Protonation and H/D exchange reactions promoted by a sulfur-rich osmium hydride complex: identification of a labile dihydrogen complex
- 29 October 2004
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Dalton Transactions
- No. 23,p. 3991-3996
- https://doi.org/10.1039/b411878b
Abstract
The sulfur-rich osmium nitrosyl complexes Bu4N[Os(NO)(buS2)2] (1) [buS2 2− = 3,5-tert-butyl-1,2-benzenedithiolate(2−)] and [Os(NO)(pybuS4)]Br (2) [pybuS4 2− = 2,6-bis(2-sulfanyl-3,5-di-tert-butylphenylthio)dimethylpyridine(2−)] have been synthesized. The molecular structure of 1 exhibits a square-pyramidal geometry with the NO group at the apical position. A pseudo-octahedral geometry with two thiolate and two thioether donors in trans configuration is found for 2. Compound 2 shows two quasi-reversible one-electron redox waves at E1/2 = 0.51 and −0.46 V vs. NHE for the redox couples [Os(NO)(pybuS4)]+1/0 and [Os(NO)(pybuS4)]0/−1, respectively. 2 reacts with NaAlH4 to produce Na[Os(H)(pybuS4)] (3), which exhibits a typical hydride resonance in the 1H NMR spectrum at δ = −15.03 ppm. Protonation of 3 with HBF4/CD3OD at 20 °C rapidly releases H2/HD to afford the dinuclear complex [Os(pybuS4)]2 (4). Low temperature 1H and 2H NMR spectra of 3 in [D8]THF with CH3OH or CD3OD at −80 °C allow the observation of the formation of [Os(H2/HD)(pybuS4)]. A 1 ∶ 1 ∶ 1 triplet at δ = −7.84 ppm [J(HD) = 31.2 Hz] and a relaxation time of T1(min) = 6 ms (−65 °C, 270 MHz) firmly establish the presence of η2-H2/HD ligand. At room temperature, 3 interacts with D2 (1 atm) and undergoes heterolytic D2 cleavage followed by H/D exchange to form Na[Os(D)(pybuS4)] (3a). A plausible cyclic mechanism has been proposed.Keywords
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