N-Triisopropylphenyl-substituted N,Npy,O pincers as supports for mononuclear palladium(II) complexes and hydrogen-bonded dimeric assemblies

Article abstract of DOI:10.1016/j.poly.2013.04.049

Treatment of the sterically bulky 2-(3-biphenyl-2-ol)-6-iminepyridine, 2-(3-C₁₂H₈-2-OH)-6-(CHN(2,4,6-i-Pr₃C ₆H₂))C₅H₃N (HL1_tripp), with Pd(OAc)₂ or (MeCN)₂PdCl₂ results in deprotonation of HL1_tripp to afford the discrete square planar O,N_py,N-pincer complexes, [(L1_tripp)Pd(OAc)] (1) and [(L1_tripp)PdCl] (2) respectively, in good yield; conversion of 1 directly to 2 using aqueous sodium chloride or to [(L1_tripp)PdI] (3) using aqueous sodium iodide has been demonstrated. Selective reduction of the imino unit in HL1_tripp with LiAlH₄ proceeds smoothly to yield the 2-(3-biphenyl-2-ol)-6-methylaminepyridine, 2-(3-C₁₂H ₈-2-OH)-6-(CH₂-NH(2,4,6-i-Pr₃C ₆H₂))C₅H₃N (HL2_tripp), which on reaction with Pd(OAc)₂ at low temperature gives [(L2 _tripp)Pd(OAc)] (4) as the sole product. Complex 4 exists as a dimeric species in the solid state in which two square planar monomers are linked together by two intermolecular NH_amine?O_acetate interactions resulting in a Pd?Pd separation of 6.255 ?. The corresponding chloride complex, [(L2_tripp)PdCl] (5), formed by reaction of 4 with aqueous sodium chloride, also exists as a dimeric assembly in the solid state but in this case the presence of two intermolecular NH _amine?O_phenolate interactions has the effect of compressing the palladium-palladium separation to 3.2580(11) ?. Single crystal X-ray diffraction studies have been performed on 1, 2·CH ₂Cl₂, 2·C₆H₆, 3, 4 and 5.

Full text of DOI:10.1016/j.poly.2013.04.049

Polyhedron 59 (2013) 124–132
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
N-Triisopropylphenyl-substituted N,Npy,O pincers as supports for
mononuclear palladium(II) complexes and hydrogen-bonded dimeric
assemblies
⇑
Warren B. Cross, Eric G. Hope, Gregory Forrest, Kuldip Singh, Gregory A. Solan
Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Treatment of the sterically bulky 2-(3-biphenyl-2-ol)-6-iminepyridine, 2-(3-C12H8-2-OH)-6-
(CH@N(2,4,6-i-Pr3C6H2))C5H3N (HL1tripp), with Pd(OAc)2 or (MeCN)2PdCl2 results in deprotonation of
HL1tripp to afford the discrete square planar O,Npy,N-pincer complexes, [(L1tripp)Pd(OAc)] (1) and
[(L1tripp)PdCl] (2) respectively, in good yield; conversion of 1 directly to 2 using aqueous sodium chloride
or to [(L1tripp)PdI] (3) using aqueous sodium iodide has been demonstrated. Selective reduction of the
imino unit in HL1tripp with LiAlH4 proceeds smoothly to yield the 2-(3-biphenyl-2-ol)-6-methylamine-
pyridine, 2-(3-C12H8-2-OH)-6-(CH2-NH(2,4,6-i-Pr3C6H2))C5H3N (HL2tripp), which on reaction with
Pd(OAc)2 at low temperature gives [(L2tripp)Pd(OAc)] (4) as the sole product. Complex 4 exists as a
dimeric species in the solid state in which two square planar monomers are linked together by two inter-
molecular NHamineÁ Á ÁOacetate interactions resulting in a PdÁ Á ÁPd separation of 6.255 Å. The corresponding
chloride complex, [(L2tripp)PdCl] (5), formed by reaction of 4 with aqueous sodium chloride, also exists as
a dimeric assembly in the solid state but in this case the presence of two intermolecular NHamineÁ Á ÁOphe-
nolate interactions has the effect of compressing the palladium–palladium separation to 3.2580(11) Å. Sin-
gle crystal X-ray diffraction studies have been performed on 1, 2ÁCH2Cl2, 2ÁC6H6, 3, 4 and 5.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 5 April 2013
Accepted 27 April 2013
Available online 6 May 2013
Keywords:
2-(3-Biphenyl-2-olate)-6-iminepyridine
2-(3-Biphenyl-2-olate)-6-
methylaminepyridine
Palladium
N-Triisopropylphenyl-substituted
Hydrogen bonding
Self-assembly
1. Introduction
it was found that the coordinated secondary amine in L2 could
indeed serve as a directional hydrogen bond donor in this case gen-
Recent years have seen a surge of interest in pyridine-based
pincer-type complexes due, in large measure, to their applications
in a variety of fields including organic synthesis, homogeneous
catalysis, bond activation, and design of new materials [1–3]. The
electronic and steric flexibility offered by the exterior donor atoms
of the terdentate ligand coupled with an appreciation of the aro-
matisation-dearomatisation processes that can occur at the pyri-
dine core during certain bond activations has no doubt lent
further impetus to the area [4–8].
erating dimeric palladium(II) assemblies linked by two intermolec-
ular NamineHÁ Á ÁOphenolate interactions [12].
To probe the scope of this chemistry and to potentially improve
the solubility of the resultant dimeric assemblies, we are con-
cerned in this note with the synthesis of palladium(II) acetate
and chloride complexes bound by the N-2,4,6-triisopropylphenyl
(tripp) derivative of L2. For purposes of comparison we also report
the corresponding coordination chemistry of imine-containing
L1tripp along with full details of the synthetic procedures employed
As part of a general study directed towards developing new ste-
rically encumbered N,Npy,O pincer ligands that can support a range
of metal-mediated catalytic processes [9–12], we have recently
been interested in adding a hydrogen bonding capacity to the role
of the pincer [13]. It was envisaged that by introducing suitably
positioned hydrogen bond donor (D) and acceptor (A) moieties
within a sterically sheltered N,Npy,O-metal pocket, self-dimerisa-
tion or non-covalent substrate binding could be promoted. As a
preliminary investigation into the palladium(II) chemistry of
monoanionic L1 and L2 (Fig. 1, Ar = 2,4,6-Me3C6H2, 2,6-i-Pr2C6H3),
to prepare HL1tripp and HL2tripp.
2. Results and discussion
The 2-(3-biphenyl-2-ol)-6-iminepyridine, 2-(3-C12H8-2-OH)-6-
(CH@N(2,4,6-i-Pr3C6H2))C5H3N (HL1tripp), has been prepared in
reasonable yield by the condensation reaction of 2-(3-biphenyl-
2-ol)-6-formylpyridine with 2,4,6-triisopropylaniline (Scheme 1).
2-(3-Biphenyl-2-ol)-6-formylpyridine is accessible via sequential
Suzuki coupling and deprotection reactions from 2-methoxybi-
phenyl-3-ylboronic acid and 2-bromo-6-formylpyridine using gen-
eral methodologies we have described elsewhere [9,12]. The imino
unit in HL1tripp could be readily reduced by addition of lithium
⇑
Corresponding author. Tel.: +44 1162 522 096; fax: +44 1162 523 789.
E-mail address: gas8@leicester.ac.uk (G.A. Solan).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.04.049

W.B. Cross et al. / Polyhedron 59 (2013) 124–132
125
moiety in reduced HL2tripp can be seen as singlet for the methylene
protons (d 4.20) and a broad singlet for the NH proton at d 3.41 in
the 1H NMR spectrum.
