Cyclooctene complexes

The cyclooctene complex was first isolated and adapted to cluster synthesis by Shapley and co-workers (156). The complex is formed by reaction of ethylene with H2Os3(CO)10 in cyclooctene, when only a trace of the vinyl adduct HOs3(CO)10-CH=CH2 is formed. The 13C-NMR spectrum indicates that substitution by the olefin of equatorial carbonyl groups on two different metal centers has occurred. The complex... 

The disubstituted acetonitrile complex has been found to undergo all the reactions cited above for the cyclooctene complex. A particular advantage of these compounds is that it is possible sequentially to replace the ligands to produce the intermediate compound [Os3(CO)10-(CN3CN)X], which may then be further reacted to give a mixed complex [Os3(CO)10XX ]. 

The Ir(III)-amido-hydrido complex 43 was isolated by reacting the electron-rich neutral phosphine-cyclooctene complex 42 according to Equation 6.13 [7] (note the cis arrangement of the hydride and amide function). Likewise, the cationic complex 44 reacted in neat aniline to afford a 50/50 mixture of the N—H (45) and C—H (46) activation products that was isolated as a light orange powder (Equation 6.14). Compound 45 was separated from 46 and purified in 49% overall yield. 

The intermediate cyclooctene complex appears to be more reactive with respect to CS coordination and more sensitive to oxidation when the arene ring bears electron-withdrawing groups (e.g., C02CH3). Dicarbonyl(methyl rj6-benzoate)-thiocarbonyl)chromium is air stable in the solid state and reasonably stable in solution.9 The infrared spectrum exhibits metal carbonyl absorptions at 1980 and 1935 cm"1 and a metal thiocarbonyl stretch at 1215 cm"1 (Nujol) (these occur at 1978, 1932, and 1912 cm"1 in CH2C12 solution).10 Irradiation of the compound in the presence of phosphite or phosphine leads to slow substitution of CO by these ligands, whereas the CS ligand remains inert to substitution. The crystal structure has been published."... 

Direct reaction between oxygen and a substrate would be expected to be more favorable when both molecules are coordinated to a metal. Indeed, hydrogen abstraction from a coordinated olefin by coordinated dioxygen was observed in the reaction of a Rh(I)-cyclooctene complex with molecular oxygen.186a,b The following mechanism was proposed ... 

For the most part, displacement of the chelating COD ligand (see Chelating Ligands) is difficult to achieve as a simple substitution under mild conditions. So, the cyclooctene complex [Ir(COE)2Cl]2 (2) is typically employed as a starting material for the preparation of [Ir(COE)(PR3)3] (12) or [Ir(PR3)3Cl] (13) complexes. In the case of PR3 = PMc3, these complexes are extremely reactive and undergo a number of oxidative addition reactions (see Oxidative Addition). 

The intermediate cw-cyclooctene complex can be prepared by the method of Fischer and Herberhold. Tricarbonyl(//-cyclopentadienyl)manganese(I)t... 

Butadiene reacts slowly with RhCls in ethanol at —5°C to yield the yellow, diamagnetic air-sensitive complex (C4H8)2RhCl (475) stable in the solid but not in solution at room temperature. The same complex is rapidly formed by reaction of C4Hg with the cyclooctene complex [(C8Hi4)2RhCl]2- X-Ray studies (475) show that the molecule (177) has Civ symmetry with Rh-C distances of about 2.2 A. The butadiene ligands... 

The trons-cycloalkenes 37a, 67, and trans-cyclononene 227 react with diironnonacarbonyl 228 to form the tetracarbonyliron(O) complexes 229-231 with the frans-cyclooctene complex 229 being significantly more stable than that of trons-cyclodecene 231 (177). The bicyclic triene 232 reacts with 228 preferentially at one of the trans double bonds of the trans, trans- cy-clodecadiene substructure. In line with the expected stability, the trans, cis-cycloocta-1,5-diene 234 and trans, ris-cycloocta-1,3-diene 236 react with 228 exclusively at the trans double bond to give the complexes 235 and 237. In the complex 238, tetracarbonyliron(O) is bonded to the bridgehead double bond of bicyclo[4.3.2]deca-7,9-diene (184b) (177). 

Another example of a geometrical photoisomerization process influenced by CD is the cis-trans photoconversion of cyclooctene in solid P-CD complexes. After prolonged irradiation of the cis-cyclooctene complex, an apparent photostationary state with a trans/cis ratio of 0.47 was detected, which was considerably smaller than that obtained in homogeneous fluid solution (0.96). This result is explained by the reduced rotational mobility of the guest in the inclusion complex. The asymmetric CD environment however, is not able to induce optical activity in the photoproduct, which shows an enantiomeric excess of only 0.24%. In this study, light of 185 nm, also absorbed by the CD, was used [302]. 

Reaction between the cyclooctene complex [(C8Hi4)2lrCl]2 and >4 equivalent of silver fluoroacetate produces a highly active system for metathesis/isomerization of... 

An interesting question remains unanswered. How largo is the heptane-Mn interaction Angelici and Loewen (14 have studied the ligand substitution of the cis-cyclooctene complex 1 by PPh3 in methylcyclohexane solution. Similarly, Butler and Sawai (161 have studied the ligand substitution of the SBu2 complex 2 by P(0-n-Bu)3 in methylcyclohexane solutioa... 

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