Inorganica Chimica Acta 362 (2009) 407–413

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Inorganica Chimica Acta

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A dinuclear vanadium compound with 24-membered macrocycle generated viaformation of S–C bonds

Lian Chen, Fei-Long Jiang, Wei-Ping Su, Cheng-Yang Yue, Da-Qiang Yuan, Mao-Chun Hong *

State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fujian, Fuzhou 350002, China

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

� 0

Article history:Received 23 January 2007Received in revised form 15 April 2008Accepted 15 April 2008Available online 22 April 2008

Keywords:Vanadium compoundS–C bondAcetylacetoneCrystal structure

0020-1693/$ - see front matter � 2008 Elsevier B.V. Adoi:10.1016/j.ica.2008.04.026

* Corresponding author. Tel.: +86 591 83792460; faE-mail address: hmc@fjirsm.ac.cn (M.-C. Hong).

A dinuclear vanadium 24-membered macrocycle with double-ring, [V2O2L2(l-CH3COO)] (H2L = 3,3 -(1,3,4-thiadiazole-2,5-diyl)bis(sulfane-diyl) bis(4-hydroxypent-3-en-2-one)), was prepared in high yieldfrom the reaction of VO2(acac) with 2,5-dimercapto-1,3,4-thiadiazole dipotassium salt (K2SSS) and ace-tylacetone (Hacac) at room temperature. Its closure of 24-membered macrocycle has resulted from theformation of U-shape units via S–C bonding between original SSS2� and acac� ligands, while the bridgingCH3COO� has created from an unexpected decomposition of Hacac. The obtained two products werecharacterized by single crystal X-ray diffraction, XRD, ESR, TGA and magnetism analyses. A possiblemechanism for formation of the bimetal 24-membered macrocycle has been discussed.

� 2008 Elsevier B.V. All rights reserved.

1. Introduction

The family of vanadium compounds has received tremendousinterest for a long time due to its rich applications in many fields[1–7]. It plays an important role in many enzymatic reactions suchas halogenation of organic substrate and fixation of nitrogen[8–10]. And in vivo, it also shows insulin-mimetic response whichcan simulate the uptake and metabolism of glucose [11–13]. One ofthe most important properties of the vanadium complexes, whichconsiderable effort has been devoted to, is that the compoundspossess versatile valence states and unusual redox ability. Com-monly, vanadium can exist with trivalence, tetravalence, pentava-lence and versatile mixed-valence states. It has been documentedthat high-valenced vanadium has strong redox ability which canlead to some important reactions [14,15]. Recently, vanadium-cat-alyzed bromination and cyclization of terpenes has been reported,showing amazing catalysis ability of this kind of high-valencedcompounds [16]. Herein, we report two novel vanadium com-pounds, (Et4N)[V2O2L2(l-CH3COO)] (1) and (Et3NH)- [V2O2L2(l-CH3COO)] � H2O (2) (H2L = 3,30-(1,3,4-thiadiazole-2,5-diyl)bis(sul-fane-diyl)bis(4-hydroxypent-3-en-2-one)), which possess a dinu-clear vanadium 24-membered macrocycle with double-ring,formed by coupling an acac ligand of VO2(acac) (acac = acetylace-tonate) with a thiolate in the high-valenced vanadium system.

Collman [17,18] and others [19] disclosed around 40 years agothat metal acetylacetonates possess quasi-aromatic properties andundergo electrophilic substitutions at the central carbon of an ace-

ll rights reserved.

x: +86 591 83714946.

tylacetonate with an array of electrophiles. Recently, these reac-tions have been used for modification of metal acetylacetonatecomplexes, for example, c-halogenation of iridium acetylaceto-nates [20] and syntheses of new compounds [21,22]. Among thesereported reactions, a C–S bond was formed from electrophilic at-tack on a metal acetylacetonate by a arylsulfenyl chloride or thio-cyanogen which are both electrophiles [18]. In our reaction systemwith the high-valenced vanadium, we have observed that a VO2-(acac) reacted with a nucleophilic thiolate, such as 2,5-dimer-capto-1,3,4-thiadiazole dipotassium salt (K2SSS), to lead to theformation of C–S bonds. Moreover, the bridging CH3COO� unitsfound in 1 and 2 are constructed through an unexpected decompo-sition of the acetylacetone.

