Pentafulvene complexes of group four metals: Versatile organometallic building blocks

A survey of the chemistry of pentafulvene complexes of group four metals is presented. Different synthetic procedures are discussed, leading to mono- and bis(η5:η1-pentafulvene)metal complexes. Due to Umpolung of the coordinated pentafulvene ligand the Cexo-atom become strong nucleophilic and a broad range of element-H activation reactions are investigated. This review covers the bond activation reactions of molecular hydrogen, N-H and C-H bond splitting reactions leading to titanium hydrides, imides and hydrazides as well as titanaaziridines, employing pentafulvene titanium complexes. A new concept of the preparation of tridentate Cp,O,P- and Cp,N,P- ligands is presented. These ligands are used for the preparation of electrophilic cationic group four metal complexes. In the case of cationic Cp,N,P-titanium complexes frustrated Lewis pair (FLP) reactivity is found.