Amido PNP complexes of iridium: Synthesis and catalytic olefin and alkyne hydrogenation

Article abstract of DOI:10.1002/jccs.201900464

In situ lithiation of HN(o-C₆H₄PPh₂)₂ (H[1a]) or HN(o-C₆H₄PiPr₂)₂ (H[1b]) with nBuLi in THF at ?35°C followed by addition of [Ir(μ-Cl)(COD)]₂ (COD = 1,5-cyclooctadiene) in toluene at ?35°C generates 5-coordinate [1a]Ir(η⁴-COD) (2a) or 4-coordinate [1b]Ir(η²-COD) (2b), respectively. Oxidative addition of N-H in H[1b] to [Ir(μ-Cl)(COD)]₂ affords square pyramidal [1b]Ir(H)(Cl) (3b). Metathetical reaction of 3b with LiBHEt₃ in the presence of 1 atm of H₂ in toluene produces [1b]Ir(H)₂ (4b). Both 2a and 4b are active for catalytic hydrogenation of olefins and alkynes under extremely mild conditions.

Full text of DOI:10.1002/jccs.201900464

Received: 30 October 2019
DOI: 10.1002/jccs.201900464
Revised: 18 November 2019
Accepted: 20 November 2019
S P E C I A L I S S U E P A P E R
Amido PNP complexes of iridium: Synthesis and catalytic
olefin and alkyne hydrogenation
1
1
1,2
Mei-Hui Huang | Xue-Ru Zou | Lan-Chang Liang
1
Department of Chemistry, National Sun
Abstract
Yat-sen University, Kaohsiung, Taiwan
2
In situ lithiation of HN(o-C H PPh ) (H[1a]) or HN(o-C H PiPr ) (H[1b])
6 4 2 2 6 4 2 2
Department of Medicinal and Applied
ꢀ
Chemistry, Kaohsiung Medical University,
Kaohsiung, Taiwan
with nBuLi in THF at −35 C followed by addition of [Ir(μ-Cl)(COD)]
2
ꢀ
(
(
COD = 1,5-cyclooctadiene) in toluene at −35 C generates 5-coordinate [1a]Ir
η -COD) (2a) or 4-coordinate [1b]Ir(η -COD) (2b), respectively. Oxidative
4
2
Correspondence
Lan-Chang Liang, Department of
Chemistry, National Sun Yat-sen
University, Kaohsiung 80424, Taiwan.
Email: lcliang@mail.nsysu.edu.tw
addition of N-H in H[1b] to [Ir(μ-Cl)(COD)] affords square pyramidal [1b]Ir
2
(
H)(Cl) (3b). Metathetical reaction of 3b with LiBHEt in the presence of 1 atm
3
of H in toluene produces [1b]Ir(H) (4b). Both 2a and 4b are active for cata-
2 2
lytic hydrogenation of olefins and alkynes under extremely mild conditions.
Funding information
Ministry of Science and Technology,
Taiwan, Grant/Award Number: MOST
K E Y W O R D S
amido, hydrogenation, iridium, PNP
108-2113-M-110-007
[
24–26]
1
| INTRODUCTION
are known,
their activities in hydrogenation cataly-
sis have yet to be explored.
Hydrogenation of unsaturated hydrocarbons is one of the
most important transition metal-catalyzed reactions in
[
1]
industry.
The search for effective catalysts in this
2 | RESULTS AND DISCUSSION
regard continues to constitute an active area of explor-
atory research.
and its cationic variations, [M(diene)L2] (M = Rh, Ir;
L = phosphine, phosphite, arsine, pyridine),
sent pioneering success. Upon hydrogenation of olefins,
these group 9 catalyst precursors were proved to trans-
form into dihydride and olefin derivatives in catalytic
cycles. We are currently exploring reaction chemistry
employing amido PNP complexes.
