e-X-

m

tes

2

ates 1,8-bis(2-diphenylarsinoethoxy)anthracene-9,10-dione (L1). L1 and 1,8-bis(2-phenylsele-noethoxy)anthraquinone (L2) reacted with bis(benzonitrile)palladium(II) chloride in 1:1 ratio yieldingPd(L1)Cl2 (1) and Pd(L2)Cl2 (2). X-ray structures of 1 and 2 revealed that L1 and L2 chelate with Pd(II)and form a convex square planar geometry. The catalytic properties of both Pd(II) complexes in the Heckreaction was investigated, and the results show that compound 2 acts as a better catalyst than 1. Theredox behavior of L1, 1 and 2 versus Ag/AgCl are also explored.

ed anthraquinone to Ag(I) and Cu(I). The selenium derivative

The hemilabile ligands [3] have the capacity to tune the catalyticactivity of a metal center due to their temporary possession ofthe coordination site before they are substituted by a substratein the sequence of a catalytic reaction. Ligands with mixed donors(phosphorous/oxygen; phosphorus/nitrogen) type have been espe-cially useful for the design of catalytically active species [4] andhave found application in many reactions. There are numerous

icinal agents, and organic materials. Transition metal-catalyzedely used in tradi-Miyaura reaction,ishi reaction. Thethis reactiopalladium

plexes used for the Heck reaction contain either palladacypalladium complex by electron-rich ligands like phosphincludes pnictogens and chalcogens as donors [7]. It was ththought worthwhile to synthesize anthraquinone based palladiumcomplexes with AsOAs or SeOSe as electron donors and studytheir catalytic properties. We report here the synthesize of L1 (AsOAs), the complexation behavior of L1 and L2 (SeOSe) with pal-ladium(II) including the X-ray structures of [PdCl2(L1)] and[PdCl2(L2)]. The catalytic efcacy of both Pd(II) complexes in theHeck reaction is also explored.

Corresponding author.E-mail address: Kadarkaraisamy.Mariappan@usd.edu (K. Mariappan).

Inorganica Chimica Acta 429 (2015) 4650

Contents lists availab

Ch

w.eserved also as chemodosimeter for the detection of Cu(II) andFe(III). Making of complexes of platinum group elements with avariety of ligands particularly hemilabile ligands, is one of thehot elds in coordination chemistry due to the catalytic propertiesof Pd(II), Rh(III) and Ru(II) complexes in many organic reactions.

cross-couplings to form CarylCaryl bonds are widtional synthetic methods [6] such as the Suzukithe Stille reaction, the Kumada reaction, and NegHeck reaction is another powerful method, andPd(0)/Pd(II) complexes as catalysts. Most of thehttp://dx.doi.org/10.1016/j.ica.2014.12.0280020-1693/ 2015 Elsevier B.V. All rights reserved.n usescom-

cles orine orerefore1. Introduction

Anthraquinone (AQ)-based ligands and their metal complexesare a rich eld of study due to their multifarious applications.[1]. We have recently reported the selective chelation of nitrogen[2a,b], sulfur [2c] and selenium derivatives [2d] of 1,8-disubstitut-

hemilabile arsenic donors that have been studied along with theircoordination chemistry [5a] in the literature; but there is a scarcityof arsenic complexes that are known as catalysts [5b].

Many methods are available to construct the carboncarbonbond, which is crucial for all of organic chemistry, but specicallythe assembly of CarylCaryl bonds in diverse natural products, med-Received 8 September 2014Received in revised form 9 December 2014Accepted 10 December 2014Available online 7 February 2015

This work is dedicated to Dr. A.Shumugasundaram, Retired professor,Department of Chemistry at VirudhunagarHindu Nadars Senthikumara Nadar College,Virudhunagar, Tamilnadu, India.

