Polyhedron 81 (2014) 203–209

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Polyhedron

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Palladium and platinum complexes of the new ligands containing P–Nand P–O bonds

http://dx.doi.org/10.1016/j.poly.2014.06.0100277-5387/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +90 232 3884000x2454; fax: +90 232 3888264.E-mail address: irislisevil@hotmail.com (S. _Iris�li).

Sevil _Iris�li a,⇑, Merve Karaman a, Nilgün Arda a, Bircan Dindar b, Orhan Büyükgüngör c

a Department of Inorganic Chemistry, Faculty of Science, Ege University, 35100 Bornova, _Izmir, Turkeyb Institute of Solar Energy, Ege University, 35100 Bornova, _Izmir, Turkeyc Department of Physics, Faculty of Science and Literature, Samsun, Turkey

a r t i c l e i n f o

Article history:Received 24 March 2014Accepted 3 June 2014Available online 11 June 2014

Keywords:Aminophosphine–phosphinitePalladium–platinum complexesSuzuki–Miyaura C–C cross couplingDiphosphinesX-ray

a b s t r a c t

A number of applications have been found for the variety complexes of Pd(II) and Pt(II) due to theirmarked catalytic activities. This study is intended to examine the seven and eight-membered novel com-plexes which have been prepared by P–N–C–C–O–P and P–N–C–C–C–O–P backbone ligands. The air-sta-ble complexes [M = Pd (1a, 3a), Pt (1b, 3b)] containing aminophosphine-phosphinite metallocyclic ringswere obtained with high yields. All the compounds were characterized by 31P{1H}, 13C{1H} and 1H NMRspectroscopy, FTIR spectroscopy and elemental analysis. Furthermore, the structure of complexes (1a and3a) were determined by X-ray crystallography. The novel complexes (1a and 3a) are very effective cata-lysts on Suzuki–Miyaura cross-coupling reactions of various aryl chlorides and aryl bromides with phen-ylboronic acid.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

The multidentate ligands which contain different donor atomssuch as phosphorus and nitrogen, and their transition metal com-plexes play an important role in organic and organometallic chem-istry, enhancing the stability of complexes and allowing themanipulation of electronic and steric parameters which controlreactivity at the metal center [1]. The phosphorus ligands are byfar the most commonly used, because they offer many more possi-bilities for modification of the structure (mono-, di-multidendate,hemilabile, hybrids, etc.), the symmetry (C2, dissymmetric, etc.),the basicity, and the chirality of the phosphorus atom [2–11]. Withregard to chelating phosphorus ligands and their complexes, thechain lengths or the bulky substituents on phosphorus atoms areof primary importance [12]. Furthermore, the chiral diphosphineligands and their ruthenium, iridium, rhodium, and palladiumcomplexes have also been reported and were essential for thedevelopment of new catalytic systems exhibiting high efficiencyand enantioselectivity [13–15].

Aminophosphine–phosphinite metal complexes have been usedin catalytic asymmetric hydrogenation [2,16,17] and hydroformyl-ation reactions [18–20]. Nevertheless, platinum complexes withchiral chelating phosphines have been shown to have a higher

stereoselectivity in hydroformylation reactions [6]. However, thecatalytic activities of such types of metal complexes in theSuzuki–Miyaura coupling reaction have not been determined inthe literature.

In this study we synthesized 1-(diphenylphosphino)piperidine-3-yl diphenylphosphinite (1), 3-[(diphenylphosphino)(methyl)amino]propyl diphenylphosphinite (2) and [1-(diphenylphosphino)piperidine-3-yl]methyl diphenylphosphinite (3) ligands, and their pal-ladium (1a and 3a) and platinum (1b and 3b) derivatives. Thestructures of the complexes were characterized by using differentspectroscopic methods. The crystal structures of 1a and 3a wereestablished by X-ray crystallography. In particular, we demon-strated the efficiency of such complexes for Suzuki–Miyaura C–Ccross coupling of activated aryl halides over palladium catalysts.

