Inorganica Chimica Acta 367 (2011) 166–172

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trans- and cis-Ru(II) aminophosphine complexes: Syntheses, X-ray structuresand catalytic activity in transfer hydrogenation of acetophenone derivatives

Murat Aydemir a,⇑, Akın Baysal a, Saim Özkar b, Leyla Tatar Yıldırım c

a Dicle University, Department of Chemistry, TR-21280 Diyarbakır, Turkeyb Middle East Technical University, Department of Chemistry, TR-06531 Ankara, Turkeyc Hacettepe University, Department of Engineering Physics, Beytepe, TR-06800 Ankara, Turkey

a r t i c l e i n f o

Article history:Received 2 June 2010Received in revised form 29 November 2010Accepted 10 December 2010Available online 24 December 2010

Keywords:Transfer hydrogenationCrystal structuresAminophosphineBis(phosphino)amineRu(II)

0020-1693/$ - see front matter � 2010 Elsevier B.V. Adoi:10.1016/j.ica.2010.12.028

⇑ Corresponding author.E-mail address: aydemir@dicle.edu.tr (M. Aydemir

a b s t r a c t

The ability of transition metal catalysts to add or remove hydrogen from organic substrates by transferhydrogenation process is a valuable synthetic tool. For this aim, a novel Ru(II) complex with the P–Nligand [(Ph2P)2NCH2–C4H3S] derived from thiophene-2-methylamine was synthesized starting with thecomplex [Ru(g6-p-cymene)(l-Cl)Cl]2 and isolated in two isomeric forms: trans- and cis-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2 and 3, respectively. The structures of both isomers were also determinedby single crystal X-ray diffraction. The cis-isomer 3 can be isolated from the solution of major trans-iso-mer 2 as yellow crystals. However, upon dissolution 3 is rapidly converted to the trans-isomer 2. The newruthenium(II) complex provides high catalytic activity in the transfer hydrogenation of acetophenonederivatives to 1-phenylethanol derivatives in the presence of 2-propanol as the hydrogen source. Thistransfer hydrogenation is characterized by low reversibility under the experimental conditions.

� 2010 Elsevier B.V. All rights reserved.

1. Introduction hydrogenation by molecular hydrogen [22,23]. In transfer hydro-

Aminophosphine ligands have been studied for the last threedecades and found to be of considerable interest due their widerange of applications in organometallic chemistry for the develop-ment of industrial processes involving a great number of catalyticreactions [1]. A large number of complexes with aminophosphineligands have been tested in different catalytic reactions includingallylic alkylation [2], amination [3], Heck [4], Sonogashira [5], Su-zuki [6], hydroformylation [7], hydrogenation [8] and polymeriza-tion [9] reactions. Some aminophosphines and derivatives havealso found application as anticancer drugs [10], herbicides andantimicrobial agents, as well as neuroactive agents [11]. To date,a number of such systems with a variety of backbone frameworkshave been synthesized and their transition metal chemistry hasbeen explored [12,13]. Aminophosphines and bis(phos-phino)amines with P–NH and P–N–P skeletons, respectively, haveproved to be much more versatile ligands, and varying the substit-uents on both the P- and N-centers gives rise the changes in the P–N–P angle and the conformation around the P-centers [14–17].Small variations in these ligands can cause significant changes intheir coordination behavior and the structural features of theresulting complexes [18–21].

Catalytic transfer hydrogenation with the aid of a stablehydrogen donor is a useful alternative method for catalytic

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).

genation, organic molecules such as primary and secondary alco-hols [24] or formic acid and its salts [25] have been employed asthe hydrogen source. The use of the hydrogen donor has someadvantages over the use of molecular hydrogen since it avoidsno risks and the constrains associated with hydrogen gas as wellas the necessity for pressure vessels and other equipments. 2-Propanol is a popular reactive solvent for transfer hydrogenationreactions since it is easy to handle and is relatively non-toxic,environmentally benign and inexpensive. The volatile acetoneby-product can also be easily removed to shift unfavorable equi-libria and can be converted to 2-propanol back by catalytichydrogenation [26]. In general, asymmetric hydrogenation ismediated by a complex bearing Rh, Ru, or Ir, among which ourfocus has been Ru. One reason is that the Ru catalysts haveexcellent performances [27,28]. Another reason is that Ru en-joyed a cost advantage relative to other asymmetric hydrogena-tion metals such as Rh [29].

In this paper, we report the ready synthesis of bis(phos-phino)amine ligand [(Ph2P)2NCH2–C4H3S] and its correspondingruthenium(II) complexes, trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2and cis-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 3. The structures of bothcomplexes were determined by single crystal X-ray diffractionanalyses. As a part of our continuing interest in developinghighly active efficient and stable catalysts [30–33], we reporthere the catalytic activity of trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2],2 complex in the transfer hydrogenation of acetophenonederivatives.

