 137.7, 138.6, 141.4, 158.6. The
determination of the molecular mass M+ of Ir(ttp)OPh by FAB or
ESI mass spectroscopy (MS) was unsuccessful, with the FABMS
only showing the metalloporphyrin peak [Ir(ttp)]+ ) 861. The
growth of a single crystal of Ir(ttp)OPh from CH2Cl2/MeOH or
CH2Cl2/hexane for X-ray diffraction crystallography was also
unsuccessful with the decomposition of Ir(ttp)OPh in the solvent.
Reaction of Ir(ttp)BF4 with Toluene: Synthesis of (5,10,15,20-
Tetrakis(p-tolyl)porphyrinato)(4-tolyl)iridium(III) [Ir(ttp)(p-tol)]
(6). Ir(ttp)BF4 [Ir(ttp)(CO)BF4/Ir(ttp)BF4 (10:1 ratio in 1H NMR)]10
(15.0 mg, 0.015 mmol) and toluene (2.0 mL) were degassed for
three freeze–thaw-pump cycles in a Teflon screw-capped tube. The
reaction mixture was covered by aluminum foil and heated at 200
°C under N2 for 2 h. The solvent was then removed under vacuum,
and the reddish brown residue was purified by column chroma-
tography over alumina (70-230 mesh), eluting with a solvent
mixture of CH2Cl2 and hexane (1:1). The major orange fraction
was collected to give 6 (3.6 mg, 0.004 mmol, 26%). Rf ) 0.40
(1:1 hexane/CH2Cl2). 1H NMR (CDCl3, 300 MHz) δ 0.47 (d, 2 H,
J ) 8.4 Hz), 1.10 (s, 3 H), 2.68 (s, 12 H, H25–28), 4.56 (d, 2 H, J
Addition of 20 Equiv of Cs2CO3. Ir(ttp)Cl(CO) (20.0 mg, 0.022
mmol), Cs2CO3 (140 mg, 0.43 mmol), and toluene (2.0 mL) were
degassed for three freeze–thaw-pump cycles in a Teflon screw-

3052 Organometallics, Vol. 27, No. 13, 2008
Cheung and Chan
capped tube. The reaction mixture was covered by aluminum foil
and heated at 200 °C under N2 for 1 h to give 2b (7.7 mg, 0.008
mmol, 37%) and Ir(ttp)Me (0.8 mg, 0.0009 mmol, 4%).
for three freeze–thaw-pump cycles in a Teflon screw-capped tube.
The reaction mixture was covered by aluminum foil and heated at
200 °C under N2 for 9 days. The solvent was then removed under
vacuum, and the reddish brown residue was purified by column
chromatography over silica gel (70-230 mesh), eluting with a
solvent mixture of CH2Cl2 and hexane (1:1). The major orange
fraction was collected. Compound 2c (23.2 mg, 0.024 mmol, 75%)
was obtained.
General Procedures for the Reactions of Ir(ttp)Cl(CO)
with 4-Fluorotoluene and Various Bases. Addition of 20
Equiv of K2CO3. Ir(ttp)Cl(CO) (20.0 mg, 0.022 mmol), K2CO3
(59 mg, 0.43 mmol), and 4-fluorotoluene (2.0 mL) were degassed
for three freeze–thaw-pump cycles in a Teflon screw-capped tube.
The reaction mixture was covered by aluminum foil and heated at
200 °C under N2 for 2 h. Compound 2c (13.6 mg, 0.014 mmol,
62%) was obtained.
Addition of 20 Equiv of NaOPh. Ir(ttp)Cl(CO) (20.0 mg, 0.022
mmol), NaOPh (50.0 mg, 0.43 mmol), and 4-fluorotoluene (2.0 mL)
were degassed for three freeze–thaw-pump cycles in a Teflon
screw-capped tube. The reaction mixture was covered by aluminum
foil and heated at 200 °C under N2 for 12 h. Compound 2c (16.6
mg, 0.017 mmol, 78%) was obtained.
Reaction of Ir(ttp)Cl(CO) with 4-Nitrotoluene. Ir(ttp)Cl(CO)
(30.0 mg, 0.032 mmol) and 4-nitrotoluene (2.0 mL) were degassed
for three freeze–thaw-pump cycles in a Teflon screw-capped tube.
The reaction mixture was covered by aluminum foil and heated at
200 °C under N2 for 1 day. Decomposition of Ir(ttp)Cl(CO) resulted.
Addition of 10 Equiv of K2CO3. Ir(ttp)Cl(CO) (30.0 mg, 0.032
mmol), K2CO3(45 mg, 0.32 mmol), and toluene (2.0 mL) were
degassed for three freeze–thaw-pump cycles in a Teflon screw-
capped tube. The reaction mixture was covered by aluminum foil
and heated at 150 °C under N2 for 2 days to give 2b (19.5 mg,
0.020 mmol, 63%) and Ir(ttp)Me (0.3 mg, 0.0003 mmol, 1%).
Addition of 20 Equiv of K2CO3. Ir(ttp)Cl(CO) (30.0 mg, 0.022
mmol), K2CO3(59 mg, 0.43 mmol), and toluene (2.0 mL) were
degassed for three freeze–thaw-pump cycles in a Teflon screw-
capped tube. The reaction mixture was covered by aluminum foil
and heated at selected temperatures under N2. At 150 °C, the
reaction was complete in 2 days to give 2b (18.8 mg, 0.020 mmol,
61%) and Ir(ttp)Me (0.9 mg, 0.0009 mmol, 3%). At 200 °C, the
reaction was complete in 3.5 h to give 2b (12.8 mg, 0.013 mmol,
61%) and Ir(ttp)Me (1.3 mg, 0.002 mmol, 7%).
