Aromatic PCN palladium pincer complexes. Probing the hemilability through reactions with nucleophiles

Article abstract of DOI:10.1021/om501231k

A series of unsymmetrical PCN pincer ligands (1-(3-((di-tert-butylphosphino)methyl)phenyl)-N,N-dialkylmethanamine) were cyclometalated with palladium to generate a series of new PCN supported Pd(II) chloro complexes, (PCN)PdCl (4-6), where alkyl = methyl, ethyl, and n-propyl, which were fully characterized by NMR spectroscopy and X-ray crystallography. The N,N-dimethyl complex 4 reacts with methyl lithium to give the corresponding methyl and dimethyl complexes (PCN)PdMe (12) and Li[(PCN)PdMe₂] (13), which could not be isolated but were characterized in solution. The substitution reactions of (PCN)PdCl (4-6) with iodide to form the corresponding iodo complexes (PCN)PdI (7-9) were investigated by use of UV-vis stopped-flow spectrophotometry. The experiments were performed in methanol over a temperature range from 293 to 325 K. The reactions are reversible and were shown to proceed exclusively via the solvento complex in two reversible consecutive steps. Activation parameters for both the forward and reverse reactions were determined, and they, together with reactivity trends, support an associative pathway. No displacement of the nitrogen donor was detected, and overall this points to a limited hemilability of the ligands on palladium.

Full text of DOI:10.1021/om501231k

Article
pubs.acs.org/Organometallics
Aromatic PCN Palladium Pincer Complexes. Probing the Hemilability
through Reactions with Nucleophiles
Andre Fleckhaus,† Abdelrazek H. Mousa, Nasir Sallau Lawal, Nitsa Kiriakidou Kazemifar,
́
and Ola F. Wendt*
Centre for Analysis and Synthesis, Department of Chemistry, Lund University, P.O. Box 124, S-221 00 Lund, Sweden
S
* Supporting Information
ABSTRACT: A series of unsymmetrical PCN pincer ligands
(1-(3-((di-tert-butylphosphino)methyl)phenyl)-N,N-dialkyl-
methanamine) were cyclometalated with palladium to generate
a series of new PCN supported Pd(II) chloro complexes,
(PCN)PdCl (4−6), where alkyl = methyl, ethyl, and n-propyl,
which were fully characterized by NMR spectroscopy and X-
ray crystallography. The N,N-dimethyl complex 4 reacts with
methyl lithium to give the corresponding methyl and dimethyl
complexes (PCN)PdMe (12) and Li[(PCN)PdMe2] (13),
which could not be isolated but were characterized in solution.
The substitution reactions of (PCN)PdCl (4−6) with iodide
to form the corresponding iodo complexes (PCN)PdI (7−9)
were investigated by use of UV−vis stopped-flow spectrophotometry. The experiments were performed in methanol over a
temperature range from 293 to 325 K. The reactions are reversible and were shown to proceed exclusively via the solvento
complex in two reversible consecutive steps. Activation parameters for both the forward and reverse reactions were determined,
and they, together with reactivity trends, support an associative pathway. No displacement of the nitrogen donor was detected,
and overall this points to a limited hemilability of the ligands on palladium.
of the kinetics and mechanism for the halide for halide
substitution.
INTRODUCTION
■
Transition metal complexes with tridentate, so-called pincer
ligands have been shown to be extremely versatile catalysts in
many transformations over the past decades.1 Thus, they have
attracted considerable interest in organometallic chemistry and
they mediate a number of interesting both stoichiometric and
catalytic transformations, including dehydrogenations,2 C−C
coupling reactions,3 and the activation of small molecules.4
They can easily be immobilized via attachment of linkers on the
ligands backbone,5 and the trans effect of the carbanionic ligand
increases the reactivity in the free coordination site.6 Most
examples include symmetric ECE type of ligands, but also
examples of unsymmetric ligands with typically one soft
phosphorus donor and one hard oxygen or nitrogen donor
exist. The most common type is the PCN ligand,7 but also, for
example, POCN,8 PCO,9 PSiN,10 and PNN11 ligands have
been reported. These complexes often show a hemilabile
character which opens up one more coordination site and gives
rise to interesting reactivity.
EXPERIMENTAL SECTION
■
General Procedures and Materials. All experiments were carried
out under an atmosphere of argon or nitrogen using standard Schlenk
or high vacuum line techniques12 unless otherwise noted. All solvents
were distilled under vacuum directly to the reaction vessel from
sodium/benzophenone ketyl radical, except dichloromethane, which
was dried over calcium hydride and methanol, which was dried over
magnesium. All chemicals were purchased from Acros, Alfa-Aesar, or
1
Sigma-Aldrich. H, 13C, and 31P NMR spectra were recorded on a
Varian Unity INOVA 500 spectrometer operating at 499.77 MHz
(1H) using C6D6 and J. Young NMR tubes unless otherwise stated.
Chemical shifts are given in ppm downfield from TMS using residual
solvent peaks (1H and 13C) or H3PO4 (31P) as reference. Multiplicities
are abbreviated as follows: (s) singlet, (d) doublet, (t) triplet, (q)
quartet, (m) multiplet, (br) broad, (v) virtual. Mass spectra were
recorded on a MICROMASS Q-Tof mass spectrometer using dilute
solutions in acetonitrile/water (50:50) containing 1% of formic acid.
Elemental analyses were performed by H. Kolbe Microanalytisches
Surprisingly, the PCN pincer ligands have not been
investigated with palladium. Here we report on the synthesis
and characterization of a number of PCN palladium pincer
complexes with different substituents on the amine function-
ality. To probe the hemilability, the reactivity of the chloride in
the fourth position toward a number of nucleophiles was
investigated and in particular we report a detailed investigation
Laboratorium, Mulheim an der Ruhr, Germany. The ligand 2 was
̈
prepared according to a literature procedure,7c as were complexes
PdCl2(MeCN)2,13 {2,6-bis[(di-tert-butylphosphino)-methyl]phenyl}
palladium(II)chloride (10),14 and the corresponding iodide 11.15
Received: December 11, 2014
© XXXX American Chemical Society
A
DOI: 10.1021/om501231k
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Ligand Synthesis. The precursors for the synthesis of ligands 1−
3, the 3-(dialkylamino)benzyl bromide·HBr salts, were synthesized
using literature procedures.16 Bromination of methyl-m-methyltoluate
followed by a reduction with DiBAl-H produces 3-(bromomethyl)-
benzyl alcohol, which reacts with the corresponding dialkylamines
(aqueous solution (40%) in the case of dimethylamine) to give the 3-
(dialkylamino)benzyl alcohols as exemplified for the di-n-propyl amine
below.