2. Experimental

2.1. Materials and measurements

All chemical reagents are commercially available without fur-ther purification except that VO2(acac) was prepared as describedin the literature [23]. The IR spectrum was recorded on a Perkin–Elmer Spectrum One FT-IR spectrometer using the KBr pellet tech-nique in range of 4000–400 cm�1. Elemental analyses of C, H and Nwere carried out by Elemental Vario EL III microanalyzer. X-raypowder diffraction patterns were taken by a Philips X’PertPW3040/X0 diffractometer with Cu Ka radiation. The polycrystal-line powder EPR spectra were recorded with a Bruker ER-420 spec-trometer employing X-band radiation and a cylindrical cavity with100 kHz magnetic field modulations. The polycrystalline magneticsusceptibility data were collected on a Quantum Design PPMS

408 L. Chen et al. / Inorganica Chimica Acta 362 (2009) 407–413

model 6000 magnetometer in the temperature range from 2 to300 K. Thermogravimetric analyses (TGA) were performed on aNETZSCH STA 449C simultaneous TG-DSC instrument.

2.2. Synthesis

2.2.1. Synthesis of (Et4N)[V2O2L2(l-CH3COO)] (1)To the solution of VO2(acac) (91 mg, 0.5 mmol) in acetonitrile

(25 ml), Hacac (0.1 ml, 0.97 mmol), K2SSS (228 mg, 1 mmol) andEt4NCl � H2O (92 mg, 0.5 mmol) were added in order and stirredat room temperature. About 30 min the reddish-brown mixturesolution slowly changed to green clear. The green filtrate was keptat room temperature for crystallization. About 1 day later, thegreen crystals of 1 (225 mg) suitable for X-ray diffraction were ob-tained. The yield was 89%. The same reaction procedure withoutacetic acid can also obtained compound 1 with the considerableyield (ca. 75%). Its purity was also confirmed by XRD powder dif-fraction (Fig. 4). Anal. Calc. for (Et4N)[V2O2L2(l-CH3COO)]: C,40.35; H, 4.68; N, 6.92. Found: C, 40.46; H, 4.83; N, 6.87%. IR(KBrpellet): 3434(br, w), 2995(w), 2927(w), 1609(vs, sh), 1567(vs),1476(m), 1410(s), 1375(vs, sh), 1337(s, sh,) 1184(w), 1075(m),1053(s, sh), 1018(m), 957(s, sh), 914(w), 698(m), 657(m),618(m), 495(s) and 456(s) cm�1.

2.2.2. Synthesis of (Et3NH)[V2O2L2(l-CH3COO)] � H2O (2)Compound 2 was prepared in an 82% yield by the similar method

using Et3N instead of Et4NCl. Anal. Calc. for (Et3NH)[V2O2L2-(l-CH3COO)] � H2O: C, 38.36; H, 4.53; N, 6.99. Found: C, 39.30; H,4.08; N, 7.19%. IR(KBr pellet): 3444(br, w), 2925(w), 1601(m),1567(vs), 1373(s, sh), 1335(s, sh),1075(w), 1057(m), 1020(w),962(m), 915(w), 699(m), 658(w),618(w), 497(m) and 458(m) cm�1.

