Abstract
The catalytic activity of the water-soluble scorpionate coordination compounds [Cu(-NN’O-Tpms)2] (1), [Mn(Tpms)2] (2) and Li[FeCl2(-NN’N’’-Tpms)] (3) [Tpms = tris(pyrazolyl)-methane sulfonate, O3SC(pz)3], were studied towards the (Henry) reaction between benzaldehyde and nitromethane or nitroethane in aqueous medium to afford, respectively, 2-nitro-1-phenylethanol or 2-nitro-1-phenylpropanol, the latter in the syn and the anti diastereoisomeric forms. Complex 1 exhibited the highest activity under the optimum experimental conditions and was used to broaden the scope of the reaction to include several aromatic aldehydes achieving yields up to 94%.
Highlights
IntroductionScorpionate is a term coined by Trofimenko [1] to describe a special class of poly(pyrazolyl) poly(pyrazolyl) compounds, which which are derived from two or more N-deprotonated pyrazole rings bound to a main group atom atom (e.g.,(e.g., boron, boron,carbon, carbon,aluminium, aluminium,indium, indium,gallium, gallium,silicon, silicon, and germanium) through one and germanium) through one of of ring nitrogens [1,2,3,4,5,6].Tris(pyrazolyl)methanes (Tpm,Figure were reported first time thethe ring nitrogens Figure 1) 1)were reported forfor thethe first time in in 1937[7]
Syntheticsynthetic protocolsprotocols to preparetoTpm compounds in high yields
tris(pyrazolyl)methane sulfonate (Tpms) have been well studied towards diverse metalmetal centers, thethe use hydrosoluble complexes complexes in aqueous aqueous medium medium catalysis catalysis is is limited limited to to scarce scarce examples, examples, in in particular particular for for hydrosoluble oxidation [16,33,34,35], hydroformylation catalytic activity of oxidation hydroformylation[19]
Summary
Scorpionate is a term coined by Trofimenko [1] to describe a special class of poly(pyrazolyl) poly(pyrazolyl) compounds, which which are derived from two or more N-deprotonated pyrazole rings bound to a main group atom atom Tpm based based complexes complexes as as catalysts catalysts due due to to their their chelating chelating versatility versatility resulting resulting from, from, e.g., e.g., aa change change between between the the bidentate. They have been reported as catalyst precursors for bidentate and andtridentate tridentatebinding bindingmodes modes[2,11,12,13,14]. [32]obtained obtainedaanovel novelclass class of of water water soluble soluble scorpionates scorpionates by by addition addition of sulfurtrioxide–trimethylamine sulfurtrioxide–trimethylamine complex complex to lithiated HC(pz) to to produce produce the the anionic anionic hydrosoluble tris(pyrazolyl)methane sulfonate (Tpms) (Scheme 1)
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