Organoosmium(IV) hydroxo complexes and the synthesis of heterobimetallic catalysts for aerobic alcohol oxidation

Chapter 1. Organometallic complexes containing terminal hydroxo ligands are reviewed to provide an adequate background for the remaining chapters. The synthesis, reactivity and structure of hydroxo complexes are discussed, as well as applications of these relatively rare complexes.;Chapter 2. The cis and trans isomers of the organometallic osmium(VI) hydroxo compound [N( n-Bu)4] [Os(N)(CH2SiMe3)2(OH) 2] result from the substitution of chloro for hydroxo ligands in precursor compounds. Depending on the molecular structure, these compounds behave as nucleophiles, Bronsted bases, or Lewis bases in their reactions. One of these, [N(n-Bu)4][cis-Os(N)(CH 2SiMe3)2(OH)2], reacts readily with CO2 to produce a carbonate compound [N(n-Bu) 4][Os(N)(CH2SiMe3)2(CO3)]. The other isomer [N(n-Bu)4][trans-Os(N)(CH 2SiMe3)2(OH)2] reacts with CO 2 to slowly form the same carbonate compound. It is protonated by other acids to give a neutral hydroxo dimer {Os(N)(CH2SiMe3) 2(micro-OH)}2. The trans isomer also reacts with K2CrO4 and acid to generate the known heterobimetallic oxidation catalyst [N(n-Bu)4][Os(N)(CH2SiMe 3)2(micro-O)2CrO2]. The anti isomer of {Os(N)(CH2SiMe3)2(micro-OH)} 2 reacts with Pd(bpy)(OSiMe3)2 to produce a coordinatively unsaturated, heterometallic complex {Os(N)(CH2SiMe3) 2}2(micro3-O)2Pd(bpy).;Chapter 3. The heterobimetallic complex [N( n-Bu)4][Os(N)(CH2 SiMe3)2(micro-O)2CrO2] catalyzes the aerobic oxidation of 5-(hydroxymethyl)-2-furfural (HMF) to 2,5-diformylfuran (DFF). The oxidation is temperature-dependent. At 65 °C and 20 psi O 2, 5 mol % [N(n-Bu)4][Os(N)(CH 2SiMe3)2(micro-O)2CrO2] catalyzes the oxidation of HMF to DFF in as high as 76% yield. Immobilization of [N(n-Bu)4] [Os(N)(CH2SiMe3 )2(micro-O)2CrO2] on silica was unsuccessful. The gray solid, [N(n-Bu)4][Os(N)(CH2SiMe 3)2CrO4](SiO2)x leaches [N(n-Bu)4][Os(N)(CH2SiMe3) 2(micro-O)2CrO2] under the conditions used for the oxidation. Currently we are exploring new methods of immobilizing [N( n-Bu)4][Os(N)(CH2SiMe3)2(micro-O) 2CrO2] on silica supports.;Chapter 4. The compounds dibenzoylmethane and N-phenylsalicylaldimine react with VOCl3 in toluene to generate complex V(O)Cl2(dbm) (dbm =C6H5C(O)CHC(O)C 6H5) and a complex of the empirical formula C13H 11Cl3NO2V. The square pyramidal complex V(O)Cl 2(dbm) is a black solid that is stable in solution, but reacts with trace water. The complex C13H11Cl3NO 2V is unstable in solution. In a solution of ether/hexane, V(O)Cl 2(dbm) reacts with NaOSiMe3 to yield the uncharacterized intermediate V(O)(dbm)(OSiMe3)2, which reacts with the organometallic dihydroxo complex [N(n-Bu)4][ cis-Os(N)(CH2SiMe3)2(OH)2] to generate Os(N)(CH2SiMe3)2(dbm).