Pd(II) and Rh(I) chelate complexes of the bidentate phosphino-thiourea ligand PhNHC(S)NHCH2CH2PPh2: Structural properties and activity in homogeneous and hybrid catalysis

Article abstract of DOI:10.1016/S0022-328X(99)00615-4

The new bifunctional ligand PhNHC(S)NHCH₂CH₂PPh₂ (Ptu), containing the thiourea and the phosphine functions, and its Pd(II) and Rh(I) complexes were prepared. Ptu behaves as a bidentate ligand forming seven-membered chelat

Full text of DOI:10.1016/S0022-328X(99)00615-4

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 593–594 (2000) 431–444
Pd(II) and Rh(I) chelate complexes of the bidentate
phosphino–thiourea ligand PhNHC(S)NHCH2CH2PPh2: structural
properties and activity in homogeneous and hybrid catalysis
Daniele Cauzzi a, Mirco Costa b, Nicola Cucci a, Claudia Graiff a, Federica Grandi a,
Giovanni Predieri a, Antonio Tiripicchio a,*, Roberto Zanoni c
a Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Uni6ersita` di Parma,
Centro di Studio per la Strutturistica Diffrattometrica del CNR, Parco Area delle Scienze 17A, I-43100 Parma, Italy
b Dipartimento di Chimica Organica e Industriale, Uni6ersita` di Parma, Parco Area delle Scienze 17A, I-43100 Parma, Italy
c Dipartimento di Chimica, Uni6ersita` di Roma ‘La Sapienza’, Piazzale Aldo Moro 5, I-00185 Rome, Italy
Received 2 August 1999; accepted 13 October 1999
Dedicated to Professor Fausto Calderazzo on the occasion of his 70th birthday, in recognition of his outstanding contributions to inorganic
and organometallic chemistry.
Abstract
The new bifunctional ligand PhNHC(S)NHCH2CH2PPh2 (Ptu), containing the thiourea and the phosphine functions, and its
Pd(II) and Rh(I) complexes were prepared. Ptu behaves as a bidentate ligand forming seven-membered chelation rings in a
boat-like conformation. In the case of palladium, this was ascertained by the X-ray determination of the structure of the
complexes [Pd(Ptu)2]Cl2·6CHCl3 (1), [Pd(Ptu)2Cl]Cl·EtOH (2) and [Pd(Ptu)2][CoCl4].CHCl3·2EtOH (3). In complexes 1 and 3, the
two ligands are related centrosymmetrically, whereas in 2 they are folded by the same side in an umbrella arrangement. The Rh(I)
complexes [Rh(cod)(Ptu)]X (X=Cl or PF6; cod=1,5-ciclooctadiene) and [Rh(cod)(Ptu)]2[CoCl4] were characterized by 31P-NMR
and FT-IR spectroscopy. The catalytic activity in homogeneous hydrogenation and hydroformylation reactions of the Pd(II) and
Rh(I) complexes was dependent on the counter-anion, being very low in the case of Cl− and high in the case of non-coordinating
anionic groups such as CoCl−4 and PF−6 . The related ligand (EtO)3Si(CH2)3NHC(S)NHCH2CH2PPh2 (SiPtu) was sol-gel
processed giving hybrid inorganic–organic xerogels (XGPtu). Anchored Pd(II) and Rh(I) complexes were obtained by two
procedures: by treating XGPtu with solution of precursor complexes or by sol-gel processing previously prepared SiPtu complexes.
Palladium complexes of the thiourea ligand (EtO)3Si(CH2)3NHC(S)NHPh (Siphtu), with different S–Pd ratios, were also sol-gel
processed. The rhodium containing xerogel was found to be an active catalyst for the hydroformylation of styrene, but metal
leaching occurred, even if to a limited extent. In the case of Pd-containing materials, it was ascertained that the heterogeneous
hydrogenating activity depends on the presence of colloidal metal particles, which form when the metal species are not adequately
surrounded by the P,S- or S-ligands. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Thiourea functions; Bidentate ligand; Umbrella arrangement; Sol-gel materials
1. Introduction
well ecological interest, to the chemical industry [1]. In
particular, the immobilization of transition metal com-
plexes to polymeric matrices leads to systems that are
able to combine the advantages of homogeneous and
heterogeneous catalysis (hybrid catalysis) [2]. In this
regard, the sol-gel process has been proved to offer the
possibility for the preparation of suitable polymeric
frameworks under smooth and low temperature condi-
tions [3].
The design and the production of new heterogeneous
catalysts are of major interest in chemistry and chemi-
cal engineering. They should allow the development of
new chemical processes which are of economical, as
* Corresponding author. Fax: +39-0521-905557.
E-mail address: tiri@unipr.it (A. Tiripicchio)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00615-4

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D. Cauzzi et al. / Journal of Organometallic Chemistry 593–594 (2000) 431–444
In previous works we have synthesized the novel
ies have been carried out on N-acylthioureas, showing
the coordination versatility of these molecules [11].
Other molecules containing the CS and P donating
groups have been studied as ligands, for instance those
of the family X2NC(S)NX2 (X=H, PR2) [12]. Further-
more, certain complexes of P,S-bidentate ligands, such
as Ph2PCH2P(S)Ph2, have displayed remarkable activity
in the catalytic carbonylation of methanol [13].
This paper deals with the synthesis and characteriza-
tion of the Pd(II) and Rh(I) complexes of Ptu and of
the hybrid materials (XGPtu) obtained by sol-gel pro-
cessing the related ligand (EtO)3Si(CH2)3NHC(S)-
NHCH2CH2PPh2 (SiPtu) and its complexes. The
catalytic activity of the molecular complexes and of the
hybrid xerogels has been tested in the hydrogenation of
phenylacetylene (Pd) and the hydroformylation of
styrene (Rh). Moreover, the hydrogenating activity of
the Pd containing xerogel catalysts has been compared
with that of the corresponding materials functionalized
with the simple thiourea function ꢀNHC(S)NHPh (XG-
phtu).
thiourea-functionalized silica xerogels represented in
the Scheme 1, in order to have polymeric materials
designed to support soft-metal species through coordi-
native linkage.
These xerogels are able to bind palladium(II) [4],
copper(I) and (II) [5], rhodium(I) [6] and metal car-
bonyl species [4], including clusters [7]. The rhodium
containing materials are effective, recyclable hydro-
formylation hybrid catalysts, styrene being quantita-
tively converted into the corresponding linear and
branched aldehydes; there is spectroscopic evidence that
anchored rhodium(I) complexes are the active species
[6b]. In further experiments [8], we have observed that
certain catalysts of this family show significant changes
in regioselectivity after consecutive catalytic runs. XPS
and EDX data strongly suggest that surface metal
leaching occurs to a certain extent, in such a way that
the hydroformylation reaction is forced to move pro-
gressively from the xerogel surface to the inside of the
matrix, where different environments could be responsi-
ble for the observed selectivity.
On the other hand, the system Pd/XGphtu behaves
as an excellent recyclable hydrogenation catalyst, show-
ing a remarkable selectivity in converting alkynes to the
corresponding alkenes [4]. TEM investigations carried
out on this system after some catalytic runs have re-
vealed the presence of colloidal palladium particles,
ranging in size from about 10–20 nm, dispersed uni-
formly throughout the siloxane matrix. In the case of
the benzoylthiourea function, the nature of the palla-
dium aggregates has been investigated by means of CO
absorption, DRIFTS, XPS and TEM techniques [9].
As an extension of these investigations, we have
synthesized the new bifunctional ligand PhN-
HC(S)NHCH2CH2PPh2 (Ptu) containing both the
thiourea and the phosphine functions. Ptu is a potential
P,S-bidentate ligand which can form seven-membered
chelation rings.
2. Experimental
2.1. Materials and analytical equipment
PhNHC(S)NHPh (Phtu) and (EtO)3Si(CH2)3NHC-
(S)NHPh (Siphtu), were prepared as reported in the
literature [6b,8]. All the other organic and organometal-
lic reagents were pure commercial products. The sol-
vents were reagent grade and were dried and distilled
by standard techniques before use. When needed, ma-
nipulations of sensitive reagents were carried out under
dry nitrogen by means of standard Schlenk-tube tech-
niques.
CHNS elemental analyses were performed with a
Carlo Erba EA 1108 automated analyzer. IR spectra
1
were recorded on a Nicolet 5PC FT spectrometer. H-
and 31P-NMR spectra were obtained with Bruker AC-
100, AC-300 and CPX-200 instruments.
Similar molecules, such as PhNHC(S)NH(CH2)3PPh2
and PhNHC(S)NH(CH2)3PHPh [10] are reported in the
literature, but, as far as we know, no metal complexes
have been structurally characterized and tested as cata-
lysts. Regarding bifunctional thioureas, systematic stud-
The hydroformylation reactions were performed in a
50 ml stainless-steel autoclave (Parr) equipped with a
magnetic stirrer and thermostated (91°C) in a silicone
oil bath (Heidolph). Analytical GLC was carried out
with a DANI 3900 chromatograph fitted with a methyl-
silicone coated capillary column (OV101).
XPS spectra were run on a Vacuum Generators
ESCALAB spectrometer, equipped with a hemispheri-
cal analyzer operated in the fixed analyzer transmission
(FAT) mode, with a pass energy of 20 or 50 eV.
Al–Ka1,2 or Mg–Ka1,2 photons (hw=1486.6 and 1253.6
eV, respectively) were used to excite photo-emission.
The binding energy (BE) scale was calibrated by taking
the Au 4f7/2 peak at 84.0 eV. Correction of the energy
shift due to static charging of the samples was accom-
Scheme 1.

