Thiourea-based ligands

Scheme 4.11 A thiourea-based ligand in carbonylative Suzuki reactions...

Bisalkoxycarbonylation of olefins commonly uses this Pd(II)-Cu(I) bimetallic catalysis some additives, such as phosphine sulfides and thiourea-based ligands, are known to facilitate the conversion. Recently Pd(II)-Cu(l)-catalyzed oxidative cyclization has been reported in the preparation of dihydrop3Ta-nones and furanones (eq 25). ... 

Thiourea-based ligands were evaluated for the palladium-catalyzed bis(methox-ycarbonylation) of terminal olefins. The best results were obtained by using tetra-substituted thioureas such as 40 and 41 (Equation 7.16) [145]. 

Preparation of trithioureacopper (I) chloride Thiourea is a soft base ligand and can stabilise Cu(I). 

This preparation is carried out in an aprotic solvent (e.g. benzene, chloroform) with no special provision other than working in a well-ventilated fume hood to avoid ill-smelling sulfur compounds. Various ligands have proved successful phosphines, pyridines, imidazoles, tetra-m ethyl thiourea, etc. When the same reaction is carried out in the absence of the Lewis base L, a dimer 6 is obtained, which is a useful catalyst in its own right and sometimes a much more active one see Section VILA. The chemical equation for that reaction is,... 

Thermodynamic data for the formation of Ag(TSC)3 are given in Table 58.437 Based on the similarity of the stability of this complex and the analogous thiourea complex, the ligand was proposed to be monodentate. The IR spectra of [Ag2(TSC)3](NC>3)2438 and of Ag(TSC)Cl439 were also interpreted in terms of silver-sulfur bonding only. 

Thiocyanate can be recovered and recycled from this solution by the precipitation of iron as iron(III) hydroxide.366 Aurocyanide can also be eluted from a strong-base resin by chemical conversion of the gold to a cationic complex with the thiourea ligand, as shown above (equation 98). This method of gold elution is favoured in the Soviet Union, but suffers from the drawback that elution of the other metal cyanide complexes is generally poor, and multi-elution procedures are necessary. 

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