Polyhedron 30 (2011) 796–804

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Polyhedron

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Ruthenium complexes of aminophosphine ligands and their use as pre-catalystsin the transfer hydrogenation of aromatic ketones: X-ray crystal structureof thiophene-2-(N-diphenylthiophosphino)methylamine

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 Physics Engineering, Beytepe, TR-06800 Ankara, Turkey

a r t i c l e i n f o

Article history:Received 5 July 2010Accepted 10 December 2010Available online 19 December 2010

Keywords:Transfer hydrogenationCatalysisAminophosphineBis(phosphino)amineX-ray diffraction

0277-5387/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.poly.2010.12.011

⇑ Corresponding author. Tel.: +90 412 248 8550; faE-mail address: aydemir@dicle.edu.tr (M. Aydemir

a b s t r a c t

Reaction of thiophene-2-methylamine with one or two equivalents of PPh2Cl in the presence of NEt3,proceeds in thf to give thiophene-2-(N-diphenylphosphino)methylamine, 1a and thiophene-2-(N,N-bis(diphenylphosphino))methylamine, 2a respectively, under anaerobic conditions. Oxidations of 1aand 2a with aqueous hydrogen peroxide, elemental sulfur or gray selenium in thf gives the correspondingoxides, sulfides and selenides [Ph2P(E)NHCH2-C4H3S] (E: O 1b, S 1c, Se 1d) and [(Ph2P(E))2NCH2-C4H3S],(E: O 2b, S 2c, Se 2d) respectively, in high yield. Furthermore, two novel Ru(II) complexes with the P–Nligands 1a and 2a were synthesized starting with the complex [Ru(g6-p-cymene)(l-Cl)Cl]2. The com-plexes were fully characterized by analytical and spectroscopic methods. 31P–{1H} NMR, DEPT, 1H–13CHETCOR or 1H–1H COSY correlation experiments were used to confirm the spectral assignments. Themolecular structure of thiophene-2-(N-diphenylthiophosphino)methylamine was also elucidated by sin-gle-crystal X-ray crystallography. Following activation by NaOH, compounds 3 and 4 catalyze the transferhydrogenation of acetophenone derivatives to 1-phenylethanol derivatives in the presence of iso-PrOH asthe hydrogen source. [Ru(Ph2PNHCH2-C4H3S)(g6-p-cymene)Cl2], 3 and [Ru((PPh2)2NCH2-C4H3S)-(g6-p-cymene)Cl]Cl, 4 complexes are suitable catalyst precursors for the transfer hydrogenation ofacetophenone derivatives in 0.1 M iso-PrOH solution. Notably 4 acts as an excellent catalyst giving thecorresponding alcohols in excellent conversions up to 99% (TOF 6 744 h�1). This transfer hydrogenationis characterized by low reversibility under the experimental conditions.

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1. Introduction

Synthesis of new aminophosphines to stabilize transition met-als in low valent states is considered to be the most challengingtask in view of their potential utility in a variety of metal-mediatedorganic transformations [1,2]. To date, a number of such systemswith a variety of backbone frameworks have been synthesizedand their transition metal chemistry has been explored [3,4].Aminophosphines and bis(phosphino)amines with P–NH andP–N–P skeletons, respectively, have proved to be versatile ligands,and varying the substituents on both to P- and N-centers gives risethe changes in the P–N–P angle and to conformation around theP-centers [5,6]. Small variations in these ligands can cause signifi-cant changes in their coordination behavior and the structuralfeatures of the resulting complexes [7].

Since its discovery, transfer hydrogenation using rutheniumcomplexes as catalysts has been an increasingly useful tool in

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organic synthesis [8,9], allowing transformations otherwise verydifficult or almost impossible to carry out. Today, the asymmetrictransfer hydrogenation [10] of prochiral ketones is one of the mostattractive methods for synthesizing optically active secondaryalcohols, which form an important class of intermediates for finechemicals and pharmaceuticals [11,12]. Catalytic transfer hydroge-nation with the aid of a stable hydrogen reservoir is a useful alter-native of using molecular hydrogen in catalytic hydrogenation[13,14]. In transfer hydrogenation, organic molecules such as pri-mary and secondary alcohols [15] or formic acid and its salts[16] have been employed as the hydrogen source. The use of ahydrogen reservoir has some advantages over the use of molecularhydrogen since it avoids risks and the constrains associated withhydrogen gas as well as the necessity for pressure vessels and otherequipments. 2-Propanol is a popular reactive solvent for transferhydrogenation reactions since it is easy to handle and is relativelynon-toxic, environmentally benign and inexpensive. The volatileacetone by-product can also be easily removed to shift unfavorableequilibria and can be hydrogenated back to 2-propanol by usingiridium catalyst at room temperature [17]. In general, asymmetric

M. Aydemir et al. / Polyhedron 30 (2011) 796–804 797

hydrogenation is mediated by a complex bearing Rh, Ru or Ir,among which our focus has been Ru. One reason is that the Ru cat-alysts have excellent performances [18,19]. Another reason is thatRu enjoyed a cost advantage relative to other asymmetric hydroge-nation metals such as Rh [20].

