Facile Cleavage of Organochalcogen Hybrid (NEEN, NEN, EN, where

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Articles Facile Cleavage of Organochalcogen Hybrid (NEEN, NEN, EN, where E ) Se or Te) Ligand C-E and E-E Bonds by Pd(II) Rupinder Kaur,† Saija C. Menon,† Snigdha Panda,† Harkesh B. Singh,†,* Rajan P. Patel,‡ and Ray J. Butcher§ Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India, Chemistry DiVision, Bhabha Atomic Research Center, Trombay, Mumbai 400 085, India, and Department of Chemistry, Howard UniVersity, Washington, D.C. 20059 ReceiVed October 23, 2008

The synthesis and characterization of chiral hybrid ligand R2*Se2 (R* ) 2-Me2NCH(Me)C6H4) (9) and some of its derivatives is described. The reaction of 9 with a Pd(II) chloride complex leads to cleavage of the Se-Se bond and formation of the corresponding areneselenenyl chloride, R*SeCl (18). However, reactions of [RS; RS] and [SR; SR] bis[2-{1-(dimethylamine)ethyl}ferrocenyl] diselenides (7 and 8) with a Pd(II) chloride complex under identical conditions afford dinuclear complexes [PdCl{(SeC5H3CH(Me)NMe2-2)Fe(C5H5)}]2 (19 and 20). Reaction of achiral ditelluride, R2Te2 (R ) 2-Me2NCH2C6H4) (10), with a Pd(II) chloride complex gives a novel dinuclear complex, [PdCl(TeC6H4CH2NMe2-2)]2 (21), and the dimeric tellurium complex (RTeCl)2 (22), whereas the reaction of chiral Schiff base tridentate tellurium ligand R′2Te (R′ ) 2-C6H4CHd NCH(Me)C6H5) (11) with a Pd(II) chloride complex produces cleaved products (R′PdCl)2 (23) and (R′TeCl)2 (24). Similarly, the reaction between the tridentate ligand R2Te (12) and Pd(COD)Cl2 gives 22 and the dimeric palladium complex (RPdCl)2 (25). The treatment of bidentate ligand RTeMe (13) results in decomposition of the ligand and precipitation of Te. All the compounds are characterized by detailed IR and NMR (1H, 13C, 77 Se, and 125Te) spectroscopic techniques, MS, and optical rotation measurements. The structures of R*SeBr (17), 21, 24, and 25 were determined by single-crystal X-ray crystallography. In 17 the coordination geometry around selenium is essentially T-shaped with a short Se · · · N distance (2.132(6) Å). The palladium tellurolato complex 21 crystallizes as a centrosymmetric dimer. Compound 23 crystallizes as a dimer in which each tellurium atom coordinates to two bridging chlorines, one nitrogen, and one carbon. Compound 25 crystallizes as a chloro-bridged centrosymmetric dimer. Introduction The coordination chemistry of transition metal ions, in particular platinum group metal ions, Pd(II) and Pt(II) with heavier organochalcogen (Se, Te) ligands has attracted considerable current interest.1 The complexes serve as precursors for the preparation of binary transition metal chalcogenides2 and have potential in homogeneous catalysis where donor selenium plays a key role.3 Whereas selenium-ligated palladium(II) * To whom correspondence should be addressed. Phone: + 91 22 2576 7190. Fax: + 91 22 2572 3480. E- mail: [email protected]. † Indian Institute of Technology Bombay. ‡ Bhabha Atomic Research Center. § Howard University. (1) (a) Hope, E. G.; Levason, W. Coord. Chem. ReV. 1993, 122, 171. (b) Arnold, J. Prog. Inorg. Chem. 1995, 43, 353. (c) Singh, A. K.; Sharma, S. Coord. Chem. ReV. 2000, 209, 49. (d) Levason, W.; Orchard, S. D.; Reid, G. Coord. Chem. ReV. 2002, 225, 159. (e) Jain, V. K.; Jain, L. Coord. Chem. ReV. 2005, 249, 3075. (2) (a) Singhal, A.; Jain, V. K.; Mishra, R.; Varghese, B. J. Mater. Chem. 2000, 1121. (b) Malik, M. A.; O’Brien, P.; Revaprasadu, N. Phosphorus, Sulfur Silicon 2005, 180, 689. (c) Kornienko, A.; Banerjee, S.; Kumar, G. A.; Riman, R. E.; Emge, T. E.; Brennan, J. G. J. Am. Chem. Soc. 2005, 127, 14008. (d) Zhang, H.; Wang, D.; Mo¨hwald, M. Angew. Chem., Int. Ed. 2006, 45, 748. (e) Kumbhare, L. B.; Jain, V. K.; Phadnis, P. P.; Nethaji, M. J. Organomet. Chem. 2007, 692, 1546, and references therein. (3) (a) Zeni, G.; Braga, A. L.; Stefani, H. A. Acc. Chem. Res. 2003, 36, 731. (b) Zeni, G.; Ludtke, D. S.; Panatieri, R. B.; Braga, A. L. Chem. ReV. 2006, 1032–1076. (c) Ranu, B. C.; Chattopadhyay, K.; Banerjee, S. J. Org. Chem. 2006, 71, 423.

complexes have received current interest in catalysis, catalysis with the tellurium analogues is rare.4 In addition to this, organotellurium compounds have been used in catalytic carbon-carbon bond formation, where these behave as aryl or vinyl carbocation equivalents. Uemura and co-workers reported palladium-catalyzed Fujiwara-Heck crosscoupling reactions between organic tellurides and alkenes (eq 1) and homocoupling reactions of an organic telluridecontaining styryl moiety (eq 2) in the presence of a catalytic amount of Pd(OAc)2 together with AgOAc.5 Comasseto and co-workers reported the alkynylation reactions of butyl vinyl tellurides catalyzed by PdCl2/CuI.6

10.1021/om801015e CCC: $40.75  2009 American Chemical Society Publication on Web 03/26/2009

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Kaur et al.

