Boronated Cyanometallates.

Thirteen boronated cyanometallates [M(CN-BR 3 ) 6 ] 3/4/5- [M = Cr, Mn, Fe, Ru, Os; BR 3 = BPh 3 , B(2,4,6,-F 3 C 6 H 2 ) 3 , B(C 6 F 5 ) 3 ] and one metalloboratonitrile [Cr(NC-BPh 3 ) 6 ] 3- 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 2g ) 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 π + B-C borane σ orbitals. CASSCF+NEVPT2 calculations including t 1u and t 2u orbitals reproduced t 1u /t 2u → t 2g excitation energies. Many [M(CN-BR 3 ) 6 ] 3/4- complexes exhibited highly electrochemically reversible redox couples. Notably, the reduction formal potentials of all five [M(CN-B(C 6 F 5 ) 3 ) 6 ] 3- anions scale with the LMCT energies, and Mn(I) and Cr(II) compounds, [K(18-crown-6)] 5 [Mn(CN-B(C 6 F 5 ) 3 ) 6 ] and [K(18-crown-6)] 4 [Cr(CN-B(C 6 F 5 ) 3 ) 6 ], are surprisingly stable. Continuous-wave and pulsed electron paramagnetic resonance (EPR; hyperfine sublevel correlation) spectra were collected for all Cr(III) complexes; as expected, 14 N hyperfine splittings are greater for (Ph 4 As) 3 [Cr(NC-BPh 3 ) 6 ] than for (Ph 4 As) 3 [Cr(CN-BPh 3 ) 6 ].