Optically active triosmium cluster with bridging terpenic thioureato-like ligand – synthesis, structure, and absolute configuration

Triosmium clusters with bridging terpenic thioureato-like ligands

“…(3aR, 3bR, 4aR, 5aS)-5a-Hydroxy-3,4,4-trimethyl3a,3b,4,4a,5,5a-hexahydrocyclopropa [3,4]-cyclopenta-[1,2-c]pyrazole-1-carbothioic acid amide Thiosemicarbazide (0.88 g, 4.5 mmol) was added to a stirred solution of the diketone (0.66 g, 4 mmol) in a mixture of methanol (25 ml) and glacial AcOH (1 ml). The reaction mixture was heated and allowed to stay under reflux for 3-4 h. The solvent was distilled off at reduced pressure; the residue was treated with water (40 ml) and extracted with CH 2 Cl 2 (2 · 30 ml).…”

“…The reaction mixture was heated and allowed to stay under reflux for 3-4 h. The solvent was distilled off at reduced pressure; the residue was treated with water (40 ml) and extracted with CH 2 Cl 2 (2 · 30 ml). The combined extracts were dried (Na 2 SO 4 ) and concentrated to give the crude product that was then purified by column chromatography (Al 2 O 3 , benzene) followed by crystallization from MeCN-CHCl 3 …”

“…These reactions proceeded quite different as compared with those of the simplest analogues. We have found CH [1] or CN [2] activation at very mild conditions and changes of the ligand coordination mode as a result of the ligands steric demands [2,3]. For example, (3bS, 4aR)-3,4,4-trimethyl-3b,4,4a,5-tetrahydro-cyclopropa [3,4] cyclopenta[1,2-c]pyrazole-1-carbothioic acid (2-methoxy-phenyl)-amide (amide 1), which contains thiourealike fragment N-C(‚S)-N, coordinates in triosmium cluster in the tautomeric N-C(‚NR)-S form [3] with the ligand coordinated only on two osmium atoms by sulphur and N 1 atoms in contrast to simple analogues bridging three metal atoms [4,5].…”

“…We have found CH [1] or CN [2] activation at very mild conditions and changes of the ligand coordination mode as a result of the ligands steric demands [2,3]. For example, (3bS, 4aR)-3,4,4-trimethyl-3b,4,4a,5-tetrahydro-cyclopropa [3,4] cyclopenta[1,2-c]pyrazole-1-carbothioic acid (2-methoxy-phenyl)-amide (amide 1), which contains thiourealike fragment N-C(‚S)-N, coordinates in triosmium cluster in the tautomeric N-C(‚NR)-S form [3] with the ligand coordinated only on two osmium atoms by sulphur and N 1 atoms in contrast to simple analogues bridging three metal atoms [4,5]. This difference could be caused by (a) involving of lone electronic N 2 atom pair into the aromatic-system of pyrazolic cycle; (b) the presence of the bulky substituent at the nitrogen atom N 3 and decreasing of electronic density on this atom owing to electronegativity of the pyrazolic cycle; (c) steric restrictions arising at coordination of bulky tricyclic ligand on cluster core.…”

“…This difference could be caused by (a) involving of lone electronic N 2 atom pair into the aromatic-system of pyrazolic cycle; (b) the presence of the bulky substituent at the nitrogen atom N 3 and decreasing of electronic density on this atom owing to electronegativity of the pyrazolic cycle; (c) steric restrictions arising at coordination of bulky tricyclic ligand on cluster core. To examine these assumptions we have investigated the reactions of cluster Os 3 (CO) 11 (NCMe) (2) with acetone-4-(2-methoxy-phenyl)thiosemicarbazone (3) and (3aR, 3bR, 4aR, 5aS)-5a-hydroxy-3,4, 4-trimethyl-3a,3b,4,4a,5,5a-hexahydro-cyclopropa [3,4] cyclopenta[1,2-c]pyrazole-1-carbothioic acid amide (4) (Scheme 1).…”