Amido PNP pincer complexes of palladium(II) and platinum(II): Synthesis, structure, and reactivity

Article abstract of DOI:10.1002/aoc.6128

The synthesis of a series of divalent palladium and platinum complexes containing amido PNP pincer ligands of the type [N(o-C₆H₄PR₂)₂]^? (R = Ph (1a), iPr (1b)) is reported. Metathetical reactions of [1a–b]PdCl or [1a–b]PtCl with a variety of alkyl Grignard reagents or LiHBEt₃ in ethereal or arene solutions generate their corresponding alkyl or hydride complexes [1a]PdR¹ (R¹ = Me, Et, nBu), [1b]PdR¹ (R¹ = Me, Et, H), [1a]PtR¹ (R¹ = Me, Et, nBu, nHexyl, H), and [1b]PtR¹ (R¹ = Me, H). Although these organometallic complexes are all thermally stable, including those containing β-hydrogen atoms even at elevated temperatures, compounds [1a]PdH and [1b]PtR¹ (R¹ = Et, nBu, nHexyl) are not isolable due to facile decomposition. The stability and reactivity of these complexes are discussed. The chloro [1a]PdCl is a superior catalyst precursor to [1b]PdCl, [1a]PtCl, and [1b]PtCl in Kumada couplings, affording, for instance, n-butyl arenes nearly quantitatively. The X-ray structures of [1b]PtCl, [1b]PtMe, [1b]PdEt, [1a]PtnBu, [1b]PdH, and [1b]PtH are presented.

Full text of DOI:10.1002/aoc.6128

Received: 22 September 2020
DOI: 10.1002/aoc.6128
Revised: 20 November 2020
Accepted: 1 December 2020
F U L L P A P E R
Amido PNP pincer complexes of palladium(II) and
platinum(II): Synthesis, structure, and reactivity
Mei-Hui Huang1 | Wei-Ying Lee1 | Xue-Ru Zou1 | Chia-Chin Lee1
Sheng-Bo Hong1 | Lan-Chang Liang1,2,3
|
1Department of Chemistry, National Sun
The synthesis of a series of divalent palladium and platinum complexes con-
taining amido PNP pincer ligands of the type [N(o-C6H4PR2)2]− (R = Ph (1a),
iPr (1b)) is reported. Metathetical reactions of [1a–b]PdCl or [1a–b]PtCl with a
variety of alkyl Grignard reagents or LiHBEt3 in ethereal or arene solutions
generate their corresponding alkyl or hydride complexes [1a]PdR1 (R1 = Me,
Et, nBu), [1b]PdR1 (R1 = Me, Et, H), [1a]PtR1 (R1 = Me, Et, nBu, nHexyl, H),
and [1b]PtR1 (R1 = Me, H). Although these organometallic complexes are all
thermally stable, including those containing β-hydrogen atoms even at ele-
vated temperatures, compounds [1a]PdH and [1b]PtR1 (R1 = Et, nBu, nHexyl)
are not isolable due to facile decomposition. The stability and reactivity of
these complexes are discussed. The chloro [1a]PdCl is a superior catalyst pre-
cursor to [1b]PdCl, [1a]PtCl, and [1b]PtCl in Kumada couplings, affording, for
instance, n-butyl arenes nearly quantitatively. The X-ray structures of [1b]PtCl,
[1b]PtMe, [1b]PdEt, [1a]PtnBu, [1b]PdH, and [1b]PtH are presented.
Yat-sen University, Kaohsiung, Taiwan
2Department of Medicinal and Applied
Chemistry, Kaohsiung Medical University,
Kaohsiung, Taiwan
3School of Pharmacy, Kaohsiung Medical
University, Kaohsiung, Taiwan
Correspondence
Lan-Chang Liang, Department of
Chemistry, National Sun Yat-sen
University, Kaohsiung 80424, Taiwan.
Email: lcliang@mail.nsysu.edu.tw
Funding information
Ministry of Science and Technology,
Taiwan, Grant/Award Number: MOST
109-2113-M-110-004
K E Y W O R D S
amido PNP pincer, Kumada coupling, olefin insertion, β-hydrogen elimination
1 | INTRODUCTION
complexes even at elevated temperatures. Olefins, such
as ethylene, 1-hexene, cycloocta-1,5-diene, norbornene,
Both β-hydrogen elimination and olefin insertion play
important roles in organometallic chemistry,[1–3] particu-
larly transition metal-mediated organic synthesis and
catalysis.[4–10] These reactions coexist in equilibrium,
with one being the reverse of the other. Understanding
and effective manipulation of these reactions have been
and methyl acrylate, readily insert into the Ni–H bond of
[1a]NiH, but similar reactions involving [1b]NiH occur
only for electronically activated olefins.[21] Consistent
with the insertion reactivity, the hydrocarbyl complexes
derived from these reactions are also thermally stable
and do not undergo β-hydrogen elimination at elevated
temperatures.
We are interested in reaction chemistry employing
amido phosphine complexes.[22–26] Whereas [1a]NiCl and
[1b]NiCl are catalytically active for Kumada couplings[20]
and [1a]PdCl is active for Heck,[27] Suzuki,[28] and
Sonogashira couplings,[29] [1a]PtMe and [1b]NiH are
capable of arene C–H bond cleavage at room temperature
in the presence of Lewis acids.[30,31] In an effort to
expand the reaction chemistry of group 10 complexes of
the essential core of
transformations.
a
number of chemical
Pincer complexes have received considerable atten-
tion in the last decades in organometallic chemistry,
catalysis, and materials science.[11–18] It is known that
organonickel complexes of amido PNP pincer ligands of
the type [N(o-C6H4PR2)2]− (R = Ph (1a), iPr (1b)) are
thermally stable, including those containing β-hydrogen
atoms.[19,20] No β-hydrogen elimination occurs for these
Appl Organomet Chem. 2020;e6128.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.6128

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HUANG ET AL.
amido PNP,[32,33] we aim in this contribution to demon-
Crystallographic Data Centre (www.ccdc.cam.ac.uk/
data_request/cif).
strate the synthetic possibilities of
a
series of
organopalladium and organoplatinum complexes of 1a
and 1b and evaluate their compatibilities in catalytic
Kumada couplings, particularly alkyl that contains
β-hydrogen atoms.
2.3 | Synthesis of [1a]PtCl
Method 1: To a THF solution (3 ml) of H[1a] (13.4 mg,
0.025 mmol) at −35ꢀC was added nBuLi (0.01 ml, 2.5 M
in n-hexane, 0.025 mmol). The reaction solution was
stirred at room temperature for 30 min and added to a
THF suspension (1 ml) of K2PtCl4 (10.4 mg, 0.025 mmol).