M. Aydemir et al. / Inorganica Chimica Acta 367 (2011) 166–172 167

2. Experimental

2.1. Materials and methods

Unless otherwise stated, all reactions were carried out under anatmosphere of argon using conventional Schlenk glass-ware, sol-vents were dried using established procedures and distilled underargon immediately prior to use. Analytical grade and deuteratedsolvents were purchased from Merck. PPh2Cl and thiophene-2-methylamine are purchased from Fluka and were used as received.[Ru(g6-p-cymene)(l-Cl)Cl]2 [34] was prepared according to litera-ture procedure. The IR spectra were recorded on a Mattson 1000ATI UNICAM FT-IR spectrometer as KBr pellets. 1H (400.1 MHz),13C NMR (100.6 MHz) and 31P-{1H} NMR spectra (162.0 MHz) wererecorded spectra on a Bruker Avance 400 spectrometer, with d ref-erenced to external TMS and 85% H3PO4 respectively. Elementalanalysis was carried out on a Fisons EA 1108 CHNS-O instrument.Melting points were recorded by Gallenkamp Model apparatuswith open capillaries.

2.2. GC analyses

GC analyses were performed on a HP 6890 N Gas Chromato-graph equipped with capillary column (5% biphenyl, 95% dimethyl-siloxane) (30 m � 0.32 mm � 0.25 lm). The GC parameters wereas follows for transfer hydrogenation of ketones; initial tempera-ture, 110 �C; initial time, 1 min; solvent delay, 4.48 min; tempera-ture ramp 80 �C/min; final temperature, 200 �C; final time,21.13 min; injector port temperature, 200 �C; detector tempera-ture, 200 �C; injection volume, 2.0 lL.

2.3. Synthesis of trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2] (2)

To a solution of [Ru(g6-p-cymene)(l-Cl)Cl]2 (149 mg,0.243 mmol) in 10 mL thf, a solution (thf, 30 mL) of (PPh2)2-NCH2–C4H3S, 1 (469 mg, 0.972 mmol) was added. The resultingreaction mixture was allowed to proceed under stirring at roomtemperature for 1 h. After this time, the solution was filtered offand the solvent evaporated under vacuum, the solid residue thusobtained was washed with diethyl ether (3 � 15 mL) and thendried under vacuum (Scheme 1). Following recrystallization fromdiethylether/CH2Cl2, a scarlet crystalline powder was obtained(yield 506 mg, 91.5%), m.p. 251–253 �C. 1H NMR (400.1 MHz,CDCl3) d = 7.11–7.56 (m, 40H, o-, m- and p- protons of phenyls),6.96 (d, 2H, 3J = 4.20 Hz, H-5), 6.60 (dd, 2H, 3J = 2.80 and 4.20 Hz,H-4), 6.43 (d, 2H, 3J = 2.80 Hz, H-3), 4.66 (t, 4H, 3J = 5.20 Hz, –

Scheme 1. Synthesis of the trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2 and cis-[Ru((PPh2)2NCequivalent [Ru(g6-p-cymene)(l-Cl)Cl]2, thf; (iii) in CH2Cl2, 48 h; (iv) 1 equivalent [Ru(g

CH2–); 13C NMR (100.6 MHz, CDCl3): d = 48.14 (–CH2–), 125.23(C-5), 126.38 (C-4), 126.78 (m-carbons of phenyls), 127.76 (C-3),129.61 (p-carbons of phenyls), 134.83 (o-carbons of phenyls),137.30 (i-carbons of phenyls), 141.16 (C-2); assignment was basedon the 1H–13C HETCOR and 1H–1H COSY spectra; 31P NMR(162 MHz, CDCl3): d = 78.05 (s); IR, (KBr): m = 993 (P–N–P), 1436(P–Ph) cm�1. Anal. Calc. for C58H50N2S2P4RuCl2 (1135.1 g/mol): C,61.37; H, 4.44; N, 2.47. Found: C, 61.29; H, 4.39; N, 2.41%.

