Amine-substituted α-N(standard)- and δ-N(remote)-pyridylidene complexes: Synthesis and bonding

Article abstract of DOI:10.1016/j.ica.2011.05.038

Reaction of ortho-amino-para-chloro- and ortho-chloro-para-amino-pyridinium triflate with tetrakis(triphenylphosphine) complexes of Ni or Pd afforded by oxidative substitution compounds that can be represented as cationic carbene complexes. NMR as well as X-ray structural studies revealed the role played by the NMe₂ and M(PPh)₂Cl (M = Ni or Pd) substituents in stabilizing the complexes by π-retro-donation and, consequently, in governing the relative importance of certain mesomeric representations describing their structures.

Full text of DOI:10.1016/j.ica.2011.05.038

Inorganica Chimica Acta 376 (2011) 87–94
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Inorganica Chimica Acta
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Amine-substituted
a-N(standard)- and d-N(remote)-pyridylidene complexes:
Synthesis and bonding
Elzet Stander-Grobler a, Christoph E. Strasser a, Oliver Schuster a, Stephanie Cronje a,b
,
Helgard Raubenheimer a,
⇑
a Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag X1, Matieland, 7602 Stellenbosch, South Africa
b Institut für Anorganische und Analytische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, D-60348 Frankfurt am Main, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Reaction of ortho-amino-para-chloro- and ortho-chloro-para-amino-pyridinium triflate with tetrakis(tri-
phenylphosphine) complexes of Ni or Pd afforded by oxidative substitution compounds that can be rep-
resented as cationic carbene complexes. NMR as well as X-ray structural studies revealed the role played
by the NMe2 and M(PPh)2Cl (M = Ni or Pd) substituents in stabilizing the complexes by p-retro-donation
and, consequently, in governing the relative importance of certain mesomeric representations describing
Received 16 March 2011
Received in revised form 20 May 2011
Accepted 31 May 2011
Available online 6 June 2011
their structures.
Keywords:
Ó 2011 Elsevier B.V. All rights reserved.
NHC
Remote pyridylidene
Amino pyridylidene
Palladium
Nickel
1. Introduction
ring related to E, indicating that charge compensation occurs pre-
dominantly via that NMe2 substituent rather than through carbe-
Complexes of type A (Scheme 1) have previously been studied
as first prototypes of N-heterocyclic carbene complexes with their
stabilising heteroatoms positioned in a distant position to the car-
bene carbon [1]. These compounds and other members of the fam-
ily, led us into the field of remote and abnormal pyridylidenes [2]
and to so-called carbene ligands with reduced heteroatom stabil-
ization in general [3]. Complex A has also been shown to be a use-
ful precatalyst in C,C-coupling reactions [4].
noid formation (which could involve p-backbonding from
platinum). Interestingly, when the NMe2 substituent is situated
in the ‘‘abnormal’’ meta-position of their bidentate ligand, no
well-defined effect is observed.
Here, by way of comparison, we report the preparation and full
characterisation of simple amine derivatives of C and E. Calcula-
tions have previously shown that the coordinated carbon in
metal-substituted pyridinium rings is a somewhat better p-acceptor
In contrast to the well-known 2-imidazolylidenes B that contain
two nitrogen atoms within a five-membered ring, such ligands fea-
ture only one (C) or no heteroatom (D and E) adjacent to the car-
in the para than in the ortho position [5]. We, therefore, posed two
questions:
bene carbon. In
a
systematic study of cationic pyridylidene
(1) Would potential p-backdonation in such amine-containing
complexes with [M] = Ni(PPh3)2Cl, we recently reported [5] that
the carbenoid canonical representations of C and E shown in
Scheme 1, are reflected by the required bond-length alternations
within the heterocyclic rings in their molecular structures as deter-
mined by X-ray diffraction.
Similar partially localised double bonds have been observed by
Bercaw and co-workers within the bidentate N-(2-pyridyl)-2-
pyridylidene ligand in a platinum complex [6]. However, upon
introduction of an additional amino group in the para-position of
the pyridylidene ring, it adopts an electronic arrangement in the
monodentate ligands again effect bond localisation within
the heterocyclic rings?
(2) Would the relative contributions to such p-backdonation (or
carbenoid formation) be determined by the manner (ortho or
para) in which the two substituents NMe2 and M(PPh3)2Cl
are positioned?
2. Results and discussion
2.1. Synthesis
⇑
The organic precursor compounds 3, 4 and 5 (Scheme 2) were
prepared by modifying Ahlbrecht’s procedures for the preparation
Corresponding author. Tel.: +27 21 808 3850; fax: +27 21 808 3849.
E-mail address: hgr@sun.ac.za (H. Raubenheimer).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.05.038

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E. Stander-Grobler et al. / Inorganica Chimica Acta 376 (2011) 87–94
of analogous compounds which can provide reactive intermediates
for the synthesis of various quinolines [7]. Aminolysis of the
dichloropyridinium triflate 2 gave the neutral hygroscopic pyridi-
neimine 3. In this case deprotonation occurred on account of the
excess of methylamine present. In contrast, the reaction of equi-
molar quantities of 2 and aniline directly yielded the cationic
para-iminium compound 5. The unexpected regioselectivity is a
key feature of this reaction and not easily rationalised. Conversions
of 2,4-dichloro-1,3-dimethylchinoliniumchloride with NH3, NH2Et
or NH2CH2Ph give exclusively the ortho products whereas the
stronger base dimethylamine affords both ortho and para products
[7], a result that supports the notion that the para preference in our
hands for 5 is not simply the result of a basicity requirement but
probably due to an interplay of electronic and steric influences.
