Synthesis of an iridium porphyrin amido complex

Article abstract of DOI:10.1139/v11-126

A synthetic route for iridium porphyrin amido complexes has been established. Treatment of a THF solution of Ir(ttp)(CO)Cl (1) (ttp = 5,10,15,20-tetrakis(p-tolyl)porphyrinato dianion) with an aqueous mixture of NaOH and NaBH₄, followed by 2-iodoethanol leads to the clean formation of the β-hydroxyethyl complex Ir(ttp)(C₂H ₄OH) (2) in 92% yield. Heating a pyridine solution of complex 2 in the presence of ca. 5-10 equiv. of phthalimide (HNC₈H ₄O₂; HPhth) leads to the formation of Ir(ttp)(C ₅H₅N)(CH₂CH₂Phth) (3). The replacement of pyridine by THF as the reaction solvent leads to the formation of the THF adduct Ir(ttp)(THF)(Phth) (4), which has been characterized spectroscopically. Heating a solution of 4 in pyridine leads to the formation of Ir(ttp)(C₅H₅N)(Phth) (5), which has been isolated in 72% yield. Complexes 3 and 5 have been characterized by X-ray crystallographic studies. Complexes 4 and 5 are rare examples of monomeric late transition metal-amido complexes and are the first examples of iridium-amido complexes featuring a porphyrin as a supporting ligand.

Full text of DOI:10.1139/v11-126

1506
Synthesis of an iridium porphyrin amido complex
Jenkins Yin Ki Tsang and Kin Shing Chan
Abstract: A synthetic route for iridium porphyrin amido complexes has been established. Treatment of a THF solution of
Ir(ttp)(CO)Cl (1) (ttp = 5,10,15,20-tetrakis(p-tolyl)porphyrinato dianion) with an aqueous mixture of NaOH and NaBH4, fol-
lowed by 2-iodoethanol leads to the clean formation of the b-hydroxyethyl complex Ir(ttp)(C2H4OH) (2) in 92% yield. Heat-
ing a pyridine solution of complex 2 in the presence of ca. 5–10 equiv. of phthalimide (HNC8H4O2; HPhth) leads to the
formation of Ir(ttp)(C5H5N)(CH2CH2Phth) (3). The replacement of pyridine by THF as the reaction solvent leads to the for-
mation of the THF adduct Ir(ttp)(THF)(Phth) (4), which has been characterized spectroscopically. Heating a solution of 4 in
pyridine leads to the formation of Ir(ttp)(C5H5N)(Phth) (5), which has been isolated in 72% yield. Complexes 3 and 5 have
been characterized by X-ray crystallographic studies. Complexes 4 and 5 are rare examples of monomeric late transition
metal-amido complexes and are the first examples of iridium-amido complexes featuring a porphyrin as a supporting ligand.
Key words: porphyrin, iridium amido, phthalimide.
Résumé : On a développé une méthode de synthèse pour les complexes iridium/porphyrine amido. Le traitement d’une so-
lution de Ir(ttp)(CO)Cl (1) (ttp = dianion 5,10,15,20-tétrakis(p-tolyl)porphyrinato) dans du THF par un mélange aqueux de
NaOH et de NaBH4, suivi d’une réaction avec le 2-iodoéthanol conduit à une formation propre du complexe b-hydroxyé-
thyle Ir(ttp)(CH2CH2OH) (2) avec un rendement de 92 %. Le chauffage du composé 2, en solution dans la pyridine, en pré-
sence d’environ 5 à 10 équivalents de phtalimide [[C6H4(C=O)2NH], PhthH] conduit à la formation du Ir(ttp)(C5H5N)
CH2CH2Phth (3). Le remplacement de la pyridine par du THF comme solvant conduit à la formation de l’adduit Ir(ttp)
(THF)Phth (4) qui a été caractérisé par des méthodes spectroscopiques. Le chauffage d’une solution du composé 4 dans de
la pyridine conduit à la formation du complexe Ir(ttp)(C5H5N)Phth (4) qui a été isolé avec un rendement de 72 %. Les com-
plexes 3 et 5 ont été caractérisés par des études de diffraction des rayons-X. Les complexes 4 et 5 correspondent à de rares
exemples de complexes monomères amido d’un métal de la fin de la période de transition et ce sont les premiers exemples
de complexes iridium-amido comportant une porphyrine comme ligand support.
Mots‐clés : porphyrine, iridium-amido, phtalimide.