Herein we describe the synthesis of two compounds thiophene-2-(N-diphenylphosphino)-methylamine (1a) and thiophene-2-(N,N-bis(diphenylphosphino))methylamine (2a) through a single stepreaction of thiophene-2-methylamine with one or two equivalentsof diphenylchlorophosphine, respectively. Oxidation of 1a and 2awith aqueous hydrogen peroxide, elemental sulfur or gray sele-nium in thf gives the corresponding oxides, sulfides andselenides [Ph2P(E)NHCH2-C4H3S] (E: O 1b, S 1c, Se 1d) and[(Ph2P(E))2NCH2-C4H3S], (E: O 2b, S 2c, Se 2d), respectively. Thecompounds were isolated from the reaction solution and fullycharacterized by elemental analysis, IR and multi-nuclear NMRspectroscopies. The X-ray crystal structure of thiophene-2-(N-diphenylthiophosphino)methylamine, [Ph2P(S)NHCH2-C4H3S] wasdetermined, and pertinent features of this structure were de-scribed. Based on these findings and our continuing interest indeveloping more efficient and stable catalysts [21–23], we alsoreport here the synthesis of Ru(II) complexes [Ru(Ph2PNHCH2-C4H3S)(g6-p-cymene)Cl2], 3 and [Ru((PPh2)2NCH2-C4H3S)(g6-p-cymene)Cl]Cl, 4 and their use as catalysts in the transfer hydroge-nation of ketones.

2. Results and discussion

2.1. Synthesis of the ligands and their chalcogenides

As shown in Scheme 1, thiophene-2-(N-diphenylphosphino)-methylamine, [Ph2PNHCH2-C4H3S] 1a and thiophene-2-(N,N-bis(diphenylphosphino))methylamine, [(Ph2P)2NCH2-C4H3S] 2awere prepared from the commercially available starting materialthiophene-2-methylamine and one or two equivalents of PPh2Clin the presence of triethylamine by aminolysis [24,25] in thf at0 �C, respectively. The 31P NMR spectra of 1a and 2a showed singleresonances at d(P) 41.70 and 59.83 ppm respectively, similar to

Scheme 1. Synthesis of thiophene-2-(N-diphenylphosphino)methylamine, [Ph2PNHCH2-C4H3S] and their chalcogenides. (i) 1 equiv. Ph2PCl, thf; (ii) 2 equiv. Ph2PCl, thf; (iii) 1 e

those found for closely related compounds [26,27]. 1a and 2a arenot stable and decompose rapidly on exposure to air or moisture.When the reactions were monitored by 31P NMR spectroscopy,the formation of P(O)Ph2PPh2 was observed, as indicated by signalsat d 34.60 (d) ppm and d�24.30 (d) ppm, {1J(PP) 226 Hz}. Solutionsof 1a and 2a in CDCl3, prepared under anaerobic conditions, arealso unstable and decompose gradually to give oxide andbis(diphenylphosphino)monoxide [P(O)Ph2PPh2] derivatives.

1a and 2a were fully characterized by multinuclear NMR, infra-red spectroscopy and microanalysis. All the compounds gave rea-sonable microanalyses results. In the 1H NMR spectrum, the NHresonance of 1a was observed as slightly broad pseudo-triplet ordoublet of triplets at 2.40 ppm due to the multiple coupling 3J(CHNH)

and 2J(NHP) and was confirmed by H/D exchange experiments. Inaddition, the methylene groups give doublet of doublet at4.28 ppm (3J 6.40 and 6.60 Hz) and triplet at 4.64 ppm (3J10.40 Hz) for 1a and 2a, respectively. The phenyls carbons,however, display well-resolved signals in their 13C-{1H} NMRspectra.

To probe the reactivity of the new ligands, reactions with aque-ous hydrogen peroxide, elemental sulfur and gray selenium werecarried out. The oxides 1b [Ph2P(O)NHCH2-C4H3S] and 2b[(Ph2P(O))2NCH2-C4H3S] were easily prepared by addition of excessaqueous hydrogen peroxide to 1a or 2a in thf, respectively. The 31PNMR spectra of 1b and 2b showed singlets (CDCl3) at d(P)23.84 ppm and 30.68 ppm which are shielded by 17.86 and29.15 ppm compared to the parent compounds 1a or 2a, respec-tively. Characteristic J(31P–13C) coupling constants of the carbonsof the phenyls rings were observed in the 13C NMR spectra, whichare consistent with the literature values [28]. In the IR spectrum,we can identify t(P@O) at 1189 and 1209 cm�1 for 1b and 2b,respectively. The sulfides 1c, 2c and selenides 1d, 2d analogs wereprepared by the addition of elemental S and gray Se to 1a and 2a inthf, respectively. The 31P NMR showed single resonances (CDCl3) atd(P) 57.78 and 71.23 ppm for 1c and 2c, respectively. The IR spec-trum of 1c and 2c exhibit characteristic band at 650 and 652 cm�1

due to t(P@S) stretching, respectively. Compounds 1d and 2d ini-tially analyzed by 31P NMR spectroscopy, which exhibited singlet

C4H3S] and thiophene-2-(N,N-bis(diphenylphosphino))methylamine, [(Ph2P)2NCH2-quiv. H2O2 or elemental S or gray Se; (iv) 2 equiv. H2O2 or elemental S or gray Se.

