Selective oxidation of (porphyrinato)iridium(III) arylethyls by nitroxide: Evidence for stabilization of carbon-centered Ir-CH2-CHR radicals by iridium

Article abstract of DOI:10.1021/om050661a

(Arylethyl)iridium(III) porphyrins were oxidized selectively with excess 2,2,6,6-tetramethylpiperidinoxy (TEMPO) at the benzylic positions to yield (2-aryl-2-oxoethyl)iridium porphyrins. Other alkyl- and PhCH₂CH ₂CH₂-substituted iridium porphyrins did not react or gave complex mixtures and low yields of indium methyl. The proposed intermediate of the carbon-centered Ir^III(CH₂CHR) radical is probably stabilized by the β iridium center, allowing the (slipped) olefin metalloradical complex Ir^II(CH₂=CHR) as a reasonable resonance structure.

Full text of DOI:10.1021/om050661a

6426
Organometallics 2005, 24, 6426-6430
Selective Oxidation of (Porphyrinato)iridium(III)
Arylethyls by Nitroxide: Evidence for Stabilization of
Carbon-Centered Ir-CH2-CHR• Radicals by Iridium
Siu Kwan Yeung and Kin Shing Chan*
Department of Chemistry, The Chinese University of Hong Kong, Shatin,
New Territories, Hong Kong, China
Received August 1, 2005
(Arylethyl)iridium(III) porphyrins were oxidized selectively with excess 2,2,6,6-tetram-
ethylpiperidinoxy (TEMPO) at the benzylic positions to yield (2-aryl-2-oxoethyl)iridium
porphyrins. Other alkyl- and PhCH2CH2CH2-substituted iridium porphyrins did not react
or gave complex mixtures and low yields of iridium methyl. The proposed intermediate of
the carbon-centered IrIII(CH2CHR•) radical is probably stabilized by the â iridium center,
allowing the (slipped) olefin metalloradical complex IrII(CH2dCHR) as a reasonable resonance
structure.
Introduction
2,2,6,6-Tetramethylpiperidinoxy (TEMPO) and re-
lated nitroxides exhibit a rich chemistry with organo-
metallic alkyls. In the determination of bond dissocia-
tion energies of transition-metal-alkyl bonds by kinetic
methods, nitroxides are efficient alkyl radical traps
which are extensively applied in the chemistry of
vitamin B12 and related models,1,2 cyclopentadienyl-
metal alkyl complexes,3 and alkylruthenium porphyrin
complexes.4,5 They also react directly as reagents with
metal alkyls bearing â-hydrogens via hydrogen atom
abstraction to produce reactive metal-centered radicals
which subsequently activate the alkyl-methine carbon-
carbon bonds of nitroxides to give new alkylrhodium
porphyrins.6,7 Some reactions of metal alkyls proceed
via initial â-hydrogen elimination to give metal hy-
drides, which subsequently react with TEMPO.8 Reac-
tions of TEMPO with rhodium and iridium porphyrin
hydrides to give their corresponding metal dimers are
known.9 TEMPO reacts with the methyl group of Ru-
(oep)Me (oep2- ) octaethylporhyrinate dianion) to give
(oep)Ru(CO). Through 13C labeling it could be proven
that the carbonyl carbon atom indeed stems from the
methyl group (lacking â-hydrogens) of the starting
Figure 1. Structure of Ir(ttp)R.
material.10 We have extended the studies of the reac-
tions of rhodium porphyrin alkyls with nitroxides6 to
that of iridium porphyrin alkyls and herein report the
unique selective oxidation of ArCH2CH2Ir(ttp) at the
benzylic position by TEMPO to give Ar(CO)CH2Ir(ttp).
In addition, this paper gives further proof for the
recently described stabilization of carbon-centered
IrIII(CH2CHR•) radicals by the iridium center, which
allows delocalization of the radical by giving access to
the (slipped) olefin metalloradical complex IrII(CH2d
CHR) as a reasonable resonance structure.11
Results and Discussion
Iridium porphyrin alkyls were synthesized in moder-
ate to good yields according to the literature method by
the reductive alkylation of Ir(ttp)(CO)Cl (ttp ) 5,10,-
15,20-tetra-4-tolylporphyrinate; Figure 1) with NaBH4
and RI/RBr (Figure 1).12,13 We investigated the reactiv-
ity of Ir(ttp)R toward TEMPO at elevated temperatures.
The reactivity toward TEMPO strongly depends on the
nature of the alkyl group R. We observed three possible
outcomes of the reaction (Scheme 1): i.e., â-carbon
* To whom correspondence should be addressed. E-mail: ksc@
cuhk.edu.hk.
(1) (a) Halpern, J. Polyhedron 1998, 7, 1483-1490. (b) Ng, F. T. T.;
Rempel, G. L.; Mancuso, C.; Halpern, J. Organometallics 1990, 9,
2762-2772.
(2) (a) Koenig, T. W.; Hay, B. P.; Finke, R. G. Polyhedron 1988, 7,
1499-1516. (b) Garr, C. D.; Finke, R. G. J. Am. Chem. Soc. 1992, 114,
10440-10445.
(3) Mancuso, C.; Halpern, J. J. Organomet. Chem. 1992, 428, C8-
C11.
(4) Collman, J. P.; McElwee, L.; Brothers, P. J.; Rose, R. J. Am.
Chem. Soc. 1986, 108, 1332-1333.