Keywords:AnthraquinoneDiphenylarsino ligandPalladium complex 2015 Elsevier B.V. All rights reserved.Article history: The reaction of the Ph As anion with 1,8-bis(2-bromoethoxy)anthracene-9,10-dione in 2:1 ratio gener-Palladium(II) complexes of anthraquinonand SeOSe type bipodands. Synthesis,and catalytic properties

Kadarkaraisamy Mariappan , Janani Sindhu RagothaMadhubabu Alaparthi, Andrew G. SykesDepartment of Chemistry, University of South Dakota, Vermillion, SD 57069, United Sta

a r t i c l e i n f o a b s t r a c t

Inorganica

journal homepage: wwbased AsOAs typeray crystallography

an, Vinothini Balasubramanian, Mariah Hoffman,

le at ScienceDirect

imica Acta

l sevier .com/locate / ica

2. Experimental

diffractometer using Mo Ka radiation. Data reduction and rene-

ArH from AQ); 7.787.80 (m, 10H, ArH from phenyl ring); 7.85

a Chment were completed using the WinGX suite of crystallographicsoftware [10,11]. Structures were solved using OLEX [12]. All hydro-gen atoms were placed in ideal positions and rened as ridingatoms with relative isotropic displacement parameters. Table 1lists additional crystallographic and renement information.

2.2. Synthesis

2.2.1. Synthesis of 1,8-bis(2-diphenylarsinoethoxy)anthracene-9,10-dione (L1)

Triphenylarsine (0.5 g, 1.62 mmol) was dissolved in 50 mL ofdry THF under a nitrogen atmosphere. A red solution was obtainedseveral minutes after adding excess lithium metal to the tripheny-larsine solution. The solution was stirred for 3 h, and the red solu-tion was transferred into another clean, dry ask using a cannulaunder nitrogen atmosphere, and mixed with 2-chloro-2-methyl-propane (0.15 g, 1.62 mmol) in THF to destroy unwanted PhLi. Asolution of 1,8-bis(2-bromoethoxy)anthracene-9,10-dione (0.37 g,0.81 mmol) made in 30 mL of THF was added to the red (Ph)2As

and the solution was stirred for 3 h. THF was evaporated underreduced pressure and the residue was puried by a silica gel col-umn using methylene chloride: ethyl acetate mixture as eluent.The yield is 0.35 g (28%) as yellow brous solid, and the meltingpoint is 137140 C. Elemental Anal. Calc. for C42H34O4As2: C,67.03; H, 4.55. Found: C, 66.94; H, 4.47%. ESI-MS: Calculated forsodiated species (1+Na+): 775.57; Found 775.48.

1H NMR (at 25 C, CDCl3): d 2.602.64 (t, J = 8 Hz, 4H, CH2-As);4.284.32 (t, J = 8 Hz, 4H, CH2-O); 7.087.10 (d, 2H, ArH fromAQ); 7.247.30 (m, 10H, ArH from phenyl ring); 7.427.52 (m,12H, ArH from phenyl ring); 7.767.78 (d, 2H, ArH from AQ).

13C NMR (at 25 C, CDCl3): 27.1; 67.7; 119.1; 119.9; 124.8;128.5; 128.7; 132.9; 133.5; 134.8; 139.4; 158.2; 182.2; 184.0.2.1. Materials and methods

1,8-bis(2-bromoethoxy)anthracene-9,10-dione [8] and 1,8-bis(2-phenylselenoethoxy)anthracene-9,10-dione (L2) [2b] weresynthesized by earlier available literature. Pd(PhCN)2Cl2 was alsosynthesized by an available procedure [9]. Triphenylarsine, lithiummetal, tetrabutylammonium hexauorophosphate and 2-chloro-2-methylpropane were purchased from Aldrich and used withoutpurication. CH3CN, THF, DMF and CH2Cl2 were purchased fromAldrich and puried using PURE SOLV solvent purication sys-tem. 1H NMR (400 MHz) and 13C NMR (100 MHz) spectra wereobtained on Bruker 400 MHz instrument at room temperatureusing deuterated solvents. Absorbance data were collected usinga HP 8452A diode array spectrophotometer and Varian Cary 50BIO. Luminescence titrations were conducted using a SPEX Fluoro-max uorimeter. Mass spectrometry was conducted using a Varian500-MS IT ESI mass spectrometer. Elemental analyses were con-ducted using an Exeter CE-440 Elemental analyzer. Melting pointswere determined using open capillaries and were uncorrected.Cyclic voltammograms were recorded in a CH instruments 660electrochemical workstation using dry methylene chloride as sol-vent and tetrabutylammonium hexauorophosphate as electrolyteunder nitrogen atmosphere.

