Boronated Cyanometallates.

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