Rearrangement of the intermediate 1,4-biradicals in photocycloaddition of cyclohex-2-enones to alkenes

Two unusual examples of enone/alkene photocycloaddition involving a rearrangement of the intermediate 1,4-biradical are presented. The first reaction proceedsvia the addition of one of the radical centers to a carbonyl C aton and subsequent bond cleavage,i.e., with rearrangement to a 1,3-biradical, while the second reaction involves abstraction of an H atom by one of the radical centers. The material was partly presented as an invited lecture by Paul Margaretha at the Sixth International Conference on the Chemistry of Carbenes and Related Intermediates (St. Petersburg, May 28–30, 1998). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 514–516, March, 1999.     

Synthesis, reactions and DNA damaging abilities of 10-membered enediyne-sulfone and related compounds

The synthesis and Myers-Saito type cycloaromatization reactions of 10-membered enediynes containing a sulfone or a sulfoxide moiety are described. These enediynes cycloaromatized smoothly under physiological conditions to generate bioactive α,3-didehydrotoluene biradicals, that showed potent DNA damaging abilities. Further, in the presence of a nucleophile such as amine or sulfide, cycloaromatization did not occur following the radical reaction pathway but ionically induced cycloaromatization took place.     

EPR Spectra of Hydrazyl Biradicals

Electron paramagnetic resonance is the most effective method of studying the electron exchange in biradicals. Experimental EPR spectra for the solutions of some hydrazyl biradicals are available in the literature (see Refs. [I,2]), however, the interpretation of the spectra is not given.     

两个氮氧自由基的合成与晶体结构：双自由基与阳离子自由基

合成并表征了2个氮氧自由基：2,2′-(2,5-二甲基苯基)-1,4-双(4,4,5,5-四甲基咪唑啉-3-氧化-1-氧基)自由基1和水合碘化m-N,N′,N″-三甲基苯铵基)-4,4,5,5-四甲基咪唑啉-3-氧化-1-氧基自由基2。双自由基1和阳离子自由基2均结晶于单斜晶系,P2₁/c空间群。通过分子间的氢键作用,2个化合物形成三维超分子体系。     

Regulating Spin Dynamics of Nitronyl Nitroxide Biradical Lanthanide Complexes through Introducing Different Transition Metals

Four biradical-Ln complexes with different transition metal ions, namely [LnM(hfac)₅(NITPh-PyPzbis)] (M^II=Mn^II and Ln^III=Gd 1 , Dy 2 ; M^II=Ni^II and Ln^III=Tb 3 , Dy 4 ), were prepared by the reaction of Ln(hfac)₃ ⋅ 2H₂O, Mn(hfac)₂ ⋅ 2H₂O or Ni(hfac)₂ ⋅ 2H₂O with NITPh-PyPzbis biradical (hfac=hexafluoroacetylacetonate, NITPh-PyPzbis=5-(3-(2-pyridinyl)-1H-pyrazol-1-yl)-1,3-bis(1’-oxyl-3’-oxido- 4’,4’,5’,5’-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene). In complexes 1 – 4 , the NITPh-PyPzbis biradical chelates one Ln^III ion by means of its aminoxyl moieties and the transition metal ion is introduced through the two N donors from the pyridyl pyrazolyl moiety. Magnetic investigations indicate that complex 4 displays visible maxima in frequency/temperature-dependent χ′′ signals with two-step relaxation processes, but complex 2 exhibits no slow magnetization relaxation. The comparison of structure parameters of both Dy complexes indicates that the symmetries of coordination spheres of two Dy ions are D_2d for 2 and C_2v for 4 , which thus probably results in different magnetic relaxation behaviors. This work provides new insight for improving properties of Ln-biradical based SMMs.     

Homobinuclear bis-3,6-di-tert-butyl-o-benzosemiquinone and bis-3,6-di-tert-butyl-o-catecholate complexes of PdII and PtII with bridging ligands. Molecular structure of (3,6-Cat)2Pd2L2 (L = dppm and dppy)

Reactions of the binuclear complexes M₂L₂Cl₂ [M = Pt or Pd, L = bis(diphenylphosphino)methane (dppm) or 2-(diphenylphosphino)pyridine (dppy)] with thallium 3,6-ditert-butyl-o-benzosemiquinone (3,6-SQ) in solutions have been studied. The formation of the corresponding bis(semiquinone) binuclear derivatives M₂L₂(SQ)₂ with retention of the metal-metal bond has been established by the ESR method. The average distances between the centers of localization of unpaired electrons, which were determined from the ESR spectral data for the complexes studied, allow conclusions about the parallel arrangement of the semiquinone ligands in skewed conformations in a square-pyramidal coordination sphere of both metal atoms. At room temperature, the biradical complexes are slowly converted to diamagnetic catecholate compounds with cleavage of the M-M bond and with retention of the bridging structure of the dppm and dppy ligands. The structures of catecholate complexes of palladium have been established by X-ray structural analysis.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 464–468, February, 1996.     

Paternò-Büchi反应的区域选择性

Paternò-Büchi(P-B)反应,即羰基-烯的[2+2]光环化加成反应,利用其特殊的区域及立体选择性可以合成一些结构精巧的取代氧杂环丁烷。随着P-B反应在有机合成中越来越广泛的应用,人们对P-B反应的区域选择性的研究也越来越深入。在P-B反应发现之初,人们一直用“最稳定的双自由基规则”解释其区域选择性,这一规则对有些体系却不适用,近年来有人开始运用“自旋化学”理论来解释区域选择性。本论文结合作者的研究工作,评述了近年来P-B反应的区域选择性的研究进展,重点阐述了反应温度、反应物的取代基对P-B反应区域选择性的影响及其规律。     

Synthesis, structure, magnetic properties and molecular mechanics study on the dinuclear copper (II) with biradical

Dinuclear copper complex with biradicals [Cu(hfac)2]2PhBNM(PhBNM = 2,5-bimethyl-1,4-bis(4,4,5,5-tetramethyllimidazoline-1-oxyl-3-oxide)phenyl,hfac=hexafluoroacetylacetonate) has been synthesized and characterized. It crystallized in the monoclinic system, with space group C2/c, a=1.9012(4), b=1.3718(3), c=2.1620(4) nm, β=97.55(3)°, Z=4. The X-ray structure analysis shows that the molecular structure consists of two kinds of conformations. The ratio of them is 7:3. The energy of two conformations, calculated with molecular mechanics, are different, E1=740 kJ/mol, and E2=771 kJ · mol-1. The CNDO/k results on the complex indicate that the orbital energy of low spin state is lower than that of high spin state, which correspond with the results of magnetic measurement.     

多自由基-金属配合物分子基铁磁体的设计

双,多自由基－金属配合物是获得具有高Ｔｃ分子铁磁体的很有潜力的一类化合物,这一新领域的研究国际上刚刚开始,但进展很快。自１９９３年Ｇａｔｔｅｓｃｈｉ Ｄ。首次报道了用稳定氮氧双自由基与Ｃｕ（Ⅱ）形成的具有铁磁耦合作用的配合物以来,掀起了双,多自由基－金属铁磁体研究的热潮,由于双或多自由基不仅能提供多个自旋中心,而且能提供多种桥联途径,因此容易获得三维网状结构的化合物。１９９６年,日本的Ｉｗａｍｕｒ