[2+ 2] Cycloaddition of Carbon Disulfide to NCN-Chelated

Sep 17, 2010 - Georgy K. Fukin , Maxim A. Samsonov , Alla V. Arapova , Anton S. Mazur , Tatiana O. Artamonova , Mikhail A. Khodorkovskiy , Aleksander ...
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Organometallics 2010, 29, 4486–4490 DOI: 10.1021/om100613x

[2 þ 2] Cycloaddition of Carbon Disulfide to NCN-Chelated† Organoantimony(III) and Organobismuth(III) Sulfides: Evidence for Terminal Sb-S and Bi-S Bonds in Solution‡ )

 Libor Dost al,*,§ Roman Jambor,§ Ales Ruzicka,§ Robert Jirasko, Eva Cerno skova,^ ^ # Ludvı´ k Benes, and Frank de Proft §

)

Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentsk a 573, CZ-53210 Pardubice, Czech Republic, Department of Analytical Chemistry, Faculty of Chemical Technology, University of Pardubice, Studetsk a 573, CZ-532 10 Pardubice, Czech Republic, ^Joint Laboratory of Solid State Chemistry of Institute of Macromolecular Chemistry of Academy of Sciences of Czech Republic, vvi and University of Pardubice, Studentsk a 84, CZ-53210 Pardubice, Czech Republic, and #Eenheid Algemene Chemie (ALGC), Vrije Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussels, Belgium Received June 24, 2010

The organoantimony(III ) and organobismuth(III ) sulfides (LMS)2 (L = NCN chelating ligand, C6H3-2,6-(CH2NMe2)2; M = Sb (1), Bi (2)) are dimeric in the solid state. Nevertheless, their monomeric structures with terminal Sb-S and Bi-S bonds present in solution were trapped by [2 þ 2] cycloaddition reactions with CS2, giving the molecular trithiocarbonates LMS2CdS (M = Sb (3), Bi (4)). Both compounds were characterized in the solid state by X-ray diffraction techniques on both single crystals and powder material and by IR spectroscopy. Carbon disulfide can be easily eliminated from the trithiocarbonates 3 and 4 by heating to 120 C ( for 3) and 160 C ( for 4) to recover the starting sulfides 1 and 2. In solution, trithiocarbonates 3 and 4 exist in equilibrium with starting sulfides 1 and 2, but this equilibrium may be shifted to pure 3 and 4 by addition of an excess of CS2, as shown by 1H NMR spectroscopy.

The preparation and characterization of compounds containing terminal (formally double) bonds between heavier main group 14 and 15 elements and chalcogens (S, Se, or Te), i.e. monomeric molecular chalcogenides, have attracted much attention recently.1 Syntheses of such compounds required using sterically overcrowded ligands for effective kinetic stabilization to prevent self-condensation and/or polymerization of these compounds to give various ring systems etc. In such a way, several terminal (double) bonds were stabilized and described.2 We have recently shown that using the NCN chelating ligand (C6H3-2,6-(CH2NMe2)2, denoted as L hereafter) enabled us to stabilize LSb-Se and LSb-Te terminal bonds, thanks to the effective rigid tridentate coordination of the ligand L. The presence of intramolecular nitrogen to antimony interactions †

NCN designates the NCN chelating ligand C6H3-2,6-(CH2NMe2)2 Dedicated to Prof. Dietmar Seyferth in recognition of his outstanding contribution to the development of Organometallics as an excellent platform for the presentation of organometallic chemistry. *To whom correspondence should be addressed. E-mail: libor. [email protected]. Fax: þ420 466037068. Tel: þ420 466037163. (1) (a) Sasamori, T.; Tokitoh, N. Dalton Trans. 2008, 1395. (b) Power, P. P. Chem. Rev. 1999, 99, 3463. (c) Tokitoh, N.; Okazaki, R. Adv. Organomet. Chem. 2001, 47, 121. (2) For example, see: (a) Saito, M.; Tokitoh, N.; Okazaki, R. J. Am. Chem. Soc. 2004, 126, 15572. (b) Tokitoh, N.; Matsumoto, T.; Okazaki, R. Bull. Chem. Soc. Jpn. 1999, 72, 1665. (c) Tokitoh, N.; Matsuhashi, Y.; Okazaki, R. Tetrahedron Lett. 1991, 32, 6151. (d) Tokitoh, N.; Saito, M.; Okazaki, R. J. Am. Chem. Soc. 1993, 115, 2065. (e) Saito, M.; Tokitoh, N.; Okazaki, R. J. Organomet. Chem. 1995, 499, 43. (f ) Suzuki, H.; Tokitoh, N.; Nagase, S.; Okazaki, R. J. Am. Chem. Soc. 1994, 116, 11578. ‡