2. Experimental

2.1. Materials and methods

Solvents were dried on suitable drying agents and purifiedunder inert conditions [21]. All synthesis was carried out usingstandard Schlenk tube techniques in an inert argon atmosphere.3-hydroxypiperidine, 3-(methylamino)propan-1-ol, 3-piperidine-methanol, diphenylchlorophosphine, and triethylamine were pur-chased from Aldrich and toluene, dichloromethane, diethylether,and acetone were purchased from Merck. The starting complexes,[PdCl2(COD)] and [PtCl2(COD)] (COD = 1,5-cyclooctadiene), which

204 S. _Iris�li et al. / Polyhedron 81 (2014) 203–209

are used for the preparation of new phosphine complexes, weresynthesized according to the method given in the literature[22,23].

31P{1H} NMR, 1H NMR and 13C NMR spectra were recorded on aVarian AS 400 MHz spectrometer. CDCl3 was employed as asolvent. J values are given in Hz. The IR spectra were obtained byPerkin-Elmer FT-IR spectrometer. Melting points were determinedusing electrothermal melting point detection apparatus. Elementalanalyses were performed by the TÜB_ITAK-Ankara Test and AnalyseLaboratories and Scientific Research and Analysis Center Labora-tory of Inönü University. The yields of catalytic experiments weremeasured by GS (Agilent Technologies 6890N-Thermo-Finniganon a HP-5 capillary column and with a FID detector). X-ray datawere measured in Ondokuz Mayis University, Turkey, by usingthe STOE IPDS II diffractometer. The thermal behavior of newlysynthesized compounds was investigated using thermogravimetry(TGA/DTG) on Perkin Elmer Pyris 6.

2.2. Synthesis of products

2.2.1. Synthesis of 3-[(diphenylphosphino)(methyl)amino]propyldiphenylphosphinite ligand (1)

Triethylamine (0.860 mL; 0.630 g; 6.20 mmol) in toluene(5.0 mL) was slowly added to a suspension of 3-(methylamino)pro-pan-1-ol (0.300 mL; 0.280 g; 3.10 mmol) in toluene (10.0 mL).Then the mixture was cooled to �78 �C. A solution of PPh2Cl(1.03 mL; 1.37 g; 6.20 mmol) in toluene (5.0 mL) was slowly addeddropwise. After addition, the mixture was stirred at room temper-ature for 24 h. Et3N�HCl was separated with canula. Toluene wasevaporated under vacuum and a light yellow oil was formed. 1HNMR (400 MHz, CDCl3, 25 �C): d = 1.78–1.83 (m, 2H, –CH2–),2.24–2.48 (m, 3H, N–CH3), 3.06–3.12 (m, 2H, N–CH2–), 3.77–3.72(m, 2H, O–CH2–), 7.06–7.70 (m, 20H, ArH). 13C{1H} NMR(100 MHz, CDCl3) ppm: d = 35.8 (d, N–CH3), 32.7 (t, –CH2–), 49.3–49.8 (dd, –CH2–N), 66.8–67.9 (dd, –CH–O), 126–140 (m, Ar–C),31P{1H} NMR (162 MHz, CDCl3): d = 113 ppm (P–O) andd = 65.3 ppm (P–N).

2.2.2. Synthesis of [1-(diphenylphosphino)piperidine-3-yl]methyldiphenylphosphinite ligand (2)

3-piperidinemethanol (0.100 mL;0.860 mmol) was dissolvedin Et3N (5.0 mL) in a standard Schlenk tube. Then, PPh2Cl(0.240 mL;1.71 mmol) in Et3N (10 mL) was added to this solution.The mixture was heated to reflux temperature for 24 h. Et3N�HClwas separated with canula. The solvent was evaporated under avacuum and an off-white viscous film was formed. (Yield 75%)1H NMR (400 MHz, CDCl3, 25 �C): d = 0.84–1.23 (m, 2H, –CH2–,piperidine), 1.60–1.69 (m, 2H, –CH2–, piperidine), 2.14–2.18(m, H, –CH–, piperidine), 2.81–2.98 (t,4H, N–CH2–), 3.38–3.73(m, 2H, O–CH2–), 7.08–7.55 (m, 20H, ArH). 31P{1H} NMR(162 MHz, CDCl3): d = 113 ppm (P–O) and d = 64.1 ppm (P–N).

