Reactivity studies of iridiuni(III) porphyrins with methanol in alkaline media

Article abstract of DOI:10.1021/om9008668

Ir(ttp)Cl(CO) (la; ttp = 5,10,15,20-tetrakis(p-tolyl)porphyrinato dianion) was found to cleave the C-O bond of CH₃OH at 200 C to give Ir(ttp)CH₃ (3a). Addition of KOH promoted the reaction rate and gave a higher yield of Ir(ttp)CH₃ in 70% yield in 1 day. Mechanistic studies suggest that, in the absence of KOH, Ir(ttp)Cl(CO) reacts with CH ₃OH initially to give Ir(ttp)OCH₃, which then undergoes β elimination to produce Ir(ttp)H (4a). Ir(ttp)H further reacts slowly to cleave the C-O bond of CH₃OH, likely via cr-bond metathesis, to give Ir(ttp)CH₃. In the presence of KOH, Ir(ttp)Cl(CO) initially reacts with KOH more rapidly to give Ir(ttp)OH, which then cleaves the 0-H bond of CH₃OH by metathesis to give Ir(ttp)OCH₃. Ir(ttp)OCH ₃ further isomerizes via /3-hydride elimination/reinsertion to give Ir(Up)CH₂OH and concurrently undergoes base-assisted /3-proton elimination to give Ir(ttp)-K+ (5a). Ir(ttp)CH.20H subsequently condenses with CH₃OH to form. Ir(Up)CH₂OCH₃ (2). Finally, Ir(ttp)-K+ cleaves the C-O bond in CH₃OH, most probably via nucleophilic substitution, to give Ir(ttp)CH₃. Ir(ttp)CH ₂OCH₃ also serves as the precursor of Ir(ttp)-K+ as it undergoes nucleophilic substitution by KOH to give Ir(ttp)-K+.

Full text of DOI:10.1021/om9008668

Organometallics 2010, 29, 1343–1354 1343
DOI: 10.1021/om9008668
Reactivity Studies of Iridium(III) Porphyrins with Methanol in
Alkaline Media
Chi Wai Cheung, Hong Sang Fung, Siu Yin Lee, Ying Ying Qian, Yun Wai Chan,
and Kin Shing Chan*
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong,
People’s Republic of China
Received October 6, 2009
Ir(ttp)Cl(CO) (1a; ttp = 5,10,15,20-tetrakis(p-tolyl)porphyrinato dianion) was found to cleave the
C-O bond of CH3OH at 200 °C to give Ir(ttp)CH3 (3a). Addition of KOH promoted the reaction
rate and gave a higher yield of Ir(ttp)CH3 in 70% yield in 1 day. Mechanistic studies suggest that, in
the absence of KOH, Ir(ttp)Cl(CO) reacts with CH3OH initially to give Ir(ttp)OCH3, which then
undergoes β-hydride elimination to produce Ir(ttp)H (4a). Ir(ttp)H further reacts slowly to cleave the
C-O bond of CH3OH, likely via σ-bond metathesis, to give Ir(ttp)CH3. In the presence of KOH,
Ir(ttp)Cl(CO) initially reacts with KOH more rapidly to give Ir(ttp)OH, which then cleaves the O-H
bond of CH3OH by metathesis to give Ir(ttp)OCH3. Ir(ttp)OCH3 further isomerizes via β-hydride
elimination/reinsertion to give Ir(ttp)CH2OH and concurrently undergoes base-assisted β-proton
elimination to give Ir(ttp)-Kþ (5a). Ir(ttp)CH2OH subsequently condenses with CH3OH to form
Ir(ttp)CH2OCH3 (2). Finally, Ir(ttp)-Kþ cleaves the C-O bond in CH3OH, most probably via
nucleophilic substitution, to give Ir(ttp)CH3. Ir(ttp)CH2OCH3 also serves as the precursor of
Ir(ttp)-Kþ as it undergoes nucleophilic substitution by KOH to give Ir(ttp)-Kþ.
Introduction
base complexes6 and porphyrins,7 have also been reported to
catalyze the aerobic oxidations of secondary alcohols to
generate the corresponding ketones. KOH can promote the
oxidation of alcohols to ketones when cobalt(II) phtha-
locyanine catalyst is used.8
One unique alcohol being investigated is methanol, as
intensive research efforts have been devoted to its catalytic
synthesis from methane.9 The stoichiometric C-H and
O-H bond cleavages of methanol have been reported with
macrocyclic rhodium(II) tetrakis(mesityl)porphyrin radical
(Rh(tmp)).10 Rh(tmp) is shown to cleave the C-H bond of
methanol to give Rh(tmp)CH2OH and Rh(tmp)H in ben-
zene or the O-H bond to give Rh(tmp)OCH3 and Rh(tmp)H
in a higher concentration of methanol in benzene.
Alcohols can in principle react with group 9 transition-
metal complexes with C-H, O-H, and C-O bond cleav-
ages. The catalytic C-H and O-H bond cleavage reactions
find many applications in organic syntheses.1 High-valent
nonmacrocyclic iridium(III) complexes are active catalysts
in the oxidations of primary and secondary alcohols to
produce aldehydes and ketones,2 N-alkylation of amines
with alcohols,3 and transfer hydrogenation of unsaturated
organic compounds.4 Alkoxy iridium(III) complexes are
proposed to be the intermediates.2 Inorganic bases have been
shown to further promote the oxidation of alcohols.2b-d,4a,b,5
Group 9 macrocyclic complexes, such as cobalt(II) Schiff
Despite the reported examples of group 9 transition-metal-
mediated C-O bond cleavages of ethers,11 esters,12 acetals,13
*To whom correspondence should be addressed. E-mail: ksc@
cuhk.edu.hk.
(1) Fujita, K.; Yamaguchi, R. Synlett 2005, 4, 560–571.
(2) (a) Fujita, K.; Furukawa, S.; Yamaguchi, R. J. Organomet. Chem.
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2002, 4, 2691–2694. (c) Hanasaka, F.; Fujita, K.; Yamaguchi, R. Organo-
(8) Sharma, V. B.; Jain, S. L.; Sain, B. Tetrahedron Lett. 2003, 44,
383–386.
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Chem. Soc. 1979, 101, 1032–1033. (b) Periana, R. A.; Taube, D. J.; Gamble,
S.; Taube, H.; Satoh, T.; Fujii, H. Science 1998, 280, 560–564. (c) Lersch, M.;
Tilset, M. Chem. Rev. 2005, 6, 2471–2526. (d) Jones, W. D. Inorg. Chem.
2005, 44, 4475–4484.
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Peris, E. Chem. Eur. J. 2008, 14, 11474–11479.
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2003, 44, 2687–2690.
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4025.
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Organometallics 1985, 4, 1504–1508. (b) Kawamoto, T.; Fujimura, Y.;
Konno, T. Chem. Lett. 2003, 32, 1058–1059. (c) Wender, P. A.; Deschamps,
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Yoshihiko, K. J. Am. Chem. Soc. 1986, 108, 385–391. (b) Sjvall, S.;
Andersson, C.; Wendt, O. F. Organometallics 2001, 20, 4919–4926.
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Chem. Commun. 2003, 1192–1193.
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4710–4712. (b) Fujita, K.; Kitatsuji, C.; Furukawa, S.; Yamaguchi, R.
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2010 American Chemical Society
Published on Web 02/15/2010
pubs.acs.org/Organometallics

1344 Organometallics, Vol. 29, No. 6, 2010
Cheung et al.
and alkyl triflates,14 the C-O bond cleavage of alcohols by
group 9 transition-metal complexes is less commonly re-
ported. To the best of our knowledge, the only example is
the iridium-catalyzed homocoupling and cross-coupling of
alcohols to give ethers with the iridium acting as the Lewis
acid.2d Transition-metal-mediated C-O bond cleavage of
methanol is an uncommon reactivity mode. A formal exam-
ple of C-O bond cleavage of methanol is the industrial
production of acetic acid by rhodium- and iridium-catalyzed
carbonylation of methanol in the Monsanto and Cativa
Processes, respectively,15 but with the prior activation of
methanol with hydroiodic acid to give methyl iodide.
In view of the successful C-H,16 Si-H,17 and C-C18 bond
activations using group 9 rhodium(III) and iridium(III)
porphyrin complexes and the recently reported C-O bond
cleavage of methanol using rhodium(III) porphyrin com-
plexes,19 we wish to explore the chemistry in the C-O bond
cleavage with iridium(III) porphyrins. We have identified the
successful base-promoted C-O bond cleavage of methanol
by high-valent iridium(III) porphyrin chloride (IrIII(ttp)Cl-
(CO), ttp = 5,10,15,20-tetrakis(p-tolyl)porphyrinato dia-
nion)20 to yield iridium(III) porphyrin methyl (IrIII(ttp)-
CH3).20a We now report the results and the mechanistic
studies.
Table 1. Base Effects on Reaction of Ir(ttp)Cl(CO) with CH3OH
base ð20 equivÞ
IrðttpÞClðCOÞ þ CH3OH
200 °C, time, N2
1a
IrðttpÞCH2OCH3 þ IrðttpÞCH3
ð1Þ
2
3a
entry
base
none
time/daysa
yield of 2/%b
yield of 3a/%b
1
2
3
4
5
6
7
8
9
5c
1
1
1
1
1
1
1
1
nil
55
57
46
62
55
43
51
57
70
NaOAc
KOAc
Na2CO3
K2CO3
Cs2CO3
K3PO4
NaOH
KOH
trace
trace
nil
trace
nil
trace
trace
nil
a All Ir(ttp)Cl(CO) was consumed. b Isolated yield. c In 1 day, Ir-
(ttp)Cl(CO) reacted with CH3OH at 200 °C to give Ir(ttp)CH3 and
Ir(ttp)H in 20% and 9% yields, respectively, with Ir(ttp)Cl(CO) recov-
ered in 37% yield.
KOAc, K2CO3, K3PO4, and NaOH also produced a trace
amount of Ir(ttp)CH2OCH3 (2)22 (Table 1, entries 2, 3, 5, 7,
and 8). The X-ray structure of Ir(ttp)CH2OCH3 is shown in
Figure 1. KOH was found to be the optimal base, as both the
reaction rate and product yield of Ir(ttp)CH3 were enhanced
(Table 1, entry 9).
Result and Discussion
Base Effect. Initially, Ir(ttp)Cl(CO) (1a) reacted with
CH3OH at 200 °C slowly in 5 days to give Ir(ttp)CH3 (3a)
in 55% yield with the cleavage of the C-O bond of CH3OH
(Table 1, eq 1, entry 1). In view of the base-promoted bond
activations with metalloporphyrins16b,c,e,17b,18c,19 and other
metal complexes,21 various base additives (Table 1, entries
2-9) were examined in the reaction of Ir(ttp)Cl(CO) with
CH3OH at 200 °C. Metal acetates, carbonates, phosphate,
and NaOH promoted the rates of reactions but had only a
slight effect on the yields (Table 1, entries 2-8). NaOAc,
The optimal amount of KOH in the C-O bond cleav-
age was then examined. KOH at 5 and 10 equiv resulted
in lower yields of Ir(ttp)CH3 (Table 2, eq 2, entries 1
and 2), whereas a higher amount of KOH at 30 equiv
did not give a higher product yield (Table 2, entry 4). Thus,
20 equiv of KOH (Table 2, entry 3) was used in further
studies.
Temperature Effect. The KOH-promoted reactions be-
tween Ir(ttp)Cl(CO) and CH3OH were studied at 150 and
200 °C. At 150 °C, Ir(ttp)Cl(CO) reacted with CH3OH and
KOH in 36 h to give Ir(ttp)CH2OCH3 in 4% yield and
Ir(ttp)CH3 in 31% yield (Table 3, eq 3, entry 1). When the
reaction temperature was increased to 200 °C, the selective
formation of Ir(ttp)CH3 in a high yield of 70% was obtained
(Table 3, entry 2). The optimal temperature was thus found
to be 200 °C.
Porphyrin Effect. The porphyrin ligand effect was also
investigated. In comparison with Ir(ttp)Cl(CO) (Table 4,
eq 4, entry 1), the more electron-rich Ir(btpp)Cl(CO) (1b,
btpp = 5,10,15,20-tetrakis(p-tert-butylphenyl)porphyrinato
dianion) (Table 4, entry 2) and the sterically more hindered
Ir(tmp)Cl(CO)23 (1c, tmp = 5,10,15,20-tetrakis(mesityl)-
porphyrinato dianion) (Table 4, entry 3) reacted with
CH3OH and KOH at 200 °C in 1 day to give Ir(btpp)CH3
(3b) and Ir(tmp)CH324 (3c) in 72% and 66% yields, respec-
tively. No significant porphyrin ligand effect on product
yield was observed. This base-promoted reaction of Ir-
(por)Cl(CO) (por = porphyrinato dianion) with CH3OH
provides a convenient synthesis of Ir(por)CH3, in contrast
with the more tedious reductive alkylation of Ir(por)Cl(CO)
using NaBH4 and MeI.20 The replacement of more toxic MeI
by CH3OH as the methylating agent also provides a green
€
(14) Nuckel, S.; Burger, P. Organometallics 2001, 20, 4345–4359.
€
(15) Thomas, C. M.; Suss-Fink, G. Coord. Chem. Rev. 2003, 243,
125–142.
(16) Aldehydic C-H bond activation of aromatic aldehydes with
Rh(ttp)Cl (ttp = 5,10,15,20-tetrakis(p-tolyl)porphyrinato dianion):
(a) Chan, K. S.; Lau, C. M.; Yeung, S. K.; Lai, T. H. Organometallics
2007, 26, 1981–1985. Benzylic C-H bond activation of toluenes with
Rh(ttp)Cl: (b) Chan, K. S.; Chiu, P. F.; Choi, K. S. Organometallics 2007,
26, 1117–1119. Alkane C-H bond activation with Rh(ttp)Cl: (c) Chan, Y. W.;
Chan, K. S. Organometallics 2008, 27, 4625–4635. Aldehydic C-H bond
activation of aromatic aldehydes with Ir(ttp)Cl(CO): (d) Song, X.; Chan,
K. S. Organometallics 2007, 26, 965–970. Benzylic C-H bond activation of
toluenes with Ir(ttp)Cl(CO): (e) Cheung, C. W.; Chan, K. S. Organometallics
2008, 27, 3043–3055.
(17) By Rh(ttp)Cl: (a) Zhang, L.; Chan, K. S. Organometallics 2006,
25, 4822–4829. By Ir(ttp)Cl(CO): (b) Li, B.; Chan, K. S. Organometallics
2008, 27, 4034–4042.
(18) C-CN bond activation of nitriles with Rh(tmp) radical (tmp =
5,10,15,20-tetrakis(mesityl)porphyrinato dianion): (a) Chan, K. S.; Li,
X. Z.; Fung, C. F.; Zhang, L. Organometallics 2007, 26, 20–21. (b) Chan,
K. S.; Li, X. Z.; Zhang, L.; Fung, C. F. Organometallics 2007, 26, 2679–
2687. C-C bond activation of ethers with Rh(tmp)Cl: (c) Lai, T. H.; Chan,
K. S. Organometallics 2009, 28, 6845–6846.
(19) Fung, H. S.; Chan, Y. W.; Cheung, C. W.; Choi, K. S.; Lee,
S. Y.; Qing, Y. Y.; Chan, K. S. Organometallics 2009, 28, 3981–3989.
(20) (a) Yeung, S. K.; Chan, K. S. Organometallics 2005, 24, 6426–
6430. (b) Ogoshi, H.; Setsune, J.-I.; Yoshida, Z.-I. J. Organomet. Chem.
1978, 159, 317–328.
(21) Harkins, S. B.; Peters, J. C. Organometallics 2002, 21, 1753–1755.
(22) The formation of Ir(ttp)CH2OCH3 was further confirmed by the
similar chemical shifts and splitting patterns in 1H NMR in both
Ir(ttp)CH2OCH3 and Rh(ttp)CH2OCH3.19 See the Experimental
Section for the 1H NMR spectroscopic data of both compounds.
(23) Collman, J. P.; Chng, L. L.; Tyvoll, D. A. Inorg. Chem. 1995, 34,
1311–1324.
(24) Zhai, H.; Bunn, A.; Wayland, B. B. Chem. Commun. 2001, 1294–
1295.