Addition of 30 Equiv of K2CO3. Ir(ttp)Cl(CO) (30.0 mg, 0.022
mmol), K2CO3(90 mg, 0.65 mmol), and toluene (2.0 mL) were
degassed for three freeze–thaw-pump cycles in a Teflon screw-
capped tube. The reaction mixture was covered by aluminum foil
and heated at 200 °C under N2 for 2 h to give 2b (18.5 mg, 0.019
mmol, 60%) and Ir(ttp)Me (2.0 mg, 0.002 mmol, 7%).
Addition of 20 Equiv of NaOPh. Ir(ttp)Cl(CO) (20.0 mg, 0.022
mmol), NaOPh (50 mg, 0.43 mmol), and toluene (2.0 mL) were
degassed for three freeze–thaw-pump cycles in a Teflon screw-
capped tube. The reaction mixture was covered by aluminum foil
and heated at 200 °C under N2 for 2 days to give 2b (16.2 mg,
0.017 mmol, 78%).
Addition of 20 Equiv of NaF. Ir(ttp)Cl(CO) (20.0 mg, 0.022
mmol), NaF (18 mg, 0.43 mmol), and toluene (2.0 mL) were
degassed for three freeze–thaw-pump cycles in a Teflon screw-
capped tube. The reaction mixture was covered by aluminum foil
and heated at 200 °C under N2 for 6 days to give 2b (19.8 mg,
0.021 mmol, 96%).
Reaction of Ir(ttp)Cl(CO) with p-Xylene. Ir(ttp)Cl(CO) (30.0
mg, 0.032 mmol) and p-xylene (2.0 mL) were degassed for three
freeze–thaw-pump cycles in a Teflon screw-capped tube. The
reaction mixture was covered by aluminum foil and heated at
200 °C under N2 for 3.5 days. The solvent was then removed under
vacuum, and the reddish brown residue was purified by column
chromatography over alumina (70-230 mesh), eluting with a solvent
mixture of CH2Cl2 and hexane (1:1) as the eluent. The major orange
fraction was collected to give 2a (17.3 mg, 0.018 mmol, 56%).
General Procedures for the Reactions of Ir(ttp)Cl(CO)
with 4-Nitrotoluene and Various Bases. Addition of 20 Equiv
of K2CO3: Synthesis of (5,10,15,20-Tetrakis(p-tolyl)porphyri-
nato)(4-nitrobenzyl)iridium(III) [Ir(ttp)Bn(p-NO2)] (2d). Ir(ttp)-
Cl(CO) (20.0 mg, 0.022 mmol), K2CO3 (59 mg, 0.43 mmol), and
4-nitrotoluene (1.0 mL) were degassed for three freeze–thaw-pump
cycles in a Teflon screw-capped tube. The reaction mixture was
covered by aluminum foil and heated at 200 °C under N2 for 5
min. The solvent was then removed under vacuum, and the reddish
brown residue was purified by column chromatography over
alumina (70-230 mesh), eluting with a solvent mixture of CH2Cl2
and hexane (1:2). The major orange fraction was collected to give
2d (17.3 mg, 0.017 mmol, 80%). Rf ) 0.50 (1:1 CH2Cl2/hexane).
1H NMR (CDCl3, 300 MHz) δ –3.84 (s, 2 H, H29), 2.70 (s, 12 H,
H28), 3.07 (d, 2 H, J ) 7.5 Hz, H30,31), 6.70 (d, 2 H, J ) 7.5 Hz,
H
32,33), 7.52 (d, 4 H, J ) 7.3 Hz, H17,19,21,23), 7.54 (d, 4 H, J ) 7.5
Hz, H18,20,22,24), 7.91 (d, 4 H, J ) 7.3 Hz, H10,12,14,16), 7.98 (d, 4 H,
J ) 7.2 Hz,H9,11,13,15), 8.50 (s, 8 H,H1–8). 13C NMR (CDCl3, 75
MHz) δ –16.7, 21.7, 121.2, 123.9, 124.2, 127.4, 127.8, 130.6, 131.5,
133.7, 133.8, 137.5, 138.6, 143.0. HRMS (FABMS): Calcd for
[C55H42N5O2Ir]+: m/z 997.2962. Found: m/z 997.2948. The single
crystal used for X-ray diffraction crystallography was grown from
CH2Cl2/MeOH.
General Procedures for the Reactions of Ir(ttp)Cl(CO)
with p-Xylene and Various Bases. Addition of 20 Equiv of
K2CO3. Ir(ttp)Cl(CO) (20.0 mg, 0.022 mmol), K2CO3 (59 mg, 0.43
mmol),andp-xylene(2.0mL)weredegassedforthreefreeze–thaw-pump
cycles in a Teflon screw-capped tube. The reaction mixture was
covered by aluminum foil and heated at 200 °C under N2 for 1 h. The
solvent was then removed under vacuum, and the reddish brown
residue was purified by column chromatography over silica gel (70-
230 mesh), eluting with a solvent mixture of CH2Cl2 and hexane (1:
1). Compound 2a and Ir(ttp)Me with the same Rf ) 0.50 (CH2Cl2/
hexane ) 1:1) were collected in one portion, and the ratio was
determined by 1H NMR spectroscopy from the integration of the
methyl protons of the Ir-CH2Ar group of 2a and the methyl protons
of the Ir-Me group of Ir(ttp)Me. Compound 2a (8.7 mg, 0.009 mmol,
41%) and Ir(ttp)Me (0.2 mg, 0.0002 mmol, 1%) were obtained.
