User-friendly aerobic reductive alkylation of iridium(III) porphyrin chloride with potassium hydroxide: Scope and mechanism

Article abstract of DOI:10.1039/c5dt03845f

Alkylation of iridium 5,10,15,20-tetrakistolylporphyrinato carbonyl chloride, Ir(ttp)Cl(CO) (1), with 1°, 2° alkyl halides was achieved to give (ttp)Ir-alkyls in good yields under air and water compatible conditions by utilizing KOH as the cheap reducing agent. The reaction rate followed the order: RCl < RBr < RI (R = alkyl), and suggests an S_N2 pathway by [Ir^I(ttp)]^-. Ir(ttp)-adamantyl was obtained under N₂ when 1-bromoadamantane was utilized, which could only undergo bromine atom transfer pathway. Mechanistic investigations reveal a substrate dependent pathway of S_N2 or halogen atom transfer.

Full text of DOI:10.1039/c5dt03845f

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User-friendly aerobic reductive alkylation of
iridium(III) porphyrin chloride with potassium
Cite this: DOI: 10.1039/c5dt03845f
hydroxide: scope and mechanism†
Huiping Zuo, Zhipeng Liu, Wu Yang, Zhikuan Zhou and Kin Shing Chan*
Alkylation of iridium 5,10,15,20-tetrakistolylporphyrinato carbonyl chloride, Ir(ttp)Cl(CO) (1), with 1°, 2°
alkyl halides was achieved to give (ttp)Ir-alkyls in good yields under air and water compatible conditions
by utilizing KOH as the cheap reducing agent. The reaction rate followed the order: RCl < RBr < RI (R =
alkyl), and suggests an SN2 pathway by [IrI(ttp)]−. Ir(ttp)-adamantyl was obtained under N2 when 1-bromo-
adamantane was utilized, which could only undergo bromine atom transfer pathway. Mechanistic investi-
gations reveal a substrate dependent pathway of SN2 or halogen atom transfer.
Received 2nd October 2015,
Accepted 26th October 2015
DOI: 10.1039/c5dt03845f
www.rsc.org/dalton
development of iridium porphyrin-based bond activation is
desirable.
Introduction
Iridium porphyrin alkyls (Fig. 1) have been applied in various
Ir(por)R have been mainly synthesized by three different
chemical areas.1–3 They are efficient catalysts for strong acti- methods: (1) transmetalation; (2) nucleophilic substitution;
vation of bonds such as the N–H4 or C–H5 bond insertion with and (3) oxidative addition (Scheme 1). Initially, Ir(oep)Me was
ethyl diazoacetate. Catalytic cyclopropanation6 and lactone for-
mation7 by Ir(por)R (por = porphyrinato dianion, R = alkyls)
provide new methods of organic transformations. Besides,
Ir(oep)H (oep = octaethylporphyrinato dianion), which acts as
a precursor of [Ir(oep)]2, catalyzes the 4-electron electrochemi-
cal reduction of O2 to H2O.8–10
We have previously reported the selective carbonyl carbon
and α-carbon bond activation (CCA) of acetophenones with
Ir(por)Me11 and carbon–carbon σ-bond hydrogenation of [2.2]-
paracyclophane with water catalyzed by Ir(ttp)-alkyls.12 There-
fore, a facile synthesis of iridium porphyrin alkyls for further
Fig. 1 Ir(ttp)R (ttp = 5,10,15,20-tetrakistolylporphyrinato dianion, R =
alkyls).
Department of Chemistry, The Chinese University of Hong Kong, Shatin,
New Territories, Hong Kong SAR, People’s Republic of China. E-mail: ksc@cuhk.edu.hk
†Electronic supplementary information (ESI) available: Table, figure, 1H and 13
C
NMR spectra. CCDC 1059004 for Ir(ttp)-c-pentyl (3i), 1048812 for Ir(ttp)-n-octyl
(3e), 1048813 for Ir(ttp)-n-pentyl (3a) and 1048814 for Ir(ttp)-adamantyl (3k). For
ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c5dt03845f
Scheme 1 Synthesis of Ir(por)R (por
alkyls).
= porphyrinato dianion, R =
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synthesized from the transmetalation between Ir(oep)(CO)Cl
and MeLi in 1978 by Ogoshi.13 Nucleophilic substitution of
Ir(ttp)(CO)Cl (1) with alkyl halides was reported as the most
general synthetic route.13 However, the generation of [IrI(ttp)]−
requires a rather expensive reducing agent: NaBH4 and an
anaerobic atmosphere. In 1986, Wayland reported an oxidative
addition of alkyl C–H bond with [Ir(oep)]2 to give Ir(oep)-alkyl.14
The base-promoted benzylic C–H bond activation of toluene by
Ir(ttp)(CO)Cl with OH− acting as a reducing agent to give Ir(ttp)-
Bn with good yields was reported by Chan in 2008.15
To expand our previously reported base-promoted carbon–
halogen bond cleavage by iridium porphyrins, we have
extended the substrate from aryl halides16,17 to alkyl halides.
Herein, we report the successful reductive alkylation of Ir(ttp)-
(CO)Cl with alkyl halides to give Ir(ttp)R (R = 1°, 2°, 3° alkyl)
using cheap KOH as the reducing agent18 under user-friendly
aerobic conditions.