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in the case of the ligand L substituted the steric (kinetic) protection of the terminal Sb-Se and Sb-Te bonds in these compounds. As a consequence of these dative connections, the Sb-Se and Sb-Te terminal bonds are strongly polarized with a partial positive charge on the antimony atom.3 Similar ligand systems using the advantage of the intramolecular chelatation of the central metal atom facilitated the preparation of other molecular main-group chalcogenides, with terminal metal-chalcogen bonds.4 In contrast to the NCN-chelated antimony selenide and telluride,3 the organoantimony5 and organobismuth6 sulfides (3) Dostal, L.; Jambor, R.; Ruzicka, A.; Lycka, A.; Brus, J.; de Proft, F. Organometallics 2008, 27, 6059. (4) For example, see: (a) Kuchta, M. C.; Parkin, G. Coord. Chem. Rev. 1998, 176, 323. (b) Kuchta, M. C.; Parkin, G. J. Am. Chem. Soc. 1994, 116, 8372. (c) Leung, W.-P.; Kwok, W.-H.; Law, L. T. C.; Zhou, Z.-Y.; Mak, T. C. W. J. Chem. Soc., Chem. Commun. 1996, 505. (d) Leung, W.-P.; Kwok, W.-H.; Zhou, Z.-Y.; Mak, T. C. W. Organometallics 2000, 19, 296. (e) Pineda, L. W.; Jancík, V.; Oswald, R. B.; Roesky, H. W. Organometallics 2006, 25, 2384. (f ) Ding, Y.; Ma, Q.; Roesky, H. W.; Uson, I.; Noltemeyer, M.; Schmidt, H. G. Dalton Trans. 2003, 1094. (g) Kuchta, M. C.; Parkin, G. Chem. Commun. 1996, 1669. (h) Kuchta, M. C.; Parkin, G. J. Chem. Soc., Chem. Commun. 1994, 1351. (i) Veith, M.; Becker, S.; Huch, V. Angew. Chem., Int. Ed. 1989, 28, 1237. ( j) Aray, P.; Boyer, J.; Carre, F.; Corriu, R.; Lanneau, G.; Lapasset, J.; Perrot, M.; Priou, C. Angew. Chem., Int. Ed. 1989, 28, 1016. (5) Dostal, L.; Jambor, R.; Ruzicka, A.; Jirasko, R.; Lochar, V.; Benes, L.; de Proft, F. Inorg. Chem. 2009, 48, 10495. (6) Breunig, H. J.; Koenigsmann, L.; Lork, E.; Nema, M.; Philipp, N.; Silvestru, C.; Soran, A.; Varga, R. A.; Wagner, R. Dalton Trans. 2008, 1831. r 2010 American Chemical Society

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Figure 1. ORTEP plot of compound 3, showing 50% probability displacement ellipsoids and the atom-numbering scheme (symmetry code: (a) -x, 1 - y, 2 - z). Hydrogen atoms are omitted for clarity. Selected bond lengths (A˚) and angles (deg): Sb(1)-C(1) = 2.146(3), Sb(1)N(1)=2.593(2), Sb(1)-N(2)=2.564(2), Sb(1)-S(1)=2.5488(7), Sb(1)-S(2)=2.5591(7), C(13)-S(1)=1.730(3), C(13)-S(2)=1.727(3), C(13)-S(3) = 1.650(3), Sb(1)-Sb(1a) = 3.8235(3); N(1)-Sb(1)-N(2) = 126.44(8), S(1)-Sb(1)-S(2) = 69.05(2), S(1)-C(1)-S(2) = 113.75(8), C(1)-Sb(1)-N(1) = 71.72(9), C(1)-Sb(1)-N(2) = 72.15(8), C(1)-Sb(1)-S(1)=97.89(6), C(1)-Sb(1)-S(2)=98.34(7). Scheme 1. Preparation of Compounds 3 and 4