in the glovebox. After evaporation, the product was obtained as a
1
colorless oil (783 mg, 75%). H NMR: δ = 7.61 (s, 1H, H1), 7.35 (d,
3JHH = 6.4 Hz, 1H, H3), 7.24−7.20 (m, 2H, H4, H5), 3.49 (s,
2H,CH2N), 2.80 (d, 2JHP = 2.0 Hz, 2H,CH2P), 2.35 (t, 3JHH = 7.3 Hz,
3
4H, N(CH2CH2CH3)2), 1.45 (tq, JHH = 7.3, 7.3 Hz, 4H,
3
N(CH2CH2CH3)2), 1.08 (d, JHP = 10.5 Hz, 18H, C(CH3)3), 0.87
3
(t, JHH = 7.4 Hz, 6H, N(CH2CH2CH3)2). 13C{1H} NMR: δ = 141.8
2
3
(d, JCP = 12.5 Hz, C2), 140.9 (s, C6), 130.5 (d, JCP = 8.7 Hz, C1),
3
4
Preparation of 3-(N,N-Di-n-propylaminomethyl)-
benzylalcohol. In a round-bottom flask 2.01 g of 3-(bromomethyl)-
benzyl alcohol (10.0 mmol) was stirred with 6.9 mL (50.0 mmol) of
di-n-propylamine for 15 h at room temperature. After removal of the
volatile compounds under reduced pressure, Et2O (100 mL) was
added and the solution was washed with aqueous KOH (10%) and
brine and dried over MgSO4 leading to 2.31 g (95%) of the crude
product in a purity of 90%. Attempts to purify it by column
chromatography led to decomposition. Therefore, it was used in the
128.5 (d, JCP = 8.8 Hz, C3), 128.3 (s, C5), 126.3 (d, JCP = 2.1 Hz,
C4), 59.4 (s, CH2N), 56.3 (s, N(CH2CH2CH3)2), 31.8 (d, 1JCP = 24.5
Hz, C(CH3)3), 29.9 (d, 2JCP = 13.5 Hz, C(CH3)3), 29.2 (d, 1JCP = 25.6
Hz, CH2P), 20.9 (s, N(CH2CH2CH3)2), 12.2 (s, N(CH2CH2CH3)2).
31P{1H} NMR: δ = 33.4 (s).
Synthesis of (PtBuCNMe)Pd-Cl (4). To a suspension of 683 mg of
(MeCN)2PdCl2 (2.63 mmol) in 40 mL of toluene in a Straus flask, 738
mg of 1 (2.50 mmol) and 520 mg of K2CO3 (3.75 mmol) were added
in the glovebox. The flask was sealed and the reaction mixture stirred
for 22 h at 120 °C. After cooling to room temperature, the flask was
opened, the mixture was filtered, and the solvents were removed under
1
next step without purification. H NMR (CDCl3): δ = 7.40−7.21 (m,
4H, Ar), 4.68 (s, 2H,CH2OH), 3.55 (s, 2H,CH2N), 2.55 (t, 3JHH = 7.3
Hz, 4H, N(CH2CH2CH3)2), 1.79 (br s, 1H, CH2OH), 1.56−1.42 (m,
1
reduced pressure, giving 1.04 g (95%) of 4 as a pale-yellow solid. H
3
4H, N(CH2CH2CH3)2), 0.86 (t, JHH = 7.4 Hz, 6H, N-
NMR (C6D6): δ = 7.00 (t, 3JHH = 7.5 Hz, 1H, H4), 6.89 (d, 3JHH = 7.5
Hz, 1H, H3), 6.69 (d, 3JHH = 7.3 Hz, 1H,H5), 3.42 (s, 2H,CH2N), 2.90
(d, 2JHP = 9.3 Hz, 2H, CH2P), 2.55 (d, 4JHP = 2.2 Hz, 6H, N(CH3)2),
1.30 (d, 3JHP = 14.0 Hz, 18H, C(CH3)3). 13C{1H}NMR: δ = 160.5 (s,
C1), 148.6 (s, C6), 147.9 (d, 2JCP = 15.2 Hz, C2), 124.7 (s, C4), 122.2
(CH2CH2CH3)2).
Preparation of 3-(N,N-Dimethylaminomethyl)benzyl bro-
mide·HBr. In a round-bottom flask, 1.02 g of 3-(N,N-
dimethylaminomethyl)benzyl alcohol (6.10 mmol) was mixed with
16 mL of HBr (48% in water) and stirred for 16 h at room
temperature. Evaporation of the solvents under high vacuum led to a
brown oil, and after stirring in 50 mL of Et2O overnight, the product
3
3
(d, JCP = 21.3 Hz,C3), 120.4 (s,C5), 72.6 (d, JCP = 2.3 Hz, CH2N),
49.7 (d, 3JCP = 2.3 Hz, N(CH3)2), 35.2 (d, 1JCP = 28.2 Hz, CH2P), 34.8
1
2
(d, JCP = 16.6 Hz, C(CH3)3), 29.2 (d, JCP = 4.5 Hz, C(CH3)3).
31P{1H} NMR: δ = 93.8 (s). Elemental analysis found (calcd for
C18H31ClNPPd): C, 49.79 (49.78); H, 7.16 (7.19); N, 3.22 (3.23).
ESI-MS: m/z 439.2 [M − Cl + MeCN]+, 398.2 [M − Cl]+.
1
precipitated as a brown solid (1.70 g, 90%). H NMR (CD3OD) δ =
7.60 (s, 1H, H1), 7.57 (d, 3JHH = 7.1 Hz, 1H, H3), 7.50 (t, 3JHH = 7.9
3
Hz, 1H, H4), 7.47 (d, JHH = 7.6 Hz, 1H, H5), 4.62 (s, 2H, CH2Br),
4.35 (s, 2H, CH2N), 2.87 (s, 6H, N(CH3)2). 13C{1H} NMR: δ =
141.1, 132.6, 132.0, 131.9, 131.6, 130.9, 61.7, 43.0, 33.1.
Synthesis of (PtBuCNEt)Pd-Cl (5). The synthesis of 5 was
performed as above using 6.4 mg (0.02 mmol) of 2, 4.4 mg (0.02
mmol) of (MeCN)2PdCl2, and triethylamine (2.7 μL, 0.02 mmol) as a
base, giving 7.3 mg (79%) of 5 as a pale-yellow solid. 1H NMR
Preparation of (PtBuCNMe)H (1). In the glovebox, 1.52 g (10.4
mmol) of di-tert-butyl phosphine was added to a solution of 1.60 g
(5.20 mmol) of 3-(dimethylaminomethyl)benzyl bromide·HBr salt in
20 mL of dry methanol. The reaction mixture was stirred for 18 h at
100 °C in a sealed Straus flask. After allowing the mixture to cool
down to room temperature, 5 mL of dry triethylamine was added and
it was stirred for 30 min. The solvents were evaporated under high
vacuum, and the flask was reintroduced into the glovebox. The solid
was treated with diethyl ether (2 × 20 mL), the suspension was
filtered, and the filtrate was evaporated under high vacuum, giving 1.35
g (89%) of the product as a pale-yellow oil. 1H NMR: δ = 7.52 (s, 1H,
H1), 7.30 (m, 1H, H3), 7.14 (m, 2H, H4, H5), 3.27 (s, 2H,CH2N),
3
3
(C6D6): δ = 6.99 (t, JHH = 7.5 Hz, 1H, H4), 6.87 (d, JHH = 7.5 Hz,
1H, H3), 6.69 (d, 3JHH = 7.4 Hz, 1H, H5), 3.55 (s, 2H, CH2N), 3.47−
2
3.39 (m, 2H, N(CH2CH3)2), 2.89 (d, JHP = 9.4 Hz, 2H, CH2P),
2.33−2.25 (m, 2H, N(CH2CH3)2), 1.37 (t, J = 7.1 Hz, 6H,
3
N(CH2CH3)2), 1.30 (d, JHP = 13.9 Hz, 18H, C(CH3)3). 13C{1H}
NMR: δ = 159.6 (s,C1), 151.2 (s, C6), 147.9 (d, 2JCP = 15.6 Hz, C2),
3
124.5 (s, C4), 121.8 (d, JCP = 21.6 Hz, C3), 119.4 (s, C5), 65.2 (d,
3JCP = 2.4 Hz, CH2N), 55.4 (s, N(CH2CH3)2), 35.2 (d, 1JCP = 22.1 Hz,
1
2
CH2P), 35.0 (d, JCP = 16.5 Hz, C(CH3)3), 29.2 (d, JCP = 4.4 Hz,
C(CH3)3), 13.6 (s, N(CH2CH3)2). 31P{1H} NMR: δ = 90.8 (s). ESI-
MS: m/z 462.0 [M + H]+, 426.0 [M − Cl]+. Elemental analysis found
(calcd for C20H35ClNPPd): C, 51.83 (51.96); H, 7.97 (7.63); N, 3.18
(3.03).
