Dilithium olefin complexes

K. Jonas, Dilithium-nickel-olefin Complexes. Novel Bimetallic Complexes From a Transition Metal and a Main Goup Metal, Angew. Chem. Int. Ed. Engl. 14, 752-753 (1975). 

The reactions described in Section II dealt with reactions of binary nickel(0)-olefin complexes with AmR, AmH, and AmPR2 and are characterized by the fact that the charge of alkali metal atoms is transferred to nickel and the respective 7r-ligands via C, H, or P atoms. That the charge from alkali metal atoms can also be directly transferred to nickel(O) -jr-lig-and systems is demonstrated in the syntheses (14, 31-33), structures (14, 34), and NMR data (18,35) of the dilithium-nickel-olefin complexes now described. 

A. Syntheses and Structures of Dilithium-Nickel-Olefin Complexes... 

The diamagnetic dilithium-nickel-olefin complexes (LiTMEDA)2-NiCDT (16) and [Li(THF)2 NiCCOD) (17) formed from CDTNi(O) (1) and (COD)2Ni(0) (2) by alkali metalation, as in Eqs. (14) and (15), represent the first examples of a new class of compounds of the d-elements in which alkali metals together with olefins are bonded to transition metals (31). 

Consequently, new dilithium-nickel-olefin complexes with tetra- or pentacoordinated nickel atoms are formed, e.g., the Li2Ni complexes Li2Ni[(CH3)2NCH2CHCHCH2N(CH3)2]3 (18), (LiTMEDA)2Ni(C2H4)3 (19), (LiTMEDA NifCVHw (20), and (LiTHF)2Ni(C4H6)3 (21), by reaction with N,N,N, TV -tetramethy lbutene-2-diamine, ethylene, norbor-nene, or butadiene (14, 31-33). 

After discovering that binary nickel(0)-olefin complexes react with lithium metal to give dilithium-nickel-olefin complexes, we were interested to find out whether alkali metal-transition metal-olefin complexes could be prepared with transition metals other than nickel. As the number of binary transition metal-olefin complexes which come into question for alkali metalation is still somewhat limited and because their preparations frequently require elaborate apparatus [co-condensation of transition metal atoms and olefins (40)], we sought a new route to this class of compounds, starting with compounds containing transition metals in higher oxidation states. 

In contrast to the dilithium-nickel-olefin complexes (Section III), the alkali metal-cobalt-olefin complexes Am[Co(C=C)4] (27) have a strong tendency to dissociate into ions just as Am[Co(CO)4] compounds do (52). The specific conductivities of 0.25 M THF solutions of 27 are x 10-3 O-1 cm-1 (-30°C). The values correspond to the values found for the saltlike nickel compounds 5 (Section II). That the complexes 27 can also... 

Two complexes containing a dilithiated stilbene fragment have been prepared and isolated from the reactions of 1,2-diphenylethane with N-chelated butyl-lithium reagents. " The molecular and crystal structures of these compounds, stilbene bis(lithium tetramethylethylenediamine) (Figure 4a) and stilbene bis(lithium pentamethyldiethylenetriamine) (Figure 4b), have been determined by X-ray diffraction techniques. Each structure contains two amine-solvated Li atoms located above and below the olefinic bond of a stilbene molecule. The stilbene molecule is planar in both structures, and is in a trans configuration about the C(7)—C(7 ) bond, which is ca. 0.01 nm longer than that in trans-stilbene. " The optical and "C n.m.r. spectra of THF solutions of the related dilithium and disodium salts of tetraphenylethylene dianion, as well as the spectra of their mixtures, have been examined. " The data can be rationalized in terms of the... 

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