2.2.3. Synthesis of 3-[(diphenylphosphino)(methyl)amino]propyldiphenylphosphinite Pd(II) chloride (1a)

PdCl2COD (0.080 g; 0.280 mmol) in CH2Cl2 (10 mL) was addedto the stirred solution in CH2Cl2 (5.0 mL) of ligand 1 (0.130 g;0.280 mmol) dropwise at room temperature. The color turned fromyellow to orange. After stirring for 24 h, CH2Cl2 was removed undervacuum. The crude product was washed with hexane (3.0 mL) andacetone (2.0 mL), and then dried using a vacuum. Yellow solid wasobtained. Yield 0.18 g, 72%, m.p = 174 �C (decomposed), 1H NMR(400 MHz, CDCl3) ppm: d = 1.81 (m, 2H, –CH2–), 2.18–2.16 (m,3H, N–CH3), 3.05–2.96 (m, 2H, –NCH2–), 3.63–3.58 (m, 2H, –OCH2–), 7.19–8.18 (m, 20H, ArH), 13C{1H} NMR (100 MHz, CDCl3)ppm: d = 36.7 (d, N–CH3), 31.4 (t, –CH2–), 49.5–49.9 (dd, –CH2–N), 67.2–67.5 (dd, –CH–O), 125–138 (m, Ar–C), 31P{1H} NMR

(162 MHz, CDCl3) ppm: d = 117 (d, P–O), and d = 91.6 (d, P–N), IR,cm�1 (CsI): 279, 317 m(Pd–Cl). Anal. Calc. for C28H29Cl2NOP2Pd(MW = 634.76): C, 52.98; H, 4.60; N, 2.21. Found: C, 52.36; H,5.01; N, 2.45%.

2.2.4. Synthesis of 3-[(diphenylphosphino)(methyl)amino]propyldiphenylphosphinite Pt(II) chloride (1b)

PtCl2COD (0.100 g; 0.270 mmol) was dissolved in CH2Cl2

(10 mL) and added dropwise to a mixture of 1 (0.120 g;0.270 mmol) dissolved in CH2Cl2 (3.0 mL). After 24 h, the raw prod-uct was concentrated with a vacuum and precipitated with hexane(10 mL). The product was dried using a vacuum. Yield 0.12 g, 62%,m.p = 186–189 �C, 1H NMR (400 MHz, CDCl3) ppm: d = 1.90 (m, 2H,–CH2–), 2.20–2.17 (m, 3H, N–CH3), 3.09–2.99 (m, 2H, –NCH2–),3.62–3.60 (m, 2H, –OCH2–), 7.22–8.19 (m, 20H, Ar–H), 13C{1H}NMR (100 MHz, CDCl3) ppm: d = 36.2 (d, N–CH3), 32.1 (t, –CH2–),49.4–49.7 (dd, –CH2–N), 66.2–66.9 (dd, –CH–O), 124–138 (m, Ar),31P{1H} NMR (162 MHz, CDCl3) ppm: d = 88.7 (d, P–O) andd = 63.6 (d, P–N), Anal. Calc. for C28H29Cl2NOP2Pt (MW = 723.47):C, 46.84; H, 4.04; N, 1.94. Found: C, 47.01; H, 4.70; N, 1.06%.

2.2.5. General procedure for the synthesis of 1-(diphenylphosphino)piperidine-3-yl diphenylphosphinite metalcomplexes [Pd (3a) and Pt (3b)]

To a suspension of 3-hydroxypiperidine (0.05 g; 0.53 mmol) intoluene (10 mL), Et3N (0.200 g; 0.200 mL; 1.00 mmol) was added.Then, the mixture was cooled to �78 �C. A solution of PPh2Cl(0.220 g; 1.00 mmol; 0.190 mL) in toluene (10 mL) was slowlyadded dropwise and stirred at �78 �C for 1 h and the temperaturewas raised to 0 �C. Stirring was maintained at 0 �C for 1 h and thenat room temperature for 30 min. For reasons concerning oxidation,the solution was not filtered. So, MCl2(COD) (0.530 mmol of PdCl2

(COD) or PtCl2(COD)) was added to the solution of in situ preparedligand, 1-(diphenylphosphino)piperidine-3-yl-diphenylphosphi-nite. The reaction mixture was heated to reflux temperature andstirred for 4 h. The solvent was removed under vacuum. The rawproduct was washed with acetone, water and Et2O, respectively.It was possible for it to be recrystallized from the dichlorometh-ane/ether (v:v = 1:3) system.