2
2.73 (d, JHP = 1.9 Hz, 2H,CH2P), 2.08 (s, 6H, N(CH3)2), 1.03 (d,
2
3JHP = 10.6 Hz, 18H, C(CH3)3). 13C{1H} NMR: δ = 142.0 (d, JCP
=
3
12.4 Hz, C2), 139.9 (s, C6), 130.6 (d, JCP = 8.6 Hz, C1), 128.8 (d,
3JCP = 8.9 Hz, C3), 128.4 (s, C5), 126.4 (d, 4JCP = 2.0 Hz, C4), 64.7 (s,
Synthesis of (PtBuCNnPr)Pd-Cl (6). The synthesis of 6 was
performed as above using 175 mg (0.50 mmol) of 3 and 109 mg (0.50
mmol) of (MeCN)2PdCl2 without the use of a base, giving 160 mg
1
CH2N), 45.5 (s, N(CH3)2), 31.8 (d, JCP = 24.5 Hz, C(CH3)3), 29.9
(d, JCP = 13.6 Hz, C(CH3)3), 29.1 (d, JCP = 25.5 Hz, CH2P).
2
1
31P{1H} NMR: δ = 33.2 (s).
(65%) of 6 as a pale-yellow solid. 1H NMR (C6D6): δ = 7.01 (t, 3JHH
=
Preparation of 3-(N,N-Di-n-propylaminomethyl)benzyl bro-
mide·HBr. Using the same procedure as above with 2.00 g of 3-(N,N-
di-n-propylaminomethyl)benzyl alcohol (9.05 mmol) and 25 mL of
HBr (48% in water) gave a brown solid, which was recrystallized from
MeOH/Et2O giving the product (2.56 g, 77%) as a light-brown
powder. 1H NMR (CD3OD): δ = 7.61 (s, 1H, H1), 7.57 (d, 3JHH = 7.5
Hz, 1H, H3), 7.50 (t, 3JHH = 7.6 Hz, 1H, H4), 7.47 (d, 3JHH = 7.6 Hz,
1H, H5), 4.63 (s, 2H, CH2Br), 4.38 (s, 2H,CH2N), 3.14−3.03 (m, 4H,
N(CH2CH2CH3)2), 1.88−1.69 (m, 4H, N(CH2CH2CH3)2), 0.99 (t,
3JHH = 7.3 Hz, 6H, N(CH2CH2CH3)2). 13C{1H} NMR: δ = 141.2 (s),
7.2 Hz, 1H, H4), 6.88 (d, 3JHH = 7.5 Hz, 1H, H3), 6.73 (d, 3JHH = 7.2
3
Hz, 1H, H5), 3.67 (s, 2H, CH2N), 3.37 (td, JHH = 11.9, 3.4 Hz, 2H,
N(CH2CH2CH3)2), 2.90 (d, 2JHP = 9.4 Hz, 2H, CH2P), 2.53−2.42 (m,
2H, N(CH2CH2CH3)2), 2.32−2.23 (m, 2H, N(CH2CH2CH3)2),
3
1.71−1.58 (m, 2H, N(CH2CH2CH3)2), 1.30 (d, JHP = 13.9 Hz,
3
18H, C(CH3)3), 0.81 (t, JHH = 7.4 Hz, 6H, N(CH2CH2CH3)2).
2
13C{1H} NMR: δ 159.6 (s, C1), 151.2 (s, C6), 147.9 (d, JCP = 15.6
3
Hz, C2), 124.6 (s, C4), 121.8 (d, JCP = 21.6 Hz, C3), 119.4 (s, C5),
3
3
66.5 (d, JCP = 2.4 Hz, CH2N), 63.7 (d JCP = 2.1 Hz,
1
1
N(CH2CH2CH3)2), 35.2 (d, JCP = 9.6 Hz, CH2P), 35.0 (d, JCP
=
132.9 (s), 132.0 (s), 131.8 (s), 131.4 (s), 130.9 (s), 57.9 (s), 55.4 (s),
33.1 (s), 18.2 (s), 11.2 (s).
2
1.5 Hz, C(CH3)3), 29.2 (d, JCP = 4.4 Hz, C(CH3)3), 21.9 (s,
N(CH2CH2CH3)2), 11.8 (s, N(CH2CH2CH3)2). 31P{1H} NMR: δ =
91.0 (s). ESI-MS: m/z 454.2 [M − Cl]+. Elemental analysis found
(calcd for C22H39ClNPPd): C, 54.75 (53.88); H, 8.17 (8.02); N, 2.94
(2.86).
Preparation of (PtBuCNnPr)H (3). In the glovebox 1.09 g of 3-
(N,N-di-n-propylaminomethyl)benzyl bromide·HBr salt (3.00 mmol)
and 875 mg of di-tert-butylphosphine (6.00 mmol) were dissolved in 5
mL of dry MeOH in a Straus flask. The sealed flask was heated to 100
°C for 38 h. After addition of 3 mL of triethylamine, it was stirred for
30 min, the volatiles were removed, and the residue filtered with Et2O
Synthesis of (PtBuCNMe)Pd-I (7). To a solution of 10.9 mg (0.025
mmol) of 4 in methanol, 44.3 mg (0.30 mmol) of NaI was added.
B
DOI: 10.1021/om501231k
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
a
Scheme 1. Synthesis of (PCN)PdCl (4−6). Complex 10 and 11 are Shown for Comparision
a
without the use of base.
After evaporation of the solvent, the residue was dissolved in benzene
and filtered through a plug of Celite. Evaporation gave 7 (12.6 mg,
96%) as a yellow solid. 1H NMR (C6D6): δ = 7.01 (t, 3JHH = 7.5, 1H,
H4), 6.88 (d, 3JHH = 7.5 Hz, 1H, H3), 6.69 (d, 3JHH = 7.4 Hz, 1H, H5),
found (calcd for C22H39INPPd): C, 45.55 (45.41); H, 6.66 (6.76); N,
2.37 (2.41).
Crystallography. XRD quality crystals of compounds 4−9 were
obtained through vapor diffusion from dichloromethane/hexane at 6
°C. Intensity data were collected with an Oxford Diffraction Excalibur
3 system, using ω-scans and Mo Kα (λ = 0.71073 Å) radiation.17 The
data were extracted and integrated using Crysalis RED.18 The
structures were solved by direct methods and refined by full-matrix
least-squares calculations on F2 using SHELXL,19 JANA2006,20 and
OLEX2.21 Molecular graphics were generated using Diamond 3.2i.22
CCDC deposition numbers 1032326−1032331.
3.42 (s, 2H,CH2N), 2.95 (d, 2JHP = 9.5 Hz, 2H, CH2P), 2.64 (d, 4JHP
=
3
2.2 Hz, 6H, N(CH3)2), 1.29 (d, JHP = 14.0 Hz, 18H, C(CH3)3).
13C{1H} NMR: δ = 165.0 (s, C1), 148.7 (s, C6), 147.6 (d, 2JCP = 15.1
3
Hz, C2), 125.0 (s, C4), 121.9 (d, JCP = 21.3 Hz, C3), 120.5 (s, C5),
72.4 (d, 3JCP = 2.8 Hz, CH2N), 51.5 (d, 3JCP = 2.8 Hz, N(CH3)2), 36.0
(d, 1JCP = 28.2 Hz, CH2P), 35.0 (d, 1JCP = 16.8 Hz, C(CH3)3), 29.6 (d,
2JCP = 4.4 Hz, C(CH3)3). 31P{1H} NMR: δ = 97.2 (s). Elemental
analysis found (calcd for C18H31INPPd): C, 40.91 (41.12); H, 5.66
(5.94); N, 2.68 (2.66).