containing ligand L were shown to be dimeric in the solid state ([LMS]2; M = Sb (1), Bi (2)) with the central M2S2 fourmembered ring (Scheme 1). Nevertheless, we have also demonstrated that the antimony sulfide [LSbS]2 (1) dissociates in solution to the monomeric species LSbS (1a) with a terminal Sb-S bond (Scheme 1).5 The dissociation energy of the dimer of 1 to monomeric units 1a was estimated to be 15.8 kcal/mol by theoretical calculations.5 In contrast to compound 1, the structure of 2 was considered as fluxional in solution at ambient temperature due to the significant broadening of the signals of both NCH2 and N(CH3)2 in the 1H NMR spectra.6,7 In this paper, we report on extended theoretical and experimental studies dealing with formation of the terminal Sb-S and Bi-S bonds in solution. Our results now show that the dissociation energy, obtained at the same level of theory, in the case of the bismuth congener 2 to the monomer 2a (Scheme 1) under the same conditions is somewhat higher, amounting to 25.4 kcal/mol, but still does not rule out the possibility of monomerization of 2 in solution. Moreover, the acetonitrile solution of 2 was measured with the ESI-MS that proved the formation of the monomeric species based on the m/z 433 [LBiS þ H]þ (100%) ion detected in the positive (7) For dimeric sulfides, where two sets of signals due to the cis-trans isomerism were observed in the 1H and 13C NMR spectra, see: (a) Dost al, L.; Jambor, R.; Ruzicka, A.; Jirasko, R.; Taraba, J.; Holecek, J. J. Organomet. Chem. 2007, 692, 3750. (b) Chovancova, M.; Jambor, R.; Ruzicka, A.; Jirasko, R.; Císarova, I.; Dostal, L. Organometallics 2009, 28, 1934. (c) Dostal, L.; Jambor, R.; Ruzicka, A.; Erben, M.; Jirasko, R.;  Cerno skova, Z.; Holecek, J. Organometallics 2009, 28, 2633.

ion full-scan mass spectrum (see the Experimental Section), while the ion corresponding to the dimer is absent. All these facts point to a possibility of formation of the monomeric 2a in solution. As proof of this hypothesis, we report here on the reactions of the sulfides 1 and 2 with carbon disulfide, which proceed in solution as a [2 þ 2] cycloaddition between the monomers 1a and 2a (present in solution) and CS2 to give the molecular trithiocarbonates ArMS2CdS (M = Sb (3), Bi (4)) (Scheme 1). A similar reaction has been recently used as proof for the terminal SndS bond in sterically protected stannanethione by Tokitoh et al.8 Treatment of 1a and 2a in CH2Cl2 solution with an excess (ca. 10 molar equiv) of CS2 resulted in an immediate reaction, as demonstrated by a significant color change (colorless to bright yellow for 1a and yellow to intense orange for 2a). The products of [2 þ 2] cycloaddition, 3 and 4, were isolated after workup (see the Experimental Section) as yellow and orange air-stable crystals in 53% and 67% yields, respectively. Both compounds displayed satisfactory elemental analysis. The structures of 3 and 4 were unambiguously determined by X-ray diffraction techniques on the single-crystal material. The identities of 3 and 4 were also corroborated by powder X-ray analysis of bulk samples after the reaction, and the observed diffractograms are essentially the same as those simulated from the single-crystal measurements (see the Supporting Information). The molecular structures of 3 and 4 are depicted in Figures 1 and 2, respectively, and the crystallographic data are summarized in the Experimental Section. Both molecular structures are quite similar. The central antimony (3) and bismuth (4) atoms are coordinated by the ligand L in a tridentate fashion through an NCN donor set. The dative Sb-N connections are Sb(1)-N(1) = 2.593(2) A˚ and Sb(1)-N(2) = 2.564(2) A˚ in 3 and the Bi-N interactions are Bi(1)-N(1) = 2.635(7) A˚ and Bi(1)-N(2) = 2.668(7) A˚ in 4. The N(1)-M(1)-N(2) angles are 126.44(8) for 3 and 126.6(3) for 4, respectively. Interestingly, the trithiocarbonate groups in the molecular structures of 3 and 4 are coordinated as terminal ligands in a chelating mode.9 To the best of our knowledge, this (8) Saito, M.; Tokitoh, N.; Okazaki, R. Organometallics 1996, 15, 4531. (9) Recently, we have observed similar terminal coordination of the carbonate ligand.7c

