Reactions of nitrogenous derivatives of substituted salicylaldehydes with cyclic ketones and enamines

The reactions of aminals, the Mannich bases, and azomethines derived from substituted salicylaldehydes were studied. Derivatives of tetrahydrocyclopenta[b]- and hexahydrocyclohepta[b]chromenes and substituted 2,2"-spirobichromenes were prepared from aminals, and substituted hexahydroxanthenes were synthesized from the Mannich bases. Azomethine derivatives of 5-nitrosalicylaldehyde and aliphatic amines react with cyclohexanone to form 4a-amino-7-nitro-2,3,4,4a-tetrahydro-1H-xanthenes. 4a-Morpholino-7-nitro-9-phenylethynyl-1,2,3,4,9,9a-hexahydroxanthene was studied by X-ray diffraction analysis.     

Pyramidane and isoelectronic pyramidal cations

Ab initio STO-3G, 4-31G and semi-empirical MINDO/3 calculations were performed on a series of C₄H₄X compounds to analyze the possibility of existence of their nonclassical C_4V pyramidal isomeric forms. It was shown that with the four-electron group X (C, N⁺, P⁺, O²⁺, S²⁺) in an apex, C_4V pyramidal structures are indeed stable, i.e., conform to local minima on the corresponding potential energy surfaces. Relative energies, molecular geometries and charge density distribution for various isomeric forms of the C₄H₄X compounds are presented. The theoretically derived strategies for an experimental trapping of the pyramidane 1, X = C and the C_4V pyramidal thiophene dication 1, X = S²⁺ are discussed.     

Conjugates of polyhedral boron compounds with carbohydrates. 2. Unexpected easy closo- to nido-transformation of a carborane-carbohydrate conjugate in neutral aqueous solution

A novel 1,2-dicarba-closo-dodecaborane-lactose conjugate 4c, when dissolved in water or methanol, is subject to unexpected deboronation in neutral conditions leading to the formation of the corresponding nido-counterpart (5) as detected by ¹¹B NMR spectroscopy. After heating the aqueous solution of the conjugate 4c at 60 °C for 17 h pure 1,2-dicarba-nido-undecaborane-lactose conjugate 5 was obtained.     

Synthesis, spectral characteristics, and crystal structure of the hexanuclear complex MeSi[η1,η5-C5H4(CO)2Fe(η1,η5-C5H5)Mn(CO)3]3

The reaction of MeSiCl₃ with 3 equivalents of LiC₅H₄(CO)₂Fe(η¹,η⁵-C₅H₄)Mn(CO)₃ afforded the hexanuclear complex MeSi[η¹,η⁵-C₅H₄(CO)₂Fe(η¹,η⁵-C₅H₅)Mn(CO)₃]3. The structure of the resulting complex was established by¹H and¹³C NMR and IR spectroscopy and by X-ray diffraction analysis. Dedicated to the memory of Academician M. I. Kabachnik on his 90th birthday. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2056–2061, October, 1998.     

Migration of the η1:η6-C6H5Cr(CO)3 ligand into the cyclopentadienyl ring during metallation of the η5-C5H5(CO)2Fe η1:η6-C6H5Cr(CO)3 binuclear complex

It was found that the ¹⁶-C₆H₅Cr(CO)₃ ligand migrates into the cyclopentadienyl ring when the ⁵-C₅H₅(CO)₂Fe ¹⁶-C₆H₅Cr(CO)₃ binuclear complex is metallated with BuⁿLi. Under the same conditions, no migration of the phenyl ligand in the ⁵-C₅H₅(CO)₂Fe ¹-C₆H₅ complex was observed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 325–326, February, 1994.     

