Organotin-Sulfur Intramolecular Interactions: An Overview of Current

Chapter 30

Organotin-Sulfur Intramolecular Interactions: An Overview of Current and Past Compounds and the Biological Implications of Sn---S Interactions Downloaded by UNIV QUEENSLAND on June 11, 2014 | http://pubs.acs.org Publication Date: December 1, 2005 | doi: 10.1021/bk-2005-0917.ch030

1

1

2

Teresita Munguia , Francisco Cervantes-Lee , LászlóPárkányi , and Keith H. Pannell * 1,

1

Deparment of Chemistry, University of Texas at El Paso, El Paso, TX 79968 Institute of Chemistry, Chemical Research Center, Hungarian Academy of Sciences, H-1525, P.O. Box 17, Budapest, Hungary

2

Lewis acid interactions of tin are of interest because it is often through intermolecular hypervalent mechanisms that organotin compounds interact with biological materials, resulting in their characteristic biocidal capabilities. We investigate the nature of the Sn---S intramolecular interactions in previously known and new organotin sulfides that may prove to be useful in modifying biocidal activity due to competition with intermolecular Sn---S biological interactions.

422

© 2006 American Chemical Society In Modern Aspects of Main Group Chemistry; Lattman, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.

423

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The restrictions on organotin antifouling paints, has lead to the search for materials that are as efficacious as the currently used formulations, but less toxic to the environment. It has been suggested that the biocidal properties of oragnotin compounds results from the ability of the tin atom to participate in intermolecular interactions, in particular with thiol groups in cystine type residues (1). For this reason, we believe it useful to investigate organotin compounds with a potential for /«/romolecular interactions with sulfur, so as to modify biocidal activity via competition between the intramolecular sulfur and biological sulfur groups, Figure 1.

Figure L Potential competition between sulfur containing biological residue and organotin compounds with intramolecular Sn—S interactions.

Biocidal Activity of Organotin Compounds Organotin compounds have found application in a large array of societal uses. They are used as stabilizers for vinyl chloride resins, catalysts, wood preservatives, antifouling agents, agrochemicals, precursors for tin oxide films, and as potentially useful therapeutic drugs. (2-5). Each usage draws upon a basic property of organotin compounds; that is, the ability of tin to become hypervalent and contain coordination numbers larger than four. However, such widespread usage has led to accumulation in the environment and their use is to be severely limited. The mammalian toxicity of organotin compounds has been well-reviewed (6). Of major concern is the recent finding by Whalen el al. that "normal" human blood samples contained concentrations varying from 64 to 155 ng/mL of tributyl tin, dibutyl tin and monobutyl tin (7). The same group has shown that tributyl tin can inhibit human natural killer lymphocyte function in vitro and since tributyl tin has been linked to neurotoxicity, hepatotoxicity, immunotoxiciy, and cutaneous toxicity in rats and mice (6) the overall finding is potentially significant.

In Modern Aspects of Main Group Chemistry; Lattman, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.

424 While different organotin toxicities are well-documented, a complete and detailed understanding of the mechanism of cell-organotin interactions is not available (8). However, histidine and cysteine residues have been implicated in binding of trialkyltin compounds in cat and rat hemoglobin (8). Cysteine in particular has the thiol group that can bind to organotin compounds, Figure 2.

H CSCH CH CHCOO" 3

2

• JiH Downloaded by UNIV QUEENSLAND on June 11, 2014 | http://pubs.acs.org Publication Date: December 1, 2005 | doi: 10.1021/bk-2005-0917.ch030

HSCH CHOO"

2

2

*ljH

3

methothionine (Met)

3

cysteine (Cys)

OOCCHCH S—SCH CHCOO 2

• NH

2

*NH

3

3

cystine (Cys-Cys)

H

H

I

I

• NH CHCH CH C—NCH—CNCH COO 3

2

COO*

2

δ

2

CH Ο 2

L glutathione (Glu-Cys-Gly) Figure 2. Biologically important sulfur-containing residues. An excellent review (8) has summarized organotin amino acid and peptide interactions. Recent studies (1,9) have illustrated a trigonal bipyramidal solution coordination geometry for di- and tri-organotin derivatives of sulfur-containing amino acids and peptides. The strong Sn—S intermolecular interactions apparently act as an anchoring site for the organotin molecules thereby permitting further coordination with neighboring Ν groups in the biological


425 residue (1). Structure and activity of organotin compounds can be condensed into three main points (8,9): • •


•

The accessibility of coordination sites at tin. The ability to create stable (but not too stable) ligand—Sn interactions via Sn—S or Sn—Ν interactions. The capability of the ligand—Sn interaction to withstand hydrolysis.