Finally, alkylation of 3 in dry CH2Cl2 with CF3SO3Me produced 4
in 83% yield. These new starting materials were fully characterised.
The Ni compounds 7a and 8a (Scheme 3) were prepared at room
temperature in THF from Ni(PPh3)4 whereas compounds 3, 4 or 5
were heated with an excess of Pd(PPh3)4 at 70 °C in THF (3) or at
60 °C in toluene (4 or 5) to afford the palladium complexes 6, 7b
and 8b. The neutral product, 6 could also serve as a precursor to
7 [1]. Both 7 and 8 may be represented as normal, cationic pyridy-
lidene complexes with the former related to A. The new transition
metal complexes are stable at room temperature and soluble in
CH2Cl2 which enabled their full characterisation.
cursors 3 and 2, respectively, it is clear that all signals appear more
downfield after aminolysis and alkylation with the exception of C4
and C6 in 5. The signals of 3 (after aminolysis) appear upfield
when compared to the cationic 2, its precursor. The signals in
the spectra of 5, 7b and 8a were unequivocally assigned using
ghsqc and ghmqc experiments. The most obvious feature is again
the exceptional (30–50 ppm) downfield change in 13C chemical
shift of the coordinated carbon atoms upon metallation. Such a
change does not occur when the neutral compound 3 is metallated
and the signal for C4 (para to N) then indeed appears somewhat
upfield.
For both the nickel and palladium compounds the chemical
shifts assigned to the carbene carbon atoms, are larger in the para
position (by ca. 10 ppm) compared to the ortho arrangement [2,5].
These resonances for the nickel complexes (d 203.5 and d 194.1) al-
ways appear downfield from their palladium analogues by ca.
10 ppm. Despite the expected double-bond character between
the ring carbon and the NMe group in 6, only one signal is observed
indicating that only one cis/trans isomer is present in solution or
that rotation about the C@NMe bond is not sufficiently hindered
to form two isomers
– a similar result has been obtained
2.2. Characterisation
The NMR data of these compounds (and their precursors) are
summarised in the Experimental Section. From comparison of
the 1H and 13C NMR spectra of 4 and 5 to the spectra of their pre-
Scheme 1.
Scheme 2.

E. Stander-Grobler et al. / Inorganica Chimica Acta 376 (2011) 87–94
89
on the chemical shifts of the carbene carbon atoms. Reported
C(carbene) chemical shifts for related simple pyridylidene com-
plexes of Ni and Pd are respectively d 205.0 and d 193.6 for nickel
and d 197.7 (now: d 194.0) and d 189.3 (now: d 182.0) for the pal-
ladium compounds [4,7,8]. These results indicate no real influence
on the metal–carbene bonding by the addition of a second nitro-
gen- containing group but probably only a better delocalisation
of formal cationic charge in 7b and 8b according to the mesomeric
structures shown in Scheme 4.
Single peaks in the 31P NMR spectra indicate single phosphorus
environments as would be expected with two mutually trans tri-
phenylphosphine groups (vide infra for conformation by X-ray
analysis of the complexes). The carbene carbons appear as triplets
in 7b as a result of coupling to two identical phosphorus atoms but
the coupling is not observed (only broadened signals) for 6, 7a, 8a
and 8b probably owing to too low sample concentrations.
The FAB mass spectra data exhibit the molecular ions of the
neutral complex 6 whereas the cations of the ion pairs of 7a and
7b are visible as peaks of low intensity. The fragmentation patterns
of the three complexes indicate the sequential loss of a PPh3 ligand,
followed by a chloride for complex 6 and a Cl, two PPh3 groups and
the metal centre for complexes 7a and 7b. Similar fragmentations
are observed for complexes 8a and 8b.
2.3. Molecular structures of 7a, 7b and 8b
The molecular structures of cationic complexes 7a, 7b and 8b
are shown in Figs. 1–3. Selected bond lengths and distances are re-
ported in Table 1.
In all three complexes the central transition metal atom adopts
the usual square planar arrangement with the pyridine ring of the
ligand placed at angles of respectively 84.0(2)°, 82.8(1)° and
87.0(1)° thereto [least squares planes P1–M1–P2–Cl1–C4/C2 and
N1–C2–C3–C4–C5–C6]. The carbene ligands in 7a, 7b and 8b are
essentially flat. In order to minimise steric repulsion, the NMe2 is
tilted away form the plane of the pyridine backbone. The amine
substituent on the pyridylidene ligand [defined by N2, C8 and C9
in 7a and 7b and by N2, C8, C9, C10, C11, C12 and C13 in 8b] forms
an angle of 43.6(1)°, 39.6(1)° or 40.0(1)°, respectively with the
plane through the pyridylidene ligand [N1, C2, C3, C4, C5 and
C6]. The same angle in the ligand precursor 5 is 45.61(5)°.
Scheme 3.
previously for a related uncomplexed compound by Ahlbrecht [10].
The fact that only one signal is seen for the two methyl groups in
each of 7a and 7b also speaks for free rotation around the
C(ring)-N bond at room temperature despite appreciable
donation from N (vide infra). Notably, the addition of another nitro-
p-back-
gen atom to the original pyridine ring has no significant influence
Scheme 4.

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E. Stander-Grobler et al. / Inorganica Chimica Acta 376 (2011) 87–94
Fig. 3. Molecular structure of the cationic complex in 8bÁ2CH2Cl2, indicating the
atom numbering scheme.