798 M. Aydemir et al. / Polyhedron 30 (2011) 796–804

resonances at 57.46 and 70.61 ppm, with 1J(31P–77Se) of 758.54 and790.56 Hz, respectively, as expected [29]. The IR spectra havet(P@Se) bands at 552 and 566 cm�1 for 1d and 2d respectively.Furthermore, in the 13C-{1H} NMR spectra of sulfides and selenides,Jð31PA13CÞ coupling constants of the carbons of the phenyls ringswere observed, which is consistent with the literature values[30,31]. In addition, the structural compositions of 1d and 2d havealso been confirmed by IR and elemental analysis. Furthermore, inthe 13C NMR spectra, the coupling between the i-carbon and phos-phorus in the oxidized P(V) compounds is quite large 1JPC = 129.78,102.81 and 90.54 Hz for 1b–d and 1JPC = 126.76, 101.61 and91.55 Hz for 2b–d respectively, corresponding to O, S, Se oxidizedspecies [32] (for details see supplementary data)

Crystal of 1c suitable for a single crystal X-ray diffraction studywas obtained by slow diffusion of diethylether into a solution ofthe compound in dichloromethane over several days. The P atomin the thiophene-2-(N-diphenylthiophosphino)methylamine,[Ph2P(S)NHCH2-C4H3S], 1c has a distorted tetrahedral coordinationsphere consisting of one N, one S and two C atoms of the phenylrings at normal bond distances. The bond angles within the coordi-nation sphere range from 101.55(17)� to 118.08(14)� (see the OR-TEP [33] in Fig. 1).

There are two H-bonds in the structure. As shown in the crystalpacking diagram (Fig. 2a), the compound 1c is made up bilateralgroup via H-bond which is lined up nearly along the b-axis of theunit cell. The first H-bond is intermolecular [N–H� � �S1i] withD� � �A distance and D–H� � �A angle of 3.617(4) Å and 168(3)�,respectively [symmetry code: (i) 1 � x, 1 � y, 1 � z]. The secondH-bond is intramolecular [C2–H2� � �S1] with D� � �A distances andD–H� � �A angle of 3.355 Å and 114�, respectively. The molecule of1c has three dimensional conformation. Dihedral angels betweenthe planar ring planes in the molecule were calculated withMERCURY [34]. Dihedral angles between planes P1–P2, P1–P3and P2–P3 are 66.77�, 43.68� and 70.91�, respectively, where P1:C1/C6; P2: C7/C12; P3: S2/C14/C17 (Fig. 2b).

2.2. Synthesis and characterization of the metal complexes

The reaction of stoichiometric amounts of [Ru(g6-p-cymene)(l-Cl)Cl]2 and [Ph2PNHCH2-C4H3S], 1a affords complex [Ru(Ph2-PNHCH2-C4H3S)(g6-p-cymene)Cl2], 3 in high yield as an air stable

Fig. 1. Molecular structure of thiophene-2-(N-diphenylthiophosphino)methylam

red microcrystalline powder (Scheme 2). 1a was expected to cleavethe [Ru(g6-p-cymene)(l-Cl)Cl]2 dimer to give the correspondingcomplex 3 via monohapto coordination of the aminophosphinegroup. The 31P NMR spectrum of 3 shows a single resonance at61.0 ppm, in line with the values previously observed for similarcompounds [35,36]. Analysis by 1H NMR reveals this compoundto be diamagnetic, exhibiting signals corresponding to the aro-matic rings for 3 at 7.97–7.42 ppm. Another set of signals consist-ing of two doublets centered at 5.29 and 5.10 ppm are due to thepresence of the aromatic protons in the p-cymene group (the pres-ence of one (broad) or two signals corresponding to CH p-cymenehydrogens in the 1H NMR spectra is consistent with a Cs symmetryof complex and with free rotation of the arene ligand [37,38]), thisinformation is complemented by the presence of signals at 2.65and 0.87 ppm due to the CH and CH3 of the iso-propyl groups ofthe p-cymene moiety. Finally, a signal due to the presence of themethyl in the p-cymene group is observed at 1.98 ppm. The NHresonance of 3 was observed slightly broad pseudo-quartet or dou-blet of triplet [39] at 3.58 ppm due to the multiple coupling 3J(CHNH)

and 2J(NHP) and was confirmed by H/D exchange experiments. Inaddition, the methylene group gives doublet of doublets at3.81 ppm (J = 6.80 and 6.40 Hz) for 3. Furthermore in the 13CNMR spectrum of 3, Jð31PA13CÞ coupling constants of the carbons ofthe phenyl rings were observed, which are consistent with the lit-erature values [30,40]. The phenyls carbons, however, display well-resolved signals in their 13C NMR spectra. In the compound 3, thecoupling between i-carbon and the phosphorus is relatively large,1J(PC) 51.6 Hz, while the coupling between o-carbon and thephosphorus relatively small 2J(PC) 10.4 Hz. The coupling betweenm-carbon and the phosphorus is 3J(PC) 10.1 Hz and the coupling be-tween p-carbon and the phosphorus is observed at 4J(PC) 6.0 Hz. Thestructure of the 3 was further confirmed by IR spectroscopy andmicroanalysis, and found to be in good agreement with thetheoretical values.

We also examined some simple coordination chemistry of 2awith [Ru(g6-p-cymene)(l-Cl)Cl]2 precursor (Scheme 2). The reac-tion between Ru(II) dimeric precursor and bis(phosphino)amine,2a is profoundly affected by the molar ratio of [Ru(g6-p-cyme-ne)(l-Cl)Cl]2 as well as the steric and electronic properties of thedonor phosphorus atoms. The reaction of 2a with 1/2 equivalent[Ru(g6-p-cymene)(l-Cl)Cl]2 yielded a dark yellow product. The

ine, [Ph2P(S)NHCH2-C4H3S] (1c), showing the atomic numbering scheme.

