Diaryltriazenido Palladium(II) complexes derived from 1-(2-bromo-4-ethoxycarbonylphenyl)-3-phenyltriazenes

Article abstract of DOI:10.1016/j.jorganchem.2019.120875

1-(2-Bromo-4-ethoxycarbonylphenyl)-3-phenyltriazene (1) can easily be deprotonated yielding the corresponding triazenides of lithium, silver, or triethylammonium. The equimolar metathesis reaction of [(Ph₃P)₂PdCl₂] with th

Full text of DOI:10.1016/j.jorganchem.2019.120875

Accepted Manuscript
Diaryltriazenido Palladium(II) complexes derived from 1-(2-bromo-4-
ethoxycarbonylphenyl)-3-phenyltriazenes
Silvio Preusser, Paul R.W. Schönherr, Helmar Görls, Wolfgang Imhof, Sven Krieck,
Matthias Westerhausen
PII:
S0022-328X(19)30315-8
DOI:
https://doi.org/10.1016/j.jorganchem.2019.120875
Article Number: 120875
Reference:
JOM 120875
To appear in: Journal of Organometallic Chemistry
Received Date: 26 March 2019
Revised Date: 18 July 2019
Accepted Date: 23 July 2019
Please cite this article as: S. Preusser, P.R.W. Schönherr, H. Görls, W. Imhof, S. Krieck,
M. Westerhausen, Diaryltriazenido Palladium(II) complexes derived from 1-(2-bromo-4-
ethoxycarbonylphenyl)-3-phenyltriazenes, Journal of Organometallic Chemistry (2019), doi: https://
doi.org/10.1016/j.jorganchem.2019.120875.
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ACCEPTED MANUSCRIPT
Diaryltriazenido Palladium(II) Complexes Derived from 1-(2-Bromo-4-
ethoxycarbonylphenyl)-3-phenyltriazenes
Silvio Preusser,a,c Paul R. W. Schönherr,a Helmar Görls,a Wolfgang Imhof,b Sven Krieck,*,a and
Matthias Westerhausen*,a
a S. Preusser, Dr. S. Krieck, P. Schönherr, Dr. H. Görls, Prof. Dr. M. Westerhausen
Institute of Inorganic and Analytical Chemistry, Friedrich Schiller University
Humboldtstraße 8, 07743 Jena (Germany)
http://www.lsac1.uni-jena.de; e-mail: m.we@uni-jena.de
b Prof. Dr. W. Imhof
Institute for Integrated Natural Sciences, Department of Chemistry
University Koblenz-Landau
Universitätsstraße 1, D-56070 Koblenz, Germany
c Present address: S. Preusser
Laborchemie Apolda GmbH
Utenbacherstraße 72-74, D-99510 Apolda, Germany
Abstract. 1-(2-Bromo-4-ethoxycarbonylphenyl)-3-phenyltriazene (1) can easily be deprotonated
yielding the corresponding triazenides of lithium, silver, or triethylammonium. The equimolar
metathesis reaction of [(Ph3P)2PdCl2] with these triazenides leads to the formation of [(Ph3P)2Pd(Ph-
N3-C6H3-2-Br-4-COOEt)Cl] (3). The addition of another equivalent yields mixtures of [(Ph3P)2Pd(Ph-N3-
C6H3-2-Br-4-COOEt)Cl] (3) and [(Ph3P)2Pd(Ph-N3-C6H3-2-Br-4-COOEt)2] (4). The reaction of 1-(2-bromo-
4-ethoxycarbonylphenyl)-3-methyl-3-phenyltriazene (2) with one quivalent of [Pd(PPh3)2] leads to an
oxidative addition of the C-Br-bond and the formation of [(Ph3P)2Pd{C6H3-2-(N=N-N(Me)Ph)-5-
COOEt}Br] (5). The palladium atoms are in square planar environments.
Keywords: Palladium(II), Triazenides, Metathesis reactions, Oxidative addition, X-ray
structures
Introduction
1,3-Diaryltriazenides of palladium(II) represent a scarce substance class despite the long tradition.
Already in 1971, the reaction of Pd(PPh3)4 with 1,3-di(para-tolyl)triazene yielded red [(Ph3P)2Pd(pTol-
N3-pTol)2] with monodentate triazenido ligands.1 First hints toward bridging triazenido ligands were
reported for [Cl(Me2PhP)Pd(Ph-N3-Ph)]2 shortly thereafter, prepared via a deprotonation of 1,3-
diphenyltriazene with a palladium-bound acetate.2 The first crystal structure determination of such a
complex revealed the monodentate binding mode of the triazenido ligand in square planar
[Cl(Ph3P)2Pd(pTol-N3-pTol)] (Pd-N 203.3(4) pm) with slight delocalization of the negative charge (N1-
N2 133.6(8), N2=N3 128.6(7) pm).3 These complexes show dynamic behavior with the Pd atoms
binding at N1 and N3 showing coalescence in NMR solution studies.

