Synthesis, coordination chemistry and bonding of strong n-donor ligands incorporating the 1h-pyridin-(2e)-ylidene (pye) motif

Article abstract of DOI:10.1002/chem.200901382

A range of N-donor ligands based on the 1H-pyridin-(2E)-ylidene (PYE) motif have been prepared, including achiral and chiral examples. The ligands incorporate one to three PYE groups that coordinate to a metal through the exocyclic nitrogen atom of each P

Full text of DOI:10.1002/chem.200901382

DOI: 10.1002/chem.200901382
Synthesis, Coordination Chemistry and Bonding of Strong N-Donor Ligands
Incorporating the 1H-Pyridin-(2E)-Ylidene (PYE) Motif
Qi Shi,[a] Robert J. Thatcher,[a] John Slattery,[a] Pardeep S. Sauari,[a]
Adrian C. Whitwood,[a] Patrick C. McGowan,[b] and Richard E. Douthwaite*[a]
Abstract: A range of N-donor ligands
based on the 1H-pyridin-(2E)-ylidene
(PYE) motif have been prepared, in-
cluding achiral and chiral examples.
The ligands incorporate one to three
PYE groups that coordinate to a metal
through the exocyclic nitrogen atom of
each PYE moiety, and the resulting
metal complexes have been character-
ised by methods including single-crystal
X-ray diffraction and NMR spectrosco-
py to examine metal–ligand bonding
and ligand dynamics. Upon coordina-
tion of a PYE ligand to a proton or
metal-complex fragment, the solid-
state structures, NMR spectroscopy
and DFT studies indicate that charge
redistribution occurs within the PYE
heterocyclic ring to give a contribution
from a pyridinium–amido-type reso-
nance structure. Additional IR spec-
troscopy and computational studies
suggest that PYE ligands are strong
donor ligands. NMR spectroscopy
shows that for metal complexes there is
restricted motion about the exocyclic
À
C N bond, which projects the hetero-
cyclic N-substituent in the vicinity of
the metal atom causing restricted
motion in chelating-ligand derivatives.
Solid-state structures and DFT calcula-
tions also show significant steric con-
gestion and secondary metal–ligand in-
teractions between the metal and
Keywords: bonding · coordination
chemistry
·
density functional
calculations · molecular dynamics ·
N ligands
À
ligand C H bonds.
Introduction
Metal complexes of nitrogen-donor ligands exhibit some of
the most interesting stoichiometric and useful catalytic
transformations described in the chemical literature. Simple
nitrogen donors based on amine, amide, imide and imine
have been extensively developed to different extents over
several decades to control the stability and reactivity of the
resulting complexes through electronic and steric modifica-
tion. Furthermore, nitrogen-donor residues in metallopro-
teins and enzymes underpin many biological processes.[1]
The compounds that are the focus of this work are based
on the 1H-pyridin-(2E)-ylidene (PYE, A in Scheme 1)
Scheme 1. Possible resonance structures of the 1H-pyridin-(2E)-ylidene
motif on coordination to a metal fragment.
motif. Although PYE-type compounds have been known for
over 80 years[2] and their organic and biological[3–13] chemis-
try and spectroscopy[14–18] has been studied, their coordina-
tion chemistry is essentially unknown.[19]
A motivation for exploring the coordination chemistry of
1H-pyridin-(2E)-ylidenes as ligands is that straightforward
modification of the pyridine and imine N substituents
should be possible, which will allow access to a range of sub-
stitution patterns including chelating and chiral derivatives.
The steric demands of the ligand can be easily modified to
give a very tuneable ligand family that has significant poten-
tial in coordination chemistry and possibly catalysis. Struc-
turally, PYE compounds resemble bulky amido ligands that
incorporate aryl substituents,[20–25] which have shown very in-
teresting reactivity, particularly in multiple bond-cleavage
and -formation processes. There is also a parallel with com-
[a] Q. Shi, R. J. Thatcher, Dr. J. Slattery, P. S. Sauari,
Dr. A. C. Whitwood, Dr. R. E. Douthwaite
Department of Chemistry, University of York
Heslington, York, YO10 5DD (UK)
Fax : (+44)1904-434183
E-mail: red4@york.ac.uk
[b] Dr. P. C. McGowan
School of Chemistry, University of Leeds
Leeds, LS2 9JT (UK)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200901382.
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Chem. Eur. J. 2009, 15, 11346 – 11360

FULL PAPER
pounds that incorporate a guanidine moiety, which have re-
cently been developed as ligands for transition-metal coordi-
nation chemistry[26–35] including bioinspired reactivity[36–40]
and catalytic applications.[41–46]
For PYE-type compounds, conjugation between the pyri-
dine and imine moieties suggests that, as ligands, these com-
pounds could exhibit strong donation owing to a contribu-
tion of the pyridinium–amido resonance structure to the
metal–ligand bond (B in Scheme 1). In this regard, a recent
report by Johnson describes the selective nickel-mediated
tion methodology,[4,6–9,12] because the alkylation of 2-amino-
pyridine[2,3] is typically unselective and condensation reac-
tions between 2-pyridinone and primary amines generally
do not occur. Consequently, none of these methods are com-
patible with the synthesis of compounds containing multiple
PYE motifs.
An alternative route derives from the amination of a 2-
chloro-1-methyl pyridinium salt I in the presence of a base
(Scheme 3),[52] and we have found that modification of this
À
C F activation of aryl fluorides by using isopropyl(1-methyl-
1H-pyridin-4-ylidene)amine (Scheme 2) and direct compari-
Scheme 2. Isopropyl(1-methyl-1H-pyridin-4-ylidene)amine.
son is made with strong donors such as N-heterocyclic car-
benes (NHCs).[47] The chemistry of strong donor ligands
such as NHCs and electron-rich phosphanes has undergone
tremendous development over recent years, particularly for
catalysis.[48–50] If PYEs are used as neutral ligands, metal–
À
ligand equilibria, which are observed for metal NHC and
metal–phosphine catalytic cycles, could also be analogously
accessible in PYE complexes.
Furthermore, structurally, PYE ligands are likely to pro-
vide a well-defined metal environment because upon coordi-
nation through the exocyclic nitrogen atom, the pyridyl N-
substituent R1 will occupy the volume close to the metal.
Free rotation and isomerisation about the exocyclic N=C
bond is not initially expected, partly because of reported
[51]
Scheme 3. Synthetic routes to PYE-containing ligands (Bn=benzyl).
À
short N C bond lengths in a related conjugate acid, and
also because the steric bulk of R1 and R2 should drive the
formation of a single isomer. With respect to steric factors,
some comparison can be made with NHCs that also contain
N substituents that point in the general direction of the
metal, whereas substituents such as tertiary phosphanes
project away from the metal, although rotation about the
procedure gave all of the target compounds (1–10 in
Scheme 3) in good yield. As may be expected, compounds
containing multiple PYE motifs are generally prepared in
lower yield and, for example, the reaction between two
À
E C (E=N or P) bonds increases the effective bulk of the
ligand.
equivalents of
methyl-1H-pyridin-(2E)-ylidene)ethane-1,2-diamine
I
and ethylenediamine gave N,N’-bis(1-
(5)
Herein we describe the synthesis and structures of achiral
and chiral examples of nitrogen-donor ligands incorporating
the PYE motif. Metal-complex derivatives have been pre-
pared for each ligand class and their spectroscopic and coor-
dination chemistry is discussed with respect to bonding and
ligand dynamics. DFT calculations have also been conducted
to compare the donor properties of PYE ligands with other
common ligand classes.
(Scheme 3) in 50% yield after recrystallisation. The synthet-
ic route is compatible with a range of amine-substitution
patterns including chiral derivatives (3,
4 and 7 in
Scheme 3), and modification of the N-heterocycle substitu-
ent can be achieved from reaction between 2-chloropyridine
and hydrocarbylbromides to give ligands such as 8 and 10,
which are derived from compound II (Scheme 3). One dis-
tinguishing feature of the synthesis of compound 9, and to a
lesser extent 10, is that the product is strongly adsorbed
onto the base, potassium carbonate. Upon filtration of the
reaction mixture, the K2CO3/9 (or 10) residue can be
washed with ether and acetonitrile, providing a convenient
work-up for the removal of organic by-products. The addi-
tion of acid to dissolve the mixture allows subsequent base
extraction and isolation of the product. All of the com-
Results and Discussion
Ligand synthesis and characterisation: There are a limited
number of methods for the preparation of hydrocarbyl-sub-
stituted PYEs, which have mainly relied on a cyclotrimerisa-
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R. E. Douthwaite et al.
pounds are very soluble in chlorinated solvents and alcohols,
and show a range of solubility in water, ethers and hydrocar-
bons. Furthermore, the exocyclic C=N bond is very resistant
to hydrolysis as shown for ligands 1 and 5, which can be
heated to reflux in D2O without decomposition as deter-
1
mined by using H NMR spectroscopy.
The characterisation data is consistent with the proposed
formulations. By taking compound 1 as a representative ex-
ample and by using the numbering scheme shown in
1
Table 1, the H NMR spectroscopy in CDCl3 shows distinc-
Table 1. 1H and 13C NMR chemical shifts of the PYE ring atoms at
298 K for selected compounds and metal complexes.[a]
Figure 1. Molecular structure of compound 7. Displacement ellipsoids are
shown at the 50% probability level. Hydrogen atoms except H(7) and
H(7’) have been omitted for clarity. Atoms marked with an apostrophe
(’) are at the symmetry positions 1+x, À1+y, Àz.
H2
H3
H4
H5
C1
C2
C3
C4
C5
2
À
shorter than 1.38 ꢁ that is typical of a single C
(sp ) N
1
6.42 6.73 5.48 6.97 150.4 115.6 133.1
6.35 6.45 5.15 6.26 149.6 115.0 132.7
99.0 139.8
98.1 139.4
bond).[56] For 7, the atoms about the C(1) N(1) bond are
also essentially planar with planes defined by C(2)-C(1)-
N(2) and C(7)-N(1)-C(1), which is twisted by approximately
6.58.
À
1[b]
8
6.45 6.70 5.46 6.80 153.3 113.6 134.3 101.1 137.9
6.36 6.90 5.60 7.11 154.3 112.6 136.1 101.3 140.7
7.20 7.89 6.91 8.43 151.7 113.0 142.7 113.3 142.6
9
11
14[b] 6.81 6.58 5.63 6.40 164.5 122.4 134.6 108.0 140.2
To aid the interpretation of the electronic and structural
features of PYE-containing complexes and to identify po-
tential decomposition products, the protonation of represen-
tative compounds 1, 5 and 9 was examined by NMR spec-
troscopy and crystals were grown after anion exchange.
Upon addition of sufficient equivalents of HBF4·OEt2 or
acetic acid to protonate each PYE group, single crystals that
were representative of each compound class were obtained
of protonated 1 [tBuN(H)][I] (11, Figure 2, Table 2), 5
18
6.95 7.33 6.31 7.24 163.2 116.7 137.7 108.6 139.9
19[c] 6.56 7.22 6.01 7.22 157.2 114.4 137.9 105.0 141.0
21[c] 6.92 7.64 6.54 7.55 162.7 116.6 141.6 110.5 142.0
[a] Chemical shift [ppm] in CD3Cl3, [b] CD3C6D5 and [c] CD3CN.
tive signals for the PYE moiety at 5.48 (H4), 6.42 (H2), 6.73
(H3) and 6.97 ppm (H5), and corresponding 13C NMR signals
at 99.0 (C4), 115.6 (C2), 133.1 (C3), 139.8 (C5) and 154.4 ppm
(C1). For all compounds, NMR spectroscopic data are con-
sistent with a single imine isomer.