Fig. 2. (a) Intermolecular hydrogen bonding geometry in the crystal packing, (b) the plane view of molecular conformation of the compound 1c.

Scheme 2. Synthesis of the [Ru(Ph2PNHCH2-C4H3S)(g6-p-cymene)Cl2], 3 and [Ru((PPh2)2NCH2-C4H3S)(g6-p-cymene)Cl]Cl, 4 complexes. (i) 1/2 equiv. [Ru(g6-p-cymene)(l-Cl)Cl]2, thf; (ii) 1/2 equiv. [Ru(g6-p-cymene)(l-Cl)Cl]2, thf; (iii)1 equiv. [Ru(g6-p-cymene)(l-Cl)Cl]2, thf.

M. Aydemir et al. / Polyhedron 30 (2011) 796–804 799

31P NMR spectrum of the product indicated that it is a mixture oftwo products, 4 and 5 as shown in (Scheme 2 and Fig. 3). In the31P NMR spectrum, a singlet at 78.1 ppm was assigned tocompound 5 [41]. Complex 4 exhibits a singlet at 88.2 ppm formonochelating [(PPh2)2NCH2-C4H3S]. Compound 4, with one[(PPh2)2NCH2-C4H3S] ligand and compound 5, with two[(PPh2)2NCH2-C4H3S] ligands, show two sets of 31P NMR reso-nances with relative intensities of 1:2 which are consistent withthese structural formulations, respectively. The compound 4 wasalso prepared in its pure form separately using different molar ra-tios (excess [Ru(g6-p-cymene)(l-Cl)Cl]2). The reaction of[(PPh2)2NCH2-C4H3S] with one equivalent of [Ru(g6-p-cyme-ne)(l-Cl)Cl]2) affords only the corresponding mono(chelate)

[Ru((PPh2)2NCH2-C4H3S)(g6-p-cymene)Cl]Cl, 4, in high yield. Com-plexation reaction was straight- forward, with coordination toruthenium being carried out at room temperature. The initial colorchange, i.e., from clear orange to deep red [42], attributed to the di-mer cleavage most probably by the bis(phosphino)amine ligand.The 31P NMR spectrum of 4 shows a single resonance at d88.2 ppm which is consistent with both the proposed structureand literature values [43,44]. In the 13C NMR spectrum through-space P–C coupling was observed, which is consistent with the lit-erature values [45,46]. Furthermore, 1H NMR spectral data of 4 isconsistent with the structure proposed. In the 1H NMR spectrum,4 is characterized by isopropyl methyl doublets, at d 1.23 ppmand g6-p-cymene doublets at d 5.45 and 5.28 ppm (for details

Fig. 3. The 31P NMR spectra of reaction mixture containing complexes 4 and 5; (i) reaction of 2a with 1/2 equiv. [Ru(g6-p-cymene)(l-Cl)Cl]2; (ii) reaction of 2a with 1 equiv.(excess) [Ru(g6-p-cymene)(l-Cl)Cl]2.

800 M. Aydemir et al. / Polyhedron 30 (2011) 796–804

see experimental). The structural composition of the complex hasalso been confirmed by IR and elemental analysis.

2.3. Catalytic transfer hydrogenation of acetophenone derivatives

Recently, we have reported that the novel half-sandwich com-plexes, based on the ligands with P–N and P–O backbone, are ac-tive catalysts in the reduction of aromatic ketones [47]. Theseligands are attractive and also widely used in ruthenium com-plexes for catalytic hydrogenations reactions [48,49]. The observedactivity of these complexes has encouraged us to investigate otheranalogous ligands and other transition metal complexes of these li-gands. So, extending our program in the design and study to devel-op useful catalysts, complexes 3 and 4 were tested as catalysts intransfer hydrogenation of aromatic ketones in iso-PrOH solution.The catalytic hydrogenation of acetophenone derivatives was con-ducted using NaOH as a promoter (Scheme 3). It was found thatboth complexes catalyze the reduction of ketones to the corre-sponding alcohols via hydrogen transfer from iso-PrOH.

The synthesized complexes 3 and 4 were used as a precursor forthe catalytic transfer hydrogenation of the acetophenone by iso-PrOH/NaOH as a reducing system. The results are summarized inTable 3. At room temperature no appreciable formation of 1-phen-ylethanol was observed (Table 3, entries 1 and 2) and also the cat-alytic activity [Ru(g6-p-cymene)(l-Cl)Cl]2 under the appliedexperimental conditions was found to be negligible. In addition,as can be inferred from the Table 3, the precatalysts as well as