The reaction vessel was sealed with a Teflon cap. The
reaction mixture was heated with stirring in an oil bath
at 110ꢀC for 20 h. After being cooled to room tempera-
ture, the reaction mixture was evaporated to dryness
under reduced pressure. Benzene (5 ml) was added. The
benzene solution was filtered through a pad of Celite and
evaporated to dryness under reduced pressure to afford
the product as a yellow solid; yield 16.1 mg (84%).
Method 2: To a THF solution (10 ml) of H[1a] (295.8 mg,
0.55 mmol) at room temperature was added yellow pow-
der PtCl2(SMe2)2 (216.1 mg, 0.55 mmol, cis/trans ratio
approximately 1:2). The reaction vessel was sealed with a
Teflon cap. The reaction mixture was heated with stirring
in an oil bath at 80ꢀC for 3 h. After being cooled to room
temperature, the reaction mixture was evaporated to dry-
ness under reduced pressure. The solid residue was tritu-
rated with n-hexane (2 ml × 3). Dichloromethane (80 ml)
was added. The dichloromethane solution was filtered
through a pad of Celite and evaporated to dryness under
reduced pressure. The solid residue was washed with
diethyl ether (3 ml × 3) to afford the product as a yellow
solid; yield 414.8 mg (98%). The NMR spectra are all
identical to those reported previously.[30]
2 | EXPERIMENTAL
2.1 | General procedures
Unless otherwise specified, all experiments were per-
formed under nitrogen using standard Schlenk or
glovebox techniques. All solvents were reagent grade or
better and purified by standard methods. Compounds H
[1a],[19,20] H[1b],[20] [1a]Li(THF)2,[19,20] [1b]Li(THF),[20]
[1a]PdCl,[27] [1b]PdCl,[29] [1a]PtCl,[30] [1a]PtMe,[30] and
[34]
PtCl2(SMe2)2
were prepared following reported proce-
dures. All other chemicals were obtained from commer-
cial vendors and used as received. Unless otherwise
noted, all NMR spectra were recorded at room tempera-
ture in specified solvents on Varian Unity or Bruker AV
instruments. Chemical shifts (δ) are listed as parts per
million downfield from tetramethylsilane. Coupling con-
stants (J) are listed in hertz. 1H NMR spectra are
referenced using the residual solvent peak at δ 7.16 for
C6D6. 13C NMR spectra are referenced using the internal
solvent peak at δ 128.39 for C6D6. The assignment of the
carbon atoms for all new compounds is based on the
DEPT 13C NMR spectroscopy. 31P NMR spectra are
referenced externally using 85% H3PO4 at δ 0. Elemental
analysis was performed on a Heraeus CHN-O Rapid ana-
lyzer. Kumada coupling reactions were analyzed by GC
on a Varian chrompack CP-3800 instrument equipped
with a CP-Sil 5 CB chrompack capillary column. Conver-
sions and yields were calculated versus n-dodecane as the
internal standard.
2.4 | Synthesis of [1b]PtCl
Method 1: Solid PtCl2(SMe2)2 (90 mg, 0.23 mmol,
cis/trans ratio approximately 1:2) was suspended in THF
(3 ml) and cooled to −35ꢀC. To this was added dropwise
a solution of [1b]Li(THF) (109.1 mg, 0.23 mmol) in THF
(20 ml) at −35ꢀC. After being stirred at room temperature
overnight, the reaction mixture was stripped to dryness
in vacuo. The residue thus obtained was triturated with
pentane (2 ml × 2), and CH2Cl2 (6 ml) was added. The
CH2Cl2 solution was filtered through a pad of Celite,
which was further washed with CH2Cl2 (2 ml) until the
washings became colorless. The filtrate and washings
were combined and evaporated to dryness under reduced
pressure. The solid thus obtained was gently washed with
pentane (2 ml × 2) and dried in vacuo to give the product
as a yellow solid; yield 123.7 mg (99%). Method 2:
2.2 | X-ray crystallography
Data were collected on a diffractometer with graphite
monochromated Mo-Kα radiation (λ = 0.7107 Å). Struc-
tures were solved by direct methods and refined by full
matrix least squares procedures against F2 using
SHELXL-97[35] or SHELXL-2014.[36] All full-weight non-
hydrogen atoms were refined anisotropically. All hydro-
gen atoms were placed in calculated positions except the
hydride ligand in [1b]PtH that was found in the differ-
ence map. CCDC 2031162–2031167 contain the supple-
mentary crystallographic data for this paper. These data
can be obtained free of charge from the Cambridge

HUANG ET AL.
3 of 11
Procedures were similar to those of Method 1 in the syn-
thesis of [1a]PtCl; yield 87%. Method 3: Procedures were
similar to those of Method 2 in the synthesis of [1a]PtCl;
yield 98%. 1H NMR (C6D6, 500 MHz) δ 7.78 (d,
2, J = 8.50, Ar), 6.96 (m, 2, Ar), 6.90 (t, 2, J = 7.50, Ar),
6.48 (t, 2, J = 7.25, Ar), 2.48 (m, 4, CHMe2), 1.40 (dd,
12, J = 16.50 and 6.60, CHMe2), 1.08 (dd, 12, J = 15.75
and 7.00, CHMe2). 31P{1H} NMR (C6D6, 202 MHz) δ 41.48
(1JPPt = 2662). 13C{1H} NMR (C6D6, 125 MHz) δ 164.40 (t,
JCP = 9.17, C), 133.45 (s, CH), 131.71 (s, CH), 120.50 (t,
JCP = 23.0, C), 118.22 (t, JCP = 3.77, CH), 116.93 (t,
(C6D6, 500 MHz) δ 7.89 (d, 2, J = 8.50, Ar), 7.03 (m,
4, Ar), 6.52 (t, 2, J = 7.25, Ar), 2.15 (m, 4, CHMe2), 1.19
(dd, 12, J = 16.25 and 7.00, CHMe2), 1.05 (dd,
3
12, J = 14.50 and 7.00, CHMe2), 0.64 (t, 3, JHP = 5.50,
PdMe). 31P{1H} NMR (C6D6, 202 MHz) δ 42.03. 13C{1H}
NMR (C6D6, 125 MHz) δ 163.22 (t, JCP = 10.38, C),
133.44 (s, CH), 131.65 (s, CH), 121.72 (t, JCP = 18.38, C),
116.25 (t, JCP = 5.19, CH), 115.94 (t, JCP = 3.06, CH),
1
2
25.16 (t, JCP = 11.50, CHMe2), 19.34 (t, JCP = 2.88,
CHMe2), 18.57 (s, CHMe2), −20.49 (t, 2JCP = 7.06, PdMe).
Anal. Calcd for C25H39NP2Pd: C, 57.53; H, 7.53; N, 2.68.
Found: C, 57.52; H, 7.29; N, 2.43.
1
JCP = 4.65, CH), 25.54 (t, JCP = 14.58, CHMe2), 18.57 (s,
CHMe2), 18.17 (s, CHMe2). Anal. Calcd for
C24H36ClNP2Pt: C, 45.68; H, 5.75; N, 2.22. Found: C,
45.47; H, 5.98; N, 2.18.
