N-H bond activation by palladium(ii) and copper(i) complexes featuring a reactive bidentate PN-ligand

Article abstract of DOI:10.1039/c2dt31009k

The first examples of reactivity at the backbone of a bidentate PN-ligand L1H relevant to N-H activation are described, leading to novel Pd^II and Cu^I amido complexes. Activation of the PN-ligand backbone led to selective dearomatization of the pyridyl ring structure. In the case of Pd ^II, the intermediate could be efficiently stabilized using PMe ₃. Selective N-H bond cleavage of e.g. trifluorosulfonylamide resulted in facile formation of mononuclear metal-amido species 2 and 4, which have been crystallographically characterized. Hydrogen-bonding dimerization is observed in these solid state structures. The results obtained with these structurally versatile and reactive scaffolds likely open up new avenues in cooperative catalysis.

Full text of DOI:10.1039/c2dt31009k

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PAPER
N–H bond activation by palladium(II) and copper(I) complexes featuring a
reactive bidentate PN-ligand†‡
Sandra Y. de Boer,a Yann Gloaguen,a Joost N. H. Reek,a Martin Lutzb and Jarl Ivar van der Vlugt*a
Received 9th May 2012, Accepted 12th June 2012
DOI: 10.1039/c2dt31009k
The first examples of reactivity at the backbone of a bidentate PN-ligand L1H relevant to N–H activation
are described, leading to novel PdII and CuI amido complexes. Activation of the PN-ligand backbone led
to selective dearomatization of the pyridyl ring structure. In the case of PdII, the intermediate could be
efficiently stabilized using PMe3. Selective N–H bond cleavage of e.g. trifluorosulfonylamide resulted in
facile formation of mononuclear metal–amido species 2 and 4, which have been crystallographically
characterized. Hydrogen-bonding dimerization is observed in these solid state structures. The results
obtained with these structurally versatile and reactive scaffolds likely open up new avenues in cooperative
catalysis.
to generate metal–amido species in a controlled manner and
Introduction
facilitate subsequent intra- and intermolecular reactions.7
In biological systems, cooperative substrate activation by earth-
abundant metals, often in combination with protein-based
ligands or other organic co-factors, is omnipresent.1 Surprisingly,
the combination of a first row transition metal and a ‘reactive
ligand’ environment acting in concert has been scarcely
exploited in a conceptual manner in synthetic chemistry,2 which
is in contrast to landmark examples for the heavier 2nd and 3rd
row metals.3
The activation of N–H bonds by transition metals (and main
group compounds) is of huge interest these days, because it
could lead to the development of new catalytic routes to functio-
nalize e.g. alkenes with amines.4 Connected to this research area
is the potential use of ammonia as an interesting substrate for
homogeneous catalysis.5 Selective N–H bond cleavage of NH3
by transition metals is a big challenge and might represent one
of the inherent limitations of this widely available compound.
The development of complexes that may engage in efficient
N–H activation and functionalization processes is therefore con-
sidered very relevant. One potential pathway for selective and
productive N–H bond activation proceeds via a cooperative
ligand–metal mechanism,6 and this may provide a viable strategy
Understanding the fundamental reactivity of metal complexes
featuring a solitary amido group (i.e. where the amido is not a
donor integrated in a ligand scaffold) is of relevance to several
elementary catalytic processes.8 Palladium amido species have
recently been studied extensively to understand C–N bond
formation via reductive elimination9 in the context of e.g.
N-amination of aryl halides10 and aza-Wacker aminations,11 but
facile and general preparative methods to obtain these amido
species are still relatively scarce. Also copper–amido species
have been implied in various functionalization reactions,12 but
despite recent reports on reactive CuI precursors (featuring
NHC-ligands), CuI–amide complexes are rare.13 Furthermore, to
date no Pd– or Cu–amido species have been prepared using a reac-
tive or cooperative ligand approach, to the best of our knowledge.14
Notably, a bifunctional activation mode might enable facile
intra- rather than intermolecular hydroaddition pathways, which
could ultimately enhance catalyst activity and selectivity pro-
nouncedly, even with cheap, earth-abundant transition metals.
We therefore started a program to explore metal–ligand bifunc-
tional reactivity with inter alia first row metals, initially focusing
on tridentate ‘pincer’15,16 PNP ligands17 that display cooperative
behaviour by deprotonation (Scheme 1).18,19 Strikingly, the
coordination chemistry of copper with any ‘pincer’ ligand is still
relatively unexplored.20 To allow for more structural versatility
as well as steric accessibility and to enhance reactivity of the
(first row) transition metal with incoming exogenous substrates
such as amines, we herein report our results on cooperative N–H
activation by Pd and Cu complexes with bidentate PN analogues
of these lutidine-derived PNP ligands. Although extensively
studied in the last decade,21 the potential cooperative character
of these PN ligands22 or related PV-phosphorane structures23 and
their application in specific bond activation processes has hardly
been exploited to date.
aSupramolecular & Homogeneous Catalysis Group, van’t Hoff Institute
for Molecular Sciences, University of Amsterdam, Science Park 904,
1098 XH Amsterdam, The Netherlands. E-mail: j.i.vandervlugt@uva.nl;
Fax: +31 20 525 5604; Tel: +31 20 525 6459
bCrystal and Structural Chemistry, Faculty of Science, University of
Utrecht, Padualaan 8, 3584 CH Utrecht, The Netherlands
†Electronic supplementary information (ESI) available: NMR and MS
spectra for all new compounds. CCDC 861127, 861128 and 861129. For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c2dt31009k
‡Dedicated to Professor David Cole-Hamilton on the occasion of his
retirement and for his outstanding contribution to transition metal
catalysis
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Scheme 2 Preparative route to ligand L1H, Pd(CH3)(Cl)(L1H)-
complex 1 and related amido-species 2.
