Tetraene complexes

However, this ligand is ideally suited for the facile preparation of purple [CotetraenCyCU, which can be easily made from [Co(NH3)5Cl]Cl2 and the amine by refluxing one day in absolute ethanol. The alcohol-insoluble product is contaminated with a trace of starting material while the mother liquor contains a green basic polynuclear by-product. Attempts to make the tetraen complex in water gave impure substances or mixtures. When aqueous tetraen was heated with Co(NH3)3(N02)3 (5 ), the flnal purple product was shown to consist of at least three different constituents, of which only about 10% seemed to be the desired material. This was demonstrated by its conversion to [CotetraenNH3]l3 with aqueous ammonia and activated carbon. 

While the chloride value checks for the tetraen complex, the nitrogen analysis is satisfactory for the penten analog. 

Attempts to prepare the tetraene complex of cobalt (III) by oxidation of the cobalt complex failed however, Goedken has succeeded in removing the tetraene from iron and then placing it on cobalt (III). 

Various reports on the synthesis and reactivity of iron complexes of trienes and tetraenes have been reported in the past 10 years. Reactivity studies of various triene and tetraene complexes predominate in the recent literature. (77-Triene)Fe(GO)3 complexes have been reported to undergo osmylation reactions with OSO4 to yield the corresponding glycols (Scheme 29). Subsequent reaction with NaI04 in THF/H20/23°C affords (dienal)Fe(GO)3 complexes. 

The skeletal rearrangement of various strained cyclic compounds is carried out with a catalytic amount of soluble complexes of PdCl2. Namely, the rearrangements of bulvalene (67) to bicyclo[4.2.2]deca-2,4,7,9-tetraene (68)[54], cubane (69) to cuneane (70)[55], hexamethyl Dewar benzene (71) to hexa-methylbenzene (72)[56], and 3-oxaquadricyclanes[57] and quadricyclane (73) to norbornadiene[58-60] take place mostly at room temperature. Reaction of iodocubane (74) with a terminal alkyne catalyzed by Pd(0) and CuBr unexpectedly affords an alkynylcyclooctatetraene 75, without giving the desired cubylalkyne 76. Probably the rearrangement is a Pd-catalyzed reaction[61]. 

Methoxyestra-l,3,5(10),14-tetraen-17-one. A solution of 9.3 g (0.0328 mole) of 3-methoxyestra-l,3,5(10),14-tetraen-17)S-ol in 300 ml of methylene dichloride is added at a rapid dropwise rate to a stirred suspension of 46.5 g (0.18 mole) of the dipyridine-chromium VI complex in 800 ml of methylene dichloride at room temperature. The mixture is stirred 45 min and then filtered. The residue is washed with ethyl acetate and the organic layers are combined. Water is added to the filtrates and sufficient ethyl acetate is added to make the organic layer less dense than water. After the organic layer is washed with water it is dried over sodium sulfate and concentrated to leave... 

Tetraene 141 has been converted into various complex polycondensed adducts by reacting with a variety of dienophiles such as maleic anhydride, N-phenylmaleimide, N-phenyltriazolinedione,p-benzoquinone and tetracyano-ethylene carried out under thermal conditions. All cycloadditions occurred facial-diastereoselectively from an outside attack and provided monocycloadducts which had an exceptionally close relationship between diene and dieno-phile and then underwent intramolecular cycloaddition [125]. The reaction between 141 and p-benzoquinone is illustrated in Scheme 2.53. 

The macrocyclic tetraene 2,3,9,10-Me4[14]tetraene (tmt) may be synthesized by a metal-directed condensation between trimethylenediamine (tn) and 2,3-butanedione in the presence of Co(OAc)2, ultimately resulting in the trans-dichloro Co111 complex [Co(tmt)Cl2]+ (59).302... 

The tetraols were found to be highly sensitive toward acidic and basic conditions. Under Bronsted acidic conditions, the hemiaminals readily eliminated to generate a tetraene, while under basic conditions, the tetraol either decomposed or epimerized to generate a mixture of diastereomers. It is speculated that the base-mediated epimerization proceeds through ring-chain tautomerization involving a putative alpha-keto amide derivative. It is also of note that simple dissolution of tetraol (+)-95 in methanol also leads to its degradation to a complex mixture of products. 

One of the most recent developments in the field of Ni-catalyzed reactions of alkyl halides with organozinc derivatives is a study of Terao et al.411 They reported the use of three additives in the couplings 1,3-butadiene, N,N-bis(penta-2,4-dienyl)benzylamine 308a, and 2,2-bis(penta-2,4-dienyl)malonic acid dimethyl ester 308b. Addition of tetraene 308b to the reaction mixtures significantly increased the product yields (Scheme 157). The remarkable effect of these additives was explained by the formation of the bis-7r-allylic complex 309 as the key intermediate (Scheme 158). 

