Transition Metal Complexes with Sulfur Ligands. 130.1 Synthesis, Structure, and Reactivity of the Sulfur-Rich Ruthenium Hydride Complexes [Ru(H)(PR3)(‘S4')]- and the η2-H2 Complex [Ru(H2)(PCy3)(‘S4')] (R = Ph, iPr, Cy; ‘S4'2- = 1,2-Bis((2-mercaptophenyl)thio)ethane(2−))

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Abstract
Hydride and η2-H2 ruthenium complexes with sulfur-rich coordination spheres were synthesized. Substitution of either DMSO or PPh3 in [Ru(DMSO)(PR3)(‘S4')] and [Ru(PPh3)2(‘S4')] by hydride anions from LiAlH4 or NaBEt3H yielded [Ru(H)(PR3)(‘S4')]- complexes (R = iPr, Ph, Cy; ‘S4'2- = 1,2-bis((2-mercaptophenyl)thio)ethane(2−)). They were isolated as [Li(THF)(Et2O)][Ru(H)(PR3)(‘S4')] (R = iPr (1a), Cy (1b), Na[Ru(H)(PCy3)(‘S4')]·2BEt3·0.5DMSO (2a), and the solvent-free Na[Ru(H)(PPh3)(‘S4')]·2BEt3 (2b). X-ray structure determinations of 1a·0.5Et2O and 1b·Et2O showed that in both complexes pseudooctahedral [Ru(H)(PR3)(‘S4')]- anions are bridged to pseudotetrahedral [Li(THF)(Et2O)] cations via the hydride ligand and one thiolate donor of the ‘S4'2- ligand (crystal data: 1a, monoclinic, P21/n, a = 1401.6(2) pm, b = 1045.2(3) pm, c = 2590.6(4) pm, β = 95.04(1)°, V = 3.780(1) nm3, Z = 4; 1b, triclinic, P1̄, a = 1264.2(1) pm, b = 1322.9(3) pm, c = 1569.5(2) pm, α = 88.96(1)°, β = 83.48(1)°, γ = 62.16(1)°, V = 2.3042(6) nm3, Z = 2). Short intramolecular C−H···H−Ru contacts (≈230 pm) between the hydride ligands, phosphine substituents, and lithium-coordinated Et2O molecules indicate “unconventional” hydrogen bonds. They potentially help to decrease the hydridic character of the hydride ligand to such an extent that no structural hydride trans influence can be observed in the solid state. In solution at room temperature, all hydride complexes 1a−2b rapidly release H2 or HD, when treated with CH3OH or CD3OD. Low-temperature 1H and 2H NMR spectroscopy between −20 and −80 °C showed that initially η2-H2 or η2-HD complexes form. Their formation explains the observed scrambling between protons and hydride ligands, which requires a heterolytic cleavage of dihydrogen. A 1:1:1 triplet at δ = −6.5 ppm (1J(HD) = 32 Hz, 2J(PH) = 5 Hz) and a relaxation time of T1(min) = 4 ms (−60 °C, 270 MHz) firmly established the formation of the η2-dihydrogen complexes. The reversibility of H2 release and uptake by [Ru(PCy3)(‘S4')] fragments and the heterolytic cleavage of H2 in [Ru(η2-H2)(PCy3)(‘S4')] was further ascertained by the reaction of [Ru(DMSO)(PCy3)(‘S4')] with H2 in the presence of NaOMe, yielding the [Ru(H)(PCy3)(‘S4')]- anion. The relevance of the complexes and their reactions for the heterolytic H2 activation at the transition metal sulfur sites of hydrogenases is discussed.