Reactions of Tp–Os nitrido complexes with the nucleophiles hydroxide and thiosulfate

Abstract

The reaction between TpOs(N)Cl 2 ( 1) [Tp = hydrotris(1-pyrazolyl)borate] and aqueous ( n Bu 4N)(OH) in THF- d 8 forms the nitrosyl complex TpOs(NO)Cl 2 ( 5) among other products, suggesting an initial hydroxide attack at the nitrido ligand. In contrast, the reaction of the acetate complex TpOs(N)(OAc) 2 ( 2) with NaOH in Me 2CO/H 2O yields the osmium bis-hydroxide complex TpOs(N)(OH) 2 ( 3), which has been structurally characterized by single-crystal X-ray diffraction. Acetate for hydroxide exchange could occur by ligand substitution or by nucleophilic attack at the carbonyl carbon of the acetate ligands (saponification). Reacting 2 with Na 18OH in H 2 18O/CD 3CN yields predominantly doubly 18O-labeled TpOs(N)( 18OH) 2 ( 3- 18 O 2 ) and unlabeled acetate, by ESI/MS and 13C{ 1H} NMR. This indicates that hydroxide reacts by substitution rather than by attack at the ligand. The reaction of 2 with the softer nucleophile thiosulfate occurs at the nitrido ligand, giving the thionitrosyl complex TpOs(NS)(OAc) 2 ( 4). Reacting 4 with NaOH in (CD 3) 2CO/D 2O also generates the bis-hydroxide complex 3.