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tionalized nanoparticles were isolated by centrifugation and
washed several times with PBS and water. The material was kept in
aqueous medium before use. HYP-[G#2]-(NH2)z (4.59 g, 2.81 mmol,
3 equiv.) was dissolved in PBS (200 mL, pH 7.2, 0.1m). Aldehyde-
functionalized nanoparticles (2.0 g, 0.94 mmol of terminal alde-
hyde, 1 equiv.) were then suspended in PBS (200 mL) and added to
the first suspension portionwise. The mixture was left to react at
RT overnight. The modified nanoparticles were isolated by centrifu-
gation and washed several times with PBS and water. Finally the
solid product Fe3O4@SiO2-HYP-NH2 was washed with methanol and
kept in this organic medium.
Synthesis of dendrimer HYP-[G#2]-(NH2)z
Preparation of Glycine-Boc adduct (Gly-Boc)
Glycine (5.0 g, 66.6 mmol) was suspended in a mixture of dioxane
(40 mL) and a solution NaOH (40 mL, 1 molLÀ1) in an ice bath. BOC
(15.99 g, 16.83 mL, 73.26 mmol) was added dropwise to the solu-
tion, and the reaction was stirred at RT for 8 h. The organic solvent
was removed under vacuum, and the pH of the resulting aqueous
phase was adjusted to 4 by the addition of a 1 molLÀ1 solution of
HCl. The aqueous layer was extracted with EtOAc (3100 mL). The
organic phase was dried with MgSO4 and concentrated and dried
1
under vacuum to give Gly-BOC as a white powder (95%). H NMR
(200 MHz, CDCl3): d=1.46 (s, 6H, ÀCH3), 1.53 (s, 3H, ÀCH3),
Preparation of Fe3O4@SiO2-HYP-N(CH2PPh2)2
3.97 ppm (d, 2H, ÀCH2).
The terminal amino groups in Fe3O4@SiO2-HYP-NH2 were subjected
to phosphinomethylation.[21] Under an inert atmosphere (N2), a mix-
ture of paraformaldehyde (1.82 mmol) and diphenylphosphine
(2.00 mmol) in methanol (5 mL) was heated at 608C for 1 h. Then,
the suspension of Fe3O4@SiO2-HYP-NH2 (1.00 g, 0.5 mmol of ÀNH2)
in a toluene (20 mL)/methanol (10 mL) solution was added to the
reaction mixture, which was stirred overnight at RT. Then, the solid,
Fe3O4@SiO2-HYP-N(CH2PPh2)2, was washed five times with toluene
and dried under vacuum.
Preparation of HYP-[G#2]-(Gly-BOC)y
HYP-[G#2]-(OH)12 (2.5 g, 2.12–25.44 mmol of OH-1 equiv.), Gly-BOC
(5.79 g, 33.07 mmol, 1.3 equiv.), DMAP (4.04 g, 33.07 mmol,
1.3 equiv.), and pyridine (10.3 mL, 127.2 mmol, 5 equiv.) were dis-
solved in dry CH2Cl2 (50 mL) in an ice bath. A solution of DCC
(6.82 g, 33.07 mmol, 1.3 equiv.) in CH2Cl2 (25 mL) was then added
dropwise. The mixture was warmed to RT and left to react for 72 h.
The urea formed and the unreacted catalyst were removed by fil-
tration. The filtrate was diluted in CH2Cl2 (1 L), and the organic
phase was washed with a 10% w/w solution of NaHSO4 (3
120 mL) and brine (1120 mL). The organic phase was dried with
MgSO4, concentrated, and dried under vacuum. The residue was
purified by liquid column chromatography on silica gel, eluting
with a 60:40 mixture of EtOAc/hexane to give HYP-[G#2]-(Gly-
Preparation of Fe3O4@SiO2-HYP-N(CH2PPh2)2Rh
Fe3O4@SiO2-HYP-N(CH2PPh2)2 was used as the support for the im-
mobilization of Rh NPs. A toluene solution that contained Rh-TOAB
NPs (ꢀ30 mL, 0.11 mmol of Rh) was added to the support
(500 mg). The mixture was stirred overnight, and the solids were
separated magnetically. After the separation, the catalyst,
Fe3O4@SiO2-HYP-N(CH2PPh2)2Rh, was washed several times with tol-
uene and dried under vacuum.
