Synthesis and characterization of novel inorganic-organic hybrid Ru(II) complexes and their application in selective hydrogenation.

Novel Ru(II) complex-based hybrid inorganic-organic materials immobilized via a diamine co-ligand site instead of the conventional diphosphine ligand have been prepared. The complexes were prepared by two different methods: sol-gel and surface modification techniques. The structures of the desired materials were deduced by several available physical measurements like elemental analyses, infrared, FAB-MS and (1)H-, (13)C- and (31)P-NMR spectroscopy. Due to a lack of solubility the structures of xerogel 3 and modified 4 were studied by solid state (13)C-, (29)Si- and (31)P-NMR spectroscopy, infrared spectroscopy and EXAFS. These materials were stable enough to serve as hydrogenation catalysts. Selective hydrogenation of functionalized carbonyls in alpha,beta-unsaturated compounds was successfully carried out under mild conditions in a basic medium using these complexes as catalysts.

1. Introduction

It has been shown that complexes containing a "class="Chemical">Ru-(class="Chemical">pan class="Disease">P-P)" (P-P = diphosphine) core per ruthenium atom are efficient catalysts in several chemical reactions [1,2,3,4,5]. As a result, several ruthenium complexes containing this motif were synthesized and their properties were studied by spectroscopic and electrochemical techniques [6,7]. Stereo-, regio- and enantioselective ruthenium-catalysis lies at the heart of current developments in pharmaceutical, agrochemical and cognate industries [8,9,10]. Recently ruthenium(II) complexes with diphosphine and diamine ligands were successfully tested as homogenous catalysts in hydrogenation of unsaturated ketones [11,12,13,14,15,16,17,18,19,20]. One of the prime concerns of industry and academia is how to transfer the active homogenous catalysts to the heterogeneous phase [20,21,22,23]. The two major problems in this field have been first that under the conditions commonly required for effective catalysis, ligand exchange reactions lead to leaching of the metal centers from the matrix, in addition to the synthetic difficulties [20,21,22,23].

The use of functionalized multidentate ligands with anchoring groups instead of the clasclass="Chemical">sical monodentate ones might limit the leaching class="Chemical">problem, but few such ligands have been described, class="Chemical">probably because of their difficult class="Chemical">preclass="Chemical">paration, sclass="Chemical">pecially when the comclass="Chemical">plexes were suclass="Chemical">pclass="Chemical">ported by the class="Chemical">pan class="Chemical">phosphine ligands site [20,21,22,23].

Our conceptual methodology was to take a homogeneous system of known catalytic behavior and, by performing suitable modifications, to tether this catalyst on class="Chemical">silica suclass="Chemical">pclass="Chemical">ports, covalent anchoring of class="Chemical">pan class="Chemical">metal complexes on such surfaces being a topic of considerable interest in catalysis [20,22]. The desired hybrid materials are able to combine the advantages of homogeneous and heterogeneous catalysis: the catalyst becomes easily separable from the reaction products and it can be reused in several runs without an essential loss in the activity due to the leaching problem [23,24,25,26].

In this work we used a class="Chemical">bidentate diphosphine ligand and class="Chemical">pan class="Chemical">diamine co-ligand with Si(OMe)3 anchoring groups; the presence of this group enables the immobilization of the ruthenium(II) complexes through simple a sol-gel process using HSi(OEt)3 as cross-linker. Another approach to achieve stable materials is to covalently bind the ligands, via the methoxy groups, to the well known silica surface instead of a sol-gel material through surface modification.

2. Results and Discussion

2.1. Synthesis of ruthenium(II) complexes [1-4]

Our approach to the preparation of the stationary phase catalyclass="Chemical">sis system is shown in Scheme 1. The class="Chemical">precursor comclass="Chemical">pound class="Chemical">pan class="Chemical">trans-Cl2Ru(dppp)2 (1) was obtained by a substitution reaction starting from Cl2Ru(PPh3)3 and dppp in dichloromethane [4,14]. Complex 2 was prepared by treating 1 with equimolar amounts of [3-(2-aminoethyl)-aminopropyl]trimethoxysilane in dichloromethane; in order to confirm this ligand exchange the reaction was monitored by 31P-NMR. One of the dppp ligands was replaced by one of the diamine ligands [4,14], giving a yellow product which were collected in excellent yield. It is soluble in chlorinated solvents such as chloroform or dichloromethane and non-soluble in polar or non-polar solvents like water, methanol or diethyl ether and n-hexane. By condensation of 2, which contains a trimethoxysilane functional group, with 10 equivalents of HSi(OEt)3 in THF/water under sol-gel conditions the xerogel 3 was prepared in good yield. In another route 2 was modified using ProntoSIL 120-5 Si (5µm) as support in toluene to produce 4. The yield of the immobilized complexes 3 and 4 was very good, but the hybrid materials were not soluble in any solvent.

