A Practical Synthesis of [(tmeda)Ni(CH3)2], Isotopically Labeled [(tmeda)Ni(13CH3)2], and Neutral Chelated-Nickel Methyl Complexes

A practical procedure for the synthesis of N,N,N′,N′-tetramethylethylene diamine nickel dimethyl, [(tmeda)­Ni­(CH3)2] (5), based on commercially available methyllithium and [(tmeda)­Ni­(acac)2] (1) (acac = acetylacetonate), [(tmeda)­Ni­(OAc)2] (2) (OAc = acetate), [(tmeda)­NiSO4] (3), or [(tmeda)­NiF2] (4) has been developed. With 2 as the starting material, reproducible isolation of >14 g (ca. 68 mmol, 85%) of 5 in one-batch reactions is feasible. This synthetic route also enables the formation and isolation of 13C-labeled [(tmeda)­Ni­(13CH3)2] (5-13CH3) starting from 13CH3I by intermediate isolation of [(tmeda)2–3(Li13CH3)4]x (10). The amount of iodide impurities in 10 to push back iodide-catalyzed decomposition of 5-13CH3 to ethane and nickel black by a Kumada-type coupling is essential for successful isolation of 5-13CH3. [(tmeda)­Ni­(OAc)2] (2) is a superior nickel precursor to 5 in comparison to [(tmeda)­Ni­(acac)2] (1), as (a) removal of lithium acetate (9) from the crude reaction mixture is much easier than removal of lithium acetylacetonate and (b) κ2-N,O-salicylaldiminato nickel methyl complexes (12) or a κ2-P,O-phosphinesulfonato nickel methyl complex (14) can be easily prepared in a one-pot procedure starting from 2, methyllithium, and salicylaldimines (11) or phosphoniumsulfonate (13), respectively. The X-ray diffraction analyses of 2, 5, and 12b-PPh3 are reported.