Article
Organometallics, Vol. 29, No. 6, 2010 1345
Figure 1. ORTEP presentation of the molecular structure with numbering scheme for Ir(ttp)CH2OCH3 (2) (30% probability
displacement ellipsoids).
Table 2. Optimization of KOH Loading
CD3OD (eq 5).
KOH ð20 equivÞ
KOH ðequivÞ
IrðttpÞClðCOÞ þ CD3OD
IrðttpÞCD3 ð5Þ
IrðttpÞClðCOÞ þ CH3OH
IrðttpÞCH3
3a
200 °C, 1 day, N2
1a
3a-d3
70%
200 °C, 1 day, N2
1a
ð2Þ
Reaction Profile. In order to gain a mechanistic under-
standing of the bond cleavage steps, the progress of the
reaction of CD3OD with Ir(ttp)Cl(CO) in a sealed NMR
tube was monitored by 1H NMR spectroscopy in both
the absence and presence of KOH. Since Ir(ttp)Cl(CO)
was nearly insoluble in CD3OD, and the suspected reaction
intermediate, Ir(ttp)D (4a-d), as well as the products, Ir-
(ttp)CD2OCD3 (2-d5) and Ir(ttp)CD3 (3a-d3), were only
sparingly soluble at room temperature, the NMR yields
of iridium porphyrin species could not be estimated accu-
rately. Instead, only the reaction sequences and the isolated
yield of Ir(ttp)CD3 could be determined. It should be noted
that the reactions conducted in sealed NMR tubes were
slower than those in Teflon screw-capped tubes at 200 °C
(Table 1), likely due to the lack of stirring in the NMR tube
experiments.
entry
amt of KOH/equiv
yield of 3a/%a
1
2
3
4
5
26
59b
70
10
20
30
66b
a Isolated yield. b A trace amount of Ir(ttp)CH2OCH3 was isolated.
Table 3. Temperature Effects
KOH ð20 equivÞ
IrðttpÞClðCOÞ þ CH3OH
temp, time, N2
1a
IrðttpÞCH2OCH3 þ IrðttpÞCH3
ð3Þ
2
3a
yield
of 2/%a
yield
of 3a/%a
total
yield/%a
(i). Without KOH. In the reaction of Ir(ttp)Cl(CO) with
CD3OD (Scheme S1, Supporting Information), Ir(ttp)Cl-
(CO) did not react with CD3OD at room temperature in
1 day. The reaction temperature was then increased to
200 °C. Ir(ttp)Cl(CO) reacted slowly with CD3OD in 4 days
to give Ir(ttp)D25 (δ(pyrrole) 8.50 ppm), with most of the
reddish purple solid, which was likely Ir(ttp)Cl(CO), remain-
ing unreacted. After a prolonged heating of 23 days, Ir-
(ttp)Cl(CO) and Ir(ttp)D were completely consumed, as
indicated by the absence of characteristic signals of Ir(ttp)Cl-
entry
temp/°C
time/h
1
2
150
200
36
24
4
0
31
70
35
70
a Isolated yield.
Table 4. Porphyrin Effects on the Base-Promoted Reaction of
Ir(por)Cl(CO) with CH3OH
KOH ð20 equivÞ
25
(CO) and Ir(ttp)D by 1H NMR spectroscopy. Ir(ttp)CD3
IrðporÞClðCOÞ þ CH3OH
IrðporÞCH3
200 °C, 1 day, N2
1
3
(δ(pyrrole) 8.46 ppm) was finally formed as a deep brown
precipitate and was isolated in 100% yield by column
chromatography (eq 6). Therefore, Ir(ttp)D is a viable inter-
mediate for Ir(ttp)CD3 formation.
ð4Þ
entry
por
yield of 3/%a
1
2
3
ttp (1a)
btpp (1b)
tmp (1c)
70 (3a)
72 (3b)
66 (3c)
200 °C
IrðttpÞClðCOÞ þ CD3OD
IrðttpÞCD3 ð6Þ
23 days
1a
3a-d3
100%
a Isolated yield.
synthetic route of Ir(por)CH3. Furthermore, Ir(ttp)CD3
in 70% yield could also be prepared at 200 °C in 1 day
from Ir(ttp)Cl(CO) and the much more easily accessible
(25) The iridium porphyrin species formed in the sealed NMR tubes
were identified by the authentic samples in CD3OD using 1H NMR
spectroscopy.

1346 Organometallics, Vol. 29, No. 6, 2010
Cheung et al.
Table 5. Effect of Time on Product Selectivity
(ii). With KOH. In the KOH-promoted reaction of Ir-
(ttp)Cl(CO) with CD3OD (Scheme S2 and Figure S1,
Supporting Information), most of the Ir(ttp)Cl(CO)
remained unreacted and a small amount of Ir(ttp)D25
KOH ð20 equivÞ
200 °C, time, N2
IrðttpÞClðCOÞ þ CH3OH
1a
25
(δ(pyrrole) 8.50 ppm) and Ir(ttp)CD2OCD3 (δ(pyrrole)
IrðttpÞCH2OCH3 þ IrðttpÞCH3
ð8Þ
8.54 ppm) was formed at room temperature after 1 day. In
order to increase the reaction rate, the reaction mixture
was heated up to 200 °C. After 30 min, Ir(ttp)-Kþ25 (5a)
(δ(o-phenyl) 7.91 ppm)26 and more Ir(ttp)CD2OCD3 ap-
2
3a
entry
time/h
yield of 2/%a
yield of 3a/%a
1
2
3
0.5
3
24
55
55
0
10
23
70
25
peared. After 90 min, a small amount of Ir(ttp)CD3
(δ(pyrrole) 8.46 ppm) was also formed. Upon further
heating for 4 days, Ir(ttp)-Kþ and Ir(ttp)CD2OCD3 were
consumed completely and Ir(ttp)CD3 was isolated in 81%
yield by column chromatography (eq 7). Thus, Ir(ttp)-Kþ
and Ir(ttp)CD2OCD3 were formed faster than Ir(ttp)CD3,
and these findings suggest that Ir(ttp)-Kþ and Ir-
(ttp)CD2OCD3 are likely intermediates for Ir(ttp)CD3
formation.
a Isolated yield.
Scheme 1. Reaction Mechanism of Ir(ttp)Cl(CO) with CH3OH
66% yield (eq 9).
IrðttpÞ ClðCOÞ þ CD3OD KOH ð20 equivÞ IrðttpÞCD3 ð7Þ
200 °C
IrðttpÞH þ CH3OH
IrðttpÞCH3
ð9Þ
200 °C, 4 days
1a
3a-d3
81%
3 days, N2
66%
In fact, Ir(ttp)OCH3 can isomerize30 via a β-hydride
elimination19 to give Ir(ttp)H and HCHO, followed by
reinsertion19 of HCHO to Ir(ttp)-H to give Ir(ttp)CH2OH
(eq 10). Indeed, the β-hydride elimination of Rh(tpp)OCH3
(tpp = 5,10,15,20-tetrakis(phenyl)porphyrinato dianion) to
give Rh(tpp)H and HCHO31 and the insertion of HCHO to
Rh(tpp)-H to give Rh(tpp)CH2OH32 have been reported.
As Ir(ttp)CD2OCD3 and Ir(ttp)CD3 did not dissolve very
well in CD3OD for accurate yield determination by 1H
NMR spectroscopy, they were quantified by isolation by
separate experiments. When Ir(ttp)Cl(CO) was heated with
KOH (20 equiv) in CH3OH for 30 min at 200 °C, Ir-
(ttp)CH2OCH3 and Ir(ttp)CH3 were produced in 55%
and 10% yields, respectively, confirming the more rapid
formation of Ir(ttp)CH2OCH3 (Table 5, eq 8, entry 1). In
3 h, the yield of Ir(ttp)CH2OCH3 remained at 55%, with
a concomitant increase in the amount of Ir(ttp)CH3 to
23% yield (Table 5, entry 2). Likely, Ir(ttp)-Kþ remains
in the alkaline reaction mixture and slowly reacts to give
more Ir(ttp)CH3. After 1 day, Ir(ttp)CH2OCH3 was con-
sumed and Ir(ttp)CH3 in 70% yield was obtained (Table 5,
entry 3).
Ir(ttp)CH2OH then further condenses with CH3OH to yield
19,33
Ir(ttp)CH2OCH3
(eq 11). Moreover, Ir(ttp)H reacted
very quickly with paraformaldehyde (17 equiv of HCHO)
in CD3OD at 200 °C in 1 day to give Ir(ttp)CH2OCD3 in 74%
yield and Ir(ttp)CD3 in 5% yield (eq 12), which was formed
by the slower reaction of Ir(ttp)H with CD3OD.
IrðttpÞOCH3 h IrðttpÞCH2OH
ð10Þ
IrðttpÞCH2OH þ CH3OH
IrðttpÞCH2OCH3 þ H2O
ð11Þ
Mechanism (No Base). On the basis of the above findings,
Scheme 1 illustrates the proposed mechanism of the reac-
tion of Ir(ttp)Cl(CO) with CH3OH. Ir(ttp)Cl(CO) initially
undergoes CO ligand dissociation to give Ir(ttp)Cl,16e
which then reacts with CH3OH via ligand substitution
to yield Ir(ttp)OCH327 and HCl28 (Scheme 1, pathway i).
Ir(ttp)OCH3 then converts to the observed Ir(ttp)H
(Table 1, entry 1) and HCHO via β-hydride elimination29
(Scheme 1, pathway ii). Finally, Ir(ttp)H cleaves the C-O
bond in CH3OH slowly, likely via σ-bond metathesis, to
yield Ir(ttp)CH3 (Scheme 1, pathway iii). Indeed, Ir(ttp)H
was found to independently react with CH3OH at
200 °C in 3 days to produce Ir(ttp)CH3 selectively in
CD3OD
IrðttpÞH þ HCHO
IrðttpÞCH2OCD3 þ IrðttpÞCD3
17 equiv
200 °C, 1 day
74%
5%
ð12Þ
However, such an isomerization does not occur, as Ir-
(ttp)CH2OCH3 was not formed in the reaction (Table 1,
entry 1). Probably, the HCl formed (Scheme 1, pathway i)
catalyzes the much faster reaction of HCHO with CH3OH to
give dimethoxymethane,34 inhibiting the reinsertion of
(30) The isomerization of Rh(tmp)OCH3 to Rh(tmp)CH2OH was
reported in a rhodium porphyrin analogue.10
(31) Collman, J. P.; Boulatov, R. Inorg. Chem. 2001, 40, 560–563.
(32) Wayland, B. B.; Vanvoorhees, S. L.; Wilker, C. Inorg. Chem.
1986, 25, 4039–4042.
(33) Rh(tpp)CH2OH (tpp = 5,10,15,20-tetrakis(phenyl)porphyrinato
dianion) has been reported to undergo condensation to give
[Rh(tpp)CH2]2O. It is likely that Ir(ttp)CH2OH prefers to undergo
condensation with excess CH3OH solvent to yield Ir(ttp)CH2OCH3,
rather than a more sterically unfavorable condensation to yield
[Ir(ttp)CH2]2O.32
(34) Lewis acid can catalyze the reaction of formaldehyde with
methanol to give dimethoxymethane. See: Danov, S. M.; Kolesnikov,
V. A.; Logutov, I. V. Russ. J. Appl. Chem. 2004, 77, 1994–1996.
(26) The characteristic upfield pyrrole proton signal of Ir(ttp)-Kþ
(δ(pyrrole) 8.11 ppm) was shielded by the upfield o-phenyl proton
signal of the porphyrin’s tolyl groups in Ir(ttp)CD2OCD3 (δ(pyrrole)
8.10 ppm). Thus, the upfield o-phenyl proton signal of Ir(ttp)-Kþ
(δ(o-phenyl) 7.91 ppm) was selected as the alternative characteristic
peak.
(27) (a) Tani, K.; Iseki, A.; Yamagata, T. Angew. Chem., Int. Ed.
1998, 37, 3381–3383. (b) Kloek, S. M.; Heinekey, D. M.; Goldberg, K. I.
Organometallics 2006, 25, 3007–3011.
(28) Jiang, B.; Feng, Y.; Ison, E. A. J. Am. Chem. Soc. 2008, 130,
14462–14464.
(29) Ofer Blum, O.; Milstein, D. J. Am. Chem. Soc. 1995, 117, 4582–
4594.