2.4. Synthesis of [Ru((PPh2)2NCH2–C4H3S)(g6-p-cymene)Cl]Cl (4)

To a solution of [Ru(g6-p-cymene)(l-Cl)Cl]2 (0.596 g,0.980 mmol) in 10 mL thf, a solution (thf, 15 mL) of [(PPh2)2NCH2–C4H3S], 1 (0.469 g, 0.980 mmol) was added. The resulting reactionmixture was allowed to proceed under stirring at room temperaturefor 1 h. After this time, the solution was filtered off and the solventevaporated under vacuum, the solid residue thus obtained waswashed with diethyl ether (3 � 15 mL) and then dried under vacuum(Scheme 2). Following recrystallization from diethylether/CH2Cl2, ared crystalline powder was obtained (yield: 0.71 g, 92%; m.p.: 250 �C(dec.); 1H NMR (d in ppm rel. to TMS, J Hz, in CDCl3): 7.72 (dd, 8H,3J = 7.2 and 13.6, o-protons of phenyls), 7.54 (dd, 4H, 3J = 6.6 and12.4, p-protons of phenyls), 7.32 (m, 8H, m-protons of phenyls),7.03 (d, 1H, 3J = 5.2 Hz, H-5), 6.66 (dd, 1H, 3J = 3.6 and 5.2 Hz, H-4),6.39 (d, 1H, 3J = 3.6, H-3), 5.45 (d, 2H, 3J = 5.6 Hz, aromatic hydrogensof p-cymene), 5.28 (d, 2H, 3J = 5.6 Hz, aromatic hydrogens of p-cym-ene), 4.45 (t, 2H, 3J = 11.6 Hz, –CH2–), 2.81 (m, 1H, –CH– of p-cym-ene), 2.26 (s, 3H, CH3-Ph of p-cymene), 1.23 (d, 6H, 3J = 6.8 Hz,(CH3)2CHPh of p-cymene); 13C NMR (d in ppm rel. to TMS, J Hz, inCDCl3): 18.63 (CH3Ph of p-cymene), 22.21 ((CH3)2CHPh of p-cym-ene), 31.01 (–C H– of p-cymene), 47.68 (–CH2–), 77.97, 79.05(aromatic carbons of p-cymene), 95.92, 100.20 (quaternary carbonsof p-cymene), 125.32 (C-5), 126.55 (C-4), 127.86 (C-3), 127.41(t, 3J = 4.0 Hz, m-carbons of phenyls), 129.84 (d, 1J = 57.3 Hz, i-car-bons of phenyls), 132.83 (t, 4J = 6.0 Hz, p-carbons of phenyls),134.31 (t, 2J = 5.5 Hz, o-carbons of phenyls), 140.54 (C-2); assign-ment was based on the 1H–13C HETCOR and 1H–1H COSY spectra;31P NMR (d in ppm rel. to H3PO4, in CDCl3): 88.21 (s); Selected IR(KBr pellet, in cm�1): m(P–N–P) 984, m(P–Ph) 1440; Anal. Calc. forC39H39NSP2RuCl2 (787.7 g/mol): C, 59.47; H, 4.99; N, 1.78. Found:C, 59.39; H, 4.93; N, 1.74%.

2.5. X-Ray Crystallography

X-ray diffraction data of single crystal for trans- and cis-[Ru((PPh2)2NCH2–C4H3S)2Cl2] were collected at room temperature

H2–C4H3S)2Cl2], 3 complexes: (i) 2 equivalent Ph2PCl, 2 equivalent Et3N, thf; (ii) 1/46-p-cymene)(l-Cl)Cl]2, thf.

Scheme 2. Hydrogen transfer from iso-PrOH to acetophenone derivatives.

168 M. Aydemir et al. / Inorganica Chimica Acta 367 (2011) 166–172

with graphite monochromated Mo Ka (k = 0.71073 Å) radiation onan Enraf-Nonius CAD4 diffractometer operating in x/2h scanmode. Unit cell parameters were refined from the setting anglesof (trans) 25 and (cis) 17 centered reflections in the range of (trans)10.00 6 h 6 18.03� and (cis) 10.10 6 h 6 17.96�. Cell refinementwas carried out using CAD-4 EXPRESS [35]. Data reduction was car-ried out using XCAD4 [36]. The structure was solved by direct meth-ods using SHELX97 and refined by the full-matrix least-squaresmethod on F2 assuming anisotropic thermal parameters for non-hydrogen atoms using SHELXL97 [37] in the WINGX package [38].Hydrogen atoms on the methylene of the trans structure were ta-ken from a difference Fourier map and refined with isotropic ther-mal parameters. All other hydrogen atoms of both molecules wereplaced geometrically and a riding model was used on their carrieratom. Selected crystal and experimental data are given in Table 1.Selected bond lengths and angles are given in Tables 2 and 3.

2.6. General procedure for the transfer hydrogenation of ketones

Typical procedure for the catalytic hydrogen transfer reaction: asolution of ruthenium complex trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2 (0.01 mmol), NaOH (0.05 mmol) and the correspond-ing ketone (1.0 mmol) in degassed iso-PrOH (10 mL) was refluxedfor 60 min for 2. After this period a sample of the reaction mixturewas taken off, diluted with acetone and analyzed immediately byGC. Conversions obtained are related to the residual unreactedketone.

Table 1Crystal data and experimental details for compounds trans- and cis-[Ru((PP

Compound trans

Formula [C58H50Cl2N2P4RuS2

Formula weight 1373.73Crystal shape/color prism/yellowCrystal size (mm3) 0.15 � 0.05 � 0.03T (K) 295(2)Crystal system/space group triclinic/P�1a (Å) 10.6451(10)b (Å) 11.459(2)c (Å) 13.580(2)a (�) 67.663(9)b (�) 75.767(7)c (�) 84.664(8)V (Å3) 1485.2(4)Z 1Dcalc (Mg/m3) 1.536l(mm�1) 0.844F(0 0 0) 698h range for data collection (�) 2.27–26.29Reflections measured 6263Independent observed reflections 5999Independent reflections [I > 2r] 4739Data/restraints/parameters 5999/5/335Rint 0.0445R indices (all data) R1 = 0.1144, wR2 = 0R indices [I > 2r(I)] R1 = 0.089, wR2 = 0.2Goodness of fit (GOF) on F2 1.069Dqmin, Dqmin (e Å�3) �2.140, 2.293