Since the early work dealing with Zeise s salt, many complexes have been prepared with the formula [PtL(C2H4)X2], where L = quinoline, pyridine, or ammonia and X=C1 , Br , I, or N()2. Similar compounds have been prepared that contain other alkenes than C2H4. Many of the complexes containing dienes, trienes, and tetraenes as ligands also contain carbonyl ligands. In fact, metal carbonyls are frequently starting complexes from which alkene complexes are obtained by substitution reactions. 

The main path of the palladium-catalyzed reaction of butadiene is the dimerization. However, the trimerization to form /j-1, 3,6,10-dodeca-tetraene takes place with certain palladium complexes in the absence of a phosphine ligand. Medema and van Helden observed, while studying the insertion reaction of butadiene to 7r-allylpalladium chloride and acetate (32, 37), that the reaction of butadiene in benzene solution at 50°C using 7r-allylpalladium acetate as a catalyst yielded w-1,3,6,10-dodecatetraene (27) with a selectivity of 79% at a conversion of 30% based on butadiene in 22 hours. 

The tetra-cA-cycIononatetracne 241 is unstable and easily rearranges at 23 °C (t /2 50 min) to the isomeric d.v-8,9-dihydroindcne 242 (equation 77)89. It is interesting, however, that the iron(III) tricarbonyl complex of tetraene 241 is stable for many days at room temperature and isomerizes to the Fe-complex of 242 only upon heating in octane at 101 °C89. The principle of stabilization of the reactive multiple bonds with metal carbonyl complexes is well-known in modem organic synthesis (e.g. see the acylation of enynes90). 

Migration of the metal along the polyene chain in (l,l- 2-l,3,5-hexatriene)CoCp occurs with an activation energy of 25.6 kcalmoT 1 (equation 15)136b. This barrier is ca 5-8 kcal mol 1 lower than that for metal migration in (triene)- or (tetraene)Fe(CO)3 complexes (see Section IV.E.l.d). 

One example of outer-sphere electron transfer is the reaction between the dipotassium cycloocta-tetraene (KjCgHg) and the cobalt complex of bis(salicylidenediamine) (Co Salen) (Levitin et al. 1971). 

Scheme 6.27 considers other, formally confined, conformers of cycloocta-l,3,5,7-tetraene (COT) in complexes with metals. In the following text, M(l,5-COT) and M(l,3-COT) stand for the tube and chair structures, respectively. M(l,5-COT) is favored in neutral (18-electron) complexes with nickel, palladium, cobalt, or rhodium. One-electron reduction transforms these complexes into 19-electron forms, which we can identify as anion-radicals of metallocomplexes. Notably, the anion-radicals of the nickel and palladium complexes retain their M(l,5-COT) geometry in both the 18- and 19-electron forms. When the metal is cobalt or rhodium, transition in the 19-electron form causes quick conversion of M(l,5-COT) into M(l,3-COT) form (Shaw et al. 2004, reference therein). This difference should be connected with the manner of spin-charge distribution. The nickel and palladium complexes are essentially metal-based anion-radicals. In contrast, the SOMO is highly delocalized in the anion-radicals of cobalt and rhodium complexes, with at least half of the orbital residing in the COT ring. For this reason, cyclooctateraene flattens for a while and then acquires the conformation that is more favorable for the spatial structure of the whole complex, namely, M(l,3-COT) (see Schemes 6.1 and 6.27). 

High-spin, five-coordinate complexes are known of type [MnLXJPFg (X = F, Cl, Br, or I and L = 2,9-dimethyl-3,10-diphenyl-1,4,8,11-tetraazacyclotetra-l,3,8,10-tetraene). Electrochemical investigation of these complexes revealed that they are surprisingly resistant to oxidation in dimethylsulfoxide." ... 

Kinetics and mechanisms of complex formation have been reviewed, with particular attention to the inherent Fe +aq + L vs. FeOH +aq + HL proton ambiguity. Table 11 contains a selection of rate constants and activation volumes for complex formation reactions from Fe " "aq and from FeOH +aq, illustrating the mechanistic difference between 4 for the former and 4 for the latter. Further kinetic details and discussion may be obtained from earlier publications and from those on reaction with azide, with cysteine, " with octane-and nonane-2,4-diones, with 2-acetylcyclopentanone, with fulvic acid, and with acethydroxamate and with desferrioxamine. For the last two systems the various component forward and reverse reactions were studied, with values given for k and K A/7 and A5, A/7° and A5 ° AF and AF°. Activation volumes are reported and consequences of the proton ambiguity discussed in relation to the reaction with azide. For the reactions of FeOH " aq with the salicylate and oxalate complexes d5-[Co(en)2(NH3)(sal)] ", [Co(tetraen)(sal)] " (tetraen = tetraethylenepentamine), and [Co(NH3)5(C204H)] both formation and dissociation are retarded in anionic micelles. 

The mechanism of the dehydrogenative transannular ring closure of cycloocta-tetraene in the presence of various inorganic reagents to provide complexes of pentalene has been the subject of debate... 

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