Zeni and co-workers have systematically studied palladiumcatalyzed coupling of vinylic tellurides for the synthesis of conjugated enyne and enediyne.7 More recently, Suzuki-Miyaura cross-coupling reactions of aryl tellurides with potassium aryltrifluoroborate salts have been reported. These are catalyzed by Pd(0) complexes.7,8 The key step of the coupling reactions was proposed to be the migration of an organic moiety (aryl/vinyl) from Te to Pd (transmetalation) in organic telluride-Pd(II) complexes to afford the organopalladium species. The proposed mechanism has been supported by interception and structural characterization of intermediates by electrospray ionization and mass and tandem mass (ESI-MS/MS) experiments.8,9 Although the intermediacy of organopalladium and organotellurium species has been proposed and the intermediates identified by ESI-MS in the catalytic cycle, the isolation and characterization of the intermediates have not been demonstrated. Although the cleavage of the C-Te bond has received current interest in the recent past due to its relevance in catalysis, the lability and cleavage of Te-C bonds in the presence of metal ions (PtII, CuII, HgII, and PdII) were observed by McWhinnie and co-workers and Levason and co-workers much earlier.10,11 A complex of ligand 1,6-bis-2-butyltellurophenyl-2,5-diazahexa1,5-diene with PtCl2 indicated loss of the butyl groups, and the early stages of dealkylation reaction were monitored by 125Te NMR and 195Pt NMR spectroscopy.10 Levason and co-workers established monodemethylation of coordinated telluroether complex 1 to give 2 (eq 3).11 2-(2-Pyridyl)(p-ethoxyphenyl)tellurium(II), (RR′Te) (3), reacted with HgCl2 at room temperature to afford 4 with a cleaved C-Te bond (eq 4).12 However, the reaction of 3 with Pd(II)Cl2 and Pt(II)Cl2 led to isolation of very complex systems.13 In no case could welldefined, crytallographically characterized cleaved products be isolated.

analogous reaction of 6 with a Pd(II) chloride complex afforded a yellow-orange solid, which was insoluble in common solvents, presumably due to formation of a polymeric complex, and further characterization could not be carried out. The cleavage of C-Te in these cases is facilitated by the strong NfTe intramolecular interaction, which involves donation of a nitrogen lone pair to the σ* orbital of the trans C-Te bond.17 Such intramolecular activation of C-Sn and C-Si bonds has earlier been used in palladiumcatalyzed cross-coupling reactions.18 In contrast to the cleavage reactions of organotellurides (R2Te), the C-E and E-E bond cleavage reactions of diorganoditellurides (R2E2) (where E ) Se/ Te) with Pd0/Pt0 complexes have been extensively studied.19 Also in comparison there are very few examples of the cleavage of the E-E bonds by Pd(II) salts.20 In continuation of our work on the application of intramolecular coordination for the isolation for hybrid multidentate liagnds, we report here reactions of a range of Se/Te ligands, e.g., (i) tetradentate dichalcogenides (7,21 8,21 9, 1022) (ii) tridentate ligands (11,23 1222), and (iii) a bidentate ligand (13),22 with Pd(II) and demonstrate that instead of the expected complexation, C-Se, C-Te, Te-Te, and Se-Se bond cleavage is more facile.

Recently, we have reported a facile C-Te bond cleavage/ transmetalation in the reaction of the 22-membered azamacrocyclic 5 with HgCl214 and Pt(COD)Cl2.15 We have also reported the facile cleavage of the C-Te bond in bis[2-(4,4-dimethyl-2-oxazolinyl)phenyl] telluride (6) on reaction with HgCl2.16 However,

Results and Discussion Synthesis of Ligands. Chiral tetradentate ligand 9 was prepared from (S)-N,N-dimethyl-1-phenylethyamine (14) following a reported procedure with slight modification (Scheme

CleaVage of Organochalcogen Hybrid Ligand Bonds

Organometallics, Vol. 28, No. 8, 2009 2365 Scheme 1

1). Wirth24 and Furukawa et al.25 have reported the preparation of the diselenides (R,R)- and (S,S)-9 independently as a yellow oil by treating chiral amine 14 with t-BuLi in pentane and s-BuLi respectively. Attempted synthesis of 9 by lithiation of the chiral amine with n-BuLi followed by addition of selenium powder gave a mixture of products 9 and 15 (inferred from 77Se NMR and MS). Repeated attempts to separate them by using column chromatography were unsuccessful. However, 9 could be isolated in the pure form by derivatizing the crude mixture product with excess bromine to give an orange precipitate of R*SeBr3 (16) (R* ) [(S)-2-Me2NCHMeC6H4]). Reduction of the tribromide with NaBH4 in methanol gave pure diselenide 9 as a solid. A similar observation has been made by Wirth and co-workers, and purification of the chiral diselenide was achieved by reducing the mixture with NaBH4 followed by reoxidation in ammonium chloride.26 The tribromide is sparingly soluble in less polar solvents such as CHCl3 but is soluble in polar solvents such as DMSO. Interestingly, when 16 was left to stand in DMSO for some time, it dissociated into the (4) Doi, T.; Mori, Y.; Asakawa, T.; Miyaki, T. Jpn. Kokai Tokkyo Koho, 2003, CODEN: JKXXAF JP 2003251191 A 20030909. CAN 139: 232187AN 2003: 702953 CAPLUS. (5) (a) Nishibayashi, Y.; Cho, C. S.; Uemura, S. J. Organomet. Chem. 1996, 507, 197. (b) Nishibayashi, Y.; Cho, C. S.; Ohe, K.; Uemura, S. J. Organomet. Chem. 1996, 526, 335. (6) Zeni, C.; Comasseto, J. V. Tetrahedron Lett. 1999, 40, 4619. (7) Zeni, G.; Menezes, P. H.; Moro, A. V.; Braga, A. L.; Silveira, C. C.; Stefani, H. A. Synlett 2001, 9, 1473. (8) Cella, R.; Cunha, R. L. O.; Reis, A. E. S.; Pimenta, D. C.; Klitzke, C. F.; Stefani, H. A. J. Org. Chem. 2006, 71, 244. (9) Raminelli, C.; Prechtl, M. H. G.; Santos, L. S.; Eberlin, M. N.; Comasseto, J. V. Organometallics 2004, 23, 3990. (10) Al-Salim, N. I.; McWhinnie, W. R. Polyhydron 1989, 8, 2769. (11) Kemmitt, T.; Levason, W.; Spicer, M. D.; Webster, M. Organometallics 1990, 9, 1181. (12) (a) Mbogo, S. A.; McWhinnie, W. R.; Lobana, T. S. J. Organomet. Chem. 1990, 384, 115. (b) Lobana, T. S.; Mbogo, S. A.; McWhinnie, W. R. J. Organomet. Chem. 1990, 390, 29. (c) Greaves, M. R.; Hamor, T. A.; Howlin, B. J.; Lobana, T. S.; Mbogo, S. A.; McWhinnie, W. R.; Povey, D. C. J. Organomet. Chem. 1991, 420, 327. (13) (a) Mbogo, S. A.; McWhinnie, W. R.; Lobana, T. S. Inorg. Chim. Acta 1992, 193, 5. (b) Mbogo, S. A.; McWhinnie, W. R.; Lobana, T. S. Inorg. Chim. Acta 1990, 172, 221. (14) Menon, S. C.; Singh, H. B.; Patel, R. P.; Kulshreshtha, S. K. J. Chem. Soc., Dalton. Trans. 1996, 1203. (15) (a) Menon, S. C.; Panda, A.; Singh, H. B.; Butcher, R. J. Chem. Commun. 2000, 143. (b) Panda, S.; Singh, H. B.; Butcher, R. J. Chem. Commun. 2004, 322. (16) Apte, S. D.; Zade, S. S.; Singh, H. B.; Butcher, R. J. Organometallics 2003, 22, 5473. (17) Tripathi, S. K.; Patel, U.; Roy, D.; Sunoj, R. B.; Singh, H. B.; Wolmersha¨user, G.; Butcher, R. J. J. Org. Chem. 2005, 70, 9237. (18) (a) Brown, J. M.; Pearson, M.; Johann, T. B. H.; van Koten, G. J. Chem. Soc., Chem. Commun. 1992, 1440. (b) Shindo, M.; Matsumoto, K.; Shishido, K. Synlett 2005, 176.

