Nickel-olefin complexes

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. 

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). 

Both complex-bonded COD molecules in 17 can be quantitatively displaced by monoolefins or dienes. 

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). 

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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). 

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

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... 

The double bond is complexed to the nickel atom. The estimated upheld shift of approximately 25 ppm is, however, relatively small for zero-valent nickel olefin complexes. 

A number of nickel-olefin complexes have been described in recent years, many of these having nickel in its zero oxidation state. 

A reversible equilibrium between nickel-olefin complexes and 7t-allylnickel hydride complexes exists at low temperature ... 

Different types of compounds are formed by reactions of nickel olefin complexes with alkali metals. In these compounds, both alkene molecules and alkali metal atoms are bonded to nickel (Figure... 

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