1
BOC)y as a yellow oil (82%). H NMR (200 MHz, CDCl3): d=0.88 (t,
3H, ÀCH3), 1.26 (m, 27H, ÀCH3), 1.44 (s, 81H, ÀCH3), 3.89 (d, 20H,
ÀCH2), 4.10 (s, 6H, ÀCH2), 4.27 (s, 36H, ÀCH2), 5.38 ppm (s, 9H,
ÀNH). 13C NMR (50 MHz, [D6]DMSO): d=17.2, 17.3, 17.6, 50.6, 50.7,
63.6, 64.2, 64.2, 64.4, 65.3, 68.5, 68.8, 70.2, 70.3, 172.9, 174.5, 174.7,
175.1 ppm; HRMS (ESI): m/z: calcd for C114H185N9O57: 2612.16
[M+Na+]; found: 2616.10.
Catalytic reactions
Catalytic experiments were performed in 100 mL homemade stain-
less-steel reactors with magnetic stirring. Reactions were followed
by using GC by sampling the liquid phase with a valved dip tube.
Typically, a mixture of toluene (20 mL), the Rh catalyst (10 mg,
1 mmol of Rh), the substrate (2.0 mmol), and dodecane (internal
standard, 1 mmol) was transferred to the reactor, which was pres-
surized to 40–60 atm with a CO/H2 mixture. The temperature (80–
1008C) was maintained with an oil bath and a hot-stirring plate
connected to a digital temperature controller. The reactions were
conducted under magnetic stirring (700 rpm). After the reaction
was performed, the reactor was cooled to RT, the pressure was re-
leased, and the catalyst was recovered magnetically with an exter-
nal magnet.
Preparation of HYP-[G#2]-(NH2)z
HYP-[G#2]-(Gly-BOC)y (2.0 g, 0.65 mmol) was dissolved in CH2Cl2
(5 mL) in an ice bath, then TFA (5 mL) and CH2Cl2 (1:1) were added
dropwise. The mixture was warmed to RT and stirred for 15 min.
The solvent and residual acid were removed by vacuum. The resi-
due, HYP-[G#2]-(NH2)z, was then stirred in the presence of ion-ex-
change resin (2 g; Amberlyst, hydroxide form) in dry methanol
(10 mL) for 15 min. 1H NMR (200 MHz, [D4]MeOD): d=0.99 (t, 3H,
ÀCH3), 1.21 (s, 9H, ÀCH3), 1.33 (m, 18H, ÀCH3), 1.60 (q, 2H, ÀCH2),
3.92 (d, 7H, ÀCH2), 4.16 (s, 6H, ÀCH2), 4.31–4.43 ppm (m, 36H,
ÀCH2); 13C NMR (50 MHz, [D6]DMSO): d=16.9, 17.5, 39.9, 46.7, 50.6,
50.8, 52.6, 64.1, 64.8, 66.7, 168.4, 173.3, 174.6 ppm; HRMS (ESI):
m/z: calcd for C73H119N11O41: 1827.42 [M+Na+]; found: 1834.84.
Characterization methods
TEM was performed by using a Jeol-2100 microscope. Samples for
TEM were prepared by placing a drop that contained the nanopar-
ticles dispersed in propan-2-ol on a carbon-coated copper grid
(Ted Pella, Inc.). The Rh content in the catalysts was measured by
using FAAS by using a Shimadzu AA-6300 Atomic Absorption Spec-
trophotometer. The Rh leaching to the supernatant solutions was
measured by using a SPECTO ARCOS ICP-OES. The products were
analyzed by using GC (Shimadzu QP2010 GC, Rtx-5MS capillary
column, flame ionization detector (FID)) and GC–MS (Shimadzu
QP2010-PLUS instrument operating at 70 eV). The conversion and
Preparation of Fe3O4@SiO2-HYP-N-(CH2PPh2)2
Preparation of Fe3O4@SiO2-HYP-NH2
In a round-bottomed flask, Fe3O4@SiO2-NH2 (200 mg; 9.4 mmol of
NH2) was suspended in a phosphate buffer solution (PBS; 40 mL;
pH 7.2, 0.1 molLÀ1) with a mechanical stirrer. A glutaraldehyde
aqueous solution (1.6 mL, 50 wt% in water) was added, and the
mixture was stirred vigorously at RT for 1.5 h. The aldehyde-func-
ChemCatChem 2016, 8, 1951 – 1960
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