X-ray quality crystals of compounds 1 and 2 were obtained byslow evaporation of a CHCl3:CH3OH solution. Crystallographic datafor 1 and 2 were collected at 100 K using a Bruker SMART APEX IIK. Mariappan et al. / Inorganic2.2.2. Synthesis of Pd(L1)Cl2 (1)L1 (0.1 g, 0.133 mmol) was dissolved in 10 mL of methylene

chloride and mixed with a solution containing 0.051 g7.87 (d, 2H, ArH from AQ).13C NMR (at 25 C, CDCl3): 22.7, 64.7, 117.8, 119.2, 128.6, 129.9,

131.0, 133.4, 133.7, 157.8, 181.2. All the peaks are very short evenafter running 5000 plus scans due to solubility issues.

2.2.3. Synthesis of Pd(L2)Cl2 (2)L2 (0.1 g, 0.163 mmol) was used instead of L1 to synthesize 2

with an identical procedure (0.063 g Pd(PhCN)2Cl2, 0.163 mmol)to 1 and crystallized using CHCl3CH3OH. Yield is 0.09 g (69%) ofdark red blocks crystals that were isolated and started decomposedabove 210 C. Elemental Anal. Calc. for C30H24O4Se2PdCl2: C, 45.97;H, 3.06. Found: C, 45.28; H, 2.96%.

1H NMR (at 25 C, CDCl3): d 2.822.88 (m, 2H, CH2-Se); 4.334.65 (m, 4H, CH2-O); 4.814.87 (m, 2H, CH2-Se); 7.128.08 (m,8H, ArH from AQ + Phenyl ring); 7.527.61 (m, 6H, ArH fromAQ + Phenyl ring); 7.827.86 (d, 2H, ArH from AQ).

13C NMR (at 25 C, CDCl3): 32.4, 66.6, 118.1, 119.2, 120.1, 129.7,133.2, 133.7, 134.7, 183.9. All the peaks are very short even afterrunning 5000 plus scans due to solubility issue.

2.2.4. Catalytic properties of 1 and 2Method A: A slight modication is done on a method available

in literature [13c]. A mixture of styrene (0.104 g, 1 mmol), bro-mobenzene (0.157 g, 1 mmol), DMF (5 mL), and complex 1 or 2in catalytic amounts (0.001 g, 0.001 mmol) was heated at100 C under inert atmosphere in the presence of a base (0.118 g,2 mmol of propyl amine) for 24 h. Stilbene formation was con-rmed by LC and GC mass spectrometry.

Method B: We were inspired by an literature report [7a] andadopted the following method. A mixture of styrene (0.208 g,2 mmol), bromobenzene (0.157 g, 1 mmol), n-butylamine(0.146 g, 2 mmol), p-xylene (3 mL) and complex 1 or 2 in catalyt-ic quantities (0.001 g, 0.001 mmol) was reuxed 24 h. Stilbenewas isolated as the product after working up the reaction usingmethylene chloride and dilute acid. Stilbene formation was con-rmed by GC MS.

Yield when using 1 as catalyst: 0%. Yield when using 2 as cata-lyst: 1020%. Stilbene yield is based on bromobenzene.

3. Results and discussion

3.1. Synthesis and NMR spectroscopy

The reaction of 1,8-bis(2-bromoethoxy)anthracene-9,10-dionewith diphenylarsino anion in THF under nitrogen (Scheme 1) givesL1 in 18% yield. Compound L1 is fully stable under ambient condi-tion and soluble in common organic solvents. The 1H NMR spec-trum of L1 has a doublet, a triplet and a doublet in the aromaticregion due to 1,8-oxydisubstitued anthraquinone derivative, andtriplets for CH2-O and CH2-As appear at 4.30 (J = 8 Hz) and 2.62

13(0.133 mmol) of Pd(PhCN)2Cl2 in 10 mL of methylene chloride.The solution was stirred for 2 h and all the solvents were evaporat-ed. The residue was dissolved in chloroform: methanol (8:2) mix-ture and evaporated slowly. Red-orange block shaped crystalswere obtained. The yield is 0.08 g of red orange blocks crystals thatwere isolated (64%) and melting point is above 160 C (dec).

