Carbon-sulfur bond cleavage with a loss of stereochemistry in the ring opening of trans-2,4-diphenylthietane by Os3(CO)10(NCMe)2

Article abstract of DOI:10.1021/om00037a024

The reaction of Os₃(CO)₁₀(NCMe)₂ with trans-2,4-diphenylthietane (2,4-DPT) at 25 °C resulted in the formation of two isomers, cis- and trans-Os₃(CO)₁₀[μ-SC(H)PhCH₂C(H)Ph] (1), in a combined yield of 76%. The cis product was characterized by single-crystal X-ray diffraction analysis and was found to contain a thiametalladiphenylcyclopentane ring formed by the opening of the thietane ring. The cis and trans isomers differ in the orientation of their phenyl substituents. The isomers are formed in approximately equal amounts in the early stages of the reaction, but the trans isomer subsequently slowly isomerizes to the cis isomer. The observed loss in stereochemistry at the carbon center is attributed to a stepwise ring-opening mechanism. When compound 1 was heated to 97 °C under a CO atmosphere, five compounds were formed: Os₃(CO)₁₀[μ-SC(H)PhC(H)=C(H)Ph[(μ-H) (2) (22%), Os₂(CO)₇[μ-SC(H)(C₆H₄)CH ₂CH₂Ph] (3) (11%), Os₃(CO)₁₁[μ-SC(H)PhCH₂C(H)Ph] (4) (39%), H₂Os₆(CO)₁₇(μ₃-S)(μ ₄-S) (5) (a trace amount), and Os₃(CO)₁₂. Compounds 3 and 5 and the known compound Os₃(CO)₉(μ₃-CO)(μ₃-S) (6) were obtained in better yields by heating 2 to 125 °C in octane solvent. Compounds 2-4 were characterized by IR, ¹H NMR, and single-crystal X-ray diffraction analyses. Compound 2 is an isomer of 1 and contains a diphenylpropenethiolate and hydride ligand formed by a β-eliminationβ transformation of the ring system in 1. The mechanism of this transformation was not established. Compound 3 contains only two metal atoms and an ortho-metalated phenyl ring. Compound 4 is a CO adduct of 1 formed by the cleavage of the sulfur-bridged metal-metal bond. Crystallographic data are as follows. cis-1: space group P2₁/c, a = 8.674 (2) A?, b = 35.09 (1) A?, c = 9.449 (2) A?, β = 106.41 (1)°, Z = 4, 2053 reflections, R = 0.033. 2: space group C2/c, a = 13.845 (2) A?, b = 14.545 (4) A? c = 28.907 (6) A?, β = 98.88 (1)°, Z = 8, 2519 reflections, R = 0.027. 3: space group P2₁/c, a = 8.337 (1) A?, b = 17.311 (4) A?, c = 16.409 (3) A?, β = 100.82 (1)°, Z = 4, 2299 reflections, R = 0.036. 4: space group P1, a = 14.319 (2) A?, b = 17.794 (5) A?, c = 12.257 (4) A?, α = 106.69 (2)°, β = 90.74 (2)°, γ = 82.56 (2)°, Z = 4, 4020 reflections, R = 0.041.