(10) Selyer, J. W.; Fanwick, P. E.; Leidner, C. R. Inorg. Chem. 1992,
31, 3699-3700.
(5) Ke, M.; Rettig, S. J.; James, B. R. Dolphin, D. J. Chem. Soc.,
Chem. Commun. 1987, 1110-1111.
(11) Hetterscheid, D. G. H.; Kaiser, J.; Reijerse, E.; Peters, T. P. J.;
Thewissen, S.; Blok, A. N. J.; Smits, J. M. M.; de Gelder, R.; de Bruin,
B. J. Am. Chem. Soc. 2005, 127, 1895-1905.
(6) Mak, K. W.; Yeung, S. K.; Chan, K. S. Organometallics 2002,
21, 2362-2364.
(7) Tse, M. K.; Chan, K. S. Dalton Trans. 2001, 510-511.
(8) Chan, K. S.; Leung, Y.-B. Inorg. Chem. 1994, 33, 3187.
(9) Albe´niz, A. C.; Espinet, P.; Lo´pez-Fernaa´dez, R.; Sen, A. J. Am.
Chem. Soc. 2002, 124, 11278-11279.
(12) Ogoshi, H.; Setsune, J.-I.; Yoshida, Z.-I. J. Organomet. Chem.
1978, 159, 317-328.
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Chem. Soc. 1975, 97, 6461-6466.
10.1021/om050661a CCC: $30.25 © 2005 American Chemical Society
Publication on Web 11/08/2005

Stabilization of Ir-CH2-CHR• by Iridium
Organometallics, Vol. 24, No. 26, 2005 6427
cleavage as was observed for Rh(ttp)CH2CHPh.6 In-
stead, A cross-couples rapidly with TEMPO,17 especially
in excess, to give the oxygenated intermediate B.
Intermediate B then decomposes with formation of the
Ir(tpp)CH2C(O)Ar products, either directly via a shift
of the remaining â-hydrogen to the attached “TEMPO”
nitrogen (with elimination of R2NH) or via abstraction
of the remaining benzylic hydrogen in B by an ad-
ditional TEMPO molecule. The ketone product could
then be obtained via elimination of a reactive free
aminyl radical which participates in hydrogen abstrac-
tion of another intermediate B. The latter possibility
would account for the observed increased rates and
yields in the presence of excess TEMPO. The mecha-
nism proposed here for the â oxidation of IrIIICH2CH2-
Ar compounds with TEMPO resembles the recently
proposed mechanism of IrII(ethene) species with O2 via
â oxidation of intermediate IrIII-CH2CH2• carbon radi-
cals.19
Scheme 1
oxidation (type 1), formation of Ir(ttp)Me (type 2), and
simple recovery of the starting material (type 3).
Type 1. Arylethyliridium porphyrins 1a-d (eq 1;
Table 1, entries 1-4) reacted cleanly with 15 equiv of
TEMPO at 80 °C in 12 days to give good yields of Ir-
(ttp)CH2COAr (8a-d). The starting materials disap-
peared rapidly within 6 days, and the rates increased
with increasing electron-rich substituents of iridium
alkyls (Table 1, entries 1-4: MeO > Me > H > Cl). In
less than 12 days, lower yields of products were obtained
together with the formation of unidentifiable, presum-
ably decomposed labile intermediates. Attempted chro-
matographic isolation of these intermediates remained
unsuccessful. A lower yield of 38% for 8b was obtained
when the reaction was carried out with 10 equiv of
TEMPO in 11 days. The structures of Ir(ttp)CH2COAr
were ascertained on the basis of spectroscopic data. In
the 1H NMR spectrum, addition of Ph3P (1 equiv) shifted
the methylene singlet of 8b at δ -3.88 ppm upfield to
-4.91 ppm and further split the singlet into a doublet
Scheme 2. Proposed Mechanism for
Formation of Ir(ttp)CH2COR
Ir(ttp)CH2CH2Ar + R2NO• f
Ir(ttp)CH2CH•Ar + R2NOH (2)
A
Ir(ttp)CH2CH•Ar + R2NO• f
Ir(ttp)CH2CCH(ONR2)Ar (3)
B
Ir(ttp)CH2CCH(ONR2)Ar + R2NO• f
Ir(ttp)CH2COAr + R2N• + R2NOH (4)
3
with JP-H ) 13.5 Hz. The possibility that 8b could be
R2NO• ) TEMPO
the other possible regioisomer, i.e., Ir(ttp)COCH2Ph
from R-carbon oxidation instead of â-carbon oxidation,
could be excluded on the basis of the magnitude of the
Type 2. Alkyliridium porphyrins bearing â-hydrogens
(Table 1, entries 5-8) reacted with TEMPO at a higher
temperature of 160 °C to give Ir(ttp)Me, with no reaction
observed at 80 °C. Propyl complex 4 reacted completely
and gave Ir(ttp)Me in 43% yield (Table 1, entry 7).
Complexes 2, 3, and 5 gave trace amounts of Ir(ttp)Me
(6), and starting materials were recovered. No iridium
porphyrin product from oxidation of the alkyl group was
isolated. Even the iridium benzylic γ-hydrogens in
PhCH2CH2CH2Ir(ttp) (5) did not undergo any oxidation.