monobromide R*SeBr (17). All the compounds were characterized by elemental analysis, mass spectrometry, and multinuclear NMR spectroscopic techniques. The 1H NMR chemical shifts of 17 are indicative of a strong Se · · · N interaction at ambient temperature, whereas two resonances were observed for the NMe2 signal (δ ) 2.53, 2.94 ppm). In the 13C NMR spectrum also the NMe2 carbons appear as a pair of lines at 41.5 and 46.3 ppm due to strong Se · · · N interactions. Palladium Complexes. Complexation reactions of multidentate chiral selenium (7, 8, 9) and chiral and achiral tellurium ligands (10-13) with Pd(II) complexes are given in Scheme 2. Addition of Pd(COD)Cl2 to a solution of 9 afforded a mixture, which upon recrystallization from dichoromethane/hexane (80: 20) gave yellow crystals of R*SeCl (18) (Scheme 2) rather than the expected Pd(II) selenolate complex. Organoselenyl chloride 18, presumably, results from the redox reaction of 9 with Pd(COD)Cl2,27 where diselenide 9 is reduced to selenolate (R*Se-) and oxidized to R*SeCl (18) (vide infra). In this case the selenolate complex could not be isolated in pure form. However, analogous reactions of 7, 8, and 10 with a Pd(II) chloride complex afforded the selenolate/tellurolate complexes as the major products. The 1H and 77Se NMR features of 18 were found to be similar to those of R*SeBr, whose X-ray structure has been determined (vide infra). A strong Se · · · N intramolecular interaction was inferred from the 1H NMR (NMe2 ) 2.51, 2.86 ppm) spectrum. The 77Se signal for 18 appears at 1021 ppm, which is the normal range for selenenyl halides and is, as expected, more downfield compared to R*SeBr (1018 ppm). (19) (a) Han, L.-B.; Choi, N.; Tanaka, M. J. Am. Chem. Soc. 1997, 119, 1795. (b) Wagner, A.; Vigo, L.; Oilunkaniemi, R.; Latinen, R. S.; Weigand, W. Dalton Trans. 2008, 3535, and references therein. (c) Jing, S.; Morley, C. P.; Webster, C. A.; Di Vaira, M. J. Organomet. Chem. 2008, 693, 2310, and references therein. (20) Dey, S.; Jain, V. K.; Varghese, B.; Schurr, T.; Niemeyer, M.; Kaim, W.; Butcher, R. J. Inorg. Chim. Acta 2006, 359, 1449, and references therein. (21) Nishibayashi, Y.; Singh, J. D.; Uemura, S.; Fukuzawa, S. Tetrahedron Lett. 1994, 35, 3115. (22) Kaur, R.; Singh, H. B.; Butcher, R. J. Organometallics 1995, 14, 4755. (23) Menon, S. C.; Singh, H. B.; Patel, R. P.; Das, K.; Butcher, R. J. Organometallics 1997, 16, 563. (24) Wirth, T. Tetrahedron Lett. 1995, 36, 7849. (25) Fukuzawa, S.; Takahashi, K.; Kato, H.; Yamazaki, H. J. Org. Chem. 1997, 62, 7711. (26) Santi, C.; Fragle, G.; Wirth, T. Tetrahedron: Asymmetry 1998, 9, 3625. (27) Drew, D.; Doyle, J. R.; Shaver, A. G. Inorg. Synth. 1991, 28, 346. (28) (a) Kaur, R.; Singh, H. B.; Patel, R. P. J. Chem. Soc., Dalton Trans. 1996, 2718. (b) Kaur, R.; Singh, H. B.; Patel, R. P.; Kulshreshtha, S. K. J. Chem. Soc., Dalton Trans. 1996, 461.


Kaur et al. Scheme 2

Interestingly, the reaction of 7 with Pd(COD)Cl2 proceeded under identical conditions to give a well-defined complex. The dark brown solid obtained after workup and purification was identified to be dimeric complex 19. The complex shows good solubility in benzene and other less polar solvents such as chloroform. It is also found to be extremely stable in solution, as no decomposition was observed even on successive recrystallizations. The mass spectrum of 19 showed the presence of the molecular ion peak at m/z 955 (100%). Complex 20, obtained by reacting the other enantiomer 8 with Pd(COD)Cl2, shows behavior identical to 19. The complexes 19 and 20 have been further examined by multinuclear NMR studies. Since 19 and 20 show identical analytical data, only 19 will be discussed. The 1H NMR behavior of 19 is significantly different from the corresponding ligand 7. A downfield shift of all peaks (except CHMe) is a result of coordination of the ligand to Pd. In addition there is evidence for a bidentate mode of coordination via Se and N. The N-methyl protons that appear as a singlet in 7 (2.19 ppm) give rise to a pair of lines in 19 (δ 2.29 and 3.04 ppm, respectively). In the 77Se NMR spectrum of 19 a significant upfield shift of the 77Se signal (-42.8 ppm) is observed compared to ligand 7 (452 ppm). The value is in the same range as the Hg complex Hg[(R,S)-(SeC5H3CHMeNMe2-2)Fe(C5H5)]2 (-64.7 ppm).28b This observation fits well with the postulated

