Platinum aminocarbenes

Thus, HCN is proposed to be formed in two competing routes, a surface-bound pathway via platinum aminocarbenes and a gas-phase channel involving successive dehydrogenation of formimine. Common to both routes is the Pt-mediated activation of methane as the first step. A crucial aspect is the remarkable selectivity observed, i.e. bare Pt+ only reacts with methane while the resulting PtCHj preferentially reacts with ammonia. Exploratory studies of other transition metals indicate that platinum... 

Scheme 8.9 Preparation of the octahedral aminocarbene rhodium(III) complexes 35 and 36 and the square-planar aminocarbene platinum(II) complex 38 from the imidoyl chloride PhC(Cl)=NMe as the precursor (for 35 PR3 = PMe2Ph for 37 and 38 PR3 = PPh3)...

From the experimental point of view, for reductions, DC-polarography at the dropping mercury electrode (DME) or cyclic voltammetry (CV) at the hanging mercury drop electrode (HMDE) were used and for controlled-potential electrolyses at negative potentials, a mercury pool electrode was employed. For both oxidative and reductive experiments, voltammetry at the platinum rotating disk electrode (RDE) and CV at the stationary platinum electrode were applied. All experiments were performed in a three-electrode system with a platinum counter electrode. For measurements in analytical scale (a standard aminocarbene concentration was 3x 10-" mol/1), an undivided cell for 5-10 ml was used and for preparative electrolyses a two-compartment cell of the H-type was employed [14]. The potentials were referred to the saturated calomel electrode (SCE), which was separated from the investigated solution by a double-frit bridge. 

Generally, during electrochemical oxidation of aminocarbene complexes the central metal atom is oxidized by one electron. The limited CV reversibility of the oxidation process, for example, of hetaryl-substituted aminocarbenes, however, points to a relatively slow follow-up reaction occurring after the primary oxidative electron transfer. During preparative electrolysis at potentials of oxidative limiting current, small bubbles were observed at the surface of the platinum electrode. The IR spectroelectrochemical experiment showed that in the course of electrochemical oxidation, the bands at 1930 cm belonging to the CO vibration disappear (Fig. 48.11). The electrochemical oxidation is thus followed by a decomposition, which is accompanied by release of CO gas. The process is faster in heterocycUc derivatives. 

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