A Convenient One-Pot Synthesis of a Sterically Demanding Aniline from Aryllithium Using Trimethylsilyl Azide, Conversion to β-Diketimines and Synthesis of a β-Diketiminate Magnesium Hydride Complex

Abstract

This work reports the one-pot synthesis of sterically demanding aniline derivatives from aryllithium species utilising trimethylsilyl azide to introduce amine functionalities and conversions to new examples of a common N,N′-chelating ligand system. The reaction of TripLi (Trip = 2,4,6-iPr3-C6H2) with trimethylsilyl azide afforded the silyltriazene TripN2N(SiMe3)2 in situ, which readily reacts with methanol under dinitrogen elimination to the aniline TripNH2 in good yield. The reaction pathways and by-products of the system have been studied. The extension of this reaction to a much more sterically demanding terphenyl system suggested that TerLi (Ter = 2,6-Trip2-C6H3) slowly reacted with trimethylsilyl azide to form a silyl(terphenyl)triazenide lithium complex in situ, predominantly underwent nitrogen loss to TerN(SiMe3)Li in parallel, which afforded TerN(SiMe3)H after workup, and can be deprotected under acidic conditions to form the aniline TerNH2. TripNH2 was furthermore converted to the sterically demanding β-diketimines RTripnacnacH (=HC{RCN(Trip)}2H), with R = Me, Et and iPr, in one-pot procedures from the corresponding 1,3-diketones. The bulkiest proligand was employed to synthesise the magnesium hydride complex [{(iPrTripnacnac)MgH}2], which shows a distorted dimeric structure caused by the substituents of the sterically demanding ligand moieties.

Alkyl backbone variations in common β-diketiminate ligands and applications to N-heterocyclic silylene chemistry

“…Installing two ethyl groups into the backbone unit, i.e. , forming EtAr nacnacH proligands, can be achieved by simply modifying a common acid-catalysed condensation reaction 22,32 according to Scheme 1. This requires stoichiometric para -toluenesulfonic acid hydrate ( p TsOH·H 2 O), an arene solvent such as toluene and heating under reflux with the use of a Dean–Stark trap to remove water from the condensation reaction system.…”

“…26,27 We have very recently introduced a one-pot condensation method to prepare iPrDip nacnacH 28 and this work expands on this backbone modification. We also consider EtAr nacnacH proligands which have been sporadically mentioned in the literature, 29–32 but in some cases without much synthetic or spectroscopic detail.…”