structure in which cleavage of the Se-Se bond leads to the formation of the chelating selenolate ligand. From the reaction of ditelluride ligand 10 with Pd(COD)Cl2 two well-defined products, dark red 21 and yellow 22, were obtained (vide supra). Complex 21 shows a weak molecular ion peak containing solvent CH2Cl2 (889, 15%). The tendency of the complex to retain the solvent molecule is reflected in the 1H NMR spectra of the complex, which shows a peak for dichloromethane (vide infra). The N-methyl signals appear as a pair of lines, and furthermore, the CH2 protons are seen as a pair of doublets, indicating diastereomerism of CH2 in the complex. The structure was unambiguously confirmed by X-ray analysis (vide infra). The Te-Te bond cleaves, leading to the formation of chelating tellurolate ligand RTe- (R ) 2-Me2NCH2C6H4). The 125Te NMR signal appears at -6 ppm and is significantly shielded with respect to the starting ditelluride 10 (354.6 ppm). Though its 1 H NMR spectrum was found to be similar to the reported literature values for RTeCl,29 the melting point was significantly different. The mass spectrum of 22 showed a peak at m/z 299 (50%), which corresponds to RTeCl and a peak at m/e ) 264 (100%, -TeR), which corresponds to the loss of one Cl atom. (29) Singh, H. B.; Sudha, N.; West, A. A.; Hamor, T. A. J. Chem. Soc., Dalton Trans. 1990, 907.


Organometallics, Vol. 28, No. 8, 2009 2367

Figure 2. ORTEP view of compound 21. Table 2. Bond Lengths [Å] and Bond Angles [deg] for 21

Figure 1. ORTEP view of compound 17. Table 1. Bond Lengths [Å] and Bond Angles [deg] for 17 Se-C1 Br-Se Se-N

1.906(7) 2.6114(12) 2.132(6)

N-Se-Br C1-Se-N C1-Se-Br

176.06(15) 82.0(3) 94.7(2)

However, the highest recorded molecular ion peak at m/e 593 (20%) corresponds to the higher homologue (RTeCl)2. This could indicate strong intermolecular contacts in the solid state, leading to a dimeric structure. Attempts to grow good quality crystals of this compound were unsuccessful. Reaction of the tridentate ligand 11 with Pd(COD)Cl2 in CHCl3 gave a mixture of products, which were inseparable. However, on reaction with Pd(C6H5CN)2Cl2 in benzene, it gave two products, 23 and 24. Compound 23 was separated as yellow precipitate during the course of the reaction. Reaction of the tridentate ligand 12 with Pd(COD)Cl2 also gave a mixture of two compounds, (RTeCl)2 (22) and (RPdCl)230 (25). These were separated on the basis of their solubility differences. The more soluble ether fraction (on the basis of elemental analysis) was assigned as 22. It is worth comparing that the reaction of 6 with HgCl2 gave monomeric R′′TeCl and R′′HgCl (R′′ ) 2-oxazolinephenyl), and no dimeric products were isolated. The reaction of bidentate ligand 13 with Pd(COD)Cl2 led to decomposition of the ligand. The ligand seems to be quite unstable, as its reaction with Cr(0) also resulted in its decomposition.22 Structure of 17. The molecular structure of 17 is shown in Figure 1, and selected molecular parameters are given in Table 1. The compound is isostructural with its achiral analogue, (2Me2NCH2C6H4)SeBr.28a The compound crystallizes as a wellseparated monomer with four molecules per unit cell. The coordination geometry around selenium is essentially T-shaped; however, the Se · · · N separation of 2.132(6) Å is shorter than the separation of 2.143(6)Å observed in the case of (2-Me2NCH2C6H4)SeBr. Another significant difference between the two structures is the less linear N-Se-Br angle (176.06(15)°) in this case, which gives rise to a shorter Se-Br distance [2.6114(12) Å] compared to (2-Me2NCH2C6H4)SeBr [N-Se-Br ) 177.6(3)°, Se-Br ) 2.634(1) Å]. This is probably a result of the reduction in the trans effect in the Br-Se · · · N fragment due to the more puckered five-membered ring in 17. The four atoms, Se, C(1), C(6), N(1), of the five-membered ring are coplanar and C(7) is out of the plane by 0.3 Å. The Se-C(1) bond distance [1.906(7) Å] is as expected. The absolute (30) Cope, A. C.; Friedrich, E. C. J. Am. Chem. Soc. 1968, 90, 909.

Pd1-N1 Te1-Pd1 Te1-Pd1A Cl1-Pd1-N1 Pd1-Te1-C1 Pd1-Te1-Pd1A Te1A-Pd1-Cl1

2.222(5) 2.5323(6) 2.5464(6) 96.69(14) 84.4(2) 97.51(7) 90.13(5)

Pd1-Cl1 Te1-C1 Te1-Pd1C Te1-Pd1-N1 Te1A-Pd1-N1 Te1-Pd1-Cl1 Te1-Pd1-Te1A

2.360(2) 2.132(6) 3.519(2) 92.17(13) 172.75(13) 169.88(5) 80.83(2)

configuration test has been performed according to Flack,31 and the configuration was confirmed to be S. In addition, the application of the Cahn, Ingold, and Prelog rule32 confirms the presence of the (S)-enantiomorph. The palladium tellurolate complex (Figure 2) crystallizes as a centrosymmetric dimer with identical coordination environment around both the palladium atoms. Complex 21 represents the second report of a crystallographically characterized example of a dinuclear Pd(II) complex containing a doubly bridged aryltellurolate ligand.20 Each palladium atom coordinates to two telluriums, one nitrogen, and one chlorine atom in a cis squareplanar MA2BC geometry. The Pd-Te (2.5323(6), 2.5464(6) Å), Pd-N (2.222(5) Å), and Pd-Cl (2.360 (2) Å) (Table 2) distances are significantly longer than the corresponding distances observed for the related [PdCl(TeCH2CH2CH2NMe2)]2.20 The two Pd-Te distances are slightly different, as they are trans to two different donors (Pd-Te, trans to Cl, 2.5323(6) Å, Pd-Te(A) trans to N, 2.5464(6) Å). The amino moiety seems to be the stronger trans influence ligand. The Pd · · · Pd distance (across the dimer) is 4.675 Å. There is a large distortion present from the normally expected square-planar geometries. The trans angles deviate considerably from 180°; Cl-Pd-Te is 169.88(5)°, while N(1)-Pd-Te(1A) is 172.75(13)°. Additionally the least plane containing Cl, Te, Te(A), and N shows the four atoms to be coplanar to (0.02 Å, while Pd is 0.06 Å out of this plane. The tellurium atom coordination is approximately pyramidal, with the bond angles in the range 84-106°. The bite angle of the chelating (Te, N) ligand is 92.2(1)°. The tellurolate ligand is also drastically distorted. The plane of the ligand is approximately perpendicular to the mean plane of the Pd atom. Some of these distortions may be due to packing forces between the molecules, as views of the unit cell diagram show weak out-of-plane interactions (3.5 Å´) between the Pd and Te atoms of adjacent molecules, giving rise to an elongated cube (Figure 3). The complex is associated with one dichloromethane (solvent) molecule, and this appears to stabilize the crystals. There are no other close contacts in the molecule. Compound 24 (Figure 4) crystallizes as a chloro-bridged dimer with two molecules per unit cell. Each unit is connected with each other through bridging chlorine atoms. The geometry (31) Flack, H. D. Acta Crystallogr. 1983, A39, 876. (32) Cahn, R. S.; Ingold, C. K.; Prelog, V. Angew. Chem., Int. Ed. 1966, 5, 385.


