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Hydrosilylation with bis(alkynyl)(1,5-cyclooctadiene) platinum catalysts: A density functional study of the initial activation

MPG-Autoren
http://pubman.mpdl.mpg.de/cone/persons/resource/persons58639

Jagadeesh,  M. N.
Research Department Thiel, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons59045

Thiel,  W.
Research Department Thiel, Max-Planck-Institut für Kohlenforschung, Max Planck Society;
Research Department Thiel, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons58707

Köhler,  J.
Research Department Thiel, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Zitation

Jagadeesh, M. N., Thiel, W., Köhler, J., & Fehn, A. (2002). Hydrosilylation with bis(alkynyl)(1,5-cyclooctadiene) platinum catalysts: A density functional study of the initial activation. Organometallics, 21(10), 2076-2087. doi:10.1021/om0200196.


Zitierlink: http://hdl.handle.net/11858/00-001M-0000-000F-99E5-A
Zusammenfassung
At elevated temperatures bis(alkynyl)(1,5- cyclooctadiene)platinum complexes catalyze the cross-linking of polyorganosiloxanes containing Si-H and vinyl groups. Density functional calculations with medium-size basis sets and effective core potentials are reported for reactions that may activate these precatalysts for hydrosilylation. For a model system consisting of the bis(ethynyl) complex, trimethylsilane, and ethylene, the computations provide two plausible pathways for gaining access to the Chalk-Harrod cycle. The first one involves a sequence of four oxidative additions and reductive eliminations, while the second one requires a reductive coupling that is induced by olefin coordination. In both cases, the initial step is rate-determining, with a computed barrier of 27 kcal/mol. Experiments for polysiloxane systems of industrial interest favor the first pathway and yield barriers of 25-30 kcal/mol. Substituents in the alkynyl groups affect the measured barriers and the barriers computed for the rate- determining initial step of the first pathway in a qualitatively similar manner. We propose that the activation of the precatalysts is initiated by oxidative addition of Si-H.