Synthetic and reactivity studies of hetero-tri-anionic sodium zincates

Francos, Javier and Kennedy, Alan R. and O'Hara, Charles T. (2016) Synthetic and reactivity studies of hetero-tri-anionic sodium zincates. Dalton Transactions, 45 (14). pp. 6222-6233. ISSN 1477-9234

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    Abstract

    The synthesis and characterisation of several sodium zincate complexes is reported. The all-alkyl monomeric sodium zincate (PMEDTA)·Na(μ-CH2SiMe3)ZntBu2 2, is prepared by combining an equimolar quantity of tBu2Zn, nBuNa and PMDETA (N,N,N′,N′′,N′′-pentamethyldiethylenetriamine)]. A similar approach was used to prepare and isolate the unusual dimeric zincate [(PMEDTA)·Na(μ-nBu)ZntBu2]2 3. When an equimolar mixture of nBuNa, tBu2Zn and TMP(H) (2,2,6,6-tetramethylpiperidine) are combined in hexane, the hetero-tri-leptic TMP(H)-solvated zincate (TMPH)Na(μ-TMP)(μ-nBu)ZntBu 4 was forthcoming. Complex 4 can also be prepared using a rational approach [i.e., utilising two molar equivalents of TMP(H)]. When TMEDA is reacted with an equimolar mixture of nBuNa, tBu2Zn and TMP(H), the monomeric sodium zincate (TMEDA)Na(μ-TMP)(μ-nBu)ZntBu 5 was obtained – this complex is structurally similar to the synthetically useful relation TMEDA)·Na(μ-TMP)(μ-tBu)Zn(tBu) 1. By changing the sodium reagent used in the synthesis of 5, it was possible to prepare (TMEDA)Na(μ-TMP)(μ-Me3SiCH2)ZntBu 6. By reacting 5 with cis-DMP(H) (cis-2,6-dimethylpiperidine), the zincate could thermodynamically function as a amide base, to give the transamination product (TMEDA)Na(μ-cis-DMP)(μ-nBu)ZntBu 7, although no crystals could be grown. However, when HMDS(H) (1,1,1,3,3,3-hexamethyldisilazane) or PEA(H) [(+)-bis[(R)-1-phenylethyl]amine] is reacted with 5, crystalline (TMEDA)Na(μ-HMDS)(μ-nBu)ZntBu 8 or (TMEDA)Na(μ-PEA)(μ-nBu)ZntBu 9 are isolated respectively. With PNA(H) (N-phenylnaphthalen-1-amine) the reaction took a different course and resulted in the formation of the dimeric sodium amide complex [(TMEDA)Na(PNA)]2 10. When reacted with benzene, it appears that a TMEDA-free variant of 5 functions thermodyanically as an nBu base to yield the previously reported (TMEDA)Na(μ-TMP)(tBu)Zn(μ-C6H4)Zn(tBu)(μ-TMP)Na(TMEDA) 11. Finally when reacted with TEMPO (2,2,6,6-tetramethylpiperidinyloxy), 5 undergoes a single electron transfer reaction to form (TMEDA)Na(μ-TMP)(μ-TEMPO)ZnnBu 12.