Group 2 metal bis(arenecarbochalcogenoate)(crown ether) complexes: isolation and structural analysis.

A series of Group 2 metal bis(arenecarbochalcogenoato)(crown ether) complexes M(EE'CAr)2(L)(L')x (M = Mg, Ca, Sr, Ba; Ar = aryl; E = S, Se; E' = O, S; L = H2O or THF; L' = 15-crown-5, 18-crown-6) were synthesized and their structures were revealed by X-ray analyses. The two carbothioato ligands in Mg, Ca and Sr 15-crown-5 complexes are located on the same side of the crown ether plane, while those in Mg, Ca, Sr, and Ba 18-crown-6 compounds are on both sides of the 18-crown-6 plane (trans relative to the plane). For the Ca 15-crown-5 complex, both carbothioato ligands are connected to the central Ca ion through an oxygen atom in a monodentate manner, and the two hydrogen atoms of the coordinated water molecule are intramolecularly hydrogen-bonded with thiocarbonyl sulfur atoms. One of the two carbothioate groups in the Ca 18-crown-6 complex is connected in a bidentate manner to the central metal, while the other is connected in a monodentate manner through an oxygen atom. The two thiocarboxylato ligands in the Sr 15-crown-5 congener are connected in a bidentate fashion to the same side of the crown ether plane. The Ca and Sr compounds are the first examples of alkali earth metal carbochalcogenoate complexes in which carbochalcogenolato ligands are connected in a monodentate manner through an oxygen atom. Both chalcogenoato ligands in Ba(SOCC6H4Me-4)2(18-crown-6) and Sr(SeOCC6H4Me-4)2(18-crown-6) are coordinated in a bidentate manner to the central metal ion.

Reaction and characterization of thioamide dianions derived from N-benzyl thioamides.

Thioamide dianions were generated by the highly efficient reaction of N-benzyl thioamides with 2 equiv of BuLi. Alkylation, allylation, and silylation took place selectively at the carbon atom adjacent to the nitrogen atom of the thioamide dianions. Oxiranes and an aldehyde were also used as electrophiles in the reaction of thioamide dianions to form N-thioacyl 1,3- or 1,2-amino alcohols. The insertion reaction of elemental sulfur to a thioamide dianion and subsequent ethylation afforded a N-thioacyl hemithioaminal. NMR studies on the thioamide mono- and dianions derived from N-benzyl 2-methoxythiobenzamide showed a linear relationship between the chemical shifts of all carbon atoms of thioamide mono- and dianions. The results also suggested that the negative charge at the benzylic carbon atom of the dianion is not fully delocalized. The charge distribution patterns of the dianion are consistent with those of pi polarization.