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Based on these initial investigations, efforts to elucidate chemical and physical properties of
triazenido-palladium complexes were intensified. Monodentate,4 bidentate5 and bridging
coordination modes5-7 were verified by X-ray crystallographic studies at single crystals as depicted in
Scheme 1. Electroneutral triazenes represent suitable Lewis bases for palladium(II) ions.8,9 These
triazenido-palladium(II) moieties are stable toward moisture (hydrolysis) and air (oxidation).
Monodentate triazenide ligands can adopt syn-E, syn-Z, anti-E or anti-Z configuration as also shown
in Scheme 1. In addition, palladium(II) complexes of the type [(Ph3P)2Pd(R-N3-R')X] (X = Cl, Br, R-N3-R')
can show cis- or favored trans-positioned phosphane bases.10 Despite the fact that these triazenide
ligands show comparable coordination behaviour as isoelectronic formamidinates and also
carboxylates, the triazenide chemistry of palladium remained strongly underdeveloped.
Scheme 1: Monodentate (left), bidentate (middle) and bridging (right) binding modes of triazenido ligands in
their palladium(II) complexes (top row) and configuration of the triazenide ligands (R, R' = aryl).
Based on this rudimentary knowledge, there are almost no applications known for these palladium(II)
triazenide complexes. During palladium-mediated conversion of 1,3-diaryl-3-methyltriazene into
benzotriazoles,11-13 such palladium complexes were discussed as intermediates in the catalytic cycle.
These studies attracted our interest and we intended to elucidate the influence of ester and bromo
substituents on the synthesis and structures of palladium-based triazenide complexes. In addition,
the formation of carboxylic amides from triazenes in the presence of carbon monoxide succeeded via
palladium(II) catalysis with yields between 70 and 93 %.14,15 Here the proposed mechanism contains
intermediately formed triazenes bound to palladium(II) followed by insertion of the Pd(II) fragment
into the N-N bond.
In this study, we investigated palladium complexes, derived from 1-(2-bromo-4-
ethoxycarbonylphenyl)-3-phenyltriazene (1)11 and 1-(2-bromo-4-ethoxycarbonylphenyl)-3-methyl-3-
phenyltriazene (2)12,13 in order to compare the products of oxidative addition of the C-Br bond on Pd
with the triazenide complexes.
Results and discussion
For a metathetical approach, 1-(2-bromo-4-ethoxycarbonylphenyl)-3-phenyltriazene (1) was
deprotonated with nBuLi or triethylamine and the triazenides of lithium, silver(I) or
triethylammonium were reacted with [(Ph3P)2PdCl2] in tetrahydrofuran according to Scheme 2. Silver
triazenide was prepared according to literature protocols from AgNO3, triethylamine and triazene.7,16
Potassium triazenides also represent suitable triazenide transfer reagents.

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Scheme 2: Synthesis of the 1-(2-bromo-4-ethoxycarbonylphenyl)-3-phenyltriazenide complexes of palladium(II)
via metathetical approaches (R' = C6H3-2-Br-4-COOEt).
Depending on the stoichiometric ratio, either the monotriazenide palladium(II) complex 3 or a
mixture of 3 and 4 were obtained. A quantitative conversion to the bis(triazenido) palladium(II)
congener 4 did not succeed via this route. The results of the metathesis reaction in dependency of E
and the stoichiometric ratio of 1 to [(Ph3P)2PdCl2] are summarized in Table 1. The route via the
reaction of silver triazenide with equimolar amounts of [(Ph3P)2PdCl2] gave the best yield (73 % of
isolated complex 3) and therefore is the preferred procedure. With the metathetical approach via
lithium triazenide, yields of only 52 % were achieved. The metathetical approach via the
triethylammonium intermediate is highly disadvantageous because unknown side products were
detected in the NMR spectra and isolation of the pure complex was very challenging leading to a low
yield of only 18 %. Mixtures of complexes 3 and 4 (obtained by metathetical approaches of
[(Ph3P)2PdCl2] with two equivalents of triazenide) could not be separated quantitatively due to very
similar solubility properties in common organic solvents like diethyl ether, alkanes, and aromatic
hydrocarbons.
Table 1: Product composition in % for the metathetical approach according to Scheme 2.

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E
Li
Amount of 1
1 equiv.
2 equiv.
1 equiv.
2 equiv.
1 equiv.
Product 3
100
Product 4
Yield (%)
-
48
-
52
-
Li
52
Ag
100
73
-
Ag
78
22
-
Et3NH
100
18
For the reaction of triazenes with palladium(0) species diverse reactivity patterns are known.
Oxidative addition of the N-H bond leads to the formation of hydridopalladium(II) triazenides
which can dismutate to palladium(II) bis(triazenides).1 The palladium-mediated oxidative
addition of the N-N bond of a triazene is discussed as an intermediate step in the
cabonylative synthesis of carboxylic acid amides from triazenes.14 Activation of aromatic C-H
groups can also be achieved with palladium compounds.4,17-19 The oxidative addition of the C-
Br bond yields arylpalladium(II) bromides and represents a well-known step in cross-coupling
reactions. In all these examples, Lewis bases like e.g. phosphanes saturate the coordination
spheres of the palladium atoms. In order to prevent the favored oxidative N-H addition we
blocked this functionality by a methyl group and used 1-(2-bromo-4-ethoxycarbonylphenyl)-
3-methyl-3-phenyltriazene (2) for our experiments.
The reduction of [(Ph3P)2Pd(OAc)2] with nBuLi or preferably with hydrazine hydrate in THF led
to intermediate formation of [Pd(PPh3)2] which subsequently reacted with one equivalent of
as depicted in Scheme 3, yielding [(Ph3P)2Pd{C6H3-2-(N=N-N(Me)Ph)-5-COOEt}Br] ( ). The use
2
5
of butyllithium as a reductant also gave minor amounts of unknown side products whereas
hydrazine hydrate reduced palladium(II) smoothly to palladium(0). However, an excess of
N2H4·H2O was disadvantageous because the released acetic acid readily formed crystalline
hydrazinium acetate (the molecular structure is shown in the ESI), hampering purification
procedures. Therefore, an electron-precise amount of half an equivalent of N2H4·H2O was
employed as shown in Scheme 3. The substrate [(Ph3P)2PdCl2] proved to be disadvantageous
because the reduction proceeded significantly slower and slightly sluggish and under these
conditions no complete reduction was achieved.
[(Ph3P)2Pd(OAc)2]
- 0.5 N2
- 2 HOAc
+ 0.5 N2H4
N
N
Me
N
N
Me
N
N
+ [Pd(PPh3)2]
THF, r.t.
PPh3
Pd Br
PPh3
Br
EtO
EtO
O
O
5
2
Scheme 3: Synthesis of the 1-(2-bromo-4-ethoxycarbonylphenyl)-3-methyl-3-phenyltriazene complex
of palladium(II) via an oxidative addition of the C-Br bond.

