Boronated Cyanometallates

Abstract

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-tometal 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 ].

Lewis‐Säure‐dekorierte Hexacyanodiboran(6)‐Dianionen

“…Die Adduktbildung von Cyanoborat‐Anionen, [5] Übergangsmetall‐(ÜM)‐cyano‐Komplexen [5d,e,h,6] und Nitrilen im Allgemeinen [5g,h,7] mit Lewis‐sauren Boranen ist eine elegante Route für die Synthese starker Oxidationsmittel [7f,g] sowie schwach koordinierender Anionen (weakly coordinating anion, WCA) [5f,h] . Addukte von Tris(pentafluorphenyl)boran (BCF) mit Tetra‐ und Hexacyanometallaten und Cyanoborat‐Anionen wurden bereits beschrieben [5d,e,f,6e,f] . Schwach koordinierende Anionen zeichnen sich durch eine effiziente Delokalisierung der negativen Ladung und ihre geringe Polarisierbarkeit aus.…”

Lewis Acid Decorated Hexacyanodiborane(6) Dianion

“…Since cyanoborate anions, [5] transition metal (TM) cyano complexes, [5d,e,h,6] and nitriles in general [5g,h,7] are known for the formation of adducts with Lewis acidic boranes, this offers an elegant route for the synthesis of strong oxidants [7f,g] or weakly coordinating anions (WCA) [5f,h] . Noteworthy, tris(pentafluorophenyl)borane (BCF) adducts of tetra‐ and hexacyanometallate and cyanoborate anions have been described in the past [5d,e,f,6e,f] . Weakly coordinating anions are characterized by efficient delocalization of the anionic charge and a small polarizability.…”

The Nephelauxetic Effect Becomes an Important Design Factor for Photoactive First‐Row Transition Metal Complexes

“…Isocyanides are strong π‐back bonders, which places them high in the nephelauxetic series of ligands. EPR studies of related isocyanoborato complexes with other first‐row transition metals suggest that nephelauxetic effects are indeed at play [39] . Until now, the focus of recent research with isocyanide d 6 metal complexes has been on emissive MLCT excited states, [40] but future studies could target the detection of MC states, for example with aliphatic isocyanides.…”

“…EPR studies of related isocyanoborato complexes with other first-row transition metals suggest that nephelauxetic effects are indeed at play. [39] Until now, the focus of recent research with isocyanide d 6 metal complexes has been on emissive MLCT excited states, [40] but future studies could target the detection of MC states, for example with aliphatic isocyanides. The monodentate arylisocyanide ligands of the [Mn-(CNdippPh OMe2 ) 6 ] + complex (Figure 6d) dissociate upon photo-irradiation, [41] analogously to what is observed with Mn I tricarbonyl diimines, [42] signaling that the role played by MC states, and possibly the nephelauxetic effect, would likely deserve greater attention.…”