The structures of 7 and 9 have been determined by using
single-crystal X-ray crytallography techniques. The molecu-
lar structure of 7 is shown in Figure 1 and selected data are
given in Table 2.[53] The asymmetric unit cell contains one
half of 7 with coincident crystallographic and molecular C2
[(MeN(H)C2H4N(H)Me)][Br]2 (12)[53] and 9 [N
AHCTUNGTRENNUNG
[CF3SO3]3 (13).[53] For all structures only protonation at N(1)
ACHTUNGTRNEN(UNG MeN(H))3]-
is observed, which is clear from the charge balance between
the number of anion equivalents in the structure and the
planarity of the heterocyclic rings. For compounds 11–13 the
bond lengths and angles within the PYE groups are essen-
tially identical.[53]
Structures 12 and 13 show evidence of hydrogen bonding
À
À
À
axes. Examination of the C C and C N bond lengths in the
PYE moiety indicates that the valence-bond structure A is
the accurate representation in
between the anion and the exocyclic N H hydrogen atom
H(1) of the cation, and both have isolated cation/anion
À
À
which C(1) C(2) and C(2)
C(3), for example, are
Table 2. Comparison of bond lengths [ꢁ] within the PYE group of compounds 7, and 11, and complexes 16,
18, 20 and 21.
1.4496(16) and 1.3527(16) ꢁ,
respectively, and the exocyclic
7
11
16[a]
18[b]
18[c]
20[a]
21[a]
À
C(1) N(1)
1.2960(15)
1.4496(16)
1.4078(14)
1.3527(16)
1.4162(17)
1.3509(17)
1.3628(14)
1.4611(16)
1.328(7)
1.407(7)
1.362(7)
1.362(2)
1.393(3)
1.348(8)
1.358(6)
1.471(7)
1.332(3)
1.424(3)
1.388(3)
1.360(3)
1.406(3)
1.350(3)
1.360(3)
1.458(3)
1.348(3)
1.414(4)
1.377(4)
1.373(4)
1.390(5)
1.354(4)
1.355(3)
1.489(3)
1.318(3)
1.430(4)
1.392(3)
1.363(4)
1.403(5)
1.354(4)
1.364(3)
1.484(3)
1.306(3)
1.447(3)
1.397(3)
1.346(4)
1.414(4)
1.355(4)
1.368(3)
1.484(3)
1.321(3)
1.426(3)
1.386(3)
1.359(4)
1.407(4)
1.346(4)
1.356(3)
1.466(3)
À
C=N bond C(1) N(1) is
À
C(1) C(2)
À
C(1) N(2)
1.2960(15) ꢁ. In contrast, the
single-crystal X-ray structure
of 2-amino pyridine exhibits all
À
C(2) C(3)
À
C(3) C(4)
À
C(4) C(5)
À
À
of the C C and C N bond
À
C(5) N(2)
À
lengths
as
approximately
C(6) N(2)
1.36 ꢁ,[54,55] including the exo-
[a] The lengths of the other PYE group are within the estimated standard deviations (esds). [b] The PYE
moiety labelled C(1) to N(2). [c] The other PYE moiety labelled with greater numbers.
À
cyclic C NH2 bond (which is
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Strong N-Donor Ligands
FULL PAPER
Table 3. Selected bond lengths [ꢁ] for the DFT optimised structures of 1
and 11 compared with those found from the X-ray crystal structure of 11.
1
9
11
11
DFT
XRD
DFT
XRD
À
C(1) N(1)
1.2813
1.4481
1.4134
1.3552
1.4147
1.3569
1.3503
1.4459
1.2934(16)
1.4514(17)
1.4069(15)
1.3533(19)
1.419(2)
1.3508(19)
1.3616(16)
1.4592(16)
1.3333
1.4115
1.3689
1.3655
1.4018
1.3561
1.3599
1.4574
1.328(7)
1.407(7)
1.362(7)
1.362(2)
1.393(3)
1.348(8)
1.358(6)
1.471(7)
À
C(1) C(2)
À
C(1) N(2)
À
C(2) C(3)
À
C(3) C(4)
À
C(4) C(5)
À
C(5) N(2)
À
C(6) N(2)
Figure 2. Molecular structure of the cation of 11. Displacement ellipsoids
are at the 50% probability level. Hydrogen atoms except H(1) and the
anion have been omitted for clarity.
and protonated derivatives are compared in Table 3. The
geometrical parameters of the optimised structures of 1 and
11 compare well with the X-ray crystal structures of 9 and
11, respectively, given that some differences are expected
between the solid-state and gas-phase structures as well as
the necessity to use experimental data from 9 because the
structure of 1 was unavailable. Analogous to the crystal-
structure data, the calculations show that significant struc-
tural changes occur upon protonation, in particular a length-
motifs.[53] Compound 12 exhibits hydrogen bonding to a bro-
À
mide with Br H(1)=2.43 ꢁ, and compound 13 exhibits hy-
drogen bonding to an oxygen atom of the triflate anion with
[53]
À
O H(1)=2.28 ꢁ. A comparison of the bond lengths and
angles between 7 and 11 (Table 2) shows that the significant
À
differences are a lengthening of C(1) N(1) (0.04 ꢁ) and a
À
À
shortening of C(1) C(2) (0.05 ꢁ) and C(1) N(2) (0.04 ꢁ)
À
À
À
À
with less change in the remaining C C and C N bonds. The
angle between the planes defined by C(2)-C(1)-N(1) and
C(1)-N(1)-C(7) for 11 is essentially equal (~6.88) to that in
compound 7, and collectively, the structural features of 11
are similar to a related compound 1-methyl-2-(2’-pyridyl)-
aminopyridinium chloride.[51]
ening of C(1) N(1) (by 0.05 ꢁ) and a shortening of C(1)
À
C(2) and C(1) N(2) (both by 0.04 ꢁ), again suggesting a
more amidopyridinium-like resonance structure.
Natural bond orbital (NBO) calculations were performed
at the PBE1PBE/TZVP level by using GAUSSIAN 03.[62]
For 1, the NBO results were based on the imine resonance
form A with substantial delocalisation of the N(2) lone pair
1
The H NMR spectroscopic investigation shows four sig-
À
À
nals for the heterocycle that are significantly downfield from
precursors 1, 5, and 9, respectively, whereas compound 11,
for example, gives signals at 6.91 (H4), 7.20 (H2), 7.89 (H3)
and 8.43 ppm (H5), which are upfield from a typical unsub-
stituted pyridinium group such as N-methylpyridinium
into the C(1) N(1) and C(4) C(5) p BD* orbitals (with the
À
À
formation of N(2) C(1) and N(2) C(5) p interactions). The
magnitude can be gauged from the resulting occupation of
the N(2) lone pair (1.555 eÀ) and the stabilisation energy of
these interactions (176 and 213 kJmolÀ1, respectively). In
iodide.[57] A broad signal at 6.53 ppm is observed for the N
addition, the C(4) C(5), C(2) C(3) and C(1) N(1) p bond-
ing orbitals are also delocalised around the aromatic system,
À
À
À
À
H(1) proton, however, the solubility of 12 and 13 restricted
the solvents that could be used to obtain the NMR spectra
to D2O or CD3OD, preventing the observation of analogous
NH signals. Furthermore, for compound 9a, proton titration
(see the Supporting Information) by using acetic acid in
CD3OD showed that up to three equivalents of protons are
consumed, which is consistent with protonation of the PYE
groups and not the tertiary amine as observed in the struc-
ture of 13. The 13C NMR spectroscopy data for 11–13
showed the most significant chemical shift changes at C3 and
C4 and surprisingly little change at C1. Representative 1H
and 13C NMR spectroscopy data of compound 11 are given
in Table 1.
À
but to a lesser extent. The C(1) N(1) p bonding orbital has
an occupation of 1.950 eÀ suggesting a large degree of
double-bond character. In contrast, the NBO results for 11
are based on the aminopyridinium resonance form B with
À
delocalisation of the N(1) lone pair into the C(1) N(2) p
BD* orbital (the N(1) lone pair occupation is 1.656 eÀ and
stabilisation energy for this interaction is 397 kJmolÀ1) to
À
give a system with significant C(1) N(1) double-bond char-
acter. In addition, the p system around the ring is signifi-
cantly delocalised. These results suggest, along with the
structural evidence, that protonation leads to a considerably
more aminopyridinium-like structure, but that the C(1)
N(1) bond retains some double-bond character.
À
DFT studies were performed on compounds 1 and 11 to
gain a greater insight into the structural and electronic
changes that occur in PYE compounds upon protonation
and that influence the subsequent coordination of metal
fragments. The geometries of 1 and 11 were optimised at
the PBE0/TZVPP level by using TURBOMOLE (using the
updated def2-TZVPP basis set), and the stationary points
were confirmed as minima by vibrational frequency analy-
ses.[58–61] Calculated and experimental bond lengths of PYE
Metal complex synthesis and characterisation: Initial com-
plexation studies have been restricted to ligands 1 and 6–10
primarily because they represent a range of substitution pat-
terns and metal-complex geometries, and the benzyl sub-
stituents of 8 and 10 aid NMR spectroscopic studies of the
ligand dynamics (see below).
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R. E. Douthwaite et al.
The reaction between 1 and [RhCl(CO)2]2 in toluene gave
complex 14 (Scheme 4) as an air-sensitive white solid in
95% yield. IR spectroscopy of complexes of the type
[RhCl(CO)2(L)] has been used to gauge the electron-donat-
ligand 11 in toluene prevented direct comparison of 1 with
14.
The reaction between [NiBr2ACTHNUGTRNEUNG(dme)] (DME=1,2-dime-
thoxyethane) and compounds 6, 7 and 8, gave complexes 15,
16 and 17, respectively, in 66–98% yield (Scheme 4). Com-
plexes 15–17 are paramagnetic dark-red (15) or dark-green
(16 and 17) solids. As solids, 15–17 are stable in air for
hours, but in solution they decompose within minutes to
give the protonated ligands as the only organic product (de-
1
termined from the H NMR spectra of the filtered samples).
The room-temperature effective magnetic moments were
measured by the Evans method[68,69] on two independent
samples for each complex to give values of 2.58, 3.01 and
3.18 mB for 15, 16 and 17, respectively, which broadly equates
to two unpaired electrons, although the origin of the much
lower moment of 15, as well as the difference in colour, is at
this time unknown. By applying basic symmetry rules and
given the observed paramagnetism of complexes 15–17,
non-square-planar coordination is expected and a single-
crystal X-ray diffraction study of complex 16 showed distort-
ed tetrahedral geometry. The molecular structure is shown
in Figure 3 and selected bond lengths and angles are given
in Tables 2 and 4, respectively.[53]
Scheme 4. Synthetic routes to metal complexes 14–20.
ing properties of L. For complex 14, IR spectroscopy in tolu-
ene shows two CO peaks at 2071 and 1992 cmÀ1, and in a
KBr matrix at 2071 and 1989 cmÀ1. Comparison with report-
ed examples in which L=pyridine (2089, 2015),[63] PPh3
(2087, 2009),[64] PMe2Ph (2089, 2002),[64] the NHCs 1,3-dime-
sitylimidazolin-2-ylidene (2081, 1996),[65] 1,3-dimethylimida-
zol-2-ylidene (2076, 2006),[66] and the acyclic carbene tert-
Figure 3. Molecular structure of complex 16. Displacement ellipsoids are
shown at the 50% probability level. Hydrogen atoms have been omitted
for clarity.
