Coordination properties of the multifunctional S,N,S zwitterionic ligand EtNHC(S)Ph2P=NPPh2C(S)NEt

The reaction of trialkylphoshanes and amino-phosphanes with isothiocyanates yields adducts containing the zwitterionic thioamidyl-phosphonium P+C(S)N− functional group. Ligands containing this group were not previously studied, probably due to their instability towards dissociation, in the presence of metal species able to coordinate the P atom. The ligand EtNHC(S)Ph2P NPPh2C(S)NEt (HEtSNS) was obtained by reaction of Ph2PNHPPh2 with ethylisothiocyanate and proved to be very versatile: it can be protonated giving cation H2EtSNS+ and deprotonated forming the dianion–cation EtSNS−. HEtSNS and its derivatives behave as ligands showing five possible coordination fashions, S,N,S tridentate and S,S-bidentate (with a bite-angle varying from 180◦ to 90◦), S-monodentate, S,S bridging andN,N,Ninteraction. Here we describe the coordination chemistry of HEtSNS, in particular towards Rh, Cu, Ag and Au, and some properties of its complexes which are still the only examples containing the P+C(S)N− zwitterionic group