Synthesis of an alkylmagnesium amide and interception of a ring-opened isomer of the important utility amide 2,2,6,6-tetramethylpiperidide (TMP)

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Kennedy, Alan and Klett, Jan and McGrath, Graeme and Mulvey, Robert and Robertson, Gemma and Robertson, Stuart and O'Hara, Charles (2014) Synthesis of an alkylmagnesium amide and interception of a ring-opened isomer of the important utility amide 2,2,6,6-tetramethylpiperidide (TMP). Inorganica Chimica Acta, 411. pp. 1-4. ISSN 0020-1693 (https://doi.org/10.1016/j.ica.2013.11.015)

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Abstract

Two new magnesium complexes containing the important utility amide 2,2,6,6-tetramethylpiperidide (TMP) have been synthesised. Treating the magnesium bis(alkyl) reagent (Me3SiCH2)2Mg with a molar equivalent of TMP(H) in hydrocarbon medium produces the dimeric alkylmagnesium amide complex [(Me3SiCH2)Mg(μ-TMP)]22, which was isolated in high yield. X-ray crystallography revealed that 2 was an unsymmetrical dimer as unusually the two TMP ligands adopt different conformations – one a chair, the other a twisted boat. Solution studies (multinuclear NMR and DOSY NMR spectroscopies) show that 2 undergoes a monomerisation and Schlenk equilibrium in d8-THF. When (Me3SiCH2)2Mg was reacted with two molar equivalents of TMP(H) in hydrocarbon medium [in an effort to prepare Mg(TMP)2] a crystalline sample of a surprising product, a tetranuclear triheteroanionic amide-alkoxide-amidoalkene [(TMP)Mg(μ-TMP){μ-N(H)C(Me)2CH2CH2CH2C(Me) = CH2}Mg(μ-OCH2SiMe3)]23 was obtained. Complex 3 contains two unexpected anions, namely the alkoxide produced via oxygen insertion into a Mg–C bond, and the primary amidoalkene which is produced via ring opening of the TMP anion.

ORCID iDs

Kennedy, Alan ORCID logoORCID: https://orcid.org/0000-0003-3652-6015, Klett, Jan, McGrath, Graeme, Mulvey, Robert ORCID logoORCID: https://orcid.org/0000-0002-1015-2564, Robertson, Gemma, Robertson, Stuart ORCID logoORCID: https://orcid.org/0000-0002-9330-8770 and O'Hara, Charles;
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