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Separation of triazene
COOEt}Br] (
Recrystallization from toluene allowed the complete removal of substrate
isolation of pure crystalline
2
and the palladium(II) complex [(Ph3P)2Pd{C6H3-2-(N=N-N(Me)Ph)-5-
5
) was quite challenging due to similar solubility in diethyl ether and ethanol.
2
and enabled the
5.
There are only very few X-ray crystal structure studies reported for triazenido palladium(II)
complexes. Therefore, we determined the structures of the complexes to and for
comparison reasons also from triazene
3
5
2.
The molecular structure and atom labelling scheme of 1-(2-bromo-4-ethoxycarbonylphenyl)-
3-methyl-3-phenyltriazene ( ) are depicted in Figure 1. The small differences between the N1-
2
N2 single and N2=N3 double bonds of only 4.4 pm and the slightly shortened N1-C6 and N3-
C7 bonds to the aryl substituents with an average value of 141.5 pm support the presence of
charge delocalization within the extended π-system. This electronic interaction leads to a
planar arrangement of the 1,3-diaryltriazene subunit.
Figure 1: Molecular structure and atom labelling scheme of 1-(2-bromo-4-ethoxycarbonylphenyl)-3-
methyl-3-phenyltriazene (2). The ellipsoids represent a probability of 30 %, H atoms are drawn with
arbitrary radii. Selected bond lengths (pm): N1-N2 132.5(3), N2-N3 128.1(3), N1-C6 141.9(3), N1-C16
146.6(4), N3-C7 141.1(4), Br1-C8 189.3(3); bond angles (deg.): N2-N1-C6 116.4(2), N2-N1-C16 121.0(2),
C6-N1-C16 122.6(2), N1-N2-N3 113.3(2), N2-N3-C7 112.1(2); dihedral angles (deg.): N2-N1-C6-C1 -
6.9(4), C6-N1-N2-N3 -179.2(2), N1-N2-N3-C7 180.0(2), N2-N3-C7-C8 173.3(2).

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Figure 2: Structural motif and atom labelling scheme of [(Ph3P)2Pd(Ph-N3-C6H3-2-Br-4-COOEt)Cl] (3). The non-
hydrogen atoms are drawn with arbitrary radii, H atoms are neglected for the sake of clarity. Selected bond
lengths (pm): Pd1-Cl1 231.3(3), Pd1-P1 231.8(3), Pd1-P2 232.2(3), Pd1-N1 201.8(11), N1-N2 129.6(16), N2-N3
130.9(16), N1-C10 144.6(17), N3-C1 141.4(17), Br1-C2 189.9(14); angles (deg.): P1-Pd1-P2 178.42(13), Cl1-Pd1-
N1 178.5(4), N1-Pd1-P1 90.2(4), N1-Pd1-P2 90.9(4), Cl1-Pd1-P1 89.59(12), Cl1-Pd1-P2 89.27(12), Pd1-N1-N2
122.0(9), Pd1-N1-C10 122.5(9), N2-N1-C10 115.4(11), N1-N2-N3 112.8(10), N2-N3-C1 109.3(10).
The molecular structures of the triazenido palladium(II) complexes contain metal centers in square
planar coordination spheres. The molecular structure and atom numbering scheme of [(Ph3P)2Pd(Ph-
N3-C6H3-2-Br-4-COOEt)Cl] (3) are shown in Figure 2. The anionic chloride and triazenide bases are
trans-positioned. The negative charge is delocalized within the triazenide moiety leading to an
average N-N distance of 130.3 pm.

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Figure 3: Molecular structure and atom labelling scheme of [(Ph3P)2Pd(Ph-N3-C6H3-2-Br-4-COOEt)2] (4). The
ellipsoids represent a probability of 30 %, H atoms are omitted for clarity reasons. Symmetry-related atoms (-
x+1.5, -y+1.5, -z+1) are marked with the letter “A”. Selected bond lengths (pm): Pd1-N1 204.8(2), Pd1-P1
236.31(9), N1-N2 130.8(4), N2-N3 130.3(4), N1-C10 142.2(4), N3-C1 140.9(4), Br1-C2 189.6(3); bond angles
(deg.): N1-Pd1-P1 90.50(8), Pd1-N1-N2 121.3(2), Pd1-N1-C10 123.7(2), N2-N1-C10 113.9(2), N1-N2-N3 114.6(2),
N2-N3-C1 109.9(3).
The molecular structure and atom labelling scheme of centrosymmetric [(Ph3P)2Pd(Ph-N3-C6H3-2-Br-
4-COOEt)2] (4) are depicted in Figure 3. The crystallographic center of symmetry enforces trans-
arranged triazenide ligands which show very similar N1-N2 and N2-N3 bond lengths verifying
delocalization of the negative charge within this triazaallyl substructure. The Pd1-P1 bond is
elongated compared to complex 3, most probably a steric consequence due to substitution of the
small chloride by another rather bulky triazenide ligand. In agreement with this interpretation also an
elongation of the Pd1-N1 distances in the more strained complex 4 is observed
The molecular structure and atom labelling scheme of [(Ph3P)2Pd{C6H3-2-(N=N-N(Me)Ph)-5-COOEt}Br]
(5) is depicted in Figure 4. The palladium(II) atom is bound to the aryl moiety and the triazene
subunit shows no short contacts to the metal atom. The N-N single and N=N double bonds differ by
almost 10 pm, a significantly larger difference than in substrate 2. This finding can be explained by
larger deviation of the diaryltriazene subunit from planarity and hence by a less effective charge
delocalization. The N-C bonds are in the same order of magnitude as observed for triazene 2. The
Pd1-C9 bond length lies in the expected range as also observed for unstrained [(Ph3P)2Pd(Ph)Br]
(199.5(6) pm)20 and dinuclear [(dppm)Pd(Ph)Br]2 (204.1(7) pm).21