Addition of 20 Equiv of NaOPh. Ir(ttp)Cl(CO) (20.0 mg, 0.022
mmol), NaOPh (50.0 mg, 0.43 mmol), and p-xylene (2.0 mL) were
degassed for three freeze–thaw-pump cycles in a Teflon screw-
capped tube. The reaction mixture was covered by aluminum foil
and heated at 200 °C under N2 for 1 h. Compound 2a (14.2 mg,
0.015 mmol, 67%) was obtained.
Addition of 20 Equiv of NaOPh. Ir(ttp)Cl(CO) (20.0 mg, 0.022
mmol), NaOPh (50.0 mg, 0.43 mmol), and 4-nitrotoluene (1.0 mL)
were degassed for three freeze–thaw-pump cycles in a Teflon
screw-capped tube. The reaction mixture was covered by aluminum
foil and heated at 200 °C under N2 for 5 min. Compound 2d (9.3
mg, 0.0093 mmol, 43%) was obtained.
Reaction of Ir(ttp)H with Toluene. Ir(ttp)H (20.0 mg, 0.023
mmol) and toluene (2.0 mL) were degassed for three freeze–thaw-
–pump cycles in a Teflon screw-capped tube. The reaction mixture
was covered by aluminum foil and heated at 200 °C under N2 for 1 h.
The solvent was then removed under vacuum, and the reddish brown
residue was purified by column chromatography over alumina (70-
230 mesh), eluting with a solvent mixture of CH2Cl2 and hexane (1:
1). Compound 2b (10.5 mg, 0.011 mmol, 48%) was obtained.
Reaction of Ir(ttp)Me with Toluene. Ir(ttp)Me16 (10.0 mg,
0.011 mmol) and toluene (2.0 mL) were degassed for three
freeze–thaw-pump cycles in a Teflon screw-capped tube. The
reaction mixture was covered by aluminum foil and heated at 200
Reaction of Ir(ttp)Cl(CO) with 4-Fluorotoluene. Ir(ttp)Cl(CO)
(30.0 mg, 0.032 mmol) and 4-fluorotoluene (2.0 mL) were degassed

Base-Promoted SelectiVe ActiVation
Organometallics, Vol. 27, No. 13, 2008 3053
°C under N2 for 14 days. The solvent was then removed under
vacuum, and the reddish brown residue was purified by column
chromatography over silica gel (70-230 mesh), eluting with a
solvent mixture of CH2Cl2 and hexane (1:1). A trace of 2b was
observed in crude 1H NMR only and could not be isolated. Ir(ttp)Me
(4.6 mg, 0.005 mmol, 46%) was recovered.
0.011 mmol), Cs2CO3 (70 mg, 0.22 mmol), and Ph13CH3 (0.10 mL)
were degassed for three freeze–thaw-pump cycles in a Teflon
screw-capped NMR tube. The reaction mixture was covered by
aluminum foil and heated at 200 °C under N2 in an oil bath for
2 h. The solvent was then removed under vacuum, and the reddish
brown residue was purified by column chromatography over
alumina (70-230 mesh), eluting with a solvent mixture of CH2Cl2
and hexane (1:1). The major orange fraction was collected to give
Ir(ttp)13CH2Ph (8%, NMR yield estimated from crude 1H NMR as
it could not be isolated) and Ir(ttp)Me (1.6 mg, 0.002 mmol, 17%).
HRMS (FABMS): Calcd for [C5413CH43N4Ir]+: m/z 953.3145.
Found: m/z 953.3154.
Reduction of Ir(ttp)Cl(CO) by Ir(ttp)H with Cs2CO3. (i)
In toluene-d8. Ir(ttp)H (15.3 mg, 0.018 mmol), Ir(ttp)Cl(CO) (4.1
mg, 0.004 mmol), Cs2CO3 (29 mg, 0.089 mmol), and toluene-d8
(0.50 mL) were degassed for three freeze–thaw-pump cycles in a
Teflon screw-capped NMR tube and then flame-sealed under
vacuum. The reaction mixture was covered by aluminum foil and
heated at 150 °C in an oil bath. Ir(ttp)H was consumed after 4
days. The crude product was dried under vacuum. The products
were purified by alumina column chromatography to give Ir(ttp)Bn-
d7 (19%, 4.0 mg, 0.004 mmol) and Ir(ttp)Me (10%, 2.0 mg, 0.002
mmol). HRMS (FABMS): Calcd for [C55H36D7N4Ir]+: m/z 959.3551.
Found: m/z 959.3554.
Reaction of Ir(ttp)Me with Toluene and K2CO3. Ir(ttp)Me
(10.0 mg, 0.011 mmol), K2CO3 (32 mg, 0.23 mmol), and toluene
(2.0 mL) were degassed for three freeze–thaw-pump cycles in a
Teflon screw-capped tube. The reaction mixture was covered by
aluminum foil and heated at 200 °C under N2 for 3 days. The solvent
was then removed under vacuum, and the reddish brown residue
was purified by column chromatography over silica gel (70-230
mesh), eluting with a solvent mixture of CH2Cl2 and hexane (1:1).
A trace of 2b was observed in crude 1H NMR only and cannot be
isolated. Ir(ttp)Me (9.2 mg, 0.011 mmol, 92%) was recovered.