An aim of our current research is the synthesis and biocidal evaluation of organotin compounds containing sulfur groups that can exhibit intramolecular Sn—S interactions. Here we present an overview of such known interactions including those exhibited by new o-thiomethylbenzyl derivatives from our laboratory.

Tin-Sulfur Intramolecular Interactions A query of non-bonded contact distances between tin and sulfur was performed using the Cambridge Crystallographic Database (10). A maximum for the sum of the van der Waals radii for Sn and S of 4.0 Â was used. We further restricted our analysis to the organotin compounds with 1,1-ditholate family and simple alkyl-alkyl or alkyl-aryl sulfides.

Intramolecular Organotin 1,1-Dithiolate Interactions The family of organotin derivatives of dithiocarbamates, xanthates, and dithiocarboxylates all have the same ligand arrangement of "S CY, where Y = aryl/alkyl, NR , and OR, respectively. Several reviews (11-13) have demonstrated the remarkable diversity in the structures of these organotin(IV) compounds; therefore our analysis of these compounds will be brief and only a few representative samples will be discussed. Ligands such as 1,1-dithiolates can coordinate with organotin compounds in three ways, Figure 3. The 1,1-ditholate ligand can be isobidentate, in which both sulfur atoms bind equally with tin, anisobidentate, in which one covalent bond has formed and the other S interacts intramolecularly to form a secondary interaction, and monodentate, in which the secondary S—Sn interaction is "too long" to contribute to changes in the coordination geometry at the tin atom. In addition, Tiekink (12, 14) found that many of the bis-( 1,1-dithiolates) adopt one of four structural arrangements that are a combination of isobidentate, anisobidentate, and monodentate. The R groups can adopt a trans or cis configuration in the distorted octahedral geometry which the bis-( 1,1-dithiolates) can form. A skew-trapezoidal bipyramidal geometry can also be formed in which the R groups lean over the longer Sn—S interactions and represents the most 2

2



426

Isobidentate

Anisobidentate

Monodentate

Figure 3. Structural motifs of organotin 1,1-dithiolates


427 commonly found bonding motif. Finally, distorted trigonal bipyramidal geometry about tin due to die monodentate binding of a second dithiolate ligand can be observed. Table 1 summarizes a selection of organotin-1,1 -ditholate compounds with their relevant Sn—S distances. The great majority of organotin-1,1 -dithiolates coordinate in an anisobidentate manner with two clearly distinguishable Sn—S atom separations. The complexes Ph Sn(S CN(Et)C6Hio) , Ph Sn(S CN[C H o]2)2 and Ph ClSnS C(C H NH ) approximate isobidentate coordination observed by the lengthening of die S=C bond and the shortening of the S—C bond. 2


2

2

6

1

5

2

2

5

3

2

2

2

Table I. Selected Organotin 1,1-dithiolates.

Sn—S Me SnS2CNMe 3

2

M-BuPh SnS CNMe2 Ph SnS CNC H Ph SnS CN(Et)2 Ph SnS CN(Me)w-Bu Ph SnS C(o-tol) Ph ClSnS C(C H NH ) («-Bu) Sn(S CNC H40) Ph Sn(S2CN[Et] ) PhzSnCSîCNlQHwfe), 2

3

2

2

3

2

3

2

3

2

4

2

2

2

5

5

3

2

2

2

4

2 2

PMn^CNiEtX^H.ok PhzSnCSzCOi-Pr^ Me Sn(S COMe) 2

2

2

PhMeSn^COMe^ Ph Sn(S COMe)2 2

2

PhSn(S C-o-Tol) 2

3

2

S->Sn S-C

2.47 2.47

3.16 3.33

2.47 2.466 2.468 2.428 2.463 2.446 2.439 2.525 2.428 2.575 2.568 2.601 2.571 2.482 2.500 2.482 2.538 2.498 2.509 2.498 2.502 2.594 2.600

3.16 3.079 3.106 3.095 3.084 3.207 2.649 3.001 3.095 2.687 2.692 2.660 2.735 3.179 3.067 2.900 —

3.019 3.089 3.126 3.042 2.813 2.751

S=C

ref

A

ft 1.80 1.78

() 1.70 1.71

1.75 1.762 1.776 1.74 1.753 1.737 1.756 1.740 1.74 1.720 1.720 1.734 1.741 1.747 1.733 1.733 1.744 1.736 1.725 1.749 1.737 1.701 1.691