Table 2 Temperature effects
Entry
Temperature (°C)
Time (h)
Yielda (%)
1
2
3
4
5
20
80
120
150
120
24
5
5
3
9
0
<10
84
73
83
a Isolated yield.
of 73% was obtained at 150 °C (Table 2, entry 4). Prolonged
heating from 5 h to 9 h had no influence on the yields of 3a
(Table 2, entries 3 and 5). Therefore, 120 °C was chosen to be
the optimal temperature.
Base effects and base, alkyl halide loading effects. As the
concentration of OH− was significant in the reported reduction
of Ir(ttp)(CO)Cl (1) to the possible intermediates [IrI(ttp)]− and
metalloradical [IrII(ttp)]•,15–17 we sought to examine the base
and base loading effects. Trace amounts of 3a were obtained
with the weak base K2CO3 or without any base (Table 3, entries
1 and 2). The stronger base KOH with 5, 10 or 20 equivalents
in loadings gave 3a in high yields (Table 3, entries 3, 5 and 6).
However, a lower loading of KOH of 1.1 equivalents decreased
the yield to 10% only (Table 3, entry 4). 20 equivalents of KOH
were chosen for further reactions.
A similar trend was observed in the alkyl halide loading
effects. An excess of n-pentyl bromide (2a) (10 equiv.) provided
the highest yield. Consequently, the reaction was conducted
with 20 equivalents of KOH and 10 equivalents of 2a.
Therefore, the reaction conditions were optimized, and
shown in eqn (4):
Results and discussion
Conditions optimization
Atmosphere, water and solvent effects. Initially, when the
reaction of Ir(ttp)(CO)Cl (1) with 1-bromopentane (2a) was con-
ducted in the presence of KOH (20 equiv.) at 120 °C in C6H6
under N2 for 5 h in a sealed glass tube, Ir(ttp)-n-pentyl (3a) was
obtained in 87% yield (Table 1, entry 1). To our delight, the
same reaction under air gave nearly the same yield (Table 1,
entry 2). Therefore, the reaction is compatible with air. When
the reaction was carried out in THF, a slightly lower 76% yield
of 3a was obtained together with some other unidentified co-
products (Table 1, entry 3), likely due to the minor carbon–
carbon bond activation (CCA)19 and carbon–hydrogen bond
activation (CHA)20 of THF.
Almost the same high yields of 3a were obtained with or
without H2O. The reaction therefore tolerates water (Table 1
entries 2, 4 and 5). For convenience, no water was added for
further investigations.
Temperature effects. The effect of temperature was further
examined. At 20 °C or 80 °C, 3a was obtained in trace amounts
(Table 2, entries 1 and 2). Increase of temperature to 120 °C
for 5 h enhanced the yield of 3a to 84%. A slightly lower yield
ð4Þ
Table 3 Base effects and base, alkyl halide loading effects
Table 1 Atmosphere, solvent and water effects
Entry
Base
m (base)
k (2a)
Time (h)
Yielda (%)
1
2
3
4
5
6
7
8
None
K2CO3
KOH
KOH
KOH
KOH
KOH
KOH
20
20
20
1.1
5
10
20
20
10
10
10
10
10
10
2
24
5
5
12
12
8
0
<10
84
10
79
80
68
80
Entry
N2/air
Solvent
n (H2O)
Time (h)
Yielda (%)
1
N2
C6H6
C6H6
THF
C6H6
C6H6
0
0
0
100
200
5
5
3
5
5
87
84
76
90
91
2
Air
Air
Air
Air
3b
4
5
5
5
5
a Isolated yield. b Co-products were observed with trace yields.
a Isolated yield.
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Substrate scope
mantane (2i) by [IrI(ttp)]− was impossible, an alternative
metalloradical mediated bromine atom abstraction operates to
yield the product 3k:
The substrate scope was examined under the optimized con-
ditions. Both primary and secondary alkyl halides worked well
with good product yields obtained (Table 4). However, tertiary
alkyl halides, 1-bromoadamantane (2i) and t-butyl chloride
(5c), did not give any Ir(ttp)-alkyls even after 48 h (Table 4,
entries 13 and 16). The reaction rate of c-hexyl-X followed the
order: X = I > Br > Cl (Table 4, entries 4, 12 and 15), which is
consistent with an SN2 mechanism.21
ð6Þ
The reaction was compatible with olefinic alkyl halides
(Table 4, entries 7 and 8) and suggests that any metalloradical
species must be low enough in concentration to disfavor the
reaction with olefin, such as 1,2-addition or the 1,2-addition is
reversible at a high temperature.22 Besides, even low boiling
alkyl halides 4a and 4c gave good yields of the alkylation pro-
ducts 3b and 3d (Table 4, entries 1 and 3).
X-ray crystallographic details
The crystallographic data of 3a, 3e, 3i·CH2Cl2 and 3k (Fig. 2–5)
are presented in the ESI (Table S1 and Fig. S1†). Table 5 lists
their selected bond lengths and angles. These Ir(ttp)-alkyls are
five-coordinated complexes in a square pyramidal geometry
and the Ir–Cα bond lengths (2.057–2.154 Å) and the average
lengths of Ir–N (2.011–2.024 Å) are consistent with the reported
data of analogous Ir(ttp)R (R = CH2OMe, Bn-p-Me).15,23 The
Synthesis of 3° alkyl-Ir(ttp)
The reaction of 1-bromoadamantane (2i) with Ir(ttp)Cl(CO) (1)
was first examined under the optimal conditions at 120 °C
under air. No Ir(ttp)-adamantyl (3k) was obtained (eqn (6)).