Complex 16 exhibits pseudo-C2 symmetry with the methyl
substituents directed above and below a metal–ligand plane
that is defined by N(1)-Ni(1)-N(3). In contrast to the struc-
tures of neutral compound 7 and pyridinium salt 12, the ni-
trogen atoms N(1) and N(3) that are coordinated to the
nickel atom exhibit distinct pyramidal geometry. For exam-
ple, the angles about N(1) are C(1)-N(1)-C(7)=115.53(16),
butyl
G
(2070,
1989),[67] indicate that by using the [Rh(CO)2Cl(L)] probe, 1
is a strongly donating ligand. An analogous complex of iso-
propyl(1-methyl-1H-pyridin-4-ylidene)amine gave stretching
frequencies at 2077 and 1998 cmÀ1,[47] indicating that 1 may
be a marginally better donor.
1
Comparison of the H and 13C NMR spectra of 14 with
C(1)-N(1)-Ni(1)=119.12(13)
and
C(7)-N(1)-Ni(1)=
ligand 1 (Table 1) in CD3C6D5 shows downfield chemical
shifts for all signals, with the most significant changes in the
1H NMR spectra for H4 (5.15 to 5.63 ppm) and H2 (6.35 to
6.81 ppm). In addition to the two signals at 182.0 (1J-
107.96(12)8, and similarly, for N(3) the sum of the angles is
approximately 3438. Comparison of the bond lengths in the
PYE groups of 7, 12[53] and 16 (Table 2) in which, for exam-
À
ple, the C(1) N(1) imine bond lengths are 1.2294(3),
A
R
1.334(4) and 1.332(3) ꢁ, respectively, indicates that the PYE
ring distances are closer to protonated ligand 12 than free
ligand 7. In comparison to the structurally related 2, 2’-bi-
pyridine and a diimine bidentate nitrogen ligands, the
nickel–nitrogen bond lengths in 16 (Table 4) are at the
were assigned to the carbon monoxide ligands, the most sig-
nificant changes in the 13C NMR spectrum are for C1 (149.6
to 164.5 ppm), C2 (115.0 to 122.4 ppm) and C4 (98.1 to
108.0 ppm). Unfortunately, poor solubility of protonated
11350
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Chem. Eur. J. 2009, 15, 11346 – 11360

Strong N-Donor Ligands
FULL PAPER
Table 4. Selected bond lengths [ꢁ] and angles [o] about the metal atoms in complexes 16, 18, 20 and 21.
16
18
20
21
À
À
À
À
Ni(1) N(1)
1.9931(16)
2.3934(3)
2.4106(4)
2.3934(3)
Pd(1) N(1)
2.041(2)
2.041(2)
2.2944(7)
2.3347(7)
Cu(1) N(1)
2.044(2)
2.038(2)
2.068(2)
2.141(2)
Zn(1) N(1)
2.0387(17)
2.0413(17)
2.0317(17)
2.1904(18)
2.2710(15)
118.76(7)
117.71(7)
118.44(7)
82.18(7)
À
À
À
À
Ni(1) N(3)
Pd(1) N(3)
Cu(1) N(3)
Zn(1) N(3)
À
À
À
À
Ni(1) Br(1)
Pd(1) Cl(1)
Cu(1) N(5)
Zn(1) N(5)
À
À
À
À
Ni(1) Br(2)
Pd(1) Cl(2)
Cu(1) N(7)
Zn(1) N(7)
À
Zn(1) O(1)
N(1)-Ni(1)-N(3)
Br(1)-Ni(1)-Br(2)
N(1)-Ni(1)-Br(1)
86.85(7)
107.433(12)
100.14(5)
N(1)-Pd(1)-N(3)
Cl(1)-Pd(1)-Cl(2)
N(1)-Pd(1)-Cl(1)
N(1)-Pd(1)-Cl(2)
79.18(9)
91.12(3)
94.44(7)
168.35(7)
77.1[a]
N(1)-Cu(1)-N(3)
N(3)-Cu(1)-N(5)
N(1)-Cu(1)-N(5)
N(1)-Cu(1)-N(7)
N(3)-Cu(1)-N(7)
N(5)-Cu(1)-N(7)
121.68(9)
117.62(9)
119.16(8)
86.56(9)
85.54(8)
85.49(9)
N(1)-Zn(1)-N(3)
N(3)-Zn(1)-N(5)
N(1)-Zn(1)-N(5)
N(1)-Zn(1)-N(7)
N(3)-Zn(1)-N(7)
N(5)-Zn(1)-N(7)
N(7)-Zn(1)-O(1)
[b]
PyeC(1)[a]-PdSqpl
82.49(7)
82.70(7)
178.13(6)
PyeC(15)[d]-PdSqpl
52.0
[a] The least-squares plane of the heterocycle containing C(1). [b] The least-squares palladium square plane. [c] The acute angle between the planes.
[d] The least-squares plane of the heterocycle containing C(15).
longer end of the observed range of diimine–dihalide com-
plexes, and the ligand bite angle N(1)-Ni(1)-N(3)=86.85(7)8
is approximately four degrees greater.[56] A nickel–aryl fluo-
ride complex of isopropyl(1-methyl-1H-pyridin-4-ylidene)a-
ligand bite angle N(1)-Pd(1)-N(3)=79.18(9)8 and identical
À
À
Pd N bond lengths at 2.041(2) ꢁ. However, the Pd Cl bond
À
À
lengths differ with Pd(1) Cl(1)=2.2944(7) and Pd(1)
Cl(2)=2.3347(7) ꢁ, which is induced by the asymmetry ob-
served in the ligand. A staggered conformation about the
mine,[47] (Figure 2) exhibits
a
trans-square-planar [Ni-
À
À
(C6F5)(F)L2] geometry and Ni N bond lengths of approxi-
C(13) C(14) bond renders the torsion angles between the
À
mately 1.925 ꢁ. The significantly longer Ni N bonds ob-
served for 16 could be attributed to the constrained chelate
ring and the non-covalent interactions between the ligand
methyl and bromine groups, but direct comparison is re-
stricted because of the different geometry and significant p
acidity of the C6F5 ligand.
palladium square plane and two heterocyclic rings that con-
tain C(1) and C(15) at approximately 77 and 528, respective-
ly. Orientation of the benzyl substituents to minimise the
À
non-covalent interactions also results in a short Pd(1) H-
(20a) length of approximately 2.38 ꢁ. The complex exhibits
pseudo-Cs symmetry, and the bond lengths within the PYE
ring moieties are similar to 16, and between free ligand 7
and protonated salt 11 (Table 2).
A
To study the spectroscopic features of the chelating biden-
tate PYE ligands, a diamagnetic palladium complex was iso-
lated from the reaction between 8 and [Pd
(COD)Cl2], which
1H NMR spectroscopy at 258C shows signals consistent
with C2v symmetry in which two singlet signals are observed
for the linker CH2 and benzyl CH2 groups at 3.67 and
6.49 ppm, respectively (Figure 5). The signals attributable to
the PYE hydrogen atoms at 6.31 (H4), 6.95 (H2), 7.24 (H5)
and 7.33 (H3) are between the corresponding signals ob-
served for free ligand 8 and the protonated salt 11 (Table 1),
with the most significant chemical-shift changes for H4 (5.46
to 6.31 ppm) and H3 (6.70 to 7.33 ppm). In the 13C NMR
spectrum a similar downfield trend in chemical shift with re-
spect to ligand 8 (Table 1) was also observed, including a
shift in the peak corresponding to C1 from 153.3 to
163.3 ppm.
gave the dark-red solid 18 (Scheme 4). The molecular struc-
ture was determined by single-crystal X-ray diffraction and
is shown in Figure 4 and selected data are provided in
Tables 2 and 4.[53] There are two molecules in the asymmet-
ric unit cell, which differ only slightly with respect to bond
lengths and angles. For the complex that contains Pd(1), the
geometry at the palladium atom is square planar with a
Variable-temperature 1H NMR spectroscopy showed sig-
nificant changes in the chemical shifts of the linker and ben-
zylic CH2 signals, but the PYE group signals remained large-
ly unchanged. At 163 K, two broad singlet signals were ob-
served at 3.05 and 4.15 ppm for the CH2 linker protons and
two doublets at 5.20 and 7.20 ppm for the benzylic CH2
groups, with coalescence occurring at 213 K, which corre-
sponds to DG°213K =37.9 kJmolÀ1. The variable-temperature
spectra are consistent with a flipping motion of the PYE
moieties above and below the palladium square plane
through a C2v intermediate, although it is unknown if the
motion of the PYE moieties is correlated. At 163 K, the ob-
servation of only two signals for the linking (CH2)2 group
rather than the four expected in a static system indicates
Figure 4. Molecular structure of complex 18. Displacement ellipsoids are
shown at the 50% probability level. Hydrogen atoms except for H(6a),
H(6b), HACHTUNGTRENNUNG(20a) and HACHTUNGTRENNUNG(20b) have been omitted for clarity.
Chem. Eur. J. 2009, 15, 11346 – 11360
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11351

R. E. Douthwaite et al.
1
Figure 5. Variable-temperature H NMR spectra of 18. (CH2-linker (#) and benzylic signals (*)).
that some motion must still be present within the five-mem-
bered metallocycle.
The reaction between 9 or 10 and [CuACHTNUGTRENNUG(MeCN)4]ACHTUNTGERN[NUGN PF6] gave
complexes 19 and 20 as diamagnetic light-brown and yellow
solids, respectively (Scheme 4). The molecular structure of
complex 20 was determined from single-crystal X-ray dif-
fraction and is shown in Figure 6 and select data are given
in Tables 2 and 4.[53] In common with a limited number of
CuI complexes of tetradentate N-donor ligands that are de-
rived from tris(2-aminoethyl)amine (TREN), complex 20 is
four coordinate.[36,70–77] The geometry about the copper atom
is very close to a trigonal pyramid with the (PYE)N-Cu-
(PYE)N angles adding to 3588 with the copper atom 0.15 ꢁ
above a plane defined by N(1)-N(3)-N(5). A pseudo-C3 ge-
ometry is adopted by the ligand with the phenyl groups of
the benzyl substituents at the periphery of the complex and
benzylic hydrogen atoms towards the centre. An unusual
À
feature is the position of the PF6 anion that is almost di-
rectly on the C3 axis as illustrated by the angle N(7)-Cu(1)-
À
P(1)=1788, and there are three short contacts F(2) H-
À
À
G
N
potentially indicating directional cation/anion interactions.
Furthermore, the remaining benzylic hydrogen atoms are
approximately 2.28 ꢁ from the copper centre.
The asymmetric unit cell contains one cation/anion pair
and, therefore, three unique PYE groups, however, there is
very little difference with respect to bond lengths and
À
angles. The bond length C(1) N(1)=1.306(3) is between the
related ligand 9 (1.2934(16) ꢁ) and the protonated analogue
13 (1.3307(19) ꢁ),[53] although in contrast to complexes 16
and 18, all bond lengths in the heterocycle are closer to the
ligand bond lengths.
