Syntheses, spectroscopy, and X-ray structures of 3-{(<i>R</i>)-(Ar)-ethylimino}-1,3-dihydro-indol-2-one (Ar = Ph, MeOC₆H₄, BrC₆H₄, 1-naphthyl) and [Rh(η⁴-cod){3-((<i>R</i>)-(Ar)-ethylimino)-3<i>H</i>-indol-2-olato}]

Abstract

Condensation of 1H-indole-2,3-dione (isatin) with (R)-(Ar)-ethylamines gives enantiopure Schiff bases, 3-{(R)-(Ar)-ethylimino}-1,3-dihydro-indol-2-one (HL) {Ar = Ph (HL1), 2-MeOC6H4 (HL2), 4-MeOC6H4 (HL3), 4-BrC6H4 (HL4), and 1-naphthyl (HL5)}. The Schiff bases readily coordinate to [Rh(μ-O2CMe)(η4-cod)]2 (cod = 1,5-cyclooctadiene) to give mononuclear [Rh(η4-cod){3-((R)-(Ar)-ethylimino)-3H-indol-2-olato}] {Ar = Ph (1), 4-MeOC6H4 (2), and 4-BrC6H4 (3)}, respectively. The Schiff bases and complexes have been fully characterized by IR, UV-Vis, 1H-NMR, mass, and circular dichroism (CD) spectrometry. Polarimetry and CD measurements show the enantiopurity of the Schiff bases as well as the complexes. 1H NMR measurements reveal slow conversion of the lactam to the enol form of the Schiff bases in solution. In the solid state the lactam form dominates as shown by crystal structures of HL1 and HL4. While gross structural features of both are similar, the molecules differ significantly in the relative orientations of the aryl and lactam rings. The difference is mostly rotation about the N2–C9 bond with different C8–N2–C9–C11 torsion angle of +89.77(12)° for HL1 and C2–N2–C9–C11 of +106.8(3)° for HL4.