A higher temperature can promote the thermal dissociation of
IrI2I(ttp)2 into [IrII(ttp)]• metalloradical species20 to facilitate
metalloradical mediated halogen atom transfer. However, no
3k was obtained at 150 °C under air (eqn (6)). Due to the high
air sensitivity of [IrII(ttp)]• metalloradical species, this reaction
was then attempted at 150 °C under N2. To our delight, Ir(ttp)-
adamantyl (3k) was finally obtained in 45% yield (eqn (6)). To
the best of our knowledge, this is the first synthesis of a ter-
tiary alkyl-Ir(por). Since SN2 backside attack of 1-bromoada-
Table 4 Substrate scope
Fig. 2 ORTEP presentation of the molecular structure with the num-
bering scheme for Ir(ttp)-n-pentyl (3a) with hydrogen atoms omitted for
clarity (50% probability displacement ellipsoids). 3a selected bond
lengths (Å): Ir(1)–C(61): 2.057(5); Ir(1)–N(1): 2.014(4); Ir(1)–N(2): 2.005(4);
Ir(1)–N(3): 2.009(4); Ir(1)–N(4): 2.015(4). Bond angles (°): Ir(1)–C(61)–
C(62): 116.7(4).
Entry
R–X
Time (h)
Ir(ttp)R
Yielda (%)
1
2
3
4
5
6
7
8
Me–I (4a)
24
2
3
3
5
5
5
5
5
5
5
5
48
24
24
48
3b
3c
3d
3j
3a
3e
3f
3g
3h
3d
3i
67
81
80
76
84
89
89
82
73b
61
85
78
0
n-C4H7–I (4b)
iPr–I (4c)
c-C6H11–I (4d)
n-C5H11–Br (2a)
n-C8H17–Br (2b)
7-Bromo-1-heptene (2c)
6-Bromo-1-hexene (2d)
Bn–Br (2e)
9
10
11
12
13
14
15
16
iPr–Br (2f)
c-C5H9–Br (2g)
c-C6H11–Br (2h)
1-Bromoadamantane (2i)
n-C8H17–Cl (5a)
c-C6H11–Cl (5b)
tBu–Cl (5c)
3j
3k
3e
3j
Fig. 3 ORTEP presentation of the molecular structure with the num-
bering scheme for Ir(ttp)-n-octyl (3e) with hydrogen atoms omitted for
clarity (50% probability displacement ellipsoids). 3e selected bond
lengths (Å): Ir(1)–C(61): 2.066(3); Ir(1)–N(1): 2.019(2); Ir(1)–N(2): 2.026(2);
Ir(1)–N(3): 2.015(2); Ir(1)–N(4): 2.025(2). Bond angles (°): Ir(1)–C(61)–
C(62): 119.2(3).
80
82
0
3l
a Isolated yields. b 73% NMR yield, 52% isolated yield due to partial
decomposition during purification by column chromatography.
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Mechanistic discussion
Based on our previously reported mechanism on the base-pro-
moted cleavage of aryl halides with Ir(ttp)(CO)Cl (1)16,17 and
recently reported base-promoted alkylation of rhodium por-
phyrins,25 Scheme 2 depicts the proposed reaction mechanism
of the alkylation reaction. Initially, Ir(ttp)(CO)Cl (1) undergoes
ligand substitution by KOH to form IrIII(ttp)OH (1a). Reductive
elimination of 1a gives H2O2 and IrI2I(ttp)2 (1b), which is in
equilibrium with the monomer: [IrII(ttp)]• (1b′).23,26 OH− is
therefore a reducing agent. The dimer 1b is further reduced by
OH− to give [IrI(ttp)]− (1c).16,17 [IrI(ttp)]− (1c) then undergoes
an SN2 reaction with alkyl halide to give Ir(ttp)-alkyl (pathway
A). Alternatively, [IrII(ttp)]• can undergo halogen atom abstrac-
tion from alkyl halide to give Ir(ttp)-X (X = halide) and an alkyl
radical, which attacks Ir2(ttp)2 to give Ir(ttp)-alkyl and
[IrII(ttp)]•. Thus, a radical chain mechanism results, like the
reported mechanism of the reaction between Rh2(oep)2 and
benzyl bromide (pathway B).22 Ir(ttp)-X (X = halide) recycles
back to Ir(ttp)OH by ligand substitution with OH−. Thus,
[IrI(ttp)]− (1c) and [IrII(ttp)]• (1b′) co-exist and are possible
intermediates for the alkylation of Ir(ttp)(CO)Cl (1). [IrI(ttp)]−
is likely more air compatible since it is a weak base.13 Two
Fig. 4 ORTEP presentation of the molecular structure with the num-
bering scheme for Ir(ttp)-c-pentyl (3i) with hydrogen atoms omitted for
clarity (50% probability displacement ellipsoids). 3i selected bond
lengths (Å): Ir(1)–C(61): 2.085(3); Ir(1)–N(1): 2.029(2); Ir(1)–N(2): 2.017(3);
Ir(1)–N(3): 2.023(2); Ir(1)–N(4): 2.019(3). Bond angles (°): Ir(1)–C(61)–
C(62): 106.1(2); Ir(1)–C(61)–C(65): 116.5(2).
