A series of functionalized 2,s-dihydro-1-hydroxy-2-R1-2-RZ-sponding nitroxide radicals. The structures of 2',5'-dihydro-4-R3-imidazoles were prepared by cyclocondensation of a-l'-hydroxy-4',5',5'-trimethylspiro[4,5-diazafluoren-9,2'-imi0x0 hydroxylamines with ketones RIRZC=O in the presence dazole] (2) and of 2-(acetoxymethyl)-2,5-dihydro-2,4,5,5-teof ammonia (R' = R2 = 2-pyridy1, 4,5-diazafluoren-9-ylene, tramethylimidazole-1-oxyl (14) were determined by X-ray R3 = Me: R' = CH20COMe, CH20COPh, 2-thienyl, CH20H, diffraction. In the crystal 2 forms one-dimensional chains C02K, R2 = R3 = Me; R1 = Py, R2 = Me, R3 = Ph; R1 = R2 = through hydrogen bonding between N atoms of the CH20COPh, CHzOH, R3 = Me) and oxidized to the corre-hydroxylamine and imidazoline groups.Because of their stability nitroxide radicals have attracted much intere~t [~,~] and have found wide application as spin markers in biochemistry, medicine, and analytical chemist r~ [~,~] .Metal complexes of nitroxide~ [~] were studied, e.g., with the goal to obtain new molecular magnetic materiaW1.The group of Volodarsky developed the chemistry of nitroxides derived from 2,5-dihydroimida~ole[~~*~I. Our Munich group studied metal complexes of nitroxides already in 1967[1°1 following the history of organic nitroxides which was founded by Piloty and Graf Schwerinr"] and Wieland[121 in Munich. We were interested in the synthesis of 2,5-dihydroimidazole-l -oxyl radicals which contain additional donor atoms (N, 0, s) for coordination of metal ions.There are two pathways for the synthesis of donor-substituted 2,5-dihydroimidazole-1 -0xyls:-Cyclocondensation of a-0x0 hydroxylamines with functionalized ketones in the presence of ammonia to 1-hydroxy-2,5-dihydroimidazoles and subsequent oxidation to nitroxides[I31.-Derivatization of nitroxides. Thus, Reznikov et al.[I4] synthesized 4-substituted 2,5-dihydroimidazole-l-oxyls by deprotonation of the 4-methyl group of 4-methyl-2,5-dihydroimidazole nitroxides and addition of electrophiles. Results and DiscussionThe 2,5-dihydro-l-hydroxyimidazoles 1-7 were synthesized according to equation (1). NH40Ac was used as base and source for ammonia. It was observed that the rate of reaction and the yield increase in the case of ketones having electron-poor carbonyl groups. Due to problems of purification the yields of 4-6 are low. Compounds 8-10 were obtained by hydrolysis of the ester group of 4-6 and of ethyl 2,5-dihydro-1 -hydroxy-2,4,5,5-tetramethylimidazole-

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Die dreizähnigen Dianionen von 2,2′‐Dihydroxyazobenzol (L1H2), 1‐(2‐Hydroxy‐4‐nitrophenylazo)‐2‐naphthol (L2H2), 1‐(2‐Hydroxy‐5‐nitrophenylazo)‐2‐naphthol (L3H2) und 1‐Phenyl‐3‐methyl‐4‐(2‐hydroxy‐5‐nitrophenylazo)‐5‐pyrazolon (L4H2) bilden mit den chloroverbrückten Komplexen [(R3P)MCl2]2 (M = Pd, Pt; R = Ph, nBu), [(n5‐C5Me5)MCl2]2 (M = Rh, Ir) sowie mit (nBu3P)2NiCl2 die Farbstoff‐Komplexe (R3P)ML (M = Ni, Pd, Pt) und (n5‐C5H5)ML (M = Rh, Ir). Die Strukturen von (Ph3P)PtL1 und (nBu3P)PdL3 wurden röntgenographisch bestimmt. Für die Komplexe (n5‐C5Me5)ML (M = Rh, Ir) mit „asymmetrischem”︁ Metallatom lassen sich NMR‐spektroskopisch zwei Diastereoisomere nachweisen, was für den „Hydrazon”︁‐Charakter der Azoliganden mit pyramidalisiertem N‐Atom spricht.

2,5-Dihydroimidazoline-l-oxyl radicals I, II with imino substituents coordinate to Pd(II) and Pt(II) complexes with formation of the N,N chelate complexes 1-6. With oxygen containing substituents either monodentate N-coordination to give 8 or N ,O chelate formation to give 9 takes place, depending on the position of the oxygen atom relative to the ring nitrogen atom. With radicals III that also have the second ring nitrogen atom oxidized and the Rh(III) or Ir(III) complexes [Cp*MCl2]2 the O , O chelates 11 -13 could be obtained, while with Na2PdCl4 the heterocycle was destroyed with formation of a N,N chelate complex 10 of an α-nitrosooxime ligand. The orthopalladated 2,2,5,5 tetramethyl-4-phenyl-2,5-dihydroimidazoline-l-oxyl complex 7a reacts with several a-amino acidates under splitting of the dichloro bridge with formation of the C,N/N,O-bis-chelate complexes 7b-f. The molecular structures of 2 and 10 were determined by X-ray diffraction.

The protection of the hydroxy group of 1-hydroxy-2.2.4.5.5-pentamethyl-3-imidazoline by a t-butyldimethylsilyl group gives the silane 1 which allows via the 4-lithium salt the preparation of 4-substituted derivatives, i. e. a dithiocarboxylic acid (2), a disulfide (3), a phosphane (4) and a thioether (5). Oxidation of 4-lithiated 1 yields under C±C coupling an ethylene bridged bis(3-imidazoline) (6). From these compounds Pd(II) and Pt(II) complexes M(4) 2 Cl 2 (M = Pd, Pt and Pd(5)Cl 2 were prepared and the structure of the dithiocarboxylate chelate complex Pd(2-H + ) 2 (7) was determined by X-ray diffraction. Cleavage of the silyl group from 7 gives complex 8 which can be oxidized to the corresponding diradical (9). Complex 9 was characterized by its EPR spectrum. Measurements of the magnetic susceptibility of 9 reveal strong antiferromagnetic coupling between the two spins at low temperatures.Neue 3-Imidazolin-Derivate und ihre Palladium(II)-Komplexe Inhaltsu È bersicht. In 1-Hydroxy-2,2,4,5,5-pentamethyl-3-imidazolin la È ût sich die Hydroxygruppe durch t-Butyldimethylsilyl schu È tzen und aus diesem Silan 1 sind u È ber das 4-LithiumSalz verschiedene 4-substituierte Imidazolin-Derivate zuga È nglich: eine Dithiocarbonsa È ure (2), ein Disulfid (3), ein Phosphan (4) und ein Thioether (5). Die Oxidation des lithierten 1 ergibt unter C±C-Kupplung ein Ethylen-verbru È cktes Bis-(3-imidazol). Mit den Liganden wurden die Pd(II)-und Pt(II)-Komplexe M(4) 2 Cl 2 (M = Pd, Pt) und Pd(5)Cl 2 erhalten. Die Struktur des Dithiocarboxylat-Komplexes Pd(2-H + ) 2 (7) wurde ro È ntgenographisch bestimmt. Der durch Abspaltung der Silylgruppe aus 7 erhaltene Komplex 8 kann zum Dinitroxid-diradikal 9 oxidiert werden. Komplex 9 wurde durch sein EPR-Spektrum charakterisiert. Magnetische Messungen zeigen fu È r 9 bei tiefen Temperaturen starke antiferromagnetische Wechselwirkungen.