Chromium complexes cycloheptatriene

A transmetalation of the styrylcarbene chromium complex 62 in the presence of stoichiometric amounts of [Ni(cod)2] to give the nickel carbene intermediate 63 was applied to the synthesis of Cr(CO)3-coordinated cycloheptatriene 64 upon reaction with terminal alkynes [57] (Scheme 37). The formation of pen-tacarbonyl(acetonitrile)chromium is expected to facilitate the metal exchange. 

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... 

Typical TLC data (silica gel, 6 1 hexanesiethyl acetate) include R - 0.61 (1-acetoxy-1,3-butadiene) 0.51, a red spot [tricarbonyl(cycloheptatriene)chromium] 0.45 a yellow spot (side product that often overlaps with the starting complex) and 0.31 a yellow spot (main intermediate chromium complex). 

Cycloheptatriene enol complexes, with chromium carbonyls,... 

The x-ray crystal analysis of thiepine 1,1-dioxide chromium complex (15) has been conducted (Figure 1) <93JA1382>. The uncomplexed S atom is puckered and the complexed C(2)-(7) atoms are in a plane. The conformation is similar to that of (cycloheptatriene)tricarbonylchromium(O). 

Hydrogen migrations in chromium complexes of cycloheptatriene are discussed. ... 

The same resolution can be efficiently carried out on structurally more complex compounds that are optically active for the helical structure of the molecule, i.e., bis(hydroxymethyl) thiaetherohelicene [160]. In this way, a nearly optically pure helical molecule can be obtained (Scheme 33). This method has been successfully applied also to resolution of organometallic compounds and a few interesting results are shown in Scheme 34. Tiicarbonyl [(ir (6)-cycloheptatriene)chromium(0)] and ferrocenyl alcohols have been examined as substrates of the lipase-catalyzed acylation, and the reaction can be accomplished in a highly enantioselective manner [161,162]. 

The metal-mediated and metal-catalyzed [6 + 2]- and [6 + 4]-cycloaddition reactions, pioneered by Pettit and co-workers105 106 and Kreiter and co-workers,107 respectively, involve the cycloaddition of metal-complexed cyclic trienes with 7r-systems such as alkenes, alkynes, and dienes. The [6 + 2]-reactions produce bicyclo[4.2.1]nonadiene derivatives and the [6 + 4]-reactions produce bicyclo[4.4.1]undecatrienes (Scheme 32). Trienes complexed to chromium, which can be prepared on large scale (40 g) as reported by Rigby and co-workers,108 react with 7r-systems upon thermolysis or irradiation.109-111 Chromium and iron-catalyzed [6 + 2]-reactions of cycloheptatrienes and disubstituted alkynes... 

Although disubstituted alkynes are used successfully as two-carbon components in chromium-mediated and -catalyzed [6 + 2]-reactions, the use of terminal alkynes produces a [6 + 2 + 2]-reaction (Section 10.13.3.7). Buono and co-workers have discovered that when a cobalt catalyst is employed, several monosubstituted alkynes can be used in [6 + 2]-cycloadditions with cycloheptatriene (Scheme 35). The use of a chiral BINOL-phosphoramidite cobalt complex affords an enantioselective [6 + 2]-cycloaddition reaction (Equation (18)).121... 

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). 

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. 

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-... 

Bis[dw-butyLphosphano] tellurium replaces norbornadiene, cycloheptatriene, acetonitrile, and dimethyl(methylene)oxosulfurane in chromium, molybdenum, and tungsten complexes. The P —Te compound acts as a bidentate ligand with the two phosphorus atoms coordinated to the metal atom1. The tetracarbonylchromium complex [R = CH(CH3)J can be recrystallized without loss of tellurium2. 

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