Rhodium and palladium complexes of a pyridyl-centred polyphenylene derivative

Article abstract of DOI:10.1039/b709818a

2-(2′-Pyridyl)-3,4,5,6-tetraphenylpyridine 2 (HL), a ligand with both N,N-bidentate and N,N,C-terdentate coordination potential, was prepared in excellent yield by the Diels-Alder [2+4] cycloaddition of 2-cyanopyridine and tetraphenylcyclopentadien-1-one. Monometallic Pd(ii) and Rh(iii) complexes were formed which exhibit both types of ligand coordination (trans-[RhCl ₂(L)(NCMe)] 3, cis-[RhCl(L)(NCMe)₂]PF₆4, cis-[RhCl₂(HL)₂]PF₆6, [RhCl(L)(HL)]PF ₆7, [Rh(L)₂]PF₆8, [Pd(OAc)(L)] 9 and [Pd(η³-methallyl)(HL)]PF₆10). The molecular structures of the ligand and six complexes, including the chloro-bridged dimer [RhCl(L)(μ-Cl)]₂5, were obtained by single crystal X-ray diffraction. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b709818a

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www.rsc.org/dalton | Dalton Transactions
Rhodium and palladium complexes of a pyridyl-centred polyphenylene
derivative†
Cecile M. A. Ollagnier, Sarath D. Perera, Christopher M. Fitchett and Sylvia M. Draper*
Received 28th June 2007, Accepted 28th September 2007
First published as an Advance Article on the web 26th October 2007
DOI: 10.1039/b709818a
2-(2ꢀ-Pyridyl)-3,4,5,6-tetraphenylpyridine 2 (HL), a ligand with both N,N-bidentate and
N,N,C-terdentate coordination potential, was prepared in excellent yield by the Diels–Alder [2+4]
cycloaddition of 2-cyanopyridine and tetraphenylcyclopentadien-1-one. Monometallic Pd(II) and
Rh(III) complexes were formed which exhibit both types of ligand coordination
(trans-[RhCl2(L)(NCMe)] 3, cis-[RhCl(L)(NCMe)2]PF6 4, cis-[RhCl2(HL)2]PF6 6, [RhCl(L)(HL)]PF6 7,
3
[Rh(L)2]PF6 8, [Pd(OAc)(L)] 9 and [Pd(g -methallyl)(HL)]PF6 10). The molecular structures of the
ligand and six complexes, including the chloro-bridged dimer [RhCl(L)(l-Cl)]2 5, were obtained by
single crystal X-ray diffraction.
Introduction
In a recent report we demonstrated the versatility of the Diels–
Alder [4+2] cycloaddition of a tetraarylcyclopenta-2,4-dien-1-
one and an appropriately substituted acetylene in the generation
of heteroatom oligo-polyphenylenes.1 The result was a new set
of propellor-like hexaaryl substituted benzenes for structural
analysis and as precursors to heteroatom graphenes.2,3 One
Scheme 2 Coordination modes of 2 to a metal centre M.
unexplored variation in the synthetic procedure was to replace
chemistry, Rh(III) and Pd(II). The coordination of bulky asym-
the acetylene with an arylcyanide to generate not superbenzenes
metric ligands to such catalytic metals has relevance to inves-
but superpyridines. In the search for such polyaromatics 2-(2ꢀ-
tigations into bond formation processes. In addition transition
pyridyl)-3,4,5,6-tetraphenylpyridine 2 (HL) is a necessary first step
metal complexes of derivatives of 6-phenyl-2,2ꢀ-bipyridine have
(Scheme 1).
shown interesting photo-physical properties4 and the coordination
chemistry of (N–N)-donor ligands such as 2,2ꢀ-bipyridine and
related ligands are well reviewed.5
Results and discussion
Synthesis of the ligand
Polyaromatic 2 (HL) has been synthesised previously6 by a similar
method,6a and by reacting 2-cyanopyridine with two equivalents
Scheme 1 Synthesis of 2 and the atom labelling used for the assignment
of NMR data.
of diphenyl acetylene in a trimerisation process6b but no complexes
were prepared. Here we report its full characterization. Data (IR,
2 is an interesting polyaromatic compound. It can be con-
1H NMR, 13C NMR, mass spectrometric, and micro-analytical)
sidered either as a substituted pyridine (2-(2ꢀ-pyridyl)-3,4,5,6-
for 2 and other compounds are given in the Experimental section;
tetraphenylpyridine) or as an asymmetrically substituted bulky
some selected proton NMR data are given in Table 1. The
bipyridine (3,4,5,6-tetraphenyl-2,2ꢀ-bipyridine). In either case the
synthetic procedure adopted in this work, the Diels–Alder [4+2]
presence of two pyridyl nitrogen atoms confers ligand potential
cycloaddition of a tetraphenylcyclopenta-2,4-dien-1-one and 2-
to the molecule and two possible coordination modes emerge:
cyanopyridine (Scheme 1) resulted in a 95% yield of 2.
(i) bidentate N,N-coordination and (ii) anionic N,N,C-terdentate
coordination via orthometallation (A and B in Scheme 2).