1
Comparison of the H NMR spectra of ligands 9 and 10
and their corresponding complexes 19 and 20 shows very
similar chemical shifts for the CH2CH2 signals and the
NCH3 signals of 9 and 19. However, a significant downfield
shift of approximately 0.5 ppm is observed for the corre-
sponding benzylic NCH2Ph signal in 20, and for both com-
plexes downfield shifts are observed for the PYE ring pro-
tons. Taking 9 and 19 as examples (Table 1), the most signifi-
cant shifts occur for H3 (6.90 to 7.22 ppm) and H4 (5.60 to
6.01 ppm) and the corresponding carbon atoms in addition
to C1. Depending on the ligand dynamics there is the poten-
tial for the benzylic CH2 protons of complex 20 to be diaste-
Figure 6. Molecular structure of complex 20. Displacement ellipsoids are
shown at the 50% probability level. Hydrogen atoms except H(6), H-
À
N
N
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Chem. Eur. J. 2009, 15, 11346 – 11360

Strong N-Donor Ligands
FULL PAPER
reotopic. At 300 K a single broad signal is observed in the
1H NMR spectrum at 5.65 ppm, which upon cooling to
220 K resolves into two doublets at 4.42 and 6.82 ppm (see
the Supporting Information), with a coalescence tempera-
ture of 270 K corresponding to DG°270K =48.2 kJmolÀ1. In
addition, at 300 K the signal at 3.15 ppm attributable to the
CH2 group adjacent to the PYE moiety resolves into two
broad signals at 220 K, whereas the CH2 group adjacent to
the amine essentially remains unchanged apart from a little
broadening. Considering the single-crystal X-ray structure,
the dynamic behaviour can be explained by an inversion of
the slightly pyramidal nitrogen atoms N(1), N(3) and N(5)
occurring in conjunction with rotation about the N-benzyl
bond. The differentiation of the CH2 groups of the TREN
moiety can be attributed to an isolated twisting libration
À
about the Cu NACHTUNGTRENNUNG(amine) bond that is independent of the
rest of the molecule. At this stage it is not known what po-
tential contribution, if any, the anion has to the activation
Figure 7. Molecular structure of complex 21. Displacement ellipsoids are
shown at the 50% probability level. Hydrogen atoms and a triflate coun-
teranion have been omitted for clarity.
1
1
energy, although no H-19F coupling is observed in the H or
19F NMR spectra.
Cyclic voltammetry of 19 and 20 in acetonitrile in each
case showed a CuII/CuI redox couple that is considered to be
quasi-reversible based on similar cathodic and anodic cur-
rents, and a peak-to-peak separation that is greater than
60 mV, which increased with scan rate. Complex 19 exhibit-
ed an E1/2 value of +120 mV (vs. Ag/AgCl with an internal
ferrocene standard at +420 mV) whereas 20 has a greater
oxidation potential at +180 mV. These values are broadly
consistent with an example of a four-coordinate copper(I)
complex derived from TREN (+130 mV),[74] however other
examples can be found at lower potentials.[74] There is no
clear correlation between different ligand sets derived from
TREN, however, the NMR spectrscopic data of 19 and 20
indicates a weaker interaction between copper(I) and ligand
20, as judged by the chemical-shift differences between the
complex and ligand. Non-covalent interactions between the
phenyl substituents and adjacent PYE groups (Figure 6) are
À
with respect to the PYE group (Table 2). The C(1) N(1)
bond lengths of 9, 13 and 21 are 1.2934(16), 1.3307(19),
1.321(3) ꢁ, respectively, and other PYE group bond lengths
show essentially the same trend as the analogous bidentate
structures 16 and 18, in which the metal complex parameters
are closer to the protonated salt structure.
The NMR spectra of 21 show signals that are downfield
of the ligand 9 and copper analogue 19 (Table 1), with the
most significant shifts in comparison to the ligand observed
for H3 (6.90 to 7.64 ppm) and H4 (5.60 to 6.54 ppm) and the
corresponding carbon atoms. Relatively significant changes
are also observed for C2 and the imine carbon C1, which is
observed at 162.7 ppm (Table 1).
Metal-ligand bonding and ligand dynamics: Clearly, a varie-
ty of ligands incorporating the PYE motif can be prepared
and coordinated to metal complexes to provide a rich coor-
dination chemistry. Examination of the spectroscopic and
structural data of the compounds and complexes indicates
that addition of a proton or metal-complex fragment to the
PYE group causes significant perturbation to the heterocy-
clic ring in addition to the exocyclic C=N bond. The length-
ening of the exocyclic C=N bond and changes in the hetero-
cyclic ring are consistent with some delocalisation of charge
onto the ligand. The metal complexes show that the greatest
À
likely to prevent shortening of the Cu N bonds that would
accompany oxidation of 20, which would account for the in-
creased oxidation potential.
Single crystals of 19 have not been obtained and, there-
fore, to examine the steric properties of ligand 9, a reaction
between [ZnACHTUNGTRENNUNG(CF3SO3)2] and 9 was attempted, which gave
complex 21 as a white powder that could be recrystallised to
give X-ray quality crystals. The molecular structure is shown
in Figure 7 and selected data are presented in Tables 2 and
4.[53] The coordination about the zinc atom is approximately
a trigonal bipyramid with the zinc atom at approximately
0.27 ꢁ above a plane defined by N(1)-N(3)-N(5), which is a
similar value to complexes that have analogous geome-
À
À
changes are a shortening of the C(1) C(2) and C(1) N(2)
À
bonds with a lesser shortening and lengthening of C(2)
À
C(3) and C(3) C4
try.[78–80] Perhaps the most notable feature is the Zn(1) O(1)
The NMR data shows that coordination of a proton or a
metal complex causes variable downfield chemical shifts in
comparison with the precursor ligand. Metal complexation
appears to be characterised by a significant shift in the
imine carbon C(1), which is not realised upon protonation.
Upon both protonation and metal complexation a chemical-
shift change similar in magnitude to that observed for C(1)
À
bond length of 2.2710(15) ꢁ, which is 0.2–0.3 ꢁ longer in
À
comparison with related Zn O bond lengths of TREN-
based ligands.[81,82] Presumably, non-covalent interactions be-
À
tween the PYE groups and the triflate anion limit the Zn O
interaction. Direct comparison of the structural data can be
made between ligand 9, protonated salt 13 and complex 21
Chem. Eur. J. 2009, 15, 11346 – 11360
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11353

R. E. Douthwaite et al.
is also observed for C(4), which is para to the imine func-
tionality, and the corresponding proton H(4) also experien-
ces the greatest change.
good correlation between n¯(CO) and d(CO) for a wide
range of ligands, and this may be a more robust measure of
donor strength. To rank the PYE ligands described in this
paper against other common ligands, n¯(CO) for the model
complex [IrCp(CO)L] was calculated for 1 and a selection
of other ligands (Figure 8) with a range of donor strengths.
Collectively, the NMR spectroscopy and X-ray crystallo-
graphic data suggest that perturbation of the PYE group
can be attributed to an electrostatic interaction, and in gen-
eral bond-length changes are broadly correlated with the
formal charge and charge density of the coordinating group.
Protonation causes the most significant changes in metrical
data with values for the metal complexes located in the
range spanned by the neutral and protonated ligand. Within
the series examined, the X-ray crystallographic data of cop-
per(I) complex 20 is distinct from that of 16, 18 and 21,
which is consistent with copper(I) behaving as a soft acid.[83]
The structural data is also supported by the NMR spectra in
which the magnitude of the chemical-shift changes are less
for 19 and 20. However, the NMR spectroscopic data for
the imine carbon C(1) is sensitive to metal coordination,
presumably because p interactions through metal-based or-
bitals can occur that are not possible for a proton.
Figure 8. A plot of n¯(CO) [cmÀ1] versus d(CO) [ꢁ] for the [IrCp(CO)L]
With respect to the donating properties of PYE-contain-
ing ligands, comparison of the IR data of 14 with literature
data would suggest that these compounds are strong donor
ligands, which was also shown for the related ligand of John-
son (Scheme 2).[47] However, some caution should be ap-
plied when interpreting data of this type in which multiple
p-acceptor ligands are present and steric factors may be im-
portant. To provide some further insight into the metal–
PYE bond, a theoretical analysis was conducted to place
PYE ligands in the context of other donors.
complexes studied.
Initial optimisations were performed at the (RI-)BP86/
SV(P) level and were followed by re-optimisation by using
the hybrid PBE0 functional in combination with the flexible
def2-TZVPP basis set. Vibrational frequencies were calcu-
lated at both levels of theory and all stationary points were
confirmed as minima by the absence of imaginary frequen-
cies. All calculations were performed by using the TURBO-
MOLE package.[58–61] As in the work of Gusev, a good corre-
lation is found between n¯(CO) and d(CO) for all of the li-
gands included in our dataset. Surprisingly, this correlation
is good, and arguably quite usable, at the relatively fast
(RI-)BP86/SV(P) level (see the Supporting Information), al-
though a slightly better correlation is found for the higher-
level calculations, which are shown in Figure 8. This suggests
that it may be possible to use relatively fast, cheap calcula-
tions for an initial assessment of donor properties of a new
ligand by using the [IrCp(CO)L] model complex. In addi-
tion to these calculations, and to rank the PYE ligand 1 with
others by using the TEP, a range of [Ni(CO)3L] complexes
with the ligands (Figure 9) were also studied at the (RI-
)BP86/SV(P) level (see the Supporting Information). As in
the work of Gusev, a plot of n¯(CO) versus d(CO) for these
complexes (Figure 9) is considerably more scattered than for
the [IrCp(CO)L] data.
The data shown in Figures 8 and 9 can be used to rank
ligand 1 and presumably the related bidentate and tridentate
ligands described in this paper to other known ligands, the
coordination and catalytic chemistries of which are more de-
veloped. The ligands lying to the left-hand side of Figures 8
and 9 with lower frequency n¯(CO) bands can be considered
as strong net donors, and those lying to the right-hand side
as weak donors with significant acceptor character. Figures 8
and 9 show the expected ranking of donor strength for
known ligands within a class, for example, PMe3 >PH3 >
The net donor strength of phosphine ligands, a combina-
tion of their s-donor and p-acceptor properties, is often de-
scribed by using Tolmanꢂs electronic parameter (TEP, the
frequency of the A1 carbonyl mode of [Ni(CO)3L] com-
plexes in dichloromethane, in which L=PR3).[84] This allows
a large range of phosphines with different substituents to be
ranked in order of their donor strength and has been hugely
important in the design of metal complexes with specific
electronic properties for catalysis. However, in addition to
the hazards associated with handling the [Ni(CO)4] precur-
sor, the suitability of TEP values for the comparison of the
donor properties of very different ligand classes (e.g., com-
parison of phosphines with carbenes and amines) has been
questioned.[85] In a recent study, Gusev proposed that densi-
ty functional methods could be used to calculate the CO
stretching frequency in a model complex [IrCp(CO)L] (L=
PR3, NR3, R2C etc.) and that this may be a more robust
measure of the relative donor properties of a wide range of
ligands than the calculated TEP.[85] His argument stems from
the fact that there should be a good correlation between the
calculated n¯(CO) and the calculated CO bond length d(CO)
in complexes that are used to probe donor properties of li-
gands. In [Ni(CO)3L] complexes, good correlation is found
for phosphine ligands, but when different classes of ligands
(e.g., carbenes and amines) are included a poor correlation
is found. The minimisation of trans effects and vibrational
coupling in calculated [IrCp(CO)L] complexes results in a
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Chem. Eur. J. 2009, 15, 11346 – 11360

Strong N-Donor Ligands
FULL PAPER
motion activation energies for 18 and 20 could be non-cova-
lent interactions between benzyl groups and chlorine atoms
À
for 18 and benzyl groups and PF6 for 20. It is not known if,
À
in solution, the PF6 anion occupies the pocket as shown in
the solid-state structure, thus increasing the free energy of
activation, but future work including anion-exchange studies
should resolve the issue. Furthermore, although an X-ray
structure of 14 has not been obtained, it is clear from assess-
À
ment of simple models that free rotation about the N M
bond is restricted owing to non-covalent interactions be-
tween the heterocyclic N-substituent and adjacent ligands, a
feature that is also common to bulky NHC ligands.
Figure 9. A plot of n¯(CO) [cmÀ1] versus d(CO) [ꢁ] for the [Ni(CO)3L]
complexes.
