Electroreduction of co-ordinated cyanide to the aminocarbyne ligand (CNH2) and a pathway for isomerisation of ligating methyleneamide (NCH2): reactions at molybdenum of relevance to cyanide reduction by nitrogenase
作者:David L. Hughes、Modher Y. Mohammed、Christopher J. Pickett
DOI:10.1039/c39890001399
日期:——
Electroreduction of trans-[Mo(CN)Cl(Ph2PCH2CH2 PPh2)2] in the presence of phenol gives trans-[Mo(CNH2)Cl(Ph2PCH2 CH2PPh2)2], this is the first example of the conversion of co-ordinatedcyanide to the aminocarbyneligand, a reaction of relevance to reduction of cyanide by nitrogenase; the methyleneamide, trans-[Mo(NCH2)Cl(Ph2PCH2 CH2PPh2)2], is oxidised to the cyanide and therefore the redox reactions
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
作者:Shirley A. Fairhurst、David L. Hughes、Saad K. Ibrahim、Marie-Laurence Abasq、Jean Talarmin、M. Arlete Queiros、Antonio Fonseca、Christopher J. Pickett
DOI:10.1039/dt9950001973
日期:——
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 [MoClNCH(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.