2.8 | Synthesis of [1b]PtMe
2.5 | General procedures for the
synthesis of alkyl complexes
The reaction was complete overnight, affording the prod-
uct as a yellowish orange solid; yield 83%. 1H NMR
(C6D6, 500 MHz) δ 7.94 (d, 2, J = 9.00, Ar), 7.05 (m,
4, Ar), 6.52 (t, 2, J = 7.25, Ar), 2.33 (m, 4, CHMe2), 1.20
(dd, 12, J = 16.00 and 7.00, CHMe2), 1.16 (t, 3, 3JHP = 5.5,
PtCH3), 1.05 (dd, 12, J = 14.50 and 7.50, CHMe2). 31P{1H}
NMR (C6D6, 202 MHz) δ 41.72 (1JPPt = 2837). 13C{1H}
NMR (C6D6, 125 MHz) δ 164.10 (t, JCP = 8.79, C), 133.73
(s, CH), 131.63 (s, CH), 122.08 (t, JCP = 22.46, C), 116.69
(t, JCP = 4.89, CH), 116.57 (t, JCP = 3.89, CH), 25.53 (t,
1JCP = 6.90, CHMe2), 18.89 (s, CHMe2), 18.44 (s, CHMe2),
−31.35 (t, 2JCP = 6.90, 1JCPt = 588.94, PtCH3). Anal. Calcd
for C25H39NP2Pt: C, 49.18; H, 6.44; N, 2.29. Found: C,
48.97; H, 6.22; N, 2.24.
The corresponding chloro complex (0.10 mmol) was dis-
solved in THF or diethyl ether (5 ml) and cooled to
−35ꢀC. To this was added Grignard reagent (1 equiv).The
reaction mixture was stirred at room temperature for a
specified period of time and evaporated to dryness under
reduced pressure. Benzene (5 ml) was added, and the
solution was filtered through a pad of Celite. Solvent was
removed in vacuo. The resulting solid was washed with
diethyl ether (1 ml × 2) and dried in vacuo to afford the
final product.
2.6 | Synthesis of [1a]PdMe
2.9 | Synthesis of [1a]PdEt
The reaction was complete in 10 min, affording the prod-
uct as a yellowish orange solid; yield 93%. 1H NMR
(C6D6, 500 MHz) δ 7.96 (t, 1, J = 3.00, Ar), 7.94 (t,
1, J = 2.75, Ar), 7.64 (td, 8, J = 6.00 and 1.50, Ar), 7.11
(m, 2, Ar), 6.98 (m, 14, Ar), 6.45 (t, 2, J = 7.00, Ar), 0.99
The reaction was complete in 30 min, affording the prod-
uct as a yellowish orange solid; yield 99%. 1H NMR
(C6D6, 500 MHz) δ 7.92 (m, 2, Ar), 7.64 (m, 8, Ar), 7.10
(m, 2, Ar), 7.00 (m, 14, Ar), 6.43 (t, 2, J = 7.25, Ar), 2.00
(m, 2, PdCH2), 1.25 (m, 3, PdCH2CH3). 31P{1H} NMR
(C6D6, 202 MHz) δ 27.54. 13C{1H} NMR (C6D6, 125 MHz)
δ 161.84 (t, JCP = 11.80, C), 136.03 (s, CH), 134.17 (t,
JCP = 7.28, CH), 133.13 (t, JCP = 21.71, C), 132.43 (s, CH),
130.48 (s, CH), 129.28 (t, JCP = 5.40, CH), 124.37 (t,
JCP = 22.59, C), 117.06 (t, JCP = 3.64, CH), 116.66 (t,
JCP = 5.52, CH), 18.79 (t, JCP = 2.70, PdCH2CH3), 5.78 (t,
JCP = 2.76, PdCH2). Anal. Calcd for C38H33NPdP2: C,
67.91; H, 4.95; N, 2.08. Found: C, 67.72; H, 4.82; N, 1.99.
3
(t, 3, JHP = 5.5, PdCH3). 31P{1H} NMR (C6D6, 202 MHz)
δ 28.46. 13C{1H} NMR (C6D6, 125 MHz) δ 162.00 (t,
JCP = 11.80, C), 136.21 (s, CH), 134.23 (t, JCP = 7.28, CH),
133.06 (t, JCP = 22.72, C), 132.50 (s, CH), 130.52 (s, CH),
129.25 (t, JCP = 4.52, CH), 124.02 (t, JCP = 22.59, C),
117.22 (t, JCP = 3.64, CH), 116.75 (t, JCP = 5.40, CH),
−10.29 (t, JCP
= 5.52, PdCH3). Anal. Calcd for
C37H31NPdP2: C, 67.54; H, 4.75; N, 2.13. Found: C,
67.41; H, 4.65; N, 2.09.
2.7 | Synthesis of [1b]PdMe
2.10 | Synthesis of [1b]PdEt
The reaction was complete in 30 min, affording the prod-
uct as a yellowish orange solid; yield 99%. 1H NMR
The reaction was complete in 20 min, affording the prod-
uct as a yellowish orange solid; yield 97%. 1H NMR

4 of 11
HUANG ET AL.
(C6D6, 500 MHz) δ 7.86 (d, 2, J = 8.50, Ar), 7.04 (t,
2, J = 7.00, Ar), 7.01 (m, 2, Ar), 6.51 (t, 2, J = 7.25, Ar),
2.19 (m, 4, CHMe2), 1.87 (m, 2, PdCH2), 1.56 (tt,
3, J = 7.75 and 2.25, PdCH2CH3), 1.22 (dd, 12, J = 15.75
and 8.00, CHMe2), 1.04 (dd, 12, J = 14.50 and 7.00,
CHMe2). 31P{1H} NMR (C6D6, 202 MHz) δ 37.55. 13C{1H}
NMR (C6D6, 125 MHz) δ 163.11 (t, JCP = 10.25, C),
133.48 (s, CH), 131.62 (s, CH), 121.23 (t, JCP = 18.44, C),
116.19 (t, JCP = 4.81, CH), 115.76 (t, JCP = 3.19, CH),
2.13 | Synthesis of [1a]PtnBu
The reaction was complete overnight, affording the prod-
uct as a yellow solid; yield 74%. 1H NMR (C6D6,
500 MHz) δ 7.95 (dt, 2, J = 4.25 and 2.50, Ar), 7.74 (m,
6, Ar), 7.14 (t, 4, J = 5.50, Ar), 7.00 (m, 10, Ar), 6.96 (t,
4, J = 8.00, Ar), 6.43 (t, 2, J = 7.25, Ar), 2.09 (m,
2
2, JHPt = 78.50, PtCH2), 1.55 (m, 2, CH2), 1.28 (m,
2, CH2), 0.72 (t, 3, J = 7.50, CH3). 31P{1H} NMR (C6D6,
202 MHz) δ 31.55 (1JPPt = 3126). 13C{1H} NMR (C6D6,
125 MHz) δ 162.55 (t, JCP = 10.42, C), 136.09 (s, CH),
134.20 (t, JCP = 6.90, CH), 132.93 (t, JCP = 26.86, C),
132.39 (s, CH), 130.74 (s, CH), 129.09 (t, JCP = 5.27, CH),
124.85 (t, JCP = 27.74, C), 117.73 (t, JCP = 4.39, CH),
117.15 (t, JCP = 4.39, CH), 38.27 (s, CH2), 29.04 (s, CH2),
14.71 (s, CH3), 0.17 (t, 2JCP = 5.15, 1JCPt = 619.47, PtCH2).