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Figure 2. ORTEP plot of compound 4 showing 50% probability displacement ellipsoids and the atom-numbering scheme (symmetry code: (a) 2 - x, -y, -z). Hydrogen atoms are omitted for clarity. Selected bond lengths (A˚) and angles (deg): Bi(1)-C(1) = 2.239(9), Bi(1)-N(1) = 2.635(7), Bi(1)-N(2) = 2.668(7), Bi(1)-S(1) = 2.674(3), Bi(1)-S(2) = 2.661(2), C(13)-S(1) = 1.719(9), C(13)S(2)=1.730(10), C(13)-S(3)=1.647(11), Bi(1)-Bi(1a)=3.8598(6); N(1)-Bi(1)-N(2)=126.6(3), S(1)-Bi(1)-S(2)=66.31(8), S(1)C(1)-S(2) =115.6(6), C(1)-Bi(1)-N(1) =71.3(3), C(1)-Bi(1)N(2) = 70.2(3), C(1)-Bi(1)-S(1) = 98.8(2), C(1)-Sb(1)-S(2) = 98.34(19).

type of coordination is quite rarely encountered, even among transition metals10 (structures determined by X-ray diffraction studies), and only two examples of such coordination were found in the field of main-group elements: a sterically protected diorganotin(IV) trithiocarbonate reported by Tokitoh8 and a bis(tetraphenylphosphonium) bis(trithiocarbonato-S,S0 )tin(IV) compound.11 Both antimony-sulfur bond distances are nearly identical: Sb(1)-S(1) = 2.5488(7) A˚ and Sb(1)-S(2) = 2.5591(7) A˚ in 3 with the bonding angle S(1)-Sb(1)-S(2) 69.05(2). The bond distances Bi(1)-S(1) = 2.674(3) A˚ and Bi(1)-S(2) = 2.661(2) A˚ in 4 are again very similar, and the S(1)-Bi(1)-S(2) angle, 66.31(8), resembles that found in 3. The bonding angles at the carbonate atom S(1)-C(13)-S(2) are significantly wider in both cases: 113.75(8) (3) and 115.6(6) (4). The most striking feature in the coordination of the trithiocarbonate moieties is the nonplanarity of the CS2M ring system. The antimony atom (3) as well as the bismuth atom (4) are significantly bent out from the plane defined by the S(1), C(13), S(2) atoms (0.574 A˚ for 3 and 0.644 A˚ for 4).12 As a possible explanation of the nonplanarity of the MCS2 ring, interesting intermolecular contacts in the structures of 3 and 4 were discovered, which allowed us to formulate dimeric structures of 3 and 4. Of particular interest is the position of the CS3 substituents in these dimeric units, because each of these groups is oriented to the central atom (10) For example, see: (a) Chen, C. H.; Chang, Y. S.; Yang, C. Y.; Chen, T. N.; Lee, C. M.; Liaw, W. F. Dalton Trans. 2004, 137. (b) Doherty, J.; Fortune, J.; Manning, A. R.; Stephens, F. S. J. Chem. Soc., Dalton Trans. 1984, 1111. (c) Simonnet-Jegat, C.; Cadusseau, E.; Dessapt, R.; Secheresse, F. Inorg. Chem. 1999, 38, 2335. (d) Aucott, S. A.; Slawin, A. M. Z.; Woollins, J. D. Polyhedron 2000, 19, 499. (e) Sendlinger, S. C.; Nicholson, J. R.; Lobkovsky, E. B.; Huffman, J. C.; Rehder, D.; Christou, G. Inorg. Chem. 1993, 32, 204. (f ) Vicente, J.; Chicote, M.-T.; Gonzalez-Herrero, P.; Jones, P. G. Inorg. Chem. 1997, 36, 5735. (g) Shaver, A.; Mouatassim, B. E.; Mortini, F.; Belanger-Gariepy, F.; Lough, A. Organometallics 2007, 26, 4229. (11) Muller, A.; Krickemeyer, E.; Katri, F. E.; Rehder, D.; Stammler, A.; Bogge, H.; Hellweg, F. Z. Anorg. Allg. Chem. 1995, 621, 1160. (12) The only comparable values with 3 and 4 were found in some molybdenum compounds: (a) Dessapt, R.; Simonnet-Jegat, C.; Secheresse, F. Bull. Pol. Acad. Sci. Chem. 2002, 50, 15. (b) Coucouvanis, D.; Draganjac, M. E.; Koo, S. M.; Toupadakis, A.; Hadjikyriacou, A. I. Inorg. Chem. 1992, 31, 1186.

Dost al et al.