Reaction of HL1tripp with either Pd(OAc)2 at 60 °C in toluene or
(MeCN)2PdCl2 in tetrahydrofuran at room temperature gave, on
work-up, [(L1tripp)Pd(OAc)] (1) and [(L1tripp)PdCl] (2), respectively,
in good yield (Scheme 2). Alternatively, 1 can be converted to 2 in
near quantitative yield by treatment of 1 with aqueous sodium
chloride followed by extraction into chloroform. Similarly, reaction
of 1 with aqueous sodium iodide gives [(L1tripp)PdI] (3). Complexes
1–3 are all air stable and have been characterised using a combina-
tion of FAB mass spectrometry, IR and 1H NMR spectroscopy and
elemental analyses (see experimental section). In addition, crystals
of each complex have been the subject of single crystal X-ray dif-
fraction studies.
A perspective view of 1 is given in Fig. 2; selected bond dis-
tances and angles are collected in Table 1. There are two pseudo
‘‘non-superimposable’’ mirror images (molecules A and B) within
the asymmetric unit with the most noticeable structural difference
between the two molecules being the relative inclination of the 3-
phenyl groups (vide infra). The structure consists of a single palla-
dium centre bound by a monoanionic 2-(3-biphenyl-2-olate)-6-
iminepyridine ligand which binds in a tridentate fashion along
with a monodentate O-bound acetate to complete a distorted
square planar geometry. Within the N,N,O-ligand there are both
5- and 6-membered chelate rings with the bite angle for the 6-
membered ring being more compatible with the geometrical
requirements of the palladium(II) centre [O(1)–Pd(1)–N(1)6-mem-
O-
N
O-
N
H
H
HN
Ar
N
Ar
H
L1
L2
Fig. 1. Monoanionic 2-(3-biphenyl-2-olate)-6-iminepyridine (L1) and 2-(3-biphe-
nyl-2-olate)-6-methylaminepyridine (L2).
aluminium hydride to yield the 2-(3-biphenyl-2-ol)-6-methyl-
aminepyridine, 2-(C12H8-2-OH)-6-(CH2-NH(2,4,6-i-Pr3C6H2))C5H3-
N (HL2tripp). Both HL1tripp and HL2tripp have been characterised
using a combination of electrospray mass spectrometry, IR, 1H
NMR and 13C NMR spectroscopy (see experimental section).
Compounds, HL1tripp and HL2tripp, either display protonated
molecular ions or peaks corresponding to their sodium adduct ions,
(M+Na)+, in their electrospray mass spectra. The phenolic hydrogen
atoms in both compounds undergo strong hydrogen bonding inter-
actions as evidenced by downfield shifted signals for the OH pro-
tons (range: d 14.2–14.8) in their 1H NMR spectra and broad
m
(OH) absorption bands centred at ca. 2600 cmÀ1 in their IR spec-
tra. Crystal structures of a series of related compounds support
these observations highlighting the presence of intramolecular
OHÁ Á ÁNpyridine hydrogen bond interactions in the solid state
[9,12,14]. In the 1H NMR spectrum of imine-based HL1tripp, the
CH@N proton is seen as a singlet at d 8.35 with the corresponding
93.8(3)A, 94.0(3)B° versus N(2)–Pd(1)–N(1)5-membered
bered
82.6(4)A, 83.4(4)B°]. Some twisting within the backbone of the
N,N,O-ligand is apparent which is most noticeable on inspection
of the relative inclination of the neighbouring phenolate and
13
imino carbon atom appearing at d 161.0 in its C NMR spectrum;
the
m
(CN)imine stretch is observable at 1649 cmÀ1. The CH2–NH
(i)
(ii), (iii)
OH
N
H
OH
N
H
OH
N
Pri
Pri
Pri
Pri
H
H
Pri
Pri
N
O
N
H
HL2tripp
HL1tripp
Scheme 1. Reagents and conditions: (i) 2,4,6-i-Pr3C6H2NH2, ethanol, 40 °C, (ii) LiAlH4, THF, À78 °C; (iii) H2O.
Pri
Pri
N
N
N
N
Pd
(i)
O
(iv)
Pd
O
Pri
Pri
OAc
I
Pri
Pri
1
3
(iii)
HL1tripp
Pri
N
N
(ii)
Pd
O
Pri
Cl
Pri
2
Scheme 2. Reagents and conditions: (i) Pd(OAc)2, toluene, 60 °C; (ii) (MeCN)2PdCl2, THF, RT; (iii) NaCl(aq), CHCl3, RT; (iv) NaI(aq), CHCl3, RT.

126
W.B. Cross et al. / Polyhedron 59 (2013) 124–132
Fig. 2. Molecular structure of 1 (molecule A) including a partial atom numbering scheme. All hydrogen atoms have been omitted for clarity.
Table 1
intermolecular contacts of note. Similar structural features can be
seen in the analogues [{2-(3-C12H8-2-O)-6-CH@N(Ar)C5H3-
N}Pd(OAc)] (Ar = 2,4,6-Me3C6H2, 2,6-i-Pr2C6H3) [12].
Selected bond distances (Å) and angles (°) for 1.
Molecule A
Molecule B
The molecular structures of halide-containing 2 [as both the
dichloromethane (2ÁCH2Cl2) and benzene (2ÁC6H6) solvates] and 3
are closely related and will be discussed together. In 2ÁC6H6 there
are two independent molecules in the unit cell (molecules A and
B) while in 3 there are three (molecules A, B and C); the main dif-
ferences between A, B and C can be attributed to a combination of
factors including the relative inclination of the N-aryl groups, the
3-phenyl groups and the inter-pyridine-phenolate plane angle.
Perspective views of 2ÁCH2Cl2 and 3 are given in Figs. 3 and 4; se-
lected bond distances and angles are collected for all structures in
Tables 2 and 3. Like 1 each structure consists of single palladium
centre bound by a tridentate 2-(3-biphenyl-2-olate)-6-iminepyri-
dine ligand but differs in that a halide [2 (Cl), 3 (I)] now fills the site
that was occupied by an acetate oxygen atom to complete a dis-
torted square planar geometry. The bite angle displayed by the
6-membered chelate ring formed by the N,N,O ligand is again bet-
ter matched to the geometrical requirements of the palladium(II)
centre [O(1)–Pd(1)–N(1)6-membered 92.71(11) (2ÁCH2Cl2), 93.0(4)A,
91.6(3)B (2ÁC6H6), 90.1(3)A, 90.9(3)B, 92.0(3)C° (3) versus N(2)–
Pd(1)–N(1)5-membered 82.28(12) (2ÁCH2Cl2), 83.5(4)A, 80.6(4)B
(2ÁC6H6), 82.6(3)A, 81.3(3)B, 81.4(4)C° (3)]. The flexibility of the
N,N,O ligand backbone is again evident with the relative inclina-
tion of the neighbouring phenolate and pyridine planes varying
anywhere between 2.6(19) and 28.4(17)° [tors. N(1)–C(13)–C(2)–
C(1) 17.5(5) (2ÁCH2Cl2), 2.6(19)A, 28.4(17)B (2ÁC6H6), 24.9(16)A,
21.3(15)B, 23.3(14)C° (3)]. Replacing an O-bound acetate in 1 for
Bond lengths
Pd(1)–O(1)
Pd(1)–O(2)
Pd(1)–N(1)
Pd(1)–N(2)
C(18)–N(2)
C(6)–C(7)
1.948(8)
1.985(7)
1.970(9)
1.980(9)
1.263(14)
1.470(18)
1.256(14)
1.211(15)
1.946(7)
1.994(7)
1.947(9)
1.978(9)
1.279(14)
1.476(18)
1.262(14)
1.222(13)
C(34)–O(2)
C(34)–O(3)
Bond angles
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–O(1)
O(1)–Pd(1)–O(2)
N(1)–Pd(1)–O(2)
N(2)–Pd(1)–O(2)
82.6(4)
93.8(3)
88.7(3)
175.1(3)
95.0(3)
83.4(4)
94.0(3)
87.6(3)
177.8(3)
95.0(3)
pyridine planes [tors. N(1)–C(13)–C(2)–C(1) 10.2(17)A, 9.6(17)B°].
