Cyclooctene complexes platinum

CkH.jP, Phosphine, dimethylphenyl-ruthenium complex 26 273 C HU, Cyclooctene platinum complex, 26 139 C,H,N, Benzene, 2-isocyano-1,3-dimethyl-iron complexes, 26 53, 57 C H N, Benzenemethanamine, N,N,2-trimethyl-... 

QH P, Phosphine, dimethylphenyl-, iron complex, 26 61 molybdenum complex, 27 11 osmium complex, 27 27 osmium-rhodium complex, 27 29 osmium-zirconium complex, 27 27 ruthenium complex, 26 273 CkH,2, 1,5-Cyclooctadiene, iridium complex, 26 122, 27 23 osmium-rhodium complex, 27 29 ruthenium complexes, 26 69-72, 253-256 CbH 20,PS, 2-Butenedioic acid, 2-(dimeth-ylphosphinothioyl)-, dimethyl ester, manganese complex, 26 163 ChH,4, Cyclooctene, platinum complex,... 

Introduction of the allene structure into cycloalkanes such as in 1,2-cyclononadiene (727) provides another approach to chiral cycloalkenes of sufficient enantiomeric stability. Although 127 has to be classified as an axial chiral compound like other C2-allenes it is included in this survey because of its obvious relation to ( )-cyclooctene as also can be seen from chemical correlations vide infra). Racemic 127 was resolved either through diastereomeric platinum complexes 143) or by ring enlargement via the dibromocarbene adduct 128 of optically active (J3)-cyclooctene (see 4.2) with methyllithium 143) — a method already used for the preparation of racemic 127. The first method afforded a product of 44 % enantiomeric purity whereas 127 obtained from ( )-cyclooctene had a rotation [a]D of 170-175°. The chirality of 127 was established by correlation with (+)(S)-( )-cyclooctene which in a stereoselective reaction with dibromocarbene afforded (—)-dibromo-trans-bicyclo[6.1 0]nonane 128) 144). Its absolute stereochemistry was determined by the Thyvoet-method as (1R, 87 ) and served as a key intermediate for the correlation with 727 ring expansion induced... 

F-Cyclooctene is chiral, and it was resolved into enantiomers by Cope and coworkers100 by separation of diasteromeric platinum complexes containing 20 and (+)-phenyl-2-aminopropane as ligands. Thermal racemization occurred around 150 °C with a rate... 

Platinum complexes incorporating an optically active amine have been employed for resolution of racemic mixtures of optically active olefins by reaction of the olefin with dichloro-platinum(II). The differing solubility of the diastereoisomers permits separation by fractional crystallization and the olefin can be recovered by reaction of the complex with aqueous alkali cyanide. Using either (-f)-l-phenyl-2-aminopropane (Dexedrine) or (-f)- or (—)-a-phenyl-ethylamine. Cope and co-workers have resolved the optical isomers of trans double bond coordinated and, with (—)-phenylethyl-amine)dichloroplatinum(II), a bridged complex with each double bond coordinated to a different platinum atom. 

Use for resolution of cycloalkenes. W s-Cycloalkenes of intermediate size (Cg-Cjo) should be capable of existing in enantiomeric forms because of the inability of the trans double bond to rotate with respect to the remainder of the molecule. But in the absence of salt-forming groups, resolution cannot be accomplished by the usual methods of forming derivatives. However, Cope et al.s found that the strong tendency of an alkene to complex with a platinum compound provides an effective method of resolution. The complex of ethylene with platinous chloride and (+) or (-)-a-methylbenzylamine exists in only one form since ethylene is symmetrical. But addition of the base to a solution of the platinum complex of trans-cyclooctene opens the way for formation of the diastereoisomeric complexes derived from the R- and S-forms of the base. Fractional crystallization at —20° (liquid at 25°) effected separation. Liberation of the (—)-hydrocarbon from the complex with potassium cyanide gave a product of aD — 411°. 

E -cyclooctene is subject to thermal racemization. The molecular motion allows the double bond to slip through the ring, giving the enantiomer. The larger and more flexible the ring, the easier the process. The rates of racemization have been measured for E-cyclooctene, Zf-cyclononene, and Zi-cyclodecene. For E-cyclooctene the half-life is Ih at 183.9° C. The activation energy is 35.6 kcal/mol. E-cyclononene, racemizes much more rapidly. The half-life is 4 min at 0° C, with an activation energy of about 20 kcal/mol. F-cyclodecene racemizes immediately on release from the chiral platinum complex used for its preparation. ... 

The ease of rotation will depend on the ring size. It is observed that trans-cyclooctene is quite stable to thermal racemization, and can be recovered with no loss in rotation after 7 days at 61°C. When the ring size is larger, it becomes easier for rotation of the plane of the double bond through the belt of the ring atoms to occur, and racemization takes place more readily. The half-life for racemization of trans-cyclononene is 5 min at 0°C. The resolution of /rans-cyclodecene has been accomplished using the techniques developed for irons-cyclooctene and trans-cyclononene, but it racemizes immediately on its release from the chiral platinum complex employed for its resolution. ... 

Other tris(olefin)platinum(0) complexes (where olefin represents a strained olefin such as bicyclo[2.2.1]heptene, dicyclopentadiene, or trans-cyclooctene) may be similarly obtained by direct displacement of 1,5-cyclooctadiene, often in quantitative yield.6... 

Distribution measurements show that the silver complex of dr-cyclo-octene is less stable than that of cycloheptene, presumably owing to more ring strain in the latter 129,130). tronr-Cyclooctene is considerably more strained than the cis isomer, and can be separated from it by extraction with 20% aqueous silver nitrate 32), but there are no quantitative measurements of the stability of the silver complex of the tram isomer. The interesting possibility of isomerizing cis to trom-cyclooctene via metal complexes has not yet been achieved. tronr-Cyclooctene has been resolved via its platinum(II) complex with the optically active amine l-phenyl-2-amino-propane (am), 7r-CgH]4PtCl2am. 29). 

An early, illustrative example of the use of chiral organometallic complexes in organic chemistry was the resolution of ra/u-cyclooctene by fractional crystallization of the diastereoisomeric tra/7i-dichloro[( + )- or (- )-a-methyl-benzylamine]platinum(Il) complexes of this olefin followed by removal of the metal with aqueous potassium cyanide (Cope et al., 1963). 

Enantiomeric (E)-cyclooctene (20E) was first resolved in 1963 through its diastereomeric platinum(II) complex. Synthesis of optically active 20E has been the subject of intensive study since 1968. The first preparation involves the treatment of enantiopure (E)-cyclooctane-l,2-thiocarbonate with triisooctyl phosphate or of (E)-cyclooatane-l,2-trithiocarbonate with l,3-dibenzyl-2-methyl-l,3,2-diazaphospholi-dine. Following analogous synthetic routes, enantiomeric (E)-cycloheptene (18E) can be produced and trapped by 2,5-diphenyl-3,4-isobenzofuran as an optically active adduct. In 1973, the circular dichroism spectrum of enantiopure 20E vapor was recorded in the vacuum UV region down to 150 nm. The first enantiodifferentiating Z-E photoisomerization of cyclooctene sensitized by chiral benzenecarboxylates appeared in 1978. Transfer of chiral information from sensitizer to substrate occurs within the exciplex intermediate. ... 

---