Dioxomolybdenum and -tungsten compounds containing sterically demanding pyrazolate ligands have been synthesised by treatment of dioxometal halides with the potassium salts of 3,5-ditert-butylpyrazole (t-Bu 2 pzH) and 3,5-di-tert-butyl-4-bromopyrazole (t-Bu 2 -4-BrpzH). The products (5) were characterised by spectroscopic techniques. The X-ray structure of complex 3 reveals a distorted trigonal prismatic geometry with two h 2 -co-ordinated pyrazolate ligands. These high-valent compounds participate in oxygentransfer reactions and catalyse the oxidation of PPh 3 with dimethyl sulphoxide. UV/VIS measurements of the oxo-transfer reactions and the kinetics of the catalytic process are described. By the reaction of 2 with three equivalents of PEt 3 or treatment of [MoOCl 2 -(PMe 3 ) 2 ] with two equivalents of t-Bu 2 pzK mononuclear mono-oxo compounds of the type [MoO(t-Bu 2 -pz) 2 (PR 3 ) 2 ] (R¼ Et 6, R¼ Me 7) were obtained and characterised by X-ray diffraction analyses. This points to biologically relevant mononuclear Mo(IV) intermediates in the catalytic process with this type of complex.

Self-assembled monolayers (SAMs) can decorate surfaces with `smart´ functional units possessing reversible stimulus-response behavior for optical, thermal, magnetic or redox-chemical stimuli. An independent performance of individual functional groups in such a film is desirable, which can be, in particular, ensured by fairly large lateral separations between tailgroups in the SAM. Adsorbate molecules with multiple attachment points are very promising in this context owing to their large surface footprint, which covers a surface area exceeding the lateral dimensions of the functional groups. To address these design constraints, novel tridentate long-chain tripodal thioether ligands with central adamantine units and a redox-active ferrocenyl tailgroup, 1-[4-(ferrocenylethynyl)phenyl]-3,5,7-tri[(4-n-octylsulfanyl)phenyl]adamantine (T8) and 1-[4-(ferrocenylethynyl)phenyl]-3,5,7-tri[(4-n-dodecylsulfanyl)phenyl]adamantine (T12), were synthesized and used as tripodal adsorbate molecules for the fabrication of redox-active ferrocenyl-terminated SAMs on Au(111). These SAMs were characterized by X-ray photoelectron spectroscopy, near edge X-ray absorption fine structure spectroscopy and sum frequency generation spectroscopy. The data suggest that T8 and T12 form almost contamination-free, wellaligned and fairly densely-packed SAMs on Au(111) with laterally separated ferrocenyl units. The SAMs show a homogeneous binding chemistry, an important requirement for high fidelity SAMs. SFG results indicate lateral interactions between neighboring molecules via the long-chain binding units.