Zinc, sulfoxide complexes

The most stable structures and formation energies of zinc thiocyanate complexes have been calculated by ab initio density functional methods. The formation energies of the linkage isomers [Zn(NCS)4]2. [Zn(NCS)2(SCN)2]2, and [Zn(SCK)4]2 were determined. A comparison of the formation energies indicated that [Zn(SCN)4]2 is the most stable isomer both in water and in dimethyl sulfoxide.567... 

However, addition of (+ )-(7 )-l-methyl-4-(mcthylsulfinyl)benzene, to aldehydes and ketones proceeds with low stereoselectivity. An improvement of the 3-syn diaslereoselectivity was found with the zinc reagent obtained by transmetalation of the lithiated sulfoxide with anhydrous zinc chloride38. An improvement of the stereoselectivity was also attained by exchange of the 4-methylphenyl substituent for a 2-methoxyphenyl or 2-pyridinyl substituent. Thus, the introduction of an additional complexing site into the aromatic part of the sulfoxide reagent enhances the stereoselectivity35. 

Much work has been devoted to the halide complexation of these elements in non-aqueous media. Equilibrium and calorimetric measurements for the formation of the [MX ](n-2) (M = Zn or Cd X = Cl, Br, I or SCN n = 1-4) anions in dimethyl sulfoxide (DMSO) have shown that stability constants follow the same order, but are much larger than those found for aqueous solution zinc exhibits an enhanced hardness as an acceptor in DMSO as compared to cadmium. Calorimetric measurements indicate a change from octahedral to tetrahedral coordination with increasing halide concentrations.1002-1006... 

Diarylacetylenes are converted in 55-90% yields into a-diketones by refluxing for 2-7 h with thallium trinitrate in glyme solutions containing perchloric acid [413. Other oxidants capable of achieving the same oxidation are ozone [84], selenium dioxide [509], zinc dichromate [660], molybdenum peroxo complex with HMPA [534], potassium permanganate in buffered solutions [848, 856, 864,1117], zinc permanganate [898], osmium tetroxide with potassium chlorate [717], ruthenium tetroxide and sodium hypochlorite or periodate [938], dimethyl sulfoxide and iV-bromosuccin-imide [997], and iodosobenzene in the presence of a ruthenium catalyst [787] (equation 143). 

To preform a strong enone sulfoxide-metal ion complex and thus possibly to increase the amount of asymmetric induction, several metal dibromides were added to eyelopentenone sulfoxide ( )-(+)-10. As shown in eq. 12, only zinc dibromide was highly effective in raising the extent of asymmetric induction during methyl Grignard conjugate addition. 

Sandstrom M (1977) An X-ray diffraction and Raman study of mercury(II) chloride complexes in aqueous solution. Evidence for the formation of polynuclear complexes. Acta Chem Scand Ser A 31 141-150 Sandstrom M, Persson I, Ahrland S (1978) On the coordination around mercuiy(II), cadmium(II) and zinc(II) in dimethyl sulfoxide and aqueous solutions. An X-ray diffraction, Raman and infrared investigation. Acta Chem Scand Ser A 32 607-625... 

Posner has also described the stereocontrolled addition of vinyl Grignard reagents to enantiomerically pure cyclopentanone sulfoxides [43,47]. The addition of vinylmagnesium bromide to (70) pre-complexed with zinc bromide, and further reaction as described in Scheme in 4.36, yielded exclusively (5,5)-3-vinylcyclopentanone (71) in 30% overall yield. 

The first example of an asymmetric directed Mizoroki-Heck reaction was published by Carretero et al., using sulfoxides as chiral auxiliaries (Scheme 7.20) [54aj. By coordination to the nitrogen, the sulfinyl group nicely directs the arylpalladium(II) complex towards one of the diastereotopic faces of the alkene, followed by diaste-reoselective C—C bond formation [54]. As an example, the reaction of 101 with iodobenzene (73a), yielding (2S, R)-102 in very good diastereomeric ratio (dr) of 94 6 which, after desulfinylation with zinc, gave (1 )-103 in excellent enantiomeric... 

Kobuke and colleagues described a complementary zinc porphyrin-magnesium phthalocyanine dimer that can be considered as a supramolecular switch (Figure 24). This switch is based on the variation of fluorescence induced by a change of ligands. More precisely, an imidazole-appended porphyrinatozinc-phthalocyaninatomagnesium complex was shown to spontaneously dimerize into a supramolecular short dimer (state I) in which the imidazole units are bound to the central magnesium atom of the Pcs. On addition of 2 equivalents (with respect to the dimer) of dimethyl sulfoxide (DMSO) or 1-methylimidazole to the dimer, a new extended dimer (state II) is formed in which... 

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