Kinetic Measurements. Reactions of 4−6 with iodide in
methanol were monitored using an Applied Photophysics Bio
Sequential SX-17 MX stopped-flow spectrophotometer. The sub-
stitution of chloride by iodide was studied in methanol by observing
the increase in absorbance at 316 nm. The complex solution (0.1 mM)
contained chloride (1−10 mM) and was mixed with at least a 10-fold
excess of iodide (2.5−50 mM), assuring the reaction is under pseudo-
first-order conditions. The kinetic traces were fitted to single
exponentials using the software provided by Applied Photophysics
spectrophotometer.23 This gave observed rate constants at different
concentrations of leaving and incoming ligands. Rate constants are
given as an average of at least 5 runs. Variable temperature
measurements were made between 20 and 52 °C. Rate laws were
fitted using KaleidaGraph 4.1. The spectra of the products were in
agreement with those prepared separately and characterized. The
reaction of 10 to give 11 was treated similarly but using a Cary 100 Bio
UV−visible spectrophotometer and following the increase in
absorbance at 330 nm.
Synthesis of (PtBuCNEt)Pd-I (8). The synthesis of 8 was performed
as above using 23.12 mg (0.05 mmol) of 5 and 74.94 mg (0.5 mmol)
1
of NaI, giving 26.3 mg (95%) of 8 as a yellow solid. H NMR (500
MHz, C6D6): δ = 7.00 (t, 3JHH = 7.5, 1H, H4), 6.86 (d, 3JHH = 7.4 Hz,
3
1H, H3), 6.65 (d, JHH = 7.4 Hz, 1H, H5), 3.82−3.71 (m, 2H,
2
N(CH2CH3)2), 3.57 (s, 2H,CH2N), 2.93 (d, JHP = 9.5 Hz, 2H,
CH2P), 2.36−2.24 (m, 2H, N(CH2CH3)2), 1.32 (t, 3JHH = 7.0 Hz, 6H,
N(CH2CH3)2), 1.30 (d, 3JHP = 14.0 Hz, 18H, C(CH3)3). The peaks of
the methyl groups of N(CH2CH3)2 and P(C (CH3)3)2 are partially
overlapping. 13C{1H} NMR: δ = 162.8 (s, C1), 152.4 (s, C6), 147.7
(d, 2JCP = 15.4 Hz, C2), 124.8 (s, C4), 121.6 (d, JCP = 21.7 Hz, C3),
3
119.0 (s, C5), 65.0 (d, J = 2.2 Hz, CH2N), 57.3 (s, N(CH2CH3)2),
1
1
35.9 (d, JCP = 27.7 Hz, CH2P), 35.3 (d, JCP = 16.5 Hz, C(CH3)3),
2
29.6 (d, JCP = 4.1 Hz, C(CH3)3), 13.9 (s, N(CH2CH3)2). 31P{1H}
NMR: δ = 93.8 (s). Elemental analysis found (calcd for
C20H35INPPd): C, 43.51 (43.38); H, 6.22 (6.37); N, 2.48 (2.53).
Synthesis of (PtBuCNnPr)Pd-I (9). The synthesis of 9 was
performed as above using 24.52 mg (0.05 mmol) of 6 and 74.94 mg
Reaction of 4 with MeLi. Method A (formation of (PCNMe)Pd-
Me (12)): In a J. Young NMR tube, 38 μL of a solution of MeLi (1.6
M in diethyl ether, 0.06 mmol, 1.2 equiv) were evaporated at the high
vacuum line. The NMR tube was reintroduced into the glovebox,
where 0.5 mL of C6D6 and 21.7 mg of 4 (0.05 mmol, 1.0 equiv) were
added. After 1 day, complete conversion to the product could be
1
(0.5 mmol) of NaI, giving 27.9 mg (96%) of 9 as a yellow solid. H
NMR (C6D6): δ = 7.02 (t, 3JHH = 8.1 Hz, 1H, H4), 6.88 (d, 3JHH = 7.4
3
Hz, 1H, H3), 6.69 (d, JHH = 7.5 Hz, 1H, H5), 3.73 (td, J = 12.1, 4.4
1
observed according to the H and 31P NMR spectra. Isolation of the
2
Hz, 2H, N(CH2CH2CH3)2), 3.68 (s, 2H,CH2N), 2.94 (d, JHP = 9.5
product was not possible, so 12 was characterized in situ by NMR
Hz, 2H,CH2P), 2.58−2.47 (m, 2H, N(CH2CH2CH3)2), 2.30−2.23
spectroscopy only. 1H NMR (C6D6): δ = 7.19−7.17 (m, 1H, H4), 7.14
(m, 2H, N(CH2CH2CH3)2), 1.55−1.43 (m, 2H, N(CH2CH2CH3)2),
3
3
(dd, JHH = 7.5, 1.1 Hz, 1H, H3), 6.98 (dd, JHH = 7.0, 1.1 Hz, 1H,
H5), 3.69 (s, 2H, CH2N), 3.27 (d, 2JHP = 9.0 Hz, 3H, CH2P), 2.40 (s,
3H, N(CH3)2), 2.39 (s, 3H, N(CH3)2), 1.25 (d, 3JHP = 13.3 Hz, 18H,
C(CH3)3), −0.01 (s, 3H, Pd-CH3). 31P{1H} NMR: δ = 93.2 (s).
Method B: In a J. Young NMR tube, 76 μL of a solution of MeLi (1.6
M in diethyl ether, 0.12 mmol, 2.4 equiv) were evaporated at the high
vacuum line. The NMR tube was reintroduced into the glovebox,
where 0.5 mL of C6D6 and 21.7 mg of 4 (0.05 mmol, 1.0 equiv) were
3
3
1.30 (d, JHP = 14.0 Hz, 18H C(CH3)3), 0.80 (t, JHH = 7.3 Hz, 6H,
N(CH2CH2CH3)2). 13C{1H} NMR: δ = 162.8 (s, C1), 152.4 (s, C6),
147.7 (d, 2JCP = 15.3 Hz, C2), 124.8 (s, C4), 121.6 (d, 3JCP = 21.6 Hz,
C3), 119.1 (s, C5), 66.5 (s, CH2N), 65.4 (s, N(CH2CH2CH3)2), 35.9
(d, 1JCP = 27.7 Hz, CH2P), 35.3 (d, 1JCP = 16.6 Hz, C(CH3)3), 29.6 (d,
2JCP = 4.1 Hz, C(CH3)3), 22.2 (s, N(CH2CH2CH3)2), 11.5 (s,
N(CH2CH2CH3)2). 31P{1H} NMR: δ= 93.9 (s). Elemental analysis
C
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reported for the palladium PCO complexes.9 The tridentate
coordination mode of the ligand was confirmed by X-ray
crystallography, and the so determined molecular structures are
shown in Figure 1. Crystal data and collection and refinement
added. After 1 h, a mixture of two compounds was formed in a ratio of
approximately 85:15 according to 1H and 31P NMR spectroscopy, and
this stayed unchanged over a period of several days. Addition of
another 76 μL of methyl lithium solution in the glovebox led to full
conversion to the minor product which decomposed after evaporation
of the solvents. Method C: In a J. Young NMR tube, 152 μL of methyl
lithium (1.6 M in diethyl ether, 0.24 mmol, 4.8 equiv) were evaporated
at the high vacuum line. The NMR tube was reintroduced into the
glovebox, where 0.5 mL of C6D6 and 21.7 mg of 4 (0.05 mmol, 1.0
equiv) were added. After 1 h, a mixture of the tridentate complex 12
and the anionic, bidentate complex 13 were formed in a ratio of
approximately 30:70 according to 1H and 31P NMR spectroscopy.
