The pursuit of single-molecule magnets (SMMs) with better performance urges new molecular design that can endow SMMs larger magnetic anisotropy. Here we report that two-coordinate cobalt imido complexes featuring highly covalent Co═N cores exhibit slow relaxation of magnetization under zero direct-current field with a high effective relaxation barrier up to 413 cm, a new record for transition metal based SMMs. Two theoretical models were carried out to investigate the anisotropy of these complexes: single-ion model and Co-N coupling model. The former indicates that the pseudo linear ligand field helps to preserve the first-order orbital momentum, while the latter suggests that the strong ferromagnetic interaction between Co and N makes the [CoN] fragment a pseudo single paramagnetic ion, and that the excellent performance of these cobalt imido SMMs is attributed to the inherent large magnetic anisotropy of the [CoN] core with |M = ± 7/2⟩ ground Kramers doublet.

Water oxidation is the key step in natural and artificial photosynthesis for solar-energy conversion. As this process is thermodynamically unfavorable and is challenging from a kinetic point of view, the development of highly efficient catalysts with low energy cost is a subject of fundamental significance. Herein, we report on iron-based films as highly efficient water-oxidation catalysts. The films can be quickly deposited onto electrodes from Fe(II) ions in acetate buffer at pH 7.0 by simple cyclic voltammetry. The extremely low iron loading on the electrodes is critical for improved atom efficiency for catalysis. Our results showed that this film could catalyze water oxidation in neutral phosphate solution with a turnover frequency (TOF) of 756 h(-1) at an applied overpotential of 530 mV. The significance of this approach includes the use of earth-abundant iron, the fast and simple method for catalyst preparation, the low catalyst loading, and the large TOF for O2 evolution in neutral aqueous media.

The reaction of the cobalt(0) alkene complex [(IMes)Co(η(2):η(2)-dvtms)] (1) (IMes = 1,3-bis(1',3',5'-trimethylphenyl)imidazol-2-ylidene, dvtms = divinyltetramethyldisiloxane) with 2 equiv of DippN3 (Dipp = 2,6-diisopropylphenyl) afforded the cobalt(IV) imido complex [(IMes)Co(NDipp)2] (2), which could be oxidized by [Cp2Fe][BAr(F)4] (Ar(F) = 3,5-di(trifluoromethyl)phenyl) to give the cobalt(V) imido species [(IMes)Co(NDipp)2][BAr(F)4] (3). The molecular structures of all these complexes were established by single-crystal X-ray diffraction studies. Characterization data and theoretical calculations suggest ground spin states of S = (1)/2 and S = 0 for the cobalt(IV) and cobalt(V) species, respectively. When heated, the cobalt(IV) imido species was converted to a cobalt(II) diamido complex via an intramolecular C-H bond amination reaction, but the cobalt(V) species was stable under similar conditions. The different outcomes suggest that a high oxidation state does not guarantee C-H bond activation reactivity of late-transition-metal imido species.

The demand for economical and environmentally benign catalysts for important chemical transformations has recently initiated great efforts on nonprecious metal-catalyzed hydrosilylation reactions. The special chemical properties of cobalt enable the development of diverse cobalt complex-based catalysts for hydrosilylation reactions. This paper reviews the significant advances of cobalt complex-catalyzed hydrosilylation of alkenes and alkynes from the early studies in the 1960s until now, with the objective of providing readers with the status of the field and the underlying late 3d metal chemistry that is meaningful for new nonprecious metal catalyst design. Progress, problems, and perspectives in this vibrant field are discussed.

The synthesis,s tructural characterization, and reactivity of the first two-coordinate cobalt complex featuring am etal-element multiple bond [(IPr)Co(NDmp)] (4;I Pr = 1,3-bis(2',6'-diisopropylphenyl)imidazole-2-ylidene;D mp = 2,6-dimesitylphenyl) is reported. Complex 4 was prepared from the reaction of [(IPr)Co(h 2 -vtms) 2 ]( vtms = vinyltrimethylsilane) with DmpN 3 .A nX -ray diffraction study revealed its linear CÀCoÀNc ore and as hort CoÀNd istance (1.691 (6) ). Spectroscopic characterization and calculation studies indicated the high-spin nature of 4 and the multiplebond character of the Co À Nbond. Complex 4 effected grouptransfer reactions to CO and ethylene to form isocyanide and imine,r espectively.I ta lso facilitated E À H( E= C, Si) s-bond activation of terminal alkyne and hydrosilanes to produce the corresponding cobalt(II) alkynyl and cobalt(II) hydride complexes as 1,2-addition products.

