Boronated Cyanometallates

Thirteen boronated cyanometallates [M(CN-BR3)6]3/4/5– (M = Cr, Mn, Fe, Ru, Os; BR3 = BPh3, B(2,4,6,-F3C6H2)3, B(C6F5)3) and one boratonitrile [Cr(NC-BPh3)6]3– have been characterized by X-ray crystallography and spectroscopy [UV-vis-NIR, NMR, IR, spectroelectrochemistry, and magnetic circular dichroism (MCD)]; CASSCF+NEVPT2 methods were employed in calculations of electronic structures. For (t2g)5 electronic configurations, the lowest energy ligand-to-metal charge transfer (LMCT) absorptions and MCD C-terms in the spectra of boronated species have been assigned to transitions from cyanide σ+π + B-C borane σ orbitals. CASSCF+NEVPT2 cal-culations including t1u and t2u orbitals reproduced t1u/t2u → t2g excitation energies. All [M(CN-BR3)6]3/4− complexes exhibited highly electrochemically reversible redox couples. Notably, the formal potentials of all five [M(CN-B(C6F5)3)6]3− anions scale with LMCT energies, and Mn(I) and Cr(II) compounds, (K(18-crown-6))5[Mn(CN-B(C6F5)3)6] and (TBA)4[Cr(CN-B(C6F5)3)6], are surprisingly stable. Continuous wave and pulsed electron paramagnetic resonance (hyperfine sublevel correlation) spectra were collected for all Cr(III) complexes; as expected, 14N hyperfine splittings are greater for (Ph4As)3[Cr(NC-BPh3)6] than for (Ph4As)3[Cr(CN-BPh3)6].