Scheme 1 (a) General concept of cooperative activation of H–E bonds,
particularly to desirable metal–amides, (b) precedent18 for CuI(PNP)
reactivity and (c) current work with a second generation cooperative
ligand system.
Pd1–N1 (2.2474(16) Å) and Pd1–C16 (2.0679(18) Å) bond
lengths are all within the expected ranges.24 The methyl ligand
is located cis to the phosphine donor (in agreement with
the doublet observed in the 1H NMR spectrum at δ 1.04
(2JPH = 1.6 Hz) and the pyridine is strongly coordinated, as also
confirmed by the IR spectrum, showing bands at 1572 and
1600 cm−1
.
Synthesis and characterization of Pd–amido species 2
Activation of this palladium complex by deprotonation–
dearomatization of the methylene CH2-group using a strong base
generated a red homogeneous solution. The relative instability of
this intermediate compared to starting compound 1 precluded its
full characterization. However, preliminary spectroscopic data
2
(δ(31P) 66 ppm and δ(1H) 3.12 ppm (d, JP–H = 8.8 Hz) for the
–CH spacer) provide support for selective dearomatization of the
ligand backbone, in agreement with reported data for related
PNP-based systems,14,17,24 with likely formation of a solvent-
stabilized Pd(L1)(CH3)-species X (Scheme 2).
Fig. 1 ORTEP plot (50% probability displacement ellipsoids) of
complex 1, Pd(CH3)Cl(L1H). Hydrogen atoms have been omitted for
clarity. Selected bond lengths (Å), angles and torsion angles (°): Pd1–P1
2.2216(5); Pd1–N1 2.2474(16); Pd1–Cl1 2.3906(5); Pd1–C16
2.0679(18); P1–C7 1.834(2); C6–C7 1.497(3); P1–Pd1–N1 82.80(4);
P1–Pd1–Cl1 170.637(19); P1–Pd1–C16 93.22(6); N1–Pd1–C16
173.19(7); P1–C7–C6–N1 26.3(2); Pd1–P1–C7–C6 −38.34(15);
Pd1–N1–C6–C7 1.5(2).
Further investigation of the species formed upon dearomatiza-
tion of the ligand backbone whilst coordinated to Pd showed that
this intermediate could be stabilized by addition of a neutral co-
ligand such as PMe3. In situ addition of trimethylphosphine
during the deprotonation of Pd-complex 1 yielded a dark-red
solution. The 31P NMR spectrum showed two doublets at δ 68.8
and −23.2 for the PtBu2 and PMe3 respectively, both with a
2
coupling constant JP–P of 439 Hz, indicative of mutual trans
disposition. The 1H NMR spectrum nicely showed a doublet
Results and discussion
(2JP–H = 7.6 Hz) at δ 3.37 for the –CH spacer and a doublet-of-
Synthesis of ligand L1H and Pd complex 1, Pd(CH3)(Cl)(L1H)
3
doublets (3JP1–H = 9.6 Hz; JP2–H = 3.6 Hz) at δ 0.56 for the
Ligand L1H, 2-(di-tert-butylphosphino)methyl-6-methyl-pyri-
dine, was prepared, following a modified literature procedure
starting from 2,6-lutidine, in a one-pot two-step reaction and
with an overall yield of 70%. The corresponding 31P NMR spec-
trum showed a singlet at δ 34.9 (C6D6) for L1H. Reaction of
this potentially bidentate PN ligand with PdCl(CH3)(cod) (cod =
1,5-cyclooctadiene) yielded a yellow solid that was fully charac-
terized as Pd(CH3)(Cl)(L1H), complex 1. X-ray crystallography
of single crystals obtained via slow diffusion of hexane into a
concentrated solution of dichloromethane resulted in the molecu-
lar structure depicted in Fig. 1.
Me-ligand at the Pd center. The formation of this species Y as
Pd(CH3)(L1)(PMe3) was also confirmed by FAB-MS spectro-
metry, showing the molecular ion peak at m/z 448.1522.
Addition of one molar equiv. of H2NTf (trifluoromethanesul-
fonamide)25 to either the initial complex X or derivative Y led to
an immediate color change from red to yellow-brown. The
31P NMR spectrum of the resultant brown solid displayed one
1
singlet at δ 75.2, and all expected signals in the H NMR spec-
trum. A doublet (2JP–H = 10.0 Hz) at δ 3.80 is nicely shown in
1
the H NMR spectrum for the –CH2 spacer of the ligand arm
and a singlet for the NH moiety at δ 3.15. Two signals indicative
of formation of the amido-species were distinctly observed
by FAB-MS, at m/z 505.0529 [M − Me] and 372.1089
[M − NHTf]. The IR spectrum displayed two peaks at ν 1600
The palladium atom displays a slightly distorted square planar
geometry, with angles P1–Pd1–N1 and P1–Pd1–Cl1 of 82.80(4)
and 170.637(19)°, respectively. The Pd1–P1 (2.2216(5) Å),
Dalton Trans.