2.3. Crystallographic studies

Intensity data were collected on a Rigaku mercury CCD diffrac-tometer with graphite-monochromated Mo Ka (k = 0.71073 Å)

Table 1Crystallographic data for compounds 1, 2 and H2L

Compound 1 2 H2L

Formula C34H47N5O12S6V2 C32H45N5O13S6V2 C24H28N4O8S6

Formula weight 1012.01 1001.99 692.86Crystal size (mm) 0.50 � 0.45 � 0.30 0.45 � 0.25 � 0.10 0.40 � 0.30

�0.10Crystal system monoclinic monoclinic monoclinicSpace group C2/c C2/m P21/na (Å) 17.7965(15) 12.7260(13) 12.9125(8)b (Å) 11.9138(9) 18.1732(14) 8.7103(5)c (Å) 21.1952(19) 11.6032(13) 13.7542(18)b (�) 101.257(4) 114.250(4) 95.274(4)V (Å3) 4407.4(6) 2446.7(4) 1540.41(16)Z 4 2 2Dc (Mg m�3) 1.525 1.360 1.494l (mm�1) 0.771 0.696 0.496F(000) 2096 1036 720T (K) 293(2) 293(2) 293(2)k (Mo Ka) (Å) 0.71073 0.71073 0.71073Reflections collected 16019 9397 11192Reflections unique 5032 2874 3505Parameters 275 171 202Goodness-of-fit on F2 1.033 1.047 1.011R1, wR2 (I > 2r(I))a 0.0420, 0.0810 0.0628, 0.1859 0.0358,

0.0940R1, wR2 (all data)b 0.0494, 0.0849 0.0698, 0.1955 0.0424,

0.0985Maximum, minimum Dq

(e �3)0.268 and �0.302 1.188 and �0.413 0.265 and

�0.166

a R1 ¼PðjjFoj � jFcjjÞ=

PjFoj.

b wR2=fP

w½ðF2o � F2

c Þ2�=P

w½ðF2oÞ

2�g1=2.

radiation by using the x–2h scan method at room temperature.The structure was solved with direct methods and refined on F2

with full-matrix least-squares methods using SHELXS-97 and SHELXL-97 programs, respectively [24,25]. All non-hydrogen atoms wererefined anisotropically. All hydrogen atoms were added in the rid-ing model and refined isotropically with C–H = 0.93 Å, N–H = 0.86 Å. The crystallographic data of 1 and 2 and the byproductH2L are summarized in Table 1, and the selected bond lengths andbond angles are listed in Table 2.

3. Results and discussion

3.1. Synthesis

The room temperature reaction of VO2(acac), SSS2� and addi-tional Hacac without the presence of acetic acid affords a dinuclearvanadium 24-membered macrocycle, [V2O2L2(l-CH3COO)]�, con-taining an acetate anion. With the addition of acetic acid to abovereaction system, the acetate containing compounds 1 and 2 canalso be obtained. The systematic experiments have been carriedout to confirm above unusual C–S bonding reaction and to findout its optimum reaction condition. The crystalline compound 1is stable in the air while compound 2 is not, but both of themcan easily be reproduced in high yields with either of K2SSS andH2SSS in CH3CN or CH2Cl2 solvents. During the course of mecha-nism research, the colorless crystalline material of H2L as an inter-mediate product has been successfully isolated from this reactionsystem,1 which is helpful for understanding the mechanism respon-sible for formation of bimetal 24-membered macrocycle.

3.2. Structural description

Since structural analyses show that compounds 1 and 2 areboth dinuclear vanadium compound and contain the same dou-ble-ring building unit [V2O2L2(l-CH3COO)]� (Fig. 1), compound 1is selected to represent their structures. It is clearly establishedthat a bidentate thiolate links to two acetylacetonates via C–Sbonding to form a U-shaped ligand L. In this anionic structure,coordination of two U-shaped L ligands to two vanadium ions gen-erates a 24-membered macrocycle that encapsulates an acetate an-ion as a guest to link two vanadium centers forming 16-membereddouble ring. Two vanadium atoms each adopts a distorted octahe-dron coordination geometry with four oxygen atoms from two L li-gands occupying equatorial positions and two oxygen atomsoccupying two axial positions, where one oxygen is terminal andthe other is from acetate anion. The axial V@O bond distance of ter-minal oxygen (1.5930(15) Å) is 0.4 Å shorter than those of equato-rial oxygen atoms (1.9956(14)–2.0121(15) Å) [26], while the otheraxial V–O bond (2.1724(14) Å) is significantly longer than equato-rial V–O bonds due to trans effect of V@O bond. The acetate anionbridges two vanadium ions and, presumably, plays the role of atemplate in forming ring. The atoms of metal acetylacetonate rings(V1/O1/O2/C2/C3/C4) are almost coplanar with the mean deviationfrom the plane 0.0407 Å, and the thiadiazole plane (S2/C13/C14/N1/N2) are nearly perpendicular to the six-membered metal ace-tylacetonate ring with the dihedral angle 85�. The bond distancesof S1–C3, S3–C8#1 are 1.7700(14) and 1.774(2) Å, respectively,which are close to the similar S–C bond distances reported in theliterature [27].