Scheme 3. Hydrogen transfer from iso-

the presence of NaOH are necessary to observe appreciable conver-sions (entries 5–12). The base facilitates the formation of ruthe-nium alkoxide by abstracting proton of the alcohol andsubsequently alkoxide undergoes b-elimination to give rutheniumhydride, which is an active species in this reaction. This is themechanism proposed by several research groups on the studiesof ruthenium catalyzed transfer hydrogenation reaction by metalhydride intermediates [50,51]. Namely, role of the base is to gener-ate a more nucleophilic alkoxide ion which would rapidly attackthe ruthenium complex responsible for dehydrogenation of iso-PrOH. As shown in Table 3, high conversions can be achieved withthe 3 and 4 catalytic systems. Next, we increased the substrate-to-catalyst ratio to observe the effect on the catalytic efficiency(entries 7–10). Increasing the substrate-to-catalyst ratio do notcause any change in conversion of the product in most cases, how-ever the reaction time was increased. Remarkably, the transferhydrogenation of acetophenone could be achieved in 99% yieldeven when the substrate-to-catalyst ratio reached 1000:1. In addi-tion, performing the reaction in air, slowed down the reaction butdid not affect yield of the product. Results obtained from optimiza-tion studies indicated clearly that the excellent yields wereachieved in the reduction of acetophenone to 1-phenylethanolwhen 3 and 4 were used as the precursor in 30 and 10 min, respec-tively, with a substrate-catalyst molar ratio (100:1) in iso-PrOH at82 �C (Table 3). It should be pointed out that complexes 3 and 4 aremore active catalysts than the parent complex: [Ru(g6-p-cyme-ne)(l-Cl)Cl]2 (41% maximum yield in 24 h) with a 1/14 complex/

PrOH to acetophenone derivatives.

M. Aydemir et al. / Polyhedron 30 (2011) 796–804 801

NaOH ratio [52]. When we compare the catalytic activity of com-plexes 3 and 4 to the other structurally similar complexes, [53–56] specially complex 4 shows higher activity [57–60].

The catalytic reduction of acetophenone derivatives were alltested with the conditions optimized for acetophenone. It is note-worthy that the complexes 3 and 4 differ in reactivity (Table 4).The reactions with the aminophosphine-Ru(II), 3 proceeds moreslowly than those with the mono-chelate(phosphino)amine-Ru(II),4. The mono-chelate(phosphino)amine-Ru(II), 4 have proved to beexcellent catalyst precursors in transfer hydrogenation of acetophe-none derivatives, leading to corresponding alcohols in 10 min. (up to95–99% yield). But, the examination of the results indicates clearlythat the highest conversion was achieved in the reduction of aceto-phenone derivatives by using mono-chelate(phosphino)amine-Ru(II), 4 as the catalyst precursor. Furthermore, complexes 3 and 4show very high activity for most of the ketones. The introductionof electron withdrawing substituents, such as F, Cl and Br to the paraposition of the aryl ring of the ketone decreases the electron densityof the C@O bond giving rise to easier hydrogenation [61–63].

3. Experimental

3.1. 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 asreceived. [Ru(g6-p-cymene)(l-Cl)Cl]2 [64] was prepared accordingto literature procedure. The IR spectra were recorded on a Mattson1000 ATI UNICAM FT-IR spectrometer as KBr pellets. 1H (400.1MHz), 13C NMR (100.6 MHz) and 31P NMR spectra (162.0 MHz)were recorded spectra on a Bruker Avance 400 spectrometer, withd referenced to external TMS and 85% H3PO4 respectively. Elemen-tal analysis was carried out on a Fisons EA 1108 CHNS-O instru-ment. Melting points were recorded by Gallenkamp Modelapparatus with open capillaries.

3.2. GC analyses

GC analyses were performed on a HP 6890N 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.

3.3. Synthesis and Characterization of ligands

3.3.1. Thiophene-2-(N-diphenylphosphino)methylamine,[Ph2PNHCH2-C4H3S], (1a)

Chlorodiphenylphosphine (0.23 g, 0.97 mmol) was added drop-wise over a period of 30 min to a stirred solution of thiophene-2-methylamine (0.11 g, 0.97 mmol) and triethylamine (0.10 g,0.97 mmol) in thf (50 mL) at 0 �C. The mixture was stirred at roomtemperature for 1 h and the white precipitate (triethylammoniumchloride) was filtered off under argon and the solvent removed un-der reduced pressure. The residue was then washed with colddiethyl ether (2 � 15 mL) and dried in vacuo to produce a clear, yel-low viscous oily compound 1a (Yield: 0.27 g, 93%); 1H NMR (d inppm rel. to TMS, J Hz, in CDCl3): 7.50 (dd, o-hydrogen of phenyls,

4H, 3J 6.80 and 14.80 Hz), 7.37–7.42 (m, m and p-hydrogen ofphenyls, 6H), 7.21 (d, H-5, 1H, 3J 4.80 Hz), 6.95 (dd, H-4, 1H, 3J3.60 and 4.80), 6.89 (d, H-3, 1H, 3J 3.60 Hz), 4.28 (dd, –CH2–, 2H,3J 6.40 and 6.60 Hz), 2.40 (t, –NH–, 1H, J 6.40 Hz); 13C NMR (d inppm rel. to TMS, J Hz, in CDCl3): 145.75 (d, C-2, 3J(31P-13C) 7.00Hz), 140.89 ppm (d, i-carbons of phenyls, 1J(31P–13C) 12.07 Hz),131.47 (d, o-carbons of phenyls, 2J(31P–13C) 20.12 Hz), 128.63 (s,p-carbons of phenyls), 128.35 (d, m-carbons of phenyls,3J(31P–13C) 6.24 Hz), 126.69 (C-4), 124.47 (C-5), 124.34 (C-3),45.16 (–CH2–); assignment was based on the 1H–13C HETCORand 1H–1H COSY spectra; 31P NMR (d in ppm rel. to H3PO4, inCDCl3): 41.70 (s). Selected IR (KBr pellet, in cm�1): t(P–N) 856,t(P–Ph) 1439, t(N–H) 3371; Anal. Calc. for C17H16NSP: C, 68.67;H, 5.42; N, 4.71; found: C, 68.53; H, 5.32; N, 4.57%.

