No abstract

A close to planar conformation is established for 2-(4-methoxyphenyl)-4,6-diphenyl-1,3,5-triazine (M-H-P) by crystal structure determination. For 2-(4-hexoxy-2-methoxyphenyl)-4,6-diphenyl-1,3,5-triazine (H-MeO-P), hydrophobic interaction between the long hexoxy groups enforces rotation of the dialkoxyphenyl ring at C6 and the C2 phenyl ring relative to the plane of the triazine ring. Time-resolved fluorescence measurements demonstrate the existence of a short-lived Franck-Condon (FC) and a longer-lived TICT (twisted intramolecular charge transfer) state, emitting at longer wavelengths, for the O-methyl derivative 2-(4-hexoxy-2-methoxyphenyl)-4,6-bis(2,4,6-trimethylphenyl)-1,3,5-triazine (H-MeO-Ms). The decay of the protontransferred (PT) fluorescence for crystalline powders of 2-(2-hydroxyphenyl)-4-(dimethylamino)-6-aryl-1,3,5triazines is shown, by the same method, to be retarded within the series phenyl f tolyl f xylyl, well in line with the gradation of quantum yields determined by steady-state methods. The high quantum yields of the PT fluorescence for triazines with only one 2-hydroxyaryl moiety on the triazine ring are reduced by 2 orders of magnitude each upon introduction of a second and a third aryl group. Most of the 2-hydroxyaryl-1,3,5triazines with additional aryl moieties at C4 and C6 show PT fluorescence, as long as the 2-hydroxyaryl and the triazine ring are more or less coplanar and the intramolecular hydrogen bond remains intact. In some cases, however, this fluorescence is very weak, or can be detected only in copolymers, in mixtures of the stabilizer with the polymer or in crystalline powders.

carbonyl ligands through the mediation of the metal centers to give isocyanates. It is also hoped that selective hydrolysis or metathesis reactions will provide a general preparative route to mixed metal carbonyl -ox0 complexes containing M-M' bonds. Furthermore, the especially volatile compounds 1 a-e, 2c, and 2 e are promising starting materials for the deposition of thin layers [M,,,M',,N,] from the gas phase using the metal-organic chemical vapor deposition technique.

No abstract

Lithium Zincate, Heteroleptic Triorganylzincate, Zincate, X-Ray, NMR Spectra Bis(trimethylsilylmethyl)-, bis[bis(trimethylsilyl)methyl]-as well as bis (2,2,4,4,6,6-hexamethyl-2,4,6-trisila-cyc/o-hexyl)zinc react with methyl lithium or phenyl lithium in the pres ence of the tridentate l,3,5-trimethyl-l,3,5-triazinane (TMTA) to yield zincates of the type LiZnR2R'-2TMTA. The compounds are colorless and insoluble in aliphatic or aromatic hydrocarbons. These zincates exist in solution as well as in the crystalline state as separated ions, as confirmed for lithium-methyl-bis(2,2,4,4,6,6-hexamethyl-2,4,6-trisila-cyc/o-hexyl)-zincate• 2TMTA by X-ray diffraction (PI; a -1139,5(3); b = 1482,4(4); c = 1528,6(5) pm; a = 95,33(2); ß = 100,13(2); y = 106,91(2)°; Z = 2). The lithium cation is six-coordinated by two TMTA ligands in a distorted anti-prismatic complex. The zinc atom displays a trigonal planar coordination with Z n -C bond lengths of 207 pm to the 2,2,4,4,6,6-hexamethyl-2,4,6-trisila-cyc/o-hexyl ligands and of 202 pm to the methyl group. One trisila-cyc/o-hexyl substi tuent exists in the chair, the other one in the twist conformation. The reaction of lithium bis(trimethylsilyl)amide with bis(trimethylsilylmethyl)zinc yields the benzene soluble lithium-bis(trimethylsilyl)amino-bis(trimethylsilylmethyl)zincate TMTA. The molecular structure was confirmed by X-ray diffraction a -1024,8(3); b = 1775,4(7), c = 1918,2(8) pm; Z = 4). The bridging bis(trimethylsilyl)amino ligand displays long Z n -N and L i-N distances of 213 and 208 pm, respectively, due to the steric inter-ligand repulsion. During the reaction of lithium bis(trimethylsilyl)amide with bis[bis(trimethylsilyl)methyl]-zinc no zincate formations observed. The decomposition products lithium bis(trimethylsilyl)-methanide and the heteroleptic bis(trimethylsilyl)amino-bis(trimethylsilyl)methylzinc were detected.Einleitung

No abstract

Trichloro‐substituted 8‐oxabicyclo[3.2.1]oct‐6‐en‐3‐ones 6 and 7 are solvolysed by methanolic sodium methoxide to form the bicyclo[3.2.1] α,α‐dimethoxy ketones 13 and 14, with preservation of one chloro substituent. In the case of 6a, prolonged reaction time with an excess of methanolic sodium methoxide provides a trimethoxy‐substituted oxanorbornene aldehyde 19 through ring contraction. Treatment of the mixture of 13 and 14 with zinc and aqueous acetic acid affords dechlorinated α‐oxo acetals 15 and 16. Starting with the [4+3] cycloadducts derived from 2‐methylfuran and tetrachloroacetones (6b and 7b), the same procedure, but with use of ethanol or trifluoroethanol, results in the corresponding ethoxy‐ and trifluoroethoxy acetals. These compounds can be converted into the oxabicyclic compounds 15, which undergo cleavage of the ether bridge on heating with KOH in methanol, thus providing 2‐alkoxy‐3‐hydroxytropones 20, which can be dealkylated to give the 2,7‐dihydroxytropones (7‐hydroxytropolones) 29. The lithium enolate generated from the α‐oxo acetal 15a can be exo‐alkylated with methyl iodide. Michael addition with 2‐nitro‐1‐butene followed by a Nef reaction furnishes the bicyclic dioxo acetal 5. Treatment of 5 with basic methanol results in an epoxyazulenone derivative 26, and a hydroxytropone 20f, which is in equilibrium with the cyclic hemiacetal form 28. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

2,4-Dichlorobicyclo[3.2.1]oct-6-en-3-one (1) and its spirocyclopropane (4) and 8-oxa analogues (15, 16) react with methanolic sodium methoxide to furnish bicyclic α-oxo-acetals (3b, 5b, 17, 18) through an enolization/ionization mechanism. With trifluoroethanol/sodium trifluoroethoxide, the corres-