Fig. 5 ORTEP presentation of the molecular structure with the num-
bering scheme for Ir(ttp)-adamantyl (3k) with solvent molecules and
hydrogen atoms omitted for clarity (50% probability displacement ellip-
soids). 3k selected bond lengths (Å): Ir(1)–C(61): 2.154(3); Ir(1)–N(1):
2.021(3); Ir(1)–N(2): 2.030(2); Ir(1)–N(3): 2.025(3); Ir(1)–N(4): 2.020(3).
Bond angles (°): Ir(1)–C(61)–C(62): 109.6(2); Ir(1)–C(61)–C(63): 110.3(2);
Ir(1)–C(61)–C(64): 111.4(2).
Ir–Cα bond length of Ir(ttp)-adamantyl (3k) (2.154 Å) is similar
to that of Ir(ttp)Ph (2.158 Å).24
The porphyrin planes of 3a, 3e, 3i·CH2Cl2 and 3k display a
slight saddle form. All iridium atoms do not lie in the defined
deviations of a 24-atom least-squares porphyrinato plane.
Particularly, the displacement of iridium in Ir(ttp)-adamantyl
3k (Dmax = −0.1708 Å) is more towards the alkyl ligand than
the others.
Scheme 2 Proposed mechanism for the alkylation of Ir(ttp)(CO)Cl with
alkyl halides.
Table 5 Selected bond lengths (Å) and angles (°) for 3a, 3e, 3i·CH2Cl2 and 3k
Length (Å)
Anglec (°)
a
b
c
Entry
Compounds
Ir–Cα
Ir–Naver
Dmax
Ir–Cα–Cβ
Ir–Cα–C′β
Ir–Cα–C″β
1
2
3
4
3a
3e
3i
2.057(5)
2.066(3)
2.085(3)
2.154(3)
2.011(16)
2.021(8)
2.022(10)
2.024(11)
−0.0349(9)
−0.0486(6)
0.0132(6)
116.7(4)
119.2(3)
106.1(2)
109.6(2)
—
—
116.5(2)
110.3(2)
—
—
—
111.4(2)
3k
−0.1708(7)
b
a Ir–Naver represents the average of four Ir–N bond lengths. Dmax means the max deviations from the iridium atom to a 24-atom least-squares
plane, and negative values corresponds to the displacement towards the alkyl ligand. c Cα–Cβ means the bond between the first and second
carbon next to the iridium atom.
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possible mechanisms are then proposed: pathway A: SN2 via side bromine atom abstraction via [IrII(ttp)]• operates to yield
[IrI(ttp)]−; pathway B: halogen atom transfer (HAT) via Ir(ttp)-adamantyl (3k).
[IrII(ttp)]•.
Since 1° and 2° alkyl halide underwent an SN2 pathway
rather than halogen atom transfer, we rationalize that
[IrI(ttp)]− is much more reactive (nucleophilic) in strongly
basic media. Any Ir2(ttp)2, with a strong Ir–Ir bond, estimated
Pathway A: SN2 via [IrI(ttp)]−
To test whether SN2 via [IrI(ttp)]− is operating, n-pentyl tosylate
(6a) was employed. The desired product Ir(ttp)(n-pentyl) (3a)
was obtained in 80% yield under the optimal conditions for
5 h (eqn (7)), and suggests an SN2 pathway via [IrI(ttp)]− in the
alkylation reaction since tosylate does not undergo homolytic
cleavage:
about 24 kcal mol−1 29 does not dissociate into [IrII(ttp)]• fast
,
and extensive enough to compete with the formation of
[IrI(ttp)]− under the strongly basic conditions. It is in contrast
with the occurrence of some extent of halogen atom transfer
for the rhodium porphyrin analogues with a weaker Rh–Rh
bond (∼16 kcal mol−1).25,29,30
For 3° alkyl halides, it undergoes base-promoted elimin-
ation by hydrodehalogenation to give an alkene like that of
tBuCl. For 1-bromoadamantane, this elimination gives a
bridge-headed olefin which is highly unfavorable. The back-
side SN2 attack by [IrI(ttp)]− is sterically impossible. [IrII(ttp)]•,
existing in equilibrium with Ir2(ttp)2, can then undergo
bromide atom abstraction to form Ir(ttp)-adamantyl (3k).
ð7Þ
Moreover, the alkylation rate followed the order: R–I > R–Br
> R–Cl (R = c-C6H11), in an established leaving group order
(Table 4, entries 4, 12 and 15), and is consistent with an
SN2 mechanism.21
To further quantify the relative reactivities of alkyl halides,
a competitive experiment was conducted. The close boiling
1-bromopentane (2a) and 1-bromocyclopentane (2g) with a
molar ratio of 1 : 1 reacted with Ir(ttp)(CO)Cl simultaneously
(eqn (8)). The ratio of 3a to 3i is 10 : 1, and is near to typical
relative SN2 rates of 16 : 1, between n-propyl and isopropyl sub-
stituted alkyl halides.21,27 The results are consistent with an
SN2 pathway:
Conclusions
In summary, a user-friendly synthesis was developed for 1°, 2°
alkyl-Ir(ttp) under the optimized conditions while the 3° alkyl-
Ir(ttp): Ir(ttp)(adamantly) (3k) was synthesized under N2 at
150 °C. Ir(ttp)R (R = 1°, 2°, 3° alkyl) were obtained in moderate
to good yields by utilizing KOH as the cheap reducing agent.