Kaur et al.

Figure 5. ORTEP view of compound 25. Table 4. Bond Lengths [Å] and Bond Angles [deg] for 25

Figure 3. ORTEP view of compound 21 showing Pd and Te atoms of adjacent molecules giving rise to an elongated cube.

Figure 4. ORTEP view of compound 24. Table 3. Bond Lengths [Å] and Bond Angles [deg] for 24 Te1-Cl1 Te1-Cl2 Te1-N1 Te1-C1 N1-Te1-C1 Cl1-Te1-C1 Cl1-Te1-N1

2.322(6) 2.471(5) 2.06(2) 1.99(2) 79.5(8) 94.8(6) 174.2(5)

Te2-Cl1 Te2-Cl2 Te2-N2 Te2-C16 Cl1-Te1-Cl2 Cl2-Te1-N1 Cl2-Te1-C1

2.464(6) 2.343(5) 2.01(2) 1.97(2) 85.3(2) 100.5(5) 172.6(6)

around the Te atom is slightly distorted square planar. This is the first example of a dimeric, chiral tellurenyl chloride of the type 12-Te-4 which is stabilized by intramolecular coordination. The most interesting feature of the structure is the formation of 12-Te-4 type species instead of 10-Te-3 type T-shaped structure, which are quite common and isolated. The two chiral centers are trans to each other, so that the dimer has a pseudocenter of inversion. The N-Te bond distances [N(1)-Te(1) 2.06(2) Å and N(2)-Te(2) 2.01(2) Å] (Table 3) are equal to the sum of covalent radii of N and Te (2.1 Å). This indicates the strong interaction between Te · · · N, leading to covalent bonding between Te and N, may be due to the presence of a Te-Cl bond and bridging of the Te to Cl. The Te-Cl bond distances of each monomer unit [Te(1)-Cl(1) 2.322(6) Å and Te(2)-Cl(2) 2.343(5) Å] are much shorter than Te-Cl bond distances in the p-PhOC6H4TeCl3 dimer33 and are equal to the sum of the covalent radii of Te and Cl (2.34 Å). There is shortening of Te-Cl (bridging) bonds [average 2.467 Å] compared to that in the case of the p-PhOC6H4TeCl3 dimer. The angle Cl(1)Te(1) · · · N(1) [174.2(5)°] is close to the linear arrangement. The Te(1) · · · N(1) and Te-Cl bond distances are shorter than the corresponding distances of phenylazophenyl(C, N′)tellurium (33) Chadha, R. K.; Drake, J. E. J. Organomet. Chem. 1985, 293, 37.

Pd-C1 Pd-ClA N-Pd-C1 ClA-Pd-N Cl-Pd-N Pd-Cl-PdA

1.970(3) 2.3290(10) 82.58(12) 177.47(8) 96.56(9) 94.04(4)

Pd-N Pd-Cl ClA-Pd-C1 Cl-Pd-C1 Pd-Cl-PdA

2.077(3) 2.4740(14) 94.89(10) 177.41(10) 94.04(5)

chloride34 [Te · · · N, 2.210(7) Å; Te-Cl, 2.533(3) Å] and 2-(2pyridyl)phenyltellurium chloride35 [Te · · · N, 2.205(11) Å; Te-Cl, 2.606(11) Å], respectively. The Te(1) · · · N(1) and Te(1)-Cl(1) bond distances are very close to the respective distances in the related compounds [2-(4,4-dimethyl-2-phenyl)oxazolinyl]tellurium chloride and [2-[1-(3,5-dimethylphenyl)-2-naphthyl]-4,5dihydro-4,4-dimethyloxazole]tellurenyl chloride.36 The X-ray structure of 25 is given in Figure 5. The organopalladium complex was characterized unambiguously by a single-crystal X-ray study. Although the structure of 25 has been recently reported by Menta and co-workers,37 we had previously solved the structure at a different temperature; hence we briefly present the salient features of the structure only. Complex 25 crystallizes as a dimer with two square-planar coordinated palladium atoms. Each palladium atom coordinates to two bridging chlorines, nitrogen, and a carbon atom in a cis square-planar MA2BC geometry. The complex is centrosymmetric and the N,N-dimethylbenzylamine ligand is coordinated to palladium through the nitrogen and the ortho carbon. The trans effect of the σ-bonded carbon is stronger than that of nitrogen as is reflected in the Pd-Cl bond lengths of the two bridging chlorines (Pd-Cl, trans to carbon, 2.4740(14) Å; Pd-ClA, trans to nitrogen, 2.3290(10) Å) (Table 4). The Pd-ClA distance is on the high side of the range of 2.24-2.45 Å reported for various Pd(II) complexes. Both five-membered chelate rings are almost planar, and the N,N-dimethylbenzylamine ligand lies in the same plane as the palladium atom.

Conclusion In summary, we have systematically explored the coordination chemistry of intramolecularly coordinating hybrid organochalcogen ligands with Pd(II). The cleavage of C-E and E-E bonds proceeded cleanly under mild conditions. In particular, the facile cleavage of C-Te bond in N,Te,N type tridentate ligands appears to be a general phenomenon. Interestingly, the stable arenetellurenyl halides (10-Te-3) are isolated as dimers to give (34) (a) Cobbledick, R. E.; Einstein, F. W. B.; McWhinnie, W. R.; Musa, F. H. J. Chem. Res. 1979, 145 (S); 1901 (M). (b) Mbogo, S. A.; McWhinnie, W. R.; Lobana, T. S. Inorg. Chim. Acta 1992, 193, 5. (35) Greaves, M. R.; Hamor, T. A.; Howlin, B. J.; Lobana, T. S.; Mbogo, S. A.; McWhinnie, W. R.; Povey, D. C. J. Organomet. Chem. 1991, 420, 327. (36) Kandasamy, K.; Kumar, S.; Singh, H. B.; Wolmersha¨user, G. Organometallics 2003, 22, 5069, and references therein. (37) Mentes, A.; Kemmit, R. D. W.; Fawcett, J.; Russell, D. R. J. Mol. Struct. 2004, 693, 241.


