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and diethylether (100 mL). The layers were separated and the
aqueous layer was extracted twice with diethylether (100 mL). The
combined organic layers were washed five times with HCl (1m),
once with saturated Na2CO3 solution and twice with brine. After
drying over MgSO4 the solvent was removed under reduced pres-
sure and a colorless solid was obtained (yield: 11.4 g, 23.6 mmol,
any loss of activity. The observed increase of reactivity during
the recycling process might indicate the formation of rhodium
nanoparticles. This indication is supported by X-ray absorption
spectroscopy. However, according to TEM investigations, the
particle diameters have to be far below 2 nm. No cleavage of
the organic ligand from the support takes place during the
catalysis and no leaching of rhodium could be detected by
AAS. We assign these findings to the strategy of synthesizing
the rhodium complex before tethering it onto the iron oxide
surface. Hereby, at least two of the phosphine units are in
close proximity to each other, stabilizing the complex on the
surface as well as the small rhodium nanoparticles. Further-
more, the phosphonate linker strongly binds to the maghemite
surface. These promising results open up new opportunities
for the immobilization of other homogenous catalysts on non-
silica-based inorganic oxides. We are currently investigating
the immobilization of different metal complexes on various
metal oxides by using the phosphonic acid bearing ligand 8.
1
75%). H NMR (400 MHz, CDCl3): d=7.83–7.76 (m, 2H, H-3), 7.37–
7.27 (m, 12H, ArH), 4.14–3.99 (m, 4H, H-9), 3.59–3.52 (m, 2H, H-6),
2.01–1.79 (m, 4H, H-7, H-8), 1.32–1.26 ppm (m, 6H, H-10);
1
13C{1H} NMR (101 MHz, CDCl3): d=167.2 (s, C-5), 141.8 (d, J(P,C)=
1
13.1 Hz, C-1), 136.5 (d, J(P,C)=10.7 Hz, C-i), 134.6 (s, C-4), 134.0 (d,
2
2J(P,C)=20.0 Hz, C-o), 133.6 (d, J(P,C)=18.9 Hz, C-2), 129.1 (s, C-p),
128.7 (d, 3J(P,C)=7.3 Hz, C-m), 127.1 (d, 3J(P,C)=6.5 Hz, C-3), 61.9
(d, 2J(P,C)=6.6 Hz, C-9), 40.3 (d, 3J(P,C)=12.1 Hz, C-6), 23.6 (d,
1J(P,C)=141.4 Hz, C-8), 22.5 (d, 2J(P,C)=4.6 Hz, C-7), 16.5 ppm (d,
3J(P,C)=6.0 Hz, C-10); 31P{1H} NMR (162 MHz, CDCl3): d=32.93 (s,
PO(OEt)2), ꢀ5.02 ppm (s, PPh2R); IR (ATR): n˜ =3287 (m) (NH), 2984
(w), 2937 (w), 1655 (vs) (CO), 1597 (m), 1550 (s), 1479 (m), 1434
(m), 1391 (m), 1302 (s), 1235 (vs), 1219 (s), 1174 (m), 1091 (m), 1023
(vs), 961 (vs), 852 (m), 817 (s), 743 (vs), 696 cmꢀ1 (vs); elemental
analysis calcd. (%) for C26H31NO4P2 (483.48): C 64.59, H 6.46, N 2.90;
found: C 64.38, H 6.60, N 2.86.
Experimental Section
(3-(4-(Diphenylphosphino)benzamido)propyl)phosphonic
acid
(8): Diethyl (3-(4-(diphenylphosphino)benzamido)propyl)phospho-
nate (7) (7.00 g, 14.5 mmol) was dissolved in dichloromethane
(60 mL). Trimethylbromosilane (7.50 mL, 56.8 mmol) was added
dropwise to the solution over a period of 1 h and the resulting
mixture was stirred for 12 h at rt. Then, the solvent and the residu-
al trimethylbromosilane were removed under reduced pressure.
The residue was combined with NaOH solution (1m, 150 mL). Di-
chloromethane (100 mL) was added to this suspension and the re-
sulting two-phase mixture was stirred vigorously for 10 min, fol-
lowed by the addition of HCl (1m) until no further precipitation of
a solid was observed and the pH value was 1. The solid was re-
moved by filtration, washed several times with water, acetone, and
dichloromethane before drying at 408C under reduced pressure.
The colorless solid is prone to oxidation and should be stored in
a cool place (yield: 6.05 g, 14.2 mmol, 98%). 1H NMR (600 MHz,
CDCl3 +CD3OD): d=7.77–7.73 (m, 2H, H-3), 7.36–7.25 (m, 12H,
ArH), 3.47–3.41 (m, 2H, H-6), 1.92–1.83 (m, 2H, H-7), 1.79–1.71 ppm
(m, 2H, H-8); 13C{1H} NMR (101 MHz, CDCl3 +CD3OD): d=169.2 (s,
C-5), 142.8 (d, 1J(P,C)=12.5 Hz, C-1), 136.8 (d, 1J(P,C)=9.9 Hz, C-i),
134.8 (s, C-4), 134.4 (d, 2J(P,C)=19.5 Hz, C-o), 133.9 (d, 2J(P,C)=
General remarks
All manipulations were performed under a nitrogen atmosphere
by using standard Schlenk techniques unless otherwise specified.