Furthermore, Ir(ttp)(5-hexenyl) (3g) was successfully syn- Mechanistic investigations suggest a substrate dependent
thesized under the optimized conditions rather than Ir(ttp) pathway of [IrI(ttp)]− mediated SN2 (1° and 2° alkyl halide) or
[IrII(ttp)]• mediated halogen atom transfer (3° alkyl halide) for
(cyclopentylmethyl) (3g′) (eqn (9)). 5-Hexenyl radical, if gener-
ated by the bromine atom abstraction via [IrII(ttp)]•, should the alkylation reaction.
have given 3g′ rapidly in view of the fast radical cyclizations.28
This rules out any bromine atom abstraction from 2d to
5-hexenyl radical which cyclizes very rapidly to give the cyclo-
Experimental section
pentamethyl radical on its way to form 3g′.
Unless otherwise specified, all reagents were purchased from
commercial suppliers and used without further purification.
Pathway B: halogen atom transfer (HAT) via [IrII(ttp)]•
The reaction of 1-bromoadamantane (2i) with Ir(ttp)Cl(CO) (1) Benzene was distilled from sodium. All reactions were pro-
at 150 °C under N2 generated the desired product: Ir(ttp)-ada- tected from light by wrapping with an aluminum foil. The
mantyl (3k) in 45% yield. For 1-bromoadamantane (2i), it reaction mixtures in Teflon screw capped pressure tubes were
cannot react by an SN2 pathway via [IrI(ttp)]− due to the heated in heat blocks on heaters and monitored by TLC until
impossible backside attack by [IrI(ttp)]−. Alternatively, front- the complete consumption of Ir(ttp)Cl(CO). Ir(ttp)Cl(CO) (1)
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was prepared according to the literature procedures.31 Hexane Methyl(5,10,15,20-tetratolylporphyrinato)iridium(III)
for chromatography was distilled from anhydrous calcium (Ir(ttp)Me) (3b)31
chloride. Thin-layer chromatography was performed on Merck
pre-coated silica gel 60 F254 plates. Silica gel (Merck, 70–230
and 230–400 mesh) was used for column chromatography in
Ir(ttp)(CO)Cl (10 mg, 0.011 mmol), KOH (12.1 mg, 0.22 mmol),
and iodomethane (15.6 mg, 0.11 mmol) were added to
benzene (1 mL). The mixture was heated at 120 °C for 24 h.
air.
Ir(ttp)Me (6.3 mg, 0.0072 mmol, 67%) was isolated. Rf = 0.70
1H NMR and proton-decoupled 13C NMR spectra were
(hexane/DCM = 1 : 1). 1H NMR (400 MHz, CDCl3): δ −6.29 (s,
recorded on a Bruker AV400 instrument at 400 and 100 MHz,
3H), 2.68 (s, 12H), 7.51 (d, J = 6.4 Hz, 8H), 8.00–8.03 (m, 8H),
8.51 (s, 8H).
respectively. Chemical shifts for 1H and 13C NMR were
reported in ppm and referenced with the residual solvent
protons in C6D6 (δ 7.15, 128.6 ppm) or in CDCl3 (δ 7.26,
77.1 ppm) as the internal standards. Coupling constants (J)
n-Butyl(5,10,15,20-tetratolylporphyrinato)iridium(III) (Ir(ttp)-
are reported in hertz (Hz). High-resolution mass spectrometry
n-butyl) (3c)
(HRMS) was performed on a Thermofinnigan MAT 95 XL
Ir(ttp)(CO)Cl (10 mg, 0.011 mmol), KOH (12.1 mg, 0.22 mmol),
and 1-iodobutane (19.8 mg, 0.11 mmol) were added to
benzene (1 mL). The mixture was heated at 120 °C for 2 h.
Ir(ttp)-n-butyl (8.0 mg, 0.0087 mmol, 81%) was isolated. Rf =
instrument in a fast atom bombardment (FAB) mode using the
3-nitrobenzyl alcohol (NBA) matrix and CH2Cl2 as the solvent
or in an electrospray ionization (ESI) mode using MeOH/
CH2Cl2 (1/1) as the solvent.
1
0.70 (hexane/DCM = 1 : 1). H NMR (400 MHz, CDCl3): δ −5.53
(t, J = 8.2 Hz, 2H), −4.46 (quint, J = 7.6 Hz, 2H), −1.54 to 1.45
(m, 2H), −0.77 (t, J = 7.3 Hz, 3H), 2.68 (s, 12H), 7.52 (t, J =
6.5 Hz, 8H), 7.97 (d, J = 7.5 Hz, 4H), 8.03 (d, J = 7.5 Hz, 4H),
8.49 (s, 8H). 13C NMR (100 MHz, CDCl3): δ −13.2, 12.4, 18.7,
21.7, 28.9, 124.4, 127.6, 127.6, 131.4, 133.6, 134.0, 137.2, 138.9,
143.5. HRMS (FABMS): calcd for [M]+: (C52H45IrN4) m/z
918.3272, found m/z 918.3274.