that iridium olefin or dihydride complexes of [N(o-
[2–8]
[9,10]
Wilkinson catalyst, RhCl(PPh ) ,
The reactions of [Ir(μ-Cl)(COD)]2 (COD = 1,5-cyclo-
3
3
+
octadiene) with [1a]Li(THF) or [1b]Li(THF), either iso-
2
[11–19]
ꢀ
repre-
lated or prepared in situ, in toluene at −35 C afford [1a]Ir
4
2
(η -COD) (2a) or [1b]Ir(η -COD) (2b), respectively
31
1
(Scheme 1). As indicated by the P{ H} NMR spectra of
reaction aliquots, the generation of 2a is clean but that of
2b is not. The isolated yield of the former is therefore
nearly quantitative while that of the latter is poor to mod-
[20–23]
We suppose
3
1
erate. Interestingly, 2a shows a singlet resonance in the
P
−
−
1
C H PPh ) ] (1a) and [N(o-C H PiPr ) ] (1b) are
{ H} NMR spectrum at 14.7 ppm whereas 2b reveals an AB
6
4
2 2
6
4
2 2
31
1
potential catalysts for hydrogenation of olefins and
alkynes. In this contribution, we aim to synthesize these
complexes and demonstrate their catalytic competence.
Though iridium complexes similar to those of 1a and 1b
quartet resonance in the P{ H} NMR spectrum centered
at 28.8 ppm, implicating different coordination geometries
for these PNP iridium complexes. A diagnostic difference
in solution NMR spectra of these complexes concerns sig-
1
nals ascribable to unbound HC=CH found in the H NMR
Dedicated to Professor Chien-Hong Cheng on the occasion of his 70th
birthday.
spectrum of 2b. The COD ligand in 2a is therefore bound
©
2019 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J Chin Chem Soc. 2019;1–8.
http://www.jccs.wiley-vch.de
1

2
HUANG ET AL.
4
2
to iridium in a η fashion whereas that in 2b is η . Though
divergent, these results are consistent with the electronic
and steric nature of their corresponding PNP ligands; 1a is
not only less electron-releasing but also less bulky than
molecular structures. Selected bond distances and angles
are summarized in Table 1.
4
As illustrated, 2a is a η -COD complex whereas 2b is a
η -COD derivative. The coordination geometry of 2a is
2
[27–32]
1b,
making 2a an 18-electron species while 2b a
6-electron complex.
best described as trigonal bipyramidal where the 1a ligand
is bound to iridium in a facial coordination mode, contra-
sting with what has been usually found for PNP as a pin-
1
Yellow crystals of 2a suitable for X-ray diffraction
[
33–38]
analysis were grown by slow evaporation of a concen-
trated benzene solution at room temperature while
orange crystals of 2b were grown from a concentrated
cer ligand.
The dihedral angle between two N-Ir-P
ꢀ
planes is 120.21 . The N donor in 1a and one of the C=C
bonds in COD are disposed axially, having the N-Ir-cen-
ꢀ
ꢀ
pentane solution at −35 C. Figures 1 and 2 depict their
troid(C37-C38) angle of 173.39 . The iridium center is dis-
placed by 0.266 Å toward the axial olefinic donor from the
ideal equatorial plane defined by P1-P2-C41-C42, due
4
likely to the constrained η -COD ring that confines the
ꢀ
centroid(C37-C38)-Ir-centroid(C41-C42) angle of 85.31 .
The displacement of iridium toward olefin instead of
amide is consistent with the π-base nature of a monovalent
group 9 metal that electronically prefers a π-acid to a
π-base. In good agreement with higher s character in
orbital hybridization composed of equatorial donors than
axial counterparts, the Ir-centroid(C41-C42) distance of
2.014 Å is shorter than the Ir-centroid(C37-C38) distance
of 2.069 Å. The C41-C42 bond distance of 1.439(7) Å is
therefore longer than the C37-C38 bond distance of 1.417
(7) Å due to better back bonding from Ir(I) to the former.
In contrast to the facial PNP found in 2a, the 1b
ligand in 2b is bound typically in a meridional fashion.
SCHEME 1 Synthesis of iridium COD complexes 2
The dihedral angle between two N-Ir-P planes is
ꢀ
1
77.84 . The core structure of 2b is best described as
square planar. Its bond distances and angles are not
exceptional.
FIGURE 1 Molecular structure of 2a with thermal ellipsoids
drawn at the 35% probability level. All hydrogen atoms are omitted
for clarity
FIGURE 2 Molecular structure of 2b with thermal ellipsoids
drawn at the 35% probability level. All hydrogen atoms are omitted
for clarity

HUANG ET AL.
