Boris Kamenar

Erythromycin series. Part 11. Ring expansion of erythromycin A oxime by the Beckmann rearrangement

The synthesis of 10-dihydro-10-deoxo-11-azaerythromycin A (11) by the Beckmann rearrangement of erythromycin A oxime (2) and reduction of the imino ether so obtained (5) is described. The structure elucidation of the new ring-expanded semisynthetic erythromycins (5) and (11) has been established on the basis of their analytical and spectral data and acid-catalysed degradation into the aglycones (7) and (13), respectively. Finally, the complete structure of ring-expanded erythronolides (7) and (13) has been determined by X-ray crystallography.

A Series of Molybdenum(VI) Complexes with Tridentate Schiff Base Ligands

Mononuclear and polynuclear dioxomolybdenum(VI) complexes with Schiff base ligands have been prepared by the reaction of [MoO2(acac)2] with salicylaldehyde (1 and 4), 2-hydroxy-1-naphthaldehyde (2 and 5) and 2-hydroxy-3-methoxybenzaldehyde (3 and 6) with addition of appropriate amine. All prepared complexes of the general formulae [MoO2LD] and [MoO2L]n consist of cis-MoO22+ core coordinated by Schiff-base ligand (L) in a tridentate manner through two deprotonated hydroxyl groups and one imino nitrogen. The usual octahedral coordination around molybdenum atom is completed by monodentate solvent molecules D (methanol, ethanol or dimethylsulphoxide). All compounds were characterized by means of chemical analysis, IR spectroscopy, thermogravimetric analysis and some of them by X-ray crystallography (1a, 2c, 3a, 4c and 6c). Eine Reihe von Molybdan(VI)-Komplexen mit dreizahnigen Schiff-Basen-Liganden Ein- und vielkernige Dioxomolybdan(VI)-Komplexe mit Schiff-Basen-Liganden wurden durch Reaktion von [MoO2(acac)2] mit Salicylaldehyd (1 und 4), 2-Hydroxy-1-naphthaldehyd (2 und 5) und 2-Hydroxy-3-methoxybenzaldehyd (3 und 6) durch Zugabe von Amin hergestellt. Alle Komplexe der allgemeinen Formeln [MoO2LD] und [MoO2L]n enthalten die cis-MoO22+-Einheit, die durch die Schiff-Basen-Liganden dreifach durch zwei deprotonierte Hydroxyl-Gruppen und durch ein Imino-Stickstoffatom koordiniert ist. Die ubliche oktaedrische Koordination am Molybdanatom wird durch einzahnige Solvens-Molekule D (Methanol, Ethanol oder Dimethylsulfoxid) erganzt. Alle Verbindungen werden durch Elementaranalysen, IR-Spektren, thermogravimetrische Analysen und einige von ihnen durch Kristallstrukturanalysen (1a, 2c, 3a, 4c und 6c) charakterisiert.

Synthesis and structure of K2[HMo6VIVVO22(NH3CH2COO)3]·8H2O: a new example of a polyoxomolybdovanadate coordinated by a glycinato ligand

Abstract A new complex of formula K2[HMo6VIVVO22(NH3CH2COO)3]·8H2O has been prepared from molybdenum(VI) oxide and vanadium(V) oxide in aqueous solution by adding glycine and potassium chloride, and its structure determined by X-ray structure analysis. The molybdovanadate anion is built up of six MoO6 edge-sharing octahedra connected into a ring centered by a VO4 tetrahedron. The MoO6 octahedra are in pairs linked by the bridging glycine-carboxylato ligands.

Metal complexes with pyrazole-derived ligands Part I. Synthesis and crystal structures of 3-amino-4-acetyl-5-methylpyrazole (L) and of the tetrahedral complexes ZnL2(NO3)2 and ML2Cl2 (M=Cu(II), Hg(II))

A new pyrazole-derived ligand 3-amino-4-acetyl-5-methylpyrazole (L) has been synthesized and structurally characterized. In order to examine its coordination properties the metal complexes ZnL2(NO3)2, CuL2Cl2 and HgL2Cl2 have been prepared and their crystal and molecular structures determined by X-ray structure analysis. The crystals of the ligand are triclinic, space group P with unit cell dimensions a=14.433(4), b=7.406(1), c=6.794(4) A, α=99.81(4), β=92.10(9), γ=105.55(6)°, V= 686.8(5) A3; ZnL2(NO3)2 is orthorhombic, space group Pbca,a=18.420(2), b=14.892(2), c=14.114(2) A, V=3872(1) A3; CuL2Cl2 is monoclinic, space group I2/a,a=13.804(3), b=8.835(1), c=14.264(4) A, β=100.50(3)°, V=1710.5(7) A3; HgL2Cl2 is monoclinic, space group I2/a,a=14.075(2), b=9.002(2), c=14.303(3) A, β=97.39(2)°, V=1797.2(6) A3. The two latter complexes are isostructural. The ligand L acts as a monodentate ligand through the tertiary ring nitrogen atom. The complexes contain metal atoms in the distorted tetrahedral coordination realized by two nitrogen atoms from the two ligands L and two nitrate-oxygen atoms in the zinc complex and two chlorine atoms in the copper and mercury complexes. All four structures are built up from individual molecules linked together by hydrogen bonding interactions NH…O achieved between ‘pyrrole’ ring nitrogens of one molecule and the acetyl-oxygen atoms from the adjacent molecules. In the free ligand the additional hydrogen bondings NH…N occur also between amino and ‘pyridine’ nitrogen atoms of the neighboring molecules. The general physicochemical characteristics as well as the IR and 1H NMR spectra are in accordance with the observed molecular structures.