General procedures for the synthesis of Ir(ttp)-alkyls
Ir(ttp)(CO)Cl (10 mg, 0.011 mmol), KOH (12.1 mg, 0.22 mmol),
and alkyl halide (0.11 mmol) were added to benzene (1 mL).
The mixture was heated at 120 °C under air. Excess benzene
was removed by rotary evaporation. The crude product was pur-
ified by pipette column chromatography (CH2Cl2 : hexane =
1 : 2) and the first dark brown band was collected.
2-Propyl(5,10,15,20-tetratolylporphyrinato)iridium(III)
(Ir(ttp)iPr) (3d)12
Conditions optimization for the synthesis of Ir(ttp)-alkyls
The optimization reactions followed the general procedures
described above with the changes of atmosphere, water
loading, solvents, temperatures, reaction times, bases, and
loadings (alkyl halide, KOH) (ESI†).
Ir(ttp)(CO)Cl (10 mg, 0.011 mmol), KOH (12.1 mg, 0.22 mmol),
and 2-iodopropane(18.3 mg, 0.11 mmol) were added to
benzene (1 mL). The mixture was heated at 120 °C for 3 h. Ir
(ttp)iPr (7.8 mg, 0.0086 mmol, 80%) was isolated. Rf = 0.79
(hexane/DCM = 1 : 1). 1H NMR (400 MHz, CDCl3): δ −5.11
Synthesis of Ir(ttp)-alkyls
3
(septet, JH–H = 6.6 Hz, 1H), −4.46 (d, J = 6.5 Hz, 6H), 2.68 (s,
The general procedures for the synthesis of Ir(ttp)-alkyls were
followed under the optimized conditions, which is 10 equiv. of
alkyl halide, with 20 equiv. of KOH at 120 °C under air con-
ditions, unless otherwise noted.
12H), 7.51 (t, J = 6.6 Hz, 8H), 8.00 (dd, J = 18.6, 7.5 Hz, 8H),
8.48 (s, 8H).
n-Octyl(5,10,15,20-tetratolylporphyrinato)iridium(III) (Ir(ttp)-
n-Pentyl(5,10,15,20-tetratolylporphyrinato)iridium(III) (Ir(ttp)-n- n-octyl) (3e)
pentyl) (3a)
Ir(ttp)(CO)Cl (10 mg, 0.011 mmol), KOH (12.1 mg, 0.22 mmol),
Ir(ttp)(CO)Cl (10 mg, 0.011 mmol), KOH (12.1 mg, 0.22 mmol), and 1-bromooctane (16.1 mg, 0.11 mmol) were added to
and 1-bromopentane (16.6 mg, 0.11 mmol) were added to benzene (1 mL). The mixture was heated at 120 °C for 5 h.
benzene (1 mL). The mixture was heated at 120 °C for 5 h. Ir(ttp)-n-octyl (9.4 mg, 0.0096 mmol, 89%) was isolated. Rf =
1
Ir(ttp)-n-pentyl (8.4 mg, 0.0091 mmol, 84%) was isolated. Rf = 0.71 (hexane/DCM = 1 : 1). H NMR (400 MHz, CDCl3): δ −5.56
1
0.76 (hexane/DCM = 1 : 1). H NMR (400 MHz, CDCl3): δ −5.55 (t, J = 8.1 Hz, 2H), −4.45 (m, 2H), −1.50 (m, 2H), −0.48 (m,
(t, J = 8.0 Hz, 2H), −4.45 (quint, J = 7.8 Hz, 2H), −1.53 (quint, 2H), 0.08 (m, 2H), 0.53 (m, 2H), 0.61 (t, J = 7.3 Hz, 3H), 0.85
J = 7.4 Hz, 2H), −0.47 to 0.41 (m, 2H), −0.21 (t, J = 7.3 Hz, 3H), (m, 2H), 2.68 (s, 12H), 7.51 (t, J = 7.0 Hz, 8H), 7.96 (d, J =
2.68 (s, 12H), 7.52 (t, J = 6.6 Hz, 8H), 7.96 (d, J = 7.4 Hz, 4H), 7.2 Hz, 4H), 8.03 (d, J = 7.6 Hz, 4H), 8.49 (s, 8H). 13C NMR
8.04 (d, J = 7.6 Hz, 4H), 8.49 (s, 8H). 13C NMR (100 MHz, (100 MHz, CDCl3): δ −12.8, 14.0, 21.7, 22.5, 25.6, 26.3, 27.6,
CDCl3): δ −12.9, 12.8, 20.8, 21.7, 26.1, 27.8, 124.3, 127.6, 127.6, 28.0, 31.4, 124.3, 127.6, 127.6, 131.4, 133.6, 134.0, 137.2, 138.9,
131.4, 133.6, 134.0, 137.2, 138.9, 143.5. HRMS (FABMS): calcd 143.5. HRMS (FABMS): calcd for [M]+ (C56H53IrN4) m/z
for [M]+ (C53H47IrN4) m/z 932.3428, found m/z 932.3434.
974.3898, found m/z 974.3896.
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6-Heptenyl(5,10,15,20-tetratolylporphyrinato)iridium(III)
(Ir(ttp)-6-heptenyl) (3f)
138.9, 143.7. HRMS (FABMS): calcd for [M]+: (C53H45IrN4) m/z
930.3272, found m/z 930.3276.
