Oxidative Addition of Alkane CH Bonds to Organometallics

Oxidative addition is a fundamental organometallic primary reaction in which an X—bond adds to a metal complex which is formally oxidized by two units [M] + X—Y X—[M]— Y. The metal coordination number 

Many examples of intramolecular oxidative addition of CH bonds have been found during the past 10 years [9]. In these cyclometallation reactions, which are apparently favoured by proximity effects, the insertion takes place into a CH bond of a ligand. Specific examples [10, 11] are illustrated by reactions 1 and 2. 

Whitesides found a large positive value for the entropy of activation for the cyclometallation of neopentyl groups on Pt(II) (reaction 2) [11] these data would indicate a rate determining reductive elimination of neopentane 

Intermolecular oxidative addition of sp CH bonds are rare [7] and, until recently, were limited to organic molecules with CH bonds activated by electronic effects (reactions 3—5) [12, 13, 14], A particular example is the hydrogen transfer reaction (reaction 4) [13] catalyzed by transition metal complexes. 

These reactions are effected by relatively electron rich metal centres for example, tungstenocene, the probable intermediate in reaction 5 [14], inserts into the weakly activated CH bond of Me4Si but not into a CH bond of neopentane. 

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