Cyclopentadiene, tetramethyl

Methylene thiirane is obtained by thermolysis of several spirothiirane derivatives which are formally Diels-Alder adducts of methylenethiirane and cyclopentadiene or anthracene <78JA7436). They were prepared via lithio-2-(methylthio)-l,3-oxazolines (c/. Scheme 121). A novel synthesis of the allene episulfide derivatives, 2-isopropylidene-3,3- dimethylthiirane (good yield) or its 5-oxide (poor yield), involves irradiation of 2,2,3,3-tetramethyl-cyclopropanethione or its 5-oxide (81AG293). Substituents on the thiirane ring may be modified to give new thiiranes (Section 5.06.3.9). The synthesis of thiirane 1-oxides and thiirane 1,1-dioxides by oxidation is discussed in Section 5.06.3.3.8 and the synthesis of 5-alkylthiiranium salts by alkylation of thiiranes is discussed in Section 5.06.3.3.4. Thiirene 1-oxides and 1,1-dioxides may be obtained by dehydrohalogenation of 2-halothiirane 1-oxides and 1,1-dioxides (Section 5.06.4.1.2). 

Perhaps chemists will be able to mimic nature without duplicating the iron-sulfur-molybdenum structure. For example, a zirconium complex with tetramethyl cyclopentadiene can bind dinitrogen in a manner that breaks the NON bond, as shown below. Treatment with hydrogen gas results in formation of small amounts of ammonia. Although the yields are too low to make this a viable commercial process, researchers hope to make the process more efficient through chemical modifications and changes in conditions. 

Reaction of Chlorodimethyl(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl)silane with Silica Materials. Chlorodimethyl-(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl)silane (excess) was added to a mixture of amine-functionalized silica with hexanes in a drybox. 2,6-Di-tert-butylpyridine (excess) was added as a proton sponge. The mixture was allowed to react while stirring for 24 h. The solid was filtered and washed with hexanes and THF in the drybox. The solid was then contacted with another aliquot of chlorodimethyl-(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl)silane and the procedure was repeated. 

The patterned aminopropyl functionalities have been tested for uniform reactivity in an effort to probe degree of site isolation (7). For example, the patterened aminopropyl functionalities quantitatively reacted with chlorodimethyl-(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl) silane (7). In our hands, a densely-loaded control material was found to have only 66% of the amine sites react with the silane functionality. This value is in line with... 

RhjC CjyH, Rhodium, di-p-chlorodichloro-bis[( 1,2,3,4,5-T )-1,2,3,4-tetramethyl-5-(trifluoromethyl)-2,4-cyclopentadien-l-yl]di-, [157997-89-2], 31 236 Rh6N015C 17H3, Rhodium, (acetonitrile)tetra-Pj-carbonylundecacarbonylhexa-, octahedro, [120292-53-7], 31 240 Rh6N2014C l8H6, Rhodium, bis(acetonitrile) tetra-pj-carbonyldecacarbonylhexa-, octahedro. [158638-72-3], 31 243 Ru2N406Cl2H6, Ruthenium, hexacaibonylbis [p-( 1 H-pyrazolato-A/1 lA lJdi-, (Ru-Ru), [109665-54-5], 31 219... 

Ozonolysis as used below is the oxidation process involving addition of ozone to an alkene to form an ozonide intermediate which eventually leads to the final product. Beyond the initial reaction of ozone to form ozonides and other subsequent intermediates, it is important to recall that the reaction can be carried out under reductive and oxidative conditions. In a general sense, early use of ozonolysis in the oxidation of dienes and polyenes was as an aid for structural determination wherein partial oxidation was avoided. In further work both oxidative and reductive conditions have been applied . The use of such methods will be reviewed elsewhere in this book. Based on this analytical use it was often assumed that partial ozonolysis could only be carried out in conjugated dienes such as 1,3-cyclohexadiene, where the formation of the first ozonide inhibited reaction at the second double bond. Indeed, much of the more recent work in the ozonolysis of dienes has been on conjugated dienes such as 2,3-di-r-butyl-l,3-butadiene, 2,3-diphenyl-l,3-butadiene, cyclopentadiene and others. Polyethylene could be used as a support to allow ozonolysis for substrates that ordinarily failed, such as 2,3,4,5-tetramethyl-2,4-hexadiene, and allowed in addition isolation of the ozonide. Oxidation of nonconjugated substrates, such as 1,4-cyclohexadiene and 1,5,9-cyclododecatriene, gave only low yields of unsaturated dicarboxylic acids. In a recent specific example... 

The synthesis of these materials starts with the reaction of chlorodimethyl-(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl)silane (Cp -silane) with the snrface amine groups. It was shown that the percentage of amine sites reactive toward the Cp -silane was significantly better for the trityl-spaced material than traditionally prepared aminosilica (77% reacted amines vs. 29% reacted amines) [19]. Also, once the Cp -silane moiety was reacted with the trityl-spaced amines, the percentage... 