Elemental Anal. Calc. for C42H34O4As2PdCl2: C, 54.24; H, 3.66.Found: C, 54.57; H, 3.70%.

1H NMR (at 25 C, CDCl3): d 3.123.16 (t, J = 8 Hz, 4H, CH2-As);4.004.04 (t, J = 8 Hz, 4H, CH2-O); 6.936.95 (d, 2H, ArH fromAQ); 7.247.37 (m, 10H, ArH from phenyl ring); 7.497.53 (t, 2H,

imica Acta 429 (2015) 4650 47(J = 8 Hz) respectively, in the aliphatic region. C NMR spectrumCH2-O and CH2-As signals appear at 67.8 ppm and 27.1 ppm. Weobserve two shorter peaks at 182.2 and 184.0 ppm that are due

Table 1Crystallographic data for 1 and 2.

1 2

Empirical formula C42H34As2O4 PdCl2 C30H24Se2O4PdCl2Wavelength Mo Ka 0.71073 Mo Ka 0.71073System SMART APEXII SMART APEXIITemperature (K) 100(2) 293(2)Crystal system monoclinic monoclinicSpace group P21/n P21/na () 10.9673(9) 10.3549(5)b () 20.3071(16) 16.4489(8)c () 17.0490(14) 32.2860(16)a () 90.00 90.00b () 105.5790(10) 92.0430(10)c () 90.00 90.00Volume (3) 3657.6(5) 5495.7(5)Z 4 8Dcalc (g cm3) 1.689 1.894Absorbtion coefcient

(mm1)2.492 3.556

F(000) 1856 3072h range 2.1725.47 1.7725.38Index ranges h(13,13), k(24,24),

l(20,20)h(12,12), k(19,19),l(38,38)

Reections collected 36346 54609Independent reections 6784 10104Observed reections 5481 9117Maximum/minimum

transition0.478/0.608 0.020.33

Data/restraints/parameters

6784/0/460 10104/0/703

Goodness-of-t 1.026 1.097Final R1 indices[I > 2r(I)] 0.0259 0.0253R1 indices (all data) 0.0403 0.0300CCDC Number 1004317 1004318

Se

O

Se

O

O

O

O O

O

O

Br Br

PhSe-

EtOH, N2

L2 CPd(PhCN)2Cl2L +

Scheme 1. Synthesis of ligand L1, L2

Fig. 1. Molecular structure of 1 (A) and 2 (B). Hydrogen atoms are not labeled. L1 andsquare planar geometry of Pd(II) in 1 is shown as insets (D).

48 K. Mariappan et al. / Inorganica ChAs

O

As

O OPh2As-

THF, N2

L1H2Cl2Pd(L)Cl2

and their palladium complexes.O

imica Acta 429 (2015) 4650to the two carbonyl groups in L1. The poor solubility of 1 and 2 inCDCl3 and in other deuterated solvent prevented a quality 13CNMR.

In the Pd(II) complex 1, the CH2-As signal in L1 deshielded by0.5 ppm (SI Fig. 5) and CH2-Se signal in L2 shifted by 0.3 ppm inthe 1H NMR spectra. These shifts support the interaction of arsenicand selenium with Pd(II). 1H and 13C NMR of L1, L2, 1 and 2 (SIFigs. 17) and LC MS of L1 (SI Fig. 8) are given as supplementarymaterial. NMR spectroscopic data, elemental analyses are in goodagreement with the structures and stoichiometry of L1, L2, 1 and2 proposed in Scheme 1.

3.2. X-ray crystallography

The molecular structures of 1 and 2 are shown in Fig 1. Crystal-lographic data for both 1 and 2 are given in Table 1, and selected

L2 formed a fourteen membered a buttery outline with Pd(II) (C). Slightly convex

Table 2Selected bond lengths () and bond angles () of 1 and 2. E = As in 1 and Se in 2.