[Traduit par la Rédaction]
amido exchange11 or insertion chemistry.10c,12 In addition,
Introduction
just like alkyl ligands, amido ligands are prone to undergo
b-elimination.13 Finally, amido ligands can also reductively
eliminate in the presence of other suitable ligands.14
Our group has been researching carbon-hydrogen bond ac-
tivation chemistry with iridium-porphyrin complexes to yield
iridium porphyrin alkyls and acyls.15 We have only once re-
ported an Ir-phenoxide complex16 but have never identified
or isolated any Ir-N covalently-bonded species. This phenom-
enon is best explained by thermodynamics that late transition
metal-carbon (alkyl or aryl) bonds are often stronger (by at
least 20 kcal/mol) than the isoelectronic amido M–N bonds
(1 cal = 4.184 J).17
Transition metal-nitrogen covalently-bonded species are an
interesting and important class of complexes.1 They have
been observed as key precursors and intermediates during
important catalytic processes, such as amination of organic
substrates,2 hydroamination of olefins,3 transfer hydrogena-
tion,4 amine dehydrogenation,5 and ammoxidation.6 In addi-
tion, metal-amidos can also effect nontrivial stoichiometric
transformations such as C–H activation.7 Late transition
metal-amidos are by far less common than their early transi-
tion metal counterparts.8 This is often rationalized by the
hard-soft-acid-base theory, that hard amido or alkoxo ligands
do not form strong bonds with late transition metals, which
are generally considered soft. More specifically, there exists
considerable electron repulsion between the filled dp orbitals
of the late transition metal and the pp electrons of the amido
ligand.9 As a result, late transition metal-amidos are often re-
active species that feature highly nucleophilic nitrogen
atoms,10 and the metal-nitrogen bonds often participate in
Results and discussion
Our research group has attempted to construct iridium-
nitrogen covalent bonds using the conventional metathesis
reactions by treatment of the iridium-chloro species Ir(ttp)
(CO)Cl15 (1; ttp = 5,10,15,20-tetrakis(p-tolylporphyrinato
Received 14 April 2011. Accepted 27 June 2011. Published at www.nrcresearchpress.com/cjc on 22 November 2011.
J.Y.K. Tsang and K.S. Chan. Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong,
People’s Republic of China.
Corresponding author: Kin Shing Chan (e-mail: ksc@cuhk.edu.hk).
This article is part of a Special Issue to commemorate the International Year of Chemistry.
Can. J. Chem. 89: 1506–1511 (2011)
doi:10.1139/V11-126
Published by NRC Research Press

Tsang and Chan
1507
Fig. 1. Structure formula for Ir(ttp)(CO)Cl (1) and phthalimide
(HPhth).
Scheme 1. Possible reaction pathways initiated by 2.
+
hydroxy
dissociation
OH-
Cl
Ir
H
N
-hydroxy
?
elimination
Ir(ttp)
O
O
N
N
Ir(ttp)C2H4OH
N
N
Ir(ttp)
OH
C
O
2
ethylene
dissociation
Ir(ttp)OH + C2H4
Phthalimide (HPhth)
Ir(ttp)(CO)Cl 1
Scheme 2. Proposed mechanism for the formation of 3.
dianion; Fig. 1) with freshly-prepared lithium anilide, lithium
diethylamide, or potassium phthalimide (KC8H4NO2; KPhth).
Disappointingly, these reactions only yielded mixtures of un-
identifiable porphyrin-containing products without the incor-
poration of the amide onto the metal.
O
O
N
HO
O
N
-H2O
N
Ir(ttp)C2H4OH
Ir(ttp)
Ir(ttp)
With complex 1 failing to serve as a viable source of a cat-
ionic iridium precursor for the synthesis of Ir-amidos, we de-
cided to seek alternatives. Treatment of a THF solution of
complex 1 with an aqueous solution of excess NaBH4 in the
presence of NaOH at 70 °C, followed by a slight excess of 2-
iodoethanol, led to the formation of the b-hydroxyethyl com-
plex Ir(ttp)(C2H4OH) (2) as a maroon solid in 92% yield
(eq. [1]). The 1H NMR spectrum of 2 closely resembles
those of our recently reported rhodium complex Rh(ttp)
(C2H4OH),18 which has been demonstrated to be a precursor
for the masked Rh(ttp)+ cation after undergoing b-hydroxy
elimination (Scheme 1).18,19 Complex 2 is also closely related
to a series of complexes with the general formula Rh(tpp)
Ir(ttp)
2
N
N
3
this product. Purification of this new product was achieved
by chromatography on Alumina, resulting in the isolation of
a red-purple powder after solvent removal. Dark-red needle-
shaped single crystals were obtained by slow diffusion of
layered hexanes into a concentrated CH2Cl2 solution. An X-
ray crystallographic analysis confirms the atom connectivity
in 3, as deduced from NMR spectroscopic data (Fig. 2). Ta-
ble 1 lists the crystal data and collection parameters. Regret-
tably, the quality of the X-ray data precludes any meaningful
discussion of metrical parameters of 3. Nevertheless, the X-
ray data indicate that the ethylene moiety has been retained.