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Figure 4: Molecular structure and atom labelling scheme of [(Ph3P)2Pd{C6H3-2-(N=N-N(Me)Ph)-5-COOEt}Br] (5).
The ellipsoids represent a probability of 30 %, H atoms are omitted for clarity reasons. The ethoxy group O2,
C15, and C16 is disordered on two position, only one position is shown. Selected bond lengths (pm): Pd1-Br1
251.91(8), Pd1-P1 231.99(18), Pd1-P2 234.52(18), Pd1-C9 202.9(6), N1-N2 125.7(7), N2-N3 135.4(7), N1-C8
141.8(8), N3-C6 140.7(9), N3-C7 146.2(8); bond angles (deg.): Br1-Pd1-P1 89.69(4), Br1-Pd1-P2 93.75(5), Br1-
Pd1-C9 174.36(17), P1-Pd1-P2 175.35(6), P1-Pd1-C9 89.47(18), P2-Pd1-C9 87.41(18), C8-N1-N2 112.6(5), N1-
N2-N3 114.4(5), N2-N3-C6 116.8(5), N2-N3-C7 120.1(6), C6-N3-C7 122.8(6).
In Table 2 selected structural parameters of palladium(II)-bound triazenides are compared.
Preferably, the triazenide ligands bind as monodentate ligands in mononuclear complexes (entries 1-
10) or as bridging ligands in di- (entries 12-20) and even tetranuclear (entry 21) palladium(II)
compounds. In contrast, the bidentate binding fashion in mononuclear derivatives is quite unique
(entry 11). The compounds [(Ph3P)2Pd(Ph-N3-C6H3-2-Br-4-COOEt)2] (4) (entry 8) and [(py)2Pd(2-FC6H4-
N3-C6H4-4-NO2)2] (entry 10) are the only known mononuclear complexes with two triazenide ligands.
In all these derivatives, the triazenide ligands have (syn-E) configuration. In mononuclear complexes
with monodentate triazenide ligands the Pd-N bond lengths vary within a rather narrow range of 202
to 205 pm (exception being entries 3 and 5 with trans-positioned aryl groups). Larger distances and a
broad variation of the Pd-N values are observed for bridging triazenide ligands. Regardless of the
binding mode, the negative charge is largely delocalized within the triazenide functionalities
supporting largely ionic interactions between the palladium(II) cation and the triazenide anion.
Furthermore, the NNN bond angles are smaller than 120° and vary in the range between 111° and
118°; steric strain induced by the bidentate coordination of the triazenide to one palladium(II) atom
leads to a smaller angle of only 106.2(4)° (entry 11) whereas in the tetranuclear congener larger
values of approx. 120° are found due to intramolecular electrostatic repulsion between the
palladium(II) cations on the one hand and between the chloride anions on the other (entry 21).
<< Insert Table 2 >>

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Selected NMR data are summarized in Table 3 to elucidate the influence of the coordination of the
triazenides at palladium(II) atoms on the chemical shifts. Formation of the palladium(II) complexes
leads to very small shifts of the 1H resonances of the N-bound methyl substituents (compounds 2 and
5) whereas the ethyl group of the ester functionality shows a larger shift toward higher field. 13C{1H}
resonances of the phenyl group of 2 are not influenced by formation of complex 5 whereas the ipso-
carbon atom of the ester-functionalized aryl substituent shows a low field shift. Formation of
triazenides 3 and 4 leads to slightly low field shifted resonances of the ipso-carbon atoms of the
phenyl group. 31P{1H} NMR shifts of 3 and 5 with palladium-bound halide ligands are very similar,
whereas the substitution of chloride by another triazenide ligand leads to a high field shifted
resonance. Resonances of very small intensity (see Figures S4 and S6 of the ESI) belong to the
isomeric form with palladium(II) bound to the nitrogen atom adjacent to the 2-bromo-4-
ethoxycarbonylphenyl group.
Table 3: Comparison of selected NMR parameters (chemical shifts, ppm) of triazenes 1 and 2 with
those of palladium(II) complexes 3 to 5.
1
2
3
4
5
Solvent
1H
[D8]THF
[D8]THF
CDCl3
CDCl3
[D8]THF
δ(NMe)
δ(MeEt)
-
3.77
1.37
4.34
-
-
3.73
1.21
4.08
1.36
4.33
1.39
4.35
1.45
4.42
δ(CH2,Et
13C{1H}
δ(MeN3)
δ(MeEt)
)
-
33.8
-
-
32.9
14.4
61.4
142.1
152.1
14.5
14.6
60.9
149.4
153.4
14.6
61.0
148.8
154.0
14,7
δ(CH2,Et
)
61.5
60.0
δ(iCPh)
145.5
151.9
146.0
158.4
δ(iCPhCOOEt
)
31P{1H}
δ(PPh3)
-
-
22.0
17.2
23.6
The cyclic voltammogram of triazene 2 shows a reversible reduction wave at -1.24 V and palladation
leads to a slight positive shift to -1.20 V in 5. An irreversible oxidation process is indicated at 0.96 V in
case of ligand 2 and 0.88 V for 5. Cyclic voltammograms of complexes with Pd–Cl bonds exhibit a
different behavior: complex 3 shows a broad irreversible oxidation wave at 0.23 V due to several
oxidation processes. Besides the oxidation of palladium(II) species, also oxidation of the chloride ion
Cl- to Cl2 occurs. This behavior was observed earlier for several dinuclear palladium(II) triazenides.7
Complex [(Ph3P)2Pd{C6H3-2-(N=N-N(Me)Ph)-5-COOEt}Br] (5) was also studied by ESI mass
spectrometry and an intensive mass was found at m/z = 650.1166 Da. In agreement with the isotopic
pattern of this signal a formula of C34H31N3O2PPd (deviation from calculated high resolution mass 1.7
ppm) can be deduced due to loss of one PPh3 ligand and the bromide anion.
TGA measurements showed that the triazenes 1 and 2 decomposed above 150 °C and 190 °C,
respectively. Formation of the palladium-bound triazenide stabilized this unit and degradation of
[(Ph3P)2Pd(Ph-N3-C6H3-2-Br-4-COOEt)Cl] (3) started above 210 °C. Contrary to this observation, the