In the solid state of compound 1, intermolecular S� � �S distance(3.493 Å) is significantly shorter than the van der Waals distance(S� � �S = 3.7 Å), indicating that S� � �S interactions exist. Thus, S� � �S

1 The H2L was obtained as a byproduct in the reaction in the crystal form. Thecrystal data were described in Table 1.

Table 2Selected bond lengths (Å) and angles (�) for (1) and (2)

Compound (1)V(1)–O(5) 1.5930(15) N(2)–C(14) 1.296(3)V(1)–O(2) 1.9956(14) N(3)–C(18) 1.513(3)V(1)–O(1) 1.9964(14) N(3)–C(18)#1 1.513(3)V(1)–O(4) 2.0004(14) N(3)–C(16) 1.520(3)V(1)–O(3) 2.0121(15) N(3)–C(16)#1 1.520(3)V(1)–O(6) 2.1724(14) C(1)–C(2) 1.496(3)S(1)–C(13) 1.747(2) C(2)–C(3) 1.421(3)S(1)–C(3) 1.7700(19) C(3)–C(4) 1.418(3)S(2)–C(13) 1.734(2) C(4)–C(5) 1.501(3)S(2)–C(14) 1.735(2) C(6)–C(7) 1.505(3)S(3)–C(14) 1.751(2) C(7)–C(8) 1.415(3)S(3)–C(8)#1 1.774(2) C(8)–C(9) 1.417(3)O(1)–C(2) 1.261(2) C(8)–S(3)#1 1.774(2)O(2)–C(4) 1.265(2) C(9)–C(10) 1.509(3)O(3)–C(7) 1.262(2) C(11)–O(6)#1 1.2515(19)O(4)–C(9) 1.260(2) C(11)–C(12) 1.512(5)O(6)–C(11) 1.2515(19) C(15)–C(16) 1.496(4)N(1)–C(13) 1.298(3) C(17)–C(18) 1.503(4)N(1)–N(2) 1.391(3)

O(5)–V(1)–O(2) 95.91(8) O(1)–C(2)–C(1) 114.9(2)O(5)–V(1)–O(1) 95.39(8) C(3)–C(2)–C(1) 120.95(19)O(2)–V(1)–O(1) 87.50(6) C(4)–C(3)–C(2) 123.95(17)O(5)–V(1)–O(4) 97.87(8) C(4)–C(3)–S(1) 118.21(16)O(2)–V(1)–O(4) 89.59(6) C(2)–C(3)–S(1) 117.82(15)O(1)–V(1)–O(4) 166.65(6) O(2)–C(4)–C(3) 123.41(19)O(5)–V(1)–O(3) 96.76(8) O(2)–C(4)–C(5) 113.8(2)O(2)–V(1)–O(3) 167.17(6) C(3)–C(4)–C(5) 122.75(19)O(1)–V(1)–O(3) 93.29(6) O(3)–C(7)–C(8) 124.2(2)O(4)–V(1)–O(3) 86.71(6) O(3)–C(7)–C(6) 114.7(2)O(5)–V(1)–O(6) 176.57(8) C(8)–C(7)–C(6) 121.1(2)O(2)–V(1)–O(6) 85.43(6) C(7)–C(8)–C(9) 123.80(18)O(1)–V(1)–O(6) 81.50(6) C(7)–C(8)–S(3)#1 118.07(17)O(4)–V(1)–O(6) 85.28(6) C(9)–C(8)–S(3)#1 118.13(17)O(3)–V(1)–O(6) 82.03(6) O(4)–C(9)–C(8) 123.7(2)C(13)–S(1)–C(3) 101.57(9) O(4)–C(9)–C(10) 114.1(2)C(13)–S(2)–C(14) 86.17(10) C(8)–C(9)–C(10) 122.2(2)C(14)–S(3)–C(8)#1 101.29(9) O(6)#1–C(11)–O(6) 123.2(3)C(2)–O(1)–V(1) 129.58(14) O(6)#1–C(11)–C(12) 118.38(14)C(4)–O(2)–V(1) 130.31(14) O(6)–C(11)–C(12) 118.38(14)C(7)–O(3)–V(1) 130.12(15) N(1)–C(13)–S(2) 114.91(17)C(9)–O(4)–V(1) 131.08(15) N(1)–C(13)–S(1) 122.52(16)C(11)–O(6)–V(1) 142.54(16) S(2)–C(13)–S(1) 122.53(11)C(13)–N(1)–N(2) 111.84(18) N(2)–C(14)–S(2) 114.58(18)C(14)–N(2)–N(1) 112.49(18) N(2)–C(14)–S(3) 122.41(17)O(1)–C(2)–C(3) 124.19(18) S(2)–C(14)–S(3) 122.99(12)