A possible explanation for the formation of 3 is the nucleo-
philic attack by phthalimido anion on the bound ethylene
(Scheme 2).12,18,19b,21 Consistent with previous related find-
ings, compound 3 is thermally stable and does not undergo
b-elimination,22 with the crude reaction mixture remaining
unchanged upon heating for a further 3 days at 150 °C.
(CH2CHROH) (tpp
= 5,10,15,20-tetraphenylporphyrinato
dianion), reported by Sanford et. al.,20 as these complexes
were synthesized via the reaction between the rhodium-
porphyrin anion Rh(tpp)– and various epoxides.
½1ꢀ
IND; r; lfÞ ¼ } : 1 :: :v11 ꢁ 126eq1:gif}
Phthalimide (HNC8H4O2; HPhth; Fig. 1) is deemed a good
initial candidate as an amido precursor, because (i) it is quite
acidic, with the pKa of the N–H of ca. 8, a desirable feature,
as the successful incorporation of the amido ligand would re-
quire the loss of this proton and (ii) the nitrogen lone pair is
delocalized in the bicyclic aromatic system, thereby greatly
reducing possible dp–pp electron repulsion in the target Ir-
phthalimido complex.
Heating a pyridine solution of 2 in an excess (10 equiv.) of
phthalimide led to formation of a new porphyrin-containing
species Ir(ttp)(C5H5N)(CH2CH2Phth) (3) in good yields
(80%, eq. [2], as evidenced by a single new b-pyrrole proton
signal at 8.50 ppm). Phthalimide has been deprotonated and
symmetrically incorporated onto the final product, as indi-
cated by a pair of 2-proton doublet of doublets at 7.07 and
7.16 ppm, respectively, attributable to the two different types
of aryl protons. These signals have been shifted upfield from
7.77 and 7.87 ppm of free phthalimide. The presence of co-
ordinated pyridine is indicated also by characteristic upfield-
shifted signals. Intriguingly, in addition to these expected
phthalimido and pyridine signals, two sets of 2-proton mul-
tiplets appear at –6.06 and –2.19 ppm, respectively. These
signals suggest that the ethylene moiety is still present in
½2ꢀ
IND; r; lfÞ ¼ } : 1 :: :v11 ꢁ 126eq2:gif}
We next employed THF, a polar aprotic but less coordinat-
ing solvent than pyridine. We reasoned that a weaker s-donor
opposite to the Ir-ethylene bond would weaken the synergic
interaction between the metal and the p-acceptor,23 thereby
rendering the ethylene more prone to dissociation to allow
preferred nucleophilic attack on the iridium centre rather
than the carbon atom. Heating a THF solution of 2 in phtha-
limide at 150 °C cleanly yielded a single porphyrin-contain-
1
ing product. Pleasingly, the H NMR spectrum of the crude
product strongly suggests the exclusive formation of Ir(ttp)
(THF)(Phth) (4) (eq. [3]). Specifically, phthalimide has been
deprotonated and symmetrically incorporated, likely directly
onto the metal center, as the aryl proton resonances now ap-
pear at 6.14 and 6.51 ppm, respectively, and are further
upfield-shifted compared with the corresponding signals in
complex 3. The presence of coordinated THF is indicated by
distinctive upfield signals at –2.33 and –0.70 ppm, respec-
1
tively. Furthermore, no ethylene signals are present in the H
Published by NRC Research Press

1508
Can. J. Chem. Vol. 89, 2011
Fig. 2. Solid-state molecular structure of 3 with 50% thermal ellip-
soids shown. Hydrogen atoms are omitted for clarity.
are currently exploring the scope of this reaction and examin-
ing the reactivity of 4 and 5.