D. Cauzzi et al. / Journal of Organometallic Chemistry 593–594 (2000) 431–444
433
plished by referencing to the C1s line from the residual
pump line oil contamination, taken at 285.0 eV. The
accuracy of reported BEs was 90.2 eV, and the repro-
ducibility of the results was within these values. XPS
atomic ratios are relative values, intrinsically affected
by a 10% error. The spectra were collected by a DAC
PDP 11/83 data system and processed by means of
commercial software.
CH2NH); 2.40
t
(2H, CH2PPh2); 1.58
m
(2H,
CH2CH2CH2); 1.19 t (9H, CH3CH2O); 0.59 t (2H,
SiCH2). 31P-NMR (l, 81 MHz, CDCl3–CHCl3): −22.3
s.
2.2.4. Preparation of
[(Ph2PCH2CH2NHC(S)NHPh)2Pd]Cl2 (PdPtu) and
crystals of 1 and 2
Energy dispersive X-ray (EDX) microanalyses were
obtained with a JEOL 6400 EDS Tracor system for
electron microscope microanalysis.
A total of 50 mg (0.28 mmol) of PdCl2 were added to
a solution of 205 mg (0.56 mmol) of Ptu in 25 ml of
dried ethanol. The stirred suspension was refluxed, until
complete dissolution of PdCl2 (4–6 h), filtered on Celite
and then evaporated in vacuo giving an orange solid
(PdPtu). A saturated ethanol solution of this solid gave
crystals of [(Ph2PCH2CH2NHC(S)NHPh)2PdCl]Cl·
EtOH (2) after 2 days at −30°C. The same reaction
could be carried out with (PhCN)2PdCl2 in chlorinated
solvents: by using CHCl3 or dissolving 2 in CHCl3 and
leaving at low temperature, crystals of [(Ph2PCH2-
CH2NHC(S)NHPh)2Pd]Cl2·6CHCl3 (1) were obtained.
IR (cm−1, KBr pellet): 3440 m, br; 3193 s, br (wNH);
3052 s (wCH arom.); 2920 (wCH alif.) 1575 vs (was
2.2. Preparations and reactions
2.2.1. Preparation of Ph2PCH2CH2NHC(S)NHPh
(Ptu)
In a 100 ml Schlenk tube, 1 g (4.36 mmol) of
Ph2PCH2CH2NH2 dissolved in 25 ml of dry ethanol
were added to 590 mg (4.36 mmol) of PhNCS. The final
solution was refluxed for 1 h. The solvent was removed
under vacuum to leave a white sticky solid which was
washed repeatedly with hexane to obtain a white pow-
der. Yield 98%. Melting point: 80–82°C. IR (cm−1
,
NCN). H-NMR (l, 100 MHz, CDCl3): 10.5 s, br (2H,
1
KBr pellet): 3380 s, 3180 s, br (wNH); 3010–3000 m
(wCH arom.); 2950 m, 2930 m (wCH alif.) 1536 vs
(wasNCN); 1495 s; 1432 m; 696 s. 1H-NMR (l, 300
MHz, CDCl3): 7.87 s (1H, NHPh); 7.44–7.12 (15H,
arom.); 6.27 t (1H, NHCH2, J=5 Hz); 3.75 m (2H,
CH2NH), 2.40 t (2H, CH2PPh2, J=7 Hz). 31P-NMR
(l, 81 MHz, CDCl3–CHCl3): −21.1 s. Elemental anal-
ysis: (%, Anal. Calc. for C21H21N2PS) C, 70.18 (69.21);
H, 5.43 (5.81); N, 7.50 (7.69); S, 8.68 (8.80).
NH); 7.50–7.02 and 6.42 d (15H, arom.); 4.14 s, br
(2H, CH2NH), 2.80 s, br (2H, CH2PPh2). 31P-NMR (l,
81 MHz, Ethanol-d5): 33.5 s; (CDCl3): 28.3 s. Elemental
analysis: (%, Anal. Calc. for C42H42Cl2N4P2PdS2·
C2H5OH) C, 56.70 (55.50); H, 5.25 (5.08); N, 5.72
(5.88); S, 7.01 (6.73).
2.2.5. Preparation of
[(Ph2PCH2CH2NHC(S)NHPh)2Pd][CoCl4] (PdPtuCo)
and crystals of 3
2.2.2. Preparation of (EtO)3Si(CH2)3NCS
A total of 200 mg (0.22 mmol) of [(Ptu)2PdCl2] were
dissolved in 10 ml of ethanol giving an orange–red
solution. A blue solution, obtained by dissolving 53 mg
(0.22 mmol) of CoCl2·6H2O in 10 ml of ethanol, was
added to the first one giving a green solution, which
was reduced in volume in vacuo giving a green crys-
talline solid (PdPtuCo). Crystals of 3 were obtained by
stratification with CHCl3 of an ethanol solution of
PdPtuCo. IR (cm−1, KBr pellet): 3223 m, br; (wNH);
3052 m (wCH arom.); 2918 m (wCH alif.) 1575 vs (was
The synthesis was performed following the published
method with minor changes [14]. Hexane instead of
diethyl ether was used to extract the liquid isothio-
cyanate which was obtained subsequently as a yellow
oil by filtering the suspension and evaporating the
solvent in vacuo.
2.2.3. Preparation of
Ph2PCH2CH2NHC(S)NH(CH2)3Si(OEt)3 (SiPtu)
In a 100 ml Schlenk tube, 1.5 g (6.54 mmol) of
Ph2PCH2CH2NH2 were mixed with 15 ml of dry
ethanol. To this solution, 1.724 g (6.54 mmol) of
(EtO)3Si(CH2)3NCS in 10 ml of dry ethanol were added
dropwise and the solution was refluxed for 1 h. The
solvent was removed under reduced pressure to give a
colorless, very viscous liquid. The product was not
purified. IR (cm−1, neat): 3270 m, br (wNH); 3055 mw
(wCH arom.); 2974 m, 2926 m, 2888 m (wCH alif.) 1551
s (wasNCN); 1079 s (wSiO). 1H-NMR (l, 100 MHz,
CDCl3): 7.43–7.10 (10H, arom.); 5.90 s, br (2H, NH);
3.80 q (6H, CH3CH2O); 3.58 m (partially covered by
the CH3CH2O peaks) (2H, PCH2CH2NH); 3.16 m (2H,
NCN). 31P-NMR (l, 81 MHz, CDCl3): 36 s (Dw1/2
=
170 Hz). Elemental analysis: (%, Anal. Calc. for
C42H42Cl4CoN4P2PdS2) C, 47.41 (48.64); H, 4.18 (4.08);
N, 5.06 (5.40); S, 6.49 (6.18).
2.2.6. Preparation of
[(Ph2PCH2CH2NHC(S)NHPh)Rh(cod)]Cl (RhPtu)
In
a Schlenk tube, 67 mg (0.136 mmol) of
[{Rh(cod)Cl}2] and 100 mg (0.272 mmol) of Ptu were
dissolved in 30 ml of CH2Cl2. The orange–yellow solu-
tion was stirred for 1 h and then reduced in vacuo to
give an orange solid (RhPtu). IR (cm−1, KBr pellet):
3400 w, br 3200 m, br (wNH); 3051 m (wCH arom.);