1.72 1.680 1.702 1.67 1.668 1.645 1.720 1.694 1.67 1.735 1.735 1.708 1.717 1.652 1.663 1.655 1.609 1.644 1.660 1.658 1.652 1.663 1.673

(15) (16) (17) (18) (19) (20) (21) (22) (23) (19) (24) (24) (25) (14) (14) (14) (21)


428 It is also important to note that the compounds with the shortest S->Sn distances have S—C—S bite angles ranging from 115.1-116.9° and S—Sn—S angles ranging from 67.26-70.65°. The compounds with longer S->Sn distances have larger S—C—S angles (117-124.4°) and smaller S—Sn—S angles (6064.64°) (14-25).


Intramolecular Organotin(IV)-SuIfide Interactions We are interested in simple alkyl/aryl sulfide systems where the soft sulfide ligand can act as a weaker donor toward tin halides, which are considered hard acids (26). A simple way to describe and assess potential intramolecular tinsulfur interactions is to monitor the progress from tetrahedral to trigonal bipyramidal geometry. Two primary methods for monitoring this transition is through Sn—S bond order (26-29) and inspection of the six bond angles of the inner tetrahedron (30, 31). Taken together, a fair assessment of the intramolecular tin-sulfur bond can be determined. The general types of such organotin sulfides are illustrated in Figure 4. The first group involves 1,5-transannular Sn—S interactions of the 8 member ring systems containing tin mid sulfur, Figure 4a (28,29, 32-36), while the others are aryl-alkyl sulfides connected to tin via flexible alkyl chains with 1-3 methylene groups, Figure 4b (26, 37, 38), and systems synthesized in our laboratory that contain an ortho benzylsulfide ligand that enables sulfur to be in close enough proximity to the tin atom, Figure 4c (39).

Compounds 1-10

Compounds 11-14

Compounds 15-19

Figure 4. a. Eight membered heterocycles of organotin compounds, Thioalkyl organotin compounds, c. (Ortho-thiomethyl)benzyl organo compounds.


429 We have also systematically increased the Lewis acidity of the tin atom by removal of the phenyl groups and addition of chlorine, i.e. Ph Sn, Ph ClSn and PhCl Sn. Table II lists the various known compounds within this general group that contain Sn—S atom distances shorter than the sum of the van der Waals radii, i.e. 4.02 Â (40). 3

2

2


Table IL Compounds Containing Tin—Sulfur Intramolecular Interactions. Compound Ε (ref) 1(32) S 2(33) S 3(28) C 4(29) S 5(29) s 6(34) s 7(34) s 8(34) s 9(35) s 10 (36) s 11 (37) 12 (38) 13 (38) 14 (26) 15 (39) 16(41) 17(41) 18(41) 19(41)

n

R

R'

Cl Ph Cl Br I Cl Br Me

Cl Ph Cl Br I Me Me Me

R"

R'"

c-Hex Ph Ph Ph Ph Ph Ph p-iBuPh /HBuPh

p-CICeH, o-NOzQH,

SCH2CH2SCH2CH2S

1 2 2 3

a c-Hex Ph Ph Cl Ph Cl Cl p-iBuPh Cl

n-Bu c-Hex Ph Ph Ph Ph Ph Cl /WBuPh p-/BuPh

2-NO2-4-CH3QH3

0-Tol

Note: Structural identification see Fig. 4; a: S P(OCH2C(Et2)CH 0); c-Hex = Cyclohexyl 2

2

The simplest and preferred way to analyze the Sn—S intramolecular interactions in these molecules is to determine their bond order (BO) and their "closeness" to tetrahedral or trigonal bipyramidal geometries. To determine the formal bond Sn—S order of the compounds we used the equation used by Drâger (26, 27): [d(Sn—E) ] + 1 - [d(Sn—E)]= BO, where Ε is the element in question, in these particular examples either C, S or halogen, and d(Sn—E) are the standard single bond distances according to O'Keeffe and Brese with corrections for electronegativity omitted (42). The distances used were Sn—S 2.4 A, Sn—C 2.15 A, Sn—CI 2.36 A, Sn—Br 2.50 A, and Sn—I 2.71 A. According to Drâger and co-workers (29), the Sn—I distance of O'Keeffe and av

av


430 Brese is too long and the distance 2.71 Â determined from Mes SnI was used instead. Here we also use this distance to simplify structural comparisons. Table III lists the tin-sulfur distances, bond orders, angle sums. 3