To explore these two facets of the ligand chemistry of 2, metal
The rhodium complexes
centres were chosen with rich coordination and orthometallation
Treatment of 2 on reflux, with one equivalent of RhCl3·xH2O in
aqueous acetonitrile results in the formation of the trans-dichloro
School of Chemistry and CRANN, University of Dublin, Trinity College,
cyclometallated product [RhCl2(L)(NCMe)] 3 which was obtained
by filtration. The monochloro cis-[RhCl(L)(NCMe)2]PF6 4 in
which one of the chloride ligands is replaced by MeCN could also
be obtained from this reaction by treatment of the mother liquor
Dublin 2, Ireland. E-mail: smdraper@tcd.ie; Fax: +353 1 671 2826;
Tel: +353 1 608 2026
† CCDC reference numbers 644544–644550. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b709818a
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with aqueous KPF6 (Scheme 3). In both cases only the mer-isomers
are produced allowing the cyclometallated ligand to be planar.
Scheme 3 (i) RhCl3·xH2O, aq. acetonitrile, reflux, 16 h, (ii) aq. KPF6,
(iii) RhCl3·xH2O, ethanol, reflux, 16 h and the atom labelling of cyclomet-
allated complexes for the assignment of NMR data.
The 1H NMR resonances of 3 are fully assigned (Fig. 1)
and evidence for the cyclometallation appears in the 13C NMR
spectrum with the 1J(RhC) coupling for the orthometallated
carbon atom occuring in the expected range7 (d 165.0 ppm,
1J(RhC) = 23.2 Hz). In the absence of a coordinating solvent such
as acetonitrile i.e. when 2 is treated with RhCl3·xH2O in aqueous
ethanol, the cyclometallated chloride-bridged dimer [RhCl(L)(l-
Cl)]2 5 (Scheme 3) is produced.
1
Fig. 1 The aromatic region of the H NMR spectrum of 3 in CDCl3 at
20 ◦C. Only the assignments made to the protons in metal coordinated
aromatic rings are presented.
On changing the stoichiometry of the reaction bis-chelate
complexes of rhodium (Scheme 4) can be formed.
Reaction of 2 with 0.33 equivalents of RhCl3·xH2O in aqueous
acetonitrile and the subsequent addition of saturated KPF6(aq.)
1
gives a mixture of products as shown by H NMR spectroscopy.
These on isolation proved to be the dichloro bis-chelate cis-
[RhCl2(HL)2]PF6 6 (43%), 3 (14%), 4 (9%), and an uniden-
tified product (33%). Reaction of 2 with 0.5 equivalent of
RhCl3·xH2O in the presence of a non-coordinating base, N-
ethylmorpholine, results in the mono-cyclometallated bis-chelate
complex [RhCl(L)(HL)]PF6 7 (67%). There was no evidence of
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and a multiplet integrating for three protons for the meta and para
protons of ring B (H16, H17 at d 6.92 ppm). The chemical shifts of
these signals are very similar to those obtained for the protons of
ring B in the ligand prior to coordination. The two more downfield
groups of signals include a multiplet integrating for four protons
at d 7.10–7.16 ppm (assigned to H18 and H12, the ortho protons
of rings A and C) and a multiplet integrating for six protons at
d 7.22–7.27 ppm (assigned to H13, H14, H19 and H20, the meta
and para protons of rings A and C). Again the chemical shifts of
these signals compare well with those of the protons of rings A
and C in the ligand prior to coordination (slight downfield shift of
about d 0.2 ppm). The proton resonances for H6 and H8 of 3 (and
also for 4 and 5) are deshielded whereas those of H3 are shielded.
The 13C NMR spectrum of 3 is very complex but shows the
expected number of signals for the quaternary (eleven, d 165.0–
135.3 ppm) and aromatic CH carbon atoms (eleven small signals
accounting for one carbon each and six larger signals accounting
for two, d 149.7–122.7 ppm) as well as a resonance for the coor-
dinated acetonitrile molecule at d 4.51 ppm. The orthometallated
carbon (C7) at d 165.0 ppm is the most downfield signal.
Scheme 4 (i) RhCl3·xH2O, aq. acetonitrile, reflux, 16 h; (ii) RhCl3·xH2O,
N-ethylmorpholine, ethanol, reflux, 3 h; (iii) AgNO3, acetone–ethanol,
reflux, 3 h; (iv) (2), reflux, 16 h; (v) aq. KPF6.
the di-cyclometallated product even on heating and in order to
generate the elusive [Rh(L)2]PF6 8 the trans dichloro ligands of 3
were first removed with silver nitrate before bringing to reflux in
the presence of one equivalent of 2.
Whereas 3 has a plane of symmetry in the plane of the tridentate
ligand due to the trans arrangement of the chloride ligands, 4 and 5
do not, increasing the number and complexity of the signals in their
1H NMR spectra. For instance, the uncoordinated phenyl rings
no longer give rise to two simple sets of spin systems. Fortunately
however, the 2-pyridyl ring and the orthometallated phenyl ring
still give rise to two distinct sets of four resonances that could
be assigned using TOCSY experiments. Table 1 summarises these
data for complexes 3, 4, 5 and 9 and 10 for comparison to the free
ligand 2.
The palladium complexes
In order to investigate the ease of formation of Pd(II) cyclome-
tallated and N-donor complexes, [Pd(OAc)2] and [(g -methallyl)-
3
Pd(l-Cl)]2 were reacted with 2 in dichloromethane in Pd : 2
ratios of 1 : 1 (Scheme 5). The result was mono-orthometallated
[Pd(OAc)(L)] 9, produced in 94% yield on reflux and the N,N-
3
chelate complex [(g -methallyl)Pd(HL)]PF6 10, produced in over
90% yield.