Scheme 1

The synthetic route used in the preparation of the hydrogenation catalyst 2, the sol-gel xerogel 3, and the modified 4.

The synthetic route used in the preparation of the pan class="Chemical">hydrogenation catalyst 2, the sol-gel xerogel 3, and the modified 4.

2.2. NMR and IR spectroscopic investigations

The stclass="Chemical">ructure of comclass="Chemical">plexes 1 and 2 described herein has been deduced from elemental analyses, infrared, class="Chemical">pan class="Gene">FAB-MS and 1H-, 13C-, H, H-COSY and 31P-NMR spectroscopy. Due to lack of solubility the structures of 3 and 4 were determined by solid state 13C-, 29Si- and 31P-NMR spectroscopy, infrared spectroscopy, and EXAFS.

Confirmation of the formation of 3 and 4 was obtained by NMR. Liquid class="Chemical">31P-NMR and solid state class="Chemical">pan class="Chemical">31P-CP/MAS-NMR measurements for both 2 and the interphased Ru(II) complexes in the hybrid xerogel 3 and surface modified 4 support the formation of the expected structural complexes whose formulae are shown in Scheme 1. The use on an asymmetric diamine caused loss of the C axis resulting in a splitting of the 31P resonance into AX patterns, as illustrated in Figure 1. The phosphorous chemical shifts and the 31P-31P coupling constants (Jpp = 35.5 Hz) suggested that the dppp ligand was positioned trans to the diamine, with trans dichloro atoms, to form the kinetically favored trans-Cl2Ru(II) isomer [14,27], while the thermodynamic favored cis-Cl2Ru(II) isomer [28,29] was not detected according to the 31P-CP/MAS-NMR data.

Figure 1

(a) 31P-CP/MAS-NMR spectrum of the modified 4, (b) 31P{1H} of complex 2 in CD2Cl2.

(a) class="Chemical">31P-CP/MAS-NMR sclass="Chemical">pectclass="Chemical">pan class="Chemical">rum of the modified 4, (b) 31P{1H} of complex 2 in CD2Cl2.

The class="Chemical">31P-MAS-NMR sclass="Chemical">pectra of the xerogel 3 and modified material 4 are class="Chemical">presented together to elucidate the stclass="Chemical">pan class="Chemical">ructural nature and integrity of the ruthenium(II) supported complexes. The 31P-MAS NMR spectrum of the modified 4 complex is presented together with the liquid 31P-NMR spectrum of 2 (Figure 1). In the case of 4 (Figure 1a) relatively broad resonances centered at 33.5, 40.1, 46.5, 51.9 ppm were observed. Fortunately, even in the presence of the line broadening the chemical shifts of 4 can be assigned, which support the formation of the expected trans Cl2Ru(II) isomer in the solid state as in liquid state (Figure 1b) and the Ru–P bond seemed to not be affected during the grafting; free ligand was not detected (δp = - 21.8 ppm) and other chemical shifts corresponding to coordination of phosphine to another species are also not recorded.

Examination of the class="Chemical">13C-class="Chemical">pan class="Chemical">CP-MAS-NMR spectrum of the modified solids along with the solution phase spectrum of the corresponding molecular precursor led to the conclusion that the organic fragments in 3 and 4 remained intact during the grafting and subsequent workup without measurable decomposition (Figure 2). The absence of the methoxy groups at δC = 50.8 ppm after the immobilization processes in 3 and 4, compared by 2, were the major differences noted between spectra, which supported the immobilization of the desired hybrid Ru(II) complexes. The total disappearance of (CH3O)3Si groups in 3 (Figure 2b), compared by 2 (Figure 2b), provides good confirmation of a sol-gel process gone to full completion.

Figure 2

(a) Dept 135 13C-NMR of 2 in CD2Cl2 (b) 13C-CP/MAS-NMR spectra of the xerogel 3.

(a) Dept 135 class="Chemical">13C-NMR of 2 in class="Chemical">pan class="Chemical">CD2Cl2 (b) 13C-CP/MAS-NMR spectra of the xerogel 3.