Anal. Calcd for C40H37NP2Pt: C, 60.91; H, 4.73; N, 1.78.
Found: C, 60.62; H, 5.02; N, 1.49.
1
2
24.88 (t, JCP = 11.19, CHMe2), 19.17 (t, JCP = 3.00,
CHMe2), 19.03 (s, PdCH2CH3), 18.25 (s, CHMe2), −6.25
2
(t, JCP
=
4.56, PdCH2CH3). Anal. Calcd for
C26H41NP2Pd: C, 58.26; H, 7.71; N, 2.61. Found: C,
58.19; H, 7.65; N, 2.50.
2.11 | Synthesis of [1a]PtEt
The reaction was complete in 48 h, affording the product
1
as a yellow solid; yield 94%. H NMR (C6D6, 300 MHz) δ
7.95 (d, 2, J = 8.37, Ar), 7.73 (m, 8, Ar), 7.13 (t,
2, J = 5.70, Ar), 6.99 (m, 14, Ar), 6.44 (t, 2, J = 7.14, Ar),
2.14 | Synthesis of [1a]PtnHexyl
3
2
2.12 (q, 2, JHH = 6.99, JHPt = 74.76, PtCH2), 1.36 (t,
The reaction was complete overnight, affording the prod-
uct as a yellowish orange solid; yield 75%. 1H NMR
(C6D6, 500 MHz) δ 7.94 (d, 2, J = 8.50, Ar), 7.74 (m,
8, Ar), 7.14 (m, 2, Ar), 7.00 (m, 14, Ar), 6.43 (t,
3, JHH = 7.53, JHPt = 54.03, PtCH2CH3). 31P{1H} NMR
(C6D6, 121 MHz) δ 30.85 (1JPPt = 3130). 13C{1H} NMR
(C6D6, 75 MHz) δ 162.25 (t, JCP = 10.19, C), 135.79 (t,
JCP = 9.83, CH), 133.89 (t, JCP = 6.45, CH), 132.60 (t,
JCP = 26.74, C), 132.05 (s, CH), 130.38 (s, CH), 128.79 (t,
JCP = 4.81, CH), 124.47 (t, JCP = 27.75, C), 117.38 (t,
JCP = 3.91, CH), 116.85 (t, JCP = 3.83, CH), 19.65 (s,
3
3
2
2, J = 7.00, Ar), 2.09 (m, 2, JHPt = 79.5, PtCH2), 1.55 (m,
2, CH2), 1.24 (m, 2, CH2), 1.12 (m, 2, CH2), 1.07 (q,
2, J = 7.00, CH2), 0.81 (t, 3, J = 7.25, CH3). 31P{1H} NMR
(C6D6, 202 MHz) δ 31.50 (1JPPt = 3128). 13C{1H} NMR
(C6D6, 125 MHz) δ 162.56 (t, JCP = 10.04, C), 136.11 (s,
CH), 134.20 (t, JCP = 6.53, CH), 132.96 (t, JCP = 26.86, C),
132.38 (s, CH), 130.73 (s, CH), 129.09 (t, JCP = 5.27, CH),
124.84 (t, JCP = 28.24, C), 117.73 (t, JCP = 4.39, CH),
117.16 (t, JCP = 4.77, CH), 36.01 (s, CH2), 35.96 (s, CH2),
32.67 (s, CH2), 23.45 (s, CH2), 14.80 (s, CH3), 0.59 (t,
2
1
PtCH2CH3), −8.81 (t, JCP = 4.16, JCPt = 612.67,
PtCH2CH3).
2.12 | Synthesis of [1a]PdnBu
1
The reaction was complete in 30 min, affording the prod-
uct as a yellowish brown solid; yield 90%. 1H NMR
(C6D6, 500 MHz) δ 7.92 (t, 1, J = 2.50, Ar), 7.91 (t,
1, J = 2.75, Ar), 7.67 (m, 8, Ar), 7.10 (m, 2, Ar), 7.00 (m,
14, Ar), 6.43 (t, 2, J = 7.50, Ar), 1.98 (m, 2, PdCH2), 1.51
2JCP = 5.27, JCPt = 613.82, PtCH2). Anal. Calcd for
C42H41NP2Pt: C, 61.76; H, 5.06; N, 1.71. Found: C,
61.45; H, 4.75; N, 1.49.
(m,
2,
PdCH2CH2CH2CH3),
1.24
J
(m,
7.50,
2.15 | Synthesis of [1a]PdH
2, PdCH2CH2CH2CH3), 0.69 (t, 3,
=
PdCH2CH2CH2CH3). 31P{1H} NMR (C6D6, 202 MHz) δ
27.95. 13C{1H} NMR (C6D6, 125 MHz) δ 161.85 (t,
JCP = 10.79, C), 135.96 (s, CH), 134.16 (t, JCP = 7.28, CH),
133.19 (t, JCP = 21.71, C), 132.44 (s, CH), 130.50 (s, CH),
129.21 (t, JCP = 5.40, CH), 124.45 (t, JCP = 23.59, C),
117.07 (t, JCP = 3.64, CH), 116.66 (t, JCP = 5.52, CH),
36.97 (t, JCP = 2.76, CH2), 28.37 (t, JCP = 2.64, CH2),
14.60 (s, CH3), 13.81 (t, JCP = 1.76, CH2). Anal. Calcd for
C40H37NPdP2: C, 68.62; H, 5.33; N, 2.00. Found: C,
68.37; H, 5.11; N, 1.92.
Method 1: To a C6D6 solution (0.35 ml) of [1a]PdCl
(3.4 mg, 5.0 μmol) at room temperature was added
LiHBEt3 (5.0 μl, 1.0 M in THF, 5.0 μmol). The solution
was transferred to an NMR tube, and the reaction was
1
examined in 10 min by H and 31P{1H} NMR spectros-
copy that showed quantitative formation of [1a]PdH.
Method 2: A similar reaction employing 100 equiv of
NaBH4 in THF at room temperature also afforded [1a]
PdH quantitatively in 1 h as indicated by the 31P{1H}
NMR spectrum of reaction aliquots. 1H NMR (C6D6,

HUANG ET AL.