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Fig. 2 ORTEP plot (50% probability displacement ellipsoids) of
complex 2, Pd(CH3)(NHTf)(L1H). Hydrogen atoms have been omitted
for clarity, except for those at C7 and N2. Selected bond lengths (Å),
angles and torsion angles (°): Pd1–P1 2.2232(10); Pd1–N1 2.191(3);
Pd1–N2 2.108(3); Pd1–C16 2.042(4); P1–C7 1.850(4); C6–C7 1.500(6);
N2–S1 1.540(4); P1–Pd1–N1 82.28(9); P1–Pd1–N2 170.03(10);
N1–Pd1–C16 175.92(15); P1–C7–C6–N1 −18.4(5); Pd1–P1–C7–C6
35.7(3); Pd1–N1–C6–C7 −10.9(4).
Fig. 3 Dimeric H-bonded structure of complex 2, with a Pd⋯Pd
[1 − x, 1 − y, 1 − z] distance of 8.4216(6) Å.
and 1564 cm−1, suggestive of rearomatization of the pyridine
moiety.18a The analogous p-toluenesulfonamide (NHTs)
complex 2A could also be prepared in a similar smooth fashion,
as indicated by the spectroscopic and mass spectrometric data
(see the experimental section).
We also have preliminary indications that e.g. 2,3,4,5,6-penta-
fluoroaniline (H2NArF5) can be activated in a similar manner,
judging from NMR spectroscopic data (i.e. δ(31P) 67.4, δ(1H)
3.04 (–NHAr)) as well as consistent MS data for derivatives of the
resulting Pd(CH3)(HNArF5)(L1H) species ([M − CH3]+ peak at
m/z 539.0872). This suggests that the potential substrate scope for
subsequent (catalytic) transformations involving N–H activation
using a bifunctional mechanism may be quite broad.
Single crystals of complex 2, suitable for X-ray crystallo-
graphic analysis, were grown by slow diffusion of pentane into a
concentrated CH2Cl2 solution (Fig. 2). The molecular structure
reveals a slightly distorted square planar geometry around the
palladium atom, with angles P–Pd–N1 and P–Pd–N2 of 82.28(9)
and 170.03(10)°, respectively. There are marginal changes for
complex 2 compared to complex 1 with respect to the Pd1–P1
(2.2232(10) Å) and Pd1–C16 (2.042(4) Å) bond lengths, but the
Pd1–N1 bond length (2.191(3) Å) is significantly smaller.
The Pd1–N2 bond length of 2.108(3) Å is typical for a palla-
dium–sulfonamide bond.26 Substitution of the halide co-ligand
has occurred with retention of configuration around the palla-
dium center, as the amide is coordinated trans to the phosphine
donor. The amide nitrogen is trigonal planar [angle sum
359(4)°]. The aromaticity of the heterocycle is restored (C7) and
the C6–C7 bond length of 1.500(6) Å is in the range for a C–C
single bond. The solid state structure of this complex reveals
intermolecular hydrogen bonding of two sulfonamide units to
generate a dimeric conformation (Fig. 3).
Scheme 3 Preparative route to [Cu(μ-Br)(L1H)]2 3 and CuI–amido
complex 4, obtained via cooperative N–H activation.
which displayed a broad signal at δ 40.1 in the 31P NMR spec-
1
2
trum. Both the H and H NMR spectra displayed a multiplet at
δ 3.80 for the –CHD (methylene) spacer, illustrating selective
reversibility of the deprotonation process, also for CuI.
Analogously to the Pd case, addition of H2NTf to this neutral
copper(I) complex yielded a broad signal at δ 31.9 in the
1
31P NMR spectrum. Also H and 13C NMR spectroscopic data
were in accord with formulation of the resulting species as
complex 4, Cu(NHTf)(L1H). The pyridine ring has undergone
rearomatization, with a doublet at δ 3.45 (JP–H = 5.6 Hz) obser-
vable for the methylene spacer of the backbone. FAB-MS
confirmed formation of Cu-complex 4, since both the molecular
ion peak [M + H] (m/z 462.0780) and the fragment peak
[M − NHTf] (m/z 314.1277) were present. Rearomatization of
the pyridine complex is also suggested by the bands at ν 1595
and 1572 cm−1 in the IR spectrum. The related NHTs-derived
complex 4A was also successfully prepared, as can be deduced
from the spectroscopic data (e.g. δ(31P) 35.3).
Single crystals of 4 were grown by slow evaporation of a con-
centrated CH2Cl2 solution of the yellow Cu–NHTf complex. The
resulting molecular structure as obtained by X-ray crystal struc-
ture determination is depicted in Fig. 4. The copper center is in a
highly distorted trigonal planar geometry (in-between the tra-
ditional Y-shape and the less common T-shape),18a as indicated
by ∠P–Cu–N2 (87.48(5)°) and ∠P–Cu–N2 (151.37(5)°). The
Cu–P and Cu–N distances are in accord with previous Cu(PNP)
complexes17 and related copper(I)–phosphine complexes.28 From
the long Cu–O2 distance of 3.2357(18) Å and the S–O–Cu
angle of only 69.40(7)°, we can exclude κ2-N,O-bonding of the
trifluorosulfonamide fragment.29 The C7 carbon bears two H
atoms and the amido nitrogen only one, showing that activation
of an N–H bond of H2NTf can occur using this Cu(L1H)
complex. In the solid state, complex 4 forms a centrosymmetric
dimer through intermolecular H-bonding interactions of the N–H
and SvO groups, as depicted in Fig. 5, with an intermolecular
Cu⋯Cu distance of 7.9744(5) Å.
