Complexes of Lithium

Many examples of the interaction between lithium and diverse it systems are documented in the literature. In the first review in this field Stucky (/) described the structure and bonding in it complexes of N-chelated lithium units. More recently, the synthesis and structure of organolithium compounds, including those containing unsaturated organic systems, have been reviewed by Wardell (2). A collection of X-ray crystal structure data of 

Copyright (0 1986 by Academic Press, Inc. All rights of reproduction in any form reserved. 

To the best of our knowledge, X-ray structural data of complexes with simple dihapto interactions between a lithium atom and the n system of an alkene or alkyne ligand are unknown, but there is some spectroscopic evidence for weak it interactions in solutions of 3-alkenyllithium compounds from 7Li-and H-NMR data (4). Interactions of this sort are presumably important in addition (polymerization) reactions between organolithium compounds and alkenes or alkynes. 

On the other hand, crystal structures of rather complicated mixed-metal organometallic it complexes are known the common feature in these species is the interaction of a lithium atom with a it ligand which is further complexed to a transition metal. Strong interactions between the lithium atoms and the transition metals are also indicated. Compounds of this type have previously been reviewed by Jonas (5,6) and by Schleyer and Setzer (3) and will not be discussed here. 

Recently, Boche et al. (5) have reported the synthesis of a highly interesting crystalline adduct of 1,3-diphenylallyllithium with diethyl ether. The crystal structure of this complex (I in Fig. 1) shows symmetrical it bonding between lithium atoms and allylic fragments. Each lithium atom interacts with two allylic 7t systems and further with the oxygen atom of a diethyl ether molecule. An exo, exo orientation of the phenyl ligands has been observed in this coordination polymer. 

---

The entrapment of lithium oxide and lithium halides by the lithium amidinate Li[Bu"C(NBu02] has been studied in detail by X-ray crystallography Interesting polycylic molecular structures have been obtained, as exemplified by the unusual sandwich complex of lithium oxide made from Li[Bu C(NBu )2l in toluene... 

Fig. 1. Energies of complex formation for complexes of lithium(I) in the gas phase with a variety of ligands. Data from Ref. (9).

It would be ideal if the asymmetric addition could be done without a protecting group for ketone 36 and if the required amount of acetylene 37 would be closer to 1 equiv. Uthium acetylide is too basic for using the non-protected ketone 36, we need to reduce the nucleophile s basicity to accommodate the acidity of aniline protons in 36. At the same time, we started to understand the mechanism of lithium acetylide addition. As we will discuss in detail later, formation of the cubic dimer of the 1 1 complex of lithium cyclopropylacetylide and lithium alkoxide of the chiral modifier3 was the reason for the high enantiomeric excess. However, due to the nature of the stable and rigid dimeric complex, 2 equiv of lithium acetylide and 2 equiv of the lithium salt of chiral modifier were required for the high enantiomeric excess. Therefore, our requirements for a suitable metal were to provide (i) suitable nucleophilicity (ii) weaker basicity, which would be... 

Many of the papers from Merck reported the 1 1 complex of lithium acetylide and lithium alkoxide of the chiral modifier as monomer and the dimer of the 1 1 complex as tetramer. 

An ab initio study of the energetics of deprotonation of cyclic vinyl ethers by organolithium reagents has clarified the ring-size-dependent competition between vinylic and allylic deprotonation.The respective transition states involve preequilibrium complexation of lithium to the electron-rich vinyl ether oxygen, prior to deprotonation via a multi-centre process free ions are not formed during the lithiation. 

In this particular case, remote control by the heteroatom of the substituent is invoked to explain the regioselectivity of the elimination. Complexation of lithium with both oxygens fixes the basic carbon atom close to the -proton . A similar model is proposed to rationalize the reversal to regiospecific a-deprotonation proximate to the hydroxyl group for oxiranes of type 23, the basic site now being close to the a-proton (Scheme 9) ° . 

The first report in this regard described a method for direct formation of the desired optically active (S)-alcohol 32a, via enantioselective reduction with a chiral amine complex of lithium aluminum hydride (Scheme 14.9). Therefore, the necessary chiral hydride complex 38 was preformed in toluene at low temperature from chiral amino alcohol 37. The resulting hydride solution was then immediately combined with ketone 31 to afford the desired (S)-alcohol 32a in excellent yield and enantiomeric excess. In addition to providing a more efficient route to the desired drug molecule, this work also led to the establishment of the absolute configuration of duloxetine (3) as S). 

In addition to the problem of the chemical bonding in metallole anions, these species may offer the promise of rich chemistry and lead to unusual structures. One example is provided by the synthesis and characterization of a novel trisgermole complex of lithium 140199 (eqUation 83). 

The phthalocyanine radical complex of lithium (PcLi ) is a member of the class of intrinsic molecular semiconductors [27]. Its preparation is carried out by electrosynthesis at 70°C under... 

The interactions between Li atom and diverse n systems yield many types of lithium n complexes. Figures 12.3.3(a)-(c) show the schematic representation of the core structures of some n complexes of lithium, and Fig. 12.3.3(d) shows the molecular structure of [C2P2(SiMe3)2]2 -2[Li+(DME)] (DME = dimethoxyethane). 

The most popular methods of preparing optically active l-octyn-3-ol involve asymmetric reduction of l-octyn-3-one with optlcally-active alcohol complexes of lithium aluminum hydride or aluminum hydride. These methods give optical purities and chemical yields similar to the method reported above. A disadvantage of these metal-hydride methods is that some require exotic chiral alcohols that are not readily available in both enantiomeric forms. Other methods include optical resolution of the racemic propargyl alcohol (100 ee) (and Note 11) and microbial asymmetric hydrolysis of the propargyl acetates (-15% ee for l-heptyn-3-ol)... 

Reductions with Complexes of Lithium Aluminum Hydride [Type 1]. 195... 

Landor and coworkers12 reasoned that, in complexes of lithium aluminum hydride with diols, the equilibrium represented by the equation would lie far to the left, and that reduction of aldehydes and... 

Evidence in favor of this theory was claimed13 when it was found that reduction of acetophenone with the 1 1 complex of lithium aluminum hydride and 5 to which one equivalent of ethanol had been... 

It was found that die stereoselectivity of reduction was increased by ethanol, and that (R)-l-phenylethanol was obtained in 70% optical yield when acetophenone (12.5 mmoles) was reduced with an ethanol-modified complex of lithium aluminum hydride with 3-O-benzyl-1,2-O-cyclohexylidene-a-D-glucofuranose prepared from the sugar derivative (26 mmoles), lithium aluminum hydride (58 mmoles), and ethanol (110 mmoles). 

Values of 7(M— C) Found for Complexes of Lithium, roron, Silicon, Germanium, Tin, Lead, Selenium, and Tellurium... 

Lithium bis(iminobenzoyl)phosphanides [41, 50] From the reaction of lithium bis(trimethylsilyl) phosphanide with two equivalents of benzonitrile at -50 °C the 1,2-dimethoxyethane complex of lithium bis(trimethylsilyliminobenzoyl)phosphanide is obtained in about 70 % yield (Eq. 19). and... 

Compared with metal enolates, there have been very few reports on the direct structural analysis and theoretical studies of ynolates. An X-ray crystal structure of a vanadium complex of lithium ynolate with a porphyrinogen ligand (56) is reported. This metal complex was incidentally formed from VCl3(THF)3 with tetralithium salt of the octaethyl-porphyrinogen ligand. In this complex, the lithium cation seems to interact with the 7T-electrons of the ynolate. The four atoms of the ynolate group in 56 are not collinear due to a partial sp character of the group in this complex. 

---