A general downfield shift is noticeable for the 2-pyridyl signals
of H6 and H5, and an upfield shift of about d 0.6 ppm for H3
in complexes 4, 5, 9 and 10 compared to the same protons in
2. This can be explained by the locked conformation of H3 on
complexation which causes it to be shielded by the adjacent phenyl
ring. The shifts for orthometallated phenyl ring protons (H8, H9,
H10, H11) are very similar in all three rhodium complexes. The
signals for the palladium complex 9 appear more upfield than that
of the rhodium complexes. In the proton NMR spectrum of 10 the
four non-equivalent proton resonances of the allyl group appeared
as broad peaks at d 3.91, 3.28, 2.51 and 1.78 ppm and are similar
to other allyl compounds reported.8
The 1H NMR spectra of complexes 6, 7 and 8 were too
complex for full assignment. However one signal is distinctive;
a multiplet integrating for one proton at d 9.58 ppm in 6 and d
8.14 ppm in 8 which is due to the H6 proton. In both spectra the
remaining twenty-three protons give rise to a number of doublets
and multiplets between d 6.37 and 7.50 ppm.
The detailed analysis of the NMR spectra allowed us to
determine which of the two possible conformations of 7 was
formed (a or b in Fig. 2). For steric reasons, conformation b is
favoured and this is supported by the 1H NMR data which show
that the most downfield signal assigned to H6B, is a doublet at d
9.94 ppm with a coupling constant J = 5.0 Hz. The deshielding
of this proton is due to its proximity to the chloride ligand. In
conformation a both H6A and H6B lie above the plane of a
pyridine ring which would be expected to shift their resonances
upfield. The inability to convert 7 to 8 also fits with the former
existing in the b conformation.
3
Scheme 5 [Pd(OAc)2], dichloromethane, reflux, 3 h; (ii) [(g -methallyl)-
Pd(l-Cl)]2, dichloromethane; (iii) NH4PF6–methanol.
Spectroscopic characterisation
The complexes were fully characterised using NMR spectroscopy,
mass spectrometry and elemental analysis. For the cationic
complexes 4, 6, 7, 8 and 10, the ESI-MS gave signals in agreement
with the theoretically expected masses and isotopic distributions
of [M − PF6]+ or [M − OAc]+. The neutral complexes 3 and 5
did not yield ESI-MS spectra. The H and 13C NMR chemical
1
shifts were assigned by performing H–H and C–H COSY and
NOE experiments. The asymmetric character of bulky 2 resulted in
complex NMR spectra and the proton chemical shifts of the mono
substituted 2-pyridyl group of 2 (H3, H4, H5, H6, see Scheme 1)
are given in Table 1 for comparison with those in the complexes.
In the 1H NMR spectrum of [Rh(L)Cl2(CH3CN)] 3 (Fig. 1) the
phenyl rings meta (A and C) and para (B) to the central pyridine
nitrogen give rise to four sets of overlapping multiplets. The two
most upfield sets of these signals include a multiplet integrating
for two protons for the ortho protons of ring B (H15 at d 6.66 ppm)
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Fig. 2 Two possible orientations for the N,N-coordinated ligand in
complex 7.
Molecular structure determination
Ligand 2 and complexes 3, 4, 5, 6, 8 and 9 were structurally char-
acterised by single crystal X-ray diffraction. The crystallographic
data are summarised in Table 2. Apart from 9 which contains a
methanol solvate per asymmetric unit, the other structures contain
a significant quantity of chlorinated solvent: dichloromethane for
2, 6 and 8 (one, one and three molecules per asymmetric unit
respectively), and deuterated chloroform for 4, 3 and 5 (2.5, four
and three molecules per asymmetric unit respectively).
The geometry of the metal centres is as expected in all structures.
The rhodium(III) complexes 3, 4, 5, 6 and 8 are octahedral and
the palladium(II) complex 9 is square planar. The octahedral
and square planar geometries are distorted primarily due to the
geometric constraints of the terdentate or bidentate ligand. The
extent of distortion is similar in the six complexes, with the smallest
angles at the metal centre ranging from 79.8(2)◦ in 3 to 80.1(2)◦ in
5 and the largest angles ranging from 99.93(2)◦ in 5 to 102.7(2)◦
in 6.
Fig. 3a gives a representation of ligand 2, with the atom
numbering and peripheral ring labelling (letters A to E) that will be
used for consistent discussion of all the structures. Fig. 3b shows
the designated numbering of the metal to ligand distances.
Fig. 3 Perspective view of the molecular structure of (a) 2 and
(b) metal–ligand distances.
Confirmation of the orthometallation in 3, 4, 5, 9 and 8
is provided from the crystallographically determined molecular
structures. These are presented in Fig. 4–6.
In the case of the chloro-bridged complex 5 (Fig. 6), there is
a centre of symmetry such that the asymmetric unit comprises
only half of the dimer (as well as three molecules of chloroform).
Despite being slightly longer than the Rh–Clterminal bonds, the Rh–
˚
˚
˚
l-Cl bonds (2.387(2) A and 2.377(2) A) are between 0.15 A and
9
˚
0.18 A shorter than Rh–l-Cl distances in the literature.
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Fig. 4 Perspective view of the molecular structure of (a) 3, (b) the cation in 4, and (c) 9.