(antimony or bismuth) of the second molecule, defining the dimer and probably (Figures 1 and 2) causing nonplanarity of the MCS2 ring. It can be anticipated that this is a result of an interaction of the CS3 backbone with the neighboring central atom. The distances Sb-C = 3.806(2) A˚ in 3 and Bi-C = 3.624(9) A˚ in 4 were observed, and both of them are frontier values of the sum of respective van der Waals radii for M-C contacts (3.7 A˚), with the Bi-C contact being slightly shorter in accord with theoretical considerations (vide infra). The intermolecular contacts between the central atoms in the dimer with the bond distances Sb(1)-Sb(1a) = 3.8235(3) A˚ and Bi(1)-Bi(1a) = 3.8598(6) A˚ were also obtained; although these are quite long, they are still significantly respective van der Waals P shorter than the sum of P ˚ radii ( vdW(Sb,Sb) = 4.52 A˚, vdW(Bi,Bi) = 4.8 A). However, these contacts were shown to be nonbonding by theoretical calculations; see further discussion.13 In order to gain additional insight into the bonding patterns of the dimeric structure of 3 and 4, we have performed a theoretical study dealing with the compounds 3 and 4.14-19 As can be seen, some deviations from the crystal structure occur in the optimized stuructures, the Sb-Sb and Bi-Bi distances now being enlarged to 4.15 and 4.25 A˚, respectively. The computed dissociation energies of the gasphase dimeric structures 3 and 4, which were corrected for the basis set superposition error using a counterpoise correction, amount to 5.0 and 8.5 kcal/mol, respectively, and in both cases the nonplanarity of the MCS2 rings is retained. In the monomeric structures, however, the MCS2 moiety is planar (this indicates that the CS3 moiety is involved in an intermolecular interaction in the present dimeric structures). Subsequent NBO analysis on 3 and 4 reveals no bonding interaction between the Sb or Bi atoms in the dimeric structures; the valence electronic configuration is 5s1.805p2.06 for Sb and 6s1.886p1.90 for Bi, and both atoms are connected with three single bonds (to the ipso carbon atom and two sulfur atoms of CS3) and contain a single lone pair which has s-type character. Both Sb and Bi have a considerably positive charge (þ1.098 and þ1.189, respectively). In compound 3, the total charge on (13) A similar Sb-Sb contact was reported for an OCO-chelated antimony compound; see: Dostal, L.; Cı´ sarova, I.; Jambor, R.; Ruzicka, A.; Jirasko, R.; Holecek, J. Organometallics 2006, 25, 4366. (14) The geometries of the dimeric structures 3 and 4 were optimized at the B3LYP15/cc-pVDZ16 level of theory (cc-pVDZ-PP17 on Sb and Bi, which uses a cc-pVDZ like basis set for the valence region, together with a small-core relativistic pseudopotential), starting from the crystal structures; the Cartesian coordinates of the resulting gas-phase optimized geometries can be found in the Supporting Information. Natural bond orbital (NBO) analysis of these structures was performed.18 All computations were performed using the Gaussian 03 program.19 (15) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785. (c) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem. 1994, 98, 11623. (16) Hydrogen and first-row: Kendall, R. A.; Dunning, T. H.; Harrison, R. J. J. Chem. Phys. 1992, 96, 6796. Second row: Woon, D. E.; Dunning, T. H. J. Chem. Phys. 1993, 98, 1358. Third row: Wilson, A. K.; Woon, D. E.; Peterson, K. A.; Dunning, T. H., Jr. J. Chem. Phys. 1999, 110, 7667. (17) Peterson, K. A. J. Chem. Phys. 2003, 119, 11099. (18) (a) Foster, J. P.; Weinhold, F. J. Am. Chem. Soc. 1980, 102, 7211– 7281. (b) Reed, A. E.; Weinhold, F. J. Chem. Phys. 1983, 78, 4066–4073. (c) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985, 83, 735– 746. (d) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88, 899– 926. (e) Weinhold, F. In Encyclopedia of Computational Chemistry; Schleyer, P. v. R., Allinger, N. L., Clark, T., Gasteiger, J., Kollman, P. A., Schaefer, H. F., III, Schreiner, P. R., Eds.; Wiley: Chichester, U.K., 1998; Vol. 3, pp 1792-1811. (19) Frisch, M. J. et al. Gaussian 03, Revision E.01; Gaussian, Inc., Wallingford, CT, 2004.