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D. Cauzzi et al. / Journal of Organometallic Chemistry 593–594 (2000) 431–444
2920 (wCH alif.) 2875 m, 2828 m (wCH cod) 1572 vs (was
NCN). 1H-NMR (l, 300 MHz, CDCl3): 10.20 s, br (1H,
NH); 9.96 s, br (1H, NH); 7.37–6.90 (15H, arom.); 5.15
s, br (2H, CH cod); 4.14 m, br (2H, CH2NH), 3.29 (2H,
CH cod) 2.65 s, br (2H, CH2PPh2); 2.28 (4H, CH2 cod);
2.00 (4H, CH2 cod). 31P-NMR (l, 81 MHz, CDCl3–
EtOH): 33.1 d (1JP, Rh=150 Hz). Elemental analysis: (%,
Anal. Calc. for C29H33ClN2PRhS.CH2Cl2) C, 54.35
(51.78); H, 5.37 (5.07); N, 4.20 (4.03); S, 4.61 (4.60). XPS
interatomic ratios: Rh/N/P/S/Cl: 1/2.1/1.0/1.2/1.2. XPS
Binding Energies (eV): P2p 132.1; S2p 162.8; N1s 400.5;
Rh3d5/2 308.9; Cl2p 198.9.
(cm−1, KBr pellet): 3322 m, br (wOH, wNH); 3071 w,
3057 w, (wCH arom); 2978 w, 2934 w, 2900 w (wCH
aliph.); 1553 m (wNCN); 1082 vs (wSiO). Elemental
analysis: (%, Anal. Calc. for C18H22N2O11.5PSSi6) C,
30.97 (31.7); H, 4.01 (3.25); N, 4.03 (4.11); S, 4.35 (4.70).
2.2.10. Preparation of XGPtu[Pd]
A total of 500 mg (1.01 mmol) of SiPtu were
dissolved in 25 ml of dry ethanol. This solution was
added to 90 mg (0.5 mmol) of PdCl2 and refluxed until
the complete dissolution of the solid. The resulting
orange solution was then filtered and dried, to give an
orange solid. A total of 1.057 g (5.07 mmol) of TEOS
and 10 ml of ethanol were added to the solid. To this
solution, 2.27 mg (0.061 mmol) of NH4F dissolved in
0.42 ml of water were added dropwise. After 30 min an
orange gel formed. The gel was left to dry for 1 week
and then roughly crushed, washed with boiling ethanol
and diethylether and dried in vacuo to give small
transparent orange monoliths. A total of 804 mg of
solid were obtained, 102.8% yield calculated on 10
SiO2·[SiO3/2(CH2)3NHC-(S)NH(CH2)2PPh2]2(PdCl2). IR
(cm−1, KBr pellet): 3393 vs, br (wOH, wNH); 3058 w
(wCH arom); 2981 w, 2943 w (wCH aliph.); 1598 s
(wNCN); 1071 vs (wSiO).
2.2.7. Preparation of
[(Ph2PCH2CH2NHC(S)NHPh)Rh(cod)]2[CoCl4]
(RhPtuCo)
A total of 150 mg (0.25 mmol) of [(Ptu)Rh(cod)]Cl
were dissolved in 20 ml of ethanol giving a yellow
solution. A blue solution, obtained by dissolving 29 mg
(0.13 mmol) of CoCl2. 6H2O in 10 ml of ethanol, was
added to the first one giving a deep green solution which
was reduced in vacuo to give a green powder. IR (cm−1
,
KBr pellet): 3256 w, br (wNH); 3051 m (wCH arom.);
2918 (wCH alif.) 2917 m, 2830 m, 2877 m (wCH cod) 1568
vs (was NCN). 31P-NMR (l, 81 MHz, CD2Cl2–CH2Cl2):
33.3 d (1JRh, P=146 Hz). Elemental analysis: (%, Anal.
Calc. for C58H66Cl4CoN4P2Rh2S2) C, 49.45 (51.5); H,
4.77 (4.92); N, 4.03 (4.14); S, 4.77 (4.74).
2.2.11. Preparation of XGPtu[PdCo]
A total of 500 mg (1.01 mmol) of SiPtu were dissolved
in 25 ml of dry ethanol. To this mixture, 90 mg (0.5
mmol) of PdCl2 were added and the solution was refluxed
until complete dissolution of the solid. To the warm
solution, 121 mg (0.5 mmol) of CoCl2·6H2O were added.
The solid dissolved rapidly and the solution color turned
green. The solution was then filtered and dried, to give
a green solid. A total of 1.057 g (5.07 mmol) of TEOS
and 10 ml of ethanol were added to the solid. To this
solution, 2.27 mg ( 0.061 mmol) of NH4F dissolved in
0.42 ml of water were added dropwise. After 30 min a
greenish yellow gel formed. The gel was left to dry for
1 week and then dried in vacuo to give small transparent
green monoliths. This xerogel, if washed with water,
releases all the Co(II) ions turning to orange; the same
happens to a less extent by using ethanol. A total of 890
mg of solid were obtained, 105% yield calculated on 10
SiO2·[SiO3/2(CH2)3NHC(S)NH(CH2)2PPh2]2(PdCoCl4).
IR (cm−1, KBr pellet): 3391 vs, br (wOH, wNH); 3058
w (wCH arom); 2947 w (wCH aliph.); 1597 m (wNCN);
1095 vs (wSiO).
2.2.8. Preparation of
[(Ph2PCH2CH2NHC(S)NHPh)Rh(cod)]PF6
(RhPtuPF6)
A total of 20 mg (0.033 mmol) of PtuRh and 20 mg
(0.11 mmol) of KPF6 were dissolved in 20 ml of ethanol
and stirred for 1 h. Ethanol was removed under reduced
pressure and the orange solid was added of CH2Cl2,
forming an orange solution and white powder (contain-
ing potassium chloride), which was filtered off. IR
(cm−1, KBr pellet): 3352 m (wNH); 3058 w (wCH arom.);
2921 m (wCH alif.) 2894 m, 2800 m, (wCH cod) 1570 vs
(was NCN); 841 vs (PF−6 ). 31P-NMR (l, 81 MHz, CDCl3):
32.8 d (1JP, Rh=151 Hz); −80 septet (1JP, F=730 Hz).
2.2.9. Preparation of 5
SiO2·SiO3/2(CH2)3NHC(S)NH(CH2)2PPh2 (XGPtu)
Conditions for gel formation were: H2O–EtO=1,
[Si]:1 mol l−1, Si(OEt)4 (TEOS)–ligand=5, Si–F=
100. A total of 1500 mg (3.04 mmol) of SiPtu were added
to 3171 mg (15.22 mmol) of TEOS and 20 ml of ethanol.
The solution was stirred and then added of 6.8 mg (0.18
mmol) of NH4F dissolved in 1.26 ml (70.02 mmol) of
water. A gel formed after 10–15 min and was left to dry
for 1 week. The white xerogel was then ground and
washed with water, ethanol and diethyl ether and dried
in vacuum. A total of 2.069 g were obtained (99.7% yield
considering complete hydrolysis and condensation). IR
2.2.12. Anchoring of Rh(I) and Pd(II) on the XGPtu
xerogel: preparation of Rh/XGPtu and Pd/XGPtu
Rhodium and palladium complexes were anchored on
XGPtu by stirring, for some hours, a suspension of
thiourea-functionalized material in a CH2Cl2 solution

