Phosphanes sulfur-containing

The trend in the few examples where an NHC is functionalised with a sulfur-containing group does not necessarily reflect the choice of scaffold seen above, but the S functionalised NHC ligands do, in part, follow the general development of an S/P exchange in conventional functionalised phosphanes. The other major source for S functionalised NHC complexes of transition metals is the replacement of sulfur by a transition metal in certain Ji-sulfurane compounds. The NHC ligand, a tetrahydro-pyrimidine derivative, is only liberated during the reaction of the sulfurane with the transition metal precursor. 

Numerous catalytic systems have been described in the literature which involve sulfur-containing ligands or which are not sensitive to the presence of sulfur atoms in the reactants. In several cases, these sulfur ligands play a spectator role. However, it is important to consider that these ancillary ligands participate, like any other more classical ligands such as phosphanes, to the coordination sphere of the metal center. Due to their electronic properties, their bulkiness. 

Reaction of phenylphosphonic dianilide with tris-(diethylamino)phosphane yields colorless crystals of compound X (m.p. 156-157 °C). Reaction of N,N -di-phenylsulfamide with the same reagent leads to compound XI, which is the first member of the class of thiadiazaphosphetidines containing tervalent phosphorus. The colorless crystals melt at 94-95 °C. With elemental sulfur the corresponding sulfide is obtained. 

Sulfur donors may also be introduced by the primary transformation of the triol into a functionalized thiethane (Equation (10)). Subsequent addition of two potentially different phosphorus nucleophiles leads to tripod ligands containing two phosphane donors together with an SH function ((84), (85), (87), (88)). 

Table 18, pp. 269/74, lists the reactions of linear, branched, and cyclic alkenes, halo-alkenes, and oxygen-, sulfur-, nitrogen-, and phosphorus-containing compounds with C=C double bonds, the reaction conditions, and the product distribution of the phosphanes obtained (abbreviations are explained in the footnotes at the end of the table). 

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