Fig. 1. Molecular structure of the cationic complex 7a (H-atoms and the triflate
counterion omitted for clarity) indicating the atom numbering scheme.
carbon meta to ring N] [8], and trans-chloro-(1-methyl-3-methyl-
quinolin-2-ylidene)bis-(triphenylphosphine)nickel(II) tetrafluoro-
borate [1.874(5) and 2.200(1) Å], (carbene carbon ortho to ring
N] [6], it is clear that in compounds where the carbene carbon
is positioned para to the ring nitrogen atom the length of the
Ni–C bond is on the short side for the Ni–C bond length range
and the Ni–Cl bond length is on the long side for the range of
Ni–Cl bonds.
Table 1
Selected bond lengths (Å) and angles (°) of 7a, 7bÁ2CH2Cl2 and 8bÁ2CH2Cl2 with
standard uncertainty in parenthesis.
7a
7bÁ2CH2Cl2
8bÁ2CH2Cl2
Bond lengths
M1–C4/C2
M1–P2
M1–P1
M1–Cl1
N2–C2/C4
N2–C8
N2–C9
N1–C6
C6–C5
C4–C5
1.844(8)
2.207(3)
2.207(3)
2.216(2)
1.357(9)
1.47(10)
1.492(8)
1.35(1)
1.35(1)
1.42(1)
1.39(1)
1.40(1)
1.990(4)
2.332(1)
2.336(1)
2.382(1)
1.360(5)
1.434(6)
1.484(6)
1.372(5)
1.360(6)
1.417(6)
1.359(6)
1.412(5)
1.368(5)
1.463(6)
1.998(3)
2.331(1)
2.335(1)
2.361(1)
1.350(4)
1.418(4)
–
1.362(4)
1.354(4)
1.413(4)
1.407(4)
1.370(4)
1.375(4)
1.469(4)
Fig. 2. Molecular structure of the cationic complex in 7bÁ2CH2Cl2 (H-atoms omitted
for clarity) showing the numbering scheme.
C4–C3
C2–C3
N1–C2
N1–C7
The two Pd–C bond distances lie well within the range previ-
ously observed for such pyridylidene complexes [2]. In accor-
dance with a comparative study of 2-, 3- and 4-pyridylidenes
[5], the Pd–Cl length in 7b [2.382(1) Å] is significantly longer
than the one in 8b [2.361(1) Å] implying that the remote type li-
gand exerts a stronger trans influence than the one in which the
carbene carbon is positioned ortho to the ring nitrogen atom.
While the same effect can be observed for the nickel complex
7a, it must be mentioned that the structural data for this com-
pound does not allow a detailed discussion of the structural
parameters. However, when the Ni–C [1.850(9) Å] and Ni–Cl
[2.219(3) Å] bonds (carbene carbon positioned para to the ring
nitrogen atom) are compared to those in other known pyridylid-
ene complexes of nickel, e.g. trans-chloro(2-chloro-1-methyl-1,4-
dihydro-pyrid-4-ylidene)bis(triphenylphosphine)nickel(II) triflate,
[1.853(2) and 2.2120(6) Å, carbene carbon para to ring N] [8],
trans-chloro(1-methyl-1,3-dihydropyrid-3-ylidene)bis(triphenyl-
phosphine)-nickel(II) triflate, [1.879(6) and 2.205(2) Å, carbene
1.385(9)
1.495(9)
Bond angles
C4/C2–M1–P2
C4/C2–M1–P1
P2–M1–P1
C4/C2–M1–Cl1
P2–M1–Cl1
P1–M1–Cl1
C2–N1–C6
C2–N1–C7
C6–N1–C7
C2/C4–N2–C8
C2–N2–C9
N1–C2–C3
C2–C3–C4
91.1(2)
89.7(2)
86.9(1)
89.3(1)
89.0(1)
89.7(1)
172.6(1)
177.7(1)
90.77(3)
90.7(3)
120.7(2)
120.8(2)
118.5(2)
129.7(3)
–
117.6(2)
123.3(3)
116.4(3)
119.3(3)
122.5(3)
172.0(1)
173.3(3)
90.32(9)
89.79(9)
120.2(7)
120.9(7)
117.9(7)
117.9(6)
120.2(6)
117.2(7)
123.6(8)
114.5(7)
121.7(8)
122.1(8)
175.91(4)
169.9(1)
91.21(4)
92.77(3)
120.1(4)
121.9(4)
117.3(4)
119.5(4)
120.9(4)
117.8(4)
122.8(4)
117.3(4)
119.8(4)
121.8(4)
C3–C4–C5
C4–C5–C6
C5–C6–N1

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91
These observations are also supported by calculations per-
4. Experimental
formed at the BP86/TZ2P level of theory, in a previous study [9],
which generally, indicated that the farther away the N-atom is
placed from the carbene carbon, the stronger the M–C bond be-
comes but the effect is weakened when the number of bonds sep-
arating the heteroatom and the carbene carbon increases above
three. Stronger M–C interaction could be correlated with a larger
trans-influence. That so-called second order effects (previously re-
ported for substituted pyridylidene complexes [6]) could become
important in catalysis, has been shown recently by Fürstner and
coworkers [11] in an innovative experimental approach that in-
volves a gold(I) complex catalyst.