For complex 3a: Yield: 0.25 g, 88%; m.p = 218–220 �C, 1H NMR(400 MHz, CDCl3): d = 1.64 (dd, 2H, –CH2–, piperidine), 2.99 (m,2H, –CH2–, piperidine), 3.25 (q, 2H, N–CH2–, piperidine), 3.60 (m,2H, –CH2–N, piperidine), 4.58 (t, 1H, CH-O, piperidine), 7.19–8.07(m, 20H, ArH), 13C{1H} NMR (100 MHz, CDCl3): d = 19.3 (s, –CH2–,piperidine), 28.9 (s, –CH2–, piperidine), 46.5 (s, N –CH2–, piperi-dine), 52.1 (s, –CH2–N, piperidine), 70.8 (d, –CH–O, piperidine),126–134 (m, Ar), 31P{1H} NMR (162 MHz, CDCl3): d = 91.7 ppm(d, P–N), 99.3 ppm (d, P–O), IR, cm�1 (CsI): 283, 306 m(Pd–Cl), Anal.Calc. For C29H29Cl2NOP2Pd (MW = 646.77): C, 57.07; H, 4.62; N,2.29. Found: C, 57.76; H, 4.68; N, 2.35%.

For complex 3b: Yield: 0.23 g; 87%; m.p = 184–185 �C, 1H NMR(400 MHz, CDCl3): d = 1.93 (dd, 2H, –CH2–, piperidine), 2.99 (m,2H, –CH2–, piperidine), d = 3.16 (q, 2H, N–CH2–, piperidine), 3.69(m, 2H, –CH2–N, piperidine), 5.03 (t, 1H, CH–O, piperidine),7.23–8.21 (m, 20H, ArH), 13C NMR (100 MHz, CDCl3): d = 19.1(s, –CH2–, piperidine), 29.1 (s, –CH2–, piperidine), 44.9 (s, N –CH2–,piperidine), 51.9 (s, –CH2–N, piperidine), 70.5 (d, –CH–O, piperi-dine), 127–134 (m, Ar–C), 31P{1H} NMR (162 MHz, CDCl3):d = 65.5 ppm (P–N), 72.0 ppm (P–O), IR, cm�1 (CsI): 285,309 m(Pt–Cl), Anal. Calc. For C29H29Cl2NOP2Pt (MW = 735.47): C,47.36; H, 3.97; N, 1.90. Found: C, 46.11; H, 4.19; N, 2.13%.

2.3. General procedure for the Suzuki–Miyaura coupling reactions

In a typical run, a two-necked 25 mL flask fitted with a refluxcondenser and septum was charged with aryl halide (1.00 mmol).

S. _Iris�li et al. / Polyhedron 81 (2014) 203–209 205

Phenylboronic acid (1.50 mmol), Cs2CO3 or K2CO3 (1.50 mmol),diethyleneglycol di-n-butyl ether (0.6 mmol, internal standard)and the palladium–phosphine catalyst (0.1 mmol%) in DMF(3.0 ml) were added, in that order. The flask was placed in a pre-heated oil bath (100 �C) under an argon atmosphere. The conver-sion was monitored using gas chromatography.

2.4. Thermal Stability (TGA) of 1a and 3a

The thermal stability of complexes (1a and 3a) was investigatedusing the method of TGA-DTG.

The thermal stabilities of these complexes were also fulfilled bya Perkin Elmer Pyris 6 TGA instrument. The analysis was carriedout using around 3.0 mg of the dry samples directly weighed onthe pans. The temperature progressed from 50 to 900 �C and itsheating rate was 20 �C min�1. The measurements were performedunder nitrogen continuous flow (100 mL/min) in the temperaturerange.

2.5. X-ray crystal structures of complex 1a and 3a

Light yellow, single crystals of compound 1a and 3a wereobtained by a slow diffussion of a 1:3 dichloromethane/diethyl-ether system at room temperature. The crystal dimensions of 1a0.34 � 0.26 � 0.10 mm and 3a 0.47 � 0.25 � 0.04 mm were usedfor data collection. Intensity data for complexes 1a and 3a werecollected on a STOE IPDS II diffractometer using graphite-monochromated Mo Ka radiation (k = 0.71073 Å) at 296 K. A totalof 8224 and 4821 reflections that had I > 2r(I) were regarded asobserved and used for complexes 1a and 3a, in the structure anal-ysis. All positional and thermal parameters were refined using theSHELXL-97 program [24]. The hydrogen atoms were identified in thedifference Fourier map and were included in the refinement pro-cess as fixed contributions. Atomic coordinates, bond lengths andangles were deposited with the Cambridge Crystallographic DataCenter, 12 Union Road, Cambridge CB2 1EZ, UK.