Article
Organometallics, Vol. 29, No. 6, 2010 1347
Scheme 2. Base-Promoted Reaction Mechanism of
Ir(ttp)Cl(CO) with CH3OH
Scheme 3. Formation of Ir(ttp)CH3 from Possible Intermediates
HCHO with Ir(ttp)H. Since Ir(ttp)H also did not react
with CH3OH at 200 °C in 1 day to yield any Ir(ttp)CH2OCH3
(eq 9), it appears that Ir(ttp)H is not a reactive intermediate
to cleave the C-H bond of CH3OH to give Ir(ttp)CH2OH.
Ir(ttp)H only cleaves the C-O bond of CH3OH to yield
Ir(ttp)CH3.
to give Ir(ttp)- and [Ir(ttp)(CD3OD)2]þ (Scheme 4, pathway i),
10
which further reacts to yield Ir(ttp)D and Ir(ttp)OCD3
(Scheme 4, pathway ii). Ir(ttp)OCD3 proceeds to undergo
β-hydride elimination19,31/reinsertion19,32 to give Ir(ttp)-
CD2OD (Scheme 4, pathway iii). Ir(ttp)CD2OD further
condenses with CD3OD to give Ir(ttp)CD2OCD333 (eq 11),
whereas Ir(ttp)D reacts more slowly with CD3OD to give
Ir(ttp)CD3 (eq 9).
However, in the presence of KOH, [Ir(ttp)]2 was observed
to form Ir(ttp)-Kþ (δ(pyrrole) 8.11 ppm) in ∼90% yield
upon heating in CD3OD at 200 °C in 5 min (Table 6, entry 2).
This likely results from the disproportionation of [Ir(ttp)]2
with CD3OD to give Ir(ttp)- and [Ir(ttp)(CD3OD)2]þ 10
(Scheme 4, pathway i), which then undergoes base-promoted
deprotonation (Scheme 4, pathway iv) and subsequent β-
proton elimination19,32 to give another Ir(ttp)- (Scheme 4,
pathway v). Prolonged heating of the reaction mixture at
200 °C in 4 days resulted in the gradual consumption of
Ir(ttp)-Kþ to give Ir(ttp)CD3 in 59% yield without any
Ir(ttp)CD2OCD3 formed (Table 6, entry 2). [Ir(ttp)]2 is
therefore not the direct intermediate in the basic medium
to give Ir(ttp)CH2OCH3 and Ir(ttp)CH3.
Mechanism (Base Promoted). Initially, Ir(ttp)Cl(CO) re-
acts with KOH via facile ligand substitution to give Ir-
(ttp)OH16e,35 (Scheme 2, pathway i), which then exchanges
rapidly with CH3OH by metathesis to afford Ir(ttp)OCH3
(Scheme 2, pathway ii). Alternatively, the deprotonation of
coordinated CH3OH10 by KOH to give Ir(ttp)OCH3 also
operates. Indeed, Ir(ttp)Cl(CO) reacted with KOH and
isopropyl alcohol at room temperature in 10 min to give
Ir(ttp)OiPr in ∼85% yield (eq 13), supporting the facile base-
promoted substitution of Ir(ttp)Cl(CO) by CH3OH to yield
Ir(ttp)OCH3. Facile isomerization30 of Ir(ttp)OCH3 via β-
hydride elimination19,31/reinsertion19,32 likely occurs to af-
ford Ir(ttp)CH2OH (eq 10), which further condenses with
CH3OH to give Ir(ttp)CH2OCH333 (eq 11; Scheme 2, path-
way iii). Concurrently, the base-assisted β-proton elimina-
tion31 of Ir(ttp)OCH3 takes place to yield Ir(ttp)-Kþ,
HCHO, and H2O (Scheme 2, pathway iv). Finally, both
Ir(ttp)CH2OCH3 and Ir(ttp)-Kþ further react with CH3OH
to give Ir(ttp)CH3 (to be discussed in the following section).
(ii). Ir(ttp)H. Ir(ttp)H (δ(pyrrole) 8.50 ppm) reacted very
slowly with CD3OD in 23 days to give Ir(ttp)CD3 in 39%
yield with some unreacted Ir(ttp)D37 (Table 6, entry 3). No
Ir(ttp)CD2OCD3 was formed in the course of reaction. In the
presence of KOH, Ir(ttp)H was rapidly deprotonated20b to
give Ir(ttp)-Kþ (δ(pyrrole) 8.11 ppm) in ∼90% yield at
200 °C in 5 min. Prolonged heating of the reaction mixture
at 200 °C over 4 days gave Ir(ttp)CD3 in 57% yield without
Ir(ttp)CD2OCD3 formation (Table 6, entry 4). The rapid
formation of Ir(ttp)CH3 from Ir(ttp)H/KOH rather than
from Ir(ttp)H suggests that Ir(ttp)-Kþ is a key and direct
intermediate to cleave the C-O bond of CH3OH to give
Ir(ttp)CH3.
IrðttpÞClðCOÞþ PrOH KOH ð25 equivÞ IrðttpÞOiPr ð13Þ
i
10 min, N2
∼85%
Since Ir(ttp)-Kþ can exist in equilibrium with CH3OH to
give Ir(ttp)H via protonation with CH3OH,36 and Ir(ttp)H is
also known to undergo fast base-promoted dehydrogenative
dimerization to give [Ir(ttp)]2,16e therefore Ir(ttp)-Kþ, Ir-
(ttp)H, and [Ir(ttp)]2 are all possible intermediates existing in
an alkaline medium (Scheme 3, pathways i and ii). The
reactivities of these three possible intermediates toward
the reaction with CH3OH to give Ir(ttp)CH2OCH3 and
Ir(ttp)CH3 were also examined in sealed NMR tubes
(Table 6, eq 14).
(i). [Ir(ttp)]2. Among the three possible intermediates,
only [Ir(ttp)]2 (δ(pyrrole) 8.71 ppm) reacted with CD3OD
at 200 °C in 16 h to give Ir(ttp)CD2OCD3 in 44% yield
accompanied by the formation of Ir(ttp)CD3 in 7% yield and
a trace amount of Ir(ttp)D37 (Table 6, entry 1). It is likely that
[Ir(ttp)]2 undergoes disproportionation with excess CD3OD
(iii). Ir(ttp)-Kþ. Ir(ttp)-Kþ (δ(pyrrole) 8.11 ppm) was
thus independently prepared in the form of Ir(ttp)-[K(18-
crown-6)]þ,38 which did react with CD3OD at 200 °C in 4
days to give only Ir(ttp)CD3 in 85% yield without the
formation of Ir(ttp)CD2OCD3 (Table 6, entry 5). Therefore,
Ir(ttp)-Kþ is also not the intermediate to give Ir(ttp)-
CH2OCH3 but the intermediate to yield Ir(ttp)CH3.
Formation of Ir(ttp)CH3. (i). From Ir(ttp)CH2OCH3. Ir-
(ttp)CH2OCH3 is thermally stable, since it was recovered
quantitatively upon heating in C6D6 at 200 °C in 14 days
(Table 7, eq 15, entry 1). When Ir(ttp)CH2OCH3 reacted
with CD3OD in the presence of KOH at 200 °C in 1 day,
small amounts of Ir(ttp)-Kþ and Ir(ttp)CD3 were formed.
Ir(ttp)CH2OCH3 also exchanged with CD3OD to yield
Ir(ttp)CH2OCD3. In 4 days, Ir(ttp)CD3 was isolated in
(35) Substitution of Ir-Cl by OH- anion to give Ir-OH has been
reported. See: (a) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman,
R. G. Acc. Chem. Res. 2002, 35, 44–56. (b) Ir(ttp)Cl(CO) wasreported to react
with NaOPh in benzene to give Ir(ttp)OPh.16e Presumably, the more nucleo-
philic KOH reacts much more quickly with Ir(ttp)Cl(CO) to give Ir(ttp)OH.
(36) Rh(TSPP)H(TSPP=tetrakis(p-sulfonatophenyl)porphyrinato) has
been reported to exist in equilibrium with Rh(TSPP)- in water. The less
acidic Ir(ttp)H is likely to be in equilibrium with Ir(ttp)- in basic medium.
See: (a) Fu, X.; Basickes, L.; Wayland, B. B. Chem. Commun. 2003, 520–521.
(b) Fu, X.; Wayland, B. B. J. Am. Chem. Soc. 2004, 126, 2623–2631.
(37) Ir(ttp)H can undergo fast proton exchange with CD3OD (50
equiv) in benzene-d6 at room temperature in 6 h to give Ir(ttp)D in 77%
yield.
(38) Ir(ttp)-[K(18-crown-6)]þ was prþep3a2red using the synthetic meth-
od to prepare Rh(ttp)-[K(18-crown-6)] .