Fig. 7 Perspective views of (a) the D and (b) K enantiomers of the cation
in 6. The solvate molecules, counter-ions and the hydrogen atoms have
been removed for clarity.
former there was some evidence of twinning and the occupational
disorder on the atoms linked to the metal is reflected in the labelling
of N68 and C44 (Fig. 5). Orthometallated complex 9 (Fig. 4c)
experienced the same type of disorder (occupancy of position 8
53% C and 47% N, occupancy of position 32 53% N and 47%
C). Complex 9 is the only complex in which the solvate molecule
hydrogen-bonds to the complex: the free oxygen of the coordinated
acetate is hydrogen-bonded to the hydroxy group of the methanol
Fig. 5 Perspective view of the molecular structure of the cation in 8 with
selected atomic labelling shown.
˚
solvate, with O50 · · · O42 = 2.696(3) A and O50–H50A · · · O42 =
164(1)◦.
Table 3 gives all the metal-atom bond distances and these
are consistent with those found in the literature.9,10 The longest
˚
˚
bonds are the metal–chlorine bonds (2.314(2) A to 2.387(2) A).
In the orthometallated complexes 3, 4 and 5, the metal–C and
metal–N bonds show the same d1 < d3 < d2 trend as the
majority of the structures known of 6-phenyl-2,2ꢀ-bipyridine and
Fig. 6 Perspective view of the molecular structure of 5.
˚
Table 3 Distances (A) from the metal atom
For the cis dichloro N,N-bidentate complex 6 (Fig. 7) there are
two independent cations, each with diad symmetry and both are
subject to space group operations which invert configuration. The
complexes containing Rh1 (Fig. 7a) and Rh2 (Fig. 7b) are the
D and K isomers respectively. In both, the free phenyl ring Eꢀ of
one ligand stacks with the 2-pyridyl ring A of the second ligand.
Measuring from the centroid of ring Eꢀ to the mean-plane of ring
d1
d2
d3
M–X
M–Cl
4
3
5
1.964(4)
1.962(4)
1.953(4)
2.119(4)
2.158(5)
2.130(4)
2.020(4)
1.994(5)
2.005(5)
2.019(4)a
2.013(4)a
2.027(4)a
2.314(2)
2.345(2)
2.337(2)
2.323(2)d
2.387(2)e
2.375(2)f
2.329(2)
2.344(2)
—
—
˚
˚
A gives stacking distances of 3.16(1) A and 3.19(1) A (Fig. 7a
and◦7brespe◦ctively). The two rings in each case are almost parallel
(8.0 , 7.9(1) ) and the centre of one ring (Eꢀ) is over the midpoint
of a C–C bond in the other (A).
6
8
9
2.086(3)
2.079(3)
1.98(2)
2.011(2)
1.964(2)
2.019(3)
2.018(3)
2.132(2)c
2.035(2)c
2.024(2)
—
—
1.99(2)c
2.090(2)c
2.070(2)
—
2.047(2)b
—
All the structures were examined for occupational CH or N
disorder. When refined as mixed occupancy (C/N), the associated
free variable was >0.9 (or <0.1) in all cases except 8 and 9. In the
a X = NCMe b X = OAc c Distances effected by disorder. d Terminal Cl.
e Bridging Cl. f Symmetry generated Cl (−x + 1, −y, −z).
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Table 4 The tilt angles made between the central ‘NC5ꢀ ring and the
peripheral aromatic rings (in ◦). The rings are identified by a letter
according to Fig. 3a
spectrometer. Tetraphenylcyclopentadienone, 2-cyanopyridine,
3
RhCl3·xH2O and [Pd(OAc)2] were purchased from Aldrich. [(g -
metallyl)Pd(l-Cl)]2 was prepared according to a literature pro-
A
B
C
D
E
cedure.12
2
3
4
5
6
8
9
53.1
16.6
12.2
11.1
15.7/15.6
17.3/18.3
7.6
62.2
65.8
69.9
71.4
74.3/73.0
81.7/68.5
89.4
61.4
75.8
83.5
80.2
73.6/66.4
80.3/88.3
88.9
61.9
81.8
89.6
74.8
71.4/72.0
89.7/87.2
86.4
51.4
10.5
8.3
6.3
67.8/70.5
8.4/14.6
10.4
Crystallography
Single-crystal analyses of ligand 2 and complexes 3, 4, 5, 6, 8
and 9 were made using a Bruker SMART APEX CCD area
detector using graphite monochromatised Mo-Ka(k = 0.71073 A)
˚
radiation at 153(2) K. The experimental and crystallographic
data are summarized in Table 2. The data reductions were
performed using SAINT.13 Intensities were corrected for Lorentz
and polarisation effects and for absorption in the case of
the complexes using multi-scan techniques. Space groups were
determined from systematic absences and checked for higher
symmetry. A full sphere of data was obtained for each using
the omega scan method. The structures were solved by direct
methods using SHELXS,14,15 and refined on F2 using all data
by full-matrix least-squares procedures with SHELXL-97.16 All
non-hydrogen atoms were refined with anisotropic displacement
parameters. Hydrogen atoms were included in calculated positions
with isotropic displacement parameters 1.2 times the isotropic
equivalent of their carrier carbons. Final Fourier syntheses showed
no significant residual electron density except in the case of 8.
Crystals of 8 were twinned; the poor nature of the data being
manifest in the refinement and thermal parameters. The resulting
structure is included for comparison only and without detailed
analysis.
its analogues,11 and reflect the trans influence of the r-C bonds.
In complex 6, the ligand is bidentate, free from the constraints
imposed by a third ligand and the distances are more similar with
d1 > d2.