3. Results and discussion

3.1. Synthesis

The new type of aminophosphine-phosphinite ligands (1 and 2)were synthesized from the commercially available 3-piperidine-methanol and 3-(methylamino) propan-1-ol. These compoundsand diphenylchlorophosphine reacted with triethylamine as a basefor tearing hydrogen (Scheme 1). Ligand 3 was synthesized as the

NH

2PPh2Cl 2Et3NHO

NH

OH

2PPh2ClE

ref

Scheme 1. Synthesis

same reaction pathway from 3-hydoxypiperidine and diphenyl-chlorophosphine but not isolated.

For reasons related to oxidation, 1-(diphenylphosphino) piperi-dine-3-yl diphenyl phosphinite ligand could not be isolated as apure product. All the isolation and purification studies failed. Also,when the solvent was removed by vacuum, the ligand wasoxidized. Because of this, there were lots of complicated peaks inthe 31P{1H} NMR spectrum of this mixture and it could not be char-acterized using any spectroscopic methods. So, the metal com-plexes, 3a and 3b were synthesized without isolation of ligand 3according to one-pot method described in the literature [25,26].

1 and 2 ligands were isolated and analyzed with 31P{1H} NMR.Both of them were overly sensitive to air. The 31P{1H} NMR spectraof 1 and 2 show two single resonances at 113 ppm (P–O) 65.3 ppm(P–N) and 113 ppm (P–O) 64.1 ppm (P–N), respectively. Phospho-rus–phosphorus couplings were not observed.

The reaction of 1 with 1:1 mole ratio proportion of PdCl2COD indichloromethane affords the chelate complex 1a in good yield. Thecomplex 1b was synthesized in a similar way to 1a with ligand 1and PtCl2COD (Scheme 2).

Complexes 3a and 3b were obtained in the reaction medium(Scheme 3). In contrast to these free ligands, which are quite sen-sitive to air, complexes (1a, 1b, 3a and 3b) are stable against airand water, and can be stored in air over long periods of time. Theresulting complexes 1a, 1b, 3a and 3b were fully characterizedusing multinuclear NMR techniques (31P{1H} NMR, 1H NMR, 13CNMR), FT-IR and elemental analysis.

For the complex 1a, the –NPPh2 resonance is 25.7 ppm down-field (d 91.6 ppm) from that of the free ligand, similarly the –OPPh2

signal shifted only 4 ppm downfield (d 117 ppm). 31P{1H} NMRspectrum of complex 3a, revealed significant shifts of the doubletsat 91.7 ppm, P(N) and 99.3 ppm, P(O) assigned to the diphenyl-phosphino groups coordinated to nitrogen and oxygen [17]. Thus,it is confirmed that the two phosphorus atoms are not magneti-cally equivalent and that the structure is not symmetric in thecomplexes 1a and 3a.

For the platinum complex 1b, the 31P{1H} NMR spectrum showstwo signals as doublets for 63.6 and 88.7 ppm for the –NPPh2 and –OPPh2 resonances whose195Pt satellites are 4037 Hz (1JPt–P(N)) and4205 Hz (1JPt–P(O)) and for 3b, 65.5 ppm and 72.0 ppm for the –NPPh2 and –OPPh2 resonances whose 195Pt satellites are 4204 Hz(1JPt, P(N)) and 4050 Hz (1JPt, P(O)), respectively. These values ofthe signals are harmonious with seven-membered aminophos-phine-phosphinite ligands with platinum complexes in the litera-ture [27,28].

IR spectra (CsI, pellet) show two distinct M–Cl stretching vibra-tions. These values are m(Pd–Cl) at 279 and 317 cm�1 (1a), m(Pd–Cl)

C6H5CH3

-78oC 1h,r.t 24h

NO

PPh2 PPh2

t3N

lux, 24hN

O

PPh2

PPh2

Ligand 1

Ligand 2

of the ligands.

NO

PPh2 PPh2

MCl2CODCH2Cl2

r.t, 24h

NO

Ph2P PPh2M

Cl Cl

1 M=Pd:1a; M=Pt:1b

Scheme 2. Synthesis of the complexes 1a and 1b.