Reaction of Ir(ttp)(p-Tol) with Toluene. Ir(ttp)(p-Tol) (5.0 mg,
mmol) and toluene (1.0 mL) was degassed for three freeze–thaw-
–pump cycles in a Teflon screw-capped tube. The reaction mixture
was covered by aluminum foil and heated at 200 °C under N2 for
1.5 days. No Ir(ttp)Bn and only unreacted Ir(ttp)(p-Tol) were
observed by thin-layer chromatography.
Reaction of Ir(ttp)Bn with 4-Fluorotoluene. Compound 2b (5.0
mg, 0.005 mmol), 4-fluorotoluene (28.9 mg, 29 µL, 0.26 mmol), and
benzene-d6 (0.50 mL) were degassed for three freeze–thaw–pump
cycles in a Teflon screw-capped NMR tube and then flame-sealed
under vacuum. The reaction mixture was covered by aluminum foil
and heated at 200 °C in a sand bath. In the course of the reaction, the
amount of 2b was decreasing, while 2c was increasing. After 6 days,
(ii) In benzene-d6. Ir(ttp)H (7.1 mg, 0.008 mmol), Ir(ttp)Cl(CO)
(1.9 mg, 0.002 mmol), Cs2CO3 (67 mg, 0.21 mmol), and benzene-
d6 (0.50 mL) were degassed for three freeze–thaw-pump cycles
in a Teflon screw-capped NMR tube and then flame-sealed under
vacuum. The reaction mixture was covered by aluminum foil and
heated at 150 °C in an oil bath. Ir(ttp)H was consumed after 11
days. Ir(ttp)Me (10%, NMR yield) was obtained using C6D6 as the
internal standard.
1
the ratio of 2b/2c was found to be 11.5:1 as observed by H NMR
spectroscopy using the ortho-phenyl protons of IrCH2Ar in 2b and
2c. After 70 days, all 2b was consumed to give 2c (92%, NMR yield)
using benzene as the internal reference.
Reduction of Ir(ttp)Cl(CO) by Ir(ttp)H. Ir(ttp)H (16.3 mg,
0.019 mmol), Ir(ttp)Cl(CO) (4.3 mg, 0.005 mmol), and toluene-d8
(0.50 mL) were degassed for three freeze–thaw-pump cycles in a
Teflon screw-capped NMR tube and then flame-sealed under
vacuum. The reaction mixture was covered by aluminum foil and
heated at 150 °C in an oil bath. Some Ir(ttp)H remained unreacted
after 7 days. The reaction temperature was increased to 200 °C for
19 days. The crude product was dried under vacuum. The products
were purified by alumina column chromatography. Ir(ttp)Bn-d7
(23%, 5.5 mg, 0.005 mmol) and Ir(ttp)Me (5%, 1.0 mg, 0.001
mmol) were obtained. Unreacted Ir(ttp)Cl(CO) (23%, NMR yield)
and Ir(ttp)H (19%, NMR yield) were estimated from crude 1H NMR.
Reaction of Ir(ttp)Cl(CO) with H2O. Ir(ttp)Cl(CO) (9.1 mg,
0.010 mmol), H2O (17.7 µL, 0.98 mmol), and benzene (1.0 mL)
were degassed for three freeze–thaw-pump cycles in a Teflon
screw-capped tube and then flame-sealed under vacuum. The
reaction mixture was covered by aluminum foil and heated at
200 °C under N2 for 8 days. No Ir(ttp)Me was generated, and
Ir(ttp)Cl(CO) remained unreacted.
Reaction of Ir(ttp)Cl(CO) with toluene-d8 and Cs2CO3. Ir(ttp)-
Cl(CO) (9.7 mg, 0.010 mmol), toluene-d8 (53 mg, 56µL, 0.52
mmol), Cs2CO3 (68 mg, 0.21 mmol), and benzene-d6 (0.50 mL)
were degassed for three freeze–thaw-pump cycles in a Teflon
screw-capped NMR tube and then flame-sealed under vacuum. The
reaction mixture was covered by aluminum foil and heated at 150
°C in an oil bath. All Ir(ttp)Cl(CO) was consumed, and Ir(ttp)H
(38%, NMR yield) and [Ir(ttp)]2 (41%, NMR yield) were obtained
after 1 h. All Ir(ttp)H was consumed in 14 days to yield Ir(ttp)Bn-
d7 (42%, NMR yield) and Ir(ttp)Me (34%, NMR yield) using
residual protons of benzene as the internal reference.
Reaction of Ir(ttp)Bn with Toluene-d8 and K2CO3. Compound
2b (6.1 mg, 0.006 mmol), toluene-d8 (32.1 mg, 34 µL, 0.32 mmol),
K2CO3 (18 mg, 0.13 mmol), and benzene-d6 (0.60 mL) were degassed
for three freeze–thaw-pump cycles in a Teflon screw-capped NMR
tube and then flame-sealed under vacuum. The reaction mixture was
covered by aluminum foil and heated at 200 °C in a sand bath. In the
course of the reaction, the amount of 2b was decreasing, while 2b-d7
was increasing. After 4 days, the ratio of 2b/2b-d7 was found to be
1
26.8:1 observed by H NMR spectroscopy (integration of benzylic
proton ) 2.000, the integration of pyrrole signal was set as 8.29). After
14 days, the ratio of 2b/2b-d7 was found to be 3.57:1 as measured by
FABMS. The recovery yield of 2b was 74% (NMR yield), and the
yield of 2b-d7 was 21% (NMR yield) using benzene as the internal
reference. The amount of toluene was increasing in the course of
reaction indicated by the increased intensity of methyl protons of
toluene at 2.70 ppm.
