Heterobimetallic Complexes That Bond Vanadium to Iron, Cobalt, and Nickel

Zero-valent iron, cobalt, and nickel were installed into the metalloligand V­[N­(<i>o</i>-(NCH₂P­(ⁱPr)₂)­C₆H₄)₃] (<b>1</b>, VL), generating the heterobimetallic trio FeVL (<b>2</b>), CoVL (<b>3</b>), and NiVL (<b>4</b>), respectively. In addition, the one-electron-oxidized analogues [FeVL]­X ([<b>2</b>^<b>ox</b>]­X, where X^– = BPh₄ or PF₆) and [CoVL]­BPh₄ ([<b>3</b>^<b>ox</b>]­BPh₄) were prepared. The complexes were characterized by a host of physical methods, including cyclic voltammetry, X-ray crystallography, magnetic susceptibility, electronic absorption, NMR, electron paramagnetic resonance (EPR), and Mössbauer spectroscopies. The CoV and FeV heterobimetallic compounds have short M–V bond lengths that are consistent with M–M multiple bonding. As revealed by theoretical calculations, the M–V bond is triple in <b>2</b>, <b>2</b>^<b>ox</b>, and <b>3</b>^<b>ox</b>, double in <b>3</b>, and dative (Ni → V) in <b>4</b>. The (d–d)¹⁰ species, <b>2</b> and <b>3</b>^<b>ox</b>, are diamagnetic and exhibit large diamagnetic anisotropies of −4700 × 10^–36 m³/molecule. Complexes <b>2</b> and <b>3</b>^<b>ox</b> are also characterized by intense visible bands at 760 and 610 nm (ε > 1000 M^–1 cm^–1), respectively, which correspond to an intermetal (M → V) charge-transfer transition. Magnetic susceptibility measurements and EPR characterization establish <i>S</i> = ¹/₂ ground states for (d–d)⁹ <b>2</b>^<b>ox</b> and (d–d)¹¹ <b>3</b>, while (d–d)¹² <b>4</b> is <i>S</i> = 1 based on Evans’ method