NH

OHPPh2Cl, MCl2COD

Et3N, C6H5CH3,ref lux, 4h N

O

PPh2

PPh2

M Cl

Cl

M=Pd:3a; M=Pt:3b

Scheme 3. Synthesis of the complexes 3a and 3b.

Table 1Crystal data, data collection and structure-refinement parameters for complex 1a and3a.

1a 3a

Empirical formula C28H29Cl2NOP2Pd C29H29Cl2NOP2PdFormula weight 634.76 646.77Crystal color light yellow light yellowCrystal size (mm) 0.34 � 0.26 � 0.10 0.47 � 0.25 � 0.04T (K) 296 296k (Å) 0.71073 0.71073Crystal system monoclinic monoclinicSpace group P21/c P21/cDescription prism prismUnit cell dimensiona (Å) 8.9898(3) 20.5304(12)b (Å) 14.4971(6) 14.4110(5)c (Å) 21.9507(7) 22.1063(15)a (�) 90.00 90.00b (�) 106.303(2) 120.557(4)c (�) 90.00 90.00�Z 4 8Absorption coefficient (mm�1) 1.009 0.986Dcalc (Mg/m3) 1.536 1.526V (Å3) 2745.72(17) 5632.1(5)Theta range (�) 1.71–28.07 1.41–27.33Index ranges �11 < h < 11, �25 < h < 25,

�18 < k < 18, �17 < k < 18,�27 < l < 27 �27 < l < 27

F(000) 1288 2624Measured reflections 29374 76053Independent reflections (Rint) 5698 (0.0399) 11668 (0.0688)Absorption correction integration Stoe

X-RED32 [29]Final R indices (all data) R1, 0.0679 0.0866R1, [I > 2r(I)] 0.0648 0.0514Goodness-of-fit (GOF) on F2 1.02 1.07Maximum/minimum trans. (e �3) 0.91/0.72 0.87/0.70

206 S. _Iris�li et al. / Polyhedron 81 (2014) 203–209

at 283 and 306 cm�1 (3a), m(Pt–Cl) at 318 and 337 cm�1 (1b),m(Pt–Cl) at 285 and 309 cm�1 (3b) consistent with a cis-MCl2

geometry. Additionally, this structure was also supported withevents of elemental analysis.

It was attempted to synthesize the pincer complexes ofpalladium and platinum by use of ligand 1 and ligand 3. For thispurpose, we changed lots of parameters such as differentsolvents (toluene, THF, dichloromethane, pentanol, chloroform–trichloroaceticacid), several bases (BuLi, Et3N, dimethylaminopyri-dine) and varied temperatures. But there was no result from theseexperiments. Also, when synthesizing of the platinum andpalladium complexes of the ligand 2, the reaction conditions (sol-vent, temperature) were changed but we were unable to achievepure products.

3.2. X-ray crystal structures of complexes 3-[(diphenylphosphino)(methyl)amino]propyl diphenylphosphinitePd(II) chloride (1a) and 1-(diphenylphosphino)piperidine-3-yldiphenylphosphinite Pd(II)chloride (3a)

The light yellow crystals of 1a and 3a were grown by a slow dif-fusion technic from a dichloromethane-diethylether (v:v = 1:3)solvent system in diffusion at room temperature. The details ofthe structure determinations are given in Table 1 and selectedbond lengths and angles are listed in Table 2. Views of the mole-cules 1a and 3a are depicted in Fig. 1 and Fig. 2, respectively,together with the numbering scheme adopted. They have seven-membered and eight-membered macrocyclic units, respectively.

Palladacycles 1a and 3a both crystallized in the monoclinic P21/c, space group. The X-ray crystal data demonstrate that each palla-dium metal is located in a distorted square-planar geometry sur-rounded by a chelating aminophosphine–phosphinite ligand andchloride anions. The assymetric unit of the structure of compound3a contains two crystallographically independent molecules.

Analysis of 1a and 3a reveals the palladium centers to belocated into a slightly distorted square planar environmentwith angles of 97.24(2)� for P(1)–Pd(1)–P(2); 85.43(2)� for P(2)–Pd(1)–Cl(2); 90.61(3)� for Cl(2)–Pd(1)–Cl(1); 86.78(2)� for

Cl(1)–Pd(1)–P(1) and 98.99(4)� for P(1)–Pd(1)–P(2); 84.78(4)� forP(2)–Pd(1)–Cl(2); 92.84(4)� for Cl(2)–Pd(1)–Cl(1); 84.72(4)�for Cl(1)–Pd(1)–P(1), respectively. Due to these steric effects, theP–Pd–P and Cl–Pd–Cl angles around the Pd center are opened upand are significantly larger than 90�.

