名称:
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
摘要:
The range of imides trans-[MoCl(NCHR(1)R(2))(dppe)(2)](+) made from the nitride trans-[MoCl(N)(dppe)(2)] (dppe = Ph(2)PCH(2)CH(2)PPh(2), R(1) = H or organic group, R(2) = organic group) has been extended; deprotonation of the imide group at the alpha-carbon gives reactive alkenylamides which have nitrogen ylide character {Mo=N+-C(-)HR} and these are attacked by electrophiles. Stepwise C-1 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(NCHCO(2)Me)(dppe)(2)] has been determined, as has that of the imide produced directly from it by C-methylation, trans [MoCl{NCH(Me)CO(2)Me}(dppe)(2)](+). Deprotonation at the alpha-carbon of an allylimide complex gives a species which is regioselectively and stereospecifically attacked by electrophiles at the gamma-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.