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influence of the insertion of Pd into the C-Br bond of the aryl group on the stability of the triazene
unit was negligible and weight loss of [(Ph3P)2Pd{C6H3-2-(N=N-N(Me)Ph)-5-COOEt}Br] (5) was
detected already above 140 °C. This finding verified the structural data which showed no significant
changes of the bonding parameters of the triazene substructure upon palladation of the aryl
substituent. The high decomposition temperatures of these diaryltriazenes are contrary to earlier
observations at 1-(2,4,6-triisopropylphenyl)-3-(2-pyridylmethyl)triazene, which eliminated dinitrogen
already under very mild conditions in hot n-pentane.27
Conclusions
The metathetical approach is a suitable pathway to prepare palladium(II) triazenides. Thus, the
equimolar reaction of [(Ph3P)2PdCl2] with deprotonated 1-(2-bromo-4-ethoxycarbonylphenyl)-3-
phenyltriazene (1) as lithium, silver, or triethylammonium salt yields the palladium(II) complex
[(Ph3P)2Pd(Ph-N3-C6H3-2-Br-4-COOEt)Cl] (3). The second reaction step with another equivalent of
triazenide proceeds less straightforward and mixtures of 3 and doubly triazenide substituted
[(Ph3P)2Pd(Ph-N3-C6H3-2-Br-4-COOEt)2] (4) are obtained.
The oxidative addition of the C-Br bond of 1-(2-bromo-4-ethoxycarbonylphenyl)-3-methyl-3-
phenyltriazene (2) on the palladium(0) species [Pd(PPh3)2] in THF yields [(Ph3P)2Pd{C6H3-2-(N=N-
N(Me)Ph)-5-COOEt}Br] (5). The N-methylated derivative has been used to avoid competitive
oxidative addition of the N-H bond on palladium.
In the molecular structures of complexes 3 and 4, the palladium-bound triazenide ligands show (syn-
E)-configuration. The negative charge of these anions is largely delocalized, leading to quite similar N-
N and N=N bond lengths and supporting a mainly ionic bonding situation in the respective palladium
complexes. In mononuclear palladium(II) compounds, the monodentate coordination mode is
preferred, the very rare bidentate binding fashion has not been observed for this 1-(2-bromo-4-
ethoxycarbonylphenyl)-3-phenyltriazenide ligand.
Experimental
General Considerations: All manipulations were carried out in a nitrogen atmosphere using standard
Schlenk techniques. The solvents THF and toluene were dried over KOH and subsequently distilled over
sodium/benzophenone under a nitrogen atmosphere prior to use. Deuterated solvents were dried over
sodium, degassed, and saturated with nitrogen. The indicated yields are not optimized and refer to
1
crystalline yields. H and 13C{1H} NMR spectra were recorded on Bruker Avance 600, 400 and Avance
250 spectrometers. Chemical shifts are reported in parts per million relative to SiMe4 as external
1
1
standard. H,13C{1H}-HSQC, H,13C{1H}-HMBC, and H,H-COSY NMR experiments were performed for the
assignment of the resonances. The residual signals of [D8]THF, CDCl3 and C6D6 were used as internal
standards. For mass spectrometric investigations the spectrometers ThermoFinnigan MAT95XL and
Finnigan SSQ710 were at our disposal. IR spectra were recorded with a Bruker ALPHA FT-IR
11
spectrometer. The compounds 1-(2-bromo-4-ethoxycarbonylphenyl)-3-phenyltriazene (
1
)
and 1-(2-
bromo-4-ethoxycarbonylphenyl)-3-methyl-3-phenyltriazene (
protocols.12,13
2) were prepared according to published