Reaction of Ir(ttp)Cl(CO) with p-Xylene in C6D6. Ir(ttp)Cl(CO)
(5.8 mg, 0.006 mmol), p-xylene (66.6 mg, 77 µL, 0.63 mmol), and
benzene-d6 (0.50 mL) were degassed for three freeze–thaw-pump
cycles in a Teflon screw-capped NMR tube and then flame-sealed
under vacuum. The reaction mixture was covered by aluminum
foil and heated at 200 °C in a sand bath. In the course of the
reaction, the amount of Ir(ttp)Cl(CO) was decreasing, while 2a was
increasing. After 22 days, 2a (47%, NMR yield) and unreacted
Ir(ttp)Cl(CO) (31%, NMR yield) were observed using the methyl
protons of p-xylene as the reference.
Reaction of Ir(ttp)Cl(CO) with Ph13CH3 and Cs2CO3. Ir(t-
tp)Cl(CO) (5.8 mg, 0.006 mmol), Ph13CH3 (29 mg, 33 µL, 0.31
mmol), Cs2CO3 (41 mg, 0.13 mmol), and benzene-d6 (0.50 mL)
were degassed for three freeze–thaw-pump cycles in a Teflon
screw-capped NMR tube and then flame-sealed under vacuum. The
reaction mixture was covered by aluminum foil and heated at
150 °C in an oil bath. Ir(ttp)H (81%, NMR yield) was observed as
an only intermediate in 30 min. Besides, Ir(ttp)Cl(CO) (10.0 mg,
Reaction of Ir(ttp)D with H2O and Cs2CO3. Ir(ttp)D (3.7 mg,
0.004 mmol), H2O (3.9 mg, 3.9µL, 0.21 mmol), Cs2CO3 (56 mg,
0.17 mmol), and benzene-d6 (0.50 mL) were degassed for three
freeze–thaw-pump cycles in a Teflon screw-capped NMR tube
and then flame-sealed under vacuum. The reaction mixture was

3054 Organometallics, Vol. 27, No. 13, 2008
Cheung and Chan
covered by aluminum foil and heated at 150 °C in an oil bath. All
Ir(ttp)D was consumed to yield Ir(ttp)H (43%, NMR yield) after
13 h using residual protons of benzene as the internal reference.
Reaction of Ir(ttp)H with D2O and Cs2CO3. Ir(ttp)H (3.2 mg,
0.004 mmol), D2O (3.7 mg, 3.3µL, 0.19 mmol), Cs2CO3 (48 mg,
0.15 mmol), and benzene-d6 (0.50 mL) were degassed for three
freeze–thaw-pump cycles in a Teflon screw-capped NMR tube
and then flame-sealed under vacuum. The reaction mixture was
covered by aluminum foil and heated at 150 °C in an oil bath. All
Ir(ttp)H was consumed to yield Ir(ttp)D (20%, NMR yield) after
36 h using residual protons of benzene as the internal reference.
Addition of 20 Equiv of Na2CO3. Ir(ttp)Cl(CO) (20.0 mg,
0.022 mmol), Na2CO3 (46 mg, 0.43 mmol), and toluene (2.0 mL)
were degassed for three freeze–thaw-pump cycles in a Teflon
screw-capped tube. The reaction mixture was covered by aluminum
foil and heated at 150 °C under N2 for 10 days to give 2b (16.2
mg, 0.017 mmol, 79%) and Ir(ttp)Me (1.9 mg, 0.002 mmol, 10%).
Addition of 20 Equiv of K2CO3. Ir(ttp)Cl(CO) (20.0 mg, 0.022
mmol), K2CO3 (60 mg, 0.43 mmol), and toluene (2.0 mL) were
degassed for three freeze–thaw-pump cycles in a Teflon screw-
capped tube. The reaction mixture was covered by aluminum foil
and heated at 150 °C under N2 for 2 days to give 2b (13.6 mg,
0.014 mmol, 66%) and Ir(ttp)Me (0.6 mg, 0.0006 mmol, 3%).
Addition of 20 Equiv of Cs2CO3. Ir(ttp)Cl(CO) (20.0 mg, 0.022
mmol), Cs2CO3 (141 mg, 0.43 mmol), and toluene (2.0 mL) were
degassed for three freeze–thaw-pump cycles in a Teflon screw-
capped tube. The reaction mixture was covered by aluminum foil
and heated at 150 °C under N2 for 1 h to give 2b (9.5 mg, 0.010
mmol, 46%) and Ir(ttp)Me (6.6 mg, 0.008 mmol, 35%).
Dehydrogentative Dimerization of Ir(ttp)H. Ir(ttp)H (4.1 mg,
0.005 mmol) and benzene-d6 (0.50 mL) were degassed for three
freeze–thaw-pump cycles in a Teflon screw-capped NMR tube
and then flame-sealed under vacuum. The reaction mixture was
covered by aluminum foil and heated at 150 °C in an oil bath.
[Ir(ttp)]2 (78%, NMR yield) was obtained after 90 min using
residual protons of benzene as the internal reference.
Reaction of [Ir(ttp)]2 with Toluene. Ir(ttp)H (19.9 mg, 0.023
mmol), TEMPO (5.0 mg, 0.032 mmol), and benzene (0.50 mL)
were stirred in a Telfon screw-capped tube for 30 min under N2 to
prepare [Ir(ttp)]2 in situ. Benzene and unreacted TEMPO were then
removed under vacuum overnight. Toluene (1.0 mL) was added to
the tube, and the reaction mixture was degassed for three
freeze–thaw-pump cycles. The reaction mixture was covered by
aluminum foil and heated at 200 °C for 90 min. Excess toluene
was removed under vaccum. The brown residue was purified by
column chromatography using CH2Cl2/hexane (1:2) as an eluent.