Compound (2)V(1)–O(3) 1.596(3) C(1)–C(2) 1.509(5)V(1)–O(2) 1.998(2) S(2)–C(6)#2 1.734(3)V(1)–O(2)#1 1.998(2) S(2)–C(6) 1.734(3)V(1)–O(1) 2.001(2) O(2)–C(4) 1.271(4)V(1)–O(1)#1 2.001(2) C(2)–C(3) 1.420(5)V(1)–O(4) 2.176(3) C(3)–C(4) 1.407(5)S(1)–C(6) 1.749(4) O(4)–C(7)#4 1.175(4)S(1)–C(3) 1.780(3) O(4)–C(7) 1.175(4)O(1)–C(2) 1.267(4) C(4)–C(5) 1.502(5)N(1)–C(6) 1.297(4) C(7)–O(4)#4 1.175(4)N(1)–N(1)#2 1.383(6) C(7)–C(8) 1.80(3)

O(3)–V(1)–O(2) 97.40(7) C(11)–N(2)–C(9)#3 99.7(19)O(3)–V(1)–O(2)#1 97.40(7) C(11)–N(2)–C(9) 99.7(19)O(2)–V(1)–O(2)#1 165.19(14) C(9)#3–N(2)–C(9) 130(3)O(3)–V(1)–O(1) 96.00(8) O(1)–C(2)–C(3) 123.4(3)O(2)–V(1)–O(1) 86.85(9) O(1)–C(2)–C(1) 115.6(3)O(2)#1–V(1)–O(1) 91.61(9) C(3)–C(2)–C(1) 121.0(4)O(3)–V(1)–O(1)#1 96.00(8) C(4)–C(3)–C(2) 124.0(3)O(2)–V(1)–O(1)#1 91.61(9) C(4)–C(3)–S(1) 118.3(3)O(2)#1–V(1)–O(1)#1 86.85(9) C(2)–C(3)–S(1) 117.6(2)O(1)–V(1)–O(1)#1 168.00(15) C(7)#4–O(4)–V(1) 159.6(4)O(3)–V(1)–O(4) 180.0 C(7)–O(4)–V(1) 159.6(4)O(2)–V(1)–O(4) 82.60(7) O(2)–C(4)–C(3) 123.9(3)O(2)#1–V(1)–O(4) 82.60(7) O(2)–C(4)–C(5) 114.9(3)O(1)–V(1)–O(4) 84.00(8) C(3)–C(4)–C(5) 121.2(3)O(1)#1–V(1)–O(4) 84.00(8) N(1)–C(6)–S(2) 115.2(3)

Fig. 1. ORTEP representation of the double-ring structure of 1. The thermal ellipsoidare drawn at 30% probability.

