Transmetallation from Mercury

It can be seen that the pseudocyclic intermediate (84a) strongly resembles the stable alkylperoxy-mercury compound (84b) prepared from the reaction of TBHP with an alkene in the presence of mercury(II) carboxylate.238 The X-ray structure of the similar BrHg CH(Ph)CH(Ph)(OOBu1) compound has clearly shown the pseudocyclic nature of this adduct by the interaction existing between mercury and the OBu1 group.259 The transmetalation of mercury by palladium in (84b) produces acetophenone in 95% yield, presumably via the formation of the pseudocyclic intermediate (85 equation 85).42... 

In the initial studies about the reaction of /V.zV-disubstituted formamides with alkaline metals to give glyoxylic amides, the participation of carbamoyl metal derivatives as intermediates was postulated83. The first preparation of the carbamoyllithium 77 was described two years later by a mercury-lithium transmetallation from compound 76 at —75 °C (Scheme 20)84. The authors proposed also an aminocarbene structure 78 and studied its reactivity with methanol, methyl iodide, carbonyl compounds, esters, acyl chlorides, mercury(II) chloride and tri-n-butyltin chloride providing compounds 79. 

Vinyl selenides have been lithiated at the a-position by LDA983,984 at —78 °C in THF to give a-(arylselanyl)vinyllithiums 680, a-(methylselanyl)vinyllithiums 681 being obtained by selenium-lithium transmetallation from l,l-bis(methylselanyl)alkenes with n-BuLi in THF or t-BuLi in ether at —78 °C985 986. These intermediates reacted with alkyl halides, epoxides, carbonyl compounds and DMF985, the final deprotection being performed by mercury(II) salts986. 

Organoaluminum compounds, particularly AlEt3, are commercially very important as activators for olefin polymerization catalysts and are produced on a large scale, in spite of their pyrophoric nature and violent reaction with water. In the laboratory organoaluminum compounds can be made from mercury alkyls by transmetallation ... 

Other small-scale laboratory procedures have been developed for the direct synthesis of the more reactive THF adducts, avoiding inconvenient high temperature treatment [59-62]. For example, the preparation of LnCl3(thf)x from metal powder and hexachloroethane is facilitated by sonication [Eq. (1)] [59]. Additional metal-based synthetic routes include the redox transmetallation with mercury(II) halides [Eq. (2)] [60] and the reaction with trimethylsilyl chloride and anhydrous methanol [Eq. (3)] [61]. Ammonia has been employed as an alternative donating solvent in the synthesis of lanthanide alkoxides starting from lanthanide chlorides [63]. 

Colourless alkyl derivatives of Na and K are obtained by transmetallation reactions starting from mercury dialkyls (equation 18.4). 

Bis(pentafluorophenyl) ytterbium is prepared similarly by transmetallation from ytterbium metal and bis(pentafluorophenyl) mercury (Deacon and Vince, 1976 Deacon et al., 1977, 1979). The complex (CgFjjjYb (THF)4 is characterized by infrared, ultraviolet, and F NMR spectra. Evidence is presented for green (CgFjjjEu (Deacon et al., 1979), and less stable derivatives (CgHF4)2Yb with the... 

Transmetallation of silylmercury compounds, which are most easily available via the reaction of a silane with (/-Bu)2llg, appears to be the most convenient method for the preparation of cyclic potassium oligosilyl compounds c-(MegSis)K (19)83c as well as c-(MenSi6)K (20)84 were obtained by Hengge and coworkers from the corresponding mercury compound by means of a Na/K alloy in THF (equation 33). 

Transmetallation is a more convenient method to obtaining divalent organolanthanide complexes from lanthanide metals. Reaction of lanthanide metal powder with a mercury alkyl or aryl complex affords the corresponding divalent lanthanide complex (Equation 8.28) [94]. The preparation of divalent perfluorophenyl lanthanide complexes Ln(C6F5)2(THF) (Ln = Eu, n = 5 Ln = Yb, n=4) is a typical example. In most cases, the addition of a small amount of Lnl3 leads to acceleration of the reaction [95]. 

Similar transmetallation reactions using mercury reagents of the form At2Hg have been performed by Clark and coworkers to deliver osmium complexes Os[77 -C,N-(2-phenylpyridyl)Cl(CO)(PPh3)2] 75 from 74 (Equation 19) <19990M2813, 2000JOM262>. 

Anhydrous lanthanide trihalides, particularly the trichlorides, are important reactants for the formation of a variety of lanthanide complexes, including organometallics. Routes for the syntheses of anhydrous lanthanide trihalides generally involve high temperature procedures or dehydration of the hydrated halides.The former are inconvenient and complex for small scale laboratory syntheses, while dehydration methods may also be complex and have limitations, for example, use of thionyl chloride. - Moreover, the products from these routes may require purification by vacuum sublimation at elevated temperatures. Redox transmetalation between lanthanide metals and mercury(II) halides was initially carried out at high temperatures. However, this reaction can be carried out in tetrahydrofuran (THF, solvent) to give complexes of lanthanide trihalides with the solvent. These products are equally as suitable as reactants for synthetic purposes as the uncomplexed... 

---