Ir(ttp)Bn (10.0 mg, 0.11 mmol, 46%) was obtained.
Reaction of Ir(ttp)Cl(CO) with toluene-d8, D2O, and
Cs2CO3. (i) D2O (20 Equiv). Ir(ttp)Cl(CO) (15.1 mg, 0.019 mmol),
toluene-d8 (1.0 mL), D2O (3.3 mg, 3.0µL, 0.16 mmol), and
Cs2CO3(106 mg, 0.33 mmol) were degassed for three freeze–thaw-
–pump cycles in a Teflon screw-capped tube. The reaction mixture
was covered by aluminum foil and heated at 150 °C under N2 for
3 h. The solvent was then removed under vacuum, and the reddish
brown residue was purified by column chromatography over
alumina (70-230 mesh), eluting with a solvent mixture of CH2Cl2
and hexane (1:2). Ir(ttp)Bn-d7 (5.1 mg, 0.005 mmol, 33%) and a
mixture of Ir(ttp)Me and Ir(ttp)CD3 (4.9 mg, 0.006 mmol, 34%)
were obtained. The ratio of Ir(ttp)Me/Ir(ttp)CD3 was found to be
5.45:1 (methyl proton from Ir(ttp)Me ) 2.535, the integration of
pyrrole signal from both Ir(ttp)Me and Ir(ttp)CD3 was set as 8.000).
(ii) D2O (50 Equiv). Ir(ttp)Cl(CO) (14.5 mg, 0.016 mmol),
toluene-d8 (1.0 mL), D2O (15.7 mg, 16 µL, 0.78 mmol), and
Cs2CO3(102 mg, 0.31 mmol) were degassed for three freeze–thaw-
–pump cycles in a Teflon screw-capped tube. The reaction mixture
was covered by aluminum foil and heated at 150 °C under N2 for
3 h. The solvent was then removed under vacuum, and the reddish
brown residue was purified by column chromatography over
alumina (70-230 mesh), eluting with a solvent mixture of CH2Cl2
and hexane (1:2). Ir(ttp)Bn-d7 (2.1 mg, 0.002 mmol, 14%) and a
mixture of Ir(ttp)Me and Ir(ttp)CD3 (3.8 mg, 0.004 mmol, 27%)
were obtained. The ratio of Ir(ttp)Me:Ir(ttp)CD3 was found to be
2.54:1 (methyl proton from Ir(ttp)Me ) 2.153; the integration of
pyrrole signal from both Ir(ttp)Me and Ir(ttp)CD3 was set as 8.000).
Reaction of Ir(ttp)H with toluene (50 Equiv) and Cs2CO3.
Ir(ttp)H (4.4 mg, 0.005 mmol), toluene (23.5 mg, 27 µL, 0.26
mmol), Cs2CO3 (33 mg, 0.10 mmol), and benzene-d6 (0.50 mL)
were degassed for three freeze–thaw-pump cycles in a Teflon
screw-capped NMR tube and then flame-sealed under vacuum. The
reaction mixture was covered by aluminum foil and heated at 150 °C
in an oil bath. Ir(ttp)H (2%, NMR yield) and [Ir(ttp)]2 (89%, NMR
yield), and Ir(ttp)Bn (4%, NMR yield) were obtained after 30 min
using residual protons of benzene as the internal reference. The reaction
was complete in 6 days to yield Ir(ttp)Bn (55%, NMR yield).
Reaction of Ir(ttp)H with and toluene (50 Equiv). Ir(ttp)H
(4.2 mg, 0.005 mmol), toluene (22.5 mg, 26 µL, 0.24 mmol), and
benzene-d6 (0.50 mL) were degassed for three freeze–thaw-pump
cycles in a Teflon screw-capped NMR tube and then flame-sealed
under vacuum. The reaction mixture was covered by aluminum
foil and heated at 150 °C in an oil bath. Ir(ttp)H (5%, NMR yield),
[Ir(ttp)]2 (66%, NMR yield), and Ir(ttp)Bn (4%, NMR yield) were
obtained after 30 min using residual protons of benzene as the internal
reference. The reaction was still complete in 6 days to yield Ir(ttp)Bn
(40%, NMR yield) and unreacted Ir(ttp)H (37%, NMR yield).
Ir(ttp)Me Generation in Reaction of Ir(ttp)Cl(CO) with
Toluene. Addition of 10 Equiv of LiOH.H2O. Ir(ttp)Cl(CO) (20.0
mg, 0.022 mmol), LiOH.H2O (9.1 mg, 0.22 mmol), and toluene
(2.0 mL) were degassed for three freeze–thaw–pump cycles in
a Teflon screw-capped tube. The reaction mixture was covered
by aluminum foil and heated at 150 °C under N2 for 3 days.
The solvent was then removed under vacuum, and the reddish
brown residue was purified by column chromatography over
alumina (70-230 mesh), eluting with a solvent mixture of CH2Cl2
and hexane (1:1). Compound 2b and Ir(ttp)Me with the same Rf
) 0.50 (CH2Cl2/hexane ) 1: 1) were collected in one portion,
and the ratio was determined by 1H NMR spectroscopy from
the integration of the methyl protons of the Ir-CH2Ar group of
2b and the methyl protons of the Ir-Me group of Ir(ttp)Me.
Compound 2b (12.8 mg, 0.013 mmol, 62%) and Ir(ttp)Me (4.4
mg, 0.005 mmol, 23%) were obtained.