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the CS3 unity is -0.887; the two S atoms connected to the Sb atom bear a charge of -0.147, C has a charge of -0.509, and the remaining S atom has a charge of -0.084. In the case of compound 4, the total charge on the CS3 unity is -0.958; the two S atoms connected to the Bi atom bear a charge of -0.168 and -0.169, C has a charge of -0.513, and the remaining S atom has a charge of -0.109. Consequently, we interpret the stabilization of the dimeric compounds 3 and 4 in these compounds as resulting from the electrostatic interaction between the Sb or Bi atoms and the C in the CS3 units. The somewhat larger charge separation in compound 4 results in an increased dissociation energy of the corresponding dimer. It should finally be noted that an NBO analysis was also performed directly on the geometries of 3 and 4 taken from the crystal structure, essentially yielding the same bonding patterns and conclusions. The thermal stability of 3 and 4 was studied by thermal analysis; it was found that evolution of CS2 started at 110 C for 3 and 147 C for 4 and the enthalpy of CS2 deliberation was found to be 127 J/g (3) and 129 J/g (4), respectively. In addition, the decomposition of 3 and 4 was accompanied by a mass loss of 17.8% for 3 (the theoretical value for loss of CS2 is 18.9%) and 11.9% (14.3%) for 4. The thermal analysis experiment was subsequently reproduced on a larger scale (ca. 200 mg) in Schlenk vessels, proving the elimination of CS2 from 3 and 4 with formation of the starting sulfides 1 and 2. The incipient sulfides 1 and 2 were characterized by the 1H NMR spectra after the experiment and, in the case of 2, also by an X-ray powder diffractogram, which is consistent with that simulated from singlecrystal measurements of 2 (see the Supporting Information).20 The volatility of the CS2 moiety in 3 and 4 is also evident from the ESI mass spectra (see the Supporting Information), where ions formed by loss of CS2 are the most abundant peaks for both compounds. Moreover, the tandem mass spectra of low-abundance protonated molecules [M þ H]þ at m/z 421 (1%) for 3 and m/z 509 (19%) for 4 were recorded for further structural confirmation. The neutral losses Δm/z 76 (CS2) and Δm/z 108 (CS3) are in agreement with the aforementioned character of the studied compounds. Trithiocarbonates 3 and 4 are both insoluble in most organic solvents. To ensure clear 1H and 13C NMR spectra, dimethyl-d6 sulfoxide (DMSO) had to be used as the solvent for NMR experiments. Dissolving compound 3 in DMSO resulted in the observation of two sets of signals in the 1H NMR spectra. One set of signals was attributed to the starting sulfide by comparison with the 1H NMR spectrum of pure sulfide 1. This means that most probably compound 3 exists in solution in equilibrium with the starting sulfide 1 and free CS2. This fact was proven by addition of an excess of CS2 to the NMR sample, which shifted the equilibrium completely to the trithiocarbonate 3. The situation is rather similar in the case of compound 4, with the difference that the sulfide 2 is completely insoluble in DMSO. Thus, after the crystals of 4 had been dissolved in DMSO, only one set of signal attributable to 4 was observed, but it was accompanied by precipitation of a significant amount of yellowish powder in the NMR tube (this powder was characterized as the sulfide 2 by 1H NMR in CDCl3). Addition of an excess of CS2 caused dissolution of the precipitate, indicating that the equilibrium was shifted to trithiocarbonate 4. (20) The characterization of sulfide 1 by X-ray powder diffraction by comparison with data from measurement of single crystals was not possible, because compound 1 crystallizes as a dichloromethane solvate and the sulfide obtained after elimination of CS2 is of course without this solvent molecule.