3
a
TABLE 1 Selected bond distances (Å) and angles (deg) of 2a, 2b, 3b, and 4b
b
Compound
Ir-N
2a
2.104(4)
2.2965(11)
2b
3b
2.035(9)
4b
2.060(6)
2.065(5)
Ir-P
2.292(2)
2.306(2)
2.034
2.290(3)
2.297(3)
2.349(4)
2.270(2)
2.275(2)
2.3607(11)
Ir-X
2.069
2
.014
1.417(7)
.439(7)
C C
1.436(15)
1
P-Ir-P
N-Ir-P
117.55(4)
78.42(10)
162.28(7)
81.41(17)
81.01(17)
85.47
164.54(12)
83.1(3)
167.69(7)
84.17(17)
83.52(17)
82.47(11)
82.3(3)
P-Ir-X
105.79
96.55(14)
98.48(14)
1
1
1
16.17
9.67
112.03
9
22.02
88.25
73.39
85.31
N-Ir-X
X-Ir-X
166.72
174.5(3)
a
X represents Cl or the centroid of a bound C C bond.
b
Data refer to the major conformation due to a disordered COD.
SCHEME 2 Synthesis of iridium
hydride complexes of 1b
The rather unsatisfactory synthesis of 2b implicates
the necessity of a second approach to iridium complexes
ligand at the apical position whereas that of 4b is trigonal
bipyramidal. Bond distances and angles of these com-
plexes are not atypical.
of 1b. Oxidative addition of H[1b] to [Ir(μ-Cl)(COD)] in
2
benzene at room temperature generates forest green [1b]
The reactivity of complexes 2a and 4b was assessed
with respect to catalytic hydrogenation of unsaturated
hydrocarbons. As summarized in Table 2, these com-
plexes are active catalyst precursors to hydrogenate ole-
fins and alkynes under extremely mild conditions.
Styrene is successfully hydrogenated to give ethylben-
zene with turnover numbers (TONs) up to 800 (entries 1–6)
under the conditions examined. Carrying an ester func-
tional group, n-butyl acrylate is quantitatively converted to
n-butyl propanoate (entries 7–8). In contrast to these termi-
nal olefins, internal alkenes are much less reactive due to
their steric hindrance. The conversions of cyclohex-2-en-
1-one, cis-cyclooctene (COE), and COD are poor to moder-
ate (entries 9–14) though these reactions proceed cleanly.
Both terminal and internal alkynes are satisfactorily
hydrogenated, having quantitative conversions to afford
their corresponding products composed of alkenes and
Ir(H)(Cl) (3b) in nearly quantitative yield (Scheme 2).
1
The H NMR spectrum of 3b shows a diagnostic triplet
2
resonance for its hydride ligand at −45.2 ppm with J
HP
of 14 Hz. Subsequent metathetical reaction of 3b with
LiBHEt in the presence of 1 atm of H in toluene at
3
2
room temperature produces red crystalline [1b]Ir(H)2
1
(
4b). Its hydride ligands resonate in the H NMR spec-
trum at −25.5 ppm.
Crystals of 3b suitable for X-ray diffraction analysis
were grown by layering pentane on top of a concentrated
ꢀ
diethyl ether solution at −35 C while those of 4b were
grown from a concentrated diethyl ether solution at
ꢀ
−
35 C. Figures 3 and 4 depict their molecular structures.
Similar to 2b, the 1b ligand in 3b and 4b is also bound in
a meridional manner. The coordination geometry of 3b is
best described as square pyramidal with its hydride

4
HUANG ET AL.
FIGURE 4 Molecular structure of 4b with thermal ellipsoids
drawn at the 35% probability level. All hydrogen atoms except
hydrides are omitted for clarity
FIGURE 3 Molecular structure of 3b with thermal ellipsoids
drawn at the 35% probability level. All hydrogen atoms are omitted
for clarity
chemicals were obtained from commercial vendors and used
as received. Unless otherwise noted, all NMR spectra were
recorded at room temperature in specified solvents on Varian
Unity or Bruker AV instruments. Chemical shifts (δ) are
listed as parts per million downfield from tetramethylsilane.