1348 Organometallics, Vol. 29, No. 6, 2010
Table 6. Relative Reactivities of Iridium Porphyrin Species
Cheung et al.
KOH ðequivÞ
200 °C, time
IrðttpÞX þ CD3OD
IrðttpÞCD2OCD3 þ IrðttpÞCD3
ð14Þ
2-d5
3a-d3
entry
Ir(ttp)X
amt of KOH/equiv
time
16 h
4 days
23 days
4 days
4 days
Ir(ttp)CD2OCD3 yield/%a
Ir(ttp)CD3 yield/%a
1
2
3
4
5
[Ir(ttp)]2c
[Ir(ttp)]2
0
20
0
20
20
44
0
0
0
0
7b
59
39
57
85
Ir(ttp)Hd
Ir(ttp)Hc
Ir(ttp)-Kþe
a Isolated yield. b A trace amount of of Ir(ttp)D was also observed by 1H NMR spectroscopy. c Ir(ttp)-Kþ was formed in ∼90% yield upon heating at
200 °C in 5 min. d Ir(ttp)H converted to Ir(ttp)D quantitatively instantaneously, and some Ir(ttp)D remained unreacted after heating for 23 days. e As
Ir(ttp)-[K(18-crown-6)]þ.
more nucleophilic Ir(ttp)(PPh3)- 40 to react more quickly
with CH3OH via an SN2 mechanism.
Scheme 4. Conversion of [Ir(ttp)]2 to Ir(ttp)OCD3,
Ir(ttp)CD2OD, and Ir(ttp)-
To ensure that Ir(ttp)H(PPh3), possibly formed in the
above reaction by protonation of Ir(ttp)(PPh3)-, did not
affect the above conclusion, the reaction of Ir(ttp)H/PPh3
(1 equiv) with CH3OH was also examined (Table 8, entry 7).
As expected, extremely slow reaction occurred in 3 days to
give Ir(ttp)CH3(PPh3) in a low yield of 24%. Therefore,
Ir(ttp)H(PPh3) is much less reactive than Ir(ttp)(PPh3)-
(Table 8, entry 4) and Ir(ttp)H as well (eq 9), presumably
due to the lack of a vacant coordination site for the σ-bond
metathesis.
To rationalize why the nucleophilic substitution of Ir-
(ttp)- with CH3OH to give Ir(ttp)CH3 is competitive with
62% yield with the unreacted Ir(ttp)CH2OCH3 and Ir-
(ttp)CH2OCD3 recovered in 4% and 24% yields, respec-
the protonation to yield Ir(ttp)H, we reason that the pro-
tonation does occur by a rapid equilibrium (Scheme 6, path-
way i). The reaction of Ir(ttp)H with CH3OH to give
tively (Table 7, entry 2). Probably, nucelophilic substitution
of the R-carbon19,39 in Ir(ttp)CH2OCH3 by KOH takes place
Ir(ttp)CH3 is shown to be very slow at 200 °C (eq 9). There-
fore, Ir(ttp)- is a viable direct intermediate (Scheme 6, path-
way ii) which reacts much more quickly with CH3OH to give
Ir(ttp)CH3 at 200 °C (Table 8, entry 6). It has been reported
that the weak base and nucleophile NH3 underwent acyl
substitution with CH3CO2H to give CH3CONH2 instead of
CH3CO2-NH4þ, which was also formed but dissociated
rapidly.41
In the base-promoted reaction of Ir(ttp)Cl(CO) with
CH3OH, the rate of formation of Ir(ttp)CH3 was slo-
wer than that of Ir(ttp)CH2OCH3 (Scheme S2 (Support-
ing Information); Table 5). This shows that the C-O
bond cleavage of CH3OH by Ir(ttp)- (Scheme 3, path-
way iii) appears to be the rate-limiting bond cleavage
step rather than the O-H and C-H bond cleavages of
CH3OH.
Methyl Group Exchange of Ir(ttp)CH3. Ir(ttp)CH3 did not
undergo any exchange with CD3OD in 1 day to yield Ir-
(ttp)CD3, with Ir(ttp)CH3 recovered in 80% yield (eq 17a).
However, extensive methyl group exchange42 of Ir(ttp)CH3
occurred with CD3OD in the presence of KOH (20 equiv) in 1
day to give Ir(ttp)CD3 in 18% yield with Ir(ttp)CH3 recovered
in 65% yield (eq 17b). These results further suggest that the
nucleophilic substitution of Ir(ttp)CH3 by KOH occurs
to give Ir(ttp)-Kþ (Scheme 7, pathway i). Ir(ttp)-Kþ
to afford Ir(ttp)-Kþ (Scheme 5), which further reacts with
CD3OD to give Ir(ttp)CD3 (Scheme 3, pathway iii). The
formation of Ir(ttp)CH3 from Ir(ttp)CH2OCH3 is slower
than that from Ir(ttp)- (Table 6, entry 5) and is likely due to
the poor leaving group of Ir(ttp)-.
(ii). From Ir(ttp)-Kþ. The puzzling suggestion that Ir-
(ttp)-Kþ reacts directly with CH3OH, likely via bimolecular
nucleophilic substitution (SN2), to yield Ir(ttp)CH3 and OH-
anion (Scheme 6, pathway ii), has been tested further experi-
mentally. At room temperature, Ir(ttp)CH3(PPh3) (3d) was
readily observed in the reaction of Ir(ttp)- with PPh3
(1 equiv) and CH3OH in 5 min (Table 8, eq 16, entry 1),
but no Ir(ttp)CH3 was formed in the absence of PPh3
(Table 8, entry 2). When the reaction temperature was
increased to 100 °C, Ir(ttp)- added with PPh3 reacted with
CH3OH in 36 h to give Ir(ttp)CH3(PPh3) in 17% yield
(Table 8, entry 1), whereas Ir(ttp)- alone gave Ir(ttp)CH3
in 9% yield in 72 h (Table 8, entry 2). The rate-promoting
effect of PPh3 on the reaction rate of Ir(ttp)- with CH3OH
was also observed at 200 °C. Ir(ttp)-/PPh3 (1 equiv) reacted
with CH3OH in 12 h at 200 °C to yield Ir(ttp)CH3(PPh3) in
52% yield (Table 8, entry 3). Ir(ttp)-/PPh3 reacted with
MeOH to give Ir(ttp)CH3(PPh3) in 77% yield upon heating
for 1 day (Table 8, entry 4). Ir(ttp)- alone reacted more
slowly with CH3OH in 12 h to yield Ir(ttp)CH3 in 28% yield
(Table 8, entry 5) and completely in 1 day to produce Ir-
(ttp)CH3 in 87% yield (Table 8, entry 6). Thus, Ir(ttp)-/PPh3
reacts more quickly than Ir(ttp)- at 200 °C. Likely, PPh3
coordinates to Ir(ttp)- to generate more electron-rich and
(40) The 1H NMR spectrum of pure Ir(ttp)(PPh3)- cannot be ob-
tained by adding 1 equiv of PPh3 to Ir(ttp)-K(18-crown-6)þ in CD3OD,
as the reaction was very fast at room temperature to give a deep purple
precipitate, which was likely Ir(ttp)CH3(PPh3).
(41) Mitchell, J. A.; Reid, E. E. J. Am. Chem. Soc. 1931, 53, 1879–
1883.
(42) Iridium porphyrin benzyl (Ir(ttp)Bn) have been shown to under-
(39) Sanford, M. S.; Groves, J. T. Angew. Chem., Int. Ed. 2004, 43,
588–590.
go base-promoted benzyl group exchange with toluene-d8.16e

Article
Organometallics, Vol. 29, No. 6, 2010 1349
Table 7. Conversion of Ir(ttp)CH2OCH3 to Ir(ttp)CH3
IrðttpÞCH2OCH3 solvent, KOH ðequivÞ IrðttpÞCH2OCH3 þ IrðttpÞCH2OCD3 þ IrðttpÞCD3
ð15Þ
200 °C, time
2
2
2-d3
3a
entry
solvent
amt of KOH/equiv
time/days
yield of 2/%
yield of 2-d3c/%
yield of 3a-d3/%
1
2
C6D6
CD3OD
0
20
14
4d
100a
4a
0
0
24a
62b
a NMR yield. b Isolated yield. c The CH3 group in Ir(ttp)CH2OCH3 exchanged with CD3OD to give Ir(ttp)CH2OCD3. d Ir(ttp)-Kþ and Ir(ttp)CD3
were formed in 1 day.
Table 8. Effect of PPh3 on Reactions of Ir(ttp)H and Ir(ttp)- with CH3OH
PPh3 ðequivÞ
IrðttpÞX þ CH3OH
IrðttpÞCH3 = IrðttpÞCH3ðPPh3Þ
ð16Þ
temp, time, N2
3a
3d
entry
Ir(ttp)X
amt of PPh3/equiv
temp/°C
time/h
yield of 3a or 3d/%a
1
2
3
4
5
6
7
Ir(ttp)-Kþ b
Ir(ttp)-Kþ b
Ir(ttp)-Kþ b
Ir(ttp)-Kþ b
Ir(ttp)-Kþ b
Ir(ttp)-Kþ b
Ir(ttp)H
1
0
1
1
0
0
1
100
100
200
200
200
200
200
36
72
12
24
12
24
72
17 (3d)c
9 (3a)d
52 (3d)e
77 (3d)
28 (3a)
87 (3a)
24 (3d)f
a Isolated yield. b As Ir(ttp)-[K(18-crown-6)]þ. c At room temperature in 5 min, Ir(ttp)CH3(PPh3) was observed by thin-layer chromatography (TLC).
d At room temperature in 5 min, no Ir(ttp)CH3 was observed by TLC. e In 1 h, Ir(ttp)CH3(PPh3) was isolated in 29% yield. f In 1.5 h, no Ir(ttp)CH3(PPh3)
was observed by TLC.
Scheme 5. Nucleophilic Substitution of Ir(ttp)CH2OCH3 by
KOH
Scheme 6. Nucleophilic Substitution of CH3OH by Ir(ttp)-Kþ
pKa of Rh(ttp)-H is lower than that of Ir(ttp)-H43 and
suggests a lower nucleophilicity of Rh(ttp)- as compared to
that of Ir(ttp)-.44 (2) As the Rh(ttp)-H bond (∼61 kcal/
mol)45 is weaker than the Ir(ttp)-H bond (∼70 kcal/mol),46
the reaction of Rh(ttp)-H with CH3-OH is likely kineti-
cally more favorable than that of Ir(ttp)-H. The CH3-OH
cleavage by Rh(ttp)H is also estimated to be thermodyna-
mically more favorable than that of Ir(ttp)H.47 Thus,
then reacts with CD3OD to yield Ir(ttp)CD3 via an SN2
mechanism (Scheme 7, pathway ii).
CD3OD, 1 day, N2
IrðttpÞCH3
IrðttpÞCH3 þ IrðttpÞCD3
ðaÞ no base
80%
65%
0%
18%
ðbÞ KOH ð20 equivÞ
ð17Þ
(43) The pKa values of the M-H bonds in group 9 transition-metal
complexes increase down the groups, and the pKa of Ir-H is reported to
be higher than that of Rh-H by around 10. Ir(ttp)H is likely to be a
weaker acid than Rh(ttp)H. See: Qi, X.-J.; Liu, L.; Fu, Y.; Guo, Q.-X.
Organometallics 2006, 25, 5879–5886.
(44) The basicity of a conjugate base is related to its nucleophilicity.
The higher the pKa of an acid, the more nucleophilic its conjugate base.
See: (a) Bordwell, F. G.; Hughes, D. L. J. Org. Chem. 1983, 48, 2206–
2215. (b) Bordwell, F. G.; Hughes, D. L. J. Am. Chem. Soc. 1984, 106,
3234–3240.
(45) Cui, W.; Wayland, B. B. J. Am. Chem. Soc. 2004, 126, 8266–8274.
(46) Bond dissociation energies (BDEs) of Ir(ttp)-H and Ir-
(ttp)-CH3 are about 70 and 62 kcal/mol, respectively: Wayland, B. B.
Personal communication, University of Pennsylvania, Philadelphia, PA,
2007.
(47) The exothermicities (ΔH) of the reactions of CH3-OH cleavage
with Rh(ttp)H and Ir(ttp)H are estimated using the bond dissociation
energies (BDEs) of Rh-H, Rh-CH3, Ir-H, Ir-CH3, CH3-OH, and
H-OH. In the Rh(ttp)H system, ΔH = BDE[Rh-H] (61) þ BDE-
[CH3-OH] (92) - BDE[Rh-CH3] (57) - BDE[H-OH] (119) = -23
kcal/mol. In the Ir(ttp)H system, ΔH = BDE[Ir-H] (70) þ BDE-
[CH3-OH] (92) - BDE[Ir-CH3] (62) - BDE[H-OH] (119) = -19
kcal/mol. BDE of Rh-H: (a) Reference 45. BDE of Rh-CH3:
(b) Wayland, B. B.; Ba, S.; Sherry, A. E. J. Am. Chem. Soc. 1991, 113,
5305–5311. BDEs of Ir-H and Ir-CH3: (c) Reference 46. BDEs of
CH3-OH and H-OH: (d) Luo, Y.-R. Handbook of Bond Dissociation
Energies in Organic Compounds; CRC Press: Boca Raton, FL, 2002.
Reactivity Comparison in Group 9 Metalloporphyrins. Our
group has reported the base-promoted reaction of CH3OH with
Rh(ttp)Cl at 150 °C, and Rh(ttp)H is proposed to be the inter-
mediate to cleave the C-O bond of CH3OH to give Rh(ttp)-
CH3.19 In the iridium porphyrin system, Ir(ttp)-Kþ (Scheme 3,
pathway iii) is shown to react with CH3OH much more quickly
than Ir(ttp)H (Scheme 3, pathway iv) to yield Ir(ttp)CH3
(Table 6, entries 3 and 5), suggesting that Ir(ttp)-Kþ rather
than Ir(ttp)H acts as the reacting species in a basic medium.
The difference in reactivities between rhodium and iridium
porphyrins is mainly due to (1) the lower nucleophilicity of
Rh(ttp)- as compared to that of Ir(ttp)- and (2) the higher
reactivitiy of Rh(ttp)H as compared to that of Ir(ttp)H. (1) It
is reported that Rh(oep)H (oep = 2,3,7,8,12,13,17,18-oc-
taethylporphyrinato dianion) dissolved readily in basic alco-
holic solution with 1 M NaOH added to give Rh(ttp)-,
whereas Ir(oep)H remained in solid form and did not form
Ir(ttp)- under the same reaction conditions.20b Indeed, Rh-
(ttp)H was readily deprotonated in the presence of weak base
of K2CO3 at 150 °C to give Rh(ttp)-.19 This shows that the