Experimental
General
Unless otherwise noted, all reagents were purchased from
commercial suppliers and directly used without further purifi-
cation. Hexanes were distilled from anhydrous CaCl2. THF
was distilled from sodium benzophenone ketyl. CDCl3, used
in the preparation of NMR samples, was distilled from CaH2.
Ir(ttp)Cl(CO) (1) was prepared according to the literature pro-
cedures.15 Neutral Alumina (Merck, 70–230 mesh) / H2O
(10:1 v/v) was used for column chromatography.
NMR spectra were recorded at room temperature (RT) on
1
Bruker DPX-300 or AV-400 spectrometers. H NMR spectra
are referenced to the residual protio isotopomer present in
CDCl3 (d = 7.26 ppm) and 13C NMR spectra are referenced
to the natural-abundance carbon signal of the same solvent
(d = 77.23 ppm). Chemical shifts (d) are reported as part
per million (ppm) in (d) scale downfield from TMS. Coupling
constants (J) were reported in Hertz (Hz). High-resolution
mass spectra (HRMS) were performed on a ThermoFinni-
gan MAT 95 XL mass spectrometer in fast atom bombard-
ment (FAB) mode using 3-nitrobenzyl alcohol (NBA)
matrix and CH2Cl2 as solvent or electrospray ionization
(ESI) mode using MeOH:CH2Cl2 (1:1) as solvent.
Single X-ray crystal data were collected at 293 K using a
Bruker AXS Kappa ApexII Duo diffractomter with Mo Κa
radiation (l = 0.71073 Å). Data collection and reduction
were performed using ApexII software. Empirical multi-
scan absorption correction was applied. Structures were
solved by direct method and refined by full-matrix least-
squares on F2, using the SHELXTL program package. The
presence of solvent accessible void was corrected by Platon/
Squeeze program. Riding refinement was used for hydrogen
treatment.
NMR spectrum of 3. Unfortunately, the physical separation
between 4 and the excess phthalimide proved to be problem-
atic. Extraction with CH2Cl2–hexanes was unsatisfactory,
washing with warm water led to the partial decomposition of
4 with the concomitant formation of new porphyrin-containing
species, and chromatography on Alumina or silica yielded
decomposition products.
½3ꢀ
IND; r; lfÞ ¼ } : 1 :: :v11 ꢁ 126eq3:gif}
Fortunately, under thermal conditions the THF ligand can
be displaced by other ligands that yield more robust com-
plexes. Thus, heating the crude mixture of 4 and phthalimide
in neat pyridine at 100 °C for 15 h led to quantitative forma-
tion of Ir(ttp)(C5H5N)(Phth) (5), which was isolated in 78%
yield as a red microcrystalline solid after chromatography on
Alumina (eq. [4]). Single rod-shaped crystals were obtained
from a CH2Cl2–hexanes bilayer, and an X-ray diffraction
study confirmed the proposed structure for 5 (Fig. 3, Table 1).
The distance between iridium and the phthalimido-N (Ir(1)–N
(5)) is 2.083(2) Å, comparable to the iridium-pyridine dis-
tance (Ir(1)–N(6)) of 2.084(2) Å. The similarity between Ir–N
covalent versus coordination bond distances has also been
observed in a few other reported systems11c,24 and could
suggest low multiple-bond character between iridium and
phthalimido. To our knowledge, complex 5 is the first ex-
ample of an iridium porphyrin amido complex, whose struc-
ture has been studied by X-ray crystallography.
Preparation of Ir(ttp)C2H4OH (2)
A 250-mL sealable round-bottomed flask, equipped with a
Rotaflo valve, was charged with Ir(ttp)(CO)Cl (46.2 mg,
50.0 mmol) and THF (50 mL). A 10 mL Schlenk tube was
charged with aqueous NaOH (1 mol/L, 3 mL) and NaBH4
(20.0 mg, 529 mmol). The two solutions were degassed sep-
arately for 15 min. The NaBH4/NaOH solution was added to
the solution of 1 using a cannula. The resulting mixture was
sealed and heated to 70 °C for 2 h, after which a color
change from red to dark orange-brown was observed. The re-
action mixture was cooled to RT, and 2-iodoethanol (100 mg,
581 mmol) was added via a micropipette. The mixture was
stirred for 15 h at RT, after which the color of the mixture
did not change significantly. Solvents were removed in vacuo
and the residue was washed with water, leaving behind
Ir(ttp)(C2H4OH) (2) as a maroon solid. Compound 2 was
further purified by chromatography on Alumina, eluting
1
with CH2Cl2/hexanes (1:1). Yield 41.7 mg (92%). H NMR
½4ꢀ
IND; r; lfÞ ¼ } : 1 :: :v11 ꢁ 126eq4:gif}
(400 MHz, CDCl3) d: –5.32 (t, 3JHH = 7.2, 2H, IrCH2CH2OH),
–2.49 (t, 3JHH = 6.0, 1H, OH), –2.20 (m, 2H, IrCH2CH2OH),
2.69 (s, 12H, CH3), 7.53 (m, 8H, Ar H), 7.97 (d, 3JHH = 7.2, 4H,
Ar H), 8.02 (d, 3JHH = 8.4, 4H, Ar H), 8.54 (s, 8H, b-pyrrole H).