As mentioned, we have shown that related but unsubstituted
metal-coordinated pyridylidenes adopt a geometry that could be
rationalised by partially localised double bonds in a predominantly
carbenoid ligand (C and E in Scheme 4) rather than as a pyridyli-
um-type ligand. While the heterocyclic rings in 7b and 8b also fea-
ture a bond-length alternation pattern, a metal–carbene resonance
structure is not supported but rather the resonance structures
7b(ii) and (iii), and 8b(iii) (Scheme 4). The positive charge in each
given ligand is, by these contributions, then divided between the
two nitrogen atoms and the barrier to rotation about the C(ring)-
NMe2 bond is still relatively low as mentioned above.
4.1. Synthesis
All reactions were carried out under nitrogen or argon using
standard vacuum-line and Schlenk techniques. All solvents were
freshly distilled under an inert atmosphere before use. THF, diethyl
ether, pentane and hexane were pre-dried over KOH and distilled
over sodium wire. Benzophenone and diethylene glycol dimethyl
ether were used as indicators for pentane and hexane and benzo-
phenone for THF and diethyl ether. Dichloromethane was dried
over KOH and distilled over CaH2 [14]. Pd(PPh3)4 was prepared
according to literature procedures [15].
Melting points were determined on a Stuart SMP3 apparatus and
are uncorrected. Mass spectra were recorded on a VG 70 SEQ (FAB,
70 eV, m-nitrobenzylalcohol matrix) instrument, and NMR spectra
on a Varian 300 FT or INOVA 600 MHz spectrometer (1H NMR at
300/600 MHz, 13C{1H} NMR at 75/150 MHz and 31P{1H} NMR at
121.5/243 MHz; d reported relative to the solvent resonance or
external reference, 85% H3PO4). Elemental analyses were carried
out at the Department of Chemistry, University of Cape Town, South
Africa and the products were evacuated under high vacuum for 5 h.
Nevertheless, the exocyclic nitrogens are bound to the ring in
7b and 8b via relatively short bonds [1.360(5) Å and 1.350(4) Å,
respectively]. These distances are much shorter than for example
the N2–C8 separation in 8b [1.418(4) Å] and do indicate apprecia-
ble double bond character. In the nickel complex, 7a, the same
bond lengths are N2–C2 1.57(9) and N2–C8 1.47(1) Å, respectively,
illustrating, at least qualitatively, the same scenario.
As shown by the structural data of 7b and 8b, the positioning of
the NMe2 substituent rather than the metal fragments determines
the bond distance alternation within the ring independent of differ-
4.2. Preparation of 2,4-dichloro-1-methylpyridinium triflate, 2 [8]
The ligand precursor, 2,4-dichloropyridine (0.70 g, 4.8 mmol),
was dissolved in 20 ml of CH2Cl2.CF3SO3Me (0.60 ml, 0.86 g,
5.2 mmol) was added dropwise with a syringe at room tempera-
ture and the solution was stirred overnight. The solvent was re-
moved under vacuum and the white residue was washed with
15 ml of diethyl ether, yielding 1.5 g (4.7 mmol) of compound 1.
Yield: 99.8%. Mp. 95.8–97.7 °C. FAB-MS, m/z (relative intensity)
for C7H6NO3SCl2F3: 163.0 [M+ÀCF3SO3, 77
(
37Cl)], 161.9
ences in
occurring in the ortho- or para-positions, respectively. We therefore
corroborate a generally stronger -retrobonding character for the
p-accepting ability of the two carbene carbon atoms when
[M+ÀCF3SO3, 100 (35Cl)]. 1H NMR (CD2Cl2, d): 9.14 (dd, 1H,
3J = 6.8 Hz, 5J = 0.4 Hz, H6), 7.99 (dd, 1H, 3J = 6.8 Hz, 4J = 2.3 Hz,
H5), 8.05 (d, 1H, 4J = 2.3 Hz, H3), 4.42 (s, 3H, NMe). 13C NMR
(CD2Cl2, d): 156.0 (s, C4), 150.0 (s, C6), 148.9 (s, C2), 130.1 (s, C3),
127.7 (s, C5), 48.1 (s, NMe). Anal. Calc. for C7H6NO3SCl2F3 (312.1):
C, 26.94; H, 1.94; N, 4.49. Found: C, 26.88; H, 1.99; N, 4.57%.
p
amino function compared to the investigated metal fragments.
It should be mentioned that 2-pyridyl metal complexes exhibit
higher basicity of the ring-nitrogen than their 4-pyridyl analogues.
The effect of amine substitution on pyridine basicity is much smal-
ler [12,13]. It remains difficult or even impossible to clearly sepa-
4.3. Preparation of [4-chloro-1-methylpyrid-2(1H)-
ylidene]methanamine, 3
rate
r- and p-influences when discussing such results.
In complex 8b as well as in its precursor 5 (compare supple-
mentary material) the external nitrogen atom in the crystalline
assembly forms a hydrogen bond with an oxygen atom of the tri-
flate counterion (NÁÁÁO distances 2.829(3) Å and 2.815(2) Å,
respectively).