A plausible mechanism for the formation of Ir(ttp)-
Me is similar to that proposed for formation of Rh(ttp)-
Me from Rh(ttp)CH2CH2R.6 Initially, Ir(ttp)CH2CH2R
reacts with TEMPO to produce an intermediate analo-
gous to A (Scheme 1). In the absence of stabilization
from the adjacent aromatic ring, the Ir(ttp)CH2CHR
radical decomposes rapidly with Ir-C cleavage to yield
an olefin and the IrII(ttp) metalloradical at higher
reaction temperatures. The IrII(ttp) metalloradical then
attacks TEMPO, resulting in methyl group transfer
from TEMPO to iridium and formation of Ir(ttp)Me.6,7
coupling constant, because the methylene signals in
3
(Ph3P)Ir(ttp)CH2CH2Ph were measured with JP-H
)
10.0 Hz without any 4JP-H observed. Furthermore, the
IR stretching frequencies of carbonyls fall at 1621-1633
cm-1 and differ from those of metal acyl complexes.
Therefore, the positions of the carbonyls were ascer-
tained to be â to iridium. The reactions were performed
strictly under a N2 atmosphere, and we can exclude that
the oxygen atoms of the â-carbonyl fragments stem from
dioxygen from air. The oxygen atoms must thus stem
from TEMPO.
Scheme 2 illustrates a proposed mechanism for the
formation of Ir(ttp)CH2COAr. TEMPO initially abstracts
the fairly weak benzylic hydrogen14 (BDE of PhCH2-H
88 kcal/mol)15 from Ir(ttp)CH2CH2Ar to generate the
IrCH2CHAr carbon-centered radical A and the reduction
product R2NOH, i.e., TEMPO-H (BDE of TEMPO-H
70 kcal/mol) (eq 2).15 Due to the Ir-C bond being
stronger compared to the Rh-C bond (an observation
generally encountered when comparing metal-ligand
bond strengths of second- and third-row transition-
metal complexes16), A does not undergo Ir-C bond
(16) Martinho Simo˜es, J. A.; Beauchamp, J. A. Chem. Rev. 1990,
90, 620-688.
(17) Browry, V. W.; Ingold, K. U. J. Am. Chem. Soc. 1992, 114,
4992-4996.
(14) (a) Connolly, T. J.; Scaiano, J. C. Tetrahedron Lett. 1997, 38,
1133-1136. (b) Bottle, S. E.; Chand, U.; Micallef, A. S. Chem. Lett.
1997, 857-858. (c) Banks, R. E.; Choudhury, D. L.; Haszeldine, R. N.
J. Chem. Soc., Perkin Trans. 1 1973, 1092-1099.
(15) Luo, Y. R. Handbook of Bond Dissociation Energies in Organic
Compounds; CRC: Boca Raton, FL, 2003.
(18) (a) Wayland, B. B.; Sherry, A. E.; Brunn, A. G. J. Am. Chem.
Soc. 1993, 115, 7675-7684. (b) Basiockes, L.; Bunn, A. G.; Wayland,
B. B. Can. J. Chem. 2001, 79, 854-856.
(19) Hetterscheid, D. G. H.; Bens, M.; de Bruin, B. Dalton Trans.
2005, 979-984.

6428 Organometallics, Vol. 24, No. 26, 2005
Table 1. Summary of Thermolysis of Ir(ttp)R with TEMPOa
Yeung and Chan
entry
RIr(ttp)
temp/°C
time/days
R′Ir(ttp), yield/%b
1
4-MeOC6H4CH2CH2Ir(ttp) (1a)
PhCH2CH2Ir(ttp) (1b)
4-MeC6H4CH2CH2Ir(ttp) (1c)
4-ClC6H4COCH2Ir(ttp) (1d)
NCCH2CH2Ir(ttp) (2)
CH3CH2Ir(ttp) (3)
80
80
1.5c
4c
3c
6c
2
4-MeOC6H4COCH2Ir(ttp)d (8a), 73
PhCOCH2Ir(ttp)d (8b), 78
4-MeC6H4COCH2Ir(ttp)d (8c), 89
4-ClC6H4CH2CH2Ir(ttp)d (8d), 75
CH3Ir(ttp) (6), trace; recovered 2, 32
CH3Ir(ttp) (6), trace; recovered 3, 69
CH3Ir(ttp) (6), 43
CH3Ir(ttp) (6); trace amount with 5, 79
recovered 6, 54
recovered 6-d3, 62
recovered 7, 79
2
3
80
4
80
5
160
160
160
160
160
160
160
6
2
7
CH3CH2CH2Ir(ttp) (4)
PhCH2CH2CH2Ir(ttp) (5)
CH3Ir(ttp) (6)
2
16
2
2
2
8
9
10
11
CD3Ir(ttp) (6-d3)e
PhCH2Ir(ttp) (7)
a 10 equiv was used unless specified. b Isolated yield after column chromatography. c Time for disappearance of starting material. d After
12 days with 15 equiv of TEMPO. e 15 equiv of TEMPO.
for further oxidation. Indeed, such RhII(por)CH2CH2 (or
RhIII(por)CH2CH2 ; por ) porphyrinato)18 and IrIICH2-
•
•
CH211 (or IrIIICH2CH2 ) species have been stabilized by
metal centers.
Figure 2. Stabilization of Ir(ttp)CH2CHR•.
