Table 1 Hydrogenation of BT with [Rh(cod)(polytriphos)]PF6 (0.94
wt%)a
Entry
t/h
ET (%) EB (%) TON (ET) Conv. (%)
1
2
3
4b
5b
2
5
10
2
48.5
62.2
74.3
47.6
48.0
2.5
4.0
5.5
3.1
3.5
97
124
349
95
51.0
66.2
79.8
50.7
51.5
2
96
a Experimental conditions: 30 mL THF, Rh 3.5 3 1022 mmol, BT 7 mmol,
ButOK 7 mmol, 160 °C, 30 bar H2, 1500 rpm; product composition
determined by GC–MS after acidification of the catalytic mixture with
aqueous HCl. b Recycling in the same conditions of entry 1.
We are grateful to Claudia Forte (ICQEM-CNR of Italy) for
assistance in recording the CP MAS 31P NMR spectra and to
MURST (Italy) for financial support (legge 95/95).
Fig. 1 CP MAS 31P NMR (121.50 MHz) spectra of polytriphos (a) and
[Rh(cod)(polytriphos)]PF6 (b).
Notes and references
† Selected NMR data for 2,2,2-tris(diphenylphosphinomethyl)ethyl
apparatus and then dried. The rhodium content in the heteroge-
neous catalysts depends on the polytriphos sample; in partic-
ular, a loading of 7.24 wt% has been found for a polymer
obtained by copolymerising TVBE and DVB in a 1+1 ratio,
while a loading of 0.94 wt% has been found for a polymer
obtained by copolymerising TVBE, DVB and styrene in a
1
3
4-vinylbenzyl ether (TVBE): H NMR (CDCl3) dH 2.57 (d, 6H, CH2P, J
2.91 Hz), 3.16 (s, 2H, OCH2C(CH3)3), 3.71 (s, 2H, OCH2Ph), 5.24 (dd, Hcis
,
CH2NCH, Jcis 10.90 Hz, Jgem 0.97 Hz), 5.74 (dd, Htrans, CH2NCH, Jtrans
17.53 Hz, Jgem = 0.97 Hz), 6.71 (dd, 1H CHNCH2), 6.91–7.31 (m, 34H, Ph).
13C{1H} NMR (CDCl3) dC 38.87 (m, CH2P), 43.58 (q, CH2C(CH2PPh2),
J(CP) 12.4 Hz), 72.50 (s, OCH2Ph), 77.19 (m, OCH2C(CH3)3), 114.03 (s,
CH2NCH), 123.48-137.42 (m, Ph), 133.92 (s, CHNCH2). 31P{1H} NMR
(CDCl3) dP 226.1 (s). Satisfactory elemental analyses were obtained for all
compounds.
0.6+1+36 ratio. The coordination of rhodium( ) to the tethered
I
phosphine is demonstrated by the low-field shift to d 28.4 of the
2
phosphorus resonance as well as the presence of the PF6
‡ Solid-state 31P NMR spectra were recorded at room temperature on a
Bruker AMX 300 WB spectrometer equipped with a 4 mm BB-CP MAS
probe at a working frequency of 121.50 MHz. The spectra were acquired
using the cross-polarisation pulse sequence under magic angle spinning at a
spinning rate of 10 kHz. The 90° pulse was 3.3 ms, and the contact pulse was
1 ms. The spectra of the supported triphosphine were collected after 400
scans with a recycle delay of 1 s and a line broadening of 30 Hz, whereas
the spectra of the supported rhodium complex were acquired with 700
scans, a recycle delay of 1 s and a line broadening of 50 Hz. H3PO4 (85%)
was used as the external standard.
sextuplet at d 2143.5 (Fig. 1b).
As an example of the great potential of polytriphos metal
complexes in heterogeneous catalysis, [Rh(cod)(polytri-
phos)]PF6 (0.94 wt%) has been employed to hydrogenate
benzo[b]thiophene (BT) in tetrahydrofuran (THF) under basic
conditions (Scheme 2).4,5
Scheme 2 Hydrogenolysis of BT to 2-ethylthiophenol and ethylbenzene.
1 Applied Homogeneous Catalysis, ed. B. Cornils and W. A. Herrmann,
VCH, Weinheim, Germany, 1996, ch. 3; E. Lindner, T. Schneller, F.
Auer and H. A. Mayer, Angew. Chem., Int. Ed., 1999, 38, 2154; E. M.
Carnahan and G. B. Jacobsen, CATTECH, 2000, 4, 74.
