Ligand-centred chemistry of molybdenum organoimides. Formation of C–C bonds via generation of nitrogen ylides, stereospecific conversion of an allylimide into alkylvinyl-imides, liberation of cyanoformate or amino acid esters

Abstract

The range of imides trans-[MoCl(NCHR¹R²)(dppe)₂]⁺ made from the nitride trans-[MoCl(N)(dppe)₂](dppe = Ph₂PCH₂CH₂PPh₂, R¹= H or organic group, R²= organic group) has been extended; deprotonation of the imide group at the α-carbon gives reactive alkenylamides which have nitrogen ylide character {MoN⁺–C^–HR} and these are attacked by electrophiles. Stepwise C₁ homologation of a methylimide to ethyl- and isopropyl-imides can be achieved by successive deprotonation and methylation steps. The crystal structure of the alkenylamide trans-[MoCl(NCHCO₂Me)(dppe)₂] has been determined, as has that of the imide produced directly from it by C-methylation, trans-[MoCl{NCH(Me)CO₂Me}(dppe)₂]⁺. Deprotonation at the α-carbon of an allylimide complex gives a species which is regioselectively and stereospecifically attacked by electrophiles at the γ-carbon; when the electrophile is the proton the overall reaction corresponds to a 1,3-prototropic rearrangement of the allylimide to the E-methylvinylimide. Electroreduction of imides in the presence of a source of protons releases the free amine; in this way esters of the amino acids glycine and DL-alanine have been synthesised. Two protons can be removed by base from imides with electron-withdrawing ester substituents and free cyanoformate esters are released from the metal centre by substitution with dinitrogen or CO.