1350 Organometallics, Vol. 29, No. 6, 2010
Cheung et al.
Scheme 7. Base-Promoted Conversion of Ir(ttp)CH3 to
Ir(ttp)CD3
mode using 3-nitrobenzyl alcohol (NBA) matrix and CH2Cl2 as
solvent and in the electrospray ionization (ESI) mode using
MeOH:CH2Cl2 (1:1) as solvent.
Preparation of Chlorocarbonyl(5,10,15,20-tetrakis(p-tert-
butylphenyl)porphyrinato)iridium(III), [Ir(btpp)Cl(CO)] (1b). Ir-
(btpp)Cl(CO) (1b) was synthesized according to the procedures
in the synthesis of Ir(ttp)Cl(CO).20a [Ir(COD)Cl]2 (437 mg, 0.65
mmol) and H2(btpp)49 (545 mg, 0.65 mmol) were heated under
reflux in p-xylene (200 mL) for 3 days. The reaction mixture
changed from deep brown to reddish brown, and it was dried
under vacuum. The product was purified by column chroma-
tography using CH2Cl2/hexane (1:2) as an eluent to remove the
initial brown fraction and purple fraction. The bright red
product fraction was then isolated using CH2Cl2/hexane (3:1)
as the eluent. The red fraction was dried and further purified by
crystallization using CH2Cl2 and methanol. Red crystalline
Rh(ttp)H reacts more quickly than Rh(ttp)-, and Ir(ttp)H
conversely reacts more slowly than Ir(ttp)-. Rh(ttp)H and
Ir(ttp)- are the reactive intermediates in the C-O bond
cleavage of CH3OH.
Conclusion
Ir(ttp)Cl(CO) successfully reacted with methanol via C-O
bond cleavage at 200 °C to give Ir(ttp)CH3. Addition of KOH
promoted the reaction rate to give a higher yield of Ir(ttp)CH3.
Mechanistic studies suggest that KOH promotes the rate of
formation of Ir(ttp)CH3 by (i) promoting the ligand substitu-
tion of Ir(ttp)Cl(CO) with CH3OH to afford the more reactive
Ir(ttp)OCH3, (ii) promoting the β-proton elimination of Ir-
(ttp)OCH3 to give Ir(ttp)-, and (iii) promoting the substitution
of Ir(ttp)CH2OCH3 to give Ir(ttp)-. Ir(ttp)H and Ir(ttp)- are
found to be the active intermediates to cleave the C-O bond in
CH3OH in the absence and presence of KOH, respectively.
Ir(ttp)H reacts with CH3OH, likely via σ-bond metathesis,
whereas Ir(ttp)-Kþ reacts with CH3OH, probably via a bimo-
lecular nucleophilic substitution, to give Ir(ttp)CH3.
1
Ir(btpp)Cl(CO) (483 mg, 0.44 mmol, 68%) was collected. H
NMR (CDCl3, 300 MHz): δ 1.62 (s, 36 H), 7.77 (d, 8 H, J =
8.1 Hz), 8.13 (d, 4 H, J = 6.9 Hz), 8.20 (d, 4 H, J = 7.2 Hz), 8.95
(s, 8 H). 13C NMR (CDCl3, 75 MHz): 31.8, 35.1, 122.3, 123.7,
124.0, 132.0, 134.3, 134.5, 135.2, 138.4, 141.3, 151.0. HRMS
(FABMS): calcd for [C61H61N4OClIr]þ ([M þ H]þ) m/z
1093.4158, found m/z 1093.4166.
Preparation of Methoxymethyl(5,10,15,20-tetrakis(p-tolyl)-
porphyrinato)iridium(III), [Ir(ttp)CH2OCH3] (2). Ir(ttp)H (4a)
(10.6 mg, 0.012 mmol), paraformaldehyde (3.7 mg, 0.12 mmol
HCHO), and methanol (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
2 h. The reaction mixture was then dried under vacuum, and it
was purified by column chromatography using alumina with a
solvent mixture of CH2Cl2 and hexane (1:4) as eluent to yield
Ir(ttp)CH2OMe (2; 4.8 mg, 0.005 mmol, 43%). 1H NMR
(CDCl3, 300 MHz): δ -2.93 (s, 2 H), -0.60 (s, 3 H), 2.68
(s, 12 H), 7.50 (d, 4 H, J = 6.0 Hz), 7.52 (d, 4 H, J = 6.0 Hz),
7.96 (d, 4 H, J = 6.7 Hz), 8.03 (d, 4 H, J = 7.2 Hz), 8.53 (s, 8 H).
1H NMR (CD3OD, 300 MHz): δ -3.20 (s, 2 H), -0.46 (s, 3 H),
2.74 (s, 12 H), 7.62 (d, 8 H, J = 8.1 Hz), 8.03 (d, 4 H, J = 7.2 Hz),
8.08 (d, 4 H, J = 6.9 Hz), 8.54 (s, 8 H). 13C NMR (CDCl3, 75
MHz): δ 21.7, 33.9, 55.9, 124.3, 127.6, 131.4, 133.6, 133.9, 137.3,
138.8, 143.5. HRMS (FABMS): calcd for [C50H42N4OIr]þ
([M þ H]þ) m/z 907.2982, found m/z 907.2958.
Experimental Section
Unless otherwise noted, all reagents were purchased from
commercial suppliers and directly used without further purifica-
tion. Hexane was distilled from anhydrous calcium chloride.
Benzene was distilled from sodium. Benzene-d6 and methanol-d4
˚
were dried in preheated 4 A molecular sieves and were stored in a
Teflon-capped tube under nitrogen prior to use. Thin-layer
chromatography was performed on precoated silica gel 60
F254 plates. H2(ttp),48 H2(btpp),49 H2(tmp),50 Ir(ttp)Cl(CO)
(1a),20a Ir(tmp)Cl(CO) (1c),23 Ir(ttp)CH3 (3a),20a Ir(tmp)CH3
(3c),24 Ir(ttp)H (4a),16e and [Ir(ttp)]2 dimer16e (6) had been
characterized, and they were prepared according to the litera-
ture procedures. Silica gel (Merck, 70-230 mesh) was used in
column chromatography to isolate Ir(por)Cl(CO) (por = ttp
(1a), btpp (1b), tmp (1c)). Neutral alumina (Merck, 70-230
mesh)/H2O (∼10:1 v/v) was used in column chromatography to
isolate Ir(ttp)CH2OCH3 (2) and Ir(por)CH3 (por = ttp (3a),
btpp (3b), tmp (3c)).
Preparation of Methyl(triphenylphosphine)(5,10,15,20-tetra-
kis(p-tolyl)porphyrinato)iridium(III), [Ir(ttp)CH3(PPh3)] (3d).
Ir(ttp)CH3 (3a; 24.4 mg, 0.028 mmol), PPh3 (68.6 mg, 0.26 mmol),
and benzene (2 mL) were degassed for three freeze-thaw-pump
cycles in a Teflon screw-capped tube. The reaction mixture was
coveredbyaluminumfoilandheatedat60°C under N2 for 2 h. The
reaction mixture was then dried under vacuum, and it was purified
by column chromatography using alumina with a solvent mixture
of CH2Cl2 and hexane (1:4) as eluent to isolate the reddish brown
fraction. The product was further crystallized using CH2Cl2/
CH3OH to obtain Ir(ttp)CH3(PPh3) (3d; 27.3 mg, 0.024 mmol,
1H NMR and 13C NMR spectra were recorded on a Bruker
DPX-300 instrument at 300 and 75 MHz, respectively, or a
Bruker AV-400 instrument at 400 and 100 MHz, respectively.
Chemical shifts were referenced with the residual solvent pro-
tons in CDCl3 (δ 7.26 ppm), C6D6 (δ 7.15 ppm), CD3OD
(δ(CH3) 3.38 ppm), THF-d8 (δ(β-CH2) 1.85 ppm), or tetra-
methylsilane (δ 0.00 ppm) as the internal standard in 1H NMR
spectra and CDCl3 (δ 77.16 ppm), C6D6 (δ 128.06 ppm), or
THF-d8 (δ(β-CH2) 25.62 ppm) as the internal standard in 13C
NMR spectra. Chemical shifts (δ) are reported as parts per
million (ppm) in δ scale downfield from TMS. Coupling con-
stants (J) are reported in hertz (Hz). High-resolution mass
spectra (HRMS) were measured on a ThermoFinnigan MAT
95 XL mass spectrometer in fast atom bombardment (FAB)
1
3
85%). H NMR (CDCl3, 300 MHz): δ -7.36 (d, 3 H, JPH
=
7.5 Hz), 2.66 (s, 12 H), 4.11 (t, 6 H, J = 8.1 Hz), 6.54 (t, 6 H, J =
7.6 Hz), 6.84 (t, 3 H, J = 7.4 Hz), 7.44 (d, 4 H, J = 7.3 Hz), 7.46
(d, 4 H, J = 7.6 Hz), 7.68 (d, 4 H, J = 7.4 Hz), 7.87 (d, 4 H,
J = 7.7 Hz), 8.38 (s, 8 H). 13C NMR (CDCl3, 75 MHz): δ -18.7
(2JPC = 118.8 Hz), 21.6, 122.5, 126.89, 126.91 (d, 3JPC = 9.4 Hz),
127.4, 127.9, 129.2 (d, 1JPC = 23.6 Hz), 130.9 (d, 2JPC = 11.2 Hz),
131.3, 133.9, 134.3, 136.8, 139.4, 142.4. HRMS (FABMS): calcd for
[C67H55N4PIr]þ ([M þ H]þ) m/z 1139.3788, found m/z 1139.3797.
Preparation of Hydrido(triphenylphosphine)(5,10,15,20-tetra-
kis(p-tolyl)porphyrinato)iridium(III), [Ir(ttp)H(PPh3)] (4b). Ir-
(ttp)H(PPh3)3 was prepared according to the procedure in the
synthesis of Ir(oep)H(PPh3) (oep = 2,3,7,8,12,13,17,18-oc-
taethylporphyrinato dianion).51 Ir(ttp)H (4a; 4.7 mg, 0.005 mmol),
(48) Alder, A. D.; Logon, F. R.; Finarelli, J. D.; Goldmacher, J.;
Assour, J.; Korsakof, L. J. Org. Chem. 1967, 32, 476.
(49) Chan, K. S.; Mak, K. W.; Tse, M. K.; Yeung, S. K.; Li, B. Z.;
Chan, Y. W. J. Organomet. Chem. 2008, 693, 399–407.
(50) Wagner, R. W.; Lawrence, D. S.; Lindsey, J. S. Tetrahedron Lett.
1987, 28, 3069–3070.
(51) Farnos, M. D.; Woods, B. A.; Wayland, B. B. J. Am. Chem. Soc.
1986, 108, 3659–3663.