Of the four bonds to palladium, the Pd(1)–O(2)acetate distance is
among the longest [1.985(7)A, 1.994(7)B Å] while the Pd(1)–
O(1)phenolate distance [1.948(8)A, 1.946(7)B Å] the shortest. The N-
tripp group is inclined up to 15.3° away from orthogonality with
regard to the neighbouring C@Nimine vector presumably, in part,
to avoid any steric interaction with the pendant acetate group.
Likewise the plane of the 3-phenyl group is tilted [tors. C(1)–
C(6)–C(7)–C(12) 44.0(17)A, 39.9(19)B°] with respect to the adjacent
phenolate unit in a manner similar to that observed in complexes
containing coordinated o-phenylphenolates [15]. There are no
Fig. 3. Molecular structure of 2ÁCH2Cl2 including a partial atom numbering scheme. All hydrogen atoms have been omitted for clarity.

W.B. Cross et al. / Polyhedron 59 (2013) 124–132
127
Fig. 4. Molecular structure of 3 (molecule A) including a partial atom numbering scheme. All hydrogen atoms have been omitted for clarity.
Table 2
Selected bond distances (Å) and angles (°) for 2ÁCH2Cl2 and 2ÁC6H6.
show some variation in the degree of tilting with respect to the
adjacent phenolate groups [tors. C(1)–C(6)–C(7)–C(12) 33.9(6)
(2ÁCH2Cl2), 55.7(19)A, 31.0(19)B (2ÁC6H6), 50.9(16)A, 46.2(14)B,
42.6(15)C° (3)]. There are no intermolecular contacts of note. The
closest structural comparators to 2 and 3 are [{2-(3-C12H8-2-O)-
6-CH@N(Ar)C5H3N}PdCl] (Ar = 2,4,6-Me3C6H2, 2,6-i-Pr2C6H3) in
which similar features are apparent [12].
2ÁCH2Cl2
2ÁC6H6
Molecule A
Molecule B
Bond lengths
Pd(1)–O(1)
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–Cl(1)
C(18)–N(2)
C(6)–C(7)
1.958(2)
1.961(7)
1.949(8)
1.992(8)
2.290(3)
1.283(13)
1.479(15)
1.965(7)
1.953(8)
2.012(9)
2.290(3)
1.250(12)
1.442(16)
1.973(3)
2.007(3)
2.2975(10)
1.280(5)
1.478(5)
The halide complexes, 2 and 3, both display molecular ion peaks
in their FAB mass spectra along with fragmentation peaks corre-
sponding to the loss of a chloride or an iodide, while acetate-con-
taining 1 instead displays a M-OAc fragmentation peak but no
parent peak. The imine stretching frequencies for 1–3 all shift by
ca. 30 cmÀ1 to lower wavenumber on imine-coordination (in com-
parison with free HL1tripp) as is seen in related palladium(II) com-
plexes [16]. In all three complexes, three distinct doublets of equal
intensity (6:6:6) are seen for the isopropyl methyl groups in their
1H NMR spectra implying free rotation for the para-isopropyl group
while the inequivalency of the ortho-isopropyl methyl groups sug-
gests restricted rotation about the N-aryl bond in solution. The ace-
tate methyl group in 1 can be seen at d 1.56 in its 1H NMR spectrum
with the MeC(O)O carbon atoms observable at d 176.4 in the 13C
NMR spectrum. In addition strong bands assignable to the sym-
Bond angles
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–O(1)
N(2)–Pd(1)–Cl(1)
O(1)–Pd(1)–Cl(1)
N(1)–Pd(1)–Cl(1)
N(2)–Pd(1)–O(1)
82.28(12)
92.71(11)
96.03(9)
88.98(7)
178.31(9)
174.57(11)
83.5(4)
93.0(4)
94.0(3)
89.9(2)
173.9(2)
175.2(4)
80.6(4)
91.6(3)
97.3(3)
90.6(2)
177.5(3)
170.4(3)
Table 3
Selected bond distances (Å) and angles (°) for 3.
Molecule A
Molecule B
Molecule C
Bond lengths
Pd(1)–O(1)
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–I(1)
C(18)–N(2)
C(6)–C(7)
metric and asymmetric m(COO) vibrations in 1, are in agreement
1.963(7)
1.992(8)
2.013(8)
2.5807(12)
1.302(11)
1.527(18)
1.964(6)
1.982(8)
2.015(8)
2.5852(12)
1.254(11)
1.431(14)
1.997(6)
1.986(9)
2.016(8)
2.5861(12)
1.289(12)
1.469(16)
with those expected for monodentate acetate ligands [17].
Complex [(L2tripp)Pd(OAc)] (4) could be prepared in good yield
by treating HL2tripp with Pd(OAc)2 at 0 °C (Scheme 3). Notably, if
the reaction was conducted at higher temperature the yield of 4
was found to significantly drop with imine 1 proving a competitive
side product [18]. Conversion of 4 to [(L2tripp)PdCl] (5) could be
readily achieved by treatment with aqueous sodium chloride at
room temperature. Complexes 4 and 5 proved highly soluble in
aromatic and chlorinated organic solvents and have been charac-
terised using a combination of FAB mass spectrometry, IR and 1H
NMR spectroscopy and elemental analyses (see experimental
section).
Bond angles
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–O(1)
N(2)–Pd(1)–I(1)
O(1)–Pd(1)–I(1)
N(1)–Pd(1)–I(1)
N(2)–Pd(1)–O(1)
82.6(3)
90.1(3)
96.4(2)
90.9(2)
179.0(3)
171.0(3)
81.3(3)
90.9(3)
97.0(2)
90.7(2)
178.1(2)
170.8(3)
81.4(4)
92.0(3)
96.8(3)
89.6(2)
174.9(3)
173.0(3)
In the electrospray mass spectra of 4 and 5 fragmentation peaks
corresponding to the loss of an acetate or chloride group from both
dimeric and monomeric species are evident, respectively. The NH
proton in each complex takes the form of a broad triplet (4) or sin-
glet (5) resonance in the 1H NMR spectra and is markedly shifted
downfield compared to that observed in free HL2tripp (from d
3.41 to d 7.58 (4) or d 5.91 (5)), supportive of both metal coordina-
tion and the probable onset of hydrogen bonding interactions. The
PyCH2 protons in the 1H NMR spectra for 4 and 5 are inequivalent
and appear as two doublet of doublets attributable to mutual
a chloride in 2 appears to have little effect on the trans Pd–N(1)pyr-
idine distance [1.970(9)A, 1.947(9)B Å (1) versus 1.973(3) (2ÁCH2Cl2),
1.949(8)A, 1.953(8)B Å (2ÁC6H6)], although a modest elongation is
apparent for iodide-containing
3
[1.992(8)A, 1.982(8)B,
1.986(9)C Å]. Despite the absence of a more sterically bulky acetate
ligand (1), the N-aryl groups in chloride 2 and iodide 3 can be in-
clined up to 19.2° away from orthogonality [tors. C(18)–N(2)–
C(19)–C(20) 79.0(5) (2ÁCH2Cl2), 75.7(13)A, 70.5(16)B (2ÁC6H6),
82.1(13)A, 86.9(12)B, 70.8(12)C° (3)]; the 3-phenyl groups also

128
W.B. Cross et al. / Polyhedron 59 (2013) 124–132
O
N
Pd
Pri
Pri
Pri
Pri
Pri
O
N
H
O
H
N
N
O
Cl
Pri
H
O
(ii)
(i)
Pri
N
Pd
Pri
Pd
O
HL2tripp
Pri
Pri
Cl
N
Pd
N
O
H
N
O
Pri
Pri
5
4
Scheme 3. Reagents and conditions: (i) Pd(OAc)2, toluene, 0 °C; (ii) NaCl(aq), CHCl3, RT.
coupling (2JHH 17.0–17.8 Hz) and coupling to the NH proton (3JHH
1.9–8.3 Hz). Each ortho-isopropyl-methyl group in 4 and 5 are also
inequivalent leading to four separate doublets consistent with re-
stricted rotation around a pyramidal NH–Pd bond. To identify the
nature of the NH hydrogen bonding interactions and likely dimeric
structure adopted in 4 and 5, single crystals of each complex were
the subject of X-ray determinations.
