2,5-Norbornadiene complexes with

The intermolecular Pauson-Khand reaction of the resulting S/P-cobalt complexes with norbornadiene was studied under thermal and A -oxide activation conditions. Thus, heating the diastereomerically pure complex (R = Ph, R = Cy) with ten equivalents of norbornadiene at 50 °C in toluene afforded the corresponding exo-cyclopentenone in a quantitative yield and with an enantio-selectivity of 99% ee. Under similar conditions, the analogous trimethylsilyl complex (R = TMS, R = Cy) afforded the expected product in a high yield but with a lower enantioselectivity of 57% ee. In order to increase this enantio-selectivity, these authors performed this reaction at room temperature in dichloromethane as the solvent and in the presence of NMO, which allowed an enantioselectivity of 97% ee to be reached. These authors assumed that the thermal activation promoted the isomerisation of the S/P ligand leading to a nonstereoselective process. 

In 1991, Park reported123 the first synthesis of iron alkynylcarbene complexes (184), involving the nucleophilic attack of a lithium acetylide on pentacarbonyl iron, followed by electrophilic quench. With such compounds in hand, he proceeded to investigate their reactivity123,124 and found that upon addition of cyclopentadiene to the alkynylcarbene complexes 184, the products formed were 774-vinylketene complexes (185). During column chromatography, some of these products (185.a and 185.b) were transformed into the tricarbonyl(norbornadiene)iron derivatives 186. Others (185.C and 185.d, not shown) were hydrolyzed as part of the workup procedure, to afford pure samples of the norbornadiene complexes 186.C and... 

The asymmetric hydrosilylation of thiochroman-4-one catalyzed by a Rh norbornadiene (nbd) complex with a mixed P and S ligand occurs with both high enantioselectivity (92%) and yield (91%) (Equation 87) <2003JA3534>. Cr complexes with amino acids effect the reduction but with only low enantioselectivity <1999TL1373, 2004TA1735>. 

RuCl2(arene)]2 complexes (1) react with 1,5-cyclooctadiene and 1,3- or 1,4-cyclohexadiene in the presence of ethanol and Na2C03 or zinc dust to give Ru°(776-arene)(V diene) compounds of type 196-198 in 60% yield [Eq. (20)] thus, this reaction appears to be the reverse of the 198-> 1 reaction [Eq. (19)]. The same reaction with ethylene leads to the bis-ethylene ruthenium(O) complex 205 (37%) (131,10). The norbornadiene complex 207 is prepared similarly from derivative 206 (125). Combination of transformations 206 - 207 [Eq. (21)] or 1 - 198 [Eq. (20)] with trans-... 

Cyclopentadienyl dithiolene complexes such as CpCo(S2C2R2) and C p2Ti-(S2C2R2) have been shown to catalyze the isomerization of quadricyclane to norbornadiene (Eq. 9) (133). The catalytic activity is closely related to the reduction potential of the complexes Complexes with higher Zs]/2 are more active. This result suggests that the reaction involves a certain degree of charge transfer between quadricyclane and the dithiolene complex. 

In contrast to its ready reaction with acetylenes, Cp2Mo2-(CO)i+ does not react with simple olefins or dienes, e.g., C2Ht+, butadiene, C2H3CN, norbornadiene, etc. With TONE (C2(CN)iJ, 1 is oxidized and [CpMo(C0)il]+ [TONE]7 may be isolated (6). Allene does react, however, to form a complex, ll, in which each of the orthogonal C=C n-bonds donates two electrons to each molybdenum. This fluxional molecule has C2 symmetry in the solid state and has a Mo-Mo bond length of 3.117(1)A (32). 

The 1,4-diphospha-l,3-butadienes are suitable as ligands for cr-coordi-nated complexes with transition metals. Attempts to carry out pericy-clic reactions with maleinic anhydride, acetylene dicarboxylate esters, dimethylbutadiene, or cyclopentadiene failed, but Diels-Alder reactions with norbornadienes were successful (94). Earlier attempts to synthesize 1,4-diphosphabuta-l,3-dienes with oxalychloride and phenyl-bis(silyl)phosphane proceeded via ring closure [Eq. (42)] (89), where R = Ph (a) or [Pg.285]

The transient electrophilic terminal phosphinidene 188, which is readily accessible by thermolysis of 7-phospha-norbornadiene complex 187 (Scheme 59), is a powerful precursor to phospholenes. For example, it reacts with ethoxyacetylene to give phosphole 189, which upon hydrolysis affords the 2-phospholene complex 190 (Scheme 59)... 

Treatment of (//, // -norbornadiene)PdCl2 complex with Ph2Hg or vinyl mercuric chloride derivatives (R R C=CH)HgCl (R ,R = H, Me, r-Bu, Cl) in THF or methanol furnished the corresponding endo,endO 3-phQny - and t/o, /6>-3-vinyl-5-nortricyclyl palladium complexes, respectively (equation 59)102,123-126 approach, employing a thio-... 

Chiral methyl chiral lactic acid (5). This labeled molecule, useful for study of stereospecificity of enzymic reactions, has been prepared in a way that allows for synthesis of all 12 possible isomers. One key step is the stereospecific debromination of 1, accomplished by conversion to the vinyl-palladium cr-complex 2 followed by cleavage with CF3COOT to give the tritium-labeled 3. The next step is the catalytic deuteration of 3, accomplished with a rhodium(I) catalyst complexed with the ligands norbornadiene and (R)-l,2-bis(diphenylphosphino)propane. This reaction gives 4 with an optical purity of 81%. The product is hydolyzed to 5, which is obtained optically pure by cr3rstallization. 

Upon treatment with 2,2 -bipyridyl (bipy) or 1,10-phenanthroline (phen), the 1,3-cyclohexadiene complex [(C6H8)Co(CO)2]2 dispropor-tionates to produce [CoL3]+[Co(CO)4] (L = bipy or phen) the analogous norbornadiene complex, however, undergoes only ligand displacement to yield [Co(CO)2L]2 (46). 

Cycloheptadiene interacts slowly with Rh(CO)2(acac), simultaneously undergoing isomerization, to give the norbornadiene complex (C7H8)Rh(acac) (74). 

The norbornadiene complexes of AgNOs (577) and AgBF4 (491) are quite analogous in stoichiometry to those of 1,3-butadiene with the same salts. A structural analysis (28) of the 1 2 complex (C7Hg)(AgNOg)2 has shown chains of silver nitrate molecules cross-linked by norbornadiene molecules (Fig. 11). In this complex, each silver ion is coordinated... 

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