The tetramethyl-Cp complex (C5Me4CH2CH2PPh2)TiCl3 has been prepared from the reaction of the trimethyl-silyl-substituted cyclopentadiene with TiCl4 and its molecular structure determined by X-ray diffraction methods. The dynamic behavior in solution has been studied by variable-temperature NMR spectroscopy.365... 

Seyferth, D., and Paetsch, J.D.H., Diels-Alder reaction in organometalhc chemistry. Part 5. Tetramethyl acetylenediphosphonate and dimethyl chloroacetylenephosphonate and their reactions with cyclopentadiene, 1,3-cyclohexadiene, and diazomethane, J. Org. Chem., 34, 1483, 1969. 

Low-temperature trapping experiments of the photolysis products of disilacycloheptene (75), which was prepared by insertion of ethyne into the Si—Si bond of l,l,2,2-tetramethyl-l,2-disilacyclopentane <75JA931>, provided evidence for the trans isomer of (75) <90JA6601>. GC-MS analyses indicated that, as the decay of trans-(75) progressed, a mixture of six dimers of mjz 368 was formed. Only one of the dimeric products was successfully isolated in pure form by preparative GC this dimer was assigned the unsymmetrical c/s,fra 5-fused cyclobutene structure (76) on the basis of NMR data. Trapping experiments of metastable trans-(75) by Diels-Alder cycloadditions with cyclopentadiene and 9,10-dihydro-l l,12-dimethylene-9,10-ethanoanthracene afforded (77) and (78), respectively. The crystal and molecular structures of (78) were determined. 

Gomplete defluorination of l,2,3,4-tetramethyl(trifluoromethyl)cyclopentadiene occurred on treatment with [Ti(NMe2)4] to give [Ti(/x-NMe2)(NMe2)(/x-E)E]6. GsMe4=G(NMe2)2 was isolated as a byproduct. 

The mixture of double bond isomers of l,2,3,4-tetramethyl-5-(trifluoro-methyl)cyclopentadiene (Cp H) is a clear, colorless liquid with a sweet ole-finic odor similar to that of pentamethylcyclopentadiene. Cp H is an air-stable compound but it should be stored in the refrigerator. Although gas chromatographic analysis shows two peaks, the presence of all three of the possible cyclopentadiene isomers is indicated by H NMR spectroscopy as three quartets for the ring protons are observed at 3.26 (Jhf = 10.0 Hz), 2.99 (Jhh = 6.7 Hz), and 2.66 ppm (Jhh = 6.8 Hz) with a relative ratio of approximately 1 16 2.4 for isomers I, II, and III, respectively. Resonances between 4.8 and 5.0 ppm are attributed to products that result from an elimination mechanism rather than cyclization in the last step of the synthesis. These impurities boil very close to that of Cp H, but they are removed by careful fractional vacuum distillation as part of the forerun. The IR spectrum (neat liquid) exhibits significant bands at 2977(vs), 2937(vs), 2884(s), 2864(s), 2751(w), 1658(m), 1599(s), 1446(s), 1384(vs), 1357(vs), 1280(s), 1258(vs), 1164(vs), 1099(vs), 1012(vs), and 686(m) cm . The syntheses of organotransi-tion metal complexes are usually carried out with the 91% purity Cp H product. Because alkali metal and thallium salts of Cp are unstable, organo-transition metal complexes are prepared from Cp H itself, as are many complexes of pentamethylcyclopentadiene and cyclopentadiene."... 

Alternatively, monomers required for the synthesis of a/r-poly(carbosilane/ siloxanes) have been prepared by formation of Si-C bonds by Pt catalyzed hydrosilation reactions. For example, Pt catalyzed hydrosilation of the C-C double bond of the Diels-Alder adduct of cyclopentadiene and maleic anhydride with sym-tetramethyldisiloxane yields a difunctional monomer 5,5 -bis(l,l,3,3-tetramethyl-l,3-disiloxanediyl)norborane-2,3-dicarboxylic anhydride, see Figure 2. Reaction of this with diamines such as 4,4 -diaminobiphenyl yields a thermally stable poIy[imide-a/r(carbosilane/siloxane)] [3]. 

Catalysis by compounds of Pt and other transition metals was used for the copolymerization of DSCBs with dimethyl[l]silaferrocenophane, in which onecy-clopentadiene cycle was unsubstituted, while in the second cyclopentadiene cycle, all hydrogen atoms were replaced by methyl groups [79]. Since the polymerization of the ferrocenophane comonomer in the presence of PtCl2 proceeded at a much higher rate than the polymerization of tetramethyl-DSCB, the polymerization of their equimolar mixture at 20°C predominantly yielded homopolymers. The random copolymer can be prepared at tetramethyl-DSCB ferrocenophane = 15 1 however, the yield of the copolymer was also low ( 21%). 

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