The metal–phosphorus bond lengths, Pd–P(O) and Pd–P(N), areslightly different from each other in complex 1a and 3a. Asexpected, the Pd–Cl bond lengths trans to –OPPh2 groups areslightly shorter than the Pd–Cl bond lengths trans to –NPPh2

groups due to the trans effect. The six-membered piperidine ringsin the two molecules of complex 3a are chair conformations.

3.3. Catalysis

The palladium-catalyzed cross-coupling of arylboronic acidswith aryl halides (bromoacetophenone, chloroacetophenone,bromoanisole, chloroanisole) has been shown to proceed under avariety of conditions; a wide range of bases and solvents, as well

Table 2Selected bond distances (Å) and angles (�) for complex 1a and 3a.

1a 3a

Bond distancesP1–Pd1 2.2368(6) P1–Pd1 2.2427(11)P2–Pd1 2.2652(6) P2–Pd1 2.2489(12)Cl1–Pd1 2.3694(6) Cl1–Pd1 2.3750(12)Cl2–Pd1 2.3516(7) Cl2–Pd1 2.3499(11)N1–P2 1.6704(19) N1–P2 1.666(4)O1–P1 1.5947(15) O1–P1 1.611(3)O1–C1 1.446(3) O1–C28 1.460(5)

Bond anglesO1–P1–Pd1 118.58(6) O1–P1–Pd1 119.52(12)N1–P2–Pd1 123.99(8) N1–P2–Pd1 117.16(14)P1–Pd1–P2 97.24(2) P1–Pd1–P2 98.99(4)P2–Pd1–Cl2 85.43(2) P2–Pd1–Cl2 84.78(4)P1–Pd1–Cl1 86.78(2) P1–Pd1–Cl1 84.72(4)Cl2–Pd1–Cl1 90.61(3) Cl2–Pd1–Cl1 92.84(4)

S. _Iris�li et al. / Polyhedron 81 (2014) 203–209 207

as catalysis [30]. The reactions are usually carried out homoge-neously in the presence of a base in an inert atmosphere. The reac-tivity of the aryl halide component decreases drastically in theorder X = Br > Cl. This optimized set of coupling reaction conditionsis used for catalytic experiments.

Fig. 1. Molecular structure of complex 1a with 30% probabilit

Fig. 2. Molecular structure of complex 3a with 30% probability level ellipso

Until now, various metal complexes of aminophosphine–phosphinites have been investigated for the asymmetric allylicalkylation, hydroformylation, and hydrogenation [6,20,31,32].However, there is no literature concerning the catalytic activityof aminophosphine-phosphinite type palladium complexes incross coupling reactions. So we have investigated the activity ofcomplexes 1a and 3a as catalysts for the coupling of various arylbromides and chlorides with phenyl boronic acid. The results ofthis study are summarized in Table 3. The conditions employedfor the catalytic experiments are depicted on Scheme 4. Better per-formances can be obtained by changing the reaction conditions.

Observations on these catalysis reactions are consistent with aclassical Pd(0)/Pd(II) catalytic cycle. Reaction mixtures begin turn-ing yellow fairly soon after being heated in an oil bath. At 100 �C,color changes became evident within about 1 min. Reaction mix-tures involving aryl chlorides slowly turned yellow at 100 �C, butno black precipitate was evident [33].

The complexes 1a and 3a were active catalysts for the Suzuki–Miyaura cross coupling reaction with tolerable yields and TON val-ues. For catalysts of 1a and 3a, the coupling of 4-bromoacetophe-none with phenylboronic acid proceeds with a 99% isolatedyield with a catalyst loading of 0.1 mmol%, while electronically

y level ellipsoids. Hydrogen atoms are omitted for clarity.

ids. Hydrogen atoms and the second molecule are omitted for clarity.

Table 3The Suzuki coupling reaction of aryl halides with phenylboronic acid of catalysts 1a and 3a (in DMF).

