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S. Siangwata et al. / Journal of Organometallic Chemistry xxx (2015) 1e7
with homogeneous catalysis, such as long chain aldehyde product
recovery. The aldehydes generated from the atom-economical
hydroformylation reaction are typically processed into valuable
consumer products in the cosmetics, bulk and fine chemicals in-
dustries [6].
Various avenues continue to be explored in order to improve
and develop the aqueous-biphasic hydroformylation process. We
have investigated the use of water-soluble Rh(I) complexes bearing
chelating N,O-bidentate ligands, as well as metallodendrimers
containing multiple peripheral active sites [7,8]. However, the
multinuclear dendritic complexes do not show any improved cat-
alytic activity from their mononuclear counterparts probably due to
poor stability of the macromolecular structures in water [8]. Ligand
modification is often of interest as, in some instances, it influences
the main catalytic centre through changing electronic and steric
factors, which in turn alters the hydroformylation rates and sub-
strate conversion [7e11].
Recent efforts in the field of catalysis involve the use of bime-
tallic catalyst precursors in various olefin transformation reactions
[12e16]. The improved catalytic properties of metalloenzymes
(bearing two or more active centres) have catapulted studies into
the application of bimetallic complexes in catalysis and medicine
amongst other fields [17,18]. The premise behind this approach is
that the addition of another metal confers unique and intriguing
chemical and catalytic behaviour to the complexes and often results
in improved activity and increased reaction rates [18]. A typical
example may involve one metal acting as the main catalytic centre
whereas the other metal serves as an electron reservoir, stabilising
the electron density around the catalytic centre. Ferrocene, a redox-
active sandwich complex, has been included in several hetero-
bimetallic complexes in combination with other transition metals,
bridged by various ligand structures. In this context, the inclusion
of ferrocene moieties modified with phosphorus donor sites is very
common [16,19,20].
To the best of our knowledge, no water-soluble ferrocenyl-based
heterobimetallic complexes containing N,O-bidentate ligands have
been reported in the literature. A combination of rhodium com-
plexes with the chemically robust and redox- active ferrocene in
forming water-soluble heterobimetallic complexes is of interest to
the continued pursuit of designing and isolating new organome-
tallic complexes with interesting properties. Moreover, the appli-
cation of such complexes in the aqueous-organic biphasic
hydroformylation of higher olefins, from an efficient catalyst design
and Green Chemistry perspective, is also intriguing. As an extension
of our previous work [8], we were prompted to evaluate the effect
of heterobimetallic complexes in the hydroformylation process. In
this paper, we report the synthesis and characterisation of a series
of new water-soluble sulfonated heterobimetallic complexes and
their reactivity as catalyst precursors in the aqueous biphasic
hydroformylation of 1-octene.
million (ppm) relative to the internal standard tetramethylsilane (d
0.00). FT-IR spectra were recorded as KBr pellets using a Perkin
Elmer 100 Spectrum One spectrometer or using Attenuated Total
Reflectance Infrared spectroscopy (ATR-IR). Melting points were
determined using a Büchi melting point apparatus B-540. Mass
spectrometry was carried out on a Waters Synapt G2 electron spray
ionisation mass spectrometer in the positive or negative-ion mode.
Elemental analyses were carried out using a Fision EA 110 CHNS
Analyser. A Perkin Elmer Clarus 580 GC instrument equipped with a
flame ionisation detector and 30 m capillary column was used for
analysing and quantifying the catalytic products. Inductively
coupled plasma optical emission spectroscopy experiments were
conducted on an ICP-OES Varian 730-ES spectrophotometer.
Preparation of monosodium-5-sulfonatosalicylaldimine (3)
Hydrazine hydrate (0.805 g, 16.07 mmol) was added to a stirring
solution of monosodium-5-sulfonato salicylaldehyde (1.80 g,
8.035 mmol)in ethanol and thereaction mixture refluxed for 1 h. The
resultant pale yellow precipitate was collected by suction filtration
while the solution was still hot, and washed with hot ethanol. Yield:
(1.50 g, 78%). M.P.: decomposes without melting, onset occurs at
394 ꢀC. 1H NMR (DMSO-d6,
d ppm): 11.51 (s, 1H, OH), 7.94 (s, 1H,
H
imine), 7.48 (d, 4J ¼ 2.0Hz,1H, Ar), 7.37 (dd, 4J ¼ 2.0Hz, 3J ¼ 8.4 Hz,1H,
Ar), 6.88 (s, 2H, NH2), 6.75 (d, 3J ¼ 8.4 Hz, 1H, Ar). 13C{1H} NMR
(DMSO-d6, d ppm): 157.1, 141.9, 139.9, 126.9, 126.0, 119.0, 115.2. FT-IR
(
nmax/cmꢁ1): 3409 (NeH), 3297 (OeH),1619 (C]N). Anal. Calcd. For:
C7H7N2NaO4S, C: 35.30, H: 2.96, N: 11.76. Found: C: 35.23, H: 2.70, N:
