Ligands thioethers

Among neutral ligands, thioethers form important complexes AuCl(SR2) (SR2, e.g. Me2S, Et2S, S(CH2CH2OH)2) that are synthetically useful since the sulphide is readily replaced by strong donors (e.g. tertiary phosphines) (sections 4.10.3 and 4.10.5). AuX(tht) (X = Cl, I) have been made. The iodide is Au(tht)2 Aul2, but the chloride and bromide are neutral AuX(tht). The iodide remarkably can be synthesized at room temperature [97] ... 

The stability of the phosphine adducts is notable as is the fact that thioethers readily form such adducts whereas ethers do not. Bis-ligand adducts of moderate stability play an important role in activating decaborane for several types of reaction to be considered in moie detail in subsequent paragraphs, e.g. ... 

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

Various thioether complexes have been synthesized for example, 6-coordination is found in [Ag(18S6)]+ and [Ag(9S3)2]+ but in [Ag(16S6)]+, tetrahedral coordination occurs, with two unused donor atoms in the ligand [59],... 

In aqueous solutions at pH 7, there is little evidence of complex formation between [MesSnflV)] and Gly. Potentiometric determination of the formation constants for L-Cys, DL-Ala, and L-His with the same cation indicates that L-Cys binds more strongly than other two amino acids (pKi ca. 10,6, or 5, respectively). Equilibrium and spectroscopic studies on L-Cys and its derivatives (S-methyl-cystein (S-Me-Cys), N-Ac-Cys) and the [Et2Sn(IV)] system showed that these ligands coordinate the metal ion via carboxylic O and the thiolic 5 donor atoms in acidic media. In the case of S-Me-Cys, the formation of a protonated complex MLH was also detected, due to the stabilizing effect of additional thioether coordination. ... 

Catalytic hydrogenation with platinum liberates the hydrocarbon from methylcobalamin (57) and from alkyl-Co-DMG complexes (161), but not from pentacyanides with primary alkyl, vinyl, or benzyl ligands, though the cr-allyl complex yields propylene (109). Sodium sand gives mixtures of hydrocarbons with the alkyl-Co-salen complexes (64). Dithioerythritol will liberate methane from a variety of methyl complexes [cobalamin, DMG, DMG-BF2, G, DPG, CHD, salen, and (DO)(DOH)pn] (156), as will 1,4-butanedithiol from the DMG complex (157), and certain unspecified thiols will reduce DMG complexes with substituted alkyl ligands (e.g., C0-CH2COOH ->CH3C00H) (163, 164). Reaction with thiols can also lead to the formation of thioethers (see Section C,3). 

Since carbohydrates constitute an inexpensive and highly modular chiral source for preparing chiral ligands," Claver et al. have reported the use of a series of thioether-phosphite" and thioether-phosphinite furanoside ligands" in the test palladium-catalysed allylic substitution reaction. In the first type of ligand, a systematic variation of the donor group attached to the carbon atom C5 indicated that the presence of a bulky phosphite functionality had a positive effect on the enantioselectivity. Indeed, the enantioselectivity was controlled mainly by the phosphite moiety. This was confirmed by the use of a ligand... 

Test reaction with furanoside thioether-phosphite or -phosphinite ligands. 

Furanoside thioether-phosphinite ligand for Pd-catalysed allylic substitutions of acyclic and cyclic allylic substrates. 

Scheme 1.33 Test reaction with (+ )-camphor-derived pyridine thioether ligand.

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