Views of 4 and 5 are shown in Figs. 5 and 6; selected bond
distances and angles are listed in Tables 4 and 5. The structure
of 4 comprises two square planar (L2tripp)Pd(OAc) monomeric
units linked together by two NamineHÁ Á ÁOacetate hydrogen bonding
interactions [N(2)Á Á ÁO(3A) 2.919 Å] [19] to form a dimeric assem-
bly in which the palladium centres are separated by a distance of
6.255 Å. Within each monomeric unit, L2tripp adopts a tridentate
bonding mode and the acetate binds as a monodentate O-bound
ligand. As with 1–3, the phenolate and pyridyl units within the
N,N,O ligand are not co-planar [tors. N(1)–C(13)–C(2)–C(1)
15.5(5)°] but are nevertheless closer to co-planarity than that
found in the previously reported dimeric species [{2-(3-C12H8-
tate oxygen that acts as the hydrogen bond acceptor. It is unclear
as to the origin of this variation in intermolecular OÁ Á ÁHN inter-
action but crystal packing effects may play a role. It is worthy
of note, that numerous crystals of 4 have been subject to single
crystal X-ray diffraction studies each revealing the structure
described.
In the structure of 5, which contains only one type of potential O-
based hydrogen bond acceptor, dimerisation does indeed occur but
in this case makes use of two intermolecular NamineHÁ Á ÁOphenolate
interactions [N(2)Á Á ÁO(1A) 3.008 Å] to link the monomeric units.
Moreover, these (L2tripp)PdCl units align in an anti-parallel fashion
allowing two metal centres to approach to
a distance of
3.2580(11) Å; a separation close to the sum of the van der Waals radii
(3.26 Å) and similar to that found in the mesityl and 2,6-diisopropyl-
phenyl analogues [12], but longer than that observed in dimeric
[Pd(OPh)2(pyrrolidine)2] (PdÁ Á ÁPd 3.0960(3) Å) in which four inter-
molecular NHÁ Á ÁO interactions exist [20]. The structural features
within the monomeric unit in 5 resemble that in 4 but it is evident
that the increased twisting of the phenolate unit with respect to
the adjacent pyridine [tors. N(1)–C(13)–C(2)–C(1) 15.5(5) (4),
27.6(6)° (5)] makes the phenolate oxygen atom more accessible to
undergo the observed intermolecular NHÁ Á ÁOphenolate interaction.
2-O)-6-(CH2-NH(Ar)C5H3N}Pd(OAc)]
[Ar = 2,6-i-Pr2C6H3
(28.9(9)°), 2,4,6-Me3C6H2 (25.0(11)°)] [12]. Indeed, in these latter
complexes it is the phenolate oxygen atom rather than the ace-
Fig. 5. Molecular structure of 4 including a partial atom numbering scheme. All
Fig. 6. Molecular structure of 5 including a partial atom numbering scheme. All
hydrogen atoms, apart from H2, have been omitted for clarity.
hydrogen atoms, apart from H2, have been omitted for clarity.

W.B. Cross et al. / Polyhedron 59 (2013) 124–132
129
Table 4
drying agents [21] or were employed directly from a Solvent Puri-
fication System (Innovative Technology, Inc). The electrospray (ESI)
mass spectra were recorded using a micromass Quattra LC mass
spectrometer with methanol as the matrix while FAB mass spectra
were recorded on Kratos Concept spectrometer with NBA as ma-
trix. The infrared spectra were recorded in the solid state with Uni-
versal ATR sampling accessories on a Perkin Elmer Spectrum One
Selected bond distances (Å) and angles (°) for 4.
Bond lengths
Pd(1)–O(1)
Pd(1)–O(2)
Pd(1)–N(1)
Pd(1)–N(2)
C(18)–N(2)
C(6)–C(7)
C(34)–O(2)
C(34)–O(3)
Pd(1)Á Á ÁPd(1A)
1.951(2)
2.013(2)
1.970(3)
2.041(3)
1.492(4)
1.486(5)
1.276(4)
1.225(4)
6.225
FTIR instrument. NMR spectra were recorded on
a Bruker
DRX400 spectrometer at 400.13 (1H) and 100.61 MHz (13C) at
ambient temperature unless otherwise stated; chemical shifts
(ppm) are referred to the residual protic solvent peaks and cou-
pling constants are expressed in hertz (Hz). Melting points (mp)
were measured on a Gallenkamp melting point apparatus (model
MFB-595) in open capillary tubes and were uncorrected. Elemental
analyses were performed at the Science Technical Support Unit,
London Metropolitan University.
Bond angles
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–O(1)
N(2)–Pd(1)–O(2)
O(1)–Pd(1)–O(2)
N(1)–Pd(1)–O(2)
N(2)–Pd(1)–O(2)
85.61(10)
94.71(10)
94.18(9)
85.62(9)
173.92(9)
94.18(9)
The reagent lithium aluminium hydride was purchased from Al-
drich Chemical Co. and used without further purification. The com-
pounds tetrakis(triphenylphosphine)palladium(0) [22], 2-(3-
biphenyl-2-ol)-6-formylpyridine [12], 2,4,6-triisopropylaniline
[23] and (MeCN)2PdCl2 [24] were prepared using literature proce-
dures. All other chemicals were obtained commercially and used
without further purification.
The ‘A’ atoms denote the neighbouring palladium atom in the dimer.
Table 5
Selected bond distances (Å) and angles (°) for 5.
Bond lengths
Pd(1)–O(1)
Pd(1)–Cl(1)
Pd(1)–N(1)
Pd(1)–N(2)
C(18)–N(2)
C(6)–C(7)
1.985(3)
2.2962(14)
1.980(3)
2.068(3)
1.507(5)
1.479(6)
3.2580(11)
4.2. Synthesis of 2-(3-C12H8-2-OH)-6-(CH@N(2,4,6-i-Pr3C6H2))C5H3N
(HL1tripp
)
To a round bottomed flask equipped with stir bar was added 2-
(3-biphenyl-2-ol)-6-formylpyridine (1.207 g, 4.38 mmol), 2,4,6-tri-
isopropylaniline (1.450 g, 6.62 mmol) and ethanol (15 ml). The
suspension was stirred and heated to 40 °C and after 15 min a cat-
alytic amount of formic acid was added. After further stirring at
40 °C overnight the solution was allowed to cool to room temper-
ature and then left to stand overnight to form a yellow precipitate.
