Cycloheptatriene, complex with

C7H7)Fe.,(CO)6]+, obtained by reaction of the cycloheptatriene complex with trityl tetrafluoroborate, shows in solution a rapid valence tautomerisrn involving diene bonding to an iron atom and Tr-allylic bonding to the other. 

The commonest method is abstraction of H from an -n cycloheptatriene complex with PhiC" (Eq. 5.48) or Et30" the oxonium cation is the reagent of choice, because the by-products, Et20 and EtH, are both volatile. 

Treatment of cycloheptatriene complexes of the type [M(tj -C7H8)(CO)3] (M = Cr, Mo, W) with Ph3C" "BF4 results in hydride abstraction to give orange-coloured tj -cycloheptatrienyl (or tropy-lium) complexes ... 

Alkoxycarbene complexes with unsaturation in the alkyl side chain rather than the alkoxy chain underwent similar intramolecular photoreactions (Eqs. 10 and 11) [60]. Cyclopropyl carbene complexes underwent a facile vinyl-cyclopropane rearrangement, presumably from the metal-bound ketene intermediate (Eqs. 12 and 13) [61]. A cycloheptatriene carbene complex underwent a related [6+2] cycloaddition (Eq. 14) [62]. 

The palladium-catalyzed trimethylenemethane reaction with tropanones was reported in 1987 by Trost and Seoane and is the first example of a [6 + 3]-cycloaddition.130 Chromium-mediated [6 + 3]-cycloadditions of two types have been described-one in which the chromium complex activates the six-carbon component and one in which the chromium complex activates the three-atom component. An example of the first type involves the reaction of a cycloheptatriene-Cr(CO)3 complex with azirines to give cyclic imines in moderate yields (Scheme 40).131... 

It was originally reported (92, 174) that the cycloheptatriene complex [Fe(CO)3(C7H8)] with triphenylmethyl fluoroborate gave a tropylium complex [Fe(CO)3(C7H7)] BF4 but subsequent work (59) has shown that an adduct [Fe(CO)3(CvH8CPh3)] BF4 (XIV R = CPh3) is formed in 96%... 

It is of interest that identical products to those derived from the metal atom technique are produced by the reduction of the metal halide (Co, Fe, Cr, V, and Ti) with PrjMgBr in the presence of cycloheptatriene (27, 85, 137). There are tentative reports of the formation of an unstable complex with chromium, possibly Cr(Tj -C7Hg)2, but these have not yet been confirmed (115, 140). 

Cycloheptatriene enol complexes, with chromium carbonyls,... 

Cycloheptatrienes with chromium, 5, 337 in molybdenum carbonyls, 5, 480 tj7-Cycloheptatrienyl complexes, with tungsten carbonyls and isocyanides, 5, 693 Cycloheptatrienyl compounds actinide complexes, 4, 227 with actinides, 4, 226 lanthanide complexes, 4, 122... 

Complexes of Cr, W, Mo, Fe, Ru, V, Mn and Rh form stable, isolable arene if -complexes. Among them, arene complexes of Cr(CO)3 have high synthetic uses. When benzene is refluxed with Cr(CO)6 in a mixture of dibutyl ether and THF, three coordinated CO molecules are displaced with six-7r-electrons of benzene to form the stable i/fi-benzene chromium tricarbonyl complex (170) which satisfies the 18-electron rule (6 from benzene + 6 from Cr(0) + 6 from 3 CO = 18). Complex formation is facilitated by electron-donating groups on benzene, and no complex of nitrobenzene is formed. Complex formation has a profound effect on reactivity of arenes, and the resulting complexes are used in synthetic reactions. The metal-free reaction products can be isolated easily after decomplexation by mild oxidation using low-valent Cr. Cycloheptatriene also forms a stable complex with Cr(CO)3 and its synthetic applications are discussed below. 

The cycloheptatriene complex undergoes cycloadditions with various unsaturated bonds, such as monoenes, dienes and alkynes, under mild conditions to afford interesting polycyclic compounds. In particular, the intramolecular version offers efficient methods for the construction of strained polycyclic skeletons, which are difficult to synthesize by other means [72]. 

Thus [6+2] cycloaddition of alkene with complex 306, bearing an optically active side chain, under irradiation at room temperature afforded the bicyclic compound 307 in 98% de [73]. According to the Woodward-Hoffmann rule, the [6+2] cycloaddition proceeds by irradiation, and is thermally forbidden. However, the cycloheptatriene complex 308 underwent 1,5-hydride shift, followed by [6+2] cycloaddition by heating, to give the tricyclic compound 309 in 90% yield [74], The cycloaddition was applied to the synthesis of /f-cedrene [75]. 

Photoreactions of [Cr(CO)3( /6-C7H8)] (41) with 6-mono- and 6,6-disub-stituted pentafulvenes (59a-59f) preferentially yield dicarbonyl complexes with substituted tj3 5-2-cyloheptadienylene-2-cyclopentadienylidenemethane chelate ligands (82,83). In the course of the reaction, C-6 of the fulvene forms a C—C bond to C-l of the 1,3,5-cycloheptatriene ligand, and one CO ligand is displaced. This reaction is of the same type as the formation of the f/3 5-[ 1 -(3-butene-1,2-diyl)-7-isopropylidenecycloheptadienyl] complexes 47c, 47e and 47t. The fulvene unit is transformed into a monosubstituted cyclo-pentadienyl entity, / -coordinated to the chromium, with the 1,3,5-cyclo-... 

While 154-157 are specific products for la, complexes of the type of 153a are the predominate products when 152 is reacted photochemically with acetylene (221), olefins (750,222,225), dienes, trienes, and tetraenes (224-226). In contrast to a previous report (227), 1,3,5-cycloheptatriene reacts with 152 like the other unsaturated hydrocarbons. Similar reaction products are obtained with lc as the diene component [Eq. (76)]. Although complexes comparable with 154,156, and 157 are missing, a trinulear species is formed... 

Other reports of (jj -allyl)Fe(CO)3R complexes are much more scattered and much less systematic. At least three general types of reactions have been observed in more than one case. First, the reaction of (diene)Fe(CO)3 complexes with electrophilic alkenes gives aUyhron complexes in two different ways. If the diene in question is acylic, electrophilic attack at C-1 of the diene gives compounds of type (158) (equation 33). In the case of substituted rj -cycloheptatriene-or azepine-Fe(CO)3 complexes, reaction... 

The reaction of 1,3-cyclohexadiene with FeCls in an ether solution of iso-C3H7MgBr produces the complex with mixed ligands (l,3-C,jHn Fe-(CflH(,) (204). Similarly by irradiation of FeClg with a mixture of 1,3,5-cycloheptatriene and 1,3-cycloheptadiene in the presence of iso-CsH7MgBr, Fischer and Muller (206) have prepared the air-sensitive and thermally unstable complex with mixed ligands (1,3,5-C7Hh)(1,3-C7Hio)Fe. Fe(CO)5 reacts with cycloheptatriene to produce not only... 

Although Able et al. (2, 8) had originally set out to prepare 7r-cyclo-heptatrienyl complexes of metals, the cycloheptatriene complexes they actually obtained served as key intermediates in forming the former complexes. In 1958 Dauben and Honnen (61) reported that cycloheptatriene-molybdenum tricarbonyl reacted with triphenylmethyl tetrafluoroborate in methylene chloride solution with abstraction of hydride ion from the molybdenum complex. The reaction products, obtained in nearly quantitative yields, were triphenylmethane and the 7r-cycloheptatrienyl complex [(7r-C7H7)Mo(CO)3]+BF4 . 

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