Selenium-containing ligands

Complexes with Sulfur- and Selenium-containing Ligands 493... 

The detection of metal-binding proteins, especially of Cd- and Hg-binding metallothioneins or of the merR protein, induced numerous studies of model compounds of Cd and Hg with more or less simple sulfur- and selenium-containing ligands. 

Goodall (53) has synthesised a series of sulphur and selenium containing ligands related to the ligands used by Kouwenhoven. These are the sulphide and selenide ligands shown in Fig. 39. 

Complexes of group VIB elements with sulfur or selenium donor atoms are mainly concerned with complexes of selenium(II), tellurium(II) and tellurium(IV). The structural chemistry of complexes of selenium and tellurium with sulfur- and selenium-containing ligands has been well reviewed in the recent past.11... 

Fig. 3 List of sulfur- or selenium-containing ligands in Pd-catalyzed reactions of 1,3-diphenylpropenyl acetates with dimethyl malonate (BSA/CH2(C02Me)2)...

Generally, the 3-values of Se in P=Se bonds of organophosphine selenides are negative. Se chemical shifts of transition metal complexes cover the whole range. In most cases the selenium atom is deshielded (3 = 200-1500) as compared to the free selenium-containing ligand but exceptions with negative complexation shifts exist. 

This attenuation of the electronegativity variation in the earlier columns of the Periodic Table is even more pronounced when S is compared with Se. A choice of selenium-containing ligands (20, 22, 23) have Xopt 0.05 to 0.1 unit below that of the corresponding sulphur-containing ligands. Before the work described in this review, the spectra of complexes of Se 2 were not known. 

The black colours of most d-group sulphides may be ascribed to collective empty orbitals to which transitions are also known in the visible of TiCla and TiBrs and in the ultra-violet of many other halides (770). Only green Mn(II) Se and pink Mn(II)S4 shows identifiable <7 transitions in the crystalline modifications of MnS. Generally, the monomeric complexes of bidentate sulphur- and selenium-containing ligands (20) have far better characterized spectra. In solids, there is a very strong tendency for sulphur and selenium to bridge two or three atoms (70) with concomitant broad absorption bands in the visible. 

Husebye. S. Recent developments in the structural chemistry of tellurium with sulfur and selenium containing ligands. Phosphorus Sulfur Silicon 1998. 136/137. 377. 

---