Os(CO)2(η2-SC5H4N(O))(η2-SC5H4N): structural evidence for the transformation of pyridine-2-thione N-oxide to pyridine-2-thiolate in osmium complexes

The reaction of Os3(CO)12 with an excess of 1-hydroxypyridine-2-thione and Me3NO gives three mononuclear osmium complexes Os(CO)2(η2-SC5H4N(O))2 (1), Os(CO)2(η2-SC5H4N(O))(η2-SC5H4N) (2), and Os(CO)2(η2-SC5H4N)2 (3). The results of single-crystal X-ray analyses reveal that complex 1 contains two O,S-chelate pyridine-2-thione N-oxide (PyOS) ligands, whereas complex 2 contains one O,S-chelate PyOS and one N,S-chelate pyridine-2-thiolate group. The unique structure of 2 provides evidence of the pathway for this transformation. When this reaction was monitored by 1H NMR spectroscopy the triosmium complexes Os3(CO)10(μ-H)(μ-η1-S-C5H4N(O)) (4) and Os3(CO)9(μ-H)(μ-η1:η2-SC5H4N(O)) (5) were identified as intermediates in the formation of the mononuclear final products 1–3. The proposed pathway is further supported by the observation of several dinuclear osmium intermediates by electrospray ionization mass spectrometry. In addition, the reaction of Os3(CO)12 with 1-hydroxypyridine-2-thione in the absence of Me3NO at 90 °C generated mononuclear complex 2 as the major product along with smaller amounts of complexes 1 and 3. These results suggest that the N-oxide facilitates the decarbonylation reaction. Crystal data for 1: monoclinic, space group C2/c, a = 26.9990(5) Å, b = 7.6230(7) Å, c = 14.2980(13) Å, β = 101.620(2)°, V = 2882.4(4) Å3, Z = 8. Crystal data for 2: monoclinic, space group C2/c, a = 5.7884(3) Å, b = 13.9667(7) Å, c = 17.2575(9) Å, β = 96.686(1)°, V = 1385.69(12) Å3, Z = 4.