D. Cauzzi et al. / Journal of Organometallic Chemistry 593–594 (2000) 431–444
435
of a weighted excess of [{Rh(cod)Cl}2] or [Pd(NCPh)2-
Cl2]. The solid was then filtered in the air and washed
repeatedly with dichloromethane. The anchoring yield
was calculated in the following way. After the an-
choring reaction, the solution was filtered quantitatively
and the solvent evaporated in vacuum. The residual
metal precursor was weighted and its quantity sub-
tracted to the starting amount, obtaining the approxi-
mate anchored quantity. The maximum theoretical
anchored amount of complex was calculated consider-
ing the mol g−1 of thioureic functions (from the XGPtu
molecular formula) and assuming the 1:1 RhꢀS coordi-
nation and the 1:2 PdꢀS coordination. In the case of
Rh/XGPtu, the anchoring yield was measured, with the
same contact time (2 h), for xerogels with different
aging times.
formed after 10–15 min. Orange, transparent, brittle
xerogels were obtained by natural drying in 20 days.
2.2.13.1. XGphtu2Pd. IR (cm−1, KBr pellet): 3250 s, br
(wOH, wNH); 1587 s (wasNCN); 1087 vs (wSiO).
2.2.13.2. XGphtu4Pd. IR (cm−1, KBr pellet): 3250 s, br
(wOH, wNH); 1575 s (wasNCN); 1085 vs (wSiO).
2.2.13.3. XGphtu6Pd. IR (cm−1, KBr pellet): 3400 s, br
(wOH, wNH); 1566 m (wasNCN); 1092 vs (wSiO).
2.2.14. Hydrogenation of phenylacetylene
Hydrogenation reactions were carried out in a
Schlenk tube connected to an atmospheric pressure gas
burette. The catalyst was disareated and then 20 ml of
dry ethanol and 0.5 ml (4.4 mmol; substrate–[Pd]=
100) of phenylacetylene were added. The solution was
thermostated at 40–50°C and left to react for 15–24 h.
The final product mixture was filtered (in the case of
the supported catalysts) and analyzed by GC.
2.2.12.1. Rh/XGPtu. A total of 300 mg (0.44 mmol of
S) of XGPtu were grinded and suspended in a solution
of 173 mg (0.35 mmol) of [{Rh(cod)Cl}2] in 10 ml of
CH2Cl2. The suspension was stirred for 10 h, the solid
filtered and washed repeatedly with CH2Cl2. Anchoring
yields (aging time): 99% (6 days); 94% (11 days); 72%
(42 days); B10% (63 days). IR (cm−1, KBr pellet):
3245 m (wOH, wNH); 3054 w (wCH arom.); 2976 w,
2940 w (wCH aliph.); 2879 w (wCH cod); 1589 s
(wasNCN); 1089 vs (wSiO). XPS interatomic ratios (ag-
ing time 6 days): Rh/N/P/S/Si/Cl: 1/1.7/1.1/1.1/7.1/1.1.
XPS Binding Energies (eV): P2p 132.1; S2p 162.8; N1s
399.9; Rh3d5/2 308.7; Cl2p 198.5.
2.2.15. Hydroformylation of styrene
In a typical run, distilled styrene (2.3 ml), toluene (3
ml) and the catalyst were introduced under nitrogen in
the autoclave to achieve the desired styrene–Rh ratio
(200–300). After some pressurization and evacuation
cycles at −20°C, the autoclave was charged at room
temperature with a 1:1 hydrogen carbon monoxide
mixture at 60 atm of pressure. The reaction mixture
was stirred at 80°C for 5–7 h and then analyzed by
GLC. In the case of the supported catalysts, the powder
was recovered by filtration in the air and washed with
dichloromethane to be reused in a further run.
The xerogel Rh/XGPtu has been used in ten runs for
a reaction time of 5 h each. A total of 150 mg of
catalyst were used at the first run and 30 mg were left
at the tenth (because of filtration loss and sampling for
FTIR and XPS analysis). Disregarding the Rh leaching,
the styrene–Rh ratio was 130 at the first run and 590 at
the tenth run.
2.2.12.2. Pd/XGPtu. A total of 500 mg (0.73 mmol of S)
of XGPtu were grinded and suspended in a solution of
280 mg (0.8 mmol) of (PhCN)2PdCl2 in 10 ml of
CH2Cl2. The suspension was stirred for 10 h. The solid
was then filtered and washed repeatedly with CH2Cl2.
Anchoring yield 50%. IR (cm−1, KBr pellet): 3299 m
(wOH, wNH); 3071 w, 3057 w (wCH arom.); 2978 w
(wCH aliph.); 1559 m (was NCN); 1089 vs (wSiO).
2.2.13. Preparation of [(xSiO2·SiO3/2(CH2)3NHC(S)-
NHPh)nPdCl2] (n=2, x=10, XGphtu[Pd2]; n=4, x=
20, XGphtu[Pd4]; x=30, n=6, XGphtu[Pd6]
2.3. Crystal structure determination of complexes 1, 2
and 3
General conditions for gel formation were: H2O–
EtO=1, [Si]:1 mol l−1, (TEOS)–ligand=5, Si–F=
100 (n=4, 6), 10 (n=2). A total of 200 mg of
(PhCN)2PdCl2 were dissolved in 10 ml of CH2Cl2. To
this solution were added 372 (n=2), 745 (n=4) or
1116 (n=6) mg of Siphtu dissolved in another 10 ml of
CH2Cl2. The solution containing the complex was evap-
orated to dryness. The orange solid was dissolved in 7,
14 or 21 ml of CH3OH and transferred to a 100 ml
becker. A total of 1085, 2170 or 3255 mg of TEOS were
added under stirring and a solution of 23.2, 4.63 or 6.95
mg of NH4F in 0.43, 0.86 or 1.30 ml of water was
rapidly added dropwise to the orange solution. A gel
The intensity data of 1 and 3 were collected at room
temperature on a Philips PW 1100 single-crystal diffrac-
tometer using a graphite monochromated Mo–Ka radi-
ation and the q/2q scan technique. The intensity data
of 2 were collected at room temperature on a Enraf
Nonius CAD 4 single-crystal diffractometer using a
graphite monochromated Cu–Ka radiation and the q/
2q scan technique. Final unit cell parameters were
obtained from a least-squares refinement using 24 (1, 2
and 3) reflections. Crystallographic and experimental
details for both structures are summarized in Table 1.