In the crystal structure of ligand 2, the peripheral rings are
tilted with respect to the central ring, with tilt angles ranging from
51.3◦ to 62.2◦. Table 4 shows how the tilt angles are affected by
coordination. The rings bound to the metal (A, and Eꢀ in the
orthometallated complexes) see their tilt angles decreased almost
to co-planarity (angles < 20◦) to accommodate the geometric
constraints of the metal. This induces an increase in the tilt angles
of all the other rings. For the non-disordered orthometallated
complexes 3, 4 and 5, the tilt angles for the orthometallated ring
Eꢀ are smaller than those for the 2-pyridyl ring A.
Conclusion
Suitable crystals of 2 and 6 were obtained by vapour diffusion
of hexane into a dichloromethane solution of the respective com-
pound. Crystals of 4 and 8 were grown by layering hexane onto a
solution of the respective complex in CDCl3 and dichloromethane
respectively. Crystals of 3 and 5 were obtained in an NMR tube by
slow evaporation of a CDCl3 solution. Crystals of 9 were grown
from dichoromethane–methanol.
2-Cyanopyridine has been shown to be an effective dieno-
phile in a [2+4] Diels–Alder cycloaddition reaction with tetra-
phenylcyclopenta-2,4-dien-1-one. The resulting formation of 2-
(2ꢀ-pyridyl)-3,4,5,6-tetraphenylpyridine in excellent yield allows
for the formation of metal complexes with potential catalytic
use. For the two types of metal centre used (Rh(III), Pd(II)) the
ligand has been shown to exhibit both N,N-bidentate and N,N,C-
orthometallated binding modes. The type of coordination can be
controlled by varying the reaction conditions. The introduction of
a base results in the preferential formation of a mono cyclomet-
allated bis chelate complex. Varying the ligand : RhCl3·xH2O
reaction stoichometry allows for the preparation of a range of
mono orthometallated products. Subsequent substitution of the
coordinated chloro or acetonitrile ligands in these complexes
generates both monometallic and dimetallic bis-orthometallated
complexes. The molecular structures of the Rh(III) complexes show
the generation of the mer isomers exclusively with similar degrees
of ring twisting.
Synthesis of [2-(2-pyridyl)-3,4,5,6-tetraphenyl]pyridine (2)
Tetraphenylcyclopentadienone (1.00 g, 2.60 mmol) and 2-
cyanopyridine (1.1 mL, 11.6 mmol) were combined and heated
to reflux (external temperature 280◦ C) under nitrogen for 48 h.
The resulting brown solution was allowed to cool to give a brown
solid, which was crystallised from dichloromethane–acetone to
give 2 as white crystals. Yield (1.13 g, 95%). IR (KBr): m 3056,
3025, 1586, 1535, 1396, 761, 698 cm−1. 1H NMR (CDCl3): d 8.48
(dm, 1H, J = 5.0 Hz, H6), 7.55 (ddd, app. td, 1H, J = 1.5, 7.5 and
7.5 Hz, H4), 7.46 (dm, 1H, J = 7.5 Hz, H3), 7.41 (m, 2H, H7), 7.18
(m, 3H, H8 and H9), 7.09 (ddd, 1H, J = 1.5, 5.0 and 7.5 Hz, H5),
6.92–7.03 (m, 13H), 6.81 (m, 2H, H15) ppm. 13C NMR: d 158.5
(Cquat, C2), 156.3 (Cquat), 155.3 (Cquat), 149.9 (Cquat), 148.3 (CH,
C6), 140.2 (Cquat), 137.8 (Cquat), 137.5 (Cquat), 137.4 (Cquat), 135.1
(CH, C4), 134.4 (Cquat), 133.9 (Cquat), 130.8 (2C, CH), 130.6 (2C,
CH), 129.9 (2C, CH, C15), 129.8 (2C, CH, C7), 127.0 (2C, CH,
C8), 126.9 (2C, CH), 126.8 (CH, C9), 126.7 (2C, CH), 126.5 (2C,
CH), 125.8 (CH), 125.8 (CH), 125.6 (CH), 124.4 (CH, C3), 121.5
(CH, C5) ppm. MS m/z: 461.1992 ([M + H]+) (calcd 461.2018);
mp 216 ◦C (lit.,6a 217–219 ◦C).
Experimental
General procedures and materials
IR spectra were recorded from KBr disks on a Perkin-Elmer
Paragon 1000 Fourier transform spectrophotometer. NMR spec-
tra were recorded on a DPX 400 spectrometer operating at
1
400.13 MHz for H, and 100.62 MHz for 13C, and were stan-
dardized with respect to TMS. Electrospray ionization mass
spectra were recorded on a micromass LCT electrospray mass
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Synthesis of [Rh(L)Cl2(CH3CN)] (3) and
[Rh(L)Cl(CH3CN)2](PF6) (4)
was heated to reflux for 16 h. After cooling, a solution of saturated
aqueous KPF6 was added to the solution. A yellow precipitate
formed, which was filtered off and washed with water and diethyl
RhCl3·xH2O (39.5 mg, 0.19 mmol) in water (1.5 mL) was added
to 2 (69.1 mg, 0.15 mmol) in acetonitrile (1.5 mL) and the mixture
was heated to reflux for 16 h, after which a yellow precipitate had
formed. The reaction mixture was cooled down on ice. The yellow
precipitate was then filtered off and washed with water and diethyl
ether to yield complex 3 (61.6 mg, 0.091 mmol, 61%). The filtrate
was evaporated, the resulting solid was dissolved in the minimum
amount of acetonitrile and a solution of saturated aqueous KPF6
was added to form a yellow precipitate. This was filtered off and
washed with water and diethyl ether to yield complex 4 (18.5 mg,
15%).