11.69. ESI-MS (m/z) ¼ 215.01 ([M] where M is the anion).
Preparation of monosodium 5-sulfonatosalicylaldimine-
ferrocenylimine (4)
Monosodium5-sulfonatosalicylaldimine (0.101 g, 0.4260 mmol)
was added to a stirring solution of ferrocenecarboxaldehyde
(9.10 ꢂ 10ꢁ2 g, 0.4260 mmol) in 20 cm3 methanol and the reaction
mixture refluxed for 48 h. The dark red solution was cooled to room
temperature and filtered under gravity. The solvent of the filtrate
was reduced to ca. 5 mL and dichloromethane was added to pre-
cipitate the product which was collected by filtration as a dark red
solid. Yield: (0.151 g, 82%). M.P.: decomposes without melting, onset
occurs at 174 ꢀC. 1H NMR (DMSO-d6,
d ppm): 11.51 (s, 1H, OH), 8.82
(s, 1H, Himine), 8.64 (s, 1H, Himine), 7.91 (d, 4J ¼ 1.4 Hz, 1H, Ar), 7.59
(dd, 3J ¼ 8.4 Hz, 4J ¼ 1.6 Hz, 1H, Ar), 6.89 (d, 3J ¼ 8.4 Hz, 1H, Ar), 4.78
(br s, 2H, HFc), 4.57 (br s, 2H, HFc), 4.27 (s, 5H, HFc). 13C{1H} NMR
(DMSO-d6,
d ppm): 164.4, 160.9, 158.9, 140.6, 130.5, 128.7, 117.7,
115.9, 77.7, 71.8, 69.8, 69.4. FT-IR (nmax/cmꢁ1): 1624 (C]N), 1589
(C]N). Anal. Calcd. For: C18H15FeN2NaO4S.4H2O, C: 42.70, H: 4.58,
N: 5.53. Found: C: 42.89, H: 4.44, N: 5.70. ESI-MS (m/z) ¼ 411.01 ([M]
where M is the anion). S25 ¼ 1.87 mg mLꢁ1 in water.
ꢀ
C
Experimental
Preparation of 3-tbutyl-5-sulfonato salicylaldimine-ferrocenylimine
complex (5)
Materials and methods
Hydrazine hydrate (0.187 g, 3.729 mmol) was added dropwise to
a stirring solution of 3-tbutyl-5-sulfonatosalicylaldehyde (1.05 g,
3.729 mmol) in methanol and the reaction heated for 6 h at 45 ꢀC.
Ferrocenecarboxaldehyde (0.799 g, 3.731 mmol) was then added
and the reaction mixture heated at 45 ꢀC for 24 h. The dark brown
solution was filtered by gravity to remove an orange precipitate, the
ferrocenylcarbaldehyde hydrazone (see supplementary material for
characterisation data). The volume of the filtrate was then reduced
to ca. 5 mL and diethyl ether was added to precipitate out a brown
solid which was collected by filtration and dried in vacuo. Yield:
(1.50 g, 82%). M.P.: decomposes without melting, onset occurs at
All reactions were carried out in air unless otherwise stated. All
solvents were reagent grade and used as received from Sigma-
eAldrich, unless otherwise stated. RhCl3.3H2O was purchased from
Heraeus South Africa. All other chemicals were purchased from
Sigma Aldrich and used as received. The sulfonated salicylaldehydes
(1 and 2) were prepared according to previously reported literature
procedures [8]. Nuclear Magnetic Resonance (NMR) spectra were
recorded on either a Bruker Ultrashield 400 Plus (1H: 400.22 MHz;
13C: 100.65 MHz) or a Bruker 300 MHz (1H: 300.08 MHz; 13C:
75.46 MHz) spectrometer. Chemical shifts werereported inparts per
j.jorganchem.2015.04.029
Siangwata, Shepherd