Solvents were dried by standard methods. Reagents were pur-
chased from ACROS, Alfa Aesar, or Sigma–Aldrich and used without
further purification, unless otherwise noted. NMR spectra were re-
corded with a Bruker DPX 400 and a Bruker Avance 600 spectro-
meter. Elemental analyses were carried out at the Fachbereich
Chemie (TU Kaiserslautern). The infrared spectra were recorded by
using a PerkinElmer FT-ATR IR 1000 spectrometer equipped with
a diamond-coated ZnSe window. Rhodium leaching was deter-
mined by atomic adsorption spectroscopy with a PERKIN ELMER
AAnalyst 300. XRD patterns were obtained on a Siemens D5005
diffractometer with Cu Ka radiation (40 kV, 30 mA, l=0,15405 nm).
Nitrogen physisorption isotherms were measured at liquid nitrogen
temperature by using a Quantachrome Autosorb 1 sorption ana-
lyzer. The specific surface areas were calculated by the BET equa-
tion at a relative pressure of 0.05 to 0.5 (p/p). Thermogravimetric
analyses (TGA) were carried out on a Setaram Setsys 16/18. TEM
images were recorded on a Philips CM 300 UltraTwin microscope
with a LaB6 cathode at an acceleration voltage of 300 kV. The sam-
ples were deposited onto commonly used copper TEM grids
coated with a continuous carbon film. For the procedures used for
the synthesis of compounds 1–6 and of the g-Fe2O3 nanoparticles,
as well as for the assignment of the NMR resonances and further
details on X-ray structure analysis and X-ray spectroscopy, see the
Supporting Information.
3
19.1 Hz, C-2), 129.7 (s, C-p), 129.2 (d, J(P,C)=7.9 Hz, C-m), 127.6 (d,
3
1
3J(P,C)=7.0 Hz, C-3), 40.8 (d, J(P,C)=17.2 Hz, C-6), 25.0 (d, J(P,C)=
138.8 Hz, C-8), 23.3 ppm (d, 2J(P,C)=3.9 Hz, C-7); 31P{1H} NMR
(243 MHz, CDCl3 +CD3OD): d=30.54 (s, PO(OH)2), ꢀ4.66 ppm (s,
PPh2R); IR (ATR): n˜ =3313 (m) (NH), 3051 (m), 2927 (m), 2693 (m)
(POH), 2205 (m), 1815 (w), 1708 (m) (CO), 1596 (m), 1541 (s), 1481
(m), 1434 (s), 1319 (m), 1278 (m), 1197 (m), 1141 (m), 1030 (m), 998
(vs), 944 (vs), 851 (m), 744 (vs), 724 (s), 692 cmꢀ1 (vs); elemental
analysis calcd. (%) for C22H23NO4P2·(CH2Cl2)0.1 (435.86): C 60.90, H
5.37, N 3.21; found: C 60.36, H 5.66, N 3.30.
Diethyl (3-(4-(diphenylphosphino)benzamido)propyl)phospho-
nate (7): Diethyl (3-aminopropyl)phosphonate hydrochloride (3)
(10.86 g, 44.6 mmol) and triethylamine (11.7 mL, 84.4 mmol) were
dissolved in dichloromethane (20 mL). In a different Schlenk tube,
4-(diphenylphosphino)benzoic acid (6) (9.60 g, 31.3 mmol), 1-ethyl-
3-(3-dimethylaminopropyl)carbodiimide (EDC, 7.20 g, 37.6 mmol),
and 4-dimethylaminopyridine (DMAP, 150 mg, 1.22 mmol) were dis-
solved in dichloromethane (50 mL). The content of the first Schlenk
tube was added to the second tube and the resulting mixture was
stirred for 72 h at rt. Then, the solvent was removed under reduced
pressure and the residue was combined with HCl (1m, 150 mL)
Carbonylchloridobis[(3-(4-(diphenylphosphino)benzamido)pro-
pyl)phosphonicacid]rhodium(I) (9): (3-(4-(Diphenylphosphino)-
benzamido)propyl)phosphonic acid (8) (220 mg, 514 mmol) was
suspended in dichloromethane (5 mL). A solution of tetracarbonyl-
di(m-chlorido)dirhodium(I) (50.0 mg, 129 mmol) in dichloromethane
(5 mL) was added to this mixture. The resulting suspension was
combined with methanol (1 mL) and the now clear yellow solution
was stirred for 40 min. After filtration and removal of the solvent
under reduced pressure, the yellow residue was washed twice with
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