ACCEPTED MANUSCRIPT
Synthesis of [(Ph3P)2Pd(Ph-N3-C6H3-2-Br-4-COOEt)Cl] (
3
): This complex can be prepared by three
methods via intermediate silver triazenide (A), via lithium triazenide (B) and via triethylammonium
triazenide. The preferred method proceeded via intermediately prepared silver triazenide. Method A:
Silver 1-(2-bromo-4-ethoxycarbonylphenyl)-3-phenyltriazenide: Sodium methanolate (0.29 g, 5.4
mmol) was dissolved in 50 mL of anhydrous ethanol and added dropwise to 1-(2-bromo-4-
ethoxycarbonylphenyl)-3-phenyltriazene (1, (1.725 g, 5.0 mmol), dissolved in 50 mL of anhydrous
dichloromethane. The resulting deep yellow-brown solution was stirred for 20 min and a solution of
silver nitrate (0.84 g, 4.9 mmol) in 13 mL of deionized and degassed water was added. Stirring
overnight led to a yellow-green suspension. The precipitate was collected and washed three times with
12 mL of ethanol. After drying in high vacuum the crude product of silver 1-(2-bromo-4-
ethoxycarbonylphenyl)-3-phenyltriazenide (1.55 g, yield: 69%) was used without further purification.
This silver triazenide (0.19 g, 0.42 mmol) was suspended in 9 mL of dichloromethane. A suspension of
0.293 g of bis(triphenylphosphane)-dichloro-palladium(II) (0.42 mmol) in 9 mL of toluene was added at
once to the silver triazenide mixture. During stirring overnight at r.t. the color of the reaction mixture
turned brown-orange and became clear. The solution was filtered through a Schlenk frit covered with
diatomaceous earth. All volatiles were removed in vacuo from the filtrate. The remaining orange
powder was extracted twice with n-hexane. After removal of the solvent, the product was dried in
vacuo. Recrystallization was possible from a saturated toluene solution by diffusion with n-hexane.
Yield: 0.31 g of
3
(73%). The methods B (52 %) and C (18 %) are described in the ESI.
: Dec. without melting. 1H NMR (400 MHz, CDCl3, 297 K): δ = 1.39 (t, J = 7.1 Hz, 3H,
Physical data of
3
COOEt CH3), 4.35 (q, J = 7.1 Hz, 2H, COOEt CH2), 6.11 (d, J = 8.5 Hz, 1H, BrArH 4-CH), 6.79 (t, J = 7.3 Hz,
1H, ArH 4-CH), 6.95 (t, J = 7.9 Hz, 2H, ArH 3,3´-CH), 7.23 (t, 12H, J = 7.6 Hz PPh3 3,3´-CH), 7.35 (t, 6H, J =
7.4 Hz PPh3 4-CH), 7.47 (m, 2H, ArH 2,2´-CH), 7.54 (dd, J = 8.5 Hz 1.9 Hz, 1H, BrArH 5-CH), 7.69 (m, 12H,
PPh3 2,2´-CH), 8.19 (d, J = 1.9 Hz, 1H, BrArH 3-CH). 13C{1H} NMR (100 MHz, CDCl3, 297 K): δ = 14.6
(COOEt CH3), 60.9 (COOEt CH2), 117.2 (BrAr 2-CBr), 119.6 (Ar 2,2´-CH), 119.7 (BrAr 6-CH), 122.7 (Ar 4-
CH), 125.2 (BrAr 4-C), 128.1 (t, 2JPC = 5.2 Hz, PPh3 2,2´-CH), 128.3 (BrAr 5-CH), 130.0 (t, 1JPC = 24.2 Hz,
PPh3 1-C), 130.6 (PPh3 4-CH), 134.4 (BrAr 3-CH), 135.0 (t, 3JPC = 5.2 Hz, PPh3 3,3´-CH), 149.4 (Ar 1-CN),
153.4 (BrAr 1-CN), 166.2 (COOEt), 31P{1H} NMR (162 MHz, CDCl3, 297 K): δ = 22.0. 1H NMR (400 MHz,
[D8]THF, 297 K): δ = 1.33 (t, J = 7.1 Hz, 3H, COOEt CH3), 4.28 (q, J = 7.1 Hz, 2H, COOEt CH2), 6.11 (d, J =
8.5 Hz, 1H, BrArH 6-CH), 6.77 (t, J = 7.3 Hz, 1H, ArH 4-CH), 6.93 (t, J = 8.0 Hz, 2H, ArH 3,3´-CH), 7.22 (t,
12H, J = 7.6 Hz PPh3 3,3´-CH), 7.36 (t, 6H, J = 7.4 Hz PPh3 4-CH), 7.50 (m, 3H, ArH 2,2´-CH, BrArH 5-CH),
7.71 (m, 12H, PPh3 2,2´-CH), 8.11 (d, J = 1.9 Hz, 1H, BrArH 3-CH), 13C{1H} NMR (101 MHz, [D8]THF, 297
K): δ = 14.6 (COOEt CH3), 60.8 (COOEt CH2), 117.7 (BrAr 2-CBr), 120.1 (Ar 2,2´-CH), 120.3 (BrAr 6-CH),
123.3 (Ar 4-CH), 126.1 (BrAr 4-C), 128.46 (t, 2JPC = 5.2 Hz, PPh3 2,2´-CH), 128.55 (BrAr 5-CH), 128.7 (Ar
3,3´-CH) 131.1 (t, 1JPC = 24.2 Hz, PPh3 1-C and s, PPh3 4-CH), 134.6 (BrAr 3-CH), 135.7 (t, 3JPC = 6.5 Hz,
PPh3 3,3´-CH), 150.4 (Ar 1-CN), 154.0 (BrAr 1-CN), 165.2 (COOEt), 31P{1H} NMR (162 MHz, [D8]THF, 297
K): δ = 25.6 (E-N1), tiny signal at δ(ppm) = 26.9 (E-N3). HR-MS (ESI, acetonitrile), [M+H]: calculated for
C51H44BrClN3O2P2Pd: 1012.0819 Da, found: 1012.0785 Da, Δm/z = 2.5 ppm. IR (ATR, cm-1): 1701, 1589,
1481, 1435, 1340, 1315, 1291, 1276, 1243, 1200, 1163, 1130, 1097, 1030, 995, 892, 840, 751, 711, 692,
618, 588, 523, 510, 496. Elemental anal. (C51H44BrClN3O2P2Pd): calcd.: C 60.43, H 4.28, Br 7.88, Cl 3.50,
N 4.15; found: C 60.62, H 4.35, Br 7.34, Cl 3.62, N 4.35. TGA-DSC (m0 = 4.8332 mg, 25 °C to 600 °C, 5
K/min): four step degradation, 1. step: –3.09 % (219.3 °C, loss of nitrogen, proceeds exothermic with
94.0 J/g), 2. step: –9.96 % (244.8 °C), 3. step: –9.43 % (300.5 °C), 4. step: –29.67 % (343.8 °C), residue:
45.58 %.
Synthesis of [(Ph3P)2Pd(Ph-N3-C6H3-2-Br-4-COOEt)2] (4): Silver 1-(2-bromo-4-ethoxycarbonylphenyl)-3-
phenyltriazenide was prepared as described above and 0.24 g of this silver salt (0.53 mmol) was
suspended in 10 mL of anhydrous dichloromethane. A suspension of 0.185 g of
bis(triphenylphosphane)-dichloro-palladium(II) (0.26 mmol) in 9 mL of toluene was added at once to
the silver triazenide. According to the same workup procedures as described for complex 3, a mixture

