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

Mononuclear 4-aminoimidazolin-2-ylidene tungsten complexes [W(CO)5{R3}] (1–10) have been synthesized by four component condensation (4CC) of [W(CN)(CO)5]− with isocyanides (CNR1; R1=Cy, tBu), aldehydes (R2CHO; R2=tBu, Ph), and amino acid ester hydrochlorides (R3NH3 +Cl−; 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 β-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{(CH2COOMe)}] (1) which reveals a C-bound five-membered heterocycle with the amino acid substituent in 1-position.