Coupling constants (J) and peak widths at half-height
alkanes (entries 15–18). The consequence that alkynes
and n-butyl acrylate are more reactive than other unsatu-
rated substrates examined in this study is ascribable
to higher π acidity of the former. Interestingly, stilbene,
though an internal olefin that is produced from hydroge-
nation of diphenylacetylene (entries 17–18), is more
reactive than styrene (entries 15–16). Attempts to hydro-
1
(Δv1/2) are listed in hertz. H NMR spectra are referenced
1
3
using the residual solvent peak at δ 7.16 for C D .
C
6
6
NMR spectra are referenced using the internal solvent
peak at δ 128.39 for C D . The assignment of the carbon
6
6
[39–46]
13
genate nitriles,
however, were not successful
atoms for all new compounds is based on the DEPT
C
3
1
(entries 19–22). Collectively, the catalytic activity of 2a is
NMR spectroscopy. P NMR spectra are referenced
comparable to that of 4b. Unsaturated substrates bearing
aryl, ester, and ketone functional groups are compatible
but nitriles are not.
externally using 85% H PO at δ 0. Routine coupling con-
3
4
stants are not listed. Elemental analysis was performed
on a Heraeus CHN-O Rapid analyzer. The hydrogenation
reactions were analyzed by GC on a Varian chrompack
CP-3800 instrument equipped with a CP-Sil 5 CB
chrompack capillary column. Conversions and yields
were calculated versus decane as the internal standard.
The identity of the hydrogenated products was confirmed
by comparison with authentic samples.
3
3
| EXPERIMENTAL
.1 | General procedures
Unless otherwise specified, all experiments were performed
under nitrogen using standard Schlenk or glovebox tech-
niques. All solvents were reagent grade or better and purified
3.2 | X-ray crystallography
[20,28]
[28]
by standard methods. Compounds H[1a],
H[1b],
[20,28]
[28]
[47]
[1a]Li(THF)2,
[1b]Li(THF), and [Ir(μ-Cl)(COD)]2
Data were collected on a diffractometer with graphite-
were prepared following reported procedures. All other
monochromated Mo-Kα radiation (λ = 0.7107 Å).

HUANG ET AL.
5
a
TABLE 2 Catalytic hydrogenation of olefins and alkynes by 2a or 4b
b
Entry
Substrate
Cat. (mol%)
2a (0.5)
4b (0.5)
2a (0.5)
4b (0.5)
2a (0.05)
4b (0.05)
2a (0.5)
4b (0.5)
2a (0.5)
4b (0.5)
2a (0.5)
4b (0.5)
2a (0.5)
Time (hr)
Conv. (%)
Product(s)
Ethylbenzene
Ethylbenzene
Ethylbenzene
Ethylbenzene
Ethylbenzene
Ethylbenzene
n-Butyl propanoate
n-Butyl propanoate
Cyclohexanone
Cyclohexanone
Cyclooctane
Cyclooctane
cis-Cyclooctene
Cyclooctane
cis-Cyclooctene
Cyclooctane
Styrene
Yield (%)
TON
38
1
2
3
4
5
6
7
8
9
Styrene
1
19
7
19
7
Styrene
1
14
Styrene
24
24
72
72
24
24
24
24
24
24
24
95
91
30
40
100
100
45
5
95
91
30
40
100
100
45
5
190
182
600
800
200
200
90
Styrene
Styrene
Styrene
n-Butyl acrylate
n-Butyl acrylate
Cyclohex-2-en-1-one
Cyclohex-2-en-1-one
cis-Cyclooctene
cis-Cyclooctene
1,5-Cyclooctadiene
10
11
12
13
10
11
10
29
11
10
9
22
20
98
20
14
2
14
15
16
17
18
1,5-Cyclooctadiene
Phenylacetylene
Phenylacetylene
Diphenylacetylene
Diphenylacetylene
4b (0.5)
2a (0.5)
4b (0.5)
2a (0.5)
4b (0.5)
24
24
24
24
24
16
36
100
100
100
100
60
40
55
45
12
88
2
280
290
376
396
Ethylbenzene
Styrene
Ethylbenzene
Stilbene
Dibenzyl
Stilbene
Dibenzyl
98
0
19
20
21
22
Benzonitrile
2a (0.5)
4b (0.5)
2a (0.5)
4b (0.5)
24
24
24
24
0
0
0
0
NA
0
0
0
0
Benzonitrile
NA
0
Benzyl cyanide
Benzyl cyanide
NA
0
NA
0
a
Conversions, product identity, and yields were characterized by GC with decane as the internal standard, average of two runs. Reaction time was not
optimized.
