The reaction of OsH6((PPr3)-Pr-i)(2) with N-acetyl-L-cysteine affords OsH2{OC(=O)CH[NHC(=O)CH3]CH2S}((PPr3)-Pr-i)(2). The molecular structure of this complex shows an unusual chelate (O, S) coordination of the cysteine ligand. The crystal structure reveals the presence of two diastereoisomers in the solid. Spectroscopic studies suggest that both independent molecules easily interconvert in solution. [GRAPHICS] ields by the thermal decomposition of H3B.NH3 under similar conditions. In both cases, borazine is the only volatile product and is obtained in excellent purity by a single vacuum fractionation. [GRAPHICS]U&?~㏃}