À
Collectively, the lack of rotation about C(1) N(1) and the
relative disposition of N(1) and R1 should allow the environ-
ment at the metal atom to be tailored to some extent. The
steric pressure exerted by the PYE ligands is also suggested
PF3, but in contrast to rankings based on the TEP, [IrCp-
(CO)L] shows pure s-donor ligands such as NMe3 as being
very strong donors. The PYE ligand 1 is found in the region
of very strong N-donor ligands and on this scale is ranked as
a stronger donor than the NHCs included in the study, for
example. In fact, the complex [IrCp(CO)1] is found to have
the second lowest n¯(CO) of all the ligands studied, which
supports the experimental IR data for analogous
[RhCl(CO)2L] complexes (see below).
Collectively, the spectroscopic and theoretical analysis
clearly appear to suggest strong donation, however, it
should be noted that strong donation gauged by CO vibra-
tional frequencies does not uniquely explain structure and,
À
by the very long Zn O bond length in complex 21, although
the strong donating ability of the PYE groups is clearly a
contributing factor, which is indicated by the four-coordi-
nate copper(I) complexes 19 and 20 that do not contain an
apical donor ligand. In addition, the relatively large oxida-
tion potentials of complexes 19 and 20 suggest that signifi-
cant steric pressure at the periphery of the complex is pres-
ent, which may prevent the formation of shorter metal–
ligand bonds that would accompany oxidation.
Conclusion
À
by extension, reactivity. For example, the Pd Cl bond
lengths of complex 18 are 0.03 ꢁ longer than in
[PdCl2(NN)] (NN=2,2’-bipyridyl or a-diimine derived li-
gands) but are on average 0.2 ꢁ shorter than several diNHC
complexes,[56] showing that as expected, the trans influence
does not reflect the CO vibrational trend.
A variety of compounds incorporating the PYE motif can
be simply prepared in a single step from the reaction be-
tween amines and 2-chloro pyridinium salts, and can act as
ligands to transition metals. Comparison of X-ray structural,
NMR spectroscopic and theoretical data of the ligand, metal
complexes and the protonated ligand show that the hetero-
cycle moiety exhibits increased pyridinium character, al-
though there is always significant double-bond character in
With respect to dynamics, variable-temperature NMR
spectroscopy has provided some useful information. There is
no evidence for rotation or significant libration about the
À
À
C(1) N(1) bond in any of the compounds or complexes at
the exocyclic C N bond. Furthermore, although significant
distortion in the bond lengths is localised about the carbon
the temperatures studied here, which agrees with the exocy-
clic C(1)-N(1) bond lengths observed in the structural data
and the ligand synthesis that exclusively results in a single
isomer. For chelate complexes such as 18 and 20, restricted
motion can be observed at lower temperatures as shown in
À
atom of the exocyclic C N bond, NMR spectroscopy shows
the most significant changes at the C(4) C(5) moiety, which
indicates significant electronic distribution within the entire
heterocycle. Variable-temperature NMR spectroscopy of the
chelating PYE complexes indicates that rotation about the
À
1
the H NMR spectra (Figure 5 and the Supporting Informa-
À
tion) in which benzylic and linker CH2 groups become dia-
stereotopic. To observe equivalence of relevant signals at
higher temperatures, both inversion at the coordinating pyr-
amidal nitrogen atoms and conformational changes within
the five-membered metallocycle(s) is required. For 20, rota-
exocyclic C N bond is absent on the NMR timescale and all
X-ray structural data shows a cis configuration between the
metal and heterocycle N-substituent, suggesting rotation
À
about C(1) N(1) does not occur. With respect to bonding,
the IR and theoretical investigations indicate that PYE li-
gands can be considered as strong donor ligands.
À
tion about the N benzyl bond is also necessary. It is not
clear at this stage if equivalence occurs through ligand disso-
ciation. The X-ray data of 18 and 20 shows that secondary
ligand–metal and ligand–anion interactions could be a fea-
ture of PYE ligands, which is also a consequence of the rela-
tive configuration of the coordinating nitrogen atom N(1)
Experimental Section
General: All manipulations were performed under argon by using stan-
dard Schlenk techniques unless stated otherwise. All solvents were dried
over the appropriate drying agent and distilled under dinitrogen accord-
and heterocyclic
Scheme 1). Therefore, additional contributions to the
N A and B in
substituent R1 (see
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11355

R. E. Douthwaite et al.
ing to literature methods.[86] Reagents were purchased from Aldrich,
Acros or Lancaster and used as supplied except K2CO3, which was
Compound 3: By using an analogous procedure to 2, a solution of 2-
chloro-1-methyl-pyridinium iodide (2.50 g, 9.79 mmol), potassium carbon-
ate (4.06 g, 29.40 mmol) and S-benzylmethyl amine (1.40 mL,
10.80 mmol) in acetonitrile (35 mL) was heated for 12 h at 808C to give 3
as a yellow viscous oil (yield: 1.67 g, 80%). 1H NMR (270 MHz, CDCl3):
heated to 1208C for at least 24 h prior to use. [PdCl2ACHTNUTRGNE(NUG COD)] was pre-
pared by using a literature method.[87] NMR spectra were recorded at the
probe temperature on a JEOL 270, JEOL 400 and Bruker AMX-500.
Chemical shifts are described in parts per million, downfield shifted from
SiMe4, and are consecutively reported as position (dH or dC), relative in-
tegral, multiplicity (s=singlet, d=doublet, t=triplet, q=quartet, m=
d=1.43 (d, 3J
(H,H)=6 Hz, 1H; CH), 5.56–5.59 (m, 1H; py-H4), 6.31 (d, J
9 Hz, 1H; py-H2), 6.82–6.85 (m, 1H; py-H3), 7.00 (d, J
(H,H)=5 Hz, 1H;
py-H5), 7.15 (t, J
(H,H)=7 Hz, 1H; PhCH), 7.27–7.30 (m, 2H; PhCH),
7.42 ppm (d, J
ACHTUNGTRENNUNG
J
N
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
multiplet, br=broad, vt=virutal triplet), coupling constant (J in HzÀ1
)
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
(H,H)=7 Hz, 2H; PhCH); 13C NMR (67.5 MHz, CDCl3):
and assignment. Proton NMR spectra were referenced to the chemical
shift of residual proton signals (CDHCl2 d=5.30, CHCl3 d=7.27, C6D5H
d=7.16 and CD2HCN d=1.94 ppm). Carbon spectra were referenced to
d=26.2 (CCH3), 39.4 (NCH3), 55.8 (CCH3), 100.2 (py-C4), 112.7 (py-C2),
125.8 (PhCH), 126.4 (PhCH), 128.0 (PhCH), 134.5 (py-C3), 139.1 (py-C5),
148.4 (PhCHipso), 153.1 ppm (py-C1); MS
ACTHNUTRGNE(UNG ESI) m/z (%): 213.0 (100)
a
13C resonance of the solvent (CD2Cl2 d=54.2, CDCl3 d=77.2, CD3CN
[M+H]+; elemental analysis calcd (%) for C14H16N2 (221.3): C 79.21, H
d=118.3 and C6D6 d=128.1 ppm). 1H-1H COSY, NOESY, 13C HSQC,
PENDANT and Gradient HMBC experiments were performed by using
standard Bruker pulse sequences. Mass spectra were recorded on a
Bruker Esquire 6000 ESI spectrometer and a Bruker microTOF instru-
ment. Electrospray (ES) mass spectra were recorded by using methanol
or acetonitrile as the mobile phase. Major fragments were given as per-
centages of the base-peak intensity (100%). Elemental analyses were
performed at the University of North London. Melting points were un-
7.60, N 13.20; found: C 79.17, H 7.59, N 13.18.
Compound 4: By using an analogous procedure to 2, a solution of 2-
chloro-1-methyl-pyridinium iodide (313 mg, 1.23 mmol), potassium car-
bonate (169 mg, 4.92 mmol) and (S)-(+)-phenylglycinol (185 mg,
1.35 mmol) in acetonitrile (8 mL) was heated for 12 h at 808C to give 4
as
CD3CN): d=3.33 (s, 3H; NCH3), 3.47–3.49 (m, 2H; CH2OH), 4.26 (dd,
a
waxy yellow solid (yield=201 mg, 72%). 1H NMR (400 MHz,
J
J
(H,H)=4 Hz, 1H; CHCH2OH), 5.60–5.62 (m, 1H; py-H4), 6.10 (d,
(H,H)=9 Hz, 1H; py-H2), 6.75–6.77 (m, 1H; py-H3), 7.12–7.14 (m, 2H;
(H,H)=7 Hz, 1H; PhCH),
corrected. Cyclic voltammetry was performed by using
a VoltaLab
PST050 potentiostat and standard three-electrode configuration with
platinum working (0.5 mm diameter wire) and counter electrodes and a
Ag/AgCl reference, which gave the FeCp+/FeCp couple at 0.42 V (DE=
76 mV). All measurements were made by using analyte (0.2 mm) in a ni-
ACHTUNGTRENNUNG
PhCH), 7.13–7.15 (m, 2H; PhCH), 7.18 (t, JACTHUNGTRENNUNG
7.25 ppm (d, JACTHNUTRGNEUNG
(H,H)=5 Hz, 1H; py-H5); 13C NMR (100 MHz CD3CN):
d=39.9 (NCH3), 63.2 (NCH), 69.7 (CH2OH), 101.9 (py-C4), 113.6 (py-
C2), 127.4 (PhCH), 128.2 (PhCH), 129.0 (PhCH), 136.3 (py-C3), 140.7
trogen-purged solution of [nBu4N]
range of scan rates from 50 to 550 mVsÀ1
Compound 1: tert-Butylamine (1 mL, 8.65 mmol) was added to an am-
poule containing 2-chloro-1-methyl-pyridinium iodide (2.00 g,
ACHTUNGTNER[NUGN PF6] (0.2m) in acetonitrile over a
(py-C5), 144.7 (PhCipso), 154.9 ppm (py-C1); MS
ACTHNUTRGNEUNG(ESI) m/z (%): 229.1
.
(100) [M+H]+; elemental analysis calcd (%) for C14H16N2O (228.2): C
73.66, H 7.06, N 12.27; found C 73.57, H 7.09, N 12.17.
7.83 mmol), potassium carbonate (3.25 g, 23.50 mmol) in acetonitrile
(25 mL) and the mixture was stirred for 4 h at 808C. After cooling to
room temperature, the volatiles were removed under reduced pressure to
give a yellow creamy solid that was washed with toluene (25 mL) and iso-
lated by filtration. The solid was then dissolved in aqueous NaOH (5m,
40 mL), extracted with toluene (3ꢃ20 mL) and dried over MgSO4. Upon
filtration, the volatiles of the filtrate were removed under reduced pres-
sure to give 1 as a yellow oil that can be distilled at 808C at 1 Torr
Compound 5: Ethylene diamine (0.55 mL, 8.25 mmol) was added to an
ampoule containing dried potassium carbonate (6.9 g, 0.05 mol), 2-
chloro-1-methyl-pyridinium iodide (4.43 g, 0.017 mol) in acetonitrile
(20 mL) and the mixture was heated at 808C with stirring for 16 h. The
volatiles were removed under reduced pressure and toluene (60 mL) and
aqueous sodium hydroxide (90 mL, 0.475 mol) were added. Upon filtra-
tion, the filtrate was left to stand at 258C for 2 h giving a yellow micro-
crystalline precipitate. The crystals were collected and dried under re-
duced pressure to give 5 as a yellow powder (yield=1.05 g, 50%). M.p.
