5445-77-2Relevant articles and documents
Structural characterisation of solution species implicated in the palladium-catalysed Heck reaction by Pd K-edge X-ray absorption spectroscopy: Palladium acetate as a catalyst precursor
Evans, John,O'Neill, Lynn,Kambhampati, Vijaya L.,Rayner, Graham,Turin, Sandra,Genge, Anthony,Dent, Andrew J.,Neisius, Thomas
, p. 2207 - 2212 (2002)
Energy dispersive EXAFS (EDE), Quick EXAFS (QEXAFS), 13C NMR and X-ray crystallography have been used to probe the co-ordination sphere of palladium in the course of the phosphine free Heck reaction. [Pd2I6][NBu3H]2 has been isolated from the precatalytic solution and its crystal structure determined. EDE and QEXAFS spectra of the complexes Pd(OAc)2, Pd(PPh3)4 and [Pd2I6][NEt3H]2 illustrated the value of the technique in structure elucidation. EXAFS of the precatalytic solution detects [Pd2I6]2- and no co-ordinated carbon. EXAFS of the catalytic solution shows a first co-ordination sphere of 2 carbon atoms and a second of 2-2.5 iodines. A scheme involving an equilibrium between the oxidative addition product and the olefin co-ordination species, has been proposed to explain these results.
A robust and stereocomplementary panel of ene-reductase variants for gram-scale asymmetric hydrogenation
Nett, Nathalie,Duewel, Sabine,Schmermund, Luca,Benary, Gerrit E.,Ranaghan, Kara,Mulholland, Adrian,Opperman, Diederik J.,Hoebenreich, Sabrina
, (2021/01/25)
We report an engineered panel of ene-reductases (ERs) from Thermus scotoductus SA-01 (TsER) that combines control over facial selectivity in the reduction of electron deficient C[dbnd]C double bonds with thermostability (up to 70 °C), organic solvent tolerance (up to 40 % v/v) and a broad substrate scope (23 compounds, three new to literature). Substrate acceptance and facial selectivity of 3-methylcyclohexenone was rationalized by crystallisation of TsER C25D/I67T and in silico docking. The TsER variant panel shows excellent enantiomeric excess (ee) and yields during bi-phasic preparative scale synthesis, with isolated yield of up to 93 % for 2R,5S-dihydrocarvone (3.6 g). Turnover frequencies (TOF) of approximately 40 000 h?1 were achieved, which are comparable to rates in hetero- and homogeneous metal catalysed hydrogenations. Preliminary batch reactions also demonstrated the reusability of the reaction system by consecutively removing the organic phase (n-pentane) for product removal and replacing with fresh substrate. Four consecutive batches yielded ca. 27 g L?1 R-levodione from a 45 mL aqueous reaction, containing less than 17 mg (10 μM) enzyme and the reaction only stopping because of acidification. The TsER variant panel provides a robust, highly active and stereocomplementary base for further exploitation as a tool in preparative organic synthesis.
Organic Ligand-Free Hydroformylation with Rh Particles as Catalyst?
Liu, Shujuan,Dai, Xingchao,Wang, Hongli,Wang, Xinzhi,Shi, Feng
, p. 139 - 143 (2020/01/03)
An efficient and organic ligand-free heterogeneous catalytic system for hydroformylation of olefins is highly desirable for both academy and industry. In this study, simple Rh black was employed as a heterogeneous catalyst for hydroformylation of olefins in the absence of organic ligand. The Rh black catalyst showed good catalytic activity for a broad substrate scope including the aliphatic and aromatic olefins, affording the desired aldehydes in good yields. Taking the hydroformylation of ethylene as an example, 86% yield of propanal and TOF of 200 h–1 were obtained, which was superior to the reported homogeneous catalytic systems. In addition, the catalyst could be reused five times without loss of activity under identical reaction conditions, and the Rh leaching was negligible after each cycle.