ACCEPTED MANUSCRIPT
of
3
and
4
(ratio of 77:23) was isolated due to an incomplete conversion and very similar solubility
properties of these complexes.
Physical data of : The resonances of
complex
are recorded here. 1H NMR (400 MHz, CDCl3, 297 K): δ = 1.45 (t, J = 7.1 Hz, COOEt CH3), 4.42
4
3 and 4 are mostly well separated. Only the signals of the
4
(q, J = 7.1 Hz, COOEt CH2), 6.50 (d, J = 8.5 Hz, BrArH 4-CH), 6.70 (t, J = 7.3 Hz, ArH 4-CH), 6.79 (t, J = 7.3
Hz, ArH 3,3´-CH), 7.11 (t, J = 7.4 Hz PPh3 3,3´-CH), 7.48 (m, PPh3 4-CH, ArH 2,2´-CH), 7.69 (m, PPh3 2,2´-
CH), 7.91 (dd, J = 8.6 Hz 1.7 Hz, BrArH 5-CH), 8.44 (d, J = 1.9 Hz, BrArH 3-CH). 13C{1H} NMR (100 MHz,
CDCl3, 297 K): δ = 14.6 (COOEt CH3), 61.0 (COOEt CH2), 117.0 (BrAr 2-CBr), 121.5 (BrAr 6-CH), 121.6 (Ar
2,2´-CH), 122.8 (Ar 4-CH), 125.4 (BrAr 4-C), 127.7 (t, 2JPC = 5.1 Hz, PPh3 2,2´-CH), 128.3 (BrAr 5-CH),
130.1 (t, 1JPC = 24.2 Hz, PPh3 1-C), 130.7 (PPh3 4-CH), 134.2 (BrAr 3-CH), 134.9 (t, 3JPC = 5.2 Hz, PPh3 3,3´-
CH), 148.8 (Ar 1-CN), 154.0 (BrAr 1-CN), 166.3 (COOEt). 31P{1H} NMR (162 MHz, CDCl3, 297 K): δ = 17.2.
Synthesis of [(Ph3P)2Pd{C6H3-2-(N=N-N(Me)Ph)-5-COOEt}Br] (5): Bis(triphenylphosphane)palladium
diacetate (315 mg, 0.42 mmol) was suspended in 10 mL of anhydrous tetrahydrofuran. After the
suspension was stirred for 10 min, hydrazine monohydrate (11 µL, 11.1 mg, 0.22 mmol) was added.
The final clear greenish brown solution was stirred for 30 min at r.t. Then 1-(2-bromo-4-
ethoxycarbonylphenyl)-3-methyl-3-phenyltriazene (2) (152.5 mg, 0.42 mmol) was dissolved in
anhydrous tetrahydrofuran (5 mL) and added via a cannula to the thus prepared palladium(0) solution.
The reaction mixture was heated to 60 °C for 4 h. After cooling to r.t. all volatiles were removed in
vacuo. The residue was washed three times with n-pentane (3x5 mL). Then the crude product was
washed twice with diethyl ether (2x3 mL). Drying in vacuo gave a grey-brown powder. Yield: 225 mg of
5
(75%). Rerystallization was achieved in toluene/n-hexane yielding orange rhombohedral crystals.
: Dec. without melting. 1H NMR (600 MHz, [D8]THF, 298 K): δ = 1.21 (t, J = 7.1 Hz, 3H,
Physical data of
5
COOEt CH3), 3.73 (s, 3H, NCH3), 4.08 (q, J = 7.1 Hz, 2H, COOEt CH2), 6.43 (d, J = 8.2 Hz, 1H, subArH 6-
CH), 7.01 (d, J = 8.2 Hz, 1H, subArH 3-CH), 7.04 (m, 1H, ArH 4-CH), 7.17 (t, J = 7.5 Hz, 12H, PPh3 2,2´-CH),
7.25 (t, J = 7.3 Hz, 6H, PPh3 4-CH), 7.30 (m, 5H, ArH 2,2´-CH, 3,3´-CH sub ArH 5-CH), 7.59 (m, 12H, PPh3
3,3´-CH). 13C{1H} NMR (150 MHz, [D8]THF, 297 K): δ = 14.7 (COOEt CH3), 32.9 (NCH3), 60.0 (COOEt CH2),
117.2 (subAr 6-CH), 117.3 (Ar 2,2´-CH), 123.6 (Ar, 4-CH), 125.1 (subAr 3-CH), 128.0 (subAr CPd), 128.2
(t, 2JPC = 5.1 Hz, PPh3 2,2´-CH), 129.5 (PPh3 4-CH), 130.2 (Ar 3,3´-CH), 132.7 (t, 1JPC = 22.9 Hz, PPh3 1-C),
135.6 (t, 3JPC = 6.3 Hz, PPh3 3,3´-CH), 139.3 (t, 5JPC = 4.6 Hz, subAr 5-CH), 146.0 (Ar 1-CN), 156.9 (t 4JPC =
2.5 Hz, subAr 4-C), 158.4 (t, 3JPC = 3.7 Hz, subAr 1-CN), 166.1 (COOEt). 31P{1H} NMR (243 MHz, [D8]THF,
297 K): δ = 23.56. HR-MS (ESI, acetonitrile), [(M-PPh3-Br)]+: calculated for C34H32N3O2PPd: 650.1196 Da,
found: 650.1219 Da, Δm/z = 5.5 ppm. IR (ATR, cm-1): 3052, 1707, 1597, 1503, 1479, 1433, 1363, 1333,
1271, 1228, 1204, 1101, 1026, 994, 825, 742, 726, 687, 608, 520, 509, 492, 453, 438, 414. Elemental
anal. (C52H46BrN3O2P2Pd): calcd.: C 62.88, H 4.67, Br 8.05, N 4.23; found: C 61.88, H 4.60, Br 7.43, N
3.75. TGA-DSC (m0 = 6.0109 mg, 25 °C to 600 °C, 5 K/min): three step degradation, 1. step: –10.31 %
(216.9 °C, proceeds exothermic with 25.9 J/g), 2. step: –31.34 % (309.3 °C), 3. step: –31.8 % (356.5 °C),
residue: 25.04 %.
Crystal structure determinations: The intensity data for the compounds were collected on a Nonius
KappaCCD diffractometer using graphite-monochromated Mo-Kα radiation. Data were corrected for
Lorentz and polarization effects; absorption was taken into account on a semi-empirical basis using
multiple-scans.28-30 The structures were solved by direct methods (SHELXS)31 and refined by full-matrix
2
least-squares techniques against Fo (SHELXL-97).31 The hydrogen atoms of HA were located by difference
Fourier synthesis and refined isotropically. All other hydrogen atoms were included at calculated positions
with fixed thermal parameters. All non-disordered, non-hydrogen atoms were refined anisotropically.31
The crystals of 3 were extremely thin and of low quality, resulting in a substandard data set; however,
the quality of the structure determination is sufficient to show connectivity and geometry despite the
high final R value. Therefore, we only publish the conformation of the molecule and the crystallographic
data. We will not deposit the data in the Cambridge Crystallographic Data Centre. Crystallographic data as

