title: Dinitrogen functionalization with bis(cyclopentadienyl) complexes of zirconium and hafnium.
abstract: The rich chemistry of substituted bis(cyclopentadienyl)zirconium and hafnium complexes bearing side-on coordinated dinitrogen ligands is highlighted in this Perspective. Our studies in this area were initially motivated by the desire to understand side-on vs. end-on dinitrogen coordination in bimetallic zirconocene and hafnocene N2 compounds. In the cases where eta2,eta2-dinitrogen compounds were isolated, both structural and computational data have established significant imido character in the metal-nitrogen bonds. This additional bonding interaction, which is diminished in end-on complexes bearing both terminal and bridging N2 ligands, facilitates dinitrogen functionalization by non-polar reagents including dihydrogen, carbon-hydrogen bonds and weak Brønsted acids such as water and ethanol. In hafnocene chemistry, where unwanted side-on, end-on isomerization is suppressed, cycloaddition of phenylisocyanate to coordinated N2 has also been accomplished. For N-H bond forming reactions involving H2, kinetic measurements, in addition to isotopic labelling and computational studies, are consistent with dinitrogen functionalization by 1,2-addition involving a highly ordered, four-centred transition structure.
authors.affiliation: Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY, USA. pc92@cornell.edu
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Chirik
mesh_terms: D003517:Cyclopentanes / Q000737:chemistry*; D006195:Hafnium / Q000737:chemistry*; D008956:Models, Chemical; D008968:Molecular Conformation; D009584:Nitrogen / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003517:Cyclopentanes; D009942:Organometallic Compounds; D015040:Zirconium; D009584:Nitrogen; D006195:Hafnium