I. Synthesis, reactivity, and structural studies of rhodium(III) and rhodium(II) complexes of novel bis(oxazoline) pincer ligands. II. Synthesis and reactivity of novel rhenium methylidene complexes

Chapter 1. A series of novel C2-symmetric bisoxazoline ligands (benbox and benboxMe₂) have been prepared. A variety of coordinatively unsaturated rhodium(III) complexes (3a–g, 4a–g ) have been isolated. Trapping reactions of the agostically-stabilized complex [RhCl₂{lcub}(S,S)-ib-benbox(Me₂){rcub}] (4d) are described. Metal-to-aryl methyl migration reactions are described for the complex [RhMe{lcub}(S,S)-ip-benbox(Me₂){rcub}][BArf] (11c). Full characterization details and reactivity studies of air-stable, isolable, mononuclear, paramagnetic rhodium(II) complexes [RhCl₂{lcub}(S,S)-tb-benbox(Me ₂){rcub}(H)] (15e) and [RhCl₂{lcub}dm-benbox(Me₂ )H{rcub}] (15g) are reported.; Chapter 2. The synthesis and structural properties of three new hydridorhodium(III) complexes are reported. Hydrogenolysis of the cyclometallated rhodium dichloride complexes [RhCl₂{lcub}(S,S )-benbox(Me₂){rcub}] (1a–c) leads to formation of the new complexes [RhCl₂(H){lcub}(S,S)-ip-benbox(Me ₂)H{rcub}] (2a–c) in 45% to 85% yield. Compounds 2a–c were found to have unusual features by NMR spectroscopy: in particular, downfield shifted aryl proton resonances (8.88–9.03 ppm) that coupled to the rhodium hydride resonances. Using X-Ray crystallographic studies and a variety of solid and solution state characterization techniques, these features were attributed to the presence of preagostic bonding in 2a–c. Preagostic bonding is a rare phenomenon that shares attributes with both agostic and hydrogen bonding interactions.; Chapter 3. A family of bis(oxazoline) complexes of coordinatively unsaturated monomeric rhodium(II) (2a,b, 3a,b) are described. These complexes serve as catalysts for cyclopropanation of olefins by ethyl diazoacetate, giving excellent yields (66–94%). Enantioselectivities for the cis product isomers are high (61–84%). The reaction shows an unusual preference for formation of the cis isomers. Catalytic asymmetric aziridination of N-aryl imines with ethyl diazoacetate is also described.; Chapter 4. The synthesis and reactivity of two novel rhenium methylidene complexes is described. Protonolysis of the new dimethylrhenium(III) compound Cp*(PMe₃)₂Re(CH₃)₂ ( 3) leads to formation of the surprising hydridorhenium methylidene compound [Cp*(PMe₃)₂Re(CH₂)(H)][OTf] ( 5), which was characterized spectroscopically at low temperature. (Abstract shortened by UMI.)...