Compound 2 (0.22 g, 0.70 mmol) was dissolved in 4 ml water at
0 °C and MeNH2 gas was bubbled through the solution until the
solution became light yellow. The excess methyl amine was re-
moved under vacuum. A light yellow precipitate formed which
was filtered off. The resulting solid was dissolved in CH2Cl2, dried
with MgSO4, filtered and dried in vacuo to yield a hygroscopic light
yellow solid (0.051 g, 0.35 mmol). Yield: 51%. Mp. 30–32 °C. FAB-
MS, m/z (relative intensity) for C7H9N2Cl: 158.1 [M+, 7 (37Cl)],
156.1 [M+, 18 (35Cl)], 90.8 (MÀ2Me–Cl, 80). 1H NMR (CD2Cl2, d):
6.99 (d, 1H, 3J = 7.3 Hz, H6), 5.65 (dd, 1H, 3J = 7.3 Hz, 4J = 2.4 Hz,
H5), 6.38 (d, 1H, 4J = 2.4 Hz, H3), 3.27 (s, 3H, NMe), 2.88 (s, 3H,
@NMe). 13C NMR (CD2Cl2, d): 153.6 (s, C4), 142.9 (s, C2), 140.1 (s,
C6), 110.1 (s, C3), 102.1 (s, C5), 39.1 (s, @NMe), 35.2 (s, NMe). Anal.
Calc. for C7H9N2Cl (156.6): C, 53.68; H, 5.79; N, 17.89. Found: C,
53.30; H, 5.88; N, 17.97%.
3. Conclusions
Metal fragments of the type M(PPh3)2Cl (M = Ni or Pd) and sim-
ple amino substituents, NMe2, determine the
p-electron distribu-
tion within functionalised pyridilium salts. Notably, such
compounds can also be represented as monodentate, cationic car-
bene or C-metal-bonded iminium complexes. When only metal
substituents are present in positions 2 or 4, the formal charge on
the pyridilium N atom is partly removed by p-backdonation from
the metal increasing the relative importance of the carbenoid
canonical representation. With NMe2 also attached to the ring,
the latter function is largely taken over by the exocyclic N atom
which acquires a partly positive charge. This result is independent
of whether the ‘carbene’ function is placed ortho or para to the N
atom within the heterocyclic ring. NMR investigation indicated,
however, that the backdonation from the amine is not sufficient
to effect hindered rotation about the C(ring)–N(external) bond.
4.4. Preparation of 4-chloro-2-(dimethylamino)-1-methylpyridinium
triflate, 4
Compound 3 (0.13 g, 0.93 mmol) was dissolved in 20 ml of dry
CH2Cl2.CF3SO3CH3 (0.18 g, 0.13 ml, 1.1 mmol) was added dropwise
and the solution was stirred overnight at room temperature. The

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E. Stander-Grobler et al. / Inorganica Chimica Acta 376 (2011) 87–94
solvent was evaporated and the residue was washed with 15 ml
dry diethyl ether and 15 ml dry pentane to yield the off-white
product, 4 (0.24 g, 0.77 mmol). Yield: 84%. Mp 57.1–58.9 °C. FAB-
MS, m/z (relative intensity) for C9H12N2O3SClF3: 173.1 [M+ÀCF3SO3,
35 (37Cl)], 171.1 [M+ÀCF3SO3, 95 (35Cl)], 157.1 (MÀMe–CF3SO3, 37).
1H NMR (CD2Cl2, d): 8.22 (d, 1H, 3J = 7.2 Hz, H6), 7.22 (dd, 1H,
3J = 7.2 Hz, 4J = 2.3 Hz, H5), 7.31 (d, 1H, 4J = 2.3 Hz, H3), 4.05 (s,
3H, NMe), 3.15 (s, 6H, NMe2). 13C NMR (CD2Cl2, d): 160.1 (s, C2),
152.7 (s, C4), 145.6 (s, C6), 119.1 (s, C5), 118.0 (s, C3), 45.4 (s,
NMe), 43.1 (s, NMe2). Anal. Calc. for C9H12N2O3SClF3 (320.7): C,
33.70; H, 3.77; N, 8.73. Found: C, 34.32; H, 3.60; N, 8.80%.
were obtained by the vapour diffusion of n-pentane into a concen-
trated CH2Cl2 solution of the product. Yield: 90%. Mp 162 °C (de-
comp.). FAB-MS, m/z (relative intensity) for C45H42N2O3P2SClF3Ni:
754.9 [M+ÀCF3SO3, 2 (35Cl, 58Ni)], 491.2 (MÀPPh3ÀCF3SO3, 4),
136.1 (MÀCl–2PPh3–Ni–CF3SO3, 77). 1H NMR (CD2Cl2, d): 7.69 (m,
12H, o-PPh3), 7.50 (m, 6H, p-PPh3), 7.38 (m, 13H, m-PPh3 and H5),
6.82 (d, 1H, 3J = 6.5 Hz, H6), 6.43 (d, 1H, 4J = 1.0 Hz, H3), 3.43 (s,
3H, NMe), 2.39 (s, 6H, NMe2). 13C NMR (CD2Cl2, d): 203.5 (s, C4),
151.8 (s, C2), 135.2 (m, o-PPh3), 134.4 (s, C6), 131.4 (s, p-PPh3),
130.5 (m, i-PPh3), 129.1 (m, m-PPh3), 127.4 (bs, C5), 125.9 (bs, C3),
42.7 (s, NMe), 42.4 (s, NMe2). 31P NMR (CD2Cl2, d): 22.8 (s, PPh3).
Anal. Calc. for C45H42N2O3P2SClF3Ni (866.0): C, 59.79; H, 4.68; N,
3.10. Found: C, 60.03; H, 4.58; N, 3.22%.
4.5. Preparation of 2-chloro-1-methyl-4-(phenylamino)pyridinium
triflate, 5
4.8. Preparation of trans-chloro[2-(dimethylamino)-1-methyl-1H-
Compound 2 (0.62 g, 2.0 mmol) was dissolved in 4 ml water at
0 °C and aniline (0.18 ml, 0.19 g, 2.0 mmol) was added drop wise.