In conclusion, we have shown that the b-hydroxyethyl
complex Ir(ttp)(C2H4OH) (2) can serve as a precursor to-
wards novel iridium-nitrogen covalently bound species. We
Published by NRC Research Press

Tsang and Chan
1509
Table 1. Crystal data and summary of data collection and refinement for 3 and 5.
Param
3
5
Color, shape
Formula
Red needles
C63H49N6O2Ir
0.40 × 0.30 × 0.20
1114.28
triclinic
P-1
11.260 (2)
13.461 (3)
18.521 (4)
89.035 (4)
73.592 (4)
81.450 (4)
2662.0 (10)
2
Red rods
C61H45N6O2Ir
0.40 × 0.30 × 0.20
1086.23
monoclinic
P2(1)/c
11.1705 (9)
17.3969 (14)
24.3961 (11)
90
100.4430 (10)
90
4662.4 (6)
4
1.547
0.71073
1.85–25.00
2184
Crystal size (mm)
Formula weight
Crystal system
Space group
A (Å)
B (Å)
C (Å)
Α (°)
Β (°)
ϒ (°)
V (Å3)
Z
Dcalcd (Mg/m3)
Radiation (l) ( Å)
q range (°)
F(000)
1.390
0.71073
1.53–25.00
1124
Reflections collected
Independent reflections
Data, restraints, parameters
Goodness of fit
29460
8540
32806
8217
8540, 0, 649
1.186
0.0735, 0.1778
0.0829, 0.1809
0.0000, 78.186
8217, 0, 631
1.088
0.0208, 0.0511
0.0273, 0.0565
0.0259, 5.1729
a
b
Final R1 , wR2 [I > 2s(I)]
a
b
Final R1 , wR2 (all data)
c
w1, w2
X
X
aR1 ¼
ðkF0j ꢁ jFckÞ=
jF0j.
X
X
1=2
bwR2 ¼ f ½wðF02 ꢁ Fc2Þ ꢀ= ½wðF02Þ ꢀg
.
2
2
2
c
Weighting scheme wꢁ1 ¼ s2ðF02Þ þ ðw1PÞ þ w2P whereP ¼ ðF02 þ 2Fc2Þ=3.
122 mmol), and pyridine (2 mL). The mixture was subjected
to three freeze-pump-thaw cycles before being heated to
150 °C for 15 h, as the color changed from red-brown to
red. Pyridine was removed in vacuo, and the mixture was an-
alyzed by NMR spectroscopy. Hexanes were added to the
CDCl3 sample, and the solution was loaded onto an Alumina
column, after which the column was eluted with CH2Cl2/hex-
anes (1:1). The major fraction was collected. Solvents were
removed in vacuo, resulting in the deposition of 3 as a red
microcrystalline powder. Yield 9.8 mg (80%). Single needle-
shaped crystals suitable for X-ray crystallography were ob-
Fig. 3. Solid-state molecular structure of 5 with 50% thermal ellip-
soids shown. Hydrogen atoms are omitted for clarity. Selected bond
distances (Å) and angles (o): Ir(1)–N(5) 2.083(2), Ir(1)–N(6) 2.084
(2), N(5)–C(61) 1.394(4), N(5)–C(68) 1.398(4), N(5)–Ir(1)–N(6)
176.51(9), C(61)–N(5)–C(68) 109.2(2), C(61)–N(5)–Ir(1) 125.75
(18), C(68)–N(5)–Ir(1) 124.69(18).