1
ether. The H NMR spectrum of this precipitate (28.5 mg) in
the H6 proton region shows a mixture of four complexes: 6 (d
H6 9.59 ppm, 43%), 4 (d H6 9.38 ppm, 9%), 3 (d H6 9.25 ppm,
15%), and another unidentified compound (d H6 8.84 ppm, 33%).
Yellow crystals of complex 6, suitable for single crystal X-ray
analysis, grew in the NMR tube by slow evaporation of the CDCl3
solution. These crystals were then collected by filtration. Yield
6.3 mg (0.0052 mmol, 10%). 1H NMR (CD3CN): d 9.58 (m, 1H,
H6), 7.34–7.40 (m, 4H), 7.32 (m, 1H), 7.21 (m, 2H), 7.08 (d, 1H,
J = 8.0 Hz), 6.95–7.04 (m, 4H), 6.92 (d, 1H, J = 7.0 Hz), 6.88 (m,
3H), 6.79–6.85 (m, 4H), 6.73 (d, 1H, J = 8.0 Hz), 6.44 (m, 2H).
MS m/z: 1093.2275 [M − PF6]+ (calcd 1093.2311).
Complex 3. 1H NMR (CDCl3): d 9.25 (m, 1H, H6), 7.87 (dd,
1H, J = 1.5 and 7.7 Hz, H8), 7.49 (m, 2H, H4 and H5), 7.22–7.27
(m, 6H, H13, H14, H19 and H20), 7.19 (m, 1H, H9), 7.10–7.16 (m,
4H, H12 and H18), 6.92 (m, 3H, H16 and H17), 6.84 (m, 1H, H3),
6.66 (m, 2H, H15), 6.62 (m, 1H, H10), 6.33 (dd, 1H, J = 1.5 Hz
and 8.4 Hz, H11), 2.66 (s, 3H, CH3CN) ppm. 13C NMR: d 165.0
(d, JRhC = 23.2 Hz, C7), 162.5 (Cquat), 156.4 (Cquat), 153.3 (Cquat),
151.7 (Cquat), 149.7 (CH, C6), 146.9 (Cquat), 137.2 (CH, C4), 136.4
(Cquat), 136.3 (Cquat), 136.0 (Cquat), 135.6 (Cquat), 135.3 (Cquat), 134.6
(CH, C8), 130.7 (CH, C9), 130.1 (2C, CH), 130.0 (2C, CH), 129.8
(2C, CH), 129.8 (CH, C11), 129.0 (2C, CH), 128.5 (2C, CH), 128.2
(CH), 127.8 (CH), 127.4 (CH, C5), 127.0 (2C, CH), 126.6 (CH),
125.8 (CH, C3), 122.7 (CH, C10), 4.51 (CH3CN) ppm. Anal. calcd
for C36H26Cl2N3Rh·1.25CDCl3: C, 54.24; H, 3.18; N, 5.09. Found:
C, 54.37; H, 2.85; N, 4.76%.
Synthesis of [Rh(HL)(L)Cl](PF6) (7)
2 (69.0 mg, 0.15 mmol) and RhCl3·xH2O (17.3 mg, 0.084 mmol)
were combined and dissolved in ethanol (12 mL) containing N-
ethylmorpholine (3 drops), and the mixture was heated to reflux for
3 h. The product was precipitated by adding a solution of saturated
aqueous KPF6. The solid was isolated via filtration, then washed
with water and diethyl ether to yield 7 as a yellow powder (67 mg,
0.056 mmol, 67%). 1H NMR (CDCl3): d 9.94 (d, 1H, J = 5.0 Hz,
H6ꢀ), 8.25 (m, 1H), 7.76 (m, 1H), 7.50–7.57 (m, 3H), 7.21–7.41 (m,
probably 11H, contains CHCl3), 7.15 (m, 2H), 7.06 (m, 4H), 6.78–
6.94 (m, 11H), 6.67–6.76 (m, 4H), 6.55–6.62 (m, 3H), 6.47 (d, 1H),
6.47 (d, 1H, J = 7.5 Hz), 6.42 (d, 1H, J = 7.5 Hz), 6.32–6.38 (m,
3H), 6.22 (d, 1H, J = 7.5 Hz) ppm. MS m/z: 1057.2549 [M − PF6]+
(calcd 1057.2544). Anal. calcd for C68H47ClF6N4PRh·CH2Cl2: C,
64.32; H, 3.83; N, 4.35. Found: C, 64.89; H, 3.49; N, 4.30%.
Complex 4. 1H NMR (CDCl3): d 9.36 (dd, 1H, J = 2.0 and
5.5 Hz, H6), 7.81 (dd, 1H, J = 1.4 and 8.2 Hz, H8), 7.66 (m, 1H,
H5), 7.56 (ddd, app. td, 1H, J = 2.0 and 8.3 Hz, H4), 7.51 (m, 1H,
Hphenyl), 7.24–7.31 (m, 6H and CHCl3, Hphenyl and H9), 7.10–7.17
(m, 4H, Hphenyl), 6.94 (m, 3H, Hphenyl), 6.85 (d, 1H, J = 8.3 Hz,
H3), 6.81 (m, 1H, Hphenyl), 6.75 (m, 1H, H10), 6.65 (m, 1H, Hphenyl),
6.33 (dd, 1H, J = 1.4 and 8.2 Hz, H11), 2.75 (s, 3H, CH3CN),
2.19 (s, 3H, CH3CN) ppm. MS m/z: 679.1164 [M − PF6]+ (calcd
679.1136). Anal. calcd for C38H29ClF6N4PRh·CDCl3: C, 49.55; H,
3.09; N, 5.93. Found: C, 50.30; H, 2.32; N, 5.10%.