Organometallics, Vol. 28, No. 8, 2009 2369

Table 5. Crystal Data and Structure Refinement of 17, 21, 24, and 25 empirical formula fw cryst color cryst syst space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z temp (K) abs coeff (mm-1) obsd reflns [I > 2σ] final R(F) [I > 2σ] wR(F2) indices [I > 2σ] abs struct param

17

21

24

25

C10H14NSeBr 307.09 yellow orthorhombic P212121 10.815(2) 9.0210(18) 11.805(2) 90 90 90 1151.7(4) 4 293(2) 6.687 1890 0.0488 0.0651 0.05(3)

C19H26Cl4N2Pd2Te2 892.22 red tetragonal P421c 14.681(2) 14.681(2) 12.538(4) 90 90 90 2702.3(10) 4 293(2) 3.852 4924 0.0364 0.0855

C30H28Cl2N2Te2 742.64 yellow monoclinic P21 10.448(2) 12.092(4) 11.143(2) 90 95.29(2) 90 1401.8(6) 2 293(2) 2.294 2734 0.645 0.1720 0.12(10)

C18H24Cl2N2Pd2 552.09 yellow monoclinic P21/c 7.8950(16) 15.751(3) 8.4150(17) 90 108.99(3) 90 989.5(3) 2 293(2) 2.089 2863 0.0384 0.0748

distorted square-planar complexes (12-Te-4). The C-Te bond cleavage has potential in palladium-catalyzed coupling reactions, and the study of coupling reactions using such ligands is in progress in our laboratory.

Experimental Section General Procedures. Solvents were predried and freshly distilled prior to use. The chemicals cis-1,5-cyclooctadiene and palladium chloride were of reagent grade and were used as received. The following starting materials were prepared according to literature methods: dichloro(η4-1,5-cyclooctadiene)palladium(II),27 dichlorobis(benzonitrile)palladium(II).38 Melting points were recorded in capillary tubes using a Veego VMP-1 melting point instrument. Elemental analyses are for the samples dried under vacuum for several hours and were performed on a Carlo-Erba model 1106 elemental analyzer. One of the palladium complexes (21) crystallizes as a partial solvate from dichloromethane, and the analytical data of this crystalline complex were calculated on the basis of dichloromethane observed in the individual sample by 1H NMR measurements. IR spectra in the range 450-100 cm-1 were recorded for solid samples as polyethylene pellets on a Bruker IFS 66V FTIR spectrometer. Nuclear magnetic resonance spectra, 1H (299.94 MHz), 13C (75.42 MHz), 77Se (57.22 MHz), and 125Te (94.75 MHz) were recorded on a Varian VXR 300S spectrometer at the indicated frequencies. Chemical shifts are cited with respect to Me4Si as internal (1H and 13C) and Me2Se (77Se) and Me2Te (125Te) as the external standard. Values quoted are using the high-frequency positive convention. FAB-MS (fast atom bombardment mass spectrometry) analyses were recorded on a Jeol SX 102/DA-6000 mass spectrometer/data system using xenon (6 kV, 10 mV) as the FAB gas. The accelerating voltage was 10 kV and the spectra were recorded at room temperature. m-Nitrobenzyl alcohol (NBA) was used as the matrix with positive ion detection. Electrospray mass spectra (ES-MS) were recorded at room temperature on a Q-Tof micro (YA-105) mass spectrometer. In the case of isotopic patterns the value given is for the most intense peak. Optical rotations were measured on a JASCO model DIP 370 digital polarimeter. Syntheses. [(S)-2-Me2NCH(Me)C6H4Se]2 (9). A stirred solution of (S)-N,N-dimethyl-1-phenethylamine (0.4 mL, 2.68 mmol) in dry ether (50 mL) was treated dropwise with a 1.6 M solution of n-butyllithium in hexane (1.68 mL, 2.68 mmol) under N2. On stirring for 24 h at room temperature, a white slurry of the lithiated product was obtained. Selenium powder (0.21 g, 2.68 mmol) was added to this under a brisk flow of N2 gas, and the stirring was (38) Doyle, J. R.; Slade, P. E.; Jonassen, H. B. Inorg. Synth. 1960, 6, 218.

continued for an additional 0.5 h. The reaction mixture was then poured into a beaker containing aqueous NaHCO3, and O2 was passed at a moderate rate for 0.5 h. The organic phase was separated from the aqueous phase, dried over anhydrous Na2SO4, and filtered. The filtrate was evaporated to dryness to give a yellow oil. All attempts to crystallize the oil were unsuccessful. The oil was dissolved in chloroform (25 mL) and treated with an excess of bromine (0.5 g, 6.0 mmol) to give an orange precipitate of the tribromide 16. This was filtered, dried, and weighed (0.88 g, 70%). Treatment of a suspension of 16 in absolute ethanol (50 mL, 0 °C) dropwise with an excess of NaBH4 (0.24 g, 6.0 mmol) gave a pale yellow solution, which was refluxed for 3 h and then poured into water (50 mL). The organic layer was extracted with ether, concentrated, and cooled to give a yellow solid of 9. Yield: 0.29 g, (47%); mp 69-70 °C); [R]25 -2.0408 (c 0.49; CHCl3); 1H NMR (CDCl3) δ 1.37-1.39 (d, 6H), 2.30 (s, 12H), 3.87 (bq, 2H), 7.08-7.20 (m, 6H), 7.84-7.87 (d, 2H); 13C NMR (CDCl3) δ 14.1, 41.0, 63.6, 125.9, 126.2, 127.6, 131.4, 133.3, 144.1; 77Se NMR (CDCl3) δ 444 ppm. Anal. Calcd (%) for [(S)-2-Me2NCHMeC6H4Se]2: C, 52.86, H, 6.16, N, 6.16. Found: C, 52.99, H, 6.26, N, 6.18. [(S)-(2-Me2NCH(Me)C6H4)]SeBr (17). Compound 17 was obtained adventitiously during attempts to obtain crystals of 16. A solution of 16 (0.88 g, 1.9 mmol) in DMSO (5 mL) was allowed to stand in a beaker for 2-3 days. Yellow crystals of 17 were found to settle down. Heating 16 in DMSO also gave 17. Yield: 0.23 g (40% based on 16); mp 138-139 °C; [R]25 -233.99 (c 0.5). Anal. Calcd (%) for C10H14NSeBr: C, 39.08, H, 4.56, N, 4.56. Found: C, 39.58, H, 4.56, N, 4.34; MS m/z 379 (M+ + Br), 307 (M+), 228 (SeC6H4CHMeNMe2), 183 (SeC6H4CHMe), 91 (C7H7), 72 (CHMeNMe2), 44 (NMe2); 1H NMR (DMSO-d6) δ 8.00-8.01(d, 1H, Ar-H), 7.20-7.93 (m, 3H, Ar-H), 4.25-4.43 (q, 1H, CH-), 2.94 (s, 3H, NMe), 2.53 (s, 3H, NMe), 1.43-1.45(d, 3H, CHMe); 13 CNMR (DMSO-d6) δ 11.8, 41.5, 41.6, 68.1, 125.8, 127.2, 129.3, 130.2, 135.6, 140.1; 77Se NMR 1018 ppm. General Methodology for Preparation of Complexes. A mixture of the appropriate ligand and Pd(COD)Cl2 (in dichloromethane and in equimolar amounts) was stirred for 2 h at room temperature. The solution volume was reduced to a few milliliters, and the product was precipitated by incremental addition of hexane. The powdered solid obtained after filtration was quickly redissolved in a minimum quantity of dichloromethane, and a top layer of an equal volume of hexane was added carefully. After 1-2 days, crystalline solids were obtained. In the case of ligands 11 and 12, a powder was obtained. This was found to be a mixture of two compounds, which were separated on the basis of their different