1
(yield=1.03 g, 80%). H NMR (270 MHz, CDCl3): d=1.27 (s, 12H; tBu),
3.27 (s, 3H; NCH3), 5.48–5.51 (m, 1H; py-H4), 6.42 (d, J
ACHTUNGTRENNUNG
1
142–1468C; H NMR (270 MHz, CDCl3): d=3.34 (s, 6H; NCH3), 3.46 (s,
1H; py-H2), 6.73–6.76 (m, 1H; py-H3), 6.97 ppm (d, J
ACHTUNGTRENNUNG
ACTHNUTRGNEUNG
4H; CH2), 5.65 (vt, 2H; py-H4), 6.57 (d, J(H,H)=9 Hz, 2H; py-H2),
py-H5); 13C NMR (67.9 MHz, CDCl3): d=30.4 (CCH3), 39.6 (NCH3), 51.4
(CCH3), 99.0 (py-C4), 115.6 (py-C2), 133.1 (py-C3), 139.8 (py-C5),
150.4 ppm (py-C1); 1H NMR (400 MHz, C6D6): d=1.48 (s, 12H; tBu),
6.88–6.90 (m, 2H; py-H3), 7.03 ppm (d,
JACTHNGUTERNNUG
(H,H)=5 Hz, 2H; py-H5);
13C NMR (67.5 MHz, CDCl3): 39.9 (NCH3), 48.9 (CH2), 101.6 (py-C4),
112.6 (py-C2), 135.0 (py-C3), 139.0 (py-C5), 154.0 ppm (py-C1); MS
ACHTUNGTRENNUNG(ESI):
2.92 (s, 3H; NCH3), 5.15–5.17 (m, 1H; py-H4), 6.26 (d, J
ACTHUNRTGNE(GNU H,H)=7 Hz,
m/z (%): 243.1 (100) [M+H]+; IR (KBR): v¯ =1641 (s), 1569 (s),
1535 cmÀ1 (s); elemental analysis calcd (%) for C14H18N4 (242.3): C 69.39,
H 7.49, N 23.12; found C 69.28, H 7.36, N 22.93.
ACHTUNGTRENNUNG
1H; py-H5), 6.35 (d, J(H,H)=10 Hz, 1H; py-H2), 6.45–6.47 ppm (m, 1H;
py-H3); 13C NMR (100 MHz, C6D6): d=30.2 (CCH3), 39.0 (NCH3), 51.1
(CCH3), 98.1 (py-C4), 115.0 (py-C2), 132.7 (py-C3), 139.4 (py-C5),
Compound 6: Triethylamine (3.600 g, 35.55 mmol) was added to an am-
poule containing activated 5 ꢁ molecular sieves (2 g), tetramethyldia-
mine (826 mg, 7.11 mmol) and 2-chloro-1-methylpyridinium iodide
(3.814 g, 14.93 mmol) in acetonitrile (80 mL) and the mixture was stirred
at 808C for 12 h. The volatiles were removed under reduced pressure and
the solid was extracted with dichloromethane (80 mL) before being fil-
tered, and the filtrate was added to aqueous sodium hydroxide (50 mL,
5m). The organic phase was separated and the aqueous phase was ex-
tracted with dichloromethane (2ꢃ30 mL). The organic phases were com-
bined and the volatiles were removed under reduced pressure. Recrystal-
lisation from acetone (100 mL) and diethyl ether (10 mL) at À308C gave
ACHTUNGTRENNUNG
149.6 ppm (py-C1); MS(ESI): m/z (%): 165.0 (100) [M+H]+; elemental
analysis calcd (%) for C10H16N2 (164.2): C 73.13, H 9.82, N 17.06; found;
C 73.14, H 9.76, N 16.98.
Compound 2: Aniline (0.8 mL, 8.65 mol) was added to an ampoule
charged with 2-chloro-1-methyl-pyridinium iodide (2.00 g, 7.83 mmol),
potassium carbonate (3.25 g, 23.50 mmol) in acetonitrile (25 mL) and the
mixture was stirred for 4 h at 808C. After cooling to room temperature
the volatiles were removed under reduced pressure to give a yellow
creamy solid that was extracted with toluene (3ꢃ20 mL) and the filtrate
was dried over MgSO4. The volatiles were removed under reduced pres-
sure to give 2 as a yellow oil (yield=1.29 g, 90%). 1H NMR (270 MHz,
CDCl3): d=3.43 (s, 3H; NCH3), 5.80–5.83 (m, 1H; py-H4), 6.31 (d,
6
as yellow microcrystals (yield=1.45 g, 66%). M.p. 220–2238C;
1H NMR (400 MHz, CDCl3): d=1.23 (s, 12H; CCH3), 3.20 (s, 6H;
NCH3), 5.35–5.37 (m, 2H; py-H4), 6.42 (d, J(H,H)=9 Hz, 2H; py-H2),
(H,H)=6 Hz, 2H; py-H5);
JACHTUNGTRENNUNG
(H,H)=10 Hz, 1H; py-H2), 6.81–6.84 (m, 1H; py-H3), 6.79–6.82 (m,
AHCTUNGTRENNUNG
JACTHNGUTERNNUG
(H,H)=5 Hz, 1H; py-H5); 13C NMR
6.64–6.66 (m, 2H; py-H3), 6.91 ppm (d,
JACHTUNGTRENNUNG
5H; PhCH), 7.29 ppm (d,
(67.5 MHz, CDCl3): d=39.5 (NCH3), 102.5 (py-C4), 113.9 (py-C2), 121.3
13C NMR (100 MHz, CDCl3): d=20.9 (CCH3), 42.0 (NCH3), 62.1
(CCH3), 107.4 (py-C4), 113.7 (py-C2), 139.1 (py-C3), 142.4 (py-C5),
(PhCH), 122.4 (PhCH), 128.8 (PhCH), 135.1 (py-C3), 138.7 (py-C5), 151.3
(PhCipso), 153.0 ppm (py-C1); MS
(ESI): m/z (%): 185.0 (100) [M+H]+; el-
ACTHNGUTERNNUG
153.0 ppm (py-C1); MS(TOFES+): m/z (%): 299.2 (100) [M+H]+; ele-
emental analysis calcd (%) for C12H12N2 (184.2): C 78.23, H 6.57, N
15.21; found C 78.31, H 6.68, N 15.17.
mental analysis calcd (%) for C18H26N4 (298.4): C 72.44, H 8.78, N 18.77;
found C 72.47, H 8.69, N 18.90.
11356
www.chemeurj.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 11346 – 11360

Strong N-Donor Ligands
FULL PAPER
Compound 7: 2-chloro-1-methyl-pyridinium iodide (4.06 g, 15.9 mmol)
was added to an ampoule containing (1R, 2R)-cyclohexane-1,2-diammo-
nium-2,3-dihydroxy succinate (2.00 g, 7.570 mmol) and potassium carbon-
ate (6.28 g, 0.045 mol) in acetonitrile (30 mL) and the mixture was
heated at 808C with stirring for 40 h. After cooling to 258C, the mixture
was filtered and the filtrate was added to an aqueous solution of sodium
hydroxide (90 mL, 0.475 mol). The aqueous phase was extracted with
acetonitrile (2ꢃ30 mL) and the volatiles were subsequently removed
under reduced pressure. Recrystallisation from acetone (20 mL) and di-
ethyl ether (5 mL) at À308C gave 7 as yellow microcrystals (yield=
1.12 g, 50%). M.p. 144–1458C; 1H NMR (400 MHz, CDCl3): d=1.29–1.49
(m, 4H; c-hex-CH2; c-hex=cyclohexyl), 1.67–1.69 (m, 4H; c-hex-CH2),
3.08 (s, 6H; NCH3), 3.24–3.26 (m, 2H; c-hex-CH), 5.31–5.33 (m, 2H; py-
1H NMR (400 MHz, [D3]MeCN): d=2.72 (dd, J
CH2), 3.13 (dd, J(H,H)=8, 6 Hz, 6H; CH2), 4.99 (s, 6H; PhCH2), 5.65–
5.67 (m, 3H; py-H4), 6.35 (d, J(H,H)=10 Hz, 3H; py-H2), 6.89 (ddd,
(H,H)=10, 6, 2 Hz, 3H; py-H3), 7.14 (ddd, J
(H,H)=7, 2, 0.5 Hz, 3H;
ACHTUNGTREN(NGNU H,H)=8, 6 Hz, 6H;
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
J
U
ACHTUNGTRENNUNG
py-H5), 7.17–7.29 ppm (m, 15H; PhCH); 13C NMR (100 MHz,
[D3]MeCN): d=47.7 (CH2), 52.8 (CH2), 57.7 (CH2), 101.6 (py-C4), 113.0
(py-C2), 128.1 (PhCH), 128.8 (PhCH), 129.3 (PhCH), 135.9 (py-C3), 139.2
(PhCipso), 139.9 (py-C5), 153.1 ppm (py-C1); MS
ACTHNUTRGNEUNG(ESI): m/z (%): 648 (25)
[M]+, 324 (100) [M]2+, 216 (5) [M]3+; IR (KBr): v¯ : 1646 (s), 1586 (s),
1560 (s), 1536 (m), 1458 (w), 1169 cmÀ1 (w); elemental analysis calcd (%)
for C42H45N7 (647.9): C 77.86, H 7.00, N 15.13; found: C 77.91, H 6.95, N
15.22.
Compound 11: HBF4·OEt2 (185 mL, 1.52 mmol) was added to a solution
of 1 (250 mg, 1.52 mmol) in methanol (1 mL) and tetramethylammonium
iodide (600 mg, 2.98 mmol). Crystals of 11 precipitated on evaporation of
methanol. 1H NMR (270 MHz, CDCl3): d=1.63 (s, 12H; CCH3), 4.43 (s,
3H, NCH3), 6.53 (brs, 1H; NH), 6.91 (t, J=5 Hz, 1H; py-H4), 7.20 (d,
J=9 Hz, 1H; py-H2), 7.89 (t, J=7 Hz, 1H; py-H3), 8.43 ppm (d, J=5 Hz,
1H; py-H5); 13C NMR (CDCl3, 67.5 MHz): d=29.3 (CCH3), 44.7
(NCH3), 54.5 (CCH3), 113.0 (py-C2), 113.3 (py-C4), 142.6 (py-C5), 142.7
H4), 6.58–6.60 (m, 4H; py-H2 and H3), 6.72 ppm (d, J
ACTHNUTRGNE(NUG H,H)=8.0 Hz, 2H;
py-H5); 13C NMR (100 MHz, CDCl3): d=25.3 (c-hex-CH2), 33.8 (c-hex-
CH2), 39.5 (NCH3), 61.8 (c-hex-CH), 99.5 (py-C4), 114.1 (py-C2), 132.7
ACTHNUTRGNEUNG
(py-C3), 138.6 (py-C5), 152.3 ppm (py-C1); MS(TOFES+): m/z (%): 298.0
(25) [M+2H]+, 297 (100) [M+H]+; elemental analysis calcd (%) for
C18H26N4 (296.4): C 72.94, H 8.16, N 18.90; found: C 73.04, H 8.19, N
18.82.
(py-C3), 151.7 ppm (py-C1); MS
ACHTUNGTRENNUNG
Compound 8: Ethylene diamine (0.033 mL, 0.5 mmol) was added to an
ampoule containing potassium carbonate (0.41 g, 3.00 mmol), N-benzyl-2-
chloro-pyridinium bromide (0.300 g, 1.05 mmol) in acetonitrile (15 mL)
and the mixture was heated at 808C with stirring for 16 h. The volatiles
were removed under reduced pressure and toluene (20 mL) and an aque-
ous solution of sodium hydroxide (30 mL, 0.15m) were added. The tolu-
ene phase was separated and the aqueous phase was washed with toluene
(2ꢃ10 mL). The collected toluene extracts were concentrated to approxi-
mately 15 mL until a yellow precipitate began to form and diethyl ether
(3 mL) was added before the mixture was cooled at À308C to give 8 as
yellow microcrystals (yield=0.16 g, 81%). M.p. 127–1318C; 1H NMR
(400 MHz, CDCl3): d=3.34 (s, 4H; CH2CH2), 4.98 (s, 4H; PhCH2), 5.46–
456.8 (30) [2M+I]+; elemental analysis calcd (%) for C10H17N2I (292.1):
C 41.11, H 5.86, N 9.59; found: C 41.00, H 5.91, N 9.50.