Addition of a drop of Et2O in the glovebox led to full conversion to the
1
anionic, bidentate complex 13. H NMR (C6D6): δ = 7.20 (d, J = 7.1
Hz, 1H), 7.01 (t, J = 7.1 Hz, 1H), 6.80 (d, J = 7.2 Hz, 1H), 4.49 (br s,
2H), 2.59 (br s, 2H), 2.05 (br s, 3H), 1.80 (br s, 3H) 1.41 (br s, 18H),
0.60 (d, J = 5.2 Hz, 3H), 0.21 (s, 3H). 31P{1H} NMR (C6D6): δ =
67.6.
Figure 1. Molecular structure of 4, 5, and 6 at the 30% probability
level. Hydrogen atoms are omitted for clarity.
details are presented in Supporting Information, Table S4, and
geometrical data are given in Table 1. The Pd(II) center has a
RESULTS AND DISCUSSION
■
Synthesis of (PCN)Pd Complexes. The new (PCN)H
ligands (1 and 3) were synthesized following the literature
procedure7c for the previously described ligand (PtBuCNEt)H
(2) with only slight modifications. After radical bromination of
methyl-m-methyltoluate and reduction of the ester group, a
sequence of three nucleophilic substitutions leads to the desired
phosphine−amine ligands. The use of different secondary alkyl
amines is tolerated, allowing for the synthesis of the differently
substituted ligands. Reaction of these ligands with
PdCl2(MeCN)2 or PdCl2(PhCN)2 at 120 °C in toluene
afforded the new (PCN)Pd-Cl complexes 4−6 in moderate
yields. Addition of base improved the reaction significantly,
leading to almost quantitative formation of the desired
products. All reactions are described in Scheme 1.
Table 1. Selected Bond Lengths (Å) and Bond Angles (deg)
with Estimated Standard Deviations for Complexes 4−6
4
5
6
bond (Å)
Pd−C1
1.9809(19)
2.1802(16)
2.2428(5)
2.4090(5)
1.9685(17)
2.1873(18)
2.2325(4)
2.4061(5)
1.981(10)
2.154(10)
2.222(3)
2.396(3)
Pd−N1
Pd−P1
Pd−Cl1
angles (deg)
C1−Pd1−N1
C1−Pd1−P1
C1−Pd1−Cl1
N1−Pd1−P1
N1−Pd1−Cl1
P1−Pd1−Cl1
81.11(7)
82.95(6)
175.69(6)
161.77(5)
94.74(5)
101.32(2)
82.85(8)
82.54(6)
83.4(4)
82.0(3)
175.85(6)
165.26(5)
94.53(5)
175.6(3)
165.1(3)
92.7(3)
The 31P{1H} NMR spectra of the (PCN)Pd chloride
complexes contain only a single resonance at 93.8 ppm for 4,
90.8 ppm for 5, and 91.0 ppm for 6. Compounds 4 and 5 are
pure as judged by microanalysis. However, satisfactory
microanalysis could not be obtained for compound 6 despite
repeated recrystallization and prolonged drying. Although these
results are outside the range viewed as establishing analytical
purity, they are provided to illustrate the best values obtained.
The 1H NMR spectrum is provided as evidence of identity and
purity (see Supporting Information, Figure S28). The chemical
shift of the phosphorus atom is thus situated between the shift
in (PCPtBu)Pd-Cl complexes (72.5 ppm)24 and (PtBuCOMe)Pd-
Cl (106.1 ppm)9 indicating that the properties of the Pd−N
bond is also somewhere in between the Pd−P and the Pd−O
100.170(18)
102.01(12)
distorted square planar coordination geometry, with P and N
being positioned trans to each other with slight distortion (P−
Pd−N 162°; C1−Pd−Cl 176°). The P−Pd bond is shortened
to 2.24 Å compared to 2.30 in 10,25 whereas the Pd−N bond is
elongated to 2.18 Å (compared to 2.10 Å in (NCN)Pd−Cl),26
showing the weaker trans effect of N compared to P. The Pd−
C1 bond length is 1.98 Å, in-between the lengths of these
complexes as well (ca. 2.03 in 10, 1.92 Å in (NCN)Pd−Cl)
The reason may be increased electrophilicity of the Pd-center
or steric in origin due to the decreased size of N compared to P.
The Pd−Cl bond of 2.41 Å (2.40 Å in 10, 2.42 Å in
(NCN)Pd−Cl), on the other hand, is almost unaffected, and
this bond also shows a variability of ca. 0.02 Å between
polymorphs of 10.25b A significant shortening of the Pd−N
distance for the n-propyl substituted chloro complex is
observed; this trend is, however, not reproduced in the iodo
complexes and probably stems from a slight disorder in the
nitrogen atom in 6 rather than any underlying chemical
difference.
1
bond. All the H NMR spectra are typical for unsymmetrically
substituted pincer complexes. The spectrum of 4, as an
example, contains three signals in the aromatic region, two
doublets at 6.89 and 6.69 ppm with a JHH coupling of 7.5 and
7.3 ppm for the protons in 3- and 5-position, and a
pseudotriplet at 6.99 ppm with a JHH coupling of 7 ppm.
The benzylic protons on the amine arm give rise to a singlet,
and on the phosphine arm they give a doublet with a JHP
3
3
2
Investigation of the Hemilabile Properties of the
(PCNMe)Pd Complex. To probe the possible hemilabile
properties of the (PCN)Pd complexes, we studied potential
decomplexation reactions starting with the reaction with strong
nucleophiles. The reactions were conveniently monitored by
31P{1H} NMR spectroscopy. Immediately after the addition of
one equivalent of methyl lithium to a solution of 4 in C6D6, we
observed two new signals in addition to the starting material.
coupling of 9.4 Hz. The N-dimethyl group is split into a
4
doublet by a JPH coupling as confirmed by a 31P decoupling
experiment. The tert-butyl protons at 1.30 ppm couple with the
3
phosphorus atom, leading to a doublet with JHP = 14.0 Hz.
3
The presence of only three aromatic protons, each showing J
coupling and the downfield shift of the phosphorus, all clearly
indicate a mer-tridentate coordination of the PCN ligand with
no indication of any dimer−monomer equilibria as previously
D
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One signal at 93.2 ppm was assigned to the expected reaction
product, the (PCN)Pd-Me complex (12). The other signal at
67.6 ppm indicated that the Pd−N bond was already cleaved
under this mild conditions, leading to the anionic, dimethyl
species 13, in strong analogy to Milstein’s observations for
platinum complexes, cf. Scheme 2.7b Notably, for the (PCN)Pd
Scheme 2. Reaction with Strong Nucleophiles
Figure 2. Molecular structure of 7, 8, and 9 at the 30% probability
level. Hydrogen atoms are omitted for clarity.
and collection and refinement details are presented in
Supporting Information, Table S5, and geometrical data are
given in Table 2. The structures of compounds 8 and 9 contain
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg)
with Estimated Standard Deviations for Complexes 7−9
complex, it was not necessary to further weaken the M−N
bond by expansion of the metallacycle from a 5-membered to a
6-membered ring.7c Keeping the reaction for a longer time
showed that the Pd−N bond cleavage was reversible by
equilibration of the reaction, leading to formation of the
(PCN)Pd-Me complex as a single product. Addition of an
excess of methyl lithium moved the equilibrium to the dimethyl
product with complete conversion to the anionic complex 13 as
could be seen by a single resonance in 31P NMR at 67.56 ppm.