Synthesis and characterization of Cu–amido species 4
Starting from complex 3, [Cu(μ-Br)(L1H)]2,27 activation of the
ligand backbone using KOtBu resulted in a characteristic color-
change from light-yellow to deep-orange, concomitant with de-
aromatization of the pyridine ring (Scheme 3).18b,c In situ addition
of DCl to this activated complex yielded a yellow solution,
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The solid state structures of complexes 2 and 4 show
H-bonding interactions between the triflic amide N–H and SvO
fragments, which leads to dimerization. The relative open and
modular coordination sphere of these hybrid bidentate PN-
ligands, especially compared to their rigid tridentate PNP ana-
logues, brings about new avenues for stoichiometric and catalytic
studies involving e.g. intra- and intermolecular amination reac-
tions, including but not limited to the hydroamidation of
alkynes.31
Experimental section
General
Solvents were either distilled over suitable drying agents or
dried using an MBraun SPS (Solvent Purification System).
All experiments were carried out under an inert-gas atmosphere
using standard Schlenk techniques. The chemicals used were
commercially available and used without further purification,
unless described otherwise. The 1H, 1H{31P}, 31P{1H} and
13C{1H} NMR spectra were recorded at 400, 162 and 100 MHz,
respectively, on a Bruker AV400 spectrometer. High resolution
mass spectra were recorded on a JEOL JMS SX/SX102A four
sector mass spectrometer; for FAB-MS 3-nitrobenzyl alcohol
was used as a matrix. IR spectra (ATR) were recorded with a
Bruker Alpha-p FT-IR spectrometer. Pd(CH3)Cl(1,5-cod) was
synthesized according to a literature procedure.32
Fig. 4 ORTEP plot (50% probability displacement ellipsoids) of
complex 4, Cu(NHTf)(L1H). All hydrogen atoms, except for those
located on C7 and N2, have been omitted for clarity. Selected bond
lengths (Å), angles and torsion angles (°): Cu1–P1 2.1980(5); Cu1–N1
2.1694(14); Cu1–N2 1.9124(16); P1–C7 1.8467(17); N2–S1 1.5416(15);
P1–Cu1–N1 87.48(5); P1–Cu1–N2 151.37(5); N1–Cu1–N2 121.13(6);
Cu1–N2–S1 123.20(10); P1–C7–C6–N1 −36.6(2); Cu1–P1–C7–C6
32.52(13); Cu1–N1–C6–C7 19.25(19).
Ligand L1H, 2-((di-tert-butylphosphino)methyl)-6-methylpyri-
dine. This is an improved procedure, modified from two litera-
ture procedures.33 Freshly distilled 2,6-lutidine (3.0 mL,
25.8 mmol) was dissolved in diethyl ether (35 mL) and then
cooled to 0 °C, whereafter n-butyllithium (2.5 M solution in
THF) (10.4 mL, 26.0 mmol) was added dropwise. The yellow-
orange solution was stirred for 1 h at 0 °C and then cooled to
−78 °C. Subsequently, di-tert-butylchlorophosphine (5.0 mL,
26.0 mmol) was added and the mixture stirred for an additional
hour at −78 °C. After this, the yellow reaction mixture was
allowed to warm up to room temperature and stirred for 18 h to
give an orange suspension. The suspension was quenched
with degassed water (40 mL) and extracted with diethyl ether
(3 × 30 mL). The ether fractions were combined and dried over
Na2SO4. Evaporation of the solvent gave a yellow-white oil. The
remaining di-tert-butylchlorophosphine was removed via flash
chromatography over basic alumina (10 : 1 hexane–ether), yield-
ing the product as a white solid (4.59 g, 70.2%). 1H NMR
(400 MHz, C6D6, ppm): δ 7.37 (d, JH = 8 Hz, 1H, pyH), 7.20
(t, JH = 7.6 Hz, 1H, pyH), 6.68 (d, JH = 7.2 Hz, 1H, pyH), 3.21
Fig. 5 Dimeric H-bonded structure of complex 4, with a Cu⋯Cu
[1 − x, 1 − y, 1 − z] distance of 7.9744(5) Å.
Conclusions
In summary, we have shown the improved synthesis of the (elec-
tron-rich) dialkylphosphinopyridine framework L1H and its
coordination as a bidentate PN-ligand to Pd(CH3)(Cl)(cod),
including a crystal structure for compound Pd(CH3)(Cl)(L1H).
Using a dearomatization–reprotonation strategy, utilizing the
reactive backbone of L1H, selective activation of N–H bonds
resulted in the formation of PdII or CuI metal–amido species.
Although the exact mechanism of the N–H bond activation is
still under investigation, the combined data as well as literature
precedent on related tridentate analogues14a,f,17 suggest a metal–
ligand bifunctional pathway. It remains to be seen whether there
are significant limitations in the N-based substrate scope in com-
bination with first-row metals, given the working hypothesis of
cooperative N–H bond rupture (on tri- as well as bidentate reac-
tive ligand scaffolds), which implies coordination of the sub-
strate to the metal center, resulting in efficient pre-activation of
the N–H bond and subsequent proton-transfer.30
(d, JPH = 2.4 Hz, 2H, CH2), 2.54 (s, 3H, CH3), 1.23 (d, JPH
=
t
10.8 Hz, 18H, Bu-H). 31P NMR (162 MHz, C6D6, ppm):
δ 34.9 (s). 13C NMR (100 MHz, C6D6, ppm): δ 161.7 (d, JPC
14.4 Hz, pyC), 157.2 (s, pyC), 135.6 (s, pyCH), 120.6 (d, JPC
=
=
9.6 Hz, pyCH), 119.3 (s, pyCH), 32.0 (d, JPC = 25.3 Hz, CH2),
t
31.5 (d, JPC = 23.8 Hz, Bu-C), 29.5 (d, JPC = 13.7 Hz,
tBu-CH3), 24.3 (s, CH3). HR-MS (FAB) (C15H26NP):
m/z calcd, 252.1881; found, 252.1884. IR (ATR, cm−1): 1592
(m), 1577 (m).
