Chelate rings convention

Coordinated thioether S is often asymmetric. In (302) the asymmetry is frozen by the configuration of the attached chelate rings but in (301) it is not and inversion is fast. Conventional resolution via diastereoisomeric salts has never been substantiated for a purely enantiomeric Co—SR Ril+ system devoid of other chirality. I3C and H studies on diastereoisomeric systems1079 however show that inversion rates are normally of the order 0.1-10 s1, which makes coordinated thioethers decidedly more configurationally labile than organic sulfonium salts. The effects of asymmetry in (302) are readily seen in diastereoisomeric systems where the lone pair on S is often stereospecifically orientated. It usually directs stereochemical change and ligand replacement processes. 

IR-9.3.4.14 Application of the skew-lines convention to conformations of chelate rings... 

For the puckered diaminoethane, there are some further observations to make. The chelate ring is more rigid than the freely-rotating unbound ligand, so that the protons on each carbon are nonequivalent, as one points essentially vertically (axial, Hax), the other sideways approximately parallel to the N—M—N plane (equatorial, Heq). Nevertheless it is sufficiently flexible that it can invert - one carbon moving upwards while the other moves downward to yield the other form. These two forms are examples of two different conformations one is called X, the other 8, by convention they are mirror images of each other. Any chelate ring that is not flat may have such conformers. 

Related to jS-diketones are metalla-/ -diketones, whose distinctive chemistry is a recent development. In these, the methine group of a conventional diketonate is replaced with an organometallic moiety such as m-Mn(CO)4, m-Re(CO)4, /<2c-Mn(CO)3(RNC) or C5H5Fe(CO).519 Exemplary is Al Mn(MeCO)2(CO)4 3, which is prepared in a two-step synthesis. Addition of methyllithium to Mn(CO)5COMe forms Li[Mn(MeCO)2(CO)4] which, when treated with aluminum chloride, provides the tris(chelate) compound.520 An X-ray study showed that the MnC202Al ring is essentially planar with Mn—C(acyl) bond distances indicative of a bond order of ca. 1.2. The O—O bite distance, 2.73 A, is about the same as that of acetylacetonate in Al(MeCOCHCOMe)3.521 As in the... 

Salts of mercury(II) and thallium(HI), such as mercury(II) acetate, Hg(OAc)2, and thallium trifluoroacetate, Tl(OCOCF3)3, are reactive electrophilic metallating species which attack benzene directly. Electron-donating groups in the aromatic ring accelerate the reaction in the conventional manner and direct attack to the ortho and para positions. In addition, metal-chelating substituents, such as amide, promote the reaction and direct attack to the 2-position in a manner similar to that seen in the directed orthometallation reaction. 

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