Table 2 (continued)

C(6)–S(1)–C(3) 101.87(14) N(1)–C(6)–S(1) 122.1(3)C(2)–O(1)–V(1) 130.5(2) S(2)–C(6)–S(1) 122.77(18)C(6)–N(1)–N(1)#2 112.0(2) O(4)#4–C(7)–O(4) 139.1(7)C(6)#2–S(2)–C(6) 85.6(2) O(4)#4–C(7)–C(8) 110.3(4)C(4)–O(2)–V(1) 130.4(2) O(4)–C(7)–C(8) 110.3(4)

Symmetry transformations used to generate equivalent atoms: #1 �x, y, �z + 1/2for 1; #1 �x, y, �z + 1; #2 x, �y + 1, z; #3 �x, �y + 1, �z + 1; #4 x, �y, z for 2.

L. Chen et al. / Inorganica Chimica Acta 362 (2009) 407–413 409

contacts link neighboring rings to afford an infinite supramolecularchain (Fig. 2.). However, as a result of difference in counter cations,no intermolecular S� � �S interaction is observed in the solid state ofcompound 2. Compounds 1 and 2 contain different counteranionswith Et4N+ for 1 and Et3NH+ for 2, respectively. To balance thecharge, the two vanadium atoms in the double-ring unit are bothconsidered to be in V4+oxidation states. The assignments are ingood agreement with the results of total bond valence calculations(4.089 for 1 and 4.074 for 2, respectively). As shown in Fig. 3, thedouble-ring building units are arranged somewhat differently intwo compounds, but both show the large one-dimensionalchannels.

3.3. XRD, EPR, magnetism and TGA

The homogeneities of compound1 is confirmed by X-ray pow-der diffraction analyses (XRD, see Fig. 4). Their peaks are in goodagreement with those calculated from X-ray single crystal diffrac-tion data. X-band EPR spectra of 1 and 2 were recorded in solidstate both at room temperature (298 K) and 77 K. As shown inFig. 5, compound 1 in the solid state give the paramagnetic signalwith g = 1.9887 and 1.9843 at 298 and 77 K, respectively, indicat-ing the existence of V4+ [28]. The EPR responds of 2 are similar to1, with g = 2.0017 and 2.1136 at 298 K and 77 K (Fig. S1).

The room temperature magnetic moments of the compoundsare given in Fig. 6. Both two compounds obey the Curie–Weisslaw and exhibit very weak antiferro-magnetic interaction withJ = �0.58(1) and �0.634(1), respectively. The effective magneticmoments of 2.46 lB for compound 1 and 2.44 lB for compound 2at 300 K are close to the theoretical value (2.44 lB) of two spin-only V4+ ions in the double ring, which confirming the valence stateassignments speculated from charge balance and bond valencecalculations.

Thermal gravimetric analyses (TGA) of compounds 1 and 2 car-ried out in a flow of air atmosphere. As shown in Fig. 7, the frame-work of structure for compound 1 remains intact when thetemperature rises up to 244 �C. Undergo several overlapping steps,the compound reaches the maximum mass loss at 553 �C. The

Fig. 2. The close S� � �S contacts linked the neighboring double-ring units forming an infinite supramolecular chain in compound 1.

Fig. 3. Different arrangement of compounds 1 and 2.

10 20 30

10 20 30

Inte

nsity

Inte

nsity

Calc.

2 (ºC)θ

Find

Fig. 4. Experimental X-ray powder pattern (top) and calculated X-ray powder pattern (bottom) of compound 1.

Fig. 5. EPR spectra of compound 1: (a) at room temperature; (b) at 77 K.

410 L. Chen et al. / Inorganica Chimica Acta 362 (2009) 407–413

Fig. 6. Temperature dependence of the corrected molar magnetic susceptibility vM and the experimental magnetic moment data of compounds 1 (top) and 2 (bottom).

0 200 400 600 800 1000Temperature /ºC

20

30

40

50

60

70

80

90

100

TG /%

2

1

Mass Change: -80.70 %

Mass Change: -82.27 %

Fig. 7. TG curves of1 and 2 measured under flowing air.

