Nathan C. Smythe

Importance of Out-of-State Spin–Orbit Coupling for Slow Magnetic Relaxation in Mononuclear FeII Complexes

Two mononuclear high-spin Fe(II) complexes with trigonal planar ([Fe(II)(N(TMS)(2))(2)(PCy(3))] (1) and distorted tetrahedral ([Fe(II)(N(TMS)(2))(2)(depe)] (2) geometries are reported (TMS = SiMe(3), Cy = cyclohexyl, depe = 1,2-bis(diethylphosphino)ethane). The magnetic properties of 1 and 2 reveal the profound effect of out-of-state spin-orbit coupling (SOC) on slow magnetic relaxation. Complex 1 exhibits slow relaxation of the magnetization under an applied optimal dc field of 600 Oe due to the presence of low-lying electronic excited states that mix with the ground electronic state. This mixing re-introduces orbital angular momentum into the electronic ground state via SOC, and 1 thus behaves as a field-induced single-molecule magnet. In complex 2, the lowest-energy excited states have higher energy due to the ligand field of the distorted tetrahedral geometry. This higher energy gap minimizes out-of-state SOC mixing and zero-field splitting, thus precluding slow relaxation of the magnetization for 2.

Iron Complex-Catalyzed Ammonia–Borane Dehydrogenation. A Potential Route toward B–N-Containing Polymer Motifs Using Earth-Abundant Metal Catalysts

Ammonia-borane (NH(3)BH(3), AB) has garnered interest as a hydrogen storage material due to its high weight percent hydrogen content and ease of H(2) release relative to metal hydrides. As a consequence of dehydrogenation, B-N-containing oligomeric/polymeric materials are formed. The ability to control this process and dictate the identity of the generated polymer opens up the possibility of the targeted synthesis of new materials. While precious metals have been used in this regard, the ability to construct such materials using earth-abundant metals such as Fe presents a more economical approach. Four Fe complexes containing amido and phosphine supporting ligands were synthesized, and their reactivity with AB was examined. Three-coordinate Fe(PCy(3))[N(SiMe(3))(2)](2) (1) and four-coordinate Fe(DEPE)[N(SiMe(3))(2)](2) (2) yield a mixture of (NH(2)BH(2))(n) and (NHBH)(n) products with up to 1.7 equiv of H(2) released per AB but cannot be recycled (DEPE = 1,2-bis(diethylphosphino)ethane). In contrast, Fe supported by a bidentate P-N ligand (4) can be used in a second cycle to afford a similar product mixture. Intriguingly, the symmetric analogue of 4 (Fe(N-N)(P-P), 3), only generates (NH(2)BH(2))(n) and does so in minutes at room temperature. This marked difference in reactivity may be the result of the chemistry of Fe(II) vs Fe(0).

Investigation of formally zerovalent Triphos iron complexes

The reduction of Triphos [PhP(CH(2)CH(2)PPh(2))(2)] iron halide complexes has been explored, yielding formally zerovalent (κ(3)-Triphos)Fe(κ(2)-Triphos) and (κ(3)-Triphos)Fe(κ(2)-Bpy). Electrochemical analysis, coupled with the metrical parameters of (κ(3)-Triphos)Fe(κ(2)-Bpy), reveal an electronic structure consistent with a π-radical monoanion bipyridine chelate that is antiferromagnetically coupled to a low spin, Fe(I) metal center.

Reactivity of (Triphos)FeBr2(CO) towards sodium borohydrides

Abstract The addition of CO to (Triphos)FeBr2 (Triphos = PhP(CH2CH2PPh2)2) resulted in formation of six-coordinate (Triphos)FeBr2(CO). This coordination compound was found to have cis-bromide ligands and a mer-Triphos ligand by single crystal X-ray diffraction. Once characterized, the reactivity of this compound toward NaEt3BH and NaBH4 was investigated. Adding 1 eq. of NaEt3BH to (Triphos)FeBr2(CO) resulted in formation of (Triphos)FeH(Br)(CO), while the addition of 2.2 eq. afforded previously described (Triphos)Fe(CO)2. In contrast, adding 2.2 eq. of NaBH4 to (Triphos)FeBr2(CO) resulted in carbonyl dissociation and formation of diamagnetic (Triphos)FeH(η2-BH4), which has been structurally characterized. Notably, efforts to prepare (Triphos)FeH(η2-BH4) following 2.2 eq. NaBH4 addition to (Triphos)FeBr2 were unsuccessful. The importance of these observations as they relate to previously reported (Triphos)Fe reactivity and recent developments in Fe catalysis are discussed.