Table III. Important Bond Distances, Angle Sums, and "Closeness" to a Trigonal Bipyramid.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

S->Sn Â 2.760 3.246 2.851 2.767 2.779 2.863 2.835 3.514 3.074 2.940 3.29 3.26 3.67 3.58 3.195 3.699 3.829 3.062 2.994 3.351

Sn—Rax BO A S-*Sn 2.392 0.64 2.156 0.15 2.449 0.55 2.545 0.63 2.786 0.62 2.444 0.54 2.582 0.57 2.147 0 2.434 0.32 2.5379 0.46 2.22 0.11 2.15 0.14 2.128 0 2.139 0 2.442 0.21 2.145 0 2.170 0 2.4130 0.34 2.4042 0.41 2.143 2.3891 0.05

BO Sn—Rax

0.91 0.99 0.99 0.96 0.92 0.92 0.92 1 0.97 0.86 0.93 1 1 1 0.92 1 1 0.95 0.96 1 0.97

2*eq

(de$ 357.1 342.9 353.6 357.1 357.2 361.2 357.9 332.2

Σα, (dec) 287.1 311.9 293.6 287.2 287.1 285.6 284.6 323.4

^eq"

Σ αχ

70 31 60 70 70 76 73 9

—

—

—

354.7 332.6 332.2 334.1 334.9 355.2 333.4 325.7 350.5 349.4 335.8 345.7

291 324.2 324.6 322.5 321.6 292.2 323.3 331.1 300.9 299.8 320.4 305.3

64 8 8 12 13 63 10 5 50 50 15 40

Note: 9 Bicapped tetrahedron; 10 1,1-dithiolate interaction not considered here; 11 and 15 have two molecules in the asymmetric unit. The transition from tetrahedral to trigonal bipyramidal geometry can be mapped by comparing the "equatorial angles" to the "axial" angles that arise as tin changes from 4 coordinate to 5; the sum of the equatorial angles change from 328.5° to 360° and the sum of the axial angles change from 328.5° to 270° in the transition of tetrahedral to trigonal bipyramidal, respectively. Angles a—Sn—b, a—Sn—c, and a—Sn—d are die "axial" angles which give lax. The equatorial angles are b—Sn—c, c—Sn—d, and b—Sn—d and give Icq. Simply taking the difference between the two sums, one can determine


431 the geometry of a compound, i.e. the sum of pure tetrahedral will be 0° and the sum of pure trigonal bipyramidal will be 90°, so the resulting value in the range 0 - 90 reflects the proximity of the structure to the tbp form. Figure 5 shows this transition and the angles in question.

J

a

d

J ,...Siu^


# C

d

* * J Sn—b C"^ ι h

b

^

I

• S Figure 5. Transitionfromtetrahedral to trigonal bypyramidal. Figure 6 maps the distortion from tetrahedral for each compound. It can be seen that long S—Stt distances give geometries that can be called distorted tetrahedral whereas short S—Sn distances begin to approximate trigonal bipyramidal geometry.


432 The Sn—S bond order increases as the intranuclear distance decreases; however, there is no significant weakening of the S n — b o n d upon complexation of tin by the sulfur. A compilation of the Sn—S and Sn— bond orders is presented in Figure 7. It is interesting to note that even for the compounds which contain one or more halogens, and therefore the largest BO for Sn—S (compounds 1 and 3-7), the corresponding S n — B O does not decrease very much if at all. Furthermore, even the strongest bonding interactions exhibit a BO of significantly less than unity. 1.2-ρ Downloaded by UNIV QUEENSLAND on June 11, 2014 | http://pubs.acs.org Publication Date: December 1, 2005 | doi: 10.1021/bk-2005-0917.ch030

1 «

0.8

0 •e α ο α

0.6

"2

0.4 0.2 0 1515 12 13 8 1911 11 2 14 9 16 1710 6 3 7

5 4 1

Compound Number ESS9 BO S->Sn •BO Sn-Rax Figure 7. Comparison ofSn—S and Sn—R bond orders. ax

Although compound 11 has Sn—S distances that at a glance look short, 3.26 and 3.39 A, it has both low bond order (0.11 and 0.13) and very little distortion about the tin atom. The short intramolecular distance is due to their only being one C atom separating tin from sulfur. Normal C—S—C bond angles and normal Sn—C and C—S bond distances will place sulfur approximately 3.1-3.4 Â apart (37). It is worth noting that the chlorinated organotin compounds, 16,17, and 19 all have relatively short S—Sn distances and significant bond orders that result in clearly observable distortions at the tin atom. It is hoped that these compounds will exhibit modified biocidal activity by challenging the manner in which the central tin atom can interact with biologically available sulfur. Tests on such activity are presently in progress.


