Synthesis, Structure, and Reactivity of Organometallic Osmium(VI) Hydroxo Compounds

The organometallic osmium(VI) hydroxo compounds [N(n-Bu)4][Os(N)(CH2SiMe3)3(OH)], cis and trans isomers of [N(n-Bu)4][Os(N)(CH2SiMe3)2(OH)2], result from the substitution of chloride for hydroxide ligands in precursor compounds. Depending on the molecular structure, these compounds behave as nucleophiles, Brønsted bases, or Lewis bases in their reactions. One of these, [N(n-Bu)4][cis-Os(N)(CH2SiMe3)2(OH)2], reacts readily with CO2 to produce the carbonate compound [N(n-Bu)4][Os(N)(CH2SiMe3)2(CO3)]. The other isomer, [N(n-Bu)4][trans-Os(N)(CH2SiMe3)2(OH)2], reacts with CO2 to slowly form the same carbonate compound. It is protonated by other acids to give the neutral hydroxo dimer {Os(N)(CH2SiMe3)2(μ-OH)}2. The anti isomer of {Os(N)(CH2SiMe3)2(μ-OH)}2 reacts with Pd(bpy)(OSiMe3)2 to produce the coordinatively unsaturated, heterometallic complex {Os(N)(CH2SiMe3)2}2(μ3-O)2Pd(bpy). The molecular structure of this complex shows two square-pyramidal osmium groups with an anti arrangement of the apical nitrido ligand and a square-planar palladium(II) center, all connected by the triply bridging oxo groups.