The precipitate was filtered, washed with ethanol and further dried
under reduced pressure to give HL1tripp as a yellow solid (0.750 g,
42%). Mp: 114–117 °C. 1H NMR (400 MHz, CDCl3): d 1.16 (d, JHH 6.8,
12H, CH(CH3)2), 1.28 (d, JHH 6.9, 6H, CH(CH3)2), 2.80–2.99 (m, 3H,
CH(CH3)2), 7.00 (s, 2H, Ar-H), 7.02 (t, JHH 7.7, 1H, Ar-H), 7.32 (t,
JHH 7.4, 1H, Ar-H), 7.40 (dd, JHH 7.4, 1.7, 1H, Ar-H), 7.42 (t, JHH 7.3,
1H, Ar-H), 7.63 (d, JHH 1.4, 2H, Ar-H), 7.85 (dd, JHH 8.1, 1.4, 1H,
Py-H), 8.00 (t, JHH 8.1, 1H, Py-H), 8.09 (d, JHH 7.6, 1H, Py-H), 8.19
(dd, JHH 7.6, 0.9, 1H, Ar-H), 8.35 (s, 1H, N@CH), 14.2 (br s, 1H,
OH). 13C{1H} NMR (100 MHz, CDCl3): d 23.5 (CH(CH3)2), 24.2
(CH(CH3)2), 28.1 (CH(CH3)2), 34.1 (CH(CH3)2), 118.9, 119.2, 120.8,
121.0, 121.2, 126.0, 127.0, 128.1, 129.5 (CH), 131.3 (C), 133.0
(CH), 136.8, 138.4 (C), 138.6 (CH),144.9, 146.0, 151.1, 157.1,
158.2 (C), 161.0 (N@C–H). IR (cmÀ1): 2957 (C–H), 2627 (br, OH),
1649 (C@Nimine), 1591 (C@Npyridine). ESIMS: m/z 477 [M+H]+. HRMS
(TOFMS ES+): Calc. C33H37N2O [M+H]+ 477.2906, found 477.2903.
Pd(1)Á Á ÁPd(1A)
Bond angles
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–O(1)
N(2)–Pd(1)–Cl(1)
O(1)–Pd(1)–Cl(1)
N(1)–Pd(1)–Cl(1)
N(2)–Pd(1)–Cl(1)
84.72(13)
91.03(12)
93.53(9)
91.00(8)
177.28(10)
93.52(9)
The ‘A’ atoms have been generated by symmetry: symmetry operation Àx + 2,
Ày + 1, Àz.
Like 1–3 the 3-phenyl groups in 4 and 5 are tilted with respect the
phenolate unit [tors. C(1)–C(6)–C(7)–C(12) 44.0(4) (4), 48.8(6)° (5)].
3. Conclusions
Protonated forms of the tripp-substituted pincer-type ligand L1
and its reduced derivative L2, have been successfully synthesised
and provide a straightforward route to square planar palladium
complexes in which the O,N,N-ligand’s substituents sterically pro-
tect the metal-bound acetate or halide site. The presence of a sec-
ondary amine donor in L2tripp has been shown to promote the self-
assembly of highly soluble dimeric species through either intermo-
lecular NHÁ Á ÁOphenolate or, for the first time, NHÁ Á ÁOacetate hydrogen
bonding interactions. Work is in progress to potentially exploit the
coordinated amine donor in L2 as a directional hydrogen bond do-
nor for a range of small organic acceptors.
4.3. Synthesis of 2-(3-C12H8-2-OH)-6-(CH2-NH(2,4,6-i-
Pr3C6H2))C5H3N (HL2tripp
)
Two Schlenk flasks equipped with stir bars were evacuated and
backfilled with nitrogen. To one of the flasks was added lithium
aluminium hydride (0.219 g, 5.77 mmol) and dry tetrahydrofuran
(10 ml) and the resulting suspension stirred and cooled to 0 °C.
To the second flask was added HL1tripp (0.550 g, 1.15 mmol) and
dry tetrahydrofuran (10 ml) and the contents stirred until dissolu-
tion. The solution of HL1tripp was then transferred via cannular
(dropwise) to the cooled LiAlH4 suspension. The reaction mixture
was allowed to warm to room temperature and stirred for
60 min. Water (1 ml) was carefully added followed by chloroform
(30 ml) and more water (20 ml). The organic phase was separated
and the aqueous layer extracted with chloroform (3 Â 10 ml). All
4. Experimental
4.1. General
All operations, unless otherwise stated, were carried out under
an inert atmosphere of dry, oxygen-free nitrogen using standard
Schlenk and cannula techniques or in a nitrogen purged glove
box. Solvents were distilled under nitrogen from appropriate

130
W.B. Cross et al. / Polyhedron 59 (2013) 124–132
organic extracts were combined and dried over magnesium sulfate.
Filtration followed by removal of the solvent under reduced pres-
sure gave a yellow brown oil which was then dissolved in a small
amount of methanol. On standing at room temperature a cream
precipitate formed which was filtered and dried affording HL2tripp
as a white solid (0.349 g, 63%). Mp: 132–135 °C. 1H NMR (400 MHz,
CDCl3): d 1.23 (d, JHH 6.9, 12H, CH(CH3)2), 1.25 (d, JHH 7.1, 6H,
CH(CH3)2), 2.86 (sept, JHH 7.1, 1H, CH(CH3)2), 3.29 (sept, JHH 7.1,
2H, CH(CH3)2), 3.41 (br s, 1H, HNCH2), 4.20 (s, 2H, HNCH2), 6.96
(s, 2H, Ar-H), 6.99 (t, JHH 7.8, 1H, Ar-H), 7.39–7.48 (m, 5H, Ar-H/
Py-H), 7.66 (dd, JHH 7.4, 0.8, 2H, Ar-H), 7.80–7.90 (m, 3H, Ar-H/
Py-H), 14.8 (br s, 1H, OH). 13C{1H} NMR (100 MHz, CDCl3): d 23.1
(CH(CH3)2), 23.3 (CH(CH3)2), 29.4 (CH(CH3)2), 33.0 (CH(CH3)2),
55.6 (HNCH2), 116.9, 117.5 (CH), 118.0 (C), 118.8, 120.5, 125.9,
126.9, 128.5 (CH), 130.1 (C), 131.4, 137.4 (CH), 137.5, 138.8,
141.8, 143.5, 155.7, 156.3, 156.7 (C). IR (cmÀ1): 2957 (C–H), 2601
(br, OH), 1595 (C@Npyridine). ESIMS (+ve): m/z 501 [M+Na]+. ESIMS
(Àve): m/z 477 [MÀH]À. HRMS (TOFMS ES+): Calc. for C33H39N2O
[M+H]+ 479.3062, found 479.3055.
>260 °C. 1H NMR (400 MHz, CDCl3): d 1.05 (d, JHH 6.9, 6H,
CH(CH3)2), 1.19 (d, JHH 6.9, 6H, CH(CH3)2), 1.33 (d, JHH 6.7, 6H,
CH(CH3)2), 2.83 (sept, JHH 7.0, 1H, CH(CH3)2), 3.20 (sept, JHH 7.0,
2H, CH(CH3)2), 6.81 (dd, JHH 8.4, 7.2, 1H, Ar-H), 6.95 (s, 2H, Ar-H),
7.14 (dd, JHH 7.4, 1.2, 1H, Ar-H), 7.28 (t, JHH 7.4, 2H, Ar-H), 7.45
(dd, JHH 7.2, 1.6, 1H, Ar-H), 7.67 (dd, JHH 7.2, 1.0, 1H, Ar-H), 7.79
(d, JHH 1.4, 1H, Ar-H), 7.81 (d, JHH 1.4, 1H, Ar-H), 7.82 (d, JHH 7.6,
1H, Py-H), 7.97 (s, 1H, N@C-H), 8.12 (dd, JHH 8.7, 7.3, 1H, Py-H),
8.47 (d, JHH 8.4, 1H, Py-H). 13C{1H} NMR (100 MHz, CDCl3): d 22.2
(CH(CH3)2), 22.9 (CH(CH3)2), 23.5 (CH(CH3)2), 27.7 (CH(CH3)2),
33.2 (CH(CH3)2), 115.3 (CH), 119.3 (C), 120.3, 123.7, 125.6, 126.1,
126.6, 127.4, 129.2, 132.9 (CH), 133.5 (C), 136.7 (CH), 138.4,
139.3, 140.6, 147.8, 151.1, 151.5, 160.1 (C), 166.5 (N@CH). IR
(cmÀ1): 2958 (C–H), 1619 (C@Nimine), 1596 (C@Npyridine). FABMS:
m/z 616 [M]+, 581 [MÀCl]+. Anal. Calc. for (C33H35N2OPdCl): C,
64.18; H, 5.71; N, 4.54. Found: C, 64.01; H, 5.72; N, 4.32%.
