Hydrosilylation of C–C multiple bonds is one of the most important applications of homogeneous catalysis in industry. The reaction is characterized by its atom-efficiency, broad substrate scope, and widespread application. To date, industry still relies on highly active platinum-based systems that were developed over half a century ago. Despite the rapid evolution of vast synthetic applications, the development of a fundamental understanding of the catalytic reaction pathway has been difficult and slow, particularly for the industrially highly relevant Karstedt’s catalyst. A detailed mechanistic study unraveling several new aspects of platinum-catalyzed hydrosilylation using Karstedt’s catalyst as platinum source is presented in this work. A combination of 2H-labeling experiments, 195Pt NMR studies, and an in-depth kinetic study provides the basis for a further development of the well-established Chalk–Harrod mechanism. It is concluded that the coordination strength of the olefin exerts a decisive effect on the kinetics of the reaction. In addition, it is demonstrated how distinct structural features of the active catalyst species can be derived from kinetic data. A primary kinetic isotope effect as well as a characteristic product distribution in deuterium-labeling experiments lead to the conclusion that the rate-limiting step of platinum-catalyzed hydrosilylation is in fact the insertion of the olefin into the Pt–H bond rather than reductive elimination of the product in the olefin/silane combinations studied.

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The reaction of cis-[Mo2(O2C-Fc)2(NCCH3)4][BF4]2 (cis-1) with two electronically different N,N'-diarylformamidinate (DArF) ligands (DArF = N,N'-bis(p-trifluoromethylphenyl)formamidinate (DTfmpF), N,N'-bis(p-anisyl)formamidinate (DAniF)) results in the isolation of the tris- and monosubstituted complexes [Mo2(DTfmpF)3(O2C-Fc)] (2a) and [Mo2(DAniF)(O2C-Fc)3] (2b). These complexes complete the series of [Mo2(DArF)n(O2C-Fc)4-n] (n = 4-0) type compounds, thus allowing for a comprehensive study. On the basis of the oxidation potential E1/2([Mo2](4+)/[Mo2](5+)) of all Mo2 complexes, ligand basicity is found to decrease in the order DAniF(-) > DTfmpF(-) > Fc-CO2(-) ≫ CH3CN. In addition, no direct electronic interaction between the trans-positioned Fc units in complex 2b is detected, which is attributed to the full overlap of all Fc oxidation processes. Furthermore, the low-energy absorption bands of compounds 2a,b are located at different positions in their respective UV-vis spectra.