Nonstabilized Alkyl Complexes and Alkyl‐Cyano‐Ate Complexes of Iron(<scp>II</scp>) and Cobalt(<scp>II</scp>) as New Reagents in Organic Synthesis

Abstract

Abstract Alkyl transition metal reagents are being increasingly used for alkylations in organic synthesis. They have various advantages over alkyllithium and alkyl‐magnesium reagents including higher selectivity, lower basicity, and—as long as the transition metal is not in its highest oxidation state—their willingness to undergo oxidative addition with electrophiles. Alkyl derivatives of Fe II and Co II , which are not stabilized by special ligands but still can be easily handled, are in many cases superior to the well‐known alkyl–Cu I and ‐Mn II reagents and can also undergo unexpected reactions. The introduction of alkyl‐cyanoate complexes of Fe II and Co II , the cyanide ligands of which (in contrast to neutral π‐acidic ligands) do not reduce the reactivity, has led to further advances. Reaction mechanisms will be discussed and comparisons will be made with alkylating reagents containing Cu I , Mn II , Ni II , or Ti IV as well as with Pd‐catalyzed coupling reactions. Furthermore, it will be shown that super‐ate Fe II complexes are almost certainly the reactive species in highly selective catalytic alkylations.