3. Results and discussion

3.1. Synthesis and characterization of the metal complexes

The ligand thiophene-2-(N,N-bis(diphenylphosphino))methyl-amine, [(Ph2P)2NCH2–C4H3S], 1 was prepared from the aminolysisof two equivalents of PPh2Cl with one equivalent thiophene-2-methylamine in the presence of triethylamine at 0 �C, as outlinedin Scheme 1 [39]. The 31P NMR spectrum of 1 gives single reso-nance at 59.83 ppm, similar to those found for closely related com-pounds [40]. 1 is not stable and rapidly oxidized to P(O)Ph2PPh2 onexposure to air or moisture as monitored by 31P NMR spectroscopy,which gives two doublets at 34.60 and �24.30 ppm with a cou-pling constant of 1J(PP) = 226 Hz.

We examined some simple coordination chemistry of 1 with[Ru(g6-p-cymene)(l-Cl)Cl]2 precursor. The reaction betweenRu(II) precursor and bis(phosphino)amine, 1 is profoundly affectedby the molar ratio of the reactants. Reaction of (PPh2)2NCH2–C4H3S,1 with [Ru(g6-p-cymene)(l-Cl)Cl]2 in thf solution in a molar ratioof 1:1/4 at room temperature for 1 h yielded trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2 as crystalline orange powders(Scheme 1). By slow diffusion of diethylether into a solution ofthe complex 2 in the dichloromethane, complex 2 was obtainedas scarlet crystals. In addition to the complex 2, a few yellow crys-tals of complex 3 were also obtained, which were suitable for X-raydiffraction studies. From these single crystals, the structures ofboth compounds were elucidated by X-ray diffraction studies.Crystal structure studies showed that major and minor productsare trans- (2) and cis- (3) isomer of [Ru((PPh2)2NCH2–C4H3S)2Cl2],respectively. The trans isomer, 2 was isolated and characterizedby observing a singlet at 78.05 ppm in the 31P NMR spectrum inline with the values previously observed for similar compounds[41,42]. This indicates that (PPh2)2NCH2–C4H3S is acting as abidendate chelating ligand. The IR bands observed at 993 and1436 cm�1 represent m(PNP) and m(PPh), respectively. The 13CNMR spectra gave signals in line with structures as explained inSection 2 [43].

h2)2NCH2–C4H3S)2Cl2].

cis

]�2(CHCl3) [C58H50Cl2N2P4RuS2]�(CH2Cl2)(C4H10O)1294.04plate/yellow0.4 � 0.4 � 0.1295(2)monoclinic/P21/c12.532(2)27.738(4)17.7547(10)90101.378(8)906050.5(14)41.4210.65426642.33–26.2912 23011855553811 855/4/6640.0704

.2802 R1 = 0.2254, wR2 = 0.1821582 R1 = 0.730, wR2 = 0.2352

1.002�1.019, 2.678

Table 2Selected bond lengths for 2 and related bond length ranges for 3 (Å).

trans cis

Ru–Cl1 2.4205(17) Ru–Cl 2.463(2)–2.464(2)Ru–P1 2.3523(17) Ru–P 2.282(2)–2.336(2)Ru–P2 2.3250(17) P–N 1.709(7)–1.743(7)P1–Ni 1.723(6) P–C 1.814(8)–1.833(9)P2–N 1.714(6) N–C 1.474(10)–1.486(9)P1–C1 1.843(8) S–C 1.645(14)–1.707(10)P1–C7 1.821(7) P���P 2.648(3)–2.656(3)P2–C13 1.807(8)P2–C19 1.830(7)N–C25 1.496(9)S–C26 1.695(10)S–C29 1.656(13)P1���P2i 2.663(3)

[i: �x, �y, �z].

Table 3Selected bond angles for 2 and related bond angle ranges for 3 (�).

trans cis

Cl1–Ru–P1 85.73(6) Cl–Ru–P (neighbor) 87.77(8)–100.71(8)Cl1–Ru–P1i 94.27(6) Cl–Ru–P (opposite) 156.08(8)–157.89(8)Cl1–Ru–P2 92.02(6) Cl1–Ru–Cl2 85.84(8)Cl1–Ru–P2i 87.98(6) P1–Ru–P2 71.18(8)P1–Ru–P2 110.61(6) P3–Ru–P4 70.13(8)P1–Ru–P2i 69.39(6) P1–Ru–P3 101.15(8)P1–N–P2i 101.5(3) P2–Ru–P3 102.68(8)Ru–P1–Ni 93.9(2) P2–Ru–P4 102.58(8)Ru–P2–N 95.1(2) P2–Ru–P4 167.66(8)C1–P1–C7 101.8(4) P–N–P 100.2(3)–100.6(3)C13–P2–C19 100.4(3) Ru–P–N 93.7(2)–95.3(2)

C–P–C 98.5(4)–99.5(4)

[i: �x, �y, �z].

