Interchange between Monolayers on Gold Formed from Unsymmetrical Disulfides and Solutions of Thiols: Evidence for Sulfur-Sulfur Bond Cleavage by Gold Metall

Chemisorption of alkanethiols, RSH, or dialkyl disulfides, RSSR, on gold gives ordered monolayers-l-S SAMs (self-assembled monolayers) formed from either precursor are believed to comprise the sattte species on the gold surface-gold(I) alkyl thiolate (RS-Aus+ on these predominately Au(111) surfaces) adsorbed epitaxially on the gold(0) substrate-but the only direct experimental eviderrce supporting this belief is the observation of indistinguishable S(2p) binding energies for both systems measured by X-ray photoelectron spectroscopy (XPS).0'z The objective of the work described in this paper was to compare the reactivity of the surface organosuHur species generated from alkanethiols and dialkyl disulfides in a iype of reaction we expected to be senstive to details of bonding to the surface-interchange of these surface organosulfur species with thiols or disulfides in solution. This study examined the reactivity of species formed on gold from an unsymmetrical disulfide LgSSMd (HO(CH21tr55(CHtsCFs; LB = long chain; Md = medium chain). We wanted to address two questions (Scheme I): (1) Are both halves of LgSSMd incorporated in the SAM to the same extent when a solution of this disufide is allowed to react with a bare gold surface? Is the snr"e result observed on a surface already covered with an alkyl thiolate? (2) Do the hypothesized surface species, LgS-AuI and MdS-AuI, behave as independent entities in their reactions with species in solution, or are their reactivities