Cyclooctadiene complexes with cobalt

Cyclooctatetraene also forms interesting complexes with cobalt, rhodium, nickel, and other transition metals, but these will not be elaborated on here. It should also be mentioned that other eight-mem-bered ring systems, such as 1,5-cyclooctadiene, 1,3,5- and 1,3,6-cyclo-octatrienes, etc., form a variety of metal, t complexes. The most recent survey of cyclooctatetraene and related metal, t complexes is the review by Fischer and Werner (100) as well as earlier reviews by these authors (99) f and Bennett (11). 

Many organometallic complexes use cod as a ligand because it can be easily substituted. For that reason, many cobalt cyclooctadiene complexes are important in catalytic reactions, particularly when used with cyclopentadienyl in complexes (Section 5.1.2). ... 

An important question in light of the ease of chelation in the synthesis of the carbonyl complexes is whether it is possible to decoordinate the phos-phane arm, possibly to create a vacant coordination site for further chemistry. The question was addressed by treatment of 327 with 1,5-cyclooctadiene under photochemical reaction conditions, using the diene as the solvent, and resulted in a 41% yield of nonchelated cyclooctadiene complex 336 (Scheme 61). Treatment of this complex with diphenylethyne under reaction conditions normally allowing alkyne di- or trimerization reactions gave tetraphenylcyclo-butadiene complex 337 in 64% yield, showing that chemistry at the cobalt atom is possible without inhibition by a chelating phosphane arm. ... 

Nickel compounds can also be employed as catalysts [161-170]. A three-component system consisting of nickel naphthenate, triethyl-aluminum, and boron trifluoride diethyletherate is used technically. The activities are similar to those of cobalt systems. The molar Al/B ratio is on the order of 0.7 to 1.4. Polymerization temperatures range from -5 to 40 °C. On a laboratory scale the synthesis of 1,4-polybutadiene with allylchloronickel giving 89% cis, 7.7% trans, and 3.4% 1,2-structures is particularly simple [8]. In nickel compounds with Lewis acids as cocatalysts, complexes with 2,6,10-dodecatriene ligands are more active than those with 1,5-cyclooctadiene (Table 4) [171]. 

These compounds have been obtained indirectly by reactions of silylated acetylenes with metal carbonyls or olefin complexes. Thus, trimethylsilylphenylacetylene reacts with rj5-cyclopentadienylcobalt dicarbonyl, cobaltocene, or rjs-cyclopentadienyl-(l,3-cyclooctadiene) cobalt, in refluxing xylene, to give a mixture of cis- and trans-bis-(trimethylsilyl)cyclobutadiene complexes (R = Me, R = Ph) 68, 127, 137) ... 

The compounds Am[Co(COD)2] (27b) react with methanol according to Eq. (30) to give the known i73-cyclooctenyl(i74-l,5-cyclooctadiene)-cobalt (55-57). This complex reacts with lithium metal in a similar way to nickel(O)-olefin complexes. Two lithium atoms are added to give 28 (46). 

Reduction of the more unsaturated 3-oxygenated menthanes is a well-known route to menthones thus treatment of pulegone (46) with cyclooctadiene and an iridium catalyst yielded 61% menthone (521) and 39% isomenthone (583). cw-Piperitol (584) was also converted to Isomenthone (583) by treatment with low-valence cobalt complexes coordinated with phosphines. ... 

Cobalt complexes of vinylketene by reaction with alkynes in the presence of 2 moles of cyclooctadiene 100°C during 20 hours resulted in moderate yields of phenols (ref. 17). This procedure represents the first synthesis of alkylphenols by the insertion of (fi -indenyl)cobalt(l) into a cyclobutenone, the latter being prepared by analogy with a method for cpCo(PPh3)2. With symmetrical alkynes (R = = Et) the yield was 65%, although with unsymmetrical compounds the... 

There is a report for the C-C bond cleavage of cyclooctadiene on cobalt by treatment with HBF4 as shown in Scheme 5 [22]. The first step of this reaction is protonation of one double bond which converts the complex to the corre-... 

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