Aminolysis of 3-alkoxysubstituted cyclobutenylidene complexes. A novel convenient route to chiral 3-aminosubstituted cyclobutenylidene complexes

Aminolysis of 3-alkoxycyclobutenylidene complexes offers a convienient and high-yield route to a variety of 3-aminocyclobutenylidene complexes. Thus, the 3-diethylaminocyclobutenylidene complexes [(CO)5CrR2)] [(4), R2(CH2)5 (a), Me2 (b), Ph2 (c)] are obtained by substitution of NEt2 of diethylamine for the ethoxy group in [(CO)5CrR2)] (3a–c). The reactions of (R)N-methyl-1-phenylethyl amine and of (S)-2-methoxymethyl-pyrrolidine with 3a–c afford the 3-N-methyl-(1-phenylethyl)amino- and 3-(2-methoxymethyl-pyrrolidino)-substituted cyclobutenylidene complexes, respectively, as mixtures of the E and Z isomers (with respect to the C3N bond). Mixtures of the E and Z isomers of 3-(amino acid ester)-substituted cyclobutenylidene complexes are obtained from 3a,b and the methylester of l-leucine, l-phenylalanine, and l-methionine in yields ranging from 82 to 94%. The E/Z ratio strongly depends on the amino acid and the substituents at the sp3-C atom of the cyclobutenylidene ring. The reactions of 3a–c with cysteine, H2NC2H4SH, proceed highly selectively. Only 3-aminocyclobutenylidene complexes are isolated in 73–86% yield. The formation of 3-organylthiocyclobutenylidene complexes has not been detected. The structure of the E-leucinyl methylester-substituted complex has been established by an X-ray structural analysis.