3.3.2. Thiophene-2-(N,N-bis(diphenylphosphino))methylamine,[(Ph2P)2NCH2-C4H3S], (2a)

Chlorodiphenylphosphine (0.45 g, 1.95 mmol) was added to astirred solution of thiophene-2-methylamine (0.11 g, 0.97 mmol)and triethylamine (0.20 g, 1.95 mmol) in thf (50 mL) at 0 �C withvigorous stirring. The mixture was stirred at room temperaturefor 2 h and the white precipitate (triethylammonium chloride)was filtered off under argon and the solvent removed under re-duced pressure. The residue was then washed with cold diethylether (2 � 15 mL) and dried in vacuo to produce a yellow viscousoily compound 2a [65] (Yield: 0.44 g, 94%); 1H NMR (d in ppmrel. to TMS, J Hz, in CDCl3): 7.38 (dd, o-hydrogen of phenyls, 8H,3J 5.60 and 7.66 Hz), 7.28–7.34 (m, m and p-hydrogen of phenyls,12H), 7.07 (d, H-5, 1H, 3J 5.20 Hz), 6.77 (dd, H-4, 1H, 3J 3.60 and5.20 Hz), 6.45 (d, H-3, 1H, 3J 3.60 Hz), 4.64 (t, –CH2–, 2H, 3J10.40 Hz); 13C NMR (d in ppm rel. to TMS, J Hz, in CDCl3): 143.01(C-2), 139.09 ppm (d, i-carbons of phenyls, 1J(31P–13C) 14.08 Hz),132.89 (d, o-carbons of phenyls, 2J(31P–13C) 22.13 Hz), 128.81 (s,p-carbons of phenyls), 128.10 (d, m-carbons of phenyls,3J(31P–13C) 6.04 Hz), 126.89 (C-3), 126.25 (C-4), 125.24 (C-5),51.53 (–CH2–); assignment was based on the 1H–13C HETCORand 1H–1H COSY spectra; 31P NMR (d in ppm rel. to H3PO4, inCDCl3): 59.83(s). Selected IR (KBr pellet, in cm�1): t(P–N–P) 814,t(P–Ph) 1439; Anal. Calc. for C29H25NSP2: C, 72.34; H, 5.23; N,2.91; found: C, 72.16; H, 5.08; N, 2.74%.

3.4. Synthesis and Characterization of ligands and their chalcogenides

See supplementary data.

3.5. Synthesis of ruthenium complexes

3.5.1. [Ru(Ph2PNHCH2-C4H3S)(g6-p-cymene)Cl2], (3)To a solution of [Ru(g6-p-cymene)(l-Cl)Cl]2 (0.30 mg, 0.49

mmol) in CH2Cl2, a solution (thf, 30 mL) of [Ph2PNHCH2-C4H3S],1a (0.29 mg, 0.98 mmol) was added. The resulting reaction mixturewas allowed to proceed with stirring at room temperature for 1 h.After this time, the solution was filtered and the solvent evapo-rated under vacuum, the solid residue thus obtained was washedwith diethyl ether (3 � 15 mL) and then dried under vacuum. Fol-lowing recrystalization from diethylether/CH2Cl2, a red crystallinepowder was obtained (yield: 0.55 g, 93%; mp: 180–182 �C); 1HNMR (d in ppm rel. to TMS, J Hz, in CDCl3): 7.97 (dd, 4H, 3J = 4.8and 9.2 Hz, o-protons of phenyls), 7.42–7.53 (m, 6H, m- and p- pro-tons of phenyls), 7.07 (d, 1H, 3J = 4.8 Hz, H-5), 6.79 (dd, 1H, 3J = 3.2and 4.8 Hz, H -4)), 6.75 (d, 1H, 3J = 3.2 Hz, H-3), 5.29 (d, 2H,3J = 6.4 Hz, aromatic hydrogens of p-cymene), 5.10 (d, 2H,3J = 6.0 Hz, aromatic hydrogens of p-cymene), 3.81 (dd, 2H,3J = 6.4 and 6.8 Hz, –CH2–), 3.58 (m, 1H, NH), 2.65 (m, 1H, –CH–of p-cymene), 1.98 (s, 3H, CH3-Ph of p-cymene), 0.87 (d, 6H,3J = 6.8 Hz, (CH3)2CHPh of p-cymene); 13C NMR (d in ppm rel. to

Table 1Crystal data and experimental details of structural analysis of thiophene-2-(N-diphenylthiophosphino)methylamine, [Ph2P(S)NHCH2-C4H3S] (1c).

Compound Ph2P(S)NHCH2-C4H3S

Formula C17H16NPS2

Formula weight 329.42Crystal system OrthorhombicSpace group Pbcaa (Å) 12.9375(16)b (Å) 13.8701(18)c (Å) 18.1301(19)Volume (Å3) 3253.4(7)Z 8Dcalc. (Mg/m3) 1.345V (mm�1) 0.418F(0 0 0) 1376h, k, l ranges 0 ? 16, �17 ? 0, 0 ? 22Reflections collected/unique 3300–2326Parameters/restrains 194/2Goodness of fit on F2 1.181R indices [I > 2r(I)] R1 = 0.0656, wR2 = 0.2304R indices [all data] R1 = 0.1024, wR2 = 0.2476(D/r)max 0.001Largest difference peak and hole (e/Å3) 0.901 and �0.786

Table 2Selected bond lengths (Å), torsion and bond angles (�) for solid state molecularstructure of 1c.

