Thio ligands

Organic thio ligands are well established, examples being the thiols RSH (R = Et, Pr", Bu, the thioethers SMe2, SEt2, tetrahy-... 

Scheme 3.10 L-Valine-derived P-amino thio ligands for addition of ZnEt2 to benzaldehyde.

Scheme 3.26 D-Mannitol P-amino thio ligands for additions of ZnEt2 to aldehydes.

Only a handful of pseudotetrahedral or octahedral oxosulfido-Mo(VI) and -Mo(V) complexes are known, and their chemistry is described in Section 11. Mononuclear sulfido-Mo(V) complexes are unstable due to their susceptibility to redox, polynucleation, and hydrolysis reactions. Trispyrazolylborate derivatives such as sfructuraUy characterized Tp Mo SX2 (X = Cl, OPh derivative X2 = bdt, catecholate) are most commonly encountered. The Tp complexes exhibit short Mo=S bonds (ca. 2.13 A), intense S(ls)- - n (Mo=S) XAS transitions characteristic of terminal thio ligands, and EPR iso see g-Factor) values substantially lower than their 0x0 analogues. ... 

Nonplanar or highly substituted Schiff bases also confer steric protection upon their rhodium(II) complexes. By contrast relatively simple thio ligands such as... 

Deactivation of oxidized xanthine oxidase by cyanide produces thiocyanate and an inactive or desulfo form of the enzyme. The oxidized desulfo enzyme contains a dioxo-Mo(VI) center. Since it is generally believed that a terminal thio ligand on Mo is removed in the cyanolysis reaction, the interaction of oxo-thio-Mo(VI) complexes with CN is worthy of investigation. In general, reactions of thio-Mo( VI) complexes (typically thiomolybdates) with cyanide leads to the formation of SCN" by formal sulfur atom transfer and reduction of the metal, e.q., Eq. (25). 

An early example involved mononuclear thiomolybdates and excess cyanide (227). In related studies, Muller and co-workers (i 75,228-230) have isolated and characterized a variety of polynuclear cyano anions of Mo(IV) and Mo(III). These complexes feature and jug-thio ligands,... 

A remarkable stabilization of selenium and tellurium dihalides is achieved if the central chalcogen atoms are coordinated with anionic (Section with neutral Lewis bases as ligands. Thio ligands,... 

MOLYBDENUM(II) CARBONYL COMPLEXES CONTAINING THIO LIGANDS AND ACETYLENE... 

Cavell et al. have synthesised and characterised a series of neutral, hexaco-ordinate phosphorus compounds containing divalent, tridentate diphenol imine, azo and thio ligands. For example, the reaction of silylated Schiff base ligands e.g. 112) with PCI5 gave the neutral, hexacoordinate compound 113 by... 

The synthesis and characterisation of neutral hexacoordinate phosphorus(V) compounds (perphosphoranides) containing divalent tridentate diphenol imino, azo and thio ligands has also been reported.The hexacoordination was revealed by their high-field 53ip values, characteristic Jpp coupling and crystal structures. Two compounds of particular interest are the trihaloperphosphoranides (77 Hal = Cl, F), with respective Ssip values of —136.4 and —136.9. 

In biological systems Mo is present as the Fe/Mo cofactor of the nitrogenase enzymes (2) and of the multitude of oxidoreductases (3). In the latter the common molybdopterin cofactor (4), in addition to a dithiolene functionalized pyranopterin (5) ligand (Fig. 1), contains terminal oxo ligands and in the case of xanthine oxidase both oxo and thio ligands. Some aspects of molybdenum sulfur chemistry discussed in this work may be relevant to the biosynthesis of the molybdopterin cofactor and the function of xanthine oxidase (6). 

A comparison of endocyclic aza and thio ligands was made through parallel studies on the diastereomeric l,3,2-thiazaphospholidin-2-ones, [16e,f] (Scheme 9a), again derived from ephedrine (Hall and Williams, 1980,... 

There are no examples of xenon bonded to sulfur or selenium and few for the halogens. The reported compounds involve the thiocyanate and selenocyanate ligands acting as pseudohalides, in the anions I(SCN)i and I(SeCN)2, for which IR and Raman spectra show the thiocyanate to have a linear S—I—S arrangement but give no definitive results for the selenocyanate, and two examples with more complex thio ligands for which crystal structures have been determined. 

Kinetics of intramolecular processes of tungsten(O) complexes of thio-ligands are mentioned in Section 8.11.2 in connection with inversion at sulfur coordinated to platinum(IV). 

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