b
Sum of reduced bond order from olefins or alkynes per catalyst precursor.
Structures were solved by direct methods and refined by
Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
2
full matrix least squares procedures against F using
[48]
[49]
SHELXL-97
or SHELXL-2014.
All full-weight non-
hydrogen atoms were refined anisotropically. Hydrogen
atoms were placed in calculated positions. The COD
ligand in 2b is disordered in a ratio of 60:40 over two con-
formations. CCDC 1961799–1961802 contain the supple-
mentary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge
4
3.3 | Synthesis of [1a]Ir(η -COD) (2a)
Solid [1a]Li(THF) (102 mg, 0.148 mmol) was dissolved in
toluene (4 ml) and cooled to −35 C. To this was added
solid [Ir(μ-Cl)(COD)] (50 mg, 0.074 mmol, 0.5 equiv).
2
ꢀ
2

6
HUANG ET AL.
The reaction mixture was stirred at room temperature for
δ 7.87 (d, 2, Ar), 7.04 (m, 2, Ar), 6.87 (t, 2, Ar), 6.52 (t,
2, Ar), 2.90 (m, 2, CHMe ), 2.44 (m, 2, CHMe ), 1.35 (dt,
1
hr and evaporated to dryness under reduced pressure. The
2
2
solid residue was extracted with benzene (5 ml), filtered
through a pad of Celite, and evaporated to dryness. The solid
thus obtained was washed with pentane (1 ml × 2) and dried
in vacuo, affording the product as a yellowish-orange solid;
6, CHMe ), 1.18 (dt, 6, CHMe ), 1.05 (dt, 6, CHMe ), 0.94
2 2 2
2
31
1
(dt, 6, CHMe ), −45.18 (t, 1, J = 14, IrH). P{ H} NMR
2
HP
13
1
(C D , 202.31 MHz) δ 44.17 (Δv = 30.3). C{ H} NMR
6
6
1/2
(C D , 125.70 MHz) δ 165.71 (t, J = 6.4, C), 133.14 (s,
6
6
CP
1
yield 122 mg (98%). H NMR (C D , 500 MHz) δ 7.75 (m,
CH), 130.87 (s, CH), 122.42 (t, JCP = 21.08, C), 118.15 (s,
6
6
4
6
2
2
2
, Ar), 7.49 (t, 2, Ar), 7.46 (m, 2, Ar), 7.37 (t, 4, Ar), 7.10 (m,
, Ar), 6.88 (t, 2, Ar), 6.82 (t, 2, Ar), 6.75 (t, 4, Ar), 6.60 (t,
, Ar), 3.77 (m, 2, CH=CHCH ), 3.17 (m, 2, CH=CHCH ),
CH), 117.57 (s, CH), 27.38 (t, JCP = 13.68, CHMe ), 25.11
2
(t, JCP = 15.56, CHMe ), 18.86 (s, CHMe ), 18.49 (s,
2
2
CHMe ). Anal. Calcd. for C H ClIrNP : C, 45.82; H,
2
2
2
24 37
2
.01 (m, 2, CH=CHCH ), 1.58 (m, 2, CH=CHCH ), 1.21 (m,
5.93; N, 2.23. Found: C, 45.94; H, 6.12; N, 1.95.