Conclusion
Type 3. Ir complexes 6, 6-d3, and 7 (Table 1, entries
9-11), lacking â-hydrogens, did not react with TEMPO
to give any isolable product. Only decomposition oc-
curred with partial recovery of starting materials. The
possibility of generation of IrII(ttp) from Ir(ttp)Me by
R-hydrogen abstraction and further decomposition or
homolysis followed by subsequent carbon-carbon bond
activation with TEMPO was ruled out by reaction of the
deuterium labeled complex 6-d3. No Ir(ttp)Me was
detected; only Ir(ttp)CD3 was recovered. Ir(ttp)Bn (7)
also did not yield any Ir(ttp)COPh.
We have reported a novel and high-yield synthesis of
Ir(ttp)CH2COAr from the oxidation of Ir(ttp)CH2CH2-
Ar with TEMPO. Non-â-aryl-substituted ethyliridium
porphyrins gave IrII(ttp), which subsequently yielded Ir-
(ttp)Me after aliphatic carbon-carbon bond activation
with excess TEMPO. Phenyl R or γ carbon-hydrogen
bonds of iridium porphyrin alkyls did not react with
TEMPO at all. These experiments give further support
that carbon-centered IrIII(CH2-CHR•) radicals are sta-
bilized by the â iridium center.
The three possible outcomes in the reactions with
TEMPO suggest that the carbon-centered radical in
IrIII(ttp)CH2CHAr is strongly stabilized by both the aryl
group and the IrIII metal center. The aryl group is well-
known for stabilization of benzylic radicals through
conjugation, but also the â-IrIII site allows the radical
to be positioned over multiple positions via the reso-
nance structures I (IrIII-CH2CHR•) and II (IrII(CH2d
CHR)) in Figure 2. The type 3 outcome of the reactions
with TEMPO reveals that neither PhCH2CH2CH2Ir(ttp)
(5) with benzylic γ-hydrogens nor Ir(ttp)Me (6) with only
R-hydrogens is oxidized by TEMPO to give an oxygen-
ated iridium alkyl. Apparently alkyl radicals from
hydrogen abstraction at the R and γ positions to the
iridium center are not easily formed, which are in
contrast with the apparent easy formation of radicals
by â-hydrogen abstraction from Ir-CH2CH2R. The type
2 outcome of the reactions reveals that radicals formed
by â-hydrogen abstraction from IrIIICH2CH2R (R )
alkyl), yielding radicals only stabilized by the â iridium
center without additional benzylic stabilization, all
decompose with formation of Ir(ttp)Me. Apparently, the
IrIIICH2CHR• (R ) alkyl) radical undergoes Ir-alkyl bond
scission more easily than the IrIIICH2CH2Ar• radical. We
interpret this different behavior by assuming that the
resonance structure I (IrIII-CH2CHR•) in Figure 2
dominates for R ) aryl, whereas resonance structure
II (IrII(CH2dCHR)) dominates for R ) alkyl. The latter
gives rise to more rapid olefin dissociation, leading to
formation of the metalloradical IrII(ttp), which subse-
quently abstracts a methyl group from TEMPO. In type
1, the combined stabilization of both the Ir center and
aryl group allow the Ir(ttp)CH2CHAr radical to be
sufficiently long-lived to be trapped by TEMPO
Experimental Section
All materials were obtained from commercial suppliers and
used without further purification, unless otherwise specified.
Benzene was distilled from sodium. Dichloromethane and
hexanes for the reaction were distilled from calcium hydride.
Hexanes for chromatography were distilled from anhydrous
calcium chloride.20 (4-Chlorophenyl)ethyl bromide, (4-meth-
ylphenyl)ethyl bromide, and (4-methoxylphenyl)ethyl bromide
were prepared according to the literature method.21
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.
1H NMR spectra were recorded on a Bru¨ker DPX 300 (300
MHz) spectrometer. Spectra were referenced internally to the
residual proton resonance in CDCl3 (δ 7.26 ppm), tetrameth-
ylsilane (TMS, δ 0.00 ppm), tetrakis(trimethylsilyl)silane
((TMS)4Si, δ 0.00 ppm), or C6D6 (δ 7.15 ppm) as the internal
standard. Chemical shifts (δ) were reported in parts per million
(ppm) in δ scale downfield from TMS or (TMS)4Si. 13C NMR
spectra were recorded on a Bruker DPX 300 (75 MHz)
spectrometer and referenced to CDCl3 (δ 77.00 ppm). Coupling
constants (J) were reported in hertz (Hz). High-resolution mass
spectra (HRMS) were performed on a Thermofinnigan MAT
95 XL instrument (FABMS).
Preparation of Chloro(5,10,15,20-tetratolylporphyri-
nato)carbonyliridium(III) (Ir(ttp)Cl(CO)). H2ttp (350 mg,
0.52 mmol) and [Ir(COD)Cl]2 (524 mg, 0.78 mmol) were added
into xylene (200 mL), and the solution was refluxed for 3 days.
The solution changed color from purple to red. The crude
mixture was dried under high vacuum and purified by silica
gel column chromatography, with a solvent mixture of hexane
(20) Perrin, D. D.; Armarego, L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon Press: Oxford, U.K., 1988.
(21) Orfanopoulos, M.; Smonou, I.; Foote, C. S. J. Am. Chem. Soc.
1990, 112, 3607-3614.