Article
Organometallics, Vol. 29, No. 6, 2010 1351
PPh3 (1.4 mg, 0.005 mmol), and benzene-d6 (0.5 mL) were added to
the Teflon screw-capped NMR tube under N2, The reaction
mixture was degassed for three freeze-thaw-pump cycles and
then flame-sealed under vacuum. The reaction mixture changed to
reddish brown instantaneously at room temperature to give Ir-
(ttp)H(PPh3) (4b) quantitatively, as no other iridium porphyrin
species were observed in 1H NMR. 1H NMR (C6D6, 300 MHz):
δ -32.57 (d, 1 H, 2JPH = 258.6 Hz), 2.38 (s, 12 H), 4.51 (br, 6 H),
6.48 (br, 6 H), 6.64 (br, 3 H), 7.31 (d, 4 H, J = 7.7 Hz), 7.81 (d, 4 H,
J = 7.7 Hz), 7.90 (d, 4 H, J = 8.0 Hz), 8.75 (s, 8 H). One set of m-
phenyl H signals was shielded by the C6H6 signal. 13C NMR
(C6D6, 75 MHz): δ 21.5, 123.6, 127.3, 131.5 (d, 2JPC = 10.1 Hz),
132.0, 134.3, 134.7, 136.8, 139.9, 143.9; ipso-, m-, and p-phenyl C
signals of coordinated PPh3 and one m-tolyl group’s C signal of
poprhyrin were shielded by the C6H6 signal. HRMS (FABMS):
calcd for [C66H52N4IrP]þ ([M]þ) m/z 1124.3553, found m/z
1124.3520.
Preparation of Potassium (18-crown-6)(5,10,15,20-tetrakis(p-
tolyl)porphyrinato)iridate(I), [Ir(ttp)-][K(18-crown-6)þ] (5b). Ir-
(ttp)-K(18-crown-6)þ (5b) was synthesized according to the
procedure in the synthesis of Rh(ttp)-K(18-crown-6)þ.32 Ir-
(ttp)H (4a; 5.0 mg, 0.006 mmol), KOH (3.3 mg, 0.058 mmol), 18-
crown-6 ether (4.6 mg, 0.017 mmol), and THF-d8 (0.5 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 in 45 min to yield Ir(ttp)-K(18-crown-6)þ
(5b) quantitatively using the residual THF’s β-protons as the
internal standard. The THF-d8 solvent in the tube could be
removed under vacuum before flame-sealing, and degassed
benzene-d6 was added to obtain stable Ir(ttp)-K(18-crown-6)þ
(5b). 1H NMR (THF-d8, 300 MHz): δ 2.62 (s, 12 H). 7.45 (d, 8 H,
J = 7.7 Hz), 7.89 (d, 8 H, J = 7.7 Hz), 8.14 (s, 8 H). 1H NMR
(C6D6, 300 MHz): δ 2.38 (s, 12 H). 7.28 (d, 8 H, J = 7.7 Hz), 7.95
(d, 8 H, J = 7.9 Hz), 8.58 (s, 8 H).
(ii). In 5 Days. Ir(ttp)Cl(CO) (1a; 15.0 mg, 0.016 mmol) and
methanol (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
5 days. All Ir(ttp)Cl(CO) (1a) was consumed. The solvent was
then removed under vacuum, and the deep brown residue was
purified by column chromatography over alumina with a sol-
vent mixture of CH2Cl2 and hexane (1:2) as eluent. The major
orange fraction was collected to give Ir(ttp)CH3 (3a; 7.8 mg,
0.009 mmol, 55%).
General Procedures for Reactions of Ir(ttp)Cl(CO) (1a) with
Methanol and Various Bases. Addition of 5 Equiv of KOH.
Ir(ttp)Cl(CO) (1a; 15.0 mg, 0.016 mmol), KOH (4.6 mg, 0.081
mmol), and methanol (2 mL) were degassed for three free-
ze-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 to give Ir(ttp)CH3 (3a; 3.7 mg,
0.004 mmol, 26%).
Addition of 10 Equiv of KOH. Ir(ttp)Cl(CO) (1a; 15.0 mg,
0.016 mmol), KOH (9.1 mg, 0.16 mmol), and methanol (2 mL)
were degassed for three freeze-thaw-pump cycles in a Teflon
screw-capped tube. The reaction mixture was covered by alu-
minum foil and heated at 200 °C under N2 for 1 day to give
Ir(ttp)CH3 (3a; 8.4 mg, 0.010 mmol, 59%) and a trace amount of
Ir(ttp)CH2OMe (2).
Addition of 20 Equiv of KOH in 30 min. Ir(ttp)Cl(CO) (1a;
15.0 mg, 0.016 mmol), KOH (18.2 mg, 0.32 mmol), and metha-
nol (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 30 min to
give Ir(ttp)CH2OMe (2; 8.1 mg, 0.009 mmol, 55%) with
CH2Cl2/hexane (1:4) as eluent and Ir(ttp)CH3 (3a; 1.4 mg,
0.002 mmol, 10%) with CH2Cl2/hexane (1:2) as eluent.
Addition of 20 Equiv of KOH in 3 h. Ir(ttp)Cl(CO) (1a;
15.0 mg, 0.016 mmol), KOH (18.2 mg, 0.32 mmol), and metha-
nol (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 3 h to give
Ir(ttp)CH3 (3a; 3.3 mg, 0.004 mmol, 23%) and Ir(ttp)CH2OMe
(2; 8.1 mg, 0.009 mmol, 55%).
Addition of 20 Equiv of KOH in 1 day. Ir(ttp)Cl(CO) (1a;
15.0 mg, 0.016 mmol), KOH (18.2 mg, 0.32 mmol), and metha-
nol (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 1 day to give
Ir(ttp)CH3 (3a; 10.0 mg, 0.011 mmol, 70%).
Addition of 20 Equiv of KOH at 150 °C. Ir(ttp)Cl(CO) (1a;
15.0 mg, 0.016 mmol), KOH (18.2 mg, 0.32 mmol), and metha-
nol (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 1.5 days
to give Ir(ttp)CH2OMe (2; 0.6 mg, 0.0007 mmol, 4%) and
Ir(ttp)CH3 (3a; 4.4 mg, 0.005 mmol, 31%).
Addition of 30 Equiv of KOH. Ir(ttp)Cl(CO) (1a; 15.0 mg,
0.016 mmol), KOH (27 mg, 0.49 mmol), and methanol (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 1 day to give
Ir(ttp)CH3 (3a; 9.4 mg, 0.011 mmol, 66%) and a trace amount of
Ir(ttp)CH2OMe (2).
Addition of 20 Equiv of NaOH. Ir(ttp)Cl(CO) (1a; 15.0 mg,
0.016 mmol), NaOH (13.0 mg, 0.32 mmol), and methanol (2 mL)
were degassed for three freeze-thaw-pump cycles in a Teflon
screw-capped tube. The reaction mixture was covered by alu-
minum foil and heated at 200 °C under N2 for 1 day to give
Ir(ttp)CH3 (3a; 8.1 mg, 0.009 mmol, 57%) and a trace amount of
Ir(ttp)CH2OMe (2).
Preparation of Isopropoxy(5,10,15,20-Tetrakis(p-tolyl)por-
phyrinato)iridium(III), [Ir(ttp)OiPr] (7). Ir(ttp)Cl(CO) (1a; 6.6 mg,
0.0071 mmol), KOH (9.9 mg, 0.18 mmol), and isopropyl alcohol
(0.50 mL) were degassed for three freeze-thaw-pump cycles in a
Teflon screw-capped NMR tube. The reaction mixture was reacted
at room temperature under N2 for 10 min. The reaction mixture was
then dried at room temperature to remove most of the solvent under
vacuum. No heating was used during the removal of solvent to avoid
any decomposition of the product. C6D6 (0.5 mL) was added into
the tube under N2, and the reaction mixture was further degassed for
three freeze-thaw-pump cycles and then flame-sealed under va-
cuum. The NMR yield of Ir(ttp)OiPr (7) was estimated to be ∼85%
using the ratios of pyrrole proton’s integrations of Ir(ttp)OiPr (7)
and unknown iridium porphyrin species (8.00:1.42). 1H NMR
(C6D6, 400 MHz): δ -3.25 (hep, 1 H, J = 6.0 Hz), -1.94 (d, 6
H, J=5.6Hz), 2.42(s, 12H),7.28(d, 4H, J= 8.8 Hz), 7.30 (d, 4 H,
J= 8.8 Hz), 8.06 (d, 4 H, J=7.6Hz),8.10(d,4H,J=7.2Hz),8.51
(s, 8 H). 13C NMR and MS cannot be obtained, due to the
decomposition of 7 upon standing under N2 over a short time.
Reaction of Ir(ttp)Cl(CO) (1a) with Methanol. (i). In 1 Day.
Ir(ttp)Cl(CO) (1a; 15.0 mg, 0.016 mmol) and methanol (2.0 mL)
were degassed for three freeze-thaw-pump cycles in a Teflon
screw-capped tube. The reaction mixture was covered by alu-
minum foil and heated at 200 °C under N2 for 1 day. The solvent
was then removed under vacuum, and the deep brown residue
was purified by column chromatography over alumina with a
solvent mixture of CH2Cl2 and hexane (1:2) as eluent. The major
orange fraction was collected to give Ir(ttp)CH3 (3a; 2.8 mg,
0.003 mmol, 20%). Unreacted Ir(ttp)Cl(CO) (1a) in 37% yield
and Ir(ttp)H (4a) in 9% yield were observed in the crude reaction
mixture by 1H NMR spectroscopy, but they cannot be isolated
over alumina, and their yields were estimated using the ratios of
pyrrole proton signals of Ir(ttp)CH3 (3a), Ir(ttp)Cl(CO) (1a),
Addition of 20 Equiv of K3PO4. Ir(ttp)Cl(CO) (1a; 15.0 mg,
0.016 mmol), K3PO4 (69 mg, 0.32 mmol), and methanol (2 mL)
were degassed for three freeze-thaw-pump cycles in a Teflon
1
and Ir(ttp)H (4a) in the crude reaction mixture by H NMR
spectroscopy and the isolated yield of Ir(ttp)CH3 (3a).