5 of 11
300 MHz) δ 7.99 (dt, 2, J = 8.52 and 2.55, Ar), 7.70 (qd,
8, J = 5.85 and 1.71, Ar), 7.04 (t, 2, J = 8.04, Ar), 6.95 (m,
with heating at 110ꢀC in a Teflon-sealed reaction vessel
for 24 h, affording the product as yellowish orange crys-
tals; yield 81.3 mg (87%). H NMR (C6D6, 500 MHz) δ
2
1
14, Ar), 6.47 (t, 2, J = 7.25, Ar), −9.78 (t, 1, JHP = 3.53,
PdH). 31P{1H} NMR (C6D6, 121 MHz) δ 34.10.
8.00 (d, 2, J = 9.00, Ar), 7.08 (t, 2, J = 7.50, Ar), 7.03 (m,
2, Ar), 6.54 (t, 2, J = 7.00, Ar), 2.10 (m, 4, CHMe2), 1.20
(dd, 12, J = 16.75 and 7.50, CHMe2), 0.96 (dd,
12, J = 15.00 and 7.50, CHMe2), −12.25 (t, 1, 2JHP = 14.5,
1JHPt = 1027, PtH). 31P{1H} NMR (C6D6, 202 MHz) δ
59.64 (1JPPt = 2780). 13C{1H} NMR (C6D6, 125 MHz) δ
164.30 (t, JCP = 9.54, JCPt = 44.80, C), 134.38 (t,
JCP = 17.44, CH), 131.98 (s, CH), 123.00 (t, JCP = 22.34,
C), 116.61 (t, JCP = 3.64, CH), 116.40 (t, JCP = 4.64, CH),
2.16 | Synthesis of [1b]PdH
To a red solution of [1b]PdCl (50 mg, 0.092 mmol) in tol-
uene (5 ml) at −35ꢀC was added LiHBEt3 (0.1 ml, 1.0 M
in THF, 0.1 mmol). The reaction mixture was stirred at
room temperature for 1 h to result in a yellow solution.
All volatiles were removed in vacuo. The residue was trit-
urated with pentane (1 ml) twice. Diethyl ether (6 ml)
was added. The diethyl ether solution was filtered
through a pad of Celite and evaporated to dryness under
reduced pressure to afford the product as a yellow solid;
1
2
25.50 (t, JCP = 16.06, JCPt = 44.93, CHMe2), 20.00 (t,
2JCP = 3.26, 3JCPt = 23.34, CHMe2), 18.71 (s, 3JCPt = 27.36,
CHMe2). Anal. Calcd for C24H37NP2Pt: C, 48.32; H,
6.25; N, 2.35. Found: C, 48.62; H, 6.34; N, 2.05.
1
yield 45.8 mg (98%). H NMR (C6D6, 500 MHz) δ 8.06 (d,
2, J = 8.50, Ar), 7.20 (t, 2, J = 7.50, Ar), 7.13 (m, 2, Ar),
6.65 (t, 2, J = 7.50, Ar), 2.13 (m, 4, CHMe2), 1.30 (dd,
12, J = 16.75 and 7.50, CHMe2), 1.05 (dd, 12, J = 15.00
and 7.00, CHMe2), −10.29 (t, 1, 2JHP = 6.50, PdH). 31P{1H}
NMR (C6D6, 202 MHz) δ 60.03. 13C{1H} NMR (C6D6,
125 MHz) δ 163.29 (t, JCP = 10.25, C), 134.09 (s, CH),
131.98 (s, CH), 122.64 (t, JCP = 17.75, C), 116.00 (t,
JCP = 5.00, CH), 115.98 (t, JCP = 2.25, CH), 24.65 (t,
2.19 | Synthesis of [1b]PtD
Procedures were similar to those of [1b]PdH except
employing [1b]PtCl (72.0 mg, 0.114 mmol) and LiAlD4
(11.0 mg, 0.262 mmol, 2.3 equiv) in THF (4 ml), affording
the product as yellowish orange crystals; yield 35.4 mg
(52%). 2H NMR (C6H6, 61 MHz) δ −12.19 (1JDPt = 156).
2
1JCP = 12.75, CHMe2), 20.15 (t, JCP = 4.06, CHMe2),
18.75 (s, CHMe2). Anal. Calcd for C24H37NP2Pd: C,
56.75; H, 7.34; N, 2.76. Found: C, 56.94; H, 7.45; N, 2.52.
2.20 | General procedures for catalytic
Kumada couplings (Table 1)
2.17 | Synthesis of [1a]PtH
A heavy wall Schlenk flask was charged with aryl bro-
mide (1.0 equiv), Grignard reagent (1.1 equiv), 1 mol%
[1a–b]MCl (M = Pd, Pt; 1.0 mg for each single experi-
ment), solvent (2 ml), and a magnetic stir bar. The flask
was sealed with a Teflon stopper and heated with stirring
in an oil bath at a prescribed temperature for a specified
period of time. After being cooled to room temperature,
the reaction mixture was quenched with deionized water
and the product was extracted with diethyl ether. The
diethyl ether solution was separated from the aqueous
layer, dried over MgSO4, and subject to GC-FID analysis
with n-dodecane as an internal standard or flash column
chromatography on silica gel with n-hexane as an eluent.
Procedures were similar to those of [1b]PdH except
employing [1a]PtCl (200 mg, 0.26 mmol) in THF (8 ml)
with heating at 100ꢀC in a Teflon-sealed reaction vessel
for 24 h, affording the product as yellowish orange crys-
tals; yield 112.5 mg (59%). H NMR (C6D6, 500 MHz) δ
8.02 (d, 2, J = 8.50, Ar), 7.76 (q, 8, J = 5.50, Ar), 7.19 (q,
1
2, J = 6.00, Ar), 7.01 (t, 2, J = 7.75, Ar), 6.94 (m, 12, Ar),
2
6.46 (t, 2, J = 7.50, Ar), −11.31 (t, JHP = 14.5,
1JHPt = 1052). 31P{1H} NMR (C6D6, 202 MHz) δ 34.79
(1JPPt = 2902). 13C{1H} NMR (C6D6, 125 MHz) δ 162.84 (t,
JCP = 10.04, C), 136.57 (s, CH), 134.57 (t, JCP = 7.30, CH),
134.11 (t, JCP = 28.36, C), 132.41 (s, CH), 130.79 (s, CH),
129.08 (t, JCP = 5.40, CH), 124.69 (t, JCP = 26.50, C),
117.93 (t, JCP = 3.60, CH), 117.160 (t, JCP = 4.50, CH).
Anal. Calcd for C36H37NP2Pt: C, 58.37; H, 5.03; N, 1.89.
Found: C, 58.09; H, 5.00; N, 2.01.
