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

The phosphines P(C6H4-4-SR)3 (R = H, Me, 2-C5H9O) and (C6H4-4-SR)2PCH2CH2P(C6H4-4-SR)2 (R = H, Me) have been synthesized. The phosphines with –SMe groups can be prepared by reaction of 4-BrC6H4SMe with either BuLi or magnesium (to generate the corresponding Grignard compound) followed by reaction with PCl3 or Cl2PCH2CH2PCl2, respectively. The methyl group can be eliminated by reaction with sodium in liquid NH3. Other methods of protection/deprotection of the thiol group failed to afford the desired compounds. Reaction of 4-BrC6H4SH with dihydropyrane afforded the protected thiol 4-BrC6H4S-2-C5H9O from which the corresponding phosphine was successfully synthesized. However, attempts to remove the tetrahydropyranyl group by reaction with AgNO3–HCl, gave an insoluble polymer as product. Reaction of P(C6H4SR)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 νCO bands were detected by grazing angle Fourier transform infrared reflection absorption spectroscopy (grazing angle FTIR-RAS). Reaction of Rh(acac)(CO)2 with P(C6H4SR)3 (R = Me) affords the complex Rh(acac)(CO)(P(C6H4SR)3) (R = Me), but if R = H a polymer insoluble in any solvent was obtained. The same occurs in the case of PtCl2(CO)(DMSO). Apparently, once P(C6H4SH)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.