Dimers organolithium reagents

Trialkylated borazines R3B3N3H3 are deprotonated by organolithium reagents, but other reaction pathways also occur.For example, the reaction of Me3B3N3H3 with one equivalent of methyllithium produces the solvated monolithium derivative [(Me3B3N3H2)Li(OEt2)]2 (9.9), which is dimeric in the solid state. The formation of di- or trilithiated derivatives. 

The reacuons of electrophihc tnflyl sources with nucleophiles were investi gated The reaction of tnfhc anhydride with an organolithium reagent is not synthetically promising because of ditnflylation and other side reactions [20] When phenyllithium reacts with tnfhc anhydnde, dimerization products and acetylenic Michael diadducts are observed [20] (equation 17), but using the sodium salt of the alkynes instead of the lithium salt provides the alkynyl tnfluoromethyl sulfones [21] (equation 18) (Table 7) Alkynyl tnfluoromethyl sulfones are of synthetic interest, because they show a pronounced reactivity toward nucleophiles in addition reactions and cyclopentadiene in Diels-Alder reactions [21] (Table 7)... 

A number of gold - -gold(I) dimers of the type [Au(o-C.P) 2 containing orf/ro-metallated arylphosphanes (see Table V) have been prepared by reaction of the organolithium reagents with [AuBr(PEt3)] in diethyl ether at low temperature... 

Wittig-type olefinations can also be performed using selenoaldehydes. Phosphorus ylides initially attack the carbon atom of the selenocarbonyl functionality.405 Aromatic selenoketones undergo reductive dimerization with organo-lithium reagents probably via an electron transfer mechanism.406 Also the addition of organolithium reagents takes... 

A peculiar property of the bis(iminophosphoryl)methanes is the facile mono and deprotonation of the methyene bridge with organolithium reagents. Thus, with H2C(NPPh2NSiMe3)2 unusual dimeric lithium complexes were obtained (Scheme 40) and Ti, Zr, Hf carbene complexes were formed with the same doubly deprotonated ligands. ... 

The anionic derivatives of cyclodiphosph(V)azanes, obtained by deprotonation of [RNH(Q)PNR]2 (Q = O, S, Se) with organolithium reagents are versatile ligands, forming unusual metal complexes. These cyclic dimers also react with A1Mc3 to form dimethylaluminum derivatives. ... 

Organolithium reagents (RLi) are tremendously important reagents in organic chemistry. In recent years, a great deal has been learned about their structure in both the solid state and in solution. X-ray analysis of complexes of n-butyllithium with A,A,A, A -tetramethylethylenediamine (TMEDA), THF, and 1,2-dimethoxyethane (DME) shows them to be dimers and tetramers [e.g., (BuLi DME)4]. X-ray analysis of isopropyllithium shows it to be a hexamer. 

As further illustrated in Scheme 2, the 1-methyl- and 1,3,3-trimethylcyclopropene are rapidly metallated with organolithium reagents in ether to afford stable solutions of the 1-lithiocyclopropenes (18) In comparison, solutions of the metallocyclopropenes (16) are significantly less stable and even at — 40°C are observed to degrade slowly to a mixture of dimeric and trimeric products apparently formed by nucleophilic addition of 16 to the highly reactive cyclopropene n system L Alkylation of 18 (R=H or Me) with methyl iodide produced 1,2-dimethyl- and 1,2,3,3-tetramethylcyclopropene . The trimethyl derivative 18 (R = Me) has also been carbonated and acylated to afford the corresponding 2,3,3-trimethylcyclopropene carboxylic acid, methyl ketone and carboxaldehyde. 

The reactivity of the organolithium compounds is increased by adding molecules capable of solvating the lithium cations. Tetramethylenediamine (TMEDA) is commonly used for organolithium reagents. This tertiary diamine can chelate lithium. The resulting complexes generally are able to effect deprotonation at accelerated rates.In the case of phenyllithium, NMR studies show that the compound is tetrameric in 1 2 ether-cyclohexane, but dimeric in 1 9 TMEDA-cyclohexane. ... 

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