Attempts to isolate this anionic complex failed so far. Both
filtration and evaporation led to decomposition forming
(PCN)Pd−Cl, a monomethyl species and the free ligand 1.
Performing the reaction in the absence of diethyl ether to get
7
8
9
bonds (Å)
Pd−C1
1.971(5)
2.187(4)
2.007(12)/
1.975(13)
1.979(6)/1.992(5)
2.194(5)/2.186(5)
Pd−N1
Pd−P1
Pd−I1
2.228(10)/
2.211(10)
2.2444(12) 2.258(4)/2.254(4) 2.2463(15)/
2.2422(16)
2.6928(5)
2.7173(12)/
2.7151(13)
2.7271(7)/
2.7282(6)
angles (deg)
C1−
80.40(18)
82.79(14)
80.0(5)/80.4(5)
81.6(4)/81.9(4)
81.9(2)/82.3(2)
Pd1−N1
1
C1−
82.95(18)/
81.93(18)
a higher quality H NMR spectrum of 13 did not lead to
Pd1−P1
complete conversion of 12 to 13. The use of 4.8 equiv of
methyl lithium resulted in a mixture of 30% of the pincer Pd
methyl complex 12 and 70% of the anionic species 13. This
ratio stays unchanged for more than 10 days, whereas the
addition of one drop of diethyl ether led to complete
conversion to 13, the more polar solvent, presumably favoring
charge separation. Performing the reaction in THF-d8, instead,
did not lead to quantitative formation of 13. Twenty minutes
after addition of 2.4 equiv of methyl lithium, a mixture of 36%
of 12 and 64% of 13 was obtained. Keeping the reaction for a
longer time led to decomposition of the anionic complex into
several phosphorus containing species.
Nucleophilic Substitution with NaI. As an additional
probe of the hemilabile character of the PCN ligand, we
decided to study nucleophilic substitution with weaker
nucleophiles. This is a type of reaction that has been studied
extensively for group 10 square planar complexes, and it
generally involves associative pathways with five-coordinate
transition states with parallel solvolytic and direct pathways.27
We reasoned that hemilability could open up possibilities for
more stable anionic intermediates, thereby favoring the direct
pathway and more closed transition states. Adding an excess of
sodium iodide to a methanol solution of 4−6 transformed them
into the corresponding iodides 7−9, which were isolated and
fully characterized. The NMR spectra of 7 show the same
features as those of the chloride complex (4). The chemical
shifts of all protons are almost exactly the same with a
maximum downfield shift of Δδ = 0.1 ppm. The biggest
differences occur in the 31P and 13C NMR spectra, with the
phosphorus signal being shifted downfield to 97.2 ppm (Δδ =
3.4 ppm) and the ipso carbon (C1) being shifted to 165.0 ppm
(Δδ = 4.6 ppm). The molecular structures were determined
using X-ray diffraction and are given in Figure 2. Crystal data
C1−
175.64(13) 177.1(4)/176.7(4) 175.33(18)/
172.39(17)
Pd1−I1
N1−
162.47(13) 161.5(3)/162.3(3) 164.81(15)/
164.01(15)
Pd1−P1
N1−
95.55(12)
97.1(3)/96.3(3)
93.47(15)/
93.49(15)
Pd1−I1
P1−
101.40(3)
101.34(10)/
101.41(11)
101.72(4)/
102.47(4)
Pd1−I1
two molecules in the asymmetric unit. As for the chloride
complexes, the (PCN)Pd-I complexes show a distorted square
planar complexation of the palladium by the tridentate ligand
and iodide. Compared to the chloride complexes, all bonds and
angles stay nearly unchanged, with only the Pd−halogen bond
being 0.2 Å longer for I than Cl.
The equilibrium reaction in Scheme 3 was conveniently
studied in methanol using UV/vis spectroscopy.
The equilibrium constants for the reactions were determined
using spectrophotometry by fitting eq 1 to the absorbance at
different temperatures and concentrations of iodide and
chloride
a
Scheme 3. Substitution Reaction of the PCN Complexes
a
No further substitution was observed.
E
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A = A0[Cl−] + A∞Keq[I−]
[Cl−] + Keq[I−]
Scheme 4. Suggested Mechanism for the Substitution
Reactions in Schemes 3 and 5
a
(1)
where A = equilibrium absorbance, A0 the absorbance of the
chloride complexes (4−6, 10), and A∞ the absorbance of the
iodide complexes (7−9, 11).28 The plotted fits (Supporting
Information, Figure S1) and all data (Supporting Information,
Table S1) are given in the Supporting Information. A van ’t
Hoff plot (Supporting Information, Figure S2) gave the
enthalpy and entropy of reaction for the equilibria involving
complexes 4−6. Equilibrium constants and thermodynamic
parameters are reported in Table 3.
Table 3. Thermodynamic Data in Methanol for the
Equilibria Involving 4−6
a
The contribution from the direct path (k12/k21) is negligible.
starting complex
K298 (M)
ΔH° (kJ mol−1
)
ΔS° (J K−1 mol−1
57
)
k23k31[Cl] + k13k32[I]
kobs = k12[I−] + k21[Cl−] +
a
4
5
6
0.91 0.30
17.2 2.5
2.3 3.0
8
k31[Cl] + k32[I]
a
(2)
1.7 0.9
12 10
82 22
a
1.5 0.7
23
7
Because the equilibrium constant is known, eq 2 can be
rearranged to a form containing only three unknowns, eq 3,
where, Keq = (k12/k21) = (k13/k23) (k32/k31) .
a
Determined from the van ’t Hoff plot. Estimated standard error from
the standard error of the individual equilibrium constants in the van ’t
Hoff plot.
kobs = k12([I] + (1/Keq[Cl]))
Time-resolved spectra (Supporting Information, Figure S3)
of the reaction in Scheme 3 display well-defined isosbestic
points, showing that it is a single reaction without intermediates
with significant concentrations. The reaction was studied under
pseudo-first-order conditions, and the so-obtained observed
rate constants as a function of iodide concentration are given in
Figure 3 and Supporting Information, Figures S4 and S5. It is
((k13/Keq)(k32/k31)[Cl]) + (k13(k32/k31)[I])
+
[Cl] + ((k32/k31)[I])
(3)
It is quite clear, though, that neither eq 2 nor eq 3 will give
rise to a saturation behavior because the k12-term will continue
to grow with increasing iodide concentrations. Accordingly,
fitting eq 3 to the data in Figure 3 gave a very poor fit with
negative fitted rate constants, large errors, and other
inconsistencies. Instead, we realized that the term for the
solvent path will level off toward k13 at high iodide
concentrations. Assuming a mechanism where only the solvent
path contributes to the reactivity (k12 and k21 are negligibly
small) gives the rate law in eq 4. Using equilibrium constants
obtained from the van ’t Hoff plot, eq 4 was fitted to the data in
Figures 3, Supporting Information, S4 and S5, giving good−
excellent fits with consistent values of k13 and k32/k31 at
different concentrations of chloride. The rate constant k23 could
also be calculated from the equilibrium constants. A variable
temperature study (at a single chloride concentration) as
shown in Figure 4 and Supporting Information, Figures S6−S7
gave activation parameters for k13 and k23 from Eyring plots
(Supporting Information, Figures S8−S10). Key kinetic data
are given in Table 4, and all data are given in the Supporting
Information.
