Assessing the reactivity of sodium zincate [(TMEDA)Na(TMP)ZntBu2] towards benzoylferrocene: deprotonative metalation vs. alkylation reactionsElectronic supplementary information (ESI) available: Full experimental details and NMR spectra. CCDC reference numbers 838243838246. For ESI and crystallographic data in CIF or other electronic format, see DOI: 10.1039/c1dt11465d

• Main Authors: Hevia, Eva, Kennedy, Alan R, McCall, Matthew D
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c1dt11465d

Exploring the reactivity of the mixed-metal reagent [(TMEDA)Na(TMP)Zn t Bu 2 ] ( 1 ) towards substituted metallocene benzoylferrocene 2 , this study has found that two competing reactivity pathways are available for the sodium TMP-zincate, namely ( i ) remote 1,6-nucleophilic addition of a tert -butyl group to the phenyl ring of 2 , and ( ii ) simultaneous alpha -deprotonation of the substituted cyclopentadienyl ring of the metallocene and alkylation (1,2-addition) across the C&z.dbd;O bond of the carbonyl group. A key organometallic intermediate [(TMEDA)Na(-TMP)Zn{OC( t Bu)(Ph)( 5 -C 5 H 3 )Fe( 5 -C 5 H 5 )}] ( 3 ), resulting from the latter reaction has been trapped and characterised by X-ray crystallography and multinuclear ( 1 H and 13 C) NMR spectroscopy. Its molecular structure revealed a unique two-fold activation of the tert -butyl groups bonded to zinc in the bimetallic base 1 , showing for the first time that each alkyl group can exhibit markedly different reactivities (deprotonation vs. 1,2-addition) towards the same substrate molecule. Iodine interception of the organometallic intermediates of the reaction between 1 and 2 allowed the isolation and characterization ( 1 H, 13 C NMR and X-ray crystallography) of the ferrocenyl derivatives [PhC(OH)( t Bu)( 5 -C 5 H 3 I)Fe( 5 -C 5 H 5 )] ( 4 ) and [4- t Bu-C 6 H 4 C(&z.dbd;O)( 5 -C 5 H 4 )Fe( 5 -C 5 H 5 )] ( 5 ) in a 29% and 24% isolated yield respectively. The low yield observed for the formation of 5 (resulting from the 1,6-addition reaction followed by spontaneous aerobic oxidation during aqueous workup) could be increased to 41% when the reaction mixture was hydrolysed in the presence of the radical oxidant TEMPO. Studies on the reactivity of sodium zincate [(TMEDA)Na(TMP)Zn t Bu 2 ] ( 1 ) with benzoylferrocene ( 2 ) have shown that the simultaneous two-fold -deprotonation/1,2-addition of the metallocene competes with a remote 1,6-addition process of a t Bu group to a phenyl group followed by aerobic oxidation.