Heterocyclic cyclopentadienyl analogs with bn frameworks
Creators: name: Ly, Hanh Vien
Publisher: name: University of Calgary
Year: 2007

description: Bibliography: p. 243-262
description: Some pages are in colour.
description: The heterocyclic cyclopentadienyl analogs have provided a fertile area of research, owing to the interest in tuning the electronic properties of cyclopentadienyl (Cp) ligands for the development of more efficient catalysts and new materials. A variety of five-membered heterocyclic Cp analogs have been synthesized by the formal replacement of ring carbon atoms with isoelectronic main group fragments. Metal complexes containing these heterocyclic ligands have proven to be feasible ancillary ligands in catalysis. The primary objective of this thesis is the development of a novel class of heterocyclic Cp ligands having ring carbon fragments (CR) formally substituted with isolobal boron (BR-) and nitrogen (NR'+) fragments. The synthesis and characterization of the 1,2-diaza-3,5-diborolyl ligands with cyclic CB2N2 frameworks is described and their coordination to a variety of metal fragments is reported. Just like cyclopentadienyl, the 1,2-diaza-3,5-diborolyl ligands are excellent 7t ligands that exhibit interesting coordination properties. Alkali metal complexes of 1,2-diaza-3,5-diborolyls were synthesized and their investigation by single-crystal X-ray diffraction analysis revealed substantial coordinative similarities, but also remarkable differences in comparison to cyclopentadienyl ligands. Sandwich complexes containing these new heterocyclic 7t ligands were synthesized by metathesis reaction of the corresponding alkali metal salts with various metal halides. The structural characterization of a series of electron-rich group 12 and 14 metallocenes, as well as metallocenes of the early and late transition metals, revealed some unique coordinative properties of the ligands: 11 1, 113, 114 and 115 -coordination modes of the 1,2-diaza-3,5-diborolyl ligands were observed, depending on the electron properties of the coordinated metals. In addition, the synthesis of the heterobicyclic l ,5-diaza-2,4,6,8-tetraborolyl ligand featuring a C2B4N2 framework is described and the structural investigation of its dipotassium salt showed that this heterobicyclic ligand is a promising re bridging linker for the construction of polydecker sandwich complexes. A triple-decker ruthenium sandwich cornplex featuring an unusual eight-membered C2 B4N2 ring as the middle deck was synthesized through the insertion of two RuCp* fragments into the N-N bond of the heterobicyclic ligand. Electrochemical studies of the triple-decker ruthenocene are presented. The coordination chemistry of the 1,2,4-triaza-3,5-diborolyl ligand, a carbon-free heterocyclic Cp analog, was also investigated. The alkali metal salts of this ligand were synthesized via selective deprotonation of the ring nitrogen utilizing appropriate metalating agents. In contrast to the fom1er ligands, the solid-state structures of the alkali metal complexes featuring these ligands are dominated by cr interactions of the ligand to the metal ions. A rhodium dimer containing 1,2,4-triaza-3,5-diborolyl ligands a-bridging two Rh( cod) fragments was synthesized and characterized. The synthesis and characterization of a tricyclic compound with a B8N4 framework consisting of fused five­and six-meri1bered rings was discussed, along with a study of its electrochemical properties.