Thioether nickel

Several extraction techniques have also been described that use enzymatic or chemical reactions to improve extraction efficiency. A technique that has been used to increase the overall recovery of the marker residue is enzymatic hydrolysis to convert specific phase II metabolites (glucuronides or sulfates) back into the parent residue. Cooper etal used a glucuronidase to increase 10-fold the concentration of chloramphenicol residues in incurred tissue. As an example of a chemical reaction, Moghaddam et al. used Raney nickel to reduce thioether bonds between benomyl and polar cellular components, and as a result achieved a substantially improved recovery over conventional solvent extraction. In choosing to use either of these approaches, thorough characterization of the metabolism in the tissue sample must be available. 

Oxygenation of the Ni1 complex (39) leads to 02 activation and 0-0 bond rupture with formation of a deep purple bis(/i-oxo)nickel(III) complex (40) supported by thioether ligands.184 Its electronic structure has been investigated by spectroscopic and DFT methods.185... 

Optically active amine-thioether ligands (492) have been investigated in nickel-catalyzed asymmetric cross-coupling reactions of Grigard reagents.1338... 

Nickel, Ni2+ (d8) 4, square planar S-Thiolate, thioether, V-i midazole, poly pyrrole Hydrogenases, hydrolases... 

Desulfuration.1 This complex as such or in combination with 2,2 -bipyridyl (bpy) or triphenylphosphine (a NiCRAL) can effect desulfuration of heteroarenes. aryl thioethers, dithioketals, sulfoxides, or sulfones in DME or THF at 63° in 1.5-30 hours. NiCRA is sufficient for aryl thioethers, dithioketals, but NiCRALs are more efficient for desulfuration of heteroarenes. Yields can be comparable with those obtained with Raney nickel. 

Synthesis. The first example of a stable, soluble pz peripherally substituted with a heteroatomic moiety involved appended thioether groups, M[pz(.V-Mc)8, as reported in 1980 by Schramm and Hoffman (2) (Scheme 9, 45-48). Mg[pz(5 -Me)s], 46, was prepared in a 60% yield by a magnesium templated macrocyclization of dinitrile, 45. Demetalation with sulfuric acid gave H2[pz(5 -Me)8], 47 (65%) and remetalation with the anhydrous acetate salts of copper and nickel gave 48 (80%) and 49 (65%). 

A novel approach to the synthesis of desoxy sugars was made by Jeanloz, Prins and Reichstein69 in 1945. In general terms, a 1,2-epoxide was cleaved with sodium thiomethoxide to give a /3-hydroxy thioether which, in turn, was hydrogenolyzed with Raney nickel. It is apparent... 

The tetradentate ligand forms monomeric square planar complexes. Synthetic and kinetic studies reveal that the coordinated mercapto group may be converted into the coordinated thioether function without breaking the metal-sulfur bond. The nucleophilic power of the coordinated mercapto group exceeds that of RSH, but depends on the metal atom. Bridging protects the sulfur atom from alkylation. In the case of nickel(ll), alkylation is accompanied by expansion of the coordination number of the nickel from 4 to 6. Ligand reactions have led to the synthesis of planar ligands completely cydized about the metal ion. 

Thioethers (sulfides) can be prepared by treatment of alkyl halides with salts of thiols (thiolate ions).7S2 R may be alkyl or aryl. As in 0-35, RX cannot be a tertiary halide, and sulfuric and sulfonic esters can be used instead of halides. As in the Williamson reaction (0-12), yields are improved by phase-transfer catalysis.753 Instead of RS ions, thiols themselves can be used, if the reaction is run in benzene in the presence of DBU (p. 1023).754 Neopentyl bromide was converted to Me3CCH2SPh in good yield by treatment with PhS in liquid NH3 at -33°C under the influence of light.755 This probably takes place by an SrnI mechanism (see p. 648). Vinylic sulfides can be prepared by treating vinylic bromides with PhS in the presence of a nickel complex,756 and with R3SnPh in the presence of Pd(PPh3)4.757 R can be tertiary if an alcohol is the substrate, e.g,758... 

Thiols and thioethers,413 both alkyl and aryl, can be desulfurized by hydrogenolysis with Raney nickel.414 The hydrogen is usually not applied externally, since Raney nickel already contains enough hydrogen for the reaction. Other sulfur compounds can be similarly desulfurized, among them ... 

Table 89 Synthetic and Structural Properties of Selected Nickel(II) Complexes with Thioether Ligands...

The coordination of methionine, MeSCH2CH2CH(NH2)C02H, to nickel has been investigated in solution. It has been found that the complex [Ni(D-Met)(L-Met)] (Met = monoanionic methionine) is a little more stable than the optically active complex. The ligand is supposed to act as tridentate with at least weak Ni—S (thioether) bonding. 72... 

Figure 5-75. The alkylation of a nickel(n) thiolate complex gives a thioether complex. There is no competitive alkylation of the pyridine nitrogen atom.

Desulfurization (13, 158-159).1 In addition to desulfurization of thiols, thioethers, sulfoxides, and sulfones, Cp2Ni-LiAlHi (1 1) can serve as a hydrogenation catalyst for reduction of alkenes it also reduces enones to ketones, but in low yield. In general, it is similar in reactivity to Raney nickel and to (2,2 -bi-... 

Treatment of the 2-pyrrolyl allyl thioether (498) with acetic anhydride and quinoline at 170 °C (or in A jV-dimethylaniline at ca. 100 °C) results in a thio-Claisen rearrangement to give the 5-(3-allyl-2-pyrrolyl) thioacetate (499), whilst peracid oxidation of (498) produces the non-rearranged sulfone in low yield and Raney nickel reduction of (498) yields 3-propylpyrrole (78CJC221). The polyphosphoric acid-catalyzed cyclization of (2-pyrrolylthio) acetic acid (501 R = R = H) somewhat unexpectedly yields (502) via the Spiro intermediate, instead of forming the expected oxothiolane (500), which can be obtained by a Dieckmann cyclization of ethyl (3-ethoxycarbonyl-2-pyrrolylthio) acetate (501 R = Et, R = C02Et) (B-77MI30506). 

---