Complex 1, Pd(CH3)Cl(L1H). Adaptation of a literature pro-
cedure.34 L1H (180.5 mg, 0.72 mmol) and Pd(CH3)Cl(1,5-cod)
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(190.4 mg, 0.72 mmol) were dissolved in dichloromethane
(5 mL) and the mixture was stirred at room temperature for 18 h.
Then, the light-yellow solution was concentrated to approxi-
mately 0.5 mL and diethyl ether (10 mL) was added under vigor-
ous stirring. The precipitate was collected by cannula-filtration
and washed with diethyl ether (3 × 5 mL). The product was
ppm): δ 75.2 (s). 13C NMR (100 MHz, (CD3)2CO, ppm): δ
161.2 (s, 1C, pyC), 159.1 (s, 1C, pyC), 138.1 (s, 1C, pyCH),
123.4 (s, 1C, pyCH), 120.5 (d, JPC = 10.4 Hz, 1C, pyCH),
t
35.1 (d, JPC = 23.9 Hz, 2C, Bu-C), 34.5 (d, JPC = 29.5 Hz, 1C,
t
CH2), 28.6 (d, JPC = 5.9 Hz, 6C, Bu-CH3), 26.0 (s, 1C, CH3),
−10.7 (s, 1C, Pd-CH3). HR-MS (FAB) (C17H30F3N2O2PPdS):
m/z calcd, 520.0753, 505.0524 (M − NHTf), 372.1072
(M − Cl); found, 505.0529 (M − NHTf), 372.1089 (M − Cl).
IR (ATR, cm−1): 1600 (m), 1564 (m).
1
obtained as an off-white powder (277.8 mg, 94.8%). H NMR
(400 MHz, CDCl3, ppm): δ 7.56 (t, JH = 8 Hz, 1H, pyH),
7.17 (d, JH = 8 Hz, 1H, pyH), 7.09 (d, JH = 7.6 Hz, 1H, pyH),
3.51 (d, JPH = 10 Hz, 2H, CH2), 3.16 (s, 3H, CH3), 1.33 (d,
PH = 14 Hz, 18H, tBu-H), 1.04 (d, JPdH = 1.6 Hz, 3H, Pd-CH3).
Complex 2A, Pd(CH3)(NHTs)(L1H). This product is syn-
thesized in the manner as complex 2 from complex 1 (69.4 mg,
0.17 mmol), KOtBu (1 M solution in THF) (0.17 mL,
0.17 mmol) and tosyl amine (29.2 mg, 0.17 mmol), and is
J
31P NMR (162 MHz, CDCl3, ppm): δ 72.8 (s). 13C NMR
(100 MHz, CDCl3, ppm): δ 162.5 (s, pyC), 158.2 (d, JPC
2.4 Hz, pyC), 137.8 (s, pyCH), 123.9 (s, pyCH), 119.9 (d, JPC
=
=
=
1
t
obtained as a sand-brown powder (78.3 mg, 84.8%). H NMR
7.5 Hz, pyCH), 35.6 (d, JPC = 16.6 Hz, Bu-C), 35.2 (d, JPC
t
(400 MHz, (CD3)2CO, ppm): δ 7.72 (t, JH = 7.6 Hz, 1H, pyH),
7.62 (d, JH = 8 Hz, 2H, TsH), 7.41 (d, JH = 9.2 Hz, 1H, pyH),
7.17 (d, JH = 7.2 Hz, 1H, pyH), 7.10 (d, JH = 8 Hz, 2H, TsH),
3.69 (d, JPH = 9.6 Hz, 2H, CH2), 3.11 (s, 3H, CH3), 2.31 (s, 3H,
20.2 Hz, CH2), 29.4 (d, JPC = 4 Hz, Bu-CH3), 27.5 (s, CH3),
−8.6 (s, Pd-CH3). HR-MS (FAB) (C16H29ClNPPd): m/z calcd,
407.0761, 372.1079 (M − Cl); found, 372.1076 (M − Cl).
IR (ATR, cm−1): 1600 (m), 1572 (m).
t
TsCH3), 2.23 (s, 1H, NH), 1.21 (d, JPH = 13.2 Hz, 18H, Bu-H),
0.36 (d, JPH = 2.4 Hz, 3H, Pd-CH3). 31P NMR (162 MHz,
(CD3)2CO, ppm): δ 73.5 (s). HR-MS (FAB) (C23H37N2-
O2PPdS): m/z calcd, 542.1348, 527.1113 (M − Me), 372.1072
Complex Y, Pd(CH3)(L1)(PMe3). To a suspension of complex
1 (47.3 mg, 0.116 mmol) in THF was added KOtBu (1 M solu-
tion in THF) (0.12 mL, 0.116 mmol) at room temperature and
the mixture, which became red immediately, was stirred for
5 min. Then, trimethylphosphine (1 M solution in toluene)
(0.12 mL, 0.116 mmol) was added and the color of the solution
changed to dark-red. The reaction was left stirring for 2 h before
the solvent was removed in vacuo. The product was obtained as
(M
− NHTs); found, 527.1121 (M − Me), 372.1075
(M − NHTs). IR (ATR, cm−1): 1601 (m), 1576 (m).
