Ligands azomethine

In a more recent publication the same group mentions that Ag(I) salts in combination with chiral phosphine ligands can catalyze the 1,3-dipolar cycloaddition involving the azomethine precursor 64b and methyl vinyl ketone (Scheme 6.43) [87]. The reaction, which presumably also required a stoichiometric amount of the catalyst, proceeds to give 65b in a good yield with 70% ee. 

Dinuclear and polynuclear complexes with azomethine ligands and tneir magnetic properties. V. A. Kogan, V. V. Zelentsov, O. A. Osipov and A. S. Burlov, Russ. Chem. Rev. (Engl. Transl.), 1979, 48,645-656 (112). 

There have been no reports of complexes of " JV-substituted thiosemicarbazones derived from 2-formylpyridine, but 2-acetylpyridine JV-methyl-thiosemicarbazone, 3a, formed [Fe(3a-H)2]C104 and [Fe(3a-H)2]FeCl4 [117]. The nature of these two species was established by partial elemental analyses, molar conductivities, magnetic moments, electronic, infrared, mass and electron spin resonance spectra. A crystal structure of a related selenosemicarbazone complex confirmed the presence of a distorted octahedral iron(III) cation coordinated by two deprotonated anions so that each ligand is essentially planar and the azomethine nitrogens are trans to each other the pyridyl nitrogen and selenium donors are both cis. 

The S-methyldithiocarbazates of both 2-picolylphenylketone, 16, and 2,6-luti-dylphenylketone, 17, yielded high spin iron(Ill) complexes, [Fe(15-H)Cl2(H20)] and [Fe(16-H)Cl2(H20)] [144]. Both complexes involve a tridentate ligand bonding via the pyridyl nitrogen, azomethine nitrogen and thiol sulfur. 

Iron(III) complexes of 2-acetylpyridine Af-oxide iV-methyl- and 3-azabicyclo[3.2.2.]nonylthiosemicarbazone, 24 and 25, respectively, have been isolated from both iron(III) perchlorate and chloride [117], The perchlorate salt yields low spin, octahedral, monovalent, cationic complexes involving two deprotonated, tridentate thiosemicarbazone ligands coordinated via the N-oxide oxygen, azomethine nitrogen and thiol sulfur based on infrared spectral studies. Their powder ESR g-values are included in Table 1 and indicate that bonding is less covalent than for the analogous thiosemicarbazones prepared from 2-acetylpyridine, 3a and 4. Starting with iron (III) chloride, compounds with the same cations, but with tetrachloroferrate(III) anions, were isolated. 

Besides complexes of thiosemicarbazones prepared from nitrogen heterocycles, iron(III) complexes of both 2-formylthiophene thiosemicarbazone, 26, and 2-acetylthiophene thiosemicarbazone, 27, have been isolated [155]. Low spin, distorted octahedral complexes of stoichiometry [Fe(26)2A2]A (A = Cl, Br, SCN) were found to be 1 1 electrolytes in nitromethane. Low spin Fe(27)3A3 (A = Cl, Br, SCN) complexes were also isolated, but their insolubility in organic solvents did not allow molar conductivity measurements. Infrared speetra indicate coordination of both via the azomethine nitrogen and thione sulfur, but not the thiophene sulfur. The thiocyanate complexes have spectral bands at 2065, 770 and 470 cm consistent with N-bonded thiocyanato ligands, but v(FeCl) and v(FeBr) were not assigned due to the large number of bands found in the spectra of the two ligands. 

Both 2-formylthiophene thiosemicarbazone, 26, and 2-acetylthiophene thiosemicarbazone, 27, form six coordinate [FeL2A2] complexes (A = Cl, Br) [156], The complexes formed with 26 are low spin, but complexes of 27 are high spin. For both ligands the bidentate coordination is via the azomethine nitrogen... 

Cu(3a)2] (BF4)2, [Cu(3a-H)Cl], and [Cu(3a)Br2], where 3a is 2-acetylpyridine N-methylthiosemicarbazone, have been prepared and studied spectroscopically [179], The former complex involves planar bonding by pyridyl and azomethine nitrogen atoms of each ligand and likely involves axial coordination of the thione sulfur atoms since v(d-d) = 15 670 cm , which is at lower energy... 

Scheme 10.12 1,3-Dipolar cycloadditions of azomethine ylides with polystyrene-supported Fesulphos ligand.

Synthesis of complex 1. The pentadentate salen catalyst 1 was synthesized as described (9). In short, the tosylated 2-[2-(2-methoxyethoxy)-ethoxy]-ethanol 2 (10) was reacted with 2,4-dihydroxybenzaldehyde 3 to yield 4-alkoxy salicylaldehyde 4 after chromatographic purification (eq. 1). Subsequent condensation of 4 with 1,3-diaminopropanol yielded water-soluble salen ligand 5 in sufficient purity and 89% yield (11). The formation of an azomethine bond is indicated by a shift of the NMR signal for the carbonyl carbon from 194.4 ppm in aldehyde 4 to 166.4 ppm for the imino carbon in 5. The pentadentate ligand 5 was then treated with copper(ll) acetate in methanol to obtain the dinuclear copper(ll) complex 1 as a green solid (eq. 2) (11). 

The basic thiosemicarbazone ligands coordinate in a N,S bidentate manner, generally via the azomethine N-donor and the thione or deprotonated amidothione group. Designating the ligands as HL, this usually results in square planar complexes [NiL2],1221-1227 [Ni(HL)2]X2,12 2,1228... 

A similar, although less marked difference characterizes the cyclopropanation of olefins 41 and 42. In the presence of either copper or copper complexes whose chelating ligands contain an azomethine moiety derived from an a-amino acid, no stereoselectivity was observed with diene 41, whereas the cyclopropanes derived from 42 occur with cisjtrans ratios of 57 43 to 69 31, depending on the catalyst93). 

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