Cycloheptatrienyl complexes reactions

Only one cycloheptatrienyl complex of the lanthanides is known nntil now. Reaction of Nd(BH4)3(THF)2 with K(C7H9) yields (THF)(BH4)2Nd(/x-) ) -C7H7)Nd (BH4)(THF)3 (Fignre 76). The X-ray stmcture determination shows a uniqne reverse-sandwich stmctnre with both Nd atoms r coordinated to the planar ligand. 

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 . 

Many cationic cycloheptatrienyl complexes are formed by reactions of various coordination compounds with CyHg in the presence of aluminum chloride or aluminum organometallic compounds/" ... 

The preparation of jr-cycloheptatrienyl complexes by ring expansion reactions is discussed in section A (c), (i). 

This review deals with metal-hydrocarbon complexes under the following headings (1) the nature of the metal-olefin and -acetylene bond (2) olefin complexes (3) acetylene complexes (4) rr-allylic complexes and (5) complexes in which the ligand is not the original olefin or acetylene, but a molecule produced from it during complex formation. ir-Cyclopentadienyl complexes, formed by reaction of cyclopentadiene or its derivatives with metal salts or carbonyls (78, 217), are not discussed in this review, neither are complexes derived from aromatic systems, e.g., benzene, the cyclo-pentadienyl anion, and the cycloheptatrienyl cation (74, 78, 217), and from acetylides (169, 170), which have been reviewed elsewhere. 

Trimetallic complexes with two identical cr,7r-bridging ring ligands having different ring sizes and numbers of tt attachments have been studied. The complexes with two bridging cyclohexadienyl (19a), cyclohepta-dienyl (19b), and cycloheptatrienyl (19c-f) ligands were synthesized by the nucleophilic addition reactions of dianionic carbonylmetallates, [M(C0)4]- (M = Os, Ru), and two equivalents of the appropriate cationic-metal allyl substrates (82). 

Reactions of anionic metal complexes with halide-bridged dimers can also be used to form a bond between two different metal atoms. Reaetion of (/j -C7H7)Fe(CO)3 with Mn2(CO)gBr2 gives ()j -C7H7)MnFe(CO)6 in which the cycloheptatrienyl ligand coordinates as a diolefin to manganese and as an allyl toward iron . 

Nucleophilic attack on coordinated unsaturated hydrocarbons is one of the fundamental and particularly well studied reactions in Organometallic Chemistry. The addition of carbonylme-tallates instead of common nucleophiles provides a directed synthesis of hydrocarbon bridged complexes. Carbonylmetallates (particularly Re(CO)5", Os(CO)4 ") add to 7C-bonded olefin, acetylene, allyl, diene, trimethylenemethane, dienyl, benzene, triene and cycloheptatrienyl ligands in cationic complexes and give hydrocarbon bridged bi- and trimetallic, homo- or he-teronuclear complexes [1]. 

Cycloheptatrienyl and cyclooctatetraene complexes may undergo oxidation and reduction reactions. In some cases, these processes are reversible ... 

Cycloheptatrienyl or cyclooctatetraene ligand displacement reactions are often utilized in the synthesis of other complexes. 

The reaction of the iron-carbene complex [[Bu C CC(OEt)=)Fe(CO)4] with 1,3-cyclohexadiene afforded223 (32), which was characterised by X-ray diffraction. The addition of the anionic derivatives of i-(diphenylmethane)-il-fluorene- and ii-(9,10-dihydroanthracene)-bis tricarbonylchromium to the hydrocarbon moiety (alkene, benzene, cyclohexadienyl, cycloheptadienyl and cycloheptatrienyl) in various cationic compounds of manganese, rhenium, iron, chromium, molybdenum, tungsten and cobalt was reported224 to provide a new route to hydrocarbon-bridged heteronuclear species such as (33). 

The thermal or photochemical Buchner reactions produce complex mixtures of cycloheptatrienyl esters, and the daunting complexity of the product mixtures was reduced or even eliminated with the advent of transition-metal catalysts, at first copper-based, then in the early 1980s rhodium(II) catalysts, which were developed by the Belgium group led by Noels and Hubert. The rhodium(II)-catalyzed cyclopropanations of aromatics, especially intramolecular cyclopropanations, have enjoyed a certain popularity due to their high regioselectivity and stereoselectivity. Since the intramolecular Buchner reaction is much more widely used in organic synthesis than the intermolecular version, the former is the focus of this review. 

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