Attachment of amino acid derivatives to tungsten carbonyl complexes via four component condensations

Mononuclear 4-aminoimidazolin-2-ylidene tungsten complexes [W(CO)5{CN(H)C(NHR1)C(R-2)NR3}] (1-10) have been synthesized by four component condensation (4CC) of [W(CN)(CO)(5)](-) with isocyanides (CNR1; R-1 = Cy, Bu-t), aldehydes ((RCHO)-C-2; R-2 = Bu-t, Ph), and amino acid ester hydrochlorides ((RNH3+Cl-)-N-3; amino acid = glycine, L-serine, L-phenylalanine, L-tyrosine, L-tryptophane, L-aspartic acid, L-glutamine). A dipeptide substituent in 1-position (8) resulted when GlyValOMe hydrochloride was employed as amine component, while two compounds with unprotected carboxylic acid groups (9, 10) were obtained from beta-alanine- and valerian acid-hydrochloride, respectively. 1,4-Terephthaldicarboxaldehyde as aldehyde component gave dinuclear bisheterocycle-bridged complexes 11-15. The claimed structure of the products is confirmed by an X-ray structure analysis of [W(CO)(5){CN(H)C((NHBu)-Bu-t)C(Bu-t)N(CH2COOMe)}] (1) which reveals a C-bound five-membered heterocycle with the amino acid substituent in 1-position. (C) 2002 Published by Elsevier Science B.V.