Stabilization of Ir-CH2-CHR• by Iridium
Organometallics, Vol. 24, No. 26, 2005 6429
and CH2Cl2 (4:1) as eluent. The fast-moving purple fraction
was discarded, and the following red fraction was collected. A
reddish purple solid (317 mg, 0.34 mmol, 66%) was obtained
by recrystallization from CH2Cl2/CH3OH. 1H NMR (CDCl3, 300
MHz): δ 2.71 (s, 8 H), 7.56 (d, 8 H, J ) 8.4 Hz), 8.08-8.16 (m,
8 H), 8.94 (s, 8 H). Anal. Calcd for C49H36N4OClIr: C, 63.66;
H, 3.92; N, 6.06. Found C, 63.48; H, 3.95; N, 5.90.
Preparation of (Porphyrinato)iridium(III) Alkyls (Ir-
(por)R). The reductive alkylation of Ir(ttp)Cl(CO) is described
as a typical example for the preparation of (porphyrinato)-
iridium(III) alkyl complexes, adapting the literature procedure
reported by Ogoshi.13
(5,10,15,20-Tetratolylporphyrinato)methyliridium-
(III) (6). A suspension of Ir(ttp)Cl(CO) (120 mg, 0.13 mmol)
in THF (50 mL) and a solution of NaBH4 (49 mg 1.30 mmol)
in aqueous NaOH (1 M, 3 mL) were purged with N2 for 15
min separately. The solution of NaBH4 was added slowly to
the suspension of Ir(ttp)Cl(CO) via a cannula. The mixture
was heated at 70 °C under N2 for 2 h in a Teflon screw-capped
tube to give a brown suspension. The mixture was then cooled
to room temperature under N2, and iodomethane (37 mg, 0.26
mmol) was added. The reaction mixture was further heated
at 70 °C under N2 for 2 h. A reddish brown suspension was
formed. The reaction mixture was worked up by extraction
with CH2Cl2/H2O. The combined organic extract was dried
(MgSO4), filtered, and rotary evaporated. The reddish orange
residue was purified by column chromatography over silica gel
(250-400 mesh), with a solvent mixture of hexane and CH2-
Cl2 (4:1) as eluent. The major red fraction was collected and
gave a reddish purple solid (63 mg, 0.07 mmol, 55%) as the
product after rotary evaporation. The product was further
purified by recrystallization from CH2Cl2/CH3OH. 1H NMR
(CDCl3, 300 MHz): δ -6.33 (s, 3 H), 2.68 (s, 12 H), 7.50 (d, 8
H, J ) 6.0 Hz), 7.19-8.04 (m, 8 H), 8.51 (s, 8 H). HRMS
(FABMS): calcd for [C49H39N4Ir]+, m/z 876.2798; found, m/z
876.2795. Anal. Calcd for C49H39N4Ir: C, 67.18; H, 4.49; N,
6.39. Found C, 67.45; H, 4.21; N, 6.00.
(5,10,15,20-Tetratolylporphyrinato)[(4-chlorophenyl)-
ethyl]iridium(III) (1d). Reddish purple solids (72%). 1H NMR
(CDCl3, 300 MHz): δ -5.38 (t, 2 H, J ) 9.0 Hz), -3.34 (t, 2 H,
J ) 9.0 Hz), 2.68 (s, 12 H), 4.81 (d, 2 H, J ) 8.4 Hz), 6.30 (d,
2 H, J ) 8.4 Hz), 7.50 (m, 8 H), 7.93 (d, 4 H, J ) 7.2 Hz), 8.03
(d, 4 H, J ) 7.2 Hz), 8.51 (s, 8 H). HRMS (FABMS): calcd for
[C56H44N4IrCl]+, m/z 1000.2878; found, m/z 1000.2891. Anal.
Calcd for C56H44N4IrCl‚CH3OH: C, 66.29; H, 4.68; N, 5.43.
Found C, 66.66; H, 4.45; N, 5.37.
(5,10,15,20-Tetratolylporphyrinato)(2-cyanoethyl)iri-
dium(III) (2). Reddish purple solids (45%). 1H NMR (CDCl3,
300 MHz): δ -6.09 to -5.94 (m, 2 H), -4.33 to -4.21 (m, 2
H), 2.68 (s, 12 H), 7.50-7.48 (m, 8 H), 7.87-7.85 (m, 8 H),
8.45 (s, 8 H). HRMS (FABMS): calcd for [C51H40N5Ir]+, m/z
915.2907; found, m/z 915.2925. Anal. Calcd for C51H40N5Ir: C,
66.94; H, 4.41; N, 7.65. Found: C, 66.82; H, 4.41; N, 7.55.
(5,10,15,20-Tetratolylporphyrinato)ethyliridium(III) (3).
1
Reddish purple solids (65%). H NMR (CDCl3, 300 MHz): δ
-5.55 (q, 2 H, J ) 9.0 Hz), -4.63 (t, 3 H, J ) 9.0 Hz), 2.68 (s,
12 H), 7.49 (t, 8 H, J ) 5.4 Hz), 7.95 (m, 8 H), 8.50 (s, 8 H).
HRMS (FABMS): calcd for [C50H41N4Ir]+, m/z 890.2957; found,
m/z 890.2966. Anal. Calcd for C50H41N4Ir‚CH3OH: C, 66.42;
H, 4.91; N, 6.08. Found: C, 66.75; H, 4.98; N, 5.93.
(5,10,15,20-Tetratolylporphyrinato)propyliridium-
1
(III) (4). Reddish purple solids (56%). H NMR (CDCl3, 300
MHz): δ -5.60 (t, 2 H, J ) 9.0 Hz), -4.40 (sextet, 2 H, J )
9.0 Hz), -1.71 (t, 3 H, J ) 9.0 Hz), 2.68 (s, 12 H), 7.50 (d, 8 H,
J ) 7.5 Hz), 7.97 (m, 8 H), 8.49 (s, 8 H). HRMS (FABMS):
calcd for [C51H43N4Ir]+, m/z 904.3118; found, m/z 904.3136.
