A complete series of stepwise oxidation of [Co(2-pyridinethiolato)(en)2]2+. Characterization of the 2-pyridinesulfenato-N,S and -N,O, 2-pyridinesulfinato-N,S and -N,O, and 2-pyridinesulfonato-N,O complexes

Abstract The H 2 O 2 oxidation of [Co(pyt)(en) 2 ] 2+ [ 1 , pyt=2-pyridinethiolate(1−) ion, en=ethylenediamine] afforded the orange [Co(pyse- N , S )(en) 2 ] 2+ [ 2 , pyse=2-pyridinesulfenate(1−) ion] complex. Irradiation of this orange complex in the solid state yielded a green complex. The molecular structure of the green complex perchlorate was determined by X-ray diffraction to be [Co(pyse- N , O )(en) 2 ](ClO 4 ) 2 ( 4 ); linkage isomerization took place upon photolysis. The crystal data and final R value for the cocrystal ( 3/5 ) are: triclinic, P 1 , a =9.374(4) A, b =11.248(4) A, c =9.238(8) A, α =95.26(4)°, β =95.14(5)°, γ =75.75(3)°, V =938(2) A 3 , Z =2 and R =0.040 for 2757 unique reflections. The pyse- N , O complex has an anomalous feature in the UV–vis spectrum. It has an extra band (16 400 cm −1 ) on the low-energy side of the first d–d absorption band (22 200 cm −1 ). This band can be rationalized as a splitting component of the first d–d band generated by the anisotropic interaction of the antibonding π* orbital of the coordinating oxygen with the t 2g orbitals on the cobalt center. Treatment of [Co(pyt)(en) 2 ] 2+ with excess H 2 O 2 afforded the yellow-orange sulfinato- N , S complex, [Co(pysi- N , S )(en) 2 ] 2+ [ 3 , pysi=2-pyridinesulfinate(1−) ion]. The molecular structure of the pysi- N , S complex was determined by X-ray diffraction to be [Co(pysi- N , S )(en) 2 ](ClO 4 ) 2 ( 3 ), which cocrystallized with the pysi- N , O complex ( 5 ). The crystal data and final R value are: monoclinic, C 2, a =28.559(8) A, b =6.960(2) A, c =10.406(3) A, β =99.90(2)°, V =2038(2) A 3 , Z =4 and R =0.040 for 2391 unique reflections. The pysi- N , S complex was unstable and was easily converted photochemically or thermally to the linkage-isomerized orange pysi- N , O complex ( 5 ). The sulfur atom becomes chiral ( R and S ) upon linkage isomerization, and two kinds of racemic salt, Λ( R )Δ( S ) and Λ( S )Δ( R ), were separated by fractional crystallization of the complex perchlorate. The molecular structure of the less soluble isomer (Λ( S )Δ( R )- 5 ) of the perchlorate was determined by X-ray diffraction to be Λ( S )Δ( R )-[Co(pysi- N , O )(en) 2 ](ClO 4 ) 2 . The crystal data and final R value are: triclinic, P 1 , a =9.384(4) A, b =11.807(8) A, c =8.640(5) A, α =98.54(5)°, β =94.40(4)°, γ =96.65(5)°, V =936(2) A 3 , Z =2 and R =0.038 for 3061 unique reflections. The two diastereomers of Λ-[Co(pysi- N , O )(en) 2 ] 2+ were separated by SP-Sephadex column chromatography, and one of them (Λ( R )- 5 ) was structurally characterized by X-ray crystallography. Λ( R )-[Co(pysi- N , O )(en) 2 ](ClO 4 ) 2 , which crystallizes as orthorhombic in space group P 2 1 2 1 2 1 with Z =4, has the cell parameters a =9.896(2) A, b =20.758(6) A, c =9.494(4) A, V =1950(2) A 3 . The final R value was 0.041 for 1543 unique reflections. Kinetic studies of reversible isomerization (epimerization) between Λ( R )- and Λ( S )-[Co(pysi- N , O )(en) 2 ] 2+ were performed in aqueous solutions at 60 °C. The rate constants were k Λ( R )→Λ( S ) =5.5×10 −6  s −1 and k Λ( S )→Λ( R ) =1.7×10 −6  s −1 . The orange-red [Co(pyso- N , O )(en) 2 ] 2+ [ 6 , pyso=2-pyridinesulfonate(1−) ion] complex was prepared by the reaction of cis -[Co{OS(O) 2 CF 3 } 2 (en) 2 ] + with the 2-pyridinesulfonate ligand or by the oxidation of [Co(pyse- N , O )(en) 2 ] 2+ ( 4 ) with H 2 O 2 . The molecular structure of the trifluoromethanesulfonate salt of complex 6 was determined by X-ray diffraction. [Co(pyso- N , O )(en) 2 ](CF 3 SO 3 ) 2 crystallizes as monoclinic in space group P 2 1 / a with Z =4. The cell parameters are a =19.079(8) A, b =16.699(6) A, c =7.462(4) A, β =100.51(4)°, V =2338(2) A 3 . The final R value was 0.050 for 3966 unique reflections. The pyso ligand has the strongest ligand field strength among the ligands studied here. A series of sulfur oxidation from [Co(pyt)(en) 2 ] 2+ to [Co(pyso- N , O )(en) 2 ] 2+ is established.