4.6. Conversion of 1 to [(L1tripp)PdX] (2 X = Cl, 3 X = I)
(a) 2 (X = Cl). A round bottomed flask equipped with stirrer bar,
and open to the air, was loaded with 1 (0.048 g, 0.07 mmol), chlo-
roform (5 ml) and a saturated solution of brine (25 ml) added. After
stirring vigorously at room temperature overnight the red solution
was extracted with chloroform (3 Â 10 ml). All organic extracts
were combined and dried over magnesium sulfate. Following fil-
tering, all volatiles were removed under reduced pressure afford-
ing 2 as a red solid (0.046 g, 99%). The spectroscopic data were
consistent with that given above.
4.4. Synthesis of [(L1tripp)Pd(OAc)] (1)
A Schlenk flask equipped with stir bar was evacuated and back-
filled with nitrogen and loaded with Pd(OAc)2 (0.065 g,
0.29 mmol), HL1tripp (0.137 g, 0.28 mmol) and dry toluene
(10 ml). After stirring at 60 °C overnight, the reaction mixture
was cooled to room temperature and filtered through celite and
the celite cake thoroughly washed with dichloromethane. All vola-
tiles were removed from the filtrate under reduced pressure and
the resultant solid dissolved in the minimum quantity of dichloro-
methane (ca. 1 ml) at which point hexane (ca. 8 ml) was added. The
resulting precipitate was filtered and dried under reduced pressure
forming 1 as a red powder (0.179 g, 96%). Red blocks suitable for an
X-ray diffraction study could be grown by slow diffusion of hexane
into a dichloromethane solution of the complex. Mp: >260 °C. 1H
NMR (400 MHz, CDCl3): d 1.11 (d, JHH 6.9, 6H, CH(CH3)2), 1.26 (d,
JHH 6.9, 6H, CH(CH3)2), 1.40 (d, JHH 6.7, 6H, CH(CH3)2), 1.56 (s, 3H,
O2C-CH3), 2.91 (sept, JHH 6.7, 1H, CH(CH3)2), 3.40 (sept, JHH 6.7,
2H, CH(CH3)2), 6.85 (t, JHH 8.1, 1H, Ar-H), 7.05 (s, 2H, Ar-H), 7.19
(tt JHH 7.3, 1H, Ar-H), 7.30 (t, JHH 7.6, 2H, Ar-H), 7.45 (dd, JHH 7.0,
1.6, 1H, Ar-H), 7.71 (dd, JHH 7.2, 1.0, 1H, Ar-H), 7.75 (d, JHH 1.3,
1H, Ar-H), 7.79 (d, JHH 1.3, 1H, Py-H), 7.91 (dd, JHH 8.7, 1.3, 1H,
Py-H), 8.07 (s, 1H, N@Cimine-H), 8.18 (t, JHH 8.4, 1H, Py-H), 8.55 (d,
JHH 8.4, 1H, Py-H). 13C{1H} NMR (100 MHz, CDCl3): d 22.1 (O2C-
CH3), 22.9 (CH(CH3)2), 24.0 (CH(CH3)2), 25.4 (CH(CH3)2), 29.7
(CH(CH3)2), 34.4 (CH(CH3)2), 115.9 (CH), 120.3 (C), 121.3, 124.5,
126.5, 126.8, 127.5, 128.4, 130.1, 133.4 (CH), 134.5 (C), 137.4
(CH), 139.9, 141.0, 149.2, 152.2, 152.7, 161.5 (C), 166.0 (Nimine-
@CH), 177.4 (O2C-CH3). IR (cmÀ1): 2958 (C–H), 1619 (C@Nimine),
1589 (COO)asymm/C@Npyridine), 1380 (COO)symm. FABMS: m/z 581
[MÀOAc]+. Anal. Calc. for (C35H38N2O3Pd): C, 65.57; H, 5.97; N,
4.37. Found: C, 65.24; H, 6.01; N, 4.18%.
(b) 3 (X = I). A round bottomed flask equipped with stirrer bar
was loaded with 1 (0.103 g, 0.16 mmol), chloroform (5 ml) and a
saturated solution of sodium iodide (25 ml) added. After stirring
vigorously at room temperature overnight the red solution was ex-
tracted with chloroform (3 Â 10 ml). All organic extracts were
combined and dried over magnesium sulfate. Following filtering,
all volatiles were removed under reduced pressure affording 3 as
a red solid (0.111 g, 97%). Orange/red plates of 3 suitable for an
X-ray diffraction study could be grown by slow diffusion of hexane
into a dichloromethane solution of the complex. Mp: >260 °C. 1H
NMR (400 MHz, CDCl3): d 1.09 (d, JHH 6.9, 6H, CH(CH3)2), 1.27 (d,
JHH 6.9, 6H, CH(CH3)2), 1.40 (d, JHH 6.8, 6H, CH(CH3)2), 2.92 (sept,
JHH 7.0, 1H, CH(CH3)2), 3.20 (sept, JHH 7.0, 2H, CH(CH3)2), 6.89
(dd, JHH 8.4, 7.2, 1H, Ar-H), 7.02 (s, 2H, Ar-H), 7.24 (dd, JHH 7.4,
1.8, 1H, Ar-H), 7.37 (t, JHH 7.7, 2H, Ar-H), 7.48 (dd, JHH 7.1, 1.7,
1H, Ar-H), 7.72 (dd, JHH 7.2, 1.0, 1H, Ar-H), 7.82 (d, JHH 1.4, 1H,
Ar-H), 7.84 (d, JHH 1.3, 1H, Ar-H), 7.92 (d, JHH 8.7, 1H, Py-H), 8.05
(s, 1H, N@C-H), 8.24 (dd, JHH 8.7, 7.2, 1H, Py-H), 8.61 (d, JHH 8.2,
1H, Py-H). 13C{1H} NMR (100 MHz, CDCl3): d 21.5 (CH(CH3)2),
23.0 (CH(CH3)2), 23.9 (CH(CH3)2), 28.7 (CH(CH3)2), 33.1 (CH(CH3)2),
115.4, 118.8, 120.8, 123.3, 125.6, 126.3, 126.5, 127.6, 129.4, 132.8
(CH), 134.0 (C), 137.1 (CH), 138.3, 138.7, 143.7, 147.9, 150.6,
150.9, 159.6 (C), 167.1 (N@CH). IR (cmÀ1): 2961 (C–H), 1611
(C@Nimine), 1589 (C@Npyridine). FABMS: m/z 709 [M]+, 581 [MÀI]+.
Anal. Calc. for (C33H35N2OPdI): C, 55.91; H, 4.98; N, 3.95. Found:
C, 56.01; H, 4.77; N, 4.21%.
