Transition metals redox-catalyzed insertion

Figure 3.9 Redox-catalyzed insertion in transition metal chemistry.

Redox reactions are considered as being able to provide versatile and efficient methods for bringing about ring transformations. Transition metal complexes in particular are able to induce or catalyze oxidative or reductive transformations of small ring compounds. Organometallics, such as metal-lacycles derived by the insertion of metal atoms into rings, are involved as key intermediates in many cases, allowing subsequent functionalization or carbon-carbon bond formation. 

Not long after transition-metal catalyzed hydrosilation took root in the 1950s as a new and powerful tool for Si-C bond formation, based on parallels drawn from TM-catalyzed hydrogenation and on the intrinsic redox properties of these metals. Chalk and Harrod proposed a simple and yet very logical catalytic cycle for TM-catalyzed hydrosilation (Scheme 1). The key steps of this cycle are (1) oxidative addition of Si-H to the metal center, (2) coordination of the olefin or other unsaturated species to the metal, (3) insertion of this usually-t/ -coordinated molecule into the M-H bond and finally, (4) reductive elimination of the Si-C pair to regenerate the catalytically active metal center. 

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