1
tained from a CH2Cl2–hexanes bilayer. H NMR (400 MHz,
CDCl3) d: –6.06 (m, 2H, IrCH2CH2), –2.19 (m, 2H,
IrCH2CH2), 2.18 (br d, 2H, py ortho H), 2.66 (s, 12H, CH3),
3
3
5.31 (t, 7.53 (m, JHH = 7.2, 2H, py meta H), 6.17 (t, JHH
=
3
4
7.6, 2H, py para H), 7.07 (dd, JHH = 5.4, JHH = 3.0, 2H,
phthalimido Ar H), 7.16 (dd, JHH = 5.4, JHH = 3.0, 2H,
phthalimido Ar H) 7.48 (m, 8H, Ar H), 7.97 (d, JHH
3
4
3
=
3
7.2, 4H, Ar H), 8.05 (d, JHH = 7.6, 4H, Ar H), 8.50 (s, 8H,
b-pyrrole H). 13C NMR (100 MHz, CDCl3) d. HRMS
(FABMS) calcd. for [C63H49N6O2Ir
1035.3119; found: m/z 1035.3130.
–
C5H5N]+: m/z
HRMS (FABMS) calcd. for [C50H41N4OIr]+: m/z 906.2904;
found: m/z 906.2912.
Preparation of Ir(ttp)(C4H8O)(NC4H8O2) (4)
A glass tube equipped with a Rotaflo valve was charged
with 2 (10.0 mg, 11.0 mmol), phthalimide (18.0 mg,
122 mmol), and THF (2 mL). The mixture was subjected to
three freeze-pump-thaw cycles before heated to 150 °C for
Preparation of Ir(ttp)(C5H5N)(CH2CH2NC4H8O2) (3)
A glass tube equipped with a Rotaflo valve was charged
with 2 (10.0 mg, 11.0 mmol), phthalimide (18.0 mg,
Published by NRC Research Press

1510
Can. J. Chem. Vol. 89, 2011
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Preparation of Ir(ttp)(C5H5N)(NC4H8O2) (5)
To a crude mixture of Ir(ttp)(C4H8O)(NC4H8O2) (4) and
phthalimide was added pyridine (2 mL). The resulting solu-
tion was subjected to three freeze-pump-thaw cycles and
then heated for 15 h at 100 °C, during which little color
change was observed. The resulting mixture was dried in va-
cuo. Compound 5 was obtained in 78% yield as a red solid
after chromatography on Alumina, eluting with CH2Cl2/hex-
anes (1:1). Single rod-shaped crystals suitable for X-ray crys-
1
tallography were grown from a CH2Cl2–hexanes bilayer. H
NMR (400 MHz, CDCl3) d: 1.13 (br d, 2H, py ortho H),
3
2.65 (s, 12H, CH3), 5.05 (t, 7.53 (m, JHH = 7.2, 2H, py
meta H), 6.06 (t, 3JHH = 7.6, 2H, py para H), 6.19 (dd, 3JHH
=
=
4
3
5.4, JHH = 3.0, 2H, phthalimido Ar H), 6.54 (dd, JHH
4
5.4, JHH = 3.0, 2H, phthalimido Ar H), 7.46 (m, 8H, Ar H),
7.86 (d, 3JHH = 7.2, 4H, Ar H), 8.10 (d, 3JHH = 7.6, 4H, Ar H),
8.64 (s, 8H, b-pyrrole H). HRMS (FABMS) calcd. for
[C61H45N6O2Ir]+: m/z 1086.3228; found: m/z 1086.3244.
Supplementary data
Text, tables, figures of crystallographic data for complexes
1
3 and 5 (CIF files), and H and 13C NMR spectra for com-
plexes are available on the journal Web site (www.nrcre-
searchpress.com/doi/suppl/10.1139/v11-126). CCDC 831991
has also been deposited with the Cambridge Crystallographic
Data Centre. These data can be obtained, free of charge, via
www.ccdc.cam.ac.uk/cgi-bin/catreq.cgi (or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1Ez, UK; fax +44 1223 336033; or e-mail
deposit@ccdc.cam.ac.uk).
Acknowledgements
We thank the Direct Grant of the Chinese University of
Hong Kong for financial support. This paper is dedicated to
Professor Tak-Hang Chan for his leadership always with
words of encouragement.
(14) (a) Fujita, K.-i.; Yamashita, M.; Puschmann, F.; Martinez
Alvarez-Falcon, M.; Incarvito, C. D.; Hartwig, J. F. J. Am.
Chem. Soc. 2006, 128 (28), 9044. doi:10.1021/ja062333n; (b)
Yamashita, M.; Hartwig, J. F. J. Am. Chem. Soc. 2004, 126
(17), 5344. doi:10.1021/ja0315107.
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