The synthesis, structure, and reactivity of some organo-iron complexes with monodentate N-heterocyclic carbene (NHC) ligation were studied. Mononuclear ferrous complexes [(IEt) 2 FeR 2 ] (IEt = 2,5-diethyl-3,4-dimethylimidazol-1-ylidene, R = Me (2a), CH 2 TMS (2b)) and [(IPr)FeMes 2 ] (3, IPr = 2,5-diisopropyl-3,4-dimethylimidazol-1-ylidene) were prepared in good yields via salt elimination reactions of [(NHC) 2 FeCl 2 ] (1) with alkylation reagents. The interaction of 1 with PhLi gave a mixture of dinuclear complexes [Cl(IEt)Fe(IEt 0 ) 2 Fe(IEt)Cl] (4a) and [Ph(IEt)Fe(IEt 0 ) 2 Fe(IEt)Ph] (4b) (IEt 0 = 3-Et-4,5-Me 2 -2-ylideneimidazolyl anion), in which NÀC(ethyl) bond cleavage of the NHC ligand was involved. Complexes 2aÀ4b were characterized by 1 H NMR, elemental analyses, and single-crystal X-ray diffraction studies. Solution magnetism measurement by Evan's method revealed the high-spin electronic configuration for the mononuclear organo-iron(II) complexes 2a, 2b, and 3. Reactivity studies showed the tetrahedral complex 2a was inert toward many unsaturated organic substrates, whereas the trigonal-planar complex 3 could react with CO and carbodiimide Pr i NdCdNPr i to yield dimesityl ketone and [(IPr)Fe(Mes)(η 2 -Pr i NC(Mes)NPr i )] (5), respectively. Relevant to iron-catalyzed Kumada couplings, both complexes 2b and 3 were found reactive with PhI to yield the corresponding carbonÀcarbon bond formation products PhÀCH 2 TMS and PhÀMes.

A three-coordinate cobalt(I) complex exhibits high catalytic efficiency and selectivity as well as good functional group compatibility in alkyne hydrosilylation. [Co(IAd)(PPh3)(CH2TMS)] (1) (IAd = 1,3-diadamantylimidazol-2-ylidene) facilitates regio- and stereoselective hydrosilylation of terminal, symmetrical internal, and trimethylsilyl-substituted unsymmetrical internal alkynes to produce single hydrosilylation products in the forms of β-(E)-silylalkenes, (E)-silylalkenes, and (Z)-α,α-disilylalkenes, respectively, in high yields. The comparable catalytic efficiency and selectivity of the Co(I) silyl complex [Co(IAd)(PPh3)(SiHPh2)] that was prepared from the reaction of 1 with H2SiPh2, and the isolation of an alkyne Co(I) complex [Co(IAd)(η(2)-PhC≡CPh)(CH2TMS)] from the reaction of 1 with the acetylene, point out a modified Chalk-Harrod catalytic cycle for these hydrosilylation reactions. The high selectivity is thought to be governed by steric factors.

The all-ferrous [Fe4S4]0 state has been demonstrated in the fully reduced Fe protein of the Azotobacter vinelandii nitrogenase complex. We seek synthetic analogues of this state more tractable than the recently prepared but highly unstable cluster [Fe4S4(CN)4]4− (Scott, Berlinguette, Holm, and Zhou, Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 9741). The N-heterocyclic carbene 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (Pri2NHCMe2) has been found to stabilize the fully reduced clusters [Fe8S8(Pri2NHCMe2)6] (4) and [Fe4S4(Pri2NHCMe2)4] (5), which are prepared by cluster assembly or phosphine substitution of FenSn (n = 8, 16) clusters. Cluster 4 is also obtained by reaction of the carbene with all-ferrous [Fe7S6(PEt3)5Cl2] (3) and cluster 5 by carbene cleavage of 4. Detailed structures of 3 (monocapped prismatic), 4, and 5 are described; the latter two are the first iron–sulfur clusters with Fe–Cσ bonds. Cluster 4 possesses the [Fe8(μ3-S)6(μ4-S)2] edge-bridged double cubane structure and 5 the cubane-type [Fe4(μ3-S)4] stereochemistry. The all-ferrous formulations of the clusters are confirmed by X-ray structure parameters and 57Fe isomer shifts. Both clusters are stable under conventional aprotic anaerobic conditions, enabling further study of reactivity. The collective properties of 5 indicate that it is a meaningful synthetic analogue of the core of the fully reduced protein-bound cluster.