The solution turned yellow and then a light yellow precipitate
formed. CH2Cl2 (20 ml) was added, the organic phase was sepa-
rated, dried with MgSO4, filtered and dried in vacuo to yield a light
orange solid (0.46 g, 1.3 mmol), the crude product. Orange needles
of complex 5 were obtained via vapour diffusion of n-pentane into
a CH2Cl2 solution of the product at À22 °C. These were used for the
crystal structure and melting point determination as well as ele-
mental analysis and MS. The crude product was used to determine
the NMR spectra. Yield: 62.5%. Mp. 98.5–102.1 °C. FAB-MS, m/z
(relative intensity) for C13H12N2O3SClF3: 221.1 [M+ÀCF3SO3, 35
pyrid-4-ylidene]bis(triphenylphosphine)-palladium(II) triflate, 7b
Compound
4 (0.17 g, 0.55 mmol) and Pd(PPh3)4 (0.66 g,
0.58 mmol) were suspended in 30 ml of toluene and stirred for
17 h at 60 °C. The white suspension in a light yellow solution was al-
lowed to cool to room temperature and filtered through Celite. The
solid on the filter was washed with 4 Â 5 ml toluene and the product
was dissolved in CH2Cl2 and filtered, to yield after solvent evapora-
tion in vacuo 0.48 g (0.50 mmol) of complex 7b. Colourless blocks
were obtained by the vapour diffusion of n-pentane into a concen-
trated CH2Cl2 solution of the product. Yield: 92%. Mp. 195 °C (de-
comp.). FAB-MS, m/z (relative intensity) for C45H42N2O3P2SClF3Pd:
801.4 [M+ÀCF3SO3, 8 (35Cl, 106Pd)], 541.2 (MÀPPh3–CF3SO3, 5),
136.1 (MÀCl–2PPh3–Pd–CF3SO3, 82). 1H NMR (CD2Cl2, d): 7.64 (m,
12H, o-PPh3), 7.50 (m, 6H, p-PPh3), 7.40 (m, 12H, m-PPh3), 6.99 (m,
2H, H5 and H6), 6.45 (d, 1H, 4J = 1.0 Hz, H3), 3.52 (s, 3H, NMe),
2.48 (s, 6H, NMe2). 13C NMR (CD2Cl2, d): 194.0 (t, 2J = 5.5 Hz, C4),
153.7 (s, C2), 136.8 (s, C6), 134.9 (m, o-PPh3), 131.3 (s, p-PPh3),
129.9 (m, i-PPh3), 128.8 (m, m-PPh3), 127.5 (bs, C5), 125.0 (t,
2J = 4.3 Hz, C3), 43.0 (s, NMe), 42.4 (s, NMe2). 31P NMR (CD2Cl2, d):
23.7 (s, PPh3). Anal. Calc. for C45H42N2O3P2SClF3Pd (913.7): C,
56.79; H, 4.45; N, 2.94. Found: C, 56.66; H, 4.54; N, 2.88%.
(
37Cl)], 219.1 [M+ÀCF3SO3, 95 (35Cl)]. 1H NMR (CD2Cl2, d): 9.67
(bs, 1H, NH), 7.53 (m, 2H, o-NPh), 7.41 (m, 1H, H3), 7.38 (m, 1H,
p-NPh), 7.31 (m, 2H, m-NPh), 7.01 (d, 1H, 4J = 2.3 Hz, H6), 6.94
(dd, 1H, 3J = 7.2 Hz, 4J = 2.3 Hz, H5), 4.11 (s, 3H, NMe). 13C NMR
(CD2Cl2, d): 151.9 (s, C2), 145.3 (s, C4), 143.3 (s, C6), 136.0 (s,
C3), 130.6 (s, o-NPh), 130.4 (s, C5), 129.6 (s, i-NPh), 129.1 (s, p-
NPh), 126.4 (s, m-NPh), 43.4 (s, NMe). Anal. Calc. for
C13H12N2O3SClF3 (368.8): C, 42.34; H, 3.28; N, 7.60. Found: C,
42.01; H, 3.12; N, 7.72%.
