Lithium-benzene complexes structure

FIGURE 15. (a) X-ray structure of the jr-complexed lithium in the monomeric benzene complex of 2,6-bis(2,4,6-tri-isopropylphenyl)phenylhthium . (b) X-ray structure of the jr-complexed lithium in the dimeric 2,6-bis(2,6-di-isopropylphenyl)phenyUithium . It is evident from the Figure that the local environments around the lithium cations are similar... 

Biphenylbis(tricarbonyt)chromium (l).1 Lithium anthracenide converts biphenyl complexed by two Cr(CO), groups into a fairly stable dianion of structure 2, in which two V-cyclohexadienyl anions are coordinated with Cr(CO)3. This dianion is alkylated by an alkyl halide to form 3, in which one benzene ring is... 

Morton et al.135,141) were the first to study the poly(butadienyl)lithium anionic chain end using (b). They found no evidence of 1,2-chain ends and concluded that only 1,4-structures having the lithium cr-bonded to the terminal carbon were present. A later study by Bywater et al.196), employing 1,1,3,4-tetradeuterobutadiene to minimize the complexity of the spectrum that arises from proton-proton coupling, found that the 1 1 adduct with d-9 fert-butyllithium in benzene exists as a mixture of the cis and trans conformers in the ratio 2.6 1. Glaze et al. 36) obtained a highly resolved spectrum of neopentylallyllithium in toluene and found a cis trans ratio of about 3 1. 

The reactions of complex metal hydrides occur by an attack of the nucleophilic hydride ion on an electrophilic center.1 Aromatic nitrogen heterocycles in which the nitrogen has contributed only one electron to the -system (1) are electrophilic as compared with benzene, and have been shown to undergo reduction by the active reducing agent, lithium aluminum hydride. The nitrogen heterocycles in which the heteroatom has contributed two electrons to the 77-system (2) are electron-rich as compared with benzene and usually do not undergo reaction by reduction with complex metal hydrides.2 A combination of these two structural features, as in oxazoles (3), usually induces sufficient electrophilicity to allow attack by the hydride ion and reduction. 

---