2.21 | Synthesis of n-butylbenzene
(Table 1, entry 12)
Isolated yield 91%. 1H NMR (CDCl3, 300 MHz) δ 7.24 (m,
2, Ar), 7.16 (m, 3, Ar), 2.59 (t, 2, J = 7.61, CH2), 1.59 (m,
2, CH2), 1.35 (m, 2, CH2), 0.93 (t, 3, J = 7.22, CH3). 13C
{1H} NMR (CDCl3, 75 MHz) δ 142.76 (C), 128.45 (CH),
128.29 (CH), 125.66 (CH), 35.86 (CH2), 33.86 (CH2), 22.52
(CH2), 14.01 (CH3).
2.18 | Synthesis of [1b]PtH
Procedures were similar to those of [1b]PdH except
employing [1b]PtCl (100 mg, 0.185 mmol) in THF (8 ml)

6 of 11
HUANG ET AL.
TABLE 1 Catalytic Kumada couplings
Entry
1
Catalyst
[1a]PdCl
[1a]PdCl
[1a]PdCl
[1a]PdCl
[1a]PdCl
[1a]PdCl
[1a]PdCl
[1a]PdCl
[1a]PdCl
[1a]PdCl
[1a]PdCl
[1a]PdCl
[1b]PdCl
[1a]PtCl
[1b]PtCl
[1a]PdCl
[1a]PdCl
[1a]PdCl
[1a]NiCl
[1b]NiCl
R
Ar
Solvent
Et2O
Temp
60
60
60
60
60
60
60
28
40
40
60
60
60
60
60
60
60
60
60
60
Time
12
12
12
12
12
12
12
40
40
84
24
36
36
36
36
36
36
36
12
12
Conva
69
R–Ar/Ar–Ar selectivitya
nBu
nBu
nBu
nBu
nBu
nBu
nBu
nBu
nBu
nBu
nBu
nBu
nBu
nBu
nBu
nBu
nBu
4-Tolyl
nBu
nBu
Ph
99/1
2
Ph
THF
94
86/14
78/22
97/3
3
Ph
DME
72
4
Ph
1,4-Dioxane
n-Hexane
Benzene
Toluene
Et2O
45
5
Ph
97
48/52
54/46
57/43
100/0
100/0
99/1
6
Ph
100
100
31
7
Ph
8
Ph
9
Ph
Et2O
50
10
11
12
13
14
15
16
17
18
19b
20b
Ph
Et2O
91
Ph
Et2O
90
99/1
Ph
Et2O
100
98
99/1
Ph
Et2O
90/10
100/0
NA
Ph
Et2O
19
Ph
Et2O
0
4-FC6H4
Et2O
100
100
83
99/1
4-MeOC6H4
Et2O
100/0
100/0
44/56
46/54
Ph
Ph
Ph
Et2O
THF
97
THF
57
Note: Unless otherwise noted, all reactions were carried out with 1 equiv of aryl bromide and 1.1 equiv of Grignard reagent in the presence of 1 mol% catalyst
(1.0 mg) in 2-ml solvent; temperature in ꢀC, time in hour, conversion in %.
aDetermined by GC, based on aryl bromide, average of two runs.
bReference Liang et al.[20]
3 | RESULTS AND DISCUSSION
3.1 | Synthesis of chloro complexes
Chloro complexes are convenient starting materials for
SCHEME 1 A facile entry to the synthesis of [1a]PtCl and
subsequent derivatization. Scheme S1 illustrates the syn-
thetic strategies to prepare [1a–b]PdCl and [1a–b]PtCl.
The synthesis of [1a]PdCl,[27] [1b]PdCl,[29] and [1a]
PtCl[30] was reported previously. In addition to these
known methods that take advantage of the enhanced
reactivity of MCl2L2 (M = Pd, L = PhCN; M = Pt,
L = SMe2), we found that the most convenient entry to
the synthesis of [1a]PtCl and [1b]PtCl perhaps involves
heating a THF suspension of K2PtCl4 in the presence of
in situ prepared lithium complexes of 1a and 1b, respec-
tively (Scheme 1). No reaction was found without heating
or prior lithiation of the protio ligands. Complex [1b]PtCl
[1b]PtCl
can be isolated in a nearly quantitative yield as a yellow
crystalline solid.
3.2 | Synthesis of alkyl and hydride
complexes
Treating [1a]PdCl in THF at −35ꢀC with R1MgCl leads
to their corresponding alkyl complexes [1a]PdR1

HUANG ET AL.
7 of 11
(R1
=
Me, Et, nBu) quantitatively in 30 min
3.3 | Structural characterization
(Scheme 2). Similar reactions employing [1b]PdCl, [1a]
PtCl, or [1b]PtCl generate successfully [1b]PdR1
(R1 = Me, Et), [1a]PtR1 (R1 = Me, Et, nBu, nHexyl), or
[1b]PtMe, respectively, though it requires >12 h to pro-
duce high yields of organoplatinum complexes [1a]PtR1
and [1b]PtMe. As a result, the alkylation of palladium
complexes [1a]PdCl and [1b]PdCl with Grignard
reagents proceeds much faster than that of platinum
complexes [1a]PtCl and [1b]PtCl. In contrast to their 1a
counterparts, no reaction occurs in attempts to prepare
higher homologs of [1b]PtMe under otherwise identical
conditions. Attempts to accelerate reactions of [1b]PtCl
with R1MgCl (R1 = Et, nBu, nHexyl) by increasing
reaction temperatures, for example, 80ꢀC, led inevitably
to a mixture of [1b]PtH (vide infra) and the presumed
[1b]PtR1 in a ratio of approximately 4:1 as indicated by
the 31P{1H} NMR spectra of reaction aliquots. The for-
mation of [1b]PtH in these alkylation reactions is
ascribed to β-hydrogen elimination of their presumed
alkyl precursors. In contrast, alkyls that contain
β-hydrogen atoms such as [1a]PdEt, [1b]PdEt, and [1a]
PtEt are all thermally stable in C6D6 (approximately
21 mM) at 80ꢀC for >30 h as evidenced by their 1H
and 31P{1H} NMR spectra. The fact that no β-hydrogen
elimination occurs for [1a]PdEt, [1b]PdEt, or [1a]PtEt
but for in situ prepared [1b]PtEt is surprising. Attempts
to selectively isolate [1b]PtEt, [1b]PtnBu, or [1b]
PtnHexyl have so far been unsuccessful.
Addition of one equivalent of LiHBEt3 or an excess
amount of NaBH4 to an arene or THF solution of [1a]
PdCl at room temperature leads to [1a]PdH quantita-
tively in 10 min or 1 h, respectively, as indicated by the
1H and 31P{1H} NMR spectra of reaction aliquots.
