Density Functional Theory Study of trans‐Dioxo Complexes of Iron, Ruthenium, and Osmium with Saturated Amine Ligands, trans‐[M(O)₂(NH₃)₂(NMeH₂)₂]²⁺ (M=Fe, Ru, Os), and Detection of [Fe(qpy)(O)₂]ⁿ⁺ (n=1, 2) by High‐Resolution ESI Mass Spectrometry

Abstract

Density functional theory (DFT) calculations on trans-dioxo metal complexes containing saturated amine ligands, trans-[M(O)2(NH3)2(NMeH2)2]2+ (M=Fe, Ru, Os), were performed with different types of density functionals (DFs): 1) pure generalized gradient approximations (pure GGAs): PW91, BP86, and OLYP; 2) meta-GGAs: VSXC and HCTH407; and 3) hybrid DFs: B3LYP and PBE1PBE. With pure GGAs and meta-GGAs, a singlet d2 ground state for trans-[Fe(O)2(NH3)2(NMeH2)2]2+ was obtained, but a quintet ground state was predicted by the hybrid DFs B3LYP and PBE1PBE. The lowest transition energies in water were calculated to be at lambda approximately 509 and 515 nm in the respective ground-state geometries from PW91 and B3LYP calculations. The nature of this transition is dependent on the DFs used: a ligand-to-metal charge-transfer (LMCT) transition with PW91, but a pi(Fe-O)-->pi*(Fe-O) transition with B3LYP, in which pi and pi* are the bonding and antibonding combinations between the dpi(Fe) and ppi(O(2-)) orbitals. The FeVI/V reduction potential of trans-[Fe(O)2(NH3)2NMeH2)2]2+ was estimated to be +1.30 V versus NHE based on PW91 results. The [Fe(qpy)(O)2](n+) (qpy=2,2':6',2'':6'',2''':6''',2''''-quinquepyridine; n=1 and 2) ions, tentatively assigned to dioxo iron(V) and dioxo iron(VI), respectively, were detected in the gas phase by high-resolution ESI-MS spectroscopy.

Ruthenium complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane for atom and group transfer reactions

“…The calculated Ru-N distances are longer by as much as 0.089Å compared with the experimental data of cis-[Ru VI (Me 3 tacn)O 2 (CF 3 CO 2 )]ClO 4 [17]. Such a large discrep- ancy has also been experienced in our previous calculation on trans-[Os VI O 2 (amine) 4 ] 2+ [59]. The largest difference between the calculated and experimental Ru-oxo distances is 0.028Å, which is of typical accuracy for metal-oxo distances obtained from DFT calculations [60].…”

cis-Oxoruthenium complexes supported by chiral tetradentate amine (N4) ligands for hydrocarbon oxidations

“…We previously reported a density functional theory (DFT) study of trans -dioxo complexes of iron, ruthenium and osmium, trans -[(NH 3 ) 2 (NMeH 2 ) 2 M VI (O) 2 ] 2+ (M = Fe, Ru, Os), where the reduction potentials of the corresponding Fe VI/V and Ru VI/V couples were estimated to be 1.3 V and 0.56 V vs. NHE, respectively. 70 This theoretical study implies that a O Fe O complex would be ∼0.7 V more oxidizing than the corresponding O Ru O complex with the same ligand system. If the same relationship can be applied to Fe/Ru(N 4 ) complexes in a cis -configuration, the potential of the redox couple cis -[(pdp)Fe V (O)(OH)] 2+ + 2e – + 2H + → cis -[(pdp)Fe III (OH)(OH 2 )] 2+ (or cis -[(pdp)Fe V (O) 2 ] + + 2e – + 2H + → cis -[(pdp)Fe III (OH) 2 ] + , depending on the p K a value) would occur at approximately 1.4–1.5 V vs. SCE at pH 4.1, which is equivalent to 1.6–1.7 V vs. SCE at pH 1.…”

Unmasking the Iron–Oxo Bond of the [(Ligand)Fe-OIAr]2+/+ Complexes

“…The enthalpy of the protonation of Fe V –dioxo species and the difference in the properties and the reactivity of Fe v -oxohydroxo and Fe V –dioxo species are still unknown. Gas-phase studies will be particularly useful on that topic because such species are too reactive and were so far never detected in solution. − …”