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Imido complexes of early transition metals are key intermediates in the synthesis of many nitrogen-containing organic compounds. The metal-nitrogen double bond of the imido moiety undergoes [2+2] cycloaddition reactions with various unsaturated organic molecules to form new nitrogen-carbon and nitrogen-heteroatom bonds. This review article focuses on reactivity of the terminal imido complexes of Group 4-6 metals, summarizing their stoichiometric reactions and catalytic applications for a variety of reactions including alkyne hydroamination, alkyne carboamination, pyrrole formation, imine metathesis, and condensation reactions of carbonyl compounds with isocyanates.

Continuous-wave electron paramagnetic resonance (EPR) spectroscopy at 35 GHz is an essential cornerstone in multi-frequency EPR studies and is crucial for differentiating multiple species in complex systems due to the improved g -tensor resolution compared to lower microwave frequencies. Especially for unstable and highly sensitive paramagnetic centers, the reliability of the measurements can be improved upon through the use of a single sample for EPR experiments at all frequencies. Besides the advantages, the lack of common availability of oversized-sample resonators at 35 GHz often limits scientists to lower frequencies or smaller sample geometries, and the latter may be non-trivial for sensitive materials. In this work, we present the design and performance of an oversized-sample 35 GHz EPR resonator with a high loaded Q value, QL , of up to 2550, well-suited for continuous-wave EPR and pulsed single-microwave-frequency experiments. The design is driven by electromagnetic field simulations, and the microwave characteristics of manufactured prototypes were found to be in agreement with the predictions. The resonator is based on a cylindrical cavity with a TE 011 mode, allowing for 3 mm sample access. The design targets that we met include high sensitivity, robustness, and ease of manufacturing and maintenance. The resonator is compatible with commercial EPR spectrometers and with helium flow, as well as with cryogen-free cryostats, allowing for measurements at temperatures down to 1.8 K. To highlight the general applicability, the resonator was tested on metal centers, as well as on organic radicals featuring extremely narrow lines. [ABSTRACT FROM AUTHOR]

The Lewis basicity of a μ3-oxo ligand for (μ3-O)[Rh(cod)]3(μ4-O)M (cod = 1,5-cyclooctadiene) complexes was controllable by metal species on the μ4-oxo ligand locating at the opposite site of the μ3-oxo ligand. Coordination of the μ3-oxo ligand of [(μ3-O){Rh(cod)}3(μ4-O){Au(PPh3)}][BF4] (1) to [Au(PPh3)]+ indicated sufficient Lewis basicity of the μ3-oxo ligand in 1 to form [{(Ph3P)Au}(μ3-O){Rh(cod)}3(μ4-O){Au(PPh3)}][BF4] (2). In contrast, the addition of Li+ to 1 induced elimination of the originally coordinated [Au(PPh3)]+ due to the weak Lewis basicity of the μ3-oxo ligand for (μ3-O){Rh(cod)}3(μ4-O)Li(THF)3, in which a pentanuclear species, [{(Ph3P)Au}(μ3-O){Rh(cod)}3(μ4-O){Li(THF)3}][BF4] (3), was assumed to be generated in situ before the dissociation of [Au(PPh3)]+. [ABSTRACT FROM AUTHOR]

We found that bis(neopentylglycolato)diboron (B2nep2) served as a bidentate ligand and a one-electron reducing agent for early transition metal chlorides to afford MCl4(B2nep2). Treatment of B2nep2 with MCl5 (M = Nb and Mo) produced MCl4(B2nep2) via two successive reactions, coordination of B2nep2 to the metal center and one-electron reduction from M(V) to M(IV), while coordination of B2nep2 to MCl4 (M = Zr, Ti) was observed without reduction of the central metals. DFT studies for the reduction of NbCl5 by B2nep2 clarified the initial formation of seven-coordinated and B2nep2-ligated Nb(V) species, NbCl5(B2nep2), and one chloride on niobium(V) moves to the Lewis acidic boron center to generate NbCl4[(B2nep2)Cl]. The chloride on the boron atom of NbCl4[(B2nep2)Cl] is trapped by the second B2nep2 to give [NbCl4(B2nep2)][ClB2nep2]. After the formation of [ClB2nep2]– as an anionic sp2–sp3 diboron adduct, one-electron reduction of the niobium(V) center produces NbCl4(B2nep2) along with [ClB2nep2]˙ as a plausible diboron species, whose decomposition affords ClBnep and B2nep2. The reduction of metal halides in the presence of B2nep2 was exemplified by green LED irradiation of TiCl4(B2nep2), producing chloride-bridged titanium(III) species, (B2nep2)TiCl2(μ-Cl)2TiCl2(B2nep2). [ABSTRACT FROM AUTHOR]

Cobalt-catalyzed hydroalkynylation of alkynes, alkenes, and imines affords internal alkynes with various functional groups adjacent to the carbon–carbon triple bond moiety in an atom-economical manner. In addition, cross-coupling of in situ generated alkynylcobalt species from terminal alkynes, haloalkynes, and metal acetylides with (hetero)aromatic compounds and organic halides selectively provides various internal aryl- and alkylalkynes. 1 Introduction 2 Hydroalkynylation of Alkynes for 1,3-Enyne Synthesis 3 Hydroalkynylation of Polar and Nonpolar Double Bonds 4 Dehydrogenative Cross-Coupling Reaction Using Terminal Alkynes with Aromatic Compounds 5 Cross-Coupling Reactions Using Haloalkynes as the Coupling Partners 6 Cross-Coupling Reactions Using Metal Acetylides 7 Conclusion [ABSTRACT FROM AUTHOR]

The steric effects of hafnocene catalysts were studied with the purpose of controlling the selectivity of 4-methyl-1-pentene formations. The analysis of relative rates reveal that the bulkiness of the cyclopentadienyl ligands as well as the structure of the growing chain significantly influence the selectivity.