4.6. Preparation of trans-chloro[1-methyl-2-(dimethylamino)-1H-
pyrid-4-ylidene]bis(triphenyl-phosphine)palladium(II) triflate, 6
4.9. Preparation of trans-chloro[1-methyl-4-(phenyl-amino)-1H-
pyrid-2-ylidene]bis(triphenylphosphine)-nickel(II) triflate, 8a
Pd(PPh3)4 (0.32 g, 0.27 mmol) and the imine ligand 3 (0.030 g,
0.19 mmol) were suspended in THF (20 ml) and the mixture was
stirred at 70 °C for 16 h. The resulting precipitate was filtered
through Celite and washed with 3 Â 5 ml THF. The white product
was dissolved in CH2Cl2, filtered and dried under high vacuum to
produce 0.085 g (0.11 mmol) of 6. Yield: 56%. Mp. 182 °C (de-
Ni(PPh3)4 (0.30 g, 0.27 mmol) and the triflate salt 5 (0.095 g,
0.26 mmol) were suspended in THF (20 ml) and the mixture was
stirred at room temperature for 17 h. The resulting yellow precip-
itate in a brown solution was filtered through Celite and washed
with 3 Â 5 ml toluene. The product was dissolved in CH2Cl2, fil-
tered and dried under high vacuum to yield 0.16 g (0.17 mmol)
of light yellow 8a. Yield: 66%. Mp 200 °C (decomp.). FAB-MS, m/z
(relative intensity) for C49H42N2O3P2SClF3Ni: 803.0 [M+ÀCF3SO3, 9
comp.). FAB-MS, m/z (relative intensity) for
C43H39N2P2ClPd:
787.0 [M+, 6, (35Cl, 106Pd)], 525.0 (MÀPPh3, 8), 489.9 (MÀCl–PPh3,
1). 1H NMR (CD2Cl2, d): 7.64 (m, 12H, o-PPh3), 7.48 (m, 6H, p-
PPh3), 7.38 (m, 12H, m-PPh3), 6.35 (dd, 1H, 3J = 6.8 Hz, 4J = 1.3 Hz,
H5), 6.17 (d, 1H, 3J = 6.8 Hz, H6), 6.00 (d, 1H, 4J = 2.3 Hz, H3), 3.52
(s, 3H, NMe), 2.48 (s, 3H, @NMe). 13C NMR (CD2Cl2, d): 148.5 (s,
C4), 134.9 (m, o-PPh3), 133.3 (s, C2), 131.2 (s, p-PPh3), 130.0 (m,
i-PPh3), 128.6 (m, m-PPh3), 129.1 (s, C6), 121.3 (bs, C5), 117.5
(bs, C3), 42.6 (s, NMe), 29.2 (s, @NMe). 31P NMR (CD2Cl2, d): 24.0
(s, PPh3). Anal. Calc. for C43H39N2P2ClPd (787.6): C, 65.57; H,
4.99; N, 3.56. Found: C, 65.31; H, 5.08; N, 3.45%.
(
35Cl, 58Ni)], 539.2 (MÀPPh3–CF3SO3, 32). 1H NMR (CD2Cl2, d):
8.56 (bs, 1H, NH), 7.60 (m, 12H, o-PPh3), 7.50 (m, 6H, p-PPh3),
7.40 (m, 12 H, m-PPh3), 7.34 (m, 2H, o-NPh and H3), 7.29 (m, 1H,
p-NPh), 6.75 (m, 3H, m-NPh and H5), 6.63 (d, 1H, 3J = 7.3 Hz, H6),
3.62 (bs, 3H, NMe). 13C NMR (CD2Cl2, d): 194.1 (s, C2), 148.0 (s,
C6), 142.6 (s, C5), 137.6 (s, C3), 134.4 (m, o-PPh3), 131.4 (s, p-
PPh3), 129.9 (s, o-NPh), 129.4 (s, C4), 129.2 (s, p-NPh), 129.1 (m,
m-PPh3), 126.2 (s, i-NPh), 125.2 (m, i-PPh3), 123.7 (s, m-NPh),
49.0 (s, NMe). 31P NMR (CD2Cl2, d): 21.0 (s, PPh3). Anal. Calc. for
4.7. Preparation of trans-chloro[2-(dimethylamino)-1-methyl-1H-
C49H42N2O3P2SClF3Ni (952.0): C, 61.82; H, 4.45; N, 2.94. Found: C,
pyrid-4-ylidene]bis(triphenylphosphine)-nickel(II) triflate, 7a
61.48; H, 4.52; N, 2.63%.
Compound 4 (0.017 g, 0.055 mmol) and Ni(PPh3)4 were dissolved
in THF and stirred for 4 h at room temperature. The solution was
then filtered through Celite, washed with 2 Â 10 ml THF and the
product was washed through with CH2Cl2 to furnish after solvent
evaporation 0.045 g (0.050 mmol) of complex 7a. Yellow needles
4.10. Preparation of trans-chloro[1-methyl-4-(phenyl-amino)-1H-
pyrid-2-ylidene]bis(triphenylphosphine)-palladium(II) triflate, 8b
The same synthetic procedure used for the preparation of
complex 7b was employed for the synthesis of 0.38 g (0.38 mmol)

E. Stander-Grobler et al. / Inorganica Chimica Acta 376 (2011) 87–94
93
Table 2
Crystal data, data collection and refinement for compounds 5, 7a, 7b and 8b.