2
2
3
1
1
, CH=CHCH ), 1.11 (m, 2, CH=CHCH ). P{ H} NMR
2
2
13
1
(C D , 202.31 MHz) δ 14.65 (Δv = 4.54). C{ H} NMR
6
6
1/2
(
C D , 125.70 MHz) δ 164.42 (d, J = 27.48, C), 139.32 (dd,
3.6 | Synthesis of [1b]Ir(H) (4b)
6
6
CP
2
JCP = 43.87 and 5.41, C), 137.79 (d, JCP = 29.24, C), 133.92 (vt,
JCP = 7.28, CH), 133.47 (s, CH), 133.09 (vt, JCP = 5.40, CH),
To a toluene solution (2 ml) of 3b (59 mg, 0.093 mmol)
1
1
30.02 (d, JCP = 53.97, C), 130.21 (s, CH), 129.42 (s, CH),
29.13 (s, CH), 128.50 (vt, JCP = 11.04, CH), 128.45 (vt,
was added LiBHEt (0.1 ml, 1.0 M in THF, 0.1 mmol) at
room temperature. The reaction solution was degassed
with three times of freeze-pump-thaw cycles and charged
3
JCP = 7.28, CH), 120.02 (d, JCP = 8.16, CH), 118.53 (d,
JCP = 2.76, CH), 65.80 (s, CH=CHCH ), 61.01 (dd, J = 28.41
with H (1 atm) at room temperature. After being stirred at
2
CP
2
and 5.41, CH=CHCH ), 32.73 (s, CH=CHCH ), 32.25
room temperature overnight, the reaction solution was
evaporated to dryness under reduced pressure. The product
was extracted with diethyl ether (10 ml). The ether extract
was filtered through a pad of Celite and evaporated to dry-
ness to afford the product as a red solid; yield 51 mg (92%).
2
2
(
s, CH=CHCH ). Anal. Calcd. for C H IrNP : C, 63.14; H,
2
44 40
2
4.82; N, 1.67. Found: C, 63.25; H, 4.88; N, 1.76.
2
1
3
.4 | Synthesis of [1b]Ir(η -COD) (2b)
H NMR (C D , 500 MHz) δ 7.88 (d, 2, Ar), 7.07 (m, 4, Ar),
6
6
6
.60 (t, 2, Ar), 2.11 (m, 4, CHMe ), 1.18 (dd, 12, CHMe ),
2
2
31
2
Procedures were similar to those of 2a with the employ-
0.96 (dd, 12, CHMe ), −25.51 (t, 2, J = 11.5, IrH2).
P
C
2
HP
1
13
ment of [1b]Li(THF) in the place of [1a]Li(THF) ,
{ H} NMR (C D , 202.31 MHz) δ 58.71 (Δv = 33.9).
2
6
6
1/2
1
1
affording the product as an orange solid; yield 40%. H
{ H} NMR (C D , 125.70 MHz) δ 166.76 (t, J = 10.98, C),
6
6
CP
NMR (C D , 200 MHz) δ 7.74 (d, 2, Ar), 6.99 (m, 4, Ar),
133.93 (s, CH), 131.40 (s, CH), 126.90 (t, JCP = 19.70, C),
6
6
6
1
.56 (t, 2, Ar), 6.06 (m, 1, unbound HC=CH), 5.82 (m,
, unbound HC=CH), 3.35 (m, 2, bound HC=CH), 2.91
118.68 (s, CH), 115.94 (t, J = 5.02, CH), 25.73 (t,
CP
1
JCP = 15.31, CHMe ), 20.46 (t, J = 3.20, CHMe ), 18.88
2
CP
2
(
m, 1, CHMe ), 2.65 (m, 1, CHMe ), 2.51 (m, 2, CHMe ),
(s, CHMe ). Anal. Calcd. for C H IrNP : C, 48.47; H,
2 24 38 2
2
2
2
2
.30 (br s, 8, CH and CHMe ), 1.72 (m, 4, CH ), 1.33
6.44; N, 2.36. Found: C, 48.59; H, 6.56; N, 2.16.
2
2
2
3
1
1
(br s, 12, CHMe ), 1.01 (br s, 8, CH and CHMe ). P{ H}
2 2 2
NMR (C D , 80.95 MHz) δ 28.77 (AB quartet). Anal.
6
6
Calcd. for C H IrNP : C, 54.84; H, 6.90; N, 2.00.
Found: C, 55.13; H, 7.12; N, 1.95.