M. Aydemir et al. / Inorganica Chimica Acta 367 (2011) 166–172 169

The reaction of 1 with 1/2 equivalent [Ru(g6-p-cymene)(l-Cl)Cl]2 yielded a dark yellow solid. The 31P NMR spectrum of thecrude product indicated that it is a mixture of two products, 2and 4 as shown in (Fig. 1). In the 31P NMR spectrum, the singletat 78.05 ppm was assigned to compound 2. Complex 4 exhibits asinglet at 88.2 ppm for monochelating (PPh2)2NCH2–C4H3S. Com-pound 4 with one (PPh2)2NCH2–C4H3S ligand and compound 2with two [C4H3S-CH2N(PPh2)2] ligands show two sets of 31P NMRresonances with relative intensities of 1:2 (approximately) whichare consistent with these structural formulae. The compound 4was also prepared in its pure form separately using different molarratios. The reaction of (PPh2)2NCH2–C4H3S with excess of [Ru(g6-p-cymene)(l-Cl)Cl]2) affords only the corresponding monochelate

Fig. 1. The 31P NMR spectra of reaction mixture containing complexes 2 and 4; (i) reactequivalent [Ru(g6-p-cymene)(l-Cl)Cl]2; (iii) reaction of 1 with 1 equivalent (excess) [Ru

[Ru((PPh2)2NCH2–C4H3S)(g6-p-cymene)Cl]Cl, 4, in high yield asthe main product (Scheme 1).

The title compounds trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2 andcis-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 3 both mononuclear Ru(II) com-plexes, crystallize in the triclinic P�1 and monoclinic P21/c spacegroup, respectively. In the trans- compound 2 the central Ru atom,which is located on an inversion center, has disordered octahedralcoordination. In the cis- compound 3 the Ru atom has highly disor-dered octahedral coordination. The ORTEP drawing [44] of the mol-ecule is shown in Fig. 2.

In compound 2, the equatorial plane consists of two P atomsand their symmetry related P atoms from N-diphenylphosphino(PPh2) ligands [Ru–P1 2.3523(17), Ru–P2 2.3250(17) Å]. The Clatom and its symmetry related atom occupy the axial positionsof the octahedron [Ru–Cl1 2.4205(17) Å]. The coordination bondangles are range of 69.39(6)–110.61(6)�. In compound 3, thereare two different coordination planes, A [P1/N1/P2/Cl2] and B[P3/N2/P4/Cl1], which are consists of three P atoms from N-diphenylphosphino (PPh2) ligands with Ru–P bond length rangeof 2.282(2)–2.336(2) Å and one Cl atom with Ru–Cl bond lengthrange of 2.463(2)–2.464(2) Å. The A and B planes are nearly per-pendicular to each other. Dihedral angle between them is 88.42�.The coordination bond angles are range of 70.13(8)–102.68(8)�.

The hydrogen bonding and molecular packing geometry wascalculated with PLATON [45]. In the crystal structure of 2 and 3, thereexists X–H���Cg (p-ring) interaction further stabilizes the structurewith the shortest intra and intermolecular hydrogen bondings. De-tails of the hydrogen bonding geometry and p-ring interactions aregiven in Tables 4 and 5, respectively.

3.2. Catalytic transfer hydrogenation of acetophenone derivatives

In a preliminary study, the obtained complex trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2 was examined in the rutheniumcatalyzed transfer hydrogenation of acetophenone to the corre-sponding alcohol in iso-PrOH solution (Scheme 2).

The activity of Ru(II) arene complexes is well known in this cat-alytic process [46,47, and references therein]. In a typical experi-ment, 0.01 mmol of the complex 2 and 1 mmol of acetophenonewere added to a solution of NaOH in iso-PrOH (0.05 mmol of NaOHin 10 mL iso-PrOH) and refluxed at 82 �C, the reaction being mon-itored by GC. With a complex/NaOH ratio of 1/5, the complex leadsto a quantitative transformation of the acetophenone in 1 h, with amoderate TOF of <100 h�1 (Table 6, entry 1). These results are sum-marized in Table 6. It should be pointed out that complex 2 is moreactive catalysts than the corresponding precursor: [Ru(g6-p-cyme-ne)(l-Cl)Cl]2 (41% maximum conversion in 24 h) with a 1/14 com-plex/NaOH ratio [48].

ion of 1 with 1/4 equivalent [Ru(g6-p-cymene)(l-Cl)Cl]2; (ii) reaction of 1 with 1/2(g6-p-cymene)(l-Cl)Cl]2.

Fig. 2. The molecular structure and atomic labeling scheme of (a) trans compound and (b) cis compound. The thermal ellipsoids are drawn at 30% probability and hydrogenatoms and solvents were omitted for clarity.

Table 4Structural parameters of hydrogen bonds between donor (D), acceptor (A) andhydrogen (H).