2370 Organometallics, Vol. 28, No. 8, 2009 solubilities. Once isolated in the crystalline form, it was difficult to redissolve the complexes in the solvent from which they were originally crystallized from. [(S)-(2-Me2NCHMeC6H4)]SeCl (18). Compound 18 was obtained adventitiously during attempts to obtain a complex of Pd(II) by the reaction of Pd(COD)Cl2 (0.38 g, 1.3 mmol) with 9 (0.58 g, 1.3 mmol) following the general procedure. An immediate color change from yellow to red was observed on addition. Recrystallization from chloroform gave yellow crystals, which were analyzed to be 18 (0.28 g, 40%, based on 9); mp 133-134 °C; [R]25 -3.999 (c 3, CHCl3). Anal. Calcd (%) for C10H14NSeCl: C, 45.62, H, 5.32, N, 5.32. Found: C, 44.22, H, 4.94, N, 5.03; 1H NMR (CDCl3) δ 8.18-8.15 (d, 1H, Ar-H), 7.38-7.05 (m, 3H, Ar-H), 4.10-4.04 (q, 1H, CH-), 2.86 (s, 3H, NMe), 2.51 (s, 3H, NMe), 1.49-1.47 (d, 3H, CHMe); 77Se NMR 1021 ppm. Pd2[7]Cl2 (19). Reaction of Pd(COD)Cl2 (0.28 g, 1 mmol) with 7 (0.67 g, 1 mmol) was carried out following the general procedure. An abrupt color change from red to deep brown was observed within seconds of the addition. On stirring for 2 h slight turbidity was observed. The reaction mixture was filtered and the filtrate was concentrated to give a brownish-black solid. Recrystallization from dichloromethane/hexane gave needle-like crystals of the pure desired compound corresponding to only one isomer. Small amounts of COD were removed by repeating the recystallisation in the same solvent system or benzene/hexane. Yield: 0.43 g, 92%; mp 112 °C (dec); [R]25 322.58 (c 0.031, CHCl3). Anal. Calcd (%) for C28H36Cl2Fe2Pd2N2Se2: C, 35.25, H, 3.77, N, 2.93. Found: C, 36.93, H, 4.25, N, 2.57. MS: m/z 955 (M+, 100%), 920 (M+ - Cl, 65%), 884 (%), 855 (10%), 762 (20%), 717 (10%), 256 (95%), 154 (C5H3SeCH, 70%), 136 (90%).107 (%), 89 (%) 65 (Cp, %); 1H NMR (CDCl3) δ 5.37 (m, 2H, C5H3-H), 4.24-4.22 (m, 2H, C5H3H), 4.21-4.18 (m, 2H, C5H3-H), 4.16 (s, 10H C5H5-H), 4.03-3.97 (q, 2H, CH), 3.04 (s, 6H, NMe), 2.29 (s, 6H, NMe), 1.46-1.43 (d, 6H, CHMe); 13C NMR (CDCl3) δ 72.4 (C1, ipso), 91.7 (C5), 66.1 (C3), 67.3 (C4), 74.2 (C2), 70.5 (Cp-C), 47.7 (CH), 39.8 (NMe2), 7.4 (CH3); 77Se NMR δ -42.8 ppm; ν /cm-1 (polyethylene) 491s (M - N), 460s (M - N), 370m (M - Se), 296s (M - Cl), 278s (M - Cl), 241s, 195s. Pd2[8]Cl2 (20). The method is the same as described for complex 19 except that the ligand used was 8. Spectroscopic data obtained are as described as 19. Yield: 0.42 g, 89%; mp 112 °C (dec). Anal. Calcd (%) for C28H36Cl2Fe2Pd2N2Se2: C, 35.25, H, 3.77, N, 2.93. Found: C, 36.33, H, 4.22, N, 2.81. [R]25 -548.38 (c 0.031, CHCl3). Pd2[2-Me2NCH2C6H4Te]2Cl2 (21). Reaction of Pd(COD)Cl2 (0.087 g, 0.3 mmol) with 10 (0.157 g, 0.3 mmol) was carried out using the general procedure. On addition, an immediate color change from yellow to red was observed. The reaction mixture was filtered and concentrated. Addition of a few drops of hexane immediately afforded dark red colored 21. The yellowish filtrate was further concentrated. After adding a few drops of hexane the solution was kept overnight in a refrigerator to afford 22. Complex 21 was recrystallized from a chloroform/hexane mixture to give red crystals. 21: Yield 0.070 g, 57%: mp 150-152 °C. Anal. Calcd (%) for C18H24Cl2N2Pd2Te2: C, 26.78, H, 2.93, N, 3.47. Found: C, 26.05, H, 2.87, N, 5.51. MS m/z 889 (M + CH2Cl2)+, 15%), 711 (80%), 675 (711 - Cl, 100%), 638 (675 - Cl, 25%); 1H NMR (CDCl3) δ 8.80-8.78 (m, 2H, Ar-H), 7.32-7.24 (m, 4H, Ar-H), 7.17-7.15 (m, 2H, Ar-H), 5.3 (CH2Cl2), 4.0 (d, 2H, CH2), 3.66 (d, 2H, CH2), 3.07 (s, 6H, NMe), 2.46 (s, 6H, NMe); 125Te NMR δ -6 ppm; ν/cm-1 (polyethylene) 499s (M - N), 469m (M - N), 326m (M - Te), 295s (M - Cl), 232 (M - Cl), 171m (M - Te). {[2-Me2NCH2C6H4]TeCl}2 (22). Yield: 25 mg, 28%; mp 136-138 °C. Anal. Calcd (%) for C18H24Cl2N2Te2: C, 36.37, H, 4.07, N, 4.71. Found: C, 36.22, H, 4.04, N, 6.34. 1H NMR (CDCl3) δ 8.05(d, 1H, Ar-H), 7.32-7.27 (m, 2H, Ar-H), 7.21-7.16 (m, 1H, Ar-H), 4.01 (s, 2H, CH2), 2.84 (s, 6H, NMe2); MS m/z 593 (M+, 15%);

