Synthesis of triarylphosphines having para –SH and –SMe groupsPreparation of their complexes and formation of a monolayer on a gold surface

Abstract

Several new aromatic phosphines bearing –SH or –SMe groups directly linked to the aromatic ring and some of their complexes have been obtained. Interaction of Ni(CO) 3 (P(4-HSC 6 H 4 ) 3 ) with a gold lamina afforded a monolayer, which was characterized by reflection–absorption IR spectroscopy. The phosphines P(C 6 H 4 -4-SR) 3 (R = H, Me, 2-C 5 H 9 O) and (C 6 H 4 -4-SR) 2 PCH 2 CH 2 P(C 6 H 4 -4-SR) 2 (R = H, Me) have been synthesized. The phosphines with –SMe groups can be prepared by reaction of 4-BrC 6 H 4 SMe with either BuLi or magnesium (to generate the corresponding Grignard compound) followed by reaction with PCl 3 or Cl 2 PCH 2 CH 2 PCl 2 , respectively. The methyl group can be eliminated by reaction with sodium in liquid NH 3 . Other methods of protection/deprotection of the thiol group failed to afford the desired compounds. Reaction of 4-BrC 6 H 4 SH with dihydropyrane afforded the protected thiol 4-BrC 6 H 4 S-2-C 5 H 9 O from which the corresponding phosphine was successfully synthesized. However, attempts to remove the tetrahydropyranyl group by reaction with AgNO 3 –HCl, gave an insoluble polymer as product. Reaction of P(C 6 H 4 SR) 3 (R = H, Me) with Ni(CO) 4 affords the corresponding mono phosphine complex quantitatively. The complex with the unprotected thiol group can be absorbed on a gold surface and the corresponding ν CO bands were detected by grazing angle Fourier transform infrared reflection absorption spectroscopy (grazing angle FTIR-RAS). Reaction of Rh(acac)(CO) 2 with P(C 6 H 4 SR) 3 (R = Me) affords the complex Rh(acac)(CO)(P(C 6 H 4 SR) 3 ) (R = Me), but if R = H a polymer insoluble in any solvent was obtained. The same occurs in the case of PtCl 2 (CO)(DMSO). Apparently, once P(C 6 H 4 SH) 3 is coordinated to a metal not in the zero oxidation state, oxidation of the thiol group to disulphide becomes very easy even in a dinitrogen atmosphere.