Addition of 10 Equiv of NaOH. Ir(ttp)Cl(CO) (20.0 mg, 0.022
mmol), NaOH (8.7 mg, 0.22 mmol), and toluene (2.0 mL) were
degassed for three freeze–thaw-pump cycles in a Teflon screw-
capped tube. The reaction mixture was covered by aluminum foil
and heated at 150 °C under N2 for 1 day to give 2b (9.1 mg, 0.010
mmol, 44%) and Ir(ttp)Me (4.0 mg, 0.005 mmol, 21%).
Addition of 10 Equiv of KOH. Ir(ttp)Cl(CO) (20.0 mg, 0.022
mmol), KOH (12.1 mg, 0.22 mmol), and toluene (2.0 mL) were
degassed for three freeze–thaw-pump cycles in a Teflon screw-
capped tube. The reaction mixture was covered by aluminum foil
and heated at 150 °C under N2 for 1 day to give 2b (5.6 mg, 0.006
mmol, 27%) and Ir(ttp)Me (4.5 mg, 0.005 mmol, 24%).
Reaction of Ir(ttp)Cl(CO) with PhCH3 and NaOPh in
C6D6. Ir(ttp)Cl(CO) (10.1 mg, 0.011 mmol), PhCH3 (100.6 mg,
116 µL, 1.09 mmol), NaOPh (25 mg, 0.11 mmol), and benzene-d6
(0.50 mL) were degassed for three freeze–thaw-pump cycles in a
Teflon screw-capped NMR tube and then flame-sealed under
vacuum. The reaction mixture was covered by aluminum foil and
heated at 200 °C in a sand bath. Ir(ttp)Cl(CO) was consumed after
2 h to give Ir(ttp)OPh (95%, NMR yield) using the methyl proton
of toluene as the internal reference.
Reaction of Ir(ttp)OPh with PhCH3 in C6D6. Ir(ttp)OPh (6.6
mg, 0.0069 mmol), PhCH3 (63.7 mg, 73.5 µL, 0.69 mmol), and

Base-Promoted SelectiVe ActiVation
Organometallics, Vol. 27, No. 13, 2008 3055
benzene-d6 (0.50 mL) were degassed for three freeze–thaw-pump
cycles in a Teflon screw-capped NMR tube and then flame-sealed
under vacuum. The reaction mixture was covered by aluminum
foil and heated at 200 °C in a sand bath. In the course of the
reaction, the amount of Ir(ttp)OPh was decreasing, while the amount
of 2b was increasing. Ir(ttp)OPh was consumed after 10 days to
yield 2b (80%, NMR yield), using methyl protons of PhCH3 as
the internal reference. No Ir(ttp)H and PhOBn were found during
the course of the reaction.
Reaction of Ir(ttp)OPh with Toluene-d8. Ir(ttp)OPh (50.0 mg,
0.052 mmol) and toluene-d8 (1.0 mL) were degassed for three
freeze–thaw-pump cycles in a Teflon screw-capped tube. The
reaction mixture was covered by aluminum foil and heated at
200 °C for 1 day. The solvent was extracted under vacuum and
trapped under liquid N2. PhOH in 31% was detected in the solvent
by GC-MS analysis using 4-tert-butylphenol as the internal standard.
Compound 2b (44.9 mg, 0.047 mmol, 90%) was obtained after
column chromatography using alumina, eluting with a mixture of
CH2Cl2/hexane (1:2).
capped tube. The reaction mixture was covered by aluminum foil
and heated at 200 °C under N2 for 1.25 h. The isotope ratio of 2b
to 2b-d7 was determined to be 2.10 (benzylic CHA, integration of
benzylic proton ) 1.354; the integration of pyrrole signal was set
1
as 8.000) by H NMR.
Competition Reactions in Base-Promoted BnCHA. Addition
of p-Xylene (100 Equiv) and Toluene (100 Equiv). Ir(ttp)Cl(CO)
(15.4 mg, 0.017 mmol), K2CO3 (46 mg, 0.33 mmol), p-xylene (177
mg, 205 µL, 1.67 mmol), toluene (154 mg, 177 µL, 1.67 mmol),
and benzene (2.0 mL) were degassed for three freeze–thaw-pump
cycles in a Teflon screw-capped tube. The reaction mixture was
covered by aluminum foil and heated at 200 °C under N2 for 6 h.
The ratio of 2a to 2b was determined to be 2.050 by 1H NMR
spectroscopy from the integration of the meta-phenyl protons of
Ir-CH2Ar group of 2a and 2b.
Addition of 4-Fluorotoluene (100 Equiv) and Toluene (100
Equiv). Ir(ttp)Cl(CO) (16.0 mg, 0.017 mmol), K2CO3 (48 mg, 0.35
mmol), p-fluorotoluene (191 mg, 191 µL, 1.73 mmol), toluene (160
mg, 184 µL, 1.73 mmol), and benzene (2.0 mL) were degassed for
three freeze–thaw-pump cycles in a Teflon screw-capped tube. The
reaction mixture was covered by aluminum foil and heated at
200 °C under N2 for 4.5 h. The ratio of 2c to 2b was determined
Isotope Effect with Ir(ttp)Cl(CO). A premixed equimolar
solvent mixture of toluene (867 mg, 1.0 mL, 9.4 mmol)/toluene-d8
(940 mg, 1.0 mL, 9.4 mmol) and Ir(ttp)Cl(CO) (30.0 mg, 0.032
mmol) were degassed for three freeze–thaw-pump cycles in a
Teflon screw-capped tube. The reaction mixture was covered by
aluminum foil and heated at 200 °C under N2 for 9 days. The isotope
ratio of 2b to 2b-d7 was determined to be 2.37 (benzylic CHA,
integration of benzylic proton ) 1.407; the integration of pyrrole
1
to be 1.303 by H NMR spectroscopy from the integration of the
meta-phenyl protons of Ir-CH2Ar groups of 2c and 2b.