1 2

C16E1 1.955(3) 1.970(3)C18E2 1.952(3) 1.972(3)C7O1 (C@O) 1.229(3) 1.224(4)C8O2 (C@O) 1.222(4) 1.219(3)PdE1 2.3889(4) 2.4252(3)PdE2 2.3999(4) 2.4336(4)PdCl1 2.3186(7) 2.2923(7)PdCl2 2.3140(7) 2.3052(8)C16E1Pd 120.60(9) 110.43(9)C18E2Pd 114.93(9 108.64(9)E1PdE2 168.332(14) 170.427(14)ClPdCl2 175.24(3) 174.06(3)

bond lengths and bond angles are given in Table 2. L1 and L2 actedas chelators and both pnictogenide and chalcogenide donors aretrans to each other in 1 and 2. The PdAs bond lengths [Pd

bonyl group in 2 is not involved in forming a coordinate covalent

A unique AsOAs ligand 1,8-bis(2-diphenylarsinoethoxy)an-thracene-9,10-dione (L1) has been prepared successfully; this isrst AQ-bipodand that contains arsenic as donors. L1 and 1,8-bis(2-phenylselenoethoxy)anthracene-9,10-dione (L2) react withbis(benzonitrile)palladium(II) chloride to form Pd(II) complexeswith the stoichiometry [PdCl2(L1)] and [PdCl2(L2)]. Relatively long

Br

+ Base, Solvent1 or 2

Scheme 2. Heck Reaction.

K. Mariappan et al. / Inorganica Chimica Acta 429 (2015) 4650 49bond with Pd(II). The selenium atoms in 2 have T shaped geome-tries and palladium(II) has a convex square planar geometry like1, but in 2, the Pd(II) geometry is closer to square which is clearlyobserved in the bond angles [Se1PdSe2 (170.427(14); Cl1PdCl2 (174.06(3)] around Pd(II).

3.3. Catalytic applications of 1 and 2

Pd(II) complexes especially with selenium donors [7] haveshown catalytic properties for the Heck reaction in the recent past,and these reports inspired us to study the catalytic properties of 1and 2 for the Heck reaction as per Scheme 2 [13c]. The catalyticproperties were studied using 0.001 mol% concentration of 1 and2 in presence of a base. Compound 2 was able to convert styreneinto stilbene (1020 yield) in both methods [SI Figs. 9 and 10]whereas compound 1 produced no stilbene [SI Fig. 10]. The solu-tion color changed from yellow-orange into brown/black afterheating when 1 was used as catalyst, and this may be due to theformation of palladium nanoparticles [14] by decomposition of 1in the course of the reaction. The crowded Pd(II) centers and for-mation of palladium NPs may be the reason for the non-catalyticactivity of 1. Having higher mol% of 1 did not improve the yieldof stilbene, and we are currently working on improving catalytic

Table 3Electrochemical data.As1 = 2.3889(4) ; PdAs2 is 2.3999(4) ] are similar to one anoth-er and match the literature [13a]. Typical PdCl interatomic [13b]distance average is 2.262.33 , and PdCl bond length in 1 alsomatches [PdCl1 = 2.3186(7) ; PdCl2 = 2.3140(7) ] an earlierreport [7a,13c]. In our previous reports [2], the intraannular car-bonyl group was involved in bonding; however, in 1 the carbonyloxygen is not involved in making a coordinate bond with Pd(II).

The arsenic atoms in 1 have a distorted tetrahedral geometryand palladium(II) has a convex square planar geometry, which isclearly reected in the bond angles [As1PdAs2 (168.332(14);Cl1PdCl2 (175.24(3)] around Pd(II). The improper square planargeometry of Pd(II) may be due to crowded arsenic donors.