Compound D–H���A D–H (Å) A���H (Å) D���A (Å) D–H���A (�)

trans (2) C2–H2���Cl14a 0.93 2.59 3.364(10) 140C14–H14���S4a 0.93 2.78 3.426(10) 128C30–H30���Cl4b 0.98 2.65 3.605(19) 164C8–H8���S 0.93 2.57 3.660(12) 168

cis (3) C2–H2���Cl2 0.93 2.77 3.496(9) 136C6–H6���S1 0.93 2.87 3.801(9) 175C12–H12���Cl1 0.93 2.52 3.410(9) 159C48–H48���Cl1 0.93 2.49 3.392(10) 164C54–H54���Cl1 0.93 2.74 3.553(10) 146C58–H58���S2 0.93 2.86 3.788(11) 173C63–H63A���Cl16a 0.97 2.56 3.418(13) 147C63–H63B���Cl26a 0.97 2.66 3.402(12) 133

Symmetry codes: [4a: 2 � x, �y, 1 � z; 4b: �1 + x, y, z; 6a: 1 � x, 1/2 + y, 1/2 � z].

Table 6Transfer hydrogenation of acetophenone with iso-PrOH catalyzed by trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2.

Entry Catalyst S/C/NaOH Time (h) Conversion (%)h TOF (h�1)i

1 3a 100:1:5 1 99 992 3b 100:1:5 1 <1 –3 3c 100:1 1 <2 –4 3d 100:1:5 1 <1 –5 3e 100:1:5 1.5 98 656 3f 100:1:5 2 97 (96, 93, 92)k 497 3g 500:1:5 3.5 99 28

a Catalyst (0.01 mmol), substrate (1.0 mmol), iso-PrOH (10 mL), NaOH(0.05 mmol), 82 �C, for 2, the concentration of acetophenone derivatives is 0.1 M.Ketone/catalyst/NaOH ratio: 100/1/5. Yields were determined by GC.

b At room temperature; acetophenone/Ru/NaOH, 100:1:5.c Refluxing in iso-PrOH; acetophenone/Ru, 100:1, in the absence of base.d Refluxing in iso-PrOH; acetophenone/Ru, 100:1:5, in the absence of catalyst.e Refluxing the reaction in air.f Added 0.1 mL of H2O.g Refluxing in iso-PrOH; acetophenone/Ru/NaOH, 500:1:5.h Determined by GC (three independent catalytic experiments).i Referred at the reaction time indicated in column; TOF = (mol product/mol

Ru(II)Cat.) � h�1.k The amount of the water in different concentrations (0.5, 1.0 and 5.0 mL).

170 M. Aydemir et al. / Inorganica Chimica Acta 367 (2011) 166–172

At room temperature no appreciable formation of 1-phenyleth-anol was observed (Table 6, entry 2) and also the catalytic activityof [Ru(g6-p-cymene)(l-Cl)Cl]2 under the applied experimentalconditions is negligible. In addition, as can be inferred from theTable 6 (entry 3 and 4), the precatalyst as well as the presence ofNaOH are necessary to observe appreciable conversion. Amazingly,the conversion was not affected in the air or with the addition ofwater. Performing the reaction in air slowed down the reactionbut did not affect conversions (Table 6, entry 5). For the transferhydrogenation of acetophenone, the catalyst system showed highactivity even in the presence of small amount (0.1 mL) of water.When we increased the amount of water in the reaction system,the high conversion remained intact (Table 6, entry 6). The transferhydrogenation of acetophenone could be achieved to up 99% con-version even when the substrate-to-catalyst ratio reached to 500:1except time of the reaction lengthened (Table 6, entry 7). Further-

Table 5Structural parameters of X–H���Cg (p-ring) interactions.

Compounds X–H ���Cg X–H (Å)

2 C8–H8���Cg41 0.93C29–H29���Cg424c 0.93

3 C31–H31���Cg61 0.93C23–H23���Cg62 0.93C41–H41���Cg62 0.93C6–H6���Cg63 0.93C58–H58���Cg64 0.93

Symmetry code: [4c: x, y, �1 + z].[Cg41 = S/C26/C27/C28/C29; Cg42 = C19/C20/C21/C22/C23/C24; Cg61 = Ru1/P1/N1/P2; C

more, in order to investigate the evolution of the catalyst, 2, 31PNMR spectrum was recorded immediately after the catalytic reac-tion. The observed singlet at 21.56 ppm is corresponding to hydro-lysis product diphenylphosphinous acid, Ph2P(O)H [49–51].

This complex was also extensively investigated with a variety ofsubstrates. Electronic properties (the nature and position) of thesubstituents on the phenyl ring of the ketone caused the changesin the reduction rate. A ortho- or para-substituted acetophenonewith an electron-donor substituent, i.e., 2-methoxy or 4-methoxyis reduced more slowly than acetophenone (Table 7, entry 4 and5) [52]. In addition, the introduction of electron withdrawing

H���Cg (Å) X���Cg (Å) X–H���Cg (�)

2.63 3.520(12) 1602.98 3.686(12) 1342.76 3.559(9) 1442.81 3.594(9) 1422.96 3.264(9) 1012.70 3.506(10) 1462.60 3.470(12) 157

g62 = Ru1/P3/N2/P4; Cg63 = S1/C14/C15/C16/C17; Cg64 = S2/C43/C44/C45/C46].

