Homo- and heteroanionic alkali metal aza-enolate aggregates derived from o-methylvalerolactim ether

Reference:

Andrews, P. C., Bull, S. and Koutsaplis, M., 2010. Homo- and heteroanionic alkali metal aza-enolate aggregates derived from o-methylvalerolactim ether. New Journal of Chemistry, 34 (8), pp. 1678-1691.

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Official URL:

http://dx.doi.org/10.1039/c0nj00088d

Abstract

The reaction of o-valerolactim ether with BuM (M = Li, Na, K) in the presence of the Lewis donors thf, tmeda, pyridine and pmdta resulted in the crystallisation and structural characterisation of a series of homo- and heteroanionic aggregates, which are also either homo or heterobimetallic. All the structures incorporate an aza-enolate (1-aza-allyl) anion (= R) derived from deprotonation of the lactim ether at the alpha-C, and its subsequent electronic rearrangement such that the metal bonds to the amido N. Lithiation resulted in crystals of [R-3{R(Me2SiO)}Li-4 center dot(thf)(4)], 1, with Me2SiO- incorporated from the base induced decomposition of silicone grease; the linked dimer [R4Li4 center dot(tmeda)(3)], 2, which has both terminal and bridging tmeda molecules; the octanuclear cluster [R-6-mu(6)-O-Li-8 center dot(pyr)(2)], 3, which is constructed around an O2- anion; and [R(CH2=CHO)(2)Li-3 center dot pmdta](2), 4, which incorporates lithium ethenolate, the base induced decomposition product of thf. Sodiation resulted in crystals of the simple dimeric complex [RNa center dot tmeda](2), 5, while potassiation resulted in the heterobimetallic cluster [R(MeO)KLi center dot(tmeda)](4), 6, incorporating a MeO anion due to its nucleophilic displacement from the valerolactim ether as MeOK by Bu-n and subsequent anion exchange with (BuOLi)-Bu-t. Solution NMR studies on the reaction between RH and (BuLi)-Bu-t in the absence of a Lewis donor revealed that both the rate of deprotonation at the alpha-carbon and nucleophilic substitution of the ether functionality decrease substantially. The cyclic 2-Bu-t-imine, as the thermodynamic product, becomes the dominant product, indicating that a Lewis donor solvent is necessary for efficient deprotonation to occur.

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