2 C. Bianchini, D. G. Burnaby, J. Evans, P. Frediani, A. Meli, W.
Oberhauser, R. Psaro, L. Sordelli and F. Vizza, J. Am. Chem. Soc., 1999,
121, 5961; C. Bianchini, V. Dal Santo, A. Meli, W. Oberhauser, R.
Psaro and F. Vizza, Organometallics, 2000, 19, 2433; C. Bianchini, P.
Barbaro, V. Dal Santo, R. Gobetto, A. Meli, W. Oberhauser, R. Psaro
and F. Vizza, Adv. Synth. Catal., 2001, 343, XX.
3 C. Bianchini, A. Meli, M. Peruzzini, F. Vizza and F. Zanobini, Coord.
Chem. Rev., 1992, 120, 193; H. A. Mayer and W. C. Kaska, Chem. Rev.,
1994, 94, 1239.
4 C. Bianchini and A. Meli, J. Chem. Soc., Dalton Trans., 1996, 801; C.
Bianchini, A. Meli, S. Moneti, W. Oberhauser, F. Vizza, V. Herrera, A.
Fuentes and R. A. Sánchez-Delgado, J. Am. Chem. Soc., 1999, 121,
7071; T. Kabe, A. Ishihara and W. Qian, Hydrodesulfurization and
Hydrodenitrogenation, Kodansha, Tokyo, Japan and Wiley-VCH,
Weinheim, Germany, 1999.
5 C. Bianchini, A. Meli, V. Patinec, V. Sernau and F. Vizza, J. Am. Chem.
Soc., 1997, 119, 4945.
6 Th. Seitz, A. Muth, G. Huttner, Th. Klein, O. Walter, M. Fritz and L.
Zsolnai, J. Organomet. Chem., 1994, 469, 155.
7 F. Benvenuti, C. Carlini, A. M. Raspolli Galletti, G. Sbrana, M.
Marchionna and R. Patrini, J. Mol. Catal. A: Chem., 1999, 137, 49.
8 C. U. Pittman, Jr., L. R. Smith and R. M. Hanes, J. Am. Chem. Soc.,
1975, 97, 1742; F. Benvenuti, C. Carlini, M. Marchionna, R. Patrini,
A. M. Raspolli Galletti and G. Sbrana, J. Inorg. Organomet. Polym.,
1997, 7, 183.
Under rather harsh experimental conditions (160 °C, 30 bar
H2), the thiophenic substrate is mainly converted to 2-ethyl-
thiophenol (ET) but appreciable formation of the desulfurised
product ethylbenzene (EB) also occurs. Interestingly, no trace
of 2,3-dihydrobenzo[b]thiophene was detected by GC. Table 1
reports catalytic data obtained for runs at 2, 5 and 10 h. In all
cases, no rhodium leaching was observed by ICP-AES ( < 1
ppm), while an effective catalyst recycling with no loss of
catalytic activity was accomplished by removing the liquid
phase via the liquid sampling valve and recharging the
autoclave with a solution containing substrate and base (entries
4 and 5).
Under comparable experimental conditions, both the aque-
ous-biphase catalyst [Rh(cod)(sulphos)] in MeOH/n-heptane
[sulphos = 2O3S(C6H4)CH2C(CH2PPh2)3]5 and the homoge-
neous catalyst [Rh(DMAD)(triphos)]PF6 in THF (DMAD =
dimethyl acetylenedicarboxylate)9 are slightly less efficient
than [Rh(cod)(polytriphos)]PF6 for the hydrogenolysis of BT to
ET (TON ca. 90 vs. 124) and cannot be recycled after
catalysis.
The data reported in Table 1 are of great relevance in the field
of model studies of heterogeneous HDS as they show that a
single metal site belonging to the class of the HDS promoters10
can open and hydrogenate a thiophenic substrate without the
need of any cooperative effect.4,5 Besides this important result,
we have succeeded for the first time in producing a polymer-
supported tripodal triphosphine ligand with which we intend to
prepare a large variety of metal catalysts and study their
performance in heterogeneous processes.
9 C. Bianchini, J. A. Casares, A. Meli, V. Sernau, F. Vizza and R. A.
Sánchez-Delgado, Polyhedron, 1997, 16, 3099.
10 H. Topsøe, B. S. Clausen and F. E. Massoth, Hydrotreating Catalysis,
Springer-Verlag, Berlin, Germany, 1996.
480
Chem. Commun., 2001, 479–480