L. Chen et al. / Inorganica Chimica Acta 362 (2009) 407–413 411

residue weight 19.3% (calcd: 18.6%) corresponds to V2O5. Com-pound 2 is less stable than 1. It starts the thermal decomposition

at 77.1 �C and gives the final product V2O5 at 422 �C with the totalmass loss of 17.7% (calculated mass loss of 17.8%).

412 L. Chen et al. / Inorganica Chimica Acta 362 (2009) 407–413

3.4. Decomposition of the acetylacetone and the formation of S–C bond

Interestingly, the unexpected CH3COO� units in 1 and 2 are cre-ated from the decomposition of the acetylacetone. However, such aphenomenon is not without precedence [29]. The acetylacetone aswell as hexafluoroacetylacetone can decompose and generate ace-tate and trifluoroacetate anion under some conditions [29,30]. Fur-thermore, alcoholysis of acetylacetone has been reported in recentyears [31]. According to these literatures, we assumed that, in oursystem, acetylacetone may undergo the retro-Claisen condensationreaction and produce a propanone and a acetate anion in the exis-tence of trace H2O which may comes from air, crystallization waterof Et4NCl and unpurified solvents (Scheme 1).

The coupling of metal acetylacetonate with a thiolate seems tobe different from electrophilic substitution on metal acetylaceto-nate reported in the literature [17–21], since the thiolate is a nucle-

Scheme 1. Decomposition of acetylacetone in the presence of trace water.

Scheme 2. Proposed route for th

ophilic reagent. In contrast, the attempted reaction of a thiolatewith a fluorinated analogues, such as (CF3COCHCOCF3)VO2, underthe same condition did not generate the expected products, sug-gesting the observed C–S formation reaction might proceedthrough electrophilic substitution process because electron-with-drawing group cause a decrease in reactivity. In view of the factthat vanadium(V) complexes can oxidize thiolates into disulfidesthrough reducing themselves to vanadium(IV) [32], we believe thata thiolate was oxidized into a disulfide in our reaction. And it wasindeed observed that the color of reaction mixture changed frombrown red to green, the characteristic color for vanadium(IV) ions,and the resulting products 1 and 2 are vanadium(IV) compounds.Thus, very likely, a disulfide acted as a real reactant and partici-pated in an electrophilic substitution reaction for C–S bond forma-tion [18]. Based on the literature precedents [33,34] and theintermediate product H2L we found in this reaction system, a rea-sonable mechanism for the production of 1 and 2 can be postulated(Scheme 2). As the redox reactions occur between the startingmaterial VO2(acac) and SSS2�, the observed U-shape H2L may formfrom disulfide and Hacac via C–S bonding, in which the thiolate–Sof disulfide substitutes the c-position of Hacac. Thus, it seems pos-sible that the U-shape dimeric product [VO(OH)]2L could be gener-ated by similar way through the VO(OH)(acac) and disulfide.Eventually, further coordination between two intermediate prod-ucts of [VO(OH)]2L and H2L in the present of CH3COO� would af-ford the final products 1 and 2.

e formation of compound 1.

L. Chen et al. / Inorganica Chimica Acta 362 (2009) 407–413 413

4. Conclusion

In summary, we have described two dinuclear vanadium com-pounds generated by coupling a metal acetylacetonate with a thio-late via C–S bond formation in high yield under the mild reactioncondition. Single crystal X-ray diffraction, XRD, ESR, TGA and mag-netism analyses have been done to characterize the compounds.Based on our observation and the relative researches reported byothers, we believe that, in this reaction system, C–S bond forma-tion results from electrophilic substitution of methine hydrogenin the metal acetylacetonate ring with disulfides, while a part ofacetylacetone is decomposed to acetate anion.

Acknowledgements

This work was supported by the Grants of 973 Program(2006CB932900), National Nature Science Foundation of Chinaand Nature Science Foundation of Fujian Province.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.ica.2008.04.026.

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