Solid-state class="Chemical">29Si-NMR class="Chemical">provided further information about the class="Chemical">pan class="Chemical">silicon environment and the degree of functionalization [30]. In all cases, the organometallic/organic fragment of the precursor molecule was covalently grafted onto the solid, and the precursors were, in general, attached to the surface of the polysiloxane (as in 3) or mesoporous oxide by multiple siloxane bridges (as in 4) as evidenced in Figure 3. The presence of Tm sites in case of xerogel 3 (with m = 2 and 3) in the spectral region of T2 at δSi = -57.8 ppm and T3 at δSi = - 67.1 ppm as expected, and no peaks belonging to Q silicon sites were detected, as in Figure 3a. Peaks assignable to Q3 at δSi = -101.9 ppm and Q4 at δSi = -109.5 ppm silicon sites of the silica framework in addition to T3 at δSi = - 67.1 ppm were discernible in modified 4, as seen in Figure 3b.

Figure 3

a) CP-MAS-29Si-NMR of xerogel 3 sol-gel functionalized complex; and b) surface modified material 4.

a) pan class="Chemical">CP-MAS-class="Chemical">pan class="Chemical">29Si-NMR of xerogel 3 sol-gel functionalized complex; and b) surface modified material 4.

The IR spectra of the complexes 2-4 in particular show four sets of characteristic absorptions in the ranges 3,336–3,319, 3,268–3,215, 3,178–3,165, and 275–254 cm-1, which can be asclass="Chemical">signed to class="Chemical">pan class="Chemical">NH2, amine-CH, phosphine-CH and RuCl stretching vibrations, respectively.

2.3. EXAFS measurement of xerogel

One of the most powerful methods to obtain interatomic distances of amorphous materials is extended X-ray absorption fine stclass="Chemical">ructure sclass="Chemical">pectroscoclass="Chemical">py (EXAFS). The xerogel 3 was chosen as an examclass="Chemical">ple to determine the bond lengths between the class="Chemical">pan class="Chemical">metal center and the coordinating atoms of the ligand. The k3 weighted EXAFS function of xerogel 3 can be described best by six different atom shells. The first intensive peak in the corresponding Fourier transform (Figure 4a) is mainly due to the nitrogen atoms. Chlorine and phosphorus atoms were found in the case of the most intense peak. For the most intense peak of the Fourier Transform, two equivalent phosphorus, two nitrogen atoms and two chlorine atoms with Ru-P, Ru-N and Ru-Cl bond distances of 2.26, 2.19 and 2.41 Å, respectively, were found (Figure 4b and Table 1). These results reveal a good agreement between the experimental and the calculated functions.

Figure 4

Experimental (solid line) and calculated (dotted line) EXAFS functions (a) and their Fourier transforms (b) for xerogel 3 measured at Ru K-edge.

Table 1

EXAFS determined structural parameters of xerogel 3.

A-Bsa	Nb	R c [Å]	σ d [Å]	ΔE0e [eV]	k-range [Å-1]	Fit-Index
Ru – N	2	2.19 ± 0.02	0.050 ± 0.005	22.72	3.0 - 16.0	32.24
Ru – P	2	2.26 ± 0.02	0.055 ± 0.006
Ru – Cl	2	2.41 ± 0.03	0.063 ± 0.007

a absorber (A) – backscatterers (Bs),b coordination number N, cinteratomic distance r, dDebye-Waller factor σ with its calculated deviation and e shift of the threshold energy ΔE0.

Experimental (solid line) and calculated (dotted line) EXAFS functions (a) and their Fourier pan class="Chemical">transforms (b) for xerogel 3 measured at class="Chemical">pan class="Chemical">Ru K-edge.

EXAFS determined stpan class="Chemical">ructural class="Chemical">parameters of xerogel 3.

2.4. Catalytic activity of complexes in the hydrogenation of α,ß-unsaturated carbonyl compounds.

The catalytic activity of the declass="Chemical">sired hybrid class="Chemical">pan class="Chemical">ruthenium(II) materials 2-4, was carried out using α,ß-unsaturated carbonyl compounds in 2-propanol as solvent, and the chosen α,ß-unsaturated carbonyl compounds allowed us to study the selectivity of the catalysts. Three different outcomes of the hydrogenation process are to be expected (Scheme 2).