1352 Organometallics, Vol. 29, No. 6, 2010
Cheung et al.
screw-capped tube. The reaction mixture was covered by alu-
minum foil and heated at 200 °C under N2 for 1 day to give
Ir(ttp)CH3 (3a; 7.2 mg, 0.008 mmol, 51%) and a trace amount of
Ir(ttp)CH2OMe (2).
Addition of 20 Equiv of Na2CO3. Ir(ttp)Cl(CO) (1a; 15.0 mg,
0.016 mmol), Na2CO3 (34 mg, 0.32 mmol), and methanol (2 mL)
were degassed for three freeze-thaw-pump cycles in a Teflon
screw-capped tube. The reaction mixture was covered by alu-
minum foil and heated at 200 °C under N2 for 1 day to give
Ir(ttp)CH3 (3a; 8.8 mg, 0.010 mmol, 62%).
Addition of 20 Equiv of K2CO3. Ir(ttp)Cl(CO) (1a; 15.0 mg,
0.016 mmol), K2CO3 (45 mg, 0.32 mmol), and methanol (2 mL)
were degassed for three freeze-thaw-pump cycles in a Teflon
screw-capped tube. The reaction mixture was covered by alu-
minum foil and heated at 200 °C under N2 for 1 day to give
Ir(ttp)CH3 (3a; 7.8 mg, 0.009 mmol, 55%) and a trace amount of
Ir(ttp)CH2OMe (2).
by aluminum foil, and no reaction occurred at room temperature in
1 day. The reaction mixture was then heated at 200 °C in an oil bath.
In 4 days, Ir(ttp)D (4a-d) was observed, and most of the undissolved
Ir(ttp)Cl(CO) remained unreacted as a reddish purple solid. After 23
days, Ir(ttp)Cl(CO) and Ir(ttp)D were consumed, and Ir(ttp)CD3
(3a-d3; 5.5 mg, 0.006 mmol, 100%) was isolated by column chro-
matography. The formation of Ir(ttp)D (4a-d) and Ir(ttp)CD3 (3a-
d3) was confirmed by the authentic samples of Ir(ttp)H (4a) and
1
Ir(ttp)CH3 (3a) in CD3OD. H NMR of Ir(ttp)H (4a) (CD3OD,
300 MHz): δ 2.74 (s, 12 H). 7.61 (d, 8 H, J = 7.5 Hz), 8.04 (d, 4 H,
J = 7.8 Hz), 8.06 (d, 4 H, J = 7.8 Hz), 8.50 (s, 8 H). No hydride
signal of Ir(ttp)H was observed due to proton exchange between
Ir(ttp)-HandCD3O-D to give Ir(ttp)D.37 1H NMR of Ir(ttp)CH3
(3a) (CD3OD, 300 MHz): δ -7.07 (s, 3 H), 2.74 (s, 12 H). 7.61 (d, 8
H, J = 7.5 Hz), 8.03 (d, 4 H, J = 9.0 Hz), 8.06 (d, 4 H, J = 8.4 Hz),
8.46 (s, 8 H).
(ii). With KOH. Ir(ttp)Cl(CO) (1a; 5.2 mg, 0.006 mmol), KOH
(6.3 mg, 0.11 mmol), and methanol-d4 (0.5 mL) were degassed for
three freeze-thaw-pump cycles in a Teflon screw-capped NMR
tube and then flame-sealed under vacuum. The course of the reaction
was monitored by 1H NMR spectroscopy. The reaction mixture was
covered by aluminum foil, and reaction occurred at room tempera-
ture in 1 day to give a small amount of Ir(ttp)D (4a-d) and
Ir(ttp)CD2OCD3 (2-d5). The reaction mixture was then heated at
200 °C in an oil bath. In 30 min, Ir(ttp)Cl(CO) was completely
consumed, and Ir(ttp)-Kþ (5a) and Ir(ttp)CD2OCD3 (2-d5) were
observed. Ir(ttp)CD3 (3a-d3) was also formed in 90 min. In 4 days,
all Ir(ttp)CD2OCD3 and Ir(ttp)-Kþ were consumed, and only
Ir(ttp)CD3 (3a-d3) (4 mg, 0.005 mmol, 81%) was isolated using
column chromatography with CH2Cl2/hexane (1:2) as the eluent. 1H
NMR of Ir(ttp)-Kþ (5a) (CD3OD, 300 MHz): δ 2.67 (s, 12 H), 7.51
(d, 8 H, J = 7.5 Hz), 7.90 (d, 8 H, J = 6.3 Hz), 8.11 (s, 8 H).
Reaction of Ir(ttp)H (4a) with Methanol. Ir(ttp)H (1a; 10.3 mg,
0.012 mmol) and methanol (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. In 1 day, some brown Ir(ttp)H remained
unreacted. In 3 days, a dark brown solid was formed. The
solvent was then removed under vacuum, and the deep brown
residue was purified by column chromatography over alumina
with a solvent mixture of CH2Cl2 and hexane (1:2) as eluent to
give Ir(ttp)CH3 (3a; 6.9 mg, 0.008 mmol, 66%).
Reactivities of Iridium Porphyrin Intermediates with Metha-
nol-d4 in Sealed NMR Tubes. (i). Ir(ttp)H (4a). Ir(ttp)H (4a;
5.0 mg, 0.006 mmol) and methanol-d4 (0.5 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 heated at 200 °C, and Ir(ttp)H turned to Ir(ttp)D
(4a-d) instantaneously.37 Upon heating for 23 days, some Ir-
(ttp)D (4a-d) remained unreacted, as was observed by 1H NMR
spsectroscopy, and a deep brown solid was formed. The solvent
was then removed under vacuum. The deep brown residue
was purified by column chromatography over alumina with a
solvent mixture of CH2Cl2 and hexane (1:2) as eluent to obtain
Ir(ttp)CD3 (3a-d3; 2.0 mg, 0.002 mmol, 39%). Unreacted Ir-
(ttp)D (4a-d) cannot be isolated by column chromatography.
(ii). Ir(ttp)H (4a) with KOH. Ir(ttp)H (4a; 5.0 mg, 0.006
mmol), KOH (6.5 mg, 0.12 mmol), and methanol-d4 (0.5 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 for 5 min to give pale brown Ir(ttp)-Kþ (5a) in ∼90%
yield and Ir(ttp)D in ∼10% yield. Ir(ttp)-Kþ (5a) and Ir(ttp)D
(4a-d) were consumed at 200 °C in 4 days, and a deep brown
solid was formed. The solvent was then removed under vacuum,
and the deep brown residue was purified by column chroma-
tography over alumina with a solvent mixture of CH2Cl2 and
hexane (1:2) as eluent to obtain Ir(ttp)CD3 (3a-d3; 2.9 mg, 0.003
mmol, 57%).
Addition of 20 Equiv of Cs2CO3. Ir(ttp)Cl(CO) (1a; 15.0 mg,
0.016 mmol), Cs2CO3 (106 mg, 0.32 mmol), and methanol
(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 1 day to give
Ir(ttp)CH3 (3a; 6.1 mg, 0.007 mmol, 43%).
Addition of 20 Equiv of NaOAc. Ir(ttp)Cl(CO) (1a; 15.0 mg,
0.016 mmol), NaOAc (27 mg, 0.32 mmol), and methanol (2 mL)
were degassed for three freeze-thaw-pump cycles in a Teflon
screw-capped tube. The reaction mixture was covered by alu-
minum foil and heated at 200 °C under N2 for 1 day to give
Ir(ttp)CH3 (3a; 8.1 mg, 0.009 mmol, 57%) and a trace amount of
Ir(ttp)CH2OMe (2).
Addition of 20 Equiv of KOAc. Ir(ttp)Cl(CO) (1a; 15.0 mg,
0.016 mmol), KOAc (31 mg, 0.32 mmol), and methanol (2 mL)
were degassed for three freeze-thaw-pump cycles in a Teflon
screw-capped tube. The reaction mixture was covered by alu-
minum foil and heated at 200 °C under N2 for 1 day to give
Ir(ttp)CH3 (3a; 6.5 mg, 0.007 mmol, 46%) and a trace amount of
Ir(ttp)CH2OMe (2).
Reaction of Ir(btpp)Cl(CO) with Methanol and KOH: Pre-
paration of Methyl(5,10,15,20-tetrakis(p-tert-butylphenyl)porp-
hyrinato)iridium(III) (3b). Ir(btpp)Cl(CO) (1b; 15.0 mg, 0.014 mmol),
KOH (15.4 mg, 0.27 mmol), and methanol (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 1 day to give Ir(btpp)CH3 (3b; 10.3 mg, 0.010 mmol,
72%). 1HNMR(THF-d8, 300 MHz): δ-6.86 (s, 3 H), 1.71 (s, 36 H),
7.88 (d, 4 H, J = 7.2 Hz), 7.91 (d, 4 H, J = 7.8 Hz), 8.15 (d, 4 H, J =
6.6 Hz), 8.17 (d, 4 H, J = 7.8 Hz), 8.54 (s, 8 H). 13C NMR (THF-d8,
100 MHz): δ -43.1, 32.3, 35.8, 124.5, 124.6, 124.7, 132.0, 134.89,
134.93, 140.5, 144.5, 151.2. HRMS (FABMS): calcd for [C61H63-
N4Ir]þ m/z 1044.4676, found m/z 1044.4646.
Reaction of Ir(tmp)Cl(CO)23 (1c) with Methanol and KOH.
Ir(tmp)Cl(CO) (1c; 15.0 mg, 0.014 mmol), KOH (16.2 mg,
0.29 mmol), and methanol (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 1 day to give Ir(tmp)CH3 (3c;24 9.4 mg,
0.010 mmol, 66%).
Reaction of Ir(ttp)Cl(CO) (1a) with Methanol-d4 and KOH.
Ir(ttp)Cl(CO) (1a; 15.0 mg, 0.016 mmol), KOH (18.2 mg,
0.32 mmol), and methanol-d4 (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 1 day to give Ir(ttp)CD3 (3a-d3; 10.0 mg,
0.011 mmol, 70%).
Reaction of Ir(ttp)Cl(CO) (1a) with Methanol-d4 in a Sealed
NMR Tube. (i). Without KOH. Ir(ttp)Cl(CO) (1a; 5.8 mg, 0.006
mmol) and methanol-d4 (0.5 mL) were degassed for three freeze-
thaw-pump cycles in a Teflon screw-capped NMR tube and then
flame-sealed under vacuum. The course of the reaction was mon-
itored by 1H NMR spectroscopy. The reaction mixture was covered