Complex 2B, Pd(CH3)(NHArF5)(L1H). To a suspension of
complex 1 (44.4 mg, 0.109 mmol) in THF was added KOtBu
(1 M solution in THF) (0.11 mL, 0.109 mmol) at room tempera-
ture and the mixture, which became red immediately, was stirred
for 5 min. Then, 2,3,4,5,6-pentafluoroaniline (H2NArF5) (20 mg,
0.109 mmol) was added and the reaction was left stirring for
0.5 h before the solvent was removed in vacuo. The product was
obtained as an orange powder (45.2 mg, 74.8 %). 1H NMR
(400 MHz, C6D6, ppm): δ 6.74 (t, JH = 7.6 Hz, 1H, pyH),
6.32 (d, JH = 7.6 Hz, 1H, pyH), 6.28 (d, JH = 7.6 Hz, 1H, pyH),
3.04 (br s, 1H, NH), 2.84 (s, 3H, CH3), 2.77 (d, JPH = 9.6 Hz,
1
a red powder (44.8 mg, 86.2 %). H NMR (400 MHz, C6D6,
ppm): δ 6.60 (ddd, JH = 8.8 Hz, JH = 6.4 Hz, JPH = 2.4 Hz, 1H,
pyH), 6.26 (d, JH = 8.8 Hz, 1H, pyH), 5.56 (d, JH = 6.4 Hz, 1H,
pyH), 3.37 (d, JH = 7.6 Hz, 1H, CH), 2.09 (s, 3H, CH3), 1.42 (d,
t
JPH = 13.2 Hz, 18H, Bu-H), 0.77 (d, JPH = 8.0 Hz, 9H,
P(CH3)3), 0.56 (dd, JP1H = 3.6 Hz, JP2H = 9.6, 3H, Pd-CH3).
2
31P NMR (162 MHz, C6D6, ppm): δ 68.8 (d, JPP = 439 Hz,
2
P1), −23.2 (d, JPP = 439 Hz, P2). 13C NMR (100 MHz, C6D6,
ppm): δ 172.8 (d, JPC = 23.2 Hz, 1C, pyC), 154.2 (s, 1C, pyC),
132.9 (s, 1C, pyCH), 111.9 (d, JPC = 19.3 Hz, 1C, pyCH), 102.4
2H, CH2), 0.97 (d, JPH = 3.2 Hz, 3H, Pd-CH3), 0.89 (d, JPH
=
t
13.2 Hz, 18H, Bu-H). 31P NMR (162 MHz, C6D6, ppm): δ
67.4 (s). 13C NMR (100 MHz, C6D6, ppm): δ 161.8 (s, 1C,
pyC), 158.9 (s, 1C, pyC), 140.4 (s, 2C, aniline-CF), 139.6 (s,
2C, aniline-CF), 138.0 (s, 1C, aniline-CF), 137.2 (s, 1C, aniline-
t
(s, 1C, pyCH), 36.7 (d, JPC = 22.7 Hz, 2C, Bu-C), 32.3 (s, 1C,
t
CH), 29.4 (d, JPC = 6.7 Hz, 2C, Bu-CH3), 27.5 (s, 1C, CH3),
13.6 (d, JPC = 26.8 Hz, 3C, P(CH3)3), −13.3 (d, JPC = 12.1 Hz,
1C, Pd-CH3). HR-MS (FAB) (C16H29ClNPPd): m/z calcd,
448.1522; found, 448.1522.
C), 136.9 (s, 1C, pyCH), 123.2 (s, 1C, pyCH), 119.5 (d, JPC
=
7.4 Hz, 1C, pyCH), 34.2 (d, JPC = 18.4 Hz, 1C, CH2), 33.9
t
(d, JPC = 15.7 Hz, 2C, Bu-C), 28.7 (d, JPC = 4.4 Hz, 6C,
tBu-CH3), 24.9 (s, 1C, CH3), −9.1 (s, 1C, Pd-CH3). 19F NMR
(282 MHz, C6D6, ppm): δ −166.8 (m), −169.7 (m), −190.2 (m).
HR-MS (FAB) (C22H30F5N2PPd): m/z calcd, 554.1102,
539.0875 (M − Me), 372.1072 (M − H2NArF5); found,
Complex 2, Pd(CH3)(NHTf)(L1H). To
a suspension of
complex 1 (63.8 mg, 0.16 mmol) in THF (15 mL) was added
KOtBu (1 M solution in THF) (0.16 mL, 0.16 mmol) at room
temperature and the mixture, which became dark red immedi-
ately, was stirred for 5 min. Then, triflic amine (23.3 mg,
0.16 mmol) was added and the color of the mixture changed to
yellowish brown. The reaction was left stirring for 2 h before the
solvent was removed in vacuo. After addition of toluene
(10 mL), the solution was filtered and evaporated. The product
was obtained as a sand-brown powder (30.0 mg, 36.8%).
1H NMR (400 MHz, (CD3)2CO, ppm): δ 7.75 (t, JH = 7.6 Hz,
1H, pyH), 7.44 (d, JH = 7.6 Hz, 1H, pyH), 7.23 (d, JH = 7.6 Hz,
1H, pyH), 3.80 (d, JPH = 10.0 Hz, 2H, CH2), 2.99 (s, 3H, CH3),
539.0872 (M
− Me), 372.1403 (M −
H2NArF5). IR
(ATR, cm−1): 1601 (m), 1573 (m).