Scheme 2

Hydrogenation of α,ß-unsaturated carbonyl compounds possibilities.

class="Chemical">Hydrogenation of α,ß-class="Chemical">pan class="Chemical">unsaturated carbonyl compounds possibilities.

The class="Chemical">Ru(II) complexes have been tested as catalyst class="Chemical">precursors for class="Chemical">pan class="Chemical">hydrogenation under mild conditions: 2 bar hydrogen pressure, six equivalents of KOH, 35 oC and with a molar substrate to catalyst (S/C) ratio of 1,000:1. The hydrogenation results are summarized in Table 2.

Table 2

Hydrogenation results of α,β-unsaturated carbonyl compounds. a

	Substrate	Complex	Conversion (%)b	C=O Selectivity (%)b	TOFc
1	Sub1	1	0	0	0
2	Sub1	2	>99	>99	1220
3	Sub2	2	>99	>99	1205
4	Sub3	2	>99	>99	1190
5	Sub1	2	0	0	0
6	Sub1	3d	98	97	113
7	Sub2	3d	95	96	120
8	Sub3	3d	93	95	108
9	Sub1	4d	97	94	128
10	Sub2	4d	95	95	102
11	Sub3	4d	96	94	110

a Two model substrate were used, reactions were conducted at 35oC, (S/C=1,000) in 50 mL of 2-propanol, PH2 =2 bar, [Ru:KOH:Sub] [1:6:1,000]. b Yield and selectivity were determined by GC. c TOF: turnover frequency (molsub mol-1cat h-1). c the same conditions of a but the reactions conversation was determined after 12 h.

class="Chemical">Hydrogenation results of α,β-class="Chemical">pan class="Chemical">unsaturated carbonyl compounds. a

a Two model substrate were used, reactions were conducted at 35oC, (S/C=1,000) in 50 mL of class="Chemical">2-propanol, Pclass="Chemical">pan class="Chemical">H2 =2 bar, [Ru:KOH:Sub] [1:6:1,000]. b Yield and selectivity were determined by GC. c TOF: turnover frequency (molsub mol-1cat h-1). c the same conditions of a but the reactions conversation was determined after 12 h.

As expected class="Chemical">RuCl2(dppp)2 1 was comclass="Chemical">pletely inactive in the class="Chemical">pan class="Chemical">hydrogenation of unsaturated ketones under the above reaction conditions (Table 2, trial 1), which was traced back to the absence of the diamine. All the trials of precursor 2 showed more than 99% activity and hydrogenation selectivity towards the C=O group in the presence of a C=C group with high TOF, (Table 2, trials 2-4). In the absence of KOH co-catalyst and under identical conditions the active precursor 2 became totally inactive (Table 2, trials 2 and 5), which supports the idea that the role of the co-catalyst is to activate the catalyst by forming the ruthenium(II) hydride intermediate [10,11,12,13,14,15,16,17,18,19,20].

All of the other class="Chemical">ruthenium(II) class="Chemical">precursors 3 and 4 disclass="Chemical">play high converclass="Chemical">pan class="Chemical">sion ratios and selectivity ~ 95% in the hydrogenation of the target substrates (Table 2, trials 6-11). Expected constant decrease in the turnover frequencies (TOFs) and the conversions were observed by comparing the homogenous 2 with the heterogeneous 3 and 4 precursors.