Kaur et al. 561 (M+ - Cl, 38%); 299 (C9H12NTeCl, 50%) 264 (C9H12NTe, 100%); 220 (C7H6Te, 18%), 134 (C9H12NTe, 55%). Synthesis of Compounds 23 and 24. Reaction of Pd(C6H5CN)2Cl2 (0.173 g, 0.45 mmol) with 11 (0.236 g, 0.45 mmol) in benzene (20 mL) immediately produced a yellow precipitate. The stirring was continued for 12 h. Hexane was added to induce precipitation of 23. This is crystallized as yellow needles from dichloromethane and ether. Concentration of the filtrate afforded 24. {[2-C6H4CHNdCH(Me)C6H5]PdCl}2 (23). The yellow precipitate was characterized as 23. Yield: 0.068 g, 40%; mp 72-75 °C; [R]25 29.999 (c 0.5, CHCl3). Anal. Calcd (%) for C30H28N2Pd2Cl2: C, 51.50, H, 4.3, N, 4.0. Found: C, 51.43, H, 4.05, N, 3.91. ES-MS m/z 735.45 (M+ + Cl); IR (neat) 1656 cm-1 (CdN stretching); 1H NMR (CDCl3) δ 7.58 (CHdN, 2H), 7.00-7.48 (m, C6H5, C6H4, 18H), 5.34 (q, CHPh, 2H), 1.80 (d, Me, 6H); 13C NMR (CDCl3) δ 172 (imine carbon), 154, 146, 139.4, 133.5, 129.98, 128.9, 128.3, 127.49, 124.764 (aromatic carbon atoms), 65.0 (CHPh), 20.73 (Me). {[2-C6H4CHNdCH(Me)C6H5]TeCl}2 (24). Concentration of the filtrate afforded 24. Yield: 0.126 g, 80%; mp 175 °C; [R]25 137.99 (c 0.5, CHCl3). Anal. Calcd (%) for C30H28N2Te2Cl2: C, 48.52, H, 3.80, N, 3.77. Found: C, 50.2, H, 3.66, N, 3.99. ES-MS m/z 765 (M+ + Na+), 665, 314 (100%) 208; 1H NMR (CDCl3) δ 9.28 (s, 1H, azomethine), 8.7-7.0 (9H, aromatic), 5.31 (1H, CH(Me), 1.91, 1.89 (d, 3H CH3); IR(neat) 1662 cm-1 (CdN stretching). Synthesis of Compounds 22-25. Reaction of Pd(COD)Cl2 (0.11 g, 0.4 mmol) with 12 (0.16 g, 0.4 mmol) gave, after few minutes of stirring, a slight turbidity. The reaction mixture was concentrated and treated with hexane to give a yellow powder, which was found to be a mixture of 22 and 25. Purification was achieved by washing the solid (put on the filter paper) first with diethyl ether (22) followed by chloroform (25). {[2-Me2NCH2C6H4]PdCl}2 (25). Yield: 23 mg, 22%; mp 142 °C (dec). Anal. Calcd (%) for C18H24Cl2N2Pd2: C, 39.13, H, 4.34, N, 5.07. Found: C, 38.76, H, 4.37, N, 4.80. 1H NMR (CDCl3) δ 7.30-7.20 (bs, 1H, Ar-H), 6.98-6.92 (m, 2H, Ar-H), 6.90-6.64 (m, 1H, Ar-H), 3.95 (s, 2H, CH2), 2.85 (s, 6H, NMe2); MS m/z 793 (20%); 551 (M+, 48%), 516 (M+ - Cl, 100%); 134 (C9H12NTe, 55%). X-ray Structure Determination. Organylselenyl bromide 17 was obtained as yellow hexagonal plates from dichloromethane/ hexane after one day at -10 °C. Red needles of complex 21 were obtained from hexane/dichloromethane after 7 h by vapor diffusion at room temperature. Yellow parallelepipeds of complex 24 were obtained similarly from hexane/chloroform. Yellow needles of 25 were obtained from chloroform/ether. Single-crystal X-ray diffraction measurements for 17, 21, and 25 were performed at room temperature (293 K) on a Siemens PC controlled R3 diffractometer and 24 on an Enraf-Nonius CAD 4 diffractometer using graphite-monochromated Mo KR radiation (R ) 0.7107). The structures were solved by direct methods. The analytical scattering factors of Cromer and Waber39 were used; real and imaginary components of anomalous scattering for the atoms were included in the calculations. All computational work was carried out using Siemens programs and SHELXTL PLUS40 and ORTEP.41 Crystal data and numerical details of measurement of intensity details are given in Table 5.

Acknowledgment. We are grateful to the Department of Science and Technology (DST), New Delhi, for the award of a Ramanna Fellowship. Additional help from the SAIF, Indian Institute of Technology (IIT), Bombay, for 300 MHz NMR and Tata Institute of Fundamental Research (TIFR), Bombay, for 500 MHz NMR spectros-


copy, and RSIC and CDRI Lucknow for FAB-MS is gratefully acknowledged. Supporting Information Available: A listing of cif files giving crystallographic data of 17, 21, 24, and 25 (CCDC 161114, 174699, (39) Cromer, D. T.; Weber, T. In International Tables for the X-ray Crystallgraphy, IV; Kynoch Press: Birmingham, England, 1974.

Organometallics, Vol. 28, No. 8, 2009 2371 174700, 174701). This material is available free of charge via Internet at http://pubs.acs.org. OM801015E (40) SHELXTL PLUS. X-ray Instruments Group; Nicolet Instruments Corp.: Madison, WI, 1983. (41) Johnson, L. K. ORTEP-11, Report ORNL-5138; Oak Ridge National Laboratory: Oak Ridge, TN, 1976.

Facile Cleavage of Organochalcogen Hybrid (NEEN, NEN, EN, where

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