The deposition and the subsequent decomposition of an organometallic precursor, (eta (3)-allyl)(eta (5)-cyclopentadienyl)palladium [Cp(allyl)Pd], on an organic surface exposed by self-assembled monolayers (SAM) was studied using X-ray photoelectron spectroscopy (XPS) and infrared reflection absorption spectroscopy (IRRAS). The interfacial chemical reactions of the vapor-deposited metal precursor with the pendant thiol group of the SAMs made from oligophenyldithiols, which are either prepared directly (terphenyldimethyldithiol, TPDMT) or by a deprotection route from SAMs formed by a monoacylated derivative of biphenyldimethyldithiol (dep. BPDMAc-1) have been studied in detail. When the TPDMT-SAMs were exposed to Cp(allyl)Pd vapor, a Pd (2+)/allyl-terminated SAM surface was obtained (to a lower extent this was also the case for dep. BPDMAc-1 SAMs), which was stable against exposure to H 2 gas. Reduction to Pd (0) by H 2 was only observed when small amounts of Pd (0) were already present, for example, after prolonged exposure to the precursor. The catalytic activity of the small Pd (0) particles also caused a decomposition of the SAMs upon exposure to air.

One of the most intriguing possibilities offered by organothiol (OT)-based self-assembled monolayers (SAMs) adsorbed on solid substrates is to create organic surfaces, the properties of which can be tailored by choosing organothiols with appropriate groups at the w-position.[1] The large variety of suitable functional groups allows for control of the physico-chemical properties of the surface. For example, the wettability can be varied smoothly between hydrophobic and hydrophilic. Presently, the possibility of chemically binding other moieties to the organic surface exposed by the SAM is attracting an increasing amount of attention, for example, in connection with the coupling of biomolecules, [2] in model studies regarding biomineralization [3] and in anchoring zeolites [4] or metal-organic frameworks.[5] A special type of surface termination, ÀSH groups, has recently attracted considerable attention with regard to metallization of SAMs. [6] In many cases the desired organic surface can be obtained by using an appropriately w-functionalized organothiol, but there are often complications resulting from undesired interactions either between the corresponding functional groups (as in the case of COOH···HOOC hydrogen bonding [7,8] or the functional group and the Au substrate [9,10] ). Recently, we have demonstrated that a protecting-group strategy can be used to avoid such problems by first fabricating a SAM from protected organothiols.[10] A subsequent deprotection carried out by immersing the SAM in a corresponding solution then yields an organic surface with the desired functionality.Herein, we demonstrate that the chemical reactions at the organic surface of the SAM proceed quite differently to the corresponding reactions in solution. Although these types of surface reactions have been studied earlier by several groups (see the papers by Sullivan and Huck [11] and Love et al. [12] for recent reviews of this field), still a careful and systematic understanding is lacking. A detailed analysis of our findings reveals that there are general phenomena resulting from confining the occurrence of a particular chemical reaction to two dimensions, which can affect reactions on highly ordered organic surfaces. We demonstrate the importance of this reduction in dimensionality for the chemical reactivity by investigating the case of removing an acetate group by a basic agent, shown schematically in Figure 1. This reaction, which is standard in solution chemistry, is found to be significantly hindered when confined to a two-dimensional system. Whereas the reaction in solution proceeds in minutes, the corresponding reaction at the organic surfaces requires, depending on the conditions, up to 84 hours. This is a surprising observation considering that the agent used for removing the protecting COCH 3 -group is a very small molecule, a hydroxide ion (OH À ). The reasons for this unexpected behavior are unraveled using IR spectroscopy, near edge X-ray absorption fine structure spectroscopy (NEXAFS) and scanning electron microscop...

Self-assembled monolayers (SAMs) on gold substrates were prepared from benzylmercaptan (BM) and para-cyanobenzylmercaptan (pCBM), and the resulting surfaces were investigated using conventional infrared reflection-absorption spectroscopy (IRRAS) as well as polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). IRRAS data are analyzed by comparison with transmission IR spectra and theoretical (DFT) simulations. The spectroscopic results indicate the presence of well-ordered monolayers of BM and pCBM with an orientation perpendicular to the surface. IRRAS and PM-IRRAS data are compared to each other and the respective merits of both methods are discussed.