Compound 12: Prepared in an analogous procedure to 11, but using tet-
ramethylammonium bromide (600 mg, 2.28 mmol). 1H NMR (D2O,
400 MHz): d=3.60 (s, 4H; CH2), 4.71 (s, 6H; NCH3), 6.80–6.82 (m, 2H;
py-H4), 7.07 (d, J=9 Hz, 2H; py-H2), 7.80 (d, J=5 Hz, 2H; py-H5), 7.81–
7.83 ppm (m, 2H; py-H3); 13C NMR (D2O, 100 MHz): d=41.1 (CH2),
41.7 (NCH3), 110.5 (py-C2), 113.5 (py-C4), 141.7 (py-C5), 143.6 (py-C3),
ACTHNUTRGNEUNG
154.0 ppm (py-C1); MS(TOFES+): m/z (%): 244 (20) [M+2H]+, 243.2
(100) [M+H]+; elemental analysis calcd (%) for C14H20B2F8N4 (417.9): C
40.23, H 4.82, N 13.41; found: C 40.16, H 4.78, N 13.54 (analysis was ob-
tained on the BF4 salt generated from protonation of 5 with HBF4.OEt2).
ACTHNUTRGNEUNG
5.48 (m, 2H; py-H4), 6.45 (d, J(H,H)=8 Hz, 2H; py-H2), 6.70–6.72 (m,
ACHTUNGTRENNUNG
2H; py-H3), 6.80 (d, J(H,H)=8 Hz, 2H; py-H5), 7.15–7.28 ppm (m, 10H;
PhCH); 13C NMR (125 MHz, CDCl3): d=49.9 (CH2CH2), 52.4 (PhCH2),
Compound 13: In an NMR tube acetic acid (68 mL, 1.19 mmol) was
added to a D2O solution (0.6 mL) of 9 (50 mg, 0.119 mmol). Crystals of
13 precipitated on standing for several days. The 1H NMR data was ob-
tained from proton titration with three equivalents of CH3CO2H.
101.1 (py-C4), 113.6 (py-C2), 127.5 (PhCH), 128.5 (PhCH), 128.7 (PhCH),
134.3 (py-C3), 137.6 (PhCipso), 137.9 (py-C5), 153.3 ppm (py-C1); MS
ACTHNUTRGNE(UNG TOF
ES+): m/z (%): 396.2 (25) [M+2H]+, 395.1 (100) [M+H]+; elemental
analysis calcd (%) for C26H26N4 (394.5): C 79.18, H 6.75, N 14.14; found:
C 79.16, H 6.64, N 14.20.
1H NMR (270 MHz, D2O): d=2.95 (t, J
(H,H)=7 Hz, 6H; CH2), 3.72 (s, 9H; CH3), 6.86 (t, J
py-H4), 7.08 (d, J
ACHTUNGTRENNUNG
J
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
Compound 9: Tris(2-aminoethyl)amine (2 g, 13.7 mmol) was added to an
ampoule charged with N-methyl-2-chloropyridinium iodide (12.23 g,
47.9 mmol), potassium carbonate (18.91 g, 136.8 mmol) in acetonitrile
(75 mL) and the mixture was heated at 808C for 12 h. After cooling to
room temperature the mixture was filtered and the residue was washed
with diethyl ether (20 mL) and dried under vacuum. The residue was
then dissolved in an aqueous solution of HCl (150 mL, 2m), filtered, and
the solution washed with ethyl acetate (6ꢃ50 mL) before the aqueous
layer was basified to pH 14 with aqueous NaOH (5m). Upon adding di-
ethyl ether (50 mL) to the solution, an oily brown solid formed at the in-
terface, which was collected by filtration, dissolved in MeOH, dried over
MgSO4 and the volatiles were removed under reduced pressure to give 9
as a brown oil (yield=4.67 g, 81%). 1H NMR (270 MHz, [D3]MeCN):
d=2.77–2.79 (m, 6H; CH2), 3.22–3.25 (m, 15H; CH2 and CH3), 5.60 (td,
and py-H5); 13C NMR (100 MHz, CD3CN): d=38.1 (CH2), 39.3 (CH3),
49.4 (CH2), 108.5 (py-C2), 111.0 (py-C4), 139.4 (py-C5), 141.2 (py-C3),
150.9 ppm (py-C1).
Complex 14: [RhCl(CO)2]2 (20 mg, 0.051 mmol) was added to a Schlenk
tube containing a solution of 1 (17 mg, 0.104 mmol) in toluene (2 mL)
and the solution was stirred for 5 min at 258C. The volatiles were re-
moved under reduced pressure to give 14 as a yellow-white powder
(yield=35 mg, 95%). 1H NMR (500 MHz, [D8]toluene): d=1.50 (s, 9H;
tBu), 3.65 (s, 3H; NCH3), 5.63–5.65 (m, 1H; py-H4), 6.40 (d, J
ACHTUNGTRENNUNG
6 Hz, 1H; py-H5), 6.58–6.60 (m, 1H; py-H3), 6.81 ppm (d, J
ACHTUNGTRENNUNG
1H; py-H2); 13C NMR (125 MHz, [D8]toluene): d=32.8 (CCH3), 44.4
(NCH3), 57.1 (CCH3), 108.0 (py-C4), 122.4 (py-C5), 134.6 (py-C3), 140.2
(py-C2), 164.5 (py-C1), 182.0 (d, 1J
1J
ACTHNUGNRTE(NUG Rh,C)=66 Hz; CO); IR (KBr): v¯ =2972, 2071, 1989, 1635, 1584, 1548,
ACHTUNGTNER(NUNG Rh,C)=78 Hz; CO), 183.8 ppm (d,
JACHTUNGTRENNUNG ACHTUNGTRENNUGN
(H,H)=7, 1 Hz, 3H; py-H4), 6.36 (d, J(H,H)=9 Hz, 3H; py-H2), 6.90
1507 cmÀ1; IR ([D8]toluene): v¯ =2071, 1992 cmÀ1; elemental analysis calcd
(%) for C12H16ClN2O2Rh (358.6): C 40.19, H 4.50, N 7.81; found: C 40.11,
H 4.46, N 7.73.
(ddd, JACHTUNGTRENNUNG AHCTUNGTREN(NGUN H,H)=7, 2 Hz,
(H,H)=10, 6, 2 Hz, 3H; py-H3), 7.11 ppm (dd, J
3H; py-H5); 13C NMR (67.5 MHz, [D3]MeCN): d=39.4 (CH3), 47.9
(CH2), 58.1 (CH2), 101.3 (py-C4), 112.6 (py-C2), 136.1 (py-C3), 140.7 (py-
ACTHNUTRGNEUNG
C5), 154.3 ppm (py-C1); MS(ESI): m/z (%): 420.2 (100) [M]+; IR (KBR):
Complex 15: A solution of [NiBr
chloromethane (10 mL) was added to
(DME)] (200 mg, 0.648 mmol) in di-
solution of (194 mg,
v¯ =1645 (s), 1564 (s), 1537 (s), 1450 (m), 1338 (m), 1281 (m), 1189 (m),
1169 (m), 1061 (m), 1048 (m), 1021 cmÀ1 (w); elemental analysis calcd
(%) for C24H33N7 (419.6): C 68.70, H 7.93, N 23.37; found: C 68.60, H
7.90, N 23.26.
a
2
0.648 mmol) in dichloromethane (10 mL) and the solution was stirred at
258C for 12 h. The volatiles were removed under reduced pressure and
the red solid was extracted with dichloromethane (20 mL) to give a red
filtrate. Removal of the volatiles gave a red solid that was washed with
diethyl ether (10 mL) to give 15 as a red powder (yield=220 mg, 66%).
Compound 10: In an analogous procedure to 9, by using and tris(2-ami-
noethyl)amine (5.22 g, 35.7 mmol), N-benzyl-2-chloropyridinium iodide
(35.55 g, 124.9 mmol) and potassium carbonate (49.34 g, 357.0 mmol) in
acetonitrile (200 mL) gave 10 as a brown wax. The ethylacetate extrac-
tion was aided by the addition of brine (50 mL; yield=9.32 g, 40%).
MSACTHNUTRGNEUNG
(TOF ES+): m/z (%): 514.0 (45) [M]+, 516.0 (100) [M+2H]+); ele-
mental analysis calcd (%) for C18H26Br2N4Ni (516.9): C 41.82, H 5.07, N
10.84; found: C 41.89, H 5.14, N 10.80.
Chem. Eur. J. 2009, 15, 11346 – 11360
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
11357

R. E. Douthwaite et al.
Complex 16: By using an analogous method to 15, compound 3 (84.2 mg,
0.284 mmol) and [NiBr2A(DME)] (87.5 mg, 0.284 mmol) give 16 as a dark
green powder (yield=143 mg, 98%). MS
(TOF ES+): m/z (%): 435.0 (5)
[MÀCuÀPF6]+; IR (KBr): v<ꢄ->=1640 (s), 1557 (s), 1530 (s), 1454
(m), 1342 (m), 1261 (m), 1175 (m), 1036 (m), 840 cmÀ1(s); elemental anal-
ysis calcd (%) for C42H45N7CuPF6 (856.4): C 58.90, H 5.30, N 11.45;
found: C 58.80, H 5.21, N 11.37.
CHTUNGTRENNUNG
AHCTUNGTRENNUNG
[MÀBr+2H]+, 297.2 (100) [MÀ2BrÀNi+H]+); elemental analysis calcd
(%) for C18H24Br2N4Ni (514.9): C 42.06, H 4.78, N 10.81; found: C 41.99,
H 4.70, N 10.88.
Complex 21: A solution of 9 (839 mg, 2 mmol) in acetonitrile (10 mL)
was added dropwise to a slurry of zinc triflate (764 mg, 2.1 mmol) in ace-
tonitrile (5 mL) and the reaction mixture was stirred at 258C for 2 h. The
volatiles were removed under reduced pressure and the residue was re-
crystallised from dichloromethane/diethyl ether to give 21 as a white
powder (yield=1.032 g, 64%). 1H NMR (270 MHz, [D3]MeCN): d=3.05
Complex 17: By using an analogous method to 15, compound 5 (127 mg,
0.322 mmol) and [NiBr2ACHTUNGTRENNUNG(DME)] (99.4 mg, 0.322 mmol) give 17 as a dark-
green powder (yield=180 mg, 90%). MSACTHNUTRGNEUNG
(TOFES+): m/z (%): 613.0 (20)
[M+3H]+; elemental analysis calcd (%) for C26H26Br2N4Ni (613.0): C
51.03, H 4.16, N 9.16; found: C 50.94, H 4.28, N 9.14.
(t, J
6.54 (td, J
(H,H)=7, 2, 3H; py-H5), 7.64 ppm (ddd, J
(dd, JACTHNUGRTENNUNG ACHTUTGNREN(NUGN H,H)=9, 7, 2, 3H; py-
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
Complex 18: [PdCl2ACHTUNGTRENNUNG(COD)] (100 mg, 0.35 mmol) and 5 (138 mg,
0.35 mmol) were added to toluene (20 mL) in a Schlenk flask and the so-
lution was heated at 708C with stirring for 2 h to give a red precipitate.
