Carbonyl complexes of chromium, molybdenum and tungsten with isocyano acetate. Reactions of coordinated isocyanoacetate. Stabilization of isocyanoacetic acid and isocyanoacetyl chloride at the metal atom. Isocyanopeptides

摘要

The reactions of [(OC)(5)MCNCH2CO2Et] (M = Cr, W) with Na[N(SiMe3)(2)] or with KOH afford the isocyanoacetate complexes [(OC)(5)MCNCH2CO2](-) (1,2). Similarly, the complex [(OC)(3)Mo(CNCH2CO2-Li+)(3)] (4) was obtained from [(OC)(3)Mo(CNCH2CO2Et)(3)] (3) and LiOH. Protonation of 1 and 2 affords the sublimable isocyanoacetic acid complexes [(OC)(5)MCNCH2CO2H] (5, 6; M = Cr, W) in which the functional isocyanide is stabilized at the metal atom. Reactions of [(OC)(5)WCNCH2CO2-K+] and of [(OC)(3)Mo(CNCH2CO2-Li+)(3)] with oxalyl dichloride give the isocyanoacetyl chloride compounds [(OC)(5)WCNCH2COCl] (9) (sublimable) and [(OC)(3)Mo(CNCH2COCl)(3)] (10); the latter (10) was not isolated. Complexes 9 and 10 were reacted in situ with beta-alanine, glycine, phenylalanine and methionine esters as well as the peptide esters GlyGlyOEt, PhePheOMe, Phe-beta-AlaOMe, and Gly-GlyGlyOMe to form the isocyanoacetyl amino acid esters (11 - 14) and the isocyanoacetyl peptide esters (15 - 18) which are stabilized at the molybdenum atom.