Article
(iii). [Ir(ttp)]2 Dimer16e (6). Ir(ttp)H (4a; 5.0 mg, 0.006 mmol)
Organometallics, Vol. 29, No. 6, 2010 1353
was covered by aluminum foil and heated at 200 °C in an oil bath
for 1 day to yield Ir(ttp)CH2OCD3 (2-d3; 3.7 mg, 0.004 mmol,
74%) and Ir(ttp)CD3 (3a-d3; 0.2 mg, 0.0003 mmol, 5%) after
column chromatography using alumina with a solvent mixture of
CH2Cl2 and hexane (1:2) as eluent.
Thermal Stability of Ir(ttp)CH2OMe (2) in C6D6. Ir-
(ttp)CH2OMe (2; 1.9 mg, 0.002 mmol) and benzene-d6 (0.5
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 for 14 days. Ir(ttp)CH2OMe (2) did not
react, and it was recovered quantitatively using residual ben-
zene’s protons as an internal standard.
and benzene (0.5 mL) were degassed for three freeze-
thaw-pump cycles in a Teflon screw-capped NMR tube.
2,2,6,6-Tetramethylpiperidinooxy (TEMPO; 1.0 mg, 0.006 mmol)
was added to the reaction mixture under N2. The reaction
mixture was then shaken for 1 min to undergo dehydrogenative
dimerization of Ir(ttp)H (4a) to yield [Ir(ttp)]2 dimer (6) quanti-
tatively. The reaction mixture was dried under vacuum in warm
water overnight. Degassed methanol-d4 (0.5 mL) was added to
the reaction mixture under N2, and the reaction mixture was
further degassed for three freeze-thaw-pump cycles and then
flame-sealed under vacuum. The reaction mixture was covered
by aluminum foil and heated at 200 °C for 16 h, and Ir-
(ttp)CD2OCD3 (2-d5), Ir(ttp)CD3 (3a-d3), and a trace amount
of Ir(ttp)D (4a-d) were observed by 1H NMR spectroscopy. The
solvent was then removed under vacuum, and the deep brown
residue was purified by column chromatography over alumina
with a solvent mixture of CH2Cl2 and hexane (1:2) as eluent to
obtain Ir(ttp)CD2OCD3 (2-d5; 2.4 mg, 0.003 mmol, 44%) and
Ir(ttp)CD3 (3a-d3; 0.4 mg, 0.0004 mmol, 7%). Unreacted Ir-
(ttp)D (4a-d) cannot be isolated by column chromatography. 1H
NMR of [Ir(ttp)]2 (6) (CD3OD, 300 MHz): δ 2.77 (s, 12 H). 7.66
(d, 8 H, J = 7.5 Hz), 8.14 (d, 8 H, J = 7.8 Hz), 8.71 (s, 8 H).
(iv). [Ir(ttp)]2 Dimer16e (6) with KOH. Ir(ttp)H (4a; 5.0 mg,
0.006 mmol) and benzene (0.5 mL) were degassed for three
freeze-thaw-pump cycles in a Teflon screw-capped NMR
tube. 2,2,6,6-Tetramethylpiperidinooxy (TEMPO; 1.0 mg,
0.006 mmol) was added to the reaction mixture under N2. The
reaction mixture was then shaken for 1 min to undergo dehy-
drogenative dimerization of Ir(ttp)H (4a) to yield [Ir(ttp)]2
dimer (6) quantitatively. The reaction mixture was dried under
vacuum in warm water overnight. Degassed methanol-d4 (0.5
mL) and KOH (6.5 mg, 0.12 mmol) were added to the reaction
mixture under N2, and the reaction mixture was further de-
gassed for three freeze-thaw-pump cycles and flame-sealed
under vacuum. The reaction mixture was covered by aluminum
foil and heated at 200 °C for 5 min to give pale brown Ir(ttp)-Kþ
(5a) in ∼90% yield with Ir(ttp)D in ∼10% yield (4a-d). Ir-
(ttp)-Kþ (5a) and Ir(ttp)D (4a-d) were consumed at 200 °C in 4
days, and a deep brown solid was formed. The solvent was then
removed under vacuum, and the deep brown residue was
purified by column chromatography over alumina with a sol-
vent mixture of CH2Cl2 and hexane (1:2) as eluent to obtain
Ir(ttp)CD3 (3a-d3; 3.0 mg, 0.003 mmol, 59%).
Reaction of Ir(ttp)CH2OMe (2) with Methanol-d4 and KOH.
Ir(ttp)CH2OMe (2; 4.3 mg, 0.005 mmol), methanol-d4 (0.4 mL),
and KOH (5.3 mg, 0.095 mmol) 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 an oil bath.
In 1 day, Ir(ttp)-Kþ (5a) and Ir(ttp)CD3 (3a-d3) were formed,
and some of the Ir(ttp)CH2OMe exchanged with CD3OD to
yield Ir(ttp)CH2OCD3 (2-d3). In 4 days, Ir(ttp)CD3 (3a-d3; 2.6
mg, 0.003 mmol, 62%) was isolated by column chromatography
using alumina with a solvent mixture of CH2Cl2 and hexane
(1:2) as eluent. Recovered Ir(ttp)CH2OMe (2; 4%, NMR yield)
and Ir(ttp)CH2OCD3 (2-d3; 24%, NMR yield) were observed in
the crude reaction mixture by 1H NMR spectroscopy but cannot
be isolated, and their yields were estimated using the integra-
tions of o-phenyl protons of total iridium porphyrin products
and the methylene and methyl protons of Ir(ttp)CH2OCH3/
Ir(ttp)CH2OCD3 in the crude reaction mixture by 1H NMR
spectroscopy.
Effect of PPh3 on the Reactions of Iridium Porphyrins and
Methanol. (i). Ir(ttp)-Kþ with PPh3 at 100 °C. Ir(ttp)H (4a;
8.1 mg, 0.009 mmol), KOH (10.5 mg, 0.19 mmol), 18-crown-6
ether (7.4 mg, 0.028 mmol), and THF (1 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 for 45 min to yield Ir(ttp)-[K(18-crown-6)]þ (5b)
quantitatively. The solvent was then removed under vacuum,
and the reaction mixture was further dried in warm water for a
few hours. PPh3 (2.5 mg, 0.009 mmol) and degassed methanol
(2 mL) were added to the tube under N2, and the tube was
further degassed for three freeze-thaw-pump cycles. Ir-
(ttp)CH3(PPh3) (3d) was observed by thin-layer chromatogra-
phy when the reaction mixture was stirred at room temperature
for 5 min. The reaction mixture was further heated at 100 °C for
36 h to give a deep purple precipitate. The reaction mixture was
dried under vacuum, and the deep purple residue was purified by
column chromatography over alumina with a solvent mixture of
CH2Cl2 and hexane (1:4) as eluent to give Ir(ttp)CH3(PPh3) (3d;
1.8 mg, 0.002 mmol, 17%).
(v). Ir(ttp)-[K(18-crown-6)]þ (5b). Ir(ttp)H (4a; 5.2 mg,
0.006 mmol), KOH (6.8 mg, 0.12 mmol), 18-crown-6 ether
(4.8 mg, 0.018 mmol), and THF (0.5 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 in an oil bath for 45 min to yield Ir(ttp)-[K(18-crown-
6)]þ (5b) quantitatively. The solvent in the tube was then
removed under vacuum, and the reaction mixture was further
dried in warm water for a few hours. Methanol-d4 (0.5 mL) was
added to the tube under N2, and the tube was further degassed
for three freeze-thaw-pump cycles and then flame-sealed
under vacuum. The reaction mixture was heated at 200 °C,
and pale brown Ir(ttp)-[K(18-crown-6)]þ (5b) was consumed in
4 days to give a deep brown solid. The reaction mixture was
dried under vacuum, and the deep brown residue was purified by
column chromatography over alumina with a solvent mixture of
CH2Cl2 and hexane (1:2) as eluent to give Ir(ttp)CD3 (3a; 4.5 mg,
0.005 mmol, 85%). 1H NMR of pure Ir(ttp)-[K(18-crown-6)]þ
(5b) in CD3OD cannot be obtained, as some of it reacted
instantaneously with CD3OD at room temperature to yield
Ir(ttp)CD3 (3a-d4).
(ii). Ir(ttp)-Kþ at 100 °C. Ir(ttp)H (4a; 8.4 mg, 0.010 mmol),
KOH (10.9 mg, 0.19 mmol), 18-crown-6 ether (7.7 mg, 0.029 mmol),
and THF (1 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 for 45 min to
yield Ir(ttp)-[K(18-crown-6)]þ (5b) quantitatively. The solvent
in the tube was then removed under vacuum, and the reaction
mixture was further dried in warm water for a few hours.
Degassed methanol (2 mL) was added to the tube under N2,
and the tube was further degassed for three freeze-thaw-pump
cycles. Ir(ttp)CH3 (3a) was not observed by thin-layer chroma-
tography when the reaction mixture was stirred at room tem-
perature for 5 min. The reaction mixture was further heated at
100 °C for 72 h. The reaction mixture was dried under vacuum,
and the deep brown residue was purified by column chromato-
graphy over alumina with a solvent mixture of CH2Cl2 and
hexane (1:3) as eluent to give Ir(ttp)CH3 (3a; 0.8 mg, 0.001
mmol, 9%).
Reactivity of Ir(ttp)H with Paraformaldehyde and Methanol-
d4. Ir(ttp)H (4a; 4.7 mg, 0.005 mmol), paraformaldehyde (2.8 mg,
0.09 mmol HCHO), and methanol-d4 (0.5 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

1354 Organometallics, Vol. 29, No. 6, 2010
Cheung et al.
(iii). Ir(ttp)-Kþ with PPh3 at 200 °C. (a). 1 h. Ir(ttp)H (4;
9.8 mg, 0.011 mmol), KOH (6.4 mg, 0.11 mmol), 18-crown-6
ether (9.0 mg, 0.034 mmol), and THF (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 150 °C in 45 min to yield Ir(ttp)-[K(18-crown-6)]þ (5)
quantitatively. The solvent in the tube was then removed under
vacuum, and the reaction mixture was further dried in warm
water for a few hours. PPh3 (3.0 mg, 0.011 mmol) and degassed
methanol (1 mL) were added to the tube under N2, and the tube
was further degassed for three freeze-thaw-pump cycles. The
reaction mixture was heated at 200 °C for 1 h to yield Ir-
(ttp)CH3(PPh3) (3d; 3.8 mg, 0.003 mmol, 29%).
and the tube was further degassed for three freeze-thaw-pump
cycles. The reaction mixture was heated at 200 °C for 1 day to
give Ir(ttp)CH3 (3a; 9.0 mg, 0.010 mmol, 87%).
(v). Ir(ttp)H with PPh3 at 200 °C. Ir(ttp)H (4a; 10.0 mg,
0.012 mmol), PPh3 (3.0 mg, 0.012 mmol), and methanol (1 mL)
were degassed for three freeze-thaw-pump cycles in a Teflon
screw-capped tube. The reaction mixture changed to reddish
brown instantaneously due to the formation of Ir(ttp)H(PPh3)
(4b).51 The reaction mixture was covered by aluminum foil and
heated at 200 °C. No Ir(ttp)CH3(PPh3) (3d) was observed in 1.5 h
by thin-layer chromatography. The reaction mixture was further
heated for 3 days to yield Ir(ttp)CH3(PPh3) (3d;3.2mg, 0.003mmol,
24%).
(b). 12 h. Ir(ttp)H (4a; 10.3 mg, 0.012 mmol), KOH (13.4 mg,
0.24 mmol), 18-crown-6 ether (9.5 mg, 0.036 mmol), and THF
(1 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 for 45 min to yield Ir(ttp)--
[K(18-crown-6)]þ (5b) quantitatively. The solvent in the tube
was then removed under vacuum, and the reaction mixture was
further dried in warm water for a few hours. PPh3 (3.1 mg, 0.012
mmol) and degassed methanol (1 mL) were added to the tube
under N2, and the tube was further degassed for three freeze-
thaw-pump cycles. The reaction was heated at 200 °C for
12 h to yield Ir(ttp)CH3(PPh3) (3d; 7.0 mg, 0.006 mmol, 52%).
(c). 24 h. Ir(ttp)H (4a; 10.4 mg, 0.012 mmol), KOH (13.5 mg,
0.24 mmol), 18-crown-6 ether (9.6 mg, 0.036 mmol), and THF
(1 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 for 45 min to yield Ir(ttp)--
[K(18-crown-6)]þ (5b) quantitatively. The solvent in the tube
was then removed under vacuum, and the reaction mixture was
further dried in warm water for a few hours. PPh3 (3.2 mg, 0.012
mmol) and degassed methanol (1 mL) were added to the tube
under N2, and the tube was further degassed for three freeze-
thaw-pump cycles. The reaction was heated at 200 °C for 1 day
to yield Ir(ttp)CH3(PPh3) (3d; 10.6 mg, 0.009 mmol, 77%).
(iv). Ir(ttp)-Kþ at 200 °C. (a). 12 h. Ir(ttp)H (4a; 9.7 mg,
0.011 mmol), KOH (12.6 mg, 0.23 mmol), 18-crown-6 ether
(8.9 mg, 0.034 mmol), and THF (1 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 for 45 min to yield Ir(ttp)-[K(18-crown-6)]þ (5b) quan-
titatively. The solvent in the tube was then removed under
vacuum, and the reaction mixture was further dried in warm
water for a few hours. Degassed methanol (1 mL) was added to
the tube under N2, and the tube was further degassed for three
freeze-thaw-pump cycles. The reaction mixture was heated at
200 °C for 12 h to give Ir(ttp)CH3 (3a; 2.8 mg, 0.003 mmol,
28%).
Study of Methyl Group Exchange of Ir(ttp)CH3 (3a) with
Methanol-d4. (i). Without Base. Ir(ttp)CH3 (3a) (11.0 mg,
0.013 mmol) and methanol-d4 (1 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. The solvent was then removed under
vacuum and the deep brown residue was purified by column
chromatography over alumina eluting with a solvent mixture of
CH2Cl2 and hexane (1:2). The major orange fraction was
collected to give only unreacted Ir(ttp)CH3 (3a) (8.8 mg, 0.010
mmol, 80%) without Ir(ttp)CD3 (3a-d3), since the intergration
signals of pyrrole: methyl = 8.00: 3.00 in the isolated product by
1H NMR spectroscopy.
(ii). With Base. Ir(ttp)CH3 (3a) (8.1 mg, 0.009 mmol), KOH
(10.5 mg, 0.19 mmol), and methanol-d4 (1 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. The solvent was then removed
under vacuum and the deep brown residue was purified by
column chromatography over alumina eluting with a solvent
mixture of CH2Cl2 and hexane (1:2). The major orange fraction
was collected to give Ir(ttp)CH3 (3a) (5.3 mg, 0.006 mmol, 65%)
and Ir(ttp)CD3 (3a-d3) (1.5 mg, 0.002 mmol, 18%) using the
ratio of 3a: 3a-d3 in the isolated product [3.6: 1.0 (integration of
methyl’s proton was set as 3.00; integration of pyrrole’s proton
1
of Ir(ttp)CH3 and Ir(ttp)CD3 = 10.23] by H NMR spectro-
scopy.
Proton Exchange of Ir(ttp)H (4a) with 50 equiv of CD3OD.
Ir(ttp)H (4a; 1.9 mg, 0.002 mmol), methanol-d4 (4.0 mg, 4.5 μL,
0.11 mmol), and benzene-d6 (0.5 mL) were degassed for three
freeze-thaw-pump cycles in a Teflon screw-capped NMR tube
and then flame-sealed under vacuum. After 6 h at room tem-
perature, Ir(ttp)D (4a-d) in 77% NMR yield was formed and
some Ir(ttp)H (4a) remained unreacted in 23% NMR yield using
residual benzene as the internal standard.
Acknowledgment. We thank the Research Grants
Council of the HKSAR, People’s Republic of China
(CUHK 400308), for financial support.
(b). 24 h. Ir(ttp)H (4a; 10.2 mg, 0.012 mmol), KOH (13.3 mg,
0.24 mmol), 18-crown-6 ether (9.4 mg, 0.035 mmol), and THF
(1 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 in 45 min to yield
Ir(ttp)-[K(18-crown-6)]þ (5b) quantitatively. The solvent in
the tube was then removed under vacuum, and the reaction
mixture was further dried in warm water for a few hours.
Degassed methanol (1 mL) was added to the tube under N2,
Supporting Information Available: Table and figure of crystal-
lographic data for complex 2 (CIF and PDF), sequence of
reactions monitored by 1H NMR, and 1H and 13C NMR
spectra. This material is available free of charge via the Internet
at http://pubs.acs.org.