Ketyl Radicals Generated from Magnesium(I) Compounds: Useful Reagents for C-C Bond Forming Reactions

The aryl ketones, 9-fluorenone (fluor), 9-xanthenone (xanth) and 9,10-anthraquinone (anth), were reacted with beta diketiminato dimagnesium(I) compounds, [{((Ar)Nacnac)Mg}(2)] ((Ar)Nacnac=[HC(MeCNAr)(2)](-), Ar= mesityl (Mes) or 2,6-diisopropylphenyl (Dip)). This gave stable magnesium ketyl complexes which are monomeric, [((Ar)Nacnac)(DMAP)Mg(fluor(center dot))] (Ar= Mes or Dip, DMAP= 4-dimethylaminopyridine) and [((Mes)Nacnac)Mg(xanth(center dot))(xanth)]; dimeric, [{((Mes)Nacnac)Mg(mu-fluor(center dot))}(2)], or tetrameric, [{((Dip)Nacnac)Mg(mu-anth(center dot))}(4)]. In contrast, di-2-pyridylketone (OCPy2) is doubly reduced with [{((Xyl)Nacnac)Mg}(2)] (Xyl= xylyl) to give a diamagnetic alkoxy/ amido complex, [{(XylNacnac)Mg}(2)(mu-OCPy2)]. These complexes have been characterized by X-ray crystallography, and in three cases, EPR spectroscopy. Regioselective C-C hetero- coupling reactions between magnesium ketyls and phenanthroline (phen) have yielded the alkoxy compounds, [(MesNacnac)Mg(OCR2-2-phen)] (OCR2= xanth, OCPh2 or OC(Ph)(2-Me Ph)). In addition, homo- C C couplings of the enones, chalcone (chalc) and dibenziylideneactetone (DBA), using magnesium(I) reducing agents, have afforded dimagnesium enolates, [{(ArNacnac)(THF)Mg}2(mu-chalc(2))] (Ar= Mes or Xyl) and [{((Dip)Nacnac)(THF)Mg}(2)(mu-DBA(2))]. A pinacol coupling reaction between [{((Dip)Nacnac)Mg}(2)] and 2-adamantanone (OAd) yielded [{((Dip)Nacnac)(OAd)Mg}(2)(mu-OAd(2))], presumably via a ketyl intermediate. This study further highlights the utility magnesium(I) compounds have as selective reducing agents in organic transformations.

Automated summary

The study shows that aryl ketones can react with beta diketiminato dimagnesium(I) compounds to form stable magnesium ketyl complexes, which can undergo selective C-C coupling reactions.