Entry Catalyst Substrat Base Time % Yield TON

1 1a 4-bromoacetophenone Cs2CO3 0.13 >99 >9900002 1a 4-chloroacetophenone Cs2CO3 10 >99 >9900003 1a 4-bromoanisole Cs2CO3 6 97 9700004 1a 4-chloroanisole Cs2CO3 24 2.5 250005 3a 4-bromoacetophenone K2CO3 1 >99 >9900006 3a 4-chloroacetophenone K2CO3 24 53 5300007 3a 4-bromoanisole K2CO3 2 89 8900008 3a 4-chloroanisole K2CO3 24 41 410000

B(OH)2 X

R

R%0.1mmol catalyst

Cs2CO3 /K2CO3DMF 100 oC

R=COCH3, OCH3X=Cl,Br

Scheme 4. The mechanism of Suzuki–Miyaura coupling reaction.

208 S. _Iris�li et al. / Polyhedron 81 (2014) 203–209

deactivated. Thus, the more challenging substrate 4-bromoanisolecan be efficiently coupled with 89% and 97% isolated yield with acatalyst loading of 0.1 mmol%, while the catalysts, 1a and 3a, aresaid to be more active compared with the amido phosphine palla-dium complex [34].

The catalytic activities of 1a and 3a, were seen to decrease fromp-bromoacetophenone to p-bromoanisole. This is ascribed to thepresence of the electron donating metoxy group which makesthe substrate less reactive in the rate determining step of the cat-alytic cycle [35]. The complex 1a efficiently catalyzes the Suzukicross-couplings of a range of aryl boronic acid and 4-chloroaceto-phenone, affording high isolated yields at a low catalyst load(0.1 mmol% 1a) to give 1-biphenyl-4-ylethanone in a good TONof >99 0000 [36].

The activity of 1a is comparable to that of some Palladium com-plexes, which catalyzed the Suzuki coupling of 4-chloroacetophe-none with phenylboronic acid, giving up to 99% yield at0.1 mmol% of 1a under ambient conditions [33,37].

Van Leeuwen and co-workers performed a study on the effect ofthe bite angle of chelating diphosphines on the activity and selec-tivity in the palladium-catalyzed cross-coupling reactions. Increas-ing the P–M–P angle of the diphosphine to even larger valuesresulted in a decrease of catalyst activity and also selectivity. So,the high catalytic activities for 1a and 3a can be explained by thesmall P–Pd–P bite angles [38–40].

Finally, complexes 1a and 3a are ideal to catalyze the couplingof electronically deactivated substrate and aryl bromides or chlo-rides as they are comparatively inexpensive and can be used togive high conversion at low concentrations of catalysts.

3.4. Thermal analysis of complexes 1a and 3a

The thermal behavior of new synthesized compounds wasinvestigated using thermogravimetry (TGA/DTG). The complexes1a and 3a were stable up to 175 and 200 �C, respectively. Bothcomplexes showed a two-step mass loss. The first stage occurredin the temperature range 175–280 and 200–330 �C with a corre-sponding weight loss of 50% and 30% for the 1a and 3a complexes,respectively. In addition, the second stages of decomposition wereobserved at 280–380 �C (25 wt.% loss) and 330–420 �C (45% wt.

loss) for the 1a and 3a complexes, respectively. The remaining25% should correspond to the mass of PdCl2.

4. Conclusion

Aminophosphine-phosphinite type ligands (1 and 2) and theirchelated Palladium (1a and 3a) and Platinum (1b and 3b) com-plexes were synthesized. The crystal structures of 1a and 3a weredetermined through X-ray crystallographic studies. 1a and 3a com-plexes were found to be active catalysts on Suzuki–Miyaura C-Ccross coupling reactions between 4-bromoacetophenone, 4-chloro-acetophenone, 4-bromoanisole and phenylboronic acid.

Acknowledgements

We are grateful to the TÜB_ITAK with science Project 110T786.Ege University/TURKEY (2009 FEN 091 and 2012 FEN 048) forfinancial support. We also wish to thank the EB_ILTEM/TURKEYfor equipment grants. The authors acknowledge the Faculty of Artsand Sciences, Ondokuz Mayis University, Turkey, for the use of theSTOE IPDS II diffractometer (purchased under Grant F.279 of theUniversity Research Fund/TURKEY).

Appendix A. Supplementary data

CCDC 920704 and 977709 contain the supplementary crystallo-graphic data for compounds 1a and 3a, respectively. These data canbe obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic DataCentre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223336 033; or e-mail: deposit@ccdc.cam.ac.uk.

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