ACCEPTED MANUSCRIPT
well as structure solution and refinement details are summarized in Table S1 (ESI). XP32 and POV-Ray33
were used for structure representations.
Electrochemistry: Electrochemical data were obtained by cyclic voltammetry using a conventional
single-compartment three-electrode cell arrangement in combination with a potentiostat ‘‘AUTOLABs,
eco chemie’’. As working electrode a 0.196 cm2 Pt disk, as auxiliary electrode was used glassy carbon
and as reference electrode Ag/AgCl (3 M KCl). The measurements were carried out in anhydrous and
nitrogen purged acetonitrile (3·10-4 M substrate concentration with 0.1 M tert-butylammonium
tetrafluoroborate as supporting electrolyte. All potentials are referenced by the ferrocenium/ferrocene
couple (E(Fc/Fc+) = 0.437 V).34
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
The work is based on industrial collaboration and we thank Laborchemie Apolda GmbH, Germany, for
generous financial support. We acknowledge the support by the NMR service platform (www.nmr.uni-
jena.de) and of the mass spectrometry platform (www.ms.uni-jena.de) of the Faculty of Chemistry and
Earth Sciences of the Friedrich Schiller University Jena.
Electronic Supporting Information (ESI)
NMR spectra, cyclovoltammograms, crystallographic and refinement details of the crystal structure
determinations, molecule representation and bonding parameters of hydrazine acetate (pdf format).
CCDC-1899309 for 2, CCDC-1899310 for 4, CCDC-1899311 for 5, and CCDC-1899364 for hydrazinium
acetate. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [E- mail: deposit@ccdc.cam.ac.uk].
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Table 2: Comparison of binding modes (see Scheme 1) and selected structural parameters (bond lengths (pm) and angles (deg.), values without e.s.d. values
were taken from the CSD database) of palladium(II)-bound triazenide ligands with the substructure Pd(R-N-N’=N’’-R’).a
Entry
1
2
3
4
5
6
7
8
R
pTol
pTol
R’
pTol
pTol
C6H4-4-F
Binding mode
Monodentate
Monodentate
Monodentate
Monodentate
Monodentate
Monodentate
Monodentate
Monodentate
Monodentate
Monodentate
Bidentate
Pd-N
203.3(4)
203.4(7)
212.0
204.0
214.9(3)
203.6
201.8(11)
N-N’
N’-N’’
128.6(7)
129.6(9)
128.3
128.3
128.7(4)
130.0
N-N’-N’’
113.0(5)
116.3(8)
111.6
112.9
112.4(2)
113.0
Ref.
3
22
23
4
133.6(8)
129.4(9)
132.4
131.8
131.3(4)
131.3
C6H4-4-F
C6H4-4-Ac
C6H4-4-NO2
C6H4-3-OMe-4-COOMe
Ph b
C6H4-4-Ac
C6H4-4-NO2
C6H4-3-OMe-4-COOMe
C6H3-2-Br-4-COOEt
C6H3-2-Br-4-COOEt
C6H4-2-F
24
4
129.6(16)
130.8(4)
133.4(6)
132.5(5)
130.6(7)
130.2(4);
130.2(5)
129.5(5);
129.4(5)
130.8(9);
128.0(8)
131.4(9);
129.3(10)
128.8(8);
130.3(8)
129.8(7);
131.0(7)
129.8(6)
130.0(8);
130.2(7)
131.3(3)
129.5;
130.9(16)
130.3(4)
128.2(6)
128.3(5)
130.8(7)
130.8(4);
131.4(6)
130.0(6);
130.6(5)
130.0(9);
130.4(9)
129.3(10);
130.4(11)
128.2(8);
128.5(8)
130.4(7);
130.6(7)
130.1(6)
131.0(8);
129.9(8)
129.3(3)
127.4;
112.8(10)
114.6(2)
111.0(4)
111.0(3)
106.2(4)
117.0(4);
117.2(4)
117.2(4);
117.7(4)
116.1(5);
116.1(5)
116.3(7);
116.5(8)
117.7(6);
116.0(5)
116.7(5);
116.8(5)
118.2(4)
116.9(6);
118.1(5)
114.3(2)
119.7;
Here
Here
24
25
5
Ph c
C6H4-4-NO2
C6H4-4-NO2
Ph
204.8(2)
204.7(5)
202.1(3)
9
10
11
12
C6H4-2-F
Ph
Ph
209.5(4), 211.7(4)
206.8(4), 209.8(4);
207.3(4), 209.0(4)
210.0(4), 216.1(4);
210.0(4), 217.6(4)
202.5(5), 214.5(5);
203.6(5), 214.5(4)
212.1(7), 214.2(7);
211.8(8), 214.4(8)
211.5(6), 217.6(6);
213.8(5), 213.6(5)
211.6(5), 213.7(5);
213.1(5), 216.0(5)
212.5(4), 215.8(4)
211.5(6), 213.0(6);
211.2(5), 214.5(5)
201.0(2), 208.7(2)
201.8, 202.3;
201.5, 203.8;
202.3, 202.3;
202.5, 201.0
Ph
Bridgingd
5
13
14
15
16
17
Ph
pTol
Ph
pTol
Bridgingd
Bridgingd
Bridgingd
Bridgingd
Bridgingd
7
22
7
pTol
pTol
oTol
oTol
7
C6H4-4-Br
C6H4-4-Br
7
18
19
C6H4-2-Br
C6H4-4-OMe
C6H4-2-Br
C6H4-4-OMe
Bridgingd
Bridgingd
7
7
20
21
pTol
pTol
C6H4-2-SMe
pTol
Bridgingd
Bridginge
26
6
129.1;
128.9;
127.9;
129.9;
128.5
120.7;
119.4;
119.9
129.0
Complex [(Ph3P)2Pd(Ph-N3-C6H3-2-Br-4-COOEt)Cl] (
a
b
c
). Complex
Abbreviations: Ac acetyl, Et ethyl, Me methyl, Ph phenyl, Tol tolyl (methylphenyl).
[(Ph3P)2Pd(Ph-N3-C6H3-2-Br-4-COOEt)2] (
3
4
). d Dinuclear palladium(II) complex. e Tetranuclear palladium(II) complex.

ACCEPTED MANUSCRIPT
Graphical Abstract
Palladium triazenides are accessible by metathetical approaches tolerating halogeno- and ester
functionalized aryl groups, whereas insertion of Pd into an aryl C-Br bond succeeds after protection
of the triazene substructure via N-methylation.

ACCEPTED MANUSCRIPT
Highlights:
•
The metathetical approach is a suitable pathway for the synthesis of palladium(II)
triazenides.
•
•
•
•
Palladium-bound triazenide ligands show perfect delocalization of the negative charge.
The Pd-triazenide interactions are mainly of ionic nature.
Triazenide anions prefer a mondentate coordination behavior toward palladium(II).
Oxidative addition of an aryl C-Br bond onto Pd(0) is tolerated by the triazene substructure.