Anal. Calcd for C51H43N4Ir: C, 67.75; H, 4.79; N, 6.19. Found:
C, 67.71; H, 4.84; N, 6.07.
(5,10,15,20-Tetratolylporphyrinato)(3-phenylpropyl)-
iridium(III) (5). Reddish purple solids (78%). 1H NMR
(CDCl3, 300 MHz): δ -5.15 (t, 2 H, J ) 9.0 Hz), -4.14 (p, 2
H, J ) 9.0 Hz), -0.35 (t, 2 H, J ) 9.0 Hz), 2.68 (s, 12 H), 5.55
(d, 2 H, J ) 6.6 Hz), 6.71-6.78 (m, 3 H), 7.48 (t, 8 H, J ) 7.8
Hz), 7.89 (d, 4 H, J ) 7.8 Hz), 8.02 (d, 4 H, J ) 7.8 Hz), 8.50
(s, 8 H). HRMS (FABMS): calcd for [C57H47N4Ir]+, m/z
980.3429; found, m/z 980.3426. Anal. Calcd for C57H47N4Ir: C,
69.84; H, 4.83; N, 5.71. Found: C, 69.63; H, 4.89; N, 5.57.
(5,10,15,20-Tetratolylporphyrinato)(methyl-d3)iridium-
(III) (6-d3). Reddish purple solids (43%). 1H NMR (CDCl3, 300
MHz): δ 2.68 (s, 12 H), 7.50 (d, 8 H, J ) 6.0 Hz), 7.19-8.04
(m, 8 H), 8.51 (s, 8 H). HRMS (FABMS): calcd for [C49H36N4D3-
Ir]+, m/z 879.2987; found, m/z 879.2971.
(5,10,15,20-Tetratolylporphyrinato)[(4-methoxyphenyl)-
ethyl]iridium(III) (1a). Reddish purple solids (65%). 1H NMR
(CDCl3, 300 MHz): δ -5.39 (t, 2 H, J ) 9.0 Hz), -3.35 (t, 2 H,
J ) 9.0 Hz), 2.68 (s, 12 H), 3.33 (s, 3 H), 4.86 (d, 2 H, J ) 8.7
Hz), 5.89 (d, 2 H, J ) 8.7 Hz), 7.49 (m, 8 H), 7.95 (d, 4 H, J )
7.5 Hz), 8.02 (d, 4 H, J ) 7.5 Hz), 8.51 (s, 8 H). HRMS
(FABMS): calcd for [C57H47N4OIr]+, m/z 996.3374; found, m/z
996.3389. Anal. Calcd for C57H47N4OIr: C, 68.72; H, 4.75; N,
5.62. Found: C, 68.34; H, 4.77; N, 5.65.
(5,10,15,20-Tetratolylporphyrinato)benzyliridium-
1
(5,10,15,20-Tetratolylporphyrinato)(phenylethyl)iri-
dium(III) (1b). Reddish purple solids (50%). 1H NMR (CDCl3,
300 MHz): δ -5.36 (t, 2 H, J ) 9.0 Hz), -3.32 (t, 2 H, J ) 9.0
Hz), 2.68 (s, 12 H), 4.94 (d, 2 H, J ) 7.5 Hz), 6.32-6.37 (m, 2
H), 6.44 (t, 1 H, J ) 6.9 Hz), 7.49-7.54 (m, 8 H), 7.95 (d, 4 H,
J ) 7.8 Hz), 8.03 (d, 4 H, J ) 7.8 Hz), 8.52 (s, 8 H). HRMS
(FABMS): calcd for [C56H45N4Ir]+, m/z 966.3268; found, m/z
966.3275. Anal. Calcd for C56H45N4Ir‚CH3OH: C, 68.58; H,
(III) (7). Reddish purple solids (66%). H NMR (CDCl3, 300
MHz): δ -3.99 (s, 2 H), 2.69 (s, 12 H), 3.16 (d, 2 H, J ) 6.9
Hz), 5.88-5.93 (m, 2 H), 6.45 (t, 1 H, J ) 7.5 Hz), 7.51 (t, 8 H,
J ) 6.0 Hz), 7.96-8.03 (m, 8 H), 8.47 (s, 8 H). HRMS
(FABMS): calcd for [C55H43N4Ir]+, m/z 925.3116; found, m/z
925.3117. Anal. Calcd for C55H43N4Ir‚3H2O: C, 65.65; H, 4.90;
N, 5.57. Found: C, 65.94; H, 4.38; N, 5.19.
