Chelated Assisted Metal-Mediated N–H Bond Activation of β‑Lactams: Preparation of Irida‑, Rhoda‑, Osma‑, and Ruthenatrinems

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)­Cl2]2 react with 2a–e, in
the presence of sodium acetate, to afford irida- and rhodatrinems
(1a–j) containing the half-sandwich
d6 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
d8 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(PiPr3)2, by reaction with 2a,b, whereas the treatment of the tetrahydroborate complexes MH­(η2-H2BH2)­(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.