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Experimental Section General Procedures. The 1H and 13C NMR spectra were recorded on a Bruker 400 spectrometer, using a 5 mm tunable broad-band probe. Appropriate chemical shifts in the 1H and 13C NMR spectra were related to the residual signals of the solvents (CDCl3, δ(1H) 7.27 ppm and δ(13C) 77.23 ppm; DMSO, δ(1H) 2.50 ppm and δ(13C) 39.51 ppm). The positive ion full-scan mass spectra were measured on an Esquire 3000 ion trap (Bruker Daltonics, Bremen, Germany). The samples were dissolved in acetonitrile and analyzed by direct infusion at a flow rate of 5 μL/min. Mass spectra were recorded in the range m/z 50-1500. The ion source temperature was 300 C, and the flow rate and pressure of nitrogen were 4 L/min and 10 psi, respectively. Infrared spectra were recorded in the range 5000-400 cm-1 as KBr pellets on a Bruker IFS 55 FT-IR spectrometer. Thermal analysis was performed with a Mettler DSC 12E Heat-Flux instrument. Starting compounds 1 and 2 were prepared by the reaction of the parent chlorides ArMCl2 (M = Sb, Bi) with an in situ prepared THF solution of Li2S, which gives better yields in our hands than reactions using insoluble sodium sulfide (Scheme 1).5,6 The THF solution of Li2S was prepared from sulfur and Li[B(Et)3H] according to the literature procedure and used in situ.21 Preparation of (ArSbS)2 (1). A solution of Li2S (4.38 mmol, prepared from 0.14 g of sulfur, and 8.8 mL of a 1 M THF solution of Li[B(Et)3H])21 in THF (20 mL) was added to a suspension of ArSbCl222 (1.46 g, 3.81 mmol) in 3 mL of CH2Cl2. Upon addition, the volume of the reaction mixture was reduced to ca. 10 mL and the remaining mixture was stirred for an additional 1 h. The insoluble yellowish precipitate was separated by decantation and washed with a THF/hexane mixture (1/1; 10 mL). The remaining solid was extracted with CH2Cl2 (40 mL), and evaporation of the extract gave compound 1 0.85 g (65%) as a slightly yellow powder. Anal. Calcd for C24H38N4S2Sb2: C, 41.8; H, 5.6. Found: C, 41.9; H, 5.8. All other data were consistent with those published earlier.5 Preparation of (ArBiS)2 (2). A solution of Li2S (2.81 mmol, prepared from 0.09 g of sulfur, and 5.6 mL of a 1 M THF solution of Li[B(Et)3H])21 in THF (20 mL) was added to a suspension of ArBiCl222 (1.15 g, 2.45 mmol) in 5 mL of CH2Cl2. Upon addition, the volume of the reaction mixture was reduced to ca. 10 mL and the remaining mixture was stirred for an additional 1 h. The insoluble yellow precipitate was separated by decantation and washed with a THF/hexane mixture (1/1; 10 mL). The remaining solid was extracted twice with warm CH2Cl2 (a total of 50 mL), and evaporation of the extract gave compound 2 0.58 g (55%), as a yellow powder. Anal. Calcd for C24H38N4S2Bi2: C, 33.3; H, 4.4. Found: C, 33.5; H, 4.6. Positiveion ESI mass spectrum: m/z 433 [LBiS þ H]þ (100%). All other data were consistent with those published earlier.6 Preparation of ArSbS2CdS (3). An excess of distilled CS2 (0.3 mL, 5 mmol) was added to a suspension of 1 (0.31 g, 0.45 mmol) in CH2Cl2 (25 mL). Immediately after addition, the solution turned bright yellow. The reaction mixture was stirred for 30 min and than evaporated to a final volume of ca. 15 mL. Several drops of hexane were added to this solution, and storage of this solution at 5 C overnight gave bright yellow single crystals of 3 suitable for X-ray diffraction. Storage of the mother liquor at -30 C provided a second crop of 3 after several days. Both crops of crystals were isolated by filtration, washed twice with diethyl ether (5 mL), and dried in vacuo. The combined yield of 3 was 0.2 g (53%). Anal. Calcd for C13H19N2S3Sb: C, 37.1; H, 4.6. Found: C, 37.3; H, 4.7. 1H NMR (DMSO; 400.13 MHz): δ (ppm) 2.10 (s (br), 6H, N(CH3)2), 2.55 (s (br), 6H, N(CH3)2), 3.64 and 4.24 (AX pattern, 4H, CH2N), 7.31 (d, 2H, (21) Herzog, U.; Lange, H.; Borrmann, H.; Walfort, B.; Lang, H. J. Organomet. Chem. 2004, 689, 4909. (22) Atwood, D. A.; Cowley, A. H.; Ruiz, J. Inorg. Chim. Acta 1992, 198-200, 271.