4.5. Synthesis of [(L1tripp)PdCl] (2)
A Schlenk flask equipped with stir bar was evacuated and back-
filled with nitrogen and loaded with (MeCN)2PdCl2 (0.062 g,
0.23 mmol), HL1tripp (0.126 g, 0.254 mmol) and tetrahydrofuran
(25 ml). After stirring overnight at room temperature, the solution
was concentrated to ca. 2 ml and hexane (15 ml) added. The resul-
tant precipitate was filtered, washed with hexane and dried under
reduced pressure to give 2 as a red solid (0.124 g, 88%). Orange/red
plates of 2ÁCH2Cl2 suitable for an X-ray diffraction study could be
grown by slow diffusion of hexane into a dichloromethane solution
of the complex. Alternatively, red needles of 2ÁC6H6 could be grown
by prolonged standing in benzene at room temperature. Mp:
4.7. Reaction of HL2tripp with Pd(OAc)2
A Schlenk flask equipped with stir bar was evacuated and back-
filled with nitrogen and loaded with Pd(OAc)2 (0.066 g,
0.29 mmol), HL2tripp (0.136 g, 0.28 mmol) and dry toluene
(10 ml). After stirring at 0 °C (cryostatically controlled) overnight,
the reaction mixture was concentrated to ca. 1 ml at which point
hexane (ca. 8 ml) was added. The resulting precipitate was filtered
and dried under reduced pressure forming 4 as a yellow powder
(0.108 g, 46%). Yellow plates suitable for an X-ray diffraction study
could be grown by slow diffusion of hexane into a dichlorometh-

W.B. Cross et al. / Polyhedron 59 (2013) 124–132
131
ane solution of the complex. Mp: >260 °C. 1H NMR (400 MHz,
CDCl3): d 1.20 (d, JHH 6.8, 3H, CH(CH3)2), 1.21 (d, JHH 7.0, 3H,
CH(CH3)2), 1.22 (d, JHH 6.9, 6H, CH(CH3)2), 1.38 (d, JHH 6.5, 3H,
CH(CH3)2), 1.59 (s, 3H, O2CCH3), 1.70 (d, JHH 6.6, 3H, CH(CH3)2),
2.85 (sept, JHH 6.7, 1H, CH(CH3)2), 3.23 (sept, JHH 6.7, 1H, CH(CH3)2),
4.29 (dd, JHH 17.1, 8.3, 1H, HN-CHaHb), 4.54 (dd, JHH 17.0, 6.9, 1H,
HN-CHaHb), 5.33 (sept, JHH 6.7, 1H, CH(CH3)2), 6.77 (dd, JHH 8.2,
7.3, 1H, Ar-H), 6.91 (d, JHH 2.1, 1H, Ar-H), 6.94 (d, JHH 7.5, 1H, Py-
H), 7.07 (d, JHH 2.0, 1H, Ar-H), 7.19 (tt, JHH 7.3, 2.0, 1H, Ar-H),
7.29 (t, JHH 7.6, 2H, Ar-H), 7.33 (dd, JHH 7.2, 1.7, 1H, Ar-H), 7.54
(dd, JHH 8.5, 1.6,1H, Ar-H), 7.58 (br t, JHH 7.5, 1H, HN-CHaHb), 7.73
(dd, JHH 8.0, 1.4, 2H, Py-H), 7.80 (dd, JHH 8.4,7.4, 1H, Py-H), 7.89
(d, JHH 8.4, 1H, Py-H). 13C{1H} NMR (100 MHz, CDCl3) d 21.4
(H3C–CO2), 22.4 (CH(CH3)2), 22.8 (CH(CH3)2), 23.7 (CH(CH3)2),
23.9 (CH(CH3)2), 25.1 (CH(CH3)2), 27.2 (CH(CH3)2), 27.8 (CH(CH3)2),
33.0 (CH(CH3)2), 62.4 (HN-CH2), 114.3, 114.9, 120.0, 122.7, 122.9,
125.2, 126.4, 128.0, 128.8, 132.1 (CH), 132.7, 134.9 (C), 137.1
(CH), 139.1, 140.0, 141.9, 146.9, 153.4, 159.3, 161.5 (C), 177.8
fusion of hexane into a dichloromethane solution of the complex.
Mp: >260 °C. 1H NMR (400 MHz, CDCl3): d 0.72 (d, JHH 6.8, 3H,
CH(CH3)2), 1.01 (br s, 3H, CH(CH3)2), 1.11 (d, JHH 6.8, 6H, CH(CH3)2),
1.22 (br s, 3H, CH(CH3)2), 1.46 (d, JHH 6.4, 3H, CH(CH3)2), 2.71 (sept,
JHH 6.5, 1H, CH(CH3)2), 3.33 (dd, JHH 17.8, 1.9, 1H, HN-CHaHb), 3.73
(br s, 1H, CH(CH3)2), 4.23 (sept, JHH 6.5, 1H, CH(CH3)2), 5.00 (dd, JHH
17.7, 9.0, 1H, HN-CHaHb), 5.91 (br s, 1H, HN-CH2), 6.54 (t, JHH 7.5,
1H, Ar-H), 6.82 (s, 1H, Ar-H), 6.87 (s, 1H, Ar-H), 7.08 (app t, JHH
7.3, 2H, Ar-H), 7.16 (d, JHH 6.9, 1H, Ar-H), 7.24 (app t, JHH 7.4, 3H,
Ar-H), 7.35 (br s, 2H, Py-H), 7.87 (d, JHH 8.3, 2H, Ar-H). 13C{1H}
NMR (100 MHz, CDCl3): d 22.2 (CH(CH3)2), 22.6 (CH(CH3)2), 22.9
(CH(CH3)2), 23.7 (CH(CH3)2), 24.5 (CH(CH3)2), 27.0 (CH(CH3)2),
27.2 (CH(CH3)2), 32.9 (CH(CH3)2), 64.2 (HN-CH2), 114.3, 114.7
(CH), 117.5 (C), 120.7, 122.4, 125.0, 126.3, 127.7, 129.5, 130.5,
135.9 (CH), 138.7, 138.8, 140.3, 140.5, 145.9, 146.4, 151.5, 164.3
(C). IR (cmÀ1): 3183 (NH), 2955 (CH), 1596 (C@Npyridine). ESIMS
(MeOH): m/z 1196 [M2À2Cl+MeOH], 583 [MÀCl]. FABMS: m/z
1202 [M2ÀCl]+, 618 [M]+, 583 [MÀCl]+. Anal. Calc. for (C33H37N2-
OPdCl): C, 63.98; H, 6.02; N, 4.52. Found: C, 64.12; H, 5.77; N,
4.41%.
(H3C–CO2). IR (cmÀ1): 3224 (NH), 2954 (C–H), 1585 (COOasymm
/
C@Npyridine), 1384 (COOsymm). ESIMS (MeOH): m/z 1196 [M2-
À2OAc+MeOH], 583 [MÀOAc]. FABMS: m/z 643 [M+H]+, 583
[MÀOAc]+. Anal. Calc. for (C35H40N2O3Pd): C, 65.38; H, 6.23; N,
4.36. Found: C, 65.13; H, 6.18; N, 4.42%.
4.9. Crystallographic studies
4.8. Conversion of 4 to [(L2tripp)PdCl] (5)
Data for 1, 2ÁCH2Cl2, 2ÁC6H6, 3, 4 and 5 were collected on a Bru-
ker APEX 2000 CCD diffractometer. Details of data collection,
refinement and crystal data are listed in Table 6. The data were cor-
rected for Lorentz and polarisation effects and empirical absorp-
tion corrections applied. Structure solution by direct methods
and structure refinement based on full-matrix least-squares on F2
employed SHELXTL version 6.10 [25] Hydrogen atoms were in-
cluded in calculated positions (C–H = 0.95–1.00 Å) riding on the
bonded atom with isotropic displacement parameters set to
1.5Ueq(C) for methyl H atoms and 1.2Ueq(C) for all other H atoms.