436
D. Cauzzi et al. / Journal of Organometallic Chemistry 593–594 (2000) 431–444
Table 1
Experimental data for the X-ray diffraction studies of 1, 2, 3
Formula
[C42H42N4P2S2Pd]
[C42H42N4P2S2Pd]Cl2·C2H6O
[C42H42N4P2S2Pd]
Cl2·6CHCl3
1622.46
293(2)
CoCl4·CHCl3·2C2H6O
2494.98
293(2)
Formula weight
Temperature
952.22
293(2)
Wavelength
Crystal system
Space group
0.71073
Monoclinic
P21/n
1.54183
Monoclinic
P21/c
0.71073
Triclinic
(
P1
Unit cell dimensions
,
a (A)
14.909(4)
19.212(5)
12.364(3)
9.407(2)
26.954(6)
18.062(4)
14.204(5)
16.610(6)
13.984(4)
105.07(2)
119.10(3)
77.89(2)
2770(2)
1
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
90.23(2)
101.36(2)
3
,
V (A )
3541(2)
2
1.521
1.156
4490(2)
4
1.409
6.268
Z
Dcalc. (Mg m−3
)
1.496
1.135
1270
Absorption coefficient v (mm−1
F(000)
)
1624
1960
Crystal size (mm)
q range (°)
0.10×0.21×0.15
3.01–25.03
0.13×0.23×0.34
3.28–70
0.15×0.28×0.31
3.02–25
Index ranges
−175h517, 05k522,
05l514
6514
−115h511, −285k532,
−185l522
8783
−165h514, −195k519,
05l516
9719
Reflections collected
Independent reflections
Observed reflections [I\2|(I)]
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I\2|(I)]
R indices (all data) a
6221 (Rint=0.0538)
2025
8514 (Rint=0.0486)
4941
9719 (Rint=0.0000)
2045
Based on F2
6221/0/360
Based on F2
8514/0/501
Based on F2
9719/0/422
0.866
1.048
0.959
R1=0.0665, wR2=0.1589
R1=0.2324, wR2=0.2374
0.613 and −0.477
R1=0.0528, wR2=0.1396
R1=0.1103, wR2=0.1981
1.141 and −1.025
R1=0.0978, wR2=0.2023
R1=0.4974, wR2=0.3837
1.159 and −0.700
Largest difference peak and hole
−3
,
(e A
)
a R1=SꢀFo−Fcꢀ/ꢀS(Fo)wR2=[S[w(Fo2−Fc2)2]/S[w(F2o)2]]1/2
.
(0.1061P)2] (1), w=1/[|2F2o+(0.0953P)2+3.2539P]
(2) and w=1/[|2Fo2 +(0.1360)2+6.1527P] (3) where
P=(F2o+2F2c)/3 was used.
All calculations were carried out on the DIGITAL
AlphaStation 255 computers of the ‘Centro di Studio
per la Strutturistica Diffrattometrica’ del CNR, Parma,
using the SHELX-97 systems of crystallographic com-
puter programs [16].
Data were corrected for Lorentz and polarization
effects in the usual manner. A correction for absorption
was made for both complexes [maximum and minimum
value for the transmission coefficient was 1.000 and
0.5401 (1), 1.000 and 0.6389 (2) and 1.000 and 0.3966
(3) [15].
The structures were solved by Patterson and Fourier
methods and refined by full-matrix least-squares proce-
dures (based on F2o) with anisotropic thermal parame-
ters in the last cycles of refinement for all the
non-hydrogen atoms excepting for the atoms of one
molecule of CHCl3 in 1 where each Cl atom was found
disordered and distributed in three positions of occu-
pancy factors 0.33, excepting for the atoms of the
solvent in 2, whereas in 3 only the Pd, N, P, S and the
C1, C2, C3 atoms, those of CoCl4 moiety and the
atoms of the three molecules of the solvents were
refined anisotropically.
3. Results and discussion
3.1. Syntheses and characterizations of ligand and
complexes
The ligand Ph2PCH2CH2NHC(S)NHPh (Ptu) is
prepared by the reaction of the amine Ph2PCH2CH2-
NH2 and the isothiocyanate PhNCS in ethanol. It is a
stable, white solid, soluble in polar and chlorinated
solvents. By the reaction with Pd(II) and Rh(I) chloride
precursors, the complexes [(Ptu)2Pd]Cl2 (PdPtu) and
[(Ptu)Rh(cod)]Cl (RhPtu) are formed. Ptu is
In all three structure, the hydrogen atoms (except
those of the solvent molecules) were introduced into the
geometrically calculated positions and refined riding on
the corresponding parent atoms. In the final cycles of
refinement,
a
weighting scheme w=1/[|2Fo2 +

D. Cauzzi et al. / Journal of Organometallic Chemistry 593–594 (2000) 431–444
437
coordinated through the P and S atoms forming seven-
3.2. X-ray structural results
membered rings (vide infra). Spectroscopic evidence for
the P,S-coordination comes from the lowfields shift of
the 31P-NMR resonance in the complexes [l 28.3 in
PdPtu and 33.1 (1JRh, P=150 Hz) in RhPtu] with re-
spect to the free molecule (−21.1), and from the blue
shift of the w(NCN) IR band (1575 cm−1 in PdPtu,
1572 in RhPtu, 1536 in Ptu). Moreover, in the 1H-
NMR spectra, the significant shifts to high frequencies
of the peaks due to the NH protons suggest thiourea
S-coordination, particularly for the NH group of the
chelation ring which moves from l 6.27 (Ptu) to 10.50
(PdPtu) and 9.96 (RhPtu).
Views of the structures of the Pd complexes 1, 2 and
3 are shown in Figs. 1–3, respectively. Selected inter-
atomic distances and angles regarding the chelation
rings are reported in Tables 2 and 3. In all the three
complexes the two bidentate ligands form two hepta-
atomic chelation rings with the donating atoms in trans
disposition and adopt a cyclohexane-like, quasi-boat
conformation, when considering the rigid thiourea
group to contribute with one side to the ring, as
outlined in the scheme attached to Table 3.
As the Ptu ligand can adopt a syn or an anti configu-
ration regarding the thiourea moiety PhNHC(S)ꢀ, com-
plex 1 contains syn-Ptu, whereas complex 2 exhibits
both the two arrangements. On the other hand, the
structure of 3 contains two independent molecules dif-
ferentiated just by the syn–anti configuration. In all
cases, the syn disposition, which should be more steri-
cally hindered, appears to be driven by the formation of
bifurcated NꢀH···Cl hydrogen bonds with isolated chlo-
ride ions, as in 1 and 2, or with the tetrachlorocobaltate
anion, as in 3.
1
The H-NMR spectra of the complexes [(Ptu)2Pd]Cl2
and [(Ptu)Rh(cod)]Cl show two CH2CH2 peaks, which
remain broad in the range of temperatures 330–233 K,
indicating a low-barrier dynamic behavior for these
groups. Regarding the PhNHC(S) moiety, which could
be present in two conformers (syn–anti ), only one NH
peak is present even at 233 K. In the Rh(I) complexes,
the vinylic protons of the coordinated cod ligand give
rise to two broad peaks corresponding to the two
halves of the ligand in trans, respectively to the P and S
atoms.
Regarding the bis-chelation configuration, while in
complexes 1 and 3 the two ligands are centrosymmetri-
callly related, in complex 2 they are folded by the same
side with respect to the coordination plane, in an
umbrella configuration sketched in Scheme 2. These
different configurations appear to affect slightly the
coordinative interactions, as in 2, differently from the
other complexes, the PdꢀS bond distances are signifi-
cantly longer than the PdꢀP ones.
The Pd and Rh complexes were reacted with CoCl2
trying to obtain bimetallic complexes by opening the
chelation ring. However, CoCl2 prefers to add Cl−
anions resulting in the formation of the ion-pair com-
plexes
[(Ptu)2Pd][CoCl4]
(PdPtuCo)
and
[(Ptu)Rh(cod)]2[CoCl4] (RhPtuCo). The 1H-NMR of
these products shows broad and overlapping peaks,
probably because of the presence of the Co(II) para-
magnetism. Nevertheless, in the case of the Rh(I) com-
pound, 31P-NMR shows a sharp doublet (l 33.1,
1JP, Rh=150 Hz) indicative of the RhꢀP coordinative
interaction), whereas the Pd(II) complex shows a large
peak (l 36.0, Dw1/2=170 Hz) at room temperature. By
lowering the temperature to 253 K, a minor sharp peak
appears at l 31.0, close to the value of the chloride
derivative (l 32.5 at 253 K). This suggests that, in
solution at least two intercoverting species could be
present, one being the Pd bis-chelate cationic complex,
and the other probably containing Co(II)ꢀP interac-
tions, giving account for the 31P line broadening [by the
way, the 31P resonance of (Ph3P)2CoCl2 is not
detectable].
This could also be related to the presence, in complex
,
2, of the Pd···Cl(1) interaction [3.026(2) A], which ap-
pears to induce a certain degree of distortion of the
square planar geometry around the metal. In fact, the
resulting coordination environment is that of an incipi-
ent trigonal bipyramid, with the two phosphorus atoms
occupying the apical positions [PꢀPdꢀP 179.5(1),
SꢀPdꢀS 160.6(1)°]. Furthermore, the proximity of the
chlorine atom Cl(1) to the metal center causes signifi-
cant modifications in the geometry of the two chelation
rings. In fact, the two methylene groups C(2a) and
C(2b) close to palladium move slightly away, as evi-
denced by the values of the distance h% and of the
torsion angles h, i and p in Table 3. However, two
weak interactions take place between the methylene
groups and the chlorine atom [e.g. Cl(1)···C(2b)
Both RhꢀCo and PdꢀCo ion-pair complexes can be
retransformed into the parent complexes, RhPtu and
PdPtu, by addition of water to their green chloroform
solutions. The aqueous layer becomes colored in pink,
indicating the presence of the Co(II) aquo-cation, while
the chloroform layer turns yellow. In the case of Rh-
Ptu, the chloride ligand is easily displaced by PF−6 , by
dissolving the complex in a concentrated solution of
KPF6, giving the cationic complex [(Ptu)Rh(cod)]PF6
(RhPtuPF6).
,
3.662(5) A, Cl(1)···H(2b1)ꢀC(2b) 132.5(5)°].
Moreover, the planarity of the thiourea moieties in 2
appears slightly affected by the umbrella configuration,
as evidenced by the values of the torsion angle k. In
addition, the values of the dihedral angle between the
main coordination plane and thiourea moieties, which
range between 43.6(3) and 47.5(5) in 1 and 3, are
significantly raised in 2 [53.3(1) (syn) and 57.5(1)°
(anti )].