Synthesis of [Rh(L)2]PF6 (8)
Complex 3 (42.2 mg, 0.068 mmol) and silver nitrate (25.5 mg,
0.15 mmol) were heated to reflux in acetone–ethanol (6 : 1, 7 mL)
under argon for 3 h. The solution was then filtered through Celite
to remove the silver chloride precipitate formed and evaporated to
dryness. The yellow oil obtained was dissolved in butanol (8 mL)
and 2 (31.3 mg, 0.068 mmol) was added. The mixture was heated to
reflux under argon for 16 h to give a yellow solution. The solution
was stirred with a saturated aqueous solution of KPF6, and a
yellow precipitate formed. This was isolated via filtration, washed
with water and diethyl ether to yield 8 (22.3 mg, 0.019 mmol, 28%).
1H NMR (CDCl3): d 8.14 (d, 1H, J = 5.0 Hz, H6), 7.49 (d, 1H,
J = 6.8 Hz), 7.44 (d, 1H, J = 7.5 Hz), 7.31–7.36 (m, 3H), 7.22–
7.29 (m, probably 5H, contains CHCl3), 7.21 (d, 1H, J = 5.4 Hz),
7.12 (m, 2H), 7.07 (m, 1H), 6.97 (m, 2H), 6.90 (d, 1H, J = 8.2),
6.84 (m, 1H), 6.80 (m, 1H), 6.44–6.51 (m, 2H), 6.37 (d, 1H, J =
8.2 Hz) ppm. 13C NMR: d 167.4 (d, JRhC = 32.8 Hz, RhC), 159.9
(Cquat), 155.2 (Cquat), 152.8 (Cquat), 149.9 (Cquat), 149.0 (CH, C6),
145.6 (Cquat), 137.1 (CH), 136.2 (Cquat), 136.1 (Cquat), 135.8 (Cquat),
135.7 (Cquat, 2 × C), 130.6 (CH), 130.4 (CH), 130.2 (CH), 130.0
(CH), 129.3 (CH), 129.2 (CH), 129.2 (CH, 2 × C), 129.1 (CH),
129.0 (CH), 128.9 (CH), 128.5 (CH), 128.4 (CH), 128.2 (CH),
128.0 (CH), 127.5 (CH), 127.4 (CH), 126.9 (CH), 126.3 (CH),
126.2 (CH), 121.9 (CH) ppm. MS m/z: 1021.2798 [M − PF6]+
Synthesis of [Rh(L)Cl(l-Cl)]2 (5)
2 (23.0 mg, 0.050 mmol) and RhCl3·xH2O (13.2 mg, 0.063 mmol)
were heated to reflux in ethanol (4 mL) for 16 h. The solvent was
removed in vacuo. Recrystallisation of the solid obtained from
dichloromethane–hexane yielded complex 5 as a yellow powder
(12.1 mg, 0.0095 mmol, 34%). 1H NMR (CDCl3): d 9.06 (ddd, 1H,
J = 0.7, 1.9 and 5.1 Hz, H6), 7.89 (dd, 1H, J = 1.5 and 7.7 Hz,
H8), 7.48 (ddd, app. td, 1H, J = 1.9 and 7.7 Hz, H4), 7.24–7.39
(m, 8H and CHCl3, Hphenyl and H5), 7.17–7.22 (m, 2H, Hphenyl), 7.08
(d, 1H, J = 7.3 Hz, Hphenyl), 6.90–7.00 (m, 3H, Hphenyl), 6.87 (m, 2H,
H3 and H9), 6.80 (d, 1H, J = 7.3 Hz, Hphenyl), 6.69 (dt, 1H, J =
1.5 and 8.0 Hz, H10), 6.63 (m, 1H, Hphenyl), 6.39 (dd, 1H, J = 1.5
and 8.0 Hz, 1H, H11) ppm.
Synthesis of [Rh(HL)2Cl2](PF6) (6)
RhCl3·xH2O (10.5 mg, 0.05 mmol) in water (1.0 mL) was added
to 2 (69.1 mg, 0.15 mmol) in acetonitrile (1.5 mL) and the mixture
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(calcd 1021.2778). Anal. calcd for C68H46F6N4PRh·2.5CH2Cl2: C,
129.3 (CH), 128.7 (CH), 128.6 (CH, 2 × C), 128.1 (CH), 127.9
(CH), 127.6 (CH, 2 × C), 127.1 (CH, 2 × C), 127.0 (CH, 2 × C),
126.7 (CH), 126.6 (CH), 125.9 (CH), 62.8 (allyl CH2), 61.5 (allyl
CH2), 22.2 (CH3) ppm. MS m/z: 621.1541 [M − PF6]+ (calcd
621.1522).
61.39; H, 3.73; N, 4.06. Found: C, 61.00; H, 3.25; N 3.96%.
