Sulfur-Coordinated Products

Triphenyllead pyridine-4-thiolate (4-Ph3PbSC5H4N) is a chain polymer resulting from intermolecular Pb-S interactions. The cyclic dithiolate 

2-diphenyl-l,3,2-dithiapliunboIane self-assembles in the solid state, forming chain structures as shown in 12. The intramolecular Pb-S bond lengths are nearly the same, 2.54 and 2.49 A, but the intermolecular Pb-S bond length is much larger, 3.55 A. 

TriphenyUead dimethyldithiophosphinate also forms polymeric structures. Here, the dithiophosphinate imsymmetrically bridges two lead atoms of adjacent units, giving a polymeric chain with pentacoordinated lead atoms (13). The coordination is best described as being distorted trigonal bipyramid with the phenyls in the equatorial and the sulfur in the axial positions. The lead-sulfur distances are 2.708 and 3.028 A. 

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Dithiothreitol is a more complex ligand than p-mercaptoethanol, and there is a corresponding increase in complexity of the solution chemistry. Two binuclear products (-352, -362 ppm -399, -526 ppm), both of V2L stoichiometry, have been identified. The individual vanadiums of each product are chemically distinct. The NMR studies [37] show that in one of the complexes, both vanadiums have a single coordinated sulfur. In the second complex, one of the two vanadiums has sulfur coordinated, whereas the second of the two has only oxygen in the coordination sphere. Neither of these compounds have been characterized by x-ray diffraction... 

Thia-6-selenaspiro[3,3]heptane with Cu(hfac)2 provided a new coordination product, [Cu(hfac)2]32SeSC5H8. This complex statistically mixes positions of the donor sulfur and selenium atoms to give an average axial Cu- S/Se contact at 2.892A <2005IC77>. The following complexes were synthesized [W(CO)5L ], [ W(CO)s 2L1],... 

Somewhat related to these studies is the proposed formation of heterobime-tallic complexes upon addition of MCI2 (M = Co, Ni, Cu) to [Zn(S2CNR2)2] (R = Me, Cy R2 = C7H14) (1895). Precise product structures are unknown, but the authors propose the formation of either binuclear complexes in which either one MCI2 unit is bound via sulfur coordination from two different dithiocarbamate ligands, or tetranuclear complexes, whereby two zinc bis(dithiocarbamate) centers are linked via two MCI2 units. 

Boron trifluoride catalyst may be recovered by distillation, chemical reactions, or a combination of these methods. Ammonia or amines are frequently added to the spent catalyst to form stable coordination compounds that can be separated from the reaction products. Subsequent treatment with sulfuric acid releases boron trifluoride. An organic compound may be added that forms an adduct more stable than that formed by the desired product and boron trifluoride. In another procedure, a fluoride is added to the reaction products to precipitate the boron trifluoride which is then released by heating. Selective solvents may also be employed in recovery procedures (see Catalysts,regeneration). 

Thiazoles are desulfurized by Raney nickel, a reaction probably initiated by coordination of the sulfur at Ni. The products are generally anions and carbonyl compounds (see Section 4.02.1.8.4). 

Examples of the C2N3S ring system containing three- or four-coordinate sulfur are also well known. The monohalogenated derivatives 12.2 (E = S, Se), are best prepared by the condensation of imidoyl amidines with SCI2 or SeCU, respectively (Scheme 12.1)." In the case of the selenium derivative, the initial product is heated at 60°C and then at 120°C in order to convert it to 12.2 (E = Se) via (PhC)2(NH)N2SeCl2. In the solid state this intermediate is a weakly associated, centrosymmetric dimer with Se-Cl and Se Cl distances of 2.42 and 3.39 A, respectively. ... 

Cases of the S-coordinated rhodium and iridium are quite scarce. To complete the picture, we next consider the possibilities of S-coordination using complicated derivatives of thiophene. 2,5-[Bis(2-diphenylphosphino)ethyl]thiophene is known to contain three potential donor sites, two phosphorus atoms and the sulfur heteroatom, the latter being a rather nucleophilic center (93IC5652). A more typical situation is coordination via the phosphorus sites. It is also observed in the product of the reaction of 2,5-bis[3-(diphenylphosphino)propyl]thiophene (L) with the species obtained after treatment of [(cod)Rh(acac)] with perchloric acid (95IC365). Carbonylation of [Rh(cod)L][C104]) thus prepared yields 237. Decarbonylation of 237 gives a mixture of 238 and the S-coordinated species 239. Complete decarbonylation gives 240, where the heterocycle is -coordinated. The cycle of carbonylation decarbonylation is reversible. 

The deprotonation of 132 is favored at Ni and the coordination of 135 occurs preferentially at 82- A second entity of 135 coordinates at N3. A computational study of thiouracil derivatives of the tungsten(O) hexacarbonyl shows that the sulfur-bound thiouracil is serving as a ir-donor during the CO dissociation (Scheme 91) [99IC4715]. DFT calculations show that 137 is significantly stabilized with respect to the alternative reaction product 138. 

The Prins reaction often yields stereospecifically the and-addition product this observation is not rationalized by the above mechanism. Investigations of the sulfuric acid-catalyzed reaction of cyclohexene 8 with formaldehyde in acetic acid as solvent suggest that the carbenium ion species 7 is stabilized by a neighboring-group effect as shown in 9. The further reaction then proceeds from the face opposite to the coordinating OH-group " ... 

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