Table 7Transfer hydrogenation results for substituted acetophenones with the catalyst system trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2.a

O

+

OH

OH

+

OCat

R R

Entry R Time (h) Conversion (%)b TOF (h�1)c

Cat: Ru(II) complex, 2

1 4-F 1 99 992 4-Cl 1 98 983 4-Br 1 98 984 2-MeO 1 97 975 4-MeO 1 95 95

a Catalyst (0.01 mmol), substrate (1.0 mmol), iso-PrOH (10 mL), NaOH (0.05 mmol), 82 �C, 1 h for 2, the concentration of acetophenone derivatives is 0.1 M.b Purity of compounds is checked by NMR and GC (three independent catalytic experiments), yields are based on methyl aryl ketone.c TOF = (mol product/mol Cat.) � h�1.

M. Aydemir et al. / Inorganica Chimica Acta 367 (2011) 166–172 171

substituents, such as F, Cl and Br to the para-position of the arylring of the ketone decreased the electron density of the C@O bondso that the activity was improved giving rise to easier hydrogena-tion [53,54].

4. Conclusion

In conclusion, the coordination geometry of the trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2 and cis-[Ru((PPh2)2NCH2–C4H3S)2Cl2] were established by single crystal X-ray crystallogra-phy. Complex 2 was investigated as precatalyst in the hydrogentransfer reaction of acetophenone derivatives in basic iso-PrOH.This compound has proved to be efficient catalyst in the transferhydrogenation reaction of ketones. Furthermore, performing thereaction in air slowed down the reaction, but the conversion wasnot affected in the air or addition of water. When we increasedthe amount of water in the reaction system, the high conversion re-mained intact.

Acknowledgements

Partial support from Dicle University (Project number: DÜAPK05-FF-27), Turkish Academy of Sciences and Hacettepe UniversityScientific Research Department (Project number: 04A602004) isgratefully acknowledged.

Appendix A. Supplementary material

CCDC 770298 and 770299 contain the supplementary crystallo-graphic data for this paper. These data can be obtained free ofcharge from The Cambridge Crystallographic Data Centre viawww.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-ated with this article can be found, in the online version, atdoi:10.1016/j.ica.2010.12.028.

References

[1] M.R.I. Zuburi, J.D. Woollins, Comments Inorg. Chem. 24 (2003) 189.[2] Y. Wang, X. Li, K. Ding, Tetrahedron Lett. 43 (2002) 159.[3] S. Urgaonkar, J.G. Verkade, Adv. Synth. Catal. 346 (2004) 611.[4] D.P. Catsoulocas, B.R. Steele, G.A. Herapoulos, M. Micha-Screttas, C.G. Screttas,

Tetrahedron Lett. 44 (2003) 4575.[5] J. Cheng, Y.H. Sun, F. Wang, M.J. Guo, J.H. Xu, Y. Pan, Z.G. Zhang, J. Org. Chem. 69

(2004) 5428.[6] M.L. Clarke, D.J. Cole-Hamilton, J.D. Woollins, J. Chem. Soc., Dalton Trans.

(2001) 2721.

[7] C. Saluzzo, J. Breuzard, S. Pellet-Rostaing, M. Vallet, F.L. Guyader, M. Lemaire, J.Organomet. Chem. 643–644 (2002) 98.

[8] N.W. Boaz, J.A. Ponasik, J. Large, E.S. Large, Tetrahedron: Asymm. 16 (2005)2063.

[9] B. Pugin, H.U. Blaser, Adv. Synth. Catal. 348 (2006) 1743.[10] J.J. Reedijk, J. Chem. Soc., Chem. Commun. (1996) 801.[11] P. Bhattacharyya, T.Q. Ly, A.M.Z. Slawin, J.D. Woollins, Polyhedron 20 (2001)

1803.[12] A.M.Z. Slawin, M.B. Smith, J.D. Woollins, J. Chem. Soc. Rev., Dalton. Trans.

(1998) 1537.[13] M.S. Balakrishna, P.P. George, S.M. Mobin, Polyhedron 24 (2005) 475.[14] M. Aydemir, A. Baysal, N. Gürbüz, _I. Özdemir, B. Gümgüm, S. Özkar, N. Çaylak,

L.T. Yıldırım, Appl. Organomet. Chem. 24 (2010) 17.[15] H.-J. Chen, J.M. Barendt, R.C. Haltiwanger, T.G. Hill, A.D. Norman, Phosphorus,

Sulfur 26 (1986) 155.[16] M. Aydemir, A. Baysal, F. Durap, B. Gümgüm, S. Özkar, L.T. Yıldırım, Appl.

Organomet. Chem. 23 (2009) 467.[17] O. Akba, F. Durap, M. Aydemir, A. Baysal, B. Gümgüm, S. Özkar, J. Organomet.