Synthesis and characterization of complexes η5,η5-(CO)3Mn(C5H4-C5H4)(CO)2Fe-η1,η5-C5H4Mn(CO)3 and μ-(C≡C)[C5H4(CO)2Fe-η1,η5-C5H4Mn(CO)3]2

The complex η⁵,η⁵-(CO)₃Mn(C₅H₄-C₅H₄)(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₃ was synthesized by the reaction of η⁵-Cp(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₃ with BuⁿLi (THF, ?78 °C) and then with anhydrous CuCl₂. The complex μ-(C≡C)[C₅H₄(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₃]₂ was prepared by the reaction of η⁵-IC₅H₄(CO)₂Fe-η¹,η⁵-C₅H₄Mn(CO)₃ with Me₃SnC≡CSnMe₃ (2:1) in the presence of Pd(MeCN)₂Cl₂.     

Investigation of the redox properties of polynuclear “ladder” complexes containing Cr,Mn, and Fe

The redox potentials of new Cr, Mn, and Fe polynuclear ladder complexes, (⁵-Cp)Fe(CO)₂(¹,⁵-C₅H₄)Fe(CO)₂(¹,⁵-C₅H₄)Mn(CO)₃, (⁵-Cp)Fe(CO)₂(¹,⁵-C₅H₄)Mn(CO)₃, (⁵-Cp)Fe(CO)₂(¹,⁶-Ph)Cr(CO)₃, (⁵-Cp)Fe(CO)₂(¹,⁵-C₅H₄)Fe(CO)₂CH₂Ph, (⁵-Cp)Fe(CO)₂(¹,⁶-CH₂Ph)Cr(CO)₃, were measured and the mechanism of their electrochemical oxidation and reduction was suggested. It was shown that the - or -bonds of the bridging ligand can be cleaved selectively by applying cathodic or anodic potentials, respectively. On the basis of the obtained electrochemical data, a mechanism is suggested for the rearrangement observed when the complexes are metallated by butyllithium.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 362–366, February, 1995.This work was carried out with financial support from the Russian Foundation for Basic Research (Project No 94-03-08628a).     

Structure of 1(5)-aryl-3-phenyl-5(1)-(2-benzothiazolyl)formazanes

1,3-Diphenyl-5-(2-benzothiazolyl)formazane exists in its crystalline state (based on x-ray crystal structure data) in the E ^1,2 Z ^2,3 Z ^3,4-conformation, which is stabilized by intramolecular hydrogen bonding (IMHB); the proton is localized on the nitrogen atom which is bound to the heterocycle. In chloroform solutions 1(5)-aryl-3-phenyl-5(1)-(2-benzothiazolyl)formazanes exist in the form of equilibrium mixtures of their chelate and open E ^1,2 Z ^2,3 Z ^3,4-forms, in which the first of these forms predominates. Based on their ¹³ C-NMR spectral data the tautomeric equilibrium involving these forms is shifted in favor of the benzothiazolylhydrazone form. The amount of tautomer containing the benzothiazolidene fragment structure increases in DMSO solution.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1268–1274, September, 1991.     

Cyclopentadienyl ring metalation in cyclopentadienyliron carbonyl complexes

The cyclopentadienyl ligands in Cp(CO)₂FePh, Cp(CO)₂FeCH₂Ph and [Cp(CO)₂Fe]₂ were metalated by BuLi in THF at ?78°C. With Cp(CO)₂FePh it was possible to employ the reaction for the synthesis of cyclopentadienyl carbonyl complexes substituted on the Cp ligands.     

Radiation-induced inactivation of angiotensin-converting enzyme in solutions

Radiation-induced inactivation of angiotensin-converting enzyme (ACE) in the low-dose range is characterized by the existence of a concentration- and pH-dependent induction period, activation, and inactivation. These effects are probably related to the change in the conformational flexibility of the active center in conjunction with the retention of the autoprotective multistep mechanism of the protection of the entire molecule. The schemes of radiation-induced reactions occurring in ACE are presented. The radiation-chemical yield of inactivation of ACE has a maximum at pH 7.5 independent of the initial concentration of the enzyme, which allows inference of a conformational transition in this pH range.For Part l, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 223–229, January, 1996.