The thermal ellipsoid diagram for 2 is shown in Fig. 1B. In 2, thePdSe bond lengths [PdSe1 = 2.4252(3) ; PdSe2 is 2.4336(4) ],and the PdCl bond lengths are [PdCl1 = 2.2923(7) ; PdCl2 = 2.3052(8) ] very similar to one another, and compare wellwith literature as well as 1 [7a,13c]. Like 1, the intraannular car-Compounds Ea1/2 (V)

Anthraquinone0/1 Anthraquinone1/2

L1 0.984 1.298L2 1.007 1.2351 1.001 1.2972 0.995 1.299

All measurements were done at room temperature using dry methylene chloride as sola Referenced vs. Ag/AgCl, glassy carbon, 1 mM in 0.1 M TBAH.b Irreversible.c Might be merged with selenium oxidation peak.4. Conclusions3.4. Cyclic voltammetry

The redox electrochemistries of L1, 1 and 2 were investigatedby means of cyclic voltammetry. Cyclic voltammetric measure-ments were carried out in 0.1 M tetrabutylammonium hex-auorophosphate (TBAH) using dry CH2Cl2 as solvent versus Ag/AgCl as the reference electrode under inert atmosphere. The anodicand cathodic peaks were used to calculate the E0 values that arelisted in Table 3. Compounds L1 (0.984 V and 1.298 V), L2(1.007 V & 1.297 V), 1 (1.001 V & 1.297 V) and 2 (0.995 V& 1.299 V) show two reversible couple, and we attribute thoseredox potentials to the anthraquinone [2c,d] moiety. L1, L2 andthe palladium complexes, 1 and 2 exhibit characteristic irreversibleoxidation peaks for arsenide and selenide [2d,15,16] moieties at+1.528, +1.224, +1.65 and +0.99 V, respectively, as expected. Palla-dium complexes 1, 2 produced additional irreversible reductionpeaks at 0.911 V and 0.732 V respectively, and an irreversibleoxidation peak at +0.61. We attribute these peaks may be due tothe palladium [17] metal center. Cyclic voltammogram of 1 isshown in Fig. 2. Cyclic voltammograms of triphenylarsine,Pd(PhCN)4Cl2 and 2 in dry methylene chloride are given in SIFig. 11.performance by synthesizing phosphorous analogue of L1 sincephosphorous ligand containing complexes are well known catalyst.

Fig. 2. Cyclic voltammogram of 1 in dry CH2Cl2 using 0.1 M TBAH vs. Ag/AgCl onglassy carbon.Arsenic/selenium oxidation Oxidation Reduction

1.528b 1.224b 1.65b +0.62 0.911b0.99b Not observedc 0.732b

vent under inert atmosphere.

PdAs and PdSe bond lengths are possibly due to the trans inu-ence of donor atoms on Pd(II). Both L1 and L2 form palladacycleswith 14 atoms in a ring, and Pd(II) roughly having a square planargeometries. Compound 2 shows a higher catalytic activity towardsthe Heck reaction than compound 1 and which may be due to itsinability to withstand high temperature which might be leadingthe formation of PdSe NPs as well crowded palladium center of 1.

Acknowledgements

Authors J.S.R. and K.M. greatly appreciate nancial support fromNSF Northern Plains Research Experience for Undergraduates(CHE-1063000), United States. NSF-EPSCoR (EPS-0554609) andthe South Dakota Governors 2010 Initiative are appreciated onaccount of the purchase of a Bruker SMART APEX II CCD diffrac-tometer. NSF-URC (CHE 0532242), United States also providedfunding for the purchase of elemental analyzer.

Appendix A. Supplementary material

CCDC 1004317 (1) and 1004318 (2) contain the supplementarycrystallographic data for this paper. These data can be obtainedfree of charge from The Cambridge Crystallographic Data Centrevia www.ccdc.cam.ac.uk/data_request/cif. Supplementary dataassociated with this article can be found, in the online version, at

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Palladium(II) complexes of anthraquinone-based AsOAs type and SeOSe type bipodands. Synthesis, X-ray crystallography and catalytic properties1 Introduction2 Experimental2.1 Materials and methods2.2 Synthesis2.2.1 Synthesis of 1,8-bis(2-diphenylarsinoethoxy)anthracene-9,10-dione (L1)2.2.2 Synthesis of Pd(L1)Cl2 (1)2.2.3 Synthesis of Pd(L2)Cl2 (2)2.2.4 Catalytic properties of 1 and 2

3 Results and discussion3.1 Synthesis and NMR spectroscopy3.2 X-ray crystallography3.3 Catalytic applications of 1 and 23.4 Cyclic voltammetry

4 ConclusionsAcknowledgementsAppendix A Supplementary materialReferences