Chem. 694 (5) (2009) 731.[18] P. Bhattacharyya, J.D. Woollins, Polyhedron 14 (1995) 3367.[19] A. Baysal, M. Aydemir, F. Durap, B. Gümgüm, S. Özkar, L.T. Yıldırım, Polyhedron

26 (2007) 3373.[20] F. Durap, N. Biricik, B. Gümgüm, S. Özkar, W. Han Ang, Z. Fei, R. Scopelliti,

Polyhedron 27 (2008) 196.[21] M. Aydemir, A. Baysal, G. Öztürk, B. Gümgüm, Appl. Organomet. Chem. 23

(2009) 108.[22] R.A.W. Johnstone, A.H. Wilby, I.D. Entwistle, Chem. Rev. 85 (1985) 129.[23] M. Yigit, B. Yigit, I. Özdemir, E. Çetinkaya, B. Çetinkaya, Appl. Organomet.

Chem. 20 (2006) 322.[24] R. Noyori, M. Yamakawa, S. Hashiguchi, Acc. Chem. Res. 23 (1990) 345.[25] S. Ram, R.E. Ehrenkaufer, Synthesis (1988) 91.[26] S. Özkar, R.G. Finke, J. Am. Chem. Soc. 127 (2005) 4800.[27] R. Noyori, T. Ohkuma, M. Kitamura, H. Takaya, N. Sayo, H. Kumobayashi, S.

Akutagawa, J. Am. Chem. Soc. 109 (1987) 5856.[28] T. Ohkuma, H. Ooka, S. Hashiguchi, T. Ikariya, R. Noyori, J. Am. Chem. Soc. 117

(1995) 2675.[29] H. Shimizu, I. Nagasaki, T. Satio, Tetrahedron 61 (2005) 5405.[30] M. Aydemir, A. Baysal, N. Meric, B. Gümgüm, J. Organomet. Chem. 694 (2009)

2488.[31] M. Aydemir, A. Baysal, Polyhedron 29 (2010) 1219.[32] M. Aydemir, A. Baysal, N. Meric, C. Kayan, M. Togrul, B. Gümgüm, Appl.

Organomet. Chem. 24 (2010) 215.[33] M. Aydemir, N. Meric, F. Durap, A. Baysal, M. Togrul, J. Organomet. Chem. 695

(2010) 1392.[34] M.A. Bennet, G.B. Robertson, A.K. Smith, J. Organomet. Chem. 43 (1972) C41.[35] Enraf-Nonius, CAD-4 Express Software, Version 1.1 Enraf-Nonius, Delft,

Netherlands, 1993.[36] XCAD4 K. Harms, S. Wocadlo, XCAD4, University of Marburg, Germany, 1995.[37] SHELX: G.M. Sheldrick, Acta Crystallogr., Sect. A64 (2008) 112.[38] WinGX: L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.[39] K. Song, H. Gao, F. Liu, J. Pan, L. Guo, S. Zai, Q. Vu, Eur. J. Inorg. Chem. (2009)

3016.[40] A.D. Burrows, M.F. Mahon, M.T. Palmer, J. Chem. Soc., Dalton Trans. (2000) 1669.[41] K.G. Gaw, M.B. Smith, A.M.Z. Slawin, New J. Chem. 24 (2000) 429.[42] L. Dahlenburg, C. Kühlein, Inorg. Chim. Acta 361 (2008) 2785.[43] P. Le Gendre, M. Offenbecher, C. Bruneau, P.H. Dixneuf, Tetrahedron: Asymm. 9

(1998) 2279.

172 M. Aydemir et al. / Inorganica Chimica Acta 367 (2011) 166–172

[44] ORTEP-3: L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.[45] PLATON: A.L. Spek, J. Appl. Crystallogr. 36 (2003) 7.[46] R. Le Lagadec, L. Rubio, L. Alexandrova, R. Toscano, E.V. Ivanova, R. Meskys, V.

Laurinavicius, M. Pfeffer, A.D. Ryabov, J. Organomet. Chem. 689 (2004) 4820.[47] A.D. Ryabov, V.S. Kurova, V. Ekaterina, R. Ivanova, R. Le Lagadec, L.

Alexandrova, Anal. Chem. 77 (2005) 1132.[48] R. Tribo, S. Munoz, J. Pons, R. Yanez, A. Alvarez-Larena, J.F. Piniella, J. Ros, J.

Organomet. Chem. 690 (2005) 4072.[49] Z. Fei, R. Scopelliti, P.J. Dyson, Inorg. Chem. 42 (2003) 2125.

[50] Z. Fei, R. Scopelliti, P.J. Dyson, Eur. J. Inorg. Chem. (2004) 530.[51] S. Berger, S. Braun, H.-O. Kolinowski, NMR-Spektroskopie von Nichtmetallen

Band 3, 31P NMR-Spektroskopie, Georg Theime Verlag, Stuttgart, New York,1993.

[52] R. Guo, X. Chen, C. Elphelt, D. Song, R.H. Morris, Org. Lett. 7 (9) (2005) 1757.[53] P. Pelagatti, M. Carcelli, F. Calbiani, C. Cassi, L. Elviri, C. Pelizzi, U. Rizzotti, D.

Rogolino, Organometallics 24 (2005) 5836.[54] J.W. Faller, A.R. Lavoie, Organometallics 20 (2001) 5245.