Ir(ttp)(CO)Cl (10 mg, 0.011 mmol), KOH (12.1 mg, 0.22 mmol),
and 7-bromo-1-heptene (19.1 mg, 0.11 mmol) were added to
benzene (1 mL). The mixture was heated at 120 °C for 5 h.
Ir(ttp)-6-heptenyl (9.2 mg, 0.0096 mmol, 89%) was isolated. Rf =
c-Hexyl(5,10,15,20-tetratolylporphyrinato)iridium(III) (Ir(ttp)-
c-hexyl) (3j)
Ir(ttp)(CO)Cl (10 mg, 0.011 mmol), KOH (12.1 mg, 0.22 mmol),
and 1-bromocyclohexane (17.6 mg, 0.11 mmol) were added to
benzene (1 mL). The mixture was heated at 120 °C for 5 h.
Ir(ttp)-c-hexyl (8.0 mg, 0.0084 mmol, 78%) was isolated. Rf =
1
0.84 (hexane/DCM = 1 : 1). H NMR (400 MHz, CDCl3): δ −5.57
(t, J = 8.2 Hz, 2H), −4.45 (quint, J = 8.0 Hz, 2H), −1.49 (quint, J =
7.5 Hz, 2H), −0.38 (quint, J = 7.7 Hz, 2H), 0.87 (m, 2H), 2.68 (s,
12H), 4.42 (d, J = 17.1 Hz, 1H), 4.52 (d, J = 9.3 Hz, 1H), 5.05–5.15
(m, 1H), 7.51 (t, J = 6.4 Hz, 8H), 7.96 (d, J = 7.4 Hz, 4H), 8.03 (d,
J = 6.8 Hz, 4H), 8.49 (s, 8H). 13C NMR (100 MHz, CDCl3):
δ −13.3, 21.7, 25.1, 26.1, 27.0, 32.6, 113.6, 124.3, 127.6, 127.6, 131.4,
133.6, 134.0, 137.3, 138.9, 143.5. [M]+ (C55H49IrN4) m/z 958.3585,
found m/z 958.3581.
1
0.73 (hexane/DCM = 1 : 1). H NMR (400 MHz, CDCl3): δ −5.02
(m, 1H), −4.15 (m, 4H), −1.15 (qt, J = 12.8, 3.3 Hz, 2H), −0.90
(qt, J = 12.8, 3.4 Hz, 1H), −0.62 (d, J = 13.5 Hz, 2H), −0.02 (d,
J = 12.7 Hz, 1H), 2.68 (s, 12H), 7.51 (m, 8H), 8.00 (m, 8H), 8.47
(s, 8H). 13C NMR (100 MHz, CDCl3): δ 9.1, 21.7, 25.2, 25.4,
32.1, 124.9, 127.5, 127.6, 131.4, 133.5, 134.1, 137.2, 138.9,
143.7. HRMS (FABMS): calcd for [M]+ (C54H47IrN4) m/z
944.3428, found m/z 944.3423.
5-Hexenyl(5,10,15,20-tetratolylporphyrinato)iridium(III) (Ir(ttp)-
5-hexenyl) (3g)
Adamantyl(5,10,15,20-tetratolylporphyrinato)iridium(III)
(Ir(ttp)-adamantyl) (3k)
Ir(ttp)(CO)Cl (10 mg, 0.011 mmol), KOH (12.1 mg, 0.22 mmol),
and 6-bromo-1-hexene (17.6 mg, 0.11 mmol) were added to
benzene (1 mL). The mixture was heated at 120 °C for 5 h.
Ir(ttp)-5-hexenyl (8.4 mg, 0.0089 mmol, 82%) was isolated. Rf =
Ir(ttp)(CO)Cl (10 mg, 0.011 mmol), KOH (12.1 mg, 0.22 mmol),
and 1-bromoadamantane (23.2 mg, 0.11 mmol) were added to
benzene (1 mL). The mixture was heated at 120 °C or 150 °C
under air for 5 h. No Ir(ttp)-adamantyl was obtained.
1
0.83 (hexane/DCM = 1 : 1). H NMR (400 MHz, CDCl3): δ −5.56
(t, J = 8.1 Hz, 2H), −4.44 (quint, J = 8.0 Hz, 2H), −1.44 (quint,
J = 7.4 Hz, 2H), 0.28 (q, J = 7.1 Hz, 2H), 2.68 (s, 12H), 4.07 (d,
J = 17.2 Hz, 1H), 4.35 (d, J = 10.1 Hz, 1H), 4.61–4.72 (m, 1H),
7.51 (t, J = 6.1 Hz, 8H), 7.97 (d, J = 7.3 Hz, 4H), 8.03 (d, J =
7.1 Hz, 4H), 8.49 (s, 8H). 13C NMR (100 MHz, CDCl3): δ −13.5,
21.7, 24.7, 25.8, 31.9, 113.3, 121.7, 124.3, 127.6, 127.6, 131.4,
133.6, 134.0, 137.3, 138.1, 138.9, 143.5. HRMS (ESIMS): calcd
for [M]+ (C54H47IrN4) m/z 944.3428, found m/z 944.3425.