P–S1 1.9549(15) N–P–C1 101.55(17)P–N 1.669(3) N–P–C7 102.26(18)P–C1 1.808(4) N–P–S1 118.08(14)P–C7 1.810(4) C1–P–C7 106.95(18)S2–C14 1.681(5) S1–P–C1 113.56(15)S2–C17 1.633(6) S1–P–C7 113.03(14)N–C13 1.488(5) P–N–C13 116.8(3)C13–C14 1.485(6) C14–S2–C17 93.4(2)C1–P–N–C13 �179.1(3) S2–C14–C13 122.7(3)C7–P–N–C13 �68.7(3) S2–C14 –C15 113.0(3)S1–P–N–C13 56.0(3) N–C13–C14 111.6(3)

Table 3Transfer hydrogenation of acetophenone with iso-PrOH catalyzed by [Ru(Ph2PNHCH2-C4H3S)(g6-p-cymene)Cl2], 3 and [Ru((PPh2)2NCH2-C4H3S)(g6-p-cymene)Cl]Cl, 4.

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

1 3a 100:1:5 1 h <12 4a 100:1:5 1 h <13 3b 100:1 1 h <54 4b 100:1 1 h <55 3c 100:1:5 30 min 98 1966 4c 100:1:5 15 min 97 3887 3d 500:1:5 2 h 97 498 4d 500:1:5 30 min 97 1949 3e 1000:1:5 3 h 96 3210 4e 1000:1:5 1 h 99 9911 3f 100:1:5 5 min (30) 23 (97) 276 (194)12 4f 100:1:5 5 min (10) 62 (97) 744 (582)13 Ru-precursorg 100:1:14 41 24 <2

Ru-precursor: [Ru(g-p-cymene)([l-Cl)Cl]2.a At room temperature; acetophenone/Ru/NaOH, 100:1:5.b Refluxing in iPrOH; acetophenone/Ru, 100:1, in the absence of base.c Refluxing the reaction in air.d Refluxing in iso-PrOH; acetophenone/Ru/NaOH, 500:1:5.e Refluxing in iso-PrOH; acetophenone/Ru/NaOH, 1000:1:5.f Refluxing in iso-PrOH; acetophenone/Ru/NaOH, 100:1:5.g [Ru(g6-p-cymene)(l-Cl)Cl]2.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.

802 M. Aydemir et al. / Polyhedron 30 (2011) 796–804

TMS, J Hz, in CDCl3): 17.49 (CH3Ph of p-cymene), 21.36((CH3)2CHPh of p-cymene), 30.09 (–C H– of p-cymene), 42.32 (–CH2–), 86.17, 91.19 (aromatic carbons of p-cymene), 94.07,108.41 (quaternary carbons of p-cymene), 124.22 (C-5), 124.75(C-3), 126.57 (C-4), 128.21 (d, 3J = 10.1 Hz, m-carbons of phenyls),130.86 (d, 4J = 6.0 Hz, p-carbons of phenyls), 132.89 (d, 2J =10.4 Hz, o-carbons of phenyls), 134.93 (d, 1J = 51.6 Hz, i-carbonsof phenyls), 143.05 (d, 3J = 7.0 Hz, C-2); assignment was based onthe 1H–13C HETCOR and 1H–1H COSY spectra; 31P NMR (d inppm rel. to H3PO4, in CDCl3): 61.0 (s); Selected IR (KBr pellet, incm�1): t(P–N) 990, t(P–Ph) 1440, t(N–H) 3301; Anal. Calc. forC27H30NPSRuCl2 (603.6 g/mol) C, 53.73; H, 5.01; N, 2.32; found:C, 53.59; H, 4.93; N 2, 29%.

3.5.2. [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], 2a (0.469 g, 0.980 mmol) was added. The resulting reactionmixture was allowed to proceed under stirring at room tempera-ture for 1 h. After this time, the solution was filtered off and thesolvent evaporated under vacuum, the solid residue thus obtainedwas washed with diethyl ether (3 � 15 mL) and then dried undervacuum. Following recrystallization from diethylether/CH2Cl2, ared crystalline powder was obtained (yield: 0.71 g, 92%; mp: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 and 12.4, p-protons of phenyls), 7.32 (m, 8H, m-protonsof phenyls), 7.03 (d, 1H, 3J = 5.2 Hz, H-5), 6.66 (dd, 1H, 3J = 3.6and 5.2 Hz, H-4), 6.39 (d, 1H, 3J = 3.6, H-3), 5.45 (d, 2H,3J = 5.6 Hz, aromatic hydrogens of p-cymene), 5.28 (d, 2H, 3J =5.6 Hz, aromatic hydrogens of p-cymene), 4.45 (t, 2H, 3J = 11.6 Hz,–CH2–), 2.81 (m, 1H, –CH– of p-cymene), 2.26 (s, 3H, CH3-Ph ofp-cymene), 1.23 (d, 6H, 3J = 6.8 Hz, (CH3)2CHPh of p-cymene); 13CNMR (d in ppm rel. to TMS, J Hz, in CDCl3): 18.63 (CH3Ph of p-cym-ene), 22.21 ((CH3)2CHPh of p-cymene), 31.01 (–CH– of p-cymene),47.68 (–CH2–), 77.97, 79.05 (aromatic carbons of p-cymene), 95.92,100.20 (quaternary carbons of 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-carbons of phenyls), 132.83 (t,4J = 6.0 Hz, p-carbons of phenyls), 134.31 (t, 2J = 5.5 Hz, o-carbonsof phenyls), 140.54 (C-2); assignment was based on the 1H–13CHETCOR and 1H–1H COSY spectra; 31P NMR (d in ppm rel. toH3PO4, in CDCl3): 88.21 (s); Selected IR (KBr pellet, in cm�1):t(P–N–P) 984, t(P–Ph) 1440; Anal. Calc. for C39H39NSP2RuCl2

(787.7 g/mol): C, 59.47; H, 4.99; N, 1.78; found: C, 59.39; H, 4.93;N, 1.74%.