All non-H atoms were refined with anisotropic displacement
A round bottomed flask equipped with stirrer bar, and open to
the air, was loaded with 4 (0.045 g, 0.07 mmol), chloroform
(5 ml) and a saturated solution of brine (25 ml) added. After stir-
ring vigorously at room temperature overnight the yellow solution
was extracted with chloroform (3 Â 10 ml). All organic extracts
were combined and dried over magnesium sulfate. Following fil-
tering, all volatiles were removed under reduced pressure afford-
ing 5 as a yellowy brown solid (0.043 g, 99%). Yellow blocks
suitable for an X-ray diffraction study could be grown by slow dif-
Table 6
Crystallographic and data processing parameters for 1, 2ÁCH2Cl2, 2ÁC6H6, 3, 4 and 5.
Complex
1
2ÁCH2Cl2
2ÁC6H6
3
4
5
Formula
M
C
71H78Cl2N2O6Pd2 C33H35ClN2OPdÁCH2Cl2 C33H35ClN4O6PdÁ2C6H6 C106H123Cl2I3N6O4Pd3 C35H40N2O3Pd
C34H39Cl3N2OPd
704.42
1367.07
702.41
773.70
2315.90
643.09
Crystal size (mm3)
Temperature (K)
Crystal system
Space group
a (Å)
0.39 Â 0.30 Â 0.05 0.43 Â 0.16 Â 0.06
0.32 Â 0.12 Â 0.06
0.20 Â 0.13 Â 0.07
0.46 Â 0.15 Â 0.08 0.41 Â 0.12 Â 0.03
150(2)
150(2)
150(2)
150(2)
150(2)
orthorhombic
Pbca
150(2)
triclinic
P1
monoclinic
P2(1)/c
24.959(5)
9.2993(19)
14.127(3)
90
99.082(4)
90
3237.8(11)
4
monoclinic
P2(1)/c
33.260(10)
21.331(6)
22.821(7)
90
124.524(6)
90
13340(7)
16
triclinic
monoclinic
P2(1)/c
ꢀ
ꢀ
P1
12.354(9)
14.641(11)
18.486(13)
75.561(14)
89.887(14)
86.015(15)
3230(4)
2
14.135(3)
20.227(5)
20.772(6)
60.961(4)
84.879(6)
71.216(4)
4900(2)
2
16.473(12)
13.926(11)
26.98(2)
90
11.897(4)
10.402(4)
29.135(8)
90
b (Å)
c (Å)
a
(o)
b (o)
90
90
113.491(11)
90
c
(o)
U (Å3)
6189(8)
8
3306.7(19)
4
Z
Dcalc (Mg mÀ3
F(000)
)
1.406
1.441
1.541
6432
0.678
1.570
2328
1.599
1.380
1.415
1412
1440
2672
1448
l
(Mo K
a
) (mmÀ1
)
0.694
0.850
0.636
0.832
Reflections collected
Independent reflections
Rint
27423
13852
0.2089
0/780
24529
6361
0.0744
0/376
51534
13086
0.2631
0/695
38282
18976
0.2088
0/1045
45864
6089
0.0918
0/377
25179
6494
0.10971
0/376
Restraints/parameters
Final R indices (I > 2
r
(I))
R1 = 0.1262
wR2 = 0.2656
R1 = 0.2128
wR2 = 0.3016
R1 = 0.0468
wR2 = 0.1170
R1 = 0.0597
wR2 = 0.1228
1.037
R1 = 0.0880
wR2 = 0.1898
R1 = 0.2300
wR2 = 0.2243
0.806
R1 = 0.0758
wR2 = 0.1447
R1 = 0.1621
wR2 = 0.1670
0.824
R1 = 0.0410
wR2 = 0.0871
R1 = 0.0597
wR2 = 0.0935
0.999
R1 = 0.0515
wR2 = 0.0829
R1 = 0.0904
wR2 = 0.0921
0.923
All data
Goodness-of-fit (GOF) on F2 1.006
(all data)
w(Fo À Fc2)2/
R
w(Fo2)2]
,
w r
À1 = [ 2(Fo)2 + (aP)2],
2
½
Data in common: graphite-monochromated Mo
Ka
radiation, k = 0.71073 Å; R1
=
R
||Fo| À |Fc||/
R
|Fo|, wR2 = [
R
(Fo À Fc2)2/(n À p)]1/2 where n is the number of reflections and p the number of
2
P = [max(Fo2,0) + 2(Fc2)]/3, where a is a constant adjusted by the program; goodness of fit = [
R
parameters.

132
W.B. Cross et al. / Polyhedron 59 (2013) 124–132
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(2011) 9042;
parameters. Disordered solvent was omitted using the SQUEEZE
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(f) W.B. Cross, E.G. Hope, Y.-H. Lin, S.A. Macgregor, K. Singh, G.A. Solan, N.
Yahya, Chem. Commun. 49 (2013) 1918.
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(1999) 2633;
Acknowledgements
We thank the University of Leicester for financial assistance.
Johnson Matthey PLC are thanked for their loan of palladium salts.
(b) Y.D.M. Champouret, J. Fawcett, W.J. Nodes, K. Singh, G.A. Solan, Inorg.
Chem. 45 (2006) 9890;
(c) C. Raminelli, Z. Liu, R.C. Larock, J. Org. Chem. 71 (2006) 4689;
(d) L. Kaczmarek, R. Balicki, J. Lipkowski, P. Borowicz, A. Grabowska, J. Chem.
Soc., Perkin Trans. 2 (1994) 1603;
Appendix A. Supplementary data
(e) I.J. Rhile, T.F. Markle, H. Nagao, A.G. DiPasquale, O.P. Lam, M.A. Lockwood,
K. Rotter, J.M. Mayer, J. Am. Chem. Soc. 128 (2006) 6075.
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(b) R.A. Kresinski, T.A. Hamor, C.J. Jones, J.A. McCleverty, J. Chem. Soc., Dalton
Trans. (1991) 603;
CCDC 932354–932359–contain the supplementary crystallo-
graphic data for 1, 2ÁCH2Cl2, 2ÁC6H6, 3, 4 and 5. This data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223 336
033; or e-mail: deposit@ccdc.cam.ac.uk.
(c) J.L. Kerschner, J.S. Yu, P.E. Fanwick, I.P. Rothwell, J.C. Huffman,
Organometallics 8 (1989) 1414;
(d) A.J. Nielson, J.A. Harrison, C. Shen, J.M. Waters, Polyhedron 25 (2006) 1729.
[16] See for example, (a) M. Lopez-Torres, P. Juanatey, J.J. Fernandez, A. Fernandez,
A. Suarez, D. Vazquez-Garcia, J.M. Vila, Polyhedron 21 (2002) 2063;
(b) H. Onoue, I. Moritani, J. Organomet. Chem. 43 (1972) 431;
(c) H. Onoue, K. Minami, K. Nakagawa, Bull. Chem. Soc. Jpn. 43 (1970) 3480.
[17] K. Nakamoto, IR and Raman Spectra of Inorganic and Coordination
Compounds, fifth ed., Wiley, New York, 1997. Part B, p. 271.
[18] The mechanism of oxidation remains unclear. Notably, palladium acetate/
pyridine mixtures have been used as catalysts to promote the aerobic
oxidation of secondary amines to imines (e.g., Ar–CH2NHPh to Ar–CH@N–
Ph): J.-R. Wang, Y. Fu, B.-B. Zhang, X. Cui, L. Liu, Q.-X. Guo, Tetrahedron Lett. 47
(2006) 8293.
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