Addition of 4-Nitrotoluene (100 Equiv) and Toluene (100
Equiv). Ir(ttp)Cl(CO) (15.8 mg, 0.017 mmol), K2CO3 (47 mg, 0.34
mmol), 4-nitrotoluene (234 mg, 1.71 mmol), toluene (158 mg, 182
µL, 1.71 mmol), and benzene (2.0 mL) were degassed for three
freeze–thaw-pump cycles in a Teflon screw-capped tube. The
reaction mixture was covered by aluminum foil and heated at
200 °C under N2 for 3.5 h. The ratio of 2d to 2b was determined
1
signal was set as 8.000) by H NMR. The isotope ratio was also
measured by FABMS to be 2.40.
Addition of 20 Equiv of K2CO3. A premixed equimolar solvent
mixture of toluene (867 mg, 1.0 mL, 9.4 mmol)/toluene-d8 (940
mg, 1.0 mL, 9.4 mmol), Ir(ttp)Cl(CO) (30.0 mg, 0.032 mmol), and
K2CO3 (88 mg, 0.64 mmol) was heated at 200 °C under N2 for
3.5 h. The isotope ratio of 2b to 2b-d7 was determined to be 2.16
(benzylic CHA, integration of benzylic proton ) 1.367; the
1
to be 5.067 by H NMR spectroscopy from the integration of the
meta-phenyl protons of Ir-CH2Ar groups of 2d and 2b.
X-ray Structure Determination. All single crystals were
immersed in Paraton-N oil and sealed under N2 in thin-walled glass
capillaries. Data were collected at 293 K on a Bruker SMART 1000
CCD diffractometer using Mo KR radiation. An empirical absorp-
tion correction was applied using the SADABS program.42 All
structures were solved by direct methods and subsequent Fourier
difference techniques and refined anisotropically for all nonhydro-
gen atoms by full-matrix least-squares calculations on F2 using the
SHELXTL program package.43 All hydrogen atoms were geo-
metrically fixed using the riding model. X-ray data are listed in
Table 5.
1
integration of pyrrole signal was set as 8.000) by H NMR. The
isotope ratio was also measured by FABMS to be 2.16.
Addition of 20 Equiv of NaOPh. A premixed equimolar solvent
mixture of toluene (867 mg, 1.0 mL, 9.4 mmol)/toluene-d8 (940
mg, 1.0 mL, 9.4 mmol), Ir(ttp)Cl(CO) (20.0 mg, 0.022 mmol), and
NaOPh (51 mg, 0.44 mmol) was heated at 200 °C under N2 for 2
days. The isotope ratio of 2b to 2b-d7 was determined to be 2.18
(benzylic CHA, integration of benzylic proton ) 1.389; the
1
integration of pyrrole signal was set as 8.000) by H NMR. The
isotope ratio was also measured by FABMS to be 2.18.
Isotope Effect with Ir(ttp)H. A premixed equimolar solvent
mixture of toluene (434 mg, 0.50 mL, 4.7 mmol)/toluene-d8 (470
mg, 0.50 mL, 4.7 mmol) and Ir(ttp)Cl(CO) (15.0 mg, 0.017 mmol)
was degassed for three freeze–thaw-pump cycles in a Teflon screw-
capped tube. The reaction mixture was covered by aluminum foil
and heated at 200 °C under N2 for 2 h. The isotope ratio of 2b to
2b-d7 was determined to be 2.30 (benzylic CHA, integration of
benzylic proton ) 1.407; the integration of pyrrole signal was set
Acknowledgment. We thank the Research Grants Council
of the HKSAR, China (CUHK 400105) for financial support.
Supporting Information Available: Text, tables, and figures
of crystallographic data for complexes 2a, 2d, and 2e (CIF and
1
PDF), H and 13C NMR spectra for 2a, 2c, 2d, 2e, Ir(ttp)H (4),
Ir(ttp)OPh (5), Ir(ttp)Ph(p-Me) (6), and 1H NMR spectrum for
[Ir(ttp)]2 (7). This material is available free of charge via the Internet
at http://pubs.acs.org.
1
as 8.000) by H NMR. The isotope ratio was also measured by
FABMS to be 2.13.
Isotope Effect with [Ir(ttp)]2. Ir(ttp)]2 was prepared in situ by
stirring Ir(ttp)H (20.8 mg, 0.024 mmol) and TEMPO (5.3 mg, 0.034
mmol) in benzene (1.0 mL) in a Teflon-screw capped tube for 0.5 h.
The solvent, unreacted TEMPO, and coproduct TEMPOH were
removed under vacuum overnight. A premixed equimolar solvent
mixture of toluene (434 mg, 0.50 mL, 4.7 mmol)/toluene-d8 (470
mg, 0.50 mL, 4.7 mmol) and [Ir(ttp)]2 prepared in situ were
degassed for three freeze–thaw-pump cycles in the Teflon screw-
OM700751H
(42) Sheldrick, G. M. SADABS: Program for Empirical Absorption
Correction of Area Detector Data; University of Gottingen: Gottingen,
Germany, 1996.
(43) Sheldrick, G. M. SHELXTL 5.10 for Windows NT: Structure
Determination Software Programs; Bruker Analytical X-ray Systems, Inc.:
Madison, WI, 1997.