Chelated assisted metal-mediated N-H bond activation of β-lactams: Preparation of irida-, rhoda-, osma-, and ruthenatrinems

Abstract

2-Azetidinones substituted with pyridine (2a), quinoline (2b), isoquinoline (2c), imidazole (2d), and benzimidazole (2e) at the 4-position of the four-membered ring have been prepared in order to synthesize tribactams containing a transition metal and its associated ligands, LnM, at the 2-position of the tricyclic skeleton. The developed procedure is compatible with a wide range of transition-metal starting complexes. Thus, the iridium and rhodium dimers [M(η5-C5Me5)Cl 2]2 react with 2a-e, in the presence of sodium acetate, to afford irida- and rhodatrinems (1a-j) containing the half-sandwich d 6 metal fragments M(η5-C5Me5)Cl (M = Ir, Rh). The reactions of [M(μ-OMe)(η4-COD)]2 (M = Ir, Rh) with 2a lead to irida- and rhodatrinems (1k,l) with the d 8 moieties M(η4-COD). The coordination sphere and oxidation state of the metal center in these compounds can be modified, without affecting the 2-azetidinone backbone, by means of substitution and oxidative addition reactions. As a proof of concept, metallatrinems with the M(CO) 2 (M = Ir (1m), Rh (1n)) and Ir(Me)I(CO)2 (1o) units are also reported. Osmatrinems 1p,q containing the d4 metal fragment OsH3(PiPr3)2 have been obtained starting from the d2 hexahydride OsH6(PiPr 3)2, by reaction with 2a,b, whereas the treatment of the tetrahydroborate complexes MH(η2-H2BH 2)(CO)(PiPr3)2 (M = Os, Ru) with 2a yields osma- and ruthenatrinems (1r,s) containing six-coordinate bis(phosphine) d6 metal fragments. The IR stretching frequency of the lactamic carbonyl, the bent angle between the five- and four-membered rings of the tricycle, and the N-CO bond length in the lactamic ring are clearly infuenced by the LnM fragment. © 2014 American Chemical Society.