3. Experimental

3.1. General remarks, materials, and instrumentation

All reactions were carried out in an inert atmosphere (class="Chemical">argon) by uclass="Chemical">pan class="Chemical">sing standard high vacuum and Schlenk-line techniques, unless otherwise noted. Prior to use CH2Cl2, n-hexane, and Et2O were distilled from CaH2, LiAlH4, and from sodium/benzophenone, respectively. 1,3−Bis(diphenyl-phosphino)propane (dppp) was prepared according to literature methods [14]. 3-(2-Aminoethyl)amino-propyl]trimethoxysilane was purchased from Acros and had to be purified by distillation and recrystallization, Elemental analyses were carried out on an Elementar Vario EL analyzer. High-resolution liquid 1H-, 13C{1H}-, DEPT 135, and 31P{1H}-NMR spectra were recorded on a Bruker DRX 250 spectrometer at 298 K. Frequencies are as follows: 1H-NMR: 250.12 MHz, 13C{1H}-NMR: 62.9 MHz, and 31P{1H}-NMR 101.25 MHz. Chemical shifts in the 1H- and 13C{1H- NMR spectra were measured relative to partially deuterated solvent peaks which are reported relative to TMS. 31P chemical shifts were measured relative to 85% H3PO4. CP/MAS solid-state NMR spectra were recorded on Bruker DSX 200 (4.7 T) and Bruker ASX 300 (7.05 T) multinuclear spectrometers equipped with wide-bore magnets. Magic angel spinning was applied at 4 kHz (29Si) and 10 kHz (13C, 31P) using (4 mm ZrO2 rotors). Frequencies and standards: 31P, 81.961 MHz (4.7 T), 121.442 MHz (7.05 T) [85% H3PO4, NH4H2PO4 (d = 0.8) as second standard]; 13C, 50.228 MHz (4.7 T), 75.432 MHz (7.05 T) [TMS, carbonyl resonance of glycine (δ = 176.05) as second standard]; 29Si, 39.73 MHz (4.7 T), 59.595 MHz (7.05 T, (Q8M8 as second standard). All samples were prepared with exclusion of molecular oxygen. IR data were obtained on a Bruker IFS 48 FT-IR spectrometer. Mass spectra: EI-MS, Finnigan TSQ70 (200 oC) and FAB-MS, Finnigan 711A (8 kV), modified by AMD and reported as mass/charge (m/z). The analyses of the hydrogenation experiments were performed on a GC 6000 Vega Gas 2 (Carlo Erba Instrument) with a FID and capillary column PS 255 [10 m, carrier gas, He (40 kPa), integrator 3390 A (Hewlett Packard)]. The EXAFS measurements were performed at the ruthenium K–edge (22118 eV) at the beam line X1.1 of the Hamburger Synchrotronstrahlungslabor (HASYLAB) at DESY Hamburg, under ambient conditions, energy 4.5 GeV, and initial beam current 120 mA. For harmonic rejection, the second crystal of the Si(311) double crystal monochromator was tilted to 30 %. Data were collected in transmission mode with the ion chambers flushed with argon. The energy was calibrated with a ruthenium metal foil of 20 μm thickness. The samples were prepared of a mixture of the samples and polyethylene.

3.2. General procedure for the preparation of the complex

class="Chemical">3-(2-Aminoethyl)aminopropyl]trimethoxysilane (0.035 mL, 0.55 mmol, 10% excess) was dissolved in class="Chemical">pan class="Chemical">dichloromethane (10 mL) and the solution was added dropwise to a stirred solution of 1 (500 mg, 0.50 mmol) in dichloromethane (10 mL) within 5 min. The mixture was stirred for ca. 2 h at room temperature while the color changed from brown to yellow. After removal of any turbidity by filtration (P4), the volume of the solution was concentrated to about 5 mL under reduced pressure. Addition of diethyl ether (40 mL) caused precipitation of a solid, which was filtered (P4). After recrystallization from dichloromethane/n-hexane, complex 2 was obtained in analytically pure form. Yield 312 mg (93%) of a yellow powder, m.p. 340 oC (dec.); 1H-NMR (CDCl3): δ (ppm) 0.11 (m, 2H, CH2Si), 0.60 (br, 2H, PCH2CH), 1.43 (br, 4H, PCHCH2), 2.07 (m, 2H, CHCH2Si), 2.45 (m, 4H, NCHN), 2.93 (m, 5H, NH2, NH, NHCH2), 3.49 (s, 9H, OCH3) 7.10- 7.60 (m, 20H, C6H5); 31P{1H}-NMR (CDCl3): δ (ppm) 33.50, 46.35, dd, Jpp =35.5 Hz; 13C{1H}-NMR (CDCl3): δ (ppm) 6.32 (s, 1C, CH2Si), 19.55 (s, 1C, PCH2H2), 21.92 (m, 1C, H2CH2Si), 27.83 (m, 2C, PCH2), 42.84 (s, 1C, NH2CH2), 49.34 (s, 1C, NHH2CH2CH2) 50.84 (s, 3C, OCH3), 54.62 (s, 1C, NH2H2CH2NH), 126.23-136.82 (m, 24C, C6H5); FAB – MS; (m/z): 806.2 (M+); Anal. Calc. C, 52.11; H, 6.00; Cl, 8.79; N, 3.47 for C35H48Cl2N2O3P2RuSi: Found C, 52.04; H, 6.22; Cl, 8.70; N, 3.35%.

