Thiophosphine ligands

Another system based on rhenium and thiophosphine ligand is also capable of reversely binding alkene moieties (Scheme 15) [42]. After electrochemical oxidation of complex 49, the ethylene is bound by the sulfur atoms of the ligand. As in complex 47, the olefin has a stronger affinity for the oxidized form 49 (i.e., 49+ and 49 +) than for the reduced complex (Kj > Kj> Kj). In the neutral species (non-oxidized forms) the equilibrium is in favor of 49 over 50 even in a large excess of ethylene. In the case of the two-electron oxidized species, the equilibrium is in full favor of 50 +, with no spectroscopic evidence of the presence of 49 +.Whenever complexes are one-electron oxidized both mono-cationic forms (49+ and 50+) are present, the ratio depending on the applied pressure of ethylene. 

Trialkylthiophosphates, (RO)3P=S (R = Et, Pr"), act as unidentate sulfur ligands.102 Dialkyl-thiophosphinates (33) react with some metal ions forming complexes (34), being concomitantly oxidized to bis(dialkylthiophosphoryl)disulfanes (35) as shown in equation (2).107 Dialkyldithio-phosphates, (RO)2P(S)SH, form complexes similar to (34). 

Only a few complexes of monothiophosphinic acids, R2P(S)OH, are known. Diphenyl-thiophosphinic acid, Ph2P(S)OH, forms polymeric complexes wiA Ni" and Al but the Cy" complex is monomeric. The Ni" complex is paramagnetic (/x, 3.86 BM) with a typically tetrahedral spectrum." Complexes of diethyldithiophosphinic add, Et2P(S)OH, with Co", Zn", In" and Pb" have been reported their degree of association in organic solvents, involving ligand brid ng, is concentration dependent. "... 

Structure 9 Cyclodextrin modified by thiophosphine or thioaminophosphine ligands (adapted from [30],... 

Table 5.3 Allylic substitution reactions with thiophosphine-thioether ligands 6...

The chiral compounds 6 have also been considered as potential ligands for palladium-catalyzed aUylic substitution. Thiophosphines have been very rarely used in asymmetric catalysis [85-89]. These compounds represent, to the best of our knowledge, only the second example of thiophosphine-thioether ligands used in asymmetric catalysis [64, 85-89]. Good catalytic activities and enantioselectivities were obtained (e.e. up to 93% for R = tBu, Table 5.3). Ligands 6 are amongst the few best S,S ligands for this reaction [90-93]. 

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