Synthesis, structure and properties of molybdenum(VI) oxalate complexes of the types M2[Mo2O5(C2O4)2(H2O)2] and M2[MoO3(C2O4)] (M=Na, K, Rb, Cs)

The reaction of molybdenum(VI) oxide with oxalic acid or alkali oxalate and alkali halides results in the formation of two series of molybdenum(VI) oxalate complexes: one of the general formula M-2[Mo2O5(C2O4)(2)(H2O)(2)] containing the Mo2O5 core and the other of the formula M-2[MoO3(C2O4)] with a MoO3 core (M = Na, K, Rb, Cs). Both series were characterized by chemical analysis, ESR, UV and IR spectroscopy, thermogravimetry, differential scanning calorimetry, X-ray powder method and some of them by single-crystal X-ray structure analysis. Complexes of the first series adopt dimeric structures, the second series infinite polymeric structures. In both types of structures molybdenum ions are six-coordinated being surrounded by terminal ore-oxygens, bridging oxygens and bidentate bonded oxalate ligands. When exposed to UV light all these complexes in the solid state exhibit photochromic behavior changing color from colorless to green-brown. These changes are remarkably more pronounced in the complexes with dimeric structures. There is definite correlation between their coloration and the UV induced ESR signal indicative for molybdenum(V). Such behavior is explained by the partial reduction of Mo(VI) to Mo(V) only at the crystal surfaces. This is also the explanation why K-2[Mo2O5(C2O4)(2)(H2O)(2)] was so far described as being red or pale reddish tan. All attempts to prepare the corresponding lithium complexes were unsuccessful. They are most probably very unstable because of the small radius of the lithium ion

New Dinuclear Molybdenum(V) Complexes With β′‐Hydroxy‐β‐enaminones Containing a 4‐Hydroxy‐2‐pyrone Ring

New dinuclear molybdenum(V) complexes of the general formula [Mo2O4L2D2], were prepared by the reaction of [Mo2O3(acac)4] (acac = acetylacetonate ion) with β′-hydroxy-β-enaminones (L). All prepared complexes consist of Mo2O42+ cores coordinated by two ligands L via two donor oxygen atoms as in the analogous β-diketonates. The usual octahedral coordination around the molybdenum atoms is completed by the monodentate solvent molecules D (methanol, ethanol, or 2-propanol). All compounds were characterized by elemental analyses, IR, one- and two-dimensional NMR spectra, and thermal analysis, and some of them by X-ray crystallography (1a, 4a, 8b, and 9a). (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Synthesis and structure of [(CH3)4N]4[H2MoV9O28]Cl·6H2O

Abstract [(CH 3 ) 4 N] 4 [H 2 MoV 9 O 28 ]Cl·6H 2 O has been synthesized from ammonium vanadate and molybdenum(VI) oxide in acidic aqueous solution by adding tetramethylammonium chloride, and its structure determined by single-crystal X-ray analysis. The polyoxomolybdovanadate anion has the structure of the decavanadate anion with the molybdenum atom substituted at one “capping” vanadium site. Owing to the 2/ m symmetry of the anion, this molybdenum atom is randomly distributed over four “capping” metal atom positions. Two hydrogen atoms are bonded to triply bridging oxygen atoms.

Synthesis, structure and ESR spectrum of (Hmorph)6[VIV, VV, Mo10)VO40] · 3H2O

Abstract The title compound has been synthesized from molybdenum(VI) oxide and ammonium vanadate in aqueous solution by adding morpholine (pH 5.8). The X-ray structural investigation shows that the polyoxometalate anion adopts a Keggin-type structure with a central tetrahedral vanadium(V) atom. The other two vanadium atoms are crystallographically disordered over 12MO 6 octahedral sites. The ESR spectrum clearly indicates that one octahedrally coordinated vanadium atom has the oxidation number +4.

1-Sulfonyl-1a,2,6,6a-tetrahydro-1H,4H-[1,3]-dioxepino[5,6-b]azirines: A novel class of fused dioxepins, potent hypoglycemic agents

Abstract The new hypoglycemics, 1-sulfonly-dioxepinoazirine 2 derived from a novel heterocyclic system, 1a,2,6,6a-tetrahydro-1H,4H-[1,3]-dioxepino[5,6-b]-azirine, have been synthesized starting from trans-6-acetylamino-5-chloro-1,3-dioxepanes 7 via azirines 3. Their structure has been confirmed by the single crystal X-ray diffiraction of 1-(4-acetylaminobenzenesulfonyl) derivative 2b.

Synthesis and characterization of octamolybdates containing co-ordinatively bound salicylideneiminato and methioninato (MetO) ligands. Crystal structures of [NH3Pr]2[Mo8O22(OH)4(OC6H4CHNPr-2)2]·6MeOH and [Hmorph]4[Mo8O24(OH)2(MetO)2]·4H2O (morph = morpholine)

The compound [MoO2(sal)2](Hsal = salicylaldehyde) reacts with n-propylamine in methanol to give [NH3Pr]2[Mo8O22(OH)4(OC6H4CHNPr-2)2]·6MeOH (1). The same complex was obtained by the reaction of ammonium paramolybdate with N-propylsalicylideneimine. The structure determined by X-ray analysis showed that the octamolybdate anion consists of eight condensed octahedra with 16 terminal positions, two of which are occupied by the salicylideneiminato ligands. The reaction of MoO2Cl2 with methionine yields the neutral complex [Mo8O20(OH)4(MetO)4]·solvent (2)(solvent = H2O or MeOH, MetO = methioninate). If the methanolic solution of (2) is neutralized with morpholine (morph) the anionic complex [Hmorph]4[Mo8O24(OH)2(MetO)2]·4H2O (3) is obtained. It has been shown by X-ray analysis that the structure of (3) is analogous to that of (1) with two MetO ligands linked to two terminal sites of the Mo8O26 core.