3.3. General procedure for sol–gel processing of xerogel

Compound 2 (300 mg, 0.235 mmol) and Hclass="Chemical">Si(OMe)3 (10 equivalents) in class="Chemical">pan class="Chemical">methanol (10 mL) were mixed together. The sol–gel took place when a THF/water mixture (4 mL, 1:1 v/v) was added to the solution. After 24 h stirring at room temperature, the precipitated gel was washed with toluene and diethyl ether (50 mL of each), and petroleum ether (40 mL). Finally the xerogel was ground and dried under vacuum for 24 h to afford after workup 500 mg of 3 as a pale yellow powder. 31P-CP/MAS-NMR: δ = 33.50, 46.35. dd, Jpp =35.5 Hz; 13C-CP/MAS NMR: δ (ppm) 4.71 (br, 1C, CH2Si), 18.19 (br, 1C, PCH2H2), 20.18 (m, 1C, H2CH2Si), 25.66 (m, 2C, PCH2), 42.31 (br, 1C, NH2CH2), 46.44 (s, 1C, NHH2CH2CH2), 53.52 (s, 1C, NH2H2CH2NH), 126.22-138.96 (m, 24C, C6H5); 29Si CP/MAS NMR: δ = –67.1 ppm (T3), –57.2 ppm (T2).

3.4. General procedure for surface modifiedmaterial

Compound 2 (0.300 mg, 0.235 mmol) dissolved in class="Chemical">CH2Cl2 (50 mL) was added droclass="Chemical">pwise to a susclass="Chemical">penclass="Chemical">pan class="Chemical">sion of ProntoSil 120-5 Si (5 mm) (0.5 g) in dry toluene (50 mL) and stirred at 25 °C for 2 h to allow the diffusion of the molecular precursor into the pore channels. The reaction mixture was then refluxed for 24 h. After filtration, the unreacted ruthenium precursor was removed by thoroughly washing the solid twice with toluene then CH2Cl2 (25 mL each). Finally, the resulting solid was dried in vacuo (~ 0.40 atm) at 30 °C to afford 620 mg of 4 as a pale white powder. 31P-CP/MAS-NMR: δ = 33.80, 46.42. dd, Jpp =35.5 Hz; 13C CP/MAS-NMR: δ (ppm) 4.82 (br, 1C, CH2Si), 18.39 (br, 1C, PCH2H2), 21.08 (m, 1C, H2CH2Si), 26.34 (m, 2C, PCH2), 42.81 (br, 1C, NH2CH2), 46.76 (s, 1C, NHH2CH2CH2), 53.82 (s, 1C, NH2H2CH2NH), 126.34-138.77 (m, 24C, C6H5); 29Si-CP/MAS- NMR: δ = –67.1 (T3) and –57.2 (T2), -101.9 ppm (Q3) and -109.5 ppm (Q4).

3.5. General procedure for the catalysis studies

The respective matrix of class="Chemical">diamine(class="Chemical">pan class="Chemical">dppp)ruthenium(II) supported complexes, (100 mg, 6% Ru) was placed in a 250 mL pressure Schlenk tube, a calculated amount of KOH (0.06 mmol, 10 equivalents) was added as co-catalyst, then trans-4-phenyl-3-butene-2-one (60 mmol, 1000 equivalents) was added. The solid mixture was magnetically stirred and warmed during the evacuation process to remove oxygen and water. Subsequently the Schlenk tube was filled with argon and 2-propanol (80 mL). The mixture was vigorously stirred, degassed by two freeze-thaw cycles, and then sonicated for 30 min (this is important to increase the homogeneity of the mixture). Finally the reaction mixture was pressurized with H2 (2 bar) after flushing with H2 three times. The reaction mixture was vigorously and magnetically stirred at 35 °C for 1−12 h. During the hydrogenation process samples were taken from the reaction mixture to check the course of the reaction. The samples were inserted by a special glass syringe into a gas chromatograph and the reaction products compared with authentic samples.

4. Conclusions

Four new complexes were prepared by a novel, fast, easy, one step ligand exchange technique and characterized. The presence of T-class="Chemical">silyl functions on the class="Chemical">pan class="Chemical">diamine co-ligand backbone enable the hybridization of these complexes in order to support them on a polysiloxane matrix through sol-gel or surface modification processes. When the polymeric complexes presented in this investigation were tested as catalysts for the hydrogenation of unsaturated ketones, they showed high degree of stability and activity as well as an excellent degree of carbonyl hydrogenation selectivity under mild conditions.