Synthesis of [Pd(L)(OAc)] (9)
A solution containing 2 (60 mg, 0.130 mmol) and [Pd(OAc)2]
(30 mg, 0.133 mmol) in dichloromethane (5 mL) was refluxed for
3 h. The solution was concentrated to a small volume (ca. 1 mL)
then methanol (2 mL) was added to give the cyclometallated Pd(II)
complex 9 as yellow crystals (76 mg, 94%). 1H NMR (CDCl3): d
8.61 (dm, 1H, J = 5.0 Hz, H6), 7.44 (td, 1H, J = 2.0 and 8.0 Hz,
H4), 7.35 (ddd, 1H, J = 1.0, 5.0 and 7.5 Hz, H5), 7.30 (dd, 1H, J =
1.5 and 7.5 Hz, H8), 7.22–7.27 (m, 6H, Hphenyl), 7.04–7.07 (m, 4H,
Hphenyl), 7.01 (td, 1H, J = 1.5 and 7.5 Hz, H9), 6.92 (m, 3H, Hphenyl),
6.68 (m, 2H, Hphenyl), 6.61 (dm, 1H, J = 8.0 Hz, H3), 6.60 (m, 1H,
H10), 5.95 (dd, 1H, J = 1.0 and 8.0 Hz, H11), 3.50 (s, 3H, CH3OH
from crystallisation), 2.30 (s, 3H, OAc), 1.20 (br. S, 1H, CH3OH
Acknowledgements
The authors are grateful to Dr John OꢀBrien for NMR support.
C.O. and C.M.F. acknowledge the Irish Research Council for
Science and Engineering for PG and PD awards. S.P. thanks
Science Foundation Ireland and CRANN for financial support.
Notes and references
1 D. J. Gregg, C. M. A. Ollagnier, C. M. Fitchett and S. M. Draper,
Chem.–Eur. J., 2006, 12, 3043.
2 S. M. Draper, D. J. Gregg and R. Madathil, J. Am. Chem. Soc., 2002,
124, 3486.
from crystallisation) ppm. 13C NMR: d 177.5 (Cquat, C O), 161.9
=
(Cquat), 155.8 (Cquat), 155.6 (Cquat), 153.6 (Cquat), 150.7 (Cquat), 149.7
(CH, C6), 147.8 (Cquat), 137.6 (CH, C4), 135.6 (Cquat), 135.5 (Cquat),
135.3 (Cquat), 135.2 (Cquat), 134.2 (Cquat), 132.8 (CH, C8), 129.4 (2C,
CH), 129.2 (2C, CH), 129.2 (CH), 129.1 (2C, CH), 128.7 (2C,
CH), 128.2 (2C, CH), 128.0 (CH), 127.9 (CH), 127.6 (CH), 126.7
(2C, CH), 126.3 (CH), 125.8 (CH, C3), 125.3 (CH, C5), 123.8
(CH, C10), 50.4 (CH3OH from crystallisation), 23.8 (CH3) ppm.
IR (Neat) 1615.7, 1592.9, 1574.8, 1369.4 and 1321.4. Anal. calcd
for C36H26N2O2Pd·2MeOH, C, 66.24; H, 4.69; N, 4.06. Found: C,
66.86; H, 4.48; N, 4.01%. MS m/z: 565.0905 [M − OAc]+ (calcd
565.0896).
3 (a) S. M. Draper, D. J. Gregg, E. R. Schofield, W. R. Browne, M. Duati,
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Synthesis of [(g3-methallyl)Pd(HL)]PF6 (10)
7 Y. Motoyama, M. Okano, H. Narusawa, N. Makihara, K. Aoki and
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3
2 (20 mg, 0.0434 mmol) and [(g -metallyl)Pd(l-Cl)]2 (8.5 mg,
0.0217 mmol) were dissolved in dichloromethane (1 mL). After
15 min, a solution of NH4PF6 (20 mg, 0.122 mmol) in methanol
(1 mL) was added to give a colourless solution. The solution was
concentrated and the residue was triturated with methanol to yield
10 as an off-white solid (30 mg, 91%). 1H NMR (CDCl3): d 8.81
(dm, 1H, J = 5.0 Hz, H6), 7.54 (ddd, app. td, 1H, J = 1.5 and
8.0 Hz, H4), 7.46 (ddd, 1H, J = 1.5, 5.0 and 7.5 Hz, H5), 7.32–7.36
(m, 3H), 7.19–7.28 (m, probably 3H, contains CHCl3), 7.06 (m,
1H), 6.95–7.03 (m, 8H), 6.91 (dm, 1H, J = 8.0 Hz, H3), 6.73–6.84
(m, 5H), 3.91 (s, 1H, Hs), 3.28 (s, 1H, Ha), 2.51 (s, 1H, Hs), 1.98
(1H, 3H, CH3), 1.78 (s, 1H, Ha) ppm. 13C NMR: d 160.3 (Cquat),
156.2 (Cquat), 154.2 (Cquat), 153.2 (CH, C6), 151.7 (Cquat), 142.7
(Cquat), 138.2 (Cquat), 137.9 (CH, C4), 137.0 (Cquat), 136.0 (Cquat),
135.9 (Cquat), 135.5 (Cquat), 133.9 (Cquat), 130.4 (CH), 130.3 (CH),
130.3 (CH), 130.2 (CH), 130.1 (CH), 130.1 (CH), 129.4 (CH),
9 (a) K. K.-W. Lo, C.-K. Li, K.-W.i Lau and N. Zhu, Dalton Trans., 2003,
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Quebatte, R. Scopelliti and K. Severin, Inorg. Chem. Commun., 2004,
7, 708; (c) Y. Motoyama, M. Okano, H. Narusawa, N. Makihara, K.
Aoki and H. Nishiyama, Organometallics, 2001, 20, 1580.
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290 | Dalton Trans., 2008, 283–290
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©