Oxido‐Hydroxido‐ and Oxido‐Aminato‐Osmium(V) Complexes with a Cyclohexanediamine‐Based Tetradentate Ligand as Active Oxidants for Dihydroxylation and Aminohydroxylation of Alkenes

• Published in: European journal of inorganic chemistry 2019-06, Vol.2019 (24), p.2891-2898
• Main Authors: Fujimoto, Tomohiro, Sugimoto, Hideki, Kai, Kenichiro, Maeda, Kazuki, Itoh, Shinobu
• Format: Article
• Language: English
• Subjects: Alkenes; Aminohydroxylation; Catalysis; Crystal structure; Dihydroxylation; Hydrogen peroxide; Inorganic chemistry; Ligands; Osmium; Oxidation; Oxidizing agents; Styrenes; Tetradentate ligands
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201900339

Six‐coordinate osmium(III) complexes coordinated by a cyclohexanediamine‐based tetradentate ligand [trans‐N,N′‐dimethyl‐N,N′‐bis(2‐pyridylmethyl)‐1,2‐cyclohexanediamine: BPMCN] are synthesized. The remaining two coordination sites are occupied by chloride (Cl–), triflate (OTf–), or hydroxide/water (OH–/H2O) to complete the octahedral osmium(III) centers; [OsIIIX2(BPMCN)]+ (X = Cl– or OTf–) and [OsIII(OH)(H2O)(BPMCN)]2+. The OsIII(OH)(H2O) complex catalyzes cis‐dihydroxylation and cis‐aminohydroxylation of styrene with hydrogen peroxide (H2O2) and chloramine‐T (TsNClNa) to yield the corresponding diol and aminoalcohol, respectively. The oxido‐hydroxido‐osmium(V) complex {[OsV(O)(OH)(BPMCN)]2+} is isolated as the active oxidant of the dihydroxylation. The oxidation of the OsIII(OH)(H2O) complex with chloramine‐T yields oxido‐aminato‐osmium(V) complex, [OsV(O)(NHTs)(BPMCN)]2+. Comparison of the crystal structure with those of the oxido‐hydroxido‐osmium(V) complex and related imido‐ and amino‐osmium complexes indicates that the –NHTs group works as a monoanionic aminate ligand and the osmium(V)–NHTs bond has a single bond character [Os–N; 2.058(4) Å]. The oxido‐aminato‐osmium(V) complex is revealed as the active oxidant for the aminohydroxylation by the direct reaction of the complex with styrene. The characterization of the complex allows us to propose the catalytic mechanism of the aminohydroxylation of alkenes. A series of Os complexes with a cyclohexanediamine‐based tetradentate ligand [trans‐N,N′‐dimethyl‐N,N′‐bis(2‐pyridylmethyl)‐1,2‐cyclohexadiamine: BPMCN] were synthesized. [OsV(O)(OH)(BPMCN)](ClO4)2 and [OsV(O)(NHTs)(BPMCN)](BF4)2 were isolated and characterized as the active oxidants for cis‐dihydroxylation and cis‐aminohydroxylation of styrene, respectively.