3.6. General procedure for the transfer hydrogenation of ketones

Typical procedure for the catalytic hydrogen transfer reaction: asolution of ruthenium complexes [Ru(Ph2PNHCH2-C4H3S)(g6-p-cymene)Cl2], 3 (0.005 mmol) or [Ru((PPh2)2NCH2-C4H3S)(g6-p-cymene)Cl]Cl, 4, NaOH (0.025 mmol) and the correspondingketone (0.5 mmol) in degassed iso-PrOH (5 mL) were refluxed for30 min for 3 and 10 min for 4. After this period a sample of thereaction mixture was taken off, diluted with acetone and analyzedimmediately by GC. Conversions obtained are related to the resid-ual unreacted ketone.

3.7. X-ray diffraction structure analysis

Intensity data of the compound 1c were measured at 295 K onan Enraf–Nonius CAD4 diffractometer fitted with graphite-mono-chromated Mo Ka (k = 0.71073 Å). The x/2h scan technique wasemployed to measure data up to a maximum Bragg angle of26.29�. The data were corrected for absorption. The structure was

Table 4Transfer hydrogenation results for substituted acetophenones with the Catalystsystems: [Ru(Ph2PNHCH2-C4H3S)(g6-p-cymene)Cl2], 3 and [Ru((PPh2)2NCH2-C4H3S)(g-p-cymene)Cl]Cl, 4.a

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

1 3 H 30 97 1942 4-F 30 99 1983 4-Cl 30 98 1964 4-Br 30 97 1945 2-MeO 30 96 1926 4-MeO 30 94 1887 4 H 10 97 5828 4-F 10 99 5949 4-Cl 10 98 58810 4-Br 10 97 58211 2-MeO 10 96 57612 4-MeO 10 95 570

a Catalyst (0.005 mmol), substrate (0.5 mmol), iso-PrOH (5 mL), NaOH(0.025 mmol), 82 �C, 30 min for 3 and 10 min for 4, respectively, the concentrationof acetophenone derivatives is 0.1 M.

b Purity of compounds is checked by NMR and GC (three independent catalyticexperiments), yields are based on methyl aryl ketone.

c TOF = (mol product/mol Cat.) � h�1.

M. Aydemir et al. / Polyhedron 30 (2011) 796–804 803

solved by direct methods using the program SHELX [66] and refinedby a full-matrix least-squares procedure based on F2. All non-hydrogen atoms were refined with anisotropic thermal parame-ters. Hydrogen atom of N were located from difference maps andrefined with isotropic thermal parameters. All other hydrogenatoms were placed on idealized positions riding on their carrieratoms with isotropic displacement parameters. The crystal dataand structure refinement details for compound 1c are given inTable 1. Selected bond distances and bond angles are listed inTable 2. Additional data, including fractional atomic co-ordinatesand their equivalent isotropic displacement parameters, hydrogenatom coordinates, anisotropic temperature factors, and a list ofobserved and calculated structure factors for compound have beendeposited from Cambridge Crystallographic Data Center as deposi-tion No: CCDC 756881 for 1c.

4. Conclusion

In summary, we have shown the facile synthesis of two amino-phosphine ligands and their derivatives including oxides, sulfidesand selenides. All these new compounds were characterized usingmulti nuclear NMR, IR spectroscopies and microanalysis and alsoone representative structure was studied by single crystal X-raydiffraction analyses. Furthermore, we synthesized two new octahe-dral Ru(II) complexes of formula [Ru(Ph2PNHCH2-C4H3S)(g6-p-cymene)Cl2] and [Ru((PPh2)2NCH2-C4H3S)(g6-p-cymene)Cl]Clwhich were fully characterized. Complexes, being stable towardsdecomposition, were tested as precatalysts in the hydrogen trans-fer reaction (HTR) of acetophenone derivatives in basic iso-PrOH.These compounds were formed to be efficient catalysts in thetransfer hydrogenation reaction of ketones. The [Ru((PPh2)2NCH2-C4H3S)(g6-p-cymene)Cl]Cl, catalytic system demonstrates remark-able catalytic activity and in a certain case, alcohols with up to 99%conversion could be obtained even when the substrate-to-catalystmolar ratio reached 1000:1. Future investigations are aiming at thedevelopment of an asymmetric version of this process.

Acknowledgement

Partial support of this work by Turkish Academy of Sciences andDicle University (Project number: DÜAPK 05-FF-27) is gratefullyacknowledged.

Appendix A. Supplementary material

CCDC 756881; contains the supplementary crystallographicdata for Compound 1c;. These data can be obtained free of chargevia http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from theCambridge Crystallographic Data Centre, 12 Union Road, CambridgeCB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.poly.2010.12.011.

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