3.7 | General procedures for catalytic
hydrogenation of olefins and alkynes
32
48
2
A Schlenk flask was charged with a benzene solution (2 ml)
of 2a or 4b (0.6 mM), olefin or alkyne, decane, and a mag-
netic stir bar (Table 2). The reaction solution was degassed
with three times of freeze-pump-thaw cycles and charged
3
.5 | Synthesis of [1b]Ir(H)(Cl) (3b)
Solid H[1b] (300 mg, 0.747 mmol) was dissolved in benzene
(
10 ml). To this was added solid [Ir(μ-Cl)(COD)] (251 mg,
with H (1 atm) at room temperature. The reaction solution
2
2
0
.373 mmol, 0.5 equiv) at room temperature. The reaction
was stirred at room temperature for a prescribed period of
time and an aliquot was taken for GC analysis.
mixture was stirred at room temperature for 1 h and evapo-
rated to dryness under reduced pressure. The solid residue
was dissolved in a mixture of pentane (8 ml) and diethyl
ether (4 ml). The solution was concentrated under reduced
pressure to ca. 0.5 ml. The solid thus precipitated was col-
lected and dried in vacuo to afford the product as a forest
4 | CONCLUSIONS
We have prepared amido PNP complexes of iridium by
oxidative addition and metathetical reactions. The facial
1
green solid; yield 445 mg (95%). H NMR (C D , 500 MHz)
6
6

HUANG ET AL.
7
coordination mode of PNP found in 5-coordinate 2a is
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unusual. Consistent with the electronic and steric nature
4
of these PNP ligands, COD in 2a is bound in a η fashion
2
whereas that in 2b is η . Not only were formally monova-
[
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lent 2a and 2b prepared, but trivalent 3b and 4b were
also characterized. Both 2a and 4b are active in catalytic
hydrogenation of olefins and alkynes under extremely
mild conditions.
1
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ACKNOWLEDGMENTS
We thank the Ministry of Science and Technology of Tai-
wan for financial support (MOST 108-2113-M-110-007)
and Mr. Ting-Shen Kuo (NTNU) for assistance on X-ray
crystallography.
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AUTHOR BIOGRAPHIES
Mei-Hui Huang received her MS in 2008 from
National Sun Yat-sen University. Her research under
the guidance of Professor Lan-Chang Liang was
focused on coordination chemistry and homogeneous
catalysis employing main group and transition metal
complexes of amido phosphine derived chelates. She
is currently a PhD student at the King Abdullah Uni-
versity of Science and Technology with Professor Kuo-
Wei Huang.
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8
HUANG ET AL.
Xue-Ru Zou is currently carrying out her PhD studies
at National Sun Yat-sen University under the guidance
of Professor Lan-Chang Liang after obtaining BS
degree in 2015 from Chia Nan University of Pharmacy
and Science. Her research interests center around
organometallic chemistry and homogeneous catalysis
with metal complexes of phenolate or anilide phos-
phine chelates.
NSYSU where his research program focuses on the
development and application of new mismatched coor-
dination compounds, particularly those competent in
inert chemical bond activation and subsequent cata-
lytic functionalization. His work has been recognized
by Thieme Chemistry Journals Award (2006), one of
top international inorganic chemists under 40 years of
age (Inorganica Chimica Acta 2007), and Chemical
Society of Japan with Distinguished Lectureship Award
Lan-Chang Liang is a Distinguished Professor of
Chemistry at National Sun Yat-sen University and a
joint Professor of Medicinal and Applied Chemistry at
Kaohsiung Medical University, Taiwan. He undertook
his PhD studies in 1995-1999 at Massachusetts Institute
of Technology with Professor Richard R. Schrock on
early transition metal chemistry of complexes con-
taining amido chelates. After a postdoctoral stay with
Professor T. Daniel P. Stack at Stanford University
studying functional molecular models of copper
oxygenases, he began his independent career in 2000 at
(
2008).
How to cite this article: Huang M-H, Zou X-R,
Liang L-C. Amido PNP complexes of iridium:
Synthesis and catalytic olefin and alkyne
hydrogenation. J Chin Chem Soc. 2019;1–8. https://
doi.org/10.1002/jccs.201900464