Attempts to isolate this hydride complex, however, were
hampered by its facile decomposition upon workup
where the solution darkened significantly to give intrac-
table materials. Similar reactions employing [1b]PdCl,
[1a]PtCl, or [1b]PtCl afford successfully their
corresponding hydride complexes in high isolated yields
though those involving platinum again proceed much
slower than palladium. For instance, the reaction of [1b]
PdCl with LiHBEt3 is complete in 1 h, but those of [1a]
PtCl or [1b]PtCl requires >12 h.
Solution structures of [1b]PtCl and organometallic com-
plexes illustrated in Scheme 2 were all characterized by
multinuclear NMR spectroscopy. Table S1 summarizes
their selected data, along with those of their protio ligands,
nickel congeners, and in situ prepared [1a]PdH and [1b]
PtR1 (R1 = Et, nBu, nHexyl). Similar to their nickel
derivatives,[19–21,37–39] these palladium and platinum com-
plexes are all C2v symmetric in solution on the NMR time-
scale, having the coordination geometry about the metal
center being square planar as evidenced by virtual triplet
resonances observed in their 13C{1H} NMR spectra for the
o-phenylene carbon atoms in these complexes.
The 31P resonances of these 4d and 5d complexes are
all shifted relatively downfield as compared with those of
their 3d analogs or protio ligands. The 31P–195Pt coupling
constants of 1a derivatives are consistently larger than
those of 1b counterparts, indicating slightly stronger P–Pt
bonds for the former. These results are in line with what
one expects for a phenyl-substituted phosphine being a
better π acid than an isopropyl-substituted phosphine.
The observed chemical shifts of Hα and Cα in alkyl com-
plexes and their corresponding coupling constants with
31P and 195Pt, if not hampered by overlaps with other sig-
nals, are all typical.[40–43] The hydride complexes exhibit
a
diagnostic triplet[44] resonance at approximately
−10 ppm for the hydride ligand in palladium derivatives
and approximately −12 ppm for platinum derivatives,
values that are both downfield shifted from those of their
nickel analogs.
Yellow crystals of [1b]PtCl suitable for X-ray diffrac-
tion analysis were grown by layering pentane on a con-
centrated diethyl ether solution at −35ꢀC whereas
yellowish orange crystals of [1b]PtMe, [1b]PdEt, [1a]
PtnBu, [1b]PdH, or [1b]PtH were grown from a concen-
trated diethyl ether or pentane solution at −35ꢀC.
Figures 1–3 and S1–S3 depict the structures of these com-
plexes. Selected bond distances and angles are summa-
rized in Tables S2 and S3, respectively, along with those
of close analogs that were known previously.
As illustrated, the coordination geometry of these
complexes is square planar, having the PNP ligand
meridionally bound to palladium or platinum,
SCHEME 2 Synthesis of isolable palladium and platinum
alkyl and hydride complexes of 1a and 1b

8 of 11
HUANG ET AL.
reminiscent of what was known for their nickel conge-
ners. The bond distances and angles about the metal cen-
ter are all comparable with those of amido or phosphine
complexes of divalent group 10 metals.[40,44] Found in the
difference map, the hydride ligand in [1b]PtH is anoma-
lously bent from the ideal position in the square coordi-
nation plane. The reason why it is bent is not clear. The
dihedral angle between the two o-phenylene planes in
these complexes is approximately 40ꢀ, whereas that
between the coordination plane and the C–N–C plane is
approximately 22ꢀ (Table S4). The N–Pt bond distance of
2.084(6) Å in [1b]PtH is slightly longer than that in [1b]
PtCl (2.029(7) Å) but somewhat shorter than that in [1b]
PtMe (2.103(5) Å), consistent with the trans influence
order of alkyl > H > Cl. Similar trends are also found for
the N–Pd bond distances: [1b]PdEt (2.097(3) Å) > [1b]
PdH (2.0881(18) Å) > [1b]PdCl (2.029(3) Å), the N–Pt
bond distances: [1a]PtnBu (2.111(15) Å) > [1a]PtMe (2.09
(2) Å) > [1a]PtCl (2.024(6) Å), and the N–Ni bond dis-
FIGURE 1 Molecular structure of [1b]PdEt with thermal
ellipsoids drawn at the 35% probability level. All hydrogen atoms
are omitted for clarity
tances: [1b]NiMe (1.945(3) Å)
> [1b]NiH (1.920
(3) Å) > [1b]NiCl (1.9030(17) Å).
The magnitude of 31P–195Pt coupling constants
observed from NMR spectroscopy has also been rational-
ized with s character involved in the corresponding P–Pt
bond; the more s character, the larger coupling con-
stant.[45] The larger C–P–C bond angles found for [1b]
PtMe than [1a]PtMe (Table S3) imply less s character
involved in the P–Pt bonds for the former, thus a smaller
31P–195Pt coupling constant (Table S1). Although this is
in good agreement with our experimental data, [1a]PtCl
instead shows larger C–P–C bond angles and a larger
31P–195Pt coupling constant than [1b]PtCl. Such inconsis-
tency led us to analyze C–P–C bond angles of all structur-
ally characterized compounds (Table S3) no matter if it is
a platinum complex. These analyses consistently show
larger C–P–C bond angles for all 1b derivatives than their
corresponding 1a counterparts, as what is anticipated
from the larger steric size of an isopropyl moiety than a
phenyl group.[46] All in all, the consequence that [1a]PtCl
has larger C–P–C bond angles than [1b]PtCl is the only
exception.
FIGURE 2 Molecular structure of [1a]PtnBu with thermal
ellipsoids drawn at the 35% probability level. All hydrogen atoms
are omitted for clarity
Atomic radii of 4d metals are larger than those of
their 3d counterparts for a larger principal quantum
number but similar to those of their 5d congeners due to
lanthanide contraction for the heavier elements. For
instance, the ionic radius of divalent nickel in a square
planar coordination geometry is 63 pm, whereas those of
palladium and platinum are 78 and 74 pm, respec-
tively.[47] As shown in Table S2, the M–N and M–P bond
distances of the hydride complexes [1b]MH increase in
the sequence of Ni < Pt < Pd. Similar trends are also
found for the M–N and M–P bond distances of [1a]MCl,
so are [1b]MCl, in spite of having one exception that the
FIGURE 3 Molecular structure of [1b]PtH with thermal
ellipsoids drawn at the 35% probability level. All hydrogen atoms
except the hydride ligand are omitted for clarity

HUANG ET AL.
9 of 11
M–N bond distances of [1b]PdCl and [1b]PtCl are coinci-
dentally identical. The M–Cl bond distance of [1a]PdCl is
similar to that of [1a]PtCl but significantly larger than
that of [1a]NiCl. A similar phenomenon is also found for
the M–Cl bond distances of [1b]MCl.
not insert into the Pt–D bond of [1b]PtD and [1b]PtEt-d1
is not kinetically accessible.
Cross-coupling catalysis has made tremendous
impacts on organic syntheses.[9,48,49] Nickel complexes of
PNP are known catalyst precursors for Kumada cou-
plings.[20] In this regard, the reactivity of their palladium
and platinum analogs was investigated. Table 1 summa-
rizes their catalytic activities.
