A mild and efficient method for the cleavage of tert-butyldimethylsilyl and tetrahydropyranyl ethers by ceric ammonium nitrate in methanol

A variety of tert-butyldimethylsilyl (TBDMS) and tetrahydropyranyl (TFP) ethers were cleaved with ceric ammonium nitrate in methanol at 0 °C in short time. It has been shown that the reaction is chemoselective in a few cases. The primary TBDMS ethers have been cleaved selectively in the presence of THP ether and ketal

Synthesis and studies of Cu(II)-thiolato complexes: bioinorganic perspectives

Ligation of thiolate sulfur to copper at the active sites of quite a number of copper proteins has been established either by X-ray crystallographic and/or by spectroscopic studies. In addition, for Cu(II)-substituted metalloproteins, the presence of Cu(II)-thiolate bonding at the active sites could be established spectroscopically. Cu(II)-thiolate bonding in different enzymes is not always very similar. Obviously, the bioinorganic significance of Cu(II)-thiolate bonding is enormous and has attracted a lot of attention to synthesize model Cu(II)-thiolato complexes as electronic structural analogues of the active sites of these biomolecules. The present review deals with (i) nature of Cu(II)-thiolate bonding present in different metalloproteins, (ii) difficulties involved in the synthesis of Cu(II)-thiolates and ways to surmount them, (iii) characterization of the Cu(II)-thiolate bonding by electronic and EPR spectroscopic techniques and (iv) electron transfer properties of the Cu(II)-thiolato complexes by cyclic voltammetric studies. The properties of the Cu(II)-thiolato complexes have been discussed as possible models for the active site(s) of copper proteins

Syntheses and X-ray structures of mixed-ligand salicylaldehyde complexes of Mn(III), Fe(III), and Cu(II) ions: reactivity of the Mn(III) complex toward primary monoamines and catalytic epoxidation of olefins by the Cu(II) complex

The Schiff base (L), synthesized from 2-(dimethylamino)ethylamine and salicylaldehyde acts as a tridentate ligand. This ligand, when stirred with 1 equiv of KOH in methanol, undergoes partial hydrolysis of the imine bond. This solution readily takes up Mn(II)/Mn(III) acetate or Fe(III) chloride/perchlorate to form mixed-ligand Mn(III) or Fe(III) complexes, respectively. The neutral dark brown complex, [Mn(L-H)(NCS){o-(CHO)C6H4O-}] (1), crystallizes in the presence of thiocyanate in the orthorhombic space group Pbca with a = 15.271(8), b = 19.522(7), c = 13.213(7) Å Z = 8; R = 0.060; and Rw = 0.062. The coordination geometry around Mn(III) ion is distorted octahedral with donation from one L-H, one salicylaldehyde and, one thiocyanate ligand. With Fe(III), the dark red complex isolated in the solid state is found to be a neutral µ-oxo Fe(III) dimer with the formula [{o-(CHO)C6H4O-}(L-H)Fe]2O (3). The structure of 3 has been solved and successfully refined in the monoclinic space group C2/c with a = 18.558(7), b = 11.231(5), c = 16.943(6) Å; β = 95.81(3)°; Z = 4; R = 0.052; and Rw = 0.055. Each of the Fe(III) ions is hexadentate with donation from one L-H and one salicylaldehyde besides the bridged O atom. The Fe(III)-O-Fe(III) angle is found to be 166.05(4)°, which is well within the normal range observed for monobridged Fe(III)-O-Fe(III) complexes. Due to structural trans effects, the coordination geometry around each metal center is distorted from the ideal octahedral geometry. Cu(II) makes the neutral complex, [Cu(L-H){o-(CHO)C6H4O-}] (2) when L, salicylaldehyde, and a Cu(II) salt are allowed to react in equimolar quantities in the presence of excess of KOH. It crystallizes in the monoclinic space group C2/c with a = 18.077(4), b = 11.514(2), c = 16.716(4) Å; β = 93.66(2)°; Z = 8; R = 0.057; and Rw = 0.061. The coordination geometry around Cu(II) is square pyramidal where, out of the four equatorial donors, three are provided by the Schiff base L and the fourth one by the phenolate O of the salicylaldehyde group. The Cu(II) ion is 0.170(5) Å above the equatorial plane and is bonded axially to the O atom of the carbonyl group of the salicylaldehyde. The bound salicylaldehyde in the Mn(III) complex 1 readily reacts with the reagents 2-aminophenol, 2-aminothiophenol, or 2-aminoethanol to form mononuclear, neutral Mn(III) complexes 4-6, respectively, with the general formula,[Mn(L-H)(L'-2H)]. The Schiff base L' is formed by condensation of the bound salicylaldehyde in 1 with the amino group of the added reagent. Complex 4 is low-spin (μeff/μB = 3.01; S = 1) at 300 K, which is quite rare. It also exhibits a pseudoreversible Mn(IV)/Mn(III) couple with E½ = 0.54 V (vs SCE) in DMF. All the other Mn complexes are high-spin (µ eff/µ B range, 4.89-4.94; S = 2) at 300 K. The μeff/μB number for 2 is 1.93 and for 3 is 1.84. Complex 2 shows catalytic activity in the oxidation of olefins to epoxides in the presence of 2-methylpropanal and molecular oxygen