Complex 3, [CuBr(L1H)]2. This product is prepared by using
a literature procedure.27 A solution of L1H (458.5 mg,
1.82 mmol) in Et2O (10 mL) was added to a suspension of
CuBrSMe2 (374.9 mg, 1.82 mmol) in Et2O (20 mL) by a
cannula at room temperature. The light yellow solution was
stirred for 16 h before all volatiles were removed in vacuo and
the product was obtained as a light-yellow powder in quantitative
yield (716.7 mg, 99.5%). 1H NMR (400 MHz, (CD3)2CO, ppm):
t
2.23 (s, 1H, NH), 1.34 (d, JPH = 13.6 Hz, 18H, Bu-H), 0.68 (d,
JPH = 1.6 Hz, 3H, Pd-CH3). 31P NMR (162 MHz, (CD3)2CO,
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Dalton Trans.

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δ 7.70 (t, JH = 7.6 Hz, 1H, pyH), 7.36 (d, JH = 7.2 Hz, 1H,
pyH), 7.20 (d, JH = 6.8 Hz, 1H, pyH), 3.39 (d, JPH = 7.6 Hz,
2H, CH2), 2.98 (s, 3H, CH3), 1.31 (d, JPH = 12.8 Hz, 18H,
tBu-H). 31P NMR (162 MHz, (CD3)2CO, ppm): δ 26.6 (br s).
13C NMR (100 MHz, (CD3)2CO, ppm): δ 159.9 (d, JPC = 17.1 Hz,
atoms were refined with anisotropic displacement parameters.
Hydrogen atoms were introduced in calculated positions
(complex 1) or located in difference Fourier maps (complexes 2
and 4). C–H hydrogen atoms were refined with a riding model,
N–H hydrogen atoms were refined freely with isotropic displace-
ment parameters. Geometry calculations and checking for higher
symmetry was performed with the PLATON program.38
pyC), 138.7 (s, pyCH), 134.5 (s, pyC), 122.8 (s, pyCH),
t
122.5 (s, pyCH), 33.5 (d, JPC = 7.8 Hz, Bu-C), 31.1 (d, JPC
=
t
11 Hz, CH2), 28.2 (d, JCH = 10.8 Hz, Bu-CH3), 26.3 (s, CH3).
HR-MS (FAB) (C30H52Br2Cu2N2P2): m/z calcd, 790.0530;
found, 790.0530. IR (ATR, cm−1): 1593 (m), 1572 (m).
Details for complex 1. C16H29ClNPPd, Fw = 408.22, yellow
block, 0.26 × 0.18 × 0.08 mm3, monoclinic, P21/n (no. 14), a =
10.0545(3), b = 15.8268(5), c = 11.3903(4) Å, β = 91.6010
(10)°, V = 1811.84(10) Å3, Z = 4, Dx = 1.497 g cm−3, μ =
1.25 mm−1. 49 119 Reflections were measured up to (sin θ/λ)max
= 0.65 Å−1. 4161 Reflections were unique (Rint = 0.022), of
which 3706 were observed [I > 2σ(I)]. 189 Parameters were
refined with no restraints. Minor disorder between chlorine and
methyl has been ignored. R1/wR2 [I > 2σ(I)]: 0.0206/0.0475.
R1/wR2 [all refl.]: 0.0263/0.0508. S = 1.108. Residual electron
density between −0.35 and 0.48 e Å−3. CCDC 861127.
Complex 4, Cu(NHTf)(L1H). To a suspension of complex 3
(32.4 mg, 0.04 mmol) in diethyl ether (30 mL) was added
KOtBu (1 M solution in THF) (0.08 mL, 0.08 mmol) at room
temperature and the mixture, which became orange immediately,
was stirred for 5 min. Then, triflic amine (12.2 mg, 0.08 mmol)
was added and the color of the mixture changed to yellow-
brown. The reaction was left stirring for 2 h before the solvent
was removed in vacuo to leave the product as a pale yellow solid
(26.4 mg, 70.0%). 1H NMR (400 MHz, (CD3)2CO, ppm): δ 7.75
(t, JH = 7.6 Hz, 1H, pyH), 7.42 (d, JH = 7.6 Hz, 1H, pyH),
7.42 (d, JH = 8 Hz, 1H, pyH), 3.45 (d, JPH = 8 Hz, 2H, CH2),
2.77 (s, 3H, CH3), 2.46 (s, 1H, NH), 1.29 (d, JPH = 13.6 Hz,
Details for complex 2. C17H30F3N2O2PPdS, Fw = 520.86,
3
ˉ
brown plate, 0.50 × 0.40 × 0.15 mm , triclinic, P1 (no. 2), a =
9.8419(3), b = 10.8652(3), c = 11.6779(4) Å, α = 109.9870(15),
β = 99.6665(15), γ = 101.8868(15)°, V = 1109.16(6) Å3, Z = 2,
Dx = 1.560 g cm−3, μ = 1.04 mm−1. The crystal was cracked
into two fragments related by a rotation of 7.1° about an arbitrary
axis. This was taken into account during the integration, which
resulted in a file in HKLF5 format.39 36 399 Reflections were
measured up to (sin θ/λ)max = 0.65 Å−1. 5033 Reflections were
unique (Rint = 0.050), of which 4207 were observed [I > 2σ(I)].
