Selective semihydrogenation of alkynes with the Mn(I) alkyl catalyst fac -[Mn(dippe)(CO) 3 (CH 2 CH 2 CH 3 )] (dippe = 1,2-bis(di- iso -propylphosphino)ethane) as a precatalyst is described. The required hydrogen gas is either directly employed or in situ-generated upon alcoholysis of KBH 4 with methanol. A series of aryl-aryl, aryl-alkyl, alkyl-alkyl, and terminal alkynes was readily hydrogenated to yield E- alkenes in good to excellent isolated yields. The reaction proceeds at 60 °C for directly employed hydrogen or at 60–90 °C with in situ-generated hydrogen and catalyst loadings of 0.5–2 mol %. The implemented protocol tolerates a variety of electron-donating and electron-withdrawing functional groups, including halides, phenols, nitriles, unprotected amines, and heterocycles. The reaction can be upscaled to the gram scale. Mechanistic investigations, including deuterium-labeling studies and density functional theory (DFT) calculations, were undertaken to provide a reasonable reaction mechanism, showing that initially formed Z- isomer undergoes fast isomerization to afford the thermodynamically more stable E- isomer.

The synthesis, characterization, and catalytic activity of low-spin {CoNO} 8 pincer complexes of the type [Co(PCP)(NO)(H)] are described. These compounds are obtained either by reacting [Co(PCP)(κ 2 -BH 4 )] with NO and Et 3 N or, alternatively, by reacting [Co(PCP)(NO)] + with boranes, such as NH 3 •BH 3 in solution. The fivecoordinate, diamagnetic Co(III) complex [Co(PCP NMe -iPr)(NO)(H)] was found to be the active species in the hydroboration of alkenes with anti-Markovnikov selectivity. A range of aromatic and aliphatic alkenes were efficiently converted with pinacolborane (HBpin) under mild conditions in good to excellent yield. Mechanistic insight into the catalytic reaction is provided by means of isotope labeling, NMR spectroscopy, and APCI/ESI-MS as well as DFT calculations.

Rationale Organometallic compounds are becoming increasingly important in their industrial application as catalysts. Mass spectrometry is an essential tool for the structural confirmation of such organometallics. Because the analysis of this class of molecules can be challenging, the ionization behavior and structural confirmation of selected transition metal catalysts are described in this work. Methods The transition metal catalysts investigated were analyzed using classical vacuum MALDI reflectron TOF‐MS as well as intermediate pressure matrix‐assisted laser desorption/ionization quadrupole time‐of‐flight mass spectrometry (MALDI QTOF‐MS). Obtained mass spectra were compared with electrospray ionization MS (ESI‐MS) already established for organometallic compounds, utilizing a QTOF mass spectrometer here. In addition, various sample preparations, including two selected MALDI matrices (trans‐2‐[3‐(4‐tert‐butylphenyl)‐2‐methyl‐2‐propenylidene]malononitrile and 2,2′:5′,2″‐terthiophene) with different solvent combinations for MALDI‐MS measurements, were investigated in detail with respect to their correct isotope distribution of the molecular ions observed. Results All investigated organometallic compounds were successfully identified by vacuum and intermediate pressure MALDI‐MS. Accurate masses of ions related to molecular ion species (e.g., [M‐Cl]+, [M]+, and [M + Na]+) could be determined by MALDI QTOF‐MS measurements with a mass error of less than ±5 ppm for all compounds. Both investigated MALDI matrices performed equally on both instruments. The impact of the analyte/matrix solvent mixtures turned out to be crucial for a successful analysis of the investigated compounds. In contrast, ESI QTOF‐MS yielded masses of ions related to molecular ion species in favorable cases. Conclusions The use of MALDI‐MS for the structural confirmation of organometallic compounds is still not widely used. Nevertheless, this work showed that this analytical technique does have some benefits. The analysis of neutral catalysts proves to be quite useful, concluding that this technique provides a complement and/or an alternative to ESI‐MS.

The selective semihydrogenation of alkynes with the Mn(I) alkyl catalyst fac-[Mn(dippe)(CO)3(CH2CH2CH3)] (dippe = 1,2-bis(di-iso-propylphosphino)ethane) as pre-catalyst is described. Hydrogen gas required for the hydrogenation is generated in situ upon alcoholysis of KBH4 with methanol. A series of aryl-aryl, aryl-alkyl, alkyl-alkyl and terminal alkynes were readily hydrogenated to yield E-alkenes in good to excellent isolated yields. The reaction proceeds at 90°C with catalyst loadings of 0.5 -2 mol%. The implemented protocol tolerates a variety of electron donating and electron withdrawing functional groups including halides, phenols, nitriles, unprotected amines and heterocycles. The reaction can be upscaled to the gram scale. Mechanistic investigations including deuterium labelling studies and DFT calculations were undertaken to provide a reasonable reaction mechanism showing that initially formed Z-isomer undergoes fast isomerization to afford the thermodynamically more stable E-isomer.

Selected organometallic compounds are nowadays extensively used as highly efficient catalysts in organic synthesis. A great variety of different ligand systems exists, of which phosphine-based ligands are a significant subgroup. While mass spectrometry, predominantly electrospray ionization mass spectrometry (ESI-MS), is a standard analytical technique for the identification of new ligands and their metal complexes, there is little information on the behavior of phosphine-based ligands/molecules by electrospray ionization collision-induced dissociation tandem mass spectrometry (ESI-CID-MS/MS) at low collision energies (<100 eV) in the literature. Here, we report a study on the identification of typical product ions occurring in tandem mass spectra of selected phosphine-based ligand systems by ESI-CID-MS/MS. The influence on the fragmentation behavior of different backbones (pyridine, benzene, triazine) as well as different spacer groups (amine, methylamine, methylene), which are directly linked to the phosphine moiety, is investigated by tandem mass spectrometry. In addition, possible fragmentation pathways are elaborated based on the assigned masses in the tandem mass spectra with high-resolution accurate mass determination. This knowledge may be particularly useful in the future for the elucidation of fragmentation pathways for coordination compounds by MS/MS, where the studied compounds serve as building blocks.