438
D. Cauzzi et al. / Journal of Organometallic Chemistry 593–594 (2000) 431–444
Packing in compound 2 is mainly driven by a net-
work of hydrogen bonds involving Cl(2), which interact
molecule behaves as acceptor in the H-bond interaction
,
N(2b)···O(1s) [2.799(7) A, 154.5(5)°].
,
with N(1a) [3.217(4) A, 154.4(4)°] and N(2a) [3.167(5)
In compound 3, the complex molecule containing the
syn thiourea moieties interacts through the NꢀH groups
with two chlorine of the [CoCl4]2− anion [N(1a)···Cl(4)
,
A, 156.7(5)°] in a bifurcated fashion (determining the
,
syn arrangement) and with N(1b) [3.233(4) A, 132.9(4)°]
,
of an adjacent molecule. The oxygen of the ethanol
3.24(2) A, 146(2)°; N(2a)···Cl(1) 3.17(2), 154(2)°]. On
Fig. 1. ORTEP diagram of the complex [Pd(Ptu)2]Cl2·6CHCl3 (1) with the atomic numbering scheme, showing 30% probability thermal ellipsoid.
Fig. 2. ORTEP diagram of the complex [Pd(Ptu)2Cl]Cl·EtOH (2) with the atomic numbering scheme, showing 30% probability thermal ellipsoid.

D. Cauzzi et al. / Journal of Organometallic Chemistry 593–594 (2000) 431–444
439
chloroform [17]. Also in this case, there is a bifurcated
hydrogen bond couple NꢀH···Cl between the syn
thiourea group and the chloride ion [N(1)···Cl 3.18(1)
,
,
A, 156(1)°; N(2)···Cl 3.16(1) A, 158(1)°]. The chloride
ion is also bound weakly to two chloroform molecules
through Cl···HꢀCCl3 interactions [Cl···C(1b) 3.61(2),
,
Cl···C(1a) 3.47(2) A].
3.3. Sol-gel preparation of silica supported Ptu
complexes
In order to produce the same Ptu complexes of Rh(I)
and Pd(II) tethered to silica xerogels, the ligand
(EtO)3Si(CH2)3NHC(S)(CH2)2PPh2 (SiPtu), or its metal
complexes, were sol-gel processed with tetraethyl or-
thosilicate (TEOS), in the desired ratio. In particular,
the 5SiO2·SiO3/2(CH2)3NHC(S)NH(CH2)2PPh2 (XG-
Ptu) xerogel was prepared, with a Si–S ratio equal to 6,
which allows satisfactory spectroscopic characterization
of the tethered species.
We used two ways of anchoring a metal complex on
silica gels: the first one (method A) implies the suspen-
sion of XGPtu in a solution containing the suitable
metal precursor; the second way (method B) consists in
the reaction of a metal precursor with the Siptu ligand
in a well defined stoichiometric ratio and in sol-gel
processing the obtained complex with TEOS. In both
cases, the integrity of the tethered ligand in the gels was
confirmed by the presence in their IR spectra of its
typical bands. Moreover, in the case of the complexes
the expected blue shift for the was(NCN) band was
observed.
With method A, the metal precursors react firstly
with the surface ligand functions, and then diffuse into
the matrix to reach the inner functional groups. This
was proved previously, in the case of Rh on XGphtu,
by comparing the Si–Rh ratios obtained by EDX
(bulk) and XPS (surface) semiquantitative analysis [8].
In the present work, we found that the amount of the
adsorbed metal depends not only on the contact time
between the xerogel and the metal precursor solution,
but also on the aging of the gel. In fact, for longer
aging times, the metal loading strongly decreases, as
reported in Table 4 for XGPtu and Rh(I). Complete
coverage of all the thiourea functions by the metal ions
is possible only for young xerogels, and not for old
ones, probably owing to the reduction of the pore size.
As a result, the metal-to-ligand ratio is out of strict
control, being possibly higher in the surface and lower
in the inner, with respect to that of the corresponding
molecular complex (e.g. 2 in the case of [Pd(Ptu)2]Cl2).
For young xerogels the anchoring yield can approach
100% in the case of Rh(I). In the case of Pd/XGPtu,
instead, the anchoring yield is never 100% but spans
from 50% (as for the materials used in catalysis) to
70–80%, suggesting that the 2/1 PꢀS/Pd coordination is
Fig. 3. ORTEP diagram of the complex [Pd(Ptu)2][CoCl4]·
CHCl3·2EtOH (3) with the atomic numbering scheme, showing 30%
probability thermal ellipsoid: (a) molecule A (syn conformation of the
thiourea groups); (b) molecule B (anti conformation).
the other hand, the second molecule containing the anti
thiourea groups interacts through the NꢀH groups with
,
the two ethanolic oxygens [N(1b)···O(2s) 2.84(2) A,
,
141(2)°; N(2b)···O(1s) 2.86(3) A, 162(2)°].
Packing in complex 1 appears quite different being
mainly due to the presence of six chloroform molecules
which give rise to a sort of clathrate compound. There
is a number of Cl···Cl interactions between adjacent
CHCl3 molecules lying in the same range of distances
,
(3.59–4.07 A) found in the crystal structure of pure