Figure 3. Observed rate constants as a function of iodide
concentration for the reaction of 5 with iodide to form 8 in methanol
at T = 25 °C. [PdTOT] = 0.1 mM. The solid lines denote the best fit to
eq 4. Different [Cl−] are indicated by colors (black, 1 mM; red 2.5
mM; blue 5 mM; green 10 mM).
((k13/Keq)(k32/k31)[Cl]) + (k13(k32/k31)[I])
kobs
=
[Cl] + ((k32/k31)[I])
(4)
clear that there is saturation behavior where the rate constants
level off at higher iodide concentrations. This cannot be
explained if the mechanism is a direct reversible substitution.
On the other hand, assuming a reversible involvement of a
solvent path (Scheme 4), as previously found in many similar
reactions, will give a rate law of the form in eq 2. This is based
upon steady-state conditions for the solvento intermediate. The
direct pathway is responsible for the first two terms and the
solvent path for the third term.29
For comparison, we decided to perform a limited study on
the substitution behavior of a (PCP)Pd complex. Thus, 10 was
reacted with iodide in methanol solution to form 11 in an
equilibrium reaction, cf. Scheme 5. Both are known
compounds, and the formation of 11 was corroborated by
NMR spectroscopy.14,15 The reaction was monitored by UV−
vis spectrometry and the equilibrium constant for the reaction
was determined as described above by fitting eq 1 to the
absorbance at different iodide concentrations, cf. Supporting
F
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Article
a
Scheme 5. Substitution Reaction of the PCP Complex
a
No further substitution was observed.
Figure 4. Observed rate constants as a function of iodide
concentration for the reaction of 5 with iodide to form 8 in methanol.
[PdTOT] = 0.1 mM. [Cl−] = 5.0 mM. The solid lines denote the best fit
to eq 4. Different temperatures (in K) are indicated by colors (black,
293.1; red 297.1; blue 301.4; green 307.8; purple 315.2).
Information, Figure S11. Plotting observed rate constants as a
function of iodide concentration at two different chloride
concentrations again gives a saturation behavior (Figure 5) as
for the PCN complexes, and eq 4 was used to evaluate the
kinetics. As expected, we therefore conclude that also for the
sterically more hindered PCP complex the substitution goes
entirely through the solvent path in Scheme 4. Kinetic and
thermodynamic data are given in Table 4.
Figure 5. Observed rate constants as a function of iodide
concentration for the reaction of 10 with iodide to form 11 in
methanol at T = 25 °C. [PdTOT] = 0.1 mM. The solid lines denote the
best fit to eq 4. Different [Cl−] are indicated by colors (black, 1 mM;
red 2.5 mM).
Thus, the substitution reactions for all the complexes
investigated are first-order in the metal complex and zero-
order in the nucleophile for both the forward and reverse
reaction. As usual for d8 square−planar complexes, we interpret
this as a nucleophilic attack by the solvent which is supported
by the fairly low activation enthalpies and negative activation
entropies. It is well-known that bulky cis-ligands and strongly
labilizing trans-ligands give rise to a lower nucleophilic
discrimination, but in platinum(II) chemistry, it is still unusual
that the solvent path completely dominates with fairly strong
nucleophiles as iodide.28,30 It can be noted that previous
examples of substitution in cyclometalated (NNC) platinum
complexes show a strong preference for the direct pathway but
no evidence for hemilability of the nitrogen donor.31 Compared
to the overwhelming amount of data on substitution reactions
in platinum(II), there is a scarcity of reports on palladium(II),
but the general trend is probably the same. Therefore, it seems
that the PCN and PCP frameworks induce an unexpected
overall decreased nucleophilic discrimination and there is no
sign that the PCN ligand opens up for direct attack by iodide or
chloride. On the contrary, the k32/k31 values indicate a lower
discriminating ability for the PCN complexes compared to 10.
This is in line with the higher reactivity of the PCN complexes,
indicating that this is not only explained by the lower steric bulk
(which should increase the nucleophilic discrimination) but
also by a more electrophilic metal center.
CONCLUSION
■
In conclusion, we present the synthesis of a number of PCN
palladium pincer complexes. With weak nucleophiles such as
iodide, there is no tendency to hemilability. On the contrary,
the PCN palladium metal centers show a low nucleophilic
discrimination where reaction with the solvent is completely
dominating over nucleophilic attack by the halide. With strong
nucleophiles, the nitrogen arm is readily displaced, more readily
than in the corresponding platinum complexes.
ASSOCIATED CONTENT
* Supporting Information
Selected NMR spectra, all kinetic data and figures, and
crystallographic tables and crystal data (CIF). This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*E-mail: ola.wendt@chem.lu.se.
■
Present Address
†University of Applied Sciences, Hochschule Emden/Leer,
Constantiaplatz 4, DE-26723 Emden, Germany.
Notes
The authors declare no competing financial interest.
a
Table 4. Kinetic Data for the Reactions in Scheme 3 and 4 in Methanol
starting complex
k13 (s−1
30
)
k23 (s−1
)
k32/k31
ΔH⧧ (kJ mol−1
)
ΔS⧧ (J K−1 mol−1
)
ΔH⧧ (kJ mol−1
)
ΔS⧧ (J K−1 mol−1
)
13
13
23
23
4
5
6
4
13.2 1.9
0.41 0.13
0.61 0.06
0.47 0.06
0.28 0.04
37
4
−93 12
51
4
−52 12
0.542 0.021
0.50 0.06
(5.4 0.2)−310
0.189 0.007
0.155 0.016
(1.5 0.2)−310
65.7 1.1
65.6 1.5
−30
−32
4
70.6 1.6
60.7 1.2
−25
−58
6
5
4
b
10
a
b
Rate constants are given at 298 K. K = 1.0 0.8.
G
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(11) (a) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D. J. Am.
Chem. Soc. 2005, 127, 12429. (b) Zhang, J.; Leitus, G.; Ben-David, Y.;
Milstein, D. Angew. Chem., Int. Ed. 2006, 45, 1113.
(12) Burger, B. J.; Bercaw, J. E. In New Developments in the Synthesis,
Manipulation and Characterization of Organometallic Compounds;
Wayda, A., Darensbourg, M. Y., Eds.; American Chemical Society:
Washington, DC, 1987; Vol. 357.
ACKNOWLEDGMENTS
■
Financial support from the Swedish Research Council, the Knut
and Alice Wallenberg Foundation, the Crafoord Foundation,
and the Royal Physiographic Society in Lund is gratefully
acknowledged.
(13) Wayland, B. B.; Schramm, R. F. Inorg. Chem. 1969, 8, 971.
REFERENCES
■
(14) Johansson, R.; Wendt, O. F. Dalton Trans. 2007, 488.
(15) Johnson, M. T.; Dzolic, Z.; Cetina, M.; Wendt, O. F.; Ohrstrom,
̈
(1) (a) Morales-Morales, D.; Jensen, C. M. (Eds.) The Chemistry of
Pincer Compounds; Elsevier: Amsterdam, The Netherlands, 2007.
(b) van Koten, G.; Milstein, D. (Eds.) Organometallic Pincer Chemistry;
Topics in Organometallic Chemistry; Springer-Verlag: Berlin−
Heidelberg, 2013, Vol. 40. (c) Szabo, K. J.; Wendt, O. F. (Eds.)
Pincer and Pincer-Type Complexes; Wiley-VCH: Weinheim, Germany,
2014.
(2) (a) Jensen, C. M. Chem. Commun. 1999, 2443. (b) Krogh-
Jespersen, K.; Czerw, M.; Zhu, K. M.; Singh, B.; Kanzelberger, M.;
Darji, N.; Achord, P. D.; Renkema, K. B.; Goldman, A. S. J. Am. Chem.