Reaction of (Porphyrinato)iridium(III) Alkyls with
TEMPO. (5,10,15,20-Tetratolylporphyrinato)(2-phenyl-2-oxo-
ethyl)iridium(III) (Ir(ttp)CH2C(O)C6H5, 8b) is described as a
typical procedure. Ir(ttp)CH2CH2C6H5 (1b), recrystallized from
CH3OH/CH2Cl2 (0.02 mmol), and TEMPO (49 mg, 0.31 mmol)
were dissolved in anhydrous benzene (1.0 mL) in a Teflon
screw-capped tube. The solution was degassed in three freeze-
thaw-pump cycles and filled with N2. The solution was
protected from light and heated in an oil bath at 80 °C. The
4.95; N, 5.61. Found: C, 68.27; H, 4.91; N, 5.95. 1H NMR (with
3
1 equiv of PPh3/CDCl3, 300 MHz): δ -6.50 (dt, 2 H, JPH
)
10.0 Hz, J ) 8.6 Hz), -3.69 (t, 2 H, J ) 8.6 Hz), 2.66 (s, 8 H),
4.11 (t, 8 H, J ) 8.0 Hz), 4.80 (d, 2 H, J ) 6.9 Hz), 6.22-6.27
(m, 9 H), 6.29 (d, 2 H, J ) 6.9 Hz), 6.52-6.56 (m, 8 H), 6.82-
6.86 (m, 4 H), 7.42 (d, 4 H, J ) 7.6 Hz), 7.4 (d, 4 H, J ) 7.6
Hz), 7.68 (d, 8 H, J ) 7.6 Hz), 7.81 (d, 8 H, J ) 7.6 Hz), 8.39
(s, 8 H).
(5,10,15,20-Tetratolylporphyrinato)[(4-methylphenyl)-
ethyl]iridium(III) (1c). Reddish purple solids (54%). 1H NMR
(CDCl3, 300 MHz): δ -5.39 (t, 2 H, J ) 9.0 Hz), -3.35 (t, 2 H,
J ) 9.0 Hz), 1.76 (s, 3 H), 2.68 (s, 12 H), 4.83 (d, 2 H, J ) 7.2
Hz), 6.14 (d, 2 H, J ) 7.2 Hz), 7.49 (m, 8 H), 7.94 (d, 4 H, J )
7.8 Hz), 8.03 (d, 4 H, J ) 7.8 Hz), 8.51 (s, 8 H). HRMS
(FABMS): calcd for [C57H47N4Ir]+, m/z 980.3424; found, m/z
980.3433. Anal. Calcd for C57H47N4Ir‚2H2O: C, 67.37; H, 5.06;
N, 5.51. Found: C, 67.34; H, 4.94; N, 5.31.
1
progress of the reaction was monitored by H NMR spectros-
copy. The crude mixture was then dried under high vacuum
and purified by silica gel column chromatography using
hexane/CH2Cl2 (4:1) as the eluent. The major red fraction was
collected. A reddish purple solid (16 mg, 0.016 mmol, 78%) was
1
obtained. H NMR (CDCl3, 300 MHz): δ -3.88 (s, 2 H), 2.68
(s, 8 H), 4.75 (d, 2 H, J ) 7.8 Hz), 6.59-6.64 (m, 2 H), 7.02 (t,
1 H, J ) 7.2 Hz), 7.48 (t, 8 H, J ) 6.8 Hz), 7.87 (d, 2 H, J )
6.8 Hz), 7.93 (d, 2 H, J ) 7.5 Hz), 8.46 (s, 8 H). IR (KBr):

6430 Organometallics, Vol. 24, No. 26, 2005
Yeung and Chan
ν(CdO) 1629 (s) cm-1. HRMS (FABMS): calcd for [C56H43N4-
OIr]+, m/z 980.3061; found, m/z 980.3070. Anal. Calcd for
C56H43N4OIr‚CH3OH: C, 67.63; H, 4.68; N, 5.54. Found: C,
67.88; H, 5.10; N, 5.33. 13C NMR (CDCl3, 75 MHz): δ 21.9,
50.8, 124.1, 125.7, 127.1, 127.7, 127.9, 130.8, 131.9, 133.9,
134.5, 137.5, 139.2, 143.4. 1H NMR (1 equiv of PPh3/CDCl3,
from light and heated in an oil bath at 160 °C for 2 days. Ir-
(ttp)Et (3; 13 mg, 53%) was recovered. H NMR (CDCl3, 300
1
MHz): δ -5.55 (q, 2 H, J ) 9.0 Hz), -4.63 (t, 3 H, J ) 9.0
Hz), 2.68 (s, 12 H), 7.49 (t, 8 H, J ) 5.4 Hz), 7.95 (m, 8 H),
8.50 (s, 8 H).
Reaction of (5,10,15,20-Tetratolylporphyrinato)pro-
pyliridium(III) (4) with TEMPO. The solution was pro-
tected from light and heated in an oil bath at 160 °C for 2
days. Ir(ttp)Me (6; 8 mg, 43%) was isolated. 1H NMR (CDCl3,
300 MHz): δ -6.33 (s, 3 H), 2.68 (s, 12 H), 7.50 (d, 8 H, J )
6.0 Hz), 7.19-8.04 (m, 8 H), 8.51 (s, 8 H).
Reaction of (5,10,15,20-Tetratolylporphyrinato)(3-phen-
ylpropyl)iridium(III) (5) with TEMPO. The solution was
protected from light and heated in an oil bath at 160 °C for 2
days. Ir(ttp)CH2CH2CH2Ph (5; 15 mg, 79%) was recovered. 1H
NMR (CDCl3, 300 MHz): δ -5.15 (t, 2 H, J ) 9.0 Hz), -4.14
(p, 2 H, J ) 9.0 Hz), -0.35 (t, 2 H, J ) 9.0 Hz), 2.68 (s, 12 H),
5.55 (d, 2 H, J ) 6.6 Hz), 6.71-6.78 (m, 3 H), 7.48 (t, 8 H, J )
7.8 Hz), 7.89 (d, 4 H, J ) 7.8 Hz), 8.02 (d, 4 H, J ) 7.8 Hz),
8.50 (s, 8 H).
