C-H Activation by Low Valent Iron Complexes

Abstract

The activation of C-H bonds by transition metal complexes is an area of considerable interest. This interest is indicated by the number of papers on the subject presented at this meeting [1]. Our work on C-H activation by Fe(dmpe)2 species (dmpe = bis (dimethyl-phosphino)ethane) has been reported elsewhere [2–5]. “Fe(dmpe)” reacts with activated sp3 [4], aromatic and non-aromatic sp2 [5], and acetylenic sp C-H [4] bonds to give new H-Fe-R species. The reactions, which involved reductive elimination of naphthalene from a hydrido-naphthyl precursor and oxidative addition of a variety of C-H bonds to the resultant, coordinatively unsaturated species, proceed through cis intermediates even when the hybride and the R-group are trans in the ultimate product. These results led us to suggest a transition state involving a three centered species such as $\mathop{1}\limits_{\sim }$. It became apparent from our work and the work of others that

there were two requirements for the oxidative addition of C-H bonds to transition metal complexes: the metal center must be a) coordinatively unsaturated, and; b) very electron rich. Continued work in low valent iron systems has led to additional insight into the activation of C-H bonds.