The mixture was filtered and the solid residue was washed with diethyl
ether (2ꢃ20 mL) to give 18 as a dark-red solid (yield=190 mg, 95%).
1H NMR (400 MHz, CDCl3, 298 K): d=3.67 (s, 4H; CH2CH2), 6.31–6.33
H3); 13C NMR (100 MHz, [D3]MeCN): d=41.8 (CH3), 48.6 (CH2), 55.5
(CH2), 110.5 (py-C4), 116.6 (py-C2), 141.6 (py-C3), 142.0 (py-C5),
162.6 ppm (py-C1); MS
ACHTUNGTRENNUNG
(KBr): v¯1640 (s), 1560 (s), 1518 (s), 1459 (s), 1343 (m), 1261 (s), 1221 (s),
1030 cmÀ1 (s); elemental analysis calcd (%) for C26H33O6N7F6S2Zn
(783.1): C 39.87, H 4.25, N 12.52; found: C 40.00, H 4.27, N 12.49.
(m, 2H; py-H4), 6.49 (s, 4H; PhCH2), 6.95 (d, 2J
(H,H)=8 Hz, 2H; py-
2
H2), 7.00 (d, J
(H,H)=7 Hz, 4H; PhCH), 7.10–7.12 (m, 4H; PhCH), 7.16
(d, 2J(H,H)=6 Hz, 2H; PhCH), 7.24 (d, 2J(H,H)=8 Hz, 2H; py-H5),
ACHTUNGTRENNUNG ACHTUNGTRENNUGN
7.33–7.35 ppm (m, 2H; py-H3); 1H NMR (400 MHz, CDCl3, 163 K) d=
Crystallographic studies: Diffraction data were collected at 110 K on a
Bruker Smart Apex diffractometer with MoKa radiation (l=0.71073 ꢁ)
by using a SMART CCD camera. Diffractometer control, data collection
and initial unit-cell determination was performed by using the SMART
programme.[88] Frame integration and unit-cell refinement was carried
out with the SAINTPLUS programme.[88] Absorption corrections were
applied by using SADABS version 2.10.[87] Structures were solved by
using SHELXS-97 and were refined by full-matrix least squares methods
by using SHELXL-97.[89] All non-hydrogen atoms were refined anisotrop-
ically. With the exception of H(1) of 11, which was found by using a dif-
ference map, hydrogen atoms were placed by using a riding model and
included in the refinement at calculated positions.
3.67 (s, 4H; CH2CH2), 6.31–6.33 (m, 2H; py-H4), 6.49 (s, 4H; PhCH2),
2
2
6.95 (d, J
7.10–7.12 (m, 4H; PhCH), 7.16 (d, 2J
2J(H,H)=8 Hz, 2H; py-H5), 7.33–7.35 ppm (m, 2H; py-H3); 13C NMR
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(H,H)=8 Hz, 2H; py-H2), 7.00 (d, J
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
(125 MHz, CDCl3, 298 K): d=53.7 (CH2CH2), 57.9 (PhCH2), 108.6 (py-
C4), 116.7 (py-C2), 128.0 (PhCH), 128.1 (PhCH), 128.1 (PhCH), 136.1
(PhCipso), 137.7 (py-C3), 139.9 (py-C5), 163.2 ppm (py-C1); MS
ACTHNUTRGNE(UNG TOF
ES+): m/z (%): 537.1 (25) [M-Cl+H]+, 499.1 (100) [MÀ2ClÀH]+); ele-
mental analysis calcd (%) for C26H26Cl2N4Pd (571.8): C 54.56, H 4.48, N
9.74; found: C 54.61, H 4.58, N 9.80.
Complex 19: A solution of 9 (315 mg, 0.75 mmol) in acetonitrile (5 mL)
was added to a solution of tetrakis(acetonitrile)copper(I) hexafluoro-
phosphate (280 mg, 0.75 mmol) in acetonitrile (10 mL) and the solution
was stirred at 258C for 12 h. The volatiles were removed under reduced
pressure to give a brown oil which was recrystallised from CH2Cl2/Et2O
The uncoordinated triflate anion of 21 was modelled as disordered over
two positions in a ratio of 76:24 with atoms F(4) and F(4a) constrained
to have equal anisotropic displacement parameters. The solvent of crys-
tallisation was modelled as a disordered mixture of acetonitrile and di-
to give 19 as
(400 MHz, [D3]MeCN): d=2.86–2.88 (m, J
3.06–3.26 (m, 15H; CH2 and CH3), 6.01–6.03 (m, 3H; py-H4), 6.56 (d,
a
light-brown solid (yield 521 mg, 88%). 1H NMR
(H,H)=6, 5 Hz, 6H; CH2),
ethyl ether in an 82:18 ratio, respectively. Atom C
be approximately isotropic.
ACHTUNGERTN(NUNG 26a) was restrained to
AHCTUNGTRENNUNG
Crystal data for 7: Colourless crystals of 7 were grown from vapour diffu-
sion of diethyl ether into an acetone solution of 7. C18H24N4; Mr =296.41;
tetragonal; space group P43212; a=b=9.8908(4), c=16.2853(8); V=
1593.16(12) ꢁ3; Z=4; size 0.27ꢃ0.20ꢃ0.17 mm; 1calcd =1.236 gcmÀ3; T=
JACHTUNGTRENNUNG
(H,H)=10 Hz, 3H; py-H2), 7.17–7.26 ppm (m, 6H; py-H5 and py-H3);
13C NMR (100 MHz, [D3]MeCN): d=40.2 (CH3), 48.9 (CH2), 54.8 (CH2),
105.0 (py-C4), 114.4 (py-C2), 137.9 (py-C3), 141.0 (py-C5). 157.2 ppm (py-
C1); MS
ACHTUNGTRENNUNG
110(2); m
pendent reflections (Rint =0.0355); wR(F2)=0.0900 (all data) and R-
AHCTUNGTREG[NNNU F>2s(F)]=0. 0397.
(MoKa)=0.075 mmÀ1; 2316 reflections measured; 2258 inde-
ACHTUNGTRENNUNG
1564 (s), 1547 (s), 1531 (s), 1470 (w), 1451 (w), 1414 (w), 1360 (w), 1325
(w), 1187 (m), 1170 (w), 1070 (w), 844 cmÀ1 (s); elemental analysis calcd
(%) for C24H33N7CuPF6 (628.1): C 45.90, H 5.30, N 15.61; found: C 45.83,
H 5.20, N 15.79.
Crystal data for 11: Colourless crystals of 11 were grown from evapora-
tion of a methanol solution of 11. C10H17N2I; Mr =292.16; orthorhombic;
space group Pnma; a=14.260(7), b=6.654(3), c=12.825(6) ꢁ; V=
Complex 20: A solution of tetrakis(acetonitrile)copper(I) hexafluoro-
phosphate (157 mg, 0.42 mmol) in acetonitrile (5 mL) was added to a so-
lution of 10 (272 mg, 0.42 mmol) in acetonitrile (15 mL). The solution
was stirred for 2 h and the volatiles were removed under reduced pres-
sure. The crude product was consecutively washed with hexane (3 mL)
and then THF (1 mL). The sample was dried in vacuo to give 20 as a
yellow solid (yield 212 mg, 49%). 1H NMR (400 MHz, [D3]MeCN,
1217.0(10) ꢁ3; Z=4; size 0.15ꢃ0.08ꢃ0.08 mm; 1=1.595 gcmÀ3
298(2); mACTHUNGTRENNNUG
;
T=
(MoKa)=2.595 mmÀ1; 1164 reflections measured; 989 independ-
ent reflections (Rint =0.032); wR(F2)=0.0755 (all data) and R
[F>2s(F)]=
AHCTUNGTRENNUNG
0.039.
Crystal data for 16: Colourless crystals of 16 were grown from evapora-
tion of an acetonitrile solution of 16. C18H24N4Br2Ni; Mr =556.00; ortho-
rhombic; space group P212121; a=9.8785(6), b=11.1592(6), c=
298 K): d=2.85 (dd, J
A
ACHTUNGTRENN(UNG H,H)=6,
5 Hz, 6H, CH2), 5.55 (s, 6H; PhCH2), 5.80 (td, JACHTUNGTRENNNUG
20.9780(12) ꢁ; V=2312.5(2) ꢁ3; Z=4; size 0.25ꢃ0.15ꢃ0.15 mm; 1calcd
=
H4), 6.27 (d, J(H,H)=9 Hz, 3H, py-H2), 6.84 (ddd, J
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
1.597 gcmÀ3
sured; 5280 independent reflections (Rint =0.0367); wR(F2)=0.0447 (all
data) and R[F>2s(F)]=0.0246; absolute structure parameter=0.000(5).
(MoKa)=4.310 mmÀ1; 5742 reflections mea-
; T=110(2); mCAHTUNTGRNUEGN
3H; py-H3), 6.96–6.98 (m, 6H; C6H5), 7.08 (ddd, J
G
1
3H; py-H5), 7.18–7.21 ppm (m, 9H; PhCH); H NMR (500 MHz, CD2Cl2,
AHCTUNGTRENNUNG
220 K): d=2.83 (brs, 6H; CH2), 2.90 (brs, 3H; CH2), 3.13 (brs, 3H;
Crystal data for 18: Colourless crystals of 18 were grown from evapora-
tion of an acetonitrile solution of 18. C26H26N4Cl2Pd·2.5.CH3CN; Mr =
1246.25; triclinic; space group P1; a=11.0952(6), b=15.1574(8), c=
CH2), 4.42 (brd, J
3H; py-H4), 6.00 (d, J
H3), 6.82 (brd, J
(H,H)=13 Hz, 3H; CH2Ph), 6.86 (d, J
PhCH), 6.98 (d, J
N
ACHTUNGTRENUN(NG H,H)=7 Hz,
ACHTUNGTRENNUNG
¯
G
ACHTUNGTRENNUNG
17.8340(9) ꢁ; a=98.7810(10), b=94.8310(10), g=110.6650(10)8; V=
2742.3(3) ꢁ3; Z=2; size 0.18ꢃ0.16ꢃ0.05 mm; 1calcd =1.509 gcmÀ3; T=
ACHTUNGTRENNUNG
110(2); m
pendent reflections (Rint =0.0237); wR(F2)=0.0891 (all data) and R-
ACHTUNGTREN[NUGN F>2s(F)]=0.0453.
(MoKa)=0.899 mmÀ1; 13033 reflections measured; 10958 inde-
ACHTUNGTRENNUNG
(py-C1); MS
N
11358
www.chemeurj.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 11346 – 11360

Strong N-Donor Ligands
FULL PAPER
Crystal data for 20: Colourless crystals of 20 were grown from vapour
diffusion of diethyl ether into an acetonitrile solution of 20.
C42H45N7PF6Cu; Mr =856.36; monoclinic; space group P21/c; a=
17.7982(13), b=10.9498(8), c=20.8145(16) ꢁ; b=101.829(2)8; V=
3970.3(5) ꢁ3; Z=4; size 0.38ꢃ0.09ꢃ0.06 mm; 1calcd =1.433 gcmÀ3; T=
110(2); m
pendent reflections (Rint =0.0581); wR(F2)=0.1339 (all data) and R-
ACHTUNGTRENNUNG[F>2s(F)]=0.0818.
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(MoKa)=0.660 mmÀ1; 9889 reflections measured; 6933 inde-
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¯
space group P1; a=10.0805(6), b=14.6697(9), c=15.0603(9) ꢁ; a=
107.5490(10), b=106.2050(10), g=108.2820(10)8; V=1836.51(19) ꢁ3;
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T=110(2);
mMoKa)=0.859 mmÀ1; 9011 reflections measured; 7060 independent re-
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Received: May 24, 2009
Published online: September 29, 2009
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