3
300 MHz): δ -4.91 (d, 2 H, JPH ) 13.5 Hz), 2.66 (s, 8 H),
3.96 (t, 8 H, J ) 7.6 Hz), 4.72 (d, 2 H, J ) 8.1 Hz), 6.65-6.56
(m, 9 H), 6.80-6.85 (m, 2 H), 6.91 (t, 1 H, J ) 7.6 Hz), 7.43 (d,
8 H, J ) 8.2 Hz), 7.58-7.81(m, 8 H), 8.40 (s, 8 H).
(5,10,15,20-Tetratolylporphyrinato)[2-(4-methoxyphen-
yl)-2-oxoethyl]iridium(III) (Ir(ttp)CH2C(O)C6H4OCH3,
1
8a). H NMR (CDCl3, 300 MHz): δ -3.85 (s, 2 H), 2.68 (s, 8
H), 3.70 (s, 3 H), 4.72 (d, 2 H, J ) 8.8 Hz), 6.09 (d, 2 H, J )
8.8 Hz), 7.49-7.53 (t, 8 H), 7.90-7.98 (m, 8 H), 8.49 (s, 8 H).
13C NMR (CDCl3, 75 MHz): δ 22.0, 30.1, 55.6, 124.2, 127.6,
127.7, 127.8, 128.0, 129.0, 131.9, 133.9, 137.6, 139.1, 140.9,
143.4. IR (KBr): ν(CdO) 1633 (s) cm-1. HRMS (FABMS): calcd
for [C57H45N4O2Ir]+, m/z 1010.3166; found, m/z 1010.3151.
(5,10,15,20-Tetratolylporphyrinato)[2-(4-methylphenyl)-
2-oxoethyl]iridium(III) (Ir(ttp)CH2C(O)C6H4CH3, 8c). 1H
NMR (CDCl3, 300 MHz): δ -3.83 (s, 2 H), 2.21 (s, 3 H), 2.69
(s, 8 H), 4.67 (d, 2 H, J ) 7.8 Hz), 6.42 (d, 2 H, J ) 7.8 Hz),
Reaction of (5,10,15,20-Tetratolylporphyrinato)(methyl-
d3)iridium(III) (6-d3) with TEMPO. The solution was
protected from light and heated in an oil bath at 160 °C for 7
7.49 (t, 8 H, J ) 6.0 Hz), 7.88-7.99 (m, 8 H), 8.49 (s, 8 H). 13
C
1
days. Ir(ttp)CD3 (6-d3; 11 mg, 62%) was recovered. H NMR
NMR (CDCl3, 75 MHz): δ 21.9, 23.2, 30.1, 124.2, 125.7, 127.7,
127.8, 128.5, 131.8, 133.8, 134.4, 137.5, 139.1, 143.4. IR
(KBr): ν(CdO) 1621 (s) cm-1. HRMS (FABMS): calcd for
[C57H45N4OIr]+, m/z 994.3217; found, m/z 994.3220.
(5,10,15,20-Tetratolylporphyrinato)[2-(4-chlorophenyl)-
2-oxoethyl]iridium(III) (Ir(ttp)CH2C(O)C6H4Cl, 8d). 1H
NMR (CDCl3, 300 MHz): δ -3.92 (s, 2 H), 2.69 (s, 8 H), 4.65
(d, 2 H, J ) 7.8 Hz), 6.58 (d, 2 H, J ) 7.8 Hz), 7.49 (d, 4 H,
J ) 7.7 Hz), 7.53 (d, 4 H, J ) 7.7 Hz), 7.87 (d, 4 H, J ) 7.7
Hz), 7.92 (d, 4 H, J ) 7.7 Hz), 8.49 (s, 8 H). 13C NMR (CDCl3,
75 MHz): δ 22.0, 30.1, 124.4, 127.0, 127.3, 127.8, 128.0, 131.9,
133.9, 134.3, 137.7, 138.9, 143.3. IR (KBr): ν(CdO) 1621 (s)
cm-1. HRMS (FABMS): calcd for [C56H42N4OClIr]+, m/z
1014.2671; found, m/z 1014.2676.
(CDCl3, 300 MHz): δ 2.68 (s, 12 H), 7.50 (d, 8 H, J ) 6.0 Hz),
7.19-8.04 (m, 8 H), 8.51 (s, 8 H).
Reaction of (5,10,15,20-Tetratolylporphyrinato)ben-
zyliridium(III) (7) with TEMPO. The solution was protected
from light and heated in an oil bath at 160 °C for 6 days. Ir-
1
(ttp)Bn (7; 13 mg, 71%) was recovered. H NMR (CDCl3, 300
MHz): δ -3.99 (s, 2 H), 2.69 (s, 12 H), 3.16 (d, 2 H, J ) 6.9
Hz), 5.88-5.93 (m, 2 H), 6.45 (t, 1 H, J ) 7.5 Hz), 7.51 (t, 8 H,
J ) 6.0 Hz), 7.96-8.03 (m, 8 H), 8.47 (s, 8 H).
Acknowledgment. We thank the Research Grants
Council of Hong Kong of the SAR of China for financial
support (Grant No. CUHK 425/01P).
Reaction of (5,10,15,20-Tetratolylporphyrinato)ethyl-
iridium(III) (3) with TEMPO. The solution was protected
OM050661A