3.4 | Reactivity studies
We began with a survey of reaction parameters.
Among seven solvents examined (entries 1–7), diethyl
ether is superior to the others in the reaction of n-
butylmagnesium chloride with phenyl bromide in the
presence of 1 mol% [1a]PdCl at 60ꢀC in 12 h in view of
their corresponding selectivity of the desired cross-
coupling product and turnover efficiency. An assessment
of temperature and time in reaction run in diethyl ether
(entries 8–12) gives an optimization of conversion and
selectivity to produce n-butylbenzene in 99% yield at
60ꢀC in 36 h (entry 12).
Under this optimized condition, [1b]PdCl shows vir-
tually identical reactivity to [1a]PdCl but somewhat less
satisfactory selectivity (entry 13). In contrast, the selectiv-
ity of the desired product derived from [1a]PtCl is excel-
lent, but its reaction rate is too slow (entry 14). No
catalytic reaction occurs, however, employing [1b]PtCl
(entry 15). Collectively, [1a]PdCl outperforms [1b]PdCl,
[1a]PtCl, and [1b]PtCl in Kumada coupling catalysis. The
low activities of [1a]PtCl and [1b]PtCl in this catalysis
are consistent with the slow reaction rates found for these
platinum complexes in their stoichiometric reactions.
The success in incorporating n-butyl that contains
β-hydrogen atoms in cross-coupling catalyzed by [1a]
PdCl, [1b]PdCl, and [1a]PtCl is in accordance with the
consequence that no β-hydrogen elimination occurs for
alkyl derivatives of these chloride precursors.
Given the results that [1a]PdEt, [1b]PdEt, and [1a]PtEt
do not undergo β-hydrogen elimination even at elevated
temperatures, we examined the reactivity of their hydride
analogs with respect to ethylene insertion. Neither [1b]
PdH nor [1a]PtH reacts with an excess amount of ethyl-
ene (1 atm), even after heating at 80ꢀC in C6D6 (29 mM)
for >30 h. No reaction was found for [1b]PtH, either,
under otherwise identical conditions. In contrast, in situ
prepared [1a]PdH reacts with ethylene in C6D6 at room
temperature to result in quantitative conversion of [1a]
PdH in 10 h and formation of a mixture in which [1a]
PdEt is one of the minor products (31P NMR evidence).
Attempts to isolate the major product (δP 7.1) of this reac-
tion were not successful. Nevertheless, ethylene insertion
into the Ni–H bond of [1a]PdH does occur though the
reaction is complicated with either the facile decomposi-
tion of [1a]PdH or other prevailed pathways involving
ethylene. The discrepancy in reactivity of these hydride
complexes with ethylene highlights the difference in elec-
trophilicity of their corresponding metal center. The con-
sequence that [1a]PdH is active toward ethylene
insertion but [1b]PdH is not is reminiscent of what was
found for their nickel analogs.[21] Decomposition of in
situ prepared [1b]PtEt, and its higher homologs, to give
[1b]PtH, however, contrasts sharply with all other group
10 complexes of PNP.[19–21] In view of the principle of
microscopic reversibility, β-hydrogen elimination of in
situ prepared [1b]PtEt is therefore thermodynamically
downhill, whereas that of [1a]PdEt is thermodynamically
uphill.
Both electronically activated and deactivated aryl bro-
mide electrophiles are compatible in this catalysis to pro-
duce n-butyl arenes satisfactorily (entries 16–17). An aryl
nucleophile such as 4-tolylmagnesium chloride also
works successfully (entry 18). Notably, [1a]PdCl is supe-
rior to nickel complexes [1a]NiCl and [1b]NiCl (entries
19–20)[20] in view of its much higher selectivity of the
desired cross-coupling product.
To gain more insights, we prepared [1b]PtD and
attempted its reaction with ethylene in order to probe the
kinetic accessibility of [1b]PtEt-d1 with which [1b]PtH
and ethylene-d1 might be observable after β-hydrogen
elimination. Complex [1b]PtD can be synthesized by
treating [1b]PtCl with LiAlD4 in THF at room tempera-
ture in 1 h. Its 2H NMR spectrum shows a diagnostic sig-
4 | CONCLUSIONS
1
nal at −12 ppm with JDPt of 156 Hz. This coupling
constant is in good agreement with that anticipated from
1JHPt in [1b]PtH and the magnetogyric ratios of these iso-
topes. No reaction was found, however, for [1b]PtD
(23 mM in C6D6) with an excess amount of ethylene
We have prepared and structurally characterized a num-
ber of divalent palladium and platinum alkyl and hydride
complexes of amido PNP pincer ligands 1a and 1b.
Though the majority of these organometallic complexes
are thermally stable, including alkyls that contain
β-hydrogen atoms even at elevated temperatures, [1a]
1
2
(1 atm) at 80ꢀC for >30 h as evidenced by H and H
NMR spectra, a result corroborating that ethylene does

10 of 11
HUANG ET AL.
PdH and [1b]PtR1 (R1 = Et, nBu, nHexyl) decompose
either during synthesis or upon workup. Among the
hydride complexes investigated in this study, [1a]PdH,
though prepared in situ, is the only one that undergoes
ethylene insertion. β-Hydrogen elimination of [1a]PdEt is
therefore thermodynamically uphill, whereas that of in
situ prepared [1b]PtEt is downhill. In addition to Heck,
Suzuki, and Sonogashira couplings, [1a]PdCl is also com-
petent in catalytic Kumada coupling. In terms of Kumada
coupling catalysis, [1a]PdCl is superior to [1b]PdCl, [1a]
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ACKNOWLEDGMENTS
We thank the Ministry of Science and Technology, Tai-
wan, for financial support (MOST 109-2113-M-110-004)
and Mr. Ting-Shen Kuo (NTNU) for assistance on X-ray
crystallography.
AUTHOR CONTRIBUTIONS
Mei-Hui Huang: Investigation. Wei-Ying Lee: Investi-
gation. Xue-Ru Zou: Investigation. Chia-Chin Lee:
Investigation. Sheng-Bo Hong: Investigation. Lan-
Chang Liang: Funding acquisition; methodology;
supervision.
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are avail-
able in the supporting information of this article.
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[29] Y.-T. Hung, M.-T. Chen, M.-H. Huang, T.-Y. Kao, Y.-S. Liu, L.-
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ORCID
Lan-Chang Liang https://orcid.org/0000-0002-8185-
2824
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How to cite this article: Huang M-H, Lee W-Y,
Zou X-R, Lee C-C, Hong S-B, Liang L-C. Amido
PNP pincer complexes of palladium(II) and
platinum(II): Synthesis, structure, and reactivity.
Appl Organomet Chem. 2020;e6128. https://doi.org/
10.1002/aoc.6128