Multidentate N -heterocyclic carbene complexes of the 3d metals: Synthesis, structure, reactivity and catalysis

N-Heterocyclic carbene (NHC) ligands are attracting worldwide interest because of their considerable scope and potential in coordination/organometallic chemistry, catalysis and materials science and this is reflected by the exponential growth in the number of relevant publications. The focus of this review is on the synthesis, structures and reactivity of 3d metals complexes with bis-NHC, tripodal NHC and tetrapodal NHC ligands. These metals are particularly relevant because of their generally lower cost and availability. The literature coverage includes the year 2015. This review is organized in six major sections, five of them are dedicated to each of the families of NHC ligands covered (chelating NHC, bridging NHC, chelating and bridging NHC, tripodal NHC and tetrapodal NHC ligands). Each section is in turn divided into subparts, one for each 3d metal. The seventh section is concerned with the catalytic applications, and we first examine C–H and C–C bond formation, the latter including polymerization, oligomerization and cross coupling reactions (Suzuki, Heck. . .). This is followed by C–N, C–O, C–B, C–Si, C–S and C–Br bond formation reactions. Reduction reactions and the conversion of sugars into 5-hydroxymethylfurfural are also discussed. After the Conclusion, a paragraph provides an update of the most recent articles that appeared in the literature after completion of the review