433


At above approximately 3.4 Â the bond order calculation, using the afore mentioned equation, begins to give negative values, which essentially means that the bond order is zero. Compounds 8,13,12, and 15 all have Sn—S bond orders of zero. Figure 8 illustrates the "cut off' distance of 3.4 Â from which a bond order can be calculated.

2.7

2.9

3.1

3.3

3.5

3.7

3.9

S—Sn Distance (À) Figure 8. S-Sn bond order as a function ofS-Sn intramolecular distance.

Each of these are triorganotin compounds, and by virtue of this, we can see how diminished the Lewis acidity of tin is in comparison to compounds such as 6, 14, and 16 which have one organic group replaced by a chloride atom and have comparably larger bond orders and shorter Sn—S distances.

Concluding Remarks Despite the simplicity of these compounds, they help provide an eloquent way to begin to understand how organotin species are able to interact with biologically important residues, namely sulfur containing residues. By analyzing what parameters are important for the coordination of tin, i.e. proximity of donor atoms and Lewis acidity of the tin center, we can perhaps bring forth some ideas into mechanisms by which these compounds work.


434

References 1. 2. 3. 4. 5.


6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

20. 21. 22. 23.

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435 24. Hall, V. J.; Tiekink, E. R. T. Main Group Metal Chemistry1995,18, 611620. 25. Donoghue, N.; Tiekink, E. R. T. Journal of Organometallic Chemistry 1991, 420, 179-184. 26. Cox, P. J.; Doidge-Harrison, S. M . S. V.; Nowell, I. W.; Howie, R. Α.; Wardell, J. L.; Wigzell, J. M . Acta Cryst. 1990, C46, 1015-1017. 27. Drager, Μ. Z. anorg.allg.Chem. 1976, 423, 53-66. 28. Jurkschat, K.; Schilling, J.; Mugge,C.; Tzschach, A. Organometallics 1988, 7, 38-46. 29. Kolb, U.; Beuter, M . ; Drager, M . Inorganic Chemistry 1994, 33, 45224530. 30. Kolb, U.; Drager, M . ; Jousseaume, B. Organometallics 1991, 10, 27372742. 31. Drager, M . Journal of Organometallic Chemistry 1983, 251, 209. 32. Drager, M . ; Engler, R. Chem. Ber. 1975, 108, 17-25. 33. Drager, M.; Guttmann, H.-J. Journal of Organometallic Chemistry 1981, 212, 171-182. 34. Kolb, U.; Beuter, M . ; Drager, M . Organometallics 1994, 13, 4413-4425. 35. Cea-Olivares, R.; Lomeli, V.; Hernandez-Ortega, S.; Haiduc, I. Polyhedron 1995, 14, 747-755. 36. Garcia y Garcia, P.; Cruz-Almanza, R.; Toscano, R.-A.; Cea-Olivares, R. Journal of Organometallic Chemistry 2000, 598, 160-166. 37. Cox, P. J.; Doidge-Harrison, S. M . S. V.; Nowell, I. W.; Howie, R. Α.; Randall, A. P.; Wardell, J. L. Inorganica Chimica Acta 1990, 172, 38. Howie, R. Α.; Wardell, J. L.; Zanetti, E.; Cox, P. J.; Doidge-Harrison, S. M . S. V. Journal of Organometallic Chemistry 1992, 431, 27-40. 39. Munguia, T.; Pavel, I. S.; Kapoor, R. N.; Cervantes-Lee, F.; Párkányi, L.; Pannell, Κ. H. Canadian Journal of Chemistry 2003, 81, 1388-1397. 40. Huheey, J. E.; Keiter, Ε. Α.; Keiter, R. L. Inorganic Chemistry: Principals of Structure and Reactivity; 4th ed.; Harper Collins College Publishers: New York, NY, 1993; pp 292. 41. Munguia, T.; Kapoor, R. N.; Cervantes-Lee, F.; Pannell, Κ. H. Unpublished Data 42. O'Keeffe, M . ; Brese, Ν. E. J. Am. Chem. Soc. 1991, 113, 3226-3229.


Organotin-Sulfur Intramolecular Interactions: An Overview of Current

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