5
7a
7b
8b
Molecular formula
Molecular weight
Crystal system
Crystal dimensions (mm)
Crystal shape and colour
Space group
a (Å)
b (Å)
c (Å)
b (°)
C
13H12ClF3N2O3S
C45H42ClF3N2NiO3P2S
903.97
C45H42ClF3N2O3P2PdSÁ2CH2Cl2
1121.5
C49H42ClF3N2O3P2PdSÁ2CH2Cl2
1169.6
368.76
monoclinic
0.40 Â 0.30 Â 0.18
light orange needle
P21/c (No. 14)
11.373(4)
7.316(3)
18.520(7)
94.242(6)
90
1537(1)
4
1.594
0.432
monoclinic
0.35 Â 0.10 Â 0.09
yellow needle
P21 (No.4)
12.590(7)
10.871(6)
15.486(9)
95.178(9)
90
2111(2)
2
1.422
0.704
monoclinic
0.15 Â 0.09 Â 0.08
colourless block
P21/c (No. 14)
17.927(2)
16.984(2)
16.266(2)
106.089(2)
90
4758.7(9)
monoclinic
0.21 Â 0.14 Â 0.07
colourless prism
P21/n (No. 14)
14.1762(9)
10.6605(7)
34.249(2)
96.183(1)
90
5145.8(6)
4
c
(°)
Volume (Å3)
Z
4
Dcalc (g cm3)
1.565
0.837
1.510
0.778
l(Mo K
a
) (mmÀ1
)
F(0 0 0)
752
936
2280
2376
h Range for data collection (°)
Index range
1.80–26.40
À11 < h < 14, À9 < k < 9,
À23 < l < 19
8412
3121 (Rint = 0.0332)
0.946 and 0.564
1.32–26.37
À14 < h < 15, À13 < k < 13,
À19 < l < 15
12 290
8038 (Rint = 0.0939)
0.939 and 0.715
1.68–26.43
À18 < h < 22, À21 < k < 21,
À19 < l < 20
27 321
9740 (Rint = 0.0446)
0.936 and 0.802
1.20–26.40
À15 < h < 17, À13 < k < 13,
À40 < l < 42
29 645
10 484 (Rint = 0.0310)
0.948 and 0.798
Number of reflections collected
Number of unique reflections
Maximum and minimum
transmission
Refinement parameters /
restraints
209 parameters, 0 restraints 526 parameters, 13 restraints
580 parameters, 0 restraints
614 parameters, 0 restraints
Goodness-of-fit (GOF) on F2
1.062
0.966
1.032
1.127
Final R-indices [I > 2
r
(I)]
R1 = 0.0409
wR2 = 0.1071
R1 = 0.475
wR2 = 0.1124
0.600 and À0.402
R1 = 0.0786
wR2 = 0.1063
R1 = 0.1562
wR2 = 0.1317
0.728 and À0.544
R1 = 0.0479
wR2 = 0.1116
R1 = 0.0687
wR2 = 0.1215
2.952 and À1.084
R1 = 0.0419
wR2 = 0.0962
R1 = 0.0477
wR2 = 0.1023
0.923 and À0.468
R indices (all data)
Largest difference in peak and
hole (e AÀ3
)
Weighing schemea
a = 0.0627/b = 0.8418
a = 0.0215/b = 0
a = 0.0585/b = 8.1515
a = 0.0427/b = 6.2334
P
P
wR2 = { [w(F2o À Fc2)2]/ [w(Fo2)2]}1/2; w = 1/[
r
2(F2o )+(aP)2 + bP + d + e sinh]; P = [f(Max(0 or Fo2)] + (1 À f) F2c .
a
of complex 8b from 0.17 g (0.45 mmol) of 5 and 0.85 g (0.74 mmol)
of Pd(PPh3)4. Yellow prisms were obtained by the vapour diffusion
of n-pentane into a concentrated CH2Cl2 solution of the product.
Yield: 83%. Mp 239 °C (decomp.). FAB-MS, m/z (relative intensity)
for C49H42N2O3P2SClF3Pd: 849.3 [M+ÀCF3SO3, 12 (35Cl, 106Pd)],
587.2 (MÀPPh3–CF3SO3, 14), 551.8 (MÀCl–PPh3–CF3SO3, 5). 1H
NMR (CD2Cl2, d): 8.63 (bs, 1H, NH), 7.56 (m, 12H, o-PPh3), 7.52
(m, 6H, p-PPh3) 7.42 (m, 12H, m-PPh3), 7.40 (m, 2H, o-NPh), 7.30
(m, 1H, p-NPh), 7.24 (m, 1H, H3), 6.79 (m, 2H, m-NPh), 6.75 (d,
1H, 3J = 2.64 Hz, H5), 6.50 (bd, 1H, H6), 3.41 (bs, 3H, NMe). 13C
NMR (CD2Cl2, d): 182.0 (s, C2), 150.2 (s, C6), 142.3 (s, C5), 137.5
(s, C3), 134.4 (m, o-PPh3), 131.6 (s, p-PPh3), 129.8 (s, o-NPh),
129.4 (s, p-NPh), 129.2 (s, m-PPh3), 128.8 (s, C4), 126.2 (s, i-NPh),
125.2 (m, i-PPh3), 123.5 (s, m-NPh), 49.4 (s, NMe). 31P NMR (CD2Cl2,
d): 22.8 (s, PPh3). Anal. Calc. for C49H42N2O3P2SClF3Pd (999.8): C,
58.87; H, 4.23; N, 2.80. Found: C, 58.80; H, 4.32; N, 2.73%.
carbon atoms as ‘‘riding model’’ for all the complexes. All non-
hydrogen atoms were refined anisotropically by full-matrix least
squares calculations on F2 using SHELX-97 [20] within the X-seed
environment [21]. Figures were generated with POV Ray for Win-
dows, with the displacement ellipsoids at 50% probability level.
Acknowledgements
We gratefully thank Sasol (ES-G), the Alexander von Humboldt
Stiftung (HGR, SC and OS), the Oppenheimer Memorial Trust (HGR)
and the NRF (National Research Foundation, South Africa – OS) for
financial support.
Appendix A. Supplementary material
CCDC 817254, 817255, 817256 and 817257 contain the supple-
mentary crystallographic data for compounds 5, 7a, 7b and 8b,
respectively. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.ica.2011.
05.038.
4.11. X-ray data collection
Crystal data collection and refinement details of compounds, 5,
7a, 7b and 8b are summarised in Table 2. Data sets were collected
on a Bruker SMART Apex CCD diffractometer with graphite mono-
chromated Mo K
measured using the
a
radiation (k = 0.71073 Å) [16]. Intensities were
-scan mode and were corrected for Lorentz
x
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synthesis (7b and 8b), which yielded the position of the metal
atom, and conventional Fourier methods. The positions of the
hydrogen atoms were calculated by assuming ideal geometry and
their coordinates were refined together with those of the attached
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