Ir(ttp)(CO)Cl (10 mg, 0.011 mmol), KOH (12.1 mg,
0.22 mmol), and 1-bromoadamantane (23.2 mg, 0.11 mmol)
were added to benzene (1 mL). The mixture was degassed for
three freeze–pump–thaw cycles, then filled with N2, heated at
150 °C for 5 h. Ir(ttp)-adamantyl (4.9 mg, 0.0049 mmol, 45%)
was isolated. Rf = 0.83 (hexane/DCM = 1 : 1). 1H NMR
(400 MHz, CDCl3): δ −3.55 (s, 6H), −0.28 (m, 6H), 0.10 (m,
3H), 2.68 (s, 12H), 7.51 (t, J = 5.6 Hz, 8H), 8.00 (m, 8H), 8.45 (s,
8H). 13C NMR (100 MHz, CDCl3): δ 19.7, 21.7, 30.2, 36.1, 44.2,
125.7, 127.5, 127.7, 131.5, 133.3, 134.2, 137.2, 139.0, 144.1.
HRMS (ESIMS): calcd for [M]+ (C58H51IrN4) m/z 996.3742,
found m/z 995.3748.
Benzyl(5,10,15,20-tetratolylporphyrinato)iridium(III) (Ir(ttp)-
benzyl) (3h)31
Ir(ttp)(CO)Cl (10 mg, 0.011 mmol), KOH (12.1 mg, 0.22 mmol),
and benzyl bromide (18.8 mg, 0.11 mmol) were added to
benzene (1 mL). The mixture was heated at 120 °C for 5 h.
Ir(ttp)-benzyl (5.4 mg, 0.0057 mmol, 52%) was isolated. Rf =
Reaction between n-pentyl tosylate and Ir(ttp)(CO)Cl
Ir(ttp)(CO)Cl (10 mg, 0.011 mmol), KOH (12.1 mg, 0.22 mmol),
and n-pentyl tosylate (6a; 26.1 mg, 0.11 mmol) were added to
benzene (1 mL). The mixture was heated at 120 °C for 5 h.
(ttp)-n-pentyl (3a; 8.5 mg, 0.0092 mmol, 80%) was isolated.
1
0.72 (hexane/DCM = 1 : 1). H NMR (400 MHz, CDCl3): δ −4.00
(s, 2H), 2.69 (s, 12H), 3.15 (d, J = 7.2 Hz, 2H), 5.90 (t, J = 7.6 Hz,
2H), 6.46 (t, J = 7.3 Hz, 1H), 7.53 (t, J = 6.4 Hz, 8H), 7.97 (d, J =
4.2 Hz, 4H), 8.01 (d, J = 4.3 Hz, 4H), 8.46 (s, 8H).
Competition reactions of 1-bromopentane (2a) and
1-bromocyclopentane (2g)
c-Pentyl(5,10,15,20-tetratolylporphyrinato)iridium(III) (Ir(ttp)-c-
pentyl) (3i)
Ir(ttp)(CO)Cl (5 mg, 0.0054 mmol), KOH (6.0 mg, 0.11 mmol),
2a (10 equiv.), and 2g (10 equiv.) were added to C6H6 (0.5 mL).
Ir(ttp)(CO)Cl (10 mg, 0.011 mmol), KOH (12.1 mg, 0.22 mmol), The mixture was heated at 120 °C for 24 h. After the starting
and 1-bromocyclopentane (16.1 mg, 0.11 mmol) were added to materials were completely consumed, the reaction was stopped
1
benzene (1 mL). The mixture was heated at 120 °C for 5 h. and tested by H NMR spectroscopy. The ratio was calculated
Ir(ttp)-c-pentyl (8.5 mg, 0.0092 mmol, 85%) was isolated. Rf = by the integration of 1H NMR spectrum. The crude product
1
0.72 (hexane/DCM = 1 : 1). H NMR (400 MHz, CDCl3): δ −5.25 was then purified by pipette column chromatography (CH2Cl2 :
(m, 1H), −4.85 (m, 2H), −3.43 (m, 2H), −0.91 (m, 4H), 2.68 (s, hexane = 1 : 3) and the first dark brown band was collected.
12H), 7.51 (t, J = 6.6 Hz, 8H), 7.97 (d, J = 7.3 Hz, 4H), 8.02 (d, The total isolated yield was 83%. The calculated yields by the
J = 7.4 Hz, 4H), 8.49 (s, 8H). 13C NMR (100 MHz, CDCl3): δ 3.6, integration of 1H NMR of 3a and 3i were 75% and 8%,
17.8, 21.7, 28.4, 124.7, 127.5, 127.6, 133.5, 131.4, 134.0, 137.2, respectively.
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14 K. J. Del Rossi and B. B. Wayland, J. Chem. Soc., Chem.
Commun., 1986, 1653–1655.
Acknowledgements
We thank the General Research Fund (no. 14300214) of 15 C. W. Cheung and K. S. Chan, Organometallics, 2008, 27,
Research Grants Council of HKSAR and Hong Kong PhD
Fellowship (WY) for financial support.
3043–3055.
16 C. W. Cheung and K. S. Chan, Organometallics, 2011, 30,
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17 Y. Y. Qian, B. Z. Li and K. S. Chan, Organometallics, 2013,
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20 Y. W. Chan and K. S. Chan, Organometallics, 2008, 27,
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