Soc. 2002, 124, 10797. (c) Goldman, A. S.; Roy, A. H.; Huang, Z.;
Ahuja, R.; Schinski, W.; Brookhart, M. Science 2006, 312, 257.
(d) Arunachalampillai, A.; Olsson, D.; Wendt, O. F. Dalton Trans.
2009, 8626. (e) Choi, J.; MacArthur, A. H. R.; Brookhart, M.;
Goldman, A. S. Chem. Rev. 2011, 111, 1761. (f) Polukeev, A. V.;
Gritcenko, R.; Jonasson, K. J.; Wendt, O. F. Polyhedron 2014, 84, 63.
(g) Jia, X.; Zhang, L.; Qin, C.; Leng, X.; Zheng, Z. Chem. Commun.
2014, 50, 11056. (h) Hu, P.; Diskin-Posner, Y.; Ben-David, Y.;
Milstein, D. ACS Catal. 2014, 4, 2649.
L.; Rissanen, K. Cryst. Growth Des. 2012, 12, 362.
(16) O’Hanlon, P. J.; Rogers, N. H. Eur. Pat. Appl. AN 406065, 1982.
(17) Crysalis CCD; Oxford Diffraction Ltd.: Abingdon, Oxfordshire,
UK, 2005.
(18) Crysalis RED; Oxford Diffraction Ltd.: Abingdon, Oxfordshire,
UK, 2005.
(19) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, A64, 112.
(20) Petricek, V.; Dusek, M.; Palatinus, L. Z. Kristallogr. 2014, 229,
345.
(21) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.;
Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339.
(22) Crystal Impact Putz H., Brandenburg K., Eds.; GbR:
Kreuzherrenstr. 102, 53227 Bonn, Germany, 2015.
(23) Bio Sequential SX-17MV Stopped-Flow ASVD Spectrophotometer,
Software Manual; Applied Photophysics Ltd.: 203/205 Kingston Road,
Leatherhead KT22 7PB, UK, 1994.
(24) Moulton, C. J.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1976,
1020.
(3) (a) Ohff, M.; Ohff, A.; van der Boom, M. E.; Milstein, D. J. Am.
Chem. Soc. 1997, 119, 11687. (b) Olsson, D.; Nilsson, P.; El
Masnaouy, M.; Wendt, O. F. Dalton Trans. 2005, 1924. (c) Nilsson, P.;
Wendt, O. F. J. Organomet. Chem. 2005, 690, 4197. (d) Serrano-
Becerra, J. M.; Morales-Morales, D. Curr. Org. Synth. 2009, 6, 169.
(e) Selander, N.; Szabo, K. J. Chem. Rev. 2011, 111, 2048.
(4) (a) Ukai, K.; Aoki, M.; Takaya, J.; Iwasawa, N. J. Am. Chem. Soc.
2006, 128, 8706. (b) Johnson, M. T.; Johansson, R.; Kondrashov, M.
V.; Steyl, G.; Ahlquist, M. S. G.; Roodt, A.; Wendt, O. F.
Organometallics 2010, 29, 3521. (c) Gutsulyak, D. V.; Piers, W. E.;
Borau-Garcia, J.; Parvez, M. J. Am. Chem. Soc. 2013, 135, 11776.
(d) Johnson, M. T.; Wendt, O. F. J. Organomet. Chem. 2014, 751, 213.
(e) Suh, H. W.; Guard, L. M.; Hazari, N. Chem. Sci. 2014, 5, 3859.
(5) Weck, M.; Jones, C. W. Inorg. Chem. 2007, 46, 1865.
(25) (a) Kimmich, B. F. M.; Marshall, W. J.; Fagan, P. J.; Hauptman,
E.; Bullock, R. M. Inorg. Chim. Acta 2002, 330, 52. (b) Johnson, M. T.;
Dzolic, Z.; Cetina, M.; Lahtinen, M.; Ahlquist, M. S. G.; Rissanen, K.;
Ohrstrom, L.; Wendt, O. F. Dalton Trans. 2013, 42, 8484.
(26) Liu, B.-B.; Wang, X.-R; Guo, Z.-F.; Lu, Z.-L. Inorg. Chem.
Commun. 2010, 13, 814.
(27) Tobe, M. L.; Burgess, J. Inorganic Reaction Mechanisms;
Longman: Amsterdam, NY, 1999; Chapter 3.3.
(28) Wendt, O. F.; Elding, L. I. Inorg. Chem. 1997, 36, 6028.
(29) Kuznik, N.; Wendt, O. F. J. Chem. Soc., Dalton Trans. 2002,
3074.
(30) (a) Cusumano, M.; Marrichi, P.; Romeo, R.; Ricevuto, V.;
Belluco, U. Inorg. Chim. Acta 1979, 34, 169. (b) Faraone, G.; Ricevuto,
V.; Romeo, R.; Trozzi, M. Inorg. Chem. 1970, 9, 1525.
(31) Romeo, R.; Plutino, M. R.; Scolaro, L. M.; Stoccoro, S.;
Minghetti, G. Inorg. Chem. 2000, 39, 4749.
̈
(6) Johansson, R.; Jarenmark, M.; Wendt, O. F. Organometallics
2005, 24, 4500.
(7) (a) Cohen, R.; Rybtchinski, B.; Gandelman, M.; Rozenberg, H.;
Martin, J. M. L.; Milstein, D. J. Am. Chem. Soc. 2003, 125, 6532.
(b) Poverenov, E.; Gandelman, M.; Shimon, L. J. W.; Rozenberg, H.;
Ben-David, Y.; Milstein, D. Chem.Eur. J. 2004, 10, 4673.
(c) Poverenov, E.; Gandelman, M.; Shimon, L. J. W.; Rozenberg,
H.; Ben-David, Y.; Milstein, D. Organometallics 2005, 24, 1082.
(d) Poverenov, E.; Leitus, G.; Shimon, L. J. W.; Milstein, D.
Organometallics 2005, 24, 5937. (e) Poverenov, E.; Efremenko, I.;
Frenkel, A. I.; Ben-David, Y.; Shimon, L. J. W.; Leitus, G.;
Konstantinovski, L.; Martin, J. M. L.; Milstein, D. Nature 2008, 455,
1093.
(8) (a) Gong, J.-F.; Zhang, Y.-H.; Song, M.-P.; Xu, C. Organometallics
2007, 26, 6487. (b) Ines, B.; San Martin, R.; Churruca, F.; Domínguez,
́
E.; Urtiaga, M. K.; Arriortua, M. I. Organometallics 2008, 27, 2833.
(c) Spasyuk, D. M.; Zargarian, D.; van der Est, A. Organometallics
2009, 28, 6531. (d) Li, J.; Siegler, M.; Lutz, M.; Spek, A. L.; Klein
Gebbink, R. J. M.; van Koten, G. Adv. Synth. Catal. 2010, 352, 2474.
(e) Zhang, B.-S.; Wang, W.; Shao, D.-D.; Hao, X.-Q.; Gong, J.-F.;
Song, M.-P. Organometallics 2010, 29, 2579. (f) Yang, M.-J-; Liu, Y.-J.;
Gong, J.-F.; Song, M.-P. Organometallics 2011, 30, 3793.
(9) Fulmer, G. R.; Kaminsky, W.; Kemp, R. A.; Goldberg, K. I.
Organometallics 2011, 30, 1627.
(10) Ruddy, A. J.; Mitton, S. J.; McDonald, R.; Turculet, L. Chem.
Commun. 2012, 48, 1159.
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DOI: 10.1021/om501231k
Organometallics XXXX, XXX, XXX−XXX