440
D. Cauzzi et al. / Journal of Organometallic Chemistry 593–594 (2000) 431–444
Table 2
a
b
Selected bond distances (A) and angles (°) in the chelation rings of 1 , 2 and 3 a (estimated standard deviations in parentheses; for the label keys
,
see the scheme below Table 3)
1 (syn)
2 (ligand a, syn)
2 (ligand b, anti )
3 (complex a, syn)
3 (complex b, anti )
Bond distances
PdꢀP
PdꢀS
SꢀC(1)
C(1)ꢀN(1)
C(1)ꢀN(2)
2.338(5)
2.327(5)
1.711(10)
1.326(11)
1.325(11)
2.316(2)
2.355(2)
1.734(8)
1.327(9)
1.331(8)
2.316(2)
2.355(2)
1.745(7)
1.312(8)
1.338(9)
2.359(6)
2.314(6)
1.67(2)
1.29(2)
1.36(2)
2.334(6)
2.337(6)
1.73(2)
1.32(2)
1.32(2)
Bond angles
PdꢀPꢀC(3)
PꢀPdꢀS
109.4(4)
94.7(1)
116.8(3)
125.5(8)
115.2(9)
119.2(8)
113.3(2)
95.69(6)
114.5(3)
122.8(6)
117.1(7)
119.8(6)
112.3(3)
94.53(7)
114.8(2)
122.8(6)
120.6(6)
116.5(5)
107.7(3)
93.3(2)
117(1)
131.2(2)
111.2(2)
118(2)
109.1(7)
95.7(2)
117(1)
126(2)
119(2)
114(2)
PdꢀSꢀC(1)
SꢀC(1)ꢀN(1)
N(1)ꢀC(1)ꢀN(2)
SꢀC(1)ꢀN(2)
a Centrosymmetrical bis-chelation.
b Umbrella bis-chelation configuration (see scheme through the text).
Table 3
,
Pd···H contacts h%, h%% (A) and torsion angles h–p (°) in the chelation rings of 1, 2 and 3 (estimated standard deviations in parentheses; for the
label keys see the schemes below) a
1
2 (ligand a)
2 (ligand b)
3 (complex a)
3 (complex b)
h%
h%%
h
2.94(1)
3.03(1)
11.5(4)
41(1)
1(2)
−96(1)
3.20(1)
3.09(1)
−8.1(2)
59.6(5)
−3.4(8)
−96.1(6)
55.4(5)
3.12(1)
2.85(1)
−3.7(2)
60.9(5)
−9.3(7)
−92.8(6)
60.2(5)
2.84(2)
3.17(2)
20(1)
34(3)
0(3)
3.06(2)
2.92(3)
4(1)
46(3)
1(3)
i
k
l
m
−97(2)
65(2)
−96(3)
56(2)
58(1)
n
41.8(8)
−69.4(4)
42.2(4)
−57.5(2)
39.6(4)
−59.9(2)
36(2)
−72(1)
42(2)
−63(1)
p
a
hardly reached, as it requires the close presence of two
Ptu functions in the xerogel matrix.
metal centers. Only with higher F−–Si ratio it was
possible to obtain gelation, but the formation of a
genuine, homogeneous gel was never achieved because
of precipitation of oligomeric substances.
With method B, the metal complex is formed in
solution and keeps its structural features when homoge-
neously dispersed in the xerogel, allowing to control
both the stoichiometry of the complex and the silica to
metal ratio.
In our previous studies with monodentate thioureas
[4,6b,8], we always used method A to anchor both
Pd(II) and Rh(I) complexes. Method B was found to be
ineffective in the case of Rh(I), probably because the
fluoride ions (used as catalyst for the sol-gel process)
are withdrawn from their task by interactions with the
Scheme 2.

D. Cauzzi et al. / Journal of Organometallic Chemistry 593–594 (2000) 431–444
441
Table 4
acetylene to styrene and ethylbenzene at atmospheric
pressure. As shown in Table 5, PdPtu exhibited a very
low activity, but the substitution of Cl− with the non
coordinating CoCl−4 anion resulted in a dramatic in-
creasing of the hydrogenating ability. This suggests the
existence in solution of interactions between the Cl−
ion and the Pd(II) center which could hinder the coor-
dination of the substrate. This kind of interaction could
be similar to that observed in the solid state structure of
compound 2. The mechanism of this reaction has not
been investigated. Apparently, the Pd complexes can be
recovered intact from the reaction mixture, but we
cannot exclude the formation of trace amounts of
colloidal metal particles, responsible for the observed
catalytic activity.
Anchoring yield a of Rh(I) on XGPtu in dependence on the aging
time of the xerogel
Aging time (days)
Anchoring yield (%)
6
11
42
63
99
94
72
B10
a Calculated according to the method reported in Section 2.2.12.
Table 5
Results a of the homogeneous hydrogenation tests with the Pd com-
plexes
PdPtu
PdPtuCo
A similar behavior was found for the complex Rh-
Ptu, which was not active in the hydroformylation of
styrene. Again, by substituting the Cl− anion with PF6−
or CoCl−4 , complete conversion of styrene to aldehydes
was observed (Table 6). It is also interesting to note the
high selectivity of the RhꢀCo compound towards the
iso aldehyde (at 80°C, iso/n=23; for comparison, the
complex [(PhNHC(S)NHPh)Rh(cod)Cl] showed iso/
n:2 [8]). After the catalysis, rhodium carbonyl com-
plexes were recovered by precipitation with a mixture
of Et2O–hexane. Their IR spectra in the carbonyl
region showed the typical two-band pattern of gem-
(CO)2 species (2024, 1975 cm−1 for the chloride and
2038, 1980 cm−1 for the chlorocobaltate derivative).
Phenylacetylene
Styrene
Ethylbenzene
91
8
B1
0
79
21
a Percentage of the substance in the product mixture.
Table 6
Results a of the homogeneous hydroformylation tests with the Rh
complexes
RhPtu
RhCoPtu
RhPtuPF6
Styrene
99
0
0
0
92
4
1
80
18
1
iso aldehyde
n aldehyde
Ethylbenzene
B 1
4
a Percentage of the substance in the product mixture.
3.5. Catalytic tests with anchored complexes
We prepared and tested in catalysis the following
materials: (i) Rh/XGPtu and Pd/XGPtu obtained by
anchoring of the metal species on the XGPtu xerogel
(method A); (ii) two Pd(II) containing xerogels using
the preformed 2:1 SiPtu complex (method B), the one
with Cl− as anion (XGPtu[Pd]) and the other with
CoCl−4 (XGPtu[PdCo]; (iii) three Pd(II) containing xe-
rogels using preformed Siphtu complexes (method B),
with a S–Pd ratio of 2 (XGphtu[Pd2]), 4 (XG-
phtu[Pd4]) and 6 (XGphtu[Pd6]) (method B). All the
xerogel materials were prepared with a Si–S ratio equal
to 6 (TEOS–thiourea=5).
In this work we prepared the Rh(I) xerogels using
method A and the Pd(II) xerogels using both methods.
The xerogels obtained by method A are yellow in the
case of rhodium and orange in the case of palladium.
The gelation of the preformed 2:1 complex of SiPtu
with Pd(II) does not need a higher quantity of F−
catalyst (probably because the Pd(II) center was pro-
tected by the ligands) and gives orange, transparent
xerogel monoliths. When gelling the complex of SiPtu
with Pd(II) and CoCl−4 as counterion, more water was
needed (instead of more catalyst) for gelation. A bright
green material is obtained which, if washed with water,
completely loses Co(II) turning orange.
3.5.1. Hydroformylation of styrene using Rh/XGPtu
The Rh(I) containing xerogel Rh/XGPtu was pre-
pared by suspending XGPtu (dried for 6 days) in a
CH2Cl2 solution of [{Rh(cod)Cl}2]. This xerogel is able
to effectively convert styrene to a mixture of iso/n
aldehydes and is easily recovered by filtration. The
surface atomic ratios resulted from XPS analysis are
reported in Table 7, together with those found after the
first, fifth and tenth catalytic runs.
In order to compare the behavior of the Ptu ligand
with that of simple thiourea ligands [4], we prepared Pd
containing xerogels following method B, using
(EtO)3Si(CH2)3NHC(S)NHPh (Siphtu) in different S–
Pd ratios (2, 4, 6).
3.4. Catalytic acti6ity tests on Ptu molecular complexes
The catalytic activity of the complexes PdPtu and
PdPtuCo was tested on the hydrogenation of phenyl-
The activity of Rh/XGPtu is in contrast with that of
the model compound [(Ptu)Rh(cod)]Cl, which is com-