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Ar-H3,5), 7.42 (t, 1H, Ar-H4). 13C NMR (DMSO; 100.63 MHz): δ (ppm) 42.2 (br, N(CH3)2), 46.2 (br, N(CH3)2), 64.0 (CH2N), 126.4 (Ar-C3,5), 129.9 (Ar-C4), 144.7 (Ar-C1), 146.6 (Ar-C2,6); CS3 was not observed, most probably due to the fast exchange with free CS2 in the NMR sample (vide infra). Positive ion ESI mass spectra: m/z 421 [M þ H]þ (1%); m/z 345 [M þ H CS2]þ (100%). MS/MS of 421: m/z 345 [M þ H - CS2]þ; m/z 313 [M þ H - CS3]þ; m/z 191 [L]þ. IR (KBr, cm-1): 1014 vs (ν(CdS)), 870 vs (νa(C-S)), 513 m (νs(C-S)).23 Preparation of ArBiS2CdS (4). An excess of distilled CS2 (0.35 mL, 5.8 mmol) was added to a solution of 2 (0.47 g, 0.54 mmol) in CH2Cl2 (25 mL). Immediately after addition, the mixture cleared up and turned orange. The reaction mixture was stirred for an additional 2 h, and during this period an orange microcrystalline material precipitated. The precipitate was separated by filtration, washed twice with diethyl ether (10 mL), and dried in vacuo. Storage of the mother liquor at 5 C provided a small second crop of 4 in the form of single crystals suitable for X-ray diffraction after several days. The yield of 4 was 0.37 g (67%). Anal. Calcd for C13H19N2S3Bi: C, 30.7; H, 3.8. Found: C, 30.6; H, 4.0. 1H NMR (DMSO; 400.13 MHz): δ (ppm) 2.19 (s (br), 6H, N(CH3)2), 2.64 (s (br), 6H, N(CH3)2), 4.11 and 4.25 (AX pattern, 4H, CH2N), 7.50 (t, 1H, Ar-H4), 7.63 (d, 2H, Ar-H3,5). 13C NMR (DMSO; 100.63 MHz): δ (ppm) 42.2 (br, N(CH3)2), 47.2 (br, N(CH3)2), 67.9 (CH2N), 127.9 (Ar-C3,5), 128.8 (Ar-C4), 152.1 (Ar-C2,6); ArC1, not detected, CS3 not observed, most probably due to the fast exchange with free CS2 in NMR sample (vide infra). Positive ion ESI mass spectra: m/z 509 [M þ H]þ (19%); m/z 433 [M þ H CS2]þ (100%). MS/MS of 509: m/z 433 [M þ H - CS2]þ. IR (KBr, cm-1): 997 vs (ν(CdS)), 866 s (νa(C-S)), 513 w (νs(C-S)).23 (23) Burke, J. M.; Fackler, J. P. Inorg. Chem. 1972, 11, 2744.

Dost al et al. Crystallographic Data. Data for 3: C13H19N2S3Sb, Mr = 421.23, monoclinic, P21/c, yellow plate, a = 11.5541(4) A˚, b = 8.7350(6) A˚, c = 18.9419(12) A˚, β = 121.371(4), V = 1632.25(18) A˚3, Z = 4, T = 150(1) K, 21 959 total reflections, 3711 independent (Rint = 0.024), R1(obsd data) = 0.022, wR2(all data) = 0.050, CCDC 771560. Data for 4: C13H19N2S3Bi, Mr = 508.46, monoclinic, P21/c, orange block, a = 11.8121(5) A˚, b = 8.8310(4) A˚, c = 18.9362(9) A˚, β = 121.873(4), V = 1667.45(15) A˚3, Z = 4, T = 150(2) K, 11 438 total reflections, 3828 independent (Rint = 0.068), R1(obsd data) = 0.043, wR2(all data) = 0.078, CCDC 771561.

 (Project No. Acknowledgment. We thank the GACR P207/10/0130) and the Ministry of Education of the Czech Republic (Project No. MSM0021627501) for financial support. R.J. acknowledges the support of Grant Project No. MSM0021627502 sponsored by the Ministry of Education, Youth and Sports of the Czech Republic. F.d.P. wishes to acknowledge the Research FoundationFlanders (FWO) and the Vrije Universiteit Brussel (VUB) for continuous support to this research group. Supporting Information Available: Text, tables, figures, and CIF files giving MS/MS spectra of protonated molecules for 3 and 4, X-ray powder diffractograms of 3 and 4 and their diffractograms after deliberation of CS2, all crystal data and structure refinement details, atomic coordinates, anisotropic displacement parameters, and geometric data for compounds 3 and 4, and details of theoretical studies. This material is available free of charge via the Internet at http:// pubs.acs.org.