Triphenylamine Derivatives with Para-Disposed Pendant Electron-Rich Organoiron Alkynyl Substituents: Defining the Magnetic Interactions in a Trinuclear Iron(III) Trication

The syntheses of two triarylamine derivatives featuring one and three electron-rich Fe(II) “(η2-dppe)(η5-C5Me5)FeCC–” pendant substituents in para position(s) on the aryl rings (1, 2) is reported, along with those of their corresponding radical tri- and monocations (1 3+ , 2 + ). The former species (1 3+ ) constitutes a new organometallic triradical. The magnetic interactions between the Fe(III) units in this novel trication were investigated by NMR and SQUID. Its ground spin state was shown to be a doublet, with a “mean” antiferromagnetic coupling constant of J ≈ −14 cm–1 between the unpaired spins, from consideration of the classic Hamiltonian for a symmetric C 3v triradical: H = −2J(S a ·S b + S b ·S c + S c ·S a ).