High-spin and low-spin iron(ii) complexes with facially-coordinated borohydride ligands

Aluminum-stabilized low-spin iron(II) hydrido complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane

We investigated herein the reactions of (Me3tacn)FeCln (1a: n = 3, 1b: n = 2) with common aluminum hydride reagents and a bulky dihydridoaluminate {Li(ether)2}{Al(OC6H3-2,6-(t)Bu2)}(μ-H)2, which yielded the diamagnetic hydrido complexes 2-4 containing Fe(II) and Al(III). In particular, the use of divalent 1b afforded excellent isolated yields. The structures of 2-4 were determined using spectroscopic and crystallographic analyses. The crystal structures showed distorted octahedral Fe centers and fairly short Fe-Al distances [2.19-2.24 Å]. The structures of cation moiety 2 and neutral complex 4 were further probed using DFT calculations, which indicated a stable low-spin Fe(II) state and strongly electron-donating nature of the (Me3tacn)FeH3 fragment toward the Al(III) center.

Density functional theory for transition metals and transition metal chemistry

We introduce density functional theory and review recent progress in its application to transition metal chemistry. Topics covered include local, meta, hybrid, hybrid meta, and range-separated functionals, band theory, software, validation tests, and applications to spin states, magnetic exchange coupling, spectra, structure, reactivity, and catalysis, including molecules, clusters, nanoparticles, surfaces, and solids.

Borane B-C Bond Cleavage by a Low-Coordinate Iron Hydride Complex and N-N Bond Cleavage by the Hydridoborate Product

The iron(II) hydride dimers [L(R)Fe(μ-H)(2)FeL(R)] (L(Me) = 2,4-bis(2,6-diisopropylphenylimino) pent-3-yl; L(tBu) = 2,2,6,6-tetramethyl-3,5-bis(2,6-diisopropylphenylimino)hept-4-yl) abstract hydrocarbyl groups from BR'(3) (R' = Et, Ph) to give L(R)FeR' and L(R)Fe(μ-H)(2)BR'(2). Mechanistic studies with R = R' = Me are consistent with a process in which the hyride dimer opens one Fe-H bond, and subsequent B-H bond formation is concerted with dissociation of an Fe-H unit. Cleavage of boron-carbon bonds is likely to proceed at least in part from transient quaternary borate anions. In a separate bond-breaking reaction, L(Me)Fe(μ-H)(2)BEt(2) reacts with N(2)H(4) to eject H(2) from the bridging hydrides and cleave the N-N bond in the diaminoborate complex L(Me)Fe(μ-NH(2))(2)BEt(2). These novel bond-breaking reactions are facilitated by the low coordination number at the iron(II) center.

A new local density functional for main-group thermochemistry, transition metal bonding, thermochemical kinetics, and noncovalent interactions

We present a new local density functional, called M06-L, for main-group and transition element thermochemistry, thermochemical kinetics, and noncovalent interactions. The functional is designed to capture the main dependence of the exchange-correlation energy on local spin density, spin density gradient, and spin kinetic energy density, and it is parametrized to satisfy the uniform-electron-gas limit and to have good performance for both main-group chemistry and transition metal chemistry. The M06-L functional and 14 other functionals have been comparatively assessed against 22 energetic databases. Among the tested functionals, which include the popular B3LYP, BLYP, and BP86 functionals as well as our previous M05 functional, the M06-L functional gives the best overall performance for a combination of main-group thermochemistry, thermochemical kinetics, and organometallic, inorganometallic, biological, and noncovalent interactions. It also does very well for predicting geometries and vibrational frequencies. Because of the computational advantages of local functionals, the present functional should be very useful for many applications in chemistry, especially for simulations on moderate-sized and large systems and when long time scales must be addressed.

Benchmarking approximate density functional theory for s/d excitation energies in 3d transition metal cations

Holthausen has recently provided a comprehensive study of density functional theory for calculating the s/d excitation energies of the 3d transition metal cations. This study did not include the effects of scalar relativistic effects, and we show here that the inclusion of scalar relativistic effects significantly alters the conclusions of the study. We find, contrary to the previous study, that local functionals are more accurate for the excitation energies of 3d transition method cations than hybrid functionals. The most accurate functionals, of the 38 tested, are SLYP, PBE, BP86, PBELYP, and PW91.