257 Parameters were refined with no restraints. R1/wR2 [I >
2σ(I)]: 0.0432/0.1061. R1/wR2 [all refl.]: 0.0579/0.1148. S =
t
18H, Bu-H). 31P NMR (162 MHz, (CD3)2CO, ppm): δ 31.9 (s).
13C NMR (100 MHz, (CD3)2CO, ppm): δ 159.0 (d, JPC
=
2.1 Hz, 1C, pyC), 158.1 (d, JPC = 2.3 Hz, 1C, pyC), 138.1
(s, 1C, pyCH), 122.0 (d, JPC = 3.8 Hz, 1C, pyCH), 121.8 (d,
JPC = 2.5 Hz, 1C, pyCH), 120.0 (s, 1C, CF3), 32.1 (d, JPC
=
t
11.1 Hz, 2C, Bu-C), 29.7 (d, JPC = 16.2 Hz, 1C, CH2), 28.5 (s,
t
6C, Bu-CH3), 24.5 (s, 1C, CH3). HR-MS (FAB) (C16H27CuF3-
N2O2PS): m/z calcd, 462.0779, 314.1099 (M − NHTf); found,
462.0780, 314.1277 (M − NHTf). IR (ATR, cm−1): 1595 (m),
1572 (m).
1.067. Residual electron density between −1.03 and 1.74 e Å−3
CCDC 861128.
.
Complex 4A, Cu(NHTs)(L1H). This product was synthesized
in the same manner as complex 4 from complex 3 (96.6 mg,
0.12 mmol), KOtBu (1 M solution in THF) (0.24 mL,
0.24 mmol) and tosyl amine (41.8 mg, 0.24 mmol), and was
Details for complex 4. C16H27CuF3N2O2PS, Fw = 462.97,
3
ˉ
green plate, 0.28 × 0.16 × 0.06 mm , triclinic, P1 (no. 2),
a = 10.6306(5), b = 10.8516(5), c = 11.2839(5) Å, α = 110.4196(13),
β = 93.6403(14), γ = 117.9401(12)°, V = 1036.42(8) Å3,
Z = 2, Dx = 1.484 g cm−3, μ = 1.27 mm−1. The crystal was
cracked into two fragments related by a rotation of 6.1° about an
arbitrary axis. This was taken into account during the integration,
which resulted in a file in HKLF5 format.39 38 810 Reflections
were measured up to (sin θ/λ)max = 0.65 Å−1. 4715 Reflections
were unique (Rint = 0.035), of which 3863 were observed
[I > 2σ(I)]. 247 Parameters were refined with no restraints.
R1/wR2 [I > 2σ(I)]: 0.0269/0.0606. R1/wR2 [all refl.]: 0.0417/
0.0650. S = 1.016. Residual electron density between −0.24
and 0.45 e Å−3. CCDC 861129.
1
obtained as a pale brown powder (63.5 mg, 53.6%). H NMR
(400 MHz, (CD3)2CO, ppm): δ 7.82 (d, JH = 8 Hz, 1H, TsH),
7.64 (t, JH = 7.6 Hz, 1H, pyH), 7.32 (d, JH = 7.6 Hz, 1H, pyH),
7.18 (d, JH = 8 Hz, 1H, TsH), 7.12 (d, JH = 8 Hz, 1H, pyH),
3.26 (d, JPH = 5.6 Hz, 2H, CH2), 2.56 (s, 3H, CH3), 2.45 (s, 1H,
t
NH), 2.34 (s, 3H, TsCH3), 1.21 (d, JPH = 12.4 Hz, 18H, Bu-H).
31P NMR (162 MHz, (CD3)2CO, ppm): δ 35.3 (br s). 13C NMR
(100 MHz, (CD3)2CO, ppm): δ 159.3 (s, pyC), 157.7 (s, pyC),
138.5 (s, TsC), 137.3 (s, pyCH), 128.0 (s, TsCH), 125.6
(s, TsCH), 121.4 (d, JPC = 5.2 Hz, pyCH), 121.0 (s, pyCH),
31.9 (d, JPC = 2.6 Hz, tBu-C), 30.1 (d, JPC = 5.2 Hz, CH2), 28.7
t
(JPC = 9.4 Hz, Bu-CH3), 24.0 (s, CH3), 20.1 (s, TsCH3).
IR (ATR, cm−1): 1590 (m), 1576 (m).
Acknowledgements
X-ray crystallography. X-ray intensities were measured on a
Bruker Kappa ApexII diffractometer with a sealed tube and a
Triumph monochromator (λ = 0.71073 Å) at a temperature of
150(2) K. Intensity data were integrated with the Saint soft-
ware.35 Absorption correction and scaling was performed with
SADABS or TWINABS.36 The structures were solved with
direct methods using the program SHELXS-9737 and refined
with SHELXL-9737 against F2 of all reflections. Non-hydrogen
This work has been financially supported by the NWO-ACTS
consortium (Advanced Chemical Technologies for Sustain-
ability) via research grant ASPECT 053.62.029, by a research
grant from the National Research School Combination Catalysis
(NRSCC), and by a European Research Council (ERC) Starting
Grant (EuReCat, Grant Agreement 279097; to J.I.v.d.V.). J.I.v.d.
V. also acknowledges the Netherlands Organisation for Scientific
Research – Chemical Sciences for an early-career VENI
Dalton Trans.
This journal is © The Royal Society of Chemistry 2012

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