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D. Cauzzi et al. / Journal of Organometallic Chemistry 593–594 (2000) 431–444
pletely inactive. We can interpret this result in two
ways: (i) the silica surface is able to interact with the
Cl− ion in order to keep it far away from the catalytic
center or (ii) Rh(I) is leached in solution in the form of
a complex with CO and/or styrene (or its aldehydes)
which is active in the hydroformylation reaction. In this
regard, it seems from the XPS data (Table 7) that
surface Rh leaching is limited compared to similar
thiourea xerogels [6b, 8]. This was confirmed by EDX
investigations which showed the bulk Si–Rh atomic
ratio to be constant after the catalytic runs. The iso/n
ratio was also found to be constant with the recycling
of the catalyst (mean value 2.390.2). This is consistent
with very low metal leaching, as for thiourea modified
xerogels, we observed a correlation between the surface
Rh leaching and the raising of the iso/n ratio [6b, 8]. In
this case, a constant iso/n ratio suggests a limited
surface leaching, lower than the intrinsic error (10%) of
the XPS obtained interatomic ratios. However, the
decomposition of the anchored complex becomes ap-
parent at the tenth run. Evidently, leaching occurs, even
if to a limited extent, therefore we cannot exclude that
the released metal species do not contribute to the
observed catalytic behavior.
stability of the anchored species which seems not to
transform in a thioureato complex as it was found for
XGbztu and XGphtu xerogels [6b, 8].
XPS binding energies are reported in Table 8. The
values of P and S binding energies in the supported
complex are in agreement with those observed in the
model compound RhPtu, whereas N and Cl binding
energies slightly differ, this discrepancy being at-
tributable to matrix effects. After five catalytic runs, the
supported catalyst shows a change in the binding en-
ergy of the P atom, probably due to the substitution of
the cod ligand by two CO ligands. After ten cycles the
surface metal complexes appear unaffected by any sig-
nificant modification, as observed also by FT-IR
spectroscopy.
3.5.2. Hydrogenation of phenylacetylene using Pd/XG-
Ptu and related species
The Pd(II) containing xerogel XGPtu[Pd] and XG-
Ptu[PdCo], obtained from the pre-formed complexes of
SiPtu (method B), are completely inactive for the hy-
drogenation of phenylacetylene. XGPtu[Pd] is a bright
orange and transparent material and keeps its physical
appearance after the catalytic run. The same happens
for XGPtu[PdCo], which is green.
Regarding the anchored metal species, as was already
found in the above mentioned works, the cod ligand is
substituted promptly by two CO molecules, as it is clear
from the appearance of the two-band pattern due typi-
cally to gem-(CO)2 rhodium species (2076, 1996 cm−1).
It is to remark that by treating a solution of the
cod-complex RhPtu with CO, nearly the same bands
are observed (2072, 1996 cm−1). The same bands are
still present after subsequent catalytic runs, showing the
On the other hand, the material obtained by an-
choring Pd(II) on XGPtu from
a
solution of
(PhCN)2PdCl2 (Pd/XGPtu, method A), is active after
an induction period of ca. 30 min at 40°C, in the same
way as the analogous materials obtained from the
xerogels containing the ꢀNHC(S)NHPh [1a] and
ꢀNHC(S)NHC(O)Ph fragments [1b]. It was demon-
strated clearly that catalytic activity in the hydrogena-
tion of phenylacetylene was possible because of the
formation of Pd colloidal particles stabilized on the
silica surface by the thiourea ligands. Also in the case
of Pd/XGPtu, the formation of colloidal particles was
observed; the xerogel color changed from orange to
dark brown during the hydrogenation reaction. It is not
clear if these particles are formed directly on the surface
of the xerogels or if Pd(II) is first leached in solution,
reduced by hydrogen and then readsorbed by the silica
matrix. The fresh material, in fact, if suspended in an
ethanol solution of phenylacetylene, slowly loses palla-
dium. Filtering this solution and exposing it to hydro-
gen resulted in some reduction of the alkyne to styrene.
After the first catalytic run, Pd/XGPtu is still active and
does not leach palladium anymore. On the contrary,
leaching was not observed for the XGPtu[Pd] material,
which contains well defined molecular complexes and,
as stated above, is inactive.
Table 7
XPS atomic ratios in the Rh/XGPtu catalyst before and after the
catalytic runs
Rh
N/Rh
P/Rh
S/Rh
Si/Rh
Rh/XGPtu
First run
Fifth run
Tenth run
1
1
1
1
1.7
2.0
1.8
3.5
1.1
0.9
1.1
1.7
1.1
0.9
0.7
1.4
7.1
7.1
6.7
10
Table 8
XPS binding energies (eV) for the Rh/XGPtu catalyst before and
after the catalytic runs
Rh
P
N
S
Cl
a
RhPtu
308.9
308.7
308.8
308.7
132.1
132.1
132.5
132.6
400.5
399.9
399.8
399.7
162.8
162.8
–
198.9
198.5
198.6
198.5
Rh/XGPtu
5th run
10th run
b
In order to gain more insight into the effect of the
surrounding ligands on the formation of colloidal parti-
cles, we prepared XGphtu[Pd2], XGphtu[Pd4] and XG-
phtu[Pd6] by sol-gel processing the preformed
Siphtu–Pd complexes with the S–Pd ratios of 2, 4 and
162.6
a Reported for comparison.
b The S2p signal was affected by low signal to noise ratio, due to
the scarce quantity of the sample.

D. Cauzzi et al. / Journal of Organometallic Chemistry 593–594 (2000) 431–444
443
6, respectively. The infrared spectra of these materials
exhibit significant differences in the thiourea bands,
suggesting the formation of different complex species.
The material XGphtu[Pd2] showed catalytic activity
and also some darkening of its color, suggesting forma-
tion of colloidal Pd particles. Its activity, though, was
lower than that of the catalyst obtained by anchoring
Pd(II) with method A [4]. The conversion of half of the
starting phenylacetylene to styrene was reached after 3
days of reaction. XGphtu[Pd4] was found less active
and no darkening of its color or Pd(II) leaching in
solution was observed. XGphtu[Pd6] showed extremely
low activity, converting only the 3% of alkyne in more
than 5 days of reaction. Even if a hexa-coordinated
thiourea–Pd complex should be excluded, it seems that
the two redundant ligands contribute to stabilize the
Pd(II), avoiding its reduction and thus its catalytic
activity.
mentary publications no. CCDC-132016 (1), no.
CCDC-132017 (2) and no. CCDC-132018 (3). Copies of
the data can be obtained free of charge on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
[fax: +44-1223-336033; e-mail: deposit@ccdc.cam.
ac.uk].
Acknowledgements
Financial support from MURST (Rome) is gratefully
acknowledged. The facilities of Centro Interdipartimen-
tale di Misure (Universita` di Parma) were used for
recording NMR and mass spectra.
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